Medications for weight reduction

Proportional Feedback Control of Energy Intake During Obesity Pharmacotherapy

OBJECTIVE

Obesity pharmacotherapies result in an exponential time course for energy intake whereby large early decreases dissipate over time. This pattern of declining drug efficacy to decrease energy intake results in a weight loss plateau within approximately 1 year. This study aimed to elucidate the physiology underlying the exponential decay of drug effects on energy intake.

METHODS

Placebo-subtracted energy intake time courses were examined during long-term obesity pharmacotherapy trials for 14 different drugs or drug combinations within the theoretical framework of a proportional feedback control system regulating human body weight.

RESULTS

Assuming each obesity drug had a relatively constant effect on average energy intake and did not affect other model parameters, our model correctly predicted that long-term placebo-subtracted energy intake was linearly related to early reductions in energy intake according to a prespecified equation with no free parameters. The simple model explained about 70% of the variance between drug studies with respect to the long-term effects on energy intake, although a significant proportional bias was evident.

CONCLUSIONS

The exponential decay over time of obesity pharmacotherapies to suppress energy intake can be interpreted as a relatively constant effect of each drug superimposed on a physiological feedback control system regulating body weight.

Alterations in hypothalamic gene expression following Roux-en-Y gastric bypass

OBJECTIVE

The role of the central nervous system in mediating metabolic effects of Roux-en-Y gastric bypass (RYGB) surgery is poorly understood. Using a rat model of RYGB, we aimed to identify changes in gene expression of key hypothalamic neuropeptides known to be involved in the regulation of energy balance.

METHODS

Lean male Sprague-Dawley rats underwent either RYGB or sham surgery. Body weight and food intake were monitored bi-weekly for 60 days post-surgery. In situ hybridization mRNA analysis of hypothalamic AgRP, NPY, CART, POMC and MCH was applied to RYGB and sham animals and compared with ad libitum fed and food-restricted rats. Furthermore, in situ hybridization mRNA analysis of dopaminergic transmission markers (TH and DAT) was applied in the midbrain.

RESULTS

RYGB surgery significantly reduced body weight and intake of a highly palatable diet but increased chow consumption compared with sham operated controls. In the arcuate nucleus, RYGB surgery increased mRNA levels of orexigenic AgRP and NPY, whereas no change was observed in anorexigenic CART and POMC mRNA levels. A similar pattern was seen in food-restricted versus ad libitum fed rats. In contrast to a significant increase of orexigenic MCH mRNA levels in food-restricted animals, RYGB did not change MCH expression in the lateral hypothalamus. In the VTA, RYGB surgery induced a reduction in mRNA levels of TH and DAT, whereas no changes were observed in the substantia nigra relative to sham surgery.

CONCLUSION

RYGB surgery increases the mRNA levels of hunger-associated signaling markers in the rat arcuate nucleus without concomitantly increasing downstream MCH expression in the lateral hypothalamus, suggesting that RYGB surgery puts a brake on orexigenic hypothalamic output signals. In addition, down-regulation of midbrain TH and DAT expression suggests that altered dopaminergic activity also contributes to the reduced intake of palatable food in RYGB rats.

Engineering of a Novel Simplified Human Insulin-Like Peptide 5 Agonist

Insulin-like peptide 5 (INSL5) has recently been discovered as only the second orexigenic gut hormone after ghrelin. As we have previously reported, INSL5 is extremely difficult to assemble and oxidize into its two-chain three-disulfide structure. The focus of this study was to generate structure-activity relationships (SARs) of INSL5 and use it to develop a potent and simpler INSL5 mimetic with RXFP4 agonist activity. A series of human and mouse INSL5 (hINSL5/mINSL5) analogues were designed and chemically synthesized, resulting in a chimeric INSL5 analogue exhibiting more than 10-fold higher potency (0.35 nM) at human RXFP4 compared with native hINSL5 (4.57 nM). The SAR study also identified a key residue (K(A15)) in the A-chain of mINSL5 that contributes to improved RXFP4 affinity and potency of mINSL5 compared with hINSL5. This knowledge ultimately led us to engineer a minimized hINSL5 mimetic agonist that retains native hINSL5-like RXFP4 affinity and potency at human RXFP4. This minimized analogue was synthesized in 17.5-fold higher yield and in less time compared with hINSL5.

Quantifying energy intake changes during obesity pharmacotherapy

OBJECTIVE

Despite the fact that most obesity drugs primarily work by reducing metabolizable energy intake, elucidation of the time course of energy intake changes during long-term obesity pharmacotherapy has been prevented by the limitations of self-report methods of measuring energy intake.

METHODS

A validated mathematical model of human metabolism was used to provide the first quantification of metabolizable energy intake changes during long-term obesity pharmacotherapy using body weight data from randomized, placebo-controlled trials that evaluated 14 different drugs or drug combinations.

RESULTS

Changes in metabolizable energy intake during obesity pharmacotherapy were reasonably well-described by an exponential pattern comprising three simple parameters, with early large changes in metabolizable energy intake followed by a slow transition to a smaller persistent drug effect.

CONCLUSIONS

Repeated body weight measurements along with a mathematical model of human metabolism can be used to quantify changes in metabolizable energy intake during obesity pharmacotherapy. The calculated metabolizable energy intake changes followed an exponential time course, and therefore different drugs can be evaluated and compared using a common mathematical framework.

Advantages of percent weight loss as a method of reporting weight loss after Roux-en-Y gastric bypass

OBJECTIVE

Although Roux-en-Y gastric bypass (RYGB) is an effective treatment for severe obesity, weight loss (WL) after this operation is highly variable. Accurate predictors of outcome would thus be useful in identifying those patients who would most benefit from this invasive therapy. WL has been characterized using several different metrics, including the number of BMI units lost (ΔBMI), percent baseline WL (%WL), and percent excess body WL (%EBWL). To identify clinically relevant predictors most sensitively, it is necessary to avoid confounding by other factors, including preoperative BMI (pBMI), the strongest known predictor of RYGB-induced WL.

DESIGN AND METHODS

To determine the WL measure least associated with pBMI, outcomes of 846 patients undergoing RYGB were analyzed.

RESULTS

Patients in this cohort had an average pBMI of 50.0 kg/m(2) at baseline. At weight nadir, they lost an average 19.4 kg/m(2), 38.7% WL, and 81.2% EBWL. pBMI was strongly and positively associated with ΔBMI at both 1 year (r = 0.56, P = 4.7 × 10(-51)) and nadir (r = 0.58, P = 2.8 × 10(-77)) and strongly but negatively associated with %EBWL at 1 year (r = -0.52, P = 3.8 × 10(-44)) and nadir (r = -0.45, P = 7.2×10(-43)). In contrast, pBMI was not significantly associated with %WL at 1 year (r = 0.04, P = 0.33) and only weakly associated at nadir (r = 0.13, P = 0.0002).

CONCLUSIONS

Of the metrics examined, %WL is the parameter describing WL after RYGB least influenced by pBMI. It thus improves comparison of WL outcomes across studies of patients undergoing surgery and facilitates the most sensitive identification of novel predictors of surgery-induced WL. We therefore is recommend that %WL be adopted more broadly in reporting weight loss after RYGB.

Weight loss after gastric bypass is associated with a variant at 15q26.1

The amount of weight loss attained after Roux-en-Y gastric bypass (RYGB) surgery follows a wide and normal distribution, and recent evidence indicates that this weight loss is due to physiological, rather than mechanical, mechanisms. To identify potential genetic factors associated with weight loss after RYGB, we performed a genome-wide association study (GWAS) of 693 individuals undergoing RYGB and then replicated this analysis in an independent population of 327 individuals undergoing RYGB. We found that a 15q26.1 locus near ST8SIA2 and SLCO3A1 was significantly associated with weight loss after RYGB. Expression of ST8SIA2 in omental fat of these individuals at baseline was significantly associated with weight loss after RYGB. Gene expression analysis in RYGB and weight-matched, sham-operated (WMS) mice revealed that expression of St8sia2 and Slco3a1 was significantly altered in metabolically active tissues in RYGB-treated compared to WMS mice. These findings provide strong evidence for specific genetic influences on weight loss after RYGB and underscore the biological nature of the response to RYGB.

Melanocortin-4 receptor signaling is required for weight loss after gastric bypass surgery

CONTEXT

Roux-en-Y gastric bypass (RYGB) is one of the most effective long-term therapies for the treatment of severe obesity. Recent evidence indicates that RYGB effects weight loss through multiple physiological mechanisms, including changes in energy expenditure, food intake, food preference, and reward pathways.

OBJECTIVE

Because central melanocortin signaling plays an important role in the regulation of energy homeostasis, we investigated whether genetic disruption of the melanocortin-4 receptor (MC4R) in rodents and humans affects weight loss after RYGB.

METHODS AND RESULTS

Here we report that MC4R(-/-) mice lost substantially less weight after surgery than wild-type animals, indicating that MC4R signaling is necessary for the weight loss effects of RYGB in this model. Mice heterozygous for MC4R remain fully responsive to gastric bypass. To determine whether mutations affect surgically induced weight loss in humans, we sequenced the MC4R gene in 972 patients undergoing RYGB. Patients heterozygous for MC4R mutations exhibited the same magnitude and distribution of postoperative weight loss as patients without such mutations, suggesting that although two normal copies of the MC4R gene are necessary for normal weight regulation, a single normal copy of the MC4R gene is sufficient to mediate the weight loss effects of RYGB.

CONCLUSIONS

MC4R is the first gene identified that is required for the sustained effects of bariatric surgery. The need for MC4R signaling for the weight loss effects of RYGB in mice underscores the physiological mechanisms of action of this procedure and demonstrates that RYGB both influences and is dependent on the normal pathways that regulate energy balance.

Heritability of the weight loss response to gastric bypass surgery

CONTEXT

The use of Roux-en-Y gastric bypass (RYGB) surgery to treat severe obesity has grown dramatically. RYGB is highly effective, but the response in individual patients varies widely, and clinical predictors have been able to explain only a fraction of this variation.

OBJECTIVE

Our objective was to determine whether there is a significant genetic contribution to weight loss after RYGB.

METHODS

We genotyped 848 patients undergoing RYGB. Using identity-by-descent methods, we identified 13 pairs of first-degree relatives. We identified an additional 10 pairs of individuals who were living together but are not genetically related and randomly paired the remaining 794 individuals. We then compared weight loss within and across pairs.

RESULTS

First-degree relative pairs had a similar response to surgery, with a 9% mean difference in excess weight loss between members of each pair. This similarity was not seen with cohabitating individuals (26% mean difference; P = 0.005 vs. first-degree pairs) or unrelated individuals (25% mean difference; P = 0.001). Cohabitating individuals had within-pair differences in weight loss no more similar than randomly paired individuals (P = 0.60). The pair relationship explained a significant portion of the variation in weight loss in first-degree relatives [intraclass correlation coefficient (ICC) = 70.4%; P = 0.02] but not in random subjects (ICC = 0.9%; P = 0.48) or genetically unrelated cohabitating individuals (ICC = 14.3%; P = 0.67).

CONCLUSIONS

Genetic factors strongly influence the effect of RYGB on body weight. Identification of the specific genes that mediate this effect will advance our understanding of the biological mechanisms of weight loss after RYGB and should help identify patients who will benefit the most from this intervention.

Pharmacology in health foods:merits and demerits of food with health claims for the prevention of metabolic syndrome

The merits and demerits of food with health claims for the prevention of metabolic syndrome (MS) are reviewed. One major underlying cause of MS is obesity. Diet and lifestyle changes remain the cornerstones of therapy for obesity, but resulting weight loss is often small and long-term success is extremely uncommon and disappointing. Many anti-obesity drugs have been associated with unintended therapeutic outcomes. Currently, only one drug (mazindol) is approved in Japan for short-term treatment of individuals with a BMI over 35 kg/m(2). Treatment with orlistat with dietary modification, caffeine, or protein supplementation; consuming a low-fat diet; adherence to physical activity routines; prolonged contact with participants; problem-solving therapy; and the alternative treatment of acupressure are efficacious in reducing weight regain after weight loss treatment. Because obesity is highly stigmatized, any effective treatment should be made available to improve quality of life and self-image. Therefore, it is necessary to provide information to consumers through the media concerning 1) basic knowledge about health foods and laws concerning them, 2) scientifically based information on safety/effectiveness of health foods and food elements, and 3) reports on health disturbances associated with health foods around the world.

Pharmacologic therapies for obesity

This article examines the transitions in pharmacological therapy for obesity. It reviews the current options approved by the Food and Drug Administration and several drugs approved for other indications that can be used to treat obesity as well. Because weight regulation is complex and redundant systems protect against perceived starvation, optimal treatment of obesity in individual patients will likely require different combinations of behavioral, nutritional, pharmacologic, endoscopic, and surgical therapies.

Behavior therapy for obesity: where are we now?

PURPOSE OF REVIEW

To describe the short-term and long-term results of lifestyle modification for obesity.

RECENT FINDINGS

Randomized controlled trials, which compared different diet and activity interventions were reviewed. Studies that investigated the efficacy of new technologies to provide lifestyle modification, such as web-based delivery, also were examined.

SUMMARY

In general, comprehensive lifestyle modification programs delivered in person induce a loss of approximately 10% of initial weight in 16-26 weeks of treatment. The use of portion-controlled diets, which typically involve the use of meal replacement products, was associated with significantly larger weight losses in the short term. In contrast, interventions delivered via the Internet induced a loss of approximately 5%. However, web-based programs appear to have potential in facilitating the continuation on patient-provider contact, which along with high levels of physical activity, appear to be key strategies for successful long-term weight control. Recent studies also have suggested that the combination of lifestyle modification with long-term use of pharmacotherapy holds promise for maximizing initial weight losses and promoting long-term maintenance.

What are the risks and the benefits of current and emerging weight-loss medications?

Obesity is epidemic; new medications and therapeutic options are urgently needed to reduce the associated health care burden. The initial clinical strategy for weight loss is lifestyle modification involving a combination of diet, exercise, and behavior change. However, it is difficult for many to achieve and maintain weight loss solely through this approach. Only two drugs, orlistat and sibutramine, have been approved by the US Food and Drug Administration (FDA) to treat obesity long term, and both medications have undesirable side effects, leaving an enormous unmet need for efficacious and safe therapy for obesity. Other medications with weight-loss effects have been approved by the FDA for short-term treatment of obesity or for disorders other than obesity, but these also have potential adverse effects. This article discusses the perceived benefits and risks of these approved medications along with emerging drugs that have shown weight-loss effects.

A randomized double-blind placebo-controlled study of the long-term efficacy and safety of diethylpropion in the treatment of obese subjects

OBJECTIVE

To evaluate the efficacy of diethylpropion on a long-term basis, with emphasis in cardiovascular and psychiatric safety aspects.

DESIGN

Randomized, double-blind, placebo-controlled trial.

MEASUREMENTS

Following a 2-week screening period, 69 obese healthy adults received a hypocaloric diet and were randomized to diethylpropion 50 mg BID (n=37) or placebo (n=32) for 6 months. After this period, all participants received diethylpropion in an open-label extension for an additional 6 months. The primary outcome was percentage change in body weight. Electrocardiogram (ECG), echocardiography and clinical chemistry were performed at baseline and every 6 months. Psychiatric evaluation and application of Hamilton rating scales for depression and anxiety were also performed by experienced psychiatrists at baseline and every 3 months.

RESULTS

After 6 months, the diethylpropion group lost an average of 9.8% (s.d. 6.9%) of initial body weight vs 3.2% (3.7%) in the placebo group (P<0.0001). From baseline to month 12, the mean weight loss produced by diethylpropion was 10.6% (8.3%). Participants in the placebo group who were switched to diethylpropion after 6 months lost an average of 7.0% (7.7%) of initial body weight. The difference between groups at month 12 was not significant (P=0.07). No differences in blood pressure, pulse rate, ECG and psychiatric evaluation were observed. Dry mouth and insomnia were the most frequent adverse events.

CONCLUSION

Diethylpropion plus diet produced sustained and clinically significant weight loss over 1 year. It seems to be safe in relation to cardiovascular and psychiatric aspects in a well-selected population.