Full-thickness human skin explants for testing the toxicity of topically applied chemicals

Ex Vivo Human Skin: An Alternative Test System for Skin Irritation and Corrosion Assays

Native human skin has been reported in the literature as being an important experimental model for studying skin biology. Studies performed by our group have shown that ex vivo skin, from elective plastic surgery, maintains the biological characteristics of native skin under specific culture conditions. As such, it might be a feasible model for the safety and efficacy testing of topical substances. While Brazil is at the forefront of global regulation implementation, Brazilian researchers are not always able to transfer certain widely used protocols to their laboratories, particularly protocols that involve the use of reconstructed tissues with limited viability, such as those for skin corrosion (OECD TG 431) and irritation testing (OECD TG 439). In this study, we investigated the applicability of the ex vivo skin model to the evaluation of irritation and corrosion potential of a number of proficiency substances described in TG 431 and TG 439. The skin fragments were standardised in size and diameter, and placed into cell culture inserts. The experimental protocol was conducted according to TG 431 and TG 439. The results obtained show that ex vivo skin could represent a promising tool for the evaluation of irritation and corrosion potential of substances (subject to inclusion and exclusion criteria), as recommended by OECD guidelines. While this is a proof-of-concept study, the use of ex vivo skin should be considered for such testing.

Simultaneous Delivery of Multiple Antimicrobial Agents by Biphasic Scaffolds for Effective Treatment of Wound Biofilms

Biofilms pose a major challenge to control wound-associated infections. Due to biofilm impenetrability, traditional antimicrobial agents are often ineffective in combating biofilms. Herein, a biphasic scaffold is reported as an antimicrobial delivery system by integrating nanofiber mats with dissolvable microneedle arrays for the effective treatment of bacterial biofilms. Different combinations of antimicrobial agents, including AgNO3 , Ga(NO3 )3 , and vancomycin, are incorporated into nanofiber mats by coaxial electrospinning, which enables sustained delivery of these drugs. The antimicrobial agents-incorporated dissolvable microneedle arrays allow direct penetration of drugs into biofilms. By optimizing the administration strategies, drug combinations, and microneedle densities, biphasic scaffolds are able to eradicate both methicillin-resistant Staphylococcus aureus (MRSA) and MRSA/Pseudomonas aeruginosa blend biofilms in an ex vivo human skin wound infection model without necessitating surgical debridement. Taken together, the combinatorial system comprises of nanofiber mats and microneedle arrays can provide an efficacious delivery of multiple antimicrobial agents for the treatment of bacterial biofilms in wounds.

Interrupting Neuron-Tumor Interactions to Overcome Treatment Resistance

Neurons in the tumor microenvironment release neurotransmitters, neuroligins, chemokines, soluble growth factors, and membrane-bound growth factors that solid tumors leverage to drive their own survival and spread. Tumors express nerve-specific growth factors and microRNAs that support local neurons and guide neuronal growth into tumors. The development of feed-forward relationships between tumors and neurons allows tumors to use the perineural space as a sanctuary from therapy. Tumor denervation slows tumor growth in animal models, demonstrating the innervation dependence of growing tumors. Further in vitro and in vivo experiments have identified many of the secreted signaling molecules (e.g., acetylcholine, nerve growth factor) that are passed between neurons and cancer cells, as well as the major signaling pathways (e.g., MAPK/EGFR) involved in these trophic interactions. The molecules involved in these signaling pathways serve as potential biomarkers of disease. Additionally, new treatment strategies focus on using small molecules, receptor agonists, nerve-specific toxins, and surgical interventions to target tumors, neurons, and immune cells of the tumor microenvironment, thereby severing the interactions between tumors and surrounding neurons. This article discusses the mechanisms underlying the trophic relationships formed between neurons and tumors and explores the emerging therapies stemming from this work.

Active neutrophil responses counteract Candida albicans burn wound infection of ex vivo human skin explants

Burn wounds are highly susceptible sites for colonization and infection by bacteria and fungi. Large wound surface, impaired local immunity, and broad-spectrum antibiotic therapy support growth of opportunistic fungi such as Candida albicans, which may lead to invasive candidiasis. Currently, it remains unknown whether depressed host defenses or fungal virulence drive the progression of burn wound candidiasis. Here we established an ex vivo burn wound model, where wounds were inflicted by applying preheated soldering iron to human skin explants, resulting in highly reproducible deep second-degree burn wounds. Eschar removal by debridement allowed for deeper C. albicans penetration into the burned tissue associated with prominent filamentation. Active migration of resident tissue neutrophils towards the damaged tissue and release of pro-inflammatory cytokine IL-1β accompanied the burn. The neutrophil recruitment was further increased upon supplementation of the model with fresh immune cells. Wound area and depth decreased over time, indicating healing of the damaged tissue. Importantly, prominent neutrophil presence at the infected site correlated to the limited penetration of C. albicans into the burned tissue. Altogether, we established a reproducible burn wound model of candidiasis using ex vivo human skin explants, where immune responses actively control the progression of infection and promote tissue healing.

The Ex Vivo Skin Model as an Alternative Tool for the Efficacy and Safety Evaluation of Topical Products

The development of alternative approaches for safety and efficacy testing that avoid the use of animals is a worldwide trend, which relies on the improvement of current models and tools so that they better reproduce human biology. Human skin from elective plastic surgery is a promising experimental model to test the effects of topically applied products. As the structure of native skin is maintained, including cell population (keratinocytes, melanocytes, Langerhans cells and fibroblasts) and dermal matrix (containing collagen, elastin, glycosaminoglycans, etc.), it most closely matches the effects of substances on in vivo human skin. In this review, we present a collection of results that our group has generated over the last years, involving the use of human skin and scalp explants, demonstrating the feasibility of this model. The development of a test system with ex vivo skin explants, of standard size and thickness, and cultured at the air–liquid interface, can provide an important tool for understanding the mechanisms involved in several cutaneous disorders.

An ex vivo Human Skin Model to Study Superficial Fungal Infections

Human skin fungal infections (SFIs) affect 25% of the world's population. Most of these infections are superficial. The main limitation of current animal models of human superficial SFIs is that clinical presentation is different between the different species and animal models do not accurately reflect the human skin environment. An ex vivo human skin model was therefore developed and standardised to accurately model SFIs. In this manuscript, we report our protocol for setting up ex vivo human skin infections and report results from a primary superficial skin infection with Trichophyton rubrum, an anthropophilic fungus. The protocol includes a detailed description of the methodology to prepare the skin explants, establish infection, avoid contamination, and obtain high quality samples for further downstream analyses. Scanning electronic microscopy (SEM), histology and fluorescent microscopy were applied to evaluate skin cell viability and fungal morphology. Furthermore, we describe a broad range of assays, such as RNA extraction and qRT-PCR for human gene expression, and protein extraction from tissue and supernatants for proteomic analysis by liquid chromatography-mass spectrometry (LC-MS/MS). Non-infected skin was viable after 14 days of incubation, expressed genes and contained proteins associated with proliferative, immune and differentiation functions. The macroscopic damage caused by T. rubrum had a similar appearance to the one expected in clinical settings. Finally, using this model, the host response to T. rubrum infection can be evaluated at different levels.

Engineered Skin Tissue Equivalents for Product Evaluation and Therapeutic Applications

The current status of skin tissue equivalents that have emerged as relevant tools in commercial and therapeutic product development applications is reviewed. Due to the rise of animal welfare concerns, numerous companies have designed skin model alternatives to assess the efficacy of pharmaceutical, skincare, and cosmetic products in an in vitro setting, decreasing the dependency on such methods. Skin models have also made an impact in determining the root causes of skin diseases. When designing a skin model, there are various chemical and physical considerations that need to be considered to produce a biomimetic design. This includes designing a structure that mimics the structural characteristics and mechanical strength needed for tribological property measurement and toxicological testing. Recently, various commercial products have made significant progress towards achieving a native skin alternative. Further research involve the development of a functional bilayered model that mimics the constituent properties of the native epidermis and dermis. In this article, the skin models are divided into three categories: in vitro epidermal skin equivalents, in vitro full-thickness skin equivalents, and clinical skin equivalents. A description of skin model characteristics, testing methods, applications, and potential improvements is presented.

Ex vivo regenerative effects of a spring water

Previous experiments by our group have indicated the regenerative effects of a spring water (Comano), which was possibly associated with the native non-pathogenic bacterial flora. The present study aimed to confirm these regenerative properties in a human ex vivo experimental model in the context of physiological wound healing. Human 6-mm punch skin biopsies harvested during plastic surgery sessions were injured in their central portion to induce skin loss and were cultured in either conventional medium (controls) or medium powder reconstituted with filtered Comano spring water (treated samples). At 24, 48 and 72 h the specimens were observed following staining with hematoxylin and eosin, Picrosirius Red, orcein and anti-proliferating cell nuclear antigen. Compared with the controls, the treated samples exhibited reduced overall cell infiltration, evidence of fibroblasts, stimulation of cell proliferation and collagen and elastic fiber regeneration. In the spring water, in addition to 12 resident non-pathogenic bacterial strains exhibiting favorable metabolic activities, more unknown non-pathogenic species are being identified by genomic analysis. In the present study, the efficacy of this ‘germ-free’, filtered spring water in wound regeneration was indicated. Thus, the Comano spring water microbiota should be acknowledged for its regenerative properties.

Topical application of RTA 408 lotion activates Nrf2 in human skin and is well-tolerated by healthy human volunteers

BACKGROUND

Topical application of the synthetic triterpenoid RTA 408 to rodents elicits a potent dermal cytoprotective phenotype through activation of the transcription factor Nrf2. Therefore, studies were conducted to investigate if such cytoprotective properties translate to human dermal cells, and a topical lotion formulation was developed and evaluated clinically.

METHODS

In vitro, RTA 408 (3-1000 nM) was incubated with primary human keratinocytes for 16 h. Ex vivo, RTA 408 (0.03, 0.3, or 3 %) was applied to healthy human skin explants twice daily for 3 days. A Phase 1 healthy volunteer clinical study with RTA 408 Lotion (NCT02029716) consisted of 3 sequential parts. In Part A, RTA 408 Lotion (0.5 %, 1 %, and 3 %) and lotion vehicle were applied to individual 4-cm(2) sites twice daily for 14 days. In Parts B and C, separate groups of subjects had 3 % RTA 408 Lotion applied twice daily to a 100-cm(2) site for 14 days or a 500-cm(2) site for 28 days.

RESULTS

RTA 408 was well-tolerated in both in vitro and ex vivo settings up to the highest concentrations tested. Further, RTA 408 significantly and dose-dependently induced a variety of Nrf2 target genes. Clinically, RTA 408 Lotion was also well-tolerated up to the highest concentration, largest surface area, and longest duration tested. Moreover, significant increases in expression of the prototypical Nrf2 target gene NQO1 were observed in skin biopsies, suggesting robust activation of the pharmacological target.

CONCLUSIONS

Overall, these data suggest RTA 408 Lotion is well-tolerated, activates Nrf2 in human skin, and appears suitable for continued clinical development.

Action of bis(betachloroethyl)sulphide (BCES) on human epidermis reconstituted in culture: Morphological alterations and biochemical depletion of glutathione

Human keratinocyte cultures were treated with bis(betachloroethyl)sulphide (BCES), an alkylating and vesicant agent. At concentrations of 5 x 10(-4) to 5 x 10(-3)m, spontaneous detachment of the epithelium from the culture plate was observed, reproducing in vitro the cutaneous vesication observed in vivo. Progressive cellular alterations were shown with increasing concentrations of BCES (5 x 10(-5) to 5 x 10(-3)m). At low concentrations (5 x 10(-5)m), lesions of the nucleus, a significant target for BCES, were observed, along with lesions in the cytoplasmic organelles. An acute, dose-dependent depletion of cellular glutathione was observed, which occurred within 1 hr of treatment. Mechlorethamine, an analogue of BCES, induced at equivalent doses the same glutathione depletion and similar spontaneous detachment in vitro. We suggest that BCES, in addition to its genetic effects, acts by direct metabolic toxicity and induces glutathione depletion by direct conjugation. The lesions obtained in vitro reproduced those observed in vivo. Human keratinocyte cultures can be proposed as a good model for the study of the mechanisms of action of BCES.

Assessment of the potential irritancy of oleic acid on human skin: Evaluation in vitro and in vivo

As skin barrier modulating compounds, fatty acids are frequently used in formulations for transdermal or topical delivery. In this study the effects of oleic acid on keratinocytes in vitro was compared with its in vivo skin irritancy in humans. Dose- and time-dependent effects of oleic acid were examined in submerged human keratinocyte cultures, in reconstructed human epidermis (RE-DED), and in excised human skin, using alterations in morphology and changes in interleukin-1alpha mRNA levels as endpoints. In vitro results were compared with responses of living human skin after topical application of oleic acid, using non-invasive bioengineering methods. Direct interaction of oleic acid and submerged keratinocyte cultures resulted in cell toxicity at very low concentrations of the fatty acid. By contrast, when oleic acid was applied topically on RE-DED or on excised skin, no alterations in morphology were observed. Modulation of stratum corneum thickness indicated a key role of the stratum corneum barrier in the control of oleic acid-induced toxicity. In agreement with these findings, no epidermal tissue damage was seen in vivo, whereas oleic acid induced a mild but clearly visible skin irritation and inflammatory cells were present in the upper dermal blood vessels. Small amounts of oleic acid induced IL-1alpha mRNA expression in submerged keratinocyte cultures, whereas in RE-DED and in excised skin, IL-1alpha mRNA levels were increased only when the concentration applied topically was at least two orders of magnitude higher. It is concluded that minute amounts of oleic acid are sufficient to cause local (i.e. inside the viable epidermis) modulation of cytokine production. These concentrations do not affect morphology but induce skin irritation in vivo. To achieve comparable effects in the skin, much higher topical doses are needed than expected according to the locally required levels, owing to the rate-limiting transport of the fatty acid across the stratum corneum barrier.

Skin explant cultures as a source of keratinocytes for cultivation

Cultivated human keratinocytes can be used successfully in the treatment of burn patients, but efforts to heal burns and other wounds can be hampered by the very small skin biopsies available for cultivation of transplantable keratinocyte sheets. A small biopsy (and correspondingly small number of enzymatically isolated keratinocytes for use in classical cultivation techniques) can lead to a low yield of multilayer sheets for clinical application or unacceptably long cultivation times. One way of addressing this is to make use of skin remnants remaining after enzymatic digestion and culture cells migrating out of these skin explants. Sufficient numbers of explant-derived keratinocytes can be obtained to facilitate additional routine cultivation of these cells. Biopsy remnants can be used to initiate explant cultures repeatedly (we were able to re-use pieces of skin 10 times and still obtain useful numbers of keratinocytes) and this "passaging" yields substantially more cells for classical cultivation than would be available from conventional methodology alone, and in a comparable timeframe. Another advantage of this method is that it does not require additional biopsies to be procured from already-compromised patients and overcomes problems associated with contamination of skin samples with resistant hospital-acquired bacterial infections common during prolonged hospitalization.

Role of MAP kinases in regulating expression of antioxidants and inflammatory mediators in mouse keratinocytes following exposure to the half mustard, 2-chloroethyl ethyl sulfide

Dermal exposure to sulfur mustard causes inflammation and tissue injury. This is associated with changes in expression of antioxidants and eicosanoids which contribute to oxidative stress and toxicity. In the present studies we analyzed mechanisms regulating expression of these mediators using an in vitro skin construct model in which mouse keratinocytes were grown at an air-liquid interface and exposed directly to 2-chloroethyl ethyl sulfide (CEES), a model sulfur mustard vesicant. CEES (100-1000 microM) was found to cause marked increases in keratinocyte protein carbonyls, a marker of oxidative stress. This was correlated with increases in expression of Cu,Zn superoxide dismutase, catalase, thioredoxin reductase and the glutathione S-transferases, GSTA1-2, GSTP1 and mGST2. CEES also upregulated several enzymes important in the synthesis of prostaglandins and leukotrienes including cyclooxygenase-2 (COX-2), microsomal prostaglandin E synthase-2 (mPGES-2), prostaglandin D synthase (PGDS), 5-lipoxygenase (5-LOX), leukotriene A(4) (LTA(4)) hydrolase and leukotriene C(4) (LTC(4)) synthase. CEES readily activated keratinocyte JNK and p38 MAP kinases, signaling pathways which are known to regulate expression of antioxidants, as well as prostaglandin and leukotriene synthases. Inhibition of p38 MAP kinase suppressed CEES-induced expression of GSTA1-2, COX-2, mPGES-2, PGDS, 5-LOX, LTA(4) hydrolase and LTC(4) synthase, while JNK inhibition blocked PGDS and GSTP1. These data indicate that CEES modulates expression of antioxidants and enzymes producing inflammatory mediators by distinct mechanisms. Increases in antioxidants may be an adaptive process to limit tissue damage. Inhibiting the capacity of keratinocytes to generate eicosanoids may be important in limiting inflammation and protecting the skin from vesicant-induced oxidative stress and injury.

Proteomic analysis of the response of EpiDermTM cultures to sodium lauryl sulphate

The analysis of EpiDerm cultures treated with the known skin irritant sodium lauryl sulphate (SLS) was performed using 2D-gel electrophoresis in order to understand the mechanism of action and thereby identify novel markers of skin irritation. A range of both broad and narrow pH gradient first-dimension gels were run (pH 4-7, 6-11, 4-5, 5-6 and 6-9) consistently followed by 12% SDS-PAGE in the second-dimension. Following treatment of EpiDerm with SLS, 67 proteins of interest were identified, of which 8 were selected as interesting: calmodulin-like skin protein, involucrin, epithelial cell marker protein, HS1, peroxiredoxin 1, serine protease inhibitor, KIAA0117 and ribosomal protein L17. Involucrin was confirmed as being up-regulated by both ELISA and Western blotting. The use of proteomics has identified a number of proteins which could be used as general markers for skin irritation and which may in particular be of value for the development of in vitro predictive models.

The human epidermis models EpiSkin, SkinEthic and EpiDerm: an evaluation of morphology and their suitability for testing phototoxicity, irritancy, corrosivity, and substance transport

The commercially available reconstructed human epidermis models EpiSkin, SkinEthic and EpiDerm demonstrate reasonable similarities to the native human tissue in terms of morphology, lipid composition and biochemical markers. These models have been identified as useful tools for the testing of phototoxicity, corrosivity and irritancy, and test protocols have been developed for such applications. For acceptance of these tests by the authorities, prevalidation or validation studies are currently in progress. Furthermore, first results also indicate their suitability for transport experiments of drugs and other xenobiotics across skin. Still, however, the barrier function of these reconstructed human epidermis models appears to be much less developed compared to native skin. Further adaptation of the models to the human epidermis, especially concerning the barrier function, therefore remains an important challenge in this area of research.

Penetration and Metabolism of Topical Retinoids in ex vivo Organ-Cultured Full-Thickness Human Skin Explants

The human epidermis contains endogenous retinoids [retinol (vitamin A) and retinyl esters] and carotenoids (mostly beta-carotene). Previous studies in the mouse have shown that the enzymes involved in retinoid metabolism are present in the epidermis. In this study, we wanted to assess the skin penetration and metabolism of topical retinoids in the human. To do this, fresh surgically excised human abdominal skin was mounted on Franz perfusion cells. Topical retinoic acid, retinal, retinol and retinyl palmitate were applied at 2.5 mg/cm(2) in oil-in-water creams containing 0.05% retinoids on the donor compartment, while the receptor compartment was filled with culture medium. The skin was incubated for 24 h at 37 degrees C, then epidermal retinoid concentrations were determined by HPLC. The same experiment was performed with mouse back skin mounted on Franz cells. Finally, topical retinoids were applied on the back of hairless mice for 24 h; then the mice were sacrificed and retinoid concentrations were assayed in the epidermis. In all three models, retinol and its esters were found to be endogenous, as was the case in previous studies in the mouse in vivo. The four applied retinoids penetrated well into the epidermis. Topical retinoic acid did not increase endogenous retinoids, whereas the latter were greatly increased following topical retinal in the mouse. Retinal was also metabolized into retinoic acid, unlike topical retinol and retinyl palmitate, which only increased endogenous retinoids. Topical retinal and retinol did undergo a higher metabolism in both mouse models than in human skin. In summary, the penetration and metabolism patterns of topical retinoids were quite similar in the two mouse models used, indicating that the Franz cells appear to be a good model to predict in vivo metabolism of topical retinoids. When applying this concept to our results obtained in Franz cells with human skin, we conclude that topical retinol and retinal load human skin with both storage and functional vitamin A.

Cleansing, dehydrating, barrier-damaging and irritating hyperaemising effect of four detergent brands: comparative studies using standardised washing models

BACKGROUND AND PROBLEM: It is well known that the damaging effect of surfactants on the stratum corneum varies according to the surfactant used. The present investigations aim to compare four standard commercial cleansing solutions (Esemptan Cleansing Lotion, Stephalen Shower Gel, Manipur Antimicrobial Cleansing Solution and Tork Mevon 55 Liquid Soap) with respect to their cleansing and skin barrier-damaging effects.

MATERIAL AND METHODS

The cleansing effect of the solutions was determined in relation to their concentrations in a first experimental series involving 15 subjects using a standardised test method. The product concentrations with the most divergent cleansing effects were tested for their dehydrating (corneometry), epidermal barrier-damaging (TEWL) and irritating effects (laser Doppler) in a standardised washing test. In a second experimental series, the concentration used for the cleansing solutions was based on the quantity of cleansing solution obtained from dispenser actuations (six actuations/L). These concentrations were used to test the cleansing and damaging effect on the stratum corneum using the same methods as in the first experimental series.

RESULTS

There were no significant differences in the first experimental series. In the second experimental series, Stephalen Shower Gel showed disadvantages in terms of a small cleansing effect, but without evidence of a smaller stratum corneum-damaging effect, and Tork Mevon 55 Liquid Soap showed advantages in terms of a smaller stratum corneum-damaging effect, but without evidence of a smaller cleansing effect.

CONCLUSIONS

These studies showed that the relationship between the cleansing and the damaging effect on the stratum corneum can be properly assessed only by testing different concentrations. Furthermore, this experimental approach allowed to differentiate the four tested cleansing solutions.

[Effects of emulsions on the stratum corneum barrier and hydration]

The appearance of the skin depends greatly on the hydration of the stratum corneum which is regulated by water binding substances of the corneocytes and also by the quality of the stratum corneum lipids. Furthermore these lipids are responsible for the barrier function. In patients with atopic dermatitis, the water binding capacity and the barrier function of the stratum corneum are reduced even in clinically healthy skin areas. Emollients can damage the stratum corneum and lead to desiccation and a disturbance of the barrier. This effect is a result of an increased permeability of the barrier lipids and direct damage to the keratinocytes and corneocytes. The degree of damage of the barrier caused by emollients in dermatological vehicles has not been sufficiently investigated. As suggested by hypothetical considerations, such an effect is not expected and cannot be demonstrated in water-in-oil-emulsions. Oil-in-water-emulsions without glycerol as well as lipophilic and hydrophilic microemulsions do damage the barrier function. Both types of microemulsions additionally lead to a dehydration of the stratum corneum. The damaging effect of oil-in-water-emulsions can be reduced by the addition of glycerol and urea.

Proteomic analysis of skin irritation reveals the induction of HSP27 by sodium lauryl sulphate in human skin

BACKGROUND

There is an increasing need for screening of mild irritants in vitro to reduce animal testing.

OBJECTIVES

Proteomics were used to search for new markers of which the expression changes after mild irritation.

METHODS

Sodium lauryl sulphate (SLS) was applied topically on excised human skin. Epidermal proteins were isolated from SLS-treated skin specimens that showed hardly any morphological changes. The proteins were analysed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and proteins that significantly increased or decreased after SLS treatment in a dose-dependent way were characterized by mass spectrometry. Subsequently, immunohistochemistry was performed on skin samples treated with SLS in vivo and nonanoic acid (NAA) or benzalkonium chloride (BC) in vitro to evaluate one of the identified proteins for its predictive value.

RESULTS

We identified seven proteins as potentially new epidermal markers for skin irritation. Among these seven proteins, the 27 kDa heat shock protein (HSP27) was identified as the most prominently upregulated protein. A strong nuclear HSP27 staining was seen in the SLS-treated skin, whereas in the vehicle controls only cytoplasmic staining was observed. Moreover, nuclear staining was also observed after topical application of SLS in vivo and after exposure to NAA and BC in vitro.

CONCLUSIONS

Our findings suggest that HSP27 may serve as a sensitive marker of skin irritation and eventually as a novel tool in clinics for testing the sensitivity of the patient for a panel of irritants.

Peripheral blood granulocyte activity following contact sensitization of rats with dinitrochlorobenzene

Contact hypersensitivity (CHS) reaction is a classic example of a cell-mediated reaction. As the afferent phase of the reaction includes inflammation, CHS is a suitable model for investigating non-specific immunity. Some aspects of granulocyte activity in the afferent phase of experimentally induced CHS to dinitrochlorobenzene (DNCB) in two genetically different rat strains, AO and DA were examined in this study. A shift in the ratio of granulocytes to lymphocytes in favour of granulocytes and an increase in granulocyte survival were noted in DA rats. Granulocytes from both strains demonstrated increased levels of NBT reduction and an increase in their adhesion to plastic. Decreased granulocyte adhesion in the presence of monoclonal antibodies to beta2 integrins (anti-CD11b/c and anti-CD18) points to the contribution of these molecules to granulocyte adhesiveness during the sensitization phase of CHS. Stimulation of adhesion in the presence of anti-CD11a antibody, points to a differential modulation of adhesion molecule activity during the afferent phase of CHS. Changes in functional activity of granulocytes demonstrated in this study might contribute to the development of CHS in rats.

p53 induction in normal human skin in vitro following exposure to solar simulated UV and UV-B irradiation

Exposure of normal human breast skin ex vivo to physiological levels of UV-B and solar simulated UV results in a UV dose- and time-dependent increase in epidermal p53, as determined by PAGE analysis. Peak p53 levels are detected 12 to 24 h post irradiation with UV-B (470-1410 mJ cm-2) and solar simulated UV (5-12 minimal erythema dose (MED) equivalents). Irradiation with an FS20 UV-B lamp, contaminated with UV-A and UV-C (74-1111 mJ cm-2), also induces peak levels after 12 h incubation at 37 degrees C but these levels persist to 36 h post UV irradiation. In all cases p53 levels start to return to normal by 48 h culture. A significant positive correlation is demonstrated between UV-B dose (47-1645 mJ cm-2) and p53 level (p < 0.01, R > 0.977) in explants cultured for 24 h at 37 degrees C post irradiation. The FS20 induces a 'UV-B' dose-dependent increase in p53 to a maximum from 370 to 1111 mJ cm-2. Similarly, solar simulated UV induces a plateau of peak p53 induction between 5 and 15 MED equivalents. Immunohistochemical analysis using microwave retrieval on 5 microns sections shows the same pattern of p53 staining with UV-B and solar UV insult, but proves unreliable as a method of quantification. These results suggest that the skin explant model may be a useful tool in the evaluation of UV-induced epidermal cell damage, providing a valuable alternative to in vivo studies.

Airway epithelial damage and release of inflammatory mediators in human lung parenchyma after sulfur mustard exposure

This study was performed to evaluate the morphological effects of sulfur mustard on human lung parenchyma in vitro and to measure the metabolites of arachidonic acid which are released during acute exposure to the alkylating agent. Histological analysis of the tissue following exposure to sulfur mustard for a period of 45 min at 10 mM revealed the presence of paranuclear vacuoles in the epithelium, specifically, in the ciliated cells. The release of metabolites of arachidonic acid were determined in the bath fluids by an enzymo-immunoassay. The basal release of prostaglandin E2 (PGE2: 1.36 +/- 0.33 ng/g tissue) and 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha: 8.83 +/- 1.17 ng/g tissue) were not modified during tissue exposure to sulfur mustard (45 min, 0.1 mM). In addition, the basal release of cysteinyl-leukotriene E4 (LTE4: 1.55 +/- 0.44 ng/g tissue) was also not altered by challenge of the tissues with sulfur mustard. In contrast, when the human lung parenchyma was stimulated with anti human IgE (anti-IgE) only the basal release of the metabolite of the 5-lipoxygenase pathway was significantly increased (LTE4: 6.84 +/- 1.57 ng/g tissue). These data suggest that sulfur mustard may produce morphological alterations in epithelial cells and at the time point studied (45 min exposure), this effect is not associated with a release of arachidonic acid metabolites. However, the increased release of LTE4 by anti-IgE suggests that the target cells for sulfur mustard and anti-IgE in the human lung may be different.

Immunologic protection afforded by sunscreens in vitro

Several studies have suggested a lack of correlation between sunscreen sun protection factor and protection of the skin immune system, potentially allowing greater damage to the skin by removing the natural protective erythemal response to sun exposure. Despite this, routine testing of immune protection afforded by sunscreens is not performed by industry. Current laboratory methods for investigating the efficacy of sunscreen protection of epidermal immune function use the induction of contact hypersensitivity or epidermal cell alloantigen presentation. Animal models, cell culture systems, and in vivo human studies are commonly employed, but all these systems have significant drawbacks for use in routine testing. The purpose of this study was to develop an in vitro system for testing the immunologic protection afforded by sunscreens in human skin. Five test sunscreens plus a vehicle control were tested in a "blind" fashion for their in vitro level of immune protection. Creams were applied in a standard manner to human whole skin explants and were irradiated over a range of physiologic doses using an Oriel solar simulator. A mixed epidermal lymphocyte reaction was used to quantify epidermal alloantigen-presenting capacity, in the presence or absence of test cream, for five explants. Results consistently demonstrated that all the test sunscreens protected beyond their designated sun protection factors, whereas the vehicle conferred no protection. The explant-mixed epidermal lymphocyte reaction system gave consistent, reproducible results and may prove useful for the allocation of an immune protection factor to all sunscreens.

Ultrastructure of the epidermal barrier after irritation

The stratum corneum (SC) controls the diffusion and penetration of chemical substances and drugs into and through the skin. Surprisingly, knowledge of the SC structure and reaction to the various irritants is still poorly understood. Routine transmission electron microscopy has not been effective in demonstrating the epidermal lipids (EL) of SC which are believed to morphologically represent the water permeability barrier. To gain a better understanding of the interaction of chemically different irritants with the SC, we investigated the ultrastructural changes of epidermal lipids resulting from the topical application of sodium dodecyl sulfate (SDS 0.5% and 1% w/v) and absolute acetone. The disturbance of barrier function by these irritants was determined by the increase of transepidermal water loss (TEWL). Punch biopsies from the treated sites showed a maximum increase of TEWL. To visualize the EL which derive from lamellar body (LB) lipids (sheets), we used a special fixation method utilizing 0.5% ruthenium tetroxide/0.25% KFe(CN)6 as the postfixative. The 0.5% SDS caused cell damage to the nucleated cells of the epidermis with disturbance of LB lipid extrusion and the transformation into the lipid bilayers. However, the upper portions of SC displayed intact intercellular lipid layers. With the acetone treatment, the EL lamellae showed disruption and loss of cohesion between the lamellae at all levels of the SC. The more polar LB lipids appeared more resistant to acetone. The results of this study suggest that different irritants induce distinct and characteristic alterations to reflect the specific interaction with the epidermal permeability barrier.

Effects of calmodulin antagonists and anesthetics on the skin lesions induced by 2-chloroethylethyl sulfide

The effects of calmodulin antagonists and anesthetics on the skin lesions induced by an alkylating vesicant, 2-chloroethylethyl sulfide, were investigated using female hairless mice. 2-Chloroethylethyl sulfide, topically applied (0.6 microliter/5 mm in diameter) on the back skin of hairless mice, induced mild to moderate petechiae on the 1st day, and ulcers with a thick scab after 3 days. The healing process started after 6 days, resulting in shedding of scabs on 9.52 days. Water-soluble ointment bases showed some beneficial effects, whereas oily bases made the skin lesions worse. Trifluoperazine (0.5-1%) and thioridazine (2%), potent calmodulin antagonists, in Pluronic F-127 base substantially prevented the development of 2-chloroethylethyl sulfide-induced skin lesions. A similar effect was achieved with pentamidine (10%), another type of calmodulin antagonist, but not with ketoconazole, a weak calmodulin antagonist. In addition, anesthetics, such as lidocaine and pentobarbital, showed some protection, although at high concentrations (> 5%). As judged by the microscopic appearance, trifluoperazine successfully reduced the hemorrhage and the infiltration of inflammatory cells in early skin lesions, and the formation of thick scabs, which leads to granulomatous scar tissue in late lesions. These results suggest that some calmodulin antagonists and anesthetics in water-soluble bases might be a choice for the treatment of 2-chloroethylethyl sulfide-induced skin burns.

Assessment of the biochemical effects of percutaneous exposure of sulphur mustard in an in vitro human skin system

1. Sulphur mustard (HD) is a potent chemical warfare agent which causes incapacitating blisters on human skin. There is no specific pretreatment nor therapy against this agent and the mechanism of dermo-epidermal cleavage is unclear. The aim of this study was to use a human skin explant system to determine the consequences of percutaneous exposure to HD. 2. Increased activities of serine proteases associated with blistering disorders in humans were detected from human skin explants after exposure to HD. The most consistent response and the highest protease activities measured were found for trypsin. This class of enzyme is therefore implicated in the dermo-epidermal separation which is associated with blistering in humans following exposure to HD. 3. An inflammatory response was observed in the skin explants exposed to HD. At low doses of HD it was characterised by the presence of neutrophils in the papillary dermis, culminating in the infiltration of the epidermis by these inflammatory cells at higher concentrations of HD. A variety of other histopathological changes in the explants was found such as focal dermo-epidermal separation, nuclear pyknosis and perinuclear vacuolation. 4. The study indicates that full thickness human skin explants can be used to investigate various aspects of the possible pathogenesis of HD-induced skin damage, including the associated inflammatory response.

Antigen-specific IgG1-mediated epidermal cell injury: a component of contact hypersensitivity reactions in guinea pigs, measurable in vitro in full-thickness skin explants

Guinea pigs were sensitized by the topical application of either dinitrochlorobenzene (DNCB) or oxazolone on days 1, 2, 3, and 10. Seventeen days after the first treatment with the sensitizer, full-thickness 1.0-cm2 explants of untreated areas of skin were topically exposed in vitro to these contactants. Compared to the response of skin from control guinea pigs, skin from specifically sensitized animals showed a dose-related increase in the number of epidermal cells containing vacuoles. A specific increase in epidermal microblistering paralleled the increase in epidermal vacuolization. In addition, skin explants from sensitized animals (exposed to the contactant) showed a specific decrease in the incorporation of [14C]leucine. Full-thickness skin explants from unsensitized guinea pigs were sensitized in vitro by the intradermal injection of serum IgG1 fraction from oxazolone-sensitized guinea pigs. In such passively sensitized explants, the specific contactant produced an increase in the number of epidermal vacuoles, an increase in the amount of microblistering, and a decrease in the number of mast cells detectable by Giemsa staining. To elicit this specific response, the concentration of the specific contactant had to be mildly injurious, as well as antigenic. This requirement for nonspecific injury could be met by topically exposing skin explants to a nonspecific irritant followed by a sub-threshold concentration of the specific contactant. In contrast to vacuole formation and blistering, contactant-specific degranulation of mast cells (measured by the decrease in their number) did not require irritant levels of the contactant. These studies show that several components of contact sensitivity reactions can be reproduced in vitro by the passive transfer of sera containing antigen-specific immunoglobulins. Banks of such sera might, therefore, be useful in identifying (in human populations) many pre-existing sensitivities to chemical compounds.

Mediators, initiating the inflammatory response, released in organ culture by full-thickness human skin explants exposed to the irritant, sulfur mustard

Mediators released from injured human skin that initiate the inflammatory response have not been adequately identified. Organ culture of full-thickness skin explants enables us to do so, because injury to the skin can be made in vitro, eliminating the rapid leakage of serum and infiltration of leukocytes that occur in vivo. In our studies, the military vesicant sulfur mustard (SM) (10 microliters of a 0.01 to 1.0% dilution) was topically applied to injure the epidermis of the explant. Then, the explants were cultured in small Petri dishes, usually for 18 h at 36 degrees C, and the organ-culture fluids were assayed for various inflammatory mediators. We found that the culture fluids from SM-exposed and control explants contained similar amounts of angiotensin-converting enzyme, trypsin-like and chymotrypsin-like proteases, acid phosphatase, beta-glucuronidase, beta-galactosidase, lysozyme, deoxyribonuclease, ribonuclease, interleukin 1, and lactic dehydrogenase. However, the culture fluids from SM-exposed explants contained increased amounts of histamine and plasminogen-activating activity, and often prostaglandin E2, when compared to culture fluids from control explants. After 3 to 4 d in culture, full-thickness human skin explants, when exposed to 0.2% SM (but not when exposed to 1.0% SM), sometimes showed separation of the epidermis and increased collagenase activity (i.e., hydroxyproline release). Thus, histamine (from local mast cells), and prostaglandin E2 and plasminogen-activating activity (probably from both mast cells and epidermal cells) are apparently involved in early mediation of the inflammatory response.