Abstract
We previously reported that squalestatin 1-mediated induction of CYP2B expression is attributable to squalene synthase inhibition and accumulation of an endogenous isoprenoid(s) that is capable of activating the constitutive androstane receptor. To determine whether squalestatin 1-mediated CYP2B induction is strictly dependent on the biosynthesis of farnesyl pyrophosphate (FPP), the substrate for squalene synthase, the effects of alendronate, a nitrogen-containing bisphosphonate inhibitor of farnesyl diphosphate synthase, on basal, squalestatin 1-inducible, and phenobarbital-inducible CYP2B expression in primary cultured rat hepatocytes were assessed. Alendronate treatment alone had no effect on CYP2B or CYP3A mRNA expression in the hepatocyte cultures, but alendronate cotreatment completely suppressed squalestatin 1-mediated CYP2B mRNA induction at concentrations (60 and 100 μM) that effectively inhibited cellular farnesyl diphosphate synthase activity, as assessed by reductions of squalestatin 1-mediated FPP accumulation, and that were not toxic to the cells, as indicated by a lack of effect on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide activity. Alendronate cotreatment also partially suppressed phenobarbital-inducible CYP2B expression, and this suppressive effect was attenuated by additional cotreatment with the upstream pathway inhibitor, pravastatin. These findings not only demonstrate that squalestatin 1-mediated CYP2B induction cannot occur in the absence of FPP biosynthesis but also indicate that one or more upstream isoprenoids, possibly isopentenyl pyrophosphate and/or dimethylallyl pyrophosphate, function to antagonize the CYP2B induction process.
Footnotes
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This work was conducted with support from National Institutes of Health Grant HL50710 and services provided by the Cell Culture and Gene Transfer Technologies Facility Core and the Imaging and Cytometry Facility Core of Environmental Health Services Center Grant ES06639.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.108.022558.
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ABBREVIATIONS: CAR, constitutive androstane receptor (or NR1I3); FPP, farnesyl pyrophosphate (or farnesyl diphosphate); FDPS, farnesyl diphosphate synthase (or farnesyl pyrophosphate synthase); GPP, geranyl pyrophosphate; IPP, isopentenyl pyrophosphate; GGPP, geranylgeranyl pyrophosphate; NBP, nitrogen-containing bisphosphonate (or aminobisphosphonate); DMAPP, dimethylallyl pyrophosphate; MTT, 3-(4,5-di methylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide; PBS, phosphate-buffered saline; PROD, pentoxyresorufin O-depentylase; ApppI, triphosphoric acid 1-adenosin-5′-yl ester 3-(3-methylbut-3-enyl) ester.
- Received May 27, 2008.
- Accepted July 8, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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