Magnetic Resonance Studies Of Cells, Organs And Animals

用于软骨细胞磁共振微成像和光谱学的生物反应器系统以及继发于创伤性损伤或退行性关节疾病的关节软骨的组织修复是一项重要的治疗挑战。尽管在了解这种高度流行疾病的发病机制方面取得了重大进展，但还没有得到广泛接受的疾病改善干预措施。开发一种灵活可靠的mri兼容软骨中空纤维生物反应器（HFBR）系统，用于新软骨生长，有可能为治疗方法做出贡献。首先，在这样一个系统中，可以深入研究促进细胞发育高质量软骨的条件，它可以完全控制发育中的新软骨暴露于生长因子、底物组成、溶解O2和CO2浓度、温度和其他环境因素。虽然从细胞（包括软骨细胞和潜在的骨髓基质细胞）在生物体中的原位软骨发育与生物反应器条件在重要方面有所不同，但体外研究将能够指出从细胞中发育功能新软骨的适当条件。其次，高质量软骨在生物反应器中的生长可能会成为实际移植的组织来源。最后，最普遍的是，不管最终软骨修复和再生过程的具体情况如何，监测组织质量的能力将是非常重要的。虽然关节镜活检提供了这样的数据，允许评估组织的生化和组织学状态，但显然更需要使用非侵入性评估方法。MRI作为一种测量软骨厚度和体积以及局部病理的无创工具越来越被人们所接受，而MRI无创评估软骨质量的能力目前是一个活跃的研究课题。在一个允许详细MRI评估的系统中产生具有广泛不同性质的软骨的高度可控系统的可用性将代表这一努力的明显进步。最后，我们注意到mri兼容的生物反应器为当前和未来的治疗药物和干预措施提供了一个灵活的试验台。总之，作为一种细胞系统，HFBR与其他3D培养系统具有支持透明软骨类型的能力。因此，我们可以评估生长条件和治疗方法对透明软骨组织而不是纤维软骨组织的影响。作为一个组织系统，HFBR允许真正的宏观生长。因此，细胞-基质相互作用和基质屏障对底物输送和代谢产物外排的影响比单层系统更真实。最后，作为生长条件和药剂的试验台，HFBR可以完全控制底物和灌注条件。

A Bioreactor System for Magnetic Resonance Microimaging and Spectroscopy of Chondrocytes and Tissue Repair of articular cartilage secondary to either traumatic injury or degenerative joint disease represents an important therapeutic challenge. In spite of significant progress in understanding the pathogenesis of this highly prevalent disease, there are no well-accepted disease-modifying interventions. The development of a flexible and reliable MRI-compatible cartilage hollow fiber bioreactor (HFBR) system for neocartilage growth has the potential to contribute to therapeutic approaches. First, conditions promoting the development of high-quality cartilage from cells can be studied intensively in such a system, which provides full control over exposure of the developing neocartilage to growth factors, substrate composition, dissolved O2 and CO2 concentrations, temperature, and other environmental factors. While in situ development of cartilage from cells, including both chondrocytes and, potentially, bone marrow stromal cells, in an organism will differ in important ways from the bioreactor conditions, in vitro studies will be able to point the way to appropriate conditions for development of functioning neocartilage from cells. Second, growth of high-quality cartilage in the bioreactor may result in a source of tissue for actual transplantation. Finally, and most generally, regardless of the specifics of eventual cartilage repair and regeneration procedures, the ability to monitor tissue quality will be of clear importance. While arthroscopic biopsies provide such data, permitting assessment of the biochemical and histologic state of the tissue, it is clearly more desirable to utilize noninvasive assessment methods. MRI is becoming increasingly accepted as a noninvasive tool for the measurement of cartilage thickness and volume and of localized pathology while the ability of MRI to noninvasively assess cartilage quality is currently a topic of active research. The availability of a highly controllable system for generating cartilage with widely varying properties in a system permitting detailed MRI assessment would represent a clear advance in this effort. Finally, we note that the MRI-compatible bioreactor provides a flexible test-bed for current and future therapeutic agents and interventions. In summary, as a cellular system, the HFBR shares with other 3D culture systems the ability to support the hyaline cartilage type. Thus, one can evaluate the effect of growth conditions and therapeutics on hyaline cartilage tissue rather than fibrocartilage. As a tissue system, the HFBR permits true macroscopic growth. Thus, cell-matrix interactions and the effects of the matrix barrier to substrate delivery and metabolic product efflux are represented much more realistically than in monolayer systems. Finally, as a test bed for growth conditions and agents, the HFBR provides full control of substrate and perfusion conditions. We have successfully demonstrated that cartilage grown from chick sternal cells in the HFBR will develop and maintain the hyaline phenotype; that morphologic measurements with MRI correlate with tissue histology; and that MRI measurements of local T1, T2, diffusion and MT correlate with biochemical assays of collagen, proteoglycans and hydration. Thus, noninvasive MRI measures provide reliable information about cartilage matrix composition. We have further demonstrated that cartilage growth in the HFBR can be modified by introduction of biologically active compounds, and that the correlations between MRI-derived parameters and biochemical results noted above are maintained in spite of the greater dynamic range of tissue characteristics resulting from these interventions. We have also utilized 31P NMR measurements of pH, inorganic phosphate (Pi) and ATP to demonstrate that the developing cartilage in the bioreactor remains metabolically stable over the typical 4 week growth period. A major focus of our work has, in addition, been to demonstrate that MRI measurements of matrix fixed density correlate with measurements of dynamic and equilibrium compressive moduli. The MRI-derived FCD values correlate with S-GAG content but not with collagen content. These correlations were found to persist even in tissue which has undergone development in the presence of chondroitinase, acting as a catabolic agent on matrix proteoglycans. Noninvasive MRI evaluation of FCD therefore has been shown to provide reliable information about cartilage matrix composition under the dynamic conditions of the HFBR in both control tissue and in tissue which has undergone degeneration analogous to that seen in osteoarthritis.