Oxidative stress promotes hypertension and albuminuria during the autoimmune disease systemic lupus erythematosus

Abstract

Several lines of evidence suggest that essential hypertension originates from an autoimmune-mediated mechanism. One consequence of chronic immune activation is the generation of oxygen-derived free radicals, resulting in oxidative stress. Renal oxidative stress has direct prohypertensive actions on renal microvascular and tubular function. Whether oxidative stress contributes to the prevalent hypertension associated with autoimmune disease is not clear. We showed previously that female NZBWF1 mice, an established model of the autoimmune disease systemic lupus erythematosus (SLE), develop hypertension associated with renal oxidative stress. In the present study we tested the hypothesis that oxidative stress contributes to autoimmune-mediated hypertension by treating SLE and control (NZW/LacJ) mice with tempol (2.0 mmol/L) and apocynin (1.5 mmol/L) in the drinking water for 4 weeks. Although the treatment did not alter SLE disease activity (assessed by plasma double-stranded DNA autoantibodies), blood pressure and renal injury (urinary albumin) were reduced in the treated SLE mice. Tempol plus apocynin-treated SLE mice had reduced expression of nitrosylated proteins in the renal cortex, as well as reduced urinary and renal cortical hydrogen peroxide, suggesting that treatment reduced renal markers of oxidative stress. These data suggest that renal oxidative stress plays an important mechanistic role in the development of autoimmune-mediated hypertension.

Figure 1. Antioxidant therapy reduces blood pressure and albuminuria in SLE mice

1A) Mean arterial pressure (mmHg) was significantly increased in SLE animals compared to controls (n = 6-20). Tempol + apocynin (T+A) decreased blood pressure in SLE animals, but not controls. *p < 0.05 vs. corresponding Control; ⁺p<0.05 vs. SLE/Vehicle. 1B) Urinary albumin excretion (μg/mg creatinine) was increased in SLE animals compared to controls (n = 8-19). Tempol + apocynin (T+A) decreased albuminuria in SLE animals, but not controls.

Figure 2. Antioxidant therapy reduces renal oxidative stress in SLE mice

Renal cortical protein expression of the 15 kDa nitrosylated protein (measured by Western blot) was increased in SLE mice compared to controls (n=3-4). Tempol + apocynin (T+A) decreased expression in SLE mice, but not controls. *p<0.05 vs. corresponding Control; ⁺p<0.05 vs. corresponding Vehicle.

Figure 3. Antioxidant therapy reduces hydrogen peroxide in SLE mice

3A and 3B) Renal cortical and urinary hydrogen peroxide was reduced in SLE mice treated with tempol and apocynin but was unchanged in control animals. *p<0.05 vs. Control.

Figure 4. Antioxidants do not affect renal cortical expression of superoxide dismutases in SLE mice

Renal cortical protein expression (measured by Western blot) of manganese superoxide dismutase (5A; MnSOD) was increased in SLE mice compared to controls (n=3-4), whereas expression of extracellular superoxide dismutase (5B; ECSOD) and copper zinc superoxide dismutase (5B; CuZnSOD) where unchanged. Tempol + apocynin (T+A) had no effect on any of the superoxide dismutases in either SLE or control animals. *p<0.05 vs. corresponding Control.

Figure 5. Antioxidant therapy increases renal cortical mRNA expression of subunits of NADPH oxidase in SLE mice

Renal cortical mRNA expression of p47phox (measured by RT-PCR) was increased in SLE mice treated with tempol + apocynin (T+A) compared to vehicle-treated SLE mice (n=3-4). Expression of p22phox and gp91 phox was not altered in mice treated with T+A. *p<0.05 vs. SLE/Vehicle.