Potential method to determine irritant potency in vitro - Comparison of two reconstructed epidermal culture models with different barrier competency.

Testing chemicals for their ability to cause skin irritation is required for all ingredients of products that come into contact with the skin. Here, we describe a potential method for determining the irritant potency of a chemical in vitro and apply the method to two different reconstructed epidermis models which exhibit different barrier properties. Two surfactants: sodium dodecyl sulphate, Triton X100 and two non-surfactants: 2-4-di-nitro-chloro-benzene, cinnamaldehyde were applied topically in a dose response for 24h. Biomarkers IL-1alpha, IL-1RA, IL-8 and MTT were assessed and EC(50) values determined. Variation in barrier properties between the epidermal models led to variation in the extent of penetration of surfactants, but not of non-surfactants which in turn influenced the EC(50) value obtained from surfactants. Furthermore, EC(50) values showed that no single biomarker could be classed as the most sensitive biomarker since biomarker sensitivity differed between the different chemicals studied. However, the ranking of the chemicals in order of strong to weak irritant was the same irrespective of the model used and also independent of the biomarker used (Triton X100>DNCB>SDS>CA). This study describes a method which not only distinguishes an irritant from a non-irritant but which may possibly also be used to determine irritant potency.

In vitro exposure effects of cyclosporin A and bis(tri-n-butyltin)oxide on lymphocyte proliferation, cytokine (receptor) mRNA expression, and cell surface marker expression in rat thymocytes and splenocytes.

Rat thymocytes and splenocytes were exposed in vitro to the model compounds Cyclosporin A (CsA), an immunosuppressive drug, and bis(tri-n-butyltin)oxide (TBTO), an immunotoxic environmental contaminant. The lymphocyte transformation test (LTT), cytokine (receptor) mRNA expression (RT-PCR and dot blot hybridisation), and flow cytometry were evaluated as assays for in vitro immunotoxicity, at dose levels that did not show effects on viability, this being the aim of the study. LTT and RT-PCR proved useful assays. Lymphocyte transformation was suppressed by both compounds, while IL-2 mRNA expression was suppressed by CsA but not by TBTO, and both compounds suppressed IL-2R mRNA expression in splenocytes but not in thymocytes. Furthermore, the data obtained suggest that antiproliferative effects may be more relevant than apoptosis induction for TBTO induced thymus atrophy.

Inter-laboratory study of the in vitro dendritic cell migration assay for identification of contact allergens.

The aim of this study was to investigate the transferability of technology and reproducibility of MUTZ-3 derived Langerhans Cell (MUTZ-LC) migration assay. The protocol was transferred from the NL-lab to two Sens-it-iv project partners (UK-lab, Italy-lab). Intra- and inter-laboratory variation with regards to MUTZ-3 progenitor culture, differentiation to MUTZ-LC, maturation and migration assay were investigated. In the transwell-migration-assay, preferential migration of sensitizer-exposed MUTZ-LC towards CXCL12 was observed (three sensitizers), whereas non-sensitizer-exposed MUTZ-LC only migrated towards CCL5 (two non-sensitizers). Four pre-pro-haptens were also identified by UK-lab. When taking the arbitrary criteria of at least two of three independent repetitions per laboratory having to have a CXCL12/CCL5 ratio>1.1 for classification as a sensitizer, all sensitizers tested in all labs were easily distinguished from all non-sensitizers. The number of repetitions giving false negative or false positive was very low (only 7 out of a total of 54 repetitions), indicating that both intra- and inter-laboratory variation was extremely low. Even though only a few chemicals were tested in this study, we show clearly that the in vitro DC migration assay is transferable between laboratories. The results were consistent between the laboratories, and the dose response data were reproduced in the three laboratories.

Autologous full-thickness skin substitute for healing chronic wounds.

BACKGROUND: Chronic wounds represent a major problem to our society. Therefore, advanced wound-healing strategies for the treatment of these wounds are expanding into the field of tissue engineering. OBJECTIVES: To develop a novel tissue-engineered, autologous, full-thickness skin substitute of entirely human origin and to determine its ability to heal chronic wounds. METHODS: Skin substitutes (fully differentiated epidermis on fibroblast-populated human dermis) were constructed from 3-mm punch biopsies isolated from patients to be treated. Acellular allodermis was used as a dermal matrix. After a prior 5-day vacuum-assisted closure therapy to prepare the wound bed, skin substitutes were applied in a simple one-step surgical procedure to 19 long-standing recalcitrant leg ulcers (14 patients; ulcer duration 0.5-50 years). RESULTS: The success rate in culturing biopsies was 97%. The skin substitute visibly resembled an autograft. Eleven of the 19 ulcers (size 1-10 cm2) healed within 8 weeks after a single application of the skin substitute. The other eight larger (60-150 cm2) and/or complicated ulcers healed completely (n = 5) or continued to decrease substantially in size (n = 3) after the 8-week follow-up period. Wound healing occurred by direct take of the skin substitute (n = 12) and/or stimulation of granulation tissue/epithelialization (n = 7). Skin substitutes were very well tolerated and pain relief was immediate after application. CONCLUSIONS: Application of this novel skin substitute provides a promising new therapy for healing chronic wounds resistant to conventional therapies.

Induction of cytokine (interleukin-1alpha and tumor necrosis factor-alpha) and chemokine (CCL20, CCL27, and CXCL8) alarm signals after allergen and irritant exposure.

The immune system is called into action by alarm signals generated from injured tissues. We examined the nature of these alarm signals after exposure of skin residential cells to contact allergens (nickel sulfate and potassium dichromate) and a contact irritant [sodium dodecyl sulfate (SDS)]. Nickel sulfate, potassium dichromate, and SDS were applied topically to the stratum corneum of human skin equivalents. A similar concentration-dependent increase in chemokine (CCL20, CCL27, and CXCL8) secretion was observed for all three chemicals. Exposure to nickel sulfate and SDS was investigated in more detail: similar to chemokine secretion, no difference was observed in the time- and concentration-dependent increase in pro-inflammatory cytokine [interleukin-1alpha (IL-1alpha) and tumor necrosis factor-alpha (TNF-alpha)] secretion. Maximal increase in IL-1alpha secretion occurred within 2 h after exposure to both nickel sulfate and SDS and prior to increased chemokine secretion. TNF-alpha secretion was detectable 8 h after chemical exposure. After allergen or irritant exposure, increased CCL20 and CXCL8, but not CCL27, secretion was inhibited by neutralizing human antibodies to either IL-1alpha or TNF-alpha. Our data show that alarm signals consist of primary and secondary signals. IL-1alpha and TNF-alpha are released as primary alarm signals, which trigger the release of secondary chemokine (CCL20 and CXCL8) alarm signals. However, some chemokines, for example, CCL27 can be secreted in an IL-1alpha and TNF-alpha independent manner. Our data suggest that skin residential cells respond to both allergen and irritant exposure by releasing mediators that initiate infiltration of immune responsive cells into the skin.

Assessment of preferential T-helper 1 or T-helper 2 induction by low molecular weight compounds using the local lymph node assay in conjunction with RT-PCR and ELISA for interferon-gamma and interleukin-4.

The local lymph node assay (LLNA) is a new and promising test in mice used to identify contact allergens by means of dermal exposure. Experimentally this assay, which comprises a sensitizing phase only, is also used to identify respiratory allergens. Another, experimentally used test in mice to identify allergens is also based on dermal exposure, but comprises both a sensitizing and effector phase. In this latter test, it has been shown that contact allergens preferentially induce a T-helper 1 (TH1) response, whereas respiratory allergens preferentially induce a T-helper 2 (TH2) response. These responses can be discriminated on the basis of cytokine production, such as IFN-gamma, which is produced by TH1 cells, and IL-4, which is produced by TH2 cells. The aim of the study was to establish whether the LLNA was sufficient to not only identify allergens but also mark them as either a contact or a respiratory allergen. To this end, LLNA responses to the contact allergen dinitrochlorobenzene (DNCB) and the respiratory allergen trimellitic anhydride (TMA) were determined using IFN-gamma and IL-4 mRNA expression and production as parameters. Topical application of TMA resulted in a threefold higher lymphocyte proliferation compared to DNCB 3 and 5 days after the first application, while a similar proliferation was found from Day 7 and onward. RT-PCR showed a similar induction of IFN-gamma and IL-4 mRNA expression. While both DNCB and TMA induced IFN-gamma production, TMA but not DNCB induced IL-4 production. Thus, only IL-4 production seemed a suitable parameter to discriminate between the two compounds. In a second study, the respiratory allergens toluene-2,4-diisocyanate (TDI) and phthalic anhydride (PA) were also assayed 7 days after the first application. Topical application of DNCB and PA resulted in a similar lymphocyte proliferation, while application of TMA and TDI resulted in a 1.8-fold higher proliferation. IFN-gamma production was similar for DNCB, TMA, and TDI, and fourfold lower for PA, while IL-4 production was similar for TMA, TDI, and PA, and 24-fold lower for DNCB. In summary, both studies showed induction of IL-4 production by respiratory allergens, with little or no induction by the contact allergen, holding promise for the possibility of identifying respiratory allergens within the LLNA by measuring IL-4 production 7 days after the first application.