RESUMEN
The total content of rat liver microsomal cytochrome P450 (CYP) significantly decreased after repeated i.p. administration of the antiviral agent tenofovir ((R)-9-[2-(phosphonomethoxy)propyl] adenine) and tenofovir disoproxil at a daily dose 25 mg/kg, although the content of liver microsomal protein did not change. The decrease of the CYP content was accompanied by concomitant increase of the amount of inactive CYP form, cytochrome P420. This effect was confirmed by a parallel study of the activities of selected CYP forms, CYP2E1 (p-nitrophenol hydroxylation) and CYP1A2 (7-ethoxyresorufin deethylation). The activity (expressed relatively to the protein content) of both CYP forms decreased significantly following the decrease of the total CYP. On the other hand, the CYP2E1 activity expressed relatively to the decreasing total CYP content remained unchanged. However, CYP1A2 activity also decreased when calculated relatively to the total native CYP content indicating lower stability of this form. Semiquantitative RT-PCR showed no significant changes in expression of major rat liver microsomal CYP forms after tenofovir treatment. In conclusion, repeated administration of tenofovir in higher doses led to significant decrease of the relative proportion of active liver microsomal CYPs accompanied by a conversion of these enzymes to the inactive form (CYP420) maintaining the sum of CYP proteins unchanged.
Asunto(s)
Adenina/análogos & derivados , Antivirales/farmacología , Citocromo P-450 CYP1A2/metabolismo , Citocromo P-450 CYP2E1/metabolismo , Hígado/efectos de los fármacos , Organofosfonatos/farmacología , Profármacos/farmacología , Adenina/administración & dosificación , Adenina/farmacología , Animales , Antivirales/administración & dosificación , Citocromo P-450 CYP1A2/genética , Citocromo P-450 CYP2E1/genética , Citocromos/metabolismo , Regulación hacia Abajo , Femenino , Inyecciones Intraperitoneales , Hígado/enzimología , Microsomas Hepáticos , Organofosfonatos/administración & dosificación , Profármacos/administración & dosificación , Desnaturalización Proteica , ARN Mensajero/metabolismo , Ratas , Ratas Endogámicas Lew , TenofovirRESUMEN
Adefovir (PMEA) and tenofovir (PMPA) and their prodrugs, adefovir dipivoxil (bisPOM-PMEA) and tenofovir disoproxil (bisPOC-PMPA), were subjected to a detailed study of their potential to inhibit the activities of human liver microsomal cytochromes P450 (CYP). The inhibition of marker enzyme activities of CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2D6, CYP2E1 and CYP3A4 was examined with high-performance liquid chromatography (HPLC) or spectroscopic (fluorescence, luminescence) detection. Adefovir and adefovir dipivoxil did not significantly influence activities of most CYP enzymes. The activity of CYP3A4 was inhibited by adefovir dipivoxil at concentrations over 100 microM. Adefovir and its prodrug inhibited CYP2C9 at concentrations below 100 microM; inhibition by adefovir was of the uncompetitive (at the lower inhibitor concentrations) or of the competitive nature with a Ki = 420 microM. Tenofovir and tenofovir disoproxil influenced the activity of CYP2C9, and competitive inhibition was found with Ki = 580 and 395 microM, respectively. Tenofovir disoproxil was shown to inhibit microsomal CYP2E1 activities by a mixed-type inhibition with Ki values at about 140 microM. The results indicate the possibility of an influence of the compounds tested on the respective CYP activities when used at high doses.