Changes in endogenous UV fluorescence and biomechanical stiffness of bovine articular cartilage after collagenase digestion are strongly correlated.

A significant source of morbidity in the elderly population of the United States is osteoarthritis (OA), a disease caused by the breakdown and loss of articular cartilage. The exact causes of OA remain unknown, though biomechanical forces and biochemical alterations are important factors. There exists an unmet need for an imaging tool to identify early lesions of OA via metabolic, chemical or structural changes. Our work aims to characterize changes in the intensity of UV fluorescent bands associated with known structural proteins of cartilage. We employed an OA model in which bovine osteochondral plugs were digested in collagenase of varying concentrations. UV fluorescence before and after proteolytic digestion was measured using a spectrofluorimeter. The elastic modulus (EM) of each sample was measured using an indentation apparatus. Hydroxypyridinoline crosslink (330/390 nm) fluorescence intensity after digestion correlated with cartilage EM (R = 0.922, p = 0.026), as did tryptophan (290/350 nm) fluorescence intensity after digestion and EM (R = 0.949, p = 0.014) and tyrosine (290/310 nm) fluorescence intensity after digestion and EM (R = 0.946, p = 0.015). Loss of endogenous UV fluorescence correlated with cartilage degradation in an in-vitro model of OA, and may serve as a sensitive optical biomarker for the state of cartilage.