The Effect of In Vitro Dieldrin Exposure on the Rat Paraoxonase 1 ( Pon1) Promoter

The legacy organochlorine insecticide, dieldrin, is still found in soil and accumulation in individuals is possible. Paraoxonase 1 hydrolyzes the oxon metabolites of organophosphorus insecticides, as well as other substrates. Putative binding sites for pregnane X receptor (PXR) exist in the paraoxonase promoter, and studies have indicated that dieldrin can activate PXR-regulated gene expression. We examined rat paraoxonase promoter activity in the presence of dieldrin alone or combined with nuclear receptors (NRs). In vitro dieldrin concentrations from 10 to 100 mu M significantly increased (p<0.05) promoter activity in the presence of Pxr or Rxr alone and when Pxr plus Rxr were on the same vector, indicating that dieldrin can increase paraoxonase promoter activity in the presence of NRs. To our knowledge, this is the first report of dieldrin increasing paraoxonase promoter activity. Since many organochlorine insecticides are in the same chemical class as dieldrin, these results could be typical of other bioaccumulative persistent pollutants.