The mechanism of accelerated corneal epithelial healing by human epidermal growth factor

The effect of biosynthetic human epidermal growth factor (hEGF) was investigated on a 10-mm diameter corneal epithelial defect model in rabbits. Topical application of over 10 micrograms/ml of hEGF five times a day significantly enhanced the epithelial healing rate, in a dose-dependent manner. The maximum healing rate was observed in eyes treated with 20 micrograms/ml of hEGF (1.59 +/- 0.26 mm2/h), whereas application of less than 5 micrograms/ml of hEGF did not increase the rate of epithelial regeneration compared statistically with control vehicles (1.03 +/- 0.24 mm2/h). S-phase analysis indicated that hEGF treatment induced a high rate of epithelial replication, particularly near the limbal region, during 12 to approximately 24 hours after wounding, followed by massive cell replication from 1 mm behind the leading edge through the limbus during 24-48 hours. The change in number and distribution of S-phase cells thereafter did not essentially differ between hEGF-treated and control groups. In concordance with the S-phase analysis, there was a statistically significant increase in the DNA content in regenerating epithelium at 48 and 72 hours in the hEGF-treated group. These findings indicate that hEGF-induced acceleration of large corneal epithelial wound healing is associated with about twofold cell replication in the regenerating epithelium during 24 to approximately 48 hours after wounding. It is concluded that cell proliferation induced by hEGF, particularly that in limbal and peripheral corneal epithelial cells, may play an important role in accelerating epithelial healing.