Xanthium strumarium L. extracts produce DNA damage mediated by cytotoxicity in in vitro assays but does not induce micronucleus in mice.

Xanthium strumarium L. is a member of the Asteraceae commonly used in Cuba, mainly as diuretic. Some toxic properties of this plant have also been reported and, to date, very little is known about its genotoxic properties. The present work aims was to evaluate the potential cytotoxic and genotoxic risk of whole extract from Xanthium strumarium L. whole extract of aerial parts. No positive response was observed in a battery of four Salmonella typhimurium strains, when exposed to concentrations up to 5 mg/plate, with and without mammalian metabolic activation (liver microsomal S9 fraction from Wistar rats). In CHO cells, high concentrations (25-100 µg/mL) revealed significant reduction in cell viability. Results from sister chromatid exchanges, chromosome aberrations, and comet assay showed that X. strumarium extract is genotoxic at the highest concentration used, when clear cytotoxic effects were also observed. On the contrary, no increase in micronuclei frequency in bone marrow cells was observed when the extract was orally administered to mice (100, 500, and 2000 mg/Kg doses). The data presented here constitute the most complete study on the genotoxic potential of X. strumarium L. and show that the extract can induce in vitro DNA damage at cytotoxic concentrations.

Sensitivity and variability of visual scoring in the comet assay. Results of an inter-laboratory scoring exercise with the use of silver staining.

Nineteen scorers from seven Cuban laboratories participated in this slide exercise designed to test the influence of the scorer on the accuracy, sensitivity and variability of the comet assay when a visual method of DNA damage evaluation is used. The assay was performed using human lymphocytes from a single donor exposed in vitro for 5 min at 0 degrees C to doses of 0, 5, 10, 25, 50, 100 and 200 microM of hydrogen peroxide. Each participant scored the same set of 14 coded slides with silver stained comets. The comets were classified visually into five categories according to the appearance resulting from the relative proportion of DNA in the tail. The extent of DNA damage was expressed in arbitrary units. At zero dose the median values of 12 scorers out of 19 were included between the values of the overall 25 and 75 per thousand. This proportion remains practically the same as the dose increases. The lowest dose detected by this method for the majority of scorers (11) was 10 microM. The coefficient of variation at the control dose was the highest (median value 26%), progressively declined to 20%, and starting from 25 microM, values are around 10%. The results of the exercise show the reliability of the silver staining and visual scoring for the comet method.