Endothelial dysfunction and oxidative stress likely play roles in PM_2.5-induced harmful effects. Epigallocatechin-3-gallate (EGCG), the major polyphenolic constituent of green tea, is a potent antioxidant that exerts protective effects on cardiovascular diseases (CVDs) in part by scavenging free radicals. The exposure to ambient fine particulate matter (PM_2.5) is responsible for certain CVDs. The aim of the present study was to investigate whether EGCG could also inhibit PM_2.5-induced oxidative stress by activating the nuclear factor E2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) pathway in human umbilical vein endothelial cells (HUVECs). PM_2.5 (200 μg/mL) increased both cell death and intracellular ROS levels significantly, whereas EGCG (50–400 μM) inhibited these effects in a concentration-dependent manner. Western blotting and PCR demonstrated that EGCG increased Nrf2 and HO-1 expression in HUVECs that had been exposed to PM_2.5. PD98059 (a selective inhibitor of extracellular signal regulated kinase [ERK]-1/2) and SB203580 (a selective inhibitor of p38 MAPK), but not SP600125 (a selective inhibitor of c-jun N-terminal kinase [JNK]), attenuated the EGCG-induced Nrf2 and HO-1 expression. In addition, silencing Nrf2 abolished EGCG-induced Nrf2 and HO-1 upregulation and enhancement of cell viability. The present study suggests that EGCG protects HUVECs from PM_2.5-induced oxidative stress injury by upregulating Nrf2/HO-1 via activation of the p38 MAPK and the ERK1/2 signaling pathways.

Quercetin is one of the most common flavonoids in the human daily diet. Its affects the coronary artery, especially L-type voltage-gated Ca²⁺ channels and voltage-gated K⁺ channels in the arterial smooth muscle cells, which are poorly understood. The present experiments were designed to study the myogenic effect of quercetin and its possible underlying mechanisms in the rat coronary artery. A wire myograph was used to observe the myogenic effects. Arterial smooth muscle cells were freshly isolated from the rat coronary artery and the intracellular free Ca²⁺ concentration was measured with molecular probe fluo-4-AM. The effects of quercetin on L-type voltage-gated Ca²⁺ channels and voltage-gated K⁺ channels were studied using a whole-cell patch clamp. Quercetin (3–30 µM) produced a depression and relaxation on the contraction induced by KCl or the thromboxane A2 analog 9,11-Dideoxy-9α,11α-methanoepoxy prostaglandin F _2α . The vasorelaxation was attenuated by 4-aminopyridine, a specific voltage-gated K⁺ channel inhibitor, but was not affected by the NG-nitro-L-arginine methylester ester (a nitric oxide synthesis inhibitor), glibenclamide (a ATP-activated K⁺ channel inhibitor), iberiotoxin (a Ca²⁺-activated K⁺ channel inhibitor), BaCl₂ (an inward rectifier K⁺ channel inhibitor), or by endothelium denudation. At the same concentrations, quercetin reduced the KCl-induced elevation of the intracellular free Ca²⁺ concentration, inhibited the inward Ca²⁺ currents through L-type voltage-gated Ca²⁺ channels, and increased the outward K⁺ currents through voltage-gated K⁺ channels in the rat coronary artery smooth muscle cells. Collectively, our results demonstrate that quercetin possesses vasospasmolytic effects in RCA and suggest that depression of the Ca²⁺ influx through L-type voltage-gated Ca²⁺ channels and augmentation of voltage-gated K⁺ channel activity in the myocytes may underlie coronary relaxation.

Farrerol, isolated from Rhododendron dauricum L., has been proven to be an important multifunctional physiologically active component, but its vasoactive mechanism is not clear. The present study was performed to observe the vasoactive effects of farrerol on rat aorta and to investigate the possible underlying mechanisms. Isolated aortic rings of rat were mounted in an organ bath system and the myogenic effects stimulated by farrerol were studied. Intracellular Ca²⁺ ([Ca²⁺]_in) was measured by molecular probe fluo-4-AM and the activities of L-type voltage-gated Ca²⁺ channels (LVGC) were studied with whole-cell patch clamp in cultured vascular smooth muscle cells (VSMCs). The results showed that farrerol significantly induced dose-dependent relaxation on aortic rings, while this vasorelaxation was not affected by N^G-nitro-l-arginine methylester ester or endothelium denudation. In endothelium-denuded aortas, farrerol also reduced Ca²⁺-induced contraction on the basis of the stable contraction induced by KCl or phenylephrine (PE) in Ca²⁺-free solution. Moreover, after incubation with verapamil, farrerol can induce relaxation in endothelium-denuded aortas precontracted by PE, and this effect can be enhanced by ruthenium red, but not by heparin. With laser scanning confocal microscopy method, the farrerol-induced decline of [Ca²⁺]_in in cultured VSMCs was observed. Furthermore, we found that farrerol could suppress Ca²⁺ influx via LVGC by patch clamp technology. These findings suggested that farrerol can regulate the vascular tension and could be developed as a practicable vasorelaxation drug.

Remote ischemic preconditioning is often performed by limb ischemic preconditioning (LIPC), which has been demonstrated to be beneficial to various cells, including endothelial cells. The mechanisms underlying the protection have not been well clarified. The present study was designed to observe the effects of sera derived from rats after LIPC on human umbilical vein endothelial cells (HUVECs) injured by hydrogen peroxide (H₂O₂) -induced oxidative stress and explore the involvement of redox state in the protection. Incubation with 1 mM H₂O₂ for 2 h induced a significant reduction in HUVECs’ viability with increased production of malondialdehyde (MDA) and reactive oxygen species (ROS). Preincubation with early preconditioning serum (EPS) or delayed preconditioning serum (DPS) derived from rats subjected to LIPC alleviated these changes. Both EPS and DPS increased the nuclear translocation of transcription factor nuclear factor E2-related factor 2 (Nrf2) and the expression of antioxidases. The protective effects of EPS and DPS were blocked neither by MEK/ERK inhibitors U0126 nor by PI3K/Akt inhibitors LY294002. In conclusion, the present study provides the evidence that LIPC protects the HUVECs from H₂O₂-induced injury by, at least partially, enhancement of Nrf2 translocation and upregulation of antioxidases via signaling pathways independent of MEK/ERK and PI3K/Akt.