Differential Effects of Commercial Polybrominated Diphenyl Ether and Polychlorinated Biphenyl Mixtures on Intracellular Signaling in Rat Brain in Vitro

Abstract

Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants and have been detected in human blood, adipose tissue, and breast milk. Developmental and long-term exposures to these contaminants may pose a human health risk, especially to children. Previously, we demonstrated that polychlorinated biphenyls (PCBs), which are neurotoxic and structurally similar to PBDEs, perturbed intracellular signaling events, including calcium homeostasis and subsequent events such as protein kinase C (PKC), which are critical for the normal function and development of the nervous system. The objective of the present study was to test whether commercial PBDE mixtures (DE-71, a pentabrominated dipheyl ether mixture, and DE-79, a mostly octabromodiphenyl ether mixture) affected intracellular signaling mechanisms in a similar way to that of PCBs and other organohalogens, as an attempt to understand the common mode of action for these persistent chemicals. PKC translocation was studied by determining ³H-phorbol ester (³H-PDBu) binding in rat cerebellar granule cells, and calcium buffering was determined by measuring ⁴⁵Ca²⁺ uptake by microsomes and mitochondria isolated from adult male rat brain (frontal cortex, cerebellum, and hippocampus). As seen with PCBs, DE-71 increased PKC translocation and inhibited ⁴⁵Ca²⁺ uptake by both microsomes and mitochondria in a concentration-dependent manner. The effect of DE-71 on ⁴⁵Ca²⁺ uptake seems to be similar in all three brain regions. Between the two organelles, DE-71 inhibited mitochondrial ⁴⁵Ca²⁺ uptake to a greater extent than microsomal ⁴⁵Ca²⁺ uptake. DE-79 had no effects on either neurochemical event even at 30 μg/ml. Aroclor 1254 altered both events to a greater extent compared to DE-71 on a weight basis. When the results were compared on a molar basis, Aroclor 1254 altered PKC translocation and microsomal ⁴⁵CaP²⁺ uptake to a greater extent than DE-71, however, Aroclor 1254 and DE-71 equally affected mitochondrial ⁴⁵Ca²⁺ uptake. These results indicate that PBDEs perturbed intracellular signaling mechanisms in rat brain as do other organohalogen compounds and the efficacy between the commercial PCB and PBDE mixtures seem to vary with different endpoints.