sb-334867-a and Obesity

INTRODUCTION. Recent research has reported the existence of a new class of neuropeptides, called orexins or hypocretins, which are produced by a small group of neurons in the hypothalamus and whose actions are mediated by two types of receptors: OX1R and OX2R. More specifically, the orexinergic neurons have been located exclusively in cells in the lateral, dorsomedial and perifornical areas of the hypothalamus. Despite this highly specific anatomical origin, the orexinergic neurons are projected widely into a number of brainstem, cortical and limbic regions. DEVELOPMENT. This fuzzy pattern of distribution of the orexinergic fibres would be indicating the involvement of this peptidic system in a wide range of functions; indeed, it has been related with the mechanisms that enable regulation of the sleep-wake cycle, the ingestion of food and drink, and some particular types of learning, such as learning certain preferences regarding tastes. It has also been suggested that upsets in the functioning of the orexinergic system would explain the appearance of certain clinical disorders like narcolepsy, obesity or addiction to drug of abuse. CONCLUSIONS. Further research will help to determine the functioning of orexinergic neurons and the interaction between the systems that regulate emotion, energetic homeostasis and the reward mechanisms, on the one hand, and the systems that regulate the sleep-wake cycle on the other. That knowledge would almost certainly make it possible to develop new drugs that, by acting upon the orexinergic system, would be effective in the treatment of sleep disorders such as insomnia or narcolepsy, eating disorders or drug addiction.. Orexina: implicaciones clinicas y terapeuticas.. Introduccion. Se ha descrito recientemente una nueva clase de neuropeptidos, las orexinas, tambien llamadas hipocretinas, producidos por un reducido grupo de neuronas hipotalamicas y cuyas acciones son mediadas por dos tipos de receptores, OX1R y OX2R. En concreto, las neuronas orexinergicas se han localizado en exclusiva en celulas de areas del hipotalamo lateral, dorsomedial y perifornical. A pesar de este origen anatomico tan localizado, las neuronas orexinergicas se proyectan ampliamente a numerosas regiones troncoencefalicas, corticales y limbicas. Desarrollo. Este patron difuso de distribucion de las fibras orexinergicas estaria indicando la intervencion de este sistema peptidico en una amplia variedad de funciones y, de hecho, se ha relacionado con los mecanismos que permiten la regulacion del ciclo sueño-vigilia, la ingesta de comida y de bebida y determinados aprendizajes como el aprendizaje de preferencias gustativas. Se ha sugerido tambien que la alteracion en el funcionamiento del sistema orexinergico explicaria la aparicion de determinados trastornos clinicos como la narcolepsia, la obesidad o la adiccion a drogas de abuso. Conclusiones. Nuevas investigaciones ayudaran a conocer el funcionamiento de las neuronas orexinergicas y la interaccion entre los sistemas que regulan la emocion, la homeostasis energetica y los mecanismos de recompensa con los sistemas que regulan el ciclo de sueño-vigilia. Se confia en que ese conocimiento permita desarrollar nuevos farmacos que, actuando sobre el sistema orexinergico, sean eficaces en el tratamiento de las alteraciones del sueño como el insomnio o la narcolepsia, de los trastornos de la alimentacion o de la drogadiccion.

Topics: Animals; Arousal; Azepines; Benzoxazoles; Disease Models, Animal; Drug Evaluation, Preclinical; Feeding and Eating Disorders; Feeding Behavior; Humans; Intracellular Signaling Peptides and Proteins; Mice; Mice, Knockout; Mice, Transgenic; Motor Activity; Naphthyridines; Narcolepsy; Neuropeptides; Obesity; Orexin Receptor Antagonists; Orexin Receptors; Orexins; Sleep Disorders, Circadian Rhythm; Sleep Disorders, Intrinsic; Substance-Related Disorders; Triazoles; Urea

Orexin-A and -B are two peptides derived by proteolytic cleavage from a 130-amino acid precursor, prepro-orexin, which were recently isolated from the rat hypothalamus. Orexin-A is fully conserved across mammalian species, whilst rat and human orexin-B differ by two amino acids. These peptides bind to two Gq-coupled receptors, termed orexin-1 and orexin-2. The receptors are 64% homologous and highly conserved across species. Orexin-A is equipotent at orexin-1 and orexin-2 receptors, whilst orexin-B displays moderate (approximately 10 fold) selectivity for orexin-2 receptors. The distribution and pharmacology of the orexin peptides and their receptors indicate that they play a role in various regulatory systems including energy homeostasis and the regulation of feeding, the evidence for which is reviewed here.

Topics: Animals; Benzoxazoles; Body Weight; Carrier Proteins; Eating; Humans; Intracellular Signaling Peptides and Proteins; Naphthyridines; Neuropeptides; Obesity; Orexin Receptors; Orexins; Receptors, G-Protein-Coupled; Receptors, Neuropeptide; Urea

Sympathetic vasomotor tone is elevated in obesity-related hypertension. Orexin importantly regulates energy metabolism and autonomic function. We hypothesized that alteration of orexin receptor in the paraventricular nucleus (PVN) of the hypothalamus leads to elevated sympathetic vasomotor tone in obesity. We used in vivo measurement of sympathetic vasomotor tone and microinjection into brain nucleus, whole-cell patch clamp recording in brain slices, and immunocytochemical staining in obese Zucker rats (OZRs) and lean Zucker rats (LZRs). Microinjection of orexin 1 receptor (OX1R) antagonist SB334867 into the PVN reduced basal arterial blood pressure (ABP) and renal sympathetic nerve activity (RSNA) in anesthetized OZRs but not in LZRs. Microinjection of orexin A into the PVN produced greater increases in ABP and RSNA in OZRs than in LZRs. Western blot analysis revealed that OX1R expression levels in the PVN were significantly increased in OZRs compared with LZRs. OX1R immunoreactivity was positive in retrogradely labeled PVN-spinal neurons. The basal firing rate of labeled PVN-spinal neurons was higher in OZRs than in LZRs. SB334867 decreased the basal firing activity of PVN-spinal neurons in OZRs but had no effect in LZRs. Orexin A induced a greater increase in the firing rate of PVN-spinal neurons in OZRs than in LZRs. In addition, orexin A induced larger currents in PVN-spinal neurons in OZRs than in LZRs. These data suggest that upregulation of OX1R in the PVN promotes hyperactivity of PVN presympathetic neurons and elevated sympathetic outflow in obesity.

Topics: Action Potentials; Animals; Benzoxazoles; Blood Pressure; Central Nervous System Agents; Disease Models, Animal; Male; Naphthyridines; Neuroanatomical Tract-Tracing Techniques; Neurons; Obesity; Orexin Receptors; Orexins; Paraventricular Hypothalamic Nucleus; Rats, Zucker; Spinal Cord; Sympathetic Nervous System; Tissue Culture Techniques; Up-Regulation; Urea

The present study was aimed to investigate the effects of orexin-A and orexin-1 receptor (OX1R) antagonist injected into the fourth ventricle of rats on food-intake and spontaneous physical activity (SPA). Obese rat model was induced by high fat diet. Different doses of orexin-A or SB334867, an OX1R antagonist, were injected into the fourth ventricle of obese and normal rats respectively. SPA and food intake were monitored for 4 h after injection in both light and dark environment. In the light measurement cycle, different doses of orexin-A significantly stimulated feeding and SPA in all injected rats, and the animals' responses showed a dose-dependent manner (P < 0.05-0.01), and compared with those of normal rats, the orexin-A induced food intake and SPA were more pronounced in obese rats. In the dark measurement cycle, different doses of orexin-A had no obvious effect on food intake and SPA in both normal and obese rats (P > 0.05). In the light cycle, different doses of SB334867 significantly decreased food intake and SPA in all rats during 0-2 h and 2-4 h after injection (P < 0.05), but the food intake and SPA in obese rats were significantly greater than those of normal rats. In the dark cycle, different doses of SB334867 showed no obvious effect on food intake and SPA of normal and obese rats (P > 0.05). These results suggest that fourth cerebral ventricle nuclei may be one target for orexin-A and light condition may play an important role in orexin-A and OX1R physiological functional processes.

Topics: Animals; Benzoxazoles; Diet, High-Fat; Eating; Fourth Ventricle; Motor Activity; Naphthyridines; Obesity; Orexin Receptor Antagonists; Orexin Receptors; Orexins; Rats; Urea

Obesity resistance due to elevated orexin signaling is accompanied by high levels of spontaneous physical activity (SPA). The behavioral and neural mechanisms underlying this observation have not been fully worked out. We determined the contribution of hypothalamic orexin receptors (OXRs) to SPA stimulated by orexin A (OXA), whether OXA-stimulated SPA was secondary to arousal and whether voluntary wheel running led to compensations in 24-h SPA. We further tested whether orexin action on dopamine one receptors (DA1R) in the substantia nigra (SN) plays an important role in the generation of SPA. To test this, SPA response was determined in lean and obese rats with cannulae targeted toward the rostral lateral hypothalamus (rLH) or SN. Sleep/wake states were also measured in rats with rLH cannula and electroencephalogram/electromyogram radiotelemetry transmitters. SPA in lean rats was more sensitive to antagonism of the OX1R and in the early response to the orexin 2 agonist. OXA increased arousal equally in lean and obese rodents, which is discordant from the greater SPA response in lean rats. Obesity-resistant rats ran more and wheel running was directly related to 24-h SPA levels. The OX1R antagonist, SB-334867-A, and the DA1R antagonist, SCH3390, in SN more effectively reduced SPA stimulated by OXA in obesity-resistant rats. These data suggest OXA-stimulated SPA is not secondary to enhanced arousal, propensity for SPA parallels inclination to run and that orexin action on dopaminergic neurons in SN may participate in the mediation of SPA and running wheel activity.

Topics: Age Factors; Animals; Benzazepines; Benzoxazoles; Body Weight; Dopamine Antagonists; Eating; Electromyography; Eye Movements; Hypothalamus; Intracellular Signaling Peptides and Proteins; Male; Motor Activity; Naphthyridines; Neuropeptides; Obesity; Orexin Receptor Antagonists; Orexins; Rats; Rats, Sprague-Dawley; Sleep; Substantia Nigra; Urea; Wakefulness

An orexin-1 receptor antagonist decreases food intake whereas orexin-A selectively induces hyperphagia to a high-fat diet. In the present study, we evaluated the effect of an orexin antagonist in two strains of rats that differ in their sensitivity to becoming obese while eating a high-fat diet. Male Osborne-Mendel (OM) and S5B/Pl (S5B) rats were treated acutely with an orexin-1 receptor antagonist (SB-334867), after adaptation to either a high-fat (56% fat energy) diet or a low-fat (10% fat energy) diet that were equicaloric for protein (24% energy). Ad libitum fed rats were injected intraperitoneally with SB-334867 at doses of 3, 10 or 30 mg/kg, or vehicle at the beginning of the dark cycle, and food intake and body weight were measured. Hypothalamic prepro-orexin and orexin-1 receptor mRNA expression were analyzed in OM and S5B rats fed at a high-fat or low-fat diet for two weeks. SB-334867 significantly decreased food intake in both strains of rats eating the high-fat diet but only in the OM rats eating the low fat diet. The effect was greatest at 12 and 24 h. Body weight was also reduced in OM rats 1d after injection of SB-334867 but not in the S5B rats. Prepro-orexin and orexin-1 receptor expression levels did not differ between strains or diets. These experiments demonstrate that an orexin antagonist (SB-334867) reduces food intake and has a greater effect in a rat strain that is susceptible to dietary-induced obesity, than in a resistant strain.

Topics: Animals; Benzoxazoles; Body Weight; Diet; Eating; Gene Expression Regulation; Hypothalamus; Male; Naphthyridines; Obesity; Orexin Receptors; Protein Precursors; Rats; Receptors, G-Protein-Coupled; Receptors, Neuropeptide; RNA, Messenger; Species Specificity; Urea

A single dose of the orexin-1 (OX1) receptor antagonist 1-(2-methylbenzoxazol-6-yl)-3-[1,5] naphthyridin-4-yl urea hydrochloride (SB-334867-A) reduces orexin-A-induced feeding and natural feeding in Sprague Dawley rats. In this study, the anti-obesity effects of SB-334867-A were determined in genetically obese (ob/ob) mice dosed with SB-334867-A (30 mg/kg, i.p.) once daily for 7 days, and then twice daily for a further 7 days. SB-334867-A reduced cumulative food intake and body weight gain over 14 days. Total fat mass gain, determined by Dual Emission X-ray Absorptiometry, was reduced, while gain in fat-free mass was unchanged. Fasting (5 h) blood glucose was also reduced at the end of the study, with a trend to reduced plasma insulin. Interscapular brown adipose tissue (BAT) weight was reduced, the tissue was noticeably darker in colour and quantitative PCR (TaqMan) analysis of this tissue showed a trend to an increase in uncoupling protein-1 mRNA expression, suggesting that SB-334867-A might stimulate thermogenesis. This was confirmed in a separate study in which a single dose of SB-334867-A (30 mg/kg, i.p.) increased metabolic rate over 4 h in ob/ob mice. OX1 receptor mRNA was detected in BAT, and its expression was increased by 58% by treatment with SB-334867-A. This is the first demonstration that OX1 receptor antagonists have potential as both anti-obesity and anti-diabetic agents.

Topics: Adipose Tissue, Brown; Animals; Benzoxazoles; Body Composition; Body Weight; Diabetes Mellitus, Type 2; Disease Models, Animal; Eating; Energy Metabolism; Female; Insulin; Mice; Mice, Inbred Strains; Naphthyridines; Obesity; Orexin Receptors; Receptors, G-Protein-Coupled; Receptors, Neuropeptide; RNA, Messenger; Urea

A variety of evidence implicates the orexins, especially orexin-A, in the regulation of food intake, but it has not been established whether this effect is mediated by the orexin-1 or orexin-2 receptor. In the present study, a selective orexin-1 receptor antagonist, 1-(2-methylbenzoxazol-6-yl)-3-[1,5]naphthyridin-4-yl urea hydrochloride (SB-334867-A), was administered intraperitoneally to rats under various conditions, and food consumption was subsequently measured over 24 h. In male rats, a single dose of SB-334867-A (30 mg/kg, i.p.) given during the light phase reduced both orexin-A-induced food intake (7 nmol, i.c.v.) and feeding stimulated by an overnight fast for 4 h. When given at the start of the dark phase, food consumption was reduced in both male and female rats over 24 h. Daily injections at the start of the dark phase for 3 days reduced natural feeding in male rats over 24 h on days one and three. These findings demonstrate direct inhibition of orexin-A induced food intake with a selective orexin-1 receptor antagonist. Furthermore, the suppression of nocturnal feeding and food intake stimulated by an overnight fast supports other evidence that orexin-A is involved in the regulation of natural feeding and suggests that orexin-1 receptor antagonists could be useful in the treatment of obesity.

Topics: Animals; Appetite Depressants; Benzoxazoles; Carrier Proteins; Darkness; Eating; Fasting; Female; Intracellular Signaling Peptides and Proteins; Male; Naphthyridines; Neuropeptides; Obesity; Orexin Receptors; Orexins; Rats; Rats, Sprague-Dawley; Receptors, G-Protein-Coupled; Receptors, Neuropeptide; Urea