Electronic Cigarettes Induce Mitochondrial DNA Damage and Trigger TLR9 (Toll-Like Receptor 9)-Mediated Atherosclerosis

Abstract

Objective: Electronic cigarette (e-cig) use has recently been implicated in promoting atherosclerosis. In this study, we aimed to investigate the mechanism of e-cig exposure accelerated atherosclerotic lesion development. Approach and Results: Eight-week-old ApoE −/− mice fed normal laboratory diet were exposed to e-cig vapor (ECV) for 2 hours/day, 5 days/week for 16 weeks. We found that ECV exposure significantly induced atherosclerotic lesions as examined by Oil Red O staining and greatly upregulated TLR9 (toll-like receptor 9) expression in classical monocytes and in the atherosclerotic plaques, which the latter was corroborated by enhanced TLR9 expression in human femoral artery atherosclerotic plaques from e-cig smokers. Intriguingly, we found a significant increase of oxidative mitochondria DNA lesion in the plasma of ECV-exposed mice. Administration of TLR9 antagonist before ECV exposure not only alleviated atherosclerosis and the upregulation of TLR9 in plaques but also attenuated the increase of plasma levels of inflammatory cytokines, reduced the plaque accumulation of lipid and macrophages, and decreased the frequency of blood CCR2 + (C-C chemokine receptor type 2) classical monocytes. Surprisingly, we found that cytoplasmic mitochondrial DNA isolated from ECV extract-treated macrophages can enhance TLR9 activation in reporter cells and the induction of inflammatory cytokine could be suppressed by TLR9 inhibitor in macrophages. Conclusions: E-cig increases level of damaged mitochondrial DNA in circulating blood and induces the expression of TLR9, which elevate the expression of proinflammatory cytokines in monocyte/macrophage and consequently lead to atherosclerosis. Our results raise the possibility that intervention of TLR9 activation is a potential pharmacological target of ECV-related inflammation and cardiovascular diseases.

Dysregulated Metabolites Serve as Novel Biomarkers for Metabolic Diseases Caused by E-Cigarette Vaping and Cigarette Smoking

“…Our previous studies described that e-cig exposure can induce oxidative stress in the mitochondrion and dysregulation of mitochondrial complexes in lung fibroblasts [39]. Furthermore, e-cig exposure causes an increased amount of damaged mitochondrial DNA in plasma as well as increases the risk of cardiovascular diseases [18]. In this study, we showed that most of the TCA cycle-related metabolites are downregulated in e-cig users while there were no changes in the cigarette smokers compared to the healthy controls.…”

“…Previous studies reported that e-cig vaping and cigarette smoking inhibited bioenergy synthesis and induced mitochondrial dysfunction [15,16]. Mitochondrial metabolism alternation in lungs was followed by cigarette smoke exposure [15,16]; e-cig exposure induced mitochondrial oxidative stress and DNA damage [17,18]. Interestingly, a previous study explained that circulated PG would be metabolized into lactic acid in the liver and go through the TCA cycle [19].…”

E-Cigarette Use: Device Market, Study Design, and Emerging Evidence of Biological Consequences

“…Taken together, macrophage-mediated inflammation and matrix remodeling promote further epithelial dysfunction, resulting in a positive feedback loop in which inflamed and damaged tissues release chemotactic signals that further recruit monocytes from the blood to the area of insult. Macrophages and monocytes also mediate dysfunction in the interior of blood vessels by promoting the development of ECA-induced atherosclerotic plaques via toll-like receptor 9 activation; blockade of this receptor ameliorated the production of inflammatory cytokines in the plasma [113].…”

Association of m.5178C>A variant with serum lipid levels: a systematic review and meta-analysis

“…A series of mouse model experiments [ 8–10 ] showed that the mtDNA damage affected lipid metabolism. For instance, the damaged mtDNA promoted lipid deposition in the atherosclerotic plaque [ 8 ], while the mtDNA dysfunction induced dyslipidemia [ 9 ].…”

“…A series of mouse model experiments [ 8–10 ] showed that the mtDNA damage affected lipid metabolism. For instance, the damaged mtDNA promoted lipid deposition in the atherosclerotic plaque [ 8 ], while the mtDNA dysfunction induced dyslipidemia [ 9 ]. Moreover, the loss of mitochondrial polymerase-γ proofreading activity (PolgD257A/D247A) and ApoE knockout (ApoE −/− ) caused severe dyslipidemia [ 10 ].…”