We present the results of the first evaluation of human placenta extracted basic fibroblast growth factor (bFGF) in a rabbit corneal epithelium wound-healing model. Healing dose-response experiments after selective epithelial wounding with iodine vapors demonstrated that bFGF accelerated the repair process in a saturable manner. Corneal binding of topically applied 125I-labeled bFGF was investigated using radioassay and autoradiographic techniques. Basic FGF was shown to bind specifically to denuded epithelial basement membrane in a very stable fashion and not to the intact epithelium. No transfer of the topical bFGF to the aqueous humor or any intraocular structure could be observed. The stability of this interaction was further demonstrated by reextracting and characterizing the labeled factor from treated corneas. The specificity of the fixation was documented by in vivo topical competition with unlabeled bFGF or heparin. We propose that bFGF-basement membrane interactions play a role in corneal wound healing.
Basic and acidic fibroblast growth factor (bFGF, aFGF) binding sites were determined in frozen sections of normal and keratoconus corneas. After incubation with I-125 radiolabelled growth factors, corneal binding sites were revealed by autoradiography. The growth factors were localized mainly to Descemet's membrane and to the epithelial basement membrane. FGF binding sites were generally similar in normal and keratoconus corneas. The binding specificity was demonstrated by competitive inhibition experiments with an excess of unlabelled growth factors. The binding sites were sensitive to pretreatment of the corneal sections with heparitinase. We have attributed FGF's basement membrane affinity to one of its constituents, proteoheparan sulfate. Proteoheparan sulfate, laminin, collagen type IV, and fibronectin were all revealed by immunofluorescent techniques. While keratoconus cornea stroma had less laminin but more fibronectin than normal corneas the main difference lied in type IV collagen which was overexpressed in keratoconus epithelium.
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