Sugar-derived glasses support thermal and photo-initiated electron transfer processes over macroscopic distances

Biodegradable Nanoparticles for Delivery of Therapeutics in CNS Infection

Despite the significant advances in neurological medicine, it remains difficult to treat ailments directly involving the brain. The blood brain barrier (BBB) is a tightly regulated, selectively permeable barrier that restricts access from the blood into the brain extracellular fluid (BEF). Many conditions such as tumors or infections in the brain are difficult to treat due to the fact that drugs and other therapeutic agents are unable to easily pass through this relatively impermeable barrier. Human Immunodeficiency Virus (HIV) presents a particular problem as it is able to remain dormant in the brain for years protected from antiretroviral drugs by the BBB. The development of nanoscale carriers over the past few decades has made possible the delivery of therapies with the potential to overcome membrane barriers and provide specific, targeted delivery. This review seeks to provide a comprehensive overview of the various aspects of nanoparticle formulation and their applications in improving the delivery efficiency of drugs, specifically antiretroviral therapeutics to the brain to treat HIV.

Chemical degradation of proteins in the solid state with a focus on photochemical reactions

Protein pharmaceuticals comprise an increasing fraction of marketed products but the limited solution stability of proteins requires considerable research effort to prepare stable formulations. An alternative is solid formulation, as proteins in the solid state are thermodynamically less susceptible to degradation. Nevertheless, within the time of storage a large panel of kinetically controlled degradation reactions can occur such as, e.g., hydrolysis reactions, the formation of diketopiperazine, condensation and aggregation reactions. These mechanisms of degradation in protein solids are relatively well covered by the literature. Considerably less is known about oxidative and photochemical reactions of solid proteins. This review will provide an overview over photolytic and non-photolytic degradation reactions, and specially emphasize mechanistic details on how solid structure may affect the interaction of protein solids with light.

Nitric oxide-releasing porous silicon nanoparticles

In this study, the ability of porous silicon nanoparticles (PSi NPs) to entrap and deliver nitric oxide (NO) as an effective antibacterial agent is tested against different Gram-positive and Gram-negative bacteria. NO was entrapped inside PSi NPs functionalized by means of the thermal hydrocarbonization (THC) process. Subsequent reduction of nitrite in the presence of d-glucose led to the production of large NO payloads without reducing the biocompatibility of the PSi NPs with mammalian cells. The resulting PSi NPs demonstrated sustained release of NO and showed remarkable antibacterial efficiency and anti-biofilm-forming properties. These results will set the stage to develop antimicrobial nanoparticle formulations for applications in chronic wound treatment.

Reverse micelles as a tool for probing solvent modulation of protein dynamics: Reverse micelle encapsulated hemoglobin

Hydration waters impact protein dynamics. Dissecting the interplay between hydration waters and dynamics requires a protein that manifests a broad range of dynamics. Proteins in reverse micelles (RMs) have promise as tools to achieve this objective because the water content can be manipulated. Hemoglobin is an appropriate tool with which to probe hydration effects. We describe both a protocol for hemoglobin encapsulation in reverse micelles and a facile method using PEG and cosolvents to manipulate water content. Hydration properties are probed using the water-sensitive fluorescence from Hb bound pyranine and covalently attached Badan. Protein dynamics are probed through ligand recombination traces derived from photodissociated carbonmonoxy hemoglobin on a log scale that exposes the potential role of both α and β solvent fluctuations in modulating protein dynamics. The results open the possibility of probing hydration level phenomena in this system using a combination of NMR and optical probes.

The potential of nitric oxide releasing therapies as antimicrobial agents

Nitric oxide (NO) is a short-lived, diatomic, lipophilic gas that plays an integral role in defending against pathogens. Among its many functions are involvement in immune cell signaling and in the biochemical reactions by which immune cells defend against bacteria, fungi, viruses and parasites. NO signaling directs a broad spectrum of processes, including the differentiation, proliferation, and apoptosis of immune cells. When secreted by activated immune cells, NO diffuses across cellular membranes and exacts nitrosative and oxidative damage on invading pathogens. These observations led to the development of NO delivery systems that can harness the antimicrobial properties of this evanescent gas. The innate microbicidal properties of NO, as well as the antimicrobial activity of the various NO delivery systems, are reviewed.

Sustained release nitric oxide from long-lived circulating nanoparticles

The current limitations of nitric oxide (NO) delivery systems have stimulated an extraordinary interest in the development of compounds that generate NO in a controlled and sustained manner with a heavy emphasis on the treatment of cardiovascular disease states. This work describes the positive physiological response to the infusion of NO-releasing nanoparticles prepared using a new platform based on hydrogel/glass hybrid nanoparticles. When exposed to moisture, these nanoparticles slowly release therapeutic levels of NO, previously generated through thermal reduction of nitrite to NO trapped within the dry particles. The controlled and sustained release of NO observed from these nanoparticles (NO-np) is regulated by its hydration over extended periods of time. In a dose-dependent manner, circulating NO-np both decreased mean arterial blood pressure and increased exhaled concentrations of NO over a period of several hours. Circulating NO-np induced vasodilatation and increased microvascular perfusion during their several hour circulation lifetime. Control nanoparticles (control-np; without nitrite) did not induce changes in arterial pressure, although a decrease in the number of capillaries perfused and an increase in leukocyte rolling and immobilization in the microcirculation were observed. The NO released by the NO-np prevents the inflammatory response observed after infusion of control-np. These data suggest that NO release from NO-np is advantageous relative to other NO-releasing compounds, because it does not depend on chemical decomposition or enzymatic catalysis; it is only determined by the rate of hydration. Based on the observed physiological properties, NO-np has clear potential as a therapeutic agent and as a research tool to increase our understanding of NO signaling mechanisms within the vasculature.

Glass matrix-facilitated thermal reduction: a tool for probing reactions of met hemoglobin with nitrite and nitric oxide

Isolating elemental steps that comprise a protein reaction in solution is a difficult process. In this study, the use of sugar-derived glass matrices is evaluated as a biophysical tool to help dissect out elemental steps and isolate intermediates. Two features of the glass are utilized in this endeavor: (i) the capacity of trehalose glass matrices to support thermal reduction over macroscopic distances; and (ii) the ability of glass matrices to significantly damp large amplitude protein dynamics. The focus of the study is on the reaction of nitric oxide (NO) with a nitrite ion coordinated to the heme iron of hemoglobin (Hb). The thermal reduction property of the glass is used to generate NO from nitrite within the glass, and the damping of protein dynamics is used to control entry of NO into the distal heme pocket of Hb, where it can either interact with bound nitrite or bind to the heme iron. The results not only relate to earlier controversial studies addressing the reactions of Hb with NO and nitrite but also raise the prospect that these properties of sugar-derived glassy matrices can be exploited as a new biophysical tool to modulate and probe reactions of NO with hemeproteins as well as a wide range of other metalloproteins.

New biomaterials for the sustained release of nitric oxide: past, present and future

Nitric oxide (NO), the 1992 'Molecule of the Year', is the focus of immense medical and scientific exploration. Interest in NO has grown exponentially since the initial and relatively recent discovery that NO is the long sought after endothelial relaxing factor. There is intense research that is continuing to expose the extensive physiologic impact of NO in virtually all organ and tissue systems under both normal and pathological conditions. Both the rate of delivery and the amount of site-specific generated NO modulate a balance between cytoregulatory and cytotoxic activities. This balancing act and the very short lifetime of NO under physiological conditions pose an extreme challenge with respect to harnessing the exceptional therapeutic potential of this molecule. Over the past two decades, the race to translate the therapeutic potential of NO to the bedside has been overwhelmingly through the development of numerous NO delivery devices/vehicles. So far no one product has emerged as a clearcut winner. This review: discusses and evaluates NO-donating platforms that are available at present; attempts to enhance delivery and efficacy through encapsulation in silane-based hydrogel matrices; and discusses and evaluates the future direction of these advances.

Reactivity of glass-embedded met hemoglobin derivatives toward external NO: implications for nitrite-mediated production of bioactive NO

Many protein reactions are exceedingly difficult to dissect under standard conditions due to low concentrations of reactants and intermediates. A case in point are several proposed reactions of hemoglobin with both nitrite and nitric oxide. In the present work, glassy matrices are used to dynamically control the rate at which externally introduced gaseous NO accesses and reacts with several different met Hb derivatives including the nitrite, nitrate, and aquomet forms. This novel yet general approach reveals a clear difference between nitrite and other ligands including nitrate, water, and an internal imidazole. For nitrate, water, and the internal distal imidazole, the observed spectral changes indicate that NO entering the distal heme pocket is effective in displacing these ligands from the ferric heme iron. In contrast, when the ligand is nitrite, the resulting initial spectra indicate the formation of an intermediate that has distinctly ferrous-like properties. The spectrum and the response of DAF fluorescence to the presence of the intermediate are consistent with a recently proposed nitrite anhydrase reaction. This proposed intermediate is especially significant in that it represents a pathway for a nitrite-dependent catalytic process whereby Hb generates relatively long-lived bioactive forms of NO such as S-nitrosoglutathione. The failure to form this intermediate either at low pH or when the glass is extensively dried is consistent with the requirement for a specific conformation of reactants and residue side chains within the distal heme pocket.

Study of the solid-matrix phosphorescence properties of a heterocyclic aromatic amine and the heat capacities of glucose glasses as the temperature decreases

The heat capacities were obtained from 294 to 133 K for four glucose-glass systems. Two of the glasses were prepared from crystalline glucose. One of the glasses contained the heavy-atom salt NaI and the other glass did not contain NaI. The other two glasses were similar, but they were prepared from glucose melts. Correlations were developed between the solid-matrix phosphorescence (SMP) lifetimes and intensities of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the glucose glasses and the heat capacities of the glucose sugar glasses as the temperature was lowered. Several plots of reciprocal SMP lifetime versus reciprocal temperature and reciprocal SMP lifetime versus reciprocal heat capacity were compared. Also, the reciprocal SMP intensity versus reciprocal temperature plots were compared with the corresponding reciprocal SMP intensity versus reciprocal heat capacity plots. In addition, basic photo-physical equations were used to develop relationships among the lifetime data, the intensity data, and the heat capacity data. The heat capacity data and SMP lifetime data, obtained as the temperature was lowered, were discussed in relationship to low-frequency vibrational modes and beta-relaxation phenomena in the glucose glasses. The discussion of these phenomena offered explanations for some of the loss of the excited triplet-state energy of PhIP in the glucose sugar glasses.

Sustained release nitric oxide releasing nanoparticles: characterization of a novel delivery platform based on nitrite containing hydrogel/glass composites

A new platform using biocompatible materials is presented for generating powders comprised of nanoparticles that release therapeutic levels of nitric oxide (NO) in a controlled and sustained manner. The capacity of these particles to retain and gradually release NO arises from their having combined features of both glassy matrices and hydrogels. This feature allows both for the generation of NO through the thermal reduction of added nitrite by glucose and for the retention of the generated NO within the dry particles. Exposure of these robust biocompatible nanoparticles to moisture initiates the sustained release of the trapped NO over extended time periods as determined both fluorimetrically and amperometrically. The slow sustained release is in contrast to the much faster release pattern associated with the hydration-initialed NO release in powders derived from glassy matrices. These glasses are prepared using trehalose and sucrose doped with either glucose or tagatose as the source of thermal electrons needed to convert nitrite to gNO. Significantly, the release profiles for the NO in the hydrogel/glass composite materials are found to be an easily tuned parameter that is modulated through the specific additives used in preparing the hydrogel/glass composites. The presented data raise the prospect that these new NO releasing nanoparticles can be easily formulated for use under a wide range of therapeutic circumstances.