Troglitazone (TGZ), a thiazolidinedione class of antidiabetic agent, causes serious idiosyncratic hepatotoxicity. TGZ is metabolized into reactive metabolites that covalently bind to cellular macromolecules, one of which is oxidation at the chromane ring, a unique structure of TGZ, and another involves oxidative cleavage of the thiazolidinedione ring, a structure common to less hepatotoxic antidiabetics, rosiglitazone and pioglitazone. TGZ is cytotoxic to HepG2 cells and rat and human hepatocytes. However, the role of the reactive metabolite on the TGZ toxicity is controversial, because there was no correlation of the generation of the reactive metabolites with susceptibility to the TGZ cytotoxicity, and chemical inhibitors of drug metabolizing enzymes could not protect the cells against the toxicity. Mitochondrial dysfunction, especially mitochondrial permeability transition, may be a pathophysiological event, which is mediated by TGZ itself and is a major non-metabolic factor. Other events such as apoptosis and PPARγ-dependent steatosis could be also mediated by TGZ, while inhibition of bile salt export pump, a cause of TGZ-induced cholestasis, may be caused by the TGZ sulfate. In conclusion, although the TGZ is biotransformed into chemically reactive metabolites, there is currently no potential evidence for involvement of the reactive metabolite in the TGZ-induced liver injury.
Pairs of forward and reverse primers and TaqMan probes specific to each of 52 human phase I metabolizing enzymes (alcohol dehydrogenase, aldehyde dehydrogenase, aldehyde oxidase, dihydropyrimidine dehydrogenase, epoxide hydrolase, esterase, flavin-containing monooxygenase, monoamine oxidase, prostaglandin endoperoxide synthase, quinone oxidoreductase, and xanthene dehydrogenase) and 48 human phase II metabolizing enzymes (acetyltransferase, acyl-CoA:amino acid N-acyltransferase, UDP-glucuronosyltransferase, glutathione S-transferase, methyltransferase, and sulfotransferase) were prepared. The mRNA expression level of each target enzyme was analyzed in total RNA from single and pooled specimens of various human tissues (adrenal gland, bone marrow, brain, colon, heart, kidney, liver, lung, pancreas, peripheral leukocytes, placenta, prostate, salivary gland, skeletal muscle, small intestine, spinal cord, spleen, stomach, testis, thymus, thyroid gland, trachea, and uterus) by real-time reverse transcription PCR using an ABI PRISM 7700 Sequence Detection System. Further, individual differences in the mRNA expression of representative human phase I and II metabolizing enzymes in the liver were also evaluated. The mRNA expression profiles of the above phase I and phase II metabolizing enzymes in 23 different human tissues were used to identify the tissues exhibiting high transcriptional activity for these enzymes. These results are expected to be valuable in establishing drug metabolism-mediated screening systems for new chemical entities in new drug development and in research concerning the clinical diagnosis of disease.
Genetic polymorphisms in xenobiotic transporters have recently been clarified to be associated with change in drug distribution and disposition. To expand on recent identification of direct interaction and functional regulation of several transporters by a PDZ (PSD95, Dlg and ZO1) domain containing protein PDZK1, the effect of mutation in PDZK1 on transport activity and subcellular localization of organic cation/carnitine transporters OCTN1 and OCTN2, and oligopeptide transporter PEPT2 was examined in the present study. HEK293 cells stably expressing a mutant transcript PDZK1-E195K (HEK293/PDZK1-E195K) were constructed, followed by transient transfection of cDNA for each transporter. Uptake of tetraethylammonium by OCTN1 was much higher in HEK293/PDZK1 cells, compared with that in the parent HEK293 cells, the uptake in HEK293/PDZK1-E195K cells showing middle range between the two values. Such difference in transport activity was accounted for the difference in transport capacity, with minimal change in affinity of OCTN1 to the substrate or other compounds. The similar difference among HEK293/PDZK1, HEK293/PDZK1-E195K and HEK293 cells was also observed in transport property of OCTN2 and PEPT2, whereas the difference was not so remarkable in each transporter with the last four amino acids deleted, that has much lower interaction potential with PDZK1. Immunohistochemical analysis indicated that OCTN1 was colocalized with PDZK1 on cell-surface, whereas colocalization with PDZK1-E195K was partially observed in cytoplasmic region. These results suggest a novel hypothesis that mutation in PDZK1 potentially changes transport property of various types of xenobiotic transporters by affecting their subcellular localization, possibly leading to change in disposition of various types of substrate drugs.
Objective: The purpose of this study was to evaluate the effect of atropine on the dose requirement of propofol for induction of anesthesia and propofol concentrations during continuous infusion. Methods: Study 1: Forty patients were randomly allocated to the control or atropine groups. Induction of anesthesia commenced 3 min following the administration of 0.9% saline or atropine (0.01 mg kg-1), using a Diprifuser set to achieve propofol concentration of 6.0 μg mL-1. The primary end point was the propofol dose per kg at the moment of loss of response to a command. Study 2: Fifteen patients undergoing elective surgery were enrolled. Propofol was administered to all subjects via target-controlled infusion to achieve a propofol concentration at 2.0 μg mL-1 after intubation. Before and after administration of atropine (0.01 mg kg-1), cardiac output (CO) was measured using indocyanine green as an indicator and blood propofol concentration was determined using high-performance liquid chromatography. Results: Study 1: The propofol dose for each group was 2.22±0.21 mg kg-1 for control group and 2.45±0.28 mg kg-1 for atropine, respectively (p=0.014). Study 2: After the administration of atropine, CO was significantly increased from 4.28±0.83 to 5.76±1.55 l min-1 (p<0.0001). Propofol concentration was significantly decreased from 2.12±0.28 to 1.69±0.27 μg mL-1 (p<0.0001). Conclusions: Following the administration of atropine, the propofol requirements for the induction of anesthesia were increased and propofol concentrations were decreased during continuous infusion by the administration of atropine.
The effect of renal failure on the pharmacokinetics and pharmacodynamics of bisoprolol was investigated in bilateral ureter-ligated (BUL) rats. The blood bisoprolol concentrations following 30-min intravenous infusion at a rate of 60 μg/kg/min were higher in renal artery-occluded (RAO) rats than in control rats, and were higher in BUL rats than in RAO rats. Increased blood bisoprolol concentrations accompanied decreased mean systemic clearances: 50.7, 36.4, and 26.2 mL/min/kg in control, RAO, and BUL rats, respectively. The finding indicated that approximately 30% of administered bisoprolol was excreted via the kidney, and that not only the renal clearance but also non-renal clearance of bisoprolol was decreased in BUL rats. The β-blocking action of bisoprolol was assessed by the reduction in isoproterenol-induced increases in the heart rate. The relationship between blood concentration and the β-blocking action of bisoprolol in BUL rats was similar to that in control rats. These results suggested that renal excretion and hepatic metabolism of bisoprolol were significantly reduced in BUL rats, but that pharmacodynamics of bisoprolol was not altered by acute renal failure.
Chimeric REP7/6 has been used as a marker of CYP2D6 deletion, such as for CYP2D6*5. However, the CYP2D6*10D (*10D) haplotype found in a Japanese population consist of CYP2D6*10B, CYP2D7P-derived 3′-flanking region, and a chimeric repetitive sequence, CYP-REP7/6 (REP7/6) (Ishiguro et al. Clin. Chim. Acta. 2004: 347, 217-221). From our analysis, REP7/6 was found in 26 out of 254 Japanese subjects. Thus, the REP7/6-containing CYP2D6 genes (2D6-REP7/6) were analyzed in detail. In order to specifically detect the 2D6-REP7/6 structure, primers were designed in CYP2D6 intron 6 and the REP7/6 3′-flanking region. Among 26 subjects analyzed by PCR, 5 had 2D6-REP7/6. The other 21 subjects were confirmed to have *5 by another *5-specific primer set. Three out of five subjects with 2D6-REP7/6 had the *10D structure. However, further analysis by PCR and sequencing revealed that their haplotypes were further divided into tandem-type *36-*10D (n=2) and single-type *10D (n=1). The remaining two subjects had a novel type of a *36-containing defective structure that consists of CYP2D6*36 and 3′-flanking REP7/6 (single-type *36-REP7/6). Then, REP7/6 sequences in *5, *10D, *36-*10D, and single-type *36 were determined and classified into 5 types: types A to D for *5, type E for *10D and *36-*10D, and type F for *36. These findings could be useful for accurate determination of *5 and REP7/6-harboring aberrant CYP2D6 haplotypes.
To assess the mechanism of gastrointestinal disorders by mycophenolate mofetil (MMF), the intestinal absorption and enterohepatic circulation of mycophenolic acid (MPA), an active metabolite of MMF, and its 7-O-glucuronide (MPAG) were investigated using rat intestinal loops and a linked-rat model. The stability of MPAG in the intestinal fluids, the toxicity of MPA and MPAG to intestinal mucosa, and biliary excretion of MPAG in rats with acute renal failure (ARF) were also characterized. MPA was rapidly and extensively absorbed from the rat intestine whereas MPAG was much less absorbable. When MPA was administered intravenously to bile-donor rats, 1.2% of dose was excreted in bile of receiver rats exclusively as MPAG during 4 h. MPAG was minimally deconjugated in the intestinal fluids. MPAG, but not MPA, significantly enhanced the release of lactate dehydrogenase from intestinal mucosa. When MPA was intravenously administered to ARF rats, the biliary excretion of MPAG significantly increased, compared with that in normal rats. These results demonstrated that MPAG accumulated in the intestinal lumen following biliary excretion and exerted some toxic effect on the intestinal mucosa. It was also suggested that enterohepatic circulation of MPAG under renal dysfunction increased the risk of gastrointestinal disorders due to MPAG.
The aim of this work is to develop a highly sensitive assay system for P-gp-mediated transport by using two methods, induction of P-gp and short-term culture of Caco-2 cells. To induce P-gp in Caco-2 cells, cells were cultured in vinblastine-containing medium. The mRNA level of P-gp was approximately 7-fold higher in Caco-2 cells cultured with vinblastine (P-gp-induced Caco-2 cells) than in control cells. Western blot analysis showed a significant increase in P-gp expression. After cell differentiation, the mRNA level of P-gp was downregulated, however, P-gp-induced Caco-2 cells still possessed a 5.6-fold higher mRNA level of P-gp compared to control cells. Polarized transport of substrate drugs was greater in the monolayer of P-gp-induced cells than in that of control cells. Moreover, we found that P-gp expression in Caco-2 cells could be further enhanced by applying the higher concentration of vinblastine. Transport activity of P-gp in Caco-2 cells cultured with higher concentration of vinblastine was markedly higher than that in P-gp-induced Caco-2 cells and was comparable with that in MDR1-MDCKII cells. In conclusion, this study provided a stable and highly sensitive in vitro assay system that can identify compounds that are subject to P-gp-mediated efflux.
The purpose of the present experiment was to examine the effects of D-tartaric acid (TA) on intestinal drug absorption under both in situ and in vitro experimental conditions. In the in vitro diffusion chamber experiments, TA (10 mM) added to the mucosal side of rat colon significantly decreased rhodamine123 (Rho 123) transport from the serosal to mucosal side. Since TA has been shown to change the integrity of the epithelial tight junctions in rat colon at low pH conditions, resulting in improved paracellular drug transport, the effect of TA on membrane resistance was examined at pH 7.4 in the present study. It was found that membrane resistance, an indicator of paracellular integrity, did not change at pH 7.4. In the in situ loop method, TA (20 mM) increased the absorption of Rho123 in both ileum and colon but not in jejunum. TA (20 mM) also increased the absorption of daunorubicin in the ileum, but TA (20 mM) did not change the expression level of P-glycoprotein (P-gp). TA (20 mM) significantly inhibited excretion of i.v.-administered Rho123 and daunorubicin into the ileal lumen. In conclusion, for the first time we demonstrated that TA increases the intestinal absorption of P-gp substrates Rho123 and daunorubicin, possibly by modulating the P-gp function without changing the expression level of P-gp in the rat intestine.
A specific, sensitive and reproducible high-performance liquid chromatographic procedure was developed for the quantitative analysis of carboplatin in human plasma. Plasma was ultrafiltered with an Amicon Centrifree system and then injected onto an analytical NH2 column. Carboplatin was monitored at 230 nm and eluted by 10 min using acetonitrile/methanol/5 mM sodium perchlorate buffer (pH 2.4) (75:15:10, v/v) as a mobile phase. The method yielded intra-day and inter-day precision and accuracy of <6% with a linearly from 0.1 to 80 μg/mL and a recovery of >98%. Plasma concentrations of intravenously administered carboplatin in three patients could be determined by this system. Slightly higher plasma concentrations of carboplatin were detected even 30 min after hyperbaric oxygenation therapy for 60 min than expected. The results suggest that this method could be applicable for measurement of carboplatin in plasma samples to evaluate carboplatin therapy together with hyperbaric oxygenation.
Interactions of DX-619, a novel fluoroquinolone antibacterial, and levofloxacin (LVFX) with the human renal organic cation transporter hOCT2 were studied. The intracellular accumulation of [14C]creatinine in stable transfectants of HEK293 cells expressing hOCT2 (hOCT2-HEK293) as well as vector-transfected HEK293 cells (VEC-HEK293) was evaluated in the presence of DX-619 and LVFX at various concentrations. When added extracellularly, both DX-619 and LVFX inhibited the uptake of [14C]creatinine (5 μM) by hOCT2-HEK293 cells in a dose-dependent manner. Unlike in hOCT2-HEK293 cells, the uptake in VEC-HEK293 cells was not inhibited by either fluoroquinolone suggesting that hOCT2 was specifically involved in the inhibition. The apparent IC50 value for the inhibition of [14C]creatinine uptake in hOCT2-HEK293 cells was 1.29±0.23 μM for DX-619 and 127±27 μM for LVFX, indicating DX-619 to be ~100-fold more potent than LVFX at inhibiting the transport of [14C]creatinine by hOCT2. A Dixon plot revealed that the inhibition by DX-619 of the hOCT2-mediated transport of [14C]creatinine was competitive. Fluoroquinolone antibacterials have the ability to inhibit the transport of creatinine by hOCT2, with DX-619 being much more effective than LVFX.