Erythrocytes increase endogenous sphingosine 1-phosphate levels as an adaptive response to SARS-CoV-2 infection.

Low plasma levels of the signaling lipid metabolite sphingosine 1-phosphate (S1P) are associated with disrupted endothelial cell (EC) barriers, lymphopenia and reduced responsivity to hypoxia. Total S1P levels were also reduced in 23 critically ill patients with coronavirus disease 2019 (COVID-19), and the two main S1P carriers, serum albumin (SA) and high-density lipoprotein (HDL) were dramatically low. Surprisingly, we observed a carrier-changing shift from SA to HDL, which probably prevented an even further drop in S1P levels. Furthermore, intracellular S1P levels in red blood cells (RBCs) were significantly increased in COVID-19 patients compared with healthy controls due to up-regulation of S1P producing sphingosine kinase 1 and down-regulation of S1P degrading lyase expression. Cell culture experiments supported increased sphingosine kinase activity and unchanged S1P release from RBC stores of COVID-19 patients. These observations suggest adaptive mechanisms for maintenance of the vasculature and immunity as well as prevention of tissue hypoxia in COVID-19 patients.

Chemerin in peritoneal sepsis and its associations with glucose metabolism and prognosis: a translational cross-sectional study.

BACKGROUND: Stress hyperglycaemia (SHG) is a common complication in sepsis associated with poor outcome. Chemerin is an adipocytokine associated with inflammation and impaired glucose homeostasis in metabolic diseases such as type 2 diabetes (T2D). We aimed to investigate how alterations of circulating chemerin levels and corresponding visceral adipose tissue (VAT) expression are linked to glucose metabolism and prognosis in sepsis. METHODS: Clinical data and tissue samples were taken from a cross-sectional study including control, T2D and sepsis patients, all undergoing laparotomy. A second independent patient cohort of patients with sepsis was included to evaluate associations with prognosis. This was complemented by a murine model of peritoneal infection and a high-fat diet. We analysed circulating chemerin by enzyme-linked immunosorbent assay and VAT messenger RNA (mRNA) expression by real-time polymerase chain reaction. RESULTS: Circulating chemerin was increased in sepsis 1.69-fold compared with controls (p = 0.012) and 1.47-fold compared with T2D (p = 0.03). Otherwise, chemerin VAT mRNA expression was decreased in patients with sepsis (p = 0.006) and in septic diabetic animals (p = 0.009). Circulating chemerin correlated significantly with intra-operative glucose (r = 0.662; p = 0.01) and in trend with fasting glucose (r = 0.528; p = 0.052). After adjusting for body mass index or haemoglobin A1c, chemerin correlated in trend with insulin resistance evaluated using the logarithmised homeostasis model assessment of insulin resistance (r = 0.539, p = 0.071; r = 0.553, p = 0.062). Chemerin was positively associated with Acute Physiology and Chronic Health Evaluation II score in patients with sepsis (p = 0.036) and with clinical severity in septic mice (p = 0.031). In an independent study population, we confirmed association of chemerin with glucose levels in multivariate linear regression analysis (ß = 0.556, p = 0.013). In patients with sepsis with SHG, non-survivors had significantly lower chemerin levels than survivors (0.38-fold, p = 0.006), while in patients without SHG, non-survivors had higher chemerin levels, not reaching significance (1.64-fold, p = 0.089). No difference was apparent in patients with pre-existing T2D (p = 0.44). CONCLUSIONS: We show, for the first time to our knowledge, that chemerin is increased in sepsis and that it associates with impaired glucose metabolism and survival in these patients. It could be further evaluated as a biomarker to stratify mortality risk of patients with SHG.

Impact of plasma histones in human sepsis and their contribution to cellular injury and inflammation.

INTRODUCTION: Circulating histones have been identified as mediators of damage in animal models of sepsis and in patients with trauma-associated lung injury. Despite existing controversies on actual histone concentrations, clinical implications and mechanism of action in various disease conditions, histone levels in human sepsis, association with disease progression and mediated effects on endothelial and immune cells remain unreported. This study aimed to determine histone levels and its clinical implication in septic patients and to elucidate histone-mediated effects ex-vivo. METHODS: Histone levels, endogenous activated protein C (APC) levels and clinical data from two independent cohorts of septic patients were obtained. Histone levels were compared with various control groups including healthy individuals, intensive care unit (ICU) patients without sepsis, ICU patients with multiple organ failure and patients with minor or multiple trauma, all without infection. Endothelial and monocytic cells were stimulated with histones. Cellular integrity and sepsis prototypical cytokines were evaluated. The mechanism of action of histones via Toll-like receptor 4 (TLR4) was evaluated using a function blocking antibody. Histone degradation in plasma was studied by immunoblotting. RESULTS: Histone H4 levels were significantly elevated in patients with sepsis (cohort I; n = 15 and cohort II; n = 19) versus ICU controls (n = 12), patients with multiple organ failure (n = 12) or minor trauma (n = 7), associated with need for renal replacement therapy and decrease in platelet count during disease progression, and remarkably were significantly associated with increased mortality rates in septic patients (ICU-, 28 day- and 90 day mortality rates). There was an inverse correlation between plasma histones and endogenous APC levels. Histone stimulation induced the release of sepsis prototypic cytokines and decreased cell integrity indicated by a significant increase of lactate dehydrogenase (LDH) and propidium iodide (PI) staining. Blocking of TLR4 decreased cellular cytotoxicity on endothelial cells. The calculated half-life of histones in spiked plasma was 4.6 minutes. CONCLUSIONS: Histone levels in septic patients are significantly increased and might mediate disease aggravation by cellular injury and inflammation via TLR4 signaling, which potentially results in multiple organ failure and fatal outcome.