Minoru Shimoda

Involvement of rat organic anion transporter 3 (rOAT3) in cephaloridine-induced nephrotoxicity: In comparison with rOAT1

This study was performed to elucidate the possible involvement of organic anion transporter 3 (OAT3) in cephaloridine (CER)-induced nephrotoxicity and compare the substrate specificity between rOAT3 and rat OAT1 (rOAT1) for various cephalosporin antibiotics, using proximal tubule cells stably expressing rOAT3 (S2 rOAT3) and rOAT1 (S2 rOAT1). S2 rOAT3 exhibited a CER uptake and a higher susceptibility to CER cytotoxicity than did mock, which was recovered by probenecid. Various cephalosporin antibiotics significantly inhibited both estrone sulfate uptake in S2 rOAT3 and para-aminohippuric acid uptake in S2 rOAT1. The Ki values of CER, cefoperazone, cephalothin and cefazolin for rOAT3- and rOAT1-mediated organic anion transport ranged from 0.048 to 1.14 mM and from 0.48 to 1.32 mM, respectively. These results suggest that rOAT3, at least in part, mediates CER uptake and CER-induced nephrotoxicity as rOAT1. There was some difference of affinity between rOAT3 and rOAT1 for cephalosporin antibiotics.

Reduced folate derivatives are endogenous substrates for cMOAT in rats

We examined the role of the canalicular multispecific organic anion transporter (cMOAT) in the biliary excretion of reduced folate derivatives in vivo and in vitro using normal [Sprague-Dawley rats (SDR)] and mutant [Eisai hyperbilirubinemic rats (EHBR)] rats whose cMOAT is hereditarily deficient. In vivo, the biliary excretion of endogenous tetrahydrofolate (H4PteGlu), 5-methyltetrahydrofolate (5-CH3-H4PteGlu), and 5,10-methylenetetrahydrofolate (5, 10-CH2-H4PteGlu) in EHBR was reduced to 8.2%, 1.9%, and 5.5% of those in SDR, respectively, whereas that of 10-formyltetrahydrofolate (10-HCO-H4PteGlu) was detected only in SDR and not in EHBR. Bile drainage caused reduction of endogenous plasma folate concentrations in SDR but not in EHBR. In vitro, significant ATP-dependent uptake of 3H-labeled 5-CH3-H4PteGlu into canalicular membrane vesicles was observed only in SDR. This ATP-dependent uptake was saturable with a Michaelis constant (Km) value of 126 microM, which was comparable with its inhibitor constant (Ki) value of 121 microM for the ATP-dependent uptake of a typical cMOAT substrate, 2,4-dinitrophenyl-S-glutathione (DNP-SG). Vice versa, DNP-SG inhibited the uptake of 5-CH3-H4PteGlu with a Ki of 35 microM, which was similar to its Km value. In addition, H4PteGlu and 5, 10-CH2-H4PteGlu also inhibited the ATP-dependent uptake of DNP-SG. These results indicate that 5-CH3-H4PteGlu and other derivatives are transported via cMOAT. Therefore, reduced folate derivatives are the first endogenous substrates for cMOAT that do not contain glutathione, glucuronide, or sulfate moieties.

Disposition Kinetics of Difloxacin in Rabbit after Intravenous and Intramuscular Injection of Dicural

This study investigated the pharmacokinetic behaviour of difloxacin following a single intravenous (i.v.) bolus and intramuscular (i.m.) administration of 5 mg/kg body weight (bw) to rabbits (n = 6). Plasma concentrations were determined in triplicate by agar plate diffusion usingE. coli (ATCC 25922) as the test organism. Difloxacin was assayed in plasma to determine its concentrations, kinetic behaviour and systemic availability. Plasma concentration–time data generated in the present study were analysed by non-compartmental methods based on statistical moment theory. Difloxacin was rapidly distributed to the tissues with a steady-state volume of distribution (Vdss) of 1.51 L/kg and the total body clearance (Cltot) was 0.59 L/kg/h. The elimination half-lives after i.v. and i.m. administration were 3.25 h and 3.82 h, respectively. After i.m. administration, difloxacin was rapidly absorbed, with mean peak plasma concentration (Cmax) of 3.85 μg/ml achieved at 1.61 h (Tmax) post administration. The extent of plasma protein binding of difloxacin in rabbits was 21.45% and the systemic bioavailability was 95.29%.

Pharmacokinetics and bioavailability of florfenicol following intravenous, intramuscular and oral administrations in rabbits.

This study examined the disposition kinetics and bioavailability of florfenicol after intravenous (i.v.), intramuscular (i.m.) and oral administration to rabbits at a dose of 30 mg/kg BW. Serial blood samples were collected through an indwelling catheter intermittently for 24 h for various routes. Plasma antibacterial concentrations were determined using a microbiological assay method withBacillus subtilis ATCC 6633 as a reference organism. Plasma concentration–time data generated in the present study were analysed by non-compartmental methods based on statistical moment theory. Following i.v. administration, the overall elimination half-life (t1/2β) was 1.54 h, mean residence time (MRT) was 1.69 h, mean volume of distribution at steady-state (Vdss) was 0.57 L/kg, and total body clearance (Cltot) was 0.34 L/kg/h. After i.m. and oral dosing, the terminal part of the curve should correspond to the absorption phase, instead of to the elimination phase, with terminal half-lives of 3.01 and 2.57 h, respectively. The mean absorption time (MAT) was 2.65 h for i.m. and 2.01 h for oral administration. Elimination rate constants differed with i.v., i.m. and oral administrations, suggesting a flip-flop situation. The observed mean peak plasma concentrations (Cmax obs) were 21.65 and 15.14 μg/ml achieved at a post-injection time (Tmax obs) of 0.5 h following i.m. and oral dosing, respectively. The absolute systemic availabilities were 88.25% and 50.79%, respectively, and the extent of plasma protein binding percent was 11.65%.

Effect of split-focus approach on producing larger coagulation in swine liver.

The split-focus approach has the potential to substantially improve the throughput of coagulation high-intensity focused ultrasound (HIFU) treatment. A prototype split-focus transducer with four elements at 4.25 MHz, combined with a small imaging probe at 6.5 MHz, was constructed for transrectal treatment of a prostate. Computer simulation predicted that 1.57 times larger acoustic power than a single-spot focus was required for a split focus to heat the tissue up to the same peak temperature at 4 s from the start of insonation. When the peak temperature was 100 degrees C, the tissue volume above 70 degrees C was predicted to be 2.3 times larger for a split focus. Swine liver lobes were intraoperatively insonated with the split-focus transducer for 4 s. A lesion of coagulation necrosis 3 to 4 times larger in volume than with a single-spot focus was formed with a split focus at the same acoustic power ratio as described above. Furthermore, a lesion about 2 times larger in volume was formed when compared at the same acoustic power. These results show the great advantage of a split-focus approach over a conventional single-spot focus in coagulation treatment.

High-performance liquid chromatography of sulphadimethoxine and its N1-glucuronide, N4-acetyl and N4-acetyl-N1-glucuronide metabolites in human plasma and urine

Sulphadimethoxine is metabolized in humans by N1-glucuronidation and by N4-acetylation. Sulphadimethoxine-N1-glucuronide can be measured by the direct high-performance liquid chromatographic analysis and without enzymic deglucuronidation. The N1-glucuronide can be measured by an isocratic as well as by a gradient mobile phase. The group contribution of the N1-glucuronide moiety to the capacity factor is a reduction of 0.24 in the isocratic system and 0.55 in the gradient system. N4-Acetylation increases the capacity factor by a factor 1.4 in the isocratic system and by 1.06 in the gradient system.

The role of plasma protein binding on the metabolism and renal excretion of sulphadimethoxine and its metabolite N4‐acetylsulphadimethoxine in pigs

The effects of plasma protein binding on the elimination of sulphadimethoxine (SDM) were examined after intravenous administration of 6.25, 12.5, 25, 50, 100 and 150 mg/kg to pigs. At an early stage of the experiment, the animals were anaesthetised by inhalation of enflurane to obtain a more exact relationship between plasma concentration and the renal excretion. SDM and its acetylated conjugate, N4-acetylsulphadimethoxine (N4-SDM) were detected in plasma and urine of all animals, and the recovery of the doses was almost complete in two animals with negligible renal excretion of SDM. The percentages of plasma protein binding of SDM and N4-SDM were almost similar, and ranged from 30 to 95%, depending on the plasma concentration. The metabolic clearance of SDM by acetylation increased when the plasma protein binding decreased. These results suggested that the main elimination route of SDM in pigs is acetylation, and that the plasma protein binding can have a large effect on the elimination of SDM in pigs. The effect of plasma protein binding on the renal clearance of SDM was not so evident, because urine pH had a much greater effect on it. The deacetylation of N4-SDM was detected after 25 mg/kg intravenous administration of N4-SDM, which suggests that the metabolic clearance of SDM is part of an acetylation-deacetylation equilibrium. Saturation of the active tubular reabsorption of SDM and of the active tubular secretion of N4-SDM was also suggested after higher doses of SDM.

Pharmacokinetics of recombinant human lipocalin-type prostaglandin D synthase/β-trace in canine

Lipocalin-type prostaglandin (PG) D synthase (L-PGDS) is identical to beta-trace, a major protein in human cerebrospinal fluid (CSF), and acts as both a PGD(2)-producing enzyme and as an extracellular transporter for lipophilic ligands. In this study, we investigated the pharmacokinetics of recombinant human L-PGDS (rh-L-PGDS) in canines. After an intravenous bolus injection of rh-L-PGDS, the serum concentration decreased bi-exponentially with a half-life of the terminal line phase of 0.77h, which was markedly shorter than that of other proteins with the same molecular weight as that of rh-L-PGDS. The distribution volume was 55.4ml/kg, which was close to the volume of canine circulation plasma, indicating that the administrated rh-L-PGDS was distributed mainly in the blood. Only 10.3% of the administered rh-L-PGDS was excreted to the urine, suggesting that rh-L-PGDS was actively degraded within the body. After an intrathecal injection, the peak serum concentration of rh-L-PGDS was observed at 4-5h. The area under the plasma concentration-time curve obtained for 12h after the intrathecal injection was one third of the value for 3h after the intravenous injection, suggesting that at least one third of the intrathecally injected rh-L-PGDS shifted to the blood.

In Vitro inhibitory potential of decursin and decursinol angelate on the catalytic activity of cytochrome P-450 1A1/2, 2D15, and 3A12 isoforms in canine hepatic microsomes

Danggui is one of the most popular herbal medicines consumed by patients in different clinical settings in Asian countries. In this study, the two major pyranocoumarin compounds extracted from the Korean Angelica gigas root decursin (DC) and decursinol angelate (DA) were examined in vitro with regard to their abilities to inhibit hepatic CYP1A1/2, CYP2D15, and CYP3A12 catalytic activities in canine liver microsomes. The two components were capable of inhibiting CYP1A1/2, CYP2D15, and CYP3A12 catalytic activities, but the potencies varied. DC and DA selectively and noncompetitively inhibited CYP1A1/2 activity, with Ki values of 90.176 and 67.560 μM, respectively. On the other hand, they exhibited slight inhibitory effects on CYP2D15 and CYP3A12 with Ki values of 666.180 and 872.502 μM, 990.500 and 909.120 μM (1’hydroxymidazolam, MDZ1’H), and 802.800 and 853.920 μM (4-hydroxymidazolam, MDZ4H), respectively. Additionally, they showed increased inhibition after preincubation, which suggests the involvement of a mechanism-based inhibition. In sum, this in vitro data should be heeded as a signal of possible in vivo interactions. The use of human liver preparations would considerably strengthen the practical impact of the data generated from this study.

Disease-induced alterations in plasma drug-binding proteins and their influence on drug binding percentages in dogs.

Summary Disease‐induced variations of plasma albumin (ALB) and alph1‐acid glycoprotein (AAG) levels were investigated in dogs. Lower ALB (sometimes >50% reduction) and higher AAG (sometimes >10‐fold increase) levels were observed in dogs with various diseases. Drug binding was determined at therapeutic concentrations using normal, low‐ALB and high‐AAG dog plasma. The binding percentages of the ALB‐binding drugs decreased in low‐ALB plasma, resulting in a large increase in unbound drug, particularly for naproxen (a 13‐fold increase). The binding percentages of all AAG‐binding drugs investigated in this study increased in high‐AAG plasma, resulting in a large decrease in unbound drug, particularly for quinidine (99% decrease). The fluctuation in the unbound fraction of drugs could affect their efficacy or could cause side‐effects. Veterinary clinicians should monitor the ALB and AAG levels in the plasma of patients and correct dosage regimens according to these levels, where field conditions permit this, in order to ensure the proper usage of drugs with high affinity for ALB or AAG.