Names | |
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Preferred IUPAC name (5Z,8Z,11Z,13E,15S)-15-Hydroxyicosa-5,8,11,13-tetraenoic acid | |
Other names 15-HETE, 15(S)-HETE, 15(S)-HETE | |
Identifiers | |
3D model (JSmol) | |
ChemSpider | |
ECHA InfoCard | 100.214.805 |
PubChem CID | |
UNII | |
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Properties | |
C20H32O3 | |
Molar mass | 320.473 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
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. [1] [2]
Some cell types (e.g. platelets) metabolize arachidonic acid to the stereoisomer of 15(S)-HpETE, 15(R)-HpETE. Both stereoisomers may also be formed as result of the metabolism of arachidonic acid by cellular microsomes or as a result of arachidonic acid auto-oxidation. Similar to 15(S)-HpETEs, 15(R)-HpETE may be rapidly reduced to 15(R)-HETE. These R,S stereoisomers differ only in having their hydroxy residue in opposite orientations. While the two R stereoisomers are sometimes referred to as 15-HpETE and 15-HETE, proper usage should identify them as R stereoisomers. 15(R)-HpETE and 15(R)-HETE lack some of the activity attributed to their S stereoisomers but can be further metabolized to bioactive products viz., the 15(R) class of lipoxins (also termed epi-lipoxins). [3]
15(S)-HETE, 15(S)-HpETE, and many of their derivative metabolites are thought to have physiologically important functions. They appear to act as hormone-like autocrine and paracrine signaling agents that are involved in regulating inflammatory and perhaps other responses. [1] [2] [4] Clinically, drugs that are stable analogs, and therefore mimic the anti-inflammatory actions of the lipoxins and drugs that block the production or actions of the pro-inflammatory eoxins may prove useful for treating acute and chronic inflammatory disorders. [5]
15(S)-HETE is unambiguously designated by a shortened version of its IUPAC name viz., 15(S)-hydroxy-5Z,8Z,11Z,13E-eicosatetraenoic acid. In this terminology S refers to the absolute configuration of the chirality of the hydroxy functional group at carbon position 15. Its 15(R) enantiomer is designated 15(R)-hydroxy-5Z,8Z,11Z,13E-eicosatetraenoic acid. Z and E give the cis–trans isomerism about each double bond at carbon positions 5, 8, 11, and 13 with Z indicating cis and E indicating trans isomerism. Both stereoisomers are produced from their corresponding S and R 15-HpETE stereoisomers, i.e. 15(S)-hydroperoxy-5Z,8Z,11Z,13E-eicosatetraenoic acid (15(S)-HpETE) and 15(R)-hydroperoxy-5Z,8Z,11Z,13E-eicosatetraenoic acid (15(R)-HpETE).
Human cells release arachidonic acid (i.e. 5Z,8Z,11Z,14Z-eicosatetraenoic acid) from its storage site in phospholipids by reactions that involve phospholipase C and/or lipase enzymes. This release is stimulated or enhanced by cell stimulation. The freed arachidonic acid is then converted to 15-hydroperoxy/hydroxy products by one or more of the following five pathways.
15-Lipoxygenase-1: Cells metabolize arachidonic acid with 15-lipoxygenase-1 (i.e., 15-LO-1, ALOX15) to form 15(S)-HpETE as a major product and 12(S)-hydroperoxy-5Z,8Z,10E,15Z-eicosatetraenoic acid (12(S)-HpETE) and 14(S),15(S)-trans-oxido-5Z,8Z,11Z-14,15-leukotriene A4 as minor products; 15(S)-HpETE and 12(S)-HpETE are rapidly converted to 15(S)-HETE and 12(S)-hydroxy-5Z,8Z,10E,15Z-eicosatetraenoic acid (12(S)-hydroxyeicosatetraenoic acid), (i.e. 12(S)-HETE), respectively, or further metabolized through other enzyme pathways; 14(S),15(S)-trans-oxido-5Z,8Z,11Z-14,15-leukotriene A4 is metabolized by 15-LO-1 to various isomers of 8,15(S)-dihydroxy-5S,8S,11Z,13S-eicosatetraenoic acids, e.g. 8,15(S)-LTB4's. [6] [7] [8] [9] [10]
15-Lipoxygenase-2: Cells also used 15-lipoxygenase 2 (i.e. 15-LOX-2 or ALOX15B) to make 15(S)-HpETE and 15(S)-HETE. However this enzyme has a preference for metabolizing linoleic acid rather than arachidonic acid. It therefore forms linoleic acid metabolites (e.g. 13-hydoxyperoxy/hydroxy-octadecadienoic and 9-hydroperoxy/hydroxyl-octadecadienoic acids) in greater amounts than 15(S)-HpETE and 15(S)-HETE. 15-LOX-2 also differs from 15-LOX-1 in that it does not make 12(S)-HpETE or the leukotriene A4 isomer cited above. [10]
Cyclooxygenase: Cells can use prostaglandin-endoperoxide synthase 1 (i.e. cyclooxygenenase-1 or COX-1) and prostaglandin-endoperoxide synthase 2 (COX-2) to metabolize arachidonic acid primarily to prostaglandins but also to small amounts of 11(R)-HETE and a racemic mixture of 15-HETEs composed of ~22% 15(R)-HETE and ~78% 15(S)-HETE. [11] When pretreated with aspirin, however, COX-1 is inactive while COX-2 attacks arachidonic acid to produce almost exclusively 15(R)-HETE along with its presumed precursor 15(R)-HpETE. [11] [12] [13]
Microsome metabolism: Human and rat microsomal cytochrome P450s, e.g. CYP2C19, metabolize arachidonic acid to a racemic mixture of 15-HETEs, i.e., 15(R,S)-HETEs, >90% of which is the 15(R) stereoisomer. [14] [15]
Autoxidation: The spontaneous and non-enzymatically induced autoxidation of arachidonic acid yields 15(R,S)-hydroperoxy-5Z,8Z,11Z,13E-eicosatetraenoic acids. This non-enzymatic reaction is promoted in cells undergoing oxidative stress. Cells forming this racemic mixture of 15-hydroperoxy products may convert then to 15(R,S)-HETEs and other products. However, the uncontrolled overproduction of the 15-hydroperoxy products may react with other elements to produce cell injury. [16] [17]
The newly formed products formed by the pathways cited in the previous section are bioactive but may also flow into down-stream pathways to form other metabolites with a different sets of bioactivity. The initially formed 15(S)-HpETE may be further metabolized by its parent cell or pass it to nearby cell by a process termed transcellular metabolism.
15(S)-HpETE may be:
15(S)-HETE may be:
15(R)-HpETE may be:
15(R)-HETE may be:
Most studies have analyzed the action of 15(S)-HETE but not that of its less stable precursor 15(S)-HpETE. Since this precursor is rapidly converted to 15(S)-HETE in cells, it is likely that the two metabolites share similar activities. In many studies, however, is not clear that these activities reflect their intrinsic action or reflect their conversion to the metabolites sited above.
15(S)-HpETE and 15(S)-HETE bind to and activate the G protein-coupled receptor, leukotriene B4 receptor 2, i.e. BLT2. [47] This receptor activation may mediate, at least in part, certain cell-stimulating activities of the two metabolites. BLT2 may be responsible in part or whole for mediating the growth-promoting and anti-apoptosis (i.e. anti-cell death) activities of 15(S)-HETE in cultured human breast cancer cells; [48] human cancer colon cells, [49] human hepatocellular HepG2 and SMMC7721 cancer cells; [50] mouse 3T3 cells (a fibroblast cell line); [51] rat PA adventitia fibroblasts; [52] baby hamster kidney cells; [53] and diverse types of vascular endothelial cells. [54] [55] [56] [57] These growth-stimulating effects could contribute to the progression of the cited cancer types in animal models or even humans [48] [49] and the excess fibrosis that causes the narrowing of pulmonary arteries in hypoxia-induced pulmonary hypertension [51] or narrowing of portal arteries in the portal hypertension accompanying liver cirrhosis. [58] 15(S)-HETE may also act through BLT2 to stimulate an immediate contractile response in rat pulmonary arteries [59] and its angiogenic effect on human umbilical [55] and dermal [54] vascular endothelial cells.
15(S)-HpETE and 15(S)-HETE also directly bind with and activate peroxisome proliferator-activated receptor gamma. [60] This activation may contribute to the ability of 15(S)-HETE to inhibit the growth of cultured human prostate cancer PC-3, LNCaP, and DU145 cell lines and non-malignant human prostate cells; [61] [62] lung adenocarcinoma A549 cells; [63] human colorectal cancer cells; [64] corneal epithelial cells; [65] and Jurkat T-cell leukemia cells. [66] The decline in the level of 15(S)-HpETE-forming enzymes and consequential fall in cellular 15-HETE production that occurs in human prostate cancer cells may be one mechanism by which this and perhaps other human cancer cells (e.g. those of the colon, rectum, and lung) avoid the apoptosis-inducing actions of 15(S)-HpETE and/or 15(S)-HETE and thereby proliferate and spread. [67] [68] In this scenario, 15(S)-HETE and one of its forming enzymes, particularly 15-LOX-2, appear to act as tumor suppressors.
Some of the inhibitory effects of 15(S)-HpETE and 15(S)-HETE, particularly when induced by high concentrations (e.g. >1-10 micromolar), may be due to a less specific mechanism: 15(S)-HpETE and to a lesser extent 15(S)-HETE induce the generation of reactive oxygen species. These species trigger cells to activate their death programs, i.e. apoptosis, and/or are openly toxic to the cells. [69] [70] [66] [71] [72] 15(S)-HpETE and 15(S)-HETE inhibit angiogenesis and the growth of cultured human chronic myelogenous leukemia K-562 cells by a mechanism that is associated with the production of reactive oxygen species. [55] [73] [74]
Several bifunctional electrophilic breakdown products of 15(S)-HpETE, e.g. 4-hydroxy-2(E)-nonenal, 4-hydroperoxy-2(E)-nonenal, 4-oxo-2(E)-nonenal, and cis-4,5-epoxy-2(E)-decanal, are mutagens in mammalian cells and thereby may contripute to the development and/or progression of human cancers. [38]
Similar to 15(S)-HpETE and 15(S)-HETE and with similar potency, 15(R)-HETE binds with and activates peroxisome proliferator-activated receptor gamma. [60] The precursor of 15(R)-HETE, 15(R)-HpETE may, similar to 15(S)-HpETE, break down to the mutagenic products 4-hydroxy-2(E)-nonenal, 4-hydroperoxy-2(E)-nonenal, 4-oxo-2(E)-nonenal, and cis-4,5-epoxy-2(E)-decanal and therefore be involved in cancer development and/or progression. [38]
In cultured human monocytes of the THP1 cell line, 15-oxo-ETE inactivates IKKβ (also known as IKK2) thereby blocking this cell's NF-κB-mediated pro-inflammatory responses (e.g. lipopolysaccharide-induced production of TNFα, interleukin 6, and IL1B) while concurrently activating anti-oxidant responses upregulated through the anti-oxidant response element (ARE) by forcing cytosolic KEAP1 to release NFE2L2 which then moves to the nucleus, binds ARE, and induces production of, e.g. hemoxygenase-1, NADPH-quinone oxidoreductase, and possibly glutamate-cysteine ligase modifier. [75] By these actions, 15-oxo-ETE may dampen inflammatory and/or oxidative stress responses. In a cell-free system, 15-oxo-ETE is a moderately potent (IC50=1 μM) inhibitor of 12-lipoxygenase but not other human lipoxygenases. [76] This effect could also have anti-inflammatory and anti-oxidative effects by blocking the formation of 12-HETE and hepoxilins. 15-Oxo-ETE is an example of an α,β unsaturated ketone electrophile. These ketones are highly reactive with nucleophiles, adducting to, for example, the cysteines in transcription and transcription-related regulatory factors and enzymes to form their alkylated and thereby often inactivated products. [76] [77] It is presumed that the preceding activities of 15-oxo-ETE reflect its adduction to the indicated elements. [75] 15-Oxo-ETE, at 2-10 μM, also inhibits the proliferation of cultured human umbilical vein endothelial cells and LoVo human colorectal cancer cells [78] [79] and at the extremely high concentration of 100 μM inhibits the proliferation of cultured MBA-MD-231 and MCF7 breast cancer cells as well as SKOV3 ovarian cancer cells. [80] They may use a similar "protein-adduction" mechanism; if so the target protein(s) for these effects have not been defined or even suggested. This 15-oxo-ETE action may prove to inhibit the remodeling of blood vessels and reduce the growth of the cited cell types and cancers. At sub-micromolar concentrations, 15-oxo-ETE has weak chemotaxis activity for human monocytes and could serve to recruit this white blood cell into inflammatory responses. [81]
5-Oxo-15(S)-hydroxy-ETE is properly a member of the 5-HETE family of agonists which binds to the oxoeicosanoid receptor 1, a G protein-coupled receptor, to activate its various target cells. As such, it is a potent stimulator of leukocytes, particularly eosinophils, as well as other OXE1-bearing cells including MDA-MB-231, MCF7, and SKOV3 cancer cells (see 5-Hydroxyicosatetraenoic acid and 5-Oxo-eicosatetraenoic acid). [82] It also binds with and activates PPARγ and thereby can stimulate or inhibit cells independently of OXE1. [80]
LXA4, LXB4, AT-LXA4, and AT-LXB4 are specialized proresolving mediators, i.e. they potently inhibit the progression and contribute to the resolution of diverse inflammatory and allergic reactions.
Eoxin A4, eoxin C4, eoxin D4, and eoxin E4 are analogs of leukotriene A4, C4, leukotriene D4, and E4. Formation of the leukotrienes is initiated by 5-lipoxygenase metabolism of arachidonic acid to form a 5,6-epoxide viz, leukotriene A4; the latter metabolite is then converted to C4, D4, and E4 in succession. Formation of the eoxins is initiated by a 15-lipoxyenase-mediated metabolism of arachiconic acid to a 14,15-epoxide, eoxin A4 followed by its serial conversion to epoxins C4, D4, and E4 using the same pathways and enzymes that metabolize leukotriene A4 to its down-stream products. Preliminary studies have found that the eoxins have pro-inflammatory actions, suggest that they are involved in severe asthma, aspirin-induced asthma attacks, and perhaps other allergic reactions. The production of eoxins by Reed-Sternburg cells has also led to suggestion that they are involve in the lymphoma of Hodgkins disease. [27] Drugs blocking the 15-lipoxygenases may be useful for inhibiting inflammation by reducing the production of the eoxins. [83]
Arachidonic acid 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 ancient Greek neologism arachis (peanut), but peanut oil does not contain any arachidonic acid.
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. Eicosanoids may also act as endocrine agents to control the function of distant cells.
A lipoxin (LX or Lx), an acronym for lipoxygenase interaction product, is a bioactive autacoid metabolite of arachidonic acid made by various cell types. They are categorized as nonclassic eicosanoids and members of the specialized pro-resolving mediators (SPMs) family of polyunsaturated fatty acid (PUFA) metabolites. Like other SPMs, LXs form during, and then act to resolve, inflammatory responses. Initially, two lipoxins were identified, lipoxin A4 (LXA4) and LXB4, but more recent studies have identified epimers of these two LXs: the epi-lipoxins, 15-epi-LXA4 and 15-epi-LXB4 respectively.
Lipoxygenases (LOX) are a family of (non-heme) iron-containing enzymes, more specifically oxidative enzymes, most of which catalyze the dioxygenation of polyunsaturated fatty acids in lipids containing a cis,cis-1,4-pentadiene into cell signaling agents that serve diverse roles as autocrine signals that regulate the function of their parent cells, paracrine signals that regulate the function of nearby cells, and endocrine signals that regulate the function of distant cells.
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.
Arachidonate 5-lipoxygenase, also known as ALOX5, 5-lipoxygenase, 5-LOX, or 5-LO, is a non-heme iron-containing enzyme that in humans is encoded by the ALOX5 gene. Arachidonate 5-lipoxygenase is a member of the lipoxygenase family of enzymes. It transforms essential fatty acids (EFA) substrates into leukotrienes as well as a wide range of other biologically active products. ALOX5 is a current target for pharmaceutical intervention in a number of diseases.
Mead acid is an omega-9 fatty acid, first characterized by James F. Mead. As with some other omega-9 polyunsaturated fatty acids, animals can make Mead acid de novo. Its elevated presence in the blood is an indication of essential fatty acid deficiency. Mead acid is found in large quantities in cartilage.
ALOX15 is, like other lipoxygenases, a seminal enzyme in the metabolism of polyunsaturated fatty acids to a wide range of physiologically and pathologically important products. ▼ Gene Function
ALOX12, also known as arachidonate 12-lipoxygenase, 12-lipoxygenase, 12S-Lipoxygenase, 12-LOX, and 12S-LOX is a lipoxygenase-type enzyme that in humans is encoded by the ALOX12 gene which is located along with other lipoyxgenases on chromosome 17p13.3. ALOX12 is 75 kilodalton protein composed of 663 amino acids.
G-protein coupled receptor 31 also known as 12-(S)-HETE receptor is a protein that in humans is encoded by the GPR31 gene. The human gene is located on chromosome 6q27 and encodes a G-protein coupled receptor protein composed of 319 amino acids.
Oxoeicosanoid receptor 1 (OXER1) also known as G-protein coupled receptor 170 (GPR170) is a protein that in humans is encoded by the OXER1 gene located on human chromosome 2p21; it is the principal receptor for the 5-Hydroxyicosatetraenoic acid family of carboxy fatty acid metabolites derived from arachidonic acid. The receptor has also been termed hGPCR48, HGPCR48, and R527 but OXER1 is now its preferred designation. OXER1 is a G protein-coupled receptor (GPCR) that is structurally related to the hydroxy-carboxylic acid (HCA) family of G protein-coupled receptors whose three members are HCA1 (GPR81), HCA2, and HCA3 ; OXER1 has 30.3%, 30.7%, and 30.7% amino acid sequence identity with these GPCRs, respectively. It is also related to the recently defined receptor, GPR31, for the hydroxyl-carboxy fatty acid 12-HETE.
5-Hydroxyeicosatetraenoic acid (5-HETE, 5(S)-HETE, or 5S-HETE) is an eicosanoid, i.e. a metabolite of arachidonic acid. It is produced by diverse cell types in humans and other animal species. These cells may then metabolize the formed 5(S)-HETE to 5-oxo-eicosatetraenoic acid (5-oxo-ETE), 5(S),15(S)-dihydroxyeicosatetraenoic acid (5(S),15(S)-diHETE), or 5-oxo-15-hydroxyeicosatetraenoic acid (5-oxo-15(S)-HETE).
Epoxygenases are a set of membrane-bound, heme-containing cytochrome P450 enzymes that metabolize polyunsaturated fatty acids to epoxide products that have a range of biological activities. The most thoroughly studied substrate of the CYP epoxylgenases is arachidonic acid. This polyunsaturated fatty acid is metabolized by cyclooxygenases to various prostaglandin, thromboxane, and prostacyclin metabolites in what has been termed the first pathway of eicosanoid production; it is also metabolized by various lipoxygenases to hydroxyeicosatetraenoic acids and leukotrienes in what has been termed the second pathway of eicosanoid production. The metabolism of arachidonic acid to epoxyeicosatrienoic acids by the CYP epoxygenases has been termed the third pathway of eicosanoid metabolism. Like the first two pathways of eicosanoid production, this third pathway acts as a signaling pathway wherein a set of enzymes metabolize arachidonic acid to a set of products that act as secondary signals to work in activating their parent or nearby cells and thereby orchestrate functional responses. However, none of these three pathways is limited to metabolizing arachidonic acid to eicosanoids. Rather, they also metabolize other polyunsaturated fatty acids to products that are structurally analogous to the eicosanoids but often have different bioactivity profiles. This is particularly true for the CYP epoxygenases which in general act on a broader range of polyunsaturated fatty acids to form a broader range of metabolites than the first and second pathways of eicosanoid production. Furthermore, the latter pathways form metabolites many of which act on cells by binding with and thereby activating specific and well-characterized receptor proteins; no such receptors have been fully characterized for the epoxide metabolites. Finally, there are relatively few metabolite-forming lipoxygenases and cyclooxygenases in the first and second pathways and these oxygenase enzymes share similarity between humans and other mammalian animal models. The third pathway consists of a large number of metabolite-forming CYP epoxygenases and the human epoxygenases have important differences from those of animal models. Partly because of these differences, it has been difficult to define clear roles for the epoxygenase-epoxide pathways in human physiology and pathology.
12-Hydroxyeicosatetraenoic acid (12-HETE) is a derivative of the 20 carbon polyunsaturated fatty acid, arachidonic acid, containing a hydroxyl residue at carbon 12 and a 5Z,8Z,10E,14Z Cis–trans isomerism configuration (Z=cis, E=trans) in its four double bonds. It was first found as a product of arachidonic acid metabolism made by human and bovine platelets through their 12S-lipoxygenase (i.e. ALOX12) enzyme(s). However, the term 12-HETE is ambiguous in that it has been used to indicate not only the initially detected "S" stereoisomer, 12S-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12(S)-HETE or 12S-HETE), made by platelets, but also the later detected "R" stereoisomer, 12(R)-hydroxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (also termed 12(R)-HETE or 12R-HETE) made by other tissues through their 12R-lipoxygenase enzyme, ALOX12B. The two isomers, either directly or after being further metabolized, have been suggested to be involved in a variety of human physiological and pathological reactions. Unlike hormones which are secreted by cells, travel in the circulation to alter the behavior of distant cells, and thereby act as Endocrine signalling agents, these arachidonic acid metabolites act locally as Autocrine signalling and/or Paracrine signaling agents to regulate the behavior of their cells of origin or of nearby cells, respectively. In these roles, they may amplify or dampen, expand or contract cellular and tissue responses to disturbances.
Eoxins are proposed to be a family of proinflammatory eicosanoids. They are produced by human eosinophils, mast cells, the L1236 Reed–Sternberg cell line derived from Hodgkin's lymphoma, and certain other tissues. These cells produce the eoxins by initially metabolizing arachidonic acid, an omega-6 (ω-6) fatty acid, via any enzyme possessing 15-lipoxygenase activity. The product of this initial metabolic step, 15(S)-hydroperoxyeicosatetraenoic acid, is then converted to a series of eoxins by the same enzymes that metabolize the 5-lipoxygenase product of arachidonic acid metabolism, i.e. 5-Hydroperoxy-eicosatetraenoic acid to a series of leukotrienes. That is, the eoxins are 14,15-disubstituted analogs of the 5,6-disubstituted leukotrienes.
Eoxin E4, also known as 14,15-leukotriene E4, is an eoxin. Cells make eoxins by metabolizing arachidonic acid with a 15-lipoxygenase enzyme to form 15(S)-hydroperoxyeicosapentaenoic acid (i.e. 15(S)-HpETE). This product is then converted serially to eoxin A4 (i.e. EXA4), EXC4, EXD4, and EXE4 by LTC4 synthase, an unidentified gamma-glutamyltransferase, and an unidentified dipeptidase, respectively, in a pathway which appears similar if not identical to the pathway which forms leukotreines, i.e. LTA4, LTC4, LTD4, and LTE4. This pathway is schematically shown as follows:
12-Hydroxyheptadecatrienoic acid (also termed 12-HHT, 12(S)-hydroxyheptadeca-5Z,8E,10E-trienoic acid, or 12(S)-HHTrE) is a 17 carbon metabolite of the 20 carbon polyunsaturated fatty acid, arachidonic acid. It was discovered and structurally defined in 1973 by P. Wlodawer, Bengt I. Samuelsson, and M. Hamberg, as a product of arachidonic acid metabolism made by microsomes (i.e. endoplasmic reticulum) isolated from sheep seminal vesicle glands and by intact human platelets. 12-HHT is less ambiguously termed 12-(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid to indicate the S stereoisomerism of its 12-hydroxyl residue and the Z, E, and E cis-trans isomerism of its three double bonds. The metabolite was for many years thought to be merely a biologically inactive byproduct of prostaglandin synthesis. More recent studies, however, have attached potentially important activity to it.
5-Oxo-eicosatetraenoic acid is a nonclassic eicosanoid metabolite of arachidonic acid and the most potent naturally occurring member of the 5-HETE family of cell signaling agents. Like other cell signaling agents, 5-oxo-ETE is made by a cell and then feeds back to stimulate its parent cell and/or exits this cell to stimulate nearby cells. 5-Oxo-ETE can stimulate various cell types particularly human leukocytes but possesses its highest potency and power in stimulating the human eosinophil type of leukocyte. It is therefore suggested to be formed during and to be an important contributor to the formation and progression of eosinophil-based allergic reactions; it is also suggested that 5-oxo-ETE contributes to the development of inflammation, cancer cell growth, and other pathological and physiological events.
5-Hydroxyeicosanoid dehydrogenase (5-HEDH) or more formally, nicotinamide adenine dinucleotide phosphate (NADP+)-dependent dehydrogenase, is an enzyme that metabolizes an eicosanoid product of arachidonate 5-lipoxygenase (5-LOX), 5(S)-hydroxy-6S,8Z,11Z,14Z-eicosatetraenoic acid (i.e. 5-(S)-HETE; see 5-HETE) to its 5-keto analog, 5-oxo-eicosatetraenoic acid (i.e. 5-oxo-6S,8Z,11Z,14Z-eicosatetraenoic acid or 5-oxo-ETE). It also acts in the reverse direction, metabolizing 5-oxo-ETE to 5(S)-HETE. Since 5-oxo-ETE is 30–100-fold more potent than 5(S)-HETE in stimulating various cell types, 5-HEDH is regarded as a regulator and promoter of 5(S)HETE's and thereby 5-LOX's influences on cell function. Although 5-HEDH has been evaluated in a wide range of intact cells and in crude microsome preparations, it has not yet been evaluated for its structure, for its gene, of in pure form; furthermore, most studies on it have been conducted in human tissues.
Epoxyeicosatetraenoic acids 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.
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