BIOTRANSFORMATION OF DRUGSContents PART A: Biotransformation reactions Introduction Phase I reactions Phase II reacions The effect of biotransformation on the biological activity of drugs: How the biological (pharmacological and toxic) activity of the metabolite compares to that of the parent compound? PART B: Alterations in biotransformation Biological alterations - Decreased biotransformation capacity in neonates - Genetic alterations in biotransformation Mutation or multiplication of genes coding for drug metabolizing enzymes – possible consequences Chemical alterations - Induction of CYP – possible consequences - Inhibition of CYP – possible consequences INTRODUCTION ELIMINATION MECHANISMS Physical mechanism: Chemical mechanism: EXCRETION BIOTRANSFORMATION CONTRIBUTION OF EXCRETION AND BIOTRANSFORMATION TO ELIMINATION OF DRUGS - examples Drugs NOT biotransformed, Drugs excreted both Drugs fully biotransformed, excreted unchanged unchanged and as metabolites excreted only as metabolites Benzylpenicilin Aminoglycosides Salicylates TCADs Metformin Acetaminophen Phenothiazines Tubocurarine Phenobarbital Chloramphenicol Amantadine The sites of biotransformation: Predominantly, the liver The liver contributes to both the presystemic and the systemic elimination of many drugs. Often other tissues, as well. e.g., in intestinal mucosa cells presystemic elimination of several drugs in renal tubular cells, etc The colon, by bacteria - e.g., azo reduction, hydrolytic reactions BIOTRANSFORMATION: classification Phase II reactions Phase I reactions (conjugations) 1. Glucuronidation 1. Oxidation 2. Sulfation 3. Conjugation with glycine (Gly) 2. Reduction 4. Conjugation with glutathione (GSH) 3. Hydrolysis 5. Acetylation 6. Methylation The chemical role of Phase I and Phase II biotransformations: An organic acid (or acetyl or methyl group) A functional group is added to the molecule is conjugated to the molecule or explored in the molecule at a preexisting functional group or at which conjugation can take place at a functional group acquired in Phase I biotransformation General examples R-O-glucuronic acid oxidation RH O R-OH R-O-sulfonic acid R-CH2-O-glucuronic acid reduction R-HC=O 2H R-CH2-OH R-CH2-O-sulfonic acid hydrolysis R-O-glucuronic acid R1-O-(C=O)-R2 HOH R1-OH R-O-sulfonic acid The pharmacological role of Phase I and Phase II biotransformations: How the fate and effect of metabolites compare to the fate and effect of the parent drug? Phase I metabolites Phase II metabolites (conjugates) Water-solubility: (slightly faster excretion) Water-solubility: for 1-4: (rapid excr.) for 5-6: (slower excretion) Biological activity: in general Biological activity: almost always but often very seldom Part A. BIOTRANSFORMATION REACTIONS 1. PHASE I BIOTRANSFORMATIONS 1.1. OXIDATION 1.1.1. Microsomal oxidation 1.1.1.1. CYP-catalyzed reactions 1.1.1.1.1. Oxigenation 1.1.1.1.1.1. Insertion of oxygen produces a stable oxigenated metabolite 1.1.1.1.1.1.1. C-hydroxylation: aliphatic hydroxylation, aromatic hydroxylation 1.1.1.1.1.1.2. N-hydroxylation 1.1.1.1.1.1.3. Epoxidation 1.1.1.1.1.2. Insertion of oxygen produces an unstable oxigenated metabolite which undergoes spontaneous cleavage into two molecules 1.1.1.1.1.2.1. Oxidative dealkylation (N- and O-dealkylation) 1.1.1.1.1.2.2. Oxidative deamination 1.1.1.1.1.2.3. Oxidative dehalogenation 1.1.1.1.1.2.4. Oxidative desulfuration 1.1.1.1.2. Dehydrogenation 1.1.1.1.3. Reduction (reductive dehalogenation) 1.1.1.2. FMO-catalyzed oxidations 1.1.2. Non-microsomal oxidation 1.1.2.1. MAO-catalyzed oxidations 1.1.2.2. Oxidations catalyzed by molydenum-containing oxidases 1.1.2.2.1. Xanthine oxidase-catalyzed oxidations 1.1.2.2.2. Aldehyde oxidase-catalyzed oxidations 1.1.2.3. Alcohol dehydrogenase and aldehyde dehydrogenase-catalyzed oxidations 1.2. REDUCTION 1.2.1. Azo-reduction 1.2.2. Nitro-reduction 1.2.3. Carbonyl-, aldehyde- and aldose-reduction (by aldo-keto reductases; AKR) 1.3. HYDROLYSIS 1.3.1. Hydrolysis by carboxylesterases 1.3.2. Hydrolysis by alkaline phosphatase 1.3.3. Hydrolysis by paraoxonases 1.3.4. Hydrolysis by epoxide hydrolase (illustrated under epoxidation) 1.3.5. Hydrolysis by microbial hydrolases in the colon 2. PHASE II BIOTRANSFORMATIONS (CONJUGATIONS) 2.1. GLUCURONIDATION 2.2. SULFATION 2.3. CONJUGATION WITH GLYCINE 2.4. CONJUGATION WITH GLUTATHIONE (Glu-Cys-Gly) 2.5. ACETYLATION 2.6. METHYLATION PHASE I BIOTRANSFORMATIONS OXIDATION - summary MICROSOMAL NON-MICROSOMAL catalyzed by: catalyzed by: Cytochrome P-450 (CYP) Monoamino-oxidases (MAO) - mitochondrial Mo-containing oxidases (cytosolic): Microsomal flavine-containing Xanthine oxidase (XO) and Aldehyde oxidase (AOX) monooxigenase (FMO) Alcohol- and aldehyde dehydrogenases (ADH, ALDH) - cytosolic OXIDATIONS CATALYZED BY CYTOCHROME P-450 (CYP) CYP is a heme-containing protein embedded in the membranes of the smooth endoplasmic reticulum (SER), the fragments of which in a tissue homogenate are sedimented after ultracentrifugation (at 100,000g) in the microsomal fraction. Origin of the name cytochrome P-450: Cytochrome: it is a coloured intracellular protein P: it is pink 450: its absorption spectrum has a maximum at 450 nm CYP constitutes a superfamily of enzymes that are classified into families (numbered) and subfamilies (marked with capital letters), the latter of which contain the individual enzymes (numbered), e.g., CYP1A2, CYP2C9, CYP2D6, CYP3A4. respectively. acetaminophen (=paracetamol). removal of 2 H atoms from a drug molecule (this is how the reactive hepatotoxic paracetamol metabolite is formed). ammonia.CYTOCHROME P-450 (CYP)-CATALYZED REACTIONS Mechanisms CYP is an extremely versatile enzyme as it can catalyze numerous types of reaction. . oxidative dehalogenation. nifedipine. Oxygenation involves insertion of an O atom (from O2) into a C-H bond. whereas the 2nd O atom is reduced to HOH by NADPH-CYP red. i. _ e II.g. As catalyzed by CYP. A hydroxylated metabolite may be stable. reductive dehalogenation of CCl4 2+ 2+ NOTE: The second electron is not Fe O2 Fe O 5 4 _ _2 transferred to the CYP-bound RH e [RH] oxygen. DEHYDROGENATION e. these reductions are also shown here. but to the drug molecule. forming a hydroxylated metabolite. forming a hydroxylated O2 HOH metabolite in step 7. such reactions are called oxidative dealkylation. From this. REDUCTION e. using 2 H atoms RH2 R from the drug molecule. Catalytic cycle (simplified): 1 Substrate (RH) Product (ROH) 3+ Fe 3+ 3+ 7 Fe In the course of oxygenation Fe 2 ROH by CYP. _ The first reactive form is e the hydroperoxy form (produced in step 5). or into a C=C double bond. OXYGENATION .the most typical CYP-catalyzed reaction CYP General scheme: RH + O2 + (NADPH + H)+ R-OH + HOH + NADP+ NADPH-CYP reductase Note: 1 atom of O2 is inserted into the drug. or unstable.g. 1 O is inserted into a water molecule (HOH). ethanol 3+ NOTE: The 2nd O atom is also (FeO)3+ Fe 6 7 reduced to water. nitro reduction of clonazepam. and oxidative desulfuration. From an unstable hydroxylated metabolite a group may break off spontaneously: an alkyl group. 2+ (FeO)3+ The second reactive form Fe 6 is the oxene (produced in step 6).e. which is then + released from CYP. I. the reactive O atom RH is inserted into a C-H bond of the drug. O2 is activated by electron RH uptake to form reactive O atoms. a halogen atom. or sulfur atom. out of which three types are presented below. RH RH 5 H + 4 NADPH-cytochrome Note that Fe represents P450 reductase the iron in CYP. thus converting it into an amino group (nitro reduction). 3 RH From this. CYP may also catalyze reduction. in a reductive dehalogenation reaction) or as many as 6 electrons to a nitro group.g. oxidative deamination. Surprisingly. H CYP-catalyzed 2+ 3+ _ Fe OOH dehydrogenation and Fe O2 reduction are explained below. CYP can also catalyze dehydrogenation. HOH III. forming an epoxide. by transferring only 1 electron to a compound (e. CYP-CATALYZED REACTIONS Overview OXYGENATION (insertion of one O atom) . Oxidative deamination ( O-containing metabolite + NH3): Amphetamine phenylacetone (-) c. † = toxic metabolite . thio-TEPA TEPA (+) DEHYDROGENATION (removal of 2 H atoms): Acetaminophen N-acetylbenzoquinone imine (†) Nifedipine (a dihydropyridine parent compund) ”pyridine” metabolite (-) REDUCTION (reductive dehalogenation. or theobromine O-dealkylation: Codeine morphine (+) Dextromethorphan dextrorphan (=D form of levorphanol) (+) Phenacetin acetaminophen (=paracetamol) (+) b. Halothane debrominated halothane free radical (†) + Br¯ For reduction of nitro group of clonazepam (or nitrazepam) to amino group by CYP. Parathion paraoxon (+). terfenadine (+).Aliphatic hydroxylation: tolbutamide (-). = inactive metabolite. INSERTION OF O PRODUCES AN UNSTABLE METABOLITE WHICH SPONTANEOUSLY BRAKES INTO TWO MOLECULES: a. propranolol (-) N-hydroxylation (insertion of O into an N-H bond): dapsone (†) b. nitro reduction): CCl4 CCl3 (†) + Cl¯. Carisoprodol meprobamate (+). Oxidative desulfuration ( O-containing metabolite + S): Thiopenthal pentobarbital (+).Aromatic hydroxylation: warfarin (-). Oxidative dehalogenation ( O-containing metabolite + HBr): Halothane trifluoroacetyl chloride (†) d. or theophylline. Oxidative dealkylation ( dealkylated metabolite + an aldehyde): N-dealkylation: Diazepam nordiazepam (+). Epoxidation (insertion of O into a C=C bond to form an epoxide): carbamazepine (-/o) 2. phenytoin (-). Amitriptyline nortriptyline (+) desmethyl-nortriptyline (-) Lidocaine monoethylglycylxylidine (+) glycylxylidine (-) Caffeine paraxanthine (-). Hydroxylation C-hydroxylation (insertion of O into a C-H bond to form a hydroxyl group): . cyclophosphamide (+) . INSERTION OF O PRODUCES A STABLE METABOLITE: a. see under nitro reduction (6-electron reduction) + = active metabolite.two variations: 1. NSERTION OF O PRODUCES A STABLE METABOLITE HYDROXYLATION = insertion of O into a C-H or N-H bond a) C-HYDROXYLATION: aliphatic O O O O CYP2C9 CH3 S NH C NH HO CH2 S NH C NH O O Tolbutamide (antidiabetic) Hydroxymethyl-tolbutamide (inactive) CH3 CH3 HOOC CH CH2 CH CH3 Ibuprofen (NSAID) CH3 CH3 CH3 CH2 OH HOOC CH CH2 C OH HOOC CH CH2 CH CH3 CH3 2-hydroxy-ibuprofen CONJUGATES 3-hydroxy-ibuprofen b) C-HYDROXYLATION: aromatic O Phenytoin O 4'-Hydroxyphenytoin (antieileptic. CYP-CATALYZED REACTIONS: 1. antiarrhythmic) (inactive) HN NH HN NH CYP2C9 C6H5 C6H5 O O OH O O HO O O CYP2C9 H H C C OH CH2 C CH3 OH CH2 C CH3 Warfarin (anticoagulant) O 7-hydroxy-warfarin O (inactive) c) N-HYDROXYLATION O O CYP2C9 H2 N S NH2 H2 N S NH OH O O Dapsone (antileprotic) Dapsone-hydroxylamine (hemotoxic and allergenic) . EPOXIDATION = insertion of O into a C=C double bond O H H CYP N N C C O NH2 O NH2 Carbamazepine Carbamazepine-10. .8-oxide benzo(a)pyrene-7.10-epoxide "ultimate carcinogen" NOTE: Leucotriene A4 (LTA4) is also an epoxide! LTA4 is converted into either LTB4 (a diol) by epoxide hydrolase.11-epoxide (antiepileptic) (less active metabolite) Epoxide O (+) CYP hydrolase CYP (+) (+) (+) HO HO O OH OH benzo(a)pyrene benzo(a)pyrene-7.8-dihydro-diol-9. or into LTC4 (a GSH conjugate) by glutathione S-transferase.8-dihydro-diol benzo(a)pyrene- 7. N-demethylation at N1 and N3 by CYP H3C N N3-demethylation N . . acetaldehyde after deethylation. Examples: CH3 H O O Other examples: N N CYP2C19 lidocaine monoethylglycylxylidine CYP3A4 imipramine desmethylimipramine Cl N Cl N erythromycine desmethylerythromycine HCHO Diazepam Nordiazepam Theophylline may undergo: O H . CYP-CATALYZED REACTIONS: 2.methylation at N7 by MT O N N H 1-Methylxanthine (25 %) O CH3 O H O H O H H3C N H3C N H3C N H3C N N1 7 MT N Hydroxylation N N3-demethylation N OH OH 3 SAM CYP3A4. N-dealkylation General scheme: NOTE: After hydroxylation at the OH R NH2 N-bound C atom of the alkyl group. the alkyl group breaks off (as an aldehyde) R NH CH3 R NH CH2 O from the N atom. etc.3-Dimethyluric acid 1-Methyluric acid (50 %) (5 %) In neonates more caffeine is formed from theophylline than H O CH3 N in adults because the CYP N1-demethylation N levels in the neonatal liver CYP1A2 O N N are low.g.. INSERTION OF O PRODUCES AN UNSTABLE METABOLITE WHICH UNDERGOES SPONTANEOUS CLEAVAGE INTO TWO MOLECULES First. an amine or alcohol/phenol).C-hydroxylation at C8 by CYP CYP1A2 . producing a H C dealkylated amine metabolite H of the drug molecule. formaldehyde after demethylation. This hydroxylated metabolite is unstable.N. It breaks spontaneously into two molecules: the dealkylated metabolite (e. CYP2E1 CYP1A2 O N N O N N O N N O N N CH3 CH3 CH3 H Caffeine Theophylline 1. however. and an aldehyde (e.. the drug becomes hydroxylated at the C atom of the alkyl group that is linked to the N (or the O) atom.g. the CH3 methyltransferase (MT) 3-Methylxanthine (15 %) levels are relatively high.). H Example: CH3 O HO Other examples: codeine morphine phenacetine paracetamol CYP2D6 HCHO N CH3 N CH3 Dextromethorphan Dextrorphan (antitussive drug) (active metabolite) . the alkyl group breaks off (as an aldehyde) R O CH3 R O CH2 O from the O atom. producing a H C dealkylated hydroxylated metabolite of the drug molecule.O-dealkylation General scheme: NOTE: After hydroxylation at the OH R OH O-bound C atom of the alkyl group. anesthetic) (active as hypnotic) The arrows point to the bond into which an O atom is inserted. (an organophosphate insecticide) an irreversible inhibitor of acethylcholinesterase) S S O O HN NH CYP HN NH HN NH O N O O N O O N O [S] H5 C2 CH CH3 H5 C 2 CH CH 3 H5 C 2 CH CH3 CH2 CH2 CH3 CH 2CH 2CH3 CH 2 CH 2 CH 3 Thiopental Pentobarbital (an i. or sulfur.Oxidative deamination OH O CYP CH2 CH CH3 CH2 C CH3 CH2 C CH3 NH2 NH2 NH3 Amphetamine Phenylacetone (centrally acting sympathomimetic) (inactive) Oxidative dehalogenation F Cl F Cl F (+) Cl C YP2E1 F C C Br F C C Br F C C O F H F OH HBr F Halothane T rifluoro-acetyl-chloride (inhalation anesthetic) binds covalently to hepatic proteins. HBr. . which then promotes cleavage of the molecule to release NH3. thus form ing a neoantigene and causing "halothane hepatitis" Oxidative desulfuration C2H 5 O S C 2H 5O S C 2H 5 O O P P O P CYP C 2H 5O O NO 2 C 2H5 O O NO 2 C 2H 5O O NO 2 [S] Paraoxon Parathion (active insecticide.v. DEHYDROGENATION General scheme: 3+ NOTE: While an oxygenation produces 1 (FeO)3+ Fe molecule hydroxylated metabolite plus 1 6 7 RH2 R molecule HOH. Thus. 2e- R-NO2 R-NO R-NH-OH R-NH2 2H+ HOH 2H+ 2H+ HOH NOTE for those interested: Homolytic cleavage occurs when a covalent bond (formed by two electrons shown as :) is cleaved in a way so that one electron remains with one of the breakage products. homolytic cleavage yields products with an unpaired electron (called free radicals). REDUCTION In CYP-catalyzed reduction. whereas the other electron will belong to the other breakage product. its reduced intermedier then undergoes a homolytic cleavage to form a free radical and a chloride anion. e. Reductive dehalogenation of carbon tetrachloride (1-electron reduction): _ Cl Cl Cl. CYP-CATALYZED REACTIONS: 3. . General scheme: 2+ 2+ 4 Fe O2 Fe O _ _2 5 RH e [RH] Examples: 1. can initiate lipid peroxidation in the liver cell membranes and can thus induce hepatic necrosis. With carbon tetrachloride. O O H C C N CH3 N CH3 NO2 NO2 CYP2E1 O O O O CYP3A4 CYP1A2 H3CO C C OCH3 H3CO C C OCH3 CYP3A4 OH O H3C CH3 H3C N CH3 N Acetaminophen N-Acetyl-p-benzo.g. but to the CYP-bound substrate. Nitro-reduction of clonazepam to 7-amino-clonazepam (6-electron reduction): H O H O N N CYP3A4 O2N N CYP2C19 H2N N Clonazepam Cl Cl 7-amino- anxiolytic and clonazepam antiepileptic drug inactive 2e. Examples: plus a dehydrogenated metabolite. carbon tetrachloride or clonazepam (see also under nitro reduction). free radical tetrachloride Cl C Cl Cl C : Cl Cl reduction initiates lipid peroxidation solvent Cl Cl Cl and liver injury 2. The reactive trichloromethyl free radical formed in the liver. 2e. Cl Tricloromethyl Carbon CYP2E1 C. dehydrogenation produces HOH 2 molecules HOH. which are reactive. the second electron is not transferred to the CYP-bound O2. H analgetic and quinoneimine antipyretic (NAPBQI) Nifedipine "Pyridine metabolite" drug hepatotoxic a dihydropyridine Ca++-channel blocker inactive Other example: Dehydrogenation of nicotine to nicotine 1’(5’) iminium ion (see under aldehyde oxidase) CYP-CATALYZED REACTIONS: 4. N atom: Nicotine → nicotine-1’-N-oxide Trimethylamine → trimethylamine N-oxide (Deficiency: Fish-odor syndrome) OXIDATIONS CATALYZED BY FMO . (water-soluble metabolite accumulates in FMO3 deficiency. OXIDATIONS CATALYZED BY MICROSOMAL FLAVIN-CONTAINING MONOOXYGENASE (FMO) FMO-CATALYZED OXIDATIONS Overview Take place on heteroatoms in drugs: Oxidation of S atom: Cimetidine → cimetidine-S-oxide Oxidation of tert.Examples: N-CN O N-CN CH2 S CH2 CH2 NH C NH CH3 CH2 S CH2 CH2 NH C NH CH3 N N FMO CH3 CH3 N N H Cimetidine H Cimetidine S-oxide (an H2-receptor antagonist) (inactive) FMO N N O N CH3 N CH3 Nicotine Nicotine-1'-N-oxide (inactive) CH3 CH3 FMO3 CH3 N CH3 N O CH3 CH3 Trimethylamine Trimethylamine N-oxide endogenous volatile compound. excreted in urine) causing fish odor syndrome . Chloral (= trichloroacetaldehyde) → trichloroethanol (+) – ADH in the reverse reaction (using NADH) can reduce chloral.Ethanol → acetaldehyde (†) → acetic acid .Dopamine → 3.4-dihydroxy-phenylacetaldehyde .MPTP → MPP+(†) – kills the DAergic neurons.4-dihydroxy-mandelic aldehyde (-) . OXIDATION CATALYZED BY MAO MAO catalyzes oxidative deamination of amines. inhibition of uric acid formation) 6-Mercaptopurine → 6-thiouric acid (-) ALDEHYDE OXIDASE-CATALYZED OXIDATION: Examples: . causing Parkinson’s disease OXIDATIONS CATALYZED BY MOLYBDENUM-CONTAINING OXIDASES: XANTHINE OXIDASE-CATALYZED OXIDATION: Examples: Hypoxanthine → xanthine → uric acid Allopurinol → alloxanthine (compet.3-Methoxy 4-hydroxy-mandelic aldehyde → VMA OXIDATIONS CATALYZED BY ALCOHOL.Norepinephrine → 3.Nicotine 1’(5’) iminium ion → cotinine .Benzaldehyde → benzoic acid . OXIDATIONS CATALYZED BY NON-MICROSOMAL ENZYMES NON-MICROSOMAL OXIDATIONS Overview The oxygen incorporated into the substrate is derived from HOH rather than O2.Methanol → formaldehyde → formic acid (†) – causes blindness . ethanol facilitates this by increasing NADH supply.AND ALDEHYDE DEHYDROGENASES: Examples: .Ethylene glycol →→ glycolic acid (†) → glyoxylic acid → oxalic acid (†) – cause renal injury .N-deisopropyl-propranolol → the respective aldehyde (-) . . Examples: . the byproducts are ammonia and HOOH! 1. R-CH=NH + H2O > R-CH(OH)-NH2 Hydration 3. R-CH(OH)-NH2 > R-CH=O + NH3 Deamination HO CH2 CH2 NH2 4. FADH2 + O2 > FAD + H2O2 FAD regeneration FAD HOOH ! 1 4 HO FADH2 O2 HO CH2 CH NH HO HOH O 2 HO CH2 C OH HO HO acid (DOPAC) NH3 O Oxidation by ALDH HO CH2 CH NH2 HO CH2 C 3 Reduction by AR OH H HO 3. R-CH2NH2 + FAD > R-CH=NH + FADH2 Dehydrogenation HO Dopamine 2.MAO-CATALYZED OXIDATIVE DEAMINATION OF AMINES INTO ALDEHYDES General scheme: FOUR STEPS .4-dihydroxy- phenylacetyl aldehyde (DOPAL) HO CH2 CH2OH alcohol Example: Propranolol N-Desisopropylpropranolol OH CH3 OH O CH2 CH CH2 NH CH O CH2 CH CH2 NH2 CH3 CYP2D6 N-dealkylation O2 + H2O CYP2D6 MAO-A aromatic hydroxylation NH3 + H2O2 OH CH3 OH O O CH2 CH CH2 NH CH O CH2 CH C H CH3 OH 4-Hydroxypropranolol Oxidation Reduction by AOX by AR Carboxylic acid Glycol . Oxygenation of aromatic (but not aliphatic) aldehydes. Therefore. Oxygenation of a C atom double-bonded to a N atom in a heterocyclic ring. (2) Thereafter. 2 H atoms are removed from the intermediary metabolite by molecular oxygen (O2). nicotine-1’(5’)-iminium ion (mainly by AOX) 2. just like cotreatment with allopurinol does. XANTHINE OXIDASE (XO) and ALDEHYDE OXIDASE (AOX) Mechanism of oxygenation by XO and AOX – two steps: NOTE: The oxygen atom incorporated into the substrate is derived from water rather than O2. in zaleplone (preferred by AOX) in the dehydrogenated nicotine metabolite. Oxygenations catalyzed by XO and/or AOX: 1.g. bone marrow depression. e. 6-mercaptopurine and 6-thioxanthine (preferred by XO). thus forming hydrogen peroxide (HOOH) and the oxygenated metabolite. such as benzaldehyde (product of benzyl alcohol oxidation by ADH – see gasping syndrome). allopurinol is contraindicated for the 6-mercaptopurine- treated patient even if hyperuricemia developed. TPMT deficiency increases the toxicity of 6MP. e. These 2 steps are shown only in the reactions presented for AOX. in purine analogues. such as: in purines. which carries now a keto- group or a carboxylic acid group. Patients have died because this contraindication was disregarded by ignorant physicians! NOTE: 6MP can also be eliminated by methylation at the SH group by thiopurine methyltransferase (TPMT. (1) A water molecule is added into the parent compound. XANTHINE OXIDASE-CATALYZED OXIDATIONS O O O H N N N HN XO HN XO HN O N N O N N O N N H O H H H H HN Hypoxanthine N Xanthine Uric acid N N H Allopurinol to decrease hyperuricemia S S S H N N N HN XO HN XO HN O N O N N O N N N H H H H H 6-Mercaptopurine 6-Thioxanthine 6-Thiouric acid antitumor drug inactive Administration of the XO inhibitor allopurinol to patients treated with 6-mercaptopurine (6MP) would decrease the elimination of 6-mercaptopurine and in turn could result in 6MP-induced toxicity. For simplicity. see later). they are not shown in the reactions presented for XO. hypoxanthine and xanthine (preferred by XO). i. . OXIDATIONS CATALYZED BY Mo-CONTAINING OXIDASES.e. forming an intermediary metabolite.g. (see gasping syndrome) NOTE: Cotinine is the main metabolite of nicotine and as such it may be used as a biomarker of nicotine exposure (i. Cotinine is conveniently analyzed from the saliva of the smoker.e.ALDEHYDE OXIDASE-CATALYZED OXIDATIONS O O O C CH3 C CH3 C CH3 N N N CH2 CH3 CH2 CH3 CH2 CH3 AOX AOX HOH O2 HOOH N N N N N N N HO N O N CN H CN H CN Zaleplon 5-hydroxy-zaleplon 5-oxo-zaleplon short-acting hypnotic NOTE: Zaleplon is also N-deethylated by CYP3A4. smoking). CYP2A6 + CYP2B6 AOX OH AOX O N N N N dehydrogenation CH3 CH3 HOH CH3 O2 CH3 N N N N HOOH Nicotine nicotine-1'(5')-iminium ion cotinine O OH O AOX AOX C C OH C H HOH H O2 HOOH OH Benzaldehyde Benzoic acid formed from benzylic alcohol. . VMA is the biomarker of E and NE production.AND ALDEHYDE DEHYDROGENASE (ALDH)-CATALYZED OXIDATIONS + + NAD NADH + H + O HOH OH NAD NADH + H + O CH3 CH2 OH CH3 C CH3 C H CH3 C ADH H OH ALDH OH Ethanol acetaldehyde DISULFIRAM acetic acid to promote alcohol withdrawal + + + + NAD NADH + H HOH OH NAD NADH + H O O CH3 OH H C H C H H C ADH H ALDH OH OH Methanol formaldehyde formic acid ETHANOL FOMEPIZOLE Formic acid causes acidosis (antidotes) and retinal injury (blindness) Rate + + NAD NADH + H limiting CH2 OH H2C OH H2C OH step HC O COOH CH2 OH ADH HC O ALDH COOH ADH COOH ALDH COOH Ethylene glycol glycolic glyoxylic oxalic glycol ETHANOL aldehyde acid acid acid FOMEPIZOLE (antidotes) Acidic metabolites cause acidosis and renal injury HO HO H3CO H3CO O O O O ALDH ALDH HO CH2 C HO CH2 C HO CH C HO CH C H OH OH H OH OH 3. . Fomepizole (=4-methylpyrazole. Urinary excretion of large amounts of VMA is a diagnostic sign for pheochromocytoma. a disulfiram-treated individual should not consume alcohol for at least a week after discontinuation of disulfiram administration. VMA is the final product of the biotransformation of epinephrine (E) and norepinephrine (NE) via the COMT – MAO – ALDH pathway. Elimination of the potentially toxic DOPAL by ALDH from nigrostriatal dopaminergic neurons is a protective mechanism. As shown in Part 6 (Appendix-2). Genetic and gender variations in the biotransformation of ethanol are presented in Part 6. Appendix-3.g.4-dihydroxy-phenylacetyl aldehyde (DOPAL) 3. Thus. For this reason. ALCOHOL DEHYDROGENASE (ADH). Inhibition of ALDH by some pesticides (e. ANTIZOL®) is a potent CH3 competitive inhibitor of ADH and is the most reliable antidote in N fomepizole poisonings with methanol or ethylene glycol. Fomepizole is also used to N 4-methylpyrazole alleviate the acetaldehyde syndrome caused by ethanol consumption in ANTIZOL H disulfiram-treated patients. 2. 5.4-dihydroxy. Vanillyl mandelic aldehyde Vanillyl mandelic acid formed by MAO phenylacetic acid formed by COMT and MAO (VMA) in dopaminergic neurons (DOPAC) from epinephrine and NE NOTES: 1. disulfiram is biotransformed into an electrophilic metabolite which covalently binds to and irreversibly inhibits aldehyde dehydrogenase. 3. the fungicide benomyl) has been speculated to be a mechanism of pesticide-induced Parkinson disease. 4. REDUCTION Overview AZO-REDUCTION (R1-N=N-R2 R1-NH2 + R2-NH2) catalyzed by microbial enzymes in the colon Prontosyl sulfanilamide + triaminobenzene Sulfasalazine (salicylazosulfapyridine) 5-aminosalycylic acid + sulfapyridine NITRO-REDUCTION (R-NO2 R-NH2): catalyzed by CYP Clonazepam 7-amino-clonazepam Chloramphenicol an arylamine metabolite (†) CARBONYL-.4-Dihydroxyphenylacetaldehyde (DOPAL. produced from DA by MAO) 3. using NADPH Haloperidol reduced haloperidol Oxcarbazepin 10-hydroxy-carbazepin (+) Doxorubicin doxorubicinol (†) 3. and ALDOSE-REDUCTION (R-C=O → R-C-OH): catalyzed by cytosolic enzymes of the aldo-keto reductase (AKR) superfamily.4-dihydroxyphenylethanol (DOPET) . ALDEHYDE-. 1939) (antibacterial. REDUCTION AZO-REDUCTION R N N R' R NH2 + R' NH2 O O H2N N N S NH2 H2N NH2 + H2N S NH2 O colonic O NH2 bacteria NH2 Prontosil tiraminobenzene sulfanilamide (Gerhard Domagk. the prototype of sulfonamides) HOOC colonic HOOC O N O N bacteria HO N N S N H HO NH2 + H2N S N H O O Sulfasalazine (Salicylazosulfapyridine) 5-aminosalycylic acid sulfapyridine (to treat ulcerative colitis) (antiinflammatory) NITRO-REDUCTION (R-NO2 R-NO R-NHOH R-NH2) Clonazepam H O H O (anxiolytic and N N antiepileptic effects) CYP3A4 O2N N CYP2C19 H2N N Cl Cl 7-amino- clonazepam (inactive) CARBONYL-REDUCTION R CH O R CH2 OH O OH OH OH C CH2 CH2 CH2 N AKR CH CH2 CH2 CH2 N Cl Cl Haloperidol reduced haloperidol F (antipsychotic) F (inactive) Oxcarbazepine O OH 10-hydroxycarbazepine (antiepileptic. (active) inactive prodrug) AKR N N C C O NH2 O NH2 O OH O O OH OH C CH2OH CH CH2OH OH OH AKR OCH3 O OH OCH3 O OH O O O O Doxorubicin CH3 CH3 doxorubicinol (antitumor drug) (cardiotoxic) HO HO NH2 NH2 AKR = aldo-keto reductase . Nobel Prize. oseltamivir – the active drugs are converted into inactive (or less active) metabolites . (+) = active metabolite. Also: heroin (+) morphine (+) HYDROLYSIS OF CARBOXYLIC ACID AMIDES: slow Example: Procainamide BY ALKALINE PHOSPHATASES: hydrolyzes phosphoric acid monoesters Examples (i. Thus BChE represents a “silent binding site” for OP insecticides and chemical warfare agents by preventing their binding to the target of toxic action. e. . or into LTC4 (a GSH conjugate) by glutathione S-transferase. bisacodyl. meperidine. tetracaine.g. ACE-inhibitor esters. the neuronal acetylcholinesterase. enalapril (-) enalaprilat (+) Antipsychotic esters. HYDROLYSIS Overview BY CARBOXYLESTERASES (CES. pipothiazine palmitate (-) pipothiazine (+) Mycophenolate mofetil (-) mycophenolic acid (+) – by CES Bambuterol terbutaline (+).v. or simvastatin (lactone) hydroxy-acid (+). remifentanil. also in plasma) HYDROLYSIS OF CARBOXYLIC ACID ESTERS: rapid Examples: . injectable prodrugs): Fosphenytoin (-) phenytoin (+) Fospropofol (-) propofol (+) Clindamycin phosphate (-) clindamycin (+) BY PARAOXONASES (Lactonases) HYDROLYSIS OF PHOSPHORIC ACID TRI-ESTERS Examples: Paraoxon and other organophosphate insecticides HYDROLYSIS OF LACTONES Examples: Statins. Spironolactone hydroxy-acid (-) BY EPOXIDE HYDROLASE: hydrolyzes the epoxide into dihydrodiols Examples: Carbamazepine-epoxide (little-reactive epoxide.g. e. fenofibrate (-) fenofibric acid (+). e.e. ASA = acetylsalicylic acid NOTE: BChE is protective against organic phosphate ester insecticides and “nerve agents” whose oxone form phosphorylates and irreversibly inactivates not only acetylcholinesterase (causing the toxicity) but also BChE. esmolol. e. active metabolite) Benzpyrene-epoxide (DNA-reactive epoxide.Drugs: Succinylcholine. sodium picosulfate (-) = inactive metabolite. lovastatin. microsomal enzymes) and/or BUTYRYLCHOLINESTERASES (BChE. BY PANCREATIC LIPASE IN THE SMALL INTESTINE Example: castor oil (ricinoleic acid-containing triglyceride) ricinoleic acid (+) BY MICROBIAL HYDROLASES IN THE COLON Examples (laxative prodrugs): Sennoside A. mutagenic and carcinogenic) NOTE: Leucotriene A4 (LTA4) is also an epoxide! It is converted into either LTB4 (a diol) by epoxide hydrolase.g.g. acetylsalicylic acid.Prodrugs: Fibrate esters. mivacurium. soluble enzymes. cocaine. procaine. clopidogrel. i. which has no role in the toxic action. . Similarly.. whereas enalaprilate is the active ACE inhibitor metabolite.m. as an oily injection once a month) S Some drugs (e. such a drug is readiliy hydrolyzed by carboxylesterase and the original organic acid (e. prodrug).HYDROLYSIS BY CARBOXYLESTERASES and/or BUTYRYLCHOLINESTERASES General scheme: R C O R' esterase R COOH + HO R' HOH O DRUGS inactivated by hydrolysis: H3C O CH3 + CH NH CH2 CH CH2 O CH2 CH2 C O CH3 CH2 C O CH2 CH2 N CH3 H3 C OH O CH3 Esmolol (short acting beta-antagonist) CH3 O + CH3 O C CH2 C O CH2 CH2 N CH3 O CH3 N CH2 CH2 C O CH3 CH3 CH2 C N O Succinylcholine O (short acting muscle relaxant) Remifentanil (short acting opioid) CH2 CH3 O H2N C O CH2 CH2 N H C O CH3 O CH2 CH3 Clopidogrel N (inhibitor of platelet aggregation) Procaine Cl (short acting local anesthetic. After absorption. rapidly hydrolyzed) S COOH O CH2 CH3 O C CH3 H2N C NH CH2 CH2 N O CH2 CH3 Acetylsalicylic acid (aspirin) Procainamide (antiarhytmic drug.g.e. slowly hydrolyzed) PRODRUGS activated by hydrolysis: O COOH C O C2H5 CH3 CH3 CH2 CH2 CH NH CH C N Cl C O C C O CH CH3 O O CH3 O CH3 Enalapril (ACE inhibitor) Fenofibrate (triglyceride-lowering drug) CH2 CH2 CH2 N CH2 CH2 O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 O O CH3 Pipothiazine palmitate N S N (PIPORTIL a depot antipsychotic. Enalapril is an inactiv drug (i. O CH3 injected i. enalaprilate from enalapril) is released. . where its hydrolysis produces morphine.. the lipophilic heroin readily diffuses into brain.g. enalapril) containing carboxyl groups are esterified with an alcohol to make them more lipophilic for better absorption by diffusion from the GI tract. respectively.-injectable forms. propofol and clindamycin. i.v. This linker group breaks off spontaneously as formaldehyde after the AP-catalyzed hydrolysis. first a -CH2-OH group had to be linked to these molecules. and the hydroxyl group of propofol is sterically hindered from phosphoric acid by the neighboring isopropyl groups. HOH spontaneous H AP H cleavage H N N N O O O OH OH N N N O CH2 O P O O CH2 OH HCHO O H HO P O OH Phosphenytoin OH Phenytoin HOH spontaneous OH AP cleavage O CH2 O P O O CH2 OH OH OH OH HCHO HO P O Phospropofol OH Propofol N N Cl HOH Cl AP N N H H O OH O HO O HO O HO P O OH SCH3 OH SCH3 OH OH Clindamycin O P O Clindamycin OH phosphate OH . into water-soluble. As phenytoin does not contain a hydroxyl group at which to esterify it with phosphoric acid. fospropofol and clindamycin phosphate are phosphate ester prodrugs that were synthesized in order to convert the poorly water-soluble phenytoin.HYDROLYSIS BY ALKALINE PHOSPHATASE (AP) NOTE: Fosphenytoin. cholesterol lowering drug) (aldosterone antagonist. an OP insecticide. K-sparing diuretic) Notes: . It functions as an antioxidant.PON is also called aromatic esterase 1 or serum aryl-dialkylphosphatase 1 .HYDROLYSIS BY PARAOXONASES (PON) Hydrolysis of phosphoric acid tri-esters: H3C CH2 O O H3C CH2 O O PON P P + HO NO2 H3C CH2 O O NO2 H3C CH2 O OH Paraoxon (the active metabolite of parathion. irreversble acethylcholinesterase inhibitor) Hydrolysis of lactone rings: HO O PON HO C O O O OH O C OH PON OH O O OH H3C H3C O active CH3 H3C CH3 lovastatin inactive spirono- O lacton H3C O S C CH3 Lovastatin Spironolactone (HMG-CoA reductase inhibitor. it is an anti-atherosclerotic component of HDL. .PON1 is synthesized in the liver and transported along with HDL in the plasma. HYDROLYSIS BY MICROBIAL HYDROLASES IN THE COLON Hydrolysis produces stimulatory laxatives in the colon OH HO Sennoside A OH O O OH HO O OH O COOH COOH COOH 2 HOH COOH COOH 2 glucose COOH O OH O O OH HO O OH HO OH antraquinone glycoside active antraquinone (prodrug) aglycone N N Bisacodyl 2 HOH O O 2 acetate H3C O O CH3 HO OH Diacetic acid ester of Active diphenol-methane diphenol-methane laxative (prodrug) laxative metabolite Sodium N N picosulfate 2 HOH O O S S 2 sulfate NaO O O ONa HO OH O O Disulfonic acid ester of Active diphenol-methane diphenol-methane laxative (prodrug) laxative metabolite . oxazepam. dapsone. + Glycine N-acyltransf. (in the endoplasmic propofol. procainamide. (in mitochondrial matrix) + Glycine nicotinic acid CONJUGATION WITH GLUTATHIONE (Glu-Cys-Gly) Enzyme Cosubstrate Substrates Glutathione S-transf. transferases acid chloramphenicol. OH-containing compounds: L-Dopa (COMT) (in cytosol) methionine N-containing compounds: histamine. furosemide. telmisartan. estradiol. epoxides (e. thyroxine reticulum = microsomes) OH-contaning metabolites: 6-OH phenytoin. endogenous compounds UDP-glucuronosyl UDP-glucuronic OH-containing compounds: morphine. LTA4) Electrophilic C-containing metabolites: N-acetyl-p-benzoquinone imine. sulfamethazine. diethylstilbestrol. hydralazine. acrolein ACETYLATION Enzyme Cosubstrate Substrates N-acetyltransferases Acetyl-CoA NH2-containing compounds: (in cytosol) NAT1 substrates: p-aminobenzoic acid. compounds: 6-mercaptopurine (TPMT) . sulfamethoxazol NAT2 substrates: isoniazid. bilirubin COOH-containing metabolites: fenofibric acid N-containing drugs: lamotrigine SULFATION Enzyme Cosubstrate Substrates Sulfotransferases PAPS OH-containing compounds: pravastatin + see above (in cytosol) OH-contaning metabolites: see above N-oxide-containing compounds: minoxidil CONJUGATION WITH GLYCINE Enzyme Cosubstrate Substrates Acyl-CoA synthetase ATP COOH-containing compounds: salicylic cid. nicotine SH-cont. Glutathione Electrophilic C-containing compounds: (in cytosol) (glu-cys-gly) ethacrinic acid. phenolphthalein. paracetamol. + CoA-SH benzoic acid. N-OH-dapsone COOH-containing compounds: valproic acid. etc. METHYLATION Enzyme Cosubstrate Substrates Methyltransferases S-adenosyl.g. diclophenac. PHASE II BIOTRANSFORMATIONS (CONJUGATIONS) GLUCURONIDATION Enzyme Cosubstrate Substrates: drugs. fenofibric acid) produced from fibric acid esters by ester hydrolysis . Estradiol .N-glucuronide formation _ COO H2N N NH2 H2N N NH2 O + N UDP-GT N N UDP-GA N HO OH Cl Cl OH Cl Cl Lamotrigine Lamotrigine N2-glucuronide (antiepileptic drug) (rapidly excreted in urine) Other: Carbamazepine ..Drugs: Acetaminophen. UGT) Cosubstrate: O UDP-glucuronic acid (UDP-GA) _ NH COO O O O O CH2 O P O P O N O _ _ HO OH O O OH OH OH Examples: . telmisartan .g. Oxazepam.Endogenous compounds: Thyroxine.. Ezetimibe.GLUCURONIDATION Enzymes: UDP-glucuronosyltransferases (UDP-GT. Morphine.Drugs: NSAID (e.Bilirubin (forms mono.g.Acidic metabolites (e. diclofenac).Ether glucuronide formation (from compounds with a hydroxyl group) _ COO O OH OH UDP-GT O2N CH CH CH2 OH O2N CH CH CH2 O HO OH UDP-GA NH C CHCl 2 NH C CHCl2 OH O O Chloramphenicol Chloramphenicol glucuronide (antibiotic) (rapidly excreted in urine) Others: . Phenolphthalein .Hydroxylated metabolites of drugs . furosemide.and diglucuronides) . Diethylstilbestrol.Ester glucuronide formation (from compounds with a carboxylic group) _ COO CH3 CH2 CH2 O CH3 CH2 CH2 O O UDP-GT CH C CH C UDP-GA HO OH CH3 CH2 CH2 OH CH3 CH2 CH2 O OH Valproic acid Valproic acid glucuronide (antiepileptic drug) (rapidly excreted in urine) Others: . . dopamine) minoxidyl (see later) hydroxylated metabolites of drugs .g.SULFATION Enzymes: Sulfotransferases (SULT) Cosubstrate: 3'-Phosphoadenosine-5'-phosphosulfate (PAPS) NH2 N N O O N O S O P O CH2 N O O O O OH PO32- Examples: NH C CH3 NH C CH3 O O SULT PAPS O OH O S O O Acetaminophen = paracetamol acetaminophen-sulfate = paracetamol-sulfate (analgetic and antipyretic) (rapidly excreted in urine) Others: catecholamines (e. CoA-SH Gly Salicylic acid Salicyl-CoA Salicyl-glycine = salicyluric acid carboxyl. (rapidly excreted in urine) esterase Acetylsalicylic acid acetylation (aspirin) and inactivation of COX ACS GNT Benzoic acid Benzoyl-CoA Benzoyl-glycine ATP. it was found in the urine of horses given benzoic acid. Then it was named hippuric acid (hippos means horse in Greek). (3) Glycine (Gly) Examples: O O O C C C OH S CoA NH CH2 COOH OH OH OH ACS GNT ATP. . (2) Coenzyme A (CoA-SH). CONJUGATION WITH GLYCINE Enzymes: (1) acyl-CoA synthetase (ACS) (2) acyl-CoA: glycine N-acyltransferase (GNT) Both enzymes are located in the mitochondrial matrix. CoA-SH Gly (hippuric acid) AOX ADH Benzadehyde Benzyl alcohol (an antiseptic. In 1830. Cosubstrates: (1) ATP. see under gasping syndrome) Note: Benzoyl-glycine was the first identified metabolite of a xenobiotic. thus it is electrophilic.. Acetaminophen-glutathione = paracetamol quinoneimine conjugate (NAPBQI) (readily excreted) ELECTROPHILIC METABOLITE MAY CAUSE HEPATIC NECROSIS .e. Examples: Compounds with electrophilic (electron deficient. CH CH2 CH2 C NH C NH CH2 COO As drugs and chemicals with elecrophilic CH atoms may also bind to protein-cysteines. electrophilic) _ atoms.. partially positive) carbon atoms O CH2 COOH O CH2 COOH Cl Cl GST GSH Cl Cl O C C CH2 CH3 O C CH CH2 CH3 (+) CH CH2 SG 2 Ethacrynic acid (EA) EA-glutathione (loop diuretic) conjugate Note: the carbon with (+) sign is electron-deficient (contains a partial positive charge). whose SH group is (active diuretic metabolite) electron-rich (nucleophilic).e. GSH conjugate a reactive electrophilic CH2 CH C GS CH2 CH2 C (detoxified) aldehyde that causes H H hemorrhagic cystitis in CP-treated patients Cyclophosphamide (CP) (antitumor drug. SH conjugation with GSH is an important . thus forming a glutathione conjugate. NH2 CH2 conjugation with glutathione prevents their covalent binding to proteins. therefore EA-Cys conjugate reactive with GSH. nucleophilic).. _ therefore it is reactive with COO O O electron-deficient (i. such as NAPBQI. protective mechanism against reactive -glutamic acid cysteine glycine electrophiles. Therefore. (+) O O Acrolein-glutathione Acrolein. a nitogen-mustard) HN C CH3 N C CH3 HN C CH3 O O O CYP2E1 GSH toxication (+) (+) detoxication SG OH O OH Acetaminophen N-acetyl-p-benzo.CONJUGATION WITH GLUTATHIONE Enzymes: Glutathione S-transfrerases (GST) Notice that the SH group in GSH Cosubstrate: Glutathione (GSH) is electron-rich (i. Sulfamethoxazole NAT2 substrates: Dapsone.ACETYLATION Enzymes: N-acetyltransferases (NAT) Cosubstrate: Acetyl coenzyme A (Ac-CoA) NH2 N N O CH3 O O N NH C CH C CH2 O P O P O CH2 N OH CH3 O O O CH2 CH2 C O O O OH NH CH2 CH2 S C CH3 - PO3H Examples: O O O C C NH NH2 NH NH C CH3 NAT2 Ac-CoA N N Isoniazid Acetylisoniazid (antituberculotic) (inactive metabolite) Others: NAT1 substrates: p-Aaminobenzoic acid. Procainamide. Sulfamethazine . Hydralazine. p-Aminosalicylic acid. but may also induce apoptosis of normal bone marrow cells as well! . 6-mercaptopurine elimination is slow. METHYLATION Enzymes: Methyltransferases (MT) Cosubstrate: S-adenosylmethionine (SAM) NH2 N N CH3 N _ OOC CH CH2 CH2 S CH2 N NH2 + O OH OH Examples: O-methylation entacapone HO CH3 O _ COMT _ HO CH2 CH COO HO CH2 CH COO SAM NH2 NH2 L-Dopa (antiparkinson drug. this drug may not cause apoptosis of leukemic cells only (which is desirable). In such patients. dopamine precursor) 3-O-Methyl-L-Dopa N-methylation CH2 CH2 NH2 CH2 CH2 NH2 HMT HN N SAM CH3 N N Histamine N-Methylhistamine S-methylation SH S CH3 N N N TPMT N SAM N N N N H H 6-Mercaptopurine (antitumor drug) 6-Methylmercaptopurine Note: In patients with thiopurine methyltransferase (TPMT) deficiency (like in patients treated with allopurinol – see earlier). TYPICALLY: ACTIVE DRUG INACTIVE METABOLITE warfarin 7-hydroxy-warfarin CYP2C9 phenytoin 4-hydroxy-phenytoin CYP2C9 theophylline 1. glyoxylic. „Non-toxic” parent compound toxic metabolite acetaminophen N-acetyl-p-benzoquinoneimine CYP2E1 halothane trifluoroacetyl chloride CYP2E1 cyclophosphamide acrolein CYP3A4. EXCEPTIONALLY: ACTIVE METABOLITE IS FORMED a. AR sulfasalazine 5-aminosalicylic acid Azo-reductase oxcarbazepine 10-hydroxy-carbazepine AK-reductase lovastatin (lactone) lovastatin (free acid) Paraoxonase enalapril (ester) enalaprilate (free acid) Esterase fenofibrate (ester) fenofibric acid (free acid) Esterase ezetimibe ezetimibe-glucuronide UDP-GT minoxidyl minoxidyl-sulfate SULT ethacrynic acid (EA) EA-cysteine GSTGGT. 2C9 carisoprodol meprobamate CYP2C19 risperidone 9-OH-risperidone (paliperidone) CYP2D6 imipramine desmethyl-imipramine CYP2D6 codeine morphine CYP2D6 diazepam nordiazepam oxazepam CYP CYP morphine morphine 6-glucuronide UDP-GT c. EFFECT OF BIOTRANSFORM ATION ON BIOLOGICAL ACTIVITY 1.oxalic acid ADH ALDH doxorubicin doxorubicinol AK-reductase .or 3-methylxanthine CYP2A1 morphine morphine-3-glucuronide UDP-GT acetaminophen acetaminophen-glucuronide UDP-GT isoniazide acetyl-isoniazide NAT2 2. Active parent compound active metabolite phenylbutazone -OH-phenylbutazone CYP2D6. DP b. Inactive parent compound (PRODRUG) active metabolite cyclophosphamide phosphoramide mustard CYP2B6 tamoxifen 4-hydroxy-tamoxifen CYP2D6 parathion paraoxon CYP3A4 terfenadine alcohol acid CYP3A4 chloral hydrate trichloroethanol ADH (rev.). 2B6 methanol formic acid ADH ALDH ethylene glycol glycolic-. OXAZEPAM). are sold as drugs. RISPERDAL). F F OH H3C N H3C N CYP2D6 N N O N O N N O N O Risperidone 9-hydroxy-risperidone (active) (antipsychotic. paliperidone. FIRST INTO ACTIVE PHASE-I METABOLITES (NORDIAZEPAM. T1/2 = 25 hrs .T1/2 = 3 hrs paliperidone (INVEGA). AND FINALLY INTO INACTIVE OXAZEPAM-GLUCURONIDE PHASE-I biotransformation Examples of drugs CH3 whose active metabolites are also drugs: O N diazepam VALIUM > oxazepam SERAX Diazepam risperidone RISPERDAL > paliperidon INVEGA (antianxiety and terfenadine TELDANE* > fexofenadine TELFAST Cl N antiepileptic drug) sulfasalazine SALAZOPYRIN > mesalazine SALOFALK active enalapril ENALAPRIL tabl > enalaprilate VASOTEC inj T1/2= 40 hrs [VALIUM] * Withdrawn .see later N-demethylation CYP2C19 CYP3A4 H O N Nordiazepam Cl N active metabolite PHASE-II biotransformation Hydroxylation CYP (conjugation) H H O O N N UDP-GT OH O -Glucuronic acid UDP-GA Cl N Cl N T1/2= 8 hrs oxazepam oxazepam-glucronide active metabolite inactive and also anti anxiety drug [SERAX] and readily excreted metabolite HYDROXYLATION OF RISPERIDONE TO AN ACTIVE METABOLITE NOTE that both risperidone and its metabolite. BIOTRANSFORMATION OF DIAZEPAM. AND A TOXIC METABOLITE (ACROLEIN) NOTE: Steps 1 and 2 Cl O O cyclophosphamide represent N-dealkylation.g. e. Cl H then chain breaking at the CYP3A4 arrow. M= N (antitumor drug) P starting with hydroxylation on N M the C atom linked to the N atom. immino- spontaneous cyclophosphamide cyclophosphamide 2 cleavage O O O O ALDH1A1 aldophosphamide C P C P O detoxication O H M HO M H2N H2N O-carboxyethyl- 3 phosphoramide mustard spontaneous cleavage O O O SG GSH C C HO P H detoxication H M H2N Acrolein Phosphoramide mustard reacts covalently with protein-SH reacts covalenly with DNA bases SPECIFIC TOXIC EFFECTS ANTITUMOR EFFECT and Liver: GENERAL TOXIC EFFECT damage to the of antitumor drugs sinusoidal endothelial cells. causing hemorrhagic cystitis . BIOTRANSFORMATION OF CYCLOPHOSPHAMIDE INTO THERAPEUTICALLY ACTIVE METABOLITE (PHOSPHORAMIDE MUSTARD). bone marrow depression causing sinusoidal obstruction sy. O O O O O O 4-hydroxy- P P P cyclo- phosphamide N M N M N M H H GS OH 4-glutathionyl. 1 CYP2C9 Here the aldehyde is CYP2B6 aldophosphamide. SOME INACTIVE METABOLITES.. and forming an aldehyde. (SOS) Bladder: damage to the urothelial cells. .BIOTRANSFORMATION OF TERFENADINE (A PRODRUG ANTIHISTAMINE THAT IS PRONE TO CAUSE POLYMORPHIC VENTRICULAR TACHYCARDIA) INTO FEXOFENADINE (AN ACTIVE ANTIHISTAMINE) Terfenadine Terfenadine is INACTIVE as an [TELDANE] antihistamine (it is a prodrug).g. ketoconazole) increased the arrhythmogenic effect of coadministered terfenadine and have caused several fatalities by precipitating polymorphic ventricular extrasystole (torsades de pointes). It has caused HO C N (CH2)3 CH C CH3 polymorphic ventricilar extrasystoles CH3 (called torsades de pointes) especially when the patient also received a CYP3A4 inhibitor drug. Hydroxylation CYP3A4 Ketoconazole Erythromycin OH CH3 HO C N (CH2)3 CH C CH2OH CH3 alcoholic metabolite Dehydrogenation Hydration CYP Dehydrogenation OH CH3 HO C N (CH2)3 CH C COOH The carboxylic acid metabolite CH3 is ACTIVE as an antihistamine! carboxylic acid Now it is marketed as metabolite fexofenadine [TELFAST] CYP3A4 inhibitors (e. terfenanidine CH3 iinhibits repolarization of cardiomyocytes OH and is arrhythmogenic. Now terfenadine is withdrawn and replaced with fexofenadine (TELFAST).. erythromycin. such as ketoconazole or erythromycin. (withdrawn) As a K+ channel inhibitor. minoxidyl-sulfate. On a similar basis. owing to inner salt formation which masks the + and – charges of this conjugate. the sulfate conjugate of 5-hydroxy-triamterene (the metabolite of the diuretic triamterene) is also an active and poorly water-soluble. O O excreted slowly) NH2 S O O The vast majority of sulfate conjugates are highly water-soluble (due to their anionic charge). is poorly water-soluble. pharmacologically inactive and readily excreted (e. in fact it may cause crystalluria by being precipitated out from the urine (see under Diuretics). In contrast. .. acetaminophen-sulfate). N inactive as a vasodilator) O NH2 PAPS Sulfotransferase N N NH2 MINOXIDIL-SULFATE N O OH NH2 S O O + N N NH3 MINOXIDIL-SULFATE inner salt form N (active vasodilator metabolite. pharmacologically active and slowly excreted.g. AN EXCEPTIONAL WAY FOR ACTIVATION OF A DRUG: THE PRODRUG MINOXIDIL FORMS AN ACTIVE SULFATE CONJUGATE N N NH2 MINOXIDIL (prodrug. AN EXCEPTIONAL WAY FOR ACTIVATION OF MORPHINE: BY CONJUGATION WITH GLUCURONC ACID AT THE 6-OH GROUP The superactive nature of Mo-6-glucuronide is explained by inner salt formation (like for minoxidyl-sulfate. intestinal tract cholesterol decreases transporter (NPC1L1) THE SERUM CHOLESTEROL LEVEL DECREASES . see above) Morphine-3-glucuronide Morphine Morphine-6-glucuronide INACTIVE ACTIVE SUPERACTIVE cannot form an inner salt can form an inner salt COOH HO O H H H O HO 3 OH H O OH H OH UDP-GT UDP-GT O O NH UDP-GA UDP-GA NH NH COOH 6 O O HO HO H H H OH H OH OH H AN EXCEPTIONAL WAY FOR ACTIVATION OF EZETIMIBE: BY FORMATION OF A GLUCURONIDE THAT REACHES AND INHIBITS THE INTESTINAL CHOLESTEROL TRANSPORTER COOH O OH O HO OH OH OH OH UDP-GT F N UDP-GA N O F O Ezetimibe-glucuronide (EG) Ezetimibe F F active metabolite produced in the enterocytes and the liver Mrp-2 transporter EG inhibits the the absorption of intestinal cholesterol Bile. INACTIVATING THESE PROTEINS (enzymes. and because (2) in the alcoholist’s liver the amount of glutathione is decreased. NAPBQI = N-acetyl-para-benzoquinoneimine . THEN NAPBQI BINDS COVALENTLY TO THIOL GROUPS IN HEPATOCELLULAR PROTEINS.) AND ULTIMATELY CAUSING LIVER NECROSIS. therefore glutathione is more readily depleted. WHEN ACETAMINOPHEN IS OVERDOSED. NAPBQI IS PRODUCED IN SO LARGE QUANTITIES THAT GLUTATHIONE BECOMES CONSUMED AND DEPLETED. etc. allowing NAPBQI to react with protein-thiols. transporters. O O O HN C CH3 N C CH3 HN C CH3 Acetaminophen toxication = Paracetamol by dehydrogenation CYP2E1 (+) (+) S protein NAPBQI OH O OH detoxication detoxication of paracetamol of NAPBQI UDP-GA glutathione UDP-GT (glu-cys-gly) O O HN C CH3 HN C CH3 S glutathione O glucuronic acid OH EXCRETION HEPATOCELLULAR NECROSIS You must know this! NAPBQI IS NORMALLY DETOXIFIED BY CONJUGATION WITH GLUTATHIONE. mitochondrial e-transport proteins. because (1) in the alcoholist’s liver the amount of CYP2E1 is increased. HOWEVER. DETOXIFICATION OF ACETAMINOPHEN (PARACETAMOL) BY GLUCURONIDATION (OR SULFATION) AT ITS HYDROXYL GROUP AND TOXIFICATION OF ACETAMINOPHEN BY CYP2E1-CATALYZED DEHYDROGENATION TO A REACTIVE ELECTROPHILIC QUINONEIMINE (NAPBQI). therefore more NAPBQI is formed. Alcoholists are hypersensitive to acetaminophen-induced liver injury. ALTERATIONS IN BIOTRANSFORMATION 1.Part B. BIOLOGICAL ALTERATIONS IN BIOTRANSFORMATION . UDP-GT Diazepam Floppy infant syndrome (see FIG) . Neonatal immaturity of biotransformation Genetic alterations: .Mutation of genes encoding drug metabolizing enzymes the mutant gene may code for an inactive or unstable enzyme protein POOR or SLOW metabolizer phenotype Such individuals may be hyperreactive to the drug if the active parent compound is slowly converted into inactive metabolite. NEONATAL IMMATURITY OF BIOTRANSFORMATION summary UDP-GT immaturity Bilirubin Physiological jaundice (see FIG) Chloramphenicol Grey baby syndrome (see FIG) Immature glycine conjugation Benzyl alcohol Gasping syndrome (see FIG) Immature CYP. .summary Age-related alterations .Multiplication of genes encoding drug metabolizing enzymes the gene in multiple copies codes for multiple amounts of enzyme protein EXTENSIVE or RAPID metabolizer phenotype Such individuals may be non-reactive to the drug if the active parent compound is rapidly converted into inactive metabolite. .UDP-GT immaturity: physiological jaundice. chloramphenicol-induced grey baby sy. Bilirubin (not excreted into bile) Bilirubin diglucuronide (excreted into bile) H H H H H H H H O N CH N CH2 N CH N O O N CH N CH2 N CH N O UDP-GT H3C H3C UDP-GA H3C H3C CH 3 CH CH2 CH 3 CH CH2 CH 2 CH CH 2 CH2 CH 3 CH 2 CH CH 2 CH2 CH 3 CH2 CH2 _ CH2 CH2 _ OOC O O COO C C C C HO O O OH O O O O OH HO HO OH HO OH Chloramphenicol (CL) Chloramphenicol glucuronide _ COO OH OH O UDP-GT O2N CH CH CH2 OH O2N CH CH CH2 O UDP-GA HO OH NH C CHCl2 NH C CHCl2 OH O O At high concentration. CL inhibits mitochondrial protein synthesis. causing: > cardiomyopathy > myopathy = GREY BABY SYNDROME Immature glycine conjugation: benzyl alcohol-induced gasping syndrome CH2 OH CYP Cytochrome P450 ADH Alcohol-dehydrogenase AOX Aldehyde-oxydase BCS Benzoyl-CoA-synthetase BC:GT Benzoyl-CoA:glycine-N-acyl-transferase Benzyl-alcohol BA accumulation acidosis LOW CAPACITY STEP gasping IN NEONATES ADH O O O O C C C C H OH S-CoA NH CH2 COOH AOX BCS BC:GT URINE CoA-SH glycine O2= benzaldehyde benzoic acid benzoyl-CoA benzoyl-glycine (BA) (hippuric acid) Note: The use of benzyl alcohol is prohibited in neonatology care units. ethanol elimination in the mother-fetus “unit” was entirely carried out by ADH in the maternal tissues. After delivery. T1/2= 40 hrs CYP2C19 SLOW STEPS CYP3A4 IN NEONATES H H H O O O N N N CYP UDP-GT OH O glucuronic acid UDP-GA Cl N Cl N Cl N T1/2= 8 hrs nordiazepam oxazepam oxazepam-glucronide active active inactive [SERAX] Immature alcohol dehydrogenase: delayed elimination of ethanol from the baby monkey whose mother received ethanol before delivery BLOOD ETHANOL CONC.Immature CYP. . UDP-GT: diazepam-induced floppy infant syndrome (FIS) CH3 O N diazepam FIS developes in a baby active whose mother received diazepam Cl N [VALIUM] before delivery. This also happens to diazepam in floppy infant sy (see above). (mg%) 140 NEONATAL MATERNAL 120 100 80 60 40 DELIVERY 20 0 0 50 100 150 200 250 300 350 TIME (min) Interpretation: Before delivery. the ethanol that remained in the baby can only be eliminated at a very slow rate because ADH is barely expressed in the neonatal tissues. Multiplication of genes encoding drug metabolizing enzymes the gene in multiple copies codes for multiple amounts of enzyme protein EXTENSIVE metabolizer (non-reactive) phenotype Multiplication of CYP2D6 gene ultrarapid metabolizer phenotype Psychotropic drugs.SSRIs (fluoxetine. paroxetine) and . e. Dihydropyrimidine dehydrogenase deficiency 5-Fluorouracyl Myelotoxicity II. . hydralazine Systemic lupus erythemathodes 4. Thiopurine methyltransferase deficiency 6-Mercaptopurine Myelotoxicity 5. NAT2 deficiency slow acetylator phenotype Isoniazide Neurotoxicity. GENETIC ALTERATIONS IN BIOTRANSFORMATION I. CYP deficiencies Adverse effects at regular dose: CYP2C9 deficiency Warfarin hydroxylation Bleeding CYP2C19 deficiency Diazepam N-demethylation Prolonged sedation CYP2D6 deficiency Debrisoquin hydroxylation Pronounced hypotension N-dealkylation of TCADs Pronounced sedation. toxicity N-dealkyl.. (most are CYP2D6 substrates) . mianserine) are all ineffective at regular doses . tics) 2. of antipsychotics Tardive dyskinesia (involuntary movements.TCADs (imipramine.Others (clozapine. Carboxylesterase (pseudocholinesterase) deficiency Succinylcholine Prolonged paralysis 3. Mutation of genes encoding drug metabolizing enzymes the mutant gene may code for an inactive or unstable enzyme protein POOR metabolizer (hyperreactive) phenotype 1. nortriptyline).g. hepatotoxicity Procainamide. . CYP3A4 is the most abundant in human liver (35% of total) and in human small intestinal mucosa cells (80% of total intestinal CYP). e. and therefore CYPs that remain uninhibited may still eliminate the drug. CYP1A2 and CYP3A4 . CYP2E CYP family members – labeled with numbers after the letter of the subfamily. CYP2 and CYP3 families are involved in biotransformation of drugs.Phenytoin and warfarin are hydroxylated by CYP2C9 .g.Diazepam is N-demethylated by CYP2C19 and CYP3A4 . CYP2D6.Dextromethorphan is O-demethylated by CYP2D6 and CYP3A4 A drug that is biotransformed by multiple CYPs. CHEMICAL ALTERATIONS IN BIOTRANSFORMATION . which often inhibit one specific CYP enzyme. is cholesterol 7- hydroxylase. CYP2C19. (CYP7A. Some drugs are biotransformed largely or exclusively by one CYP. CYP2C.. For example: .Acetaminophen is dehydrogenated by CYP2E1 (mostly). CYP3A4 Of all the CYPs. 2. CYP2C9. is typically less susceptible to pharmacokinetic interactions by CYP inhibitors. CYP superfamily organization: CYP families – labeled with numbers.g. for example. For example: . CYP inducers and inhibitors thus may significantly affect the fate and the effect of other drugs that are biotransformed by CYP enzymes. e.Halothane is oxidatively debrominated by CYP2E1 Other drugs may be biotransformed by several CYPs. CYP2B.summary Overexpression of enzymes by inducers Inhibition of enzymes by inhibitors Cytochrome P450 enzymes are often induced or inhibited by certain drugs or other chemicals. the rate limiting enzyme of bile acid synthesis.) CYP subfamilies – labeled with capital letters. only CYP1. Inducers may induce multiple CYP members. although CYP2E1 is not truly induced by ethanol but is stabilized by it. Induction is usually caused by increased gene transcription. The inducer is a drug or other chemical which binds as a ligand to the ligand- activated transcription factor (intracellular receptor) and activates it. phenobarbital. constitutive androstane receptor (CAR) and pregnane X receptor (PXR). etc. thus promoting the transcription of such genes. John's wort).ENZYME INDUCTION: Induction means increased synthesis of the enzyme protein. ultimately increasing CYP protein synthesis. which is mediated by ligand-activated transcription factors. (see the table on the next page). For example. hyperforin (St. PXR = Pregnane X receptor RXR = Retinoid X receptor . The activated transcription factor (with its dimerizing partner) binds to a cognate sequence in the regulatory region of one or more CYP genes. such as aryl hydrocarbon receptor (AhR).) THE MECHANISM OF CYP3A4 INDUCTION BY DRUGS: Increased CYPA4 gene transcription by activated pregnane X-receptor (PXR) Xenobiotic* (Ligand) Increased expression of CYP3A4 PXR Increased transcription of CYP3A4 mRNA Plasma membrane DNA ER6 CYP3A4 (CYP3A7) Nucleus RXR *Ligands: rifampicin. whereas ethanol induces only CYP2E1 (called ethanol-inducible CYP form. phenobarbital induces CYP2 members (except CYP2D) and CYP3A4. nisoldipine. venlafaxine. encainide. Aryl acetaminophen TCDD. atorvastatin. receptor C19: moclobemide desipramine. ster) tacrolimus. dapsone. Miscellaneous drugs: codeine. warfarin. acetaminophen. Statins: hyperforin (an naringenin: a flvonoid. bupropion. indole-3-carbinol hydrocarbon cimetidine (in brussels sprouts. cabbage) CYP2 B6: cyclophosphamide. diazepam. dextromethorphan. bufuralol. sirolimus. ondansetron. Others: buspirone. fluvoxamine broiled meat. tizanidine. inducible) fluoxetine propafenone. C19: CAR: B6: clopidogrel C9: phenytoin. metoprolol. clomipramine. simvastatin. (CYP2D6 is NOT terbinafine propranolol. E1: ethanol. acyclovir receptor broccoli. taxol John's wort) in grapefruit juice) . Drugs: omeprazole AHR: A2: ciprofloxacine CYP1 Others: PAHs (charcoal- A2: caffeine. prazepam. clonazepam. spironolactone inhibitor contrac. nifedipine HIV protease inhib verapamil. fluvastatin rifampin Constitutive C9: amiodarone D6: Psychotropic drugs: SSRI (citalopram. nelfinavir. tolbutamide phenobarbital ticlopidin C19: omeprazole. HIV antivirals: indinavir. felodipine. paroxetine debrisoquine. fluoxetine. nifedipine. triazolam. isoniazide D6: cimetidine mianserine. nortriptyline). flurazepam. halazepam. Calcium channel phenytoin Pregnane X Azole antifungals blockers: amlodipine. rifabutin PXR: A4: clorazepate. diazepam. fluconazole paroxetine). antidepressant in St -cumarin (both present codeine. mirtazapine. unless induced. dextromethorphan. ritonavir. theophylline. rifampin. diltiazem. Immunesuppressive drugs: cyclosporine. B6: phenytoin androstane (+D6). erythromycin. phenformin E1: disulfiram E1: halothane. carbamazepine receptor Macrolide antibiot. Steroids: estradiol. timolol).CYP Inducer Inducer Inhibitors (often Drug substrates family chemicals receptors (TFs) competing substrates) A1: barely expressed. isradipine. simvastatin Dietary chemicals: hydrocortisone. flecainide. phenobarbital Drugs: (3A4) midazolam. imipramine. bergamottin: a furano lovastatin. C9. lercanidipine. TCAD (amitriptyline. progesterone. testosterone. ketamine B6. methadone. nitrendipine. dexamethasone Gestodene (suicide saquinavir. theophylline CYP3 Benzodiazepines: alprazolam. Macrolide antibiotics: lovastatin clarithromycin. clozapine. smoking). Cardiovascular quinidine drugs: -blockers (alprenolol. Barbiturates (both substrates and inducers of CYP2 and CYP3A4) Meprobamate (both substrate and inducer of CYP) 2. tacrolimus.g. phenytoin. a CYP3A4 substrate) INSUFFICIENT CONTRACEPTIVE EFFECT of the contraceptive UNWANTED PREGNANCY.g.CONSEQUENCES OF CYP INDUCTION: 1. all are CYP3A4 substrates) INSUFFICIENT IMMUNOSUPPRESSION TRANSPLANT REJECTION. thus the inducer accelerates the biotransformation of the coadministered drug into inactive metabolites diminished effect e. rifampin. CYP2C9 inducers (phenobarbital.g. cyclosporine A. carbamazepine) + immunophyllin-binding immunosuppressive drug (e. sirolimus. CYP2C9 substrate) INSUFFICIENT ANTICOAGULANT EFFECT of warfarin! THROMBOSIS. carbamazepine) + an oral contraceptive (contains ethinyl estradiol. Enhanced toxification of a coadministered drug after repeated administration of the inducer Occurs when the inducer drug induces a CYP which transforms the coadministered drug into a toxic metabolite. Enhanced inactivation of some coadministered drugs after repeated administration of the inducer Occurs when the inducer drug induces a CYP which transforms the coadministered drug into inactive metabolite. rifampin) + warfarin (anticoagulant. despite immunosuppressive therapy! 3. despite taking a contraceptive! CYP3A4 inducers (phenobarbital. rifampin. Enhanced inactivation of a drug after repeated administration Occurs when the drug is both a substrate and an inducer of a CYP. phenytoin.) increased formation of N-acetyl-p-benzoquinone imine (NAPBQI) HEPATIC NECROSIS! Another cause of increased susceptibility of drinkers to paracetamol- induced liver injury: lower hepatic GSH detoxication of NAPBQI CYP2E1 inducer (ethanol) + halothane anesthesia increased formation of trifluoroacetyl chloride the probability for halothane HEPATITIS may increase! . thus the inducer accelerates the biotransformation of the coadministered drug into toxic metabolites increased toxicity e.g. CYP2E1 inducer (ethanol) + acetaminophen overdose (CYP2E1 substr. despite warfarin therapy! CYP3A4 inducers (phenobarbital. thus it accelerates its own biotransformation into inactive metabolites diminished effect (self-induced tolerance) e.. itraconazole.g. Decreased inactivation of an active drug increased adverse effect: e.CONSEQUENCES OF CYP INHIBITION: 1. effect: e. CYP2D6 substrate) decreased conversion into 4-hydroxytamoxifen (active antiestrogen) – see FIGURE Thus.g. itraconazole. a CYP3A4 inhibitor (e. erythromycin) + terfenadine (a withdrawn antihistamin. CYP3A4 substrate) POLYMORPHIC VENTRICULAR ES!– see FIG. HYPOTENSION! – see FIG. a CYP3A4 inhibitor (e. CYP3A4 substr.g. a CYP1A2 inhibitor (e. fluvoxamine) + tizanidine (a central muscle relaxant 2-receptor agonist. CYP1A2 substr. Decreased inactivation of an active drug increased therap.. bergamottin) + a CYP3A4 substrate statin (not pravastatin. fluoxetine or paroxetine) + tamoxifen (an antiestrogen prodrug.) oral bioavailability and elimination of CsA Two consequences (Two birds are killed with one stone!): effectiveness (dose reduction saving on the drug) the antifungal ketokonazole prevents fungal infection of the immunosuppressed patient 2.. CYP2D6 inhibitors can compromise the effectiveness of tamoxifen against estrogen-dependent breast cancers! 4.. Decreased toxification of a drug decreased toxic effect e.g.g. CYP2E1 substrate) decreased conversion into trifluoroacetyl chloride (reactive metab. ketoconazole) + cyclosporine A (CsA.g. fluvastatin. amiodarone) + the oral anticoagulant warfarin BLEEDING! a CYP3A4 inhibitor (e.g. .. ciprofloxacin.g. a CYP2D6 inhibitior (e. a CYP2C9 inhibitor (e. an immunosuppressive drug..) Thus..g. CYP2E1 inhibitior (disulfiram) + halothan (an inhalation anesthetic. clarithromycin.) HYPOGLYCEMIA! a CYP3A4 inhibitor (e. ketoconazole.g. disulfiram pretreatment before halothane anesthesia could be used to decrease the likelihood of halothane hepatitis. rosuvastatin) MYOTOXICITY! – see FIG. 3.) EXCESSIVE SEDATION.. clarithromycin) + the oral antidiabetic repaglinide (CYP3A4 substr. Decreased activation of a prodrug decreased therapeutic effect e.g. . gemfibrozil). 1998. etc.) may increase the myotoxicity of statins by diminishing their elimination by CYP3A4. OATP inhibitors. A PRODRUG) AND ITS ACTIVE METABOLITE SIMVASTATIN ACID SEVERAL FOLD.. itraconazole. 64: 477-483. Pharmacol.) 30 15 Simvastatin acid (ng/ml) 25 Simvastatin (ng/ml) 20 grapefruit juice + SV 10 grapefruit juice + SV 15 10 5 water + SV water + SV 5 0 0 0 2 4 6 8 10 12 14 16 18 20 22 24 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (h) Time (h) BIOTRANSFRORMATION PATHWAYS FOR THE CHOLESTEROL-LOWERING DRUG SIMVASTATIN INTO ACTIVE SIMVASTATIN ACID BY PARAOXONASE AND INACTIVE METABOLITES BY CYP3A4 HO O HO COOH O OH O O Paraoxonase O O HOH Simvastatin Simvastatin acid (inactive) (active) CYP3A4 naringenin. may also increase the myotoxicity of statins by diminishing their hepatic uptake mediated by OATP.GRAPEFRUIT JUICE (contains bergamottin which inhibits CYP3A4 as well as the OATP transporter-mediated hepatic uptake of statins) INCREASES THE PLASMA CONCENTRATION OF SIMVASTATIN (SV. Clin. such as constiuents of grapefruit juice (naringenin and bergamottin) as well as drugs (itraconazole. verapamyl. . erythromycin. Ther. bergamottin.g. (Lilja et al. verapamil HO O HO O HO O O O O O O O O O O HO OH H2C 6'-hydroxy SV 3'-hydroxy SV 6'-exomethylene SV CYP3A4 inhibitors. such as the grapefruit juice constituent bergamottin and the fibrate- type triglyceride-lowering drugs (e. . such as ketoconazole or erythromycin. terfenanidine CH3 iinhibits repolarization of cardiomyocytes OH and is arrhythmogenic.g. erythromycin. Now terfenadine is withdrawn and replaced with fexofenadine (TELFAST). Hydroxylation CYP3A4 Ketoconazole Erythromycin OH CH3 HO C N (CH2)3 CH C CH2OH CH3 alcoholic metabolite Dehydrogenation Hydration CYP Dehydrogenation OH CH3 HO C N (CH2)3 CH C COOH The carboxylic acid metabolite CH3 is ACTIVE as an antihistamine! carboxylic acid Now it is marketed as metabolite fexofenadine [TELFAST] CYP3A4 inhibitors (e.BIOTRANSFORMATION OF TERFENADINE (A PRODRUG ANTIHISTAMINE THAT IS PRONE TO CAUSE POLYMORPHIC VENTRICULAR TACHYCARDIA) INTO FEXOFENADINE (AN ACTIVE ANTIHISTAMINE) Terfenadine Terfenadine is INACTIVE as an [TELDANE] antihistamine (it is a prodrug) (withdrawn) As a K+ channel inhibitor. It has caused HO C N (CH2)3 CH C CH3 polymorphic ventricilar extrasystoles CH3 (called torsades de pointes) especially when the patient also received a CYP3A4 inhibitor drug. . ketoconazole) increased the arrhythmogenic effect of coadministered terfenadine and have caused several fatalities by precipitating polymorphic ventricular extrasystole (torsades de pointes). a centrally acting muscle relaxant. which is a 2-receptor agonist like N clonidine. Therefore.7) and rapid Cl N elimination (T1/2 = 2. ROFECOXIB OH Tizanidine. CIPROFLOXACIN. CYP2D6 used against breast cancer) tamoxifen (prodrug) SSRI (e. ------------------------------------------------------------------------------------------------------------------- O CH3 O CH3 N N CH3 CH3 -hydroxytamoxifen (active antiestrogen. drugs that inhibit CYP1A2 (e. fluoxetine or paroxetine) can compromise the therapeutic effectiveness of tamoxifen against estrogen-dependent breast cancer because they inhibit the conversion of tamoxifen into 4- hydroxytamoxifen. ..5 hrs) of tizanidine.g. tizanidine.g. This is responsible for both its S hepatic presystemic elimination (F = 0. the active antiestrogen metabolite of tamoxifen. ciprofloxacin. At high level. is rapidly N biotransformed by CYP1A2. fluvoxamine. fluoxetine OH paroxetine) CYP2D6 inhibitors (e. can cause marked hypotension. bradycardia and sedation. H N NH rofecoxib) can increase the AUC of tizanidine several fold. N N N S S S Cl N Cl N Cl N hydroxylation dehydrogenation H H H N NH CYP1A2 N CYP1A2 N NH NH N Tizanidine N N HO O hydroxylation CYP1A2 FLUVOXAMINE..g. Some cephalosporins: cefamandol. but a CYP inhibitor as well.Procarbazine .Chloramphenicol . like disulfiram does. 1-methyltetrazole-5-thiol.g.Metronidazole .g.) .. moclobemide) – to treat major depression MAO B inhibitors (e. cefoperazone (Their metabolite.THERAPEUTIC USE OF ENZYME INHIBITORS CYP inhibitors: Ketoconazol – to increase effectiveness of cyclosporine (to save on the drug) Disulfiram – to decrease the likelihood of • halothane hepatitis or • acetaminophen-induced hepatic necrosis MAO inhibitors: MAO A inhibitors (e.. selegiline) – to treat Parkinson's disease COMT inhibitors: Entacapone – to treat Parkinson's disease XO inhibitors: allopurinol – to decrease uric acid formation (in gout) (BUT: it decreases the elimination and thus increases the toxicity of 6-mercaptopurine!) Alcohol dehydrogenase inhibitors: Fomepizol. Drugs with unwanted ”disulfiram-like effect”: . disulfiram is not only an irreversible ALDH inhibitor. ethanol – to treat methanol or ethylene glycol intoxication Aldehyde dehydrogenase (ALDH) inhibitors: Disulfiram – to induce „acetaldehyde syndrome” and thus promote alcohol withdrawal Note. inhibits aldehyde dehydrogenase.