Vascular Calcification in a Mouse Model of Chronic Kidney Disease and in Human Peripheral Arterial Disease

Vascular calcification is a process in which calcium and phosphate crystallize to form hydroxyapatite in the extracellular matrix of blood vessels. There are two forms of arterial calcification: intimal and medial, which occur via different etiologies. Intimal calcification is associated with atherosclerosis and occurs in the layer of endothelial cells adjacent to the artery lumen. Medial arterial calcification (MAC) is independent of atherosclerosis and occurs in the middle, muscular layer of the artery. MAC is strongly associated with aging, diabetes mellitus, and chronic kidney disease (CKD). MAC is frequently in patients with peripheral arterial disease (PAD). Most studies to date have either focused on atherosclerosis and plaque calcification or have not differentiated between intimal and medial calcification. This study aims to characterize the mechanical effects of vascular calcification and its removal in arteries. We also investigated the use of lower limb calcification score in risk stratifying patients with PAD undergoing treatment by femoral endarterectomy (FEA). To characterize the mechanical behavior of healthy arteries, the femoral, popliteal, and tibial arteries of porcine hind limbs were biaxially tested under in vivo conditions. Our study documented differences in mechanical properties and histology of these three arteries. A mouse model of chronic kidney disease, which is strongly associated with MAC, was used to investigate differences in the mechanical behaviors of the abdominal aorta of the diseased mouse and healthy wild type mice. Biaxial mechanical testing showed differences in in vivo axial stretch ratio, diameter, compliance, and active stress generation. After examining the differences between healthy and calcified arteries in mice, we used cadaveric human leg arteries to determine whether calcification can be reversed and mechanical properties restored to baseline levels. Our results indicate that ethylene-diamine-tetra-acetic acid (EDTA) chelation can change the mechanical response of calcified human femoropopliteal artery to resemble the response of healthy porcine femoropopliteal arteries. This study shows promising pilot results for the reversal of vascular calcification with chelation therapy. Blood from patients with PAD who underwent FEA to improve blood flow to the lower leg was collected, and six protein biomarkers were quantified. The volume of calcium in the lower limb arterial tree was quantified from patient computed tomographic angiograms. We found that fetuin A and osteoprotegerin correlate with the volume of arterial calcification in the legs. Multivariate logistic regression of the biomarker, demographic, and clinical data from the patients shows that the inclusion of calcium volume does not always improve the ability to classify patients according to adverse outcomes after FEA. The panel of six protein biomarkers, however, showed strong discriminatory capability. These results indicate a potential for a blood biopsy test to assist patients and physicians to assess the risk of FEA, although this needs further investigation in a larger population.