Decreased incidence of renal tumors in DMN treated Balb/C mice after orchiectomy

Dimethylnitrosamine (DMN) induced a significant incidence (45.5%) of kidney epithelial tumors in adult male Balb/C mice. The proportion of mice with renal tumors orchiectomized after DMN injection was reduced to 25.6%; whereas the proportion of tumor bearing animals at other sites, such as lung, liver, and lymphatic tissue, increased compared to intact DMN treated animals and controls. This experiment confirms other studies in rats and mice showing that androgens play a role in initiation and progression of nitrosamine induced renal cancer, paralleling the finding of increased male susceptibility in human renal cancer.     

Stability of activating systems for in vitro mutagenesis assays: Enzyme activity and activating ability following long-term storage at - 85°c

Activating systems for in vitro mutagenesis assays are commonly prepared and stored at low temperature until required. The objective of the studies reported here was to determine the long-term stability of activating systems stored at - 85°C. A broad range of microsomal enzymes in the postmitochondrial supernatant (PMS) and the microsomal fraction of livers from Aroclor 1254 treated rats were studied in conjunction with the ability of these fractions to catalyse the conversion of dimethylnitrosamine (DMN) and benzo(a)pyrene (B(a)P) to products mutagenic to Chinese hamster ovary (CHO) cells and Salmonella typhimurium TM677. Biphenyl-2- and biphyeny 1-4-hydroxylase showed a rapid decline in activity on storage, epoxide hydratase activity increased with storage and other enzyme activities studied were relatively stable for up to 32 weeks. No consistent trends in the ability of either the microsomes or the PMS to catalyze DMN or B(a)P induced mutation were observed for up to 12 weeks with CHO cells and 24 weeks with bacteria. It is concluded that low temperature storage of activating systems is an acceptable procedure. However, the results also indicate that certain enzyme activities change during storage, suggesting that aberrant results may be obtained when stored activiating systems are used in in vitro tests to screen for mutagens.     

茵陈蒿汤干预二甲基亚硝胺大鼠肝硬化效应的方证病理学基础研究

目的基于清热利湿与滋养肝肾不同功效古典方剂的干预效应,探讨二甲基亚硝胺(dimethylni-trosamine,DMN)诱导大鼠肝硬化的方证病理学基础。方法腹腔注射DMN4周制备大鼠肝硬化模型,造模2周末取6只模型大鼠作给药前观察,其余模型大鼠随机分为模型对照组、茵陈蒿汤(yinchenhao Decoc-tion,YCHD)组及一贯煎(yiguanjian,YGJ)组;各组于继续造模同时给予不同方剂的煎剂经口灌胃2周,正常大鼠与模型对照组给予同量等渗盐水,4周末处死大鼠,获取血清与肝组织样品,观测肝功能、肝组织病理学、α-平滑肌肌动蛋白(α-smooth muscle actin,α-SMA)与羟脯氨酸(hydroxyproline,Hyp)含量,检测肝组织丙二醛(malondialdehyde,MDA)、谷胱甘肽(glutathione,GSH)含量,谷胱甘肽S转移酶(glutathione S-transferase,GST)活性;免疫印迹检测肝组织α-SMA、肿瘤坏死因子α(tumor necrosis factor-alpha,TNF-α)、血小板衍生生长因子(platelete-derived growth factor,PDGF)以及肝脂肪酸结合蛋白(liver fatty acid bindingprotein,L-FABP)、转铁蛋白(transferrin,Tf)表达的变化。结果与模型对照组比较,YCHD组肝功能显著改善;肝组织Hyp含量与α-SMA蛋白表达显著降低(P0.05),显著抑制DMN大鼠肝硬化的形成,而YGJ无明显作用。肝组织TNF-α与PDGF表达在YCHD组显著减少,而YGJ组TNF-α进一步增加,PDGF无明显变化;YCHD组肝组织MDA含量与GST活性显著降低(P0.01或P0.05),GSH含量、L-FABP及Tf蛋白表达显著增加(P0.05),而YGJ组仅见GSH显著增加(P0.05)。结论茵陈蒿汤显著抑制DMN大鼠肝硬化的形成;DMN大鼠肝硬化形成期的肝组织炎性病变及其过氧化损伤是茵陈蒿汤清热利湿效应的方证病理学基础。     

System issues: Organ variation in the mutagenicity of dimethylnitrosamine in Big Blue® mice

Organ specificity in the lacl mutant frequency (MF) induced by dimethylnitrosamine (DMN) was analyzed in lung, liver, kidney, bone marrow, urinary bladder, and testis of Big Blue® mice. Cell proliferative activity was also analyzed in some of these tissues by immunohistochemical staining of proliferating cell nuclear antigen (PCNA). Clastogenicity of DMN was concomitantly analyzed by the peripheral blood micronucleus assay with the same animals used for the lacl mutation assay. Five daily intraperitoneal (ip) treatments with DMN (1 mg/kg) increased MF in liver (6.2 × control), kidney (2.4 × control), and lung (2.1 × control). These are known target organs for DMN carcinogenesis. No MF increase was observed in nontarget organs studied, i.e., bone marrow, bladder, and testis. Single ip treatment with DMN also increased lacl MF in liver but the increases were smaller than in a 5-daily-treatment regimen. This result suggests that multiple dosing is more effective in the transgenic mutation assay. The enhancement of cell proliferation observed was in bronchial epithelia 7 days after treatment. No micronucleus induction in peripheral blood was observed 24 hours after 2 and 3 daily ip treatments with 1 mg/kg DMN. An increase in the incidence of micronucleated reticulocytes in peripheral blood was observed 48 hours after single ip treatment with 5 or 10 mg/kg DMN. The present study demonstrated organ-specific induction of gene mutations by DMN, which suggests a relevance of this assay for the prediction of organ-specific carcinogenesis. © 1996 Wiley-Liss, Inc.