Influence of acute tryptophan depletion on gastric sensorimotor function in humans

Effect of intracolonic volume on gastric sensory-motor responses in constipation-predominant irritable bowel syndrome

BACKGROUND

Interaction between gut stimuli may induce symptom overlap in patients with functional gastrointestinal disorders. The aim is to determine the effect of increased volumes of colonic contents on gastric sensory/motor responses and satiety in patients with constipation-predominant irritable bowel syndrome (IBS-C) and overlapping dyspeptic symptoms, and a cohort of healthy subjects.

METHODS

In 15 patients with IBS-C and 10 healthy subjects, the effect of real versus sham colonic filling with gas (1080 ml) on gastric sensitivity (measured by stepwise distensions of the stomach), gastric compliance, abdominal perception, and nutrient drink tolerance was studied on separate days.

RESULTS

In healthy subjects, colonic gas filling induced an increment in gastric sensitivity to distension (mean score 2.0 ± 0.2 before, and 3.0 ± 0.4 after; p = 0.038). In IBS, basal sensitivity was greater and remained unchanged after colonic gas filling (score 4.0 ± 0.1 and 3.8 ± 0.3, respectively; p < 0.001 vs. basal in health). Colonic gas infusion induced abdominal symptoms that were significantly greater in IBS-C (score 2.6 ± 0.1) than in health (score 1.7 ± 0.4; p = 0.027), with minor changes in gastric tone, and no changes in gastric compliance in both groups. Colonic filling produced a profound reduction in nutrient drink tolerance in IBS (791 ± 87 ml sham filling, 491 ± 58 ml gas filling; p < 0.001) but only a minor reduction in health (940 ± 70 ml sham filling, 860 ± 94 ml gas filling; p = 0.223).

CONCLUSIONS & INFERENCES

The volume of the colonic contents modulates satiety in patients with IBS-C, due to a general visceral pan-hypersensitivity. These effects should be considered in the choice of treatment for constipation in these patients.

Circadian Rhythms and Melatonin Metabolism in Patients With Disorders of Gut-Brain Interactions

Circadian rhythms are cyclic patterns of physiological, behavioural and molecular events that occur over a 24-h period. They are controlled by the suprachiasmatic nucleus (SCN), the brain’s master pacemaker which governs peripheral clocks and melatonin release. While circadian systems are endogenous, there are external factors that synchronise the SCN to the ambient environment including light/dark cycles, fasting/fed state, temperature and physical activity. Circadian rhythms also provide internal temporal organisation which ensures that any internal changes that take place are centrally coordinated. Melatonin synchronises peripheral clocks to the external time and circadian rhythms are regulated by gene expression to control physiological function. Synchronisation of the circadian system with the external environment is vital for the health and survival of an organism and as circadian rhythms play a pivotal role in regulating GI physiology, disruption may lead to gastrointestinal (GI) dysfunction. Disorders of gut-brain interactions (DGBIs), also known as functional gastrointestinal disorders (FGIDs), are a group of diseases where patients experience reoccurring gastrointestinal symptoms which cannot be explained by obvious structural abnormalities and include functional dyspepsia (FD) and irritable bowel syndrome (IBS). Food timing impacts on the production of melatonin and given the correlation between food intake and symptom onset reported by patients with DGBIs, chronodisruption may be a feature of these conditions. Recent advances in immunology implicate circadian rhythms in the regulation of immune responses, and DGBI patients report fatigue and disordered sleep, suggesting circadian disruption. Further, melatonin treatment has been demonstrated to improve symptom burden in IBS patients, however, the mechanisms underlying this efficacy are unclear. Given the influence of circadian rhythms on gastrointestinal physiology and the immune system, modulation of these rhythms may be a potential therapeutic option for reducing symptom burden in these patients.

Gastric Motor Functions in Patients With Mood Disorders and Functional Gastroduodenal Symptoms

OBJECTIVE

Functional gastroduodenal symptoms (FGDSs) may result from perturbations in gastric emptying (GE) and gastric accommodation (GA), which are variably affected by acute stress. This study aimed to examine whether individuals who have both mood disorder and FGDS exhibit differences in GE and GA using standardized, validated, and reproducible noninvasive methods.

METHODS

Using a data retrieval program, 1554 individuals at a single center were identified after having undergone measurements of GE by scintigraphy of a 99mTc-radiolabeled egg (320 kcal, 30% fat meal) and GA by single-photon emission computed tomography to assess the underlying pathophysiology in FGDS. An extensive medical record review identified 267 of these individuals as having diagnoses of depression, anxiety, or comorbid anxiety/depression (CAD). Differences in GE and GA as related to the presence of anxiety or depressive disorders were analyzed using one-way analysis of variance on ranks and Mann-Whitney tests for the two-group comparisons.

RESULTS

Sixty-three patients with anxiety, 134 with depression, and 70 with CAD were identified. GE at 1 hour was slower (p = .04) and GE at 2 hours numerically decreased (p = .07) for depression compared with anxiety. GA was diminished for CAD compared with anxiety (p = .04) and depression (p = .009). There were no differences in fasting gastric volume or GE at 4 hours.

CONCLUSIONS

In this study examining GE and GA in anxiety and depressive disorders among patients with FGDS, the combined presence of anxiety and depression was associated with impaired GA compared with patients with depression or anxiety alone, and early GE seemed to be slower in those with depression compared with patients with anxiety.

Effects of Acute Tryptophan Depletion on Human Taste Perception

Taste perception has been reported to vary with changes in affective state. Distortions of taste perception, including blunted recognition thresholds, intensity, and hedonic ratings have been identified in those suffering from depressive disorders. Serotonin is a key neurotransmitter implicated in the etiology of anxiety and depression; systemic and peripheral manipulations of serotonin signaling have previously been shown to modulate taste detection. However, the specific effects of central serotonin function on taste processing have not been widely investigated. Here, in a double-blind placebo-controlled study, acute tryptophan depletion was used to investigate the effect of reduced central serotonin function on taste perception. Twenty-five female participants aged 18-28 attended the laboratory on two occasions at least 1 week apart. On one visit, they received a tryptophan depleting drink and on the other, a control drink was administered. Approximately, 6 h after drink consumption, they completed a taste perception task which measured detection thresholds and supra-threshold perceptions of the intensity and pleasantness of four basic tastes (sweet, sour, bitter, and salt). While acutely reducing central levels of serotonin had no effect on the detection thresholds of sweet, bitter, or sour tastes, it significantly enhanced detection of salt. For supra-threshold stimuli, acutely reduced serotonin levels significantly enhanced the perceived intensity of both bitter and sour tastes and blunted pleasantness ratings of bitter quinine. These findings show manipulation of central serotonin levels can modulate taste perception and are consistent with previous reports that depletion of central serotonin levels enhances neural and behavioral responsiveness to aversive signals.

The Role of GI Peptides in Functional Dyspepsia and Gastroparesis: A Systematic Review

Functional dyspepsia (FD) and gastroparesis (GP) are common disorders of the upper gastrointestinal tract. The pathophysiology of these conditions is likely to be heterogenous, and factors such as altered motility, sensitivity and response to nutrition have been identified as putative underlying mechanisms. Motility, sensitivity as well as responses to nutrition can be influenced or mediated by peptide hormones and serotonin released from the gastrointestinal mucosa. This review summarizes the role of GI peptides in functional dyspepsia and gastroparesis. In most studies, the levels of somatostatin, ghrelin, and motilin did not differ between healthy volunteers and FD or GP patients, but higher symptom burden was often correlated with higher peptide levels. Ghrelin and motilin receptor agonists showed promising results in improvement of the gastric emptying, but the link with improvement of symptoms is less predictable. Serotonin agonists have a potential to improve symptoms in both FD and idiopathic gastroparesis. Drugs acting on the GLP-1 and on the PYY receptors deserve further investigation. There is a need for systematic large scale studies.

NPs/NPRs Signaling Pathways May Be Involved in Depression-Induced Loss of Gastric ICC by Decreasing the Production of mSCF

It is well known that natriuretic peptides (NPs) are involved in the regulation of gastrointestinal motility. Interstitial cells of Cajal (ICC) are the pacemaker cells of gastrointestinal motility and gastrointestinal dyskinesia is one of the important digestive tract symptoms of depression. However, it is unclear whether they are involved in depression-induced loss of ICC. The aim of the present study was to investigate the relationship between the natriuretic peptide signaling pathway and depression-induced loss of gastric ICC in depressed rats. These results showed that the expression of c-kit and stem cell factor (SCF) in smooth muscle layers of stomach were down-regulated in depressed rats at the mRNA and protein levels. The expression of natriuretic peptide receptor (NPR)-A, B and C were up-regulated in the stomach of depressed rats at the mRNA and protein levels. NPR-A, B and C can significantly decrease the expression of SCF to treat cultured gastric smooth muscle cells (GSMCs) obtained from normal rats with different concentrations of C-type natriuretic peptide (CNP). Pretreatment of cultured GSMCs with 8-Brom-cGMP (8-Br-cGMP, a membrane permeable cGMP analog), cANF (a specific NPR-C agonist) and CNP (10⁻⁶ mol/L) demonstrated that 8-Br-cGMP had a similar effect as CNP, but treatment with cANF did not. The results of the methyl thiazolyl tetrazolium bromide (MTT) assay indicated that high concentrations of cANF (10⁻⁶ mol/L) restrained the proliferation of cultured GSMCs. Taken together, these results indicate that the up-regulation of the NPs/NPR-C and NPs/NPR-A, B/cGMP signaling pathways may be involved in depression-induced loss of gastric ICC.

Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis

The serotonergic system forms a diffuse network within the central nervous system and plays a significant role in the regulation of mood and cognition. Manipulation of tryptophan levels, acutely or chronically, by depletion or supplementation, is an experimental procedure for modifying peripheral and central serotonin levels. These studies have allowed us to establish the role of serotonin in higher order brain function in both preclinical and clinical situations and have precipitated the finding that low brain serotonin levels are associated with poor memory and depressed mood. The gut-brain axis is a bi-directional system between the brain and gastrointestinal tract, linking emotional and cognitive centres of the brain with peripheral functioning of the digestive tract. An influence of gut microbiota on behaviour is becoming increasingly evident, as is the extension to tryptophan and serotonin, producing a possibility that alterations in the gut may be important in the pathophysiology of human central nervous system disorders. In this review we will discuss the effect of manipulating tryptophan on mood and cognition, and discuss a possible influence of the gut-brain axis.

Effects of L-tryptophan on gastric emptying evaluated by breath test in relation to gastric accommodation evaluated by Barostat in rats

Gastric emptying has been known to correlate the pyloric sphincter contractile function and distention-induced gastric relaxation (gastric accommodation). In the present study, the effects of L-tryptophan on the gastric emptying and accommodation were evaluated by breath test using [1-(13)C]acetic acid and Barostat study, respectively, in rats. L-Tryptophan significantly decreased Cmax and AUC120min and delayed Tmax, indicating the inhibition of gastric emptying. L-Tryptophan significantly enhanced the gastric accommodation. These findings show that L-tryptophan may inhibit the gastric emptying through the enhanced gastric accommodation. Therefore, L-tryptophan may be useful for the therapy of postprandial dyspepsia, especially for early satiety.

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 ¹³C 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.

Applying novel nutrient drink to clinical trial of functional dyspepsia

Background/Aims

The drink test has been regarded as a surrogate marker of gastric accommodation. The aims of this study were to develop a novel nutrient drink test (NDT) protocol and investigate its potential for application to a clinical trial of functional dyspepsia (FD).

Methods

A novel NDT was designed, involving drinking 125 mL of nutrient 4 times at 5-minute intervals or until maximal tolerability. Healthy volunteers and patients with FD rated their symptoms every 5 minutes for 20 minutes in a developmental study. Patients with FD were enrolled in an open trial of itopride for 4 weeks. NDT was performed before and after treatment. Improvement of integrative symptoms score during NDT after treatment for more than 50% compared with baseline was defined as responder.

Results

Total aggregate symptom scores, sum of symptom scores measured during NDT, were higher in FD patients (n = 40, 368.1 ± 245.3) than in controls (n = 19, 215.9 ± 171.2) (P = 0.018) in a developmental study. In an open trial of itopride, symptom scores measured during NDT decreased significantly at all time points after treatment in responders (n = 49), whereas did not in non-responders (n = 25). Total aggregate symptom score for NDT correlated significantly with integrative dyspeptic symptom score, sum of 8 symptom scores of NDI questionnaire, at baseline (r = 0.374, P = 0.001) and after treatment (r = 0.480, P < 0.001).

Conclusions

Our novel NDT can quantify dyspeptic symptoms and reflected therapeutic effects of itopride treatment in a clinical trial of FD patients. This NDT can be used as an effective parameter in clinical trials or drug development programs for assessing effects of novel therapies on postprandial symptoms.

Gastroduodenal mechanisms underlying functional gastric disorders

Functional dyspepsia (FD), a disorder thought to originate from the gastroduodenum, is one of the most prevalent functional gastrointestinal disorders. In this review, we focused on gastroduodenal mechanisms involved in the pathophysiology of FD. The roles of impaired gastric accommodation, delayed gastric emptying, hypersensitivity to gastric distention and to luminal agents, altered mucosal integrity, low-grade inflammation and psychological stress are reviewed. The underlying pathophysiology in FD is probably multifactorial, involving a combination of several of these factors, ultimately leading to symptom pattern and severity.

Association between the serotonin transporter triallelic genotype and eating problems is moderated by the experience of childhood trauma in women

OBJECTIVE

This study investigated a potential interaction between the triallelic polymorphism of the serotonin transporter gene (SLC6A4) promoter and the experience of childhood trauma on the number of problem eating behaviors.

METHOD

The study sample was comprised of 439 (64.7% female) Caucasian college students (mean age = 22.49, SD = 6.12). Participants completed questionnaires that assessed eating problems and experience of trauma in childhood (ages 0-12) and donated cheek cells for 5-HTTLPR and rs25531 genotyping.

RESULTS

Women carrying a lower expressing allele (i.e., L(G) or S) who were exposed to higher levels of childhood trauma reported significantly higher mean numbers of eating problems (gender × genotype × trauma interaction, p = .006).

DISCUSSION

These results are consistent with findings that the lower expressing alleles of the SLC6A4 promoter are associated with increased sensitivity to the negative impact of childhood stressors on adult behavioral outcomes.

Does acute tryptophan depletion affect peripheral serotonin metabolism in the intestine?

BACKGROUND

Serotonin (5-hydroxytryptamine; 5-HT), a tryptophan metabolite, plays an important regulatory role in the human central nervous system and in the gastrointestinal tract. Acute tryptophan depletion (ATD) is currently the most widely established method to investigate 5-HT metabolism.

OBJECTIVE

The aim of this study was to assess the effect of an acute decrease in the systemic availability of tryptophan on intestinal 5-HT metabolism and permeability.

DESIGN

Thirty-three healthy volunteers (17 with ATD, 3 of whom dropped out; 16 placebo) participated in this randomized placebo-controlled study. Plasma and duodenal mucosal concentrations of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), and kynurenic acid (KA) were measured by HPLC-mass spectrometry. Intestinal barrier function was assessed with a multisugar plasma test, and analysis of tight junction transcription was performed in duodenal biopsy samples obtained by gastroduodenoscopy.

RESULTS

Mucosal 5-HT, 5-HIAA, and KA concentrations remained unaltered by ATD. In contrast, ATD significantly decreased plasma 5-HT (P < 0.05) and 5-HIAA (P < 0.0001) concentrations. After endoscopy, a significant increase in plasma 5-HT concentrations was observed in the placebo group (P = 0.029) compared with the ATD group. Moreover, a significant increase in plasma KA concentrations over time was found in the placebo group (P < 0.05). No changes in intestinal barrier function were observed.

CONCLUSIONS

An acute decrease in precursor availability does not affect mucosal concentrations of serotonergic metabolites, in contrast with systemic concentrations. ATD alters biochemical responses to acute stress from the endoscopic examination reflected by lower 5-HT concentrations. Changes in 5-HT concentrations were paralleled by alterations in KA concentrations, which suggest competition between the 2 metabolic pathways for the mutual precursor. This trial was registered at clinicaltrials.gov as NCT00731003.

Functional dyspepsia

PURPOSE OF REVIEW

This review summarizes the recent progress in the epidemiology, pathophysiology and treatment of functional dyspepsia.

RECENT FINDINGS

Epidemiological, pathophysiological and therapeutic studies continue to examine the Rome III-proposed subdivision of functional dyspepsia into epigastric pain syndrome and postprandial distress syndrome. Although epidemiological studies support the subdivision, studies in patient samples show major overlap. Several studies identified overlapping functional disorders and psychosocial comorbidity as major contributors to the severity of functional dyspepsia and its impact on quality of life. Central processing of visceral stimuli, and its role in the pathogenesis of functional dyspepsia, as well as low-grade inflammation in the duodenum are important emerging topics in pathophysiology research. Therapeutic studies have reported on prokinetic and fundus-relaxing drugs. Acotiamide is a first-in-class drug with both prokinetic and fundus-relaxing properties that was evaluated in the recent phase 2 and phase 3 trials in functional dyspepsia.

SUMMARY

There is gradual progress in our understanding of the symptom pattern, impact and pathophysiology of functional dyspepsia. The areas of recent advances including the recognition of low-grade duodenal inflammation, central nervous system processing and the exploration of novel pharmacotherapeutic approaches are summarized in this review.

WITHDRAWN: Is acute tryptophan depletion a valid method to assess central serotonergic function?

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