Maria Francesca Ottaviani

Interactions between dendrimers and heparin and their implications for the anti-prion activity of dendrimers

Heparin is involved in the pathogenesis of prion diseases, affecting the process of fibril formation. It has been shown that whether it accelerates or inhibits fibrilogenesis depends on its concentration: prion peptide PrP 185-208 aggregates in the presence of 0.04 mg ml−1 heparin, but concentrations ten times lower or higher cause no aggregation. Polyamidoamine, polypropyleneimine and phosphorus dendrimers that previously exhibited anti-prion activity have been shown to interact with heparin. The interactions between cationic dendrimers and anionic heparin are mainly electrostatic. The present study shows that these interactions are indirectly responsible for the inhibition or enhancement of fibril formation by dendrimers.

Characterization of the Nonionic Microemulsions by EPR. I. Effect of Solubilized Drug on Nanostructure

The effect of the solubilized model drug, carbamazepine, on the internal structure of fully dilutable nonionic microemulsions was examined for the first time using electron paramagnetic resonance (EPR). Systems containing different surfactant to oil ratios, at two different pH values (4.6 and 8.5), with continuous dilution implementing structural transformations (micellar solution-W/O-bicontinuous-O/W) were investigated. The internal order, micropolarity, and microviscosity were scrutinized utilizing pH-dependent amphiphilic probe 5-doxylstearic acid (5-DSA). In the basic environment, the probe explored the vicinity of the surfactant head region; the deeper hydrophobic region of the surfactant tails was investigated in the acidic milieu. The study demonstrated that the EPR technique enables efficient monitoring of structural changes and examination of drug influence on structure in surfactant-poor systems. Lower order and microviscosity values were obtained in surfactant-poor systems in comparison to surfactant-rich systems. The drug functioned as a spacer of the surfactant molecules or as a cosurfactant depending on the formed microemulsion structure and the surfactant to oil ratio. The structural changes, pH variation, and presence of the drug did not alter the polarity parameter, indicating that the probe most likely does not sense a water environment in any of the examined systems. Under the basic conditions, higher microviscosity and order values were obtained in comparison to those at low pH, suggesting a higher order packing of the surfactant chains near the surfactant heads. The structural changes initiated in the vicinity of the surfactant heads, therefore, are more apparent in the basic environment. The ability to control and monitor the intramicellar interactions within drug carrier systems may be of significant interest for understanding the kinetics of drug release.

Do food microemulsions and dietary mixed micelles interact

Using microemulsions (ME) as delivery vehicles requires understanding whether water-insoluble molecules are delivered by an interaction of the ME system with the dietary mixed micelles (DMM) in the small intestine to give new mixed micelles, or by alternate paths. Diluted DMM and ME systems were mixed at various weight ratios to address this question. The individual and mixed systems were characterized by physical techniques that address this interaction from different aspects. This research showed that increased DMM concentration in ME/DMM mixed systems caused: (1) increased conformational order of the acyl chains and perturbed hydrogen bonds between the ethoxylate headgroups (based on ATR-FTIR results); (2) significant increase in microviscosity (from 1.7 to 3.3ns) (based on EPR results); (3) increased diffusivity of the surfactant molecules compared to their diffusivity in pure ME droplets, and decreased diffusivity of the taurochenodeoxycholate molecules compared to their diffusivities in pure DMM micelles (based on PGSE-NMR results); (4) formation or modification of intramolecular interactions (based on NOESY-NMR results); (5) decreased average droplet diameter and increased droplet density per unit area compared to pure ME systems (based on DLS and cryo-TEM results); and (6) fluorescence resonance energy transfer between two dyes (diphenylhexatriene and Nile Red), which were solubilized in each system separately (based on fluorescence resonance energy transfer results). These results show that DMM and ME interact to create ME-DMM mixed micelles, providing a potential pathway for delivering solubilized molecules.

Characterization of nonionic microemulsions by EPR. Part II. The effect of competitive solubilization of cholesterol and phytosterols on the nanostructure.

One of the theories for the reduction of cholesterol (CH) in the blood stream by the consumption of phytosterols (PS) states that these two types of sterols compete for solubilization within the dietary mixed micelles (DMM). In this study, a fully dilutable nonionic microemulsion system was used as a model to explain a possible competitive solubilization mechanism of CH and PS molecules using an electron paramagnetic resonance (EPR) technique that reveals relevant intramicellar properties. The effect of the solubilized sterols on the structural changes occurring in the vicinity of the surfactant head groups or closer to the oil phase was examined by controlling the pH of the environment, which influences the probe locus between the surfactant molecules. The results indicate that the structure transformations in the surfactant layer closer to the vicinity of the head groups region are more pronounced than the structural changes occurring in the region between the surfactant tails closer to the oil phase, except for the oil-in-water (O/W) micelles region. The study also shows that when each of the sterols is solubilized alone, they occupy different solubilization sites within the microemulsion nanostructures, in comparison to their solubilization together. This behavior is most pronounced in 3:1 (wt ratio) CH/PS systems. The main conclusion is that cosolubilization of these sterols leads to competitive solubilization between the surfactant tails closer to the oil phase locus, where the CH molecules are pushed toward the interface by the PS molecules. This conclusion might better explain the competitive solubilization of the two sterols in the human digestive tract.

Copper(II) complexes with 4-carbomethoxypyrrolidone functionalized PAMAM-dendrimers: an EPR study.

The internal flexibility and interacting ability of PAMAM-dendrimers having 4-carbomethoxypyrrolidone-groups as surface groups (termed Gn-Pyr), which may be useful for biomedical purposes, and ion traps were investigated by analyzing the EPR spectra of their copper(II) complexes. Increasing amounts (with respect to the Pyr groups) of copper(II) gave rise to different signals constituting the EPR spectra at room and low temperature corresponding to different coordinations of Cu(2+) inside and outside the dendrimers. At low Cu(2+) concentrations, CuN4 coordination involving the DAB core is preferential for G3- and G5-Pyr, while G4-Pyr shows a CuN3O coordination. CuN2O2 coordination into the external dendrimer layer was also contributing to G3- and G4-Pyr spectra. The structures of the proposed copper-dendrimer complexes were also shown. G4-Pyr displays unusual binding ability toward Cu(II) ions. Mainly the remarkably low toxicity shown by G4-Pyr and its peculiar binding ability leads to a potential use in biomedical fields.

Morpho-chemical characterization and surface properties of carcinogenic zeolite fibers.

Erionite belonging to the zeolite family is a human health-hazard, since it was demonstrated to be carcinogenic. Conversely, offretite family zeolites were suspected carcinogenic. Mineralogical, morphological, chemical, and surface characterizations were performed on two erionites (GF1, MD8) and one offretite (BV12) fibrous samples and, for comparison, one scolecite (SC1) sample. The specific surface area analysis indicated a larger availability of surface sites for the adsorption onto GF1, while SC1 shows the lowest one and the presence of large pores in the poorly fibrous zeolite aggregates. Selected spin probes revealed a high adsorption capacity of GF1 compared to the other zeolites, but the polar/charged interacting sites were well distributed, intercalated by less polar sites (Si-O-Si). MD8 surface is less homogeneous and the polar/charged sites are more interacting and closer to each other compared to GF1. The interacting ability of BV12 surface is much lower than that found for GF1 and MD8 and the probes are trapped in small pores into the fibrous aggregates. In comparison with the other zeolites, the non-carcinogenic SC1 shows a poor interacting ability and a lower surface polarity. These results helped to clarify the chemical properties and the surface interacting ability of these zeolite fibers which may be related to their carcinogenicity.

Comparative EPR studies of Cu(II)-conjugated phosphorous-dendrimers in the absence and presence of normal and cancer cells

Comparative electron paramagnetic resonance (EPR) studies of both Cu(II)-conjugated phosphorous-dendrimers and the corresponding Cu(II)-monomers bearing different ligand moieties are presented, showing that the coordination mode, the chemical structure, the flexibility and the stability of these complexes strongly depend on different parameters such as the nature of the ligands, the size (generation) of the dendrimer, and the molar ratio between Cu(II) and the ligands. Studies are performed in the presence of HCT-116 cancer cells, and MRC-5 normal cells allowing us to clarify the interaction mode of the Cu(II) ions in a biological medium at different equilibration times. These studies point out the particular behavior of the Cu(II)-conjugated phosphorous-dendrimer at generation 3, decorated with N-(di(pyridine-2-yl)methylene)ethanamine moiety (termed G3B). The G3B–Cu(II) complex shows strong anticancer activity. The EPR analysis helped to clarify the unusual properties of this complex in the absence and presence of normal and cancer cells.

Effect of Hydrogenated Cardanol on the Structure of Model Membranes Studied by EPR and NMR

Hydrogenated cardanol (HC) is known to act as an antiobesity, promising antioxidant, and eco-friendly brominating agent. In this respect, it is important to find the way to transport and protect HC into the body; a micellar structure works as the simplest membrane model and may be considered a suitable biocarrier for HC. Therefore, it is useful to analyze the impact of HC in the micellar structure and properties. This study reports a computer aided electron paramagnetic resonance (EPR) and (1)H NMR investigation of structural variations of cetyltrimetylammonium bromide (CTAB) micelles upon insertion of HC at different concentrations and pH variations. Surfactant spin probes inserted in the micelles allowed us to get information on the structure and dynamics of the micelles and the interactions between HC and CTAB. The formation of highly packed HC-CTAB mixed micelles were favored by the occurrence of both hydrophobic (chain-chain) and hydrophilic (between the polar and charged lipid heads) interactions. These interactions were enhanced by neutralization of the acidic HC heads. Different HC localizations into the micelles and micellar structures were identified by changing HC/CTAB relative concentrations and pH. The increase in HC concentration generated mixed micelles characterized by an increased surfactant packing. These results suggested a rod-like shape of the mixed micelles. The increase in pH promoted the insertion of deprotonated HC into less packed micelles, favored by the electrostatic head-head interactions between CTAB and deprotonated-HC surfactants.

Original Contribution: Stearic acid delivery to corneum from a mild and moisturizing cleanser

Objective  A mild moisturizing body wash with stearic acid, a key component of corneum lipids, and emollient soybean oil has been introduced in the market place. The objectives of this study are to determine the amount and the location of the stearic acid in the corneum after in vivo cleansing by the formulation.

W/O microemulsions as dendrimer nanocarriers: an EPR study.

A complex system, based on a dendrimer solubilized in the aqueous core of water-in-oil microemulsion, may combine the advantages of both dendrimers and microemulsions to provide better control of drug release. We report for the first time the use of EPR technique to determine the effect of solubilized dendrimer on the structure of the microemulsion. The solubilized poly(propyleneimine) (PPI-G2) interacts with sodium bis(2-ethylhexyl) sulfosuccinate (AOT). EPR analysis provided information on polarity, microviscosity, and molecular order of the systems. Polarity and microviscosity increased from unloaded water-in-oil microemulsion to the system loaded with 0.2 wt % PPI-G2, but remained unchanged with higher PPI-G2 loads. The degree of order also increased with 0.2 wt % PPI-G2 with only minor additional increase with larger quantities (25 wt %) of PPI-G2. Variations in pH only slightly affected the structure of microemulsion in the absence and presence of the loaded dendrimers. Aliphatic oils with longer lipophilic chains enhanced the structural order of the microemulsion. On increasing water content, polarity and degree of order increased. PPI-G2 dendrimer in small loads is attracted by the negatively charged AOT and thus intercalates in the interface of the droplets. Yet, at higher PPI-G2 loads, the excess molecules are solubilized in the water core.