A kinetic study of phosphate adsorption by boehmite.

Rates of phosphate adsorption to PT-A (a new type of aluminium oxide hydroxide) and ALG (aluminum hydroxide gel) from a pH 3 phosphate solution were measured by a batch method. Phosphate uptake progressed mainly by the adsorption mechanism for PT-A, but dissolution of aluminum and precipitation of aluminum phosphate took place in addition to phosphate adsorption for ALG. The intraparticle diffusivities (Dp'S) of phosphate were evaluated from the time courses of adsorption using the model of pore diffusion with a Freundlich-type adsorption isotherm. The Dp values were approximately 7 x 10(-7) cm2 S-1 for PT-A and 1 x 10(-6) cm2 s(-1) for ALG. The tortuosity factors calculated from a model of parallel plate pore were 5.1 for PT-A and 6.7 for ALG; these values resembled those for porous inorganic ion exchangers. The adsorption rates are high enough for each of the samples to be utilized as a phosphate adsorbent to prevent hyperphosphatemia in patients on chronic dialysis. PT-A is favored as a phosphate adsorbent because of its high chemical stability against acid.

[Phosphate ion-exchange with hydrotalcite-like compound in the presence of trypsin].

A Cl(-)-intercalated hydrotalcite-like compound (HTAL) is a promising material as a better phosphate adsorbent for further clinical use than the currently marketed aluminum hydroxide gels. In the preceding study, we found that Cl- ions in the interlayer of HTAL can be exchanged with phosphate ions equivalently. In the present study, we have investigated the adsorption of porcine pancreas trypsin on HTAL and the influence of trypsin adsorption on the phosphate/Cl- ion-exchange properties of HTAL. The isotherm for trypsin adsorption at 310K and pH 8.4 showed the curve of BDDT V type and gave an adsorption capacity of 88.6 mg/g for trypsin. The zeta-potential analysis of HTAL suggested that the trypsin adsorption on HTAL at pH 8.4 was restrained by the electrostatic repulsion between HTAL surface and trypsin with positive charge. XRD and nitrogen adsorption studies showed that trypsin was adsorbed on the external surface of HTAL by occupying the area (ca. 22 nm2) per trypsin molecule. The phosphate/Cl- ion-exchange reaction with HTAL was not affected by the presence of trypsin; the phosphate ion-exchange capacity reached 73.6 mg P/g from the solution containing 3200 mg trypsin/dm3. On the other hand, the trypsin adsorption was significantly depressed by the loading of phosphate ions. The XRD analysis of the phosphate-loaded HTAL revealed that the layered structure of hydrotalcite holds after the phosphate ion-exchange, but shows a slight increase of the interlayer distance from 0.3 nm to 0.5 nm by the intercalation of phosphate ions.

Mechanism of phosphate adsorption to a three-dimensional structure of boehmite in the presence of bovine serum albumin.

A new microcrystalline boehmite (tentatively named PT-A) was synthesized as an efficient phosphate adsorbent to replace aluminum hydroxide gel. The characteristic structure of PT-A was examined by nitrogen adsorption/desorption, X-ray diffraction, deviation microscopy, and scanning electron microscopy to establish a pore structural model of PT-A. With this model structure, the details of the mechanism of interaction between PT-A and phosphate in the presence of bovine serum albumin (BSA) are discussed. PT-A is a spherical particle with a diameter of approximately 100 microns and a porous surface structure, and its inside is packed with boehmite microcrystals (crystallite size, 2 nm). PT-A has three types of pores in its structure: a micropore with a narrow size-distribution, a mesopore with a broad size-distribution, and a macropore (radii of pores are 0.7, 1-20, and approximately 300 nm, respectively). When phosphate was incubated with PT-A in human gastric and intestinal juices or in an aqueous solution containing BSA, the amounts of phosphate adsorbed by PT-A were not affected by the presence of proteins. The nitrogen adsorption/desorption isotherms and energy dispersive X-ray analyses demonstrated that phosphate could diffuse to the smaller tunnels freely even if the external surface of PT-A was covered with BSA. It was also demonstrated that the main site of adsorption for phosphate was in micropores of PT-A, whereas BSA was adsorbed only to the external surface and none entered inside smaller tunnels consisting of micro- and mesopores.

Interaction of bovine serum albumin with the surface of a microcrystalline aluminum oxide hydroxide compound: a possible new type of phosphate adsorbent.

Aluminum hydroxide gel (ALG) has been effective for ameliorating acidosis associated with phosphatemia caused by hemodialysis. However, aluminum accumulation in the body causes severe side effects. As substitute for ALG, a new type of aluminum oxide hydroxide (tentatively named PT-A) was prepared with the hope of future clinical use. PT-A has a microcrystalline structure with a high resistance to pH change and has more phosphate-binding efficacy than ALG. It was tested for possible interaction with protein by adsorption test, zeta-potential analysis, X-ray diffraction, and scanning electron microscopy. Bovine serum albumin (BSA) was chosen as a model protein. The interaction of BSA with PT-A depended on the amount of adsorbent. Protein adsorption occurred rapidly and reached the maximal level at near neutral pHs. Phosphate adsorption was not affected by the presence of BSA, but the interaction of BSA with PT-A was significantly reduced by the presence of phosphate. Zeta-potential changes on the surface of PT-A indicated that the positively charged surface of PT-A was covered with negatively charged phosphate ions that repelled negatively charged BSA molecules. X-ray diffraction patterns indicated no observable structural alteration caused by adsorption of BSA or phosphate, and scanning electron microscopy revealed that BSA covered the outer surface of PT-A but did not cover small pores, where phosphate can freely penetrate.

Immunohistochemical localization of physiologic urinary proteins in Wistar rats.

Rat physiologic urinary proteins were immunohistochemically localized. In male Wistar rats, urinary protein antigens were present in both hepatic and epithelial cells of the salivary ducts, the coagulating gland, and the prostate gland. In female rats, urinary protein antigens were present in the same proportion of the salivary glands as in males and in the uterine glands, but to a lesser extent than in salivary glands. The results of this study indicate multiple origins of rat urinary proteins. It remains to be determined if female uterine glands contribute to urinary proteins.

Phosphate and pepsin adsorptions by a new boehmite compound and aluminum hydroxide.

A new microcrystalline compound of aluminum oxide hydroxide (tentatively named PT-A) was synthesized in the hope of providing a better phosphate adsorbent for future clinical use than the currently marketed aluminum hydroxide gels (ALG). An X-ray diffraction study demonstrated a boehmite structure in PT-A but an amorphous structure in ALG. PT-A was more stable in pH change than ALG; in elution tests in artificial gastric and intestinal solutions, aluminum ion eluted from PT-A was maximally 10% of the amount from ALG at pH 1.2; and was undetectable at pH 6.8, at which point ALG still showed some aluminum elution. Phosphate-adsorbing efficacy of PT-A and ALG in vitro was about the same at pH 1.2; however, it was four times greater in PT-A than in ALG at pH 6.8, indicating that PT-A will be effective in the intestine. PT-A also adsorbed pepsin but the amount was at most the same or much less than that adsorbed by ALG, which depended on pH in solution.