Rodent bone marrow assays, chromosome

No genotoxicity of an aqueous extract of Indian tinospora was observed in any of four different genotoxicity tests. Tests included the Ames test with Salmonella typhimurium strains TA97a, TA98, TAIOO, TA102, and TA1535 at concentrations of extract up to 5000 pg/plate, the chromosome aberration assay, the rodent bone marrow micronucleus assay, and the comet assay. For the bone marrow micronucleus and comet assays, mice were orally administered the extract for 7 days at doses of 150, 200, and 250 mg/kg (Chandrasekaran et al. 2009). 

The in vivo micronucleus test is used for the detection of damage to chromosomes as well as the mitotic apparatus in bone marrow or peripheral blood cells of rodents. The assay system has been well standardized.14-17 The basic features of the test system are (1) the effect of the test chemical is observed in anucleated polychromatic erythrocytes (PCEs) (2) PCEs have a relatively short lifespan, so that any micronuclei they contain must have been generated as a result of recently induced chromosome damage (3) micronuclei are readily identifiable and their distribution is well defined and (4) the frequency of induced micronuclei in PCEs is dependent on sampling times. 

EGBE did not induce sister chromatid exchanges or chromosomal aberrations in mammalian cell assays in vitro, and in vivo it did not induce micronuclei in bone marrow cells of rodents. It was not mutagenic in bacterial assays with or without metabolic activation. ... 

Metabolism and genetic toxicity have been reported to differ with the isomer of nitro-toluene. p-Nitrotoluene was not mutagenic in bacterial assays, but it did increase sister chromatid exchange frequencies and chromosomal aberrations in vitro-, in vivo it did not increase the frequency of micronuclei in bone marrow of treated rodents. Similar findings were reported for the ortho isomer, except that it did not induce chromosomal aberrations in vitro. Only the ortho isomer induces DNA excision repair in the in vivo-in vitro hepatocyte unscheduled DNA synthesis assay. Furthermore, ort/jo-nitrotoluene binds to hepatic DNA to a much greater extent than meta- or para-nitrotoluene, and investigators suggest that it may act similarly to the rodent hepatocarcino-gen 2,6-dinitrotoluene. ... 

The principle techniques of the micronucleus assay can be applied at the end of a subacute/sub chronic study in the bone marrow of rodents (princliples are described in the section on genotoxicity elsewhere in this book). Usually, only bone marrow from one femur is used for histopathology, thus, the marrow from the second femur can be used for the micronucleus assay. It is not recommended to perform chromosomal analysis in animals from short-term or sub-chronic studies because this technique requires the in vivo treatment with antimitotic agents to arrest the mitotic stage of cell division. 

In contrast to in vitro tests, most in vivo assays in rodents have failed to show evidence of antimony s genotoxicity. Antimony trioxide tested negative (no evidence of clastogenicity) in the mouse bone marrow micronucleus assay and in the rat liver DNA repair assay (Elliott et al. 1998), and failed to induce micronuclei or chromosomal aberrations in the bone marrow of rats in a subchronic dosing study (Kirkland et al. 2007). 

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