Caffeine -DNA Interactions: Biochemical Investigations Comprising DNA-Repair Enzymes and Nucleic Acid Synthesis

Abstract

Chicken embryo cells were treated with caffeine (0.5-8.0 mᴍ) alone or combined with various chemical and physical DNA - and/or chromatin-interactive agents. Analytical procedures comprised scheduled (SDS) and unscheduled (UDS) DNA synthesis, RNA synthesis (RNS), the activities of O6-alkylguanine-DNA alkyltransferase (AT) and poly (ADP-ribose) polymerase (PARP) as well as nucleoid sedimentation. Additional investigations were done in rat thymic and splenic cells. The effect of caffeine on DNase-I activity served as an in vitro-model system.- When present in the PARP-, SDS-, UDS- and RNS-assays, caffeine inhibited the corresponding tracer (14C-NAD, dT-3H, 3H-U) incorporation in a dose-dependent manner. The AT activity was slightly stimulated. At concentrations of 0.06-0.3 mᴍ, caffeine inhibited DNase-I activity by excess substrate. No specific effects of caffeine could be shown by nucleoid sedimentation.- Besides the reduced permeability of the cells to nucleic acid precursors, the results obtained with the PARP- and DNase-I assays give evidence for the formation of a DNA-caffeine adduct as a prominent mechanism of cellular caffeine effects including DNA repair inhibition.