Objective Colorimetric Evaluation of Aging-related Articular Cartilage Degeneration

Aging is a primary risk factor for the development of osteoarthritis (OA). Recently, advanced glycation end products (AGEs) have received much attention in relation to aging and OA. Some AGEs are reported to be brownish, but the association between AGE levels and browning in articular cartilage is unknown. The purposes of this study were first, to develop a colorimetric device to evaluate the quality and aging of the articular cartilage, and second, to investigate the relationship between AGE levels and color of articular cartilage by using this device without enzymatic digestion of the articular surface.

Open-label, single-center, prospective study Methods: Seven patients with OA (1 man, 6 women; mean age, 74.4 years; age range 58-81 years) who underwent primary total knee arthroplasty at our university hospital between July and December 2014 were enrolled in the study. Articular cartilage was harvested from the femur and tibia during surgery. The color and chromaticity of the articular cartilage was assayed by using a newly developed device with high validity. The characteristics of the articular cartilage were examined using the CIE XYZ Color Coordinate System (International Commission on Illumination, Vienna, Austria), and the color indicative of browning of the cartilage was defined on the X- and Y-axes. The brightness was adjusted and the specimen was photographed submerged in distilled water and the color was measured using a commercial luminance and color analyzer. Measurement of X and Y was repeated 3 times per site at 9 different points on the articular cartilage surface, and the mean value per specimen was calculated. Pentosidine (a well characterized biomarker of AGEs) levels and hydroxyproline content in articular cartilage were determined by high-performance liquid chromatography (HPLC). The correlation between age, articular cartilage AGE levels, and browning was analyzed using Spearman's rank correlation coefficient. The association between the degree of macroscopic degeneration and AGE levels was analyzed using one-way analysis of variance.

Age was positively correlated with pentosidine levels in articular cartilage (r_s=0.322) and browning of articular cartilage (r_s=0.261). However, a weak negative correlation was observed between pentosidine levels and browning of articular cartilage (r_s=-0.564, p=0.004). No positive relationship was observed between pentosidine levels and browning of articular cartilage in the visible spectrum.

This study developed an original colorimetric device with high validity. Browning of articular cartilage increased with age, but this study did not detect pentosidine-caused browning. Further study is needed to clarify the factors associated with browning of cartilage.