Cartilage calcification studied by proton nuclear magnetic resonance microscopy

Detection and characterization of mineralo-organic nanoparticles in human kidneys

Ectopic calcification is associated with various human diseases, including atherosclerosis, cancer, chronic kidney disease, and diabetes mellitus. Although mineral nanoparticles have been detected in calcified blood vessels, the nature and role of these particles in the human body remain unclear. Here we show for the first time that human kidney tissues obtained from end-stage chronic kidney disease or renal cancer patients contain round, multilamellar mineral particles of 50 to 1,500 nm, whereas no particles are observed in healthy controls. The mineral particles are found mainly in the extracellular matrix surrounding the convoluted tubules, collecting ducts and loops of Henle as well as within the cytoplasm of tubule-delineating cells, and consist of polycrystalline calcium phosphate similar to the mineral found in bones and ectopic calcifications. The kidney mineral nanoparticles contain several serum proteins that inhibit ectopic calcification in body fluids, including albumin, fetuin-A, and apolipoprotein A1. Since the mineralo-organic nanoparticles are found not only within calcified deposits but also in areas devoid of microscopic calcifications, our observations indicate that the nanoparticles may represent precursors of calcification and renal stones in humans.

Total-body irradiation produces late degenerative joint damage in rats

PURPOSE

Premature musculoskeletal joint failure is a major source of morbidity among childhood cancer survivors. Radiation effects on synovial joint tissues of the skeleton are poorly understood. Our goal was to assess long-term changes in the knee joint from skeletally mature rats that received total-body irradiation while skeletal growth was ongoing.

MATERIALS AND METHODS

14 week-old rats were irradiated with 1, 3 or 7 Gy total-body doses of 18 MV X-rays. At 53 weeks of age, structural and compositional changes in knee joint tissues (articular cartilage, subchondral bone, and trabecular bone) were characterized using 7T MRI, nanocomputed tomography (nanoCT), microcomputed tomography (microCT), and histology.

RESULTS

T2 relaxation times of the articular cartilage were lower after exposure to all doses. Likewise, calcifications were observed in the articular cartilage. Trabecular bone microarchitecture was compromised in the tibial metaphysis at 7 Gy. Mild to moderate cartilage erosion was scored in the 3 and 7 Gy rats.

CONCLUSIONS

Late degenerative changes in articular cartilage and bone were observed after total-body irradiation in adult rats exposed prior to skeletal maturity. 7T MRI, microCT, nanoCT, and histology identified potential prognostic indicators of late radiation-induced joint damage.

Novel mineral contrast agent for magnetic resonance studies of bone implants grown on a chick chorioallantoic membrane

Magnetic resonance imaging (MRI) studies of tissue engineered constructs prior to implantation clearly demonstrate the utility of the MRI technique for studying the bone formation process. To test the utility of our MRI protocols for explant studies, we present a novel test platform in which osteoblast-seeded scaffolds were implanted on the chorioallantoic membrane of a chick embryo. Scaffolds from the following experimental groups were examined by high-resolution MRI: (a) cell-seeded implanted scaffolds (CIM), (b) unseeded implanted scaffolds (UCIM), (c) cell-seeded scaffolds in static culture (CIV) and (d) unseeded scaffolds in static culture (UCIV). The reduction in water proton transverse relaxation times and the concomitant increase in water proton magnetization transfer ratios for CIM and CIV scaffolds, compared to UCIV scaffolds, were consistent with the formation of a bone-like tissue within the polymer scaffold, which was confirmed by immunohistochemistry and fluorescence microscopy. However, the presence of angiogenic vessels and fibrotic adhesions around UCIM scaffolds can confound MRI findings of bone deposition. Consequently, to improve the specificity of the MRI technique for detecting mineralized deposits within explanted tissue engineered bone constructs, we introduce a novel contrast agent that uses alendronate to target a Food and Drug Administration-approved MRI contrast agent (Gd-DOTA) to bone mineral. Our contrast agent termed GdALN was used to uniquely identify mineralized deposits in representative samples from our four experimental groups. After GdALN treatment, both CIM and CIV scaffolds, containing mineralized deposits, showed marked signal enhancement on longitudinal relaxation time-weighted (T1W) images compared to UCIV scaffolds. Relative to UCIV scaffolds, some enhancement was observed in T1W images of GdALN-treated UCIM scaffolds, subjacent to the dark adhesions at the scaffold surface, possibly from dystrophic mineral formed in the fibrotic adhesions. Notably, residual dark areas on T1W images of CIM and UCIM scaffolds were attributable to blood inside infiltrating vessels. In summary, we present the efficacy of GdALN for sensitizing the MRI technique to the deposition of mineralized deposits in explanted polymeric scaffolds.

Characterization of granulations of calcium and apatite in serum as pleomorphic mineralo-protein complexes and as precursors of putative nanobacteria

Calcium and apatite granulations are demonstrated here to form in both human and fetal bovine serum in response to the simple addition of either calcium or phosphate, or a combination of both. These granulations are shown to represent precipitating complexes of protein and hydroxyapatite (HAP) that display marked pleomorphism, appearing as round, laminated particles, spindles, and films. These same complexes can be found in normal untreated serum, albeit at much lower amounts, and appear to result from the progressive binding of serum proteins with apatite until reaching saturation, upon which the mineralo-protein complexes precipitate. Chemically and morphologically, these complexes are virtually identical to the so-called nanobacteria (NB) implicated in numerous diseases and considered unusual for their small size, pleomorphism, and the presence of HAP. Like NB, serum granulations can seed particles upon transfer to serum-free medium, and their main protein constituents include albumin, complement components 3 and 4A, fetuin-A, and apolipoproteins A1 and B100, as well as other calcium and apatite binding proteins found in the serum. However, these serum mineralo-protein complexes are formed from the direct chemical binding of inorganic and organic phases, bypassing the need for any biological processes, including the long cultivation in cell culture conditions deemed necessary for the demonstration of NB. Thus, these serum granulations may result from physiologically inherent processes that become amplified with calcium phosphate loading or when subjected to culturing in medium. They may be viewed as simple mineralo-protein complexes formed from the deployment of calcification-inhibitory pathways used by the body to cope with excess calcium phosphate so as to prevent unwarranted calcification. Rather than representing novel pathophysiological mechanisms or exotic lifeforms, these results indicate that the entities described earlier as NB most likely originate from calcium and apatite binding factors in the serum, presumably calcification inhibitors, that upon saturation, form seeds for HAP deposition and growth. These calcium granulations are similar to those found in organisms throughout nature and may represent the products of more general calcium regulation pathways involved in the control of calcium storage, retrieval, tissue deposition, and disposal.

Magnetic resonance microscopy of collagen mineralization

A model mineralizing system was subjected to magnetic resonance microscopy to investigate how water proton transverse (T(2)) relaxation times and magnetization transfer ratios can be applied to monitor collagen mineralization. In our model system, a collagen sponge was mineralized with polymer-stabilized amorphous calcium carbonate. The lower hydration and water proton T(2) values of collagen sponges during the initial mineralization phase were attributed to the replacement of the water within the collagen fibrils by amorphous calcium carbonate. The significant reduction in T(2) values by day 6 (p < 0.001) was attributed to the appearance of mineral crystallites, which were also detected by x-ray diffraction and scanning electron microscopy. In the second phase, between days 6 and 13, magnetic resonance microscopy properties appear to plateau as amorphous calcium carbonate droplets began to coalesce within the intrafibrillar space of collagen. In the third phase, after day 15, the amorphous mineral phase crystallized, resulting in a reduction in the absolute intensity of the collagen diffraction pattern. We speculate that magnetization transfer ratio values for collagen sponges, with similar collagen contents, increased from 0.25 +/- 0.02 for control strips to a maximum value of 0.31 +/- 0.04 at day 15 (p = 0.03) because mineral crystals greatly reduce the mobility of the collagen fibrils.

Evaluation of bioreactor-cultivated bone by magnetic resonance microscopy and FTIR microspectroscopy

We present a three-dimensional mineralizing model based on a hollow fiber bioreactor (HFBR) inoculated with primary osteoblasts isolated from embryonic chick calvaria. Using non-invasive magnetic resonance microscopy (MRM), the growth and development of the mineralized tissue around the individual fibers were monitored over a period of 9 weeks. Spatial maps of the water proton MRM properties of the intact tissue, with 78 microm resolution, were used to determine changes in tissue composition with development. Unique changes in the mineral and collagen content of the tissue were detected with high specificity by proton density (PD) and magnetization transfer ratio (MTR) maps, respectively. At the end of the growth period, the presence of a bone-like tissue was verified by histology and the formation of poorly crystalline apatite was verified by selected area electron diffraction and electron probe X-ray microanalysis. FTIR microspectroscopy confirmed the heterogeneous nature of the bone-like tissue formed. FTIR-derived phosphate maps confirmed that those locations with the lowest PD values contained the most mineral, and FTIR-derived collagen maps confirmed that bright pixels on MTR maps corresponded to regions of high collagen content. In conclusion, the spatial mapping of tissue constituents by FTIR microspectroscopy corroborated the findings of non-invasive MRM measurements and supported the role of MRM in monitoring the bone formation process in vitro.

Nanostructure of the neurocentral growth plate: Insight from scanning small angle X-ray scattering, atomic force microscopy and scanning electron microscopy

In this study, the experimental techniques scanning electron microscopy (SEM) including energy-dispersive X-ray analysis, atomic force microscopy (AFM) and scanning small angle X-ray scattering (SAXS) have been exploited to characterize the organization of large molecules and nanocrystallites in and around the neurocentral growth plate (NGP) of a pig vertebrae L4. The techniques offer unique complementary information on the nano- to micrometer length scale and provide new insight in the changes in the matrix structure during endochondral bone formation. AFM and SEM imaging of the NGP reveal a fibrous network likely to consist of collagen type II and proteoglycans. High-resolution AFM imaging shows that the fibers have a diameter of approximately 100 nm and periodic features along the fibers with a periodicity of 50-70 nm. This is consistent with the SAXS analysis that yields a cross-sectional diameter of the fibers in the range of 90 to 112 nm and a predominant orientation in the longitudinal direction of the NGP. Furthermore, we find inhomogeneities around 7 nm in the NGP by SAXS analysis. Moving towards the bone in the direction perpendicular to the growth plate, a systematic change in apparent thickness is observed, while the large-scale structural features remain constant. In the region of bone, the apparent thickness equals the mean mineral thickness and increases from 2 nm to approximately 3.5 nm as a function distance from the NGP. The mineral particles are organized as plates in a rather compact network structure. We have demonstrated that SEM, AFM and SAXS are valuable tools for the investigation of the organization of large molecules and nanocrystallites in the NGP and adjacent trabecular bone. Our findings will be an important basis for future work into identifying the defects on nanometer length scale responsible for idiopathic scoliosis and other growth-plate-related diseases.

Nondestructive evaluation of osteogenic differentiation in tissue-engineered constructs

Conventional measurements of osteogenesis in tissue-engineered constructs are destructive to living cells and incapable to provide three-dimensional information. In the present study, noninvasive magnetic resonance (MR) microscopy was used to evaluate osteogenic differentiation in vitro in human mesenchymal stem cell-based tissue-engineered constructs. The constructs were prepared by seeding the cells (10(6)cells/ml) on 4 x 4 x 4 mm gelatin sponge cubes and subsequently exposing them to osteogenic differentiation or basic medium. During the 4-week experiment, alkaline phosphatase (ALP) activity and calcium content of differentiated constructs were significantly increased compared to the basic medium controls. The T1, T2, and apparent diffusion coefficient (ADC) of differentiated constructs were significantly lower than those of the control group at each time point (p < 0.05). The MR parameters of constructs were significantly correlated to their ALP activities (r to T1, T2, and ADC = -0.57, -0.78, and -0.81, respectively) and calcium content (r to T1, T2, and ADC = 0.48, 0.90, and 0.92, respectively) measured by biochemical techniques. MR microscopy can be a promising tool for noninvasive assessment of osteogenic differentiation and to provide three-dimensional information about tissue-engineered constructs.

MR Assessment of Osteogenic Differentiation in Tissue-Engineered Constructs

Bone marrow stromal cells (MSC) are a promising source of osteoprogenitor cells for bone tissue engineering. However, the population of the osteoprogenitor cells and their differentiation potentials change with the gender, age, and health of the donor. Development of a noninvasive method to assess osteogenic progression is critical for successful bone tissue regeneration. High-resolution magnetic resonance imaging (MRI) (at 11.7 T, with spatial resolution of 62.5 x 62.5 microm in 500 microm slices) is used in the present study to monitor osteogenic differentiation of tissue-engineered constructs prepared by seeding human bone MSCs on gelatin sponge scaffolds. Quantitative measurements of the MR relaxation times (T1, T2) and the apparent diffusion coefficient (ADC) were performed for four successive weeks on control tissue constructs and constructs exposed to osteogenic differentiation medium. The T1 and T2 relaxation times and ADC were found to decrease as osteogenic progression proceeded in samples exposed to osteogenic differentiation medium. At week 4, the T1, T2, and ADC of TE constructs were 1.81 +/- 0.11 s, 19.5 +/- 11.02 ms, and 1.01 +/- 0.47 x 10(3) mm(2)/s, respectively, for osteogenic differentiated constructs, significantly different from control constructs 2.22 +/- 0.08 s, 50.39 +/- 5.57 ms, and 1.86 +/- 0.18 x 107(3) mm(2)/s (p < 0.05). The MR parameters were also highly correlated with the cell seeding densities and alkaline phosphatase (ALP) activities of the osteogenic constructs. In conclusion, periodic measurements of MR parameters (T1, T2, and ADC) provide a promising method for noninvasive monitoring of the status of tissue-engineered bone growth and differentiation.

Non-destructive studies of tissue-engineered phalanges by magnetic resonance microscopy and X-ray microtomography

One of the intents of tissue engineering is to fabricate biological materials for the augmentation or replacement of impaired, damaged, or diseased human tissue. In this context, novel models of the human phalanges have been developed recently through suturing of polymer scaffolds supporting osteoblasts, chondrocytes, and tenocytes to mimic bone, cartilage, and tendon, respectively. Characterization of the model constructs has been accomplished previously through histological and biochemical means, both of which are necessarily destructive to the constructs. This report describes the application of two complementary, non-destructive, non-invasive techniques, magnetic resonance microscopy (MRM) and X-ray microtomography (XMT or quantitative computed tomography), to evaluate the spatial and temporal growth and developmental status of tissue elements within tissue-engineered constructs obtained after 10 and 38 weeks of implantation in athymic (nude) mice. These two times represent respective points at which model middle phalanges are comprised principally of organic components while being largely unmineralized and later become increasingly more mineralized. The spatial distribution of mineralized deposits within intact constructs was readily detected by XMT (qCT) and was comparable to low intensity zones observed on MRM hydration maps. Moreover, the MRM-derived hydration values for mineralized zones were inversely correlated with mineral densities measured by XMT. In addition, the MRM method successfully mapped fat deposits, collagenous tissues, and the hydration state of the soft tissue elements comprising the specimens. These results support the application of non-destructive, non-invasive, quantitative MRM and XMT for the evaluation of constituent tissue elements within complex constructs of engineered implants.

Design and assessment of a tissue-engineered model of human phalanges and a small joint

OBJECTIVES

To develop models of human phalanges and small joints by suturing different cell-polymer constructs that are then implanted in athymic (nude) mice.

DESIGN

Models consisted of bovine periosteum, cartilage, and/or tendon cells seeded onto biodegradable polymer scaffolds of either polyglycolic acid (PGA) or copolymers of PGA and poly-L-lactic acid (PLLA) or poly-epsilon-caprolactone (PCL) and PLLA. Constructs were fabricated to produce a distal phalanx, middle phalanx, or distal interphalangeal joint.

SETTING AND SAMPLE POPULATION

Studies of more than 250 harvested implants were conducted at the Northeastern Ohio Universities College of Medicine.

EXPERIMENTAL VARIABLE

Polymer scaffold, cell type, and implantation time were examined.

OUTCOME MEASURE

Tissue-engineered specimens were characterized by histology, transmission electron microscopy, in situ hybridization, laser capture microdissection and qualitative and quantitative polymerase chain reaction analysis, magnetic resonance microscopy, and X-ray microtomography.

RESULTS

Over periods to 60 weeks of implantation, constructs developed through vascularity from host mice; formed new cartilage, bone, and/or tendon; expressed characteristic genes of bovine origin, including type I, II and X collagen, osteopontin, aggrecan, biglycan, and bone sialoprotein; secreted corresponding proteins; responded to applied mechanical stimuli; and maintained shapes of human phalanges with small joints.

CONCLUSION

Results give insight into construct processes of tissue regeneration and development and suggest more complete tissue-engineered cartilage, bone, and tendon models. These should have significant future scientific and clinical applications in medicine, including their use in plastic surgery, orthopaedics, craniofacial reconstruction, and teratology.

Bone formation in polymeric scaffolds evaluated by proton magnetic resonance microscopy and X-ray microtomography

Magnetic resonance microscopy (MRM) and X-ray microtomography (XMT) were used to investigate de novo bone formation in porous poly(ethyl methacrylate) (PEMA) scaffolds, prepared by a novel co-extrusion process. PEMA scaffolds were seeded with primary chick calvarial osteoblasts and cultured under static conditions for up to 8 weeks. Bone formation within porous PEMA scaffolds was confirmed by the application of histologic stains to intact PEMA disks. Disks were treated with Alizarin red to visualize calcium deposits and with Sirius red to visualize regions of collagen deposition. DNA analysis confirmed that cells reached confluence on the scaffolds after 7 weeks in static culture. The formation of bone in PEMA scaffolds was investigated with water proton MRM. Quantitative MRM maps of the magnetization transfer ratio (MTR) yielded maps of protein deposition, and magnetic resonance (MR) relaxation times (T1 and T2) yielded maps of mineral deposition. The location of newly formed bone and local mineral concentrations were confirmed by XMT. By comparing MRM and XMT data from selected regions-of-interest in one sample, the inverse relationship between the MR relaxation times and mineral concentration was validated, and calibration curves for estimating the mineral content of cell-seeded PEMA scaffolds from quantitative MRM images were developed.