Cigarette Smoking Potentiates Endothelial Dysfunction of Forearm Resistance Vessels in Patients With Hypercholesterolemia

TLDR

Risk factors such as hypercholesterolemia and hypertension are linked to endothelial dysfunction, but how these factors interact to affect endothelial function remains unclear. The study examined how long‑term smoking and hypercholesterolemia together influence endothelial function of forearm resistance vessels and their association with plasma autoantibodies against oxidized LDL. Forearm blood flow responses to acetylcholine and sodium nitroprusside were measured in normal controls, hypercholesterolemic patients, long‑term smokers, and hypercholesterolemic smokers after drug infusion into the brachial artery using venous occlusion plethysmography. Acetylcholine‑induced forearm blood flow was significantly blunted in all patient groups, most markedly in hypercholesterolemic smokers, while nitroprusside responses were unchanged; plasma oxidized‑LDL autoantibody titers were inversely correlated with acetylcholine responses and elevated in the combined‑risk group, indicating synergistic endothelial dysfunction.

Abstract

Background Risk factors for atherosclerosis such as hypercholesterolemia and hypertension are associated with endothelial dysfunction of conduit and resistance vessels; however, the interaction of these risk factors and underlying mechanisms affecting endothelial function remain to be determined. The present study investigated the role of long-term smoking and hypercholesterolemia and their impact on endothelial function of peripheral resistance vessels in relation to plasma levels of autoantibodies against oxidized LDL, which has been implicated in the development of endothelial dysfunction and atherosclerosis. Methods and Results The vascular responses to the endothelium-dependent agent acetylcholine (7.5, 15, 30, and 60 μg/min) and the endothelium-independent agent sodium nitroprusside (1, 3, and 10 μg/min) were studied in normal control subjects (n=10), patients with hypercholesterolemia (n=15), long-term smokers (n=15), and hypercholesterolemic patients who smoked (n=15). Drugs were infused into the brachial artery, and forearm blood flow (FBF) was measured by venous occlusion plethysmography. The FBF responses to acetylcholine were significantly blunted in all three patient groups compared with normal control subjects ( P <.05). The acetylcholine-induced increase in FBF was significantly attenuated in patients with hypercholesterolemia who smoked compared with hypercholesterolemic nonsmokers and normocholesterolemic smokers ( P <.05 for both). The response to sodium nitroprusside was not statistically different in all four groups. Plasma levels of autoantibody titer against oxidized LDL were inversely related to acetylcholine-induced changes in FBF ( r =−.53, P <.002) and were substantially increased in the group with both risk factors. Conclusions These results demonstrate that cigarette smoking and hypercholesterolemia synergistically impair endothelial function and that their combined presence is associated with increased plasma levels of autoantibodies against oxidized LDL. These observations raise the possibility that long-term smoking potentiates endothelial dysfunction in hypercholesterolemic patients by enhancing the oxidation of LDL.