Role of eicosanoids in the pathogenesis of atopic dermatitis

Avena Rhealba Inhibits A23187-Stimulated Arachidonic Acid Mobilization, Eicosanoid Release, and cPLA2 Expression in Human Keratinocytes: Potential in Cutaneous Inflammatory Disorders

The aim of the present study was to examine the effects of Avena Rhealba (AR) oatmeal extract on the metabolism of arachidonic acid (AA) and eicosanoids as well as on the expression of cytosolic phospholipase A(2 )(cPLA(2)) in the human keratinocyte cell line HaCaT. For this purpose, we examined the effects of AR on basal and A23187-triggered release of [(3)H]-AA from phospholipids and on the production of [(3)H]-labeled metabolites of the cyclooxygenase (CO) and 5-lipoxygenase (LO) pathways. AR was found to inhibit A23187-triggered [(3)H]-AA mobilization from phospholipids (p<0.05) and production of [(3)H]-labeled metabolites of CO (p<0.05) and LO (p<0.05) pathways. These results suggest AR decreases PLA(2)-dependent mobilization of AA from phospholipids. A closer examination of the effects of AR on prostaglandin 6KF1alpha (6KPGF1alpha), the stable metabolite of prostacyclin, revealed dose-dependent inhibition of this AA metabolite. AR also decreased A23187- and tumor necrosis factor alpha-induced cPLA(2) overexpression, as shown by cPLA(2) immunodetection and mRNA expression. These results demonstrate the high potential of AR in the treatment of inflammatory diseases of the skin.

Effects of n-3 polyunsaturated fatty acids on dermatitis in NC/Nga mice

The administration of n-3 polyunsaturated fatty acids (PUFAs) is known to be effective against allergic diseases by suppressing the production of eicosanoids derived from arachidonic acid. To investigate the mechanisms and efficacy of n-3 PUFA treatment in patients with atopic dermatitis (AD), we administered four different formulas of alpha-linolenic acid for 6 weeks in an AD model using NC/Nga mice. According to the doses of alpha-linolenic acid given, the levels of alpha-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid in the red blood cell membranes increased while the levels of linoleic acid and arachidonic acid decreased. However, there was no significant difference among the four dose groups in clinical skin severity score, histopathological findings of skin lesions, or levels of total plasma IgE. Moreover, there was no significant difference in the production of leukotriene B(4) and Leukotriene C(4) from skin lesions after stimulation with A23187 among the groups, although the production of prostaglandin E(2) (PGE(2)) was significantly reduced and skin blood flow in the ear was significantly higher in the group given the highest dose of alpha-linolenic acid. Our results suggest that the administration of alpha-linolenic acid can change the fatty acid composition, PGE(2) production, and skin blood flow but may not prevent the development of dermatitis in NC/Nga mice.

Pathophysiological role of leukotrienes in dermatological diseases: potential therapeutic implications

In vitro and in vivo data have demonstrated that leukotrienes play a key role not only in allergic airway diseases but also in inflammatory reactions of the skin. Antileukotriene drugs, i.e. leukotriene receptor antagonists and synthesis inhibitors, are a new class of anti-inflammatory drugs that have shown clinical efficacy in the management of asthma, allergic rhinitis and inflammatory bowel disease. To address the question of the validity and applicability of published evidence of the use of antileukotriene drugs in dermatological diseases, we reviewed data concerning the pathophysiological effect of leukotrienes in the skin and in skin diseases, and the experience with antileukotriene treatment that has been published. In vivo and in vitro data suggest that antileukotriene treatment may have efficacy in atopic dermatitis, different types of urticaria or psoriasis and other skin diseases such as bullous skin diseases, collagenoses, Sjogren-Larsson syndrome or Kawasaki disease. Nevertheless, published evidence is very limited and before any conclusions can be drawn, additional basic research needs to be performed with regard to the role of different leukotrienes and leukotriene receptors in skin diseases. On the basis of these data, randomised and placebo-controlled clinical trials with leukotriene antagonists and synthesis inhibitors should be performed. Moreover, future studies investigating the additive benefit of antileukotriene drugs are warranted, e.g. in combination with antihistamines, corticosteroids or other anti-inflammatory drugs.

Psoriasis and the arachidonic acid cascade

Arachidonic acid (5.8,11,14-eicosatetraenoic acid C20:4, n-6) is released from the cell membrane by the action of phospholipases on membrane phospholipids. Metabolites of arachidonic acid, which are generically termed eicosanoids, including prostaglandins, thromboxane, leukotrienes and hydroxyeicosatetraenoic acids, have been implicated as mediators or modulators of a number of physiological functions and pathological conditions in both normal and diseased human skin. Particularly, eicosanoids have been suspected to play an important role in the pathogenesis of psoriasis, because a number of phenomena observed in psoriasis can be explained, at least in part, by the action of eicosanoids. This review will focus on recent progress regarding the significance of eicosanoids in the pathogenesis of psoriasis. Recent developments in the molecular biology in the eicosanoids have renewed interest in the role of eicosanoids in psoriasis. New understanding of the etiology of psoriasis and advances in its treatment due to recent progress in eicosanoid biology will also be presented.

Leukotriene A4 hydrolase in peripheral leukocytes of patients with atopic dermatitis

We examined the enzymatic activity of leukotriene (LT) A4 hydrolase, which catalyzes the conversion of LTA4 to LTB4, in peripheral leukocytes of patients with atopic dermatitis. The patients were divided into three categories (severe, moderate and mild) on the basis of clinical severity. The LTA4 hydrolase activities in the supernatant fraction of peripheral blood polymorphonuclear leukocytes (PMN) were significantly higher in preparations of cells from severe atopic dermatitis patients (123.94 +/- 16.61 pmol/10(6) cells per min) than in those from moderate (49.03 +/- 9.43 pmol/ 10(6) cells per min; P < 0.01) and mild (28.75 +/- 11.42 pmol/10(6) cells per min; P < 0.01) atopic dermatitis patients and normal controls (15.14 +/- 1.74 pmol/10(6) cells per min; P < 0.01). LTA4 hydrolase activities were also higher in peripheral blood mononuclear cells (PBMC) from severe atopic dermatitis patients (27.81 +/- 8.28 pmol/10(6) cells per min) than in those from moderate (11.31 +/- 2.11 pmol/10(6) cells per min; P < 0.05) and mild (6.16 +/- 2.62 pmol/10(6) cells per min; P < 0.05) atopic dermatitis patients and normal controls (11.17 +/- 0.83 pmol/10(6) cells per min; P < 0.05). LTA4 hydrolase activities in PMN were reduced after improvement of the disease in eight patients with severe or moderate atopic dermatitis. These results suggest that LTA4 hydrolase, which synthesizes LTB4, plays a significant role in the pathogenesis and development of atopic dermatitis.

Leukotriene A4 hydrolase in human skin

The biochemical properties and immunohistochemical localization of leukotriene (LT) A4 hydrolase were investigated in human skin. The activity of LTA4 hydrolase, which catalyzes the hydrolysis of LTA4 to LTB4, the most chemotactic compound known, was detected in the 100,000 x g supernatant of homogenates of human epidermis and a transformed epidermal cell line (HSC-1). No significant LTA4 hydrolase activity was detected in human whole skin or dermis. The enzymatic properties of LTA4 hydrolase isolated from human keratinocytes and peripheral leukocytes were similar. Their activities were inhibited by bestatin and captopril, and they were completely absorbed by anti-human LTA4 hydrolase antibody. By immunoblotting analysis using this antibody, LTA4 hydrolase was detected as a 70-kDa protein in human epidermis and HSC-1 and was found to be similar to the enzyme detected in peripheral mononuclear leukocytes. In human dermis, LTA4 hydrolase was barely detected by Western blotting. On the other hand, LTA4 hydrolase was demonstrated in the cytoplasm of keratinocytes in the epidermis, and in fibroblasts, infiltrating and endothelial cells in the dermis of normal human skin by immunohistochemical analysis using the immunoperoxidase method. These results suggest that LTB4 can be generated from LTA4 by LTA4 hydrolase in keratinocytes as well as fibroblasts, infiltrating and endothelial cells in the dermis of human skin.