Folic acid reverts dysfunction of endothelial nitric oxide synthase

5-Methyltetrahydrofolate (MTHF), the active form of folic acid, has been re ported to restore NO status in hypercholesterolemic patients. The mechanism of this effect remains to be established. We assessed the effects of L- an d D-MTHF on tetrahydrobiopterin (BH4)-free and partially BH4-repleted endot helial NO synthase (eNOS). Superoxide production of eNOS and the rate const ants for trapping of superoxide by MTHF were determined with electron param agnetic resonance using 5-diethoxyphosphoryl-5-methyl-1-pynoline-N-oxide (D EPMPO) as spin trap for superoxide. NO production was measured with [H-3]ar ginine-citrulline conversion or nitrite assay. The rate constants for scave nging of superoxide by L- and D-MTHF were similar, 1.4X10(4) ms(-1). In BH4 -free eNOS, L- and D-MTHF have no effect on enzymatic activity. In contrast , in partially BH4-repleted eNOS, we observe a 2-fold effect of MTHF on the enzymatic activity. First, superoxide production is reduced. Second, NO pr oduction is enhanced. In cultured endothelial cells, a sim., In the present study, we show direct effects of MTHF on the enzymatic activity of NO synt hase both in recombinant eNOS as well as in cultured endothelial cells, whi ch provides a plausible explanation for the previously reported positive ef fects of MTHF on NO status in vivo.