Consistent antioxidant and antihypertensive effects of oral sodium nitrite in DOCA-salt hypertension

Abstract

Hypertension is a common disease that includes oxidative stress as a major feature, and oxidative stress impairs physiological nitric oxide (NO) activity promoting cardiovascular pathophysiological mechanisms. While inorganic nitrite and nitrate are now recognized as relevant sources of NO after their bioactivation by enzymatic and non-enzymatic pathways, thus lowering blood pressure, mounting evidence suggests that sodium nitrite also exerts antioxidant effects. Here we show for the first time that sodium nitrite exerts consistent systemic and vascular antioxidant and antihypertensive effects in the deoxycorticosterone-salt (DOCA-salt) hypertension model. This is particularly important because increased oxidative stress plays a major role in the DOCA-salt hypertension model, which is less dependent on activation of the renin-angiotensin system than other hypertension models. Indeed, antihypertensive effects of oral nitrite were associated with increased plasma nitrite and nitrate concentrations, and completely blunted hypertension-induced increases in plasma 8-isoprostane and lipid peroxide levels, in vascular reactive oxygen species, in vascular NADPH oxidase activity, and in vascular xanthine oxidoreductase activity. Together, these findings provide evidence that the oral administration of sodium nitrite consistently decreases the blood pressure in association with major antioxidant effects in experimental hypertension.

Keywords: DOCA-salt; Hypertension; Nitric oxide; Nitrite; Oxidative stress.

Graphical abstract

Fig. 1

Systolic blood pressure measured by non-invasive tail-cuff method (mmHg; panel A) and body weight changes (g; panel B) throughout the study. (A) Data are shown as mean±S.E.M (n=8–10 per group). *P<0.05 for DOCA+vehicle versus vehicle group; ^#P<0.05 for DOCA+nitrite group versus DOCA+vehicle group. (B) *P<0.05 for DOCA groups versus control groups.

Fig. 2

Plasma nitrite and NO_x levels at end of the treatments. (A) This panel shows plasma nitrite concentration (µmol/l) assessed by reductive chemiluminescence. (B) This panel shows plasma NO_x concentrations assessed by Griess reaction. Data are shown as mean±S.E.M. (n=5–7 per group). *P<0.05 Versus vehicle group; ^#P<0.05 versus respective control group.

Fig. 3

Effects of nitrite treatment on systemic markers of oxidative stress. Panel A shows plasma 8-isoprostanes concentrations (pg/ml) and panel B shows plasma lipoperoxide concentrations expressed in terms of malondialdehyde (MDA) (nmol/ml) in all experimental groups. Data are shown as mean±S.E.M. (n=4–6 per group). *P<0.05 versus vehicle; ^#P<0.05 versus DOCA+vehicle group.

Fig. 4

Effects of nitrite treatment on in situ vascular O₂^•− production assessed by dihydroethidium (DHE) fluorescence. Panel A shows the fluorescence intensity in each experimental group. Data are shown as mean±S.E.M. (n=5–7 per group). *P<0.05 versus vehicle; ^#P<0.05 versus DOCA+vehicle group. Panel B shows representative photomicrographs (original magnification ×400) of arteries incubated in the presence of DHE, which produces a red fluorescence when oxidized to hydroxyethidium by O₂^•−.

Fig. 5

Sodium nitrite decreases vascular NADPH and xanthine oxidase activities. (A) NADPH oxidase activity in the aortas from rats in all experimental groups was measured by lucigenin chemiluminescence. *P<0.05 versus vehicle group; ^#P<0.05 versus vehicle group and DOCA+vehicle group. (B) Xanthine oxidase activity in aortas from rats in all experimental groups. *P<0.05 versus vehicle group; ^#P<0.05 versus DOCA+vehicle group. Data are shown as means±S.E.M. (n=5 per group).