Chemistry of Antibiotics: Cell Wall Synthesis

Introduction

In this post we will continue our exploration of the chemistry of antibiotics with a look at drugs that interrupt wall synthesis and how bacteria develop resistance to these drugs.

The target of these antibiotics is crucial because it explains how antibiotics can attack bacteria without affecting human cells. Bacterial cells, unlike animal cells, have cell walls. Therefore, a drug that attacks cell walls will not be able to impact human cells. Bacterial cell walls are essentially a peptidoglycan layer that is composed of units of peptides (proteins) and glycans (sugars). This layer is the primary and most important component of the cell wall.

β-lactam Antibiotics

The most common class of antibiotics that interferes with cell wall synthesis are the β-lactam antibiotics, which

include penicillin. These types of antibiotics function by impeding the synthesis of the peptidoglycan of the bacterial cell wall. There are multiple ways to inhibit the synthesis of the peptidoglycan layer but the most common is by means of destroying the enzymes that do so. If the antibiotic does not function by destroying synthetic enzymes, it could also destroy the enzymes that convert the polymers into a layer of the cell wall. β-lactam antibiotics inhibit cell wall synthesis by preventing the assembly of the peptidoglycan layer. This is done when the antibiotic competes with the polymer at the site of binding.

This video gives a general overview of how peptidoglycans are inhibited by the mechanisms of a beta-lactam antibiotic:

 The Chemistry of Penicillin

 

Penicillin is one of the most common β-lactam antibiotics, and is characterized by three structural requirements: one fused β-lactam structure, a free carboxylic acid group, and one or more substituted amino acid side chains. Penicillin’s structure prevents the cross linking of peptide chains – weaker cell walls will allow water to flow into the cell freely and the cell will swell and burst, causing cell death. If you change the side R-group chain on the penicillin, the penicillin can possess different properties, such as acidity or penicillinase resistance.

The β-lactam ring in the penicillin reacts with an enzyme that is used for building the cell wall called DD-transpeptidase. Resemblances between a segment of the penicillin structure and the backbone of a peptide chain of the bacterial cell wall have been used to explain the mechanism of beta-lactam antibiotics.

Bacteria Fighting Back

Bacteria have a number of ways to evolve and beat our human antibiotics. One method that bacteria employ in order to fight drugs that interrupt cell wall synthesis, is changing the structure of their cell walls. One instance of this is mutation of pathogenic bacteria. Bacteria that colonize the mucosal pathways, such as nostrils, lips and eyelids, must undergo changes in order to avoid the antimicrobials of the host. In particular, they must avoid lysozyme, an enzyme that destroys the cell walls of bacteria. The activity of lysozyme is similar to β-lactam antibiotics since they both attack the cell walls of bacteria. Since the muramidase activity of lysozyme leads to hydrolysis of the β-1,4 glycosidic bond between the C-1 carbon of N-acetyl muramic acid (MurNAc) and the C-4 carbon of N-acetylglucosamine (GlcNAc), that is the bond that the bacteria have to change in order to survive.Streptococcus pneumoniae and bacillus anthracis, two lysozyme resistant bacteria, have peptidoglycan cell walls that are N-deacetylated, which means that the composition and structure of the sugar component of the cell wall is changed. It was shown that N-acetylating them caused them to be more susceptible to lysozyme. Therefore, it was concluded that N-deacetylating the caused lysozyme resistance. This shows that through changes in structure, bacteria can evade agents that inhibit their cell wall synthesis. When this happens, we too must evolve and change our tactics. This is why new drugs always need to be developed. Bacteria develop resistance, and we must develop new antibiotics.

Want to know more about different classes of antibiotics that inhibit cell wall synthesis? Check out thislink to learn about glycopeptide antibiotics. Of course that’s not enough to satisfy the hunger of your mind, so here is a website that goes further in-depth regarding the processes of cell wall synthesis.

Local Anesthetics: The Caine Family

As seen in the previous post, local anesthetics generally work to prevent only a small area of the body from experiencing pain by inhibiting the flow of sodium ions (preventing action potential thus preventing nerve activity) through sodium channels embedded in the cell membrane of neurons. More specifically, the local anesthetic will bind to a receptor inside the sodium channels and antagonize it, therefore closing the sodium channels thus creating the halt in the influx of ions through the channels as seen in the diagram below.

 .

Many local anesthetics commonly bind to the N-methyl-D-aspartate (NMDA) receptor (an image of how the anesthetic might bind to a receptor through the polar attractions between the receptor and anesthetics is shown here), such as the constituents of the Caine family: a category of local anesthetic compounds that share similar qualities (i.e. similar receptors and mechanism of actions) and end in the suffix “caine”. The following will consist of descriptions of three different local anesthetics, particularly from the Caine family, to demonstrate the functional and molecular diversity in the compounds of local anesthesia.

Cocaine:

Cocaine, otherwise known as benzoylmethylecgonine, can be used as a type of local anesthetic, but for the past several decades it has reached the headlines for different reasons. Cocaine was used historically as an eye and nose anesthetic, used to block nerve signals during surgery, but side effects of cocaine exposure during surgery include intense vasoconstriction and cardiovascular toxicity. It is a powerful nervous system stimulant, and above all, it is extremely addictive. Repeated use of the drug can cause strokes, cardiovascular disease, and several hundred other afflictions such as gingivitis, lupus, and an increased chance for heart attacks. Cocaine can be administered in many different ways, most commonly through insufflation, injection, and in the case of crack cocaine, inhalation. Cocaine is a controlled substance around the world due to its addictive properties and terrible side effects of constant use.

How To Use It:

Most users of pure cocaine are drug addicts, but cocaine hydrochloride is still used as a topical anesthetic. It is applied through the mouth, or the nose using a cotton swab to numb the area. It should not be used in the eye or injected, and rarely, addictive behavior will be expressed by the patient. Use the medication as specified by a healthcare professional, and do not use more frequently or longer than specified.

Molecular Structure:

Cocaine usually contains pure C17H21NO4 from the leaves of the coca plant.]

2D structure                                              3D structure

Properties:

• The molecular weight of cocaine is 303.35 g/mol.
• The molecular formula is C17H21NO4
• The systematic name is Methyl (1R,2R,3S,5S)-3-(benzoyloxy)-8-methyl-8-azabicyclo[3.2.1]octane-2-carboxylate
• Approximately 35.9 million Americans aged 12 and older have tried cocaine at least once in their lifetime, according to a national survey, and about 2.1 million Americans are regular users

Novocain (Procaine):

First synthesized in 1905, novocain (the trade name of procaine) is an ester-type local anesthetic that is able to induce a loss of sensation when injected, as opposed to oral intake which has been stated to wield therapeutic values. The first synthetic local anesthetics to be produced, novocain was primarily utilized for oral surgeries in dentistry however due to ester-type anesthetics having generally a high potential of causing allergic reactions, it eventually became obsolete and eventually replaced by a more effective anesthetic known as lidocaine. Ester-type anesthetics are more prone causing allergic reactions compared to Amide-type anesthetics because when they metabolize in the body, they form a compound known as para-aminobenzoic acid (PABA). PABA has a documented history of causing allergic reactions that range from urticaria to anaphylaxis. Generally, the adverse side effects of using novocain include heartburn, migraines, nausea, and can induce a serious condition known as systemic lupus erythematosus (SLE), therefore it is highly advised that intake is performed by a healthcare professional. However, novocain also retains the property and advantage of constricting blood vessels, reducing bleeding unlike many other local anesthetics.

How To Use It:

The common and primary method of intake of novocain for its anesthetic properties is through injection in solution state. However, if novocain is present in capsule or tablet form, oral ingestion can also performed though its properties and effects will be greatly mitigated and may induce therapeutic rather than anesthetic conditions.  An informative video of how novocain is administered in oral surgeries of dentistry can be found  below.

Molecular Structure:

Novocain contains pure C13H20N2O2.

2D structure                            3D structure

Properties:

• The molecular weight of novocain is 236.31 g/mol.
• The molecular formula is C13H20N2O2.
• The systematic name is 2-(diethylamino)ethyl 4-aminobenzoate
• The melting point of novocain is approximately 61 °C while its pKa value at 15 °C is 8.05

 

Tetracaine:

Tetracaine is a type of local anesthetic and it is used as a numbing medication. It is generally used for surface and spinal anesthesia and it works by blocking the nerve signals in your body. There most used type of tetracaine medication is cream and ointment. It’s primary use is to reduce pain or discomfort caused by minor skin irritations, cold sores or fever blisters, sunburn or other minor burns, insect bites or stings, and many other sources of minor pain on a surface of the body. The reason why this medication is given is to lessen the pain caused by the insertion of a medical instrument such as a scope or a tube. Although in most situations tetracaine is used on the skin, it can also be used on the eye. This eye medication is in the form of drops and it is used to decrease the feeling in your eyes right before going through surgery or perhaps a test or procedure involving the eyes.

How To Use It:

The eye drops medication should be issued by the clinic and after going through the procedure, the patient must refrain from touching his or her eye until the medication is no longer in effect and in some cases, an eye patch is required. The Tetracaine topical gel is applied by very small amounts only necessary to cover the area and should not be used more than four times a day unless the doctor specifies otherwise.

Molecular Structure:

Tetracaine contains more than 98 percent of .C15H24N2O2  calculated on the dried basis..

2D structure                                                      3D structure

Properties:

• The molecular weight of tetracaine is 264.36 g/mol.
• The molecular formula is C15H24N2O2.
• The systematic name is 2-(dimethylamino)ethyl 4-(butylamino)benzoate.
• The boiling point of tetracaine is between 362.4 degrees Celsius and 416.4 degrees Celsius at the standard 1 ATM.

Problems Arise: Balloons are Inflating the Helium Shortage

 

              It sounds ridiculous to think that something used everyday in birthday parties is in a serious shortage, but helium, an element used in applications ranging from balloons to MRI scanners, is now getting very difficult to find.  That means that very soon, your cousin may have a very disappointing birthday party. Yet that is the least of our problems.

              The most surprising thing about this shortage is that helium is the second most abundant element in our universe.  However, most of this helium is, practically speaking, way out of our reach.  Let’s embark on an exploration of helium to see why it is so hard to find, what Helium does for us, and what we can do in the future to make the search for it a little easier.

              The main trouble that arises when trying to obtain helium is that it’s less dense than air. This means that any helium trapped under the Earth’s surface eventually diffuses into the atmosphere. Once it’s in the air, it’s out of reach; we have yet to create a feasible means of collecting all of this diffused helium.  Currently, a huge build-up of Helium-4 (He-4) is being released in Yellowstone and about 60 tons of helium are released every year.  Some of this helium is diluted into the atmosphere, but the rest of it escapes the atmosphere into space.  Although it seems like we are letting this helium go to waste, there is just simply no viable way to collect it.

                                                                                                                                                                                                                      Yellowstone National Park

              Yet there are other factors that contribute to Helium’s shortage. For one, the production of Helium as a by-product of nuclear decay is not a heavily invested means of production. This is largely because it is not an economically viable option (along with capturing the diffused Helium in the air as mentioned before); however as we will see, the value of Helium just may be priceless.  Another factor contributing to the shortage is the fact that in the past few decades, the demand and use of Helium has skyrocketed, largely ascribed to our squandering ways. With a limited amount, prices of Helium have soared as well.

              So why exactly is helium important anyway?  Helium has a multitude of applications, but its main application is its use to cool superconducting magnets in MRI (magnetic resonance imaging) scanners. Superconducting magnets are magnets that can produce immense magnetic fields, which MRI scanners require to operate and use to construct images of the body. MRIs use superconducting magnets because below a certain temperature, known as a critical temperature, a metal loses its resistance (The reason this happens at low temperatures is because there are lower energy and less frequent atomic collisions). This temperature needed for superconductivity requires cryogenic temperatures.  That’s where helium comes in.  Liquid helium, due to its extremely low (4.2 K) boiling point and high thermal conductivity, is very efficient at capturing heat and is the only medium that can induce superconductivity in metal alloys. In MRI scanners, the wires are bathed in liquid helium at -269.1 °C to capture heat and remove it from the system. This effectively removes the wires’ resistance and allows them to become superconductors. However, a normal MRI scanner uses 1,700 liters of helium which periodically has to be changed. This is a huge amount of helium, especially with the impending shortage. A new method of superconductor cooling was recently developed by a company known as Cryogenic. This method uses a significantly lower amount of helium and may soon significantly reduce the amounts of helium that we waste.

                                                                 

                                                                                 MRI Scanner

              Another important application of helium is its use in oxygen tanks for underwater diving.  Normally air is comprised of approximately 20% oxygen gas and 80% nitrogen gas. Nitrogen gas is a lot more soluble than Helium, and is especially soluble at high pressures – which essentially keeps the gases in solution. The difference in solubility between the two plays a key role in why Helium is used, and is due to their difference in size. In order to dissolve any substance into a solvent, the solute and solvent must have interactions with one another. For non-polar gases like N2 and He, it becomes difficult to create the interactions with polar water molecules. To actually bring one of these gases into solution, an induced dipole must be created in the gas. An induced dipole becomes increasingly easier as the molar mass of the substance increases. This is because there are then more electrons to shift between the atoms thereby creating a strong bond between the solute and solvent. Between N2 and He, nitrogen gas clearly dominates in molar mass and strength of LDF forces. So at these high pressures below the water, the nitrogen gas becomes highly soluble in the bloodstream inducing nitrogen narcosis, a state with similar effects to those of alcohol. Furthermore, as divers begin to rise from the water, the solubility of nitrogen decreases and begin to bubble out of solution (the blood). This is extremely dangerous as it can create bubbles in the bloodstream which wouldn’t be able to pass through fine capillaries in the body. The condition, called the Bends, is life threatening. To prevent this from happening, Helium is used. As stated previously, Helium is less soluble than Nitrogen, so less Helium would get into the bloodstream. Furthermore, Helium is an inert gas, so its narcotic properties are negligible and do not pose any problems of toxicity like Nitrogen does. Helium continues to be the most ideal gas for diving tanks, and the shortage poses a serious threat to the maritime industries.

              With such versatility it seems more likely that the United States will take on currently, non-viable means to produce Helium rather than drastically cut down on usage. There will likely be 3 primary sources that will serve the United States in the future as a source of Helium. As stated before the first source would be through nuclear reactions.  One reaction that results in a formation of a helium atom is plutonium decomposition (Pu-239).  A plutonium nucleus decays into an alpha particle and a uranium nucleus.  The alpha particle immediately captures 2 electrons from the nearby plutonium metal and becomes a helium atom in the midst of a plutonium lattice.  There are 2 main problems with this method of producing helium.  Firstly, this process has a half-life of 24,100 years.  Using the half-life formula for first-order reactions, one could calculate k to be (ln2)/t_1/2 = (ln2)/24,100= 2.88 x 10-5.  Using the first-order integrated rate law, one could determine that in a year, 10,000 g of plutonium will decompose to 10,000 x e^{-2.88×10^-5} = 9,999.71 g.  Therefore, in a year, 10,000 g of plutonium will only decompose to 0.29 g of decay.  That’s a measly 0.0029% decay after an entire year.  This makes generating a profitable amount of helium unfeasible to say the least.  The second problem with this method is that once the helium is produced, it is stuck in the plutonium lattice.  This makes it become very difficult to isolate and extract

              The second source is actually through natural gas. Some natural gas contains amounts of Helium that can be extracted through a complicated process. The reason it is not widely used today is because the extraction process requires strict criteria and many samples of natural gas only contain about 0.3-1.9 percent Helium by volume. Furthermore, there are many economic considerations before uptaking such a project as the extraction process requires facilities. However, in essence there are 3 steps to the extraction process. The first step is to remove the impurities from the natural gas such as water, carbon dioxide and hydrogen sulfide through means such as amine and glycol adsorption. The second step is to extract the high molecular-weight hydrocarbons. Finally, through cryogenic processing the remaining methane gas is extracted. This works because Helium has the lowest freezing point of any element. So as the temperature is sufficiently reduced, all other substances will freeze and can be filtered out. What’s left is crude Helium, containing approximately 50-70% Helium and the rest is Nitrogen gas and other traces of gases. To further purify the Helium to approximately 99.99% purity, Pressure-Swing Adsorption (PSA) is used. PSA separates different gases from each other based on the premise that each gas has a different affinity for different adsorbent materials, and have different vapor pressures. Due to the varying vapor pressures, one gas can be completely transformed into the gas phase at one temperature and pressure and then extracted, while the other gas would remain largely as a liquid.

                                                                                                                                             Pressure Swing Absorption Process

              The final source will actually be where Helium is most abundant: outer space. Observations from lunar missions have concluded that there are about 22 grams of helium in every cubic meter of lunar soil. In the future, if Helium were to ever run dry on Earth, this alternative would likely create a madman’s dash to the Moon in search of this precious yet scarce gas.

              In essence, our lavish uses of Helium without a steady state of supply has caused a shortage that affects many scientific disciplines that rely on the unique characteristics of Helium. As a human race, we must either cut down on our uses of Helium in some shape or form, or begin taking measures to create more Helium for use in the future. Without Helium, many of the opportunities and technology today will float adrift tomorrow, just an arm’s length away from humanity’s struggling grasp for the resources we use so plentifully.

Synthesis of Antibiotics

     Antibiotics are agents that are used to kill microorganisms or inhibit their growth. They can either occur naturally or can be synthetically produced. Extremely common today are semi-synthetic modifications of natural compounds. These chemical, biosynthetic antibacterial compounds are classified according to their biological effect on microorganisms. Bactericidal agents kill bacteria altogether while bacteriostatic agents slow down or stall bacterial growth. One specific semisynthetic antibiotic is what is known as Erythromycin.

     Erythromycin is what is considered a macrolide antibiotic. Macrolide antibiotics slow the growth of and often kill sensitive bacteria by reducing the production of important proteins needed by the bacteria to survive. This drug is notorious for being similar to penicillin in what it is used for and how it is synthesized. Often it is used as a substitute for people who are allergic to penicillin being that penicillin is such a common allergy. It is commonly used to treat respiratory tract infections, acne, Gonorrhea, Chlamydia, and other STDs. It is also applied to the eyes of newborn babies in order to prevent ophthalmia neonatorum. Erythromycin works by improving gastric emptying as well as its symptoms, though oral use of this drug is generally for short term use rather than long term.

     The chemical structure of Erythromycin, C38H69NO12, is extremely complicated and elaborate. Its synthesis published by Robert B. Woodward in 1981, the drug consists of a 14-membered lactone ring along with ten asymmetric centers and two sugars, L-cladinose and D-desosamine. The compound’s complexity makes it extremely hard to produce synthetically therefore it is produced by the bacterium Saccharopolyspora erythraea. Synthesis of this drug includes an intricate series of reactions. Reactions include hydrolysis and stereospecific aldolization. Oxidations and reductions are also involved in the synthesis by the pure enone’s conversion to desired dithiadecalin product. This product is further converted to ketone as well as an aldehyde. Overall, the synthesis contains roughly 50 steps split into 4 parts.

     Erythromycin comes in 4 forms: Erythromycin A, B, C and D. Erythromycin A is known for being the most antibacterial, with B, C and D following respectively. As discussed previously, this drug is considered to inhabit bacteriostatic activity, otherwise it inhibits growth of bacteria rather than stopping it or killing in completely. Its bacteriostatic capability is most displayed at high concentrations by interfering with aminoacyl translocation. This process objects to the functionality of important proteins, which is overall how antimicrobial action is put in place. One should be aware of the side effects erythromycin may cause, for example, abdominal pain, nausea, diarrhea, and vomiting.

     Zithromax is a semi-synthetic antibiotic, an example of the subclass, azalides and slightly differs in structure from the classical macrolides. It is used to treat and prevent infection within an area thought to be caused by bacteria. Like all other antibiotics, zithromax has an active ingredient, which in this case is azithromycin, a subclass of macrolide antibiotics. Azithromycin is derived from erythromycin but differs chemically from erythromycin in that a methyl-substituted nitrogen atom is incorporated into the lactone ring and is has improved activity through its glycosylated side chains. In this form, it has a molecular formula of C38H72N2O12. However, when Azithromycin is a dihydrate, which means it contains two molecules of water or its elements, it has a molecular formula of C38H72N2O12*2H2O. Also, Azithromycin contains inactive ingredients such as pregelatinized starch, lactose, sucrose, sodium phosphate, hydroxypropyl cellulose, or xanthan gum that all supplement the active ingredient.

 

     Azithromycin binds to 50s ribosomes and interferes with protein synthesis but does not affect nucleic acid synthesis. It binds to the 23S rRNA of the bacterial 50S ribosomal subunit, which includes the activities such as catalyzation of  peptide bond formation, prevention of premature polypeptide hydrolysis, provision of a binding site for the G-protein factors, assistance of protein folding after synthesis. blocking of protein synthesis by inhibiting the transpeptidation or translocation step of protein synthesis and by inhibiting the assembly of the 50S ribosomal subunit. Azithromycin was the target of an enantioselective synthesis, which is a chemical reaction where one or more new elements of chirality,a molecule that has a non-superposable mirror image, are formed in a substrate molecule and which produces the stereoisomeric products in unequal amounts are formed in a substrate molecule and produces the stereoisomeric products in unequal amounts. Also, all the stereogenic quaternary carbon centers were enhanced by the desymmetrization of 2-substituted glycerols using a chiral imine/CuCl catalyst, otherwise known as copper (I) chloride.

   

     Synthesis of antibiotics such as erythromycin and azithromycin shows how the chemical structure and formula can be modified in order to change its function and its effect on the body accordingly. Although erythromycin was created first, scientists and doctors were able to enhance its molecular formula in order to enhance the process and activity in which it deals with an infected area. Also, these synthetic drugs offset and affect series of reactions such as hydrolysis, which can either interfere or not affect other processes. Overall, the synthesis of such antibiotics require much difficulty due to the fact that many factors such as the complexity of the compound or different incorporated ingredients that change the orientation of each function and process.

The Antidepressant

Kinetic and mechanistic evaluation of antidepressant medication

A Brief Overview 

Neurons in the human brain transfer information through an electrochemical process that culminates in the brain interpreting the transmitted data.  Between normal human neurons there exists a synapse through which envoy neurochemicals cross. The presynaptic, or initial neuron taking part in communication, produces chemical courier neurotransmitters. After being transported to the neuron’s external surface, these neurotransmitters are sent into the synapse and find a receptor area on the secondary, or postsynaptic, neuron. By doing so, the chemical messengers have now relayed their message, which will catalyze processes in the secondary neuron, among which include further construction of new neurotransmitters. When a surplus amount of neurotransmitters are put into the synapse, the initial neuron has the ability to reclaim this excess. Portions that go through reuptake are destroyed in the neuron and used as crude product for future undertakings. At the origin of antidepressants were the monoamine oxidase inhibitors, or MAOIs, which stemmed from the tuberculosis drug iproniazid. This medication became a treatment for depression, having the ability to obstruct the elimination of recycled neurotransmitters. A heightened sense of positive mood and energy in those who were medicated came from blockage of the enzyme that disintegrated norepinephrine, serotonin and dopamine.

Tricyclic antidepressants

In an analogous manner, tricyclic antidepressants hinder reprocessing of norepinephrine and serotonin, both expanding the success of the message in traveling to the second neuron and permitting neurotransmitter excess to remain in the synapses. Tricyclic antidepressants (TCAs) categorize a set of antidepressant medications that have homologous chemical structures and efficacy. Due to depression’s perceived roots in the disproportion of neurotransmitter levels, tricyclic antidepressants promote levels of norepinephrine and serotonin while impeding the function of acetylcholine. Anafranil, Elavil, Norpramin, Pamelor, Sinequan, and Tofranil are all
commercial names of tricyclic antidepressanst that are currently on the market, representing a now aged class of treatments combating depression. Muscarinic, histaminergic and α1-adrenergic receptors are antagonized in the action of classical TCA drugs, leading to anticholinergic (rendering inactive the neurotransmitter acetylcholine), sedative, and cardiovascular effects. In vitro, fluoxetine unites with the aforesaid receptors in the brain tissue with less efficacy than TCA drugs. As identifiable through their names, these TCAs have a three-ring chemical structure. For example,

in imipramine (tofranil), the crucial portions of antidepressant activity include the ring system, sidechain extent, and location of the substituent groups. In this way, the most vigorously occupied compounds are the secondary methylamines (organic compound) and a small amount of primary amines (functional group with a atom of nitrogen coupled with a lone pair). In terms of sedative action apart from imipramine’s antidepressant properties, the tertiary amines deal with this mechanism while not taking part in the prime purpose.

Mechanism of Action in Tricyclic Antidepressants

Selective Serotonin Reuptake Inhibitors

As opposed to TCAs, there exists a class of compounds termed selective serotonin reuptake inhibitors(SSRIs), now the most prescribed antidepressant medications in numerous countries. In the creation of the SSRIs the method of rational drug design was used for the first time among the psychotropic drug class (psychoactive drugs traverse the blood-brain barrier, affecting the central nervous system of the human body and altering brain activity), where a definitive biological mark was identified and made an objective to a treatment.  An example of a prominent selective serotonin reuptake inhibitor, working by delaying the reuptake of serotonin into the human platelets so the serotonin that is released remains for a longer period of time, is Prozac. The chemical formula of Prozac is C₁₇H₁₈F₃NO (systematic name: N-Methyl-3-phenyl-3-[4-(trifluoromethyl)phenoxy]-1-propanamine. Prozac is the trade name for Fluoxetine.  The fluoxetine molecule contains a variety of functional groups. There are two phenyl groups (benzene rings), an ether, and an amine.  Prozac is also a chiral molecule, meaning that they display a symmetry to their mirror image, often caused by the location of an asymmetric carbon atom in the general structure. This is a feature to be noted due to its usages in inorganic, organic, physical, and biological chemistry. It is metabolized by CYP2D6 by the liver, characterized by its slow rate and a long half-life in the confines of the system. Slow aggregation leads to delay in the manifestation of meaningful effect. It is also an agonist for 5HT2C receptors, linking back to the first blog post on beta-agonists.

Agonists, as aforementioned in the previous post, are chemical compounds that bind to receptor area and initiate the receptor to a form of action. Contrary to an antagonist which thwarts an action, the agonist strength is strongly linked to its half maximal effective concentration, otherwise known as EC50. This is the concentration of the substance that causes an intermediate effect between a minimum and maximal point after a definite period of time. In research regimens that follow a dose response, this represents the 50% efficacy point, and correlates to the IC50 that ascertains a substance’s inhibition. The slowing of the increasing ligand concentration response is an inflection point at which the EC50 occurs. This is pertinent due to the fact that the ligand is the functional group molecule or ion that connects to a center metal atom in the creation of a coordination complex, where there is a transfer of electron pairs from the ligand to the metal element. The bonds created in the process can be characterized as ranging from the covalent strength to ionic bonds, while the bond order is conventionally from one 1-3. In most circumstances, these ligands are also Lewis bases, and in Gilbert N. Lewis’ definition, are characterized as electron-pair acceptors that have the capacity to react with a Lewis base and result in the Lewis adduct. Furthermore, the ligand is what prescribes the reactivity of the central metal atom and redox. In conditions where the oxidation state is unclear, the ligand is non-innocent, present in heme proteins and with redox not focused on the ligand. (The innocent ligand does not change in oxidation state, for example in the the reduction of MnO₄^– to MnO₄^2-. As you can see, the transformation occurs in the change in oxidation state of manganese from 7+ to 6+. The oxide ligand remains at an oxidation state of 2-, though a meticulous analysis would show that the ligand is changed in an alternate way by the redox).

3D animated view of Prozac Molecule

The Mechanism of Prozac

 

In this post we will discuss antibiotic resistance and how different ‘superbugs’ are being created because of continued use of antibiotics.

Antibiotic resistance is the ability of bacteria to resist the effects of an antibiotic. This usually occurs when bacteria change in some way that reduces or eliminates the effectiveness of drugs, chemicals, or other agents designed to cure infections. These bacteria survive and continue to multiply, causing more harm. This resistance can cause significant danger for people who have common infections that were once easily treatable with antibiotics. Every time a person takes antibiotics, sensitive bacteria are killed, but resistant germs may be left to grow and multiply.

Here is an interesting TED Talk by Dr. Karl Klose, which describes the ‘superbug’ and how different bacteria evolve into ‘antibiotic-resistant menaces’.

The big question is how bacteria become resistant to antibiotics. There are two answers to this question. One way that bacteria become resistant to antibiotics is by mutations in DNA. These mutations occur spontaneously and can have two different effects. A change in DNA of bacteria could lead to the prevention of bacterial protein synthesis. In our previous post we discussed how antibiotics target and attack these proteins. However, if the bacteria is active without the protein, there will be nothing for the antibiotics to attack. Mutations causing variations in the shape or size of the protein prevent antibiotics from being able to properly bind to the target protein. Another change in the DNA of bacteria could lead to the overproduction of protein enzymes. This overproduction could lead to various issues. Firstly, a particular dose of antibiotics would not be able to deactivate an overproduction of protein enzymes. Furthermore, some of the proteins produced may be alter the permeability of the cell membrane of cell wall of the bacteria. Aside from spontaneously occurring mutations in the DNA of bacteria, bacteria can become resistant to antibiotics as a result of gene borrowing. According to microbiologist Doctor John Turnidge,  “They’re the original life forms almost, so for thousands of millions of years they’ve had a chance to work out ways to survive and one of those is to borrow genes from other bacteria to survive.” Antibiotic resistance can result from DNA mutations or gene sharing among bacteria. The image below explains how the population of antibiotic resistant bacteria has increased tremendously. For more information regarding the process and causes of antibiotic resistance, check out this website. 

Since the advent of penicillin in the 1940s, antibiotic use has been steadily increasing. Antibiotics are used far more than necessary; they are used as a precautionary measure ‘just in case’ or as a comfort to patients who have viral or fungal infections. According to the CDC, 50 million of the 150 million prescriptions for antibiotics annually are unnecessary. Doctors would rather sign off on a prescription than spend the extra time trying to educate patients on the strengths and weaknesses of antibiotics. In addition to that, increasing use of hand sanitizer and antibacterial cleaning agents also contributes to the development of superbugs. The excessive use of antibiotics has already started to have devastating effects. But why? In the body, antibiotics kill enough bacteria so that the body can finish the job. Shouldn’t more antibiotics just kill more bacteria? It would seem that we should always take antibiotics and heed the adage ‘better safe than sorry’, right? Wrong.

That type of thinking will only drive us towards the edge faster, and here’s why: As soon as researchers develop new antibiotics, there are always already bacteria with the capabilities to defeat them. These resistant bacteria survive the antibiotic agents to multiply and divide, passing on their antibiotic resistanceto their progeny. As a result, the same antibiotics become less effective with time and it becomes harder and harder to develop antibiotics for these so called ‘superbugs’. The most famous strain of bacteria that has risen due to increasing antibiotic use is methicillin-resistant Staphylococcus aureus, or MRSA.

The CDC is currently working to reduce the amount of antibiotics used, because unchecked, it could become a serious public health issue. Already, 2 million people in the US are infected annually by antibiotic resistant bacteria. Should antibiotics continue to be prescribed at such an alarming rate, we could face a post-antibiotic age, in which antibiotics have been rendered useless.

The Mysterious Shortage

If you’ve recently watched NBC Nightly News you may have heard of the impending helium shortage (the topic for our next post), but there is another shortage, perhaps as equally impacting as the helium shortage, that most people have not heard about. That’s because this shortage happens all the time. It is the drug shortage. Where did all the drugs go? They didn’t go to Colorado as some might suspect with the recent legalization of marijuana. These are prescription, FDA-approved drugs that are on shortage, not recreational drugs normally run by drug cartels. But what’s even more interesting is that the drug shortage isn’t a normal shortage. As explained before, these shortages occur all the time, but only to a select number of prescription drugs, and these shortages are much more temporary compared to the helium or Plutonium-238 shortage. Nevertheless, that doesn’t mitigate the impact of this constant shortage. So why is there a drug shortage? As the FDA explains, these drug shortages are due to a number of reasons, most commonly manufacturing or quality problems. As we explore both of these factors, and examples of current drug shortages, you will see how both issues can affect a large population, not tomorrow or in 2025, but now.

To understand a little more about the underpinnings of this unknown shortage, you must first understand how competitive and difficult it is to bring a drug to market. The process often takes a couple of years and a couple billion dollars. The tests for safety are rigorous and lengthy and the paperwork fills dictionaries. It is no wonder why drugs are so expensive and why drug companies will do everything they can to make more money…

So what goes into this testing process regulated by the seemingly “devilish” FDA? Once a company has created a new drug, it can begin the FDA’s Drug Review Process. To start, there are preclinical animal testings. This phase is simply to identify whether the drug is lethal at its prescribed dosage. If it kills a mouse, you certainly do not want to give it to a human. Results must be shown to and reviewed by the FDA before human trials can begin. This transition to human clinical trials is marked by an Investigational New Drug (IND) Application. The first human trial is called Phase 1 where 20-80 healthy patients are given the drug simply to gauge the drug’s safety in humans and discern how the drug is metabolized and excreted. If it is determined that there isn’t an unreasonable toxicity Phase 2 trials begin. Phase 2 tests the effectiveness of the drug compared to placebos in treating a certain ailment. Typically a few dozen to 300 patients partake in Phase 2. If the drug is determined as effective, Phase 3 begins. Phase 3 are mass testings, often with a few thousand participants. This phase tests the drug’s interaction with other drugs and once again the drug is reviewed for its safety and effectiveness. The results are reviewed and finally all phases, trials and results are reviewed in a New Drug Application (NDA). Not so bad? The entire process can take up to 12 years, and drugs have a 1 in 5000 chance of making it through the process.

What does this have to do with the problem at hand? Well, besides bankrupting any small company, the FDA regulates drugs on a much lower frequency once a drug is brought to market with the thought that these drugs are safe. However, this means that your safety is not guaranteed. Often times a demand for a drug will increase, while just as frequently a manufacturing company may close down thereby decreasing supply. This is how a manufacturing and consumerism problem can lead to a shortage. But remember, the drug company just paid, on average, 4 billion dollars to bring that drug to market, there is no way a small manufacturing problem is going to stop the drug company from selling their drug. So what might a drug company do? Come up with a cheaper, more efficiently manufactured formula for the drug and begin manufacturing that. What’s to stop them? The FDA is not due for a visit in another year – hopefully the new formula won’t hurt anyone. And that’s how quality problems arise. A simple change in the formula harms a select, but noticeable, clientele and they report the problem to the FDA. That’s when the FDA’s visit to the drug company is unexpected and a lot sooner than their annual or biannual visit. The FDA will halt all production of the drug, and begin running testings and reviews of the drug once more. So as you can see the two factors – manufacturing and quality – are interlinked and sometimes a drug company will simply pick the lesser of two evils. This makes for a very harmful shortage not only when the formula of the drug is changed, but also in either scenario when production of the drug is slowed or halted and the patientneeding the drug cannot get it.

So what are some current drug shortages, what do the drugs do and who do the shortages affect? An interesting one with many applications is Dexamethasone Sodium Phosphate Injections.

[1]

Dexamethasone is a potent glucocorticoid (the term glucocorticoid is interchangeable with corticoid or corticosteroid) and the injection of Dexamethasone Sodium Phosphate is used to treat allergic reactions, arthritis, blood diseases, breathing problems, eye diseases, intestinal disorders and more. It can also be used to diagnose an adrenal gland disorder (Cushing’s disease) since the adrenal gland is responsible for secreting corticoids. Dexamethasone and other corticoids are anti-inflammatory and is the reason why they can be used to treat ailments like allergic reactions, arthritis or skin disorders (such as bug bites). This is because dexamethasone binds to the glucocorticoid receptor – since they are complementary in structural shape [1] – which is responsible for suppressing the immune system (and heightening awareness). During times of stress, the adrenal gland releases corticoids, which bind to the glucocorticoid receptor. The body suppresses all non-essential functions (i.e. the immune system) and heightens all functions beneficial to survival (i.e. attention). This natural phenomena is used to stop inflammation, a natural immune response. It is also the reason why withdrawing from dexamethasone or any other corticoids can cause weakness and tiredness.

Because of its versatility, the dexamethasone sodium phosphate injection shortage affects many people who need a wide variety of treatments. There are 4 manufacturers of the dexamethasone sodium phosphate injection, but over half of the concentrations of the injection are unavailable from all suppliers. One concentration from a certain supplier may not recover until April, 2014 because of increased demand. Most of these backorders or unavailability began in January of 2013.

Calcium chloride injections are also in shortage, and while they aren’t as widely applicable as Dexamethasone Sodium Phosphate injections, their absence is just as life-threatening. Calcium chloride (CaCl2) is normally a crystal structure as depicted in the below two pictures.

Its crystal structure forms a rather unique cubic unit cell with a total of 2 Calcium atoms and 4 Chloride atoms – appropriately so since there should be twice as many Chloride atoms as there are Calcium atoms. 8 Calcium atoms reside in each corner of the unit cell, and since each contribute 1/8 to the unit cell, that is a total of 1 Calcium atom. Another Calcium atom resides in the center of the unit cell. What makes this unit cell so interesting though is the placement of the Chloride atoms make this cubic unit cell neither a face-centered unit cell nor a body-centered unit cell. 2 Chloride atoms reside completely within the unit cell, while 4 Chloride atoms reside on the faces, each contributing 1/2 to the unit cell which accounts for the 4 total Chloride atoms that are within the cubic unit cell.

As a solid, Calcium chloride is commonly used as brine for refrigeration plants, salt on roads to prevent ice, and desiccation, or the removal of water by chemical means. However as a liquid, the Calcium chloride injection is used for immediate treatment of hypocalcemic tetany, uncontrollable muscle contractions and spasms due to a lack of Calcium in the body, treatment for insect bites, aid for depression due to an overdose of Magnesium sulfate (which happens to be another drug currently on shortage – not because of an increase in overdoses, and the two shortages are not related) and to improve weak or ineffective myocardial  contractions when epinephrine (in injection form is also on shortage. Again, the two shortages are not related) has failed to due so (usually after open heart surgery). Calcium chloride injections are vital to both hypocalcemic tetany, since the cause of the illness is a lack of calcium, and recoveries from open heart surgeries. Again, while both diseases are rare and far less common than the diseases dexamethasone sodium phosphate injections treat, this shortage can have detrimental effects. The shortage began in December of 2012, and still has yet to recover since half the suppliers have either discontinued manufacturing calcium chloride injections, or were having trouble manufacturing enough for the increased demand.

 The final shortage worth touching upon is the copper injection shortage which is often delivered as cupric sulfate (Cu(II)SO4).

This interesting cubic unit cell is even more complex than that of calcium chloride. Again it is neither a simple cubic, face-centered cubic nor body-centered cubic unit cell but rather a combination of them all “plus more”. The copper ions reside in the corners of the unit cell, the edge of the unit cell, the face of the unit cell and in the center of the unit cell. A copper ion resides on each corner and since each contribute one eighth of an ion (8*1/8₎ that amounts to 1 ion. Next there are 4 edge cells which contribute one fourth of an ion (4*1/4) which totals another ion. Then there are 2 face centered ions which each contribute half an ion (2*1/2) which is another ion. Finally there resides one copper ion in the center of the unit cell. In total there are 4 copper ions. Further evaluation of the unit cell concludes in the fact that there are 4 sulfur ions and 16 oxygen ions within the unit cell, or otherwise 4 sulfate (SO₄^-2) ions. This makes sense since the ratio of copper to sulfur to oxygen ions is 1:1:4 and the ratio of copper ions to sulfate ions is 1:1.

Copper injections are used in IV therapies (Intravenous therapies) as a part of total parenteral nutrition (TPN). Copper is necessary, in small quantities, in a human diet and when a patient cannot eat, it is required that they receive their nutrients in another manner; IV therapies. IV therapies are used often in hospitals so this shortage may have a significant impact on hospital patients and is the reason why this may be the most urgent shortage mentioned in this blog. The shortage is not only life threatening to those who need it, but it also affects a large population. The shortage began in April of January and the sole manufacturer has halted production of the injection. The only signs of hope are Cupric Chloride injections, another form of copper injections which are expected to recover from their own shortage sometime this quarter.

Hopefully, as you can begin to see, the fairly unknown drug shortage, is a very serious problem. Luckily most shortages are due to manufacturing delays and not quality problems (perhaps drug companies are not as greedy as the public might believe), but the shortages which can last months, are still detrimental to those who need the drugs. As the problem continues unnoticed by the general public, the best we can hope for is a revamping of manufacturing of dozens of drugs on shortage to satiate the ever-increasing demand for drugs.

Manufacture of Local Anesthesia: Cocaine

by: Sol Lim, Anthony Xu, Miguel Zevallos

Introduction:

Cocaine, also known as benzoylmethylecgonine, is a very controversial drug today because although it can  be used as a local anesthetic, usually in optic or nasal surgery, it is actually used primarily as an expensive, addictive, and extremely detrimental illegal substance. It is usually seen as a white powder; typically cocaine is transported as a salt known as cocaine hydrochloride.Cocaine is a powerful nerve stimulant, as referenced in the last post, and is usually associated with euphoria, alertness, and increased energy. However, its side effects include cardiac arrests, myocardial infarctions, hallucinations, hypothermia, and through chronic usage, most likely death.

Origins:

The production of cocaine begins from the leaves of a South American plant known as the Erythroxylon coca, or coca plant. The indigenous peoples of South America have been chewing the leaves of the coca leaf for centuries, as they contain many vital nutrients, as well as several alkaloids, precursors to cocaine. The leaves of the coca plant are consumed by millions of people in the Andes, where it grows, and has no negative side effects. In fact, coca leaves are prescribed to help with altitude sickness, dizziness, and headaches. It is considered a staple crop in the countries surrounding the Andes Mountains and sold in various forms.

However, complete isolations of the cocaine alkaloid from the coca leaves was not achieved until the mid-1850’s by Friedrich Gaedcke. Throughout the late 1800’s, doctors and businessmen alike became interested in both the medicinal and the economic potential of the isolated cocaine molecule. By the early 1900’s, cocaine had become a widespread local anesthetic, and was sold commercially until its prohibition in the later 20th century.

Synthesis of Cocaine:

The illicit synthesis of cocaine involves three primary steps:

1. Extraction of crude coca paste from the coca leaf

2. Purification of coca paste to coke base

3. Conversion of coke base to cocaine hydrochloride.

Extraction: 

The most popular way of producing coca paste is through the solvent extraction technique.

In this process, coca leaves are macerated, dampened, and placed in a maceration pit. Alternately, there is a pre-mixed aqueous solution of the inorganic base which is then poured over the macerated leaves, ensuring that the cocaine is in its free-base form. A water-immiscible organic solvent such as gasoline is later added  to the already dampened coca leaves. This mixture is then either stirred occasionally for the process of 3 days or vigorously mixed, taking only several hours. One of the biggest determinants in the extraction is highly dependant on how fine the leaves were chopped up because this increases the efficiency of the transferring of the cocaine base to the solvent. After the extraction process is complete, the solvent is then removed from the mixture causing the new solution to be mostly organic with the occasional aqueous layer. this new large volume of organic solvent is then back-extracted with a significantly smaller volume of dilute sulfuric acid. This acid is essential because it converts the cocaine-free base into a new substance, that dissolves in the aqueous layer, called cocaine sulfate. The organic solvent then separates, which leaves only the dilute sulfuric acid solution of cocaine sulfate, forming a new solution called “agua rica”. An excess of base is then slowly added to the solution while stirring. This base is responsible for the neutralization of the sulfuric acid, converting the cocaine sulfate back to the free base, which leaves the solution due to its precipitation. This free base, however, precipitates out of the solution in solid form with moldy and yellowish complexion. This is what is known as the coca paste. After this process is done, the coca paste is then dried, filtered, packaged, and is ready to bes sent a lab for the next step.

Purification:

Once the coca paste is made, the next step is to convert this paste to what is known as the coke base through a purification process. The level of cocaine purity once the coca paste is made lies between 30 and 80%. The rest is made up of alkaloidal impurities and inorganic salts that are alter to be removed in order for there to be the highest possible concentration of purified cocaine. The first step in the conversion to the coke base is to redissolve the coca paste in dilute sulfuric acid. The solution formed is then titrated with a fairly concentrated aqueous solution of a powerful oxidizing agent called potassium permanganate.  This potassium permanganate is reduced to manganese dioxide when it reacts with the oxidizable alkaloidal impurities of the coca paste. Once this manganese dioxide is formed in the solution, it quickly proceeds to precipitate out of the solution. The best way to do this reaction is by slowly adding the solution of potassium permanganate to the solution of dissolved coca paste in dilute sulfuric acid and vigorously stirring. The key is to add the exact amount of potassium permanganate so that the final solution is colorless, indicating that the manganese dioxide is fully precipitated out of the solution. If too much potassium permanganate is added, it can cause in decomposition and loss of cocaine, which is the ultimate goal of the entire process. After the solution is complete, it is still acidic and therefore needs to be treated by stirring with a solution of base, for the most part ammonia. The ammonia neutralizes any and all of the remaining sulfuric acid as well as the cocaine sulfate. This final product is called the coke base and is dried, filtered, and packaged.

Conversion:

The final step is known as conversion, where the cocaine base is undergoes several chemical procedures to finally synthesize cocaine hydrochloride in its crystalline form. Unlike the previous steps, cocaine hydrochloride processing is much more dangerous as it requires the use of hazardous, rare chemicals and equipment. In order to convert cocaine base to cocaine hydrochloride, the base is dissolved into diethyl ether to create a solution, allowing the extraction of any impurities or undesirable material from the solution through filtration.  Next, hydrochloric acid is diluted in acetone and the resulting solution is mixed with the cocaine solution. The presence of hydrochloric acid allows ion-pairs to be formed with the cocaine base, precipitating cocaine hydrochloride out of the mixed solution as shiny white, flaky crystals. This precipitation process usually takes between 3 to 6 hours to fully complete the crystallization process. However, if time is limited, the rate of ion-pair reaction can be accelerated by placing the solution in a hot water bath called a “bańo maria”. Though the total reaction time is reduced to a favorable 30 minutes, the use of this technique has been reported to demean the quality of cocaine hydrochloride. After crystallization, the cocaine hydrochloride is then dried using heat lamps or microwaves and prepared for distribution.  Illicitly synthesized cocaine hydrochloride usually ranges 80%-97% purity, with many alkaloidal impurities (present in the coke base) appearing in the final product.

Bańo maria pictured above

Especially in South America, the acquiring of the solvents used in this step (diethyl ether and acetone) is difficult therefore manufacturers resort to alternatives that will be an adequate substitution. When choosing the alternatives, the manufacturers must keep three concepts in mind in order to successfully synthesize cocaine hydrochloride:

1.       Solubility of coke base in diethyl ether alternative

2.       Miscibility of acetone alternative with hydrochloric acid

3.       Insolubility of cocaine hydrochloride in combined solvent mixture (diethyl ether alternative + acetone alternative)

The most common substitutes for the solvents include methyl ethyl ketone, ethyl acetate, toluene, and so forth.

Crack Cocaine:

               A rising, popular trend in modern society is to convert cocaine hydrochloride into crack cocaine: a more potent form of cocaine has been recorded to induce a very intense high within a matter of seconds. Though the response is immediate making it addictive, it is short lived and followed by an intense period of depression and desire for more. Common impurities within crack also release toxic fumes when combusted therefore posing a health risk to using crack cocaine. Opposed to powder cocaine hydrochloride, crack cocaine vaporizes (90^o C) at a much lower temperature therefore allowing it to be inhaled and triggering an immediate response by the body to its effects. The cause for this change in melting point is a result of how crack cocaine is produced. Crack cocaine is synthesized by dissolving cocaine hydrochloride in a mixture of water and baking soda and heating the solution until all the hydrochloride is removed. The remaining product is a waxy substance that hardens when dried: crack cocaine.  The color generally ranges from white to a yellowish cream to a light brown.

Biochemistry of Morphine: How It Can Help and Hurt

In our previous blog post, we discussed the structure of morphine and other opioid analgesics.  These substances all have similar chemical structures, and these structural similarities lead to the similar effects that these opioids have.  In this post, we’ll be specifically discussing the effects of morphine on the body.  From our previous entries, it is known that morphine’s chemical formula is C₁₇H₁₉NO₃.  These elements are organized in a way often called the morphine rule, and other opioids also obey this rule. Additionally, the structures of morphine and the opioids that are derived from it are similar to endorphins and enkephalins, which are substances that the brain naturally produces. These natural substances also have analgesic effects, and since opioids are similar in structure to them, opioids also can stimulate pain receptors in the way that endorphins and enkephalins can. However, since opioids do not have exactly the same structure as endorphins and enkephalins, they are able to cause side effects. Let’s examine some of these effects.

 Biochemistry of Morphine’s Positive Effects

Pain is caused by intense or damaging stimuli. To avoid this unpleasant feeling of pain, people use morphine. Morphine is capable of blocking the pain receptor sites on the nerve cells. It is considered one of the most powerful pain relievers available, but what is the reason behind it being so effective? In this case, since the topic is about the interaction between a chemical and some receptor, there is a lock-and-key mechanism at effect. A molecule which can bind to a receptor is called a ligand, so in this case morphine is a ligand. The circumstances of the ligand being able to bind to the receptor are specific to the size, shape, and charge composition of both. There lies the idea behind the key, the molecule, and the lock, the receptor. If a ligand has the correct structure and charge to fit into a specific site on the receptor, known as the active site, it will bind to the receptor and effect some characteristic of the receptor cell, but we won’t go too deep into that. We’re here to talk about the chemistry of morphine, so let’s take a look at how morphine is the key to blocking pain receptors.

The structure of morphine is reproduced to the right. It is known as acentrally acting analgesic, a category of analgesics that includes opioids and acts on primarily on the brain and spinal cord, making it so capable of being a painkiller. As is apparent from its structure, it contains a benzene ring and various other chemical groups, such as a hydroxyl group and other carbon rings. The morphine needs a specific receptor to bind to in order to be effective. Morphine is known to bind to a specific subset of receptors known as opioid receptors. There are different types of opioid receptors such as kappa (κ)-,mu (μ)-, and delta (δ)- receptors, which differ by functional properties, side effect profiles, genes and proteins, and tissue expression patterns. These receptors are found on nociceptors, the sensory neuron cells that are responsible for sending pain signals to the brain as a response to damaging stimuli. Now that both the key and lock have been defined, the process of binding can take effect. The important characteristic to note in the structure of morphine is that the benzene ring is contained in one plane, so it is completely flat. It is perfect because it is then able to fit snugly against a flat section of the receptor’s active site. The rest of molecule falls into place easily. The neighboring carbon atoms fit into a nearby groove, while the nitrogen atom is able to attach to a negatively-charged group on the receptor, thus binding the ligand to the receptor.

The ligand has been bound to the nociceptor, so the morphine is able to work about dulling the pain. It accomplishes that by simply blocking the pain signals from being sent by the pre-synaptic neuron on the nociceptor. This is done by activating the opioid receptors, causing a reactionary change in the cell, which inhibits the production of substance P, a compound that is responsible for the synaptic transmission of pain and nerve impulses. Refer to the diagram to see a visualization of this process. However, it is a dangerous effect since the slowing of the nerve cell’s function and impulse release could lead to slowing in vital processes such as respiration, resulting in respiratory depression, a negative side effect amongst many.

This diagram is a visual interpretation of the process of blocking the release of substance P by activating opioid receptors, which morphine and endorphins can both do.

 Neurological Side-Effects and Addiction

In addition to stimulating the receptors that process pain signals, morphine is capable of stimulating other regions of the brain, especially the ventral tegmental area of the brain, which processes the release of reward compounds that are released when the human does something that aids survival. Doses of morphine are able to inhibit a process called long-term potentiation, in which the connections between neurons, or synapses, are made stronger through repeated simulation. As a result of long-term potentiation, the brain’s memory capacity is reinforced and made stronger as a result, since strengthened synapses are the basis for memory. Specifically, morphine effects the synapses between inhibitor neurons and dopamine neurons in the ventral tegmental area of the brain.

Pictured here is a dopamine neuron releasing dopamine, depicted as yellow-green circles, to a nearby neuron. Dopamine is responsible for making humans feel “good.”

Dopamine is a reward compound in the brain, being released whenever a human does something that makes them feel good, and inhibitor neurons serve to control the release of dopamine. The morphine removes the link between the inhibitor neuron and the dopamine neurons, so the dopamine neurons produce dopamine uninhibited with the connection to the inhibitor being removed. Thus, the human feels more rewarded since more dopamine is being processed by their receptors, but it takes more dopamine for the human to feel satisfied since the increased dopamine levels of the brain are imprinted into the memory since the morphine stimulates the synapse. Morphine chemically changes the brain by doing this, and it can cause dependence and addiction because of this.

Other Negative Side-Effects

Although morphine and other opioid analgesics primarily work with the brain, some of the side-effects of ingesting these substances affect different areas of the body.  These effects have a variety of causes, and many of these are independent from the structure of the opioid, contrary to the neurological effects.  Similar substances such as morphine, methadone, oxycodone, and hydrocodone can cause serious consequences as side-effects.  Some may even say that these unfortunate effects may render these drugs “not worth it.”  Many of the positive effects of these helpful drugs are only temporary.  For example, when morphine is used as a pain-killer, it is often used for only a short period of time.  The pain is temporary, and once it is relieved, the medication is no longer needed.  However, many of these side-effects are chronic.  As mentioned earlier, addiction can be caused by prolonged usage of opioids.  One’s body becomes trained to require treatment and medication in a process of addiction.  When these substances cease to be taken, the body undergoes withdrawal and many related side-effects.

Pictured here is a woman who is suffering from opioid-induced hyperalgesia after long-term opioid use.

After long-term opioid use, the body can become extra-sensitive to painful stimulation.  This condition is known as opioid-induced hyperalgesia, and although it is induced by nociceptive sensitization in the brain, it affects the entire body.  This state is caused by the inhibition of pain signals, and the alteration of the responsible receptors due to exposure to opioids.  Another long-term side-effect is particularly rampant in males.  This is the lowered production of sex hormones, notably testosterone.  Opioid-induced hypogonadism, as it is called, relates to the inhibition of the endocrine system after long exposure to opioid analgesics.  Consequently, when the body is subject to an imbalance of hormones, a domino-like effect can be caused, and in the case of opioids, people can develop osteoporosis.

These effects, both good and bad, show just some of the things that opioids can do to the human body.  Although these drugs are often used to ward off pain in medical circumstances, if used incorrectly, much like any medication, they can be devastating.  Avoid overdosing or becoming addicted to these substances, and only use them when told by a doctor.  Come back next time to read about methamphetamine, the most abused hard drug in the world, as declared by the U.N. World Drug Report in 2006, and how Heisenberg created it on the hit show Breaking Bad.

Midazolam: The Anesthetic That Makes You Forget

  It is amazing how far medicine has progressed. Can you imagine that only a little over 100 years ago the most common form of treating an illness was bloodletting? Today there are thousands of different medications and drugs available to make a successful treatment. For example, midazolam, often called by its brand name Versed, is a type of oral or injectable drug that is used prior to medical procedures. It is well known for its fast-acting anxiolytic and amnestic properties (MedlinePlus). “I use it for all of my cases from simple hernia operations to complex cardiac procedures…and I imagine [it is used in] over 95% of all cases done in the OR,” says Dr. Kaya Sarier, an anesthesiologist at the Hackensack University Medical Center. This common yet crucial anesthetic causes drowsiness, reduces anxiety, and most interestingly erases the memory of an event. How exactly? Let’s take a closer look.

The Molecule

The molecular formula for midazolam is C₁₈H₁₃ClFN₃. This specific structure with the core of a benzene ring bonded to a diazepine ring allows it to be categorized as a benzodiazepine. If you are interested, this article from the Handbook of Experimental Pharmacology gives a general background on benzodiazepine.

When midazolam is taken, it moves through the body and into the cerebrospinal fluid. There, cytochrome P450 3A4 enzymes metabolize the midazolam. The end product binds to the gamma-aminobutyric acid (GABA) receptor on a neuron. This opens up a channel, and higher concentrations of GABA are released, which bind to the GABA receptors. As a result, this causes chlorine ions to enter the neuron, and the sudden presence of electronegative chlorine ions in the neuron stops the neuron from sending signals to the brain. The neural inhibition that results is the reason why midazolam relaxes the mind and makes you forget the events that transpire under its effects. Check out the animation in this link to see how benzodiazepines react with GABA receptors.

Action Potentials

Now that the general pharmacokinetics of midazolam have been established, let’s compare it to the regular process of a neuron’s response to stimuli. Neurons have a certain point called rest potential, which is the potential difference between two sides of a neuronal membrane when the neuron is not transmitting a signal. The approximate rest potential is -70mV. Neurons naturally respond to events in the environment by depolarization, which starts by the opening of Na⁺ channels. If enough pass through the membrane and reach -55mV, the neuron will proceed to send the signal. This point is called the action threshold. Voltage-gated channels will allow more Na⁺ ions to increase the interior potential to +30mV. Then repolarization starts. The voltage-gated channels of Na⁺ close while those of K⁺ open. The K⁺ ion channels are much slower than the Na⁺ channels, and so more K⁺ions can leave the neuron. The repolarization aims to go back to rest potential, but the process will typically go to -90mV. This is called hyperpolarization. What this does is stops the neuron from receiving and transmitting any other source of stimuli during this time besides the one it is in the process of sending. If hyperpolarization did not occur, the first stimulus that is being sent may change directions and be sent back down the axon to the neuron instead of to the brain; the result would be an unceasing loop of stimuli never being processed and transmitted. The releasing and receiving of K⁺and Na⁺ ions by diffusion eventually bring the neuron back to its rest potential, the stimulus information sent. However, if the interior potential incessantly decreases, the neuron will forever be in hyperpolarization and cease to carry out its functions. A step-by-step description of this process is available on this link and this video as well.

How does this tie into midazolam? Midazolam causes hyperpolarization. The Cl^– ions that are released due to the GABA are brought into the neuron via the GABA receptors. These chlorine ions have a negative charge, causing hyperpolarization in neurons at rest potential and increasing the time needed to send a signal when a neuron is in the process of sending an impulse to the brain. Therefore, the anxiolytic and amnestic effects of midazolam at the correct dosage are not damaging, as all neurons themselves go through hyperpolarization. The main difference is that midazolam causes hyperpolarization in neurons that are not even active, eradicating any chance of an impulse being sent. This is why no stimuli are being received while under the drug’s effects, no memories to remember.

Production of Midazolam

Since midazolam is such a common drug, it is made through a relatively simple process called a condensation reaction. This process is used for producing most benzodiazepine rings, and it involves reacting two amine groups with a ketone. During this reaction, water is lost, classifying it as a condensation reaction. Sulfamic acid is used as a catalyst during the reaction to help the reactants bond and to stabilize the complex.

For the reaction itself, two amine groups bond to the ketone, forming a double bond between the nitrogen and carbon atoms. Then an intramolecular reaction occurs that forms the diazepine ring. The resulting products are benzodiazepine and water. The figure to the below shows the synthesis of a benzodiazepine from o-phenylenediamine.

Drawbacks and the Antidote

While midazolam has its benefits, there are many cases of overdosage due to various factors, such as the patient’s age and metabolism. “The most common side effect would be hypoventilation,” says Dr. Sarier. “This can happen quite often. [The anesthesiologist] would assist in the patient’s ventilation and could administer oxygen via a nasal cannula or place a mask over both the mouth and nose to force oxygen into the lungs.”

In addition to this method, research in the British Journal of Clinical Pharmacology shows that a rising alternative solution is the use of a GABA receptor antagonist/ partial agonist called flumazenil. This drug works by binding to the GABA receptors, thereby reducing the amount of receptors that the midazolam binds to. This reverses the effects of midazolam with proven swiftness of recovering from the side effects. Therefore, flumazenil has been called the “antidote” to any benzodiazepine. For more information on flumazenil, take a look at Netdoctor and PubChem.