Scott W. Altmann

Niemann–Pick C1 Like 1 (NPC1L1) an intestinal sterol transporter

Niemann-Pick C1 Like 1 (NPC1L1) has been identified and characterized as an essential protein in the intestinal cholesterol absorption process. NPC1L1 localizes to the brush border membrane of absorptive enterocytes in the small intestine. Intestinal expression of NPC1L1 is down regulated by diets containing high levels of cholesterol. While otherwise phenotypically normal, Npc1l1 null mice exhibit a significant reduction in the intestinal uptake and absorption of cholesterol and phytosterols. Characterization of the NPC1L1 pathway revealed that cholesterol absorption inhibitor ezetimibe specifically binds to an extracellular loop of NPC1L1 and inhibits its sterol transport function. Npc1l1 null mice are resistant to diet-induced hypercholesterolemia, and when crossed with apo E null mice, are completely resistant to the development of atherosclerosis. Intestinal gene expression studies in Npc1l1 null mice indicated that no exogenous cholesterol was entering enterocytes lacking NPC1L1, which resulted in an upregulation of intestinal and hepatic LDL receptor and cholesterol biosynthetic gene expression. Polymorphisms in the human NPC1L1 gene have been found to influence cholesterol absorption and plasma low density lipoprotein levels. Therefore, NPC1L1 is a critical intestinal sterol uptake transporter which influences whole body cholesterol homeostasis.

Deficiency of Niemann-Pick C1 Like 1 Prevents Atherosclerosis in ApoE−/− Mice

Objective—The objective of this study was to determine whether the deficiency of Niemann-Pick C1 Like 1 (Npc1l1) prevents atherosclerosis in apoE null mice. Methods and Results—Npc1l1−/−/apoE null−/− mice were generated and found to have a significant reduction in cholesterol absorption (−77%) compared with wild-type or apoE−/− mice. Npc1l1/apoE−/− mice were fed a chow or Western diet for 24 weeks, then lipoprotein, hepatic, and biliary cholesterol, and atherosclerosis development was compared with apoE−/−, Npc1l1−/−, wild-type, and ezetimibe-treated apoE−/− mice. Chylomicron remnant/ VLDL cholesterol levels were reduced 80% to 90% in both chow and Western diet-fed Npc1l1/apoE−/− mice relative to apoE−/− mice. Male Npc1l1−/− and Npc1l1/apoE−/− mice were completely resistant to diet induced hypercholesterolemia, and both male and female mice were completely resistant to increases in hepatic and biliary cholesterol levels. Atherosclerosis was reduced 99% in aortic lesion surface area, 94% to 97% in innominate artery intimal lesion area, and >90% in aortic root lesion area in both male and female Npc1l1/apoE−/− mice relative to apoE−/− mice. Conclusions—Lack of Npc1l1, the molecular target of the cholesterol absorption inhibitor ezetimibe, in apoE−/− mice results in a significant reduction in cholesterol absorption and plasma cholesterol levels, and causes a nearly complete protection from the development of atherosclerosis, under both cholesterol-fed and non-cholesterol-fed conditions.

Cholesterol homeostasis by the intestine: lessons from Niemann-Pick C1 Like 1 [NPC1L1).

Ezetimibe is a selective cholesterol absorption inhibitor, which potently inhibits the uptake and absorption of biliary and dietary cholesterol from the small intestine without affecting the absorption of fat-soluble vitamins, triglycerides or bile acids. Identification and characterization of Niemann-Pick C1 Like 1 (NPC1L1) has established NPC1L1 as an essential protein in the intestinal cholesterol absorption process. While otherwise phenotypically normal, Npc1l1 null mice exhibit a significant reduction in the intestinal uptake and absorption of cholesterol and phytosterols. Characterization of the NPC1L1 pathway revealed that ezetimibe specifically binds to NPC1L1 and inhibits its sterol transport function. Npc1l1 null mice were resistant to diet-induced hypercholesterolemia, and when crossed with apoE null mice, were completely resistant to the development of atherosclerosis. In Npc1l1/apoE null mice or apoE null mice treated with ezetimibe plasma cholesterol levels were reduced primarily in the apoB48 containing chylomicron remnant lipoproteins relative to untreated apoE null mice. SR-B1 has been proposed to play a role in intestinal cholesterol uptake, but in Npc1l1/SR-B1 double null mice intestinal cholesterol absorption was not different than Npc1l1 null alone mice. Therefore, NPC1L1 is the critical intestinal sterol transporter which influences whole body cholesterol homeostasis, and is the molecular target of ezetimibe.

Synthesis of fluorescent biochemical tools related to the 2-azetidinone class of cholesterol absorption inhibitors.

Fluorescent analogues of the cholesterol absorption inhibitor (CAI), Sch 58235, have been designed and synthesized as single enantiomers. Biological testing reveals that they are potent CAIs and are suitable tools for the investigation of the azetidinone CAI mechanism of action (MOA).