Immunomodulatory effects of arginine supplementation in colitis and colon cancer

描述（由申请人提供）：炎症性肠病（IBD）由溃疡性结肠炎（UC）和克罗恩病组成，是美国140万人发病的重要来源，并可发展为结肠癌。它很难治疗，昂贵的免疫疗法只在不到一半的病例中诱导缓解。我们一直专注于半必需氨基酸，l -精氨酸（L-Arg）作为补充和替代药物的作用。我们已经证明了l -精氨酸在体外和结肠炎中的有益作用机制。阳离子氨基酸转运蛋白2 （CAT2）、l -精氨酸诱导转运蛋白以及l -精氨酸的摄取在小鼠结肠炎中上调，口服l -精氨酸补充可有效治疗葡聚糖硫酸钠（DSS）诱导的上皮损伤和炎症，这是一种模拟UC的模型。UC组织中CAT2表达、L-Arg摄取和L-Arg水平均降低。在azoxymethane (AOM)-DSS结肠炎（CAC）模型中，CAT2-/-小鼠表现出明显的DSS结肠炎加重和结肠肿瘤发生。在DSS结肠炎模型中，CAT2-/-小鼠对补充l -精氨酸没有反应，这表明单独使用l -精氨酸作为人类UC的治疗可能不足以克服其转运到组织中的受损。伤口修复模型中的结肠上皮恢复依赖于CAT2，这是由于精氨酸酶利用l -精氨酸生成l -鸟氨酸（L-Orn），其可被鸟氨酸脱羧酶（ODC）代谢生成多胺，或鸟氨酸转氨酶（OAT）代谢生成l -脯氨酸（L-Pro）。虽然精氨酸酶的抑制或精氨酸酶1 （Arg1）的敲低会阻止恢复，但在L-精氨酸存在的情况下，当添加L- orn或L- pro时，这种恢复可以完全恢复。OAT而不是ODC的下调阻止了l -精氨酸对恢复的有益作用，暗示OAT参与维持上皮功能。此外，ODC+/-小鼠在DSS结肠炎中表现出改善，组织巨噬细胞NO产生增加，调节性T细胞和巨噬细胞反应增强，表明多胺在该模型中具有有害作用。我们假设l -精氨酸在结肠炎和结肠炎相关肿瘤发生中的益处依赖于CAT2和下游效应物，以改善上皮恢复、先天免疫功能和适应性免疫。在我们的具体目标中，我们将确定：1)由于CAT2的缺失和l -精氨酸可用性的丧失导致DSS结肠炎的恶化

DESCRIPTION (provided by applicant): Inflammatory bowel disease (IBD), consisting of ulcerative colitis (UC) and Crohn's disease, is a source of substantial morbidity for 1.4 million people affected in the USA, and it can progress to colon cancer. It is difficult to treat, with cosly immunotherapies only inducing remission in less than half of cases. We have been focusing on the role of the semi-essential amino acid, L-arginine (L-Arg) as a complementary and alternative medicine. We have demonstrated mechanisms for beneficial effects of L-Arg in vitro and in colitis. Cationic amino acid transporter 2 (CAT2), the inducible transporter of L-Arg, and uptake of L-Arg are upregulated in murine colitis, and oral L-Arg supplementation is effective as a treatment for epithelial injury and inflammation induced by dextran sulfate sodium (DSS), a model that mimics UC. CAT2 expression, L-Arg uptake, and L-Arg levels are all decreased in UC tissues. CAT2-/- mice exhibit marked exacerbation of DSS colitis, and colon tumorigenesis in the azoxymethane (AOM)-DSS model of colitis-associated carcinoma (CAC). CAT2-/- mice do not respond to L-Arg supplementation in the DSS colitis model, suggesting that L-Arg alone as a therapy for human UC may not be sufficient to overcome its impaired transport into tissues. Colonic epithelial restitution in a wound repair model is dependent on CAT2 and this is due to utilization of L-Arg by arginase that generates L-ornithine (L-Orn), which can be metabolized by either ornithine decarboxylase (ODC) to generate polyamines, or ornithine aminotransferase (OAT) to generate L-proline (L-Pro). While inhibition of arginase or knockdown of arginase 1 (Arg1) prevented restitution, this could be completely restored, in the presence of L- Arg, when either L-Orn or L-Pro was added. Knockdown of OAT, but not ODC, prevented beneficial effects of L-Arg on restitution, implicating OAT in the maintenance of epithelial function. Additionally, ODC+/- mice exhibit improvement in DSS colitis, with increased tissue macrophage NO production, and enhanced regulatory T cell and macrophage responses, indicating a deleterious role for polyamines in this model. We hypothesize that benefits of L-Arg in colitis and colitis-associated tumorigenesis depend on CAT2 and downstream effectors to improve epithelial restitution, innate immune function, and adaptive immunity. In our Specific Aims we will determine if: 1) exacerbation of DSS colitis due to deletion of CAT2 and loss of L-Arg availability that mimics human UC is due to an epithelial or macrophage defect and if this is ameliorated by supplementation of L-Orn or L-Pro in combination with L-Arg; 2.) improvement in DSS colitis in ODC+/- mice is due to an epithelial or macrophage effect and if it results from enhanced L-Arg availability for iNOS and/or OAT; 3.) accelerated tumorigenesis with CAT2 deletion is due to an epithelial or macrophage defect and if this process can be beneficially modulated by downregulation of ODC or supplementation of L-Orn or L-Pro in combination with L- Arg. Through investigation of epithelial and immune function, these studies seek to provide new macronutrient- based strategies for treatment of IBD and prevention of colitis-associated dysplasia and carcinoma.