Smoking without exception adversely affects vascular structure and function in apparently healthy Chinese: Implications in global atherosclerosis prevention

Age and sex differences in the effects of short- and long-term exposure to air pollution on endothelial dysfunction

BACKGROUND

The effects of air pollution on endothelial function remain unclear across populations. We aimed to use brachial artery flow-mediated dilatation (FMD) to identify demographic differences in the effects of air pollution exposure on endothelial dysfunction.

METHODS

We measured FMD in 850 participants from October 2016 to January 2020. Location-specific concentrations of fine particulate matter < 2.5 μm aerodynamic diameter (PM2.5), inhalable particulate matter < 10 μm aerodynamic diameter (PM10), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3) measured by fixed ambient air monitoring stations were collected for short- and long-term exposure assessment. Multiple linear regression models and restricted cubic splines were used to assess the associations before and after stratification by age and sex.

RESULTS

This study eventually included 828 participants [551 (66.5%) younger than 65 years and 553 (66.8%) men]. Each 10 µg/m3 increase in 7-day exposure to PM2.5 and PM10 was significantly linearly associated with a 0.07% (β = -0.07, 95% CI: -0.13 to -0.004) and 0.05% (β = -0.05, 95% CI: -0.10 to -0.004) decrease in FMD in the fully adjusted model. After full adjustment, long-term exposure to all air pollutants was significantly associated with impaired FMD. Each 10 µg/m3 increase in long-term exposure to PM2.5 and PM10 was significantly associated with a -0.18% (95% CI: -0.34 to -0.03) and - 0.23% (95% CI: -0.40 to -0.06) change in FMD, respectively. After stratification, the associations of lower FMD with long-term exposure to PM2.5, PM10, SO2, NO2, and CO significantly persisted in men and participants younger than 65 years instead of women or older participants. For short-term exposure, we observed differences consistent with long-term exposure and a stronger effect of 7-day exposure to SO2 in men due to a significant interaction effect.

CONCLUSION

Short- and long-term exposure to different air pollutants are strongly associated with decreased endothelial function, and susceptibility to air pollution varies significantly with age and sex.

Vitamins B-12 and C Supplementation Improves Arterial Reactivity and Structure in Passive Smokers: Implication in Prevention of Smoking-Related Atherosclerosis

BACKGROUND

Atherosclerosis is an important medical problem of modern society. High environmental tobacco smoke in casino is associated with an accelerated atherogenic process. We have previously shown vitamin B12 and C supplementation improves vascular reactivity and may be beneficial in vascular protection.

OBJECTIVE

To evaluate the impact of vitamin supplementation on atherosclerosis (brachial artery reactivity FMD and carotid intima-media thickness IMT) in subjects exposed to high environmental tobacco smoke.

DESIGN

Double-blind 2x2 factorial design fashion.

SETTING

Computer randomization in 4 treatment groups: placebo (n=24), vitamin B12 (n=21), vitamin C (n=23) and vitamin B12+C (n=23) groups.

PARTICIPANTS

91 passive-smoking casino employees (19.2% male, mean age 45.0±8.2 years).

INTERVENTION

Subjects were randomized to receive vitamin B12 (500µg daily), vitamin C (200mg daily), vitamin B12+C or image-matched placebo capsules for 1 year.

MEASUREMENT

Brachial FMD and carotid IMT (surrogate atherosclerotic markers) were measured by ultrasound at baseline and on completion at 12 months.

METHODS

91 passive smoking casino employees (19.2% male, mean age 45.0±8.2 years) were randomized to receive vitamin B12 (500µg daily), vitamin C (200mg daily), vitamin B12+C or image-matched placebo capsules in double-blind 2 x 2 factorial design fashion for 1 year. Brachial FMD and carotid IMT (surrogate atherosclerotic markers) were measured by ultrasound at baseline and 12 months.

RESULTS

Of the 78 (85.7%) passive-smoking employees completed the study, 11.5% had hypertension, 5.1% diabetes mellitus and 15.4% hypercholesterolemia. There were no significant changes in their blood pressures, lipid profiles, glucose and body mass index after supplementation for 1 year, but mild decrease in DBP (p<0.001) and blood creatinine (p<0.01) after combined vitamin B12 and C, and significant increase in blood B12 after vitamin B12 (p<0.01) and vitamin B12+C supplementations (p<0.001). Brachial FMD and cartotid IMT improved after the 3 vitamin supplementations (p<0.001), but not after placebo, being more significant after combined vitamin supplementations (p<0.0001). No adverse effects were reported.

CONCLUSION

Vitamin B12 or C supplementation in passive smokers improved vascular reactivity and structures at 1 year, with implication in long term atherosclerosis prevention.

A greater burden of atrial fibrillation is associated with worse endothelial dysfunction in hypertension

Atrial fibrillation (AF) and hypertension often co-exist and both are associated with endothelial dysfunction. We hypothesised that AF would further worsen endothelium-dependent flow-mediated dilatation (FMD) in hypertension patients compared to those without AF. In a cross-sectional comparison, we measured brachial artery diameter at rest and during reactive hyperaemia following 5 min of arterial occlusion in two patient groups: AF (and hypertension) (n = 61) and hypertension control groups (n = 33). The AF (and hypertension) subgroups: permanent AF (n = 30) and paroxysmal AF (n = 31) were also assessed. The permanent AF patients received heart rate and blood pressure (BP) control optimisation and were then followed up after eight weeks for repeat FMD testing. There was no significant difference in FMD between AF (and hypertension) group and hypertension control group (4.6%, 95% CI [2.6-5.9%] vs 2.6%, 95% CI [1.9-5.3%]; p = 0.25). There was a significant difference in FMD between permanent AF and paroxysmal AF groups (3.1%, 95% CI [2.3-4.8%] vs 5.9%, 95% CI [4.0-8.1%]; p = 0.02). Endothelium-dependent FMD response showed a non-significant improvement trend following eight weeks of heart rate and BP optimisation (3.1%, 95% CI [2.3-4.8%] (baseline) vs 5.2%, 95% CI [3.9-6.5%] (follow up), p = 0.09). Presence of AF generally does not incrementally worsen endothelial dysfunction in hypertension patients, although the duration and frequency of AF (paroxysmal AF to permanent AF) does lead to worsening endothelial function. Eight weeks of BP optimisation did not significantly improve endothelial dysfunction as measured by FMD.

Mediating effects of lipids on the association between smoking and coronary artery disease risk among Chinese

Objective

The mechanism between smoking and coronary artery disease (CAD) remains unclear. It is likely that lipid (including triglycerides (TG), total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C), high density lipoprotein-cholesterol (HDL-C)) have been functioning as one of the mediators between smoking and the CAD occurrence. The study aimed to investigate the mediating effect of lipid on the relationship between smoking and CAD risk.

Methods

The case-control study included 2048 subjects. General linear regression analysis was used to corroborate the association between smoking and lipid levels. Univariate and multivariate logistic regression analysis were performed to reveal the relationship between smoking, lipid and the risk of CAD. Mediation analysis was used to investigate whether the association between smoking and CAD risk was mediated by lipid.

Results

Smoking was found to be associated with the risk of CAD (odds ratio (OR) = 1.34, 95% confidence interval (CI): 1.05–1.71, P = 0.019). Regression analysis showed that TG, TC and HDL-C were associated with CAD (OR = 2.69, 95%CI: 2.12–3.40, P < 0.001; OR = 0.34, 95%CI: 0.29–0.43, P < 0.001; OR = 0.37, 95%CI: 0.30–0.47, P < 0.001). Moreover, the ratio of TG to HDL-C (TG/HDL-C) was also related to CAD (OR = 4.45, 95%CI: 3.52–5.64, P < 0.001). Mediation analysis showed that among the effects of smoking on CAD, 17.52% was mediated by lipid, in which HDL-C accounted for 11.16% and TG accounted for 6.36%. Further analysis showed that the effect was also partially mediated by TG/HDL-C, which was accounted for 28%.

Conclusions

Lipid plays a partial mediation on the association between smoking and CAD risk. The study provides a clue on the mediation effect of lipids on the relationship between smoking and CAD risks, which is a novel insight to the progression of CAD.

Endothelial function in patients with atrial fibrillation

Atrial fibrillation (AF) is the most common heart arrhythmia and is associated with poor outcomes. The adverse effects of AF are mediated through multiple pathways, including endothelial dysfunction, as measured by flow-mediated dilatation. Flow-mediated dilatation has demonstrated endothelial dysfunction in several conditions and is associated with poor outcomes including mortality, yet can be improved with medical therapy. It is thus a useful tool in assessing endothelial function in patients. Endothelial dysfunction is present in patients with AF and is associated with poor outcomes. These patients are generally older and have other co-morbidities such as hypertension, hypercholesterolaemia and diabetes. The precise process by which AF is affiliated with endothelial damage/dysfunction remains elusive. This review explores the endothelial structure, its physiology and how it is affected in patients with AF. It also assesses the utility of flow mediated dilatation as a technique to assess endothelial function in patients with AF. Key MessagesEndothelial function is affected in patients with atrial fibrillation as with other cardiovascular conditions.Endothelial dysfunction is associated with poor outcomes such as stroke, myocardial infarction and death, yet is a reversible condition.Flow-mediated dilatation is a reliable tool to assess endothelial function in patients with atrial fibrillation.Patients with atrial fibrillation should be considered for endothelial function assessment and attempts made to reverse this condition.

The impact of tetrahydrobiopterin administration on endothelial function before and after smoking cessation in chronic smokers

Cardiovascular disease mortality is reduced following smoking cessation but the reversibility of specific atherogenic risk factors such as endothelial dysfunction is less established. We assessed brachial artery flow-mediated dilation (FMD) in 57 chronic smokers and 15 healthy controls, alone and after oral tetrahydrobiopterin (BH4) administration, to assess the extent to which reduced bioactivity of BH4, a cofactor for the endothelial nitric oxide synthase enzyme (eNOS), contributes to smoking-associated reductions in FMD. Thirty-four smokers then ceased cigarette and nicotine use for 1 week, after which FMD (±BH4 administration) was repeated. Brachial artery FMD was calculated as the peak dilatory response observed relative to baseline (%FMD). Endothelium-independent dilation was assessed by measuring the dilatory response to sublingual nitroglycerin (%NTG). Chronic smokers exhibited reduced %FMD relative to controls: (5.6±3.0% vs. 8.1±3.7%; P<0.01) and %NTG was not different between groups (P=0.22). BH4 administration improved FMD in both groups (P=0.03) independent of smoking status (P=0.78) such that FMD was still lower in smokers relative to controls (6.6±3.3% vs. 9.8±3.2%; P<0.01). With smoking cessation, FMD increased significantly (from 5.0±2.9 to 7.8±3.2%;P<0.01); %NTG was not different (P=0.57) and BH4 administration did not further improve FMD (P=0.33). These findings suggest that the blunted FMD observed in chronic smokers, likely due at least in part to reduced BH4 bioactivity and eNOS uncoupling, can be restored with smoking cessation. Post-cessation BH4 administration does not further improve endothelial function in chronic smokers, unlike the effect observed in nonsmokers, indicating a longer-term impact of chronic smoking on vascular function that is not acutely reversible.

Effects of active and passive smoking on the development of cardiovascular disease as assessed by a carotid intima-media thickness examination in patients with type 2 diabetes mellitus

Carotid intima-media thickness has been widely used as a surrogate end-point for cardiovascular disease, myocardial infarction, and stroke. This study aimed to assess the effects of active and passive smoking exposure on the development of cardiovascular disease in patients with type 2 diabetes mellitus. Seven hundred twenty-two patients with type 2 diabetes mellitus were recruited for the study. A standardized questionnaire on smoking status, pack-years of smoking, and the number of years of smoking cessation was provided to the patients, and their responses were collected for analysis. The carotid intima-media thickness, carotid plaque, and the internal diameter of the common carotid artery were determined by high-resolution B-mode ultrasonography. Compared to non-smokers, passive female smokers had a higher risk of cardiovascular disease (odds ratio = 3.50, 95% confidence interval: 1.29-9.49, P = 0.009); they also had a significantly larger common carotid artery (P = 0.041) and risk of carotid plaque (odds ratio = 2.20, 95% confidence interval: 1.1980-4.0505, P = 0.01). Both active and passive male smokers had a significantly greater carotid intima-media thickness than non-smokers (P = 0.003 and P = 0.005, respectively). Male active smokers had a significantly higher risk of carotid plaque (odds ratio = 2.88, 95% confidence interval: 1.4788-5.6094, P = 0.001). In conclusion, cumulative active and passive smoking exposures are significant risk factors for carotid atherosclerosis in patients with type 2 diabetes mellitus. Our results highlight the importance of endorsing a smoke-free environment for patients with type 2 diabetes mellitus.

Extending the Bayesian Adjustment for Confounding algorithm to binary treatment covariates to estimate the effect of smoking on carotid intima-media thickness: the Multi-Ethnic Study of Atherosclerosis

We illustrate the application of the Bayesian Adjustment for Confounding (BAC) algorithm when the treatment covariate is binary. Using data from the Multi-Ethnic Study of Atherosclerosis, we estimate the effect of ever smoking on common carotid artery intimal medial thickness among adult Caucasian participants (n=1378). Our novel implementation of the BAC algorithm is performed first from an outcome model perspective and second from a treatment model perspective with both inverse probability weighting and doubly-robust estimation techniques. The BAC results are compared with the results obtained using standard model averaging and full model strategies, giving a range of adjusted estimates between 45.50 and 65.30 μm for increased common carotid artery intimal medial thickness among ever smokers. For both perspectives, we observe that BAC offers similar performance to using the fully specified outcome and/or treatment model (the full outcome model ever smoking effect is 48.61 μm; 95% CI: (0.62, 96.60)). We then redo the analyses for the African American, Hispanic, and Chinese adult participants to study the robustness of these findings with reduced sample size. For the Chinese subcohort, which corresponds to the smallest sample size (n=436), we find that, from a treatment model perspective, BAC reduces the variability of the estimates in comparison with using a full model approach. This suggests that the use of BAC in conjunction with inverse probability weighting and doubly-robust estimation can be advantageous when applied to relatively small sample sizes. This conjecture is subsequently verified on the basis of three simulated experiments.

Smoking in Asians: it doesn't stop at vascular endothelium

Smoking is a global risk factor for atherosclerosis, affecting societies all over the world. Smoking exerts its pro-atherogenic effects by triggering the generation of free radicals and by modifying vascular redox signaling. These abnormal vascular responses to cigarette smoking result into impaired endothelial function, decreased nitric oxide bioavailability, increased intima media thickness and finally atherosclerotic plaque formation in human arteries. Importantly, evidence suggests that cigarette smoking may have an effect on vascular smooth muscle cells function, leading to impaired endothelium-independent dilation in response to nitrate, in the brachial artery of healthy smokers. Taken together, it is now well established that smoking induces functional and structural abnormalities in the vascular wall, by mechanisms involving endothelial dysfunction and impairment of vascular smooth muscle cells in human arterial tree.