Evaluation of alamar blue reduction for the in vitro assay of hepatocyte toxicity.

Alamar Blue (AB) reduction is a promising new in vitro assay which is simple to conduct and amenable to repeated measurements and high-throughput screening; however, evaluation with hepatocytes has not been reported. Accordingly, we compared AB reduction with established markers of hepatocyte viability and cell density. Primary rat hepatocytes were allowed to adhere to collagen-coated 96-well plates, then exposed for 16 hours to culture medium, 0.7% dimethyl sulfoxide (DMSO) in medium, 500 mum CCl(4), 500 mum eugenol or 15 or 150 mum of a novel substituted indoline (the latter three in medium with 0.7% DMSO; medium also contained hydrocortisone during exposure period). Using a spectrophotometric plate reader, AB reduction was compared with lactate dehydrogenase release (LDH) release, neutral red (NR) uptake, total protein (TP) and cell seed density. AB reduction showed a linear relationship and good correlation with NR uptake, LDH release, TP and cell density. AB assay precision varied with cell density, but was similar to other assays in cytotoxicity screening. Good correlation with cell density indicates AB to have the potential for assessment of hepatocyte proliferation. From the results reported here, we recommend further evaluation and optimization of a protocol for application of AB reduction as a test for cytotoxicity and proliferation in primary hepatocyte cultures.