Serum Albumin Binding at Cytotoxic Concentrations of Chemicals As Determined with a Cell Proliferation Assay

The aim of the present study was to measure the influence of albumin binding on cytotoxic concentrations of chemicals and to determine binding parameters which can be used for quantitative in vitro-in vivo extrapolations. Protein binding parameters were determined from cytotoxic potencies measured with Balb/c 3T3 cells cultured in the presence of 18 and 600 microM bovine serum albumin (BSA). A subset of 27 chemicals from the Multicenter Evaluation of In Vitro Cytotoxicity (MEIC) project was investigated. At 18 microM BSA the EC(50)-values ranged from 2.54 microM (As(III)) to 527 mM (ethylene glycol). Increasing the BSA concentration either decreased the cytotoxic potency (12 compounds) by factors up to 34 (pentachlorophenol), had no effect (14 compounds), or increased the cytotoxicity (paraquat). Calculated molar ratios of binding ranged from 0.05 (Hg(2+)) to 4.8 moles per mole albumin (acetylic salicylic acid). At 18 microM BSA fractional binding of most of these compounds was low (<25%) but increased up to > or =90% (hexachlorophene, mercuric chloride, thioridazine, pentachlorophenol) at 600 microM BSA. The results obtained in general were compatible with available protein binding data and can be used to calculate equipotent concentrations of chemicals in biological systems containing different albumin concentrations.