Combined Administration of Metformin and Amprolium to Rats Affects Metabolism of Free Amino Acids in the Brain, Altering Behavior, and Heart Rate

The risk of developing diabetes and cardiometabolic disorders is associated with increased levels of alpha-aminoadipic acid and disturbances in the metabolism of branched-chain amino acids. The side effects of the widely used antidiabetic drug metformin include impaired degradation of branched-chain amino acids and inhibition of intracellular thiamin transport. These effects may be interconnected, as thiamine deficiency impairs the functioning of thiamine diphosphate (ThDP)-dependent dehydrogenases of 2-oxo acids involved in amino acids degradation, while diabetes is often associated with perturbed thiamine status. In this work, we investigate the action of metformin in rats with impaired thiamine availability. The reduction in the thiamine influx is induced by simultaneous administration of the thiamine transporters inhibitors metformin and amprolium. After 24 days of combined metformin/amprolium administration, no significant changes in the total brain levels of ThDP or activities of ThDP-dependent enzymes of central metabolism are observed, but the affinities of transketolase and 2-oxoglutarate dehydrogenase to ThDP increase. The treatment also significantly elevates the brain levels of free amino acids and ammonia, reduces the antioxidant defense, and alters the sympathetic/parasympathetic regulation, which is evident from changes in the ECG and behavioral parameters. Strong positive correlations between brain ThDP levels and contents of ammonia, glutathione disulfide, alpha-aminoadipate, glycine, citrulline, and ethanolamine are observed in the metformin/amprolium-treated rats, but not in the control animals. Analysis of the obtained data points to a switch in the metabolic impact of ThDP from the antioxidant and nitrogen-sparing in the control rats to the pro-oxidant and hyperammonemic in the metformin/amprolium-treated rats. As a result, metformin administration along with the amprolium-reduced thiamine supply significantly perturb the metabolism of amino acids in the rat brain, altering behavioral and ECG parameters.