Hideaki Fujisaki

The potency of substituted benzimidazoles such as E3810, omeprazole, RO 18-5364 to inhibit gastric H+,K+-ATPase is correlated with the rate of acid-activation of the inhibitor

The half maximal inhibitory concentrations (IC50) of substituted benzimidazoles for the H+, K(+)-ATPase in hog gastric vesicles were measured by using the pyruvate kinase-lactate dehydrogenase-linked system in which hydrolysis of ATP was coupled with the oxidation of NADH. The vesicles were incubated in a solution containing a high concentration of KCl, valinomycin and Mg-ATP, and the intravesicular medium was acidified. The inhibitor was activated in the acidic medium and reacted with SH groups on the luminal (intravesicular) side of the ATPase. The active compound formed in the extravesicular medium (pH 6.11) was quenched by GSH. Under these conditions, IC50 of new compound E3810, 2[(4-(3-methoxypropoxy)-3-methylpyridine-2-yl)methyl-sulfinyl]-1H- benzimidazole sodium salt, was 0.072 microM and that of omeprazole was 0.47 microM at 25 degrees. On the other hand, the rates of formation of active compounds, tetracyclic sulfenamide derivatives, from original substituted benzimidazoles in 0.1 N HCl (k) were determined by measuring optical density at the characteristic wavelengths of the active compounds. There was a good correlation between IC50 and k for various substituted benzimidazoles including E3810, methoxy derivative of E3810, omeprazole, Ro 18-5364, H compound, picoprazole and timoprazole. This fact suggest that the rate of the formation of the acid-activated compound is a main factor determining the potency of the inhibitor.

Inhibitions of acid secretion by E3810 and omeprazole, and their reversal by glutathione

A substituted benzimidazole ([4-(3-methoxypropoxy)-3-methylpyridine-2-yl]methylsulfinyl)- 1H-benzimidazole sodium salt (E3810), is a gastric proton pump (H+, K(+)-ATPase) inhibitor. E3810 and omeprazole inhibited acid accumulation dose dependently as measured with aminopyrine uptake in isolated rabbit gastric glands, their IC50 values being 0.16 and 0.36 microM, respectively. The addition of exogenous reduced glutathione (GSH) to the gland suspension reactivated dose dependently the acid secretion which had been inhibited by 2 microM E3810 or omeprazole as a function of the incubation time. Furthermore, GSH at 1 and 3 mM reversed the antisecretory effect of E3810 more quickly than it did that of omeprazole. The antisecretory effect of E3810 was slightly greater than that of omeprazole in histamine-stimulated fistula dogs in vivo. The duration of the antisecretory activity of E3810 at concentrations of 2 and 4 mg/kg was shorter than that of omeprazole at the same concentrations in pentagastrin-stimulated fistula dogs. The reversal of the antisecretory activity of the inhibitors in dogs is suggested to be due to the action of endogenous extracellular GSH, in addition to de novo synthesis of the proton pump, because bullfrog gastric mucosae were found in the present study to secrete GSH into the mucosal solution at the rate of about 0.25 nmol/min/g tissue.

Effects of the Proton Pump Inhibitor, E3810, on Gastric Secretion and Gastric and Duodenal Ulcers or Erosions in Rats

SummaryThe effects of E3810, a potent proton pump inhibitor, on gastric secretion and gastric or duodenal ulcers or erosions were studied in rats. Intraduodenal administration of E3810 dose dependently inhibited gastric secretion (volume and acid outputs) in pylorus-ligated rats. The effective dose required to inhibit volume output by 50% (ED50) was 12 mg/kg and that for acid output was 3.4 mg/kg. Acutely induced gastric ulcers or erosions, such as cold-restraint stress erosions, Shay ulcers and mercaptamine (cysteamine)-induced duodenal ulcers, were significantly inhibited by oral, intraduodenal or subcutaneous administration of E3810 at 1 to 100 mg/kg. The protective effects of E3810 in these acute models were compared with those of omeprazole at the same doses. At low doses, 10 mg/kg (intraduodenally) in Shay ulcers and 3 mg/kg (subcutaneously) in mercaptamine-induced ulcers, E3810 was significantly more effective than omeprazole. But at high doses, there was no significant difference between the 2 drugs in efficacy. In the cold stress erosion model, the drugs were equally effective.

E3710, a new proton pump inhibitor, with a long lasting inhibitory effect on gastric acid secretion

We have investigated the pharmacology of sodium (R)-2-[4-(2,2-dimethyl-1,3-dioxan-5-yl) methoxy-3,5-dimethylpyridin-2-yl]methylsulfinyl-1H-benzimidazol (E3710), a new proton pump inhibitor (PPI), and its effect on gastric acid secretion. E3710 irreversibly inhibited H+,K+-ATPase activity in pig gastric vesicles with an acidic internal environment with an IC50 of 0.28 μM. Administration of E3710 (0.1, 0.2, 0.4, and 0.8 mg/kg; n = 6) intraduodenally in a gastric fistula model in dogs inhibited histamine-stimulated gastric acid secretion at 0 to 2 and 24 to 26 h after administration with ED50 values of 0.18 and 0.22 mg/kg, respectively. The inhibition by E3710 was 2.3 times more potent than that of another representative PPI, esomeprazole (0.2, 0.4, 0.8, and 1.6 mg/kg; n = 6) at 0 to 2 h after administration (ED50 = 0.40 mg/kg) and 2.8 times more potent at 24 to 26 h (ED50 = 0.71 mg/kg). In the gastric fistula dogs, the intragastric pH was ≥4 for 17% (n = 27) of a 24-h period with vehicle alone, but when E3710 was administered, at 0.2 (n = 4), 0.4 (n = 8), and 0.8 mg/kg (n = 5), the pH was ≥4 for 40, 79, and 88% of a day, respectively. The corresponding values for esomeprazole at 0.8 (n = 4) and 1.6 mg/kg (n = 8) were 55 and 59%, respectively. In a crossover study with vehicle, E3710 at 0.4 mg/kg and esomeprazole at 1.6 mg/kg (n = 6), E3710 increased the intragastric pH to >4 for 82% of a day compared with 61% of a day with esomeprazole. These results show that E3710 is a long-acting inhibitor of gastric acid secretion and a promising novel therapy for acid-related diseases, such as gastroesophageal reflux disease.

Effect of secretin on stress-induced gastric bleeding in rats

The effect of secretin on gastric bleeding induced by water (20°C) immersion stress was studied by means of either perfusion of hydrochloric acid (0.13 N) or instillation of hydrochloric acid solution (0.4 N) into the rat stomach. When the stomach was perfused with acid solution, gastric bleeding occurred 20 min after the stress of water immersion and the amount of bleeding increased with time. It was found that integrated amounts of gastric bleeding after stress were more significantly decreased in the secretin-treated group (7.5 clinical units/kg/hr) than the saline control. On the other hand, intraduodenal administration of cimetidine (100 mg/kg) or propantheline (30 mg/kg) did not affect gastric bleeding. It was also revealed that the total amount of glycoprotein in the 4-hr perfusate was decreased 30% by the water immersion, but that secretin treatment prevented the 30% decrease in glycoprotein in the perfusate. In experiments on intragastric instillation of hydrochloric acid solution, it was found that gastric bleeding was seen only when the concentration of hydrochloric acid solution was higher than 0.4 N. However, the bleeding was also significantly prevented by treatment with secretin (2.5 and 7.5 clinical units/kg/hr). In conclusion, secretin prevents stress-induced gastric bleeding at least in part by increasing glycoprotein secretion in the gastric mucosa in the rat.

E3710, Long-Acting PPI as New Approach for the Treatment of Unmet Medical Needs for GERD

Gastroesophageal reflux disease (GERD) is a spectrum of multifunctional disorder caused by the failure of the normal antireflux mechanism with frequent acid reflux. Patients with GERD experience primary symptoms of heartburn and/or acid regurgitation. The patients with GERD have erosive esophagitis, peptic strictures, Barrett esophagus or evidence of extraesophageal diseases such as chest pain, pulmonary symptoms or symptoms in ear, nose and throat symptoms, while others have no apparent mucosal injury by endoscopic diagnosis (non-erosive GERD) [Armstrong, 2005]. GERD is a chronic, relapsing disorder requiring long term management. The pathophysiological mechanism of GERD is complicated. The decreased lower esophageal sphincter pressure, night time reflux, impaired mucosal defense factors, bile reflex, delayed gastric emptying, visceral hypersensitivity, hiatal hernia, insufficient esophageal clearance, physiological comorbidity and concomitant functional bowl diseases are implicated in the refractory mechanism of GERD [Castell et al., 2004; Fass and Sifrim, 2009].