Effect of Collagen Peptide-containing Diet on Hepatic Gene Expressions in Mouse

Ingestion of collagen peptide elicits beneficial effects on the body. Improvement of blood lipid is one of the effects, but its mechanism remains unclear. Male BALB/cCrSlc mice were bred with the AIN-93M diet containing 14% casein or AIN-93M-based low-protein diet containing 10% casein or diet containing 6% casein+4% collagen peptide (n=12/group) for 10 weeks．Total, free, and esterified cholesterol levels in the blood decreased in the collagen peptide group. DNA microarray analysis of the liver revealed that expression of the genes related to lipid metabolic process, such as PPAR signaling pathway and fatty acid metabolism, increased in the collagen peptide group compared to the 10% casein group. In contrast, expression of the genes related to unfolded protein response (UPR) and protein level of phospho-IRE1 decreased. Our data suggest that lipid metabolism in the liver was altered by collagen ingestion, which probably results in the decreased levels of blood cholesterol. Male 6-week-old BALB/cCrSlc mice were purchased from Japan SLC, Inc. (Shizuoka, Japan) and acclimatized to breeding conditions for 1 week in the laboratory animal facilities of Rakuno Gakuen University. They were divided into three groups (12 mice per group) based on body weight so that the average body weight did not differ significantly among groups. The mice were individually housed under conventional conditions (20±2°C, 12 h light/12 h dark cycle) with free access to water and diet. The basic powder diet AIN-93M-based low-protein diets containing 10% casein (10C) or 6% casein plus 4% collagen peptide (fish-derived, MW 4,000~6,000, Nippi Inc., Tokyo, Japan) (6C+4CP) were prepared by Oriental Yeast Co., Ltd. (Tokyo, Japan). Cornstarch was used to compensate for the decreased protein in the low-protein diets. Body weight, food and water intake were measured once a week. After 10 weeks of the breeding, sampling was performed in the morning after starvation for 3 h. After anesthesia with 50mg/kg sodium pentobarbital, blood was collected from the right ventricle with a heparinized syringe, and plasma was stored at -80°C. Three mice of medium food efficiency (weight gain/food intake) were selected in each group for further analysis. Whole liver was removed and a portion of the first leaf (ca. 5 × 5 × 3 mm) was kept in RNAlater (Ambion, Austin, TX, USA) to isolate total RNA. This study was conducted in accordance with the Act on Welfare and Management of Animals in Japan (Act No. 105 of October 1, 1973; partly revised on June 22, 2005), the Standards Relating to the Care and Management of Laboratory Animals and Relief of Pain (Notice No. 88 of the Ministry of the Environment, dated April 28, 2006), and the Guidelines for Methods of Animal Disposition Procedures (Prime Minister’s Office Notification No. 40, dated July 4, 1995; partly revised on November 12, 2007: Notice No. 105 of the Ministry of the Environment). The study protocol was approved by the Ethics Committee of Rakuno Gakuen University (No. VH23A8).