|Symbols||; 12-LOX; 15-LOX-1; 15LOX-1|
|External IDs||ChEMBL: GeneCards:|
|RNA expression pattern|
Arachidonate 15-lipoxygenase is an enzyme (molecular weight of 75 kDa) that in humans is encoded by the ALOX15 gene. ALOX15 is also known as 15-lipoxygenase-1 (15-LO-1 or 15-LOX-1) and is distinguished from its related oxygenase, ALOX15B or 15-lipoxygenase-2.
15-lipoxygenase is a lipoxygenase-type enzyme that metabolizes arachidonic acid primarily to a 15-hydroperoxy product. The enzyme was initially named arachidonate 15-lipoxygenase but subsequent studies uncovered a second enzyme with 15-lipoxygenase-like activity; consequently, the ALOX15 product is now referred to as arachidonate-15-lipoxygenase-1, 15-lipoxygenase-1, 15-LOX-1, 12/15-lipoxygenase, arachidonate 12-lipoxygenase, leukocyte-type, or arachidonate omega-6 lipoxygenase while the second discovered 15-lipoxygenase, a product of the ALOX15B gene, is termed arachidonate 15-lipoxygenase 2, 15-lipoxygenase-2, 15-LOX-2, arachidonate 15-lipoxygenase type II, arachidonate 15-lipoxygenase, second type, or arachidonate 15-lipoxygenase, platelet type. Human 15-LOX-1 and 15-LOX-2 genes are both located on chromosome 17 but their encoded lipoxygenases have an amino acid sequence identity of only ~38%, differ in the polyunsaturated fatty acids that they prefer as substrates, and exhibit somewhat different product profiles when acting on the same substrates.
Human tissue distribution
15-LOX-1 protein is highly expressed in circulating blood eosinophils, bronchial airway epithelial cells, mammary epithelial cells, the Reed-Sternberg cells of Hodgkin's lymphoma, cornea epithelial cells, reticulocytes, and dendritic cells; it is less strongly expressed in alveolar macrophages, tissue mast cells, tissue fibroblasts, circulating blood neutrophils, vascular endothelial cells, joint Synovial membrane cells, seminal fluid, prostate epithelium cells, and mammary ductal epithelial cells.
Human 15-LOX-1 attaches molecular oxygen (O
2) to the 15th or 12th carbon of arachidonic acid and then adds a hydrogen atom to the attached O
2 to form 15(S)-hydroperoxy-5Z,8Z,11Z,13E-eicosatetraenoic acid (15(S)-HpETE) and 12(S)-hydroperoxy-5Z,8Z,10E,15S-eicosatetraenoic acid (12(S)-HpETE), respectively, in a 15(S)-HpETE to 12(S)-HpETE product ratio of ~4-9 to 1. Both products may be rapidly reduced by ubiquitous cellular enzymes with peroxide-reducing activity to form their corresponding hydroxy analogs, 15(S)-HETE (see 15-hydroxyicosatetraenoic acid) and 12(S)-HETE (see 12-Hydroxyeicosatetraenoic acid). 15-(S)-HpETE and/or 15(S)-HETE may then be further metabolized by 15-LOX-1 or other lipoxygenases to various di-hydroxy and tri-hydroxy compounds, e.g., 8(S),15(S)-dihydroxy-eicosatetraenoic acid (8(S),15(S)-diHETE), 8(R),15(S)-diHETE, 5(S),15(S)-diHETE, 14(R),15(S)-diHETE, and various lipoxins. Alternatively, 15-LOX-1 can further metabolize 15(S)-HpETE to its 14,15-epoxide and then to various 14,15-hepoxilins or to various eoxins.
However, 15-LOX-1 prefers linoleic acid over arachidonic acid as its primary ω-6 polyunsaturated fatty acid (see Omega-6 fatty acid) substrate, oxygenating it at carbon 13 to form 13(S)-hydroperoxy-9Z,11E-octadecaenoic acid (13-HpODE or 13(S)-HpODE) which is then reduce to the corresponding hydroxy derivative, 13(S)-HODE or 13-HODE (see 13-Hydroxyoctadecadienoic acid). Non-human 15-LOX1 orthologs such as mouse 12/15-LOX and soybean 15-LOX form, in addition to 13(S)-HODE, metabolize linoleic acid to 9-hydroperoxy-10E,12Z-octadecaenoic acid (9-HpODE or 9(S)-HpODE), which in mice is rapidly converted to 9(S)-HODE (9-HODE). These arachidonic and linoleic acid metabolites have significant bioactivities and potential but unproven clinical relevancies.
Human 15-LOX-1 also acts on ω-3 polyunsaturated fatty acids (see Omega-3 fatty acid): it metabolizes α-linolenic acid to 13(S)-hydroperoxy-9Z,11E,15Z)-octadecatrienoic acid; eicosapentaenoic acid to 15(S)-hydroperoxy-5Z,8Z,11Z,13E,17Z-eicosatetraenoic acid (15(S)-HpEPA) and docosahexaenoic acid to 17(S)-hydroperoxy-4Z,7Z,10Z,13Z,15E,19Z-docosahexaenoic acid (17-HpDHA) and to neuroprotectin D1 (i.e. 10(R),17(S)-dihydroxy-4Z,7Z,11E,13E,15Z,19Z-docosahexaenoic acid, also designated protectin D1). 15(S)-HpEPA and 17(S)-HpDHA are reduced to 15(S)-hydroxy-5Z,8Z,11Z,13E,17Z-eicosatetraenoic acid (15-HEPA or 15(S)-HEPA) and 17(S)-hydroxy-4Z,7Z,10Z,13Z,15E,19Z-docosahexaenoic acid (17-HDHA or 17(S)-HDHA), respectively; all of these metabolites possess various and often overlapping bioactivities.
15-LOX-1 also works in conjunction with other oxygenating enzymes to form a wide range of products that inhibit, limit, and resolve inflammatory reactions. 15-LOX-1 acts in series with: a) 5-LOX to metabolize arachidonic acid to lipoxins; b) with 5-LOX to metabolize docosahexaenoic acid to resolvins D1, D2, D3, D4, D5, and D6; and c) aspirin-treated cyclooxygenase-2 or cytochrome P450 enzymes to metabolize eicosapentaenoic acid to resolvin E3.
A huge and growing number of studies in animal models suggest that 15-LOX-1 and its lipoxin, resolvin, and protectin metabolites act to inhibit, limit, and resolve diverse inflammatory diseases including periodontitis, peritonitis, sepsis, and other pathogen-induced inflammatory responses, eczema, arthritis, asthma, cystic fibrosis, atherosclerosis, adipose tissue inflammation and subsequent insulin resistance that occurs in obesity, diabetes and the metabolic syndrome, and Alzheimer's disease. While these studies have not yet been shown to translate to human diseases, first and second generation synthetic resolvins and lipoxins have been made and may prove in future studies of clinical use for treating one or more of such diseases.
By metabolizing ω-3 polyunsaturated fatty acids, eicosapentaenoic acid and docosahexaenoic acid, into lipoxins, resolvins, and protectins, 15-LOX-1 is thought to be one mechanism by which dietary ω-3 polyunsaturated fatty acids, particularly fish oil, may act to reduce inflammation and inflammation-related diseases.
While studies have shown that 5-lipoxygenase and its Leukotriene and possibly 5-oxo-eicosatatraenoic acid (see 5-Hydroxyicosatetraenoic acid) metabolites contribute to, and are important pharmacological in the treatment of, severe human allergen-induced asthma and aspirin-induced asthma, recent work suggests that 15-LOX-1 and its eoxin metabolites may also be contributors to these diseases. Further work on this issue is needed.
In colorectal, breast, and kidney cancers, 15-LOX-1 levels are low or absent compared to the cancers' normal tissue counterparts and/or these levels sharply decline as the cancers progress. These results, as well as a 15-LOX-1 transgene study on colon cancer in mice suggests but do not prove that 15-LOX-1 is a tumor suppressor.
By metabolizing ω-3 polyunsaturated fatty acids, eicosapentaenoic acid and docosahexaenoic acid, into lipoxins and resolvins, 15-LOX-1 is thought to be one mechanism by which dietary ω-3 polyunsaturated fatty acids, particularly fish oil, may act to reduce the incidence and/or progression of certain cancers. Indeed, the ability of docosahexaenoic acid to inhibit the growth of cultured human prostate cancer cells is totally dependent upon the expression of 15-LOX-1 by these cells and appears due the this enzyme's production of docosahexaenoic acid metabolites such as 17(S)-HpETE, 17(S)-HETE, and/or and, possibly, an isomer of protectin DX (10S,17S-dihydroxy-4Z,7Z,11E,13Z,15E,19Z-docosahexaenoic acid)
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