The glycosaminoglycans of the different layers of bovine articular cartilage in relation to age. II. Incorporation of 35s-sulphate in vitro into different fractions of chondroitin sulphate

T1rho mapping of entire femoral cartilage using depth- and angle-dependent analysis

Objectives

To create and evaluate normalized T1rho profiles of the entire femoral cartilage in healthy subjects with three-dimensional (3D) angle- and depth-dependent analysis.

Methods

T1rho images of the knee from 20 healthy volunteers were acquired on a 3.0-T unit. Cartilage segmentation of the entire femur was performed slice-by-slice by a board-certified radiologist. The T1rho depth/angle-dependent profile was investigated by partitioning cartilage into superficial and deep layers, and angular segmentation in increments of 4° over the length of segmented cartilage. Average T1rho values were calculated with normalized T1rho profiles. Surface maps and 3D graphs were created.

Results

T1rho profiles have regional and depth variations, with no significant magic angle effect. Average T1rho values in the superficial layer of the femoral cartilage were higher than those in the deep layer in most locations (p < 0.05). T1rho values in the deep layer of the weight-bearing portions of the medial and lateral condyles were lower than those of the corresponding non-weight-bearing portions (p < 0.05). Surface maps and 3D graphs demonstrated that cartilage T1rho values were not homogeneous over the entire femur.

Conclusions

Normalized T1rho profiles from the entire femoral cartilage will be useful for diagnosing local or early T1rho abnormalities and osteoarthritis in clinical applications.

Key Points

• T1rho profiles are not homogeneous over the entire femur.

• There is angle- and depth-dependent variation in T1rho profiles.

• There is no influence of magic angle effect on T1rho profiles.

• Maps/graphs might be useful if several difficulties are solved.

Chondroitin sulphate: an effective joint lubricant?

OBJECTIVE

The effect of chondroitin sulphate (CS) treatment on the friction and deformation characteristics of native and glycosaminoglycan (GAG) deficient articular cartilage was investigated.

METHODS

Friction tests were conducted at 0.4 MPa load, in Static and Dynamic models, to determine the startup coefficient of friction (COF) and dynamic COF, respectively. Native cartilage: For each cartilage pin and plate couple, the COF was determined under three consecutive tests - (1) baseline COF in PBS (2) COF in CS lubricant and (3) COF again in PBS, after 24h CS treatment. GAG deficient cartilage: For each cartilage pin and plate couple, the baseline COF was determined in PBS initially and again following enzymatic treatment to deplete GAGs. The specimens were then soaked in CS solution for 24h and the COF determined again in PBS. In a similar manner, friction tests were replaced with indentation tests to study the deformation of the tissue.

RESULTS

CS at 50mg/ml significantly lowered the startup COF of native cartilage both as a lubricant and a treatment solution. In the dynamic model, where the fluid load support is sustained at a high level, CS failed to have any effect on the COF of native cartilage. GAG depletion raised the friction and deformation levels of cartilage, and subsequent CS treatment failed to lower them to their native levels.

CONCLUSION

CS proved to be an effective lubricant for cartilage under mixed-mode lubrication conditions. However, supplemental CS that diffused into the specimens had no influence on the fluid load support of cartilage.

Structure of proteoglycans from different layers of human articular cartilage

Full-depth plugs of adult human articular cartilage were cut into serial slices from the articular surface and analysed for their glycosaminoglycan content. The amount of chondroitin sulphate was highest in the mid-zone, whereas keratan sulphate increased progressively through the depth. Proteoglycans were isolated from each layer by extraction with 4M-guanidinium chloride followed by centrifugation in 0.4M-guanidinium chloride/CsCl at a starting density of 1.5 g/ml. The efficiency with which proteoglycans were extracted depended on slice thickness, and extraction was complete only when cartilage from each zone was sectioned at 20 microns or less. When thick sections (250 microns) were extracted, hyaluronic acid was retained in the tissue. Most of the proteoglycans, extracted from each layer under optimum conditions, could interact with hyaluronic acid to form aggregates, although the extent of aggregation was less in the deeper layers. Two pools of proteoglycan were identified in all layers by gel chromatography (Kav. 0.33 and 0.58). The smaller of these was rich in keratan sulphate and protein, and gradually increased in proportion through the cartilage depth. Chondroitin sulphate chain size was constant in all regions. The changes in composition and structure observed were consistent with the current model for hyaline-cartilage proteoglycans and were similar to those observed with increasing age in human articular cartilage.

Studies on the in vitro incubation procedure for [35S]sulphate labelling of articular cartilage glycosaminoglycans

Articular cartilage from cow and calf femoral condyles was incubated in Tyrodes solution containing [35S]sulphate for different periods up to 80 min. Glycosaminoglycans from the cartilage tissue and incubation medium were fractionated on Cetylpyridinium chloride and ECTEOLA cellulose microcolumns. The incorporation of [35S]sulphate into all individual fractions of chondroitin sulphate and keratan sulphate was found to be linear from 20 to 80 min incubation time. As a rule the total specific activities of keratan sulphate and chondroitin sulphate were similar for both calves and cows. The proteoglycan material recovered from the medium amounted to about 1% of the tissue dry weight and was found to have a higher chondroitin sulphate: keratan sulphate ratio than the corresponding cartilage tissue for both calf and cow. The solubility profiles for the newly synthesised glycosaminoglycans, obtained from determination of the radioactivity in the individual fractions, were compared with those of glycosaminoglycans already present. These curves indicated that newly synthesised chondroitin sulphate had a higher average molecular size than that present in the tissue whereas the newly synthesised keratan sulphate had a smaller average molecular size. These newly synthesised components were also detected in the proteoglycans recovered from the incubation medium.

The metabolic heterogeneity of glycosaminoglycans of the different zones of the epiphyseal growth plate and the effect of ethane-1-hydroxy-1, 1-diphosphonate (EHDP) upon glycosaminoglycan synthesis in vivo

The synthesis of total and unextractable glycosaminoglycans of rabbit epiphyseal growth plate was studied by determination of the incorporation in vivo of 35S-sulphate into various glycosaminoglycans separated by microfractionation procedures using CPC and ECTEOLA columns. In the narrow hypertrophic zone, hyaluronic acid and chondroitin sulphate of low molecular weight were found to be unextractable with 3M guanidinium chloride for 24 h, thus being firmly bound within the tissue. While the unextractable chondroitin sulphate showed a sharply reduced synthesis rate in the hypertrophic zone compared with that in the columnar and resting zones, a rapid increase in the synthesis of extractable chondroitin sulphate toward the calcification front is indicated. At microfractionation, solubility profiles indicated that the unextractable chondroitin sulphate was of predominantly lower molecular weight and/or charge density compared to that of the whole tissue, most evident in the hypertrophic zone. The distribution pattern of incorporated 35S showed a close correspondence to the distribution of the various chondroitin sulphate fractions both for extracted and unextracted tissue. In the hypertrophic zone, higher radioactivity was found for chondroitin sulphate of predominantly low molecular weight and/or charge density in extracted compared to unextracted tissue. Low doses of EHDP caused no change of distribution of the various glycosaminoglycans but generally inhibited their synthesis.

Chondrocyte mitosis in the articular cartilage of femoral heads with various diseases

Autoradiographic studies using thymidine-3H reveal the mitosis of chondrocytes in degenerated joints, i.e. joints having secondary osteoarthritis or aseptic necrosis of the femoral head. The findings obtained provide additional support for the recent investigations regarding chondrocyte mitosis in primary osteoarthritic cartilage. Histologic and histochemical examinations suggest that a loss of glycosaminoglycans in the matrix is evidence for conversion of chondrocyte activity to mitosis which occurs, however, within the limit of "the point of irreversibility", analogous to the observations from the biochemical point of view. Biomechanical and nutritional factors are also discussed in relation to the results obtained from cartilages of the femoral heads in cases of femoral neck fracture and aseptic necrosis of the femoral head.

Calf articular cartilage in organ culture in a chemically defined medium. 2. Concentrations of glycosaminoglycans and [35S]-sulfate incorporation at different oxygen tensions

Articular cartilage from 6-month-old calves was maintained in organ culture in Eagle's minimum essential medium at different oxygen tensions between 20 and 50%. When well standardized cartilage pieces of about 1 mm thickness were used the results showed a high degree of reproducibility. The glycosaminoglycans were studied using the cetylpyridinium chloride cellulose and epichlorohydrin triethanolamine (ECTEOLA) column techniques on a microscale. In some experiments the cartilage was labelled with [35S]sulfate. Small alterations of the concentrations and distribution of different glycosaminoglycans were found and were not affected by various oxygen tensions for up to 4 weeks. A small increase was found in the fractions containing low molecular weight chondroitin sulfate. Devitalized cartilage, maintained under identical conditions, remained largely unaltered during the 4 weeks. The [35S]sulfate activity calculated per mole of hexosamine showed a general decrease during culture maintenance. High specific activities in the fractions containing low molecular weight chondroitin sulfate and keratan sulfate were found between 1 and 3 weeks of maintenance in 20% oxygen. Maintenance in 50% oxygen resulted in severely disturbed synthesis of glycoaminoglycans. The results are interpreted as showing that the synthesis pattern of glycosaminoglycans in articular cartilage can be altered by other factors and without the prior loss of glycosaminoglycans.

Calf anticular cartilage in organ culture in a chemically defined medium. I. Autoradiographic study after [35S]sulfate labeling

Articular cartilage from 5-month-old calves survived for 4 weeks in organ culture in a chemically defined medium. The viability was assessed by calculating the labeling frequency of chondrocytes on autoradiograms after [35S]sulfate labeling. The survival rate of chondrocytes was highest in 20% oxygen tension, whereas 50% oxygen resulted in chondrocyte death after 2 weeks. The survival rate was improved by using 1-mm thick standardized pieces of cartilage. The cells of the superficial layer showed a higher proportion of living chondrocytes than the cells in the deeper layers. No differentiation, dedifferentiation, or outgrowth of cells occurred during the experimental period.

Chondroitin sulphate of calf knee-joint cartilage

Chondroitin sulphate from different layers of calf knee-joint cartilage has been isolated and purified. Analysis for hexosamine, uronic acid, sulphate and relative proportions of the 4- and 6-isomers revealed no differences between the layers. However, an increase in the average molecular weight of the chondroitin sulphate was found to correspond with distance from the articular surface. In particular, the average molecular weight in the epiphyseal cartilage was significantly higher than that in the articular cartilage. The chondroitin sulphate of the 40-mu-mthick articular surface layer was found to have a higher molecular weight than the rest of the articular part of the cartilage and also to be more polydisperse. These results, regarding molecular size, are in agreement with the cetylpyridinium chloride cellulose microcolumn fractionation patterns.