Aldose Reductase Inhibition Attenuates TNF- and High Glucose–induced Cytotoxic Signals in Human Lens Epithelial Cells

Abstract

Abstract: : Purpose: Stress signals by the cytokines such as TNF-α (elevated during diabetes) and hyperglycemia are the major contributors to inflammation and secondary diabetic complications. It is believed that the cytotoxicity is mediated by increased oxidative stress that causes lipid peroxidation and generation of lipid derived aldehydes (LDA) which are reduced by aldose reductase (AR). The purpose of this study was to investigate the mechanisms through which AR mediates the high glucose and TNF-α signals that cause cytotoxicity to human lens epithelial cells (HLEC). Methods: Growth arrested HLEC were cultured without or with AR inhibitors followed by stimulation with TNF-α or high glucose. The apoptosis was determined by caspase-3 activation and nucleosomal degradation. Electrophoretic mobility gel shift assays were performed to determine the activation of NF-ΚB. Western blot analyses were carried out to identify JNK, p38 MAPK and IΚB-α using respective antibodies. Results: Inhibition of AR by sorbinil/ tolrestat or antisense ablation attenuated TNF-α and hyperglycemia-induced apoptosis in HLEC. Further, TNF-α and high glucose-induced PKC activation /IΚB-α phosphorylation and NF-ΚB activation were attenuated by inhibition of AR. Inhibition of AR also inhibited the phosphorylation of JNK and P38 MAPK. However, the Phorbol ester-induced PKC activation and down stream signals were not affected by AR inhibition suggesting that AR is an obligatory mediator of cytokine and hyperglycemic signals that act upstream to PKC. Similarly, we have shown that AR mediates the mitogenic and cytotoxic signals in vascular smooth muscle cells and vascular endothelial cells. Conclusions: Our results identify a novel mechanism of the pathophysiology of diabetic complications mediated by AR, possibly upstream of PKC.

Keywords: apoptosis/cell death • signal transduction • diabetes