Department of Pharmaceutical Sciences, University of Connecticut School of Pharmacy, Storrs, Connecticut, USA.
J Pharmacol Exp Ther. 2012 May;341(2):447-54. doi: 10.1124/jpet.111.191122. Epub 2012 Feb 10.
Small intestinal mucosal injury is a frequent adverse effect caused by nonsteroidal anti-inflammatory drugs (NSAIDs). The underlying mechanisms are not completely understood, but topical (luminal) effects have been implicated. Many carboxylic acid-containing NSAIDs, including diclofenac (DCF), are metabolized to acyl glucuronides (AGs), and/or ether glucuronides after ring hydroxylation, and exported into the biliary tree. In the gut, these conjugates are cleaved by bacterial β-glucuronidase, releasing the potentially harmful aglycone. We first confirmed that DCF-AG was an excellent substrate for purified Escherichia coli β-D-glucuronidase. Using a previously characterized novel bacteria-specific β-glucuronidase inhibitor (Inhibitor-1), we then found that the enzymatic hydrolysis of DCF-AG in vitro was inhibited concentration dependently (IC₅₀ ∼164 nM). We next hypothesized that pharmacologic inhibition of bacterial β-glucuronidase would reduce exposure of enterocytes to the aglycone and, as a result, alleviate enteropathy. C57BL/6J mice were administered an ulcerogenic dose of DCF (60 mg/kg i.p.) with or without oral pretreatment with Inhibitor-1 (10 μg per mouse, b.i.d.). Whereas DCF alone caused the formation of numerous large ulcers in the distal parts of the small intestine and increased (2-fold) the intestinal permeability to fluorescein isothiocyanate-dextran, Inhibitor-1 cotreatment significantly alleviated mucosal injury and reduced all parameters of enteropathy. Pharmacokinetic profiling of DCF plasma levels in mice revealed that Inhibitor-1 coadministration did not significantly alter the C(max), half-life, or area under the plasma concentration versus time curve of DCF. Thus, highly selective pharmacologic targeting of luminal bacterial β-D-glucuronidase by a novel class of small-molecule inhibitors protects against DCF-induced enteropathy without altering systemic drug exposure.
小肠黏膜损伤是一种常见的非甾体抗炎药（NSAIDs）的不良反应。其潜在机制尚未完全阐明，但局部（腔道）效应已被牵涉其中。许多含有羧酸的 NSAIDs，包括双氯芬酸（DCF），在环羟化后被代谢为酰基葡萄糖醛酸（AGs）和/或醚葡萄糖醛酸，然后被输出到胆管树。在肠道中，这些共轭物被细菌β-葡萄糖醛酸酶裂解，释放出潜在有害的糖苷配基。我们首先证实 DCF-AG 是纯化大肠杆菌β-D-葡萄糖醛酸酶的优良底物。然后，使用以前表征的新型细菌特异性β-葡萄糖醛酸酶抑制剂（Inhibitor-1），我们发现 DCF-AG 的体外酶水解被浓度依赖性抑制（IC₅₀∼164 nM）。接下来，我们假设抑制细菌β-葡萄糖醛酸酶的药理学作用将减少肠细胞暴露于糖苷配基，从而减轻肠病。C57BL/6J 小鼠接受了致溃疡剂量的 DCF（60 mg/kg 腹腔注射），并同时或分别用 Inhibitor-1（每只小鼠 10 μg，每日两次）进行口服预处理。单独给予 DCF 会在小肠远端形成许多大溃疡，并使荧光素异硫氰酸酯-葡聚糖的肠道通透性增加（增加 2 倍），而 Inhibitor-1 共同处理则显著减轻了黏膜损伤并降低了所有肠病参数。在小鼠中对 DCF 血浆水平的药代动力学分析表明，Inhibitor-1 共同给药并没有显著改变 DCF 的 Cmax、半衰期或血浆浓度-时间曲线下面积。因此，通过新型小分子抑制剂对腔道细菌β-D-葡萄糖醛酸酶进行高度选择性的药理学靶向作用，可防止 DCF 诱导的肠病，而不会改变全身药物暴露。
