Abstract 328: 5-Methyl-Tetrahydrofolate Increases eNOS Activity By Preventing Peroxynitrite-Induced Oxidation Of Tetrahydrobiopterin In Human Vessels
Background: 5-methyltetrahydrofolate (5MTHF), the active form of folic acid, reduces homocysteine but its direct effects on vascular function are unclear. We hypothesized that 5MTHF may improve endothelial function by effects on the eNOS co-factor tetrahydrobiopterin (BH4).
Methods: Saphenoud veins (SV) and internal mammary arteries (IMA) were obtained from 56 patients undergoing CABG. Vasomotor responses to acetylcholine (ACh) were evaluated at baseline and after 45 minutes incubation with 5MTHF 0 or 1 μM. Vascular peroxynitrite (ONOO-) production was measured using luminol chemiluminescence, in paired segments of SV and IMA, after incubation with 5MTHF 0 or 1 μM. Vascular eNOS activity was estimated by radio-labeled arginine/citrulline conversion and the direct ONOO- scavenging capacity of 5MTHF was quantified using SIN-1 and uric acid as positive control.
Results. 5MTHF rapidly improved the vasomotor responses of SV to ACh (Fig. a⇓) and increased eNOS activity in human IMA (from 0.14 ± 0.02%/g to 0.20±0.03%/g tissue p<0.05). 5MTHF decreased ONOO-production in both SV (from 1.3±0.3 to 0.1±0.07 RLU/Sec/mg) and IMA (from 1.6±0.4 to 0.2±0.1 RLU/Sec/mg, p<0.05 for both), and increased intravascular BH4 (Fig b⇓). 5MTHF was a potent direct scavenger of ONOO- (Fig c⇓) and reversed ONOO-induced oxidation of BH4.
Conclusions. 5MTHF directly improves endothelial function in human vessels by protecting the peroxynitrite-induced oxidation of BH4, leading to an increase of eNOS activity.