1.1 Inflammaging

Aging is multifactorial process characterized by the gradual decline of physiological functions and increased vulnerability to a range of chronic diseases. Among the concepts emerging to explain the biological underpinnings of aging, “inflammaging” has garnered significant attention. Inflammaging describes the chronic, low-grade inflammation that develops with age and contributes to the pathogenesis of age-related diseases, including cardiovascular diseases (CVDs) [1]. This concept was grounded in observations that aging is accompanied by unbalanced systemic cytokine secretion, with increased levels of the most relevant pro-inflammatory cytokines in the serum of older but apparently healthy individuals [2,3,4]. The elevated secretion of interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor α (TNF-α), along with the subsequent increase in inflammatory markers such as C-reactive protein (CRP) and serum amyloid A (SAA), has been documented [5,6,7]. Concurrently, a reduction in the levels of anti-inflammatory cytokines, including interleukin-10 (IL-10) and transforming growth factor-beta (TGF-β), has also been observed [6, 7] This chronic inflammatory state is thought to result from a combination of genetic, environmental and lifestyle factors, including the accumulation of cellular debris, senescent cells and changes in the gut microbiota.

The molecular mechanisms underlying inflammaging are complex and its effects involve multiple pathways and cellular processes. Chronic inflammation is involved in accelerated biological aging and age-related diseases, particularly CVDs, atherosclerosis, osteoporosis and osteoarthritis, type 2 diabetes, metabolic syndrome, neurodegeneration, sarcopenia or cancer [7,8,9]. Inflammaging is driven by a variety of molecular age-related mechanisms, leading to cellular senescence [10], including impaired mitochondrial function, oxidative stress, DNA damage, inflammasome activation, and telomere shortening [10, 11]. The changes of the immune system (IS) occurring with age and characterizing immunosenescence should be considered as a dynamic process modulated by exogenous and endogenous detrimental stimuli to which our body is exposed lifelong and the major contributor to inflammaging [1, 12, 13].

Inflammaging could be considered as the result of the imbalance between inflammatory and anti-inflammatory networks, in the framework of the aging of the immune system [6]. However, after 20 years from its discovery, several biological mechanisms beyond immunosenescence have been described as contributors of inflammaging: (i) accumulation of senescent cells secreting pro-inflammatory mediators, which have the potential to propagate the senescent phenotype to neighboring cells [14] promoting age-related diseases [15]; (ii) reactive oxygen species (ROS) and other agents can cause nuclear DNA damage, often associated with telomere shortening, triggering DNA repair response and the production of pro-inflammatory compounds [16] (iii) age-related accumulation of damage-associated molecular patterns (DAMPs), such as nucleic acids, mitochondrial DNA (mtDNA), cardiolipin, mitochondria, Heat Shock Proteins, and other proteins, can trigger innate immunity and the production of pro-inflammatory cytokines [13,17]; (iv) pro-inflammatory circulating microRNA, which enhances inflammatory response [18]; (v) age-related accumulation of pro-inflammatory agalactosylated N-glycans in the blood, which represent one of the most powerful markers of biological age in humans [19]; (vi) enhanced activation of the coagulation pathway, that increases the risk for arterial and venous thrombosis in older people; (vii) age-related gut microbiota dysbiosis, which represents an important source of inflammatory stimuli during the aging [20].

Among them, of particular relevance in the framework of CVD are cellular senescence, the oxidative stress caused by mitochondrial dysfunction, the release of DAMPs, the dysregulation of proinflammatory microRNAs.

The accumulation of senescent cells is a hallmark of aging and significantly contributes to inflammaging. In response to various stressors, such as DNA damage, oxidative stress, and telomere shortening, cells undergo irreversible growth arrest. Unlike apoptotic cells, they remain metabolically active and secrete a wide range of bioactive molecules. This secretory activity gives rise to the senescence-associated secretory phenotype (SASP), characterized by the secretion of pro-inflammatory cytokines (e.g., IL-6, IL-1β, TNF-α), chemokines (e.g., MCP-1, IL-8), growth factors (e.g., vascular endothelial growth factor -VEGF), and proteases (e.g., matrix metalloproteases, MMPs). This secretome can vary depending on the cell type, the nature of the senescence trigger, and the tissue microenvironment. The SASP factors can autocrinally reinforce the senescent state or paracrinely influence neighboring cells and tissues [2] Although SASP secretome is highly variable, it usually includes many proinflammatory molecules and can contribute to create a pro-inflammatory environment that affects neighboring cells and leads to tissue dysfunction. Senescent cells accumulate in various tissues with age and are implicated in the development of age-related diseases. In the cardiovascular system, senescent endothelial cells and vascular smooth muscle cells contribute to atherosclerosis by promoting inflammation, extracellular matrix remodeling, and plaque instability [3] The SASP factors, such as IL-6, IL-1β, and TNF-α, play pivotal roles in these processes by attracting immune cells to the site of senescent cells and enhancing the local inflammatory response. Senescent leukocytes have been correlated with the formation of atherosclerotic plaques, reinforcing the idea that changes related to inflammaging contributes to the onset of CVD [21]

Oxidative stress is characterized by an imbalance between the production of reactive oxygen species (ROS) and the body's ability to neutralize them. Mitochondria are the major sources of ROS, and their dysfunction is a hallmark of aging. Mitochondrial dysfunction leads to increased ROS production, which can damage cellular components, including lipids, proteins, and DNA, further promoting cellular senescence and inflammation [4].

ROS can activate various signaling pathways, such as NF-κB and MAPK (Mitogen-activated protein kinase), which are involved in the expression of pro-inflammatory genes. Moreover, mitochondrial DNA (mtDNA) released into the cytoplasm can act as a DAMP, activating the innate immune system and contributing to chronic inflammation [5].

Oxidative stress has serious implications in the development of CVD. Atherosclerosis is common in the aging population and can be exacerbated by oxidative stress. Low density lipoprotein (LDL) cholesterol can be oxidized in the initial stage of atherogenesis, leading to the activation of endothelium and the initiation of immune system response. Inflammatory cells such as monocytes and T cells adhere and migrate into the arterial intima. The oxidized LDL is then phagocytosed, inducing macrophages to release ROS and pro-inflammatory markers, which in turn promote further LDL oxidation, thereby initiating a vicious circle [22] which leads to the progression of atherosclerosis [23]. Dysfunction of the endothelium can be attributed to ROS produced via the electron transport chain in the mitochondria. Under a physiological state, nitric oxide (NO) is a key regulator of endothelial function. However, under the condition in which there is an increase in ROS levels, NO is oxidized leading to additional oxidation and cell damage [23] NOX enzymes expressed in vascular tissue produce ROS that are linked to CVD [23]. Superoxid dismutase (SOD) has also been implicated in vascular disease in response to oxidative stress [24]. Particularly, SOD1 plays a key role in maintaining the endothelial function by protecting the NO availability. In atherosclerosis, SOD1 has been shown to decrease the levels of O2•−, to maintain normal vascular function. This is evident in the aging populations who are constantly exposed to oxidative elements such as angiotensin II and LPS [25]. A deficiency in SOD ultimately leads to heightened levels of vasoconstriction and endothelium malfunction. Oxidative stress can also increase the load on the innate immune system which increases the incidence of chronic inflammation and induce atherosclerosis [26].

Finally, epigenetic modifications, including DNA methylation, histone modifications, and non-coding RNA expression, play crucial roles in gene regulation and are significantly altered with aging. In particular, large amounts of some crucial microRNAs regulating inflammation, named inflammamiRs have been implicated in inflammaging [27]. This is important because microRNA modulates mitochondrial activity, contributing to inflammaging and furthering susceptibility to CVD [28]. Some inflammamiRs target the NF-κB and (NOD)-like receptor protein 3 (known as NLRP3) pathways, and have been identified as a crucial component of the extracellular vesicle [29]. These changes can promote a pro-inflammatory phenotype, contributing to inflammaging. For instance, age-related hypomethylation of promoter regions of pro-inflammatory genes can lead to their increased expression [30]. Similarly, through chromatin remodeling, atypical cellular expression of inflammatory genes leads to aberrant molecular pathways therefore increasing vulnerability to CVD. Histone modifications that promote inflammatory gene expression are more prevalent in aged cells.

Although inflammaging is a process inevitably associated with aging and observed in all elderly subjects, some of them have mechanisms that can counterbalance the harmful effects given by the low-grade inflammatory state that characterizes inflammaging. In particular, centenarians, represent the best example of successful aging. These exceptional subjects have a large amount of circulating anti-inflammatory, molecules such as Transforming Growth Factor-(TGF)-β1, IL-10, IL-1 receptor antagonist (IL-1Ra), adiponectin, cortisol, anti-inflammatory arachidonic acid compounds, including HETE and EET, mitokines (FGF21, GDF15 and HN) [31,32,33]. These molecules counterbalance the concomitant increased levels of the aforementioned inflammatory ones, mitigating the inflammaging [6, 32,34]. Thus, the development of age-related diseases and frailty is a result of excessive stimulation of pro-inflammatory responses and also of an ineffective anti-inflammatory reaction [35]. Conversely, the attaining of longevity and successful aging is determined by a reduced stimulation of inflammatory pathways together with an effective anti-inflammatory response.

1.2 Cardiovascular Senescence in Women

The understanding of the aging process was improved by the Strehler’s enunciation [36] of the so-called 4 rules of aging. This rule states that aging processes are universal, progressive, intrinsic and deleterious [37], occurring in different patterns across individuals. There are scientific studies that have observed inflammation and cardiovascular senescence [38, 39]. As previously highlighted, Franceschi et al. [6] coined the term “inflammaging” to describe the chronic, low-grade, systemic inflammation which develops with age in the absence of overt infections (thus, sterile inflammation)[40].

Women can experience unique inflammatory responses and cardiovascular changes due to hormonal fluctuations, particularly during events like pregnancy and menopause [41, 42]. Studies proved that women may exhibit different inflammatory markers compared to men, influenced by factors like genetics, hormonal levels, and lifestyle [43, 44]. For example, higher levels of certain pro-inflammatory cytokines have been observed in women, particularly following menopause, which may contribute to increased cardiovascular risks [45].

There are evidence suggesting that women may develop cardiovascular diseases later than men, but when they do, they may experience more severe symptoms and outcomes, related to specific pathophysiological processes [46, 47]. For instance, women often present with microvascular dysfunction rather than the typical macrovascular disease seen in men [48].

Research has increasingly linked menopause and the accompanying hormonal changes to higher risks of cardiovascular diseases. Studies have indicated that postmenopausal women see an increase in inflammatory markers, which are associated with cardiovascular events. For instance, the Women’s Health Initiative study has provided important insights into how hormone replacement therapy may impact cardiovascular health [49, 50]. Moreover, recent studies have explored the differences in immune responses between men and women. It has been found that women may have a stronger inflammatory response, which could influence the development of autoimmune diseases and cardiovascular issues [51].

In addition, research has shown that women, particularly younger and postmenopausal women, may be more susceptible to microvascular dysfunction, which is an important factor in cardiovascular diseases [52]. This dysfunction can be linked to chronic inflammation and can often lead to heart failure with preserved ejection fraction (known as HFpEF), a condition that is increasingly recognized as a significant issue in women [53].

Menopausal hormonal changes include changes in cortisol secretion. The body may adapt to stress differently, which can lead to elevated levels of cortisol, particularly in response to psychological and physical stressors. Cortisol is a steroid hormone that has a complex role in the inflammatory process. It is generally known for its anti-inflammatory effects, but chronic high levels of cortisol can lead to a paradoxical pro-inflammatory state. Elevated cortisol can disrupt the balance of immune responses and increase the production of pro-inflammatory cytokines, which may contribute to chronic inflammation. Moreover, elevated cortisol levels can impact several cardiovascular risk factors, such as increased blood pressure, dyslipidemia (abnormal lipid levels), and arterial stiffness. These factors collectively contribute to an increased risk of cardiovascular diseases, including heart disease and stroke [54]. Postmenopausal women may also experience increased psychological stress, which can further elevate cortisol levels. The relationship between stress, cortisol, and inflammation is well-documented; chronic stress can lead to sustained high levels of cortisol, perpetuating an inflammatory vicious cycle that negatively affects cardiovascular health [55,56,57].

Longitudinal studies, such as the Framingham Heart Study, have provided evidence of how inflammatory markers change over time in women and how they correlate with cardiovascular events [49, 58].

Endothelial dysfunction during senescence is a peculiar sign of aging and age-related cardiovascular diseases. Low grade inflammation can exacerbate the decline in endothelial function. A major player in this inflammatory environment is the enzyme NADPH oxidase (NOX), which, when overactive, leads to the excessive production of reactive oxygen species (ROS) [59].

1.

Endothelial dysfunction in senescence

Endothelial cells regulate vascular tone, blood flow and overall cardiovascular health [59]. With aging, endothelial cells enter a state of senescence, with an impaired function, leading to dysregulated vascular homeostasis. This can manifest as reduced nitric oxide (NO) bioavailability, impaired vasodilation, increased vascular stiffnessand pro-inflammatory signaling. Estrogens play a fundamental role in promoting endothelial function, by increasing the NO production [60].

A key factor in this dysfunction is the increased production of ROS, which contributes to oxidative stress, DNA damage, and a further decline in endothelial cell function. Moreover, NOX, generating superoxide (O2•−), by transferring electrons from NADPH to oxygen, enhance inflammation in endothelial cells. During senescence and chronic inflammation, NOX can become overactive, leading to excessive ROS generation [61]. Over time, this ROS-mediated endothelial dysfunction contributes to the pathogenesis of atherosclerosis, hypertension, and other cardiovascular diseases. It also accelerates vascular aging, characterized by arterial stiffness, reduced regenerative capacity of endothelial cells, and impaired angiogenesis [62].

2.

Inflammation and cardiovascular comorbidities: chained conditions

Some pathological conditions, such as osteoporosis, cancer and autoimmune disorders can indeed exacerbate cardiovascular impairment in women after menopause. These conditions add additional layers of risk that compound the already increased susceptibility to CVDs in postmenopausal women [50]. Osteoporosis and cardiovascular disease share many common risk factors, including age, inflammation, hormonal changes and oxidative stress, all of which become more prevalent after menopause. A decline in estrogen increases the risk of both osteoporosis (due to loss of bone density) and endothelial dysfunction.

In osteoporosis, calcium is often leached from bones and can accumulate in arterial walls, leading to vascular calcification. This stiffens blood vessels and impairs their ability to regulate blood pressure, contributing to hypertension and increasing the risk of cardiovascular events such as heart attacks or strokes [63, 64].

Furthermore, cancer and cardiovascular diseases frequently rise from the same risk factors, unhealthy behavior and pathophysiological basis. Some sex-specific tumors (e.g. ovarian cancer, breast cancer) are nowadays treated using some heart-harmful agents which could further impair cardiovascular conditions [65, 66]. Indeed, cancer therapies, including chemotherapy, radiation, and certain targeted therapies, can have cardiotoxic effects that exacerbate cardiovascular problems, particularly in postmenopausal women who already have higher baseline risk due to age and loss of estrogen. Moreover, cancer often induces a pro-inflammatory state, which promotes endothelial dysfunction and atherosclerosis. Elevated levels of inflammatory markers like CRP are associated with both cancer and cardiovascular disease, creating a bidirectional risk [67].

Autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus (SLE), and psoriasis, which show a higher prevalence among middle-aged women, are known to significantly increase the risk of cardiovascular disease [