Epidermal Langerhans cell apoptosis is induced in vivo by nonanoic acid but not by sodium lauryl sulphate

Dermatologic reactions to disinfectant use during the COVID-19 pandemic

Infection preventive practice of using disinfectants against SARS-CoV-2 has become the new normal due to the COVID-19 pandemic. Although disinfectants may not be applied directly to the human body, it remains at high risk of exposure including close skin contact on disinfected surfaces or during handling. This dermal contact, on a regular basis, can induce hazardous skin reactions like irritation, inflammation, and burning in severe conditions. Disinfectants are germicide chemicals that can penetrate the skin and create skin reactions that are usually regarded as irritant and allergic contact dermatitis. More importantly, disinfectants can react with skin components (proteins and lipids) to facilitate their skin penetration and disrupt the skin barrier function. Whereas the antimicrobial actions of disinfectants are well understood, much less is known regarding their dermatologic reactions, including but not limited to irritation and hypersensitivity. We reviewed the skin reactions created by those disinfectants against SARS-CoV-2 approved by the European Chemical Agency and the US Environmental Protection Agency.

In Vitro Evaluation of Chemically Analyzed Hypericum Triquetrifolium Extract Efficacy in Apoptosis Induction and Cell Cycle Arrest of the HCT-116 Colon Cancer Cell Line

Naturally derived drugs and plant-based products are attractive commodities that are being explored for cancer treatment. This in vitro study aimed to investigate the role of Hypericum triquetrifolium (50% ethanol: 50% water) extract (HTE) treatment on apoptosis, cell cycle modulation, and cell cycle arrest in human colon cancer cell line (HCT-116). HTE induced cell death via an apoptotic process, as assayed by an Annexin V-Cy3 assay. Exposing HCT-116 cells to 0.064, 0.125, 0.25, and 0.5 mg/mL of HTE for 24 h led to 50 ± 9%, 71.6 ± 8%, 85 ± 5%, and 96 ± 1.5% apoptotic cells, respectively. HCT-116 cells treated with 0.25 and 0.5 mg/mL HTE for 3 h resulted in 38.9 ± 1.5% and 57.2 ± 3% cleavage of caspase-3-specific substrate, respectively. RT-PCR analysis revealed that the HTE extract had no effect on mRNA levels of Apaf-1 and NOXA. Moreover, the addition of 0.125 mg/mL and 0.25 mg/mL HTE for 24 h was clearly shown to attenuate the cell cycle progression machinery in HCT-116 cells. GC/MS analysis of the extract identified 21 phytochemicals that are known as apoptosis inducers and cell cycle arrest agents. All the compounds detected are novel in H. triquetrifolium. These results suggest that HTE-induced apoptosis of human colon cells is mediated primarily through the caspase-dependent pathway. Thus, HTE appears to be a potent therapeutic agent for colon cancer treatment.

Development of 3D imaging technique of reconstructed human epidermis with immortalized human epidermal cell line

The epidermis, the outermost layer of the skin, retains moisture and functions as a physical barrier against the external environment. Epidermal cells are continuously replaced by turnover, and thus to understand in detail the dynamic cellular events in the epidermis, techniques to observe live tissues in 3D are required. Here, we established a live 3D imaging technique for epidermis models. We first obtained immortalized human epidermal cell lines which have a normal differentiation capacity and fluorescence-labelled cytoplasm or nuclei. The reconstituted 3D epidermis was prepared with these lines. Using this culture system, we were able to observe the structure of the reconstituted epidermis live in 3D, which was similar to an in vivo epidermis, and evaluate the effect of a skin irritant. This technique may be useful for dermatological science and drug development.

Differential regulation of free radicals (reactive oxygen and nitrogen species) by contact allergens and irritants in human keratinocyte cell line

Immune responses to chemicals resulting in sensitization and the appearance of allergic responses following subsequent exposures are dependent upon activation of T lymphocytes. On the contrary, irritant responses are independent of immune response. The aim of this project was to identify the differential signaling cascade operated in allergic and irritant contact dermatitis. Recently, we have shown that keratinocyte cell line A431 can function as an antigen presenting cell (APC) and hence can be used as a model to differentiate between an allergen and irritant molecule. Allergen- and irritant-induced regulation of reactive oxygen species (ROS) and nitric oxide (NO) has been explored. Irritants induce release of ROS even at noncytotoxic concentration. ROS generation by allergens was not detected at nontoxic concentration but as the concentration was increased to a toxic dose there was a drastic increase in the ROS level compared to the untreated cells. Hence, the regulation of ROS is not significant in allergic responses but important in irritant responses. The major difference exists in the fact that the source of ROS for irritants is mitochondria, while that of allergens is mostly cytosolic. Antioxidant-induced protection from irritant-induced cell death has also been demonstrated. NO level was found to increase by allergens and irritants in a concentration-dependent manner. Hence, the regulation of ROS and NO can be used as important mediators in contact allergic and irritant dermatitis.

Final Report of the Cosmetic Ingredient Review Expert Panel on the Safety Assessment of Pelargonic Acid (Nonanoic Acid) and Nonanoate Esters

Pelargonic acid and its esters function as skin-conditioning agents in cosmetics. Molecular weight (mw) and octanol–water partition coefficient data suggest that dermal penetration is possible. The biohandling of branched-chain fatty acids is not the same as for straight-chain fatty acids, but the differences are not significant to the conclusion that they all are readily metabolized to nontoxic moieties. Limited data suggested that the penetration of other ingredients may be enhanced if these ingredients are present in the same formulation. These ingredients are not significant oral or dermal toxicants in animal studies. They are not reproductive/developmental toxicants or genotoxic/carcinogenic in animal studies. The available data suggested that product formulations containing these ingredients would be nonirritating and nonsensitizing to human skin, but formulators were cautioned to consider the penetration enhancement potential. The Cosmetic Ingredient Review (CIR) Expert Panel concluded that these ingredients are safe in the present practices of use and concentration.

Skin irritants and contact sensitizers induce Langerhans cell migration and maturation at irritant concentration

Skin irritants and contact allergens reduce the number of Langerhans cells (LCs). It has been assumed that this reduction is due their migration to the draining lymph node (LN) for initiating immune sensitization in a host. Skin irritation, however, as opposed to contact allergy is not considered to be an immunological disease. Nevertheless, skin irritants are also known for their adjuvant-like effects on contact allergy, resulting in skin hypersensitivity reactions like toxic dermatitis. The human organotypic skin explant culture (hOSEC) model is used to study the characteristics of chemical-induced migration of CD1a(+) LCs out of the epidermis in relation to irritancy or toxicity. We analysed cells emigrating out of hOSEC for CD1a(+) LCs, CD83(+) mature dendritic cells (DCs) and CCR7(+) LN homing cells. After exposure to a toxic concentration of a non-immunogenic irritant, an increase of CD1a(+)CD83(+) LCs was found in the culture medium. A non-toxic concentration of an sensitizer induced an increase of CD1a(+) cells. About 50% of skin emigrating CD1a(+) LCs were CD83(-) (immature) but all were CCR7(+). Skin irritation by both non-allergenic and allergenic compounds induces LC migration and maturation. In contrast, only allergenic compounds induced LC migration with partial maturation at subtoxic concentration. This effectively demonstrates that irritation is physiologically needed stimuli for inducing LC maturation.

Surfactant Sodium Lauryl Sulfate Enhances Skin Vaccination

The skin is a highly accessible organ and thus provides an attractive immune environment for cost-effective, simple, and needle-free delivery of vaccines and immunomodulators. In this study, we pretreated mouse skin with an anionic surfactant, sodium lauryl sulfate (SLS), for a short period of time (10 min) followed by epicutaneous vaccination with hen egg lysozyme antigen. We demonstrated for the first time that pretreatment of skin with surfactant SLS significantly enhances the production of antibody to hen egg lysozyme. Short term pretreatment with SLS disorganized the stratum corneum, extracted partial lamellar lipids, induced the maturation of Langerhans cells, and did not result in epidermis thickening. To reveal the mechanism underlying these changes, particularly at the molecular level, we used a novel proteomic technique using ultrafiltration capillaries and mass spectrometry to identify in vivo proteins/peptides secreted in the SLS-pretreated skin. Two secretory proteins, named as calcium-binding protein S100A9 and thymosin beta4, were identified by this novel technique. These two proteins thus may provide new insight into the enhancing effect of surfactants on skin vaccination.

Assessment of contact allergens by dissociation of irritant and sensitizing properties

The human organotypic skin explant culture (hOSEC) model is a promising alternative in vitro model for screening contact allergens. In this model, the chemical-induced migration of Langerhans cells (LCs) out of the epidermis, evaluated after a 24-h exposure period, is used as a measure of sensitizer potential. As skin irritants can also induce LC migration it is essential that concentrations of test chemicals are used that are not even weakly irritant. Using the hOSEC irritation model chemicals are classified as weak irritants if they are toxic after a 48-h exposure period. Toxicity is determined by methyl green-pyronine (MGP) staining of hOSEC. We studied three frequently used non-sensitizing skin irritants and six potent or frequent human sensitizers in a dose-response. A complete discrimination between non-sensitizers and contact sensitizers was obtained for the chemicals tested when the concentrations used were lower than the weak irritant concentrations. Frequency of positive allergen reactions in patch test of human populations correlated with the difference between weak irritant concentrations and the lowest concentration inducing significant LC migration. Sensitizer potency correlated with chemical irritancy as determined by keratinocyte death. For the compounds tested, the hOSEC model predicted allergenicity in humans better than the guinea pig maximization test and the mouse local lymph node assay.

In vitro cell death induced by irradiation and chemicals relevant for dental applications; dose-response and potentiation effects

Resin-based dental materials polymerized using blue light are frequently used in dental practice and may come in contact with the oral mucosa. Remnants from oral hygiene product ingredients, such as sodium lauryl sulfate (SLS), add to the chemical exposure of the mucosa. The aim of the present in vitro study was to elucidate the cytotoxic effects in terms of apoptosis and necrosis after exposures to combinations of an adhesive (0.5% and 0.6%), SLS (concentration range 0.0025%-0.0075%), and irradiation from a dental curing lamp (radiant exposure of 8 J cm(-2)). The test system chosen was rat submandibular salivary gland acinar cells, and the cytotoxic effects were measured by fluorescence microscopy and flow cytometry methods. Cytotoxicity was observed as a result of irradiation. The most pronounced cytotoxic effects were seen in cells exposed to a combination of adhesive and SLS compared with those exposed to either agent alone. Necrosis was the dominating form of cell death for all exposures, except for the highest concentration of SLS. Apoptosis was dose-dependent on SLS in the rat submandibular acinar cells. Cytotoxic considerations of dental materials should include contributions from irradiation and other chemicals that might be present in the oral cavity.

Nonanoic acid - an experimental irritant

Irritant contact dermatitis is defined as a non-immunological skin reaction following exposure to various chemical, mechanical and physical factors. It is known that the skin response to irritants depends on the irritant applied and differs between chemically different irritants. Sodium lauryl sulfate (SLS) is an anionic detergent and the most frequently used substance in experimental irritant contact dermatitis. In 1980, it was suggested that nonanoic acid (NNA) could be used as a positive control when patch testing. Since then, NNA has been used as an experimental irritant in several studies and has been used as a chemically different substance compared to SLS. The present article presents a review of the application of NNA in studies on skin irritancy and experimental irritant contact dermatitis.

Assessment of irritant skin reactions using electrical impedance--a comparison between 2 laboratories

To assess interlaboratory variability in the measurement of skin electrical impedance (IMP), we evaluated irritant reactions to sodium lauryl sulfate (SLS) (2%) and nonanoic acid (NAA) (40%) in 2 laboratories. We studied the patch test responses in 40 healthy male and female volunteers between 20 and 30 years of age (20 in each laboratory) with an instrument for measuring IMP. 2 other bioengineering methods and visual scoring were also used to facilitate further illumination of any findings. A strict protocol including all details of the measurement procedure was carefully implemented in both laboratories. The skin reactions were evaluated at 23 h and at 3, 7 and 14 days after exposure. Our findings show that both irritants caused distinct dynamic responses detectable with the bioengineering techniques. Interestingly, the IMP baseline values varied between the 2 laboratories. Moreover, at early stages in the development of irritation (day 1), the irritants induced changes in IMP indices in the opposite direction, which accords with the concept of various IMP patterns of contact dermatitis caused by different irritants. Although the absolute values of IMP differed in both laboratories, the dynamic response patterns were the same.