Add time:08/03/2019         Source:sciencedirect.com

Benz[a]anthracene (BA) and its derivatives containing methyl and/or ethyl groups in the 7 and/or 12 positions were tested for their ability to induce chromosome aberrations (CA) in rat bone marrow cells and for their mutagenicity to Salmonella typhimurium TA100 or TA98. The incidence of aberrant cells induced by the BA derivatives, given in lipid emulsion as a single-pulse dose of 50 mg/kg body weight into the caudal vein, was in the order: DMBA > EMBA > MEBA > other BA derivatives = control. The alkyl groups, at least 1 methyl group, at the 7 and 12 positions of BA seemed to be necessary to induce CA, although DEBA having ethyl groups at both the 7 and 12 positions of BA did not induce CA. DMBA or EMBA induced not only gaps and breaks but also exchanges and multiple CA, while the CA induced by other BA derivatives consisted of only gaps and breaks. 7MBA and 12MBA which exhibit carcinogenic activity intermediate between that of DMBA and BA induced few CA in the present system. However, the correlation coefficient between the logarithm incidence of aberrant cells and the carcinogenicity index calculated from the data of 9 BA derivatives including both 7MBA and 12MBA was 0.792.The relative mutagenicities of the BA derivatives with TA100 in the presence of hepatic S9 from polychlorinated biphenyl (PCB)-treated rats were in the order: BA > 7MBA > DMBA > 12MBA > 7EBA > EMBA > MEBA > 12EBA = DEBA = control. The results with TA98 were essentially the same as those with TA100. The results with TA100 in the presence of hepatic S9 from phenobarbital (PB)-treated rats were in the order: DMBA > 12MBA > 7MBA > 7EBA > BA > EMBA = MEBA > 12EBA = DEBA = control. These findings reveal no obvious relation between the mutagenic activities of the BA derivatives with the PCB-S9 or PB-S9 activating systems and their capacities to induce CA or their reported carcinogenicities.The incidence of CA induced by the dihydrodiols implicated as the metabolic precursors of the active diol epoxide metabolites of several of these BA derivatives was also tested. BA 3,4-dihydrodiol, like BA itself, induced few CA. However, the corresponding dihydrodiols of DMBA, 12MBA and 7MBA, induced relatively high levels of CA. The present results are consistent with the hypothesis that induction of CA by diol epoxide metabolites is involved in the mechanism of PAH carcinogenesis, but do not rule out the possibility that other electrophilic metabolites are also involved.

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