Infectious diseases remain a major health problem, and sepsis and other severe infectious diseases are common causes of morbidity and mortality. There is a need for clinical and laboratory tools to identify patients with severe infections early and to distinguish between bacterial and nonbacterial conditions. Heparin‐binding protein (HBP), also known as azurocidin or cationic antimicrobial protein of 37 KDa, is a promising biomarker to distinguish between patients with these conditions. It is biologically plausible that HBP is an early and predictive biomarker because it is prefabricated and rapidly mobilized from migrating neutrophils in response to bacterial infections. HBP induces vascular leakage and oedema formation and has a pro‐inflammatory effect on a variety of white blood cells and epithelial cells. The dysregulation of vascular barrier function and cellular inflammatory responses can then lead to organ dysfunction. Indeed, it has been shown that patients with sepsis express elevated levels of HBP in plasma several hours before they develop hypotension or organ dysfunction. HBP has a major role in the pathophysiology of severe bacterial infections and thus represents a potential diagnostic marker and a target for the treatment of sepsis.

Introduction: Apolipoprotein M (apoM) is present in 5% of high-density lipoprotein (HDL) particles in plasma. It is a carrier of sphingosine-1-phosphate (S1P), which is important for vascular barrier protection. The aim was to determine the plasma concentrations of apoM during sepsis and systemic inflammatory response syndrome (SIRS) and correlate them to levels of apolipoprotein A-I (apoA1), apolipoprotein B (apoB), HDL-, and low-density lipoprotein (LDL)-cholesterol. Methods: Plasma samples from patients with (1), severe sepsis with shock (n = 26); (2), severe sepsis without shock (n = 44); (3), sepsis (n = 100); (4), infections without SIRS (n = 43); and (5) SIRS without infection (n = 20) were analyzed. The concentrations of apoM, apoA1, and apoB were measured with enzyme-linked immunosorbent assays (ELISAs). Total, HDL-, and LDL-cholesterol concentrations were measured with a commercial HDL/LDL cholesterol test. Results: ApoM concentrations correlated negatively to acute-phase markers. Thus, apoM behaved as a negative acute-phase protein. Decreased values were observed in all patient groups (P < 0.0001), with the most drastic decreases observed in the severely sick patients. ApoM levels correlated strongly to those of apoA1, apoB, HDL, and LDL cholesterol. The HDL and LDL cholesterol levels were low in all patient groups, as compared with controls (P < 0.0001), in particular, HDL cholesterol. ApoA1 and apoB concentrations were low only in the more severely affected patients. Conclusions: During sepsis and SIRS, the plasma concentrations of apoM decrease dramatically, the degree of decrease reflecting the severity of the disease. As a carrier for barrier-protective S1P in HDL, the decrease in apoM could contribute to the increased vascular leakage observed in sepsis and SIRS.

The incorporation of machine learning methods into proteomics workflows improves the identification of disease-relevant biomarkers and biological pathways. However, machine learning models, such as deep neural networks, typically suffer from lack of interpretability. Here, we present a deep learning approach to combine biological pathway analysis and biomarker identification to increase the interpretability of proteomics experiments. Our approach integrates a priori knowledge of the relationships between proteins and biological pathways and biological processes into sparse neural networks to create biologically informed neural networks. We employ these networks to differentiate between clinical subphenotypes of septic acute kidney injury and COVID-19, as well as acute respiratory distress syndrome of different aetiologies. To gain biological insight into the complex syndromes, we utilize feature attribution-methods to introspect the networks for the identification of proteins and pathways important for distinguishing between subtypes. The algorithms are implemented in a freely available open source Python-package (https://github.com/InfectionMedicineProteomics/BINN).

Introduction: Rapid detection of, and optimized treatment for, severe sepsis and septic shock is crucial for successful outcome. Heparin-binding protein (HBP), a potent inducer of increased vascular permeability, is a potentially useful biomarker for predicting outcome in patients with severe infections. Our aim was to study the systemic release and dynamics of HBP in the plasma of patients with severe sepsis and septic shock in the ICU. Methods: A prospective study was conducted of two patient cohorts treated in the ICU at Karolinska University Hospital Huddinge in Sweden. A total of 179 patients was included, of whom 151 had sepsis (126 with septic shock and 25 patients with severe sepsis) and 28 a non-septic critical condition. Blood samples were collected at five time points during six days after admission. Results: HBP levels were significantly higher in the sepsis group as compared to the control group. At admission to the ICU, a plasma HBP concentration of ≥15 ng/mL and/or a HBP (ng/mL)/white blood cell count (10⁹/L) ratio of >2 was found in 87.2% and 50.0% of critically ill patients with sepsis and non-septic illness, respectively. A lactate level of >2.5 mmol/L was detected in 64.9% and 56.0% of the same patient groups. Both in the sepsis group (n = 151) and in the whole group (n = 179), plasma HBP concentrations at admission and in the last measured sample within the 144 hour study period were significantly higher among 28-day non-survivors as compared to survivors and in the sepsis group, an elevated HBP-level at baseline was associated with an increased case-fatality rate at 28 days. Conclusions: Plasma HBP levels were significantly higher in patients with severe sepsis or septic shock compared to patients with a non-septic illness in the ICU. HBP was associated with severity of disease and an elevated HBP at admission was associated with an increased risk of death. HBP that rises over time may identify patients with a deteriorating prognosis. Thus, repeated HBP measurement in the ICU may help monitor treatment and predict outcome in patients with severe infections.

Early identification of patients with infection and at risk of developing severe disease with organ dysfunction remains a difficult challenge. We aimed to evaluate and validate the heparin-binding protein, a neutrophil-derived mediator of vascular leakage, as a prognostic biomarker for risk of progression to severe sepsis with circulatory failure in a multicenter setting. A prospective international multicenter cohort study. Seven different emergency departments in Sweden, Canada, and the United States. Adult patients with a suspected infection and at least one of three clinical systemic inflammatory response syndrome criteria (excluding leukocyte count). None. Plasma levels of heparin-binding protein, procalcitonin, C-reactive protein, lactate, and leukocyte count were determined at admission and 12–24 hours after admission in 759 emergency department patients with suspected infection. Patients were defined depending on the presence of infection and organ dysfunction. Plasma samples from 104 emergency department patients with suspected sepsis collected at an independent center were used to validate the results. Of the 674 patients diagnosed with an infection, 487 did not have organ dysfunction at enrollment. Of these 487 patients, 141 (29%) developed organ dysfunction within the 72-hour study period; 78.0% of the latter patients had an elevated plasma heparin-binding protein level (> 30 ng/mL) prior to development of organ dysfunction (median, 10.5 hr). Compared with other biomarkers, heparin-binding protein was the best predictor of progression to organ dysfunction (area under the receiver operating characteristic curve = 0.80). The performance of heparin-binding protein was confirmed in the validation cohort. In patients presenting at the emergency department, heparin-binding protein is an early indicator of infection-related organ dysfunction and a strong predictor of disease progression to severe sepsis within 72 hours.

Elevated plasma levels of heparin-binding protein (HBP) are associated with risk of organ dysfunction and mortality in sepsis, but little is known about causality and mechanisms of action of HBP. The objective of the present study was to test the hypothesis that HBP is a key mediator of the increased endothelial permeability observed in sepsis and to test potential treatments that inhibit HBP-induced increases in permeability. Association between HBP at admission with clinical signs of increased permeability was investigated in 341 patients with septic shock. Mechanisms of action and potential treatment strategies were investigated in cultured human endothelial cells and in mice. Following adjustment for comorbidities and Acute Physiology and Chronic Health Evaluation (APACHE) II, plasma HBP concentrations were weakly associated with fluid overload during the first 4 days of septic shock and the degree of hypoxemia (PaO2/FiO2) as measures of increased systemic and lung permeability, respectively. In mice, intravenous injection of recombinant human HBP induced a lung injury similar to that observed after lipopolysaccharide injection. HBP increased permeability of vascular endothelial cell monolayers in vitro, and enzymatic removal of luminal cell surface glycosaminoglycans (GAGs) using heparinase III and chondroitinase ABC abolished this effect. Similarly, unfractionated heparins and low molecular weight heparins counteracted permeability increased by HBP in vitro. Intracellular, selective inhibition of protein kinase C (PKC) and Rho-kinase pathways reversed HBP-mediated permeability effects. HBP is a potential mediator of sepsis-induced acute lung injury through enhanced endothelial permeability. HBP increases permeability through an interaction with luminal GAGs and activation of the PKC and Rho-kinase pathways. Heparins are potential inhibitors of HBP-induced increases in permeability.