Biotransformation Biotransformation Siva Nageswararao Mekala Assistant Professor Dept. of clinical Pharmacology

Biotransformation It is the chemical transformation of the It is the chemical transformation of the drug within the living organism drug within the living organism

What happens to metabolized drug ? Lipid soluble and Unionized compounds Converted Converted Water soluble or more ionized compounds Water soluble or more ionized compounds reducing renal tubular reabsorption reducing renal tubular reabsorption facilitating their excretion facilitating their excretion  Drug metabolism does not always result in detoxification and inactivation of drugs

 Foreign chemicals or xenobiotics (substances foreign to the body)  Environmental contaminants as well as in our diets.  Plants (phytoallexins) eg, poisonous mushrooms  Drugs are considered xenobiotics Most are extensively metabolized in humans. Most are extensively metabolized in humans.

Humans exposed exposed Environmental pollution, food additives, cosmetic products, agrochemicals, processed foods, and drugs. Environmental pollution, food additives, cosmetic products, agrochemicals, processed foods, and drugs. ( lipophilic chemicals) ( lipophilic chemicals) If there is absence of metabolism accumulate in the body, accumulate in the body, Resulting in toxicity

 Biotransformation reactions may have four different consequences with respect to pharmacologic activity: i. i. ACTIVATION: An inactive precursor is converted into pharmacologically An inactive precursor is converted into pharmacologically active drug active drug L-dopa (inactive) to Dopamine(active) L-dopa (inactive) to Dopamine(active) prednisone(inactive) to prednisolone(active) prednisone(inactive) to prednisolone(active) Such inactive drugs are known as PRODRUGS Such inactive drugs are known as PRODRUGS

Prodrugs have following advantages: Prodrugs have following advantages: Active form is more stable Active form is more stable Better bioavailability Better bioavailability Desired pharmacokinetics Desired pharmacokinetics Less side effects and toxicity Less side effects and toxicity e.g., Enalapril – Enalaprilat e.g., Enalapril – Enalaprilat Bacampicillin – Ampicillin Bacampicillin – Ampicillin Acyclovir- Acyclovir triphosphate Acyclovir- Acyclovir triphosphate

ii. MAINTENANCE OF ACTIVITY: An active substance is converted into active metabolite An active substance is converted into active metabolite e.g: Diazepam to Oxazepam e.g: Diazepam to Oxazepam Codeine to Morphine Codeine to Morphine iii. INACTIVATION: An active drug is converted to inactive products An active drug is converted to inactive products e.g: Pentobarbital to Hydroxypentobarbital e.g: Pentobarbital to Hydroxypentobarbital iv. ACTIVE DRUG TO HIGHLY TOXIC METABOLITE : eg: Paracetamole converts N-acetyl-p-benzoquinoneimine eg: Paracetamole converts N-acetyl-p-benzoquinoneimine

Sites  Metabolizing enzymes are found in most tissues in the body with the highest levels located in the tissues of the gastrointestinal tract [liver, small and large intestines]  For orally administered drug---- LIVER Lower gut Lower gut  In addition, drugs may be metabolized by gastric acid (eg, penicillin)  digestive enzymes (eg, polypeptides such as insulin)  enzymes in the wall of the intestine (eg, sympathomimetic catecholamines

 Other organs that contain significant xenobiotic- metabolizing enzymes include the tissues of the nasal metabolizing enzymes include the tissues of the nasal mucosa and lung mucosa and lung

 Biotransformation reactions can be assigned to two major categories: categories:  PHASE - I (NON-SYNTHETIC REACTIONS): Convertion of the parent drug to a more polar metabolite by introducing or unmasking a functional group (–OH, –NH2, –SH). Convertion of the parent drug to a more polar metabolite by introducing or unmasking a functional group (–OH, –NH2, –SH).  PHASE - II(SYNTHETIC REACTIONS): Enzymes form conjugate of the substrate Enzymes form conjugate of the substrate

2/16/2016 NOTE: Drugs originally containing reactive groups NH 2, OH or COOH - can undergo direct phase 2 reactions COOH - can undergo direct phase 2 reactions

PHASE I In this enzymes carry out  Oxidation: Addition of Oxygen and/or removal of Hydrogen. It is the most Addition of Oxygen and/or removal of Hydrogen. It is the most important and common metabolic reaction. important and common metabolic reaction.  Reduction: Removal of oxygen or addition of hydrogen Removal of oxygen or addition of hydrogen  Hydrolytic reactions: Breakdown of the compound by addition of water Breakdown of the compound by addition of water  Cyclization: This is formation of ring structure from a straight chain This is formation of ring structure from a straight chain compound compound  Decyclization : This is opening up of ring structure of the cyclic drug molecule. This is opening up of ring structure of the cyclic drug molecule.

 OXIDATIVE REACTIONS: Eg: Phenytoin,Phenobarbitone,Propranolol, pentobarbitone Eg: Phenytoin,Phenobarbitone,Propranolol, pentobarbitone  REDUCTION REACTIONS: Eg: Chloramphenicol, methadone, Halothane,Warfarin Eg: Chloramphenicol, methadone, Halothane,Warfarin  HYDROLYSIS REACTION: Eg: Esters: Procaine, Succinylcholine Eg: Esters: Procaine, Succinylcholine Amides: lignocaine,Procainamide Amides: lignocaine,Procainamide  CYCLIZATION: Proguanil  DECYCLIZATION: Barbiturates,phynytoin 2/16/2016

Classes of enzymes: Classes of enzymes: i. Cytochrome P450s (P450 or CYP), ii Flavin-containing monooxygenases (FMO) iii Epoxide hydrolases - Hydrolysis of epoxides (mES, sES) 2/16/2016

CYTOCHROME P(CYP ) CYTOCHROME P(CYP )  The CYPs are a superfamily of enzymes, all of which contain a molecule of heme that is noncovalently bound to the polypeptide chain  CYPs use O2, plus H+ derived from the NADPH to carry out the oxidation of substrates 2/16/2016

CYPs Specificity metabolism of bile acids such as steroids, estrogens synthesis of endogenous compounds metabolism of dietary and xenobiotic CYPs (> 50)

CYP 19 Testosterone Testosterone Estrogen(estradiol) Aromatase ( member of the cytochrome P450 superfamily)

CYP3A4 family 3 subfamily A gene number 4

 In humans the 12 CYPs that are important are: CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4, and 3A5 CYP1A1, 1A2, 1B1, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4, and 3A5 CYP1A2, 15% CYP2A6, 4% CYP2C9, 20% CYP2D6, 5% CYP2E1, 10% CYP3A4 30%

PHASE II In Phase II consists of Conjugation reaction. In Phase II consists of Conjugation reaction. Phase 2 "transferases“  Sulfotransferases Addition of sulfate (SULT) (SULT)  UDP-glucuronosyl Addition of glucuronic acid transferases (UGT) transferases (UGT)  Glutathione-S- Addition of glutathione transferases (GST) transferases (GST)  N-acetyltransferases Addition of acetyl group (NAT) (NAT)  Methyltransferases Addition of methyl group (MT) (MT)

PHASE II REACTIONS PHASE II REACTIONS  Parent drugs or their phase I metabolites undergo coupling or conjugation reactions with an endogenous substance to yield drug conjugate  Conjugates are polar molecules that are readily excreted and often inactive. 2/16/2016

Type of Endogenous Examples Type of Endogenous Examples Conjugation Reactant Conjugation Reactant  Glucuronidation UDP glucuronic acid morphine (Hydroxyl or carboxyl acid group) diazepam (Hydroxyl or carboxyl acid group) diazepam  Acetylation Acetyl-CoA isoniazid, dapsone (Amino or hydrazine residues) (Amino or hydrazine residues)  Glutathione Glutathione Acetaminophen Conjugation (GSH), Conjugation (GSH), (Quinone or epoxide reactive intermediates) (Quinone or epoxide reactive intermediates)

Type of Endogenous Examples Conjugation Reactant Conjugation Reactant  Glycine GlycineAcyl -CoA Salicylic acid Conjugation nicotinic acid (Having carboxylic acid group)-minor pathway  Sulfation Phosphoadenosyl Estrone (Phenolic or steroids) phosphosulfate methyldopa (Phenolic or steroids) phosphosulfate methyldopa  Methylation S-Adenosyl Dopamine methionine, epinephrine, histamine methionine, epinephrine, histamine (Amines and phenols)  Water Water Benzopyrene Conjugation Leukotriene A4 Conjugation Leukotriene A4

Phenytoin Phenytoin 4-hydroxyphenytoin (highly lipophilic) (Slightly water soluble) 4-hydroxyphenytoin beta-d-glucuronide (highly water soluble) CYP (PHASE I) UGT+UDP-GA (PHASE II)

Drug metabolizing enzymes Drug metabolizing enzymes Microsomal Non microsomal Located in smooth ER Catalyzes phaseI and Phase II glucuronidation Cytoplasm and mitochondria Catalyzes all conjugation reactions except glucuronidation INDUCIBLE BY DRUGSNON- INDUCIBLE BY DRUGS

Hofmann Elimination  Inactivation of a drug in the body fluids by spontaneous molecular rearrangement without the agency of enzyme (Non molecular rearrangement without the agency of enzyme (Non enzymatic degradation in the plasma) enzymatic degradation in the plasma) E.g., ATRACURIUM E.g., ATRACURIUM - cleavage of the N-alkyl portion in the benzylisoquinoline - cleavage of the N-alkyl portion in the benzylisoquinoline

ENZYME INDUCTION Repeated administration of certain drugs increases the synthesis of microsomal enzymes - Chemically induce P450 Repeated administration of certain drugs increases the synthesis of microsomal enzymes - Chemically induce P450 enhancing the rate of its synthesis reducing its rate of degradation

 Induction involves microsomal enzymes in liver and other organs organs  It increases rate of metabolism by 2-4 fold

 Various substrates inducing P450 are Drugs: inducing CYP3A4 are Drugs: inducing CYP3A4 are Barbiturates, carbamazepine, phenytoin, rifampin Barbiturates, carbamazepine, phenytoin, rifampin Environmental pollutants: induce CYP1A1/2 enzymes- Environmental pollutants: induce CYP1A1/2 enzymes- activation of procarcinogens activation of procarcinogens Eg: tobacco smoke, charcoal-broiled meat, Eg: tobacco smoke, charcoal-broiled meat, polycyclic hydrocarbons polycyclic hydrocarbons

Clinical relevance of enzyme induction a) Drug drug interactions: Oral contraceptive and rifampicin : Oral contraceptive and rifampicin : Rifampicin induces the drug metabolizing enzyme of oral Rifampicin induces the drug metabolizing enzyme of oral contraceptives, thus enhancing the metabolism and leading to contraceptives, thus enhancing the metabolism and leading to contraceptive failure. contraceptive failure. Phenytoin accelerates metabolism of vit.D3 and lead to Phenytoin accelerates metabolism of vit.D3 and lead to osteomalacia osteomalacia

c) Therapeutic benefits: To treat neonatal jaundice To treat neonatal jaundice - phenobarbitone can be given to infant soon after birth to - phenobarbitone can be given to infant soon after birth to induce hepatic glucuronyl transferase induce hepatic glucuronyl transferase (Bilirubin is conjugated and excreted) (Bilirubin is conjugated and excreted)

- In Cushing’s syndrome (Abnormally high levels of cortisol) phenytoin may reduce the manifestations by enhancing phenytoin may reduce the manifestations by enhancing degradation of steroids degradation of steroids - Chronic poisoning : faster metabolism of accumulated poisonous substance poisonous substance - Vegetables like cabbage,spinach etc can induce microsomal enzymes and promotes the rapid elimination of the drugs enzymes and promotes the rapid elimination of the drugs

ENZYME INHIBITION  Certain drug substrates inhibit cytochrome P450 enzyme activity activity cimetidine and ketoconazole cimetidine and ketoconazole bind tightly to the P450 heme iron bind tightly to the P450 heme iron reduce the metabolism of endogenous substances reduce the metabolism of endogenous substances competitive inhibition. competitive inhibition.

Factors affecting drug biotransformation  AGE: Increased susceptibility to the pharmacologic or toxic activity Increased susceptibility to the pharmacologic or toxic activity of drugs is seen in young and very old patients compared with of drugs is seen in young and very old patients compared with young adults.In neonates mainly due to diminished activity of young adults.In neonates mainly due to diminished activity of hepatic microsomal enzymes. hepatic microsomal enzymes.  SEX: dependent differences in drug metabolism exist in humans for ethanol, propranolol, some benzodiazepines, estrogens, and salicylates. dependent differences in drug metabolism exist in humans for ethanol, propranolol, some benzodiazepines, estrogens, and salicylates. N-Demethylation of erythromycin F>M. N-Demethylation of erythromycin F>M. Propranolol oxidation M>F. This is most probably due to hormonal differences Propranolol oxidation M>F. This is most probably due to hormonal differences

DIET AND ENVIRONMENTAL FACTORS DIET AND ENVIRONMENTAL FACTORS Charcoal-broiled foods and cruciferous vegetables induce Charcoal-broiled foods and cruciferous vegetables induce CYP1A enzymes CYP1A enzymes Grapefruit juice inhibits the CYP3A metabolism of Grapefruit juice inhibits the CYP3A metabolism of coadministered drug substrates coadministered drug substrates Cigarette smokers metabolize some drugs more rapidly than Cigarette smokers metabolize some drugs more rapidly than nonsmokers because of enzyme induction nonsmokers because of enzyme induction

DRUG DRUG INTERACTIONS DURING METABOLISM:DRUG DRUG INTERACTIONS DURING METABOLISM:  Enzyme-inducing drugs like sedative-hypnotics, antipsychotics, anticonvulsants, the sedative-hypnotics, antipsychotics, anticonvulsants, the antitubercular drug rifampin, and insecticides may increase antitubercular drug rifampin, and insecticides may increase the requirement dose of drugs like warfarin the requirement dose of drugs like warfarin

DISEASES AND METABOLISMDISEASES AND METABOLISM  Disease like alcoholic hepatitis, cirrhosis impair hepatic drug metabolising enzymes metabolising enzymes E.g. half-life of diazepam in patients with liver abnormality are E.g. half-life of diazepam in patients with liver abnormality are greatly increased, with a corresponding prolongation of their greatly increased, with a corresponding prolongation of their effects effects

GENETIC VARIATION (Pharmacogenetics)GENETIC VARIATION (Pharmacogenetics)  Genetic factors that affect enzyme level leads to difference in metabolism

 Defect Enzyme Drug Clinical Involved Consequences Involved Consequences N-Acetylation N-acetyl Isoniazid Peripheral N-Acetylation N-acetyl Isoniazid Peripheral transferase neuropathy transferase neuropathy Ester Plasma Sch Prolonged Ester Plasma Sch Prolonged hydrolysis cholinesterase apnea hydrolysis cholinesterase apnea G6PD Deficiency –Hemolysis when exposed to certain drugs like Sulphonamides, Salicylates G6PD Deficiency –Hemolysis when exposed to certain drugs like Sulphonamides, Salicylates

THANK YOU…! THANK YOU…! 2/16/2016