High-Resolution X-Ray Microtomography Is a Sensitive Method to Detect Vascular Calcification in Living Rats With Chronic Renal Failure

Abstract

Objective-Chronic renal failure (CRF) is associated with a 10-to 20-fold increase in cardiovascular risk. Vascular calcification is a prominent feature of cardiovascular disease in patients with end-stage renal failure and contributes to the excess mortality in this population. In this study, we explored in vivo X-ray microtomography (micro-CT) as a tool to detect and follow-up vascular calcifications in the aorta of living rats with adenine-induced CRF. Methods and Results-With in vivo micro-CT, calcification of the aorta in uremic rats was clearly discernible on transversal virtual cross-sections. Micro-CT findings correlated well with tissue calcium content and histology.Repetitive scans in animals with light, moderate, and severe vascular calcification showed good reproducibility with minimal interference of motion artifacts. Moreover, both calcified volume and area could be quantified with this method. Key Words: ectopic calcification Ⅲ imaging Ⅲ micro-CT Ⅲ renal failure Ⅲ kidney C hronic renal failure (CRF) is associated with a 10-to 20-fold increase in cardiovascular risk, which is responsible for Ϸ50% of the mortality in hemodialysis patients. 1 Goodman et al demonstrated that vessel calcification is already present in young hemodialysis patients and shows rapid progression. 2 In addition to increased calcification of atherosclerotic plaques, patients on dialysis also show characteristic calcifications of the vascular media, 3 which were recently shown to contribute significantly to the excess cardiovascular mortality observed in uremic patients. 4 Epidemiological studies identified elevated serum phosphate levels, increased calcium phosphate product and secondary hyperparathyroidism as risk factors for mortality in the hemodialysis population. 5,6 The causative roles of phosphate and calcium in the calcification process were elegantly demonstrated by in vitro studies showing that blockage of the Na-phosphate co-transporter in cultured vascular smooth muscle cells inhibited the calcification process induced by either elevated phosphate 7 or calcium levels. 8 Katsumata et al recently described adenine-induced CRF as a suitable animal model for uremia-related vascular calcification. 9 The availability of such a model allows for studies investigating how pharmacological agents, such as the recently developed alternative therapies to control hyperphosphatemia and secondary hyperparathyroidism, influence the CRF-related vascular calcification process and the mediators involved in it. Conclusions-InIn the present study, we evaluated whether vascular calcifications in a rat model of CRF can be visualized by in vivo high-resolution X-ray microtomography (micro-CT). This technique has recently been introduced as a promising noninvasive imaging technique in living rats and mice. Micro-CT proved to be most suitable for the visualization of bones and other calcified tissues. 10 Additionally, recent studies showed that noninvasive soft tissue imaging of the chest area was possible in living animals despite cardiac an...

Chondrocyte Rather Than Osteoblast Conversion of Vascular Cells Underlies Medial Calcification in Uremic Rats

“…Previous studies 21,22 in our laboratory demonstrated that the induction of CRF with an adenine-rich diet containing a normal protein content results in calcification of the aortic tunica media in approximately 50% of the animals after 4 to 6 weeks. However, lowering the protein content from 19% to 2.5% during the 4-week adenine treatment period resulted in a remarkably increased prevalence of severe medial calcifications up to 100% in rats with CRF.…”

“…21 Therefore, a separate group of rats with CRF (nϭ10) was scanned at 1, 2, 3, 4, 6, and 8 weeks after the induction of CRF.…”

Vascular Calcification in Chronic Renal Failure

“…With regard to future studies aiming to investigate the reversal of vascular calcification, in vivo microtomography scanning has been shown to be a sensitive tool for the follow-up of aortic calcification in living rats. 149 …”

PA21, a New Iron-Based Noncalcium Phosphate Binder, Prevents Vascular Calcification in Chronic Renal Failure Rats

“…The degree of von Kossa positivity was scored semiquantitatively, with scores ranging from 0 to 3 depending on the surface of von Kossa positivity. Score 0 indicated no von Kossa positivity; score 1, focal von Kossa positivity, larger than or not overlying a cell nucleus; score 2, partially circumferential von Kossa positivity in the tunica media of the vessel; and score 3, von Kossa positivity in the tunica media spanning the complete circumference of the vessel (Persy et al, 2006a;Neven et al, 2010).…”

“…The aortic rings visible on a 40Â magnification were captured on a microcomputer equipped with Leica software (Leica Microsystems, Buffalo Grove, IL) and analyzed by a computerized image analysis program. Semiquantitative assessments of nitrotyrosine and CD68 expressions were done by semiautomatic quantification of brown-field expression specifically inside aorta media, as described previously Persy et al, 2006a). Data were expressed as the relative proportion (percentage) of the positive staining area of the aorta media to total surface area of each ring.…”