Adsorption of biometals to monosodium titanate in biological environments

Estimation of Calcium Titanate or Erbium Oxide Nanoparticles Induced Cytotoxicity and Genotoxicity in Normal HSF Cells

Extensive uses of calcium titanate nanoparticles (CaTiO₃-NPs) and erbium oxide nanoparticles (Er₂O₃-NPs) increase their release into the environment and human exposure, particularly through skin contact. However, there are almost no studies available on the effect of these nanoparticles on skin integrity. Therefore, this study was undertaken to estimate CaTiO₃-NP- or Er₂O₃-NP-induced cytotoxicity and genotoxicity in normal human skin fibroblast (HSF) cells. Cell viability was measured using sulforhodamine B (SRB) assay, while the level of DNA damage was detected using the alkaline comet assay. The intracellular levels of reactive oxygen species (ROS) as well as the expression level of p53, Bax, and Bcl2 genes were detected. Although the viability of HSF cells was non-markedly changed after 24 h, prolonged treatment with CaTiO3-NPs or Er2O3-NPs for 72 h induced concentration-dependent death of HSF cells. Treatment of normal HSF cells with IC50/72 h of CaTiO3-NPs or Er2O3-NPs did not cause marked changes in the intracellular level of ROS, DNA damage parameters, and expression levels of apoptosis genes compared to their values in the untreated HSF cells. We thus concluded that CaTiO3-NPs or Er2O3-NPs cause time- and concentration-dependent cytotoxicity toward normal HSF cells. However, safe and non-genotoxic effects were demonstrated by the apparent non-significant changes in intracellular ROS level, DNA integrity, and apoptotic genes' expression after exposure of normal HSF cells to nanoparticles. Thus, it is recommended that further studies be conducted to further understand the toxic and biological effects of CaTiO₃-NPs and Er2O3-NPs.

Gold Complexes in Anticancer Therapy: From New Design Principles to Particle-Based Delivery Systems

The discovery of the medicinal properties of gold complexes has fuelled the design and synthesis of new anticancer metallodrugs, which have received special attention due to their unique modes of action. Current research in the development of gold compounds with therapeutic properties is predominantly focused on the molecular design of drug leads with superior pharmacological activities, e.g., by introducing targeting features. Moreover, intensive research aims at improving the physicochemical properties of gold compounds, such as chemical stability and solubility in the physiological environment. In this regard, the encapsulation of gold compounds in nanocarriers or their chemical grafting onto targeted delivery vectors could lead to new nanomedicines that eventually reach clinical applications. Herein, we provide an overview of the state-of-the-art progress of gold anticancer compounds, andmore importantly we thoroughly revise the development of nanoparticle-based delivery systems for gold chemotherapeutics.

Induction of oxidative DNA damage, cell cycle arrest and p53 mediated apoptosis by calcium titanate nanoparticles in MCF-7 breast cancer cells

Background

The distinctive properties and high activity of calcium titanate nanoparticles (CaTiO₃-NPs) increase their use in many products. However, the cytotoxic and genotoxic effects of CaTiO₃-NPs in human cancer cell lines have not been well studied. Therefore, this study was conducted to explore CaTiO₃-NPs induced cytotoxicity, genomic instability and apoptosis in human breast cancer (MCF-7) cells.

Methods

Sulforhodamine B (SRB) and the alkaline comet assays were done to study cell viability and DNA damage induction, respectively. Apoptosis induction and cell cycle distribution were analyzed using flow cytometry. The level of intracellular reactive oxygen species (ROS) was studied, and the expression levels of p53, Bax and Bcl2 genes were also measured.

Results

The results of the Sulforhodamine B (SRB) cytotoxicity assay showed that viability of MCF-7 cells was not affected by CaTiO₃-NPs treatment for 24 h, however, exposure to CaTiO₃-NPs for 72 h caused concentrations dependent death of MCF-7 cells. Treatment with CaTiO₃-NPs for 72 h caused marked increases in intracellular ROS level and induced DNA damage. Treatment of MCF-7 cells with CaTiO₃-NPs also caused MCF-7 cell cycle arrest at the G0 and S phases and s triggered apoptosis of MCF-7 cells by causing simultaneous increases in the expression levels of apoptotic p53 and Bax genes and a decrease in the expression level of anti-apoptotic Bcl2 gene.

Conclusion

Collectively, it was concluded that CaTiO₃-NPs cause time- and concentration-dependent cytotoxic effects in human MCF-7 cells through induction of ROS generation, genomic instability and apoptosis. Thus it is recommended that further in vitro and in vivo studies are therefore recommended to understand the cytotoxic and biological effects of CaTiO₃-NPs.

Cytotoxicity of Titanate-Calcium Complexes to MC3T3 Osteoblast-Like Cells

Monosodium titanates (MST) are a relatively novel form of particulate titanium dioxide that have been proposed for biological use as metal sorbents or delivery agents, most recently calcium (II). In these roles, the toxicity of the titanate or its metal complex is crucial to its biological utility. The aim of this study was to determine the cytotoxicity of MST and MST-calcium complexes with MC3T3 osteoblast-like cells; MST-Ca(II) complexes could be useful to promote bone formation in various hard tissue applications. MC3T3 cells were exposed to native MST or MST-Ca(II) complexes for 24–72 h. A CellTiter-Blue® assay was employed to assess the metabolic activity of the cells. The results showed that MST and MST-Ca(II) suppressed MC3T3 metabolic activity significantly in a dose-, time-, and cell-density-dependent fashion. MST-Ca(II) suppressed MC3T3 metabolism in a statistically identical manner as native MST at all concentrations. We concluded that MST and MST-Ca(II) are significantly cytotoxic to MC3T3 cells through a mechanism yet unknown; this is a potential problem to the biological utility of these complexes.

Biomedical applications of nano-titania in theranostics and photodynamic therapy

Titanium dioxide (TiO₂) is one of the most abundantly used nanomaterials for human life. It is used in sunscreen, photovoltaic devices, biomedical applications and as a food additive and environmental scavenger.

Titanates and Titanate-Metal Compounds in Biological Contexts

Metal ions are notorious environmental contaminants, some causing toxicity at exquisitely low (ppm-level) concentrations. Yet, the redox properties of metal ions make them attractive candidates for bio-therapeutics. Titanates are insoluble particulate compounds of titanium and oxygen with crystalline surfaces that bind metal ions; these compounds offer a means to scavenge metal ions in environmental contexts or deliver them in therapeutic contexts while limiting systemic exposure and toxicity. In either application, the toxicological properties of titanates are crucial. To date, the accurate measurement of the in vitro toxicity of titanates has been complicated by their particulate nature, which interferes with many assays that are optical density (OD)-dependent, and at present, little to no in vivo titanate toxicity data exist. Compatibility data garnered thus far for native titanates in vitro are inconsistent and lacking in mechanistic understanding. These data suggest that native titanates have little toxicity toward several oral and skin bacteria species, but do suppress mammalian cell metabolism in a cells-pecific manner. Titanate compounds bind several types of metal ions, including some common environmental toxins, and enhance delivery to bacteria or cells. Substantial work remains to address the practical applicability of titanates. Nevertheless, titanates have promise to serve as novel vehicles for metal-based therapeutics or as a new class of metal scavengers for environmental applications.

In vitro biological response of micro- and nano-sized monosodium titanates and titanate-metal compounds

Previous studies report that microsized monosodium titanates (MSTs) deliver metal ions and species to mammalian cells and bacteria with cell-specific and metal-specific effects. In this study, we explored the use of MST and a new synthesized nanosized monosodium titanate (nMST) to deliver gold(III), cisplatin, or platinum(IV) to two human cell lines with different population doubling times, in vitro. The effect was measured using a fluorescent mitochondrial activity assay (CellTiter-Blue(®) Assay). This fluorescence assay was implemented to mitigate optical density measurement errors owing to particulate titanate interference and allowed for the studies to be extended to higher titanate concentrations than previously possible. Overall, native MST significantly (p < 0.05) decreased mitochondrial activity of both cell types by 50% at concentrations of >50 mg/L. Native nMST significantly suppressed the rapidly dividing cell line (by 50%) over untreated cultures, but had no effect on the more slowly dividing cells. For both cell types, increased titanate concentrations resulted in increased effects from delivered metals. However, there was no difference in the effect of metal delivered from micro- versus nano-sized MST.

Peroxotitanate- and monosodium metal-titanate compounds as inhibitors of bacterial growth

Sodium titanates are ion-exchange materials that effectively bind a variety of metal ions over a wide pH range. Sodium titanates alone have no known adverse biological effects but metal-exchanged titanates (or metal titanates) can deliver metal ions to mammalian cells to alter cell processes in vitro. In this work, we test a hypothesis that metal-titanate compounds inhibit bacterial growth; demonstration of this principle is one prerequisite to developing metal-based, titanate-delivered antibacterial agents. Focusing initially on oral diseases, we exposed five species of oral bacteria to titanates for 24 h, with or without loading of Au(III), Pd(II), Pt(II), and Pt(IV), and measuring bacterial growth in planktonic assays through increases in optical density. In each experiment, bacterial growth was compared with control cultures of titanates or bacteria alone. We observed no suppression of bacterial growth by the sodium titanates alone, but significant (p < 0.05, two-sided t-tests) suppression was observed with metal-titanate compounds, particularly Au(III)-titanates, but with other metal titanates as well. Growth inhibition ranged from 15 to 100% depending on the metal ion and bacterial species involved. Furthermore, in specific cases, the titanates inhibited bacterial growth 5- to 375-fold versus metal ions alone, suggesting that titanates enhanced metal-bacteria interactions. This work supports further development of metal titanates as a novel class of antibacterials.

Titanate particles as agents to deliver gold compounds to fibroblasts and monocytes

Titanates are inorganic compounds with high affinity for specific metal ions or metal compounds, including gold. We have previously demonstrated that both monosodium titanate (MST) and amorphous peroxo-titanate (APT) alone do not suppress cellular metabolism of several cell types, and we have shown that MST and APT adsorb and release gold compounds in biological salt solutions. In the current study, we extend this work and show that MST and APT loaded with two gold compounds deliver sufficient levels of these compounds to alter the metabolism of mammalian cells. Fibroblasts (L929) or monocytes (THP1) were exposed to MST and APT loaded with either Au(III) or Auranofin(R), a Au(I)-organic compound, for 24-72 h, after which succinate dehydrogenase (SDH) activity of the cells was measured using the MTT method. MST or APT alone did not suppress SDH activity of either cell type. AF and Au(III) alone suppressed SDH activity completely above 2 muM or 300 muM, respectively. APT and MST loaded with either gold compound suppressed L929 fibroblast SDH activity by 30-80% after 72 h, but Au(III)-loaded APT was more potent than AF-loaded APT. Monocyte SDH activity was not affected by any loaded titanate. Our results suggest that titanates could be used for solid phase delivery of metal compounds to affect mammalian cell function of some types of cells.

Titanates deliver metal ions to human monocytes

Amorphous peroxotitantes (APT) are insoluble titanium-based particles that bind a variety of metal compounds with high affinity; these particles could be sequestered locally in a solid phase to deliver metal-based drugs. Previous studies have confirmed the 'biodelivery' of metals from metal-APT complexes to fibroblasts, but not monocytes. Our goal in the current study was to use monocytic cytokine secretion to assess delivery of gold or platinum-based compounds from APT to human THP1 monocytes. Cytokine secretion was not triggered by APT alone or metal-APT complexes. In monocytes activated by lipopolysaccharide (LPS), APT alone enhanced or suppressed IL1beta or IL6 secretion, yet TNFalpha secretion was unaffected. Complexes of APT and Au(III) or cis-platin altered LPS-activated IL6 or IL1beta secretion most, TNFalpha least. Our results suggest that the APT deliver metals to monocytes.

Peroxotitanates for biodelivery of metals

Metal-based drugs are largely undeveloped in pharmacology. One limiting factor is the systemic toxicity of metal-based compounds. A solid-phase, sequestratable delivery agent for local delivery of metals could reduce systemic toxicity, facilitating new drug development in this nascent area. Amorphous peroxotitanates (APT) are ion-exchange materials with high affinity for several heavy metal ions and have been proposed to deliver or sequester metal ions in biological contexts. In the current study, we tested a hypothesis that APTs are able to deliver metals or metal compounds to cells. We exposed fibroblasts (L929) or monocytes (THP1) to metal-APT materials for 72 h in vitro and then measured cellular mitochondrial activity (SDH-MTT method) to assess the biological impact of the metal-APT materials versus metals or APT alone. APT alone did not significantly affect cellular mitochondrial activity, but all metal-APT materials suppressed the mitochondrial activity of fibroblasts (by 30-65% of controls). The concentration of metal-APT materials required to suppress cellular mitochondrial activity was below that required for metals alone, suggesting that simple extracellular release of the metals from the metal-APT materials was not the primary mechanism of mitochondrial suppression. In contrast to fibroblasts, no metal-APT material had a measurable effect on THP1 monocyte mitochondrial activity, despite potent suppression by metals alone. This latter result suggested that "biodelivery" by metal-APT materials may be cell type-specific. Therefore, it appears that APTs are plausible solid-phase delivery agents of metals or metal compounds to some types of cells for potential therapeutic effect.

In vitro biological effects of sodium titanate materials

Monosodium titanate (MST) particles effectively bind specific metals and are therefore promising compounds for delivery or sequestration of metals in biological contexts. Yet, the biological properties of MST are largely unexplored. Our previous study showed that the cytotoxicity of these compounds was mild, but the nature of the dose response curves suggested that residual titanates in culture may have interfered with the assay. In the current study, we assessed the importance of these artifacts, and extended our previous results using fibroblasts for biological evaluation. We also assessed the biological response to a new type of titanate (referred to as amorphous peroxo-titanate or APT) that shows more promising metal binding properties than MST.

METHODS

The degree of titanate-induced interference in the MTT (mitochondrial activity assay) was estimated by means of cell-free assays with and without a final centrifugation step to remove residual titanate particulate. Cytotoxic responses to titanates were assessed by measuring succinate dehydrogenase activity (by MTT) in THP1 monocytes or L929 fibroblasts after 24-72 h exposures. Monocytic activation by APT was assessed by TNFalpha secretion (ELISA) from monocytes with or without lipopolysaccharide (LPS) activation.

RESULTS

We confirmed that residual titanate particulates may alter the SDH activity assay, but that this effect is eliminated by adding a final centrifugation step to the standard MTT procedure. Addition of MST or APT at concentrations up to 100 mg/L altered succinate dehydrogenase activity by < 25% in both monocytes and fibroblasts. Fibroblasts displayed time-dependent adaptation to the MST. APT did not trigger TNFalpha secretion or modulate LPS-induced TNFalpha secretion from monocytes.

CONCLUSIONS

Although further in vitro and in vivo assessment is needed, MST and APT exhibit biological properties that are promising for their use as agents to sequester or deliver metals in biological systems.