Yusaku Komoike

Inhibition of both COX-1 and COX-2 is required for development of gastric damage in response to nonsteroidal antiinflammatory drugs.

We examined the gastric ulcerogenic property of selective COX-1 and/or COX-2 inhibitors in rats, and investigated whether COX-1 inhibition is by itself sufficient for induction of gastric damage. Animals fasted for 18 h were given various COX inhibitors p.o., either alone or in combination, and they were killed 8 h later. The nonselective COX inhibitors such as indomethacin, naproxen and dicrofenac inhibited PG production, increased gastric motility, and provoked severe gastric lesions. In contrast, the selective COX-2 inhibitor rofecoxib did not induce any damage in the stomach, with no effect on the mucosal PGE(2) contents and gastric motility. Likewise, the selective COX-1 inhibitor SC-560 also did not cause gastric damage, despite causing a significant decrease in PGE(2) contents. The combined administration of SC-560 and rofecoxib, however, provoked gross damage in the gastric mucosa, in a dose-dependent manner. SC-560 also caused a marked gastric hypermotility, whereas rofecoxib had no effect on basal gastric motor activity. On the other hand, the COX-2 mRNA was expressed in the stomach after administration of SC-560, while the normal gastric mucosa expressed only COX-1 mRNA but not COX-2 mRNA. These results suggest that the gastric ulcerogenic property of conventional NSAIDs is not accounted for solely by COX-1 inhibition and requires the inhibition of both COX-1 and COX-2. The inhibition of COX-1 up-regulates the COX-2 expression, and this may counteract the deleterious influences, such as gastric hypermotility and the subsequent events, due to a PG deficiency caused by COX-1 inhibition.

Up-regulation of COX-2 by inhibition of COX-1 in the rat: a key to NSAID-induced gastric injury

A recent study demonstrated that inhibition of both cyclooxygenase (COX)‐1 and COX‐2 is required for the development of nonsteroidal anti‐inflammatory drug (NSAID)‐induced gastric lesions. However, the role of COX‐1 or COX‐2 inhibition in the pathogenisis of these lesions remains unclear.

Lack of Gastric Toxicity of Nitric Oxide-Releasing Indomethacin, NCX-530, in Experimental Animals

The effects of a nitric oxide (NO) releasing derivative of indomethacin (NCX-530) on gastric ulcerogenic and healing responses were evaluated in rats and mice, in comparison with the parent compound indomethacin. Indomethacin (per os) produced damage in the rat stomach in a dose-dependent manner. NCX-530 (per os) itself, however, was not ulcerogenic and even showed a dose-dependent protection against HCl/ethanol-induced lesions in the rat stomach. Likewise, indomethacin given repeatedly delayed healing of gastric ulcers induced in mice by thermal cauterization, while NCX-530 did not affect the healing response and significantly promoted the healing as compared to indomethacin. These actions of NCX-530 were mimicked by the combined administration of a NO donor NOR-3 with indomethacin. The amount of NO metabolites was increased in both the gastric contents and serum when NCX-530, but not indomethacin, was given in pylorus-ligated stomachs. Neither indomethacin nor NCX-530 influenced gastric acid secretion and transmucosal potential difference, yet NCX-530 caused a marked increase of gastric mucosal blood flow, which was preventable by carboxy-PTIO, a scavenger of NO. Gastric motility was increased by indomethacin but not by NCX-530. In addition, NCX-530 inhibited PGE2 generation in both the intact and ulcerated gastric mucosa and showed antiinflammatory action on carrageenan-induced rat paw edema, as effectively as indomethacin. These results suggest that unlike indomethacin, NCX-530 caused neither an irritating action on the stomach nor healing impairment effect on the preexisting gastric ulcers, but conferred gastric protection against HCl/ethanol, despite causing cyclooxygenase inhibition and antiinflammatory action, as effectively as indomethacin. This NO-releasing indomethacin, probably by releasing NO, exerts protective influences, such as an increase of gastric mucosal blood flow, that counteract the potential damaging effects of cyclooxygenase inhibition by indomethacin.

Healing of Duodenal Ulcers Is Not Impaired by Indomethacin or Rofecoxib, the Selective COX-2 Inhibitor, in Rats

Background/Aim: Studies have demonstrated an important role for endogenous PG and NO in the healing of chronic gastric ulcers. We investigated the effects of COX and NOS inhibitors on the healing of duodenal ulcers, in comparison with gastric ulcers, in rats. Methods: Gastric and duodenal ulcers were induced by serosal application of acetic acid (0.1 ml of 100% acetic acid) for 60 and 20 s, respectively. Indomethacin (a nonselective COX inhibitor) or rofecoxib (a selective COX-2 inhibitor) was given p.o. once daily for 14 days from 3 days after ulcer induction, while NG-nitro-L-arginine methyl ester (L-NAME: a nonselective NOS inhibitor) or aminoguanidine (a relatively selective iNOS inhibitor) was given s.c. twice daily during this period. Results: Both gastric and duodenal ulcers induced by acetic acid healed spontaneously within 17 days to a minimal size. Daily administration of indomethacin or rofecoxib significantly delayed the healing of gastric but not duodenal ulcers. In contrast, the healing of both gastric and duodenal ulcers was delayed by repeated administration of either L-NAME or aminoguanidine. Ulceration markedly increased the PGE2 content of the ulcerated mucosa in both the stomach and duodenum, and the increased PG biosynthetic response was inhibited by either indomethacin or rofecoxib in both tissues. The expression of both COX-2 and iNOS mRNAs was upregulated in the ulcerated mucosa of the stomach and duodenum. Conclusion: These results suggest that COX-2/PG is actively involved in the healing of gastric but not duodenal ulcers, although the mRNA for COX-2 is expressed in the duodenal mucosa after ulceration, as potently as in the gastric mucosa. In contrast, NO produced by both cNOS and iNOS plays a role in the healing of both gastric and duodenal ulcers.

Selective cyclooxygenase-2 inhibitor induces gastric mucosal damage in adrenalectomized rats

We investigated gastric ulcerogenic properties of the selective COX-2 inhibitor in adrenalectomized rats. SC-560 (selective COX-1 inhibitor) or celecoxib (selective COX-2 inhibitor) was given to sham-operated and adrenalectomized rats, with or without corticosterone replacement 11 days after the surgery, and gastric lesions were estimated 8 h later. Neither SC-560 nor celecoxib alone induced any gross damage in the gastric mucosa in sham-operated rats. In adrenalectomized rats, however, celecoxib did provoke gross damage that was prevented by corticosterone pellets. Mucosal PGE2 content was increased 3-fold after adrenalectomy, and this response was prevented by both celecoxib and corticosterone pellets. The COX-2 mRNA was up-regulated in the stomach of adrenalectomized rats, but this expression was suppressed by corticosterone replacement. These results support our hypothesis that adrenalectomy increases gastric mucosal PGE2 due to COX-2 expression, and the selective COX-2 inhibitor produces gastric lesions by inhibiting the additional PGE2 production in adrenalectomized rats.

Prevention by Parenteral Aspirin of Indomethacin-Induced Gastric Lesions in Rats Mediation by Salicylic Acid

Nonsteroidal antiinflammatory drugs (NSAIDs) produce gastric damage in experimental animals, irrespective of the route of administration. However, aspirin (ASA) causes damage only when it is given orally. In the present study, we examined the gastric ulcerogenic effect of subcutaneously administered ASA in rats, in comparison with various NSAIDs, and investigated the reason why ASA does not cause damage in the stomach, in relation to its metabolite salicylic acid (SA). Since the antiinflammatory action of SA is known to be mediated, partly, by endogenous adenosine (AD), we also examined the possible involvement of AD in the protective action of SA. Various NSAIDs (indomethacin, flurbiprofen, naproxen, diclrofenac, ASA, SA) were administered subcutaneously, and the gastric mucosa was examined macroscopically 4 hr later. All NSAIDs tested, except ASA and SA, caused hemorrhagic lesions in the stomach, with a marked gastric hypermotility and a decrease of mucosal PGE2 contents. These ulcerogenic and motility responses caused by NSAIDs were blocked by pretreatment with atropine or PGE2. ASA, although inhibiting PGE2 generation, caused neither hypermotility nor damage in the stomach. On the other hand, SA alone inhibited basal gastric motility without any effect on mucosal PGE2 contents, and this agent, when given together with indomethacin, prevented gastric hypermotility and lesion formation in response to indomethacin, without affecting the reduced PGE2 contents. Likewise, ASA inhibited these responses to indomethacin, yet the effects appeared later than those of SA. Following administration of ASA, the blood SA levels reached a peak within 30 min and remained elevated for 4 hr. In addition, the protective effect of SA was not significantly influenced by either the AD deaminase or the AD-receptor antagonists. These results suggest that the failure of parenteral ASA to induce gastric damage may be explained by a protective action of SA metabolized from ASA. SA has a cytoprotective action against NSAID-induced gastric lesions, and this action is not mediated by endogenous AD but may be functionally associated with inhibition of the gastric motility response.

Protection by aspirin of indomethacin-induced small intestinal damage in rats: mediation by salicylic acid

Most of non-steroidal anti-inflammatory drugs (NSAIDs) except aspirin (ASA) produce intestinal damage in rats. In the present study, we re-examined the intestinal toxic effect of ASA in rats, in comparison with various NSAIDs, and investigated why ASA does not cause damage in the small intestine, in relation to its metabolite salicylic acid (SA). Various NSAIDs (indomethacin; 10 mg/kg; flurbiprofen; 20 mg/kg; naproxen; 40 mg/kg; dicrofenac; 40 mg/kg; ASA; 20-200 mg/kg) were administered s.c., and the small intestinal mucosa was examined macroscopically 24 h later. All NSAIDs tested, except ASA, caused hemorrhagic lesions in the small intestine, with a decrease of mucosal PGE(2) contents. ASA did not provoke any damage, despite inhibiting (prostaglandin) PG production, and prevented the occurrence of intestinal lesions induced by indomethacin, in a dose-related manner. This protective action of ASA was mimicked by the equimolar doses of SA (17.8-178 mg/kg). Indomethacin caused intestinal hypermotility, in preceding to the occurrence of lesion, and this event was followed by increases of enterobacterial translocation in the mucosa. Both ASA and SA prevented both the intestinal hypermotility and the bacterial translocation seen after indomethacin treatment. In addition, the protective effect of SA was not significantly influenced by either the adenosine deaminase or the adenosine receptor antagonists. Following administration of ASA, the blood SA levels reached a peak within 30 min and remained elevated for more than 7 h. These results suggest that SA has a cytoprotective action against indomethacin-induced small intestinal lesions, and this action may be associated with inhibition of the intestinal hypermotility and the bacterial translocation, but not mediated by endogenous adenosine. Failure of ASA to induce intestinal damage may be explained, at least partly, by a protective action of SA, the metabolite of ASA.

Permissive role of neutrophils in pathogenesis of indomethacin-induced gastric lesions in rats

INTRODUCTION We examined the possible role of neutrophils in the pathogenesis of indomethacin-induced gastric lesions, in comparison with prostaglandin (PG) deficiency. MATERIAL AND METHODS Rats were given indomethacin (35 mg/kg, s.c.) and killed 4 hr later. Gastric motility, mucosal PGE2 levels, and myeloperoxidase (MPO) activity were measured following indomethacin. Atropine was given s.c. 30 min before administration of indomethacin, while 16, 16-dimethyl PGE2 (dmPGE2) or anti-rat neutrophil antiserum (ANS) was given i.v. 10 min or 1 hr, respectively, before indomethacin treatment. RESULTS Indomethacin reduced PGE2 contents in the stomach and produced hemorrhagic lesions in the stomach, with an increase of gastric motility and MPO activity. Indomethacin-induced gastric lesions were significantly prevented by dmPGE2 as well as atropine, at any time points during a 4 hr-test period. By contrast, the pretreatment of ANS did not prevent the development of gastric lesions when examined at either 1, 2 or 3 hr following indomethacin, but significantly reduced the severity of these lesions at 4 hr after indomethacin treatment. Both dmPGE2 and atropine inhibited the increase of gastric motility and MPO activity in response to indomethacin, whereas ANS prevented the increase of MPO activity, without any effect on the gastric hypermotility. CONCLUSION These results confirmed that indomethacin-induced gastric lesions occurred in association with gastric hypermotility, in both atropine and PG-sensitive manners, and further suggest that the neutrophil activation/migration is not sufficient by itself to induce damage in the stomach and may be implicated in the process of later extension of damage.

Gastric Cytoprotection by Prostaglandin E2 - Relation to EP Receptor Subtypes -

This article overviews our recent studies on the relation between EP receptor subtypes and gastric cytoprotection afforded by endogenous and exogenous PGE2, using rats and EP-receptor knockout mice. Exogenous PGE2 dose-dependently reduced the severity of HCl/ethanol-in-duced gastric lesions. This action of PGE2 was mimicked by another E type prostanoids such as sulprostone (EP1/EP3) and 17-phenyl PGE2 (EP1) but not by butaprost (EP2), ONO-NT-012 (EP3) or 11-deoxy PGEl (EP3/EP4), and significantly attenuated by ONO-AE-829 the selective EP1 antagonist. Similar results were obtained in EP-receptor knockout mice, and PGE2 inhibited these lesions in both wild type and EP3-receptor knockout mice but not in the animals lacking EP1-receptors. HCl/ethanol-induced gastric lesions were also prevented by mild irritants such 20 mM taurocholate (TC). This effect was accompanied by an increase of mucosal PGE2 production, attenuated by indomethacin as well as ONO-AE-829, and disappeared in EP1-receptor knockout mice. On the other hand, capsaicin also protected the stomach against HCl/ethanol, without increase of mucosal PGE2 production. This action was totally attenuated by chemical ablation of afferent neurons, partially mitigated by indomethacin but not by ONO-AE-829. Attenuation by indomethacin of the capsaicin protection was recoverd in the presence of butaprost but not other EP agonists. In addition, capsaicin exihibited gastric protection in knockout mice lacking EP1- and EP3-receptors but not in IP-receptor knockout mice.

Role of endogenous prostacyclin in gastric ulcerogenic and healing responses: A study using IP-receptor knockout mice

mg/kg), a NO donor, significantly prevented the development of gastric lesions induced by ASA, irrespective of whether or not ASA was given together with HCI. Gastric mucosal application of ASA for 30 min caused a marked reduction of transmucosal potential difference (PD) with a minimal effect on gastric mucosal blood flow in both normal and cirrhotic rats, while that of NCX-4016 did not cause a PD reduction and produced a marked increase in the mucosal blood flow in both groups of rats. Conclusion: These results suggest that 1) the gastric mucosal susceptibility to ASA-induced damage is increased in both cirrhotic and arthritic rats, the process being partly accounted for by acid hypersecretion observed in these animals, 2) NCX-4016 has less gastric toxicity even in both cirrhotic and arthritic rats, and 3) the gastric sparing effect of NCX-4016 is due, at least partly, to increase of gastric mucosal blood flow, mediated by NO released from this drug.