Abstract 1466: Intravenous Infusion Of 5-Methyl-Tetrahydrofolate Rapidly Improves eNOS Coupling In Human Vessels By Increasing Tetrahydrobiopterin Bioavailability
Background: Uncoupled endothelial nitric oxide synthase (eNOS) is a source of superoxide radicals (O2-) in human atherosclerosis, while folates appear to improve endothelial function. We examined the effects of 5-methyl-tetrahydrofolate (5MTHF), the circulating form of folic acid, on eNOS coupling and the eNOS cofactor tetrahydrobiopterin (BH4) in human vessels.
Methods: Fifty-six patients undergoing CABG were randomized to receive intravenous 5MTHF (0.13 mg/Kg, n=24) or placebo (n=32) preoperatively, 45 minutes before graft harvesting. Vascular O2- was determined in paired samples of saphenous veins (SV) and internal mammary arteries (IMA) using lucigenin chemiluminescence, in the presence or absence of NOS inhibitor LNAME. Vasomotor responses of SV to acetylcholine (ACh) and nitroprusside (SNP) were determined in an organ bath, while vascular 5-MTHF and biopterins were measured by HPLC.
Results: 5MTHF improved vasomotor response to ACh (Fig a⇓) and decreased O2- production in both SV and IMA (1.0±0.15 and 0.97±0.15 RLU/sec/mg in 5MTHF vs 2.27±0.37 and 5.01±0.62 RLU/sec/mg in placebo, p<0.01 for both). LNAME reduced O2- in both SV and IMA in placebo group suggesting eNOS uncoupling, that was reversed by 5MTHF (Fig b⇓). 5MTHF increased BH4 and BH4/total biopterin ratio (Fig c⇓). Moreover, vascular 5MTHF levels correlated with BH4/tBio ratio (r=0.406, p=0.001 in SV and r=0.334 p=0.043 in IMA respectively) and with maximum relaxations to Ach (r=0.314, p=0.016).
Conclusions: Intravenous administration of 5MTHF rapidly increases NO bioavailability, improves eNOS ‘coupling’ and decreasees O2- production in human vessels, through effects on intracellular BH4 oxidation.