Epigallocatechin gallate changes mRNA expression level of genes involved in cholesterol metabolism in hepatocytes.

Catechins, compounds derived from green tea, have been shown to improve cholesterol metabolism in animal studies, but the molecular mechanisms underlying this function have not been fully understood. We performed DNA microarray analysis in order to clarify the effects of epigallocatechin gallate (EGCG), the dominant catechin in green tea, on cholesterol metabolism in HepG2 hepatocytes. This revealed that the expression levels of several genes related to cholesterol metabolism, including the LDL receptor, were changed by EGCG treatment. Using a real-time PCR technique, we confirmed that EGCG treatment up-regulated mRNA expression level of the LDL receptor. Moreover, EGCG decreased extracellular apoB levels. These findings indicated that EGCG improves cholesterol metabolism through the up-regulation of LDL receptor and also reduces extracellular apoB levels.

Effects of dipeptides having a C-terminal lysine on the cholesterol 7alpha-hydroxylase mRNA level in HepG2 cells.

Inducing expression of the cholesterol-catabolizing enzyme cholesterol 7alpha-hydroxylase (CYP7A1) in the liver can be an effective strategy in preventing hypercholesterolemia and atherosclerosis. We used HepG2 cells to investigate the effects of 1 mM dipeptides having a C-terminal lysine group on the CYP7A1 mRNA level. We found that the dipeptides Asp-Lys, Glu-Lys, and Trp-Lys significantly increased the CYP7A1 mRNA level.

A novel regulatory pathway for cholesterol degradation via lactostatin.

Our group previously discovered a novel hypocholesterolemic pentapeptide (IIAEK: Ile-Ile-Ala-Glu-Lys, or what we describe as "lactostatin") derived from bovine milk beta-lactoglobulin. To clarify the mechanism of the hypocholesterolemic action of lactostatin, we screened the target gene and signal transducing pathway induced by lactostatin in HepG2, a human liver cell line. Unexpectedly, we found that water-soluble lactostatin can activate cholesterol 7alpha-hydroxylase (CYP7A1) gene expression. Treatment with mitogen-activated protein kinase (MAPK) inhibitor or calcium (Ca2+) channel blocker blocked this activation. We also found that lactostatin regulates the phosphorylation of extracellular signal-regulated kinase (ERK) and intracellular Ca2+ concentration. Here, we show the involvement of a new regulatory pathway in the calcium-channel-related MAPK signaling pathway of lactostatin-mediated cholesterol degradation. Oligopeptide shows promise as a new molecule for the development of medicines and functional foods to prevent and improve hypercholesterolemia and atherosclerosis.

A novel protein C-phycocyanin plays a crucial role in the hypocholesterolemic action of Spirulina platensis concentrate in rats.

This study was designed to clarify the mechanisms of the hypocholesterolemic action of Spirulina platensis concentrate (SPC) and identify the novel hypocholesterolemic protein derived from SPC. We investigated the effects of casein or SPC on the solubility of cholesterol, taurocholate binding capacity in vitro, cholesterol absorption in Caco-2 cells, and cholesterol metabolism in rats for 10 d. We also evaluated the effects of SPC, C-phycocyanin (PHY), and PHY residue on cholesterol metabolism in rats fed a high-cholesterol diet for 5 d, and SPC or SPC-acetone extract for 10 d. SPC had a significantly greater bile acid-binding capacity than casein in vitro. Micellar cholesterol solubility and cholesterol uptake by Caco-2 cells was significantly lower in the presence of SPC compared with casein. Fecal excretion of cholesterol and bile acids was significantly greater in rats fed the SPC-supplemented diet than in those fed the casein control diet. Serum and liver cholesterol concentrations were significantly lower in rats fed SPC than in those fed casein. Thus, the hypocholesterolemic action of SPC may involve the inhibition of both jejunal cholesterol absorption and ileal bile acid reabsorption. Although no studies to date have found a hypocholesterolemic protein among the algal proteins, we report here the discovery of a hypocholesterolemic effect in the novel protein C-phycocyanin. This study provides the first direct evidence that PHY, a novel hypocholesterolemic protein derived from Spirulina platensis, can powerfully influence serum cholesterol concentrations and impart a stronger hypocholesterolemic activity than SPC in animals.