Liposomal methemoglobin as a potent antidote for hydrogen sulfide poisoning.

Hydrogen sulfide (HS) induces acute and lethal toxicity at high concentrations. However, no specific antidotes for HS poisoning have been approved. Liposomal methemoglobin (metHb@Lipo) was developed as an antidote for cyanide poisoning. As the toxic mechanism of HS poisoning is the same as that of cyanide poisoning, metHb@Lipo could potentially be used as an antidote for HS poisoning. In this study, we evaluated the antidotal efficacy of metHb@Lipo against HS poisoning. Stopped-flow rapid-scan spectrophotometry clearly showed that metHb@Lipo scavenged HS rapidly. Additionally, metHb@Lipo showed cytoprotective effects against HS exposure in H9c2 cells by maintaining mitochondrial function. MetHb@Lipo treatment also improved the survival rate after HS exposure in vivo, with the maintenance of cytochrome c oxidase activity and suppression of metabolic acidosis. Moreover, metHb@Lipo therapy maintained significant antidotal efficacy even after 1-year-storage at 4-37 °C. In conclusion, metHb@Lipo is a candidate antidote for HS poisoning.