In one specific project, we sought to assess the reliability in measurement of evolving sulfated glycosaminoglycan (GAG) content in a clinically applicable tissue engineered cartilage system using magnetic resonance imaging (MRI). Samples of the hydrogel, poly(ethylene oxide) diacrylate (PEODA) were used to encapsulate bovine chondrocytes ( 2.4 million cells/ sample). The fixed charge density (FCD) of the developing cartilage was determined using the MRI gadolinium exclusion method. MRI experiments were performed on samples following 9, 16, 29, 36, 43 and 50 days of incubation. Samples from these timepoints were subsequently analyzed via biochemical procedures in order to correlate the MRI-derived FCD measurements with the true GAG content in the tissue. Histological sections of the samples were also processed to reveal temporal differences in the GAG concentration. We found a strong correlation (R2 = 0.85) between FCD and GAG content was determined up to 36 days. However, when extended to 50 days, the correlation decreased significantly (R2 = 0.54). From this, we conclude that FCD of chondrocyte-encapsulated hydrogel constructs correlate well with true GAG content during the first 36 days of incubation. This study demonstrates that MRI-derived FCD measurements can be reliably interpreted in the early stage evaluation ( 5 weeks) of injectable cartilage tissue engineering systems. In further work, we sought to define the distribution of cells within tissue engineered constructs. This is difficult to study through non-destructive means, such as would be required after implantation. However, cell labeling with iron-containing particles may prove to be a useful approach to this problem, since regions of such labeled cells have been shown to be readily detectable using magnetic resonance imaging. In this study, we used the FDA-approved superparamagnetic iron oxide (SPIO) agent, Feridex, in combination with transfection agents to label and visualize with MRI chondrocytes in two different tissue engineered constructs. Correspondence between labeled cell location as determined by MRI and by histology was established. The phenotype, viability and production of major cartilage matrix constituents were found to be unaffected by the SPIO-labeling process. We believe that this method of visualizing and tracking chondrocytes may be useful in the further development of cartilage tissue engineering therapeutics. Lastly, MR is an excellent modality for detailed metabolic investigations in human subject. We were interested in the link between body weight, lipid metabolism, and health risks. This is poorly understood and difficult to study. Magnetic resonance spectroscopy (MRS) permits non-invasive investigation of lipid metabolism. We extended existing two-dimensional MRS techniques to permit quantification of intramyocellular (IMCL) and extramyocellular (EMCL) lipid compartments and their degree of unsaturation in human subjects, and correlated these results with BMI. Using muscle creatine (Cr) for normalization, a statistically significant (p <0.01) increase in IMCL/Cr with BMI (n=8 subjects per group) was observed, with values of 5.9 1.7 (BMI <25), 10.9 1.82 (25 30). Similarly, the degree of IMCL unsaturation decreased significantly (p <0.01) with BMI, with respective values of 1.51 0.08, 1.30 0.11, and 0.90 0.14. We conclude that important aspects of lipid metabolism can be evaluated with 2-dimensional MRS and propose that degree of unsaturation measured noninvasively may serve as a biomarker for lipid metabolic defects associated with obesity.

National Institute of Health (NIH)
National Institute on Aging (NIA)
Investigator-Initiated Intramural Research Projects (ZIA)
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National Institute on Aging
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Cameron, Donnie; Bouhrara, Mustapha; Reiter, David A et al. (2017) The effect of noise and lipid signals on determination of Gaussian and non-Gaussian diffusion parameters in skeletal muscle. NMR Biomed :
Reiter, David A; Magin, Richard L; Li, Weiguo et al. (2016) Anomalous T2 relaxation in normal and degraded cartilage. Magn Reson Med 76:953-62
Makrogiannis, S; Fishbein, K W; Moore, A Z et al. (2016) Image-Based Tissue Distribution Modeling for Skeletal Muscle Quality Characterization. IEEE Trans Biomed Eng 63:805-13
Bouhrara, Mustapha; Spencer, Richard G (2015) Incorporation of nonzero echo times in the SPGR and bSSFP signal models used in mcDESPOT. Magn Reson Med 74:1227-35
Celik, Hasan; Bouhrara, Mustapha; Reiter, David A et al. (2013) Stabilization of the inverse Laplace transform of multiexponential decay through introduction of a second dimension. J Magn Reson 236:134-9
Spencer, Richard G; Pleshko, Nancy (2013) How do statistical differences in matrix-sensitive magnetic resonance outcomes translate into clinical assignment rules? J Am Acad Orthop Surg 21:438-9
Irrechukwu, Onyi N; Reiter, David A; Lin, Ping-Chang et al. (2012) Characterization of engineered cartilage constructs using multiexponential T? relaxation analysis and support vector regression. Tissue Eng Part C Methods 18:433-43
Makrogiannis, Sokratis; Serai, Suraj; Fishbein, Kenneth W et al. (2012) Automated quantification of muscle and fat in the thigh from water-, fat-, and nonsuppressed MR images. J Magn Reson Imaging 35:1152-61
Lin, Ping-Chang; Irrechukwu, Onyi; Roque, Remy et al. (2012) Multivariate analysis of cartilage degradation using the support vector machine algorithm. Magn Reson Med 67:1815-26
Reiter, David A; Irrechukwu, Onyi; Lin, Ping-Chang et al. (2012) Improved MR-based characterization of engineered cartilage using multiexponential T2 relaxation and multivariate analysis. NMR Biomed 25:476-88

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