Cytochrome P450 4F2 (CYP4F2) is a human enzyme belonging to the cytochrome P450 (CYP) superfamily. It regulates inflammation by inactivating leukotriene B4, a potent inflammatory mediator, and genetic variations in its encoding gene (CYP4F2, part of a cluster of cytochrome P450 genes on chromosome 19) affect the dosing of the anticoagulant warfarin.
CYP enzymes function primarily as monooxygenases, adding a hydroxy group to their substrates. They are most highly expressed in the liver and are responsible for about 80% of oxidative metabolism and about 50% of the elimination of commonly used drugs in humans.
The primary substrate of CYP4F2 is leukotriene B4 (LTB4), an eicosanoid inflammatory mediator. By hydroxylating LTB4 to its inactivated form 20-hydroxy-LTB4, the enzyme helps regulate inflammation. CYP4F2 also metabolizes other eicosanoids derived from arachidonic acid in white blood cells.
CYP4F2 also metabolizes certain fatty acids and fat-soluble vitamins, including vitamin E and vitamin K, and bioactivates prodrugs such as pafuramidine. Genetic variations in CYP4F2 affect enzymatic activity, with implications for vitamin K bioavailability and the dosing of vitamin K antagonists like warfarin.
Gene The cytochrome P450 4F2 protein is encoded by the CYP4F2 gene in humans.
CYP4F2 is part of a cluster of cytochrome P450 genes located on chromosome 19, with another closely related gene, CYP4F11, located approximately 16 kbp away. The CYP4F2 gene is composed of no fewer than 13 exons. The protein-coding sequence of the gene is from the second through the thirteenth exon, whereas the first exon contains a 49‑base‑pair segment forming part of the 5′ untranslated region, which makes the overall genomic organization of CYP4F2 very similar to that of CYP4F3.
Gene polymorphisms (variants) in CYP4F2 affect liver mRNA levels and enzymatic activity of the protein encoded.
The analysis of the gene on a molecular level presents several difficulties: CYP4F2 is highly polymorphic, meaning that many genetic variants are present within the population; this makes it challenging to identify specific causal variants responsible for phenotypic effects or disease associations. CYP4F2 is located within a cluster of genes of the CYP4F subfamily; these genes exhibit high homology, which can lead to difficulties in distinguishing between different subfamily members during genetic analysis, including distinguishing functional genes from pseudogenes within the cluster. The genes of the CYP4F subfamily tend to be closely linked on the chromosome and inherited together due to linkage disequilibrium, making it challenging to differentiate one gene's sequence from closely related genes or pseudogenes.
Protein The crystal structure of CYP4F2 has not been experimentally determined. Researchers have used homology modeling and molecular docking to construct theoretical models of the enzyme's structure and predict how it interacts with its substrates.
Species The CYP4F subfamily is conserved across vertebrates, including mammals, birds, amphibians, and ray-finned fishes. However, CYP4F2 is a human gene designation; other species have their own CYP4F genes with different numbers (for example, the mouse ortholog is Cyp4f14). The CYP4 family has also been identified in invertebrate groups such as Ascidiacea, Echinoidea, Gastropoda, and Insecta, though these organisms have distinct CYP4 subfamily members rather than direct CYP4F2 equivalents.
CYP4 enzymes from the same subfamily are often assumed to have similar functions across species, but this may not hold true, as CYP4 enzymes may have diverged in their biochemical properties and gene expression patterns over evolutionary time.
Tissue and subcellular distribution
In humans, CYP4F2 is expressed in various tissues, including the liver, duodenum, small intestine, kidney, bone marrow, epididymis, and prostate, with the highest expression in the liver. CYP4F2 expression can be influenced by various factors, such as genetic variations, dietary intake, drug interactions, and inflammatory conditions.
The CYP4F2 protein localizes to the endoplasmic reticulum (ER) membrane. Specifically, CYP4F2 resides in the smooth endoplasmic reticulum, where it interacts with electron transfer partners such as NADPH-cytochrome P450 reductase and cytochrome b5. The Human Protein Atlas has not yet completed experimental immunofluorescence imaging for CYP4F2 in its cell line panel.
Function The cytochrome P450 superfamily
CYP4F2 is a member of the cytochrome P450 (CYP) superfamily, a group of hemoprotein enzymes bound to cell membranes that are most abundant in the liver. CYP enzymes are involved in cellular metabolism, hormone synthesis, and cholesterol metabolism, and are responsible for about 80% of oxidative metabolism and about 50% of drug elimination in humans. CYP enzymes are frequently targeted in drug development due to their roles in vascular function, sex hormone biosynthesis, and inflammatory response.
The CYP4F subfamily The CYP4F subfamily of CYP enzymes exhibits diverse metabolic specificities, but is characterized by the ω-hydroxylation of very long-chain fatty acids (VLCFA), eicosanoids, lipophilic (fat-soluble) vitamins, and hydroxyeicosatetraenoic acids (HETEs). The cytochrome P450 4F2 protein is an enzyme also known as "leukotriene-B4 ω-hydroxylase 1", because it starts the process of inactivating and degrading leukotriene B4 (LTB4), a potent mediator of inflammation, by ω-hydroxylating it to 20-hydroxy-LTB4.
CYP4F2 and CYP4F3 catalyze the omega-hydroxylation of pro- and anti-inflammatory leukotrienes, modulating their biological activities. Other CYP4F subfamily members have related but distinct roles: CYP4F8 and CYP4F12 metabolize prostaglandins and arachidonic acid, while CYP4F11 and CYP4F12 can also hydroxylate xenobiotics such as certain drugs. The related CYP4X and CYP4Z subfamilies remain classified as "orphan" enzymes with incompletely characterized physiological functions.
The CYP4F subfamily plays a role in the development of cancer. Enzymes such as CYP4F2 and CYP4F3B convert arachidonic acid into 20-Hydroxyeicosatetraenoic acid (20-HETE), an eicosanoid metabolite of arachidonic acid. This metabolite impacts the progression of tumors, the formation of new blood vessels (angiogenesis), and the regulation of blood pressure in blood vessels and kidneys.
CYP4F2 within the subfamily Beyond its role in degrading LTB4, CYP4F2 metabolizes various endogenous substrates including fatty acids, eicosanoids, and fat-soluble vitamins. It regulates the bioavailability of vitamin E by catalyzing the rate-limiting step in vitamin E catabolism, and also regulates the bioavailability of vitamin K, a co-factor required for blood clotting.
Gene polymorphisms in CYP4F2 affect enzymatic activity. Variations that alter vitamin K bioavailability also affect the dosing of vitamin K antagonists such as warfarin, coumarin, or acenocoumarol.
CYP4F2 also regulates the bioactivation of certain drugs, such as the anti-parasitic prodrug pafuramidine, by catalyzing the initial oxidative O-demethylation in human liver and intestinal microsomes to produce its active form, furamidine. The enzyme additionally plays a role in renal water homeostasis through its production of 20-HETE.
Metabolism of leukotriene B4 Biosynthesis of leukotriene B4 from arachidonic acid Leukotriene B4 (LTB4) is a type of lipid mediator that belongs to the family of leukotrienes, which are derived from arachidonic acid by the action of 5-lipoxygenase (5-LOX).
Arachidonic acid is a polyunsaturated fatty acid that is present in the phospholipids of cell membranes. This fatty acid can be released from the membrane by the action of phospholipase A2, a peripheral membrane protein, which is activated by stimuli such as hormones, cytokines, growth factors and stress. Arachidonic acid can then be metabolized by three major pathways: the cyclooxygenase (COX) pathway, the lipoxygenase (LOX) pathway, and the cytochrome P450 (CYP) pathway. These pathways produce different types of lipid mediators, which are collectively called eicosanoids.
Eicosanoids are a group of bioactive molecules that have diverse and potent effects on physiological and pathological processes such as inflammation, immunity, pain, fever, blood pressure, blood clotting, reproduction and cancer. There are multiple types of eicosanoids, such as prostaglandins, leukotrienes, hydroxyeicosatetraenoic acids (HETEs), and so on.
Leukotriene B4 (LTB4) is one of the eicosanoids that is produced by the LOX pathway. LTB4 is synthesized from arachidonic acid by the sequential actions of 5-LOX, 5-lipoxygenase-activating protein, and leukotriene A4 hydrolase.
LTB4 is produced by activated innate immune cells, such as neutrophils, macrophages and mast cells. It induces the activation of polymorphonuclear leukocytes, monocytes and fibroblasts, the production of superoxide and the release of cytokines to attract neutrophils.
The role of leukotriene B4 in inflammatory response LTB4 initiates and maintains inflammation, as it can recruit and activate immune cells such as neutrophils, macrophages, mast cells, monocytes and fibroblasts. LTB4 also stimulates the production of reactive oxygen species, cytokines, chemokines and cell adhesion molecules, which further amplify the inflammatory response.
Inactivation of leukotriene B4 by CYP4F2
Excessive or prolonged inflammation can be harmful to the host, as it can cause tissue damage and chronic diseases, so that the inflammatory process must be tightly regulated and resolved in a timely manner. One of the mechanisms that contributes to the resolution of inflammation is the enzymatic inactivation and degradation of LTB4 by the cytochrome P450 (CYP) family of enzymes. CYP enzymes are mainly expressed in the liver, but they can also be found in other tissues, such as the lungs, kidneys, intestines, and skin.
Among the CYP enzymes, CYP4F2 is the most important for the metabolism of LTB4. It catalyzes the omega-hydroxylation of LTB4 as the first step of inactivation, converting it to 20-hydroxy-LTB4, which has much lower biological activity. CYP4F2 then converts 20-hydroxy-LTB4 to 20-oxo-LTB4 and then to 20-carboxy-LTB4, which are both inactive and can be excreted from the body.
Fatty acid ω-hydroxylation
CYP4F2 belongs to cytochrome P450 omega hydroxylase set of enzymes that catalyze the addition of a hydroxy functional group (−OH) to a molecule of the fatty acid substrate. Specifically, CYP4F2 performs ω-hydroxylation of fatty acids, which means that the functional group is added to the ω- or (ω-1)-C atom. In the context of fatty acids, the ω (omega) atom refers to the carbon atom (C) at the end of the hydrocarbon chain, furthest from the carboxyl group, so that the ω- or (ω-1)-C atom refers to the last carbon atom or the second-to-last carbon atom in the hydrocarbon chain of the fatty acid: the hydroxy group (−OH) is added to one of these atoms during the ω-hydroxylation process.
The enzymes which are members of the CYP4A and CYP4F sub-families, including CYP4F2, may ω-hydroxylate and thereby reduce the activity of fatty acid metabolites of arachidonic acid such as LTB4, 5-HETE, 5-oxo-eicosatetraenoic acid, 12-HETE, and several prostaglandins. These enzymatic reactions lead to the production of metabolites involved in regulating inflammatory and vascular responses in animals and humans. By reducing the activity of these fatty acid metabolites, ω-hydroxylation plays a role in dampening inflammatory pathways and maintaining immune system balance.
Certain single-nucleotide polymorphisms (SNPs) in the CYP4F2 have been associated with human diseases like Crohn's disease and Coeliac disease. These genetic variations may impact the function or expression level of the enzyme, influencing its ability to perform ω-hydroxylation reactions effectively.