Serum aminotransferase activity as a predictor for estimation of total clearance of hepatically metabolized drugs in rats with acute hepatic failure

Altered tolbutamide pharmacokinetics by a decrease in hepatic expression of CYP2C6/11 in rats pretreated with 5-fluorouracil

1. We investigated the change in the pharmacokinetic profile of tolbutamide (TB), a substrate for CYP2C6/11, 4 days after single administration of 5-fluorouracil (5-FU), and the hepatic gene expression and activity of CYP2C6/11 were also examined in 5-FU-pretreated rats. 2. Regarding the pharmacokinetic parameters of the 5-FU group, the area under the curve (AUC) was significantly increased, and correspondingly, the elimination rate constant at the terminal phase (k_e) was significantly decreased without significant change in the volume of distribution at the steady state (Vd_ss). 3. The metabolic production of 4-hydroxylated TB in hepatic microsomes was significantly reduced by the administration of 5-FU. 4. The expression level of mRNAs for hepatic CYP2C6 and CYP2C11 was significantly lower than in the control group when the rats were pretreated with 5-FU. 5. These results demonstrated that the pharmacokinetic profile of TB was altered by the treatment with 5-FU through a metabolic process, which may be responsible for the decreased CYP2C6/11 expression at mRNA levels.

Decreased elimination clearance of midazolam by doxorubicin through reductions in the metabolic activity of hepatic CYP3A in rats

1. We examined the effects of doxorubicin (DOX) on the expression level and metabolic activity of CYP3A in the liver as well as on the pharmacokinetics of midazolam (MDZ), a probe for CYP3A, in rats. Changes in the hepatic status of DOX-treated rats were confirmed. 2. Serum levels of the biomarkers of hepatic impairment were elevated by the DOX treatment, which was consistent with the results obtained from a histopathological evaluation of the liver. 3. No significant difference was observed in the expression of proteins for hepatic CYP3A1 and CYP3A2 between the DOX and control groups. The metabolic production of 1'-hydroxylated and 4'-hydroxylated MDZ by hepatic microsomes was significantly lower in DOX-treated rats than in control rats. 4. The area under the curve (AUC) and the half-life (t1/2) of intravenously administered MDZ were significantly increased, and the total clearance (CLtot) and the elimination rate constant at the terminal phase (ke) were significantly decreased without significant changes in the volume of distribution at a steady state (Vdss). 5. These results indicated that a DOX-induced depression in the metabolic activity, but not expression level of CYP3A contributed to a decrease in the elimination clearance of MDZ, and also that reduced CYP3A function may be associated with the hepatotoxicity of DOX.

Improved efficacy and reduced toxicity of doxorubicin encapsulated in sulfatide-containing nanoliposome in a glioma model

As a glycosphingolipid that can bind to several extracellular matrix proteins, sulfatide has the potential to become an effective targeting agent for tumors overexpressing tenasin-C in their microenvironment. To overcome the dose-limiting toxicity of doxorubicin (DOX), a sulfatide-containing nanoliposome (SCN) encapsulation approach was employed to improve treatment efficacy and reduce side effects of free DOX. This study analysed in vitro characteristics of sulfatide-containing nanoliposomal DOX (SCN-DOX) and assessed its cytotoxicity in vitro, as well as biodistribution, therapeutic efficacy, and systemic toxicity in a human glioblastoma U-118MG xenograft model. SCN-DOX was shown to achieve highest drug to lipid ratio (0.5∶1) and a remarkable in vitro stability. Moreover, DOX encapsulated in SCN was shown to be delivered into the nuclei and displayed prolonged retention over free DOX in U-118MG cells. This simple two-lipid SCN-DOX nanodrug has favourable pharmacokinetic attributes in terms of prolonged circulation time, reduced volume of distribution and enhanced bioavailability in healthy rats. As a result of the improved biodistribution, an enhanced treatment efficacy of SCN-DOX was found in glioma-bearing mice compared to the free drug. Finally, a reduction in the accumulation of DOX in the drug's principal toxicity organs achieved by SCN-DOX led to the diminished systemic toxicity as evident from the plasma biochemical analyses. Thus, SCN has the potential to be an effective and safer nano-carrier for targeted delivery of therapeutic agents to tumors with elevated expression of tenascin-C in their microenvironment.

Use of hepatotoxic drugs in chronic liver disease

Cirrhosis and chronic liver disease are common illnesses that cause high mortality and require treatment. Medication use in these patients may be challenging because of idiosyncratic or dose-dependent drug toxicity. Therefore, drug choice and drug dose adaptations play an important role. The objective of this clinical review is to discuss the literature about and challenges in drug use in patients with chronic liver disease. To make good decisions regarding drug choice and dose adjustments in these patients, well-defined clinical information about diagnoses and laboratory results (creatinine, international normalized ratio, bilirubin, and serologies) as well as in some instances, pathological findings like liver biopsies are needed. In a second step, these data should be organized in electronically supported clinical decision systems, which can then assist providers in making choices about medication selection and dosage. In summary, although substantial research has been done in the field of drug use in patients with liver dysfunction, a great deal also remains to be learned. Although many of these patients can now be identified, it is still very difficult to assess their individual level of hepatic function. The degree of risk associated with drug use and how best to use medications in these patients represents an important area for further study. In the future, pharmacogenomics and electronic linking of clinical data may well prove helpful for making decisions about optimal drug choices in this complex group of patients.

Influence of chronic hepatic failure on disposition kinetics of valproate excretion through a phase II reaction in rats treated with carbon tetrachloride

The influence of chronic hepatic failure on the disposition kinetics of valproate (VPA) excretion via a phase II reaction was examined in rats treated with carbon tetrachloride (1.0 mg/kg, s.c., 3 times a week) for 2 or 3 months. There was no significant difference in the plasma concentration-time courses of VPA among the control and two treated groups up to 120 min after i.v. administration of VPA (75 mg/kg), but subsequently the plasma concentrations of the treated groups declined significantly below the control levels. Expression of Mrp2 mRNA in the liver of the treated groups was significantly lower than in the control group; conversely that in the kidney was significantly higher. The enzyme activity of UGTs in the liver of the treated groups decreased significantly, but UGT1A8 mRNA expression in the duodenum was increased about 3-fold. Cumulative excretion of VPA glucuronide (VPA-G) in bile of the treated groups was reduced significantly, while that in urine was markedly increased. In conclusion, the area under the VPA plasma concentration-time curve was decreased significantly in rats with chronic hepatic failure owing to increased excretion of VPA-G via the kidney as a result of induction of Mrp2, and inhibition of enterohepatic circulation of VPA-G.