MMP9 and acute respiratory distress syndrome: To prove the critical roles of MMP-2 and MMP-9 in H2S-induced ALI, we indicated that the MMP inhibitor DOX obviously attenuated H2S-induced ALI via the direct suppression of MMP-2 and MMP-9, which was consistent with other studies that DOX inhibited the mRNA and protein expression of MMP-2 and MMP-9, and attenuated the symptoms of ALI including aggravating alveolar destruction, neutrophil migration to the airspaces of lung and protein leakage in BAFL [33], [34], [53], [54].