Serotonin Metabolism Research Articles

Vitamin C improved anxiety and depression like behavior induced by chronic unpredictable mild stress in adolescent rats by influencing on oxidative stress balance, neurotransmitter systems, and inflammatory response

ABSTRACT Objectives: Stress is an adaptive response to different events in daily life that could strain physically, emotionally, or psychologically. Adolescence is an important developmental period due to physical, psychological, and social maturation. The aim of our study is to state whether chronic unpredictable mild stress (CUMS) during adolescence in male rats can cause anxiety and depression in adulthood and whether vitamin C (Vit C) can prevent this problem or not. Methods: For this purpose, we performed behavioral tests, including open field test, elevated plus maze, and forced swimming test. In addition, we investigated the metabolism of serotonin, the level of inflammation, oxidative stress and brain-derived neurotrophic factor (BDNF) in the brain cortex tissue of animals. Results: Results indicated that CUMS exacerbates mood-related behaviors by affecting the brain oxidative stress balance, inflammatory response, and serotonin metabolism. Moreover, we found that CUMS-Vit C co-treatment could significantly reverse CUMS-induced complications by restoration of the mentioned biochemical parameters. Discussion: Taken together, we would like to suggest the use of Vit C supplementation as a safe, inexpensive, and effective strategy for the management of CUMS.

Effects of Different Photoperiods on Peripheral 5-Hydroxytryptamine Metabolism, Breast Muscle Glucose Metabolism, and Myopathies in Broilers.

Background: There is a close relationship between breast muscle glucose metabolism, peripheral 5-hydroxytryptamine (5-HT), and myopathies in animals. Here, this study aimed to investigate the effects of different photoperiods on peripheral 5-HT metabolism, white striping (WS), and wooden breast (WB) in broilers. Methods: A total of 216 healthy 5-day-old (d) Arbor Acres (AA) male broilers were randomly assigned to 12L:12D, 18L:6D, and 24L:0D photoperiods for 4 weeks. Results: Compared with the 12L:12D photoperiod, we found the WB score in broilers was significantly increased in the 18L:6D and 24L:0D photoperiod at week 4 (p < 0.05). Muscle glycogen was significantly reduced (p < 0.05) and glycolysis was promoted in the breast muscles of broilers under the 18L:6D and 24L:0D photoperiods at week 2 and 4. Peripheral 5-HT concentrations, the mRNA expression of tryptophan hydroxylase 1 (TPH1) and serotonin transporter (SERT) in the cecal mucosa, and 5-hydroxytryptamine receptor 2A (5-HTR2A) mRNA expression in the breast muscle of broilers significantly up-regulated in the 18L:6D and 24L:0D photoperiod at week 2 and 4 (p < 0.05). Conclusions: Our findings revealed that extending the photoperiod improved the breast muscle growth rate, but up-regulated 5-HT synthesis and secretion to higher peripheral 5-HT, induced breast muscle glucose metabolism disorder, and increased WB incidence rates in broilers.

FMT intervention decreases urine 5-HIAA levels: a randomized double-blind controlled study.

Autism spectrum disorder (ASD) is often linked to gastrointestinal issues and altered serotonin metabolism. Emerging evidence suggests gut microbiota influence both, with fecal microbiota transplantation (FMT) offering a potential therapeutic approach. However, its impact on serotonin metabolism and ASD symptoms is not well understood. In this study, we aimed to evaluate the clinical effects of FMT and examine changes in specific urinary metabolites in children with ASD. A randomized double-blind controlled trial was performed to evaluate the clinical effects of FMT on GI and ASD-related symptoms. Gastrointestinal symptoms were assessed using the Gastrointestinal Symptom Rating Scale (GSRS), and the ASD-related symptoms were assessed using the Childhood Autism Rating Scale (CARS), Aberrant Behavior Checklist (ABC), and Social Responsiveness Scale (SRS) scores. Urinary metabolites were analyzed by homogeneous enzyme immunoassay using commercially available kits. Significant improvements in GI and core ASD symptoms were observed following FMT intervention. The average GSRS scores decreased from 30.17 (before) to 19 (after; p < 0.0001), CARS scores decreased from 36.22 to 33.33 (p < 0.0001), SRS scores decreased from 151.17 to 137.5 (p = 0.0002), and the ABC scores decreased 76.39 to 53.17 (p < 0.0001) in the FMT group. However, in the placebo group, GSRS, CARS, and SRS scores showed no significant changes, while ABC scores decreased from 72 to 58.75 (p = 0.034). The FMT group also showed a significant reduction in urinary 5-hydroxyindoleacetic acid (5-HIAA) levels from 8.6 to 7.32 mg/L (p = 0.022), while other metabolites showed no significant changes. FMT is a safe and effective treatment for improving GI and core symptoms in children with ASD, with 5-HIAA showing potential as a urinary biomarker for treatment response.

Intergenerational neurotoxicity of polystyrene nanoplastics in offspring mice is mediated by dysfunctional microbe-gut-brain axis

Nanoplastics (NPs) are ubiquitous in daily life, posing potential risks to the environment and human. While their negative effects on parental organisms have been extensively studied, intergenerational effects are still in the early stages of investigation. Here, we aimed to investigate the impact of maternal exposure to an environmentally relevant level of polystyrene NPs (PSNPs, 100 nm) during gestation and lactation (∼32 days, 50 μg/mouse/day) on neurotoxicity mediated by the microbe-gut-brain axis in offspring mice. Maternal PSNPs exposure significantly increased brain TNF-α level and microglia by 1.43 and 1.48 folds respectively, compared to control, accompanied by nuclear pyknosis and cell vacuolization in cortex and hippocampus. Targeted neurotransmitter metabolomics analysis revealed dysregulation in dopamine and serotonin metabolism. Specifically, dopamine levels increased significantly from 0.007 ng/L to 0.015 ng/L, while N-acetylseroton and 3,4-dihydroxyphenylacetic acid decreased significantly from 0.002 and 0.929 ng/L to 0.001 and 0.680 ng/L, respectively. Through a combination of 16S rRNA sequencing and biochemical analysis, we discovered that maternal PSNPs exposure led to a depletion of anti-inflammatory bacteria and an enrichment of pro-inflammatory bacteria resulting in intestinal barrier damage, elevated levels of lipopolysaccharide in blood, and subsequent activation of neuroinflammation. Meanwhile, gut bacteria dysbiosis interfered with communication between gut and brain by dysregulating neurotransmitter synthesis, as evidenced by significant associations between neurotransmitter-related bacteria (Akkermansia, Family_XIII_AD3011_group, Lachnoclostridium) and dopamine/serotonin related metabolites. Furthermore, transcriptional alterations in dopamine and serotonin related pathways were observed in the enteric nervous system, suggesting abnormal signal transduction from gut to brain contributes to neurotoxicity. This study provides new insights into NPs-induced neurotoxicity within the context of microbe-gut-brain axis and highlights the risk of cerebral dysfunction in offspring with maternal NPs exposure.

Prebiotic inulin alleviates anxiety and depression-like behavior in alcohol withdrawal mice by modulating the gut microbiota and 5-HT metabolism

BackgroundAlcohol dependence (AD) is a common psychiatric disorder, often accompanied by anxiety and depression. These comorbidities are linked to disturbances in serotonin (5-HT) metabolism and gut microbiota dysbiosis. Clinical studies suggest that inulin, a prebiotic, can alleviate anxiety and depression in AD patients by affecting the gut microbiota, although the mechanisms remain unclear. PurposeThe purpose of this study is to investigate the potential mechanisms by which inulin, a prebiotic, improves anxiety and depression-like behaviors in AD withdrawal mice. This research is based on the drug and food homology and intestinal treatment of encephalopathy, with the goal of developing new clinical strategies for AD treatment. Study DesignFor this purpose, fecal samples from AD patients were analyzed to identify microorganisms associated with AD. An AD withdrawal mouse model was created, with inulin as the intervention and fluvoxamine maleate as the control. Techniques such as 16S microbiome sequencing and UPLC-TQMS-targeted metabolomics were used to assess gut microbiota, short-chain fatty acids (SCFAs) levels, and 5-HT metabolism. MethodsThe AD withdrawal model was built using the "Drinking-in-the-dark" protocol over 6 weeks. Inulin (2 g/kg/day) and fluvoxamine maleate (30 mg/kg/day) were administered for 4 weeks. The open field test, forced swim test, and tail suspension test were used to evaluate anxiety and depression-like behaviors in mice. ELISA and qRT-PCR assessed 5-HT metabolism in the colon, blood, and prefrontal cortex, while 16S microbiome sequencing analyzed changes in gut microbiota and UPLC-TQMS examined SCFAs levels. Immunohistochemistry was used to study intestinal barrier integrity. ResultsAD patients showed reduced SCFA-producing bacteria such as Faecalibacterium and Roseburia. In mice, AD withdrawal led to anxiety, depression-like behaviors, disrupted 5-HT metabolism, and gut microbiota dysbiosis. Inulin supplementation alleviated these behaviors, increased 5-HT and 5-hydroxytryptophan (5-HTP) levels, upregulated colonic tryptophan hydroxylase 1 (TPH1) expression, and promoted the growth of beneficial bacteria such as Faecalibacterium and Roseburia, while also increasing SCFAs levels. ConclusionInulin increases the abundance of Faecalibacterium and Roseburia, enhances SCFAs production, and regulates 5-HT metabolism, improving anxiety and depression-like behaviors in AD withdrawal mice. These findings suggest that inulin may serve as a nutritional intervention for mental health in AD patients by targeting the microbiome-gut-brain axis.

6817 Metabolomics Analysis Reveals Disordered Serotonin Metabolism as a Novel Therapeutic Target for Post-Bariatric Hypoglycemia

6817 Metabolomics Analysis Reveals Disordered Serotonin Metabolism as a Novel Therapeutic Target for Post-Bariatric Hypoglycemia

Boosting Serotonin Synthesis Is Not Sufficient to Improve Motor Coordination of Mecp2 Heterozygous Mouse Model of Rett Syndrome.

Motor deficit is a core symptom of Rett syndrome, a rare neurological disease caused in most cases by mutations of the methyl-CpG-binding protein2 (MECP2) gene. Serotonin reuptake inhibitors improve motor coordination in Mecp2 heterozygous (Het) mice and serotonin depletion prevented this effect. Here, we assess alterations in indole levels in various brain regions and whether boosting brain serotonin synthesis with the serotonin precursors tryptophan, 5-hydroxytryptophan and α-lactalbumin rescued motor coordination deficit of Mecp2 Het mice. Motor coordination was assessed in the accelerated rotarod during and after systemic administration of serotonin precursors for 2-3 weeks. Since no data are available, the effect of α-lactalbumin on tryptophan, serotonin and 5-hydroxyindoleacetic acid levels was evaluated in various brain regions in order to identify the dose of ALAC to evaluate on motor coordination. As compared to WT, Mecp2 Het mice show reduced levels of serotonin in the whole brain, hippocampus, brainstem and cerebral cortex, but not the striatum. Reduced levels of 5-hydroxyindoleacetic acid were observed in the hippocampus and brainstem. Doses of serotonin precursors increasing brain tryptophan and/or serotonin production and metabolism had no effect on motor coordination. The results indicate that boosting serotonin synthesis is not sufficient to improve motor coordination of Mecp2 Het mice.

Metformin reprograms tryptophan metabolism via gut microbiome-derived bile acid metabolites to ameliorate depression-Like behaviors in mice

As an adjunct therapy, metformin enhances the efficacy of conventional antidepressant medications. However, its mode of action remains unclear. Here, metformin was found to ameliorate depression-like behaviors in mice exposed to chronic restraint stress (CRS) by normalizing the dysbiotic gut microbiome. Fecal transplants from metformin-treated mice ameliorated depressive behaviors in stressed mice. Microbiome profiling revealed that Akkermansia muciniphila (A. muciniphila), in particular, was markedly increased in the gut by metformin and that oral administration of this species alone was sufficient to reverse CRS-induced depressive behaviors and normalize aberrant stress-induced 5-hydroxytryptamine (5-HT) metabolism in the brain and gut. Untargeted metabolomic profiling further identified the bile acid metabolites taurocholate and deoxycholic acid as direct A. muciniphila-derived molecules that are, individually, sufficient to rescue the CRS-induced impaired 5-HT metabolism and depression-like behaviors. Thus, we report metformin reprograms 5-HT metabolism via microbiome-brain interactions to mitigate depressive syndromes, providing novel insights into gut microbiota-derived bile acids as potential therapeutic candidates for depressive mood disorders from bench to bedside.

Postprandial metabolomics analysis reveals disordered serotonin metabolism in post-bariatric hypoglycemia.

Bariatric surgery is a potent therapeutic approach for obesity and type 2 diabetes but can be complicated by post-bariatric hypoglycemia (PBH). PBH typically occurs 1 to 3 hours after meals, in association with exaggerated postprandial levels of incretins and insulin. To identify mediators of disordered metabolism in PBH, we analyzed plasma metabolome in fasting state and 30 and 120 minutes after mixed meal in 3 groups: PBH (n = 13), asymptomatic post-RYGB (n = 10), and non-surgical controls (n = 8). In the fasting state, multiple tricarboxylic acid cycle intermediates and the ketone beta-hydroxybutyrate were increased by 30% to 80% in PBH vs. asymptomatic. Conversely, multiple amino acids (BCAA, tryptophan) and polyunsaturated lipids were reduced by 20% to 50% in PBH versus asymptomatic. Tryptophan-related metabolites, including kynurenate, xanthurenate, and serotonin, were reduced by 2- to 10-fold in PBH in fasting state. Postprandially, plasma serotonin was uniquely increased by 1.9-fold in PBH versus asymptomatic post-RYGB. In mice, serotonin administration lowered glucose and increased plasma insulin and GLP-1. Moreover, serotonin-induced hypoglycemia in mice was blocked by the nonspecific serotonin receptor antagonist cyproheptadine and the specific serotonin receptor 2 antagonist ketanserin. Together these data suggest that increased postprandial serotonin may contribute to the pathophysiology of PBH and provide a potential therapeutic target. NIH grant R01 DK121995, NIH grant P30 DK036836 (Diabetes Research Center grant, Joslin Diabetes Center), and Fundação de Amparo à Pesquisa do Estado de São Paulo-FAPESP grant 2018/22111-2.

The Effect of Chronic Treatment with the Inhibitor of Phosphodiesterase 5 (PDE5), Sildenafil, in Combination with L-DOPA on Asymmetric Behavior and Monoamine Catabolism in the Striatum and Substantia Nigra of Unilaterally 6-OHDA-Lesioned Rats.

The use of phosphodiesterase inhibitors in the treatment of Parkinson's disease is currently widely discussed. The study aimed to investigate the impact of acute and chronic treatment with the phosphodiesterase 5 inhibitor, sildenafil, at low and moderate doses of 2 mg/kg and 6 mg/kg, and L-DOPA (12.5 mg/kg), alone or in combination, on asymmetric behavior and dopamine (DA) and serotonin metabolism in the striatum and substantia nigra of unilaterally 6-OHDA-lesioned rats. Acute administration of sildenafil at both tested doses jointly with L-DOPA significantly increased the number of contralateral rotations during a 2 h measurement compared to L-DOPA alone. The effect of a lower dose of sildenafil combined with L-DOPA was much greater in the second hour of measurement. However, the acute combined administration of a higher dose of sildenafil with L-DOPA resulted in an immediate and much stronger increase in the number of contralateral rotations compared to L-DOPA alone, already visible in the first hour of measurement. Interestingly, the chronic combined administration of 2 mg/kg of sildenafil and L-DOPA significantly reduced the number of contralateral rotations, especially during the first hour of measurement, compared to the long-term treatment with L-DOPA alone. Such an effect was not observed after the long-term combined treatment of a higher dose of sildenafil and L-DOPA compared to L-DOPA alone. The concentration of DA in the ipsilateral striatum and substantia nigra after the last combined chronic dose of sildenafil (2 or 6 mg/kg) and L-DOPA (12.5 mg/kg) was significantly higher than after L-DOPA alone. In spite of much stronger increases in the DA concentration in the ipsilateral striatum and substantia nigra, the number of contralateral rotations was reduced in the group of rats treated with the combination of 2 mg/kg sildenafil and L-DOPA compared to the group receiving L-DOPA alone. Moreover, the combined treatment with a low dose of sildenafil and L-DOPA had an opposite effect on DA catabolism, as assessed by DOPAC/DA and HVA/DA indexes, and these indexes were reduced in the ipsilateral striatum but increased in the contralateral striatum and substantia nigra compared to the treatment with L-DOPA alone. The results of the present study show that the addition of a low dose of a PDE5 inhibitor to the standard L-DOPA therapy differently modulates rotational behavior, the tissue DA concentration and its catabolism in the striatum and substantia nigra.

Mental disorders of the depressive and anxiety spectrum in neuroendocrine tumors: prevalence, pathogenesis, clinical particulars

Neuroendocrine tumors (NETs) are a heterogeneous group of slowly progressing tumors from neuroendocrine cells able to secrete biologically active substances. The most striking clinical manifestation of functioning NETs is the carcinoid syndrome, which is caused by serotonin overproduction and is most often associated with hot flashes, diarrhea, and abdominal pain. The prevalence of depressive and anxiety spectrum disorders in NETs patients can amount to 30–50%. The development of depressive and anxiety spectrum disorders in NETs can occur both through a nosogenic mechanism facilitated by a long pre-diagnostic stage, the presence of a serious disease with severe somatic symptoms and resulting significant decrease in quality of life. The mental disorders may be a result of somatogenic factors, which include an imbalance of significant mediators in the central nervous system (in particular, serotonin), as well as chronic inflammation and abnormalities of the body's immune defense. In the treatment of patients with NETs and verified anxiety and depressive disorders, special attention is paid to the safety of prescribing the first-line therapy, the selective serotonin reuptake inhibitors. The side effects of these agents are related to the activity of serotonin receptor agonists in the gut, which results in diarrhea and increased gastrointestinal motility, the symptoms similar to the carcinoid syndrome manifestations. The accumulated evidence allows concluding on the relative safety of serotoninergic antidepressants in NETs patients, but does not exclude some groups of patients with an increased risk of complications related to an additional effect on serotonin metabolism. Current knowledge on the prevalence, pathogenesis and treatment of depressive and anxiety spectrum disorders, comorbid to NETs, are limited and contradictory. Therefore, further studies with a larger patient samples are required to identify key factors of the pathophysiology and manifestation of mental disorders in NETs patients, which would generally facilitate the optimization of their treatment.

Discovery of MAO-A Inhibitors as Antidepressant Based on Virtual Screening

Aim: Major depression and anxiety have increased significantly worldwide since the 2019 outbreak of COVID-19. The development of highly effective antidepressants with low side effects is attracting researchers. Methods: Monoamine oxidase A (MAO-A) is a key enzyme that catalyzes the metabolism of norepinephrine (NE), dopamine (DA), and serotonin (5-HT), etc. Elevated level of MAO-A would lead to increased metabolism of its substrates, thereby causing a decrease in the levels of these neurotransmitter monoamines in the brain leading to depression. Consequently, inhibition of MAO-A was thought to be an effective strategy, as this would treat the root cause of depression. Results and Discussion: Based on the crystal structure of MAO-A, 4 star-hits, as potential MAO-A inhibitors was screened from the compound libraries with central nervous system (CNS) activity by using various computational techniques. Molecular dynamics simulation was used to verify the stability of the ligand- receptor complexes. Conclusion: Furthermore, the ADMET (absorption, distribution, metabolism, excretion and toxicity properties) of the virtual hits were predicted in order to evaluate their lead-like properties and safety. This work provides ideas for the drugs discovery of antidepressant.

Prophylactic effects of supplementation of a combination of Lactobacillus lactis WHH2078 and saffron on depressive-like behaviors in mice exposed to chronic stress.

Depression is one of the most common psychiatric conditions worldwide, with an annual escalation in prevalence. The serotonin (5-Hydroxytryptamine [5-HT]) metabolism through the gut-brain axis has been revealed to be related to the development of depression. Our previous study demonstrated that Lactococcus lactis WHH2078 alleviated depression in mice by shaping the gut microbiome composition and 5-HT metabolism. However, little research has explored the synergistic effects of probiotics and natural mental health-improving products. In this study, three natural products (saffron, l-theanine, and phosphatidylserine), either individually or in combination, were orally administrated for 4 weeks in chronic restraint stress (CRS)-induced mice, and their depressive behaviors, hippocampal 5-HT, and serum corticosterone were assessed. Saffron demonstrated improvement of the depressive-like behaviors via multiple behavioral tests and reversed the declined concentration of 5-HT and increased concentration of corticosterone. Following an initial screening, saffron was chosen to be combined with WHH2078, referred to as WHHMOOD™. Furthermore, the effects of WHHMOOD were evaluated in mice with depressive-like behaviors. WHHMOOD reduced immobility time in the forced swimming test and tail suspension test, increased the time spent in the central area in open field test, and reduced the serum corticosterone level. Besides, WHHMOOD improved the CRS-induced gut microbial dysbiosis by reversing gut microbial diversity and the abundances of Ligilactobacillus, Candidatus Arthromitus, and Erysipelatoclostridium. Compared to WHH2078, WHHMOOD treatment significantly increased the travel distance and hippocampal 5-HT level in mice. In conclusion, WHHMOOD exhibited prophylactic effects on depressive-like in CRS mice, which may act as a promising agent for improving the symptoms of depression.

Infant Microbiota Communities and Human Milk Oligosaccharide Supplementation Independently and Synergistically Shape Metabolite Production and Immune Responses in Healthy Mice

BackgroundMultiple studies have demonstrated associations between the early-life gut microbiome and incidence of inflammatory and autoimmune disease in childhood. Although microbial colonization is necessary for proper immune education, it is not well understood at a mechanistic level how specific communities of bacteria promote immune maturation or drive immune dysfunction in infancy. ObjectivesIn this study, we aimed to assess whether infant microbial communities with different overall structures differentially influence immune and gastrointestinal development in healthy mice. MethodsGerm-free mice were inoculated with fecal slurries from Bifidobacterium longum subspecies infantis positive (BIP) or B. longum subspecies infantis negative (BIN) breastfed infants; half of the mice in each group were also supplemented with a pool of human milk oligosaccharides (HMOs) for 14 d. Cecal microbiome composition and metabolite production, systemic and mucosal immune outcomes, and intestinal morphology were assessed at the end of the study. ResultsThe results showed that inoculation with a BIP microbiome results in a remarkably distinct microbial community characterized by higher relative abundances of cecal Clostridium senu stricto, Ruminococcus gnavus, Cellulosilyticum sp., and Erysipelatoclostridium sp. The BIP microbiome produced 2-fold higher concentrations of cecal butyrate, promoted branched short-chain fatty acid (SCFA) production, and further modulated serotonin, kynurenine, and indole metabolism relative to BIN mice. Further, the BIP microbiome increased the proportions of innate and adaptive immune cells in spleen, while HMO supplementation increased proliferation of mesenteric lymph node cells to phorbol myristate acetate and lipopolysaccharide and increased serum IgA and IgG concentrations. ConclusionsDifferent microbiome compositions and HMO supplementation can modulate SCFA and tryptophan metabolism and innate and adaptive immunity in young, healthy mice, with potentially important implications for early childhood health.

Antidepressant effect of new coumarin derivatives

BACKGROUND: The incidence of bipolar disorder is increasing worldwide. The search for new compounds with antidepressant activity and milder adverse drug reactions is an urgent task of modern psychopharmacology. AIM: This study aimed to analyze the effect of new neuroactive coumarin derivatives on the level of depressive behavior and monoamine metabolism in the brain structures of rats. MATERIALS AND METHODS: The antidepressant effects of LVM-091, LVM-099, LVM-S144, and IEM-2886 were evaluated in rats subjected to the Porsolt forced swimming test and the metabolism of monoamines in brain structures (LVM-099) using high-performance liquid chromatography. RESULTS: LVM-091, LVM-099, LVM-S144, and IEM-2886, synthesized from coumarin, decreased the immobilization time of the experimental rats in the Porsolt forced swimming test, indicating the antidepressant effect of these substances. The administration of LVM-099 at a dose of 10 mg/kg increased the level of homovanillic acid and the homovanillic acid-to-dopamine ratio in the nucleus accumbens. LVM-099 also increased 5-hydroxyindoleacetic acid levels and the 5-hydroxyindoleacetic acid-to-serotonin ratio in the nucleus accumbens. In the amygdala, the levels of norepinephrine, dopamine, serotonin, and their metabolites did not change after LVM-099 administration. CONCLUSIONS: New coumarin derivatives exert antidepressant effects and increase the metabolism of dopamine and serotonin in rat nucleus accumbens, which can be used in the development of new highly effective antidepressants.

The Influence of BMP6 on Serotonin and Glucose Metabolism.

Previous studies have suggested a potential role of bone morphogenetic protein 6 (BMP6) in glucose metabolism, which also seems to be regulated by serotonin (5-hydroxytryptamine, 5HT), a biogenic amine with multiple roles in the organism. In this study, we explored possible interactions between BMP6, serotonin, and glucose metabolism regulation. The effect of BMP6 or 5HT on pancreatic β-cells has been studied in vitro using the INS-1 832/13 rat insulinoma cell line. Studies in vivo have been performed on mice with the global deletion of the Bmp6 gene (BMP6-/-) and included glucose and insulin tolerance tests, gene expression studies using RT-PCR, immunohistochemistry, and ELISA analyses. We have shown that BMP6 and 5HT treatments have the opposite effect on insulin secretion from INS-1 cells. The effect of BMP6 on the 5HT system in vivo depends on the tissue studied, with no observable systemic effect on peripheral 5HT metabolism. BMP6 deficiency does not cause diabetic changes, although a mild difference in insulin tolerance test between BMP6-/- and WT mice was observed. In conclusion, BMP6 does not directly influence glucose metabolism, but there is a possibility that its deletion causes slowly developing changes in glucose and serotonin metabolism, which would become more expressed with ageing.

Effects of dietary tryptophan levels on growth performance, serotonin metabolism, brain 5-HT and cannibalism activities in tiger puffer, Takifugu rubripes fingerlings

Essential amino acid (EAA) requirements of aquaculture fish species can be used as a guideline for commercial feed formulation. Several EAA requirements have been quantified in tiger puffer (Takifugu rubripes). However, as the third limiting amino acid (AA) of many plant protein sources, tryptophan requirement of this species has yet to be quantified. This study was conducted to determine dietary tryptophan requirement of tiger puffer, and investigate the effect of dietary tryptophan supplementation on the cannibalism, brain serotonin (5-hydroxytryptpamine, 5-HT) metabolism and serum cortisol levels. Six experimental diets were prepared using fish meal, gelatin and corn protein concentrate as intact protein, and then supplemented with crystalline AA premix. The analyzed tryptophan levels in the experimental diets were 3.5, 4.1, 4.5, 5.5, 7.0 and 11.8 g/kg of dry diet. Experimental diets were randomly fed in triplicate to tiger puffer (initial average weight of 17.5 g) for 58 days. The weight gain (WG), feed conversion ratio (FCR) and protein efficiency ratio (PER) were significantly affected by dietary tryptophan, and the break points were observed at 5.07, 4.82 and 4.99 g/kg of dry diet, respectively. Compared to the basal diet, the cannibalism (the rate of bite mark appearance) was significantly lower and survival rate was significantly higher when fish were given diets containing 7.0 and 11.8 g/kg tryptophan. The concentrations of free tryptophan and phenylalanine in the brain exhibited a nonlinear increase in response to the incremental levels of dietary tryptophan. Brain 5-HT concentration was significantly affected by dietary tryptophan levels, but did not show a significant dose-dependent response. The expression of genes related to 5-HT metabolism (tph1a, ddc and aldh) and serotonin reuptake (sert) in the brain varied significantly and exhibited a nonlinear relationship with the graded levels of dietary tryptophan. In addition, serum cortisol levels showed a decreasing trend till the 5.5 g/kg tryptophan inclusion level, at which point there appeared to be the lowest level. In conclusion, based on nonlinear regression analysis of the WG, FCR and PER, dietary tryptophan requirement of tiger puffer was determined to be range between 4.82 and 5.07 g/kg of dry diet (10.48–11.03 g/kg of dietary protein). Dietary tryptophan supplementation above requirement could mitigate cannibalism and improve the survival of tiger puffer, which may be attributed to regulating the synthesis and catabolism of 5-HT and its availability in the synaptic cleft, and subsequently the reduction of serum cortisol content.

Differential roles of serotonin receptor subtypes in regulation of neurotrophin receptor expression and intestinal hypernociception.

Aberrant serotonin (5-hydroxytryptamine, 5-HT) metabolism and neurite outgrowth were associated with abdominal pain in irritable bowel syndrome (IBS). We previously demonstrated that 5-HT receptor subtype 7 (5-HT₇) was involved in visceral hypersensitivity of IBS-like mouse models. The aim was to compare the analgesic effects of a novel 5-HT₇ antagonist to reference standards in mouse models and investigate the mechanisms of 5-HT₇-dependent neuroplasticity. Two mouse models, including Giardia post-infection combined with water avoidance stress (GW) and post-resolution of trinitrobenzene sulfonic acid-induced colitis (PT) were used. Mice were orally administered CYY1005 (CYY, a novel 5-HT₇ antagonist), alosetron (ALN, a 5-HT₃ antagonist), and loperamide (LPM, an opioid receptor agonist) prior to measurement of visceromotor responses (VMR). Levels of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin receptors (NTRs) were assessed. Peroral CYY was more potent than ALN or LPM in reducing VMR values in GW and PT mice. Increased mucosal 5-HT₇-expressing nerve fibers were associated with elevated Gap43 levels in the mouse colon. We observed higher colonic Ntrk2 and Ngfr expression in GW mice, and increased Bdnf expression in PT mice compared with control mice. Human SH-SY5Y cells stimulated with mouse colonic supernatant or exogenous serotonin exhibited longer nerve fibers, which CYY dose-dependently inhibited. Serotonin increased Ntrk1 and Ngfr expression via 5-HT₇ but not 5-HT₃ or 5-HT₄, while Ntrk2 upregulation was dependent on all three 5-HT receptor subtypes. Stronger analgesic effects by peroral CYY were observed compared with reference standards in two IBS-like mouse models. The 5-HT₇-dependent NTR upregulation and neurite elongation may be involved in intestinal hypernociception.

Quantitative Analysis of 5-hydroxyindoleacetic Acid in Rat Urine by High-performance Liquid Chromatography Method

ABSTRACT Background: 5-hydroxyindoleacetic acid (5-HIAA) is a metabolite of serotonin, a neurotransmitter primarily associated with regulating mood, appetite, and sleep. When serotonin is broken down in the body, it forms 5-HIAA, which is then excreted in urine. Quantification of 5-HIAA levels in urine is often used as a diagnostic tool for certain conditions, particularly carcinoid tumors, which can produce excess serotonin. Elevated levels of 5-HIAA in urine can indicate increased serotonin production, which may be indicative of carcinoid tumors or other conditions affecting serotonin metabolism. However, there is limited work on employing high-performance liquid chromatography (HPLC)–ultraviolet to estimate monoamines in biological samples. Aim and Objectives: The present study explores the detection of 5-HIAA in rat urine samples, developing an easy, precise validated HPLC method. Materials and Methods: Mobile phase combination acetonitrile and o-phosphoric acid in the ratio of 30:70% v/v and flow rate 0.5 mL/min was able to separate 5-HIAA distinctly. Results: The detection was observed at λmax 277 nm with better sensitivity. According to the parameters indicated in the international council for harmonisation of technical requirements for pharmaceuticals for human use guidelines (Q2A; Q2B), the procedure was verified. The linearity range was selected from 20 to 45 μg/mL, r 2 = 0.992, limit of detection (4.65 μg/mL), limit of quantification (15.52 μg/mL), retention time (6.3 min). Conclusion: The technique has demonstrated that it is repeatable and recoverable within the given range. Thus can be used for routine analysis of 5-HIAA in urine samples.

Serotonin signalling in cancer: Emerging mechanisms and therapeutic opportunities

AbstractBackgroundSerotonin (5‐hydroxytryptamine) is a multifunctional bioamine serving as a neurotransmitter, peripheral hormone and mitogen in the vertebrate system. It has pleiotropic activities in central nervous system and gastrointestinal function via an orchestrated action of serotonergic elements, particularly serotonin receptor‐mediated signalling cascades. The mitogenic properties of serotonin have garnered recognition for years and have been exploited for repurposing serotonergic‐targeted drugs in cancer therapy. However, emerging conflicting findings necessitate a more comprehensive elucidation of serotonin's role in cancer pathogenesis.Main body and conclusionHere, we provide an overview of the biosynthesis, metabolism and action modes of serotonin. We summarise our current knowledge regarding the effects of the peripheral serotonergic system on tumourigenesis, with a specific emphasis on its immunomodulatory activities in human cancers. We also discuss the dual roles of serotonin in tumour pathogenesis and elucidate the potential of serotonergic drugs, some of which display favourable safety profiles and impressive efficacy in clinical trials, as a promising avenue in cancer treatment.Key points Primary synthesis and metabolic routes of peripheral 5‐hydroxytryptamine in the gastrointestinal tract. Advanced research has established a strong association between the serotonergic components and carcinogenic mechanisms. The interplay between serotonergic signalling and the immune system within the tumour microenvironment orchestrates antitumour immune responses. Serotonergic‐targeted drugs offer valuable clinical options for cancer therapy.