The plasticizer dibutyl phthalate (DBP) potentiates chemical allergen-induced THP-1 activation.

Recent studies suggest that phthalates may have a role in the development of allergic diseases, probably due to an adjuvant effect. The present study aimed to investigate the possible adjuvant effect of dibutyl phthalate (DBP) in two in vitro models of contact-allergen induced cell activation, namely the NCTC 2544 IL-18 assay and the THP-1 activation assay. Results show no adjuvant effect in the human keratinocyte cell line NCTC 2544, indicated by lack of increase in interleukin 18 (IL-18) production after exposure to p-Phenylenediamine (PPD) in association with DBP. On the contrary, increased upregulation of CD86 and interleukin 8 (IL-8) production were observed in THP-1 cells exposed to combinations of citral (Cit) or imidazolidinyl urea (IMZ) with DBP, indicative of an adjuvant effect. Additionally, higher production of reactive oxygen species (ROS) in THP-1 cells treated with DBP associated to Cit supports that oxidative stress could be part of the molecular mechanism of the observed adjuvant effect. In conclusion, we demonstrate that DBP presents in vitro an adjuvant effect for immune stimulation in dendritic cells but not in keratinocytes. Future studies are necessary to elucidate the precise mechanism underlying the adjuvant effect of DBP in vitro and in vivo.

Establishment of an in vitro photoassay using THP-1 cells and IL-8 to discriminate photoirritants from photoallergens.

At present, there are no in vivo or in vitro methods developed which has been adopted by regulatory authorities to assess photosensitization induced by chemicals. Recently, we have proposed the use of THP-1 cells and IL-8 release to identify the potential of chemicals to induce skin sensitization. Based on the assumption that sensitization and photosensitization share common mechanisms, the aim of this work was to explore the THP-1 model as an in vitro model to identify photoallergenic chemicals. THP-1 cells were exposed to 7 photoallergens and 3 photoirritants and irradiated with UVA light or kept in dark. Non phototoxic allergens or irritants were also included as negative compounds. Following 24h of incubation, cytotoxicity and IL-8 release were measured. At subtoxic concentrations, photoallergens produced a dose-related increase in IL-8 release after irradiation. Some photoirritants also produced a slight increase in IL-8 release. However, when the overall stimulation indexes of IL-8 were calculated for each chemical, 6 out of 7 photoallergens tested reached a stimulation index above 2, while the entire set of negative compounds had stimulation indexes below 2. Our data suggest that this assay may become a useful cell-based in vitro test for evaluating the photosensitizing potential of chemicals.

Further development of the NCTC 2544 IL-18 assay to identify in vitro contact allergens.

Several European Union legislations request the use of in vitro methods for toxicological evaluations, including sensitization, in order to increase consumer safety but also to reduce the use of animals. The EU project SENS-IT-IV addresses the need of developing predictive in vitro tests to assess contact and respiratory hypersensitivity reactions. In this context, we have recently reported the possibility to use IL-18 production in the human keratinocyte cell line NCTC 2544 to discriminate contact sensitizer from irritants and low molecular weight respiratory allergens. The aims of the present study were to further develop this assay in order to optimize experimental conditions; to develop a 96-well plate format to establish a high throughput assay; to test the performance of other available keratinocyte cell lines, and to understand the signal transduction pathway involved in p-phenylenediamine (PPD)-induced IL-18 production. If cells reach confluence at the moment of treatment, the ability to identify contact allergens is lost; therefore a careful check for the optimal cell density using PPD as reference contact allergen is critical. In our hands, a cell density of 1-2.5 × 10(5)cells/ml gave optimal stimulation. In order to develop a high throughput test, cells seeded in 96-well plate were exposed to contact allergens (2,4-dinitrochlorobenzene, p-phenylenediamine, isoeugenol, cinnamaldehyde, tetramethylthiuram disulfite, resorcinol, cinnamic alcohol and eugenol), irritants (phenol, sodium laurel sulphate, lactic acid and salicylic acid) and respiratory allergens (hexachloroplatinate, diphenylmethane diisocyanate, trimellitic anhydride). A selective increase in total (intracellular plus released) IL-18 was observed 24h later in cells treated with contact allergens, whereas no changes were observed following treatment with respiratory allergens and irritants, confirming previous results obtained in a 24-well format assay. A selective induction of IL-18 was also obtained testing with PPD other keratinocyte cell lines, namely HPKII and HaCaT, with the HPKII showing the highest stimulation index. Regarding the signal transduction pathway, we could demonstrate using selective inhibitors a role for oxidative stress, NF-κB and p38 MAPK activation in PPD-induced IL-18 production. In conclusion, results obtained suggest that the production of IL-18 represents a promising endpoint for the screening of potential contact allergens. The assay can be performed in a 96-well plate format, different keratinocyte cell lines can be used, and a role for oxidative stress in contact allergen-induced IL-18 was demonstrated.

Use of IL-8 release and p38 MAPK activation in THP-1 cells to identify allergens and to assess their potency in vitro.

The local lymph node assay (LLNA) has been developed to assess skin sensitization, and based on the EC3 value, it can also be used to evaluate allergen potency. Therefore, in the development of in vitro alternatives to the LLNA assay, one should not only consider the hazard identification but also the possibility to classify allergens relatively to their potency. We have recently described a selective release of interleukin-8 (IL-8) by chemical allergens in THP-1 cell line, and identified the activation of p38 mitogen-activated protein kinase (p38 MAPK) as a common pathway. Therefore, the purpose of this study was to expand the number of chemicals tested and to investigate whether IL-8 production and p38 MAPK activation can be used to classify allergens according to their potency. THP-1 cells were exposed to the contact allergens (p-benzoquinone, 2-aminophenol, isoeugenol, diethyl maleate, citral and imidazolidinyl urea), selected according to their potency in the LLNA, and to lactic acid and propylene glycol as non-sensitizers. p38 MAPK activation was evaluated 5-15 min after treatment by FACS analysis, while IL-8 release was assed by ELISA following 24h of incubation. p38 MAPK was activated by all contact allergens, including the pro-apten isoeugenol, whereas IL-8 release was significantly increased after stimulation with all allergens tested, except for isoeugenol. The failure of isoeugenol may be due to decrease in the stability of IL-8 mRNA. Irritants exposure, as expected, failed to induce both p38 MAPK activation and IL-8 release. A significant correlation between IL-8 release and the LLNA EC(3) was found (Pearson correlation r=0.743, p=0.0036, n=12). On the contrary, the activation of p38 MAPK showed no significant correlation between LLNA data and vigor of p38 MAPK activation. Overall, data presented confirm our previous observations and reveal IL-8 as potential tool not only to identify sensitizers, with the exception of pro-haptens, but also to classify them according to their potency, while p38 MAPK activation allows the identification of all sensitizers, including pro-haptens, but was not useful for potency classification.

Hand impairment in systemic sclerosis: association of different hand indices with organ involvement.

OBJECTIVE: To evaluate the association between the assessment tools used to quantify hand impairment and organ involvement in patients with systemic sclerosis (SSc). METHODS: Eighty consecutive SSc patients were assessed for hand impairment using the Hand Anatomic Index (HAI), finger-to-palm distance in flexion (FTP), and the Hand Mobility in Scleroderma (HAMIS) test. Cluster analysis was used to identify patients having similar characteristics on the basis of the pattern of organ involvement in order to create clinically homogeneous groups, and to correlate these clusters with the measures of hand involvement. Finally, we evaluated the discriminating ability of the indices to identify the patients whose clinical condition was more severe. RESULTS: Two major clusters were identified by cluster analysis on the basis of organ involvement. The first (cluster A) included 61 patients and the second (cluster B) 19 patients characterized by minor and major extent of organ involvement, respectively. The extent of organ involvement and the hand impairment were related. The scores of hand indices were lower in cluster B. The area under the receiver operating characteristic (ROC) curve (C-index) for the logistic model including all three indices was 0.85 (95% confidence interval 0.74­0.95). CONCLUSION: The seriousness of hand involvement as measured by the three indices was associated with the extent of organ involvement. Further studies of hand impairment scales are needed to provide validated guidance as meaningful clinical measures.