Detection of glycosaminoglycan loss in articular cartilage by fluorescence lifetime imaging

Abstract

Glycosaminoglycan (GAG) loss is an early marker of osteoarthritis, which is a clinical late stage disease that affects millions of people worldwide. The goal of our study was to evaluate the ability of a fiber-based fluorescence lifetime imaging (FLIm) technique to detect GAG loss in articular cartilage. Native bovine cartilage explants (n ¼ 20) were exposed to 0 (control), 0.5 (low), or 1 U∕mL (high) concentrations of chondroitinase ABC (cABC) to create samples with different levels of GAG loss. FLIm assessment (excitation: 355 nm; detection: channel 1: 375 to 410 nm, channel 2: 450 to 485 nm, channel 3: 530 to 565 nm) was conducted on depthresolved cross-sections of the cartilage sample. FLIm images, validated with histology, revealed that loss of GAG resulted in a decrease of fluorescence lifetime values in channel 2 (Δ ¼ 0.44 ns, p < 0.05) and channel 3 (Δ ¼ 0.75 ns, p < 0.01) compared to control samples (channel 2: 6.34 ns; channel 3: 5.22 ns). Fluorescence intensity ratio values were lower in channel 1 (37%, p < 0.0001) and channel 2 (31% decrease, p < 0.0001) and higher in channel 3 (23%, p < 0.0001) relative to control samples. These results show that FLIm can detect the loss of GAG in articular cartilage and support further investigation into the feasibility of in vivo FLIm arthroscopy.

Autofluorescence Lifetime Reports Cartilage Damage in Osteoarthritis

“…Inducing proteolytic damage in cartilage tissue resulted in significant decrease in AFL in murine, porcine and human joints. These measurements confirmed previous observations 15,24 , demonstrating that AFL is sensitive to biochemical alterations in the cartilage ECM caused by disruption of collagen crosslinks or aggrecan depletion from tissue. In particular, we observed a decrease in the AFL of fresh human metatarsophalangeal articular cartilage treated with RA.…”

“…We have previously reported that AFL can report proteolytic damage of ex vivo cartilage tissue that includes aggrecan degradation in porcine cartilage pieces 15 . Similar work by others demonstrated that AFL can report glycosaminoglycan (GAG) depletion in bovine articular cartilage 24 . In this study, we investigated the potential of AFL to report areas of proteolytically damaged human cartilage.…”

Non‐destructive detection of matrix stabilization correlates with enhanced mechanical properties of self‐assembled articular cartilage

“…In contrast, native cartilage has a large depth‐dependent variation in biochemical composition. When we subjected native tissue to enzymatic treatments to deplete matrix content, we found lower than expected differences in fluorescence signal in cartilage imaged perpendicular to the tissue surface as compared with cartilage imaged in cross section (Zhou et al, ).…”

Real‐time fiber‐based fluorescence lifetime imaging with synchronous external illumination: A new path for clinical translation

“…To illustrate the potential to report intrinsic contrast in a clinically relevant application, porcine articular cartilage samples were mapped before and after localized treatment with bacterial collagenase (see Figures , S10‐S14 and Video S4) to promote cleavage of collagen type II fibrils and depletion of proteoglycan content, which are known to affect the fluorescence lifetime of cartilage . Before treatment (see Figure A,C,E), we measured an average lifetime of 6.89 ± 0.45 ns over the entire sample, for a total acquisition time of 30.8 seconds (n = 1528 measurements, resulting in an average TCSPC rate of 49.6 Hz).…”