Cytochrome P450 3A4 (abbreviated CYP3A4) () is an important
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
in the body, mainly found in the liver and in the intestine. It
oxidizes
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
small foreign organic molecules (
xenobiotic
A xenobiotic is a chemical substance found within an organism that is not naturally produced or expected to be present within the organism. It can also cover substances that are present in much higher concentrations than are usual. Natural compo ...
s), such as
toxin
A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849– ...
s or drugs, so that they can be removed from the body. It is highly homologous to
CYP3A5
Cytochrome P450 3A5 is a protein that in humans is encoded by the ''CYP3A5'' gene.
Tissue distribution
''CYP3A5'' encodes a member of the cytochrome P450 superfamily of enzymes. Like most of the cytochrome P450, the CYP3A5 is expressed in the ...
, another important CYP3A enzyme.
While many drugs are deactivated by CYP3A4, there are also some drugs which are ''activated'' by the enzyme. Some substances, such as some drugs and
furanocoumarin
The furanocoumarins, or furocoumarins, are a class of organic chemical compounds produced by a variety of plants. Most of the plant species found to contain furanocoumarins belong to a handful of plant families. The families Apiaceae and Rutacea ...
s present in
grapefruit
The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink.
Grapefruit is ...
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
Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...
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
A hemeprotein (or haemprotein; also hemoprotein or haemoprotein), or heme protein, is a protein that contains a heme prosthetic group. They are a very large class of metalloproteins. The heme group confers functionality, which can include oxygen ...
, i.e. a
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
containing a
heme
Heme, or haem (pronounced / hi:m/ ), is a precursor to hemoglobin, which is necessary to bind oxygen in the bloodstream. Heme is biosynthesized in both the bone marrow and the liver.
In biochemical terms, heme is a coordination complex "consisti ...
group with an iron atom. In humans, the CYP3A4 protein is encoded by the ''CYP3A4''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.
This gene is part of a cluster of cytochrome P
450 genes on
chromosome 7q22.1.
Function
CYP3A4 is a member of the
cytochrome P450
Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...
superfamily
SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...
of
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...
s. The cytochrome P450 proteins are
monooxygenase
Monooxygenases are enzymes that incorporate one hydroxyl group (−OH) into substrates in many metabolic pathways. In this reaction, the two atoms of dioxygen are reduced to one hydroxyl group and one H2O molecule by the concomitant oxidation o ...
s that catalyze many reactions involved in
drug metabolism
Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set of ...
and synthesis of cholesterol, steroids, and other lipids components.
The CYP3A4 protein localizes to the
endoplasmic reticulum
The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...
, and its expression is induced by
glucocorticoid
Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebr ...
s and some pharmacological agents. Cytochrome P450 enzymes metabolize approximately 60% of prescribed drugs, with CYP3A4 responsible for about half of this metabolism; substrates include acetaminophen (paracetamol), codeine, ciclosporin (cyclosporin), diazepam, and erythromycin. The enzyme also metabolizes some steroids and carcinogens.
Most drugs undergo deactivation by CYP3A4, either directly or by facilitated
excretion
Excretion is a process in which metabolic waste
is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks after lea ...
from the body. Also, many substances are
bioactivated
Activation, in chemistry and biology, is the process whereby something is prepared or excited for a subsequent reaction.
Chemistry
In chemistry, "activation" refers to the reversible transition of a molecule into a nearly identical chemical or ...
by CYP3A4 to form their active compounds, and many protoxins being
toxicated
Toxication, toxification or toxicity exaltation is the conversion of a chemical compound into a more toxic form in living organisms or in substrates such as soil or water. The conversion can be caused by enzymatic metabolism in the organisms, as we ...
into their toxic forms ''(for examples – see table below)''.
CYP3A4 also possesses
epoxygenase
Epoxygenases are a set of membrane-bound, heme-containing cytochrome P450 (CYP P450 or just CYP) enzymes that metabolize polyunsaturated fatty acids to epoxide products that have a range of biological activities. The most thoroughly studied substr ...
activity in that it metabolizes
arachidonic acid
Arachidonic acid (AA, sometimes ARA) is a polyunsaturated omega-6 fatty acid 20:4(ω-6), or 20:4(5,8,11,14). It is structurally related to the saturated arachidic acid found in cupuaçu butter. Its name derives from the New Latin word ''arachi ...
to
epoxyeicosatrienoic acid
The epoxyeicosatrienoic acids or EETs are signaling molecules formed within various types of cells by the metabolism of arachidonic acid by a specific subset of Cytochrome P450 enzymes termed cytochrome P450 epoxygenases. These nonclassic eicosa ...
s (EETs), i.e. (±)-8,9-, (±)-11,12-, and (±)-14,15-epoxyeicosatrienoic acids. The EETs have a wide range of activities including the promotion of certain types of cancers (see
epoxyeicosatetraenoic acid
Epoxyeicosatetraenoic acids (EEQs or EpETEs) 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 ...
). 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. The cytochrome P450 is also reported to have fatty acid monooxgenase activity for metabolizing arachidonic acid to
20-Hydroxyeicosatetraenoic acid
20-Hydroxyeicosatetraenoic acid, also known as 20-HETE or 20-hydroxy-5''Z'',8''Z'',11''Z'',14''Z''-eicosatetraenoic acid, is an eicosanoid metabolite of arachidonic acid that has a wide range of effects on the vascular system including the regula ...
(20-HETE).
20-HETE has a wide range of activities that also include growth stimulation in breast and other types of cancers (see
12-hydroxyeicosatetraenoic acid).
Evolution
The CYP3A4 gene exhibits a much more complicated upstream regulatory region in comparison with its
paralogs
Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a spec ...
.
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.
Chimpanzee
The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...
and human CYP3A4 are highly conserved in metabolism of many
ligands
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electro ...
, although four amino acids positively selected in humans led to a 5-fold
benzylation of
7-BFC in the presence of the
hepatotoxic
Hepatotoxicity (from ''hepatic toxicity'') implies chemical-driven liver damage. Drug-induced liver injury is a cause of acute and chronic liver disease caused specifically by medications and the most common reason for a drug to be withdrawn fro ...
secondary
bile acid
Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver. Bile acids are conjugated with taurine or glycine residues to give anions called bile salts.
Primary b ...
lithocholic acid
Lithocholic acid, also known as 3α-hydroxy-5β-cholan-24-oic acid or LCA, is a bile acid that acts as a detergent to solubilize fats for absorption. Bacterial action in the colon produces LCA from chenodeoxycholic acid by reduction of the hydrox ...
.
This change in consequence contributes to an increased human defense against
cholestasis
Cholestasis is a condition where bile cannot flow from the liver to the duodenum. The two basic distinctions are an obstructive type of cholestasis where there is a mechanical blockage in the duct system that can occur from a gallstone or malignan ...
.
Tissue distribution
Fetus
A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...
es tend to not express CYP3A4 in their liver tissue, but rather
CYP3A7
CYP3A7 is an enzyme belonging to the cytochrome P450 family. It is 503 amino acids in size and shares 87% of its sequence with CYP3A4. It carries out a similar role in fetuses that CYP3A4 serves in adults. The gene location is 7q22.1.
The CYP3A ...
(), which acts on a similar range of substrates. CYP3A4 is absent in fetal liver but increases to approximately 40% of adult levels in the fourth month of life and 72% at 12 months.
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. CYP3A4 in the intestine plays an important role in the metabolism of certain drugs. Often this allows
prodrug
A prodrug is a medication or compound that, after intake, is metabolized (i.e., converted within the body) into a pharmacologically active drug. Instead of administering a drug directly, a corresponding prodrug can be used to improve how the drug ...
s to be activated and absorbed – as in the case of the
histamine H1-receptor antagonist terfenadine
Terfenadine is an antihistamine formerly used for the treatment of allergic conditions. It was brought to market by Hoechst Marion Roussel (now Sanofi-Aventis) and was marketed under various brand names, including Seldane in the United States, Tr ...
.
Recently CYP3A4 has also been identified in the brain, however its role in the
central nervous system
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
is still unknown.
Mechanisms
Cytochrome P450
Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...
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
In chemistry, hydroxylation can refer to:
*(i) most commonly, hydroxylation describes a chemical process that introduces a hydroxyl group () into an organic compound.
*(ii) the ''degree of hydroxylation'' refers to the number of OH groups in a ...
,
epoxidation
In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale for ...
of olefins, aromatic
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
, heteroatom oxidations, N- and O- dealkylation reactions, aldehyde oxidations,
dehydrogenation
In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. At ...
reactions, and aromatase activity.
Hydroxylation of an sp
3 C-H bond is one of the ways in which CYP3A4 (and cytochrome P450 oxygenases) affects its ligand.
In fact, hydroxylation is sometimes followed by dehydrogenation, leading to more complex metabolites.
An example of a molecule that undergoes more than one reaction due to CYP3A4 includes
tamoxifen
Tamoxifen, sold under the brand name Nolvadex among others, is a selective estrogen receptor modulator used to prevent breast cancer in women and treat breast cancer in women and men. It is also being studied for other types of cancer. It has b ...
, which is hydroxylated to 4-hydroxy-tamoxifen and then dehydrated to 4-hydroxy-tamoxifen quinone methide.
Two mechanisms have been proposed as the primary pathway of hydroxylation in P450 enzymes.
![Hydroxylation Mechanisms of Cytochrome P450 Enzymes](https://upload.wikimedia.org/wikipedia/commons/2/21/Hydroxylation_Mechanisms_of_Cytochrome_P450_Enzymes.png)
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 In chemistry, a radical clock is a chemical compound that assists in the indirect methodology to determine the kinetics (chemistry), kinetics of a free-radical reaction. The radical-clock compound itself reacts at a known rate, which provides a cali ...
".
Inhibition through fruit ingestion
In 1998, various researchers showed that
grapefruit
The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink.
Grapefruit is ...
juice, and grapefruit in general, is a potent inhibitor of CYP3A4, which can affect the metabolism of a variety of drugs, increasing their
bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is the fraction (%) of an administered drug that reaches the systemic circulation.
By definition, when a medication is administered intravenously, its bioavailability is 100%. H ...
.
In some cases, this can lead to a fatal interaction with drugs like
astemizole
Astemizole (marketed under the brand name Hismanal, developmental code R43512) was a second-generation antihistamine drug that has a long duration of action. Astemizole was discovered by Janssen Pharmaceutica in 1977. It was withdrawn from the ma ...
or
terfenadine
Terfenadine is an antihistamine formerly used for the treatment of allergic conditions. It was brought to market by Hoechst Marion Roussel (now Sanofi-Aventis) and was marketed under various brand names, including Seldane in the United States, Tr ...
.
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.
In addition to grapefruit, other fruits have similar effects.
Noni
''Morinda citrifolia'' is a fruit-bearing tree in the coffee family, Rubiaceae. Its native range extends across Southeast Asia and Australasia, and was spread across the Pacific by Polynesian sailors. The species is now cultivated throughout th ...
(''Morinda citrifolia''), for example, is a
dietary supplement
A dietary supplement is a manufactured product intended to supplement one's diet by taking a pill, capsule, tablet, powder, or liquid. A supplement can provide nutrients either extracted from food sources or that are synthetic in order ...
typically consumed as a juice and also inhibits CYP3A4.
Pomegranate
The pomegranate (''Punica granatum'') is a fruit-bearing deciduous shrub in the family Lythraceae, subfamily Punicoideae, that grows between tall.
The pomegranate was originally described throughout the Mediterranean Basin, Mediterranean re ...
juice has shown some inhibition in limited studies, but has not yet demonstrated the effect in humans.
Variability
While over 28
single nucleotide polymorphism
In genetics, a single-nucleotide polymorphism (SNP ; plural SNPs ) is a germline substitution of a single nucleotide at a specific position in the genome. Although certain definitions require the substitution to be present in a sufficiently larg ...
s (SNPs) have been identified in the ''CYP3A4'' gene, it has been found that this does not translate into significant interindividual variability . It can be supposed that this may be due to the induction of CYP3A4 on exposure to substrates.
CYP3A4 alleles which 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
Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...
and
nifedipine
Nifedipine (3,5-dimethyl 2,6-dimethyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3,5-dicarboxylate), sold under the brand name Adalat and Procardia, among others, is a calcium channel blocker medication used to manage angina, high blood pressure, Ra ...
in comparison to wild-type metabolism.
By contrast, ''CYP3A4*1G'' allele has more potent enzymatic activity compared to ''CYP3A4*1A'' (the wild-type allele).
[Alkattan A, Alsalameen E. Polymorphisms of genes related to phase-I metabolic enzymes affecting the clinical efficacy and safety of clopidogrel treatment. Expert Opin Drug Metab Toxicol. 2021 Apr 30. doi: 10.1080/17425255.2021.1925249. Epub ahead of print. PMID 33931001.]
Variability in CYP3A4 function can be determined noninvasively by the
erythromycin breath test (ERMBT). The ERMBT estimates CYP3A4 activity by measuring the radiolabelled carbon dioxide exhaled after an intravenous dose of (
14C-''N''-methyl)-
erythromycin
Erythromycin is an antibiotic used for the treatment of a number of bacterial infections. This includes respiratory tract infections, skin infections, chlamydia infections, pelvic inflammatory disease, and syphilis. It may also be used duri ...
.
Induction
CYP3A4 is
induced
Induce may refer to:
* Induced consumption
* Induced innovation
* Induced character
* Induced coma
* Induced menopause
* Induced metric
* Induced path
* Induced topology
* Induce (musician), American musician
See also
* Inducement (disambiguation ...
by a wide variety of
ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
s. These ligands bind to the
pregnane X receptor
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 ' ...
(PXR). The activated PXR complex forms a heterodimer with the
retinoid X receptor
The retinoid X receptor (RXR) is a type of nuclear receptor that is activated by 9-cis retinoic acid, which is discussed controversially to be of endogenous relevance, and 9-''cis''-13,14-dihydroretinoic acid, which is likely to be the major e ...
(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
Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including:
Genetics
* Transcription (biology), the copying of DNA into RNA, the fir ...
of the CYP3A4 promoter region and gene. Ligand binding increases when in the presence of CYP3A4 ligands, such as in the presence of
aflatoxin
Aflatoxins are various poisonous carcinogens and mutagens that are produced by certain molds, particularly ''Aspergillus'' species. The fungi grow in soil, decaying vegetation and various staple foodstuffs and commodities such as hay, sweetcorn ...
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.
Induction of CYP3A4 has been shown to vary in humans depending on sex. Evidence shows an increased
drug clearance
In pharmacology, clearance is a pharmacokinetic measurement of the volume of plasma from which a substance is completely removed per unit time. Usually, clearance is measured in L/h or mL/min. The quantity reflects the rate of drug elimination d ...
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
In molecular biology, messenger ribonucleic acid (mRNA) is a single-stranded molecule of RNA that corresponds to the genetic sequence of a gene, and is read by a ribosome in the process of Protein biosynthesis, synthesizing a protein.
mRNA is ...
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.
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
Rifampicin, also known as rifampin, is an ansamycin antibiotic used to treat several types of bacterial infections, including tuberculosis (TB), mycobacterium avium complex, ''Mycobacterium avium'' complex, leprosy, and Legionnaires’ disease. ...
and human PXR is not activated by pregnenalone 16α-carbonitrile
In order to facilitate study of CYP3A4 functional pathways ''in vivo,'' mouse strains have been developed using
transgene
A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another. The introduction of a transgene, in a process known as transgenesis, has the potential to change the ...
s 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.
This effect has been attributed to CYP3A4 regulation by the
growth hormone
Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in h ...
signal transduction pathway.
In addition to providing an ''in vivo'' model, humanized CYP3A4 mice (hCYP3A4) have been used to further emphasize gender differences in CYP3A4 activity.
CYP3A4 activity levels have also been linked to diet and environmental factors, such as duration of exposure to xenobiotic substances.
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.
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.
Turnover
Estimates of the
turnover rate of human CYP3A4 vary widely. For hepatic CYP3A4, ''in vivo'' methods yield estimates of enzyme
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
mainly in the range of 70 to 140 hours, whereas ''in vitro'' methods give estimates from 26 to 79 hours.
Turnover of gut CYP3A4 is likely to be a function of the rate of
enterocyte
Enterocytes, or intestinal absorptive cells, are simple columnar epithelial cells which line the inner surface of the small and large intestines. A glycocalyx surface coat contains digestive enzymes. Microvilli on the apical surface increase its ...
renewal; an indirect approach based on recovery of activity following exposure to grapefruit juice yields measurements in the 12- to 33-hour range.
Technology
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.
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
Surface plasmon resonance (SPR) is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity material in a particle stimulated by incident light. SPR is the basis of many standard tools for measu ...
spectroscopy (LSPR).
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
Solid-state NMR (ssNMR) spectroscopy is a technique for characterizing atomic level structure in solid materials e.g. powders, single crystals and amorphous samples and tissues using nuclear magnetic resonance (NMR) spectroscopy. The anisotropic pa ...
, redox potentiometry, and
steady-state enzyme kinetics.
Ligands
Following is a table of selected
substrates,
inducers and
inhibitors of CYP3A4. Where classes of agents are listed, there may be exceptions within the class.
Inhibitors of CYP3A4 can be classified by their
potency
Potency may refer to:
* Potency (pharmacology), a measure of the activity of a drug in a biological system
* Virility
* Cell potency, a measure of the differentiation potential of stem cells
* In homeopathic dilutions, potency is a measure of how ...
, such as:
*Strong inhibitor being one that causes at least a 5-fold increase in the plasma
AUC values, or more than 80% decrease in
clearance.
[
*Moderate inhibitor being one that causes at least a 2-fold increase in the plasma AUC values, or 50-80% decrease in clearance.][
*Weak inhibitor being one that causes at least a 1.25-fold but less than 2-fold increase in the plasma AUC values, or 20-50% decrease in clearance.][ Retrieved on December 25, 2008.]
Interactive pathway map
See also
*List of drugs affected by grapefruit
A ''list'' is any set of items in a row. List or lists may also refer to:
People
* List (surname)
Organizations
* List College, an undergraduate division of the Jewish Theological Seminary of America
* SC Germania List, German rugby union ...
References
External links
PharmGKB: Annotated PGx Gene Information for CYP3A4
CYP3A4 substrate prediction
*
*
{{DEFAULTSORT:Cyp3a4
3
EC 1.14.14