Curcumin longa extract-loaded nanoemulsion improves the survival of endotoxemic mice by inhibiting nitric oxide-dependent HMGB1 release

Abstract

Background High mobility group box 1 (HMGB1) is a well-known damage-related alarmin that participates in cellular inflammatory responses. However, the mechanisms leading to HMGB1 release in inflammatory conditions and the therapeutic agents that could prevent it remain poorly understood. This study attempted to examine whether the Curcumin longa herb, which is known to have anti-inflammatory property, can modulate cellular inflammatory responses by regulating HMGB1 release. Methods The murine macrophage RAW264.7 cells were treated with lipopolysaccharide (LPS) and/or a C. longa extract-loaded nanoemulsion (CLEN). The levels of released HMGB1, nitric oxide (NO) production, inducible NO synthase (iNOS) expression, and phosphorylation of mitogen-activated protein kinases were analyzed in RAW264.7 macrophages. The effects of CLEN on survival of endotoxemic model mice, circulating HMGB1 levels, and tissue iNOS expression were also evaluated. Results We have shown that a nanoemulsion loaded with an extract from the C. longa rhizome regulates cellular inflammatory responses and LPS-induced systemic inflammation by suppressing the release of HMGB1 by macrophages. First, treatment of RAW264.7 macrophages with the nanoemulsion significantly attenuated their LPS-induced release of HMGB1: this effect was mediated by inhibiting c-Jun N-terminal kinase activation, which in turn suppressed the NO production and iNOS expression of the cells. The nanoemulsion did not affect LPS-induced p38 or extracellular signal-regulated kinase activation. Second, intraperitoneal administration of the nanoemulsion improved the survival rate of LPS-injected endotoxemic mice. This associated with marked reductions in circulating HMGB1 levels and tissue iNOS expression. Discussion The present study shows for the first time the mechanism by which C. longa ameliorates sepsis, namely, by suppressing NO signaling and thereby inhibiting the release of the proinflammatory cytokine HMGB1. These observations suggest that identification of agents, including those in the herb C. longa, that can inhibit HMGB1 production and/or activity may aid the treatment of endotoxemia.