Impact of 5-HT3 receptor blockade on colonic haemodynamic responses to ischaemia and reperfusion in the rat

Anti-inflammatory effects of alosetron mediated through 5-HT3 receptors on experimental colitis

Development of new medicine with fewer deleterious effects and more efficacies for treatment of inflammatory bowel disease is needed. 5-Hydroxytryptamine 3 receptor (5-HT₃R) antagonists have exhibited analgesic and anti-inflammatory features in vitro and in vivo. The present study was designed to evaluate the anti-inflammatory effect of alosetron, a 5-HT₃R antagonist, on trinitrobenzenesulfonic acid (TNBS)-induced ulcerative colitis in rats. Two h subsequent to induce colitis (intracolonic instillation of TNBS, 50 mg/kg) in male Wistar rats, alosetron (1 mg/kg), dexamethasone (1 mg/kg), meta-chlorophenylbiguanide (mCPBG, a 5-HT₃R agonist, 5 mg/kg), or alosetron + mCPBG were administrated intraperitoneally for 6 days. Animals were thereafter sacrificed and the efficacy of drugs was evaluated macroscopically, histologically, and biochemically (myeloperoxidase, tumor necrosis factor-alpha, interleukin-6, and interleukin-1 beta) on distal colon samples. Treatment with alosetron and dexamethasone improved macroscopic and microscopic colonic damages significantly and decreased myeloperoxidase activity and colonic levels of inflammatory cytokines. The profitable effects of alosetron were antagonized by concurrent administration of mCPBG. Our data provided evidence that the protective effects of alosetron on TNBS-induced colitis can be mediated by 5- HT3R.

Partial agonism of 5-HT3 receptors: a novel approach to the symptomatic treatment of IBS-D

Irritable bowel syndrome (IBS) is a functional bowel disorder characterized by abdominal pain, discomfort, and altered bowel habits, which have a significant impact on quality of life for approximately 10-20% of the population. IBS can be divided into three main types IBS-D (diarrhea predominant), IBS-C (constipation predominant), and mixed or alternating IBS. 5-HT(3) receptor antagonism has proved to be an efficacious treatment option for IBS-D. For example, alosetron displays efficacy in the treatment of multiple symptoms, including abdominal pain, discomfort, urgency, stool frequency and consistency. However, significant constipation occurred in approximately 25% of patients, leading to withdrawal of up to 10% of patients in clinical trials. Targeting compounds with partial agonist activity at the 5-HT(3) receptor represents a mechanistic departure from the classic 5-HT(3) receptor antagonist approach and should result in agents that are applicable to a broader array of IBS patient populations. Attenuation of the activity of the ion channel without completely abolishing its function may control or normalize bowel function without leading to a total block associated with severe constipation. We have identified a new class of selective, orally active 5-HT(3) receptor ligands with high 5-HT(3) receptor affinity and low partial agonist activity currently in preclinical development that should offer a significant advantage over existing therapies.

The risk of ischaemic colitis in irritable bowel syndrome patients treated with serotonergic therapies

Ischaemic colitis (IC) is the most common form of ischaemic injury to the gastrointestinal (GI) tract. IC typically presents with the sudden onset of lower abdominal pain, cramping and rectal bleeding, and is usually self-limited with low morbidity, although it may cause gangrenous or fulminant colitis, especially when the right colon is involved. Multiple medical conditions, as well as several pharmacological agents, are associated with IC, including irritable bowel syndrome (IBS) and drugs used for its treatment that act on gut serotonin 5-HT receptors. These include the selective 5-HT(3) receptor antagonist alosetron, currently approved for the treatment of severe diarrhoea-predominant IBS in women who fail to respond to conventional treatment, and cilansetron, another 5-HT(3) receptor antagonist that is no longer in clinical development. In addition, the 5-HT(4) receptor partial agonist tegaserod, which was approved for the treatment of constipation-predominant IBS in women, was associated with IC in the postmarketing setting, as was renzapride, a 5-HT(4) agonist/5-HT(3) antagonist. Although several hypotheses have been proposed, the pathophysiological basis for development of IC with 5-HT(3) receptor antagonists or 5-HT(4) receptor agonists remains unknown. Of interest, several population-based studies demonstrated that a diagnosis of IBS (independent of serotonergic therapies) increases the risk of developing IC 2- to 4-fold. As a result, IBS patients with the acute onset of abdominal pain, tenderness, diarrhoea or lower intestinal bleeding, especially those with predisposing conditions or medications, should be evaluated promptly for IC. The management of IC remains supportive; most cases of non-gangrenous IC, as seen in the alosetron and tegaserod databases, have been transient and have resolved spontaneously without complications or death. Despite the small number of deaths associated with alosetron in patients with complications of constipation and because of the ongoing requirement to prescribe alosetron under a risk management plan, misconceptions persist regarding the definition, incidence, severity and outcome of IC in clinical trials and the postmarketing setting. In this article, the frequency and clinical characteristics of IC associated with the use of alosetron and other serotonergic agents are examined, evidence of an association between IC and IBS is reviewed, and a scoring system to aid in the diagnosis of IC in any clinical situation is proposed.

Ischemic colitis and complications of constipation associated with the use of alosetron under a risk management plan: clinical characteristics, outcomes, and incidences

OBJECTIVES

Alosetron is a potent, selective 5-HT(3) receptor antagonist prescribed for women with severe diarrhea-predominant irritable bowel syndrome (IBS-D) under a risk management plan (RMP). The RMP was implemented following cases of ischemic colitis (IC) and complications of constipation (CoC) associated with the use of alosetron. The objectives of this study were to characterize IC and CoC clinical features, outcomes, and incidence rates in the new restricted patient population to evaluate the effectiveness of the RMP in the prevention of serious outcomes.

METHODS

Safety data from adverse event reporting from November 2002 through June 2008 were reviewed for probable and possible IC and CoC using the US Food and Drug Administration/sponsor-defined criteria and definitions. Evidence for IC included medical documentation, colonoscopy, and sigmoidoscopy+/-biopsy. Evidence for CoC included medical history and confirmation from health-care professionals.

RESULTS

Within the inclusion dates, 29,072 patients received 203,939 alosetron prescriptions. Although the absolute numbers of IC and CoC cases have declined, the incidence rates for IC and CoC (0.95 and 0.36 cases per 1,000 patient-years, respectively) were similar to rates during the postmarketing cycle before alosetron withdrawal. In patients with severe IBS-D receiving alosetron (n=998) or placebo (n=411) in clinical trials since reintroduction, incidence rates for IC were 4 and 2 cases per 1,000 patients, respectively. Rates for CoC were 2 and 0 cases per 1,000 patients in the alosetron and placebo groups, respectively. No mesenteric ischemia, surgeries, transfusions, or deaths occurred in patients with IC and no cases of CoC were associated with toxic megacolon, perforation, surgeries, transfusions, or deaths. IC and CoC cases were typically of short duration and all improved on prompt withdrawal of alosetron.

CONCLUSIONS

Serious outcomes associated with IC and CoC appear to be mitigated since introduction of alosetron under the RMP.

Alosetron for severe diarrhea-predominant irritable bowel syndrome: safety and efficacy in perspective

Irritable bowel syndrome affects 5-10% of North Americans, with an estimated one-third having a diarrhea-predominant form. Alosetron hydrochloride (Lotronex) is a serotonin receptor type 3 antagonist approved in early 2000 for use in women with diarrhea-predominant irritable bowel syndrome (IBS-D). Initial use was widespread, but infrequent serious adverse events of ischemic colitis and severe constipation-related complications prompted alosetron's voluntary withdrawal from the US market in November 2000. Unprecedented public request prompted its reintroduction in 2002 under a Risk Management Plan, including a more restricted indication and a Prescribing Program for Lotronex. Despite these measures, the use of alosetron has been very limited since its reintroduction. Possible deterrents to its use include concerns over safety and the possible medical-legal implications raised by the Risk Management Plan. It is also possible that changes in the natural history and/or diagnosis of IBS-D have reduced the target population. Given the unique regulatory history of alosetron, these issues continue to engender controversy. This article profiles these concerns and reviews the pharmacology, clinical efficacy and safety, and post-marketing experience with alosetron. Myths and misconceptions related to alosetron use, or lack thereof, are addressed to provide the reader with the evidence needed to make informed treatment decisions for their female patients with severe IBS-D.

Alosetron, cilansetron and tegaserod modify mesenteric but not colonic blood flow in rats

BACKGROUND AND PURPOSE

As the use of the 5-HT(3) receptor antagonist alosetron (GlaxoSmithKline) and the 5-HT(4) receptor agonist tegaserod (Novartis) in patients with irritable bowel syndrome has been associated with cases of ischaemic colitis, the effects of alosetron, cilansetron (Solvay) and tegaserod on the rat splanchnic circulation were evaluated.

EXPERIMENTAL APPROACH

Phenobarbital-anaesthetised rats were instrumented to record blood flow in the superior mesenteric artery and transverse colon and to calculate mesenteric and colonic vascular conductance.

KEY RESULTS

Intravenous alosetron (0.03-0.3 mg.kg(-1)) did not alter blood pressure or heart rate but reduced mesenteric blood flow and vascular conductance by 15-20%. This activity profile was also seen after intraduodenal alosetron and shared by the 5-HT(3) receptor antagonist cilansetron. In contrast, blood flow, vascular conductance and intraluminal pressure in the colon were not modified by alosetron and cilansetron. Intravenous or intraduodenal tegaserod (0.3-1.0 mg.kg(-1)) had no inhibitory effect on mesenteric and colonic blood flow. Peroral treatment of rats with alosetron or tegaserod for 7 days did not modify mesenteric haemodynamics at baseline and after blockade of nitric oxide synthesis. Mild inflammation induced by dextran sulphate sodium failed to provoke a vasoconstrictor effect of cilansetron in the colon.

CONCLUSIONS AND IMPLICATIONS

Alosetron and cilansetron, not tegaserod, caused a small and transient constriction of the rat mesenteric vascular bed, whereas blood flow in the colon remained unaltered. The relevance of these findings to the treatment-associated occurrence of ischaemic colitis in patients with irritable bowel syndrome remains open.

Endoscopic findings and clinicopathologic characteristics of ischemic colitis: a report of 85 cases

Ischemic colitis is the most common type of intestinal ischemia and has a clinical spectrum of injury that ranges from mild and transient ischemia to acute fulminant colitis. The aim of this study was to explore endoscopic findings and clinicopathologic characteristics of ischemic colitis and be accurate enough to avoid missed diagnosis or misdiagnosis. A retrospective analysis was undertaken of endoscopy findings and clinicopathologic characteristics of 85 cases of ischemic colitis from March 2005 to April 2008 in the endoscopy center of our hospital. All cases underwent colonoscopy with biopsy within 2 weeks of the onset of symptoms, and all specimens with forceps were stained with hematoxylin-eosin and observed under light microscopy. Of the 85 cases of ischemic colitis (24 men and 61 women, average age 61.36 +/- 14.49 years old, range 29-84), 71 were over 50 years of age. These cases were associated with the basal diseases such as hypertension, cardiovascular disorders, diabetes, and hematological diseases as well as a history of abdominal operation. The clinical features usually presented with sudden onset of abdominal pain, diarrhea, and hematochezia. Ischemic lesions were located mainly in the left colon with segmental form (only descending colon affected 16%, only splenic flexure 14%, and only sigmoid colon 23%). The 85 patients consisted of the non-gangrenous type (82), which were composed of reversible IC (76) and chronic IC (6), and the gangrenous type (3). Endoscopic appearance of the transient ischemic colitis consisted of petechial hemorrhages, edematous and fragile mucosa, segmental erythema, scattered erosion, longitudinal ulcerations, and sharply defined segment of involvement. Ischemic colitis of stricture was characterized by full-thickness mucosa, lumens stricture, and diseased haustrations. The mucosa of gangrenous colitis with cyanotic and pseudopolyps was endoscopically observed as well. Clinicopathologic characteristics showed mucosal inflammation accompanied by erosion, granulation tissue hyperplasia and gland atrophy, lamina propria hemorrhage, and macrophages with hemosiderin pigmentation in submucosa in particular. Although endoscopy findings and clinicopathologic characteristics of ischemic colitis are nonspecific, colonoscopy with biopsy plays a vital role in the early diagnosis of ischemic colitis.

A novel herbal preparation desensitizes mesenteric afferents to bradykinin in the rat small intestine

Herbal preparations are evolving as promising agents for the treatment of functional gastrointestinal disorders which are considered to be secondary to visceral hypersensitivity. We aimed to determine whether a new combination of six herbal extracts reduces the sensitivity of intestinal afferents in rat. Male Wistar rats (250-350 g, n = 6 per group) were gavaged with either vehicle or 2.5, 5 or 10 mL kg(-1) of STW 5-II, a herbal preparation which contains six extracts. Two hours later, animals were anaesthetized and extracellular multi-unit mesenteric afferent nerve recordings were obtained in the proximal jejunum in vivo. Afferent discharge to 5-hydroxy-tryptamine (5-HT) (5, 10, 20 and 40 microg kg(-1), i.v.), luminal distension (0-60 mmHg) and bradykinin (BK) (15, 30 and 60 microg kg(-1), i.v.) was recorded. At baseline, spontaneous afferent discharge was not different following pretreatment with the various doses of STW 5-II compared with vehicle. The pressure-dependent increase in afferent discharge to intraluminal ramp distension and the dose-dependent increase in afferent firing following 5-HT were also uninfluenced by STW 5-II pretreatment. In contrast, the afferent nerve responses to 15, 30 and 60 microg kg(-1) of BK were reduced following 10 mL kg(-1) STW 5-II with peaks at 106 +/- 19, 153 +/- 22 and 156 +/- 25 imp s(-1) compared with 160 +/- 15, 228 +/- 14 and 220 +/- 16 imp s(-1) following vehicle pretreatment (mean +/- SEM, P < 0.05). Intestinal afferent sensitivity to BK which plays a prime role in nociception was reduced following STW 5-II. Thus, STW 5-II may be of therapeutic use for conditions that involve neuronal hypersensitivity and the release of BK in the intestine.

Serotonin in the gastrointestinal tract

PURPOSE OF REVIEW

To assess the role of serotonin and its control in the manifestations and treatment of lower functional gastrointestinal disorders.

RECENT FINDINGS

Recent literature has explored several novel concepts in the association of serotonin and symptoms, alterations in tissue levels of serotonin and its reuptake protein, aspects of the genetic determinants of serotonergic function (particularly 5-HTTLPR) and its relationship to gastrointestinal motor and sensory functions, and novel serotonergic agents used in therapy of lower functional gastrointestinal disorders. The most consistent findings are the increase in plasma 5-hydroxytryptamine (5-HT) in diarrheal diseases and reduction in constipation. The serotonin transporter in platelets has an impact on the circulating level of 5-HT. Meta-analysis shows that 5-HTTLPR genotype is not significantly associated with irritable bowel syndrome in Whites or Asians. New 5-HT3 antagonists and 5-HT4 agonists are efficacious and promise to provide relief for patients if they can pass regulatory hurdles.

SUMMARY

Although the most relevant implication for clinical practice remains the evidence that serotonergic agents are efficacious in the treatment of chronic constipation, chronic diarrhea and irritable bowel syndrome, the role of genetic control of 5-HT and its receptors is the subject of ongoing research, and is likely to enhance understanding of the mechanisms and treatment of these diseases.