Normal Physiological Conditions Maintain the Biological Characteristics of Porcine Aortic Heart Valves: An Ex Vivo Organ Culture Study

Abstract

The aortic valve functions in a complex mechanical environment which leads to force-dependent cellular and tissue responses. Characterization of these responses provides a fundamental understanding of valve pathogenesis. The aim of this work was to study the biological characteristics of native porcine aortic valves cultured in an ex vivo pulsatile organ culture system capable of maintaining physiological pressures (120/80 mmHg) and cardiac output (4.2 l/min). Collagen, sGAG and elastin contents of the valve leaflets were measured and cusp morphology, cell phenotype, cell proliferation and apoptosis were examined. Presence of endothelial cells (ECs) on the leaflet surface was also evaluated. The differences in collagen, sGAG and elastin contents were not significant (p > 0.05) between the cultured and fresh valve leaflets. The cultured valves maintained the native ECM composition of the leaflets while preserving the morphology and cell phenotype. Cell phenotype in leaflets incubated statically under atmospheric conditions decreased compared to fresh and cultured valve leaflets, indicating the importance of mechanical forces in maintaining the natural biology of the valve leaflets. ECs were retained on the surfaces of cultured leaflets with no remodeling of the leaflets. The number of apoptotic cells in the cultured leaflets was significantly (p < 0.05) less than in the statically incubated leaflets and comparable to fresh leaflets. The sterile ex vivo organ culture system thus maintained the viability and native biological characteristics of the aortic valves that were cultured under dynamic conditions for a period of 48 h.

Elevated cyclic stretch alters matrix remodeling in aortic valve cusps: implications for degenerative aortic valve disease

“…Each experiment was run for either 24 or 48 h, with 12-15 cusp sections for each experimental run. These time points were chosen based on previous studies as necessary and sufficient to observe acute responses in valve cusps (2,13,16,20,38). All samples were stretched in normal Dulbecco's modified Eagle's medium (DMEM; Sigma), supplemented with 10% fetal bovine serum (FisherScientific), 50 mg/l ascorbic acid, 3.7 g/l sodium bicarbonate, 1% (vol/vol) nonessential amino acid solution, and 1% (vol/vol) antimycotic-antibiotic solution (all Sigma).…”

The Porcine Aortic Tissue Culture System in vitro for Stem Cell Research

“…Endothelial cells were retained on the surfaces of cultured leaflets with no remodeling of the leaflets for a period of 48 hours (17). However, vessel tissue itself has not yet been cultured.…”

“…However, the materials that are commonly used lack growth potential, and long-term results have revealed several material-related failures, such as stenosis, thromboembolization, calcium deposition, and risk of infection (13). Previously, organ cultures such as heart valves were developed to study the biological characteristics of native aortic valves cultured in vitro and understand fundamental valve pathogenesis (14)(15)(16)(17). An organ culture maintains cells within their na- tive microstructural environment, and thus offers greater potential.…”

Cyclic strain inhibits acute pro-inflammatory gene expression in aortic valve interstitial cells

“…Once the valve is implanted it will be exposed to a demanding and highly complex mechanical environment. Previous studies have demonstrated that this environment is important in maintaining homeostasis in the aortic valve and the absence of these forces causes structural and phenotypical changes in the tissue (Balachandran et al 2006;Konduri et al 2005;Weston and Yoganathan 2001;Xing et al 2004). Additionally, mechanical pre-conditioning of tissue engineered valves improves microstructure, mechanical properties, and extracellular matrix formation (Hoerstrup et al 2000;Ku et al 2006).…”

“…Studies have shown that these stimuli are necessary to maintain homeostasis and correct functioning of the valve. Their absence results in a decrease in α-smooth muscle actin expression, significant changes in extra cellular matrix composition and altered DNA synthesis (Konduri et al 2005;Weston and Yoganathan 2001). Consequently, it has long been accepted that in vitro biomimetic mechanical preconditioning greatly enhances the development of tissue engineered heart valves by increasing collagen and DNA content relative to static controls (Hoerstrup et al 2002(Hoerstrup et al , 2000.…”