Sex Differences in Oxidative Stress-Mediated Reductions in Microvascular Endothelial Function in Young Adult e-Cigarette Users

Cardiovascular health effects of vaping e-cigarettes: a systematic review and meta-analysis

BACKGROUND

There is substantial interest in the cardiovascular effects of e-cigarette use, highlighting the need to update our knowledge on the subject. We conducted this review to analyse whether e-cigarette use increases cardiovascular health risks and how these risks vary among different populations.

METHODS

We searched six databases and included peer-reviewed human, animal, cell/in vitro original studies but excluded qualitative studies, which were published between July 2021 and December 2023. Three types of e-cigarette exposure were examined: acute, short-to-medium term and long term. Different risk of bias tools were used for assessing the quality of the included human studies and we conducted meta-analysis when possible.

RESULTS

We included 63 studies in the main analysis, 12 studies in the meta-analysis and 32 studies in the sociodemographic factor-based subgroup analysis. Over half of the human studies had low risk of bias. Acute exposure to e-cigarette was associated with increased heart rate (HR) (mean difference (MD) 11.329, p<0.01) and blood pressure (BP) (MD 12.856, p<0.01 for systolic; MD 7.676, p<0.01 for diastolic) compared with non-use. While HR was lower after acute exposure to e-cigarettes compared with cigarettes (MD -5.415, p<0.01), no significant difference in systolic or diastolic BP was observed. Non-smoker current vapers had no significant differences in resting HR and BP compared with non-users but lower resting HR (MD -2.608, p<0.01) and diastolic BP (MD -3.226, p<0.01) compared with non-vaper current smokers. Despite some association between e-cigarette and endothelial dysfunction, short-to-medium-term transition from cigarettes to e-cigarettes may improve blood flow and BP, particularly among females and younger individuals. There is lack of evidence supporting any association of e-cigarette use with cardiovascular diseases and cardiac dysfunction or remodelling.

CONCLUSIONS

This review highlighted several important cardiovascular impacts of e-cigarette use compared with non-use and cigarette smoking. However, the evidence is still limited and requires future research.

PROSPERO REGISTRATION NUMBER

CRD42023385632.

E-cigarette-induced changes in cell stress and mitochondrial function

Inhaling aerosols from electronic nicotine delivery systems, such as e-cigarettes (e-cigs), may pose health risks beyond those caused by nicotine intake. Exposure to e-cig aerosols can lead to the release of exosomes and metabolites into the bloodstream, potentially affecting mitochondrial physiology across the body, leading to chronic inflammatory diseases. In this study we assessed the effects of e-cig use by young healthy human subjects on the circulating exosome profile and markers of cell stress, and also defined the effects of e-cig user plasma on mitochondrial function in endothelial cells (EA. Hy 926) and epithelial cells (A549) via adoptive transfer. E-cig users had altered plasma exosome profiles, with significantly increased levels of cell free mitochondrial DNA (mtDNA), protein carbonyls, and 4-HNE relative to non-users. Plasma from e-cig users decreased maximal mitochondrial respiration and spare capacity of cells, while also increasing metabolic stress, as evidenced by changes in mitochondrial phenotype from basal to stressed in both endothelial and epithelial cells, which was corroborated by electron microscopy demonstrating structural changes in mitochondria. Mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) levels significantly increased in e-cig plasma-subjected cells. Overall, we identified alterations in plasma exosome profiles and increased markers of mitochondrial stress in e-cig users and evidence that circulating factors within plasma from e-cig users drives metabolic stress in endothelial and epithelial cells. Our results imply that e-cig use adversely affects mitochondrial function, leading to stress and potentially chronic inflammation across the body.

Quantification and interpretation of nitric oxide-dependent cutaneous vasodilation during local heating

Human cutaneous microdialysis approaches for assessing nitric oxide (NO)-dependent blood flow include local heating (LH) of the skin until a plateau is reached, followed by infusion of a NO synthase inhibitor such as NG-nitro-l-arginine methyl ester (l-NAME); however, varied methods of quantifying and expressing NO-dependent vasodilation can obfuscate data interpretation and reproducibility. We retrospectively assessed NO-dependent vasodilation during LH to 39°C or 42°C, calculated as the 1) absolute contribution of the NO-dependent component (along with baseline and the non-NO-dependent component) to the total cutaneous vascular conductance (CVC) response to LH, normalized to maximal CVC (%CVCmax); 2) difference in %CVCmax (Δ%CVCmax) between the LH plateau and post-NO synthase inhibition (l-NAME plateau; Δ%CVCmax = LH plateau - l-NAME plateau); 3) percentage of the LH plateau attributable to Δ%CVCmax (%plateau = Δ%CVCmax/LH plateau × 100); and 4) %plateau when correcting for baseline. The LH plateaus during 39°C and 42°C were 48 ± 17%CVCmax (9 ± 5% baseline; 2 ± 4% non-NO dependent; 36 ± 15% NO dependent) and 88 ± 10%CVCmax (15 ± 8% baseline; 9 ± 10% non-NO dependent; 64 ± 13% NO dependent), respectively. The absolute contributions of the non-NO-dependent and NO-dependent components of the response (P < 0.0001) and the Δ%CVCmax (66 ± 14 vs. 38 ± 15%) were greater during 42°C compared with 39°C (all P ≤ 0.02); however, there were no differences between the two protocols in %plateau (75 ± 13 vs. 80 ± 10%; P = 0.57) or %plateauBL (88 ± 14 vs. 95 ± 8%; P = 0.31). For both protocols, the values were greater for %plateauBL versus Δ%CVCmax and %plateau (P ≤ 0.0001), and for %plateau versus Δ%CVCmax (P ≤ 0.05). Quantification of NO-dependent skin vasodilation responses to LH is dependent upon the mathematical approach and verbal description, which can meaningfully impact data interpretation and reproducibility.NEW & NOTEWORTHY Local heating protocols are commonly used in conjunction with intradermal microdialysis for assessing nitric oxide (NO)-dependent microvascular function in humans, but various methods used to quantify and describe NO-dependent vasodilation may impact data interpretation. We compared four approaches for quantifying NO-dependent cutaneous vasodilation during local heating at 39°C and 42°C. We identify discrepancies in calculated NO-dependent dilation responses that are dependent upon the mathematical approach and meaningfully impact data interpretation and reproducibility.

Maternal use of electronic cigarettes and impact on offspring: a double-hit model

Endothelial dysfunction is a predictor for cardiovascular disease. Preclinical data suggest longstanding cardiovascular and cerebrovascular dysfunction occurs in offspring with perinatal electronic cigarette (Ecig) exposure. Furthermore, direct use of Ecigs increases reactive oxygen species and impairs cerebrovascular function, but the combined effect of direct use in offspring with a history of perinatal exposure (i.e. double-hit condition) is not known. We tested the hypothesis that offspring with double-hit Ecig exposure will lead to greater cerebrovascular and neurocognitive dysfunction compared with in utero exposure only. Male and female offspring were obtained from time-mated Sprague Dawley female rats exposed to air (n = 5 dams) or Ecig exposed (n = 5 dams) and studied at either 3 or 6 mo after birth. Ecig exposure for double-hit offspring began at 1-mo before the timepoints and lasted 4 wk (5 days/wk with 90-min exposure/day). We found double-hit offspring (Ecig:Ecig = exposure dam:offspring) sustained further blunted middle cerebral artery (MCA) reactivity, increased severity of neuronal damage, and increased interactions of astrocytes and endothelial cells compared with offspring with maternal (Ecig:Air) or direct (Air:Ecig) exposure only. Circulating extracellular vesicles (EVs) were increased, whereas sirtuin 1 (SIRT1) was decreased, in all Ecig-exposed groups compared with controls (Air:Air), with Ecig:Ecig group showing the greatest respective change for each. Electron paramagnetic resonance (EPR) spectroscopy revealed oxidative stress was the highest in the plasma of Ecig:Ecig group (P < 0.05) than the other groups. These data show that a double-hit exposure in adolescent or adult offspring results in a greater decline in cerebrovascular function, biomarkers of neuronal dysfunction, and increased circulation of EVs compared with a single-hit exposure.NEW & NOTEWORTHY These data add to the growing body of literature demonstrating that electronic cigarette (Ecig) use during pregnancy (even without nicotine) is not safe, and primes offspring to have worse cardiovascular health outcomes in early and adult life. A key finding from this work is that a second insult from direct vaping in offspring with prior in utero exposure induces greater vascular dysfunction, increased oxidative stress, and shows evidence of neuronal dysfunction compared with either direct- or maternal-only exposure.

Young users of electronic cigarettes exhibit reduced cardiorespiratory fitness

Electronic nicotine delivery systems, often referred to as e-cigarettes, are popular tobacco products frequently advertised as safer alternatives to traditional cigarettes despite preliminary data suggesting a potential negative cardiovascular impact. Cardiorespiratory fitness is a critical cardiovascular health marker that is diminished in individuals who consume traditional tobacco products. Whether the use of e-cigarettes impacts cardiorespiratory fitness is currently unknown. Thus, the purpose of this study was to investigate the impact of regular e-cigarette use on cardiorespiratory fitness in young healthy adults. Twenty-six users of e-cigarettes (ECU, 13 males, and 13 females; age: 24 ± 3 yr; e-cigarette usage 4 ± 2 yr) and 16 demographically matched nonusers (NU, 6 males, and 10 females; age: 23 ± 3 yr) participated in this study. Cardiorespiratory fitness was measured by peak oxygen consumption (V̇o2peak) during a cardiopulmonary exercise test. Measurements of chronotropic response, hemodynamic, oxygen extraction, and utilization were also evaluated. Our results suggest that regular users of e-cigarettes exhibited significantly lower peak oxygen consumption when compared with nonusers, even when controlled by fat-free mass and lean body mass. Hemodynamic changes were not different between both groups during exercise, whereas lower chronotropic responses and skeletal muscle oxygen utilization were observed in users of e-cigarettes. Results from the present study demonstrate that young, apparently healthy, regular users of e-cigarettes exhibit significantly reduced cardiorespiratory fitness, lower chronotropic response, and impaired skeletal muscle oxygen utilization during exercise. Overall, our findings contribute to the growing body of evidence that supports adverse effects of regular e-cigarette use on cardiovascular health.NEW & NOTEWORTHY E-cigarettes are tobacco products frequently used by youth and young adults. Little is known about the long-term health effects of their prolonged use. Results from the present study demonstrate that young, apparently healthy, regular users of e-cigarettes exhibit significantly reduced cardiorespiratory fitness, a marker of cardiovascular health and a predictor of all-cause mortality. We also identified that the young users of e-cigarettes present with lower chronotropic response and impaired skeletal muscle oxygen utilization during exercise.

Evidence of premature vascular dysfunction in young adults who regularly use e-cigarettes and the impact of usage length

BACKGROUND

Electronic (e-) cigarettes are increasingly popular tobacco products on the US market. Traditional tobacco products are known to cause vascular dysfunction, one of the earliest indicators of cardiovascular disease (CVD) development. However, little is known about the effect of regular e-cigarette use on vascular function. The purpose of this study was to investigate the impact of regular e-cigarette use on vascular function and cardiovascular health in young, healthy adults.

METHODS

Twenty-one regular users of e-cigarettes (ECU) and twenty-one demographically matched non-users (NU) completed this study. Vascular health was assessed in the cutaneous microcirculation through different reactivity tests to evaluate overall functionality, endothelium-dependent vasodilation (EDD), and endothelium-independent vasodilation (EID). Macrovascular function was assessed using flow-mediated dilation (FMD).

RESULTS

Our results suggest that regular users of e-cigarettes present with premature microvascular impairment when compared to non-users. Specifically, they exhibit lower hyperemic (p = 0.003), thermal (p = 0.010), and EDD (p = 0.004) responses. No differences in EID between the groups were identified. We also identified that individuals who use e-cigarettes for longer than 3 years also present with systemic manifestations, as observed by significantly reduced macrovascular (p = 0.002) and microvascular (p ≤ 0.044) function.

CONCLUSIONS

Our novel data suggests that young, apparently healthy, regular users of e-cigarettes present with premature vascular dysfunction in the microcirculation when compared to non-users. We have also identified systemic vascular dysfunction affecting both the micro and macrovasculature in those young individuals who used e-cigarettes for longer than 3 years. Taken together, these findings associate regular e-cigarette use with premature vascular dysfunctions and adverse cardiovascular outcomes.