Mitochondrial dysfunction has a significant role in the development and complications of diabetic cardiomyopathy. Mitochondrial dysfunction and mitochondrial DNA (mtDNA) mutations are also associated with different types of cancer and neurodegenerative diseases. The goal of this study was to determine if chronically elevated glucose increase in mtDNA damage contributed to mitochondrial dysfunction and identify the underlying basis for mtDNA damage. H9c2 myotubes (a cardiac-derived cell line) were studied in the presence of 5.5, 16.5, or 33.0 mM glucose for up to 13 days. Tests of mitochondria function (Complex I and IV activity and ATP generation) were all significantly depressed by elevated media glucose. Intramitochondrial superoxide and intracellular superoxide levels were transiently increased during the experimental period. AnnexinV binding (a marker of apoptosis) was significantly increased after 7 and 13 days of high glucose. Thirteen days of elevated glucose significantly increased mtDNA damage globally and across the region encoding for the three subunits of cytochrome oxidase. Using mitochondria isolated from cells chronically exposed to elevated glucose, we observed significant increases in topoisomerase-linked DNA cleavage. Mitochondria-dependent DNA cleavage was significantly exacerbated by H(2)O(2) and that immunoprecipitation of mitochondrial extracts with a mtTOP1 antibody significantly decreased DNA cleavage, indicating that at least part of this activity could be attributed to mtTOP1. We conclude that even mild increases in glucose presentation compromised mitochondrial function as a result of a decline in mtDNA integrity. Separate from a direct impact of oxidative stress on mtDNA, ROS-induced alteration of mitochondrial topoisomerase activity exacerbated and propagated increases in mtDNA damage. These findings are significant in that the activation/inhibition state of the mitochondrial topoisomerases will have important consequences for mitochondrial DNA integrity and the well being of the myocardium.
Type II diabetes increases mitochondrial DNA mutations in the left ventricle of the Goto-Kakizaki diabetic rat. Am J Physiol Heart Circ Physiol 304: H903-H915, 2013. First published February 1, 2013 doi:10.1152/ajpheart.00567.2012.-Mitochondrial dysfunction has a significant role in the development of diabetic cardiomyopathy. Mitochondrial oxidant stress has been accepted as the singular cause of mitochondrial DNA (mtDNA) damage as an underlying cause of mitochondrial dysfunction. However, separate from a direct effect on mtDNA integrity, diabetic-induced increases in oxidant stress alter mitochondrial topoisomerase function to propagate mtDNA mutations as a contributor to mitochondrial dysfunction. Both glucose-challenged neonatal cardiomyocytes and the diabetic GotoKakizaki (GK) rat were studied. In both the GK left ventricle (LV) and in cardiomyocytes, chronically elevated glucose presentation induced a significant increase in mtDNA damage that was accompanied by decreased mitochondrial function. TTGE analysis revealed a number of base pair substitutions in the 3' end of COX3 from GK LV mtDNA that significantly altered the protein sequence. Mitochondrial topoisomerase DNA cleavage activity in isolated mitochondria was significantly increased in the GK LV compared with Wistar controls. Both hydroxycamptothecin, a topoisomerase type 1 inhibitor, and doxorubicin, a topoisomerase type 2 inhibitor, significantly exacerbated the DNA cleavage activity of isolated mitochondrial extracts indicating the presence of multiple functional topoisomerases in the mitochondria. Mitochondrial topoisomerase function was significantly altered in the presence of H 2O2 suggesting that separate from a direct effect on mtDNA, oxidant stress mediated type II diabetesinduced alterations of mitochondrial topoisomerase function. These findings are significant in that the activation/inhibition state of the mitochondrial topoisomerases will have important consequences for mtDNA integrity and the well being of the diabetic myocardium. diabetic cardiomyopathy; type 2 diabetes; mitochondrial DNA damage; mitochondrial dysfunction CARDIOVASCULAR DISEASE is responsible for a higher incidence of mortality in diabetics than the general population. Diabetic cardiomyopathy (DCM) is characterized by the development of a myopathy that manifests initially as diastolic dysfunction, but evolves into increased cavitary dilation and mural thinning, which is reflective of decompensated eccentric hypertrophy. DCM is considered to be independent of atherosclerosis or hypertension but is exacerbated by either (94). Mitochondrial dysfunction has long been known to have a significant role in the development and complications of DCM (32,46,66,82,92). Mitochondrial dysfunction is also associated with other pathologies including cancer, skeletal muscle disorders, and neurodegenerative diseases such as Wolfram syndrome or Leber's hereditary optic neuropathy (LHON) (18,36,54,104).Separate from inborn errors, mitochondrial DNA (mtDNA) mutations are thought to accumul...
Hemoglobin (Hb)-based oxygen carriers (HBOCs) are being developed as a potential therapy for increasing tissue oxygenation, yet they have not reached their full potential because of unwanted hemodynamic side effects (vasoconstriction, low cardiac output, and oxygen delivery) due in part to nitric oxide (NO) scavenging by cell-free Hb. It may be possible to overcome the NO scavenging effect by coinfusing S-nitrosylated (SNO) HBOC along with unmodified HBOC. SNO-HBOC, like free Hb, may act as an NO donor in low-oxygen conditions. We hypothesized that an unaltered HBOC, polymerized bovine Hb (PBvHb), coinfused with an SNO-PBvHb, would improve hemodynamics and oxygen delivery during hypoxia. Vascular oxygen content and hemodynamics were determined after euvolemic rats were infused (3 ml) with lactated Ringer's solution, PBvHb, SNO-PBvHb, or PBvHb plus SNO-PBvHb (1:10) during normoxia or acute hypoxia (fraction of inspired oxygen = 10%, 120 min). Hemodynamic side effects resulting from PBvHb infusion (vasoconstriction, elevated pulmonary blood pressure, and reduced cardiac output) were offset by SNO-PBvHb in acute hypoxic, but not normoxic, conditions. These data support the potential use of HBOC mixed with SNO-HBOC for the treatment of conditions in which acute hypoxia is present, such as tumor oxygenation, wound healing, hemorrhagic trauma, and sickle cell and hemolytic anemia.
Mitochondrial dysfunction has a significant role in the development of diabetic cardiomyopathy. Using neonatal cardiomyocytes and the Goto‐Kakizaki (GK) rat as models of type II diabetes, we investigated if mitochondrial topoisomerases contributed to mitochondrial dysfunction. In cardiomyocytes elevated glucose significantly decreased ATP production and cytochrome oxidase (COX) activity. Diabetes significantly decreased cytochrome oxidase activity in GK left ventricle (LV). Diabetes significantly increased mtDNA damage, in both glucose‐challenged cardiomyocytes and GK LV. TTGE analysis of COX3 identified nucleotide substitutions in the GK LV mtDNA that altered the primary protein sequence. In isolated mitochondria, diabetes increased DNA cleavage activity and incubation with topoisomerase inhibitors significantly altered this response. Immunoprecipitation with a mtTOP1 antibody partially blocked DNA cleavage. The presence of 60 μM H2O2 increased mitochondrial topoisomerase dependent DNA cleavage: implicating ROS as a modifier of topoisomerase function. Separate from a direct impact of oxidative stress on mtDNA, ROS‐induced alteration of mitochondrial topoisomerase function propagated mtDNA damage. Our findings suggest that mitochondrial topoisomerase dysfunction contributes to the development and complications of diabetic cardiomyopathy. Supported in part by NIH HD065551.
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