Francisco M. Goycoolea

Astaxanthin: A Review of its Chemistry and Applications

Astaxanthin is a carotenoid widely used in salmonid and crustacean aquaculture to provide the pink color characteristic of that species. This application has been well documented for over two decades and is currently the major market driver for the pigment. Additionally, astaxanthin also plays a key role as an intermediary in reproductive processes. Synthetic astaxanthin dominates the world market but recent interest in natural sources of the pigment has increased substantially. Common sources of natural astaxanthin are the green algae Haematococcus pluvialis, the red yeast, Phaffia rhodozyma, as well as crustacean byproducts. Astaxanthin possesses an unusual antioxidant activity which has caused a surge in the nutraceutical market for the encapsulated product. Also, health benefits such as cardiovascular disease prevention, immune system boosting, bioactivity against Helycobacter pylori, and cataract prevention, have been associated with astaxanthin consumption. Research on the health benefits of astaxanthin is very recent and has mostly been performed in vitro or at the pre-clinical level with humans. This paper reviews the current available evidence regarding astaxanthin chemistry and its potential beneficial effects in humans.

Chitosan-alginate blended nanoparticles as carriers for the transmucosal delivery of macromolecules.

Nanoparticles intended for use in the transmucosal delivery of macromolecules were prepared by the ionic gelation of chitosan (CS) hydrochloride with pentasodium tripolyphosphate (TPP) and concomitant complexation with sodium alginate (ALG). The incorporation of a small proportion of ALG of increasing molecular weight (M(w); from 4 to 74 kDa) into the nanoparticles led to a monotonic increase in colloidal size from ∼260 to ∼525 nm. This increase in size was regarded as a consequence of the formation of gradually more expanded structures. Insulin, taken as a model peptide, was associated to CS-TPP-ALG nanoparticles with efficiencies in the range of ∼41 to ∼52%, irrespective of the M(w) of the ALG incorporated in the formulation. These CS-TPP-ALG nanoparticles exhibited a capacity to enhance the systemic absorption of insulin after nasal administration to conscious rabbits. Interestingly, it was observed that the duration of the hypoglycaemic response was affected by the ALGs M(w). Briefly, this work describes a new nanoparticulate composition of potential value for increasing nasal insulin absorption.

Antibacterial and free‐radical scavenging activities of Sonoran propolis

Aims:  To evaluate the antibacterial and free‐radical scavenging (FRS) activities of propolis collected from three different areas of Sonoran Desert in northwestern Mexico [Pueblo de Alamos (PAP), Ures (UP) and Caborca (CP)].

Rheology of okra (Hibiscus esculentus L.) and dika nut (Irvingia gabonensis) polysaccharides

Abstract Polysaccharide extracts were prepared from two traditional food thickeners with extensive domestic use in central and western parts of Africa: okra (Hibiscus esculentis L.) and the seed kernel from ‘dika nut’ (Irvingia gabonensis). Both demonstrated typical polyelectrolyte behaviour in solution, and were therefore studied under fixed ionic conditions (0.1 M NaCl), yielding intrinsic viscosities of [η] = 7.6 dl g−1 for okra and [η] = 4.4 dl g−1 for dika. Concentrated solutions gave mechanical spectra typical of entangled networks, with close Cox-Merz superposition of η(ω) and η(γ). The variation of ‘zero-shear’ specific viscosity with degree of space-occupancy (c[η]) was also broadly similar to the general form observed for most disordered polysaccharides, but with greater separation of c ∗ and c ∗∗ and steeper slope of log ηsp vs. log c above c ∗ (~4.0 for okra and ~4.6 for dika, in comparison with the usual value of ~3.3). As found for normal disordered polysaccharides, the shear-thinning behaviour of dika gum could be reduced to a single ‘master-curve’ for all concentrations above c ∗∗ , but the absolute value of the terminal slope of log (η-ηs) vs. log ⋗g was unusually low (~0.58, in comparison with the normal value of ~0.76). Terminal slopes for okra gum were also unusually low, and varied systematically with polymer concentration. These departures from normal solution properties are tentatively ascribed to compact macromolecular structures, coupled, in the case of okra gum, with a strong tendency to self-association.

Solution rheology of mesquite gum in comparison with gum arabic

Abstract Commercial samples of mesquite gum and food-grade gum arabic were purified by filtration, alcohol precipitation, and extensive dialysis, and their Theological properties were characterised over the full range of concentrations at which solutions could be prepared (up to ~50% w/w). Both gave typical solution-like mechanical spectra, with close Cox-Merz superposition of η (⋗g) and η ∗ (ω) and only slight shear thinning at the highest accessible concentrations, and (ln η rel ) c varied linearly with log c from below 2% w/w to above 50%. The intrinsic viscosity of mesquite gum ([η]≈ 0.11 dl g −1 ) was appreciably lower than that of gum arabic ([η]≈ 0.19 dl g −1 in 0.1 m NaCl at 20 °C), and was independent of ionic strength above I ≈ 0.05, indicating a compact structure capable of only limited contraction. Departures from dilute-solution behaviour (η ~ c 1.4 ) occurred at c [η]≈ 1 for both materials, with a progressive increase in concentration dependence at higher space-occupancy, behaviour typical of soft, deformable particles, rather than of interpenetrating macromolecules. The increase in viscosity with increasing concentration was steeper for mesquite, consistent with evidence from size-exclusion chromatography and dynamic light scattering that the larger (and presumably more deformable) ‘wattle blossom’ component of gum arabic was absent from the mesquite gum sample.

Structure of chitosan determines its interactions with mucin.

Synthetic and natural mucoadhesive biomaterials in optimized galenical formulations are potentially useful for the transmucosal delivery of active ingredients to improve their localized and prolonged effects. Chitosans (CS) have potent mucoadhesive characteristics, but the exact mechanisms underpinning such interactions at the molecular level and the role of the specific structural properties of CS remain elusive. In the present study we used a combination of microviscosimetry, zeta potential analysis, isothermal titration calorimetry (ITC) and fluorescence quenching to confirm that the soluble fraction of porcine stomach mucin interacts with CS in water or 0.1 M NaCl (at c < c*; relative viscosity, η(rel), ∼ 2.0 at pH 4.5 and 37 °C) via a heterotypic stoichiometric process significantly influenced by the degree of CS acetylation (DA). We propose that CS-mucin interactions are driven predominantly by electrostatic binding, supported by other forces (e.g., hydrogen bonds and hydrophobic association) and that the DA influences the overall conformation of CS and thus the nature of the resulting complexes. Although the conditions used in this model system are simpler than the typical in vivo environment, the resulting knowledge will enable the rational design of CS-based nanostructured materials for specific transmucosal drug delivery (e.g., for Helicobacter pylori stomach therapy).

Chitosan nanocapsules: Effect of chitosan molecular weight and acetylation degree on electrokinetic behaviour and colloidal stability

In recent years, chitosan nanocapsules have shown promising results as carriers for oral drug or peptide delivery. The success in their applicability strongly depends on the stability of these colloidal systems passing through the digestive tract. In gastric fluids, clear stability comes from the high surface charge density of the chitosan shell, which is completely charged at acidic pH values. However, in the intestinal fluid (where the pH is almost neutral) the effective charge of these nanocapsules approaches zero, and the electrostatic forces cannot provide any stabilization. Despite the lack of surface charge, chitosan nanocapsules remain stable in simulated intestinal fluids. Recently, we have demonstrated that this anomalous stability (at zero charge) is owed to short-range repulsive forces that appear between hydrophilic particles when immersed in saline media. The present work examines the influence of the chitosan hydrophobicity, as well as molecular weight, in the stability of different chitosan nanocapsules. A study has been made of the size, polydispersity, electrophoretic mobility, and colloidal stability of eight core-shell nanocapsule systems, in which the chitosan-shell properties have been modified using low-molecular-weight (LMW) and high-molecular-weight (HMW) chitosan chains having different degrees of acetylation (DA). With regard to the stability mediated by repulsive hydration forces, the LMW chitosan provided the best results. In addition, contrary to initial expectations, greater stability (also mediated by hydration forces) was found in the samples formed with chitosan chains of high DA values (i.e. with less hydrophilic chitosan). Finally, a theoretical treatment was also tested to quantify the hydrophilicity of the chitosan shells.

Protein delivery based on uncoated and chitosan-coated mesoporous silicon microparticles

Mesoporous silicon is a biocompatible, biodegradable material that is receiving increased attention for pharmaceutical applications due to its extensive specific surface. This feature enables to load a variety of drugs in mesoporous silicon devices by simple adsorption-based procedures. In this work, we have addressed the fabrication and characterization of two new mesoporous silicon devices prepared by electrochemistry and intended for protein delivery, namely: (i) mesoporous silicon microparticles and (ii) chitosan-coated mesoporous silicon microparticles. Both carriers were investigated for their capacity to load a therapeutic protein (insulin) and a model antigen (bovine serum albumin) by adsorption. Our results show that mesoporous silicon microparticles prepared by electrochemical methods present moderate affinity for insulin and high affinity for albumin. However, mesoporous silicon presents an extensive capacity to load both proteins, leading to systems were protein could represent the major mass fraction of the formulation. The possibility to form a chitosan coating on the microparticles surface was confirmed both qualitatively by atomic force microscopy and quantitatively by a colorimetric method. Mesoporous silicon microparticles with mean pore size of 35 nm released the loaded insulin quickly, but not instantaneously. This profile could be slowed to a certain extent by the chitosan coating modification. With their high protein loading, their capacity to provide a controlled release of insulin over a period of 60-90 min, and the potential mucoadhesive effect of the chitosan coating, these composite devices comprise several features that render them interesting candidates as transmucosal protein delivery systems.

Systemic heparin delivery by the pulmonary route using chitosan and glycol chitosan nanoparticles

The aim of this study was to evaluate the performance of chitosan (CS) and glycol chitosan (GCS) nanoparticles containing the surfactant Lipoid S100 for the systemic delivery of low molecular weight heparin (LMWH) upon pulmonary administration. These nanoparticles were prepared in acidic and neutral conditions using the ionotropic gelation technique. The size and zeta potential of the NPs were affected by the pH and also the type of polysaccharide (CS or GCS). The size (between 156 and 385 nm) was smaller and the zeta potential (from +11 mV to +30 mV) higher for CS nanoparticles prepared in acidic conditions. The encapsulation efficiency of LMWH varied between 100% and 43% for the nanoparticles obtained in acidic and neutral conditions, respectively. X-ray photoelectron spectroscopy studies indicated that the surfactant Lipoid S100 was localized on the nanoparticles surface irrespective of the formulation conditions. In vivo studies showed that systems prepared in acidic conditions did not increase coagulation times when administered to mice by the pulmonary route. In contrast, Lipoid S100-LMWH GCS NPs prepared in neutral conditions showed a pharmacological efficacy. Overall, these results illustrate some promising features of CS-based nanocarriers for pulmonary delivery of LMWH.

Physicochemical and biological characterization of chitosan-microRNA nanocomplexes for gene delivery to MCF-7 breast cancer cells.

Cancer gene therapy requires the design of non-viral vectors that carry genetic material and selectively deliver it with minimal toxicity. Non-viral vectors based on cationic natural polymers can form electrostatic complexes with negatively-charged polynucleotides such as microRNAs (miRNAs). Here we investigated the physicochemical/biophysical properties of chitosan–hsa-miRNA-145 (CS–miRNA) nanocomplexes and the biological responses of MCF-7 breast cancer cells cultured in vitro. Self-assembled CS–miRNA nanocomplexes were produced with a range of (+/−) charge ratios (from 0.6 to 8) using chitosans with various degrees of acetylation and molecular weight. The Z-average particle diameter of the complexes was <200 nm. The surface charge increased with increasing amount of chitosan. We observed that chitosan induces the base-stacking of miRNA in a concentration dependent manner. Surface plasmon resonance spectroscopy shows that complexes formed by low degree of acetylation chitosans are highly stable, regardless of the molecular weight. We found no evidence that these complexes were cytotoxic towards MCF-7 cells. Furthermore, CS–miRNA nanocomplexes with degree of acetylation 12% and 29% were biologically active, showing successful downregulation of target mRNA expression in MCF-7 cells. Our data, therefore, shows that CS–miRNA complexes offer a promising non-viral platform for breast cancer gene therapy.