Abstract 1809: Increased eNOS Coupling Protects Against Vein Graft Accelerated Atherosclerosis in ApoE-KO Mice
Accelerated atherosclerosis, a principal cause of vein graft (VG) failure, is associated with eNOS uncoupling and increased vascular superoxide (O2−). Tetrahydrobiopterin (BH4) is a required cofactor for endothelial NO synthase (eNOS) which promotes eNOS coupling. We aimed to investigate the importance of eNOS uncoupling in vein graft atherosclerosis using a transgenic mouse with endothelial-targeted overexpression of the rate-limiting enzyme in BH4 synthesis, GTP-cyclohydrolase I (GCH).
METHODS AND RESULTS: Transgenic mice crossed onto ApoE-KO background (GCH/ApoE-KO) or ApoE-KO littermates underwent interposition bypass grafting of donor caval vein to the carotid artery. VGs were harvested 28 or 56 days post surgery. VG lesion area was reduced by 61% at 28 days (*P < 0.01) and 46% at 56 days (#P<0.01) in GCH/ApoE-KO mice compared to ApoE-KO controls. BH4 levels in VGs were 8-fold higher in GCH/ApoE-KO mice (P < 0.01). NO synthesis, measured using arginine to citrulline conversion and electron paramagnetic resonance in aortas of experimental animals was not different between groups. However, O2− production was significantly attenuated in GCH/ApoE-KO mice measured by both dihydroethidium fluorescence and lucigenin enhanced chemilluminescence. eNOS inhibition by L-NAME reversed these effects indicating the endothelium as the source of O2− and preserved eNOS coupling.
CONCLUSION: These results indicate that the reduction in VG atherosclerosis is conferred by reduced endothelial O2− production. These findings highlight the importance of eNOS regulation by BH4, in vein graft atherosclerosis.