In vivo approach for the evaluation of mechanism-based inhibition of cytochrome P450 3A in rats.

1. There have been no reports showing that the area under the concentration-time curve (AUC) of a probe drug is elevated due to mechanism-based inhibition (MBI) of drug-metabolizing enzymes in animals. This study ascertained that mechanism-based inhibitors reported to induce drug-drug interactions (DDIs) in humans also caused MBI in rats. 2. Midazolam (MDZ), mainly metabolized by cytochrome P450 3A in rats, and mibefradil, which showed the most intense time-dependent inhibition among the inhibitors tested, were selected as the probe and the inhibitor, respectively. Following pretreatment of mibefradil at 24 h before MDZ administration in rats, the C(max) and AUC values of MDZ were significantly elevated in comparison with the control. The free plasma concentration of mibefradil was substantially lower than the IC(50) value observed in the in vitro inhibition study, suggesting that the DDI was due to MBI. 3. It is concluded that the evaluation of MBI in rats in vivo in combination with in vitro data using human enzymes could be useful to evaluate risk in clinical studies.

Antiatherogenic effects of the antioxidant BO-653 in three different animal models.

Antioxidants have been proposed to have antiatherogenic potential by their inhibition of low density lipoprotein (LDL) oxidation. Here, we report an antioxidant, BO-653 (2,3-dihydro-5-hydroxy-2, 2-dipentyl-4,6-di-tert-butylbenzofuran), designed to exhibit antioxidative potency comparable to that of alpha-tocopherol, but yet possess a high degree of lipophilicity comparable to that of probucol. BO-653 exhibits a high affinity for LDL and is well distributed in aortic vessels in vivo. In atherosclerosis models of rabbits and mice, BO-653 has been shown to be able to suppress the formation of atherosclerotic lesions without untoward side effects. Specifically, there was no reduction of high density lipoprotein levels. This antioxidant provides additional evidence in support of the oxidized-LDL hypothesis, and itself is a promising candidate antioxidant for clinical use.

[Recovered state of iron in female blood donors--after taking an iron supplement].

An iron supplement was given to female blood donors to prevent iron deficiency after blood donation. The levels of items related to red blood cells and serum ferritin (S-Fer) among 17 iron-takers and 31 non-iron-takers were analyzed continuously. In most of the non-iron-takers, the S-Fer levels did not recover within four weeks after the donation of 200ml or 400ml of blood. In the approximately half of the donors, hemoglobin (Hb) levels did not recover either. However, in 59% of those taking iron supplements three times the amount of iron lost by donation, the levels of Hb and S-Fer recovered within two weeks. In the remaining 41%, the Hb levels recovered within four weeks by taking the iron supplement. Four weeks after blood donation, the incidence of iron deficiency anemia among the non-iron-takers increased from 13% to 23% and the incidence of latent iron deficiency among the non-iron-takers increased from 32% to 42%. However, the incidence of iron deficiency anemia among the iron-takers remained 0% and the incidence of latent iron deficiency among the iron-takers decreased from 12% to 6%.

Comparison of the effects of bifemelane hydrochloride and indeloxazine hydrochloride on scopolamine hydrobromide-induced impairment in radial maze performance.

The antiamnesic effects of bifemelane hydrochloride (bifemelane) and indeloxazine hydrochloride (indeloxazine) on radial maze performance in rats were assessed. This performance was dependent on working memory and spatial memory, without aversive electric stimuli. When administered alone, neither bifemelane nor indeloxazine had an effect on the task performance of normal rats. However, impairment of the performance of rats induced by scopolamine hydrobromide (scopolamine) injection was dose-dependently reduced by oral treatment with bifemelane. On the other hand, indeloxazine, which was reported to enhance the learning behavior in a passive avoidance test, did not improve the radial maze task performance of scopolamine-treated rats. It has been shown that dysfunction of the cholinergic neuronal system plays an important role in memory loss and that bifemelane induces recovery of reduced cerebral cholinergic neuronal activity associated with brain ischemia or aging. In accordance with these previous findings, our results suggest that bifemelane is useful in the treatment of memory loss and cognitive dysfunction in patients with dementia and cerebrovascular disease.

Differences in the acquisition process and the effect of scopolamine on radial maze performance in three strains of rats.

The acquisition process and the effect of scopolamine (SCOP) on the radial maze task were studied in 3 strains of male rats, Fischer 344 (F344), Sprague-Dawley (SD) and Wistar. The pretraining level of locomotor activity was measured and performance was quantitatively and qualitatively evaluated. The highest pretraining locomotor activity was observed in Wistar rats. In this experiment, rats were allowed to select each arm successively. The changes in the number of correct choices during the first eight selections, error choice in a trial and the total duration of a trial differed with the strain in the first 5 training sessions. Acquisition curve for F344 rats gradually rose. Wistar rats made many error choices. However, during the final 5 sessions, only the total duration of a trial differed with the strain. Wistar rats took the shortest time to finish a trial, but the number of sessions taken to acquire this task was the fewest with F344 rats, and the most with Wistar rats. The effect of SCOP differed among strains in all the above 3 indexes. Generally, the Wistar rat was the most affected by the injection of SCOP. Moreover, the change of the choice accuracy and the spatial strategy by the administration of SCOP were investigated. SD and Wistar rats showed a dose-dependent decrease in choice accuracy in the earlier selection. The spatial strategy was changed in every strain by the injection of SCOP. These findings do not support the previous finding that a high level of locomotor activity yields fast acquisition of this task or that Wistar rats are better in learning than SD, but indicates that SCOP affects not only the working memory but also the motivational factor.

Selective suppression of schedule-induced ethanol drinking by antialcoholic drugs in rats.

Effects of disulfiram and calcium cyanamide, antialcoholic drugs, on schedule-induced ethanol drinking as well as on schedule-controlled response (lever-pressing) under a fixed interval 1 min schedule of food reinforcement were investigated in Wistar strain rats. When ethanol solution was available, the schedule-induced ethanol drinking decreased depending on the ethanol concentration (2-8%). However, the dose of ethanol intake during the 1 hr experimental session was at maximum (2.8 g/kg) when 4% ethanol solution was available. Thereafter, 4% ethanol solution was used in the experiment for studying the effects of disulfiram and calcium cyanamide on the schedule-induced ethanol drinking. Disulfiram (100-200 mg/kg, p.o.), pretreated at 1 hr before the start of the experiment, tended to suppress schedule-induced water drinking. However, the same treatment of calcium cyanamide (5-10 mg/kg, p.o.) did not produce a marked change in it. In contrast, disulfiram (100 and 200 mg/kg) and calcium cyanamide (5 and 10 mg/kg) markedly suppressed schedule-induced ethanol drinking without eliciting a marked change in schedule-controlled response. The present results suggest that both disulfiram and calcium cyanamide selectively suppress ethanol drinking in rats.