Pharmacokinetic disposition of anagliptin, a novel dipeptidyl peptidase-4 inhibitor, in rats and dogs.

The pharmacokinetic disposition of anagliptin, an orally active and highly selective dipeptidyl peptidase-4 (DPP-4) inhibitor was evaluated in male rats and dogs. Anagliptin was well absorbed in dogs (70.4 %) and moderately to well absorbed in rats ranging from 38.1 to 85.5 % depending on the dose. In situ testing indicated that anagliptin absorption from rat intestine was apparently limited by P-glycoprotein. The absorbed radioactivity was distributed rapidly throughout the body, and high levels of radioactivity were found in the tissues expressing DPP-4 at high levels, especially small intestine, kidney and liver. In both species, the major circulating component was unchanged anagliptin; major circulating metabolites were M1 resulting from hydrolysis of the cyano group and M6 and M7, both of which resulting from the oxidation-cleavage of the methylene function adjacent to the amine. After intravenous dosing, urinary excretion of radioactivity was the major route of elimination for rats (64.6 %) and dogs (66.2 %), and biliary excretion was demonstrated to be an important pathway in rats (25.2 %). The total recovery was good (97.5-99.5 %) and most of the radioactivity was excreted by 24 h in both species. The renal clearance of unbound anagliptin in rats (91.7 ml/min/kg) was much higher than the glomerular filtration rate, indicative of active renal elimination.

Effect of a newly developed ketolide antibiotic, telithromycin, on metabolism of theophylline and expression of cytochrome P450 in rats.

The effects of a newly-developed ketolide antibiotic, telithromycin, on the metabolism of theophylline and the expression of hepatic cytochrome P450 (CYP) 1A2 and CYP3A2 were investigated in rats. Telithromycin at a high dose (100 mg/kg of body weight) was injected intraperitoneally once a day for 3 days. Twenty-four hours (day 4) after the final administration of telithromycin, theophylline (10 mg/kg) was administered intravenously. The presence of telithromycin significantly delayed the disappearance of theophylline from plasma. Parameters related to the pharmacokinetic interaction between theophylline and telithromycin were examined by noncompartmental methods. A significant decrease in the systemic clearance of theophylline was observed in the presence of telithromycin. Pretreatment with telithromycin significantly decreased the metabolic clearance of the major metabolites, 1-methyluric acid and 1,3-dimethyluric acid, with no change in the renal clearance of theophylline, suggesting that the decreased systemic clearance of theophylline by telithromycin is due to reduction of their metabolic clearance. Pretreatment with telithromycin significantly decreased the activity of 7-ethoxyresorufin O-deethylation and testosterone 6 beta-hydroxylation, suggesting that telithromycin decreases the activity of hepatic CYP1A2 and CYP3A2. Western blot analysis revealed that telithromycin significantly decreased the protein levels of CYP1A2 and CYP3A2 in the liver, which could explain the observed decreases in the systemic clearance of theophylline and metabolic clearance of 1-methyluric acid and 1,3-dimethyluric acid. The present study suggests that telithromycin at the dose used in this study alters the pharmacokinetics and metabolism of theophylline, due to reductions in the activity and expression of hepatic CYP1A2 and CYP3A2.

Role of tumor necrosis factor-alpha in down-regulation of hepatic cytochrome P450 and P-glycoprotein by endotoxin.

We investigated the role of tumor necrosis factor-alpha (TNF-alpha) in the down-regulation of hepatic P-glycoprotein and cytochrome P450 (CYP) by endotoxin, using TNF-alpha gene-deficient (TNF-alpha-/-) mice. In the case of P-glycoprotein, endotoxin (10 mg/kg) significantly decreased the expression of hepatic P-glycoprotein in wild-type mice 6 h, but not 24 h, after intraperitoneal injection, with no significant differences in the constitutional expression of P-glycoprotein between wild-type mice and TNF-alpha-/- mice. However, endotoxin had no effect on the expression of P-glycoprotein in TNF-alpha-/- mice either 6 or 24 h after injection. When doxorubicin was administered intravenously to TNF-alpha-/- mice treated 6 h earlier with and without endotoxin, no significant differences in the plasma concentrations of doxorubicin 3 h after injection were observed between endotoxin-treated and untreated TNF-alpha-/- mice. These results suggest that TNF-alpha plays a pivotal role in the down-regulation of P-glycoprotein by endotoxin. In the case of CYP, the constitutive expression of hepatic CYP3A2 and CYP2C11 had a tendency to decline in TNF-alpha-/- mice compared with that in wild-type mice. Endotoxin significantly decreased the expression of hepatic CYP3A2 and CYP2C11 in wild-type mice 24 h after injection, and that decreased expression was significantly greater in TNF-alpha-/- mice than wild-type mice. When antipyrine was administered intravenously to wild-type mice and TNF-alpha-/- mice treated 24 h earlier with endotoxin, the plasma concentrations of antipyrine in TNF-alpha-/- mice 3 h after injection were significantly higher than those in wild-type mice. These findings suggest that TNF-alpha plays a key role in endotoxin-induced down-regulation of hepatic P-glycoprotein, as well as plays a protective role in the regulation of hepatic CYP3A2 and CYP2C11 against endotoxin-induced acute inflammatory response. In TNF-alpha-/- mice, other cytokines appear to function as compensation for the lack of endogenous TNF-alpha.

Possible involvement of P-glycoprotein in renal excretion of pazufloxacin in rats.

The present study aims to investigate whether pazufloxacin, a new quinolone antimicrobial agent, is a substrate for P-glycoprotein in vitro, and whether it is excreted from kidney by P-glycoprotein and/or multidrug resistance-associated protein (Mrp2) in vivo. The in vitro experiments showed that the intracellular accumulation of pazufloxacin in adriamycin-resistant human chronic myelogenous leukemia cells (K562/ADR) overexpressing P-glycoprotein was significantly lower than that in human chronic myelogenous leukemia cells (K562/S) not expressing P-glycoprotein. When rats received an intravenous injection of pazufloxacin in combination with or without cyclosporine, cyclosporine significantly delayed the disappearance of pazufloxacin from plasma and decreased the systemic clearance and volume of distribution at steady state of pazufloxacin to 50% and 70% of the corresponding control values, respectively. Renal handling experiments revealed that the renal clearance of pazufloxacin was 75% of that corresponding to the systemic clearance, suggesting that the main route of pazufloxacin elimination is the kidney. Cyclosporine significantly increased the steady-state concentration of pazufloxacin in plasma by decreasing the tubular secretion clearance and glomerular filtration rate. These results suggest the possibility that pazufloxacin is excreted into the urine via P-glycoprotein. No significant differences in the renal and tubular secretion clearances of pazufloxacin were observed between normal rats and Eisai hyperbilirubinemic rats (EHBR), which have a hereditary deficiency in Mrp2, indicating the lack of the involvement of Mrp2 in the renal excretion of pazufloxacin. Sparfloxacin, a P-glycoprotein substrate, also significantly decreased the renal and tubular secretion clearances of pazufloxacin, suggesting that pazufloxacin and sparfloxacin share the same transporters, including P-glycoprotein. The present study at least suggests that pazufloxacin is excreted into the urine via P-glycoprotein and some active drug transporters other than Mrp2.

Azithromycin reverses anticancer drug resistance and modifies hepatobiliary excretion of doxorubicin in rats.

The present study aims to investigate whether azithromycin reverses P-glycoprotein-dependent anticancer drug resistance in vitro and modifies the hepatobiliary excretion of doxorubicin, a substrate for P-glycoprotein in vivo. Azithromycin increased dose-dependently the intracellular accumulation of doxorubicin in adriamycin-resistant human myelogenous leukemia cells (K562/ADR) with no effect on the expression of P-glycoprotein in the cells. However, the inhibitory effect was much weaker than that of cyclosporin A and was comparable to that of erythromycin. When Sprague-Dawley (SD) rats, which have drug transporting P-glycoprotein and multidrug resistance-associated protein 2 (Mrp2) in the bile canalicular membrane of hepatocytes, received an infusion of doxorubicin, the steady-state biliary clearance of doxorubicin was significantly decreased for 40 min after a single intravenous injection of azithromycin. However, azithromycin did not increase the plasma concentration of doxorubicin. The biliary clearance of doxorubicin in Eisai hyperbilirubinemic rats (EHBRs), which have a hereditary deficiency in Mrp2, was significantly decreased compared with that in Sprague-Dawley rats, suggesting the involvement of Mrp2 in the biliary excretion of doxorubicin. The present findings suggest that azithromycin overcomes P-glycoprotein-dependent anticancer drug resistance of tumors by inhibiting the binding of doxorubicin to P-glycoprotein in K562/ADR cells and inhibits the hepatobiliary excretion of drugs that are substrates for P-glycoprotein and Mrp2.