UC是一种迄今为止病因不明的慢性非特异性肠道炎症疾病,临床主要表现为反复发作腹痛、腹泻、黏液脓血便等,属炎症性型肠病(Inflammatory bowel disease, IBD)的一种。UC好发于乙状结肠和直肠,严重者可引起全结肠甚至回肠末端病变。UC主要表现于结肠粘膜和粘膜下层,甚至整个结肠的持续性、融合性炎症反应,且发病过程中以复发与缓解交替为病变特点[1, 2],在全球的发病率不断上升[3]。本病病情发展较复杂,具有难治愈,易复发的特点,会严重影响患者的正常工作和生活,被WHO列为难治疾病之一,且被认为与结肠癌的发病相关。UC的发病机制是多因素的,涉及免疫系统失调、上皮屏障缺陷、肠道微生物组、遗传因素、饮食因素、和环境因素等[3]。由于病因不明、复发风险高、预后不佳,UC已逐渐成为临床治疗的一个重要问题[4]。目前,5-氨基水杨酸、皮质类固醇激素、硫嘌呤、生物制剂药物和抗细胞因子疗法是治疗 UC 的主要药物疗法[5-8]。然而,由于药物治疗费用高昂且存在负面影响,长期使用受到限制。因此,迫切需要发现更有效、更安全的治疗药物。
PPARγ是一种依赖配体的转录因子,是核受体超家族的成员。作为激素、维生素、内源性代谢物和外源化合物的传感器,核受体控制着大量基因的表达。PPARγ调节脂肪细胞分化、脂肪酸储存和葡萄糖代谢,是抗糖尿病药物的靶点[9, 10]。最近,人们认识到PPARγ通过抑制炎症细胞因子的表达和指导免疫细胞向抗炎表型分化的能力,在免疫反应中起着至关重要的作用。PPARγ的一个特点是其配体的结构多样性,包括内源性代谢物、膳食化合物和合成药物。炎症和过敏性疾病的高发病率和不断增加的发病率,加上最近临床试验的令人鼓舞的结果,表明食物中发现的天然PPARγ激动剂可能作为抗炎分子对人类健康有益。因此,PPARγ不仅是制药工业的目标,而且对食品工业也有很大的潜在兴趣,因为它是由几种天然膳食成分激活的。在过去几年中,饮食干预炎症性疾病的前景有所改善。经典的激素激活受体,如雌激素受体,位于细胞质中,与激活配体结合后易位到细胞核中,而PPARγ受体则位于细胞核中,与DNA应答元件结合[11]。PPARγ受体的核位置是典型的代谢物激活核受体。PPARγ受体有三种形式:α、β / δ和γ[12]。在炎症过程中,PPARγ通过拮抗其他转录因子如NF-κB和AP-1家族成员的活性,以配体依赖的方式直接负调控促炎基因的表达[13]。PPARγ是一种核受体,最近被认为对抑制肠道炎症反应和保护细胞免受氧化损伤很重要。
核因子κB(nuclear factor kappa-B,NF-κB)是与多种细胞炎症和免疫反应相关的重要转录因子,被认为是治疗各种疾病的关键靶点[14]。在炎症、先天免疫和组织完整性的调节中起着关键作用。正常情况下,NF-κB及NF-κB的抑制蛋白(inhibitor of NF-κB, IκB)以惰性状态储存在细胞质中。内外源刺激下,NF-κB激活信号可诱导IκB磷酸化而泛素化。当机体或细胞受到外界刺激后,NF-κB结合的IκB被IκB激酶(Inhibitor of Kappa B Kinase, IKK)复合物磷酸化,磷酸化后发生泛素化,泛素化的IκB分子构象发生改变,迅速被蛋白酶体识别和降解,IκB的降解导致NF-κB易位至细胞核[15]并介导调节下游靶基因的转录。NF-κB进入细胞核诱导促炎细胞因子、粘附分子和趋化因子的释放,如iNOS、COX-2、TNF-α和IL-1β等,这些都与结肠炎的发病有关[16]。我们的研究结果表明,在DSS诱导的UC大鼠中,18β-GA处理通过抑制IκB-α磷酸化有效地抑制了NF-κB的活化。
甘草中国传统医学中最常用的草药之一,素有国老之称,有温中益气,清热解毒,调和诸药,解毒等功效。甘草性味甘、平,主要治疗咽喉肿痛,消化性溃疡以及食物中毒等。GR具有多种生物活性成分,包括皂苷、类黄酮、香豆素saponins, flavonoids, and coumarins等[17],现代研究表明,甘草提取物具有抗肿瘤[18, 19]、抗微生物[20, 21]、抗病毒[22, 23]、抗炎[24, 25]、免疫调节[26]和神经保护作用[27]。GR含有20多种三萜和近300种黄酮类化合物。18β-GA是在甘草中发现的一种三萜皂苷,是甘草酸的水解代谢产物。18β-GA具有抗氧化、抗炎、抗病毒、抗肿瘤和免疫调节特性[17]。
尽管如此,18β-GA对实验诱导的UC的作用及潜在机制尚不清楚。因此我们使用DSS诱导的UC小鼠模型和细胞共培养体系进行药效研究,通过网络药理学和分子对接实验预测其作用靶点,并通过细胞转染技术、WB等实验进行验证,为在临床上使用18β-GA治疗UC提供了实验和理论基础。
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