The 3T3 neutral red uptake (NRU) phototoxicity assay

Method Description

The 3T3 Neutral Red Uptake (NRU) assay is based on an immortalised mouse fibroblast cell line called Balb/c 3T3. The method is based on a comparison of the cytotoxicity of a chemical when tested in the presence or absence of exposure to a non-cytotoxic dose of simulated solar light (i.e. ultra-violet light). Cytotoxicity in this test is expressed as a concentration-dependent reduction of the uptake of the vital dye neutral red when measured 24 hours after treatment with the test chemical and irradiation. The test chemical together with the irradiation may alter the cell surface and in effect may result in a decreased uptake and binding of the neutral red dye. Differences in this uptake can be measured with a spectrophotometer, which allows the distinction and quantification between viable, damaged or dead cells.