Pka. Lasson et al., EFFECTS OF 1-CHLORO-2,4,6-TRINITROBENZENE ON 5-LIPOXYGENASE ACTIVITY AND CELLULAR LEUKOTRIENE SYNTHESIS, Biochemical pharmacology, 55(6), 1998, pp. 863-871
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.