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PURPOSE - Restructuring of extracellular matrix at actively extending blood vessel tips involves secretion of plasminogen activator (PA). Findings in earlier studies conducted in the authors' laboratory have suggested that angiostatic steroids suppress the PA activity essential for the invasive aspect of angiogenesis by increasing synthesis of plasminogen activator inhibitor (PAI)-1. This experiment was designed to test the effect of administration of exogenous PAI-1 on retinal neovascularization (NV) in an animal model of retinopathy of prematurity (ROP).
METHODS - At birth, Sprague-Dawley rats were placed into incubators and exposed to an atmosphere alternating between 50% and 10% O(2) every 24 hours. After 14 days, the animals were removed to room air, at which time each received a single intravitreal injection of 5 microL of buffer vehicle or one of five doses of PAI-1, ranging from 3.0 microg/mL to 2.0 mg/mL. Animals were killed 6 days later, and retinal NV was assessed using adenosine diphosphatase (ADPase) histochemical staining.
RESULTS - Retinal neovascularization decreased with increasing PAI-1 dosage. The most effective dose tested (2.0 mg/mL) caused a 52% reduction in retinal NV relative to vehicle (P < 0.005). Normal vasculogenesis, as determined by measuring retinal vascular area, was unaffected.
CONCLUSIONS - PAI-1 inhibits pathologic angiogenesis without adversely affecting normal vasculogenesis, an attractive feature for ROP therapies. Moreover, PAI's relationship to matrix metalloproteinases, which are also implicated in angiogenesis, suggests that the proteolytic aspect of the process may provide additional downstream therapeutic targets.