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DNA Damage and Cellular Stress Responses

Mitochondria Are an Essential Mediator of Nitric Oxide/Cyclic Guanosine 3',5'-Monophosphate Blocking of Glucose Depletion–Induced Cytotoxicity in Human HepG2 Cells

¹ Institute of Pharmacology, School of Medicine, National Yang-Ming University and Departments of ² Medical Research and Education and ³ Surgery, Taipei Veterans General Hospital, Taipei, Taiwan

Requests for reprints: Chin-Wen Chi, Department of Medical Research and Education, Taipei Veterans General Hospital, 201, Sec 2, Shih-Pai Road, Taipei 11217, Taiwan. Phone: 886-2-28757627; Fax: 886-2-28751562. E-mail: cwchi{at}vghtpe.gov.tw

It is well known that glucose is a major energy source in tumors and that mitochondria are specialized organelles required for energy metabolism. Previous studies have revealed that nitric oxide (NO) protects against glucose depletion–induced cytotoxicity in mouse liver cells and in rat hepatocytes, but the detailed mechanism is not well understood. Therefore, we investigated the involvement of mitochondria in the NO protective effect in human hepatoma HepG2 cells. In this study, we showed that glucose depletion resulted in a time-dependent decrease in intracellular NO and in the protein expression of NO synthases. This glucose depletion–induced decrease in NO was blocked by NO donors. Next, we showed that the cytoprotective effect of NO is via a cyclic guanosine 3',5'-monophosphate–dependent pathway. Additionally, SNP blocked a glucose depletion–induced decrease in mitochondrial mass, mitochondrial DNA copies, and ATP level in HepG2 cells. Moreover, glucose depletion decreased the expression of various mitochondrial proteins, including cytochrome c, complex I (NADH dehydrogenase), complex III (cytochrome c reductase), and heat shock protein 60; these glucose depletion–induced effects were blocked by SNP. Furthermore, we found that rotenone and antimycin A (mitochondria complex I and III inhibitors, respectively) blocked SNP cytoprotection against glucose depletion–induced cytotoxicity. Taken together, our results indicated that the mitochondria serve as an important cellular mediator of NO during protection against glucose deprivation–induced damage. (Mol Cancer Res 2007;5(9):923–32)