EFSA Pilot Project on New Approach Methodologies (NAMs) for Tebufenpyrad Risk Assessment. Part 2. Hazard characterisation and identification of the Reference Point

Abstract

This Project was performed to provide an in vitro Point of Departure (PoD) for an Adverse Outcome Pathway (AOP)‐informed Integrated Approach to Testing and Assessment (IATA), concerning a potential risk of parkinsonian motor deficits after long‐term exposure to Tebufenpyrad. The AOP considered was AOP:3. Assays were performed for Key Event (KE) 1, KE2 (mitochondrial dysfunction) and KE4 of the AOP, based on the use of human dopaminergic neurons (LUHMES cells). KE1 (inhibition of complex I of the mitochondrial respiratory chain) was considered equivalent to the molecular initiating event (MIE). KE4 (dopaminergic cell degeneration) was considered as alternative AO (target cell degeneration). All necessary and linear steps of the AOP (i.e. KE2,3,4) were investigated by experimental test methods. The three major objectives were: (i) generation of potential PoD data from each assay; (ii) evaluation and optimization of the consistency of these data; (iii) selection of a PoD to be used for further risk assessment. During the optimization phase, assay conditions that reflect brain metabolism (MitoMet conditions) were implemented, and degeneration of neurites was considered the most relevant neuropathological endpoint. With this setting, the potential PoD ranged from 6 nM to 45 nM. The selection of the PoD put emphasis on more chronic effects and on the assay closest to the AO. Thus the KE4 assay, measuring neurite degeneration under MitoMet conditions was chosen, and the PoD was 8 nM. This value has a confidence interval of about one log10‐fold change from the lowest to the highest estimate (range: 3 nM – 30 nM), based on the experimental variations we observed. Some biokinetics measurements were undertaken to help estimating cell concentrations. These data had a high uncertainty concerning the measurements and the model assumptions. Based on the assumptions we consider most realistic and robust, we suggest a cell/tissue (brain) concentration of 8‐40 nM to be associated with a potential onset of toxicity of Tebufenpyrad.

Mapping of Data Requirements and Assessment Methodologies Linked to the Regulatory Frameworks and Remits of the Relevant EU Agencies (ECHA, EFSA and EMA) and EC Scientific Committees (SCCS and SCHEER)

“…An EFSA guidance for RAx is currently in preparation 159 . With respect to the even more daunting NAMs and their implementation into modern assessment a road map for their implementation (Escher et al, 2022) and first results of the respective pilot project were published (Alimohammadi et al, 2023;Henri et al, 2023). It is understood that the use of RAx is currently limited to some areas within EFSA's remit of activity, such as food flavourings and in the assessment of metabolites of PPPR substances (Chesnut et al, 2018).…”

Ten Years of Using Key Characteristics of Human Carcinogens to Organize and Evaluate Mechanistic Evidence in IARC Monographs on the Identification of Carcinogenic Hazards to Humans: Patterns and Associations

“…Use of high-throughput in vitro toxicity screening data in cancer hazard evaluations by IARC Monographs was pioneered together with Key Characteristics (Chiu et al 2018) and was among the first examples of these data being used in decision-making. Indeed, the wide recognition of the greater role for mechanistic evidence in cancer hazard identification, as well as in other areas of regulatory decisions for industrial (U.S. EPA 2021, 2022), food-use (Alimohammadi et al 2023) and drugs (Strauss et al 2021), has been catalyzed by both the time and expense of human epidemiology and chronic animal studies, considerations of animal welfare, and advances in computational and in vitro models in toxicology (Andersen and Krewski 2010;Kavlock et al 2018;Krewski et al 2020;Sturla et al 2014). In fact, there has been was not certified by peer review) is the author/funder.…”