Constitutive basal and stimulated human small bowel contractility is enhanced in obesity

Understanding the gastrointestinal tract in obesity: From gut motility patterns to enzyme secretion

BACKGROUND AND PURPOSE

The pathophysiology of obesity has been the product of extensive research, revealing multiple interconnected mechanisms contributing to body weight regulation. The regulation of energy balance involves an intricate network, including the gut-neuroendocrine interplay. As a consequence, research on the gut-brain-microbiota axis in obesity has grown extensively. The physiology of the gastrointestinal tract, far from being underexplored, has significant implications for the development of specific complications in people living with obesity across the fields of gastroenterology, nutrition, and pharmacology. Clinical research indicates higher fasting bile acids serum levels, and blunted postprandial increases in bilious secretions in people living with obesity. Findings are less straightforward for the impact of obesity on gastric emptying with various studies reporting accelerated, normal, or delayed gastric emptying rates. Conversely, the effect of obesity on gastrointestinal pH, gastrointestinal transit, and gastric and pancreatic enzyme secretion is largely unknown. In this review, we explore the current evidence on the gastrointestinal physiology of obesity.

Characterizing the Suture Pullout Force for Human Small Bowel

Performing a small bowel anastomosis, or reconnecting small bowel segments, remains a core competency and critical step for the successful surgical management of numerous bowel and urinary conditions. As surgical education and technology moves toward improving patient outcomes through automation and increasing training opportunities, a detailed characterization of the interventional biomechanical properties of the human bowel is important. This is especially true due to the prevalence of anastomotic leakage as a frequent (3.02%) postoperative complication of small bowel anastomoses. This study aims to characterize the forces required for a suture to tear through human small bowel (suture pullout force, SPOF), while analyzing how these forces are affected by tissue orientation, suture material, suture size, and donor demographics. 803 tests were performed on 35 human small bowel specimens. A uni-axial test frame was used to tension sutures looped through 10 × 20 mm rectangular bowel samples to tissue failure. The mean SPOF of the small bowel was 4.62±1.40 N. We found no significant effect of tissue orientation (p = 0.083), suture material (p = 0.681), suture size (p = 0.131), age (p = 0.158), sex (p = .083), or body mass index (BMI) (p = 0.100) on SPOF. To our knowledge, this is the first study reporting human small bowel SPOF. Little research has been published about procedure-specific data on human small bowel. Filling this gap in research will inform the design of more accurate human bowel synthetic models and provide an accurate baseline for training and clinical applications.

The Influence of Obesity on Small Bowel Capsule Endoscopy

Objective

Intestinal motility may be different in obese and nonobese patients, but this has not been determined. Here, we sought to evaluate the effect of obesity on small bowel capsule endoscopy (SBCE). Patients and Methods. We retrospectively analyzed the cases of the 340 patients who underwent SBCE for small intestinal disease (excluding cases of unobservable total small bowel, small bowel stenosis, and bowel resection) at our hospital during the period January 2014 to December 2020 to extract patient background factors and the bowel transit times of SBCE according to the presence/absence of obesity (defined as a body mass index (BMI) ≥ 25 kg/m²).

Results

The obese group was 54 patients (nonobese, n = 286). The small bowel transit time (SBTT) was significantly shorter in the obese patients compared to the nonobese patients (p = 0.0026), and when we divided the patients by their short/long SBTTs using 216.5 min as the cutoff, we observed significant between-group differences in the patients' age (≥60 years) and in the patients' hospitalization status at the time of the SBCE examination. A multivariate analysis revealed that hospitalized status at the examination is a factor contributing significantly to a long SBTT (OR 0.25, 95% CI: 0.15–0.42, p < 0.0001). An analysis using the outpatient/inpatient conditions showed that obesity was an independent factor in the inpatient status at the SBCE examination with a significant short SBTT (OR 2.91, 95% CI: 1.06–7.97, p = 0.0380). Constipation at the examination was also a factor contributing to a long SBTT (OR 0.26, 95% CI: 0.07–0.99, p = 0.0493).

Conclusion

The SBTT of the SBCE was significantly shorter in the obese patients. This tendency was especially evident in the hospitalized state.

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.

Effect of obesity on gastrointestinal transit, pressure and pH using a wireless motility capsule

BACKGROUND

Despite the increasing prevalence and medical burden of obesity, the understanding of gastrointestinal physiology in obesity is scarce, which hampers drug development.

AIM

To investigate the effect of obesity and food intake on gastrointestinal transit, pressure and pH.

MATERIAL AND METHODS

An exploratory cross-sectional study using a wireless motility capsule (SmartPill©) was performed in 11 participants with obesity and 11 age- and gender-matched participants with normal weight (group) in fasted and fed state (visit). During the first visit, the capsule was ingested after an overnight fast. During a second visit, the capsule was ingested after a nutritional drink to simulate fed state. Linear mixed models were constructed to compare segmental gastrointestinal transit, pressure and pH between groups (obesity or control) and within every group (fasted or fed).

RESULTS

Food intake slowed gastric emptying in both groups (both P < 0.0001), though food-induced gastric contractility was higher in participants with obesity compared to controls (P = 0.02). In the small intestine, a higher contractility (P = 0.001), shorter transit (P = 0.04) and lower median pH (P = 0.002) was observed in participants with obesity compared to controls. No differences were observed for colonic measurements.

CONCLUSION

Obesity has a profound impact on gastrointestinal physiology, which should be taken into account for drug development.

Gastrointestinal Physiology Before and After Duodenal Switch with Comparisons to Unoperated Lean Controls: Novel Use of the SmartPill Wireless Motility Capsule

Purpose

Bariatric surgery alters gastrointestinal anatomy. In this exploratory study, the SmartPill® wireless motility capsule (WMC) was used to study changes in gastrointestinal physiology following biliopancreatic diversion with duodenal switch (BPD/DS).

Material and Methods

Twenty-eight BPD/DS patients (35 ± 11 years, 50% females, body mass index [BMI] 56 ± 5) were to be examined preoperatively and postoperatively. In addition to transit time, appetite control and gastrointestinal symptoms were studied by patient-scored questionnaires (visual analogue scale and Gastrointestinal Symptom Rating Scale (GSRS)). Data was compared to 41 lean unoperated controls.

Results

About 1.8 years postoperatively, 18 patients (BMI 35.8 ± 8.3) returned for a second WMC test. As expected, small bowel transit time was reduced, from 3.9 ± 1.6 h to 2.8 ± 2.0, p = 0.02, and at both these time points, it was shorter than in lean controls (5.4 ± 1.9 h, p = 0.001). Postoperatively, a trend towards reduced colon and whole gut transit times was seen in BPD/DS-patients, thus approaching those of lean controls. Surprisingly, BPD/DS patients scored higher satiety than controls preoperatively as well as increased hunger and desire to eat postoperatively. Compared to lean, BPD/DS patients reported a higher total GSRS score at both time points (1.2 ± 0.2 vs 1.7 ± 0.6 and 2.3 ± 0.5, p < 0.001). Postoperatively, the scores for diarrhea and indigestion increased.

Conclusions

The novel use of the SmartPill system in BPD/DS patients gave the expected readouts. Although small bowel transit time was further shortened after BPD/DS, whole gut transit time did not differ from controls. Typical gastrointestinal symptoms were reported postoperatively.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11695-021-05452-4.

The effects of antibiotics and melatonin on hepato-intestinal inflammation and gut microbial dysbiosis induced by a short-term high-fat diet consumption in rats

High-fat diet (HFD) consumption leads to metabolic disorders, gastrointestinal dysfunction and intestinal dysbiosis. Antibiotics also disrupt the composition of intestinal microbiota. The aim of the present study was to investigate the impact of a short-term feeding with HFD on oxidative status, enteric microbiota, intestinal motility and the effects of antibiotics and/or melatonin treatments on diet-induced hepato-intestinal dysfunction and inflammation. Male Sprague-Dawley rats were pair-fed with either standard chow or HFD (45 % fat) and were given tap water or melatonin (4 mg/kg per d) or melatonin plus antibiotics (ABX; neomycin, ampicillin, metronidazole; each 1 g/l) in drinking water for 2 weeks. On the 14th day, colonic motility was measured and the next day intestinal transit was assessed using charcoal propagation. Trunk blood, liver and intestine samples were removed for biochemical and histopathological evaluations, and faeces were collected for microbiota analysis. A 2-week HFD feeding increased blood glucose level and perirenal fat weight, induced low-level hepatic and intestinal inflammation, delayed intestinal transit, led to deterioration of epithelial tight junctions and overgrowth of colonic bacteria. Melatonin intake in HFD-fed rats reduced ileal inflammation, colonic motility and perirenal fat accumulation. ABX abolished increases in fat accumulation and blood glucose, reduced ileal oxidative damage, suppressed HFD-induced overgrowth in colonic bacteria, and reversed HFD-induced delay in intestinal transit; however, hepatic neutrophil accumulation, hepatic injury and dysfunction were further enhanced. In conclusion, the results demonstrate that even a short-term HFD ingestion results in hepato-intestinal inflammatory state and alterations in bacterial populations, which may be worsened with antibiotic intake, but alleviated by melatonin.

Characteristics of Intestinal Myoelectrical and Motor Activities in Diet-Induced Obese Rats: Obesity and Motility

BACKGROUND

Gastrointestinal motility has been reported to be altered in obesity. However, it is unknown whether intestinal myoelectrical activity (IMA) is also changed in obesity.

AIMS

The aim of this study was to characterize intestinal myoelectrical and motility activities in the fasting state, during feeding, and postprandial state after various test meals in diet-induced obese (DIO) rats in comparison with regular rats.

METHODS

IMA was recorded in the fasting, feeding, and postprandial states in DIO and regular rats. Regular laboratory chow, high-fat solid food, and high-fat liquid food were used to test IMA responses to different meals.

RESULTS

(1) The intestinal slow waves in the DIO rats were not different from those in normal rats in the fasting or postprandial state. Neither intestinal transit nor the number of intestinal contractions per minute was altered in DIO rats although gastric emptying was accelerated. (2) Both DIO rats and normal rats showed altered IMA during the first minute of feeding (cephalic stimulation). (3) The intestinal slow waves in both DIO rats and regular rats were impaired slightly but significantly after intake of a high-fat meal.

CONCLUSIONS

Our study demonstrates that intestinal myoelectrical activity is not altered in DIO rats and its postprandial responses to various meals are not altered either. High-fat meals induce intestinal dysrhythmia but do not have a chronic impact on intestinal slow waves in DIO rats.

Fecal Microbiota Transplantation Can Alleviate Gastrointestinal Transit in Rats with High-Fat Diet-Induced Obesity via Regulation of Serotonin Biosynthesis

AIM

We tested the hypothesis that fecal microbiota transplantation (FMT) could regulate the biotransformation of bile acids, such as deoxycholic acid (DCA) and cholic acid (CA), which in turn regulate the biosynthesis of serotonin in the gut and relieve gastrointestinal dysmotility in high-fat diet- (HFD-) induced obesity in rats.

METHODS

Male Sprague-Dawley rats were randomly divided into the control diet group, HFD group, and HFD-fed with receiving FMT. HFD was fed for 12 weeks. At the end of two-week HFD, FMT was carried out for two weeks. The gastrointestinal transit, serotonin concentration, the expression of tryptophan hydroxylase 1 (TPH1) and serotonin reuptake transporter (SERT), and the levels of bile acids in intestinal contents were examined.

RESULTS

Compared with the control group, the gastrointestinal transit and small intestinal serotonin concentration of HFD-fed rats were increased. In HFD-fed rats, TPH1 protein expression was increased significantly, while SERT protein expression was decreased, but not significant. The levels of CA and DCA in intestinal contents were also significantly increased in HFD-fed rats compared with the control group. After HFD-fed rats receiving FMT treatment, the gastrointestinal transit, small intestinal serotonin concentration, and TPH1 expression were decreased, while SERT expression was not affected. Moreover, the levels of CA and DCA in intestinal contents were also decreased.

CONCLUSIONS

FMT could alleviate small intestinal transit in the HFD-fed rats by regulating the serotonin biosynthesis. In this process, CA and DCA may be related to the regulation of synthesis of serotonin.

Gastrointestinal Transit Time, Glucose Homeostasis and Metabolic Health: Modulation by Dietary Fibers

Gastrointestinal transit time may be an important determinant of glucose homeostasis and metabolic health through effects on nutrient absorption and microbial composition, among other mechanisms. Modulation of gastrointestinal transit may be one of the mechanisms underlying the beneficial health effects of dietary fibers. These effects include improved glucose homeostasis and a reduced risk of developing metabolic diseases such as obesity and type 2 diabetes mellitus. In this review, we first discuss the regulation of gastric emptying rate, small intestinal transit and colonic transit as well as their relation to glucose homeostasis and metabolic health. Subsequently, we briefly address the reported health effects of different dietary fibers and discuss to what extent the fiber-induced health benefits may be mediated through modulation of gastrointestinal transit.

Dietary Genistein Influences Number of Acetylcholine Receptors in Female Diabetic Jejunum

BACKGROUND

Intestinal dysfunction in the ob/ob mouse model of diabetes mimics that seen clinically.

METHODS

We determined the effects of a 4-week genistein diet (600 mg genistein/kg food) on intestinal function (contractility, morphology, AChR, and motility) in female ob/ob and lean mice.

RESULTS

Contractility of the jejunum in response to incrementally increasing concentrations of KCl was comparable in ob/ob females and lean controls regardless of a genistein-diet. There were no changes in the wall thickness measured. We assessed the number of clusters of AChR in the jejunum wall; AChR were decreased by 48% in ob/ob mice versus leans, and the genistein diet reversed this. In utilizing a video-imaging system to evaluate gastrointestinal motility, we determined that the distance between consecutive contractile events was significantly increased by 1.87-fold in ob/ob mice versus leans, and the genistein diet was without effect.

CONCLUSIONS

These data suggest that slowed intestinal transit in the diabetic ob/ob mouse may be due in part to decreased AChR and decreased contraction events occurring per unit time. A genistein diet rescues the number of AChR to levels of leans yet did not change the number of contractile events. Feeding ob/ob mice a genistein-rich diet has potential therapeutic benefits towards improving the debilitating diabetes-related gastrointestinal dysfunction.

Translational neuropharmacology: the use of human isolated gastrointestinal tissues

Translational sciences increasingly emphasize the measurement of functions in native human tissues. However, such studies must confront variations in patient age, gender, genetic background and disease. Here, these are discussed with reference to neuromuscular and neurosecretory functions of the human gastrointestinal (GI) tract. Tissues are obtained after informed consent, in collaboration with surgeons (surgical techniques help minimize variables) and pathologists. Given the difficulties of directly recording from human myenteric neurones (embedded between muscle layers), enteric motor nerve functions are studied by measuring muscle contractions/relaxations evoked by electrical stimulation of intrinsic nerves; responses are regionally dependent, often involving cholinergic and nitrergic phenotypes. Enteric sensory functions can be studied by evoking the peristaltic reflex, involving enteric sensory and motor nerves, but this has rarely been achieved. As submucosal neurones are more accessible (after removing the mucosa), direct neuronal recordings are possible. Neurosecretory functions are studied by measuring changes in short-circuit current across the mucosa. For all experiments, basic questions must be addressed. Because tissues are from patients, what are the controls and the influence of disease? How long does it take before function fully recovers? What is the impact of age- and gender-related differences? What is the optimal sample size? Addressing these and other questions minimizes variability and raises the scientific credibility of human tissue research. Such studies also reduce animal use. Further, the many differences between animal and human GI functions also means that human tissue research must question the ethical validity of using strains of animals with unproved translational significance.

A quantitative model of human jejunal smooth muscle cell electrophysiology

Recently, a number of ion channel mutations have been identified in the smooth muscle cells of the human jejunum. Although these are potentially significant in understanding diseases that are currently of unknown etiology, no suitable computational cell model exists to evaluate the effects of such mutations. Here, therefore, a biophysically based single cell model of human jejunal smooth muscle electrophysiology is presented. The resulting cellular description is able to reproduce experimentally recorded slow wave activity and produces realistic responses to a number of perturbations, providing a solid platform on which the causes of intestinal myopathies can be investigated.

Duodenum electrical stimulation delays gastric emptying, reduces food intake and accelerates small bowel transit in pigs

Duodenum electrical stimulation (DES) has been shown to delay gastric emptying and reduce food intake in dogs. The aim of this study was to investigate the effects of DES on gastric emptying, small bowel transit and food intake in pigs, a large animal model of obesity. The study consisted of three experiments (gastric emptying, small bowel transit, and food intake) in pigs implanted with internal duodenal electrodes for DES and one or two duodenal cannulas for gastric emptying and small bowel transit. We found that (i) gastric emptying was dose-dependently delayed by DES of different stimulation parameters; (ii) small bowel transit was significantly accelerated with continuous DES in proximal intestine but not with intermittent DES; (iii) DES significantly reduced body weight gain with 100% duty cycle (DC), but not with DES with 40% DC. A marginal difference was noted in food intake among 100% DC session, 40% DC session, and control session. DES with long pulses energy-dependently inhibits gastric emptying in pigs. DES with appropriate parameters accelerates proximal small bowel transit in pigs. DES reduces body weight gain in obese pigs, and this therapeutic effect on obesity is mediated by inhibiting gastric emptying and food intake, and may also possibly by accelerating intestinal transit. DES may have a potential application to treat patients with obesity.

Cyclic AMP-mediated chloride secretion is induced by prostaglandin F2alpha in human isolated colon

BACKGROUND AND PURPOSE

Prostaglandin F(2alpha) (PGF(2alpha)) is implicated in the pathogenesis of inflammatory bowel disease and colorectal cancer. This study investigates the effects of PGF(2alpha) on electrophysiological parameters in isolated human colonic mucosa.

EXPERIMENTAL APPROACH

Ion transport was measured as changes in short-circuit current across human colonic epithelia mounted in Ussing chambers. Colonic crypts were isolated by calcium chelation and cyclic adenosine monophosphate (cAMP) was measured by ELISA.

KEY RESULTS

PGF(2alpha) stimulated chloride secretion in a concentration-dependent manner with an EC(50) of 130 nM. The PGF(2alpha) induced increase in chloride secretion was inhibited by AL8810 (10 microM), a specific PGF(2alpha) receptor antagonist. In addition, PGF(2alpha) (1 microM) significantly increased levels of cAMP in isolated colonic crypts.

CONCLUSIONS AND IMPLICATIONS

PGF(2alpha) stimulated chloride secretion in samples of human colon in vitro through a previously unrecognizd cAMP-mediated mechanism. These findings have implications for inflammatory states.