HISTOCHEMICAL ANALYSIS OF GAGS IN ALTERED TENDON: A MEANS TO EVALUATE THE DEGREE OF PATHOLOGY

IntroductionThe social and economic consequences of injured tendons have long been recognised. In particular, patellar tendinopathy is often recalcitrant to standard treatment, highlighting the need for prevention and therapeutic strategies that aim at minimising tissue alteration and protecting tendon structure and function. This relies on a pertinent diagnostic of the degree of pathology. A means to correlate anatomical and biochemical properties of injured tendon to the extent of the pathology is thus important to acquire. Sulfated glycosaminoglycans (GAGs), along with the proteoglycan aggrecan, are known to increase with tendon pathology, indicating a shift of tenocytes towards a chondroïd phenotype. It could be postulated that the amount of GAGs correlates with the degree of pathology of patellar tendon assessed by the VISA Score.MethodsAnalysis of total and specific GAGs using a DiMethyl Methylene Blue histochemical technique and immuno-histological technique with antibodies against Dermatan Sulfate, Chondroitin Sulfate, Heparan Sulfate and proteoglycans (PG) (decorin, versican and aggrecan) respectively were performed on normal and pathological tendon sections from rat supraspinatus and human patellar tendons.ResultsAs observed in rat overused supraspinatus tendon, total GAGs as well as Dermatan and Chondroitin sulfate were increased in human pathological patellar tendon. Correlatively, PGs such as decorin, and above all versican and aggrecan were also enhanced. Amounts of GAGs and aggrecan found in tendons changed with the Visa score of patellar tendons. A correlation was established between VISA score and the amount of GAGs. This correlation allowed us to verify the correct sampling of patient tendons and was predictive for the extent of pathology of unclassified tendon samples.ConclusionThis study underscores the importance of excessive GAGs in relation to tendon pain and function. Accurate GAG assessment would represent a help in establishing a reliable diagnostic of patellar tendinopathy as a complement of the Visa score. This knowledge may be useful in stimulating the development of more sensitive imaging modalities capable of detecting early changes in the composition of tendon extracellular matrix.