Douglas S Compton

Diet-induced obese mice develop peripheral, but not central, resistance to leptin.

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 < 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 < 0.00001) and body weight (P < 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.

Comparison of the activity and disposition of the novel cholesterol absorption inhibitor, SCH58235, and its glucuronide, SCH60663.

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. To understand the increased potency of the glucuronide, the metabolism and distribution of SCH58235 and SCH60663 were studied in bile duct‐cannulated rats. One minute after intraduodenal delivery of SCH58235, significant levels of compound were detected in portal plasma; >95% 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, >95% of the compound remained in the intestinal lumen and wall, which may explain its increased potency. Significant 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. 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 (ID50=0.0015 mg kg−1) and rhesus monkey (ID50=0.0005 mg kg−1).

Ezetimibe selectively inhibits intestinal cholesterol absorption in rodents in the presence and absence of exocrine pancreatic function

Ezetimibe potently inhibits the transport of cholesterol across the intestinal wall, thereby reducing plasma cholesterol in preclinical animal models of hypercholesterolemia. The effect of ezetimibe on known absorptive processes was determined in the present studies. Experiments were conducted in the hamster and/or rat to determine whether ezetimibe would affect 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 flow, was established in the rat. Ezetimibe reduced plasma cholesterol and hepatic cholesterol accumulation in cholesterol‐fed hamsters with an ED50 of 0.04 mg kg−1. Utilizing cholesteryl esters labelled on either the cholesterol or the fatty acid moiety, we demonstrated that ezetimibe did not affect 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 affect the ability of ezetimibe to block absorption of free cholesterol (−94%). Ezetimibe did not affect the absorption of triglyceride, ethinylestradiol, progesterone, vitamins A and D, and taurocholic acid in rats. Ezetimibe is a potent inhibitor of intestinal free cholesterol absorption that does not require exocrine pancreatic function for activity. Ezetimibe does not affect the absorption of triglyceride as a pancreatic lipase inhibitor (Orlistat) would, nor does it affect the absorption of vitamin A, D or taurocholate, as a bile acid sequestrant (cholestyramine) would.

Hypocholesterolemic activity of a novel inhibitor of cholesterol absorption, SCH 48461

The amount of cholesterol that circulates in the plasma as lipoproteins can be affected by the balance of cholesterol metabolism within and between the intestines and liver. In the present report, we describe a novel hypocholesterolemic agent and document its pharmacological effects in animal models of hypercholesterolemia. The oral administration of (3R,4S)-1,4-bis-(4-methoxyphenyl)-3-(3-phenylpropyl)-2-azetidinone (SCH 48461) reduced plasma cholesterol concentrations in cholesterol-fed hamsters, rats and rhesus monkeys with ED50s of 1, 2 and 0.2 mg/kg per day, respectively, SCH 48461 was also highly effective in reducing hepatic cholesteryl ester accumulation in cholesterol-fed hamsters and rats after 7 days of treatment. In one 3 week study, rhesus monkeys were fed a 0.25% cholesterol/22% saturated fat diet with or without SCH 48461. At the end of the 3 week period the control groups VLDL + LDL-cholesterol increased to 180 Mg/dl from a baseline of approximately 65 mg/dl while plasma apolipoprotein B levels had doubled. Animals treated daily with 1 mg/kg SCH 48461 maintained their baseline levels of VLDL + LDL-cholesterol, HDL-cholesterol, and plasma apolipoproteins B and A-I. After 3 weeks the diets of the two groups were switched. Within 1 week SCH 48461 (1 mg/kg per day) rapidly reversed the elevated VLDL + LDL-cholesterol levels of the previous control group to near baseline values. SCH 48461 exerted its hypocholesterolemic effect through the inhibition of cholesterol absorption. A dose of 10 mg/kg per day inhibited cholesterol absorption in cholesterol-fed hamsters by 68% while a similar reduction was achieved in chow-fed monkeys with 3 mg/kg per day. This latter dose inhibited cholesterol absorption in cholesterol-fed monkeys by 95%. Treatment of cholesterol-fed monkeys with 10 mg/kg per day SCH 48461 significantly increased fecal neutral sterol excretion (52 vs. 32 mg/kg) but had no effect on acidic sterol excretion. Using a 2-h absorption model in cholesterol-fed hamsters, SCH 48461 caused a 46% inhibition of unesterified [14C]cholesterol accumulation in the intestinal wall and a 90% inhibition of cholesteryl ester formation at a dose of 10 mg/kg. Similar data were observed when the plasma radioactivity was assessed, indicating inhibition of both free (61%) and esterified (85%) cholesterol appearance. In contrast, CI-976, a potent acyl-CoA:cholesterol acyltransferase (ACAT) inhibitor, did not affect the uptake of free cholesterol into the intestines while inhibiting cholesterol esterification (98% inhibition).(ABSTRACT TRUNCATED AT 400 WORDS)

The cholesterol absorption inhibitor, ezetimibe, decreases diet-induced hypercholesterolemia in monkeys

Ezetimibe (1-(4-fluorophenyl)-(3R)-[3-(4-fluorophenyl)-(3S)-hydroxypropyl]-(4S)-(4-hydroxyphenyl)-2-azetidinone) potently and selectively inhibits the intestinal absorption of cholesterol, thereby reducing plasma cholesterol in preclinical models of hypercholesterolemia. In rhesus monkeys fed a diet containing 375 mg/day of cholesterol, 0.1 mg/kg of ezetimibe completely prevented the doubling of plasma cholesterol normally induced under these dietary conditions (ED(50)=0.0005 mg/kg). Low-density lipoprotein cholesterol (LDL) was dose-dependently reduced, while high-density lipoprotein cholesterol (HDL) and plasma triglyceride were unchanged. A single dose of an ezetimibe analog administered to cynomolgus monkeys fed a single cholesterol-containing meal caused a significant reduction (-69%) of cholesterol in chylomicrons during the postprandial phase without affecting triglyceride content. In rhesus monkeys, apolipoprotein (apo) B(48) concentrations in chylomicrons did not differ between control and the ezetimibe analog, but apo B(100) was significantly reduced in LDL (-41%). These data indicate that these cholesterol absorption inhibitors reduce cholesterol content in chylomicrons, which indirectly leads to a decrease in LDL cholesterol and particle number.

Ezetimibe potently inhibits cholesterol absorption but does not affect acute hepatic or intestinal cholesterol synthesis in rats

Ezetimibe (1‐(4‐fluorophenyl)‐(3R)‐[3‐(4‐fluorophenyl)‐(3S)‐hydroxypropyl]‐(4S)‐(4‐hydroxyphenyl)‐2‐azetidinone) and its analog SCH48461 are potent and selective cholesterol absorption inhibitors that inhibit the transport of cholesterol across the intestinal wall, thereby lowering plasma cholesterol. After a dose response for ezetimibe in rats was established, experiments were conducted to determine whether acute administration could alter hepatic or intestinal cholesterol synthesis. To determine whether this class of intestinal cholesterol absorption inhibitors could discriminate between newly synthesized cholesterol in the intestine versus exogenously administered cholesterol, rats were intraduodenally dosed with 14C‐cholesterol and 3H‐mevalonate, and mesenteric lymph was analyzed for radiolabeled cholesterol and cholesteryl ester content. Ezetimibe attenuated diet‐induced hypercholesterolemia 60–94% at doses of 0.1–3 mg kg−1 in rats. A single administration of ezetimibe did not have a direct effect on intestinal or hepatic cholesterol synthesis, while ketoconazole significantly inhibited cholesterol synthesis after a single dose. The ezetimibe analog, SCH48461, inhibited the movement of exogenously administered cholesterol into lymph, but did not affect the appearance of newly synthesized cholesterol into lymph. These data suggest that this class of cholesterol absorption inhibitors does discriminate by blocking the movement of exogenous cholesterol in the enterocyte before it reaches the intracellular cholesterol pool to be incorporated into intestinal lipoproteins, without affecting the incorporation of newly synthesized cholesterol into intestinal lipoproteins.

Metabolism and structure activity data based drug design: discovery of (−) SCH 53079 an analog of the potent cholesterol absorption inhibitor (−) SCH 48461

Abstract Based on the metabolism of the potent cholesterol absorption inhibitor (−) SCH48461 and structure activity relationship information, we designed and evaluated (−)SCH 53079. This compound was found to be equipotent to (−)SCH 48461 in both the cholesterol-fed hamster and rhesus monkey assays. Importantly, (−)SCH 53079 was metabolically more stable than (−)SCH 48461 and as desired had very low plasma levels and did not cause hepatic enzyme induction.

(−)-SCH 57939: synthesis and pharmacological properties of a potent, metabolically stable cholesterol absorption inhibitor

Abstract Previous SAR studies of C-3 side chain modified analogs of (−)-SCH 48461, 1,3,4 as well as information concerning the metabolic stability this series, enabled us to design a cholesterol absorption inhibitor (i.e., (−) 2a, SCH 57939) with tenfold higher potency and greatly enhanced metabolic stability. The synthesis and pharmacological profile, including the role of relative stereochemistry at both the C3 and 1′ positions in determining the SAR of these compounds, will be discussed.