Effects of an alpha(2)-adrenergic agonist on gastrointestinal transit, colonic motility, and sensation in humans

Ischemic Colitis Secondary to Olanzapine and Clonidine Use in a Patient With a History of Laxative Abuse

Ischemic colitis is the most common type of intestinal ischemia and is caused by an acute arterial occlusion, thrombosis, or hypoperfusion of the mesenteric vasculature. This case centers around a 39-year-old female with a past medical history significant for a 20-year history of stimulant laxative abuse, chronic constipation, bipolar disorder, and anxiety that presented with ischemic colitis following 21 days of obstipation. At the time of presentation, the patient was taking olanzapine 15 mg daily for the treatment of bipolar disorder and clonidine 0.2 mg three times daily for anxiety. Over the course of her hospitalization, the patient was found to have a high stool burden, including calcified stool, contributing to ischemic colitis. She was successfully treated with a clonidine taper, multiple enemas, and laxatives. Pharmacological agents that induce constipation have been shown to increase the risk of colonic ischemia by increasing intraluminal pressure in the colon. Atypical antipsychotics block peripheral anticholinergic and anti-serotonergic receptors, limit gastrointestinal muscle contractions, and delay intestinal transit.

Pharmacological modulation of colorectal distension evoked potentials in conscious rats

BACKGROUND

Cerebral evoked potentials (CEP) induced by colorectal distension (CRD) in conscious rats provides a novel method in studies of visceral sensitivity. The aim of this study was to explore the pharmacological effect on CEP of compounds known to reduce the visceromotor response to CRD.

METHODS

Epidural electrodes were chronically implanted in eight female Sprague-Dawley rats. Evoked potentials were elicited by colorectal rapid balloon distensions (100 ms, 80 mmHg) and the effect of WIN55 (cannabinoid CB receptor agonist), clonidine (adrenergic α₂ receptor agonist), MPEP (mGluR5 receptor antagonist), pregabalin (ligand of α₂δ subunits in voltage-gated calcium channels) and baclofen (GABA-B receptor agonist) on amplitudes and latency of CEP were determined.

RESULTS

WIN55 (0.1 μmol kg^-1), clonidine (0.05 μmol kg^-1), MPEP (10 μmol kg^-1) and pregabalin (200 μmol kg^-1) caused a significant, p < 0.05, reduction of the N2 to P2 peak-to-peak amplitude by 23 ± 8%, 25 ± 8%, 39 ± 5%, and 47 ± 6% respectively. Baclofen (9 μmol kg^-1) induced a prolongation of the N2 peak latency of 18 ± 4% but had no significant effect on the amplitudes.

CONCLUSION

The obtained results suggest that MPEP, WIN55, clonidine, and pregabalin reduce visceral nociceptive input to the brain, whereas the lack of effect of baclofen on CRD evoked CEP amplitudes suggest that the effect on VMR is not due to a direct analgesic effect. Brain responses to colorectal distension provide a useful tool to evaluate pharmacological effects in rats and may serve as a valuable preclinical model for understanding pharmacological mechanisms related to visceral sensitivity.

Increased Sympathetic Outflow Induces Adaptation to Acute Experimental Pain

BACKGROUND

There are interrelationships between the autonomic nervous system and pain. This study aims to explore the effect of different autonomic manipulations on pain perception and modulation.

METHODS

Twenty healthy subjects (10 men and 10 women, mean age 25 ± 3 years) participated in this single-blinded, semi-randomized, controlled study, which included 2 study visits. Warm detection thresholds, heat pain thresholds, conditioned pain modulation (CPM), and pain adaptation were tested before and after administration of phenylephrine, clonidine, yohimbine, and saline.

RESULTS

Changes in heart rate and blood pressure were found after all the pharmacological interventions. The only effect on pain measures was that yohimbine enhanced pain adaptation capacity while phenylephrine reduced it (P = 0.032). Several significant correlations were found between autonomic and pain parameters; greater decreases in heart rate after phenylephrine were associated with reduced pain ratings (r² = 0.288, P = 0.018). In addition, enhanced pain adaptation was associated with higher total vascular resistance (r² = 0.442, P = 0.01).

CONCLUSIONS

Different effects of acute autonomic manipulations on experimental pain were found: an increase in sympathetic tone induced by yohimbine led to reduced pain sensitivity; a decrease in sympathetic tone with no effect on vagal-parasympathetic tone induced by phenylephrine led to reduction in pain adaptation capacity; and a decrease in sympathetic tone and increase in vagal parasympathetic tone by clonidine led to no change in pain adaptation capacity. While increased sympathetic outflow does facilitate pain adaptation, activation of either the sympathetic or parasympathetic limbs of the autonomic nervous system does not affect pain thresholds or CPM. Finally, a correlation exists between nociception and cardiovascular parameters only due to baroreflex activation.

Pharmacogenetics and the treatment of functional gastrointestinal disorders

The diagnosis and management of functional gastrointestinal disorders (FGIDs) remain very challenging. In the era of precision medicine, it is important to individualize the treatment of these conditions by providing targeted and effective therapies while minimizing the risk of medication side effects. By using genetic information that predicts and affects the responses to specific medications, it is anticipated that the science of pharmacogenetics in FGIDs will advance the practice of precision medicine. The pathophysiology of FGIDs is complex, involving the interaction between predisposing genetic and environmental factors. Studies have shown that genetic polymorphisms may contribute to the variable responses to specific medications among individuals with FGIDs. Genetic variations in the CYP450 system can affect the metabolism and, hence, the pharmacokinetics of drugs used to treat FGIDs. Polymorphisms in the genes controlling proteins that are involved in the direct action of medications targeting the serotonergic, cannabinoid, adrenergic and bile acid pathways can affect the pharmacologic effects of the medications. In this review, we summarize the published literature on the pharmacogenetics of FGIDs and address the potential clinical utility and future challenges in this field. Since it was the dominant topic in the majority of the articles relevant to FGIDs, our review will focus on irritable bowel syndrome.

Pharmacological Approach for Managing Pain in Irritable Bowel Syndrome: A Review Article

Context

Visceral pain is a leading symptom for patients with irritable bowel syndrome (IBS) that affects 10% - 20 % of the world population. Conventional pharmacological treatments to manage IBS-related visceral pain is unsatisfactory. Recently, medications have emerged to treat IBS patients by targeting the gastrointestinal (GI) tract and peripheral nerves to alleviate visceral pain while avoiding adverse effects on the central nervous system (CNS). Several investigational drugs for IBS also target the periphery with minimal CNS effects.

Evidence of Acquisition

In this paper, reputable internet databases from 1960 - 2016 were searched including Pubmed and ClinicalTrials.org, and 97 original articles analyzed. Search was performed based on the following keywords and combinations: irritable bowel syndrome, clinical trial, pain, visceral pain, narcotics, opioid, chloride channel, neuropathy, primary afferent, intestine, microbiota, gut barrier, inflammation, diarrhea, constipation, serotonin, visceral hypersensitivity, nociceptor, sensitization, hyperalgesia.

Results

Certain conventional pain managing drugs do not effectively improve IBS symptoms, including NSAIDs, acetaminophen, aspirin, and various narcotics. Anxiolytic and antidepressant drugs (Benzodiazepines, TCAs, SSRI and SNRI) can attenuate pain in IBS patients with relevant comorbidities. Clonidine, gabapentin and pregabalin can moderately improve IBS symptoms. Lubiprostone relieves constipation predominant IBS (IBS-C) while loperamide improves diarrhea predominant IBS (IBS-D). Alosetron, granisetron and ondansetron can generally treat pain in IBS-D patients, of which alosetron needs to be used with caution due to cardiovascular toxicity. The optimal drugs for managing pain in IBS-D and IBS-C appear to be eluxadoline and linaclotide, respectively, both of which target peripheral GI tract.

Conclusions

Conventional pain managing drugs are in general not suitable for treating IBS pain. Medications that target the GI tract and peripheral nerves have better therapeutic profiles by limiting adverse CNS effects.

Evaluating the safety and the effects on colonic compliance of neostigmine during motility testing in patients with chronic constipation

BACKGROUND

Neostigmine, an acetyl cholinesterase inhibitor, stimulates colonic motor activity and may induce vagally mediated cardiovascular effects. Our aim was to evaluate effects of i.v. neostigmine on colonic compliance and its safety in patients with chronic constipation.

METHODS

We retrospectively reviewed medical records of a selected group of 144 outpatients with chronic constipation who were refractory to treatment. These patients had undergone intracolonic motility and compliance measurements with an infinitely compliant balloon linked to a barostat. Data abstracted included barostat balloon mean volumes with increases in pressure (4 mmHg steps from 0 to 44 mmHg) before and after i.v. neostigmine. Vital signs and oxygen saturation before and after neostigmine were recorded.

KEY RESULTS

Of the 144 patients, 133 were female, mean age was 41.0 ± 15.4 years (SD), and duration of constipation was 12.9 ± 13.8 years. Among patients who had undergone colonic transit measurement by scintigraphy, the overall colonic transit at 24 h (geometric center, GC24 [n = 115]) was 1.5 ± 0.7 (normal >1.3), and at 48 h (GC48 [n = 75]) it was 2.3 ± 0.9 (normal >1.9). Neostigmine decreased colonic compliance at lower distension pressures (e.g., 12 and 20 mmHg [both p < 0.001]), but not at 40 mmHg. There were expected minor changes in vital signs in response to neostigmine in 144 patients; however, one patient developed unresponsiveness, significant bradycardia, hypotension, and muscular rigidity that responded to 400 mcg i.v. atropine.

CONCLUSIONS & INFERENCES

Neostigmine significantly decreases colonic compliance in patients with refractory chronic constipation. Symptomatic bradycardia in response to neostigmine should be promptly reversed with atropine.

What about clonidine for diarrhoea? A systematic review and meta-analysis of its effect in humans

BACKGROUND

Clonidine is considered an alternative treatment for refractory diarrhoea. The evidence in the literature is scarce and not conclusive. The present paper's purpose is to gather available evidence and provide a systematic answer regarding the effectiveness of clonidine for diarrhoea.

METHOD

We performed a systematic review of clonidine and its effect on diarrhoea. Meta-analysis was performed with a random effects model of the standardized mean difference (SMD) or the weighted mean difference and heterogeneity was quantified with I (2) and publication bias was assessed with Egger's and Begg's test. Subgroup analyses and meta-regression were performed to investigate sources of heterogeneity. Any empirical study describing use of clonidine for diarrhoea in humans independent of age was included. For the meta-analysis, papers had to provide sufficient data to produce an effect measure, while case reports were not included in the meta-analysis and are discussed narratively only.

RESULTS

A total of 24 trials and seven case reports were identified. Clonidine (median dose 300 μg/day) has been used for treatment of diarrhoea in irritable bowel syndrome, faecal incontinence, diabetes, withdrawal-associated diarrhoea, intestinal failure, neuroendocrine tumours and cholera; studies were also performed on healthy volunteers. Results indicate a strong effect of clonidine on diarrhoea (SMD = -1.02, 95% confidence interval [CI] -1.46 to -0.58) with a decrease of stool volume by 0.97 l/day, stool frequency by 0.4 times/day and increase in transit time by 31 minutes. In a sensitivity analysis of studies with functional diarrhoea and sample size over 10 subjects, the effect was similar -0.99 (95% CI -1.54 to -0.43). There is however significant heterogeneity and publication bias. Heterogeneity decreased in subgroup analyses by condition but not with other factors examined. A limitation of the present study includes small study effects.

CONCLUSION

Clonidine is effective for treatment of diarrhoea and should be considered as an alternative when all other medications have failed.

Role of sympathetic nervous system in rat model of chronic visceral pain

BACKGROUND

Changes in central pain modulation have been implicated in generalized pain syndromes such as irritable bowel syndrome (IBS). We have previously demonstrated that reduced descending inhibition unveils a role of sympathoneuronal outflow in decreasing peripheral sensory thresholds, resulting in stress-induced hyperalgesia. We investigated whether sympathetic nervous system (SNS) exacerbation of pain sensation when central pain inhibition is reduced is relevant to chronic pain disorders using a rat colon irritation (CI) model of chronic visceral hypersensitivity with hallmarks of IBS.

METHODS

Rats were treated to a series of colorectal balloon distensions (CRD) as neonates resulting in visceral and somatic hypersensitivity and altered stool function that persists into adulthood. The visceral sensitivity was assessed by recording electromyographic (EMG) responses to CRD. Somatic sensitivity was assessed by paw withdrawal thresholds to radiant heat. The effects on the hypersensitivity of (i) inhibiting sympathoneuronal outflow with pharmacological and surgical interventions and (ii) enhancing the outflow with water avoidance stress (WAS) were tested.

KEY RESULTS

The alpha2-adrenergic agonist, clonidine, and the alpha1-adrenergic antagonist, prazosin, reduced the visceral hypersensitivity and WAS enhanced the pain. Chemical sympathectomy with guanethidine and surgical sympathectomy resulted in a loss of the chronic visceral hypersensitivity.

CONCLUSIONS & INFERENCES

The results support a role of the SNS in driving the chronic visceral and somatic hypersensitivity seen in CI rats. The findings further suggest that treatments that decrease sympathetic outflow or block activation of adrenergic receptors on sensory nerves could be beneficial in the treatment of generalized pain syndromes.

Novel nervous system mechanisms in visceral pain

Visceral hypersensitivity is an important factor underlying abdominal pain in functional gastrointestinal disorders such as irritable bowel syndrome (IBS) and can result from aberrant signaling from the gut to the brain or vice versa. Over the last two decades, research has identified several selective, intertwining pathways that underlie IBS-related visceral nociception, including specific receptors on afferent and efferent nerve fibers such as transient receptor potential channels (TRP) channels, opioid, and cannabinoid receptors. In this issue of Neurogastroenterology and Motility Gil et al. demonstrate that in an animal model with reduced descending inhibitory control, the sympathetic nervous system outflow is enhanced, contributing to visceral and somatic hypersensitivity. They also provide evidence that interfering with the activation of adrenergic receptors on sensory nerves can be an interesting new strategy to treat visceral pain in IBS. This mini-review places these findings in a broader perspective by providing an overview of promising novel mechanisms to alter the nervous control of visceral pain interfering with afferent or efferent neuronal signaling.

Genetics and pharmacogenetics of aminergic transmitter pathways in functional gastrointestinal disorders

Functional gastrointestinal disorders (FGIDs) are highly prevalent syndromes, without evident underlying organic causes. Their pathogenesis is multifactorial in nature, with a combination of environmental and genetic factors contributing to their clinical manifestations, for which most of current treatments are not satisfactory. It is acknowledged that amine mediators (noradrenaline, dopamine and serotonin) play pivotal regulatory actions on gut functions and visceral sensation. In addition, drugs of therapeutic interest for FGIDs act on these transmitter pathways. The present article reviews current knowledge on the impact of genetics and pharmacogenetics of aminergic pathways on FGID pathophysiology, clinical presentations, symptom severity and medical management, in an attempt of highlighting the most relevant evidence and point out issues that should be addressed in future investigations.

Effects of clonidine in women with fecal incontinence

BACKGROUND & AIMS

Some women with urge-predominant fecal incontinence (FI) have diarrhea-predominant irritable bowel syndrome and a stiffer and hypersensitive rectum. We evaluated the effects of the α2-adrenergic agonist clonidine on symptoms and anorectal functions in women with FI in a prospective, placebo-controlled trial.

METHODS

We assessed bowel symptoms and anorectal functions (anal pressures, rectal compliance, and sensation) in 43 women (age, 58 ± 2 y) with urge-predominant FI, randomly assigned to groups given oral clonidine (0.1 mg, twice daily) or placebo for 4 weeks. Before and after administration of the medication, anal pressures were evaluated by manometry, and rectal compliance and sensation were measured using a barostat. Anal sphincter injury was evaluated by endoanal magnetic resonance imaging. Bowel symptoms were recorded in daily and weekly diaries. The primary end point was the FI and Constipation Assessment symptom severity score.

RESULTS

FI scores decreased from 9.1 ± 0.3 to 7.6 ± 0.5 among subjects given placebo and from 8.1 ± 0.4 to 6.5 ± 0.6 among patients given clonidine. Clonidine did not affect FI symptom severity, bowel symptoms (stool consistency or frequency), anal pressures, rectal compliance, or sensation compared with placebo. However, when baseline data were used to categorize subjects as those with or without diarrhea, clonidine reduced the proportion of loose stools in patients with diarrhea only (P = .018). Clonidine also reduced the proportion of days with FI in patients with diarrhea (P = .0825).

CONCLUSIONS

Overall, clonidine did not affect bowel symptoms, fecal continence, or anorectal functions, compared with placebo, in women with urge-predominant FI. Among patients with diarrhea, clonidine increased stool consistency, with a borderline significant improvement in fecal continence. ClinicalTrials.gov, Number NCT00884832.

Expression of β2 adrenoceptors within enteric neurons of the horse ileum

The activity of the gastrointestinal tract is regulated through the activation of adrenergic receptors (ARs). Since data concerning the distribution of ARs in the horse intestine is virtually absent, we investigated the distribution of β2-AR in the horse ileum using double-immunofluorescence. The β2-AR-immunoreactivity (IR) was observed in most (95%) neurons located in submucosal plexus (SMP) and in few (8%) neurons of the myenteric plexus (MP). Tyrosine hydroxylase (TH)-IR fibers were observed close to neurons expressing β2-AR-IR. Since β2-AR is virtually expressed in most neurons located in the horse SMP and in a lower percentage of neurons in the MP, it is reasonable to retain that this adrenergic receptor could regulate the activity of both secretomotor neurons and motor neurons innervating muscle layers and blood vessels. The high density of TH-IR fibers near β2-AR-IR enteric neurons indicates that the excitability of these cells could be directly modulated by the sympathetic system.

Translational aspects of rectal evoked potentials: a comparative study in rats and humans

Inconsistencies between species has stunted the progress of developing new analgesics. To increase the success of translating results between species, improved comparable models are required. Twelve rats received rectal balloon distensions on 2 different days separated by 24.3 (SD 24.6) days. Rectal balloon distensions were also performed in 18 humans (mean age: 34 yr; range: 21-56 yr; 12 men) on two separate occasions, separated by 9.3 (SD 5.5) days. In rats, cerebral evoked potentials (CEPs) were recorded by use of implanted skull-electrodes to distension pressure of 80 mmHg. In humans surface electrodes and individualized pressure, corresponding to pain detection threshold, were used. Comparison of morphology was assessed by wavelet analysis. Within- and between-day reproducibility was assessed in terms of latencies, amplitudes, and frequency content. In rats CEPs showed triphasic morphology. No differences in latencies, amplitudes, and power distribution were seen within or between days (all P ≥ 0.5). Peak-to-peak amplitude between the first positive and negative potential were the most reproducible characteristic within and between days (evaluated by intraclass correlation coefficients, ICC) (ICC = 0.99 and ICC = 9.98, respectively). In humans CEPs showed a triphasic morphology. No differences in latencies, amplitudes, or power distribution were seen within or between days (all P ≥ 0.2). Latency to the second negative potential (ICC = 0.98) and the second positive potential (ICC = 0.95) was the most reproducible characteristic within and between days. A unique and reliable translational platform was established assessing visceral sensitivity in rats and humans, which may improve the translational process of developing new drugs targeting visceral pain.

Cannabinoid receptor 1 gene and irritable bowel syndrome: phenotype and quantitative traits

Genetic variations in metabolism of endocannabinoids and in CNR1 (gene for cannabinoid 1 receptor) are associated with symptom phenotype, colonic transit, and left colon motility in irritable bowel syndrome (IBS). Our aim was to evaluate associations between two variations in CNR1 genotype (rs806378 and [AAT]n triplets) with symptom phenotype, small bowel and colonic transit, and rectal sensations in 455 patients with IBS and 228 healthy controls. Small bowel and colonic transit were measured by scintigraphy, rectal sensation by isobaric distensions. Associations with genotype were assessed by χ(2) test (symptom phenotype) and ANCOVA (quantitative traits) based on a dominant genetic model. Significant association of CNR1 rs806378 (but not CNR1 [AAT]n) genotype and symptom phenotype was observed (χ(2) P = 0.028). There was significant association of CNR1 rs806378 (P = 0.014; CC vs. CT/TT) with colonic transit in IBS-diarrhea (IBS-D) group; the TT group had the fastest colonic transit at 24 and 48 h. There was significant overall association of CNR1 rs806378 with sensation rating of gas (P = 0.025), but not pain; the strongest associations for gas ratings were in IBS-D (P = 0.002) and IBS-alternating (P = 0.025) subgroups. For CNR1 (AAT)n, gene-by-phenotype interactions were observed for colonic transit at 24 (P = 0.06) and 48 h (P = 0.002) and gas (P = 0.046, highest for IBS-D, P = 0.034), but not pain sensation; the strongest association with transit was in controls, not in IBS. These data support the hypothesis that cannabinoid receptors may play a role in control of colonic transit and sensation in humans and deserve further study as potential mediators or therapeutic targets in lower functional gastrointestinal disorders.

Drug development for the irritable bowel syndrome: current challenges and future perspectives

Medications are frequently used for the treatment of patients with the irritable bowel syndrome (IBS), although their actual benefit is often debated. In fact, the recent progress in our understanding of the pathophysiology of IBS, accompanied by a large number of preclinical and clinical studies of new drugs, has not been matched by a significant improvement of the armamentarium of medications available to treat IBS. The aim of this review is to outline the current challenges in drug development for IBS, taking advantage of what we have learnt through the Rome process (Rome I, Rome II, and Rome III). The key questions that will be addressed are: (a) do we still believe in the "magic bullet," i.e., a very selective drug displaying a single receptor mechanism capable of controlling IBS symptoms? (b) IBS is a "functional disorder" where complex neuroimmune and brain-gut interactions occur and minimal inflammation is often documented: do we need to target gut motility, visceral sensitivity, or minimal inflammation? (c) are there validated biomarkers (accepted by regulatory agencies) for studies of sensation and motility with experimental medications in humans? (d) do animal models have predictive and translational value? (e) in the era of personalized medicine, does pharmacogenomics applied to these medications already play a role? Finally, this review will briefly outline medications currently used or in development for IBS. It is anticipated that a more focused interaction between basic science investigators, pharmacologists, and clinicians will lead to better treatment of IBS.

Functional diarrhea

Chronic diarrhea is a frequent and challenging problem in clinical medicine. In a considerable subgroup of these, no underlying cause is identified and this is referred to as functional diarrhea. A consensus definition for functional diarrhea is based on loose stool consistency and chronicity and absence of coexisting irritable bowel syndrome. Underlying pathophysiology includes rapid intestinal transit, which may be worsened by stress or be triggered by a preceding infectious gastroenteritis. Diagnostic work-up aims at exclusion of underlying organic disease. Treatment starts with dietary adjustments, aiming at decreasing nutrients that enhance transit and stool and at identifying precipitating food items.

Sensations of gas and pain and their relationship with compliance during distension in human colon

BACKGROUND

Colonic mechanosensory afferents 'in parallel' to circular muscle activate prevertebral ganglion reflexes; 'in series', afferents convey visceral sensation to the central nervous system; and pain receptors are activated with muscle distension. Our aim was to analyze the relationships of gas and pain sensations during graded distensions, and the association of sensations with colonic compliance in conscious humans.

METHODS

The data were acquired in a prior study performed on 60 healthy volunteers (aged 18-75 years) under baseline conditions. Colonic compliance was measured in response to 4 mmHg stepwise balloon distensions to estimate pressure at half-maximum volume (Pr(50%)). Sensation ratings for gas and pain were averaged over distensions at 16, 24, 30 and 36 mmHg above baseline operating pressure. Associations between mean gas and pain ratings, and colonic compliance were assessed with Pearson correlations.

KEY RESULTS

Gas and pain sensations were significantly correlated at all levels of distension (all P < 0.001). Significant inverse correlations between Pr(50%) and sensations of gas and pain were observed, suggesting that lower compliance was associated with lower sensations. Up to 25% of the variance in sensation may be attributed to colonic compliance.

CONCLUSIONS & INFERENCES

These data are consistent with the hypothesis that, if circumferential colonic receptors are stimulated by distension to mediate gas and pain in humans, they are, at least partly, arranged 'in parallel' to the muscle layer.

Irritable bowel syndrome: methods, mechanisms, and pathophysiology. Genetic epidemiology and pharmacogenetics in irritable bowel syndrome

The objectives of this review are twofold. Our first objective is to evaluate the evidence supporting a role for genetics in irritable bowel syndrome (IBS). Specific examples of the associations of genetic variation and symptoms, syndromes, and intermediate phenotypes, including neurotransmitter (serotonergic, α(2)-adrenergic, and cannabinoid) mechanisms, inflammatory pathways (IL-10, TNFα, GNβ3, and susceptibility loci involved in Crohn's disease), and bile acid metabolism, are explored. The second objective is to review pharmacogenetics in IBS, with the focus on cytochrome P-450 metabolism of drugs used in IBS, modulation of motor and sensory responses to serotonergic agents based on the 5-hydroxytryptamine (5-HT) transporter-linked polymorphic region (5-HTTLPR) and 5-HT(3) genetic variants, responses to a nonselective cannabinoid agonist (dronabinol) based on cannabinoid receptor (CNR1) and fatty acid amide hydrolase (FAAH) variation, and responses to a bile acid (sodium chenodeoxycholate) and bile acid binding (colesevelam) based on klothoβ (KLB) and fibroblast growth factor receptor 4 (FGFR4) variation. Overall, there is limited evidence of a genetic association with IBS; the most frequently studied association is with 5-HTTLPR, and the most replicated association is with TNF superfamily member 15. Most of the pharmacogenetic associations are reported with intermediate phenotypes in relatively small trials, and confirmation in large clinical trials using validated clinical end points is still required. No published genome-wide association studies in functional gastrointestinal or motility disorders have been published.

Effect of nifedipine on anorectal sensorimotor functions in health and fecal incontinence

The mechanisms of increased rectal stiffness in women with fecal incontinence (FI) and rectal urgency are not understood. Our hypothesis was that distention-induced activation of mechanosensitive L-type calcium channels in smooth muscle contributes to increased rectal stiffness in FI. Anal pressures, rectal distensibility (compliance, capacity, and contractile response to sinusoidal oscillation), and rectal sensation were assessed before and after oral nifedipine (30 + 10 mg) or placebo in 16 women with FI and 16 asymptomatic women. At baseline, FI patients had a lower anal pressure increment during squeeze (health, 66.9 ± 7.6: FI, 28.6 ± 5.9, mean ± SE, P ≤ 0.01), lower rectal capacity (P = 0.052), and higher rectal pressures during sinusoidal oscillation (health, 13.7 ± 3.2: FI, 21.7 ± 1.4, mean ± SE, P = 0.02) than the healthy women, which suggests an exaggerated rectal contractile response to distention. Nifedipine decreased mean BP, increased heart rate (P = 0.01 vs. placebo), and reduced anal resting pressure (P ≤ 0.01) but did not significantly modify rectal distensibility in health or FI. Plasma nifedipine concentrations (health, 103 ± 21 ng/ml: FI, 162 ± 34 ng/ml) were correlated with increased rectal compliance (r = 0.6, P = 0.02) in all study participants and, in healthy subjects, with decreased rectal pressures during sinusoidal oscillation (r = 0.86, P = 0.01), indicative of reduced stiffness. No consistent effects on rectal perception were observed. These observations confirm that FI is associated with anal weakness and increased rectal stiffness. At therapeutic plasma concentrations, nifedipine reduced anal resting pressure but did not improve rectal distensibility in FI, outcomes that argue against a predominant contribution of myogenic L-type calcium channels to reduced rectal distensibility in FI.

Opioid-induced constipation: challenges and therapeutic opportunities

There has been an alarming increase in the prescription of opiates and opioids for chronic non-cancer pain in the past 15 years. It is estimated that opiate-induced constipation (OIC) is experienced by ~40% of these patients, and that constipation and other gastrointestinal symptoms may dissuade patients from using the required analgesic dose to achieve effective pain relief. Opiates have several effects on gastrointestinal functions, and the inhibition of colonic transit and intestinal and colonic secretion results in constipation. Several different pharmacological approaches are being developed to prevent or treat OIC: prolonged release formulations that contain naloxone (a less specific opiate antagonist that is widely distributed) and a new class of peripherally restricted μ-opiate receptor antagonists, including methylnaltrexone, alvimopan, tapentadol, NKTR-118, and TD-1211. Novel patient response outcomes have been developed to facilitate demonstration of efficacy and safety of drugs in development for OIC.

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.

Investigational agents for the irritable bowel syndrome

IMPORTANCE OF THE FIELD

Irritable bowel syndrome (IBS) is a common disorder with significant health and economic consequences. The etiology of IBS is complex and appears to be multifactorial. Traditional IBS therapies have been directed primarily at the relief of individual symptoms but have been largely disappointing. This has triggered the search for newer treatment strategies with improved patient outcomes.

AREAS COVERED IN THIS REVIEW

Enhanced knowledge about the putative pathophysiology of IBS has allowed the identification of new mechanistic targets for treatment. Our aim is to review emerging and promising drugs in the treatment of IBS based on disease pathophysiology. Data were extracted using Medline and PubMed search engines until January 2010. Abstracts were identified through 'Web of Science' and abstract supplements of major gastrointestinal scientific meetings. Drugs were classified according to mechanism of action and those with efficacy in trials involving human subjects examined.

WHAT THE READER WILL GAIN

Additional insight into the pathophysiology as well as current and prospective treatments of IBS.

TAKE HOME MESSAGE

A multitude of putative drug targets have been identified and some novel treatments have progressed through to human clinical trials, but very few will be approved for the market in the near future. Moreover, and in keeping with the complex and multifactorial nature of this syndrome, it is unlikely that there will be one dominant and universally effective form of therapy for all IBS patients.

Investigation of the distribution and function of alpha-adrenoceptors in the sheep isolated internal anal sphincter

BACKGROUND AND PURPOSE

We have investigated the distribution of alpha-adrenoceptors in sheep internal anal sphincter (IAS), as a model for the human tissue, and evaluated various imidazoline derivatives for potential treatment of faecal incontinence.

EXPERIMENTAL APPROACH

Saturation and competition binding with (3)H-prazosin and (3)H-RX821002 were used to confirm the presence and density of alpha-adrenoceptors in sheep IAS, and the affinity of imidazoline compounds at these receptors. A combination of in vitro receptor autoradiography and immunohistochemistry was used to investigate the regional distribution of binding sites. Contractile activity of imidazoline-based compounds on sheep IAS was assessed by isometric tension recording.

KEY RESULTS

Saturation binding confirmed the presence of both alpha(1)- and alpha(2)-adrenoceptors, and subsequent characterization with sub-type-selective agents, identified them as alpha(1A)- and alpha(2D)-adrenoceptor sub-types. Autoradiographic studies with (3)H-prazosin showed a positive association of alpha(1)-adrenoceptors with immunohistochemically identified smooth muscle fibres. Anti-alpha(1)-adrenoceptor immunohistochemistry revealed similar distributions of the receptor in sheep and human IAS. The imidazoline compounds caused concentration-dependent contractions of the anal sphincter, but the maximum responses were less than those elicited by l-erythro-methoxamine, a standard non-imidazoline alpha(1)-adrenoceptor agonist. Prazosin (selective alpha(1)-adrenoceptor antagonist) significantly reduced the magnitude of contraction to l-erythro-methoxamine at the highest concentration used. Both prazosin and RX811059 (a selective alpha(2)-adrenoceptor antagonist) reduced the potency (pEC(50)) of clonidine.

CONCLUSIONS AND IMPLICATIONS

This study shows that both alpha(1)- and alpha(2)-adrenoceptors are expressed in the sheep IAS, and contribute (perhaps synergistically) to contractions elicited by various imidazoline derivatives. These agents may prove useful in the treatment of faecal incontinence.

The effects of clonidine on symptoms and anorectal sensorimotor function in women with faecal incontinence

BACKGROUND

Women with faecal incontinence and rectal urgency have increased rectal stiffness and sensation.

AIM

To evaluate the effects of clonidine, an alpha(2) -adrenergic agonist, in faecal incontinence.

METHODS

In this open-label uncontrolled study, bowel symptoms and anorectal functions (anal pressures, rectal compliance, and sensation) were assessed before and during treatment with transdermal clonidine (0.2 mg daily, 4 weeks) in 12 women with urge-predominant faecal incontinence.

RESULTS

Clonidine reduced the frequency (17.8 +/- 3.1 before vs. 8.8 +/- 3.9 after, P = 0.03) and number of days with faecal incontinence (11.8 +/- 1.6 before vs. 6.1 +/- 1.8 after, P = 0.02), faecal incontinence symptom severity score (max = 13, 8.3 +/- 0.7 vs. 5.6 +/- 0.9, P < 0.01), and allowed patients to defer defecation for a longer duration (P = 0.03). Although overall effects on anorectal functions were not significant, the treatment-associated reduction in faecal incontinence episodes was associated with increased rectal compliance (r = -0.58, P < 0.05) and reduced rectal sensation. (r = -0.73, P = 0.007 vs. desire to defecate pressure threshold).

CONCLUSIONS

Clonidine improves symptoms in women with faecal incontinence; this improvement is associated with increased rectal compliance and reduced rectal sensitivity. A controlled study is necessary to confirm these observations.

Pharmacogenetics of low dose clonidine in irritable bowel syndrome

Adrenergic and serotonergic (ADR-SER) mechanisms alter gut (gastrointestinal, GI) sensorimotor functions. We aimed to determine whether candidate ADR-SER genes affect GI responses to low dose clonidine (CLO) in humans. Forty healthy and 120 irritable bowel syndrome (IBS) participants received CLO, 0.1 mg or 0.15 mg b.i.d., for 6 days. At baseline and post-CLO, we measured: gastric volume (GV); satiation volume; rectal compliance, sensation thresholds and ratings with distensions. Genetic variations tested were: alpha2A (C-1291G), alpha2C (Del 322-325), GNbeta3 (C825T) and solute carrier family 6 (neurotransmitter transporter, serotonin), member 4 (SLC6A4) (serotonin transporter linked polymorphic region). CLO reduced volume to satiation (P = 0.002), postprandial GV (P < 0.001), sensation threshold for pain (<0.001); CLO increased rectal compliance (P = 0.024). There were significant associations between post-CLO responses and gene variations for DeltaGV (alpha2A and SLC6A4), rectal sensation of gas (alpha2A, GNbeta3), urgency (alpha2A); and pain (GNbeta3 and SLC6A4); and rectal compliance (SLC6A4). alpha2A, GNbeta3 and SLC6A4 genotypes significantly modify responses to CLO on sensory and motor GI functions in health and IBS.

Effect of a chloride channel activator, lubiprostone, on colonic sensory and motor functions in healthy subjects

Lubiprostone, a bicyclic fatty acid chloride channel activator, is efficacious in treatment of chronic constipation and constipation-predominant irritable bowel syndrome. The study aim was to compare effects of lubiprostone and placebo on colonic sensory and motor functions in humans. In double-blind, randomized fashion, 60 healthy adults received three oral doses of placebo or 24 microg lubiprostone per day in a parallel-group, placebo-controlled trial. A barostat-manometry tube was placed in the left colon by flexible sigmoidoscopy and fluoroscopy. We measured treatment effects on colonic sensation and motility with validated methods, with the following end points: colonic compliance, fasting and postprandial tone and motility indexes, pain thresholds, and sensory ratings to distensions. Among participants receiving lubiprostone or placebo, 26 of 30 and 28 of 30, respectively, completed the study. There were no overall effects of lubiprostone on compliance, fasting tone, motility indexes, or sensation. However, there was a treatment-by-sex interaction effect for compliance (P = 0.02), with lubiprostone inducing decreased fasting compliance in women (P = 0.06) and an overall decreased colonic tone contraction after a standard meal relative to fasting tone (P = 0.014), with greater effect in women (P < 0.01). Numerical differences of first sensation and pain thresholds (P = 0.11 in women) in the two groups were not significant. We concluded that oral lubiprostone 24 microg does not increase colonic motor function. The findings of decreased colonic compliance and decreased postprandial colonic tone in women suggest that motor effects are unlikely to cause accelerated colonic transit with lubiprostone, although they may facilitate laxation. Effects of lubiprostone on sensitivity deserve further study.

Candidate genes and sensory functions in health and irritable bowel syndrome

Adrenergic and serotonergic (ADR-SER) mechanisms alter gut (GI) function; these effects are mediated through G protein transduction. Candidate genetic variations in ADR-SER were significantly associated with somatic scores in irritable bowel syndrome (IBS) and gastric emptying but not small bowel or colonic transit. Our aim was to assess whether candidate ADR-SER genes are associated with motor and sensory GI functions in IBS and subgroups on the basis of bowel dysfunction. In 122 patients with IBS and 39 healthy controls, we assessed gastrointestinal somatic symptoms and affect by validated questionnaires. We measured: gastric volume (GV), maximum tolerated volume, rectal compliance, sensation thresholds and ratings, and genetic variations including alpha2A (C-1291G), alpha2C (Del 332-325), GNbeta3 (C825T), and 5-HTTLPR. Demographics and genotype distributions were similar in the patients with IBS subgrouped on bowel function. There were significant associations between 5-HTTLPR SS genotype and absence of IBS symptoms and between 5-HTTLPR LS/SS genotype and increased rectal compliance and increased pain ratings, particularly at 12 and 24 mmHg distensions. GNbeta3 was associated only with fasting GV; we did not detect associations between alpha2A genotype and the gastrointestinal sensory or motor functions tested. We concluded that 5-HTTLPR LS/SS genotype is associated with both increased pain sensation and increased rectal compliance though the latter effect is unlikely to contribute to increased pain sensation ratings with LS/SS genotype. The data suggest the hypotheses that the endophenotype of visceral hypersensitivity in IBS may be partly related to genetic factors, and the association of GNbeta3 with fasting GV may explain, in part, the reported association of GNbeta3 with dyspepsia.

Updates on treatment of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a highly prevalent gastrointestinal disorder characterized by abdominal pain and discomfort in association with altered bowel habits. It is estimated to affect 10%-15% of the Western population, and has a large impact on quality of life and (in)direct healthcare costs. IBS is a multifactorial disorder involving dysregulation within the brain-gut axis, and it is frequently associated with gastrointestinal motor and sensory dysfunction, enteric and central nervous system irregularities, neuroimmune dysregulation, and post-infectious inflammation. As with other functional medical disorders, the treatment for IBS can be challenging. Conventional therapy for those with moderate to severe symptoms is largely unsatisfactory, and the development of new and effective drugs is made difficult by the complex pathogenesis, variety of symptoms, and lack of objective clinical findings that are the hallmark of this disorder. Fortunately, research advances over the past several decades have provided insight into potential mechanisms responsible for the pathogenesis of IBS, and have led to the development of several promising pharmaceutical agents. In recent years there has been much publicity over several of these new IBS medications (alosetron and tegaserod) because of their reported association with ischemic colitis and cardiovascular disease. While these agents remain available for use under restricted prescribing programs, this highlights the need for continued development of safe and effective medication for IBS. This article provides a physiologically-based overview of recently developed and frequently employed pharmaceutical agents used to treat IBS, and discusses some non-pharmaceutical options that may be beneficial in this disorder.

Comparison of mathematical methods for calculating colonic compliance in humans: power exponential, computer-based and manual linear interpolation models

Measuring compliance allows differentiation of sensory changes from changes in thresholds because of altered compliance. As compliance of the colorectum is sigmoidal, a power exponential analysis was recommended. We aimed to develop and validate simpler measurements of compliance. Forty subjects (23 female, 17 male) underwent colonic barostat procedures comparing dronabinol vs placebo. Results of the effects on compliance were reported elsewhere. Compliance was determined as volume response to pressures ranging from 0 to 36 mmHg. Pressures corresponding to 10%, 50% and 90% (Pr10, Pr50 and Pr90) of maximum volume at 36 mmHg were estimated using a power exponential model, computer-based and manual linear interpolation. Data were compared and concordance evaluated. Pr50 and Pr90 were not significantly different by all methods for baseline and post-treatment. Respectively, concordance correlation coefficients were: pretreatment, 0.879, 0.464 and post-treatment, 0.879, 0.623. There is larger variation in Pr10 comparing all methods and manual calculations allow for the closest fit to the data. Concordance correlation coefficients were pretreatment = 0.189 and post-treatment = 0.322. There were no gender differences in compliance measurements. Results of compliance are highly concordant amongst all models. However, computer-based or manual interpolations appear superior to power exponential models for estimating Pr10.

Current treatments in functional dyspepsia

By nature of the definition of functional dyspepsia (FD), organic causes have to be ruled out before therapy can be directed. However, in uninvestigated dyspepsia in the absence of alarm features, Helicobacter pylori "test and treat" or an empiric trial of acid suppression therapy for 4 to 8 weeks is reasonable. If alarm symptoms or signs are present, or if the dyspepsia symptoms first occur in those aged greater than 55 years, prompt esophagogastroduodenoscopy is mandatory to exclude serious disease and positively diagnose FD. Empiric acid suppression with H(2)-receptor antagonists or proton-pump inhibitors is superior to placebo in treatment of FD, but those patients with meal-related symptoms are least likely to respond. Helicobacter pylori eradication in FD benefits a minority of cases but is worthwhile, as response may be maintained. There is increasing evidence that some prokinetics may be superior to placebo in treatment of FD, but probably only a minority respond; those with meal-related symptoms may have the best response. Antidepressant therapy may have a place in management of difficult cases, but adequate randomized controlled trials are unavailable.

Effects of glucagon-like peptide-1 and sympathetic stimulation on gastric accommodation in humans

In humans, glucagon-like peptide-1 (GLP-1) delays gastric emptying by inhibiting vagal activity and also increases gastric volumes, by unclear mechanisms. Because GLP-1 inhibits intestinal motility by stimulating the sympathetic nervous system in rats, we assessed the effects of a GLP-1 agonist and yohimbine, an alpha(2)-adrenergic antagonist, on gastric volumes in humans. In this double-blind study, 32 healthy volunteers were randomized to placebo, a GLP-1 agonist, yohimbine or GLP-1 and yohimbine. Gastric volumes (fasting predrug and postdrug, and postprandial postdrug) were measured by (99m)Tc single photon emission computed tomography imaging. Plasma catecholamines and haemodynamic parameters were assessed. Compared with placebo, GLP-1 increased (P = 0.03) but yohimbine did not affect fasting gastric volume. However, GLP-1 plus yohimbine increased (P < 0.001) postprandial gastric accommodation vs placebo and vs GLP-1 alone [postprandial volume change = 542 +/- 29 mL (mean +/- SEM, placebo), 605 +/- 31 mL (GLP-1), 652 +/- 54 mL (yohimbine) and 810 +/- 37 mL (GLP-1 and yohimbine)]. Plasma noradrenaline and dihydroxyphenylglycol concentrations were higher for yohimbine vs placebo and for GLP-1 and yohimbine vs GLP-1. Yohimbine stimulates central sympathetic activity and in combination with GLP-1, augments postprandial accommodation in humans.

Mechanisms of Disease: genetics of functional gastrointestinal disorders—searching the genes that matter

There is evidence to suggest that genetic factors contribute to the manifestation of functional gastrointestinal disorders (FGID). As such, it is important to note that FGID are heterogeneous; they have quite different clinical features and (probably) different underlying pathophysiologic mechanisms. Evidence from family and twin studies indicates that there is clustering of FGID in families and increased concordance in monozygotic compared with dizygotic twins. The clinical features of FGID implicate polymorphisms in the genes that encode adrenergic, opioidergic or serotonergic receptors, as well as in the G-protein beta3 subunit (GNB3) gene and serotonin-transporter genes, in their manifestations. As mediators or regulators of mucosal inflammation can trigger events that ultimately result in manifestations of FGID, polymorphisms in genes that encode proteins with immunomodulatory and/or neuromodulatory features (e.g. OPRM1, IL4, IL4R, TNF) might also have a role in the manifestation of FGID. A two-step model for the role of genetic factors in the manifestation of functional gastrointestinal pain can, therefore, be proposed. In the presence of specific hereditary factors, environmental factors that do not usually cause long-term functional alterations are linked to the manifestation of symptoms.

Clonidine reduces diarrhea and sodium loss in patients with proximal jejunostomy: a controlled study

BACKGROUND

Patients with short bowel syndrome have significant fluid losses. This represents a significant management problem, especially in patients with minimal residual intestine. We determined whether clonidine, an alpha2-adrenergic agonist, is effective in decreasing fecal water and sodium (Na) losses in patients with proximal jejunostomy. Eight parenteral nutrition (PN)-dependent subjects (3 men, 5 women), aged 49.9+/-10.2 years, with a residual small bowel length of 71.8+/-152.0 cm that ended in a jejunostomy, were studied.

METHODS

Subjects were admitted to the North-western General Clinical Research Center (GCRC) for a 2-day equilibrium period while receiving a self-selected 100 g fat diet with protein 1.5 g/kg/d and 30 kcal/kg/d and 1 L/d of oral rehydration solution. A D-xylose test was performed after an overnight fast. On days 3-5, all stool and urine were collected for volume, weight, fat, nitrogen, energy, sodium, magnesium, potassium, and calcium. Meals were provided in duplicate and the equivalent portions consumed by each patient were analyzed for fluid volume, fat, nitrogen, energy, sodium, magnesium, calcium, and potassium in order to calculate nutrient balances. At the conclusion of the stool and urine collections (day 6), a clonidine (0.3 mg) patch was applied to the shoulder. Subjects were restudied after 1 week.

RESULTS

Daily fecal volume and weight were 4.514+/-1.769 L/d and 4394+/-1727 g/d, respectively, at baseline. Five subjects were net "secretors" in that excreted fecal volume exceeded oral intake. Fecal volume decreased by 427+/-562 mL/d (8.9%, p=.07). Fecal weight decreased by 438+/-527 g/d (9.4%, p=.05). Urine volume correspondingly increased by 747+/-1934 mL (18.9%, p=not significant [NS]). The increase in urine output was weakly and negatively correlated with the decrease in fecal volume and weight (r=-0.37 and -0.41, respectively, p=NS). Oral fluid intake decreased slightly from 3.328+/-1.246 L/d baseline to 3.203+/-1.119 L/d with clonidine therapy (-3.8%, p=NS). Fecal Na loss was significantly decreased from baseline (887+/-996 mg/d, 11.2+/-12.3%; p=.036). This was not related to decreased oral Na intake, which actually increased from baseline (3.799+/-2.271 g/d) to 3.933+/-1.314 g/d after clonidine therapy (p=NS). No patient developed hypotension.

CONCLUSIONS

Our results show the transdermal administration of clonidine is associated with a modest but clinically significant decrease in fecal output in patients with short bowel syndrome and high-output proximal jejunostomy that require chronic parenteral fluid infusion. This is accompanied by decreased fecal Na loss.

Irritable bowel syndrome: recent and novel therapeutic approaches

Irritable bowel syndrome (IBS) is a highly prevalent functional gastrointestinal disorder affecting up to 3-15% of the general population in Western countries. It is characterised by unexplained abdominal pain, discomfort and bloating in association with altered bowel habits. The pathophysiology of IBS is considered to be multifactorial, involving disturbances of the brain-gut-axis: IBS has been associated with abnormal gastrointestinal motor functions, visceral hypersensitivity, psychosocial factors, autonomic dysfunction and mucosal inflammation. Traditional IBS therapy is mainly symptom oriented and often unsatisfactory. Hence, there is a need for new treatment strategies. Increasing knowledge of brain-gut physiology, mechanisms, and neurotransmitters and receptors involved in gastrointestinal motor and sensory function have led to the development of several new therapeutic approaches. This article provides a systematic overview of recently approved or novel medications that show promise for the treatment of IBS; classification is based on the physiological systems targeted by the medication. The article includes agents acting on the serotonin receptor or serotonin transporter system, novel selective anticholinergics, alpha-adrenergic agonists, opioid agents, cholecystokinin antagonists, neurokinin antagonists, somatostatin receptor agonists, neurotrophin-3, corticotropin releasing factor antagonists, chloride channel activators, guanylate cyclase-c agonists, melatonin and atypical benzodiazepines. Finally, the role of probiotics and antibacterials in the treatment of IBS is summarised.

Irritable bowel syndrome: update on colonic neuromuscular dysfunction and treatment

Recent discoveries regarding the relatively autonomous workings of the enteric nervous system have expanded our understanding of the pathophysiology of irritable bowel syndrome (IBS). However, the heterogeneity of the pathogenesis of IBS continues to create unique challenges for clinicians who care for these patients. Advances in our understanding of the structure and functions of the brain-gut axis and its interplay with other potentially important factors, such as genetic predisposition, inflammation, and psychological unrest, have led to new developments in the field of targeted pharmacotherapy for IBS sufferers. Therapies designed specifically to modulate gut motility, secretion, and/or sensation have been created and introduced into the marketplace in recent years, and additional designer formulations are in various stages of development. Concurrently, new discoveries of potentially beneficial effects of agents approved for other, often non-gastroenterologic, conditions continue to be reported. This article reviews the accumulating body of evidence supporting the importance of neuromuscular dysfunction as a central cause of IBS symptoms and provides a rationale for the discussion of current and future drug development.

Current gut-directed therapies for irritable bowel syndrome

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that can present with a wide array of symptoms that make treatment difficult. Current therapies are directed at relieving symptoms of abdominal pain or discomfort, bloating, constipation, and diarrhea. Pharmacologic agents used to treat IBS-associated pain include myorelaxants, peppermint oil, and peripherally acting opiates. Dicyclomine and hyoscyamine, the two myorelaxants available in the United States, have not been proven effective in reducing abdominal pain in patients with IBS. The efficacy of peppermint oil is debated, but methodological problems with existing studies preclude definitive judgment. Loperamide is ineffective for relief of abdominal pain. For IBS patients with excessive abdominal bloating, a small number of studies suggest that bacterial eradication with gut-directed antibiotics and bacterial reconstitution with nonpathogenic probiotics may reduce flatulence. For constipation-predominant (C-IBS) symptoms, current treatment options include fiber supplementation, polyethylene glycol, and tegaserod. Soluble fibers (ispaghula, calcium polycarbophil, psyllium) are more effective than insoluble fibers (wheat bran, corn fiber) in alleviating global symptoms and relieving constipation, although fiber in general has marginal benefit in treatment of overall IBS symptoms. Polyethylene glycol increases bowel frequency in chronic constipation, but its overall efficacy against IBS is unclear. Tegaserod, a 5-HT(4) agonist, demonstrates superiority over placebo in improving bowel frequency and stool consistency and alleviating abdominal pain and bloating in women with C-IBS. Overall global symptoms are modestly improved with tegaserod when compared with placebo. Additional agents under investigation for C-IBS include the ClC(2) chloride channel opener lubiprostone, mu-opioid receptor antagonist alvimopan, and 5-HT(4) agonist renzapride. For diarrhea-predominant (D-IBS) symptoms, available therapies include loperamide, alosetron, and clonidine. Alosetron, a 5-HT(3) antagonist, is superior to placebo for reducing bowel frequency, improving stool consistency, and relieving abdominal pain in women with D-IBS. However, alosetron is available under a restricted license because of concerns for ischemic colitis and severe constipation necessitating colectomy. Clonidine may be helpful in alleviating global symptoms for D-IBS patients.

Treatments targeting putative mechanisms in irritable bowel syndrome

The pathophysiology of irritable bowel syndrome (IBS) is heterogeneous; it is possible for several mechanisms to be disturbed in the same patient. Isolating a single target for pharmacological manipulation is also difficult because of the complexity and overlap of the neural circuitry in the enteric and central nervous system. This review summarizes the rationale and efficacy of current and future therapies for IBS, on the basis of putative pathophysiological models. The modulation of gastrointestinal sensorimotor function, intestinal gas handling, the gastrocolonic reflex, neurohormonal stress responses, central processing of afferent information, and microbial flora are the current frontiers for experimental therapeutics for IBS. Patients presumed to have POSTINFECTIOUS IBS have also been targeted as a distinct group. In the very near future, it is unlikely that a single drug will come to the fore as a suitable and successful treatment for everyone with IBS, but new data on potential therapeutic targets lend hope for the improved long-term management of IBS. Disease modification rather than just symptom-based treatments must remain the goal.

Meta-analysis: The treatment of irritable bowel syndrome

To evaluate therapies available for the treatment of irritable bowel syndrome, and provide consensus recommendations for their use, a total of 51 double-blind clinical trials using bulking agents, prokinetics, antispasmodics, alosetron, tegaserod and antidepressants were selected. The quality of studies was assessed using 5-point scale. Meta-analyses were performed on all studies, and on 'high-quality studies'. The efficacy of fibre in the global irritable bowel syndrome symptoms relief (OR: 1.9; 95% CI:1.5-2.4) was lost after exclusion of low-quality trials (OR: 1.4; 95% CI: 1.0-2.0, P = 0.06). When excluding the low-quality trials, an improvement of global irritable bowel syndrome symptoms with all antispasmodics (OR: 2.1; 95% CI:1.8-2.9) was maintained only for octylonium bromide, but on the basis of only two studies. Antidepressants were effective (OR: 2.6, 95% CI: 1.9-3.5), even after exclusion of low-quality studies (OR: 1.9, 95% CI: 1.3-2.7). Alosetron (OR: 2.2; 95% CI: 1.9-2.6) and tegaserod (OR: 1.4; 95% CI: 1.2-1.5) showed a significant effect in women. We recommend the use of tegaserod for women with irritable bowel syndrome with constipation and alosetron for women with severe irritable bowel syndrome with diarrhoea. Antidepressants can be beneficial for irritable bowel syndrome with diarrhoea patients with severe symptoms. Loperamide can be recommended in painless diarrhoea. Evidence is weak to recommend the use of bulking agents in the treatment of irritable bowel syndrome with constipation.

Management of Functional Abdominal Pain

The diagnosis of functional abdominal pain should be made based on the Rome II symptom criteria with only limited testing to exclude other disease. During physical examination the clinician may look for evidence of pain behavior which would be supportive of the diagnosis. Reassurance and proper education regarding the clinical entity of functional abdominal pain is critical for successful treatment and good patient satisfaction. Education should include validation that symptoms are real, and that other individuals experience similar symptoms. No further treatment may be required for those with mild symptoms. For patients with more severe symptoms, a long-term management plan of either pharmacological or psychological treatments is warranted. This will require a commitment by both the patient and the physician to engage in a partnership with active involvement and responsibility by both individuals. The goal of treatment--to decrease pain and increase function over time, not to cure the disorder-- should be explained. Strong consideration should be made for the use of an antidepressant to treat analgesic effects. Tricyclic antidepressants are the mainstay of therapy for functional pain disorders. The analgesic effect is generally quicker in onset and occurs at a lower dose than their effect on mood. To maximize patient compliance, patients should be told the rationale behind their use, warned of the potential side effects, and reassured that many of the side effects will disappear with time. Choice of an antidepressant should be based on the presence of concomitant symptoms (eg, depression), cost, and physician familiarity with specific agents. All patients with functional abdominal pain should be screened for underlying psychiatric disturbance as an untreated mood disorder will adversely affect response to treatment. If a concurrent mood disorder is found, it should be treated by either using a higher dose of the tricyclic antidepressant or by adding another antidepressant agent. Psychological interventions such as cognitive behavioral therapy may be important as adjuvant therapy or as an alternative to treatment with antidepressants for those patients who find antidepressants ineffective or are intolerant to them. Narcotics and benzodiazepines should not be used to treat chronic abdominal pain due to the high risk of physical and psychological dependence.

Treating irritable bowel syndrome: overview, perspective and future therapies

This article summarizes the ongoing challenges in irritable bowel syndrome and the exciting opportunities for development of novel therapies for this common, enigmatic condition. The challenges include insufficient understanding of mechanisms, lack of specificity of symptoms, differentiation from other conditions, and lack of availability of noninvasive tests to identify dysfunctions. However, significant opportunities are reflected by the advances in clinical trial design and, particularly, clinically relevant end points for such trials, and the increasing understanding of basic neuroenteric science. The latter has delivered two new medications to the practice (alosetron and tegaserod), and other candidate therapies (other serotonergic, tachykininergic, opioid, cannabinoid modulators) are being carefully appraised as potential drugs for the future.

Evaluation of drug treatment in irritable bowel syndrome

The irritable bowel syndrome (IBS) remains a therapeutic challenge in part because of the limited understanding of the pathophysiology. The placebo response rate varies in randomized controlled trials from 20 to 70%, and can persist for up to at least 1 year. It is contentious whether dietary fibre and bulking agents relieve the symptoms of IBS; constipation probably improves. Anticholinergic and antispasmodic agents are of questionable benefit in IBS despite positive meta-analyses of poor quality trials. A meta-analysis concluded that the tricyclic antidepressants were superior to placebo in IBS, although the individual trial results were variable. Selective serotonin reuptake inhibitors are of uncertain benefit. Laxatives are used for constipation but probably poorly control the IBS symptom complex. Loperamide is superior to placebo in improvement of diarrhoea but not abdominal pain in IBS. Tegaserod is a well- tolerated aminoguanidine indole derivative of serotonin that is a partial 5HT4-receptor agonist with prokinetic properties; a therapeutic gain over placebo of 5% to 15% has been observed in constipation-predominant IBS in females. Alosetron is a 5HT3-receptor antagonist that is efficacious in females with diarrhoea-predominant IBS, with a 12% to 17% therapeutic gain; the risk of ischaemic colitis is 1 in 350, with very severe constipation occurring in about 1 in 1000. Optimizing study design remains a challenge in IBS. New visceral analgesic and motility modifying agents, as well as anti-inflammatory agents are in trials, and hopefully additional efficacious therapeutic options for patients with IBS will soon emerge.

Effects of a kappa-opioid agonist, asimadoline, on satiation and GI motor and sensory functions in humans

To compare the effects of the kappa-opioid agonist asimadoline and placebo on visceral sensation and gastrointestinal (GI) motor functions in humans, 91 healthy participants were randomized in a double-blind fashion to 0.15, 0.5, or 1.5 mg of asimadoline or placebo orally twice a day for 9 days. We assessed satiation (nutrient drink test), colonic compliance, tone, perception of colonic distension (barostat), and whole gut transit (scintigraphy). Treatment effect was assessed by analysis of covariance. Asimadoline increased nutrient drink intake (P = 0.03). Asimadoline decreased colonic tone during fasting (P = 0.03) without affecting postprandial colonic contraction, compliance, or transit. Gas scores in response to colonic distension were decreased with 0.5 mg of asimadoline at low levels (8 mmHg above operating pressure) of distension (P = 0.04) but not at higher levels of distension. Asimadoline at 1.5 mg increased gas scores at 16 mmHg of distension (P = 0.03) and pain scores at distensions of 8 and 16 mmHg (P = 0.003 and 0.03, respectively) but not at higher levels of distension. Further studies of this compound in diseases with altered satiation or visceral sensation are warranted.

New developments in the treatment of functional dyspepsia

Functional dyspepsia is a clinical syndrome defined by chronic or recurrent pain or discomfort in the upper abdomen of unknown origin. Although generally accepted, investigators differently interpret this definition and clinical trials are often biased by inhomogeneous inclusion criteria. The poorly defined multifactorial pathogenesis of dyspeptic symptoms has hampered efforts to develop effective treatments. A general agreement exists on the irrelevant role played by Helicobacter pylori in the pathophysiology of functional dyspepsia. Gastric acid secretion is within normal limits in patients with functional dyspepsia but acid related symptoms may arise in a subgroup of them. Proton pump inhibitors appear to be effective in this subset of patients with dyspepsia. Non-painful dyspeptic symptoms are suggestive of underlying gastrointestinal motor disorders and such abnormalities can be demonstrated in a substantial proportion of patients. Postprandial fullness and vomiting have been associated with delayed gastric emptying of solids, and early satiety and weight loss to postcibal impaired accommodation of the gastric fundus. Prokinetics have been shown to exert beneficial effects, at least in some patients with dyspepsia. In contrast, drugs enhancing gastric fundus relaxation have been reported to improve symptoms, although conflicting results have also been published. An overdistended antrum may also generate symptoms, but its potential pathogenetic role and the effects of drugs on this abnormality have never been investigated formally. Visceral hypersensitivity plays a role in some dyspeptic patients and this abnormality is also a potential target for treatment. Both chemo- and mechanoreceptors can trigger hyperalgesic responses. Psychosocial abnormalities have been consistently found in functional digestive syndromes, including dyspepsia. Although useful in patients with irritable bowel syndromes (IBS), antidepressants have been only marginally explored in functional dyspepsia. Among the new potentially useful agents for the treatment of functional dyspepsia, serotonin 5-HT(4) receptor agonists have been shown to exert a prokinetic effect. Unlike motilides, 5-HT(4) receptor agonists do not appear to increase the gastric fundus tone and this may contribute to improve symptoms. 5-HT(3) receptor antagonists have been investigated mainly in the IBS and the few studies performed in functional dyspepsia have provided conflicting results. Also, kappa-opioid receptor agonists might be useful for functional digestive syndromes because of their antinociceptive effects, but available results in functional dyspepsia are scanty and inconclusive. Other receptors that represent potential clinical targets for antagonists include purinoceptors (i. e., P2X2/3 receptors), NMDA receptors (NR2B subtype), protease-activated receptor-2, the vanilloid receptor-1, tachykinin receptors (NK(1)/NK(2)) and cholecystokinin (CCK)(1) receptors.