The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of the NTP or the U.S. Government.
2-Methoxy-4-nitroaniline is used in dying textiles, as a dye in the printing industry, and as an intermediate in the synthesis of azo dyes that have applications in tattoo inks, emulsion paints, and toy enamels. Azo dyes are reported to induce cross-sensitization and allergic contact dermatitis in people exposed to products containing the dyes (Nakagawa et al. 1996). An extensive retrospective analysis of clinical data and animal studies involving aniline, the parent compound for MONA, and other aminobenzene-based dyes concluded that aniline is a weak sensitizer that likely cross-reacts with other aminobenzene compounds (Uter et. al., 2007). However, 4-nitroaniline failed to induce sensitization in a guinea pig occlusion patch test (Kleniewska and Maibach, 1980). In a survey of "tie and dye" industry workers in India, 26 people with dermatitis associated with contact with dye solutions were patch tested. Of the 14 people who had positive reactions to specific dyes, one individual tested positive for the "red base" dye (0.2% patch) made from MONA; this individual also tested positive for two other aminobenzene-based dyes (Mathur et. al., 1985). A series of animal studies measuring the irritancy and sensitization potential of MONA were reviewed by Chemie (1995), and MONA was identified as non-irritating to the skin (at 500 mg) and the eye (at 100 mg) based on studies in rabbits. A single rabbit in one of two studies developed "very slight" erythema and edema, and the highest irritation index score recorded in the eye was 5 out of 100 at one hour, with reversal after that point. Sensitization was evaluated using the Magnusson-Kligman Maximization Test in guinea pigs; no sensitization to MONA was observed (Chemie, 1995). However, the GPMT has limitations in both sensitivity and specificity, and it poses many technical challenges that can result in false negative/false positive reactions. Recently, two computational (quantitative) structure-activity relationship [(Q)ASAR] models were used to predict the chemical classification for inducing allergic contact dermatitis. These models, which have correct classification rates of 73-83%, have classified MONA as a probable chemical for both skin irritation and sensitization (Fedorowicz et. al., 2005). Based on the variability of the previously conducted animal studies and the possibility of MONA-associated human allergic contact dermatitis, this compound has been selected by the NTP to be tested for potential contact hypersensitivity effects following dermal application.
The objective of this study was to determine the sensitizing potential of MONA when applied dermally to female BALB/c mice. Measurement of the contact hypersensitivity response was initially accomplished using the combined local lymph node assay and irritancy assay. The exposure levels recommended by the sponsor for testing the dermal sensitizing capability of MONA in the LLNA were: 50%, 25%, 10%, 5%, and 2.5% (w/v). In the first LLNA study, there were decreases in lymph node cell proliferation in 25% and 50% MONA-treated animals when compared to the vehicle control. In the second LLNA, although mice treated with 25% MONA had an increase in lymph node cell proliferation that was above the three-fold level of the vehicle response, there were no statistically significant changes in lymph node cell proliferation. In the third study, mice treated with 10 - 25% MONA had increases in lymph node cell proliferation with statistically significant changes observed at levels of 25% and 50%, but they were below the three-fold level of the vehicle response. MONA was not an irritant at concentrations tested, as demonstrated by a lack of significant changes in ear thickness at 24 hours following the last dermal exposure in the IRR assay.
The Mouse Ear Swelling Test was performed to further investigate the potential contact hypersensitivity effects of MONA. In the sensitization phase, three concentrations of MONA (10%, 25%, and 50%) were used, and a concentration of 25% was applied during the challenge phase. Sensitization and subsequent challenge with MONA had no effect on ear thickness at either 24 hours post-challenge or 48 hours post-challenge when compared to the Vehicle Irritancy Control group.
Overall, the results from these studies in BALB/c mice have demonstrated that MONA at 2.5% - 50% produced equivocal results in the LLNA and no effects in the MEST. In addition, MONA was negative in the irritancy assay.
Nakagawa M., Kawai K., & Kawai K. (1996). Multiple azo disperse dye sensitization mainly due to group sensitizations to azo dyes. Contact Dermatitis 34: 6-11.
Uter W., Stropp G., Schnuch A., & Lessmann H. (2007). Aniline-a “historical” contact allergen? Current data from the IVDK and review of the literature. Ann Occup Hyg. 51(2):219-226.
Kleniewska D. & Maibach H. (1980). Allergenicity of aminobenzene compounds: structure-function relationships. Derm. Beruf. Umwelt. 28(1):11-13.
Mathur N.K., Mathur A., & Banerjee K. (1985). Contact dermatitis in tie and dye industry workers. Contact Dermatitis 12: 38-41.
Chemie B.G. (1999). 2-Methoxy-4-nitroaniline. In: Toxicology Evaluation, Vol 14, Springer, pp. 59-68.
Fedorowicz A., Singh H., Soderholm S., & Dumchuk E. (2005). Structure-activity models for contact sensitization. Chem Res Toxicol. 18:954-969.