Combination amino acids and glucose effects on insulin and GLP-1 secretion

Dietary nutrients such as amino acids possess an insulinogenic effect. However, not all amino acids were meticulously investigated for their effect on both insulin and incretin secretion, and the effect of amino acids given in different combinations remained incompletely characterized. In the present work, we reported the quantitative effect of individual and combinatorial amino acids in conjunction with low and high glucose, respectively, on insulin secretion from human islets and on glucagon-like peptide-1 (GLP-1) secretion from secretin tumor cell (STC-1). STC-1 cells were incubated with amino acid treatment solutions individually and in combinations at low and high glucose to investigate GLP-1 secretion. Batches of 15 islets were sequentially treated with 3 mM glucose, combinatorial amino acid treatment solutions at low and high glucose, and finally 25 mM KCl to quantify insulin secretion. Lysine, threonine, tryptophan, phenylalanine, and aspartic acid significantly increased GLP-1 secretion in STC-1 cells compared with negative control. Branched-chain amino acids (BCAAs) stimulated greater GLP-1 secretion only at high glucose and significantly induce insulin secretion in islets even in low glucose. Other amino acid combinations tested were able to augment GLP-1 secretion even in the absence of glucose but failed to further stimulate insulin secretion in human islets when given concurrently at higher glucose concentrations. In conclusion, the findings from our work could be used to infer the expected insulinogenic effect and glycemic response for proteins with different amino acid compositions.