Gas chromatography-mass spectrometry for metabolite profiling of Japanese medaka (Oryzias latipes) juveniles exposed to malathion.

Purpose: We evaluate malathion toxicity to Japanese medaka (Oryzias latipes) juveniles by using a mass spectrometry combined with gas chromatography (GC/MS) metabolomics approach.

Methods: Medaka were exposed to low (L) and high (H) concentrations (nominally 20 and 2,000 μg/L, respectively) of water-borne malathion. Metabolites were extracted from the fish, derivatized, and analyzed by GC/MS. Identified metabolites were subjected to one-way analysis of variance and principal component analysis (PCA). We examined the variations in the amounts of the metabolites during the exposure period.

Results And Discussion: At 24 h, control, L, and H groups were separated along PC1, suggesting that the effects of malathion depended on exposure concentration. The PCA results at 96 h suggest that the metabolite profiles variations of the L and H groups differed, and thus that the effects of malathion in groups differed. At 24 h, the amounts of amino acids in both exposed groups were lower than the control group amounts, perhaps owing to accelerated protein synthesis. At 96 h, the amounts of almost all the amino acids increased in the L group but decreased in the H group relative to the control group amounts, suggesting the proteolysis occurred in the L group while protein synthesis continued in the H group, that the high malathion exposure affected the fish. In addition, at 96 h, gluconeogenesis may have been induced in the L group but not in H group.

Conclusions: Malathion exposure may have altered the balance between protein synthesis and degradation and induced gluconeogenesis in medaka. Our results suggest that metabolomics will be useful for comprehensive evaluation of toxicity.