Pentapeptide IIAEK ameliorates cholesterol metabolism via the suppression of intestinal cholesterol absorption in mice.

Dietary protein-derived peptides are effective in improving dyslipidemia and hypercholesterolemia. We previously identified a novel cholesterol-lowering pentapeptide IIAEK from milk beta-lactoglobulin. However, it remains unclear whether IIAEK affects the micellar solubility of cholesterol and the bile acid-binding ability to lower cholesterol. Moreover, there is no direct evidence that IIAEK inhibits intestinal cholesterol absorption and affects hepatic cholesterol and fecal steroid excretion in vivo. Herein, we showed that IIAEK did not affect the micellar solubility of cholesterol and the bile acid-binding ability. However, we found that IIAEK decreased serum and liver cholesterol levels and increased fecal steroid excretion in mice. Interestingly, IIAEK markedly suppressed the intestinal absorption of [3H]-cholesterol in mice. In conclusion, we found that IIAEK ameliorated cholesterol metabolism by suppressing intestinal cholesterol absorption without affecting in vitro micellar solubility of cholesterol and the bile acid-binding ability in mice.

Protamine-derived peptide RPR (Arg-Pro-Arg) ameliorates oleic acid-induced lipogenesis via the PepT1 pathway in HepG2 cells.

The protamine-derived peptide arginine-proline-arginine (RPR) can ameliorate lifestyle-related diseases such as obesity and hypercholesterolemia. Thus, we hypothesized that the hypolipidemic activity of RPR could attenuate events leading to non-alcoholic fatty liver disease. Addition of 2 m m oleic acid (OA) to the culture medium induced fatty liver conditions in HepG2 cells. The OA + RPR group showed significantly decreased cellular or medium triglyceride (TG) level compared with the OA group. Stearoyl-CoA desaturase-1 (SCD1) or sterol regulatory element-binding protein 1 (SREBP1) protein level was significantly lower in the OA + RPR group than in the OA group. In the R + P + R amino acid mixture-treated group, the TG level was not significantly different from that in the OA-treated group. The OA + RP- or OA + PR-treated groups showed significantly decreased cellular TG level compared with the OA group. Moreover, the effect of RPR disappeared when the peptide transporter 1 (PepT1) was knocked down with a siRNA. Collectively, our results demonstrated that RPR effectively ameliorated hepatic steatosis in HepG2 cells via the PepT1 pathway.

Eugeniin improves cholesterol metabolism in HepG2 cells and Caco-2 cells.

Considering the absence of prior studies on the cholesterol metabolism-improving effects of eugeniin, the present investigation aimed to explore the potential impact of eugeniin on cholesterol metabolism. This study sought to elucidate the molecular mechanisms involved in this process using HepG2 and Caco-2 cells treated with 5 µm eugeniin. The intracellular cholesterol levels in HepG2 and Caco-2 cells were significantly decreased in the 24-h eugeniin-treated group. The protein and messenger ribonucleic acid (mRNA) levels of the low-density lipoprotein receptor (LDLR) were increased, while 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase protein and mRNA levels were decreased in HepG2 cells 6 h of the eugeniin-treated group. Additionally, LDLR protein and mRNA levels were increased in HepG2 cells after 24 h of eugeniin treatment. In Caco-2, the protein and mRNA levels of ATP-binding cassette transporter 1 were increased after 24 h eugeniin treatment. This novel finding indicates that eugeniin improves cholesterol metabolism in human cell cultures.

The physiological blood concentration of phenylalanine-proline can ameliorate cholesterol metabolism in HepG2 cells.

We have previously reported that the dipeptide Phe-Pro affects lipid metabolism in vivo and in vitro, but very little is known regarding the mechanism of action of Phe-Pro after it is absorbed by the intestines via PepT1. In this study, we administered a single oral dose of Phe-Pro to rats and quantified its concentration in the portal plasma using LC-TOF/MS analysis. Additionally, the physiological blood concentration of Phe-Pro was added to the lipid accumulation model of HepG2 cells to decrease intracellular cholesterol and increase the expression of CYP7A1 and PPARα mRNA levels. Moreover, we analyzed the binding of PPARα and Phe-Pro using AlphaFold2. We found that Phe-Pro is a ligand for PPARα. To the best of our knowledge, this is the first study that shows Phe-Pro to be present in the portal plasma. We found for the first time that Phe-Pro ameliorated cholesterol metabolism in HepG2 cells.

Rose polyphenols exert antiobesity effect in high-fat-induced obese mice by regulating lipogenic gene expression.

Obesity presents a major risk factor in the development of cardiovascular diseases. Recent reports indicate that many kinds of polyphenols have the potential to prevent metabolic diseases. We hypothesized that rose polyphenols (ROSE) have the effect of improvement in lipid metabolism. In this study, we investigated whether rose polyphenols affected lipid metabolism and exerted antiobesity. To clarify the mechanism, C57BL/6J mice were fed a high-fat diet containing 0.25% ROSE for 35 days. Compared with the control group, body weight gain and adipose tissue weight in the 0.25% ROSE group were significantly decreased. Serum cholesterol and hepatic triglyceride concentrations significantly decreased, whereas fecal triglyceride was significantly increased in the 0.25% ROSE group. Liver stearoyl-CoA desaturase 1 (Scd1), 3-hydroxy-3-methylglutaryl-CoA reductase (Hmgcr), and acyl-CoA:cholesterol acyltransferase 1 (Acat1) mRNA as well as protein stearoyl-CoA desaturase 1 concentrations were significantly lower in the 0.25% ROSE group than that in the control group. The mRNA and the protein concentrations of adipose triglyceride lipase, hormone-sensitive lipase, and peroxisomal acylcoenzyme A oxidase 1 in white adipose tissue were significantly higher in the 0.25% ROSE group than that in the control group. The components in rose polyphenols were quantified by liquid chromatography-tandem mass spectrometry, and we consider that ellagic acid plays an important role in an antiobesity effect because the ellagic acid content is the highest among polyphenols in rose polyphenols. In summary, rose polyphenols exhibit antiobesity effects by influencing lipid metabolism-related genes and proteins to promote lipolysis and suppress lipid synthesis.

Anti-Obesity and Hypocholesterolemic Actions of Protamine-Derived Peptide RPR (Arg-Pro-Arg) and Protamine in High-Fat Diet-Induced C57BL/6J Mice.

Dietary protamine can ameliorate hyperlipidemia; however, the protamine-derived active peptide and its hypolipidemic mechanism of action are unclear. Here, we report the discovery of a novel anti-obesity and hypocholesterolemic peptide, RPR (Arg-Pro-Arg), derived from protamine in mice fed a high-fat diet for 50 days. Serum cholesterol levels were significantly lower in the protamine and RPR groups than in the control group. White adipose tissue weight was significantly decreased in the protamine and RPR groups. The fecal excretion of cholesterol and bile acid was significantly higher in the protamine and RPR groups than in the control group. We also observed a significant decrease in the expression of hepatic SCD1, SREBP1, and adipocyte FAS mRNA, and significantly increased expression of hepatic PPARα and adipocyte PPARγ1 mRNA in the protamine group. These findings demonstrate that the anti-obesity effects of protamine are linked to the upregulation of adipocyte PPARγ1 and hepatic PPARα and the downregulation of hepatic SCD1 via SREBP1 and adipocyte FAS. RPR derived from protamine has a crucial role in the anti-obesity action of protamine by evaluating the effective dose of adipose tissue weight loss.

Identification of a novel cholesterol-lowering dipeptide, phenylalanine-proline (FP), and its down-regulation of intestinal ABCA1 in hypercholesterolemic rats and Caco-2 cells.

There has been no report about in vivo active cholesterol-lowering dipeptide in any protein origin, despite their potential health benefits. Cattle heart protein hydrolysate ultra-filtrate (HPHU, molecular weight < ca. 1,000 Da peptide mixture) exhibits cholesterol-lowering activity in hypercholesterolemic rats, but the active peptide in HPHU that lowers serum cholesterol levels and its molecular mechanism are unknown. In this study, we separated and purified HPHU to identify a novel cholesterol-lowering dipeptide (phenylalanine-proline, FP) and characterized the mechanism underlying its effects in vivo and in vitro. We identified FP as an active peptide from HPHU by MALDI-TOF mass spectrometry. FP significantly decreased serum total and non-HDL cholesterol and hepatic cholesterol levels in rats. FP significantly increased serum HDL cholesterol, accompanied by a significant decrease in the atherogenic index. FP also significantly increased fecal cholesterol and acidic steroid excretion. Moreover, FP significantly decreased ATP-binding cassette transporter A1 (ABCA1) expression in the rat jejunum and reduced cholesterol absorption in Caco-2 cells. We found a novel cholesterol-lowering dipeptide FP that could improve cholesterol metabolism via the down-regulation of intestinal ABCA1. The cholesterol-lowering action induced by FP was disappeared in PepT1KO mice. FP-induced cholesterol-lowering action is mediated via PepT1 in mice.