Effects of tropisetron, a 5-HT3 receptor antagonist, on proximal gastric motor and sensory function in nonulcer dyspepsia

Dietary Lipid Modulation of Intestinal Serotonin in Ballan Wrasse (Labrus bergylta)-In Vitro Analyses

Serotonin (5-HT) is pivotal in the complex regulation of gut motility and consequent digestion of nutrients via multiple receptors. We investigated the serotonergic system in an agastric fish species, the ballan wrasse (Labrus bergylta) as it represents a unique model for intestinal function. Here we present evidence of the presence of enterochromaffin cells (EC cells) in the gut of ballan wrasse comprising transcriptomic data on EC markers like adra2a, trpa1, adgrg4, lmxa1, spack1, serpina10, as well as the localization of 5-HT and mRNA of the rate limiting enzyme; tryptophan hydroxylase (tph1) in the gut epithelium. Second, we examined the effects of dietary marine lipids on the enteric serotonergic system in this stomach-less teleost by administrating a hydrolyzed lipid bolus in ex vivo guts in an organ bath system. Modulation of the mRNA expression from the tryptophan hydroxylase tph1 (EC cells isoform), tph2 (neural isoform), and other genes involved in the serotonergic machinery were tracked. Our results showed no evidence to confirm that the dietary lipid meal did boost the production of 5-HT within the EC cells as mRNA tph1 was weakly regulated postprandially. However, dietary lipid seemed to upregulate the post-prandial expression of tph2 found in the serotonergic neurons. 5-HT in the intestinal tissue increased 3 hours after "exposure" of lipids, as was observed in the mRNA expression of tph2. This suggest that serotonergic neurons and not EC cells are responsible for the substantial increment of 5-HT after a lipid-reach "meal" in ballan wrasse. Cells expressing tph1 were identified in the gut epithelium, characteristic for EC cells. However, Tph1 positive cells were also present in the lamina propria. Characterization of these cells together with their implications in the serotonergic system will contribute to broad the scarce knowledge of the serotonergic system across teleosts.

Immune-Kynurenine Pathways and the Gut Microbiota-Brain Axis in Anxiety Disorders

Anxiety disorders are a complex set of illnesses in which genetic factors, particularly stress, play a role in the etiopathogenesis. In recent years, inflammation and intestinal microbiota have also been included in this complex network of relationships. The functions associated with tryptophan catabolism and serotonin biosynthesis have long been associated with anxiety disorders. Tryptophan catabolism progresses toward the path of the kynurenine in the presence of stress and inflammation. The catabolism of kynurenine is a pathway in which many enzymes play a role and a large number of catabolites with neuroactive properties occur. The body's serotonin biosynthesis is primarily performed by enterochromaffin cells located in the intestines. A change in the intestinal microbiota composition (dysbiosis) directly affects the serotonin biosynthesis. Stress, unhealthy nutrition, and the use of antibiotics cause dysbiosis. In the light of this new perspective, the role of dysbiosis-induced inflammation and kynurenine pathway catabolites activated sequentially come into prominence in the etiopathogenesis of anxiety disorders.

Influence of the 5-HT3 receptor antagonist ondansetron on gastric sensorimotor function and nutrient tolerance in healthy volunteers

BACKGROUND

Serotonin is believed to be involved in the regulation of the gastric accommodation reflex in man however which receptor subtype(s) are involved remains to be elucidated.

METHODS

Eleven healthy subjects (nine men, age 19-30) underwent a gastric barostat and a drinking test after treatment with either placebo or ondansetron (8 mg intravenously). During the barostat protocol an intragastric flaccid bag was stepwise distended (2 mmHg increments 2 min) to determine gastric compliance and sensitivity to distention. Subsequently, the pressure level was set at intra-abdominal pressure +2 mmHg while volume was followed before and after administration of a liquid meal (200 mL; 300 kcal). During the drink test volunteers drank at a rate of 15 mL min(-1) until maximal satiation. Results (mean ± SEM) were compared using t-tests and mixed model analysis.

KEY RESULTS

Gastric compliance was not significantly altered by ondansetron (51.5 ± 5.6 vs 49.2 ± 5.2 mL mmHg(-1)), neither were the pressure thresholds for first perception or discomfort. Ondansetron treatment did not affect basal gastric tone (173 ± 14 vs 156 ± 12 mL), neither did it affect the amplitude of the meal-induced relaxation (160 ± 52 vs 131 ± 43 mL) or the maximum volume increase after the meal (264 ± 54 mL vs 234 ± 51 mL). During the drinking test the amount of liquid meal ingested at maximum satiation was significantly increased by ondansetron (784 ± 74 vs 907 ± 64 mL, P < 0.05).

CONCLUSIONS & INFERENCES

These data suggest that 5-HT acting at 5-HT(3) receptors is not involved in the control of gastric sensorimotor function, but contributes to the regulation of hunger and satiation in man.

The effects of acute citalopram dosing on gastric motor function and nutrient tolerance in healthy volunteers

BACKGROUND

It is unclear whether endogenous serotonin release is involved in the regulation of gastric motility and food intake.

AIM

To study the effect of acute administration of the selective serotonin reuptake inhibitor citalopram on gastric motor function in man.

METHODS

Nineteen healthy volunteers underwent a gastric barostat, gastric emptying and/or a drinking test after dosing with either placebo or citalopram (20 mg intravenously). In the barostat protocol, a flaccid bag was introduced in the stomach and inflated at intra-abdominal pressure +2 mmHg, volume was recorded before and after administration of a liquid meal (300 kcal). Gastric emptying for solids and liquids was simultaneously assessed using the ¹⁴C-octanoic acid/¹³C-glycine breath test. During the drink test, volunteers drank at a rate of 15 mL/min until maximal satiation. Citalopram was compared with placebo using t-tests and mixed model analysis.

RESULTS

Citalopram induced a significant preprandial gastric relaxation (volume increase of 154 ± 55 mL vs. -38 ± 33 mL after placebo dosing; P < 0.05), whereas the postprandial volume increase was significantly decreased after citalopram treatment (F₁₂.₈₀ = 4.78, P < 0.0001; maximum volume increase was 304 ± 40 vs. 201 ± 54 mL after placebo and citalopram treatment respectively). Citalopram enhanced solid (123 ± 17 vs. 77 ± 6 min, P < 0.05) but not liquid emptying (62 ± 6 vs. 57 ± 4 min). Satiation scores during the drink test were lower after citalopram (F₁₉.₁₅₃ = 2.02, P = 0.01; volunteers drank 998 ± 129 vs. 765 ± 79 mL after citalopram and placebo treatment respectively).

CONCLUSION

The observed effects indicate a role for serotonin in the control of gastric motility and food intake.

Spinal NMDA NR1 subunit expression following transient TNBS colitis

BACKGROUND

N-methyl-D-aspartic acid (NMDA) receptors play an important role in the development of hypersensitivity to visceral and somatic stimuli following inflammation or tissue injury. Our objective was to investigate the role of NMDA NR1 receptors in the spinal cord (T10-L1; L4-S1) of a subset of rats that remain hypersensitive following the histological resolution of TNBS-induced colitis compared to saline treated rats and rats that had recovered both behaviorally and histologically. We hypothesized that NMDA NR1 subunit expression mediates hypersensitivity following transient TNBS colitis.

METHODS

Male Sprague-Dawley rats (150 g-250 g) received 20 mg/rat intracolonic trinitrobenzene sulfonic acid (TNBS) in 50% ethanol or saline. Animals underwent nociceptive visceral/somatic pain testing 16 weeks after resolution of TNBS colitis. Animals were sacrificed and their spinal cords (T10-L1; L4-S1) were retrieved and 2-dimensional polyacrylamide gel electrophoresis and immunohistocytochemistry techniques were used to investigate spinal-NMDA receptor expression.

RESULTS

NR1(001) was the only NMDA NR1 receptor subunit that was expressed in recovered and control rats, whereas hypersensitive animals expressed NR1(011) and NR1(111) as well as NR1(001) subunits. Immunohistochemistry analysis demonstrated increased expression of NMDA NR1-N1, C1, and C2-plus expression in laminae I and II of the spinal cord (T10-L1; L4-S1) in hypersensitive rats but not in recovered/control rats.

CONCLUSIONS

Selective increases in the expression of the NMDA NR1 splice variants occur in hypersensitive rats following resolution of TNBS colitis. This suggests that the NMDA NR1 receptor plays an important role in the development of neuronal plasticity and central sensitization. The recombination of NR1 splice variants may serve as a key functional protein that maintains hypersensitivity following resolution of TNBS colitis.

Effect of the 5-HT3 receptor antagonist, ondansetron, on gastric size in dyspeptic patients with impaired gastric accommodation

BACKGROUND

A reduction of gastric accommodation after a meal has been documented in patients with idiopathic dyspepsia. In these patients the administration of a 5-HT3 receptor antagonist may reduce some of the dyspeptic symptoms; it is not clear however, whether these drugs influence gastric adaptation to distension as well.

AIM

To evaluate the effects of the 5-HT3 receptor antagonist, ondansetron, on gastric distension after a liquid meal in dyspeptic patients with reduced gastric accommodation.

METHODS

Before and after a 500 ml water load, gastric accommodation (area of the proximal and distal stomach) was evaluated using real-time ultrasonography in 21 idiopathic dyspepsia patients and 26 healthy controls. In dyspeptic patients, the test was repeated twice: after the administration of placebo and after ondansetron 8 mg i.v. (in both cases, 15 min prior to the water load). Secondary outcomes were epigastric pain, fullness and nausea as assessed by a visual analogue scale at basal and after ondansetron.

RESULTS

Fasting gastric size was similar in dyspeptic and controls. Compared with controls, dyspeptic patients showed a statistically significant smaller area of the proximal stomach (14.7+/-1.2 cm(2) vs. 18.6+/-1.4 cm(2), respectively; p=0.0247). In dyspeptic patients, gastric proximal and distal size did not change significantly following placebo, whereas after the administration of ondansetron the mean area of the proximal and distal stomach significantly increased (proximal stomach: 14.6+/-1.6 cm(2) placebo, 20.4+/-1.9 cm(2) ondansetron, p=0.0095; distal stomach: 8.9+/-0.9 placebo, 11.4+/-1.2cm(2) ondansetron, p=0.0409). Of the symptoms, only nausea was significantly reduced after ondansetron.

CONCLUSION

In dyspeptic patients with impaired gastric accommodation, ondansetron reverts gastric accommodation to within the range of controls.

Serotonergic and non-serotonergic targets in the pharmacotherapy of visceral hypersensitivity

Visceral hypersensitivity is considered a key mechanism in the pathogenesis of functional gastrointestinal (GI) disorders. Targeting visceral hypersensitivity seems an attractive approach to the development of drugs for functional GI disorders. This review summarizes current knowledge on targets for the treatment of visceral hypersensitivity, and the status of current and future drug and probiotic treatment development, and the role of pharmacogenomic factors.

The serotonin signaling system: from basic understanding to drug development for functional GI disorders

Serotonin is an important gastrointestinal signaling molecule. It is a paracrine messenger utilized by enterochromaffin (EC) cells, which function as sensory transducers. Serotonin activates intrinsic and extrinsic primary afferent neurons to, respectively, initiate peristaltic and secretory reflexes and to transmit information to the central nervous system. Serotonin is also a neurotransmitter utilized by a system of long descending myenteric interneurons. Serotonin is synthesized through the actions of 2 different tryptophan hydroxylases, TpH1 and TpH2, which are found, respectively, in EC cells and neurons. Serotonin is inactivated by the serotonin reuptake transporter (SERT)-mediated uptake into enterocytes or neurons. The presence of many serotonin receptor subtypes enables selective drugs to be designed to therapeutically modulate gastrointestinal motility, secretion, and sensation. Current examples include tegaserod, a 5-HT(4) partial agonist, which has been approved for treatment of irritable bowel syndrome (IBS) with constipation in women and for chronic constipation in men and women. The 5-HT(3) antagonists, granisetron and ondansetron, are useful in combating the nausea associated with cancer chemotherapy, and alosetron is employed in the treatment of IBS with diarrhea. Serotonergic signaling abnormalities have also been putatively implicated in the pathogenesis of functional bowel diseases. Other compounds, for which efficacy has not been rigorously established, but which may have value, include tricyclic antidepressants and serotonin selective reuptake inhibitors to combat IBS, and 5-HT(1) agonists, which enhance gastric accommodation, to treat functional dyspepsia. The initial success encountered with serotonergic agents holds promise for newer and more potent insights and therapies of brain-gut disorders.

Review article: drugs interfering with visceral sensitivity for the treatment of functional gastrointestinal disorders--the clinical evidence

At present, the concept of visceral hypersensitivity provides the leading hypothesis regarding the generation of symptoms in functional gastrointestinal disorders. This paper discusses the current clinical evidence for drugs that have been proposed to interfere with visceral sensitivity in functional gastrointestinal disorders. Several possible pharmacological targets have been identified to reduce visceral pain and to reverse the processes underlying the persistence of visceral hypersensitivity. However, most of the available evidence comes from experimental animal models and cannot simply be extrapolated to patients with functional gastrointestinal disorders. In this review, we selected five drug classes that have been shown to exhibit visceral analgesic properties in experimental studies, and of which data were available regarding their clinical efficacy. These included opioid substances, serotonergic agents, antidepressants, somatostatin analogues and alpha(2)-adrenergic agonists. Although clinical trials show a limited benefit, in particular for serotonergic agents, the evidence illustrating that these effects result from normalization of visceral sensation is currently lacking. Therefore, we conclude that the concept of targeting visceral hypersensitivity as a treatment for functional gastrointestinal disorders is still controversial. Future evaluations require patient selection based on the presence of visceral hypersensitivity and application of compounds that exhibit 'true' viscerosensory effects.

Functional dyspepsia: motor abnormalities, sensory dysfunction, and therapeutic options

Functional dyspepsia is a common condition, but as yet, the underlying etiology is unclear. In this article, upper gastrointestinal motor and sensory physiology are reviewed and the current evidence for motor and/or sensory functional abnormalities causing dyspeptic symptoms is presented. The complex interrelationship between abnormal motor activity and sensation is explored, as well as the potential roles for autonomic dysfunction and psychological state in modulating gastrointestinal sensation and motor function. Finally, based on clinical trial evidence, a treatment pathway for functional dyspepsia is suggested.

A dose-ranging, placebo-controlled, randomized trial of alosetron in patients with functional dyspepsia

BACKGROUND

Functional dyspepsia is characterized by upper abdominal pain or discomfort.

AIM

To assess the benefit of the 5-HT3-receptor antagonist alosetron in a pilot, dose-ranging, placebo-controlled, multicentre, randomized clinical trial.

METHODS

A total of 320 functional dyspepsia patients received placebo (n=81), or alosetron 0.5 mg b.d. (n=77), 1.0 mg b.d. (n=79) or 2.0 mg b.d. (n=83) for 12 weeks, followed by 1 week of follow-up. Primary efficacy was the 12-week average rate of adequate relief of upper abdominal pain or discomfort. Secondary endpoints assessed pain and upper gastrointestinal symptoms.

RESULTS

Twelve-week average rates of adequate relief of pain or discomfort were 46% (95% CI: 37-54%), 55% (95% CI: 46-63%), 55% (95% CI: 47-64%) and 47% (95% CI: 38-55%) in the placebo, 0.5 mg, 1.0 mg and 2.0 mg alosetron groups, respectively. Alosetron 0.5 mg or 1.0 mg showed potential benefit over placebo for early satiety and postprandial fullness. Females showed greater responses compared to males. Patients with adequate relief had significantly (P < 0.001) greater reductions in severity and frequency of functional dyspepsia symptoms than those without adequate relief. Constipation was the most commonly reported adverse event.

CONCLUSIONS

Alosetron showed potential benefit in relieving functional dyspepsia symptoms compared to placebo. Patients with adequate relief of upper abdominal pain or discomfort showed improvements in multiple functional dyspepsia symptoms.

Effects of nutrients and serotonin 5-HT3 antagonism on symptoms evoked by distal gastric distension in humans

Distal gastric distension may contribute to meal-related dyspeptic symptoms. This study's aims were to determine the effects of distinct nutrient classes on symptoms induced by distal gastric distension and their dependence on 5-hydroxytryptamine(3) (5-HT3) receptors. Nine healthy subjects rated pain, nausea, and bloating induced by isobaric distal gastric distensions (6-24 mmHg) during duodenal lipid, carbohydrate, protein, or saline perfusion after treatment with placebo or the 5-HT3 receptor antagonist granisetron (10 microg/kg iv). Distensions produced greater pain, nausea, and bloating with lipid at 1.5 kcal/min compared with saline (P < or = 0.02), primarily because of greater distal gastric volumes at each distending pressure. In contrast, carbohydrate and protein had no significant effect. At 3 kcal/min, lipid increased symptoms through a volume-independent as well as a volume-dependent effect. Granisetron did not affect symptom perception or gastric pressure-volume relationships. In conclusion, isobaric distal gastric distension produces more intense symptoms during duodenal lipid compared with saline perfusion. Symptom perception during distal gastric distension is unaffected by 5-HT3 receptor antagonism.

Effects of the 5-HT3 antagonist cilansetron vs placebo on phasic sigmoid colonic motility in healthy man: a double-blind crossover trial

AIMS

5-hydroxytryptamine3 receptor antagonists act antiemetically and slow colonic transit. This study evaluated effects of the high-affinity 5-HT3 antagonist, cilansetron, on fasting, meal-and anticholinesterase-stimulated phasic contractile activity of the human sigmoid colon as well as on bowel habits and stool consistency.

METHODS

Five female and seven male healthy volunteers received, during three 7 day periods separated by 7 day wash-out periods, 4 mg cilansetron, 8 mg cilansetron or placebo three times daily orally under random, double-blind, crossover conditions. On day 8 of each treatment period, motility 20-40 cm from the anal verge was recorded using five pressure sensors spaced at 5 cm intervals. After a basal 30 min, subjects swallowed a further dose of the scheduled treatment; 60 min later, blood was taken for the determination of plasma cilansetron levels. Thereafter, subjects ingested a 4200 kJ meal and 250 ml sweetened mallow tea (166 kJ); 90 min after meal onset, 1 mg neostigmine was administered intramuscularly and motility recording was continued for 60 min

RESULTS

Phasic contractile activity and intraluminal base-line pressure increased postprandially and more so after neostigmine. With cilansetron, the area under the pressure curve as the primary outcome variable and the number of contractions were significantly greater than with placebo (P = 0.005), amplitude and duration of contractions and base-line pressure were not affected. The effects of the two cilansetron dosages did not differ. With cilansetron, stool tended to become firmer. No adverse effects were observed. Plasma levels were highest with 8 mg cilansetron.

CONCLUSIONS

Cilansetron slightly augments meal-stimulated and markedly neostigmine-stimulated phasic motility of the sigmoid colon. When administered over 7 days, it tends to increase stool consistency and is well tolerated.