Targeting HO-1 by Epigallocatechin-3-Gallate Reduces Contrast-Induced Renal Injury via Anti-Oxidative Stress and Anti-Inflammation Pathways

Both oxidative stress and inflammation are involved in the pathogenesis of contrast-induced nephropathy (CIN). Epigallocatechin-3-gallate (EGCG), a purified catechin from green tea, has antioxidant and anti-inflammatory effects. However, it is unknown whether or not EGCG is effective in treating CIN. Our present study found that intravenous administration of EGCG, either before or just after the establishment of CIN, had a protective effect, determined by normalization of serum creatinine and blood urea nitrogen levels, improvement in renal histopathological scoring and alleviation of apoptosis, accompanied by decreased oxidative stress and inflammation. Because EGCG is a potent inducer of the antioxidant heme oxygenase-1 (HO-1), we studied HO-1 signaling in CIN. HO-1 levels were increased in CIN; treatment with EGCG further increased HO-1 levels, accompanied by an increase in Nrf2, a regulator of antioxidant proteins. Interestingly, blockade of HO-1 with protoporphyrin IX zinc(II) (ZnPP) prevented the protective effect of EGCG on CIN. ZnPP also blocked the ability of EGCG to increase the activity of an antioxidant (superoxide dismutase), and decrease markers of oxidative stress (myeloperoxidase and malondialdehyde) and inflammation (myeloperoxidase and IL-1β), indicating that HO-1 is the upstream molecule that regulates the EGCG-mediated protection. To determine further the role of HO-1 on the EGCG-mediated inhibition of inflammation, we studied the effect of EGCG on the NLRP3 inflammasome, an upstream signaling of IL-1β. EGCG down-regulated NLRP3 expression, which was blocked by ZnPP, indicating that HO-1 links EGCG with NLRP3. Therefore, EGCG, via up-regulation of HO-1, protects against CIN by amelioration of oxidative stress and inflammation.氧化应激与炎症均参与造影剂肾病（contrast-induced nephropathy, CIN）的发病机制。表没食子儿茶素没食子酸酯（epigallocatechin-3-gallate, EGCG）是一种从绿茶中纯化得到的儿茶素类物质，具备抗氧化与抗炎活性。然而，目前尚不清楚EGCG是否可有效治疗CIN。本研究发现，在CIN造模前或造模即刻静脉给予EGCG，可发挥肾脏保护作用，具体表现为血清肌酐与血尿素氮水平恢复正常、肾脏病理评分改善以及细胞凋亡减轻，同时伴随氧化应激与炎症水平的降低。由于EGCG是抗氧化蛋白血红素氧合酶-1（heme oxygenase-1, HO-1）的强效诱导剂，本研究针对CIN模型中的HO-1信号通路展开了探究。CIN模型中HO-1表达水平升高，而EGCG处理可进一步上调HO-1表达，同时伴随抗氧化蛋白调控因子核因子E2相关因子2（nuclear factor erythroid 2-related factor 2, Nrf2）水平的升高。值得注意的是，使用原卟啉IX锌(II)（protoporphyrin IX zinc(II), ZnPP）阻断HO-1后，EGCG对CIN的保护作用被完全抵消。ZnPP同样可阻断EGCG上调抗氧化酶超氧化物歧化酶（superoxide dismutase, SOD）活性的能力，同时抑制EGCG降低氧化应激标志物髓过氧化物酶（myeloperoxidase, MPO）与丙二醛（malondialdehyde, MDA）、以及炎症标志物髓过氧化物酶与白细胞介素1β（interleukin-1β, IL-1β）的作用，这表明HO-1是调控EGCG介导的肾脏保护作用的上游分子。为进一步明确HO-1在EGCG抑制炎症过程中的作用，本研究探究了EGCG对NLRP3炎症小体（NLRP3 inflammasome）的影响——该复合体是IL-1β的上游调控信号通路。EGCG可下调NLRP3的表达，而该效应可被ZnPP阻断，这提示HO-1将EGCG与NLRP3通路关联起来。综上，EGCG可通过上调HO-1的表达，减轻氧化应激与炎症反应，从而发挥对CIN的保护作用。