N-acetylcysteine decreases binge eating in a rodent model

Systematic Review of Binge Eating Rodent Models for Developing Novel or Repurposing Existing Pharmacotherapies

Recent advances in developing and screening candidate pharmacotherapies for psychiatric disorders have depended on rodent models. Eating disorders are a set of psychiatric disorders that have traditionally relied on behavioral therapies for effective long-term treatment. However, the clinical use of Lisdexamfatamine for binge eating disorder (BED) has furthered the notion of using pharmacotherapies for treating binge eating pathologies. While there are several binge eating rodent models, there is not a consensus on how to define pharmacological effectiveness within these models. Our purpose is to provide an overview of the potential pharmacotherapies or compounds tested in established rodent models of binge eating behavior. These findings will help provide guidance for determining pharmacological effectiveness for potential novel or repurposed pharmacotherapies.

The Potential of N-acetyl Cysteine in Behavioral Addictions and Related Compulsive and Impulsive Behaviors and Disorders: a Scoping Review

Purpose of Review

Behavioral addictions (also termed disorders due to addictive behaviors) contain impulsive and compulsive features and have been shown to involve glutamate dysregulation. N-acetylcysteine (NAC), a well-tolerated cysteine pro-drug and antioxidant, may reduce addictive behaviors by restoring glutamate homeostasis. The current review details and discusses the use of NAC in behavioral addictions and related impulsive and compulsive behaviors, including gambling disorder, problematic use of the internet, problematic video gaming, compulsive sexual behavior, problematic shopping/buying, problematic stealing, repetitive self-injurious behavior, and binge eating disorder.

Recent Findings

Preliminary results have indicated the usefulness of NAC in gambling disorder, self-injurious behaviors, and compulsive sexual behaviors. Preclinical studies indicate that NAC is effective in improving binge eating behavior, but clinical trials are limited to a small open-label trial and case report. Studies are lacking on the efficacy of NAC in problematic use of the internet, problematic video gaming, problematic stealing, and problematic shopping/buying.

Summary

NAC demonstrates potential for use in behavioral addictions and compulsive behaviors, particularly in gambling disorder and self-injury. However, more studies are needed to assess the effectiveness of NAC in other behavioral addictions and the mechanisms by which NAC improves these conditions.

Cardiac and respiratory muscle responses to dietary N-acetylcysteine in rats consuming a high-saturated fat, high-sucrose diet

NEW FINDINGS

What is the central question of this study? This study addresses whether a high-fat, high-sucrose diet causes cardiac and diaphragm muscle abnormalities in male rats and whether supplementation with the antioxidant N-acetylcysteine reverses diet-induced dysfunction. What is the main finding and its importance? N-Acetylcysteine attenuated the effects of high-fat, high-sucrose diet on markers of cardiac hypertrophy and diastolic dysfunction, but neither high-fat, high-sucrose diet nor N-acetylcysteine affected the diaphragm. These results support the use of N-acetylcysteine to attenuate cardiovascular dysfunction induced by a 'Western' diet.

ABSTRACT

Individuals with overweight or obesity display respiratory and cardiovascular dysfunction, and oxidative stress is a causative factor in the general aetiology of obesity and of skeletal and cardiac muscle pathology. Thus, this preclinical study aimed to define diaphragmatic and cardiac morphological and functional alterations in response to an obesogenic diet in rats and the therapeutic potential of an antioxidant supplement, N-acetylcysteine (NAC). Young male Wistar rats consumed ad libitum a 'lean' or high-saturated fat, high-sucrose (HFHS) diet for ∼22 weeks and were randomized to control or NAC (2 mg/ml in the drinking water) for the last 8 weeks of the dietary intervention. We then evaluated diaphragmatic and cardiac morphology and function. Neither HFHS diet nor NAC supplementation affected diaphragm-specific force, peak power or morphology. Right ventricular weight normalized to estimated body surface area, left ventricular fractional shortening and posterior wall maximal shortening velocity were higher in HFHS compared with lean control animals and not restored by NAC. In HFHS rats, the elevated deceleration rate of early transmitral diastolic velocity was prevented by NAC. Our data showed that the HFHS diet did not compromise diaphragmatic muscle morphology or in vitro function, suggesting other possible contributors to breathing abnormalities in obesity (e.g., abnormalities of neuromuscular transmission). However, the HFHS diet resulted in cardiac functional and morphological changes suggestive of hypercontractility and diastolic dysfunction. Supplementation with NAC did not affect diaphragm morphology or function but attenuated some of the cardiac abnormalities in the rats receiving the HFHS diet.

Prefrontal Cortical Control of Activity in Nucleus Accumbens Core Is Weakened by High-Fat Diet and Prevented by Co-Treatment with N-Acetylcysteine: Implications for the Development of Obesity

A loss of neuroplastic control on nucleus accumbens (NAc) neuronal activity exerted by the medial prefrontal cortex (mPFC) through long-term depression (LTD) is involved in triggering drug-seeking behavior and relapse on several substances of abuse due to impaired glutamate homeostasis in tripartite synapses of the nucleus accumbens (NAc) core. To test whether this maladaptive neuroplastic mechanism underlies the addiction-like behavior induced in young mice by a high-fat diet (HFD), we utilized 28-days-old male mice fed HFD ad-libitum over 2 weeks, followed by 5 days of HFD abstinence. Control groups were fed a regular diet. HFD fed mice showed increased ΔFosB levels in the NAc core region, whereas LTD triggered from the mPFC became suppressed. Interestingly, LTD suppression was prevented by an i.p. injection of 100 mg/kg N-acetylcysteine 2.5 h before inducing LTD from the mPFC. In addition, excessive weight gain due to HFD feeding was diminished by adding 2mg/mL N-acetylcysteine in drinking water. Those results show a loss of neuroplastic mPFC control over NAc core activity induced by HFD consumption in young subjects. In conclusion, ad libitum consumption of HFD can lead to neuroplastic changes an addiction-like behavior that can be prevented by N-acetylcysteine, helping to decrease the rate of excessive weight gain.

Compulsive-like eating of high-fat high-sugar food is associated with 'addiction-like' glutamatergic dysfunction in obesity prone rats

Chronic overeating is a core feature of diet-induced obesity. There is increasing evidence that in vulnerable individuals, such overeating could become compulsive, resembling an addictive disorder. The transition to compulsive substance use has been linked with changes at glutamatergic synapses in the nucleus accumbens. In this study, we investigated a potential link between such glutamatergic dysregulation and compulsive-like eating using a rat model of diet-induced obesity. A conditioned suppression task demonstrated that diet-induced obese rats display eating despite negative consequences, as their consumption was insensitive to an aversive cue. Moreover, nucleus accumbens expression of GluA1 and xCT proteins was upregulated in diet-induced obese animals. Lastly, both a computed 'addiction score' (based on performance across three criteria) and weight gain were positively correlated with changes in GluA1 and xCT expression in the nucleus accumbens. These data demonstrate that the propensity for diet-induced obesity is associated with compulsive-like eating of highly palatable food and is accompanied by 'addiction-like' glutamatergic dysregulation in the nucleus accumbens, thus providing neurobiological evidence of addiction-like pathology in this model of obesity.

Obesity-induced astrocyte dysfunction impairs heterosynaptic plasticity in the orbitofrontal cortex

Overconsumption of highly palatable, energy-dense food is considered a key driver of the obesity pandemic. The orbitofrontal cortex (OFC) is critical for reward valuation of gustatory signals, yet how the OFC adapts to obesogenic diets is poorly understood. Here, we show that extended access to a cafeteria diet impairs astrocyte glutamate clearance, which leads to a heterosynaptic depression of GABA transmission onto pyramidal neurons of the OFC. This decrease in GABA tone is due to an increase in extrasynaptic glutamate, which acts via metabotropic glutamate receptors to liberate endocannabinoids. This impairs the induction of endocannabinoid-mediated long-term plasticity. The nutritional supplement, N-acetylcysteine rescues this cascade of synaptic impairments by restoring astrocytic glutamate transport. Together, our findings indicate that obesity targets astrocytes to disrupt the delicate balance between excitatory and inhibitory transmission in the OFC.

N-acetylcysteine reduces addiction-like behaviour towards high-fat high-sugar food in diet-induced obese rats

Compulsive forms of eating displayed by some obese individuals share similarities with compulsive drug-taking behaviour, a hallmark feature of substance use disorder. This raises the possibility that drug addiction treatments may show utility in the treatment of compulsive overeating. N-Acetylcysteine (NAC) is a cysteine pro-drug which has experienced some success in clinical trials, reducing cocaine, marijuana and cigarette use, as well as compulsive behaviours such as gambling and trichotillomania. We assessed the impact of NAC on addiction-like behaviour towards highly palatable food in a rat model of diet-induced obesity. Adult male Sprague-Dawley rats were placed on a high-fat high-sugar diet for 8 weeks and then assigned to diet-induced obesity-prone (DIO) or diet-induced obesity-resistant (DR) groups based on weight gain. DIO and DR rats were subjected to an operant conditioning paradigm whereby rats could lever press for high-fat high-sugar food pellets. This alternated with periods of signalled reward unavailability. Before treatment DIO rats ate more in their home cage, earned more food pellets in operant sessions, and responded more during periods that signalled reward unavailability (suggestive of compulsive-like food seeking) compared with DR rats. This persistent responding in the absence of reward displayed by DIO rats was ameliorated by daily injections of NAC (100 mg/kg, i.p.) for 14 days. By the end of the treatment period, lever-pressing by NAC-treated DIO rats resembled that of DR rats. These findings suggest that NAC reduces addiction-like behaviour towards food in rats and supports the potential use of this compound in compulsive overeating.

A combination of an antioxidant with a prebiotic exerts greater efficacy than either as a monotherapy on cognitive improvement in castrated-obese male rats

Previous studies by ourselves and others have demonstrated that both obesity and testosterone deprivation have been related to cognitive decline. We have also shown that a prebiotic and n-acetyl cysteine (NAC) improved cognitive dysfunction in obese rats and castrated-male rats. However, the effects of NAC, a prebiotic (inulin), and a combination of the two on cognition in castrated-obese rats has never been investigated. The hypothesis was that NAC and inulin attenuated cognitive decline in castrated-obese rats by improving gut dysbiosis, and decreasing oxidative stress, glial activation and apoptosis. Male Wistar rats (n = 36) were fed with either a normal diet (ND: n = 6) or a high-fat diet (HFD: n = 30) for twenty-eight weeks. The resultant obese rats had a bilateral orchiectomy (ORX) and were randomly divided into five subgroups (n = 6/ subgroup). Each subgroup was treated with one of five therapies: a vehicle; testosterone replacement (2 mg/kg/day); NAC (100 mg/kg); inulin (10%, w/w), or a combination of the NAC and inulin for four weeks. The results demonstrated that castrated-obese rats developed gut dysbiosis, metabolic disturbance, brain pathologies, and cognitive decline. All of the pathological conditions in the brain were ameliorated to an equal extent by testosterone replacement, NAC, and inulin supplementation. Interestingly, a combination of NAC and inulin had the greatest beneficial effect on cognitive function by synergistically reducing hippocampal inflammation and ameliorating glial dysmorphology. These findings suggest that a combination of NAC and inulin may confer the greatest benefits in improving cognitive function in castrated-obese male rats.

Acute Blockade of PACAP-Dependent Activity in the Ventromedial Nucleus of the Hypothalamus Disrupts Leptin-Induced Behavioral and Molecular Changes in Rats

Leptin signaling pathways, stemming primarily from the hypothalamus, are necessary for maintaining normal energy homeostasis and body weight. In both rodents and humans, dysregulation of leptin signaling leads to morbid obesity and diabetes. Since leptin resistance is considered a primary factor underlying obesity, understanding the regulation of leptin signaling could lead to therapeutic tools and provide insights into the causality of obesity. While leptin actions in some hypothalamic regions such as the arcuate nuclei have been characterized, less is known about leptin activity in the hypothalamic ventromedial nuclei (VMN). Recently, pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to reduce feeding behavior and alter metabolism when administered into the VMN in a pattern similar to that of leptin. In the current study, we examined whether leptin and PACAP actions in the VMN share overlapping pathways in the regulation of energy balance. Interestingly, PACAP administration into the VMN increased STAT3 phosphorylation and SOCS3 mRNA expression, both of which are hallmarks of leptin receptor activation. In addition, BDNF mRNA expression in the VMN was increased by both leptin and PACAP administration. Moreover, antagonizing PACAP receptors fully reversed the behavioral and cellular effects of leptin injections into the VMN. Electrophysiological studies further illustrated that leptin-induced effects on VMN neurons were blocked by antagonizing PACAP receptors. We conclude that leptin dependency on PACAP signaling in the VMN suggests a potential common signaling cascade, allowing a tonically and systemically secreted neuropeptide to be more precisely regulated by central neuropeptides.

Increased Fear Memory and Glutamatergic Modulation in Compulsive Drinker Rats Selected by Schedule-Induced Polydipsia

Compulsive behavior is observed in several neuropsychiatric disorders such as obsessive-compulsive disorder (OCD), anxiety, depression, phobia, and schizophrenia. Thus, compulsivity has been proposed as a transdiagnostic symptom with a highly variable pharmacological treatment. Recent evidence shows that glutamate pharmacotherapy may be of benefit in impaired inhibitory control. The purpose of the present study was: first, to test the comorbidity between compulsivity and other neuropsychiatric symptoms on different preclinical behavioral models; second, to assess the therapeutic potential of different glutamate modulators in a preclinical model of compulsivity. Long Evans rats were selected as either high (HD) or low (LD) drinkers corresponding with their water intake in schedule-induced polydipsia (SIP). We assessed compulsivity in LD and HD rats by marble burying test (MBT), depression by forced swimming test (FST), anxiety by elevated plus maze (EPM) and fear behavior by fear conditioning (FC) test. After that, we measured the effects of acute administration (i.p.) of glutamatergic drugs: N-Acetylcysteine (NAC; 25, 50, 100 and 200 mg/kg), memantine (3.1 and 6.2 mg/kg) and lamotrigine (15 and 30 mg/kg) on compulsive drinking on SIP. The results obtained showed a relation between high compulsive drinking on SIP and a higher number of marbles partially buried in MBT, as well as a higher percentage of freezing on the retrieval day of FC test. We did not detect any significant differences between LD and HD rats in FST, nor in EPM. The psychopharmacological study of glutamatergic drugs revealed that memantine and lamotrigine, at all doses tested, decreased compulsive water consumption in HD rats compared to LD rats on SIP. NAC did not produce any significant effect on SIP. These results indicate that the symptom clusters of different forms of compulsivity and phobia might be found in the compulsive phenotype of HD rats selected by SIP. The effects of memantine and lamotrigine in HD rats point towards a dysregulation in the glutamatergic signaling as a possible underlying mechanism in the vulnerability to compulsive behavior on SIP. Further studies on SIP, could help to elucidate the therapeutic role of glutamatergic drugs as a pharmacological strategy on compulsive spectrum disorders.

N-acetylcysteine Treatment Reduces Age-related Hearing Loss and Memory Impairment in the Senescence-Accelerated Prone 8 (SAMP8) Mouse Model

Age-related hearing loss (ARHL) is the most common sensory disorder in the elderly population. SAMP8 mouse model presents accelerated senescence and has been identified as a model of gerontological research. SAMP8 displays a progressive age-related decline in brain function associated with a progressive hearing loss mimicking human aging memory deficits and ARHL. The molecular mechanisms associated with SAMP8 senescence process involve oxidative stress leading to chronic inflammation and apoptosis. Here, we studied the effect of N-acetylcysteine (NAC), an antioxidant, on SAMP8 hearing loss and memory to determine the potential interest of this model in the study of new antioxidant therapies. We observed a strong decrease of auditory brainstem response thresholds from 45 to 75 days of age and an increase of distortion product amplitudes from 60 to 75 days in NAC treated group compared to vehicle. Moreover, NAC treated group presented also an increase of memory performance at 60 and 105 days of age. These results confirm that NAC delays the senescence process by slowing the age-related hearing loss, protecting the cochlear hair cells and improving memory, suggesting that antioxidants could be a pharmacological target for age-related hearing and memory loss.

A narrative review of potential treatment strategies for food addiction

The concept of food addiction (FA) remains controversial with research being in the nascent stages; FA like any addiction can have a devastating impact on the lives of those afflicted. There exists a clinical need for treatment strategies for those affected. This article reviews potential treatment strategies for FA. The treatment strategies target four core behaviours of the addiction phenotype specifically craving through the opioid system, impulsivity as a personality trait, compulsivity through the serotonergic system and lastly motivation through the dopaminergic system. A range of pharmacological and psychological interventions are reviewed. Future research should seek to test and validate the proposed clinical treatment strategies.