Glycosaminoglycan-degrading enzymes in porcine aortic heart valves: implications for bioprosthetic heart valve degeneration.
OBJECTIVE
Glutaraldehyde (GA)-fixed aortic valves used in heart valve replacement surgery have limited durability due to tissue degeneration and calcification. Despite their structural and functional importance, very little is known about the fate of glycosaminoglycans (GAGs) within the extracellular matrix of bioprosthetic heart valves. The study aim was to investigate the stability of GAGs in GA-fixed tissues and to identify enzymatic mechanisms that may be responsible for GAG degeneration.


METHODS
Porcine aortic valve cusps were fixed with GA and implanted subdermally in rats for 21 days. Fresh, fixed and explanted cusps were analyzed for GAG content by hexosamine determination, and GAG-degrading enzyme activity was evaluated using zymography. GAG classes in fresh cusps were also assessed by flurorophore-assisted carbohydrate electrophoresis. Fresh and GA-fixed cusps were also exposed in vitro to hyaluronidase and chondroitinase in order to test the susceptibility of cusp GAGs towards enzymatic degradation.


RESULTS
Native aortic cusps contained -3.5% GAGs by dry weight, consisting of hyaluronic acid, chondroitin sulfate and dermatan sulfate. Significantly lower GAG levels were found in aortic cusps after fixation with GA, and even lower levels were found after subdermal implantation in rats. GAG levels in GA-fixed cusps were also significantly reduced by in-vitro incubation with hyaluronidase and chondroitinase. Novel GAG-degrading enzymes were detected in considerable levels in native cusps, in lower levels in GA-fixed cusps and significantly increased levels after subdermal implantation of GA-fixed cusps.


CONCLUSIONS
The combined action of active GAG-degrading enzymes and the failure of GA to stabilize GAGs towards enzymatic digestion may contribute significantly to bioprosthetic heart valve degeneration and subsequent structural failure.
Simionescu
Dan T
DT
Cardiovascular Implant Research Laboratory, Department of Bioengineering, Clemson University, Clemson, South Carolina 29634, USA.
Lovekamp
Joshua J
JJ
Vyavahare
Narendra R
NR
D000818:Animals; D001021:Aortic Valve / Q000187:drug effects* / Q000201:enzymology* / Q000473:pathology; D001705:Bioprosthesis; D002114:Calcinosis / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D002118:Calcium / Q000378:metabolism; D002810:Chondroitinases and Chondroitin Lyases / Q000187:drug effects / Q000378:metabolism; D004195:Disease Models, Animal; D004198:Disease Susceptibility; D004586:Electrophoresis; D005404:Fixatives / Q000494:pharmacology; D018093:Gelatinases / Q000187:drug effects / Q000378:metabolism; D005976:Glutaral / Q000494:pharmacology; D006025:Glycosaminoglycans / Q000378:metabolism*; D006349:Heart Valve Diseases / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D006350:Heart Valve Prosthesis; D006821:Hyaluronoglucosaminidase / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008955:Models, Cardiovascular; D010758:Phosphorus / Q000378:metabolism; D011475:Prosthesis Failure; D051381:Rats; D017207:Rats, Sprague-Dawley; D013552:Swine
D005404:Fixatives; D006025:Glycosaminoglycans; D010758:Phosphorus; D006821:Hyaluronoglucosaminidase; D018093:Gelatinases; D002810:Chondroitinases and Chondroitin Lyases; D002118:Calcium; D005976:Glutaral