EU-ToxRisk - Repeated dose toxicity (RDT)/ Developmental and reproductive toxicity (DART) – Mitochondrial toxicity. The case of mitochondrial complex I inhibitors: deguelin and rotenone.

Keywords

REACH, read-across, RDT, DART, NAM, AOP

Objective

There is an anticipated hazard for agrochemicals that inhibit complex I of the mitochondrial respiratory chain to cause toxicity to the nigrostriatal neurons leading to symptoms that reflect Parkinson's disease. This effect has been comprehensively described in an OECD-validated AOP (Terron et al. 2019). This case study aims to assess the application of an AOP approach in a read-across safety assessment of structurally related mitochondrial complex I inhibitors, deguelin, and rotenone.
Epidemiological studies indicate that exposure of workers to rotenone is statistically associated with an increased incidence of Parkinson's disease; moreover, rotenone is known to induce parkinsonian phenotypes in experimental animals. Therefore, rotenone was used as the source substance. Deguelin can induce parkinsonian-like phenotypes in rats. Whether deguelin has such a parkinsonian hazard liability in humans is currently unclear and therefore deguelin was the target substance for this case study.

Testing Strategy

Based on the AOP, structural modelling approaches were applied to define the binding of rotenone and deguelin to mitochondrial complex I, the molecular initiating event of the AOP. Then, previously established and routinely applied assays that reflect the various key events in this AOP were defined. Multiple human-based in vitro test systems to monitor mitochondrial effects of rotenone and deguelin were additionally integrated. To assess the effect on neuron toxicity, high-content imaging approaches to measure degeneration of neuronal neurites were applied. Finally, both biokinetic evaluation of cellular exposure to rotenone and deguelin, as well as PBPK modelling, were used to evaluate the relevance of observed effects in vitro towards a likely in vivo exposure situation. Both substances inhibit complex I activity and cause mitochondrial dysfunction. Similarly, rotenone is also more potent than deguelin in disrupting neurites.
The target compound deguelin displayed a similar mode-of-action as rotenone, but with minor potency. The case study showed how practical application of an AOP approach through the integration of specific technologies and test systems might find broader application in a read-across safety assessment of structurally related substances.

Publications

Wink et al. 2018 [link]; Hiemstra et al. 2019 [link]; Delp et al. 2018 [link]; Terron et al. 2019 [link]; van der Stel W et al. 2020 [link]; Fisher et al. 2017 [link]; Delp et al. 2019 [link]; Hemmerich et al. 2020 [link]; Troger et al. 2020 [link]; Delp et al. 2019 [link]; Delp et al. 2018 [link]; Delp et al. 2021 [link]; Hemmerich et al. 2020 [link]; van der Stel et al. 2021 [link]; van der Stel et al. 2020 [link]; Troger et al. et al. 2020 [link]; Vrijenhoek et al. 2022 [link]; Escher et al. 2019 [link]; Rovida et al. 2021 [link]