New advances in models and strategies for developing anti-obesity drugs

Introduction: Obesity is a worldwide pandemic. Obesity-related health and economic costs are staggering. Existing strategies to combat obesity through lifestyle improvements and medical intervention have had limited success. Pharmacotherapy, in combination with lifestyle modification, may play a vital role in reversing the disease burden. However, past and current weight-loss medications have had serious safety risks, notably cardiovascular and psychiatric events.

Areas covered: The authors review the strategies for designing new anti-obesity drugs by describing those currently in development. They describe their target, mechanism of action and developmental or regulatory status. Furthermore, they discuss the problem of weight regain following weight loss, and its relevance to the long-term success of anti-obesity pharmacotherapy.

Expert opinion: For weight management drugs to achieve the safety and efficacy required to be impactful, current studies are uncovering and characterizing new targets, including new signaling circuits and hormones regulating appetite and metabolism, and re-evaluating the role of pharmacotherapy in weight management. To avoid the safety failures of many past weight-loss drugs, the models and strategies covered in this article incorporate recent advances in knowledge and technology. We discuss the emergence of cGMP signaling as a potentially transformative target in weight management. Modulating cGMP signaling may represent an ideal goal for an anti-obesity pharmacotherapy, reflecting some of the major themes described in the present review: targeting pathways that are newly realized as relevant for weight management; promoting safety by re-purposing drugs that are safe, proven, and approved for clinical use; and having a synergistic effect on multiple, reinforcing pathways.     

Evaluation of lorcaserin on progression of prediabetes to type 2 diabetes and reversion to euglycemia

Objectives: Lorcaserin is a selective 5-HT_2C (5-hydroxytryptamine 2C) receptor agonist indicated for weight management. Here, we assess the impact of lorcaserin on progression from prediabetes to type 2 diabetes (T2D) and on reversion from prediabetes to euglycemia.

Methods: This is a post hoc analysis of pooled data from two Phase 3 studies, BLOOM and BLOSSOM (N = 6136), evaluating the impact of lorcaserin on weight and glycemic parameters over 52 weeks in the subpopulation of obese/overweight subjects with prediabetes, alternately defined by fasting plasma glucose (FPG) 100–125 mg/dl or glycated hemoglobin (HbA1c) 5.7–6.4% at baseline.

Results: At Week 52, in the subpopulation with prediabetes, nearly twice as many lorcaserin-treated subjects achieved ≥5% weight loss versus placebo (HbA1c: 55.6% vs. 27.5%, p < 0.001; FPG: 52.8% vs. 28.8%, p < 0.001), and a significantly lower percentage of lorcaserin-treated subjects progressed to T2D versus placebo based on HbA1c (lorcaserin 3.2%, placebo 5.0%, p = 0.032) but not FPG (lorcaserin 1.6%, placebo 2.6%, p = 0.227). A significantly greater proportion of lorcaserin-treated subjects versus placebo also reverted to euglycemia based on both HbA1c (lorcaserin 40%, placebo 29.5%, p < 0.001) and FPG (lorcaserin 52.4%, placebo 46.5%, p = 0.047).

Conclusion: In subjects with prediabetes, lorcaserin may contribute to weight loss and improve glycemic parameters, and thus may help with preventing progression to T2D and promoting reversion to euglycemia.

Clinical trial registration: www.clinicaltrials.gov identifiers are NCT00395135 (BLOOM) and NCT00603902 (BLOSSOM)     

The endocannabinoid system: A new pharmacological target for obesity treatment?

Being a great threaten for human health, obesity has become a pandemic chronic disease. There have been several therapeutic treatments for this social health issue, including diet and exercise therapy, medication and surgery, among which the diet is still the most common way. However, none of these therapeutic measures available is ideal, making it necessary to find an effective medical treatment. The endocannabinoid system, which is well known for its contributions in certain mental processes such as relaxation, amelioration of pain and anxiety, and sedation initiation, has been recently reported to play an essential role in regulating appetite and metabolism to maintain energy balance, leading to the belief that endocannabinoid system is closely related to obesity. This new discovery deepens our understanding of obesity, and provides us with a new direction for clinical obesity treatment. Rimonabant is an antagonist for CB1, and has entered the market in some countries. However, although effective as an anti-obesity drug, rimonabant also causes obviously adverse side-effects, thus is being doubted and denied for medical usage.     

Anti-Obesity Effects of Onion Extract in Zucker Diabetic Fatty Rats

Anti-obesity effects of onion extract were determined in obesity and diabetes-prone Zucker diabetic fatty rats by measuring the efficacy of markers concerned with diabetes and obesity. Body and adipose tissue weights in 5% of onion extract-fed group were found to be significantly lower than the control group without onion extract. Fasting blood glucose and HOMA-IR levels were also improved, although the serum insulin and leptin levels did not show any remarkable difference. Serum triglyceride and free fatty acid levels in both the 3% and 5%-fed group were found to be reduced compared to the control group. Additionally the feeding of the onion extract increased the glucose tolerance. These results suggest that dietary onion extract is beneficial for improving diabetes by decreasing lipid levels. We also examined differentiation ability of rat white preadipocyte cells using the onion extract and its sulfur-containing components. Cycloalliin, S-methyl-L-cysteine, S-propyl-L-cysteine sulfoxide, dimethyl trisulfide, especially S-methyl-L-cysteine sulfoxide were reported to be effective in inhibiting formation of oil drop in the cells, suggesting that these compounds may be involved in the anti-obesity effect of the onion extract.     

绿茶及其成分对小鼠体重、脂肪沉积和肝脏脂肪代谢酶活性的影响

目的研究绿茶及其成分的减肥作用机制。方法 50只雌性昆明小鼠随机分成5组,分别为对照组、2%绿茶组、0.05%咖啡碱组、0.3%儿茶素组及0.05%咖啡碱+0.3%儿茶素组。混合饲料投喂8 w后,摘取肝脏和腹腔脂肪(IPAT)并称重。分析血清中血糖、甘油三酯(TG)、总胆固醇、瘦素及胰岛素浓度和肝脏中脂类含量。测定肝脏中脂肪酸合成酶(FAS)、肉毒碱脂酰转移酶(CAT)和酰基辅酶A氧化酶(ACO)的活性。结果绿茶、咖啡碱、咖啡碱+儿茶素组体重增加和IPAT重量比对照组明显减少,特别是咖啡碱+儿茶素效果极显著。咖啡碱+儿茶素显著降低血中TG和瘦素浓度。绿茶、儿茶素、咖啡碱+儿茶素组小鼠肝脏中TG含量显著减少。咖啡碱+儿茶素明显降低肝脏中FAS活性,提高CAT和ACO的活性。结论咖啡碱和儿茶素组合通过调节脂肪代谢酶活性,抑制脂肪沉积和体重增加,并且咖啡碱和儿茶素对降脂减肥有协同作用。[营养学报,2012,34(6):605-608,612]     

Mechanism of the anti-obesity effects induced by a novel Melanin-concentrating hormone 1-receptor antagonist in mice

Background and purpose:

Melanin-concentrating hormone (MCH) is an orexigenic neuropeptide expressed in the lateral hypothalamus that is involved in feeding and body weight regulation. Intracerebroventricular infusion of a peptidic MCH1 receptor antagonist ameliorated obesity in murine models. Recently, small molecule MCH1 receptor antagonists have been developed and characterized for the treatment of obesity. However, little is known of the mechanism of the anti-obesity effects of MCH1 receptor antagonists.

Experimental approach:

To examine the mechanisms of action of the anti-obesity effect of MCH1 receptor antagonists more precisely, we conducted a pair-feeding study in mice with diet-induced obesity (DIO), chronically treated with an orally active and highly selective MCH1 receptor antagonist and examined changes in mRNA expression levels in liver, brown and white adipose tissues. We also assessed the acute effects of the MCH1 receptor antagonist in energy expenditure under thermoneutral conditions.

Key results:

Treatment with the MCH1 receptor antagonist at 30 mg·kg⁻¹ for 1 month moderately suppressed feeding and significantly reduced body weight by 24%. In contrast, pair-feeding resulted in a smaller weight reduction of 10%. Treatment with the MCH1 receptor antagonist resulted in a higher body temperature compared with the pair-fed group. TaqMan and calorimetry data suggested that the MCH1 receptor antagonist also stimulated thermogenesis.

Conclusions and implications:

Our results indicate that an MCH1 receptor antagonist caused anti-obesity effects im mice by acting on both energy intake and energy expenditure.     

A novel fluorophosphonate inhibitor of the biosynthesis of the endocannabinoid 2-arachidonoylglycerol with potential anti-obesity effects

Background and Purpose

The development of potent and selective inhibitors of the biosynthesis of the endocannabinoid 2-arachidonoylglycerol (2-AG) via DAG lipases (DAGL) α and β is just starting to be considered as a novel and promising source of pharmaceuticals for the treatment of disorders that might benefit from a reduction in endocannabinoid tone, such as hyperphagia in obese subjects.

Experimental Approach

Three new fluorophosphonate compounds O-7458, O-7459 and O-7460 were synthesized and characterized in various enzymatic assays. The effects of O-7460 on high-fat diet intake were tested in mice.

Key Results

Of the new compounds, O-7460 exhibited the highest potency (IC₅₀ = 690 nM) against the human recombinant DAGLα, and selectivity (IC₅₀ > 10 μM) towards COS-7 cell and human monoacylglycerol lipase (MAGL), and rat brain fatty acid amide hydrolase. Competitive activity-based protein profiling confirmed that O-7460 inhibits mouse brain MAGL only at concentrations ≥10 μM, and showed that this compound has only one major ‘off-target’, that is, the serine hydrolase KIAA1363. O-7460 did not exhibit measurable affinity for human recombinant CB₁ or CB₂ cannabinoid receptors (K_i > 10 μM). In mouse neuroblastoma N18TG2 cells stimulated with ionomycin, O-7460 (10 μM) reduced 2-AG levels. When administered to mice, O-7460 dose-dependently (0–12 mg·kg⁻¹, i.p.) inhibited the intake of a high-fat diet over a 14 h observation period, and, subsequently, slightly but significantly reduced body weight.

Conclusions and Implications

O-7460 might be considered a useful pharmacological tool to investigate further the role played by 2-AG both in vitro and in vivo under physiological as well as pathological conditions.

Linked Articles

This article is part of a themed section on Cannabinoids. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-4 & http://dx.doi.org/10.1111/bph.2012.167.issue-8