Claudin 5 (Cldn5) is a critical tight junction protein essential for maintaining paracellular barrier integrity across endothelial and epithelial cells in barrier-forming tissues, including the blood–brain barrier and blood–retinal barrier. Cldn5 plays a central role in regulating vascular permeability, immune responses, and tissue homeostasis. The complex distribution and organ-specific regulation of Cldn5 underscore its potential as a promising therapeutic target. This review comprehensively analyzes the role of Cldn5 in endothelial and epithelial barrier function, its regulation of vascular permeability, and the discrepancies in the literature regarding its expression, regulation, and function in both physiological and pathological conditions across multiple organ systems, including the retina, brain, lung, heart, gut, kidney, liver, skin, and peripheral nerves, while emphasizing its tissue-specific expression patterns. We discuss how both reduced and excessive expressions of Cldn5 can disrupt barrier integrity and contribute to the pathogenesis of ischemic retinopathies, neuroinflammation, cardiovascular injury, and other forms of barrier dysfunction. Furthermore, we explore the dual role of Cldn5 as both a biomarker and a therapeutic target, highlighting emerging strategies such as RNA silencing, pharmacological stabilizers, and transcriptional modulators in controlling barrier leakage in disease conditions.

Urinary bladder cancer (UBC) holds a potentially profound social burden and affects over 573,278 new cases annually. The disease’s primary risk factors include occupational tobacco smoke exposure and inherited genetic susceptibility. Over the past 30 years, a number of treatment modalities have emerged, including cisplatin, a platinum molecule that has demonstrated effectiveness against UBC. Nevertheless, it has severe dose-limiting side effects, such as nephrotoxicity, among others. Since intracellular accumulation of platinum anticancer drugs is necessary for cytotoxicity, decreased uptake or enhanced efflux are the root causes of platinum resistance and response failure. Evidence suggests that genetic variations in any transporter involved in the entry or efflux of platinum drugs alter their kinetics and, to a significant extent, determine patients’ responses to them. This review aims to consolidate and describe the major transporters and their polymorphic variants in relation to cisplatin-induced toxicities and resistance in UBC patients. We concluded that the efflux transporters ABCB1, ABCC2, SLC25A21, ATP7A, and the uptake transporter OCT2, as well as the organic anion uptake transporters OAT1 and OAT2, are linked to cisplatin accumulation, toxicity, and resistance in urinary bladder cancer patients. While suppressing the CTR1 gene’s expression reduced cisplatin-induced nephrotoxicity and ototoxicity, inhibiting the expression of the MATE1 and MATE2-K genes has been shown to increase cisplatin’s nephrotoxicity and resistance. The roles of ABCC5, ABCA8, ABCC10, ABCB10, ABCG1, ATP7B, ABCG2, and mitochondrial SLC25A10 in platinum-receiving urinary bladder cancer patients should be the subject of further investigation.

The blood–retinal barrier (BRB) maintains neurovascular homeostasis by regulating solute and ion exchange between the retina and circulation. This selectivity depends on tight junctions (TJs), with claudin (Cldn) proteins forming the core structure that defines paracellular permeability. Distinct Cldn isoforms show cell-specific expression, with Cldn-5 predominating in the endothelial cells of the inner BRB and Cldn-19 is the signature Cldn in the retinal pigment epithelium forming the outer BRB. Disruption of these isoforms contributes to vascular leakage, inflammation, and neuronal loss across various ocular diseases. Cldn function in vascular homeostasis is multifaceted; barrier dysfunction does not always result from Cldn loss, as excessive expression or mislocalization, particularly of Cldn-5, can also impair BRB integrity. Cldns act as dynamic signaling hubs that respond to metabolic, oxidative, and mechanical stress and are regulated through VEGF, Wnt/β-catenin, and RhoA/ROCK pathways. This review summarizes current understanding of Cldn biology in retinal vascular regulation and highlights emerging therapeutic strategies aimed at stabilizing Cldn expression and junctional localization. Small molecules and blocking antibodies that enhance localization or prevent degradation are redefining barrier repair. Key questions remain regarding isoform specificity, inter-barrier communication, and systemic safety. Integrative omics and spatial imaging may reveal disease-specific Cldn signatures and guide molecular restoration of BRB integrity.

This study investigates the hormonal responses to academic stress by measuring Oxytocin (OXT) and cortisol levels in saliva among male university students. This research discusses how academic examination is a form of stress influencing the levels of hormones associated with general and social anxiety. The male participants involved in this experiment were between the ages of 20 and 26 years and met the highest criteria in terms of health. There were saliva collections, first during the non-examination period and then during an examination period. Cortisol and OXT levels were quantified using ELISA. Anxiety was assessed using Westside Test Anxiety Scale and the Liebowitz Social Anxiety Scale (LSAS). Results implied a significant rise in cortisol level in exams, especially among high-anxiety students, indicating a large amount of developed stress. Conversely, OXT levels decreased during exams, where the biggest decline occurred among high anxiety individuals. Data support the inverse association of anxiety level and OXT pointing toward the role of oxytocin as an anxiolytic. These results emphasize both the physiological impacts of academic stress and the differential involvement of cortisol and OXT in the responses to stress and anxiety, especially in highly anxious individuals. These effects should be further explored according to gender and during extended time under stress.