The anti-mutagenic and antioxidant effects of bile pigments in the Ames Salmonella test

The aim of this study was to explore the potential pro- and anti-mutagenic effects of endogenous bile pigments unconjugated bilirubin (BR), biliverdin (BV) and a synthetic, water soluble conjugate, bilirubin ditaurate (BRT) in the Ames Salmonella test. The bile pigments were tested over a wide concentration range (0.01-2 μmol/plate) in the presence of three bacterial strains (TA98, TA100, TA102). A variety of mutagens including benzo[α]pyrene (B[α]P), 2,4,7 trinitrofluorenone (TNFone), 2-aminofluorene (2-AF), sodium azide (NaN3) and tertiary-butyl hydroperoxide (t-BuOOH), were used to promote the formation of mutant revertants. Tests were conducted with (B[α]P, 2-AF, t-BuOOH) and without (TNFone, NaN3, t-BuOOH) metabolic activation incorporating the addition of the microsomal liver preparation, S9. The bile pigments alone did not induce mutagenicity in any of the strains tested (p > 0.05). Anti-mutagenic effects of the bile pigments were observed in the presence of all mutagens except for NaN3 and the anti-mutagenic effects appeared independent of the strain tested. For TNFone induced genotoxicity, the order of effectiveness was BR ≥ BRT > BV. However, the order was BV ≥ BRT ≥ BR for 2-AF. Antioxidant testing in the TA102 strain revealed bile pigments could effectively inhibit the genotoxic effect of t-BuOOH induced oxidative stress. The apparent antioxidant and anti-mutagenic behaviour of bile pigments further suggests their presence in biological systems is of possible physiological importance.