Endothelial glycocalyx

1. Dr Vinoth Natarajan MD DNB
Sri Narayani Hospital & Research centre, Vellore

2.  Definition – what is it?
 Composition
 Physiologic Functions
 Scenarios of degradation of EG
 Strategies to prevent EG degradation
 Conclusion

3.  Gel like layer rich in carbohydates lining the luminal surface of healthy vascular
endothelium
 Danielli in 1940 – existence of this layer
 After 40 years – Copley studied its structure and function with help of Electron
microscope.
 Dimensions vary 0.2 µm to 2 µm – according to the type of vasculature

4.  Consists of various types of glycosaminoglycans covalently attached to plasma
membrane (of endothelial cell) bound core proteoglycans.
PROTEOGLYCANS – proteins that are heavily glycosylated
GLYCOSAMINOGLYCAN – Unbranched polysaccharides consisting of repeated
disaccharide unit (amino sugar with uronic acid)

6.  Glycosaminoglycans – Heparan sulfate (70-90%), the reminder is the mixture of
chondroitin, Dermatan, Keratan sulfates and hyaluronic acid. (Negatively
charged)
 Proteoglycans – Syndecans (Single membrane spanning domain) and Glypicans
(GPI anchored) provide the membrane tethered scaffold for these GAGs
 In addition EG also consists – many biologically active molecule like Superoxide
dismutase, Lipoprotin lipase, various cytokines and regulators of coagulation.

8.  In a healthy vasculature
 EG forms the main skeleton and Plasma constituents of blood (mainly albumin) are in
dynamic equilibrium with their circulating portion in blood.
Endothelial Glycocalyx
Plasma constituents
of blood
Endothelial surface
layer (ESL)

9.  EG is also not a static structure and it is also in equilibrium with continuous shear
induced degradation and synthesis.
 This constant state is quite vulnerable to various stressors like
1) Ischemia reperfusion injury,
2) Oxidative stress,
3) Hypervolemia,
4) Endotoxins,
5) Diabetic angiopathy and
6) other pro-inflammatory stimuli

11.  Vascular permeability
 Mechanotransduction
 Role in blood cell and endotheial cell interaction (Coagulation
cascade/Inflammation)

13.  The net fluid flux across the inter-endothelial junction determined by hydrostatic pressure
and oncotic pressure gradients.
 High hydrostatic pressure in vascular lumen drives the fluid to interstial space, whereas the
lower oncontic pressure in interstial space compared to plasma results in opposing force for
hydrostatic pressure.

14.  Classic principle – hydrostatic pressure decrease from arteriolar side to venule: fluid is
filtered to interstitum from arterioloar side and resorbed back in the venules. But, Later
studies – the return of fluid to venous side is by lymphatic drainage.
 Levick quantitative studies 1991 – the net fluid filtration is far excess that of the
observed lymphatic flow. Moreover, when interstitial oncotic pressure was raised,
increase in net fluid filtration is much smaller than the expected values.
 Led to the conclusion that the interstial oncotic pressure play only a minor role in
vascular permeability.
Levick JR. Capillary filtration-absorption balance reconsidered
in light of dynamic extravascular factors. Experimental Physiology
1991; 76: 825–57.

15.  Levick also suggested that the effective oncotic pressure gradient opposing the
hydrostatic forces is mainly due to the oncotic pressure exerted by protein content of
endothelial glycocalyx and revised the law as

16.  Enzymatic removal of EG components results in increased hydraulic conductivity,
protein flux, albumin excretion, and edema.
 When the negative charge of the EG was removed, increased permeability to
albumin or dextrans were observed. This evidence indicates that EG is a major
determinant of vascular permeability.
van Haaren PM, VanBavel E, Vink H, Spaan JA. Charge modification of the endothelial
surface layer modulates the permeability barrier of
isolated rat mesenteric small arteries. Am J Physiol Heart Circ Physiol 2005; 289: H2503-7
Adamson RH. Permeability of frog mesenteric capillaries after partial pronase digestion of the
endothelial glycocalyx. J Physiol 1990; 428:
1-13.
Huxley VH, Williams DA. Role of a glycocalyx on coronary arteriole permeability to proteins:
evidence from enzyme treatments. Am J
Physiol Heart Circ Physiol 2000; 278: H1177-85.

17.  EG functions as a sensor of mechanical shear stress force exerted on the endothelial surface in
concert with other sensors like G protein coupled receptors, stretch sensitive ion channels,
rheological properties of plasma membrane, caveolar structures, integrins and focal adhesion
molecules.
mechanosensors
Intracellular
signalling
Increase in cytosolic
calcium
Activation of eNOS
Release of NO which has a crucial role in vascular tone regulation, permeability and inflammation

18.  The intact EG shields the vascular endothelium from interactions with leukocytes
and platelets whereas shedding of EG facilititates it.
 Play a mojor role in rolling and margining of leukocytes in acute inflammation
and platelet adhesion.

19. TNF alpha
EG Degradation
Neutrophills
and mast
cells
Variety of
enzymes and
reactive oxygen
species
Matrix
metalloproteinases
- syndecans
Vascular
endothelium
Exocytosis of
weibel palade
bodies

20.  Acute degradation –
a) major surgery (cardiac),
b) major trauma and
c) sepsis.
 Scenarios of intraoperative damage
a) Ischemia/reperfusion,
b) major haemorrhage/bleeding,
c) Use of CPB pump
c) Hypervolemia,
d) Hyperglycaemia and
e) Oxidative stress

21. CPB
Atherosclerosis
and diabetes
Sepsis/
Endotoxins
Inflammation at
vascular endothelial
sites
Major
hemorrhage
Integrity of
endothelium itself
lost
Hypervolemia
On pump
CABG
Ischemia/Reperfusion
lifting and displacement
of heart to expose
coronaries
stretch of
atrium
release of ANP.
ANP causes the rapid shedding of EG via cGMP linked proteolytic pathway.
EG LOSS

22.  Avoiding hypervolemia
 Plasma albumin
 Hydrocortisone
 Other pharmacological methods

23.  Detrimental effect due to ANP
 Preloading – not recommended as considering the role of EG in vascular permeability.
Moreover, it does not prove to be effective in many clinical trials.
 Liberal perioperative fluid administration leading to a positive fluid balance has been
associated with increased morbidity.
 Perioperative degradation of the EG may provide one rationale for restrictive fluid
administration by a goal-directed protocol; however, the clinical impact of liberal
versus restrictive fluids needs more extensive discussion

24.  Protection against oxidative damage, excessive attachment of blood cells and shear
mediated vasodilataion
 Provide the constituents for intercalation with GAGs increasing the stability of
Endothelial surface layer.
 In animal models of heart transplantations, HTK containing albumin reduce EG
degradation.
 Experimental model of massive haemorrhage, Albumin >> colloid – EG degradation
 Paucity of direct clinical evidence

25.  Protective effects against I/R injury and inflammation in general.
 Prevention of migration of leukocytes by blocking the synthesis of various
cytokines and chemokines.
 Mat cell stabilization
 Animal models – preconditioning with hydrocortisone reduce EG degradation
following I/R injury and inflammation
 Septic shock – role controversial.

26.  MMP inhibitor – doxycycline
 TNF alpha analogue – etanercept
 Volatile anaesthetic agents
 Liposomal nanocarriers of preassembled glyocalyx
 Sulodexide – 8:2 mixture of fast moving heparin and dermatan sulfate found to restore
the degraded EG in severe sepsis - phase 2 trial successful
 Clinically, Broekhuizen et al demonstrated that oral sulodexide administration for two
months partially restored the thickness of the EG in patients with type 2 diabetes
using sidestream dark field imaging of sublingual microcirculation. But potential side
effect – bleeding should be considered before applying in perioperative settings.
 chemically modified, non-anticoagulant variants of heparin could be fascinating
candidates for the protection of EG – phase 2 trials going on.

27.  Currently, no pharmacological tools for the restoration of EG are clinically
available. However, attempts to minimize EG degradation, including avoidance of
hypervolemia, and reducing the stress response and systemic inflammation,
should be adopted by anesthesiologists.
 For now, it is difficult to make any hard recommendations but we may respect the
presence of ENDOTHELIAL GLYCOCALYX, promote the things to prevent its
degradation in perioperative settings.