GABAergic and glutamatergic modulation in binge eating: therapeutic approach

Emerging Evidence for the Widespread Role of Glutamatergic Dysfunction in Neuropsychiatric Diseases

The monoamine model of depression has long formed the basis of drug development but fails to explain treatment resistance or associations with stress or inflammation. Recent animal research, clinical trials of ketamine (a glutamate receptor antagonist), neuroimaging research, and microbiome studies provide increasing evidence of glutamatergic dysfunction in depression and other disorders. Glutamatergic involvement across diverse neuropathologies including psychoses, neurodevelopmental, neurodegenerative conditions, and brain injury forms the rationale for this review. Glutamate is the brain's principal excitatory neurotransmitter (NT), a metabolic and synthesis substrate, and an immune mediator. These overlapping roles and multiple glutamate NT receptor types complicate research into glutamate neurotransmission. The glutamate microcircuit comprises excitatory glutamatergic neurons, astrocytes controlling synaptic space levels, through glutamate reuptake, and inhibitory GABA interneurons. Astroglia generate and respond to inflammatory mediators. Glutamatergic microcircuits also act at the brain/body interface via the microbiome, kynurenine pathway, and hypothalamus-pituitary-adrenal axis. Disruption of excitatory/inhibitory homeostasis causing neuro-excitotoxicity, with neuronal impairment, causes depression and cognition symptoms via limbic and prefrontal regions, respectively. Persistent dysfunction reduces neuronal plasticity and growth causing neuronal death and tissue atrophy in neurodegenerative diseases. A conceptual overview of brain glutamatergic activity and peripheral interfacing is presented, including the common mechanisms that diverse diseases share when glutamate homeostasis is disrupted.

Negative Modulation of the Metabotropic Glutamate Receptor Type 5 as a Potential Therapeutic Strategy in Obesity and Binge-Like Eating Behavior

Obesity is a multifactorial disease, which in turn contributes to the onset of comorbidities, such as diabetes and atherosclerosis. Moreover, there are only few options available for treating obesity, and most current pharmacotherapy causes severe adverse effects, while offering minimal weight loss. Literature shows that metabotropic glutamate receptor 5 (mGluR5) modulates central reward pathways. Herein, we evaluated the effect of VU0409106, a negative allosteric modulator (NAM) of mGluR5 in regulating feeding and obesity parameters. Diet-induced obese C57BL/6 mice were treated for 14 days with VU0409106, and food intake, body weight, inflammatory/hormonal levels, and behavioral tests were performed. Our data suggest reduction of feeding, body weight, and adipose tissue inflammation in mice treated with high-fat diet (HFD) after chronic treatment with VU0409106. Furthermore, a negative modulation of mGluR5 also reduces binge-like eating, the most common type of eating disorder. Altogether, our results pointed out mGluR5 as a potential target for treating obesity, as well as related disorders.

Investigational drugs for the treatment of binge eating disorder (BED): an update

Introduction: Binge eating disorder (BED) is the most common eating disorder and is frequently associated with psychiatric and medical comorbidities and functional impairment. Although psychological treatments have been the cornerstones of BED treatment, pharmacologic interventions also play an important part of the multimodal management of this condition.Areas covered: This review examines investigational, approved and other pharmacological agents for the treatment of BED. We searched PubMed and clinicaltrials.gov to identify pharmacological interventions for the management of this condition.Expert opinion: BED pharmacological studies have incorporated new drug targets based on our enhanced understanding of the pathophysiology of BED. Neurobiological dysregulation in the reward center and impulse control circuitry and related disturbances in dopamine neurotransmission are among the neurobiological explanations that have been suggested for BED. These mechanisms serve as a pharmacodynamic foundation for the development of new compounds such as lisdexamfetamine (LDX) and dasotraline. Despite these advances, pharmacological trials in BED have numerous challenges that must be overcome. For most compounds studied, larger and more definitive trials is a high priority.

Shared Behavioral and Neurocircuitry Disruptions in Drug Addiction, Obesity, and Binge Eating Disorder: Focus on Group I mGluRs in the Mesolimbic Dopamine Pathway

Accumulated data from clinical and preclinical studies suggest that, in drug addiction and states of overeating, such as obesity and binge eating disorder (BED), there is an imbalance in circuits that are critical for motivation, reward saliency, executive function, and self-control. Central to these pathologies and the extensive topic of this Review are the aberrations in dopamine (DA) and glutamate (Glu) within the mesolimbic pathway. Group I metabotropic glutamate receptors (mGlus) are highly expressed in the mesolimbic pathway and are poised in key positions to modulate disruptions in synaptic plasticity and neurotransmitter release observed in drug addiction, obesity, and BED. The use of allosteric modulators of group I mGlus has been studied in drug addiction, as they offer several advantages over traditional orthosteric agents. However, they have yet to be studied in obesity or BED. With the substantial overlap between the neurocircuitry involved in drug addiction and eating disorders, group I mGlus may also provide novel targets for obesity and BED.

Does compulsive behavior in Anorexia Nervosa resemble an addiction? A qualitative investigation

The characteristic relentless self-starvation behavior seen in Anorexia Nervosa (AN) has been described as evidence of compulsivity, with increasing suggestion of parallels with addictive behavior. This study used a thematic qualitative analysis to investigate the parallels between compulsive behavior in AN and Substance Use Disorders (SUD). Forty individuals currently suffering from AN completed an online questionnaire reflecting on their experience of compulsive behavior in AN. Eight main themes emerged from thematic qualitative analysis; compulsivity as central to AN, impaired control, escalating compulsions, emotional triggers, negative reactions, detrimental continuation of behavior, functional impairment, and role in recovery. These results suggested that individuals with AN view the compulsive nature of their behavior as central to the maintenance of their disorder, and as a significant barrier to recovery. The themes that emerged also showed parallels with the DSM-V criteria for SUDs, mapping onto the four groups of criteria (impaired control, social impairment, risky use of substance, pharmacological criteria). These results emphasize the need for further research to explore the possible parallels in behavioral and neural underpinnings of compulsivity in AN and SUDs, which may inform novel treatment avenues for AN.

Nucleus accumbens AMPA receptor involvement in cocaine-conditioned place preference under different dietary conditions in rats

RATIONALE

When ad libitum-fed (AL) rats undergo cocaine place preference conditioning (CPP) but are switched to food restriction (FR) for testing, CPP is enhanced and preference scores correlate with phosphorylation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor GluA1 at Ser845 in nucleus accumbens (NAc) core.

OBJECTIVES

The present study tested whether a similar association exists in AL rats and whether an inhibitor of Ca(2+)-permeable AMPARs blocks CPP expression in either diet group.

MATERIALS AND METHODS

In experiments 1-3, AL rats were conditioned with cocaine (12.0 mg/kg, i.p.). Three weeks later, CPP was tested daily and brains were harvested after the fifth test. Western analyses were used to probe for levels of AMPA receptors in NAc. In experiment 4, AL rats were conditioned, half were switched to FR for testing, and half in each diet group received NAc core microinjection of 1-naphthylacetyl spermine (NASPM (NASPM) (25.0 μg) prior to each test.

RESULTS

In experiment 1, CPP expression in AL rats was associated with elevated pSer845-GluA1, GluA1, and GluA2 in NAc. In experiment 2, the correlation between pSer845-GluA1 and CPP was localized to NAc core. In experiment 3, pSer845-GluA1 following a CPP test was higher in NAc synaptic membranes of FR relative to AL rats. In experiment 4, NASPM blocked CPP expression in both diet groups.

CONCLUSIONS

Results support a scheme in which pSer845-GluA1 in NAc core underlies expression of cocaine CPP and does so by stabilizing or trafficking Ca(2+)-permeable AMPARs to the synaptic membrane. The more robust CPP of FR rats may result from upregulation of stimulus-induced pSer845-GluA1.

Hungry for reward: How can neuroscience inform the development of treatment for Anorexia Nervosa?

Dysfunctional reward from the pursuit of thinness presents a major challenge to recovery from Anorexia Nervosa (AN). We explore the neuroscientific basis of aberrant reward in AN, with the aim of generating novel hypotheses for translational investigation, and elucidate disease mechanisms to inform the development of targeted interventions. Relevant neuroimaging and behavioural studies are reviewed. These suggest that altered eating in AN may be a consequence of aberrant reward processing combined with exaggerated cognitive control. We consider evidence that such aberrant reward processing is reflected in the compulsive behaviours characterising AN, with substantial overlap in the neural circuits implicated in reward processing and compulsivity. Drawing on contemporary neuroscientific theories of substance dependence, processes underpinning the shift from the initially rewarding pursuit of thinness to extreme and compulsive weight control behaviours are discussed. It is suggested that in AN, weight loss behaviour begins as overtly rewarding, goal-directed and positively reinforced, but over time becomes habitual and increasingly negatively reinforced. Excessive habit formation is suggested as one underlying mechanism perpetuating compulsive behaviour. Ongoing research into the behavioural and neural basis of aberrant reward in AN is required to further elucidate mechanisms. We discuss clinical and transdiagnostic implications, and propose that future treatment innovation may benefit from the development of novel interventions targeting aberrant reward processing in AN.

Compulsivity in anorexia nervosa: a transdiagnostic concept

The compulsive nature of weight loss behaviors central to anorexia nervosa (AN), such as relentless self-starvation and over-exercise, has led to the suggestion of parallels between AN and other compulsive disorders such as obsessive-compulsive disorder (OCD) and addictions. There is a huge unmet need for effective treatments in AN, which has high rates of morbidity and the highest mortality rate of any psychiatric disorder, yet a grave paucity of effective treatments. Viewing compulsivity as a transdiagnostic concept, seen in various manifestations across disorders, may help delineate the mechanisms responsible for the persistence of AN, and aid treatment development. We explore models of compulsivity that suggest dysfunction in cortico-striatal circuitry underpins compulsive behavior, and consider evidence of aberrancies in this circuitry across disorders. Excessive habit formation is considered as a mechanism by which initially rewarding weight loss behavior in AN may become compulsive over time, and the complex balance between positive and negative reinforcement in this process is considered. The physiological effects of starvation in promoting compulsivity, positive reinforcement, and habit formation are also discussed. Further research in AN may benefit from a focus on processes potentially underlying the development of compulsivity, such as aberrant reward processing and habit formation. We discuss the implications of a transdiagnostic perspective on compulsivity, and how it may contribute to the development of novel treatments for AN.

Lamotrigine use in patients with binge eating and purging, significant affect dysregulation, and poor impulse control

OBJECTIVE

Some patients with symptoms of binge eating and purging are successfully treated with specific serotonin reuptake inhibitors (SSRIs), but others experience only partial or no benefit. Significant affect dysregulation and poor impulse control may be characteristics that limit responsiveness.

METHOD

We report on the treatment of five patients with bulimia nervosa (BN), anorexia nervosa-binge/purge type (AN-B/P) or eating disorder not otherwise specified (EDNOS), using the anticonvulsant lamotrigine after inadequate response to SSRIs.

RESULTS

Following addition of lamotrigine to an antidepressant in four cases, and switch from an antidepressant to lamotrigine in one case, patients experienced substantial improvement in mood reactivity and instability, impulsive drives and behaviors, and eating-disordered symptoms.

DISCUSSION

These findings raise the possibility that lamotrigine, either as monotherapy or as an augmenting agent to antidepressants, may be useful in patients who binge eat and purge, and have significant affect dysregulation with poor impulse control.

Lamotrigine in binge-eating disorder associated with bipolar II depression and treatment-resistant type 2 diabetes mellitus: a case report

BACKGROUND

Lamotrigine (LMG) is an anticonvulsant currently registered for the treatment of bipolar disorder (BP) depression. We report the case of a 61-year-old woman with comorbid binge-eating disorder (BED), BP depression, and treatment-resistant type 2 diabetes mellitus (T2DM), in which LMG showed significant efficacy against BED and BP depression and resulted in a drastic decrease in plasma glucose levels.

CASE REPORT

The patient had had untreated BP depression, BED, and T2DM for more than 30 years. We prescribed LMG at 25 mg/d for BP depression and titrated it up to 50 mg/d over 4 weeks, then maintained this dose for the next 16 weeks. At follow-up after the first 4-week period, she reported a significant decrease in compulsive eating impulses and depressive mood, and her positive reports were consistent in the following months. Hemoglobin A1c levels at National Glycohemoglobin Standardization Program decreased drastically from 9.6% to 7.1% over the 20 weeks after initiating treatment.

CONCLUSION

This case suggests that LMG might be beneficial for BED with concomitant BP depression, and potentially for treatment-resistant T2DM, if this refractoriness is identified to result from comorbidity of BED and BP.

Psychopharmacologic treatment of obesity and eating disorders in children and adolescents

This review discusses the evidence base for medications that are currently used for obesity and eating disorders, including their Food and Drug Administration approval status by disorder and age group, contraindications, and major adverse effects. Investigational agents currently being considered, issues related to psychiatric and medical comorbidity, limitations of pharmacologic strategies, and recommendations for treatment are also addressed.

Rationale and consequences of reclassifying obesity as an addictive disorder: neurobiology, food environment and social policy perspectives

The rapid increase in the prevalence of obesity is a priority for investigators from across numerous disciplines, including biology, nutritional science, and public health and policy. In this paper, we systematically examine the premise that common dietary obesity is an addictive disorder, based on the criteria for addiction described in the Diagnostic and Statistical Manual (DSM) of Mental Disorders of the American Psychiatric Association, version IV, and consider the consequences of such a reclassification of obesity for public policy. Specifically, we discuss evidence from both human and animal studies investigating the effects of various types and amounts of food and the food environment in obese individuals. Neurobiological studies have shown that the hedonic brain pathways activated by palatable food overlap considerably with those activated by drugs of abuse and suffer significant deficits after chronic exposure to high-energy diets. Furthermore, food as a stimulus can induce the sensitization, compulsion and relapse patterns observed in individuals who are addicted to illicit drugs. The current food environment encourages these addictive-like behaviors where increased exposure through advertisements, proximity and increased portion sizes are routine. Taking lessons from the tobacco experience, it is clear that reclassifying common dietary obesity as an addictive disorder would necessitate policy changes (e.g., regulatory efforts, economic strategies, and educational approaches). These policies could be instrumental in addressing the obesity epidemic, by encouraging the food industry and the political leadership to collaborate with the scientific and medical community in establishing new and more effective therapeutic approaches.

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.

Effects of GABAB receptor agonists and antagonists on glycemia regulation in mice

γ-Aminobutyric acid (GABA) inhibits insulin secretion through GABA(B) receptors in pancreatic β-cells. We investigated whether GABA(B) receptors participated in the regulation of glucose homeostasis in vivo. BALB/c mice acutely pre-injected with the GABA(B) receptor agonist baclofen (7.5mg/kg, i.p.) presented glucose intolerance and diminished insulin secretion during a glucose tolerance test (GTT, 2g/kg body weight, i.p.). The GABA(B) receptor antagonist 2-hydroxysaclofen (15 mg/kg, i.p.) improved the GTT and reversed the baclofen effect. Also a slight increase in insulin secretion was observed with 2-hydroxysaclofen. In incubated islets 1.10(-5)M baclofen inhibited 20mM glucose-induced insulin secretion and this effect was reversed by coincubation with 1.10(-5)M 2-hydroxysaclofen. In chronically-treated animals (18 days) both the receptor agonist (5mg/kg/day i.p.) and the receptor antagonist (10mg/kg/day i.p.) induced impaired GTTs; the receptor antagonist, but not the agonist, also induced a decrease in insulin secretion. No alterations in insulin tolerance tests, body weight and food intake were observed with the treatments. In addition glucagon, insulin-like growth factor I, prolactin, corticosterone and growth hormone, other hormones involved in glucose metabolism regulation, were not affected by chronic baclofen or 2-hydroxysaclofen. In islets obtained from chronically injected animals with baclofen, 2-hydroxysaclofen or saline (as above), GABA(B2) mRNA expression was not altered. Results demonstrate that GABA(B) receptors are involved in the regulation of glucose homeostasis in vivo. Treatment with receptor agonists or antagonists, given acutely or chronically, altered glucose homeostasis and insulin secretion alerting to the need to evaluate glucose metabolism during the clinical use of these drugs.