[Show abstract][Hide abstract] ABSTRACT: We document in vitro and in vivo effects of a novel, selective cannabinoid CB(1) receptor inverse agonist, Imidazole 24b (5-(4-chlorophenyl)-N-cyclohexyl-4-(2,4-dichlorophenyl)-1-methyl-imidazole-2-carboxamide). The in vitro binding affinity of Imidazole 24b for recombinant human and rat CB(1) receptor is 4 and 10 nM, respectively. Imidazole 24b binds to human cannabinoid CB(2) receptor with an affinity of 297 nM; in vitro, it is a receptor inverse agonist at both cannabinoid CB(1) and CB(2) receptors as it causes a further increase of forskolin-induced cAMP increase. Oral administration of Imidazole 24b blocked CP-55940-induced hypothermia, demonstrating cannabinoid CB(1) receptor antagonist efficacy in vivo. Using ex vivo autoradiography, Imidazole 24b resulted in dose-dependent increases in brain cannabinoid CB(1) receptor occupancy (RO) at 2h post-dosing in rats, indicating that approximately 50% receptor occupancy is sufficient for attenuation of receptor agonist-induced hypothermia. Imidazole 24b administered to C57Bl/6 mice and to dietary-induced obese (DIO) Sprague-Dawley rats attenuated overnight food intake with a minimal effective dose of 10 mg/kg, p.o. Administration had no effect in cannabinoid CB(1) receptor-deficient mice. DIO rats were dosed orally with vehicle, Imidazole 24b (1, 3 or 10 mg/kg), or dexfenfluramine (3 mg/kg) for 2 weeks. At 3 mg/kg, Imidazole 24b reduced cumulative food intake, leading to a non-significant decrease in weight gain. Imidazole 24b at 10 mg/kg and dexfenfluramine treatment inhibited food intake and attenuated weight gain. These findings suggest that selective cannabinoid CB(1) receptor inverse agonists such as Imidazole 24b have potential for the treatment of obesity.
Full-text · Article · Feb 2008 · European Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: A series of 2-aminoquinoline compounds was prepared and evaluated in MCH1R binding and functional antagonist assays. Small dialkyl, methylalkyl, methylcycloalkyl, and cyclic amines were tolerated at the quinoline 2-position. The in vivo efficacy of compound 12 was explored and compared to that of a related inactive analog to determine their effects on food intake and body weight in rodents.
[Show abstract][Hide abstract] ABSTRACT: Central administration of the neuropeptide melanin-concentrating hormone (MCH) stimulates feeding in rodents. We studied the effects of intracerebroventricular (i.c.v.) administration of an MCH-1 receptor agonist (Compound A) and an MCH-1 receptor antagonist (Compound B) on feeding in satiated rats. Compound B (10 microg, i.c.v.) blocked the acute orexigenic effect of Compound A (5 microg, i.c.v.). In an experiment designed to either stimulate or inhibit MCH-1 receptor signaling over an extended period, rats received continuous i.c.v. infusions of vehicle (saline), Compound A (30 microg/day), Compound B (30 or 48 microg/day) or neuropeptide Y (24 microg/day, as positive control) via implantable infusion pumps. Continuous MCH-1 receptor activation recapitulated the obese phenotype of MCH-over-expressor mice, manifest as enhanced feeding (+23%, P<0.001), caloric efficiency and body weight gain (+38%, P<0.005) over the 14-day period relative to controls. Chronic MCH-1 receptor activation also elevated plasma insulin and leptin levels significantly. Conversely, continuous MCH-1 receptor antagonism led to sustained reductions in food intake (-16%, P<0.001), body weight gain (-35%, P<0.01), and body fat gain relative to controls, without an effect on lean mass. Antagonism of the MCH-1 receptor may be an effective approach for the treatment of obesity.
No preview · Article · Aug 2003 · European Journal of Pharmacology
[Show abstract][Hide abstract] ABSTRACT: We measured plasma concentrations of agouti-related protein (AGRP) in humans and rats and determined whether these were affected by ingestion of a meal after fasting. In 17 healthy human subjects, the mean plasma concentration of AGRP was lower in the fed state than in the fasted state. Two hours after a breakfast meal, AGRP levels dropped by 39%. By contrast, a continued fast for 2 h increased the average AGRP concentration by 73%. In rats with diet-induced obesity, refeeding resulted in a 50% decrease in plasma AGRP concentrations following a fasting-refeeding protocol. Our results support the notion that plasma AGRP may serve as a biomarker for the transition from a fasted to the satiated state.
No preview · Article · Sep 2002 · Journal of Neuroendocrinology
[Show abstract][Hide abstract] ABSTRACT: Agouti-related protein (AgRP), a neuropeptide abundantly expressed in the arcuate nucleus of the hypothalamus, potently stimulates
feeding and body weight gain in rodents. AgRP is believed to exert its effects through the blockade of signaling by α-melanocyte-stimulating
hormone at central nervous system (CNS) melanocortin-3 receptor (Mc3r) and Mc4r. We generated AgRP-deficient (Agrp−/−) mice to examine the physiological role of AgRP. Agrp−/− mice are viable and exhibit normal locomotor activity, growth rates, body composition, and food intake. Additionally, Agrp−/− mice display normal responses to starvation, diet-induced obesity, and the administration of exogenous leptin or neuropeptide
Y (NPY). In situ hybridization failed to detect altered CNS expression levels for proopiomelanocortin, Mc3r, Mc4r, or NPY
mRNAs in Agrp−/− mice. As AgRP and the orexigenic peptide NPY are coexpressed in neurons of the arcuate nucleus, we generated AgRP and NPY
double-knockout (Agrp−/−;Npy−/−) mice to determine whether NPY or AgRP plays a compensatory role in Agrp−/− or NPY-deficient (Npy−/−) mice, respectively. Similarly to mice deficient in either AgRP or NPY, Agrp−/−;Npy−/− mice suffer no obvious feeding or body weight deficits and maintain a normal response to starvation. Our results demonstrate
that neither AgRP nor NPY is a critically required orexigenic factor, suggesting that other pathways capable of regulating
energy homeostasis can compensate for the loss of both AgRP and NPY.
Full-text · Article · Aug 2002 · Molecular and Cellular Biology
[Show abstract][Hide abstract] ABSTRACT: Melanin-concentrating hormone (MCH) is a cyclic 19-aa hypothalamic neuropeptide derived from a larger prohormone precursor of MCH (Pmch), which also encodes neuropeptide EI (NEI) and neuropeptide GE (NGE). Pmch-deficient (Pmch-/-) mice are lean, hypophagic, and have an increased metabolic rate. Transgenic mice overexpressing Pmch are hyperphagic and develop mild obesity. Consequently, MCH has been implicated in the regulation of energy homeostasis. The MCH 1 receptor (MCH1R) is one of two recently identified G protein-coupled receptors believed to be responsible for the actions of MCH. We evaluated the physiological role of MCH1R by generating MCH1R-deficient (Mch1r-/-) mice. Mch1r-/- mice have normal body weights, yet are lean and have reduced fat mass. Surprisingly, Mch1r-/- mice are hyperphagic when maintained on regular chow, and their leanness is a consequence of hyperactivity and altered metabolism. Consistent with the hyperactivity, Mch1r-/- mice are less susceptible to diet-induced obesity. Importantly, chronic central infusions of MCH induce hyperphagia and mild obesity in wild-type mice, but not in Mch1r-/- mice. We conclude that MCH1R is a physiologically relevant MCH receptor in mice that plays a role in energy homeostasis through multiple actions on locomotor activity, metabolism, appetite, and neuroendocrine function.
Full-text · Article · Apr 2002 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: We examined the effectiveness of sibutramine to modulate food intake and body composition in rats with two levels of adiposity imposed by the duration of their maintenance on a moderate-fat diet.
Male Sprague--Dawley rats were fed a 32% fat diet from weaning until 2 or 4 months of age, at which point, body fat was either 15% or 25%, respectively, as measured by DXA. Sibutramine (0.6 or 2 mg/kg, orally) was then given daily for 2 weeks.
Food intake and body weight decreased acutely in a dose-related manner in both groups with sibutramine treatment. In all rats, food intake suppression was attenuated after multiple days of sibutramine. Both 15%- and 25%-fat rats had a persistent decrease in weight gain over the 2-week period in response to sibutramine. The older, 25%-fat rats were more sensitive to sibutramine than the younger, 15%-fat rats with regard to the magnitude of overall food intake inhibition, decrease in body weight gain, and caloric efficiency. Despite these differences, sibutramine produced the same relative reductions in fat mass and had no effect on lean mass in the two groups.
Thus, sibutramine produced equivalent efficacy on carcass fat loss in both groups, despite less inhibition of feeding and body weight gain in leaner rats. Whether these changes are a result of the leaner rats being younger and on a steeper growth curve compared with older, fatter rats or whether this is a direct function of their level of adiposity remains to be determined.
[Show abstract][Hide abstract] ABSTRACT: Genetic1,
8 and pharmacological6,
studies have defined a role for the melanocortin-4 receptor (Mc4r) in the
regulation of energy homeostasis. The physiological function of Mc3r, a melanocortin
receptor expressed at high levels in the hypothalamus13, has
remained unknown. We evaluated the potential role of Mc3r in energy homeostasis
by studying Mc3r-deficient (Mc3r
and compared the functions of Mc3r and Mc4r in mice deficient
for both genes. The 4−6-month Mc3r
mice have increased fat mass, reduced lean mass and higher feed efficiency
than wild-type littermates, despite being hypophagic and maintaining normal
metabolic rates. (Feed efficiency is the ratio of weight gain to food intake.)
Consistent with increased fat mass, Mc3r
mice are hyperleptinaemic and male Mc3r
mice develop mild hyperinsulinaemia. Mc3r
mice did not have significantly altered corticosterone or total thyroxine
(T4) levels. Mice lacking both Mc3r and Mc4r become significantly
heavier than Mc4r
-/- mice. We conclude that
Mc3r and Mc4r serve non-redundant roles in the regulation of energy homeostasis.
[Show abstract][Hide abstract] ABSTRACT: We evaluated the role of the melanocortin-4 receptor (MC-4R) in the control of metabolic rate and food intake in mice. Intraperitoneal administration of the non-selective MC-R agonist melanotan II (MT-II; a cyclic heptapeptide) increases metabolic rate in wildtype mice, while MC-4R knockout mice are insensitive to the effects of MT-II on metabolic rate. MC-4R knockout mice are also insensitive to the effects of MT-II on reducing food intake. We conclude that MC-4R can mediate control of both metabolic rate and food intake in mice. We infer that a role for MC-3R in mediating the acute effects of MT-II on basal metabolic rate and food intake in wildtype mice seems limited.
No preview · Article · Mar 2000 · Transgenic Research