Human internal thoracic arteries from diabetic patients are resistant to endothelial dysfunction

Impact of type 2 diabetes on vascular reactivity to cGMP generators in human internal thoracic arteries

OBJECTIVE

The balance between nitric oxide (NO)-sensitive and -insensitive forms of soluble guanylate cyclase (sGC) has been demonstrated to be disrupted in certain lifestyle-related diseases. However, it remains unclear whether type 2 diabetes results in a shift of sGC to the NO-insensitive form. This study addressed this issue in the human blood vessel.

METHODS

Internal thoracic arteries were obtained from patients undergoing coronary artery bypass grafting. Helically cut strips of the arteries were suspended in organ chambers, and relaxant responses to nitroglycerin (NO-sensitive sGC stimulant) and BAY 60-2770 (NO-insensitive sGC stimulant) were assessed.

RESULTS

The patients were divided into two groups according to the presence of type 2 diabetes (HbA1c: 7.0±0.3%) or its absence (HbA1c: 5.6±0.1%). Nitroglycerin-induced relaxation was not different in the arteries obtained from type 2 diabetic and non-diabetic patients. In addition, the relaxant response to BAY 60-2770 in type 2 diabetics was comparable to that observed in non-diabetics. Although the patients enrolled often had vascular risk factors other than type 2 diabetes, the relaxant responses were still in the same range in a comparison based on the number of risk factors. However, in separate experiments, the relaxant response to nitroglycerin was attenuated by pre-incubation of the arteries with ODQ (sGC imbalance inducer), whereas the relaxant response to BAY-60-2770 was augmented.

CONCLUSIONS

These findings suggest that type 2 diabetes does not affect the balance between NO-sensitive and -insensitive sGC in human internal thoracic artery grafts.

Reactive oxygen species mediate functional differences in human radial and internal thoracic arteries from smokers

OBJECTIVE

Smoking not only increases the risk that coronary heart disease will develop but also morbidity and mortality in patients with known coronary atherosclerosis and after coronary artery bypass grafting. Excessive generation of reactive oxygen species (ROS) has been implicated as the final common pathway for the development of endothelial dysfunction in various cardiovascular risk factors. This study assessed the influence of smoking on two different human arteries routinely used as coronary artery bypass graft conduits.

METHODS

Isometric tension was recorded on discarded segments of human left internal thoracic artery (ITA) and the radial artery (RA) from smokers and nonsmokers.

RESULTS

The contractile response to endothelin-1 was significantly stronger in arteries from smokers than in those from nonsmokers. By contrast, endothelium-dependent relaxant responses to acetylcholine were attenuated in RA rings but enhanced in ITA rings from smokers. In additional experiments, 5-(&6)-chloromethyl-2'-7'-dichlorodihydro-fluorescein diacetate (DCDHF) was used to photochemically detect ROS by confocal imaging of intact ITA and RA. Enhanced production of ROS was induced by exposure of tissues to 28 degrees C. While during exposure to 28 degrees C, basal fluorescence emission was unchanged in ITA rings, it increased significantly in RA rings, indicating enhanced formation of ROS in this peripheral artery.

CONCLUSIONS

Data suggest that smoking induces endothelial dysfunction by increasing vascular ROS production. Different levels of endogenous antioxidant enzyme activities and the degree of atherosclerotic changes might modulate physiologic and pharmacologic vasoreactivity and be responsible for decreased graft patency of RA compared with ITA conduits, especially in active smokers.