Neutralisation of TGF beta or binding of VLA-4 to fibronectin prevents rat tendon adhesion following transection.

Following tendon injury, severe loss of function often occurs either as a result of obliteration of the synovial canal with fibrous scar tissue or from rupture of the repaired tendon. The role of cell engineering in tendon repair is to promote strong and rapid healing of tendon whilst at the same time facilitating rapid reconstitution of the synovial canal. Modification of the immediate inflammatory response around healing tendon has been found to be of value. Experimentally this has been achieved by neutralisation of transforming growth factor-beta over the first 3 days following injury, or by blockade of inflammatory cell binding to the CS-1 locus on fibronectin with an anti-VLA-4 antibody, or with the synthetic VLA-4 inhibitor, CS-1 peptide, in a rat model of tendon transection. It is concluded from this pilot study that the treatments described hold promise in improving outcomes of the common clinical problem of tendon injury in man.

Expression of nitric oxide synthase and transforming growth factor-beta in crush-injured tendon and synovium.

This study examined the expression of inducible nitric oxide synthase (iNOS) and transforming growth factor-beta (TGF-beta) in macrophage infiltrates within crush-injured digital flexor tendon and synovium of control rats and rats treated with N(G)-nitro-1-arginine methyl ester (L-NAME) (5 mg/kg). Release of TGF-beta from organ cultures of tendon, muscle, and synovium, and the effects of L-NAME treatment (in vitro and in vivo), on adhesion of peritoneal macrophages to epitenon monolayers were also investigated. The results showed that during normal tendon healing the levels of TGF-beta are high at first and gradually decrease after 3 weeks of injury to slightly above control uninjured levels. However, when L-NAME was administered at the time of injury, the macrophage infiltrates were expressing high levels of TGF-beta even at 5 weeks after the injury, with no evidence of reduction. In the standard injury, iNOS activity was greatest at the acute phase of the inflammatory response and then gradually returned to normal. Treatment with L-NAME, however, resulted in inhibition of iNOS activity at 3 days and a reduction in the activity at the later time points examined after injury. We also found greatly increased levels of adhesion of peritoneal macrophages from L-NAME-treated rats to epitenon monolayers in vitro, which reflect a chronic imbalance in expression of TGF-beta, which is overexpressed, and nitric oxide, which is underexpressed. The results of the current study show that formation of nitric oxide is an important event in the course of tendon healing since its inhibition results in chronic inflammation and fibrosis due to an imbalance in TGF-beta expression in vivo.