CYP2D6

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Cytochrome P450 2D6 (CYP2D6) is an enzyme that in humans is encoded by the CYP2D6 gene. CYP2D6 is primarily expressed in the liver. It is also highly expressed in areas of the central nervous system, including the substantia nigra.

CYP2D6, a member of the cytochrome P450 mixed-function oxidase system, is one of the most important enzymes involved in the metabolism of xenobiotics in the body. In particular, CYP2D6 is responsible for the metabolism and elimination of approximately 25% of clinically used drugs, via the addition or removal of certain functional groups – specifically, hydroxylation, demethylation, and dealkylation.[1] CYP2D6 also activates some prodrugs. This enzyme also metabolizes several endogenous substances, such as hydroxytryptamines, neurosteroids, and both m-tyramine and p-tyramine which CYP2D6 metabolizes into dopamine in the brain and liver.[1][2]

Considerable variation exists in the efficiency and amount of CYP2D6 enzyme produced between individuals. Hence, for drugs that are metabolized by CYP2D6 (that is, are CYP2D6 substrates), certain individuals will eliminate these drugs quickly (ultrarapid metabolizers) while others slowly (poor metabolizers). If a drug is metabolized too quickly, it may decrease the drug's efficacy while if the drug is metabolized too slowly, toxicity may result.[3] So, the dose of the drug may have to be adjusted to take into account of the speed at which it is metabolized by CYP2D6.[4]

Other drugs may function as inhibitors of CYP2D6 activity or inducers of CYP2D6 enzyme expression that will lead to decreased or increased CYP2D6 activity respectively. If such a drug is taken at the same time as a second drug that is a CYP2D6 substrate, the first drug may affect the elimination rate of the second through what is known as a drug-drug interaction.[3]

Gene[edit | edit source]

The gene is located near two cytochrome P450 pseudogenes on chromosome 22q13.1. Alternatively spliced transcript variants encoding different isoforms have been found for this gene.[5]

Genotype/phenotype variability[edit | edit source]

CYP2D6 shows the largest phenotypical variability among the CYPs, largely due to genetic polymorphism. The genotype accounts for normal, reduced, and non-existent CYP2D6 function in subjects. Pharmacogenomic tests are now available to identify patients with variations in the CYP2D6 allele and have been shown to have widespread use in clinical practice.[6] The CYP2D6 function in any particular subject may be described as one of the following:[7]

  • poor metabolizer – little or no CYP2D6 function
  • intermediate metabolizers – metabolize drugs at a rate somewhere between the poor and extensive metabolizers
  • extensive metabolizer – normal CYP2D6 function
  • ultrarapid metabolizer – multiple copies of the CYP2D6 gene are expressed, so greater-than-normal CYP2D6 function occurs

A patient's CYP2D6 phenotype is often clinically determined via the administration of debrisoquine (a selective CYP2D6 substrate) and subsequent plasma concentration assay of the debrisoquine metabolite (4-hydroxydebrisoquine).[8]

The type of CYP2D6 function of an individual may influence the person's response to different doses of drugs that CYP2D6 metabolizes. The nature of the effect on the drug response depends not only on the type of CYP2D6 function, but also on the extent to which processing of the drug by CYP2D6 results in a chemical that has an effect that is similar, stronger, or weaker than the original drug, or no effect at all. For example, if CYP2D6 converts a drug that has a strong effect into a substance that has a weaker effect, then poor metabolizers (weak CYP2D6 function) will have an exaggerated response to the drug and stronger side-effects; conversely, if CYP2D6 converts a different drug into a substance that has a greater effect than its parent chemical, then ultrarapid metabolizers (strong CYP2D6 function) will have an exaggerated response to the drug and stronger side-effects.[9]

Genetic basis of variability[edit | edit source]

The genetic basis for CYP2D6-mediated metabolic variability is the CYP2D6 allele, located on chromosome 22. Subjects possessing certain allelic variants will show normal, decreased, or no CYP2D6 function, depending on the allele. Pharmacogenomic tests are now available to identify patients with variations in the CYP2D6 allele and have been shown to have widespread use in clinical practice.[6]

CYP2D6 enzyme activity for selected alles[10][11]
Allele CYP2D6 activity
CYP2D6*1 normal
CYP2D6*2 normal
CYP2D6*3 none
CYP2D6*4 none
CYP2D6*5 none
CYP2D6*6 none
CYP2D6*7 none
CYP2D6*8 none
CYP2D6*9 decreased
CYP2D6*10 decreased
CYP2D6*11 none
CYP2D6*12 none
CYP2D6*13 none
CYP2D6*14 none
CYP2D6*15 none
CYP2D6*17 decreased
CYP2D6*19 none
CYP2D6*20 none
CYP2D6*21 none
CYP2D6*29 decreased
CYP2D6*31 none
CYP2D6*38 none
CYP2D6*40 none
CYP2D6*41 decreased
CYP2D6*42 none
CYP2D6*68 none
CYP2D6*92 none
CYP2D6*100 none
CYP2D6*101 none
CYP2D6 duplication increased

Ethnic factors in variability[edit | edit source]

Race is a factor in the occurrence of CYP2D6 variability. The lack of the liver cytochrome CYP2D6 enzyme occurs approximately in 7–10% in white populations, and is lower in most other ethnic groups such as Asians and African-Americans at 2% each.[12] The occurrence of CYP2D6 ultrarapid metabolizers appears to be greater among Middle Eastern and North African populations.[13]

Caucasians with European descent predominantly (around 71%) have the functional group of CYP2D6 alleles, while functional alleles represent only around 50% of the allele frequency in populations of Asian descent.[14]

This variability is accounted for by the differences in the prevalence of various CYP2D6 alleles among the populations–approximately 10% of whites are intermediate metabolizers, due to decreased CYP2D6 function, because they appear to have the non-functional CYP2D6*4 allele,[10] while approximately 50% of Asians possess the decreased functioning CYP2D6*10 allele.[10]

Ligands[edit | edit source]

Following is a table of selected substrates, inducers and inhibitors of CYP2D6. Where classes of agents are listed, there may be exceptions within the class.

Inhibitors of CYP2D6 can be classified by their potency, such as:

  • Strong inhibitor being one that causes at least a 5-fold increase in the plasma AUC values of sensitive substrates metabolized through CYP2D6, or more than 80% decrease in clearance thereof.[15]
  • Moderate inhibitor being one that causes at least a 2-fold increase in the plasma AUC values of sensitive substrates metabolized through CYP2D6, or 50-80% decrease in clearance thereof.[15]
  • Weak inhibitor being one that causes at least a 1.25-fold but less than 2-fold increase in the plasma AUC values of sensitive substrates metabolized through CYP2D6, or 20-50% decrease in clearance thereof.[15]
Selected inducers, inhibitors and substrates of CYP2D6
Substrates
↑ = bioactivation by CYP2D6		 Inhibitors Inducers

Strong

Moderate

Weak

Unspecified potency

Strong

Unspecified potency

Dopamine biosynthesis[edit | edit source]

Biosynthetic pathways for catecholamines and trace amines in the human brain[39][40][20]
The image above contains clickable links
In humans, catecholamines and phenethylaminergic trace amines are derived from the amino acid phenylalanine. It is well established that dopamine is produced from L-tyrosine via L-dopa; however, recent evidence has shown that CYP2D6 is expressed in the human brain and catalyzes the biosynthesis of dopamine from L-tyrosine via p-tyramine.[20] Similarly, CYP2D6 also metabolizes m-tyramine into dopamine.[20]


References[edit | edit source]

  1. ↑ 1.0 1.1 , New insights into the structural characteristics and functional relevance of the human cytochrome P450 2D6 enzyme, Drug Metabolism Reviews, 2009, Vol. 41(Issue: 4), pp. 573–643, DOI: 10.1080/03602530903118729, PMID: 19645588,
  2. ↑ , The endogenous substrates of brain CYP2D, European Journal of Pharmacology, Vol. 724 pp. 211–8, DOI: 10.1016/j.ejphar.2013.12.025, PMID: 24374199,
  3. ↑ 3.0 3.1 , Pharmacogenomics of CYP2D6: molecular genetics, interethnic differences and clinical importance, Drug Metabolism and Pharmacokinetics, 2012, Vol. 27(Issue: 1), pp. 55–67, DOI: 10.2133/dmpk.DMPK-11-RV-121, PMID: 22185816,
  4. ↑ , Use of CYP2D6 genotyping in practice: tamoxifen dose adjustment, Pharmacogenomics, Vol. 13(Issue: 6), pp. 691–7, DOI: 10.2217/pgs.12.27, PMID: 22515611,
  5. ↑ Entrez Gene: CYP2D6 cytochrome P450, family 2, subfamily D, polypeptide 6 Full text, ,
  6. ↑ 6.0 6.1 , The role of pharmacogenomic testing in psychiatry: Real world examples, The Australian and New Zealand Journal of Psychiatry, Vol. 48(Issue: 8), pp. 778, DOI: 10.1177/0004867413520050, PMID: 24413808,
  7. ↑ , Molecular genetics of CYP2D6: clinical relevance with focus on psychotropic drugs, British Journal of Clinical Pharmacology, Vol. 53(Issue: 2), pp. 111–22, DOI: 10.1046/j.0306-5251.2001.01548.x, PMID: 11851634, PMC: 1874287,
  8. ↑ , Pharmacogenetics of debrisoquine and its use as a marker for CYP2D6 hydroxylation capacity, Pharmacogenomics, Vol. 10(Issue: 1), pp. 17–28, DOI: 10.2217/14622416.10.1.17, PMID: 19102711,
  9. ↑ , The effect of cytochrome P450 metabolism on drug response, interactions, and adverse effects, American Family Physician, Vol. 76(Issue: 3), pp. 391–6, PMID: 17708140,
  10. ↑ 10.0 10.1 10.2 , Comparison of three CYP2D6 probe substrates and genotype in Ghanaians, Chinese and Caucasians, Pharmacogenetics, Vol. 8(Issue: 4), pp. 325–33, DOI: 10.1097/00008571-199808000-00006, PMID: 9731719,
  11. ↑ CYP2D6 allele nomenclature Full text, ,
  12. ↑ Linda Lane, Scott, Julie, Beth, Pharmacology and the Nursing Process, Toronto:Mosby Elsevier, 2007, ISBN 9780779699711, Pages: 25,
  13. ↑ , Frequent occurrence of CYP2D6 gene duplication in Saudi Arabians, Pharmacogenetics, Vol. 7(Issue: 3), pp. 187–91, DOI: 10.1097/00008571-199706000-00003, PMID: 9241658,
  14. ↑ , CYP2D6 allele frequency in European Caucasians, Asians, Africans and their descendants, Pharmacogenomics, Vol. 3(Issue: 2), pp. 229–43, DOI: 10.1517/14622416.3.2.229, PMID: 11972444,
  15. ↑ 15.00 15.01 15.02 15.03 15.04 15.05 15.06 15.07 15.08 15.09 15.10 15.11 15.12 15.13 15.14 15.15 15.16 15.17 15.18 15.19 15.20 15.21 15.22 15.23 15.24 15.25 15.26 15.27 15.28 15.29 15.30 15.31 15.32 15.33 15.34 15.35 15.36 15.37 15.38 15.39 15.40 15.41 15.42 15.43 15.44 15.45 15.46 15.47 15.48 15.49 15.50 15.51 15.52 15.53 15.54 15.55 15.56 15.57 15.58 15.59 15.60 15.61 15.62 15.63 15.64 15.65 15.66 15.67 15.68 15.69 15.70 15.71 15.72 15.73 15.74 15.75 15.76 15.77 15.78 15.79 15.80 15.81 15.82 15.83 15.84 15.85 15.86 Drug Interactions: Cytochrome P450 Drug Interaction Table Full text, Flockhart DA, , Indiana University School of Medicine, Retrieved in July 2011
  16. ↑ 16.00 16.01 16.02 16.03 16.04 16.05 16.06 16.07 16.08 16.09 16.10 16.11 16.12 16.13 16.14 16.15 16.16 16.17 16.18 16.19 16.20 16.21 16.22 16.23 16.24 16.25 16.26 16.27 16.28 16.29 16.30 16.31 16.32 FASS (drug formulary): Swedish environmental classification of pharmaceuticals Facts for prescribers (Fakta för förskrivare), retrieved July 2011
  17. ↑ 17.0 17.1 , Pharmacogenetics and pharmacogenomics, Pediatric Clinics of North America, Vol. 48(Issue: 3), pp. 765–81, DOI: 10.1016/S0031-3955(05)70338-2, PMID: 11411304,
  18. ↑ Hydrocodone Full text, , Drugbank,
  19. ↑ , CYP2D6 and tamoxifen: DNA matters in breast cancer, Nature Reviews. Cancer, Vol. 9(Issue: 8), pp. 576–86, DOI: 10.1038/nrc2683, PMID: 19629072,
  20. ↑ 20.0 20.1 20.2 20.3 20.4 , The endogenous substrates of brain CYP2D, European Journal of Pharmacology, Vol. 724 pp. 211–218, DOI: 10.1016/j.ejphar.2013.12.025, PMID: 24374199,
  21. ↑ 21.0 21.1 DILTIAZEM HCL CD- diltiazem hydrochloride capsule, coated, extended release Full text, DailyMed, 2017-02-01, Accessed on: 2019-01-31.
  22. ↑ NIFEDIPINE EXTENDED RELEASE- nifedipine tablet, extended release Full text, DailyMed, 2012-11-29, Accessed on: 2019-02-01.
  23. ↑ , Inhibition of CYP2D6 activity by bupropion, Journal of Clinical Psychopharmacology, Vol. 25(Issue: 3), pp. 226–9, DOI: 10.1097/01.jcp.0000162805.46453.e3, PMID: 15876900,
  24. ↑ , Pathway-specific inhibition of primaquine metabolism by chloroquine/quinine, Malaria Journal, Vol. 15 pp. 466, DOI: 10.1186/s12936-016-1509-x, PMID: 27618912, PMC: 5020452,
  25. ↑ Medical Cannabis Adverse Effects & Drug Interactions Full text, ,
  26. ↑ , Interaction of buprenorphine and its metabolite norbuprenorphine with cytochromes p450 in vitro, Drug Metabolism and Disposition, Vol. 31(Issue: 6), pp. 768–72, DOI: 10.1124/dmd.31.6.768, PMID: 12756210,
  27. ↑ 27.0 27.1 Citalopram Oral Solution Full text, ,
  28. ↑ Escitalopram-drug-information Full text, UpToDate, Accessed on: 2019-05-22.
  29. ↑ , Methylphenidate and Its Under-recognized, Under- explained, and Serious Drug Interactions: A Review of the Literature with Heightened Concerns, German Journal of Psychiatry, pp. 29–42, Full text,
  30. ↑ Bailey, David G., Erythromycin-felodipine interaction: Magnitude, mechanism, and comparison with grapefruit juice*, Clinical Pharmacology and Therapeutics, 1996, Vol. 60(Issue: 1), pp. 25–33, DOI: 10.1016/s0009-9236(96)90163-0, PMID: 8689808,
  31. ↑ Lown, K S, Grapefruit juice increases felodipine oral availability in humans by decreasing intestinal CYP3A protein expression., The Journal of Clinical Investigation, Vol. 99(Issue: 10), pp. 2545–2553, DOI: 10.1172/jci119439, PMID: 9153299, PMC: 508096,
  32. ↑ Guengerich, FP, Oxidation of dihydropyridine calcium channel blockers and analogues by human liver cytochrome P-450 IIIA4., Journal of Medicinal Chemistry, 1991, Vol. 34(Issue: 6), pp. 1838–44, DOI: 10.1021/jm00110a012, PMID: 2061924,
  33. ↑ Owen, J. Randall, New antidepressants and the cytochrome P450 system: Focus on venlafaxine, nefazodone, and mirtazapine, Depression and Anxiety, Vol. 7(Issue: SUPPL. 1), pp. 24–32, DOI: 10.1002/(SICI)1520-6394(1998)7:1+3.0.CO;2-F, PMID: 9597349, Full text,
  34. ↑ 34.0 34.1 34.2 34.3 FASS, The Swedish official drug catalog > Kodein Recip Last reviewed 2008-04-08
  35. ↑ , In Vitro Activity of St. John's Wort Against Cytochrome P450 Isozymes and P-Glycoprotein, Pharmaceutical Biology, 2008, Vol. 42(Issue: 2), pp. 159–69, DOI: 10.1080/13880200490512034,
  36. ↑ , Inhibitory effects of H1-antihistamines on CYP2D6- and CYP2C9-mediated drug metabolic reactions in human liver microsomes, European Journal of Clinical Pharmacology, Vol. 57(Issue: 12), pp. 847–51, DOI: 10.1007/s00228-001-0399-0, PMID: 11936702,
  37. ↑ 37.0 37.1 , Inhibition of human P450 enzymes by nicotinic acid and nicotinamide, Biochemical and Biophysical Research Communications, Vol. 317(Issue: 3), pp. 950–6, DOI: 10.1016/j.bbrc.2004.03.137, PMID: 15081432,
  38. ↑ , Pharmacokinetics of haloperidol: an update, Clinical Pharmacokinetics, Vol. 37(Issue: 6), pp. 435–56, DOI: 10.2165/00003088-199937060-00001, PMID: 10628896,
  39. ↑ , The vascular effects of trace amines and amphetamines, Pharmacology & Therapeutics, Vol. 125(Issue: 3), pp. 363–375, DOI: 10.1016/j.pharmthera.2009.11.005, PMID: 19948186,
  40. ↑ , A renaissance in trace amines inspired by a novel GPCR family, Trends in Pharmacological Sciences, Vol. 26(Issue: 5), pp. 274–281, DOI: 10.1016/j.tips.2005.03.007, PMID: 15860375,


Further reading[edit | edit source]

, 

 Molecular genetics of the human cytochrome P450 monooxygenase superfamily, 
 Xenobiotica, 
  
 Vol. 28(Issue: 12), 
 pp. 1129–65, 
 DOI: 10.1080/004982598238868, 
 PMID: 9890157,

, 

 Cytochrome P450 CYP2D6, 
 IARC Scientific Publications, 
 1999, 
 (Issue: 148), 
 pp. 209–29, 
  
 PMID: 10493260,

, 

 Human extrahepatic cytochromes P450: function in xenobiotic metabolism and tissue-selective chemical toxicity in the respiratory and gastrointestinal tracts, 
 Annual Review of Pharmacology and Toxicology, 
 2003, 
 Vol. 43 
 pp. 149–73, 
 DOI: 10.1146/annurev.pharmtox.43.100901.140251, 
 PMID: 12171978,

, 

 Galantamine--a novel cholinergic drug with a unique dual mode of action for the treatment of patients with Alzheimer's disease, 
 CNS Drug Reviews, 
 2006, 
 Vol. 8(Issue: 2), 
 pp. 159–76, 
 DOI: 10.1111/j.1527-3458.2002.tb00221.x, 
 PMID: 12177686, 
 PMC: 6741688,

, 

 Polymorphic cytochrome P450 2D6: humanized mouse model and endogenous substrates, 
 Drug Metabolism Reviews, 
  
 Vol. 36(Issue: 2), 
 pp. 243–77, 
 DOI: 10.1081/DMR-120034000, 
 PMID: 15237854, 
  
  
 Full text,

, 

 CYP2D6 gene variants: association with breast cancer specific survival in a cohort of breast cancer patients from the United Kingdom treated with adjuvant tamoxifen, 
 Breast Cancer Research, 
 2010, 
 Vol. 12(Issue: 4), 
 pp. R64, 
 DOI: 10.1186/bcr2629, 
 PMID: 20731819, 
 PMC: 2949659,

, 

 CYP2D6 gene variants and their association with breast cancer susceptibility, 
 Cancer Epidemiology, Biomarkers & Prevention, 
  
 Vol. 20(Issue: 6), 
 pp. 1255–8, 
 DOI: 10.1158/1055-9965.EPI-11-0321, 
 PMID: 21527579,

External links[edit | edit source]




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