Quercetin Protects Intestinal Barrier Integrity in Inflammation and Oxidative Stress

Background/Objective: An obesogenic diet triggers intestinal inflammation and oxidative stress, leading to epithelial barrier dysfunction and increased risk of metabolic disorders. This study investigated the mechanisms by which quercetin protects intestinal integrity in high-fat diet (HFD)-fed mice. Methods: Mice were fed an HFD or a low-fat diet (LFD) with or without 1% quercetin, intestinal gene and protein expression, microRNA levels, permeability, and circulating intestinal biomarkers were assessed. Results: Mice fed an HFD with quercetin (HFDQ) showed a 17% improvement in intestinal barrier integrity with increased expression of tight junction and mucin genes and proteins. The nuclear translocation of the nuclear factor-κB (NF-κB) p65 subunit in the ileum decreased by 34%, whereas its acetylation was reduced by 50-57% throughout the intestine, with downregulation of NF-κB-regulated pro-inflammatory genes and proteins. Quercetin increased the nuclear factor erythroid 2-related factor 2 (NRF2) by ~ 25% across intestinal segments and upregulated antioxidant enzyme genes. It suppressed toll-like receptor 4 (TLR4) by 50% and restored AMP-activated protein kinase (AMPK) and sirtuin 1 to levels comparable to those in LFD mice. Altered microRNAs (miRNA-16, 200b, 122, 34a, and 21) supported these molecular changes. Quercetin also restored short-chain fatty acid receptors and serotonin transporters that were affected by HFD. Plasma lipopolysaccharide (LPS), cluster of differentiation 14, LPS-binding protein, and myeloperoxidase activity decreased by 36, 31, 42, and 37%, while glucagon-like peptide-1 increased by 23%. Conclusions: Quercetin protects epithelial barrier integrity against HFD-induced intestinal inflammation and oxidative stress via the AMPK-mediated NF-κB and NRF2 signaling pathways.