Photothermal conversion efficiency and cytotoxic effect of gold nanorods stabilized with chitosan, alginate and poly(vinyl alcohol)

Gold nanorods (GNR) use has been proposed in medical applications because of their intrinsic photothermal properties. However, the presence of CTAB molecules adsorbed onto the surface of GNRs results in a highly cytotoxic GNR system. In this work we replace the CTAB molecules with a thiolated chitosan. Once chitosan coated GNRs (Chi-SH-GNR) were attained, a film of alginate (Alg-Chi-SH-GNR) or polyvinyl alcohol (PVA-Chi-SH-GNR) was deposited onto the surface of Chi-GNR by a layer-by-layer process. The photothermal conversion efficiency for the GNR systems was determined irradiating the GNRs suspended in aqua media with a CW 808nm diode laser (CNI, China). The cytotoxicity effect and the photothermal cellular damage of GNR systems were evaluated on a breast cancer cell line. Results show that polymer coats did not affect the transduction photothermal efficiency. Values around 50% were obtained for the different coated gold nanorods. The cytotoxicity of coated gold nanorods diminished significantly compared with those GNR stabilized with CTAB. The laser irradiation of cells treated with gold nanorods showed a decrease in their viability compared with the cells treated but no irradiated.

Oligomers, protofibrils and amyloid fibrils from recombinant human lysozyme (rHL): fibrillation process and cytotoxicity evaluation for ARPE-19 cell line

Amyloid-associated diseases, such Alzheimer's, Huntington's, Parkinson's, and type II diabetes, are related to protein misfolding and aggregation. Herein, the time evolution of scattered light intensity, hydrophobic properties, and conformational changes during fibrillation processes of rHL solutions at 55 °C and pH 2.0 were used to monitor the aggregation process of recombinant human lysozyme (rHL). Dynamic light scattering (DLS), thioflavin T (ThT) fluorescence, and surface tension (ST) at the air-water interface were used to analyze the hydrophobic properties of pre-amyloid aggregates involved in the fibrillation process of rHL to find a correlation between the hydrophobic character of oligomers, protofibrils and amyloid aggregates with the gain in cross-β-sheet structure, depending on the increase in the incubation periods. The ability of the different aggregates of rHL isolated during the fibrillation process to be adsorbed at the air-water interface can provide important information about the hydrophobic properties of the protein, which can be related to changes in the secondary structure of rHL, resulting in cytotoxic or non-cytotoxic species. Thus, we evaluated the cytotoxic effect of oligomers, protofibrils and amyloid fibrils on the cell line ARPE-19 using the MTT reduction test. The more cytotoxic protein species arose after a 600-min incubation time, suggesting that the hydrophobic character of pre-amyloid fibrils, in addition to the high prevalence of the cross-β-sheet conformation, can become toxic for the cell line ARPE-19.

Interaction of N-nitrosodiethylamine/bovine serum albumin complexes with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine monolayers at the air-water interface

We report the effect of N-nitrosodiethylamine (NDA) on the interaction between bovine serum albumin (BSA) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine monolayers (DPPC) at the air-water interface. We prepared aqueous solutions of NDA/BSA complexes maintaining a constant concentration of BSA of 1.49 x 10(-9) M and using NDA concentrations to obtain 2000, 4000, 6000, 12,500, and 25,000 NDA/BSA molar ratios. The hysteresis area and the compressional modulus of the compression-expansion cycles performed at different times were dependent on the NDA concentration. The cycles performed demonstrate the stability of the new phase of DPPC/BSA and DPPC/NDA/BSA monolayers. This was achieved probably because the BSA concentration used was lower than the one needed for BSA to inhibit the return of DPPC molecules to the interface. Results of the compressional modulus at the onset of the new phase, obtained around 17 mN/m, 15 min and 1, 3, 5, and 12 h after DPPC deposition, indicated that the 3.0 x 10(-6) M NDA concentration produced a more rigid film, probably due to the higher alpha-helix content of BSA. AFM images were obtained for DPPC/BSA and two DPPC/NDA/BSA complexes. Our images show that 12,500 NDA/BSA molecules were mostly adsorbed in the liquid condensed phase. However, BSA molecules were distributed more homogeneously.

Chitosan−Cholesterol and Chitosan−Stearic Acid Interactions at the Air−Water Interface

We report in this work the isotherms of cholesterol and stearic acid at the air-water interface modified by different chitosans (chitosan chloride, hydrophobic modified chitosan, and medium and high molecular weight chitosans) in the aqueous subphase. The Langmuir-Blodgett films of the complexes cholesterol-chitosan and stearic acid-chitosan are analyzed by atomic force microscopy (AFM), and a molecular simulation was performed to visualize the chitosan-lipid interactions. Strong modifications are obtained in the isotherms as a result of the chitosan interactions with cholesterol and stearic acid at the air-water interface. These modifications were dependent on the type and concentration of chitosan. Severe modifications of all phases were noticed with larger molecular areas, and the observed changes in the compressional modulus were dependent on the type of chitosan used. The complexes of chitosan-stearic acid were more flexible than the ones of chitosan-cholesterol. The AFM images demonstrated that chitosan was disaggregated by the cholesterol and stearic acid interactions producing more homogeneous surfaces in some cases. The hydrophobic chitosan showed more affinity with stearic acid, while both medium and high molecular weight chitosans produced homogeneous surfaces with cholesterol. The simulated chitosan chains interacting with cholesterol and stearic acid demonstrated the possibility of specific sites of electrostatic bonds between these molecules. Adsorption of cholesterol on the different powdered chitosans, performed by HPLC, showed that the medium and high molecular weight chitosans could retain higher proportions of cholesterol compared with the other analyzed samples.