NPY5R antagonism does not augment the weight loss efficacy of orlistat or sibutramine

Exploratory Literature Meta-Analysis to Characterize the Relationship Between Early and Longer Term Body Weight Loss for Antiobesity Compounds

The presented analysis was performed to characterize the relationship between treatment-related early (week 4) and longer term (3-6 months) weight loss to understand the potential utility of 4-week proof-of-mechanism studies in the early decision-making process during clinical development of new antiobesity compounds. A regression-based meta-analysis was performed leveraging publically available clinical outcomes data to (1) characterize the within-trial relationship between treatment-related early and longer term body weight loss and (2) identify and quantify key covariate effects on this relationship. Data from 89 randomized clinical trials with 209 treatment arms, representing observations from 54 461 patients and 9 treatments, were available for the meta-analysis. Results indicated that (1) there is a correlation between treatment-related early and longer term body weight loss (r > 0.9), (2) baseline body weight influences the relationship between early and longer term weight loss, whereas comorbidity such as type 2 diabetes mellitus, class of drugs including GLP-1 analogues and the antiobesity compounds lorcaserin or phentermine/topiramate showed no significant effects on this relationship. The model was externally evaluated with data from the investigational compound beloranib, for which longer term weight loss could be successfully predicted based on early response data. Based on these results, the identified strong relationship between treatment-related early and longer term weight loss appears to be independent of mechanism of action. Thus, findings from this analysis can optimize design of clinical studies and facilitate development of new anti-obesity compounds.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

Can neuropeptides treat obesity? A review of neuropeptides and their potential role in the treatment of obesity

Obesity is a major worldwide public health issue. The physiological systems that regulate body weight are thus of great interest as targets for anti-obesity agents. Peptidergic systems are critical to the regulation of energy homeostasis by key regions in the hypothalamus and brainstem. A number of neuropeptide systems have therefore been investigated as potential treatments for obesity. Blocking orexigenic peptide signals such as neuropeptide Y, melanin-concentrating hormone, orexins, relaxin-3 and galanin-like peptide or stimulating anorectic signalling pathways used by peptides such as the melanocortins, ciliary neurotrophic factor and brain-derived neurotrophic factor, are approaches that have shown some promise, but which have also highlighted possible concerns. Manipulation of central peptidergic systems poses a number of therapeutic problems, including brain access and side effects. Given that the homeostatic defence of body weight may limit the effectiveness of any single-target therapy developed, a combination therapy approach may offer the best hope for the effective prevention and treatment of obesity.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Imaging of brain dopamine pathways: implications for understanding obesity

Obesity is typically associated with abnormal eating behaviors. Brain imaging studies in humans implicate the involvement of dopamine (DA)-modulated circuits in pathologic eating behavior(s). Food cues increase striatal extracellular DA, providing evidence for the involvement of DA in the nonhedonic motivational properties of food. Food cues also increase metabolism in the orbitofrontal cortex indicating the association of this region with the motivation for food consumption. Similar to drug-addicted subjects, striatal DA D2 receptor availability is reduced in obese subjects, which may predispose obese subjects to seek food as a means to temporarily compensate for understimulated reward circuits. Decreased DA D2 receptors in the obese subjects are also associated with decreased metabolism in prefrontal regions involved in inhibitory control, which may underlie their inability to control food intake. Gastric stimulation in obese subjects activates cortical and limbic regions involved with self-control, motivation, and memory. These brain regions are also activated during drug craving in drug-addicted subjects. Obese subjects have increased metabolism in the somatosensory cortex, which suggests an enhanced sensitivity to the sensory properties of food. The reduction in DA D2 receptors in obese subjects coupled with the enhanced sensitivity to food palatability could make food their most salient reinforcer putting them at risk for compulsive eating and obesity. The results from these studies suggest that multiple but similar brain circuits are disrupted in obesity and drug addiction and suggest that strategies aimed at improving DA function might be beneficial in the treatment and prevention of obesity.

The role of neuropeptide Y in energy homeostasis

When administered into the brain, NPY acts at Y1 and Y5 receptors to increase food intake. The response occurs with a short latency and is quite robust, such that exogenous NPY is generally considered to be the most potent of a growing list of orexigenic compounds that act in the brain. The role of endogenous NPY is not so straightforward, however. Evidence from diverse types of experiments suggests that rather than initiating behavioral eating per se, endogenous NPY elicits autonomic responses that prepare the individual to better cope with consuming a calorically large meal.

Sympathetic nervous system in obesity-related hypertension: mechanisms and clinical implications

Obesity markedly increases the risk of hypertension and cardiovascular disease, which may be related to activation of the sympathetic nervous system (SNS). Sympathetic overactivity directly and indirectly contributes to blood pressure (BP) elevation in obesity, including stimulation of the renin-angiotensin-aldosterone system (RAAS). The adipocyte-derived peptide leptin suppresses appetite, increases thermogenesis, but also raises SNS activity and BP. Obese individuals exhibit hyperleptinemia but are resistant to its appetite-suppressing actions. Interestingly, animal models of obesity exhibit preserved sympathoexcitatory and pressor actions of leptin, despite resistance to its anorexic and metabolic actions, suggesting selective leptin resistance. Disturbance of intracellular signaling at specific hypothalamic neural networks appears to underlie selective leptin resistance. Delineation of these pathways should lead to novel approaches to treatment. In the meantime, treatment of obesity-hypertension has relied on antihypertensive drugs. Although sympathetic blockade is mechanistically attractive in obesity-hypertension, in practice its effects are disappointing because of adverse metabolic effects and inferior outcomes. On the basis of subgroup analyses of obese patients in large randomized clinical trials, drugs such as diuretics and RAAS blockers appear superior in preventing cardiovascular events in obesity--hypertension. An underused alternative approach to obesity-hypertension is induction of weight loss, which reduces circulating leptin and insulin, partially reverses resistance to these hormones, decreases sympathetic activation and improves BP and other risk factors. Though weight loss induced by lifestyle is often modest and transient, carefully selected pharmacological weight loss therapies can produce substantial and sustained antihypertensive effects additive to lifestyle interventions.

The role of NPY in hypothalamic mediated food intake

Neuropeptide Y (NPY) is a highly conserved neuropeptide with orexigenic actions in discrete hypothalamic nuclei that plays a role in regulating energy homeostasis. NPY signals via a family of high affinity receptors that mediate the widespread actions of NPY in all hypothalamic nuclei. These actions are also subject to tight, intricate regulation by numerous peripheral and central energy balance signals. The NPY system is embedded within a densely-redundant network designed to ensure stable energy homeostasis. This redundancy may underlie compensation for the loss of NPY or its receptors in germline knockouts, explaining why conventional knockouts of NPY or its receptors rarely yield a marked phenotypic change. We discuss insights into the hypothalamic role of NPY from studies of its physiological actions, responses to genetic manipulations and interactions with other energy balance signals. We conclude that numerous approaches must be employed to effectively study different aspects of NPY action.

N-Heteroaryl glycinamides and glycinamines as potent NPY5 antagonists

Subtype specific ligands are needed to evaluate the therapeutic potential of modulating the brain's neuropeptide Y system. The benzothiazepine glycinamide 1a was identified as an NPY5 antagonist lead. While having acceptable solubility, the compound was found to suffer from high clearance and poor exposure. Optimization efforts are described targeting improvements in potency, microsomal stability, and PK properties. The low microsomal stability and poor PK properties were addressed through the optimization of the sulfonyl urea and replacement of the benzothiazepinone with other N-heteroaryl glycinamides. For example, the analogous benzoxazine glycinamide 2e has improvements in both affinity (human Y5 K(i) 4 nM vs 1a 27 nM) and microsomal stability (human CL(int) 2.5 L/min vs 1a 35L/min). However the brain penetration (B/P 43/430 nM at 10 mg/kg PO) remained an unresolved issue. Further optimization by decreasing the hydrogen bond donating properties and PSA provided potent and brain penetrant NPY5 antagonists such as 5f (human Y5 K(i) 9 nM, B/P 520/840 nM 10 mg/kg PO).

Early weight loss and outcome at one year in obese adolescents treated with orlistat or placebo

BACKGROUND

Pharmacotherapy, associated with a comprehensive weight loss intervention, has emerged as a promising therapeutic approach in adolescents. Identification of subjects who best respond to a pharmacological intervention remains difficult.

OBJECTIVE

To compare the value of early weight loss after 12 weeks of treatment with placebo or orlistat (120 mg three times a day) in predicting treatment outcome after 52 weeks.

METHODS

Secondary analysis of a randomized control trial in 182 placebo-treated and 357 orlistat-treated obese adolescents (Body mass index [BMI] ≥ 2 kg/m(2) above the 95(th) percentile).

RESULTS

Percent weight change at 12 weeks was positively correlated with percent change in weight (r(2) ≥ 0.41), BMI (r(2) ≥ 0.33) and waist circumference (r(2) ≥ 0.20) at 52 weeks in both the placebo and orlistat groups (P < 0.001). A weight loss ≥ 5% of baseline weight at 12 weeks was associated with a mean weight loss of 8.1% (95% CI: 6.4 to 9.7) at the study end that was independent of treatment. Subjects in the orlistat group were 2.44 times (95% CI: 1.34 to 4.46) more likely to experience a weight loss ≥ 5% after 12 weeks than subjects in the placebo group (P = 0.0028).

CONCLUSIONS

Early weight loss predicts a favourable outcome in both placebo-treated and orlistat-treated subjects but is more than 2 times more likely to occur in the orlistat group. Addition of orlistat should be considered as part of a weight loss intervention but reevaluated after 3 months of treatment.

Synthesis and structure-activity relationship of N-(3-azabicyclo[3.1.0]hex-6-ylmethyl)-5-(2-pyridinyl)-1,3-thiazol-2-amines derivatives as NPY Y5 antagonists

A novel class of small molecule NPY Y5 antagonists based around an azabicyclo[3.1.0]hexane scaffold was identified through modification of a screening hit. Structure-activity relationships and efforts undertaken to achieve a favourable pharmacokinetic profile in rat are described.

The use of sibutramine in the management of obesity and related disorders: an update

Aims:

To review the major trials that evaluated the efficacy and safety of the use of sibutramine for weight loss and the impact of this agent on obesity-related disorders.

Methods and results:

The most important articles on sibutramine up to January 2009 were located by a PubMed and Medline search. Sibutramine reduces food intake and body weight more than placebo and has positive effects on the lipid profile (mainly triglycerides and high density lipoprotein cholesterol), glycemic control and inflammatory markers in studies for up to one year. Preliminary studies showed that sibutramine may also improve other obesity-associated disorders such as polycystic ovary syndrome, left ventricular hypertrophy, binge eating disorder and adolescent obesity. The high discontinuation rates and some safety issues mainly due to the increase in blood pressure and pulse rate have to be considered. Additionally, it has not yet been established that treatment with sibutramine will reduce cardiovascular events and total mortality.

Conclusions:

Sibutramine, in conjunction with lifestyle measures, is a useful drug for reducing body weight and improving associated cardiometabolic risk factors and obesity-related disorders. Studies of longer duration are required to determine the precise indications of the drug, to evaluate safety issues and to assess its efficacy on cardiovascular mortality.

Effects of a novel Y5 antagonist in obese mice: combination with food restriction or sibutramine

OBJECTIVE

To further address the function of the Y5 receptor in energy homeostasis, we investigated the effects of a novel spironolactone Y5 antagonist in diet-induced obese (DIO) mice.

METHODS AND PROCEDURES

Male C57BL/6 or Npy5r(-/-) mice were adapted to high-fat (HF) diet for 6-10 months and were submitted to three experimental treatments. First, the Y5 antagonist at a dose of 10 or 30 mg/kg was administered for 1 month to DIO C57BL/6 or Npy5r(-/-) mice. Second, the Y5 antagonist at 30 mg/kg was administered for 1.5 months to DIO C57BL/6 mice, and insulin sensitivity was evaluated using an insulin tolerance test. After a recovery period, nuclear magnetic resonance measurement was performed to evaluate body composition. Third, DIO mice were treated with the Y5 antagonist alone, or in combination with 10% food restriction, or with another anorectic agent, sibutramine at 10 mg/kg, for 1.5 months. Plasma glucose, insulin, and leptin levels, and adipose tissue weights were quantified.

RESULTS

The spironolactone Y5 antagonist significantly reduced body weight in C57BL DIO mice, but not in Npy5r(-/-) DIO mice. The Y5 antagonist produced a fat-selective loss of body weight, and ameliorated obesity-associated insulin resistance in DIO mice. In addition, the Y5 antagonist combined with either food restriction or sibutramine tended to produce greater body weight loss, as compared with single treatment.

DISCUSSION

These findings demonstrate that the Y5 receptor is an important mediator of energy homeostasis in rodents.

Update on obesity

Endocrinologists have unique skills in evaluating and caring for patients with metabolic diseases. As such, they have a special role to play within the organizations in which they work as leaders in the approach to managing obese patients. Recent epidemiological data demonstrate that the prevalence of obesity is beginning to plateau. However, the rate of severe obesity in adults and the prevalence of overweight among children continue to grow, suggesting that in the future there will be an increasing burden of obesity-related illnesses. A number of recent studies have identified a number of novel mechanisms that predispose to obesity including several newly identified genes, the role of intestinal microflora, and even social networks. The selection of treatment for obese patients remains a complex issue. Recent studies demonstrate that a range of dietary approaches including the Atkins diet can provide modest weight loss, although the key feature appears to be adherence in the dietary strategy. High levels of physical activity appear to be necessary to maintain a reduced state, although modest increases in activity improve fitness. Although the new understanding of biology of weight regulation has provided a wide range of potential drug targets, available pharmacotherapy options remain limited although a number of potential targets show promise. Recent data provides the most enthusiasm for surgical treatment of obesity. Several recent studies demonstrate a reduction in mortality and dramatic benefits in diabetes in obese patients treated surgically. Questions remain as to the best surgical approach and the cost effectiveness. Research advances in obesity continue to move at a rapid pace and raise hopes for more effective management strategies in the future.