Royal jelly (RJ) intake lowers serum
cholesterol levels in animals and humans, but the active component in RJ that lowers serum
cholesterol level and its molecular mechanism are unclear. In this study, we set out to identify the
bile acid-
binding protein contained in RJ, because dietary
bile acid-binding proteins including
soybean protein and its
peptide are effective in ameliorating
hypercholesterolemia. Using a
cholic acid-conjugated column, we separated some
bile acid-binding proteins from RJ and identified the major RJ
protein 1 (MRJP1), MRJP2, and MRJP3 as novel
bile acid-binding proteins from RJ, based on matrix-assisted
laser desorption ionization time-of-flight mass spectrometry. Purified MRJP1, which is the most abundant
protein of the
bile acid-binding proteins in RJ, exhibited
taurocholate-binding activity in vitro. The micellar solubility of
cholesterol was significantly decreased in the presence of MRJP1 compared with
casein in vitro. Liver
bile acids levels were significantly increased, and
cholesterol 7α-hydroxylase (CYP7A1)
mRNA and
protein tended to increase by MRJP1 feeding compared with the control. CYP7A1
mRNA and
protein levels were significantly increased by MRJP1 tryptic hydrolysate treatment compared with that of
casein tryptic hydrolysate in hepatocytes. MRJP1 hypocholesterolemic effect has been investigated in rats. The
cholesterol-lowering action induced by MRJP1 occurs because MRJP1 interacts with
bile acids induces a significant increase in fecal
bile acids excretion and a tendency to increase in fecal
cholesterol excretion and also enhances the hepatic
cholesterol catabolism. We have identified, for the first time, a novel hypocholesterolemic
protein, MRJP1, in RJ. Interestingly, MRJP1 exhibits greater hypocholesterolemic activity than the medicine β-
sitosterol in rats.