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

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.