Comparative NMR-based metabonomic investigation of the metabolic phenotype associated with tienilic acid and tienilic acid isomer.

An NMR-based metabonomic approach was applied to study the systems level metabolic effects of two closely related thiophene compounds, tienilic acid (TA) and tienilic acid isomer (TAI). The metabonomic data were anchored with traditional clinical chemistry and histopathologic analyses. TA was removed from the market as a result of suspected immune-mediated hepatotoxicity, whereas TAI is an intrinsic hepatotoxin. Equimolar doses of TA and TAI were administered to Sprague-Dawley rats, and sampling was conducted at 2, 6, and 24 h post-treatment. Histopathologic analyses revealed development of a significant hepatic lesion 24 h post-TAI treatment with a parallel increase in plasma alanine aminotransferase (ALT) activity. In contrast, TA was not associated with the development of a hepatic lesion or an increase in plasma ALT activity. High-resolution NMR spectral metabolic profiles were generated for liver extracts, plasma, and urine at multiple time points. Multivariate statistical tools were applied to model the metabolic profiles and identify discriminatory metabolites that reflected both the adaptation to TA administration and the onset and progression of TAI-induced hepatotoxicity. TAI was shown to induce marked metabolic effects on the metabolome at all time points, with dramatic metabolic perturbations at 24 h post-treatment correlating with the histopathologic and clinical chemistry evidence of a hepatic lesion. The TAI-induced metabolic perturbations provided evidence for the generation of electrophilic reactive metabolites and a significant impairment of bioenergetic metabolic pathways. TA induced early metabolic perturbations that were largely resolved by 24 h post-treatment, suggesting the reestablishment of metabolic homeostasis and the ability to adapt to the intervention, with hepatic hypotaurine potentially representing a means of assessment of hepatic adaptation. This comparative metabonomic approach enabled the discrimination of metabolic perturbations that were common to both treatments and were interpreted as nontoxic thiophene-induced perturbations. Importantly, this approach enabled the identification of temporal metabolic perturbations that were unique to TAI or TA treatment and hence were of relevance to the development of toxicity or the ability to adapt. This approach is applicable to the future study of pharmacologically and structurally similar compounds and represents a refined means of identification of biomarkers of toxicity.