Degenerative calcification occurring in failing heart bioprosthetic valves is still poorly understood. In "in vivo" calcification models, mineralization onset takes place at level of cells (1) or cell nuclei (2). In porcine aortic valves subdermally implanted in rat subcutis for 6 weeks, we found that calcification correlates with the presence of peculiar acidic phospholipid layers (PPLs) surrounding cells and matrix vesicles (3-5). Here, we investigated valve mineralization after shorter implantation times to understand how PPLs form and correlate with mineralization progress. Chemical analyses revealed initial calcium deposition before 2-day-long implantation and its linear increase with time. Ultrastructural observations revealed lipid accumulation within more and more numerous vacuoles filling cell cytoplasm in 2-day and and 1-week implanted valves. Initial PPL formation was observed in 1-week implanted valves, whereas PPLs involved most cells after longer implantation times. These data suggest that (a) direct correlation does exist between calcification rate and acidic phospholipid accumulation and (b) PPL genesis is due to distinct intracellular modifications which seem to depend on a peculiar pattern of phospholipidosis. (1) Schoen FJ, Levy RJ, Nelson AC et al. Lab Invest, 5: 523-532; 1985. (2) Girardot MN, Torrianni M, Dillehay D et al. , 29: 793-801; 1995. (3) Ortolani F, Petrelli L, Tubaro F et al. Connect Tiss Res, 43: 44-55; 2002. (4) Ortolani F, Tubaro F, Petrelli L et al. Histochem J, 34: 41-50; 2002. (5) Ortolani F, Petrelli L, Nori SL et al. Histol Histopathol, in press; 2003.
