Macrophage preconditioning with synthetic malaria pigment reduces cytokineproduction via heme iron-dependent oxidative stress

Hemozoin (malaria pigment), a polymer of hematin (ferri-protoporphyrin IX) derived from hemoglobin ingested by intraerythrocytic plasmodia, modulates cytokine production by phagocytes. Mouse peritoneal macrophages (PM) fed wi th synthetic beta -hematin (BH), structurally identical to native hemozoin, no longer produce tumor necrosis factor alpha (TNF alpha) and nitric oxide (NO) in response to lipopolysaccharide (LPS). Impairment of NO synthesis i s due to inhibition of inducible nitric oxide synthase (iNOS) production. B H-mediated inhibition of PM functions cannot he ascribed to iron release fr om BH because neither prevention by iron chelators nor down-regulation of i ron-regulatory protein activity was detected. Inhibition appears to be rela ted to pigment-induced oxidative stress because (a) thiol compounds partial ly restored PM functions, (b) heme oxygenase (HO-1) and catalase mRNA level s were up-regulated, and (c) free radicals production increased in BH-treat ed cells. The antioxidant defenses of the cells determine the response to B H: microglia cells, which show a lower extent of induction of HO-1 and cata lase mRNAs and lower accumulation of oxygen radicals, are less sensitive to the inhibitory effect of BH on cytokine production. Results indicate that BH is resistant to degradation by HO-1 and that heme-iron mediated oxidativ e stress may contribute to malaria-induced immunosuppression. This study ma y help correlate the different clinical manifestations of malaria, ranging from uncomplicated to severe disease, with dysregulation of phagocyte funct ions and promote better therapeutic strategies to counteract the effects of hemozoin accumulation.