Regulation of GLUT4 translocation in an in vitro cell model using postprandial human serum ex vivo.

NEW FINDINGS: What is the research question? This study employed a novel experimental model in which culture media is conditioned with human serum ex vivo to investigate nutrient-mediated regulation of GLUT4 translocation in skeletal muscle cells in vitro. What is the main finding and importance? Human serum stimulated GLUT4 translocation, an effect differentially modulated by whether the culture media is conditioned with fasted serum, or serum collected after feeding of intact or hydrolysed whey protein. Conditioning cell culture media with human serum ex vivo represents a new approach to elucidate the effects of ingesting specific nutrients on skeletal muscle cell metabolism.

ABSTRACT: Aim : Individual amino acids (AA), AA mixtures and protein hydrolysates stimulate glucose uptake in multiple experimental models. To better replicate in vitro the dynamic postprandial response to feeding in vivo, the current study investigated the effects of culture media conditioned with fasted and postprandial human serum on GLUT4 translocation in L6-GLUT4myc myotubes.

METHODS: Serum samples were collected from healthy male participants (n = 8) at baseline (T0), 60 (T60) and 120 min (T120) after the ingestion of 0.33 g·kg BM-1 of intact (WPC) or hydrolysed (WPH) whey protein, and an isonitrogenous non-essential amino acid control (NEAA). L6-GLUT4myc myotubes were serum- and AA-starved for 1 h prior to 1 h incubation in media containing 1% postprandial human serum after which GLUT4 translocation was determined via colorimetric assay.

RESULTS: Media conditioned with fasted human serum at concentrations of 5-20% increases cell surface GLUT4myc abundance. Incubation with serum collected following the ingestion of WPH increased cell surface GLUT4myc at T60 relative to T0 [mean (lower, upper 95% CI); 1.13 (1.05, 1.22)], whereas WPC [0.98 (0.90, 1.07)] or NEAA [1.02 (0.94, 1.11)] did not. The differential increases in cell surface GLUT4myc abundance were not explained by differences in serum concentrations of total, essential, and branched chain amino acids, or insulin, GLP-1, and GIP.

CONCLUSION: Using a novel ex vivo/in vitro approach, cell culture media conditioned with postprandial serum following the ingestion of a whey protein hydrolysate increased GLUT4 translocation in skeletal muscle cells. This article is protected by copyright. All rights reserved.