Omar Mertins

Spray-dried indomethacin-loaded polyester nanocapsules and nanospheres: development, stability evaluation and nanostructure models.

The industrial development of polymeric nanoparticle suspensions, as drug delivery systems, is limited due to the problems in maintaining stability of suspensions. In this work, a spray-drying technique was applied to dry nanocapsule and nanosphere suspensions prepared by nanoprecipitation of polyesters using SiO(2) as adjuvant. Powders obtained from nanocapsules presented stable drug recoveries and morphological characteristics after 5 months. For nanocapsules, nanostructures around 200 nm were observed by scanning electron microscopy (SEM) on the surface of microparticles of SiO(2), whereas for the nanosphere formulation, nanostructures with a reduced diameter (60-90 nm) were observed, despite the particle sizes of each original suspension being similar, when measured by photon correlation spectroscopy (PCS). In order to investigate the morphological aspects of nanocapsule and nanosphere powders, several nanosphere formulations were spray-dried using different concentrations of SiO(2) and a comparative study of the different colloidal systems (nanocapsules, nanospheres, nanoemulsion or nanodispersion) was carried out by PCS. SEM analyses showed that nanostructures with reduced diameter are formed independently of the adjuvant concentration. The dynamic properties of these systems allowed to suggest that the structure of the nanosphere particle (polymer, sorbitan monostearate and polysorbate 80) was a polymeric matrix dispersing the sorbitan monostearate which, when submitted to the spray-drying process in the presence of SiO(2), gave nanostructures presenting diameters around 80 nm covering the microparticles due to the release of lipophilic surfactant from the polymeric matrix.

Interaction between phospholipids bilayer and chitosan in liposomes investigated by 31P NMR spectroscopy

The interaction between chitosan and the polar head of phosphatidylcholine (PC) is discussed for a composite nanovesicle obtained by incorporating chitosan in the organic phase before PC self-assembling. Nanovesicles free of chitosan are studied in parallel to allow the comparison concerning modifications produced on the composite system. Zeta Potential increases in the presence of chitosan and with the increase in its concentration proving the localization of the polymer over the external surface of the vesicle as one interaction site. A (31)P resonance around 0 ppm, characteristic of the system, is reduced with addition of chitosan at 25 degrees C, indicating motional freedom reduction of the polar head phosphate group. The same resonance signal remains almost constant after increasing the temperature to 60 degrees C, suggesting that chitosan shields the phospholipids polar heads as a consequence of the electrostatic interactions leading to an increase in the thermodynamic stability of the composite.

Physical Damage on Giant Vesicles Membrane as a Result of Methylene Blue Photoirradiation

In this study we pursue a closer analysis of the photodamage promoted on giant unilamellar vesicles membranes made of dioleoyl-sn-glycero-3-phosphocholine (DOPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), by irradiating methylene blue present in the giant unilamellar vesicles solution. By means of optical microscopy and electro-deformation experiments, the physical damage on the vesicle membrane was followed and the phospholipids oxidation was evaluated in terms of changes in the membrane surface area and permeability. As expected, oxidation modifies structural characteristics of the phospholipids that lead to remarkable membrane alterations. By comparing DOPC- with POPC-made membranes, we observed that the rate of pore formation and vesicle degradation as a function of methylene blue concentration follows a diffusion law in the case of DOPC and a linear variation in the case of POPC. We attributed this scenario to the nucleation process of oxidized species following a diffusion-limited growth regime for DOPC and in the case of POPC a homogeneous nucleation process. On the basis of these premises, we constructed models based on reaction-diffusion equations that fit well with the experimental data. This information shows that the outcome of the photosensitization reactions is critically dependent on the type of lipid present in the membrane.

Membrane changes under oxidative stress: the impact of oxidized lipids

Studying photosensitized oxidation of unsaturated phospholipids is of importance for understanding the basic processes underlying photodynamic therapy, photoaging and many other biological dysfunctions. In this review we show that the giant unilamellar vesicle, when used as a simplified model of biological membranes, is a powerful tool to investigate how in situ photogenerated oxidative species impact the phospholipid bilayer. The extent of membrane damage can be modulated by choosing a specific photosensitizer (PS) which is activated by light irradiation and can react by either type I and or type II mechanism. We will show that type II PS generates only singlet oxygen which reacts to the phospholipid acyl double bond. The byproduct thus formed is a lipid hydroperoxide which accumulates in the membrane as a function of singlet oxygen production and induces an increase in its area without significantly affecting membrane permeability. The presence of a lipid hydroperoxide can also play an important role in the formation of the lipid domain for mimetic plasma membranes. Lipid hydroperoxides can be also transformed in shortened chain compounds, such as aldehydes and carboxylic acids, in the presence of a PS that reacts via the type I mechanism. The presence of such byproducts may form hydrophilic pores in the membrane for moderate oxidative stress or promote membrane disruption for massive oxidation. Our results provide a new tool to explore membrane response to an oxidative stress and may have implications in biological signaling of redox misbalance.

Caracterização da pureza de fosfatidilcolina da soja através de RMN de ¹H e de 31P

A strategy is proposed to evaluate the purity of phosphatidylcholine from soybean lecithin, obtained by extraction or column chromatography, using the integrals ratio of 1H NMR spectra. Integrals of methylene signals, around 1.3 and 1.6 ppm, are added and divided by the integral of the choline methyl groups, around 3.3 ppm. Before purification, a ratio of 19.68±1.37 was determined. Using extraction, a ratio of 10.70±0.61 was found, while from column chromatography, a value of 2.99±0.25 was detected. 31P NMR of standard phosphatidylcholine showed signals at -0.2 and -0.9 ppm, whereas the purified one showed a single signal at -0.9 ppm.

Electroformation of Giant Vesicles from an Inverse Phase Precursor

We discuss a simple modification of the well-known method of giant vesicle electroformation that allows for a direct addition of water-soluble species to the phospholipid bilayers. Using this modified method, we prepare phospholipid vesicles decorated with chitosan, a water-soluble polysaccharide currently investigated for potential pharmacological applications. We find that the method allows this polysaccharide with primary amino groups on every glucose subunit to be tightly bound to the membrane, rather than simply being encapsulated.

Effective protection of biological membranes against photo-oxidative damage: Polymeric antioxidant forming a protecting shield over the membrane

We have prepared a chitosan polymer modified with gallic acid in order to develop an efficient protection strategy biological membranes against photodamage. Lipid bilayers were challenged with photoinduced damage by photosensitization with methylene blue, which usually causes formation of hydroperoxides, increasing area per lipid, and afterwards allowing leakage of internal materials. The damage was delayed by a solution of gallic acid in a concentration dependent manner, but further suppressed by the polymer at very low concentrations. The membrane of giant unilamellar vesicles was covered with this modified macromolecule leading to a powerful shield against singlet oxygen and thus effectively protecting the lipid membrane from oxidative stress. The results have proven the discovery of a promising strategy for photo protection of biological membranes.

Massive parasitism by Gussevia tucunarense (Platyhelminthes: Monogenea: Dactylogyridae) in fingerlings of bujurqui-tucunare cultured in the Peruvian Amazon

A high infestation of the monogenean Gussevia tucunarense in a cultivation of bujurqui-tucunare was reported. The prevalence was 100%. The mean intensity and abundance of the parasite was 164.4 of parasites per individual. This is the first report of a high infestation by G. tucunarense in C. semifasciatus cultured from the Peruvian Amazon.

Targeted Drug Delivery and Treatment of Endoparasites with Biocompatible Particles of pH-Responsive Structure

Biomaterials conceived for vectorization of bioactives are currently considered for biomedical, biological, and environmental applications. We have produced a pH-sensitive biomaterial composed of natural source alginate and chitosan polysaccharides for application as a drug delivery system via oral administration. The composite particle preparation was in situ monitored by means of isothermal titration calorimetry. The strong interaction established between the macromolecules during particle assembly led to 0.60 alginate/chitosan effective binding sites with an intense exothermic effect and negative enthalpy variation on the order of a thousand kcal/mol. In the presence of model drugs mebendazole and ivermectin, with relatively small and large structures, respectively, mebendazole reduced the amount of chitosan monomers available to interact with alginate by 27%, which was not observed for ivermectin. Nevertheless, a state of intense negative Gibbs energy and large entropic decrease was achieved, providing evidence that formation of particles is thermodynamically driven and favored. Small-angle X-ray scattering provided further evidence of similar surface aspects independent of the presence of drug. The physical responses of the particles to pH variation comprise partial hydration, swelling, and the predominance of positive surface charge in strong acid medium, whereas ionization followed by deprotonation leads to compaction and charge reversal rather than new swelling in mild and slightly acidic mediums, respectively. In vivo performance was evaluated in the treatment of endoparasites in Corydoras fish. Systematically with a daily base oral administration, particles significantly reduced the infections over 15 days of treatment. The experiments provide evidence that utilizing particles granted and boosted the action of the antiparasitic drugs, leading to substantial reduction or elimination of infection. Hence, the pH-responsive particles represent a biomaterial with prominent characteristics that is promising for the development of targeted oral drug delivery.

Phospholipid/chitosan self‐assemblies analyzed by SAXS and Light Scattering

Self‐assemblies of phospholipids in an organic solvent (ethyl acetate) and their interaction with a cationic polysaccharide (chitosan) were appraised by scattering techniques. The investigations allowed following the formation of the self‐assemblies and their dimensions as a function of components concentration over time.