Citation:

Frank, C., J. Brown, K. Wallace, W. Mundy, I. Shah, AND Tim Shafer. Defining toxicological tipping points using microelectrode array recordings of developing neural networks. American Society for Cellular and Computational Toxicology, RTP, NC, September 29 - 30, 2016.

Impact/Purpose:

This work is being conducted to develop assays to screen and prioritize compounds for the potential to cause developmental neurotoxicity. This work presents an analysis of "tipping points" from the data which may be useful for compound prioritization.

Description:

Current guideline studies for developmental neurotoxicology (DNT) hazard are resource intensive and time-consuming, and therefore have only been conducted for a limited set of compounds. The EPA is developing more efficient methods to screen and prioritize the thousands of chemicals with undefined DNT hazard. In vitro microelectrode array recording of cellular electrical activity is a promising assay for development of functional neuronal networks that is amenable to high-throughput screening. We have used this approach on developing cultures of primary rat cortical neurons to derive 16 network parameters that quantify aspects of network activity and coordination during exposure to a library of 70 compounds. Assessing these 16 parameters at four times across 7 concentrations for each compound produced a rich dataset of 31,360 total endpoints. To prioritize compounds for further investigation, we have developed two complimentary methods to quantify the potency of each compound in producing network effects. An area-under-the-curve metric applied to network parameter values over time simplifies concentration-response modeling without loss of developmental delay effects, and allows for estimation of concentration where 50% of network activity is lost (EC50) for each network parameter. To integrate data across network parameters and model network adaptive response to exposure, we also calculated the total scalar perturbation at each timepoint. This allows for estimation of system velocities indicating whether a given concentration causes network failure or allows for recovery by adaptive response. Critical concentrations (i.e, tipping points) that mark the point at which toxicity begins to overwhelm the system were defined from the system velocities of 35 compounds. Comparison of these DNT tipping points to network and cell viability EC50 estimates for the same compounds suggests tipping points are often more sensitive than individual network parameters, capture selective effects, and may be useful to prioritize compounds for DNT hazard. (This abstract does not represent EPA Policy).

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