iTRAQ-based proteomic analysis reveals alterations in the liver induced by restricted meal frequency in a pig model

Objective: The present study was conducted to investigate the effects of meal frequency on metabolite levels in pig plasma and hepatic proteome by isobaric tags for relative and absolute quantitation (iTRAQ) analysis. Methods: Twenty-four pigs (60.7 +/- 1.0 kg) consumed the same amount of feed either in 2 (M2, n = 12) or 12 (M12, n = 12) meals per day. After an 8-wk feeding period, plasma concentrations of metabolites and hormones, hepatic biochemical traits, and proteome (n = 4 per group) were measured. Results: Pigs on the M12 regimen had lower average daily gain and gain-to-feed ratio than pigs fed the M2 regimen. The M2 regimen resulted in lower total lipid, glycogen, and triacylglycerol content in the liver and circulating triacylglycerol concentration than that in the M12 pigs. The metabolic hormone concentrations were not affected by meal frequency, with the exception of elevated fibroblast growth factor 21 concentrations in the M2 regimen compared with the M12 regimen. The iTRAQ-based proteomic analysis revealed 35 differentially expressed proteins in the liver between pigs fed two and 12 meals per day, and these differentially expressed proteins were involved in the regulation of general biological process such as glucose and energy metabolism, lipid metabolism, protein and amino acid metabolism, stress response, and cell redox homeostasis. Conclusion: Altogether, the proteomic results provide insights into the mechanism mediating the beneficial effects of restricted meal frequency on the metabolic fitness. (C) 2016 Elsevier Inc. All rights reserved.