Methotrexate (MTX) was investigated for possible effect on the metabolism of ethoxyresorufin, pentoxyresorufin and ethjxycoumarin, the model substrates of cytochrome P450. The investigation was carried out in liver microsomes of rats pretreated with classical inducers of cytochrome P450 as well as in microsomes of two human livers. Firthermore, we measured the conversion of MTX (100 ^M) to its main metabolite, 7-hydroxymethotrexate (7-OHMTX), in microsomes and cytosolic fractions of rat and human livers. The inhibition of 7-OHMTX formation by menadion (inhibitor of aldehyde oxidase) and allopurinol (inhibitor of xanthine oxidase) was studied in the cytosol of rat and human livers. In both species, MTX in the concentration range 0.5-500 /¿M exerted no inhibitory effect on enzymatic activities associated with cytochrome P450. Moreover, we did not observe any measurable formation of 7-OHMTX in liver microsomes. MTX was metabolized at a similar rate in the cytosol of rat and human liver. Allopurinol (100 /iM) reduced the rate of MTX hydroxylation by 31.5 % in the cytosol of human livers but had no effect in the rat. Menadion (100 y/M) decreased the rate of 7-OHMTX formation in the cytosol of human and rat liver by 69 % and 94 %, respectively. Our results confirmed that MTX is oxidized by a soluble enzymatic system in both the rat and human liver. In human tissues, both aldehyde oxidase and xanthine oxidase may play an important role in the metabolism of MTX. Depression of cytochrome P450 and related enzymatic activities observed in vivo cannot be explained by a direct inhibitory action of MTX on cytochrome P450
The present study was undertaken to evaluate the use of cortisol 6b-hydroxylation in defining the effect of amiodarone on cytochrome CYP3A activity. To accomplish this goal, the in vivo activity of CYP3A was estimated by measuring the 24-hour urinary excretion of 6b-hydroxycortisol (6b-OHC) and by calculating 24-hour ratio of 6b-hydroxycortisol to urinary free cortisol (6b-OHC/UFC ratio). Nine cardiac patients scheduled for amiodarone treatment were recruited to participate in this study. Urine was collected over a 24-hour period from each subject before the first amiodarone administration and during the third day of oral administration of amiodarone (200 mg four times daily as a loading dose). Three days of amiodarone treatment caused a significant decrease (p<0.05) in both the 6b-OHC/UFC ratio and the 24-hour urinary excretion of 6b-OHC. These results suggest that amiodarone is an inhibitor of CYP3A activity., S. Mičuda, M. Hodač, L. Šišpera, P. Pařízek, M. Pleskot, G. Zimová, J. Cerman, J. Martínková, V. Pinderman., and Obsahuje bibliografii