Biochemical and pharmacological characteristics of a newly synthesized H+-K+ ATPase inhibitor, YJA20379-1, 2-amino-4,5-dihydro-8-phenylimidazole[2,1-b]thiazolo[5,4-g]benzothiazol e.

The biochemical and pharmacological characteristics of a newly synthesized H+-K+ ATPase inhibitor, 2-amino-4,5-dihydro-8-phenylimidazole[2,1-b]thiazolo[5,4-g]benzothiazole (YJA20379-1), were investigated. In the pig gastric microsomes, YJA20379-1 inhibited the gastric H+-K+ ATPase regardless of pH condition, IC50 values being 21 and 24 microM at pH 6.4 and 7.4, respectively. The inhibitory activity of YJA20379-1 was antagonized by dithiothreitol treatment but could not be reversed by dilution and washing of the enzyme preparation. In Sprague-Dawley rats, YJA20379-1, administered i.d., p.o, i.v., or s.c., significantly inhibited basal gastric acid secretion, with ED50 values of 4.7, 20.2, 6.3, and 13.4 mg/kg, respectively. The antisecretory action of YJA20379-1 was short lasting (less than 7 h at an oral dosing of 30 mg/kg). Oral administration of YJA20379-1 also prevented the formation of ethanol, indomethacin, and water immersion stress induced gastric lesions and mepirizole-induced duodenal ulcers in rats. Furthermore, YJA20379-1 accelerated the healing of acetic acid induced chronic gastric ulcers in rats. In conclusion, these results suggest that YJA20379-1 has a potent inhibitory activity on the gastric H+-K+ ATPase but much shorter duration of antisecretory action than omeprazole, thereby exerting its anti-ulcer effects partly with cytoprotective activity.

Role of active oxygen species and lipid peroxidation in mepirizole-induced duodenal ulcers in rats.

The role of active oxygen species and lipid peroxidation in the pathogenesis of duodenal ulcers induced by mepirizole was investigated in rats. Oral administration of mepirizole (200 mg/kg) resulted in ulcer lesions in the proximal duodenum. Thiobarbituric acid-reactive substances (TBA-reactive substances), an indicator of lipid peroxidation, also significantly increased in the duodenal mucosa. Myeloperoxidase (MPO) activity in the duodenal mucosa, a sign of polymorphonuclear leukocyte (PMN) accumulation, significantly increased. Combination treatment with polyethylene glycol-modified Serratia Mn-SOD and catalase significantly decreased the size of the ulcers and TBA-reactive substances in the duodenal mucosa. Allopurinol, a xanthine oxidase inhibitor, also reduced the size of duodenal ulcers. Both the size of the ulcers and the increase in TBA-reactive substances in the duodenal mucosa were significantly lower in PMN-depleted rats. Mepirizole increased the surface expression of adhesion molecule CD18 on PMNs in vitro. These results suggest that lipid peroxidation, mediated by active oxygen species generated from xanthine oxidase and PMNs, plays an important role in the pathogenesis of duodenal ulcers induced by mepirizole.

The biochemical and pharmacological properties of a newly synthesized H+-K+ ATPase inhibitor, 2-dimethylamino-4,5-dihydrothiazolo[4,5:3,4]pyridol-[1,2-a]benzimidazol e.

This study was designed to determine the effect of a newly synthesized proton pump inhibitor, 2-dimethylamino-4,5-dihydrothiazolo[4,5:3,4]pyridol[1,2-a]be nzimidazole (YJA20379-2), on gastric H(+)-K(+) ATPase activity, acid secretion, and experimental gastroduodenal lesions or ulcers in rats. YJA20379-2 inhibited in a concentration-dependent manner the proton pump (H(+)-K(+) ATPase) activity in isolated hog gastric mucosal microsomes, therefore, confirming its classification as a proton pump inhibitor. The inhibitory efficacy of YJA20379-2 on the proton pump was about eight times higher than that of omeprazole at pH 7.4. The activity of the inhibited enzyme was not restored by dilution and washout method, so this implied that the inhibition of YJA20379-2 is not reversible. YJA20379-2, given intraduodenally or orally, potently suppressed acid secretion in pylorus-ligated rats, with ED50 values of 3.6 and 7.7 mg.kg(-1), respectively. Pretreatment with YJA20379-2 dose dependently protected the gastric mucosa from damage induced by absolute ethanol, water-immersion stress, indomethacin, and the duodenal mucosa from damage induced by mepirizole in rats, with ED50 values of 11.0, 21.0, 0.5, and 18.7 mg.kg(-1), respectively. Repeated administration of YJA20379-2 also dose dependently accelerated spontaneous healing of acetic acid induced gastric ulcers. These results suggest that YJA20379-2 has potent antisecretory and antiulcer effects, which are exerted by suppression of H(+)-K(+) ATPase activity in gastric parietal cells, such that YJA20379-2 may be useful for the clinical treatment of peptic ulcer diseases.

Studies on antiulcer agents. IV. Antiulcer effects of 2-benzylthio5,6,7,8-tetrahydro-4(3H)-quinazolinones and related compounds.

With a view to finding more effective antiulcer agents, a series of 2-benzylthio-5,6,7,8-tetrahydro-4(3H)-quinazolinones and related compounds were synthesized and evaluated in a histamine-stimulated gastric secretion model. The sodium salt of the 2-(dimethylamino)benzylthio derivative (8) showed gastric mucosal protection and gastric antisecretion activities, and was also effective against experimental gastric and duodenal ulcers induced by some ulcerogenic agents. Based on a comparison of the antiulcer properties of 8 with those of the lead compounds (1 and 2) and cimetidine, it appears that, for improvement of antiulcer activity, the reduction of gastric acidity is a more important factor than the reduction of gastric volume output or gastric total acid output.

Effect of NG-nitro-L-arginine methyl ester, the nitric oxide synthase inhibitor, on duodenal alkaline secretion and mepirizole-induced duodenal lesions in rats.

We investigated the HCO3- stimulatory mechanism of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) in the anesthetized rat duodenum and examined whether L-NAME protects against mepirizole-induced duodenal damage. The proximal duodenal loop was perfused with saline and HCO3- secretion was measured at pH 7.0 using a pH-stat with added HCl (10 mM). L-NAME (1-5 mg/kg, i.v.) increased HCO3- secretion in a dose-dependent manner, with concomitant elevation in arterial blood pressure and an apparent decrease in heart rate. These changes were mimicked by another NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA; 50 mg/kg, i.v.) but not by NG-nitro-D-arginine methyl ester (D-NAME), and were all antagonized by co-administration of L-arginine but not by D-arginine (200 mg/kg, i.v.). The HCO3- stimulatory effect of L-NAME was also inhibited by vagotomy and pretreatment with atropine (1 mg/kg, s.c.) or indomethacin (5 mg/kg, s.c.). Vagotomy and atropine did not affect blood pressure response, but both inhibited the decrease of heart rate caused by L-NAME, whereas indomethacin did not affect either of these changes. In addition, L-NAME increased HCO3- secretion in the presence of mepirizole (200 mg/kg, s.c.) and prevented duodenal lesions caused by this agent. These results suggest that L-NAME stimulates duodenal HCO3- secretion in association with the inhibition of endogenous NO production, mediated by neural reflex through vagal efferent nerves, resulting from the pressor response to this agent, and may protect the duodenal mucosa against acid-related damage.

Effect of duodenal ulcerogens mepirizole and propionitrile on small intestinal and liver alkaline phosphatase activity in rats.

Duodenal ulcer could be induced in rats by a single subcutaneous injection of the anti-inflammatory agent mepirizole (M) or by the alkyl chemical propionitrile (P). Contrary to M, P provokes HCl hypersecretion as well. We used these animal models of duodenal ulcer to study the preulcerogenic molecular changes in the mucosal cells and their causal relationship to HCl hypersecretion. It was found that M and P induced the dose- and time-dependent decrease of duodenal alkaline phosphatase (DAP) activity. The decrease was detected at 4 h, with a nadir at 12 h after the injection of both drugs. The decrease of alkaline phosphatase activity was organ-specific after P administration and it was even regional-specific along the small intestine after M administration. At the level of mucosal cells of duodenum the effect of the ulcerogens was enzyme-selective. Both ulcerogens decreased protein and alkaline phosphatase activities; however, they had no effect on lysosomal acid phosphatase. Contrary to cysteamine (C), the effect of M and P on DAP depletion could not be reproduced under in vitro conditions. An interference of P and a slight additive effect of C on DAP depletion after simultaneous subcutaneous administration with M to the rats was found. The results indicate that the DAP depletion after in vivo administration of the three duodenal ulcerogens could be provoked by at least two different mechanisms. The decrease of DAP activity seems to be a general property of the duodenal ulcerogens independent of their effects on gastric acid secretion or on the suppression of alkaline secretion in the duodenum. As a late molecular event most probably elicited by the early morphological changes, the decrease of DAP activity could rather be related to ulcer healing than to its pathogenesis.

Effects of TY-10957, a stable PGI2 derivative, on gastroduodenal lesions and secretory responses in the rat.

The effects of TY-10957, a stable PGI2 derivative, on gastroduodenal lesions and secretory responses were examined in rats and compared with those of ornoprostil, a PGE1 derivative. Orally administered TY-10957 dose dependently prevented gastric lesions induced by ethanol/HC1 (60% ethanol in 150 mM HCl) and duodenal ulcers induced by mepirizole (200 mg/kg); a significant effect was obtained at 3 micrograms/kg or greater in the former and at 300 micrograms/kg in the latter. Intraduodenally administered TY-10957 had minimal effects on gastric acid secretion, and at the highest dose (300 micrograms/kg) both the basal acid output and that stimulated by histamine (20 mg/kg) were significantly reduced by about 40%. TY-10957 (30-300 micrograms/kg s.c.) produced a marked increase of alkaline secretion in both stomach and duodenum of anesthetized rats, and these effects were significant at 30 micrograms/kg in the stomach and at 100 micrograms/kg in the duodenum. On the other hand, ornoprostil produced a potent and significant inhibition against ethanol/HCl-induced lesions (greater than 1 microgram/kg), but had no effect on mepirizole-induced duodenal ulcers. This PGE1 derivative had no influence on both basal and stimulated acid secretion and did not significantly affect alkaline secretion even at 100 micrograms/kg. These results suggest that TY-10957 has a protective action on both gastric and duodenal mucosa. The mechanism of duodenal antiulcer effect may involve both inhibition of acid and stimulation of alkaline secretion, while the gastroprotective action of this agent may be attributed to other factors.

The relationship of intraduodenal pH and delayed gastric emptying in duodenal ulceration induced by mepirizole or cysteamine in rats.

Subcutaneous administration of mepirizole (60 and 200 mg/kg) and cysteamine (100 and 300 mg/kg) to fasted rats consistently induced localized villous damage to the proximal duodenum after 6 to 8 hr. The severity of the damage in animals treated with the low doses remained unchanged at 12 hr. With the high doses, however, well-defined deep ulcers were evident by that time, the incidence being high. The agents caused a significant accumulation of highly acidic gastric contents for 6 to 8 hr, but the accumulated gastric contents had markedly decreased by 12 hr. The intraduodenal pH in these animals was significantly lowered for 8 hr with the low doses, but for 12 hr with the high doses. Both mepirizole and cysteamine significantly delayed gastric emptying which was quantitated by weighing the food residue in refed animals. This delay in emptying was observed for 6 to 8 hr with the low doses and for 12 hr with the high doses. We conclude that this prolonged accumulation of gastric contents for up to 8 hr, resulting in a continuous lowering of the intraduodenal pH for 12 hr, is a crucial factor for the progression from duodenal villous damage to visible ulcers in response to mepirizole and cysteamine.

Pathogenesis of the earliest epithelial cell damage induced by mepirizole and cysteamine in the rat duodenum.

Mepirizole (200 mg/kg) and cysteamine (100 mg/kg) induced epithelial cell damage in the proximal duodenum of rats within 30 min after s.c. administration. The injury induced was severe 60 min later. Gastric acid secretion determined in intact animals was stimulated by these agents 30 and 60 min later when the intraluminal pH of the duodenum was significantly decreased. Duodenal blood flow was significantly decreased beginning 5 min after administration up to 60 min. Oral treatment with sodium bicarbonate (300 mg/kg), cimetidine (100 mg/kg), omeprazole or NC-1300 (gastric proton pump inhibitors, 30 mg/kg) and 16,16-dimethyl prostaglandin E2 (10 micrograms/kg) protected the epithelium from damage induced by the two duodenal ulcerogens. Epithelial cell damage in the duodenum in response to mepirizole and cysteamine appears to be related to the increased gastric acid secretion followed by lowered intraduodenal pH of the duodenum having decreased blood flow.

Pathogenesis of duodenal ulcer in the rat: dissociation of acid load and blood flow.

Duodenal mucosal blood flow (DMBF) and duodenal acid load were studied in nonanesthetized rats. Four groups of animals were injected with an ulcerogenic dose of mepirizole [1-(4-methoxy-6-methyl-2-pyrimidinyl)-3-methyl-5-methoxypyrazole] and were studied at 3, 6, 12, and 24 h after drug administration. Three additional groups were given an injection of the vehicle used to solubilize the drug and were studied 3, 12, and 24 h later. All animals studied 24 h after mepirizole showed ulceration of the proximal duodenum. DMBF in animals that received vehicle averaged 141 +/- 12 ml.100 g-1.min-1. A significant duodenal hyperemia was observed 3 and 6 h after mepirizole (498 +/- 113 and 377 +/- 92 ml.100 g-1.min-1, respectively). A large increase in duodenal acid load was also found at these times (47.6 +/- 2.6 and 46.4 +/- 7.3 mueq/h, respectively). DMBF declined progressively afterwards to reach subnormal levels at 24 h after mepirizole. Acid load, however, remained at a high level throughout the 24 h of observation. In contrast, no significant changes in blood flow were observed in pancreas, jejunum, ileum, or colon. In animals with a duodenal ligature 5 mm distal to the pylorus, a hyperemia was observed in the portion of duodenum in continuity with the stomach. This phenomenon was absent in the duodenum distal to the ligature. It is concluded that the high duodenal acid load observed in the face of decreasing DMBF could explain the occurrence of duodenal damage between 12 and 24 h after mepirizole administration.

Effect of duodenal ulcerogens cysteamine, mepirizole, and MPTP on duodenal myoelectric activity in rats.

Increased gastric acid secretion, enhanced acid delivery to the duodenum, and reduced alkaline secretion in the proximal duodenum are relatively well-established pathophysiologic abnormalities in duodenal ulcer. Impaired duodenal motility, however, may also contribute to duodenal ulceration by altering the distribution of acid and alkaline secretions along the upper digestive tract. We tested the hypothesis that the duodenal ulcerogens cysteamine, MPTP, and mepirizole modify duodenal motility in the rat and that motility changes might be a common and early alteration in experimental duodenal ulceration. All three duodenal ulcerogens rapidly produced extensive changes in duodenal myoelectric activity and reduced the frequency of myoelectric slow waves. Cysteamine induced marked hypermotility for at least 6 hr; MPTP rapidly decreased motility and fragmented the myoelectric migrating pattern. Mepirizole induced biphasic changes: an early hypermotility phase of about 30 min was followed by profound hypomotility. These results indicate that marked alterations of duodenal motility are common during experimental duodenal ulceration. In light of the differential effect of the ulcerogens on duodenal motility, it remains to be determined how these changes influence acid neutralization in the proximal duodenum. Nevertheless, our results suggest that all three duodenal ulcerogens, which are different in structure, alter duodenal motility.

Selective decrease of duodenal phosphoprotein phosphatase activity is a general property of duodenal ulcerogens.

A phosphoprotein phosphatase (PPPase) is inhibited in rat duodenal mucosal cells very early after a single s. c. injection of the duodenal ulcerogens cysteamine, propionitrile and mepirizole. The effect seems to be independent of their effects on gastric acid secretion and on duodenal suppression of alkaline secretion. The enzyme inhibition is dose- and time-dependent under in vivo conditions. The inhibition of the PPPase activity is enzyme-selective at the level of mucosal cells in the duodenum. Under in vitro conditions, none of the duodenal ulcerogens inhibited PPPase activity. The results indicate that the effect of the ulcerogens on PPPase activity is probably exerted indirectly. When given simultaneously in vivo, propionitrile attenuated the inhibitory effects of cysteamine on the PPPase activity. However, both propionitrile and cysteamine potentiated the effect of mepirizole on PPPase depletion. These data indicate that cysteamine and propionitrile may act through the same mechanism when depleting PPPase activity. The mechanism of the decrease of duodenal protein phosphatase activity by mepirizole is probably different from the other duodenal ulcerogens.

Role of prostanoids in experimental duodenal ulcer in rat.

The purposes of this study were to determine whether inhibition of cyclooxygenase is a mechanism by which cysteamine and mepirizole produce duodenal ulcers, identify qualitative or quantitative differences in prostanoid production between gastric mucosa and duodenum, and determine whether differences in cyclooxygenase sensitivity to inhibition by aspirin exist between these two tissues. In fed female rats, gastric mucosal prostaglandin E2 (PGE2) and prostacyclin (PGI2) generation was 235 +/- 25 and 832 +/- 40 ng/g/min, respectively, whereas full-thickness duodenal PGE2 and PGI2 generation was 665 +/- 46 and 662 +/- 49 ng/g/min, respectively. Over an intraperitoneal dose range of 0-25 mg/kg, aspirin-induced cyclooxygenase inhibition was dose-dependent and similar for the two tissues. Duodenal ulceration (16.7 mm2) produced by cysteamine, 425 mg/kg, was associated with a 46% reduction in duodenal PGE2 generation, while having no effect on PGI2 generation; however, cysteamine, 213 mg/kg, produced no visible duodenal mucosa injury yet reduced duodenal PGE2 generation 39% compared to control values. In fed male rats, gastric mucosal PGE2 and PGI2 generation was 179 +/- 18 and 813 +/- 61 ng/g/min, respectively, whereas duodenal PGE2 and PGI2 generation was 321 +/- 27 and 454 +/- 38 ng/g/min, respectively. Duodenal ulceration (7.7 +/- 2.3 mm2) produced by oral mepirizole was associated with a 63% reduction in duodenal PGE2 generation compared to control values, while having no effect on PGI2 generation. Subcutaneous aspirin, 100 mg/kg, which reduced duodenal PGE2 generation to a greater degree than either ulcerogen, given in conjunction with pentagastrin, did not produce visible duodenal ulceration.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandin deficiency by itself is not the cause of mepirizole-induced duodenal ulcers in rats.

The purpose of these studies was to determine the role played by endogenous prostaglandins in the development of gastric ulcers produced by indomethacin, and of duodenal ulcers produced by mepirizole in rats. Indomethacin (10 mg/kg subcutaneously) produced gastric ulcers, whereas mepirizole (100 mg/kg subcutaneously) produced exclusively duodenal ulcers. Both drugs, given at ulcerogenic doses, reduced the gastric and duodenal generation of PGE2, PGF2 alpha, 6-keto-PGF1 alpha, and thromboxane B2. In this regard, the extent of reduction was more pronounced after indomethacin than after mepirizole. Despite this greater inhibition of prostaglandin synthesis by indomethacin, this drug did not produce duodenal ulcers, whereas mepirizole was duodenoulcerogenic. In addition, mepirizole increased gastric acid secretion by 74%, whereas indomethacin had no effect on acid secretion. Oral administration of 16,16-dimethyl PGE2, given at nonantisecretory doses (0.5-5 micrograms/kg), prevented formation of indomethacin-induced gastric ulcers, whereas antisecretory doses were required to prevent formation of mepirizole-induced duodenal ulcers. We conclude that a reduction of prostaglandin formation in the duodenal mucosa is not by itself sufficient to induce duodenal ulcers. We hypothesize that three changes, produced by mepirizole, must be present for duodenal ulcers to develop: increased gastric acid secretion, decreased duodenal bicarbonate secretion (as demonstrated earlier), and decreased duodenal content of prostaglandins. The decreased prostaglandin formation, although not causing duodenal ulcers, may lower the resistance of duodenal mucosa to the hyperacidity induced by mepirizole. On the other hand, in the case of gastric ulcers following administration of indomethacin, a decrease in gastric mucosal levels of prostaglandins may play a more important role than changes in gastric acidity.

Pathogenic mechanisms involved in mepirizole-induced duodenal damage in the rat.

Mepirizole (60 and 200 mg/kg) administered s.c. induced damage in the surface epithelial cells of the rat proximal duodenum as early as 2 hr after the treatment. 16,16-Dimethyl prostaglandin E2 (dmPGE2, 30 micrograms/kg) administered s.c. significantly protected the duodenal mucosa against mepirizole-induced damage for up to 6 hr. Gastric acid secretion in acute fistula preparations was significantly reduced 1 hr after administration of mepirizole (60 and 200 mg/kg). The secretion reverted to the control level 2 hr later. In the 60 mg/kg-treated group, however, there was a significant increase in the acid output for up to 6 hr. Duodenal HCO3- secretion, stimulated with 10 mM HCl was significantly inhibited with mepirizole (60 and 200 mg/kg). Mepirizole (60 and 200 mg/kg) significantly increased the amount of acid in the duodenum for 2 to 6 hr after the treatment. dmPGE2 (30 micrograms/kg) significantly inhibited gastric acid secretion, stimulated duodenal HCO3- secretion, and reduced the increased amount of acid in the duodenum in response to mepirizole. Endogenous prostaglandin E2 and 6-keto prostaglandin F1 alpha in the duodenal mucosa were significantly reduced by mepirizole (200 mg/kg) 1 to 2 hr later. Mepirizole-induced duodenal damage appears to be caused by the increased amount of acid in the duodenum.

Species and strain differences in mepirizole-induced duodenal and gastric lesions.

Species and strain differences in mepirizole-induced duodenal and gastric lesions were studied. Mepirizole at 200 mg/kg given orally induced deep duodenal ulcers and gastric erosions in nonfasted Sprague-Dawley, Fisher, Wistar, and Donryu rats at an incidence of over 75%. Mepirizole at 300 mg/kg given orally also induced penetrating duodenal ulcers in nonfasted rabbits at an incidence of 50%. There was little or no damage to the duodenum and stomach in mice and dogs given 200-300 mg/kg of mepirizole orally or subcutaneously. The stomachs of fasted guinea pigs given 200 mg/kg of mepirizole had superficial erosions at a high incidence (93.3%). Mepirizole at 200 mg/kg given intraduodenally significantly reduced the volume of gastric juice but increased the acidity and pepsin activity in both pylorus-ligated and acute fistula rats. In chronic fistula rabbits, however, the agent at 200 mg/kg given orally reduced the volume and acidity, but increased the pepsin activity. The mechanism of duodenal ulceration by mepirizole differs slightly in rats and rabbits.