Grouping of chemicals for safety assessment: the importance of toxicokinetic properties of salicylate esters.

Grouping of chemicals has been proposed as a strategy to speed up the screening and identification of potential substances of concern among the broad chemical universe under REACH. Such grouping is usually based on shared structural features and should only be used for the prioritization objectives. However, additional considerations (as well as structural similarity) are needed, e.

Incorporating Singaporean habits and practices for cosmetics and personal care products into a global consumer aggregate exposure model.

Understanding consumer habits and practices of cosmetics and personal care products (PCP) is essential to generate realistic product exposure data for the safety assessment of ingredients such as fragrance materials. Product usages can vary across regions due to differences in cultural norms, seasonal and climate conditions, and the availability of different product forms, yet there is limited data published on cosmetics and PCP use outside of North America and Europe. This study reports the habits and practices of cosmetics and PCP (such as frequency and amount of use) in Singapore where participants (n = 494, aged 21-64 years) recorded their product usages and had their products weighed over a two-week period.

Predicting points of departure and potency categories for fragrance ingredients by integrating OECD in vitro models.

Continuous potency assessment is crucial for conducting quantitative risk assessment (QRA) of sensitizers. Quantitative regression models, based on in vitro methods, have been developed to calculate points of departure for use in skin sensitization QRA. These models calculate a point of departure as a predicted value for Local Lymph Node Assay (LLNA) EC3 or potency value (PV), integrating data from the kinetic Direct Peptide Reactivity Assay (kDPRA), KeratinoSens (KS) assay, and human Cell Line Activation Test (h-CLAT).

Updating Reaction Mechanistic Domains for Skin Sensitization: 1. Nucleophilic Skin Sensitizers.

It has long been recognized that skin sensitizers either are electrophilic or can be activated to electrophilic species. Several nonanimal assays for skin sensitization are based on this premise. In the course of a project to update dermal sensitization thresholds (DST), we found a substantial number of sensitizers, with no electrophilic or pro-electrophilic alerts, that could be simply explained in terms of the sensitizer acting as a nucleophile.

Assessment of genotoxic potential of fragrance materials in the chicken egg assays.

The genotoxic and clastogenic/aneugeneic potentials of four α,β-unsaturated aldehydes, 2-phenyl-2-butenal, nona-2-trans-6-cis-dienal, 2-methyl-2-pentenal, and p-methoxy cinnamaldehyde, which are used as fragrance materials, were assessed using the Chicken Egg Genotoxicity Assay (CEGA) and the Hen's egg micronucleus (HET-MN) assay, respectively. Selection of materials was based on their chemical structures and the results of their previous assessment in the regulatory in vitro and/or in vivo genotoxicity test battery. Three tested materials, 2-phenyl-2-butenal, nona-2-trans-6-cis-dienal, and 2-methyl-2-pentenal, were negative in both, CEGA and HET-MN assays.

In vitro to in vivo extrapolation to derive a metabolism factor for estimating the aggregate exposure to salicylic acid after dermal exposure of its esters.

As part of the safety assessment of salicylate esters in cosmetics, we developed a metabolism factor based on in vitro to in vivo extrapolation (IVIVE) to provide a better estimation of the aggregate internal exposure to the common metabolite, salicylic acid. Optimal incubation conditions using human liver S9 were identified before measuring salicylic acid formation from 31 substances. Four control substances, not defined as salicylic esters but which could be mistaken as such due to their nomenclature, did not form salicylic acid.

GARDskin dose-response assay and its application in conducting Quantitative Risk Assessment (QRA) for fragrance materials using a Next Generation Risk Assessment (NGRA) framework.

Development of New Approach Methodologies (NAMs) capable of providing a No Expected Sensitization Induction Level (NESIL) value remains a high priority for the fragrance industry for conducting a Quantitative Risk Assesment (QRA) to evaluate dermal sensitization. The in vitro GARDskin assay was recently adopted by the OECD (TG 442E) for the hazard identification of skin sensitizers. Continuous potency predictions are derived using a modified protocol that incorporates dose-response measurements.

Detailed aggregate exposure analysis shows that exposure to fragrance ingredients in consumer products is low: Many orders of magnitude below thresholds of concern.

The Research Institute for Fragrance Materials (RIFM) and Creme Global Cremeglobal.com partnered to develop an aggregate exposure model for fragrance ingredients. The model provides a realistic estimate of the total exposure of fragrance ingredients to individuals across a population.

Utility of ToxTracker in animal alternative testing strategy for fragrance materials.

To determine the utility of the ToxTracker assay in animal alternative testing strategies, the genotoxic potential of four fragrance materials (2-octen-4-one, lauric aldehyde, veratraldehyde, and p-methoxy cinnamaldehyde) were tested in the ToxTracker assay. These materials have been previously evaluated in an in vitro as well as in vivo micronucleus assay, conducted as per OECD guidelines. In addition to these studies, reconstructed human skin micronucleus studies were conducted on all four materials.

An End Point-Specific Framework for Read-Across Analog Selection for Human Health Effects.

Integrating computational chemistry and toxicology can improve the read-across analog approach to fill data gaps in chemical safety assessment. In read-across, structure-related parameters are compared between a target chemical with insufficient test data and one or more materials with sufficient data. Recent advances have focused on enhancing the grouping or clustering of chemicals to facilitate toxicity prediction via read-across.

A Cautionary tale for using read-across for cancer hazard classification: Case study of isoeugenol and methyl eugenol.

Chemical grouping and read-across are frequently used non-animal alternatives for filling toxicological data gaps. When grouping chemicals, it is critical to define the applicability domain because minor differences in chemical structure can lead to significant differences in toxicity. Here, we present a case study on isoeugenol and methyl eugenol, which are scheduled for review by IARC in June 2023, to illustrate that structural similarity alone may not be sufficient to group chemicals for hazard classification.

Updating the Dermal Sensitisation Thresholds using an expanded dataset and an in silico expert system.

The Dermal Sensitisation Thresholds (DST) are Thresholds of Toxicological Concern, which can be used to justify exposure-based waiving when conducting a skin sensitisation risk assessment. This study aimed to update the published DST values by expanding the size of the Local Lymph Node Assay dataset upon which they are based, whilst assigning chemical reactivity using an in silico expert system (Derek Nexus). The potency values within the expanded dataset fitted a similar gamma distribution to that observed for the original dataset.

Expansion of the Cosmetics Europe skin sensitisation database with new substances and PPRA data.

The assessment of skin sensitisation is a key requirement in all regulated sectors, with the European Union's regulation of cosmetic ingredients being most challenging, since it requires quantitative skin sensitisation assessment based on new approach methodologies (NAMs). To address this challenge, an in-depth and harmonised understanding of NAMs is fundamental to inform the assessment. Therefore, we compiled a database of NAMs, and in vivo (human and local lymph node assay) reference data.

Implementation of a dermal sensitization threshold (DST) concept for risk assessment: structure-based DST and data-based DST.

Skin sensitization resulting in allergic contact dermatitis represents an important toxicological endpoint as part of safety assessments. When available substance-specific sensitization data are inadequate, the dermal sensitization threshold (DST) concept has been proposed to set a skin exposure threshold to provide no appreciable risk of skin sensitization. Structure-based DSTs, which include non-reactive, reactive, and high potency category (HPC) DSTs, can be applied to substances with an identified chemical structures.

The BlueScreen HC assay to predict the genotoxic potential of fragrance materials.

BlueScreen HC is a mammalian cell-based assay for measuring the genotoxicity and cytotoxicity of chemical compounds and mixtures. The BlueScreen HC assay has been utilized at the Research Institute for Fragrance Materials in a safety assessment program as a screening tool to prioritize fragrance materials for higher-tier testing, as supporting evidence when using a read-across approach, and as evidence to adjust the threshold of toxicological concern. Predictive values for the BlueScreen HC assay were evaluated based on the ability of the assay to predict the outcome of in vitro and in vivo mutagenicity and chromosomal damage genotoxicity assays.

Weight of Evidence Approach for Skin Sensitization Potency Categorization of Fragrance Ingredients.

Background: Reliable human potency data are necessary for conducting quantitative risk assessments, as well as development and validation of new nonanimal methods for skin sensitization assessments. Previously, human skin sensitization potency of fragrance materials was derived primarily from human data or the local lymph node assay.

Objectives: This study aimed to define skin sensitization potency of fragrance materials via weight of evidence approach, incorporating all available human, animal, in vitro, in chemico, and in silico data.

Identifying a reference list of respiratory sensitizers for the evaluation of novel approaches to study respiratory sensitization.

The induction of immunological responses that trigger bio-physiological symptoms in the respiratory tract following repeated exposure to a substance, is known as respiratory sensitization. The inducing compound is known as a respiratory sensitizer. While respiratory sensitization by high molecular weight (HMW) materials is recognized and extensively studied, much less information is available regarding low molecular weight (LMW) materials as respiratory sensitizers.

Benchmarking performance of SENS-IS assay against weight of evidence skin sensitization potency categories.

Potency determination of potential skin sensitizers in humans is essential for quantitative risk assessment and proper risk management. SENS-IS is an in vitro test based on a reconstructed human skin model, that was developed to predict the hazard and potency of potential skin sensitizers. The performance of the SENS-IS assay in potency prediction for 174 materials was evaluated for this work.

Use of alternative test methods in a tiered testing approach to address photoirritation potential of fragrance materials.

The safety assessment of fragrance materials for photoirritation utilized by The Research Institute for Fragrance Materials has recently been modified and is described in detail. Materials demonstrating significant absorbance in the ultraviolet and visible light (UV/VIS) range (290-700 nm) may present a concern for photoirritation and require further investigation. If there are no photoirritation data or data are insufficient, then data on read-across materials are considered before a tiered approach for testing begins.

Assessment of the skin sensitization potential of fragrance ingredients using the U-SENS™ assay.

The U-SENS™ assay was developed to address the third key event of the skin sensitization adverse outcome pathway (AOP) and is described in OECD test guideline 442E, Annex II. A dataset of 68 fragrance ingredients comprised of 7 non-sensitizers and 61 sensitizers was tested in the U-SENS™ assay. The potential for fragrance ingredients to activate dendritic cells, measured by U-SENS™, was compared to the sensitization potential determined by weight of evidence (WoE) from historical data.

Use of the EpiDermTM 3D reconstructed skin micronucleus assay for fragrance materials.

In order to evaluate the utility of the 3D reconstructed skin micronucleus assay (3DRSMN) to assess clastogenic/aneugenic potential of the fragrance chemicals, a set of 22 fragrance materials were evaluated in 3DRSMN assay. These materials evaluated were also evaluated in an in vitro as well as in vivo micronucleus assay, conducted as per Organisation for Economic Co-operation and Development guidelines. The results of the RSMN assay were in 100% agreement with the in vivo micronucleus assay results.

Derivation of the no expected sensitization induction level for dermal quantitative risk assessment of fragrance ingredients using a weight of evidence approach.

Some fragrance ingredients may have the potential to induce skin sensitization in humans but can still be safely formulated into consumer products. Quantitative Risk Assessment (QRA) for dermal sensitization is required to determine safe levels at which potential skin sensitizers can be incorporated into consumer products. The no expected sensitization induction level or NESIL is the point of departure for the dermal QRA.

Assessment of the genotoxic potential of mintlactone.

Mintlactone (chemical name 3,6-dimethyl-5,6,7,7a-tetrahydro-1-benzofuran-2(4H)-one, CAS Number 13341-72-5) is a fragrance and flavor ingredient with reported uses in many different cosmetics, personal care, and household products. In order to evaluate the genotoxic potential of mintlactone, in vitro and in vivo genotoxicity tests were conducted. Results from bacterial mutagenicity tests varied across different batches of differing purity with positive results observed in TA98 only.

Dietary administration of -ionone epoxide to Sprague-Dawley rats for 90 days.

In a 90-day GLP-compliant study groups of Sprague-Dawley rats (10/sex/group) were fed diets containing β-ionone epoxide, a fragrance material and a flavoring substance, at dietary concentrations providing target intakes of 0, 20, 40 and 80 mg/kg bw/day. There were no deaths and no adverse changes in clinical observations, ophthalmological examinations, body weight, body weight gain, food consumption, food efficiency; hematology, serum chemistry, urinalysis parameters; or in macroscopic findings attributable to β-ionone epoxide administration. Increased absolute and relative liver weights in high dose females without correlating hepatic histopathological findings were considered non-adverse.

Internal Threshold of Toxicological Concern (iTTC): Where We Are Today and What Is Possible in the Near Future.

The Threshold of Toxicological Concern (TTC) is a risk assessment tool for evaluating low-level exposure to chemicals with limited toxicological data. A next step in the ongoing development of TTC is to extend this concept further so that it can be applied to internal exposures. This refinement of TTC based on plasma concentrations, referred to as internal TTC (iTTC), attempts to convert the chemical-specific external NOAELs (in mg/kg/day) in the TTC database to an estimated internal exposure.