Pu-erh Tea Extract Attenuates Nicotine-Induced Foam Cell Formation in Primary Cultured Monocytes: An in Vitro Mechanistic Study

In this study, the mechanisms by which pu-erh tea extract (PETE) attenuates nicotine-induced foam cell formation were investigated. Monocytes were purified from healthy individuals using commercial antibodies coated with magnetic beads. We found that the nicotine-induced (1-10 μM) expression of oxidized low-density lipoprotein receptors (ox-LDLRs) and α9-nAchRs in monocytes was significantly attenuated by 24 h of PETE (10 μg/mL; ∗, p < 0.05) cotreatment. Nicotine (1 μM for 24 h) significantly induced the expression of the surface adhesion molecule ICAM-1 and the monocyte integrin adhesion molecule (CD11b) by human umbilical vein endothelial cells (HUVECs) and triggered monocytes to differentiate into macrophages via interactions with the endothelium. After treatment with nicotine (0.1-10 μM for 24 h), the HUVECs released chemotactic factors (IL-8) to attract monocytes into the tunica intima of the artery, and the monocytes then transformed into foam cells. We demonstrated that PETE treatment (>1 μg/mL for 24 h; ∗, p < 0.05) significantly attenuates nicotine-induced (1 μM) monocyte migration toward HUVECs and foam cell formation. This study suggests that tea components effectively attenuate the initial step (foam cell formation) of nicotine-induced atherosclerosis in circulating monocytes.