GLP-1 and estrogen conjugate acts in the supramammillary nucleus to reduce food-reward and body weight

Anti-Obesity Therapy: from Rainbow Pills to Polyagonists

With their ever-growing prevalence, obesity and diabetes represent major health threats of our society. Based on estimations by the World Health Organization, approximately 300 million people will be obese in 2035. In 2015 alone there were more than 1.6 million fatalities attributable to hyperglycemia and diabetes. In addition, treatment of these diseases places an enormous burden on our health care system. As a result, the development of pharmacotherapies to tackle this life-threatening pandemic is of utmost importance. Since the beginning of the 19th century, a variety of drugs have been evaluated for their ability to decrease body weight and/or to improve deranged glycemic control. The list of evaluated drugs includes, among many others, sheep-derived thyroid extracts, mitochondrial uncouplers, amphetamines, serotonergics, lipase inhibitors, and a variety of hormones produced and secreted by the gastrointestinal tract or adipose tissue. Unfortunately, when used as a single hormone therapy, most of these drugs are underwhelming in their efficacy or safety, and placebo-subtracted weight loss attributed to such therapy is typically not more than 10%. In 2009, the generation of a single molecule with agonism at the receptors for glucagon and the glucagon-like peptide 1 broke new ground in obesity pharmacology. This molecule combined the beneficial anorectic and glycemic effects of glucagon-like peptide 1 with the thermogenic effect of glucagon into a single molecule with enhanced potency and sustained action. Several other unimolecular dual agonists have subsequently been developed, and, based on their preclinical success, these molecules illuminate the path to a new and more fruitful era in obesity pharmacology. In this review, we focus on the historical pharmacological approaches to treat obesity and glucose intolerance and describe how the knowledge obtained by these studies led to the discovery of unimolecular polypharmacology.

The impact of ERα action on muscle metabolism and insulin sensitivity - Strong enough for a man, made for a woman

Background

The incidence of chronic disease is elevated in women after menopause. Natural variation in muscle expression of the estrogen receptor (ER)α is inversely associated with plasma insulin and adiposity. Moreover, reduced muscle ERα expression levels are observed in women and animals presenting clinical features of the metabolic syndrome (MetSyn). Considering that metabolic dysfunction impacts nearly a quarter of the U.S. adult population and elevates chronic disease risk including type 2 diabetes, heart disease, and certain cancers, treatment strategies to combat metabolic dysfunction and associated pathologies are desperately needed.

Scope of the review

This review will provide evidence supporting a critical and protective role for skeletal muscle ERα in the regulation of metabolic homeostasis and insulin sensitivity, and propose novel ERα targets involved in the maintenance of metabolic health.

Major conclusions

Studies identifying ERα-regulated pathways essential for disease prevention will lay the important foundation for the rational design of novel therapeutics to improve the metabolic health of women while limiting secondary complications that have plagued traditional hormone replacement interventions.

Lateral hypothalamic GLP-1 receptors are critical for the control of food reinforcement, ingestive behavior and body weight

Increased motivation for highly rewarding food is a major contributing factor to obesity. Most of the literature focuses on the mesolimbic nuclei as the core of reward behavior regulation. However, the lateral hypothalamus (LH) is also a key reward-control locus in the brain. Here we hypothesize that manipulating glucagon-like peptide-1 receptor (GLP-1R) activity selectively in the LH can profoundly affect food reward behavior, ultimately leading to obesity. Progressive ratio operant responding for sucrose was examined in male and female rats, following GLP-1R activation and pharmacological or genetic GLP-1R blockade in the LH. Ingestive behavior and metabolic parameters, as well as molecular and efferent targets, of the LH GLP-1R activation were also evaluated. Food motivation was reduced by activation of LH GLP-1R. Conversely, acute pharmacological blockade of LH GLP-1R increased food motivation but only in male rats. GLP-1R activation also induced a robust reduction in food intake and body weight. Chronic knockdown of LH GLP-1R induced by intraparenchymal delivery of an adeno-associated virus-short hairpin RNA construct was sufficient to markedly and persistently elevate ingestive behavior and body weight and ultimately resulted in a doubling of fat mass in males and females. Interestingly, increased food reinforcement was again found only in males. Our data identify the LH GLP-1R as an indispensable element of normal food reinforcement, food intake and body weight regulation. These findings also show, for we believe the first time, that brain GLP-1R manipulation can result in a robust and chronic body weight gain. The broader implications of these findings are that the LH differs between females and males in its ability to control motivated and ingestive behaviors.

Estradiol and the control of feeding behavior

This review lays out the evidence for the role of E2 in homeostatic and hedonic feeding across several species. While significant effort has been expended on homeostatic feeding research, more studies for hedonic feeding need to be conducted (i.e. are there increases in meal size and enhanced motivation to natural food rewards). By identifying the underlying neural circuitry involved, one can better delineate the mechanisms by which E2 influences feeding behavior. By utilizing more selective neural targeting techniques, such as optogenetics, significant progress can be made toward this goal. Together, behavioral and physiological techniques will help us to better understand neural deficits that can increase the risk for obesity in the absence of E2 (menopause) and aid in developing therapeutic strategies.

Progress and challenges in anti-obesity pharmacotherapy

Obesity is a serious and growing worldwide health challenge. Healthy lifestyle choices are the foundation of obesity treatment. However, weight loss can lead to physiological adaptations that promote weight regain. As a result, lifestyle treatment alone typically produces only modest weight loss that is difficult to sustain. In other metabolic diseases, pharmacotherapy is an accepted adjunct to lifestyle. Several anti-obesity drugs have been approved in the USA, European Union, Australia, and Japan including sympathomimetics, pancreatic lipase inhibitors, GABA_A receptor activators, a serotonin 2C receptor agonist, opioid antagonist, dopamine-norepinephrine reuptake inhibitor, and glucagon-like peptide-1 (GLP-1) receptor agonists. These drugs vary in their efficacy and side-effect profiles but all provide greater weight loss than do lifestyle changes alone. Even though obesity is widespread and associated with adverse health consequences, and anti-obesity drugs can help people to lose weight, very few patients use these drugs partly because of concerns about safety and efficacy, but also because of inadequate health insurance coverage. Despite great advances in our understanding of the biology of weight regulation, many clinicians still believe that patients with obesity should have the willpower to eat less. The tendency to hold the patient with obesity responsible for their condition can be a barrier to greater acceptance of anti-obesity drugs as appropriate options for treatment. Physicians should be comfortable discussing the risks and benefits of these drugs, and health insurance companies should provide reasonable coverage for their use in patients who are most likely to benefit. Although few promising anti-obesity medications are in the drug-development pipeline, the most promising drugs are novel molecules that are co-agonists for multiple gut hormones including GLP-1, glucagon, and gastric inhibitory peptide.

Gut hormone polyagonists for the treatment of type 2 diabetes

Chemical derivatives of the gut-derived peptide hormone glucagon-like peptide 1 (GLP-1) are among the best-in-class pharmacotherapies to treat obesity and type 2 diabetes. However, GLP-1 analogs have modest weight lowering capacity, in the range of 5-10%, and the therapeutic window is hampered by dose-dependent side effects. Over the last few years, a new concept has emerged: combining the beneficial effects of several key metabolic hormones into a single molecular entity. Several unimolecular GLP-1-based polyagonists have shown superior metabolic action compared to GLP-1 monotherapies. In this review article, we highlight the history of polyagonists targeting the receptors for GLP-1, GIP and glucagon, and discuss recent progress in expanding of this concept to now allow targeted delivery of nuclear hormones via GLP-1 and other gut hormones, as a novel approach towards more personalized pharmacotherapies.

Hypothalamic effects of thyroid hormone

Thyroid hormone (TH) is a key driver of metabolism in mammals. Plasma concentrations of TH are kept within a narrow range by negative feedback regulation in the hypothalamus-pituitary-thyroid (HPT) axis. Plasma TH concentrations are an important determinant of metabolic processes in liver and brown adipose tissue (BAT). In addition to endocrine effects of TH derived from the circulation, recent studies have demonstrated additional neural routes for intrahypothalamic thyroid hormone to regulate metabolism in liver and BAT via the sympathetic and parasympathetic branch of the autonomic nervous system (ANS). This review provides an overview of studies reporting metabolic effects of selective administration of T3 within hypothalamic nuclei including the paraventricular nucleus (PVN), the ventromedial nucleus (VMH), the arcuate nucleus (Arc), and the anterior hypothalamic area (AHA). This overview of the literature suggests that intrahypothalamic T3 can have profound effects on hepatic glucose production and insulin sensitivity, energy expenditure in BAT, cardiovascular function and feeding behavior. As the experiments have been performed in experimental animals exclusively, and the timing and route of T3 administration may be an important determinant of effect size, the clinical relevance of these metabolic effects in the chronic setting remains to be established.

Estradiol modulates the anorexic response to central glucagon-like peptide 1

Estrogens suppress feeding in part by enhancing the response to satiation signals. Glucagon-like peptide 1 (GLP-1) acts on receptor populations both peripherally and centrally to affect food intake. We hypothesized that modulation of the central GLP-1 system is one of the mechanisms underlying the effects of estrogens on feeding. We assessed the anorexic effect of 0, 1, and 10μg doses of GLP-1 administered into the lateral ventricle of bilaterally ovariectomized (OVX) female rats on a cyclic regimen of either 2μg β-estradiol-3-benzoate (EB) or oil vehicle 30min prior to dark onset on the day following hormone treatment. Central GLP-1 treatment significantly suppressed food intake in EB-treated rats at both doses compared to vehicle, whereas only the 10μg GLP-1 dose was effective in oil-treated rats. To follow up, we examined whether physiologic-dose cyclic estradiol treatment influences GLP-1-induced c-Fos in feeding-relevant brain areas of OVX females. GLP-1 significantly increased c-Fos expression in the area postrema (AP) and nucleus of the solitary tract (NTS), and the presence of estrogens may be required for this effect in the paraventricular nucleus of the hypothalamus (PVN). Together, these data suggest that modulation of the central GLP-1 system may be one of the mechanisms by which estrogens suppress food intake, and highlight the PVN as a region of interest for future investigation.

Ghrelin's control of food reward and body weight in the lateral hypothalamic area is sexually dimorphic

Ghrelin is a stomach-produced hormone that stimulates ingestive behavior and increases motivated behavior to obtain palatable foods. Ghrelin receptors (growth hormone secretagogue receptors; Ghsr) are expressed in the lateral hypothalamic area (LHA), and LHA-targeted ghrelin application increases ingestive behavior in male rodents. However, the effects of LHA ghrelin signaling in females are unexplored. Here we investigated whether LHA ghrelin signaling is necessary and sufficient for control of ingestive and motivated behavior for food in male and female rats. Ghrelin delivered to the LHA increased food intake and motivated behavior for sucrose in both male and female rats, whereas increased food-seeking behavior and body weight were only observed in females. Females had slightly higher Ghsr levels in the LHA compared to males, and importantly, acute blockade of the Ghsr in the LHA significantly reduced food intake, body weight, and motivated behavior for sucrose in female but not male rats. Chronic LHA Ghsr reduction in female rats achieved by RNA inference-mediated Ghsr knockdown, resulting in a 25% reduction in LHA Ghsr mRNA, abolished the reward-driven behavioral effects of LHA-targeted ghrelin, but was not sufficient to affect baseline food intake or food reward responding. Collectively we show that ghrelin acts in the LHA to alter ingestive and motivated behaviors in a sex-specific manner.

The Role of Skeletal Muscle Estrogen Receptors in Metabolic Homeostasis and Insulin Sensitivity

Women in the modern era are challenged with facing menopausal symptoms as well as heightened disease risk associated with increasing adiposity and metabolic dysfunction for up to three decades of life. Treatment strategies to combat metabolic dysfunction and associated pathologies have been hampered by our lack of understanding regarding the biological causes of these clinical conditions and our incomplete understanding regarding the effects of estrogens and the tissue-specific functions and molecular actions of its receptors. In this chapter we provide evidence supporting a critical and protective role for skeletal muscle estrogen receptor α in the maintenance of metabolic homeostasis and insulin sensitivity. Studies identifying the critical ER-regulated pathways essential for disease prevention will lay the important foundation for the rational design of novel therapeutic strategies to improve the health of women while limiting secondary complications that have plagued traditional hormone replacement interventions.