Mechanisms of bioprosthetic heart valve failure: Fatigue causes collagen denaturation and glycosaminoglycan loss

Abstract

Bioprosthetic heart valve (BPHV) degeneration, characterized by extracellular matrix deterioration, remodeling, and calcification, is an important clinical problem accounting for thousands of surgeries annually. Here we report for the first time, in a series of in vitro accelerated fatigue studies (5-500 million cycles) with glutaraldehyde fixed porcine aortic valve bioprostheses, that the mechanical function of cardiac valve cusps caused progressive damage to the molecular structure of type I collagen as assessed by Fourier transform IR spectroscopy (FTIR). The cyclic fatigue caused a progressive loss of helicity of the bioprosthetic cuspal collagen, which was evident from FTIR spectral changes in the amide I carbonyl stretching region. Furthermore, cardiac valve fatigue in these studies also led to loss of glycosaminoglycans (GAGs) from the cuspal extracellular matrix. The GAG levels in glutaraldehyde crosslinked porcine aortic valve cusps were 65.2 +/- 8.66 microg uronic acid/10 mg of dry weight for control and 7.91 +/- 1.1 microg uronic acid/10 mg of dry weight for 10-300 million cycled cusps. Together, these molecular changes contribute to a significant gradual decrease in cuspal bending strength as documented in a biomechanical bending assay measuring three point deformation. We conclude that fatigue-induced damage to type I collagen and loss of GAGs are major contributing factors to material degeneration in bioprosthetic cardiac valve deterioration.

Periodate-mediated glycosaminoglycan stabilization in bioprosthetic heart valves

“…1,2 Thus, the spongiosa layer plays a significant role in reducing valve mechanical fatigue. 1,2 Moreover, this layer is constantly remodeled in native valves to maintain the valve's mechanical properties. 1 Conventional glutaraldehyde crosslinking of porcine aortic valves significantly reduces flexural properties of native valves.…”

“…[1][2][3] We have recently reported that glycosaminoglycans (GAGs) present in the middle spongiosa layer of BPHV leach out under in vitro cyclic fatigue, resulting in a significant reduction in cuspal stiffness, thus making BPHV cusps vulnerable to material failure. 2 In the native valve, highly hydrated GAGs present in the middle spongiosa layer allow shearing between the two outer layers, the fibrosa and ventricularis, during valve function. 1,2 Conventional glutaraldehyde crosslinking does not stabilize GAGs present in BPHVs because the structures of hyaluronic acid (HA) and dermatan sulphate (the major GAGs present in the BPHV cusps) do not have the amine functionalities necessary to react with glutaraldehyde.…”

“…2 In the native valve, highly hydrated GAGs present in the middle spongiosa layer allow shearing between the two outer layers, the fibrosa and ventricularis, during valve function. 1,2 Conventional glutaraldehyde crosslinking does not stabilize GAGs present in BPHVs because the structures of hyaluronic acid (HA) and dermatan sulphate (the major GAGs present in the BPHV cusps) do not have the amine functionalities necessary to react with glutaraldehyde. 2,4 Moreover, unlike other GAG molecules, HA is not linked to a protein.…”

“…1,2 Conventional glutaraldehyde crosslinking does not stabilize GAGs present in BPHVs because the structures of hyaluronic acid (HA) and dermatan sulphate (the major GAGs present in the BPHV cusps) do not have the amine functionalities necessary to react with glutaraldehyde. 2,4 Moreover, unlike other GAG molecules, HA is not linked to a protein. In addition, the devitalized nature of BPHVs after glutaraldehyde treatment prevents any cellmediated remodeling of the extracellular matrix (ECM) that would otherwise maintain GAG concentrations.…”

Valve proteoglycan content and glycosaminoglycan fine structure are unique to microstructure, mechanical load and age: Relevance to an age-specific tissue-engineered heart valve

“…Altered proportions of selected PGs and GAGs are found in myxomatous MV disease [5], are probably responsible for the altered material properties of these swollen tissues [6], and are possibly involved in the disease pathogenesis. The loss of the GAG-and PG-rich spongiosa layer, which normally provides shear between the outer valve layers and thus enables complex valve leaflet movement [7], from porcine bioprosthetic aortic valves (AVs) is thought to be instrumental in the failure of these devices [8]. Overall, knowledge of the composition and distribution of the various GAGs and PGs within heart valves appears to be essential for understanding and recapitulating the complex mechanics of the heart valve leaflets.…”