基于4%中性甲醛固定肝组织的大鼠肝微核实验方法的建立与验证

Establishment and validation of liver micronucleus assay in rats using 4%neutral formaldehyde-fixed tissues

目的建立并验证基于4%中性甲醛固定肝组织制备肝细胞的大鼠肝微核实验(LMNT)方法(甲醛固定-LMNT法)。方法(1)SD大鼠分为雌性和雄性组,然后分别随机分为溶剂对照组和肝微核阳性化合物N-亚硝基二乙胺(DEN)12.5 mg·kg^(-1)组,每组5只,分别ig给予生理盐水和DEN,每天1次,连续14 d后取肝组织,同时用胶原酶消化-LMNT法和甲醛固定-LMNT法检测微核化肝细胞数量和处于有丝分裂期肝细胞数,分别计算肝细胞微核率和有丝分裂指数,肝细胞微核率>0.07%判定为阳性结果。(2)雄性SD大鼠分为喹啉(30,60和120 mg·kg^(-1))组、N-亚硝基吡咯烷(NPYR,25,50和100 mg·kg^(-1))组、各自溶剂对照组(NPYR,去离子水;喹啉,玉米油)及阳性对照DEN(12.5 mg·kg^(-1))组,每组5~6只,连续ig 15 d。每日记录体重,实验结束取肝记录肝总重,计算肝系数。自动生化分析仪检测肝功能相关血清生化指标谷丙转氨酶(GPT)、谷草转氨酶(GOT)活性和血清总胆红素(T-BIL)、直接胆红素(D-BIL)的水平。采用胶原酶消化-LMNT法和甲醛固定-LMNT法测定肝细胞微核率,用外周血微核实验和肝彗星实验评价喹啉和NPYR遗传毒性。结果(1)与各自溶剂对照组的肝细胞微核率(0.069%和0.030%)相比,甲醛固定-LMNT法测得的DEN组雄性大鼠肝细胞微核率为1.10%,雌性大鼠为0.82%,均显著升高(P<0.05);与各自溶剂对照组(0.060%和0.030%)相比,胶原酶消化法-LMNT法测得的DEN组雄性大鼠肝细胞微核率为1.45%,雌性大鼠为0.46%,均显著升高(P<0.05),判定为阳性。2种方法中雄性大鼠的肝细胞微核率均显著高于雌性(P<0.05)。与各自溶剂对照组相比,2种方法测得的DEN组雄性和雌性大鼠肝细胞有丝分裂指数均无明显差异。(2)与溶剂对照组相比,NPYR 50和100 mg·kg^(-1)组大鼠体重在ig第7~14天显著降低(P<0.01),DEN组在ig第8~14天显著降低(P<0.01);喹啉120 mg·kg^(-1)组大鼠在ig第4~14天显著降低(P<0.01),DEN组在ig第10~14天显著降低(P<0.05)。与溶剂对照组相比,NPYR 100 mg·kg^(-1)组(P<0.01)和DEN组(P<0.05)的肝重和肝系数均显著降低;喹啉60和120 mg·kg^(-1)组肝重(P<0.01)和肝系数(P<0.05)均显著增加。与溶剂对照组相比,DEN组大鼠血清T-BIL水平显著升高(P<0.01),NPYR 100 mg·kg^(-1)组GPT、GOT活性和D-BIL、T-BIL水平均显著升高(P<0.01),NPYR 25,50 mg·kg^(-1)和喹啉各剂量组则均无显著差异。甲醛固定-LMNT法测得的NPYR组肝细胞微核率较胶原酶消化-LMNT法略高,均判定为阳性;与溶剂对照组相比,2种方法测得的NPYR组肝细胞微核率均显著增加(P<0.05),喹啉组结果相当,均判定为阳性;2种方法测得的喹啉组肝细胞微核率均显著增加(P<0.05)。2种方法测得的NPYR和喹啉组肝细胞微核率相关性较好(R2分别为0.8614和0.9279)。NPYR组外周血微核实验为阴性,彗星实验结果为阳性;喹啉组外周血微核实验和彗星实验结果均为阴性。结论初步建立并验证了甲醛固定-LMNT法,且该方法检测肝致癌物的灵敏度与胶原酶-LMNT法相近。

OBJECTIVE To establish and validate a rat liver micronucleus test(LMNT)method based on fixation of liver tissue with 4%neutral formaldehyde(HCHO fixation)for preparation of hepa-tocytes(HEPs).METHODS①The LMNT based on neutral HCHO fixation(HCHO fixation-LMNT)was established using the liver micronucleus positive compound N-nitrosodiethylamine(DEN).SD rats were divided into female and male groups,and each group was randomly subdivided into the vehicle control group and DEN 12.5 mg·kg^(-1) group,with five rats in each.The rats were ig administered with normal saline and DEN once a day for 14 consecutive days,after which liver tissues were collected.Some of the tissue was digested with collagenase to prepare HEP suspension,and the remaining tissue was used to prepare HEP suspension with HCHO fixation.After staining with SYBR Gold,the number of micronucleated hepatocytes(MN-HEP)and the number of HEPs in the mitotic phase were counted under a microscope.The micronucleus rate of HEP(MN-HEP rate)and the mitotic index were calculated,and an MN-HEP rate>0.07%was considered positive.②Male SD rats were divided into the quinoline(30,60,120 mg·kg^(-1))group,N-nitrosoopyrrolidine(NPYR,25,50,100 mg·kg^(-1))group,vehicle control group(deionized water for NPYR,and corn oil for quinoline),and positive control DEN(12.5 mg·kg^(-1))group,with 5-6 rats per group,and were ig administrated for 15 consecutive days.Body mass was recorded daily,and at the end of the experiment,the liver was removed to record the total liver weight,and calculate the liver coefficient.Liver function-related serum biochemical indicators including glutamic-pyruvic transaminase(GPT),glutamic-oxaloacetic transaminase(GOT)activities,and levels of total bili-rubin(T-BIL)were measured and direct bilirubin(D-BIL)using an automatic biochemical analyzer.The MN-HEP rate was determined using the collagenase digestion and HCHO fixation methods,and the peripheral blood MN assay and hepatocellular carcinoma comet assay were conducted to evaluate the genotoxicity of quinoline and NPYR.RESULTS①Compared with the corresponding vehicle control groups(0.069%and 0.030%),the MN-HEP rate of male rats treated with DEN by formalin-LMNT was 1.10%,and the MN-HEP rate of female ones was 0.82%,both significantly increased(P<0.05).Com-pared with corresponding vehicle control groups(0.060%and 0.030%),the MN-HEP rate of male rats treated with DEN by collagenase digestion-LMNT was 1.45%,and that of female rats was 0.46%,both significantly increased(P<0.05),which were considered positive.The MN-HEP rate of male rats was significantly higher than that of females with both methods(P<0.05).There was no significant differ-ence in mitotic indexes between the DEN groups by collagenase digestion-LMNT and HCHO fixation-LMNT in male and female rats compared to corresponding vehicle control groups.②Compared to the vehicle control group,the body mass of rats in the NPYR 50 and 100 mg·kg^(-1) groups was significantly reduced 7 to 14 days into the ig administration(P<0.01),and the DEN group showed a significant reduction at days 8 to 14(P<0.01).The body mass of rats in the quinoline 120 mg·kg^(-1) group was signifi-cantly reduced 4 to 14 days into the ig administration(P<0.01),and the DEN group showed a signifi-cant reduction at days 10 to 14(P<0.05).Compared to the vehicle control group,both the liver weight and liver coefficient were significantly reduced in the NPYR 100 mg·kg^(-1) group(P<0.01)and the DEN group(P<0.05).The liver weight(P<0.01)and liver coefficient(P<0.05)were significantly increased in the quinoline 60 and 120 mg·kg^(-1) groups.Compared to the vehicle control group,the serum T-BIL level was significantly increased in the DEN group(P<0.01),and the activities of GPT and GOT,as well as the levels of D-BIL and T-BIL,were significantly increased in the NPYR 100 mg·kg^(-1) group(P<0.01).There were no significant changes in the NPYR 25,50 mg·kg^(-1) groups or any of the dose groups of quinoline.The MN-HEP rate by HCHO fixation-LMNT for NPYR was slightly higher than that by collage-nase digestion-LMNT,both considered positive.Compared with corresponding control group,the MN-HEP rate by formalin-LMNT for NPYR and the MN-HEP rate by collagenase digestion for NPYR were both significantly increased(P<0.05).The MN-HEP rate by HCHO fixation-LMNT for quinoline was comparable to that by collagenase digestion-LMNT,both considered positive.Compared with corresponding vehicle control group,the MN-HEP rate by HCHO fixation-LMNT for quinoline and the MN-HEP rate by collagenase digestion-LMNT for quinoline were both significantly increased(P<0.05).The correlation between the MN-HEP rates based on HCHO fixation and collagenase digestion for NPYR and quinoline was good(R2=0.8614 and 0.9279,respectively).In the NPYR groups,the periph-eral blood micronucleus assay were negative,while the comet assay results were positive.In the quino-line group,both the peripheral blood micronucleus assay and the comet assay results were negative.CON-CLUSION The HCHO fixation-LMNT has been established and validated,and the sensitivity of the LMNT method based on HCHO fixation-LMNT for detection of hepatocarcinogens is higher than that of collagenase digestion-LMNT.