Zinc treatment is beneficial for infectious diarrhea or colitis. This study aims to characterize the pathomechanisms of the epithelial barrier dysfunction caused by alpha-hemolysin (HlyA)-expressing Escherichia coli in the colon mucosa and the mitigating effects of zinc ions.

We performed Ussing chamber experiments on porcine colon epithelium and infected the tissues with HlyA-producing E. coli. Colon mucosa from piglets was obtained from a feeding trial with defined normal or high dose zinc feeding (pre-conditioning). Additional to the zinc feeding, zinc was added to the luminal compartment of the Ussing chamber. Transepithelial electrical resistance (TER) was measured during the infection of the living tissue and subsequently the tissues were immuno-stained for confocal microscopy.

Zinc applied to the luminal compartment was effective in preventing from E. coli-induced epithelial barrier dysfunction in Ussing chamber experiments. In contrast, zinc pre-conditioning of colon mucosae when zinc ions were missing subsequently in the luminal compartment was not sufficient to prevent epithelial barrier impairment during E. coli infection. The pathological changes caused by E. coli HlyA were alterations of tight junction proteins claudin-4 and claudin-5, focal leak formation, and cell exfoliation which reflected the paracellular barrier defect measured by a reduced TER. In microscopic analysis of luminal zinc-treated mucosae these changes were absent.

In conclusion, continuous presence of unbound zinc ions in the luminal compartment is essential for the protective action of zinc against E. coli HlyA. This suggests the usage of zinc as therapeutic regimen, while prophylactic intervention by high dietary zinc loads may be less useful.

锌治疗有益于感染性腹泻或结肠炎。这项研究旨在表征结肠粘膜中表达α-溶血素（HlyA）的大肠杆菌引起的上皮屏障功能障碍的致病机理和锌离子的缓解作用。

我们在猪结肠上皮细胞上进行了Ussing室实验，并用产生HlyA的大肠杆菌感染了组织。来自仔猪的结肠粘膜是从饲喂试验中获得的，该饲喂试验具有确定的正常或高剂量锌喂养（预处理）。除了补锌外，还向锌制室的腔室中添加了锌。在活组织感染期间测量跨上皮电阻（TER），随后对组织进行免疫染色以进行共聚焦显微镜检查。

在Ussing室实验中，将锌应用于腔室可有效预防大肠杆菌诱导的上皮屏障功能障碍。相反，当随后在管腔隔室中缺少锌离子时，结肠粘膜的锌预处理不足以防止大肠杆菌感染期间的上皮屏障损伤。大肠杆菌HlyA引起的病理变化是紧密连接蛋白claudin-4和claudin-5的改变，局灶性漏液形成和细胞脱落，反映出TER减少所测量的细胞旁屏障缺陷。在腔内锌处理的粘膜的显微镜分析中，没有这些变化。

总之，在腔室内连续存在未结合的锌离子对于锌对大肠杆菌HlyA的保护作用至关重要。这表明使用锌作为治疗方案，而高饮食锌负荷的预防干预可能不太有用。