Glycocalyx Perturbation in Patients with Sickle Cell Disease: Association with Disease Morbidity.
Authors: Beers van Eduard J. , Landburg Pearl , Nieuwdorp Max , Duits Ashley L. , Vink Hans , Evers Ludo M. , Biemond Bart J. 
Published: April 2020

Abstract
Activated endothelium plays a pivotal role in the pathogenesis of sickle cell disease (SCD). The activation of the endothelium is caused by hypoxia reperfusion damage, high shear rates and pro-inflammatory mediators, like thrombin and TNF-alpha. The central role of the glycocalyx (a layer of hyaluronan and proteoglycans covering the endothelium) has been established as an antithrombotic and antiadhesive endothelial barrier. Recently, a technique to determine the total systemic volume of the endothelial glycocalyx in humans has been validated. Using this technique, we demonstrated that the glycocalyx volume is strongly diminished in diabetic patients and even more in diabetic patients with microangiopathy. In the present study, we measured the glycocalyx volume in 20 sickle cell patients (14 HbSS/Sβ0 and 6 HbSC) and 10 carriers of sickle cell disease. To assess whether the glycocalyx perturbation may also contribute to disease morbidity in SCD, disease morbidity score (DMS) was calculated according to predefined criteria. In addition, we determined plasma levels of the matrix metalloproteases (MMP-2 and MMP-9) and the tissue inhibitors of MMP (TIMP-1 and TIMP-2) and compared these levels with the glycocalyx volume. The total systemic glycocalyx volume was measured by subtracting the intravascular distribution volume of a glycocalyx impermeable tracer (autologous labelled erythrocytes) from that of a glycocalyx permeable tracer (dextran 40). DMS was calculated by adding up individual prevalence (present or absent) of organ damage (microalbuminuria, pulmonary hypertension, retinopathy, perceptive hearing loss, iron overload, avascular osteonecrosis, renal failure and leg ulcers) and history of sickle cell related complications (acute chest syndrome, stroke, &gt; 2 vaso-occlusive crises/year, and cholelithiasis ). Patients with SCD (HbSS/Sβ0 and HbSC) demonstrated to have a significant reduced glycocalyx volume compared to sex and age-matched sickle cell traits 0.48 ± 0.14 and 0.5 ± 0.36 versus 1.26 ± 0.27 liters (mean ± SEM), p=0.025. Interestingly, the glycocalyx volume was associated with DMS. Patients with high (severe)DMS had a significant lower glycocalyx volume than patients with a low(mild) DMS (0.81 ± 0.26 versus 0.18 ± 0.26 liters, p=0.047). No associations between glycocalyx volume and serum levels of MMP-2, MMP-9, TIMP-1 or TIMP-2 were found. The strongly diminished glycocalyx volume in sickle cell patients resembles the chronic state of activation of the endothelium in SCD that may also may be responsible for the enhanced adhesion of leukocytes and erythrocytes as well as the prothrombotic state of these patients Since the glycocalyx layer serves as an important barrier between the endothelium and the circulating blood cells to prevent the adhesion of leukocytes, therapies that may restore or preserve glycocalyx function are warranted in SCD.
Figure. Disease severity and glycocalyxvolum Figure. Disease severity and glycocalyxvolum