A tiered approach to the use of alternatives to animal testing for the safety assessment of cosmetics: Skin irritation

Replacing Animal Testing with Stem Cell-Organoids : Advantages and Limitations

Various groups including animal protection organizations, medical organizations, research centers, and even federal agencies such as the U.S. Food and Drug Administration, are working to minimize animal use in scientific experiments. This movement primarily stems from animal welfare and ethical concerns. However, recent advances in technology and new studies in medicine have contributed to an increase in animal experiments throughout the years. With the rapid increase in animal testing, concerns arise including ethical issues, high cost, complex procedures, and potential inaccuracies.Alternative solutions have recently been investigated to address the problems of animal testing. Some of these technologies are related to stem cell technologies, such as organ-on-a-chip, organoids, and induced pluripotent stem cell models. The aim of the review is to focus on stem cell related methodologies, such as organoids, that can serve as an alternative to animal testing and discuss its advantages and limitations, alongside regulatory considerations.Although stem cell related methodologies has shortcomings, it has potential to replace animal testing. Achieving this requires further research on stem cells, with potential societal and technological benefits.

Machine-learning based prediction models for assessing skin irritation and corrosion potential of liquid chemicals using physicochemical properties by XGBoost

Skin irritation test is an essential part of the safety assessment of chemicals. Recently, computational models to predict the skin irritation draw attention as alternatives to animal testing. We developed prediction models on skin irritation/corrosion of liquid chemicals using machine learning algorithms, with 34 physicochemical descriptors calculated from the structure. The training and test dataset of 545 liquid chemicals with reliable in vivo skin hazard classifications based on UN Globally Harmonized System [category 1 (corrosive, Cat 1), 2 (irritant, Cat 2), 3 (mild irritant, Cat 3), and no category (nonirritant, NC)] were collected from public databases. After the curation of input data through removal and correlation analysis, every model was constructed to predict skin hazard classification for liquid chemicals with 22 physicochemical descriptors. Seven machine learning algorithms [Logistic regression, Naïve Bayes, k-nearest neighbor, Support vector machine, Random Forest, Extreme gradient boosting (XGB), and Neural net] were applied to ternary and binary classification of skin hazard. XGB model demonstrated the highest accuracy (0.73-0.81), sensitivity (0.71-0.92), and positive predictive value (0.65-0.81). The contribution of physicochemical descriptors to the classification was analyzed using Shapley Additive exPlanations plot to provide an insight into the skin irritation of chemicals.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-022-00168-8.

Evaluation of Two Novel Hydantoin Derivatives Using Reconstructed Human Skin Model EpiskinTM: Perspectives for Application as Potential Sunscreen Agents

This study aimed to assess two novel 5-arylideneimidazolidine-2,4-dione (hydantoin) derivatives (JH3 and JH10) demonstrating photoprotective activity using the reconstructed human skin model Episkin^TM. The skin permeability, irritation, and phototoxicity of the compounds was evaluated in vitro. Moreover, the in vitro genotoxicity and human metabolism of both compounds was studied. For skin permeation and irritation experiments, the test compounds were incorporated into a formulation. It was shown that JH3 and JH10 display no skin irritation and no phototoxicity. Both compounds did not markedly enhance the frequency of micronuclei in CHO-K1 cells in the micronucleus assay. Preliminary in vitro studies with liver microsomes demonstrated that hydrolysis appears to constitute their important metabolic pathway. Episkin^TM permeability experiments showed that JH3 permeability was lower than or close to currently used UV filters, whereas JH10 had the potential to permeate the skin. Therefore, a restriction of this compound permeability should be obtained by choosing the right vehicle or by optimizing it, which should be addressed in future studies.

Design and Synthesis of New Quinoxaline Derivatives as Potential Histone Deacetylase Inhibitors Targeting Hepatocellular Carcinoma: In Silico, In Vitro, and SAR Studies

Guided by the structural optimization principle and the promising anticancer effect of the quinoxaline nucleus, a new series of novel HDAC inhibitors were designed and synthesized. The synthesized compounds were designed to bear the reported pharmacophoric features of the HDAC inhibitors in addition to an extra moiety to occupy the non-used vacant deep pocket of the HDAC receptor. The newly prepared compounds were evaluated for their in vitro anti-proliferative activities against HepG-2 and HuH-7 liver cancer cell lines. The tested compounds showed promising anti-proliferative activities against both cell lines. The most active ten candidates (6 c , 6 d , 6 f , 6 g , 6 k , 6 l , 7 b , 8, 10 h , and 12) were further evaluated for their effect on the gene expression levels of Bax as an apoptotic marker and Bcl-2 as an anti-apoptotic one. Moreover, they were evaluated for their ability to inhibit histone deacetylase (HDAC1, HDAC4, and HDAC6) activities. Compound 6 c achieved the best cytotoxic activities on both HepG-2 and HuH-7 cell lines with IC50 values of 1.53 and 3.06 µM, respectively, and also it showed the most inhibitory activities on HDAC1, HDAC4, and HDAC6 with IC50 values of 1.76, 1.39, and 3.46 µM, respectively, compared to suberoylanilide hydroxamic acid (SAHA) as a reference drug (IC50 = 0.86, 0.97, and 0.93 µM, respectively). Furthermore, it achieved a more characteristic arrest in the growth of cell population of HepG-2 at both G0/G1 and S phases with 1.23-, and 1.18-fold, respectively, compared to that of the control, as determined by cell cycle analysis. Also, compound 6 c showed a marked elevation in the AnxV-FITC apoptotic HepG-2 cells percentage in both early and late phases increasing the total apoptosis percentage by 9.98-, and 10.81-fold, respectively, compared to the control. Furthermore, docking studies were carried out to identify the proposed binding mode of the synthesized compounds towards the prospective target (HDAC4). In silico ADMET and toxicity studies revealed that most of the synthesized compounds have accepted profiles of drug-likeness with low toxicity. Finally, an interesting SAR analysis was concluded to help the future design of more potent HDACIs in the future by medicinal chemists.

Paving the way for application of next generation risk assessment to safety decision-making for cosmetic ingredients

Next generation risk assessment (NGRA) is an exposure-led, hypothesis-driven approach that has the potential to support animal-free safety decision-making. However, significant effort is needed to develop and test the in vitro and in silico (computational) approaches that underpin NGRA to enable confident application in a regulatory context. A workshop was held in Montreal in 2019 to discuss where effort needs to be focussed and to agree on the steps needed to ensure safety decisions made on cosmetic ingredients are robust and protective. Workshop participants explored whether NGRA for cosmetic ingredients can be protective of human health, and reviewed examples of NGRA for cosmetic ingredients. From the limited examples available, it is clear that NGRA is still in its infancy, and further case studies are needed to determine whether safety decisions are sufficiently protective and not overly conservative. Seven areas were identified to help progress application of NGRA, including further investments in case studies that elaborate on scenarios frequently encountered by industry and regulators, including those where a ‘high risk’ conclusion would be expected. These will provide confidence that the tools and approaches can reliably discern differing levels of risk. Furthermore, frameworks to guide performance and reporting should be developed.

Construction of Vascularized Oral Mucosa Equivalents Using a Layer-by-Layer Cell Coating Technology

There have been many advances in tissue engineering with respect to in vitro and in vivo models of oral mucosa equivalents (OMEs). To apply in vitro reconstructed oral mucosa models to regenerative medicine and alternatives to animal testing, it is necessary to develop the technology of reconstructing different types of oral tissues, such as control of epithelial differentiation and introduction of appendages. We previously reported that functional three-dimensional (3D) tissue models could be quickly constructed by using a layer-by-layer (LbL) cell coating technique that assembles extracellular matrix (ECM) nanofilms to a cell surface. In this study, 3D human OMEs composed of lamina-propria, keratinized or non-keratinized epithelium, and blood capillaries were constructed by using the LbL cell coating technology. Human oral mucosal fibroblasts (HOMFs) were coated with ECM nanofilms and accumulated for the construction of oral mucosal lamina-propria. To construct OMEs with keratinized or non-keratinized epithelium, human oral keratinocytes isolated from gingiva (human oral gingival keratinocytes: HOGKs) or human oral keratinocytes isolated from oral mucosa (human oral mucosal keratinocytes: HOMKs) were used in this study. We further studied the construction of epithelialized OMEs with density- and size-controlled blood capillary networks by using human umbilical vein endothelial cells (HUVECs). It was revealed that these constructions had barrier functions in accordance with their histological characterization. The OMEs with keratinization (K-OMEs) showed higher transepithelial electrical resistance (TEER) values compared with OMEs with non-keratinization (N-OMEs). The constructed epithelialized OMEs with blood capillaries are useful for in vitro/ex vivo research models and regenerative medicine as in oral tissue regeneration. The results suggest that OMEs with oral tissue appendages are more promising alternatives to animal testing and can be applied to the design of in vitro oral models that mimic human tissue organs.

Mixture Toxicity of Methylisothiazolinone and Propylene Glycol at a Maximum Concentration for Personal Care Products

Methylisothiazolinone (MIT) has been used in combination with methylchloroisothiazolinone (CMIT) for cosmetic products such as shampoo, body lotion, and skin care products. The mixture of CMIT/MIT has been found to cause allergic contact dermatitis and is thus no longer permitted for use as a preservative in leave-on cosmetics. However, MIT itself was approved as a stand-alone preservative at a maximum concentration of 100 ppm as the toxicity was derived from CMIT rather than MIT. However, in many countries, allergic skin irritation caused by MIT remains a social concern. In this study, skin irritation was assessed for the presence of MIT, propylene glycol, and their mixture using a 3D human skin model EpiDerm™. Although non-diluted MIT causes serious skin toxicity, skin irritation was not observed at a concentration of 100 ppm, the maximum permissible level for cosmetics and personal care products according to European regulations. Propylene glycol, the most widely used vehicle for MIT, did not cause skin irritation in the 3D skin model. The results are expected to provide information for regulatory policies and guidelines on the use of biocides in consumer products.

Skin and Eye Irritation Assessment of Oil Palm (Elaeis guineensis) Leaf Extract for Topical Application

Many types of phytochemicals have been found to be present in oil palm leaf and could potentially be used as functional ingredients for skincare product. However, as of today, there is no published report on hazard identification and safety assessment of oil palm ( Elaeis guineensis) leaf extract (OPLE), particularly on skin and eye irritation. In this study, potential hazard of OPLE on skin and eye irritation was evaluated as an initial step to the safety assessment of OPLE. In vitro cell viability study of OPLE on normal human dermal fibroblasts showed that OPLE was nontoxic to the cells with percentage viability more than 90% after 24 and 48 hours of incubation. Skin irritation potential of OPLE was evaluated using in vitro SkinEthic reconstructed human epidermis (RHE) model (Organization for Economic Cooperation and Development [OECD] Test Guideline 439, 2015), while eye irritation potential was evaluated using in vitro SkinEthic Human corneal epithelium (HCE) model (OECD test guideline 492, 2017). Hazard identification results showed that OPLE at 1%, 5%, and 10% (wt/wt) was classified as nonirritant to the skin and eye where mean tissue viabilities of SkinEthic RHE and SkinEthic HCE were more than 50% and 60%, respectively. Therefore, we recommend a further safety assessment, such as human patch testing, to confirm the nonirritant of OPLE.

A β-galactosidase-expressing E. coli culture as an alternative test to identify skin sensitizers and non-sensitizers

Although the Organization for Economic Cooperation and Development (OECD) has adopted several in vitro methods with reasonable predictive capacity, alternative methods for identifying skin sensitizers and non-sensitizers with reliability and simplicity are still required for more efficient and economic prediction. The present study was to design an in vitro system with the use of a β-galactosidase-expressing E. coli culture for simpler but sufficiently accurate classification of skin sensitizers and non-sensitizers. A LacZ gene-containing E. coli strain that is capable of producing β-galactosidase enzyme was induced by isopropyl β-D-1-thiogalactopyranoside with concomitant treatment with test chemicals. After 6-hr incubation, cells were lysed and β-galactosidase enzyme activity was monitored colorimetrically by using O-nitrophenyl-D-galactopyranoside as a substrate. Following optimization of several experimental conditions, 22 skin sensitizers and 11 non-sensitizers were examined to assess predictive capacity of this method. The results indicated that predictivity was as follows: 90.9% sensitivity, 81.8% specificity, and 87.9% accuracy, when 17.3% of control activity was used as the cut-off value to separate sensitizers from non-sensitizers. Data suggested that the current bacterial system expressing β-galactosidase may serve as a useful alternative test for classifying skin sensitizers and non-sensitizers, without the utilization of animals or mammalian cell cultures.

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.

The potential of tissue engineering for developing alternatives to animal experiments: a systematic review

An underexposed ethical issue raised by tissue engineering is the use of laboratory animals in tissue engineering research. Even though this research results in suffering and loss of life in animals, tissue engineering also has great potential for the development of alternatives to animal experiments. With the objective of promoting a joint effort of tissue engineers and alternative experts to fully realise this potential, this study provides the first comprehensive overview of the possibilities of using tissue-engineered constructs as a replacement of laboratory animals. Through searches in two large biomedical databases (PubMed, Embase) and several specialised 3R databases, 244 relevant primary scientific articles, published between 1991 and 2011, were identified. By far most articles reviewed related to the use of tissue-engineered skin/epidermis for toxicological applications such as testing for skin irritation. This review article demonstrates, however, that the potential for the development of alternatives also extends to other tissues such as other epithelia and the liver, as well as to other fields of application such as drug screening and basic physiology. This review discusses which impediments need to be overcome to maximise the contributions that the field of tissue engineering can make, through the development of alternative methods, to the reduction of the use and suffering of laboratory animals.

Assuring consumer safety without animals: Applications for tissue engineering

Humans are exposed to a variety of chemicals in their everyday lives through interactions with the environment and through the use of consumer products. It is a basic requirement that these products are tested to assure they are safe under normal and reasonably foreseeable conditions of use. Within the European Union, the majority of tests used for generating toxicological data rely on animals. However recent changes in legislation (e.g., 7(th) amendment of the Cosmetics Directive and REACH) are driving researchers to develop and adopt non-animal alternative methods with which to assure human safety. Great strides have been made to this effect, but what other opportunities/technologies exist that could expedite this? Tissue engineering has increasing scope to contribute to replacing animals with scientifically robust alternatives in basic research and safety testing, but is this application of the technology being fully exploited? This review highlights how the consumer products industry is applying tissue engineering to ensure chemicals are safe for human use without using animals, and identifies areas for future development and application of the technology.

Chemicals inducing acute irritant contact dermatitis mobilize intracellular calcium in human keratinocytes

Intracellular Ca(2+) increase is a common feature of multiple cellular pathways associated with receptor and channel activation, mediator secretion and gene regulation. We investigated the possibility of using this Ca(2+) signal as a biomarker for a reaction to chemical irritants of normal human keratinocytes (NHK) in submerged primary cell culture. We tested 14 referenced chemical compounds classified as strong (seven), weak (four) or non- (three) irritants in acute irritant contact dermatitis. We found that the strong irritant compounds tested at 20-40 mM induced an intracellular Ca(2+) increase measurable by spectrofluorimetry in an automated test. Weak and non-irritant compounds however did not increase intracellular Ca(2+) concentration. We further investigated the mechanisms by which the amine heptylamine, classified as a R34 corrosive compound, increases intracellular Ca(2+). Heptylamine (20mM) induced an ATP release that persisted in the absence of intra- and extra-cellular Ca(2+). In addition, we found that this ATP activates NHK purinergic receptors that subsequently cause the increase in intracellular Ca(2+) from sarcoplasmic reticular stores. We conclude that measuring the intracellular Ca(2+) concentration in NHK is a suitable and easy way of determining any potential reaction to soluble chemical compounds.

Short term study of human skin irritation by single application closed patch test: assessment of four multiple emulsion formulations loaded with botanical extracts

BACKGROUND

Assessment of skin irritation potential is a major concern in safety assessment of cosmetics, when long-term use of these products are expected. Non-invasive bioengineering probes have been used previously to measure skin irritation potential of cosmetic ingredients.

OBJECTIVES

Experimentation carried out to weigh up the skin irritation potential of four multiple emulsion formulations via visual and non-invasive measurements. Immediate effects of formulations and comparison of two assessment techniques were also tried to establish.

METHODS

Four multiple emulsion formulations one control (without botanical active) and three containing the functional botanical actives plus additives were tested in this study using the following techniques: transepidermal water loss (TEWL), COLIPA visual scoring method (CVSM), Mexameter MPA 5 (Courage + Khazaka, Germany) and capacitance [Corneometer MPA 5 (Courage + Khazaka, Germany)]. Visual examination and non-invasive measurements were performed at baseline and after 24 h. The formulations were applied on the forearm of 12 healthy volunteers of same sexes aged 20-25 years.

RESULTS

We found that none of the formulation produced irritation both on visual and instrumental evaluation. However, formulations MeB and MeC have comparable immediate effects on dryness, erythema, melanin and TEWL. Formulation MeC produced more effective results on different parameters, may be due to synergistic effect of two extracts, while MeA failed to produce any immediate effects on skin parameters. Moreover results of both assessment methods are parallel to each other.

CONCLUSIONS

None of the formulation produce irritant effects, barrier impairment effects or immediate effects except for the formulation MeC which produced appreciable results than other formulations but statistically these results were insignificant (p > 0.05). Based on these results, it could be concluded that formulations may be implied safely as skin rejuvenating candidates.

Solid lipid nanoparticles suspension versus commercial solutions for dermal delivery of minoxidil

Solid lipid nanoparticles have been reported as possible carrier for skin drug delivery. Solid lipid nanoparticles are produced from biocompatible and biodegradable lipids. Solid lipid nanoparticles made of semi-synthetic triglycerides stabilized with a mixture of polysorbate and sorbitan oleate were loaded with 5% of minoxidil. The prepared systems were characterized for particle size, pH and drug content. Ex vivo skin penetration studies were performed using Franz-type glass diffusion cells and pig ear skin. Ex vivo skin corrosion studies were realized with a method derived from the Corrositex(®) test. Solid lipid nanoparticles suspensions were compared to commercial solutions in terms of skin penetration and skin corrosion. Solid lipid nanoparticles suspensions have been shown as efficient as commercial solutions for skin penetration; and were non-corrosive while commercial solutions presented a corrosive potential. Solid lipid nanoparticles suspensions would constitute a promising formulation for hair loss treatment.