Burstein D, Gray M L, Hartman A L, Gipe R, Foy B D
Department of Radiology, Charles A. Dana Research Institute, Beth Israel Hospital, Boston, MA 02215.
J Orthop Res. 1993 Jul;11(4):465-78. doi: 10.1002/jor.1100110402.
The ability of water and solutes to move through the cartilage matrix is important to the normal function of cartilage and is presumed to be altered in degenerative diseases of cartilage such as osteoarthritis and rheumatoid arthritis. Nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) techniques were used to measure a self diffusion coefficient (D) for small solutes in samples of explanted cartilage for diffusion times ranging from 13 ms to 2 s. With a diffusion time of 13 ms, the intratissue diffusivity of several small solutes (water, Na+, Li+, and CF3CO2-) was found consistently to be about 60% of the diffusivity of the same species in free solution. Equilibration of the samples at low pH (which titrates the charge groups so that the net matrix charge of -300 mM at pH 8 becomes approximately -50 mM at pH 2) did not affect the diffusivity of water or Na+. These data, and the similarity between the D in cartilage relative to free solution for water, anions, and cations, are consistent with the view that charge is not an important determinant of the intratissue diffusivity of small solutes in cartilage. With 35% compression, the diffusivity of water and Li+ dropped by 19 and 39%, respectively. In contrast, the diffusivity of water increased by 20% after treatment with trypsin (to remove the proteoglycans and noncollagenous proteins). These data and the lack of an effect of charge on diffusivity are consistent with D being dependent on the composition and density of the solid tissue matrix. A series of diffusion-weighted proton images demonstrated that D could be measured on a localized basis and that changes in D associated with an enzymatically depleted matrix could be clearly observed. Finally, evidence of restriction to diffusion within the tissue was found with studies in which D was measured as a function of diffusion time. The measured D for water in cartilage decreased with diffusion times ranging from 25 ms to 2 s, at which point the measured D was roughly 40% of the diffusivity in free solution. Although changes in matrix density by compression or digestion with trypsin led to a decrease or increase, respectively, in the measured D, the functional change in measured diffusivity with diffusion time remained essentially unchanged. In a different type of study, in which bulk transport could be observed over long periods of time, cartilage was submerged in 99% D2O and MRI studies were performed to demonstrate the bulk movement of water out of the cartilage matrix.(ABSTRACT TRUNCATED AT 400 WORDS)
水和溶质在软骨基质中移动的能力对软骨的正常功能很重要，并且据推测在诸如骨关节炎和类风湿性关节炎等软骨退行性疾病中会发生改变。核磁共振（NMR）光谱和磁共振成像（MRI）技术被用于测量外植软骨样品中小溶质在13毫秒至2秒的扩散时间范围内的自扩散系数（D）。在扩散时间为13毫秒时，发现几种小溶质（水、Na⁺、Li⁺和CF₃CO₂⁻）在组织内的扩散率始终约为其在自由溶液中扩散率的60%。在低pH值下使样品平衡（这会滴定电荷基团，使得pH值为8时净基质电荷为 -300 mM在pH值为2时变为约 -50 mM）不会影响水或Na⁺的扩散率。这些数据，以及软骨中相对于自由溶液的水、阴离子和阳离子的D值之间的相似性，与电荷不是软骨中小溶质组织内扩散率的重要决定因素这一观点一致。在35%压缩下，水和Li⁺的扩散率分别下降了19%和39%。相比之下，用胰蛋白酶处理（以去除蛋白聚糖和非胶原蛋白）后水的扩散率增加了20%。这些数据以及电荷对扩散率缺乏影响与D值取决于固体组织基质的组成和密度一致。一系列扩散加权质子图像表明，可以在局部基础上测量D值，并且可以清楚地观察到与酶促耗尽的基质相关的D值变化。最后，通过将D值作为扩散时间的函数进行测量的研究发现了组织内扩散受限的证据。在软骨中测量的水的D值随着扩散时间从25毫秒到2秒而降低，此时测量的D值约为自由溶液中扩散率的40%。尽管通过压缩或用胰蛋白酶消化导致的基质密度变化分别导致测量的D值降低或增加，但测量的扩散率随扩散时间的功能变化基本保持不变。在另一项不同类型的研究中，其中可以长时间观察到大量运输，将软骨浸入99% D₂O中并进行MRI研究以证明水从软骨基质中的大量移动。（摘要截断于400字）
