Synergistic effect between tannic acid and X-rays detected by the Tradescantia-micronucleus assay

Tannic acid (TA), a complex mixture of polyphenolics, exhibited synergism with 4-nitroquinoline 1-oxide (4-NQO), methyl methanesulfonate (MMS) and cis-platinum (cis-DDP) in a recent study on w/w+ somatic mutation in the eye pigment of Drosophila, although several studies indicated that tannic acid is an antimutagen in cultured mammalian cells. The goal of this study was to determine the genotoxicity of tannic acid alone and its possible synergistic effect with X-rays using the Tradescantia-micronucleus (Trad-MCN) bioassay. Plant cuttings were irradiated with 35 R of X-rays (80 kV, 5 mA) and followed by a series of increasing dosages (0.1, 0.5, 0.75, 1.0, 1.25, 1.50 mM) of TA treatment (24 h) and in some cases TA treatment was followed by X-irradiation. Inflorescences were fixed after a 24-h recovery period and slides were prepared for scoring MCN frequencies. Four series of experiments were conducted and the results of Trad-MCN tests on X-rays alone yielded an average of 47.5 MCN/100 tetrads (SE = 6.08), and 1.0 mM TA alone yielded an average of 8.95 MCN/100 tetrads (SE = 0.1), while the combined treatments (35 R X-rays plus 1.0 mM TA) yielded an average of 126.95 MCM/100 tetrads (SE = 13.69). The MCN frequency of the negative control was around 4.6 MCN/100 tetrads (SE = 0.75). This kind of synergism was exhibited through all the increasing dosages around 1.0 mM or higher. The synergistic effect of these two agents remained at the same level when TA was followed by X-irradiation. When a 12-h repairing period was allowed after X-irradiation in the combined treatment, the MCN frequency was similar to that of the X-ray treatment alone. The synergistic effect in the cases where the TA exposure was given immediately after X-irradiation could be attributed to the inhibitory action of TA on the DNA repair process.