welcome back everyone this is pup age 462 and this is topic three bio transformation so in the previous topic we learned about absorption distribution and elimination and one of the important factors in ade is the fact that the chemical property of the xenobiotic is going to have a huge influence on whether that xenobiotic is going to be absorbed or not so if it's lipophilic it's much more likely to be absorbed and distributed today's topic biotransformation is in some ways continuation from the last topic because biotransformation is part of the illumination route so we are exposed to numerous foreign chemicals and this may include both man-made or anthropogenic or even obviously natural chemicals and this could be drugs industrial chemicals pesticides pollutants byproducts of combustion even through cooking process some kind of plant alkaloids and other kinds of toxins that are produced whether it is intentionally or unintentionally we are exposed to these kind of xenobiotics all the time now if some of these antibiotics were actually very lipid soluble and we absorb it and if we don't have a real good mechanism to eliminate them they will accumulate in our bodies and will become very very toxic and there's no way without biotransformation that humans can live up to 75 years old 76 years old and the fact of matter is that we're able to live this long because we're able to remove these lipophilic xenobiotics so biotransformation is really the process in which we're able to eliminate fat-soluble or lipophilic xenobiotics from our bodies so this is a very important process and this is a topic for today's lecture so the first thing that we're going to do is actually talk about the steps in the biotransformation we'll talk about phase one versus phase two and we'll distinguish the two and how they are similar yet very different and in terms of discussing phase one we'll also talk about how phase one metabolized can result in bioactivation or detoxification so bioactivation meaning that the metabolite becomes more toxic than the parent chemical or xenobiotic that you initially absorbed so in bioactivation process the biotransform product or the metabolite is more toxic whereas in detoxification we'll talk about examples where biotransformation will reduce toxicity it will detoxify so the metabolite is less toxic than the parent compound and lastly we'll talk about factors that modify biotransformation age sex nutritional status existing disease genetic variability are various reasons why people have different abilities to biotransform these xenobiotics alright so in topic two we spent most of our time talking about toxic kinetics that is how things are absorbed we didn't really talk about the rate themselves because that would be beyond the scope of this course but we talked about some of the characteristics that will enhance absorption distribution storage and ultimate elimination the only part that we actually skipped is this biotransformation which is part of the elimination so what is biotransformation simply said it is a process that changes substances you may want to call it xenobiotics maybe chemicals that you are exposed to whatever it may be we are changing the xenobiotics so that they become more water soluble so in essence we're changing these substances from hydrophobic also known as lipophilic to hydrophilic because if you can change it into a more water-soluble chemical then you can actually eliminate or enhance the elimination through urination or even through feces this is through bile so biotransformation is a process that changes substance from hydrophobic to hydrophilic to aid in elimination obviously hydrophobic means that it hates water and hydrophilic means that it likes water and as briefly mentioned xenobiotics that are more water soluble are more likely to be eliminated by urine we can divide biotransformation process to two steps phase one biotransformation and phase two biotransformation we can't necessarily completely separate these two phases because phase one and phase two may happen at the same time matter of fact these are two separate processes with two different goals so whether we're talking about phase one or phase two the ultimate goal is to eliminate phase one reaction uses these three chemical reactions known as oxidation reduction or hydrolysis to make the xenobiotic slightly more polar usually there are always exceptions to this and also produces something we call handle where on this handle you can add a big piece of molecule which makes the chemical much more water soluble and this is what we call the phase two reaction or conjugation process so without this handle you really cannot continue phase two reaction once a xenobiotic has gone through phase two it becomes very polar and then it's much more likely to be eliminated a chemical just go through phase one and be eliminated sure that's a possibility but if the chemical does go through second phase it's going to be much more water soluble and i do want to mention that phase one can either be bioactivation or detoxification whereas in phase two this is usually detoxification yes there are exceptions to every rule but generally speaking phase one could be either activation or detoxification whereas in phase two in most cases it is a detoxification process so let's say that the chemical that you absorb initially we call this the parent compound was very toxic but if it's gone through a phase two reaction it's no longer toxic so hence it's a detoxification process so here is an example we've actually talked about benzene benzene occurs naturally as well as anthropogenically whenever there is a fire or when there are volcanic activities benzene will be produced benzene is also a very important industrial chemical often it is a starting material for producing more complex chemical products it's colorless it has a little bit of sweet odor we call these aromatics benzene is a class of compound also known as aromatics so this is what benzene looks like it has three double bonds and they rotate around hence we just make it into a circle right and sometimes we call this aromatics because it has sort of aromatic sweet fragrance and benzene is also very volatile it's highly flammable benzene according to epa is also a probable carcinogen meaning that we pretty much know that benzene is able to cause cancer in humans right we didn't have to test it on humans but with lots of epidemiologic data and with animal studies we know that benzene is a probable carcinogen well what's interesting is that benzene as a parent compound so benson here is the parent compound that's what we are often absorbing i think i did mention that benzene is also found as a contaminant in gasoline you probably know that when you're pumping gas you can actually smell sort of the fragrance of gasoline if you're smelling it you are probably exposing yourself to the toxic chemical as mentioned one of the outcomes from benzene exposure is cancer so but what's interesting as i mentioned is that benzene as a parent is not very toxic not in this form but what happens is that once we absorb benzene into our bodies and it goes into for example the liver then it goes through biotransformation one of the first things that actually happen is an oxidation process where it adds a hydroxyl group this is one of the phase one reaction or this benzene as it's going through the biotransformation can actually break open and this will be elimination safely eliminated also in this process of biotransformation benzene can add this large water-soluble molecule and become eliminated once again safely however if it happens that the byproduct of this phase one reaction is a pheno group and phenol can eventually be once again eliminated safely however if it happens to go through random reaction to produce hydroquinone and then it becomes benzoquinone this is pathway to dna mutation so in essence this guy or you can call it this guy are the more toxic form that eventually cause toxicity in this case cancer now this bioactivation process is one of various biotransformation pathways out of maybe 15-20 different biotransformation pathways there's one pathway that will lead to toxicity and this happens to be the one and everything else it's going to lead to safe elimination of the absorb benzene now when we talk about biotransformation what is a source of allowing the absorbed xenobiotic being changed into a metabolite well the answer is these are enzymes enzymes are proteins that have specific function if the xenobiotic is a substrate to the enzyme the enzyme itself then catalyze a reaction really speed up the process of the reaction to modify the substrate in this case apparent compound so this modified product is what we call the metabolite or the biotransform product so let's talk a little bit more about enzymes because if we want to understand biotransformation we have to know what enzymes are here's a good video that you can watch to help you understand what enzymes are enzymes are biological catalysts catalysts are catalysts unable reactions to occur very quickly and enzymes are what we call biological catalysts so in a chemical reaction we can add a chemical to catalyze a reaction for example by adding a little bit of heat or by adding a little bit of uv light you can actually start the reaction well that uv light or that fire may act as a catalyst now enzymes are biological catalysts so this biotransformation of xenobiotics are accomplished by various enzymes many many many different kinds of enzymes so for example what do enzymes actually do well in this case here is a substrate and in order for the substrate to do its thing it needs to break apart but on its own it's not going to break apart now in order to catalyze this break apart reaction the substrate needs to fit into the enzyme so this is like key and a lock the substrate has to have certain specific chemical 3d structure that will fit into the active site of the enzyme and if it does the enzyme itself will catalyze the reaction and then it can actually make these two things separate apart right and let's say that this is one of the active substrate that eventually will will produce something important the thing is without the enzyme the substrate will not break apart on its own it's the enzyme that catalyzes the reaction on the other hand you can also have similar reaction but in a reverse order so let's say that there are two substrates well once so this is the enzyme once these two substrates are bound then the substrate will be fused together through this enzyme so the enzyme in this case is catalyzing reaction where it's binding two different chemicals into one once again this is also an enzyme reaction so we talked about benzene already and i did mention that the benzene the parent compound itself is not the ultimate toxic agent it's not the one that actually caused cancer right it's the metabolite that does one of the elimination pathways for benzene is adding these two hydroxyl groups and once these two hydroxyl groups are added to benzene we call this chemical a catechol so how does this occur well once again it uses enzyme this is the enzyme and benzene is the substrate once again it's like key and a lot right the shape has to fit with one another once the enzyme binds to the substrate in this case benzene this enzyme is able to catalyze the reaction in which it adds two hydroxyl groups once the hydroxyl groups are added then the catechol is released and then it frees up the enzyme again to go through another enzymatic reaction and this is once again another elimination pathway so when we talk about the workhorse of all biotransformation process or reaction is carried out by these enzymes whether it is phase one or phase two another example of an enzyme this time it's called cytochrome p450 sometimes this this is one of the most important enzymes in phase one reaction we sometimes call this the sip enzyme or cyp enzyme or we call these p450 enzymes they're really the same thing same same you don't actually have to understand this enzyme reaction but i'm trying to kind of show you what these enzymes do so this is a little more detailed than the previous slide in the center of the p450 or sip enzyme is this iron and this iron has oxidation state of three plus and this is when it's not bound to a substrate the goal of this phase 1 reaction is to add a hydroxyl group or this oh group initially when the substrate binds to this p450 enzyme it did not have oh okay it only has h like carbon to hydrogen once it is bound it goes through a complex process and this happens very very quickly there's addition of an electron and there's addition of oxygen there's addition of another electron another hydrogen and etc water is released and so on eventually the substrate leaves the enzyme with this hydroxyl group attached this is one of the functions of the sip or p450 enzyme it adds that hydroxyl group this hydroxyl group increases water solubility because that oxygen as we learned from the previous topic that oxygen increases water solubility at the same time this hydroxyl group will act as a handle handle that can be used for phase 2 reaction later or if it is needed this is another example of an enzyme this is what actually happens in the liver where most sib enzymes reside so when we talk about biotransformation we're not just talking about one enzyme we're talking about various enzymes many many different enzymes so in the liver there are many enzymes and you may in fact have different metabolites depending on what that xenobiotic comes across now this is very random process let's say the chemical that you're exposed to is amylin this is your xenobiotic or this is your parent compound aniline is a chemical that is clear to slightly yellow liquid and has certain odor it's not very water soluble as you can see the only thing that will make it watercycle is that nitrogen aniline is used to make a wide variety of products such as polyurethane foam agricultural chemicals synthetic dyes antioxidant stabilizers for rubber industry herbicides varnishes and explosives now this aniline whether you're exposed through dermal pathway or whether it's exposed orally or even inhaling it's relatively toxic chemical and the disease that it causes is known as met hemoglobinemia now in red blood cells usually you have a lot of hemoglobin that allows the blood to absorb oxygen gas and release the oxygen gas to all the cells that are needed when aniline is bioactivated and cause hemoglobinemia oxygen will bind to this modified hemoglobin but it won't easily come off so that oxygen is not released to the cells that are needed hence it causes oxygen deprivation in the human now depending on what enzyme aniline come across for example if it comes in contact with this particular enzyme called anhydroxylase it turns into phenohydroxamine once it's turned into phenohydroxamine it causes met hemoglobinemia however if aniline comes across p450 or the sieve enzyme really did really they're the same thing then it ends up producing a compound known as aminophenol and aminophenol is less toxic metabolic compared to phenohydroxamine therefore this is safer pathway unfortunately the liver doesn't really have a brain it doesn't choose p450 to come in contact with andolin this is all random chance if aniline happens to contact anhydroxylase then it forms a toxic chemical if it happens to come across p450 then it forms less toxic chemical normal blood has this color but with increased hemoglobin the color of the blood changes to more like a dark chocolate brownish color it's a sign that the hemoglobin has been modified and that modified hemoglobin cannot release oxygen very well hence it's not distributing the oxygen gas so let's talk about phase one and phase two reactions and i did mention that phase one reaction increases polarity slight polarity slightly increase water solubility right whereas in phase two is large increase right so phase one reaction adds a handle and usually this handle has a polar atom hence adding a polar atom makes the xenobiotic more water soluble and these handles sometimes more formally we call these functional groups can be this oh group known as hydroxyl sh group known as a thio group nh2 known as amino group or cooh known as carboxyl group all of these are functional groups they become a handle but in addition to becoming a handle they also increase the water solubility slightly and i'll try to explain these functional groups or handle using an analogy of this a trailer hitch phase 2 reaction also involves enzymes but we call this a conjugation phase or conjugation process it adds a large bulky water-soluble molecule called conjugate and by adding this large bulky water-soluble molecule to the xenobiotic the whole molecule becomes very water soluble and phase two is often known as detoxification process because adding that large water soluble molecule makes it no longer toxic so this is one way to describe this biotransformation enzymatic reactions phase one and phase two let's say the xenobiotic that you're exposed to let's say it's benzene well benzene is very very lipophilic right if it's lipophilic it's much more likely to be absorbed even without carriers or channels through passive diffusion it will be absorbed and it will be distributed and if you have no way of eliminating benzene and there's accumulation of benzene in your body after a while it's going to cause toxicity and you can die from it right even before you get cancer that's chronic exposure you'll have acute exposure because of the fact that you cannot eliminate it okay so this biotransformation process will enable an organism to remove these lipophilic xenobiotics so a benzene is very lipophilic but in order for an organism to eliminate it you have to turn that into hydrophilic why does the xenobiotic have to be hydrophilic in order to eliminate it why can't you eliminate it when it is lipophilic well think about the elimination pathways what are the major routes of elimination the first one is urination urine that's one of the most important elimination pathway number two is your feces number three is respiratory out of these three urine is the most important feces is also very important too and in order to eliminate xenobiotic the xenobiotic has to dissolve in urine and also in feces now this is in the form of bile so in order to eliminate the xenobiotics we have to make it more water soluble so the biotransformation process makes the xenobiotic more water soluble so what was very lipophilic if it goes through phase one it becomes slightly more water-soluble right so at the end of phase one process it may be sufficient enough that it could be dissolving water maybe not okay it's less lipophilic it's slightly more hydrophilic and these are the oxidation reduction hydrolysis so it could be eliminated but if it's not water soluble enough it's going to have to go through multiple phase one reactions or a conjugation reaction where at the end of the conjugation or phase two reaction the metabolite or the modified compound becomes very hydrophilic very water soluble so that it can be excreted so in order for an organism to excrete the xenobiotics that are very lipophilic we have to turn them into more water-soluble product and this is what biotransformation does so here's an analogy that i'm going to use to help you understand this concept of biotransformation let's say that the xenobiotic that you are exposed to is like a truck and this truck or the xenobiotic is very lipophilic it's not charged it's not water soluble because it's not water soluble it's poorly excretable we can easily absorb it but we can't really get rid of it so how can we get rid of this truck or xenobiotic well we have to make it more water soluble how do we do this the first step is to add a hitch meaning that this hitch is acts like a handle because ultimately what you might need to do is to add a conjugate molecule in order to add the conjugate molecule you need to have a hitch and phase one reaction adds or exposes a functional group which we also call it a handle or a hitch okay so what is added after the phase one reaction is this hitch an example of a hitch is a hydroxyl group and that oxygen makes it more water soluble so the product after the phase one reaction is slightly more water soluble but probably still lipophilic it could be also more reactive or could be more toxic or it could be less toxic and most likely because it's not water soluble enough that it's still very poorly excretable and the phase one reaction is often catalyzed by p450 or sip enzyme or something right so chances are you might not be able to eliminate it just going through the phase one reaction the next step in the biotransformation is to go through the second phase and using the hitch you're able to add a bulky groove by adding this trailer now to the hitch now the whole compound is no longer lipophilic it's now water soluble and usually it's not reactive because because phase two reaction usually causes detoxification and it's very excretable because it's more water soluble now that the xenobiotic has gone through both phase one and phase two the modified xenobiotic or the metabolite is now more water soluble more excretable and less toxic this is biotransformation well now let's use benzene as an example instead of the truck this benzene is like a truck right it's very lipophilic right it's not charged it's not water soluble and it's poorly excretable when it goes to the phase one reaction it adds a functional group in this case it's a hydroxyl group so adding that oxygen makes it slightly more water soluble but chances are it's not water soluble enough to eliminate this phenol this is phenol but this hydroxyl group can also act as a handle or a hitch now it's able to go through phase two reaction where sorry i accidentally erased it now when it goes through the phase two reaction and on this handle you can add a very bulky water soluble group in this case it's a sulfonation group or sulfate group you can see that all of these are water soluble or polar atoms right so the whole thing now becomes much more water soluble you can actually now put this in water it's no longer lipophilic it's not used reactive and it's also excretable hence you're able to get rid of the xenobiotic in this case benzene that you initially were exposed to watch this video it's very important for you to understand the biotransformation process what phase one means and what phase two means okay let's go into a little more detail about phase one reactions i mentioned that some of the reactions that are involved in phase one are these three types the most important phase one reaction is called oxidation one of the easiest way to think of oxidation is that oxygen is added or you can also think in terms of when hydrogen is removed then it could also be an oxidation process as well hydrolysis is addition of water and you're in in essence you're adding oxygen reduction is a little bit more complicated but the best way to think about reduction is is a process in which electrons are added and easiest way to visualize reduction is when hydrogen is added when hydrogens are added it means that usually electrons are also added another way to think about it is when oxygen is removed but this isn't a chemistry class i'm not really going to ask you whether there was an oxidation reaction or reduction process but remember that oxidation hydrolysis and reduction chemical reactions are all phase one reactions and what's really happening here is that of course in most cases it increases the water solubility slightly but not always sometimes reduction process can make it less water soluble but the important thing in all of these chemical reactions is that they all add a handle in the case of reduction it actually reveals a handle so these are some of the functional groups these are handles handles that you need to know right you should be able to pick out these handles from a chemical structure one of the most important handle or the functional group that you'll typically come across is this oh group it's also known as hydroxyl group okay you may also have this cooh also known as carboxyl group so this whole thing is a handle right this whole thing is the end you can also have an amino group nh3 nh2 you can also have a sulfur hydro group also known as thio group or you can have a phosphate group this r represents some kind of carbon a chain of carbon you can also have an mi group is another functional group or handle you can also have a sulfate group so these are all examples of functional groups so in phase one reaction these functional groups will be added or revealed so handle is in essence created and in most cases to modify the xenobiotic or the metabolism itself becomes slightly more water soluble what are some of the functional groups that you see here there's the amino group known as amine here's the hydroxyl group here's the mi group here's a carboxyl group and here's another carboxyl group so this chemical is known as folic acid in glutathione which we'll talk about in phase two here you have the carboxyl group now sometimes it's a little bit more challenging because you look at the hydroxyl group it's like oh this is hydroxyl group but in fact if it's bound to carbon and double bond oxygen like this you have to think of it as oh this is carboxyl okay here's the amino group there's the ani group there's a sulfur hydro or thio group here's another amide here's another carboxyl group glutathione is very very waterside but in fact one of the conjugate molecules that's used in the phase two reaction to make it like a trailer in the analogy that i previously discussed is a glutathione because glutathione as you can see it's very very water soluble fad is another molecule i'm not going to go through all these but you've got now lots of hydroxyl groups here you've got the phosphate groups you have the amino group and you've got more hydroxyl groups okay so all of these are functional groups and through the phase one reaction you can add these functional groups or reveal these functional groups so let me provide you with some phase one oxidation reactions at this side represents just a phase one reaction right after you go through the phase one reaction you make it slightly more water soluble it could also be a little bit more toxic or in fact it could be less toxic hypoxanthine is a naturally occurring trend derivative when it is oxidized it can become xenthine xenthine is a precursor to some stimulants like caffeine but addition of this oxygen is therefore an oxidation process here's second oxidation process has another oxygen group there right by adding oxygen it's an oxidation process as i mentioned oxidation either adds oxygen or removes hydrogen lignocaine is also known as lidocaine it's used as a local anesthetic when lignochain goes through the phase one of the biotransformation it becomes hydroxyl linokine and in this case you add this hydroxyl group so this is an oxidation process it increases slightly the water solubility but it also produces a handle carbero is an insecticide when carburetor is biotransform through phase 1 reaction you add a hydroxyl group in this case it's a 4-hydroxyl carbaryl it's gone through an oxidation process you've added an oxygen in this case in the form of a functional group known as hydroxyl group four hydroxyl carbaryl is more water soluble than the parent compound carbero so this is slightly different looking reaction codeine is a pro drug once coating is metabolized it becomes morphine so this is also an oxidation reaction known as oxidative de-alkylation so what's happening is that you're removing this ch3 group and it becomes this well you're not really adding oxygen but i did mention that another way for the oxidation process to occur is when you remove hydrogens so in fact not only have you removed carbon but also you removed two hydrogens in the process and hence this is an oxidation process what it has done is that it has revealed the handle and also made it slightly more water soluble aflatoxin is a putin liver carcinogen it is produced by mold but like benzene the parent compound is not the ultimate toxicant it's not the one actually that causes cancer the ethyl toxin itself is not toxic but once it goes through the biotransformation in this case through phase one reaction it's done by p450 enzyme it forms an intermediate in which it can bind to the dna of liver cells and the binding of this highly active intermediate known as aflatoxin b189 epoxide will cause mutation and it leads to cancer so he adds this epoxide this funky looking chemical is an epoxide sorry i'm just redrawing this and the epoxide themselves are very temporary it's quite reactive and if this ethyltophane b189 epoxide did not come in contact with the dna it would actually break apart and it will become most likely like this by adding another oxygen group and in that case it becomes less toxic but in this epoxide form it can actually bind to dna and cause mutation but i guess the point of this reaction is to show you that we've added the oxygen group and this is oxidation process another reaction category within phase one is known as hydrolysis hydrolysis is basically adding water and often by adding water you break apart the chemical and when you break apart the chemical you end up producing or revealing the functional groups or the handles like lidocaine procaine it's also a local anesthetic when it goes through the phase one reaction in this case hydrolysis by adding that water you actually break this bond and you form protein into two separate compounds one has a hydroxyl handle and the other has carboxyl handle reduction as i mentioned is a little bit more complicated it's harder to catch but the best way to think about reduction is when you see hydrogen being added it's usually a reduction process protocell is an antibacterial drug and then it becomes less active when it is reduced through phase one reaction in this case the nitrogen will break and the hydrogens will be added so one of the things that happened in this reduction reaction is that it produced two handles we've created two amine or amino groups okay it's a reduction process because you added four hydrogens here is another reduction process here's antibiotic as well and this reduction process by adding hydrogen you once again reveal this amino group we talked a little bit about aniline right how it causes met hemoglobinemia the precursor molecule in mass-producing aniline is nitrobenzene nitrobenzene goes through reduction process eventually you've added the hydrogen groups and this is the functional group right amino group that's added addition of these hydrogen groups is known as reduction process hello peridol is a antipsychotic drug and this goes through a reduction phase one reaction this is how oxygen that's double bound carbon then is reduced to a hydroxyl group hydroxyl remember that hydrogen is added that makes it reduction process here's another example you've got this aldehyde group c double bond to oxygen it is reduced to the hydroxyl group once again you've added that hydrogen oops added that hydrogen that makes it reduction process i don't expect you to recognize reduction process that's a little bit more challenging but at least you should know the oxidation process once you when you see an oxygen or a hydroxyl handle being added you should know that is an oxidation process in terms of reduction it's probably a little bit more complicated and beyond the scope of this course but you should know that reduction is part of the phase one reaction so i mentioned that the most important enzymes that's used in the phase 1 reactions are these sip enzymes or also known as p450 enzymes cytochrome p450 enzymes are the most important in biotransformation in terms of catalytic versatility and the number of xenobiotics that can metabolize and most of these sip enzymes are in the liver in the endoplasmic reticulum there are many different families of the sip enzymes or p450 enzymes sorry i tend to just interchangeably use p450 and sip there are actually 36 families and in total there are more than 400 different kinds of unique sit enzymes but there are a few that are really important compared to others for example sit1a2 is one of the most important sip enzymes it will metabolize many things like caffeine tylenol and other kinds of xenobiotics including different kinds of drugs so depending on what type of chemical it is and what its structure is it's going to use various different kinds of sit enzymes and one of the important functions of the liver is to bio transform these xenobiotics so that we can eliminate them safely so there are various enzymes that's involved in the phase one reaction as i mentioned about sip 1a1 also two very important sip enzymes include sip to c9 and sip to d6 so these three will really catalyze many of the phase 1 reactions so most phase 1 reactions are catalyzed by sip or p450 enzymes but there are some non-zip enzymes or non p450 enzymes that's also catalyzes phase one reaction which we won't really go into another important process that happens during biotransformation that we need to touch upon is something called enzyme induction enzyme induction is an increase in enzyme concentration that's caused by exposure to a drug or some kind of environmental xenobiotic so let's say that you're exposed to certain type of chemicals and there's some forest fire and maybe you're barbecuing and you are exposed to lots of these combustible byproduct known as polycyclic aromatic hydrocarbons or known as pahs well phs are also carcinogens so as soon as you absorb phs in order to protect your body your body needs to eliminate it and phs are very very lipophilic so it's a c1a2 enzyme that biotransforms the phs well when you are exposed to high levels of phs what ends up happening is that the large presence of phs in your liver causes the induction of the sip 182 enzyme meaning that your liver will recognize that there are many phs and then it calls for backup the receptor will tell the dna to produce more c1a2 enzyme and in short period of time more of these sip1a2 enzymes will be available to metabolize the pahs right the sip 1a2 is induced in order to protect the organism because there's high presence of pahs another example of induction is that when you drink alcohol initially your body doesn't have a lot of alcohol dehydrogenase alcohol dehydrogenase is one of the phase one enzymes once there's high presence of alcohol in the liver your liver will induce the production of more alcohol dehydrogenase so that you can break down all of the alcohol that are absorbed into the blood okay it's an induction process phenobarbital is a sedative to treat anxiety epilepsy and insomnia rifampin is an antibiotic that's used to treat tuberculosis and both of these drugs are metabolized by sib 269 and they are able to induce sib-269 so in the case of drugs you would rather not have induction right because the induction of c2c9 enzyme will lower the bioavailability of phenobarbital and rifampin but your liver really doesn't have a brain it doesn't really are able to tell difference between toxic chemical or non-toxic or beneficial drug the only thing that i really wants to do is to make them more water-soluble to get rid of them not only is there induction there's also inhibition so certain type of chemicals can inhibit the action of enzymes so enzyme is in essence blocked by certain chemicals and this inhibition sometimes can be useful so if you can inhibit sip to c9 enzyme and increase the bioavailability of phenobarbital and rifampin i suppose that's good right but once again trying to purposefully inhibit enzymes is like treading on a thin ice it's like a double-edged sword one of the well-known chemical that can inhibit multiple enzymes is found in grapefruit in fact this chemical is able to inhibit sip3a4 it inactivates metabolizing intestinal enzymes not only are sip enzymes found just in liver civ enzymes are found in kidneys they're fine in the respiratory epithelial tissue as well as in the small intestine well grapefruit inactivates metabolizing intestinal enzymes that can result in intense activity and possible toxicity when a pharmaceutical company designs a drug and the dosage of the drug it includes the fact that it expects certain amount of the drug will be metabolized in the intestine now if a person drinks grapefruit at the same time taking this drug grapefruit will inactivate let's say sip 3a4 in the intestinal enzyme and now there's higher bioavailability of this drug and more of it will enter into the bloodstream can cause toxicity because now this can lead to overdose right can you see how dangerous this could be enzyme inhibition caused by drinking a cup of grapefruit can last as long as 72 hours so many hospitals and health care centers have taken grapefruit products off the menu entirely if they know that there's interaction between the drug and the enzymes that are inhibited by grapefruit they will tell the patients not to drink grapefruit besides grapefruit there are other drugs that can interact with enzymes as well for example cipro is one of the antibiotics will inhibit sib1a2 enzyme meaning that if you are exposed to other xenobiotics that are supposed to be metabolized by sit 1a2 but if you were to take cipro at the same time c1a2 in your liver will be deactivated or inhibited and now there's going to be higher bioavailability of other drugs that are supposed to be metabolized by c1a2 so these are the drugs that are known to interact with grapefruit juice here's an interesting video from fda anxiety drugs like xanax depression drugs allergies medicine like allegra cough medicine uh drugs for hiv asthma ideophiline is one of the drugs that's used in asthma treatment a lot of people take medication for high cholesterol lipitor is one of them and grapefruit interacts with enzyme that is supposed to metabolize lipitor and other kinds of heart disease drugs so grapefruit juice can interfere with many drugs that are commonly used by many people now let's talk about the second phase of the biotransformation process known as phase two it's also known as conjugation reaction xerobiotic that have gone through phase one biotransformation and it adds this handle you know what in fact the xenobiotic may already have a handle even before it has gone through phase one in that case phase two can happen right away because the handle is already present so on this polar handle you can add a conjugate group after a xenobiotic has gone through the phase one reaction the metabolite is now slightly more hydrophilic in nature but often it's not hydrophilic enough so that it requires the second phase of the biotransformation process hence the conjugation process it's like adding that big trailer that makes the whole thing very water soluble so these are the common chemical groups that are added in the phase ii reaction and these are all relatively very water soluble not all of them are completely water soluble you'll find that some of them like acetyl group is not as water soluble as some of the other ones but typically the idea is that they're increasing the water solubility of the xenobiotic glutathione is one of the most important conjugate chemicals and another important conjugate molecule is glucuronide amino acid and the sulfate group so this addition of very water-soluble chemical groups to a lipid-soluble xenobiotic or metabolite that has gone through a phase one reaction makes the whole molecule very water soluble so that you can eliminate it via kidney or via feces through bio all right let's talk about how glucuronide is conjugated to a xenobiotic we call this process glucuronidation here's an enzyme called transferase and this transferase will transfer the glucuronide molecule to the xenobiotic and this transferase is known as ugt so in the first example here is a benzoic acid remember this is your carboxyl handle on this carboxyl handle the transferase will add this glucuronide to benzoic acid here's the glucuronide group and it adds it to the carboxyl handle benzoic acid was slightly water soluble because the carboxyl group now that you've added the glucuronide now the whole thing is much more water soluble glucuronide is in essence a glucose like sugar and sugar has many hydroxyl groups that makes it very water cyber like sugar dissolving in water here's another example ph stands for a phenyl group an example a phenyl group is an aromatic group you can add the glucuronide group to this amino group so this transferase will add glucuronide group to the xenobiotic and now everything is much more water soluble although they look slightly different it's just the way you draw these structures but they're actually the same thing here's another transferase that can transfer the sulfate group we call this sulfonation or sulfation here's an example here's a phenol and what the transfer is you're able to add onto this handle this sulfate group and we call this sulfonation or sulfation mdma which later we'll talk about is also known as ecstasy when ecstasy is orally absorbed phase one reaction will occur viacip enzyme and here is the metabolite after the phase one reaction you reveal these two handles now you have two handles where you can add the conjugate group so in the phase two reaction you can see that you can add a sulfate group here or here so this phase two sulfation reaction has occurred now the whole thing is much more water soluble acetylation is another phase two reaction in which it has an acetyl group an acetyl group looks something like this as you can see right here and in this reaction it adds an acetyl group to lysine one of the amino acids and this is your acetyl group unlike other conjugate reactions acetylation doesn't increase the water solubility dramatically not by much however it is considered one of the phase two conjugate reactions now glutathione conjugation is one of the most important conjugate reactions glutathione is a very very large molecule that is very water soluble this whole structure is actually glutathione and because glutathione is a such large water soluble molecule instead of writing the whole or drawing the structure we often use g to refer to glutathione group as such so if x is your xenobiotic and this is your glutathione then the conjugate reaction will result in the glutathione plus the xenobiotic and we can in some ways we can also say it looks like this that would represent the glutathione conjugate this is a metabolite of benzoate pyrene which we have briefly mentioned and once one of the intermediates and one way to eliminate this very lipophilic compound although there are three oxygens here it's just not water soluble enough by adding glutathione to one of the handles you can make the whole thing very water soluble so that g represents once again glutathione and the last conjugate reaction is known as amino acid conjugation many amino acids are water soluble and by adding a water-soluble amino acid group you can actually help increase the water solubility of the xenobiotic complex an example of amino acids that can be added include glycine taurine as was glutamine here is your xenobiotic and you ultimately add glycine to this compound and it makes it much more water soluble in this reaction you're adding aspartate another very water-soluble amino acid okay so this amino acid conjugation like other conjugation process it's adding a trailer and it's making the whole thing much more water-soluble all right so this is an example of combination of phase one and phase two reactions the r represents some kind of carbon so so it could be a chain of carbon so that's why we don't actually use c in this case so r represents a chain of carbons and if it's chain of carbons you know that this is very lipophilic so the phase one reaction if this is an oxidation process it will add a hydroxyl group and by adding hydroxyl group sometimes we call this hydroxylation but it's an oxidation process so you've added the hydroxyl group now that you have the handle it can go through the second phase of the biotransformation is this more water soluble than this yes slightly but probably not water soluble enough for an organism to eliminate it in urine so using the handle it can go through the second phase and there are many choices so this upper pathway is able to transfer a sulfate group and onto that hydroxyl handle you've added a sulfate group or it can also go through glucuronidation or you're adding a glucuronide to the handle so here's the handle and this is your glucuronidal now the whole thing is water soluble one more example you've got a different kind of xenobiotic and this is very lipophilic in this case instead of adding a hydroxyl group you've added an oxygen in this you guys remember what this is called this is called epoxide oxide is relatively reactive okay but you've added that oxygen in so it's an oxidation process now with that as a handle you can add a glutathione group so this whole thing is the glutathione group now the complex itself is much more likely to be water-soluble so you can eliminate it in urine this table provides a brief summary of phase 1 and phase 2 reactions so what are some differences between phase one and phase two phase one includes hydrolysis oxidation of course there's also reduction right phase two is known as conjugation increase in water solubility is very small for phase one reaction but it's much larger for phase two reaction the general mechanism for phase one is that it adds a functional group or exposes a functional group but in phase two reaction it adds a large polar compound or molecule to the functional group or this handle that was created in phase one so it makes it much more water soluble the consequence is that after phase one it's slightly more water-soluble probably but it also may result in bioactivation or the metabolite could be more toxic than the parent compound or it could be less toxic detoxification and but in phase two it's usually detoxification in addition it facilitates the excretion so this is an important diagram that you need to understand this summarizes all of the potential not all but the important pathways of xenobiotic elimination so let's talk about some of these different pathways let's say that your xenobiotic is already water soluble right if it's water soluble then it may not need to go through any of those biotransformation reactions so in fact even without biotransformation it could be eliminated why because the xenobiotic was already water soluble right that's one pathway what's another pathway well let's say the xenobiotic is very lipophilic but somehow it was able to pass through the liver without being biotransformed so instead of being eliminated it gets stored let's say in adipose tissue or fat tissue so that's another pathway let's suppose that the xenobiotic is very lipophilic right the xenobiotic in fact has low handle okay in that case because it has no handle and because it's very lipophilic right that it would have to go through the phase one reaction to add a functional group so let's say a hydroxyl group is added depending on the size of the xenobiotic perhaps adding just one hydroxyl group can be eliminated that's one pathway however if the x the xenobiotic itself is relatively large and adding one hydroxyl group isn't really going to increase the water solubility then it would have to go through eventually phase two reaction well of course one pathway this doesn't include is that it can go through additional phase one it can go through multiple phase one right and even without going through the phase two reaction perhaps having multiple phase one reactions might be enough for it to solubilize so that's a pathway that's not actually included in this schematic but to keep things simple right after the xenobiotic has gone through one phase one reaction and it's not enough to be water-soluble then it has to go through phase two reaction once it has gone through phase two reaction you've added the conjugate group and now it's water soluble then it could be eliminated so that's sort of the second pathway now another pathway let's say the xenobiotic already has a handle so if it has a handle then now it has a possibility of going through the phase two reaction so that's one mechanism so just because a xenobiotic already has a handle does it mean that it cannot go through a phase one reaction no it can actually go through another phase one reaction and add another let's say handle okay that's a possibility and if this product is water soluble enough that you might be able to eliminate it if not it needs to go through the phase two reaction and then it's eliminated right so that's the same pathway once again what i didn't mention is that yes it can go through multiple phase one reactions right so does that make sense it's this is an important diagram that you need to understand all the major important biotransformation pathways