Identification and characterization of calcifying valve cells from human and canine aortic valves

Background and aim of the study: Cardiac valve calcification is the predomi nant pathology in patients needing valve replacement. The aim of this study was to determine if aortic valve cells calcify spontaneously and, if so, t o characterize the nodular complex and response to growth factors. Methods: Aortic valves were obtained from humans undergoing surgical valve replacement, and from female dogs. The valvular endothelium was removed and explants cultured in medium. Results: A population of valvular interstitial cells spontaneously formed d istinct calcified nodules containing hydroxyapatite within two to three wee ks in canine and within six weeks in human aortic valves. The nodules conta ined an inner ring of dead cells surrounded by an outer ring of living cell s. Cells associated with nodules had osteoblast-like characteristics and st ained positively for extracellular bone matrix proteins. Incubating canine cells with potential calcifying stimuli tested the stimulus for calcificati on. The rate of nodule formation was increased with transforming growth fac tor beta-1 (+25 nodules), 25-hydroxycholesterol (+9 nodules) and bone morph ogenetic protein 2 (+4 nodules) as compared with vehicle control (+3 nodule s) over 25 days. Conclusions: We identified a population of valvular interstitial cells with osteoblast-like characteristics that spontaneously form calcific nodules i n cell culture. In addition, the rate of calcific nodule formation was incr eased with transforming growth factor beta-1 and 25-hydroxycholesterol. Fur ther study of these 'calcifying valve cells' may yield a new in vitro model for testing therapy aimed at preventing calcific valve stenosis.