Elevated capillary tube hematocrit reflects degradation of endothelial cell glycocalyx by oxidized LDL

Abstract

Proteoglycans and plasma proteins bound to the endothelial cell glycocalyx are essential for vascular function, but at the same time, they lower capillary tube hematocrit by reducing capillary volume available to flowing blood. Because oxidized low-density lipoproteins (oxLDL) reduce the effective thickness of the glycocalyx (Vink H, Constantinescu AA, and Spaan JAE. Circulation 101: 1500-1502, 2000), we designed the present study to determine whether this is caused by pathological degradation of glycocalyx constituents or increased glycocalyx deformation by elevated shear forces of flowing blood. Capillaries from the right cremaster muscle of 24 hamsters were examined by using intravital microscopy after systemic administration of normal LDL (n = 4), moderate oxLDL (6-h oxidation with CuSO(4), n = 7), severe oxLDL (18-h oxidation, n = 5), and moderate oxLDL plus superoxide dismutase (SOD) and catalase (n = 8). Capillary tube hematocrit increased from 0.16 +/- 0.03 to 0.37 +/- 0.05 and from 0.15 +/- 0.01 to 0.31 +/- 0.03 after moderate oxLDL and severe oxLDL, respectively. These changes were paralleled by increases in red blood cell flux from 8.7 +/- 1.9 to 13.8 +/- 3 and from 10.7 +/- 2.1 to 16.3 +/- 3.2 cells/s after moderate oxLDL and severe oxLDL, respectively, in the absence of changes in anatomic capillary diameter. Red blood cell velocity, as a measure for the shear forces on the glycocalyx, was not affected by oxLDL, whereas tissue pretreatment with SOD and catalase completely abolished the effects of oxLDL on glycocalyx thickness, capillary hematocrit, and red blood cell flux. We conclude that elevation of capillary tube hematocrit by oxLDL reflects degradation of the endothelial glycocalyx by oxygen-derived free radicals.

Damage of the Endothelial Glycocalyx in Dialysis Patients

“…The presence of glycocalyx prevents RBCs from approximating the endothelium very closely. 5,21,22 Previous studies, in which microvascular glycocalyx was assessed in humans by SDF imaging of the sublingual microvasculature, 20 together with previous experimental studies 11,23 have led to the concept that perturbation of the glycocalyx is associated with an impairment of its RBCs-excluding properties, affecting the temporal and spatial variations of the microvascular RBC column width. Similarly, recent experimental studies showed that enzymatic degradation of glycocalyx is followed by increases in PBR.…”

“…5 It is involved in mediating shear-induced release of nitric oxide and contributes to the endothelial permeability barrier, the regulation of redox state, and the inhibition of coagulation as well as leukocyte and platelet adhesion. [6][7][8][9] Perturbation of glycocalyx occurs after provocation with inflammatory or atherogenic stimuli (such as ischemia reperfusion, 10 infusion of oxidized LDL, 9,11 administration of TNFa 12 or endotoxin, 13 and during hyperglycemia 14 ) and after stimulation with thrombin, 15 atrial natriuretic peptide, 16 or abnormal blood shear stress. 17,18 Consequences of glycocalyx perturbation include a wide range of vascular abnormalities in experimental models, including increased vascular permeability followed by generation of tissue edema, 19 increased rolling and adhesion of leukocytes, 6 and increased platelet adhesion.…”

Commentary: On the Pathophysiology of Coronary Heart Disease

“…There is thinning of the glycocalyx in diabetes [2] and heterozygous familial hypercholesterolemia [9], both diseases characterised by proneness to coronary disease. Constantinescu et al [10] demonstrated thinning of the glycocalyx by oxidised LDL.…”

Microcirculatory dysfunction and tissue oxygenation in critical illness

“…The release of inflammatory mediators induces morphological changes of the endothelium and its protective glycocalyx 30, 31. Endothelial exposure to oxidative stress, oxidized lipoproteins,32, 33, 34 and hyperglycemia35 cause further glycocalyx injury which in turn give rise to profound changes in capillary flows and hematocrit 33, 36. The glycocalyx constitutes a fluid barrier, and degradation of the glycocalyx is hence associated with edema and capillary compression 37, 38…”