Development of a Gal-free Calcification Resistant Porcine Pericardial Heart Valve: Establishment of Biological Tissue Equivalence.

心脏瓣膜控制着血液通过肺部和身体的正常流动。这些瓣膜可能会因为出生缺陷、衰老或感染而受损。这种损害可能需要用人工瓣膜替换心脏瓣膜，以提高心脏瓣膜病患者的生活质量或挽救他们的生命。全球每年约有30万例心脏瓣膜置换手术。替换瓣膜要么是机械的，由碳和金属制成，要么是生物的，通常是由猪或牛的非生物组织制成的。患者和医生倾向于使用生物心脏瓣膜(BHV)，因为它们通常不需要血液稀释剂，而机械瓣膜需要血液稀释剂。在年龄较小的患者(60岁)和儿童中，BHV磨损更快，有时在5年内。BHV失败是因为它们形成了骨状的钙沉积，这会削弱瓣膜，导致撕裂，或者在钙沉积阻止瓣膜打开时阻碍血液流动。长期以来，科学家和商业瓣膜公司一直在寻求生产不会钙化的BHV，因为它们可以用于更年轻的患者，而不需要血液稀释剂。到目前为止，钙化阻断治疗已经能够在动物身上测试时减少瓣膜钙化，但还不能阻止患者的钙化，也不能可靠地允许年轻人使用BHV。我们确定了一种排斥反应，使BHV材料中的钙化变得更糟。这种排斥反应是人类独有的，因为人类的免疫系统会与一种名为Gal的物质发生反应，这种物质存在于BHV上。为了阻止这种排斥反应，我们用转基因猪来制造被称为Gal基因敲除猪的BHV。Gal基因敲除猪是健康和正常的，它们的无Gal组织减少了钙化。在将Gal基因敲除组织用于患者之前，我们需要确保Gal基因敲除猪的基因变化没有对用于制造这些BHV的组织产生破坏性影响。我们比较了当前标准BHV和Gal基因敲除BHV中的组织，并使用了简单的测试，例如测量组织拉伸和撕裂的难度，以查看Gal基因敲除组织的机械性能是否保持坚固和不变。我们还用目前的标准组织和Gal基因敲除组织制作了BHV，并在实验室机器上模拟它们在心脏中的功能进行了测试。这两种类型的BHV在这些测试中的表现相似。目前的项目是比较Gal基因敲除组织在标准工业动物模型中作为BHV的效果。这项测试是确定瓣膜在体内是否正常工作以及是否能够控制心脏中正常血液流动的唯一方法。成功地进行国际标准要求的这项测试，是制造新的BHV的重要一步，这种新的BHV可以减少钙化，并可用于年轻患者。这种新的BHV将极大地提高患者的生活质量。如果成功，我们希望推出一种新的Gal基因敲除的心脏瓣膜，用于人类的临床测试。

Heart valves control the normal flow of blood through the lungs and body. These valves may be damaged because of birth defects, old age, or infection. This damage may require heart valves to be replaced with artificial valves to improve the quality of life of heart valve disease patients or to save their lives. There are about 300,000 heart valve replacements worldwide each year. Replacement valves are either mechanical, made of carbon and metal, or biological, made of non-living tissue generally obtained from pigs or cows. Patients and doctors tend to prefer biological heart valves (BHVs) because they generally do not require blood thinners, which are needed with mechanical valves. In younger patients (<60 years) and in children, BHVs wear out more rapidly, sometimes within 5 years. BHVs fail because they build up bone-like deposits of calcium, which weaken the valve, leading to tears, or obstructed blood flow as the calcium deposits block the opening of the valve. Scientists and commercial valve companies have long sought to produce BHVs, which do not calcify, because these could be used in younger patients without the need for blood thinners. So far, calcification-blocking treatments have been able to reduce valve calcification when tested in animals, but have not been able stop calcification in patients or reliably allow the use of BHVs in younger adults. We identified a type of rejection that makes calcification worse in BHV material. This rejection is unique to humans as the human immune system reacts with a substance, called Gal present on BHVs. To block this rejection reaction we have genetically altered pigs that can be used to make BHVs called Gal knockout pigs. The Gal knockout pigs are healthy and normal and their Gal-free tissue has reduced calcification. Before using Gal knockout tissue in patients, we need to be certain the genetic change in Gal knockout pigs has not had a damaging effect on the tissues used to make these BHVs. We have compared the tissues in current standard and Gal knockout BHVs and used simple tests, such as measuring how hard it is to stretch and tear the tissue, to see if the mechanical properties of Gal knockout tissue remain strong and unchanged. We have also made BHVs using both current standard and Gal knockout tissue, and tested them in a laboratory machine that mimics their function in the heart. Both types of BHVs performed similarly in these tests. This current project is to compare how well the Gal knockout tissue works as a BHV in the standard industry animal model. This test is the only way of determining if the valve works well inside of the body and can function to control the normal flow of blood in the heart. Successfully performing this test, which is required by International standards, is a major step forward to making a new BHV, which reduces calcification and be usable in younger patients. Such a new BHV would greatly increase the quality of life for patients. If successful, we hope to advance a new Gal knockout heart valve for a clinical test in man.