ANALYSIS OF MICRONUCLEI AND DNA SINGLE-STRAND BREAKS IN MOUSE SPLENOCYTES AND PERIPHERAL LYMPHOCYTES AFTER ORAL-ADMINISTRATION OF TETRAMETHYLTHIURAM DISULFIDE (THIRAM)

The fungicide thiram (tetramethylthiuram disulfide, TMTD) was administ ered by repeated oral intubations to groups of male B6C3F(i) mice at 1 00, 300 and 900 mg/kg body weight for 4 consecutive days, or at 300 mg /kg for 8 and 12 days. 24 hr after the last treatment animals were kil led, and splenocyte cultures were set up for the analysis of micronucl ei by the cytokinesis-block method. DNA single strand breaks (ssb) and alkali labile sites were also analysed by the single cell gel electro phoresis (Comet) assay in splenocytes and lymphocytes of animals recei ving the 8- and 12-day treatments. Parallel experiments with human per ipheral lymphocytes were carried out to assess the ability of thiram t o induce micronuclei and DNA ssb and alkaline labile sites under in vi tro conditions. No;significant increase of micronucleated splenocytes was observed in treated animals, despite some evidence of treatment-re lated cellular toxicity. A borderline excess of DNA damage was suggest ed by the Comet assay on circulating lymphocytes, whereas negative res ults were obtained with splenocytes. In vitro, positive results with b oth genetic end points were obtained in assays with human lymphocytes in the dose ranges 0.5-24 mu g/ml and 0.1-8 mu g/ml for micronucleus a nd Comet assays, respectively. These results suggest that thiram, desp ite its established genotoxicity in vitro, is devoid of appreciable cl astogenic and/or aneugenic activity in vivo after oral administration to mice at the maximum tolerated dose. (C) 1998 Elsevier Science Ltd. All rights reserved.