OVEREXPRESSION OF ALDEHYDE REDUCTASE PROTECTS PC12 CELLS FROM THE CYTOTOXICITY OF METHYLGLYOXAL OR 3-DEOXYGLUCOSONE

The glycation reaction (Maillard reaction) plays a major role in diabe tic complications, since some reaction intermediates are responsible f or the modification and cross-linking of long-lived proteins, resultin g, in turn, in a deterioration of normal cell function. The reaction i ntermediates include methylglyoxal (MG) and 3-deoxyglucosone (3-DG), b oth of which are cytotoxic dicarbonyl compounds and are elevated durin g hyperglycemia. Aldehyde reductase (ALR) catalyzes the reduction of b oth compounds. To examine the intracellular role of ALR in the diabeti c complications of neural cells, its gene was overexpressed in rat phe ochromocytoma PC12 cells, which normally express a low level of ALR. W estern blot analysis showed that ALR protein in the ALR gene-transfect ed cells was more than twice as much as in the control cells. In the p arental cells, cytotoxicity, including apoptotic cell death, which was determined by fluorescent microscopy using the fluorescent DNA bindin g dye Hoechst 33258, was observed at 100 mu M MG. In the ALR gene-tran sfected cells, the cytotoxicity of both MG and 3-DG and apoptotic cell death were decreased. This suggests that intracellular ALR protects n eural cells from the cytotoxicity of 3-DG or MG, and that neural cells , which normally express a low level of ALR, might be susceptible to d iabetic complications caused by intermediate products of the Maillard reaction, such as 3-DG and MG.