Gene:

CYP4F2

cytochrome P450, family 4, subfamily F, polypeptide 2

Cytochrome p450, family 2, subfamily F, polypeptide 2 catalyzes the NADPH-dependent oxidation of the terminal carbon of long and very long-chain fatty acids, the side chains of vitamin K (K ₁, K ₂ ) and vitamin E (tocopherols and tocotrienols), arachidonic acid (AA), and leukotriene B ₄ (LTB ₄). CYP4F2 localizes to the endoplasmic reticulum of cells. Although it is predominantly expressed in the liver and kidneys, there is some evidence that CYP4F2 is expressed in human enteric microsomes [Articles:17709372, 24870542]. In the liver and kidneys CYP4F2 catalyzes the synthesis of 20-hydroxyeicosatetraeonic acid (20-HETE) from AA. Hepatic CYP4F2 also regulates the bioavailability of vitamin K and vitamin E, catalyzes the inactivation of LTB ₄, and the bioactivation of the anti-malarial drug pafuramidine. Although initial studies of CYP4F2 were focused on its role as a regulator of LTB ₄ and 20-HETE levels, current investigations focus on how genetic variants of CYP4F2 affect warfarin drug dosing and safety.

Substrates of CYP4F2

Fatty Acids
Fatty acids (FA) can be degraded by α, β, and ω-oxidation of their carbon chains. The preferred pathway of fatty acid degradation is β-oxidation in the mitochondria and peroxisomes. Very long chain fatty acids (VLCFAs), which are fatty acids with more than 22 carbons in their chain, cannot be β-oxidized and must be chain-shortened before they can be oxidized by the mitochondria. CYP4F2 contributes to FA oxidation by catalyzing the ω-oxidation and chain shortening of VLCFAs [Articles:18182499, 18433732]. Under normal physiologic conditions, ω-hydroxylation contributes somewhere between 4-15% of FA metabolism, but there is evidence supporting an increasingly larger role for CYP4F2 in FA metabolism during periods of fasting, upon administration of lovastatin, and as a rescue pathway in disorders of peroxisomal β-oxidation [Articles:18433732, 17786636, 22484021].

Eicosanoids
AA is a precursor of the eicosanoids, which are signaling molecules that mediate the inflammation and immune response. Acute inflammation at the site of injury or infection protects the body from pathogens but prolonged inflammation damages healthy cells and tissue; thus inflammation must be tightly controlled. LTB ₄ is a pro-inflammatory eicosanoid that induces activation of polymorphonuclear leukocytes, monocytes, and fibroblasts, generation of superoxide, and the release of cytokines to attract neutrophils [Article:16926051]. ω -oxidation of LTB ₄ is catalyzed by multiple members of the CYP4F family, but in the liver CYP4F2 is the principle enzyme to ω -oxidize LTB ₄ to 20-OH LTB ₄ , a far less potent eicosanoid metabolite [Articles:18433732, 17341693, 9799565, 11368003].

CYP4F2 also catalyzes the ω-oxidation of AA, which converts it to the signaling molecule 20-hydroxyeicosatetraeonic acid (20-HETE). 20-HETE promotes vasoconstriction by contributing to the myogenic response and by inducing alterations smooth muscle calcium homeostasis, which sensitize the smooth muscle to constrictor stimuli such as angiotensin II, phenylephrine and endothelin. In the nephron, 20-HETE is present in the proximal tubules, the thick ascending loop of Henle (TALH), and the glomerulus and it promotes natriuresis by acting on various ion transporters [Articles:23584425, 16258232]. Because 20-HETE is both vasoconstrictive and natriuretic its overall effect on arterial blood pressure depends on where it is acting, but the mechanism regulating the localization of its expression is still unknown.

Studies in rats and mice have shown that decreased levels of renal 20-HETE are associated with salt-sensitive hypertension whereas increased levels of renal 20-HETE are associated with other types of hypertension (e.g. spontaneous or androgen induced hypertension) [Articles:12874093, 20930591]. Multiple studies have reported that urinary 20-HETE is positively associated with hypertension in humans. If urinary 20-HETE reflects vascular 20-HETE levels it would provide a reasonable explanation for the positive association between urinary 20-HETE and increased blood pressure [Articles:18235092, 24984178, 18391101] or impaired vascular function [Article:15262846]. Unfortunately, the relationship between urinary 20-HETE levels and CYP4F2 enzyme activity is equivocal. One study reported that a haplotype shown to increase CYP4F2 expression (which is presumed to increase renal 20-HETE formation) was associated with increased urinary 20-HETE excretion and increased risk for hypertension [Article:18235092]. A second study reported that a single nucleotide polymorphism (SNP) in CYP4F2, which has been shown to decrease 20-HETE formation in vitro [Article:17341693], was also associated with increased urinary 20-HETE and increased blood pressure [Article:18391101].

Blood pressure is a sexually dimorphic characteristic; on average men under the age of 60 have higher blood pressure than age-matched pre-menopausal women [Articles:7875754, 18259027]. A study in male Sprague-Dawley rats showed that administration of 5 α -dihydrotestosterone stimulated production of 20-HETE in the renal vasculature, which preceded a statistically significant rise in systolic blood pressure. The rise in systolic blood pressure was abrogated upon administration of a 20-HETE antagonist [Article:21321301]. Several studies have also reported sex-specific associations between certain genetic variants of CYP4F2 with blood pressure, vascular function and risk of cerebral infarction [Articles:18391101, 15262846, 18787519, 18971550].

Vitamin E
Vitamin E is the name given to eight fat-soluble tocopherols and tocotrienols. Tocopherols are the most investigated form of vitamin E. Vitamin E is best known as a free-radical scavenger that prevents cellular peroxidation of polyunsaturated fatty acids (PUFA). Vitamin E is especially important for protecting the cell membranes of neurons and patients with perturbations in vitamin E absorption are at an increased risk of peripheral neuropathy and ataxia [Article:21664268]. α-tocopherol is the most biologically active of the four isomers of tocopherol: α, β, γ, δ. Each isomer differs in both the placement, and the number of hydroxyl groups on their chromanol rings. Studies have shown that regardless of the isoform of vitamin E consumed, the α-tocopherol isoform is always the predominant isoform in plasma and tissue [Article:23505319]. Tocopherols, like LCFAs and VLCFAs, are metabolized by chain shortening [Articles:15753130, 11997390]. Parker RS et al. were the first to report that the γ and δ tocopherols are preferentially catabolized over α-tocopherol, which promotes the retention of α-tocopherol in plasma and tissues. CYP4F2 is the only known enzyme to ω-hydroxylate vitamin E (tocotrienols as well as tocopherols), thus making it a critical modulator of circulating plasma vitamin E levels [Articles:15753130, 18433732, 20861217].

Vitamin K
Vitamin K refers to a group of fat-soluble derivatives of naphthoquinones, which differ in the number of double bonds present in their hydrocarbon chains. Plants synthesize vitamin K1 (VK ₁), also known as phylloquinone. VK ₁ is highly concentrated in leaves where it acts as an electron acceptor in the light dependent reactions of photosynthesis. Menaquinones, also known as vitamin K ₂, are the main form of vitamin K in animals and the most common form is menaquinone 4 (MK-4), which can be synthesized from VK ₁, and obtained by eating dark green leafy vegetables. Animals also obtain menaquinones from eating fermented food, and animal products [Article:18841274]. Both types of vitamin K can act as co-factors for γ-glutamyl carboxylase (GGCX), which catalyzes the biochemical activation of proteins involved in blood clotting, and bone mineralization. CYP4F2 ω-hydroxylates and inactivates vitamin K, which makes CYP4F2 an important negative regulator of vitamin K levels [Articles:23132553, 19297519, 24138531].

Anti-Parasitic Drugs
Pafuramidine (DB289), is a pro-drug of the anti-parasitic drug furamidine (DB75). Two studies identified CYP4F2 as one of the enzymes responsible for catalyzing the first-pass biotransformation of pafuramidine to furamidine in human liver microsomes and human enteric microsomes [Articles:17709372, 16997912].

The CYP4F2 Gene
CYP4F2 is part of a cluster of CYP4F genes on chromosome 19p13. The genetic architecture of all CYP4F genes is highly similar and the genes are thought to have evolved by duplication. Human CYP4F2 spans 2.2 kB, has thirteen exons, twelve introns, and its open reading frame is encoded between exons two and thirteen [Article:10492403]. The amino acid sequences of CYP4F2 and CYP4F3 are reported to be between 81-93% similar [Articles:17786636, 18662666, 10492403]. Analyses of the upstream 5' regions of CYP4F2 show that there are putative RXRα and RARα response elements (RARE), sterol regulatory element binding protein elements (SREBPE), nuclear factor κ Β and Myb response elements [Articles:18235092, 10492403, 18662666].

Hirani and colleagues (2008) developed a targeted polyclonal antibody of CYP4F2 to quantify CYP4F2 protein levels in human liver and kidney cortex samples [Article:18662666]. With this antibody substantial inter-individual variability in CYP4F2 expression from liver and kidney samples was discovered. Microsomal protein levels of CYP4F2 ranged between 0-80.1 pmol/mg protein in liver and between 0-11.3 pmol/ mg protein in kidney cortex. Total hepatic microsomal immunoreactive CYP4F (CYP4F3b, CYP4F11, CYP4F12) protein was present in all patients, even those without detectable CYP4F2 protein. This evidence suggests that CYP4F2 may be regulated in a different manner than other CYP4F family members [Article:18662666].

Inducers and inhibitors of CYP4F2
The molecular mediators that regulate CYP4F2 expression have only been elucidated in in vitro systems. Studies in hepatoblastoma cell lines (HepG2) have shown that retinoic acid regulates CYP4F2 transcription through the RXRα and RARα nuclear receptors. A study using a luciferase reporter system in HepG2 cells that were transiently transfected with the upstream CYP4F2 regions -506/6 and -1726/6 revealed that co-transfection with human RXR α, and all-trans retinoic acid (ATRA), or 9-cis-retinoic acid (9cRA) stimulated reporter activity [Article:11162441]. In contrast, co-transfection of either 9cRA or ATRA and RAR α, or RXR α/RAR α heterodimers attenuated the observed increase in promoter activity. The same study also identified several putative retinoic response elements (RARE) near CYP4F2, but none were confirmed RAREs. Although both retinoic acids induced promoter construct activity, only 9cRA was capable of inducing protein translation of CYP4F2 [Article:1116244]. Saturated fatty acids, such as lauric acid and stearic acid also induced CYP4F2 expression in HepG2 cells [Article:10860554]. The promoter region of CYP4F2 contains multiple sterol regulatory element binding protein (SREBP) elements. SREBP-2 was found to mediate lovastatin-induced expression of CYP4F2 in primary human hepatocytes, and in SREBP-1a transfected HepG2 cells SREBP-1a was found to mediate lovastatin-induced expression of CYP4F2 [Article:17142457]. None of these findings have been confirmed in clinical studies, although a few case studies provide some evidence that co-administration of lovastatin and warfarin is associated with longer prothrombin time in patients [Article:14998226].

Peroxisomal proliferators, such as clofibrate, WY14,643, and PDFO, were shown to inhibit CYP4F2 gene expression [Articles:10860554, 17142457]. The anti-fungal drug ketoconazole and sesamin, a molecule found in sesame oil, also inhibit ω-hydroxylation of tocopherols in rat and human liver microsomes, as well as in HepG2 cells. Studies with recombinant CYP4F2 expressed in insect cells demonstrated that CYP4F2 is enzymatically inhibited by both ketoconazole and sesamin [Articles:15753130, 11997390, 11061988].

Genetic variants of CYP4F2
Initially investigated due to its role in eicosanoid metabolism, rs2108622 was later discovered to have a small, albeit significant, role in affecting warfarin dose in several populations, most notably in Han Chinese and several different White populations. The rs2108622 (NT_011295.11:g.7253233C>T, V433M) polymorphism was initially reported in a screen of CYP4F2 in an effort to discover SNPs associated with alterations in AA metabolism [Article:17341693]. The T allele at rs2108622 is also associated with increased blood pressure [Articles:24984178, 18391101] and decreased vitamin E metabolism [Articles:20861217, 21729881].

A study in Han Chinese reported that a seven SNP haplotype (Haplotype I) in the proximal regulatory region of CYP4F2 that included the A allele at rs3093105 (NC_000019.10:g.15897578A>C, W12G) was associated with increased urinary 20-HETE and increased risk of hypertension in case-control studies. Haplotype I was also transmitted more frequently to hypertensive offspring in family association studies [Article:18235092]. In vitro assays showed that Haplotype I was associated with increased basal, as well as LPS-induced expression of CYP4F2 when compared to Haplotype II, which included the C allele at rs3093105. Sequence analysis and functional studies showed that a second SNP in Haplotype II, rs3093098 (NC_000019.10:g.15897702A>G), eliminated a putative nuclear factor κB binding site, which provides a plausible explanation for the decrease in basal and LPS-induced expression associated with Haplotype II as compared to Haplotype I. A separate study in Japanese patients reported that when it is part of a haplotype with two other SNPS (rs1558139 A and rs2108622 C) the A allele at rs3093105 was protective against hypertension in men [Article:18971550].