Evaluation of auricular lymph node cell lymphocyte proliferation and cytokine production as non-radioactive endpoints during murine contact allergy

Introducing the antibacterial and photocatalytic degradation potentials of biosynthesized chitosan, chitosan-ZnO, and chitosan-ZnO/PVP nanoparticles

The development of nanomaterials has been speedily established in recent years, yet nanoparticles synthesized by traditional methods suffer unacceptable toxicity and the sustainability of the procedure for synthesizing such nanoparticles is inadequate. Consequently, green biosynthesis, which employs biopolymers, is gaining attraction as an environmentally sound alternative to less sustainable approaches. Chitosan-encapsulated nanoparticles exhibit exceptional antibacterial properties, offering a wide range of uses. Chitosan, obtained from shrimp shells, aided in the environmentally friendly synthesis of high-purity zinc oxide nanoparticles (ZnO NPs) with desirable features such as the extraction yield (41%), the deacetylation (88%), and the crystallinity index (74.54%). The particle size of ZnO NPs was 12 nm, while that of chitosan-ZnO NPs was 21 nm, and the bandgap energies of these nanomaterials were 3.98 and 3.48, respectively. The strong antibacterial action was demonstrated by ZnO NPs, chitosan-ZnO NPs, and chitosan-ZnO/PVP, particularly against Gram-positive bacteria, making them appropriate for therapeutic use. The photocatalytic degradation abilities were also assessed for all nanoparticles. At a concentration of 6 × 10-5 M, chitosan removed 90.5% of the methylene blue (MB) dye, ZnO NPs removed 97.4%, chitosan-coated ZnO NPs removed 99.6%, while chitosan-ZnO/PVP removed 100%. In the case of toluidine blue (TB), at a concentration of 4 × 10-3 M, the respective efficiencies were 96.8%, 96.8%, 99.5%, and 100%, respectively. Evaluation of radical scavenger activity revealed increased scavenging of ABTS and DPPH radicals by chitosan-ZnO/PVP compared to individual zinc oxide or chitosan-ZnO, where the IC50 results were 0.059, 0.092, 0.079 mg/mL, respectively, in the ABTS test, and 0.095, 0.083, 0.061, and 0.064 mg/mL in the DPPH test, respectively. Moreover, in silico toxicity studies were conducted to predict the organ-specific toxicity through ProTox II software. The obtained results suggest the probable safety and the absence of organ-specific toxicity with all the tested samples.

Combinative ex vivo studies and in silico models ProTox-II for investigating the toxicity of chemicals used mainly in cosmetic products

Human data on remains sparse and of varying quality and reproducibility. Ex vivo experiments and animal experiments currently is the most preferred way to predict the skin sensitization approved by the regulatory agencies across the world. However, there is a constant need and demand to reduce animal experiments and provide the scope of alternative methods to animal testing. In this study, we have compared the predictive performance of the published computational tools such as ProTox-II, SuperCYPsPred with the data obtained from ex-vivo experiments. From the results of the retrospective analysis, it can be observed that the computational predictions are in agreement with the experimental results. The computational models used here are generative models based on molecular structures and machine learning algorithms and can be applied also for the prediction of skin sensitization. Besides prediction of the toxicity endpoints, the models can also provide deeper insights into the molecular mechanisms and adverse outcome pathways (AOPs) associated with the chemicals used in cosmetic products.

The 21st Century movement within the area of skin sensitization assessment: From the animal context towards current human-relevant in vitro solutions

In a regulatory context, skin sensitization hazard and risk evaluations of manufactured products and their ingredients (e.g. cosmetics) are mandatory in several regions. Great efforts have been made within the field of 21st Century Toxicology to provide non-animal testing approaches to assess the skin allergy potential of materials (e.g. chemicals, mixtures, nanomaterials, particles). Mechanistic understanding of skin sensitization process through the adverse outcome pathway (AOP) has promoted the development of in vitro methods, demonstrating accuracies superior to the traditional animal testing. These in vitro testing approaches are based on one of the four AOP key events (KE) of skin sensitization: formation of immunogenic hapten-protein complexes (KE-1 or the molecular initiating event, MIE), inflammatory keratinocyte responses (KE-2), dendritic cell activation (KE-3), and T-lymphocyte activation and proliferation (KE-4). This update provides an overview of the historically used in vivo methods as well as the current in chemico and in cell methods with and without OECD guideline designations to analyze the progress towards human-relevant in vitro test methods for safety assessment of the skin allergenicity potential of materials. Here our focus is to review 96 in vitro testing approaches directed to the KEs of the skin sensitization AOP.

Use of the LLNA:BrdU-ELISA for Skin Sensitization Hazard Assessment

Allergic contact dermatitis (ACD) continues to be an occupational and environmental health issue. Consequently, there is a need to employ predictive tests to reduce the incidence of skin sensitization leading to clinical manifestations of ACD. For more than a decade, the murine local lymph node assay (LLNA) has been the method of choice for the identification of skin sensitizers. While the original LLNA protocol has been extensively evaluated and subjected to exhaustive validation, the use of radioisotope (i.e., tritiated thymidine; 3HTdR) has discouraged utilization of this powerful assay in some countries. To promote further utilization of this method, the original LLNA protocol was refined to use 5-bromo-2'-deoxyuridine, a nonradioactive analog of 3HTdR. The LLNA:BrdU-ELISA has been reviewed, validated, and approved for use internationally, and its performance is regarded as equivalent to the traditional LLNA. Here, we provide guidance on how to perform and interpret data from this assay.

Utilization of the Ex Vivo LLNA

Dermal exposure to chemicals may result in allergic or irritant contact dermatitis. In this study, we performed ex vivo local lymph node assay: bromodeoxyuridine-enzyme-linked immunosorbent assay (LLNA: BrdU-ELISA) to compare the differences between irritation and sensitization potency of some chemicals in terms of the 3 end points: lymphocyte proliferation, cytokine profiles (interleukin 2 [IL-2], interferon-γ (IFN-γ), IL-4, IL-5, IL-1, and tumor necrosis factor α [TNF-α]), and ear swelling. Different concentrations of the following well-known sensitizers and irritant chemicals were applied to mice: dinitrochlorobenzene, eugenol, isoeugenol, sodium lauryl sulfate (SLS), and croton oil. According to the lymph node results; the auricular lymph node weights and lymph node cell counts increased after application of both sensitizers and irritants in high concentrations. On the other hand, according to lymph node cell proliferation results, there was a 3-fold increase in proliferation of lymph node cells (stimulation index) for sensitizer chemicals and SLS in the applied concentrations; however, there was not a 3-fold increase for croton oil and negative control. The SLS gave a false-positive response. Cytokine analysis demonstrated that 4 cytokines including IL-2, IFN-γ, IL-4, and IL-5 were released in lymph node cell cultures, with a clear dose trend for sensitizers whereas only TNF-α was released in response to irritants. Taken together, our results suggest that the ex vivo LLNA: BrdU-ELISA method can be useful for discriminating irritants and allergens.

Development and utilization of an ex vivo bromodeoxyuridine local lymph node assay protocol for assessing potential chemical sensitizers

The murine local lymph node assay (LLNA) is widely used to identify chemicals that may cause allergic contact dermatitis. Exposure to a dermal sensitizer results in proliferation of local lymph node T cells, which has traditionally been measured by in vivo incorporation of [(3) H]methyl thymidine. A more recent non-isotopic variation of the assay utilizes bromodeoxyuridine (BrdU) incorporation in vivo. To further improve the utility of this assay, we developed an ex vivo BrdU labeling procedure eliminating the need for in vivo injections. The results of this assay correctly identified a strong sensitizer (i.e., trimellitic anhydride) as well as weak/moderate sensitizers (i.e., eugenol, cinnamaldehyde and hexylcinnaminic aldehyde). As anticipated, neither non-sensitizers isopropanol and lactic acid nor the false negative chemical nickel II sulfate hexahydrate induced a positive threshold response in the assay. The results of this assay are in close agreement with those of the in vivo LLNA:BrdU-enzyme-linked immunosorbent assay labeling procedure. We also used the ex vivo BrdU LLNA procedure to evaluate ammonium hexachloroplatinate, ammonium tetrachloroplatinate and cis-diamminedichloroplatinum(II) and the assay correctly identified them as sensitizers based on the calculation of EC2 values. We conclude that this ex vivo BrdU labeling method offers predictive capacity comparable to previously established LLNA protocols while eliminating animal injections and the use of radioisotope. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Evaluation of non-radioactive endpoints of ex vivo local lymph node assay-BrdU to investigate select contact sensitizers

The present study sought to verify the utility of the non-radioactive endpoints LLNA BrdU (5-bromo-2'-deoxyuridine) ex vivo incorporation and cytokine release using auricular lymph node cells isolated from BALB/c mice topically treated with a strong (formaldehyde or p-phenylene-diamine [PPD]), moderate sensitizer (cinnamal), or weak sensitizer (eugenol). Stimulation index (SI) and EC₃ values were calculated for each agent. Based on the results of ex vivo LLNA-BrdU assays, EC₃ values were calculated to be 0.29, 0.09, 1.91, and 16.60% for formaldehyde, PPD, cinnamal, and eugenol, respectively. These results were in good agreement with data from previous standard radioactive LLNA. Cytokine analyses indicated T(H)1 and T(H)2 cytokine involvement in the regulation of murine contact allergy and these could be utilized as endpoints in assessments of contact allergy in mice. In conclusion, the current study provided evidence that the non-radioactive endpoint LLNA BrdU ex vivo incorporation could be of use as a viable alternative approach to assess the skin sensitization potential of test compound with respect to improving animal welfare. This is of particular importance in the case of any laboratory where it might be difficult to handle and/or readily employ radioisotopes. Further studies will be required to confirm--across test agents--the reproducibility as well as the limits of utility of this new ex vivo BrdU method.