Human Skin Sensitization Research Articles

Isolating the independent effect of decreasing mean skin temperature on local thermal sensitivity of human hands and feet during cold stress

Whether reductions in whole‐body mean skin temperature (Tsk), with no concurrent changes in core temperature (Tc), alter local thermal sensitivity (TS) of human skin is currently unknown. On 4 separate occasions, 8 males (27±5y) underwent a 30‐min whole‐body cooling protocol (water‐perfused suit: ~5°C), during which a quantitative thermo‐sensory test, consisting of reporting (visual analogue scale) perceived magnitude of local warm (38°C) and cold (22°C) thermal stimuli (25‐cm2 thermal probe) applied to hand (palm/dorsum) and foot (sole/dorsum), was performed before cooling and every 10min thereafter. The cooling protocol resulted in large progressive reductions in Tsk (10min: −3.36±0.67°C; 20min: −5.21±1.00°C; 30min: −6.32±1.14°C; p<0.001), with minimal changes in Tc (10min: −0.08±0.04°C; 20min: −0.07±0.07°C; 30min: −0.07±0.09°C; p<0.001). While no differences in TS to the local cold stimulus were observed for any skin region at any stage of the cooling protocol (ΔTS from baseline; 10min: −2.05±5.9%; 20min: −0.3±7.8%; 30min: −1.1±8.5%; p=0.790), a significant and progressive increase in warm TS occurred at each level of Tsk for all skin regions (10min: +4.9±7.5; 20 min: +6.1±4.5; 30 min: +7.9±6.1%; p=0.004). A significant association between decreasing levels of Tsk and increases in warm TS was observed (y= −1.217x+0.2139; R2=0.98; p=0.003), indicating a 1.4% increase in warm TS per 1°C drop in whole‐body Tsk. Overall, the same local warm stimulus (hence same increase in skin temperature) was perceived to be warmer with progressive reductions in whole‐body Tsk, indicating that, independently of Tc, decreases in whole‐body Tsk significantly alter local warmth, but not cold, TS of human hands and feet.Support or Funding InformationMr Morris was supported by a University of Sydney International Postgraduate Research Scholarship (IPRS). Dr Filingeri was supported by a Government of Australia Endeavour Fellowship

Safety Evaluation of Cosmetic Ingredients Regarding Their Skin Sensitization Potential

Up to today, product safety evaluation in the EU is predominantly based on data/information on their individual ingredients. Consequently, the quality and reliability of individual ingredient data is of vital interest. In this context, the knowledge about skin sensitization potential is an explicit need for both hazard and risk assessment. Proper skin sensitization data of the individual chemicals is essential, especially when dermal contact is intended, like for cosmetics. In some cases, e.g., in the presence of irritating chemicals, the combination of individual ingredients may also need to be evaluated to cover possible mixture effects. Today, it seems unlikely or even impossible that skin sensitization in humans can be adequately described by a single test result or even by a simple combination of a few data points (in vivo or in vitro). It is becoming evident that a set of data (including human data and market data) and knowledge about the ingredient’s specific sensitizing potency needs to be taken into account to enable a reliable assessment of skin sensitization. A more in-depth understanding on mechanistic details of the Adverse-Outcome-Pathway of skin sensitization could contribute key data for a robust conclusion on skin sensitization.

Filaggrin genotype does not determine the skin's threshold to UV-induced erythema

Filaggrin genotype does not determine the skin's threshold to UV-induced erythema

QSAR models of human data can enrich or replace LLNA testing for human skin sensitization.

Skin sensitization is a major environmental and occupational health hazard. Although many chemicals have been evaluated in humans, there have been no efforts to model these data to date. We have compiled, curated, analyzed, and compared the available human and LLNA data. Using these data, we have developed reliable computational models and applied them for virtual screening of chemical libraries to identify putative skin sensitizers. The overall concordance between murine LLNA and human skin sensitization responses for a set of 135 unique chemicals was low (R = 28-43%), although several chemical classes had high concordance. We have succeeded to develop predictive QSAR models of all available human data with the external correct classification rate of 71%. A consensus model integrating concordant QSAR predictions and LLNA results afforded a higher CCR of 82% but at the expense of the reduced external dataset coverage (52%). We used the developed QSAR models for virtual screening of CosIng database and identified 1061 putative skin sensitizers; for seventeen of these compounds, we found published evidence of their skin sensitization effects. Models reported herein provide more accurate alternative to LLNA testing for human skin sensitization assessment across diverse chemical data. In addition, they can also be used to guide the structural optimization of toxic compounds to reduce their skin sensitization potential.

QSAR models of human data can enrich or replace LLNA testing for human skin sensitization

QSAR models of human data can enrich or replace LLNA testing for human skin sensitization

Evaluation of an optimized protocol using human peripheral blood monocyte derived dendritic cells for the in vitro detection of sensitizers: Results of a ring study in five laboratories

Allergic contact dermatitis is a delayed T-cell mediated allergic response associated with relevant social and economic impacts. Animal experiments (e.g. the local lymph node assay) are still supplying most of the data used to assess the sensitization potential of new chemicals. However, the 7th amendment to the EU Cosmetic Directive have introduced a testing ban for cosmetic ingredients after March 2013.We have developed and optimized a stable and reproducible in vitro protocol based on human peripheral blood monocyte derived dendritic cells to assess the sensitization potential of chemicals. To evaluate the transferability and the predictivity of this PBMDCs based test protocol, a ring study was organized with five laboratories using seven chemicals with a known sensitization potential (one none-sensitizer and six sensitizers, including one pro-hapten).The results indicated that this optimized test protocol could be successfully transferred to all participating laboratories and allowed a correct assessment of the sensitization potential of the tested set of chemicals. This should allow a wider acceptance of PBMDCs as a reliable test system for the detection of human skin sensitizers and the inclusion of this protocol in the toolbox of in vitro methods for the evaluation of the skin sensitization potential of chemicals.

Using novel in vitro methods to predict of the skin sensitization potential of botanical mixtures

Determination of skin sensitization is a critical toxicological endpoint in the safety evaluation of botanical ingredients. With the European Union regulatory ban of animal testing for cosmetic ingredients, and many companies proactively choosing to eliminate animal testing due to ethical considerations, non-animal methods are increasingly being used for safety assessments. The KeratinoSens assay is a cell-based reporter gene assay which may be used to assess the potential of chemicals to induce skin sensitization in humans. A feature all chemical allergens have in common is their intrinsic electrophilicity, or their potential to be transformed to electrophilic chemicals. The Nrf-2-electrophile sensing pathway comprised of the repressor protein Keap1, the transcription factor Nrf2 and the antioxidant response element (ARE), is capable of detecting skin sensitizers. In the KeratinoSens assay, the induction of a luciferase gene under the control of the antioxidant response element derived from the human gene AKR1C2 gene is quantified. Botanical mixtures were tested in the KeratinoSens assay and the resulting data compared to available historical animal data or clinical data. Since the botanical extract portion may only be a small fraction of the complete mixture, as a proof of concept low levels of known sensitizers were spiked into botanical mixtures with different excipient solvent systems and luciferase induction and cytotoxicity measured. Even at levels as low as 1%, the assay was capable of detecting the spiked sensitizers. These data suggest that the KeratinoSens assay has the potential to identify electrophile allergens within a botanical extract mixture.

Evaluation of combinations of in vitro sensitization test descriptors for the artificial neural network-based risk assessment model of skin sensitization.

The skin sensitization potential of chemicals has been determined with the use of the murine local lymph node assay (LLNA). However, in recent years public concern about animal welfare has led to a requirement for non-animal risk assessment systems for the prediction of skin sensitization potential, to replace LLNA. Selection of an appropriate in vitro test or in silico model descriptors is critical to obtain good predictive performance. Here, we investigated the utility of artificial neural network (ANN) prediction models using various combinations of descriptors from several in vitro sensitization tests. The dataset, collected from published data and from experiments carried out in collaboration with the Japan Cosmetic Industry Association (JCIA), consisted of values from the human cell line activation test (h-CLAT), direct peptide reactivity assay (DPRA), SH test and antioxidant response element (ARE) assay for chemicals whose LLNA thresholds have been reported. After confirming the relationship between individual in vitro test descriptors and the LLNA threshold (e.g. EC3 value), we used the subsets of chemicals for which the requisite test values were available to evaluate the predictive performance of ANN models using combinations of h-CLAT/DPRA (N = 139 chemicals), the DPRA/ARE assay (N = 69), the SH test/ARE assay (N = 73), the h-CLAT/DPRA/ARE assay (N = 69) and the h-CLAT/SH test/ARE assay (N = 73). The h-CLAT/DPRA, h-CLAT/DPRA/ARE assay and h-CLAT/SH test/ARE assay combinations showed a better predictive performance than the DPRA/ARE assay and the SH test/ARE assay. Our data indicates that the descriptors evaluated in this study were all useful for predicting human skin sensitization potential, although combinations containing h-CLAT (reflecting dendritic cell-activating ability) were most effective for ANN-based prediction.

Correlation between experimental human and murine skin sensitization induction thresholds

Quantitative risk assessment for skin sensitization is directed towards the determination of levels of exposure to known sensitizing substances that will avoid the induction of contact allergy in humans. A key component of this work is the predictive identification of relative skin sensitizing potency, achieved normally by the measurement of the threshold (the “EC3” value) in the local lymph node assay (LLNA). In an extended series of studies, the accuracy of this murine induction threshold as the predictor of the absence of a sensitizing effect has been verified by conduct of a human repeated insult patch test (HRIPT). Murine and human thresholds for a diverse set of 57 fragrance chemicals spanning approximately four orders of magnitude variation in potency have been compared. The results confirm that there is a useful correlation, with the LLNA EC3 value helping particularly to identify stronger sensitizers. Good correlation (with half an order of magnitude) was seen with three-quarters of the dataset. The analysis also helps to identify potential outlier types of (fragrance) chemistry, exemplified by hexyl and benzyl salicylates (an over-prediction) and trans-2-hexenal (an under-prediction).

Derek Nexus predicts human skin sensitisation accurately. What is the rationale behind its predictive performance?

Domiphen bromide and didecyl dimethylammonium bromide were widely used environmental chemicals with potent activity on blockade of human ether-a-go-go related gene (HERG) channels. But the mechanism of their action is not clear. The kinetics of block of HERG channels by domiphen bromide and didecyl dimethylammonium bromide was studied in order to characterize the inhibition of HERG currents by these quaternary ammonium compounds (QACs). Domiphen bromide and didecyl dimethylammonium bromide inhibited HERG channel currents in a dose-dependent manner with IC50 values of 9 nM and 5 nM, respectively. Block of HERG channel by domiphen bromide and didecyl dimethylammonium bromide was voltage-dependent and use-dependent. Domiphen bromide and didecyl dimethylammonium bromide caused substantial negative shift of the activation curves, accelerated activated process, but had no effects on the deactivation and reactivation processes. The docking models implied that these two compounds bound to PAS domain of HERG channels and inhibited its function. Our data demonstrated that domiphen bromide and didecyl dimethylammonium bromide blocked the HERG channel with a preference for the activated channel state.

Applying the skin sensitisation adverse outcome pathway (AOP) to quantitative risk assessment

As documented in the recent OECD report ‘the adverse outcome pathway for skin sensitisation initiated by covalent binding to proteins’ (OECD, 2012), the chemical and biological events driving the induction of human skin sensitisation have been investigated for many years and are now well understood. Several non-animal test methods have been developed to predict sensitiser potential by measuring the impact of chemical sensitisers on these key events (Adler et al., 2011; Maxwell et al., 2011); however our ability to use these non-animal datasets for risk assessment decision-making (i.e. to establish a safe level of human exposure for a sensitising chemical) remains limited and a more mechanistic approach to data integration is required to address this challenge.Informed by our previous efforts to model the induction of skin sensitisation (Maxwell and MacKay, 2008) we are now developing two mathematical models (‘total haptenated protein’ model and ‘CD8+ T cell response’ model) that will be linked to provide predictions of the human CD8+ T cell response for a defined skin exposure to a sensitising chemical. Mathematical model development is underpinned by focussed clinical or human-relevant research activities designed to inform/challenge model predictions whilst also increasing our fundamental understanding of human skin sensitisation. With this approach, we aim to quantify the relationship between the dose of sensitiser applied to the skin and the extent of the hapten-specific T cell response that would result. Furthermore, by benchmarking our mathematical model predictions against clinical datasets (e.g. human diagnostic patch test data), instead of animal test data, we propose that this approach could represent a new paradigm for mechanistic toxicology.

Development and evaluation of an in vitro skin sensitization assay based on primary monocyte-derived dendritic cells (P6376)

Abstract Allergic contact dermatitis is a delayed T-cell mediated allergic response associated with relevant social and economic impacts. Until now, animal experiments (e.g. the local lymph node assay) are supplying most of the data used to assess the sensitization potential of new chemicals. However, becoming effective in March 2013, the 7th amendment to the EU Cosmetic Directive introduced an animal testing ban for the endpoint skin sensitisation for cosmetic ingredients. In vitro alternative methods are thus being actively developed. Although promising results have been obtained with cell lines, their reduced functionality and inherent genomic instability led us to reinvestigate the use of peripheral blood monocyte-derived dendritic cells (PBMDCs) for the establishment of a reliable in vitro sensitization test. We successfully solved the issues associated with the use of primary cells (optimized cytokine concentrations, incubation time, readout, pooled vs. single donors and cytoxicity) resulting in a stable and reproducible protocol. Here, we report on the adaption of the protocol to the 96-well format, allowing for a higher and cost-effective throughput of test substances. Comparative analyses of the effect of several skin sensitizers on CD86 expression display similar results for 24- and 96-well format. Upscaling of the PBMDCs advances its applicability for the reliable detection of human skin sensitizers.

A Bayes Linear Approach to Weight-of-Evidence Risk Assessment for Skin Allergy

We introduce a strategy for quantifying and synthesising uncertainty about elements of a risk assessment using Bayes linear methods. We view the population of subjective belief structures and the use of Bayes linear adjustments as a flexible and transparent tool for risk assessors who want to quantify their uncertainty about hazard based on disparate sources of information. For motivation, we use an application of the strategy to human skin sensitisation risk assessment where there are many competing sources of information available.

Highly sensitive tactile sensors integrated with organic transistors

This paper presents a highly sensitive capacitive pressure sensor composed of a polymer dielectric film with a nano-needle structure. The nano-needle polymer films were prepared by facile fabrication methods including breath figures formation followed by stamping. The pressure sensitivity of the sensor reached 1.76 kPa−1 in the low pressure range (<1 kPa), which is comparable to the sensitivity of human skin. Analysis of the geometries and densities effect was shown, and the nano-needle film showed better sensitivity in comparison to films with hemispherical or conical structures. The pressure sensors were integrated with printed organic thin film transistors to enable flexible, large-area tactile sensing applications.

Proteomic allergen–peptide/protein interaction assay for the identification of human skin sensitizers

Modification of proteins by skin sensitizers is a pivotal step in T cell mediated allergic contact dermatitis (ACD). In this process small reactive chemicals interact covalently or non-covalently with cellular or extracellular skin self-proteins or self-peptides to become recognized by the human immune system. Aiming to develop a novel non-animal in vitro test system for predicting sensitization potential of small reactive chemicals in human skin the allergen–peptide/protein interaction assay (APIA) has been developed. By applying modern proteomic technologies together with a target peptide containing all amino acids, the assay permits the profiling of all amino acid specific allergen–peptide interactions. Moreover, potentially crucial allergen-specific Cys-modifications are qualitatively monitored by mass spectrometry and confirmed by a dual peptide approach. Assay conditions chosen mimic the distinct human epidermal reactivity compartments of the skin surface (pH 5.5), stratum basale (pH 6.8), and typical physiological conditions (pH 7.4). An extreme as well as a moderate human contact sensitizer produced Cys-specific mass shifts, whereas a skin irritant did not. Our data indicate that MALDI–MS based and skin-related in vitro technology platforms – like the APIA – are promising tools in developing alternative non-animal allergen assays. This will assist in chemical classification and next generation risk assessment strategies, including REACH and experimental immunotoxicology.

Hairy electronic sensors rival the sensitivity of human skin

Sensors inspired by beetle hairs could bring a more nuanced sense of touch to robots and wearable electronics.

Determining Epidermal Disposition Kinetics for Use in an Integrated Nonanimal Approach to Skin Sensitization Risk Assessment

Development of risk assessment methods for skin sensitization in the absence of toxicological data generated in animals represents a major scientific and technical challenge. The first step in human skin sensitization induction is the transport of sensitizer from the applied dose on the skin surface to the epidermis, where innate immune activation occurs. Building on the previous development of a time course in vitro human skin permeation assay, new kinetic data for 10 sensitizers and 2 nonsensitizers are reported. Multicompartmental modeling has been applied to analyze the data and determine candidate dose parameters for use in integrated risk assessment methods: the area under the curve (AUC) and maximum concentration (C(max)) in the epidermis. A model with two skin compartments, representing the stratum corneum and viable skin (epidermis and dermis), was chosen following a formal model selection process. Estimates of the uncertainty, as well as average values of the epidermal disposition kinetics parameters, were made by fitting to the time course skin permeation data from individual skin donors. A potential reduced time course method is proposed based on two time points at 4 and 24 h, which gives results close to those from the full time course for the current data sets. The time course data presented in this work have been provided as a resource for development of predictive in silico skin permeation models.

In vitro detection of contact allergens: Development of an optimized protocol using human peripheral blood monocyte-derived dendritic cells

Allergic contact dermatitis is a delayed T-cell mediated allergic response associated with relevant social and economic impacts. Animal experiments (e.g. the local lymph node assay) are still supplying most of the data used to assess the sensitization potential of new chemicals. However, the 7th amendment to the EU Cosmetic Directive will introduce a testing ban for cosmetic ingredients after 2013. In vitro alternative methods are thus being actively developed. Although promising results have been obtained with cell lines, their reduced functionality and inherent genomic instability led us to reinvestigate the use of peripheral blood monocyte-derived dendritic cells (PBMDCs) for the establishment of a reliable in vitro sensitization test. To solve the issues associated with the use of primary cells, the culture and exposure conditions (cytokine concentrations, incubation time, readout, pooled vs. single donors and cytotoxicity) were re-assessed and optimized. Here we propose a stable and reproducible protocol based on PBMDCs. This should allow a wider acceptance of PBMDCs as a reliable test system for the detection of human skin sensitizers and the inclusion of this protocol in an integrated testing strategy.

RESEARCH ON THE INFLUENCE OF ORTHOPAEDIC INSERTS ON PRESSURE DISTRIBUTION IN THE FOOT

The article examines the influence of individual orthopaedic inserts on pressure distribution in the foot. Feet deformations, types of orthopaedic inserts, materials and pressure in the foot testing methods are discussed. Experimental computer measurements of pressure in the foot before and after the use of inserts have been done. During research, the inserts made of different kinds of materials selected according to human weight, pathology, skin sensitivity and many other reasons has been used. It has been determinated that orthopaedic inserts have a more noticeable impact on children whose feet is adjusted easier if compared with those of adults.

Porcine Skin as a Model System for Studies of Adverse Effects of Narrow-Band UVB Pulses on Human Skin

Ultraviolet (UV) radiation has been widely used in medicine, and in recent years there has been a growing interest in narrow-band UVB therapies, especially those employing pulses of the 308-nm line of XeCl excimer lasers. Comparative studies in several skin pathologies showed that narrow-band UVB was more effective than classical broad-band UVB radiation. Simultaneously, UVB is carcinogenic and there is a need for data to establish the risk associated with phototherapies involving irradiations of human skin with different doses of narrow- and broad-band UVA and/or UVB radiation. Relevant data are sparse predominantly due to a lack of suitable model systems for study of this phenomenon. Our comparative study of human and porcine skin responses to pulses of narrow-band UVB radiation demonstrated that for doses ranging from 5 to 10,000 mJ/cm2 both skin types have similar susceptibility to UVB-induced breaking of nuclear DNA, indicating that pig skin might serve as good model for studies of sensitivity of human skin to UVB radiation.