Evaluation of the genotoxic potential of the natural neurotoxin Tetrodotoxin (TTX) in a battery of in vitro and in vivo genotoxicity assays.

The genotoxic potential of the natural neurotoxin Tetrodotoxin (TTX) was evaluated in a battery of in vitro and in vivo genotoxicity assays. These comprised a bacterial reverse-mutation assay (Ames test), an in vitro human lymphocyte chromosome-aberration assay, an in vivo mouse bone-marrow micronucleus assay and an in vivo rat-liver UDS assay. Maximum test concentrations in in vitro assays were determined by the TTX limit of solubility in the formulation vehicle (0.02% acetic acid solution). In the Ames test, TTX was tested at concentrations of up to 200 microg/plate. In the chromosome-aberration assay human lymphocytes were exposed to TTX at concentrations of up to 50 microg/ml for 3 and 20 h in the absence of S9, and for 3h in the presence of S9. For the in vivo assays, maximum tested dose levels were determined by the acute lethal toxicity of TTX after subcutaneous administration. In the mouse micronucleus assay TTX dose levels of 2, 4 and 8 microg/kg were administered to male and female animals, and bone-marrow samples taken 24 and 48 h (high-dose animals only) after administration. In the UDS assay, male rats were given TTX on two occasions with a 14-h interval at dose levels of 2.4 and 8 microg/kg, the last dose being administered 2h before liver perfusion and hepatocyte culturing. Relevant vehicle and positive control cultures and animals were included in all assays. TTX was clearly shown to lack in vitro or in vivo genotoxic activity in the assays conducted in this study. The results suggest that administration of TTX as a therapeutic analgesic agent would not pose a genotoxic risk to patients.

In vivo genotoxic evaluation of the furylethylene derivative 1-(5-bromofur-2-yl)-2-nitroethene in mouse bone marrow.

The genotoxic potential of the compound 1-(5-bromofur-2-yl)-2-nitroethene (2-ßNF) has been tested by using the in vivo mouse bone marrow micronucleus assay. Its ability to induce clastogenicity or aneugenicity, through the induction of micronucleated polychromatic erythrocytes (MNPCE) in the bone marrow cells has been evaluated. Treatment groups of five CD-1 male mice were administered once intraperitoneally at the doses of 10, 20, and 30mg/kg, and their bone marrows were sampled at 24 and 48h after the administration, at the first sampling time animals administered with the three doses were used, and in the second sampling time, only animals administered with the highest dose were used. All animals treated with the highest dose of the test compound (30mg/kg) showed evident clinical symptoms of toxicity such as irritation, hunched posture, slight ataxia, dyspnoea, piloerection, and palpebral ptosis. However, no marked depression of bone marrow cell proliferation was observed, and no significant increases in the frequency of MNPCE were obtained in any of the concentrations tested at any sampling times. The positive control treated-animals were administered with cyclophosphamide at the dose of 40mg/mL. The compound caused a significant increase in the number of MNPCE in all treated animals, demonstrating the sensitivity of the mouse strain used. From the results obtained, it is concluded that the compound 2-ßNF is neither clastogenic nor aneugenic in the erythrocytes from the bone marrow of treated mice at the doses tested.