Oltea Murariu

Peptidic Targeting of Phosphatidylserine for the MRI Detection of Apoptosis in Atherosclerotic Plaques

Molecular and cellular imaging of atherosclerosis has garnered more interest at the beginning of the 21st century, with aims to image in vivo biological properties of plaque lesions. Apoptosis seems an attractive target for the diagnosis of vulnerable atherosclerotic plaques prone to a thrombotic event. The aim of the present work was to screen for apoptosis peptide binders by phage display with the final purpose to detect apoptotic cells in atherosclerotic plaques by magnetic resonance imaging (MRI). A phosphatidylserine-specific peptide identified by phage display was thus used to design an MRI contrast agent (CA), which was evaluated as a potential in vivo reporter of apoptotic cells. A library of linear 6-mer random peptides was screened in vitro against immobilized phosphatidylserine. Phage DNA was isolated and sequenced, and the affinity of peptides for phosphatidylserine was evaluated by enzyme-linked immunosorbent assay. The phosphatidylserine-specific peptide and its scrambled homologue were attached to a linker and conjugated to DTPA-isothiocyanate. The products were purified by dialysis and by column chromatography and complexed with gadolinium chloride. After their evaluation using apoptotic cells and a mouse model of liver apoptosis, the phosphatidylserine-targeted CA was used to image atherosclerotic lesions on ApoE(-/-) transgenic mice. Apoptotic cells were detected on liver and aorta specimens by the immunostaining of phosphatidylserine and of active caspase-3. Sequencing of the phage genome highlighted nine different peptides. Their alignment with amino acid sequences of relevant proteins revealed a frequent homology with Ca2+ channels, reminiscent of the function of annexins. Alignment with molecules involved in apoptosis provides a direct correlation between peptide selection and utility. The in vivo MRI studies performed at 4.7 T provide proof of concept that apoptosis-related pathologies could be diagnosed by MRI with a low molecular weight paramagnetic agent. The new CA could have real potential in the diagnosis and therapy monitoring of atherosclerotic disease and of other apoptosis-associated pathologies, such as cancer, ischemia, chronic inflammation, autoimmune disorders, transplant rejection, neurodegenerative disorders, and diabetes mellitus. The phage display-derived peptide could also play a potential therapeutic role through anticoagulant activity by mimicking the role of annexin V, the endogenous ligand of phosphatidylserine.

How to quantify iron in an aqueous or biological matrix: a technical note

Iron oxide (nano)particles are powerful contrast agents for MRI and tags for magnetic cellular labeling. The need for quantitative methods to evaluate the iron content of contrast media solutions and biological matrixes is thus obvious. Several convenient methods aiming at the quantification of iron from iron oxide nanoparticle-containing samples are presented.

Effect of incorporation of POSS compounds and phosphorous hardeners on thermal and fire resistance of nanofilled aeronautic resins

The aim of this work is the identification of the best strategy for improving thermal, fire resistance and electrical conductivity of an epoxy resin for aeronautic applications. The effect of DodecaPhenyl POSS (DPHPOSS), Epoxycyclohexyl POSS (ECPOSS), Glycidyl POSS (GPOSS) and TriglycidylCyclohexyl POSS (TCPOSS) to act as flame retardants of the resin was evaluated. Flame retardancy tested by the limiting oxygen index (LOI) indicated that GPOSS has meaningful effects on the flame retardancy of the epoxy mixture. The incorporation of 5 wt% of GPOSS into the epoxy matrix resulted in a LOI value of 33 with respect to 27 of the pure epoxy mixture. The trend observed by LOI tests was confirmed by mass loss calorimetry measurements: a decrease from 540 kW m−2 down to 327 kW m−2 was observed in the peak of heat release rate (PHRR). LOI and PHRR values were compared with those obtained for the same resin replacing the 4,4′-diaminodiphenyl sulfone (DDS) with the bis(3-aminophenyl) phenylphosphineoxide (BAPPO) and the bis(3-aminophenyl) methyl phosphine oxide (BAMPO). BAMPO and BAPPO proved to be more effective than POSS compounds to increase LOI values. Carbon nanotubes (CNTs), embedded inside the epoxy resin to enhance electrical conductivity, are found to affect significantly fire properties of epoxy systems mainly by preventing the epoxy systems from forming intumescent charring.

In vitro biomedical applications of functionalized iron oxide nanoparticles, including those not related to magnetic properties.

Superparamagnetic iron oxide nanoparticles (SPION) are very promising contrast media, especially for molecular imaging, due to their superior NMR efficacy. They even have wider biomedical applications such as in drug and gene delivery, tissue engineering and bioseparation, or as sensitive biological nanosensors. By coupling them to affinity ligands, SPION can bind to drugs, proteins, enzymes, antibodies or nucleotides. For in vitro biomedical applications, the detection of molecular interaction is possible by using a diversity of systems capable of sensing the magnetic properties of these materials. The goal of the present work was to develop and validate various in vitro biomedical applications of ultrasmall superparamagnetic particles of iron oxide (USPIO), including some that are not related to their magnetic properties. USPIO coated with dextran, starch or bisphosphonate exposing carboxylate groups were synthesized and some of them were functionalized by conjugating various biomolecules, such as biotin, streptavidin and apoptosis, or VCAM-1 specific peptides. The in vitro biomedical applications assessed in the present work included: (1) the relaxometric measurement of antibody concentration, cell receptor expression, molecular interaction, and enzymatic activity in aqueous suspensions; (2) MRI visualization of cells and detection of molecular interaction in an ELISA system; (3) ELISA applications of USPIO derivatives; and (4) detection of specific biomolecules by histochemistry. Our results confirm that rapid and simple in vitro detection of a diversity of functionalized SPION with relevance in medicine is possible by the existing NMR techniques and by chemical staining reactions. The protocols can be applied to minimally prepared biological samples (e.g. whole blood, blood plasma or serum, cell suspensions, biopsies, histological preparations, etc.), and often do not need complicated systems of signal amplification. The use of SPION labeled compounds could furthermore contribute to cost reductions in the diagnosis and in patient care.

Polyethylene-polyaniline Nanofiber Composites: Evaluation of Experimental Conditions of in situ Polymerization

The difficult processability of polyaniline (PAni) can be overcome by preparing composites with high density polyethylene (HDPE), resulting in a conducting material with improved mechanical properties. PAni nanofibers were synthesized in this research using a rapid mixing method, while HDPE/PAni composites were prepared by in situ polymerization using Cp2ZrCl2/MAO as a catalyst system. Different experimental conditions for polymerization and an electrochemical study were performed. The findings confirmed that the addition of small amounts of Pani (up to 7%) and longer impregnation (120 min) with methylaluminoxane (MAO) before polymerization are important factors contributing to increased catalytic activity. Analysis by cyclic and differential pulse voltammetry indicates that MAO reacts with the PAni in the ethylene polymerization process, and forms active species in the presence of the catalyst. Changes in catalytic activity may be due to the kinetic consumption of the active species, which become less important in the presence of PAni.

Thermal Degradation and fire properties of epoxy modified resins

The flammability of the resin is a major limitation in the aeronautic applications where new developed materials for primary and secondary structures must fulfill special regulation in order to demonstrate that their level of fire safety is equivalent to a conventional transport (aluminum) material. In this paper, the attention is focused on the thermal properties and the fire behavior of TGMDA based epoxy resins in which carbon nanotubes and POSS have been dispersed at nanometric or molecular level. The effect of the hardener, the diluent and the nanoparticles on the thermal properties has been investigated. Thermogravimetric data have been modeled according to the Coats and Redfen equations which provide a fast method for the determination of the kinetics of thermal degradation of polymers. The char yield has been used as criteria for evaluating limiting oxygen index (LOI) of the resin in accordance with Van Krevelen and Hoftyzer equation and the results have been compared with the experimental LOI dataThe flammability of the resin is a major limitation in the aeronautic applications where new developed materials for primary and secondary structures must fulfill special regulation in order to demonstrate that their level of fire safety is equivalent to a conventional transport (aluminum) material. In this paper, the attention is focused on the thermal properties and the fire behavior of TGMDA based epoxy resins in which carbon nanotubes and POSS have been dispersed at nanometric or molecular level. The effect of the hardener, the diluent and the nanoparticles on the thermal properties has been investigated. Thermogravimetric data have been modeled according to the Coats and Redfen equations which provide a fast method for the determination of the kinetics of thermal degradation of polymers. The char yield has been used as criteria for evaluating limiting oxygen index (LOI) of the resin in accordance with Van Krevelen and Hoftyzer equation and the results have been compared with the experimental LOI data