Eosinophil Peroxidase in Allergic Inflammation

描述（由申请人提供）：嗜酸性粒细胞（EO）吞噬细胞可以破坏宿主组织，并有助于过敏性炎症性疾病的发病机制，如哮喘和炎症性肠病（IBD）。EO特异性颗粒具有丰富的EO过氧化物酶（EPO）和强烈的呼吸爆发，产生H2O2，为其他氧化剂的生成提供燃料。然而，关于epo介导的氧化损伤对嗜酸性炎症状态病理的贡献知之甚少。我们发现三种不寻常的底物——溴化物（Br-）、亚硝酸盐（NO2-）和硫氰酸盐（SCN-）——在H2O2存在的生理液体中竞争EPO的氧化，分别产生HOBr、NO2和HOSCN。这些氧化剂对人体细胞的相对毒性为HOBr > NO2 >> HOSCN；然而EPO优先氧化SCN- > NO2- > Br-。我们假设SCN-“缓冲液”可以抑制EPO产生更具有细胞毒性的NO2和Br基氧化剂，因此血清SCN-水平（由饮食决定）可能调节EPO的毒性。我们提出的工作的总体目标是检验epo产生的氧化剂以底物决定的方式对宿主组织和EOs本身施加损害的假设。我们的第一个具体目标是在小鼠硫酸葡聚糖模型中验证通过膳食补充硫氰酸盐或其代谢前体氰样化合物来调节EPO毒性的假设，从而改善炎症性肠病的严重程度。我们的第二个具体目标是验证以下假设：在一种新的小鼠IL- 5/Eotaxin-2 （I5/E2）转基因哮喘模型中，1)与EPO-/-小鼠杂交，2)药理抑制EPO酶活性，以及3)饮食中添加SCN-均可改善这些动物自发和卵清蛋白（OVA）致敏和激发后发生的严重哮喘表型。第三个具体目的是验证EPO/H2O2/SCN-系统通过NF- b依赖机制抑制嗜酸性粒细胞凋亡和有害的继发性坏死脱粒的假设。这些研究如果成功，将证明epo介导的氧化损伤在哮喘和IBD发病机制中的作用，并提出一种简单的治疗策略，即在饮食中补充廉价且无害的SCN/，这可以应用于这些和其他过敏性炎症疾病，甚至在贫困社区。

DESCRIPTION (provided by applicant): Eosinophil (EO) phagocytes can damage host tissue and contribute to the pathogenesis of allergic inflammatory diseases such as asthma and inflammatory bowel diseases (IBD). EO specific granules are endowed with abundant amounts of EO peroxidase (EPO) and a vigorous respiratory burst that generates H2O2 to fuel the generation of other oxidants. However, little is known about the contribution of EPO-mediated oxidative damage to the pathology of eosinophilic inflammatory states. We find that three unusual substrates -- bromide (Br-), nitrite (NO2-), and thiocyanate (SCN-) -- compete for oxidation by EPO in physiologic fluids in the presence of H2O2, yielding, respectively, HOBr, NO2, and HOSCN. The relative toxicity of these oxidants for human cells is HOBr > NO2 >> HOSCN; yet EPO preferentially oxidizes SCN- > NO2- > Br-. We hypothesize that SCN- "buffers" against generation by EPO of the more cytotoxic NO2-- and Br-- based oxidants and consequently serum SCN- levels, which are dietarily determined, may modulate EPO toxicity. The overall goal of our proposed work is to examine the hypothesis that that EPO-generated oxidants impose damage in a substrate-determined manner to host tissue and EOs themselves. Our first specific aim s to test the hypothesis that substrate modulation of EPO toxicity by dietary supplementation with either thiocyanate or its metabolic precursors, cyanide-like compounds, ameliorates the severity of inflammatory bowel disease in a murine dextran sulfate model. Our second specific aim is to test the hypothesis that in a novel murine IL- 5/Eotaxin-2 (I5/E2) transgenic model of asthma, 1) crossbreeding with EPO-/- mice, 2) pharmacologic inhibition of EPO enzymatic activity, and 3) dietary SCN- supplementation all ameliorate the severe asthmatic phenotype which develops in these animals both spontaneously and after ovalbumin (OVA) sentitization and challenge. The third specific aim is to test the hypothesis that the EPO/H2O2/SCN- system functions through an NF-(B-dependent mechanism to inhibit eosinophil apoptosis and deleterious secondary necrotic degranulation. These studies, if successful, will prove a role for EPO-mediated oxidant damage in the pathogenesis of asthma and IBD and suggest a simple strategy for its treatment-- i.e., dietary supplementation with inexpensive and innocuous SCN/-- that could be applied to these and other allergic inflammatory diseases even in impoverished communities. PUBLIC HEALTH RELEVANCE: In this grant we will test whether thiocyanate, a simple, inexpensive and non-toxic chemical compound found in vegetables, can be ingested to treat asthma and ulcerative colitis, two serious allergic diseases. We believe this is possible because thiocyanate blunts tissue damage caused by eosinophils, a type of white cell that causes allergic symptoms and diseases. If these studies succeed, we will have discovered a simple, cheap and safe way to treat allergies.