The current study aimed to investigate the relationship between a prolonged D2B time and eGC damage in the case of cardiogenic shock during STEMI. Particular attention was paid to the relationships between eGC damage and endothelial dysfunction with regard to the D2B. Multiple studies have demonstrated the importance of the shortest possible period of time between the first medical contact and revascularization in acute myocardial infarction9,18, but to our knowledge there is no published data showing a temporal link between myocardial infarction and endothelial injury. Acute ischemic syndromes such as STEMI ultimately lead to cardiogenic shock with advancing time.19 A cut-off of < 60 min D2B time was used in accordance with the current guidelines and an overall association of a D2B over 60 min with higher morbidity and mortality.20,21
Using AFM for quantifying the nanomechanical properties (height/stiffness) of the eGC, our data shows that the endothelial surface is injured during STEMI, causing deterioration of the eGC. For the first time we could demonstrate that a shorter D2B time is associated both with fewer changes in the nanomechanical properties of the eGC (r = .516) and lower concentrations of syndecan-1 (r = .637), indicating less damage to the eGC. The eGC damage and loss of endothelial function was significantly lower in the group of patients with a D2B of under 60 min. Furthermore, shorter D2B resulted in a shorter hospitalization. Although it has been shown that cardiac I/R severely damages the eGC, which can be detected by increased circulating levels of its principal constituents13,22, until now there were no published data that have demonstrated a temporal relationship between eGC components and the D2B. A prolonged D2B may thus cause more severe damage to the eGC, which might be the “stumbling block” to severe cardiac IRI ultimately leading to cardiogenic shock.
A reduction in eGC height and stiffness indicates eGC shedding 23. Shedding of eGC is known to be caused by different factors that are elevated and activated during cardiac IRI and cardiogenic shock24. Those factors are associated with cardiac mechanical stress, generalized vascular trauma, and an increased inflammatory response11,25, as indicated by proinflammatory mediators such as interleukins26, catecholamines27, angiopoetin-228, CRP29, leukocytes25, matrix metalloproteinases (MMP)26, or the complement system.30 This inflammation-mediated response results in cell death of the ischemic tissue and subsequent long-term consequences such as postinfarction heart failure with the hallmarks of cardiac fibrosis and heart dysfunction.31 In the present study, the strong correlations between eGC impairment and the elevated levels of CRP, leukocyte count, and elevation of the complement anaphylatoxins indicate a proinflammatory response. The process of eGC shedding is further underpinned by elevated levels of the eGC components (syndecan-1, heparan sulfate, and hyaluronic acid) measured in the STEMI sera, indicating elevated levels of MMPs, and by the strong correlation between eGC height and stiffness (r = .918).
High syndecan-1 levels have been found to be an independent predictor for outcome in patients with STEMI independent of the infarct-related myocardial injury13 and are an independent predictor of mortality in cardiogenic shock.32 Compared to healthy individuals, syndecan-1 concentrations were significantly higher in STEMI patients. This effect is mostly explained by the activation of MMPs, which have been shown to be commonly upregulated in cardiac IRI triggering glycocalyx damage.33 The exact physiological and pathophysiological role of syndecan-1 in cardiac IRI are beyond the scope of this paper; however, this matter was dealt with in detail in previous work of our group.11 In this context, it can be hypothesized that increased syndecan-1 indicates eGC shedding after STEMI, impairing eGC and vascular function and leading to adverse outcomes. The same applies to increased levels of other eGC components such as heparan sulfate or hyaluronic acid. Syndecan-1 levels > 120 ng/ml have been shown to be independently associated with higher 6-month mortality after STEMI13. In our cohort 54% of the STEMI patients showed an elevation of this magnitude. Without analyzing mortality as an endpoint in this study, a prolonged hospital stay suggests that patients with an elevated syndecan-1 level > 120ng/ml were significantly more severely ill than patients with lower syndecan-1 levels. Likewise, there was a strong interaction between nanomechanical properties of the eGC and syndecan-1 levels, which further correlated with a prolonged D2B time, indicating a time dependency of the eGC damage during STEMI. This time dependency of eGC damage could be explained by an overall prolonged inflammatory response in the phase of chronic inflammation after myocardial ischemia.34
The deterioration of the eGC also correlated with the degree of NO release - the hallmark for endothelial dysfunction.35 In a functional endothelium NO is released by the endothelial cells themselves and diffuses to adjacent vascular smooth muscle cells (VSMC) where it triggers vasodilation via cyclic guanosine monophosphate (cGMP)-dependent pathways.36 Here, the reduction in NO production demonstrates the link between the altered nanomechanical properties of the eGC and the beginning of endothelial dysfunction during STEMI.
The disruption in eGC integrity in cardiac IRI has been documented in the meantime2, but, to date, no satisfactory cardioprotective therapy against IRI is available for daily clinical practice37. Here, protecting the eGC in the case of STEMI and cardiogenic shock leads to less eGC damage, resulting in turn in less cardiac IRI, which has previously been demonstrated by using a recombinant syndecans-1 as an eGC recovering agent.11
Our study has established the basis for further investigations to illustrate the important role that the eGC plays in the development of cardiac IRI. Despite all previous knowledge, the eGC still represents an underestimated factor in the development of cardiac IRI. On the one hand, this is due to the complex and multi-layered cell biological background and mechanisms of eGC damage in cardiac IRI3, but, on the other, also to the limited translatability from basic research to clinical practice, both for diagnostic options and pharmacological approaches to managing IRI.37
Our AFM-based methodology is time consuming and sophisticated, which precludes analyzing considerably larger, random sets of samples; however, there are approaches for meaningful analysis of the eGC status that can be probed in everyday clinical practice: For example, by visualizing the sublingual microcirculation the integrity of the glycocalyx could be assessed indirectly and could represent an important diagnostic tool to measure eGC integrity in the future and further predict the outcome of STEMI patients.38 The association between sublingual microcirculation parameters and eGC dimensions has already been demonstrated for critically ill patients.39 It is now known that the study of microcirculation parameters and eGC dimensions is an important part of the assessment of septic patients.40 So far, however, this need has not been demonstrated for patients in cardiogenic shock. Here, we establish the basis for further investigations and illustrate the important role the eGC condition plays in the development of cardiac IRI in the event of STEMI.