Effect of polychlorinated biphenyls on production of reactive oxygen species (ROS) in rat synaptosomes

In this paper the effect of polychlorinated biphenyls (PCBs) on the production of reactive oxygen species (ROS) in rat synaptosomes is elucidated. The effect of methylmercury (MeHg) on rat synaptosomes was included as a positive control since several studies have investigated the ability of this substance to produce ROS. The exposure of the synaptosomes to the congener 2,2-dichlorobiphenyl (2,2'-DCB; 12.5 mu M) produced a linear increase in the formation of 2',7'-dichlorofluorescein (DCF) as a measure for the production of ROS. The congeners 2,2'-DCB (12.5 mu M) and 3,3'-DCB (12.5 mu M) stimulated, as expression of ROS production, a significant increase in DCF formation formation compared to the control. The congeners 2-chlorobiphenyl (2-CB) and 2,2',6-trichlorobiphenyl (2,2,6'-TCB) were active at 50 mu M, whereas 2,2',4,4',5,5'-hexachlorobiphenyl (2,2',4,4',5,5'-HCB), 4,4'-DCB and 2,2',6,6'-tetrachlorobiphenyl (2,2',6,6'-TeCB) were not active at this concentration. The increased formation of ROS in response to 2,2'-DCB and MeHg in the synaptosomes was dependent on extracellular Ca2+. A phospholipase C inhibitor, U73122, was shown to significantly decrease the ROS formation induced by 2,2'-DCB, but did not reduce the ROS formation induced by MeHg. Ethanol (1%), a phospholipase D modulator, reduced the ROS formation induced by MeHg and by 2,2'-DCB by 33 and 52%, respectively. Wortmannin (25 nM), an inhibitor of phosphatidylinositol 3-kinase, completely inhibited the ROS formation induced by MeHg and 2,2'-DCB. It appears that the ROS-stimulating PCBs are the same congeners found to be neuroactive in other types of study. Phospholipase C and D and phosphatidylinositol 3-kinase seem to be involved in the intracellular signalling system that leads to ROS formation during PCB exposure.