In Vivo Assays for Amyloid-Related Diseases

Amyloid-related diseases, such as Alzheimer's and Parkinson's disease, are devastating conditions caused by the accumulation of abnormal protein aggregates known as amyloid fibrils. While assays involving animal models are essential for understanding the pathogenesis and developing therapies, a wide array of standard analytical techniques exists to enhance our understanding of these disorders. These techniques provide valuable information on the formation and propagation of amyloid fibrils, as well as the pharmacokinetics and pharmacodynamics of candidate drugs. Despite ethical concerns surrounding animal use, animal models remain vital tools in the search for treatments. Regardless of the specific animal model chosen, the analytical methods used are usually standardized. Therefore, the main objective of this review is to categorize and outline the primary analytical methods used in in vivo assays for amyloid-related diseases, highlighting their critical role in furthering our understanding of these disorders and developing effective therapies.

Proximity-Induced Pharmacology for Amyloid-Related Diseases

Proximity-induced pharmacology (PIP) for amyloid-related diseases is a cutting-edge approach to treating conditions such as Alzheimer's disease and other forms of dementia. By bringing small molecules close to amyloid-related proteins, these molecules can induce a plethora of effects that can break down pathogenic proteins and reduce the buildup of plaques. One of the most promising aspects of this drug discovery modality is that it can be used to target specific types of amyloid proteins, such as the beta-amyloid protein that is commonly associated with Alzheimer's disease. This level of specificity could allow for more targeted and effective treatments. With ongoing research and development, it is hoped that these treatments can be refined and optimized to provide even greater benefits to patients. As our understanding of the underlying mechanisms of these diseases continues to grow, proximity-induced pharmacology treatments may become an increasingly important tool in the fight against dementia and other related conditions.

Trioleyl Pyridinium, a Cationic Transfection Agent for the Lipofection of Therapeutic Oligonucleotides into Mammalian Cells

BACKGROUND

One of the most significant limitations that therapeutic oligonucleotides present is the development of specific and efficient delivery vectors for the internalization of nucleic acids into cells. Therefore, there is a need for the development of new transfection agents that ensure a proper and efficient delivery into mammalian cells.

METHODS

We describe the synthesis of 1,3,5-tris[(4-oelyl-1-pyridinio)methyl]benzene tribromide (TROPY) and proceeded to the validation of its binding capacity toward oligonucleotides, the internalization of DNA into the cells, the effect on cell viability, apoptosis, and its capability to transfect plasmid DNA.

RESULTS

The synthesis and chemical characterization of TROPY, which can bind DNA and transfect oligonucleotides into mammalian cells through clathrin and caveolin-mediated endocytosis, are described. Using a PPRH against the antiapoptotic survivin gene as a model, we validated that the complex TROPY-PPRH decreased cell viability in human cancer cells, increased apoptosis, and reduced survivin mRNA and protein levels. TROPY was also able to stably transfect plasmid DNA, as demonstrated by the formation of viable colonies upon the transfection of a dhfr minigene into dhfr-negative cells and the subsequent metabolic selection.

CONCLUSIONS

TROPY is an efficient transfecting agent that allows the delivery of therapeutic oligonucleotides, such as PPRHs and plasmid DNA, inside mammalian cells.

Three to Tango: Inhibitory Effect of Quercetin and Apigenin on Acetylcholinesterase, Amyloid-β Aggregation and Acetylcholinesterase-Amyloid Interaction

One of the pathological hallmarks of Alzheimer's disease (AD) is the formation of amyloid-β plaques. Since acetylcholinesterase (AChE) promotes the formation of such plaques, the inhibition of this enzyme could slow down the progression of amyloid-β aggregation, hence being complementary to the palliative treatment of cholinergic decline. Antiaggregation assays performed for apigenin and quercetin, which are polyphenolic compounds that exhibit inhibitory properties against the formation of amyloid plaques, reveal distinct inhibitory effects of these compounds on Aβ40 aggregation in the presence and absence of AChE. Furthermore, the analysis of the amyloid fibers formed in the presence of these flavonoids suggests that the Aβ40 aggregates present different quaternary structures, viz., smaller molecular assemblies are generated. In agreement with a noncompetitive inhibition of AChE, molecular modeling studies indicate that these effects may be due to the binding of apigenin and quercetin at the peripheral binding site of AChE. Since apigenin and quercetin can also reduce the generation of reactive oxygen species, the data achieved suggest that multitarget catechol-type compounds may be used for the simultaneous treatment of various biological hallmarks of AD.

Activity of Antibiotics and Potential Antibiofilm Agents against Biofilm-Producing Mycobacterium avium-intracellulare Complex Causing Chronic Pulmonary Infections

Nontuberculous mycobacteria (NTM) cause lung infections in patients with underlying pulmonary diseases (PD). The Mycobacteriumavium-intracellulare complex (MAC) is the most frequently involved NTM. The MAC-PD treatment is based on the administration of several antibiotics for long periods of time. Nonetheless, treatment outcomes remain very poor. Among the factors involved is the ability of MAC isolates to form biofilm. The aim of the study was to assess the in vitro activity of different antibiotics and potential antibiofilm agents (PAAs) against MAC biofilm. Four antibiotics and six PAAs, alone and/or in combination, were tested against planktonic forms of 11 MAC clinical isolates. Biofilm was produced after 4 weeks of incubation and analyzed with the crystal violet assay. The antibiotics and PAAs were tested by measuring the absorbance (minimum biofilm inhibition concentrations, MBICs) and by performing subcultures (minimum biofilm eradication concentrations, MBECs). The clarithromycin/amikacin and clarithromycin/ethambutol combinations were synergistic, decreasing the MBECs values compared to the individual antibiotics. The amikacin/moxifloxacin combination showed indifference. The MBIC values decreased significantly when PAAs were added to the antibiotic combinations. These results suggest that antibiotic combinations should be further studied to establish their antibiofilm activity. Moreover, PAAs could act against the biofilm matrix, facilitating the activity of antibiotics.

Targeting transthyretin in Alzheimer's disease: Drug discovery of small-molecule chaperones as disease-modifying drug candidates for Alzheimer's disease

Transthyretin (TTR) has a well-established role in neuroprotection in Alzheimer's Disease (AD). We have setup a drug discovery program of small-molecule compounds that act as chaperones enhancing TTR/Amyloid-beta peptide (Aβ) interactions. A combination of computational drug repurposing approaches and in vitro biological assays have resulted in a set of molecules which were then screened with our in-house validated high-throughput screening ternary test. A prioritized list of chaperones was obtained and corroborated with ITC studies. Small-molecule chaperones have been discovered, among them our lead compound Iododiflunisal (IDIF), a molecule in the discovery phase; one investigational drug (luteolin); and 3 marketed drugs (sulindac, olsalazine and flufenamic), which could be directly repurposed or repositioned for clinical use. Not all TTR tetramer stabilizers behave as chaperones in vitro. These chemically diverse chaperones will be used for validating TTR as a target in vivo, and to select one repurposed drug as a candidate to enter clinical trials as AD disease-modifying drug.

Prussian Blue: A Safe Pigment with Zeolitic-Like Activity

Prussian blue (PB) and PB analogues (PBA) are coordination network materials that present important similarities with zeolites concretely with their ability of adsorbing cations. Depending on the conditions of preparation, which is cheap and easy, PB can be classified into soluble PB and insoluble PB. The zeolitic-like properties are mainly inherent to insoluble form. This form presents some defects in its cubic lattice resulting in an open structure. The vacancies make PB capable of taking up and trapping ions or molecules into the lattice. Important adsorption characteristics of PB are a high specific area (370 m2 g-1 determined according the BET theory), uniform pore diameter, and large pore width. PB has numerous applications in many scientific and technological fields. PB are assembled into nanoparticles that, due to their biosafety and biocompatibility, can be used for biomedical applications. PB and PBA have been shown to be excellent sorbents of radioactive cesium and radioactive and nonradioactive thallium. Other cations adsorbed by PB are K+, Na+, NH4+, and some divalent cations. PB can also capture gaseous molecules, hydrocarbons, and even luminescent molecules such as 2-aminoanthracene. As the main adsorptive application of PB is the selective removal of cations from the environment, it is important to easily separate the sorbent of the purified solution. To facilitate this, PB is encapsulated into a polymer or coats a support, sometimes magnetic particles. Finally, is remarkable to point out that PB can be recycled and the adsorbed material can be recovered.

Prussian blue nanoparticles: synthesis, surface modification, and biomedical applications

Prussian blue nanoparticles (PBNPs) are a nanomaterial that presents unique properties and an excellent biocompatibility. They can be synthesized in mild conditions and can be derivatized with polymers and/or biomolecules. PBNPs are used in biomedicine as therapy and diagnostic agents. In biomedical imaging, PBNPs constitute contrast agents in photoacoustic and magnetic resonance imaging (MRI). They are a good adsorbent to be used as antidotes for poisoning with cesium and/or thallium ions. Moreover, the ability to convert energy into heat makes them useful photothermal agents (PAs) in photothermal therapy (PTT) or as nonantibiotic substances with antibacterial properties. Finally, PBNPs can be both reduced to Prussian white and oxidized to Prussian green. A large window of redox potential exists between reduction and oxidation, which result in the enzyme-like characteristics of these NPs.

Facile Synthesis of Novel Prussian Blue-Lipid Nanocomplexes

Prussian blue (PB) is known for its multiple applications ranging from fine arts to therapeutics. More recently, PB nanoparticles have been pointed to as appealing photothermal agents (PA) when irradiated with wavelengths corresponding to the biological windows, namely regions located in the near infrared (NIR) zone. In addition, the combination of PB with other components such as phospholipids boosts their therapeutical potential by facilitating, for instance, the incorporation of drugs becoming suitable drug delivery systems. The novelty of the research relies on the synthesis procedure and characterization of hybrid lipid-PB nanoparticles with a high yield in a friendly environment suitable for photothermal therapy. This goal was achieved by first obtaining insoluble PB coated with oleylamine (OA) to facilitate its combination with lipids. The resulting lipid-PB complex showed a monomodal distribution of sizes with an overall size of around 100 nm and a polydispersity index of about 0.200. It highlights one critical step in the synthesis procedure that is the shaking time of the mixture of PB-OA nanoparticles with the lipid, which was found to be 48 h. This time assured homogeneous preparation without the need of further separation stages. Samples were stable for more than three months under several storage conditions.

Bacterial Inclusion Bodies for Anti-Amyloid Drug Discovery: Current and Future Screening Methods

Amyloid aggregation is linked to an increasing number of human disorders from nonneurological pathologies such as type-2 diabetes to neurodegenerative ones such as Alzheimer or Parkinson's diseases. Thirty-six human proteins have shown the capacity to aggregate into pathological amyloid structures. To date, it is widely accepted that amyloid folding/aggregation is a universal process present in eukaryotic and prokaryotic cells. In the last decade, several studies have unequivocally demonstrated that bacterial inclusion bodies - insoluble protein aggregates usually formed during heterologous protein overexpression in bacteria - are mainly composed of overexpressed proteins in amyloid conformation. This fact shows that amyloid-prone proteins display a similar aggregation propensity in humans and bacteria, opening the possibility to use bacteria as simple models to study amyloid aggregation process and the potential effect of both anti-amyloid drugs and pro-aggregative compounds. Under these considerations, several in vitro and in cellulo methods, which exploit the amyloid properties of bacterial inclusion bodies, have been proposed in the last few years. Since these new methods are fast, simple, inexpensive, highly reproducible, and tunable, they have aroused great interest as preliminary screening tools in the search for anti-amyloid (beta-blocker) drugs for conformational diseases. The aim of this mini-review is to compile recently developed methods aimed at tracking amyloid aggregation in bacteria, discussing their advantages and limitations, and the future potential applications of inclusion bodies in anti-amyloid drug discovery.

Iron Oxide Nanoparticles in Photothermal Therapy

Photothermal therapy is a kind of therapy based on increasing the temperature of tumoral cells above 42 °C. To this aim, cells must be illuminated with a laser, and the energy of the radiation is transformed in heat. Usually, the employed radiation belongs to the near-infrared radiation range. At this range, the absorption and scattering of the radiation by the body is minimal. Thus, tissues are almost transparent. To improve the efficacy and selectivity of the energy-to-heat transduction, a light-absorbing material, the photothermal agent, must be introduced into the tumor. At present, a vast array of compounds are available as photothermal agents. Among the substances used as photothermal agents, gold-based compounds are one of the most employed. However, the undefined toxicity of this metal hinders their clinical investigations in the long run. Magnetic nanoparticles are a good alternative for use as a photothermal agent in the treatment of tumors. Such nanoparticles, especially those formed by iron oxides, can be used in combination with other substances or used themselves as photothermal agents. The combination of magnetic nanoparticles with other photothermal agents adds more capabilities to the therapeutic system: the nanoparticles can be directed magnetically to the site of interest (the tumor) and their distribution in tumors and other organs can be imaged. When used alone, magnetic nanoparticles present, in theory, an important limitation: their molar absorption coefficient in the near infrared region is low. The controlled clustering of the nanoparticles can solve this drawback. In such conditions, the absorption of the indicated radiation is higher and the conversion of energy in heat is more efficient than in individual nanoparticles. On the other hand, it can be designed as a therapeutic system, in which the heat generated by magnetic nanoparticles after irradiation with infrared light can release a drug attached to the nanoparticles in a controlled manner. This form of targeted drug delivery seems to be a promising tool of chemo-phototherapy. Finally, the heating efficiency of iron oxide nanoparticles can be increased if the infrared radiation is combined with an alternating magnetic field.

Effect of PEGylation on Ligand-Targeted Magnetoliposomes: A Missed Goal

We tested the targeting efficiency of magnetoliposomes (MLPs) labeled with tripeptide arginine-glycine-aspartic acid (RGD) on two types of cells: HeLa cells expressing RGD receptors and 3T3 cells lacking RGD receptors. The targeting ability of RGD-MLPs was compared to that of bare MLPs and MLPs stabilized with poly(ethylene glycol) (PEG). Cellular internalization of these liposomes was determined by flow cytometry and confocal microscopy, which showed that both types of cells took up more nontargeting MLPs than targeting RGD-MLPs or PEG-MLPs, with PEG-MLPs showing the lowest degree of internalization. The presence of specific receptors on HeLa cells did not facilitate the binding of RGD-MLPs, probably due to the presence of PEG chains on the liposomal surface. The polymer increases the circulation time of the liposomes in the organism but reduces their interactions with cells. Despite the localization of the RGD peptide on the tip of PEG in RGD-MLPs, the interaction between the liposome and cell was still limited. To avoid this drawback, targeting drug delivery systems can be prepared with two types of PEG: one of a short length to enable biocompatibility and the other of a longer chain to carry the ligand.

Magnetic Nanoemulsions: Comparison between Nanoemulsions Formed by Ultrasonication and by Spontaneous Emulsification

Nanoemulsions are particularly suitable as a platform in the development of delivery systems. The type of nanoemulsion with a higher stability will offer an advantage in the preparation of a delivery system for lipophilic drugs. Nanoemulsions can be fabricated by different processing methods, which are usually categorized as either high- or low-energy methods. In this study, a comparison between two methods of preparing magnetic oil-in-water (O/W) nanoemulsions is described. The nanoemulsions were formed by sonication (the high-energy method) or by spontaneous emulsification (the low-energy method). In both cases, the oil phase was olive oil, and a phospholipid and a pegylated phospholipid were used as emulsifiers. To favor the comparison, the amounts of the components were the same in both kinds of nanoemulsions. Moreover, nanoemulsions were loaded with hydrophobic superparamagnetic nanoparticles and indomethacin. In vitro, releases studies indicated a short drug burst period followed by a prolonged phase of dissolutive drug release. The Korsmeyer-Peppas model can fit the associated kinetics. The results showed that such nanoemulsions are suitable as a platform in the development of delivering systems for lipophilic drugs. The long-term stability was also examined at different temperatures, as well as the interaction with plasma proteins. Nanoemulsion obtained by the low-energy method showed a great stability at 4 °C and at ambient temperature. Its size and polydispersity did not change over more than two months. The spontaneous emulsification method therefore has great potential for forming nanoemulsion-based delivery systems.

Evidence of Protein Adsorption in Pegylated Liposomes: Influence of Liposomal Decoration

In order to contribute to a better knowledge of the events involved in the formation of the protein corona when nanoparticles (NPs) come in contact with proteins, we report a study about the changes on the physicochemical properties of pristine, PEGylated and Cyclic Arginine-Glycine-Aspartate peptide (RGD)-functionalized large unilamelar liposomes (LUVs) or magnetoliposomes (MLs) upon incubation with Bovine Serum Albumin (BSA). The main phospholipid component of both LUVs and MLs was l-α-phosphatydylcholine (PC) or 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) with 20% of cholesterol. The most obvious indication of the interaction of BSA-nanosystems is given by changes in the hydrodynamic diameter of the particles but other evidence is needed to corroborate the process. Our findings indicate that size modification is a process that is accomplished in few hours and that is strongly dependent not only on the surface decoration but also of the lipid composition of both LUVs and MLs. Fluorescence quenching experiments as well as cryogenic transmission electron microscopy (Cryo-TEM) images assessed these changes and confirmed that although each system has to be studied in a particular way, we can establish three distinctive features that turn into more reactive systems: (a) compositions containing PC compared with their DMPC counterparts; (b) the presence of PEG and/or RGD compared to the pristine counterparts; and (c) the presence of SPIONs: MLs show higher interaction than LUVs of the same lipid composition. Consequently, PEGylation (that is supposed to make stealth NPs) actually fails in preventing complete protein binding.

Liposomes Loaded with Hydrophobic Iron Oxide Nanoparticles: Suitable T₂ Contrast Agents for MRI

There has been a recent surge of interest in the use of superparamagnetic iron oxide nanoparticles (SPIONs) as contrast agents (CAs) for magnetic resonance imaging (MRI), due to their tunable properties and their low toxicity compared with other CAs such as gadolinium. SPIONs exert a strong influence on spin-spin T₂ relaxation times by decreasing the MR signal in the regions to which they are delivered, consequently yielding darker images or negative contrast. Given the potential of these nanoparticles to enhance detection of alterations in soft tissues, we studied the MRI response of hydrophobic or hydrophilic SPIONs loaded into liposomes (magnetoliposomes) of different lipid composition obtained by sonication. These hybrid nanostructures were characterized by measuring several parameters such as size and polydispersity, and number of SPIONs encapsulated or embedded into the lipid systems. We then studied the influence of acyl chain length as well as its unsaturation, charge, and presence of cholesterol in the lipid bilayer at high field strength (7 T) to mimic the conditions used in preclinical assays. Our results showed a high variability depending on the nature of the magnetic particles. Focusing on the hydrophobic SPIONs, the cholesterol-containing samples showed a slight reduction in r₂, while unsaturation of the lipid acyl chain and inclusion of a negatively charged lipid into the bilayer appeared to yield a marked increase in negative contrast, thus rendering these magnetoliposomes suitable candidates as CAs, especially as a liver CA.

Key Points Concerning Amyloid Infectivity and Prion-Like Neuronal Invasion

Amyloid aggregation has been related to an increasing number of human illnesses, from Alzheimer’s and Parkinson’s diseases (AD/PD) to Creutzfeldt-Jakob disease. Commonly, only prions have been considered as infectious agents with a high capacity of propagation. However, recent publications have shown that many amyloid proteins, including amyloid β-peptide, α-synuclein (α-syn) and tau protein, also propagate in a “prion-like” manner. Meanwhile, no link between propagation of pathological proteins and neurotoxicity has been demonstrated. The extremely low infectivity under natural conditions of most non-prion amyloids is far below the capacity to spread exhibited by prions. Nonetheless, it is important to elucidate the key factors that cause non-prion amyloids to become infectious agents. In recent years, important advances in our understanding of the amyloid processes of amyloid-like proteins and unrelated prions (i.e., yeast and fungal prions) have yielded essential information that can shed light on the prion phenomenon in mammals and humans. As shown in this review, recent evidence suggests that there are key factors that could dramatically modulate the prion capacity of proteins in the amyloid conformation. The concentration of nuclei, the presence of oligomers, and the toxicity, resistance and localization of these aggregates could all be key factors affecting their spread. In short, those factors that favor the high concentration of extracellular nuclei or oligomers, characterized by small size, with a low toxicity could dramatically increase prion propensity; whereas low concentrations of highly toxic intracellular amyloids, with a large size, would effectively prevent infectivity.

Magnetic Nanoparticles Cross the Blood-Brain Barrier: When Physics Rises to a Challenge

The blood-brain barrier is a physical and physiological barrier that protects the brain from toxic substances within the bloodstream and helps maintain brain homeostasis. It also represents the main obstacle in the treatment of many diseases of the central nervous system. Among the different approaches employed to overcome this barrier, the use of nanoparticles as a tool to enhance delivery of therapeutic molecules to the brain is particularly promising. There is special interest in the use of magnetic nanoparticles, as their physical characteristics endow them with additional potentially useful properties. Following systemic administration, a magnetic field applied externally can mediate the capacity of magnetic nanoparticles to permeate the blood-brain barrier. Meanwhile, thermal energy released by magnetic nanoparticles under the influence of radiofrequency radiation can modulate blood-brain barrier integrity, increasing its permeability. In this review, we present the strategies that use magnetic nanoparticles, specifically iron oxide nanoparticles, to enhance drug delivery to the brain.

Kinetics characterization of c-Src binding to lipid membranes: Switching from labile to persistent binding

Cell signaling by the c-Src proto-oncogen requires the attachment of the protein to the inner side of the plasma membrane through the myristoylated N-terminal region, known as the SH4 domain. Additional binding regions of lower affinity are located in the neighbor intrinsically disordered Unique domain and the structured SH3 domain. Here we present a surface plasmon resonance study of the binding of a myristoylated protein including the SH4, Unique and SH3 domains of c-Src to immobilized liposomes. Two distinct binding processes were observed: a fast and a slow one. The second process lead to a persistently bound form (PB) with a slower binding and a much slower dissociation rate than the first one. The association and dissociation of the PB form could be detected using an anti-SH4 antibody. The kinetic analysis revealed that binding of the PB form follows a second order rate law suggesting that it involves the formation of c-Src dimers on the membrane surface. A kinetically equivalent PB form is observed in a myristoylated peptide containing only the SH4 domain but not in a construct including the three domains but with a 12-carbon lauroyl substituent instead of the 14-carbon myristoyl group. The PB form is observed with neutral lipids but its population increases when the immobilized liposomes contain negatively charged lipids. We suggest that the PB form may represent the active signaling form of c-Src while the labile form provides the capacity for fast 2D search of the target signaling site on the membrane surface.

Amyloids in solid-state nuclear magnetic resonance: potential causes of the usually low resolution

Amyloids are non-crystalline and insoluble, which imply that the classical structural biology tools, ie, X-ray crystallography and solution nuclear magnetic resonance (NMR), are not suitable for their analysis. In the last years, solid-state NMR (ssNMR) has emerged as an alternative tool to decrypt the structural signatures of amyloid fibrils, providing major contributions to our understanding of molecular structures of amyloids such as β-amyloid peptide associated with Alzheimer’s disease or fungal prions, among others. Despite this, the wide majority of amyloid fibrils display low resolution by ssNMR. Usually, this low resolution has been attributed to a high disorder or polymorphism of the fibrils, suggesting the existence of diverse elementary β-sheet structures. Here, we propose that a single β-sheet structure could be responsible for the broadening of the line widths in the ssNMR spectra. Although the fibrils and fibers consist of a single elementary structure, the angle of twist of each individual fibril in the mature fiber depends on the number of individual fibrils as well as the fibril arrangement in the final mature fiber. Thus, a wide range of angles of twist could be observed in the same amyloid sample. These twist variations involve changes in amino acid alignments that could be enough to limit the ssNMR resolution.

Gelatin-based nanoparticles as DNA delivery systems: Synthesis, physicochemical and biocompatible characterization

The rapidly rising demand for therapeutic grade DNA molecules requires associated improvements in encapsulation and delivery technologies. One of the challenges for the efficient intracellular delivery of therapeutic biomolecules after their cell internalization by endocytosis is to manipulate the non-productive trafficking from endosomes to lysosomes, where degradation may occur. The combination of the endosomal acidity with the endosomolytic capability of the nanocarrier can increase the intracellular delivery of many drugs, genes and proteins, which, therefore, might enhance their therapeutic efficacy. Among the suitable compounds, the gelification properties of gelatin as well as the strong dependence of gelatin ionization with pH makes this compound an interesting candidate to be used to the effective intracellular delivery of active biomacromolecules. In the present work, gelatin (either high or low gel strength) and protamine sulfate has been selected to form particles by interaction of oppositely charged compounds. Particles in the absence of DNA (binary system) and in the presence of DNA (ternary system) have been prepared. The physicochemical characterization (particle size, polydispersity index and degree of DNA entrapment) have been evaluated. Cytotoxicity experiments have shown that the isolated systems and the resulting gelatin-based nanoparticles are essentially non-toxic. The pH-dependent hemolysis assay and the response of the nanoparticles co-incubated in buffers at defined pHs that mimic extracellular, early endosomal and late endo-lysosomal environments demonstrated that the nanoparticles tend to destabilize and DNA can be successfully released. It was found that, in addition to the imposed compositions, the gel strength of gelatin is a controlling parameter of the final properties of these nanoparticles. The results indicate that these gelatin-based nanoparticles have excellent properties as highly potent and non-toxic intracellular delivery systems, rendering them promising DNA vehicles to be used as non-viral gene delivery systems.

Miscibility and Langmuir Studies of the Interaction of E2 (279-298) Peptide Sequence of Hepatitis G Virus/GB Virus-C with Dipalmitoylphosphatidyl Choline and Dimiristoylphosphatidyl Choline Phospholipids

Mixed monolayers of E2(279-298), a synthetic peptide belonging to the structural protein E2 of the GB virus C (GBV-C), formerly know as hepatitis G virus (HGV), and the phospholipids dipalmitoylphosphatidyl choline (DPPC) and dimiristoylphosphatidyl choline (DMPC),which differ in acyl chains length, were obtained at the A/W interface (monolayers of extension) in order to provide new insights on E2/phospholipids interaction. Analysis of the surface pressure-area isotherms, Brewster angle microscopy images, relative thickness, and mean areas per molecule has allowed us to establish the conditions under which the mixed components of the monolayer are miscible or immiscible and know how the level of the E2/phospholipid interaction varies with the composition of the mixed films, the surface pressure, and the hydrocarbon chains length of the phospholipids. The steric hindrance caused by the penetration of the polymer strands into the more or less ordered hydrocarbon chains of the phospholipids was suggested to explain the differences in the peptide interaction with the phospholipids studied. Therefore, the novelty of results obtained with the Langmuir film balance technique, supplemented with BAM images allow us to achieve a deeper understanding of the interaction.

Predicting the aggregation propensity of prion sequences

The presence of prions can result in debilitating and neurodegenerative diseases in mammals and protein-based genetic elements in fungi. Prions are defined as a subclass of amyloids in which the self-aggregation process becomes self-perpetuating and infectious. Like all amyloids, prions polymerize into fibres with a common core formed of β-sheet structures oriented perpendicular to the fibril axes which form a structure known as a cross-β structure. The intermolecular β-sheet propensity, a characteristic of the amyloid pattern, as well as other key parameters of amyloid fibril formation can be predicted. Mathematical algorithms have been proposed to predict both amyloid and prion propensities. However, it has been shown that the presence of amyloid-prone regions in a polypeptide sequence could be insufficient for amyloid formation. It has also often been stated that the formation of amyloid fibrils does not imply that these are prions. Despite these limitations, in silico prediction of amyloid and prion propensities should help detect potential new prion sequences in mammals. In addition, the determination of amyloid-prone regions in prion sequences could be very useful in understanding the effect of sporadic mutations and polymorphisms as well as in the search for therapeutic targets.

Nanoparticles in magnetic resonance imaging: from simple to dual contrast agents

Magnetic resonance imaging (MRI) has become one of the most widely used and powerful tools for noninvasive clinical diagnosis owing to its high degree of soft tissue contrast, spatial resolution, and depth of penetration. MRI signal intensity is related to the relaxation times (T₁, spin–lattice relaxation and T₂, spin–spin relaxation) of in vivo water protons. To increase contrast, various inorganic nanoparticles and complexes (the so-called contrast agents) are administered prior to the scanning. Shortening T₁ and T₂ increases the corresponding relaxation rates, 1/T₁ and 1/T₂, producing hyperintense and hypointense signals respectively in shorter times. Moreover, the signal-to-noise ratio can be improved with the acquisition of a large number of measurements. The contrast agents used are generally based on either iron oxide nanoparticles or ferrites, providing negative contrast in T₂-weighted images; or complexes of lanthanide metals (mostly containing gadolinium ions), providing positive contrast in T₁-weighted images. Recently, lanthanide complexes have been immobilized in nanostructured materials in order to develop a new class of contrast agents with functions including blood-pool and organ (or tumor) targeting. Meanwhile, to overcome the limitations of individual imaging modalities, multimodal imaging techniques have been developed. An important challenge is to design all-in-one contrast agents that can be detected by multimodal techniques. Magnetoliposomes are efficient multimodal contrast agents. They can simultaneously bear both kinds of contrast and can, furthermore, incorporate targeting ligands and chains of polyethylene glycol to enhance the accumulation of nanoparticles at the site of interest and the bioavailability, respectively. Here, we review the most important characteristics of the nanoparticles or complexes used as MRI contrast agents.

Potential applications of magnetic particles to detect and treat Alzheimer's disease

Nanotechnology is an exciting and promising scientific discipline. At the nanoscale, a material displays novel physical properties that offer many new and beneficial products and applications. In particular, magnetic nanoparticles - a core/shell nanoparticle - present considerable diagnostic and therapeutic potentials, and superparamagnetic iron oxide nanoparticles (SPIONs) are considered promising theranostic tools. Alzheimer's disease (AD) is a neurodegenerative disorder that predominantly affects people over 65 years of age. The disease is characterized by the presence of extracellular plaques in the brain which are formed by interwoven fibrils composed of variants of the β-amyloid peptide. Medication can temporarily retard worsening of symptoms, but only in the first stages of the disease; early detection is thus of crucial importance. This minireview covers the progress made in research on the use of magnetic nanoparticles for ex vivo and/or in vivo detection and diagnosis of AD by means of magnetic resonance imaging (MRI), or to label peptides and fibrils. Of particular importance is the use of these nanoparticles to detect AD biomarkers in biological fluids. A description is given of the bio-barcode amplification assay using functionalized magnetic particles, as well as the use of such nanoparticles as a system for inhibiting or delaying the assembly of peptide monomers into oligomers and fibrils. Lastly, a brief overview is given of possible future lines of research in this.

Spectroscopic analysis of the interaction of a peptide sequence of Hepatitis G virus with bilayers

Merocyanine 540 (MC540) has been used as external probe to determine the interaction of the peptide sequence 125-139 corresponding to the E2 protein of Hepatitis G virus, with lipid bilayers. The probe was incorporated into large unilamellar vesicles (LUVs) or small unilamellar vesicles (SUVs) of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). When incorporated into bilayers, MC540 shows two absorption maxima corresponding to the monomer (570 nm) and dimer (530 nm) form of the probe. Changes in the probe microenvironment are reflected by a modification in the position and/or intensity of these maxima. Addition of increasing amounts of peptide resulted in a slight decrease of the ratio A570/A530 thus indicating a change in MC540 partition into the membrane, going from a hydrophobic to a more hydrophilic environment. This effect was concomitant with an increase in dimer formation as stated from the values of the apparent dimerization constant (K(app)) obtained. Fluorescence spectra as well as steady state anisotropy measurements were in agreement with the above results indicating that the peptide was able to relocate the probe and displacing MC540 from its initial location into the bilayer. Results with SUVs or LUVs were similar for what curvature does not seem to play any role on peptide activity. These results reflect the ability of peptide to interact with biomimetic membranes in the lipid head group region.

Interaction of two overlapped synthetic peptides from GB virus C with charged mono and bilayers

The physical chemistry properties and interactions of E2 (125-139) and E2 (120-139) peptide sequences from GB virus C with model cell membranes were investigated by means of several biophysical techniques in order to gain better understanding of the effect of peptide length and lipid charge on membrane binding. The peptides, having one net negative charge at the pH of the assays, interacted with monolayers of all the phospholipids regardless of the charge but with more extent with the cationic DPTAP thus indicating that the interaction had both a hydrophobic and an electrostatic component as has been observed for other peptides of the same family. The peptides were able to leakage contents of liposomes and showed fluorescence energy transfer in vesicles depending on the vesicles lipid composition. On another hand, circular dichroism has shown that the peptides exist mainly as a mixture of disordered structure and β-type conformations in aqueous solution but diminished its unstructured content, folding preferentially into α-helical conformation upon interaction with hydrophobic solvents or positively charged lipid surfaces. Altogether, results of this work indicate that the peptides interact at a surface level, penetrate into bilayers composed of fluid lipids and that conformational changes could be responsible for this effect.

Disturbance of erythrocyte lipid bilayer by amino acid-based surfactants

In an attempt to increase our knowledge regarding the mechanisms of surfactant membrane interaction, we studied the action of several anionic and cationic amino acid-based surfactants on membrane fluidity using fluorescence anisotropy. Anisotropy measurements demonstrated that almost all of the surfactants studied disturbed the external region of the erythrocyte membrane without affecting the core of the bilayer. How the physico-chemical properties and structure of these compounds affect dynamics of the lipid bilayer is discussed in detail.

Study of Adsorption and Penetration of E2(279−298) Peptide into Langmuir Phospholipid Monolayers

The peptide corresponding to the sequence (279-298) of the Hepatitis G virus (HGV/GBV-C) E2 protein was synthesized, and surface activity measurements, pi-A compression isotherms, and penetration of E2(279-298) into phospholipid monolayers spread at the air-water interface were carried out on water and phosphate buffer subphases. The results obtained indicated that the pure E2(279-298) Langmuir monolayer exhibited a looser packing on saline-buffered than on pure water subphase and suggest that the increase in subphase ionic strength stabilizes the peptide monolayer. To better understand the topography of the monolayer, Brewster angle microscopy (BAM) images of pure peptide monolayers were obtained. Penetration of the peptide into the pure lipid monolayers of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine (DMPC) and into mixtures of dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol (DMPC/DMPG) at various initial surface pressures was investigated to determine the ability of these lipid monolayers to host the peptide. The higher penetration of peptide into phospholipids is attained when the monolayers are in the liquid expanded state, and the greater interaction is observed with DMPC. Furthermore, the penetration of the peptide dissolved in the subphase into these various lipid monolayers was investigated to understand the interactions between the peptide and the lipid at the air-water interface. The results obtained showed that the lipid acyl chain length is an important parameter to be taken into consideration in the study of peptide-lipid interactions.

Ocular photodynamic therapy with verteporfin for choroidal neovascularization secondary to ocular histoplasmosis syndrome

PURPOSE

To evaluate the use of ocular photodynamic therapy (OPT) with verteporfin in patients with choroidal neovascularization (CNV) from ocular histoplasmosis syndrome (OHS) and to compare these results with those for a natural history group.

METHODS

A retrospective chart review was performed to identify cases of CNV secondary to OHS treated with OPT. Complete data were available for 38 of 41 eligible eyes. Data regarding the following variables were abstracted from the patient charts: demographic characteristics, previous surgery, angiographic features, number and timing of treatments with OPT, follow-up time, and visual acuity. The visual acuity results of eyes receiving photodynamic therapy were compared with those for a natural history cohort.

RESULTS

On average, OHS patients who received treatment developed 0.88 line of visual improvement. Visual acuity improved or stayed the same in 69% (22 of 32) of eyes, improved by > or = 2 lines in 44% (14 of 32), and improved by > or = 4 lines in 22% (7 of 32). Patients who received OPT were 2.07 times more likely to have improved or constant vision than were those in the natural history group as described in one retrospective series (odds ratio = 2.07; 95% confidence interval, 0.78-5.56; P = 0.162). Thirty-eight percent (12 of 32) of eyes had undergone submacular surgery for CNV before any OPT.

CONCLUSIONS

Ocular photodynamic therapy with verteporfin may be beneficial in patients with CNV secondary to OHS, even in the setting of previous submacular surgery.

Interaction study of peptide from VP3 capsid protein of hepatitis A virus through monolayers and fluorescence spectroscopy

A synthetic peptide with the sequence [Lys113]VP3(110--121): FWRKDLVFDFQV, corresponding to an epitope of the VP3 capsid protein of hepatitis A virus (HAV), was synthesized by solid phase and characterized. To obtain insight into its physicochemical properties and to understand its possible mechanism of action at the membrane level, interaction with DPPC or DPPC/DPPG (95/5) liposomes and lipid monolayers of DPPC, DPPG, SA, PS, PA and SM were studied by fluorescence spectroscopy and Langmuir--Blotgett films technique, respectively. Fluorescence studies showed that the peptide was in a hydrophobic environment when DPPC liposomes were used. The addition of a 5% of a charged lipid, DPPG, to the preparations changed the preference of the peptide towards a polar surrounding. However, the peptide had a high surface activity (nmol/L) and was able to incorporate into lipid monolayers. Interaction was higher with charged phospholipids than with neutral ones. These results may have physiological significance in the mechanism of infection of host hepatic cells by HAV.

Interaction of VP3(110-121) Peptide with Hepatocyte and Erythrocyte Membrane Models

The use of synthetic peptides in the goal of developing a new, inexpensive vaccine against hepatitis A virus is one of the encouraging approaches followed by many laboratories. These peptides have to be well characterized, being their physicochemical properties one of the most relevant points to control. In that sense, one can consider the study of the peptide interaction with lipid monolayers by means of the Wilhelmy plate method, to gain insight into the possible mechanism of action at the membrane level. The peptide chosen corresponds to the lineal epitope of hepatitis A virus VP3(110-121). As far as the lipids used are concerned, they were selected according to the composition of hepatocytes and erythrocytes because these structures seem to play an important role in hepatitis proliferation and infection. The peptide was able to accommodate into lipid monolayers. Interaction was slightly lower in the hepatocyte model than in the erythrocyte model, probably due to the presence of cholesterol in the hepatocyte membrane. Copyright 1999 Academic Press.

pH-induced destabilization of lipid bilayers by a peptide from the VP3 protein of the capsid of hepatitis A virus

The membrane destabilizing and fusogenic properties of the synthetic peptide VP3(110-121), corresponding to an immunogenic sequence of the hepatitis A virus (HAV) VP3 capsid protein, were studied. By tryptophan fluorescence and acryalmide quenching it was demonstrated that the peptide binds liposomes of POPC-SM-DPPE (47 + 39 + 14) and POPC-SM-DPPE-DOTAP (40 + 33 + 12 + 15) and penetrates the membrane, at both neutral and acidic pH (POPC = 1-palmitoyl-2-oleoylglycero-sn-3-phosphocholine; SM = sphingomyelin; DPPE = 1,2-dipalmitoylphosphatidylethanolamine; DOTAP = 1,2-dioleoyl-3-trimethylammoniumpropane). VP3(110-121) did not have membrane-destabilizing properties at neutral pH. Acid-induced destabilization of the vesicles was demonstrated by fluorescence techniques and dynamic light scattering. VP3(110-121) induced aggregation of POPC-SM-DPPE-DOTAP (40 + 33 + 12 + 15) vesicles, lipid mixing and leakage of vesicle contents, all consistent with fusion of vesicles. In POPC-SM-DPPE (47 + 39 + 14) vesicles, at acidic pH, VP3(110-121) induced membrane destabilization with leakage of contents but without aggregation of vesicles or lipid mixing. The peptide only showed fusogenic properties when bound to the vesicles at neutral pH before acidification to pH below 6.0, and no effect was seen if the peptide was added to vesicles already set at acidic pH. These results may have physiological significance in the mechanism of infection of host hepatic cells by HAV.

Thermodynamic analysis of the interaction between a bactericidal antibody and a PorA epitope of Neisseria meningitidis

An antibody-peptide model system was used to study the binding characteristics between a bactericidal antibody (MN12H2) and the P1. 16 epitope of class 1 outer membrane protein PorA of Neisseria meningitidis by means of a thermodynamic approach. A series of four linear peptides and three "head-to-tail" cyclic peptides (with ring sizes of 9, 15 and 17 amino acids) were synthesized and evaluated as ligands. The peptides contain a fluorescein label and the core determinant amino acid sequence TKDTNNN (residues 180-186) of the PorA P1.16 epitope of meningococcal strain H44/76. Thermodynamic data of the binding of the peptide homologs of the epitope by MN12H2 were assessed by measuring affinity constants (Ka) over a temperature range of 4-55 degrees C, using fluorescence spectroscopy. Curvilinear plots of ln Ka versus T (K) revealed strong temperature dependencies of enthalpy (DeltaH) and entropy (DeltaS). The Gibbs free energy change (DeltaG) was only weakly temperature dependent. The large negative enthalpy value indicated the importance of polar interactions in the binding of both linear and cyclic peptides by MN12H2. Sturtevant's analysis of the thermodynamic parameters showed large unfavorable vibrational contributions to the binding for all linear peptides [Sturtevant, J. M. (1977) Proc. Natl. Acad. Sci.U.S.A. 74, 2236-2240]. The large hydrophobic contribution compensating these vibrational modes was partially attributed to aspecific interaction of the fluorescein label with the antibody. Binding of MN12H2 to conformationally restricted epitope sequences was characterized by a dramatic reduction in the size of unfavorable vibrational components of the thermodynamic parameters. Substitution of individual charged amino acids of the P1.16 epitope sequence revealed that aspartate-182 was essential for the binding. The pH profile observed for the MN12H2-peptide complexes with a midpoint pH of approximately 8.5 suggests a positively charged histidine from the antibody binding site to be involved in a charge interaction with Asp-182. These findings are consistent with the results from the crystal structure of the Fab fragment of MN12H2 in complex with a linear fluorescein-conjugated peptide homolog of the P1.16 epitope [van den Elsen et al. (1997) Proteins (in press)], thereby identifying the basis of an increased incidence of endemic disease in England and Wales since 1981 caused by a mutant meningococcal strain.

Interaction of opiate molecules with lipid monolayers and liposomes

The interaction of opiate molecules (buprenorphine, codeine, dextromethorphan, diprenorphine, etorphine, meperidine, methadone, morphine, and naloxone) with lipids (phosphatidylcholine, phosphatidylinositol, phatidylinositol, phosphatidylserine, and cholesterol) by using liposomes and monomolecular layers as membrane models is described. The ability of opiates to induce leakage of carboxyfluorescin from liposomes is highly dependent on the hydrophobicity of the opiate molecules. Buprenorphine and etorphine increased the membrane permeability in all the experiments. On the contrary, naloxone, morphine, and codeine only caused a slight release of the entrapped dye in the presence of acidic phospholipids. Moreover, the leakage of carboxyfluorescein is directly related to the concentration of drug in the incubation media. Studies of the kinetics of the surface penetration of these molecules into monolayers of phospholipids were performed. Again, in this system, buprenorphine and etorphine exhibited stronger interactions than the most hydrophilic opiates. Nevertheless, in these experiments, differences among the opiate molecules are not so high as in the liposomes. The time course of the penetration of all of these molecules in the monolayers fits the Lineweaver-Burk equation. This fact suggests a lack of specific interactions and the predominance of hydrophobic factors. Moreover, the high percentage of release of entrapped dye caused by some opiate molecules suggests a possible toxic side-effect for these agents.

A synthetic glycopeptide of substance P analogue (SP6-11) with enhanced NK-1 receptor specificity

A new glycopeptide analogue of substance P (6-11) (SP6-11), namely, N1,6 (beta-D-glucopyranosyl) [Glu6, Pro9]SP6-11, has been synthesized and found to be water soluble. The in vitro biological activity of this glycopeptide was determined for spasmogenic activity in the guinea pig ileum and for potentiation of electrically evoked contractions in the rat vas deferens. Thus, activities on NK-1, NK-2, and NK-3 receptor types have been differentiated by two assays and, in the case of NK-1 and NK-3, receptors in guinea pig ileum (GPI) were assayed using specific pharmacological procedures. The ED50 values for the analogue and reference peptides substance P (SP), neurokinin A(NKA), and neurokinin B (NKB) were determined and potencies relative to SP were calculated. The analogue is three times more potent than the potent NK-1 agonist SP on NK-1 receptors. Moreover, this glycopeptide proved to be as selective for the NK-1 receptor as the specific agonist SPOMe (the methyl ester of substance P).

Preparation and in vitro activity of liposome encapsulated opioids

Four opiate molecules: morphine, naloxone, meperidine and codeine have been encapsulated in liposomes. The encapsulation efficiency has been studied as a function of the following parameters: liposome preparation method, lipid composition and opioid molecule hydrophobicity. The most important parameter as far as the entrapment efficiency is concerned is the liposome preparation method. The opioid activity of these molecules in vitro (Guinea Pig Ileum preparation) has been determined. No differences in the IC50 values could be found between encapsulated and free drug molecules.