Preclinical and clinical evidence for a distinct regulation of mu opioid and type 1 cannabinoid receptor genes expression in obesity

Among endogenous signaling networks involved in both rewarding and homeostatic mechanisms of obesity, a relevant role is played by the endocannabinoid (ECS) and the opioid (EOS) systems. We here studied the transcriptional regulation of ECS and EOS genes in the hypothalamus of Diet-induced obesity rats, a preclinical model of obesity, as well as in humans with obesity and healthy controls. A significant and selective increase in type 1 cannabinoid receptor gene (Cnr1) expression was observed at the beginning of obesity development (5 weeks on high fat diet) as well as after 21 weeks of high diet exposure. After 5 weeks on high fat diet, selective up-regulation of mu opioid receptor gene (Oprm1) expression was also observed. Consistently, epigenetic studies showed a selective and significant decrease in DNA methylation at specific CpG sites at both gene promoters in overweight rats, but only after 5 weeks on high fat diet. Moreover, significantly lower levels of DNA methylation were observed at selected CpG sites of both receptor gene promoters, analyzed in peripheral blood mononuclear cells from younger (<30 years old) humans with obesity, as well as in those with shorter time length from disease onset. Taken together, we here provide evidence of selective, synergistic and time-dependent transcriptional regulation of CNR1 and OPRM1 genes in overweight rats, as well as in human subjects. These alterations in genes regulation could contribute to the development of the obese phenotype, and we thus suggest CNR1 and OPRM1 epigenetic modulation as possible biomarkers of obesity development. Due to the reversible nature of the epigenetic hallmark, our data might also open new avenue to early environmental strategies of intervention

Modulation of pain sensitivity by chronic consumption of highly palatable food followed by abstinence: emerging role of fatty acid amide hydrolase

There is a strong relationship between palatable diet and pain sensitivity, and the cannabinoid and opioid systems might play an important role in this correlation. The palatable diet used in many animal models of obesity is the cafeteria (CAF) diet, based on human food with high sugar, salt, and fat content. In this study, we investigated whether long-term exposure to a CAF diet could modify pain sensitivity and explored the role of the cannabinergic system in this modification. Male Sprague–Dawley rats were divided into two groups: one fed with standard chow only (CO) and the other with extended access (EA) to a CAF diet. Hot plate and tail flick tests were used to evaluate pain sensitivity. At the end of a 40-day CAF exposure, EA rats showed a significant increase in the pain threshold compared to CO rats, finding probably due to up-regulation of CB1 and mu-opioid receptors. Instead, during abstinence from palatable foods, EA animals showed a significant increase in pain sensibility, which was ameliorated by repeated treatment with a fatty acid amide hydrolase inhibitor, PF-3845 (10 mg/kg, intraperitoneally), every other day for 28 days. Ex vivo analysis of the brains of these rats clearly showed that this effect was mediated by mu-opioid receptors, which were up-regulated following repeated treatment of PF-3845. Our data add to the knowledge about changes in pain perception in obese subjects, revealing a key role of CB1 and mu-opioid receptors and their possible pharmacological crosstalk and reinforcing the need to consider this modulation in planning effective pain management for obese patients

EXTRA-HYPOTHALAMIC CRF-1 RECEPTOR MECHANISMS IN A MODEL OF BINGE-LIKE PALATABLE FOOD CONSUMPTION IN FEMALE RATS

Purpose: The present study evaluated the effect of the corticotrophin releasing factor (CRF)1 receptor antagonist R121919 and the corticosterone synthesis inhibitor metyrapone in female rats, in which binge eating for highly palatable food was evoked by frustration stress and cycles of food restrictions. Methods: We used 4 groups of rats that were first exposed or not exposed to repeated intermittent cycles of regular chow food restriction during which they were also given intermittent access to high-caloric palatable food. On the test day, we either exposed or did not expose the rats to the sight of the palatable food for 15 min, without allowing access to it (frustration stress) before assessing food consumption for 2 h. Results: We found that systemic injections of the CRF1 receptor antagonist R121919 but not of the metyrapone blocked binge-like eating behavior. Moreover, corticosterone injection did not induce binge eating in non-stressed rats. Restricted and stressed rats showed up regulation of CRH1 receptor mRNA signal in dorsal BNST and in CeA but not in PVN. Injection of CRF receptor antagonist D-Phe-CRF(12– 41) in CeA blocked binge-like eating behavior. Conclusions: These findings demonstrate that extra-hypothalamic CRF1 receptors, rather than those involved in endocrine functions, are involved in binge eating. Selective antagonism at CRF1 receptor may represent a novel pharmacological treatment for bingeing-related eating disorders

Regulation of adenosine A2A receptor gene expression in a model of binge eating in the amygdaloid complex of female rats

Background: Pharmacological treatment approaches for eating disorders, such as binge eating disorder and bulimia nervosa, are currently limited. Methods and aims: Using a well-characterized animal model of binge eating, we investigated the epigenetic regulation of the A2A Adenosine Receptor (A2AAR) and dopaminergic D2 receptor (D2R) genes. Results: Gene expression analysis revealed a selective increase of both receptor mRNAs in the amygdaloid complex of stressed and restricted rats, which exhibited binge-like eating, when compared to non-stressed and non-restricted rats. Consistently, pyrosequencing analysis revealed a significant reduction of the percentage of DNA methylation but only at the A2AAR promoter region in rats showing binge-like behaviour compared to the control animals. Focusing thus on A2AAR agonist (VT 7) administration (which inhibited the episode of binge systemically at 0.1 mg/kg or intra-central amygdala (CeA) injection at 900 ng/side) induced a significant increase of A2AAR mRNA levels in restricted and stressed rats when compared to the control group. In addition, we observed a significant decrease in A2AAR mRNA levels in rats treated with the A2AAR antagonist (ANR 94) at 1 mg/kg. Consistent changes in the DNA methylation status of the A2AAR promoter were found in restricted and stressed rats after administration of VT 7 or ANR 94. Conclusion: We confirm the role of A2AAR in binge eating behaviours, and we underline the importance of epigenetic regulation of the A2AAR gene, possibly due to a compensatory mechanism to counteract the effect of binge eating. We suggest that A2AAR activation, inducing receptor gene up-regulation, could be relevant to reduction of food consumption