The curative effect of fucoidan on visceral leishmaniasis is mediated by activation of MAP kinases through specific protein kinase C isoforms.

Fucoidan can cure both antimony-sensitive and antimony-resistant visceral leishmaniasis through immune activation. However, the signaling events underlying this cellular response remain uncharacterized. The present study reveals that fucoidan induces activation of p38 and ERK1/2 and NF-κB DNA binding in both normal and Leishmania donovani-infected macrophages, as revealed by western blotting and electrophoretic mobility shift assay (EMSA), respectively. Pharmacological inhibition of p38, ERK1/2 or the NF-κB pathway markedly attenuated fucoidan-induced pro-inflammatory cytokine synthesis and inducible nitric oxide synthase (iNOS) gene transcription, resulting in a reduction of parasite clearance. To decipher the underlying mechanism of fucoidan-mediated parasite suppression, the expression and functionality of various protein kinase C (PKC) isoforms were evaluated by immunoblotting and enzyme activity assay. Fucoidan elicited an increase in expression and activity of PKC-α, -βI and -βII isoforms in infected macrophages. Functional knockdown of PKC-α and -β resulted in downregulation of p38 and ERK1/2, along with a marked reduction of IL-12 and TNF-α production in fucoidan-treated infected macrophages. Collectively, these results suggest that the curative effect of fucoidan is mediated by PKC-dependent activation of the mitogen-activated protein kinase (MAPK)/NF-κB pathway, which ultimately results in the production of nitric oxide (NO) and disease-resolving pro-inflammatory cytokines.