IN VIVO MUTAGENICITY AND CARCINOGENICITY OF HETEROCYCLIC AMINES IN TRANSGENIC MIC

2-氨基-3，8-二甲基咪唑并[4，5-f]喹喔啉（MeIQx）是一种存在于熟肉制品中的具有致突变性和致癌性的杂环胺。在携带lacZ突变报告基因的小鼠（MutaTM小鼠）和过表达c-myc癌基因的双转基因小鼠中检查了MeIQx的体内致突变性和肝癌性。饲养C57 Bl/lacZ和双转基因c-myc（白蛋白启动子）/lacZ小鼠，并断奶至含有0.06%（w/w）MeIQx的AIN-76基饮食或对照饮食。饮食30周后，只有MeIQx的雄性双转基因小鼠发生肝细胞癌（100%发病率），表明c-myc过表达和MeIQx之间存在协同作用。到40周时，给予MeIQx（或对照）饮食的雄性/雌性c-myc/lacZ和C57 Bl/lacZ小鼠的肝肿瘤发生率分别为100%/75%（17%/0%）和44%/17%（0%/0%），表明单独的MeIQx或c-myc过表达最终诱导肝肿瘤。在任一时间点，在lacZ基因的突变频率是至少40倍高，在MeIQx处理的小鼠比对照小鼠的任一菌株。这些发现表明，MeIQx诱导的肝癌发生与MeIQx诱导的突变有关。MeIQx处理的小鼠中突变频率升高也伴随着MeIQx-鸟嘌呤加合物的形成而发生，如通过32P-后标记测定检测到的。无论菌株或饮食，从雄性小鼠肝脏的lacZ突变体的序列分析表明，主要的序列改变是一个单一的鸟嘌呤碱基取代。然而，腺嘌呤突变仅在对照饮食的动物中检测到。携带c-myc癌基因的MeIQx喂养小鼠的lacZ基因突变频率比未携带转基因的小鼠高1.4 - 2.6倍。虽然在c-myc小鼠中存在更高加合物水平的趋势，但在饮食30周后，c-myc/lacZ和C57 Bl/lacZ小鼠之间的MeIQx-DNA加合物水平没有显著差异。因此，似乎除了MeIQx-DNA加合物水平之外的因素，例如与c-myc过表达相关的增殖速率增强，可能导致c-myc小鼠中较高的突变频率。在对照饮食组中，c-myc/lacZ小鼠的lacZ突变频率显著高于C57 Bl/lacZ小鼠。这些发现与c-myc过表达与突变增加相关的观点一致。c-myc过表达似乎协同增强MeIQx的基因突变和肝致癌性。- 杂环胺，LacZ，突变，报告基因，转基因小鼠，肝癌发生，

2-Amino-3, 8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is a mutagenic and carcinogenic heterocyclic amine found in cooked meat. The in vivo mutagenicity and hepatocarcinogenicity of MeIQx were examined in mice harboring the lacZ mutation reporter gene (MutaTM Mice) and bitransgenic mice over-expressing the c-myc oncogene. C57Bl/ lacZ and bitransgenic c-myc (albumin promoter)/ lacZ mice were bred and weaned onto an AIN-76 based diet containing 0.06% (w/w) MeIQx or onto control diet. After 30 weeks on diet, only male bitransgenic mice on MeIQx developed hepatocellular carcinoma (100% incidence) indicating that there was synergism between c-myc over-expression and MeIQx. By 40 weeks, hepatic tumor incidence was 100 %/75% (17%/0%) and 44%/17% (0%/0%) in male/female c-myc/ lacZ and C57Bl/ lacZ mice given MeIQx (or control) diet, respectively, indicating that either MeIQx or c-myc over-expression alone eventually induced hepatic tumors. At either time point, mutant frequency in the lacZ gene was at least 40-fold higher in MeIQx-treated mice than in control mice of either strain. These findings suggest that MeIQx-induced hepatocarcinogenesis is associated with MeIQx-induced mutations. Elevated mutant frequency in MeIQx- treated mice also occurred concomitant with the formation of MeIQx- guanine adducts as detected by the 32P-postlabeling assay. Irrespective of strain or diet, sequence analysis of the lacZ mutants from male mouse liver showed that the principal sequence alteration was a single guanine-base substitution. Adenine mutations, however, were detected only in animals on control diet. MeIQx-fed mice harboring the c-myc oncogene showed a 1.4-2.6-fold higher mutant frequency in the lacZ gene than mice not carrying the transgene. Although there was a trend toward higher adduct levels in c-myc mice, MeIQx-DNA adduct levels were not significantly different between c-myc/ lacZ and C57Bl/ lacZ mice after 30 weeks on diet. Thus, it appeared that factors in addition to MeIQx- DNA adduct levels, such as the enhanced rate of proliferation associated with c-myc over-expression, may have accounted for a higher mutant frequency in c-myc mice. In the control diet groups, the lacZ mutant frequency was significantly higher in c-myc/ lacZ mice than in C57Bl/ lacZ mice. The findings are consistent with the notion that c- myc over-expression is associated with an increase in mutagenesis. The c-myc over-expression appears to synergistically enhance gene mutations and hepatocarcinogenicity by MeIQx. - c-myc, Heterocyclic Amines, LacZ, Mutagenesis, Reporter gene, Transgenic Mice, Hepatocarcinogenesis,