Influence of sibutramine on energy expenditure in African American women

Role of serotonin in body weight, insulin secretion and glycaemic control

Obesity and type 2 diabetes are key healthcare challenges of the 21st century. Subsequent to its discovery in 1948, serotonin (5-hydroxytryptamine; 5-HT) has emerged as a principal modulator of energy homeostasis and body weight, prompting it to be a target of weight loss medications (eg, fenfluramine, D-fenfluramine, fenfluramine-phentermine and sibutramine). The potential risk of off-target effects led to these medications being withdrawn from clinical use and spurred drug discovery into 5-HT receptor selective ligands. The serotonin 2C receptor (5-HT_2C R) is the primary receptor through which 5-HT impacts feeding and body weight and 5-HT_2C R agonist lorcaserin was released for obesity treatment in 2012. Obese patients with type 2 diabetes prescribed medications that produce weight loss commonly observe improvements in type 2 diabetes. However, recent research has provided compelling evidence that 5-HT_2C R agonists produce effects on blood glucose and insulin sensitivity independent of weight loss. As such, neuroactive 5-HT_2C R agonists are a potential new category of type 2 diabetes medications. 5-HT is also expressed within pancreatic β cells, is co-released with insulin and may have a role in modulating insulin secretion. This review highlights the latest advances in the function of 5-HT in body weight, insulin release and glycaemic control.

Long-term effects of weight-reducing drugs in people with hypertension

BACKGROUND

This is the third update of this review, first published in July 2009. All major guidelines on treatment of hypertension recommend weight loss; anti-obesity drugs may be able to help in this respect.

OBJECTIVES

Primary objectives: To assess the long-term effects of pharmacologically-induced reduction in body weight in adults with essential hypertension on all-cause mortality, cardiovascular morbidity, and adverse events (including total serious adverse events, withdrawal due to adverse events, and total non-serious adverse events).. Secondary objectives: To assess the long-term effects of pharmacologically-induced reduction in body weight in adults with essential hypertension on change from baseline in systolic and diastolic blood pressure, and on body weight reduction.

SEARCH METHODS

For this updated review, the Cochrane Hypertension Information Specialist searched the following databases for randomised controlled trials up to March 2020: the Cochrane Hypertension Specialised Register, CENTRAL, MEDLINE (from 1946), Embase (from 1974), the World Health Organization International Clinical Trials Registry Platform, and ClinicalTrials.gov. The searches had no language restrictions. We contacted authors of relevant papers about further published and unpublished work.

SELECTION CRITERIA

Randomised controlled trials of at least 24 weeks' duration in adults with hypertension that compared approved long-term weight-loss medications to placebo.  DATA COLLECTION AND ANALYSIS: Two review authors independently selected studies, assessed risks of bias, and extracted data. Where appropriate and in the absence of significant heterogeneity between studies (P > 0.1), we pooled studies using a fixed-effect meta-analysis. When heterogeneity was present, we used the random-effects method and investigated the cause of the heterogeneity.

MAIN RESULTS

This third update of the review added one new trial, investigating the combination of naltrexone/bupropion versus placebo. Two medications, which were included in the previous versions of this review (rimonabant and sibutramine) are no longer considered relevant for this update, since their marketing approval was withdrawn in 2010 and 2009, respectively. The number of included studies in this review update is therefore six (12,724 participants in total): four RCTs comparing orlistat to placebo, involving a total of 3132 participants with high blood pressure and a mean age of 46 to 55 years; one trial comparing phentermine/topiramate to placebo, involving 1305 participants with high blood pressure and a mean age of 53 years; and one trial comparing naltrexone/bupropion to placebo, involving 8283 participants with hypertension and a mean age of 62 years. We judged the risks of bias to be unclear for the trials investigating orlistat or naltrexone/bupropion. and low for the trial investigating phentermine/topiramate. Only the study of naltrexone/bupropion included cardiovascular mortality and morbidity as predefined outcomes. There were no differences in the rates of all-cause or cardiovascular mortality, major cardiovascular events, or serious adverse events between naltrexone/bupropion and placebo. The incidence of overall adverse events was significantly higher in participants treated with naltrexone/bupropion. For orlistat, the incidence of gastrointestinal side effects was consistently higher compared to placebo. The most frequent side effects with phentermine/topiramate were dry mouth and paraesthesia. After six to 12 months, orlistat reduced systolic blood pressure compared to placebo by mean difference (MD) -2.6 mm Hg (95% confidence interval (CI) -3.8 to -1.4 mm Hg; 4 trials, 2058 participants) and diastolic blood pressure by MD -2.0 mm Hg (95% CI -2.7 to -1.2 mm Hg; 4 trials, 2058 participants). After 13 months of follow-up, phentermine/topiramate decreased systolic blood pressure compared to placebo by -2.0 to -4.2 mm Hg (1 trial, 1030 participants) (depending on drug dosage), and diastolic blood pressure by -1.3 to -1.9 mm Hg (1 trial, 1030 participants) (depending on drug dosage). There was no difference in the change in systolic or diastolic blood pressure between naltrexone/bupropion and placebo (1 trial, 8283 participants). We identified no relevant studies investigating liraglutide or lorcaserin in people with hypertension.

AUTHORS' CONCLUSIONS

In people with elevated blood pressure, orlistat, phentermine/topiramate and naltrexone/bupropion reduced body weight; the magnitude of the effect was greatest with phentermine/topiramate. In the same trials, orlistat and phentermine/topiramate, but not naltrexone/bupropion, reduced blood pressure. One RCT of naltrexone/bupropion versus placebo showed no differences in all-cause mortality or cardiovascular mortality or morbidity after two years. The European Medicines Agency refused marketing authorisation for phentermine/topiramate due to safety concerns, while for lorcaserin the application for European marketing authorisation was withdrawn due to a negative overall benefit/risk balance. In 2020 lorcaserin was also withdrawn from the US market. Two other medications (rimonabant and sibutramine) had already been withdrawn from the market in 2009 and 2010, respectively.

Long-term effects of weight-reducing drugs in people with hypertension

BACKGROUND

All major guidelines on antihypertensive therapy recommend weight loss; anti-obesity drugs may be able to help in this respect.

PRIMARY OBJECTIVES

To assess the long-term effects of pharmacologically induced reduction in body weight in adults with essential hypertension on all-cause mortality, cardiovascular morbidity, and adverse events (including total serious adverse events, withdrawal due to adverse events, and total non-serious adverse events).

SECONDARY OBJECTIVES

To assess the long-term effects of pharmacologically induced reduction in body weight in adults with essential hypertension on change from baseline in systolic blood pressure, change from baseline in diastolic blood pressure, and body weight reduction.

SEARCH METHODS

We obtained studies using computerised searches of the Cochrane Hypertension Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), Ovid MEDLINE, Ovid EMBASE, the clinical trials registry ClinicalTrials.gov, and from handsearches in reference lists and systematic reviews (status as of 13 April 2015).

SELECTION CRITERIA

Randomised controlled trials in hypertensive adults of at least 24 weeks' duration that compared long-term pharmacologic interventions for weight loss with placebo. 

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, assessed risk of bias, and extracted data. Where appropriate and in the absence of significant heterogeneity between studies (P > 0.1), we pooled studies using fixed-effect meta-analysis. When heterogeneity was present, we used the random-effects method and investigated the cause of heterogeneity.

MAIN RESULTS

After updating the literature search, which was extended to include four new weight-reducing drugs, we identified one additional study of phentermine/topiramate, bringing the total number of studies to nine that compare orlistat, sibutramine, or phentermine/topiramate to placebo and thus fulfil our inclusion criteria. We identified no relevant studies investigating rimonabant, liraglutide, lorcaserin, or naltrexone/bupropion. No study included mortality and cardiovascular morbidity as predefined outcomes. Incidence of gastrointestinal side effects was consistently higher in those participants treated with orlistat versus those treated with placebo. The most frequent side effects were dry mouth, constipation, and headache with sibutramine, and dry mouth and paresthaesia with phentermine/topiramate. In participants assigned to orlistat, sibutramine, or phentermine/topiramate body weight was reduced more effectively than in participants in the usual-care/placebo groups. Orlistat reduced systolic blood pressure as compared to placebo by -2.5 mm Hg (mean difference (MD); 95% confidence interval (CI): -4.0 to -0.9 mm Hg) and diastolic blood pressure by -1.9 mm Hg (MD; 95% CI: -3.0 to -0.9 mm Hg). Sibutramine increased diastolic blood pressure compared to placebo by +3.2 mm Hg (MD; 95% CI: +1.4 to +4.9 mm Hg). The one trial that investigated phentermine/topiramate suggested it lowered blood pressure.

AUTHORS' CONCLUSIONS

In people with elevated blood pressure, orlistat and sibutramine reduced body weight to a similar degree, while phentermine/topiramate reduced body weight to a greater extent. In the same trials, orlistat and phentermine/topiramate reduced blood pressure, while sibutramine increased it. We could include no trials investigating rimonabant, liraglutide, lorcaserin, or naltrexone/bupropion in people with elevated blood pressure. Long-term trials assessing the effect of orlistat, liraglutide, lorcaserin, phentermine/topiramate, or naltrexone/bupropion on mortality and morbidity are unavailable and needed. Rimonabant and sibutramine have been withdrawn from the market, after long-term trials on mortality and morbidity have confirmed concerns about the potential severe side effects of these two drugs. The European Medicines Agency refused marketing authorisation for phentermine/topiramate due to safety concerns, while the application for European marketing authorisation for lorcaserin was withdrawn by the manufacturer after the Committee for Medicinal Products for Human Use judged the overall benefit/risk balance to be negative.

Assessment of acute and chronic pharmacological effects on energy expenditure and macronutrient oxidation in humans: responses to ephedrine

Evidence of active brown adipose tissue in human adults suggests that this may become a pharmacological target to induce negative energy balance. We have explored whole-body indirect calorimetry to detect the metabolic effects of thermogenic drugs through administration of ephedrine hydrochloride and have assessed ephedrine's merits as a comparator compound in the evaluation of novel thermogenic agents. Volunteers randomly given ephedrine hydrochloride 15 mg QID (n = 8) or placebo (n = 6) were studied at baseline and after 1-2 and 14-15 days of treatment. We demonstrate that overnight or 23-hour, 2% energy expenditure (EE) and 5% fat (FO) or CHO oxidation effects are detectable both acutely and over 14 days. Compared to placebo, ephedrine increased EE and FO rates overnight (EE 63 kJ day 2, EE 105 kJ, FO 190 kJ, day 14), but not over 23 h. We conclude that modest energy expenditure and fat oxidation responses to pharmacological interventions can be confidently detected by calorimetry in small groups. Ephedrine should provide reliable data against which to compare novel thermogenic compounds.

Metabolic testing in the office

The three most commonly used metabolic tests are the Resting Metabolic Rate, Anaerobic Threshold Testing, and V.O2max. For several decades, these metabolic tests have been confined to the setting of university-based physiology laboratories and cardiopulmonary environments, i.e., metabolic carts in the intensive care units. The information gathered is used as a research and clinical tool in evaluating metabolic activity in a variety of physiological states from a body at rest, to exercise (aerobic and anaerobic), in certain medical states like illness, fed/starvation, and medicinal or supplementation affective states. Over the last decade, as technology has improved, so have the metabolic testing carts. They have become widely available for mainstream use by a variety of health care professionals. The purpose of this article is to review these three tests and how they may be useful in a medical practice.

Chronic 5-HT6 receptor modulation by E-6837 induces hypophagia and sustained weight loss in diet-induced obese rats

E-6837 is a novel, selective and high-affinity 5-HT(6) receptor ligand (pK(i): 9.13) which in vitro demonstrates partial agonism at a presumably silent rat 5-HT(6) receptor and full agonism at a constitutively active human 5-HT(6) receptor by monitoring the cAMP signaling pathway.The effects of chronic treatment with E-6837 were determined in diet-induced obese (DIO)-rats on changes in body weight, food and water intake, plasma indices of comorbid risk factors, and weight regain on compound withdrawal. The centrally acting antiobesity drug, sibutramine, was used as the reference comparator. Sustained body weight loss and decreased cumulative food intake of DIO-rats was observed with E-6837 (30 mg kg(-1), p.o., twice a day) during the 4-week treatment period. The onset of the E-6837 effect on body weight was slower than that of sibutramine (5 mg kg(-1), p.o.), while its maximal effect was greater, that is -15.7 versus -11.0%.E-6837-induced weight loss was exclusively mediated by a decrease (31.7%) in fat mass, with a concomitant reduction (49.6%) in plasma leptin. Reduced obesity was also reflected in improved glycemic control. Although weight regain occurred after withdrawal from either compound, the body weights after E-6837 (-6.6%) remained lower than after sibutramine (-3.8%) indicating that the greater efficacy of the former did not result in profound rebound hyperphagia/weight gain. These results show that the 5-HT(6) receptor partial agonist, E-6837, is a promising new approach to the management of obesity with the potential to produce greater sustained weight loss than sibutramine.

Sibutramine and the management of obesity

Sibutramine is a selective serotonin and noradrenaline re-uptake inhibitor approved for the long-term management of obesity. Its primary mechanism of action is increased satiety, although some evidence also suggests increased energy expenditure could play a role in sibutramine-induced weight loss. It has established general efficacy in long-term trials, with clinically-approved doses of 10 and 15 mg. Sibutramine has also been studied in a number of unique populations, including obese controlled hypertensives, diabetics and ethnic minorities, further establishing its effectiveness. However, it does have a consistent effect of increasing blood pressure and pulse. Thus, blood pressure and heart rate should be monitored in patients using sibutramine and it may not be applicable in obese patients with significant cardiovascular disease.

The discovery and status of sibutramine as an anti-obesity drug

Sibutramine is a serotonin-norepinephrine reuptake inhibitor indicated for the management of obesity in conjunction with a reduced calorie diet. Though sibutramine was originally evaluated for possible use as an antidepressant, its research development was eventually redirected to evaluate it as an anorexiant. The pharmacological mechanisms by which sibutramine exerts its weight loss effect are likely due to a combination of reduced appetite, feelings of satiety, and possibly the induction of thermogenesis. Its efficacy for inducing an initial weight-loss and the subsequent maintenance of the weight-loss is well proven in short- and long-term clinical trials of up to 2 years duration. In general, sibutramine has been well tolerated. Increases in blood pressure and heart rate are possible adverse effects that require regular monitoring. Sibutramine is one of the few established and well-proven agents for obesity available for use today and should be considered effective in the management of patients requiring pharmacotherapy as part of the multi-modal approach to weight-loss.