Do corticotropin releasing factor-1 receptors influence colonic transit and bowel function in women with irritable bowel syndrome?

The newly developed CRF1-receptor antagonists, NGD 98-2 and NGD 9002, suppress acute stress-induced stimulation of colonic motor function and visceral hypersensitivity in rats

Corticotropin releasing factor receptor 1 (CRF₁) is the key receptor that mediates stress-related body responses. However to date there are no CRF₁ antagonists that have shown clinical efficacy in stress-related diseases. We investigated the inhibitory effects of a new generation, topology 2 selective CRF₁ antagonists, NGD 98-2 and NGD 9002 on exogenous and endogenous CRF-induced stimulation of colonic function and visceral hypersensitivity to colorectal distension (CRD) in conscious rats. CRF₁ antagonists or vehicle were administered orogastrically (og) or subcutaneously (sc) before either intracerebroventricular (icv) or intraperitoneal (ip) injection of CRF (10 µg/kg), exposure to water avoidance stress (WAS, 60 min) or repeated CRD (60 mmHg twice, 10 min on/off at a 30 min interval). Fecal pellet output (FPO), diarrhea and visceromotor responses were monitored. In vehicle (og)-pretreated rats, icv CRF stimulated FPO and induced diarrhea in >50% of rats. NGD 98-2 or NGD 9002 (3, 10 and 30 mg/kg, og) reduced the CRF-induced FPO response with an inhibitory IC₅₀ of 15.7 and 4.3 mg/kg respectively. At the highest dose, og NGD 98-2 or NGD 9002 blocked icv CRF-induced FPO by 67–87% and decreased WAS-induced-FPO by 23–53%. When administered sc, NGD 98-2 or NGD 9002 (30 mg/kg) inhibited icv and ip CRF-induced-FPO. The antagonists also prevented the development of nociceptive hyper-responsivity to repeated CRD. These data demonstrate that topology 2 CRF₁ antagonists, NGD 98-2 and NGD 9002, administered orally, prevented icv CRF-induced colonic secretomotor stimulation, reduced acute WAS-induced defecation and blocked the induction of visceral sensitization to repeated CRD.

Behavioral, biological, and chemical perspectives on targeting CRF(1) receptor antagonists to treat alcoholism

BACKGROUND

Alcohol use disorders are chronic disabling conditions for which existing pharmacotherapies have only modest efficacy. In the present review, derived from the 2012 Behavior, Biology and Chemistry "Translational Research in Addiction" symposium, we summarize the anti-relapse potential of corticotropin-releasing factor type 1 (CRF(1)) receptor antagonists to reduce negative emotional symptoms of acute and protracted alcohol withdrawal and stress-induced relapse to alcohol seeking.

METHODS

We review the biology of CRF(1) systems, the activity of CRF(1) receptor antagonists in animal models of anxiolytic and antidepressant activity, and experimental findings in alcohol addiction models. We also update the clinical trial status of CRF(1) receptor antagonists, including pexacerfont (BMS-562086), emicerfont (GW876008), verucerfont (GSK561679), CP316311, SSR125543A, R121919/NBI30775, R317573/19567470/CRA5626, and ONO-2333Ms. Finally, we discuss the potential heterogeneity and pharmacogenomics of CRF(1) receptor pharmacotherapy for alcohol dependence.

RESULTS

The evidence suggests that brain penetrant-CRF(1) receptor antagonists have therapeutic potential for alcohol dependence. Lead compounds with clinically desirable pharmacokinetic properties now exist, and longer receptor residence rates (i.e., slow dissociation) may predict greater CRF(1) receptor antagonist efficacy. Functional variants in genes that encode CRF system molecules, including polymorphisms in Crhr1 (rs110402, rs1876831, rs242938) and Crhbp genes (rs10055255, rs3811939) may promote alcohol seeking and consumption by altering basal or stress-induced CRF system activation.

CONCLUSIONS

Ongoing clinical trials with pexacerfont and verucerfont in moderately to highly severe dependent anxious alcoholics may yield insight as to the role of CRF(1) receptor antagonists in a personalized medicine approach to treat drug or alcohol dependence.

Corticosterone mediates stress-related increased intestinal permeability in a region-specific manner

BACKGROUND

Chronic psychological stress (CPS) is associated with increased intestinal epithelial permeability and visceral hyperalgesia. It is unknown whether corticosterone (CORT) plays a role in mediating alterations of epithelial permeability in response to CPS.

METHODS

Male rats were subjected to 1-h water avoidance (WA) stress or subcutaneous CORT injection daily for 10 consecutive days in the presence or absence of corticoid receptor antagonist RU-486. The visceromotor response (VMR) to colorectal distension (CRD) was measured. The in situ single-pass intestinal perfusion was used to measure intestinal permeability in jejunum and colon simultaneously.

KEY RESULTS

We observed significant decreases in the levels of glucocorticoid receptor (GR) and tight junction proteins in the colon, but not the jejunum in stressed rats. These changes were largely reproduced by serial CORT injections in control rats and were significantly reversed by RU-486. Stressed and CORT-injected rats demonstrated a threefold increase in permeability for PEG-400 (MW) in colon, but not jejunum and significant increase in VMR to CRD, which was significantly reversed by RU-486. In addition, no differences in permeability to PEG-4000 and PEG-35 000 were detected between control and WA groups.

CONCLUSIONS & INFERENCES

Our findings indicate that CPS was associated with region-specific decrease in epithelial tight junction protein levels in the colon, increased colon epithelial permeability to low molecular weight macromolecules which were largely reproduced by CORT treatment in control rats and prevented by RU-486. These observations implicate a novel, region-specific role for CORT as a mediator of CPS-induced increased permeability to macromolecules across the colon epithelium.

Pharmacodynamic and clinical endpoints for functional colonic disorders: statistical considerations

BACKGROUND

Intra- and inter-subject coefficients of variation (COV) of scintigraphic colonic transit (SCT) are well characterized. SCT response to therapy predicts clinical efficacy of experimental medications in lower functional gastrointestinal disorders (FGID).

AIM

To compare COVs for bowel function with pharmacodynamic (PD) colonic transit geometric center (GC) as endpoints in lower FGID studies.

METHODS

We evaluated data from placebo arm of 9 phase IIA, parallel-group, clinical trials of PD effects of linaclotide, dexloxiglumide, renzapride, elobixibat, ROSE 010, and chenodeoxycholate in lower FGID with constipation, and pexacerafont, VSL#3, and colesevelam in lower FGID with diarrhea. Patients completed daily diaries for at least 7 days of stool frequency, consistency (7-point Bristol Stool Form Scale), and ease of passage (7-point scale from manual disimpaction to incontinence). Seventeen patients received placebo in 2 separate studies allowing assessment of intra-patient COVs. We calculated sample sizes required to demonstrate a 30 % effect size for colonic transit, stool frequency, consistency and ease of passage for patients with lower FGID with constipation and, separately, diarrhea.

RESULTS

COV(inter) from 87 patients and COV(intra) from 17 patients are reported. Generally, COV(intra) is somewhat greater than COV(inter). The COVs for PD endpoints are lower than for clinical endpoints; however, clinically relevant effects can be identified with modest (~50 %) increases in the sample size using parallel-group design studies.

CONCLUSION

Phase IIA studies that incorporate clinical and PD endpoints are feasible in lower FGID associated with constipation or diarrhea. Crossover design would require lower sample size for most endpoints compared to parallel-group studies.

Metabolic and toxicological considerations for the latest drugs used to treat irritable bowel syndrome

INTRODUCTION

The high prevalence of irritable bowel syndrome (IBS), a chronic gastrointestinal (GI) disorder, its lack of satisfactory effective drugs and its complicated pathophysiology lead to the demand of new therapeutic agents. During a new drug development process, the pharmacokinetic profiling is of a great considerable importance comparable to drug's efficacy. This involves the drug's absorption, distribution, metabolism and excretion, all of which are crucial to its usefulness. In addition, the toxicological profile and possible adverse reactions of the drug should be identified. Also its interactions should be identified at different phases of trials. Several pharmacokinetic studies are carried out to achieve drugs with the best absorption and bioavailability and the least adverse effects and lowest toxicity.

AREAS COVERED

To make an update on new clinically introduced drugs for IBS and their dynamics and kinetics data, the present systematic review was accomplished. All relevant bibliographic databases were searched from the year 2003 up to May 2012 to identify all clinical trials that evaluated the potential efficacy of a novel agent in IBS.

EXPERT OPINION

Some evaluated drugs, such as ramosetron (5-HT3 antagonist) and pexacerfont (CRF1 receptor antagonist), have shown some benefits in diarrhea-predominant IBS (D-IBS), while, prucalopride and mosapride (5-HT4 agonist) with prokinetic effect were found useful in constipation-predominant IBS (C-IBS). Besides, dexloxiglumide, lubiprostone and linaclotide have shown beneficial effects in C-IBS patients. Melatonin regulates GI tract motility and, asimadoline, gabapentin and pregabalin show reduction of pain threshold and visceral hypersensitivity. Glucagon-like peptide analog, calcium-channel blockers and neurokinin receptor antagonists have shown benefits in pain attacks. More time is required to indicate both efficacy and safety in long-term treatment due to multifactorial pathophysiology, variations in individual responses and insufficient assessment methods, which limit the right decision-making process about the efficacy and tolerability of these new drugs.

New treatments for IBS

IBS is a common disorder that affects approximately 5-20% of the populations of Western countries; the main symptoms are abdominal pain and erratic, altered bowel habits, often accompanied by bloating. Despite an array of available pharmacological and nonpharmacological treatments aimed at a wide variety of gastrointestinal and brain targets, many patients do not report adequate symptom relief. The effect of IBS on an individual can be enormous, and the societal and financial costs overall are high, which is indicative of an unmet need for effective IBS treatments. Intense research efforts are ongoing that range from the development of new molecules for pharmacological therapies to testing the utility of internet technology to facilitate widespread delivery of efficacious behavioural therapy. This Review discusses the latest treatments for IBS, including novel nonpharmacological and pharmacological approaches. We have included estimates of the number needed to treat and the number needed to harm for selected treatments. Emerging and potential future treatments are included, with the data supporting an optimistic view about the future of IBS therapeutics. The ability to optimize therapy by individualizing management whilst also avoiding harm remains the key to achieving the best possible outcomes with currently available therapeutics.

Effect and mechanism of acupuncture on gastrointestinal diseases

Acupuncture modulates various biomechanical responses, such as prokinetic, antiemetic, and antinociceptive effects. Acupuncture treatment involves the insertion of thin needles into the skin and underlying muscle and the needles are stimulated manually or electrically. Thus, acupuncture stimulates the somatic afferent nerves of the skin and muscles. The somatic sensory information from the body is carried to the cortex area of the brain. Somatic sensory fibers also project to the various nuclei, including the brain stem, periaqueductal gray (PAG), and paraventricular nucleus (PVN) of the hypothalamus. Somatosensory pathways stimulated by acupuncture activate these nuclei. Activation of the brain stem modulates the imbalance between sympathetic activity and parasympathetic activity. Opioid released from the PAG is involved in mediating antiemetic and antinociceptive effects of acupuncture. Oxytocin release from the PVN mediates antistress and antinociceptive effects of acupuncture. Acupuncture may be effective in patients with functional gastrointestinal (GI) disorders because of its effects on GI motility and visceral pain. It is expected that acupuncture is used in the treatment of patients with functional GI disorders.

Emerging role for corticotropin releasing factor signaling in the bed nucleus of the stria terminalis at the intersection of stress and reward

Stress and anxiety play an important role in the development and maintenance of drug and alcohol addiction. The bed nucleus of the stria terminalis (BNST), a brain region involved in the production of long-term stress-related behaviors, plays an important role in animal models of relapse, such as reinstatement to previously extinguished drug-seeking behaviors. While a number of neurotransmitter systems have been suggested to play a role in these behaviors, recent evidence points to the neuropeptide corticotropin releasing factor (CRF) as being critically important in BNST-mediated reinstatement behaviors. Although numerous studies indicate that the BNST is a complex brain region with multiple afferent and efferent systems and a variety of cell types, there has only been limited work to determine how CRF modulates this complex neuronal system at the circuit level. Recent work from our lab and others have begun to unravel these BNST neurocircuits and explore their roles in CRF-related reinstatement behaviors. This review will examine the role of CRF signaling in drug addiction and reinstatement with an emphasis on critical neurocircuitry within the BNST that may offer new insights into treatments for addiction.

Association of HLA-DQ gene with bowel transit, barrier function, and inflammation in irritable bowel syndrome with diarrhea

Patients with irritable bowel syndrome (IBS) with diarrhea (IBS-D) carrying human leukocyte antigen (HLA)-DQ2/8 genotypes benefit from gluten withdrawal. Our objective was to compare gastrointestinal barrier function, mucosal inflammation, and transit in nonceliac IBS-D patients and assess association with HLA-DQ2/8 status. In 45 IBS-D patients who were naive to prior exclusion of dietary gluten, we measured small bowel (SB) and colonic mucosal permeability by cumulative urinary lactulose and mannitol excretion (0-2 h for SB and 8-24 h for colon), inflammation on duodenal and rectosigmoid mucosal biopsies (obtained in 28 of 45 patients), tight junction (TJ) protein mRNA and protein expression in SB and rectosigmoid mucosa, and gastrointestinal and colonic transit by validated scintigraphy. SB mucosal biopsies were stained with hematoxylin-eosin to assess villi and intraepithelial lymphocytes, and immunohistochemistry was used to assess CD3, CD8, tryptase, and zonula occludens 1 (ZO-1); colonic biopsy intraepithelial lymphocytes were quantitated. Associations of HLA-DQ were assessed using Wilcoxon's rank-sum test. Relative to healthy control data, we observed a significant increase in SB permeability (P < 0.001), a borderline increase in colonic permeability (P = 0.10), and a decrease in TJ mRNA expression in rectosigmoid mucosa in IBS-D. In HLA-DQ2/8-positive patients, ZO-1 protein expression in the rectosigmoid mucosa was reduced compared with that in HLA-DQ2/8-negative patients and colonic transit was slower than in HLA-DQ2/8-negative patients. No other associations with HLA genotype were identified. There is abnormal barrier function (increased SB permeability and reduced mRNA expression of TJ proteins) in IBS-D relative to health that may be, in part, related to immunogenotype, given reduced ZO-1 protein expression in rectosigmoid mucosa in HLA-DQ2/8-positive relative to HLA-DQ2/8-negative patients.

Pharmacological and behavioral characterization of the novel CRF1 antagonist BMS-763534

BMS-763534 is a potent (CRF(1) IC(50) = 0.4 nM) and selective (>1000-fold selectivity vs. all other sites tested) CRF(1) receptor antagonist (pA2 = 9.47 vs. CRF(1)-mediated cAMP production in Y79 cells). BMS-763534 accelerated the dissociation of (125)I-o-CRF from rat frontal cortex membrane CRF(1) receptors consistent with a negative allosteric modulation of CRF binding. BMS-763534 produced dose-dependent increases in CRF(1) receptor occupancy and anxiolytic efficacy; lowest effective anxiolytic dose = 0.56 mg/kg, PO, which was associated with 71 ± 5% CRF(1) receptor occupancy of frontoparietal CRF(1) receptors. Sedative/ataxic effects of BMS-763534 were only observed at high dose multiples (54-179×) relative to the lowest dose required for anxiolytic efficacy. At doses of 5- to 18-fold higher than the lowest efficacious dose in the anxiety assay, BMS-763534 shared subjective effects with the benzodiazepine chlordiazepoxide. Interestingly BMS-790318, the O-demethylated metabolite of BMS-763534, showed weak affinity for the TBOB site of the GABA(A) receptor (67% inhibition at 10 μM) and augmented GABA evoked currents (EC(50) = 1.6 μM). Thus, the unanticipated signal in the drug discrimination assay may have resulted from an interaction of the metabolite BMS-790318 with the TBOB site on the GABA(A) channel where it appears to behave as an allosteric potentiator of GABA evoked currents.

Methods for the assessment of small-bowel and colonic transit

Transit assessment of the small intestine and colon is relevant in the study of physiology, pathophysiology, and pharmacodynamics, and there is increasing use of small-bowel and colonic transit measurements in clinical practice as well. The main methods that are applied in clinical practice are substrate-hydrogen breath tests for small-bowel transit and radiopaque markers for colonic transit. Over the past 2-3 decades, scintigraphy has become the preferred standard in research studies, particularly for studies of pathophysiology and pharmacodynamics. New approaches include experimental stable isotope measurement of orocecal transit and the recently approved method using a wireless motility capsule that is validated as an accurate measurement of small-bowel and colonic transit.

Psychopharmacological treatment and psychological interventions in irritable bowel syndrome

Irritable bowel syndrome (IBS) accounts for 25% of gastroenterology output practice, making it one of the most common disorders in this practice. Psychological and social factors may affect the development of this chronic disorder. Furthermore, psychiatric symptoms and psychiatric diseases are highly prevalent in this condition, but the approach to treating these is not always straightforward. As emphasized in the biopsychosocial model of IBS, with regard to the modulatory role of stress-related brain-gut interactions and association of the disease with psychological factors and emotional state, it proves useful to encourage psychopharmacological treatments and psychosocial therapies, both aiming at reducing stress perception. The aim of this paper is to analyze the effectiveness of psychopharmacological treatment and psychological interventions on irritable bowel syndrome.

Brain-Gut Interactions in IBS

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder with an estimated prevalence of 10–20%. Current understanding of the pathophysiology of IBS is incomplete due to the lack of a clearly identified pathological abnormality and due to the lack of reliable biomarkers. Possible mechanisms believed to contribute to IBS development and IBS like symptoms include physical stressors, such as infection or inflammation, psychological, and environmental factors, like anxiety, depression, and significant negative life events. Some of these mechanisms may involve the brain-gut axis (BGA). In this article we review the current knowledge on the possible involvement of the BGA in IBS and discuss new directions for potential future therapies of IBS.

In vitro and in vivo metabolism and pharmacokinetics of BMS-562086, a potent and orally bioavailable corticotropin-releasing factor-1 receptor antagonist

The absorption, distribution, metabolism, and excretion (ADME) and the pharmacokinetic characteristics of BMS-562086 [pexacerfont; 8-(6-methoxy-2-methyl-3-pyridinyl)-2,7-dimethyl-N-[(1R)-1-methylpropyl]pyrazolo(1,5-a)-1,3,5-triazin-4-amine (DPC-A69448)] were investigated in vitro and in animals to support its clinical development. BMS-562086 was orally bioavailable in rats, dogs, and chimpanzees, with an absolute oral bioavailability of 40.1, 58.8, and 58.5%, respectively. BMS-562086 was extensively metabolized in hepatocytes from all species and completely metabolized in rats. The primary biotransformation pathways found for BMS-562086 in both liver microsomal and hepatocyte preparations and in rats were similar. These included O-demethylation, hydroxylation at the N-alkyl side chain and N-dealkylation. Multiple cytochromes P450 including CYP3A4/5 were involved in the metabolic clearance of BMS-562086. Both renal and biliary excretion played a significant role in elimination of the metabolites of BMS-562086. The involvement of other metabolic enzymes in addition to CYP3A4/5 in elimination of BMS-562086 suggests a reduced potential for drug-drug interaction through modulation of CYP3A4/5. Chimpanzees proved to be a good animal model in predicting BMS-562086 human clearance. Virtual clinical trials performed with a population-based ADME simulator suggested that a minimal dose of 100 mg daily would provide sufficient drug exposure to achieve plasma concentrations above the projected human efficacious plasma concentration of BMS-562086 (> 500 nM). In summary, BMS-562086 exhibited favorable ADME and pharmacokinetic properties for further development.

Peripheral α-helical CRF (9-41) does not reverse stress-induced mast cell dependent visceral hypersensitivity in maternally separated rats

BACKGROUND

Acute stress-induced hypersensitivity to colorectal distention was shown to depend on corticotropin releasing factor (CRF)-induced mast cell degranulation. At present it remains unclear whether CRF also induces chronic poststress activation of these cells. Accordingly, the objective of this study was to compare pre- and poststress CRF-receptor antagonist treatment protocols for their ability to, respectively, prevent and reverse mast cell dependent visceral hypersensitivity in a rat model of neonatal maternal separation.

METHODS

The visceromotor response to colonic distention was assessed in adult maternally separated and non-handled rats before and at different time points after 1 h of water avoidance (WA). Rats were treated with the mast cell stabilizer doxantrazole and the CRF receptor-antagonist α-helical-CRF (9-41). Western blotting was used to assess mucosal protein levels of the mast cell protease RMCP-2 and the tight junction protein occludin.

KEY RESULTS

In maternally separated, but not in non-handled rats, WA induced chronic hypersensitivity (up to 30 days) to colorectal distention. Visceral hypersensitivity was prevented, but could not be reversed by administration of α-helical-CRF (9-41). In contrast, however, the mast cell stabilizer doxantrazole reversed visceral hypersensitivity. Compared with vehicle-treated rats, pre-WA α-helical-CRF (9-41) treated animals displayed higher mucosal RMCP-2 and occludin levels.

CONCLUSIONS & INFERENCES

Water avoidance-stress leads to persistent mast cell dependent visceral hypersensitivity in maternally separated rats, which can be prevented, but not reversed by blockade of peripheral CRF-receptors. We conclude that persistent poststress mast cell activation and subsequent visceral hypersensitivity are not targeted by CRF-receptor antagonists.

Corticotropin-releasing factor receptor 1 antagonist alters regional activation and effective connectivity in an emotional-arousal circuit during expectation of abdominal pain

Alterations in corticotropin-releasing factor (CRF) signaling pathways have been implicated in irritable bowel syndrome (IBS) pathophysiology. We aimed to (1) determine the effect of the selective CRF receptor 1 antagonist (CRF(1)) GW876008 relative to placebo, on regional activation and effective connectivity of a stress-related emotional-arousal circuit during expectation of abdominal pain using functional magnetic resonance imaging in human subjects with a diagnosis of IBS and healthy controls (HCs), and (2) examine GW876008 effects on state-trait anxiety and hypothalamic-pituitary-adrenal (HPA) axis response. Although there were no drug-related effects on peripheral HPA activity, significant central effects were observed in brain regions associated with the stress response. Effective connectivity analysis showed drug-induced normalizations between key regions of the emotional-arousal circuit in patients. During pain expectation, orally administered GW876008 relative to placebo produced significant blood oxygen level-dependent (BOLD) signal reductions in the amygdala, hippocampus, insula, anterior cingulate, and orbitomedial prefrontal cortices across groups. Patients showed significantly greater BOLD responses in the left locus coeruleus and hypothalamus after placebo compared with HCs, and BOLD signal decreases in the left hypothalamus after drug. The inhibitory effects of GW876008 in the hypothalamus in patients were moderated by anxiety; patients having average and high levels of state anxiety showed drug-related BOLD decreases. GW876008 represents a novel tool for elucidating the neuronal mechanisms and circuitry underlying hyperactivation of CRF/CRF(1) signaling and its role in IBS pathophysiology. The unique state anxiety effects observed suggest a potential pathway for therapeutic benefit of CRF(1) receptor antagonism for patients with stress-sensitive disorders.

Pharmacologic and complementary and alternative medicine therapies for irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by episodic abdominal pain or discomfort in association with altered bowel habits (diarrhea and/or constipation). Other gastrointestinal symptoms, such as bloating and flatulence, are also common. A variety of factors are believed to play a role in the development of IBS symptoms, including altered bowel motility, visceral hypersensitivity, psychosocial stressors, altered brain-gut interactions, immune activation/low grade inflammation, alterations in the gut microbiome, and genetic factors. In the absence of biomarkers that can distinguish between IBS subgroups on the basis of pathophysiology, treatment of this condition is predicated upon a patient's most bothersome symptoms. In clinical trials, effective therapies have only offered a therapeutic gain over placebos of 7-15%. Evidence based therapies for the global symptoms of constipation predominant IBS (IBS-C) include lubiprostone and tegaserod; evidence based therapies for the global symptoms of diarrhea predominant IBS (IBS-D) include the probiotic Bifidobacter infantis, the nonabsorbable antibiotic rifaximin, and alosetron. Additionally, there is persuasive evidence to suggest that selected antispasmodics and antidepressants are of benefit for the treatment of abdominal pain in IBS patients. Finally, several emerging therapies with novel mechanisms of action are in development. Complementary and alternative medicine therapies including probiotics, herbal therapies and acupuncture are gaining popularity among IBS sufferers, although concerns regarding manufacturing standards and the paucity of high quality efficacy and safety data remain.

Corticotropin releasing factor receptor antagonists for major depressive disorder

INTRODUCTION

Major depressive disorder is a serious and common psychiatric illness, and many of the depressive patients benefit from pharmacological treatment. Available antidepressants produce remission in only about 30 -- 40% of the patients. Therefore, new concepts are being explored for the development of innovative antidepressants with higher efficacy.

AREAS COVERED

The use of corticotropin releasing factor type 1 (CRF1) receptor antagonists for depression is supported by abundant evidence of target validation, the availability of in vitro and in vivo assays and specific small ligands. Some of these compounds have advanced to clinical studies, with discouraging results so far in depression. This review covers the development of CRF1 receptor antagonists at different stages of the development pipeline of the pharmaceutical industry and its bottlenecks. Most of the available CRF1 receptor antagonists known so far share a common chemical scaffold. We present possible strategies to overcome obstacles in the discovery and development process at the levels of library screenings and clinical studies to find more diverse compounds.

EXPERT OPINION

CRF1 receptor antagonists are expected to be beneficial only for those patients with CRF overexpression and the need for tests to identify these individuals is discussed. New technical developments and diagnostic tools might eventually lead to a more successful treatment of major depression with CRF1 receptor antagonists.

Treatment of irritable bowel syndrome in women

Irritable bowel syndrome (IBS) is a complex clinical process with multiple pathophysiologic mechanisms. There has recently been a shift in the treatment of patients with severe IBS symptoms to disease-modifying therapies as opposed to symptomatic treatment. Because pathophysiologic differences exist between men and women, so does the efficacy of treatment options. These differences could further explain gender-related differences in disease prevalence and treatment response. A brief discussion of the definition, epidemiology, and diagnostic criteria of IBS is followed by a comprehensive review of the current treatment choices and potential future therapeutic options of IBS in women.

Activation of corticotropin-releasing factor receptor 2 mediates the colonic motor coping response to acute stress in rodents

BACKGROUND & AIMS

Corticotropin-releasing factor receptor-1 (CRF(1)) mediates the stress-induced colonic motor activity. Less is known about the role of CRF(2) in the colonic response to stress.

METHODS

We studied colonic contractile activity in rats and CRF(2)-/-, CRF-overexpressing, and wild-type mice using still manometry; we analyzed defecation induced by acute partial-restraint stress (PRS), and/or intraperitoneal injection of CRF ligands. In rats, we monitored activation of the colonic longitudinal muscle myenteric plexus (LMMP) neurons and localization of CRF(1) and CRF(2) using immunohistochemical and immunoblot analyses. We measured phosphorylation of extracellular signal-regulated kinase 1/2 by CRF ligands in primary cultures of LMMP neurons (PC-LMMPn) and cyclic adenosine monophosphate (cAMP) production in human embryonic kidney-293 cells transfected with CRF(1) and/or CRF(2).

RESULTS

In rats, a selective agonist of CRF(2) (urocortin 2) reduced CRF-induced defecation (>50%), colonic contractile activity, and Fos expression in the colonic LMMP. A selective antagonist of CRF(2) (astressin(2)-B) increased these responses. Urocortin 2 reduced PRS-induced colonic contractile activity in wild-type and CRF-overexpressing mice, whereas disruption of CRF(2) increased PRS-induced colonic contractile activity and CRF-induced defecation. CRF(2) colocalized with CRF(1) and neuronal nitric oxide synthase in the rat colon, LMMP, and PC-LMMPn. CRF-induced phosphorylation of extracellular signal-regulated kinase in PC-LMMPn; this was inhibited or increased by a selective antagonist of CRF(1) (NBI35965) or astressin(2)-B, respectively. The half maximal effective concentration, EC(50), for the CRF-induced cAMP response was 8.6 nmol/L in human embryonic kidney-293 cells that express only CRF(1); this response was suppressed 10-fold in cells that express CRF(1) and CRF(2).

CONCLUSIONS

In colon tissues of rodents, CRF(2) activation inhibits CRF(1) signaling in myenteric neurons and the stress-induced colonic motor responses. Disruption of CRF(2) function impairs colonic coping responses to stress.

Activation of corticotropin-releasing factor receptor 2 mediates the colonic motor coping response to acute stress in rodents

BACKGROUND & AIMS

Corticotropin-releasing factor receptor-1 (CRF(1)) mediates the stress-induced colonic motor activity. Less is known about the role of CRF(2) in the colonic response to stress.

METHODS

We studied colonic contractile activity in rats and CRF(2)-/-, CRF-overexpressing, and wild-type mice using still manometry; we analyzed defecation induced by acute partial-restraint stress (PRS), and/or intraperitoneal injection of CRF ligands. In rats, we monitored activation of the colonic longitudinal muscle myenteric plexus (LMMP) neurons and localization of CRF(1) and CRF(2) using immunohistochemical and immunoblot analyses. We measured phosphorylation of extracellular signal-regulated kinase 1/2 by CRF ligands in primary cultures of LMMP neurons (PC-LMMPn) and cyclic adenosine monophosphate (cAMP) production in human embryonic kidney-293 cells transfected with CRF(1) and/or CRF(2).

RESULTS

In rats, a selective agonist of CRF(2) (urocortin 2) reduced CRF-induced defecation (>50%), colonic contractile activity, and Fos expression in the colonic LMMP. A selective antagonist of CRF(2) (astressin(2)-B) increased these responses. Urocortin 2 reduced PRS-induced colonic contractile activity in wild-type and CRF-overexpressing mice, whereas disruption of CRF(2) increased PRS-induced colonic contractile activity and CRF-induced defecation. CRF(2) colocalized with CRF(1) and neuronal nitric oxide synthase in the rat colon, LMMP, and PC-LMMPn. CRF-induced phosphorylation of extracellular signal-regulated kinase in PC-LMMPn; this was inhibited or increased by a selective antagonist of CRF(1) (NBI35965) or astressin(2)-B, respectively. The half maximal effective concentration, EC(50), for the CRF-induced cAMP response was 8.6 nmol/L in human embryonic kidney-293 cells that express only CRF(1); this response was suppressed 10-fold in cells that express CRF(1) and CRF(2).

CONCLUSIONS

In colon tissues of rodents, CRF(2) activation inhibits CRF(1) signaling in myenteric neurons and the stress-induced colonic motor responses. Disruption of CRF(2) function impairs colonic coping responses to stress.

Targeting the 5-HT(3) receptor in the treatment of irritable bowel syndrome

Irritable bowel syndrome, which affects 5-10% of the population includes around 25% with predominantly diarrhoea (IBS-D). Several lines of evidence suggest an increase in mucosal 5-HT availability in IBS-D including a decrease in the serotonin transporter (SERT) which is also seen following acute diverticulitis. 5-HT(3) receptor antagonists have proved effective in suppressing urgency, prolonging small and large bowel transit and relieving symptoms in IBS-D. Alosetron continues to be used under restricted availability without any serious morbidity despite ischemic colitis which occurs at a rate of <1/1000 patient year. Other agents such as ramosetron and ondansetron are still in use and have not been associated with ischemic colitis. 5-HT(3) receptor agonists stimulate intestinal motility, shorten transit times and in a pilot trial accelerated transit in patients with IBS-C.

Emerging pharmacological therapies for the irritable bowel syndrome

The irritable bowel syndrome (IBS) is a symptom-based disorder defined by the presence of abdominal pain and altered bowel habits. Clinical presentations of IBS are diverse, with some patients reporting diarrhea, some constipation, and others a mixture of both. Like the varied clinical phenotypes, the pathogenesis of IBS is also diverse. IBS is not a single disease entity, but rather likely consists of several different disease states. This fact has important implications for the choices and efficacy of IBS treatment. This article reviews the IBS drugs that have reached phase II or III clinical trials.

Treatment of irritable bowel syndrome: beyond fiber and antispasmodic agents

Irritable bowel syndrome (IBS) is a chronic functional disorder of the gastrointestinal tract of unknown etiology. The diagnosis of IBS is made clinically, using symptom-based criteria such as the Manning or Rome criteria. Medical therapy for this condition has traditionally been directed towards symptom relief, using fiber or antispasmodic agents. In recent years, emerging data have confirmed the efficacy of antidepressants, psychological therapies, 5-HT(3) antagonists, 5-HT(4) agonists, and probiotics in the short-term treatment of IBS, although whether these therapies influence the long-term course of the disease is unknown. Increasing knowledge regarding the pathophysiological mechanisms underlying IBS has resulted in a number of novel molecular treatments, which show promise. These include therapies targeting gastrointestinal mucosal chloride channels and guanylate cyclase-C receptors, as well as highly selective agents influencing serotonergic transmission that, at the time of writing, do not appear to have any severe deleterious effects. In this article we provide a summary of current and emerging therapies in this field.

Corticosterone mediates reciprocal changes in CB 1 and TRPV1 receptors in primary sensory neurons in the chronically stressed rat

BACKGROUND & AIMS

Chronic stress is associated with visceral hyperalgesia in functional gastrointestinal disorders. We investigated whether corticosterone plays a role in chronic psychological stress-induced visceral hyperalgesia.

METHODS

Male rats were subjected to 1-hour water avoidance (WA) stress or subcutaneous corticosterone injection daily for 10 consecutive days in the presence or absence of corticoid-receptor antagonist RU-486 and cannabinoid-receptor agonist WIN55,212-2. The visceromotor response to colorectal distension was measured. Receptor protein levels were measured and whole-cell patch-clamp recordings were used to assess transient receptor potential vanilloid type 1 (TRPV1) currents in L6-S2 dorsal root ganglion (DRG) neurons. Mass spectrometry was used to measure endocannabinoid anandamide content.

RESULTS

Chronic WA stress was associated with visceral hyperalgesia in response to colorectal distension, increased stool output and reciprocal changes in cannabinoid receptor 1 (CB1) (decreased) and TRPV1 (increased) receptor expression and function. Treatment of WA stressed rats with RU-486 prevented these changes. Control rats treated with serial injections of corticosterone in situ showed a significant increase in serum corticosterone associated with visceral hyperalgesia, enhanced anandamide content, increased TRPV1, and decreased CB1 receptor protein levels, which were prevented by co-treatment with RU-486. Exposure of isolated control L6-S2 DRGs in vitro to corticosterone reproduced the changes in CB1 and TRPV1 receptors observed in situ, which was prevented by co-treatment with RU-486 or WIN55,212-2.

CONCLUSIONS

These results support a novel role for corticosterone to modulate CB1 and TRPV1-receptor pathways in L6-S2 DRGs in the chronic WA stressed rat, which contributes to visceral hyperalgesia observed in this model.

The brain-gut axis in abdominal pain syndromes

The importance of bidirectional brain-gut interactions in gastrointestinal (GI) illness is increasingly recognized, most prominently in the area of functional GI syndromes such as irritable bowel syndrome (IBS), functional dyspepsia, and functional chest pain. The brain receives a constant stream of interoceptive input from the GI tract, integrates this information with other interoceptive information from the body and with contextual information from the environment, and sends an integrated response back to various target cells within the GI tract. This system is optimized to assure homeostasis of the GI tract during physiological perturbations and to adapt GI function to the overall state of the organism. In health, the great majority of interoceptive information reaching the brain is not consciously perceived but serves primarily as input to autonomic reflex pathways. In patients with functional abdominal pain syndromes, conscious perception of interoceptive information from the GI tract, or recall of interoceptive memories of such input, can occur in the form of constant or recurrent discomfort or pain. This is often associated with alterations in autonomic nervous system output and with emotional changes. A model is proposed that incorporates reported peripheral and central abnormalities in patients with IBS, extrapolates similar alterations in brain-gut interactions to patients with other chronic abdominal pain syndromes, and provides novel treatment targets.

Corticotropin-releasing factor signaling and visceral response to stress

Stress may cause behavioral and/or psychiatric manifestations such as anxiety and depression and also impact on the function of different visceral organs, namely the gastrointestinal and cardiovascular systems. During the past years substantial progress has been made in the understanding of the underlying mechanisms recruited by stressors. Activation of the corticotropin-releasing factor (CRF) signaling system is recognized to be involved in a large number of stress-related behavioral and somatic disorders. This review will outline the present knowledge on the distribution of the CRF system (ligands and receptors) expressed in the brain and peripheral viscera and its relevance in stress-induced alterations of gastrointestinal and cardiovascular functions and the therapeutic potential of CRF(1) receptor antagonists.

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.

Therapeutic utility of non-peptidic CRF1 receptor antagonists in anxiety, depression, and stress-related disorders: evidence from animal models

Adaptive responding to threatening stressors is of fundamental importance for survival. Dysfunctional hyperactivation of corticotropin releasing factor type-1 (CRF(1)) receptors in stress response system pathways is linked to stress-related psychopathology and CRF(1) receptor antagonists (CRAs) have been proposed as novel therapeutic agents. CRA effects in diverse animal models of stress that detect anxiolytics and/or antidepressants are reviewed, with the goal of evaluating their potential therapeutic utility in depression, anxiety, and other stress-related disorders. CRAs have a distinct phenotype in animals that has similarities to, and differences from, those of classic antidepressants and anxiolytics. CRAs are generally behaviorally silent, indicating that CRF(1) receptors are normally in a state of low basal activation. CRAs reduce stressor-induced HPA axis activation by blocking pituitary and possibly brain CRF(1) receptors which may ameliorate chronic stress-induced pathology. In animal models sensitive to anxiolytics and/or antidepressants, CRAs are generally more active in those with high stress levels, conditions which may maximize CRF(1) receptor hyperactivation. Clinically, CRAs have demonstrated good tolerability and safety, but have thus far lacked compelling efficacy in major depressive disorder, generalized anxiety disorder, or irritable bowel syndrome. CRAs may be best suited for disorders in which stressors clearly contribute to the underlying pathology (e.g. posttraumatic stress disorder, early life trauma, withdrawal/abstinence from addictive substances), though much work is needed to explore these possibilities. An evolving literature exploring the genetic, developmental and environmental factors linking CRF(1) receptor dysfunction to stress-related psychopathology is discussed in the context of improving the translational value of current animal models.

Challenges and prospects for pharmacotherapy in functional gastrointestinal disorders

Functional gastrointestinal disorders, such as irritable bowel syndrome and functional dyspepsia, are complex conditions with multiple factors contributing to their pathophysiology. As a consequence they are difficult to treat and have posed significant challenges to the pharmaceutical industry when trying to develop new and effective treatments. This review provides an overview of these difficulties and how the industry is reshaping its drug developmental strategies. It describes some of the more significant and encouraging advances that have occurred, and discusses how future research might embrace the opportunities provided by advances in genetic and in particular, epigenetic research.

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.

Pain is a salient "stressor" that is mediated by corticotropin-releasing factor-1 receptors

Corticotropin-releasing factor (CRF) plays a major role in controlling the body's response to stress. Because painful conditions are inherently stressful, we hypothesize that CRF may act via CRF-1 receptors to contribute to the pain experience. Studies were designed to investigate whether blocking CRF-1 receptors with selective antagonists or reducing their expression with CRF-Saporin, would attenuate ulcer, inflammatory- and neuropathic-like pain. Five experimental designs were undertaken. In experiment 1, ulcer pain was induced in mice following oral administration of indomethacin, while in experiments 2 and 3, inflammatory pain was induced in rats with either carrageenan or FCA, respectively. For these studies, animals were dosed with CP-154,526 (3, 10, 30 mg/kg) and NBI 27914 (1-30 mg/kg) 1 h prior to the assessment of tactile, thermal or mechanical hypersensitivity, respectively. In experiment 4, neuropathic pain was induced. Twenty-one days following spinal nerve ligation (SNL), animals received CRF-Saporin or control. Three weeks later tactile allodynia was assessed. Similarly, in experiment 5, a separate set of rats received CRF-Saporin or control. Twenty-one days later, mechanical hyperalgesia was assessed following intraplantar carrageenan. Results from the antagonist studies showed that CP-154,526 and NBI 27914 either fully or partially reversed the referred ulcer pain with minimal effective doses (MED) equal to 3 and 10 mg/kg, respectively. Similarly, both NBI 27914 and CP-154,526 reversed the thermal and mechanical hypersensitivity elicited by carrageenan and FCA with MEDs </= 5 and 10 mg/kg, respectively. Findings from the two CRF-Saporin studies determined that pre-treatment with this toxin significantly attenuated SNL- and carrageenan-induced tactile hypersensitivity. Together, these findings suggest that CRF-1 receptors mediate pain and implicate CRF in this regard.

Performance characteristics of scintigraphic colon transit measurement in health and irritable bowel syndrome and relationship to bowel functions

BACKGROUND

The inter- and intra-subject variations of scintigraphy, which are used to identify colonic transit disturbances in irritable bowel syndrome (IBS), are unclear. The relationship between colonic transit and bowel functions is incompletely understood. To assess inter- and intra-subject variations of scintigraphic colonic transit measurements in 86 IBS patients and 17 healthy subjects and to quantify the relationship between colonic transit and bowel symptoms in 147 IBS patients and 46 healthy subjects.

METHODS

Data from participants with multiple colonic transit measurements were analysed. Primary end points were colonic filling at 6 h (CF6h) and geometric center (GC) at 24 and 48 h for colonic transit. Bowel functions were assessed by daily stool diaries.

KEY RESULTS

Inter- and intra-subject variations were greater for small intestinal than colonic transit. Overall, inter- and intra-subject variations were relatively narrow for colonic transit (both GC24h and GC48h, with lower COV at 48 h); there was little intra-subject variation in health and IBS-constipation over a period of <or=3 weeks and over 2.0 years (median, range 0.1, 11.0 years). Significant intra-individual differences in GC24h were observed only in IBS-D patients. Colonic transit was significantly associated with stool form (accounting for 19-27% of the variance), frequency (19%), and ease of stool passage (12%).

CONCLUSIONS & INFERENCES

Despite inter-subject variation in scintigraphic colonic transit results, the intra-subject measurements are reproducible over time in healthy volunteers and patients with IBS; significant changes in colonic transit at 24 h were observed only in IBS-D. Colonic transit is associated with stool form, frequency and ease of passage.

Lower functional gastrointestinal disorders: evidence of abnormal colonic transit in a 287 patient cohort

BACKGROUND Abnormalities of colonic motility were reported in relatively small studies of patients with lower functional gastrointestinal disorders (FGID) including irritable bowel syndrome (IBS). The influence of gender and body mass on the observed motor pathophysiology is unclear. We sought to compare colonic transit in patients within different lower FGID subgroups and healthy controls, controlling for gender and BMI, and to determine whether BMI independently influences colonic motility. METHODS We evaluated a scintigraphic gastrointestinal and colonic transit database of 287 lower FGID patients associated with constipation (IBS-C, or functional constipation, n = 118), diarrhoea (IBS-D or functional diarrhoea, n = 139) or mixed bowel function (IBS-M, n = 30) and 170 healthy controls. We measured colon filling at 6 h (CF 6 h), and overall colonic transit at 8, 24 and 48 h. KEY RESULTS Colon filling at 6 h did not differentiate health from FGID. Colonic transit was abnormal at 24 h (GC24 of <1.50 or >3.86) in 29.7% of all lower FGID patients. There was a significant overall association between colonic transit and subject group (healthy controls and FGID subgroups) at 8 (P = 0.01), 24 (P < 0.001) and 48 h (P < 0.001) in particular for those with diarrhoea or constipation at 24 and 48 h (P < 0.05), even after adjusting for age, gender and BMI. In addition, BMI was associated with colonic transit after adjusting for age, gender and subject group. CONCLUSIONS & INFERENCES Abnormal transit is documented non-invasively with scintigraphy in 30% of lower FGID patients; transit measurement may help document pathophysiology and inform selection of therapy in lower FGID.

Linaclotide - a secretagogue and antihyperalgesic agent - what next?

Ongoing clinical trials suggest that linaclotide, a first-in-class, 14-amino acid peptide guanylate cyclase-C (GC-C) receptor agonist and intestinal secretagogue is an effective treatment for chronic constipation. A study in this issue of the Journal suggests that linaclotide also has antihyperalgesic effects in three common rat models of inflammation- and stress-induced hypersensitivity (i.e., acute trinitrobenzene sulfonic acid colitis, water avoidance stress [WAS], and restraint-induced stress) but not in naïve animals. In mice, linaclotide at least partly reduces hyperalgesia via GC-C receptors. Dose-effect relationships of linaclotide were complicated and non-linear. This viewpoint discusses human clinical trials with linaclotide and the results of this study. Potential mechanisms and clinical significance of these findings are explored. Collectively, these data suggest that GC-C receptors exert other, as yet poorly understood, effects on gastrointestinal sensitivity in conditions associated with inflammation and/or stress-induced increased intestinal permeability. However, the data need to be confirmed in humans and in long-term animal models. Further studies are also necessary to elucidate the mechanisms as these effects cannot be explained by linaclotide's known effects on epithelial GC-C receptors.

Review article: new receptor targets for medical therapy in irritable bowel syndrome

BACKGROUND

Despite setbacks to the approval of new medications for the treatment of irritable bowel syndrome, interim guidelines on endpoints for irritable bowel syndrome (IBS) trials have enhanced interest as new targets for medical therapy are proposed based on novel mechanisms or chemical entities.

AIMS

To review the approved lubiprostone, two targets that are not meeting expectations (tachykinins and corticotrophin-releasing hormone), the efficacy and safety of new 5-HT(4) agonists, intestinal secretagogues (chloride channel activators, and guanylate cyclase-C agonists), bile acid modulation, anti-inflammatory agents and visceral analgesics.

METHODS

Review of selected articles based on PubMed search and clinically relevant information on mechanism of action, safety, pharmacodynamics and efficacy.

RESULTS

The spectrum of peripheral targets of medical therapy addresses chiefly the bowel dysfunction of IBS and these effects are associated with pain relief. The pivotal mechanisms responsible for the abdominal pain or visceral sensation in IBS are unknown. The new 5-HT(4) agonists are more specific than older agents and show cardiovascular safety to date. Secretory agents have high specificity, low bioavailability and high efficacy. The potential risks of agents 'borrowed' from other indications (such as hyperlipidaemia, inflammatory bowel disease or somatic pain) deserve further study.

CONCLUSIONS

There is reason for optimism in medical treatment of IBS with a spectrum of agents to treat bowel dysfunction. However, visceral analgesic treatments are still suboptimal.

What we have learned about colonic motility: normal and disturbed

PURPOSE OF REVIEW

Disorders of colonic motor and sensory function are common among children and adults and pose significant diagnostic and therapeutic challenges; the purpose of this review, therefore, was to critically assess the recent literature on this topic.

RECENT FINDINGS

Considerable progress has been made at the ultrastructural, molecular and electrophysiological level in understanding the normal functions of the muscles, nerves and interstitial cells that generate and control colonic motility. Furthermore, abnormalities in these cell types and in the interstitial cells of Cajal, in particular, have been identified in a number of disease states. Testing of colonic motor and sensory function in clinical practice continues to be a challenge due, in part, not only to the technical issues presented by accessing the organ but also to the intrinsic variability of its physiology. These have not been auspicious times for advances in the therapy of disturbed colonic motility; new agents or new applications for 'old' agents continue to be explored as are more innovative approaches such as those based on neural stimulation and cell therapy.

SUMMARY

Considerable progress has been made in understanding the basic pathophysiology of colonic dysmotility; clinical diagnostics and therapeutics continue to lag behind.

Corticotropin releasing factor signaling in colon and ileum: regulation by stress and pathophysiological implications

It is well established that central corticotropin releasing factor (CRF) signaling mediates the gastrointestinal responses to stress. However, as shown in the brain, both CRF receptors and ligands are also widely expressed in the colon and the ileum of humans and rodents, and stress modulates their expression. Several functional studies documented that peripheral injection of CRF or urocortin stimulates colonic transit, motility, Fos expression in myenteric neurons, and defecation through activation of CRF(1) receptors, whereas it decreases ileal contractility via CRF(2) receptors. Additionally, intraperitoneal administration of CRF induces colonic mast cells degranulation via both CRF(1) and CRF(2) receptors and increases ion secretion and mucosal permeability to macromolecules, which can in turn promote intestinal inflammation and alter visceral sensitivity. Most peripheral CRF-induced alterations of colonic and ileal functions mimic effects which are observed after stress exposure, and CRF receptor antagonists given peripherally prevent stress-induced GI dysfunction. Furthermore, CRF peptides can reproduce secretomotor and mucosal alterations in vitro. Therefore, accumulated clinical and preclinical evidence supports in addition to the brain, a role for peripheral CRF signaling in mediating stress-induced effects on gastrointestinal sensorimotor, mucosal and immune functions, that may be components of underlying mechanisms involved in stress-related impact on inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS).

A role for corticotropin-releasing factor in functional gastrointestinal disorders

Functional gastrointestinal disorders (FGIDs), which include irritable bowel syndrome (IBS), encompass a heterogeneous group of diseases identified by chronic or recurrent symptom-based diagnostic criteria. Psychosocial factors are key components in the outcome of clinical manifestations of IBS symptoms. Anxiogenic and endocrine responses to stress are mediated by the corticotropin-releasing factor (CRF)-CRF1 receptor pathway. Preclinical studies show that activation of the CRF1 receptor by exogenous CRF or stress recapitulates many functional symptoms of IBS diarrhea-predominant patients as related to anxiogenic/hypervigilant behavior, autonomic nervous system alterations, induction of diarrhea, visceral hyperalgesia, enhanced colonic motility, mucus secretion, increased permeability, bacterial translocation, and mast cell activation, which are all alleviated by selective CRF1 receptor antagonists. Clinical studies also support that CRF administration can induce IBS-like symptoms in healthy subjects and heighten colonic sensitivity in IBS patients. Yet to be ascertained is whether CRF1 receptor antagonists hold promise as a new therapy in IBS treatment.

Cortagine, a CRF1 agonist, induces stresslike alterations of colonic function and visceral hypersensitivity in rodents primarily through peripheral pathways

Corticotropin-releasing factor (CRF) 1 receptor (CRF(1)) activation in the brain is a core pathway orchestrating the stress response. Anatomical data also support the existence of CRF signaling components within the colon. We investigated the colonic response to intraperitoneal (ip) injection of cortagine, a newly developed selective CRF(1) peptide agonist. Colonic motor function and visceral motor response (VMR) were monitored by using a modified miniaturized pressure transducer catheter in adult conscious male Sprague-Dawley rats and C57Bl/6 mice. Colonic permeability was monitored by the Evans blue method and myenteric neurons activation by Fos immunohistochemistry. Compared with vehicle, cortagine (10 microg/kg ip) significantly decreased the distal colonic transit time by 45% without affecting gastric transit, increased distal and transverse colonic contractility by 35.6 and 66.2%, respectively, and induced a 7.1-fold increase in defecation and watery diarrhea in 50% of rats during the first hour postinjection whereas intracerebroventricular (icv) cortagine (3 microg/rat) had lesser effects. Intraperitoneal (ip) cortagine also increased colonic permeability, activated proximal and distal colonic myenteric neurons, and induced visceral hypersensitivity to a second set of phasic colorectal distention (CRD). The CRF antagonist astressin (10 mug/kg ip) abolished ip cortagine-induced hyperalgesia whereas injected icv it had no effect. In mice, cortagine (30 microg/kg ip) stimulated defecation by 7.8-fold, induced 60% incidence of diarrhea, and increased VMR to CRD. Stresslike colonic alterations induced by ip cortagine in rats and mice through restricted activation of peripheral CRF(1) receptors support a role for peripheral CRF(1) signaling as the local arm of the colonic response to stress.