Mechanisms of methyl dithiocarbamate immunotoxicity

说明(由申请人提供)：甲基二硫代氨基甲酸钠(SMD，又称灭百虫)是美国第三大最常用的传统农业杀虫剂。它自发分解形成甲基异硫氰酸酯(MTC)，已被加利福尼亚州环保局列为有毒空气污染物，与SMD具有一些免疫调节作用。SMD和MITC均可改变小鼠腹膜巨噬细胞的Toll样受体信号，并导致细菌脂多糖(IPS)处理的小鼠IL-10浓度显著增加，IL-12(以及其他促炎细胞因子和趋化因子)显著降低。SMD还大大降低了小鼠对大肠杆菌腹膜炎的先天抵抗力。其他一些化学品和药物会导致IL-10表达增加，IL-12表达减少。由于这些变化往往会降低先天免疫力，因此了解SMD和MITC影响这些参数的机制对人类健康具有广泛的影响，即使是对没有接触SMD或MITC的人也是如此。本项目将验证以下假设：SMD通过TLR4改变信号以减少IL-12的产生，并通过改变细胞氧化还原平衡、改变铜的可获得性和诱导应激介质来增加IL-10的产生。这些效应在降低对大肠杆菌感染的先天抵抗力方面起着关键作用。本研究将从三个方面对本项目的假说进行验证：特异性目标1-确定丹参和米非司酮增加内毒素诱导的巨噬细胞产生IL-10和降低内毒素诱导的巨噬细胞产生IL-12的机制(S)。特定目的2-确定SMD改变参与IL-10和IL-12表达的上游激酶激活的机制(S)，并确定IL-10表达增加在SMD和MITC诱导的IL-12表达下降中的作用。具体目标3-确定在目标1和2中评估的每个机制在SMD或MITC处理的小鼠对大肠杆菌腹膜炎抵抗力降低中的作用。在每个目标中，要研究的机制都是假说中提到的机制(氧化还原平衡改变，铜的可获得性改变，以及应激介质的诱导)。在目标3中，将开发数学模型来预测或描述信号、基因表达和寄主抗性变化之间的关系。这些结果将代表免疫毒理学的一种新的(系统生物学)方法。这些结果将首次为SMD和MITC提供基于机制的风险评估。对三个重要作用机制的详细研究也有望推广到改变这些参数的其他情况或毒物，这些机制将在每个目标中加以研究。

DESCRIPTION (provided by applicant): Sodium methyldithiocarbamate (SMD, also called metam sodium) is the third most abundantly used conventional agricultural pesticide in the U.S. It spontaneously breaks down to form methylisothiocyanate MTC), which has been classified a toxic air contaminant by the California EPA and which shares some immunomodulatory actions, with SMD. Both SMD and MITC alter toll-like receptor signaling in mouse peritoneal macrophages and cause substantial increases in the concentration of IL-10 and substantial decreases in IL-12 (and other pro-inflammatory cytokines and chemokines) in mice treated with bacterial lipopolysaccharide (IPS). SMD also substantially reduces innate resistance to Escherichia coli peritonitis in mice. A number of other chemicals and drugs cause increased expression of IL-10 and decreased expression of IL-12. Because these changes would tend to decrease innate immunity, understanding the mechanisms by which SMD and MITC affect these parameters has broad implications for human health, even for persons not exposed to SMD or MITC. This project will test the following hypothesis: SMD alters signaling through TLR4 to decrease the production of IL-12 and to increase IL-10 production by altering cellular redox balance, altering copper availability, and inducing stress mediators. These effects play key roles in decreasing innate resistance to infection with E. coli. Three aims will be used to test the hypothesis of this project: Specific Aim 1- Determine the mechanism(s) by which SMD and MITC increase LPS-induced IL-10 production and decrease LPS-induced IL-12 production by peritoneal macrophages. Specific Aim 2- Determine the mechanism(s) by which SMD alters activation of upstream kinases involved in IL-10 and IL-12 expression and determine the role of increased IL-10 expression in the SMD and MITC-induced decreases in IL-12 expression. Specific Aim 3- Determine the role of each of the mechanisms evaluated in Aims 1 and 2 in the decreased resistance to E. coli peritonitis in SMD or MITC treated mice. In each Aim the mechanisms to be investigated are those noted in the hypothesis (altered redox balance, altered copper availability, and induction of stress mediators). In Aim 3, mathematical models will be developed to predict or describe the relationships between changes in signaling, gene expression, and host resistance. These results will represent a new (systems biology) approach to immunotoxicology. These results will allow mechanism based risk assessment for SMD and MITC for the first time. It is also expected that the detailed study of three important mechanisms of action, which will be examined in each aim, can be generalized to other situations or toxicants that alter these parameters.