Colchicine inhibits arachidonate release and 5-lipoxygenase action in alveolar macrophages

Although colchicine is known to inhibit leukotriene synthesis in neutrophils, its effect on other aspects of arachidonic acid (AA) metabolism as well as its mechanism of action are unknown. To address these questions, we investigated the effects of colchicine on resident rat alveolar macrophages (AM), cells that generate a variety of lipoxygenase and cyclooxygenase products after stimulation. Pretreatment of AM with 10 microM colchicine for 1 h dramatically inhibited the synthesis of all 5-lipoxygenase (5-LO) metabolites from endogenous AA in ionophore A-23187-stimulated cells. In addition, colchicine inhibited the total release 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 particulate agonist zymosan was inhibited as well. A selective inhibitory effect of colchicine on the 5-LO pathway was demonstrated by monitoring the synthesis of 5-LO products from exogenously supplied AA. Cell-free enzyme assays showed that this effect was not through a direct inhibition of the 5-LO enzyme. Moreover, colchicine did not affect the translocation of 5-LO to the nuclear envelope. We next evaluated the effect of colchicine on the levels of the two 5-LO cofactors, ATP and Ca2+. Although colchicine did not affect ATP levels, it did abrogate the ionophore-induced increase in intracellular Ca2+ concentration; the inhibitory effect of colchicine on 5-LO metabolism in AM was partially overcome by stimulation with higher doses of A-23187. We conclude that microtubular disruption inhibits agonist-induced increase in intracellular Ca2+ concentration, with multiple consequences for AA metabolism. These include a reduction in the liberation of AA from membrane phospholipids as well as the selective inhibition of processing of AA by 5-LO.