Degradation of endothelial glycocalyx provides new insights in the pathogenesis of septic shock microvascular failure

Introduction

Glycocalyx (GLX) is implicated in mechanotransduction of shear stress and microvascular blood flow. We tested whether GLX loss accounts for the microvascular dysfunction in sepsis and whether activated protein C (APC) preserves endothelial GLX integrity.

Methods

Endotoxin LPS (10 mg/kg) was infused in rats treated or not with APC (240 μg/kg/hour). Changes in GLX were assessed by circulating levels of hyaluronan (a GLX constituent) and by GLX apparent thickness evaluated using intravital microscopy by comparing 4 and 150 kDa dextran distribution as markers of GLX permeable and impermeable tracers, respectively. Intravital microscopy was used to characterize mesentery functional capillary density. Because glycocalyx is extremely sensitive to free radical, oxidative stress was evaluated by oxidation of dihydrorhodamine (DHR) in microvascular beds and by concentrations of heart malondialdehyde (MDA) and plasma carbonyl proteins (CP).

Results

LPS elicited a 4 hours later profound reduction in GLX layer thickness and increase in plasma hyaluronan levels. LPS rats had decreases in capillary continuous flow, and significant increases in intermittent and stopped flow capillaries compared with controls. The pressor responses to norepinephrine were greatly reduced, indicative of vascular hyporeactivity. In vivo oxidation of DHR and levels of heart MDA and plasma CP were all increased in LPS-treated rats. Interestingly, in LPS rats, APC reduced plasma hyaluronan levels and GLX destruction, which was accompanied with major improvements in vasopressor response and functional capillary density. APC treatment also prevented increases in biochemical and in vivo microvascular oxidative stress markers.

Conclusion

In our model of septic shock, increased plasma hyluronan levels and reduction in endothelial layer thickness indicated GLX degradation. APC prevented vascular oxidative stress and limited GLX loss. GLX degradation plays a critical role in the septic vasculature and generation of free radicals during septic shock is potentially toxic to GLX function.