COLCHICINE INHIBITS ARACHIDONATE RELEASE AND 5-LIPOXYGENASE ACTION INALVEOLAR MACROPHAGES

Although colchicine is known to inhibit leukotriene synthesis in neutr ophils, its effect on other aspects of arachidonic acid (AA) metabolis m as well as its mechanism of action are unknown. To address these que stions, we investigated the effects of colchicine on resident rat alve olar macrophages (AM), cells that generate a variety of lipoxygenase a nd cyclooxygenase products after stimulation. Pretreatment of AM with 10 mu M colchicine for 1 h dramatically inhibited the synthesis of all 5-lipoxygenase (5-LO) metabolites from endogenous AA in ionophore A-2 3187-stimulated cells. In addition, colchicine inhibited the total rel ease of AA as well as prostanoids to a lesser extent. Similar effects were observed with the other microtubule-disruptive agents nocodazole and vinblastine, and 5-LO product formation stimulated by the particul ate agonist zymosan was inhibited as well. A selective inhibitory effe ct of colchicine on the 5-LO pathway was demonstrated by monitoring th e synthesis of 5-LO products from exogenously supplied AA. Cell-free e nzyme assays showed that this effect was not through a direct inhibiti on of the 5-LO enzyme. Moreover, colchicine did not affect the translo cation of 5-LO to the nuclear envelope. We next evaluated the effect o f colchicine on the levels of the two 5-LO cofactors, ATP and Ca2+ Alt hough colchicine did not affect ATP levels, it did abrogate the ionoph ore-induced increase in intracellular Ca2+ concentration; the inhibito ry effect of colchicine on 5-LO metabolism in AM was partially overcom e by stimulation with higher doses of A-23187. We conclude that microt ubular disruption inhibits agonist-induced increases in intracellular Ca2+ concentration, with multiple consequences for AA metabolism. Thes e include a reduction in the liberation of AA from membrane phospholip ids as well as the selective inhibition of processing of AA by 5-LO.