Pathological mechanisms of cigarette smoking, dietary and sedentary lifestyle risks in vascular dysfunction: mitochondria as a common target of risk factors

Abstract

In the past century, the lifespan of human population has dramatically increased to 80s, but it is hindered by limited healthspan to 60s due to epidemic increase in the cardiovascular disease which is a main cause of morbidity and mortality. We cannot underestimate the progress in understanding the major cardiovascular risk factors which include cigarette smoking, dietary and sedentary lifestyle risks. Despite their clinical significance, these modifiable risk factors are still the major contributors to cardiovascular disease. It is, therefore, important to understand the specific molecular mechanisms behind their pathological effects to develop new therapies to improve the treatment of cardiovascular disease. In recent years our group and others have made a progress in understanding how these risk factors can promote endothelial dysfunction, smooth muscle dysregulation, vascular inflammation, hypertension, lung and heart diseases. These factors, despite differences in their nature, lead to stereotypical alterations in vascular metabolism and function. Interestingly, cigarette smoking has a tremendous impact on a very distant site from the initial epithelial exposure, namely circulation and vascular cells mediated by a variety of stable cigarette smoke components which promote vascular oxidative stress, alter vascular metabolism and function. Similarly, dietary and sedentary lifestyle risks facilitate vascular cell metabolic reprograming promoting vascular oxidative stress and dysfunction. Mitochondria are critical in cellular metabolism and in this work we discuss a new concept that mitochondria are a common pathobiological target for these risk factors and mitochondria-targeted treatments may have therapeutic effect in the patients with cardiovascular disease.

Introduction

Vascular dysfunction plays a key role in the pathogenesis of cardiovascular disease which is a leading cause of death [97]. Multiple risk factors contribute to the development of cardiovascular disease and many of them are preventable such as cigarette smoking, dietary and sedentary lifestyle risk factors [94]. In 2020, global smoking prevalence was 32.6% in men and 6.5% among women [27]. In 2021, tobacco use caused 3 million of cardiovascular deaths and dietary risks accounted for 6.6 million cardiovascular deaths [100]. Reduction in salt intake of 3 g per day could save up to 392,000 quality-adjusted life-years and $24 billion in health care costs annually [13]. Despite recent descending trend in cardiovascular disease, it remains the main cause of morbidity and mortality. Although smoking cessation, reduced salt consumption, increased fruit and vegetables in the diet and regular physical activity have been shown to reduce the risk of cardiovascular disease, it is important to recognize that risk for cardiovascular diseases remains elevated long after quitting smoking or diet modifications [50,104]. Understanding the specific molecular pathological mechanisms of these risk factors can help to develop new therapies for treatment of cardiovascular disease.

Several cluster of modifiable cardiovascular risk factors have been identified including behavioral, metabolic, socio-economic and environmental risk clusters [110]. These groups indicate the interaction of different factors within cluster such as smoking and physical activity or hypertension and metabolic conditions. The complex interaction of metabolic, socio-economic and environmental risk factors contributes to cardiovascular disease [71]. Therefore, these risk factors contribute to an increased risk of disease both collectively and synergistically due to the interactions between individual factors.

Vascular dysfunction includes numerous conditions affecting blood vessels including conduit and microvascular arteries, veins and lymph vessels. It can be mediated by various alterations in endothelial, smooth muscle or inflammatory cells. Each type of vascular cells plays an important role in vascular homeostasis, and alterations in any of these cells may contribute to vascular dysregulation and disease. For example, endothelial cells provide barrier function, regulate vascular tone, cell proliferation and control vascular inflammation and remodeling [63]. Meanwhile, endothelial dysfunction has the profound prognostic implication predicting adverse cardiovascular events [87,85]. Endothelial dysfunction and hypertension are integrally related and represent the major risk factors for cardiovascular disease. Despite great burden, only 1 in 4 patients have their blood pressure under control [20]. There is an urgent need for new therapies which can reduce pathological effects of these risk factors.

Tobacco smoking is strongly associated with the oxidative stress [67]. Clinical studies showed that accumulation of lipid peroxidation product malondialdehyde in blood plasma of smokers was increased by 2.5-fold while activity of major antioxidant enzymes catalase, superoxide dismutase and glutathione peroxidase were significantly reduced [62]. This leads to oxidation of cysteine and glutathione, and the level of reduced glutathione is diminished in kidney by 2-fold in mice exposed to cigarette smoke for four days.[83] The resultant alteration in the thiol redox status impairs cellular redox signaling and can cause cellular dysfunction. Indeed, smoking a single cigarette rapidly reduces endothelial nitric oxide production and significantly diminishes blood plasma antioxidants [99]. It has been proposed that cigarette smoke induces ${\mathrm{O}}_2^{\underset{¯}{•}}$ production in endothelial cells leading to nitric oxide inactivation and nitric oxide synthase uncoupling [81]. Indeed, treatment of cultured endothelial cells with cigarette smoke condensate or smokers’ blood plasma increases cellular ${\mathrm{O}}_2^{\underset{¯}{•}}$ production and reduces nitric oxide synthase activity [48,75]. The specific mechanisms of smoking mediated endothelial dysfunction and hypertension however remain unclear.

Clinical studies show that increased levels of cholesterol, fatty acids and sugar in circulation increases risks of vascular disease [89]. Meanwhile, this pathology is mediated not only by eating diet rich in saturated fats, trans fat, or cholesterol but also depends on the individual metabolic rate which declines with age and promotes metabolic imbalance [5]. This metabolic condition can be further exacerbated by sedentary lifestyle at any age. Interestingly, there is a connection between and dietary alterations since both cause metabolic dysregulation as well as oxidative stress. These have been previously related to systemic metabolic conditions and inflammation [10]. New studies indicate that these alterations can occur in a cell- and tissue-specific fashion and may not necessarily be represented as a systemic disorder. Therefore, the interplay between risk factors and genetic background can lead to a cell-specific pathological condition in endothelium, smooth muscle, or heart. Recent studies suggest that these cardiovascular risk factors may have a common target – mitochondria [96]. Indeed, mitochondria play a critical role in cellular metabolism and production of reactive oxygen species, therefore, mitochondrial dysfunction contributes to both cellular metabolic dysregulation and oxidative stress, however, there is not currently available mitochondria-targeted treatment. In this work we discuss cellular pathways and the role of mitochondria which can be targeted for development of new treatments (Figure 1).

Figure 1.

Mitochondria are the common pathophysiological target for cardiovascular risk factors which promote metabolic alterations and oxidative stress driving vascular epigenetic and phenotypic dysregulation. This increases vascular inflammation and permeability, impairs vascular relaxation, and plasticity, accelerates vascular senescence and disease.

In this work we discuss a new concept that mitochondria are a common pathobiological target for these risk factors, how specific risk factor impact mitochondria, and how mitochondria-targeted therapies may improve treatment of cardiovascular disease.

Cigarette smoking and hypertension

Despite recent decline in cigarette smoking rate, it is estimated that 12.5% of U.S. adults are currently cigarette smokers [25]. Cigarette smoking remains the leading cause of preventable disease and death in the United States. Smoking increases blood pressure both in normotensive and hypertensive subjects [42,64]; however, smoking cessation success is very limited (7%) [79,30] and risk for cardiovascular diseases remains elevated long after quitting smoking [50,104]. Furthermore, hypertensive patients with smoking have significantly reduced responses to common classes of antihypertensive drugs such as diuretics, ACE-inhibitors and beta-blockers due to metabolic interference between cigarette smoking and drugs [55]. Meanwhile, there have been no mechanistically novel treatments for hypertension in the past 30 years. There is an urgent need for new therapies that could improve treatment of hypertension and cardiovascular diseases in patients with the history of smoking.

The deleterious effect of cigarette smoking on cancer development and pulmonary diseases has been extensively documented [1]. Our Vanderbilt University research team provided an important contribution in understanding the molecular mechanism of how cigarette smoke induces metabolic reprogramming and tissue hypertrophy in these pathological conditions [82]. The specific mechanism of smoking mediated endothelial dysfunction and hypertension however remains unclear.

Cigarette smoking and oxidative stress

It has been previously suggested that cigarette smoke exposure increases oxidative stress in the lung, and this contributes to the development of lung cancer, pulmonary hypertension, and cardiovascular disease [19]. Indeed, cigarette fume contains reactive oxygen species which can cause epithelial oxidative injury. Meanwhile, these fume oxidants are short lived and cannot account for the deleterious effects of smoking in the distant tissue in the heart and circulation [92]. It was found that these pathogenic cardiovascular effects of smoking can be reproduced by exposure to the stable products present in the cigarette smoke which are frequently called cigarette smoke extracts [75]. It does not contain reactive oxygen species but its stable components like nicotine can induce metabolic and genetic dysregulations in circulation and heart [18]. It has been previously shown that serum plasma of smokers reduces nitric oxide production by human endothelial cells indicating endothelial dysfunction [99]. Meanwhile, the specific mechanisms of smoking mediated endothelial dysfunction and hypertension remain elusive.

Cigarette smoking increases systemic markers of oxidative stress such as blood plasma F2-isoprostanes [67]. This can be mediated by activation of NADPH oxidases [51] and redox cycling components [75]. Mitochondria are an important source of ${\mathrm{O}}_2^{\underset{¯}{•}}$ [15], and we have shown that scavenging mitochondrial ${\mathrm{O}}_2^{\underset{¯}{•}}$ improves endothelial function and attenuates hypertension [34,33]. Nicotine and other cigarette smoke components stimulate production of mitochondrial ${\mathrm{O}}_2^{\underset{¯}{•}}$ [57,3]. Genetic manipulation of mitochondrial antioxidant enzyme superoxide dismutase (SOD2) affects blood pressure, and mitochondria-targeted therapies such as SOD2 mimetics effectively lower blood pressure [34,33]. We have tested if cigarette smoking impairs SOD2 activity. Indeed, substantially reduced expression and activity of mitochondrial deacetylase Sirtuin 3 lead to SOD2 acetylation [32]. SOD2 is inactivated by acetylation [95,72] and deacetylation by mitochondrial Sirt3 restores SOD2 activity [111]. The activity of Sirtuins is regulated by reversible S-glutathionylation at Cys204 in the catalytic region [16] and redox inactivation of Sirt3 by S-glutathionylation may contribute to vascular dysfunction and development of hypertension [35]. Indeed, mice with mitochondria-targeted catalase were protected from cigarette smoke induced oxidative stress, endothelial dysfunction and hypertension [32].

Metabolic alterations in cigarette smoking

Cigarette smoke condensate promotes cellular metabolic reprograming which down regulates mitochondrial respiration and increases the glucose consumption and lactate production [82,2]. This results in phenotypic alterations such as epithelial-to-mesenchymal transition in non-small cell lung cancer through HDAC-mediated downregulation of E-cadherin [68]. The same mechanisms can be responsible for epigenetic reprograming associated with smoking [60]. DNA methylation changes associated with maternal smoking persist over years of life and prenatal environmental exposure in children leads to chromatin transitions into a hyperactive state [12]. This increases the cardiovascular risks factors not only for the mother but also for children [9]. Metabolic alterations are not limited to epithelial cells but also can be found in the vascular cells and the heart [32]. This is evident by increased oxidant production in the vasculature, elevated biomarkers of mitochondrial oxidative stress in the heart, reduced expression of key regulator of mitochondrial metabolism, Sirtuin 3, and inactivation of essential mitochondrial superoxide dismutase by acetylation [32]. This brings us to the question why smoking induces metabolic alterations. We suggest that cigarette smoke causes mitochondrial dysfunction due to increased oxidative stress. Indeed, our studies showed that mCAT mice expressing H₂O₂ scavenger, catalase, in the mitochondria are protected from deleterious effects of cigarette smoke. Vascular oxidative stress, endothelial dysfunction and cigarette smoke-induced hypertension were significantly reduced in mCAT mice [32]. It is possible that crosstalk between metabolic alterations and mitochondrial oxidative stress contributes to cigarette smoke induced end-organ dysfunction and hypertension [31].

Cigarette smoking and inflammation

Inflammation plays a key role in vascular dysfunction, hypertension and cardiovascular disease [105] and cigarette smoke exposure increases vascular inflammation and dysfunction [21]. This can be mediated by multiple pathways but given the fact that cigarette smoke promotes oxidative stress in the circulation, we will discuss a potential role of recently discovered mechanism of immune cell activation mediated by dicarbonyl lipid peroxidation products, isolevuglandins [29]. It was found that isolevuglandins protein adducts stimulate dendritic cell leading to of T cell activation and ultimately to hypertension [52]. Isolevuglandins also contribute to autoimmunity and systemic lupus [74]. Interestingly, scavenging of isolevuglandins with 2-hydroxybenzylamine prevents dendritic cell activation, preserves vascular function, attenuates hypertension, and reduces cardiac dysfunction [52,69]. Lipid peroxidation is substantially increased in smokers [66], therefore, we propose a novel approach to target cytotoxic and proinflammatory dicarbonyl lipid peroxidation products to reduce vascular inflammation and cardiovascular disease associated with cigarette smoking.

Smooth muscle cells and cigarette smoking

Cigarette smoking plays an important role in pulmonary and peripheral vascular remodeling and contributes to the development and progression of various cardiovascular diseases, including pulmonary hypertension associated with chronic lung diseases, atherosclerosis, abdominal aortic aneurism, and hypertension [90,102]. Crucial components for smoking associated vascular remodeling are smooth muscle cells (SMCs) contractile tonus, proliferation, migration, apoptosis, and phenotyping changes [8]. In normal conditions, all these processes are regulated by endothelial cells and via complex intercellular signaling processes and balance of various relaxing, contracting, and angiogenic factors, including nitric oxide, endothelin-1, prostacyclin and vascular endothelial growth factor [39,98]. Therefore, endothelial dysfunction has various direct (increased permeability, pro-inflammatory signaling, etc.) and indirect (realized via smooth muscle cells regulation) effects on vasculature remodeling (Figure 2.

Figure 2.

Endothelial cell-smooth muscle cell regulatory interactions and impact sites for harmful components of cigarette smoke on smooth muscle cells contractile tonus, proliferation, migration, and phenotyping changes. In addition to endothelial dysfunction, oxidative stress in smooth muscle cells is driving vascular remodeling.

At the same time, various components of cigarette smoke directly contribute to pulmonary arterial remodeling through increased cell senescence and vascular tone alterations that lead to vasoconstriction and SMCs hypertrophy and proliferation [22,106,101]. While other components can be absorbed into blood stream and have systemic effects, including abnormal regulation of SMCs in peripheral arteries [103,65]. Cigarette smoke can lead to vascular dysfunction through increased mitochondrial superoxide levels and reduced antioxidant defenses in SMCs [101,91]. Oxidative stress can induce changes in the degree of various functions of SMCs such as contractility, proliferation, migration, and the synthesis of inflammatory mediators [54]. Cigarette smoke increases SMCs proliferation and migration via activation of the platelet-derived growth factor–protein kinase C pathway [106] and polycyclic aromatic hydrocarbons of cigarette smoke activate aryl hydrocarbon receptor inducing iNOS and intimal thickening [6]. Thus, multiple mechanisms could explain why cigarette smoke is a major risk factor for pulmonary hypertension, atherosclerosis and sequential heart diseases, stroke, and hypertension (Figure2) [93].

Dietary and sedentary risk factors

Diet high in saturated fats, trans fat, and cholesterol has been linked to heart disease and related conditions, such as atherosclerosis [88]. This diet has been related to excessive calorie intake. Indeed, reduced calorie consumption and increased physical activity (increased energy utilization) are beneficial for vascular health and reduces cardiovascular risks [59]. Meanwhile, high salt (sodium) diet increases blood pressure despite potential increase in the energy utilization. This may potentially contradict with the notion that excessive calorie intake drives these risk factors despite the well-known association of metabolic conditions and vascular disfunction. Instead, mitochondrial dysfunction associated with many risk factors [80] leads to imbalance between energy demand and energy production. This will cause cell and tissue specific metabolic dysregulation which may not necessarily represent as a systemic metabolic disorder. For example, sedentary lifestyle leads to excessive accumulation of mitochondrial metabolites and overreduction of mitochondria due to low energy demand leading to mitochondrial dysfunction because of overproduction of mitochondrial oxidants and inhibition of mitochondrial metabolism. This can be mediated by accumulation of fatty acids in the cells and mitochondria since fatty acid is one of the primary mitochondrial substrates [73]. Low mitochondrial activity can lead to excessive accumulation of fatty acid intermediates despite normal diet. This does not mean that fatty acids are bad for endothelial and vascular function. In fact, mitochondrial metabolism is essential for endothelial barrier function and vasorelaxation [47,53] and we showed that endothelial dysfunction is linked to mitochondrial impairment [38]. Furthermore, endothelial specific impairment of fatty acid metabolism induces endothelial dysfunction [107]. These studies provide a basis for a new concept indicating that multiple risk factors co-operatively promote mitochondrial dysfunction which contributes to endothelial dysfunction and cardiovascular disease [31]. This can be mediated by impairment of multiple mitochondrial metabolic and antioxidant pathways [49] including deacetylase Sirtuin 3 [36,76] which may represent an attractive target for the development of future cardiovascular treatments.

Therapeutic effects of calorie restriction on inflammation and vascular function

Clinical studies demonstrate beneficial effects of calorie restriction beyond the level expected from reduced metabolic body mass [40,44]. Animal studies showed that reduced calory consumption increases eNOS expression, promotes mitochondrial biogenesis [70], attenuates hypertension and cardiac hypertrophy [37]. Interestingly, calorie restriction reduces oxidative stress by SIRT3-mediated SOD2 deacetylation [78]. It is important to note that moderate calory restriction (25%) diet increased expression of SIRT1 and SIRT3 in myocardium, whereas the 45% calorie restriction diet decreased in Sirt1 and Sirt3 expression indicating that excessive calorie restriction may be harmful to health [108]. It has been proposed that Sirtuin agonists can be used as a calorie restriction mimetics [43].

Future clinical translation

As we described above, mitochondria represent an important target for these cardiovascular risk factors (Figure 3). Unfortunately, there is no clinically approved mitochondria-targeted treatments. Therefore, we can discuss life-style modification and currently available therapies or supplements that can help to correct the mitochondrial function. One of the most popular life-style intervention is physical exercise. Exercise training improves the local and systemic antioxidative capacity, increases anabolic signaling in muscle and improves compliance of the vascular system. Therefore, regular exercise seems to protect long-term smokers against some consequences of smoking and studies suggest that it is important to start exercise training as early as possible [61].

Figure 3.

Multiple cardiovascular risk factors such as aging, smoking, diet, and sedentary lifestyle promote mitochondrial dysfunction which can be attenuate by lifestyle modifications, dietary supplements, NAD donors, TERT agonists and future mitochondria-targeted treatments to improve mitochondrial and vascular function.

Calorie restriction is a little bit controversial in smokers. Smokers often gain weight when they quit, and it was suggested that diet and calorie restriction can help to offset these metabolic effects. Meanwhile, it was found that moderate calorie restriction was associated with increase in cigarette smoking suggesting that dieting may increase smoking behavior and impede smoking-cessation [23]. Indeed, nicotine increases energy expenditure and reduce appetite which can explain why smokers tend to have lower body weight compared with nonsmokers [24]. Several pharmacotherapies were evaluated for preventing post-cessation weight gain such as bupropion, nicotine-replacement medications, fluoxetine, and varenicline, however, they appear to delay, rather than prevent, post-cessation weight gain [7]. One potential solution is to improve the quality of diet enriched in the natural antioxidants and polyphenols to offset some deleterious effects of smoking rather than reduce calorie consumption [45]. Several natural polyphenols including honokiol, resveratrol, curcumin and quercetin are able to increase Sirt3 expression and activity and supplementation with these natural Sirt3 agonists could improve mitochondrial and vascular function in smokers [46].

There are several NAD+ donors including niacin, nicotinamide mononucleotide, nicotinamide riboside which could be beneficial in cigarette smokers. They increase the cellular NAD+ promoting Sirtuins activity, however, the results are widely varying, and further studies required for a better understanding of the therapeutic role of NAD+ donors in human diseases [14]. Recent studies show that metformin activates protective mechanisms through Nrf2 pathway which significantly reduces cigarette smoke-induced inflammation, oxidative stress, and cerebrovascular toxicity [77]. Metformin was recently proposed for treatment of pulmonary arterial hypertension [17] and it could also ameliorate other pathological conditions associated with cigarette smoking [58]. Resent clinical studies showed accelerated vascular aging in smokers and that it is associated with the telomere shortening [11], meanwhile, increasing telomerase expression (TERT) may improve the mitochondrial and microvascular function [4].

On the basis of presented pathophysiological role of mitochondrial dysfunction, we propose several currently available therapeutics as a promising approach to improve the mitochondrial function in cardiovascular conditions. First, there are several supplements available, including nicotinamide and nicotinamide mononucleotide [86], resveratrol and other polyphenols stimulating Sirtuin functions [26,56], and telomerase activator cycloastragenol [109]. Second, an AMPK activator metformin was recently proposed to correct the mitochondrial function [17]. Finally, new mitochondria-targeted emerges such as mitoQ and SS31 that shows cardioprotective effects [84,41].

Future translational studies must define the most important molecular targets and most effective therapeutic approaches to offset the pathological mechanisms responsible for cardiovascular risk factors (Figure 3). It should include preventive measures for lifestyle correction, supplementations with essential nutrients which can be depleted with age and disease as well as pharmacological therapy such as mitochondria-targeted treatments.