Bisphenol A 3,4-quinone induces the conversion of xanthine dehydrogenase into oxidase in vitro

In the present study, we assessed the influence of bisphenol A (BPA) and bisphenol A 3,4-quinone (BPAQ) on the conversion of xanthine dehydrogenase (XD) into xanthine oxidase (XO) in the rat liver in vitro. BPA up to 100 micromol/L did not affect the XO and XD activities in the partially purified cytosolic fraction from rat liver, whereas BPAQ (2-10 micromol/L) dose-dependently enhanced the XO activity concomitant with a decrease in the XD activity, implying that BPAQ, but not BPA, can convert XD into the reactive oxygen species (ROS) producing the form XO. Furthermore, it was found that BPAQ could increase the generation of ROS and oxidize the guanine moiety of deoxyguanosine in the DNA of primary rat hepatocyte cultures. These results suggest that BPAQ has the potential to convert XD into XO in the liver, which in turn may lead to ROS generation and oxidative DNA damage in this region.

Selenite induces oxidative DNA damage in primary rat hepatocyte cultures

The effects of selenite ions on oxidative DNA damage in primary rat hepatocyte cultures were examined. Selenite ions dose-dependently stimulated 8-hydroxydeoxyguanosine formation in DNA from the hepatocyte cultures at concentrations of 1, 5 and 10 micromol/L (1.6-, 2.5- and 3.6-fold). Selenite ions also induced DNA fragmentation in nucleus from the hepatocyte cultures at concentrations of 5 and 10 micromol/L. Selenite ions could not affect protein expression levels of 8-oxoguanine DNA glycosylase 1 which is responsible for excision of 8-hydroxydeoxyguanosine from DNA, but could increase 2',7'-dichlorofluorescein-fluorescence intensity from 2',7'-dichlorodihydrofluorescein, an indicator of reactive oxygen species generation, at concentrations of 5 and 10 micromol/L. Furthermore, an increase in 8-hydroxydeoxyguanosine induced by selenite ions (10 micromol/L) was inhibited by free radical scavengers (alpha-tocopherol, N-acetyl-L-cysteine, and melatonin) at concentrations more than 50 micromol/L. These observations imply that selenite ions have the potential to induce oxidative DNA damage in the liver through an increase in reactive oxygen species formation, but not a decrease in 8-oxoguanine DNA glycosylase 1 protein expression levels.

The regulation of formation of prostaglandins and arachidonoyl-CoA from arachidonic acid in rabbit kidney medulla microsomes by linoleic acid hydroperoxide

Under physiological conditions, small amounts of free arachidonic acid (AA) are released from membrane phospholipids, and cyclooxygenase (COX) and acyl-CoA synthetase (ACS) competitively act on this fatty acid to form prostaglandins (PGs) and arachidonoyl-CoA (AA-CoA). In the present study, we investigated the effects of linoleic acid (LA) and 13-hydroperoxyoctadecadienoic acid (13-HPODE) on the PG and AA-CoA formation from high and low concentrations of AA (60 and 5 microM) in rabbit kidney medulla microsomes. The kidney medulla microsomes were incubated with 60 or 5 microM [(14)C]-AA in 0.1M Tris-HCl buffer (pH 8.0) containing cofactors of COX (reduced glutathione and hydroquinone) and cofactors of ACS (ATP, MgCl(2) and CoA). After incubation, PG (as total PGs), AA-CoA and residual AA were separated by selective extraction using petroleum ether and ethyl acetate. LA (10-50 microM) reduced only PG formation from both 60 and 5 microM AA. 13-HPODE (10-50 microM) also reduced PG formation from 60 and 5 microM AA, but the inhibitory potency was much stronger than that by LA. Furthermore, 13-HPODE had the potential to increase the AA-CoA formation with a decrease in the PG formation from 5 microM AA. These results suggest that 13-HPODE, but not LA, may shift AA away from COX pathway into ACS pathway under low substrate concentration (near physiological concentration of AA).