Phorbol ester-induced formation of clastogenic factor from human monocytes.

Phorbol-12-myristate-13-acetate (PMA) acts as a tumor promoter on mouse skin. It induces inflammation and leukocyte-mediated clastogenicity which appears to be related to rapid changes in lipid metabolism. To identify lipids possessing clastogenic and/or tumor-promoting properties, we have characterized the metabolism and release of arachidonic acid (AA) and related lipids during the formation of lipophilic clastogenic factors by PMA-treated human monocytes. In 1 h, [3H]AA-labeled monocytes spontaneously released significant amounts of their total radioactivity (4%) which increased nearly 4-fold (15%) with PMA (30 ng/ml) treatment. Eighty-five per cent of extracellular 3H-label from both control and PMA-treated monocytes was composed of free AA (plus AA-metabolites), while the remaining radioactivity was incorporated in phospholipids and mono- and diacylglycerols. Treated and non-treated cells released essentially the same kind of metabolites but PMA induced a 3- to 4-fold increase in total amounts. The major products consisted of prostaglandins F2 alpha and E2, thromboxane B2, 12-hydroxy-5,8,10-heptadecatrienoic acid and 5-, 11- and 15-hydroxyeicosatetraenoic acids. PMA also induced increases in the levels of three unidentified products. Neither leukotrienes nor 4-hydroxynonenal, a major alkenal degradation product of AA, were found in medium from PMA-treated monocytes. PMA, in contrast to the first-stage tumor promoter calcium ionophore A23187, failed to stimulate the release of platelet activating factor. The increased formation of phorbol ester-induced AA metabolites was proportional to the increase in free extracellular AA. The source of AA from treated and untreated monocytes consisted of cellular phospholipids with phosphatidylcholine and phosphatidylethanolamine accounting for 85%.