We investigated the molecular mechanism underlying the role of transient receptor potential vanilloid type 1 (TRPV1), a Ca²⁺-permeable non-selective cation channel, in the activation of endothelial nitric oxide (NO) synthase (eNOS) in endothelial cells (ECs) and mice. In ECs, TRPV1 ligands (evodiamine or capsaicin) promoted NO production, eNOS phosphorylation, and the formation of a TRPV1–eNOS complex, which were all abrogated by the TRPV1 antagonist capsazepine. TRPV1 ligands promoted the phosphorylation of Akt, calmodulin-dependent protein kinase II (CaMKII) and TRPV1, and increased the formation of a TRPV1–Akt–CaMKII complex. Removal of extracellular Ca²⁺ abolished the ligand-induced increase in the phosphorylation of Akt and CaMKII, formation of a TRPV1–eNOS complex, and eNOS activation. Inhibition of PI3K and CaMKII suppressed the ligand-induced increase in TRPV1 phosphorylation, formation of a TRPV1–eNOS complex, and eNOS activation. TRPV1 activation increased the phosphorylation of Akt, CaMKII, and eNOS in the aortas of wild-type mice but failed to activate eNOS in TRPV1-deficient aortas. Additionally, TRPV1 ligand-induced angiogenesis was diminished in eNOS- or TRPV1-deficient mice. When compared with apolipoprotein E (ApoE)-deficient mice, ApoE/TRPV1-double-knockout mice displayed reduced phosphorylation of eNOS, Akt, and CaMKII in aortas but worsened atherosclerotic lesions. TRPV1 activation in ECs may trigger Ca²⁺-dependent PI3K/Akt/CaMKII signalling, which leads to enhanced phosphorylation of TRPV1, increased TRPV1–eNOS complex formation, eNOS activation and, ultimately, NO production.

Although a link between toxic smoke and oxidant lung vascular injury has been indicated, the cellular mechanisms of smoke-induced injury to lung endothelial cells are unknown. We investigated oxidative stress and apoptosis induced by wood smoke extract (SE) in human pulmonary artery endothelial cells (HPAECs) and delineated their relationship. We found that SE increased intracellular reactive oxygen species (ROS), depleted intracellular glutathione, and upregulated Cu/Zn superoxide dismutase and heme oxygenase-1 (2 antioxidant enzymes), but it failed to alter the expression of catalase and glutathione peroxidase. In addition, SE promoted apoptosis as indicated by the external exposure of membrane phosphatidylserine, the loss of mitochondrial membrane potential, an increase in the level of Bax (a proapoptotic protein), and enhanced DNA fragmentation. This apoptosis was associated with mitochondrial-to-nuclear translocation of apoptosis-inducing factor (AIF) and endonuclease G (EndoG) (2 apoptogenic proteins) but was independent of caspase cascade activation. Whereas N-acetylcysteine (an antioxidant) effectively reversed the SE-induced increase in ROS and depletion of glutathione, it also suppressed SE-induced nuclear translocation of either AIF or EndoG and prevented the enhanced DNA fragmentation that would have resulted from this. We conclude that 1) although SE upregulates Cu/Zn superoxide dismutase and heme oxygenase-1, it nevertheless increases intracellular oxidative stress in HPAECs, and 2) SE promotes oxidative stress-mediated caspase-independent HPAEC apoptosis that involves mitochondrial-to-nuclear translocation of AIF and EndoG. Thus modulations of the expression of antioxidant enzymes and the caspase-independent apoptotic pathway are possible target choices for potential therapeutic regimes to treat smoke-induced lung injury.

Cigarette smoking causes persistent lung inflammation that is mainly regulated by redox-sensitive pathways. We have previously reported that cigarette smoke (CS) activates reactive oxygen species- (ROS-) sensitive mitogen-activated protein kinases (MAPKs)/nuclear factor-κB (NF-κB) signaling leading to induction of lung inflammation. Paeonol, the main phenolic compound present in the Chinese herbPaeonia suffruticosa, has antioxidant and anti-inflammatory properties. However, whether paeonol has similar beneficial effects against CS-induced lung inflammation remains unclear. Using a murine model, we showed that chronic CS exposure for 4 weeks caused pulmonary inflammatory infiltration, increased lung vascular permeability, elevated lung levels of chemokines, cytokines, and 4-hydroxynonenal (an oxidative stress biomarker), and induced lung inflammation; all of these CS-induced events were suppressed by chronic treatment with paeonol. Using human bronchial epithelial cells (HBECs), we demonstrated that cigarette smoke extract (CSE) sequentially increased extracellular and intracellular levels of ROS, activated the MAPKs/NF-κB signaling, and induced interleukin-8 (IL-8); all these CSE-induced events were inhibited by paeonol pretreatment. Our findings suggest a novel role for paeonol in alleviating the oxidative stress and lung inflammation induced by chronic CS exposurein vivoand in suppressing CSE-induced IL-8in vitrovia its antioxidant function and an inhibition of the MAPKs/NF-κB signaling.