F.L. Harwood

Controlled-Release Kinetics and Biologic Activity of Platelet-Derived Growth Factor-BB for Use in Flexor Tendon Repair

PURPOSE Surgically repaired intrasynovial tendons are at greatest risk of failure in the first 3 weeks after surgery. Attempts to improve the strength of repair by modifying rehabilitation parameters have not always been successful. Manipulation of the biological environment of the sutured tendon holds great promise for accelerating the repair process. The goals of this study were to examine (1) the range of conditions (eg, dosage, delivery system formulation, presence of cells) over which delivery of platelet-derived growth factor-BB (PDGF-BB) can be sustained from fibrin matrices using a heparin-binding delivery system (HBDS) and (2) the biological activity of the PDGF-BB released from this system on canine tendon fibroblasts in vitro. METHODS We examined in vitro release kinetics from cellular and acellular fibrin matrices using enzyme-linked immunosorbent assays. We examined the biologic activity of the PDGF-BB in vitro by measuring cell proliferation (ie, total DNA) and collagen synthesis (ie, proline incorporation). RESULTS The acellular release kinetics of PDGF-BB was modulated by varying the ratio of PDGF-BB to heparin (PDGF-binding sites) or the dose of PDGF-BB in the presence of the delivery system. In the presence of canine tendon fibroblasts, the delivery system prolonged the duration of PDGF-BB release from fibrin matrices, thus demonstrating that cells are able to liberate PDGF-BB retained by the HBDS. Sustained delivery of PDGF-BB promoted increased cell proliferation at doses of 0.125 microg/mL and 1.25 microg/mL compared to fibrin without delivery system. Collagen synthesis was enhanced by PDGF-BB at doses of 0.125 microg/mL and 1.25 microg/mL; however, there was an enhancement over fibrin without the delivery system only at the lower dose. CONCLUSIONS These results demonstrate that the PDGF-BB released from fibrin matrices containing an HBDS is biologically active and can modulate both cell proliferation and extracellular matrix synthesis, both of which are key factors in the process of tendon repair.

Chondrocyte apoptosis and regional differential expression of nitric oxide in the medial meniscus following partial meniscectomy

Partial medial meniscectomy leads to tibial articular cartilage degeneration. Nitric oxide (NO) production increases with the development of osteoarthritis (OA) and has been shown to have a catabolic effect on chondrocytes. Since distribution of chondrocytic and fibroblastic cell types within the total cell population comprising meniscus is region‐specific, we compared NO production in the peripheral and central regions of the medial meniscus 12 weeks after partial medial meniscectomy and assessed chondrocyte apoptosis and NO production in the tibial articular cartilage. Additionally, transcriptional gene expression of inducible nitric oxide synthetase (iNOS) and immunohistochemical staining of nitrotyrosine were examined. The results showed that following partial medial meniscectomy, NO production in the central region of the medial meniscus and in the tibial articular cartilage were significantly higher than respective NO levels in normal and sham‐operated controls. Reverse transcription polymerase chain reaction (RT‐PCR) revealed a high transcriptional expression of the iNOS gene in the central region of the meniscus and in tibial articular cartilage following partial medial meniscectomy. Nitrotyrosine immunoreactivity was prominent in the central region of the medial meniscus and in the deep layer of the tibial articular cartilage and apoptotic cells were also detected in situ in the superficial zone of the tibial articular cartilage and central regions of the medial meniscus following partial medial meniscectomy. These observations suggest that the central region of the meniscus is responsible for NO synthesis associated with apoptosis in both meniscal and articular cartilage cells following partial meniscectomy.

Quantitative Assessment by Competitive ELISA of Fibronectin (Fn) in Tendons and Ligaments

A method utilizing the enzyme-linked immunosorbent assay (ELISA) is presented for quantitating fibronectin in periarticular soft tissues from rabbits. The concentrations of fibronectin were determined in the medial collateral ligament, anterior cruciate ligament, posterior cruciate ligament, and patellar tendon. The anterior cruciate and posterior cruciate ligaments, surrounded by a synovial sheath, had similar amounts of fibronectin that were each over twice as high as that found in either medial collateral ligament or patellar tendon which have no sheath covering.