Effects of decabrominated diphenyl ether (PBDE 209) on voltage-gated sodium channels in primary cultured rat hippocampal neurons.

Polybrominated diphenyl ethers (PBDEs) are widely used as flame-retardant additives. But the application of PBDEs has been challenged due to their toxicity, especially neurotoxicity. In this study, we investigated the effects of decabrominated diphenyl ether (PBDE 209), the major PBDEs product, on voltage-gated sodium channels (VGSCs) in primary cultured rat hippocampal neurons. Employing the whole-cell patch-clamp technique, we found that PBDE 209 could irreversibly decrease voltage-gated sodium channel currents (I(Na)) in a very low dose and in a concentration-dependent manner. We had systematically explored the effects of PBDE 209 on I(Na) and found that PBDE 209 could shift the activation and inactivation of I(Na) toward hyperpolarizing direction, slow down the recovery from inactivation of I(Na), and decrease the fraction of activated sodium channels. These results suggested that PBDE 209 could affect VGSCs, which may lead to changes in electrical activities and contribute to neurotoxicological damages. We also showed that ascorbic acid, as an antioxidant, was able to mitigate the inhibitory effects of PBDE 209 on VGSCs, which suggested that PBDE 209 might inhibit I(Na) through peroxidation. Our findings provide new insights into the mechanism for the neurological symptoms caused by PBDE 209.

Effects of decabrominated diphenyl ether (PBDE 209) exposure at different developmental periods on synaptic plasticity in the dentate gyrus of adult rats In vivo.

Polybromininated diphenyl ethers (PBDEs) are widely used as flame-retardant additives. Previous studies have demonstrated that PBDEs exposure can lead to neurotoxicity. However, little is known about the effects of PBDE 209 on synaptic plasticity. This study investigated the effect of decabrominated diphenyl ether (PBDE 209), a major PBDEs product, on synaptic plasticity in the dentate gyrus of rats at different developmental periods. We examined the input/output functions, paired-pulse reactions, and the long-term potentiation of the field excitatory postsynaptic potential slope and the population spike amplitude in vivo. Rats were exposed to PBDE 209 during five different developmental periods: pregnancy, lactation via mother's milk, lactation via intragastric administration, after weaning, and prenatal to life. We found that exposed to PBDE 209 during different developmental periods could impair the synaptic plasticity of adult rats in different degrees. The results also showed that PBDE 209 might cause more serious effects on the postsynaptic cell excitability in synaptic plasticity, and the lactation period was the most sensitive time of development towards PBDE 209.

Epigallocatechin-3-gallate induced primary cultures of rat hippocampal neurons death linked to calcium overload and oxidative stress.

Epigallocatechin-3-gallate (EGCG), a catechin polyphenols component, is the main ingredient of green tea extract. It has been reported that EGCG is a potent antioxidant and beneficial in oxidative stress-related diseases, but others and our previous study showed that EGCG has pro-oxidant effects at high concentration. Thus, in this study, we tried to examine the possible pathway of EGCG-induced cell death in cultures of rat hippocampal neurons. Our results showed that EGCG caused a rapid elevation of intracellular free calcium levels ([Ca(2+)](i)) in a dose-dependent way. Exposure to EGCG dose- and time-dependently increased the production of reactive oxygen species (ROS) and reduced mitochondrial membrane potential (Deltapsi(m)) as well as the Bcl-2/Bax expression ratio. Importantly, acetoxymethyl ester of 5,5'-dimethyl-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, ethylene glycol-bis-(2-aminoethyl)-N,N,N',N'-tetraacetic acid, and vitamin E could attenuate EGCG-induced apoptotic responses, including ROS generation, mitochondrial dysfunction, and finally partially prevented EGCG-induced cell death. Furthermore, treatment of hippocampal neurons with EGCG resulted in an elevation of caspase-3 and caspase-9 activities with no significant accompaniment of lactate dehydrogenase release, which provided further evidence that apoptosis was the dominant mode of EGCG-induced cell death in cultures of hippocampal neurons. Taken together, these findings indicated that EGCG induced hippocampal neuron death through the mitochondrion-dependent pathway.

Involvement of cyclin D1/CDK4 and pRb mediated by PI3K/AKT pathway activation in Pb2+ -induced neuronal death in cultured hippocampal neurons.

Lead (Pb) is widely recognized as a neurotoxicant. One of the suggested mechanisms of lead neurotoxicity is apoptotic cell death. And the mechanism by which Pb(2+) causes neuronal death is not well understood. The present study sought to examine the obligate nature of cyclin D1/cyclin-dependent kinase 4 (CDK4), phosphorylation of its substrate retinoblastoma protein (pRb) and its select upstream signal phosphoinositide 3-kinase (PI3K)/AKT pathway in the death of primary cultured rat hippocampal neurons evoked by Pb(2+). Our data showed that lead treatment of primary hippocampal cultures results in dose-dependent cell death. Inhibition of CDK4 prevented Pb(2+)-induced neuronal death significantly but was incomplete. In addition, we demonstrated that the levels of cyclin D1 and pRb/p107 were increased during Pb(2+) treatment. These elevated expression persisted up to 48 h, returning to control levels after 72 h. We also presented pharmacological and morphological evidences that cyclin D1/CDK4 and pRb/p107 were required for such kind of neuronal death. Addition of the PI3K inhibitor LY294002 (30 microM) or wortmannin (100 nM) significantly rescued the cultured hippocampal neurons from death caused by Pb(2+). And that Pb(2+)-elicited phospho-AKT (Ser473) participated in the induction of cyclin D1 and partial pRb/p107 expression. These results provide evidences that cell cycle elements play a required role in the death of neurons evoked by Pb(2+) and suggest that certain signaling elements upstream of cyclin D1/CDK4 are modified and/or required for this form of neuronal death.