Microsomal enzyme induction

microsomal enzyme induction

1. Microsomal Enzymes Dr. Renu Yadav Resident Pharmacology

2. Learning Objectives Introduction Biotransformation Microsomal enzymes Cytochrome p450 enzymes Clinical relevance of drug metabolism Conclusion

3. Bio-transformation DEFINITION : Chemical alteration of the drug in the body. Non-polar compounds to polar (lipid-insoluble) compounds . SITES : liver kidney intestine lungs

4. Actions Inactivation EG : Ibuprofen, lidocaine, propranolol 2. Active metabolite from active drug Active drug Active metabolite Morphine Morphine-6-glucoronide Codeine Morphine Amitryptiline Nortriptiline Spironolactone Canrenone Imipramine Desimipramine

5. 3. Active metabolite from inactive drug Prodrug Active form Levodopa Dopamine Enalapril Enalaprilat Prednisone Prednisolone Sulfasalazine 5-aminosalicylic acid Acyclovir Acyclovir triphosphate

6. Bio-transformation Phases Phase 1 Phase 2 Non-Synthetic/functionalization reactions Metabolite may be active or inactive O xidation R eduction H ydrolysis C yclization D e-cyclization ( O n R ace H onda CD ) Synthetic / conjugation reaction Mostly inactive G lucuronide conjugation A cetylation M ethylation S ulphate conjugation G lycine conjugation G lutathione conjugation R ibonucleotide/nucleotide synthesis ( G et A M otor S cooter, G o G et R acing)

7. ENZYME INDUCTION Microsomal Non-microsomal Smooth endoplasmic reticulum( in liver, kidney, intestine, lungs) Cytoplasm and m itochondria (in liver) Eg : Monooxygenases, CYP450, UGT, epoxide hydrolases etc. Esterases , amidases, some flavoprotein, most conjugases Catalyzes oxidation, reduction, glucoronide conjugation etc. All conjugation except glucoronidation Inducible Non-inducible

8. Microsomal Enzymes Microsomes : E R is isolated by homogenization and fractionation of cells reform into V esicles known as microsomes

9. They are inducible by drugs and environmental factors and some dietary constituents. For e,g A component of grapefruit juice inhibits drug metabolism (leading to potentially disastrous consequences, including cardiac dysrhythmias) Brussel sprouts and cigarette smoke induce P450 enzymes. Components of the herbal medicine St John’s wort induces CYP450 isoenzymes as well as P-glycoprotein (P- gp )

10. Different Microsomal Enzymes Flavin monooxygenases Cytochrome p450 UDP glucoronosyl transferases Glutathione s transferases Epoxide hydrolases Carboxyl esterases

11. Cytochrome P450 Cytochrome P450 enzymes are heme proteins, comprising a large family (‘superfamily’) each referred to as CYP followed by a defining set of numbers and a letter. P450 because reduced heme protein binds with CO to form a complex that absorbs light maximally at 450nm. Not all 57 human CYPs are involved in drug metabolism. CYP enzymes in families 1–3 mediate 70%–80% of all drug metabolism. Twelve CYPs accounted for 93.0% of drug metabolism.

12. Nomenclature

13. Cyp Isoforms found in liver are Cyp1a2, Cyp2a6, cyp2b6, cyp2c9, cyp2c18, cyp2c19, cyp2d6, cyp2e1 Cyp3a4, cyp3a5 cyp4a11 Cyp7 The most active CYPs for drug metabolism are of cyp 2c, cyp 2d, and cyp 3a subfamilies.

14. Cytochrome P450 Inducers C arbamazepines R ifampicin A lcohol P henytoin G riseofulvin P henobarbitone S ulphonylureas (CRAP GPS)

15. Enzyme Induction Enzyme induction Substrate metabolism Non active metabolite or Reactive metabolite Pharmacological action Pharmacological action/ toxic effects

16. Drug interaction due to enzyme induction Auto-induction : Because the inducing agent is often itself a substrate for the induced enzymes, the process can result in slowly developing tolerance Eg : carbamazepine, rifampicin, nevirapine dose needed to be doubled after 2 weeks. Enzyme induction can increase toxicity of an active metabolite of paracetamol by its metabolite N-acetyl-P-benzoquinone imine (NAPQI). The risk of serious hepatic injury following paracetamol overdose is increased in patients in whom CYP has been induced, for example, by chronic alcohol Consumption. Antibiotic rifampicin , given for 3 days, reduces the effectiveness of warfarin as an anticoagulant.

17. Effect of rifampicin on the metabolism and anticoagulant action of warfarin.

18. Therapeutic Uses Of Enzyme Induction Non-hemolytic anemia : Its due to deficient glucuronidation of bilirubin, phenobarbitone hastens its clearance. Cushings syndrome : Phenytoin may reduce the manifestation by enhancing degradation of adrenal steroids. Chronic poisoning Liver diseases .

19. Enzyme Inhibition Competitive inhibition of co-administered drug : Cimetidine , Ketoconazole, Erythromycin Suicidal inhibition : Chloramphenicol Clopidogrel Ritonavir

20. Cytochrome P450 Inhibitors S odium valproate C hloramphenicol I soniazid E rythromycin C imetidine S ulfonamides K etoconazole C iprofloxacin F luconazole O meprazole A lcohol & grapefruit juice M etronidazole ( SICKFACES.COM )

21. Drug Interaction Due To Enzyme Inhibition Several inhibitors of drug metabolism influence the metabolism of different stereoisomers selectively. Examples of drugs that inhibit the metabolism of the active (S) and less active (R) isomers of warfarin Inhibition of metabolism drugs Stereoselective for ( S ) isomer Phenylbutazone Metronidazole Sulfinpyrazone Trimethoprim– sulfamethoxazole Disulfiram Stereoselective for ( R ) isomer Cimetidine Omeprazole Non-stereoselective amiodarone

22. Cyp 3a4 SUBSTRATE INDUCERS INHIBITORS A cetaminophen B uspirone C isapride D iazepam E thinyl Estradiol E rythromycin F elodipine S tatins T erbinafine S ildenafil ( ABCDEF Short Too Sweet) C arbamazepine R ifampicin P henytoin P henobarbitone E favirenz G lucocorticoids S t. Johns Wart (Chronic Routine PEGS) G rapefruit Juice C imetidine A zoles M acrolide P rotease Inhibitor (Go CAMP)

23. Udp Glucoronosyl Transferases(UGT) Catalyse phase II reaction - Glucuronidation Glucoronides excreted via – Intestine via bile (majority) Kidney (minority) Glucoronides are cleaved by beta-glucuronidase found in bacteria of lower GIT – enterohepatic circulation of drugs eg. OCPs UGT 1 – drugs metabolism UGT 2 – endogenous substrate metabolism

24. Flavin Monooxygenases Phase I reaction 6 families are present FMO 3 is most abundant in human liver They are not induced or inhibited by any drug Not involved in drug-drug interaction

25. Epoxide Hydrolases Carry out hydrolysis of epoxide, many of which are produced by CYP It metabolises very few drugs eg. Carbamazepine

26. Glutathione S Transferases (GST) Found in both ER and cytosol Microsomal form – metabolism of endogenous leukotrienes and prostaglandins Cytosolic form – conjugation, reduction, isomerization reaction of drug metabolism.

27. Factors Affecting Drug Metabolism Genetic Factors Non-genetic Factors Genetic polymorphism Commensal Gut Microflora Diet And Envt Factors Age And Sex Concurrent Exposure To Inhibitors or Inducers Diseases

28. Genetic Polymorphism Definition : o ccurrence of a variant allele of a gene at a population frequency more than 1%, resulting in altered expression of functional activity of the gene product, or both. Based on metabolic ratio, individuals are divided into 1 - Poor metabolisers 2 - Extensive metabolisers 3 - Ultra rapid metabolisers Metabolic Ratio = Percentage of dose excreted as unchanged drug Percent of dose excreted as metabolite in urine

29. Conclusion Understanding drug metabolism and interaction within the body allows principles of biotransformation to be applied in better designing and therapeutic uses of drug. Increased understanding of biotransformation based on pharmacogenomics will also render pharmacologic treatment of disease more individualised, efficacious and safe.

30. Thank you