Impaired pancreatico-biliary response to vagal stimulation and to cholecystokinin in human 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.

Targeting bile acid metabolism in obesity reduction: A systematic review and meta-analysis

A systematic review and meta-analysis was conducted of studies that address the association of bile acid (BA) with obesity and of studies on the effects of treatment in patients with obesity on BA metabolism, assessed from systemic BA, fibroblast growth factor 19 (FGF19), 7α-hydroxy-4-cholesten-3-one (C4) level, and faecal BA. We searched PubMed, Embase, and the Cochrane Library from inception to 1 August 2019 using the keywords obesity, obese, body mass index, and overweight with bile acid, FGF19, FXR, and TGR5. Two reviewers independently searched, selected, and assessed the quality of studies. Data were analysed using either fixed or random effect models with inverse variance weighting. Of 3771 articles, 33 papers were relevant for the association of BA with obesity of which 22 were included in the meta-analysis, and 50 papers were relevant for the effect of obesity interventions on BA of which 20 were included in the meta-analysis. Circulating fasting total BA was not associated with obesity. FGF19 was inversely and faecal BA excretion was positively associated with obesity. Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) modulated BA metabolism, ie, increased BA and FGF19. Our results indicate that BA metabolism is altered in obesity. Certain bariatric surgeries including RYGB and SG modulate BA, whether these underlie the beneficial effect of the treatment should be investigated.

Single vagus nerve stimulation reduces early postprandial C-peptide levels but not other hormones or postprandial metabolism

A recent study in rheumatoid arthritis (RA) patients using electrical vagus nerve stimulation (VNS) to activate the inflammatory reflex has shown promising effects on disease activity. Innervation by the autonomic nerve system might be involved in the regulation of many endocrine and metabolic processes and could therefore theoretically lead to unwanted side effects. Possible effects of VNS on secretion of hormones are currently unknown. Therefore, we evaluated the effects of a single VNS on plasma levels of pituitary hormones and parameters of postprandial metabolism. Six female patients with RA were studied twice in balanced assignment (crossover design) to either VNS or no stimulation. The patients selected for this substudy had been on VNS therapy daily for at least 3 months and at maximum of 24 months. We compared 10-, 20-, and 30-min poststimulus levels to baseline levels, and a 4-h mixed meal test was performed 30 min after VNS. We also determined energy expenditure (EE) by indirect calorimetry before and after VNS. VNS did not affect pituitary hormones (growth hormone, thyroid stimulating hormone, adrenocorticotropic hormone, prolactin, follicle-stimulating hormone, and luteinizing hormone), postprandial metabolism, or EE. Of note, VNS reduced early postprandial insulin secretion, but not AUC of postprandial plasma insulin levels. Cortisol and catecholamine levels in serum did not change significantly. Short stimulation of vagal activity by VNS reduces early postprandial insulin secretion, but not other hormone levels and postprandial response. This suggests VNS as a safe treatment for RA patients.

Surgery for Gastroesophageal Reflux Disease in the Morbidly Obese Patient

The prevalence of gastroesophageal reflux disease (GERD) has mirrored the increase in obesity, and GERD is now recognized as an obesity-related comorbidity. There is growing evidence that obesity, specifically central obesity, is associated with the complications of chronic reflux, including erosive esophagitis, Barrett's esophagus, and esophageal adenocarcinoma. While fundoplication is effective in creating a competent gastroesophageal junction and controlling reflux in most patients, it is less effective in morbidly obese patients. In these patients a bariatric operation has the ability to correct both the obesity and the abnormal reflux. The Roux-en-Y gastric bypass is the preferred procedure.

Lifestyle measures in the management of gastro-oesophageal reflux disease: clinical and pathophysiological considerations

Several lifestyle and dietary factors are commonly cited as risk factors for gastro-oesophageal reflux disease (GORD) and modification of these factors has been advocated as first-line measures for the management of GORD. We performed a systematic review of the literature from 2005 to the present relating to the effect of these factors and their modification on GORD symptoms, physiological parameters of reflux as well as endoscopic appearances. Conflicting results existed for the association between smoking, alcohol and various dietary factors in the development of GORD. These equivocal findings are partly due to methodology problems. There is recent good evidence that weight reduction and smoking cessation are beneficial in reducing GORD symptoms. Clinical and physiological studies also suggest that some physical measures as well as modification of meal size and timing can also be beneficial. However, there is limited evidence for the role of avoiding alcohol and certain dietary ingredients including carbonated drinks, caffeine, fat, spicy foods, chocolate and mint.

Deficits in gastrointestinal responses controlling food intake and body weight

The gastrointestinal tract serves as a portal sensing incoming nutrients and relays mechanical and chemosensory signals of a meal to higher brain centers. Prolonged consumption of dietary fat causes adaptive changes within the alimentary, metabolic, and humoral systems that promote a more efficient process for energy metabolism from this rich source, leading to storage of energy in the form of adipose tissue. Furthermore, prolonged ingestion of dietary fats exerts profound effects on responses to signals involved in termination of a meal. This article reviews the effects of ingested fat on gastrointestinal motility, hormone release, and neuronal substrates. It focuses on changes in sensitivity to satiation signals resulting from chronic ingestion of high-fat diet, which may lead to disordered appetite and dysregulation of body weight.

LJ, Aguero GC, Alvariz Â, Schechter RB. Maior prevalência de obesidade na doença do refluxo gastroesofagiano erosiva

CONTEXTO: Existe uma noção geral de que indivíduos obesos desenvolvem mais freqüentemente a doença do refluxo gastroesofagiano, sendo a orientação de perder peso parte integrante do seu tratamento. Entretanto, uma base científica para esta associação não está plenamente estabelecida. OBJETIVOS: Avaliar a prevalência de obesidade e sobrepeso em pacientes com sintomas típicos de refluxo, com e sem esofagite erosiva. Analisar a prevalência de hérnia hiatal e a intensidade do refluxo anormal em relação ao índice de massa corporal nos dois grupos de pacientes. MÉTODOS: Foram examinadas retrospectivamente 362 pHmetrias de pacientes com pirose, todos com endoscopia digestiva alta prévia, definindo-se esofagite erosiva pela presença de erosões esofagianas macroscópicas e hérnia de hiato quando à junção esôfago-gástrica estava 2 cm ou mais acima do pinçamento diafragmático. Pacientes com esôfago de Barrett ou estenose péptica foram excluídos. A população foi dividida em três grupos de acordo com o índice de massa corpórea: peso normal, com índice de massa corporal entre 20 e 24,9, sobrepeso, com 25 e 29,9 e obesos com índice superior a 30. O diagnóstico de refluxo gastroesofagiano anormal com sua intensidade foi avaliado de acordo com os resultados de pHmetrias, analisados nos grupos de pacientes com e sem esofagite erosiva em relação ao índice de massa corporal. RESULTADOS: Entre os 362 pacientes, havia 148 (41%) com e 214 (59%) sem esofagite erosiva, sendo a pHmetria anormal em 100% e 57% dos pacientes, retrospectivamente. Entre os 148 (61% do sexo masculino, mediana de idade de 50 anos), 41 (28%) apresentavam peso normal, 82 (55%) sobrepeso e 25 (17%) eram obesos. Havia 88 (60%) com hérnia hiatal, sendo 29 (71% dos pacientes com peso normal), 45 (55% dos com sobrepeso) e 14 (56% dos obesos). Nos 121 indivíduos sem esofagite erosiva e com pHmetria anormal, diagnosticados como doentes com doença do refluxo não-erosiva (38% masculino, mediana de idade de 50 anos), havia 51 (42%) pacientes com peso normal, 55 (46%) com sobrepeso e 15 (12%) eram obesos. Detectou-se hérnia de hiato em 52 (43%) dos 121 pacientes, sendo 21 (41% dos indivíduos com peso normal), 24 (44% dos com sobrepeso) e 7 (47% dos obesos). Naqueles 93 pacientes sem esofagite erosiva e com pHmetria normal (39% homens, mediana de idade de 43 anos) havia 43 (46%) pacientes com peso normal, 38 (41%) com sobrepeso e 12 (13%) obesos, sendo 26 (28%) com hérnia hiatal. A prevalência de hérnia de hiato, assim como o número de pacientes com obesidade e sobrepeso foi significantemente maior no grupo de doença do refluxo erosiva, quando comparado ao grupo sem esofagite erosiva. A intensidade do refluxo, assim como a prevalência de hérnia hiatal foram similares nos pacientes com peso normal, sobrepeso e obesos, em ambos os grupos. CONCLUSÃO:A prevalência de obesidade e sobrepeso é maior em indivíduos com doença do refluxo erosiva do que naqueles sem esofagite erosiva. Não houve diferença na intensidade do refluxo entre as várias categorias de índice de massa corporal, em nenhum dos grupos estudados. Embora a hérnia hiatal seja mais prevalente na doença do refluxo erosiva, esta superioridade não se relacionou ao excesso de peso.

A systematic review and meta-analysis of the risk of increasing adiposity on Barrett's esophagus

OBJECTIVES

Esophageal adenocarcinoma and its precursor lesion, Barrett's esophagus, are increasing in incidence in western populations. Gastroesophageal reflux disease (GERD) and high body mass index (BMI) are known risk factors, but it is unclear whether BMI mediates its risk on Barrett's esophagus independently. This systematic review and meta-analysis investigated whether increasing BMI is associated with Barrett's esophagus as compared to general population and GERD controls.

METHODS

Search strategies were conducted in MEDLINE (U.S. National Library of Medicine, Bethesda, MD) (1966-2005) and EMBASE (Reed Elsevier PLC, Amsterdam, The Netherlands) (1980-2005). Studies to be included were required to present "current" BMI data for consecutively recruited Barrett's esophagus patients and appropriate comparison arms with a minimum number of 30 subjects in each.

RESULTS

The literature search produced 5,501 hits from which 295 papers were extracted. Only 10 studies met the criteria for inclusion. The Statistics/Data Analysis (STATA) program was used to conduct random effects meta-analyses. Nine studies comparing the BMI of the Barrett's esophagus and GERD groups produced a pooled odds ratio (OR) of 0.99 per kg/m2 (95% confidence interval [CI] 0.97-1.01, I2= 52%), while the pooled estimate of three studies comparing Barrett's esophagus with general population controls was 1.02 per kg/m2 (95% CI 1.01-1.04, I2= 0%).

CONCLUSIONS

Increasing adiposity is only an indirect risk factor of Barrett's esophagus through the precursor lesion of GERD. Hence, BMI status has no predictive value with respect to GERD patients and their risk of progression to Barrett's esophagus.

Implications of altered gastrointestinal motility in obesity

The onset of obesity occurs as a result of an imbalance between nutrient consumption/absorption and energy expenditure. Gastrointestinal (GI) motility plays a critical role in the rate of consumption of foods, digestion, and absorption of nutrients. Various segments of the GI tract coordinate in a complex yet precise way, to control the process of food consumption, digestion, and absorption of nutrients. GI motility not only regulates the rates at which nutrients are processed and absorbed in the gut, but also, via mechanical and neurohormonal methods, participates in the control of appetite and satiety. Altered GI motility has frequently been observed in obese patients, the significance of which is incompletely understood. However, these alterations can be considered as potential contributing factors in the development and maintenance of obesity and changed eating behavior. Therapies aimed at regulating or counteracting the observed changes in GI motility are being actively explored and applied clinically in the management of obese patients.

Gastro-oesophageal reflux disease in obesity: pathophysiological and therapeutic considerations

Gastro-oesophageal reflux disease (GERD) is common in obese patients. Apart from the physical discomfort and the economic burden, GERD may increase morbidity and mortality through its association with oesophageal carcinoma. The pathophysiology of GERD differs between obese and lean subjects. First, obese subjects are more sensitive to the presence of acid in the oesophagus. Second, hiatal hernia, capable of promoting GERD by several mechanisms, is more prevalent among the obese. Third, obese subjects have increased intra-abdominal pressure that displaces the lower oesophageal sphincter and increases the gastro-oesophageal gradient. Finally, vagal abnormalities associated with obesity may cause a higher output of bile and pancreatic enzymes, which makes the refluxate more toxic to the oesophageal mucosa. The altered body composition associated with obesity affects the pharmacokinetics of drugs. There are no data regarding the efficacy of any of the drugs used for GERD treatment. The dosages of cimetidine and ranitidine should be calculated according to the patient's ideal body weight, not their actual weight. Of the operative procedures used for weight loss, Roux-en-Y gastric bypass was found to be most effective for GERD, while gastric banding was associated with a high prevalence of reflux. This review outlines the pathophysiology and the treatment of GERD in obesity with emphasis on the therapeutic considerations in this population of patients.

Gastrointestinal motility in obesity

Gastrointestinal motility is closely linked to the rate at which nutrients become systemically available. Regulation of gastric emptying represents the most important brake against delivery of nutrients to the intestine in excess of digestive and absorptive capacity. In man, gastric emptying is slowed in proportion to the energy density of the meal, which will level out the rate of energy delivery to the duodenum. Studies suggest a more rapid gastric emptying in obesity, although the opposite has been reported in some experimental settings. Moreover, gastric volume is larger in obese individuals and appropriate satiety signals are not triggered in response to gastric distension. Postprandial intestinal transit time in obesity is similar to that in normal-weight subjects, however, despite this fact, intestinal absorption of nutrients is more efficient in obesity. Several regulatory mechanisms for gastrointestinal motility, such as the autonomous and enteric nervous systems and gastrointestinal regulatory peptides, are also of importance for feeding behaviour and metabolism. Dysfunction of the autonomous nervous system has been observed, the sensitivity to cholecystokinin is decreased in obesity, and plasma concentrations of somatostatin and neurotensin are lower than in normal-weight subjects. These changes in regulatory mechanisms favour rapid gastrointestinal transit of ingested nutrients and promote rapid intestinal absorption in obesity and decreased satiety in response to ingested food. It is presently not known whether the observed changes in gastrointestinal motility in obesity represent a primary feature linked to the pathogenesis of such disease.

Whole body autoradiography of CCK-8 in rats

Rats were given i.v., intranasal or intraperitoneal doses of CCK-8 (sulfated) labelled with 125I-labeled Bolton and Hunter reagent. Radioactivity was found mainly in the liver, kidney, and the intestinal contents. No radioactivity was detected in the brain. In animals dosed i.v., specific localization occurred in the tissue of the pyloric region of the stomach, and in the pancreas. Label persisted within the pyloric region of the stomach for longer than 30 min, in spite of the reported half-life of CCK-8 in plasma of approximately 1 min. Intranasal and intraperitoneal doses had limited bioavailability. The binding to the sites in the pyloric region of the stomach, which required systemic delivery, may have identified receptors associated with appetite control.

Effect of a satiating meal on the concentrations of procolipase propeptide in the serum and urine of normal and morbidly obese subjects

The effect of a satiating meal on the serum and urinary concentrations of procolipase propeptide (Ala-Pro-Gly-Pro-Arg, APGPR) immunoreactivity, as measured by enzyme linked immunosorbent assay (ELISA) specific for free APGPR, has been studied in normal and morbidly obese human subjects. The normal subjects displayed a biphasic response with coordinate increases in both serum and urine APGPR immunoreactivity both occurring within the first two hours after the meal. In two of three of the morbidly obese subjects, this early rise in APGPR concentration in urine was not seen but was followed by a slow rise in urinary APGPR immunoreactivity at four to six hours. In both the normal and obese groups, the urinary immunoreactive signal was found to coelute with synthetic APGPR on gel chromatography. In rats, procolipase propeptide (Val-Pro-Asp-Pro-Arg, VPDPR) specifically inhibits fat intake early in the postprandial period when given peripherally or centrally. This study suggests that in humans APGPR reaches the circulation shortly after feeding and is excreted in the urine. These findings are consistent with the hypothesis that human procolipase propeptide may also act as a satiety signal. In addition the late appearance of the peptide in some of the morbidly obese patients could be associated with perturbation of appetite control in these subjects.

Gastrointestinal disturbances with obesity

Steatosis and steatohepatitis are associated with obesity. Despite florid histological changes, patients with non-alcoholic steatohepatitis generally remain asymptomatic, and it usually runs a relatively benign course. An elevated insulin level may be important in the pathogenesis. There is a marked regression of fatty changes after weight reduction. In obese subjects the risk of developing gallstones is increased due to an increased saturation of gallbladder bile with cholesterol and possible gallbladder stasis. During weight reduction with very low calorie diets the incidence in gallstones increases probably because of an increased saturation of bile during the loss of weight. Ursodeoxycholic acid appears to be a promising prophylactic agent. Chenodeoxycholic acid is not useful for these subjects. There is controversy over whether obesity contributes to gastroesophageal reflux and gastric emptying disturbances. There are changes in gastrointestinal peptide plasma levels in obesity but it is not clear if this contributes to its development. The risk for high-risk colorectal adenomas and carcinomas is reported to be increased in obese males. Vertical banded gastroplasty and gastric bypass procedures are nowadays the surgical options for the treatment of obesity. Nutritional deficiencies, particularly of vitamin B12, folate and iron are common after gastric bypass and must be sought and treated. Dumping is another potential complication of this operation. If stenosis and gastric outlet obstruction develop endoscopic dilatation is a good therapeutic option.

Gastrointestinal function in obesity: motility, secretion, and absorption following a liquid test meal

Digestive responses to a 300-mL liquid fat-rich meal (432 kcal) in a group of massively obese patients were compared with those observed in a group of healthy lean subjects of variable body weight. Gastric and intestinal propulsion, digestive secretions, and absorption in the proximal 70 cm of intestine were measured using a multiple-marker dilution method. The average gastric emptying of energy, acid, volumes, and meal marker were similar in the two groups 80 minutes after intake, justifying a comparison of intestinal processing of the meal. Compared with lean subjects, the obese subjects responded with less pancreatic secretion (P less than .05) and gallbladder emptying, but absorbed a larger proportion of the emptied energy in the test segment (P less than .01) during a similar or shorter transit time. In addition, when the entire meals were compared, the obese group generally absorbed the test meal more effectively and rapidly in the upper part of the intestine. As a consequence, the flow volumes at the exit of the test segment were lower (P less than .05), and less of the test meal was propulsed to distal parts of the intestine. In the lean subjects, the body weight or height correlated positively with the gastric emptying rate, peak gastric acid output, and pancreatic responses, and negatively with (P less than .05) the segment transit time. The taller the subject, the greater the proportion of the meal which was rapidly propulsed unabsorbed to lower parts of the intestine, indicating that a large intestinal area was exposed for rapid energy uptake. No such correlations were observed in the obese group.

Plasma concentrations of regulatory peptides in obseity following modified sham feeding (MSF) and a liquid test meal

Plasma concentrations of regulatory peptides were monitored in groups of obese and normal-weight subjects following modified sham feeding and a liquid fatty meal. Following modified sham feeding a significant increase in immunoreactive cholecystokinin (CCK) in plasma was recorded in both groups. In the obese subjects, however, the concentrations following sham feeding were significantly lower than in normal-weight subjects, and the initial part of the response was negative. Basal and modified sham feeding stimulated immunoreactive pancreatic polypeptide (PP) concentrations in plasma did not differ between the groups. After the liquid fatty meal plasma CCK concentrations increased similarly in both groups. In contrast immunoreactive neurotensin and somatostatin concentrations following the meal were lower in the obese group, and a changed concentration-time pattern for somatostatin was observed in the obese group. Postprandial concentrations of PP and immunoreactive gastrin were not different in the groups. The results indicate that the plasma concentration patterns of CCK, somatostatin and NT are disarranged in obesity. The changes may promote rapid propulsion and absorption of ingested food, and facilitate deposition of fat in adipose tissue in obesity and thus may be of pathophysiological importance.

Pancreatic procolipase propeptide, enterostatin, specifically inhibits fat intake

Pancreatic procolipase is activated by trypsin forming colipase, a cofactor for pancreatic lipase involved in intestinal fat digestion and a pentapeptide named enterostatin. Enterostatin with the sequence Val-Pro-Asp-Pro-Arg (VPDPR) was previously shown to decrease food intake in rats both after peripheral and central injection. In this work enterostatin has been shown to reduce specifically the consumption of a high-fat diet as opposed to a low-fat diet after central injection of Sprague-Dawley rats. After starvation for 18 hours the rats were given a free choice of a low-fat diet (5.2% fat by weight; 14.1% by energy) and a high-fat diet (17.8% fat by weight; 32.8% by energy) in separate containers. After injection of 200 ng of VPDPR into the lateral ventricle, the rats selectively decreased the intake of the high-fat diet by 45% (p less than 0.005), while the intake of the low-fat diet was unaffected compared to saline injection. VPDP after intracerebroventricular injection had totally lost the selective effect on the consumption of a high- fat and a low-fat diet. It is suggested that enterostatin formed during fat digestion from pancreatic procolipase may provide a feed-back signal for the intake of lipid.