Important role of 5-hydroxytryptamine in glucocorticoid-induced insulin resistance in liver and intra-abdominal adipose tissue of rats

Fresh insights into glucocorticoid-induced diabetes mellitus and new therapeutic directions

Glucocorticoid hormones were discovered to have use as potent anti-inflammatory and immunosuppressive therapeutics in the 1940s and their continued use and development have successfully revolutionized the management of acute and chronic inflammatory diseases. However, long-term use of glucocorticoids is severely hampered by undesirable metabolic complications, including the development of type 2 diabetes mellitus. These effects occur due to glucocorticoid receptor activation within multiple tissues, which results in inter-organ crosstalk that increases hepatic glucose production and inhibits peripheral glucose uptake. Despite the high prevalence of glucocorticoid-induced hyperglycaemia associated with their routine clinical use, treatment protocols for optimal management of the metabolic adverse effects are lacking or underutilized. The type, dose and potency of the glucocorticoid administered dictates the choice of hypoglycaemic intervention (non-insulin or insulin therapy) that should be provided to patients. The longstanding quest to identify dissociated glucocorticoid receptor agonists to separate the hyperglycaemic complications of glucocorticoids from their therapeutically beneficial anti-inflammatory effects is ongoing, with selective glucocorticoid receptor modulators in clinical testing. Promising areas of preclinical research include new mechanisms to disrupt glucocorticoid signalling in a tissue-selective manner and the identification of novel targets that can selectively dissociate the effects of glucocorticoids. These research arms share the ultimate goal of achieving the anti-inflammatory actions of glucocorticoids without the metabolic consequences.

Mechanisms for Improving Hepatic Glucolipid Metabolism by Cinnamic Acid and Cinnamic Aldehyde: An Insight Provided by Multi-Omics

Cinnamic acid (AC) and cinnamic aldehyde (AL) are two chemicals enriched in cinnamon and have been previously proved to improve glucolipid metabolism, thus ameliorating metabolic disorders. In this study, we employed transcriptomes and proteomes on AC and AL treated db/db mice in order to explore the underlying mechanisms for their effects. Db/db mice were divided into three groups: the control group, AC group and AL group. Gender- and age-matched wt/wt mice were used as a normal group. After 4 weeks of treatments, mice were sacrificed, and liver tissues were used for further analyses. Functional enrichment of differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) were performed using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. DEPs were further verified by parallel reaction monitoring (PRM). The results suggested that AC and AL share similar mechanisms, and they may improve glucolipid metabolism by improving mitochondrial functions, decreasing serotonin contents and upregulating autophagy mediated lipid clearance. This study provides an insight into the molecular mechanisms of AC and AL on hepatic transcriptomes and proteomes in disrupted metabolic situations and lays a foundation for future experiments.

The Levels of Serum Serotonin Can Be Related to Skin and Pulmonary Manifestations of Systemic Sclerosis

Background and Objective: The most prominent feature of systemic sclerosis (SSc), besides vasculopathy and autoimmune disorders, is excessive fibrosis. Serotonin affects hemostasis and can induce vasoconstriction, which is presumed to be one of the pathophysiological patterns in SSc that leads to fibrosis. Our aim was to explore the possible association of serotonin with some of the clinical features of SSc in our cohort of patients. Materials and Methods: We measured serotonin levels in sera of 29 female SSc patients. Patients were 41–79 years old, their average disease duration was 9 years. Serotonin values were analyzed in correlation with clinical and laboratory parameters, such as modified Rodnan skin score (mRSS), digital ulcers (DU), and spirometry parameters-forced expiratory volume in the first second (FEV1), forced vital capacity (FVC), and lung diffusion capacity of carbon monoxide (DLCO). Statistical analyses were performed using statistical software Statistica. Results: We found correlation of serotonin level with mRSS (r = 0.388, p = 0.038). The highest values of serotonin were documented in patients with refractory DU, but this was not statistically significant. We also found a negative correlation between serotonin and FVC (r = −0.397), although it did not reach the level of significance (p = 0.114). Conclusions: Our study suggests that levels of serum serotonin could affect the course of skin fibrosis and partially restrictive pulmonary dysfunction in patients with SSc. We assume that serotonin might have influence on several features of SSc, but more studies are needed to reveal those relations.

Role of 5-HT degradation in acute liver injury induced by carbon tetrachloride

5-hydroxytryptamine (5-HT) is involved in the pathological processes of several liver diseases. Acute liver injury underlies the development of many liver diseases, but the mechanism remains unclear. We aimed to investigate the role of 5-HT in carbon tetrachloride (CCl4)-induced acute liver injury. Acute liver injury was induced with CCl4 (10 mg/kg) in mice pretreated with the 5-HT2A receptor antagonist sarpogrelate hydrochloride (SH) and the 5-HT synthesis inhibitor carbidopa (CDP). LO2 cells were treated with CCl4, 5-HT or 2,5-dimethoxy-4-idopametamine and pretreated with SH, CDP or the monoamine oxidase A (MAO-A) inhibitor clorgyline. Hematoxylin-eosin staining, immunohistochemistry, Real-time quantitative PCR, western blotting, fluorescent probe and biochemical markers were used to evaluate liver compromise. 5-HT2A receptor, 5-HT synthetase and MAO-A were expressed in hepatocytes; their gene and protein expression were upregulated by CCl4, which led to the degradation of mitochondrial 5-HT and overproduction of reactive oxygen species (ROS). Hepatic injury may be aggravated by ROS, which induce oxidative stress and the phosphorylation of p38 mitogen-activated protein kinase, Jun N-terminal kinase, extracellular regulated protein kinase, signal transducer and activator of transcription 3 and nuclear factor kappa-B. 5-HT2A receptor may contribute to acute liver injury by modulating 5-HT synthase and MAO-A expression. The synergistic action of SH and CDP treatment may inhibit CCl4-induced acute liver injury in a dose-dependent manner. Hence, CCl4-induced acute liver injury is due to an increase in mitochondrial ROS production caused by increased 5-HT degradation and probably involves increases in 5-HT2A receptor expression and 5-HT synthesis.

5-HT2A Receptor and 5-HT Degradation Play a Crucial Role in Atherosclerosis by Modulating Macrophage Foam Cell Formation, Vascular Endothelial Cell Inflammation, and Hepatic Steatosis

Aim: Previously, we found that diabetes-related liver dysfunction is due to activation of the 5-HT _2A receptor (5-HT _2A R) and increased synthesis and degradation of 5-HT. Here, we investigated the role of 5-HT in the development of atherosclerosis.

Methods: The study was conducted using high-fat diet-fed male ApoE ^−/− mice, THP-1 cell-derived macrophages, and HUVECs. Protein expression and biochemical indexes were determined by Western blotting and quantitative analysis kit, respectively. The following staining methods were used: oil red O staining (showing atherosclerotic plaques and intracellular lipid droplets), immunohistochemistry (showing the expression of 5-HT _2A R, 5-HT synthase, and CD68 in the aortic wall), and fluorescent probe staining (showing intracellular ROS).

Results: In addition to improving hepatic steatosis, insulin resistance, and dyslipidemia, co-treatment with a 5-HT synthesis inhibitor and a 5-HT _2A R antagonist significantly suppressed the formation of atherosclerotic plaques and macrophage infiltration in the aorta of ApoE ^−/− mice in a synergistic manner. Macrophages and HUVECs exposed to oxLDL or palmitic acid in vitro showed that activated 5-HT _2A R regulated TG synthesis and oxLDL uptake by activating PKCε, resulting in formation of lipid droplets and even foam cells; ROS production was due to the increase of both intracellular 5-HT synthesis and mitochondrial MAO-A-catalyzed 5-HT degradation, which leads to the activation of NF-κB and the release of the inflammatory cytokines TNF-α and IL-1β from macrophages and HUVECs as well as MCP-1 release from HUVECs.

Conclusion: Similar to hepatic steatosis, the pathogenesis of lipid-induced atherosclerosis is associated with activation of intracellular 5-HT _2A R, 5-HT synthesis, and 5-HT degradation.

Serotonin Regulates De Novo Lipogenesis in Adipose Tissues through Serotonin Receptor 2A

BACKGROUND

Obesity is defined as excessive fat mass and is a major cause of many chronic diseases such as diabetes, cardiovascular disease, and cancer. Increasing energy expenditure and regulating adipose tissue metabolism are important targets for the treatment of obesity. Serotonin (5-hydroxytryptophan [5-HT]) is a monoamine metabolite of the essential amino acid tryptophan. Here, we demonstrated that 5-HT in mature adipocytes regulated energy expenditure and lipid metabolism.

METHODS

Tryptophan hydroxylase 1 (TPH1) is the rate-limiting enzyme during 5-HT synthesis in non-neural peripheral tissues. We generated adipose tissue-specific Tph1 knockout (Tph1 FKO) mice and adipose tissue-specific serotonin receptor 2A KO (Htr2a FKO) mice and analyzed their phenotypes during high-fat diet (HFD) induced obesity.

RESULTS

Tph1 FKO mice fed HFD exhibited reduced lipid accumulation, increased thermogenesis, and resistance to obesity. In addition, Htr2a FKO mice fed HFD showed reduced lipid accumulation in white adipose tissue and resistance to obesity.

CONCLUSION

These data suggest that the inhibition of serotonin signaling might be an effective strategy in obesity.

Alternate-day fasting alleviates diabetes-induced glycolipid metabolism disorders: roles of FGF21 and bile acids

Glycolipid metabolism disorder is one of the causes of type 2 diabetes (T2D). Alternate-day fasting (ADF) is an effective dietary intervention to counteract T2D. The present study is aimed to determine the underlying mechanisms of the benefits of ADF metabolic on diabetes-induced glycolipid metabolism disorders in db/db mice. Here, leptin receptor knock-out diabetic mice were subjected to 28 days of isocaloric ADF. We found that ADF prevented insulin resistance and bodyweight gain in diabetic mice. ADF promoted glycogen synthesis in both liver and muscle. ADF also activated recombinant insulin receptor substrate-1 (IRS-1)/protein kinase B (AKT/PKB) signaling，inactivated inflammation related AMP-activated protein kinase (AMPK) and the inflammation-regulating nuclear factor kappa-B (NF-κB) signaling in the liver. ADF also suppressed lipid accumulation by inactivating the expression of peroxisome proliferator-activated receptor gamma (PPAR-γ) and sterol regulatory element-binding protein-1c (SREBP-1c). Furthermore, ADF elevated the expression of fibroblast growth factor 21 (FGF21) and down-stream signaling AMPK/silent mating type information regulation 2 homolog 1 (SIRT1)/peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) in the liver of diabetic mice. The mitochondrial biogenesis and autophagy were also stimulated by ADF. Interestingly, ADF also enhanced the bile acids (BAs) metabolism by generating more cholic acid (CA), deoxycholic acid (DCA) and tauroursodeoxycholic acid (TUDCA) in db/db mice. In conclusion, ADF could significantly inhibit T2D induced insulin resistance and obesity, promote insulin signaling，reduce inflammation, as well as promote glycogen synthesis and lipid metabolism. It possibly depends on FGF21 and BA metabolism to enhance mitochondrial biosynthesis and energy metabolism.

Role of murine macrophage in temporal regulation of cortisol- and serotonin-induced adipogenesis in pre-adipocytes when grown together

Regulation of adipogenesis, the root cause for obesity, is very poorly understood. However, studies have presented evidence of immuno-metabolic regulation of adipose tissue during periods of chronic psychological stress, leading to adverse conditions related to stress manifestation, including visceral obesity and atherosclerosis. Despite pronounced association of hormonal markers of stress with dys-regulated metabolic states, the contributing signalling events are yet to be established. It is apparent that to understand contributing signalling events we need a model. Although an in vivo model is preferred, it is difficult to establish. The current report, therefore, presents an in vitro model system for the simulation of adipose tissue in a chronic stress micro-environment by growing pre-adipocytes with macrophages in the presence and absence of stress hormones. In this report, effects of cortisol and serotonin on the kinetics of immune and metabolic changes in adipocytes and macrophage (alone and co-cultured) was studied through whole genome transcriptome profiling. A transition from pro- to anti-inflammatory response in the immune profile of pre-adipocytes, with increasing time in co-culture with macrophages, was observed. This transition was reversed by stress hormones cortisol and/or serotonin.

Summary: Stress-induced obesity is poorly understood in vivo at the molecular level. The current report established a novel molecular basis of adipogenesis in vitro.

Kynurenines: Tryptophan's metabolites in exercise, inflammation, and mental health

Kynurenine metabolites are generated by tryptophan catabolism and regulate biological processes that include host-microbiome signaling, immune cell response, and neuronal excitability. Enzymes of the kynurenine pathway are expressed in different tissues and cell types throughout the body and are regulated by cues, including nutritional and inflammatory signals. As a consequence of this systemic metabolic integration, peripheral inflammation can contribute to accumulation of kynurenine in the brain, which has been associated with depression and schizophrenia. Conversely, kynurenine accumulation can be suppressed by activating kynurenine clearance in exercised skeletal muscle. The effect of exercise training on depression through modulation of the kynurenine pathway highlights an important mechanism of interorgan cross-talk mediated by these metabolites. Here, we discuss peripheral mechanisms of tryptophan-kynurenine metabolism and their effects on inflammatory, metabolic, oncologic, and psychiatric disorders.

Selection of Suitable Reference Genes for Quantitative Real-Time PCR Normalization in Three Types of Rat Adipose Tissue

Quantitative real-time PCR (qRT-PCR) is the most classical technique in the field of gene expression study. This method requires an appropriate reference gene to normalize mRNA levels. In this study, the expression stability of four frequently-used reference genes in epididymal white adipose tissue (eWAT), inguinal beige adipose tissue (iBeAT) and brown adipose tissue (BAT) from obese and lean rats were evaluated by geNorm, NormFinder and BestKeeper. Based on the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines, the two most stable reference genes were recommended in each type of adipose tissue. Two target genes were applied to test the stability of the reference genes. The geNorm and NormFinder results revealed that GAPDH and 36B4 exhibited the highest expression stabilities in eWAT, while 36B4 and β-actin had the highest expression stabilities in iBeAT and BAT. According to the results of the BestKeeper analysis, 36B4 was the most stable gene in eWAT, iBeAT and BAT, in terms of the coefficient of variance. In terms of the coefficient of correlation, GAPDH, 36B4 and β-actin were the most stable genes in eWAT, iBeAT and BAT, respectively. Additionally, expected results and statistical significance were obtained using a combination of two suitable reference genes for data normalization. In conclusion, 36B4 and GAPDH, in combination, are the best reference genes for eWAT, while 36B4 and β-actin are two most suitable reference genes for both iBeAT and BAT. We recommend using these reference genes accordingly.

Effective treatment with combination of peripheral 5-hydroxytryptamine synthetic inhibitor and 5-hydroxytryptamine 2 receptor antagonist on glucocorticoid-induced whole-body insulin resistance with hyperglycemia

AIMS/INTRODUCTION

Our previous study found that dexamethasone-induced insulin resistance (IR) was involved in 5-hydroxytryptamine (5-HT) synthesis and 5-hydroxytryptamine 2 receptor (5-HT₂ R) in the periphery. The present study examined the effects of inhibitions of both peripheral 5-HT synthesis and 5-HT₂ R on dexamethasone-induced IR.

MATERIALS AND METHODS

Male rats were exposed to dexamethasone for 10 days, then treated with or without a 5-HT₂ R antagonist, sarpogrelate, a 5-HT synthetic inhibitor, carbidopa, alone or in combination for 20 days.

RESULTS

Dexamethasone-induced whole-body IR, with glucose intolerance, decreased insulin sensitivity, hyperglycemia, hyperinsulinemia and dyslipidemia, could be effectively abolished by sarpogrelate or/and carbidopa, whereas IR-related actions of dexamethasone in tissues were accompanied by increased 5-HT synthesis in the liver and visceral adipose, and upregulated 5-HT₂ R (5-HT_2A R and 5-HT_2B R) expression in these two tissues as well as in skeletal muscle. Sarpogrelate or/and carbidopa treatment significantly abolished dexamethasone-caused tissue-specific IR. In the liver, increased gluconeogenesis, triglycerides and very low-density lipoprotein syntheses with steatosis, and downregulated expression of plasmalemmal glucose transporter-2 were markedly reversed. In the visceral adipose and skeletal muscle, downregulated expression of plasmalemmal glucose transporter-4 was significantly reversed, and increased lipolysis was also reversed in the visceral adipose. Dexamethasone-induced activations of hepatic mammalian target of rapamycin serine²⁴⁴⁸ , and S6K threonine^389/412 phosphorylation were also abolished markedly by sarpogrelate or/and carbidopa. Co-treatment with sarpogrelate and carbidopa showed a synergistic effect on suppressing dexamethasone actions.

CONCLUSION

Inhibitions of both peripheral 5-HT synthesis and 5-HT₂ R are expected to be a dependable target for treatment of steroid-induced diabetes.

Important role of 5-hydroxytryptamine in glucocorticoid-induced insulin resistance in liver and intra-abdominal adipose tissue of rats

Aim/Introduction

Both glucocorticoids and 5‐hydroxytryptamine (5‐HT) have been shown to induce insulin resistance (IR) in hepatocytes and adipocytes. Here, we explore whether there is a correlation between them.

Materials and Methods

Except for the control group, male rats were exposed to dexamethasone treated with or without para‐chlorophenylalanine (pCPA), or carbidopa for 20 days. Except for the control group, buffalo rat liver 3A (BRL‐3A) cells were exposed to dexamethasone for 24 h, treated with or without pCPA, carbidopa, or clorgiline for 48 h, or exposed to 5‐HT treated with or without fluoxetine for 48 h. Whole‐body IR was determined by both glucose tolerance test and measurement of fasting blood glucose and insulin, whereas hepatocytes or adipocytes IR was determined by examining either hepatic gluconeogenesis, steatosis and glucose transporter 2 expression or lipolysis.

Results

Dexamethasone‐induced whole‐body IR, liver and intraabdominal adipose IR were accompanied by upregulated expressions of tryptophan hydroxylase‐1 and aromatic amino acid decarboxylase with increased 5‐HT level in both tissues, which were attenuated significantly by pCPA, inhibiting tryptophan hydroxylase‐1, or carbidopa, inhibiting aromatic amino acid decarboxylase. [Correction added on 22 September 2015, after first online publication: ‘inhibiting aromatic amino acid decarboxylase’ was duplicated and has been replaced by ‘tryptophan hydroxylase‐1’.] In the BRL‐3A cells, dexamethasone‐induced IR was also accompanied by upregulated 5‐HT synthesis in dose‐ and time‐dependent manners, and was attenuated by pCPA or carbidopa, but exacerbated by clorgiline, inhibiting monoamine oxidase‐A to further increase 5‐HT level. Dexamethasone also enhanced 5‐HT 2A and 2B receptor expressions in both tissues and BRL‐3A cells. Additionally, blocking 5‐HT transporter with fluoxetine significantly suppressed 5‐HT‐induced IR in BRL‐3A cells.

Conclusion

Enhancement of 5‐HT synthesis in liver and intra‐abdominal adipose is an important reason for glucocorticoids‐induced IR.