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Purpose: To determine the effect of decorin on oxidative stress and apoptosis of human lens epithelial (HLE) cells under high glucose condition. Methods: HLE cell line (HLEB3) was incubated in normal glucose (5.5 mM) or high glucose (60 mM) medium. Decorin (50 nM) was applied 2 hours before high glucose medium was added. Apoptosis detection was executed by flow cytometry and western blotting (analysis of bcl-2 and bax). Oxidative stress level was measured by the generation of reactive oxygen species (ROS), glutathione peroxidase (GSH) and superoxide dismutase (SOD). P38 mitogen-activated protein kinase (MAPK) phosphorylation, the expression of p22phox of HLE cells and human lens anterior capsules were detected by western blotting. Small interfering RNA transfection to p22phox and p38 MAPK was also carried out on HLEB3. Results: High glucose caused HLE cells oxidative stress and apoptosis exhibiting the increase of apoptotic cells and ROS production and decrease of bcl-2/bax ratio, GSH/GSSG ration and SOD activity. P22phox and phospho-p38 MAPK were upregulated in high glucose treated HLEB3 cells. Knocking down p22phox or p38 by siRNAs can reduce high glucose induced cell apoptosis and oxidative stress level. Silencing p22phox by siRNA can downregulate the phosphorylation of p38 MAPK. Decorin can inhibit the apoptosis, oxidative stress level and the induction of p22phox and phospho-p38 of HLEB3 induced by high glucose. Furthermore, the expression of p22phox and p38 were found significantly increased in lens anterior capsules of diabetic cataract patients compared to that of normal age-related cataract patients. Conclusions: Results showed that p22phox-p38 pathway may be participated in high glucose induced lens epithelial cell injury, decorin may inhibit the high glucose induced apoptosis and oxidative stress injury by suppressing this pathway in part. [ABSTRACT FROM AUTHOR]