Endothelial dysfunction in the microcirculation of patients with obstructive sleep apnea

Abstract

Rationale: Obstructive sleep apnea (OSA) is a risk factor for cardiovascular disease. We hypothesized that patients with OSA and no cardiovascular disease have oxidant-related microcirculatory endothelial dysfunction.

Objectives: To evaluate the microcirculation in OSA.

Methods: This study included seven patients with OSA and seven age- and weight-matched control subjects (mean age, 38 yr; mean body mass index, 32.5 kg/m²). All participants were free of cardiovascular risk factors. Participants received measurement of brachial artery flow-mediated dilation and forearm subcutaneous biopsy. Patients underwent repeated tests 12 weeks after treatment. Microcirculatory endothelial cells were isolated, and immunohistochemistry staining for peroxynitrite in the microcirculation was performed.

Measurements and main results: Flow-mediated dilation was lower in patients than in control subjects at baseline (mean ± SEM: 5.7 ± 0.5 vs. 9.5 ± 0.6; P = 0.02) and increased after treatment (5.7-7.3; change, 1.7 ± 0.6; P = 0.04). Microcirculatory peroxynitrite deposit was higher in patients compared with control subjects (44.0 ± 1.6 vs. 21.8 ± 1.9 stain density units; P < 0.001) and decreased after treatment from 44.0 to 30.5 stain density units (change, -13.5 ± 2.9; P = 0.009). In patients, transcription of endothelial nitric oxide synthase decreased from 5.2 to -1.3 after treatment (change, 6.5 ± 2.5; P = 0.05), and transcription of superoxide dismutase1 decreased from -4.0 to -12.3 after treatment (change, -8.3 ± 2.1; P = 0.01). These changes persisted after adjustment for weight and underlying severity of OSA.

Conclusions: This is the first direct evaluation of the microcirculation in OSA. Patients with OSA with low cardiovascular risk status had increased oxidant production in the microcirculation and endothelial dysfunction, both of which improved with treatment. Endothelial nitric oxide synthase transcription decreased with treatment.

Figure 1.

Microcirculatory endothelial cell isolation. (A) In fluorescein-labeled UEA I–stained arterioles, localization of stain in microcirculatory endothelial cells is performed to enable cell selection by laser capture microdissection. (B) Area selected and marked for capture and RNA isolation for creation of cDNA library.

Figure 2.

Peroxynitrite deposit in a microcirculatory vessel of a patient with obstructive sleep apnea. Brown stain indicates nitrated tyrosine residues in microcirculation. (A) Section of pretreatment tissue stained with antinitrotyrosine antibody. (B) Section of post-treatment tissue stained with antinitrotyrosine antibody.

Figure 3.

Peroxynitrite deposits in the microvascular walls of patients with obstructive sleep apnea and control subjects. Peroxynitrite stain density in the microcirculation decreased with continuous positive airway pressure treatment from 44.0 ± 1.6 stain density units (SDU) to 30.5 ± 2.3 SDU, with a difference of −13.5 ± 2.9 SDU (P < 0.01). Microcirculatory peroxynitrite stain density was increased in patients with obstructive sleep apnea compared with control subjects (44.0 ± 1.6 SDU vs. 21.8 ± 1.9 SDU, with a difference of −22.3 ± 2.6 SDU; P < 0.001).

Figure 4.

Superoxide dismutase transcription in microvascular endothelial cells of patients and matched control subjects. Quantitative PCR measurement of superoxide dismutase 1 revealed a decrease in expression with treatment of obstructive sleep apnea from −4.0 to −12.1 ΔCt, with a difference of −8.3 ± 2.1 ΔCt (P = 0.011).

Figure 5.

Endothelial nitric oxide transcription in microvascular endothelial cells of patients and matched control subjects. There was a decrease in eNOS transcription with continuous positive airway pressure treatment from 5.2 to −1.3 ΔCt, with a difference of −6.5 ± (2.5) ΔCt (P = 0.05).