Abstract

Steamed red rice has been served in local religious ceremonies in Japan and is mainly consumed in Asian countries. However, only a few detailed chemical and biological studies have been performed on red rice to date. The present study aimed to clarify the chemical structure of red pigment and examined its effects on lipid metabolism, such as hepatic β-oxidation, in mice. The results obtained showed that red pigment up-regulated the mRNA expression of enzymes involved in lipid metabolism, such as acyl CoA oxidase 1 (ACOX-1), peroxisome proliferator-activated receptor β (PPAR β), and AMP-activated protein kinase (AMPK), which decompose fatty acids. Furthermore, the redcolored extract was fractionated by ACOX-1-enhancing activity to provide the proanthocyanidins involved in cytosolic β-oxidation. Spectroscopic data on proanthocyanidins revealed detailed characteristic structures, including 3- to 10- mer polymerization, a 3,4-cis configuration, more C4-C8 than C4-C6 linkages, and the existence of a B-ring bearing three hydroxy groups with/without a methyl moiety. In conclusion, red rice bran comprising proanthocyanidins has potential in the treatment of fatty liver and hyperlipidemia.

Keywords: Red rice bran; Proanthocyanidin; β -oxidation; ACOX-1