17,18-EEQ | |
Identifiers | |
---|---|
| |
3D model (JSmol) |
|
ChEBI |
|
PubChem CID |
|
| |
| |
Properties | |
C20H30O3 | |
Molar mass | 318.457 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
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 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. [1] [2]
EPA is a straight-chain, 20 carbon omega-3 fatty acid containing cis double bonds between carbons 5 and 6, 8 and 9, 11 and 12, 14 and 15, and 17 and 18; each of these double bonds is designated with the notation Z to indicate its cis configuration in the IUPAC Chemical nomenclature used here. EPA is therefore 5Z,8Z,11Z,14Z,17Z-eicosapentaenoic acid. Certain cytochrome P450 epoxygenases metabolize EPA by converting one of these double bounds to an epoxide thereby forming one of 5 possible eicosatetraenoic acid epoxide regioisomers. These regioisomers are: 5,6-EEQ (i.e. 5,6-epoxy-8Z,11Z,14Z,17Z-eicosatetraenoic acid), 8,9-EEQ (i.e. 8,9-epoxy-5Z,11Z,14Z,17Z-eicosatetraenoic acid), 11,12-EEQ (i.e. 11,12-epoxy-5Z,8Z,14Z,17Z-eicosatetraenoic acid), 14,15-EEQ (i.e. 14,15-epoxy-5Z,8Z,11Z,17Z-eicosatetraenoic acid), and 17,18-EEQ (i.e. 17,18-epoxy-5Z,8Z,11Z,14Z-eicosatetraenoic acid). The epoxydases typically make both R/S enantiomers of each epoxide. For example, they metabolize EPA at its 17,18 double bond to a mixture of 17R,18S-EEQ and 17S,18R-EEQ. [3] [4] The EEQ products therefore consist of as many as ten isomers.
Cellular cytochrome P450 epoxygenases metabolize various polyunsaturated fatty acids to epoxide-containing products. They metabolize the omega-6 fatty acids arachidonic acid, which possess four double bonds, to 8 different epoxide isomers which are termed epoxyeicosatrienoic acids or EETs and linoleic acid, which possess two double bonds, to 4 different epoxide isomers, i.e. two different 9,10-epoxide isomers termed coronaric acids or leukotoxins and two different 12,13-epoxides isomers termed vernolic acids or isoleukotoxins. They metabolize the omega-3 fatty acid, docosahexaenoic acid, which possesses six double bonds, to twelve different epoxydocosapentaenoic acid (EDPs) isomers. In general, the same epoxygenases that accomplish these metabolic conversions also metabolize the omega-6 fatty acid, EPA, to 10 epoxide isomers, the EEQs. These epoxygenases fall into several subfamilies including the cytochrome P4501A (i.e.CYP1A), CYP2B, CYP2C, CYP2E, and CYP2J subfamilies, and within the CYP3A subfamily, CYP3A4. In humans, CYP1A1, CYP1A2, CYP2C8, CYP2C9, CYP2C18, CYP2C19, CYP2E1, CYP2J2, CYP3A4, and CYP2S1 metabolize EPA to EEQs, in most cases forming principally 17,18-EEQ with smaller amounts of 5,6-EEQ, 8,9-EEQ, 11,12-EEQ, and 14,15-EEQ isomers. [5] [6] [7] However, CYP2C11, CYP2C18, and CYP2S1 also form 14,15-EEQ isomers while CYP2C19 also forms 11,12-EEQ isomers. [7] [8] The isomers formed by these CYPs vary greatly with, for example, the 17,18-EEQs made by CYP1A2 consisting of 17R,18S-EEQ but no detectable 17S,18R-EEQ and those made by CYP2D6 consisting principally of 17R,18S-EEQ with far smaller amounts of 17S,18R-EEQ. [9] In addition to the cited CYP's, CYP4A11, CYP4F8, CYP4F12, CYP1A1, CYP1A2, and CYP2E1, which are classified as CYP monooxygenase rather than CYP epoxygenases because they metabolize arachidonic acid to monohydroxy eicosatetraenoic acid products (see 20-Hydroxyeicosatetraenoic acid), i.e. 19-hydroxyeicosatetraenoic acid and/or 20-hydroxyeicosatetranoic acid, take on epoxygenase activity in converting EPA primarily to 17,18-EEQ isomers (see Epoxyeicosatrienoic acid). [7] 5,6-EEQ isomers are generally either not formed or formed in undetectable amounts while 8,9-EEQ isomers are formed in relatively small amounts by the cited CYPs. [5] The EET-forming CYP epoxygenases often metabolize EPA to EEQs (as well as DHA to EDPs) at rates that exceed their rates in metabolizing arachidonic acid to EETs; that is, EPA (and DHA) appear to be preferred over arachidonic acid as substrates for many CYP epoxygenases. [6]
The EEQ-forming cytochromes are widely distributed in the tissues of humans and other mammals, including blood vessel endothelium, blood vessel atheroma plaques, heart muscle, kidneys, pancreas, intestine, lung, brain, monocytes, and macrophages. [1] [6] [10] [11] These tissues are known to metabolize arachidonic acid to EETs; it has been shown or is presumed that they also metabolize EPA to EEQs. Note, however, that the CYP epoxygenases, similar to essentially all CYP450 enzymes, are involved in the metabolism of xenobiotics as well as endogenously-formed compounds; since many of these same compounds also induce increases in the levels of the epoxygenases, CYP oxygenase levels and consequently EEQ levels in humans vary widely and are highly dependent on recent consumption history; numerous other factors, including individual genetic differences, also contribute to the variability in CYP450 epoxygenase expression. [12]
In cells, EEQs are rapidly metabolized by the same enzyme that similarly metabolizes other epoxy fatty acids including the EETs viz., cytosolic soluble epoxide hydrolase [EC 3.2.2.10.] (also termed sEH or the EPHX2), to form their corresponding vicinal diol dihydroxyeicosatetraenoic acids (diHETEs). The omega-3 fatty acid epoxides, EEQs and EPAs, appear to be preferred over EETs as substates for sEH. [6] sEH converts 17,18-EEQ isomers to 17,18-dihydroxy-eicosatrienoic acid isomers (17,18-diHETEs), 14,15-EEQ isomers to 14,15-diHETE isomers, 11,12-EEQ isomers to 11,12-diHETE isomers, 8,9-EEQ isomers to 8,9-diHETE isomers, and 5,6-EEQ isomers to 5,6-diHETE isomers. [13] The product diHETEs, like their epoxy precursors, are enantiomer mixtures; for instance, sEH converts 17,18-EEQ to a mixture of 17(R),18(R)-diHETE and 17(S),18(S)-diHETE. [4] Since the diHETE products are as a rule generally far less active than their epoxide precursors, the sEH pathway of EET metabolism is regarded as a critical EEQ-inactivating pathway. [13] [14] [15]
Membrane-bound microsomal epoxide hydrolase (mEH or epoxide hydrolase 2 [EC 3.2.2.9.]) can metabolize EEQs to their dihydroxy products but is regarded as not contributing significantly to EEQ inactivation in vivo except possibly in rare tissues where the sEH level is exceptionally low while the mEH level is high. [2]
In addition to the sEH pathway, EETs may be acylated into phospholipids in an acylation-like reaction. This pathway may serve to limit the action of EETs or store them for future release. [4] EETs are also inactivated by being further metabolized through three other pathways: beta oxidation, omega oxidation, and elongation by enzymes involved in fatty acid synthesis. [2] [16]
EEQs, similar to EDPs, have not be studied nearly as well as the epoxyeicosatrienoic acids (EETs). In comparison to the many activities attributed to the EETs in animal model studies, a limited set of studies indicate that EEQs (and EPAs) mimic EETs in their abilities to dilate arterioles, reduce hypertension, inhibit inflammation (the anti-inflammatory actions of EEQ are less potent than those of the EETs) and thereby reduce occlusion of arteries to protect the heart and prevent strokes (see Epoxyeicosatrienoic acid § Clinical significance sections on a) Regulation of blood pressure, b) Heart disease, c) Strokes and seizures, and d) Inflammation); they also mimic EETs in possessing analgesia properties in relieving certain types of pain. [6] Often, the EEQs (and EPAs) exhibit greater potency and/or effectiveness than EET in these actions. [17] [6] [18] In human studies potentially relevant to one or more of these activities, consumption of long chain omega-3 fatty acid (i.e. EPA- and DHA-rich) diet produced significant reductions in systolic blood pressure and increased peripheral arteriole blood flow and reactivity in patients at high to intermediate risk for cardiovascular events; an EPA/DHA-rich diet also reduced the risk while high serum levels of DHA and EPA were associated with a low risk of neovascular age-related macular degeneration. [19] [20] Since such diets lead to large increases in the serum and urine levels of EPAs, EEQs, and the dihydroxy metabolites of these epoxides but relatively little or no increases in EETs or lipoxygenase/cyclooxygenase-producing metabolites of arachidonic acid, DHA, and/or EEQs, it is suggested that the diet-induced increases in EPAs and/or EEQs are responsible for this beneficial effects. [6] [21] [22] In direct contrast to the EETs which have stimulating effects in the following activities (see Epoxyeicosatrienoic acid § Cancer), EEQs (and EPAs) inhibit new blood vessel formation (i.e. angiogenesis), human tumor cell growth, and human tumor metastasis in animal models implanted with certain types of human cancer cells. [6] The possible beneficial effects of omega-3 fatty acid-rich diets in pathological states involving inflammation, hypertension, blood clotting, heart attacks and other cardiac diseases, strokes, brain seizures, pain perception, acute kidney injury, and cancer are suggested to result, at least in part, from the conversion of dietary EPA and DHA to EEQs and EPAs, respectively, and the cited subsequent actions of these metabolites. [7] [23] [24] [2] [25] [17]
Arachidonic acid is a polyunsaturated omega−6 fatty acid 20:4(ω−6), or 20:4(5,8,11,14). If its precursors or diet contains linoleic acid it is formed by biosynthesis and can be deposited in animal fats. It is a precursor in the formation of leukotrienes, prostaglandins, and thromboxanes.
Eicosanoids are signaling molecules made by the enzymatic or non-enzymatic oxidation of arachidonic acid or other polyunsaturated fatty acids (PUFAs) that are, similar to arachidonic acid, around 20 carbon units in length. Eicosanoids are a sub-category of oxylipins, i.e. oxidized fatty acids of diverse carbon units in length, and are distinguished from other oxylipins by their overwhelming importance as cell signaling molecules. Eicosanoids function in diverse physiological systems and pathological processes such as: mounting or inhibiting inflammation, allergy, fever and other immune responses; regulating the abortion of pregnancy and normal childbirth; contributing to the perception of pain; regulating cell growth; controlling blood pressure; and modulating the regional flow of blood to tissues. In performing these roles, eicosanoids most often act as autocrine signaling agents to impact their cells of origin or as paracrine signaling agents to impact cells in the proximity of their cells of origin. Some eicosanoids, such as prostaglandins, may also have endocrine roles as hormones to influence the function of distant cells.
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.
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. They are nonclassic eicosanoids.
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 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.
Hepoxilins (Hx) are a set of epoxyalcohol metabolites of polyunsaturated fatty acids (PUFA), i.e. they possess both an epoxide and an alcohol residue. HxA3, HxB3, and their non-enzymatically formed isomers are nonclassic eicosanoid derived from acid the (PUFA), arachidonic acid. A second group of less well studied hepoxilins, HxA4, HxB4, and their non-enzymatically formed isomers are nonclassical eicosanoids derived from the PUFA, eicosapentaenoic acid. Recently, 14,15-HxA3 and 14,15-HxB3 have been defined as arachidonic acid derivatives that are produced by a different metabolic pathway than HxA3, HxB3, HxA4, or HxB4 and differ from the aforementioned hepoxilins in the positions of their hydroxyl and epoxide residues. Finally, hepoxilin-like products of two other PUFAs, docosahexaenoic acid and linoleic acid, have been described. All of these epoxyalcohol metabolites are at least somewhat unstable and are readily enzymatically or non-enzymatically to their corresponding trihydroxy counterparts, the trioxilins (TrX). HxA3 and HxB3, in particular, are being rapidly metabolized to TrXA3, TrXB3, and TrXC3. Hepoxilins have various biological activities in animal models and/or cultured mammalian tissues and cells. The TrX metabolites of HxA3 and HxB3 have less or no activity in most of the systems studied but in some systems retain the activity of their precursor hepoxilins. Based on these studies, it has been proposed that the hepoxilins and trioxilins function in human physiology and pathology by, for example, promoting inflammation responses and dilating arteries to regulate regional blood flow and blood pressure.
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 2S1 is a protein that in humans is encoded by the CYP2S1 gene. The gene is located in chromosome 19q13.2 within a cluster including other CYP2 family members such as CYP2A6, CYP2A13, CYP2B6, and CYP2F1.
Cytochrome P450 4F8 is a protein that in humans is encoded by the CYP4F8 gene.
Cytochrome P450 4F12 is a protein that in humans is encoded by the CYP4F12 gene.
Epoxygenases are a set of membrane-bound, heme-containing cytochrome P450 enzymes that metabolize polyunsaturated fatty acids (PUFAs) to epoxide products that have a range of biological activities.
15-Hydroxyeicosatetraenoic acid (also termed 15-HETE, 15(S)-HETE, and 15S-HETE) is an eicosanoid, i.e. a metabolite of arachidonic acid. Various cell types metabolize arachidonic acid to 15(S)-hydroperoxyeicosatetraenoic acid (15(S)-HpETE). This initial hydroperoxide product is extremely short-lived in cells: if not otherwise metabolized, it is rapidly reduced to 15(S)-HETE. Both of these metabolites, depending on the cell type which forms them, can be further metabolized to 15-oxo-eicosatetraenoic acid (15-oxo-ETE), 5(S),15(S)-dihydroxy-eicosatetraenoic acid (5(S),15(S)-diHETE), 5-oxo-15(S)-hydroxyeicosatetraenoic acid (5-oxo-15(S)-HETE), a subset of specialized pro-resolving mediators viz., the lipoxins, a class of pro-inflammatory mediators, the eoxins, and other products that have less well-defined activities and functions. Thus, 15(S)-HETE and 15(S)-HpETE, in addition to having intrinsic biological activities, are key precursors to numerous biologically active derivatives.
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.
Cytochrome P450 omega hydroxylases, also termed cytochrome P450 ω-hydroxylases, CYP450 omega hydroxylases, CYP450 ω-hydroxylases, CYP omega hydroxylase, CYP ω-hydroxylases, fatty acid omega hydroxylases, cytochrome P450 monooxygenases, and fatty acid monooxygenases, are a set of cytochrome P450-containing enzymes that catalyze the addition of a hydroxyl residue to a fatty acid substrate. The CYP omega hydroxylases are often referred to as monoxygenases; however, the monooxygenases are CYP450 enzymes that add a hydroxyl group to a wide range of xenobiotic and naturally occurring endobiotic substrates, most of which are not fatty acids. The CYP450 omega hydroxylases are accordingly better viewed as a subset of monooxygenases that have the ability to hydroxylate fatty acids. While once regarded as functioning mainly in the catabolism of dietary fatty acids, the omega oxygenases are now considered critical in the production or break-down of fatty acid-derived mediators which are made by cells and act within their cells of origin as autocrine signaling agents or on nearby cells as paracrine signaling agents to regulate various functions such as blood pressure control and inflammation.
Jorge H. Capdevila is an American biochemist and professor emeritus of medicine at Vanderbilt University Medical School. He was named fellow of the American Heart Association in 2002 and received the 2004 American Heart Association's "Novartis Excellence Award for Hypertension Research" for his contributions to our understanding of the molecular basis of hypertension. Capdevila's identification of roles for Cytochrome P450 (P450) in the metabolism of arachidonic acid (AA) and of the physiological and pathophysiological importance of these enzymes and their products were recognized in a special section honoring him at the 14th International Winter Eicosanoid Conference (2012). Capdevila received an "Outstanding Achievement Award" from the Eicosanoid Research Foundation at their 15th International Bioactive Lipid Conference (2017),.