In vitro testing of basal cytotoxicity: Establishment of an adverse outcome pathway from chemical insult to cell death

Abstract

In this paper, an in vitro basal cytotoxicity testing strategy is described for new chemical entities that lack any pre-existing information on potential toxicity. Special attention is paid to the selection of the cellular system, cytotoxicity assay and exposure conditions. This approach is based on a newly proposed generic adverse outcome pathway from chemical insult to cell death that consists of 3 steps, including initial cell injury, mitochondrial dysfunction and cell demise. The suggested strategy to consider in vitro basal cytotoxicity as a first step in evaluating the toxicity of new chemical entities can be placed in a tiered strategy that could be continued by evaluating more specific types of toxicity.

Keywords: Adverse outcome pathway; Basal cytotoxicity; Chemical; In vitro experimentation.

Figure 1. Generic adverse outcome pathway from chemical insult to cell death.

The first step or the MIE involves initial cell injury, whereby the parent chemical and/or its metabolites cause narcosis, directly impair mitochondrial function or induce decompartmentalization. In the second step, which is a KE, a MPT process takes place as a consequence of the primary insult. This ultimately leads to cell death by apoptosis or necrosis in the third step, being the actual AO.

Figure 2. Mechanisms of initial injury leading to basal cytotoxicity.

Chemicals can harm plasma membrane integrity through accumulation and binding to the phospholipid bilayer, called narcosis. Chemicals can negatively affect cellular energy supplies by targeting mitochondria. Chemicals can compromise subcellular architectural organization, called decompartmentalization.