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1 From the Department of Dermatology, University of California, Davis.
2 Supported by research grant AM 30679 from the US Public Health Service.
3 Address reprint requests to VA Ziboh, Department of Dermatology, TB-192, One Shields Avenue, School of Medicine, University of California, Davis, CA 95616. E-mail: vaziboh{at}ucdavis.edu.
| ABSTRACT |
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-linolenic acid, it is transformed by epidermal 15-lipoxygenase to mainly 13-hydroxyoctadecadienoic acid, which functionally exerts antiproliferative properties in the tissue. In contrast, compared with LA, arachidonic acid (AA) is a relatively minor 20-carbon n-6 PUFA in the skin and is metabolized via the cyclooxygenase pathway, predominantly to the prostaglandins E2, F2
, and D2. AA is also metabolized via the 15-lipoxygenase pathway, predominantly to 15-hydroxyeicosatetraenoic acid. At low concentrations, the prostaglandins function to modulate normal skin physiologic processes, whereas at high concentrations they induce inflammatory processes. PUFAs derived from other dietary oils are also transformed mainly into monohydroxy fatty acids. For instance, epidermal 15-lipoxygenase transforms dihomo-
-linolenic acid (20:3n-6) to 15-hydroxyeicosatrienoic acid, eicosapentaenoic acid (20:5n-3) to 15-hydroxyeicosapentaenoic acid, and docosahexaenoic acid (22:6n-3) to 17-hydroxydocosahexaenoic acid, respectively. These monohydroxy acids exhibit antiinflammatory properties in vitro. Thus, supplementation of diets with appropriate purified vegetable oils, fish oil, or both may generate local cutaneous antiinflammatory and antiproliferative metabolites which could serve as less toxic in vivo monotherapies or as adjuncts to standard therapeutic regimens for the management of inflammatory skin disorders.
Key Words: Arachidonic acid dihomo-
-linolenic acid DGLA docosahexaenoic acid DHA essential fatty acid eicosapentaenoic acid EPA
-linolenic acid GLA 13-hydroxyoctadecadienoic acid 13-HODE 13-HODE-substituted diacylglycerol leukotriene B4 LTB4 prostaglandin E2 PGE2 protein kinase C polymorphonuclear cell polyunsaturated fatty acid PUFA
| INTRODUCTION |
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| BIOLOGICAL SIGNIFICANCE OF 18-CARBON POLYUNSATURATED FATTY ACIDS IN THE EPIDERMIS |
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Generation of 13-hydroxyoctadecadienoic acid by 15-lipoxygenase: role in epidermal hyperproliferation
Although the feeding of LA to EFA-deficient animals is known to reverse the major cutaneous symptoms of EFA deficiency (which include hyperproliferation and increased transepidermal water loss), the mechanism for such a reversal has remained unknown. As a first step towards elucidating the reversal of hyperproliferative scaly skin lesions by dietary LA, we incubated LA with soybean 15-lipoxygenase (EC 1.13.11.33) or 15-lipoxygenase prepared from skin epidermis. The major metabolite identified in these incubations was 13-hydroxyoctadecadienoic acid (13-HODE) and a minor metabolite was 9-HODE. The skin epidermis is unique in that it preferentially metabolizes LA to 13-HODE with a negligible amount transformed to
-linolenic acid (GLA), suggesting that this metabolite may play a role in vivo. Similarly, the feeding of corn oil to normal guinea pigs led to enhanced amounts of 13-HODE in the skin epidermis. A schematic illustration of the metabolism of dietary LA and GLA in the epidermis is shown in Figure 1
. In attempts to identify a mode of action, subsequent studies revealed that 13-HODE was incorporated into epidermal phosphatidylinositol 4,5-bisphosphate, resulting in epidermal phospholipase Ccatalyzed release of 13-HODE into a novel 13-HODE-containing diacylglycerol (1-acyl-213-HODE-glycerol) (11). The possibility now exists that this novel 13-HODE-containing diacylglycerol could function to modulate the activity of epidermal protein kinase C (PKC) and epidermal hyperproliferation and differentiation.
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. The resulting data revealed marked inhibition of total PKC activity with substantial selectivity for inhibition of PKC-ß but a negligible effect on PKC-
(12). Thus, 13-HODEsubstituted diacylglycerol had a selective inhibitory effect on the activity of a major epidermal PKC isozyme. These results suggest that 13-HODEcontaining diacylglycerol can modulate epidermal PKC activity and expression, which are purportedly associated with epidermal hyperproliferation.
Possible in vivo regulatory role of 13-HODEsubstituted diacylglycerol
To ascertain the in vivo relevance of 13-HODEsubstituted diacylglycerol, we determined whether 13-HODE and 13-HODEsubstituted diacylglycerol accumulate in the skin epidermis of guinea pigs after feeding with safflower oil containing LA. To accomplish this, guinea pigs were made EFA-deficient by feeding them a basal diet supplemented with 4% hydrogenated coconut oil for 8 wk. Tissue concentrations of putative 13-HODEsubstituted diacylglycerol and PKC isozymes, tissue hyperproliferation (determined by 3H-thymidine uptake), and histologic evaluations were determined in epidermal preparations from guinea pigs fed 1) safflower oil (controls), 2) only the EFA-deficient diet, and 3) the EFA-deficient diet followed by safflower oil for 2 wk (reversed guinea pigs). Our findings revealed that cutaneous 13-HODE and 13-HODEsubstituted diacylglycerol were significantly lower in EFA-deficient animals than in normal safflower-oilfed animals. The 13-HODE and 13-HODEsubstituted diacylglycerol reductions paralleled both epidermal hyperproliferation (scaly lesions) and elevated expression and activities of PKC-
and -ß in the EFA-deficient animals. Refeeding the animals with safflower oil for 2 wk replenished tissue concentrations of 13-HODE and 13-HODEsubstituted diacylglycerol, which inversely correlated with the selective down-regulation of PKC-ß expression as well as suppression of epidermal hyperproliferation. In contrast, the expression and activity of PKC-
were elevated in the epidermis of the EFA-deficient guinea pigs, but were not down-regulated after refeeding with the safflower-oil diet (13). A summary of data derived from these studies is shown in Figure 2
. These results suggest that the epidermal concentration of 13-HODE, which is derived from dietary LA, plays a role in vivo in modulating cutaneous hyperproliferation via the generation of 13-HODEsubstituted diacylglycerol and its selective suppression of PKC-ß. A speculative scenario describing the association of dietary LA-enriched oil with elevation of 13-HODE in the tissue, the generation of putative 13-HODEsubstituted diacylglycerol, and its down-regulation of PKC-ß is illustrated in Figure 3
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| BIOLOGICAL SIGNIFICANCE OF 20-CARBON PUFAS IN THE EPIDERMIS |
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610% of the total fatty acids in the epidermal phospholipids of guinea pigs and
9% in human skin (14). The functional role of AA depends largely on its generation of biologically potent oxidative metabolites, namely prostaglandins and hydroxy fatty acids. When released after catalytic hydrolysis by epidermal cytosolic phospholipase A2, AA undergoes oxidative transformations via the cyclooxgenase pathway and generates prostaglandin E2 (PGE2), PGF2
, and PGD2. The major lipoxygenase pathway enzyme in the epidermis is epidermal 15-lipoxygenase, which catalyzes the generation of 15-hydroxyeicosatetraenoic acid (15-HETE) from AA. Interestingly, leukotriene-A4 hydrolase (EC 3.3.26), the enzyme that transforms leukotriene A4 (LTA4) to LTB4, has also been identified in the epidermis and presumably functions to transform polymorphonuclear-cellderived LTA4 into LTB4 (15), a proinflammatory metabolite. This latter possibility explains, at least in part, the elevated LTB4 concentrations in leukocyte-infiltrated cutaneous inflammatory reactions in psoriasis. The amount of 5-lipoxygenase in the epidermis is negligible and thus this enzyme does not appreciably transform AA to LTB4. Therefore, a major lipoxygenase metabolite from AA in the epidermis is 15-HETE.
Dihomo-
-linolenic acid
Dihomo-
-linolenic acid (DGLA; 20:3n-6), although a small constituent of normal epidermis, is formed as an elongation product of dietary
-linolenic acid (GLA; 18:3n-6). When its concentration is elevated in the tissue, it is metabolized by epidermal cyclooxygenase to prostaglandin of the 1-series (PGE1) and also by 15-lipoxygenase to 15-hydroxyeicosatrienoic acid (15-HETrE). Human epidermis and guinea pig epidermis both contain an active elongase enzyme that converts the dietary precursor GLA to DGLA (16). For instance, supplementation of human (17) or guinea pig (18) diets with evening primrose or borage oil (vegetable oils that contain GLA) raises epidermal PGE1 and 15-HETrE concentrations. Interestingly, as shown in Figure 1
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5-desaturase enzyme is deficient in the epidermis and thus dietary GLA is not metabolized in significant amounts to AA. Because evening primrose oil has been used in the clinical management of inflammatory hyperproliferative disorders of the skin (19, 20), its reported beneficial effects may be due, at least in part, to epidermal generation of PGE1 and 15-HETrE from elevated tissue DGLA concentrations.
Eicosapentaenoic acid and docosahexaenoic acid
Eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) are the 2 major PUFAs derived from fish oils. They are not present in normal epidermis. Although
-linolenic acid (18:3n-3) and its oxidative metabolites, EPA and DHA, are absent in normal epidermis, both EPA and DHA are metabolized by skin epidermal 15-lipoxygenase to predominantly monohydroxylated metabolites: 15-hydroxyeicosapentaenoic acid (15-HEPE) and 17-hydroxydocosahexaenoic acid (17-HoDHE), respectively. Interestingly, it was reported that these metabolites accumulated in the epidermis after ingestion of fish oils (21, 22). This possibility may explain, at least in part, the beneficial effects of dietary fish oil on cutaneous inflammation.
Attenuation of the proinflammatory mediator LTB4 generated from arachidonic acid by dietary PUFAs
To evaluate whether these 20-carbon monohydroxy fatty acids exert effects on inflammatory processes, we tested the in vitro effects of 15-HETE (derived from AA), 15-HETrE (derived from DGLA), 15-HEPE (derived from EPA) and 17-HoDHE (derived from DHA) on the biosynthesis of polymorphonuclear-cellderived proinflammatory LTB4 (22). The data shown in Figure 4
revealed that 15-HETrE derived from dietary GLA was most potent at lower concentrations.
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| DISCUSSION |
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Additionally, although the 18-carbon 13-HODE derived from LA exerts moderate antiinflammatory effects in vitro, it exerts potent antiproliferative effects in vivo, as evidenced by the reduction of epidermal scaly lesions (13). Overall, these findings underscore the significance of 15-lipoxygenase monohydroxylated metabolites generated from PUFAs in the skin, indicating that they may play important roles in vivo. These metabolites may, in concert with other cellular processes, attenuate inflammatory and proliferative cutaneous disorders. In Figure 5,
a speculative scenario of the possible modulatory effects of the constituent PUFAs and their 15-lipoxygenase metabolites from vegetable and fish oils on the generation of pro-inflammatory leukotrienes from AA is shown.
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| REFERENCES |
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-linolate. Biochim Biophys Acta 1985;834:35763.[Medline]
-linolenic acid by guinea pig epidermis: evidence of generation of anti-inflammatory products. Prostaglandins 1988; 35:91738.[Medline]
-linolenic acidenriched oils on human polymorphonuclear-neutrophil biosynthesis of leukotriene B4. Am J Clin Nutr 1992;55:3945.This article has been cited by other articles:
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A. Friedman and S. Moe Review of the Effects of Omega-3 Supplementation in Dialysis Patients Clin. J. Am. Soc. Nephrol., March 1, 2006; 1(2): 182 - 192. [Abstract] [Full Text] [PDF] |
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C. J. van Gool, C. Thijs, C. J. Henquet, A. C van Houwelingen, P. C Dagnelie, J. Schrander, P. P. Menheere, and P. A van den Brandt {gamma}-Linolenic acid supplementation for prophylaxis of atopic dermatitis--a randomized controlled trial in infants at high familial risk Am. J. Clinical Nutrition, April 1, 2003; 77(4): 943 - 951. [Abstract] [Full Text] [PDF] |
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C. N. Serhan, S. Hong, K. Gronert, S. P. Colgan, P. R. Devchand, G. Mirick, and R.-L. Moussignac Resolvins: A Family of Bioactive Products of Omega-3 Fatty Acid Transformation Circuits Initiated by Aspirin Treatment that Counter Proinflammation Signals J. Exp. Med., October 21, 2002; 196(8): 1025 - 1037. [Abstract] [Full Text] [PDF] |
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S. MADANI, A. HICHAMI, A. LEGRAND, J. BELLEVILLE, and N. A. KHAN Implication of acyl chain of diacylglycerols in activation of different isoforms of protein kinase C FASEB J, December 1, 2001; 15(14): 2595 - 2601. [Abstract] [Full Text] [PDF] |
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G. Liu, D. M. Bibus, A. M. Bode, W.-Y. Ma, R. T. Holman, and Z. Dong Omega 3 but not omega 6 fatty acids inhibit AP-1 activity and cell transformation in JB6 cells PNAS, June 19, 2001; 98(13): 7510 - 7515. [Abstract] [Full Text] [PDF] |
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