Digoxin Attenuates Ocular Hypertension via Ferroptosis Inhibition: Mechanistic Insights and Research Implications

Study Background and Research Question

Glaucoma is the leading cause of irreversible blindness worldwide, with primary open-angle glaucoma (POAG) representing its most prevalent and insidious form. Elevated intraocular pressure (IOP)—primarily due to impaired aqueous humor outflow—remains the central risk factor for POAG progression. Dysfunction of trabecular meshwork cells (TMCs), including aberrant extracellular matrix (ECM) turnover and heightened oxidative stress, has been increasingly implicated as a driver of this resistance and subsequent IOP elevation. Despite advances in understanding glaucoma's pathophysiology, the precise molecular mechanisms underlying TMC injury and IOP dysregulation remain incompletely defined.

Emerging evidence points to ferroptosis, an iron-dependent form of regulated cell death characterized by excessive lipid peroxidation, as a key pathway in TMC damage. The reference study (Zhou et al., 2026) directly addresses whether targeting ferroptosis could offer a therapeutic strategy for POAG, and whether small-molecule inhibitors such as digoxin can modulate this process to protect TMCs and reduce IOP.

Key Innovation from the Reference Study

The primary innovation of Zhou et al. lies in establishing a causal and functional link between iron-mediated ferroptosis and trabecular meshwork dysfunction in POAG, and in identifying digoxin—a cardiac glycoside and ATPase inhibitor—as an effective therapeutic candidate for inhibiting ferroptosis in this context. This work integrates Mendelian randomization (MR) genetic data, clinical biomarker analysis, transcriptomic profiling, and small-molecule screening to delineate the ferroptosis pathway in glaucoma and to validate a novel intervention.

Methods and Experimental Design Insights

The study employed a multi-tiered experimental design, combining population genetics, patient-derived biospecimens, bioinformatics, and in vitro/in vivo functional validation:

• Mendelian Randomization (MR) Analysis: East Asian genome-wide association study data were interrogated to explore the causal relationship between blood metal levels (particularly iron) and POAG risk.
• Biochemical Measurement in Human Samples: Aqueous humor from POAG patients was assayed for ferroptosis-related biomarkers—iron, malondialdehyde (MDA), glutathione peroxidase 4 (GPX4), and glutathione (GSH)—using ELISA.
• Transcriptomic Integration and Network Analysis: Differential gene expression analysis of trabecular meshwork tissue was cross-referenced with ferroptosis-related gene sets (FerrDb), followed by protein–protein interaction (PPI) analysis to identify functional hubs.
• Compound Screening and Molecular Docking: The CMap platform and structural modeling were used to identify small molecules targeting the key ferroptosis pathway. Digoxin emerged as a lead candidate.
• In Vitro Validation: Human trabecular meshwork cells (HTMCs) exposed to H₂O₂ were used to model oxidative injury and ferroptosis. The protective effects of digoxin were examined by measuring MDA and GPX4 levels and assessing cell viability.
• In Vivo Efficacy: Digoxin was formulated as topical ophthalmic drops and administered to chronic ocular hypertension (COH) rat models. IOP was monitored to assess therapeutic benefit.

Protocol Parameters

• MR data analysis: Based on East Asian GWAS datasets; assess serum iron association with POAG risk.
• Biomarker quantification: ELISA-based measurement of iron, MDA, GPX4, and GSH in aqueous humor from POAG patients and controls.
• In vitro ferroptosis model: Treat HTMCs with H₂O₂ (concentration typically 100–500 μM) to induce oxidative stress and ferroptosis.
• Compound application: Digoxin dosing in vitro and in vivo based on prior pharmacodynamic studies; topical administration to rats twice daily for up to 2 weeks.
• Cell viability measurement: Employ sensitive assays (e.g., water-soluble tetrazolium salt-based methods) to quantify live cell populations post-treatment.

Core Findings and Why They Matter

The reference study provides several pivotal discoveries:

• MR analysis revealed that elevated serum iron is causally linked to increased POAG risk.
• Patients with POAG displayed higher iron and MDA and lower GPX4 and GSH in their aqueous humor, consistent with active ferroptotic injury.
• Transcriptomics identified 14 differentially expressed, ferroptosis-related genes in TM tissue. Hub genes—SLC2A3, SCD, and HBA1—emerged as key regulators linking ferroptosis to TMC dysfunction.
• CMap and docking analyses pinpointed digoxin as a potential ferroptosis inhibitor. Functionally, digoxin reduced MDA accumulation and restored GPX4 expression in H₂O₂-stressed HTMCs, thereby protecting against ferroptotic cell death.
• Topical digoxin treatment significantly lowered IOP in COH rat models, supporting in vivo efficacy.

These results highlight ferroptosis as a central mechanism in POAG pathogenesis and establish digoxin as a promising candidate for repurposing in glaucoma therapy. The mechanistic pathway—centered on SLC2A3/SCD/HBA1—offers new molecular targets for future drug discovery and biomarker development.

Comparison with Existing Internal Articles

Several recent internal articles have explored the value of advanced cell viability assays in mechanistic research, including the study of ferroptosis and related cell death pathways. For example, "Cell Counting Kit-8 (CCK-8): Unveiling Ferroptosis and Inflammation in Cell Viability Assays" details how sensitive, water-soluble tetrazolium salt-based assays enable quantitative analysis of ferroptosis in vitro, paralleling the methodologies used in the reference study. Similarly, "Rethinking Cell Viability: Mechanistic Insights and Strategic Approaches" underscores the importance of reproducible cell viability measurement for translational discovery in oxidative stress and neurodegenerative models.

While these articles focus on assay platform optimization and workflow strategy, the Zhou et al. study provides a direct translational link by demonstrating how targeted inhibition of ferroptosis with a clinically approved drug can impact disease-relevant endpoints such as IOP. Integrating sensitive cell proliferation and cytotoxicity detection kits into such workflows, as recommended in internal resources, is essential for robust mechanistic validation of therapeutic hypotheses.

Limitations and Transferability

Despite its comprehensive approach, the study has notable limitations. First, the in vivo efficacy of digoxin was demonstrated only in a rat model of chronic ocular hypertension, which may not fully recapitulate the complexity of human POAG. Second, while hub genes were identified via transcriptomic analysis, causal relationships between specific genetic variants and therapeutic response require further validation in larger, diverse patient cohorts. Third, the safety and pharmacokinetic profile of topical digoxin in human eyes remains unexplored, and off-target effects beyond TM cells warrant careful evaluation.

Transferability to other contexts (e.g., non-POAG forms of glaucoma, other neurodegenerative diseases) should be approached cautiously. The mechanistic insights regarding iron metabolism, lipid peroxidation, and ferroptosis, however, are likely relevant to multiple forms of oxidative tissue injury.

Why this cross-domain matters, maturity, and limitations

The cross-domain application of cardiovascular drugs (digoxin) to ophthalmic disease highlights the growing convergence between systemic pharmacology and localized cell death modulation. However, this bridge is currently supported only by preclinical and genetic data, and clinical translation will require rigorous safety and efficacy trials. As such, the maturity of this therapeutic approach is promising but still experimental.

Research Support Resources

For researchers seeking to investigate ferroptosis, oxidative stress, or cell viability in glaucoma or related models, robust quantitative methods are essential. The Cell Counting Kit-8 (CCK-8) (SKU K1018) from APExBIO provides a sensitive, water-soluble tetrazolium salt-based assay suitable for evaluating cell proliferation and cytotoxicity in vitro. Such platforms, as discussed in internal articles, are invaluable for mechanistic studies into ferroptosis and can facilitate workflow optimization in preclinical glaucoma research.