PCB 136 Atropselectively Alters Morphometric and Functional Parameters of Neuronal Connectivity in Cultured Rat Hippocampal Neurons via Ryanodine Receptor-Dependent Mechanisms

Abstract

We recently demonstrated that polychlorinated biphenyl (PCB) congeners with multiple ortho chlorine substitutions sensitize ryanodine receptors (RyRs), and this activity promotes Ca²⁺-dependent dendritic growth in cultured neurons. Many ortho-substituted congeners display axial chirality, and we previously reported that the chiral congener PCB 136 (2,2',3,3',6,6'-hexachlorobiphenyl) atropselectively sensitizes RyRs. Here, we test the hypothesis that PCB 136 atropisomers differentially alter dendritic growth and other parameters of neuronal connectivity influenced by RyR activity. (-)-PCB 136, which potently sensitizes RyRs, enhances dendritic growth in primary cultures of rat hippocampal neurons, whereas (+)-PCB 136, which lacks RyR activity, has no effect on dendritic growth. The dendrite-promoting activity of (-)-PCB 136 is observed at concentrations ranging from 0.1 to 100 nM and is blocked by pharmacologic RyR antagonism. Neither atropisomer alters axonal growth or cell viability. Quantification of PCB 136 atropisomers in hippocampal cultures indicates that atropselective effects on dendritic growth are not due to differential partitioning of atropisomers into cultured cells. Imaging of hippocampal neurons loaded with Ca²⁺-sensitive dye demonstrates that (-)-PCB 136 but not (+)-PCB 136 increases the frequency of spontaneous Ca²⁺ oscillations. Similarly, (-)-PCB 136 but not (+)-PCB 136 increases the activity of hippocampal neurons plated on microelectrode arrays. These data support the hypothesis that atropselective effects on RyR activity translate into atropselective effects of PCB 136 atropisomers on neuronal connectivity, and suggest that the variable atropisomeric enrichment of chiral PCBs observed in the human population may be a significant determinant of individual susceptibility for adverse neurodevelopmental outcomes following PCB exposure.

Effect of Pregnancy on the Disposition of 2,2′,3,5′,6-Pentachlorobiphenyl (PCB 95) Atropisomers and Their Hydroxylated Metabolites in Female Mice

“…Further studies are therefore needed to advance our understanding of the complex processes contributing to species differences in the disposition of PCB atropisomers, especially in light of the growing evidence demonstrating that the developmental neurotoxicity of chiral PCBs is atropselective. 16–18 …”

“…Specifically, chiral PCBs atropselectively interfere with cellular targets implicated in cellular calcium homeostasis 16, 17 and, as we have shown recently, atropselectively affect neuronal connectivity in cultured rat hippocampal neurons. 18 …”

“…Such differences are expected to be toxicologically relevant because PCBs atropselectively affect molecular and cellular targets implicated in PCB developmental neurotoxicity. 16–18 …”

Chiral polychlorinated biphenyls: absorption, metabolism and excretion—a review

“…Recent studies with pure C-PCB atropisomers showed that (−)-PCB 136 activates ryanodine receptors (RyRs) (Pessah et al 2009), microsomal Ca 2+ channels that are widely expressed in the mammalian brain and skeletal muscle. Moreover, (−)-PCB 136 enhances dendritic growth in primary cultured rat hippocampal neurons by mechanisms involving RyRs (Yang et al 2014). In contrast, (+)-PCB 136 lacked activity towards RyRs and had no effect on dendritic growth.…”

Reference compounds for alternative test methods to indicate developmental neurotoxicity (DNT) potential of chemicals: Example lists and criteria for their selection and use_suppl

“…To an even greater extent, the same holds true for identification of general toxicity mechanisms (Fritsche et al, 2005;Gassmann et al, 2010Gassmann et al, , 2014Langeveld et al, 2012;Lein et al, 2007;Waldmann et al, 2014;Yang et al, 2014;Zimmer et al, 2011a) or for development of toxicant classifiers (Krug et al, 2013b;Rempel et al, 2015), as the selected compounds are the main anchoring point of such studies.…”