NMR Studies of Cartilage – Dynamics, Diffusion, Degradation

Abstract

An increasing number of people is suffering from rheumatic diseases, and, therefore, methods of early diagnosis of joint degeneration are urgently required. For their establishment, however, an improved knowledge about the molecular organisation of cartilage would be helpful. Cartilage consists of three main components: Water, collagen and chondroitin sulfate (CS) that is (together with further polysaccharides and proteins) a major constituent of the proteoglycans of cartilage.

¹H and ¹³C MAS (magic-angle spinning) NMR (nuclear magnetic resonance) opened new perspectives for the study of the macromolecular components in cartilage. We have primarily studied the mobilities of CS and collagen in bovine nasal and pig articular cartilage (that differ significantly in their collagen/polysaccharide content) by measuring ¹³C NMR relaxation times as well as the corresponding ¹³C CP (cross polarisation) MAS NMR spectra. These data clearly indicate that the mobility of cartilage macromolecules is broadly distributed from almost completely rigid (collagen) to highly mobile (polysaccharides), which lends cartilage its mechanical strength and shock-absorbing properties.

Additionally, the diffusion behaviour of ions and polymers in cartilage was also studied by PFG (pulsed-field gradient) NMR to clarify the influence of charges and a varying molecular weight of the diffusing species: Only at longer observation times, however, structural parameters of cartilage play a significant role, whereas at shorter observation times, the water content has the most tremendous impact on diffusion, equally what kind of molecule is observed.

Finally, it will also be shown that both - NMR spectroscopy in solution as well as in the solid state - are very promising tools to investigate the molecular pathways of cartilage degradation in rheumatic diseases.