RESUMEN
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 (apoE-/-) mice. Cholesterol absorption was inhibited by >90% at doses of ezetimibe >3 mg/kg in apoE-/- mice. Atherosclerosis and lipoprotein changes were determined in apoE-/- 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 apoE-/- mice. Although apoE-/- 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.
Asunto(s)
Anticolesterolemiantes/farmacología , Arteriosclerosis/prevención & control , Azetidinas/farmacología , Colesterol/farmacocinética , Administración Oral , Animales , Aorta Abdominal/patología , Aorta Torácica/patología , Apolipoproteínas E/deficiencia , Arteriosclerosis/patología , HDL-Colesterol/sangre , HDL-Colesterol/efectos de los fármacos , VLDL-Colesterol/sangre , VLDL-Colesterol/efectos de los fármacos , Dieta con Restricción de Grasas , Progresión de la Enfermedad , Ezetimiba , Absorción Intestinal/efectos de los fármacos , Lipoproteínas/sangre , Hígado/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones MutantesRESUMEN
1. 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. 2. 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. 3. Ezetimibe reduced plasma cholesterol and hepatic cholesterol accumulation in cholesterol-fed hamsters with an ED(50) 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. 4. 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.
Asunto(s)
Anticolesterolemiantes/farmacología , Azetidinas/farmacología , Colesterol/farmacocinética , Absorción Intestinal/efectos de los fármacos , Mucosa Intestinal/metabolismo , Páncreas/fisiología , Animales , Procedimientos Quirúrgicos del Sistema Biliar/métodos , Radioisótopos de Carbono , Colesterol/sangre , Ésteres del Colesterol/farmacocinética , Colesterol en la Dieta/administración & dosificación , Colesterol en la Dieta/farmacocinética , Cricetinae , Relación Dosis-Respuesta a Droga , Etinilestradiol/farmacocinética , Ezetimiba , Hígado/efectos de los fármacos , Hígado/metabolismo , Masculino , Mesocricetus , Progesterona/farmacocinética , Ratas , Ratas Sprague-Dawley , Ácido Taurocólico/farmacocinética , Trioleína/farmacocinética , Tritio , Vitamina A/farmacocinética , Vitamina D/farmacocinéticaRESUMEN
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.
Asunto(s)
Anticolesterolemiantes/farmacología , Azetidinas/farmacología , Colesterol en la Dieta/administración & dosificación , Hipercolesterolemia/prevención & control , Animales , Colesterol/sangre , Ésteres del Colesterol/sangre , HDL-Colesterol/sangre , HDL-Colesterol/efectos de los fármacos , LDL-Colesterol/sangre , LDL-Colesterol/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Ezetimiba , Femenino , Hipercolesterolemia/sangre , Hipercolesterolemia/inducido químicamente , Macaca fascicularis , Macaca mulatta , Masculino , Factores de Tiempo , Triglicéridos/sangreRESUMEN
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 (ID(50) = 0.0015 mg kg(-1)) and rhesus monkey (ID(50) = 0.0005 mg kg(-1)).
Asunto(s)
Anticolesterolemiantes/farmacología , Azetidinas/farmacología , Colesterol/metabolismo , Absorción Intestinal/efectos de los fármacos , Animales , Anticolesterolemiantes/metabolismo , Anticolesterolemiantes/farmacocinética , Autorradiografía , Azetidinas/metabolismo , Azetidinas/farmacocinética , Bilis/metabolismo , Conductos Biliares/efectos de los fármacos , Conductos Biliares/metabolismo , Cateterismo , Cromatografía Líquida de Alta Presión , Ezetimiba , Inyecciones Intravenosas , Intestinos/efectos de los fármacos , Intestinos/patología , Masculino , Ratas , Ratas Sprague-Dawley , Factores de Tiempo , TritioRESUMEN
Glucagon-like peptide (7-36) amide (GLP-1) acutely inhibits food and water consumption in rats after intracerebroventricular (icv) administration. To assess the potential for desensitization of these effects, we investigated the effects of chronic icv administration of GLP-1 on food consumption and body weight in Sprague-Dawley (SD) rats and Zucker (fa/fa) obese rats. In vitro functional densensitization of the GLP-1 receptor was not observed after overnight exposure of Rin m5F insulinoma cells to GLP-1 at concentrations up to 10 nM. Administration of GLP-1 to SD rats (30 microg icv twice a day for 6 days) resulted in significant reductions in 24-hour food consumption each day (25 +/- 1%). Continuous icv infusion of GLP-1 for 7 and 14 days significantly inhibited cumulative food consumption and reduced body weight in SD rats. In the genetically obese Zucker rat, chronic dosing with GLP-1 (30 microg icv) once a day for 6 days caused significant reductions in food consumption each day and a reduction in body weight. These results indicate that the GLP-1 pathways in the central nervous system controlling food consumption do not desensitize after chronic exposure to GLP-1 and suggest that agonists of the central GLP-1 receptor may be effective agents for the treatment of obesity.
Asunto(s)
Peso Corporal/efectos de los fármacos , Ingestión de Alimentos/efectos de los fármacos , Neurotransmisores/farmacología , Obesidad/fisiopatología , Fragmentos de Péptidos/farmacología , Animales , Glucagón , Péptido 1 Similar al Glucagón , Receptor del Péptido 1 Similar al Glucagón , Péptidos Similares al Glucagón , Inyecciones Intraventriculares , Insulinoma/metabolismo , Masculino , Neoplasias Pancreáticas/metabolismo , Fragmentos de Péptidos/administración & dosificación , Ratas , Ratas Sprague-Dawley , Ratas Zucker , Receptores de Glucagón/efectos de los fármacos , Receptores de Glucagón/metabolismo , Células Tumorales CultivadasRESUMEN
SCH48461 is a selective and highly potent inhibitor of cholesterol absorption. In rats, SCH48461 is rapidly and completely metabolized in the first pass through the body. To compare the activity of the metabolites of SCH48461 with SCH48461 itself, an intestinally cannulated, bile duct-cannulated rat model for cholesterol absorption was developed. SCH48461 inhibited the absorption of cholesterol by 70%, whereas bile containing the metabolites of SCH48461 (henceforth, "metabolite bile") inhibited the absorption by greater than 95%. Very little of the recovered radioactive dose of SCH48461 was located in the intestinal lumen (7%) or wall (4%), whereas 85% appeared in bile. However, in rats treated with metabolite bile, 62% of the dose remained in the lumen, 13% was associated with the wall and only 24% reappeared in bile, which suggests that the activity of the metabolite bile may be related to its higher retention in the intestinal wall. Rats treated with metabolite bile had 64% and 84% less drug-related radioactivity in their plasma and livers, respectively, compared with animals treated with SCH48461, which indicates that the metabolites are systemically less available than SCH48461. The metabolites in bile were separated by high-performance liquid chromatography; the most active fraction in the bile duct-cannulated rat model was identified by mass spectrometry as the glucuronide of the C4-phenol of SCH48461. The other fractions had moderate or no activity. Through the identification of the most active biliary metabolites of SCH48461 in the rat, we have discovered SCH58235, a novel cholesterol absorption inhibitor which is 400 times more potent than SCH48461 in the cholesterol-fed rhesus monkey.
Asunto(s)
Anticolesterolemiantes/farmacología , Azetidinas/metabolismo , Azetidinas/farmacología , Colesterol/metabolismo , Absorción , Animales , Anticolesterolemiantes/metabolismo , Bilis/metabolismo , LDL-Colesterol/sangre , Relación Dosis-Respuesta a Droga , Ezetimiba , Macaca mulatta , Masculino , Ratas , Ratas Sprague-DawleyRESUMEN
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.
Asunto(s)
Obesidad/tratamiento farmacológico , Proteínas/administración & dosificación , Proteínas/uso terapéutico , Animales , Regulación del Apetito/efectos de los fármacos , Peso Corporal/efectos de los fármacos , Grasas de la Dieta/administración & dosificación , Grasas de la Dieta/efectos adversos , Relación Dosis-Respuesta a Droga , Resistencia a Medicamentos , Ingestión de Alimentos/efectos de los fármacos , Conducta Alimentaria/efectos de los fármacos , Leptina , Estudios Longitudinales , Masculino , Ratones , Ratones Endogámicos AKR , Ratones Endogámicos C57BL , Obesidad/sangre , Proteínas/análisis , Factores de TiempoRESUMEN
Brain and whole body localization and distribution of 125I-leptin was determined after intraperitoneal administration to ob/ob and db/db mice, and was compared to inhibition of food intake. Food intake was not significantly inhibited at3 hours post-injection, but was decreased significantly at 6 h (p < 0.0007) and 24 h (p < 0.02) in ob/ob mice, times at which > 97 % of the radioactive dose was found in the urine. The highest concentrations of 125I-leptin at all time-points were found in the serum, liver and kidneys. These findings were verified by whole body autoradiography. Virtually no 125I-leptin was found in the CNS at later timepoints in either ob/ob or db/db mice. Coronal sectioning of entire brains from ob/ob and db/db mice revealed 125I radioactivity localized to the choroid plexus and in the ventricular space, but not in other CNS regions. No differences in localization, accumulation, or clearance of 125I-leptin in ob/ob vs. db/db mice were found in any of the tissues studied. The present studies demonstrate that the inhibitory effect of leptin on food intake in the ob/ob mouse persists for up to 24 hours after a single dose, despite the complete degradation and elimination of the labeled leptin during the first several hours after injection.
Asunto(s)
Ingestión de Alimentos/efectos de los fármacos , Obesidad/metabolismo , Proteínas/farmacología , Proteínas/farmacocinética , Tejido Adiposo/metabolismo , Animales , Autorradiografía , Encéfalo/metabolismo , Ventrículos Cerebrales/metabolismo , Plexo Coroideo/metabolismo , Femenino , Humanos , Inyecciones Intraperitoneales , Mucosa Intestinal/metabolismo , Radioisótopos de Yodo , Riñón/metabolismo , Cinética , Leptina , Hígado/metabolismo , Ratones , Ratones Obesos , Proteínas/administración & dosificación , Distribución TisularRESUMEN
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 group's 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)