Energy metabolism profile of the effects of amino acid treatment on hepatocytes: Phenylalanine and phenylpyruvate inhibit glycolysis of hepatocytes

Amino acids are not only the building blocks of proteins, but also can be metabolized to energy substances or function as signaling molecules. The aim of this study was to profile whether amino acid treatment (essential amino acids and alanine) affects the energy metabolism (glycolysis, mitochondrial respiration) of cultured hepatocytes. AML12 hepatocytes were treated with 5 mM of each amino acid for 1 h and the energy metabolism was then measured by using an extracellular flux analyzer. The results showed that phenylalanine and lysine decreased the extracellular acidification rate (ECAR), an indirect indicator of glycolysis, whereas isoleucine and histidine increased the ECAR. Amino acids did not affect the oxygen consumption rate, an indirect indicator of mitochondrial respiration. The glycolysis stress test revealed that treatment of the hepatocytes with phenylalanine inhibited glycolysis when the concentration of the substrate for glycolysis was sufficient in cultured media. We also investigated the effect of metabolites derived from conversion of phenylalanine on glycolysis in hepatocytes and found that phenylpyruvate inhibited glycolysis, whereas tyrosine and phenylethylamine did not affect glycolysis. The findings from the present study complement basic knowledge of the effects of amino acid treatment on energy metabolism in cultured hepatocytes and indicate that phenylalanine and phenylpyruvate inhibit glycolysis.