The peritoneal microvascular endothelial glycocalyx in peritoneal dialysis patients

Patients treated with chronic peritoneal dialysis (PD) develop alterations in
peritoneal transport rates and ultrafiltration failure. Morphologically these
are associated with vascular alterations that are partly diabetiform and partly
atherosclerotic. The glycocalyx is a negatively charged mesh of membranous
glycoproteins, proteoglycans and glycosaminoglycans situated at the luminal
side of all blood vessels. It exerts a wide range of vasculoprotective effects
like inhibition of coagulation, inhibition of leucocyte and platelet adhesion,
regulation of redox state, shear-induced release of NO, regulation of
endothelial permeability, being an important factor in vascular homeostasis.
The glycocalyx is very sensitive to inflammatory mediators and hyperglycaemia,
which alter the transendothelial permeability, probably leading to changes in
the underlying cell-interstitial matrix, which in turn affects peritoneal
transport. No information is available on the peritoneal microcirculatory
glycocalyx and its evolution in time during PD. Since this entity appears to
influence transendothelial solute and water transport in many tissues
throughout the body, it will be important to include the glycocalyx in studies
of the peritoneal barrier and its pathophysiology.

The aim of the study is to investigate the changes in peritoneal endothelial
glycocalyx in end-stage renal disease (ESRD), with the duration of peritoneal
dialysis, and relate these changes to alterations in peritoneal transport and
morphology. Defining the role of the glycocalyx in this condition will guide
further strategies on its preservation. The changes in the sublingual
endothelial glycocalyx with time on renal replacement therapy (PD and
transplantation) will also be investigated.

We will perform a cross-sectional observational study with invasive
measurements.
Measurements of the peritoneal microvascular glycocalyx thickness will be done
in:
- patients with ESRD starting PD or undergoing preemptive kidney
transplantation,
- stable, prevalent PD patients free of acute inflammatory conditions and
malignancy, undergoing any procedure involving the opening of the peritoneal
cavity (kidney transplantation, incidental abdominal condition, PD related
problems (excluding recent peritonitis), e.g. catheter replacement, catheter
removal because of membrane failure),
- sex and age matched controls with normal renal function.
In incident peritoneal dialysis patients, OPS imaging of the peritoneal
microvasculature will be done during the implantation of the peritoneal
catheter by laparotomy. This will be repeated at the time of transplantation.
In addition, in prevalent peritoneal dialysis patients measurements of the
peritoneal microvascular glycocalyx will be performed at the time of
transplantation. Peritoneal transport function is assessed on a yearly basis
using the Standard Peritoneal permeability Analysis (SPA) as part of regular
follow-up of patients. Peritoneal biopsies will be performed in all
participants except the PD patients undergoing a cadaveric kidney
transplantation, at the time of surgery.
Relationships between peritoneal microvascular glycocalyx and parameters of
peritoneal transport and morphology will be investigated.
For reference data on peritoneal glycocalyx, we will do measurements in
otherwise healthy individuals, kidney donors undergoing nephrectomy.
All participants will undergo OPS imaging of sublingual microvasculature before
surgery. In patients, this will be repeated at 3 and 12 months.
Furthermore, measurements of glycocalyx constituents (hyaluronan,
heparansulphate) and their regulating enzymes (hyaluronidase, heparanase), will
be done in plasma and dialysate (when applicable).

The study consists of the following measurements which will all take place
during the admission in the hospital: measurements of the sublingual
endothelial glycocalyx, measurements of the peritoneal endothelial glycocalyx,
body weight, blood pressure and blood sampling. The inform consent will be
signed during a previous visit at the outpatient clinic.
Measurements of the sublingual endothelial glycocalyx will be repeated in
patients during future visits at the outpatient (at 3months and 1year).
In all participants, in addition to the regular blood samples which are taken
during their hospital admission or outpatient clinic visit, 20.5 ml of extra
blood will be drawn once via vena puncture, and stored for analysis.
All PD patients will undergo a Standard Peritoneal permeability Analysis test
(SPA). This test is performed in the AMC on a yearly basis as part of the
regular follow-up of PD patients. It allows measurements of small solute
transport, transport of proteins, and fluid kinetics. The methodology is well
established. In patients who receive a kidney transplant and do not have a SPA
performed in the last 3 months before the intervention, a SPA will be performed
one week before surgery. PD patients coming from other hospitals for
transplantation will also be invited to undergo a SPA one week before surgery.
Since its introduction in the mid nineties more than 800 SPAs have been
performed without problems, especially no anaphylactic reactions have occurred.
Peritoneal biopsy will be performed during surgery. There is a small risk of
bleeding after biopsy but local hemostasis is applied. There is also a risk of
leakage. As the chances of primary graft function in living-related transplant
recipients are very high (more than 90%), and PD is discontinued immediately,
the risk of leakage is acceptable. Above all, in most of these cases the
peritoneal catheter is removed during transplantation. In the case of
post-mortal transplantation, a peritoneal biopsy will not be performed due to
the risk of delayed graft function, necessitating the continuation of PD
postoperatively.