Department of Gastroenterology, The Second Hospital of Hebei Medical University, Hebei Key Laboratory of Gastroenterology, Hebei Institute of Gastroenterology, No,215 Heping West Road, 050000, Shijiazhuang, China.
BMC Gastroenterol. 2012 May 30;12:57. doi: 10.1186/1471-230X-12-57.
Intestinal hyper-permeability plays a critical role in the etiopathogenesis of inflammatory bowel disease (IBD) by affecting the penetration of pathogens, toxic compounds and macromolecules. 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the active form of vitamin D, has been shown to be an important regulator of IBD and recent epidemiology suggests that patients with IBD have an impaired vitamin D status. The purpose of this study is to investigate the possible protective effects of 1,25(OH)2D3 on mucosal injury and epithelial barrier disruption on dextran sulfate sodium (DSS)-induced acute colitis model.
We used DSS-induced acute colitis model to investigate the protective effects of 1,25(OH)2D3 on mucosal injury and epithelial barrier integrity. Severity of colitis was evaluated by disease activity index (DAI), body weight (BW) change, colon length, histology, myeloperoxidase (MPO) activity, and proinflammatory cytokine production including tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). In vitro the protective role of 1,25(OH)2D3 was assessed by incubating Caco-2 cells with or without DSS and measuring transepithelial electrical resistance (TEER) and fluorescein isothiocyanate dextran (FITC-D). The intestinal permeability was analyzed by FITC-D, bacterial translocation and measurement of lipopolysaccharide (LPS). Ultrastructural features of the colon tissue and Caco-2 cell monolayer were observed by electron microscopy. Expressions of tight junction (TJ) proteins in the colon mucosa and Caco-2 cells were detected by immunohistochemistry, immunofluorescence, Western blot and real-time fluorescent quantitative PCR, respectively.
DSS-induced acute colitis model was characterized by a reduced BW, AUC of BW, serum calcium, higher DAI, AUC of DAI, shortened colon length, elevated MPO activity, worsened histologic inflammation, increased mononuclear cell numbers in mesenteric lymph nodes (MLNs) and colonic lamina propria (LP), and enhanced proteins and mRNA levels of TNF-α and IFN-γ. 1,25(OH)2D3 markedly increased expressions of TJ proteins and mRNA and decreased the FITC-D permeability and the level of LPS. Furthermore, 1,25(OH)2D3 abrogated bacterial translocation to MLNs and ameliorated ultrastructural features of the colon epithelium by scanning electron microscopy (SEM). In vitro, 1,25(OH)2D3 increased TEER, TJ proteins and mRNA expressions, decreased the FITC-D permeability, and preserved structural integrity of the TJ in Caco-2 cells.
1,25(OH)2D3 may play a protective role in mucosal barrier homeostasis by maintaining the integrity of junction complexes and in healing capacity of the colon epithelium. 1,25(OH)2D3 may represent an attractive and novel therapeutic agent for the adjuvant therapy of IBD.
肠道通透性在炎症性肠病（IBD）的发病机制中起着关键作用，通过影响病原体、有毒化合物和大分子的渗透。1,25-二羟维生素 D3[1,25(OH)2D3]，维生素 D 的活性形式，已被证明是 IBD 的重要调节剂，最近的流行病学研究表明，IBD 患者存在维生素 D 状态受损。本研究旨在探讨 1,25(OH)2D3 对葡聚糖硫酸钠（DSS）诱导的急性结肠炎模型中粘膜损伤和上皮屏障破坏的可能保护作用。
我们使用 DSS 诱导的急性结肠炎模型来研究 1,25(OH)2D3 对粘膜损伤和上皮屏障完整性的保护作用。通过疾病活动指数（DAI）、体重（BW）变化、结肠长度、组织学、髓过氧化物酶（MPO）活性以及肿瘤坏死因子-α（TNF-α）和干扰素-γ（IFN-γ）等促炎细胞因子的产生来评估结肠炎的严重程度。在体外，通过用或不用 DSS 孵育 Caco-2 细胞来评估 1,25(OH)2D3 的保护作用，并测量跨上皮电阻（TEER）和荧光素异硫氰酸酯右旋糖（FITC-D）。通过 FITC-D、细菌易位和测量脂多糖（LPS）分析肠道通透性。通过电子显微镜观察结肠组织和 Caco-2 细胞单层的超微结构特征。通过免疫组织化学、免疫荧光、Western blot 和实时荧光定量 PCR 分别检测结肠黏膜和 Caco-2 细胞中紧密连接（TJ）蛋白的表达。
DSS 诱导的急性结肠炎模型的特征是 BW、BW 的 AUC、血清钙降低，DAI、AUC 的 DAI 升高，结肠长度缩短，MPO 活性升高，组织学炎症恶化，肠系膜淋巴结（MLNs）和结肠固有层（LP）中的单核细胞数量增加，TNF-α 和 IFN-γ 的蛋白和 mRNA 水平升高。1,25(OH)2D3 显著增加 TJ 蛋白和 mRNA 的表达，降低 FITC-D 通透性和 LPS 水平。此外，1,25(OH)2D3 可阻止细菌易位至 MLNs，并通过扫描电子显微镜（SEM）改善结肠上皮的超微结构特征。在体外，1,25(OH)2D3 增加 TEER、TJ 蛋白和 mRNA 的表达，降低 FITC-D 的通透性，并保持 Caco-2 细胞中 TJ 的结构完整性。
1,25(OH)2D3 通过维持连接复合物的完整性和结肠上皮的愈合能力，在粘膜屏障稳态中发挥保护作用。1,25(OH)2D3 可能是 IBD 辅助治疗的一种有吸引力的新型治疗药物。
