The Food Environment, Preference, and Experience Modulate the Effects of Exendin-4 on Food Intake and Reward

The interplay between leptin, glucocorticoids, and GLP1 regulates food intake and feeding behaviour

Nutritional, endocrine, and neurological signals converge in multiple brain centres to control feeding behaviour and food intake as part of the allostatic regulation of energy balance. Among the several neuroendocrine systems involved, the leptin, glucocorticoid, and glucagon-like peptide 1 (GLP1) systems have been extensively researched. Leptin is at the top hierarchical level since its complete absence is sufficient to trigger severe hyperphagia. Glucocorticoids are key regulators of the energy balance adaptation to stress and their sustained excess leads to excessive adiposity and metabolic perturbations. GLP1 participates in metabolic adaptation to food intake, regulating insulin secretion and satiety by parallel central and peripheral signalling systems. Herein, we review the brain and peripheral targets of these three hormone systems that integrate to regulate food intake, feeding behaviour, and metabolic homeostasis. We examine the functional relationships between leptin, glucocorticoids, and GLP1 at the central and peripheral levels, including the cross-regulation of their circulating levels and their cooperative or antagonistic actions at different brain centres. The pathophysiological roles of these neuroendocrine systems in dysregulated intake are explored in the two extremes of body adiposity - obesity and lipodystrophy - and eating behaviour disorders.

Meta-analysis of pre-clinical studies on the effects of opioid receptor ligands on food intake, motivation, and choice

The opioid receptors (OR) regulate food intake. Still, despite extensive pre-clinical research, the overall effects and individual contribution of the mu (MOR), kappa (KOR), and delta (DOR) OR subtypes to feeding behaviors and food intake remain unclear. To address this, we conducted a pre-registered systematic search and meta-analysis of rodent dose-response studies to evaluate the impact of central and peripheral administration of non-selective and selective OR ligands on intake, motivation, and choice of food. All studies had a high bias risk. Still, the meta-analysis confirmed the overall orexigenic and anorexigenic effects of OR agonists and antagonists, respectively. Our results support a larger orexigenic role for central MOR agonists among OR subtypes and that peripheral OR antagonists reduce motivation for and intake of preferred foods. In binary food choice studies, peripheral OR agonists selectively increase the intake of fat-preferred foods; in contrast, they did not increase the intake of sweet carbohydrate-preferred foods. Overall, these data support that OR regulation of intake, motivation, and choice is influenced by food macronutrient composition.

Antismoking agents do not contribute synergistically to semaglutide's ability to reduce alcohol intake in rats

Preclinical studies have identified glucagon-like peptide-1 receptor (GLP-1R) agonists, and the antismoking agents varenicline and bupropion as tentative agents for treatment of alcohol use disorder (AUD). Combining different medications is a recent approach that has gained attention regarding heterogenous and difficult-to-treat diseases, like AUD. Successfully, this approach has been tested for the combination of varenicline and bupropion as it prevents relapse to alcohol drinking in rats. However, studies assessing the effects of the combination of semaglutide, an FDA-approved GLP-1R agonist for diabetes type II, and varenicline or bupropion to reduce alcohol intake in male and female rats remains to be conducted. Another approach to influence treatment outcome is to combine a medication with feeding interventions like high fat diet (HFD). While HFD reduces alcohol intake, the ability of the combination of HFD and semaglutide to alter alcohol drinking is unknown and thus the subject for a pilot study. Therefore, three intermittent alcohol drinking experiments were conducted to elucidate the effectiveness of these treatment combinations. We show that semaglutide, bupropion or HFD reduces alcohol intake in male as well as female rats. While various studies reveal beneficial effects of combinatorial pharmacotherapies for the treatment of AUD, we herein do not report any additive effects on alcohol intake by adding either varenicline or bupropion to semaglutide treatment. Neither does HFD exposure alter the ability of semaglutide to reduce alcohol intake. Although no additive effects by the combinatorial treatments are found, these findings collectively provide insight into possible monotherapeutical treatments for AUD.

Semaglutide reduces alcohol intake and relapse-like drinking in male and female rats

BACKGROUND

Glucagon-like peptide1 receptor (GLP-1R) agonists have been found to reduce alcohol drinking in rodents and overweight patients with alcohol use disorder (AUD). However, the probability of low semaglutide doses, an agonist with higher potency and affinity for GLP-1R, to attenuate alcohol-related responses in rodents and the underlying neuronal mechanisms is unknown.

METHODS

In the intermittent access model, we examined the ability of semaglutide to decrease alcohol intake and block relapse-like drinking, as well as imaging the binding of fluorescently marked semaglutide to nucleus accumbens (NAc) in both male and female rats. The suppressive effect of semaglutide on alcohol-induced locomotor stimulation and in vivo dopamine release in NAc was tested in male mice. We evaluated effect of semaglutide on the in vivo release of dopamine metabolites (DOPAC and HVA) and gene expression of enzymes metabolising dopamine (MAOA and COMT) in male mice.

FINDINGS

In male and female rats, acute and repeated semaglutide administration reduced alcohol intake and prevented relapse-like drinking. Moreover, fluorescently labelled semaglutide was detected in NAc of alcohol-drinking male and female rats. Further, semaglutide attenuated the ability of alcohol to cause hyperlocomotion and to elevate dopamine in NAc in male mice. As further shown in male mice, semaglutide enhanced DOPAC and HVA in NAc when alcohol was onboard and increased the gene expression of COMT and MAOA.

INTERPRETATION

Altogether, this indicates that semaglutide reduces alcohol drinking behaviours, possibly via a reduction in alcohol-induced reward and NAc dependent mechanisms. As semaglutide also decreased body weight of alcohol-drinking rats of both sexes, upcoming clinical studies should test the plausibility that semaglutide reduces alcohol intake and body weight in overweight AUD patients.

FUNDING

Swedish Research Council (2019-01676), LUA/ALF (723941) from the Sahlgrenska University Hospital and the Swedish brain foundation.

Impact of short and long exposure to cafeteria diet on food intake and white adipose tissue lipolysis mediated by glucagon-like peptide 1 receptor

Introduction

The modern food environment facilitates excessive calorie intake, a major driver of obesity. Glucagon-like peptide 1 (GLP1) is a neuroendocrine peptide that has been the basis for developing new pharmacotherapies against obesity. The GLP1 receptor (GLP1R) is expressed in central and peripheral tissues, and activation of GLP1R reduces food intake, increases the expression of thermogenic proteins in brown adipose tissue (BAT), and enhances lipolysis in white adipose tissue (WAT). Obesity decreases the efficiency of GLP1R agonists in reducing food intake and body weight. Still, whether palatable food intake before or during the early development of obesity reduces the effects of GLP1R agonists on food intake and adipose tissue metabolism remains undetermined. Further, whether GLP1R expressed in WAT contributes to these effects is unclear.

Methods

Food intake, expression of thermogenic BAT proteins, and WAT lipolysis were measured after central or peripheral administration of Exendin-4 (EX4), a GLP1R agonist, to mice under intermittent-short exposure to CAF diet (3 h/d for 8 days) or a longer-continuous exposure to CAF diet (24 h/d for 15 days). Ex-vivo lipolysis was measured after EX4 exposure to WAT samples from mice fed CAF or control diet for 12 weeks. .

Results

During intermittent-short exposure to CAF diet (3 h/d for 8 days), third ventricle injection (ICV) and intra-peritoneal administration of EX4 reduced palatable food intake. Yet, during a longer-continuous exposure to CAF diet (24 h/d for 15 days), only ICV EX4 administration reduced food intake and body weight. However, this exposure to CAF diet blocked the increase in uncoupling protein 1 (UCP1) caused by ICV EX4 administration in mice fed control diet. Finally, GLP1R expression in WAT was minimal, and EX4 failed to increase lipolysis ex-vivo in WAT tissue samples from mice fed CAF or control diet for 12 weeks. .

Discussion

Exposure to a CAF diet during the early stages of obesity reduces the effects of peripheral and central GLP1R agonists, and WAT does not express a functional GLP1 receptor. These data support that exposure to the obesogenic food environment, without the development or manifestation of obesity, can alter the response to GLP1R agonists. .

Brain site-specific regulation of hedonic intake by orexin and DYN peptides: role of the PVN and obesity

The orexin peptides promote hedonic intake and other reward behaviors through different brain sites. The opioid dynorphin peptides are co-released with orexin peptides but block their effects on reward in the ventral tegmental area (VTA). We previously showed that in the paraventricular hypothalamic nucleus (PVN), dynorphin and not orexin peptides enhance hedonic intake, suggesting they have brain-site-specific effects. Obesity alters the expression of orexin and dynorphin receptors, but whether their expression across different brain sites is important to hedonic intake is unclear. We hypothesized that hedonic intake is regulated by orexin and dynorphin peptides in PVN and that hedonic intake in obesity correlates with expression of their receptors. Here we show that in mice, injection of DYN-A_1-13 (an opioid dynorphin peptide) in the PVN enhanced hedonic intake, whereas in the VTA, injection of OXA (orexin-A, an orexin peptide) enhanced hedonic intake. In PVN, OXA blunted the increase in hedonic intake caused by DYN-A_1-13. In PVN, injection of norBNI (opioid receptor antagonist) reduced hedonic intake but a subsequent OXA injection failed to increase hedonic intake, suggesting that OXA activity in PVN is not influenced by endogenous opioid activity. In the PVN, DYN-A_1-13 increased the intake of the less-preferred food in a two-food choice task. In obese mice fed a cafeteria diet, orexin 1 receptor mRNA across brain sites involved in hedonic intake correlated with fat preference but not caloric intake. Together, these data support that orexin and dynorphin peptides regulate hedonic intake in an opposing manner with brain-site-specific effects.

Early Postoperative Exposure to High-Fat Diet Does Not Increase Long-Term Weight Loss or Fat Avoidance After Roux-en-Y Gastric Bypass in Rats

Background

Bariatric surgery alters food preferences in rats and reportedly decreases desire to consume high-fat high-sugar food in humans. The aim of this study was to investigate whether early post-operative exposure to high-fat food could increase body weight loss after Roux-en-Y gastric bypass (RYGB) by triggering fat avoidance.

Methods

Male Wistar rats underwent either RYGB (n = 15) or sham-operations (n = 16). Preoperatively a standardized 4-choice cafeteria diet [dietary options: low-fat/low-sugar (LFLS), low-fat/high-sugar (LFHS), high-fat/low-sugar (HFLS), high-fat/high-sugar (HFHS)] was offered. First, each option was available for 4 days, thereafter rats were offered the 4 options simultaneously for 3 days preoperatively. Post-surgery, 8 rats in the RYGB- and 8 in the sham-group were exposed to a high-fat content diet (Oatmeal + 30% lard, OM+L) for 10 days, while 7 RYGB rats and 8 sham-rats received OM alone. From the 11th postoperative day, the 4-choice cafeteria diet was reintroduced for 55-days. The intake of all available food items, macronutrients and body weight changes were monitored over 8 weeks. Main outcomes were long-term body-weight and daily change in relative caloric intake during the postoperative cafeteria period compared to the preoperative cafeteria.

Results

During the first 12 days of postoperative cafeteria access, RYGB-rats exposed to OM+L had a higher mean caloric intake per day than RYGB rats exposed to OM alone (Δ10 kCal, P_adj = 0.004), but this difference between the RYGB groups disappeared thereafter. Consequently, in the last 33 days of the postoperative cafeteria diet, the mean body weight of the RYGB+OM+L group was higher compared to RYGB+OM (Δ51 g, P_adj < 0.001). RYGB rats, independently from the nutritional intervention, presented a progressive decrease in daily consumption of calories from fat and increased their daily energy intake mainly from non-sugar carbohydrates. No such differences were detected in sham-operated controls exposed to low- or high fat postoperative interventions.

Conclusion

A progressive decrease in daily fat intake over time was observed after RYGB, independently from the nutritional intervention. This finding confirms that macronutrient preferences undergo progressive changes over time after RYGB and supports the role of ingestive adaptation and learning. Early postoperative exposure to high-fat food failed to accentuate fat avoidance and did not lead to superior weight loss in the long-term.

Gut peptide regulation of food intake - evidence for the modulation of hedonic feeding

The number of people living with obesity has tripled worldwide since 1975 with serious implications for public health, as obesity is linked to a significantly higher chance of early death from associated comorbidities (metabolic syndrome, type 2 diabetes, cardiovascular disease and cancer). As obesity is a consequence of food intake exceeding the demands of energy expenditure, efforts are being made to better understand the homeostatic and hedonic mechanisms governing food intake. Gastrointestinal peptides are secreted from enteroendocrine cells in response to nutrient and energy intake, and modulate food intake either via afferent nerves, including the vagus nerve, or directly within the central nervous system, predominantly gaining access at circumventricular organs. Enteroendocrine hormones modulate homeostatic control centres at hypothalamic nuclei and the dorso-vagal complex. Additional roles of these peptides in modulating hedonic food intake and/or preference via the neural systems of reward are starting to be elucidated, with both peripheral and central peptide sources potentially contributing to central receptor activation. Pharmacological interventions and gastric bypass surgery for the treatment of type 2 diabetes and obesity elevate enteroendocrine hormone levels and also alter food preference. Hence, understanding of the hedonic mechanisms mediated by gut peptide action could advance development of potential therapeutic strategies for the treatment of obesity and its comorbidities.

Liraglutide changes body composition and lowers added sugar intake in overweight persons with insulin pump-treated type 1 diabetes

AIMS

To present secondary outcome analyses of liraglutide treatment in overweight adults with insulin pump-treated type 1 diabetes (T1D), focusing on changes in body composition and dimensions, and to evaluate changes in food intake to identify potential dietary drivers of liraglutide-associated weight loss.

MATERIALS AND METHODS

A 26-week randomized placebo-controlled study was conducted to investigate the efficacy and safety of liraglutide 1.8 mg daily in 44 overweight adults with insulin pump-treated T1D and glucose levels above target, and demonstrated significant glycated haemoglobin (HbA1c)- and body weight-reducing effects. For secondary outcome analysis, dual X-ray absorptiometry scans were completed at Weeks 0 and 26, and questionnaire-based food frequency recordings were obtained at Weeks 0, 13 and 26 to characterize liraglutide-induced changes in body composition and food intake.

RESULTS

Total fat and lean body mass decreased in liraglutide-treated participants (fat mass -4.6 kg [95% confidence interval {CI} -5.7; -3.5], P < 0.001; lean mass -2.5 kg [95% CI -3.2;-1.7], P < 0.001), but remained stable in placebo-treated participants (fat mass -0.3 kg [95% CI -1.3;0.8], P = 0.604; lean mass 0.0 kg [95% CI -0.7;0.7]; P = 0.965 [between-group P values <0.001]). Participants reduced their energy intake numerically more in the liraglutide arm (-1.1 MJ [95% CI -2.0;-0.02], P = 0.02) than in the placebo arm (-0.9 MJ [95% CI -2.0;0.1], P = 0.22), but the between-group difference was statistically insignificant (P = 0.42). However, energy derived from added sugars decreased by 27% in the liraglutide arm compared with an increase of 14% in the placebo arm (P = 0.004).

CONCLUSIONS

Liraglutide lowered fat and lean body mass compared with placebo. Further, liraglutide reduced intake of added sugars. However, no significant difference in total daily energy intake was detected between liraglutide- and placebo-treated participants.

Macronutrient intake, appetite, food preferences and exocrine pancreas function after treatment with short- and long-acting glucagon-like peptide-1 receptor agonists in type 2 diabetes

AIM

To clarify the distinct effects of a long-acting (liraglutide) and a short-acting (lixisenatide) glucagon-like peptide-1 receptor agonist (GLP-1 RA) on macronutrient intake, gastrointestinal side effects and pancreas function.

MATERIALS AND METHODS

Fifty participants were randomized to either lixisenatide or liraglutide for a treatment period of 10 weeks. Appetite, satiety, macronutrient intake, gastrointestinal symptoms and variables related to pancreatic function and gastric emptying were assessed at baseline and after treatment.

RESULTS

Both GLP-1 RAs reduced macronutrient intake similarly. Weight loss and appetite reduction were not related to the delay in gastric emptying or gastrointestinal side effects (P > .05). Lipase increased significantly with liraglutide treatment (by 18.3 ± 4.1 U/L; P = .0001), but not with lixisenatide (-1.8 ± 2.4 U/L; P = .46). Faecal elastase and serum ß-carotin levels (indicators for exocrine pancreas function) improved in both groups (P < .05). Changes in lipase activities did not correlate with gastrointestinal symptoms (P > .05 for each variable).

CONCLUSIONS

Both GLP-1 RAs comparably affected body weight, energy and macronutrient intake. Both treatments were associated with indicators of improved exocrine pancreas function. Reductions in appetite and body weight as a result of treatment with short- or long-acting GLP-1 RAs are not driven by changes in gastric emptying or gastrointestinal side effects.

Can GLP-1 Be a Target for Reward System Related Disorders? A Qualitative Synthesis and Systematic Review Analysis of Studies on Palatable Food, Drugs of Abuse, and Alcohol

The role of glucagon-like peptide 1 (GLP-1) in insulin-dependent signaling is well-known; GLP-1 enhances glucose-dependent insulin secretion and lowers blood glucose in diabetes. GLP-1 receptors (GLP-1R) are also widely expressed in the brain, and in addition to its role in neuroprotection, it affects reward pathways. This systematic review aimed to analyze the studies on GLP-1 and reward pathways and its currently identified mechanisms.

Methods: “Web of Science” and “Pubmed” were searched to identify relevant studies using GLP-1 as the keyword. Among the identified 26,539 studies, 30 clinical, and 71 preclinical studies were included. Data is presented by grouping rodent studies on palatable food intake, drugs of abuse, and studies on humans focusing on GLP-1 and reward systems.

Results: GLP-1Rs are located in reward-related areas, and GLP-1, its agonists, and DPP-IV inhibitors are effective in decreasing palatable food intake, along with reducing cocaine, amphetamine, alcohol, and nicotine use in animals. GLP-1 modulates dopamine levels and glutamatergic neurotransmission, which results in observed behavioral changes. In humans, GLP-1 alters palatable food intake and improves activity deficits in the insula, hypothalamus, and orbitofrontal cortex (OFC). GLP-1 reduces food cravings partially by decreasing activity to the anticipation of food in the left insula of obese patients with diabetes and may inhibit overeating by increasing activity to the consumption of food in the right OFC of obese and left insula of obese with diabetes.

Conclusion: Current preclinical studies support the view that GLP-1 can be a target for reward system related disorders. More translational research is needed to evaluate its efficacy on human reward system related disorders.

GLP-1/dexamethasone inhibits food reward without inducing mood and memory deficits in mice

BACKGROUND

Pharmacotherapies targeting motivational aspects of feeding and palatable food reward, while sparing mood and cognitive function, represent an alluring approach to reverse obesity and maintain weight loss in an obesogenic environment. A novel glucagon-like peptide-1/dexamethasone (GLP-1/Dexa) conjugate, developed to selectively activate glucocorticoid receptors in GLP-1 receptor-expressing cells was shown to decrease food intake and lower body weight in obese mice. Here, we investigate if this novel drug candidate modulates the rewarding properties of food and if it affects behavioral indices of mood and memory.

METHODS

C57Bl6 mice treated with the GLP-1/Dexa conjugate, GLP-1 or vehicle lever-pressed for high-fat, high sugar (HFHS) food rewards in an operant task. Alterations in food-motivated behavior were also assessed following a HFHS diet withdrawal manipulation (switch to chow). The effects of repeated GLP-1/Dexa conjugate, GLP-1 or vehicle on free-feeding intake, body weight, anxiodepressive behaviors (elevated-plus maze, open field test & forced swim test), memory (novel object recognition) and mRNA expression of reward-relevant markers in the nucleus accumbens were also evaluated in mice fed a HFHS diet for 12 weeks.

RESULTS

Mice treated with a GLP-1 analogue displayed a transient (4 h) reduction in their motivation to lever press for HFHS reward, whereas treatment with equimolar doses of GLP-1/Dexa delivered a superior and sustained (20 h) suppression of food-motivated behavior. GLP-1/Dexa also inhibited food reward following withdrawal from the HFHS diet. These benefits coincided with related transcriptional changes of dopaminergic markers in the nucleus accumbens. Importantly, repeated GLP-1/Dexa treatment during a HFHS diet caused weight loss without affecting anxiodepressive behavior and memory.

CONCLUSION

Via its actions to blunt the rewarding effects of palatable food without affecting mood and recognition memory, GLP-1-directed targeting of dexamethasone may serve as a promising and safe anti-obesity strategy.

Updates on the neurobiology of food reward and their relation to the obesogenic environment

PURPOSE OF REVIEW

To summarize recent findings about the neurobiological control of food reward and discuss their relevance for hedonic food intake and obesity in our current obesogenic environment.

RECENT FINDINGS

Recent data show new roles for circuits involving neuronal subpopulations within the central amyglada (CeA) and lateral hypothalamus in the regulation of feeding and reward in rodents under free and operant conditions and also in restrain from reward consumption. Recent work also shows that the orbitofrontal cortex (OFC) codes for subjective perception of food features during reward assessment of individual foods and that activity in the nucleus accumbens (NAc) codes for anticipation for reward, which can be blocked by time-locked neurostimulation of NAc.

SUMMARY

New data illustrates that different aspects of hedonic intake and food reward are coded in a distributed brain network. In particular, as our obesogenic environment facilitates access to palatable food and promotes cue-induced feeding, neuronal circuits related to control of impulsivity, food valuation and duration of hedonic intake episodes might have a significant role in our ability to control food intake and development of obesity by excess intake.