Quercetin improves and protects Calu-3 airway epithelial barrier function.

Introduction: In light of the impact of airway barrier leaks in COVID-19 and the significance of vitamin D in COVID-19 outcomes, including airway barrier protection, we investigated whether the very common dietary flavonoid quercetin could also be efficacious in supporting airway barrier function. Methods: To address this question, we utilized the widely used airway epithelial cell culture model, Calu-3. Results: We observed that treating Calu-3 cell layers with quercetin increased transepithelial electrical resistance while simultaneously reducing transepithelial leaks of 14C-D-mannitol (Jm) and 14C-inulin. The effects of quercetin were concentration-dependent and exhibited a biphasic time course. These effects of quercetin occurred with changes in tight junctional protein composition as well as a partial inhibition of cell replication that resulted in decreased linear junctional density. Both of these effects potentially contribute to improved barrier function. Quercetin was equally effective in reducing the barrier compromise caused by the pro-inflammatory cytokine TNF-α, an action that seemed to derive, in part, from reducing the elevation of ERK 1/2 caused by TNF-α. Discussion: Quercetin improved Calu-3 barrier function and reduced TNF-α-induced barrier compromise, mediated in part by changes in the tight junctional complex.

Zinc Gluconate Induces Potentially Cancer Chemopreventive Activity in Barrett's Esophagus: A Phase 1 Pilot Study.

BACKGROUND: Chemopreventive effects of zinc for esophageal cancer have been well documented in animal models. This prospective study explores if a similar, potentially chemopreventive action can be seen in Barrett's esophagus (BE) in humans. AIMS: To determine if molecular evidence can be obtained potentially indicating zinc's chemopreventive action in Barrett's metaplasia. METHODS: Patients with a prior BE diagnosis were placed on oral zinc gluconate (14 days of 26.4 mg zinc BID) or a sodium gluconate placebo, prior to their surveillance endoscopy procedure. Biopsies of Barrett's mucosa were then obtained for miRNA and mRNA microarrays, or protein analyses. RESULTS: Zinc-induced mRNA changes were observed for a large number of transcripts. These included downregulation of transcripts encoding proinflammatory proteins (IL32, IL1ß, IL15, IL7R, IL2R, IL15R, IL3R), upregulation of anti-inflammatory mediators (IL1RA), downregulation of transcripts mediating epithelial-to-mesenchymal transition (EMT) (LIF, MYB, LYN, MTA1, SRC, SNAIL1, and TWIST1), and upregulation of transcripts that oppose EMT (BMP7, MTSS1, TRIB3, GRHL1). miRNA arrays showed significant upregulation of seven miRs with tumor suppressor activity (-125b-5P, -132-3P, -548z, -551a, -504, -518, and -34a-5P). Of proteins analyzed by Western blot, increased expression of the pro-apoptotic protein, BAX, and the tight junctional protein, CLAUDIN-7, along with decreased expression of BCL-2 and VEGF-R2 were noteworthy. CONCLUSIONS: When these mRNA, miRNA, and protein molecular data are considered collectively, a cancer chemopreventive action by zinc in Barrett's metaplasia may be possible for this precancerous esophageal tissue. These results and the extensive prior animal model studies argue for a future prospective clinical trial for this safe, easily-administered, and inexpensive micronutrient, that could determine if a chemopreventive action truly exists.

Cobalt chloride compromises transepithelial barrier properties of CaCo-2 BBe human gastrointestinal epithelial cell layers.

BACKGROUND: Elevation of the transcription factor HIF-1 is a prominent mediator of not only processes that accompany hypoxia, but also the tumor microenvironment and tissue regeneration. This study uses mediators of "chemical hypoxia" to ask the question whether HIF-1α elevation in a healthy epithelial cell layer leads to leakiness in its tight junctional seals. METHODS: Transepithelial electrical resistance and transepithelial diffusion of 14C-D-mannitol and other radiolabeled probes are used as indicators of transepithelial barrier function of CaCo-2 BBe human gastrointestinal epithelial cell layers cultured on permeable supports. Western immunoblot analyses of integral tight junctional proteins (occludin and claudins) are used as further indicators of barrier function change. RESULTS: Cobalt, an inhibitor of the prolyl hydroxylase enzymes governing HIF-1α breakdown in the cell, induces transepithelial leakiness in CaCo-2 BBe cell layers in a time and concentration-dependent manner. This increased leakiness is accompanied by significant changes in certain specific integral tight junctional (TJ) proteins such as a decreased level of occludin and increased level of claudin-5. Similar results regarding barrier function compromise also occur with other chemical inhibitors of HIF-1α breakdown, namely ciclopiroxolamine (CPX) and dimethyloxalylglycine (DMOG). The increased leak is manifested by both decreased transepithelial electrical resistance (Rt) and increased paracellular diffusion of D-mannitol (Jm). The induced transepithelial leak shows significant size selectivity, consistent with induced effects on TJ permeability. Less-differentiated cell layers were significantly more affected than well-differentiated cell layers regarding induced transepithelial leak. A genetically modified CaCo-2 variant with reduced levels of HIF-1ß, showed reduced transepithelial leak in response to cobalt exposure, further indicating that elevation of HIF-1α levels induced by agents of "chemical hypoxia" is responsible for the compromised barrier function of the CaCo-2 BBe cell layers. CONCLUSIONS: Exposure to inducers of chemical hypoxia elevated HIF-1α levels and increased transepithelial leak. The degree of epithelial differentiation has significant effects on this action, possibly explaining the varying effects of HIF-1 modulation in epithelial and endothelial barrier function in different physiological and pathophysiological conditions.