Rapid and complete degradation of thymidine by human peripheral blood platelets: implications for genotoxicity assays

Small-scale washed cell preparations obtained by Percoll density-gradient fractionation of whole blood were used to study the metabolic fate of [3H]thymidine supplied to isolated human blood mononuclear cells and platelets incubated for up to 24 h in vitro. Two cell fractions were monitored: low molecular weight compounds which were soluble in Triton X-100 and TCA were investigated by thin-layer chromatography, and high molecular weight components, distinguished by their Triton and TCA insolubility, were examined by agarose-gel electrophoresis. Under the conditions used, greater than 99% of added [3H]thymidine was very rapidly degraded. Catabolites were recovered in the Triton-soluble (cytoplasmic) fraction and the extracellular medium. A negligible proportion of added label was associated with Triton- and TCA-insoluble cell fractions. These results confirm and clarify previous data and have important implications for genotoxicity tests which employ in vitro leukocyte cultures.