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 The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009.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.
Diisopropylcarbodiimide was selected for evaluation as a sensitizing agent for contact hypersensitivity in mice. It is most commonly used in the area of protein synthesis. It has application in the chemical and pharmaceutical industries as well as laboratory usage in the area of recombinant DNA and bioenergetics. Occupational exposure to these compounds occurs primarily by inhalation or skin exposure. Very little data is available on the toxicological properties of DIC.
DIC was obtained from Aldrich Chemical Company as a clear liquid. Dilutions were made in acetone which served as the vehicle. Three assays were used in this assessment, a primary irritancy study, to screen for toxicity and determine the Minimal Irritating Concentration and the Maximal Non-Irritating Concentration and two assays, the Mouse Ear Swelling Test and the local lymph node assay, to test the dermal sensitizing potential of DIC group.
For irritancy testing, in two separate studies, three mice per group using both ears (N=6) were used to test seven concentrations of test article in vehicle, vehicle alone and untreated controls. Animals were dosed on 4 consecutive days and checked daily for signs of morbidity. The lowest concentration of test article demonstrating significant irritation when compared to vehicle controls, as determined by the percent ear swelling at 24 hrs post last treatment, was considered the MIC. The highest concentration not to demonstrate a significant irritation over the vehicle controls was considered the MNC. Doses chosen for the hypersensitivity assays were based on the MIC and MNC. Pre-, 24 and 48 hr post treatment ear measurements were taken and used to calculate the percen t ear swelling. Measurements from animals dosed with varying concentrations of test article were compared to the DIC background control for significance. When a no effect level was not determined in the first study a second study was run using decreasing concentrations of DIC. After 3 consecutive days of dosing, animals were rested for 1 day and then injected with 31-1-thymidine, draining auricular lymph nodes dissected out 5 hours later and radiciassayed. Chemical exposed groups were compared to vehicle controls for statistical significance.
In the irritancy studies, morbidity was seen in animals dosed with 20% Irritating Concentration was determined to be 10% and the Maximal Non-Irritating Concentration to be 3%. A statistically significant contact hypersensitivity response was demonstrated by the MEST in mice sensitized with concentrations as low as .3% DIC. The positive control group produced a .25% and statistically significant contact hypersensitivity response at a sensitizing concentration of challenge concentration of .5% DNFB as compared to the .5% DNFB challenge only group. In the LLNA, concentrations as low as 10% DIC and .25% DNFB (the positive control) caused a significant response as compared to the vehicle treated group.
Morbidity was seen in animals dosed with 20% DIC. The Minimal Irritating Concentration of DIC was determined to be 10%. DIC was identified as a potential contact sensitizer by both the MEST and the LLNA. The MEST appeared to be a more sensitive indicator, detecting a sensitizing potential at concentrations as low as .3% as compared to detection by the LLNA at a concentration of 10%.