Iqra Vaid

Background: Diabetic retinopathy (DR) is a leading cause of vision loss, affecting nearly one-third of individuals with type I and II diabetes.¹ It results from chronic hyperglycemia, which induces oxidative stress and microvascular damage in the retina. A major source of reactive oxygen species (ROS) in this process is the NADPH oxidase (NOX) enzyme family, particularly NOX4, which is overactivated in diabetic retinal endothelial cells.² NOX4-driven ROS production contributes to vascular leakage, inflammation, and abnormal neovascularization.¹ While current treatments, such as anti-VEGF therapy, provide some benefit, they are limited by incomplete response rates and high treatment burden with repetitive injections. This underscores the need to target upstream drivers like oxidative stress for prevention and treatment. Inhibiting NOX4 may offer a more effective and durable strategy for managing DR and preventing vision loss.

Objective: To evaluate the therapeutic potential of NOX4 inhibitors in the treatment of diabetic retinopathy.

Search Methods: A PubMed search (2018–2025) was conducted using the keywords: “NOX4,” “diabetic retinopathy,” “oxidative stress,” “NADPH oxidase,” and “retinal vascular dysfunction.”

Results: Evidence strongly implicates NOX4 as a key driver. Genome-wide association studies have identified NOX4 gene variants that correlate with severity of DR.³ In endothelial cells, NOX4 overexpression increases oxidative stress, promotes vascular leakage, and induces apoptosis.⁴ Conversely, NOX4 knockout in diabetic animal models significantly reduces oxidative stress, VEGF expression, and retinal vascular damage.³ Under hyperglycemic conditions, NOX4 activation mediated by CCN1 disrupts VE-cadherin, a key protein maintaining endothelial junctions.⁶ Disruption of this blood-retinal barrier (BRB), an early feature of DR, leads to vascular leakage and macular edema, which can distort and impair central vision. Selective NOX4 inhibitors, such as GLX7013114 and GKT137831, help preserve vascular integrity and show promise in slowing DR progression.⁵⁻⁷ Emerging delivery methods, including topical and oral formulations, offer less invasive alternatives, though further DR-specific clinical trials are needed to confirm their safety and efficacy.

Conclusions:

NOX4 upregulation contributes to oxidative stress, VEGF overexpression, and vascular damage in diabetic retinopathy. While current anti-VEGF therapies have limitations, selective NOX4 inhibition offers a promising alternative. Targeting NOX4 may improve clinical outcomes by addressing upstream oxidative mechanisms activated by hyperglycemia. Future research should focus on clinical translation, safety, and delivery strategies of NOX4 inhibition.

Works Cited:

1. Tang Q, Buonfiglio F, Böhm EW, Zhang L, Pfeiffer N, Korb CA, Gericke A. Diabetic Retinopathy: New Treatment Approaches Targeting Redox and Immune Mechanisms. Antioxidants. 2024; 13(5):594. https://doi.org/10.3390/antiox13050594
2. Peng J-J, Xiong S-Q, Ding L-X, Peng J, Xia X-B. Diabetic retinopathy: Focus on NADPH oxidase and its potential as therapeuticEuropean Journal of Pharmacology. 2019;853:381-387. doi:10.1016/j.ejphar.2019.04.038
3. Meng W, Shah KP, Pollack S, et al. A genome-wide association study suggests new evidence for an association of the NADPH Oxidase 4 (NOX4) gene with severe diabetic retinopathy in type 2 diabetes. Acta Ophthalmol. 2018;96(7):e811-e819. doi:10.1111/aos.13769
4. Tang X, Wang J, Abboud HE, Chen Y, Wang JJ, Zhang SX. Sustained upregulation of endothelial Nox4 mediates retinal vascular pathology in type 1 diabetes. Diabetes. 2023;72(1):112-125. doi:10.2337/db22-0194. PMID: 36321974; PMCID: PMC9797318.
5. Dionysopoulou S, Wikstrom P, Bucolo C, et al. Topically administered NOX4 inhibitor, GLX7013114, is efficacious in treating the early pathological events of diabetic retinopathy. 2023;72(5):638-652. doi:10.2337/db22-0515
6. Li H, Li T, Wang H, et al. Diabetes promotes retinal vascular endothelial cell injury by inducing CCN1 expression. Front Cardiovasc 2021;8:689318. doi:10.3389/fcvm.2021.689318
7. Appukuttan B, Ma Y, Stempel A, Ashander LM, Deliyanti D, Wilkinson-Berka JL, Smith JR. Effect of NADPH oxidase 1 and 4 blockade in activated human retinal endothelial cells. Clin Exp Ophthalmol. 2018;46(6):652-660. doi:10.1111/ceo.13155