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89th Annual Meeting Abstracts

An Investigation Of Efficiency Of AAV2-VEGF And AAV2-bFGF Gene Delivery To Enhance Strength Of Injured Tendons: An In Vivo Study
Wu Ya Fang, MD1, Chuan Hao Chen, MD1, Yi Cao, MD1, You Lang Zhou, MS1, Xiao Tian Wang, MD2, Paul Y. Liu, MD2, Jin Bo Tang, MD1.
1Affiliated Hospital of Nantong University, Nantong, China, 2Roger Williams Medical Center, Providence, RI, USA.

Delivery of growth factor genes into tissues may enhance healing strength. Intrasynovial tendons have low resident cell populations and low growth factor activities. We have used adeno-associated viral (AAV2) vector mediated bFGF or VEGF gene transfer to enhance the healing strength of cleanly lacerated tendon. In this study, we investigated the efficiency of these gene transfers in enhancing tendon healing strength and effects on adhesion formation around the tendons in a chicken laceration/repair model of intrasynovial tendons.
Sixty-four flexor digitorum profundus tendons of 32 chickens were divided into three groups: AAV2-bFGF injection group, AAV2-VEGF injection group, sham vector group, and non-injection control group. In the two experimental groups, AAV2-bFGF or AAV2-VEGF was injected into 4 sites of the tendon stump immediately after tendon transection. The tendon was subsequently repaired with a modified Kessler method. In the sham vector and non-injection control groups, the tendon was cut and repaired similarly, with injection of the AAV2-GFP, or without injection of vectors. Four and six weeks later, the tendons were harvested and were subjected to load-to-failure testing and work of digital flexion in an Instron tensiometer, and the tendon samples were analyzed for expression of transgene and extracellular matrix genes by real-time PCR.
At four weeks, compared with the non-injection control tendons, the tendons injected with AAV2-bFGF and AAV2-VEGF had a significantly greater tensile strength of 140% and 220% (p < 0.01, p < 0.001, respectively); the increase in the strength of the tendon injected with AAV2-VEGF was greater than that after AAV2-bFGF injection. At week six, the tendon strengths after injection of the AAV2-bFGF and the AAV2-VEGF were increased significantly compared with the control group, but no significant differences were found between tendons injected with two growth factor vectors. At week six, work of digital flexion was significantly greater in the AAV2-VEGF injected tendons, and adhesions in these tendons were also significantly more severe. No differences in the strength and work obtained in the sham vector and non-injection control groups. Since the transgene was of rat (bFGF) or the human (VEGF) origin, we could detect the presence of the xenogene in all tendon samples. Real-time PCR analysis showed increased expression of tissue inhibitor of metalloproteinase (TIMP) gene.
AAV2-bFGF and AAV2-VEGF can effectively improve the healing strength of the injured digital flexor tendon in an in vivo animal model. However, work of digital flexion was significantly increased in the toes injected with AAV2-VEGF compared with that injected with AAV2-bFGF. Morphologically, adhesion formations around the tendons were more severe in the AAV2-VEGF injected groups. TIMP may serve to decrease the activities of metalloproteinase and ensure accumulation of tendon collagen. We conclude that AAV2-bFGF may be more preferable for flexor tendon gene therapy to improve tendon healing strength, while not significantly increasing adhesion formation.


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