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Numerous xenobiotics are toxic to human and animal cells by interacting with their metabolism, but the precise metabolic step affected and the biochemical mechanism behind such a toxicity remain often unknown. In an attempt to reduce the ignorance in this field, we have developed a new approach called cellular metabolomics. This approach, developed in vitro, provides a panoramic view not only of the pathways involved in the metabolism of physiological substrates of any normal or pathological human or animal cell but also of the beneficial and adverse effects of xenobiotics on these metabolic pathways. Unlike many cell lines, precision-cut tissue slices, for which there is a renewed interest, remain metabolically differentiated for at least 24-48 h and allow to study the effect of xenobiotics during short-term and long-term incubations. Cellular metabolomics (or metabolic flux analysis), which combines enzymatic and carbon 13 NMR measurements with mathematical modeling of metabolic pathways, is illustrated in this brief chapter for studying the effect of insulin on glucose metabolism in rat liver precision-cut slices and of valproate on glutamine metabolism in human renal cortical precision-cut slices. The use of very small amounts of test compounds allows to predict their toxic effect and eventually their beneficial effects very early in the research and development processes. Cellular metabolomics is complementary to other omics approaches, but, unlike them, provides functional, mechanistic, and dynamic pieces of information by measuring enzymatic fluxes.

Sodium valproate is a drug widely used for the treatment of epilepsy and mood disorders. We studied the effect of valproate on cerebral energy metabolism by incubating rat brain slices with 5 mM [3-(13)C]glutamate in the absence and the presence of 1 mM valproate. Substrate removal and product formation were measured by enzymatic and carbon 13 NMR methods. Fluxes through the enzymatic steps involved were calculated with an original mathematical model. We demonstrate that, in the presence of valproate, glutamate consumption and aspartate accumulation and labeling were inhibited, whereas GABA accumulation and labeling were increased. Consistent with these observations, this drug inhibited the unidirectional flux from glutamate to α-ketoglutarate and fluxes through several enzymes (gamma aminobutyric acid aminotransferase, α-ketoglutarate dehydrogenase, succinate dehydrogenase, malate dehydrogenase, aspartate aminotransferase, malic enzyme, pyruvate dehydrogenase, pyruvate carboxylase and citrate synthase). By contrast, glutamic acid decarboxylase flux was increased. With 2 mM glutamate+1 mM valproate and with 5 mM glutamate+2 mM valproate, GABA and aspartate labelings were similarly altered. On the basis of the effects of valproate, it is concluded that our cellular model and our cellular metabolomic approach appear suitable to study the beneficial and adverse interactions of neurotropic compounds with the cerebral metabolic pathways., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Numerous xenobiotics are toxic to human and animal cells by interacting with their metabolism, but the precise metabolic step affected and the biochemical mechanism behind such a toxicity often remain unknown. In an attempt to reduce the ignorance in this field, we have developed a new approach called cellular metabolomics. This approach, developed in vitro, provides a panoramic view not only of the pathways involved in the metabolism of physiologic substrates of any normal or pathologic human or animal cell but also of the beneficial and adverse effects of xenobiotics on these metabolic pathways. Unlike many cell lines, precision-cut tissue slices, for which there is a renewed interest, remain metabolically differentiated for at least 24-48 h and allow to study the effect of xenobiotics during short-term and long-term incubations. Cellular metabolomics (or cellular metabonomics), which combines enzymatic and carbon 13 NMR measurements with mathematical modeling of metabolic pathways, is illustrated in this brief chapter for studying the effect of insulin on glucose metabolism in rat liver precision-cut slices, and of valproate on glutamine metabolism in human renal cortical precision-cut slices. The use of very small amounts of test compounds allows to predict their toxic effect and eventually their beneficial effects very early in the research and development processes. Cellular metabolomics is complementary to other omics approaches, but, unlike them, provides functional and dynamic pieces of information by measuring enzymatic fluxes.