Exploratory aspirin resistance trial in healthy Japanese volunteers (J-ART) using platelet aggregation as a measure of thrombogenicity.

Aspirin prevents the production of thromboxane A2 (TXA2) by irreversibly inhibiting platelet cyclooxygenase, exhibiting antiplatelet actions. This agent has been reported to prevent relapse in patients with ischemic heart disease or cerebral infarction via this action mechanism. However, there are individual differences in this action, and aspirin is not effective in some patients, which is referred to as 'aspirin resistance'. In this study, we analyzed laboratory aspirin resistance by platelet aggregation in 110 healthy adult Japanese males using 24 single-nucleotide polymorphisms (SNPs) of nine genes involved in platelet aggregation/hemorrhage. Among SNPs involved in platelet aggregation, aspirin was less effective for 924T homozygote of a TXA2 receptor, 924T>C, and 1018C homozygote of a platelet membrane glycoprotein GPIbalpha, 1018C>T, suggesting that 924T and 1018C alleles are involved in aspirin resistance.

Studies on the first-pass metabolism of ebastine in rats.

The metabolic conversion of ebastine (CAS 90729-43-4, LAS-90), an antiallergic agent, to its active principle carebastine (CAS 90729-42-3) in the rat intestine and liver was investigated using intravenous-intraportal infusion techniques and jejunum loop preparations. The steady state blood concentrations of ebastine and carebastine were determined during continuous intravenous or intraportal infusion of ebastine to evaluate their respective activity to metabolize ebastine in the intestine and liver. Total body clearance of ebastine was calculated to be approximately 22-26 ml/ min. The intestinal and hepatic clearances were 6.7 ml/min and 15.4 ml/min, respectively, accounting for about 32% and 60% of the total clearance, respectively. The ratio of the concentrations of carebastine in portal blood to that in arterial blood was 1.41 during intravenous infusion, suggesting the single-pass metabolic conversion of ebastine to carebastine in the intestine. The ratio of the arterial blood concentration of carebastine during intraportal infusion to that during intravenous infusion was 1.88, suggesting the single-pass metabolic conversion in the liver. The contribution of the intestine to form carebastine from ebastine present in the systemic circulation was thus about 1/2 (0.41/0.88) of that of the liver under these conditions. When [14C]ebastine was administered in the jejunal loop, carebastine was detected in the mesenteric plasma circulated from the loop, as the major component accounting for approximately 56% of the plasma radioactivity, while the unchanged ebastine was only about 13%. Therefore, the jejunal tissue converted > 1/2 of the permeated fraction of ebastine to carebastine under these conditions. The results in the infusion studies suggested that metabolic potential to convert ebastine to carebastine was higher in the liver than in the intestine. However, since after oral administration all of the drug appeared in the systemic circulation firstly permeated the mucosa of small intestine and then passed through the liver, the contribution of the small intestine in the metabolic conversion of ebastine given orally would be greater than that of the liver, as suggested by the above in situ jejunum loop study.

Identification of rat faecal metabolites of ebastine by B/E linked scanning liquid secondary ion mass spectrometry.

The identification of rat faecal metabolites of a new antihistaminic agent, ebastine, 4'-tert-butyl-4-[4-(diphenylmethoxy)piperidino]butyrophenone, is presented. After oral administration of (14C)ebastine (20 mg kg-1) to rats, 84% of the radioactive dose was excreted in the 24 h faeces. Unchanged drug and five metabolites were isolated from the faeces by thin-layer chromatography and solid-phase extraction, and their structures were identified by liquid secondary ion mass spectrometry using the B/E linked scanning technique. The main metabolic pathways were oxidation of a terminal methyl group to give the hydroxymethyl and carboxyl derivatives, and hydroxylation of a phenyl ring in the diphenylmethoxy moiety. In addition to the oxidative mechanism, metabolism of ebastine involved sulphate conjugation. It is noteworthy that M-4, having both phenolic and alcoholic hydroxyl groups, was sulphated selectively in the latter position.

Absorption, distribution, metabolism and excretion of [14C]ebastine after a single administration in rats.

Absorption, distribution, metabolism and excretion of ebastine (4'-tert-butyl-4-[4-(diphenylmethoxy)piperidino]butyrophenone, LAS-90, CAS 90729-43-4), a novel antihistamine, were investigated with 14C-labeled compound in rats after a single oral or intravenous administration, in comparison with [14C]carebastine, an active metabolite of ebastine. After intravenous administration of [14C]ebastine at 2 mg/kg, the plasma level of radioactivity decreased biphasically with alpha-phase half-life (t1/2 alpha) of 1.6 h and beta-phase half-life (t1/2 beta) of 3.1 h. After administration of [14C]carebastine, a similar plasma level-time profile was observed with t1/2 alpha of 0.7 h and t1/2 beta of 2.1 h. Following oral administration of [14C]ebastine at a dose of 2 mg/kg, the plasma level reached the maximum (Cmax) of 102 ng eq./ml at 2 h and decreased monophasically with t1/2 of 3.9 h. At 20 mg/kg, a monophasic decrease was also observed with Cmax of 1110 ng eq./ml at 4 h and with t1/2 of 4.0 h. After oral administration of [14C]carebastine at 2 mg/kg, the plasma level reached Cmax of 129 ng eq/ml at 2 h, followed by a monophasic decrease with t1/2 of 2.9 h. Half-lives after administration of [14C]ebastine were somewhat longer than those after administration of [14C]carebastine. The level of [14C]ebastine radioactivity in the liver was about 36 times higher, and in kidney, mesenteric lymph nodes, lung, adrenal, submaxillary gland or pancreas 2-4 times higher than in plasma at 2 h after oral administration. The brain level was lower than the reliable limit of measurement. Other tissue levels were similar to or lower than plasma level. Radioactivity in most tissues decreased essentially in parallel with that in plasma. In pregnant rats, [14C]ebastine radioactivity level in fetus was about 1/4 of the maternal plasma level 1 h after administration. In lactating rats, milk levels of [14C]ebastine radioactivity were similar to maternal plasma levels over 8 h. Serum protein binding of [14C]ebastine was more than 99.8%. After intravenous administration of [14C]ebastine, about 6% of the dose was excreted in the urine and about 93% in the feces. Similar results were observed after oral administration at 0.2, 2 and 20 mg/kg. Following administration of [14C]carebastine, the recovery of radioactivity in urine and feces were around 2% and 96% of the dose, respectively, irrespective of administration route. In the plasma 2 h after oral administration of [14C] ebastine, carebastine and the polar metabolite(s) were observed as major components, whereas ebastine was hardly detected.(ABSTRACT TRUNCATED AT 400 WORDS)

Absorption, distribution, metabolism and excretion of [14C]ebastine after repeated oral administration in rats.

Absorption, distribution, metabolism and excretion of ebastine (4'-tert-butyl-4-[4-(diphenylmethoxy)piperidino]butyrophenone, LAS-90, CAS 90729-43-4), a new potent histamine H1-receptor antagonist, were studied with 14C-labeled compound in male rats during and after 21 consecutive daily oral administrations at a dose of 2 mg/kg/d. Plasma levels at 2 h after each administration were virtually constant in the range of 81-166 ng eq./ml for 21 days. The plasma levels at 24 h following each administration were lower than the reliable limit of radioactivity measurements during the course of the experiment. Plasma level reached the maximum (Cmax) of 109 ng eq./ml at 2 h after the 21st administration and decreased monophasically with a half-life (t1/2) of 2.5 h, which was similar to the results in the previous single dose study. [14C]Ebastine radioactivity was distributed to the liver, kidney, submaxillary gland, hypophysis, adrenal, lung and pancreas twice as high or more, and to others including brain similarly as or lower than in plasma, at 1 h after the last administration. At 168 h, radioactivity was detected at low levels in several tissues such as liver, kidney, submaxillary gland, etc. and not in other examined tissues. About 2-3% and more than 90% of the daily dose were excreted in urine and feces, respectively, within 24 h after each administration and radioactivity was virtually completely excreted within 120 h after the last administration. The analysis by thin-layer chromatography revealed that the composition of radioactive metabolites in plasma, urine and feces after repeated administration was similar to that in the single dose study.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption, distribution, metabolism and excretion of [carbonyl-14C]mosapride citrate after repeated oral administration in rats.

Absorption, distribution, metabolism and excretion of mosapride citrate ((+/-)-4-amino-5-chloro-2-ethoxy-N [[4-(4-fluorobenzyl)-2-morpholinyl]methyl]benzamide citrate, AS-4370, CAS 112885-42-4), a novel gastrokinetic agent, were studied with 14C-labeled compound in male rats during and after 21 consecutive daily oral administration at a dose of 10 mg/kg/d. After the first administration, plasma radioactivity concentrations were essentially equal to those in the single dose experiment, including the maximum concentration (Cmax; 1130 ng eq./ml) at 1 h. Plasma concentrations at 1 h after each administration were virtually constant in the range of 770-1350 ng eq./ml for 21 days. On the other hand, the plasma concentration at 24 h gradually increased for 6-7 days to about 120 ng eq./ml and became substantially constant, suggesting that apparent steady state was achieved by around 7 consecutive daily administration. Plasma concentration reached Cmax of 1230 ng eq./ml at 0.5 h after the 21st administration and decreased biphasically with half-lives of 3.4 h (t1/2 alpha) and 14.9 h (t1/2 beta). t1/2 alpha was virtually similar but t1/2 beta was about 2 times longer compared with single dose experiment. About 40% and 55% of dose radioactivity were excreted in urine and feces, respectively, for 21 days and radioactivity was almost completely excreted within 168 h after the last administration. The analysis by thin layer chromatography elucidated that composition of radioactive metabolites in plasma and urine after repeated administration was similar to that in the single dose study.(ABSTRACT TRUNCATED AT 250 WORDS)

Dependence of cellular energy metabolism on the intracellular pH of isolated rabbit parietal cells.

The cellular energy metabolism under various extracellular pH (pHe) was investigated in parietal cells isolated from rabbit gastric mucosae. Activity of parietal cells was checked by measuring effects of histamine and db-cAMP on the accumulation of aminopyrine in the intracellular canaliculi. The relationship between the intracellular pH (pHi) and pHe was determined by using a fluorescence probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) in suspensions of isolated parietal cell. The pHi was a linear function of pHe and it changed by 0.63 pH unit per 1.0 unit change in pHe. The internal [H+] was equal to the external [H+] at approximately pH 7.0. The respiratory rate of the cell depended on pHi. Values of [ATP] + [ADP] and intracellular inorganic phosphoric acid [Pi] were almost independent of pHi, whereas the [ATP]/[ADP] ratio decreased with increase in pHi. In addition, the standard free energy of ATP(delta Go'ATP) decreases as pHi increases. The calculated available free energy of ATP, which is the sum of delta Go'ATP and -RTlog[ATP]/([ADP] [Pi]), was independent of pHi in the range from pHi 6.2 to 7.6 and its value was about -11.7 kcal/mol. Furthermore, [ATP], [ADP], and [Pi] in the intracellular space were not affected by the presence of histamine or dibutyryl cAMP in media. It was indicated that the available free energy of ATP did not change in the transformation from resting to acid-secreting states, and the phosphorylation potential might have an important role in control of homeostasis in energy metabolism.