Abstract 17272: Cardiomyocyte-Specific Overexpression of Human GTP Cyclohydrolase 1 Gene Restores Ischemic Preconditioning-Elicited Myocardial and Mitochondrial Protection Impaired by Hyperglycemia
Background: Previous studies indicate that cardioprotection by ischemic preconditioning (IPC) is blocked by acute hyperglycemia with decreased intracellular tetrahydrobiopterin (BH4), an essential cofactor for nitric oxide synthase. We hypothesized that increased BH4 by cardiomyocyte-specific overexpression of human GTP cyclohydrolase 1 (GTPCH-1) gene rescues IPC-induced cardioprotection impaired by hyperglycemia.
Methods: Myocardial BH4 concentration was determined by HPLC. Transgenic mice overexpressing human GTPCH-1 gene and their wild-type littermates were subjected to 30 min of coronary artery occlusion followed by 2 h of reperfusion. IPC was elicited with 4 consecutive periods of 5 min of ischemia/5 min of reperfusion in the presence or absence of dextrose (2 g/kg, i.p) to produced acute hyperglycemia. Mitochondria were isolated 5 min after reperfusion to assess the Ca2+ loading required to open the mitochondrial permeability transition pore (mPTP).
Results: Overexpression of human GTPCH-1 gene in cardiomyocytes did not alter expression of mouse GTPCH-1 mRNA. Myocardial BH4 content was increased to 265 ± 58 pmols mg−1 protein in transgenic mice compared to 5 ± 1 pmols mg−1 protein (n = 5, P < 0.05) in wild-type mice. Infarct size was decreased by IPC in both wild-type (56 ± 3% in control vs. 33 ± 4% of risk region in IPC, P < 0.05) and transgenic (45 ± 3% in control vs. 29 ± 4% of risk region in IPC, n = 8 mice/group, P < 0.05) mice. The concentration of Ca2+ needed to open mPTP were increased by IPC in both wild-type (142 ± 10 in control vs. 184 ± 14 μmols CaCl2 mg−1 protein in IPC; P< 0.05) and transgenic (136 ± 11 in control vs. 193 ± 12 μmols CaCl2 mg−1 protein in IPC; n = 10, P< 0.05) mice. These beneficial actions of IPC were abrogated by hyperglycemia in wild-type but rescued in transgenic mice. Cardioprotection by IPC in hyperglycemic, transgenic mice was blocked by administration of NG-nitro-L-arginine methyl ester (1 mg/kg, i.p.), a nitric oxide synthase inhibitor.
Conclusions: Increased BH4 by cardiomyocyte-specific overexpression of human GTPCH-1 gene preserves the ability of IPC to elicit cardioprotection and inhibit mPTP opening impaired by hyperglycemia. Nitric oxide is involved in cardioprotection by IPC in hyperglycemic, transgenic GTPCH-1 mice.
- © 2010 by American Heart Association, Inc.