Calendula officinalis flower extracts are used to cure inflammatory and
infectious diseases, for wound healing and even
cancer with partial objective evidence of its therapeutic properties or toxic effects, many of which can be attributed to the presence of
flavonols. We studied whether C. officinalis extracts induce unscheduled
DNA synthesis (UDS) in rat liver cell cultures, and if these extracts can reverse
diethylnitrosamine (DEN)-induced UDS. Four different flower extracts were prepared: aqueous (AE), aqueous-
ethanol (AEE),
ethanol (EE) and
chloroform (CE). AE and AEE were evaporated to 6.72 and 4.54 mg of solid material per ml, respectively and final
ethanol concentration in AEE was 0.8%. EE and CE were dried and resuspended in
dimethyl sulfoxide (
DMSO) to 19.2 and 10 mg of solid material per ml.
Ethanol residue of EE was 0.34%. In the UDS assay in liver cell cultures, DEN at 1.25 microM produced a maximal increase of 40% (3)H-thymidine ((3)HdTT) incorporation, and both, AE and AEE showed complete reversion of the DEN effect at around 50 ng/ml and between 0.4 to 16 ng/ml, respectively. In the absence of DEN, these two polar extracts induced UDS at concentrations of 25 microg for AE and 3.7 microg/ml for AEE to 100 microg/ml in rat liver cell cultures. Concentrations producing genotoxic damage were three orders of magnitude above concentrations that conferred total protection against the DEN effect. Thus, at the lower end, ng/ml concentrations of the two polar extracts AE and AEE conferred total protection against the DEN effect and at the higher end, g/ml concentrations produced genotoxic effects. These results justify the study of C. officinalis flower extracts to obtain products with
biological activity and to define their genotoxic or chemopreventive properties.