Cationic Dendrimers Research Articles

Dendrimer-Induced Leukocyte Procoagulant Activity Depends on Particle Size and Surface Charge

Thrombogenicity associated with the induction of leukocyte procoagulant activity (PCA) is a common complication in sepsis and cancer. Since nanoparticles are increasingly used for drug delivery, their interaction with coagulation systems is an important part of the safety assessment. The purpose of this study was to investigate the effects of nanoparticle physicochemical properties on leukocyte PCA, and to get insight into the mechanism of PCA induction. A total of 12 formulations of polyamidoamine (PAMAM) dendrimers, varying in size and surface charge, were studied in vitro using recalcification time assay. Irrespective of their size, anionic and neutral dendrimers did not induce leukocyte PCA in vitro. Cationic particles induced PCA in a size- and charge-dependent manner. The mechanism of PCA induction was similar to that of doxorubicin. Cationic dendrimers were also found to exacerbate endotoxin-induced PCA. PAMAM dendrimer-induced leukocyte PCA depends on particle size, charge and density of surface groups.

Synthesis of Cationic Carbosilane Dendrimers via Click Chemistry and Their Use as Effective Carriers for DNA Transfection into Cancerous Cells

New amine-terminated carbosilane dendrimers have been prepared by a Huisgen cycloaddition ("click chemistry" reaction) of azide-terminated carbosilane dendrimers with two different propargyl amines. The corresponding cationic derivatives with peripheral ammonium groups were obtained by subsequent addition of MeI. Quaternized dendrimers are soluble and stable in water or other protic solvents for long time periods, and have been studied as nonviral vectors for the transfection of DNA to cancer cells. In this study DNA-dendrimeric nanoparticles (dendriplexes) formulated with two different families of cationic carbosilane dendrimers (family 1 (G1, G2 and G3) and family 2 (G1, G2)) were characterized and evaluated for their ability to transfect cells in vitro and in vivo. Dendriplex derived from second generation dendrimer of family 1 (F1G2 5/1 (+/-)) increased the efficiency of plasmid-mediated gene transfer in HepG2 cells as compared to naked DNA and the commercial control dendrimer. Also, intravenously administered dendriplex F1G3 20/1 (+/-) is superior in terms of gene transfer efficiency in vivo.

Phosphorus Dendrimers Affect Alzheimer’s (Aβ1–28) Peptide and MAP-Tau Protein Aggregation

Alzheimer's disease (AD) is characterized by pathological aggregation of β-amyloid peptides and MAP-Tau protein. β-Amyloid (Aβ) is a peptide responsible for extracellular Alzheimer's plaque formation. Intracellular MAP-Tau aggregates appear as a result of hyperphosphorylation of this cytoskeletal protein. Small, oligomeric forms of Aβ are intermediate products that appear before the amyloid plaques are formed. These forms are believed to be most neurotoxic. Dendrimers are highly branched polymers, which may find an application in regulation of amyloid fibril formation. Several biophysical and biochemical methods, like circular dichroism (CD), fluorescence intensity of thioflavin T and thioflavin S, transmission electron microscopy, spectrofluorimetry (measuring quenching of intrinsic peptide fluorescence) and MTT-cytotoxicity assay, were applied to characterize interactions of cationic phosphorus-containing dendrimers of generation 3 and generation 4 (CPDG3, CPDG4) with the fragment of amyloid peptide (Aβ(1-28)) and MAP-Tau protein. We have demonstrated that CPDs are able to affect β-amyloid and MAP-Tau aggregation processes. A neuro-2a cell line (N2a) was used to test cytotoxicity of formed fibrils and intermediate products during the Aβ(1-28) aggregation. It has been shown that CPDs might have a beneficial effect by reducing the system toxicity. Presented results suggest that phosphorus dendrimers may be used in the future as agents regulating the fibrilization processes in Alzheimer's disease.

Synthesis and fluorescent properties of cationic carbosilane dendrimers containing eugenol linkers for their use in biomedical applications

A synthetic strategy has been carried out to prepare a new family of dendrimers containing eugenol linkers between the carbosilane scaffold and the peripheral amine or ammonium groups, of type Gn-[Si(CH2)3C6H3(OMe){O(CH2)2NMe2}]m or Gn-[Si(CH2)3C6H3(OMe){O(CH2)2NMe3+I−}]m respectively. Cationic carbosilane dendrimers have shown fluorescent properties due to the presence of the aromatic rings. A preliminary study of the interaction of dendrimers with two model drugs as examples of Active Pharmaceutical Ingredients (APIs) has been performed by fluorescence and NMR methods. This study determines the ability of these dendrimers to interact with potassium phenoxymethylpenicillin (Penicillin VK) as an example of an anionic low molecular weight drug entity or bovine serum albumin (BSA) as a biopharmaceutical drug protein entity, affording an appropriate dendritic system for its use in certain biological applications like drug delivery.

Interactions between oppositely charged dendrimers

The interactions between cationic (G3, G4, and G5) and anionic (G4.5) poly(amidoamine) (PAMAM) dendrimers were investigated by isothermal titration calorimetry (ITC), photometric titration, nuclear magnetic resonance (NMR), and dynamic light scattering (DLS) studies. The results suggest that the formation of anionic–cationic dendrimer aggregates is an enthalpy-driven process. Ionic interactions occur between the cationic and anionic dendrimers, followed by the formation of supramolecular aggregates and precipitates. The phase separation of the resulting aggregate depends on dendrimer generation, surface charge density, anionic–cationic dendrimer molar ratio, and solution pH values. G5, with a relatively rigid structure, displayed a different binding behavior with G4.5 as compared to the G3 and G4 dendrimers with more flexible scaffolds. G4.5 and G5 with a molar ratio of 0.5 : 1 form the largest aggregates among the investigated G4.5–G5 molar ratios. G4.5 and G5 form aggregates in a size range of 300–3000 nm depending on the G4.5–G5 molar ratio. The G4.5–G5 supramolecular aggregates are not stable and will disassemble after several days of incubation. The results help us to understand the interactions between globular polyelectrodes as well as oppositely charged biomacromolecules.

Dendrimers and dendrons for siRNA binding: computational insights

Short double-stranded RNAs, known as short interfering RNA (siRNA), can be used to specifically down-regulate the expression of targeted genes in a process known as RNA interference (RNAi). However, the success of gene-silencing applications based on the use of synthetic siRNA critically depends on efficient intracellular delivery. In recent years, particular attention has been paid to the use of dendritic scaffolds, in particular dendrimers and dendrons, which are hyper-branched polymers characterized by a well-defined structure and whose surface can be functionalized in many different ways. These structures serve as a base to construct efficient siRNA as well as DNA nanocarriers. In fact, their multivalent character allows the creation of multiple binding sites between the positively charged groups that decorate the surface of cationic dendrons and dendrimers and the negatively charged phosphate groups present on the strands of siRNA and DNA. Despite their great number of potential applications, few attempts have been made so far to study in detail the molecular mechanism underlying the complexation process between these dendritic structures and siRNAs, and the engineering of “ideal dendritic candidates” to deliver and release genetic materials into cells still remains a non-trivial task. In this context, molecular simulation represents a “virtual bridge” between experimental approaches and theoretical models, providing a microscopic view of the molecular requirements of the interaction of RNA-based therapeutics and dendrimers.

Impact of maltose modified poly(propylene imine) dendrimers on liver alcohol dehydrogenase (LADH) internal dynamics and structure

The toxicity of cationic dendrimers is one of their most important drawbacks. Modification of the surface of those dendrimers is a way to obtain compounds that are tolerable by living organisms. However, the sole knowledge how such modifications influence the toxicity of dendrimers is not enough. It is also important to know how such modifications influence the ability of dendrimers to interact with biomolecules, as such interactions may be responsible for dendrimers fate in vivo. In this study the ability of poly(propylene imine) dendrimers of the fourth generation (G4 PPI) with surface modified with maltose moieties to interact with horse liver alcohol dehydrogenase (LADH) was examined. Fluorescence, room temperature tryptophan phosphorescence (RTTP), circular dichroism (CD), dynamic light scattering (DLS) and zeta potential measurements were applied to fully investigate those interactions. As a result, an ability of all studied G4 PPI dendrimers to interact with LADH was shown. However, the differences in the strength of influence of dendrimers on different parts of protein, depending on the dendrimer surface structure, were observed. All dendrimers increased flexibility of the core part of LADH to a similar degree. However, changes in LADH secondary structures upon the interaction with dendrimers depended on the type of the dendrimer. Additionally, experiments performed allowed us to propose the most probable part of LADH that is the subject of the structural changes as the cleft between catalytic and coenzyme binding subdomains of LADH.

Exploiting Dendrimer Multivalency To Combat Emerging and Re-Emerging Infectious Diseases

The emergence and re-emergence of bacterial strains that are resistant to current antibiotics reveal the clinical need for new agents that possess broad-spectrum antibacterial activity. Furthermore, bacteriophobic coatings that repel bacteria are important for medical devices, as the lifetime, reliability, and performance of implant devices are hindered by bacterial adhesion and infection. Dendrimers, a specific class of monodisperse macromolecules, have recently shown potential to function as both antibacterial agents and antimicrobial surface coatings. This review discusses the limitations with currently used antibacterial agents and describes how various classes of dendrimers, including glycodendrimers, cationic dendrimers, anionic dendrimers, and peptide dendrimers, have the potential to improve upon or replace certain antibiotics. Furthermore, the unexplored areas in this field of research will be mentioned to present opportunities for additional studies regarding the use of dendrimers as antimicrobial agents.

Effect of phosphorus dendrimers on DMPC lipid membranes

Large unilamellar liposomes and multilamellar vesicles consisting of DMPC interacted with cationic phosphorus-containing dendrimers CPDs G3 and G4. DSC and ζ-potential measurements have shown that liposomal-dendrimeric molecular recognition probably occurs due to the interaction between the complementary surface groups. Calorimetric studies indicate that the enthalpy of the transition of the lipids that interact with CPDs is dependent on the dendrimers generation.These results can be used in order to rationally design mixed modulatory liposomal locked-in dendrimeric, drug delivery nano systems.

Supporting the Design of Efficient Dendritic DNA and siRNA Nano-Carriers with Molecular Modeling

The design of macromolecules able to generate a stable binding with nucleic acids is of great interest for their possible application in gene delivery. During the last years particular attention has been addressed to the use of dendritic scaffolds as a base to construct efficient DNA and siRNA nano-carriers. Dendrimers and dendrons are hyperbranched polymers characterized by a well-defined structure and by the possibility to functionalize their surface in many different ways. In particular, their multivalent character allows the creation of multiple binding sites between the positively charged groups that decorate the surface of cationic dendrons and dendrimers and the negatively charged phosphate groups present on the strands of DNA and siRNA. The engineering of "ideal dendritic candidates" to deliver and release genetic materials into cells is, however, not trivial due to the huge distance that exists between the design phase and the real application of such molecules. A different architecture of the dendritic scaffold (flexible or rigid) can strongly modify the binding efficiency, but, at the same time, is influenced by the interactions with the external solution. In this context, molecular simulation can represent a "virtual bridge" between the design and the comprehension of the real behavior of such macromolecules.

Systemic Administration of Combinatorial dsiRNAs via Nanoparticles Efficiently Suppresses HIV-1 Infection in Humanized Mice

We evaluated the in vivo efficacy of structurally flexible, cationic PAMAM dendrimers as a small interfering RNA (siRNA) delivery system in a Rag2(-)/-γc-/- (RAG-hu) humanized mouse model for HIV-1 infection. HIV-infected humanized Rag2-/-γc-/- mice (RAG-hu) were injected intravenously (i.v.) with dendrimer-siRNA nanoparticles consisting of a cocktail of dicer substrate siRNAs (dsiRNAs) targeting both viral and cellular transcripts. We report in this study that the dendrimer-dsiRNA treatment suppressed HIV-1 infection by several orders of magnitude and protected against viral induced CD4(+) T-cell depletion. We also demonstrated that follow-up injections of the dendrimer-cocktailed dsiRNAs following viral rebound resulted in complete inhibition of HIV-1 titers. Biodistribution studies demonstrate that the dendrimer-dsiRNAs preferentially accumulate in peripheral blood mononuclear cells (PBMCs) and liver and do not exhibit any discernable toxicity. These data demonstrate for the first time efficacious combinatorial delivery of anti-host and -viral siRNAs for HIV-1 treatment in vivo. The dendrimer delivery approach therefore represents a promising method for systemic delivery of combinations of siRNAs for treatment of HIV-1 infection.

Molecular Structure Encodes Nanoscale Assemblies: Understanding Driving Forces in Electrostatic Self-Assembly

Supramolecular nanoparticles represent a key field in recent research as their synthesis through self-assembly is straightforward and they often can respond to external triggers. A fundamental understanding of structure-directing factors is highly desirable for a targeted structure design. This contribution demonstrates a quantitative relation between the size of supramolecular self-assembled nanoparticles and the free energy of association. Nanoparticles are prepared by electrostatic self-assembly of cationic polyelectrolyte dendrimers as model macroions and oppositely charged di- and trivalent organic dye molecules relying on the combination of electrostatic and π-π-interactions. A systematic set of sulfonate-group carrying azo-dyes was synthesized. Light scattering and ζ-potential measurements on the resulting nanoparticles yield hydrodynamic radii between 20 nm < R(H) < 50 nm and positive ζ-potential values indicating a positive particle charge. Studies on dye self-aggregation and dendrimer-dye association by isothermal titration calorimetry (ITC) and UV-vis spectroscopy allow for the correlation of the thermodynamic parameters of dendrimer-dye association with the size of the particles, showing that at least a free energy gain of ΔG ≈ - 32 kJ mol(-1) is necessary to induce dendrimer interconnection. Structural features of the azo dyes causing these to favor or prevent nanoparticle formation have been identified. The dye-dye-interaction was found to be the key factor in particle size control. A simple model yields a quantitative relation between the free energy and the particle sizes, allowing for predicting the latter based on thermodynamic measurements. Hence, a set of different molecular "building bricks" can be defined where the choice of building block determines the resulting assembly size.

Nanoparticle size and surface charge determine effects of PAMAM dendrimers on human platelets in vitro.

Blood platelets are essential in maintaining hemostasis. Various materials can activate platelets and cause them to aggregate. Platelet aggregation in vitro is often used as a marker for materials' thrombogenic properties, and studying nanomaterial interaction with platelets is an important step toward understanding their hematocompatibility. Here we report evaluation of 12 formulations of PAMAM dendrimers varying in size and surface charge. Using a cell counter based method, light transmission aggregometry and scanning electron microscopy, we show that only large cationic dendrimers, but not anionic, neutral or small cationic dendrimers, induce aggregation of human platelets in plasma in vitro. The aggregation caused by large cationic dendrimers was proportional to the number of surface amines. The observed aggregation was not associated with membrane microparticle release, and was insensitive to a variety of chemical and biological inhibitors known to interfere with various pathways of platelet activation. Taken in context with previously reported studies, our data suggest that large cationic PAMAM dendrimers induce platelet aggregation through disruption of membrane integrity.

Design of interior-functionalized fully acetylated dendrimers for anticancer drug delivery

In this study, dendrimers was synthesized by introducing functional groups into the interior pockets of fully acetylated dendrimers. NMR techniques including COSY and 2D-NOESY revealed the molecular structures of the synthesized dendrimers and the encapsulation of guest molecule such as methotrexate within their interior pockets. The synthesized polymeric nanocarriers showed much lower cytotoxicity on two cell lines than cationic dendrimers, and exhibited better performance than fully acetylated dendrimers in the sustained release of methotrexate. The results provided a new strategy in the design of non-toxic dendrimers with high performance in the delivery of anti-cancer drugs for clinical applications.

Fourth Generation Phosphorus-Containing Dendrimers: Prospective Drug and Gene Delivery Carrier

Research concerning new targeting delivery systems for pharmacologically active molecules and genetic material is of great importance. The aim of the present study was to investigate the potential of fourth generation (P4) cationic phosphorus-containing dendrimers to bind fluorescent probe 8-anilino-1-naphthalenesulfonate (ANS), anti-neoplastic drug cisplatin, anti-HIV siRNA siP24 and its capability to deliver green fluorescent protein gene (pGFP) into cells. The interaction between P4 and ANS (as the model drug) was investigated. The binding constant and the number of binding centers per one molecule of P4 were determined. In addition, the dendriplex between P4 and anti-HIV siRNA siP24 was characterized using circular dichroism, fluorescence polarization and zeta-potential methods; the average hydrodynamic diameter of the dendriplex was calculated using zeta-size measurements. The efficiency of transfection of pGFP using P4 was determined in HEK293 cells and human mesenchymal stem cells, and the cytotoxicity of the P4-pGFP dendriplex was studied. Furthermore, enhancement of the toxic action of the anti-neoplastic drug cisplatin by P4 dendrimers was estimated. Based on the results, the fourth generation cationic phosphorus-containing dendrimers seem to be a good drug and gene delivery carrier candidate.

Interaction of cationic phosphorus dendrimers with lipid membranes

Large unilamellar liposomes and multilamellar vesicles consisting of DMPC interacted with cationic phosphorus-containing dendrimers CPDs G3 and G4. DSC and ζ -potential measurements have shown that liposomal-dendrimeric molecular recognition occurs due to the interaction between the complementary surface groups. Calorimetric studies indicate that the enthalpy of the transition of the lipids that interact with CPDs is dependent on the dendrimers generation. These results can be used in order to rationally design mixed modulatory liposomal locked-in dendrimeric, drug delivery nano systems.

Effect of Polyelectrolyte Architecture and Size on Macroion–Dye Assemblies

This study describes the influence of polyelectrolyte building block nature on the formation of supramolecular polyelectrolyte-dye nanoparticles self-assembled through electrostatic interactions of the oppositely charged building units and π-π interactions in-between dye molecules ("electrostatic self-assembly"). The anionic azo dye Acid Red 26 (Ar26) is combined with cationic polyamidoamine dendrimers of generations G0, G2, G4, G6, and G8 and linear polycations polylysine (PolyLys) and polyallylamine hydrochloride (PAH). Light scattering reveals defined supramolecular particles with hydrodynamic radii R(H) = 15 nm to R(H) = 50 nm for slight excess of G2-G8 dendrimers. G0 does not yield stable assemblies. Linear polyelectrolytes form assemblies with hydrodynamic radii from R(H) = 20 nm to R(H) = 200 nm. Thermodynamic measurements by isothermal titration calorimetry (ITC) show that all macroions bind dye molecules up to about charge stoichiometry, and assembly formation is predominantly enthalpically driven. Differences in dye-dye interactions are related to structural features by analyzing endothermic heats of aggregate disruption through excess macroion addition. A simple model connects thermodynamic parameters with the internal assembly structure.

Effects of PAMAM Dendrimer Salt Solutions on Protein Stability

Dendrimers are widely used for biological applications. However, their effect on protein stability has not been studied extensively. Typically, charged cationic dendrimers such as PAMAM dendrimers tend to destabilize proteins due to the cooperative binding of surface groups to the protein surface. We have studied the effect of PAMAM dendrimer salt solutions on protein stability both experimentally and computationally. We show that the effect of dendrimers on protein stability depends on the choice of counterion (e.g., dihydrogen phosphate salts reduce the rate of protein aggregation, while chloride salts increase the rate of protein aggregation). In the presence of dihydrogen phosphate and sulfate counterions, the binding of dendrimers to the protein surface is limited (when compared to chloride and thiocyanate), which enhances the conformational stability of proteins. To the best of the authors’ knowledge, this is the first study that has shown that PAMAM dendrimer salts can significantly suppress the ag...

Structure-Skin Permeability Relationship of Dendrimers

To investigate skin penetration of poly (amidoamine) (PAMAM) dendrimers as a function of surface charge and molecular weight in presence and absence of iontophoresis. Dendrimers were labeled with fluoroisothiocynate (FITC); skin penetration of dendrimers was studied using excised porcine skin in-vitro. Skin penetration of FITC-labeled dendrimers was quantified using confocal laser scanning microscope (CLSM). G2-G6 NH(2), G3.5-COOH and G4-OH dendrimers were used. Cationic dendrimers showed higher skin penetration than neutral and anionic dendrimers. Skin penetration of cationic dendrimer increased linearly with increase in treatment time. Iontophoresis enhanced skin penetration of cationic and neutral dendrimers. Increase in current strength and current duration increased skin transport of dendrimers. Passive and iontophoretic skin penetration of cationic dendrimers was inversely related to their molecular weight. Dendrimer penetrated the skin through intercellular lipids and hair follicles. With iontophoresis, dendrimer was also found in localized skin regions. The study demonstrates that the physicochemical properties of dendrimers influence their skin transport. Findings can be used to design dendrimer-based nanocarriers for drug delivery to skin.

Effects of a cationic PAMAM dendrimer on photosynthesis and ROS production of Chlamydomonas reinhardtii

Poly(amidoamine) (PAMAM) dendrimers hold great promises for biomedicine. This study sought to examine the toxicity of generation 4 (G4) cationic PAMAM dendrimer to the green microalga, Chlamydomonas reinhardtii, using physiological and molecular biomarkers. Results revealed that the G4 dendrimer at 15 and 25 nM stimulated the photosynthetic process and the production of reactive oxygen species (ROS) in algae. However, the over-production of ROS did not induce the expression of antioxidant enzyme genes, catalase and glutathione peroxidase. In addition, genes encoding light-harvesting proteins (lhca and lhcb), a ferredoxin (fdx) and an oxygen-evolving enhancer protein (psb) involved in photosynthesis were repressed after treatment. Nevertheless, the expression of the lhcbm9 gene, encoding a major light harvesting polypeptide, was increased. These results suggest that the strong modulation of photosynthesis induced by the dendrimer could lead to elevated ROS levels in microalgae.