Proteoglycan Content Of Articular Cartilage Research Articles

A Platelet-Rich Plasma-Derived Biologic Clears Staphylococcus aureus Biofilms While Mitigating Cartilage Degeneration and Joint Inflammation in a Clinically Relevant Large Animal Infectious Arthritis Model.

The leading cause of treatment failure in Staphylococcus aureus infections is the development of biofilms. Biofilms are highly tolerant to conventional antibiotics which were developed against planktonic cells. Consequently, there is a lack of antibiofilm agents in the antibiotic development pipeline. To address this problem, we developed a platelet-rich plasma (PRP)-derived biologic, termed BIO-PLY (for the BIOactive fraction of Platelet-rich plasma LYsate) which has potent in vitro bactericidal activity against S. aureus synovial fluid free-floating biofilm aggregates. Additional in vitro studies using equine synoviocytes and chondrocytes showed that BIO-PLY protected these cells of the joint from inflammation. The goal of this study was to test BIO-PLY for in vivo efficacy using an equine model of infectious arthritis. We found that horses experimentally infected with S. aureus and subsequently treated with BIO-PLY combined with the antibiotic amikacin (AMK) had decreased bacterial concentrations within both synovial fluid and synovial tissue and exhibited lower systemic and local inflammatory scores compared to horses treated with AMK alone. Most importantly, AMK+BIO-PLY treatment reduced the loss of infection-associated cartilage proteoglycan content in articular cartilage and decreased synovial tissue fibrosis and inflammation. Our results demonstrate the in vivo efficacy of AMK+BIO-PLY and represents a new approach to restore and potentiate antimicrobial activity against synovial fluid biofilms.

Effect of cells on spatial quantification of proteoglycans in articular cartilage of small animals

ABSTRACT Objective Histochemical characterization of proteoglycan content in articular cartilage is important for the understanding of osteoarthritis pathogenesis. However, cartilage cells may interfere with the measurement of matrix proteoglycan content in small animal models (e.g. mice and rats) due to the high cell volume fraction (38%) in mice compared to human tissue (~1%). We investigated whether excluding the cells from image analysis affects the histochemically measured proteoglycan content of rat knee joint cartilage and assessed the effectiveness of a deep learning algorithm-based tool named U-Net in cell segmentation. Design Histological sections were stained with Safranin-O, after which optical densities were measured using digital densitometry to estimate proteoglycan content. U-Net was trained with 600 annotated Safranin-O cartilage images for exclusion of cells from the cartilage extracellular matrix. Optical densities of the ECM with and without cells were compared as a function of normalized tissue depth. Results U-Net cell segmentation was accurate, with the measured cell area fraction following largely that of ground-truth images (average difference: 4.3%). Cell area fraction varied as a function of tissue depth and took up 8–21% of the tissue area. The exclusion of cells from the analysis led to an increase in the analyzed depth-dependent optical density of cartilage by approximately 0.6–1.8% (p < 0.01). Conclusions Although the effect of cells on the analyzed proteoglycan content is small, it should be considered for improved sensitivity, especially at the onset of the disease during which cells may proliferate in small animals.

Characterization of connective tissues using near-infrared spectroscopy and imaging.

Near-infrared (NIR) spectroscopy is a powerful analytical method for rapid, non-destructive and label-free assessment of biological materials. Compared to mid-infrared spectroscopy, NIR spectroscopy excels in penetration depth, allowing intact biological tissue assessment, albeit at the cost of reduced molecular specificity. Furthermore, it is relatively safe compared to Raman spectroscopy, with no risk of laser-induced photothermal damage. A typical NIR spectroscopy workflow for biological tissue characterization involves sample preparation, spectral acquisition, pre-processing and analysis. The resulting spectrum embeds intrinsic information on the tissue's biomolecular, structural and functional properties. Here we demonstrate the analytical power of NIR spectroscopy for exploratory and diagnostic applications by providing instructions for acquiring NIR spectra, maps and images in biological tissues. By adapting and extending this protocol from the demonstrated application in connective tissues to other biological tissues, we expect that a typical NIR spectroscopic study can be performed by a non-specialist user to characterize biological tissues in basic research or clinical settings. We also describe how to use this protocol for exploratory study on connective tissues, including differentiating among ligament types, non-destructively monitoring changes in matrix formation during engineered cartilage development, mapping articular cartilage proteoglycan content across bovine patella and spectral imaging across the depth-wise zones of articular cartilage and subchondral bone. Depending on acquisition mode and experiment objectives, a typical exploratory study can be completed within 6 h, including sample preparation and data analysis.

Arp2/3 inactivation causes intervertebral disc and cartilage degeneration with dysregulated TonEBP-mediated osmoadaptation

Extracellular matrix and osmolarity influence the development and homeostasis of skeletal tissues through Rho GTPase-mediated alteration of the actin cytoskeleton. This study investigated whether the actin-branching Arp2/3 complex, a downstream effector of the Rho GTPases Cdc42 and Rac1, plays a critical role in maintaining the health of matrix-rich and osmotically loaded intervertebral discs and cartilage. Mice with constitutive intervertebral disc- and cartilage-specific deletion of the critical Arp2/3 subunit Arpc2 (Col2-Cre; Arpc2fl/fl) developed chondrodysplasia and spinal defects. Since these mice did not survive to adulthood, we generated mice with inducible Arpc2 deletion in disc and cartilage (Acan-CreERT2; Arpc2fl/fl). Inactivation of Arp2/3 at skeletal maturity resulted in growth plate closure, loss of proteoglycan content in articular cartilage, and degenerative changes in the intervertebral disc at 1 year of age. Chondrocytes with Arpc2 deletion showed compromised cell spreading on both collagen and fibronectin. Pharmacological inhibition of Cdc42 and Arp2/3 prevented the osmoadaptive transcription factor TonEBP/NFAT5 from recruiting cofactors in response to a hyperosmolarity challenge. Together, these findings suggest that Arp2/3 plays a critical role in cartilaginous tissues through the regulation of cell-extracellular matrix interactions and modulation of TonEBP-mediated osmoadaptation.

Synchrotron MicroCT Reveals the Potential of the Dual Contrast Technique for Quantitative Assessment of Human Articular Cartilage Composition.

ABSTRACTDual contrast micro computed tomography (CT) shows potential for detecting articular cartilage degeneration. However, the performance of conventional CT systems is limited by beam hardening, low image resolution (full‐body CT), and long acquisition times (conventional microCT). Therefore, to reveal the full potential of the dual contrast technique for imaging cartilage composition we employ the technique using synchrotron microCT. We hypothesize that the above‐mentioned limitations are overcome with synchrotron microCT utilizing monochromatic X‐ray beam and fast image acquisition. Human osteochondral samples (n = 41, four cadavers) were immersed in a contrast agent solution containing two agents (cationic CA4+ and non‐ionic gadoteridol) and imaged with synchrotron microCT at an early diffusion time point (2 h) and at diffusion equilibrium (72 h) using two monochromatic X‐ray energies (32 and 34 keV). The dual contrast technique enabled simultaneous determination of CA4+ (i.e., proteoglycan content) and gadoteridol (i.e., water content) partitions within cartilage. Cartilage proteoglycan content and biomechanical properties correlated significantly (0.327 < r < 0.736, p < 0.05) with CA4+ partition in superficial and middle zones at both diffusion time points. Normalization of the CA4+ partition with gadoteridol partition within the cartilage significantly (p < 0.05) improved the detection sensitivity for human osteoarthritic cartilage proteoglycan content, biomechanical properties, and overall condition (Mankin, Osteoarthritis Research Society International, and International Cartilage Repair Society grading systems). The dual energy technique combined with the dual contrast agent enables assessment of human articular cartilage proteoglycan content and biomechanical properties based on CA4+ partition determined using synchrotron microCT. Additionally, the dual contrast technique is not limited by the beam hardening artifact of conventional CT systems. © 2019 The Authors. Journal of Orthopaedic Research® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 38:563–573, 2020

T1 and T2 mapping of articular cartilage and menisci in early osteoarthritis of the knee using 3-Tesla magnetic resonance imaging

Purpose3-Tesla magnetic resonance imaging (MRI) T1 and T2 mapping to detect and quantify cartilage matrix and meniscal degeneration between normal healthy volunteers and early osteoarthritis patients.Material and methodsA prospective study including 25 patients and 10 healthy volunteers was done. Patients with symptoms of early osteoarthritis and Kellgren-Lawrence grade I-II on plain radiograph were included for MRI knee. Patients with inflammatory arthritis, infection, trauma, and history of knee surgery were excluded. Healthy, normal adult volunteers (preferably age and sex matched) without symptoms of osteoarthritis of the knee were drawn from patient’s relatives/hospital employees/colleagues for MRI knee.ResultsT1 and T2 relaxation time values of articular cartilage and menisci were significantly higher in osteoarthritis patients as compared to healthy volunteers. No significant difference was found in morphological thickness of articular cartilage and menisci in early osteoarthritis patients and healthy volunteers.ConclusionsT1 and T2 mapping are noninvasive MRI techniques reflecting changes in the biochemical composition of cartilage and menisci. T1 values reflect changes in proteoglycan content, and T2 values are sensitive to interaction between water molecules and collagen network. Mapping techniques assess early cartilage and meniscal matrix degeneration in osteoarthritis of the knee, and help in initiating treatment and monitoring disease progression. MRI is a sensitive modality for assessment of pathological changes in articular cartilage. With use of T1 and T2 mapping techniques, it is possible to evaluate the collagen network and proteoglycan content in articular cartilage and meniscal matrix.

Evaluation of Normal Ankle Cartilage by Magnetic Resonance Imaging (MRI) T1ρ Mapping

Category: Ankle Introduction/Purpose: With the recent remarkable progresses in image diagnosis using magnetic resonance imaging (MRI), it could be possible to evaluate articular cartilage in detail. T1ρ mapping by MRI has recently drawn attention as a noninvasive cartilage evaluation method. While its validity has been proven, there are no reports describing T1ρ mapping for the ankle; therefore, in this present study, T1ρ values of the articular cartilage surfaces of the talar dome were measured in healthy individuals. Methods: The study sample comprised 10 ankles from 10 healthy volunteers (4 male and 6 female), with a mean age of 32.2 years. Images taken using a 3.0 T MRI device, manufactured by Philips, were processed using the PRIDE software (Philips, Inc.) and analyzed using Image J, a specialized analysis software. Evaluations were performed using slices in the coronal plane from the trochlear ridge of the talus and slices 10 mm anterior and posterior of the ridge. Each slice was divided into three equal parts including the medial, central, and lateral areas of cartilage on the articular surface of the trochlea tali, to totally yield 9 regions of interests where T1ρ values (ms) were measured. Furthermore, values were measured thrice for each region in each volunteer, and the mean was calculated. Results: T1ρ values for the medial, central, and lateral regions were 31.0 ± 6.4 ms, 31.2 ±7 .2 ms, and 32.2 ± 6.9 ms, respectively for the anterior talus; 24.2 ± 4.2 ms, 21.7 ± 5.6 ms, and 25.1 ± 5.5 ms, respectively for the trochlear ridge of the talus; and 33.8 ± 4.8 ms, 31.9 ± 4.5 ms, and 35.1 ± 4.8 ms, respectively for the posterior talus. T1ρ values were significantly lower in the anterior and posterior areas of the talar dome than in the trochlear ridge of the talus (p &lt; 0.05). Conclusion: Proteoglycan content of articular cartilage in the talar dome was determined to be low in the anterior and posterior areas, that reveals load application might be concentrate on these areas.

Spatial mapping of proteoglycan content in articular cartilage using near-infrared (NIR) spectroscopy.

Diagnosis of articular cartilage pathology in the early disease stages using current clinical diagnostic imaging modalities is challenging, particularly because there is often no visible change in the tissue surface and matrix content, such as proteoglycans (PG). In this study, we propose the use of near infrared (NIR) spectroscopy to spatially map PG content in articular cartilage. The relationship between NIR spectra and reference data (PG content) obtained from histology of normal and artificially induced PG-depleted cartilage samples was investigated using principal component (PC) and partial least squares (PLS) regression analyses. Significant correlation was obtained between both data (R(2) = 91.40%, p<0.0001). The resulting correlation was used to predict PG content from spectra acquired from whole joint sample, this was then employed to spatially map this component of cartilage across the intact sample. We conclude that NIR spectroscopy is a feasible tool for evaluating cartilage contents and mapping their distribution across mammalian joint.

A5.3 Elevated levels of BMP2 compensate for loss of TGF-BETA on proteoglycan level in articular cartilage during experimental osteoarthritis

Purpose We demonstrated earlier that in aging articular cartilage TGF-beta signalling via Smad2/3 is drastically reduced and loss of Smad2/3signalling predisposed cartilage for OA. We showed that TGF-beta inhibition reduced...

A Comparison of the Histochemical and Image-Derived Proteoglycan Content of Articular Cartilage

There are several methods for determining the proteoglycan content of cartilage in biomechanics experiments. Many of these include assay-based methods and the histochemistry or spectrophotometry protocol where quantification is biochemically determined. More recently a method based on extracting data to quantify proteoglycan content has emerged using the image processing algorithms, e.g., in ImageJ, to process histological micrographs, with advantages including time saving and low cost. However, it is unknown whether or not this image analysis method produces results that are comparable to those obtained from the biochemical methodology. This paper compares the results of a well-established chemical method to those obtained using image analysis to determine the proteoglycan content of visually normal (n=33) and their progressively degraded counterparts with the protocols. The results reveal a strong linear relationship with a regression coefficient (R2) = 0.9928, leading to the conclusion that the image analysis methodology is a viable alternative to the spectrophotometry.

MRI of Hip Cartilage: Joint Morphology, Structure, and Composition

Accurate, reproducible, and noninvasive assessment of hip cartilage is clinically relevant and provides a means by which to assess the suitability of candidates for arthroscopic or open surgical procedures and the response to such interventions over time. Given the relatively thin cartilage of the hip and the complex spherical anatomy, however, accurately assessing the cartilage poses a challenge for traditional MRI techniques. We assessed the current status of imaging articular cartilage of the hip through a comprehensive review of recent literature. We performed a literature review using PubMed. Topics included quantitative MRI, imaging of the hip cartilage and labrum, femoroacetabular impingement syndrome, and osteoarthritis of the hip. WHERE ARE WE NOW?: With the use of high in-plane and through-plane resolution, reproducible assessment of hip cartilage and labrum is clinically feasible. More recent quantitative MR techniques also allow for noninvasive assessment of collagen orientation and proteoglycan content in articular cartilage, thus providing insight into early matrix degeneration. These techniques can be applied to cohorts at risk for osteoarthritis, helping to predict cartilage degeneration before symptoms progress and osteoarthritic changes are visible on radiographs. WHERE DO WE NEED TO GO?: Prospective longitudinal data registries are necessary for developing predictive models of osteoarthritis and subsequent joint failure to assess the results of surgical intervention and predict the timing of arthroplasty. HOW DO WE GET THERE?: By establishing more hip cartilage registries, a correlation can be made between subjective measures and morphologic MRI to assess the cartilage, labrum, bone, and synovial lining of the hip.

Species‐specific biological effects of FGF‐2 in articular cartilage: Implication for distinct roles within the FGF receptor family

Existing literature demonstrates that fibroblast growth factor-2 (FGF-2) exerts opposing, contradictory biological effects on cartilage homeostasis in different species. In human articular cartilage, FGF-2 plays a catabolic and anti-anabolic role in cartilage homeostasis, driving homeostasis toward degeneration and osteoarthritis (OA). In murine joints, however, FGF-2 has been identified as an anabolic mediator as ablation of the FGF-2 gene demonstrated increased susceptibility to OA. There have been no previous studies specifically addressing species-specific differences in FGF-2-mediated biological effects. In this study, we provide a mechanistic understanding by which FGF-2 exerts contradictory biological effects in human versus murine tissues. Using human articular cartilage (ex vivo) and a medial meniscal destabilization (DMM) animal model (in vivo), species-specific expression patterns of FGFR receptors (FGFRs) are elucidated between human and murine articular cartilage. In the murine OA model followed by intra-articular injection of FGF-2, we further correlate FGFR profiles to changes in behavioral pain perception, proteoglycan content in articular cartilage, and production of inflammatory (CD11b) and angiogenic (VEGF) mediators in synovium lining cells. Our results suggest that the fundamental differences in cellular responses between human and murine tissues may be secondary to distinctive expression patterns of FGFRs that eventually determine biological outcomes in the presence of FGF-2. The complex interplay of FGFRs and the downstream signaling cascades induced by FGF-2 in human cartilage should add caution to the use of this particular growth factor for biological therapy in the future.

Effects of chondroitin sulfate-C on bradykinin-induced proteoglycan depletion in rats.

Depletion of the proteoglycan content of articular cartilage was induced by injecting bradykinin (30-300 mumol/l, 50 microliters/knee) into the left knee articular cavities of rats 3 times a day for 2 days. The degree of the reduction in the intensity of histopathological safranin O staining was used as an index of proteoglycan depletion. Bradykinin reduced the cartilage proteoglycan contents of the knee joints of non-injected limbs in a dose-dependent manner and at 300 mumol/l markedly reduced these contents, but evoked no inflammatory changes. The extent of the reduction of the cartilage proteoglycan contents induced by bradykinin injection depended on the dose and injection frequency. Chondroitin sulfate-C (CAS 25322-46-7, Chondroitin ZS Tab) (30-1,000 mg/kg/day) administered orally to rats for 14 days inhibited the bradykinin-induced proteoglycan depletion of the articular cartilage in a dose-dependent manner. These results suggest that a reduction of the proteoglycan content of cartilage, like that associated with osteoarthritis, was induced by injecting bradykinin into the knee articular cavities of rats and chondroitin sulfate-C protected against this effect.

Apelin plays a catabolic role on articular cartilage: In vivo and in vitro studies

Adipokines play key roles in the regulation of bone growth, obesity, diabetes mellitus type 2, and HIV infection. As a newly discovered hormone in the adipokine family, the precise role of apelin on articular cartilage metabolism is not yet clear. The aim of this study was to evaluate the role of apelin on articular cartilage. In vitro, we examined the effects of apelin on normal chondrocyte proliferation and gene expression of metalloproteinases (MMPs) and interleukin-1beta (IL-1beta). In vivo, by intra-articular injection with apelin, we examined MMP-3, -9, collagen II and IL-1beta at both gene and protein levels. Furthermore, we measured the messenger RNA (mRNA) expression of ADAMTS-4 and -5 (a disintegrin and metalloproteinase with thrombospondin motifs 4 and 5) and the proteoglycan content in articular cartilage. Apelin stimulated the proliferation of chondrocytes and significantly increased mRNA levels of MMP-1, -3, -9 and IL-1beta in vitro. Intra-articular injection with apelin in vivo up-regulated the expression of MMP-3, -9, and IL-1beta as well as decreased the level of collagen II. Additionally, after treatment with apelin, mRNA levels of ADAMTS-4 and -5 markedly increased and depletion of proteoglycan in articular cartilage was found by histological assessment. These findings suggest that apelin plays a catabolic role in cartilage metabolism and is a risk factor in the pathophysiology of osteoarthritis.

Blood Induced Cartilage Changes in a Hemophilia A Murine Model.

Background: Hemophilia A results from a congenital deficiency of clotting factor VIII. Patients with hemophila are unable to generate adequate thrombin during blood coagulation and therefore have a bleeding diathesis. Degenerative joint disease is the largest source of morbidity for hemophilic patients. The pathophysiology of this process is poorly understood but clinically, repeated bleeding into a joint leads to changes in the synovium, articular cartilage and underlying bone. It is not well known how quickly cartilage changes occur or if animal age has any impact on susceptibility to blood induced cartilage damage.Materials and Methods: The E16 fVIII knockout mouse is a well-established model for hemophilia research. These mice contain a targeted disruption of the factor VIII gene at exon 16 (E16) in a C57BL/6 background. Despite having no detectable circulating fVIII activity they rarely suffer from spontaneous hemarthroses. Therefore hemarthroses was mimicked by injecting 5 μL of autologous whole blood into the hind knee. Six male mice per group in each of three ages; 12, 24 and 52 weeks were utilized. The animals were sacrificed 48 hours after injection. The injected and control contralateral knee joint from each animal was fixed in 10% formalin and then mounted in paraffin. After decalcification, five micrometer sections through the joint were obtained. Joint architecture was examined after hematoxylin and eosin staining. Proteoglycan content of articular cartilage was evaluated after alcian blue staining as part of the modified Mankin score. The pathologic specimens were also scored utilizing Valentino's visual bleeding score. The Student's t-test was utilized for significance testing.Results: All mice showed evidence of blood remaining in the injected joint at 48 hours. The mean visual bleeding score was significantly higher for the injected knees versus the control knees of all age groups p<0.001. The mean visual bleeding score was significantly between the 12 and 24 week animals p=0.0112 and the 12 and 52 week animals p=0.0379, but not between the 24 and 52 week animals p=0.5423. The modified Mankin score was significantly higher between the injected and control knees of all age groups as seen in Figure 1 where the mean and standard deviation is shown for 6 animals in each group. Interestingly, one control knee in a 24 week old animal demonstrated synovial hyperplasia and decreased proteoglycan staining but had no evidence of blood in the joint. This likely represented a previous spontaneous hemorrhage. The modified Mankin score was highest for the 12 week old animals and lowest for the 52 week animals but did not achieve statistical significance p=0.5746.Conclusions: Injection of autologous blood mimicked clinical hemarthrosis. Evidence of decreased proteoglycan staining of articular cartilage was evident within 48 hours of blood exposure. Additionally, there was a trend toward more prominent proteoglycan loss in the youngest animals. [Display omitted]

Measuring fixed charge density of goat articular cartilage using indentation methods and biochemical analysis

An important indicator of osteoarthritis (OA) progression is the loss of proteoglycan (PG) aggregates from the cartilage tissue. Using the indentation creep test, two analytical methods, as previously developed by Lu et al. [Lu, X. L., Miller, C., Chen, F. H., Guo, X. E., Mow, V. C., 2007. The generalized triphasic correspondence principle for simultaneous determination of the mechanical properties and proteoglycan content of articular cartilage by indentation. Journal of Biomechanics 40, 2434–2441 (EPub).], for predicting the fixed charge density (FCD) of goat knee articular cartilage in the normal (control) and degenerated states were compared: (1) a “dual-stage” method to calculate FCD from the mechanical properties of the tissue when tested in isotonic and hypertonic solutions; and (2) a “single-stage” method to predict FCD (as in (1)) assuming an intrinsic Poisson's ratio of 0.05 in the hypertonic state. A biochemical analysis using 1,9-dimethylmethylene blue (DMMB) assay was conducted to directly measure PG content, and hence FCD. The association between the FCD and the aggregate modulus of the tissue was also explored. The mean (±S.D.) FCD values measured using the dual-stage method were the closest (control: 0.129±0.039, degenerated: 0.046±029) to the DMMB results (control: 0.125±0.034, degenerated: 0.057±0.024) as compared to those of the single-stage method (control: 0.147±0.035, degenerated: 0.063±0.026). The single-stage method was more reliable ( r 2=0.81) when compared to the dual-stage method ( r 2=0.79). A prediction of FCD from the aggregate modulus generated the least reliable FCD prediction ( r 2=0.68). Because both the dual- and single-stage methods provided reliable FCD estimates for normal and degenerated tissue, the less time-consuming single-stage method was concluded to be the ideal technique for predicting FCD and hence PG content of the tissue.

The generalized triphasic correspondence principle for simultaneous determination of the mechanical properties and proteoglycan content of articular cartilage by indentation

The triphasic mixture theory has been used to describe the mechanical and physicochemical behaviors of articular cartilage under some specialized loading conditions. However, the mathematical complexities of this theory have limited its applications for theoretical analyses of experimental studies and models for predicting cartilage and other biological tissues’ deformational behaviors. A generalized correspondence principle has been established in the present study, and this principle shows that the equilibrium deformational behavior of a charged-hydrated material under loading is identical to that of an elastic medium without charge. A set of explicit formulas has been derived to correlate the mechanical properties of an equivalent material with the intrinsic elastic moduli, fixed charge density and free-ion concentration within the cartilage tissue. The validity of these formulas is independent of the deformation state of the elastic solid matrix under an infinitesimal strain. Therefore they can be employed for any loading conditions, such as confined or unconfined compression, tension, and indentation tests, etc. In the current study, the fixed charge density of bovine cartilage is determined from the indentation creep data using this generalized correspondence principle. The proteoglycan content results were then compared with those from biochemical assay, yielding a linear regression slope of 1.034. Additionally a correspondence principle within a framework of cubic symmetry and a bilinear response in tension-compression (the conewise linear elasticity model) has also been developed to demonstrate the potential application of current methodology for inhomogeneous, anisotropic and nonlinear situations.

Assessment of Human Disc Degeneration and Proteoglycan Content Using T1ρ-weighted Magnetic Resonance Imaging

T1rho relaxation was quantified and correlated with intervertebral disc degeneration and proteoglycan content in cadaveric human lumbar spine tissue. To show the use of T1rho-weighted magnetic resonance imaging (MRI) for the assessment of degeneration and proteoglycan content in the human intervertebral disc. Loss of proteoglycan in the nucleus pulposus occurs during early degeneration. Conventional MRI techniques cannot detect these early changes in the extracellular matrix content of the disc. T1rho MRI is sensitive to changes in proteoglycan content of articular cartilage and may, therefore, be sensitive to proteoglycan content in the intervertebral disc. Intact human cadaveric lumbar spines were imaged on a clinical MR scanner. Average T1rho in the nucleus pulposus was calculated from quantitative T1rho maps. After MRI, the spines were dissected, and proteoglycan content of the nucleus pulposus was measured. Finally, the stage of degeneration was graded using conventional T2 images. T1rho decreased linearly with increasing degeneration (r = -0.76, P < 0.01) and age (r = -0.76, P < 0.01). Biochemical analysis revealed a strong linear correlation between T1rho and sulfated-glycosaminoglycan content. T1rho was moderately correlated with water content. Results from this study suggest that T1rho may provide a tool for the diagnosis of early degenerative changes in the disc. T1rho-weighted MRI is a noninvasive technique that may provide higher dynamic range than T2 and does not require a high static field or exogenous contrast agents.

MRI heterogeneity of articular cartilage in strong magnetic fields: Dependence on proteoglycan content

AbstractArticular cartilage is a thin heterogeneous tissue (typical thickness of less than 2 mm) composed of collagen, proteoglycan, and water that coats skeletal joint surfaces. Its physical and chemical integrity are essential for maintaining normal joint articulation. MR imaging techniques are being developed to visualize articular cartilage for the purpose of assessing changes in its structure that occur with age and the onset of joint disease. Emerging high‐field MR systems (greater than 4 T) have a higher signal‐to‐noise ratio, which can be used to improve the spatial resolution for imaging articular cartilage beyond that available in most clinical systems. In this study, we examined the effect of changing the proteoglycan content of articular cartilage on high‐resolution (40 × 40 × 100 μm) T1‐ and T2‐weighted images acquired at 11.74 T (500 MHz for protons). Susceptibility artifacts were observed near the cartilage‐bone interface that were verified by separating the cartilage from the bone. MR image heterogeneity of articular cartilage was observed as a function of depth and in the transverse directions of the sample. Enzymatic depletion of cartilage proteoglycan demonstrated that the MR image heterogeneity is due in part to variation of the proteoglycan content in different regions of the cartilage. The apparent diffusion coefficient (ADC) was measured as a function of depth in the cartilage. The ADC varied from the subchondral bone to the articular surface for both normal and digested cartilage. In addition, the ADC increased by 20% after 6 hours of enzymatic digestion of proteoglycan. These results suggest a role for high‐field MRI of articular cartilage in the management and staging of osteoarthritis and other joint diseases. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 23B: 33–43, 2004

Degradation of cartilage type II collagen precedes the onset of osteoarthritis following anterior cruciate ligament rupture.

To determine if degradation of cartilage matrix in primary osteoarthritis (OA) or in OA secondary to rupture of the anterior cruciate ligament (ACL) is a gradual response to excessive loading or an early, initiating event in the disease process. Biopsy samples were obtained from the low-weight-bearing articular cartilage of the intercondylar notch, in patients undergoing knee arthroscopy (ACL injury) or arthroplasty (late-stage primary OA) or in controls. In some cases, biopsy samples were also removed from the high-weight-bearing articular cartilage of the femoral condyles. Biopsy specimens were extracted and assayed for total and denatured type II collagen (CII) by inhibition enzyme-linked immunosorbent assay and for proteoglycan using a colorimetric method. All patients were assessed radiographically for cartilage erosion. In addition, the cartilage of patients with ACL injury was assessed at arthroscopy, and the knee function of patients with primary OA was assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Increased CII degradation was detected in the low- as well as the high-weight-bearing cartilage of patients with late-stage OA, and there was a positive correlation between the percentage denatured collagen and the WOMAC score. Most of the patients with ACL injury had no clinical signs of OA or macroscopic cartilage erosion. However, the low-weight-bearing articular cartilage from these patients showed a significant increase in CII degradation, similar to that observed in late-stage OA. The proteoglycan content of articular cartilage did not change significantly in patients with OA or ACL injury compared with controls. CII degradation is an early event following ACL injury and is unlikely to be a direct result of mechanical loading, since it was observed in cartilage obtained from a low-weight-bearing site.