Read-across and new approach methodologies applied in a 10-step framework for cosmetics safety assessment - A case study with parabens.

Parabens are esters of para-hydroxybenzoic acid that have been used as preservatives in many types of products for decades including agrochemicals, pharmaceuticals, food and cosmetics. This illustrative case study with propylparaben (PP) demonstrates a 10-step read-across (RAX) framework in practice. It aims at establishing a proof-of-concept for the value added by new approach methodologies (NAMs) in read-across (RAX) for use in a next-generation risk assessment (NGRA) in order to assess consumer safety after exposure to PP-containing cosmetics. In addition to structural and physico-chemical properties, in silico information, toxicogenomics, in vitro toxicodynamic, toxicokinetic data from PBK models, and bioactivity data are used to provide evidence of the chemical and biological similarity of PP and analogues and to establish potency trends for observed effects in vitro. The chemical category under consideration is short (C1-C4) linear chain n-alkyl parabens: methylparaben, ethylparaben, propylparaben and butylparaben. The goal of this case study is to illustrate how a practical framework for RAX can be used to fill a hypothetical data gap for reproductive toxicity of the target chemical PP.

Assessment of consumer exposure to boron in cleaning products: a case study of Canada.

Boron is an essential mineral for plants, and as such, is a normal dietary constituent for humans. Humans may be naturally exposed to boron through food and drinking water, or via anthropogenic sources such as consumer products. The World Health Organisation established an acceptable safe range of population mean intakes for boron of 1-13 mg/day. Most studies of dietary boron intake show a range of 1-2 mg/day. Consumer products have been estimated to contribute a geometric mean daily intake of 0.1 mg to total boron exposure; however, there are few published surveys of consumer exposure to boron from use of cleaning products. The Government of Canada published a draft screening assessment report of boric acid, its salts and precursors that included estimates of consumer exposure to boron found as ingredients in consumer products. The manufacturers of consumer cleaning products conducted a survey of boron content of current products and estimated exposure using the publicly available exposure tool ConsExpo Web. Dermal exposures to boron during cleaning product use were estimated to result in annual internal exposures ranging from ≪0.001 to 0.36 µg/kg bw/day based on dermal absorption of 0.5%. Using a conservative point of departure for hazard assessment (2,900 µg boron/kg bw/day), estimated margins of exposure for dermal exposures to boron from cleaning product use range from 8,056 to >1,000,000. This work demonstrates that exposure to boron from cleaning product use is very low and essentially insignificant when compared to other (e.g. dietary) sources of boron intake by Canadian consumers.

Towards grouping concepts based on new approach methodologies in chemical hazard assessment: the read-across approach of the EU-ToxRisk project.

Read-across is one of the most frequently used alternative tools for hazard assessment, in particular for complex endpoints such as repeated dose or developmental and reproductive toxicity. Read-across extrapolates the outcome of a specific toxicological in vivo endpoint from tested (source) compounds to "similar" (target) compound(s). If appropriately applied, a read-across approach can be used instead of de novo animal testing. The read-across approach starts with structural/physicochemical similarity between target and source compounds, assuming that similar structural characteristics lead to similar human hazards. In addition, similarity also has to be shown for the toxicokinetic and toxicodynamic properties of the grouped compounds. To date, many read-across cases fail to demonstrate toxicokinetic and toxicodynamic similarities. New concepts, in vitro and in silico tools are needed to better characterise these properties, collectively called new approach methodologies (NAMs). This white paper outlines a general read-across assessment concept using NAMs to support hazard characterization of the grouped compounds by generating data on their dynamic and kinetic properties. Based on the overarching read-across hypothesis, the read-across workflow suggests targeted or untargeted NAM testing also outlining how mechanistic knowledge such as adverse outcome pathways (AOPs) can be utilized. Toxicokinetic models (biokinetic and PBPK), enriched by in vitro parameters such as plasma protein binding and hepatocellular clearance, are proposed to show (dis)similarity of target and source compound toxicokinetics. Furthermore, in vitro to in vivo extrapolation is proposed to predict a human equivalent dose, as potential point of departure for risk assessment. Finally, the generated NAM data are anchored to the existing in vivo data of source compounds to predict the hazard of the target compound in a qualitative and/or quantitative manner. To build this EU-ToxRisk read-across concept, case studies have been conducted and discussed with the regulatory community. These case studies are briefly outlined.

Development of a physiologically-based pharmacokinetic model of 2-phenoxyethanol and its metabolite phenoxyacetic acid in rats and humans to address toxicokinetic uncertainty in risk assessment.

2-Phenoxyethanol (PhE) has been shown to induce hepatotoxicity, renal toxicity, and hemolysis at dosages ≥ 400 mg/kg/day in subchronic and chronic studies in multiple species. To reduce uncertainty associated with interspecies extrapolations and to evaluate the margin of exposure (MOE) for use of PhE in cosmetics and baby products, a physiologically-based pharmacokinetic (PBPK) model of PhE and its metabolite 2-phenoxyacetic acid (PhAA) was developed. The PBPK model incorporated key kinetic processes describing the absorption, distribution, metabolism and excretion of PhE and PhAA following oral and dermal exposures. Simulations of repeat dose rat studies facilitated the selection of systemic AUC as the appropriate dose metric for evaluating internal exposures to PhE and PhAA in rats and humans. Use of the PBPK model resulted in refinement of the total default UF for extrapolation of the animal data to humans from 100 to 25. Based on very conservative assumptions for product composition and aggregate product use, model-predicted exposures to PhE and PhAA resulting from adult and infant exposures to cosmetic products are significantly below the internal dose of PhE observed at the NOAEL dose in rats. Calculated MOEs for all exposure scenarios were above the PBPK-refined UF of 25.

A strategy for safety assessment of chemicals with data gaps for developmental and/or reproductive toxicity.

Alternative methods for full replacement of in vivo tests for systemic endpoints are not yet available. Read across methods provide a means of maximizing utilization of existing data. A limitation for the use of read across methods is that they require analogs with test data. Repeat dose data are more frequently available than are developmental and/or reproductive toxicity (DART) studies. There is historical precedent for using repeat dose data in combination with a database uncertainty factor (UF) to account for missing DART data. We propose that use of the DART decision tree (Wu et al., 2013), in combination with a database UF, provides a path forward for DART data gap filling that better utilizes all of the data. Our hypothesis was that chemical structures identified by the DART tree as being related to structures with known DART toxicity would potentially have lower DART NOAELs compared to their respective repeat dose NOAELs than structures that lacked this association. Our analysis supports this hypothesis and as a result also supports that the DART decision tree can be used as part of weight of evidence in the selection of an appropriate DART database UF factor.

A framework to facilitate consistent characterization of read across uncertainty.

A process for evaluating analogues for use in structure activity relationship (SAR) assessments was previously published (Wu et al., 2010) and tested using a series of case studies (Blackburn et al., 2011). SAR-based "read across" approaches continue to be broadly used to address toxicological data gaps. The potential additional uncertainty introduced into risk assessments as a result of application of read across approaches to fill data gaps has been widely discussed (OECD, 2007; ECETOC, 2012; Patlewicz et al., 2013), but to date a systematic framework to guide the characterization of uncertainty in read across assessments has not been proposed. The current manuscript presents both a systematic framework to describe potential areas of additional uncertainty that may arise in read across (evaluated based on the number and suitability of analogues contributing data, severity of the critical effect, and effects and potency concordance), as well as a questionnaire for evaluating and documenting consideration of these potential additional sources of uncertainty by risk assessors. Application of this framework represents a next step in standardizing the read across process, both by providing a means to transparently assign a level of uncertainty to a SAR-based read across assessment and by facilitating consistency in read across conclusions drawn by different risk assessors.

Relevance and Application of Read-Across - Mini Review of European Consensus Platform for Alternatives and Scandinavian Society for Cell Toxicology 2017 Workshop Session.

Structure activity relationship (SAR)-based read-across is an effective approach for addressing data gaps in human health risk assessment for 'data-poor' chemicals. In read-across, available data on chemical structural analogues are used to predict the toxicity potential of the data-poor chemical. This approach has long been recognized by regulatory agencies and used by industry to evaluate the hazards of chemicals for which there are limited direct data. Construction of a scientifically robust SAR-based read-across hazard assessment is a complex and iterative process involving multiple considerations in each step. Traditional in vivo data generated using regulatory guideline compliant study designs typically forms the basis for read-across assessments. Recently, however, new data streams have been explored and incorporated to enhance read-across predictivity. These in vitro and omics data streams may be used in different ways involving identification of hazards or to provide insight into modes of action for observed toxicological responses. These 'new approach methods' can also enable comparison of biological responses across analogues or a category of structurally related chemicals in order to establish a pattern of biological similarity in addition chemical similarity and/or to help address potency differences across a category. The purpose of this workshop session was to inform on practical considerations in conducting SAR-based read-across assessments and to review recent activities related to application of new approach methods to the practice of read-across.

Toward Good Read-Across Practice (GRAP) guidance.

Grouping of substances and utilizing read-across of data within those groups represents an important data gap filling technique for chemical safety assessments. Categories/analogue groups are typically developed based on structural similarity and, increasingly often, also on mechanistic (biological) similarity. While read-across can play a key role in complying with legislations such as the European REACH regulation, the lack of consensus regarding the extent and type of evidence necessary to support it often hampers its successful application and acceptance by regulatory authorities. Despite a potentially broad user community, expertise is still concentrated across a handful of organizations and individuals. In order to facilitate the effective use of read-across, this document aims to summarize the state-of-the-art, summarizes insights learned from reviewing ECHA published decisions as far as the relative successes/pitfalls surrounding read-across under REACH and compile the relevant activities and guidance documents. Special emphasis is given to the available existing tools and approaches, an analysis of ECHA's published final decisions associated with all levels of compliance checks and testing proposals, the consideration and expression of uncertainty, the use of biological support data and the impact of the ECHA Read-Across Assessment Framework (RAAF) published in 2015.

The safety of ethyl oleate is supported by a 91-day feeding study in rats.

The purpose of this study was to determine the safety of ethyl oleate (EO) in a 91-day feeding study in Sprague-Dawley rats. EO was mixed into AIN-93G purified diet at levels of 0, 3.3, 6.7, and 10% by weight (the high-dose males and females consumed 5.5 and 6.1g/kg/day EO, respectively). All diets were calorie- and fat-matched using high oleic safflower oil (HOSO) as the control fat. The study design followed the 1993 FDA draft "Redbook II" guidelines (Toxicological Principles for the Safety Assessment of Direct Food Additives and Color Additives Used in Food). There were 20 male and 20 female rats per group. EO in the diet was well tolerated and there were no toxicologically significant findings in any of the measured parameters (clinical observations, body weight gains, appearance of the feces, ophthalmic examinations, hematology, clinical chemistry, urinalysis, organ weights, histopathology, or male and female reproductive assessments). Mortality was limited to three males during the course of the study whose cause of death was unrelated to test material administration. The terminal body weight of the mid- and high-dose females was approximately 10% lower than that of the control group. This finding does not represent a toxicologically significant effect because rats on the EO diets gained more weight during the course of the study than historical control data on this strain of rats. The lower body weight relative to control rats is directly related to lower food consumption relative to the controls. The lower food consumption relative to controls is fully consistent with a decrease in the palatability of the EO-containing food versus the triglyceride-containing food. This conclusion is based on (1) a decrease in food consumption was noted within the first week (consistent with palatability preferences), (2) there was not a dose-response with regard to food consumption (mid-dose consumed less than high-dose), (3) the lack of cumulative decreases in food consumption which often are observed with toxicity, and (4) anecdotal experiences in our lab show that rats prefer diets containing high triglyceride fat over high EO-fat. Hepatocellular vacuolation typical of fat accumulation was noted for both control and high-dose animals. The incidence and severity of the vacuolation were higher for animals given 10% HOSO (controls) than for the animals given 10% EO. Serum calcium and phosphorous levels in high dose males were slightly, but statistically significantly, lower than in the controls. There was a dose-related increase in fecal fat concentration in both sexes from approximately 9% (control) to 18% in males, and from 4 (control) to 13% in females There were no visually obvious differences with regard to feces quality or quantity at any level of EO in the diet (i.e., color, diarrhea, weight, etc.). The increase in fat most likely represents small amounts of unabsorbed EO at the mid- and high-dose (estimates of EO absorption in this study are >80%). The No Observable Adverse Effect Level was determined to be 10% EO when administered daily in the diet for 91-days (approximately 6g EO/kg bw/day).