Aliphatic β-nitro alcohols for non-enzymatic collagen cross-linking of scleral tissue

The success of riboflavin photochemical cross-linking of the cornea in treating keratoconus and post-surgical keratectasia has prompted interest in cross-linking scleral tissue with a potential application to stabilize myopic progression. Applying an UVA light source to the sclera is difficult, particularly in the posterior region. An alternate pharmacologic approach to scleral cross-linking may be possible. The present study was undertaken in order to identify nitrite related compounds capable of inducing scleral tissue cross-linking and to gain information regarding the possible chemical mechanisms involved. 8 × 4 mm strips of porcine and human sclera were incubated in various concentrations of nitrite related agents (1–100 mM) at 37 °C. pH 7.4 was used for all experiments except those involving NaNO2. Following a 24–96 h incubation period, the samples were tested for cross-linking effects using thermal shrinkage temperature (Ts) analysis. Several compounds were studied including NaNO2, 2-nitroethanol, 2-nitro-1-propanol, 3-nitro-2-pentanol, 2-nitrophenol, 2-nitroethane, 2-aminoethanol, isopentyl nitrite, DPTA/NO, DETA/NO, and urea, a nitrous acid trap. The results indicate that short chain aliphatic β-nitro alcohols (2-nitroethanol, 2-nitro-1-propanol, and 3-nitro-2-pentanol) are particularly effective cross-linking agents at pH 7.4, showing both time and concentration dependent effects. Furthermore, nitrosation does not appear to induce tissue cross-linking. In conclusion, aliphatic β-nitro alcohols can cross-link scleral tissue at physiologic pH and temperature. Since β-nitro alcohols are known to have reasonable toxicity profiles, these agents could find utility as pharmacologic cross-linking agents for scleral thinning disease.