| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2001: ¥1,700,000 (Direct Cost: ¥1,700,000)
Fiscal Year 2000: ¥2,100,000 (Direct Cost: ¥2,100,000)
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| Research Abstract |
Cytochrome P450s including in the CYP3A subfamily are involved in metabolism of numbers of clinically relevant substrates as well as numerous endogenous compounds. CYP3A forms are induced by treatment with various drugs, but those induction profiles differ between experimental animals and humans. Recently, a novel orphan receptor, pregnane X receptor (PXR) has been isolated and reported to make a heterodimer with retinoid X receptera (RXRa). In our experiment, co-expression of human PXR (hPXR) with RXRa did not show the CYP3A1 gene activation by treatment with rifampicin. When hPXR co-expressed with other orphan receptors, COUPs, apolipoprotein AI regulatory protein 1 (ARP-1) and v-ErbA-related protein 3, the CYP3A1 gene expression was activated by rifampicin in HepG2 cells. On the contrary, neither co-expression of PXR with RXRa nor with COUPs showed the CYP3A4 gene activation by the treatment, although the activation was observed on single expression of hPXR in HepG2 cells. On the ot
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her hand, both CYP3A1 and CYP3A4 inductions through hPXR activation by rifampicin were basically similar at the level of their cis-elements. The transactivation of the CYP3A4 gene is mainly mediated through dNR-1 locating around at its -7600 bp and enhance through ER-6. To further verify the in vivo activation of the CYP3A4 gene expression by drugs, adenovirus expression vectors, AdCYP3A4-362 and AdCYP3A4-362-7k, were constructed with the proximal promoter (+11 to -364) and the enhancer (-7.2 k to -7.8 k) regions of the CYP3A4 gene, respectively. AdCYP3A4-362 infection to HepG2 cells showed the CYP3A4 gene activation by treatment with clotrimazole and dexamethsone. The gene activation was enhanced by co-infection of AdhPXR. AdCYP3A4-362-7k infection to HepG2 cells showed the CYP3A4 gene activation not only by clotrimazole but also by rifampicin. Therefore in vivo experiment of the CYP3A4 gene activation by use of AdCYP3A4-362-7k was carried out in mouse and rat. Strong CYP3A4 gene activation was observed in mouse livers by administration of all drugs used in this experiment. The activation was strongly enhanced in both animal livers treated only with rifampicin by co-transfection of AdhPXR. These results suggest that PXR is one of essential factors for the CYP3A induction, and others factors are also predicted from our experiment. Less
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