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Improving in vitro to in vivo extrapolation (IVIVE) by incorporation of toxicokinetic measurements: a case study with lindane induced seizures.
Citation:
CROOM, E. L., TIM SHAFER, W. R. MUNDY, A. F. JOHNSTONE, C. M. MACK, B. ROBINETTE, R. A. PEGRAM, AND R. A. PEGRAM. Improving in vitro to in vivo extrapolation (IVIVE) by incorporation of toxicokinetic measurements: a case study with lindane induced seizures. Presented at Society of Toxicology (SOT) Annual Meeting, San Francisco, CA, March 11 - 15, 2012.
Impact/Purpose:
This abstract describes the in vitro toxicokinetics of lindane in MEA cultures of primary neurons to develop an improved basis for in vitro to in vivo extrapolation. The in vitro results compare favorably with in vivo lindane levels associated with seizures , thus demonstrating the efficacy of this approach and the predictive capability of MEA results.
Description:
In vitro toxicokinetic assessments are needed to maximize the capability of in vitro toxicity assays to predict in vivo outcomes. The purpose of this study was to determine the in vitro distribution of lindane, a non-competitive GABAA receptor antagonist, in rat primary neocortical neuron cultures and characterize its concentration dependent effects on neural network activity as measured with microelectrode arrays (MEAs). These data were then compared to published in vivo blood and brain lindane concentrations associated with seizures. Using "faux MEAs" (identical culture dishes, but with no electrodes), the time (5-20 min) and concentration (0.1-250 uM) dependent accumulation of lindane into the neurons and the amount of lindane in the media and wells was determined by GC-uECD. Approximately 70% of the lindane was in the media while the amount in the cells never exceeded 5%. After the media and cells were removed, ~15% of the total applied dose was recovered from the wells when fresh media was added. Lindane accumulation in the cells was time and concentration dependent. Cell lindane levels were ~20-fold higher than the media concentration at the EC50, which was determined to be 1.9uM(0.58ug/ml for an increased mean spike rate of spontaneous network electrical activity in rat primary neurons cultured on MEAs. The human (0.2-1.2 ug/ml) and rat (1.7-1.9 ug/ml) blood lindane levels associated with seizures were similar to the actual effective media levels determined in these experiments (0.4 ug/ml at the EC50). The published rat brain lindane levels associated with seizures in vivo (5-11 ug/ml) were also similar to levels detected in the cells at the EC50 dose (11.1 ug/ml). These findings indicate that careful in vitro toxicokinetic measurements can greatly facilitate IVIVE and that in vitro MEA results are predictive of the in vivo dose-response neurotoxicity of lindane in rodents and humans. (This abstract does not reflect US EPA policy.)