Apatite Containing Aspartic Acid for Selective Protein Loading

Abstract

Physico-chemical modifications of hydroxyapatite (HAp) materials are considered as pre-requisites for the development of new bioactive carrier materials for drug delivery and tissue engineering applications. Since acidic amino acids have well-documented affinities to both HAp and basic proteins, HAp modified by aspartic acid (Asp, acidic amino acid) might be one of the candidate substrates for a basic protein carrier. Here, we synthesized HAp in the presence of various concentrations of Asp and observed that HAp crystallinity and other physico-chemical properties were effectively modulated. Detailed studies indicated that Asp was not incorporated in the HAp crystal lattice, but rather was trapped in HAp crystals. Protein adsorption studies indicated that the HAp particles modified by Asp had a selective loading capacity for basic protein. Therefore, HAp particles containing Asp might have potential in drug delivery applications, especially as the carrier of basic proteins including bFGF and BMP.

Modulating protein adsorption onto hydroxyapatite particles using different amino acid treatments

“…The presence of Asp and Ser during HA preparation substantially reduced the crystallinity of HA (figure 2). Our results are in good agreement with the data reported by Uddin et al [19] in which the surface area increased twofold when 0.2 M Asp was added during HA preparation and the size of particles had an inverse relationship with their specific surface area. In a separate study, Gonzalez-McQuire et al [20] showed that the presence of amino acids inhibited the crystal growth of HA.…”

“…For example, the calculated 1/n for the lysozyme adsorption onto Asp-HA is 0.848 (table 2), which shows a relatively high degree of homogeneity. For the BSA adsorption on Asp-HA, the Q m value was 16.23 mg g -1 (table 1), which is higher than that reported by Uddin et al [19] ). The extent of the first adsorbed protein layer (both BSA and lysozyme) onto HA depends on the strength of proteins -surface electrostatic interactions.…”

“…This could be explained in terms of favourable electrostatic interaction of the enhanced negative charge sites of Asp-HA (PO 3À 4 and additional two 2COO 2 groups on Asp-HA surface) towards the positive region ðÀNH þ 3 ) of lysozyme. A similar approach was applied to increase the adsorption of basic protein (cytochrome C) by adding Asp into HA, whereby more than twofold increase of cytochrome c binding was reported [19]. Uddin et al [19] further investigated the influence of -COO 2 groups on protein-binding by blocking the -COO 2 groups on Asp-HA surface with the excess of ÀNH þ 3 .…”

“…A similar approach was applied to increase the adsorption of basic protein (cytochrome C) by adding Asp into HA, whereby more than twofold increase of cytochrome c binding was reported [19]. Uddin et al [19] further investigated the influence of -COO 2 groups on protein-binding by blocking the -COO 2 groups on Asp-HA surface with the excess of ÀNH þ 3 . Consequently, the binding of cytochrome c was significantly reduced.…”

In situ synthesis carbonated hydroxyapatite layers on enamel slices with acidic amino acids by a novel two-step method

“…In fact, the interaction of HA with biological macromolecules, such as amino acids, is a promising method to control the surface charge of HA and thus influence the morphology of synthesized HA powder [23][24][25][26]. However, major aspects of the formation mechanism of enamel-like HA crystal synthesized on enamel are still unclear, e.g., HA nucleation, crystal growth and crystal orientation.…”