Lack of Evidence for Involvement of P-Glycoprotein in Brain Uptake of the Centrally Acting Analgesic, Tramadol in the Rat

Purpose. Tramadol Hydrochloride is a widely-used centrally acting analgesic drug, which has some features of being a P-gp substrate. The present study evaluates the functional involvement of P-gp in CNS distribution of tramadol. Methods. The possibe involvement of P-glycoprotein in brain distribution of tramadol was evaluated using a pharmacokinetic approach in two groups of Pgp-inhibited and control rats. Six male Sprague-Dawley rats were used in each group to collect plasma and brain at 1, 5, 10, and 30 min following two tramadol doses of 1 and 10 mg/kg. Results. The brain uptake clearances of tramadol in Pgp-inhibited and control rats were 2.47±0.56 and 2.34±0.56 ml min-1g-1, respectively, for 1 mg/kg and 3.50±0.60 and 3.14±1.02 mlmin-1g-1, respectively, for 10 mg/kg dose. The brain-to-plasma concentration ratio (Kp,app) of more than 1 in all the time points following both the high and low dose cases (sometimes more than 3) indicated the brain accumulation of the drug. Linear correlation was found between tramadol dose and both corresponding plasma and brain concentrations, but the presence of a dose-dependency was not confirmed by the data obtained for brain-to-plasma concentration ratio. Conclusion. Considering the results of the previous studies and the present research, it seems that the brain accumulation of tramadol is not affected by P-gp inhibition which implies that there may be some other transport mechanisms involved in BBB transport of tramadol. This article is open to POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page

Imatinib Metabolism and Disposition in Isolated Rat Perfused Liver: Imatinib Metabolism and Disposition in Isolated Rat Perfused Liver

Imatinib is an orally administered tyrosine kinase inhibitor which inhibits the Bcr-Abl protein-tyrosine kinase with high selectivity. Imatinib is rapidly absorbed from the gut, after oral intake and has an almost absolute bioavailability of 98%. The metabolism of imatinib is mediated by the cytochrome P450 (CYP) isoenzymes in the liver and gut wall. CGP74588 is a major active metabolite of imatinib. The study was performed on Male Sprague-Dawley rats (250-300 g) housing under artificial light on a 12-h light/dark cycle with free access to standard laboratory chow and water. Re-circulating (at imatinib concentration of 1 and 5 μg/ml) and single-pass (imatinib dose of 1mg) perfusion modes in the presence and absence of BSA were tested. Throughout the experiment, perfusate temperature (37± 0.5 C°), pH (7.4±0.2) and liver viability (ALT and AST) were monitored. The concentrations of imatinib and its main metabolite in perfusion buffer and liver homogenate were determined by a validated HPLC method.No metabolite was detected in outlet perfusate in all conditions. However, negligible amounts of metabolite were found in liver homogenate at 1 and 5 μg/ml imatinib concentrations in re-circulating perfusion mode. The rapid and remarkable disappearance of imatinib from perfusate was related to its accumulation in liver. Statistical moment definition was used to calculate some pharmacokinetic parameters. These calculations also confirmed liver accumulation and slow and sustained dissociation of imatinib from liver

Effect of 3,4-Methylenedioxymethamphetamine on Liver CYP2C19 Enzyme Activity in Isolated Perfused Rat Liver Using Omeprazole Probe

Background and purpose: This study aimed at investigating the effects of 3,4-Methyl​enedioxy​methamphetamine (MDMA) on liver cytochrome 2C19 enzyme activity, which is a major liver enzyme in the metabolism of a wide range of drugs, using omeprazole as a probe of the CYP2C19 activity in isolated perfused rat liver. Materials and methods: This experimental study was done in 20 male Sprague–Dawley (SD) rats (weighing 250–300 g). After isolating the animal liver, omeprazole was administered at 400 μm and the concentration of omeprazole and its metabolite were determined. The liver was then washed with perfusion buffer, and MDMA was transferred at 300 ng/ml unilaterally from the same liver for 30 minutes. After re-washing the liver with perfusion buffer, omeprazole was passed through the liver for second time and the metabolic ratio was determined after exposure to MDMA. This process was also done in a group of animals at 600 ng/ml of MDMA. Results: Analysis of data from three end-time intervals after exposure to liver at 300 and 600 ng/ml of MDMA, showed 26.6% and 20.6% reduction in the activity of CYP2C19. Findings showed that MDMA administration could significantly reduce the activity of CYP2C19. Conclusion: According to this study, liver exposure to MDMA can significantly reduce cytochrome 2C19 activity, but, further studies are needed to examine this issue more closely

A RAPID AND SENSITIVE HPLC-FLUORESCENCE METHOD FOR DETERMINATION OF MIRTAZAPINE AND ITS TWO MAJOR METABOLITES IN HUMAN PLASMA

A rapid and sensitive HPLC method has been developed for the quantification of mirtazapine (MRZ), a noradrenergic and specific serotonergic inhibitor antidepressant (NaSSA) and its two major metabolites N-desmethylmirtazapine (NDM) and 8-hydroxymirtazapine (8-OHM) in human plasma. The separation was achieved using Chromolith C18 columns and a mobile phase of acetonitrile: phosphate buffer (pH=3, 20:80, v/v) in isocratic mode at a flow rate of 2 ml/min. A fluorescence detector was set at 290 and 350 nm for excitation and emission, respectively. Zolpidem was used as the internal standard. Liquid-liquid extraction was applied for sample clean up. All analytes were eluted in less than 5 minutes with LOQ of 1 ng/ml for MRZ and 2 ng/ml for both NDM and 8-OHM . The developed method was successfully applied to quantify MRZ and its metabolites in plasma of a healthy volunteer

Study the effect of 3,4-Methylenedioxy methamphetamine on cytochrome P450 2E1 activity

Evaluating the effects of ecstasy on CYP2E1 activity is of great concern, mainly due to growing trends in abuse and co-administration of MDMA with ethanol and the dominant role of this isoenzyme on ethanol metabolism. This study aimed to evaluate the effects of MDMA on CYP2E1 activity. A total of 24 male rats were selected and divided into three groups. The first and second groups consisted of 12 rats and were employed to optimize the perfusion method, and the third group was employed for studying the alteration of CYP2E1 activity after liver exposure to MDMA (300 and 600 ng/ml). The amount of chlorzoxazone and 6-hydroxy chlorzoxazone in a sample obtained from liver perfusion before and after exposure to a buffer containing MDMA was determined by HPLC-FL. The enzymatic activity of rat CYP2E1 decreased after liver perfusion with a buffer containing 600 ng/ml of MDMA. However, no significant changes were observed in chlorzoxazone and 6-hydroxy chlorzoxazone concentration in perfusate before and after liver perfusion with a buffer containing 300 ng/ml of MDMA. Our findings suggest that the activity of CYP2E1 in rats might decrease only after administration of MDMA at a lethal dose. However, further animal and human studies are needed to confirm our assumption