Browsing by Subject "Drugs--Metabolism"

Now showing 1 - 3 of 3

Effect of immunosuppressive agents on drug metabolism in rats
(2001) Bai, Shuang; Brunner, Lane J.
The effects of cyclosporine on drug metabolism in rats and its mechanism
(2002-08) Liu, Jingrong; Brunner, Lane J.
Immunosuppressant cyclosporine (CsA) is primarily metabolized by cytochrome P450 3A (CYP3A), and a substrate for P-glycoprotein (P-gp). The large variability in CsA pharmacokinetics makes predicting CsA effects and toxicity difficult, which may be related to CsA-induced alterations in CYP3A or Pgp. Based on recent studies on the pregnane X receptor (PXR) in CYP3A induction and the role of cAMP in CYP regulation, we hypothesized that cAMP regulates PXR and CYP3A induction and that PXR and cAMP/CREB pathways are involved in CsA-induced CYP3A alterations. The objective of this work was to study the effects of chronic CsA administration on drug metabolism in rats and the possible mechanisms of CsA-induced CYP3A alterations in cells. Our in vivo results demonstrated that large doses of CsA significantly suppressed hepatic CYP3A but induced hepatic P-gp after rats were given CsA orally or subcutaneously for 28 days. In contrast, chronic oral administration of CsA increased small intestinal CYP3A. These data suggested that the differential effects of CsA on CYP3A and P-gp in the liver and small intestine may contribute to the variability of CsA pharmacokinetics. Our in vitro data demonstrated that CsA significantly decreased CYP3A expression and cAMP levels in CV-1 cells. To study whether PXR and/or cAMP/CREB pathways are involved in CsA-induced CYP3A modulation, we transfected a mouse PXR expression vector and the (CYP3A1DR3)2-tk-CAT reporter gene into HepG2, Caco-2, and CV-1 cells and measured the levels of phosphorylated cAMP response element-binding protein (phosphoCREB) in CV-1 cells. The results showed that CsA significantly suppressed PXR activation in these three cell lines and elevated phosphoCREB in CV-1 cells. Moreover, cAMP analog 8-Br-cAMP significantly upregulated phosphorylation of CREB and induced PXR activation and CYP3A expression. These results suggest that PXR and the cAMP/CREB pathways are critical in CYP3A alterations. However, CsA decreased cAMP content but increased phosphoCREB levels, thus suggesting that another pathway might be involved in CsA-induced CYP3A alteration. Together, these studies identified factors that are involved in the variability of CsA pharmacokinetics and elucidated mechanisms of CsA-induced CYP3A alterations in drug metabolism, thus providing a mechanistic interpretation of metabolism-mediated variation of CsA pharmacokinetics.
Recombinant adenoviral-meditated alterations of cytochrome P450 3A2 and 2C11
(2005) Callahan, Shellie Marie; Croyle, Maria A.
Recombinant adenovirus serotype 5 (Ad) is a key vector extensively employed in gene therapy clinical trials and vaccine development protocols. Although this vector has a natural tropism for the liver, there is limited understanding of how Ad infection affects one of the primary hepatic processes, drug metabolism. Preliminary data investigating the effect of a single dose of 5.7 x 1012 adenovirus particles/kilogram on the hepatic cytochrome P450 enzyme system (CYP) revealed not only that significant suppression occurs following systemic administration, but also that enzymatic activity remains suppressed for 14 days. In addition to the vector dose, various components of the virus (transgene, virus gene expression and capsid-receptor interactions) viii could be responsible for the observed suppression in hepatic CYP. Investigation of treatment (5.7 x 1010-5.7 x 1012 vp/kg) of a recombinant vector expressing a non-therapeutic transgene significantly suppressed CYP3A2 expression (mean value of 39%) and function (mean value of 41%) four days after administration. Doses in the range of 5.7 x 106-5.7 x 109 vp/kg did not alter CYP3A2 expression or function, but significantly increased CYP2C11 one day after administration. Expression levels (mean value of 88%) and activity levels (mean value of 93%) were markedly increased. Doses of vectors expressing self transgenes and no transgene revealed that CYP is altered regardless of the transgene cassette used. Treatment with the Null vector, a vector without a transgene cassette, significantly altered CYP3A2 activity throughout the duration of the study (14 days) and CYP2C11 activity at early time points (6 and 24 hours). In addition, modifications at the molecular and macromolecular level do not eliminate aberrations in CYP following Ad administration. Treatment with an adenoviral vector lacking all viral genes markedly suppressed both CYP isoforms, at the transcriptional and translational level, for 14 days. The data presented here suggest that the binding of Ad to cell surface receptors and subsequent internalization of the virion significantly alters posttranslational CYP function, possibly through altered signal transduction pathways. In addition these studies show that shifts in cellular machinery to support the production of the transgene product, and not the transcription of viral genes, also repress CYP transcription.