Region-Specific Quantification of 2-Hydroxyglutarate Enantiomers in Murine Brain during Mitochondrial Complex I Deficiency

The <i>Ndufs4</i>^-/- mouse is a model of mitochondrial Complex I deficiency that contributes to altered production of the tricarboxylic acid cycle metabolites. We hypothesized that l-2-hydroxyglutarate (l-2-HG) levels would be elevated in the pathologically affected regions of the <i>Ndufs4</i>^-/- mouse brain in parallel with metabolic acidosis. We employed a stable isotope dilution method for the concurrent quantification of l-lactate and the distinct 2-HG enantiomers in isolated mouse brain regions. While lactate levels were elevated, as expected in the <i>Ndufs4</i>^-/- brain, the levels of l-2-HG and the enantiomer d-2-HG were markedly reduced in a region-specific manner, and this decrease was also reproduced in the <i>Ndufs4</i>^-/- serum. The specific and reproducible decreases in 2-HG quantified in Complex I deficiency may have utility as a unique disease biomarker. Quantitative analysis of the mitochondrial proteome of the <i>Ndufs4</i>^-/- mouse brainstem indicated an increased abundance of l-2-HG dehydrogenase, suggesting that 2-HG enantiomers are metabolized in the <i>Ndufs4</i>^-/- mouse yielding FADH₂ to alleviate the bioenergetic deficit.