Metabolomic Profiles of Siberian Wood Frog Rana amurensis in Hypoxia and Upon Reoxygenation

Hypoxia poses a serious challenge for all animals; however, certain animals exhibit a remarkable resilience in the case of prolonged and severe hypoxia. The Siberian wood frog Rana amurensis is a unique amphibian capable of surviving for up to several months at almost complete anoxia. We investigated changes in the metabolome of R. amurensis at the onset of hypoxia (day 1) and within 1 h of reoxygenation after a long-term hypoxia using ¹H NMR. We compared our results to the data obtained for animals exposed to 17 days of hypoxia and controls. Despite the differences between the samples analyzed in three different experimental series, we were able to obtain some interesting insights. In most studied vertebrates, succinate accumulates under hypoxic conditions and undergoes rapid conversion upon reoxygenation. We found that reoxygenation caused a decrease in the succinate content in the brain, but not in the liver, where it remained unchanged, suggesting an existence of a mechanism that inhibits succinate conversion. Furthermore, we observed intriguing differences in the behavior of two substances with unknown functions: glycerol and 2,3-butanediol. Glycerol exhibited rapid accumulation during hypoxia and equally rapid processing during reoxygenation. In contrast, 2,3-butanediol required an extended period of time to accumulate, yet persisted after reoxygenation. Overall, our data demonstrate rapid accumulation of most substances during exposure to hypoxia followed by their slower processing upon reoxygenation.