Hyaluronan suppresses fibronectin fragment-mediated damage to human cartilage explant cultures by enhancing proteoglycan synthesis.

Hyaluronic acid, recently renamed hyaluronan, has been used as a therapeutic intervention in the treatment of osteoarthritis. We have reported that high-molecular-weight (800 kDa) hyaluronan is effective in blocking the catabolic action of fibronectin fragments in explant cultures of bovine cartilage and in an experimental in vivo model of damage to the rabbit knee joint. The fibronectin fragments induce catabolic cytokines in human cartilage, which, in turn, suppress proteoglycan synthesis and induce matrix metalloproteinases to decrease the proteoglycan content. Since the clinical target of high-molecular-weight hyaluronan is human cartilage, which may differ in certain ways from bovine cartilage, we tested the effect on human knee cartilage. We found that 1 mg/ml hyaluronan completely blocked fibronectin fragment-mediated decreases in proteoglycan content in five of five specimens of cartilage from the human knee. This was associated with binding of exogenous hyaluronan to the superficial surface, suppressed penetration of the fibronectin fragment into the cartilage, decreased expression for the first week in culture of one of the matrix metalloproteinases involved in cartilage degradation, matrix metalloproteinase-3, and proteoglycan synthesis rates that increased to supernormal levels. However, the appearance of the NITEGE and VDIPEN neoepitopes, indices of cartilage degradation, was not blocked but was delayed by 1 week. The addition of hyaluronan to cartilage previously damaged by the fibronectin fragments or to osteoarthritic cartilage fully restored the proteoglycan content to control levels. We conclude that hyaluronan blocked damage at least partly by blocking penetration of the fibronectin fragments and slowing matrix metalloproteinase expression. However, the major effect on blocking damage and promoting repair may be through enhanced proteoglycan synthesis, a mechanism that requires further study. Nonetheless, these data clearly demonstrate that hyaluronan completely protected human cartilage in explant culture and facilitated a full restoration of proteoglycan in damaged cartilage.

Agents that block fibronectin fragment-mediated cartilage damage also promote repair.

OBJECTIVE AND DESIGN: The objective was to determine if agents that suppress catabolism might also enhance repair of irreversibly damaged cartilage. MATERIAL: Articular cartilage from bovine metacarpophalangeal joints was studied in explant culture. TREATMENT: Fibronectin fragments or IL-1 alpha, which potently cause proteoglycan (PG) loss from cartilage, were added to cultures also containing the catabolism-blocking agents: insulin-like growth factor-1, or N-acetylcysteine, or Arg-Gly-Asp-Ser peptide, and the effects of these agents on blocking PG loss determined. To test for repair or restoration of PG, cartilage was first damaged, damage agents removed and inhibitory agents added. METHODS: Each mean and SD value for cartilage PG content was determined by assays of papain digests of cartilage from three similar cultures. RESULTS: The agents either partially or fully blocked PG loss and promoted repair. CONCLUSIONS: Normally irreversible cartilage damage was reversed by slowing ongoing catabolic processes during attempted repair. Thus, catabolic inhibitors have reparative potential.

Generación de factores quimiotácticos para macrófagos alveolares, después de la instilación con asbesto crisotilo / Generation of chemotactic factors for alveolar macrophages after chrysotile asbestos instillation

Los modelos experimentales de asbestosis han demostrado que la respuesta inflamatoria inicial está mediada por macrófagos alveolares (MA). Aunque la atracción y acumulación de MA vistos en nuestros modelos está fundamentalmente mediada por el complemento, se ha sugerido la participación de otros factores quimiotácticos no bien caracterizados. En este trabajo, buscamos la presencia de factores quimiotácticos en ratas instiladas con asbesto en forma aguda. Demostramos morfoñlógicamente que el depósito de fibras, la respuesta macrofágica y las lesiones inducidas, son equivalentes a lo reportado en modelos por inhalación. Evaluamos la actividad quimiotáctica en el lavado broncoalveolar (LBA) fraccionado de acuerdo a su peso molecular (PM), y la presencia de albúmina y complemento. Encontramos actividad quimiotáctica en las fracciones del LBA correspondientes a picos de alto y bajo PM. La actividad del primer pico se atribuyó al complemento. La actividad del segundo, aumentó conforme al tiempo de exposición y no parece estar relacionada con complemento. Para identificar otros factores quimiotácticos diferentesa complemento, determinamos la presencia de factor de necrosis tumoral (TNFÿ) y fibronectina (FN) en los LBA no fraccionados. No se detectaron diferencias en la cantidad de TNF presente en los diferentes grupos. Observamos un incremento en la concentración de FN en relación al tiempo de exposición. Aunque la presencia de fracciones de FN pudiera explicar parcialmente el fenómeno quimiotáctico observado con el pico de bajo úPM, no podemos descartar la participación de otros factores no identificados

Thrombogenicity of a fibronectin-coated, experimental polytetrafluoroethylene graft.

To determine if pretreatment of polytetrafluoroethylene (PTFE) vascular grafts with fibronectin (FN) increased platelet adherence to them and adversely affected their patency, we labeled autologous canine platelets with indium III-oxine and interposed a FN-coated, experimental, 4 mm inner diameter, 10 cm long PTFE prosthesis into one carotid artery of 10 dogs. An identical graft, lacking only the FN coating, was implanted as a control in the contralateral carotid artery. A second group of 10 dogs was similarly treated, but each animal received 2 grains of aspirin and 50 mg of dipyridamole (Persantine) daily, beginning 3 days before surgery and continuing for the duration of the experiment. By means of a quantitative, gamma-camera, platelet adherence to the grafts was studied for 5 days after implantation. Graft patency was assessed with the Doppler velocity meter and was confirmed by surgical reexploration when thrombosis was suspected. FN coating increased platelet adhesion to the grafts in animals untreated with aspirin by a factor of threefold to fivefold. In those animals receiving antiplatelet drugs, patency of FN-coated grafts at 5 days was significantly (p less than 0.05) higher (80%) than in untreated animals (27.2%). In addition, mean platelet deposition on the grafts in these animals was reduced compared with untreated controls. Thus although FN coating of PTFE grafts significantly increases their affinity for platelets, this effect can be effectively abolished by pretreatment with aspirin and dipyridamole.