Green Tea Catechins as Therapeutic Antioxidants for Glaucoma Treatment

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TL;DR

This review summarizes the chemistry, pharmacokinetics, and therapeutic properties of green tea catechins, particularly EGCG, in the context of glaucoma. Preclinical evidence from cellular and animal models shows that green tea catechins can reduce oxidative stress and inflammation, protect retinal ganglion cells, and improve survival after injury. Clinical studies suggest potential benefits, such as improved electroretinogram amplitudes and reduced intraocular pressure, but further trials are needed to confirm efficacy and safety.

Full summary

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**Background:** Glaucoma is a leading cause of irreversible blindness, affecting over 80 million people worldwide, with projections exceeding 100 million by 2040. The disease is characterized by progressive loss of retinal ganglion cells (RGCs) and their axons, driven by oxidative stress and inflammation. Current treatments focus on lowering intraocular pressure (IOP), but many patients continue to experience RGC degeneration despite good IOP control. Green tea catechins, especially epigallocatechin-3-gallate (EGCG), are potent antioxidants and anti-inflammatory agents that may offer neuroprotection. This review examines the chemistry, pharmacokinetics, and therapeutic potential of green tea catechins for glaucoma.

**Methods:** The authors conducted a narrative review of the literature, summarizing studies on green tea catechin chemistry, pharmacokinetics in ocular tissues, and therapeutic effects in cellular and animal models of glaucoma. They also reviewed clinical trials and epidemiological studies related to green tea consumption and glaucoma risk. Key data sources included in vitro studies using RGC-5 cells, animal models (NMDA excitotoxicity, optic nerve axotomy/crush, acute and chronic IOP elevation), and human clinical trials.

**Key Results:** - **Chemistry and Pharmacokinetics:** EGCG is the most abundant and biologically active catechin, with eight hydroxyl groups that scavenge reactive oxygen species. Its standard reduction potential (0.104 V) is lower than glutathione (0.310 V), indicating high antioxidant activity. After oral administration, catechins are absorbed in the small intestine, undergo extensive metabolism, and have low bioavailability. In rats, a single dose of 550 mg/kg green tea extract (GTE) distributed catechins to ocular tissues, with maximum concentrations (Cmax) of GC and ECG reaching hundred micromolar levels in choroid–sclera and retina, but only 1.5 μM in the lens. EGCG levels in fetal eye reached 0.83 μM. Elimination rates varied; for example, GC elimination rate was 0.2–2.4 h⁻¹ in retina, while ECG in vitreous humor was 0.04–0.2 h⁻¹. - **Therapeutic Properties:** Catechins exhibit both antioxidant and pro-oxidant effects. EGCG activates Nrf2/HO-1 pathways and suppresses NF-κB and MAPK signaling, reducing inflammatory cytokines (IL-1β, TNF-α, IL-6). In a rat model, GTE suppressed microglial activation and reduced pro-inflammatory cytokines in retina and vitreous humor after LPS induction. GTE also attenuated uveitis in a murine model of experimental autoimmune uveoretinitis. - **Cellular Models:** In RGC-5 cells, 50 μM EGCG significantly reduced apoptosis and ROS production induced by 400 μM hydrogen peroxide. EGCG (2.5–10 μg/mL) improved cell survival after hydrogen peroxide and UV insults. EGCG IC50 for lipid peroxidation was 0.8–2.5 μM. - **Animal Models:** In NMDA-induced excitotoxicity, intraperitoneal EGCG (25 mg/kg) increased ganglion cell layer density. In optic nerve axotomy, 50 mg/kg EGCG attenuated RGC loss by 12% and reduced neuronal NOS and Bax expression. In optic nerve crush, EGCG-treated rats showed significantly higher RGC density at days 7, 14, and 28 post-injury. In chronic IOP elevation (microbead injection), mice fed EGCG-supplemented water had higher RGC density at days 15 and 27. In acute IOP elevation (150 mm Hg for 60 min), 50 mg/kg EGCG reduced RGC death by 10%. In rabbits, 15 mg/kg EGCG reduced TUNEL-positive cells and increased Nrf2 nuclear translocation. - **Clinical Studies:** A randomized placebo-controlled trial (NCT00476138) in POAG patients found that oral EGCG (200 mg/day for 3 months) increased pattern-evoked electroretinogram amplitudes compared to placebo, but standard automated perimetry showed no significant changes. A study in Lithuania reported that 400 mg GTE or EGCG reduced IOP after 1–2 hours. Epidemiological data from the Nurses’ Health Study and Health Professionals Follow-up Study showed that consuming ~2 cups of tea daily was associated with an 18% lower POAG risk, and the US NHANES 2005–2006 reported a 74% decreased odds of glaucoma with daily hot tea consumption. However, the Korea NHANES and Rotterdam Study found no significant associations.

**Clinical Implications:** Green tea catechins, particularly EGCG, demonstrate neuroprotective effects in preclinical glaucoma models by reducing oxidative stress, inflammation, and RGC death. Clinical evidence is limited but suggests potential benefits in improving retinal function and lowering IOP. However, challenges include low bioavailability, potential hepatotoxicity at high doses, and the need for more rigorous clinical trials. The authors propose that green tea catechins could serve as co-adjuvant therapy alongside IOP-lowering treatments, but caution that further research is needed to establish optimal dosing, safety, and efficacy.