Effect of Iron Oxide Nanoparticles on the Oxidation and Secondary Structure of Growth Hormone

Oxidation of therapeutic proteins (TPs) can lead to changes in their pharmacokinetics, biological activity and immunogenicity. Metal impurities such as iron are known to increase oxidation of TPs, but nanoparticulate metals have unique physical and chemical properties compared to the bulk material or free metal ions. Iron oxide nanoparticles (lONPs) may originate from equipment used in the manufacturing of TPs or from needles during injection. In this study, the impact of lONPs on oxidation of a model protein, rat growth hormone (rGH), was investigated under chemical stress. Hydrogen peroxide (H(2)O(2))- and 2,2′-azobis (2-methylpropionamidine) dihydrochloride (AAPH) oxidized methionine residues of rGH, but unexpectedly, oxidation was suppressed in the presence of lONPs compared to a phosphate buffer control. Fourier transform infrared (FTIR) spectroscopy indicated splitting of the α-helical absorbance band in the presence of lONPs, while CD spectra showed a reduced α-helical contribution with increasing temperature for both rGH and rGH-IONP mixtures. The results collectively indicate that lONPs can increase the chemical stability of rGH by altering the kinetics and preference of amino acid residues that are oxidized, although the changes in protein secondary structure by lONPs may lead to alterations of physical stability.