Fluvoxamine exerts anorexic effect in 5-HT2C receptor mutant mice with heterozygous mutation of beta-endorphin gene

Association of serotonin receptor gene polymorphisms with anorexia nervosa: a systematic review and meta-analysis

PURPOSE

Several studies have investigated the association between anorexia nervosa and polymorphisms of genes regulating serotonin neurotransmission, with a focus on the rs6311 polymorphism of 5-HTR2A. However, inconsistent results of these studies and conflicting conclusions of existing meta-analyses complicate the understanding of a possible association. We have updated these results and evaluated the involvement of other serotonin receptor gene polymorphisms in anorexia nervosa.

METHODS

Adhering to PRISMA guidelines, we have searched studies on anorexia nervosa and serotonin-regulating genes published from 1997 to 2022, selected those concerning receptor genes and meta-analyzed the results from twenty candidate gene studies on the 5-HTR2A rs6311 polymorphism and the 5-HTR2C rs6318 polymorphism.

RESULTS

Present analyses reveal an association for the 5-HTR2A rs6311 polymorphism, with G and A alleles, across eighteen studies (2049 patients, 2877 controls; A vs. G allele, Odds Ratio = 1.24; 95% Confidence Interval = 1.06-1.47; p = 0.009). However, after geographic subgrouping, an association emerged only in a Southern European area, involving five studies (722 patients, 773 controls; A vs. G allele, Odds Ratio = 1.82; 95% Confidence Interval = 1.41-2.37; p < 0.00001). No association was observed for the 5-HTR2C rs6318 polymorphism across three studies.

CONCLUSIONS

To date, the involvement in the pathophysiology of anorexia nervosa of the 5-HTR2A rs6311 polymorphism appears limited to a specific genetic and/or environmental context, while that of the 5-HTR2C rs6318 polymorphism seems excluded. Genome-wide association studies and epigenetic studies will likely offer deeper insights of genetic and environmental factors possibly contributing to the disorder.

LEVEL OF EVIDENCE

III Evidence obtained from well-designed cohort or case-control analytic studies. Clinical trial registration PROSPERO registration number: CRD42021246122.

The Regulatory Role of the Central and Peripheral Serotonin Network on Feeding Signals in Metabolic Diseases

Central and peripheral serotonin (5-hydroxytryptamine, 5-HT) regulate feeding signals for energy metabolism. Disruption of central 5-HT signaling via 5-HT2C receptors (5-HT2CRs) induces leptin-independent hyperphagia in mice, leading to late-onset obesity, insulin resistance, and impaired glucose tolerance. 5-HT2CR mutant mice are more responsive than wild-type mice to a high-fat diet, exhibiting earlier-onset obesity and type 2 diabetes. High-fat and high-carbohydrate diets increase plasma 5-HT and fibroblast growth factor-21 (FGF21) levels. Plasma 5-HT and FGF21 levels are increased in rodents and humans with obesity, type 2 diabetes, and non-alcohol fatty liver diseases (NAFLD). The increases in plasma FGF21 and hepatic FGF21 expression precede hyperinsulinemia, insulin resistance, hyperglycemia, and weight gain in mice fed a high-fat diet. Nutritional, pharmacologic, or genetic inhibition of peripheral 5-HT synthesis via tryptophan hydroxylase 1 (Tph1) decreases hepatic FGF21 expression and plasma FGF21 levels in mice. Thus, perturbing central 5-HT signaling via 5-HT2CRs alters feeding behavior. Increased energy intake via a high-fat diet and/or high-carbohydrate diet can upregulate gut-derived 5-HT synthesis via Tph1. Peripheral 5-HT upregulates hepatic FGF21 expression and plasma FGF21 levels, leading to metabolic diseases such as obesity, insulin resistance, type 2 diabetes, and NAFLD. The 5-HT network in the brain–gut–liver axis regulates feeding signals and may be involved in the development and/or prevention of metabolic diseases.

Effects of adjunctive fluvoxamine on metabolic parameters and psychopathology in clozapine-treated patients with schizophrenia: A 12-week, randomized, double-blind, placebo-controlled study

OBJECTIVE

Numerous studies have demonstrated that fluvoxamine has considerable pharmacokinetic and pharmacodynamic interactions with clozapine. We conducted a 12-week, randomized, double-blind, placebo-controlled study to evaluate the effects of fluvoxamine on metabolic parameters and psychopathology in clozapine-treated patients with schizophrenia.

METHODS

We recruited 85 patients who received a DSM-IV diagnosis of schizophrenia. Eligible patients were randomized to receive fluvoxamine 50mg/day plus clozapine 100mg/day or clozapine 300mg/day. We studied metabolic parameters, psychopathology, and drug levels at baseline and 4, 8, and 12weeks after the intervention. Plasma levels of clozapine, norclozapine, clozapine N-oxide, and fluvoxamine were determined using high-performance liquid chromatography with ultraviolet detection.

RESULTS

No significant difference was observed in baseline characteristics between the two groups. Clozapine-fluvoxamine combined treatment significantly attenuated the increments in body weight, insulin resistance, and levels of insulin, glucose, and triglycerides compared with clozapine monotherapy. Both groups exhibited significant improvements in their Positive and Negative Syndrome Scale (PANSS) total and negative scores. The combined treatment group showed significant reduction in the PANSS general psychopathology scores compared with the monotherapy group. No difference was observed in the plasma clozapine level between the two groups. The monotherapy group showed higher levels of norclozapine and clozapine N-oxide than the combined group.

CONCLUSIONS

Compared with clozapine monotherapy, treatment with adjunctive fluvoxamine with clozapine for 12weeks can alleviate body weight gain and metabolic abnormalities in patients with schizophrenia, without sacrificing the clinical effect. Clinicians should interpret these findings cautiously considering the short duration of this study. The study was registered at www.clinicaltrials.gov (NCT01401491).

Appetite-Enhancing Effects: The Influence of Concentrations of Benzylacetone and trans-Cinnamaldehyde and Their Inhalation Time, as Well as the Effect of Aroma, on Body Weight in Mice

Benzylacetone has appetite-enhancing and locomotor-reducing effects. The effective doses for these two outcomes overlap, and the weight gain of mice exposed to benzylacetone is caused by both appetite-enhancement and a reduction in locomotor activity. The appetite-enhancing effects of trans-cinnamaldehyde and benzylacetone have been reported previously. In this study, these appetite-enhancing effects were seen in mice after short-term, high-dose exposure.

The acute anorexic effect of liraglutide, a GLP-1 receptor agonist, does not require functional leptin receptor, serotonin, and hypothalamic POMC and CART activities in mice

The acute anorexic effect of liraglutide, a GLP-1 receptor agonist, did not require functional leptin receptor, serotonin, and hypothalamic proopiomelanocortin and cocaine amphetamine regulated transcript activities in mice, although decrease in functional hypothalamic orexin activity might be involved in the acute anorexic effect of liraglutide.

Endogenous opioids and feeding behavior: A decade of further progress (2004-2014). A Festschrift to Dr. Abba Kastin

Functional elucidation of the endogenous opioid system temporally paralleled the creation and growth of the journal, Peptides, under the leadership of its founding editor, Dr. Abba Kastin. He was prescient in publishing annual and uninterrupted reviews on Endogenous Opiates and Behavior that served as a microcosm for the journal under his stewardship. This author published a 2004 review, "Endogenous opioids and feeding behavior: a thirty-year historical perspective", summarizing research in this field between 1974 and 2003. The present review "closes the circle" by reviewing the last 10 years (2004-2014) of research examining the role of endogenous opioids and feeding behavior. The review summarizes effects upon ingestive behavior following administration of opioid receptor agonists, in opioid receptor knockout animals, following administration of general opioid receptor antagonists, following administration of selective mu, delta, kappa and ORL-1 receptor antagonists, and evaluating opioid peptide and opioid receptor changes in different food intake models.

Long-term consequences of chronic fluoxetine exposure on the expression of myelination-related genes in the rat hippocampus

The selective serotonin reuptake inhibitor (SSRI) fluoxetine is widely prescribed for the treatment of symptoms related to a variety of psychiatric disorders. After chronic SSRI treatment, some symptoms remediate on the long term, but the underlying mechanisms are not yet well understood. Here we studied the long-term consequences (40 days after treatment) of chronic fluoxetine exposure on genome-wide gene expression. During the treatment period, we measured body weight; and 1 week after treatment, cessation behavior in an SSRI-sensitive anxiety test was assessed. Gene expression was assessed in hippocampal tissue of adult rats using transcriptome analysis and several differentially expressed genes were validated in independent samples. Gene ontology analysis showed that upregulated genes induced by chronic fluoxetine exposure were significantly enriched for genes involved in myelination. We also investigated the expression of myelination-related genes in adult rats exposed to fluoxetine at early life and found two myelination-related genes (Transferrin (Tf) and Ciliary neurotrophic factor (Cntf)) that were downregulated by chronic fluoxetine exposure. Cntf, a neurotrophic factor involved in myelination, showed regulation in opposite direction in the adult versus neonatally fluoxetine-exposed groups. Expression of myelination-related genes correlated negatively with anxiety-like behavior in both adult and neonatally fluoxetine-exposed rats. In conclusion, our data reveal that chronic fluoxetine exposure causes on the long-term changes in expression of genes involved in myelination, a process that shapes brain connectivity and contributes to symptoms of psychiatric disorders.

Pharmacological stimulation of serotonin 5-HT1B receptors enhances increases in plasma active glucagon-like peptide-1 levels induced by dipeptidyl peptidase-4 inhibition independently of feeding in mice

AIM

Glucagon-like peptide-1 (GLP-1), an incretin hormone, is released from intestinal L cells in response to nutrient ingestion. Dipeptidyl peptidase-4 (DPP-4) rapidly degrades the active form of GLP-1 to an inactive form in the bloodstream. The present study aimed to investigate the role of serotonin (5-HT)1B receptors in the regulation of plasma active GLP-1 levels and glucose tolerance under DPP-4 inhibition.

METHODS

C57BL6J mice treated with or without alogliptin, a highly selective DPP-4 inhibitor, for 4 days were intraperitoneally injected with either saline, the 5-HT1B/2C receptor agonist meta-chlorophenylpiperazine (mCPP) at 2.5mg/kg and 5mg/kg or the selective 5-HT1B receptor agonist CP94253 at 2.5mg/kg and 5mg/kg, and food-deprived after treatment. An hour later, plasma active GLP-1 levels were determined. Also, a glucose tolerance test was done by injecting D-glucose (2g/kg) following the injection of saline or CP94253 (5mg/kg) in mice treated with alogliptin.

RESULTS

Intraperitoneal injection of mCPP (2.5 and 5mg/kg) or CP94253 (2.5 and 5mg/kg) in mice treated with alogliptin for 4 days significantly increased plasma active GLP-1 levels compared with saline controls in mice that were food-deprived after the injections. While intraperitoneal injection of either mCPP or CP94253 alone had no significant effect on plasma active GLP-1 levels, the injection of CP94253 improved glucose tolerance in mice treated with alogliptin compared with saline.

CONCLUSION

These findings suggest that pharmacological stimulation of 5-HT1B receptors enhances the increases in plasma active GLP-1 induced by DPP-4 inhibition independently of feeding and also improves glucose tolerance in mice.

The genetics of selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are among the most widely prescribed drugs in psychiatry. Based on the fact that SSRIs increase extracellular monoamine levels in the brain, the monoamine hypothesis of depression was introduced, postulating that depression is associated with too low serotonin, dopamine and noradrenaline levels. However, several lines of evidence indicate that this hypothesis is too simplistic and that depression and the efficacy of SSRIs are dependent on neuroplastic changes mediated by changes in gene expression. Because a coherent view on global gene expression is lacking, we aim to provide an overview of the effects of SSRI treatment on the final targets of 5-HT receptor signal transduction pathways, namely the transcriptional regulation of genes. We address gene polymorphisms in humans that affect SSRI efficacy, as well as in vitro studies employing human-derived cells. We also discuss the molecular targets affected by SSRIs in animal models, both in vivo and in vitro. We conclude that serotonin transporter gene variation in humans affects the efficacy and side-effects of SSRIs, whereas SSRIs generally do not affect serotonin transporter gene expression in animals. Instead, SSRIs alter mRNA levels of genes encoding serotonin receptors, components of non-serotonergic neurotransmitter systems, neurotrophic factors, hypothalamic hormones and inflammatory factors. So far little is known about the epigenetic and age-dependent molecular effects of SSRIs, which might give more insights in the working mechanism(s) of SSRIs.

Serotonin conflict in sleep-feeding

Short sleep duration has been suggested to be a risk factor for weight gain and adiposity. Serotonin (5-HT) substantially contributes to the regulation of sleep and feeding behavior. Although 5-HT predominately promotes waking and satiety, the effects of 5-HT depend on 5-HT receptor function. The 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2C, 5-HT6, and 5-HT7 receptors reportedly contribute to sleep-waking regulation, whereas the 5-HT1B and 5-HT2C receptors contribute to the regulation of satiety. The 5-HT1B and 2C receptors may therefore be involved in the regulation of sleep-feeding. In genetic studies, 5-HT1B receptor mutant mice display greater amounts of rapid eye movement sleep (REMS) than wild-type mice, while displaying no effects on waking or slow wave sleep (SWS). On the other hand, 5-HT2C receptor mutant mice exhibit increased wakefulness and decreased SWS, without any effect on REMS. Moreover, the 5-HT2C receptor mutants display leptin-independent hyperphagia, leading to a middle-aged onset of obesity, whereas 5-HT1B receptor mutants do not display any effect on food intake. Thus, the genetic deletion of 5-HT2C receptors results in sleep loss-associated hyperphagia, leading to the late onset of obesity. This is a quite different pattern of sleep-feeding behavior than is observed in disturbed leptin signaling, which displays an increase in sleep-associated hyperphagia. In pharmacologic studies, 5-HT1B and 5-HT2C receptors upregulate wakefulness and downregulate SWS, REMS, and food intake. These findings suggest that 5-HT1B/2C receptor stimulation induces sleep loss-associated anorexia. Thus, the central 5-HT regulation of sleep-feeding can be dissociated. Functional hypothalamic proopiomelanocortin and orexin activities may contribute to the dissociated 5-HT regulation.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Hypothalamic orexin and pro-opiomelanocortin activities are essential for the anorexic effects of m-chlorophenylpiperazine in mice

Hypothalamic pro-opiomelanocortin (POMC) activity is reportedly essential for satiety signalling downstream of serotonin (5-HT). Here we show that food-restricted wild-type mice, which exhibited decreased hypothalamic POMC expression and increased hypothalamic orexin expression, were responsive to m-chlorophenylpiperazine (m-CPP), a 5-HT(2C/1B) receptor agonist, leading to anorexia, whereas food-restricted A(y) mice with decreased hypothalamic POMC and orexin expression, were not. Injection of POMC small interfering RNA (siRNA) oligonucleotide+orexin siRNA oligonucleotide into the third cerebral ventricle was unresponsive to mCPP-induced anorexia, whereas a single injection of POMC or orexin siRNA oligonucleotides elicited a response. The injection of POMC siRNA oligonucleotides suppressed the anorexic effects of sibutramine, a serotonin and noradrenaline re-uptake inhibitor. The injection of orexin siRNA oligonucleotides suppressed the hyperphagia induced by the injection of POMC siRNA oligonucleotides. These findings suggest that functional hypothalamic POMC and orexin activity has a critical role in satiety signalling of mCPP in mice.

Effect of serotonergic anorectics on food intake and induction of Fos in brain of mice with disruption of melanocortin 3 and/or 4 receptors

Previous studies have indicated that type 3 or 4 melanocortin receptors (MCR) are downstream of the critical anorectic action of drugs that stimulate 5-HT(2C) receptors. To characterize further the receptor types involved, we have studied the effect of serotonergic anorectics in mice with genomic disruption of either MC3R or MC4R, or their combined knockout. In a first experiment, we showed that wild type (WT) and MC4R-/- mice showed comparable inhibition of food intake following acute treatment with dexnorfenfluramine. In a second experiment using WAY-161503, a 5-HT receptor full agonist with selectivity for 2B and 2C subtypes, we found that MC4R-/- responded comparably to WT, while MC3R-/- had reduced sensitivity. Double receptor knockout (DKO) mice responded comparably to WT and MC4R-/-. Surprisingly, brain Fos-ir was not strongly induced in any brain region by WAY-16103 with the exception of the paraventricular nucleus of DKO. These data suggest that MC3Rs may be involved in the response to serotonergic anorectic agents, and more generally in control of food intake.

Rikkunshito and 5-HT2C receptor antagonist improve cisplatin-induced anorexia via hypothalamic ghrelin interaction

Circulating ghrelin concentration regulates appetite behavior, but no study thus far has focused on the role of central ghrelin in anorexia after chemotherapy. To clarify the action mechanisms of rikkunshito (RKT), a traditional Japanese medicine, on cisplatin-induced anorexia, we attempted to elucidate its effect on hypothalamic ghrelin receptor expression in cisplatin-induced anorexia. We first examined the effects of an intracerebroventricular (ICV) injection of exogenous ghrelin on food intake with or without cisplatin treatment, and the effects of cisplatin or m-chlorophenylpiperazine (mCPP), a 5-HT2C receptor agonist, on hypothalamic growth hormone secretagogue receptor 1a (GHS-R1a) mRNA expression. To identify the mechanism of cisplatin-induced decrease in hypothalamic GHS-R1a mRNA expression, we evaluated the effects of SB242084HCl, a 5-HT2C receptor antagonist, and RKT on hypothalamic GHS-R1a gene expression, along with the effect of coadministration of a GHS-R1a antagonist on decreased food intake. Compared to vehicle controls, an ICV-injected rat ghrelin failed to inhibit the decrease in food intake in cisplatin-treated rats. Hypothalamic GHS-R1a gene expression was significantly reduced after cisplatin or mCPP treatment, and the induced decrease was reversed by SB242084HCl or RKT, but not granisetron or ondansetron, both of which are 5-HT3 receptor antagonists. Their suppressive effect on the decrease in food intake was abolished by coadministration of the GHS-R1a antagonist. Administration of RKT or SB242084HCl reversed the decrease in food intake induced by mCPP injection. The improvement by RKT on decreased food intake after cisplatin treatment was partly mediated by hesperidin and isoliquiritigenin, components of RKT. Cisplatin-induced anorexia may worsen because of decreased hypothalamic GHS-R1a gene expression. A 5-HT2C receptor antagonist and RKT suppressed cisplatin-induced anorexia by inhibiting reduction of GHS-R1a signal transduction in the hypothalamus.