Protectiveness of NAM-based hazard assessment – which testing scope is required?

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Walter Zobl , Annette Bitsch, Jonathan Blum, Jan J. W. A. Boei, Liliana Capinha, Giada Carta, Jose V. Castell, Enrico Davoli, Christina Drake, Ciaran P. Fisher, Muriel M. Heldring, Barira Islam, Paul Jennings, Marcel Leist, Damiano Pellegrino-Coppola, Johannes P. Schimming, Kirsten E. Snijders, Laia Tolosa, Bob van de Water, Barbara M. A. van Vugt-Lussenburg, Paul Walker, Matthias M. Wehr, Lukas S. Wijaya, Sylvia E. Escher
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Hazard assessment requires toxicity tests to allow deriving protective points of departure (PoDs) for risk assessment irrespective of a compound’s mode of action (MoA). The scope of in vitro test batteries (ivTB) needed to assess systemic toxicity is still unclear. We explored the protectiveness regarding systemic toxicity of an ivTB with a scope that was guided by previous findings from rodent studies, where examining six main targets, including liver and kidney, was sufficient to predict the guideline scope-based PoD with high probability. The ivTB comprises human in vitro models representing liver, kidney, lung, and the neuronal system covering transcriptome, mitochondrial dysfunction, and neuronal outgrowth. Additionally, 32 CALUXR- and 10 HepG2 BAC-GFP reporters cover a broad range of disturbance mechanisms. Eight compounds were chosen for causing adverse effects such as immunotoxicity or anemia in vivo, i.e., effects not directly covered by assays in the ivTB. PoDs derived from the ivTB and from oral repeated dose studies in rodents were extrapolated to maximum unbound plasma concentrations for comparison. The ivTB-based PoDs were one to five orders of magnitude lower than in vivo PoDs for six of eight compounds, implying that they were protective. The extent of in vitro response varied across test compounds. Especially for hematotoxic substances, the ivTB showed either no response or only cytotoxicity. Assays better capturing this type of hazard would be needed to complement the ivTB. This study highlights the potentially broad applicability of ivTBs for deriving protective PoDs of compounds with unknown MoA.

Plain language summary
Animal tests are used to determine how much of a chemical is toxic (threshold of toxicity) and which organs are affected. In principle, the threshold can also be derived solely from tests with cultured cells. However, only a limited number of cell types can practically be tested, so one challenge is to determine how many and which types shall be tested. In animal tests, only few organs including liver and kidney are regularly among those most sensitively affected. We explored whether a cell-based test battery representing these sensitive organs and covering important mechanisms of toxicity can be used to derive protective human thresholds. To challenge this approach, eight chemicals were tested that primarily cause effects in organs not directly represented in our test battery. Results provided protective thresholds for most of the investigated compounds and gave indications how to further improve the approach towards a full-fledged replacement of animal tests.

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Zobl, W. (2024) “Protectiveness of NAM-based hazard assessment – which testing scope is required?”, ALTEX - Alternatives to animal experimentation, 41(2), pp. 302–319. doi: 10.14573/altex.2309081.

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