Detection of in vitro genotoxicity of pro-mutagens using the comet assay under human and rat liver S9 fractions

Abstract

Genotoxicity tests are used to detect mutagens and carcinogens, study the mechanisms of chemical mutagenesis and carcinogenesis, and assess the genotoxic and carcinogenic hazards of chemicals to humans. Genotoxicity tests also play a critical role in drug development. For all those uses, data is usually obtained from experimental organisms and extrapolated to humans. Pro-mutagens are inactive until enzymes transform them to electrophilic species capable of covalently binding to DNA, so metabolic activation is a critical step in mutagenesis.1 Metabolic activation systems are necessary for testing the potential genotoxicity of pro-mutagens. Cytochrome P450 (CYP) in liver S9 fractions plays an important role in activating promutagens to proximate and/or ultimate mutagens.1,2 Liver S9 prepared from rats pretreated with phenobarbital/5,6-benzoflavone (PB/BF) or Aroclor 1254 is routinely used for that purpose in genotoxicity tests because they are simple, convenient and cost-effective.2,3 Human liver S9, however, are known to behave differently than rat liver S9 in the activation of four compounds and cigarette smoke condensate.4