APPLICATION OF TRANSGENIC MICE TO THE TOXICOLOGICAL TESTING

我们有六种携带人类CYP3A7 cDNA的转基因小鼠。在M10小鼠中，CYP3A7在小肠中表达，在肾脏中不表达，而M2小鼠在肾脏中表达CYP3A7。HITEC小鼠是一种用于检测体内多种化学物质致突变性的转基因小鼠。将这两株小鼠杂交，建立CYP3A7/HITEC小鼠。将M10/HITEC小鼠小肠制备的9000 × g上清液加入到鼠伤寒沙门菌TA98培养液中，进行黄曲霉毒素B_1 （AEB_1）致诱变活性的Ames试验，发现M10/HITEC小鼠小肠制备的9000 × g上清液致诱变活性比HITEC小鼠高1.7倍。在M10/HITEC小鼠和HITEC小鼠肾脏的9000 x g上清部分中，没有观察到这种激活AFB1能力的差异。8周龄雄性CYP3A7/HITEC小鼠单次腹腔注射AFB1 （8 mg/kg体重）。分析了引入的rpsL基因在小肠和肾脏基因组DNA中的突变。M10/HITEC小鼠小肠的突变频率显著高于HITEC小鼠（p<0.05），而两株小鼠肾脏的突变频率相似。另一方面，M2/HITEC小鼠肾脏rpsL基因的突变频率倾向于高于HITEC小鼠。这些结果提供了人类CYP3A7在体内代谢激活AFB1的第一个证据。综上所述，CYP3A7/HITEC小鼠是一种有用的模型，可以通过代谢激活来检测化学物质诱导的体内突变。

We have six lines of transgenic mice carrying human CYP3A7 cDNA.In M10 mouse, CYP3A7 is expressed in the small intestine but not in the kidney, while M2 mouse expresses CYP3A7 in the kidney. HITEC mouse is a transgenic mouse developed to detect mutagenic potency of various chemicals in vivo. The CYP3A7/HITEC mice were established by crossmating of these two strains of mice. When a 9,000 x g supernatant fraction prepared from the small intestine of M10/HITEC mouse was added to an incubation mixture for Ames test with Salmonella typhimurium TA98 strain to examine the mutagen-producing activity from aflatoxin B_1 (AEB_1) , the mutagen-producing activities of the 9,000 x g supernatant fraction from the small intestine was found to be 1.7-fold higher in the M10/HITEC mice than that seen with HITEC mice. Such a difference in the capacity to activate AFB1 was not seen with the 9,000 x g supernatant fraction from the kidney from M10/HITEC mice and HITEC mice. Male CYP3A7/HITEC mice of 8 weeks old were treated with a single i. p. injection of AFB1 (8 mg/kg body weight). The mutation of the introduced rpsL gene in the genomic DNA from the small intestine and the kidney was analyzed. The mutation frequency in the small intestine of M10/HITEC mice was significantly higher (p<0.05) than that of HITEC mice, while the mutation frequency in both strains was similar in the kidney. On the other hand, the mutation frequency of the rpsL gene from the kidney of M2/HITEC mice tended to be higher than that of HITEC mice. These results provide the first evidence that human CYP3A7 metabolically activate AFB1 in vivo.In conclusion, the CYP3A7/HITEC mice is a useful model to detect mutations in vivo induced by chemicals through the metabolic activations.