Use of HPLC/UPLC-spectrophotometry for detection of formazan in in vitro Reconstructed human Tissue (RhT)-based test methods employing the MTT-reduction assay to expand their applicability to strongly coloured test chemicals

Vitro UPLC analysis and mass method identification, and in vivo or cellular immune anti-inflammatory function of Sanhuang Xiexin Decoction (SHXD)

ETHNOPHARMACOLOGICAL RELEVANCE

Sanhuang Xiexin Decoction (SHXD), consisting of Coptis chinensis Franch., Scutellaria baicalensis Georgi and Rheum palmatum L., is traditionally used for relieving fever, purging fire for removing toxins, eliminating phlegm and haemostasis, eliminating the wetness-evil from the upper warmer, clearing away the heat-evil and expelling superficial evils. Each of the three herbs contained in SHXD has been indicated to have anti-inflammatory effects in vivo, but its effects on rat NK-cell phenotypes remain unexplored, and the comprehensive mechanism of this compound SHXD in curing the inflammation induced by lipopolysaccharides (LPS) remains to be revealed.

AIM OF THE STUDY

The study aim was to assess the effect of SHXD on LPS-induced fever and inflammation in a rat model, reduce NLRP3 activation in NK cells expressing specific cell phenotype antibodies and determine the therapeutic value of this approach in vivo.

MATERIALS AND METHODS

SHXD extract was prepared and analysed by the developed ultra-performance liquid chromatography (UPLC) method for the simultaneous detection of 14 compounds. The main peaks were firstly identified on an Orbitrap via high resolution tandem mass spectrometry (MS). Then, the extract was used in the rat model of LPS-induced inflammation and fever for pharmacologically study the effects of drug treatment. Peripheral blood lymphocyte cells were isolated from the animals, including those subjected to the SHXD extract treatment, and the cell phenotype was determined prior to cell culture and after treating the cell cultures with the extract. The phenotypes of cells harvested using CD3, CD4, CD8a, CD81, CD161 and CD86 antibodies were used to verify the enhanced memory of the peripheral blood lymphocytes cells (PBMC) that were induced into nature killer (NK) cells.

RESULTS

The SHXD extract was prepared, analysed and identified via quality control equipment and was observed to have pharmacological effects that reduced NLRP3 activation and fever in rats. The production of NK cells and peripheral blood lymphocytes was induced by the SHXD extract, which manifested as increased levels of CD4+, CD8a+, CD81+, CD161+ and CD86+ cells. The levels of CD3+ cells were significantly different between the model group and the drug-treated or control groups (p < 0.01) with dose independence, while the levels of CD4+ cells were not significantly different between the drug-treated and control groups, with a trend towards lower levels in the model group with dose independence. The levels of CD4+ cells was significantly different between the drug-treated group and the model groups with dose independence (p < 0.05). The levels of CD86+ cells were not significantly different between the drug-treated group and the model and control groups. The levels of CD8a + cells was significantly different between the model group and the drug and control groups (p < 0.05, dose 2.0 μg/ml), with higher levels in the drug-treated group. The levels of CD3+, CD4+, CD8a + cells in the drug treated group have dose dependence with SHXD.

CONCLUSIONS

This experiment revealed that SHXD reduced NLRP3 activation in the blood of LPS-treated rats, which occurred through the activation of NK cells that expressed CD3, CD8a and CD161. SHXD may possess anti-inflammatory effect via activacting the one of major pharmacology effcet of NK cells that expressed CD3, CD8a and CD161 phenotypes expression. This result demonstrates that SHXD may possess ability to enhance the memory of peripheral blood lymphocytes and natural killer cells.

Amending the U-SENS™ skin sensitization test method for interfering auto-fluorescent chemicals

Limitations of the applicability domain of new approach methodologies (NAM) present a major challenge for the testing of cosmetic ingredients in Europe, as the regulation does not allow to resort to in vivo test method. Therefore, research focused on overcoming such limitations of established in vitro test methods is frequently conducted. Here, we address a limitation of the U-SENS™, an in vitro skin sensitization test method that addresses the key event 3 on activation of dendritic cells of the adverse outcome pathway (AOP) for skin sensitization. The applicability domain of the U-SENS™ excludes autofluorescent substances that can interfere with the measurement of the expression of CD86, i.e., the primary readout. An evaluation of several fluorochromes identified APC as most suitable for testing auto-fluorescent chemicals. Acceptance criteria were reproducibly met when using the APC-labelled antibody. Equivalent performance in terms of reproducibility and skin sensitisation hazard assessment of the standard FITC-labelled antibodies and the APC-labelled antibodies was demonstrated by testing 40 substances. Finally, the value of the expanded technical applicability domain was highlighted with a case study using sulfuretin. In conclusion, we successfully demonstrated the expansion of the U-SENS™ applicability domain to interfering auto-fluorescent chemicals by using APC-labelled antibodies.

ChemSkin Reference Chemical Database for the Development of an In Vitro Skin Irritation Test

Since the animal test ban on cosmetics in the EU in 2013, alternative in vitro safety tests have been actively researched to replace in vivo animal tests. For the development and evaluation of a new test method, reference chemicals with quality in vivo data are essential to assess the predictive capacity and applicability domain. Here, we compiled a reference chemical database (ChemSkin DB) for the development and evaluation of new in vitro skin irritation tests. The first candidates were selected from 317 chemicals (source data n = 1567) searched from the literature from the last 20 years, including previous validation study reports, ECETOC, and published papers. Chemicals showing inconsistent classification or those that were commercially unavailable, difficult or dangerous to handle, prohibitively expensive, or without quality in vivo or in vitro data were removed, leaving a total of 100 chemicals. Supporting references, in vivo Draize scores, UN GHS/EU CLP classifications and commercial sources were compiled. Test results produced by the approved methods of OECD Test No. 439 were included and compared using the classification table, scatter plot, and Pearson correlation analysis to identify the false predictions and differences between in vitro skin irritation tests. These results may provide an insight into the future development of new in vitro skin irritation tests.

Immortalized keratinocytes cells generates an effective model of Epidermal Human Equivalent for irritation and corrosion tests

Three-dimensional skin models, also named 3D skin models, human skin equivalents (HSEs), or Human Epidermal Equivalents (HEEs), have been increasingly used for chemical assessments in terms of efficacy and safety. Considering this, we developed an HEE model using immortalized HaCaT cells, aiming to overcome the limitation of primary tissue source. Our 3D model (HaCaT-HEE) exhibited important markers of cell differentiation (CK10, CK14, involucrin, and filaggrin), although the stratum corneum was shown to be modest. Besides, the model showed a good prediction potential considering membrane permeability, sensitivity, specificity, and accuracy in distinguishing irritant and corrosive effects after exposure to selected chemicals recommended by the OECD protocols. We also validated the formazan determination for the MTT method using High-Performance Liquid Chromatography (HPLC). For that, we considered carry over, linearity, reproducibility/robustness, accuracy, precision, selectivity, and matrix effect, according to the Food and Drug Administration (FDA) guideline. Based on our results, we can conclude that our model has an acceptable predictive value for the safety evaluation of compounds after skin exposure, with the great advantage of being constructed using immortalized cells.

Employment of cytology for in vitro skin irritation test using a reconstructed human epidermis model, Keraskin™

Skin irritation tests using reconstructed human epidermis (RhE) employ viability as an endpoint, but color interference or borderline results are often problematic. We examined whether the cytology of cells from treated RhE could determine skin irritancy. Six chemicals (three irritants; DnP, 1-B, PH, three non-irritants; DP, APA, HS) were evaluated in a RhE, Keraskin™. DP, HS, and PH were clearly classified with viability, but DnP, 1-B, and APA were often falsely determined, due to borderline values falling near the cutoff, 50%. In histology, the tissues treated with DnP, 1-B, and PH showed erosion of the stratum corneum, vacuolization, and necrosis in the basal layer. DP- and HS-treated tissues showed relatively normal morphology but APA induced necrosis similar to irritants. Cytology revealed that DnP, 1-B or PH depleted cells and induced irregular and abnormal cell shapes. In contrast, relatively regular and normal shapes and clear distinction between the nucleus and cytoplasm was observed for DP, APA and HS. To further confirm it, additional 10 substances, including false positives from OECD TG 439, were tested. Overall (16 substances in total), cytology: total area predicted the skin irritancy of test chemicals with the highest accuracy (87.5%) followed by cytology: cell count (81.3%), histology (75%) and viability (68.8%), confirming the utility of cytology as an alternative endpoint in the skin irritation test using RhE.

Development and validation of UPLC method for WST-1 cell viability assay and its application to MCTT HCE™ eye irritation test for colorful substances

WST-1 [Water Soluble Tetrazolium-1; 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt)] is widely used in the cell viability assays replacing MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). A water-soluble formazan dye (4-[1-(4-Iodophenyl)-5-(4-nitrophenyl)formaz-3-yl]-1,3-benzene disulfonate, disodium salt) is produced from the reduction of WST-1 tetrazolium, of which optical density at 450 nm is measured to evaluate cell viability. Colorful substances may interfere with spectrometric measurement, and a method to specifically detect WST-1 formazan is required. Here, a simple, rapid, sensitive, and specific ultra-performance liquid chromatography coupled to UV detector (UPLC-UV) was developed and validated for the WST-1 formazan. For the application to cell viability assay, the supernatant from WST-1 assay was injected without sample preparation procedure and a single run was completed within 5 min. Chromatographic separation was achieved on BEH C18 column (1.7 μm, 2.1 × 50 mm) using gradient elution with the mobile phase of water and acetonitrile. The standard curves were linear over the concentration range of 2.5-120 μg/mL WST-1 formazan, which encompasses WST-1 formazan concentrations from 2% cell viability to 2 fold of 100% cell viability. The intra- and inter-day precisions were measured to be below 5% and accuracies were within the range of 91.8-104.9%. The validated method was successfully applied to the test of colorful substances in vitro eye irritation test with a human cornea-like epithelium, and in vitro cytotoxicity in HaCaT, human keratinocyte cell line.

Alternative Methods to Animal Testing for the Safety Evaluation of Cosmetic Ingredients: An Overview

The safety of cosmetics sold in Europe is based on the safety evaluation of each individual ingredient conducted by those responsible for putting the product on the market. However, those substances for which some concern exists with respect to human health (e.g., colorants, preservatives, UV-filters, nanomaterials) are evaluated at the European Commission level by a scientific committee, currently called the Scientific Committee on Consumer Safety (SCCS). According to the Cosmetics Regulation (European Commission, 2009), it is prohibited in the European Union (EU) to market cosmetic products and ingredients that have been tested on animals. However, the results of studies performed before the ban continue to be accepted. In the current study, we evaluated the use of in vitro methods in the dossiers submitted to the SCCS in the period between 2013 and 2016 based on the published reports issued by the scientific committee, which provides a scientific opinion on these dossiers. The results of this evaluation were compared with those of an evaluation conducted four years previously. We found that, despite a slight increase in the number of studies performed in vitro, the majority of studies submitted to the SCCS is still done principally in vivo and correspond to studies performed before the ban.

Evaluation of ocular irritancy of coal-tar dyes used in cosmetics employing reconstructed human cornea-like epithelium and short time exposure tests

Coal-tar dyes in cosmetics may elicit adverse effects in the skin and eyes. Countries, like the US, have banned the use of coal-tar dyes in cosmetics for the eye area due to the potential for ocular irritation. We evaluated the eye irritation potential of 15 coal-tar dyes permitted as cosmetic ingredients in reconstructed human cornea-like epithelium (RhCEs [EpiOcular™ and MCTT HCE™]) tests and the short time exposure (STE) test. Eosin YS, phloxine B, tetrachlorotetrabromofluorescein, and tetrabromofluorescein were identified as irritants in RhCEs; dibromofluorescein and uranine yielded discrepant results. STE enabled further classification in accordance with the UN Globally Harmonized System of Classification and Labelling of Chemicals, as follows: eosin YS as Cat 2; phloxine B, Cat 1; and tetrachlorotetrabromofluorescein and tetrabromofluorescein, Cat 1/2. STE indicated dibromofluorescein (irritant in EpiOcular™) and uranine (irritant in MCTT HCE™) as No Cat, resulting in the classification of "No prediction can be made." based on bottom-up approach with each model. These results demonstrated that in vitro eye irritation tests can be utilized to evaluate the potential ocular irritancy of cosmetic ingredients and provide significant evidence with which to determine whether precautions should be given for the use of coal-tar dyes in cosmetics or other substances applied to the eye area.

Cosmetics Europe compilation of historical serious eye damage/eye irritation in vivo data analysed by drivers of classification to support the selection of chemicals for development and evaluation of alternative methods/strategies: the Draize eye test Reference Database (DRD)

A thorough understanding of which of the effects assessed in the in vivo Draize eye test are responsible for driving UN GHS/EU CLP classification is critical for an adequate selection of chemicals to be used in the development and/or evaluation of alternative methods/strategies and for properly assessing their predictive capacity and limitations. For this reason, Cosmetics Europe has compiled a database of Draize data (Draize eye test Reference Database, DRD) from external lists that were created to support past validation activities. This database contains 681 independent in vivo studies on 634 individual chemicals representing a wide range of chemical classes. A description of all the ocular effects observed in vivo, i.e. degree of severity and persistence of corneal opacity (CO), iritis, and/or conjunctiva effects, was added for each individual study in the database, and the studies were categorised according to their UN GHS/EU CLP classification and the main effect driving the classification. An evaluation of the various in vivo drivers of classification compiled in the database was performed to establish which of these are most important from a regulatory point of view. These analyses established that the most important drivers for Cat 1 Classification are (1) CO mean ≥ 3 (days 1-3) (severity) and (2) CO persistence on day 21 in the absence of severity, and those for Cat 2 classification are (3) CO mean ≥ 1 and (4) conjunctival redness mean ≥ 2. Moreover, it is shown that all classifiable effects (including persistence and CO = 4) should be present in ≥60 % of the animals to drive a classification. As a consequence, our analyses suggest the need for a critical revision of the UN GHS/EU CLP decision criteria for the Cat 1 classification of chemicals. Finally, a number of key criteria are identified that should be taken into consideration when selecting reference chemicals for the development, evaluation and/or validation of alternative methods and/or strategies for serious eye damage/eye irritation testing. Most important, the DRD is an invaluable tool for any future activity involving the selection of reference chemicals.