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.

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.