Effects of amino acid transport limitations on cultured hepatocytes.

Amino acid supplementation has been shown to enhance the liver-specific functions of cultured hepatocytes during plasma exposure. However, their transport through the cell membrane may restrict their availability for hepatic metabolism. Here, we focus on transport constraints related to uptake of the neutral amino acids and their impact on hepatic metabolism and liver-specific functions. Under varying combinations of their medium concentrations, we found that transport competition exists among the three amino acids alanine, serine and glutamine and that the resulting capacity constraints affect the urea and albumin production of cultured hepatocytes. Regression equations were developed to quantify these constraints and were incorporated with other constraints (mass balance, measured flux data and reaction directionality) within a multi-objective flux balance framework to understand how amino acid transport constraints propagate through central hepatic metabolism and to predict refined amino acid supplementations for specific hepatocyte design objectives.