High Immobilization Efficiency of Basic Protein within Heparin-Immobilized Calcium Phosphate Nanoparticles

Previously, we achieved one-pot fabrication of heparin-immobilized calcium phosphate (CaP) nanoparticles with high dispersibility by a precipitation process in a highly supersaturated reaction solution. In this study, we revealed that the heparin-immobilized CaP nanoparticles have a greater co-immobilizing capacity for basic proteins than for acidic proteins. In this process, heparin acted as not only a particle-dispersing agent but also as an immobilizing agent for basic proteins; it remarkably (approximately three-fold) improved the immobilization efficiency of cytochrome C (a model basic protein) within the CaP nanoparticles. The content of cytochrome C immobilized within the nanoparticles was increased with an increase in cytochrome C concentration in the reaction solution and by aging the nanoparticles. The obtained nanoparticles were dispersed well in water owing to their large negative zeta potentials derived from heparin, irrespective of the content of cytochrome C. Similar results were obtained also for another basic protein, lysozyme, but not for an acidic protein, albumin; the immobilization efficiency of albumin within the nanoparticles was decreased by heparin. These findings provide new insights into the co-immobilization strategy of proteins within heparin-immobilized CaP nanoparticles and will be useful in the design and fabrication of nanocarriers for protein delivery applications.

Surface-Functionalized Silica-Coated Calcium Phosphate Nanoparticles Efficiently Deliver DNA-Based HIV-1 Trimeric Envelope Vaccines against HIV-1

Human immunodeficiency virus type 1 (HIV-1) infection remains one of the worst crises in global health. The prevention of HIV-1 infection is a crucial task that needs to be addressed due to the absence of a licensed vaccine against HIV-1. DNA vaccines present a promising alternative approach to combat HIV-1 infection due to their excellent safety profile, lack of severe side effects, and relatively rapid fabrication. Traditional vaccines composed of a monomeric envelope or peptide fragments have been indicated to lack protective efficacy mediated by inducing HIV-1-specific neutralizing antibodies in clinical trials. The immunogenicity and protection against HIV-1 induced by DNA vaccines are limited due to the poor uptake of these vaccines by antigen-presenting cells and their ready degradation by DNases and lysosomes. To address these issues of naked DNA vaccines, we described the feasibility of CpG-functionalized silica-coated calcium phosphate nanoparticles (SCPs) for efficiently delivering DNA-based HIV-1 trimeric envelope vaccines against HIV-1. Vaccines comprising the soluble BG505 SOSIP.664 trimer fused to the GCN4-based isoleucine zipper or bacteriophage T4 fibritin foldon motif with excellent simulation of the native HIV-1 envelope were chosen as trimer-based vaccine platforms. Our results showed that SCP-based DNA immunization could significantly induce both broad humoral immune responses and potent cellular immune responses compared to naked DNA vaccination in vivo. To the best of our knowledge, this study is the first to assess the feasibility of CpG-functionalized SCPs for efficiently delivering DNA vaccines expressing a native-like HIV-1 trimer. These CpG-functionalized SCPs for delivering DNA-based HIV-1 trimeric envelope vaccines may lead to the development of promising vaccine candidates against HIV-1.

Biological and Medical Applications of Calcium Phosphate Nanoparticles

Calcium phosphate nanoparticles have a high biocompatibility and biodegradability due to their chemical similarity to human hard tissue, for example, bone and teeth. They can be used as efficient carriers for different kinds of biomolecules such as nucleic acids, proteins, peptides, antibodies, or drugs, which alone are not able to enter cells where their biological effect is required. They can be loaded with cargo molecules by incorporating them, unlike solid nanoparticles, and also by surface functionalization. This offers protection, for example, against nucleases, and the possibility for cell targeting. If such nanoparticles are functionalized with fluorescing dyes, they can be applied for imaging in vitro and in vivo. Synthesis, functionalization and cell uptake mechanisms of calcium phosphate nanoparticles are discussed together with applications in transfection, gene silencing, imaging, immunization, and bone substitution. Biodistribution data of calcium phosphate nanoparticles in vivo are reviewed.

Biodegradable calcium phosphate nanoparticles for cancer therapy

Calcium phosphate is the inorganic mineral of hard tissues such as bone and teeth. Due to their similarities to the natural bone, calcium phosphates are highly biocompatible and biodegradable materials that have found numerous applications in dental and orthopedic implants and bone tissue engineering. In the form of nanoparticles, calcium phosphate nanoparticles (CaP's) can also be used as effective delivery vehicles to transfer therapeutic agents such as nucleic acids, drugs, proteins and enzymes into tumor cells. In addition, facile preparation and functionalization of CaP's, together with their inherent properties such as pH-dependent solubility provide advantages in delivery and release of these bioactive agents using CaP's as nanocarriers. In this review, the challenges and achievements in the intracellular delivery of these agents to tumor cells are discussed. Also, the most important issues in the design and potential applications of CaP-based biominerals are addressed with more focus on their biodegradability in tumor microenvironment.

Reduction of inflammation in a chronic periodontitis model in rats by TNF-α gene silencing with a topically applied siRNA-loaded calcium phosphate paste

We developed a calcium phosphate-based paste containing siRNA against TNF-α and investigated its anti-inflammatory and bone-healing effects in vitro and in vivo in a rat periodontitis model. The bioactive spherical CaP/PEI/siRNA/SiO₂ nanoparticles had a core diameter of 40-90 nm and a positive charge (+23 mV) that facilitated cellular uptake. The TNF- α gene silencing efficiency of the nanoparticles in J774.2 monocytes, gingival-derived cells, and bone marrow-derived cells was 12 ± 2%, 36 ± 8%, and 35 ± 22%, respectively. CaP/PEI/siRNA/SiO₂ nanoparticles cancelled the suppression of alkaline phosphatase (ALP) activity in LPS-stimulated bone marrow-derived cells. In vivo, ALP mRNA was up-regulated, TNF-α mRNA was down-regulated, and the amount of released TNF-α was significantly reduced after topical application of the calcium phosphate-based paste containing siRNA-loaded nanoparticles. The number of TNF-α-positive cells in response to CaP/PEI/siRNA/SiO₂ nanoparticle application was lower than that observed in the absence of siRNA. Elevated ALP activity and numerous TRAP-positive cells (osteoclasts) were observed in response to the application of all calcium phosphate pastes. These results demonstrate that local application of a paste consisting of siRNA-loaded calcium phosphate nanoparticles successfully induces TNF-α silencing in vitro and in vivo and removes the suppression of ALP activity stimulated by inflammation. STATEMENT OF SIGNIFICANCE: We developed a calcium phosphate-based paste containing nanoparticles loaded with siRNA against TNF-α. The nanoparticles had a core diameter of 40-90 nm and positive charge (+23 mV). The anti-inflammatory and osteoinductive effects of the paste were investigated in vitro and in vivo in a rat periodontitis model. In vitro, the TNF-α gene silencing efficiency of the nanoparticles in J774.2 monocytes, gingival-derived cells, and bone marrow-derived cells was 12 ± 2%, 36 ± 8%, and 35 ± 22%, respectively. The ALP activity of bone marrow-derived cells was recovered. In vivo, TNF-α mRNA was down-regulated and the amount of released TNF-α was significantly reduced, whereas the ALP mRNA was up-regulated. Elevated ALP activity and TRAP-positive cells were observed by immunohistochemistry.

Functionalized calcium orthophosphates (CaPO4) and their biomedical applications

Due to the chemical similarity to natural calcified tissues (bones and teeth) of mammals, calcium orthophosphates (abbreviated as CaPO₄) appear to be good biomaterials for creation of artificial bone grafts. However, CaPO₄ alone have some restrictions, which limit their biomedical applications. Various ways have been developed to improve the properties of CaPO₄ and their functionalization is one of them. Namely, since surfaces always form the interfaces between implanted grafts and surrounding tissues, the state of CaPO₄ surfaces plays a crucial role in the survival of bone grafts. Although the biomedically relevant CaPO₄ possess the required biocompatible properties, some of their properties could be better. For example, functionalization of CaPO₄ to enhance cell attachment and cell material interactions has been developed. In addition, to prepare stable formulations from nanodimensional CaPO₄ particles and prevent them from agglomerating, the surfaces of CaPO₄ particles are often functionalized by sorption of special chemicals. Furthermore, there are functionalizations in which CaPO₄ are exposed to various types of physical treatments. This review summarizes the available knowledge on CaPO₄ functionalizations and their biomedical applications.

Calcium phosphate nanocarriers for drug delivery to tumors: imaging, therapy and theranostics

Calcium phosphate (CaP) was engineered as a drug delivery nanocarrier nearly 50 years ago due to its biocompatibility and biodegradability. In recent years, several approaches have been developed for the preparation of size-controllable, stable and multifunctional CaP nanocarriers, and several targeting moieties have also been decorated on the surface of these nanocarriers for active targeting. The CaP nanocarriers have been utilized for loading probes, nucleic acids, anticancer drugs and photosensitizers for cancer imaging, therapy and theranostics. Herein, we reviewed the recent advances in the preparation strategies of CaP nanocarriers and the applications of these nanocarriers in tumor diagnosis, gene delivery, drug delivery and theranostics and finally provided perspectives.

Dual delivery of nucleic acids and PEGylated-bisphosphonates via calcium phosphate nanoparticles

Despite many years of research and a few success stories with gene therapeutics, efficient and safe DNA delivery remains a major bottleneck for the clinical translation of gene-based therapies. Gene transfection with calcium phosphate (CaP) nanoparticles brings the advantages of low toxicity, high DNA entrapment efficiency and good endosomal escape properties. The macroscale aggregation of CaP nanoparticles can be easily prevented through surface coating with bisphosphonate conjugates. Bisphosphonates, such as alendronate, recently showed promising anticancer effects. However, their poor cellular permeability and preferential bone accumulation hamper their full application in chemotherapy. Here, we investigated the dual delivery of plasmid DNA and alendronate using CaP nanoparticles, with the goal to facilitate cellular internalization of both compounds and potentially achieve a combined pharmacological effect on the same or different cell lines. A pH-sensitive poly(ethylene glycol)-alendronate conjugate was synthetized and used to formulate stable plasmid DNA-loaded CaP nanoparticles. These particles displayed good transfection efficiency in cancer cells and a strong cytotoxic effect on macrophages. The in vivo transfection efficiency, however, remained low, calling for an improvement of the system, possibly with respect to the extent of particle uptake and their physical stability.

Biomolecule-assisted green synthesis of nanostructured calcium phosphates and their biomedical applications

Calcium phosphates (CaPs) are ubiquitous in nature and vertebrate bones and teeth, and have high biocompatibility and promising applications in various biomedical fields. Nanostructured calcium phosphates (NCaPs) are recognized as promising nanocarriers for drug/gene/protein delivery owing to their high specific surface area, pH-responsive degradability, high drug/gene/protein loading capacity and sustained release performance. In order to control the structure and surface properties of NCaPs, various biomolecules with high biocompatibility such as nucleic acids, proteins, peptides, liposomes and phosphorus-containing biomolecules are used in the synthesis of NCaPs. Moreover, biomolecules play important roles in the synthesis processes, resulting in the formation of various NCaPs with different sizes and morphologies. At room temperature, biomolecules can play the following roles: (1) acting as a biocompatible organic phase to form biomolecule/CaP hybrid nanostructured materials; (2) serving as a biotemplate for the biomimetic mineralization of NCaPs; (3) acting as a biocompatible modifier to coat the surface of NCaPs, preventing their aggregation and increasing their colloidal stability. Under heating conditions, biomolecules can (1) control the crystallization process of NCaPs by forming biomolecule/CaP nanocomposites before heating; (2) prevent the rapid and disordered growth of NCaPs by chelating with Ca2+ ions to form precursors; (3) provide the phosphorus source for the controlled synthesis of NCaPs by using phosphorus-containing biomolecules. This review focuses on the important roles of biomolecules in the synthesis of NCaPs, which are expected to guide the design and controlled synthesis of NCaPs. Moreover, we will also summarize the biomedical applications of NCaPs in nanomedicine and tissue engineering, and discuss their current research trends and future prospects.

CaP coated mesoporous polydopamine nanoparticles with responsive membrane permeation ability for combined photothermal and siRNA therapy

Combined photothermal and gene therapy provides a promising modality toward cancer treatment, yet facile integration and controlled codelivery of gene payloads and photothermal conversion agents (PTCAs) remains a great challenge. Inspired by the robust wet adhesion of marine mussels, we present a rationally designed nanosystem constructed by using hybrid mesoporous polydopamine nanoparticles (MPDA) with sub-100 nm sizes and a high photothermal conversion efficiency of 37%. The surface of the particles were modified with tertiary amines by the facile Michael addition/Schiff base reactions of PDA to realize high siRNA loading capacity (10 wt%). Moreover, a successful calcium phosphate (CaP) coating via biomineralization was constructed on the cationic nanoparticle to prohibit premature release of siRNA. The CaP coating underwent biodegradation in weakly-acidic subcellular conditions (lysosomes). The synergistic integration of tertiary amines and catechol moieties on the subsequently exposed surfaces was demonstrated to feature the destabilization/disruption ability toward model cellular membranes via the greatly enhanced interfacial adhesion and interactions. Consequently, sufficient permeability of lysosomal membranes, and in turn, a high lysosomal escape efficiency, was realized, which then resulted in high gene silencing efficiencies via sufficient cytosolic delivery of siRNA. When an efficient knocking down (65%) of survivin (an inhibitor of apoptosis proteins) was combined with a subsequent photothermal ablation, remarkably higher therapeutic efficiencies were observed both in vitro and in vivo, as compared with monotherapy. The system may help to pave a new avenue on the utilization of bio-adhesive surfaces for handling the obstacles of combined photothermal and gene therapy. STATEMENT OF SIGNIFICANCE: Polydopamine (PDA) based porous photothermal-conversion agent (PTCA) with sufficiently high conversion efficiency was employed to deliver photothermal/gene therapy modalities towards cancer treatment. CaP coating via PDA-induced biomineralization was constructed to prohibit premature release of siRNA loaded in the pore space of the nanocarriers. Responsive degradation of CaP also led to the exposure of membrane-lytic surfaces built through the synergistic integration of tertiary amines and catechol moieties, and in turn the significantly enhanced lysosomal escape and cytosol siRNA delivery. Therapeutic targeting of survivin was successfully applied for activation of apoptosis and programmed cell death. Combined photothermal and gene therapy improved therapeutic effectiveness.

Functionalization of titania nanotubes with electrophoretically deposited silver and calcium phosphate nanoparticles: Structure, composition and antibacterial assay

Herein TiO₂ nanotubes (NTs) were fabricated via electrochemical anodization and coated with silver and calcium phosphate (CaP) nanoparticles (NPs) by electrophoretic deposition. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) revealed that Ag and CaP NPs were successfully deposited onto the TiO₂ NTs. Using X-ray diffraction, only anatase and Ti were observed after deposition of Ag and CaP NPs. However, X-ray photoelectron spectroscopy (XPS) analysis revealed that the binding energy (BE) of the Ag and CaP NP core levels corresponded to metallic Ag, hydroxyapatite and amorphous calcium phosphate, based on the knowledge that CaP NPs synthesized by precipitation have the nanocrystalline structure of hydroxyapatite. The application of Ag NPs allows for decreasing the water contact angle and thus increasing the surface free energy. It was concluded that the CaP NP surfaces are superhydrophilic. A significant antimicrobial effect was observed on the TiO₂ NT surface after the application of Ag NPs and/or CaP NPs compared with that of the pure TiO₂ NTs. Thus, fabrication of TiO₂ NTs, Ag NPs and CaP NPs with PEI is promising for diverse biomedical applications, such as in constructing a biocompatible coating on the surface of Ti that includes an antimicrobial effect.

Nanonized tetracycline cures deadly diarrheal disease 'shigellosis' in mice, caused by multidrug-resistant Shigella flexneri 2a bacterial infection

We reported earlier about nano-formulation of tetracycline through its entrapment within calcium-phosphate nano-particle (CPNP) and about killing of pathogenic bacterium Shigella flexnari 2a, resistant to tetracycline (and 9 other antibiotics), by the nanonized antibiotic (Tet-CPNP). Here, we report on therapeutic role of Tet-CPNP against deadly diarrheal disease 'shigellosis' in mice, caused by Shigella infection. Our findings revealed that occurrence of mushy-stool excretion, colon-length shortening, weight-loss and bacterial colonization in gastrointestinal tract of mice due to shigellosis was significantly reduced by Tet-CPNP treatment. Histo- and immuno-logical studies showed that changes in morphology and level of inflammatory cytokines TNF-α, IL-1β and IFN-γ in intestinal tissue of Shigella-infected mice were reverted to almost normal features by Tet-CPNP treatment. Bulk tetracycline had no anti-shigellosis action. Thus, nanonization of tetracycline rejuvenated the old, cheap, broad-spectrum antibiotic from obsolescence (due to resistance generation), making it highly beneficial for diarrhea-prone developing countries with limited health-care budgets.

Dendrimer as a new potential carrier for topical delivery of siRNA: A comparative study of dendriplex vs. lipoplex for delivery of TNF-α siRNA

Topical delivery of siRNA is challenging task due to complex barrier property of stratum corneum and cationic lipid based carriers have been widely explored for this purpose due to improved permeation through skin. For gene delivery application, dendrimers are considered as efficient carrier due to their cationic nature and well-defined surface groups. However, they are not well explored for topical delivery. This work compares the suitability of PAMAM dendrimer with DOTAP liposome for topical delivery of siRNA against TNF-α. The particle size, zeta potential and entrapment efficiency of dendriplex were 99.80 ± 1.80 nm, 13.40 ± 4.84 mV and 98.72 ± 2.02% whereas for lipoplex were 174.80 ± 0.80 nm, 29.96 ± 0.51 mV and 94.99 ± 5.01% respectively. Both the formulations were stable in serum and in the presence of RNAse. TNF-α is inflammatory cytokine, hence the in vivo efficacy of developed formulations was determined using psoriatic plaque model. Results suggested improved phenotypic and histopathological features and reduced levels of IL-6, TNF-α, IL-17 and IL-22 for dendriplex and lipoplex treated groups in comparison to Imiquimod treated group. These findings suggest that dendrimer can be a potential carrier for topical gene delivery.

Therapeutic approaches for the delivery of TNF-α siRNA

Immune-mediated diseases are emerging as a major healthcare concern in the present era. TNF-α, a proinflammatory cytokine, plays a major role in the manifestation of these diseases by mediating different pathways and inducing the expression of other cytokines. In last decades, monoclonal antibodies and extracellular portion of human TNF-α receptors are explored in this area; however, the risk of immunological response and undesired effects urge a need to develop more effective therapies to control TNF-α levels. siRNA therapeutic strategies are emerging for the treatment of myriad of diseases, but the delivery challenges associated with siRNA require the development of suitable delivery vectors. For delivery of TNF-α siRNA, both viral and nonviral vectors are explored. This review attempts to describe different delivery approaches for TNF-α siRNA with special focus on nonviral delivery vectors.

Calcium-based biomaterials for diagnosis, treatment, and theranostics

Calcium-based biomaterials with good biosafety and bio-absorbability are promising for biomedical applications such as diagnosis, treatment, and theranostics.

Interfacing DNA Oligonucleotides with Calcium Phosphate and Other Metal Phosphates

Calcium phosphate (CaP) has long been used for DNA delivery, although its fundamental interaction with DNA, especially with single-stranded DNA oligonucleotides, remains to be fully understood. Using fluorescently labeled oligonucleotides, we herein studied DNA adsorption isotherm and the effect of DNA length and sequence. Longer DNAs are adsorbed more strongly, and at neutral pH, poly-C DNAs are adsorbed more than the other three DNA homopolymers. However, at near pH 11, the pH of CaP synthesis, T₃₀ DNA is adsorbed more strongly than C₃₀ or A₃₀. This can explain why T₃₀ and G₃₀ can fully inhibit the growth of CaP, while A₃₀ and C₃₀ only retarded its growth kinetics. DNA adsorption also reduces aggregation of CaP. DNA desorption experiments were carried out using concentrated urea, thymidine, or inorganic phosphate as competitors, and desorption was observed only in the presence of phosphate, suggesting that DNA uses its phosphate backbone to interact with the CaP surface. Desorption was also promoted by raising the NaCl concentration suggesting the electrostatic nature of interaction. Finally, ten different metal phosphate materials were synthesized by co-precipitating each metal ion (Ce³⁺, Fe³⁺, Ca²⁺, Ni²⁺, Zn²⁺, Mn²⁺, Ba²⁺, Cu²⁺, Sr²⁺, Co²⁺), and DNA adsorption by these phosphate precipitants was found to be related to their surface charge and metal chemistry. This work has revealed fundamental surface science of DNA adsorption by CaP and other metal phosphate salts, and this knowledge might be useful for gene delivery, biomineralization, and DNA-directed assembly of metal phosphate materials.

Functional calcium phosphate composites in nanomedicine

Calcium phosphate (CaP) materials have many peculiar and intriguing properties. In nature, CaP is found in nanostructured form embedded in a soft proteic matrix as the main mineral component of bones and teeth. The extraordinary stoichiometric flexibility, the different stabilities exhibited by its different forms as a function of pH and the highly dynamic nature of its surface ions, render CaP one of the most versatile materials for nanomedicine. This review summarizes some of the guidelines so far emerged for the synthesis of CaP composites in aqueous media that endow the material with tailored crystallinity, morphology, size, and functional properties. First, we introduce very briefly the areas of application of CaP within the nanomedicine field. Then through some selected examples, we review some synthetic routes where the presence of functional units (small templating molecules like surfactants, or oligomers and polymers) assists the synthesis and at the same time impart the functionality or the responsiveness desired for the end-application of the material. Finally, we illustrate two examples from our laboratory, where CaP is decorated by biologically active polymers or prepared within a thermo- and magneto-responsive hydrogel, respectively.

Live-cell imaging to compare the transfection and gene silencing efficiency of calcium phosphate nanoparticles and a liposomal transfection agent

The processing of DNA (for transfection) and short interfering RNA (siRNA; for gene silencing), introduced into HeLa cells by triple-shell calcium phosphate nanoparticles, was followed by live-cell imaging. For comparison, the commercial liposomal transfection agent Lipofectamine was used. The cells were incubated with these delivery systems, carrying either enhanced green fluorescent protein (eGFP)-encoding DNA or siRNA against eGFP. In the latter case, HeLa cells that stably expressed eGFP were used. The expression of eGFP started after 5 h in the case of nanoparticles and after 4 h in the case of Lipofectamine. The corresponding times for gene silencing were 5 h (nanoparticles) and immediately after incubation (Lipofectamine). The expression of eGFP was notably enhanced 2-3 h after cell division (mitosis). In general, the transfection and gene silencing efficiencies of the nanoparticles were lower than those of Lipofectamime, even at a substantially higher dose (factor 20) of nucleic acids. However, the cytotoxicity of the nanoparticles was lower than that of Lipofectamine, making them suitable vectors for in vivo application.

Characterization of Calcium Phosphate Nanoparticles Based on a PEGylated Chelator for Gene Delivery

Calcium phosphate (CaP) nanoparticles are promising gene delivery carriers due to their bioresorbability, ease of preparation, high gene loading efficacy, and endosomal escape properties. However, the rapid aggregation of the particles needs to be addressed in order to have potential in vivo. In addition, there is a need to better understand the relationship between CaP nanoparticle properties and their interactions with cells. Here, a new synthesis route involving click chemistry was developed to prepare the PEGylated chelator PEG-inositol 1,3,4,5,6-pentakisphosphate (PEG-IP5) that can coat and stabilize CaP nanoparticles. Two methods (1 and 2) differing on the time of addition of the PEGylated chelator were employed to produce stabilized particles. Method 1 yielded amorphous aggregated spheres with a particle size of about 200 nm, whereas method 2 yielded 40 nm amorphous loose aggregates of clusters, which were quickly turned into needle bundle-like crystals of about 80 nm in a few hours. Nanoparticles prepared by method 1 were internalized with significantly higher efficiency in HepG2 cells than those prepared by method 2, and the uptake was dramatically influenced by the reaction time of Ca²⁺ and PO₄^3- and sedimentation of the particles. Interestingly, morphological transformations were observed for both types of particles after different storage times, but this barely influenced their in vitro cellular uptake. The transfection efficiency of the particles prepared by method 1 was significantly higher, and none of the formulations tested showed signs of cytotoxicity. This study provides a better understanding of the properties (e.g., size, morphology, and crystallinity) of PEGylated CaP nanoparticles and how these influence the particles' in vitro uptake and transfection efficiency.

Calcium phosphate-quercetin nanocomposite (CPQN): A multi-functional nanoparticle having pH indicating, highly fluorescent and anti-oxidant properties

Calcium phosphate quercetin nanocomposite (CPQN) i.e., quercetin entrapped in calcium phosphate nanoparticle was synthesized by a precipitation method at 80°C, taking ammonium hydrogen phosphate, calcium nitrate and quercetin as precursors and sodium citrate as stabilizer. The nanocomposite suspension had different color at different pH values, a property that could render the nanoparticle a pH indicator. Besides color, the particles also had different size, shape, stability and quercetin content with change of pH. In addition, the CPQN was highly fluorescent having two sharp emission peaks at 460 and 497nm, when excited at 370nm; by this property it behaved as an effective fluorophore to label biological cell. Moreover, the nanocomposite had potential anti-oxidant property, for which mortality of mouse neuroblastoma cell N2A, by H₂O₂-induced oxidative stress, was found to be lowered by the pre-treatment of the cells with CPQN.

Tetracycline-loaded calcium phosphate nanoparticle (Tet-CPNP): Rejuvenation of an obsolete antibiotic to further action

BACKGROUND

Increasing resistance in bacteria towards antibiotics has made it imperative to research on their revitalization to combat infectious diseases. This study dealt with synthesis of a nano-form of the antibiotic tetracycline, its characterization and potency of killing different multi-drug resistant diarrhea-causing bacteria.

METHODS

Nano-formulation was done by loading tetracycline within biocompatible calcium phosphate nanoparticle. The synthesized tetracycline-loaded calcium phosphate nanoparticle (Tet-CPNP) was characterized by the techniques like TEM, DLS, EDS, FTIR, spectrofluorimetry and dialysis. Bactericidal activity of nano-particulate tetracycline was investigated by agar plating, spectrophotometry, phase contrast-fluorescence-atomic force microscopy and flow cytometry techniques.

RESULTS

The Tet-CPNPs were 8±5nm in size and nearly spherical in shape, efficiency of tetracycline loading in CPNP was about 20% and the release of antibiotic from Tet-CPNPs was sustainable during 7days. Minimum inhibitory concentration (MIC) of Tet-CPNP on multiple antibiotic (including tetracycline) resistant bacteria like Escherichia coli, Salmonella kentuckey and Shigella flexneri was in the range of 20-40μg/ml, whereas MIC of free tetracycline was in the range of 150-180μg/ml. NP-mediated cell filamentation and cell membrane disintegration caused cell killing. Moreover, death of Shigella-infected Zebra fish larvae was stalled by Tet-CPNP treatment. CPNP itself had no toxic effect on bacteria as well as on Zebra fish.

CONCLUSION

Our nano-formulation of tetracycline might reclaim a nearly obsolete antibiotic to further potential function.

GENERAL SIGNIFICANCE

Such a study on revival of an old, cheap, broad-spectrum antibiotic to further action is highly beneficial to developing countries with limited health care budgets.

Biomimetic synthesis of needle-like fluorescent calcium phosphate/carbon dot hybrid composites for cell labeling and copper ion detection

We report a biomimetic method to synthesize needle-like calcium phosphate (CaP) using carbon dots (CDs) and sodium carboxymethylcellulose as dual templates. The CaP/CDs were capable of cell labeling and selective detection of copper ions in drinking water.

Gene silencing of the pro-inflammatory cytokine TNF-α with siRNA delivered by calcium phosphate nanoparticles, quantified by different methods

The expression of the proinflammatory cytokine TNF-α was efficiently downregulated with nanoparticles, opening a way to combat inflammatory reactions.

Protein–calcium phosphate nanocomposites: benchmarking protein loading via physical and chemical modifications against co-precipitation

This study benchmarks the co-precipitation, physical and chemical methods used for protein loading enhancement on calcium phosphate.

Quantification of volume and size distribution of internalised calcium phosphate particles and their influence on cell fate

We report preliminary findings suggesting that the diameter of the internalised calcium phosphate particles is critical to cell fate with particles/aggregates of particles of larger than 1.5 μm not processed by lysosomes leading to cell death. This has significant implications for the design of medical materials even from those consisting of non-toxic calcium phosphate salts.

Efficient gene delivery and multimodal imaging by lanthanide-based upconversion nanoparticles

Nanoparticles have been explored as nonviral gene carriers for years because of the simplicity of surface modification and lack of immune response. Lanthanide-based upconversion nanoparticles (UCNPs) are becoming attractive candidates for biomedical applications in virtue of their unique optical properties and multimodality imaging ability. Here, we report a UCNPs-based structure with polyethylenimine coating for both efficient gene transfection and trimodality imaging. Cytotoxicity tests demonstrated that the nanoparticles exhibited significantly decreased cytotoxicity compared to polyethylenimine polymer. Further, in vitro studies revealed that the gene carriers are able to transfer the enhanced green fluorescence protein (EGFP) plasmid DNA into Hela cells in higher transfection efficiency than PEI. Gene silencing was also examined by delivering bcl-2 siRNA into Hela cells, resulting in significant downregulation of target bcl-2 mRNA. More importantly, we demonstrated the feasibility of upconversion gene carriers to serve as effective contrast agents for MRI/CT/UCL trimodality imaging both in vitro and in vivo. The facile fabrication process, great biocompatibility, enhanced gene transfection efficiency, and great bioimaging ability can make it promising for application in gene therapy.

Calcium phosphate nanoparticles: a study of their synthesis, characterization and mode of interaction with salmon testis DNA

Calcium phosphate nanoparticles (CPNPs) are presently emerging as a second generation vector for efficient delivery and stabilization of nucleic acids inside cells, although the detailed mode of interaction between CPNPs and DNA is still obscure. This study discloses some features of the interaction. For this study, we synthesized CPNPs by a modified co-precipitation method and characterized the particles by different techniques such as dynamic light scattering, X-ray diffraction, electron dispersive spectroscopy, Fourier transform infra-red spectroscopy, differential thermal and thermo-gravimetric analysis, and atomic force, scanning and transmission electron microscopy. The characterization studies showed that the nanoparticles were spherical in shape, about 45 nm in size and were composed of the hydroxyapatite form of calcium phosphate; almost 90% of the starting materials were converted to nanoparticles (NPs). The different aspects of the interaction between CPNPs and salmon testis DNA were investigated using techniques such as UV-Vis spectrophotometry, circular dichroism, Fourier transform infra-red spectrometry, thermal denaturation, microviscometry, agarose gel electrophoresis, cyclic voltammetry and atomic force microscopy. The results revealed that CPNPs interacted with DNA with ~1 : 3.3 stoichiometry with a binding constant of the order of 10(4) M(-1) through groove-interacting mode and a single nanoparticle covered about 6.2 base pairs of the DNA chain. Moreover, the binding interaction was spontaneous, cooperative, exothermic and enthalpy-driven and some electrostatic nature of the binding was also evident; however, the non-polyelectrolyte contribution was dominant. The binding interaction finally caused an increase in the melting temperature of DNA from 70.8 °C to 75 °C and alteration of its secondary structure from the naturally occurring B-form to C-form.

Soft Hybrid Nanoparticles: from Preparation to Biomedical Applications

Hybrid particles are a class of materials that include both organic and inorganic moieties at the same time and possess interesting magnetic, optical and mechanical properties. Extensive research is being carried out to develop soft hybrid nanoparticles utilizing their superparamagnetic, biodegradable and fluorescence properties and to explore their biomedical applications. This chapter discusses the important methods for the development of different types of soft hybrid nanoparticles, including polymer immobilization on preformed particles, adsorption of polymers on colloidal particles, adsorption of polymers via layer-by-layer self-assembly, adsorption of nanoparticles on colloidal particles, chemical grafting of preformed polymers, polymerization from and on to colloidal particles, click chemistry, atom-transfer radical polymerization (ATRP), reversible addition–fragmentation chain-transfer radical (RAFT) polymerization, nitroxide-mediated polymerization (NMP) and conventional seed radical polymerization. With current rapid advances in nanomedicine, colloidally engineered hybrid particles are gaining immense importance in fields such as cancer therapy, gene therapy, disease diagnosis and bioimaging. The applications of soft hybrid nanoparticles with respect to diagnosis are discussed briefly and a comprehensive account of their applications in the capture and extraction of nucleic acids, proteins and viruses is presented in this chapter.

Enhancing endosomal escape for nanoparticle mediated siRNA delivery

Gene therapy with siRNA is a promising biotechnology to treat cancer and other diseases. To realize siRNA-based gene therapy, a safe and efficient delivery method is essential. Nanoparticle mediated siRNA delivery is of great importance to overcome biological barriers for systemic delivery in vivo. Based on recent discoveries, endosomal escape is a critical biological barrier to be overcome for siRNA delivery. This feature article focuses on endosomal escape strategies used for nanoparticle mediated siRNA delivery, including cationic polymers, pH sensitive polymers, calcium phosphate, and cell penetrating peptides. Work has been done to develop different endosomal escape strategies based on nanoparticle types, administration routes, and target organ/cell types. Also, enhancement of endosomal escape has been considered along with other aspects of siRNA delivery to ensure target specific accumulation, high cell uptake, and low toxicity. By enhancing endosomal escape and overcoming other biological barriers, great progress has been achieved in nanoparticle mediated siRNA delivery.

Colloidal micro- and nano-particles as templates for polyelectrolyte multilayer capsules

Colloidal particles play an important role in various areas of material and pharmaceutical sciences, biotechnology, and biomedicine. In this overview we describe micro- and nano-particles used for the preparation of polyelectrolyte multilayer capsules and as drug delivery vehicles. An essential feature of polyelectrolyte multilayer capsule preparations is the ability to adsorb polymeric layers onto colloidal particles or templates followed by dissolution of these templates. The choice of the template is determined by various physico-chemical conditions: solvent needed for dissolution, porosity, aggregation tendency, as well as release of materials from capsules. Historically, the first templates were based on melamine formaldehyde, later evolving towards more elaborate materials such as silica and calcium carbonate. Their advantages and disadvantages are discussed here in comparison to non-particulate templates such as red blood cells. Further steps in this area include development of anisotropic particles, which themselves can serve as delivery carriers. We provide insights into application of particles as drug delivery carriers in comparison to microcapsules templated on them.

Targeting and activation of antigen-specific B-cells by calcium phosphate nanoparticles loaded with protein antigen

Cross-linking of the B-cell receptors of an antigen-specific B-cell is the initial signal for B-cell activation, proliferation, and differentiation into antibody secreting plasma cells. Since multivalent particulate structures are efficient activators of antigen-specific B-cells, we developed biodegradable calcium phosphate nanoparticles displaying protein antigens on their surface and explored the efficacy of the B-cell activation after exposure to these nanoparticles. The calcium phosphate nanoparticles were functionalized with the model antigen Hen Egg Lysozyme (HEL) to take advantage of a HEL-specific B-cell receptor transgenic mouse model. The nanoparticles were characterized by scanning electron microscopy and dynamic light scattering. The functionalized calcium phosphate nanoparticles were preferentially bound and internalized by HEL-specific B-cells. Co-cultivation of HEL-specific B-cells with the functionalized nanoparticles also increased surface expression of B-cell activation markers. Functionalized nanoparticles were able to effectively cross-link B-cell receptors at the surface of antigen-matched B-cells and were 100-fold more efficient in the activation of B-cells than soluble HEL. Thus, calcium phosphate nanoparticles coated with protein antigens are promising vaccine candidates for induction humoral immunity.

Modeling biominerals formed by apatites and DNA

Different aspects of biominerals formed by apatite and DNA have been investigated using computer modeling tools. Firstly, the structure and stability of biominerals in which DNA molecules are embedded into hydroxyapatite and fluoroapatite nanopores have been examined by combining different molecular mechanics methods. After this, the early processes in the nucleation of hydroxyapatite at a DNA template have been investigated using molecular dynamics simulations. Results indicate that duplexes of DNA adopting a B double helix can be encapsulated inside nanopores of hydroxyapatite without undergoing significant distortions in the inter-strand hydrogen bonds and the intra-strand stacking. This ability of hydroxyapatite is practically independent of the DNA sequence, which has been attributed to the stabilizing role of the interactions between the calcium atoms of the mineral and the phosphate groups of the biomolecule. In contrast, the fluorine atoms of fluoroapatite induce pronounced structural distortions in the double helix when embedded in a pore of the same dimensions, resulting in the loss of its most relevant characteristics. On the other hand, molecular dynamics simulations have allowed us to observe the formation of calcium phosphate clusters at the surface of the B-DNA template. Electrostatic interactions between the phosphate groups of DNA and Ca(2+) have been found to essential for the formation of stable ion complexes, which were the starting point of calcium phosphate clusters by incorporating PO3(4) from the solution.

Nanoparticles for gene delivery

Nanocarriers are a new type of nonviral gene carriers, many of which have demonstrated a broad range of pharmacological and biological properties, such as being biodegradable in the body, stimulus-responsive towards the surrounding environment, and an ability to specifically targeting certain disease sites. By summarizing some main types of nanocarriers, this Concept considers the current status and possible future directions of the potential clinical applications of multifunctional nanocarriers, with primary attention on the combination of such properties as biodegradability, targetability, transfection ability, and stimuli sensitivity.

F127/Calcium phosphate hybrid nanoparticles: a promising vector for improving siRNA delivery and gene silencing

Calcium phosphate-based transfection method had been used to transfer DNA into living cells. However, it had so far not been studied in detail to what extend siRNA delivery system. In this study, Pluronic F127/calcium phosphate hybrid nanoparticles (F127/CaP) were prepared by a facile room temperature method and employed as carriers to deliver siRNA to silence tumor cell. The morphology of the F127/CaP hybrid nanoparticles was investigated with TEM. In order to determine the ratio of F127 to CaP in the hybrid nanoparticles, TGA (the thermogravimetric analysis) was applied. MTT assays confirmed that the F127/CaP hybrid nanoparticles were quite safe. The hybrid F127/CaP nanoparticles obtained were 120-210 nm in diameter, and they were applied as siRNA carriers for siRNA loading and in vitro transfection. The siRNA encapsulating efficiency was 91.5 wt.% with a loading content of 6.5 wt.%. Compared to traditional CaP transfection method, the siRNA-loaded F127/CaP exhibited higher gene inhibition efficiency, and this was supported by fluorescence microscopy. Quantitative analysis of GFP silencing efficiency of various siRNA formulations was measured by using FACS flow cytometry analysis. Additionally, both custom CaP and F127/CaP are biocompatible and biodegradable, thus the as-prepared F127/CaP hybrid nanoparticles are promising for siRNA delivery.

Intracellular cleavable poly(2-dimethylaminoethyl methacrylate) functionalized mesoporous silica nanoparticles for efficient siRNA delivery in vitro and in vivo

A low cytotoxicity and high efficiency delivery system with the advantages of low cost and facile fabrication is needed for the application of small interfering RNA (siRNA) delivery both in vitro and in vivo. For these prerequisites, cationic polymer-mesoporous silica nanoparticles (ssCP-MSNs) were prepared by surface functionalized mesoporous silica nanoparticles with disulfide bond cross-linked poly(2-dimethylaminoethyl methacrylate) (PDMAEMA). In vitro and in vivo evaluations were performed. The synthesized ssCP-MSNs are 100-150 nm in diameter with a pore size of 10 nm and a positively charged surface with a high zeta potential of 27 mV. Consequently, the ssCP-MSNs showed an excellent binding capacity for siRNA, and an enhancement in the cell uptake and cytosolic availability of siRNA. Furthermore, the intracellular reducing cleavage of the disulfide bonds cross-linking the PDMAEMA segments led to intracellular cleavage of PDMAEMA from ssCP-MSNs, which facilitated the intracellular triggered release of siRNA. Therefore, promoted RNA interference was observed in HeLa-Luc cells, which was equal to that of Lipofectamine 2000. Significantly, compared to Lipofectamine 2000, the ssCP-MSNs were more biocompatible, with low cytotoxicity (even non-cytotoxicity) and promotion of cell proliferation to HeLa-Luc cells. The in vivo systemic distribution studies certified that ssCP-MSNs/siRNA could prolong the duration of siRNA in vivo, and that they accumulated in the adrenal gland, liver, lung, spleen, kidney, heart and thymus after intravenous injection. Encouragingly, with the ability to deliver siRNA to a tumor, ssCP-MSNs/siRNA showed a tumor suppression effect in the HeLa-Luc xenograft murine model after intravenous injection. Therefore, the ssCP-MSNs cationic polymer-mesoporous silica nanoparticles with low cytotoxicity are promising for siRNA delivery.

New developments in polymer-controlled, bioinspired calcium phosphate mineralization from aqueous solution

The polymer-controlled and bioinspired precipitation of inorganic minerals from aqueous solution at near-ambient or physiological conditions avoiding high temperatures or organic solvents is a key research area in materials science. Polymer-controlled mineralization has been studied as a model for biomineralization and for the synthesis of (bioinspired and biocompatible) hybrid materials for a virtually unlimited number of applications. Calcium phosphate mineralization is of particular interest for bone and dental repair. Numerous studies have therefore addressed the mineralization of calcium phosphate using a wide variety of low- and high-molecular-weight additives. In spite of the growing interest and increasing number of experimental and theoretical data, the mechanisms of polymer-controlled calcium phosphate mineralization are not entirely clear to date, although the field has made significant progress in the last years. A set of elegant experiments and calculations has shed light on some details of mineral formation, but it is currently not possible to preprogram a mineralization reaction to yield a desired product for a specific application. The current article therefore summarizes and discusses the influence of (macro)molecular entities such as polymers, peptides, proteins and gels on biomimetic calcium phosphate mineralization from aqueous solution. It focuses on strategies to tune the kinetics, morphologies, final dimensions and crystal phases of calcium phosphate, as well as on mechanistic considerations.

siRNA transfection with calcium phosphate nanoparticles stabilized with PEGylated chelators

Despite the enormous therapeutic potential of siRNAs, their delivery is still problematic due to unfavorable biodistribution profiles and poor intracellular bioavailability. Calcium phosphate co-precipitate has been used for nearly 40 years for in vitro transfection due to its non-toxic nature and simplicity of preparation. However, rapid particle growth has largely prevented the translation of this method for in vivo purposes. It has recently been shown that bisphosphonate derivatives can physically stabilize calcium phosphate nanoparticles while still allowing for efficient cell transfection with plasmid DNA. Herein, two novel PEGylated chelating agents (PEG-alendronate and PEG-inositolpentakisphosphate) with enhanced stabilizing properties are introduced, and it is demonstrated that the bisphosphonate-stabilized nanoparticles can efficiently deliver siRNA in vitro. The nanoparticles are mainly taken up by clathrin-dependent endocytosis, and acidification of the endosomal compartment is required to release the entrapped siRNA into the cytosol. Furthermore, particle uptake enhances the inhibition of the mevalonate pathway by the bisphosphonate in macrophages.

Recent advances in nonviral vectors for gene delivery

Gene therapy has long been regarded a promising treatment for many diseases, whether acquired (such as AIDS or cancer) or inherited through a genetic disorder. A drug based on a nucleic acid, however, must be delivered to the interior of the target cell while surviving an array of biological defenses honed by evolution. Successful gene therapy is thus dependent on the development of an efficient delivery vector. Researchers have pursued two major vehicles for gene delivery: viral and nonviral (synthetic) vectors. Although viral vectors currently offer greater efficiency, nonviral vectors, which are typically based on cationic lipids or polymers, are preferred because of safety concerns with viral vectors. So far, nonviral vectors can readily transfect cells in culture, but efficient nanomedicines remain far removed from the clinic. Overcoming the obstacles associated with nonviral vectors to improve the delivery efficiency and therapeutic effect of nucleic acids is thus an active area of current research. The difficulties are manifold, including the strong interaction of cationic delivery vehicles with blood components, uptake by the reticuloendothelial system (RES), toxicity, and managing the targeting ability of the carriers with respect to the cells of interest. Modifying the surface with poly(ethylene glycol), that is, PEGylation, is the predominant method used to reduce the binding of plasma proteins to nonviral vectors and minimize clearance by the RES after intravenous administration. Nanoparticles that are not rapidly cleared from the circulation accumulate in the tumors because of the enhanced permeability and retention effect, and the targeting ligands attached to the distal end of the PEGylated components allow binding to the receptors on the target cell surface. Neutral and anionic liposomes have been also developed for systemic delivery of nucleic acids in experimental animal models. Other approaches include (i) designing and synthesizing novel cationic lipids and polymers, (ii) chemically coupling the nucleic acid to peptides, targeting ligands, polymers, or environmentally sensitive moieties, and (iii) utilizing inorganic nanoparticles in nucleic acid delivery. Recently, the different classes of nonviral vectors appear to be converging, and the ability to combine features of different classes of nonviral vectors in a single strategy has emerged. With the strengths of several approaches working in concert, more hurdles associated with efficient nucleic acid delivery might therefore be overcome. In this Account, we focus on these novel nonviral vectors, which are classified as multifunctional hybrid nucleic acid vectors, novel membrane/core nanoparticles for nucleic acid delivery, and ultrasound-responsive nucleic acid vectors. We highlight systemic delivery studies and consider the future prospects for nucleic acid delivery. A better understanding of the fate of the nanoparticles inside the cell and of the interactions between the parts of hybrid particles should lead to a delivery system suitable for clinical use. We also underscore the value of sustained release of a nucleic acid in this endeavor; making vectors targeted to cells with sustained release in vivo should provide an interesting research challenge.