Plant protection products (PPPs) consist of one or more active substances and several co-formulants. Active substances provide the functionality of the PPP and are consequently evaluated according to ...standard test methods set by legal data requirements before approval, whereas co-formulants' toxicity is not as comprehensively assessed. However, in some cases mixture effects of active substances and co-formulants might result in increased or different forms of toxicity. In a proof-of-concept study we hence built on previously published results of Zahn et al. (201838) on the mixture toxicity of Priori Xtra
and Adexar
to specifically investigate the influence of co-formulants on the toxicity of these commonly used fungicides. Products, their respective active substances in combination as well as some co-formulants were applied to human hepatoma cell line (HepaRG) in several dilutions. Cell viability analysis, mRNA expression, abundance of xenobiotic metabolizing enzymes and intracellular concentrations of active substances determined by LC-MS/MS analyses demonstrated that the toxicity of the PPPs is influenced by the presence of co-formulants
. PPPs were more cytotoxic than the mix of their active substances. Gene expression profiles of cells treated with the PPPs were similar to those treated with their respective mixture combinations with marked differences. Co-formulants can cause gene expression changes on their own. LC-MS/MS analyses revealed higher intracellular concentrations of active substances in cells treated with PPPs compared to those treated with the respective active substances' mix. Proteomic data showed co-formulants can induce ABC transporters and CYP enzymes. Co-formulants can contribute to the observed increased toxicity of PPPs compared to their active substances in combination due to kinetic interactions, necessitating a more comprehensive evaluation approach.
NAMs: Beta testing needed Bloch, Denise; Marx-Stoelting, Philip; Tralau, Tewes
Current opinion in toxicology,
September 2024, 2024-09-00, Letnik:
39
Journal Article
Recenzirano
Odprti dostop
A variety of new approach methodologies (NAMs) have already been developed for acute systemic and short-term toxicity, including in vitro, in silico, and omics methods. To advance their regulatory ...implementation, we suggest that beta testing of these methods in regulatory settings is urgently needed. There are several limitations to the use of NAMs for acute systemic and short-term toxicity, such as the lack of definitions for applicability domains, skewed reference data for validation, and the absence of representation of kinetic processes and multi-organ complexity. These limitations may lead to risks associated with the ordinary regulatory implementation, such as the application of methods to substances outside of their intended applicability domain or reduced predictivity due to a lack of mechanistic information or consideration of kinetics. We argue that this could be avoided by beta testing. Further benefits of beta testing would be the filling of in vivo data gaps and potentially improved validation with regard to human relevance of methods. In order to enhance the improvement, familiarisation, and acceptance of NAMs in the near future, it is essential for such concept of beta testing to rely on feedback loops between method testers and developers.
•Beta Testing new approach methodologies will accelerate their acceptance.•Acute systemic and short-term toxicity are ready for beta testing.•Advantages include familiarisation and identification of data gaps.•Feedback loops ensure constant method improvement.
Authorisation of ready to use plant protection products (PPPs) usually relies on the testing of acute and local toxicity only. This is in stark contrast to the situation for active substances where ...the mandatory data set comprises a most comprehensive set of studies. While the combination of certain active ingredients and co-formulants may nevertheless result in increased toxicity of the final product such combinations have never been evaluated systematically for complex and long-term toxicological endpoints. We therefore investigated the effect of three frequently used co-formulants on the toxicokinetic and toxicodynamic of the representative active substance combination of tebuconazol (Teb) and prothioconazol (Pro) or of cypermethrin (Cpm) and piperonyl butoxide (Pip), respectively. With all four active substances being potential liver steatogens, cytotoxicity and triglyceride accumulation in HepaRG were used as primary endpoints. Concomitantly transcriptomics and biochemical studies were applied to interrogate for effects on gene expression or inhibition of CYP3A4 as key enzyme for functionalization. Some of the tested combinations clearly showed more than additive effects, partly due to CYP3A4 enzyme inhibition. Other effects comprised the modulation of the expression and activity of steatosis-related nuclear key receptors. Altogether, the findings highlight the need for a more systematic consideration of toxicodynamic and toxicokinetic mixture effects during assessment of PPPs.
•Authorisation of plant protection products (PPPs) relies on the testing of acute and topological toxicity.•The combination of certain active ingredients and co-formulants may result in increased toxicity of the final product.•We therefore investigated the effect of three frequently used co-formulants on representative active substance combinations.•Some of the tested combinations showed more than additive effects on primary endpoints, partly due to CYP3A4 enzyme inhibition.•Altogether, the findings highlight the need for a more systematic consideration of toxicodynamic and toxicokinetic mixture effects during assessment of PPPs.
Currently, the authorisation process for plant protection products (PPPs) relies on the testing of acute and topological toxicity only. Contrastingly, the evaluation of active substances includes a ...more comprehensive set of toxicity studies. Nevertheless, mixture effects of active ingredients and co-formulants may result in increased toxicity. Therefore, we investigated effects of surface active co-formulants on the toxicity of two PPPs focussing on qualitative and quantitative toxicokinetic effects on absorption and secretion. The respective products are based on the active substances abamectin and fluroxypyr-meptyl and were tested for cytotoxicity in the presence or absence of the corresponding surfactants and co-formulants using Caco-2 cells. In addition, the effect of co-formulants on increased cellular permeation was quantified using LC–MS/MS, while potential kinetic mixture effects were addressed by fluorescence anisotropy measurements and ATPase assays. The results show that surface active co-formulants significantly increase the cytotoxicity of the investigated PPPs, leading to more than additive mixture effects. Moreover, analytical investigations show higher efflux ratios of both active substances and the metabolite fluroxypyr upon combination with certain concentrations of the surfactants. The results further point to a significant and concentration-dependent inhibition of Pgp transporters by most of the surfactants as well as to increased membrane fluidity. Altogether, these findings strongly support the hypothesis that surfactants contribute to increased cytotoxicity of PPPs and do so by increasing the bioavailability of the respective active substances.
In light of an ever-increasing exposure to chemicals, the topic of potential mixture toxicity has gained increased attention, particularly as the toxicological toolbox to address such questions has ...vastly improved. Routinely toxicological risk assessments will rely on the analysis of individual compounds with mixture effects being considered only in those specific cases where co-exposure is foreseeable, for example for pesticides or food contact materials. In the field of pesticides, active substances are summarized in so-called cumulative assessment groups (CAG) which are primarily based on their toxicodynamic properties, that is, respective target organs and mode of action (MoA). In this context, compounds causing toxicity by a similar MoA are assumed to follow a model of dose/concentration addition (DACA). However, the respective approach inherently falls short of addressing cases where there are dissimilar or independent MoAs resulting in wider toxicokinetic effects. Yet, the latter are often the underlying cause when effects deviate from the DACA model. In the present manuscript, we therefore suggest additionally to consider toxicokinetic effects (especially related to xenobiotic metabolism and transporter interaction) for the grouping of substances to predict mixture toxicity. In line with the concept of MoA-based CAGs, we propose common kinetics groups (CKGs) as an additional tool for grouping of chemicals and mixture prioritization. Fundamentals of the CKG concept are discussed, along with challenges for its implementation, and methodological approaches and examples are explored.
Like many other consumer and occupational products, pesticide formulations may contain active ingredients or co-formulants which have the potential to cause skin sensitisation. Currently, there is ...little evidence they do, but that could just reflect lack of clinical investigation. Consequently, it is necessary to carry out a safety evaluation process, quantifying risks so that they can be properly managed. A workshop on this topic in 2022 discussed how best to undertake quantitative risk assessment (QRA) for pesticide products, including learning from the experience of industries, notably cosmetics, that already undertake such a process routinely. It also addressed ways to remedy the matter of clinical investigation, even if only to demonstrate the absence of a problem. Workshop participants concluded that QRA for skin sensitisers in pesticide formulations was possible, but required careful justification of any safety factors applied, as well as improvements to the estimation of skin exposure. The need for regulations to stay abreast of the science was also noted. Ultimately, the success of any risk assessment/management for skin sensitisers must be judged by the clinical picture. Accordingly, the workshop participants encouraged the development of more active skin health monitoring amongst groups most exposed to the products.
•Quantitative risk assessment is pre-eminent for skin sensitiser safety evaluation.•Plant protection products may contain sensitising actives and/or co-formulants.•An expert workshop reviewed clinical and toxicological aspects of the issue.•The workshop recommended PPP safety assessment evolve to use QRA.•The workshop noted the paucity of skin allergy to PPPs required an evidence base.
Exposure to multiple substances is a challenge for risk evaluation. Currently, there is an ongoing debate if generic “mixture assessment/allocation factors” (MAF) should be introduced to increase ...public health protection. Here, we explore concepts of mixture toxicity and the potential influence of mixture regulation concepts for human health protection. Based on this analysis, we provide recommendations for research and risk assessment. One of the concepts of mixture toxicity is additivity. Substances may act additively by affecting the same molecular mechanism within a common target cell, for example, dioxin-like substances. In a second concept, an “enhancer substance” may act by increasing the target site concentration and aggravating the adverse effect of a “driver substance”. For both concepts, adequate risk management of individual substances can reliably prevent adverse effects to humans. Furthermore, we discuss the hypothesis that the large number of substances to which humans are exposed at very low and individually safe doses may interact to cause adverse effects. This commentary identifies knowledge gaps, such as the lack of a comprehensive overview of substances regulated under different silos, including food, environmentally and occupationally relevant substances, the absence of reliable human exposure data and the missing accessibility of ratios of current human exposure to threshold values, which are considered safe for individual substances. Moreover, a comprehensive overview of the molecular mechanisms and most susceptible target cells is required. We conclude that, currently, there is no scientific evidence supporting the need for a generic MAF. Rather, we recommend taking more specific measures, which focus on compounds with relatively small ratios between human exposure and doses, at which adverse effects can be expected.
Both because of the shortcomings of existing risk assessment methodologies, as well as newly available tools to predict hazard and risk with machine learning approaches, there has been an emerging ...emphasis on probabilistic risk assessment. Increasingly sophisticated AI models can be applied to a plethora of exposure and hazard data to obtain not only predictions for particular endpoints but also to estimate the uncertainty of the risk assessment outcome. This provides the basis for a shift from deterministic to more probabilistic approaches but comes at the cost of an increased complexity of the process as it requires more resources and human expertise. There are still challenges to overcome before a probabilistic paradigm is fully embraced by regulators. Based on an earlier white paper (Maertens et al., 2022), a workshop discussed the prospects, challenges and path forward for implementing such AI-based probabilistic hazard assessment. Moving forward, we will see the transition from categorized into probabilistic and dose-dependent hazard outcomes, the application of internal thresholds of toxicological concern for data-poor substances, the acknowledgement of user-friendly open-source software, a rise in the expertise of toxicologists required to understand and interpret artificial intelligence models, and the honest communication of uncertainty in risk assessment to the public.
PDF
