Charge density and particle size effects on oligonucleotide and plasmid DNA binding to nanosized hydrotalcite

Spectrophotometric and nucleic acid-binding properties of halloysite clay nanotubes and kaolinite

Halloysite particles (HNTs) are naturally occurring aluminosilicate nanotubes of low toxicity that have shown great promise for drug and biomolecule delivery into human and animal cells. Kaolinite particles retain the same layered structure as HNT, but do not form nanotubes. In this study, the spectrophotometric and sedimentation properties of the two clays in aqueous solutions and their abilities to associate with both small and large nucleic acids have been investigated. Both clays scattered ultraviolet light strongly and this characteristic of HNT was not affected by either vacuum treatment to remove trapped gases or by sonication. Vacuum treatment increased the binding of small nucleic acids to HNT and this association was further enhanced by addition of divalent metal ions. By contrast, only small RNAs were bound efficiently by kaolinite in the presence of Mg²⁺ ions. Large linear double-stranded DNAs and circular plasmid DNAs bound poorly to kaolinite under all conditions, but these nucleic acids could form strong associations with HNT. Differences in binding data were largely consistent with measurements of the available surface areas of each clay. These results demonstrate that interactions with each clay are critically dependent on both the type and the conformation of each nucleic acid.

Topology dependent modification of layered double hydroxide for therapeutic and diagnostic platform

Layered double hydroxide is a family of two-dimensional materials with wide range of compositions. Recently, its ability to accommodate various chemical species and biocompatibility have been attracted in the biomedical applications to develop drug delivery system and nanodiagnostics. In this review, we categorized biomedical approaches of layered double hydroxide with respect to the three topologies of, namely, interlayer space, outer surface with particle edge, and the lattice points. There have been extensive researches on the intercalation of drug or tracing to make use of interlayer space of layered double hydroxide for drug stabilization, sustained release, cellular delivery and etc. Outer surface or edge has been utilized to immobilization of large therapeutic moieties and to attach tracing moiety. Lattice points consisting of various metal species could be utilized for the specific metal species like paramagnetic elements or radioisotopes. Based on these topologies in layered double hydroxide, both the synthetic routes and the achieved functionalities in terms of biomedical application will be discussed.

Layered Double Hydroxide as a Potent Non-viral Vector for Nucleic Acid Delivery Using Gene-Activated Scaffolds for Tissue Regeneration Applications

Nonviral vectors offer a safe alternative to viral vectors for gene therapy applications, albeit typically exhibiting lower transfection efficiencies. As a result, there remains a significant need for the development of a nonviral delivery system with low cytotoxicity and high transfection efficacy as a tool for safe and transient gene delivery. This study assesses MgAl-NO₃ layered double hydroxide (LDH) as a nonviral vector to deliver nucleic acids (pDNA, miRNA and siRNA) to mesenchymal stromal cells (MSCs) in 2D culture and using a 3D tissue engineering scaffold approach. Nanoparticles were formulated by complexing LDH with pDNA, microRNA (miRNA) mimics and inhibitors, and siRNA at varying mass ratios of LDH:nucleic acid. In 2D monolayer, pDNA delivery demonstrated significant cytotoxicity issues, and low cellular transfection was deemed to be a result of the poor physicochemical properties of the LDH–pDNA nanoparticles. However, the lower mass ratios required to successfully complex with miRNA and siRNA cargo allowed for efficient delivery to MSCs. Furthermore, incorporation of LDH–miRNA nanoparticles into collagen-nanohydroxyapatite scaffolds resulted in successful overexpression of miRNA in MSCs, demonstrating the development of an efficacious miRNA delivery platform for gene therapy applications in regenerative medicine.

Dentifrice Based on Fluoride-Hydrotalcite Compounds: Characterization and Release Capacity Evaluation by Novel In Vitro Methods

Anti-caries activity of fluoride ions is due to the protection against demineralization and the enhancement of remineralization of tooth enamel. Dentifrices available on the market contain sodium fluoride, sodium monofluorophosphate, stannous fluoride, and amine fluoride as source of these ions. A new compound working both as fluoride ion source and as abrasive was projected. Hybrids based on F^- ions intercalated between the lamellae of hydrotalcite-like compounds (HTlc-F), namely MgAl-HTlc-F and ZnAl-HTlc-F, were prepared and characterized. Then, three different percentages (2, 3, and 4%) of both HTlc-F compounds were assayed. After the rheological characterization, the dentifrices containing 3 and 4% of MgAl-HTlc-F and ZnAl-HTlc-F, respectively, resulted to be the most suitable ones. Two novel in vitro methods, "rotary toothbrush method" and "manual brushing method," were developed and used in order to study the F^- ions release from the prepared dentifrices. The obtained results showed that the dentifrice containing ZnAl-HTlc-F (4%) was the most effective in releasing fluoride ions. The "rotary toothbrush method" resulted to be the most suitable as the simulation of the brushing movements is standardizable and reproducible.

Factors affecting the association of single- and double-stranded RNAs with montmorillonite nanoclays

Montmorillonite (MMT) nanoclays exist as single and stacked sheet-like structures with large surface areas that can form stable associations with many naturally occurring biomolecules, including nucleic acids. They have been utilized successfully as vehicles for delivery of both drugs and genes into cells. Most previous studies have focused on interactions of MMT with DNA. In the current study, we have investigated the binding of small RNAs similar to those used for RNA interference (RNAi) therapy to two major forms of the clay, Na-MMT and Ca-MMT. Association of both forms of MMT with several double-stranded RNAs (dsRNAs), including 25mers, 54mers and cloverleaf-shaped transfer RNAs, was weak and increased only slightly after addition of Mg2+ ions to the binding reactions. By contrast, ssRNA 25mers and 54mers bound poorly to Na-MMT but interacted strongly with Ca-MMT. The weak binding of ssRNAs to Na-MMT could be strongly enhanced by addition of Mg2+ ions. The strength of MMT-ssRNA interactions was also examined using inorganic anion competition and displacement assays, as well as electrophoretic mobility shift assays (EMSAs). The aggregate results point to a cation-bridging mechanism for binding of ssRNAs, but not dsRNAs, in the presence of divalent metal cations.

Inhibition of mTOR signaling Confers Protection against Cerebral Ischemic Injury in Acute Hyperglycemic Rats

Hyperglycemia is known to exacerbate neuronal death resulted from cerebral ischemia. The mechanisms are not fully understood. The mammalian target of rapamycin (mTOR) pathway regulates cell growth, division and apoptosis. Recent studies suggest that activation of mTOR may mediate ischemic brain damage. The objective of the present experiment is to explore whether mTOR mediates ischemic brain damage in acute hyperglycemic animals. Rats were subjected to 10 min of forebrain ischemia under euglycemic, hyperglycemic and rapamycin-treated hyperglycemic conditions. The rat brain samples were collected from the cortex and hippocampi after 3h and 16h of reperfusion. The results showed that hyperglycemia significantly increased neuronal death in the cortex and hippocampus and the exacerbation effect of hyperglycemia was associated with further activation of mTOR under control and/or ischemic conditions. Inhibition of mTOR with rapamycin ameliorated the damage and suppressed hyperglycemia-elevated p-MTOR, p-P70S6K and p-S6. In addition, hyperglycemia per se increased the levels of cytosolic cytochrome c and autophagy marker LC3-II, while rapamycin alleviated these alterations. It is concluded that activation of mTOR signaling may play a detrimental role in mediating the aggravating effect of hyperglycemia on cerebral ischemia.

Impact of size, secondary structure, and counterions on the binding of small ribonucleic acids to layered double hydroxide nanoparticles

Use of ribonucleic acid (RNA) interference to regulate protein expression has become an important research topic and gene therapy tool, and therefore, finding suitable vehicles for delivery of small RNAs into cells is of crucial importance. Layered double metal hydroxides such as hydrotalcite (HT) have shown great promise as nonviral vectors for transport of deoxyribose nucleic acid (DNA), proteins, and drugs into cells, but the adsorption of RNAs to these materials has been little explored. In this study, the binding of small RNAs with different lengths and levels of secondary structure to HT nanoparticles has been analyzed and compared to results obtained with small DNAs in concurrent experiments. Initial experiments established the spectrophotometric properties of HT in aqueous solutions and determined that HT particles could be readily sedimented with near 100% efficiencies. Use of RNA+HT cosedimentation experiments as well as electrophoretic mobility shift assays demonstrated strong adsorption of RNA 25mers to HT, with twofold greater binding of single-stranded RNAs relative to double-stranded molecules. Strong affinities were also observed with ssRNA and dsRNA 54mers and with more complex transfer RNA molecules. Competition binding and RNA displacement experiments indicated that RNA-HT associations were strong and were only modestly affected by the presence of high concentrations of inorganic anions.

Effect of Isomorphous Substitution on the Thermal Decomposition Mechanism of Hydrotalcites

Hydrotalcites have many important applications in catalysis, wastewater treatment, gene delivery and polymer stabilization, all depending on preparation history and treatment scenarios. In catalysis and polymer stabilization, thermal decomposition is of great importance. Hydrotalcites form easily with atmospheric carbon dioxide and often interfere with the study of other anion containing systems, particularly if formed at room temperature. The dehydroxylation and decomposition of carbonate occurs simultaneously, making it difficult to distinguish the dehydroxylation mechanisms directly. To date, the majority of work on understanding the decomposition mechanism has utilized hydrotalcite precipitated at room temperature. In this study, evolved gas analysis combined with thermal analysis has been used to show that CO₂ contamination is problematic in materials being formed at RT that are poorly crystalline. This has led to some dispute as to the nature of the dehydroxylation mechanism. In this paper, data for the thermal decomposition of the chloride form of hydrotalcite are reported. In addition, carbonate-free hydrotalcites have been synthesized with different charge densities and at different growth temperatures. This combination of parameters has allowed a better understanding of the mechanism of dehydroxylation and the role that isomorphous substitution plays in these mechanisms to be delineated. In addition, the effect of anion type on thermal stability is also reported. A stepwise dehydroxylation model is proposed that is mediated by the level of aluminum substitution.