| Abstract: | Neutrophils which ingest particles (serum-treated zymosan, monosodium urate crystals) or are exposed to calcium ionophore A23187 generate leukotriene B4 (LTB4). Earlier work has shown that cells exposed to colchicine before exposure to monosodium urate crystals produce less LTB4; the formation of 5-HETE is unaffected. To determine whether inhibition by colchicine of LTB4 generation was stimulus-specific and was mediated by microtubule integrity, the effects of colchicine (10 microM, 60 min) on the release of lipoxygenase products from neutrophils exposed to ionophore A23187 (10 microM, 5 min) were examined. In the presence of exogenous arachidonic acid (100 microM, 15 min), colchicine decreased LTB4 to 48% +/- 11.7 of control and 5-HETE to 60.5% +/- 5.7 of control (mean +/- SEM); 15-HETE was also decreased to 61% +/- 10.3 of control. In the absence of exogenous arachidonate, LTB4 was decreased to 22.2% +/- 11.7 of control and 5-HETE to 13% +/- 4.8 of control. Lumicolchicine did not significantly affect formation of 5-HETE or LTB4. However, vinblastine sulfate (20 microM, 60 min), another microtubule-disruptive agent, decreased the formation of both 5-lipoxygenase products. The effects of colchicine and vinblastine were not due to impairment of cell viability because the release of cytoplasmic lactic dehydrogenase was unaffected. Ultrastructural analysis of centriolar microtubules showed that decrements in microtubule numbers of colchicine- and vinblastine-treated cells paralleled decrements in 5-lipoxygenase products. These pharmacologic manipulations suggested that functional microtubules might be required for optimal lipoxygenase activity. Consequently, we prepared neutrophil-derived cytoplasts, devoid of an intact microtubule system. No significant decreases in the 5- or 15-lipoxygenase products were found when cytoplasts were exposed to colchicine in the presence of exogenous arachidonate and A23187. The data show that colchicine inhibits the formation of lipoxygenase products from neutrophils stimulated with A23187, most likely via its effect on microtubules, the integrity of which appears necessary for full expression of 5- and 15-lipoxygenases. |
