Cytochrome P450 family 2 subfamily C member 9 (abbreviated CYP2C9) is an enzyme protein. The enzyme is involved in the metabolism, by oxidation, of both xenobiotics, including drugs, and endogenous compounds, including fatty acids. In humans, the protein is encoded by the CYP2C9 gene. [5] [6] The gene is highly polymorphic, which affects the efficiency of the metabolism by the enzyme. [7]
CYP2C9 is a crucial cytochrome P450 enzyme, which plays a significant role in the metabolism, by oxidation, of both xenobiotic and endogenous compounds. [7] CYP2C9 makes up about 18% of the cytochrome P450 protein in liver microsomes. The protein is mainly expressed in the liver, duodenum, and small intestine. [7] About 100 therapeutic drugs are metabolized by CYP2C9, including drugs with a narrow therapeutic index such as warfarin and phenytoin, and other routinely prescribed drugs such as acenocoumarol, tolbutamide, losartan, glipizide, and some nonsteroidal anti-inflammatory drugs. By contrast, the known extrahepatic CYP2C9 often metabolizes important endogenous compounds such as serotonin and, owing to its epoxygenase activity, various polyunsaturated fatty acids, converting these fatty acids to a wide range of biologically active products. [8] [9]
In particular, CYP2C9 metabolizes arachidonic acid to the following eicosatrienoic acid epoxide (EETs) stereoisomer sets: 5R,6S-epoxy-8Z,11Z,14Z-eicosatetraenoic and 5S,6R-epoxy-8Z,11Z,14Z-eicosatetraenoic acids; 11R,12S-epoxy-8Z,11Z,14Z-eicosatetraenoic and 11S,12R-epoxy-5Z,8Z,14Z-eicosatetraenoic acids; and 14R,15S-epoxy-5Z,8Z,11Z-eicosatetraenoic and 14S,15R-epoxy-5Z,8Z,11Z-eicosatetraenoic acids. It likewise metabolizes docosahexaenoic acid to epoxydocosapentaenoic acids (EDPs; primarily 19,20-epoxy-eicosapentaenoic acid isomers [i.e. 10,11-EDPs]) and eicosapentaenoic acid to epoxyeicosatetraenoic acids (EEQs, primarily 17,18-EEQ and 14,15-EEQ isomers). [10] Animal models and a limited number of human studies implicate these epoxides in reducing hypertension; protecting against myocardial infarction and other insults to the heart; promoting the growth and metastasis of certain cancers; inhibiting inflammation; stimulating blood vessel formation; and possessing a variety of actions on neural tissues including modulating neurohormone release and blocking pain perception (see epoxyeicosatrienoic acid and epoxygenase). [9]
In vitro studies on human and animal cells and tissues and in vivo animal model studies indicate that certain EDPs and EEQs (16,17-EDPs, 19,20-EDPs, 17,18-EEQs have been most often examined) have actions which often oppose those of another product of CYP450 enzymes (e.g. CYP4A1, CYP4A11, CYP4F2, CYP4F3A, and CYP4F3B) viz., 20-Hydroxyeicosatetraenoic acid (20-HETE), principally in the areas of blood pressure regulation, blood vessel thrombosis, and cancer growth (see 20-Hydroxyeicosatetraenoic acid, epoxyeicosatetraenoic acid, and epoxydocosapentaenoic acid sections on activities and clinical significance). Such studies also indicate that the eicosapentaenoic acids and EEQs are: 1) more potent than EETs in decreasing hypertension and pain perception; 2) more potent than or equal in potency to the EETs in suppressing inflammation; and 3) act oppositely from the EETs in that they inhibit angiogenesis, endothelial cell migration, endothelial cell proliferation, and the growth and metastasis of human breast and prostate cancer cell lines whereas EETs have stimulatory effects in each of these systems. [11] [12] [13] [14] Consumption of omega-3 fatty acid-rich diets dramatically raises the serum and tissue levels of EDPs and EEQs in animals as well as humans, and in humans is by far the most prominent change in the profile of polyunsaturated fatty acids metabolites caused by dietary omega-3 fatty acids. [11] [14] [15]
CYP2C9 may also metabolize linoleic acid to the potentially very toxic products, vernolic acid (also termed leukotoxin) and coronaric acid (also termed isoleukotoxin); these linoleic acid epoxides cause multiple organ failure and acute respiratory distress in animal models and may contribute to these syndromes in humans. [9]
The CYP2C9 gene is highly polymorphic. [16] At least 20 single nucleotide polymorphisms (SNPs) have been reported to have functional evidence of altered enzyme activity. [16] In fact, adverse drug reactions (ADRs) often result from unanticipated changes in CYP2C9 enzyme activity secondary to genetic polymorphisms. Especially for CYP2C9 substrates such as warfarin and phenytoin, diminished metabolic capacity because of genetic polymorphisms or drug-drug interactions can lead to toxicity at normal therapeutic doses. [17] [18] Information about how human genetic variation of CYP2C9 affects response to medications can be found in databases such PharmGKB, [19] Clinical Pharmacogenetics Implementation Consortium (CPIC). [20]
The label CYP2C9*1 is assigned by the Pharmacogene Variation Consortium (PharmVar) to the most commonly observed human gene variant. [21] Other relevant variants are cataloged by PharmVar under consecutive numbers, which are written after an asterisk (star) character to form an allele label. [22] [23] The two most well-characterized variant alleles are CYP2C9*2 (NM_000771.3:c.430C>T, p.Arg144Cys, rs1799853) and CYP2C9*3 (NM_000771.3:c.1075A>C, p. Ile359Leu, rs1057910), [24] causing reductions in enzyme activity of 30% and 80%, respectively. [16]
On the basis of their ability to metabolize CYP2C9 substrates, individuals can be categorized by groups. The carriers of homozygous CYP2C9*1 variant, i.e. of the *1/*1 genotype, are designated extensive metabolizers (EM), or normal metabolizers. [25] The carriers of the CYP2C9*2 or CYP2C9*3 alleles in a heterozygous state, i.e. just one of these alleles (*1/*2, *1/*3) are designated intermediate metabolizers (IM), and those carrying two of these alleles, i.e. homozygous (*2/*3, *2/*2 or *3/*3) – poor metabolizers (PM). [26] [27] As a result, the metabolic ratio – the ratio of unchanged drug to metabolite – is higher in PMs.
A study of the ability to metabolize warfarin among the carriers of the most well-characterized CYP2C9 genotypes (*1, *2 and *3), expressed as a percentage of the mean dose in patients with wild-type alleles (*1/*1), concluded that the mean warfarin maintenance dose was 92% in *1/*2, 74% in *1/*3, 63% in *2/*3, 61% in *2/*2 and 34% in 3/*3. [28]
CYP2C9*3 reflects an Ile359-Leu (I359L) change in the amino acid sequence, [29] and also has reduced catalytic activity compared with the wild type (CYP2C9*1) for substrates other than warfarin. [30] Its prevalence varies with race as:
| Allele frequencies (%) of CYP2C9 polymorphism | |||||
|---|---|---|---|---|---|
| African-American | Black-African | Pygmy | Asian | Caucasian | |
| CYP2C9*3 | 2.0 | 0–2.3 | 0 | 1.1–3.6 | 3.3–16.2 |
The Association for Molecular Pathology Pharmacogenomics (PGx) Working Group in 2019 has recommended a minimum panel of variant alleles (Tier 1) and an extended panel of variant alleles (Tier 2) to be included in assays for CYP2C9 testing.
CYP2C9 variant alleles recommended as Tier 1 by the PGx Working Group include CYP2C9 *2, *3, *5, *6, *8, and *11. This recommendation was based on their well-established functional effects on CYP2C9 activity and drug response availability of reference materials, and their appreciable allele frequencies in major ethnic groups.
The following CYP2C9 alleles are recommended for inclusion in tier 2: CYP2C9*12, *13, and *15. [16]
CYP2C9*13 is defined by a missense variant in exon 2 (NM_000771.3:c.269T>C, p. Leu90Pro, rs72558187). [16] CYP2C9*13 prevalence is approximately 1% in the Asian population, [31] but in Caucasians this variant prevalence is almost zero. [32] This variant is caused by a T269C mutation in the CYP2C9 gene which in turn results in the substitution of leucine at position-90 with proline (L90P) at the product enzyme protein. This residue is near the access point for substrates and the L90P mutation causes lower affinity and hence slower metabolism of several drugs that are metabolized CYP2C9 by such as diclofenac and flurbiprofen. [31] However, this variant is not included in the tier 1 recommendations of the PGx Working Group because of its very low multiethnic minor allele frequency and a lack of currently available reference materials. [16] As of 2020 [update] the evidence level for CYP2C9*13 in the PharmVar database is limited, comparing to the tier 1 alleles, for which the evidence level is definitive. [21]
Not all clinically significant genetic variant alleles have been registered by PharmVar. For example, in a 2017 study, the variant rs2860905 showed stronger association with warfarin sensitivity (<4 mg/day) than common variants CYP2C9*2 and CYP2C9*3. [33] Allele A (23% global frequency) is associated with a decreased dose of warfarin as compared to the allele G (77% global frequency). Another variant, rs4917639, according to a 2009 study, has a strong effect on warfarin sensitivity, almost the same as if CYP2C9*2 and CYP2C9*3 were combined into a single allele. [34] The C allele at rs4917639 has 19% global frequency. Patients with the CC or CA genotype may require decreased dose of warfarin as compared to patients with the wild-type AA genotype. [35] Another variant, rs7089580 with T allele having 14% global frequency, is associated with increased CYP2C9 gene expression. Carriers of AT and TT genotypes at rs7089580 had increased CYP2C9 expression levels compared to wild-type AA genotype. Increased gene expression due to rs7089580 T allele leads to an increased rate of warfarin metabolism and increased warfarin dose requirements. In a study published in 2014, the AT genotype showed slightly higher expression than TT, but both much higher than AA. [36] Another variant, rs1934969 (in studies of 2012 and 2014) have been shown to affect the ability to metabolize losartan: carriers of the TT genotype have increased CYP2C9 hydroxylation capacity for losartan comparing to AA genotype, and, as a result, the lower metabolic ratio of losartan, i.e., faster losartan metabolism. [37] [38]
Most inhibitors of CYP2C9 are competitive inhibitors. Noncompetitive inhibitors of CYP2C9 include nifedipine, [39] [40] phenethyl isothiocyanate, [41] medroxyprogesterone acetate [42] and 6-hydroxyflavone. It was indicated that the noncompetitive binding site of 6-hydroxyflavone is the reported allosteric binding site of the CYP2C9 enzyme. [43]
Following is a table of selected substrates, inducers and inhibitors of CYP2C9. Where classes of agents are listed, there may be exceptions within the class.
Inhibitors of CYP2C9 can be classified by their potency, such as:
| Substrates | Inhibitors | Inducers |
|---|---|---|
| Strong
Moderate
Weak Unspecified potency
| Strong Weak |
CYP2C9 attacks various long-chain polyunsaturated fatty acids at their double (i.e. alkene) bonds to form epoxide products that act as signaling molecules. It along with CYP2C8, CYP2C19, CYP2J2, and possibly CYP2S1 are the principle enzymes which metabolizes 1) arachidonic acid to various epoxyeicosatrienoic acids (also termed EETs); 2) linoleic acid to 9,10-epoxy octadecenoic acids (also termed vernolic acid, linoleic acid 9:10-oxide, or leukotoxin) and 12,13-epoxy-octadecenoic (also termed coronaric acid, linoleic acid 12,13-oxide, or isoleukotoxin); 3) docosahexaenoic acid to various epoxydocosapentaenoic acids (also termed EDPs); and 4) eicosapentaenoic acid to various epoxyeicosatetraenoic acids (also termed EEQs). [9] Animal model studies implicate these epoxides in regulating: hypertension, Myocardial infarction and other insults to the heart, the growth of various cancers, inflammation, blood vessel formation, and pain perception; limited studies suggest but have not proven that these epoxides may function similarly in humans (see epoxyeicosatrienoic acid and epoxygenase pages). [9] Since the consumption of omega-3 fatty acid-rich diets dramatically raises the serum and tissue levels of the EDP and EEQ metabolites of the omega-3 fatty acid, i.e. docosahexaenoic and eicosapentaenoic acids, in animals and humans and in humans is the most prominent change in the profile of polyunsaturated fatty acids metabolites caused by dietary omega-3 fatty acids, eicosapentaenoic acids and EEQs may be responsible for at least some of the beneficial effects ascribed to dietary omega-3 fatty acids. [11] [14] [15]
Cytochromes P450 are a superfamily of enzymes containing heme as a cofactor that mostly, but not exclusively, function as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are important for the clearance of various compounds, as well as for hormone synthesis and breakdown. In 1963, Estabrook, Cooper, and Rosenthal described the role of CYP as a catalyst in steroid hormone synthesis and drug metabolism. In plants, these proteins are important for the biosynthesis of defensive compounds, fatty acids, and hormones.
Pharmacogenomics, often abbreviated "PGx," is the study of the role of the genome in drug response. Its name reflects its combining of pharmacology and genomics. Pharmacogenomics analyzes how the genetic makeup of a patient affects their response to drugs. It deals with the influence of acquired and inherited genetic variation on drug response, by correlating DNA mutations with pharmacokinetic, pharmacodynamic, and/or immunogenic endpoints.
Cytochrome P450 3A4 is an important enzyme in the body, mainly found in the liver and in the intestine, which in humans is encoded by CYP3A4 gene. It oxidizes small foreign organic molecules (xenobiotics), such as toxins or drugs, so that they can be removed from the body. It is highly homologous to CYP3A5, another important CYP3A enzyme.
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.
Cytochrome P450 2E1 is a member of the cytochrome P450 mixed-function oxidase system, which is involved in the metabolism of xenobiotics in the body. This class of enzymes is divided up into a number of subcategories, including CYP1, CYP2, and CYP3, which as a group are largely responsible for the breakdown of foreign compounds in mammals.
Cytochrome P450 1A2, a member of the cytochrome P450 mixed-function oxidase system, is involved in the metabolism of xenobiotics in the human body. In humans, the CYP1A2 enzyme is encoded by the CYP1A2 gene.
Cytochrome P450 2C19 is an enzyme protein. It is a member of the CYP2C subfamily of the cytochrome P450 mixed-function oxidase system. This subfamily includes enzymes that catalyze metabolism of xenobiotics, including some proton pump inhibitors and antiepileptic drugs. In humans, it is the CYP2C19 gene that encodes the CYP2C19 protein. CYP2C19 is a liver enzyme that acts on at least 10% of drugs in current clinical use, most notably the antiplatelet treatment clopidogrel (Plavix), drugs that treat pain associated with ulcers, such as omeprazole, antiseizure drugs such as mephenytoin, the antimalarial proguanil, and the anxiolytic diazepam.
Cytochrome P4502C8 (CYP2C8) is a member of the cytochrome P450 mixed-function oxidase system involved in the metabolism of xenobiotics in the body. Cytochrome P4502C8 also possesses epoxygenase activity, i.e. it metabolizes long-chain polyunsaturated fatty acids, e.g. arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and Linoleic acid to their biologically active epoxides.
Cytochrome P450, family 1, subfamily A, polypeptide 1 is a protein that in humans is encoded by the CYP1A1 gene. The protein is a member of the cytochrome P450 superfamily of enzymes.
Cytochrome P450 3A5 is a protein that in humans is encoded by the CYP3A5 gene.
The human gene VKORC1 encodes for the enzyme, Vitamin K epOxide Reductase Complex (VKORC) subunit 1. This enzymatic protein complex is responsible for reducing vitamin K 2,3-epoxide to its active form, which is important for effective clotting (coagulation). In humans, mutations in this gene can be associated with deficiencies in vitamin-K-dependent clotting factors.
Cytochrome P450 2J2 (CYP2J2) is a protein that in humans is encoded by the CYP2J2 gene. CYP2J2 is a member of the cytochrome P450 superfamily of enzymes. The enzymes are oxygenases which catalyze many reactions involved in the metabolism of drugs and other xenobiotics) as well as in the synthesis of cholesterol, steroids and other lipids.
Cytochrome P450 2C18 is a protein that in humans is encoded by the CYP2C18 gene.
Cytochrome P450 4A11 is a protein that in humans is codified by the CYP4A11 gene.
Cytochrome P450 4F2 is a protein that in humans is encoded by the CYP4F2 gene. This protein is an enzyme, a type of protein that catalyzes chemical reactions inside cells. This specific enzyme is part of the superfamily of cytochrome P450 (CYP) enzymes, and the encoding gene is part of a cluster of cytochrome P450 genes located on chromosome 19.
Cytochrome P450 4F8 is a protein that in humans is encoded by the CYP4F8 gene.
Epoxygenases are a set of membrane-bound, heme-containing cytochrome P450 enzymes that metabolize polyunsaturated fatty acids to epoxide products that have a range of biological activities. The most thoroughly studied substrate of the CYP epoxylgenases is arachidonic acid. This polyunsaturated fatty acid is metabolized by cyclooxygenases to various prostaglandin, thromboxane, and prostacyclin metabolites in what has been termed the first pathway of eicosanoid production; it is also metabolized by various lipoxygenases to hydroxyeicosatetraenoic acids and leukotrienes in what has been termed the second pathway of eicosanoid production. The metabolism of arachidonic acid to epoxyeicosatrienoic acids by the CYP epoxygenases has been termed the third pathway of eicosanoid metabolism. Like the first two pathways of eicosanoid production, this third pathway acts as a signaling pathway wherein a set of enzymes metabolize arachidonic acid to a set of products that act as secondary signals to work in activating their parent or nearby cells and thereby orchestrate functional responses. However, none of these three pathways is limited to metabolizing arachidonic acid to eicosanoids. Rather, they also metabolize other polyunsaturated fatty acids to products that are structurally analogous to the eicosanoids but often have different bioactivity profiles. This is particularly true for the CYP epoxygenases which in general act on a broader range of polyunsaturated fatty acids to form a broader range of metabolites than the first and second pathways of eicosanoid production. Furthermore, the latter pathways form metabolites many of which act on cells by binding with and thereby activating specific and well-characterized receptor proteins; no such receptors have been fully characterized for the epoxide metabolites. Finally, there are relatively few metabolite-forming lipoxygenases and cyclooxygenases in the first and second pathways and these oxygenase enzymes share similarity between humans and other mammalian animal models. The third pathway consists of a large number of metabolite-forming CYP epoxygenases and the human epoxygenases have important differences from those of animal models. Partly because of these differences, it has been difficult to define clear roles for the epoxygenase-epoxide pathways in human physiology and pathology.
CYP2U1 is a protein that in humans is encoded by the CYP2U1 gene
Epoxide docosapentaenoic acids are metabolites of the 22-carbon straight-chain omega-3 fatty acid, docosahexaenoic acid (DHA). Cell types that express certain cytochrome P450 (CYP) epoxygenases metabolize polyunsaturated fatty acids (PUFAs) by converting one of their double bonds to an epoxide. In the best known of these metabolic pathways, cellular CYP epoxygenases metabolize the 20-carbon straight-chain omega-6 fatty acid, arachidonic acid, to epoxyeicosatrienoic acids (EETs); another CYP epoxygenase pathway metabolizes the 20-carbon omega-3 fatty acid, eicosapentaenoic acid (EPA), to epoxyeicosatetraenoic acids (EEQs). CYP epoxygenases similarly convert various other PUFAs to epoxides. These epoxide metabolites have a variety of activities. However, essentially all of them are rapidly converted to their corresponding, but in general far less active, vicinal dihydroxy fatty acids by ubiquitous cellular soluble epoxide hydrolase. Consequently, these epoxides, including EDPs, operate as short-lived signaling agents that regulate the function of their parent or nearby cells. The particular feature of EDPs distinguishing them from EETs is that they derive from omega-3 fatty acids and are suggested to be responsible for some of the beneficial effects attributed to omega-3 fatty acids and omega-3-rich foods such as fish oil.
Epoxyeicosatetraenoic acids are a set of biologically active epoxides that various cell types make by metabolizing the omega 3 fatty acid, eicosapentaenoic acid (EPA), with certain cytochrome P450 epoxygenases. These epoxygenases can metabolize EPA to as many as 10 epoxides that differ in the site and/or stereoisomer of the epoxide formed; however, the formed EEQs, while differing in potency, often have similar bioactivities and are commonly considered together.
This article incorporates public domain material from "CYP2C9". National Center for Biotechnology Information, U.S. National Library of Medicine. National Center for Biotechnology Information. 29 March 2021. This gene encodes a member of the cytochrome P450 superfamily of enzymes. The cytochrome P450 proteins are monooxygenases that catalyze many reactions involved in drug metabolism and synthesis of cholesterol, steroids, and other lipids. This protein localizes to the endoplasmic reticulum and its expression is induced by rifampin. The enzyme is known to metabolize many xenobiotics, including phenytoin, tolbutamide, ibuprofen, and S-warfarin. Studies identifying individuals who are poor metabolizers of phenytoin and tolbutamide suggest that this gene is polymorphic. The gene is located within a cluster of cytochrome P450 genes on chromosome 10q24.
This article incorporates text from this source, which is in the public domain . This article incorporates text from this source, which is in the public domain . | This 'further reading' section may need cleanup.(November 2020) |
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