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 The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009.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.
2,3-Pentanedione is used as a substitute for 2,3-butanedione to impart a butter, strawberry, caramel, fruit, rum, or cheese flavor in beverages, ice cream, candy, baked goods, gelatins, and puddings (Day et al., 2011). The US Food and Drug Administration granted PTD Generally Recognized As Safe status as a food additive (21 CFR.172.515), and consumption of low levels of PTD have not been reported to cause adverse health effects. However, inhalation of PTD has been shown to be toxic to the respiratory tract in rodents. Hubbs et al. (2010) have reported that PTD inhalation resulted in injury to airway epithelium, predominantly in the nose. However, there is limited data available regarding the potential sensitizing effects of PTD. Therefore, PTD has been nominated by the National Toxicology Program to be tested for its potential to induce contact hypersensitivity following dermal application.
The objective of this study was to determine the sensitizing potential of PTD 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. A previous NTP study conducted at Virginia Commonwealth University has indicated that treatment with 2,3-butanedione, a compound with chemical structure similar to PTD, increased lymph node proliferation at 1% - 25% (v/v) as compared to vehicle control in female BALB/c mice after 3 consecutive days of dermal application. Based on the apparent similarity in dermal absorption, the exposure levels recommended by the sponsor for testing the dermal sensitizing capability of PTD in the LLNA were: 25%, 10%, 5%, 2.5% and 1% (v/v). Results indicated that PTD at 5% - 25% induced significant increases in lymph node cell proliferation at levels above 3-fold of the vehicle control in the LLNA. Treatment with PTD at 2.5% also significantly increased lymph node cell proliferation; however, the increase was below 3-fold of the vehicle control response. PTD was not an irritant at concentrations up to 25%, as demonstrated by a lack of significant changes in ear thickness at 24 hr following the last dermal exposure in the IRR assay.
To further confirm the positive LLNA response, the Mouse Ear Swelling Test was conducted following exposure to PTD. In the sensitization phase, three concentrations of PTD (5%, 10% and 25%) were used, and a concentration of 25% was applied during the challenge phase. In total, three MEST studies were conducted. Mice that were sensitized with 10% and 25% PTD followed by 25% PTD challenge exhibited statistically significant increases in percent ear swelling at either 24 or 48 hr post-challenge in two out of the three studies when compared to the vehicle irritancy control. In the second MEST (Study 3), the percent ear swelling in mice that received 5 - 25% PTD for sensitization and 25% PTD for challenge were also increased when compared to the VHIC group at both 24 and 48 hr post-challenge; however, none of increases reached the levels of statistical significance. There was a statistically significant increase in the percent ear swelling of the VHIC group (which received challenge only with 25% PTD) when compared to the vehicle control group in one of the MEST studies (Study 2). However, this increase was not observed in the other MEST studies or in the IRR.
Overall, the results from these studies in BALB/c mice have demonstrated that PTD at 5% - 25% produced increases in lymph node cell proliferation that were above the level of 3-fold enhancement over the vehicle control in the LLNA. Furthermore, PTD challenge at 25% induced a biologically significant increase in percent ear swelling when the mice were sensitized with PTD at 25% as evaluated using MEST. In contrast, PTD was negative in the irritancy assay.
Day G., LeBouf R., Grote A., Pendergrass S., Cummings K., Kreiss K., & Kullman G. (2011). Identification and measurement of diacetyl substitutes in dry bakery mix production. J Occup Environ Hyg. 8(2):93-103.
Hubbs A.F., Moseley A.E., Goldsmith W.T., Jackson M.C., Kashon M.L., Batteli L.A., Schwegler-Berry D., Goravanahally M.P., Frazer D., Fedan J.S., Kreiss K., & Castranova V. The Toxicologist, 2010. 114, S-1, 319.