Arachidonic acid metabolism by polymorphonuclear leukocytes in psoriasis.

The metabolism of endogenous arachidonic acid by human polymorphonuclear leukocytes (PMNL) isolated from peripheral blood has been studied in 19 patients with chronic plaque psoriasis and 19 healthy controls. Using calcium ionophore A23187 as a stimulus, the PMNL synthesized leukotriene B4 (LTB4), 6-trans-leukotriene B4, 12-epi-6-trans-LTB4, and 5-hydroxy-6,8,11,14-eicosatetraenoic acid. There was no significant difference in the amounts of the products formed between the psoriatic and control groups. The elevated levels of LTB4 that have been described in psoriatic skin may therefore be due to the PMNL infiltrate or to enhanced synthesis by another cell type. The reported increase in activity of the circulating PMNL in psoriasis does not appear to be due to increased 5-lipoxygenase activity in these cells.

Arachidonic acid metabolism by peripheral blood cells in psoriasis.

The metabolism of arachidonic acid by mixed suspensions of leukocytes and platelets prepared from peripheral blood has been studied in 20 patients with psoriasis and 21 healthy controls. A lipoxygenase-derived product, identified as 12,20-dihydroxy-5,8,10,14-eicosatetraenoic acid was formed in increased amounts by the cell suspension from the psoriatic patients. This product results from the metabolism of platelet-derived 12-hydroxy-5,8,10,14-eicosatetraenoic acid by the polymorphonuclear leukocyte 20-hydroxylase enzyme. By contrast, synthesis of the cyclo-oxygenase products 12-hydroxy-5,8,10-heptadecatrienoic acid and thromboxane B2 was diminished. Benoxaprofen, which is known to be beneficial in psoriasis, diminished the levels of 12,20-dihydroxy-5,8,10,14-eicosatetraenoic acid formed in vitro.

The effects of dietary supplementation with fish oil in patients with psoriasis.

Ten patients with psoriasis resistant to conventional topical treatment were given dietary supplements of fish oil, providing approximately 12 g of eicosapentaenoic acid daily for a period of at least 6 weeks. In eight patients there was a modest improvement in their psoriasis, the principal effects being a diminution of erythema and scaling. The dietary treatment resulted in a substantial inhibition of leukotriene B4 production by the peripheral blood polymorphonuclear leukocytes in vitro. The discrepancy between the high degree of inhibition of leukotriene B4 synthesis and the modest therapeutic effect suggests that leukotriene B4 is not the only mediator involved in the development of the psoriatic lesion. Furthermore, the in vivo cutaneous levels of leukotriene B4 might not have been inhibited to the same extent as the polymorphonuclear leukocyte levels in vitro. Further studies on the use of fish oil supplements, both on their own and in conjunction with other forms of treatment in psoriasis are warranted. It will also be important to determine whether the altered profile of 5-lipoxygenase products found in the blood is also seen in the skin.