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. 2001 Oct 23;98(22):12479-84.
doi: 10.1073/pnas.221471898. Epub 2001 Oct 16.

Water magnetic relaxation dispersion in biological systems: the contribution of proton exchange and implications for the noninvasive detection of cartilage degradation

U Duvvuri  1 , A D Goldberg, J K Kranz, L Hoang, R Reddy, F W Wehrli, A J Wand, S W Englander, J S Leigh
Affiliations

Water magnetic relaxation dispersion in biological systems: the contribution of proton exchange and implications for the noninvasive detection of cartilage degradation

U Duvvuri et al. Proc Natl Acad Sci U S A. .

Abstract

Magnetic relaxation has been used extensively to study and characterize biological tissues. In particular, spin-lattice relaxation in the rotating frame (T(1rho)) of water in protein solutions has been demonstrated to be sensitive to macromolecular weight and composition. However, the nature of the contribution from low frequency processes to water relaxation remains unclear. We have examined this problem by studying the water T(1rho) dispersion in peptide solutions ((14)N- and (15)N-labeled), glycosaminoglycan solutions, and samples of bovine articular cartilage before and after proteoglycan degradation. We find in model systems and tissue that hydrogen exchange from NH and OH groups to water dominates the low frequency water T(1rho) dispersion, in the context of the model used to interpret the relaxation data. Further, low frequency dispersion changes are correlated with loss of proteoglycan from the extra-cellular matrix of articular cartilage. This finding has significance for the noninvasive detection of matrix degradation.

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Figures

Figure 1
Figure 1
Dependence of water R1ρ dispersion on peptide concentration. The dispersion of the buffer (▴), attributed to natural abundance H217O effects, increases in 0.9 mM 14N-peptide solution (■) and 1.6 mM 14N-peptide solution (⧫). The dispersion of the 1.6 mM 15N-peptide solution (●) is only 10% less than that of 1.6 mM 14N-peptide solution, indicating that 14N relaxation is not the dominant mechanism modulating the interaction between NH and water protons.
Figure 2
Figure 2
Dependence of water R1ρ dispersion on CS concentration. (A) The dispersion of the buffer (▴) is less than that of 2 (⧫), 5 (●), and 10% (■) solutions of CS. The correlation time of these dispersion plots is in agreement with literature values for hydroxyl exchange times, under similar conditions. B shows the dependence of R1ρ with CS concentration at various spin-lock amplitudes: 314 rad/s (●), 930 rad/s (■), 4,650 rad/s (▴), and 1.1 × 104 rad/s (⧫).
Figure 3
Figure 3
Dependence of water R1ρ relaxation and dispersion in articular cartilage on PG loss. This figure shows the water dispersion profile of a representative sample of cartilage before (●), after 28% PG depletion (■), and after 60% PG depletion (▴). The error bar of measurement is about 0.5%. Solid lines represent fits to a bi-Lorentzian function. The low frequency dispersion is attributed to proton exchange from NH and OH groups, whereas the high frequency dispersion is the result of the exchange of entire water molecules (see text).
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