Hydrogen sulfide modulates chromatin remodeling and inflammatory mediator production in response to endotoxin, but does not play a role in the development of endotoxin tolerance

BACKGROUND: Pretreatment with low doses of LPS (lipopolysaccharide, bacterial endotoxin) reduces the pro-inflammatory response to a subsequent higher LPS dose, a phenomenon known as endotoxin tolerance. Moreover, hydrogen sulfide (H(2)S), an endogenous gaseous mediator (gasotransmitter) can exert anti-inflammatory effects. Here we investigated the potential role of H(2)S in the development of LPS tolerance. THP1 differentiated macrophages were pretreated with the H(2)S donor NaHS (1 mM) or the H(2)S biosynthesis inhibitor aminooxyacetic acid (AOAA, 1 mM). METHODS: To induce tolerance, cells were treated with a low concentration of LPS (0.5 μg/ml) for 4 or 24 h, and then treated with a high concentration of LPS (1 μg/ml) for 4 h or 24 h. In in vivo studies, male wild-type and CSE(-/-) mice were randomized to the following groups: Control (vehicle); Endotoxemic saline for 3 days before the induction of endotoxemia with 10 mg/kg LPS) mg/kg; Tolerant (LPS at 1 mg/kg for 3 days, followed LPS at 10 mg/kg). Animals were sacrificed after 4 or 12 h; plasma IL-6 and TNF-α levels were measured. Changes in histone H3 and H4 acetylation were analyzed by Western blotting. RESULTS: LPS tolerance decreased pro-inflammatory cytokine production. AOAA did not affect the effect of tolerance on reducing cytokine production. Treatment of the cells with the H(2)S donor reduced cytokine production. Induction of the tolerance increased the acetylation of H3; AOAA reduced histone acetylation. H(2)S donation increased histone acetylation. Tolerance did not affect the responses to H(2)S with respect to histone acetylation. CONCLUSIONS: In conclusion, both LPS tolerance and H(2)S donation decrease LPS-induced cytokine production in vitro and modulate histone acetylation. However, endogenous, CSE-derived H(2)S does not appear to play a significant role in the development of LPS tolerance.