Both dietary supplementation with monosodium L-glutamate and fat modify circulating and tissue amino acid pools in growing pigs, but with little interactive effect

Abstract

Background: The Chinese population has undergone rapid transition to a high-fat diet. Furthermore, monosodium L-glutamate (MSG) is widely used as a daily food additive in China. Little information is available on the effects of oral MSG and dietary fat supplementation on the amino acid balance in tissues. The present study aimed to determine the effects of both dietary fat and MSG on amino acid metabolism in growing pigs, and to assess any possible interactions between these two nutrients.

Methods and results: Four iso-nitrogenous and iso-caloric diets (basal diet, high fat diet, basal diet with 3% MSG and high fat diet with 3% MSG) were provided to growing pigs. The dietary supplementation with fat and MSG used alone and in combination were found to modify circulating and tissue amino acid pools in growing pigs. Both dietary fat and MSG modified the expression of gene related to amino acid transport in jejunum.

Conclusions: Both dietary fat and MSG clearly influenced amino acid content in tissues but in different ways. Both dietary fat and MSG enhance the absorption of amino acids in jejunum. However, there was little interaction between the effects of dietary fat and MSG.

Figure 1. Dietary fat and MSG supplementation for one month effect the concentrations of serous biochemical parameters in growing pigs (n = 8).

Abbreviation, ALB: Albumin, ALT: Alanine transaminase, AST: Aspartate aminotransferase.

Figure 2. Dietary fat and MSG supplementation changed the express profiles of free AA-sensing genes, T1R1 (A), CaR (B) and GPRC6A (C) (n = 8).

The results were normalized by the expression of β-actin. Abbreviations, T1R1: Taste receptor type 1 member 1, CaR: Ca²⁺-sensing receptor and GPRC6A: G-protein-coupled receptor family C member 6A.

Figure 3. Dietary fat and MSG supplementation changed the express profiles of AA and peptide transporters in intestine: Duodenum (A), Jejunum (B), Ileum (C) and Colon (D) (n = 8).

The results were normalized by β-actin. Abbreviation, EAAC1: Excitatory amino-acid carrier 1, LAT1: L-type AA transporter 1, B⁰⁺: B⁰⁺ AA transporter, ASCT2: ASC-like Na⁺-dependent neutral AA transporter 2 and PEPT1: Intestinal H⁺/peptide co-transporter.