Synthesis of connective-tissue components. The effect of retinol and hydrocortisone on cultured limb-bone rudiments

Effect of retinoic acid in combination with platelet-derived growth factor-BB or transforming growth factor-beta on tissue inhibitor of metalloproteinases and collagenase secretion from human skin and synovial fibroblasts

This report shows for the first time that platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-beta (TGF-beta) can interact in a synergistic manner with retinoic acid to stimulate the production of tissue inhibitor of metalloproteinases (TIMP) from human skin and synovial fibroblasts. When cells are treated with 1, 10, and 100 ng/ml of either of these growth factors in combination with 10(-5) M retinoic acid, this results in a dose-dependent synergistic induction of TIMP protein secretion which is greater than the additive effect of the agents by up to fourfold. These responses can be inhibited by the presence of specific neutralising antibodies to the growth factors, demonstrating that they are not the result of an experimental artefact such as contamination with bacterial endotoxin. The mechanisms of these synergistic responses may involve the induction of receptors for retinoic acid, PDGF, or TGF-beta or may result from synergistic effects on TIMP gene transcription. We have also found that retinoic acid potently down-regulates PDGF-BB-stimulated collagenase in both types of fibroblast and that the effect of PDGF-BB alone on collagenase secretion from skin fibroblasts is biphasic. Finally, this study reports that retinoic acid and TGF-beta do not act in an additive fashion to inhibit the production of collagenase from skin fibroblasts.

Intra-articular corticosteroid reduces joint stiffness after an experimental periarticular fracture

Early care after surgery or trauma to the extremities often includes a period of immobilization. The resultant joint stiffness may require extensive rehabilitation and may permanently limit function of the limb. Posttraumatic joint stiffness is particularly vexing in the small joints. In an experimental model, we tested the effects of intra-articular corticosteroid injections on stiffness in a joint at risk of posttraumatic joint stiffness. Triamcinolone was injected into ankle joints of rabbits after distal tibial fractures. Three weeks after injury, joint stiffness increased 34% in ankles injected with the steroid. Stiffness in ankles injected with saline solution and in ankles treated with no injection increased 133% and 224%, respectively. Limb swelling and tibial torsional strength to failure were not significantly affected by either of the treatments.

Triamcinolone hexacetonide protects against fibrillation and osteophyte formation following chemically induced articular cartilage damage

Although corticosteroids have been shown to cause articular cartilage degeneration, recent studies of experimentally induced osteoarthritis indicate that under certain conditions they may protect against cartilage damage and osteophyte formation. The present study examines the in vivo effect of triamcinolone hexacetonide on the degeneration of articular cartilage which occurs following intraarticular injection of sodium iodoacetate. Three weeks after a single injection of iodoacetate into the knees of guinea pigs, ipsilateral femoral condylar cartilage exhibited fibrillation, loss of staining with Safranin O, depletion of chondrocytes, and prominent osteophytes. In striking contrast, when triamcinolone hexacetonide was injected into the ipsilateral knee 24 hours after the intraarticular injection of iodoacetate, fibrillation was noted in only 1 of 6 samples, osteophytes were much less prominent, pericellular staining with Safranin O persisted, and cell loss was less extensive. Knees of animals which received only one-tenth as much intraarticular triamcinolone hexacetonide after the iodoacetate injection also exhibited marked reduction in size and extent of osteophytes. However, the degree of fibrillation, loss of Safranin O staining, and chondrocyte depletion was similar to that observed in animals injected with iodoacetate but not treated with intraarticular steroid. No apparent morphologic or histochemical changes were observed after intraarticular injection of the steroid preparation alone. Thus, triamcinolone hexacetonide produced a marked, dose-dependent protective effect in this model of chemically induced articular cartilage damage.

Retinoids inhibit the differentiation of embryonic-mouse mesenchymal cells in vitro

The influence of all-trans retinoic acid, 13-cis retinoid acid and two aromatic retinoids (Ro 10-1670, Ro 11-1430) on the chondrogenic differentiation of mesenchymal cells in vitro was studied electron-microscopically. Organ cultures of limb buds from mouse embryos (Day 11) and high-density cultures of embryonic-mouse mesenchymal cells (Day 12) were used as experimental models. After a 6-day culture in the control medium, the development of hyaline cartilage was observed in both systems. In cultures which were treated with retinoids from Day 1 through Day 3 and then incubated in the control medium for 3 more days, the mesenchymal cells still maintained the morphological features of the blastema stage; cartilage synthesis was reduced (low retinoid concentrations) or completely absent (high retinoid concentrations). These findings indicate that the treatment of embryonic-mouse mesenchymal cells with retinoids induces a persistent and dose-dependent inhibition of chondrogenic differentiation, which in quantitative terms, is variably expressed during treatment with different retinoids. These inhibitory effects of retinoids on chondrogenesis are probably implicated in the pathogenetic mechanisms of their teratogenic action in vivo.

The effect of synovial tissue on the synthesis of proteoglycan by the articular cartilage of young pigs

Explants of pig articular cartilage were grown in organ culture in the presence of synovial tissue; controls consisted of paired explants that were cultivated in isolation. To find whether the synovial tissue affected synthesis of sulfated proteoglycan by the cartilage, 35SO4 was added to the medium and its incorporation into the cartilage examined by both biochemical assay and autoradiography. The synovial tissue severely inhibited the uptake of 35SO4, but if the synovium was removed after 8 days cultivation and the cartilage was grown in isolation for a further 4 days, incorporation of 35SO4 equalled and sometimes surpassed that of controls which had been grown without synovium continuously for 12 days. Synovium did not prevent the formation of new cartilage on the cut surfaces of the explants, but it reduced the incidence of newly formed cartilage.

Effect of homologous synovial membrane on adult human articular cartilage in organ culture, and failure to influence it with D-penicillamine

Adult human articular cartilage has been maintained in organ culture for 8 days, and the culture medium, which was changed on alternate days, was pooled. Normal and rheumatoid cartilage was obtained from patients and 4 types of culture were prepared: (1) cartilage alone; (2) cartilage + D-penicillamine; (3) cartilage + homologous synovium; (4) cartilage, synovium, and D-penicillamine. The hexosamines and hexuronic acid were measured in the cartilage explants and in the medium. The quantity released was divided by the amount measured in the original cartilage explant and the different culture variables were compared. D-penicillamine did not alter the release of cartilage proteoglycan, but the addition of synovium did. The rheumatoid cartilage released significantly more proteoglycan than normal cartilage whether or not homologous synovium was present.

The effect of hypervitaminosis A on rat palatal development

Retinoic acid or retinyl acetate was administered to pregnant rats in doses sufficient to induce a 90% incidence of cleft palate. In another study, a delay in the reorientation of the palatal shelves was observed to be longer with the more potent teratogen, retinoic acid. On day 16 of gestation, 24 hours after final dosage with vitamin A, the synthesis of DNA and protein was studied in fetal carcass, mandible, and palate, and that of sulfated mucopolysaccharides (S-MPS) and glycoproteins (GP) in fetal head, mandible, and palate. Increases in DNA synthesis in fetal palate and in GP synthesis in fetal palate were found; thus, the mechanism of action of vitamin A in inducing cleft palates in rats may be caused by interference with the normal biochemical synthetic pattern of the palatal shelves.

Synthesis of glycosaminoglycan in adult human articular cartilage in organ culture from patients with rheumatoid arthritis

Hyaline cartilage was obtained from patients undergoing synovectomy of the knee joint for rheumatoid arthritis. Eroded cartilage from beneath the invading pannus and relatively normal cartilage from the same joint were maintained in organ culture for three days. During the first 48 hours in culture the explants were exposed to 35SO4 in the medium. The equivalent layers of normal and eroded cartilage were analysed for DNA uronic acid and 35SO4 incorporation. There was a decrease in the DNA and uronic acid of the eroded cartilage, although only the latter reached statistical significance. The uptake of radioactive sulphate was significantly greater in explants taken from the eroded site than from normal areas. This increase in metabolic activity could well be a protective phenomenon.

The effect of D-penicillamine of the skeletal development of rat foetuses

Rats received 20, 50 or 100 mg/animal D-penicillamine i.p. twice daily on days 15, 16, 17, 18, and 19 of gestation, i.e. a total dose of 200, 500 resp. 1000 mg/animal. At all dosages the number of fetal resorptions did not increase significantly. Weight of the 20 day old embryos as well as length of the long bones in the extremities in the 100 mg-group showed a significant decrease. Numerous skeletal alterations could be observed in the 1000 mg-group such as absence, deformations or incomplete mineralisation of bones. Light microscopic examinations revealed an inhibition of the ossification as well as a decrease of number and size of the trabecula and of the thickness of the perichondrial bone sheath. A swelling of the collagenous fibrils can be demonstrated with the electron microscope. The first apatite crystals aggregate in collagen-free areas. The fusion of these aggregates to homogenously mineralized trabecula is inhibitied. In contrast to bones from untreated embryos, mineralized areas show varying content of collagen and apatide crystals. A regular spatial relationship between apatite crystals and collagenous fibrils does not develop. These findings show that even after the so-called "critical period" malformations can be pproduced by substances which disturb synthesis and maturation of the mesenchymal intercellular substance.

Vitamin A: concentration in the rat liver Golgi apparatus

Vitamin A compounds (principally as retinyl esters) are concentrated in Golgi apparatus fractions from rat liver. The amounts vary with the vitamin A status of the liver and show an inverse relation to the concentration of ubiubinone. The results suggest a specific role of the Golgi apparatus in the mobilization or action, or both, of vitamin A compounds.

Role of biological membranes in some skeletal reactions

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On the mechanisms of bone resorption. The action of parathyroid hormone on the excretion and synthesis of lysosomal enzymes and on the extracellular release of acid by bone cells

Bone resorption, characterized by the solubilization of both the mineral and the organic components of the osseous matrix, was obtained in tissue culture under the action of parathyroid hormone (PTH). It was accompanied by the excretion of six lysosomal acid hydrolases, which was in good correlation with the progress of the resorption evaluated by the release of phosphate, calcium 45 or hydroxyproline from the explants; there was no increased excretion of two nonlysosomal enzymes, alkaline phosphatase, and catalase. Balance studies and experiments with inhibitors of protein synthesis indicated that the intracellular stores of the acid hydrolases excreted were maintained by new synthesis. The release was not due to a direct disruption of the lysosomal membrane by PTH; it is presumed to result from an exocytosis of the whole lysosomal content and to involve mechanisms similar to those controlling the secretion of this content into digestive vacuoles. The resorbing explants acidified their culture fluids at a faster rate and released more lactate and citrate than the controls; this release was in good correlation, in the PTH-treated cultures, with the resorption of the bone mineral, but the amount of citrate released was considerably smaller than that of lactate. The acid released could account for the resorption of the mineral. It is proposed, as a working hypothesis, that the acid hydrolases of the lysosomes are active in the resorption of the organic matrix of bone and that acid, originating possibly from the stimulation of glycolysis, cares for the concomitant solubilization of bone mineral while also favoring the hydrolytic action of the lysosomal enzymes.

Cellular control of macromolecular synthesis: rates of synthesis of extracellular macromolecules during and after depletion by papain

Papain was administered in doses of 1.6, 8.0 or 80.0 μ g/ml. of synthetic medium for 24 h to 11- to 12-day embryonic chicken tibiae grown in organ culture. This treatment caused: (1) a decrease in length and weight, (2) loss of cells and total protein, (3) little change in hydroxyproline content, and (4) release of large amounts of glycosaminoglycans. When subcultured and allowed to recover in normal medium for periods of up to 144 h the explants increased in length and weight and partially replaced the lost material. In response to the depletion of the glycosaminoglycans, primarily chondroitin sulphate and keratan sulphate, from the extracellular matrix the cells of the treated explants synthesized both precursor hexosamine and the requisite polymerized glycosaminoglycans more rapidly than control explants. This increased rate of synthesis occurred whether or not the glycosaminoglycans were incorporated into the matrix; indeed, during recovery after treatment with the 80 μ g/ml. dose the tissue was unable to accept the newly synthesized macromolecules even though the matrix was very deficient in these substances, and the glycosaminoglycans were released into the medium. Large amounts of the monomer precursors of hexosamine also were released into the medium before they could be assembled into the polymer glycosaminoglycans. The results showed that the cell compensates for its loss of extracellular material by increased synthesis of the depleted macromolecules; after treatment with 8.0 μ g/ml. the rate of production of hexosamine was over three times that of the control explants.