Proteoglycan synthesis by human corneal explants submitted to laser in situ keratomileusis (LASIK)

PURPOSE To evaluate the acute effects of laser in situ keratomileusis (LASIK) upon the synthesis of proteoglycans (PGs) and collagen fibril organization in human corneal explants. METHODS Human corneas that had been rejected for transplants were obtained at Banco de Olhos of Hospital São Paulo. For each eye pair, one cornea was submitted to refractive surgery, and the other was used as its matched control. After surgery, the corneas were excised from the eyes and immediately placed in a Ham F-12 nutrient mixture containing (35)S-sulfate for the metabolic labeling of PGs. After 24 h incubation, PGs were extracted and identified by a combination of agarose gel electrophoresis and enzymatic degradation with protease and specific glycosaminoglycan lyases. Histopathological and birefringence analysis were performed in fixed tissue slices. RESULTS A marked decrease in (35)S-sulfate incorporation in PGs was observed in corneal explants that received LASIK, especially concerning dermatan sulfate-PGs, with keratan sulfate- and heparan sulfate-PG synthesis reduced to a lower degree. Only low molecular weight PGs were present in the corneas, both before and 24 h after LASIK. No sign of wound healing processes were observed, but a marked change in corneal birefringence was seen following LASIK treatment. CONCLUSIONS Laser application led to decreased PG biosynthesis in human corneal explants, with marked changes in the collagen fibril organization, as revealed by changes in the tissue birefringence.