Troponin elevation in acute stroke : clinical characteristics and the link to cancer-associated neutrophil extracellular traps

Abstract: Elevated plasma levels of troponin, a marker of myocardial injury, are a frequent observation in stroke patients. Despite several reports on an adverse short-term prognosis, however, the significance of troponin elevation in stroke is still controversial, and the myocardial injury often lacks a clear etiology. The aim of this thesis was to determine patient characteristics, including long-term prognosis, in these patients, as well as to explore possible underlying pathomechanisms. In a retrospective cohort analysis of 247 stroke patients (Study I), troponin elevation was significantly associated with age, comorbidity burden, and stroke severity. Stroke patients with troponin elevation also had a higher prevalence of electrocardiographic changes suggestive of myocardial ischemia on admission. A 5-year follow-up period revealed an almost 2-fold increased risk of mortality, with an adjusted hazard ratio of 1.90 (95% CI 1.34- 2.70). In an explorative case-control study (Study II), we furthermore suggest that cancer may be a contributing factor to the poor prognosis in these patients, showing a significant prevalence of underlying cancer among ischemic stroke patients with high troponin elevations. Plasma analyses were strongly supportive of a hypercoagulable state in these patients, and histopathological investigations revealed widespread arterial microthrombi in several organs including the heart. Neutrophil activation, with the release of highly pro-coagulant extracellular chromatin, referred to as neutrophil extracellular traps (NETs), has recently been proposed to play a central role in cancer-associated venous thromboembolism. We therefore proceeded to investigate the role of NETs in the cancer-associated hypercoagulable state seen in the ischemic stroke patients with high levels of plasma troponin as well as an underlying malignancy. As with markers of coagulation, plasma markers of NETs were significantly elevated in these patients, and there were significant positive correlations between the two. Histopathological investigations further supported the role of NETs in the thrombotic state by immunodetection of NET markers in arterial microthrombi. To assess a circulating NET burden in these patients, a novel ELISA-based assay to quantify the NETspecific marker H3Cit in plasma was developed, and subsequently standardized and methodologically validated (Study III) revealing a high specificity, precision and stability of the assay. These results support cardiologic work-up and more aggressive prevention measures in stroke patients with troponin elevation. They furthermore suggest that an underlying cancer should be considered in ischemic stroke patients with unexplainably high plasma levels of troponin. Finally, we link this hypercoagulable state to NETs, and therefore encourage further studies to explore whether markers of NETs could serve as novel diagnostic and prognostic tools in the setting of cancer-associated arterial thrombosis. To this end, we suggest a novel ELISAbased assay to quantify the NET-specific marker H3Cit in plasma.