SIRT1 and serum lipopolysaccharide activity: SIRT1 inhibited LPS- or TNF-α-induced HMGB1 release from macrophages by directly interacting with HMGB1 in an acetylation-dependent manner; therefore, we next analyzed whether SIRT1 affected the circulating HMGB1 level during endotoxemia, a standard model of systemic inflammation.