Spatial Raman Spectroscopy to Characterize (Sulfated) Glycosaminoglycans in Human Articular Cartilage

Raman spectroscopy allows for analyzing local molecular matrix components while preserving spatial resolution in tissue samples. The aim of this study was to use Raman line scans to discriminate between healthy and diseased cartilage tissue based on the depth-dependent sulfated glycosaminoglycans (sGAG) and total GAGs distribution. Full-thickness articular cartilage tissue was harvested from human individuals at different maturation stages (skeletally immature, skeletally mature) and from patients with diagnosed osteoarthritis. Raman spectroscopic line scans (30 µm step size) were utilized to analyze the sub-zonal sGAG (1062 cm^-1) and total GAG (1370-1380 cm^-1) distribution relative to the organic matrix (CH₂ band 1430-1480 cm^-1). We found a linear trend of the sGAG/CH₂ ratio over the tissue depth in all samples (p < 0.0001). The total GAG/CH₂ ratio of the skeletally immature and mature cartilage showed a characteristic non-linear behavior over the tissue distance. The elderly osteoarthritic cartilage exhibited lower total GAG/CH₂ ratios compared to the ratios of the skeletally immature and mature samples, without a pronounced increase in the superficial area. Raman spectroscopic line scans are a fast and representative method allowing us to identify the local and tissue depth-dependent distribution of GAGs at higher specificity and resolution compared to histological staining.