Mechanisms of Coronary Thrombosis in Cigarette Smoke Exposure

Cigarette smoking and cardiovascular events: role of inflammation and subclinical atherosclerosis from the MultiEthnic Study of Atherosclerosis

OBJECTIVES

To examine the contemporary effect of smoking in a multiethnic sample, and to explore the respective contributions of inflammation and subclinical atherosclerosis to the cardiovascular consequences of smoking.

APPROACH AND RESULTS

We studied 6814 participants free of cardiovascular disease and coronary heart disease (CHD) from the Multiethnic Study of Atherosclerosis. Smoking status and cumulative exposure were determined by self-report and confirmed by urinary cotinine. Multivariable Cox regression was used to estimate the association between smoking parameters and all-cause cardiovascular disease, all-cause CHD, and hard CHD events. We further adjusted for high-sensitivity C-reactive protein and coronary artery calcium (CAC) in hierarchical Cox models. We identified 3218 never smokers, 2607 former smokers, and 971 current smokers. Median follow-up was 10.2 years. Compared with never smokers, adjusted hazard ratios in current smokers were 1.7 (95% confidence interval, 1.3-2.2) for all-cause cardiovascular disease, 1.6 (1.1-2.1) for all-cause CHD, and 1.7 (1.2-2.4) for hard CHD. Similarly, among current smokers, hazard ratios were higher in the 4th versus 1st quartile of pack-years (eg, all-cause CHD hazard ratio=2.7 [1.1-6.6]). Both CAC>100 and high-sensitivity C-reactive protein ≥3 mg/L identified higher relative risk among current smokers (eg, all-cause CHD hazard ratio of 3.0 [1.5-6.0, compared with CAC=0] and 2.6 [1.4-4.8, compared with high-sensitivity C-reactive protein <2 mg/L], respectively). However, CAC was a stronger mediator of events and adversely modified the effect of smoking on events (eg, P-interaction=0.02 for hard CHD). Compared with never smokers, former smokers (median cessation interval=22 years) had similar adjusted hazard for events.

CONCLUSIONS

In this multiethnic cohort, current smoking and cumulative exposure remain important modifiable determinants of cardiovascular disease. Both high-sensitivity C-reactive protein ≥3 mg/L and, particularly, CAC>100 identified high-risk smokers who may benefit from more intensive smoking-cessation efforts.

Elucidating mechanisms of toxicity using phenotypic data from primary human cell systems--a chemical biology approach for thrombosis-related side effects

Here we describe a chemical biology approach for elucidating potential toxicity mechanisms for thrombosis-related side effects. This work takes advantage of a large chemical biology data set comprising the effects of known, well-characterized reference agents on the cell surface levels of tissue factor (TF) in a primary human endothelial cell-based model of vascular inflammation, the BioMAP^® 3C system. In previous work with the Environmental Protection Agency (EPA) for the ToxCast™ program, aryl hydrocarbon receptor (AhR) agonists and estrogen receptor (ER) antagonists were found to share an usual activity, that of increasing TF levels in this system. Since human exposure to compounds in both chemical classes is associated with increased incidence of thrombosis-related side effects, we expanded this analysis with a large number of well-characterized reference compounds in order to better understand the underlying mechanisms. As a result, mechanisms for increasing (AhR, histamine H1 receptor, histone deacetylase or HDAC, hsp90, nuclear factor kappa B or NFκB, MEK, oncostatin M receptor, Jak kinase, and p38 MAPK) and decreasing (vacuolar ATPase or V-ATPase) and mTOR) TF expression levels were uncovered. These data identify the nutrient, lipid, bacterial, and hypoxia sensing functions of autophagy as potential key regulatory points controlling cell surface TF levels in endothelial cells and support the mechanistic hypothesis that these functions are associated with thrombosis-related side effects in vivo.

Plasma Fibrinolysis Parameters in Smokers and Non-smokers of the Ludwigshafen Risk and Cardiovascular Health (LURIC) Study

Cardiovascular diseases (CVD) are an important cause of morbidity and mortality worldwide. Parameters of coagulation and fibrinolysis are risk factors of CVD and might be affected by cigarette smoking. Aim of our study was to analyze the effect of cigarette smoking on parameters of fibrinolysis in active smokers (AS) and life-time non-smokers (NS) of the Ludwigshafen Risk and Cardiovascular Health (LURIC) Study as well as the use of these parameters for risk prediction. We determined plasminogen activator inhibitor-1 (PAI-1), tissue plasminogen activator antigen (t-PA), protein C activity, and D-dimers in 3,316 LURIC patients. Smoking status was assessed by a questionnaire and measurement of plasma cotinine concentration. Cox regression was used to assess the effect of parameters on mortality. We found that of the 3,316 LURIC patients 777 were AS and 1,178 NS. Within the observation period of 10 years (median) 221 AS and 302 NS died. In male AS vs. NS, PAI-1 (19.0 (10.0-35.0) vs. 15.0 (9.0-29.0) U/ml; p=0.026) and t-PA antigen (12.7 (9.6-16.3) vs. 11.6 (8.9-14.6) μg/l; p=0.020) were slightly increased, while t-PA activity was slightly decreased (0.63 (0.30-1.05) vs. 0.68 (0.42-1.10) U/l; p=0.005). In female AS vs. NS, t-PA antigen (10.5 (8.3-13.9) vs. 11.5 (8.8-15.0) μg/l; p=0.025) and protein C (108.0±24.1% vs. 118.0±25.7%; p=0.004) were decreased. All parameters except for protein C were predictive for mortality in AS. Fully adjusted hazard ratios (95% CI) were 1.14 (1.04-1.25), 1.19 (1.06-1.34), and 1.29 (1.11-1.49) per 1SD increase for D-dimer, t-PA, and PAI-1, respectively. Including fibrinolysis parameters in risk prediction models for mortality improved the area-under-the-curve (AUC) significantly compared with the conventional risk factors. In conclusion, we found alterations in the fibrinolytic system in smokers, which were more pronounced in male AS. PAI-1, t-PA and D-dimers were significant predictors of mortality in AS in LURIC and should be included into the assessment of cardiovascular risk particularly in patients at risk.

Secondhand smoke exposure and endothelial stress in children and adolescents

OBJECTIVE

Links between secondhand smoke exposure and cardiovascular disease in adults are well established. Little is known about the impact of this exposure on cardiovascular status during childhood. The purpose of this study was to investigate relationships between secondhand smoke exposure in children and adolescents and cardiovascular disease risk--systemic inflammation, endothelial stress, and endothelial repair.

METHODS

A total of 145 subjects, aged 9 to 18 years, were studied. Tobacco smoke exposure was determined by hair nicotine level. Cardiovascular risk was assessed by markers of systemic inflammation (C-reactive protein [CRP] and adiponectin); by soluble intercellular adhesion molecule 1 (s-ICAM1), which measures endothelial activation after surface vascular injury; and by endothelial repair. This was measured by prevalence of endothelial progenitor cells (EPCs), which are bone marrow-derived cells that home preferentially to sites of vascular damage.

RESULTS

Hair nicotine was directly correlated with s-ICAM1 (r = 0.4090, P < .0001) and negatively correlated with EPC prevalence (r = -0.2002, P = .0195). There was no relationship between hair nicotine and CRP, and a trend toward a weak relationship with adiponectin. Hair nicotine and body mass index were independent variables in a multivariate model predicting s-ICAM1; hair nicotine was the only significant variable in a model predicting EPC prevalence.

CONCLUSIONS

Secondhand smoke exposure during childhood and adolescence is detrimental to vascular health because s-ICAM1 is a marker for endothelial activation and stress after vascular surface injury, and EPCs contribute to vascular repair. The fact that body mass index is also a factor in the model predicting s-ICAM1 is concerning, in that 2 risk factors may both contribute to endothelial stress.

NADPH oxidase and the cardiovascular toxicity associated with smoking

Smoking is one of the most serious but preventable causes of cardiovascular disease (CVD). Key aspects of pathological process associated with smoking include endothelial dysfunction, a prothrombotic state, inflammation, altered lipid metabolism, and hypoxia. Multiple molecular events are involved in smokinginduced CVD. However, the dysregulations of reactive oxygen species (ROS) generation and metabolism mainly contribute to the development of diverse CVDs, and NADPH oxidase (NOX) has been established as a source of ROS responsible for the pathogenesis of CVD. NOX activation and resultant ROS production by cigarette smoke (CS) treatment have been widely observed in isolated blood vessels and cultured vascular cells, including endothelial and smooth muscle cells. NOX-mediated oxidative stress has also been demonstrated in animal studies. Of the various NOX isoforms, NOX2 has been reported to mediate ROS generation by CS, but other isoforms were not tested thoroughly. Of the many CS constituents, nicotine, methyl vinyl ketone, and α,β-unsaturated aldehydes, such as, acrolein and crotonaldehyde, appear to be primarily responsible for NOX-mediated cytotoxicity, but additional validation will be needed. Human epidemiological studies have reported relationships between polymorphisms in the CYBA gene encoding p22phox, a catalytic subunit of NOX and susceptibility to smoking-related CVDs. In particular, G allele carriers of A640G and -930^A/G polymorphisms were found to be vulnerable to smoking-induced cardiovascular toxicity, but results for C242T studies are conflicting. On the whole, evidence implicates the etiological role of NOX in smoking-induced CVD, but the clinical relevance of NOX activation by smoking and its contribution to CVD require further validation in human studies. A detailed understanding of the role of NOX would be helpful to assess the risk of smoking to human health, to define high-risk subgroups, and to develop strategies to prevent or treat smoking-induced CVD.

Genetic variants in PLG, LPA, and SIGLEC 14 as well as smoking contribute to plasma plasminogen levels

Plasminogen is the precursor of the serine protease plasmin, a central enzyme of the fibrinolytic system. Plasma levels of plasminogen vary by almost 2-fold among healthy individuals, yet little is known about its heritability or genetic determinants in the general population. In order to identify genetic factors affecting the natural variation of plasminogen levels, we performed a genome-wide association study and linkage analysis in a sample of 3456 young healthy individuals who participated in the Genes and Blood Clotting Study (GABC) or the Trinity Student Study (TSS). Heritability of plasminogen levels was 48.1% to 60.0%. Tobacco smoking and female sex were associated with higher levels of plasminogen. In the meta-analysis, 11 single-nucleotide polymorphisms (SNPs) in 2 regions reached genome-wide significance (P < 5.0E-8). Of these, 9 SNPs were near the PLG or LPA genes on Chr6q26, whereas 2 were on Chr19q13 and 5' upstream of SIGLEC14. These 11 SNPs represented 4 independent signals and collectively explained 6.8% of plasminogen level variation in the study populations. The strongest association was observed for a nonsynonymous SNP in the PLG gene (R523W). Individuals bearing an additional copy of this allele had an average decrease of 13.4% in plasma plasminogen level.

Caffeic acid inhibits the formation of 7-carboxyheptyl radicals from oleic acid under flavin mononucleotide photosensitization by scavenging singlet oxygen and quenching the excited state of flavin mononucleotide

We examined the effects of caffeic acid (CA) and related compounds on 7-carboxyheptyl radical formation. This analysis was performed using a standard D₂O reaction mixture containing 4.3 mM oleic acid, 25 μM flavin mononucleotide (FMN), 160 mM phosphate buffer (pH 7.4), 10 mM cholic acid, 100 mM α-(4-pyridyl-1-oxide)-N-tert-butylnitrone, and 1 mM Fe(SO₄)₂(NH₄)₂ during irradiation with 7.8 J/cm² at 436 nm. 7-Carboxyheptyl radical formation was inhibited by CA, catechol, gallic acid, chlorogenic acid, ferulic acid, noradrenalin, 2-hydroxybenzoic acid, 3-hydroxybenzoic acid, and 4-hydroxybenzoic acid. Quinic acid, benzoic acid, and p-anisic acid had no effect on radical formation. These results suggest that a phenol moiety is essential for these inhibitory effects. The fluorescence intensity of FMN decreased by 69% ± 2% after CA addition, suggesting that CA quenches the singlet excited state of FMN. When 1 mM CA was added to a standard reaction mixture containing 25 μM FMN, 140 mM phosphate buffer (pH 7.4), and 10 mM 4-oxo-2,2,6,6-tetramethylpiperidine, the electron spin resonance signal of 4-oxo-2,2,6,6-tetramethylpiperidinooxy disappeared. This finding suggests that singlet oxygen was scavenged completely by CA. Therefore, CA appears to inhibit 7-carboxyheptyl radical formation by scavenging singlet oxygen and quenching the excited state of FMN.

Genetic etiology of coronary artery disease considering NOS 3 gene variant rs1799983

Reduced production of nitric oxide due to rs1799983 single nucleotide polymorphism in nitric oxide synthase 3 gene (NOS3) may enhance the risk of coronary artery disease. The association of rs1799983 polymorphism with coronary artery disease was investigated in the local population of Pakistan. Study consisted of 376 individuals, out of which 198 were coronary artery disease patients and 178 were normal healthy individuals. Allele-specific polymerase chain reaction (PCR) based strategy was used for the detection of different genotypes of rs1799983 polymorphism. PCR amplification results were obtained for 354 samples. Frequency of T allele was higher as compared to G allele in our population. Strong association between rs1799983 and coronary artery disease was observed (p < 0.01). TT genotype was found to enhance 5.717 times the risk of coronary artery disease (odds ratio (OR): 5.717; 95% confidence interval (95% CI) 3.586-9.115). On the basis of present results, it can be concluded that rs1799983 is strongly associated with coronary artery disease in our population and TT genotype of this polymorphism enhanced the risk of coronary artery disease in Pakistani population.

Mechanisms of Plaque Formation and Rupture

Atherosclerosis causes clinical disease through luminal narrowing or by precipitating thrombi that obstruct blood flow to the heart (coronary heart disease), brain (ischemic stroke), or lower extremities (peripheral vascular disease). The most common of these manifestations is coronary heart disease, including stable angina pectoris and the acute coronary syndromes. Atherosclerosis is a lipoprotein-driven disease that leads to plaque formation at specific sites of the arterial tree through intimal inflammation, necrosis, fibrosis, and calcification. After decades of indolent progression, such plaques may suddenly cause life-threatening coronary thrombosis presenting as an acute coronary syndrome. Most often, the culprit morphology is plaque rupture with exposure of highly thrombogenic, red cell–rich necrotic core material. The permissive structural requirement for this to occur is an extremely thin fibrous cap, and thus, ruptures occur mainly among lesions defined as thin-cap fibroatheromas. Also common are thrombi forming on lesions without rupture (plaque erosion), most often on pathological intimal thickening or fibroatheromas. However, the mechanisms involved in plaque erosion remain largely unknown, although coronary spasm is suspected. The calcified nodule has been suggested as a rare cause of coronary thrombosis in highly calcified and tortious arteries in older individuals. To characterize the severity and prognosis of plaques, several terms are used. Plaque burden denotes the extent of disease, whereas plaque activity is an ambiguous term, which may refer to one of several processes that characterize progression. Plaque vulnerability describes the short-term risk of precipitating symptomatic thrombosis. In this review, we discuss mechanisms of atherosclerotic plaque initiation and progression; how plaques suddenly precipitate life-threatening thrombi; and the concepts of plaque burden, activity, and vulnerability.

Phenotypic screening of the ToxCast chemical library to classify toxic and therapeutic mechanisms

Addressing the safety aspects of drugs and environmental chemicals has historically been undertaken through animal testing. However, the quantity of chemicals in need of assessment and the challenges of species extrapolation require the development of alternative approaches. Our approach, the US Environmental Protection Agency's ToxCast program, utilizes a large suite of in vitro and model organism assays to interrogate important chemical libraries and computationally analyze bioactivity profiles. Here we evaluated one component of the ToxCast program, the use of primary human cell systems, by screening for chemicals that disrupt physiologically important pathways. Chemical-response signatures for 87 endpoints covering molecular functions relevant to toxic and therapeutic pathways were generated in eight cell systems for 641 environmental chemicals and 135 reference pharmaceuticals and failed drugs. Computational clustering of the profiling data provided insights into the polypharmacology and potential off-target effects for many chemicals that have limited or no toxicity information. The endpoints measured can be closely linked to in vivo outcomes, such as the upregulation of tissue factor in endothelial cell systems by compounds linked to the risk of thrombosis in vivo. Our results demonstrate that assaying complex biological pathways in primary human cells can identify potential chemical targets, toxicological liabilities and mechanisms useful for elucidating adverse outcome pathways.

α,β-Unsaturated aldehyde crotonaldehyde triggers cardiomyocyte contractile dysfunction: role of TRPV1 and mitochondrial function

Recent evidence has suggested that cigarette smoking is associated with an increased prevalence of heart diseases. Given that cigarette smoking triggers proinflammatory response via stimulation of the capsaicin-sensitive transient receptor potential cation channel TRPV1, this study was designed to evaluate the effect of an essential α,β-unsaturated aldehyde from cigarette smoke crotonaldehyde on myocardial function and the underlying mechanism with a focus on TRPV1 and mitochondria. Cardiomyocyte mechanical and intracellular Ca2+ properties were evaluated including peak shortening (PS), maximal velocity of shortening/relengthening (±dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR90), fura-2 fluorescence intensity (FFI), intracellular Ca2+ decay and SERCA activity. Apoptosis and TRPV1 were evaluated using Western blot analysis. Production of reactive oxygen species (ROS) and DNA damage were measured using the intracellular fluoroprobe 5-(6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate and 8-hydroxy-2'-deoxyguanosine (8-OHdG), respectively. Our data revealed that crotonaldehyde interrupted cardiomyocyte contractile and intracellular Ca2+ property including depressed PS, ±dL/dt, ΔFFI and SERCA activity, as well as prolonged TR90 and intracellular Ca2+ decay. Crotonaldehyde exposure increased TRPV1 and NADPH oxidase levels, promoted apoptosis, mitochondrial injury (decreased aconitase activity, PGC-1α and UCP-2) as well as production of ROS and 8-OHdG. Interestingly, crotonaldehyde-induced cardiac defect was obliterated by the ROS scavenger glutathione and the TRPV1 inhibitor capsazepine. Capsazepine (not glutathione) ablated crotonaldehyde-induced mitochondrial damage. Capsazepine, glutathione and the NADPH inhibitor apocynin negated crotonaldehyde-induced ROS accumulation. Our data suggest a role of crotonaldehyde compromises cardiomyocyte mechanical function possibly through a TRPV1- and mitochondria-dependent oxidative stress mechanism.

Smoking and Cardiovascular Disease

Smoking represents one of the most important preventable risk factors for the development of atherosclerosis. The present review aims at providing a comprehensive summary of published data from clinical and animal studies, as well as results of basic research on the proatherogenic effect of smoking. Extensive search and review of literature revealed a vast amount of data on the influence of cigarette smoke and its constituents on early atherogenesis, particularly on endothelial cells. Vascular dysfunction induced by smoking is initiated by reduced nitric oxide (NO) bioavailability and further by the increased expression of adhesion molecules and subsequent endothelial dysfunction. Smoking-induced increased adherence of platelets and macrophages provokes the development of a procoagulant and inflammatory environment. After transendothelial migration and activation, macrophages take up oxidized lipoproteins arising from oxidative modifications and transdifferentiate into foam cells. In addition to direct physical damage to endothelial cells, smoking induces tissue remodeling, and prothrombotic processes together with activation of systemic inflammatory signals, all of which contribute to atherogenic vessel wall changes. There are still great gaps in our knowledge about the effects of smoking on cardiovascular disease. However, we know that smoking cessation is the most effective measure for reversing damage that has already occurred and preventing fatal cardiovascular outcomes.

Lung deposition analyses of inhaled toxic aerosols in conventional and less harmful cigarette smoke: a review

Inhaled toxic aerosols of conventional cigarette smoke may impact not only the health of smokers, but also those exposed to second-stream smoke, especially children. Thus, less harmful cigarettes (LHCs), also called potential reduced exposure products (PREPs), or modified risk tobacco products (MRTP) have been designed by tobacco manufacturers to focus on the reduction of the concentration of carcinogenic components and toxicants in tobacco. However, some studies have pointed out that the new cigarette products may be actually more harmful than the conventional ones due to variations in puffing or post-puffing behavior, different physical and chemical characteristics of inhaled toxic aerosols, and longer exposure conditions. In order to understand the toxicological impact of tobacco smoke, it is essential for scientists, engineers and manufacturers to develop experiments, clinical investigations, and predictive numerical models for tracking the intake and deposition of toxicants of both LHCs and conventional cigarettes. Furthermore, to link inhaled toxicants to lung and other diseases, it is necessary to determine the physical mechanisms and parameters that have significant impacts on droplet/vapor transport and deposition. Complex mechanisms include droplet coagulation, hygroscopic growth, condensation and evaporation, vapor formation and changes in composition. Of interest are also different puffing behavior, smoke inlet conditions, subject geometries, and mass transfer of deposited material into systemic regions. This review article is intended to serve as an overview of contributions mainly published between 2009 and 2013, focusing on the potential health risks of toxicants in cigarette smoke, progress made in different approaches of impact analyses for inhaled toxic aerosols, as well as challenges and future directions.