Differential effects of polybrominated diphenyl ethers and polychlorinated biphenyls on [3H]arachidonic acid release in rat cerebellar granule neurons

Abstract

Polybrominated diphenyl ethers (PBDEs), which are widely used as flame-retardants, have been increasing in environmental and human tissue samples during the past 20-30 years, while other structurally related, persistent organic pollutants such as polychlorinated biphenyls (PCBs) and polychlorinated dibenzo-p-dioxins (on a TEQ basis), have decreased. PBDEs have been detected in human blood, adipose tissue, and breast milk, and developmental and long-term exposure to these contaminants may pose a human health risk, especially to children. Previously, we demonstrated that PCBs, which cause neurotoxic effects, including changes in learning and memory, stimulated the release of [3H]arachidonic acid ([3H]AA) by a cPLA2/iPLA2-dependent mechanism. PLA2 (phospholipase A2) activity has been associated with learning and memory, and AA has been identified as a second messenger involved in synaptic plasticity. The objective of the present study was to test whether PBDE mixtures (DE-71 and DE-79), like other organohalogen mixtures, have a similar action on [3H]AA release in an in vitro neuronal culture model. Cerebellar granule cells at 7 days in culture were labeled with [3H]AA for 16-20 h and then exposed in vitro to PBDEs. DE-71, a mostly pentabromodiphenyl ether mixture, significantly stimulated [3H]AA release at concentrations as low as 10 μg/ml, while DE-79, a mostly octabromodiphenyl ether mixture, did not stimulate [3H]AA release, even at 50 μg/ml. The release of [3H]AA by DE-71 is time-dependent, and a significant increase was seen after only 5-10 min of exposure. The removal and chelation of calcium from the exposure buffer, using 0.3 mM EGTA, significantly attenuated the DE-71-stimulated [3H]AA release; however, only an 18% inhibition of the release was demonstrated for the calcium replete conditions at 30 μg/ml DE-71. Methyl arachidonylfluorophosphonate (5 μM), an inhibitor of cPLA2/iPLA2, completely attenuated the DE-71-stimulated [3H]AA release. Further studies focused on comparing the effects of DE-71 with PCB mixtures such as Aroclors 1016 and 1254. Both PCB mixtures stimulated [3H]AA release in a concentration-dependent manner; however, the effect for PCBs was about two times greater than that of the PBDEs on a weight basis, but was comparable on a molar basis. These results indicate that PBDEs stimulated the release of [3H]AA by activating PLA2, which is similar to the effect of other organohalogen mixtures.