The Role of Proteinase in Acanthamoeba keratitis and the Effect of Amniotic Membrane as a Proteinase Inhibitor

ABSTRACT

This study was performed to investigate the biochemical properties of Acanthamoeba proteinase, its role in the pathogenesis of Acanthamoeba keratitis and the therapeutic effect of the homogenate of amniotic membrane as a proteinase inhibitors. Acanthamoeba castellanii isolated from the keratitis patient was cultured in PYG medium, in which the excretory and secretory products were analysed. The secretory proteinases of A. castellanii wre identified using in vitro azocasein assay, activity-PAGE, and various protein substrate degradation assays, and one of them was purified and characterized. The pruified secretory proteinase was a kind of serine proteinase. Its molecular weight was 105 kDa and optimal pH was 8.5. It was able to degrade the various protein substrates such as fibronectin, IgA, IgG, fibrinogen. The various proteinase ingibitors and the amniotic membrane homogenates were tested in vitro against the purified seirne proteinase. The amniotic membrane homegenates markedly showed the inhibitory effect against the enzyme activity and this inhibitory effect was also revealed in animal study. In vivo study, this purified proteinase was infected into 14 pigmented rabbit corneas, pretreated with steroids. The corneal lesions induced by both of the purified proteinase and A. castellanii, showed similar clinical findings each other, in which the stromal infiltration and opacity with epithelial defect was revealed. These corneal lesions were significantly inhibited without any side effects of the amniotic membrane homogenates. Conclusively, Acanthamoeba proteinase was closely associated with the pathogenesis of Acanthamoeba keratitis. This study provides a successful animal model of Acanthamoeba keratitis using pigmented rabbit. And the fact that Acanthamoeba-induced corneal lesions were inhibited by the amniotic membrane homogenate, suggested that the amniotic membrane homogenate have the ability of the serine protinase inhibition further investigative studies are also necessary.