Hypolipidemic Roles of Casein-Derived Peptides by Regulation of Trans-Intestinal Cholesterol Excretion and Bile Acid Synthesis

Abstract

Hyperlipidemia, a syndrome characterized by an abnormal elevation of blood lipids, causes chronic lethal metabolic disorders. Although statins are regularly prescribed to patients, an alternative to treat the burden of excessive lipids is required for cholesterol control. In this study, it was found that the treatment of casein hydrolyzed by pepsin and trypsin induced trans-intestinal cholesterol excretion (TICE) through ATP-binding cassette subfamily G members 5 (ABCG5) expression. Next, we analyzed sequences of the peptides responsible for TICE induction, synthesized artificial peptides based on the sequences, and the hypolipidemic effects of the peptide treatments were assessed in both in vitro and in vivo models. We determined that two bioactive peptides contained in casein hydrolysates (SQSKVLPVPQK and HPHPHLSF) induced TICE through the expression of ABCG5 in enterocytes and suppressed hepatic mRNA expression of cytochrome P450 family 7 subfamily A member 1 (CYP7A1) and CYP8B1by ileal FGF19 expression both in an liver X receptor α (LXRα)-mediated manner. In the hyperlipidemic mouse models, the oral administration of peptides reduced serum cholesterol levels through elevation of the ABCG5 expression in proximal intestine and fecal cholesterol secretion. Besides this, peptides induced ileal expression of fibroblast growth factor 15/19 (FGF15/19) and inhibited hepatic bile acid synthesis. We found that the oral treatment of casein-derived bioactive peptides could improve hyperlipidemia by regulating intestinal excretion and hepatic synthesis of cholesterols.

Soybean-Derived Peptides Attenuate Hyperlipidemia by Regulating Trans-Intestinal Cholesterol Excretion and Bile Acid Synthesis

“…Consequently, we discovered 11 peptide sequences in fraction #2 ( Table 2 ). To prove the effects of these 11 synthetic peptides for ABCG5 and ABCG8 regulation, we performed analysis by using 1 μg/mL in distilled water of each peptide to treat Caco-2 cells [ 20 , 33 ]. We confirmed that peptides 1 and 8 significantly upregulated ABCG5 and ABCG8 expression by 1.5-fold ( Figure 2 D).…”

“…Consistent with previous studies, TICE steadily decreased upon movement toward the distal intestine and peptide-derived TICE increased only in the proximal intestine. Therefore, peptide-mediated ABCG5 and ABCG8 upregulation effectively increased fecal cholesterol excretion [ 10 , 20 ]. Our in vivo results showed that peptide 1 and 8 downregulated the serum cholesterol levels while increasing the fecal cholesterol levels.…”

“…For soybean hydrolysis, pepsin and trypsin treatments were performed as previously described [ 20 ]. Briefly, the soy solution was prepared at 5 mg/mL in distilled water.…”

“…Following a previous study, Caco-2 cells were incubated on the insert of the transwell and differentiated for 7 days [ 20 , 28 ]. To prepare a media containing cholesterol, MEM media was supplemented with monoolein (30 μM), sodium taurocholate (500 μM) and/or cholesterol (100 μM) and subsequently sonicated for 15 min to form micelles.…”

“…Bioactive polypeptides have diverse functions, including anti-cancer [ 17 ], hypertensive [ 18 ], and immunoregulatory effects [ 19 ]. In addition, our previous study showed that casein-derived bioactive peptides affect TICE and bile acid metabolism [ 20 ].…”