Glutathione may prevent age-related, oxidative damage to ocular tissues but has poor corneal penetration. Hydrogel formulations were investigated to determine an optimized ocular delivery system. The rheology and texture profile of formulations were investigated at 25°C. The 1% w/v glutathione was incorporated into systems demonstrating desirable characteristics for ocular vehicles and physical characteristics re-determined. In vitro cumulative glutathione delivery across the bovine cornea was measured over 8 hours at 32°C in Franz diffusion cells. Carbopol-containing Poloxamer systems exhibited shear-thinning behavior desirable for ocular formulations whilst Polyvinyl alcohol (PVA) and Polyacrylic acid (PAA) systems exhibited Newtonian behavior. Of the glutathione-containing systems, 0.2% w/v Carbopol 1342 was the most viscous with a viscosity of 960 cP at a shear rate of 100 sec-1. All formulations significantly increased the amount of glutathione delivered across the cornea (relative to an aqueous solution of glutathione) with the exception of 0.1% w/v Carbopol 940 (p=0.12). Formulations containing 0.1% w/v Carbopol 934, 0.1% w/v Carbopol 1342 and 0.2% w/v Carbopol 940 improved penetration dramatically (ca. 30%); but were not significantly different from each other. Therefore, Carbopol and Poloxamer formulations demonstrated enhanced penetration of glutathione across the cornea. The 0.2% w/v C940-containing-Poloxamer formulation was determined to be the most promising drug delivery system for ocular delivery of glutathione.
Guanyu Chen, Teresa Hawke, Diana Wong, Jonathon Hwang, Katarina Jeftic, Min Hao Zhan and Jingyuan Wen*