The administration of folic acid reduces intravascular oxidative stress in diabetic rabbits

There is evidence that plasma homocysteine augments angiopathy in patients with diabetes mellitus. Although lowering homocysteine with folic acid improves endothelial function, the precise mechanisms underlying this effect are unknown. To study this area further, the effect of administration of folic acid to diabetic rabbits on intraaortic oxidative stress was studied by assessing the formation of superoxide (O(2)(-)), 8-isoprostane F(2alpha) (8-IPF(2alpha)), and prostacyclin (as 6-keto-PGF(1alpha)) as well as acetylcholine-stimulated relaxation and gp47(phox) content. Nonketotic diabetes mellitus was induced in New Zealand rabbits with alloxan, and low- and high-dose folic acid was administered daily for 1 month. Rabbits were killed, aortae were excised, and rings were prepared. Rings were mounted in an organ bath, and relaxation was elicited with acetylcholine. The O(2)(-) release was measured spectrophotometrically; the gp47(phox) expression, by Western blotting; and the 8-IPF(2alpha) and 6-keto-PGF(1alpha) formation, by enzyme-linked immunosorbent assay. Blood was collected for measurement of homocysteine, red blood cell folate, and glucose. In aortae from the diabetic rabbits, acetylcholine-induced relaxation was significantly impaired compared with that in untreated controls. The O(2)(-) release, p47(phox) expression, and 8-IPF(2alpha) formation were all enhanced and 6-keto-PGF(1alpha) formation was reduced compared with controls. All these effects were reversed by both low- and high-dose folic acid. Plasma total homocysteine was reduced by high-dose, but not low-dose, folic acid. Red blood cell folate was elevated in both groups. The improvement of endothelial function in patients receiving folic acid may be due to inhibition of nicotinamide adenine nucleotide phosphate oxidase (NADPH) oxidase expression and therefore conservation of nitric oxide and prostacyclin bioavailability, 2 vasculoprotective factors.