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Biomedical subjects

A Maroudas

Publications and source records attributed to A Maroudas.

At least 55 records · Page 3Linked to original sources
PubMed1977

Chemical composition and swelling of normal and osteoarthrotic femoral head cartilage. I. Chemical composition.

Radiochemical and biochemical methods were used to characterize post-mortem and osteoarthrotic femoral head cartilage. Fixed charge density measurements were correlated with glycosaminoglycan content as estimated by uronic acid and hexosamine analyses. In post-mortem cartilage water content decreased from a maximum at the surface to a minimum in the deep zones. In the osteoarthrotic specimens water content was greatest in the middle zones. Glycosaminoglycan content increased with depth and in the osteoarthrotic specimens was reduced throughout the depth of the cartilage. With increasing degeneration there was an increase in water content and decrease in glycosaminoglycan content. The difference in the water content profile in osteoarthrotic cartilage was explained in terms of damage to the collagen network. In osteoarthrosis the latter is no longer capable of restraining the swelling pressure produced by the glycosaminoglycans and swelling is greatest in the midzones, where glycosaminoglycan content is highest.

Body Water↗
PubMed1977

Chemical composition and swelling of normal and osteoarthrotic femoral head cartilage. II. Swelling.

Studies of the equilibrium, partition, and diffusion of tritiated water were carried out on normal and osteoarthrotic cartilage as well as on cartilage from which proteoglycans had been extracted chemically. All the water was found to be freely exchangeable in both normal and degenerate specimens. The diffusiviity of the water was equal to about 40% of the value in free solution, with an activation energy equal to that in free solution. It was concluded that the swelling of degenerate tissue is not due to any changes in the state of the water, but to a failure of the damaged collagen network to oppose the swelling pressure of the proteoglycans. Swelling similar to that observed in fibrillated cartilage was also found in initially normal specimens treated with collagenase.

Cartilage, Articular↗
PubMed1976

The distribution of serum albumin in human normal and degenerate articular cartilage.

A method for studying the distribution of a high molecular weight solute (serum albumin) between physiological saline and human articular cartilage is described. Samples of normal and fibrillated articular cartilage from both femoral condyles and femoral heads have been studied. Limited studies have also been performed where the glycosaminoglycan content of normal cartilage has been reduced by chemical or enzymic methods. With naturally occurring cartilage a wide range of partition coefficients (0.3 to less than 0.002) was obtained. The partition coefficients are very dependent upon proteoglycan concentration, with the partition coefficient decreasing with increasing fixed charge density. An attempt is made to interpret the observed partitioning in terms of the steric exclusion by the proteoglycans.

Binding Sites↗
PubMed1976

Transport of solutes through cartilage: permeability to large molecules.

A review of the transport of solutes through articular cartilage is given, with special reference to the effect of variations in matrix composition. Some physiological implications of our findings are discussed. Also, results of an experimental study of the permeability of articular cartilage to large globular proteins are presented. Because of the very low partition coefficients of large solutes between cartilage and an external solution new experimental techniques had to be devised, particularly for the study of diffusion. The partition coefficients of solutes were found to decrease very steeply with increase in size, up to serum albumin. There was, however, no further decrease for IGG. The diffusion coefficient of serum albumin in cartilage was relatively high (one quarter of the value in aqueous solution). These two facts taken together suggest that there may be a very small fraction of relatively large pores in cartilage through which the transport of large molecules is taking place. The permeability of cartilage to large molecules is extremely sensitive to variations in the glycosaminoglycan content: for a threefold increase in the latter there is a hundredfold decrease in the partition coefficient. For cartilage of fixed charge density around 0-19 m-equiv/g, there is no penetration at all of globular proteins of size equal to or larger than serum albumin.

Biological Transport↗
PubMed1975

Glycosaminoglycan turn-over in articular cartilage.

Glycosaminoglycan turn-over has been studied both in vivo and in vitro, by using sodium [35S]sulphate as a precursor. The in vivo experiments were performed on rabbits and dogs, taking special care to monitor the 35S radioactivity in the serum throughout the experiment and to measure the radioactivity due to unincorporated inorganic [35S]sulphate in cartilage at the end of each experiment, in addition to that due to incorporated sulphate. The inorganic sulphate content of the serum was also determined as well as the distribution coefficient for the inorganic sulphate ion between cartilage and serum. From this information it was possible to calculate accurately the rate of sulphate uptake by cartilage in vivo and hence the turn-over rate. Experiments were then performed in vitro on cartilage from rabbits and dogs and the in vivo and in vitro results were compared. A very good agreement was obtained between the two sets of results. Studies were then carried out under exactly the same in vitro conditions on human articular cartilage and it was thus possible to obtain a turn-over rate for the latter which one could trust was close to the actual in vivo value. The mean half-lives thus obtained varied from 45 days for the young rabbit to 150 days for the adult dog and 800 days for the human femoral head. In human cartilage there were considerable variations in turn-over rate within a single joint as a function of depth below the surface, and between different joints. Thus, while the mean half-life for the human femoral head is 800 days, that for the femoral condyle is 300 days. Cartilage from osteoarthrosic femoral heads did not appear to differ much with respect to sulphate uptake from the normal specimens although the turn-over rates were somewhat higher.

Adult↗
PubMed1975

Cartilage of the patella. Topographical variation of glycosaminoglycan content in normal and fibrillated tissue.

The variation in the glycosaminoglycan content was studied at different sites of the patella, both where the cartilage was intact and where it showed varying degrees of fibrillation. It was found that when the cartilage surface was intact the glycosaminoglycan content was the same at the different sites of the patella. Local fibrillation always gave rise to a local lowering of fixed charge density, the magnitude of the latter correlating well with the visual assessment of the severity of the lesion. Even in the presence of severe lesions, if there was a site left on the patella where the cartilage was visually normal, its fixed charge density was also at a normal level. Thus, the depletion of glycosaminoglycans is a local phenomenon, limited to the area of fibrillation. The glycosaminoglycan content of normal cartilage is lower in the knee joint than in the hip. This fact, together with the existence of high pressure during load bearing, may be responsible for the greater frequency of destructive lesions affecting the cartilage of the patella compared with that of the hip.

Adolescent↗
PubMed1975

Factors involved in the nutrition of the human lumbar intervertebral disc: cellularity and diffusion of glucose in vitro.

Post-mortem specimens of the human lumbar (L4-L5) intervertebral disc have been studied histologically and physico-chemically. Blood vessels were found only at the margin of the anulus fibrosus and in the vertebral marrow spaces. Contact between disc tissue and marrow spaces occupied about 10% of the bone-cartilage interface. The disc was most cellular at the periphery of the anulus fibrosus and in the hyaline cartilage next to the vertebral bone. Cellularity declined towards the nucleus pulposus where it achieved a low constant value. The cell density of the disc as a whole was about 60000 cells/mm3. For glucose, the diffusion coefficient of the anulus fibrosus and hyaline cartilage end plate was 2.5 cm2/sec and 2.4 cm2/sec respectively at 37 degrees C, comparable to that of cartilage elsewhere. The permeability of the bone-cartilage interface was low, particularly in the peripheral part. Calculations, based on the present findings and derived values for glucose utilization in disc tissue, indicate that nutritional conditions in the intervertebral disc are more critical than, for example, in articular cartilage.

Adolescent↗
PubMed1970

Distribution and diffusion of solutes in articular cartilage.

An experimental study was made on the distribution of solutes between articular cartilage and external solution, and on their diffusivity in cartilage. The solutes were classed as small ions, small uncharged molecules, and uncharged molecules of increasing size ranging from glucose to hemoglobin. The distribution of sodium and chloride ions obeys the Donnan equilibrium when cartilage is equilibrated in physiological saline solution. However, in cartilage immersed in dilute solution the concentration of chloride ions is higher than predicted. This is probably due to the presence in cartilage of some microscopic regions depleted of mucopolysaccharide in which the Donnan exclusion does not operate. The molal distribution coefficients of small uncharged molecules like urea are close to unity, which indicates that all water in cartilage seems to behave as solvent water. For larger molecules the distribution as well as the diffusion coefficients decrease with increase in molecular weight and are very sensitive to variations in fixed charge density. The results have been interpreted on the basis of the "steric exclusion" principle. The largest molecules which can penetrate into cartilage are of the size of the hemoglobin molecule.

Cartilage↗