Medium-term effects of a new 5HT3 antagonist, alosetron, in patients with carcinoid diarrhoea

Treatment for gastrointestinal and pancreatic neuroendocrine tumours: a network meta-analysis

BACKGROUND

Several available therapies for neuroendocrine tumours (NETs) have demonstrated efficacy in randomised controlled trials. However, translation of these results into improved care faces several challenges, as a direct comparison of the most pertinent therapies is incomplete.

OBJECTIVES

To evaluate the safety and efficacy of therapies for NETs, to guide clinical decision-making, and to provide estimates of relative efficiency of the different treatment options (including placebo) and rank the treatments according to their efficiency based on a network meta-analysis.

SEARCH METHODS

We identified studies through systematic searches of the following bibliographic databases: the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library; MEDLINE (Ovid); and Embase from January 1947 to December 2020. In addition, we checked trial registries for ongoing or unpublished eligible trials and manually searched for abstracts from scientific and clinical meetings.

SELECTION CRITERIA

We evaluated randomised controlled trials (RCTs) comparing two or more therapies in people with NETs (primarily gastrointestinal and pancreatic).

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies and extracted data to a pre-designed data extraction form. Multi-arm studies were included in the network meta-analysis using the R-package netmeta. We separately analysed two different outcomes (disease control and progression-free survival) and two types of NET (gastrointestinal and pancreatic NET) in four network meta-analyses. A frequentist approach was used to compare the efficacy of therapies.

MAIN RESULTS

We identified 55 studies in 90 records in the qualitative analysis, reporting 39 primary RCTs and 16 subgroup analyses. We included 22 RCTs, with 4299 participants, that reported disease control and/or progression-free survival in the network meta-analysis. Precision-of-treatment estimates and estimated heterogeneity were limited, although the risk of bias was predominantly low. The network meta-analysis of progression-free survival found nine therapies for pancreatic NETs: everolimus (hazard ratio [HR], 0.36 [95% CI, 0.28 to 0.46]), interferon plus somatostatin analogue (HR, 0.34 [95% CI, 0.14 to 0.80]), everolimus plus somatostatin analogue (HR, 0.38 [95% CI, 0.26 to 0.57]), bevacizumab plus somatostatin analogue (HR, 0.36 [95% CI, 0.15 to 0.89]), interferon (HR, 0.41 [95% CI, 0.18 to 0.94]), sunitinib (HR, 0.42 [95% CI, 0.26 to 0.67]), everolimus plus bevacizumab plus somatostatin analogue (HR, 0.48 [95% CI, 0.28 to 0.83]), surufatinib (HR, 0.49 [95% CI, 0.32 to 0.76]), and somatostatin analogue (HR, 0.51 [95% CI, 0.34 to 0.77]); and six therapies for gastrointestinal NETs: 177-Lu-DOTATATE plus somatostatin analogue (HR, 0.07 [95% CI, 0.02 to 0.26]), everolimus plus somatostatin analogue (HR, 0.12 [95%CI, 0.03 to 0.54]), bevacizumab plus somatostatin analogue (HR, 0.18 [95% CI, 0.04 to 0.94]), interferon plus somatostatin analogue (HR, 0.23 [95% CI, 0.06 to 0.93]), surufatinib (HR, 0.33 [95%CI, 0.12 to 0.88]), and somatostatin analogue (HR, 0.34 [95% CI, 0.16 to 0.76]), with higher efficacy than placebo. Besides everolimus for pancreatic NETs, the results suggested an overall superiority of combination therapies, including somatostatin analogues. The results indicate that NET therapies have a broad range of risk for adverse events and effects on quality of life, but these were reported inconsistently. Evidence from this network meta-analysis (and underlying RCTs) does not support any particular therapy (or combinations of therapies) with respect to patient-centred outcomes (e.g. overall survival and quality of life).

AUTHORS' CONCLUSIONS

The findings from this study suggest that a range of efficient therapies with different safety profiles is available for people with NETs.

Randomised study: effects of the 5-HT4 receptor agonist felcisetrag vs placebo on gut transit in patients with gastroparesis

BACKGROUND

Gastroparesis is defined by delayed gastric emptying with associated symptoms in the absence of mechanical obstruction.

AIM

To evaluate pharmacokinetics and pharmacodynamics of felcisetrag, a highly selective 5-HT₄ receptor agonist, on total gut transit in patients with documented delayed gastric emptying of solids.

METHODS

Single-centre, placebo-controlled study of 36 participants receiving placebo, 0.1mg, 0.3mg or 1.0mg of felcisetrag I.V. infusion, daily, for 3 days. At baseline, each participant completed a 4h, ^99m Tc-egg meal (300 kcal, 30% fat) gastric emptying test. Following infusion (Day 2), gastric, small bowel and colonic transit of solids were measured over 48h (same meal plus ¹¹¹ In-charcoal delivered in methacrylate-coated capsule). Samples were collected for pharmacokinetics. The primary endpoint was gastric emptying T_1/2 . Statistical analysis used baseline parameters as covariates (ANCOVA).

RESULTS

Patients (22 idiopathic, 14 diabetic gastroparesis) were randomised to felcisetrag (0.1 mg, n = 10; 0.3 mg, n = 9; 1.0 mg, n = 7) or placebo (n = 10). Compared to placebo, felcisetrag significantly accelerated gastric emptying T_1/2 , colonic filling at 6h, and 10% small bowel transit time (overall P < 0.01; all three doses individually Bonferroni corrected P < 0.05) for all three measurements. Ascending colon emptying (T_1/2 ) was significantly accelerated (all doses), and colonic transit at 48 hours was accelerated with 0.1 mg and 0.3 mg felcisetrag compared to placebo. Pharmacokinetic results were dose proportional. Felcisetrag was well tolerated with no clinically significant findings from clinical laboratory, vital signs or ECG.

CONCLUSION

I.V. felcisetrag significantly accelerated gastric, small bowel and colonic transit in patients with gastroparesis, and should be further evaluated for short-term treatment of gastric and intestinal motility disorders. ClinicalTrials.gov #NCT03281577.

Therapeutic Options for Neuroendocrine Tumors: A Systematic Review and Network Meta-analysis

IMPORTANCE

Multiple therapies are currently available for patients with neuroendocrine tumors (NETs), yet many therapies have not been compared head-to-head within randomized clinical trials (RCTs).

OBJECTIVE

To assess the relative safety and efficacy of therapies for NETs.

DATA SOURCES

PubMed, Embase, the Cochrane Central Register of Controlled Trials, trial registries, meeting abstracts, and reference lists from January 1, 1947, to March 2, 2018, were searched. Key search terms included neuroendocrine tumors, gastrointestinal neoplasms, therapy, and randomized controlled trial.

STUDY SELECTION

Randomized clinical trials comparing 2 or more therapies in patients with NETs (primarily gastrointestinal and pancreatic) were evaluated. Thirty RCTs met the selection criteria.

DATA EXTRACTION AND SYNTHESIS

Pairs of independent reviewers screened studies, extracted data, and assessed the risk of bias. A network meta-analysis with a frequentist approach was used to compare the efficacy of therapies; the Preferred Reporting Items for Systematic Reviews and Meta-analyses guideline was used.

MAIN OUTCOMES AND MEASURES

Disease control, progression-free survival, overall survival, adverse events, and quality of life.

RESULTS

The systematic review identified 30 relevant RCTs comprising 3895 patients (48.4% women) assigned to 22 different therapies for NETs. These therapies showed a broad range of risk for serious and nonserious adverse events. The network meta-analyses included 16 RCTs with predominantly a low risk of bias; nevertheless, precision-of-treatment estimates and estimated heterogeneity were limited. The network meta-analysis found 7 therapies for pancreatic NETs: everolimus (hazard ratio [HR], 0.35 [95% CI, 0.28-0.45]), everolimus plus somatostatin analogue (HR, 0.35 [95% CI, 0.25-0.51]), everolimus plus bevacizumab plus somatostatin analogue (HR, 0.44 [95% CI, 0.26-0.75]), interferon (HR, 0.37 [95% CI, 0.16-0.83]), interferon plus somatostatin analogue (HR, 0.31 [95% CI, 0.13-0.71]), somatostatin analogue (HR, 0.46 [95% CI, 0.33-0.66]), and sunitinib (HR, 0.42 [95% CI, 0.26-0.67]), and 5 therapies for gastrointestinal NETs: bevacizumab plus somatostatin analogue (HR, 0.22 [95% CI, 0.05-0.99]), everolimus plus somatostatin analogue (HR, 0.31 [95% CI, 0.11-0.90]), interferon plus somatostatin analogue (HR, 0.27 [95% CI, 0.07-0.96]), Lu 177-dotatate plus somatostatin analogue (HR, 0.08 [95% CI, 0.03-0.26], and somatostatin analogues (HR, 0.40 [95% CI, 0.21-0.78]) with higher efficacy than placebo and suggests an overall superiority of combination therapies.

CONCLUSIONS AND RELEVANCE

The findings from this study suggest that a range of efficient therapies with different safety profiles is available for patients with NETs.

Management of carcinoid syndrome: a systematic review and meta-analysis

Carcinoid syndrome (CS) is a debilitating disease caused by functional neuroendocrine tumors. Several treatment options are available to alleviate the hormonal symptoms, but their relative efficacy is unknown. Online databases were searched for publications on the treatment of CS symptoms. Independent reviewers assessed relevant publications for study quality and outcome. Meta-analysis of the outcomes of the intervention on CS-related symptoms was stratified by the type of treatment. We found 3682 therapeutic interventions on CS-specific outcomes were collected from 93 studies. Overall, the study qualities were poor with only six randomized controlled clinical trials. The somatostatin analogs octreotide and lanreotide induced symptomatic improvement in 65-72% and biochemical response in 45-46% of patients. An increase in dose or frequency or interclass switch led to a reduction of flushes and/or diarrhea in 72-84% of cases. Retrospective, institutional series showed that liver-directed therapy can improve symptoms in 82% of CS patients with a liver-dominant disease. The serotonin synthesis inhibitor telotristat ethyl reduced bowel movements in 40% of patients with diarrhea refractory to somatostatin analogs. Interferon-alpha controlled CS symptoms in 45-63% of cases. Favorable response has been noted after radionuclide therapy in subgroup analyses of studies not specifically involving CS patients. Chemotherapy and everolimus did not induce a significant response in the CS. We conclude that several treatment lines can be offered to patients suffering from the carcinoid syndrome. Initiation of randomized controlled trials with a primary outcome on carcinoid syndrome symptoms is strongly recommended.

Management of carcinoid syndrome: a systematic review and meta-analysis

Carcinoid syndrome (CS) is a debilitating disease caused by functional neuroendocrine tumors. Several treatment options are available to alleviate the hormonal symptoms, but their relative efficacy is unknown. Online databases were searched for publications on the treatment of CS symptoms. Independent reviewers assessed relevant publications for study quality and outcome. Meta-analysis of the outcomes of the intervention on CS-related symptoms was stratified by the type of treatment. We found 3682 therapeutic interventions on CS-specific outcomes were collected from 93 studies. Overall, the study qualities were poor with only six randomized controlled clinical trials. The somatostatin analogs octreotide and lanreotide induced symptomatic improvement in 65–72% and biochemical response in 45–46% of patients. An increase in dose or frequency or interclass switch led to a reduction of flushes and/or diarrhea in 72–84% of cases. Retrospective, institutional series showed that liver-directed therapy can improve symptoms in 82% of CS patients with a liver-dominant disease. The serotonin synthesis inhibitor telotristat ethyl reduced bowel movements in 40% of patients with diarrhea refractory to somatostatin analogs. Interferon-alpha controlled CS symptoms in 45–63% of cases. Favorable response has been noted after radionuclide therapy in subgroup analyses of studies not specifically involving CS patients. Chemotherapy and everolimus did not induce a significant response in the CS. We conclude that several treatment lines can be offered to patients suffering from the carcinoid syndrome. Initiation of randomized controlled trials with a primary outcome on carcinoid syndrome symptoms is strongly recommended.

Management of the hormonal syndrome of neuroendocrine tumors

Gastroenteropancreatic neuroendocrine tumors (GEP/NET) are unusual and rare neoplasms that present many clinical challenges. They characteristically synthesize store and secrete a variety of peptides and neuroamines which can lead to the development of distinct clinical syndrome, however many are clinically silent until late presentation with mass effects. Management strategies include surgery cure and cytoreduction with the use of somatostatin analogues. Somatostatin have a broad range of biological actions that include inhibition of exocrine and endocrine secretions, gut motility, cell proliferation, cell survival and angiogenesis. Five somatostatin receptors (SSTR1-SSTR5) have been cloned and characterized. Somatostatin analogues include octreotide and lanreotide are effective medical tools in the treatment and present selectivity for SSTR2 and SSTR5. During treatment is seen disapperance of flushing, normalization of bowel movements and reduction of serotonin and 5-hydroxyindole acetic acid (5-HIAA) secretion. Telotristat represents a novel approach by specifically inhibiting serotonin synthesis and as such, is a promising potential new treatment for patients with carcinoid syndrome. To pancreatic functionig neuroendocrine tumors belongs insulinoma, gastrinoma, glucagonoma and VIP-oma. Medical management in patients with insulinoma include diazoxide which suppresses insulin release. Also mTOR inhibitors may inhibit insulin secretion. Treatment of gastrinoma include both proton pump inhibitors (PPIs) and histamine H2 - receptor antagonists. In patients with glucagonomas hyperglycaemia can be controlled using insulin and oral blood glucose lowering drugs. In malignant glucagonomas smatostatin analogues are effective in controlling necrolytic migratory erythemia. Severe cases of the VIP-oma syndrome require supplementation of fluid losses. Octreotide reduce tumoral VIP secretion and control secretory diarrhoea.

Serotonin is a sword and a shield of the bowel: serotonin plays offense and defense

The gut contains the bulk of the body's serotonin (5-hydroxytryptamine, 5-HT); nevertheless, the physiological role that enteric 5-HT plays has not been determined. 5-HT is linked to gastrointestinal (GI) motility; increased intraluminal pressure causes enterochromaffin (EC) cells to secrete 5-HT, which stimulates intrinsic primary afferent neurons that initiate peristaltic reflexes. 5-HT is also an enteric neurotransmitter. Surprisingly, deletion of tryptophan hydroxylase-1 (TPH1), upon which 5-HT biosynthesis in EC cells depends, does not alter constitutive GI motility, whereas deletion of TPH2, upon which biosynthesis of neuronal 5-HT depends, slows intestinal transit and accelerates gastric emptying. TPH1 deletion, however, protects mice from experimental inflammation; 5-HT potentiation and TPH2 deletion each make inflammation more severe. Neuronal 5-HT is neuroprotective and recruits stem cells to give rise to new enteric neurons in adult mice. Mucosal 5-HT, therefore, may mobilize inflammatory effectors, which protect the gut from invasion, whereas neuronal 5-HT shields enteric neurons from inflammatory damage.

Potential biomarkers

A "biomarker" (biological marker) is an indicator of a bodily function that can be objectively measured. A wide range of possible biomarkers for IBS have been considered but at present only gut transit measured using radio-isotope markers meet the criteria of reproducibility and availability. While barostat studies perform reasonably in expert centers, to do them reproducibly requires considerable effort and standardization. This makes them unsuitable for widespread use. However radio-isotope tests are expensive and of limited availability so the search for other more convenient markers including blood and stool tests is still an important goal for the future.

LX-1031, a tryptophan 5-hydroxylase inhibitor, and its potential in chronic diarrhea associated with increased serotonin

LX-1031 is an oral, small molecule tryptophan 5-hydroxylase (TPH) inhibitor that reduces serotonin (5-HT) synthesis peripherally. It has potential for illnesses characterized by excess 5-HT, such as diarrhea-predominant irritable bowel syndrome (IBS-D) and carcinoid diarrhea. In vitro, inhibition of TPH1 occurred in 10(-8) -10(-7) mol L(-1) range. In vivo in rodents, LX-1031 has no effect on brain 5-HT while dose-dependently reducing 5-HT, particularly in the small bowel. After oral LX1031 in humans, systemic exposure is very low, plasma concentrations are linear in dose range 250-750 mg q.i.d.; the median T(1/2) for elimination is ∼ 20 h, and repeat administration for 14 days doubles C(max) . In ascending-single-dose and multiple-dose (14 days) trials in healthy volunteers, LX-1031, 2-4 g day(-1) significantly reduced urinary 5-hydroxyindoleacetic acid (5-HIAA) starting by Day 5, and persisting over the 14 day exposure. There are no dose-limiting toxicities in healthy subjects or remarkable adverse effects in clinical trials to date. Over a 28-day treatment period, LX-1031 was associated with improved weekly global scores (2/4 weeks) and improved stool consistency with lower urinary 5-HIAA excretion. LX-1031 appears promising for chronic diarrhea associated with increased 5-HT expression including IBS-D. Optimal doses, efficacy and safety in IBS clinical trials need to be fully elucidated; low systemic exposure, selectivity for TPH1 over TPH2, and lack of effect on brain 5-HT in several species suggest that LX-1031 is unlikely to cause affective disorders.

Serotonin and GI clinical disorders

Serotonin is widely distributed throughout the gut within both the enteric nerves and enterochromaffin (EC) cells. EC cells are located in the gut mucosa with maximal numbers in the duodenum and rectum where they act as signal transducers, responding to pressure and luminal substances both bacterial and dietary. Activation leads to serotonin release which acts on a range of receptors on mucosal afferent and myenteric interneurones to initiate secretomotor reflexes. These cause nausea and vomiting as well as intestinal secretion, propulsion and if pronounced, diarrhoea. Inflammation in animal models acts via T lymphocytes to increase EC cell numbers and mucosal serotonin (5-HT) content while inflammatory cytokines decrease serotonin transporter (SERT) function. Inflammation due to coeliac disease and following gastrointestinal infection increases mucosal 5-HT availability by a combination of increased EC cells and depressed SERT. Irritable bowel syndrome (IBS) developing after gastrointestinal infection and IBS with diarrhoea is associated with excess 5-HT. The associated diarrhoeal symptoms respond well to 5-HT(3) receptor antagonists. These drugs also inhibit the nausea and vomiting occurring in patients undergoing chemotherapy which cause a marked increase in release of 5-HT as well as other mediators. Other conditions including IBS-C and constipation may have inadequate 5-HT release and benefit from both 5-HT(3) and 5-HT(4) receptor agonists.

Purinergic receptors and gastrointestinal secretomotor function

Secretomotor reflexes in the gastrointestinal (GI) tract are important in the lubrication and movement of digested products, absorption of nutrients, or the diarrhea that occurs in diseases to flush out unwanted microbes. Mechanical or chemical stimulation of mucosal sensory enterochromaffin (EC) cells triggers release of serotonin (5-HT) (among other mediators) and initiates local reflexes by activating intrinsic primary afferent neurons of the submucous plexus. Signals are conveyed to interneurons or secretomotor neurons to stimulate chloride and fluid secretion. Inputs from myenteric neurons modulate secretory rates and reflexes, and special neural circuits exist to coordinate secretion with motility. Cellular components of secretomotor reflexes variably express purinergic receptors for adenosine (A1, A2a, A2b, or A3 receptors) or the nucleotides adenosine 5'-triphosphate (ATP), adenosine diphosphate (ADP), uridine 5'-triphosphate (UTP), or uridine diphosphate (UDP) (P2X(1-7), P2Y(2), P2Y(4), P2Y(6), P2Y(12) receptors). This review focuses on the emerging concepts in our understanding of purinergic regulation at these receptors, and in particular of mechanosensory reflexes. Purinergic inhibitory (A(1), A(3), P2Y(12)) or excitatory (A(2), P2Y(1)) receptors modulate mechanosensitive 5-HT release. Excitatory (P2Y(1), other P2Y, P2X) or inhibitory (A(1), A(3)) receptors are involved in mechanically evoked secretory reflexes or "neurogenic diarrhea." Distinct neural (pre- or postsynaptic) and non-neural distribution profiles of P2X(2), P2X(3), P2X(5), P2Y(1), P2Y(2), P2Y(4), P2Y(6), or P2Y(12) receptors, and for some their effects on neurotransmission, suggests their role in GI secretomotor function. Luminal A(2b), P2Y(2), P2Y(4), and P2Y(6) receptors are involved in fluid and Cl(-), HCO(3) (-), K(+), or mucin secretion. Abnormal receptor expression in GI diseases may be of clinical relevance. Adenosine A(2a) or A(3) receptors are emerging as therapeutic targets in inflammatory bowel diseases (IBD) and gastroprotection; they can also prevent purinergic receptor abnormalities and diarrhea. Purines are emerging as fundamental regulators of enteric secretomotor reflexes in health and disease.

Mechanisms of hypersensitivity in IBS and functional disorders

General introduction The concept of visceral hypersensitivity is accepted as being germane to several functional gastrointestinal disorders (FGIDs). The causes or risk factors associated with this hypersensitivity are unclear. This article addresses the proposed mechanisms leading to hypersensitivity: from genetic to inflammatory disorders, from central to peripheral alterations of function. However, in order to place visceral hypersensitivity in a more global perspective as an aetiological factor for FGIDs, it also provides a review of recent evidence regarding the role of other peripheral mechanisms (the intraluminal milieu), as also genetic factors in the pathophysiology of these disorders. The article has been divided into five independent sections. The first three sections summarize the evidence of visceral hypersensitivity as a biological marker of functional gut disorders, the peripheral and central mechanisms involved, and the role of inflammation on hypersensitivity. In opposition to visceral hypersensitivity as an isolated phenomenon in functional gut disorders, the last two sections focus on the importance of peripheral mechanisms, like motor disturbances, specifically those resulting on altered transport of intestinal gas, and alterations of the intraluminal milieu and genetics.

Adaptive changes of the enterochromaffin and gastrin cells in the rat gastrointestinal tract following subtotal colectomy

OBJECTIVE

Colectomized patients often have diarrhoea and increased gastric acid secretion. Although serotonin influences gastrointestinal (GI) motility and secretion, GI serotonin-producing enterochromaffin (EC) cells have not been investigated after colectomy, nor have the antral gastrin cells. The aim of this experimental study was to investigate the GI tract in rats 8 weeks after subtotal colectomy, with particular emphasis on the frequency and distribution of EC and gastrin cells.

MATERIAL AND METHODS

Immunohistochemical techniques were used to identify the two endocrine cell types.

RESULTS

The colectomized animals had diarrhoea. Body-weight was lower and the small intestine shorter in the colectomized animals compared with sham-operated and untreated controls. In the two surgically treated groups, the antral mucosa was thinner and the small intestinal mucosa was thicker compared with that of the untreated rats, whereas the thickness of the rectum of the colectomized rats was increased compared with that of the control groups. In the colectomized animals, the number of EC cells was increased in the small intestine and rectum, whereas the numbers of both EC and gastrin cells were decreased in the antrum.

CONCLUSIONS

The results indicate that colectomy exerts a significant influence on the GI mucosa and on the endocrine cell systems studied. An increased number of EC cells can result in alterations in motility and secretion, which may be important in the pathogenesis of the diarrhoea that often occurs after colectomy.

Tumours of the midgut (jejunum, ileum and ascending colon, including carcinoid syndrome)

(Neuro-)endocrine tumours of the gastrointestinal tract are also called 'carcinoids'. (Neuro-)endocrine midgut tumours can be categorized according to their clinical behaviour. Most tumours are non-functioning. Functioning tumours are responsible for the carcinoid syndrome. The carcinoid syndrome is almost uniquely associated with midgut carcinoids. Symptoms of the carcinoid syndrome are caused by an excess of biogenic amines, peptides and other factors in the circulation. The typical symptoms of the carcinoid syndrome are diarrhoea, flushing, and carcinoid heart disease. Carcinoid heart disease involves the tricuspid and pulmonary valves and the endocardium. Serum chromogranin A and urinary excretion of 5-hydroxy-indoleacetic acid (5-HIAA) are biochemical markers. Carcinoid tumours express large numbers of high-affinity somatostatin receptors. These can bind the currently available octapeptide somatostatin analogues. In inoperable patients, biotherapy with somatostatin analogues and interferon-alpha is the treatment of choice. Somatostatin analogues and interferon-alpha significantly improve symptoms.

Short-chain fatty acids stimulate colonic transit via intraluminal 5-HT release in rats

We studied whether physiological concentration of short-chain fatty acids (SCFAs) affects colonic transit and colonic motility in conscious rats. Intraluminal administration of SCFAs (100-200 mM) into the proximal colon significantly accelerated colonic transit. The stimulatory effect of SCFAs on colonic transit was abolished by perivagal capsaicin treatment, atropine, hexamethonium, and vagotomy, but not by guanethidine. The stimulatory effect of SCFAs on colonic transit was also abolished by intraluminal pretreatment with lidocaine and a 5-hydroxytryptamine (HT)(3) receptor antagonist. Intraluminal administration of SCFAs provoked contractions at the proximal colon, which migrated to the mid- and distal colon. SCFAs caused a significant increase in the luminal concentration of 5-HT of the vascularly isolated and luminally perfused rat colon ex vivo. It is suggested that the release of 5-HT from enterochromaffin cells in response to SCFAs stimulates 5-HT(3) receptors located on the vagal sensory fibers. The sensory information is transferred to the vagal efferent and stimulates the release of acetylcholine from the colonic myenteric plexus, resulting in muscle contraction.

Effect of alosetron on left colonic motility in non-constipated patients with irritable bowel syndrome and healthy volunteers

BACKGROUND

Alosetron is a 5-hydroxytryptamine-3 receptor antagonist reducing symptoms in female patients with diarrhoea-predominant irritable bowel syndrome, and is known to increase the colonic transit time.

AIM

To study the effect of alosetron on left colonic phasic motility in ambulant non-constipated patients with irritable bowel syndrome and healthy volunteers.

METHODS

In a double-blind, randomized, crossover design, 10 patients with irritable bowel syndrome and 12 sex- and age-matched volunteers were treated for two 7-day periods with alosetron, 4 mg b.d., or placebo b.d. On day 6 of each treatment period, a six-channel solid-state manometric catheter was positioned in the left colon and 24 h motility was studied on day 7. The periprandial phasic motility around dinnertime was evaluated in the descending and sigmoid colon. The high-amplitude propagated contraction frequency and characteristics were calculated.

RESULTS

Alosetron appeared to increase the overall periprandial frequency in the sigmoid colon (P=0.043) and the mean amplitude of colonic contractions in the descending colon (P=0.007). The high-amplitude propagated contraction frequency was higher on alosetron during the second half of the day for patients with irritable bowel syndrome (P=0.002), with increased mean propagation length of high-amplitude propagated contractions (P=0.001). The stool frequency (P=0.024) and stool consistency score (P=0.002) were decreased by alosetron.

CONCLUSIONS

The 5-hydroxytryptamine-3 receptor antagonist alosetron marginally increased left colonic periprandial phasic motility. Alosetron increased the number and propagation length of high-amplitude propagated contractions, which were paradoxically accompanied by a decrease in stool frequency and a firming of stool consistency.

Small bowel review: normal physiology part 1

In the past year there have been many advances in the area of small bowel physiology and pathology and therapy. In preparation for this review, over 1500 papers were assessed. The focus is on presenting clinically useful information for the practising gastroenterologist. Selected important clinical learning points include the following: (1) glucose absorption mediated by SGLT1 is controlled by mRNA abundance, as well as by posttranscriptional processes including protein trafficking; (2) inducers of cytochrome P-450 decrease glucose and fructose absorption and increase glucose consumption in the intestine; (3) the regulated release of nutrients from the stomach into the upper intestine ensures that the modest intestinal transport reserve capacity is not exceeded; (4) hepatocyte growth factor and short-chain fatty acids may enhance intestinal adaptation and prevent the atrophy seen when total parenteral nutrition is infused; (5) inhibitors of pancreatic lipase and phospholipase H2 may be useful clinically to reduce absorption as part of a treatment program for obesity and hyperlipidemia; (6) several membrane-bound and cytosolic proteins have been identified in the enterocyte as well as in the hepatocyte and may be the target for the future therapeutic manipulation of bile acid metabolism and control of hyperlipidemia; (7) suspect bile acid malabsorption in the patient with otherwise unexplained chronic diarrhea; (8) a proportion of lipid absorption is protein-mediated, and this opens the way to targeting these proteins and thereby therapeutically modifying lipid absorption; (9) a high protein diet may be useful to increase the intestinal absorption of drugs transported by the H+/dipeptide cotransporter; (10) a metal transporter DCT1 has been identified, and this may open the way to a better understanding of disorders of, for example, iron and zinc metabolism; (11) the nutrient transporters such as SGLT1 are responsible for a portion of the intestinal absorption of water; (12) the influence of nitric oxide on intestinal water absorption and secretion depends on its concentration; (13) a trial of bile acid-sequestering agent may prove useful in the treatment of the patient who experiences diarrhea while taking an enteral diet; (14) a proteolytic extract from pineapple stems may prove to be useful to treat diarrhea, although the mechanism of this effect remains to be established; and (15) the antisecretory effect of the new peptide, sorbin, needs to be tested in a clinical situation on patients with diarrhea. Other new and promising antidiarrheal agents include bromelain, an extract from pineapple stems, and igmesine, a final sigma ligand.

Effects of alosetron on spontaneous migrating motor complexes in murine small and large bowel in vitro

Alosetron (Lotronex) is a serotonin subtype 3 (5-HT3) receptor antagonist that alleviates symptoms of irritable bowel syndrome (IBS) in female patients. Alosetron may act centrally, involve the alteration of ascending pain sensation, or modulate peristaltic, secretory, or sensory function. To investigate further the mechanisms underlying its action and gender selectivity we recorded the effect of increasing concentrations of alosetron or ondansetron on spontaneous migrating motor complexes (MMCs) from isolated terminal ileum or colon from C57BL/6 mice. Both antagonists inhibited MMC frequency before affects on duration or amplitude. The threshold of inhibition for alosetron was 100-fold less in small intestine from females (20 nM) than from males. The opposite effect of gender was observed with ondansetron in the colon. All MMCs were abolished by either drug at 10 microM. Our results demonstrate that alosetron selectively inhibits MMC frequency in isolated preparations of murine bowel. Because contractile events in the ileum correlate with symptoms of IBS in humans, the gender selectivity of alosetron may be caused by a direct action within the small intestine.

Mechanical stimulation activates Galphaq signaling pathways and 5-hydroxytryptamine release from human carcinoid BON cells

5-Hydroxytryptamine (5-HT) released from enterochromaffin cells activates secretory and peristaltic reflexes necessary for lubrication and propulsion of intestinal luminal contents. The aim of this study was to identify mechanosensitive intracellular signaling pathways that regulate 5-HT release. Human carcinoid BON cells displayed 5-HT immunoreactivity associated with granules dispersed throughout the cells or at the borders. Mechanical stimulation by rotational shaking released 5-HT from BON cells or from guinea pig jejunum during neural blockade with tetrodotoxin. In streptolysin O-permeabilized cells, guanosine 5'-O- (2-thiodiphosphate) (GDP-beta-S) and a synthetic peptide derived from the COOH terminus of Galphaq abolished mechanically evoked 5-HT release, while the NH(2)-terminal peptide did not. An antisense phosphorothioated oligonucleotide targeted to a unique sequence of Galphaq abolished mechanically evoked 5-HT release and reduced Galphaq protein levels without affecting the expression of Galpha(11). Depletion and chelation of extracellular calcium did not alter mechanically evoked 5-HT release, whereas depletion of intracellular calcium stores by thapsigargin and chelation of intracellular calcium by 1,2-bis (o-Aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetra (acetoxymethyl) ester (BAPTA-AM) reduced 5-HT release. Mechanically evoked 5-HT release was inhibited by somatostatin-14 in a concentration-dependent manner. The results suggest that mechanical stimulation of enterochromaffin-derived BON cells directly or indirectly stimulates a G protein-coupled receptor that activates Galphaq, mobilizes intracellular calcium, and causes 5-HT release.

Gender-related differences in slowing colonic transit by a 5-HT3 antagonist in subjects with diarrhea-predominant irritable bowel syndrome

OBJECTIVE

To evaluate the influence of gender on the effect of a 5-HT3 antagonist, alosetron, 1 mg b.i.d., on GI and colonic transit in D-IBS.

METHODS

Thirty patients (15 male, 15 female) with D-IBS received 1 mg b.i.d. alosetron for 6 wk. Transit was measured by scintigraphy at baseline and at the end of treatment.

RESULTS

Alosetron, 1 mg b.i.d., significantly retarded small bowel and, proximal and overall colonic transit in the 30 patients with D-IBS. The effect of alosetron on the primary endpoint, colonic geometric center at 24 h, was significantly greater in females than in males (p < 0.05). However, two females showed no slowing of colonic transit on treatment. Among male patients, two of 15 had a slowing of colonic transit at 24 h that was greater than the mean change in female patients, suggesting responsiveness to alosetron among a subgroup of males.

CONCLUSION

A 5-HT3 antagonist, alosetron, significantly retards small intestinal and colonic transit in diarrhea-predominant IBS patients, with significantly greater female to male responsiveness. Gender partly contributes to differences in the serotonergic control of intestinal and colonic transit in patients with D-IBS.

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.

Small-bowel motility

Advances in the field of small-bowel motility in the last few years include the delineation of the role of the intrinsic primary afferent neuron in eliciting the peristaltic reflex, the genetic control of the development of the enteric nervous system, and the potential role of the interstitial cells of Cajal as pacemakers of the intestine and colon. New promising molecules have been developed for therapeutic purposes, particularly in the modulators of serotonin receptors. Their effects on sensory and motor function has allowed a better recognition of the important role of 5-hydroxytryptamine in several disorders, especially in irritable bowel syndrome. In this brief review, we have elected to appraise the advances pertaining to human studies, with emphasis on novel methodologies, disease manifestations, and novel therapeutic strategies.

Effects of a serotonin 5-HT(4) receptor antagonist SB-207266 on gastrointestinal motor and sensory function in humans

BACKGROUND

Serotonin 5-HT(4) receptors are located on enteric cholinergic neurones and may regulate peristalsis. 5-HT(4) receptors on primary afferent neurones have been postulated to modulate visceral sensation. While 5-HT(4) agonists are used as prokinetic agents, the physiological role of 5-HT(4) receptors in the human gut is unknown.

AIMS

Our aim was to characterise the role of 5-HT(4) receptors in regulating gastrointestinal motor and sensory function in healthy subjects under baseline and stimulated conditions with a 5-HT(4) receptor antagonist.

METHODS

Part A compared the effects of placebo to four doses of a 5-HT(4) receptor antagonist (SB-207266) on the cisapride mediated increase in plasma aldosterone (a 5-HT(4) mediated response) and orocaecal transit in 18 subjects. In part B, 52 healthy subjects received placebo, or 0.05, 0.5, or 5 mg of SB-207266 for 10-12 days; gastric, small bowel, and colonic transit were measured by scintigraphy on days 7-9, and fasting and postprandial colonic motor function, compliance, and sensation during distensions were assessed on day 12.

RESULTS

Part A: 0.5, 5, and 20 mg doses of SB-207266 had significant and quantitatively similar effects, antagonising the cisapride mediated increase in plasma aldosterone and acceleration of orocaecal transit. Part B: SB-207266 tended to delay colonic transit (geometric centre of isotope at 24 (p=0.06) and 48 hours (p=0.08)), but did not have dose related effects on transit, fasting or postprandial colonic motor activity, compliance, or sensation.

CONCLUSION

5-HT(4) receptors are involved in the regulation of cisapride stimulated orocaecal transit; SB 207266 tends to modulate colonic transit but not sensory functions or compliance in healthy human subjects.

Effects of alosetron on gastrointestinal transit time and rectal sensation in patients with irritable bowel syndrome

BACKGROUND

Alosetron, a 5-HT3-receptor antagonist, relieves abdominal pain and improves bowel function in non-constipated, female patients with irritable bowel syndrome. 5-HT3 antagonists delay colonic transit, increase colonic compliance, and increase small intestinal water absorption.

AIM

To evaluate the effects of alosetron on gastrointestinal and colonic transit, rectal compliance and rectal sensation in irritable bowel syndrome.

METHODS

A double-blind, placebo-controlled, two-dose study of alosetron was performed in 25 non-constipated irritable bowel syndrome patients, with paired studies before and after 4 weeks of treatment with placebo (n=5), 1 mg alosetron (n=10) or 4 mg (n=10) alosetron b.d. Gastrointestinal and colonic transit were measured by scintigraphy. Rectal compliance and sensation were assessed by rectal balloon distention with a barostat.

RESULTS

There was a trend (P=0.06) for 1 mg alosetron to increase rectal compliance (median pressure at half maximum volume 11 mmHg after alosetron vs. 15.6 mmHg before alosetron). The 1 mg b.d. alosetron dose non-significantly retarded proximal colonic transit. Alosetron and placebo reduced sensory scores relative to baseline values; none of the changes induced by alosetron was significant relative to placebo.

CONCLUSIONS

Alosetron had no significant effect on gastrointestinal transit or rectal sensory and motor mechanisms in non-constipated irritable bowel syndrome patients in this study. Alosetron's effects on colonic sensorimotor function and central sensory mechanisms deserve further evaluation.

Alosetron

Each month, subscribers to The Formulary® Monograph Service receive five to six researched monographs on drugs that are newly released or are in late Phase III trials. The monographs are targeted to your Pharmacy and Therapeutics Committee. Subscribers also receive monthly one-page summary monographs on the agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation (DUE) is also provided each month. The monographs are published in printed form and on diskettes that allow customization. Subscribers to the The Formulary Monograph Service also receive access to a pharmacy bulletin board called The Formulary Information Exchange (The F.I.X). All topics pertinent to clinical pharmacy are discussed on The F.I.X.

Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The June 2000 Formulary monographs are on pantoprazole, oral and intravenous; meloxicam; zonisamide; gentuzum-ab zogamicin; and vertiporfin. The DUE is on meloxicam.

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.

Alosetron

Alosetron is a potent and highly selective serotonin 5-HT3 receptor antagonist which has been evaluated for the management of irritable bowel syndrome (IBS). It blocked the fast 5HT3-mediated depolarisation of guinea-pig myenteric and submucosal neurons in vitro, with half-maximal inhibition at approximately 55 nmol/L. Alosetron attenuated the visceral nociceptive effect of rectal distension in conscious or anaesthetised dogs. It increased the compliance of the colon to distension in patients with IBS and delayed colonic transit in patients with IBS or carcinoid diarrhoea and in healthy volunteers. A single dose of alosetron 4 mg increased in vivo fluid absorption in normal human small intestine. In clinical trials in patients with IBS, alosetron 1 mg twice daily was effective in relieving abdominal pain and discomfort. Alosetron was most effective in female patients and particularly in those with diarrhoea-predominant IBS. In patients with IBS and healthy volunteers who received alosetron, the most common adverse event was constipation.

Pharmacology and clinical experience with alosetron

Alosetron (Lotronex) is a potent, highly selective 5-HT(3) antagonist. Animal models have shown it to be active in anxiety, psychosis, cognitive impairment, emesis and drug withdrawal, though its application in humans has been almost entirely restricted to irritable bowel syndrome (IBS). Alosetron does not cause adverse pharmacodynamic effects, is absorbed rapidly after oral administration and is widely distributed throughout tissues after oral or iv. dosing in animals. Its metabolism is rapid and extensive with N-demethylation, hydroxylation and oxidation. The drug, or its two principal metabolites, is equally excreted through the biliary tract and kidneys. Alosetron has proved safe in a range of toxicity studies; at high repeated dosing, clinical signs were transient and repeated administration produced no significant adverse effects on fertility, reproductive performance or fetal development. In pharmacokinetic studies, bioavailability of alosetron in healthy volunteers is approximately 60% and the plasma half-life is about 1.5 h. There are some gender differences in the pharmacokinetic profile, with 30 - 50% higher alosetron concentrations in females. No consistent differences in alosetron serum concentrations between the young and elderly were observed. The pharmacokinetics of single, oral doses of alosetron are linear up to 8 mg. In human pharmacodynamic studies, alosetron increased basal jejunal water and electrolyte absorption, increased colonic transit time and, consequently, whole gut transit time. Alosetron has been evaluated in two large Phase II trials (randomised, double-blinded, placebo-controlled) and in Phase III trials which included a four-week observation period after cessation. Dose response studies suggested that the effective dosages could be between 1 and 2 mg, twice-daily. In Phase II trials, alosetron, 1 mg b.i.d., resulted in a greater proportion of non-constipated IBS patients reporting adequate relief of pain and discomfort, as well as improvement of bowel symptoms, frequency, urgency and stool consistency when compared with placebo. However, this beneficial effect was seen exclusively among females. Phase III studies evaluated exclusively females with non-constipated IBS and confirmed the results of the Phase II studies. Alosetron was well-tolerated in all studies, with the most frequently recorded adverse event being constipation. Thus, alosetron appears promising in the treatment of abdominal pain and discomfort and normalising of bowel function in patients with non-constipated IBS. It also improves quality of life, has a high degree of tolerability and has an excellent safety profile to date.

Review article: the therapeutic potential of 5-HT3 receptor antagonists in the treatment of irritable bowel syndrome

There is evidence from studies, in both animals and humans, that 5-HT3 receptor blockade has potential value in the treatment of irritable bowel syndrome, particularly in those patients with diarrhoea-predominant bowel habits. New findings suggest that 5-HT3 receptors exist on gut afferent neurones and that their activation by locally released 5-HT leads to visceral nociceptive stimulation, in addition to increased neuronally-mediated motor and secretory activity. If this concept is validated, it will provide a rationale for the use of 5-HT3 receptor antagonists in patients with increased gut motility, reduced fluid absorption and low nociceptive thresholds leading to abdominal pain. Alosetron is a highly selective, potent 5-HT3 receptor antagonist which is well absorbed with a long pharmacodynamic half-life. Its ability to provide long-lasting blockade of 5-HT3 receptors throughout the body make it an ideal candidate within its class to evaluate the clinical hypothesis that sustained and ubiquitous 5-HT3 receptor blockade is of value in the treatment of IBS.