The changes in free and peptide form of amino acid concentration in plasma of NAFLD prevention rat by oral administration of brown rice

Although the number of patients with non-alcoholic fatty liver disease (NAFLD) is increasing globally, a comprehensive treatment strategy has not been established. Therefore, it is important to prevent the development of NAFLD through dietary habits. In our previous study, feeding brown rice to Zucker fatty rats for 10 weeks prevented NAFLD and suppressed the accumulation of lipid droplets in the liver. The objective of this study was to identify the active component for elucidation the mechanisms of NAFLD preventation by brown rice. We focused on rice-derived protein components and examined the changes in free and peptide forms of amino acids in the blood of rats fed a diet with brown rice or rice bran. Zucker fatty rats (7-week-old males) were fed AIN-93G (control) or AIN-93G containing white rice (WR), brown rice (BR), or bran for 10 weeks. Analyses of free and peptide forms of amino acids in rat plasma were conducted by high-performance liquid chromatography introduced with phenylisothiocyanate derivatization. The free Val concentration in rat blood samples from the WR, BR, and bran groups decreased to 73%, 58%, and 15%, respectively, of the concentration in the control group, which developed NAFLD. No significant changes in peptide-form amino acids between groups indicated that the peptides derived from BR or bran may have already been metabolized, and no trace remained in the blood after administration. Therefore, we examined the free and peptide forms of amino acids in rat plasma 30 and 45 min after the administration of rice protein prepared from defatted bran as a byproduct of rice oil. The concentrations of all peptide-form amino acids increased, with Gly (0.80 μmol/mL) showing the highest concentration. These results show that peptides containing Gly may be one of the active components responsible for the prevention of NAFLD development.