BIOL 480 Final Presentation

1. BIOL 480 Final Presentation Brant Dye Apr. 8, 2005

2. Question: • Are there common inter-racial genetic variations that affect the metabolism of drugs and should be taken into account when determining safe dosage concentrations?

3. Outline of Presentation • Basics of Drug Metabolism • Cytochrome P450 enzymes • Conclusion • Works Cited • Questions

4. Metabolism: The Purpose? • Metabolism = alteration of covalent bonds • Generally considered a defensive mechanism. • Makes xenobiotic less toxic and easier to excrete. • The liver is the main organ involved in metabolism. • The intestine, lung, kidney, and skin play minor roles.1 • Rate of metabolism can very greatly from one individual to the next.2 1 Landis and Yu (1999) 2 Lu and Kacew (2002)

5. Metabolism (Cont’) • Metabolic activation: • Metabolism converts a xenobiotic into a more reactive form.1 • Xenobiotic metabolism can be broken down into two different phases. • Phase I and Phase II metabolism. 1 Landis and Yu (1999)

6. Phase I Metabolism • Main types of reactions include oxidations, reductions, and hydrolysis.1 • Generally considered to be degradation reactions.1 • Adds functional groups.2 • Convert xenobiotics into directly excretable compounds or into substrates for phase II metabolism.1 1 Lu and Kacew (2002) 2 Landis and Yu (1999)

7. Phase II Metabolism • Conjugation reactions.1 • Adds a water soluble group.1 • Usually added to a functional group. • Makes xenobiotic more water soluble.1 • Favors excretion. 1 Lu and Kacew (2002)

8. Goals of A Manufactured Drug! • Want drug to be receptor-specific.1 • Enzymes involved in basic metabolism can alter the structure or function of a drug.1 • Metabolic activation of a pro-drug. 1 Albert (1987)

9. Environmental Factors:1 Climate Diet Pollutants Previous Exposure Biological Factors:1 Age Genetic Variations Gender Smoking Alcohol Drugs Disease Ethnicity Variation of drug response! 1 Amudha et al. (2003)

10. What are the Cytochrome P450 enzymes? • They are a family of microsomal enzymes mainly found in the liver.1 • Over 400 different enzymes in the Cytochrome P450 Superfamily. (~40-50 a species) • Many of the enzymes are inducible. • They mostly metabolize xenobiotics through oxidation reactions.1 • Most of the medicine we consume is metabolized by these enzymes.2 1 Lu and Kacew (2002) 2 Ma et al. (2002)

11. How Cytochrome P450 enzymes are named? • Root: CYP • Family: CYP2 • Subfamily: CYP2D • Gene:CYP2D6 • Wild-type allele: CYP2D6*1 • Mutant Allele: CYP2D6*2-? • Gene = Italicized • Protein = non-italicized

12. Basic Metabolic Terms: • Poor Metabolizers (PMs) • More likely to develop adverse effects and/or toxicity from high levels of unmetabolized drugs. • Extensive Metabolizers (EMs) • More likely to be non-responders at the usual therapeutic dose range. • Wild-type • Predominant genotype or phenotype.

13. Genetic Variations Among Ethnic Groups • The main genetic variations are found in Cytochrome P450 enzymes (Phase I Metabolism)! • Mainly: • CYP2C19 • CYP2C9 • CYP2D6 These CYP450 enzymes are responsible for metabolizing the majority of clinically useful drugs! Ma et al. (2002)

14. Common Inter-racial Genetic Variations Common inter-racial genetic variations can be found within particular races, especially when comparing Caucasians, Asians, and African Americans. Ma et al. (2002); Xie et al. (2001)

15. CYP2C19 • Drugs metabolized by CYP2C19.1 • Omeprazole • Diazepam (Valium) • 15-25% incidence of PMs in Asians vs. 2-5% incidence of PMs in Caucasians and African-Americans.2 • PM phenotype is the result of two nonfunctional alleles.1 • Drugs should be initially prescribed in lower doses to Asians to safeguard against the higher frequency of PMs in the Asian population. • Nine mutant alleles have been identified as the cause of PMs.3 1 Ma et al. (2002) 2 Anderson (2005) 3 Xie et al. (2001)

16. Diazepam(Valium) • Used primarily for short-term relief of anxiety • Also used to relieve muscle spasms, acute-alcohol withdrawal, and control epilepsy. • It has been noted that Hong Kong physicians normally prescribe smaller doses of diazepam for Chinese patients than for Caucasians.1 • PMs of CYP2C19 may be at higher risk for diazepam toxicity.1 1 Xie et al. (2001)

17. CYP2C9 • Makes up ~20% of total P450 hepatic content.1 • Drugs metabolized by CYP2C9 include:1 • S-warfarin • Phenytoin • Non-steroidal anti-inflammatory drugs (NSAIDs). • Ibuprofen, etc… • Six allelic variants have been identified as the cause of reduced enzyme activity.2 • CYP2C9*2-6 • *2 and *3 mutant alleles are most common. 1 Xie et al. (2002) 2 Amudha et al. (2003)

18. CYP2C9 (cont’) • CYP2C9*2 mutant allele occurs in ~8-20% of Caucasians, ~3% of African-Americans, and is extremely rare in Asians.1 • The CYP2C9*3 mutant allele occurs in ~8% of Caucasians, ~2% of Asians, and ~1% of African Americans.2 • Caucasians have a higher frequency (~10%) of the CYP2C9*2 and *3 alleles.1 1 Xie et al. (2001) 2 Ma et al. (2002)

19. S-warfarin • Prevents the formation of blood clots or existing clots from getting larger.1 • Individuals with a high frequency of CYP2C9 mutant alleles require lower doses of S-warfarin.1 • Caucasians 10%. • CYP2C9*2 and CYP2C9*3 are associated with a 5.5- and 27.0-fold decrease in the intrinsic clearance of S-warfarin, when compared to the wild-type allele.1 1 Ma et al. (2002)

20. CYP2D6 • Metabolizes 25-30% of clinically useful drugs.1 • Less than 1% of Asians, 2-5% of African Americans, and 6-10% of Caucasians are PMs.1 • PMs possess two nonfunctional alleles. • Drugs metabolized by CYP2D6.1 • Anti-depressants • Nortriptyline • Antipsychotics • Haloperidol • At least seventy allelic variants have been identified that cause reduced or a complete loss of enzyme activity.2 1 Ma et al. (2002) 2 Xie et al. (2001)

21. CYP2D6 (cont’) • Genotypes for this enzyme have been useful in predicting adverse effects associated with anti-depressants.1 • Preliminary dosage recommendations based on CYP2D6 genotypes are available for anti-depressants.1 • Asian and African-American populations tend to have reduced CYP2D6 activity compared with Caucasians because of a lower occurrence of nonfunctional alleles, but a higher frequency of alleles associated with reduced activity.1 1 Ma et al. (2002)

22. Conclusion • Inter-racial genetic similarities are not consistent enough across the board that safe and effective drug dosages can be adequately determined for an entire race. • Intra-racial genetic similarities cause observable trends within certain races, but inter-racial genetic differences make it difficult to apply these trends to the entire race.

23. Conclusion (con’t) • However, an understanding of common inter-racial genetic variations can aid doctors in correctly determining safe and effective drug dosage levels for an individual. • Valium (lower doses prescribed for Chinese). • High frequency of PMs. • The advancements in our understanding of the human genome will allow us in the future to determine and utilize an individual’s genotype to determine safe and effective drug dosage levels for that individual. • The use of genotypes will enable doctors to determine if an individual is a PM or EM for a certain drug. • Dosage levels can be adjusted. • Alternative treatments.

24. Works Cited Albert A. 1987. Xenobiosis: Food, drugs, and poisons in the human body. New York, NY; Chapman and Hall Limited, 367p. Amudha K, Wong LP, Choy AJ, Lang CC. 2003. Ethnicity and Drug Therapy for Hypertension. Current Pharmaceutical Design 9(1): 1691-1701. Anderson GD. 2005. Sex and Racial Differences in Pharmacological Response: Where Is the Evidence? Pharmacogenetics, Pharmacokinetics, and Pharmacodynamics. Journal of Women's Health 14(1): 19-29. Landis WG, Yu M. 1999. Introduction to Environmental Toxicology: Impacts of Chemicals Upon Ecological Systems. Boca Raton, FL; Lewis Publishers, 390p. Lu FC, Kacew S. 2002. Lu's Basic Toxicology: Fundamental, target organs, and risk assessment. New York, NY; Taylor and Francis, 392p. Ma MK, Woo MH, McLeod HL. 2002. Genetic basis of drug metabolism. American Journal of Health-System Pharmacists 59(1): 2061-2069. Xie H, Kim RB, Wood AJ, Stein CM. 2001. Molecular Basis of Ethnic Differences in Drug Disposition and Response. Annual Review Pharmacology and Toxicology 41(1): 815-850. Xie H, Prasad HC, Kim RB, Stein CM. 2002. CYP2C9 allelic variants: ethnic distribution and functional significance. Advanced Drug Delivery Reviews 54(1): 1257-1270.

25. ?’s