Results suggest that 25% restriction in food intake increased median life span and delayed the onset of signs of chronic disease in these dogs.

The criteria offer, for the first time, a set of quantitative and objective means to subdivide the tissue thickness into the zones in histology and in MRI. It is shown that the microMRI zones based on the T(2)characteristics are statistically equivalent to the histological zones based on the collagen fibre orientation (t-probabilities of 0.730, 0.973, 0.647, 0.850 for the superficial, transitional, radial zones and the total thickness).

Composites of chondrocytes and polymerised fibrin were supplemented with insulin-like growth factor-I (IGF-I) during the arthroscopic repair of full-thickness cartilage defects in a model of extensive loss of cartilage in horses. Repairs facilitated with IGF-I and chondrocyte-fibrin composites, or control defects treated with chondrocyte-fibrin composites alone, were compared before death by the clinical appearance and repeated analysis of synovial fluid, and at termination eight months after surgery by tissue morphology, collagen typing, and biochemical assays. The structure of cartilage was evaluated histologically by Toluidine Blue reaction and collagen type-I and type-II in situ hybridisation and immunohistochemistry. Repair tissue was biochemically evaluated by DNA assay, proteoglycan quantitation and characterisation, assessment of collagen by reverse-phase high-performance liquid chromatography, and collagen typing using cyanogen bromide digestion and peptide separation by polyacrylamide gel electrophoresis. The results at eight months showed that the addition of IGF-I to chondrocyte grafts enhanced chondrogenesis in cartilage defects, including incorporation into surrounding cartilage. Gross filling of defects was improved, and the tissue contained a higher proportion of cells producing type-II collagen. Measurements of collagen type II showed improved levels in IGF-I-treated defects, supporting in situ hybridisation and immunohistochemical assessments of the defects. IGF-I improves the repair capabilities of chondrocyte-fibrin grafts in large full-thickness repair models.

To understand the origin of the laminated appearance of cartilage in MRI (the magic angle effect), microscopic MRI (mu MRI) experiments were performed at 14-microns pixel resolution on normal canine articular cartilage from the shoulder joints. Two-dimensional images of the spin-spin relaxation time (T2) of the cartilage-bone plug at two angles (0 degree and 55 degrees) were calculated quantitatively. A distinct T2 anisotropy was observed as a function of the cartilage tissue depth. The surface and the deep regions exhibit strong orientational dependence of T2, whereas the upper-middle region exhibits little orientational dependence of T2. These three mu MRI regions correspond approximately to the three histologic zones in cartilage tissue. The results from the bulk T2 measurements agreed with these mu MRI results. Our studies show that the laminated appearance of cartilage in MRI is caused by T2 anisotropy of the tissue. We further suggest that the molecular origin of the T2 anisotropy is the nuclear dipolar interaction. The structure of the cartilage tissue indicates that the collagen meshwork defines this T2 anisotropy. The results show that the T2 anisotropy provides an indirect but sensitive indicator for the orientation of macromolecular structures in cartilage. The clinical implications of this anisotropy are discussed.

A decrease in chondrocyte numbers is one characteristic of osteoarthritic cartilage. This decrease may be the result of apoptosis or other forms of cell death induced by mechanical damage. Furthermore, cell death may contribute to the structural and metabolic changes found in osteoarthritic cartilage. Therefore, we investigated cell viability and the mode of cell death in cartilage subjected to an increasing severity of impact loads expected to cause compositional damage and osteoarthritic-like metabolic alterations. Canine cartilage explants were subjected to cyclic indentation impacts of 5 megapascals at 0.3 Hz for 0,2,20, and 120 min and then kept in culture for 2, 4, 48, and 144 h. Cell death was assessed by the TUNEL assay and by uptake of propidium iodide. Viable cells were detected by the ability to metabolize fluorescein diacetate. Nuclear morphology and ultrastructure of the cell were examined using Hoechst 33342 fluorescent staining and transmission electron microscopy (TEM). As controls for necrosis and apoptosis, cartilage was, respectively, frozen and thawed or incubated with mitomycin-C, an apoptosis inducer. In cartilage that had been loaded for 2 h, 32% of the chondrocytes in the loaded core took up propidium iodide within 2 h after loading. Most of these were in the middle to superficial zones and reflected leaky cell membranes usually characteristic of necrosis. Less than 1% of these chondrocytes were positive in the TUNEL assay after 4 h. After additional culture for 2 days, however, the proportion of chondrocytes which were positive in the TUNEL assay reached 73%. A dose dependent response to duration of loading was detected with the TUNEL assay at this time. The TUNEL assay was not specific for apoptosis since 92% of chondrocytes in freezekhawed cartilage were TUNEL positive. However, some cells with apoptotic bodies and chromatin condensation characteristic of apoptosis were found in the transition zone between necrotic and normal chondrocytes, but not in the superficial and upper zones, in impact damaged cartilage. We concluded that in this study, necrosis occurred first, followed by apoptosis. 0