[Pharmacological and clinical profile of linaclotide (Linzess®), a novel therapeutic agent for irritable bowel syndrome with constipation and chronic constipation].

Linaclotide (Linzess® tablets 0.25 mg) is a guanylate cyclase-C (GC-C) agonist with high selectivity and binding affinity to GC-C. In Japan, linaclotide was approved for 〝irritable bowel syndrome with constipation (IBS-C)〟 in December 2016 and 〝chronic constipation (CC) (excluding constipation due to organic disease)〟 in August 2018. Non-clinical studies demonstrated that linaclotide binding to GC-C increases intracellular cyclic guanosine monophosphate (cGMP), resulting in increased fluid secretion and gastrointestinal transit. In rats with colonic hyperalgesia, but not in normal rats, linaclotide suppressed the visceral nociceptive response, mediated by increased submucosal cGMP. In clinical studies in Japan, improvements were observed in the responder rates for global assessment of IBS symptom relief, complete spontaneous bowel movements in patients with IBS-C, and the frequency of spontaneous bowel movement in patients with CC, which were maintained during long-term treatment. Additionally, abdominal bloating, which has been associated with lower quality of life (QOL) and lower satisfaction with other approved therapies, and IBS QOL were improved throughout treatment with linaclotide. Diarrhea, a consequence of linaclotide's mechanism of action, was observed during the clinical studies, but was generally controllable by decreasing the linaclotide dose. No drug resistance was observed during the clinical studies, unlike some other approved agents. These results of non-clinical and clinical studies demonstrate that linaclotide can improve constipation, various abdominal symptoms, and QOL with a favorable safety profile in patients with IBS-C and CC.

Inhibitory effect of the selective serotonin 5-HT3 receptor antagonist ramosetron on duodenal acidification-induced gastric hypersensitivity in rats.

Irritable bowel syndrome (IBS) and functional dyspepsia (FD) are both functional gastrointestinal disorders and frequently co-occur in patients. While one cause of FD appears to be gastric hypersensitivity, whether the hypersensitivity is affected by IBS treatments remains unclear, given the lack of appropriate animal models for testing. Here, we established an experimental model of duodenal acidification-induced gastric hypersensitivity in conscious rats. The model involved duodenal acidification induced by the infusion of hydrochloric acid into the proximal duodenum, with the nociceptive response being determined as the change in mean arterial pressure (MAP) during gastric distension via an indwelling latex balloon. Using our model we evaluated the effects of duodenal acidification, increased distension pressure, and orally administered therapeutic agents for IBS with diarrhea (IBS-D). Duodenal acidification enhanced the pressor response during gastric distension, and pretreatment with the opioid κ-receptor agonist fedotozine (10mg/kg, intra-arterial) inhibited the pressor response. Pressure levels of 15-60 mm Hg increased MAP in response to gastric distension. The serotonin 5-HT3 receptor antagonist ramosetron (30 µg/kg) inhibited MAP increase induced by duodenal acidification, with no other IBS-D therapeutic agents showing any effect. In contrast, the serotonin 5-HT3 receptor agonist m-chlorophenylbiguanide (1mg/kg) significantly enhanced the pressor response during gastric distension. These findings indicate that the serotonin 5-HT3 receptor plays a key role in duodenal acidification-induced gastric hypersensitivity in rats, suggesting that ramosetron may reduce FD symptoms by ameliorating sensitized gastric perception.

Effects of novel TRPA1 receptor agonist ASP7663 in models of drug-induced constipation and visceral pain.

Constipation is a major gastrointestinal motility disorder with clinical need for effective drugs. We previously reported that transient receptor potential ankyrin 1 (TRPA1) is highly expressed in enterochromaffin (EC) cells, which are 5-hydroxytryptamine (5-HT)-releasing cells, and might therefore be a novel target for constipation. Here, we examined the effects of ASP7663, a novel and selective TRPA1 agonist, in constipation models as well as an abdominal pain model. ASP7663 activated human, rat, and mouse TRPA1 and released 5-HT from QGP-1 cells, and oral but not intravenous administration of ASP7663 significantly improved the loperamide-induced delay in colonic transit in mice. While pretreatment with the TRPA1 antagonist HC-030031 and vagotomy both inhibited the ameliorating effect of oral ASP7663 on the colonic transit, both orally and intravenously administered ASP7663 significantly inhibited colorectal distension (CRD)-induced abdominal pain response in rats. Taken together, these results demonstrate that ASP7663 exerts both anti-constipation and anti-abdominal pain actions, the former is likely triggered from the mucosal side of the gut wall via activation of vagus nerves while the latter is assumed to be provoked through systemic blood flow. We conclude that ASP7663 can be an effective anti-constipation drug with abdominal analgesic effect.

Inhibitory effect of ramosetron on corticotropin releasing factor- and soybean oil-induced delays in gastric emptying in rats.

BACKGROUND AND AIM: Symptoms of functional dyspepsia (FD) are highly prevalent in patients with irritable bowel syndrome (IBS). However, the effects of therapeutic agents for IBS on the pathophysiology of FD are unclear. In this study, therefore, we examined the effects of ramosetron, a serotonin 5-HT(3) receptor antagonist, on corticotropin releasing factor (CRF)- and soybean oil-induced delays in gastric emptying of rats, in comparison with anti-diarrheal agent and spasmolytics. The involvement of 5-HT and the 5-HT(3) receptor in delayed gastric emptying was also evaluated. METHODS: Corticotropin releasing factor was administered intravenously to rats 10min before oral administration of 0.05% phenol red solution, and the amount remaining in the stomach was measured after 30min. Soybean oil was administered orally with glass beads, and the number of residual beads in the stomach was counted 1h later. RESULTS: Both CRF and soybean oil inhibited gastric emptying dose-dependently. Ramosetron and itopride, a gastro-prokinetic agent, significantly reduced both CRF- and soybean oil-induced delays in gastric emptying, while an anti-diarrheal agent and spasmolytics aggravated them. Pretreatment with p-chlorophenylalanine for 2days to reduced the synthesis of endogenous 5-HT diminished the effects of both CRF and soybean oil on gastric emptying. A 5-HT(3) receptor agonist m-chlorophenylbiguanide suppressed gastric emptying of both phenol red and glass beads, and those effects were reversed by ramosetron. CONCLUSIONS: These results suggest that CRF and soybean oil suppress gastric emptying in rats by activating 5-HT(3) receptors, and that by antagonizing these receptors, ramosetron may ameliorate symptoms of FD in clinical settings.

Effects of serotonin 5-HT(3) receptor antagonists on CRF-induced abnormal colonic water transport and defecation in rats.

The effects of corticotropin releasing factor (CRF) and serotonin (5-HT)(3) receptor antagonists on intestinal water transport are not well understood. Hence, we established a CRF-induced abnormal water transport model in rat colon, and evaluated the effects of 5-HT(3) receptor antagonists including ramosetron, alosetron, and cilansetron, and the antidiarrheal agent loperamide, in this model. In addition, the effects of 5-HT(3) receptor antagonists and loperamide on abnormal defecation induced by CRF in rats were examined. Colonic water transport was measured in colonic loops in conscious rats. Centrally administered CRF (3-30 microg/kg) markedly decreased colonic fluid loss, whereas oral administration of ramosetron (3, 30 microg/kg), alosetron (300 microg/kg), cilansetron (300 microg/kg), or loperamide (3 mg/kg) significantly inhibited it. Ramosetron (1-10 microg/kg), alosetron (10-100 microg/kg), cilansetron (10-100 microg/kg), or loperamide (0.3-3 mg/kg) also showed dose-dependent inhibition of CRF-induced defecation in rats. These results suggest that 5-HT(3) receptors are involved in both abnormal colonic water transport and defecation induced by CRF, and that the inhibitory effects of 5-HT(3) receptor antagonists on CRF-induced abnormal defecation partly result from their ameliorating action on colonic water transport.

Inhibitory effects of ramosetron, a potent and selective 5-HT3-receptor antagonist, on conditioned fear stress-induced abnormal defecation and normal defecation in rats: comparative studies with antidiarrheal and spasmolytic agents.

We examined the effect of ramosetron, a potent serotonin (5-HT)(3)-receptor antagonist for irritable bowel syndrome with diarrhea, on conditioned fear stress (CFS)-induced defecation and normal (non-stressed) defecation in rats and compared ramosetron with the antidiarrheal agent loperamide and the spasmolytic agents trimebutine and tiquizium. Ramosetron, loperamide, trimebutine, and tiquizium significantly inhibited CFS-induced defecation in a dose-dependent manner with ED(50) (95% confidence limit) values of 0.019 (0.01 - 0.028), 9.4 (4.0 - 22), 850 (520 - 2,400), and 300 (190 - 450) mg/kg, respectively. A significant effect of ramosetron on CFS-induced defecation appeared at 10 min after dosing and was sustained for 8 h. In contrast, loperamide, trimebutine, and tiquizium significantly inhibited CFS-induced defecation between 1 - 8, 1 - 4, and 1 - 8 h after administration, respectively. High doses of ramosetron did not affect normal defecation, whereas loperamide, trimebutine, and tiquizium significantly inhibited this process. In conclusion, ramosetron has potent, rapid-onset, and long-lasting inhibitory effects on CFS-induced defecation in rats, but does not influence normal defecation. The present findings indicate that ramosetron will be a useful therapeutic agent for irritable bowel syndrome with diarrhea, showing greater efficacy and safety than other antidiarrheal and spasmolytic agents.

Effect of ramosetron on conditioned emotional stress-induced colonic dysfunction as a model of irritable bowel syndrome in rats.

The aim of this study was to establish a pathophysiologic model of irritable bowel syndrome, and then to evaluate the pharmaceutical efficacy of ramosetron, a potent serotonin 3 (5-HT(3)) receptor antagonist, and other anti-irritable bowel syndrome agents in this model. Rats stressed by a conditioned stress procedure exhibited marked prolongation of freezing time, an index of fear level, and an increase in the frequency of defecation (P<0.01). A corticotropin-releasing factor (CRF) antagonist, alpha-helical CRF, inhibited both defecation and freezing behavior, while the antidiarrheal loperamide inhibited defecation only. The 5-HT(3) receptor antagonists ramosetron, cilansetron and alosetron also inhibited defecation (ED(50) values: 0.012, 0.094, 0.078 mg/kg p.o., respectively) without affecting freezing behavior. Ramosetron showed longer-lasting effect on defecation than cilansetron. Stress also resulted in increases in both proximal and distal colonic transit rates. Ramosetron and other 5-HT(3) receptor antagonists at doses inhibiting stress-induced defecation also ameliorated both stress-stimulated colonic transit rates. These results suggest that ramosetron, as well as agents used for the treatment of irritable bowel syndrome with diarrhea, has beneficial effects against emotional stress-induced colonic dysfunction. Furthermore, this emotional stress model may be useful in evaluation of drugs to treat irritable bowel syndrome presenting with diarrhea.

Evaluation of the pharmacological profile of ramosetron, a novel therapeutic agent for irritable bowel syndrome.

We examined the pharmacological profile of ramosetron, a 5-HT(3)-receptor antagonist for irritable bowel syndrome with diarrhea, comparing it with those of other 5-HT(3)-receptor antagonists, alosetron and cilansetron, and the anti-diarrheal agent loperamide. Ramosetron showed high affinity for cloned human and rat 5-HT(3) receptors, with K(i) values of 0.091 +/- 0.014 and 0.22 +/- 0.051 nmol/L, respectively, while its affinities for other receptors, transporters, ion channels, and enzymes were negligible. Dissociation of ramosetron from the human 5-HT(3) receptor was extremely slow (t(1/2) = 560 min), while alosetron (t(1/2) = 180 min) and cilansetron (t(1/2) = 88 min) dissociated relatively rapidly. Ramosetron competitively inhibited 5-HT-induced contraction of isolated guinea-pig colon, with pA(2) values of 8.6 (8.5 - 9.0). Ramosetron given orally also dose-dependently inhibited the von Bezold-Jarisch reflex in rats, with an ED(50) value of 1.2 (0.93 - 1.6) microg/kg. In addition, oral ramosetron dose-dependently inhibited restraint stress-induced defecation in rats, with an ED(50) value of 0.62 (0.17 - 1.2) microg/kg. In all of these experiments, the potencies of ramosetron were greater than those of alosetron, cilansetron, or loperamide. These results indicate that ramosetron is a highly potent and selective 5-HT(3)-receptor antagonist, with beneficial effects against stress-induced abnormal defecation in rats.

Mucosal acid causes gastric mucosal microcirculatory disturbance in nonsteroidal anti-inflammatory drug-treated rats.

The mechanism by which nonsteroidal anti-inflammatory drugs (NSAIDs) suppress gastric mucosal blood flow is not fully understood, although the depletion of mucosal prostaglandin E2 has been proposed as one possible explanation. We investigated the role of gastric acid on gastric mucosal blood flow in NSAID-treated rats. A rat stomach was mounted in an ex vivo chamber, and gastric mucosal blood flow was measured sequentially in a 5-mm2 area of the gastric corpus using a scanning laser Doppler perfusion image system. Results showed that diclofenac (5 mg/kg s.c.) and indomethacin (10 mg/kg s.c.) did not affect gastric mucosal blood flow, although both strongly decreased mucosal prostaglandin E2 when saline was instilled into the gastric chamber. On replacement of the saline in the chamber with 100 mM hydrochloric acid, these drugs caused a decrease in gastric mucosal blood flow levels within 30 min. The specific cyclooxygenase (COX)-2 inhibitors celecoxib (50 mg/kg s.c.) and rofecoxib (25 mg/kg s.c.) did not affect mucosal prostaglandin E2 level, nor did they decrease gastric mucosal blood flow, even when hydrochloric acid was added to the chamber. Furthermore, measurement of vasoconstrictive factors present in the mucosa showed that endothelin-1 levels increased after administration of diclofenac s.c. in the presence of intragastric hydrochloric acid. This indicates that the presence of mucosal hydrochloric acid plays an important role in the NSAID-induced decrease in gastric mucosal blood flow, while the COX-1-derived basal prostaglandin E2, which is unlikely to control gastric mucosal blood flow itself, protects microcirculatory systems from mucosal hydrochloric acid.

Influence of Helicobacter pylori infection on healing and relapse of acetic acid ulcers in Mongolian gerbils.

Both Helicobacter pylori and NSAIDs play important roles in the healing and relapse of peptic ulcers in man. We examined how H. pylori infection, indomethacin, and their combination affects the healing of gastric ulcers and whether or not such factors provoke a relapse of healed gastric ulcers in Mongolian gerbils. Gastric ulcers were induced by serosal application of an acetic acid solution. H. pylori (ATCC43504) was orally administered once into animals with active and healed ulcers. Ulcers healed within eight weeks and remained healed for the following six months. H. pylori infection significantly delayed ulcer healing four weeks following infection. Indomethacin treatment showed a tendency to delay ulcer healing. Ulcer healing in H. pylori-infected Mongolian gerbils was significantly delayed by indomethacin. H. pylori infection resulted in a relapse of healed ulcers from one to six months after infection, with a gradual increase in size. By the fourth month following a relapse, the serum gastrin level had significantly increased. H. pylori-induced ulcers in the posterior wall coexisted with relapsed ulcers in the anterior wall five and six months later. Omeprazole markedly prevented the ulcer relapse caused by H. pylori infection. It is concluded that, in Mongolian gerbils, H. pylori infection delayed the healing of preexisting gastric ulcers and resulted in the relapse of healed ulcers, yet indomethacin had little or no effect on ulcer healing or relapse.