Labonté Eric D, Howles Philip N, Granholm Norman A, Rojas Juan C, Davies Joanna P, Ioannou Yiannis A, Hui David Y
Department of Pathology (ML0507), Genome Research Institute, University of Cincinnati, 2120 E. Galbraith Rd., Cincinnati, OH 45237, USA.
Biochim Biophys Acta. 2007 Sep;1771(9):1132-9. doi: 10.1016/j.bbalip.2007.03.002. Epub 2007 Mar 16.
Recent studies have documented the importance of Niemann-Pick C1-like 1 protein (NPC1L1), a putative physiological target of the drug ezetimibe, in mediating intestinal cholesterol absorption. However, whether NPC1L1 is the high affinity cholesterol binding protein on intestinal brush border membranes is still controversial. In this study, brush border membrane vesicles (BBMV) from wild type and NPC1L1-/- mice were isolated and assayed for micellar cholesterol binding in the presence or absence of ezetimibe. Results confirmed the loss of the high affinity component of cholesterol binding when wild type BBMV preparations were incubated with antiserum against the class B type 1 scavenger receptor (SR-BI) in the reaction mixture similar to previous studies. Subsequently, second order binding of cholesterol was observed with BBMV from wild type and NPC1L1-/- mice. The inclusion of ezetimibe in these in vitro reaction assays resulted in the loss of the high affinity component of cholesterol interaction. Surprisingly, BBMVs from NPC1L1-/- mice maintained active binding of cholesterol. These results documented that SR-BI, not NPC1L1, is the major protein responsible for the initial high affinity cholesterol ligand binding process in the cholesterol absorption pathway. Additionally, ezetimibe may inhibit BBM cholesterol binding through targets such as SR-BI in addition to its inhibition of NPC1L1.
近期研究已证明尼曼匹克C1样1蛋白(NPC1L1)在介导肠道胆固醇吸收中的重要性,NPC1L1是药物依泽替米贝的假定生理靶点。然而,NPC1L1是否为肠道刷状缘膜上的高亲和力胆固醇结合蛋白仍存在争议。在本研究中,分离了野生型和NPC1L1基因敲除小鼠的刷状缘膜囊泡(BBMV),并在有或没有依泽替米贝的情况下检测其对胶态胆固醇的结合。结果证实,与之前的研究类似,当野生型BBMV制剂在反应混合物中与抗B类1型清道夫受体(SR-BI)的抗血清孵育时,胆固醇结合的高亲和力成分丧失。随后,在野生型和NPC1L1基因敲除小鼠的BBMV中观察到胆固醇的二级结合。在这些体外反应试验中加入依泽替米贝导致胆固醇相互作用的高亲和力成分丧失。令人惊讶的是,NPC1L1基因敲除小鼠的BBMV保持了对胆固醇的活性结合。这些结果证明,在胆固醇吸收途径中,负责初始高亲和力胆固醇配体结合过程的主要蛋白是SR-BI,而非NPC1L1。此外,依泽替米贝除了抑制NPC1L1外,还可能通过SR-BI等靶点抑制BBM对胆固醇的结合。