Calprotectin predicts mortality after ischemic stroke and is present in the thrombus

Abstract Background- Inflammatory response plays an important role in many processes related to acute ischemic stroke (AIS). Calprotectin (S100A8/S100A9), released by monocytes and neutrophils, is a key protein in the regulation of inflammation and thrombosis. The purpose of this study is to evaluate the association of circulating calprotectin with other inflammatory biomarkers and AIS prognosis, as well as the calprotectin content in stroke thrombi.Methods- Among the 748 patients treated at a comprehensive stroke centre between 2015-2017, 413 patients with confirmed acute ischemic injury were evaluated. Patients with systemic inflammation or infection at onset were excluded. Plasma calprotectin was measured by ELISA in blood samples of AIS patients within the first 24h. Univariate and multivariate logistic regression models were performed to evaluate its association with mortality and functional independence (FI) at 3-months (defined as modified Rankin Scale<2), and intracranial haemorrhage (ICH) after stroke. Further, S100A9 was localized by immunostaining in stroke thrombi (n=44). Results- Higher calprotectin levels were associated with 3-month mortality and ICH, while lower calprotectin levels were documented in patients with 3-month FI. After adjusting for potential confounders, plasma calprotectin levels remained associated with 3-month mortality [OR (95%CI); 3.06, (1.67-5.61)]. Patients with calprotectin≥2.26 µg/mL were 4-times more likely to die [OR 3.98, (1.88-8.41)]. Likewise, Neutrophil-Lymphocyte Ratio (NLR) and C-Reactive Protein (CRP) were also associated with 3-month mortality [OR 1.98, (1.17-3.35); and 1.39, (1.02-1.89) respectively]. A multimarker approach demonstrated that patients with increased calprotectin, CRP and NLR had the poorest outcome with a mortality rate of 42.3% during follow-up. S100A9 protein, as part of the heterodimer calprotectin, was present in all thrombi retrieved from AIS patients. Mean S100A9 content was 3.5% and tended to be higher in patients who died (p=0.09). Moreover, it positively correlated with platelets (Pearson r 0.46, p<0.002); leukocytes (0.45, p<0.01) and neutrophil elastase (0.70, p<0.001) thrombi content. Conclusions- Plasma calprotectin is an independent predictor of 3-month mortality and provides complementary prognostic information to identify patients with poor outcome after AIS. Presence of S100A9 in stroke thrombi suggests a possible inflammatory mechanism in clot formation and further studies are needed to determine its influence in resistance to reperfusion.