Toxic actions of dinoseb in medaka ( Oryzias latipes) embryos as determined by in vivo 31P NMR, HPLC-UV and 1H NMR metabolomics

Abstract

Changes in metabolism of Japanese medaka ( Oryzias latipes) embryos exposed to dinoseb (2- sec-butyl-4,6-dinitrophenol), a substituted dinitrophenol herbicide, were determined by in vivo 31P NMR, high-pressure liquid chromatography (HPLC)-UV, and 1H NMR metabolomics. ATP and phosphocreatine (PCr) metabolism were characterized within intact embryos by in vivo 31P NMR; concentrations of ATP, GTP, ADP, GDP, AMP and PCr were determined by HPLC-UV; and changes in numerous polar metabolites were characterized by 1H NMR-based metabolomics. Rangefinding exposures determined two sublethal doses of dinoseb, 50 and 75 ppb, in which embryos survived from 1-day post fertilization (DPF) through the duration of embryogenesis. In vivo 31P NMR data were acquired from 900 embryos in 0, 50, and 75 ppb dinoseb at 14, 62, and 110 h ( n = 6 groups) after initiation of exposure. After 110 h, embryos were observed for normal development and hatching success, then either preserved in 10% formalin for growth analysis or flash frozen and extracted for HPLC-UV and 1H NMR analysis. Dinoseb exposure at both concentrations resulted in significant declines in [ATP] and [PCr] at 110 h as measured by in vivo 31P NMR ( p < 0.01), HPLC-UV ( p < 0.001) and NMR-based metabolomics. Reduced eye growth and diminished heart rate occurred in a concentration-dependent fashion. Metabolic effects measured by in vivo 31P NMR showed a significant increase in orthophosphate levels (P i; p < 0.05), and significant decreases in [ATP], [PCr] and the PCr/P i ratio ( p < 0.05). Metabolomics revealed a dose–response relationship between dinoseb and endogenous metabolite changes, with both dinoseb concentrations producing significantly different metabolic profiles from controls ( p < 0.05). Metabolic changes included decreased concentrations of ATP, PCr, alanine and tyrosine, and increased concentrations of lactate with medaka embryotoxicity. This study demonstrated that medaka embryos respond to dinoseb with significant changes in metabolism, reduced growth and heart rates, and increased abnormal development and post-exposure mortality. All three analytical methods confirmed similar trends, and utilization of PCr to compensate for ATP loss was found to be a consistent indicator of sublethal stress—one that could be used to quantify stress associated with medaka embryotoxicity.