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Review
. 2023 Jun 21;12(7):1320.
doi: 10.3390/antiox12071320.

Green Tea Catechins as Therapeutic Antioxidants for Glaucoma Treatment

Tsz Kin Ng  1   2 , Kai On Chu  2   3 , Chi Chiu Wang  3 , Chi Pui Pang  1   2
Affiliations
Review

Green Tea Catechins as Therapeutic Antioxidants for Glaucoma Treatment

Tsz Kin Ng et al. Antioxidants (Basel). .

Abstract

Glaucoma is the leading cause of irreversible blindness and visual impairment, affecting more than 80 million individuals worldwide. Oxidative stress and inflammation-induced neurodegenerative insults to retinal ganglion cells are the main pathogenesis of glaucoma. Retinal ganglion cells, the retinal neurons transmitting the visual signals to the visual cortex in the brain, have very limited regeneration or recovery capacity after damages. Apart from intraocular pressure-lowering treatments, there is still no clinically effective treatment to rescue the degeneration of retinal ganglion cells in glaucoma. Dietary antioxidants are easily accessible and can be applied as supplements assisting in the clinical treatments. Catechins, a chemical family of flavonoids, are the phenolic compounds found in many plants, especially in green tea. The anti-oxidative and anti-inflammatory properties of green tea catechins in vitro and in vivo have been well proven. They could be a potential treatment ameliorating retinal ganglion cell degeneration in glaucoma. In this review, the chemistry, pharmacokinetics, and therapeutic properties of green tea catechins were summarized. Research updates on the biological effects of green tea catechins in cellular and animal experimental glaucoma models were reviewed. In addition, clinical potentials of green tea catechins for glaucoma treatment were also highlighted.

Keywords: EGCG; anti-inflammation; anti-oxidation; glaucoma; green tea; retinal ganglion cells.

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Conflict of interest statement

The authors declare no potential conflict of interest.

Figures

Figure 1
Figure 1
Structures of polyphenols, amino acids, and alkaloids that are present in green tea.
Figure 2
Figure 2
Resonance structures of epigallocatechin-3-gallate after reaction with reactive oxygen species.
Figure 3
Figure 3
Epigallocatechin-3-gallate interacts with various receptor/mediators to relieve inflammation and oxidation. The green arrow indicates the effects of EGCG on the oxidative stress.
Figure 4
Figure 4
The exposure level, maximum concentration, and elimination of total catechins in the plasma, ocular fluid, and tissues of Sprague–Dawley rats. (A) Relative area under the curve (AUC) levels of different catechins in the plasma after normalization by the corresponding input catechin dose in the GTE. Non-gallated levels were higher than of the gallated derivatives while epimers were higher than the non-epimers. (B) Relative AUC levels of catechins in vitreous and aqueous humor. Vitreous humor was selective to non-epimer but showed no selectivity on gallated and non-gallated catechins. No particular trend of catechin selectivity appeared in the aqueous humor. (C) Relative AUC levels of catechins in the retina, lens, cornea, and choroid–sclera. (D) Maximum concentration of catechins in the plasma, aqueous and vitreous humors, and (E) eye tissues after a single dose of 550 mg/kg of Sunphenon DCF-1 green tea extract administrated orally to rats. Star: the level of an epimer was significantly higher than the corresponding non-epimer or vice versa in the same ocular compartment (p < 0.05); Droplet: the level of a catechin was higher than the corresponding gallate derivative or vice versa in the same compartment; Oval: the level of one of the catechins was significantly higher in one compartment than the other compartment (p < 0.05). GC: (−)-gallocatechin; EGC: (−)-epigallocatechin; C: (+)-catechin; EC: (−)-epicatechin; EGCG: (−)-epigallocatechin-3-gallate; GCG: gallocatechin-3-gallate; and ECG: (−)-epicatechin-3-gallate.
Figure 5
Figure 5
Pathophysiological conditions in glaucoma and the retinal ganglion cell protective effect of green tea catechins in glaucoma. RGC: retinal ganglion cell; and IOP: intraocular pressure.
See this image and copyright information in PMC

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