Lead inhibits oxidative metabolism of macrophages exposed to macrophage-activating factor

Abstract

The present experiments were designed to evaluate the effect of lead on the capacity of macrophages to respond to activating signals by increased respiratory-burst activity. When mouse peritoneal macrophages were exposed for 24 h to macrophage-activating factor (MAF) and/or bacterial lipopolysaccharide in the presence of lead acetate, a marked inhibition of their oxidative metabolism was observed. The hexosemonophosphate-shunt (HMPS) activity and the release of oxygen derivatives upon triggering by phorbol myristate acetate (PMA) were impaired. Treatment with the metal for 1 h led, however, to stimulation rather than inhibition of the PMA-triggered superoxide production, suggesting that the metal interfered with neither the triggering steps nor the activity of the NADPH oxidase. Moreover, the lead-induced inhibition of macrophage oxidative metabolism did not result from blockade of enzymes of the HMPS pathway. Glucose-6-phosphate dehydrogenase in macrophage extracts, as well as CO2 production from glucose, remained unaffected by the presence of lead, and extracts of lead-treated macrophages were as active as extracts from control cells in those two assays. Lead appeared to interfere with an early event in the MAF-induced activation process. In addition, lead decreased the uptake of 2-deoxyglucose by macrophages, suggesting that the metal might inhibit trans-membrane glucose-transport systems, a phenomenon that might explain in part the metabolic inhibition observed in lead-treated cells.