Antimutagenic effects and possible mechanisms of action of vitamins and related compounds against genotoxic heterocyclic amines from cooked food

Possible antimutagenic activity of 26 vitamins and related compounds — ascorbic acid, β-carotene, cyanocobalamin, folic acid, nicotinic acid, nicotinamide, pantothenic acid, pyridoxale, pyridoxamine, pyridoxine, retinal, retinol, retinoic acid, retinyl acetate, retinyl palmitate, riboflavin, riboflavin 5′-phosphate, flavin adenine dinucleotide (FAD), α-tocopherol, α-tocopherol acetate, vitamins K 1, K 3, K 4, 1,4-naphthoquinone, and coenzyme Q 10 — was tested against six heterocyclic amine (HCA) mutagens, i.e., 2-amino-3-methyl-imidazo[4,5- f]quinoline (IQ), 2-amino-3,4-dimethyl-imidazo[4,5- f]quinoline (MeIQ), 2-amino-3,8-dimethyl-imidazo[4,5- f]quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine (PhIP), 2-amino-6-methyl-dipyrido[1,2- a:3′,2′- d]imidazole (Glu-P-1) and 3-amino-1-methyl-5 H-pyrido[4,3- b]indole (Trp-P-2) in the Salmonella/reversion assay using tester strains Salmonella typhimurium TA 98 and TA 100. Retinol, retinal, riboflavin, riboflavin 5′-phosphate, FAD, vitamins K 1, K 3, K 4, 1,4-naphthoquinone, and coenzyme Q 10 caused a concentration-dependent decrease in the mutagenicity of all six mutagens in both tester strains. Quantification of antimutagenic potencies by calculating ID 50 values (inhibitory dose for 50% reduction of mutagenic activity) from dose–response curves resulted in the following data (nmol/plate): retinol: 480–1400; retinal: 268–441; riboflavin: 25–>100; riboflavin 5′-phosphate: 800–4723; FAD: 970–>1000; vitamin K 1: 401–740; vitamin K 3 (menadione): 85–590; vitamin K 4: 45–313; 1,4-naphthoquinone: 170–290; coenzyme Q 10: 490–860. In general, there were no major differences between HCAs tested except in part with Trp-P-2 nor between the two tester strains. In enzyme kinetic experiments with Salmonella, retinol, vitamins K 3, and K 4 behaved as competitive inhibitors of IQ induced mutagenesis. However, at the highest concentration of menadione (200 nmol/plate) and of riboflavin 5′-phosphate (2000 nmol/plate), non-competitive inhibition was observed. At other concentrations of riboflavin 5′-phosphate and at all concentrations of FAD, meaningful interpretation of enzyme kinetics were not possible. Reduction of the activity of 7-ethoxy- and 7-methoxyresorufin- O-dealkylases with IC 50 values of 2.03–30.8 μM indicated strong inhibition of 1A1 and 1A2 dependent monooxygenases by menadione and retinol. Riboflavin 5′-phosphate and FAD were less effective (IC 50: 110–803.7 μM). Nicotinamide-adenine-dinucleotide