NADPH oxidase-derived reactive oxygen species contribute to impaired cutaneous microvascular function in chronic kidney disease

Abstract

Oxidative stress promotes vascular dysfunction in chronic kidney disease (CKD). We utilized the cutaneous circulation to test the hypothesis that reactive oxygen species derived from NADPH oxidase and xanthine oxidase impair nitric oxide (NO)-dependent cutaneous vasodilation in CKD. Twenty subjects, 10 stage 3 and 4 patients with CKD (61 ± 4 yr; 5 men/5 women; eGFR: 39 ± 4 ml·min(-1)·1.73 m(-2)) and 10 healthy controls (55 ± 2 yr; 4 men/6 women; eGFR: >60 ml·min(-1)·1.73 m(-2)) were instrumented with 4 intradermal microdialysis fibers for the delivery of 1) Ringer solution (Control), 2) 10 μM tempol (scavenge superoxide), 3) 100 μM apocynin (NAD(P)H oxidase inhibition), and 4) 10 μM allopurinol (xanthine oxidase inhibition). Skin blood flow was measured via laser-Doppler flowmetry during standardized local heating (42°C). N(g)-nitro-l-arginine methyl ester (L-NAME; 10 mM) was infused to quantify the NO-dependent portion of the response. Cutaneous vascular conductance (CVC) was calculated as a percentage of the maximum CVC achieved during sodium nitroprusside infusion at 43°C. Cutaneous vasodilation was attenuated in patients with CKD (77 ± 3 vs. 88 ± 3%, P = 0.01), but augmented with tempol and apocynin (tempol: 88 ± 2 (P = 0.03), apocynin: 91 ± 2% (P = 0.001). The NO-dependent portion of the response was reduced in patients with CKD (41 ± 4 vs. 58 ± 2%, P = 0.04), but improved with tempol and apocynin (tempol: 58 ± 3 (P = 0.03), apocynin: 58 ± 4% (P = 0.03). Inhibition of xanthine oxidase did not alter cutaneous vasodilation in either group (P > 0.05). These data suggest that NAD(P)H oxidase is a source of reactive oxygen species and contributes to microvascular dysfunction in patients with CKD.

Keywords: cutaneous vasodilation; kidney disease; nitric oxide; oxidative stress.

Fig. 1.

Original recording of the skin blood flow response to local heating. Baseline measurements are made taken for ∼30 min at a local temperature of 33°C. An initial peak occurs upon increasing the local temperature to 42°C, followed by a sustained plateau that is primarily mediated by nitric oxide (NO). Once a stable plateau has been established, N^g-nitro-l-arginine methyl ester (l-NAME) is delivered through the microdialysis fiber to inhibit NO synthase (NOS). Following a stable post-l-NAME plateau, sodium nitroprusside is delivered through the fiber and the local temperature is increased to 43°C to cause a maximal dilation response.

Fig. 2.

Initial peak responses to tempol, apocynin, and allopurinol. Filled bars, healthy control (HC) responses; open bars, chronic kidney disease (CKD) responses. Values are means ± SE. *P < 0.05 vs. HC Ringer. †P < 0.05 vs. CKD Ringer.

Fig. 3.

Plateau responses and NO contribution. A: plateau responses in HC and CKD. B: post l-NAME plateau responses in HC and CKD. C: NO contribution in HC and CKD. Filled bars, HC responses; open bars, CKD responses. Values are means ± SE. *P < 0.05 vs. HC Ringer. †P < 0.05 vs. CKD Ringer.

Fig. 4.

Plasma asymmetric dimethylarginine (ADMA) and l-arginine levels. A: plasma ADMA levels. B: plasma l-arginine levels. C: l-arginine/ADMA ratio. Values are means ± SE. *P < 0.05 vs. HC.