Size-tunable LDH-protein hybrids toward the optimization of drug nanocarriers.

Layered double hydroxides (LDHs) are extensively investigated as drug nanocarriers due to their anion exchange properties and potential capacity to achieve enhanced cellular trafficking and targeted delivery. In this work, LDH-protein hybrids with controlled particle size were obtained by modulation of the charge and hydrophobicity of LDH matrixes. In order to do that, bovine serum albumin (BSA) adsorption was studied in LDH matrixes intercalated with chloride and dodecylsulfate (DS-) in different ratios and its dependence on pH and ionic strength was determined. Positively charged LDH-Cl matrixes in aqueous solution changed from micro- to nano-size when adsorbing BSA molecules at pH values higher than the isoelectric point of the protein. On the other hand, the low BSA hybridization with a negatively charged LDH-DS matrix was not enough to reduce its particle size. However, a fine tuning of the physicochemical properties of the LDH-Cl matrix by controlled DS- incorporation and pH and ionic strength conditions allowed LDH-BSA nanohybrids to be partially intercalated with the surfactant that exhibited colloidal stability at high ionic strength (similar to that of biological fluids).

Adsorption of IgG onto hydrophobic teflon. Differences between the F(ab) and F(c) domains.

The effect of differences in the degree of hydrophobicity of protein patches/fragments on the adsorption behaviour of the protein is investigated. The adsorption isotherm of a monoclonal mouse anti-human immunoglobulin G (isotype 2b) onto hydrophobic Teflon particles is measured using a depletion method. The adsorption-induced denaturation of the immunoglobulin as a function of the adsorbed amount is studied by differential scanning calorimetry, and the corresponding rearrangements in the secondary structure of the whole IgG molecule and its F(ab) and F(c) fragments are determined by circular dichroism spectroscopy. The effects of adsorption on the F(ab) and F(c) fragments in the intact IgG molecule occur independently. Adsorption of the whole IgG molecule leads to denaturation of the F(ab) fragments, whereas the F(c) fragment remains unperturbed; adsorption of the isolated fragments results in structural changes in both F(ab) and F(c). The surface hydrophobicity of the isolated fragments was studied by HPLC. These experiments support the hypothesis that differences in the degree of denaturation between F(ab) and F(c) are due to the higher degree of hydrophobicity of the F(ab) fragment. The adsorption-induced changes in the secondary structure are more prominent for the isolated fragments as compared to intact IgG. This is ascribed to the higher flexibility of the isolated fragment, as compared to the fragment in the whole molecule.

BSA structural changes during homomolecular exchange between the adsorbed and the dissolved states.

The secondary structure and the thermostability of bovine serum albumin (BSA), before adsorption and after homomolecular displacement from silica and polystyrene particles, are studied by circular dichroism spectroscopy and differential scanning calorimetry. The structural perturbations induced by the hydrophilic silica surface are reversible, i.e. BSA completely regains the native structure and stability after being exchanged. On the other hand, the adsorption on, and subsequent desorption from, polystyrene particles causes irreversible changes in the stability and (secondary) structure of BSA. The exchanged proteins have a higher denaturation temperature and a lower enthalpy of denaturation than native BSA. The alpha-helix content is reduced while the beta-turn fraction is increased in the exchanged molecules. Both effects are more pronounced when the protein is displaced from less crowded sorbent surfaces. The irreversible surface-induced conformational change may be related to some aggregation of BSA molecules after being exposed to a hydrophobic surface.