A comparison of macroscopic lipid content within porcine pulmonary and aortic valves: Implications for bioprosthetic valves

AbstractLipid droplets have been demonstrated within both explanted porcine bioprostheses and normal porcine aortic valves. Because of the increasing interest in pulmonary valves as an allograft or xenograft aortic valve substitute, we examined the incidence and distribution of such lipid deposits in 50 porcine aortic valves and 50 matched porcine pulmonary valves. All 300 cusps were removed with surgical scissors and, under a dissecting microscope, the ventricularis layer was removed to expose the spongiosal layer. Macroscopic extracellular lipid droplets were exposed. The position and amount of the visible unstained droplets were analyzed by means of a dissecting microscope with an eyepiece grid and stereology point-counting techniques to provide an area-density average spatial probability map for each cusp. Only 8% of porcine aortic valves were free of lipid, with the distribution of the lipids being 52% ± 14% right coronary cusp, 90% ± 8% left coronary cusp, and 68% ± 13% noncoronary cusp. Of the pulmonary valves, 60% were free of lipid, with the incidence of lipids being 26% ± 12% left cusp, 6% ± 7% right cusp, and 12% ± 9% anterior cusp. Subsequently, lipid cluster samples underwent thin-layer chromatography, which showed them to be phospholipids, oleic acid (fatty acid), triglycerides, and unesterified cholesterol. One primary mode of bioprosthetic valve failure is leaflet calcification. The similarity of distribution within the spongiosal layer between leaflet calcification and intrinsic cusp lipids suggests that the observed lipids might act as a nucleation site for calcification. The substantially lower incidence of lipid in pulmonary valves therefore may represent a potential benefit when these valves are considered for use as aortic valve replacements. (J THORAC CARDIOVASC SURG 1995;110:1756-61

Vascular smooth muscle cells as a valvular interstitial cell surrogate in heart valve tissue engineering

Background: Vascular smooth muscle cells (VSMCs) are a potential autologous cell source for aortic valve tissue engineering, but have a phenotype that differs from that of valvular interstitial cells in vivo. We hypothesized that combining basic fibroblast growth factor (bFGF), epidermal growth factor (EGF), or platelet-derived growth factor (PDGF) with transforming growth factor beta-1 (TGF-β1) would achieve a valvular interstitial cell-like phenotype of VSMCs. Methods: VSMC phenotype was assessed by immunofluorescence, proliferation was measured by the tetrazolium reduction (MTT) assay, and extracellular matrix gene expression was determined by real-time polymerase chain reaction. Results: Combinations of growth factors that included PDGF showed the greatest increases in proliferation. Immunofluorescence for α-smooth muscle actin demonstrated an inverse correlation between proliferation and a myofibroblast-like phenotype, while combinations of TGF-β1+ EGF+bFGF (TEF) and TGF-β1+EGF+PDGF (TEP) induced the greatest change of α-smooth muscle actin expression compared to untreated controls. Finally, TEP treatment showed an increase in versican, fibronectin, and type I collagen mRNA expression, while decreasing matrix metalloproteinase 1 expression. Conclusions: Combination of TGF-β1 with EGF and PDGF induces VSMC proliferation and expression of extracellular matrix constituents found in the aortic valve. In vitro preconditioning of VSMCs provides a potentially viable surrogate cell source for developing a valve graft. © 2009, Mary Ann Liebert, Inc