MAGNETIZATION-TRANSFER IN CARTILAGE AND ITS CONSTITUENT MACROMOLECULES

The goal of this work was to investigate magnetization transfer (MT) in cartilage by measuring water proton signals M(s)/M(o), as an indicator of MT, in (i) single-component systems of the tissue's constituent macromolecules and (ii) intact cartilage under control conditions and after two pathomimetic interventions, M(s)/M(o) was quantified with a 12-mu T saturation pulse applied 6 kHz off resonance, Both glycosaminoglycans (GAG) and collagen exhibited concentration dependent effects on M(s)/M(o), being approximately linear for GAG solutions (M(s)/M(o) = -0.0137[% GAG] + 1.02) and exponential for collagen suspensions (M(s)/M(o) = 0.80 x exp[-(%collagen)/6.66] + 0.20); the direct saturation of water could not account for the measured M(s)/M(o). Although the effect of collagen on M(s)/M(o) is much stronger than for a corresponding concentration of GAG, M(s)/M(o) is not very sensitive to changes in collagen concentration in the physiological range, Tissue degradation with 25 mg/ml trypsin led to an increase inM(s)/M(o) from the baseline value of 0.2 (final/initial values = 1.15 +/- 0.13, n = 11, P < 0.001), In contrast, a 10-day treatment of cartilage with 100 ng/ml of interieukin-1 beta (IL-1 beta) caused a 19% decrease in M(s)/M(o) (final/initial values = 0.81 +/- 0.08, n = 3, P = 0.085), The changes in hydration and macromolecular content for the two treatments were comparable, suggesting that M(s)/M(o) is sensitive to macromolecular structure as well as concentration, In conclusion, whereas the baseline M(s)/M(o) value in cartilage may be primarily due to the tissue collagen concentration, changes in M(s)/M(o) may be due to physiological or pathophysiological changes in GAG concentration and tissue structure, and the measured M(s)/M(o) may differentiate between various pathomimetic degradative procedures.