Skin sensitisation – Moving forward with non-animal testing strategies for regulatory purposes in the EU

Preparation and in vitro characterization studies of astaxanthin-loaded nanostructured lipid carriers with antioxidant properties

The purpose of this study was to evaluate the astaxanthin-loaded nanostructured lipid carriers (ASX-NLC) prepared using a high-pressure homogenization transport system for local application of astaxanthin. Dynamic light scattering (DLS) and X-ray diffraction (XRD) were used to study the effect of microencapsulation on the properties of ASX-NLC. The mean size of ASX-NLC was about 108.43 ± 0.26 nm and PdI was 0.176 ± 0.002. The ASX-NLC had high encapsulation efficiency which was 95.69 ± 0.13%. Good light stability and temperature stability were shown at the ASX-NLC, indicating that the preparation process was feasible. The 2,2-diphenyl-1-pyridylohydrazinyl (DPPH) scavenging test showed that ASX-NLC could still play an antioxidant role. In vitro release studies showed that compared with an astaxanthin ethanol solution, an ASX-NLC could maintain astaxanthin release more effectively. In vitro permeation studies showed that ASX-NLC could increase astaxanthin retention in the skin. In conclusion, ASX-NLC could significantly enhance astaxanthin accumulation during dermal applications. The research results have important reference significance for local skin applications and provide a basis for the development of nanostructured lipid carriers. ASX-NLC might be suitable carriers for the local application of astaxanthin.

A critical review of the kinetic direct peptide reactivity assay (kDPRA) for skin sensitizer potency assessment - taking it forward

It is widely recognized that the ability of chemicals to sensitize, and the potency of those chemicals that are sensitizers, is related to their ability to covalently modify protein in the skin. With the object of putting non-animal-based prediction of skin sensitization on a more quantitative footing, a recent paper describes the development of the kinetic Direct Protein Reactivity Assay (kDPRA), in which a matrix of peptide depletion values for different reaction times and test chemical concentrations is generated and analyzed so as to derive a reactivity parameter, logk_max, which is used to classify chemicals into one of two potency categories. The present paper demonstrates that the reaction chemistry is not always consistent with the mathematical analysis of the data matrix and the kDPRA protocol does not identify such cases. Consequently the derived logk_max value is not always mechanistically meaningful and its application to predict potency can lead to misleading conclusions. It is shown that by adopting a data analysis protocol based on conventional kinetics practice, the kDPRA can be made to provide more reliably meaningful and more extensive information that can be used for purposes such as potency estimation for deriving No Expected Sensitization Induction Level (NESILs) required for quantitative risk assessment (QRA), deriving quality specifications in terms of acceptable impurity levels, and development of structure-activity relationships. Secondly, the paper addresses applicability domain issues, in particular the problem of deciding whether or not the kDPRA is applicable for a given chemical.

Nanostructured-lipid carriers-Chitosan hydrogel beads carrier system for loading of resveratrol: A new method of topical application

The aim of this study was to develop nanostructured-lipid carriers (NLC) encapsulated by Chitosan hydrogel beads for the efficient topical carrier. Dynamic light scattering (DLS), X-ray diffraction (XRD), Differential scanning calorimetry (DSC), and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) were conducted to study the influence of the encapsulation on the characteristic of resveratrol-loaded NLC, and the results showed that there was no impact on resveratrol-loaded NLC. Chitosan hydrogel beads could significantly improve the physical stability of resveratrol-loaded NLC. In vitro release study revealed that resveratrol-loaded NLC-Chitosan hydrogel beads had a more significant sustained-release effect on resveratrol. In vitro transdermal studies suggested that the skin permeation of resveratrol was promoted by the effect of Chitosan hydrogel beads and increased resveratrol distribution in the skin. In vitro cytotoxicity showed that resveratrol-loaded NLC-Chitosan hydrogel beads did not exert a hazardous effect on L929 cells. Hence, NLC-Chitosan hydrogel beads might be a promising method for topical applications of resveratrol.

Extraction With Sweat-Sebum Emulsion as a New Test Method for Leachables in Patch-Based Medical Devices, Illustrated by Assessment of Isobornylacrylate (IBOA) in Diabetes Products

BACKGROUND

The increasing offering of patch-based medical devices is accompanied by growing numbers of reported adverse skin reactions. Procedures for testing leachables according to ISO 10993 may not be optimal for lipophilic substances that can be mobilized on skin by sweat and sebum. We propose an improved extraction method for targeted analysis of leachables using low volumes of a sweat-sebum emulsion. The approach is illustrated by the analysis of isobornylacrylate (IBOA), a compound found in some devices and suspected for allergenic potential.

METHOD

Three patch-based products were tested: an implantable device for continuous glucose monitoring (CGM), an intermittently scanned CGM (isCGM) device, and a micro-insulin pump. Quantification of IBOA was performed by gas chromatography and allergenic potential of IBOA levels was assessed by the KeratinoSens cell assay. Different combinations were used for extraction solvent (isopropanol, 5% ethanol-water solution, and sweat-sebum emulsion), extraction volumes (complete immersion vs partial immersion in 2 mm of solvent), and extraction time (3, 5, and 14 days).

RESULTS

Isobornylacrylate was only found in the isCGM device. About 20 mg/L IBOA were eluted after 3 days in isopropanol but only about 1 mg/L in ethanol-water. Sweat-sebum emulsion dissolves IBOA better and gives a more stable solution than ethanol-water. Decomposition of IBOA solutions requires adjusted extraction timing or correction of results. In the sweat-sebum extract, IBOA levels were about 20 mg/L after 3 days and about 30 mg/L after 5 days, clearly above the threshold found in the KerationSens assay for keratinocyte activation (10 mg/L).

CONCLUSION

Extraction by low volumes of sweat-sebum emulsion can be a superior alternative for the targeted simulating-use assessment of leachables in patch-based medical devices.

Skin Sensitization Tests: The LLNA and the RhE IL-18 Potency Assay

Contact allergy is of considerable importance to the toxicologist, and regulatory authorities worldwide require testing for skin sensitization potential and appropriate hazard labeling to enable management of the risk to human health. Although traditionally the identification of skin-sensitizing chemicals has been carried out using animal models, in Europe legislative changes have promoted, and now require, the use of non-animal methods (i.e., Cosmetic Directive, REACH). Several in vitro alternatives for hazard identification have now been validated, but do not provide information on the potency of a skin sensitizer. Here, we describe an animal model, the local lymph node assay (LLNA), and an in vitro model, the RhE IL-18 potency assay, in the context of the identification and potency classification of skin sensitizers. These two assays have been chosen among the different available tests as representative of an alternative in vivo model (the LLNA) and a promising in vitro method with the potential of both hazard identification and potency classification.

A direct peptide reactivity assay using a high-throughput mass spectrometry screening platform for detection of skin sensitizers

Chemical-peptide conjugation is the molecular initiating event in skin sensitization. The OECD test guideline uses a high-performance liquid chromatography/ultraviolet (HPLC/UV) detection method to quantify chemical-peptide conjugation in a direct peptide reactivity assay (DPRA), which measures the depletion of two synthetic peptides containing lysine or cysteine residues. To improve assay throughput, sensitivity and accuracy, an automated 384-well plate-based RapidFire solid-phase extraction (SPE) system coupled with tandem mass spectrometry (MS/MS) DPRA was developed and validated in the presence of a newly designed internal standard. Compared to the HPLC/UV-based DPRA, the automated SPE-MS/MS-based DPRA improved throughput from 16 min to 10 s per sample, and substrate peptides usage was reduced from 100 mM to 5 μM. When implementing the SPE-MS/MS-based DPRA into a high-throughput platform, we found 10 compounds that depleted lysine peptide and 24 compounds that depleted cysteine peptide (including 7 unreported chemicals from 55 compounds we tested) in a concentration-response manner. The adduct formation between cysteine and cinnamic aldehyde and ethylene glycol dimethacrylate were further analyzed using high-performance liquid chromatography time-of-flight mass spectrometry (HPLC-TOF-MS) to confirm the conjugation. Overall, the automated SPE-MS/MS-based platform is an efficient, economic, and accurate way to detect skin sensitizers.

Applying non-animal strategies for assessing skin sensitisation report from an EPAA/cefic-LRI/IFRA Europe cross sector workshop, ECHA helsinki, February 7th and 8th 2019

Four years on since the last cross sector workshop, experience of the practical application and interpretation of several non-animal assays that contribute to the predictive identification of skin sensitisers has begun to accumulate. Non-animal methods used for hazard assessments increasingly are contributing to the potency sub-categorisation for regulatory purposes. However, workshop participants generally supported the view that there remained a pressing need to build confidence in how information from multiple methods can be combined for classification, sub-categorisation and potency assessment. Furthermore, the practical experience gained over the last few years, highlighted the overall high potential value of using the newly validated methods and testing strategies, but also that limitations for certain substance/product classes may become evident with further use as had been the case with other new regulatory methods. As the available information increases, review of the data and collated experience could further determine strengths and limitations leading to more confidence in their use. Finally, the need for a substantial and universally accepted dataset of non-sensitisers and substances of different sensitising potencies, based on combined human and in vivo animal data for validation of methods and test strategies was re-emphasised.

Multi-Descriptor Read Across (MuDRA): A Simple and Transparent Approach for Developing Accurate Quantitative Structure-Activity Relationship Models

Multiple approaches to quantitative structure-activity relationship (QSAR) modeling using various statistical or machine learning techniques and different types of chemical descriptors have been developed over the years. Oftentimes models are used in consensus to make more accurate predictions at the expense of model interpretation. We propose a simple, fast, and reliable method termed Multi-Descriptor Read Across (MuDRA) for developing both accurate and interpretable models. The method is conceptually related to the well-known kNN approach but uses different types of chemical descriptors simultaneously for similarity assessment. To benchmark the new method, we have built MuDRA models for six different end points (Ames mutagenicity, aquatic toxicity, hepatotoxicity, hERG liability, skin sensitization, and endocrine disruption) and compared the results with those generated with conventional consensus QSAR modeling. We find that models built with MuDRA show consistently high external accuracy similar to that of conventional QSAR models. However, MuDRA models excel in terms of transparency, interpretability, and computational efficiency. We posit that due to its methodological simplicity and reliable predictive accuracy, MuDRA provides a powerful alternative to a much more complex consensus QSAR modeling. MuDRA is implemented and freely available at the Chembench web portal ( https://chembench.mml.unc.edu/mudra ).

Evaluation of 5-methylcytosine and 5-hydroxymethylcytosine as potential biomarkers for characterisation of chemical allergens

Epigenetic regulation of gene expression plays a pivotal role in the orchestration of immune responses. Chemical allergens form two categories: skin sensitizing chemicals associated with allergic contact dermatitis, and chemicals that cause sensitization of the respiratory tract and occupational asthma. In mice these are characterized by different T helper (Th) cell responses. Changes in DNA methylation in particular have been implicated in the in vivo responses to chemical allergy. As such it was hypothesised that differentially methylated regions (DMR) may provide candidates biomarkers of chemical allergy To examine this, mice were exposed to 2,4-dinitrochlorobenzene (DNCB; a contact allergen) or trimellitic anhydride (TMA; a respiratory allergen). DNA from draining lymph nodes was processed for methylated (5mC) and hydroxymethylated (5hmC) DNA immunoprecipitation (MeDIP/hMeDIP) then selected DMR analysed by qPCR. We describe a number of DMRs which, by combined analysis of 5mC and 5hmC, differentiate between responses induced by DNCB and those by TMA. Furthermore, these changes in methylation are specific to the draining lymph node. The Gmpr DMR is suggested as a possible biomarker for contact allergen-induced immune responses; it is characterised by divergent levels of 5mC and 5hmC DNCB-treated mice only. In contrast, the Nwc DMR was characterised by divergent 5mC and 5hmC specifically in response to TMA, highlighting its possible utility as a biomarker for responses induced by chemical respiratory allergens. These data not only represent novel analysis of 5hmC in response to chemical allergy in vivo, but with further investigation, may also provide a possible basis for differentiation between classes of chemical allergens.

Transdermal solid delivery of epigallocatechin-3-gallate using self-double-emulsifying drug delivery system as vehicle: Formulation, evaluation and vesicle-skin interaction

The present study investigated a self-double-emulsifying drug delivery system loaded with epigallocatechin-3-gallate to improve epigallocatechin-3-gallate skin retention. The long chain solid lipids (cetostearyl alcohol) and macadamia oil were utilized as a carrier to deliver the bioactive ingredient. Response surface methodology was used to optimize the formulation, and the solid lipid to total lipid weight ratio, concentration of epigallocatechin-3-gallate and hydrophilic surfactant on skin retention were found to be the principal factors. The optimum formulation with high encapsulation efficiency (95.75%), self-double-emulsification performance (99.58%) and skin retention (87.24%) were derived from the fitted models and experimentally examined, demonstrating a reasonable agreement between experimental and predicted values. Epigallocatechin-3-gallate-self-double-emulsifying drug delivery system was found to be stable for 3 months. Transdermal studies could explain a higher skin diffusion of epigallocatechin-3-gallate from the self-double-emulsifying drug delivery system compared with EGCG aqueous solution. In vitro cytotoxicity showed that epigallocatechin-3-gallate-self-double-emulsifying drug delivery system did not exert hazardous effect on L929 cells up to 1:10.

The European Long-range Research Initiative (LRI): A decade of contributions to human health protection, exposure modelling and environmental integrity

The European Long-range Research Initiative (LRI) was launched in 2000. The objective of this programme is to provide increased understanding of the potential impact of chemicals on human health and the environment. The aim has been to reduce uncertainty associated with innovation, and to promote evidence-based decision making. In pursuing these objectives the LRI has commissioned independent scientific research in institutions throughout Europe and beyond. The portfolio of research supported by the LRI has delivered significant contributions to risk assessment sciences. In addition, the LRI programme has benefited the broader scientific community. In this review article members of the Cefic European Scientific Advisory Panel (ESAP), the body charged with providing oversight of the LRI programme, illustrate some of those achievements by reference to specific areas of research (respiratory allergy, human biomonitoring, environment and wildlife), and also the contribution made to the development of European scientists through the annual LRI Award Programme.

Mechanism-Based QSAR Modeling of Skin Sensitization

Many chemicals can induce skin sensitization, and there is a pressing need for non-animal methods to give a quantitative indication of potency. Using two large published data sets of skin sensitizers, we have allocated each sensitizing chemical to one of 10 mechanistic categories and then developed good QSAR models for the seven categories that have a sufficient number of chemicals to allow modeling. Both internal and external validation checks showed that each model had good predictivity.

Toxicology: a discipline in need of academic anchoring--the point of view of the German Society of Toxicology

The paper describes the importance of toxicology as a discipline, its past achievements, current scientific challenges, and future development. Toxicological expertise is instrumental in the reduction of human health risks arising from chemicals and drugs. Toxicological assessment is needed to evaluate evidence and arguments, whether or not there is a scientific base for concern. The immense success already achieved by toxicological work is exemplified by reduced pollution of air, soil, water, and safer working places. Predominantly predictive toxicological testing is derived from the findings to assess risks to humans and the environment. Assessment of the adversity of molecular effects (including epigenetic effects), the effects of mixtures, and integration of exposure and biokinetics into in vitro testing are emerging challenges for toxicology. Toxicology is a translational science with its base in fundamental science. Academic institutions play an essential part by providing scientific innovation and education of young scientists.

LuSens: a keratinocyte based ARE reporter gene assay for use in integrated testing strategies for skin sensitization hazard identification

Allergic contact dermatitis can develop following repeated exposure to allergenic substances. To date, hazard identification is still based on animal studies as non-animal alternatives have not yet gained global regulatory acceptance. Several non-animal methods addressing key-steps of the adverse outcome pathway (OECD, 2012) will most likely be needed to fully address this effect. Among the initial cellular events is the activation of keratinocytes and currently only one method, the KeratinoSens™, has been formally validated to address this event. In this study, a further method, the LuSens assay, that uses a human keratinocyte cell line harbouring a reporter gene construct composed of the antioxidant response element (ARE) of the rat NADPH:quinone oxidoreductase 1 gene and the luciferase gene. The assay was validated in house using a selection of 74 substances which included the LLNA performance standards. The predictivity of the LuSens assay for skin sensitization hazard identification was comparable to other non-animal methods, in particular to the KeratinoSens™. When used as part of a testing battery based on the OECD adverse outcome pathway for skin sensitization, a combination of the LuSens assay, the DPRA and a dendritic cell line activation test attained predictivities similar to that of the LLNA.

Towards AOP application--implementation of an integrated approach to testing and assessment (IATA) into a pipeline tool for skin sensitization

Since the OECD published the Adverse Outcome Pathway (AOP) for skin sensitization, many efforts have focused on how to integrate and interpret nonstandard information generated for key events in a manner that can be practically useful for decision making. These types of frameworks are known as Integrated Approaches to Testing and Assessment (IATA). Here we have outlined an IATA for skin sensitization which focuses on existing information including non testing approaches such as QSAR and read-across. The IATA was implemented into a pipeline tool using OASIS technology to provide a means of systematically collating and compiling relevant information which could be used in an assessment of skin sensitization potential. A test set of 100 substances with available skin sensitization information was profiled using the pipeline IATA. In silico and in chemico profiling information alone was able to correctly predict skin sensitization potential, with a preliminary accuracy of 73.85%. Information from other relevant endpoints (e.g., Ames mutagenicity) was found to improve the accuracy (to 87.6%) when coupled with a reaction chemistry mechanistic understanding. This pipeline platform could be useful in the assessment of skin sensitization potential and marks a step change in how non testing approaches can be practically applied.

Development of a multiparametric in vitro model of skin sensitization

Most animal experiments on cosmetics safety are prohibited and since March 2013, this obligation includes sensitization tests. However, until now there has been no validated alternative in vitro method. In this work, 400 compounds used in the cosmetic industry were selected to cover the greatest diversity of structures, biological activities and sensitizing potential. These molecules were submitted to a series of tests aimed at reproducing essential steps in sensitization and to distinguish between sensitization and irritations, i.e., transcutaneous permeation (factor A), haptenation (factor B), sensitization cytokines production (factor C) and acute toxicity (factor D). The transcutaneous diffusion was measured on human skin explants using Franz cells. Haptenation was tested in solution on human serum albumin. Sensitization cytokine production was investigated by measurement of interleukin-18 release by keratinocytes. Acute toxicity was determined using an 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(75) cell viability test. As only sufficiently stable, soluble and detectable compounds are usable, 33, 72, 68 and 68 molecules were finally tested on factors A, B, C and D, respectively, and 32 were completely screened by the four factors. The individual correlation of the four factors with the reference in vivo tests was limited but the combination of these factors led to a correlation between in vivo and in vitro assays of 81.2% and the safety of the test (risk of false negative) reached 96.8%. The techniques employed are simple and inexpensive and this model of four tests appears as a promising technique to evaluate in vitro the skin sensitization potential of unknown molecules.