Chronic renal failure is associated with a strong increase in cardiovascular risk, which is responsible for approximately 50 % of the mortality in the hemodialysis population.
Vascular disease in uremic patients is characterized by calcification of the vessel wall.
Recently, Goodman et al. [1] used electron beam tomography to demonstrate the presence of vascular calcifications and their rapidly progressive character in young dialysis patients.
In addition to increased calcification of atherosclerotic plaques, patients on dialysis also show characteristic calcifications of the vascular media, which were shown to contribute significantly to the excess cardiovascular mortality in this population [2].
Both in vivo and in vitro evidence indicates that ectopic calcification is a tightly regulated process that results from an imbalance between inhibitors (such as fetuin and matrix Gla protein) and inducers of mineralisation, such as cbfa-1 and osteocalcin.
In vitro studies stress the role of elevated phosphate levels in the development of vascular calcification [3].
In order to study factors that can modulate uremia-related vascular calcification in vivo, a suitable animal model is necessary. A recent study by Katsumata et al. [4] indicates that rats fed a diet supplemented with 0.75% adenine for 4 weeks develop severe calcifications of the aortic media over the next 5 weeks. High adenine feeding causes the production of 2,8-dihydroxyadenine, which forms crystals in the renal tubules, with subsequent tubular injury and inflammation, obstruction, fibrosis and renal function impairment.
In the present study, two different high phosphate diets were used to induce vascular calcification in rats made uremic with a diet containing 0.75% adenine.
The aim of the present study was to evaluate whether in vivo micro-CT scanning can be used to detect vascular calcification in rats with chronic renal failure.

Micro-CT, macroscopic and microscopic aspect of the thoracic aorta of the same animal



The used micro-CT scanning protocol allowed clear detection of the calcified aortic wall (see insert).
The thickening of the aortic wall at the ventral side correlated well with the presence of macroscopic calcification shown in panel B.



Thick calcified rings - that could be observed macroscopically - were found along the aortas of animals with massive calcification.



Von Kossa stained microscopic sections of the same animal.
Calcified tissue is stained black with Von Kossa's method.
The left panel shows that calcification is circumferential, whereas the right panel shows that a calcified band is present in the tunica media of the vessel, surrounded by 'cartilage-like' cells (arrow), which are in turn flanked at both sides by apparently normal vascular smooth muscle cells.

V. Persy¹, A. Postnov², E. Neven¹, G. Dams¹, M. De Broe,¹, P. D'Haese¹ and N. De Clerck²
Departments of Nephrology¹ and Microtomography², University of Antwerp, Belgium

References
[1] Goodman et al. Coronary-artery calcification in young adults with end-stage renal disease who are undergoing dialysis. New Engl J Med 342:1478-83, 2001.
[2] London et al. Arterial media calcification in end-stage renal disease: impact on all-cause and cardiovascular mortality. Nephrol Dial Transpl 18: 1731- 40, 2003.
[3] Jono et al. Phosphate regulation of vascular smooth muscle cell calcification. Circ Res 87: E10-E17, 2000.
[4] Katsumata et al. Sevelamer hydrochloride prevents ectopic calcification and renal osteodystrophy in chronic renal failure rats. Kidney Int 64: 441-50, 2003.