Serotonin availability in rat colon is reduced during a Western diet model of obesity

Overweight/bowel dysmotility crosslinking and analogous laxative actions of two edible wild fruits in obese/constipated rats

BACKGROUND

The prompt development of obesity/constipation is the most serious problem for both children and adults. Limited studies suggested an association between them but lacked preclinical studies. This study allows to evaluate their crosslink and to compare the aqueous extracts laxative actions of two edible wild fruits of Arbutus unedo (AUAE) and Crataegus monogyna (CMAE) in constipated high-fat diet (HFD) rats.

METHODS

Wistar rats were divided into experimental groups for 13 weeks: standard (SD) and HFD groups. SD-rats were randomly redivided into 2 groups: SD and SD + Loperamide (LOP, 3 mg/kg, b.w.). HFD-rats were randomly reseparated into HFD-group, (HFD + LOP)-group, [HFD + Yohimbine (YOH, 2 mg/kg, b.w.)]-group, [HFD+ LOP]-groups+ various doses of AUAE or CMAE (75, 150, and 300 mg/kg, b.w.). Diversified indicators were investigated to achieve the expected objectives, including; fecal parameters, gastrointestinal transit (GIT), gastric emptying (GE), oxidative stress-(OxS), blood biochemical analysis, and accompanied small/large bowel histological modification.

KEY RESULTS

The liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS) analysis of AUAE and CMAE allowed the identification of 11 and 6 phenolic compounds, respectively. In HFD-rats, the subsequent dysregulation of GI motility was markedly aggravated. More importantly, with the same way (CMAE and AUAE)-treated groups showed alleviated outcomes for the following: most stool parameters, GIT, and GE were remarkably recovered; a similar recovery pattern was observed in the histopathological structure, OxS, and blood biochemical indicators.

CONCLUSIONS & INFERENCES

Our results experimentally confirmed the crosslink between overweight and constipation and both fruits have potential as functional foods to reduce metabolic risk of the obesity associated with bowel dysmotility.

Association of Ultra-processed Food and Unprocessed or Minimally Processed Food Consumption With Bowel Habits Among U.S. Adults

BACKGROUND & AIMS

Ultra-processed foods (UPFs) may have a negative impact on bowel habits. We aimed to assess the association between UPF and unprocessed or minimally processed food (MPF) intake and bowel habits among adults in the United States (U.S.).

METHODS

We performed a cross-sectional study using data from the National Health and Nutrition Examination Survey (2005-2010). We used two 24-hour dietary recalls and, based on the Nova classification, calculated intakes of UPFs and MPFs. Constipation and diarrhea were defined using the Bristol Stool Form Scale and stool frequency. We performed survey-weighted logistic regression and substitution analysis to estimate the odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Among 12,716 U.S. adults, there were 1290 cases of constipation and 1067 cases of diarrhea. Median UPF and MPF intakes were 26.5% and 66.2% of total grams per day, respectively. Greater UPF consumption (in % gram/d) was associated with higher odds of constipation (adjusted OR [aORQ4 vs Q1], 2.20; 95% CI, 1.76-2.74) (Ptrend < .001) but not diarrhea (aORQ4 vs Q1, 0.82; 95% CI, 0.62-1.09) (Ptrend = .12). Increased MPF consumption was associated with lower odds of constipation (aORQ4 vs Q1, 0.46; 95% CI, 0.370-0.57) (Ptrend < .001). Associations with constipation were attenuated after adjusting for diet quality (aORQ4 vs Q1, UPF, 1.53; MPF, 0.69). Substituting 10% of UPF intake with an equivalent proportion of MPFs was associated with lower odds of constipation (aOR, 0.90; 95% CI, 0.87-0.93).

CONCLUSIONS

UPF intake was associated with higher odds of constipation, whereas the odds were lower with greater MPF consumption. The effect of food processing on bowel habits was independent of diet quality.

Similarities and differences in constipation phenotypes between Lep knockout mice and high fat diet-induced obesity mice

CRISPR-Cas9-mediated leptin (Lep) knockout (KO) mice exhibited prominent phenotypes for constipation, even though they were not compared with other model animals. This study compared the stool excretion, gastrointestinal motility, histological structure, mucin secretion, and enteric nerve function in Lep KO and high fat diet (HFD)-treated mice to determine if there were differences in their phenotypes for constipation. Most obesity phenotypes, including fat weight, adipocyte size, expression of lipolytic proteins (HSL, perilipin, and ATGL), and glucose concentrations, were detected similarly in the Lep KO and HFD-treated mice. They showed a similar decrease in the excretion parameters, including the stool number, weight, and water content, while the same pattern was detected in the gastrointestinal motility and intestinal length. A similar decrease in the mucosal layer thickness, muscle thickness, ability for mucin secretion, and expression of water channel (aquaporin 3 and 8) genes was detected in the mid-colon of the Lep KO and HFD-treated mice, but the alteration rate in some levels was greater in the HFD-treated group than the Lep KO mice. On the other hand, the levels of c-kit, nNOS, NSE, and PGP9.5 expression for the enteric neurons and intestitial cells of Cajal (ICC) were remarkably lower in the mid-colon of the HFD-treated mice than in the Lep KO mice, but the level of most proteins in both groups remained lower than those in the control group. A similar alteration pattern in the expression of muscarinic acetylcholine receptors (mAChRs) and serotonin receptors was detected in the Lep KO and HFD-treated mice. These results suggest that most phenotypes for obesity-induced constipation were similarly detected in the Lep KO and HFD-treated mice, but there was a difference in the regulatory function of the enteric nervous system (ENS).

Effect of chronic restraint stress and western-diet feeding on colonic regulatory gene expression in mice

BACKGROUND

Diet-induced obesity (DIO) and psychological stress are significant independent regulators of gastrointestinal physiology; however, our understanding of how these two disorders influence the host-microbe interface is still poorly characterized. The aim of this study was to assess the combined influences of diet-induced obesity and psychological stress on microbiome composition and colonic gene expression.

METHODS

C57BL/6J mice (n = 48) were subject to a combination of 22 weeks of Western diet (WD) feeding and a chronic restraint stressor (CRS) for the last 4 weeks of feeding. At the end of the combined intervention, microbiome composition was determined from cecal contents, and colonic tissue gene expression was assessed by multiplex analysis using NanoString nCounter System and real-time qPCR.

RESULTS

WD feeding induced a DIO phenotype with increased body weight, worsened metabolic markers, and alterations to microbiome composition. CRS reduced body weight in both dietary groups while having differential effects on glucose metabolism. CRS improved the Firmicutes/Bacteroidetes ratio in WD-fed animals while expanding the Proteobacteria phyla. Significantly lower expression of colonic Tlr4 (p = 0.008), Ocln (p = 0.004), and Cldn3 (p = 0.004) were noted in WD-fed animals compared to controls with no synergistic effects observed when combined with CRS. No changes to colonic expression of downstream inflammatory mediators were observed. Interestingly, higher levels of expression of Cldn2 (p = 0.04) and bile acid receptor Nr1h4 (p = 0.02) were seen in mice exposed to CRS.

CONCLUSION

Differential but not synergistic effects of WD and CRS were noted at the host-microbe interface suggesting multifactorial responses that require further investigation.

High-fat diets on the enteric nervous system: Possible interactions and mechanisms underlying dysmotility

Obesity is a chronic disease that affects various physiological systems. Among them, the gastrointestinal tract appears to be a main target of this disease. High-fat diet (HFD) animal models can help recapitulate the classic signs of obesity and present a series of gastrointestinal alterations, mainly dysmotility. Because intestinal motility is governed by the enteric nervous system (ENS), enteric neurons, and glial cells have been studied in HFD models. Given the importance of the ENS in general gut physiology, this review aims to discuss the relationship between HFD-induced neuroplasticity and gut dysmotility observed in experimental models. Furthermore, we highlight components of the gut environment that might influence enteric neuroplasticity, including gut microbiota, enteric glio-epithelial unit, serotonin release, immune cells, and disturbances such as inflammation and oxidative stress.

Serotonin Deficiency Is Associated With Delayed Gastric Emptying

BACKGROUND & AIMS

Gastrointestinal (GI) motility is regulated by serotonin (5-hydroxytryptamine [5-HT]), which is primarily produced by enterochromaffin (EC) cells in the GI tract. However, the precise roles of EC cell-derived 5-HT in regulating gastric motility remain a major point of conjecture. Using a novel transgenic mouse line, we investigated the distribution of EC cells and the pathophysiologic roles of 5-HT deficiency in gastric motility in mice and humans.

METHODS

We developed an inducible, EC cell-specific Tph1CreERT2/+ mouse, which was used to generate a reporter mouse line, Tph1-tdTom, and an EC cell-depleted line, Tph1-DTA. We examined EC cell distribution, morphology, and subpopulations in reporter mice. GI motility was measured in vivo and ex vivo in EC cell-depleted mice. Additionally, we evaluated 5-HT content in biopsy and plasma specimens from patients with idiopathic gastroparesis (IG).

RESULTS

Tph1-tdTom mice showed EC cells that were heterogeneously distributed throughout the GI tract with the greatest abundance in the antrum and proximal colon. Two subpopulations of EC cells were identified in the gut: self-renewal cells located at the base of the crypt and mature cells observed in the villi. Tph1-DTA mice displayed delayed gastric emptying, total GI transit, and colonic transit. These gut motility alterations were reversed by exogenous provision of 5-HT. Patients with IG had a significant reduction of antral EC cell numbers and 5-HT content, which negatively correlated with gastric emptying rate.

CONCLUSIONS

The Tph1CreERT2/+ mouse provides a powerful tool to study the functional roles of EC cells in the GI tract. Our findings suggest a new pathophysiologic mechanism of 5-HT deficiency in IG.

Altered intestinal epithelial nutrient transport: an underappreciated factor in obesity modulated by diet and microbiota

Dietary nutrients absorbed in the proximal small intestine and assimilated in different tissues have a profound effect on overall energy homeostasis, determined by a balance between body's energy intake and expenditure. In obesity, altered intestinal absorption and consequently tissue assimilation of nutrients may disturb the energy balance leading to metabolic abnormalities at the cellular level. The absorption of nutrients such as sugars, amino acids and fatty acids released from food digestion require high-capacity transporter proteins expressed in the intestinal epithelial absorptive cells. Furthermore, nutrient sensing by specific transporters/receptors expressed in the epithelial enteroendocrine cells triggers release of gut hormones involved in regulating energy homeostasis via their effects on appetite and food intake. Therefore, the intestinal epithelial cells play a pivotal role in the pathophysiology of obesity and associated complications. Over the past decade, gut microbiota has emerged as a key factor contributing to obesity via its effects on digestion and absorption of nutrients in the small intestine, and energy harvest from dietary fiber, undigested component of food, in the large intestine. Various mechanisms of microbiota effects on obesity have been implicated. However, the impact of obesity-associated microbiota on the intestinal nutrient transporters needs extensive investigation. This review marshals the limited studies addressing the altered structure and function of the gut epithelium in obesity with special emphasis on nutrient transporters and role of diet and microbiota. The review also discusses the thoughts and controversies and research gaps in this field.

Molecular Characterization of Constipation Disease as Novel Phenotypes in CRISPR-Cas9-Generated Leptin Knockout Mice with Obesity

(1) Background: We characterized a novel animal model with obesity-induced constipation because constipation is rarely known in genetically engineered mice (GEM); (2) Methods: The changes in the constipation parameters and mechanisms were analyzed in CRISPR-Cas9-mediated leptin (Lep) knockout (KO) mice from eight to 24 weeks; (3) Results: Significant constipation phenotypes were observed in the Lep KO mice since 16 weeks old. These mice showed a significant decrease in the gastrointestinal motility, mucosal layer thickness and ability for mucin secretion as well as the abnormal ultrastructure of Lieberkühn crypts in the transverse colon. The density or function of the enteric neurons, intestinal Cajal cells (ICC), smooth muscle cells, and the concentration of gastrointestinal (GI) hormones for the GI motility were remarkably changed in Lep KO mice. The downstream signaling pathway of muscarinic acetylcholine receptors (mAChRs) were activated in Lep KO mice, while the expression of adipogenesis-regulating genes were alternatively reduced in the transverse colon of the same mice; (4) Conclusions: These results provide the first strong evidence that Lep KO mice can represent constipation successfully through dysregulation of the GI motility mediated by myenteric neurons, ICC, and smooth muscle cells in the transverse colon during an abnormal function of the lipid metabolism.

High-Fat Diet Causes Constipation in Mice via Decreasing Colonic Mucus

BACKGROUND

Constipation is one of the most common gastrointestinal complaints. Although the causes of constipation are varied, dietary habits have a significant influence. Excessive fat intake is suggested as one of the main causes of constipation; however, the exact mechanism is unknown.

AIMS

To investigate whether a high-fat diet (HFD) causes constipation in mice and to clarify the underlying mechanism, focusing on the amount of colonic mucus.

METHODS

Six-week-old male C57BL/6 mice were randomly divided into two groups: mice fed with HFD and those with normal chow diet (NCD). Fecal weight, water content, total gastrointestinal transit time, and colon transit time were measured to determine whether the mice were constipated. The colonic mucus was evaluated by immunostaining and quantified by spectrometry. Malondialdehyde (MDA) was measured using the thiobarbituric acid (TBA) test as a marker for oxidative stress.

RESULTS

Compared to the NCD group, the weight of feces was less in the HFD group. In the functional experiment, the total gastrointestinal transit time and colon transit time were longer in the HFD group. Furthermore, HFD significantly reduced the amount of colonic mucus. In addition, the reduction in colonic mucus caused by surfactant resulted in constipation in the NCD group.

CONCLUSIONS

HFD causes constipation with delayed colon transit time possibly via the reduction in colonic mucus in mice.

Gut-Derived Serotonin Contributes to the Progression of Non-Alcoholic Steatohepatitis via the Liver HTR2A/PPARγ2 Pathway

The precipitous increase in occurrence of non-alcoholic steatohepatitis (NASH) is a serious threat to public health worldwide. The pathogenesis of NASH has not yet been thoroughly studied. We aimed to elucidate the interplay between serotonin (5-hydroxytryptamine, 5-HT) and NASH. The serum 5-HT levels in patients with non-alcoholic fatty liver disease (NAFLD) and a rat fed with high fat-sucrose diet (HFSD) were evaluated using liquid chromatography-hybrid quadrupole time-of-flight mass spectrometry (LC-QTOF MS)/MS. The peripheral Tph1 inhibitor, LP533401, and a tryptophan (TRP)-free diet were administered to rats with NASH, induced by HFSD. BRL-3A cells were treated with 1 mM free fatty acids (FFAs) and/or 50 μM 5-HT, and then small interfering RNA (siRNA) targeting the 5-HT2A receptor (HTR2A) and the PPARγ pharmaceutical agonist, pioglitazone, were applied. We found a marked correlation between 5-HT and NASH. The absence of 5-HT, through the pharmaceutical blockade of Tph1 (LP533401) and dietary control (TRP-free diet), suppressed hepatic lipid load and the expression of inflammatory factors (Tnfα, Il6, and Mcp-1). In BRL-3A cells, 50 μM 5-HT induced lipid accumulation and upregulated the expression of lipogenesis-ralated genes (Fas, Cd36, and Plin2) and the inflammatory response. Specifically, HTR2A knockdown and evaluation of PPARγ agonist activity revealed that HTR2A promoted hepatic steatosis and inflammation by activating PPARγ2. These results suggested that duodenal 5-HT was a risk factor in the pathological progression of NASH. Correspondingly, it may represent an attractive therapeutic target for preventing the development of NASH via the regulation of the HTR2A/PPARγ2 signaling pathway.

Effects of purified fibre-mixture supplementation of gestation diet on gut microbiota, immunity and reproductive performance of sows

This experiment was conducted to investigate the effects of a purified fibre-mixture (FM, 50% guar gum, 50% cellulose) supplementation of gestation diet on the immunity, faecal microbial composition and reproductive performance of sows. A day after breeding, 68 multiparous sows were randomly allocated to receive treatment with a control (CON) diet or a diet containing 3% FM (FM diet). Results showed the FM diet to be associated with a significant increase in the number of live-born piglets relative to CON (13.65 vs. 12.47, p < .05). In addition, this FM diet coincided with significantly increased faecal concentrations of butyrate on day 30 and propionate on day 100 (p < .05), with trends towards increased propionate on day 30 and increased short-chain fatty acids (SCFAs) on days 30 and 110 (p < .1). Meanwhile, FM addition markedly increased the abundance of representative SCFAs producing-related genera as Roseburia on days 30 and 110 (p < .05), Eubacterium-hallii-group on days 30 and 110 (p < .05), and Bacteroides on day 110 of gestation (p < .05). The serotonin concentration on day 110 of gestation had increased (p < .05) and that on day 30 of gestation (p < .1) exhibited a tendency to increase with the FM-supplemented diet in comparison with the CON. Besides, FM supplementation caused an increase in serum interleukin-10 concentrations on days 30 (p < .05) and 110 of gestation (p < .1), and a decrease in interferon-γ concentration on day 30 of gestation (p < .05). Together these results indicated that purified FM was able to improve sow reproductive performance through a mechanism potentially linked with a bias towards type-2 helper T-cell differentiation that supported embryonic survival and thereby improve reproductive yields. Changes in metabolites produced by the intestinal microbiome may thus have an impact on host immunity and reproductive performance.

Prevalence of Functional Constipation and Relationship with Dietary Habits in 3- to 8-Year-Old Children in Japan

Objectives

To determine the prevalence and effect of dietary habits on functional constipation in preschool and early elementary school children in Japan.

Study Design

A total of 3595 children aged 3 to 8 years from 28 nursery schools and 22 elementary schools in Yokohama City, Kanagawa Prefecture, Japan, were evaluated. The subjects were divided into a functional constipation group and a nonfunctional constipation group according to the Rome III criteria. Dietary intake data were collected using a brief-type, self-administered, diet-history questionnaire validated for Japanese preschool-aged children.

Results

Of the 3595 subjects evaluated, 718 (20.0%) had functional constipation. The association between functional constipation and gender was not statistically significant (p = 0.617). A decrease in bowel frequency was observed in 15.9% of those with functional constipation. There was no significant difference in the proportion of participants in the constipation group by age (p = 0.112). Binomial logistic regression analysis indicated that only fat per 100 kcal positively correlated with functional constipation [odds ratio = 1.216, 95% confidence interval: 1.0476–1.412].

Conclusions

Functional constipation is common among children in preschool and early elementary school in urban areas of Japan. Parents should pay attention to constipation-related symptoms other than defecation frequency. A high-fat diet should be avoided to prevent functional constipation.

Is There a Role for Bioactive Lipids in the Pathobiology of Diabetes Mellitus?

Inflammation, decreased levels of circulating endothelial nitric oxide (eNO) and brain-derived neurotrophic factor (BDNF), altered activity of hypothalamic neurotransmitters (including serotonin and vagal tone) and gut hormones, increased concentrations of free radicals, and imbalance in the levels of bioactive lipids and their pro- and anti-inflammatory metabolites have been suggested to play a role in diabetes mellitus (DM). Type 1 diabetes mellitus (type 1 DM) is due to autoimmune destruction of pancreatic β cells because of enhanced production of IL-6 and tumor necrosis factor-α (TNF-α) and other pro-inflammatory cytokines released by immunocytes infiltrating the pancreas in response to unknown exogenous and endogenous toxin(s). On the other hand, type 2 DM is due to increased peripheral insulin resistance secondary to enhanced production of IL-6 and TNF-α in response to high-fat and/or calorie-rich diet (rich in saturated and trans fats). Type 2 DM is also associated with significant alterations in the production and action of hypothalamic neurotransmitters, eNO, BDNF, free radicals, gut hormones, and vagus nerve activity. Thus, type 1 DM is because of excess production of pro-inflammatory cytokines close to β cells, whereas type 2 DM is due to excess of pro-inflammatory cytokines in the systemic circulation. Hence, methods designed to suppress excess production of pro-inflammatory cytokines may form a new approach to prevent both type 1 and type 2 DM. Roux-en-Y gastric bypass and similar surgeries ameliorate type 2 DM, partly by restoring to normal: gut hormones, hypothalamic neurotransmitters, eNO, vagal activity, gut microbiota, bioactive lipids, BDNF production in the gut and hypothalamus, concentrations of cytokines and free radicals that results in resetting glucose-stimulated insulin production by pancreatic β cells. Our recent studies suggested that bioactive lipids, such as arachidonic acid, eicosapentaneoic acid, and docosahexaenoic acid (which are unsaturated fatty acids) and their anti-inflammatory metabolites: lipoxin A4, resolvins, protectins, and maresins, may have antidiabetic actions. These bioactive lipids have anti-inflammatory actions, enhance eNO, BDNF production, restore hypothalamic dysfunction, enhance vagal tone, modulate production and action of ghrelin, leptin and adiponectin, and influence gut microbiota that may explain their antidiabetic action. These pieces of evidence suggest that methods designed to selectively deliver bioactive lipids to pancreatic β cells, gut, liver, and muscle may prevent type 1 and type 2 DM.

Other Risks/Possible Benefits of Obesity

Obesity is not a cosmetic or social issue; it is an animal health issue. The metabolic effects of obesity on insulin resistance and development of hyperlipidemia and the mechanical stress excess weight places on the musculoskeletal system are well established in the literature. Additional health risks from obesity, such as fatty accumulation in the liver, intestinal bacterial dysbiosis, and changes to renal architecture, are less well understood, but have been demonstrated to occur clinically in obese animals and may lead to deleterious long-term health effects. Keeping dogs and cats lean lowers their risk for development of certain diseases and leads to a longer and better quality of life.

Association of high dietary saturated fat intake and uncontrolled diabetes with constipation: evidence from the National Health and Nutrition Examination Survey

BACKGROUND

Constipation is highly prevalent in the United States. The association of dietary fat intake with constipation has not been well studied. We recently reported that mice fed a high-fat diet had higher incidence of constipation than regular diet fed mice. The aim of this study was to assess if increased intake of dietary saturated fat in humans is also associated with higher risk of constipation and reduced stool frequency.

METHODS

Analyses were based on data from 6207 adults (≥20 years) from the 2005-2006 and 2007-2008 cycles of the National Health and Nutrition Examination Surveys who had completed the bowel health questionnaire. Constipation was defined as a stool frequency of less than three times per week. Multivariable logistic regression analysis was used to calculate adjusted prevalence odds ratio (OR) estimates. Statistical analyses were performed using R and RStudio softwares.

KEY RESULTS

The prevalence of constipation in this sample was 3.1%. After multivariable adjustment high saturated fat remained associated with constipation. The OR for high saturated fat intake associated with constipation was much higher in diabetics above 65 years, especially in non-Hispanic blacks, females, and those with poor glycemic control, compared to the control group.

CONCLUSIONS & INFERENCES

To the best of our knowledge, this is the first report to investigate the association of high saturated fat diet, bowel frequency, and diabetes. This study demonstrates that a high dietary saturated fat intake is associated with significant increase in the prevalence of constipation, especially in the uncontrolled diabetic, non-Hispanic black, female patients.

Association of obesity with serum leptin, adiponectin, and serotonin and gut microflora in beagle dogs

Background

Serotonin (5‐hydroxytryptamine, 5HT) is involved in hypothalamic regulation of energy consumption. Also, the gut microbiome can influence neuronal signaling to the brain through vagal afferent neurons. Therefore, serotonin concentrations in the central nervous system and the composition of the microbiota can be related to obesity.

Objective

To examine adipokine, and, serotonin concentrations, and the gut microbiota in lean dogs and dogs with experimentally induced obesity.

Animals

Fourteen healthy Beagle dogs were used in this study.

Methods

Seven Beagle dogs in the obese group were fed commercial food ad libitum, over a period of 6 months to increase their weight and seven Beagle dogs in lean group were fed a restricted amount of the same diet to maintain optimal body condition over a period of 6 months. Peripheral leptin, adiponectin, 5HT, and cerebrospinal fluid (CSF‐5HT) levels were measured by ELISA. Fecal samples were collected in lean and obese groups 6 months after obesity was induced. Targeted pyrosequencing of the 16S rRNA gene was performed using a Genome Sequencer FLX plus system.

Results

Leptin concentrations were higher in the obese group (1.98 ± 1.00) compared to those of the lean group (1.12 ± 0.07, P = .025). Adiponectin and 5‐hydroytryptamine of cerebrospinal fluid (CSF‐5HT) concentrations were higher in the lean group (27.1 ± 7.28) than in the obese group (14.4 ± 5.40, P = .018). Analysis of the microbiome revealed that the diversity of the microbial community was lower in the obese group. Microbes from the phylum Firmicutes (85%) were predominant group in the gut microbiota of lean dogs. However, bacteria from the phylum Proteobacteria (76%) were the predominant group in the gut microbiota of dogs in the obese group.

Conclusions and Clinical Importance

Decreased 5HT levels in obese group might increase the risk of obesity because of increased appetite. Microflora enriched with gram‐negative might be related with chronic inflammation status in obese dogs.

Association of central serotonin transporter availability and body mass index in healthy Europeans

Serotonin-mediated mechanisms, in particular via the serotonin transporter (SERT), are thought to have an effect on food intake and play an important role in the pathophysiology of obesity. However, imaging studies that examined the correlation between body mass index (BMI) and SERT are sparse and provided contradictory results. The aim of this study was to further test the association between SERT and BMI in a large cohort of healthy subjects.

METHODS

127 subjects of the ENC DAT database (58 females, age 52 ± 18 years, range 20-83, BMI 25.2 ± 3.8 kg/m(2), range 18.2-41.1) were analysed using region-of-interest (ROI) and voxel-based approaches to calculate [(123)I]FP-CIT specific-to-nonspecific binding ratios (SBR) in the hypothalamus/thalamus and midbrain/brainstem as SERT-specific target regions.

RESULTS

In the voxel-based analysis, SERT availability and BMI were positively associated in the thalamus, but not in the midbrain. In the ROI-analysis, the interaction between gender and BMI showed a trend with higher correlation coefficient for men in the midbrain albeit not significant (0.033SBRm(2)/kg, p=0.1).

CONCLUSIONS

The data are in agreement with previous PET findings of an altered central serotonergic tone depending on BMI, as a probable pathophysiologic mechanism in obesity, and should encourage further clinical studies in obesity targeting the serotonergic system.

Leptin, adiponectin and serotonin levels in lean and obese dogs

Background

Serotonin (5-hydroytryptamine or 5HT) is associated with numerous behavioral and psychological factors and is a biochemical marker of mood. 5HT is involved in the hypothalamic regulation of energy consumption. 5HT controls appetite in the central nerve system (CNS) and stimulates intestinal mobility. There are few studies looking at the role of 5HT and the relationship between peripheral circulating serotonin and obesity. The aim of this study was to find any differences in leptin, adiponectin, and 5HT between lean and obese dogs and to identify correlations among these factors.

Results

Leptin, triglyceride (TG) and cholesterol levels were higher in the obese group (all p < 0.01). Adiponectin and 5HT levels were higher in the lean group compared to the obese group (p < 0.01). Leptin (r = 0.628, p < 0.01), TG (r = 0.491, p < 0.01) and cholesterol (r = 0.419, p < 0.01) were positively correlated with body condition score (BCS), and adiponectin (r = -0.446, p < 0.01) and 5HT (r = -0.490, p < 0.01) were negatively correlated with BCS. Leptin was negatively correlated with adiponectin (r = -0.294, p < 0.01) and 5HT (r = -0.343, p < 0.01). 5HT was negatively correlated with leptin (r = -0.343, p < 0.01), TG (r = -0.268, p < 0.05) and cholesterol (r = -0.357, p < 0.05).

Conclusions

5HT is an important appetite control neurotransmitter, but there are limited studies for 5HT levels related to obesity in dogs. To the best of our knowledge, this is the first study to evaluate peripheral 5HT levels in obese dogs. From this research, we can assume that 5HT may be correlated with canine obesity. Further studies will be needed to further elucidate the role of low serum 5HT levels in canine obesity.

MicroRNA 375 mediates palmitate-induced enteric neuronal damage and high-fat diet-induced delayed intestinal transit in mice

BACKGROUND & AIMS

A high-fat diet (HFD) can cause serious health problems, including alteration of gastrointestinal transit, the exact mechanism of which is not clear. Several microRNAs (miRNAs) are involved in energy homeostasis, lipid metabolism, and HFD-induced weight gain. We investigated the role of miRNAs in HFD-induced damage to the enteric nervous system.

METHODS

Male mice were fed a HFD (60% calories from fat) or regular diets (18% calories from fat) for 11 weeks. Mice on regular diets and HFDs were given intraperitoneal injections of Mir375 inhibitor or a negative control. Body weights, food intake, stool indices, and gastrointestinal transit (following Evans blue gavage) were measured. An enteric neuronal cell line (immorto-fetal enteric neuronal) and primary enteric neurons were used for in vitro studies.

RESULTS

HFD delayed intestinal transit, which was associated with increased apoptosis and loss of colonic myenteric neurons. Mice fed a low-palmitate HFD did not develop a similar phenotype. Palmitate caused apoptosis of enteric neuronal cells associated with mitochondrial dysfunction and endoplasmic reticulum stress. Palmitate significantly increased the expression of Mir375 in vitro; transfection of cells with a Mir375 inhibitor prevented the palmitate-induced enteric neuronal cell apoptosis. Mir375 expression was increased in myenteric ganglia of mice fed HFD and associated with decreased levels of Mir375 target messenger RNAs, including Pdk1. Systemic injection of a Mir375 inhibitor for 5 weeks prevented HFD-induced delay in intestinal transit and morphologic changes.

CONCLUSIONS

HFDs delay colonic transit, partly by inducing apoptosis in enteric neuronal cells. This effect is mediated by Mir375 and is associated with reduced levels of Pdk1. Mir375 might be targeted to increase survival of enteric neurons and gastrointestinal motility.

Properties of myenteric neurones and mucosal functions in the distal colon of diet-induced obese mice

Colonic transit and mucosal integrity are believed to be impaired in obesity. However, a comprehensive assessment of altered colonic functions, inflammatory changes and neuronal signalling of obese animals is missing. In mice, we studied the impact of diet-induced obesity (DIO) on: (i) in vivo colonic transit; (ii) signalling in the myenteric plexus by recording responses to nicotine and 2-methyl-5-hydroxytryptamine (2-methyl-5-HT), together with the expression of tryptophan hydroxylase (TPH) 1 and 2, serotonin reuptake transporter, choline acetyltransferase and the paired box gene 4; and (iii) expression of proinflammatory cytokines, epithelial permeability and density of macrophages, mast cells and enterochromaffin cells. Compared with controls, colon transit and neuronal sensitivity to nicotine and 2-methyl-5-HT were enhanced in DIO mice fed for 12 weeks. This was associated with increased tissue acetylcholine and 5-hydroxytryptamine (5-HT) content, and increased expression of TPH1 and TPH2. In DIO mice, upregulation of proinflammatory cytokines was found in fat tissue, but not in the gut wall. Accordingly, mucosal permeability or integrity was unaltered without signs of immune cell infiltration in the gut wall. Body weight showed positive correlations with adipocyte markers, tissue levels of 5-HT and acetylcholine, and the degree of neuronal sensitization. DIO mice fed for 4 weeks showed no neuronal sensitization, had no signs of gut wall inflammation and showed a smaller increase in leptin, interleukin-6 and monocyte chemoattractant protein 1 expression in fat tissue. DIO is associated with faster colonic transit and impacts on acetylcholine and 5-HT metabolism with enhanced responsiveness of enteric neurones to both mediators after 12 weeks of feeding. Our study demonstrates neuronal plasticity in DIO prior to the development of a pathological histology or abnormal mucosal functions. This questions the common assumption that increased mucosal inflammation and permeability initiate functional disorders in obesity.