Risk Assessment of Nongenotoxic Carcinogens Based upon Cell Proliferation/Death Rates in Rodents

Increased cell proliferation increases the opportunity for transformations of normal cells to malignant cells via intermediate cells. Nongenotoxic cytotoxic carcinogens that increase cell proliferation rates to replace necrotic cells are likely to have a threshold dose for cytotoxicity below which necrosis and hence, carcinogenesis do not occur. Thus, low dose cancer risk estimates based upon nonthreshold, linear extrapolation are inappropriate for this situation. However, a threshold dose is questionable if a nongenotoxic carcinogen acts via a cell receptor. Also, a nongenotoxic carcinogen that increases the cell proliferation rate, via the cell division rate and/or cell removal rate by apoptosis, by augmenting an existing endogenous mechanism is not likely to have a threshold dose. Whether or not a threshold dose exists for nongenotoxic carcinogens, it is of interest to study the relationship between lifetime tumor incidence and the cell proliferation rate. The Moolgavkar–Venzon–Knudson biologically based stochastic two-stage clonal expansion model is used to describe a carcinogenic process. Because the variability in cell proliferation rates among animals often makes it impossible to detect changes of less than 20% in the rate, it is shown that small changes in the cell proliferation rate, that may be obscured by the background noise in rates, can produce large changes in the lifetime tumor incidence as calculated from the Moolgavkar–Venzon–Knudson model. That is, dose response curves for cell proliferation and tumor incidence do not necessarily mimic each other. This makes the use of no observed effect levels (NOELs) for cell proliferation rates often inadmissible for establishing acceptable daily intakes (ADIs) of nongenotoxic carcinogens. In those cases where low dose linearity is not likely, a potential alternative to a NOEL is a benchmark dose corresponding to a small increase in the cell proliferation rate, e. g., 1%, to which appropriate safety (uncertainty) factors can be applied to arrive at an ADI.     

植物原生质体培养及应用

综述了原生质体培养的研究进展,原生质体培养在理论上和品种改良中的应用。在理论研究中的应用有三个方面：1、细胞生理现象的研究;2、细胞核与细胞质相互关系的研究;3、病毒侵染与复制机理的研究。在品种改良中的应用采用的方法包括二个方面：1、遗传操作;2、突变体的筛选。     

Carcinogenicity Studies on MTBE: Critical Review and Interpretation

Chronic inhalation of toxic concentrations of MTBE caused renal tubular cell neoplasms in male Fischer 344 rats and hepatocellular adenomas in female CD-1 mice. In Sprague-Dawley rats the oral administration of MTBE was associated with increased incidences of Leydig cell tumors and of lymphomas and leukemias (combined) in males and females, respectively. Neither lymphomas nor leukemias were individually increased in treated females. Leydig cell tumors are common in rats and do not predict human responses to drugs and chemicals. Neither MTBE nor its metabolite, t -butyl alcohol, possess mutagenic potential and a second metabolite, formaldehyde, is mutagenic in vitro but in vivo results are equivocal. MTBE-induced neoplasms are most likely produced through a nongenetic mechanism which requires chronic exposure to toxic doses. Because of the intense odor (and taste) of MTBE, humans will not tolerate either air or water concentrations sufficient to produce the cytotoxic precursors required to promote cellular proliferation.     

新金属菌绿素对HL-60肿瘤细胞光毒作用的参数研究

细菌叶绿素锌作为一类潜在的长波长光敏剂,具有重要生物医学研究价值.采用MTT法研究Zn-BCA-PDT灭杀HL-60细胞的浓度、暗孵育时间、照光时间和光波长等参数,总结对HL-60白血病肿瘤细胞进行Zn-BCA-PDT的较佳处理方案：细胞密度1×105个/mL,Zn-BCA浓度10μg/mL,暗室孵育3 h,照光时间50 min,光源波长为800 nm.     

Expectation maximization estimates of the offspring probabilities in a class of multitype branching processes with binary family trees

When proliferating cells are counted in several independent colonies at some time points, the maximum likelihood estimates of the parameters of the multitype branching process are obtained trough an expectation maximization algorithm. In the case of an offspring distribution governed by a Markov branching process with binary family trees, this method, relying then on a partial knowledge of the tree, yields the same estimates as those computed with the complete knowledge of the tree.     

小檗碱透皮制剂对小鼠骨髓细胞的微核效应

本文采取小鼠骨髓细胞微核试验方法,研究小檗碱透皮制剂对体细胞的诱变性。结果表明：阴性对照组微核率为1．125±0．9％,环磷酰胺阳性对照组的微核率为5．125±0.976％,与阴性对照组比较,差异极显著（P＜0．01）;小檗碱透皮制剂低、中、高剂量组微核率分别为1．125±0．69%、1．5±0．9%、1.875±0．787‰,与阴性对照比较,差异均不显著（P＞0．06）,试验结果为阴性。小檗碱透皮制剂对小鼠骨髓细胞不具诱变性。     

MRI在骨巨细胞瘤诊断中的价值

目的 探讨骨巨细胞瘤的表现特点.方法 搜集经手术证实的40例骨巨细胞瘤患者资料,分析MRI征象并与病理结果对照.结果 所有病例在T1WI表现为等、低信号,T2WI为不均匀高信号,Gd-DTPA增强扫描呈中度或明显强化,并可显示瘤内坏死、囊变、出血、含铁血黄素沉着及液-液平面等.结论 MRI对骨巨细胞瘤的内部组织情况及周边情况显示良好,信息全面,可提高骨巨细胞瘤诊断的准确性,对临床治疗方案的选择提供重要依据.     

燃料电池发动机优化控制的建模与蚂蚁算法研究

以某燃料电池发动机为原型,将神经网络辨识方法应用到其非线性系统的建模中.仿真结果表明,方法可行,建立的模型精度较高.在此模型的基础上,为了缩短发动机在常温启动时的暖机时间(升温至正常工作温度范围)和提高其输出功率以及在高温怠速加速时,保持其升温的平稳性和缩短达到额定输出功率的时间,将蚂蚁算法应用于发动机的优化控制问题.最后通过对模型的测试,采用蚂蚁算法优化后的控制方法基本达到了要求目标,与传统PID控制方法相比较,显示了其优越性.     

锂电池用SnO基复合氧化物负极材料的研究

将SnCl2、FeCl2及CuCl2按一定比例进行混合并水解，得到Sn基氧化物与其他惰性材料（FeO,CuO）的混合物，将其在还原性气氛（Ar96% H24%）中进行热处理，以获得具有高容量及更好的循环性能的负极材料。研究结果表明：热处理温度对首次循环的库仑效率影响不大，但对循环稳定性有明显影响。复合材料电极的可逆容量起过381mAh/g。Sn-Fe体系在400℃热处理2h，获得的材料具有优异的循环稳定性，但首次循环的库仑效率仅24．91％。     

PEMFC膜电极制作工艺的研究

提出了新的膜电极结构模式──双网络Ｎａｆｉｏｎ被覆膜电极。该模型的催化剂由具有高气体扩散率的薄层Ｎａｆｉｏｎ被覆Ｐｔ／Ｃ催化剂网络与具有高质子传导率的厚层Ｎａｆｉｏｎ被覆碳黑电解质网络互联套构而成。通过优化ＰＥＭＦＣ膜电极制作工艺条件,制得了活性面积５ｃｍ~２,Ｐｔ载量０．１ｍｇ／ｃｍ~２的双网络膜电极。