Acute lung injury (ALI) is still a leading cause of morbidity and mortality in
critically ill patients. Inhaled
nitric oxide (NO) has been reported to ameliorate ALI. However,
reactive nitrogen species produced by NO can cause
lung injury. Because
hydrogen gas (H2) is reported to eliminate
peroxynitrite, it is expected to reduce the adverse effects of NO. Moreover, we have found that H2 inhalation can attenuate
lung injury. Therefore, we hypothesized that combination
therapy with NO and H2 might afford more potent therapeutic strategies for ALI. In the present study, a mouse model of ALI was induced by intratracheal administration of
lipopolysaccharide (LPS). The animals were treated with inhaled NO (20 ppm), H2 (2%), or NO + H2, starting 5 min after LPS administration for 3 h. We found that LPS-challenged mice exhibited significant
lung injury characterized by the deterioration of histopathology and histologic scores, wet-to-dry weight ratio, and oxygenation index (ratio of
oxygen tension to inspired
oxygen fraction [Pao2/Fio2]), as well as total
protein in the bronchoalveolar lavage fluid (BALF), which was attenuated by NO or H2 treatment alone. Combination
therapy with NO and H2 had a more beneficial effect with significant interaction between the two. While the
nitrotyrosine level in lung tissue was prominent after NO inhalation alone, it was significantly eliminated after breathing a mixture of NO with H2. Furthermore, NO or H2 treatment alone markedly attenuated LPS-induced lung neutrophil recruitment and
inflammation, as evidenced by downregulation of lung
myeloperoxidase activity, total cells, and polymorphonuclear neutrophils in BALF, as well as proinflammatory
cytokines (
tumor necrosis factor α,
interleukins 1β and 6, and high-mobility group box 1) and
chemokines (keratinocyte-derived
chemokine,
macrophage inflammatory proteins 1α and 2, and
monocyte chemoattractant protein 1) in BALF. Combination
therapy with NO and H2 had a more beneficial effect against lung inflammatory response. Moreover, combination
therapy with NO and H2 could more effectively inhibit LPS-induced pulmonary early and late nuclear factor κB activation as well as pulmonary cell apoptosis. In addition, combination treatment with inhaled NO and H2 could also significantly attenuate
lung injury in polymicrobial
sepsis. Combination
therapy with subthreshold concentrations of NO and H2 still had a significantly beneficial effect against
lung injury induced by LPS and polymicrobial
sepsis. Collectively, these results demonstrate that combination
therapy with NO and H2 provides enhanced therapeutic efficacy for ALI.