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Aroclor 1254 is a widely studied commercial polychlorinated biphenyl (PCB) mixture which, by definition, contains 54% chlorine by weight. Recent reports indicate substantial differences in the congener composition among Aroclor [...]

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. [ABSTRACT FROM PUBLISHER]

PCBs have been shown to alter several neurochemical end-points and are implicated in the etiology of some neurological diseases. Recent in vivo studies from our laboratory indicated that developmental exposure to a commercial PCB mixture, Aroclor 1254, caused perturbations in calcium homeostasis and changes in protein kinase C (PKC) activities in rat brain. However, it is not known which molecular substances are targets for PCB-induced developmental neurotoxicity. Since the PKC signaling pathway has been implicated in the modulation of motor behavior as well as learning and memory, and the roles of PKC are subspecies specific, the present study attempted to analyze the effects on selected PKC isozymes in the cerebellum and the hippocampus following developmental exposure (gestational day 6 through postnatal day 21) to a PCB mixture, Aroclor 1254. The results indicated that the developmental exposure to PCBs caused significant hypothyroxinemia and age-dependent alterations in the translocation of PKC isozymes; the effects were greatly significant at postnatal day (PND) 14. Immunoblot analysis of PKC-alpha (alpha) from both cerebellum and hippocampus revealed that developmental exposure to Aroclor 1254 caused a significant decrease in cytosolic fraction and an increase in particulate fraction. There was no significant difference between these two brain regions on the level of fractional changes. However, the ratio between the fractions (particulate/cytosol) from cerebellum only was increased in a dose-dependent manner. Analysis of PKC-gamma (gamma) in cerebellum on PND14 showed a decrease in cytosolic fraction in both dose groups and an increase in particulate fraction at high dose (6 mg/kg) only. The ratio between the two fractions was increased in a dose-dependent manner. In the hippocampus, there was a significant decrease in PKC-gamma in cytosolic fraction of the high-dose group and a significant increase in particulate fraction of the low-dose group. But, the ratio between the fractions showed a significant increase (2.6-fold increase in high dose on PND14). Analysis of PKC-epsilon (epsilon) in cerebellum showed a significant decrease in cytosolic fraction at PND14, while particulate PKand an increase in ratio between fractions at 6 mg/kg on PND14. The results from this study indicate that the patterns of subcellular distributions of PKC isoforms following a developmental PCB exposure were PKC isozyme- and developmental stage-specific. Considering the significant role of PKC signaling in motor behavior, learning and memory, it is suggested that altered subcellular distribution of PKC isoforms at critical periods of brain development may be a possible mechanism of PCB-induced neurotoxic effects and that PKC-alpha, gamma, and epsilon may be among the target molecules implicated with PCB-induced neurological impairments during developmental exposure. It is believed that this is the first report successfully identifying PKC isoforms responding to PCBs during developmental exposure.