CYP3A4 | |||||||||
---|---|---|---|---|---|---|---|---|---|
Identifiers | |||||||||
EC no. | 1.14.14.56 | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
|
Cytochrome P450 3A4 (abbreviated CYP3A4) (EC 1.14.13.97) 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.
While many drugs are deactivated by CYP3A4, there are also some drugs that are activated by the enzyme. Some substances, such as some drugs and furanocoumarins present in grapefruit juice, interfere with the action of CYP3A4. These substances will, therefore, either amplify or weaken the action of those drugs that are modified by CYP3A4.
CYP3A4 is a member of the cytochrome P450 family of oxidizing enzymes. Several other members of this family are also involved in drug metabolism, but CYP3A4 is the most common and the most versatile one. Like all members of this family, it is a hemoprotein, i.e. a protein containing a heme group with an iron atom. In humans, the CYP3A4 protein is encoded by the CYP3A4 gene. [3] This gene is part of a cluster of cytochrome P450 genes on chromosome 7q22.1. [4] Previously another CYP3A gene, CYP3A3, was thought to exist; however, it is now thought that this sequence represents a transcript variant of CYP3A4. Alternatively-spliced transcript variants encoding different isoforms have been identified. [5]
CYP3A4 is 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 steroids (including cholesterol), and other lipids. [5]
The CYP3A4 protein localizes to the endoplasmic reticulum, and its expression is induced by glucocorticoids and some pharmacological agents. [5] Cytochrome P450 enzymes metabolize approximately 60% of prescribed drugs, with CYP3A4 responsible for about half of this metabolism; [6] substrates include acetaminophen (paracetamol), codeine, ciclosporin (cyclosporin), diazepam, erythromycin, and chloroquine. [5] The enzyme also metabolizes some steroids and carcinogens. [7] Most drugs undergo deactivation by CYP3A4, either directly or by facilitated excretion from the body. Also, many substances are bioactivated by CYP3A4 to form their active compounds, and many protoxins are toxicated into their toxic forms (see table below for examples).
CYP3A4 also possesses epoxygenase activity in that it metabolizes arachidonic acid to epoxyeicosatrienoic acids (EETs), i.e. (±)-8,9-, (±)-11,12-, and (±)-14,15-epoxyeicosatrienoic acids. [8] EETs have a wide range of activities including the promotion of certain types of cancers (see epoxyeicosatetraenoic acid). CYP3A4 promotes the growth of various types of human cancer cell lines in culture by producing (±)-14,15-epoxyeicosatrienoic acids, which stimulate these cells to grow. [9] The CYP3A4 enzyme is also reported to have fatty acid monooxgenase activity for metabolizing arachidonic acid to 20-Hydroxyeicosatetraenoic acid (20-HETE). [10] 20-HETE has a wide range of activities that include growth stimulation in breast and other types of cancers (see 12-hydroxyeicosatetraenoic acid).
The CYP3A4 gene exhibits a much more complicated upstream regulatory region in comparison with its paralogs. [11] This increased complexity renders the CYP3A4 gene more sensitive to endogenous and exogenous PXR and CAR ligands, instead of relying on gene variants for wider specificity. [11] Chimpanzee and human CYP3A4 are highly conserved in metabolism of many ligands, although four amino acids positively selected in humans led to a 5-fold benzylation of 7-BFC in the presence of the hepatotoxic secondary bile acid lithocholic acid. [12] This change in consequence contributes to an increased human defense against cholestasis. [12]
Fetuses do not express CYP3A4 in their liver tissue, but rather CYP3A7 (EC 1.14.14.1), which acts on a similar range of substrates. CYP3A4 increases to approximately 40% of adult levels in the fourth month of life and 72% at 12 months. [13] [14]
Although CYP3A4 is predominantly found in the liver, it is also present in other organs and tissues of the body, where it may play an important role in metabolism. CP3A4 is the major CYP enzyme in the intestine. [15] CYP3A4 in the intestine plays an important role in the metabolism of certain drugs. Often this allows prodrugs to be activated and absorbed, as in the case of the histamine H1-receptor antagonist terfenadine.
Recently CYP3A4 has also been identified in the brain, but its role in the central nervous system is still unknown. [16]
Cytochrome P450 enzymes perform an assortment of modifications on a variety of ligands, utilizing its large active site and its ability to bind more than one substrate at a time to perform complicated chemical alterations in the metabolism of endogenous and exogenous compounds. These include hydroxylation, epoxidation of olefins, aromatic oxidation, heteroatom oxidations, N- and O- dealkylation reactions, aldehyde oxidations, dehydrogenation reactions, and aromatase activity. [17] [18]
Hydroxylation of an sp3 C-H bond is one of the ways in which CYP3A4 (and cytochrome P450 oxygenases) affects its ligand. [19] In fact, hydroxylation is sometimes followed by dehydrogenation, leading to more complex metabolites. [18] An example of a molecule that undergoes more than one reaction due to CYP3A4 includes tamoxifen, which is hydroxylated to 4-hydroxy-tamoxifen and then dehydrated to 4-hydroxy-tamoxifen quinone methide. [18]
Two mechanisms have been proposed as the primary pathway of hydroxylation in P450 enzymes.
The first pathway suggested is a cage-controlled radical method ("oxygen rebound"), and the second involves a concerted mechanism that does not utilize a radical intermediate but instead acts very quickly via a "radical clock". [19]
In 1998, various researchers showed that grapefruit juice, and grapefruit in general, is a potent inhibitor of CYP3A4, which can affect the metabolism of a variety of drugs, increasing their bioavailability. [20] [21] [22] [23] [24] In some cases, this can lead to a fatal interaction with drugs like astemizole or terfenadine. [21] The effect of grapefruit juice with regard to drug absorption was originally discovered in 1989. The first published report on grapefruit drug interactions was in 1991 in the Lancet entitled "Interactions of Citrus Juices with Felodipine and Nifedipine", and was the first reported food-drug interaction clinically. The effects of grapefruit last from 3–7 days, with the greatest effects when juice is taken an hour previous to administration of the drug. [25]
In addition to grapefruit, other fruits have similar effects. Noni (Morinda citrifolia), for example, is a dietary supplement typically consumed as a juice and also inhibits CYP3A4. [26] Pomegranate juice has shown some inhibition in limited studies, but has not yet demonstrated the effect in humans. [27] [28]
While over 28 single nucleotide polymorphisms (SNPs) have been identified in the CYP3A4 gene, it has been found that this does not translate into significant interindividual variability in vivo. It can be supposed that this may be due to the induction of CYP3A4 on exposure to substrates.
CYP3A4 alleles that have been reported to have minimal function compared to wild-type include CYP3A4*6 (an A17776 insertion) and CYP3A4*17 (F189S). Both of these SNPs led to decreased catalytic activity with certain ligands, including testosterone and nifedipine in comparison to wild-type metabolism. [29] By contrast, CYP3A4*1G allele has more potent enzymatic activity compared to CYP3A4*1A (the wild-type allele). [30]
Variability in CYP3A4 function can be determined noninvasively by the erythromycin breath test (ERMBT). The ERMBT estimates in vivo CYP3A4 activity by measuring the radiolabelled carbon dioxide exhaled after an intravenous dose of (14C-N-methyl)-erythromycin. [31]
CYP3A4 is induced by a wide variety of ligands. These ligands bind to the pregnane X receptor (PXR). The activated PXR complex forms a heterodimer with the retinoid X receptor (RXR), which binds to the XREM region of the CYP3A4 gene. XREM is a regulatory region of the CYP3A4 gene, and binding causes a cooperative interaction with proximal promoter regions of the gene, resulting in increased transcription and expression of CYP3A4. Activation of the PXR/RXR heterodimer initiates transcription of the CYP3A4 promoter region and gene. Ligand binding increases when in the presence of CYP3A4 ligands, such as in the presence of aflatoxin B1, M1, and G1. Indeed, due to the enzyme's large and malleable active site, it is possible for the enzyme to bind multiple ligands at once, leading to potentially detrimental side effects. [32]
Induction of CYP3A4 has been shown to vary in humans depending on sex. Evidence shows an increased drug clearance by CYP3A4 in women, even when accounting for differences in body weight. A study by Wolbold et al. (2003) found that the median CYP3A4 levels measured from surgically removed liver samples of a random sample of women exceeded CYP3A4 levels in the livers of men by 129%. CYP3A4 mRNA transcripts were found in similar proportions, suggesting a pre-translational mechanism for the up-regulation of CYP3A4 in women. The exact cause of this elevated level of enzyme in women is still under speculation, however studies have elucidated other mechanisms (such as CYP3A5 or CYP3A7 compensation for lowered levels of CYP3A4) that affect drug clearance in both men and women. [33]
CYP3A4 substrate activation varies amongst different animal species. Certain ligands activate human PXR, which promotes CYP3A4 transcription, while showing no activation in other species. For instance, mouse PXR is not activated by rifampicin and human PXR is not activated by pregnenolone 16α-carbonitrile [34] In order to facilitate study of CYP3A4 functional pathways in vivo, mouse strains have been developed using transgenes in order to produce null/human CYP3A4 and PXR crosses. Although humanized hCYP3A4 mice successfully expressed the enzyme in their intestinal tract, low levels of hCYP3A4 were found in the liver. [34] This effect has been attributed to CYP3A4 regulation by the growth hormone signal transduction pathway. [34] In addition to providing an in vivo model, humanized CYP3A4 mice (hCYP3A4) have been used to further emphasize gender differences in CYP3A4 activity. [34]
CYP3A4 activity levels have also been linked to diet and environmental factors, such as duration of exposure to xenobiotic substances. [35] Due to the enzyme's extensive presence in the intestinal mucosa, the enzyme has shown sensitivity to starvation symptoms and is upregulated in defense of adverse effects. Indeed, in fatheaded minnows, unfed female fish were shown to have increased PXR and CYP3A4 expression, and displayed a more pronounced response to xenobiotic factors after exposure after several days of starvation. [35] By studying animal models and keeping in mind the innate differences in CYP3A4 activation, investigators can better predict drug metabolism and side effects in human CYP3A4 pathways.
Estimates of the turnover rate of human CYP3A4 vary widely. For hepatic CYP3A4, in vivo methods yield estimates of the enzyme half-life mainly in the range of 70 to 140 hours, whereas in vitro methods give estimates from 26 to 79 hours. [36] Turnover of gut CYP3A4 is likely to be a function of the rate of enterocyte renewal; an indirect approach based on the recovery of activity following exposure to grapefruit juice yields measurements in the 12- to 33-hour range. [36]
Due to membrane-bound CYP3A4's natural propensity to conglomerate, it has historically been difficult to study drug binding in both solution and on surfaces. Co-crystallization is difficult since the substrates tend to have a low KD (between 5–150 μM) and low solubility in aqueous solutions. [37] A successful strategy in isolating the bound enzyme is the functional stabilization of monomeric CYP3A4 on silver nanoparticles produced from nanosphere lithography and analyzed via localized surface plasmon resonance spectroscopy (LSPR). [38] These analyses can be used as a high-sensitivity assay of drug binding, and may become integral in further high-throughput assays utilized in initial drug discovery testing. In addition to LSPR, CYP3A4-Nanodisc complexes have been found helpful in other applications including solid-state NMR, redox potentiometry, and steady-state enzyme kinetics. [38]
Following are lists of selected substrates, inducers and inhibitors of CYP3A4. Where classes of agents are listed, there may be exceptions within the class.
The substrates of CYP3A4 are:
Inhibitors of CYP3A4 are classified by potency:
The inhibitors of CYP3A4 are the following substances.
Strong and moderate CYP3A4 inducers are drugs that decrease the AUC of sensitive substrates of a given pathway where CYP3A4 is involved by ≥80 percent and ≥50 to <80 percent, respectively. [83] [123] Weak inducers decrease the AUC by ≥20 to <50 percent. [123]
The inducers of CYP3A4 are the following substances.
Click on genes, proteins and metabolites below to link to respective articles. [§ 1]
Cimetidine, sold under the brand name Tagamet among others, is a histamine H2 receptor antagonist that inhibits stomach acid production. It is mainly used in the treatment of heartburn and peptic ulcers.
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.
In pharmaceutical sciences, drug interactions occur when a drug's mechanism of action is affected by the concomitant administration of substances such as foods, beverages, or other drugs. A popular example of drug–food interaction is the effect of grapefruit on the metabolism of drugs.
Dextromethorphan (DXM), sold under the trade name Robitussin among others, is a cough suppressant used in many cough and cold medicines. It affects serotonin, norepinephrine, NMDA, and sigma-1 receptors in the brain, all of which have been implicated in the pathophysiology of depression. In 2022, the FDA approved the combination dextromethorphan/bupropion to serve as a rapid acting antidepressant in patients with major depressive disorder.
Naringin is a flavanone-7-O-glycoside between the flavanone naringenin and the disaccharide neohesperidose. The flavonoid naringin occurs naturally in citrus fruits, especially in grapefruit, where naringin is responsible for the fruit's bitter taste. In commercial grapefruit juice production, the enzyme naringinase can be used to remove the bitterness (debittering) created by naringin. In humans naringin is metabolized to the aglycone naringenin by naringinase present in the gut.
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.
Some fruit juices and fruits can interact with numerous drugs, in many cases causing adverse effects. The effect is most studied with grapefruit and grapefruit juice, but similar effects have been observed with certain other citrus fruits.
Cytochrome P450 family 2 subfamily C member 9 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. The gene is highly polymorphic, which affects the efficiency of the metabolism by the enzyme.
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.
In the field of molecular biology, the pregnane X receptor (PXR), also known as the steroid and xenobiotic sensing nuclear receptor (SXR) or nuclear receptor subfamily 1, group I, member 2 (NR1I2) is a protein that in humans is encoded by the NR1I2 gene.
Cytochrome P450 17A1 is an enzyme of the hydroxylase type that in humans is encoded by the CYP17A1 gene on chromosome 10. It is ubiquitously expressed in many tissues and cell types, including the zona reticularis and zona fasciculata of the adrenal cortex as well as gonadal tissues. It has both 17α-hydroxylase and 17,20-lyase activities, and is a key enzyme in the steroidogenic pathway that produces progestins, mineralocorticoids, glucocorticoids, androgens, and estrogens. More specifically, the enzyme acts upon pregnenolone and progesterone to add a hydroxyl (-OH) group at carbon 17 position (C17) of the steroid D ring, or acts upon 17α-hydroxyprogesterone and 17α-hydroxypregnenolone to split the side-chain off the steroid nucleus.
The erythromycin breath test (ERMBT) is a method used to measure metabolism (oxidation and elimination from the system) by a part of the cytochrome P450 system. Erythromycin produces 14CO2, and this 14CO2 can be measured to study drugs that interact with the cytochrome P450 system. Erythromycin is tagged with carbon-14 and given as an intravenous injection; after 20 minutes the subject blows up a balloon and the carbon dioxide exhaled that is tagged with carbon-14 shows the activity of the CYP3A4 isoenzyme on the erythromycin. ERMBT can be used to determine how drugs that the CYP3A4 isoenzyme metabolizes will function in a given individual.
Bergamottin (5-geranoxypsoralen) is a natural furanocoumarin found in the pulp of pomelos and grapefruits. It is also found in the peel and pulp of the bergamot orange, from which it was first isolated and from which its name is derived.
Cytochrome P450 2B6 is an enzyme that in humans is encoded by the CYP2B6 gene. CYP2B6 is a member of the cytochrome P450 group of enzymes. Along with CYP2A6, it is involved with metabolizing nicotine, along with many other substances.
Cytochrome P450 3A5 is a protein that in humans is encoded by the CYP3A5 gene.
Cytochrome P450, family 3, subfamily A, also known as CYP3A, is a human gene locus. A homologous locus is found in mice.
Cobicistat, sold under the brand name Tybost, is a medication for use in the treatment of human immunodeficiency virus infection (HIV/AIDS). Its major mechanism of action is through the inhibition of human CYP3A proteins.
The Cooperstown cocktail refers to a panel of four drug probes used in human pharmacokinetic studies to determine the activity of drug metabolising enzymes. The terminology 'cocktail' refers to the fact that the drug probes are given together.
In biochemistry, cytochrome P450 enzymes have been identified in all kingdoms of life: animals, plants, fungi, protists, bacteria, and archaea, as well as in viruses. As of 2018, more than 300,000 distinct CYP proteins are known.
Metabolized primarily by CYP3A4 and, to a lesser degree, by CYP1A2 and the extrahepatic isoform CYP1A1
Drug Interactions: Nifedipine is mainly eliminated by metabolism and is a substrate of CYP3A. Inhibitors and inducers of CYP3A can impact the exposure to nifedipine and, consequently, its desirable and undesirable effects. In vitro and in vivo data indicate that nifedipine can inhibit the metabolism of drugs that are substrates of CYP3A, thereby increasing the exposure to other drugs. Nifedipine is a vasodilator, and coadministration of other drugs affecting blood pressure may result in pharmacodynamic interactions.
Erythromycin 500 mg three-four times daily for 6-7 days markedly increased lovastatin exposure (≈6-fold increase in AUC)
Ginko Biloba has been shown to contain the potent inhibitor amentoflavone
This article incorporates text from the United States National Library of Medicine, which is in the public domain.