Effect of high polyol concentrations on the neutral red absorption assay and tetrazolium-MTT test of rat hepatocytes in primary culture.

The effects of three polyols, mannitol, sorbitol and xylitol, on primary cultures of rat hepatocytes were studied with the aid of two cytotoxicity markers, the MTT test and the neutral red assay. A dose-related increase in the uptake of neutral red (up to approximately 60%) was observed in comparison with untreated cells, whereas the MTT test was unaffected by concentrations of polyols up to 330 mM (620 mOsmol/litre). The increase in neutral red uptake does not indicate cellular toxicity as it was reversible and was shown to be due to an increase in the size of lysosomes. For compounds acting on cellular metabolism, such as phenol, mercuric chloride and pentobarbital, it was shown that the increase in neutral red uptake may minimize any cytotoxic effect of these compounds. The neutral red assay should therefore be used with caution when testing compounds that provoke lysosomal swelling. We recommend the use of multiple, mechanistically different, cytotoxicity markers for the evaluation of xenobiotic cytotoxicity.