Question

As a toxicologist, you are given the assignment of determining whether a new chemical is capable of producing dermal sensitization. Explain how you would test for this. Include in your explanation the model/test system you would use and a brief description of how the test is run and interpreted.

Hint: You will need to use resources outside the textbook to answer this. There are many standardized protocols that will be easy to find. Please include in your answer why you picked the test(s) you selected.

Answer 1

The dermal sensitivity can be done using 2 models in-vitro and in-vivo

In-vitro first by treating the new chemical in different concentrations to the dermal cell lines such as the keratinocytes, fibroblasts and the endothelial cells . The cells were seeded onto a tissue culture plate and left for attachment overnight in a carbon di oxide incubator. The next day the cells were treated with different concentrations of the given chemical. After 24, 48 and 72 hours of incubation the plates are treated with MTT ( 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). This is then incubated for 3 hours after which the formazan crystals formed when the dye reacts with the NADPH of live cells is dissolved using DMSO and the readings are recorded at 570nm. If the chemical is toxic to the cell , then the reading of the sample will be lesser than that of the control or it will be more than that of the control. The cytokines released from the cells after treatment can also be monitored to check the sensitivity

In-vivo test is carried out on guinea pigs. The pigs are divided into 3 wide groups the positive control , placebo ( negative control), sample ( chemical) . About 4 cm × 6 cm size of region on the back of the guinea pigs is shaved and used as experimental are. The animals in the positive control is treated with  0.1% w/v 1-chloro-2,4-dinitrobenzene (CDNB) in 10% propylene glycol , the placebo group received only the vehicle solvent in which the chemical was made in , the sample group is treated with the chemical itself. The samples were changed for every 7 days and were kept for nearly 28 days, after this the sample was completely removed , after removal of the samples the animal was noted for 24, 48 and 72 hours and the observations were recorded . If the animal didn't loose any weight abnormally, if there are no redness on the skin observed and no allergies on the skin is found then the applied chemical is said to be safe for the skin

The test is mentioned in the OECD Guidelines for the Testing of Chemicals and hence this test was selected