Adduct‐forming tendencies of cationic triarylmethane dyes with proteins: Metabolic and toxicological implications

The formation of colorless adducts by four cationic triarylmethane dyes (TAM + s), methyl green (MeG + ), malachite green (MG + ), pararosaniline (PR + ), and crystal violet (CV + ) was studied spectrophotometrically at 25°C, in 50 mM 3‐(N‐morpholino)propanesulfonic acid (MOPS) buffer (pH 8), by monitoring the loss in TAM + color in the absence and presence of human serum proteins as potential addends. Unfractionated serum caused a rapid bleaching of MeG + and MG + , while PR + and CV + were unaffected. Sephacryl S200 HR chromatographic screening of the serum revealed two composite peaks of MeG + ‐bleaching activity. The major peak ( M r range, 40,000–130,000) overlapped with and extended on either side of the albumin peak. The minor peak corresponding to ca. 10% of the total MeG + ‐bleaching capacity had M r > 230,000. MG + ‐bleaching activity dominated the entire chromatographic profile and implicated a multitude of minority proteins with a high capacity to form colorless MG adducts. It is concluded that highly electrophilic TAM + s such as MeG + and MG + must be quantitatively trapped in the form of dye–protein adducts in biological fluids and that the primary in vivo effects (e.g. toxicity) of such dyes most likely arise from ligand‐type effects on multiple protein targets. Mechanisms that call for unmodified TAM + structure (radical‐mediated redox changes, DNA intercalation) may be more relevant to the in vivo impact of dyes such as PR + and CV + that have a lower tendency to form adducts. © 2004 Wiley Periodicals, Inc. J Biochem Mol Toxicol 18:253–256, 2004 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20034