Heparin-binding protein and endothelin-1 in acute inflammation and trauma

Inflammation in sepsis and trauma is a clinical challenge and despite advances in supportive care, morbidity and mortality are high. The mechanisms behind this inflammation are extremely complicated, involving numerous molecular pathways. One of the crucial consequences of sepsis is macro-and microcirculatory failure which sometimes leads to dysfunction in multiple organs, partly dependent on a progressive capillary leak resulting in oedema and fluid overload. Heparin-binding protein (HBP) originating from polymorphonuclear leukocytes is an inflammatory protein, a mediator of vascular permeability and is associated with sepsis and organ dysfunction. Endothelin-1 (ET-1) is a potent endothelium-derived vasoconstrictor with pro-inflammatory properties. Elevated levels of ET-1 are found in patients with sepsis and other inflammatory conditions. This thesis focuses on HBP and ET-1 in acute inflammation and trauma with the overall aim to gain further knowledge on their role in acute inflammation and study them as possible biomarkers in clinical circumstances.

Study I investigated the association between HBP and ET-1 during porcine endotoxemia and the effects of a dual ETA and ETB receptor antagonist (tezocentan) were studied. The animals developed pulmonary dysfunction and evidence of increased pulmonary oedema, measured with single thermal indicator dilution (STID) and by gravimetrical assessment. We found that plasma levels of HBP and ET-1 gradually increased during endotoxemia. When the dual ET receptor antagonist tezosentan was administered, it prevented a further increase in HBP and pulmonary oedema. Moreover, we investigated the effects of graded challenge with the ETA and ETB agonist ET-1 and the selective ETB agonist sarafotoxin 6c in animals not receiving endotoxin. Plasma HBP levels increased dose-dependently with both ET-1 and sarafotoxin 6c infusions and to similar levels as seen in endotoxin challenge. These findings show beneficial effects of ET receptor antagonism in experimental sepsis and a possible link between ET-1 and HBP.

In study II we measured HBP in trauma patients admitted to the intensive care unit (ICU) with the aim to evaluate HBP as a predictor of post-injury sepsis. We measured HBP on ICU-day one, three and five. The cohort consisted of severely injured patients, and we found that the HBP levels were higher in those with higher injury scores, shock at admission to the trauma centre, and in patients needing massive blood transfusion. Similarly, patients who developed multiple organ failure during the first week had higher HBP at ICU admission. Heparin-binding protein was weakly associated with the development of sepsis and only at a later stage of the observation period of one week.

We assessed and compared the predictive performance of HBP, C-reactive protein (CRP) and white blood cell count (WBC) for sepsis development in the following two days after blood sampling. None of the biomarkers regardless of the sample day could predict development of sepsis in the subsequent two days. The results indicate that HBP is weakly associated with post-injury sepsis and shows poor discriminatory properties as an early biomarker of post-injury sepsis. Trauma-induced inflammation may blunt the sepsis predictive performance of HBP.

In study III we wanted to investigate if heparins in clinical use affect plasma levels of HBP. In this pilot study we measured HBP repeatedly in three different patient groups receiving unfractionated heparins intravenously or low molecular weight heparin (LMWH) subcutaneously. We found a dose-dependent, rapid (minutes) and substantial (six- to nine-fold) increase in HBP after heparin administration during vascular and cardiac surgery. When patients received LMWH, the levels of HBP increased but to a lower degree and reached their maximum value in three hours.

We also compared a recent point-of-care device (Joinstar FIC-Q100) to the standard commercial Axis-Shield ELISA and found a strong correlation between the two methods. However, the plasma HBP levels measured with the standard ELISA method were consistently lower compared to the point-of-care device.

In study IV we measured plasma HBP and ET-1 levels at ICU admission in patients with critical COVID-19 disease. We investigated their association with mortality or invasive mechanical ventilation (IMV). The cohort was characterised by severe respiratory failure where 64 % of the patients were subject to IMV during their ICU stay. Plasma HBP was markedly increased in the COVID-19 cohort, but we did not find any association with 60-day mortality or need of IMV. Endothelin-1 levels were modestly elevated, and the levels were significantly higher in patients needing IMV compared to those who did not but when adjusted for age, sex and body mass index, there was no association with either need of IMV or 60-day mortality. In addition, we did not find a correlation between HBP and ET-1 values. In our group of critical COVID-19 patients treated in the ICU, HBP and ET-1 do not seem to be associated with the need of IMV or 60-day mortality.

List of scientific papers

I. Heparin-binding protein (HBP/CAP37) - a link to endothelin-1 in endotoxemia-induced pulmonary oedema? B. P. Persson, H. Halldorsdottir, L. Lindbom, P. Rossi, H. Herwald, E. Weitzberg, A. Oldner Acta Anaesthesiologica Scand, 2014; 58: 549-559. https://doi.org/10.1111/aas.12301

II. Heparin-binding protein as a biomarker of post-injury sepsis in trauma patients. H. D. Halldorsdottir, J. Eriksson, B. P. Persson, H. Herwald, L. Lindbom, E. Weitzberg, A. Oldner Acta Anaesthesiologica Scand, 2018; 62: 962-973. https://doi.org/10.1111/aas.13107

III. The effect of heparins on plasma concentration of heparin- binding protein: a pilot study. H. Halldorsdottir, L. Lindbom, A. Ebberyd, A. Oldner, E. Weitzberg BJA Open. 2024, 27; 9: 100256. https://doi.org/10.1016/j.bjao.2023.100256

IV. Heparin-binding protein and Endothelin-1 in critical COVID-19. H. Halldorsdottir, J. Eriksson, O. Rooyackers, J. Grip, J. Mårtensson, E. Weitzberg *, A. Oldner *. [Manuscript] *Equal contribution