Influence of a lipase inhibitor on gastric sensitivity and accommodation to an orally ingested meal

Mechanisms Underlying Food-Triggered Symptoms in Disorders of Gut-Brain Interactions

There has been a dramatic increase in clinical studies examining the relationship between disorders of gut-brain interactions and symptoms evoked by food ingestion in the upper and lower gastrointestinal tract, but study design is challenging to verify valid endpoints. Consequently, mechanistic studies demonstrating biological relevance, biomarkers and novel therapeutic targets are greatly needed. This review highlights emerging mechanisms related to nutrient sensing and tasting, maldigestion, physical effects with underlying visceral hypersensitivity, allergy and immune mechanisms, food-microbiota interactions and gut-brain signaling, with a focus on patients with functional dyspepsia and irritable bowel syndrome. Many patients suffering from disorders of gut-brain interactions exhibit these mechanism(s) but which ones and which specific properties may vary widely from patient to patient. Thus, in addition to identifying these mechanisms and the need for further studies, biomarkers and novel therapeutic targets are identified that could enable enriched patient groups to be studied in future clinical trials examining the role of food in the generation of gut and non-gut symptoms.

The Role of Gasotransmitters in Gut Peptide Actions

Although gasotransmitters nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H₂S) receive a bad connotation; in low concentrations these play a major governing role in local and systemic blood flow, stomach acid release, smooth muscles relaxations, anti-inflammatory behavior, protective effect and more. Many of these physiological processes are upstream regulated by gut peptides, for instance gastrin, cholecystokinin, secretin, motilin, ghrelin, glucagon-like peptide 1 and 2. The relationship between gasotransmitters and gut hormones is poorly understood. In this review, we discuss the role of NO, CO and H₂S on gut peptide release and functioning, and whether manipulation by gasotransmitter substrates or specific blockers leads to physiological alterations.

The Role of Duodenal Inflammation in Functional Dyspepsia

Functional dyspepsia (FD) is common and significantly impairs quality of life. Symptoms of FD are considered to originate from the gastroduodenal region, classified by the Rome criteria as disorders of brain-gut interaction without structural alteration. However, it is now apparent that FD is a number of syndromes, the epigastric pain syndrome (bothersome epigastric pain or epigastric burning) and the postprandial distress syndrome (with bothersome postprandial fullness or early satiation) and there are wide-ranging symptoms and severity. The origin of these troublesome symptoms is now considered to be a result of disrupted gastroduodenal neuropathophysiology. The complexity of the syndrome indicates that there must be different triggers, supported by the limited efficacy of the many treatments available. Current research based on evidence by association suggests that duodenal contents, including the duodenal microbiome, pathogens, and allergy may be triggers of FD. Recent studies have also shown that systemic responses of increased circulating lymphocytes and elevated proinflammatory cytokines and subtle inflammation in the duodenum may accompany the onset and persistence of symptoms. This inflammatory phenotype is characterized by innate inflammation, an eosinophil infiltrate in the duodenum in FD in those with postprandial distress syndrome. Routine histopathology practice does not quantify these cells so the status of FD is not yet appreciated as an inflammatory condition. Thus functional is becoming inflammatory and this breakthrough in understanding that functional does not necessarily mean no, but subtle pathology, may improve therapeutic options, which are currently aimed at symptom relief rather than targeted at underlying pathology.

Gastric sensitivity and reflexes: basic mechanisms underlying clinical problems

Both reflex and sensory mechanisms control the function of the stomach, and disturbances in these mechanisms may explain the pathophysiology of disorders of gastric function. The objective of this report is to perform a literature-based critical analysis of new, relevant or conflicting information on gastric sensitivity and reflexes, with particular emphasis on the comprehensive integration of basic and clinical research data. The stomach exerts both phasic and tonic muscular (contractile and relaxatory) activity. Gastric tone determines the capacity of the stomach and mediates both gastric accommodation to a meal as well as gastric emptying, by partial relaxation or progressive recontraction, respectively. Perception and reflex afferent pathways from the stomach are activated independently by specific stimuli, suggesting that the terminal nerve endings operate as specialized receptors. Particularly, perception appears to be related to stimulation of tension receptors, while the existence of volume receptors in the stomach is uncertain. Reliable techniques have been developed to measure gastric perception and reflexes both in experimental and clinical conditions, and have facilitated the identification of abnormal responses in patients with gastric disorders. Gastroparesis is characterised by impaired gastric tone and contractility, whereas patients with functional dyspepsia have impaired accommodation, associated with antral distention and increased gastric sensitivity. An integrated view of fragmented knowledge allows the design of pathophysiological models in an attempt to explain disorders of gastric function, and may facilitate the development of mechanistically orientated treatments.

Changes in gastrointestinal tract function and structure in functional dyspepsia

Functional dyspepsia is an extremely common disorder of gastrointestinal function. The disorder is thought to be heterogeneous, with different pathophysiological mechanisms underlying varied symptom patterns. A diversity of changes in gastrointestinal tract function and structure has been described in functional dyspepsia. These involve alterations in the stomach, such as impaired accommodation, delayed gastric emptying and hypersensitivity, and alterations in the duodenum, such as increased sensitivity to duodenal acid and/or lipids and low-grade inflammation. In this Review, we summarize all these abnormalities in an attempt to provide an integrated overview of the pathophysiological mechanisms in functional dyspepsia.

Dyspepsia: organic versus functional

Dyspepsia is the medical term for difficult digestion. It consists of various symptoms in the upper abdomen, such as fullness, discomfort, early satiation, bloating, heartburn, belching, nausea, vomiting, or pain. The prevalence of dyspepsia in the western world is approximately 20% to 25%. Dyspepsia can be divided into 2 main categories: "organic" and "functional dyspepsia" (FD). Organic causes of dyspepsia are peptic ulcer, gastroesophageal reflux disease, gastric or esophageal cancer, pancreatic or biliary disorders, intolerance to food or drugs, and other infectious or systemic diseases. Pathophysiological mechanisms underlying FD are delayed gastric emptying, impaired gastric accommodation to a meal, hypersensitivity to gastric distension, altered duodenal sensitivity to lipids or acids, altered antroduodenojenunal motility and gastric electrical rhythm, unsuppressed postprandial phasic contractility in the proximal stomach, and autonomic nervous system-central nervous system dysregulation. Pathogenetic factors in FD are genetic predisposition, infection from Helicobacter pylori or other organisms, inflammation, and psychosocial factors. Diagnostic evaluation of dyspepsia includes upper gastrointestinal endoscopy, abdominal ultrasonography, gastric emptying testing (scintigraphy, breath test, ultrasonography, or magnetic resonance imaging), and gastric accommodation evaluation (magnetic resonance imaging, ultrasound, single-photon emission computed tomography, and barostat). Antroduodenal manometry can be used for the assessment of the myoelectrical activity of the stomach, whereas sensory function can be evaluated with the barostat, tensostat, and satiety test. Management of FD includes general measures, acid-suppressive drugs, eradication of H. pylori, prokinetic agents, fundus-relaxing drugs, antidepressants, and psychological interventions. This review presents an update on the diagnosis of patients presenting with dyspepsia, with an emphasis on the pathophysiological and pathogenetic mechanisms of FD and the differential diagnosis with organic causes of dyspepsia. The management of uninvestigated and FD, as well as the established and new pharmaceutical agents, is also discussed.

Review article: the role of gastric motility in the control of food intake

BACKGROUND

From a classical point of view, gastric motility acts to clear the stomach between meals, whereas postprandial motility acts to provide a reservoir for food, mixing and grinding the food and to assure a controlled flow of food to the intestines.

AIM

To summarise findings that support the role of gastric motility as a central mediator of hunger, satiation and satiety.

METHODS

A literature review using the search terms 'satiety', 'satiation' and 'food intake' was combined with specific terms corresponding to the sequence of events during and after food intake.

RESULTS

During food intake, when gastric emptying of especially solids is limited, gastric distension and gastric accommodation play an important function in the regulation of satiation. After food intake, when the stomach gradually empties, the role of gastric distension in the determination of appetite decreases and the focus will shift to gastric emptying and intestinal exposure of the nutrients. Finally, we have discussed the role of the empty stomach and the migrating motor complex in the regulation of hunger signals.

CONCLUSIONS

Our findings indicate that gastric motility is a key mediator of hunger, satiation and satiety. More specifically, gastric accommodation and gastric emptying play important roles in the regulation of gastric (dis)tension and intestinal exposure of nutrients and hence control satiation and satiety. Correlations between gastric accommodation, gastric emptying and body weight indicate that gastric motility can also play a role in the long-term regulation of body weight.

Early weight loss and outcome at one year in obese adolescents treated with orlistat or placebo

BACKGROUND

Pharmacotherapy, associated with a comprehensive weight loss intervention, has emerged as a promising therapeutic approach in adolescents. Identification of subjects who best respond to a pharmacological intervention remains difficult.

OBJECTIVE

To compare the value of early weight loss after 12 weeks of treatment with placebo or orlistat (120 mg three times a day) in predicting treatment outcome after 52 weeks.

METHODS

Secondary analysis of a randomized control trial in 182 placebo-treated and 357 orlistat-treated obese adolescents (Body mass index [BMI] ≥ 2 kg/m(2) above the 95(th) percentile).

RESULTS

Percent weight change at 12 weeks was positively correlated with percent change in weight (r(2) ≥ 0.41), BMI (r(2) ≥ 0.33) and waist circumference (r(2) ≥ 0.20) at 52 weeks in both the placebo and orlistat groups (P < 0.001). A weight loss ≥ 5% of baseline weight at 12 weeks was associated with a mean weight loss of 8.1% (95% CI: 6.4 to 9.7) at the study end that was independent of treatment. Subjects in the orlistat group were 2.44 times (95% CI: 1.34 to 4.46) more likely to experience a weight loss ≥ 5% after 12 weeks than subjects in the placebo group (P = 0.0028).

CONCLUSIONS

Early weight loss predicts a favourable outcome in both placebo-treated and orlistat-treated subjects but is more than 2 times more likely to occur in the orlistat group. Addition of orlistat should be considered as part of a weight loss intervention but reevaluated after 3 months of treatment.

Contribution of different triggers to the gastric accommodation reflex in humans

Accommodation of the stomach consists of a vagally mediated relaxation of the proximal stomach, providing the meal with a reservoir. Our aim was to study whether, similar to other vagally mediated processes, the accommodation reflex is also determined by cephalic, oropharyngeal, gastric, and intestinal phases. Eleven healthy subjects underwent in randomized order five gastric barostat studies and two satiety drinking tests. In all studies, isobaric tone measurements (at minimal distending pressure + 2 mmHg) were performed 20 min before and 20 min after a nutrient stimulus. The stimuli included only visual and olfactory exposure to a meal (cephalic stimulation), taking liquid nutrient in the mouth without swallowing (sham feeding), ingestion of a 200-ml 300-kcal nutrient meal with blocked outflow to the pylorus (gastric retention), and meal infusion through a nasointestinal tube (duodenal instillation), or normal ingestion (control). During satiety testing, subjects ingested liquid nutrient at a fixed rate of 15 ml/min until maximum satiety, with an inflated or deflated intrapyloric balloon assembly. Progressively bigger gastric relaxatory responses were seen with cephalic stimulation (18 +/- 19 ml), sham feeding (54 +/- 21 ml), gastric retention (95 +/- 47), duodenal instillation (144 +/- 33), and control (232 +/- 33 ml). The amount of nutrient ingested at maximum satiety was significantly lower with an inflated intrapyloric balloon (1,223 +/- 103 vs. 1,392 +/- 124 ml, P < 0.05). The accommodation reflex in humans lacks a cephalic phase, but it can be activated from the oropharynx, the stomach, and the duodenum. Blocking passage to the duodenum significantly decreases the amplitude of the accommodation reflex and induces early satiety.

Functional dyspepsia: mechanisms of symptom generation and appropriate management of patients

With the exception of predominant heartburn, the management of upper abdominal symptoms not caused by an organic disorder remains a challenge. Systematic reviews of large trials show that suppressing acid secretion and eradicating Helicobacter pylori, prokinetics, and antidepressants have inconsistent effects on the treatment of functional dyspepsia. This inconsistent therapeutic efficacy has been attributed to the heterogeneity of patients, and the contribution of multiple mechanisms to development of symptoms. To achieve greater therapeutic efficacy, it may be necessary to target the therapeutic approach to a specific pathophysiology, such as impaired gastric emptying.

Appetite suppression through delayed fat digestion

High-fat diets are often associated with greater caloric intake and weight gain. Since satiety during fat intake is induced by fat in the intestine we investigated the efficiency of a lipid compound that retards fat digestion to regulate fat intake. We found this compound to reduce high-fat food intake, body weight and blood lipids in Sprague-Dawley rats, without causing steatorrhea. The absence of steatorrhea is explained by an increased pancreatic lipase/colipase secretion, compensating the impaired lipolysis by the added compound. The animals also had an elevated CCK secretion. The satiety for fat may be the consequence of elevated CCK and procolipase/enterostatin levels. We conclude that compounds can be found that delay intestinal fat digestion and control high-fat food intake through the release of satiety signals, without causing steatorrhea. The absence of steatorrhea makes such compounds advantageous over lipase inhibitors in the treatment of obesity.

Dietary factors in functional dyspepsia

Functional dyspepsia (FD) is characterized by upper gastrointestinal symptoms, which are frequently exacerbated by meal ingestion. While subgroups of FD patients exhibit a range of disturbances in upper gastrointestinal motor function, including delayed gastric emptying and abnormal intragastric meal distribution, which may reflect impaired proximal gastric relaxation and/or antral dysmotility, the association between symptoms and abnormalities in motor function appears to be relatively weak. More recently, the concept of visceral hypersensitivity to mechanical and chemical/nutrient stimuli has been promoted as important in the aetiology of dyspeptic symptoms. Somewhat surprisingly, the role of 'dietary' factors, that is, those factors, related directly to food ingestion, including patterns of nutrient intake, potential intolerance to specific foods or macronutrients, as well as cognitive factors, have been largely ignored. Moreover, presently available treatments fail to take into account the fact that symptoms are frequently induced by eating. This review focuses on the relevance of 'dietary' factors to FD.

Nutrition and motility disorders

The purpose of this article is to give an overview of the relation between feeding and gastrointestinal symptoms and complaints, and to review different motility disorders that have implications for food intake. We also report the consequences for nutrition state and the evidence-based principles of dietary modification in patients with motility disorders.

Gastric motor and sensory function

PURPOSE OF REVIEW

Abnormalities of gastric sensory and motor function are considered key players in the pathogenesis of upper gastrointestinal symptoms in functional dyspepsia and in gastroparesis. This review summarizes recent progress in our understanding of normal and pathologic gastric sensory and motor function.

RECENT FINDINGS

Several novel tests have been developed to study gastric sensitivity and meal-induced accommodation, including scintigraphic analysis of meal distribution within the stomach, single photon emission computed tomography of gastric volumes, and nutrient or water challenge tests. Several studies have reported on the occurrence of delayed gastric emptying in functional dyspepsia and in gastroparesis, but the correlation with symptoms was generally poor. The pathways and neurotransmitter involved in gastric hypersensitivity are progressively being unraveled. Several studies have confirmed and focused on increased symptom occurrence after nutrient challenge in functional dyspepsia. The role of the proximal stomach in the control of food intake and the stomach as a target in the treatment of obesity are areas of intense research. Studies have reported on pharmacologic approaches as well as electric stimulation in the treatment of gastric sensorimotor dysfunction.

SUMMARY

Progress in our understanding of normal and abnormal gastric sensory and motor function may lead to new or improved treatment modalities. Areas of major advances are the study of meal-induced symptoms in functional dyspepsia, unraveling of the role of the stomach in the control of food intake, and the use of gastric electric stimulation in gastroparesis and in obesity.

Nutrients and dyspepsia: paradigms and reality

PURPOSE OF REVIEW

Dyspepsia is a common disorder that presents as persistent or recurrent abdominal pain or discomfort in the upper abdomen and originates from organic or functional causes. Heterogeneous disorders, physiopathological, psychosomatic, sociocultural, demographic and genetic components have a great impact on its presentation. Physiopathological elements and the influence of nutrients on symptomatology are discussed to help establish clearer guidelines for treatment.

RECENT FINDINGS

Gastric emptying is affected by physiological, pharmacological and dietary factors and is translated into symptoms and signs such as anorexia, nausea, vomiting, weight loss and abdominal pain. Liquid or solid meals may cause early or delayed emptying, which is associated with symptoms of postprandial fullness. Abnormal glucose and electrolyte serum values may also cause transitory emptying delay. Fatty and acid nutrients have also been reported to aggravate symptoms of functional dyspepsia, especially after large meals. Studies have also pointed at food sensibility and the effect of Helicobacter pylori infection on gastric emptying in symptomatic patients. Patients may suffer antral hypomotility and total/partial postingestion pattern conversion. Spinal brain axis dysfunction caused by peripheral inflammation is associated with gastric dysmotility. An association between symptoms and functional polymorphisms is pending further clarification. It has been questioned whether the genotype is associated with a specific physiopathological mechanism, postinfectious functional disorders or psychological/social alterations.

SUMMARY

The treatment of dyspepsia is empiric and is directed at improving symptoms associated with alterations in emptying, postprandial accommodation, hypersensibility and hyperalgesia. Further studies are required to correlate symptoms with food kinetics at the initial postfood ingestion stages.

Pathophysiology of functional dyspepsia

Functional dyspepsia is a highly prevalent symptom complex and a heterogeneous disorder. Recent studies showed potential associations between specific pathophysiologic disturbances and dyspeptic symptoms. Delayed gastric emptying reported in about 30% of patients with functional dyspepsia is associated with the symptoms of postprandial fullness, nausea, and vomiting. Impaired gastric accommodation present in 40% of functional dyspepsia patients is found to be associated with early satiety. Hypersensitivity to gastric distension is observed in 37% of functional dyspepsia patients and associated with the symptoms of postprandial pain, belching, and weight loss. Psychosocial factors and altered response to duodenal lipids or acid have also been identified as pathophysiologic mechanisms.