Production of DNA single-strand breaks in unstimulated splenocytes by dimethylnitrosamine

Abstract

In an attempt to elucidate the mechanism whereby primary hepatocytes, but not liver S9 homogenates, generate immunosuppressive metabolites of dimethylnitrosamine (DMN), the production of DNA single-strand breaks (SSB) in unstimulated splenocytes was investigated with alkaline-elution analysis. Both hepatocytes and S9 hormogenates induced SSB in cultured splenocytes by DMN — minimum detectable doses with the two metabolic activation systems (MAS) were 1 μM and 5 mM, respectively. DNA elution profiles were linear in splenocytes co-cultured with DMN and hypatocytes and convex in splenocytes incubated with DMN and S9 homogenates. Aminoacetonitrile (AAN; 10 mM), a DMN demethylase inhibitor, reversed SSB in splenocytes when incubated with either MAS. Addition of exogenous calf-thymus DNA to the hepatocyte co-culture medium did not affect the production of SSB. Rocking the hepatocyte-splenocyte cultures changed the elution profile from linear to convex. All of these treatments have been previously shown to block the immunosuppressive by DMN in the hepatocyte co-culture system. These results indicate that the immunosuppressive by DMN is not related to DNA damage, as measured by the production of SSB, and suggest that the metabolism of DMN to intermediates capable of producing genotoxicity and immunotoxicity may be qualitatively and/or quantitatively different.