Introduction: Corneal diseases cause inflammation and vascularization that can result loss of vision and bacterial growth. Catechin is one of the polyphenol molecules from nature that has advantageous biochemical properties such as anti-angiogenesis, anti-oxidant, and anti-inflammatory that are suitable for corneal treatment for clear vision. Despite the advantageous properties and biocompatibility of polyphenols, catechin has not been used in corneal treatment as an eyedrop-based formulation due to very low solubility. We anticipated that increase of catechin solubility would increase bioavailability as a corneal drug that requires optical transparency. In this study, we have enhanced the solubility of catechin in aqueous with poly(ethylene glycol) (PEG) through complex (PEG/catechin) formation by simple mixing. The advantageous biochemical properties of catechin remained effective which was confirmed from in vivo study.
Materials and Methods: Catechin and PEG (M.W. 4400 Da) were purchased from Sigma-Aldrich. Catechin was dissolved in methanol at concentration of 10 mg/ml. PEG was dissolved in distilled and deionized water (DDW) at various concentrations of 2, 4, 10, 20 mg/ml, respectively. Catechin solution to PEG solution (1:5 v/v) are mixed vigorously for 5 min to make PEG/catechin weight ratios of 1, 2, 5, and 10, respectively. After homogeneously mixing, methanol was evaporated by Centrifan at 50 oC for 120 min. Finally the remaining solution was lyophilized and kept in moisture-free desiccator before use. The powder was then re-solubilized in DDW for measuring the solubility test by UV-vis spectroscopy and morphologies by TEM, DLS. Also, we performed in vivo test for corneal regenerations. PEG/catechin is applied on damaged rabbit cornea for four times a day for a week.
Results: PEG/catechin 5 and 10 show excellent solubility of 50 mg/ml as shown in Fig 1. The relative transmittance is close to 1 which indicates the transparency is similar to DDW. PEG/catechin 2 showed lower solubility of < 10 mg/ml. Catechin and PEG/catechin 1 showed very low solubility of < 1 mg/ml. The morphology of PEG/catechin shows that particle is formed with size of about 100~200 nm regardless of weight ratio of PEG/catechin. Particle is not observed for pure catechin. In vivo study on rabbit corneal model shows the damaged area is reduced by PEG/catechin.
Discussion: The solubility of catechin is increased as the weight ratio of PEG/catechin is increased. PEG/catechin 5 and 10 increase solubility of catechin a hundred times. The optimal weight ratio of PEG/catechin is determined to be 5 because catechin is dissolved at high concentration. TEM analysis shows that particle is formed from PEG/catechin, yet, the size of particle is independent from the weight ratio. The formation of PEG/catechin is probably due to hydrogen bonding between oxygen of PEG and hydroxyl of catechin. Reduced damaged area of rabbit cornea indicates that anti-inflammatory and anti-angiogenic properties of catechin is effective.
Conclusion: In this study, we have developed solubilized catechin for ocular drugs by adding PEG. The PEG/catechin exhibits a hundred times increase in solubility (50 mg/ml). The PEG/catechin complex maintains advantageous properties. Therefore, bioavailability of catechin is enhanced and broadened its application.
References:
[1] H. Mok et al. PEG-Assisted DNA Solubilization in Organic Solvents for Preparing Cytosol Specifically Degradable PEG/DNA Nanogels, Bioconjugate Chemistry 2006, 17, 1369-1372