Emerging Role of GLP-1 Agonists in Obesity: A Comprehensive Review of Randomised Controlled Trials

Obesity is a chronic disease with high prevalence and associated comorbidities, making it a growing global concern. These comorbidities include type 2 diabetes, hypertension, ventilatory dysfunction, arthrosis, venous and lymphatic circulation diseases, depression, and others, which have a negative impact on health and increase morbidity and mortality. GLP-1 agonists, used to treat type 2 diabetes, have been shown to be effective in promoting weight loss in preclinical and clinical studies. This review summarizes numerous studies conducted on the main drugs in the GLP-1 agonists class, outlining the maximum achievable weight loss. Our aim is to emphasize the active role and main outcomes of GLP-1 agonists in promoting weight loss, as well as in improving hyperglycemia, insulin sensitivity, blood pressure, cardio-metabolic, and renal protection. We highlight the pleiotropic effects of these medications, along with their indications, contraindications, and precautions for both diabetic and non-diabetic patients, based on long-term follow-up studies.

Impact of dose-escalation schemes and drug discontinuation on weight loss outcomes with liraglutide 3.0 mg: A model-based approach

AIMS

To investigate the impact on weight loss of the treatment changes in overweight or obese people that may be needed in case of gastrointestinal (GI) tolerability issues during escalation of the glucagon-like peptide-1 analogue liraglutide.

MATERIALS AND METHODS

The individual longitudinal body weight data from the main trial periods of three phase II/III trials in overweight or obese patients (56-week treatment with once-daily liraglutide 1.2, 1.8, 2.4 or 3.0 mg or placebo, n = 4952) were analysed using a non-linear mixed-effect modelling approach. Individual pharmacokinetic profiles were derived based on published pharmacokinetic models. Baseline body weight, baseline glycated haemoglobin (HbA1c), age, gender, diabetes status (no diabetes, prediabetes or type 2 diabetes), race and trial region were investigated as covariates. As a form of external validation, the model was used to predict the weight regain after treatment cessation at week 56 (data not included in model development).

RESULTS

A pharmacokinetic/pharmacodynamic model provided an adequate description of the weight loss trajectories for all studied doses. Gender and diabetes status were identified as the most influential covariates, and an underlying seasonal weight fluctuation was identified. Slower than that recommended, one-week dose-escalation algorithms led up to 2 weeks slower initial weight loss but similar long-term weight loss trajectories.

CONCLUSIONS

The relationship between liraglutide systemic exposure and weight loss was successfully established in overweight or obese people. The model could predict the time course of weight regain after treatment cessation and suggests that GI tolerability can be mitigated by slower escalation with only minor impact on the weight loss trajectory.

The gut sensor as regulator of body weight

The gastrointestinal (GI) tract comprises a large endocrine organ that regulates not only nutrient sensing and metabolising but also satiety and energy homeostasis. More than 20 hormones secreted from the stomach, intestine, and pancreas as well as signaling mediators of the gut microbiome are involved in this process. A better understanding of how related pathways affect body weight and food intake will help us to find new strategies and drugs to treat obesity. For example, weight loss secondary to lifestyle intervention is often accompanied by unfavorable changes in multiple GI hormones, which may cause difficulties in maintaining a lower body weight status. Conversely, bariatric surgery favorably changes the hormone profile to support improved satiety and metabolic function. This partially explains stronger sustained body weight reduction resulting in better long-term results of improved metabolic functions. This review focuses on GI hormones and signaling mediators of the microbiome involved in satiety regulation and energy homeostasis and summarizes their changes following weight loss. Furthermore, the potential role of GI hormones as anti-obesity drugs is discussed.

Tolerability of nausea and vomiting and associations with weight loss in a randomized trial of liraglutide in obese, non-diabetic adults

BACKGROUND

Liraglutide 3.0 mg, with diet and exercise, produced substantial weight loss over 1 year that was sustained over 2 years in obese non-diabetic adults. Nausea was the most frequent side effect.

OBJECTIVE

To evaluate routinely collected data on nausea and vomiting among individuals on liraglutide and their influence on tolerability and body weight.

DESIGN

A randomized, placebo-controlled, double-blind 20-week study with an 84-week extension (sponsor unblinded at 20 weeks, open-label after 1 year) in eight European countries (Clinicaltrials.gov: NCT00422058).

SUBJECTS

After commencing a 500-kcal/day deficit diet plus exercise, 564 participants (18-65 years, body mass index (BMI) 30-40 kg m(-2)) were randomly assigned (after a 2-week run-in period) to once-daily subcutaneous liraglutide (1.2, 1.8, 2.4 or 3.0 mg), placebo or open-label orlistat (120 mg × 3 per day). After 1 year, participants on liraglutide/placebo switched to liraglutide 2.4 mg, and subsequently, to liraglutide 3.0 mg (based on 20-week and 1-year results, respectively).

RESULTS

The intention-to-treat population comprised 561 participants (n=90-98 per arm, age 45.9±10.3 years, BMI 34.8±2.7 kg m(-2) (mean±s.d.)). In year 1, more participants reported ⩾1 episode of nausea/vomiting on treatment with liraglutide 1.2-3.0 mg (17-38%) than with placebo or orlistat (both 4%, P⩽0.001). Most episodes occurred during dose escalation (weeks 1-6), with 'mild' or 'moderate' symptoms. Among participants on liraglutide 3.0 mg, 48% reported some nausea and 13% some vomiting, with considerable variation between countries, but only 4 out of 93 (4%) reported withdrawals. The mean 1-year weight loss on treatment with liraglutide 3.0 mg from randomization was 9.2 kg for participants reporting nausea/vomiting episodes, versus 6.3 kg for those with none (a treatment difference of 2.9 kg (95% confidence interval 0.5-5.3); P=0.02). Both weight losses were significantly greater than the respective weight losses for participants on placebo (P<0.001) or orlistat (P<0.05). Quality-of-life scores at 20 weeks improved similarly with or without nausea/vomiting on treatment with liraglutide 3.0 mg.

CONCLUSION

Transient nausea and vomiting on treatment with liraglutide 3.0 mg was associated with greater weight loss, although symptoms appeared tolerable and did not attenuate quality-of-life improvements. Improved data collection methods on nausea are warranted.

Pharmacological management of binge eating disorder: current and emerging treatment options

Growing evidence suggests that pharmacotherapy may be beneficial for some patients with binge eating disorder (BED), an eating disorder characterized by repetitive episodes of uncontrollable consumption of abnormally large amounts of food without inappropriate weight loss behaviors. In this paper, we provide a brief overview of BED and review the rationales and data supporting the effectiveness of specific medications or medication classes in treating patients with BED. We conclude by summarizing these data, discussing the role of pharmacotherapy in the BED treatment armamentarium, and suggesting future areas for research.

Is there altered sensitivity to ghrelin-receptor ligands in leptin-deficient mice?: importance of satiety state and time of day

BACKGROUND

Several fine-tuned and interconnected hypothalamic peptidergic systems orchestrate the regulation of energy homeostasis in the body. The orexigenic peptide ghrelin and the anorexigenic peptide leptin are among the most important, and both have been implicated in the development of eating disorders from obesity to anorexia nervosa.

OBJECTIVES

The goal of these studies was to examine the response of leptin-deficient ob/ob mice in ghrelin-receptor ligands in a food intake task.

METHODS

Changes in cumulative food intake were measured after peripheral administration of ghrelin (1 and 2 nmol/10 g) and the ghrelin-receptor antagonist (D-Lys(3))-GHRP-6 (66.6 and 133.3 nmol/10 g) in obese and lean control mice during the light and dark cycle as well as in a state of food restriction. Hypothalamic ghrelin and ghrelin-receptor expression was measured in ob/ob and lean mice at two different timepoints.

RESULTS

Ghrelin increased food intake in lean and obese mice in the light and dark cycle, whereas the ghrelin-receptor antagonist caused significantly stronger reduction in food intake in obese mice only in the dark cycle. After fasting, ob/ob mice displayed decreased light cycle sensitivity to the anorexigenic effects of the ghrelin-receptor antagonist. Hypothalamic expression levels of ghrelin were unaltered during the light cycle but decreased during the dark cycle in ob/ob mice; whereas, although unchanged in the light cycle, ghrelin-receptor expression was increased in the dark cycle in obese mice.

CONCLUSION

The functionality and sensitivity of the ghrelinergic system is dependent on the time of day and the satiety state in leptin-deficient ob/ob mice.

Gliptins: a new class of oral antidiabetic agents

India has the largest population of patients with type 2 diabetes mellitus. The conventional agents used to treat type 2 diabetes frequently exhibit reduced efficacy over time leading to inadequate glycaemic control and are also associated with adverse effects. Hence, there is a need for alternative therapies that can overcome the limitations associated with conventional antidiabetic agents. This review focuses on Gliptins, which have become a research area of intense focus and present an alternative therapeutic strategy for patients with type 2 diabetes. Gliptins show significant improvements in glycaemic control and are well tolerated, particularly with regard to weight change and hypoglycemia. Hence, gliptins are considered as useful agents for the treatment of type 2 diabetes mellitus.

The effects of increasing water content to reduce the energy density of the diet on body mass changes following caloric restriction in domestic cats

Caloric restriction induces body mass loss that is often regained when restriction ends. This study aimed to determine if dietary energy density modulates the extent of post-restriction body mass regain. Water (20% wt:wt) was added to a standard dry commercially available feline diet. Twenty-seven domestic short-haired cats underwent a 20% caloric restriction on this diet. Following restriction, cats were offered the same dry diet ad libitum either without additional water or with 40% added water, therefore maintaining macronutrient composition whilst manipulating energy density. Despite no significant difference in energy intake during ad libitum consumption, post-restriction body mass regain was greater on the high energy dense (0% hydrated), compared to the low energy dense (40% hydrated) diet. The same protocol was repeated with a separate cohort of 19 cats with additional measures of physical activity, gut transit time and energy digestibility. Activity levels on the low energy dense diet were significantly higher than in cats on the high energy dense diet (p=0.030) and were similar to those recorded during caloric restriction. These results suggest that body mass gain following caloric restriction is ameliorated, and physical activity enhanced, by feeding a diet which is low in energy density due to the addition of 40% water.

Reversal of obesity and insulin resistance by a non-peptidic glucagon-like peptide-1 receptor agonist in diet-induced obese mice

BACKGROUND

Glucagon-like peptide-1 (GLP-1) is recognized as an important regulator of glucose homeostasis. Efforts to utilize GLP-1 mimetics in the treatment of diabetes have yielded clinical benefits. A major hurdle for an effective oral therapy has been the difficulty of finding a non-peptidic GLP-1 receptor (GLP-1R) agonist. While its oral bioavailability still poses significant challenges, Boc5, one of the first such compounds, has demonstrated the attainment of GLP-1R agonism in diabetic mice. The present work was to investigate whether subchronic Boc5 treatment can restore glycemic control and induce sustainable weight loss in diet-induced obese (DIO) mice, an animal model of human obesity and insulin resistance.

METHODOLOGY/PRINCIPAL FINDINGS

DIO mice were treated three times a week with Boc5 (0.3, 1 and 3 mg) for 12 weeks. Body weight, body mass index (BMI), food intake, fasting glucose, intraperitoneal glucose tolerance and insulin induced glucose clearance were monitored regularly throughout the treatment. Glucose-stimulated insulin secretion, β-cell mass, islet size, body composition, serum metabolic profiles, lipogenesis, lipolysis, adipose hypertrophy and lipid deposition in the liver and muscle were also measured after 12 weeks of dosing. Boc5 dose-dependently reduced body weight, BMI and food intake in DIO mice. These changes were associated with significant decreases in fat mass, adipocyte hypertrophy and peripheral tissue lipid accumulation. Boc5 treatment also restored glycemic control through marked improvement of insulin sensitivity and normalization of β-cell mass. Administration of Boc5 (3 mg) reduced basal but enhanced insulin-mediated glucose incorporation and noradrenaline-stimulated lipolysis in isolated adipocytes from obese mice. Furthermore, circulating leptin, adiponectin, triglyceride, total cholesterol, nonesterified fatty acid and high-density lipoprotein/low-density lipoprotein ratio were normalized to various extents by Boc5 treatment.

CONCLUSIONS/SIGNIFICANCE

Boc5 may produce metabolic benefits via multiple synergistic mechanisms and may represent an attractive tool for therapeutic intervention of obesity and diabetes, by means of non-peptidic GLP-1R agonism.

Dietary and physical activity patterns in children with obstructive sleep apnea

OBJECTIVE

To assess dietary and physical activity patterns and morning circulating blood levels of the orexigenic hormones ghrelin and visfatin in children with either obesity, obstructive sleep apnea (OSA), or both conditions.

STUDY DESIGN

In this cross-sectional design, 5- to 9-year-old participants (n = 245) from the community were identified. After overnight polysomnography, caregivers filled out a food and physical activity questionnaire, and the child underwent a fasting blood draw for ghrelin and visfatin plasma levels.

RESULTS

Compared with control subjects, obese children with OSA ate 2.2-times more fast food, ate less healthy food such as fruits and vegetables, and were 4.2-times less frequently involved in organized sports. OSA was positively correlated with plasma ghrelin levels (R(2), 0.73; P < .0001), but not visfatin levels, particularly when obesity was present.

CONCLUSION

OSA and obesity in children may adversely impact dietary preferences and may be particularly detrimental to daily physical activity patterns. Furthermore, increased ghrelin levels support the presence of increased appetite and caloric intake in obese patients with OSA, which in turn may further promote the severity of the underlying conditions.

The fermentable fibre inulin increases postprandial serum short-chain fatty acids and reduces free-fatty acids and ghrelin in healthy subjects

It is thought that diets high in dietary fibre are associated with reduced risk for type 2 diabetes, at least in part because the short-chain fatty acids (SCFAs) produced during the colonic fermentation of fibre beneficially influence circulating concentrations of free-fatty acids (FFAs) and gut hormones involved in the regulation of blood glucose and body mass. However, there is a paucity of data showing this sequence of events in humans. Thus, our objective was to determine the effect of the fermentable fibre inulin on postprandial glucose, insulin, SCFA, FFA, and gut hormone responses in healthy subjects. Overnight fasted healthy subjects (n = 12) were studied for 6 h after consuming 400 mL drinks, containing 80 g high-fructose corn syrup (80HFCS), 56 g HFCS (56HFCS), or 56 g HFCS plus 24 g inulin (Inulin), using a randomized, single-blind, crossover design. A standard lunch was served 4 h after the test drink. Glucose and insulin responses after Inulin did not differ significantly from those after 80HFCS or 56HFCS. Serum acetate, propionate, and butyrate were significantly higher after Inulin than after HFCS drinks from 4-6 h. FFAs fell at a similar rate after all 3 test drinks, but were lower after Inulin than after 56HFCS at 4 h (0.40 +/- 0.06 vs. 0.51 +/- 0.06 mmol*L-1; p < 0.05). Compared with 56HFCS, Inulin significantly increased plasma glucagon-like peptide-1 concentrations at 30 min, and reduced ghrelin at 4.5 h and 6 h. The results are consistent with the hypothesis that dietary fibre increases the production of colonic SCFAs, which may reduce type 2 diabetes risk by reducing postprandial FFAs and favorably affecting gut hormones, which regulate food intake.

Approved and Off-Label Uses of Obesity Medications, and Potential New Pharmacologic Treatment Options

Available anti-obesity pharmacotherapy options remain very limited and development of more effective drugs has become a priority. The potential strategies to achieve weight loss are to reduce energy intake by stimulating anorexigenic signals or by blocking orexigenic signals, and to increase energy expenditure. This review will focus on approved obesity medications, as well as potential new pharmacologic treatment options.

Endocannabinoid system in food intake and metabolic regulation

PURPOSE OF REVIEW

As the incidence of obesity and the metabolic syndrome has increased, research has focused on the importance of the endocannabinoid system in the brain and peripheral tissues. Rimonabant, an inverse agonist of the CB1 receptor is being used therapeutically. This review presents recent advances in endocannabinoid physiology.

RECENT FINDINGS

The endocannabinoid system interacts with other anorexigenic and orexigenic pathways to regulate food intake in the hypothalamus, and the hedonistic value of food in the mesolimbic system. Endocannabinoid system overactivity contributes to hepatic steatosis, increased adipose tissue inflammation, dysregulated insulin signalling in the pancreas and disturbed oxidative pathways in skeletal muscle. The breakdown pathways for anandamide and 2-arachidonoylglycerol, the endocannabinoid receptor ligands, are reviewed, and the recent discoveries of endocannabinoid receptor polymorphisms and their relationship to obesity and metabolic disease noted. The favourable effect of rimonabant on fat mass glycaemic control, lipid metabolism and overall cardiovascular risk must be tempered by adverse effects on mood.

SUMMARY

The ubiquitous role of the endocannabinoid system in food intake and energy metabolism is now established. Drugs that manipulate different aspects of this system may benefit subjects with the metabolic and cachectic syndromes.