Ju-Hee Oh

Effects of experimental hyperlipidaemia on the pharmacokinetics of docetaxel in rats

Hyperlipidaemia correlates with an increased risk of occurrence of various cancers. In this study, the effects of hyperlipidaemia on the pharmacokinetics of docetaxel, a member of the taxane class of anti-cancer drugs, were investigated in rats with experimental hyperlipidaemia; we focused on the alterations in docetaxel metabolism and plasma distribution. Docetaxel (5 mg/kg intravenously (i.v.) and 40 mg/kg per oral (p.o.)) was administered to control rats and rats with poloxamer-407 (P-407)–induced hyperlipidaemia (1 g/kg, intraperitoneally). In vitro studies were conducted on hepatic metabolism in S9 fractions and plasma protein binding using the ultrafiltration method. Hyperlipidaemia dramatically increased the area under the plasma concentration–time curve from time 0 to infinity (AUC0–∞) of docetaxel after i.v. (1.86-fold) or p.o. (10.8-fold) administration and decreased total body clearance (0.574-fold) and apparent volume of distribution at steady state (0.615-fold) of docetaxel after i.v. administration. Compared with the control rats, the metabolism of docetaxel by hepatic S9 fractions and the unbound fraction in the plasma in the hyperlipidaemic rats were decreased, i.e., by 20.1 and 79.8%, respectively. In conclusion, the alterations in docetaxel pharmacokinetics in rats with P-407-induced hyperlipidaemia may be due, at least in part, to a decrease in hepatic metabolism and the unbound fraction of docetaxel in the plasma. These findings have potential therapeutic implications for predicting human pharmacokinetic responses to hyperlipidaemia.

Danshen extract does not alter pharmacokinetics of docetaxel and clopidogrel, reflecting its negligible potential in P-glycoprotein- and cytochrome P4503A-mediated herb–drug interactions

Danshen (Salvia miltiorrhiza) contains tanshinones, which inhibit P-glycoprotein (P-gp) and the cytochrome P450 (CYP) system. In the present study, we evaluated the possible pharmacokinetic interactions of Danshen extract with docetaxel and clopidogrel in rats. Docetaxel (5 mg/kg intravenously and 40 mg/kg orally) or clopidogrel (30 mg/kg orally) was administered to rats with or without oral co-administration of Danshen (400 mg/kg). Co-administration of Danshen did not affect the plasma concentration profiles and pharmacokinetic parameters of docetaxel and clopidogrel, whereas cyclosporine A, a P-gp and CYP3A inhibitor, significantly influenced the pharmacokinetics of co-administered docetaxel and clopidogrel. Orally administered Danshen had no substantial effect on the pharmacokinetics of docetaxel and clopidogrel, suggesting the negligible safety concern of Danshen in P-gp- and CYP3A-mediated interactions in vivo.

Sample preparation for liquid chromatographic analysis of phytochemicals in biological fluids.

INTRODUCTION Natural products have been used traditionally for the treatment and prevention of diseases for thousands of years and are nowadays consumed as dietary supplements and herbal medicine. To ensure the safe and effective use of these herbal products, information about bioavailability of active compounds in plasma or target tissues should be provided via validated analytical methods combined with appropriate sampling methods. OBJECTIVE To provide comprehensive and abridged information about sample preparation methods for the quantification of phytochemicals in biological samples using liquid chromatography analysis. METHODS Sample pre-treatment procedures used in analytical methods for in vivo pharmacokinetic studies of natural compounds or herbal medicines were reviewed. These were categorised according to the biological matrices (plasma, bile, urine, faeces and tissues) and sample clean-up processes (protein precipitation, liquid-liquid extraction and solid-phase extraction). RESULTS Although various kinds of sample pre-treatment methods have been developed, liquid-liquid extraction is still widely used and solid-phase extraction is becoming increasingly popular because of its efficiency for extensive clean up of complex matrix samples. However, protein precipitation is still favoured due to its simplicity. CONCLUSION Sample treatment for phytochemical analysis in biological fluids is an indispensable and critical step to obtain high quality results. This step could dominate the overall analytical process because both the duration of the process as well as the reliability of the data depend in large part on its efficiency. Thus, special attention should be given to the choice of a proper sample treatment method that targets analytes and their biomatrix.

The Increased Cellular Uptake and Biliary Excretion of Curcumin by Quercetin: A Possible Role of Albumin Binding Interaction

Curcumin and quercetin are natural compounds with a wide spectrum of activities, including antioxidant and anticancer activities. In this study, the combined effect of the two compounds was investigated, with special emphasis on the pharmacokinetics of curcumin by the quercetin-induced changes in the albumin binding of curcumin. We evaluated the effect of quercetin on the binding of curcumin to albumin and on the uptake of curcumin into the cells of the human colon carcinoma cell line WiDr. In addition, we also investigated changes in the in vivo pharmacokinetics of curcumin and curcumin sulfate (the major metabolite of curcumin) coadministered with quercetin. We found that quercetin inhibited the binding of curcumin to albumin and increased the uptake of curcumin into WiDr cells, the human colon carcinoma cell. The quercetin-induced increased uptake (1.6-fold) of curcumin into WiDr cells was also confirmed by an ex vivo study. The in vivo pharmacokinetics of curcumin showed obvious changes when it was coadministered with quercetin, with the significantly lower plasma concentration and greater biliary excretion of curcumin and curcumin sulfate. The present study suggests that quercetin could enhance the cellular uptake of curcumin and modulate in vivo pharmacokinetics of curcumin, and it could be related to albumin-binding interaction.

Low-dose probenecid selectively inhibits urinary excretion of phenolsulfonphthalein in rats without affecting biliary excretion

Renal organic anion transport systems play an important role in the excretion of anionic drugs and toxic compounds. Probenecid has been used as a potent inhibitor of urinary and biliary excretion of anionic compounds mediated by transporters such as organic anion transporters and multidrug resistance‐associated protein 2 (Mrp2). The purpose of this study was to optimize the dose of probenecid required for selective inhibition of urinary excretion of anionic compounds in rats, without inhibition of biliary excretion. Phenolsulfonphthalein (PSP), a model anionic compound that is excreted in urine and bile, was intravenously administered to rats after intraperitoneal injection of different doses of probenecid (0, 0.2, 2, 10, 100, 200 and 400 mg kg−1). Treatment with 100, 200 or 400 mg kg−1 probenecid decreased both renal clearance (CLr) and biliary clearance (CLb) of PSP, whereas 0.2 mg kg−1 probenecid did not have any effect. Probenecid administered at doses of 2 and 10 mg kg−1 decreased only CLr. The median effective doses of probenecid for inhibiting CLr and CLb were 0.925 and 23.9 mg kg−1, respectively. These data suggest that a low dose of probenecid selectively inhibits urinary excretion of PSP that may be mediated by organic anion transporters, without affecting biliary excretion that may be mediated by Mrp2. Copyright

Comparative pharmacokinetic study of paclitaxel and docetaxel in streptozotocin-induced diabetic rats.

The pharmacokinetics of paclitaxel and docetaxel were compared in diabetic rats induced by streptozotocin (DMIS rats) and the impact of altered expression of cytochrome P450 3A (Cyp3A) and P‐glycoprotein (P‐gp) in the diabetic state. The pharmacokinetics of paclitaxel and docetaxel were determined after intravenous (5 mg/kg) and oral (30 and 40 mg/kg, respectively) administration to both groups and the mRNA expression levels of Cyp3A isozymes and Mdr1a and Mdr1b in the liver and small intestine were determined in control and DMIS rats. After intravenous administration, the AUC and clearance of paclitaxel and docetaxel were not significantly different in DMIS vs control rats. After oral administration, the AUC and Cmax of paclitaxel in DMIS rats were significantly greater than those in the control rats, whereas those of docetaxel was not changed significantly. The mRNA expression levels of hepatic Cyp3A1, Cyp3A9 and Mdr1b were significantly increased in DMIS compared with the control rats. In the intestine, Cyp3A62 expression decreased in the DMIS rats compared with the controls. Thus the pharmacokinetic changes of taxanes observed in the DMIS rats were attributed to changes in P‐gp and Cyp3A, predominant factors that control the absorption of paclitaxel and docetaxel, respectively. It seemed that there were different susceptibilities to intestinal P‐gp and Cyp3A between the two taxanes. Copyright

Dose-dependent pharmacokinetics of toxic metabolites is not related to increased toxicity following high-dose valproic acid in rats

It has been reported that urinary excretion of two metabolites of valproic acid (VPA), 4‐ene‐valproic acid (4‐VPA) and 2,4‐diene‐valproic acid (2,4‐VPA), increased exponentially with the administration of high doses of VPA, and this increased formation of toxic metabolites could be related to VPA hepatotoxicity in humans. The aim of this study was to investigate whether the plasma level of 4‐VPA and 2,4‐VPA in rats corresponds to the urinary data for the same metabolites in humans. After the oral administration of VPA at doses of 20, 100 and 500 mg kg−1 in rats, the AUC0–24 h, 4‐VPA/AUC0–24 h, VPA ratios (0.0399, 0.0120 and 0.0100 for 20, 100 and 500 mg kg−1, respectively) and AUC0–24 h, 2,4‐VPA/AUC0–24 h, VPA ratios (0.00104, 0.00201 and 0.00141, respectively) did not increase with increasing doses of VPA in rats. Thus, the plasma exposure of toxic metabolites normalized by dose remained unchanged (for 2,4‐VPA) or even decreased (for 4‐VPA) following high‐dose VPA administration; this contradicts the findings of previous studies. Our results suggest that toxicity induced by high doses of VPA cannot be explained by a nonlinear increase of toxic metabolites in rats. Copyright

Biliary clearance of bromosulfophthalein in anesthetized and freely moving conscious rat.

The aim of this study was to investigate the effect of anesthesia on the pharmacokinetics of bromosulfophthalein (BSP) with focus on biliary clearance. The plasma concentration profile and biliary clearance of intravenously administered BSP was compared in conscious freely moving bile duct catheterized rats and rats anesthetized with ketamine or Zoletil. The plasma concentration of BSP in conscious rats was similar to that of anesthetized rats, irrespective of the anesthetic used. There was no significant difference in the volume of distribution, total body clearance and mean residence time of BSP between the groups. The biliary clearance of BSP in rats anesthetized using ketamine or Zoletil was also similar to that of conscious rats. Only bile flow was increased under anesthetization compared with conscious rats. These results demonstrate that the pharmacokinetics of BSP, including biliary clearance, in ketamine or Zoletil anesthetized rats is virtually identical to that in conscious rats and it may be related to blood flow limited hepatic disposition of BSP. Furthermore, they suggest the conscious rat model does not offer methodological advantage and the anesthesia model is suitable for a realistic approximation of the hepatobiliary transport of BSP.

Designing of the fixed-dose gastroretentive bilayer tablet for sustained release of metformin and immediate release of atorvastatin

Abstract Patients with type 2 diabetes mellitus have a high risk of cardiovascular disease mainly caused by dyslipidemia. Metformin and atorvastatin are preferentially used to treat type 2 diabetes mellitus and dyslipidemia, respectively. The aim of this study was to develop a once-a-day fixed-dose combination tablet containing metformin and atorvastatin. For this purpose, we designed gastroretentive bilayer tablets consisting of 500 mg metformin in a sustained release layer and 10 mg atorvastatin in an immediate release layer. In addition, we modified the formulation to maintain a dual release pattern for the kinetically different layers for once-daily dosing. The gastroretentive bilayer tablet was developed using polyethylene oxide as a swellable polymer and ammonium methacrylate copolymer as a granule-coating polymer with minimal use of excipients. In vitro release patterns of metformin and atorvastatin from the developed formulation were similar to those of the reference drugs, Glucophage XR for metformin and Lipitor for atorvastatin, with satisfactory dissolution similarity factor (f2) values. The pharmacokinetic study showed the sustained and immediate absorptions of metformin and atorvastatin, respectively, in beagle dogs. The 90% confidence intervals of the ratios of ln values of AUCs of test formulation F3 and respective reference formulations of metformin and atorvastatin were 0.93–1.12 and 0.89–1.17, respectively, compared with their respective reference drugs. This formulation could contribute to improving the compliance and therapeutic outcome of patients with metabolic diseases.

Pharmacokinetic interactions of clopidogrel with quercetin, telmisartan, and cyclosporine A in rats and dogs

In this study, we investigated pharmacokinetic drug interactions of clopidogrel with P-gp inhibitors in rats and dogs. Following the oral administration of clopidogrel with or without the P-gp inhibitors, quercetin (250 mg/kg), telmisartan (8 mg/kg), and cyclosporine A (10 mg/kg), in rats and dogs, the plasma concentration-time profiles of clopidogrel carboxylic acid, a surrogate marker for the bioavailability of clopidogrel, were determined. Co-administration of the quercetin, telmisartan and cyclosporine A significantly increased the area under the curve and peak plasma concentration of clopidogrel carboxylic acid in rats. However, in dogs, the plasma concentrations of clopidogrel carboxylic acid were not considerably changed by the coadministration of three different kinds of P-gp inhibitors. These findings suggest potential interaction of clopidogrel with quercetin, telmisartan, and cyclosporine A, although there are differences between animal models. Follow-up clinical study is needed to explore the meaning of this remarkable species differences in the P-gp-mediated interaction.