Research scrutinizes lyophilization method
Lyophilization, a method once thought to inactivate retroviruses such as HIV from bones and connective tissues used in transplant procedures, may not be quite as effective as originally thought, researchers at Michigan State University have concluded.
In a paper to be presented at an upcoming meeting of the American Orthopaedic Society for Sports Medicine, MSU scientists said their research shows the method, known as lyophilization or freeze-drying, does not improve the safety of bones and tissues for transplantation, something that could affect thousands of transplant recipients.
"We were able to demonstrate that this type of tissue processing does not inactivate systemically infected tendon and bone tissues," said Steven P. Arnoczky, the Wade O. Brinker Endowed Professor of Surgery in MSU's College of Veterinary Medicine and one of the lead researchers in the project. "Contrary to currently held clinical beliefs, lyophilization should not be relied upon as an extra measure of security for processing connective tissue allografts."
Bones, ligaments and other tissues that will be used for orthopedic transplants frequently are treated with gamma irradiation or a chemical "cocktail" in an effort to remove any bacteria or viruses which may have evaded the rigorous donor-screening process.
However, these methods can create additional problems, as they sometimes change the tissue's biological and biomechanical properties.
A clinical study published in 1985 suggested that lyophilization may inactivate HIV. Therefore, many surgeons who were seeking an extra measure of protection for their patients would specifically request tissues that had gone through the lyophilization process.
"This has completely changed a long-held belief," Arnoczky said, "and it's a very important contribution, as it got rid of the false sense of security people had with that process."
In their experiment, Arnoczky and his colleagues at the Laboratory for Comparative Orthopaedic Research (LCOR) put five samples each of bone and tissue that were infected with feline leukemia virus, a retrovirus similar to human immunodeficiency virus, or HIV, through the lyophilization process. In every case, the virus survived the process.
The feline leukemia virus, Arnoczky said, has a structure and replication cycle very similar to human immunodeficiency virus, making it an excellent model for HIV.
"The results of this in vitro study clearly demonstrated that neither freezing nor freeze-drying of systemically infected bone and tendon samples had any effect on inactivating the (feline leukemia) retrovirus," Arnoczky and colleagues wrote in their accompanying paper, which will soon be published in The American Journal of Sports Medicine.
The chance of contracting a bacterial or viral infection from a connective tissue transplant, while rare, is still a possibility, Arnoczky said. In 1999, for example, more than 700,000 bone and connective tissue transplant procedures were performed in the United States.
"In one case report from 1985," Arnoczky said, "distribution of tissues from a single HIV-infected donor resulted in the dissemination of 52 virus-contaminated allografts. However, using current screening methods and testing protocols, the risk of implanting tissue from an infected HIV donor is less than one in a million."
This work earned LCOR the 2004 Cabaud Award, an honor given by the American Orthopaedic Society for Sports Medicine to laboratories that usually do research that benefits humans.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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