Research Article: Whey Protein Hydrolysate Increases Translocation of GLUT-4 to the Plasma Membrane Independent of Insulin in Wistar Rats

Date Published: August 30, 2013

Publisher: Public Library of Science

Author(s): Priscila Neder Morato, Pablo Christiano Barboza Lollo, Carolina Soares Moura, Thiago Martins Batista, Rafael Ludemann Camargo, Everardo Magalhães Carneiro, Jaime Amaya-Farfan, Angel Nadal.

http://doi.org/10.1371/journal.pone.0071134

Abstract

Whey protein (WP) and whey protein hydrolysate (WPH) have the recognized capacity to increase glycogen stores. The objective of this study was to verify if consuming WP and WPH could also increase the concentration of the glucose transporters GLUT-1 and GLUT-4 in the plasma membrane (PM) of the muscle cells of sedentary and exercised animals. Forty-eight Wistar rats were divided into 6 groups (n = 8 per group), were treated and fed with experimental diets for 9 days as follows: a) control casein (CAS); b) WP; c) WPH; d) CAS exercised; e) WP exercised; and f) WPH exercised. After the experimental period, the animals were sacrificed, muscle GLUT-1 and GLUT-4, p85, Akt and phosphorylated Akt were analyzed by western blotting, and the glycogen, blood amino acids, insulin levels and biochemical health indicators were analyzed using standard methods. Consumption of WPH significantly increased the concentrations of GLUT-4 in the PM and glycogen, whereas the GLUT-1 and insulin levels and the health indicators showed no alterations. The physical exercise associated with consumption of WPH had favorable effects on glucose transport into muscle. These results should encourage new studies dealing with the potential of both WP and WPH for the treatment or prevention of type II diabetes, a disease in which there is reduced translocation of GLUT-4 to the plasma membrane.

Partial Text

Different food proteins may affect muscle metabolism in different fashions, as shown when the effects of whey proteins (WP) are compared to those of casein (CAS) [1]–[3]. One difference between WP and CAS is that WP stimulates an increase of fatty acid synthesis in the muscle accompanied by a concomitant decrease in fatty acid synthesis in the liver, considered to be a positive effect on lipid metabolism [4]. Hydrolysis of the protein alone could alter the biological function of the protein, thus affecting the metabolism [5]. For example, it has been suggested that a slight change in the physicochemical form of the protein when presented to the animal can be enough to influence the general metabolism, apparently as a result of the various peptides that are generated during partial enzymatic hydrolysis of whey proteins (WPH) [3], [6]–[8]. The bioactive peptides present in WPH might be capable of reducing the levels of creatine kinase in soccer players [9].

Forty-eight male Wistar rats (∼150 g; n = 8 per group) were divided into sedentary and exercised groups, and each group was fed casein (CAS, control), whey protein (WP) or whey protein hydrolysate (WPH) as their dietary protein source for a total of 9 days. All the animals were fasted overnight to arrive at similar glycogen reserves, but two hours before sacrifice, each received 2 g of the appropriate experimental diet (Figure 1). Food consumption was determined every other day, and body mass was monitored weekly. When the animals reached ∼150 g, they were randomly assigned to groups and body mass gain was checked after one week. The research methodology was approved by the Ethics Committee on Animal Experimentation (CEEA-UNICAMP, protocol 2376-1/2011).

The consumption of whey protein (WP) and whey protein hydrolysate (WPH) for 9 days resulted in a significant increase (p<0.05) in GLUT-4 translocation to the plasma membrane (Figure 2A). It was evident that exercise had a magnifying effect on translocation for all food proteins, but particularly for the whey proteins. Phosphorylation of Akt at serine 473 (Figure 2E) was increased (p<0.05) by the consumption of whey protein hydrolysate in both groups, sedentary and exercised, whereas there was no difference in the serum insulin concentrations between the control group (CAS, with casein as dietary protein) and the WPH group. However, the consumption of WPH also increased glycogen concentrations in the heart, skeletal muscle and liver (Figure 2G–I). Based on previous findings by the present [3], [7], [8] and other [10], [23] authors clearly showing that the consumption of WP and WPH raised muscle and hepatic glycogen levels, the objective of the present study was to verify the effect that the consumption of WP and WPH had on the translocation of the glucose transporters GLUT-4 and GLUT-1 to the plasma membrane (PM), as compared to rats fed a standard diet (AIN93-G) with casein as the protein source. The results showed clearly that the consumption of WP and WPH increased the translocation of GLUT-4 (Figure 2A) when compared to the casein-fed animals, whereas GLUT-1 (Figure 2B) was not responsive to the different proteins. This increase in GLUT-4 in the PM was consistent with increases in glycogen (Figure 2G–I) because with more glucose transporters in the cell PM, the availability of glucose and synthesis of glycogen could both increase. Physical exercise is known to increase the potential for the translocation of GLUT-4 to the membrane [16], [24], and for all diets, the exercised animals demonstrated higher levels of GLUT-4 in the PM.   Source: http://doi.org/10.1371/journal.pone.0071134