Early effects of Lansoprazole orally disintegrating tablets on intragastric pH in CYP2C19 extensive metabolizers

AIM： To compare rabeprazole （RPZ; 10 mg） with Lansoprazole orally disintegrating tablets （LPZ; 30 mg OD） in terms of antisecretory activity and blood drug concentration after a single dose. METHODS： Eight H pylori-negative cytochrome P450 （CYP） 2C19 extensive metabolizers were assigned to receive a single oral dose of RPZ 10 mg or LPZ 30 mg OD. Twelve hour intragastric pH monitoring was performed on the day of treatment. Blood samples were also collected after the administration of each drug. RESULTS： LPZ 30 mg OD induced a significantly earlier rise in blood drug concentration than RPZ 10 mg; consequently, LPZ 30 mg OD induced a significantly earlier rise in median pH in the third and fourth hours of the study. CONCLUSION： In H pylori-negative CYP2C19 extensive metabolizers, LPZ 30 mg OD induced a significantly faster inhibition of gastric acid secretion than RPZ 10 mg.     

The novel and orally active thrombin receptor antagonist E5555 (Atopaxar) inhibits arterial thrombosis without affecting bleeding time in guinea pigs

Thrombin is a powerful agonist for platelets, the action of which is mediated by the thrombin receptor protease-activated receptor-1 (PAR-1). Recently, we discovered that E5555 (1-(3-tert-butyl-4-methoxy-5-morpholinophenyl)-2-(5,6-diethoxy-7-fluoro-1-imino-1,3-dihydro-2H-isoindol-2-yl) ethanone hydrobromide) is a potent thrombin receptor antagonist. We evaluated the anti-platelet and anti-thrombotic effects of E5555. E5555 inhibited the binding of a high-affinity thrombin receptor-activating peptide ([(3)H]haTRAP) to PAR-1 with a half maximal inhibitory concentration (IC(50)) value of 0.019μM. E5555 showed potent inhibitory effects on human platelet aggregation induced by thrombin and TRAP with IC(50) values of 0.064 and 0.031μM, respectively, but had no effect on platelet aggregation induced by either ADP or collagen. Similarly, E5555 showed potent and selective inhibitory effects on guinea pig platelet aggregation induced by thrombin and TRAP with IC(50) values of 0.13 and 0.097μM, respectively. The antithrombotic activity of E5555 in vivo was evaluated in a photochemically-induced thrombosis (PIT) model using guinea pigs. Oral administration of E5555 at 30 and 100mg/kg prolonged the time to occlusion by 1.8-fold and 2.4-fold, respectively, compared with controls. Furthermore, E5555 did not prolong bleeding time in guinea pigs at the highest tested dosage of 1000mg/kg. The drug interactions between E5555 and tissue plasminogen activator (tPA) were evaluated. Intravenous administration of 1mg/kg tPA significantly prolonged bleeding time, and its effects were not altered by the oral co-administration of 300mg/kg E5555. These results suggest that E5555 could be a therapeutic option for atherothrombotic disease.     

Differential development of carbachol-induced desensitization in receptor-mediated Ca2+ influx and Ca2+ release pathways in smooth muscle of guinea-pig taenia caeci

1. We have found that development of carbachol (CCh)-induced desensitization to receptor agonists, but not to receptor by-passed stimulation, is transiently interrupted by a Ca2+-dependent resensitization during the early stage in the smooth muscle of guinea-pig taenia caeci. To further characterize the receptor-mediated signal transduction pathways involved in this peculiar desensitization process, we examined the desensitization processes during Ca2+ influx- and Ca2+ release-mediated contractions in response to activation of muscarinic receptors or histamine H1 receptors. 2. Desensitization treatment with 10(-4) mol/L CCh for 30 min in the presence of extracellular Ca2+ resulted in desensitization to the muscarinic agonists McN-A-343 or AHR-602, which are known to induce contraction only in the presence of extracellular Ca2+ in taenia caeci. The development of desensitization to these agonists was interrupted by a transient resensitization at 1 min. In contrast, the transient resensitization phase was lost following removal of extracellular Ca2+ during the desensitization treatment with CCh; under these conditions, the desensitization developed gradually without an apparent resensitization phase. 3. Contractions to 10(-4) mol/L CCh and 10(-4) mol/L histamine in the absence of extracellular Ca2+ were gradually desensitized without a resensitization phase following the CCh desensitization treatment, irrespective of the presence or absence of extracellular Ca2+ during CCh treatment, although the onset of the desensitization was delayed under Ca2+-free conditions. 4. These results suggest that the receptor-mediated Ca2+ influx and Ca2+ release pathways are differentially desensitized to CCh and that the transient resensitization appears to regulate the desensitization process in response to Ca2+ influx-mediated contraction. Such differential processes of desensitization in receptor-mediated bifurcated signalling pathways may determine cellular responsiveness to certain types of stimuli, depending on the different Ca2+ sources required for contraction.