Effects of poly-gamma-glutamic acid on serum and brain concentrations of glutamate and GABA in diet-induced obese rats

Abstract

Poly-gamma-glutamic acid (gamma-PGA) is a mucilaginous and biodegradable compound produced by Bacillus subtilis from fermented soybeans, and is found in the traditional Korean soy product, cheongkukjang. This study was carried out to evaluate the effects of gamma-PGA from a food source on the concentration of the neurotransmitter GABA and its metabolic precursor glutamate in diet-induced obese rats. Eight-week old male Sprague-Dawley rats (n=60) were used. The rats were divided into two groups and obesity was induced by providing either a 10% control fat or 45% high fat diet for 5 weeks. The rats were then blocked into 6 groups and supplemented with a 0.1% gamma-PGA diet for 4 weeks. After sacrifice, brain and serum GABA and glutamate concentrations were analyzed by high performance liquid chromatography with fluorometric detection. The rats fed the high fat diet had significantly increased body weights. gamma-PGA supplementation significantly increased serum concentrations of glutamate and GABA in the control fat diet groups while this effect was not found in the high fat groups. In the brain, glutamate concentrations were significantly higher in the gamma-PGA supplemented groups both in rats fed the normal and high fat diets than in the no gamma-PGA controls. GABA concentrations showed the same tendency. The results indicated that gamma-PGA intake increased GABA concentrations in the serum and brain. However, the effects were not shown in obese rats.

Keywords: Poly-gamma-glutamic acid (γ-PGA); glutamate; γ-aminobutyric acid (GABA).

Fig. 1

Changes of body weight during the experimental period. CC: 10% fat control, CP: 10% fat with γ-PGA, HC: High fat control, HP: High fat with γ-PGA, HCC: 45% to 10% fat control, HCP: 45% to 10% fat with γ-PGA. All points represent means, n=10 rats per group. Different letters in the same week indicate significantly different values assessed by Duncan's multiple range test (P < 0.05).

Fig. 2

Chromatograms of NDA derivatives of glutamate and GABA. (A) Standard solution, 10 ug of glutamate (retention time: 3.752 min) and GABA (retention time: 8.338 min) injected onto the column. Conditions as described in the text. (B) Example of a brain sample from a CP group rat showing glutamate (8.8 mg/g tissue) and GABA (1.6 mg/g tissue).

Fig. 3

Chromatograms of OPA derivatives of glutamate and GABA. (A) Standard solution, 10 ug of glutamate (retention time: 1.833 min) and GABA (retention time: 2.478 min) injected onto the column. Conditions as described in the text. (B) Example of a serum sample from a CP group rat showing glutamate (9.8 ug/ml) and GABA (60.4 ug/ml).