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Folic acid reduces intravascular oxidative stress in diabetic rabbits There is evidence that plasma homocysteine (Hcy) augments angiopathy in patients with diabetes mellitus (DM; Shukla et al., 2003). Although lowering Hcy with folic acid (FA) improves endothelial function, the precise mechanisms underlying this effect are unknown. It has been demonstrated, however, that Hcy augments superoxide (O2▪-) formation and reduces NO-mediated relaxation in aortae from diabetic rabbits. O2▪- reacts with NO thereby reducing the bioavailability of NO). The source of O2▪- is NADPH oxidase (NOX). In order to study this area further, the effect of administration FA to diabetic rabbits on intravascular (aortic) oxidative stress was studied by assessing O2▪- and 8-isoprostane F2α (8-IPF2α ) formation, acetycholine (Ach)-stimulated (NO-dependent) relaxation and gp47phox expression (Shukla et al., 2006). Non-ketotic DM was induced in New Zealand White rabbits (3 kg) with an i.v. injection of alloxan (60mg/kg). FA (0.5 mg / kg) was administered orally to one DM group. After one month, plasma samples were taken, rabbits killed with a barbiturate overdose and aortae excised and rings prepared. Rings were mounted in an organ bath and contraction elicited with phenylephrine (10-4M) and relaxation with Ach (10-9 – 10-5M). Superoxide dismutase (SOD)-inhibitable O2▪- release was measured, gp47phox expression with western blotting and 8-IPF2α with ELISAs. Data are expressed as mean ± s.e.mean; n = 6. One-way ANOVA was used for statistical analysis. All studies were carried out in accordance with the Animal (Scientific Procedures) Act, 1986. After one month, in aortae from the DM group: i) Ach-induced relaxation was significantly impaired in the DM group (38.4 ± 4%) compared to controls (68 ± 6%) which was reversed by FA administration (58 ± 7%), ii) O2▪- release was significantly enhanced (0.68 ± 0.3 nmoles / mg tissue / hr) compared to controls (0.09 ± 0.003 nmoles / mg tissue / hr), an effect again reversed by FA (0.095 ± 0.01 nmoles/mg tissue/hr), iii) gp47phox expression was increased (relative OD: 268 ± 39 %) compared to controls, an effect reversed by FA (relative OD: 35 ± 9 %), iv) 8-IPF2α formation was enhanced (14.8 pmoles / mg / tissue / min) compared to controls (0.3 pmoles / mg / tissue / min), an effect reduced by FA (3.9 pmoles / mg / tissue / min). This study consolidates that DM augments the formation of arterial O2▪- which in turn reduces NO bioavailability and that the source of this O2▪- is NOX. The data indicate that the improvement of endothelial cell function reported in diabetic patients receiving oral administration of FA is due, in part, to an inhibition of NOX expression. Apart from preventing endothelial cell dysfunction, the inhibition of NOX by FA has other therapeutic implications for preventing DM-associated disorders, including accelerated atherosclerosis, impaired wound healing, retinopathy and neuropathy. Shukla N, et al. (2006) Eur J Pharmacol, 531 : 201-208. |
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