Does the Animal Origin Influence the Calcification of Xenograft Tissue Heart Valve Substitutes? Comparison between Bovine and Camel Pericardium in a Subcutaneous Rat Model

Fatima Al Harmoodi,Olivier Jegaden,Salah Al Shafy,Francoise Thivolet,Jean-Jacques Lebrun,Michel Guichardant

doi:10.4236/ijcm.2015.69093

Abstract

Objective: To validate the hypothesis that camel pericardium could be more protected than bovine pericardium against calcification process according to the huge difference in their respective lifestyle and lifetime. Methods: Glutaraldehyde (GA) fixed bovine and camel pericardium samples (BP and CP respectively) were both implanted in 30 New Zealand white rats (2 BP and 2 CP matched specimens in each animal) and explanted after 60 days. Unimplanted GA-fixed samples of both species served as control. Matched implanted samples and unimplanted samples were randomly submitted to elemental analysis by spectroscopy, phospholipid extraction, macroscopic and X-ray examination and histology. Results: At 60 days, calcium and phosphorus content were respectively 9.54% ± 3.1% and 4.79% ± 1.4% of tissue dry weight in BP, and 12.52% ± 2.7% and 6.14% ± 1.3% of tissue dry weight in CP (ns). In X-ray analysis, the calcification score was 1.28 ± 0.45 and 2.14 ± 0.98 in BP and CP samples respectively without significant difference (p < 0.08). In histology, calcifications were lower in BP than in CP: 1.37 ± 0.85 vs 2.28 ± 0.83 (ns); collagen fibers were better conserved in BP than in CP: 2.4 ± 0.48 vs 1.87 ± 0.78 (ns), and less disoriented: 25% vs 62% (ns). In unimplanted samples, there was a higher but not significant rate of extracted lipids in CP: 5.7 ± 1.8 vs 9.5 ± 3.8 nanomoles in PS fraction and 11.3 ± 3.7 vs 19 ± 7.7 nanomoles in total fatty acids, in BP and CP samples respectively. All results were in conjunction and demonstrated a higher but not significant rate of mineralization in camel pericardium after implantation, which could be related to a higher but not significant basic rate of phospholipid and fatty acids. Conclusion: This experiment study in a subcutaneous rat model has failed to valid our hypothesis. Because the differences observed between bovine and camel pericardium did not reach the significance, at the best, there is no difference between both species and at the worst, camel pericardium has a higher rate of the phosphatidylserine fraction of phospholipid, and is more sensitive and prompt to calcification.

Highlights

Structural dysfunction, due to calcification and non-calcific deterioration, is the major cause of failure of bioprosthetic heart valves
Because the differences observed between bovine and camel pericardium did not reach the significance, at the best, there is no difference between both species and at the worst, camel pericardium has a higher rate of the phosphatidylserine fraction of phospholipid, and is more sensitive and prompt to calcification
Regardless of the fixation and the post-fixation treatments of the pericardium, we have considered that the animal origin of the xenograft could influence the process of calcification and we have tested this hypothesis in a comparison between bovine and camel origin

Summary

Introduction

Structural dysfunction, due to calcification and non-calcific deterioration, is the major cause of failure of bioprosthetic heart valves. Glutaraldehyde (GA) was introduced for fixation of bioprosthetic valves to decrease immunogenecity, increase crosslinking of connective tissue proteins, and increase strength and durability [1]. It has been used extensively for the preservation of bovine pericardium derived valves and porcine aortic valves. It has been found that GA fixation stimulates dystrophic calcification, as a consequence of xenograft cells devitalization and a toxic effect of unstable cross-linking. Despite the controversies around the different effects of GA on the calcification process [4] [5], GA-fixed tissue remains the basic concept of xenograft engineering and GA is the standard fixative with no alternative in view. Additional anticalcificant treatments have been developed to block calcification at the cellular level and to provide better structural integrity [6] [7]

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Results

Conclusion