Citation:

Shafer, Tim, J. Brown, B. Lynch, S. Davila-Montero, K. Wallace, AND K. Paul-Friedman. Evaluation of Chemical Effects on Network Formation in Cortical Neurons Grown on Microelectrode Arrays. TOXICOLOGICAL SCIENCES. Society of Toxicology, RESTON, VA, 169(2):436-455, (2019). https://doi.org/10.1093/toxsci/kfz052

Impact/Purpose:

The need to define developmental neurotoxicity (DNT) hazard for thousands of chemicals is a challenge not only for the EPA but for regulatory agencies world-wide. To develop this information, an assay battery of in vitro screening assays is being developed and evaluated. The assays in this battery evaluate chemical effects on a variety of processes critical to development of the nervous system, such as the proliferation of neuroprogenitor cells, outgrowth of neurites, establishment of chemical synapses and formation of functional networks. In the current study, 136 unique chemicals were evaluated for their effects on the formation of functional networks in primary cultures of cortical neurons. The results demonstrate that this assay is sensitive to effects of chemicals known to have acute effects on the nervous system. In addition, for a small subset of chemicals where sufficient information was available to make in vitro to in vivo comparisons, that the assay detects effects on network formation at concentrations that are relevant to in vitro exposures. This work will be of interest to those working under TSCA and FIFRA, as well as for decision makers who need to have information about potential DNT hazard as part of their decision-making process.

Description:

Thousands of chemicals to which humans are potentially exposed have not been evaluated for developmental neurotoxicity (DNT) potential, driving efforts to develop a battery of in vitro screening approaches for DNT hazard. Here, 136 unique chemicals were evaluated for potential DNT hazard using a network formation assay (NFA) in cortical cells grown on microelectrode arrays (MEAs). The effects of chemical exposure from 2 hr post-plating through 12 days in vitro (DIV) on network formation were evaluated at DIV 5, 7, 9 and 12, with cell viability assessed at DIV 12. Only 82 chemicals altered at least one network development parameter. Assay results were reproducible; 10 biological replicates yielded qualitative results that were 100% concordant, with consistent potency values. Toxicological tipping points were determined for 58 chemicals, and were similar to or lower than the lowest 50% effect concentrations (EC50) for all parameters. When EC50and tipping point values from the NFA were compared to the range of potencies observed in ToxCast assays, the NFA EC50¬ values were less than the lower quartile for ToxCast assay potencies for a subset of chemicals, many of which are acutely neurotoxic in vivo. For 13 chemicals with available in vivo DNT data, estimated administered equivalent doses based on NFA results were similar to or lower than administered doses in vivo. Collectively, these results indicate that the NFA is sensitive to chemicals acting on nervous system function and will be a valuable contribution to an in vitro DNT screening battery.

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