Low-field and variable-field NMR relaxation studies of H(2)O and D(2)O molecular dynamics in articular cartilage

Osteoarthritis (OA) as the main degenerative disease of articular cartilage in joints is accompanied by structural and compositional changes in the tissue. Degeneration is a consequence of a reduction of the amount of macromolecules, the so-called proteoglycans, and of a corresponding increase in water content, both leading to structural weakening of cartilage. NMR investigations of cartilage generally address only the relaxation properties of water. In this study, two-dimensional (T(1)-T(2)) measurements of bovine articular cartilage samples were carried out for different stages of hydration, complemented by molecular exchange with D(2)O and treatment by trypsin which simulates degeneration by OA. Two signal components were identified in all measurements, characterized by very different T(2) which suggests liquid-like and solid-like dynamics. These measurements allow the quantification of separate hydrogen components and their assignment to defined physical pools which had been discussed repeatedly in the literature, i.e. bulk-like water and a combination of protein hydrogens and strongly bound water. The first determination of (2)H relaxation dispersion in comparison to (1)H dispersion suggests intramolecular interactions as the dominating source for the pronounced magnetic field dependence of the longitudinal relaxation time T(1).