探討雞肝水解物於高脂飲食下脂質恆定功效

Abstract

於國人十大死因中，至少有五項為肥胖相關之代謝性疾病所引起。其中心血管疾病(cardiovascular diseases, CVDs)、高血脂症及非酒精性脂肪肝(nonalcoholic fatty liver, NAFLD)之形成與高脂飲食下之血脂異常、肝臟脂肪堆積及氧化壓力有高度相關性。根據本實驗室先前之研究結果，利用pepsin水解雞肝蛋白，能有效製備具抗氧化能力之雞肝水解物(chicken-liver hydrolysates, CLHs)，且補充CLHs於D-半乳糖(D-galactose)誘導之氧化壓力小鼠模式中，亦能展現其抗氧化能力。故本研究目標為評估CLHs補充於高脂飲食倉鼠模式下之抗氧化與脂質平衡調節之效。 雞肝水解物之游離胺基酸主要組成為Glu、Arg、Ala、Leu、及Lys。比較CLHs與原雞肝蛋白之游離胺基酸組成後發現：牛磺酸(taurine)與雙胜肽-肌肽(carnosine, CNS)與甲肌肽(anserine)之含量在水解後大幅增加。經體外試驗結果發現：雞肝水解物具有胰脂解酶活性抑制能力與膽酸結合能力(p<0.05)。本研究欲進一步評估CLHs於倉鼠模式下之補充效果。48隻敘利亞黃金鼠(Golden Syrian hamsters)隨機分至下列組別：(1) Control：chow diet + (normal distilled water, NDW)；(2) HFD：高脂飼糧(high-fat diet, HFD) + NDW；(3) 1X CLH：HFD + 1X CLH (100 mg CLH/kg BW)；(4) 2X CLH：HFD + 2X CLH (200 mg CLH/kg BW)；(5) 4X CLH：HFD + 4X CLH (400 mg CLH/kg BW)；(6) CNS：HFD + CNS (200 mg CNS/kg BW)。動物試驗結果顯示：CLHs與CNS之補充能顯著提高(p<0.05)血中總抗氧化能力(trolox equivalent antioxidative capacity, TEAC)、減緩氧化壓力(p<0.05)及改善(p<0.05)血脂組成(膽固醇、三酸甘油酯、高密度脂蛋白膽固醇與低密度脂蛋白膽固醇)。CLHs之補充亦能顯著提高(p<0.05)肝臟抗氧化酵素之活性(超氧歧化酶、過氧化氫酶及麩胱甘肽過氧化酶)與總抗氧化力(TEAC)，改善(p<0.05)肝臟脂質堆積(膽固醇與三酸甘油脂)、氧化壓力及細胞激素(TNF-α與IL-1β)之含量。而上述改善效果可能來自於脂質生合成相關基因表現(SREBP 1c、ACC、FAS、SREBP2及HMGCoA reductase)之調降(p<0.05)以及能量代謝(PPARα、RARα、CPT1及UCP2)與膽固醇代謝相關基因(LDL receptor與CYP7A1)表現之提升(p<0.05)。此外，CLHs之補充亦會促進高脂飲食倉鼠之膽酸排出(p<0.05)，有助於降低肝臟及血中膽固醇含量。 綜觀上述研究結果，於高脂飲食下補充CLHs具有抗氧化及脂質調節之能力，且保護效果優於CNS之補充效果。表示CLHs之益處不僅僅來自於CNS之提供，可能與其中之游離胺基酸組成與潛在活性胜肽有關。

Among 10 major causes of death in Taiwan, there are at least 5 causes related to obesity. High-fat diet not only increases serum lipid levels or hepatic lipid accumulation, but also produces reactive oxygen-species (ROS) which result in cardiovascular diseases, hyperlipidemia, and non-alcoholic fatty liver disease (NAFLD). According to a previous research from our lab, antioxidant chicken-liver hydrolysates (CLHs) can be manufactured by pepsin digestion and also demonstrate an antioxidant activity in oxidative-stressed mice. Hence, we aimed to evaluate the effects of pepsin-digested CLHs on lipid homeostasis and antioxidant activity in high-fat-diet fed hamsters. Regarding the free-amino-acid profile, Glu, Arg, Ala, Leu and Lys were majorities in CLHs. The contents of taurine and dipeptides, i.e. anserine and carnosine (CNS), had been greatly elevated after the hydrolysis. CLHs also exhibited the in vitro bile-acid binding ability and pancreatic lipase inhibitory activity (p<0.05). Furthermore, an evaluation of in vivo effects of CLHs was constructed. Forty-eight male Golden Syrian hamsters were assigned randomly to the following dietary groups: (1) chow diet and NDW (Control); (2) high-fat diet (HFD) and NDW; (3) HFD and 1X CLH (100 mg CLH/kg BW); (4) HFD and 2X CLH (200 mg CLH/kg BW); (5) HFD and 4X CLH (400 mg CLH/kg BW); (6) HFD and CNS (200 mg CNS/kg BW). In high-fat diet groups, supplementing CLHs and CNS apparently alleviated (p<0.05) the oxidative stress and improved (p<0.05) the lipid profile in serum. CLHs also improved (p<0.05) the antioxidant ability, and decreased (p<0.05) lipid accumulation, oxidative stress, and cytokine levels (TNF-α and IL-1β) in livers. Those beneficial effects might result from downregulations (p<0.05) of lipogenesis related gene expressions (SREBP1c, ACC, FAS, SREBP2, and HMGCoA reductase) but upregulations (p<0.05) of β-oxidation related gene expressions (PPARα, RXRα, CPT1, and UCP2) and cholesterol metabolism related gene expressions (LDL receptor and CYP7A1). Moreover, supplementing CLHs increased (p<0.05) fecal bile-acid outputs which also contributed decreased serum and liver cholesterol contents in high-fat-diet fed hamsters. In summary, CLHs possess lipid-homeostasis and antioxidant abilities in the high-fat dietary habit and its functional effects seem better than CNS. Those benefits might be due to its free-amino-acid profile in CLHs other than carnosine only.