To explore the role of endogenous and exogenous hydrogen sulfide (H2S) in lipopolysaccharide (LPS)-induced acute lung injury (ALI) in rats and the underlying mechanisms.
120 Sprague-Dawley rats were randomly divided into four groups: control, LPS (instilled intratracheally to induce ALI), NaHS (H2S donor) + LPS, and propargylglycin (PPG) + LPS. Animals were sacrificed at 4 h or 8 h after agent administration. Lung weight/body weight ratio (LW/BW) was measured and calculated. Morphological changes of lung tissues were observed. H2S concentration, NO concentration (NO) and carbon monoxide (CO) level in plasma were tested. Malondialdehyde (MDA) content, CSE activity, inducible nitric oxide synthase (iNOS) activity and hemeoxygenase (HO) activity of the lung were determined. PMN and protein content in BALF were also tested. Immunohistochemisty technique was performed to examine the expression of iNOS and HO-1 protein in lung tissues. The correlation of H2S content with the above indices was analyzed.
Compared with control conditions, severe injuries of lung tissues and a raised LW/BW, MDA content, PMN and protein content in BALF were observed in rats treated with LPS. LPS also lead to a drop in plasma H2S concentration and lung CSE activity. The enzyme activity of iNOS and HO, the protein expression of them and plasma NO, CO level increased after LPS instillation. Administration of NaHS before LPS could attenuated the changes induced by LPS. Pre-administration of PPG exacerbated the injuries induced by LPS, increased PMN and protein content in BALF, the plasma NO level, lung iNOS activity and its protein expression, but there was no prominent variation in CO level, HO activity and HO-1 protein expression compared with those of LPS group. The H2S content was positively correlated with CSE activity, CO content and HO-1activity (r = 0.945-0.987, P < 0.01), and negatively correlated with the other indices (r = -0.994 - -0.943, P < 0.01).
Downregulation of H2S/CSE was involved in the pathogenesis of acute lung injury induced by LPS. Endogenous and exogenous H2S provided protection against the lung injuries, which might be explained by its anti-oxidative effects, attenuating inflammatory over-reaction in lung induced by PMN,the downregulation NO/iNOS system and the upregulation of CO/HO-1 system.