etters

Abstracts / Toxicology L

and toxicity and selecting inducers or inhibitors for theseenzymes.

doi:10.1016/j.toxlet.2008.06.480

K06Inhibition with spontaneous reactivation of esterases byorganophosphorus compounds: Paraoxon as a model

Jorge Estévez ∗, Adolfo García, José Barril, Eugenio Vilanova

Universidad Miguel Hernández de Elche, Elche, Alicante, Spain

The kinetic analysis of the inhibition of esterases by organophos-phorus compounds is sometimes unable to yield consistent resultsby fitting simple inhibition kinetic models to experimental dataof complex systems. In this work kinetic data were obtainedfor different paraoxon concentrations incubated for up to threehours with soluble fraction of chicken peripheral nerve. A kineticmodel equation was deduced assuming a multienzymatic systemwith three different molecular phenomena occurring simultane-ously: (1) inhibition; (2) simultaneous spontaneous reactivation;(3) ongoing inhibition (inhibition during the substrate reaction).A three-dimensional fit of the model was applied for analysingthe experimental data. The best fitting model is compatible witha resistant component (22%) and two sensitive enzymatic entities(37% and 41%). The corresponding second order rate constants ofinhibition (ki = 1.8 × 109 and 5.1 × 106 M−1 min−1, respectively) andthe spontaneous reactivation constants (kr = 0.428 and 0.011 min−1,respectively) were estimated. These parameters were similar tothose deduced in spontaneous reactivation experiments of pre-inhibited samples with paraoxon. The consistency of results in bothexperiments was considered an internal validation of the method-ology. The results were also consistent with a significant ongoinginhibition. The proportion of enzymatic components showed in thiswork by the inhibition and reactivation of paraoxon is similar tothose previously observed in inhibition experiments with mipafox,demonstrating that this kinetic approach gives consistent results incomplex enzymatic systems.

doi:10.1016/j.toxlet.2008.06.481

K07Modulating effects of vitamin E on drug metabolizing enzymesin iodine-deficient rats

Pinar Erkekoglu, Aydan Caglayan ∗, Belma Giray, Filiz Hincal

Hacettepe University, Faculty of Pharmacy, Ankara, Turkey

This study has been undertaken to investigate the modulatingeffects of vitamin E on drug metabolizing enzymes in iodine defi-cient rat livers. Wistar rats were divided into four groups [control,vitamin E control (V), iodine deficient (ID) and vitamin E plus iodinedeficient (ID-V) groups]. Iodine deficient rats received 1% sodiumperchlorate containing water for 7 weeks and the rats in V grouptreated with a loading dose of 100 mg/kg/day, i.e., vitamin E incorn oil for 3 days in the last week of feeding period and thenreceived a single maintenance dose of 40 mg/kg on the 4th day. Thelevels of total microsomal cytochrome P450 and cytochrome b5,activities of microsomal CYP2E1, PROD, NADPH cytochrome P450reductase (P450R) and cytosolic GST in hepatic tissues were deter-mined. Total hepatic P450 levels and P450R activities did not changein ID, whereas a significant increase in CYP b5 levels (∼30%) and sig-nificant decreases in GST (∼80%), PROD (∼30%) and CYP2E1 (∼30%)activities were observed. Vitamin E treatment alone caused a sig-nificant increase in total hepatic P450 (∼40%) and CYPb5 (∼55%)

180S (2008) S32–S246 S91

concentrations, but did not effect PROD, CYP2E1 and GST activi-ties. However, in IDV rats, significant enhancement in GST activity(∼155%) and CYP b5 levels were observed compared to ID group.These results suggest that vitamin E may modulate hepatic xeno-biotic metabolizing enzyme systems in iodine deficiency as well asnormal subjects and may cause alterations on the metabolism ofconcomitantly exposed xenobiotics including drugs.

doi:10.1016/j.toxlet.2008.06.482

K08Organic cation transporters 1 and 2 mediate pralidoxime renalsecretion

Maya Kayouka, Pascal Houzé ∗, Patricia Risède, SalvatoreCisternino, Frédéric Baud

INSERM U705, Paris, France

Objective: Pralidoxime (PRX) is an organic cation used to treatorganophosphate poisoning. PRX elimination is characterized byfast renal excretion. In rodents, we studied the role of organic cationtransporters (Oct) in the renal secretion of PRX using specific Octsubstrates (TEA) and KO mice (Oct 1/2−/−; Oct 3−/−).

Methods: Male Sprague–Dawley rats received a loading dose ofPRX followed by a continuous infusion to achieve a plasma PRXconcentration of 10 mg/l during 180 min. Then, blood and urinewere collected. In rats, the pharmacokinetics of PRX (50 mg/kg,30 min perfusion) was determined 15 min after TEA treatment(75 mg/kg, IM). Knock-out and wild type mice received a PRX injec-tion (50 mg/kg, IM), blood samples were taken at 45 and 90 minpost-injection. Results are expressed as mean ± S.E.M. Statisticalanalysis used t-test and ANOVA on log transformed data withp < 0.05.

Results: PRX renal clearance was 3-fold than creatinine clearanceevidencing PRX renal secretion. Pretreatment by TEA significantlymodifies the PRX pharmacokinetic, increasing the beta half-life(224 vs. 39 min−1) and decreasing the clearance (3.6 vs. 2.2 l/h/kg)without modification of the volume of distribution. The defi-ciency in Oct 1 and 2 in mice resulted in a significant increasein plasma pralidoxime concentrations at 45 min (6.40 ± 0.46 vs.2.37 ± 0.13 mg/l) and 90 min (2.83 ± 0.17 vs. 1.47 ± 0.07). Lack in Oct3 did not change the plasma PRX concentrations.

Conclusion: Our data show that PRX is secreted in urine by anactive process involving Oct 1 and 2.

doi:10.1016/j.toxlet.2008.06.483

K09Comparative metabolism of insecticide benfuracarb by human,mouse and rat liver microsomes

Chul-Hee Chang 1, Jeong-Han Kim 1,∗, Joon-Kwan Moon 1, Hwa-Gyung Lee 1, Joo-Hee Lee 1, Hee-Won Park 1, Byeong-Soo Park 1,Hye-Suk Lee 2, Kwang-Hyeon Liu 3

1 School of Agricultural Biotechnology, College of Agriculture and LifeSciences, Seoul National University, San 56-1, Sillim-dong,Gwanak-gu, Seoul 151-742, Republic of Korea, 2 College of Pharmacy,Wonkwang University, Shinyong-dong, Iksan 570-749, Republic ofKorea, 3 Department of Pharmacology, College of Medicine, InjeUniversity, Kaekum-dong, Jin-Gu, Busan 614-735, Republic of Korea

The metabolism of insecticide benfuracarb by human, mouse andrat liver microsomes was performed and, the CYP450 isozymesthat are involved in the corresponding metabolic reactions werecharacterized. Benfuracarb was metabolized through two path-