Direct effect of branched‐chain amino acids on the growth and metabolism of cultured human hepatocellular carcinoma cells

Abstract

Little is known about the influence of amino acid imbalance by supplementation of branched‐chain amino acids (BCAAs) on human hepatocellular carcinoma (HCC). We investigated the effect of various BCAA concentrations in culture medium on the growth and metabolism of two human HCC cell lines: Hep G2 and KYN‐1. DNA and protein syntheses were studied by radiolabeled thymidine and leucine uptake. Amino acid concentrations in cell and medium were measured with an amino acid analyzer. Expression and excretion of transforming growth factor (TGF)‐α and TGF‐β1 were studied by immunostaining and enzyme‐linked immunosorbent assay methods. The cell growth was suppressed in media with higher and lower BCAA concentrations than Dulbecco ‘s modified Eagle's medium, and this was grossly correlated with the incorporation of [3H] thy mi‐dine into DNA and incorporation of [3H]leucine into intra‐cellular protein. Pretreatment with 10,000 nmol/ml of BCAA did not suppress the cell growth in subsequent culture in the standard Dulbecco's modified Eagle's medium, indicating that the effect of BCAAs was not cytocidal but cytostatic and reversible. BCAA and aromatic amino acid concentrations in cells increased in parallel as the BCAA level in medium was increased, despite the fixed aromatic amino acid level. Intracellular expression and extracellular excretion of TGF‐a were higher at BCAA concentrations of 100 and 1,000 nmol/ml than at 10 or 1,000 nmol/ml. The present finding that the in vitro growth of HCC can be suppressed by enriched BCAA levels in medium may indicate that amino acid‐imbalanced therapy with enriched BCAAs is useful in the treatment of HCC.