以Caco-2細胞模式篩選具有減少吸收膽固醇能力之乳酸菌株

Abstract

高膽固醇血症是導致心血管疾病的關鍵因素之一，家族性高膽固醇血症的低診斷率，加上不正常的飲食與運動習慣，使高膽固醇血症成為現代一大問題。已知特定的益生菌菌株具有降低腸道和血漿中膽固醇濃度的能力，益生菌可藉由膽鹽水解酶的活性和降低與膽固醇代謝相關的基因（例如NPC1L1，ABCG5，ABCG8和HMGCR）表現來降低腸細胞的膽固醇吸收，故益生菌可能是一種預防高膽固醇血症與心血管疾病的新方法。本研究的目的是以Caco-2細胞模式篩選具有降低膽固醇吸收能力的乳酸菌株，從克弗爾粒中分離出總共29株乳酸菌株，篩選出對Caco-2腸上皮細胞無細胞毒性的菌株，並評估其降低膽固醇吸收的能力。並以即時定量聚合酶連鎖反應進一步定量Caco-2細胞中與膽固醇代謝相關的基因之表現量。結果顯示Lactococcus lactis subsp. lactis YPK20和YPK23可以降低Caco-2細胞對膽固醇的吸收，並非透過細菌的膽鹽水解酶活性或細菌吸附膽固醇微胞的能力。以Lc. lactis subsp. lactis YPK20和YPK23預處理細胞，可以下調Caco-2細胞中NPC1L1基因的表達，而YPK23也可以降低Caco-2細胞中HMGCR基因的表現。此外，此二分離菌株在pH3環境下具有耐酸性，菌株代謝物具有抗病原菌活性。總的來說，本研究建構了一個檢測Caco-2細胞吸收膽固醇的模型，並發現Lc. lactis subsp. lactis YPK20和YPK23具有調節腸道上皮細胞基因表達和降低膽固醇吸收的潛在能力。

Hypercholesterolaemia is one of the critical factors that cause cardiovascular disease (CVD). The low diagnosis of familial cholesterolaemia, abnormal diet, and exercise habits make cholesterolaemia become a big problem in modern life. It was reported that specific strains of probiotics had abilities to lower intestinal and plasma cholesterol levels, and supposed that probiotics would be a novel method to prevent hypercholesterolaemia and CVD. Probiotics lower cholesterol absorption of enterocytes by the activity of bile salt hydrolase (BSH) and down-regulation of the gene related to cholesterol metabolism, such as NPC1L1, ABCG5, ABCG8 and HMGCR. The aim of this study was to screen lactic acid bacterial strains with abilities to reduce cholesterol absorption in Caco-2 cells. A total of 29 lactic acid bacterial strains were isolated from kefir grains, and the strains without cytotoxicity to Caco-2 cells were selected. The isolates were evaluated by reduction of cholesterol absorption through an in vitro model. The expressions of several candidate genes that associated with cholesterol metabolism in Caco-2 cells were further quantified by real-time PCR. The results showed that Lactococcus lactis subsp. lactis YPK20 and YPK23 could reduce cholesterol absorption by Caco-2 cells. Not by BSH activity or assimilation of cholesterol by bacteria, pre-treatment with Lc. lactis subsp. lactis YPK20 and YPK23 could down-regulate NPC1L1 gene expression in Caco-2 cells, and down-regulation of HMGCR gene in Caco-2 cells was also observed by pre-treatment with Lc. lactis subsp. lactis YPK23. Furthermore, these two isolates showed anti-pathogenic activities by metabolites and acid tolerance at pH3. In conclusion, this study constructed a model for detecting cholesterol absorption by Caco-2 cells, and found that Lc. lactis subsp. lactis YPK20 and YPK23 possess potential abilities to regulate gene expressions and lower cholesterol absorption in Caco-2 cells.