Role of the glycocalyx in pre-eclampsia

Pre-eclampsia is a potentially life threatening disorder affecting 2-7% of
pregnant nulliparous women and is a leading cause of maternal and neonatal
morbidity and mortality in the Netherlands. Hallmarks of pre-eclampsia are a
systemic increase in vascular permeability and vasomotor tone, proteinuria and
a prothrombotic state. Maternal death is in most cases attributable to
cerebrovascular complications, believed to result from impaired cerebral
autoregulation and increased permeability of the blood-brain barrier. Even
after delivery, patients with a history of pre-eclampsia remain at increased
risk for future cardiovascular complications and have a disturbed flow mediated
vasodilatation.
The glycocalyx is a layer of complex sugars lining the endothelium and
a critical determinant of vascular homeostasis in humans. The glycocalyx
regulates vascular permeability for macromolecules particularly in the
glomerulus and is involved in vessel tone regulation by mediating
shear-dependent NO release.In addition, the glycocalyx has potent
anti-thrombotic effects. Because of recent experiments and previous
observations we believe that damage to the endothelial glycocalyx may play a
pivotal role in pre-eclampsia.
First, artificial degradation of the glycocalyx in mice by
hyaluronidase infusion, leads to a profound increase in proteinuria and
systemic vascular leakage thereby resembling the findings of pre-eclampsia.
Second, mRNA expression of various (placental) glycoproteins is up to 32 fold
up-regulated in placental tissue from pre-eclamptic women compared to placental
tissue from women with healthy pregnancy supporting a role for the glycocalyx
in pre-eclampsia. Third, the glycocalyx is intimately involved in VEGF and
TGF-beta signaling by mediating their binding to the endothelial cell surface
receptor, FLT-1 and endoglin respectively. The soluble circulating form of
these cell-surface receptors are associated with an increased risk of
pre-eclampsia. Perturbation of the glycocalyx may very well result in the
release of these receptors from the endothelial cell surface and thereby
provide an alternative explanation for the association between these soluble
antiangiogenic factors and the risk of pre-eclampsia.
Based on these observations we hypothesize that perturbation of the
endothelial glycocalyx is important in the pathogenesis of pre-eclampsia and is
associated with increased vascular permeability, vasomotor tone and
coagulation.

The principal aim of this study is to elucidate the role of the glycocalyx in
the pathogenesis of pre-eclampsia by assessing:
- Whether the glycocalyx is affected in pre-eclampsia and is related to its
severity.
- Whether glycocalyx perturbation is associated with increased permeability,
vasomotor tone and coagulation in pre-eclampsia.
- Whether glycocalyx perturbation is associated with disturbances in cerebral
autoregulation
- Whether glycocalyx perturbation is associatied with soluble FLT-1 and
Endoglin, the circulating membrane receptors of VEGF and TGF-beta

A case-control design is chosen to compare patients with pre-eclampsia and
healthy pregnant controls matched for maternal and gestational age. Patients
with pre-eclampsia and healthy pregnant controls will be approached to
participate in the study. They will be informed about the rationale of this
study, possible risks and study burden. Eligible candidates who are willing to
participate will be asked to provide informed consent. The study consists of
three visits: one screening visit, one visit for non-invasive measurements
within 24 hrs after the screening visit and one visit 12 weeks after delivery.
During the screening visit a brief history and physical examination will be
performed. At the second and at the third visit a 24 hour urine sample will be
collected and the following non-invasive measurements will be performed: 1.
conventional sphygmomanometry will be used to measure BP, 2. glycocalyx
dimensions will be visualized using SDF imaging, 3. noninvasive finger arterial
pressure waveform registration by Nexfin (BMeye, Amsterdam, The Netherlands)
will be used for continuous monitoring of heart rate, blood pressure, cardiac
stroke volume, cardiac output, and peripheral vascular resistance, 4.
transcranial Doppler (TCD) measurement will be performed to assess cerebral
blood flow velocity of the medial cerebral artery. Finally, a blood sample will
be drawn for standard laboratory assessments, measurement of coagulation,
glycocalyx constituents and enzymes, and anti-angiogenic agents. A third visit
will be planned 12 weeks after delivery of the baby. During this final visit
the same procedures will be undertaken as in the second visit. In addition to
these measurements flow mediated vasodilatation will be non-invasively assessed
by foreman plethysmography.

Participants will be asked to spend approximately 2 hours spread over 3 visits
to the measurements. At 2 visits a blood sample will be drawn via a venous
puncture totalling 100 ml (50 ml at each visit). These wil be combined if
possible with routine blood sample collection. There are no risks besides a
mild sore spot or hematoma at the site of the venipuncture. All other
measurements are non-invasive and are not harmful to mother and child.