Serum Tricarboxylic Acid Cycle Intermediates: Potential Biomarker for Hyperammonemic Metabolic Dysregulation in Human Cirrhosis

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Introduction. Hyperammonemia is a consistent abnormality in cirrhosis and the skeletal muscle functions as a metabolic partner in ammonia disposal in liver disease. Skeletal muscle ammonia disposal is mediated by conversion of a-ketoglutarate (aKG) a critical intermediate in the tricarboxylic acid (TCA) cycle to glutamate and glutamine. We have previously reported low skeletal muscle TCA cycle intermediates during hyperammonemia. Since TCA cycle intermediates can leak into the circulation, we hypothesized that plasma TCA cycle intermediates will be lower in cirrhosis. We also hypothesized that branched chain amino acids (BCAA) that serve as anaplerotic (entry of TCA cycle intermediates) substrates will reverse this abnormality. Materials and Methods. In 6 well compensated, stable alcoholic cirrhotic patients and 8 controls, serial plasma samples were obtained before and 1h, 3h, 6h after a single oral BCAA mixture enriched with leucine (BCAA/ Leu). Intermediary metabolites extracted using ethyl acetate and Tertbutyldimethylsilyl derivatives generated and quantified by gas chromatography-mass spectrometry using protocols established in our laboratory. All experiments were performed in at least 6 experimental replicates for each sample and the data expressed as percentage mean±SD after normalization with the concentration of control. Results. Surprisingly, plasma concentrations of all TCA cycle intermediates in cirrhotic patients were consistently higher at baseline and remained elevated at 1h, 3h, and 6h after a single oral BCAA mixture enriched with leucine (BCAA/Leu) compared to controls (Table). Conclusion. Elevated plasma TCA cycle intermediates are potential biomarkers for metabolic perturbations in cirrhosis. Identifying the molecular and biochemical mechanisms for elevated plasma TCA cycle intermediates, lack of response to BCAA/Leu and the source of intermediates in circulation will be necessary to restore anaplerosis/cataplerosis homeostasis in cirrhosis.


Poster Abstract #751 presented at the 68th Annual Meeting of the American Association for the Study of Liver Diseases (AASLD).