Regulation of energy balance and body weight by the brain: a distributed system prone to disruption

Position statement on nutrition therapy for overweight and obesity: nutrition department of the Brazilian association for the study of obesity and metabolic syndrome (ABESO-2022)

Obesity is a chronic disease resulting from multifactorial causes mainly related to lifestyle (sedentary lifestyle, inadequate eating habits) and to other conditions such as genetic, hereditary, psychological, cultural, and ethnic factors. The weight loss process is slow and complex, and involves lifestyle changes with an emphasis on nutritional therapy, physical activity practice, psychological interventions, and pharmacological or surgical treatment. Because the management of obesity is a long-term process, it is essential that the nutritional treatment contributes to the maintenance of the individual's global health. The main diet-related causes associated with excess weight are the high consumption of ultraprocessed foods, which are high in fats, sugars, and have high energy density; increased portion sizes; and low intake of fruits, vegetables, and grains. In addition, some situations negatively interfere with the weight loss process, such as fad diets that involve the belief in superfoods, the use of teas and phytotherapics, or even the avoidance of certain food groups, as has currently been the case for foods that are sources of carbohydrates. Individuals with obesity are often exposed to fad diets and, on a recurring basis, adhere to proposals with promises of quick solutions, which are not supported by the scientific literature. The adoption of a dietary pattern combining foods such as grains, lean meats, low-fat dairy, fruits, and vegetables, associated with an energy deficit, is the nutritional treatment recommended by the main international guidelines. Moreover, an emphasis on behavioral aspects including motivational interviewing and the encouragement for the individual to develop skills will contribute to achieve and maintain a healthy weight. Therefore, this Position Statement was prepared based on the analysis of the main randomized controlled studies and meta-analyses that tested different nutrition interventions for weight loss. Topics in the frontier of knowledge such as gut microbiota, inflammation, and nutritional genomics, as well as the processes involved in weight regain, were included in this document. This Position Statement was prepared by the Nutrition Department of the Brazilian Association for the Study of Obesity and Metabolic Syndrome (ABESO), with the collaboration of dietitians from research and clinical fields with an emphasis on strategies for weight loss.

Sex and Species Differences in the Development of Diet-Induced Obesity and Metabolic Disturbances in Rodents

Prevalence and health consequences of obesity differ between men and women. Yet, most preclinical studies investigating the etiology of obesity have, to date, been conducted in male rodents. Notably, diet is a major determinant of obesity, but sex differences in rodent models of diet-induced obesity, and the mechanisms that underlie such differences, are still understudied. Here, we aim to determine whether time course and characteristics of diet-induced obesity differ between sexes in rats and mice, and to investigate the potential causes of the observed divergence. To achieve this, we offered the most commonly tested rodents of both sexes, SD rats and C57BL/6 mice, a free choice of 60 % high-fat diet (HFD) and regular chow; body weight, food intake, fat mass, brown adipose responses, locomotor activity and glucose tolerance were assessed in a similar manner in both species. Our results indicate that overall diet-induced hyperphagia is greater in males but that females display a higher preference for the HFD, irrespective of species. Female rats, compared to males, showed a delay in diet-induced weight gain and less metabolic complications. Although male rats increased brown adipose tissue thermogenesis in response to the HFD challenge, this was not sufficient to counteract increased adiposity. In contrast to rats, female and male mice presented with a dramatic adiposity and impaired glucose tolerance, and a decreased energy expenditure. Female mice showed a 5-fold increase in visceral fat, compared to 2-fold increase seen in male mice. Overall, we found that male and female rodents responded very differently to HFD challenge, and engaged different compensatory energy expenditure mechanisms. In addition, these sex differences are divergent in rats and mice. We conclude that SD rats have a better face validity for the lower prevalence of overweight in women, while C57BL/6 mice may better model the increased prevalence of morbid obesity in women.

Biased Ghrelin Receptor Signaling and the Dopaminergic System as Potential Targets for Metabolic and Psychological Symptoms of Anorexia Nervosa

Anorexia Nervosa (AN) is a complex disease that impairs the metabolic, mental and physiological health of affected individuals in a severe and sometimes lethal way. Many of the common symptoms in AN patients, such as reduced food intake, anxiety, impaired gut motility or overexercising are connected to both the orexigenic gut hormone ghrelin and the dopaminergic system. Targeting the ghrelin receptor (GhrR) to treat AN seems a promising possibility in current research. However, GhrR signaling is highly complex. First, the GhrR can activate four known intracellular pathways Gαq, Gαi/o, Gα12/13 and the recruitment of β-arrestin. Biased signaling provides the possibility to activate or inhibit only one or a subset of the intracellular pathways of a pleiotropic receptor. This allows specific targeting of physiological functions without adverse effects. Currently little is known on how biased signaling could specifically modulate GhrR effects. Second, GhrR signaling has been shown to be interconnected with the dopaminergic system, particularly in the context of AN symptoms. This review highlights that a biased agonist for the GhrR may be a promising target for the treatment of AN, however extensive and systematic translational studies are still needed and the connection to the dopaminergic system has to be taken into account.

Copper Ionophores as Novel Antiobesity Therapeutics

The therapeutic utility of the copper ionophore disulfiram was investigated in a diet-induced obesity mouse model (C57BL/6J background), both through administration in feed (0.05 to 1% (w/w)) and via oral gavage (150 mg/kg) for up to eight weeks. Mice were monitored for body weight, fat deposition (perigonadal fat pads), metabolic changes (e.g., glucose dyshomeostasis) and pathologies (e.g., hepatic steatosis, hyperglycaemia and hypertriglyceridemia) associated with a high-fat diet. Metal-related pharmacological effects across major organs and serums were investigated using inductively coupled plasma mass spectrometry (ICP-MS). Disulfiram treatments (all modes) augmented hepatic copper in mice, markedly moderated body weight and abolished the deleterious systemic changes associated with a high-fat diet. Likewise, another chemically distinct copper ionophore H2(gtsm), administered daily (oral gavage), also augmented hepatic copper and moderated mouse body weight. Postmortem histological examinations of the liver and other major organs, together with serum aminotransferases, supported the reported therapeutic safety of disulfiram. Disulfiram specifically altered systemic copper in mice and altered hepatic copper metabolism, perturbing the incorporation of copper into ceruloplasmin (holo-ceruloplasmin biosynthesis) and subsequently reducing serum copper concentrations. Serum ceruloplasmin represents a biomarker for disulfiram activity. Our results establish copper ionophores as a potential class of antiobesity agents.

Combined Amylin/GLP-1 pharmacotherapy to promote and sustain long-lasting weight loss

A growing appreciation of the overlapping neuroendocrine mechanisms controlling energy balance has highlighted combination therapies as a promising strategy to enhance sustained weight loss. Here, we investigated whether amylin- and glucagon-like-peptide-1 (GLP-1)-based combination therapies produce greater food intake- and body weight-suppressive effects compared to monotherapies in both lean and diet-induced obese (DIO) rats. In chow-maintained rats, systemic amylin and GLP-1 combine to reduce meal size. Furthermore, the amylin and GLP-1 analogs salmon calcitonin (sCT) and liraglutide produce synergistic-like reductions in 24 hours energy intake and body weight. The administration of sCT with liraglutide also led to a significant enhancement in cFos-activation in the dorsal-vagal-complex (DVC) compared to mono-therapy, suggesting an activation of distinct, yet overlapping neural substrates in this critical energy balance hub. In DIO animals, long-term daily administration of this combination therapy, specifically in a stepwise manner, results in reduced energy intake and greater body weight loss over time when compared to chronic mono- and combined-treated groups, without affecting GLP-1 receptor, preproglucagon or amylin-receptor gene expression in the DVC.

Stress-Induced Synaptic Dysfunction and Neurotransmitter Release in Alzheimer's Disease: Can Neurotransmitters and Neuromodulators be Potential Therapeutic Targets?

The communication between neurons at synaptic junctions is an intriguing process that monitors the transmission of various electro-chemical signals in the central nervous system. Albeit any aberration in the mechanisms associated with transmission of these signals leads to loss of synaptic contacts in both the neocortex and hippocampus thereby causing insidious cognitive decline and memory dysfunction. Compelling evidence suggests that soluble amyloid-β (Aβ) and hyperphosphorylated tau serve as toxins in the dysfunction of synaptic plasticity and aberrant neurotransmitter (NT) release at synapses consequently causing a cognitive decline in Alzheimer's disease (AD). Further, an imbalance between excitatory and inhibitory neurotransmission systems induced by impaired redox signaling and altered mitochondrial integrity is also amenable for such abnormalities. Defective NT release at the synaptic junction causes several detrimental effects associated with altered activity of synaptic proteins, transcription factors, Ca2+ homeostasis, and other molecules critical for neuronal plasticity. These detrimental effects further disrupt the normal homeostasis of neuronal cells and thereby causing synaptic loss. Moreover, the precise mechanistic role played by impaired NTs and neuromodulators (NMs) and altered redox signaling in synaptic dysfunction remains mysterious, and their possible interlink still needs to be investigated. Therefore, this review elucidates the intricate role played by both defective NTs/NMs and altered redox signaling in synaptopathy. Further, the involvement of numerous pharmacological approaches to compensate neurotransmission imbalance has also been discussed, which may be considered as a potential therapeutic approach in synaptopathy associated with AD.

Beyond glycaemic control: A cross-over, double-blinded, 24-week intervention with liraglutide in type 1 diabetes

AIMS

To investigate the effects of 24 weeks of treatment with liraglutide added to basal/bolus insulin on anthropometric and metabolic parameters in overweight participants with type 1 diabetes.

METHODS

In a double-blinded cross-over fashion, 15 participants were randomly assigned (1:1) to receive placebo (saline solution) or liraglutide for 24 weeks including a 1-month titration period from 0.6 to 1.2 to 1.8 mg, in addition to their insulin. The treatment was followed by a 1-month wash-out period. Participants were then assigned to the other treatment for another 24 weeks. Paired rank tests were used to compare the metabolic parameters.

RESULTS

There was no treatment effect on HbA1c nor on insulin dose. Heart rate was increased by about 8 beats per minute with liraglutide. There were significant reductions in metabolic measures: weight, body mass index, waist and hip circumferences, body fatness, computed tomography scan abdominal and mid-thigh measurements, systolic and diastolic blood pressures (all P ≤ .05). There was no increase in time spent in hypoglycaemia with liraglutide.

CONCLUSIONS

The addition of liraglutide to basal/bolus insulin therapy for 24 weeks in overweight/obese individuals with type 1 diabetes improved the anthropometric and metabolic profiles without an increase in hypoglycaemia. Clinical Trials.gov No: NCT01787916.

Mitochondrial dysfunction in obesity

Obesity leads to various changes in the body. Among them, the existing inflammatory process may lead to an increase in the production of reactive oxygen species (ROS) and cause oxidative stress. Oxidative stress, in turn, can trigger mitochondrial changes, which is called mitochondrial dysfunction. Moreover, excess nutrients supply (as it commonly is the case with obesity) can overwhelm the Krebs cycle and the mitochondrial respiratory chain, causing a mitochondrial dysfunction, and lead to a higher ROS formation. This increase in ROS production by the respiratory chain may also cause oxidative stress, which may exacerbate the inflammatory process in obesity. All these intracellular changes can lead to cellular apoptosis. These processes have been described in obesity as occurring mainly in peripheral tissues. However, some studies have already shown that obesity is also associated with changes in the central nervous system (CNS), with alterations in the blood-brain barrier (BBB) and in cerebral structures such as hypothalamus and hippocampus. In this sense, this review presents a general view about mitochondrial dysfunction in obesity, including related alterations, such as inflammation, oxidative stress, and apoptosis, and focusing on the whole organism, covering alterations in peripheral tissues, BBB, and CNS.

Biological control of appetite: A daunting complexity

OBJECTIVE

This review summarizes a portion of the discussions of an NIH Workshop (Bethesda, MD, 2015) titled "Self-Regulation of Appetite-It's Complicated," which focused on the biological aspects of appetite regulation.

METHODS

This review summarizes the key biological inputs of appetite regulation and their implications for body weight regulation.

RESULTS

These discussions offer an update of the long-held, rigid perspective of an "adipocentric" biological control, taking a broader view that also includes important inputs from the digestive tract, from lean mass, and from the chemical sensory systems underlying taste and smell. It is only beginning to be understood how these biological systems are integrated and how this integrated input influences appetite and food eating behaviors. The relevance of these biological inputs was discussed primarily in the context of obesity and the problem of weight regain, touching on topics related to the biological predisposition for obesity and the impact that obesity treatments (dieting, exercise, bariatric surgery, etc.) might have on appetite and weight loss maintenance. Finally considered is a common theme that pervaded the workshop discussions, which was individual variability.

CONCLUSIONS

It is this individual variability in the predisposition for obesity and in the biological response to weight loss that makes the biological component of appetite regulation so complicated. When this individual biological variability is placed in the context of the diverse environmental and behavioral pressures that also influence food eating behaviors, it is easy to appreciate the daunting complexities that arise with the self-regulation of appetite.

Hindbrain DPP-IV inhibition improves glycemic control and promotes negative energy balance

The beneficial glycemic and food intake-suppressive effects of glucagon-like peptide-1 (GLP-1) have made this neuroendocrine system a leading target for pharmacological approaches to the treatment of diabetes and obesity. One strategy to increase the activity of endogenous GLP-1 is to prevent the rapid degradation of the hormone by the enzyme dipeptidyl peptidase-IV (DPP-IV). However, despite the expression of both DPP-IV and GLP-1 in the brain, and the clear importance of central GLP-1 receptor (GLP-1R) signaling for glycemic and energy balance control, the metabolic effects of central inhibition of DPP-IV activity are unclear. To test whether hindbrain DPP-IV inhibition suppresses blood glucose, feeding, and body weight gain, the effects of 4th intracerebroventricular (ICV) administration of the FDA-approved DPP-IV inhibitor sitagliptin were evaluated. Results indicate that hindbrain delivery of sitagliptin improves glycemic control in a GLP-1R-dependent manner, suggesting that this effect is due at least in part to increased endogenous brainstem GLP-1 activity after sitagliptin administration. Furthermore, 4th ICV injection of sitagliptin reduced 24h body weight gain and energy intake, with a selective suppression of high-fat diet, but not chow, intake. These data reveal a novel role for hindbrain GLP-1R activation in glycemic control and also demonstrate that DPP-IV inhibition in the caudal brainstem promotes negative energy balance.

Neuronal Regulation of Energy Homeostasis: Beyond the Hypothalamus and Feeding

The essential role of the brain in maintaining energy homeostasis has motivated the drive to define the neural circuitry that integrates external and internal stimuli to enact appropriate and consequential metabolic and behavioral responses. The hypothalamus has received significant attention in this regard given its ability to influence feeding behavior, yet organisms rely on a much broader diversity and distribution of neuronal networks to regulate both energy intake and expenditure. Because energy balance is a fundamental determinant of survival and success of an organism, it is not surprising that emerging data connect circuits controlling feeding and energy balance with higher brain functions and degenerative processes. In this review, we will highlight both classically defined and emerging aspects of brain control of energy homeostasis.

Early leptin intervention reverses perturbed energy balance regulating hypothalamic neuropeptides in the pre- and postnatal calorie-restricted female rat offspring

Pre- and postnatal calorie restriction is associated with postnatal growth restriction, reduced circulating leptin concentrations, and perturbed energy balance. Hypothalamic regulation of energy balance demonstrates enhanced orexigenic (NPY, AgRP) and diminished anorexigenic (POMC, CART) neuropeptide expression (PN21), setting the stage for subsequent development of obesity in female Sprague-Dawley rats. Leptin replenishment during the early postnatal period (PN2-PN8) led to reversal of the hypothalamic orexigenic:anorexigenic neuropeptide ratio at PN21 by reducing only the orexigenic (NPY, AgRP), without affecting the anorexigenic (POMC, CART) neuropeptide expression. This hypothalamic effect was mediated via enhanced leptin receptor (ObRb) signaling that involved increased pSTAT3/STAT3 but reduced PTP1B. This was further confirmed by an increase in body weight at PN21 in response to intracerebroventricular administration of antisense ObRb oligonucleotides (PN2-PN8). The change in the hypothalamic neuropeptide balance in response to leptin administration was associated with increased oxygen consumption, carbon dioxide production, and physical activity, which resulted in increased milk intake (PN14) with no change in body weight. This is in contrast to the reduction in milk intake with no effect on energy expenditure and physical activity observed in controls. We conclude that pre- and postnatal calorie restriction perturbs hypothalamic neuropeptide regulation of energy balance, setting the stage for hyperphagia and reduced energy expenditure, hallmarks of obesity. Leptin in turn reverses this phenotype by increasing hypothalamic ObRb signaling (sensitivity) and affecting only the orexigenic arm of the neuropeptide balance.

Insulin Resistance, Metabolic Syndrome, and Polycystic Ovary Syndrome in Obese Youth

School nurses are well aware of the childhood obesity epidemic in the United States, as one in three youth are overweight or obese. Co-morbidities found in overweight or obese adults were not commonly found in youth three decades ago but are now increasingly "normal" as the obesity epidemic continues to evolve. This article is the second of six related articles discussing the co-morbidities of childhood obesity and discusses the complex association between obesity and insulin resistance, metabolic syndrome, and polycystic ovary syndrome. Insulin resistance increases up to 50% during puberty, which may help to explain why youth are more likely to develop co-morbidities as teens. Treatment of these disorders is focused on changing lifestyle habits, as a child cannot change his or her pubertal progression, ethnicity, or family history. School nurses and other personnel can assist youth with insulin resistance, metabolic syndrome, and polycystic ovary syndrome by supporting their efforts to make changes, reinforcing that insulin resistance is not necessarily type 2 diabetes even if the child is taking medication, and intervening with negative peer pressure.

Adiponectin in eating disorders

PURPOSE

To elucidate the possible role of adiponectin, an adipokine secreted by white adipose tissue that plays an important role in the neuromodulation of food intake, in the pathogenesis of eating disorders.

METHODS

A comprehensive review of the available literature via MedLine is done using the term "adiponectin" in association with one of the following terms: "anorexia nervosa", "bulimia nervosa", "binge eating disorder" or "eating disorders".

RESULTS

The majority of studies evaluating serum adiponectin levels in patients with eating disorders show that serum adiponectin levels are increased in patients with anorexia nervosa. After refeeding, adiponectin levels tend to rejoin the levels of healthy individuals. Data concerning serum adiponectin levels in patients with bulimia nervosa show that these levels can be equal, higher or lower than those found in healthy controls and lower than those found in anorexia nervosa patients. Binge eating disorder is accompanied with lower serum adiponectin levels than normal. Adiponectin receptor type 1 seems to be more related to the central pathological effect of adiponectin on eating behavior.

CONCLUSION

The potential role that plays adiponectin in the pathogenesis of eating disorders needs to be elucidated by further studies.

Towards a 'systems'-level understanding of the nervous system and its disorders

It is becoming clear that nervous system development and adult functioning are highly coupled with other physiological systems. Accordingly, neurological and psychiatric disorders are increasingly being associated with a range of systemic comorbidities including, most prominently, impairments in immunological and bioenergetic parameters as well as in the gut microbiome. Here, we discuss various aspects of the dynamic crosstalk between these systems that underlies nervous system development, homeostasis, and plasticity. We believe a better definition of this underappreciated systems physiology will yield important insights into how nervous system diseases with systemic comorbidities arise and potentially identify novel diagnostic and therapeutic strategies.

Exenatide-induced reduction in energy intake is associated with increase in hypothalamic connectivity

OBJECTIVE

Glucagon-like peptide-1 receptor agonists such as exenatide are known to influence neural activity in the hypothalamus of animals and to reduce energy intake. In humans, however, significant weight loss has been observed in only a subgroup of patients. Why only some individuals respond with weight loss and others do not remains unclear. In this functional magnetic resonance imaging (fMRI) study, we investigated differences in hypothalamic connectivity between "responders" (reduction in energy intake after exenatide infusion) and "nonresponders."

RESEARCH DESIGN AND METHODS

We performed a randomized, double-blinded, placebo-controlled, cross-over fMRI study with intravenous administration of exenatide in obese male volunteers. During brain scanning with continuous exenatide or placebo administration, participants rated food and nonfood images. After each scanning session, energy intake was measured using an ad libitum buffet. Functional hypothalamic connectivity was assessed by eigenvector centrality mapping, a measure of connectedness throughout the brain.

RESULTS

Responders showed significantly higher connectedness of the hypothalamus, which was specific for the food pictures condition, in the exenatide condition compared with placebo. Nonresponders did not show any significant exenatide-induced changes in hypothalamic connectedness.

CONCLUSIONS

Our results demonstrate a central hypothalamic effect of peripherally administered exenatide that occurred only in the group that showed an exenatide-dependent anorexigenic effect. These findings indicate that the hypothalamic response seems to be the crucial factor for the effect of exenatide on energy intake.

Divergent circuitry underlying food reward and intake effects of ghrelin: dopaminergic VTA-accumbens projection mediates ghrelin's effect on food reward but not food intake

Obesity has reached global epidemic proportions and creating an urgent need to understand mechanisms underlying excessive and uncontrolled food intake. Ghrelin, the only known circulating orexigenic hormone, potently increases food reward behavior. The neurochemical circuitry that links ghrelin to the mesolimbic reward system and to the increased food reward behavior remains unclear. Here we examine whether VTA-NAc dopaminergic signaling is required for the effects of ghrelin on food reward and intake. In addition, we examine the possibility of endogenous ghrelin acting on the VTA-NAc dopamine neurons. A D1-like or a D2 receptor antagonist was injected into the NAc in combination with ghrelin microinjection into the VTA to investigate whether this blockade attenuates ghrelin-induced food reward behavior. VTA injections of ghrelin produced a significant increase in food motivation/reward behavior, as measured by sucrose-induced progressive ratio operant conditioning, and chow intake. Pretreatment with either a D1-like or D2 receptor antagonist into the NAc, completely blocked the reward effect of ghrelin, leaving chow intake intact. We also found that this circuit is potentially relevant for the effects of endogenously released ghrelin as both antagonists reduced fasting (a state of high circulating levels of ghrelin) elevated sucrose-motivated behavior but not chow hyperphagia. Taken together our data identify the VTA to NAc dopaminergic projections, along with D1-like and D2 receptors in the NAc, as essential elements of the ghrelin responsive circuits controlling food reward behavior. Interestingly results also suggest that food reward behavior and simple intake of chow are controlled by divergent circuitry, where NAc dopamine plays an important role in food reward but not in food intake.