Glycation에 의한 세포사멸 및 손상에서 mitochondrial NADP+-dependent isocitrate dehydrogenase의 방어 작용
Protective role of mitochondrial NADP+-dependent isocitrate dehydrogenase against glycation0induced apoptosis and oxidative damage+
효소 Glycation mitochondrial NADP+-dependent isocitrate dehydrogenase;
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High glucose concentrations have been implicated as a casual factor in the initiation and progression of diabetes and there is evidence to suggest that hyperglycemia increases the production of free radicals and oxidant stress. In addition, glucose can undergo autooxidation, leading to the production of intermediates that the result in reactive oxygen spies (ROS) generation. And proteins undergo glycation when exposed to reducing sugars, initially with the formation of Schiff bases and then with the Amadori product on free amino groups, which ultimately undergo molecular rearrangement to form irreversible advanced glycation end products (AGEs). During the glycation reaction, ROS are generated from intermediates such as the Amadori product, and the resulting AGEs cause aggregation and insolubility of the target proteins. Reactive oxygen species (ROS) such as superoxide anion, nitric oxide and hydrogen peroxide are generated by glycation. These oxygen species can cause cell apoptosis and widespread damage to biological macromolecules leading to lipid peroxidation, protein oxidation, and DNA base modifications and strand breaks. Biological systems have evolved an effective and complicated network of defense mechanism which enable cells to cope with lethal oxidative environments. These defense mechanisms involve antioxidant enzymes such as superoxide dismutases (SODs), catalase, glucose 6-phosphate dehydrogenase, glutathione reductase. Recently, the importance of isocitrate dehydorgenase (ICDH) as antioxidant enzymes has been demonstrated in various types of cells. In the present study, ICDH, especially mitochondrial NADP^(+)- dependent isocitrate dehydrogenase (IDPm), in the cellular defense against glycation was investigated. The protective role of IDPm against glycation induced apoptosis and damage was investigated in transfectant Hek 293 cell line (vector, IDPm-sense and IDPm-antisense strains). In transfectant Hek 293 cell line, upon exposure to 50 mM high glucose, there was a distinct difference among these three strains in intracellular ROS level, NADPH level, GSSG level, death signal pathway, DNA fragmentation, apoptotic signaling, mitochondria membrane potential and cell membrane permeability. And, upon exposure to 100 mM high glucose, there was a distinct difference among these three strains in viability, intracellular ROS level, NADPH level, GSSG level, intracellular lipid peroxidation, the level of protein carbonyl content, which was the indicative marker of oxidative damage to protein and DNA damage. In addition, higher level of other antioxidant enzymes were maintained in sense strain. These results suggest that IDPm may play a important role in cellular defense against glycation, presumably functioning as an antioxidant protein. In conclusion, results of this study indicate that IDPm play an important role as antioxidant enzyme in cellular defense against glycation through the removal of reactive oxygen species.