Kazuhiko Hanada

Decreased Expression of Cytochromes P450 1A2, 2E1, and 3A4 and Drug Transporters Na+-Taurocholate-Cotransporting Polypeptide, Organic Cation Transporter 1, and Organic Anion-Transporting Peptide-C Correlates with the Progression of Liver Fibrosis in Chronic Hepatitis C Patients

Patients with chronic hepatitis C viral infection underwent liver biopsies and laboratory studies for evaluation and to determine subsequent treatment. Changes in status of drug metabolism and disposition may vary with chronic hepatitis C stage and should be assessed. Total RNA was extracted from liver biopsy specimens (n = 63) and reverse transcribed to yield cDNA. Relative mRNA levels of drug-metabolizing enzymes, transporters, nuclear receptors, and proinflammatory cytokines were analyzed with normalization to glyceraldehyde 3-phosphate dehydrogenase expression. mRNAs encoding cytochromes P450 1A2, 2E1, and 3A4, and drug transporters, Na+-taurocholate-cotransporting polypeptide, organic anion-transporting peptide-C, and organic cation transporter 1 showed remarkable decreases, and tumor necrosis factor-α showed an increase according to fibrosis stage progression. HepG2 cells and primary hepatocytes of two human individuals were treated with interleukin 1β, interleukin 6, or tumor necrosis factor-α. CYP1A2 and Na+-taurocholate-cotransporting polypeptide mRNA levels significantly decreased in HepG2 cells with interleukin 1β and interleukin 6 treatments. CYP2E1 and organic cation transporter 1 mRNA levels significantly decreased with tumor necrosis factor-α treatment only in HepG2. These results suggested that down-regulation of CYP1A2, 2E1, and 3A4, and drug transporters, Na+-taurocholate-cotransporting polypeptide, organic anion-transporting peptide-C, and organic cation transporter 1, manifested in livers of patients with chronic hepatitis C viral infection, was associated, at least in part, with the elevated production of proinflammatory cytokines, including tumor necrosis factor-α.

Comparison of Pharmacokinetics and Pharmacodynamics of Docetaxel and Cisplatin in Elderly and Non-Elderly Patients: Why Is Toxicity Increased in Elderly Patients?

PURPOSE Following phase I studies of docetaxel and cisplatin in patients with non-small-cell lung cancer, the recommended doses of docetaxel were different for elderly (> or = 75 years) and non-elderly (< 75 years) patients. To elucidate the mechanism of the difference, the pharmacokinetics of docetaxel and cisplatin were investigated in two phase II studies separately conducted in elderly and non-elderly patients. PATIENTS AND METHODS Twenty-seven elderly and 25 non-elderly patients were treated with three weekly administrations of docetaxel and cisplatin every 4 weeks. Doses of docetaxel were 20 and 35 mg/m(2) for elderly and non-elderly patients, respectively. All patients received 25 mg/m(2) of cisplatin. The pharmacokinetics and pharmacodynamics of docetaxel and cisplatin were compared in elderly and non-elderly patients. RESULTS There were no differences in pharmacokinetics of docetaxel or cisplatin between elderly versus non-elderly patients with regard to clearance and volume of distribution. In the pharmacodynamic analysis, neutropenia was positively correlated with the area under the concentration-time curve for docetaxel but not for cisplatin. In evaluating the relationship between neutropenia and the area under the concentration-time curve of docetaxel, elderly patients experienced greater neutropenia than those predicted by a pharmacodynamic model developed in non-elderly patients; the residual for prediction of the percent change in neutrophil count was -11.2% (95% CI, -21.8 to -0.5%). CONCLUSION The pharmacokinetics of docetaxel and unchanged cisplatin were not different between elderly and non-elderly patients. The elderly patients were more sensitive to docetaxel exposure than the non-elderly patients, resulting in the different recommended doses for the phase II studies.

Enantioselective Binding of Propranolol, Disopyramide, and Verapamil to Human α1‐Acid Glycoprotein

We investigated the binding of propranolol (PL), disopyramide (DP), and verapamil (VP) enantiomers by human alpha(1)-acid glycoprotein (AGP; also called orosomucoid) and the relationships between the extent of drug binding and lipophilicity, desialylation, and genetic variants of AGP. Desialylation had little effect on the affinity of AGP for the drugs tested. The percentage binding correlated significantly with the partition coefficients for the drugs tested. Each enantiomer was competitively displaced from AGP by another enantiomer of the same drug, suggesting that they bind to the same site. However, the enantiomers bound to AGP with stereospecific affinities; the (-)-isomers of DP and VP had higher Kd values (4.27 and 4.97 microM, respectively) than the (+)-isomers (1.51 and 2.48 microM, respectively). When enantiomers of the different drugs were used in competitive binding experiments, VP binding was only partially inhibited by DP. This result suggested that drug binding is specific to different variants of AGP (A, F1, S). DP was found to specifically bind to variant A, whereas PL and VP bind to both A and F1/S variants.

Enantioselective tissue distribution of the basic drugs disopyramide, flecainide and verapamil in rats : Role of plasma protein and tissue phosphatidylserine binding

AbstractPurpose. The stereoselective distribution of three basic drugs, disopyramide (DP), flecainide (FLC) and verapamil (VP), was studied to clarify the relationships between the tissue-to-unbound plasma concentration ratio (Kpf) and drug lipophilicity and binding to phosphatidylserine (PhS), which are possible factors determining the tissue distribution of these drug enantiomers. Methods. The drug enantiomer or racemate was administered to rats by intravenous constant infusion. Their concentrations in plasma and tissues were determined using enantioselective high-performance liquid chromatography. Plasma protein binding, and buffer-octanol and buffer-hexane containing PhS partition coefficients were also determined. Results. The stereoselectivity of the tissue-to-plasma concentration ratio (Kp) was partly associated with that of serum protein binding. However, the Kpf value of R( + )-VP in the lung was significantly higher than that of S(−)-VP. A linear correlation was observed between the Kpf values of these drug enantiomers in brain, heart, lung and muscle, and their buffer-hexane containing PhS partition coefficients. The in vitrodata for the binding of these drugs to PhS suggest that stereoselective binding of VP to PhS may correspond to its stereoselective tissue binding. Conclusions. Our findings provide some evidence for a role of tissue PhS in the tissue distribution of basic drugs with respect to stereoselectivity of drug enantiomers distribution.

Effects of Indoxylsulfate on the in vitro Hepatic Metabolism of Various Compounds Using Human Liver Microsomes and Hepatocytes

Background: Alterations of hepatic drug metabolism in patients with renal failure are poorly understood. In this study, the effects of uremic substances that can be removed by hemodialysis on in vitrohepatic drug metabolism were studied using human liver microsomes and hepatocytes. Methods: The metabolism of various compounds that undergo oxidation and glucuronidation in the liver was studied using human liver microsomes and hepatocytes in the presence of 11 uremic substances removable by hemodialysis. Results: The formation of resorufin from ethoxyresorufin was inhibited by 3-indoxylsulfate and 3-indoleacetic acid. The formation of 6β-hydroxytestosterone from testosterone was inhibited only by 3-indoxylsulfate. These uremic substances reduced the maximum metabolic rate but not the affinity, suggesting that the inhibitory mechanism was noncompetitive. The inhibition of formation of resorufin and 6β-hydroxytestosterone by 3-indoxylsulfate was also observed in human hepatocytes. The elimination of nicardipine in liver microsomes was decreased significantly in the presence of 3-indoxylsulfate and 3-indoleacetic acid. Conclusion: The hepatic metabolism of certain drugs may be inhibited directly by uremic substances such as 3-indoxylsulfate that accumulate in the plasma in patients with chronic renal failure.

Intestinal first-pass metabolism of eperisone in the rat.

AbstractPurpose. The purpose of this study was to clarify quantitatively the contribution of the intestine to the first-pass metabolism of eperisone in rats. Methods. The systemic availabilities of eperisone were estimated by administering the drug into the duodenum, portal vein, and femoral vein in rats in vivo. The first-pass metabolism of eperisone was confirmed in the perfused rat small intestine in situ. Metabolism of eperisone to an ω-1-hydroxylated metabolite (HMO), the first step of eperisone metabolism, was studied using rat intestinal microsomes in vitro. Results. The bioavailabilities in the intestine were 0.176 and 0.0879 at administration rates of 100 and 25 mg/h/kg, respectively, whereas those in the liver were 0.532 and 0.486, respectively. In the intestinal perfusion experiment, the appearance clearance to the portal vein from the intestinal lumen was much lower than the elimination clearance from the intestinal lumen, resulting in high metabolic clearance of eperisone in the small intestine. Eperisone was biotransformed to HMO by rat intestinal microsomes, and this was inhibited by α-naphthoflavone and an anti-rat CYP1A antibody. Conclusions. Those data strongly suggest that eperisone may be metabolized to HMO by CYP1A in rat intestinal microsomes during the first-pass through the epithelium of the small intestine.

Quantitative determination of unchanged cisplatin in rat kidney and liver by high-performance liquid chromatography

A quantitative analytical method for measuring unchanged cisplatin (CDDP) and high- and low-molecular-mass metabolites (fixed and mobile metabolites) in rat kidney and liver was developed. Unchanged CDDP, separated from fixed and mobile metabolites in tissue homogenates by consecutive procedures of fractionation and ultrafiltration, was determined by high-performance liquid chromatography (HPLC) with post-column derivatization. Although unchanged CDDP was found to be partly metabolized to fixed metabolites during the preparation of cytosolic ultrafiltrates, the recovery of unchanged CDDP gave a constant value (about 70%), which was independent of tissue type and CDDP concentration (from 1 to 10 micrograms/ml). The detection limit for unchanged CDDP in the cytosolic ultrafiltrate was 20 ng/ml, corresponding to a concentration detection limit of 65 ng Pt per g of tissue in the kidney and liver. The concentrations of fixed and mobile metabolites were determined as platinum concentrations in the tissue homogenate and in the cytosolic ultrafiltrate using atomic absorption spectrometry after correcting for transformation of unchanged CDDP to fixed metabolites. The distribution of unchanged CDDP, mobile metabolites and fixed metabolites in rat kidney and liver, after bolus injection of CDDP (5 mg/kg), was determined using this method.

Pharmacokinetics and toxicodynamics of cisplatin and its metabolites in rats : Relationship between renal handling and nephrotoxicity of cisplatin

The renal handling of cisplatin and its metabolites and the relationship between the pharmacokinetics of these platinum species in the kidney and nephrotoxicity in rats were studied by carrying out pharmacokinetic‐pharmacodynamic analysis.

Effect of trimethoprim on the renal clearance of lamivudine in rats.

Lamivudine undergoes minimal metabolism and renal clearance of the unchanged drug is the predominant mechanism of clearance. The effect of trimethoprim on the renal clearance of lamivudine was investigated in rats in‐vivo.

Stereoselective First-Pass Metabolism of Verapamil in the Small Intestine and Liver in Rats

Verapamil (VP) is used as a racemate but shows stereoselective pharmacokinetics and pharmacodynamics. It undergoes extensive first-pass metabolism. Stereoselective first-pass metabolism in the intestine and liver was investigated in vivo and in vitro to determine its impact on the disposition of VP and its main metabolite, norverapamil (NVP). VP racemate was administered to rats i.v., p.o., and via the portal vein. The formation rates of the main metabolites of the VP enantiomers were estimated in an in vitro intestinal microsomal study. The hepatic bioavailability of VP showed saturable metabolism, and the hepatic bioavailability of R-VP was higher than that of S-VP. Conversely, the intestinal bioavailability of R-VP was lower than that of S-VP, resulting in a higher systemic bioavailability of S-VP. The pharmacokinetics of the NVP enantiomers was similar. These results suggest that the stereoselectivity of the total bioavailability of VP is determined by first-pass metabolism in the small intestine and liver, and that the NVP enantiomers observed in the systemic circulation after p.o. administration of VP racemate originate mainly from the liver in rats.