Verification of Lactobacillus brevis tolerance to simulated gastric juice and the potential effects of postbiotic gamma-aminobutyric acid in streptozotocin-induced diabetic mice

The therapeutic effect of gamma-aminobutyric acid (GABA) on diabetes was spread as one of the alarming epidemics worldwide. The study aims to investigate the function of Lactobacillus brevis KLDS1.0727 and KLDS1.0373 strains as glutamic acid decarboxylase 65 (GAD65) carriers capable of generating GABA by comparing in vitro free and freeze-dried models and GABA intervention in vivo. PCR amplification of gad and in vitro i.e., (growth rate, viability at different pH, bile tolerance, and survivability in simulated gastric juice) were performed. In vivo experiments were conducted in 7 groups of C57BL/6J mice. Each group was injected with streptozotocin (ContSTZ, INSSTZ, LAC1STZ, LAC1MFDSTZ, LAC2STZ, LAC2MFDSTZ) daily except for the control (Cont). One group was injected with insulin (INSSTZ). The body weight and hyperglycemia in the blood were assessed weekly, post-euthanasia blood plasma parameters, insulin, and histological examination were evaluated. Results indicated L. brevis strains demonstrated a great tolerance to bile and simulated gastric juice in vitro (P < 0.05). ContSTZ had the highest average glucose level (6.84 ± 6.46) mmol/L while INSSTZ expressed dramatically decreed in glucose level and displayed a significant decline in the average of weekly blood glucose (−5.74 ± 3.08) mmol/L. The lowest body weight (ContSTZ) was (19.30 ± 0.25) g. Based on the blood plasma analysis, L. brevis strains improved good cholesterol properties, liver and kidney functions, where most of these parameters fall within the average the reference range and prevent the development of symptoms of type 1 diabetes in vivo. As recommended, L. brevis should be commonly distributed as a postbiotic GABA in pharmaceutical and nutritional applications.