Degradation of elastic fiber and elevated elastase expression in long head of biceps tendinopathy

Tendinopathy of the long head of the biceps (TLHB) involves various types of extracellular matrix degeneration, but previous studies have not evaluated elastic fibers. The purpose of this study was to investigate elastic fiber distribution in long head of the biceps (LHB). The TLHB tendons of 16 consecutive patients (eight men and eight women; average age of 55.75 years; age range of 40-71 years) were transected and harvested. Three cadaveric LHB tendons were used as the control group. The expression of collagen type I was decreased, but type III was increased in TLHB. Disruption of elastic fibers was particularly observed in grade II specimens where the level of elastase-positive staining was significantly higher than in grade I specimens. Elastic fibers were not observed in the grade III area, implying a higher expression of elastase than in the grade I area. Results of Western blotting showed that the expression of elastin was higher in the control group and the levels of elastin significantly decreased in grades II and III of TLHB. Levels of osteopontin and elastase were increased in primary culture of human tenocytes after experiencing elastic derived peptide treatment. These results suggested that elastase may be caused by the disruption of elastic fibers in the development of chronic tendinopathy and that elastic derived peptide may enhance elastase and osteopontin expression. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1919-1926, 2017.