Dietary l-lysine supplementation altered the content of pancreatic polypeptide, enzymes involved in glutamine metabolism, and β-actin in rats

Abstract

This study investigated the effects of Lys supplementation on serum pancreatic polypeptide (PP), glutamine (Gln) levels and the expression of PP, Gln synthetase (GlnS), glutaminase (Gls) and β-actin in different tissues such as pancreas, skeletal muscle, liver and kidney in rats. Male Sprague-Dawley rats were fed diets containing 7% casein supplemented with either 0% (Control), 1%, 1.5%, 3% Lys or 3% Lys with 1.5% Arg for a week. All rats were necropsied for collection of blood and tissues. Expression of PP, GlnS, Gls, and β-actin in tissues were determined using Western blotting. The results showed that the rats fed 3% supplemental Lys had significantly lower body weight gain (BWG) and food intake than the ≤ 1.5% Lys groups (P < 0.05). Supplementation with ≥ 1% Lys increased serum PP level (P < 0.05), but had no significant effect on pancreatic PP abundance (P > 0.05). GlnS expression was significantly lowered in skeletal muscle by ≥ 1.5% supplemental Lys compared to the Control (P < 0.05). The expression of Gls in the kidney was increased by the addition of 1.5% Arg to 3% Lys diet (P < 0.05). Liver β-actin significantly increased with both Lys and Arg supplementation and muscle β-actin significantly decreased (P < 0.05) with ≥ 1.5% supplemental Lys. Kidney β-actin significantly increased with Arg supplementation vs 3% Lys alone (P < 0.05). These results showed that dietary supplementation with ≥ 1.5% Lys significantly suppressed GlnS expression in the skeletal muscle, which may contribute to the decreased serum Gln levels, and that increased serum PP by Lys may be due to suppressed catabolism rather than increased synthesis of PP. Lys-induced PP may play a role in reducing food intake and BWG.

Impacts of essential amino acids on energy balance

“…Overall, except for Met [ 104 ] and Val [ 105 ], supplementation with other EAAs has been reported to reduce body weight under certain conditions [ 2 , [106] , [107] , [108] , [109] , [110] , [111] , [112] , [113] , [114] , [115] , [116] , [117] , [118] , [119] ]. However, the results are inconsistent.…”

“…In general, when there are effects of an EAA supplementation on weight loss, the underlying mechanisms could involve decreased food intake and/or increased energy expenditure. Lys [ 106 , 107 ], His [ 108 , 109 ], and Phe [ 110 ] supplementation suppresse food intake. Although excess Leu intake [ [114] , [115] , [116] ] does not affect food intake under HFD, it increases energy expenditure.…”

“…Two mechanisms have been proposed for the effects of Lys supplementation [ 106 , 107 ]. First, the effects of Lys supplementation may be partially a result of intracellular l -arginine (Arg) deficiency, as the addition of Arg could reverse the effects of Lys supplementation on food intake and body weight reduction.…”

“…Second, studies have revealed that Lys supplementation increases the serum levels of pancreatic polypeptide (PP), a hormone mainly produced by the pancreas in response to ingestion of food. Overexpression of PP decreases body weight and food intake [ 107 ]. These indicate that increased PP may mediate the effects of Lys supplementation on hypophagia and weight loss.…”