Atherosclerosis is known as a chronic inflammatory disease (1). Endothelial dysfunction, characterized by oxidative stress and increased expression of adhesion molecules and chemokines as well as reduced expression of nitric oxide, is regarded as a pivotal stage in the initiation of atherogenesis (2). Oxidation inherently interacts with inflammation in the pathogenesis of endothelial dysfunction. Leukocyte adherence and infiltration into the vessel wall (3) has been shown to stimulate vascular reactive oxygen species (ROS) production by both infiltrating immune cells and activated vascular cells (4, 5). Increased superoxide production is a critical step in endothelial dysfunction (4, 6–9). At the same time low grade inflammation is a hallmark of cardiovascular disease (CVD). Recent clinical trials including CANTOS [Canakinumab Anti-inflammatory Thrombosis Outcome Trial (10)], as well as COLCOT (Colchicine Cardiovascular Outcomes Trial) and LoDoCo2 (low-dose colchicine trial) (11, 12) have demonstrated proof of principle of potential targeting of the inflammatory mechanisms in cardiovascular risk. These are supported by mechanistic evidence in murine and human studies linking systemic inflammation to local events in the vessel wall (13).

Inflammation can be a cause and a consequence of heart failure (HF), and it contributes to disease pathogenesis and progression. The hemodynamic stress associated with HF induces inflammation by eliciting the release of proinflammatory cytokines by cardiomyocytes and cardiac fibroblasts, including TNF-α, IL-6, IL-1β as well as angiotensin II, and myostatin. HF also causes mitochondrial dysfunction, reactive oxygen species generation, and leads to activation of the NLRP3 inflammasome, with subsequent production of proinflammatory cytokines (14–16). The proinflammatory cytokines IL-1β and TNF-α may induce systolic and diastolic dysfunction, TNF-α also stimulates cardiac remodeling (17). Additionally, comorbidities that commonly coexist with HF including diabetes, obesity, and chronic kidney disease are associated with chronic low-grade inflammation, which may have detrimental effects on cardiac structure and function (18). A recently published analysis of the CANTOS trial found that, anti-IL-1β therapy was associated with a significant reduction in HF hospitalizations and a reduction in the composite of HF hospitalizations and all-cause death, in participants who had a reduction in hs-CRP to <2 mg/L compared with placebo (19).

In light of these relationships, it becomes essential to identify biomarkers that could reflect vascular inflammation as well as related pathogenetic mechanisms of vascular dysfunction (20–22). While increased levels of circulating biomarkers such as IL-6 as well as hs-CRP independently predict the risk of cardiovascular diseases (23, 24), it remains unclear to what extent they represent local processes occurring in the vessel wall.

Accordingly, as there are regional differences in arterial vessels in susceptibility to atherosclerosis, and different pathological pathways might be involved in different vessels, yet some systemic markers of inflammation have been reported to be associated with increased risk of CVD. We sought to investigate whether levels of circulating inflammatory cytokines (TNF-α, IL-6 and IL-1β) reflect the local vascular expression of these inflammatory molecules in different types of blood vessels (internal mammary artery and left anterior descending artery) of patients with advanced cardiovascular diseases [coronary artery disease patients undergoing coronary artery bypass graft (CABG) surgery, and patients with end-stage heart failure undergoing heart transplantation]. We also investigated whether oxidative stress is associated with inflammation in atherosclerosis resistant artery (internal mammary artery) in patients with coronary artery disease (CAD). We chose these blood vessels as a model as they represent different aspects of the spectrum of susceptibility to atherosclerosis. While human internal mammary arteries do not develop atherosclerosis in spite of overt endothelial dysfunction, coronary arteries are an essential site of atherosclerosis development (25).

In this study we demonstrate that the levels of systemic TNF-α, IL-1β and IL-6 do not reflect their vascular mRNA expression in patients with advanced cardiovascular diseases, and that vascular expression of these cytokines is not associated with increased ROS generation in IMA in patients with coronary artery disease. Interestingly, we found that proinflammatory cytokine TNF-α positively correlated with high sensitivity C-reactive protein in patients with advanced heart failure undergoing heart transplantation. In CABG cohort the positive correlation of hs-CRP with TNF-α and IL-6 was observed. Serum CRP is considered as a marker of inflammation as well as a predictor of the development of cardiovascular events (29, 30). Our results are consistent with previous published data. It has been shown that human coronary artery smooth muscle cells are able to produce CRP in response to proinflammatory cytokines including TNF-α, IL-1β and IL-6 (29). Interestingly, locally produced CRP participated in the atherogenesis (29, 30). CRP was increased in patients with coronary artery lesions. Moreover, CRP positively correlated with IL-6 (31–33) and TNF-α (33–35).

In our study we observed no correlation between systolic blood pressure and systemic or vascular inflammatory cytokines. However, we found the correlation between diastolic blood pressure and vascular expression of TNF-α and IL-6. Previously, it has been shown that IL-6 and TNF-α, positively correlated with blood pressure in pregnancy induced hypertension (36, 37). Moreover, the positive correlation between IL-1β and mean blood pressure in patients with essential hypertension has been demonstrated (38). However, it should be noted that IL-1β inhibition by canakinumab reduces adverse cardiovascular events but this mechanism is not associated with changes in blood pressure (39). These discrepancies may be related to the fact that patients in our study had more advanced CVD, and comorbidities and medications may influence the relationship between blood pressure and inflammatory markers.

Previous studies have confirmed the role of TNF-α in vascular pathology (40, 41). TNF-α is synthesized initially by activated macrophages and T cells, it acts by binding to one of two types of receptors: TNFR1 or TNFR2 (tumor necrosis factor receptor) (42), and employs the stimulation of the release of IL-1β and IL-6, as well as upregulation of the expression of chemokines and endothelial adhesion molecules, and coordination of the migration of leukocytes to the inflamed targeted organs (40). In humans, evidence points towards TNF-α playing an important role in stimulating endothelial dysfunction. The positive correlation between increased plasma TNF-α levels and reduced reactivity to acetylcholine has been observed previously (41). In diabetic patients, TNF-α induces endothelial dysfunction, which is reversed by the PPAR-γ agonist (43). Moreover, the TNF-α inhibitors are particularly effective in blood pressure lowering in animal studies (44). ROS appears to be one of the key mediators involved in TNF-α induced endothelial activation. Mycophenolic acid, active metabolite of mycophenolate mofetil inhibits TNF-α-stimulated ROS generation in human aortic endothelial cells (45). TNFRs activate transcription factor NF-κB (nuclear factor-κB). ROS also function as second messengers in several signal transduction pathways including NF-κB signaling (46). ROS trigger activation of NF-κB but may also inhibit NF-κB activity. These opposite effects seem to be time and context dependent (47). In our study the vascular TNF expression (dCT) in IMA negatively correlated with vascular superoxide production, but this interaction did not reach the statistical significance. No correlation of TNF with maximal relaxation was found. Interestingly, we observed the strong negative correlation of plasma IL-1β with the maximal relaxation. This observation is consistent with previous study showing the link between IL-1β and coronary endothelial dysfunction (48).

Discordance between levels of systemic cytokines and their vascular expression may be partially explained by the complexity of the inflammatory process. Cytokines are local mediators, and their production can be compartmentalized (49). Patterns of cytokine production differ under various clinical conditions, particularly in low-grade chronic inflammation, and cellular mRNA may not correspond to circulation proteins. Although elevations in inflammatory markers commonly occur together, they may not be synchronized. Additionally, concentrations of some inflammatory markers change relatively slowly, while other can change rapidly. Accurate detection of cytokines is challenging because of their dynamic secretion processes and short half-lives. The majority of cytokines have a short half-life in vivo and may be subjected to immediate degradation during sample collection and preparation (50).

Interestingly, multiple distinct endothelial cells subtypes have been revealed in aorta by single-cell sequencing (51). At the same time, vascular dysfunction can correlate between different arteries, as well as between venous and arterial endothelium, suggesting that endothelial dysfunction may be systemic (52). Furthermore, genetic and epigenetic modifications may influence endothelial function both in healthy individuals and in patients with cardiovascular diseases (53). Immune response can also vary within the individual, between local and systemic scales and across the tissues.

The analysis of biomarkers in patients with atrial fibrillation (AF) has revealed compelling associations between various mechanisms and cardiovascular death. These mechanisms include oxidative stress, cardiorenal dysfunction, inflammation, vascular and renal dysfunction, calcium balance, apoptosis, and fibrinolysis (54). Additionally, the associations between biological processes related to IFN-γ production, T-cell co-stimulation, and all-cause mortality have been demonstrated. In light of these findings, the potential therapeutic targets may involve enhancing IFN-γ production and targeting CD28, CD70, TNF superfamily member-14 (TNFSF14), and inducible costimulator ligand (ICOSLG) (55). Furthermore, it is worth noting that circulating cardiovascular disease biomarkers may also be associated with an increased risk of cancer and overall mortality (56).

Our study does have certain limitations. Firstly, we have evaluated the association of plasma biomarker concentrations and their vascular mRNA expression but not vascular protein level. It should be noted that during the surgery there were collected very small fragments of the vessel, and we were unable to perform the additional analyses, including the measurements of cytokine vascular protein levels. This may be the limitation of our study. On the other hand, cytokines are small, secreted proteins, which are produced by immune cells as well as a number of vascular cells (57). For this reason, the vascular cytokine mRNA expression may be more representative than its vascular protein level. Moreover, examining mRNA levels could offer valuable insights into the interplay between inflammation and oxidation, as ROS may regulate cytokine transcription in vascular cells. In addition, no histological data were available on the human vessels.

Secondly, it is important to note that the patients included in our study had advanced CVD and multimorbidity, which indicates the presence of several potential confounding factors that could influence the systemic levels of peripheral inflammatory markers more than local vascular expression. These confounders may include factors such as adipose tissue in obesity, medication usage, and other comorbidities. We do not have data on the imaging of other arteries which could show the extent of atherosclerosis. Although, it may be speculated that presence of clinical atherosclerosis in one vascular territory largely indicates an increased likelihood of its presence in other vessels.

Another limitation is a relatively small number of HTx patients included for this study. We have collected 17 samples of the left anterior descending artery from HTx cohort. However, it should be noted that, other studies on the human cardiac tissue and coronary arteries were performed on a smaller number of samples, collected from 10 to 14 patients (27, 58, 59).

Furthermore, our study involved a single systemic cytokine measurement. This may partially explain the lack of relationship observed with local production, as systemic levels can vary depending on environmental and other factors. Therefore, our analysis may not fully capture the potential variability over time. However, it is worth noting that in practical terms, our aim was to identify biomarkers that could be implemented clinically without the need for multiple consecutive measurements. Requiring frequent measurements could hinder their feasibility and practical use in a clinical setting.

In conclusion, our findings suggest that while individual cytokines show correlation within their respective compartments, indicating consistency in local processes, we observed a lack of correlation between cytokine levels across compartments. This lack of correlation between local cytokine expression and their circulating levels highlights the complex nature of inflammation, which may involve intricate aspects that cannot be fully captured by measuring circulating inflammatory cytokines.