Influence of concurrent and staggered dosing of semi-solid nutrients on the pharmacokinetics of orally administered carbamazepine in rats.

In the present study, we examined the effects of concurrent and staggered dosing of PG-soft ace-MP TM (PG), novel semi-solid enteral nutrients, on the pharmacokinetics of orally administered carbamazepine (CBZ) in rats due to the high possibility of drug interaction during the absorption process. The pharmacokinetic behavior of CBZ was considerably altered when administered concurrently with PG. The maximum serum CBZ concentration (Cmax) significantly decreased and the mean residence time (MRT) significantly increased. The elimination constant (ke) also significantly increased, but there were no significant changes in the area under the serum CBZ concentration versus time curve (AUC) and the time to reach Cmax (Tmax). However, these changes in the pharmacokinetic parameters were eliminated by waiting 20 min, the time interval equivalent to the Tmax described above, between CBZ administration and PG dosing. This study suggested that PG interferes with CBZ absorption from the digestive tract, although staggered administration of CBZ and PG prevented their interaction.

Reduced cytotoxicity in doxorubicin-exposed HepG2 cells pretreated with menthol due to upregulation of P-glycoprotein.

The aim of the present study was to examine changes in the expression and activity of P-glycoprotein (P-gp) in human hepatocellular carcinoma HepG2 cells after exposure to menthol, and their relationship to the cytotoxicity of and apoptotic responses to doxorubicin (DOX), a substrate of P-gp, in the cells. The expression of P-gp in HepG2 cells was significantly increased by menthol treatment. Intracellular accumulation of DOX in HepG2 cells was significantly lower in the menthol-treated group than in the control group, but this phenomenon was abolished in the presence of verapamil. Decreased cell viability by DOX was significantly attenuated by 24-h menthol treatment prior to DOX exposure, which coincided with the changes in mRNA expression of Bcl-xl and caspase-3. These results demonstrate that menthol causes hepatocellular carcinoma cells to acquire resistance to DOX by increasing its efflux through the upregulation of P-gp.

Downregulation of organic cation transporter 1 and breast cancer resistance protein with the induction of Pregnane X receptor in rat kidney impaired by doxorubicin.

Transporters expressed in the kidney play an important role in the excretion of endogenous substances and chemical drugs. The Pregnane X receptor (PXR) has been reported to be involved in regulating the expression of numerous transporters. In the present study, we examined the alteration in expression level of PXR, organic cation transporter 1 (OCT1) and breast cancer resistance protein (BCRP) in renal cell lines of rat origin and the kidney of rats when damaged by doxorubicin (DOX). The expression level of PXR in renal tubular epithelium NRK-52E cells was significantly increased by DOX at a concentration confirmed to cause cellular damage. The expression levels of OCT1 and BCRP were significantly lower in the DOX-treated cells than in the untreated cells. In model rats with DOX-induced nephrotoxicity, the alterations in renal expression of PXR, OCT1 and BCRP were similar to those in NRK-52E cells, although there was a difference in the degree of the changes.

Higher gene expression of CYP1A2, 2B1 and 2D2 in the brain of female compared with male rats.

Cytochrome P450 (CYP) in the brain plays an essential role in the local metabolism of various compounds, including clinically used drugs, toxins, and endogenous substances. In the present study, we compared the expression profiles of mRNAs for several CYP subtypes in the brain between male and female rats. The expression of CYP1A2, CYP2B1, and CYP2D2 in females was significantly higher than that in males. On the other hand, the expression level of the other CYP subtypes examined in the male brain was similar to that in the female brain. These results strongly suggest that marked gender differences exist in the expression profiles of some CYP subtypes in rat brain.

Taurine as a protective agent for 5-fluorouracil-induced hepatic damage related to oxidative stress.

5-Fluorouracil (5-FU) is a pyrimidine analog widely used for the treatment of various cancers, but often causes hepatic damage in clinical practice. In this study, we examined the influence of taurine on 5-FU-induced hepatotoxicity in mice with respect to changes in oxidative stress. Elevations in the aspartate aminotransferase and alanine aminotransferase serum levels after 5-FU administration were significantly suppressed in a dosedependent manner by concurrent treatment with taurine. The activity of superoxide dismutase and reduced glutathione content in the liver were significantly decreased following treatment with 5-FU alone, but these changes were markedly inhibited by the administration of taurine. Our findings suggest that taurine protects against 5-FU-induced hepatotoxicity by suppressing oxidative stress.