Malarial pigment activates p38 MAPK and NF-kappaB pathways in human monocytes: effects on degranulation and inflammatory response.

INTRODUCTION. Phagocytosis of malarial pigment (HZ, hemozoin) impairs several functions of human monocytes by enhancing release of pro-inflammatory molecules (i.e. TNFalpha, IL-1beta, MIP-1alpha) and of enzymes stored in gelatinase granules (i.e. MMP-9, TIMP-1, lysozyme). Here the mechanisms underlying HZ-dependent enhanced release of these molecules were investigated. METHODS. Human monocytes were fed with HZ and treated with/without SB203580 (inhibitor of p38 MAPK phosphorylation) or quercetin, artemisinin and parthenolide (inhibitors of cytosolic I-kappaBalpha phosphorylation/degradation, p50/p65 NF-kappaB subunits nuclear translocation, and p65/DNA binding, respectively). Thereafter, we studied in cell lysates the following parameters: cytosolic phospho-p38 MAPK, phospho-I-kappaB and I-kappaB or nuclear p50/p65 protein levels by WB and p65/DNA binding by EMSA. Meanwhile, in cell supernatants we studied the release of the following proteins: TNFalpha, IL-1beta, and MIP-1alpha by ELISA; MMP-9 by gelatin zymography; TIMP-1 by WB; lysozyme by spectrometric assay. RESULTS. HZ promoted p38 MAPK phosphorylation, I-kappaB phosphorylation/degradation, p50/p65 nuclear translocation, p65/DNA binding. As expected, p38 MAPK signalling was inhibited by SB203580, while quercetin, artemisinin and parthenolide blocked NF-kappaB pathway activation. All these inhibitors abrogated the HZ-enhanced release of TNFalpha, IL-1beta, MIP-1alpha, MMP-9, TIMP-1 and lysozyme. CONCLUSION. In human monocytes, HZ promotes release of pro-inflammatory factors and degranulation of enzymes stored in gelatinase granules by activating p38MAPK and NF-kappaB pathways. These findings provide new information useful to clarify mechanisms of malaria pathogenesis, and to design specifically targeted adjuvant therapy in complicated malaria.