Role of different phosphate binders on absorption of vitamin K, metabolism of matrix *-carboxy-glutamaat (Gla) proteïne (MGP).

Vascular calcification are a common problem within dialysis population and are
associated with higher mortality risk. Fifty percent of dialysis patients
eventually pass away due to vascular calcification. A lot of dialysis patients
use vitamin K antagonist which promote vascular calcification. In this project
we try to comprehend which factors play a role in this process.
New bio marker involved in vascular calcification is matrix *-
carboxy-glutamatee(Gla) protein (MGP) will be measured when different phosphate
binders are used and PIVKA-II will be measured to see if there is a vitamin K
deficiency.
Hypothesis is that different phosphate binders bind vitamin K in a different
way in the intestinal tract. MGP is a vitamin K dependant factor and therefore
expectataion is that MGP expression will be variable with different phosphate
binders.
MGP will be measured as unphosphorylated, uncarboxylated MGP (dp-ucMGP) which
is a free fraction and higher in dialysis patients with vascular calcification.

This research will have as aim to look at progression or decrease of vascular
calcification in dialysis population with use of different phosphate binders.
There is a possibility that differect phosphate binders bind vitamin K in a
different way in intestinal tract and thereby cause different level of
calcification.
Level of calcification will be measured by dp-ucMGP which is used as markers
for vascular calcification. Because of the fact that ucMGP en dp-ucMGP are
vitamin K dependant PIVKA-II will be measured as well.
Better insight in mechanisms of vascular calcification under different
circumstance can lead to therapeutic options which inhibit calcification and
benefit survival of dialysis patients.

Prospective open cohort study in which used phosphate binders (usually a
combination of a few binders) will be replaced by calciumcarbonate or
lanthanumcarbonate (Fosrenol®) monotherapy for eight weeks only in patients
which don't use vitamin K antagonists.
Choice for calciumcarbonate 3 dd 1000 mg or lanthanumcarbonate 3 dd 1000 mg as
initial therapy will be randomized. After eight weeks the first phosphate
binder will be replaced by the other one for once again a period of eight weeks.
After the initial 16 weeks a period of 4 weeks will follow with suppletion of
menaquinon (vitamin K2).

Randomization between calciumcarbonate and lanthanumcarbonate with collection
of blood samples. Blood will be drawn from hemodialysis shunt or catheter. And
after 16 weeks a period of four weeks supplementation of menaquinone once daily
360 micrograms with continuation of the last phosphate binder.

There is no risk in participation in this research blood sampels will be drawn
frequently and medication will be adjusted.