Investigation of TNF-α release as a measure of skin irritancy

A Comprehensive Assessment of the Biocompatibility and Safety of Diamond Nanoparticles on Reconstructed Human Epidermis

Diamond nanoparticles, also known as nanodiamonds (NDs), exhibit remarkable, awe-inspiring properties that make them suitable for various applications in the field of skin care products. However, a comprehensive assessment of their compatibility with human skin, according to the irritation criteria established by the Organization for Economic Cooperation and Development (OECD), has not yet been conducted. The purpose of this study was to evaluate if diamond nanoparticles at a concentration of 25 μg/mL, incubated with reconstituted human epidermis (EpiDermTM) for 18 h, conform to the OECD TG439 standard used to classify chemical irritants. For this purpose, a cell viability test (MTT assay), histological assessment, and analysis of pro-inflammatory cytokine expression were performed. The results indicated that NDs had no toxic effect at the tested concentration. They also did not adversely affect tissue structure and did not lead to a simultaneous increase in protein and mRNA expression of the analyzed cytokines. These results confirm the safety and biocompatibility of NDs for application in skincare products, thereby creating a wide range of possibilities to exert an impact on the advancement of contemporary cosmetology in the future.

Interleukin-1α and Interleukin-8 Release by Human Keratinocyte Cell Culture Treated with Surfactants

The effects of four cosmetic surfactants on interleukin (IL)-1α and IL-8 release from human keratinocytes were studied to investigate the feasibility of using these effects for the prediction of the irritation potential of chemicals. After exposure of cells to surfactants, the amounts of IL-1α and IL-8 released into culture medium were measured by ELISA. Cytotoxicity was evaluated by using the neutral red uptake (NRU) cytotoxicity assay. Cytokine release was increased 7–15 times by sodium lauryl sulphate (SLS), laurtrimonium chloride, cocamidopropyl betaine (CPB) and Oleth-5 at cytotoxic concentrations. IL-8 release was increased 3–4 times by SLS, CPB and Oleth-5 at subcytotoxic concentrations. After exposure to SLS, IL-1α was released within 1 hour, suggesting that IL-1α release is associated with membrane damage, whereas IL-8 release continued for 24 hours, suggesting that IL-8 was produced within the cells. Cytotoxicity tests and IL-8 release assays were also performed on seven other surfactants. The results show that moderate irritants CPB and PEG-4 dioleate, which have weak cytotoxic effects, significantly increased IL-8 release from human keratinocytes. It is suggested that measurement of IL-8 release is useful for predicting the irritation potential of chemicals which cannot be detected by using the NRU cytotoxicity assay.

Thymic stromal lymphopoietin induction by skin irritation is independent of tumour necrosis factor-α, but supported by interleukin-1

BACKGROUND

Thymic stromal lymphopoietin (TSLP) is an extensively studied cytokine linked to the pathogenesis of allergic diseases, but the inherent activities behind TSLP expression are not well defined.

OBJECTIVES

To explore the conditions favourable to TSLP induction outside of a typically allergic set-up and determine the associated mechanisms, and to assess whether TSLP is similarly controlled in murine and human skin.

METHODS

A combination of primary keratinocytes, skin explants/epidermal sheets and in vivo strategies was employed. The skin of wild-type and tumour necrosis factor knockout (TNF-/-) mice was subjected to acute irritation. Cells and specimens were stimulated with a range of TSLP inducers in the presence or absence of neutralizing antibodies. TSLP was quantitated by quantitative reverse-transcriptase polymerase chain reaction, enzyme-linked immunosorbent assay and immunohistochemistry.

RESULTS

In addition to cytokines, skin irritation brought about by various causes (e.g. shaving, scratching and chemical perturbation) elicited uniformly high-level production of TSLP, which entered the circulatory system. Despite the potency of TNF-α as an in vitro TSLP inducer, the use of TNF-/- mice revealed that this mechanism was completely independent of endogenous TNF-α. Conversely, irritation-elicited TSLP depended on interleukin (IL)-1, which had a more pronounced influence in human skin than in murine skin. Murine and human skin differed considerably regarding TSLP regulation.

CONCLUSIONS

Thymic stromal lymphopoietin is a general responder to disrupted skin homeostasis and may have a role in triggering the alarm system of the skin. TSLP induction is rapid, transient and driven by a mechanism that does not involve TNF-α, but partially relies on the evolutionarily ancient IL-1 system. The irritated skin secretes TSLP into the circulatory system. TSLP regulation varies between species.

Is protein phosphatase inhibition responsible for the toxic effects of okadaic Acid in animals?

Okadaic acid (OA) and its derivatives, which are produced by dinoflagellates of the genera Prorocentrum and Dinophysis, are responsible for diarrhetic shellfish poisoning in humans. In laboratory animals, these toxins cause epithelial damage and fluid accumulation in the gastrointestinal tract, and at high doses, they cause death. These substances have also been shown to be tumour promoters, and when injected into the brains of rodents, OA induces neuronal damage reminiscent of that seen in Alzheimer’s disease. OA and certain of its derivatives are potent inhibitors of protein phosphatases, which play many roles in cellular metabolism. In 1990, it was suggested that inhibition of these enzymes was responsible for the diarrhetic effect of these toxins. It is now repeatedly stated in the literature that protein phosphatase inhibition is not only responsible for the intestinal effects of OA and derivatives, but also for their acute toxic effects, their tumour promoting activity and their neuronal toxicity. In the present review, the evidence for the involvement of protein phosphatase inhibition in the induction of the toxic effects of OA and its derivatives is examined, with the conclusion that the mechanism of toxicity of these substances requires re-evaluation.

Relationship between 2,4-dinitrochlorobenzene elicitation responses and individual irritant threshold

Contact dermatitis shows significant interindividual variation. We studied the relationship between an individual's irritant threshold and the elicitation of experimentally induced allergic sensitization. The results suggest that there is an association between reactivity to an irritant and the likelihood of positive elicitation reactions to lower hapten concentrations. This novel finding would be compatible with the proposal that contact allergy is best explained using a danger model with cutaneous irritancy determining sensitization. However, the enhanced allergic reactivity of individuals with a lower irritant threshold was not apparent on visual inspection, suggesting that the determinants of skin reactivity to haptens are multifactorial.