Vascular generation of tumor necrosis factor-α reduces nitric oxide availability in small arteries from visceral fat of obese patients

Abstract

Objectives: The aim of this study was to assess whether small arteries from visceral fat of obese patients show a reduced nitric oxide (NO)-dependent relaxation, as compared with lean control subjects, focusing on the role of the pro-inflammatory cytokine tumor necrosis factor (TNF)-α.

Background: Visceral obesity is characterized by endothelial dysfunction.

Methods: Small arteries from 14 obese (body mass index 48.4 ± 11 kg/m(2)) and 14 control subjects (body mass index 24.9 ± 2 kg/m(2)), dissected after a visceral fat biopsy (laparoscopy), were evaluated on a pressurized micromyograph. Endothelium-dependent relaxation was assessed by acetylcholine. The NO availability, superoxide production, and inflammation were assessed by testing acetylcholine under the nitric oxide synthase (NOS) inhibitor N(ω)-nitro-L-arginine methylester, tempol (superoxide scavenger), and infliximab (monoclonal anti-TNF-α antibody), respectively. The roles of nicotinamide adenine dinucleotide phosphate oxidase and inducible nitric oxide synthase (iNOS) were assessed by their selective inhibitors apocynin and S-methylisothiourea (SMT), respectively. Vascular superoxide generation (dihydroethidium staining) protein expression of TNF-α and NOS isoforms (Western Blot) and TNF-α localization (immunohistochemistry) were assessed.

Results: Vessels from obese patients displayed a blunted relaxation to acetylcholine and a reduced inhibitory effect of N(ω)-nitro-L-arginine methylester. These alterations were normalized by tempol or infliximab while being partly ameliorated by apocynin and SMT. Vascular superoxide generation was increased (p < 0.01) in obese patients. This condition was abrogated by both tempol and infliximab and partly (p < 0.05 vs. control subjects) reduced by apocynin or SMT. Enhanced TNF-α and iNOS expression together with increased TNF-α localization in the vascular media were detected.

Conclusions: Small arteries from visceral fat of obese patients are characterized by an increased TNF-α production, which reduces NO availability by promoting superoxide generation via nicotinamide adenine dinucleotide phosphate oxidase and iNOS activation.