Roux-En-Y Gastric Bypass (RYGB) Surgery during High Liquid Sucrose Diet Leads to Gut Microbiota-Related Systematic Alterations.

Roux-en-Y gastric bypass (RYGB) surgery has been proven successful in weight loss and improvement of co-morbidities associated with obesity. Chronic complications such as malabsorption of micronutrients in up to 50% of patients underline the need for additional therapeutic approaches. We investigated systemic RYGB surgery effects in a liquid sucrose diet-induced rat obesity model. After consuming a diet supplemented with high liquid sucrose for eight weeks, rats underwent RYGB or control sham surgery. RYGB, sham pair-fed, and sham ad libitum-fed groups further continued on the diet after recovery. Notable alterations were revealed in microbiota composition, inflammatory markers, feces, liver, and plasma metabolites, as well as in brain neuronal activity post-surgery. Higher fecal 4-aminobutyrate (GABA) correlated with higher Bacteroidota and Enterococcus abundances in RYGB animals, pointing towards the altered enteric nervous system (ENS) and gut signaling. Favorable C-reactive protein (CRP), serine, glycine, and 3-hydroxybutyrate plasma profiles in RYGB rats were suggestive of reverted obesity risk. The impact of liquid sucrose diet and caloric restriction mainly manifested in fatty acid changes in the liver. Our multi-modal approach reveals complex systemic changes after RYGB surgery and points towards potential therapeutic targets in the gut-brain system to mimic the surgery mode of action.

The effects of 5-hydroxytryptophan in combination with different Fatty acids on gastrointestinal functions: a pilot experiment.

Background. Fat affects gastric emptying (GE). 5-Hydroxythryptophan (5-HTP) is involved in central and peripheral satiety mechanisms. Influence of 5-HTP in addition to saturated or monounsaturated fatty acids (FA) on GE and hormone release was investigated. Subjects/Methods. 24 healthy individuals (12f : 12m, 22-29 years, BMI 19-25.7 kg/m²) were tested on 4 days with either 5-HTP + short-chain saturated FA (butter), placebo + butter, 5-HTP + monounsaturated FA (olive oil), or placebo + olive oil in double-blinded randomized order. Two hours after FA/5-HTP or placebo intake, a (13)C octanoid acid test was conducted. Cortisol, serotonin, cholecystokinin (CCK), and ghrelin were measured, as were mood and GE. Results. GE was delayed with butter and was normal with olive (P < 0.05) but not affected by 5-HTP. 5-HTP supplementation did not affect serotonin levels. Food intake increased plasma CCK (F = 6.136; P < 0.05) irrespective of the FA. Ghrelin levels significantly decreased with oil/5-HTP (F = 9.166; P < 0.001). The diurnal cortisol profile was unaffected by FA or 5-HTP, as were ratings of mood, hunger, and stool urgency. Conclusion. Diverse FAs have different effects on GE and secretion of orexigenic and anorexigenic hormones. Supplementation of 5-HTP had no effect on plasma serotonin and central functions. Further studies are needed to explain the complex interplay.

Effect of tryptophan supplementation on diet-induced non-alcoholic fatty liver disease in mice.

Intestinal serotonin (5-hydroxytrypamine, 5-HT) metabolism is thought to play a role in gut functions by regulating motility, permeability and other functions of the intestine. In the present study, we investigated the effect of tryptophan (TRP), the precursor of 5-HT, supplementation on intestinal barrier functions and non-alcoholic fatty liver disease (NAFLD). An established mouse model of NAFLD induced by feeding a fructose-rich diet (N group) was used in the present study. TRP was administered orally for 8 weeks to C57BL/6J control or NAFLD mice. NAFLD-related liver parameters (hepatic TAG and Oil Red O staining), intestinal barrier parameters (tight-junction protein occludin and portal plasma lipopolysaccharides (LPS)) and 5-HT-related parameters (5-HT, 5-HT transporter (SERT) and motility) were measured. We observed reduced duodenal occludin protein concentrations (P= 0·0007), high portal plasma LPS concentrations (P= 0·005) and an elevated liver weight:body weight ratio (P= 0·01) in the N group compared with the parameters in the control group. TRP supplementation led to an increase in occludin concentrations (P= 0·0009) and consecutively reduced liver weight:body weight ratio (P= 0·009) as well as overall hepatic fat accumulation in the N group (P= 0·05). In addition, the N group exhibited reduced SERT protein expression (P= 0·002), which was normalised by TRP supplementation (P= 0·02). For the first time, our data indicate that oral TRP supplementation attenuates experimental NAFLD in mice. The underlying mechanisms are not clear, but probably involve stabilisation of the intestinal barrier in the upper small intestine and amelioration of the dysregulated intestinal serotonergic system.

Role of serotonin in fatty acid-induced non-alcoholic fatty liver disease in mice.

BACKGROUND: Saturated fatty acids are thought to be of relevance for the development of non-alcoholic fatty liver disease and obesity. However, the underlying mechanisms are poorly understood. In previous studies we found that food-derived carbohydrates such as fructose alter the intestinal serotonergic system while inducing fatty liver disease in mice. Here, we examined the effect of fatty acid quantity (11% versus 15%) and quality (saturated, monounsaturated, or polyunsaturated fatty acids) on hepatic fat accumulation, intestinal barrier and the intestinal serotonergic system. METHODS: C57BL/6 mice had free access to diets enriched with one of the three fatty acids or standard diet, for 8 weeks. In an additional experiment mice were fed diets enriched with saturated, monounsaturated fatty acids or standard diet supplemented with tryptophan (0.4 g/(kg.d), 8 weeks) or not. Hepatic fat accumulation, small intestinal barrier impairment and components of the serotonergic system were measured with RT-PCR, western blot or immunoassays. For statistical analysis t-test and one-way ANOVA with Tukey's post hoc test and Bartlett's test for equal variances was used. RESULTS: Hepatic triglycerides, liver weight and liver to body weight ratio were significantly changed depending on the fat quality but not fat quantity. In contrast, fat quantity but not quality decreased the expression of the tight junction proteins occludin and claudin-1 in the small intestine. These changes seemed to result in enhanced portal vein endotoxin concentrations and fatty liver disease after feeding diet enriched with saturated and monounsaturated fatty acids but not polyunsaturated fatty acids. Neither fatty acid quantity nor quality significantly influenced the intestinal serotonergic system. Similarly, tryptophan supplementation had no impact on small intestinal barrier or fatty liver disease. CONCLUSION: In conclusion, diets rich in saturated or monounsaturated fatty acids promote the development of fatty liver disease in mice, likely by a dysfunction of the small intestinal mucosal barrier.

Serotonin receptor type 3 antagonists improve obesity-associated fatty liver disease in mice.

Obesity is a major cause for nonalcoholic fatty liver disease (NAFLD). Previous studies suggested that alterations in intestinal motility and permeability contribute to the development of NAFLD. Serotonin and serotonin receptor type 3 (5-HT(3)R) are key factors in the regulation of intestinal motility and permeability. Therefore, we studied the effect of the 5-HT(3)R antagonists tropisetron and palonosetron on the development of NAFLD in leptin-deficient obese mice. Four-week-old ob/ob mice and lean controls were treated for 6 weeks orally with tropisetron or palonosetron at 0.2 mg/kg per day. We determined markers of liver damage and inflammation, portal endotoxin levels, and duodenal concentrations of serotonin, serotonin-reuptake transporter (SERT), occludin, and claudin-1. Tropisetron treatment significantly reduced liver fat content (-29%), liver inflammation (-56%), and liver cell necrosis (-59%) in ob/ob mice. The beneficial effects of tropisetron were accompanied by a decrease in plasma alanine aminotransferase and portal vein plasma endotoxin levels, an attenuation of enhanced MyD88 and tumor necrosis factor-α mRNA expression in the liver, and an increase of tight junction proteins in the duodenum. Tropisetron treatment also caused a reduction of elevated serotonin levels and an increase of SERT in the duodenum of ob/ob mice. Palonosetron had similar effects as tropisetron with regard to the reduction of liver fat and other parameters. Tropisetron and palonosetron are effective in attenuating NAFLD in a genetic mouse model of obesity. The effect involves the intestinal nervous system, resulting in a reduction of endotoxin influx into the liver and subsequently of liver inflammation and fat accumulation.