Leptin administration reduces obesity in leptin-deficient ob/ob mice; its effects in obese humans, who have high circulating leptin levels, remain to be determined. This longitudinal study was designed to determine whether diet-induced obesity in mice produces resistance to peripheral and/or central leptin treatment. Obesity was induced in two strains of mice by exposure to a 45% fat diet. Serum leptin increased in proportion to body weight ( P Ͻ 0.00001). Whereas C57BL/6 mice initially responded to peripherally administered leptin with a marked decrease in food intake, leptin resistance developed after 16 d on high fat diet; mice on 10% fat diet retained leptin sensitivity. In AKR mice, peripheral leptin significantly decreased food intake in both 10 and 45% fat-fed mice after 16 d of dietary treatment. However, after 56 d, both groups became resistant to peripherally administered leptin. Central administration of leptin to peripherally leptin-resistant AKR mice on 45% fat diet resulted in a robust response to leptin, with a dose-dependent decrease in food intake ( P Ͻ 0.00001) and body weight ( P Ͻ 0.0001) after a single intracerebroventricular infusion. These data demonstrate that, in a diet-induced obesity model, mice exhibit resistance to peripherally administered leptin, while retaining sensitivity to centrally administered leptin. ( J. Clin. Invest. 1997. 99:385-390.) Key words: leptin resistance • high fat diet • food intake • C57BL/6 • AKR

1 Previous studies described the metabolism-based discovery of a potent, selective inhibitor of intestinal absorption of cholesterol, SCH58235 (Ezetimibe). Here we demonstrate that the phenolic glucuronide (SCH60663) of SCH58235, was more potent at inhibiting cholesterol absorption in rats than SCH58235, when administered by the intraduodenal route. 2 To understand the increased potency of the glucuronide, the metabolism and distribution of SCH58235 and SCH60663 were studied in bile duct-cannulated rats. 3 One minute after intraduodenal delivery of SCH58235, signi®cant levels of compound were detected in portal plasma; 495% was glucuronidated, indicating that the intestine was metabolizing SCH58235 to its glucuronide. When intraduodenally delivered as SCH58235, the compound was glucuronidated, moved through the intestinal wall, into portal plasma, through the liver, and into bile. However, when delivered as SCH60663, 495% of the compound remained in the intestinal lumen and wall, which may explain its increased potency. Signi®cant inhibition of cholesterol absorption and glucuronidation of SCH58235 occurred when SCH58235 was intravenously injected into bile duct-cannulated rats. Autoradiographic analysis demonstrated that drug related material was located throughout the intestinal villi, but concentrated in the villus tip. 4 These data indicate that (a) SCH58235 is rapidly metabolized in the intestine to its glucuronide; (b) once glucuronidated, the dose is excreted in the bile, thereby delivering drug related material back to the site of action and (c) the glucuronide is more potent than the parent possibly because it localizes to the intestine. Taken together, these data may explain the potency of SCH58235 in the rat (ID 50 =0.0015 mg kg 71) and rhesus monkey (ID 50 =0.0005 mg kg 71 ).

Abstract-Ezetimibe (SCH58235) is a potent, selective, cholesterol absorption inhibitor. The objective of this study was to determine whether ezetimibe reduces plasma cholesterol and inhibits atherogenesis in apolipoprotein E knockout (apoEϪ/Ϫ) mice. Cholesterol absorption was inhibited by Ͼ90% at doses of ezetimibe Ͼ3 mg/kg in apoEϪ/Ϫ mice. Atherosclerosis and lipoprotein changes were determined in apoEϪ/Ϫ mice fed a high-fat (0.15% cholesterol) "western" diet, a low-fat (0.15% cholesterol) diet, or a semisynthetic cholesterol-free diet with or without ezetimibe (5 mg/kg per day) for 6 months. Ezetimibe reduced plasma cholesterol levels from 964 to 374 mg/dL, from 726 to 231 mg/dL, and from 516 to 178 mg/dL in the western, low-fat, and cholesterol-free diet groups, respectively. The reductions occurred in the very low density and low density lipoprotein fractions, whereas high density lipoprotein cholesterol levels were increased by ezetimibe treatment. Ezetimibe reduced aortic atherosclerotic lesion surface area from 20.2% to 4.1% in the western diet group and from 24.1% to 7.0% in the low-fat cholesterol diet group. Ezetimibe reduced carotid artery atherosclerotic lesion cross-sectional area by 97% in the western and low-fat cholesterol groups and by 91% in the cholesterol-free group. Ezetimibe inhibits cholesterol absorption, reduces plasma cholesterol, increases high density lipoprotein levels, and inhibits the progression of atherosclerosis under western, low-fat, and cholesterol-free dietary conditions in apoEϪ/Ϫ mice. Although apoEϪ/Ϫ mice are more hypercholesterolemic than are humans and low density lipoprotein reductions with ezetimibe are not as pronounced clinically, ezetimibe may inhibit atherogenesis in individuals consuming restricted-fat or western diets. Key Words: cholesterol absorption Ⅲ ezetimibe Ⅲ atherosclerosis Ⅲ hypercholesterolemia T he abnormal metabolism and elevation of plasma cholesterol and lipoproteins are well-documented risk factors for the development of atherosclerosis. Evidence from clinical trials indicates that reducing plasma cholesterol by dietary and/or pharmacological means leads to reductions in the incidence of death from cardiovascular disease. 1-4 Present pharmacological interventions include the inhibition of cholesterol biosynthesis by inhibiting 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase (statins) either alone or in combination with other agents. Ezetimibe (SCH58235) is the first of a new class of selective cholesterol absorption inhibitors that may represent a new option for the pharmacological treatment of hypercholesterolemia. 5,6 Ezetimibe selectively inhibits the intestinal uptake and absorption of dietary and biliary cholesterol at the brush border of small intestinal enterocytes, confining cholesterol to the intestinal lumen for subsequent excretion. 6,7 Results from preclinical studies in various animal models have demonstrated the lipid-lowering properties of ezetimibe as a single agent [5][6][7][8][9] and the synergistic cholesterol-lowering...

Although several studies implicate small declines in blood glucose levels as stimulus for spontaneous meal initiation, no mechanism is known for how these dips might initiate feeding. To assess the role of ventromedial hypothalamus (VMH) (arcuate plus ventromedial nucleus) glucosensing neurons as potential mediators of spontaneous and glucoprivic feeding, meal patterns were observed, and blood and VMH microdialysis fluid were sampled in 15 rats every 10 min for 3.5 h after dark onset and 2 h after insulin (5 U/kg, i.v.) infusion. Blood glucose levels declined by 11% beginning ϳ5 min before 65% of all spontaneous meals, with no fall in VMH levels. After insulin, blood and VMH glucose reached nadirs by 30 -40 min, and the same rats ate 60% faster and spent 84% more time eating during the ensuing hypoglycemia. Although 83% of first hypoglycemic meals were preceded by 5 min dips in VMH (but not blood) glucose levels, neither blood nor VMH levels declined before second meals, suggesting that low glucose, rather than changing levels, was the stimulus for glucoprivic meals. Furthermore, altering VMH glucosensing by raising or lowering glucokinase (GK) activity failed to affect spontaneous feeding, body or adipose weights, or glucose tolerance. However, chronic depletion by 26 -70% of VMH GK mRNA reduced glucoprivic feeding. Thus, although VMH glucosensing does not appear to be involved in either spontaneous feeding or long-term body-weight regulation, it does participate in glucoprivic feeding, similar to its role in the counter-regulatory neurohumoral responses to glucoprivation.

1 Ezetimibe potently inhibits the transport of cholesterol across the intestinal wall, thereby reducing plasma cholesterol in preclinical animal models of hypercholesterolemia. The e ect of ezetimibe on known absorptive processes was determined in the present studies. 2 Experiments were conducted in the hamster and/or rat to determine whether ezetimibe would a ect the absorption of molecules other than free cholesterol, namely cholesteryl ester, triglyceride, ethinylestradiol, progesterone, vitamins A and D, and taurocholic acid. In addition, to determine whether exocrine pancreatic function is involved in the mechanism of action of ezetimibe, a biliary anastomosis model, which eliminates exocrine pancreatic function from the intestine while maintaining bile¯ow, was established in the rat. 3 Ezetimibe reduced plasma cholesterol and hepatic cholesterol accumulation in cholesterol-fed hamsters with an ED 50 of 0.04 mg kg 71 . Utilizing cholesteryl esters labelled on either the cholesterol or the fatty acid moiety, we demonstrated that ezetimibe did not a ect cholesteryl ester hydrolysis and the absorption of fatty acid thus generated in both hamsters and rats. The free cholesterol from this hydrolysis, however, was not absorbed (92 ± 96% inhibition) in the presence of ezetimibe. Eliminating pancreatic function in rats abolished hydrolysis of cholesteryl esters, but did not a ect the ability of ezetimibe to block absorption of free cholesterol (794%). Ezetimibe did not a ect the absorption of triglyceride, ethinylestradiol, progesterone, vitamins A and D, and taurocholic acid in rats. 4 Ezetimibe is a potent inhibitor of intestinal free cholesterol absorption that does not require exocrine pancreatic function for activity. Ezetimibe does not a ect the absorption of triglyceride as a pancreatic lipase inhibitor (Orlistat) would, nor does it a ect the absorption of vitamin A, D or taurocholate, as a bile acid sequestrant (cholestyramine) would.