Endothelial nitric oxide synthase uncoupling: A novel pathway in OSA induced vascular endothelial dysfunction

• OSA patients underwent endothelial reactivity studies and subcutaneous biopsies.
• We evaluated endothelial nitric oxide synthase function in patient tissue before and after treatment.
• eNOS uncoupling is the cause of endothelial dysfunction and
• O2− overproduction in OSA patients.
• Tetrahydrobioterin restored eNOS function in OSA patients’ tissue.
• The findings provide a potential pharmacological target to decrease vascular disease in OSA.

The mechanism of vascular endothelial dysfunction (VED) and cardiovascular disease in obstructive sleep apnea (OSA) is unknown. We performed a comprehensive evaluation of endothelial nitric oxide synthase (eNOS) function directly in the microcirculatory endothelial tissue of OSA patients who have very low cardiovascular risk status. Nineteen OSA patients underwent gluteal biopsies before, and after effective treatment of OSA. We measured superoxide (O2
• −) and nitric oxide (NO) in the microcirculatory endothelium using confocal microscopy. We evaluated the effect of the NOS inhibitor l-Nitroarginine-Methyl-Ester (l-NAME) and the NOS cofactor tetrahydrobiopterin (BH4) on endothelial O2
• − and NO in patient endothelial tissue before and after treatment. We found that eNOS is dysfunctional in OSA patients pre-treatment, and is a source of endothelial O2
• − overproduction. eNOS dysfunction was reversible with the addition of BH4. These findings provide a new mechanism of endothelial dysfunction in OSA patients and a potentially targetable pathway for treatment of cardiovascular risk in OSA.