Cutaneous responses to 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) and 5,12-dihydroxyeicosatetraenoic acid (leukotriene B4) in psoriasis and normal human skin

Bioactive Lipid Mediator Profiles in Human Psoriasis Skin and Blood

Psoriasis is a chronic immune-mediated disease that represents a unique model for investigating inflammation at local and systemic levels. Bioactive lipid mediators (LMs) are potent compounds reported to play a role in the development and resolution of inflammation. Currently, it is not known to what extent these LMs are involved in psoriasis pathophysiology and related metabolic dysfunction. Here, we use targeted and untargeted liquid chromatography-tandem mass spectrometry approaches to quantify LMs in skin and peripheral blood from psoriasis patients and compared them with those of healthy individuals. Lesional psoriasis skin was abundant in arachidonic acid metabolites, as 8-, 12- and 15-hydroxyeicosatetraenoic acid, compared with adjacent nonlesional and skin from healthy individuals. Additionally, a linoleic acid-derived LM, 13-hydroxyoctadecadienoic acid, was significantly increased compared with healthy skin (607.9 ng/g vs. 5.4 ng/g, P = 0.001). These psoriasis skin differences were accompanied by plasma decreases in antioxidant markers, including glutathione, and impaired lipolysis characterized by lower concentrations of primary and secondary bile acids. In conclusion, our study shows that psoriasis skin and blood have disease-specific phenotype profiles of bioactive LMs represented by omega-6 fatty acid-oxidized derivatives. These findings provide insights into psoriasis pathophysiology that could potentially contribute to new biomarkers and therapeutics.

Monohydroxy fatty acids esterified to phospholipids are decreased in lesional psoriatic skin

Because of the increasing number of reports of the important roles of monohydroxy derivatives of poly-unsaturated fatty acids in the regulation of cell function, we determined the pools of unesterified and esterified monohydroxy fatty acids (MHFAs) in keratomed epidermal slices, taken from lesional and non-lesional psoriatic skin. Extracted phospholipids were separated by thin-layer chromatography. The isolated fractions of phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidyl-ethanolamine (PE) were treated with phospholipase A2 to release fatty acids in the sn-2 position. Released MHFAs were separated by reversed-phase and straight-phase high-performance liquid chromatography and identified as the linoleic acid derivatives 9-hydroxy-octadecadienoic acid (9-HODE) and 13-hydroxy-octadecadienoic acid (13-HODE) and as the arachidonic acid derivative 15-hydroxy-eicosatetraenoic acid (15-HETE). These findings are consistent with the presence of unesterified 9-HODE, 13-HODE and 15-HETE. In contrast, 12-hydroxy-eicosatetraenoic acid (12-HETE), although found to be present in high amounts as unesterified 12-HETE, was not detectable in the phospholipids. When compared with non-lesional psoriatic skin, the levels of 9-HODE, 13-HODE and 15-HETE esterified to the sn-2 position of PC, PI and PE in lesional psoriatic skin were significantly decreased (to 28-78% of those in non-lesional skin). This depletion of MHFAs in specific phospholipids may be due to an imbalance between phospholipase and acyltransferase activities. Because the levels of esterified MHFAs may influence signal transduction and eicosanoid metabolism the described changes may be relevant for the inflammatory processes occurring in psoriasis.

Defect of epidermal 12(S)-hydroxyeicosatetraenoic acid receptors in psoriasis

12-hydroxyeicosatetraenoic acid (12-HETE) is assumed to play a central role in the pathophysiology of psoriasis. Since its effects in skin are mediated by specific high-affinity receptors, we studied the receptor characteristics in cultured epidermal cells from involved and apparently healthy skin of psoriasis patients by radioligand binding assay. Involved and uninvolved psoriatic epidermal cells showed a fourfold decrease in the number of 12-HETE binding sites as compared with normal healthy individuals and patients with atopic dermatitis, while receptor affinity remained unchanged. The decrease in receptor number was evident in psoriatic cells even in long-term culture and was not due to receptor down-regulation, defective response to interferon gamma or to protease degradation of receptor protein. The decrease in the number of 12-HETE receptors detectable even in clinically normal psoriatic skin functionally leads to diminished 12-HETE uptake and may thus represent a primary central molecular defect in the pathophysiology of the disease.

Leukotriene B4 and platelet-activating factor in human skin

Acute inflammatory reactions are characterized by leukocyte infiltration associated with increases in vascular permeability and in local blood flow. Leukocyte infiltration can be induced by chemotactic factors such as leukotriene B4 (LTB4) and paf-acether (formerly known as platelet-activating factor) that can be generated within inflammatory lesions. Vascular permeability and increase in blood flow are also affected by LTB4 and paf-acether, as well as by several other substances, including histamine and prostaglandins. Derived from arachidonic acid via the 5 lipo-oxygenase pathway, LTB4 is one of the most potent leukocyte chemotactic substances known. Intradermal injections of LTB4 induce dermal neutrophil infiltration in animal models and in humans. Topical application of LTB4 to human skin induces intraepidermal micro-abscesses containing numerous intact neutrophils. LTB4 has been found to be increased in psoriatic lesions, but its synthesis by epidermal cells remains undecided. Like other leukotrienes, LTB4 can stimulate DNA synthesis in cultured human epidermal keratinocytes. However, receptors for LTC4 but not for LTB4 have been found on human keratinocytes in culture. Paf-acether is an ether-linked phospholipid identified as 1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine and is considered to be one of the most potent mediators of acute allergic and inflammatory reactions. For instance, intradermal injection of paf-acether induces inflammatory events such as neutrophil infiltration and increase in vascular permeability. Recent data suggest that cutaneous cells, such as fibroblasts and keratinocytes, are capable of producing paf and that paf is released during the development of allergic cutaneous reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of arachidonic acid by human epidermal cells depends upon maturational stage

Synthesis of 12- and/or 15-HETE by human epidermal cells was investigated after separating basal cells from suprabasal epidermal cell layers. We found that the main metabolite of 3H-arachidonic acid (3H-AA), formed by freshly prepared upper epidermal layers (stratum granulosum and spinosum), upon RP-HPLC co-eluted with authentic 3H-12-HETE. A 3H-15-HETE co-eluting peak selectively occurred in chromatograms obtained from supernatants of fractions containing basal cells. Supernatants of freshly prepared suspensions rich in basal keratinocytes appeared to contain 3H-15-HETE as their main 3H-AA metabolite, by far exceeding the recovered amounts of 3H-12-HETE. Moreover, keratinocytes cultured for 1 week or longer were found to produce predominantly a 3H-AA metabolite co-eluting with 3H-15-HETE. In supernatants of cultured cells, little if any 3H-12-HETE was detectable. Cultured human skin fibroblasts were not found to produce relevant amounts of HETE. Genuine tissue rich in basal cells, i.e., cells of hair follicles, were found to form twice as much 3H-15-HETE as 3H-12-HETE (3H-15-HETE/3H-12-HETE-ratio = 1.9 +/- 0.8; n = 7). Apparently, different epidermal layers are able to produce a characteristic pattern of 3H-AA metabolites. 3H-15-HETE generation seems to be a marker for proliferating keratinocytes, whereas 3H-12-HETE formation appears to be typical for differentiating suprabasal epidermal cells. Our results may explain the heretofore varying patterns of AA-metabolites by keratinocytes reported in the literature.

Cellular, immunologic and biochemical characterization of topical retinoic acid-treated human skin

Histologic and clinical improvement of sun-exposed skin following topical treatment with retinoic acid has been reported. Daily application of retinoic acid typically results within 2-5 d in an erythematous scaling reaction, which lessens with continued usage. The cellular, immunologic, and biochemical basis of this retinoid reaction and its role in the repair of photodamaged skin are not known. To investigate the retinoid reaction in man, we have treated non-sun-exposed skin with 0.1% retinoic acid cream (Retin-A, Ortho Pharmaceutical Corporation, Raritan, NJ) under occlusion for 4 d to induce erythema and then examined changes in 1) histology, 2) expression of cell-surface molecules, 3) the enzymes and second messengers of the phospholipase C/protein kinase C signal-transduction system, 4) levels of eicosanoids, and 5) levels of interleukin-1 protein and mRNA. These parameters were chosen for measurement both because they are indicators of epidermal function and previous studies suggest they may be responsive to retinoic acid treatment. Epidermal cell growth as judged by increased epidermal thickness and mitotic figures was significantly increased in retinoic acid-treated skin compared to vehicle-treated controls. Increased numbers of CD4+ T cells accompanied by prominence of dermal dendrocytes in the papillary dermis and focal keratinocyte expression of intercellular adhesion molecule-1 were observed in retinoic acid-treated biopsies. Phosphoinositide-specific phospholipase C activity and 1,2-diacylglycerol content were also elevated in retinoic acid-treated epidermis. Protein kinase C activity was reduced by one third in both the soluble and membrane fraction, suggesting down-regulation. Surprisingly, in view of the inflammatory nature of the retinoid reaction, no increases were observed in arachidonic acid, its metabolites, interleukin-1 alpha, or interleukin-1 beta. To examine the specificity of the retinoid reaction, subjects were treated with the irritant sodium lauryl sulfate, under conditions that resulted in a reaction clinically similar to that observed with retinoic acid. The histologic alterations induced by sodium lauryl sulfate were found to be indistinguishable from those induced by retinoic acid. These data indicate that, although a wide range of cellular and molecular alterations occur in retinoic acid-treated skin, these changes may not be necessarily specific or unique for retinoic acid.

Regulation of 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE) binding sites on human epidermal cells by interferon-gamma

We recently detected specific high-affinity binding sites for 12(S)-HETE, the main arachidonic acid metabolite in skin, on epidermal cells. The putative receptor is involved in keratinocyte chemotaxis toward 12(S)-HETE, which points to its participation in wound healing. In an effort to further characterize the 12(S)-HETE receptor, we investigated its regulation by various cytokines. Of the tested cytokines, only interferon (IFN)-gamma led to a massive induction of the 12(S)-HETE receptors. The effect was dose and time dependent and blocked by cycloheximide. The up-regulation of 12(S)-HETE receptors by IFN-gamma may represent an amplification mechanism of the assumed role of 12(S)-HETE in skin wound repair.

12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid is a more potent neutrophil chemoattractant than the 12(R) epimer in the rat cornea

12(R)-hydroxy-5,8,10,14-eicosatetraenoic acid [12(R)-HETE] is reported to be more potent than its epimer 12(S)-HETE as a chemoattractant for human neutrophils in vitro and following topical application to the skin. To assess the in vivo neutrophil chemoattractant potencies of 12(S)-HETE and 12(R)-HETE in the rat, we injected 1 microgram, 5 micrograms, or 10 micrograms of these eicosanoids into the corneal stroma. Rats were killed 12-15 hours after injection, and the number of neutrophils in the stroma was counted in a histological section of the cornea including the injection site. The number of neutrophils was significantly increased in corneas injected with 5 micrograms (+103% of control) or 10 micrograms (+456% of control) of 12(S)-HETE and in those injected with 10 micrograms of 12(R)-HETE (+111% of control). The neutrophilic infiltrate in corneas injected with 1 microgram or 5 micrograms of 12(S)-HETE was not significantly different from that in corneas injected with 1 microgram of leukotriene B4. The data for the 10 micrograms injections indicate that 12(S)-HETE is a more potent neutrophil chemoattractant than 12(R)-HETE in the rat cornea. Our results suggest that species or tissue specificity may determine the relative potencies of 12-HETE epimers as chemoattractants for neutrophils, and that 12(S)-HETE may be an important inflammatory mediator in the rat cornea.

12-Hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) does not stimulate proliferation of human neonatal keratinocytes

We have developed an assay to study the effect of drugs on the proliferation of neonatal human skin-derived keratinocytes in vitro. Expanding populations of neonatal keratinocytes were cultured in low concentrations (0.5%) of fetal calf serum for up to 12 d. Growth of the cultures was determined by measurement of DNA using a sensitive fluorimetric assay. Addition of 10(-9)-10(-6) M 12(RS)-hydroxy-5,8,10,14-eicosatetraenoic acid (12(RS)-HETE) neither stimulated keratinocyte proliferation nor enhanced the incorporation of [3H]thymidine. The ability of neonatal keratinocytes in low serum medium to respond to exogenous factors was demonstrated by increased growth in response to a mixture of cholera toxin, hydrocortisone, and epidermal growth factor. Confluent keratinocyte cultures in 10% human AB serum exposed to 12(S)-HETE for 72 h also showed no changes in DNA, [3H]thymidine incorporation, or labeling index. Metabolism of 12(S)-[3H]HETE was greater in cultures containing low concentrations of serum but there was no evidence for the formation of 12,20-dihydroxyeicosatetraenoic acid.