In the present study, we have shown for the first time that sarcoidosis is characterized by an unfavorably altered thrombin generation profile, reflected by the higher ETP and peak TG and extended ttPeak as compared to well-matched controls. Thus, our results provide evidence for a prothrombotic state in clinically stable, non-active pulmonary sarcoidosis, which is consistent with previous epidemiological cohort studies, ,  and systematic reviews ,  demonstrating an increased risk of cardiovascular events in that disorder.
Interestingly, higher serum IL-6, blood platelet count, and FVIII activity were independent predictors of increased thrombin formation in sarcoidosis. At the same time, demographic factors, such as age, gender, and BMI, had no impact. Indeed, IL-6 is a robust prothrombotic agent, increasing TF expression on monocytes and endothelial cells and promoting their activation. Furthermore, IL-6 may enhance the production of fibrinogen, FVIII, and platelets , which secrete proinflammatory and procoagulant mediators, such as P-selectin, platelet-activating factor, and thromboxane after activation . Likewise, elevated FVIII may promote thrombin formation in response to inflammation or endothelial injury, further enhancing the prothrombotic state.
Our results mirror previously published data on increased thrombin generation in other chronic inflammatory diseases, such as asthma, rheumatoid arthritis, systemic sclerosis, and systemic lupus erythematosus. They all point to the complex nature of the coagulation pathway control; however, inflammation and endothelial damage were essential prothrombotic determinants in most of them. On the contrary, discretion concerns demographic factors, such as age and BMI, which were predictors of CAT assay parameters, e.g., in asthma . That discrepancy suggests that in sarcoidosis, the role of inflammatory response is much more significant ,  and outweighs other less critical variables. Furthermore, our results indicate that even in a clinically non-active disease, the local or low-grade systemic inflammation may contribute to the prothrombotic plasma properties with potential clinical outcomes. Moreover, the patients with a more severe form of the disease, e.g., with lung function changes or requiring systemic corticosteroids, might be at a higher risk of thromboembolic complications. However, chronic exposure to corticosteroids poses increased cardiovascular risk and could be an independent variable contributing to the observed cardiovascular changes.
Our results do not explain how lung inflammatory granulomas drive the prothrombotic state. One possible explanation might be related to the activity of Rac-1, a small G-coupled protein, a molecular switcher regulating cell adhesion, proliferation, migration, and chemotaxis. It has been demonstrated that Rac-1 implies T-cell and macrophage to sarcoid granulomas formation . Furthermore, a murine model of sepsis provides a piece of evidence that it also activates a coagulation pathway . In turn, generated active coagulation factors, such as thrombin, may aggravate local or systemic inflammation by protease-activated receptors (PARs), located on inflammatory, epithelial, and endothelial cells in the lungs. PARs are triggered by several proteases, including neutrophil elastase, granzymes of cytotoxic lymphocyte, and thrombin, enhancing local inflammatory response . Moreover, it has been documented that activating PAR-1 on monocytes and macrophages upregulates the production of oncostatin M, a pleiotropic cytokine implicated in the pathology of the heart and vascular damage .
As expected, increased ETP was related to the higher serum triglycerides. However, in our study, that association was more potent than previously reported in the general population. Therefore, it may underline the importance of strict dyslipidemia management in sarcoidosis patients. In turn, the inverse relationship between thrombin generation and kidney function is well-known and mirrors other reports , .
Another important issue that merits comment is a higher circulating VCAM-1 in sarcoidosis patients with extrapulmonary lymphadenopathy. VCAM-1 is an endothelial cell biomarker, which appears on these cells after activation. Therefore, its higher blood concentration might suggest endothelial injury. However, it has been previously shown that increased VCAM-1 on endothelial cells is the first step of signaling mechanisms in lymph nodes, leading to lymphocyte accumulation and lymph nodes enlargement . Therefore, one may speculate that increased VCAM-1 in our study does not necessarily indicate vascular damage. Instead, its higher level, interestingly related to the lower lymphocyte count in peripheral blood (data not shown), may reflect vascular susceptibility to the lymphocyte homing into the sarcoid lymph nodes.
In turn, the second analyzed endothelial damage biomarker, thrombomodulin, was higher in patients with hypercalcemia. Hypercalcemia affects about 20% of sarcoidosis individuals. The majority of those cases can be explained by the overproduction of 1,25(OH)2D3 by activated macrophages. Of note, the active form of vitamin D3 stimulates osteoblasts to synthesize thrombomodulin. Thus, higher thrombomodulin in hypercalcemia might also be related to the macrophage stimulation in sarcoid granulomas.
The last issue for discussion in our data is echocardiographic findings. In comparison to the controls, the patient group had enlarged dimensions of the right ventricle, left atrium, and thicker LV walls. Furthermore, sarcoidosis was related to diastolic cardiac dysfunction and the increased probability of pulmonary hypertension. Apart from cardiological cases, diastolic LV impairment is often demonstrated in pulmonary patients, particularly those with COPD or sleep apnea syndrome, . It is related to heart wall relaxation disorders, LV mass hypertrophy, and myocardial fibrosis, leading to increased LV filling pressure, left atrium pressure, and, consequently, pulmonary hypertension, which ultimately causes clinical symptoms . Additionally, a postulated mechanism underlying cardiac diastolic failure is endothelial dysfunction of the coronary microcirculation due to increased circulating inflammatory cytokines (e.g., IL-6, TNF-α, pentraxin-3) , . Furthermore, coronary circulation's endothelial damage likely induces cardiomyocyte hypertrophy and increased collagen production in interstitial tissue.
Documented echocardiographic features seem not clinically significant; however, they might increase the risk of cardiovascular events in sarcoidosis. Moreover, the elevated left atrial volume index has been shown as an independent predictor of adverse cardiovascular outcomes. While cardiac sarcoidosis is asymptomatic in 95% of the affected patients, untreated inflammation and progressive myocardial fibrosis can lead to heart chamber abnormalities and dysfunction. It is possible, that described diastolic dysfunction may be a consequence of undetected cardiac sarcoidosis. Of note, the diagnosis of this abnormality is difficult. Identified electrocardiographic or echocardiographic findings can often be explained by comorbidities such as hypertension or coronary heart disease. At the same time, the sensitivity and specificity of the standard two-dimensional (2D) echocardiography are limited. However, new techniques, such as speckle tracking echocardiography, cardiac magnetic resonance, and positron emission tomography, can be beneficial in the early detection of inflammatory and fibrotic changes of the heart and thus need to be recommended in patients with suspected cardiac sarcoidosis –.