Methods to Improve Vitamin C Stability in Hydrogel Vitreous Substitutes to Prevent Cataract

Abstract

Purpose : Vitamin C (ascorbic acid) has recently been noted as a vital antioxidant in the vitreous humor, and its levels are significantly depleted after vitrectomy. We have explored adding vitamin C to hydrogel vitreous substitutes as a potential cataract-preventing therapeutic. However, vitamin C degrades rapidly in solution, limiting its long-term effectiveness. This study aims to extend vitamin C stability to at least two weeks by physical and chemical means, encapsulating therapeutic in multilayered particles and blending with glutathione.

Methods : Copolymers of poly(ethylene glycol) methacrylate (PEGMA) and poly(ethylene glycol) diacrylate (PEGDA) were synthesized and loaded with physiological levels of vitamin C (2 mM). For physical protection of vitamin C, nanoparticles were prepared by crosslinking chitosan with sodium tripolyphosphate, loading with vitamin C, and coating with alternating layers of alginate and chitosan. Alternatively, glutathione solutions (1, 2, 4, 10 mM) were used to chemically “recycle” vitamin C, as glutathione is naturally found in the lens. Particles and vitamin C solutions were incubated at 37^oC. At predetermined times (0, 1, 2, 3, 4, 7, 8, 9, 11, and 14 days), vitamin C remaining was determined using a microplate reader at 265 nm wavelength.

Results : PEGDA and PEGDA-co-PEGMA hydrogels were injectable and had similar optical and mechanical properties as the natural vitreous humor. When vitamin C was added in solution, it degraded completely by day 5. The hydrogels and particles provided some protection to vitamin C, extending release to 7 days. Glutathione provided the longest extension to vitamin C efficacy, with 70% remaining after 14 days when the glutathione concentration was at least 4 mM.

Conclusions : While multilayered particles provided some protection to vitamin C, mixing with glutathione significantly improved the stability of vitamin C, enabling release for at least two weeks. These results indicate glutathione might be an effective addition to current vitamin C-loaded hydrogel vitreous substitutes to improve the stability of vitamin C and potentially prevent oxidative stress after vitrectomy.

This is a 2020 ARVO Annual Meeting abstract.

 

Vitreous substitutes retained gel-like consistency after injection (A) and appeared to be similar to the natural vitreous (B). Encapsulating in particles and mixing with glutathione both improved stability of vitamin C, although chemical protection was more effective (C).