EFFECTS OF 1-CHLORO-2,4,6-TRINITROBENZENE ON 5-LIPOXYGENASE ACTIVITY AND CELLULAR LEUKOTRIENE SYNTHESIS

5-Lipoxygenase (EC 1.13.11.34) is the key enzyme in the regulation of leukotriene synthesis. Here, the effects of various substituted nitrob enzene compounds on 5-lipoxygenase activity and the formation of leuko triene B-4 (LTB4) were studied in polymorphonuclear leukocytes (PMNL), B lymphocytes, and human whole blood. 1-Chloro-2,4,6-trinitrobenzene (TNCB) was found to inhibit calcium ionophore A23187-induced leukotrie ne synthesis in PMNL in a biphasic manner. Thus, 1.0 mu M TNCB caused 50% inhibition of LTB4 formation, but only 16% inhibition was found at 10 times higher concentration. In contrast, this higher concentration of TNCB activated the synthesis of LTB4 when PMNL were stimulated wit h arachidonic acid alone, demonstrating that TNCB can exert both stimu latory and inhibitory effects on leukotriene synthesis depending on th e experimental conditions. The inhibitory effect of 1.0 mu M TNCB on i onophore A23187-induced leukotriene synthesis could be circumvented by addition of exogenous arachidonic acid. At high concentrations of TNC B (25-100 mu M), the drug blocked ionophore A23187-induced leukotriene synthesis. TNCB also inhibited LTB4 formation in B lymphocytes, as we ll as in human whole blood. The activity of recombinant 5-lipoxygenase was inhibited by TNCB, and reduced glutathione or beta-mercaptoethano l counteracted this inhibition. This suggests that TNCB might inhibit 5-lipoxygenase by alkylating thiol groups. TNCB possessed a high speci ficity for 5-lipoxygenase with only modest inhibitory effects on 12-li poxygenase (EC 1.13.11.31), 15-lipoxygenase (EC 1.13.11.12), and phosp holipase A(2) (EC 3.1.1.4) activities. Taken together, these results s how that TNCB can both specifically inhibit and stimulate leukotriene formation and might be useful in further studies on the regulation of 5-lipoxygenase. (C) 1998 Elsevier Science Inc.