Abstract
Introduction: The pathogenesis of chronic tendinopathy is unclear. A role for increased apoptosis of tenocytes has been suggested. Nitric oxide is thought to be a mediator of apoptosis and nitric oxide synthase (NOS) isoforms have been shown to be up regulated in rotator cuff tendons as a result of chronic overuse. We found, the same up regulation of NOS in the Achilles tendon in non-insertional Achilles tendinopathy in a previous study.
The purpose of this study was to investigate whether apoptotic cells were present in these tissues with raised endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS) levels.
Methods: Consent was obtained preoperatively from all patients and the research and ethics committee granted ethical approval. Samples were obtained from the Achilles Tendons of patients with non-insertional Achilles tendinopathy who had failed conservative treatment for at least six months and were undergoing a surgical procedure. Several biopsies were taken of the visibly abnormal tendon tissue. Control samples were taken from macroscopically normal tendon correlating with areas of normal tissue on MRI. Standard immunohistochemical techniques were used to identify the expression of eNOS and iNOS. Apoptotic cells were identified using terminal deoxynucleotidyl transferase-mediated dUTP neck end labelling (TUNEL reaction) with TdT-FragEL and the demonstration of Caspase-3 activation.
Results: Significant differences were found between the diseased tendon and the controls for all of the parameters measured. The mean Caspase-3 cell count for diseased tendon was 51.9 compared to 28.3 for the controls (p=0.000001). The mean TUNEL cell count for diseased tendon was 24.1 compared to 14.8 (p=0.00014). iNOS densitometry revealed a mean of 26.1 for the diseased tissue verses 15.0 for the controls (p=0.000009) and the values for eNOS were 48.3 and 23.7 respectively (p=0.015).
Conclusions: Apoptosis clearly plays a role in the development of non-insertional Achilles tendinopathy and appears to be related to the presence of raised eNOS and iNOS levels. It is possible that, by blocking the apoptotic pathway, the tendinopathic process could be halted. This may lead to the development of treatments strategies for early Achilles tendinopathy.
Correspondence should be addressed to A.H.N. Robinson, BOX 37, Department of Orthopaedics, Addenbrooke’s Hospital, Cambridge University Hospitals NHS Trust, Hills Road, Cambridge. CB2 0QQ, England.
