GABAA receptor and cell membrane potential as functional endpoints in cultured neurons to evaluate chemicals for human acute toxicity

Abstract

Toxicity risk assessment for human health mainly relies on data obtained from animal experimentation and human experimental studies and epidemiology. Validated alternative test methods are required for safety toxicology of drugs and chemicals. Studies have demonstrated that there is ~70% correlation between in vitro cytotoxic concentracions and in vivo LD50 or human lethal concentracions. Multiple reasons may account for this failing to predict acute toxicity in 20 – 30 % of the tested chemicals: i) chemical metabolism, ii) barrier passage, iii) biokinetics and iv) organ-specific toxicity (neurotoxicity, hepatotoxicity, nephrotoxicity, etc). The nervous system is particularly vulnerable to chemical exposure; its complexity results in multiple potential target sites with different toxicity demonstration. We are developing a neurotoxicity testing strategy that could identify factors to improve the correlation between in vitro data and human acute toxicity and alerts for the identification of outliers. A set of pharmaceutical, industrial, biocide and drug abuse chemicals have been tested against GABAA receptor activity, GABA and glutamate transport , acetylcholinaesterase activity and membrane potential in primary neuronal cultures, in the frame of the European project AcuteTox. GABAA receptor-mediated chloride influx was inhibited by compounds for which seizures have been observed after severe human poisoning. Abuse drugs inhibit [3H]GABA uptake but not [3H]aspartate uptake. Exposure to organophosphorus compounds for 48 hours resulted in higher inhibition of acetylcholinaesterase activity than shorter exposure for 30 – 60 minutes, suggesting that primary cortical neurons have metabolic capacity. Most neurotoxic compounds altered membrane potential. Cell viability was not reduced at concentrations that were effective against neuronal endpoints. Acetaminophen and acetylsalicylic acid did not modify any of the endpoints assayed. These results show that in vitro evaluation of neural endpoints may identify compounds that produce acute neurotoxicity in humans, provided that relevant in vitro models for acute neural disfunctions are used.