Cyclic Pressure Affects the Biological Properties of Porcine Aortic Valve Leaflets in a Magnitude and Frequency Dependent Manner

Abstract

An understanding of how mechanical forces impact cells within valve leaflets would greatly benefit the development of a tissue-engineered heart valve. Previous studies by this group have shown that exposure to constant static pressure leads to enhanced collagen synthesis in porcine aortic valve leaflets. In this study, the effect of cyclic pressure was evaluated using a custom-designed pressure system. Different pressure magnitudes (100, 140, and 170 mmHg) as well as pulse frequencies (0.5, 1.167, and 2 Hz) were studied. Collagen synthesis, cell proliferation, sGAG synthesis, alpha-SMC actin expression, and extracellular matrix (ECM) structure were chosen as markers for valvular biological responses. Results showed that aortic valve leaflets responded to cyclic pressure in a magnitude and frequency-dependent manner. Increases in pressure magnitude (with the frequency fixed at 1.167 Hz) resulted in significant increases in both collagen and sGAG synthesis, while DNA synthesis remained unchanged. Responses to pulse frequency (with the magnitude fixed at 100 mmHg) were more complex. Collagen and sGAG synthesis were increased by 25 and 14% respectively at 0.5 Hz; but were not affected at 1.167 and 2 Hz. In contrast, DNA synthesis increased by 72% at 2 Hz, but not at 0.5 and 1.167 Hz. Under extreme pressure conditions (170 mmHg, 2 Hz), collagen and sGAG synthesis were increased but to a lesser degree than at 170 mmHg, and 1.167 Hz. Cell proliferation was not affected. A notable decline in a-SMC actin was observed over the course of the experiments, although no significant difference was observed between the cyclic pressure and control groups. It was concluded that cyclic pressure affected biosynthetic activity of aortic valve leaflets in a magnitude and frequency dependent manner. Collagen and sGAG synthesis were positively correlated and more responsive to pressure magnitude than pulse frequency. DNA synthesis was more responsive to pulse frequency than pressure magnitude. However, when combined, pressure magnitude and pulse frequency appeared to have an attenuating effect on each other. The number of alpha-SMC actin positive cells did not vary with cyclic pressure, regardless of pulse frequency and pressure magnitude.

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).…”

“…Anti-bromodeoxyuridine (Sigma) immunohistochemistry (38) was used to visualize proliferating cells, whereas a terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling fluorescence kit (Roche Applied Science, Indianapolis, IN) was used to identify apoptotic cells. For the cell proliferation analysis, experiments were run with 5 mg/l bromodeoxyuridine included in the DMEM for the last 24 h of the experiment.…”

The Contribution of Whole Blood Viscosity to the Process of Aortic Valve Sclerosis

“…Additionally, it has been claimed that mechanical forces such as blood pressure, membrane tension, and fluid shear stress contribute to the calcification of the aortic valve (AV) [3]. Lesions frequently occur at the aortic side of the leaflets, an area of high turbulent flow and tensile stress with oscillatory shear stress [4].…”

Dynamic deformation characteristics of porcine aortic valve leaflet under normal and hypertensive conditions

“…Furthermore, in a manner similar to the correlation between adverse hemodynamic/mechanical environment and atherosclerosis formation (9,10), data in the literature suggest that adverse mechanical forces may elicit pathological responses of AV leaflets. Isolated mechanical forces, including stretch, pressure, and fluid shear, have been shown to affect the remodeling activity in AV tissues (3,32,33). Butcher et al (6) compared transcriptional profiles of porcine AV endothelial cell cultures in vitro and found that exposure to shear stress was protective against inflammatory and oxidative gene expressions, compared with static culture.…”