Effects of asimadoline, a kappa-opioid agonist, on satiation and postprandial symptoms in health

Recent Advances in Peripheral Opioid Receptor Therapeutics

PURPOSE OF REVIEW

Although opioids are excellent analgesics, they are associated with severe short- and long-term side effects that are especially concerning for the treatment of chronic pain. Peripherally acting opioid receptor agonists promise to mitigate the more serious centrally mediated side effects of opioids, and the goal of this paper is to identify and elaborate on recent advances in these peripheral opioid receptor therapeutics.

RECENT FINDINGS

Peripheral opioid receptor agonists are effective analgesics that at the same time circumvent the problem of centrally mediated opioid side effects by (1) preferentially targeting peripheral opioid receptors that are often the source of the pain and (2) their markedly diminished permeability or activity across the blood-brain barrier. Recent novel bottom-up approaches have been notable for the design of therapeutics that are either active only at inflamed tissue, as in the case of fentanyl-derived pH-sensitive opioid ligands, or too bulky or hydrophilic to cross the blood-brain barrier, as in the case of morphine covalently bound to hyperbranched polyglycerols. Recent innovations in peripheral opioid receptor therapeutics of pH-sensitive opioid ligands and limiting opioid permeability across the blood-brain barrier have had promising results in animal models. While this is grounds for optimism that some of these therapeutics will be efficacious in human subjects at a future date, each drug must undergo individualized testing for specific chronic pain syndromes to establish not only the nuances of each drug's therapeutic effect but also a comprehensive safety profile.

Efficacy of opioid receptor modulators in patients with irritable bowel syndrome: A systematic review and meta-analysis

BACKGROUND

While irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal diseases in clinical practice, it has diverse pathogenesis. Because of its sudden and lingering intractable symptoms, it seriously affects patients work and life. Opioid receptors are G protein-coupled receptors distributed across the brain, spinal cord, skin, and gastrointestinal tract, and each of the subtypes has a unique role and specific distribution. They play a role in regulating gastrointestinal motility, secretion, and visceral sensations in the gastrointestinal tract. Therefore, this meta-analysis aims to evaluate the effects of opioid receptor modulators on improving the symptoms of IBS.

METHODS

Searching the key words (Irritable Bowel Syndromes or Syndrome, Irritable Bowel OR Syndromes, Irritable Bowel OR Colon, Irritable OR Irritable Colon OR Colitis, Mucous OR Colitides, Mucous OR Mucous Colitides OR Mucous Colitis) AND (opioid receptor modulators OR eluxadoline OR Viberzi OR asimadoline OR loperamide), a preliminary search on PubMed (English), EMBASE (English), Cochrane Library (English), China National Knowledge Infrastructure Database (CNKI, Chinese), WanFang (Chinese), VIP citation databases (Chinese) and SinoMed (Chinese) databases yielded 1023 papers published in English and Chinese from inception to July 1, 2019. Nine studies were included in the final meta-analysis. Because this is a systematic review and meta-analysis, ethical approval is not necessary.

RESULTS

The random-effects meta-analysis based on these 9 studies and their 4156 patients found that opioid receptor modulators have a statistically significant beneficial effect on IBS global symptoms (RR = 0.85, 95%CI = 0.79-0.92, P < .01) and bowel movement frequency (SMD = -1.26, 95%CI = -2.49--0.04, P < .05), and while there was an improvement trend in stool consistency and quality of life, these findings were not statistically significant.

CONCLUSIONS

This is the first meta-analysis to examine the use of opioid receptor modulators in IBS, and few adverse events were reported in the available trials. Compared with the control group, eluxadolin has a better effect in improving IBS global symptoms and abdominal pain and has statistical significance and showed a low rate of constipation development in IBS patients in comparison with known effects of other opioid receptor modulators. However, current findings are based on a considerably limited evidence base with marked heterogeneity. Future studies should aim to identify subpopulations of patients with IBS and need to evaluate the long-term safety of these therapies.PROSPERO registration number: CRD42020141597.

Use of Molecular Imaging in Clinical Drug Development: a Systematic Review

Background

Molecular imaging such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT) can provide the crucial pharmacokinetic-pharmacodynamic information of a drug non-invasively at an early stage of clinical drug development. Nevertheless, not much has been known how molecular imaging has been actually used in drug development studies.

Methods

We searched PubMed using such keywords as molecular imaging, PET, SPECT, drug development, and new drug, or any combination of those to select papers in English, published from January 1, 1990, to December 31, 2015. The information about the publication year, therapeutic area of a drug candidate, drug development phase, and imaging modality and utility of imaging were extracted.

Results

Of 10,264 papers initially screened, 208 papers met the eligibility criteria. The more recent the publication year, the bigger the number of papers, particularly since 2010. The two major therapeutic areas using molecular imaging to develop drugs were oncology (47.6%) and the central nervous system (CNS, 36.5%), in which efficacy (63.5%) and proof-of-concept through either receptor occupancy (RO) or other than RO (29.7%), respectively, were the primary utility of molecular imaging. PET was used 4.7 times more frequently than SPECT. Molecular imaging was most frequently used in phase I clinical trials (40.8%), whereas it was employed rarely in phase 0 or exploratory IND studies (1.4%).

Conclusions

The present study confirmed the trend that molecular imaging has been more actively employed in recent clinical drug development studies although its adoption was rather slow and rare in phase 0 studies.

Caloric intake capacity as measured by a standard nutrient drink test helps to predict weight loss after bariatric surgery

BACKGROUND

Instruments that enable to select individuals that will benefit most from bariatric surgery (BS) are necessary to increase its cost-efficiency. Our goal was to assess if intake capacity, measured with a standardized test, predicts response to BS.

METHODS

Patients with criteria for BS were randomly allocated to laparoscopic gastric bypass (LRYGB) or sleeve gastrectomy (LSG). We measured caloric intake capacity before and 1 year after surgery using a standardized nutrient drink test. We evaluated if pre-surgery satiation could predict satiation and weight loss (%) 1 year after surgery using multiple regression modeling. Descriptive statistics are given as mean ± SD.

RESULTS

Fourteen women (48 ± 9 years old, BMI 41 ± 3 kg/m(2)) were evaluated before and 11 ± 2.6 months after surgery (seven LRYGB, seven LSG). Caloric intake capacity diminished after surgery (-950 ± 85 kcal on average [70 ± 8 % decrease over basal intake capacity]; p=0.002) and similarly in both LRYGB (72 ± 7 % decrease) and LSG groups (68 ± 8 % decrease); p=0.5. There was a significant weight reduction after surgery (-32 ± 10 kg [30 ± 8 % of total basal weight]) with a mean post-surgery BMI of 29 ± 2 kg/m(2). The best predictive model of weight loss (%) after surgery (R (2)=89 %, p=0.0009) included: BMI (p=0.0004), surgery type (p=0.01) and pre-surgery intake capacity (p=0.006). Weight loss was higher in heavier patients and those undergoing LRYGB. Patients with higher intake capacity had a poorer outcome independently of basal BMI and surgery type.

CONCLUSIONS

Caloric intake capacity, as measured by a standard nutrient drink test, helps to predict weight loss after bariatric surgery. This test might be useful in algorithms of obesity treatment decision.

The safety of novel drugs used to treat irritable bowel syndrome

INTRODUCTION

Irritable bowel syndrome (IBS) is a chronic gastrointestinal (GI) disorder with a high prevalence. Besides efficacy, the safety of each drugs used to treat GI disorders is an important issue in the drug development process.

AREAS COVERED

This article reviews all Phase I to IV clinical trials or case reports with results related to the safety of novel GI drugs. The drugs are currently approved or under evaluation for approval.

EXPERT OPINION

Most of the reported adverse events were related to the GI tract with mild-to-moderate severity. Diarrhea was significantly higher versus placebo following use of linaclotide and renzapride, similar to that of constipation with ramosetron. Lubiprostone, linaclotide and rifaximin with low systemic bioavailability have less adverse events and exert more advantageous results. Asimadoline acts peripherally on κ-opioid receptors and is not associated with CNS side effects. As lubiprostone and linaclotide cause dose-dependent adverse events, starting the treatment with the lowest effective doses is advised. Ramosetron is under evaluation for diarrhea-predominant IBS due to its acceptable safety and tolerability, besides its efficacy. Rifaximin, asimadoline and renzapride are still in need of more long-term studies regarding their safety.

Chronic methadone use, poor bowel visualization and failed colonoscopy: A preliminary study

AIM: To examine effects of chronic methadone usage on bowel visualization, preparation, and repeat colonoscopy.

METHODS: In-patient colonoscopy reports from October, 2004 to May, 2009 for methadone dependent (MD) patients were retrospectively evaluated and compared to matched opioid naive controls (C). Strict criteria were applied to exclude patients with risk factors known to cause constipation or gastric dysmotility. Colonoscopy reports of all eligible patients were analyzed for degree of bowel visualization, assessment of bowel preparation (good, fair, or poor), and whether a repeat colonoscopy was required. Bowel visualization was scored on a 4 point scale based on multiple prior studies: excellent = 1, good = 2, fair = 3, or poor = 4. Analysis of variance (ANOVA) and Pearson χ² test were used for data analyses. Subgroup analysis included correlation between methadone dose and colonoscopy outcomes. All variables significantly differing between MD and C groups were included in both univariate and multivariate logistic regression analyses. P values were two sided, and < 0.05 were considered statistically significant.

RESULTS: After applying exclusionary criteria, a total of 178 MD patients and 115 C patients underwent a colonoscopy during the designated study period. A total of 67 colonoscopy reports for MD patients and 72 for C were included for data analysis. Age and gender matched controls were randomly selected from this population to serve as controls in a numerically comparable group. The average age for MD patients was 52.2 ± 9.2 years (range: 32-72 years) years compared to 54.6 ± 15.5 years (range: 20-81 years) for C (P = 0.27). Sixty nine percent of patients in MD and 65% in C group were males (P = 0.67). When evaluating colonoscopy reports for bowel visualization, MD patients had significantly greater percentage of solid stool (i.e., poor visualization) compared to C (40.3% vs 6.9%, P < 0.001). Poor bowel preparation (35.8% vs 9.7%, P < 0.001) and need for repeat colonoscopy (32.8% vs 12.5%, P = 0.004) were significantly higher in MD group compared to C, respectively. Under univariate analysis, factors significantly associated with MD group were presence of fecal particulate [odds ratio (OR), 3.89, 95% CI: 1.33-11.36, P = 0.01] and solid stool (OR, 13.5, 95% CI: 4.21-43.31, P < 0.001). Fair (OR, 3.82, 95% CI: 1.63-8.96, P = 0.002) and poor (OR, 8.10, 95% CI: 3.05-21.56, P < 0.001) assessment of bowel preparation were more likely to be associated with MD patients. Requirement for repeat colonoscopy was also significant higher in MD group (OR, 3.42, 95% CI: 1.44-8.13, P = 0.01). In the multivariate analyses, the only variable independently associated with MD group was presence of solid stool (OR, 7.77, 95% CI: 1.66-36.47, P = 0.01). Subgroup analysis demonstrated a general trend towards poorer bowel visualization with higher methadone dosage. ANOVA analysis demonstrated that mean methadone dose associated with presence of solid stool (poor visualization) was significantly higher compared to mean dosage for clean colon (excellent visualization, P = 0.02) or for those with liquid stool only (good visualization, P = 0.01).

CONCLUSION: Methadone dependence is a risk factor for poor bowel visualization and leads to more repeat colonoscopies. More aggressive bowel preparation may be needed in MD patients.

Drug management of visceral pain: concepts from basic research

Visceral pain is experienced by 40% of the population, and 28% of cancer patients suffer from pain arising from intra- abdominal metastasis or from treatment. Neuroanatomy of visceral nociception and neurotransmitters, receptors, and ion channels that modulate visceral pain are qualitatively or quantitatively different from those that modulate somatic and neuropathic pain. Visceral pain should be recognized as distinct pain phenotype. TRPV1, Na 1.8, and ASIC3 ion channels and peripheral kappa opioid receptors are important mediators of visceral pain. Mu agonists, gabapentinoids, and GABAB agonists reduce pain by binding to central receptors and channels. Combinations of analgesics and adjuvants in animal models have supra-additive antinociception and should be considered in clinical trials. This paper will discuss the neuroanatomy, receptors, ion channels, and neurotransmitters important to visceral pain and provide a basic science rationale for analgesic trials and management.

Current and emerging therapies in irritable bowel syndrome: from pathophysiology to treatment

Irritable bowel syndrome is a common functional gastrointestinal disorder with characteristic symptoms of abdominal pain/discomfort with a concurrent disturbance in defecation. It accounts for a significant healthcare burden, and symptoms may be debilitating for some patients. Traditional symptom-based therapies have been found to be ineffective in the treatment of the entire syndrome complex, and do not modify the natural history of the disorder. Although the exact etiopathogenesis of IBS is incompletely understood, recent advances in the elucidation of the pathophysiology and molecular mechanisms of IBS have resulted in the development of novel therapies, as well as potential future therapeutic targets. This article reviews current and emerging therapies in IBS based upon: IBS as a serotonergic disorder; stimulating intestinal chloride channels; modulation of visceral hypersensitivity; altering low-grade intestinal inflammation; and modulation of the gut microbiota.

Current and novel therapeutic options for irritable bowel syndrome management

Irritable bowel syndrome is a 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 irritable bowel syndrome is multifactorial involving disturbances of the brain-gut axis. The pathophysiology provides the rationale for pharmacotherapy: abnormal gastrointestinal motor functions, visceral hypersensitivity, psychosocial factors, autonomic dysfunction, and mucosal immune activation. Understanding the mechanisms, and their mediators or modulators including neurotransmitters and receptors have led to several therapeutic approaches including agents acting on the serotonin receptor or serotonin transporter system, antidepressants, novel selective anticholinergics, alpha-adrenergic agonists, opioid agents, cholecystokinin-antagonists, neurokinin-antagonists, somatostatin receptor agonists, corticotropin releasing factor antagonists, chloride channel activators, guanylate cyclase-c agonists, melatonin, atypical benzodiazepines, antibiotics, immune modulators and probiotics. The mechanisms and current evidence regarding efficacy of these agents are reviewed.

Effect of a kappa-opioid agonist, i.v. JNJ-38488502, on sensation of colonic distensions in healthy male volunteers

Kappa-opioid receptors are located on visceral pain fibres. JNJ-38488502 is a highly selective tetrapeptide kappa-opioid agonist with little access to the central nervous system and low risk of central nervous system side effects. The aim of the study was to evaluate the effects of i.v. JNJ-38488502 on sensations, including pain, during colonic distension. In a single-centre study, 23 healthy adult males underwent a single-dose, randomized, double-blind crossover study of JNJ-38488502 (0.42 mg kg(-1) i.v. infusion) vs placebo on left colon compliance, sensory thresholds and ratings during standard distensions. One participant could not undergo sensation studies. In the other 22, JNJ-38488502 increased colonic compliance (pressure at half-maximum volume 17.9 +/- 0.8 mmHg) compared to placebo (21.6 +/- 0.9 mmHg, P = 0.007). There was no significant effect on sensory thresholds which, however, were not reached by 44 mmHg in >50% of participants in both treatment phases. There were no significant treatment effects on sensory ratings to distensions at 8, 16, 24, 32 and 36 mmHg above baseline operating pressure. JNJ-38488502 was associated with increased urine output and plasma prolactin, consistent with kappa-opioid receptor activation. This study concluded that i.v. JNJ-38488502 induced kappa-opioid effects, but did not attenuate colonic sensations following random order colonic distension. Further studies of effects on pain sensations in health and disease are required.

Challenges to the therapeutic pipeline for irritable bowel syndrome: end points and regulatory hurdles

Recent advances in our understanding of basic neuroenteric mechanisms and the role of effectors and transmitters in the brain-gut axis have provided opportunities to develop new therapeutic agents for irritable bowel syndrome (IBS). Furthermore, human pharmacodynamic studies utilizing transit, colonic, or rectal sensitivity and brain imaging have been useful in determining therapeutic efficacy (particularly for drugs that act on motor function). This review provides an overview of medications that have not yet been approved for treatment of patients with IBS yet have shown promise in phase IIB trials. These include drugs that act on the serotonin receptor and transporter system: antidepressants, norepinephrine reuptake inhibitors, opioids, cholecystokinin antagonists, neurokinin-antagonists, chloride channel activators, guanylate cyclase C agonists, atypical benzodiazepines, probiotics, and antibiotics. The changing landscape in the regulatory approval process has impacted the development of IBS drugs. Guidance documents from regulatory agencies in Europe and the United States have focused on patients' reported outcomes and associated quality of life. After a decade of experience with different end points that have generated some data on psychometric validation and unprecedented information about responsiveness of the binary or global end points to drug therapy, it is necessary to pursue further validation studies before or during pivotal phase IIB or III trials. The hope of providing relief to patients should galvanize all parties to achieve these goals.

Role of endogenous opioids in the control of gastric sensorimotor function

Endogenous opioids have been implicated not only in the process of feeding but also in the control of gastric sensitivity and gastric motor responses, and impairment of antinociceptive opioid pathways has been hypothesized to contribute to the pathogenesis of functional dyspepsia. Our aim was to study the effect of suppression of endogenous opioid action by naloxone on gastric sensorimotor function in healthy volunteers. During intravenous administration of saline or naloxone (0.4 mg intravenous bolus followed by continuous infusion 20 microg kg(-1) h(-1)), sensitivity to gastric distension, gastric accommodation and fundic phasic contractility were evaluated by barostat in 15 subjects. Nutrient tolerance and meal-related symptoms were assessed using a satiety drinking test (n = 13), and solid and liquid gastric emptying were evaluated by breath test (n = 14). Naloxone did not influence gastric compliance and sensitivity. No effect on preprandial gastric tone was found but meal-induced accommodation was significantly inhibited by naloxone (P = 0.031). Subjects receiving naloxone demonstrated a higher motility index before (20.8 +/- 2.4 vs 28.0 +/- 1.9 mL s(-1), P = 0.007) and after (15.2 +/- 2.0 vs 22.7 +/- 1.5 mL s(-1), P = 0.0006) the meal. Naloxone significantly decreased the amount of food ingested at maximum satiety (715.4 +/- 77.7 vs 617.3 +/- 61.3 mL, P = 0.03). No effect of naloxone on gastric emptying was observed and intensity of postprandial symptoms was unchanged. These observations suggest that endogenous opioids are involved in the control of gastric accommodation and phasic contractility but not in the control of sensitivity to gastric distension or gastric emptying in healthy volunteers.

Novel pharmacology: asimadoline, a kappa-opioid agonist, and visceral sensation

Asimadoline is a potent kappa-opioid receptor agonist with a diaryl acetamide structure. It has high affinity for the kappa receptor, with IC(50) of 5.6 nmol L(-1) (guinea pig) and 1.2 nmol L(-1) (human recombinant), and high selectively with kappa : micro : delta binding ratios of 1 : 501 : 498 in human recombinant receptors. It acts as a complete agonist in in vitro assay. Asimadoline reduced sensation in response to colonic distension at subnoxious pressures in healthy volunteers and in irritable bowel syndrome (IBS) patients without alteration of colonic compliance. Asimadoline reduced satiation and enhanced the postprandial gastric volume (in female volunteers). However, there were no significant effects on gastrointestinal transit, colonic compliance, fasting or postprandial colonic tone. In a clinical trial in 40 patients with functional dyspepsia (Rome II), asimadoline did not significantly alter satiation or symptoms over 8 weeks. However, asimadoline, 0.5 mg, significantly decreased satiation in patients with higher postprandial fullness scores, and daily postprandial fullness severity (over 8 weeks); the asimadoline 1.0 mg group was borderline significant. In a clinical trial in patients with IBS, average pain 2 h post-on-demand treatment with asimadoline was not significantly reduced. Post hoc analyses suggest that asimadoline was effective in mixed IBS. In a 12-week study in 596 patients, chronic treatment with 0.5 mg and 1.0 mg asimadoline was associated with adequate relief of pain and discomfort, improvement in pain score and number of pain-free days in patients with IBS-D. The 1.0 mg dose was also efficacious in IBS-alternating. There were also weeks with significant reduction in bowel frequency and urgency. Asimadoline has been well tolerated in human trials to date.

Asimadoline, a kappa-opioid agonist, and satiation in functional dyspepsia

BACKGROUND

Asimadoline, a kappa-opioid agonist, reduces visceral sensitivity in experimental animal models and may decrease satiation and postprandial fullness in healthy individuals. However, its effect on satiation in functional dyspepsia is unclear, and any symptom benefit has not been explored.

AIM

To evaluate the effects of asimadoline on satiation volume and postchallenge symptoms in functional dyspepsia.

METHODS

A randomized, double-blind trial evaluated gastric satiation and symptoms before and after 8 weeks of asimadoline 0.5 mg (n = 13) or 1.0 mg (n = 13) or placebo (n = 14) b.d. in patients with functional dyspepsia (Rome II). Gastrointestinal Symptom Rating Scale and Nepean Dyspepsia Index were used to assess symptoms during the 8-week treatment.

RESULTS

Over 8 weeks of treatment, asimadoline had no significant effect on maximum-tolerated volume or aggregate symptom score with nutrient drink challenge, and on the mean of the total daily symptom severity score compared to placebo. In a post hoc analysis, asimadoline 0.5 mg significantly increased the maximum-tolerated volume (1217 mL +/- 90.2) compared to placebo (807 mL +/- 111.8) in patients with higher postprandial fullness scores (P = 0.01).

CONCLUSION

Asimadoline overall did not significantly alter maximum-tolerated volume, symptoms postnutrient challenge or symptoms over 8 weeks in functional dyspepsia.

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.

Impaired drinking capacity in patients with functional dyspepsia: intragastric distribution and distal stomach volume

The water drink test is a good tool to evoke dyspeptic symptoms. To what extent these symptoms are related to altered gastric distribution is not clear. Therefore, we determined gastric volumes after a drink test using SPECT. After a baseline scan 20 healthy volunteers (HV) and 18 patients with functional dyspepsia (FD) underwent a drink test (100 mL min(-1)) followed by five scans up to 2 h. Dyspeptic symptoms were scored before every scan. A Wilcoxon signed rank test (P < 0.05) and a mixed effects model were used for statistical analyses. Fasting volumes were significantly higher in FD compared to HV for total, proximal and distal stomach (P < 0.001). Functional dyspeptic patients ingested significantly less water (P < 0.001) and had an impaired filling of the distal part of the stomach (P = 0.001) after the drink test. In FD, bloating (prox. 80%, dist. 56%), pain (prox. 87%, dist. 62%) and fullness (prox. 80%, dist. 59%) were determined more by proximal stomach volume rather than distal stomach volume. These data suggest that drinking capacity is mainly determined by antral volume, with a reduced antral filling in FD compared to HV. The persisting symptoms of bloating, pain and fullness in FD are predominantly associated with proximal stomach volume.

Efficacy of on-demand asimadoline, a peripheral kappa-opioid agonist, in females with irritable bowel syndrome

BACKGROUND & AIMS

In experimental animal models of irritable bowel syndrome (IBS) and human studies, peripheral kappa opioid agonists have been shown to decrease sensation to colonic distention. The aim of this study was to compare the effects of the kappa opioid agonist, asimadoline, and placebo on episodes of abdominal pain in patients with IBS.

METHODS

After a 2-week run-in period, 100 patients with IBS were randomized (3:2 ratio) to receive asimadoline, up to 1 mg 4 times daily, or placebo for 4 weeks in a double-blind study. Pain was scored by daily diary using a 100-mm visual analogue scale. During pain episodes, patients recorded the pain severity, took study medication, and recorded their pain score 2 hours later. The primary end point was the average reduction in pain severity 2 hours after treatment.

RESULTS

The average pain reduction 2 hours posttreatment was not significantly different between the groups. Post hoc analyses suggest asimadoline was effective in mixed IBS (P = .003, unadjusted), but may be worse in diarrhea-predominant IBS (P = .065 unadjusted). The anxiety score was reduced modestly by asimadoline (P = .053). No significant adverse effects were noted.

CONCLUSIONS

An on-demand dosing schedule of asimadoline was not effective in reducing severity of abdominal pain in IBS. Further studies in visceral pain and IBS appear warranted.

Functional Dyspepsia: A New Rome III Paradigm

Functional dyspepsia (FD) is a condition commonly seen in gastroenterological practice. With the introduction of Rome III criteria in 2006, a new approach for categorizing patients has been recommended. The diagnostic criteria suggest that meal-related and pain-predominant symptom groupings that presumably have distinct pathophysiologic mechanisms and potentially different therapeutic targets exist. The new classification is in the early stages of testing; in the meantime, the umbrella term of FD should continue to be utilized in clinical practice. Treatment of FD remains a major challenge. Unfortunately, most of the agents used in practice have limited or no evidence of efficacy, and the results typically are short-lived once therapy is ceased. Appropriate therapy currently is based on a consideration of putative pathophysiologic mechanisms. Testing for and eradicating Helicobacter pylori is a first-line strategy irrespective of the symptom pattern. In patients who have epigastric pain, antisecretory agents are recommended. Antacids, bismuth, and sucralfate seem to be no better than placebo. For meal-related symptoms such as postprandial fullness or early satiety, prokinetics may confer some benefit. However, few choices are available, and the efficacy for those drugs on the market is limited at best. Antidepressants are of uncertain efficacy but are widely used. Psychological therapies seem promising and may confer benefits on both pain and meal-related symptoms. Efficacy of complementary medicines has been suggested in controlled trials, but more data are needed. Emerging treatments include gastric fundus relaxors and visceral analgesics, although their application in FD is still in the preliminary stages.

Recent insights into digestive motility in functional dyspepsia

Functional gastrointestinal disorders, such as functional dyspepsia (FD) and irritable bowel syndrome, are common pathologies of the gut. FD is a clinical syndrome defined as chronic or recurrent pain or discomfort of unknown origin in the upper abdomen. The pathophysiological mechanisms responsible for FD have not been fully elucidated, but new ideas regarding its pathophysiology and the significance of the pathophysiology with respect to the symptom pattern of FD have emerged. In particular, there is growing interest in alterations in gastric motility, such as accommodation to a meal or gastric emptying, and visceral sensation in FD. The mechanisms underlying impaired gastroduodenal motor function are unclear, but possible factors include abnormal neurohormonal function, autonomic dysfunction, visceral hypersensitivity to acid or mechanical distention, Helicobacter pylori infection, acute gastrointestinal infection, psychosocial comorbidity, and stress. Although the optimum treatment for FD is not yet clearly established, acid-suppressive drugs, prokinetic agents, eradication of H. pylori, and antidepressants have been widely used in the management of patients with FD. The therapeutic efficacy of prokinetics such as itopride hydrochloride and mosapride citrate in the treatment of FD is supported by the results of relatively large and well-controlled studies. In addition, recent research has yielded new therapeutic agents and modalities for dysmotility in FD, including agonists/antagonists of various sensorimotor receptors, activation of the nitrergic pathway, kampo medicine, acupuncture, and gastric electric stimulation. This review discusses recent research on the pathophysiology of and treatment options for FD, with special attention given to digestive dysmotility.

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.

Review article: current and emerging therapies for functional dyspepsia

Functional dyspepsia represents a heterogeneous group of gastrointestinal disorders marked by the presence of upper abdominal pain or discomfort. Although its precise definition has evolved over the last several decades, this disorder remains shrouded in controversy. The symptoms of functional dyspepsia may overlap with those of other functional bowel disorders including irritable bowel syndrome and non-erosive reflux disease. There may be coexistent psychological distress or disease complicating its presentation and response to therapy. Given the prevalence and chronicity of functional dyspepsia, it remains a great burden to society. Suspected physiological mechanisms underlying functional dyspepsia include altered motility, altered visceral sensation, inflammation, nervous system dysregulation and psychological distress. Yet the exact pathophysiological mechanisms that cause symptoms in an individual patient remain difficult to delineate. Numerous treatment modalities have been employed including dietary modifications, pharmacological agents directed at various targets within the gastrointestinal tract and central nervous system, psychological therapies and more recently, complementary and alternative treatments. Unfortunately, to date, all of these therapies have yielded only marginal results. A variety of emerging therapies are being developed for functional dyspepsia. Most of these therapies are intended to normalize pain perception and gastrointestinal motor and reflex function in this group of patients.

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.

Early satiety in cancer patients: a common and important but underrecognized symptom

INTRODUCTION

The severity of anorexia correlates with the presence of early satiety. The sense of fullness limits nutritional intake. The symptom is poorly understood because most assessment questionnaires do not include early satiety.

METHODS

Patients rarely volunteer early satiety. Central and peripheral mechanisms may be involved in the genesis of early satiety. These would include central sensory specific satiety, food aversions, diurnal changes in intake, gastric motility and accommodation and as gastrointestinal hormones.

CONCLUSIONS

Prokinetic medications, such as metoclopramide are used to treat early satiety. However, other medications which influence gastric accommodation such as clonidine, sumatriptan, or sildenafil, or diminish enteric afferent output such as kappa opioid receptor agonists, may favorably influence early satiety and should be subject to future research. Translational research is needed to understand the relationship of early satiety to gastric motility and accommodation.

Treatment of functional dyspepsia

Functional dyspepsia (FD) is a common reason a patient presents with upper gastrointestinal symptoms for medical care. Although treatment of FD remains expensive, the agents are rarely used in a systematic manner; the majority of treatments are empirical and the results short lived once therapy is ceased. This is partly due to the lack of consistent pathophysiologic markers in FD, so therapy is symptom driven. This review appraises the best evidence on available interventions. A structured scheme for deciding on appropriate therapies is to consider the possible putative pathophysiologic mechanisms. Eradicating Helicobacter pylori, if present, is a first-line strategy. In patients who have symptoms suggesting excessive gastric acid secretion, particularly epigastric pain, antisecretory agents are recommended. Prokinetics may confer benefits on symptoms suggestive of upper gastrointestinal dysmotility, like fullness or early satiety. However, their use is limited due to availability issues. The expanding field of psychologic therapies provides a promising avenue of treatment. Complementary medicines are now widely use and their benefits have been suggested in recent controlled trials. Emerging treatments include cholecystokinin 1 blockers, opioid receptor agonists, and serotonergic agents, although their application in FD is in the preliminary stages.

Peripheral opioids for functional GI disease: a reappraisal

Opioids have been used medicinally and recreationally for thousands of years. The clinical use of opioids for gastrointestinal conditions has been limited by central nervous system side effects. A new generation of peripheral opioid receptor ligands free of central nervous system side effects is being developed. Clinical trials with the peripherally acting mu opioid receptor antagonists' alvimopan and N-methylnaltrexone show promise for improving postoperative ileus- and opioid-induced constipation. Likewise, preliminary studies with the peripherally acting kappa opioid agonist fedotozine showed promise in the treatment of irritable bowel syndrome (IBS) and functional dyspepsia. Further studies are on hold presumably due to lack of efficacy in subsequent studies. However, clinical studies are underway for newer kappa opioid agonists such as asimadoline and ADL 10-0101.

Contribution of ascites to impaired gastric function and nutritional intake in patients with cirrhosis and ascites

BACKGROUND & AIMS

Protein calorie malnutrition and weight loss are common among patients with cirrhosis and ascites. The cause of these symptoms is unclear, with several putative mechanisms proposed. The primary aims of this study were to compare gastric volumes and accommodation between patients with cirrhosis complicated by ascites and healthy controls, and to evaluate the effect of large-volume paracentesis in the patient group.

METHODS

Patients with cirrhosis and ascites underwent assessment of gastric volumes as measured by single-photon emission computed tomography, gastric sensation assessed by a validated nutrient drink test, and a 3-day assessment of caloric intake before and after large-volume paracentesis. Age- and sex-adjusted linear regression models were used to compare gastric volumes and accommodation ratios between patients and healthy volunteers. Paired Wilcoxon rank-sum tests were used to compare gastric measures before and after paracentesis among the patient group.

RESULTS

Fifteen patients (median age, 54 y) were compared with 112 healthy (age- and sex-matched) controls. Median postprandial gastric volumes (627 mL patients vs 721 healthy controls) and gastric accommodation were reduced significantly in patients compared with healthy controls (P = .02 and .006, respectively). After paracentesis: (1) fasting gastric volumes were increased (median 312 mL post- vs 241 mL pre-, P = .04), (2) patients tolerated ingestion of larger maximum volumes (median 964 mL post- vs 738 mL pre-, P = .04), and (3) caloric intake was increased (median 34% kcal post- vs 3110 kcal pre-, P = .005).

CONCLUSIONS

Postprandial gastric volumes and accommodation ratios are reduced in patients with cirrhosis and ascites compared with healthy controls. In addition, large-volume paracentesis increases fasting gastric volumes, volumes ingested until maximal satiation, and caloric intake.

Functional dyspepsia pathogenesis and therapeutic options--implications for management

Functional dyspepsia is far more common than dyspepsia due to organic disease, both in the community and general practice. Proposed aetiopathogenic factors include gastric acid, Helicobacter pylori infection, delayed emptying, hypersensitivity or impaired accommodation of the stomach, dysfunction of the duodenum or brain-gut axis, psychosocial morbidity and post-infective mucosal damage. More effective therapy will depend on the development of drugs targeted at these putative pathophysiological mechanisms. On current evidence tricyclic antidepressants appear to be more effective than either acid suppressants or H. pylori eradication.

Does the nutrient drink test accurately predict postprandial gastric volume in health and community dyspepsia?

Nutrient drink tests have been proposed as a surrogate for measurement of gastric accommodation. To study the relationship of maximum tolerated volume (MTV) during nutrient drink test and gastric volumes measured by single-photon emission computed tomography (SPECT) in healthy controls and functional dyspepsia (FD) patients. We reviewed data from 85 healthy controls and 35 FD residents of south-eastern Minnesota. All underwent standardized nutrient drink and SPECT studies between August 2000 and June 2003. To test for associations between nutrient drink test and SPECT gastric volumes, we used multiple linear regression and partial regression analyses, assigning age, gender, dyspepsia status and postprandial symptoms as covariates in the model. In the combined group (healthy and FD), MTV was weakly associated with fasting gastric volume (r = 0.43, P = 0.0001) and with volume response to feeding (r = 0.25, P = 0.006). In the FD group, associations were similar (fasting r = 0.53, P = 0.001; postmeal r = 0.32, P = 0.06). After accounting for covariates, MTV only explained 13 and 3% of variations in fasting and postprandial volumes measured by SPECT. MTV during the nutrient drink test does not accurately reflect gastric volume measurements by SPECT in healthy controls and a sample of people in the community with FD.

Contributions of gastric volumes and gastric emptying to meal size and postmeal symptoms in functional dyspepsia

BACKGROUND & AIMS

The aim was to assess relative contributions of gastric volumes (GV) and gastric emptying (GE) to meal size and postprandial symptoms in patients with functional dyspepsia.

METHODS

Patients with chronic upper gastrointestinal symptoms were prospectively evaluated. GV during fasting and after 300 mL Ensure was measured with 99m Tc-single-photon emission computed tomography imaging and solid GE (99m Tc-egg) by scintigraphy. Maximum tolerated volume (MTV) and symptoms were measured after Ensure challenge.

RESULTS

Of 57 adult patients evaluated, 39 (23 women, 16 men) met Rome II criteria for functional dyspepsia and had no other diagnosis to account for dyspepsia. The most frequent symptoms were abdominal pain (90%), pain predominantly after meals (76%), nausea (85%), and early fullness after meals (79%). Relative to established laboratory normal values, MTV was abnormal in 82%, aggregate symptom score >209 in 72%, GE (at 1 hour) accelerated in 41%, GE (at 4 hours) delayed in 41%, and postmeal GV reduced in 52%. Lower body mass was associated with lower MTV and higher postchallenge symptoms. Lower fasting (not postprandial) GV and faster GE were independent predictors of lower MTV, explaining 18% of the variance after adjusting for body weight (32% of variance). GE was an independent predictor of postchallenge symptoms (10% of variance) after adjusting for volume ingested (10%), age (20%), and weight (10%).

CONCLUSIONS

In adults with functional dyspepsia seen in a tertiary referral practice, decreased meal size and postmeal symptoms are associated with low fasting GV and faster GE. These data provide physiologic targets for ameliorating symptoms of functional dyspepsia.

Opioids and the gut: pharmacology and current clinical experience

This article reviews the pharmacology and physiology of opiate receptors and the current and potential uses of opioid agonists and antagonists in clinical gastroenterology. Mu-receptors are involved in motor and sensory functions, and their modulation is established for treatment of diarrhea. Mu-antagonists have potential to reverse endogenous (e.g., postoperative ileus) or iatrogenic dysmotility (e.g., opioid bowel dysfunction). Modulation of the function of kappa-receptors may be a novel approach to control visceral pain in functional gut disorders. Results of formal testing of novel opioid modulators are keenly awaited.

Treatment of Functional Dyspepsia

Functional dyspepsia is a common chronic condition. It can have a major impact on quality of life and remains a large burden on healthcare resources. Its underlying mechanisms are not fully understood and therapies are mainly empirical. In this review, we summarize the best evidence on available therapeutic interventions in functional dyspepsia. Helicobacter pylori eradication, for those infected, is likely a safe and cost-effective strategy but benefits only a minority. Antisecretory agents such as proton-pump inhibitors and histamine-2 receptor antagonists have shown some benefit and are recommended as the first-line option in the absence of H. pylori infection. There is a lack of strong evidence of benefit from prokinetic agents, and cisapride, the most studied agent, is largely unavailable. Antidepressants need to be adequately tested in functional dyspepsia, but both psychotherapy and hypnotherapy interventions have shown promising results. Herbal therapies need further study in these patients. 5-Hydroxytryptamine3 (5-HT(3)) and 5-HT(4) receptor antagonists, and cholecystokinin type A and neurokinin receptor antagonists remain promising emerging therapies.

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.