Sulfhydryl reagents as model substances for eicosanoid research.

The rate of eicosanoid synthesis is controlled by the availability of free arachidonic acid. Recently we showed that inhibition of reacylation of liberated fatty acids by the sulfhydryl group-blocking agent thimerosal increased prostaglandin as well as leukotriene synthesis. In order to gain further insight into the basic regulatory mechanisms controlling cellular eicosanoid production, the effects of different sulfhydryl reagents on prostaglandin E2 synthesis in the macrophage-like cell line P388D1 were investigated. As these cells exhibit an enormous acyl turnover of cellular phospholipids even under basal conditions, any interference with their fatty acid deacylation-reacylation cycle should lead to a change in intracellular concentrations of the eicosanoid precursor arachidonic acid. Therefore, arachidonic acid release from prelabelled cells as well as arachidonic acid incorporation into different phospholipid species under the influence of mercuric chloride (HgCl2), ethylmercurithiosalicylate (thimerosal), p-hydroxymercuribenzoic acid (PHMB), 0-(3-hydroxymercuri-3-methoxypropyl)carbamoyl-phenoxyacetic acid (mersalyl), N-ethylmaleimide (NEM), and ethacrynic acid were examined. Additionally, direct effects of those substances on corresponding enzyme activities, i.e. phospholipase A2 (PLA2), acyl-CoA synthetase, and lysophospholipid acyltransferase (LAT), on glutathione levels, and on cell viability were estimated. The results demonstrate that the organic mercury compound thimerosal was the most effective in enhancing free arachidonic acid levels, and concomitantly prostaglandin E2 synthesis in P388D1 cells, as result of a rather selective inhibition of the fatty acid reacylating enzyme LAT.