Comparative NMR-Based
Metabonomic Investigation of
the Metabolic Phenotype Associated with Tienilic Acid and Tienilic
Acid Isomer
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Abstract
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