Pharmacokinetics and disposition of CS-8958, a long-acting prodrug of the novel neuraminidase inhibitor laninamivir in rats

CS-8958, a prodrug of laninamivir (R-125489), is currently under development as an inhaled anti-influenza drug. In this study, the pharmacokinetics and disposition of CS-8958 were characterized in rats. After intratracheal administration of 14C-CS-8958, radioactivity was retained over long periods in the target tissues (trachea and lung) as its active metabolite R-125489 - 19.12% of the dose was retained in the lung at 24 h. After intratracheal administration of CS-8958, plasma R-125489 concentration was slowly eliminated, and its half-life (14.1 h) was considerably longer than that after intravenous administration of R-125489. The radioactivity of intratracheally administered 14C-CS-8958 was mainly excreted into the urine (67.5% of dose), and this excretion lasted over long periods. R-125489 accounted for most of the urinary radioactivity recovered after 24 h. These results demonstrated that CS-8958 administered intratracheally to rats was converted/hydrolysed to R-125489 in the target tissues, and that the R-125489 was slowly excreted into the urine via an absorption rate-limiting process. Such distinctive pharmacokinetics attributed to the slow release of R-125489 suggests the potential for a long-acting anti-influenza drug.

Identification of valproic acid glucuronide hydrolase as a key enzyme for the interaction of valproic acid with carbapenem antibiotics

Plasma levels of valproic acid (VPA) are decreased by concomitant use with carbapenem antibiotics, such as panipenem (PAPM). One of the plausible mechanisms of this interaction is the inhibition of VPA glucuronide (VPA-G) hydrolysis by carbapenems in the liver. To elucidate this interaction mechanism, we purified VPA-G hydrolase from human liver cytosol, in which the hydrolytic activity was mainly located. After chromatographic purification, the VPA-G hydrolase was identified as acylpeptide hydrolase (APEH). APEH-depleted cytosol, prepared by an immunodepletion method, completely lacked the hydrolytic activity. These results demonstrate that APEH is a single enzyme involved in PAPM-sensitive VPA-G hydrolysis in cytosol. In addition, the hydrolytic activity of recombinant human APEH was inhibited by PAPM and the inhibition profile by typical esterase inhibitors (diisopropyl fluorophosphate, 5,5'-dithiobis(2-nitrobenzoic acid), p-chloromercuribenzoic acid, and d-saccharic acid 1,4-lactone) was similar to that of human liver cytosol. Cytosolic VPA-G hydrolase activity was slightly inhibited by cholinesterase and carboxylesterase inhibitors. beta-Glucuronidase activity remained in APEH-depleted cytosol, whereas VPA-G hydrolase activity was completely abolished. Thus, either cholinesterase, carboxylesterase, or beta-glucuronidase in cytosol would not be involved in VPA-G hydrolysis. Taken together, APEH plays a major role in the PAPM-sensitive VPA-G hydrolysis in the liver. These findings suggest that APEH could be a key enzyme for the drug interaction of VPA with carbapenems via VPA-G hydrolysis.

Identification of the human cytochrome P450 enzymes involved in the two oxidative steps in the bioactivation of clopidogrel to its pharmacologically active metabolite

The aim of the current study is to identify the human cytochrome P450 (P450) isoforms involved in the two oxidative steps in the bioactivation of clopidogrel to its pharmacologically active metabolite. In the in vitro experiments using cDNA-expressed human P450 isoforms, clopidogrel was metabolized to 2-oxo-clopidogrel, the immediate precursor of its pharmacologically active metabolite. CYP1A2, CYP2B6, and CYP2C19 catalyzed this reaction. In the same system using 2-oxo-clopidogrel as the substrate, detection of the active metabolite of clopidogrel required the addition of glutathione to the system. CYP2B6, CYP2C9, CYP2C19, and CYP3A4 contributed to the production of the active metabolite. Secondly, the contribution of each P450 involved in both oxidative steps was estimated by using enzyme kinetic parameters. The contribution of CYP1A2, CYP2B6, and CYP2C19 to the formation of 2-oxo-clopidogrel was 35.8, 19.4, and 44.9%, respectively. The contribution of CYP2B6, CYP2C9, CYP2C19, and CYP3A4 to the formation of the active metabolite was 32.9, 6.76, 20.6, and 39.8%, respectively. In the inhibition studies with antibodies and selective chemical inhibitors to P450s, the outcomes obtained by inhibition studies were consistent with the results of P450 contributions in each oxidative step. These studies showed that CYP2C19 contributed substantially to both oxidative steps required in the formation of clopidogrel active metabolite and that CYP3A4 contributed substantially to the second oxidative step. These results help explain the role of genetic polymorphism of CYP2C19 and also the effect of potent CYP3A inhibitors on the pharmacokinetics and pharmacodynamics of clopidogrel in humans and on clinical outcomes.

Biotransformation of prasugrel, a novel thienopyridine antiplatelet agent, to the pharmacologically active metabolite

Prasugrel, a novel thienopyridine antiplatelet agent, undergoes rapid hydrolysis in vivo to a thiolactone, R-95913, which is further converted to its thiol-containing, pharmacologically active metabolite, R-138727, by oxidation via cytochromes P450 (P450). We trapped a sulfenic acid metabolite as a mixed disulfide with 2-nitro-5-thiobenzoic acid in an incubation mixture containing the thiolactone R-95913, expressed CYP3A4, and NADPH. Further experiments investigated one possible mechanism for the conversion of the sulfenic acid to the active thiol metabolite in vitro. A mixed disulfide form of R-138727 with glutathione was found to be a possible precursor of R-138727 in vitro when glutathione was present. The rate constant for the reduction of the glutathione conjugate of R-138727 to R-138727 was increased by addition of human liver cytosol to the human liver microsomes. Thus, one possible mechanism for the ultimate formation of R-138727 in vitro can be through formation of a sulfenic acid mediated by P450s followed possibly by a glutathione conjugation to a mixed disulfide and reduction of the disulfide to the active metabolite R-138727.

Human carboxymethylenebutenolidase as a bioactivating hydrolase of olmesartan medoxomil in liver and intestine

Olmesartan medoxomil (OM) is a prodrug type angiotensin II type 1 receptor antagonist widely prescribed as an antihypertensive agent. Herein, we describe the identification and characterization of the OM bioactivating enzyme that hydrolyzes the prodrug and converts to its pharmacologically active metabolite olmesartan in human liver and intestine. The protein was purified from human liver cytosol by successive column chromatography and was identified by mass spectrometry to be a carboxymethylenebutenolidase (CMBL) homolog. Human CMBL, whose endogenous function has still not been reported, is a human homolog of Pseudomonas dienelactone hydrolase involved in the bacterial halocatechol degradation pathway. The ubiquitous expression of human CMBL gene transcript in various tissues was observed. The recombinant human CMBL expressed in mammalian cells was clearly shown to activate OM. By comparing the enzyme kinetics and chemical inhibition properties between the recombinant protein and human tissue preparations, CMBL was demonstrated to be the primary OM bioactivating enzyme in the liver and intestine. The recombinant CMBL also converted other prodrugs having the same ester structure as OM, faropenem medoxomil and lenampicillin, to their active metabolites. CMBL exhibited a unique sensitivity to chemical inhibitors, thus, being distinguishable from other known esterases. Site-directed mutagenesis on the putative active residue Cys¹³² of the recombinant CMBL caused a drastic reduction of the OM-hydrolyzing activity. We report for the first time that CMBL serves as a key enzyme in the bioactivation of OM, hydrolyzing the ester bond of the prodrug type xenobiotics.

Derive right precordial leads at higher intercostal spaces from 12-lead system for diagnosis of Brugada syndrome

Recording the right procordial leads at higher intercostal spaces (ICS) can raise the sensitivity of the diagnosis on Brugada syndrome using ECG. However, the directive measurement of the right precordial leads at the higher ICSs is tedious and impractical. In this paper, we proposed a derivation method based on the information redundancy in the 12-lead system to study the possibility of deriving the right precordial leads at the higher ICSs from the commonly used Mason-Likar 12-lead ECGs. Through the evaluation based on the simulated Brugada-type ECGs and recorded ECGs from BS subjects, we found that the BS characteristic J wave and coved type ST elevation in the right precordial leads at the higher ICSs could be satisfyingly derived from the 12-lead ECGs. It is concluded that the derived precordial leads at the higher ICSs may serve as an assistant diagnosis tool to unmask Brugada syndrome.

A possible mechanism for the differences in efficiency and variability of active metabolite formation from thienopyridine antiplatelet agents, prasugrel and clopidogrel

The efficiency and interindividual variability in bioactivation of prasugrel and clopidogrel were quantitatively compared and the mechanisms involved were elucidated using 20 individual human liver microsomes. Prasugrel and clopidogrel are converted to their thiol-containing active metabolites through corresponding thiolactone metabolites. The formation rate of clopidogrel active metabolite was much lower and more variable [0.164 + or - 0.196 microl/min/mg protein, coefficient of variation (CV) = 120%] compared with the formation of prasugrel active metabolite (8.68 + or - 6.64 microl/min/mg protein, CV = 76%). This result was most likely attributable to the less efficient and less consistent formation of clopidogrel thiolactone metabolite (2.24 + or - 1.00 microl/min/mg protein, CV = 45%) compared with the formation of prasugrel thiolactone metabolite (55.2 + or - 15.4 microl/min/mg protein, CV = 28%). These differences may be attributed to the following factors. Clopidogrel was largely hydrolyzed to an inactive acid metabolite (approximately 90% of total metabolites analyzed), and the clopidogrel concentrations consumed were correlated to human carboxylesterase 1 activity in each source of liver microsomes. In addition, 48% of the clopidogrel thiolactone metabolite formed was converted to an inactive thiolactone acid metabolite. The oxidation of clopidogrel to its thiolactone metabolite correlated with variable activities of CYP1A2, CYP2B6, and CYP2C19. In conclusion, the active metabolite of clopidogrel was formed with less efficiency and higher variability than that of prasugrel. This difference in thiolactone formation was attributed to hydrolysis of clopidogrel and its thiolactone metabolite to inactive acid metabolites and to variability in cytochrome P450-mediated oxidation of clopidogrel to its thiolactone metabolite, which may contribute to the poorer and more variable active metabolite formation for clopidogrel than prasugrel.

Highly frequent anti-idiotype antibody in cynomolgus monkeys developed against mouse-derived regions of anti-Fas antibody humanized by complementarity determining region grafting

BACKGROUND AND PURPOSE

We investigated the immunogenicity of a humanized anti-human Fas monoclonal antibody, R-125224, in cynomolgus monkeys to estimate its efficacy, as well as its toxicity in clinical situations.

EXPERIMENTAL APPROACH

R-125224 was intravenously administered to cynomolgus monkeys at single doses of 0.4, 1.2, 6 and 30 mg kg(-1), and the plasma concentrations of R-125224 and anti-R-125224 antibody (ARA) were measured. We conducted a competitive enzyme-linked immunosorbent assay to determine which part of R-125224 was recognized by ARA. We also examined the retention of radioactivity in mononuclear cells and granulocytes after the injection of [(125)I]-R-125224 to a collagen-induced arthritis monkey model.

KEY RESULTS

After i.v. administration of R-125224, the elimination of the plasma R-125224 concentrations was accelerated at around 10 days post-dose, and 10 of 12 monkeys were ARA positive. From an epitope analysis of ARA, the ARA produced in monkeys recognized the mouse-derived regions located in complementarity determining regions, but could not recognize the human IgG. After the injection of [(125)I]-R-125224 to a collagen-induced arthritis monkey model, a significantly longer retention of the radioactivity in mononuclear cells compared to granulocytes was observed.

CONCLUSIONS AND IMPLICATIONS

In monkeys, the development of antibodies against R-125224 is rapid and highly frequent. Our hypothesis is that this highly frequent development of ARA might be due to the binding of R-125224 to immune cells, and its circulation in monkey blood might contribute to an increase in its chances of being recognized as an immunogen.

11C-methionine PET of acute myocardial infarction

Tissue uptake of l-[methyl-(11)C]-methionine ((11)C-methionine) has been used to monitor amino acid metabolism and protein synthesis. We examined whether (11)C-methionine was retained in areas of myocardial infarction after successful reperfusion.

METHODS

Nine patients with infarction in the left anterior descendent region underwent percutaneous transluminal coronary artery intervention within 24 h and (201)Tl SPECT, (18)F-FDG PET, and (11)C-methionine PET within 2 wk of infarction onset. The standardized uptake values of the infarcted area and of the normal area were measured.

RESULTS

The (11)C-methionine images showed increased uptake in the infarcted area, whereas the (201)Tl SPECT and (18)F-FDG PET images showed decreased uptake. The highest accumulation of (11)C-methionine in the infarcted area was observed during the early phase of AMI.

CONCLUSION

(11)C-methionine uptake is elevated in infarcted areas and may reflect the early acute phase of damage healing, that is, the initial process of remodeling.

Metabolism of ticlopidine in rats: identification of the main biliary metabolite as a glutathione conjugate of ticlopidine S-oxide

We have identified several novel metabolites of ticlopidine, a well known antiplatelet agent and have revealed its metabolic route in rats. The main biliary metabolite of ticlopidine was characterized as a glutathione (GSH) conjugate of ticlopidine S-oxide, in which conjugation had occurred at carbon 7a in the thienopyridine moiety. Quantitative analysis revealed that 29% of the dose was subjected to the formation of reactive intermediates followed by conjugation with GSH after oral administration of ticlopidine (22 mg/kg) to rats. In vitro incubation of ticlopidine with rat liver 9000 g supernatant fraction (S9) fractions led to the formation of multiple metabolites, including 2-oxo-ticlopidine, the precursor for the pharmacologically active ticlopidine metabolite, [1-(2-chlorobenzyl)-4-mercaptopiperidin-(3Z)-ylidene] acetic acid. A novel thiophene ring-opened metabolite with a thioketone group and a carboxylic acid moiety has also been detected after incubation of 2-oxo-ticlopidine with rat liver microsomes or upon incubation of ticlopidine with rat liver S9 fractions.

Culture period-dependent change of function and expression of ATP-binding cassette transporters in Caco-2 cells

The objective of this study was to determine an appropriate culture period to assess whether a compound of interest is transported by efflux transporters such as human multidrug resistance 1 (hMDR1), human multidrug resistance-associated protein 2 (hMRP2), and human breast cancer resistance protein (hBCRP) in Caco-2 cells. Caco-2 cells were cultured on a Transwell for 1 to 6 weeks. The expression of these transporters in the mRNA and protein levels was examined using a real-time polymerase chain reaction and Western blotting, respectively. Transcellular transport activities using digoxin, ochratoxin A, olmesartan, and estrone-3-sulfate were also examined. Except for digoxin, the permeability coefficient (P(app)) ratio of the three compounds at 2 weeks was the highest in the periods tested. The P(app) ratio of digoxin at 2 weeks was higher than that at 3 weeks. The temporal expression profile of each transporter in the mRNA level was similar to that in the protein level, and the functions of hMRP2 and hBCRP were roughly correlated with the expression in the mRNA and protein levels, but that of hMDR1 was not. These data suggest that among all the culture periods evaluated a 2-week culture is the best culture period for transport studies to identify whether a compound is a substrate for hMDR1, hMRP2, and hBCRP.

Exercise-induced QTc-interval changes for predicting improvement in regional blood flow in ischemic myocardium and cardiac output after coronary angioplasty in patients with right bundle-branch block

BACKGROUND

We have previously shown that QT-interval changes are more useful than ST-T changes in evaluating the severity of exercise-induced myocardial ischemia in patients with right bundle-branch block (RBBB).

HYPOTHESIS

The purpose of this study was to evaluate whether the improvement in regional myocardial blood flow (RMBF) in ischemic areas and cardiac output after percutaneous transluminal coronary angioplasty (PTCA) can be predicted by exercise-induced QT-interval changes prior to PTCA.

METHODS

The RMBF and cardiac output were quantified with nitrogen-13 ammonia positron emission tomography at rest and during exercise in 20 patients with RBBB and ischemic heart disease before and 6 months after PTCA, and in 9 healthy volunteers.

RESULTS

Before PTCA, exercise-induced prolongation by < 20 ms or shortening of the Bazett-corrected QT (QTc) interval (454 +/- 38 to 451 +/- 41 ms, p = NS) was observed in 13 patients (Group 1) and prolongation by > or = 20 ms (429 +/- 44 to 466 +/- 50 ms, p < 0.002) was observed in 7 (Group 2). The number of regions of exercise-induced ischemia was significantly greater in Group 2 than in Group 1 (4.0 +/- 1.2 vs. 2.1 +/- 1.2, p < 0.01). The RMBF in regions of exercise-induced ischemia and cardiac output at rest was not significantly different between Groups 1 and 2, whereas during exercise both the parameters were significantly lower in Group 2 than in Group 1 (both p < 0.05). After successful PTCA, RMBF both at rest and during exercise improved significantly in Group 1 (0.67 +/- 0.04 to 0.71 +/- 0.06 ml/min/g, 0.74 +/- 0.05 to 0.84 +/- 0.08 ml/min/g; both p < 0.0001), but did not improve significantly in Group 2 (0.63 +/- 0.05 to 0.65 +/- 0.07 ml/min/g, 0.65 +/- 0.04 to 0.69 +/- 0.11 ml/ min/g; both p = NS). Cardiac output during exercise improved significantly in Group 1 (6.4 +/- 0.7 to 7.4 +/- 0.9 l/min; p < 0.002) but not in Group 2 (5.7 +/- 0.6 to 5.9 +/- 0.6 l/min; p = NS).

CONCLUSIONS

Our results suggest that the marked prolongation of the QTc interval induced by pre-PTCA exercise may predict a lack of improvement in RMBF in ischemic areas and cardiac output after PTCA in patients with RBBB and ischemic heart disease.