Comparison of Phosphate Binding Capacities of PA21, A Novel Phosphate Binder, with those of other Phosphate Binders in vitro and in vivo.

PURPOSE: The phosphate binding capacity of PA21, a novel phosphate binder, was compared with those of other phosphate binders in vitro and in vivo. METHODS: 1) For in vitro studies, PA21, sevelamer hydrochloride, lanthanum carbonate hydrate, calcium carbonate, and ferric citrate hydrate were incubated with a phosphate solution at 37°C for 2 h. Phosphate binding capacity was assessed at simulated gastrointestinal tract pH levels of 2, 5, and 8 for estimation of clinical effects, and the quantity of phosphate adsorbed by each phosphate binder was determined. 2) For in vivo studies, rats were orally administered various phosphate binders after the oral administration of phosphate solution (100 mg/kg) adjusted to pH 2, 5, or 8, and the effects of PA21 and other phosphate binders on the serum phosphorus level of the rats were investigated. RESULTS: 1) The in vitro studies revealed that PA21 and sevelamer hydrochloride adsorbed phosphate better at all tested pH levels than lanthanum carbonate hydrate, calcium carbonate, and ferric citrate hydrate, and PA21 showed the most potent phosphate binding capacity among the tested compounds. 2) The in vivo studies showed that PA21 dose-dependently inhibited the increase in the serum phosphorus level after the administration of phosphate solution and no difference in the extent of inhibition by PA21 was observed at the different pH levels (in contrast to other phosphate binders). CONCLUSION: These results indicated that PA21 has a phosphate binding capacity over the entire pH range of the GI tract.

Cryoscanning electron microscopy of loaded articular cartilage with special reference to the surface amorphous layer.

The surface layer (i.e. the surface lamina) of articular cartilage, which is devoid of a collagen fibril network or cells, was investigated in the pig and human. It overlies the collagenous main part of the articular cartilage which contains chondrocytes and is thought to be important biomechanically. In order to examine morphological changes in this layer when under load, knee articular cartilage of the pig, along with the underlying subchondral bone, was compressed with a cylindrical indenter. The specimen was frozen by immersion in liquid nitrogen to maintain the loaded condition and was then freeze-fractured at the indented region. The fracture face was examined with a cryoscanning electron microscope. The surface layer was compressed beneath the indenter regardless of loading pressure or period and was expanded around the indenter to form a triangular bulge in cross section. The height of the bulge was related to the applied pressure and not to the loading period. Recovery of the cartilage from indentation was also examined. Immediately after removal of the indenter, the bulge of the surface layer moved back into the previously indented region. The region was covered by a thick surface layer after 2 s. The response of the surface layer to and recovery from indentation was largely instantaneous and elastic. Under heavy load conditions, the main part of the cartilage under the indenter was observed to have a striped pattern which was made up of bands of densely packed collagen fibrils with fibrillar networks remaining between them. These morphological findings agree well with previously reported biomechanical hypotheses and can be explained by the flow of interstitial fluid provoked by stress application.

Cryoscanning electron microscopic study of the surface amorphous layer of articular cartilage.

In order to elucidate the structure near the articular surface, frozen unfixed hydrated articular cartilage with subchondral bone from the pig knee was examined using a cryoscanning electron microscope (cryo-SEM). This method is considered to reduce the introduction of artefacts due to fixation and drying. An amorphous layer, without a collagen-fibril network or chondrocytes, covered most of the surface of the cartilage. This layer was termed the surface amorphous layer. It showed various appearances, which were classified into 4 groups. The average thickness of the layer did not differ among the 8 anatomical regions from which the specimens were taken. The thickness of the layer was found to correlate with the type of appearance of the layer. The 4 appearances associated with thicknesses in descending order are: 'streaked', 'foliate', 'spotted', and 'vestigial'. The surface layer observed in the cryo-SEM was thicker than that observed by a conventional SEM. This difference may be attributable to dehydration of the specimen used in specimen preparation for the latter technique. The layer was also observed in articular cartilage taken from human and rabbit knees. The layer was found to be unstable and to have very variable features. Its thickness and appearance may be influenced by various factors such as dehydration, fluid absorption or mechanical stress.