Epithelial barrier (EB)

The epithelial barrier is a complex physiological structure composed of a continuous layer of epithelial cells and the apical junctional complexes that seal the paracellular space between them [4, 7]. It functions as a selective filter that allows the absorption of essential nutrients, water, and ions while simultaneously acting as a physical defense against the translocation of pathogens, environmental toxins, and dietary antigens into the systemic circulation [8, 12]. This integrity is primarily maintained by a network of transmembrane proteins, including claudins, occludin, and junctional adhesion molecules (JAMs), which are anchored to the intracellular cytoskeleton by scaffolding proteins like zonula occludens (ZO-1, ZO-2) [4, 14]. Dysfunction of this barrier, characterized by increased permeability (hyperpermeability), is a central feature in the pathogenesis of several chronic inflammatory and autoimmune conditions, such as inflammatory bowel disease, celiac disease, and asthma [5, 16]. Therapeutically, the epithelial barrier is targeted through various strategies aimed at restoring or reinforcing junctional integrity and mucosal health [9, 11]. Pharmacological agents such as larazotide acetate directly modulate tight junction proteins to reduce paracellular permeability, while drugs like lubiprostone and growth factor analogs like teduglutide promote mucosal healing and junctional assembly [6, 7, 10]. Additionally, indirect therapeutic effects are achieved using biologics like anti-TNF antibodies or JAK inhibitors, which reduce local inflammation and thus permit the natural regeneration of the barrier [8, 16]. Monitoring the efficacy of these treatments involves the use of diverse biomarkers, including serum levels of zonulin, intestinal fatty acid-binding protein (I-FABP), and citrulline, which reflect junctional regulation and epithelial cell mass [1, 3, 5]. Safety concerns associated with targeting the barrier include the potential for disrupting normal nutrient absorption and the risk of off-target effects in different epithelial tissues such as the kidney or the blood-brain barrier [8, 14].

Other names

Intestinal barrierMucosal barrierAirway epithelial barrierSkin barrierTight junction complexApical junctional complexGut barrier

Enhancement of epithelial barrier integrity via direct modulation of tight junction assembly (e.g., targeting ZO-1 and claudins), inhibition of paracellular leak pathways through myosin light chain kinase (MLCK) regulation, and secondary restoration through the neutralization of proinflammatory cytokines (e.g., TNF-alpha, IL-13) that trigger junctional disassembly.