Loss of stromal glycosaminoglycans during corneal edema

This study tried to determine if glycosaminoglycans (GAGs) are released from the rabbit stroma during corneal edema. The GAGs of rabbit corneas were labeled in situ using anterior-chamber injections of 35S-sulfate and 3H-glucosamine. Labeled corneal pairs were excised and the endothelium perfused in vitro in the specular microscope. Edema was induced in one cornea by perfusion with a calcium-free balanced salt solution; the control cornea was perfused with glutathione bicarbonate Ringer's (GBR). Corneal thickness was measured every 15 minutes during the 3-hour perfusion period, and perfusate fractions were collected from each cornea and analyzed for the presence of GAGs. Edematous corneas swelled from 438 +/- 14.8 microns to 688 +/- 10.6 microns compared with control corneas (427 +/- 4.7 microns to 454 +/- 7.2 microns). Total 3H-glucosamine (4.00 +/- 0.68%) and 35S-sulfate (10.36 +/- 0.92%) released from the edematous corneas during perfusion exceeded that lost by control corneas (1.92 +/- 0.18% for 3H-glucosamine; 3.23 +/- 0.52% for 35S-sulfate). Enzymatic digestion studies showed the presence of keratan sulfate in the edematous perfusates. The results suggest that increased loss of radiolabeled components from edematous corneas represent a loss of stromal GAGs and possibly GAG fragments. Therefore, corneal edema involves loss of GAGs and water uptake.