Abstract 2670: Molecular Basis of Atrial Nitroso-Redox Imbalance in Permanent Human Atrial Fibrillation
Purpose. Increased atrial NOX2/NADPH oxidase activity is an early event in the natural history of atrial fibrillation (AF) and an independent risk factor for post-operative AF. These findings suggest that NADPH oxidases may represent a novel therapeutic target in AF; however, whether atrial superoxide (O2−) production and its enzymatic sources remain unchanged with the duration of AF remains to be established.
Methods. NO synthase (NOS) and arginase activity (HPLC), the NOS cofactor tetrahydrobiopterin (BH4) and the enzymatic sources of O2− release (lucigenin-enhanced chemiluminescence) were assessed in right atrial appendage homogenates from 15 patients with permanent AF and 17 matched patients in sinus rhythm undergoing cardiac surgery.
Results. AF was associated with increased atrial O2− production (110±61%, P<0.001). Inhibiting NOS or mitochondrial oxidases normalized O2− release the fibrillating myocardium, whereas NADPH oxidase inhibition had no effect. mRNA (real-time RT-PCR) and protein level (immunoblotting) of NOX2 and NOX5 and the NOX2 glycosylated/deglycosylated ratio were unaltered in AF, whereas NOX4 mRNA was increased. The mitochondria-derived increase in O2− production in AF was accompanied by a significant increase in mitochondrial complexes 1–5 and peroxiredoxin-3, whereas NOS ‘uncoupling’ was associated with a 40% reduction (P<0.05) in tissue BH4, in the absence of changes in arginase activity or eNOS protein level and phosphorylation. A persistent reduction in NO synthesis after BH4 saturation was due to a significant reduction in nNOS protein level (by ca. 40%), despite an increase nNOS mRNA.
Conclusions. Activation of atrial NOX2/NADPH oxidase is an early but transient event in AF. Once atrial structural remodeling has taken place, preserving nNOS degradation and function and/or restoring mitochondrial function may restore the atrial nitroso-redox imbalance in the fibrillating atria and its negative impact on myocardial function and structure.