■尼古丁是香烟烟雾的主要成分,具有各种有害的心血管作用,包括心脏氧化应激的增加。α2-肾上腺素能受体(ARs)的激动剂,如右美托咪定,已被证明对氧化应激和相关的细胞凋亡和坏死发挥心脏保护作用。α2-AR是主要激活Gi/o蛋白的膜驻留G蛋白偶联受体(GPCRs)。他们还经历了GPCR-激酶(GRK)-2依赖性脱敏,这需要GRK2对激动剂激活的受体进行磷酸化,以诱导其与G蛋白解耦,从而终止α2AR介导的G蛋白信号传导。
■在本研究中,我们试图研究尼古丁对α2AR信号的影响以及暴露于H2O2诱导氧化细胞损伤的H9c2心肌细胞的影响。
■如预期的那样,用H2O2处理H9c2心肌细胞显著降低细胞活力,增加氧化应激,通过活性氧(ROS)相关荧光水平(DCF测定)和超氧化物歧化酶活性评估。在对照心肌细胞中,溴莫尼定的α2AR激活部分挽救了两种H2O2作用,但在用尼古丁预处理24小时的细胞中却没有。其中溴莫尼定不能减少H2O2诱导的细胞死亡和氧化应激。这是由于严重的α2AR脱敏,表现为溴莫尼定对Gi蛋白的低活化,在尼古丁处理的心肌细胞中伴有GRK2上调。最后,腺苷酸环化酶(AC)的药理学抑制阻断尼古丁预处理的H9c2心肌细胞中H2O2依赖性氧化损伤,表明α2AR激活通过其与Gai介导的AC抑制的经典偶联来保护氧化损伤。
■尼古丁可以抵消α2AR激动剂对氧化损伤的心脏保护作用,这可能对使用这类药物治疗的慢性吸烟者患者有重要意义。
UNASSIGNED: Nicotine is a major component of cigarette smoke with various detrimental cardiovascular effects, including increased oxidative stress in the heart. Agonism of α2-adrenergic receptors (ARs), such as with dexmedetomidine, has been documented to exert cardioprotective effects against oxidative stress and related apoptosis and necroptosis. α2-ARs are membrane-residing G protein-coupled receptors (GPCRs) that primarily activate Gi/o proteins. They are also subjected to GPCR-kinase (GRK)-2-dependent desensitization, which entails phosphorylation of the agonist-activated receptor by GRK2 to induce its decoupling from G proteins, thus terminating α2AR-mediated G protein signaling.
UNASSIGNED: In the present study, we sought to examine the effects of nicotine on α2AR signaling and effects in H9c2 cardiomyocytes exposed to H2O2 to induce oxidative cellular damage.
UNASSIGNED: As expected, treatment of H9c2 cardiomyocytes with H2O2 significantly decreased cell viability and increased oxidative stress, as assessed by reactive oxygen species (ROS)-associated fluorescence levels (DCF assay) and superoxide dismutase activity. Both H2O2 effects were partly rescued by α2AR activation with brimonidine in control cardiomyocytes but not in cells pretreated with nicotine for 24 hours, in which brimonidine was unable to reduce H2O2-induced cell death and oxidative stress. This was due to severe α2AR desensitization, manifested as very low Gi protein activation by brimonidine, and accompanied by GRK2 upregulation in nicotine-treated cardiomyocytes. Finally, pharmacological inhibition of adenylyl cyclase (AC) blocked H2O2-dependent oxidative damage in nicotine-pretreated H9c2 cardiomyocytes, indicating that α2AR activation protects against oxidative injury via its classic coupling to Gai-mediated AC inhibition.
UNASSIGNED: Nicotine can negate the cardioprotective effects of α2AR agonists against oxidative injury, which may have important implications for patients treated with this class of drugs that are chronic tobacco smokers.