Differential cytotoxicity and particle action of hydroxyapatite nanoparticles in human cancer cells

The multifunctional role of hydroxyapatite nanoparticles as an emerging tool in tumor therapy

Hydroxyapatite nanoparticles (HANPs) are well-known nanomaterials for bone regeneration or repair. In recent years, HANPs have emerged as a potential tool in tumor therapy because of the numerous advantages the nanoparticles offer, including the diverse physicochemical properties, the selective anti-tumor effect, intrinsic immunomodulatory activity, ability to reverse of drug or immune tolerance, allowance of ion substation, good drug-loading capabilities, etc. Notably, the physicochemical properties of the particles, such as size and shape, significantly influence their anti-tumor efficacy. Therefore, to offer a comprehensive understanding of the key properties of HANPs and the involving molecular mechanisms, and provide crucial cues for rational design and development of novel HANPs-based anti-tumor platforms, this review summarizes various synthesis methods of HANPs with controlled physiochemical characteristics and highlights the multifaceted effects such as interactions with tumor cells and immune cells, regulation of the tumor microenvironment (TME), overcoming drug or immune resistance, and their potentials as effective drug carriers. This review also outlines the emerging strategies leveraging HANPs for tumor therapy and diagnostic imaging. At last, we discuss the challenges HANPs face when used for tumor treatment. STATEMENT OF SIGNIFICANCE: Hydroxyapatite nanoparticles (HANPs) have emerged as a promising tool in tumor therapy without compromising biocompatibility. This review highlights the unique and multifaceted features of HANPs in tumor therapy, including the selective induction of tumor cell apoptosis, engagement in immune regulation, reversal of drug or immune resistance, and the loading of diverse anti-tumor drugs or biomaterials. Additionally, this review emphasizes the influence of the intrinsic physicochemical properties of HANPs on their anti-tumor activity, and explores the emerging strategies that leverage HANPs for tumor therapy and diagnostic imaging. In summary, this work aims to provide a comprehensive and deep understanding of the role of HANPs in tumor therapy and is significant for the improved design of HANP-based platforms for tumor therapy.

Advancements in nanohydroxyapatite: synthesis, biomedical applications and composite developments

Nanohydroxyapatite (nHA) is distinguished by its exceptional biocompatibility, bioactivity and biodegradability, qualities attributed to its similarity to the mineral component of human bone. This review discusses the synthesis techniques of nHA, highlighting how these methods shape its physicochemical attributes and, in turn, its utility in biomedical applications. The versatility of nHA is further enhanced by doping with biologically significant ions like magnesium or zinc, which can improve its bioactivity and confer therapeutic properties. Notably, nHA-based composites, incorporating metal, polymeric and bioceramic scaffolds, exhibit enhanced osteoconductivity and osteoinductivity. In orthopedic field, nHA and its composites serve effectively as bone graft substitutes, showing exceptional osteointegration and vascularization capabilities. In dentistry, these materials contribute to enamel remineralization, mitigate tooth sensitivity and are employed in surface modification of dental implants. For cancer therapy, nHA composites offer a promising strategy to inhibit tumor growth while sparing healthy tissues. Furthermore, nHA-based composites are emerging as sophisticated platforms with high surface ratio for the delivery of drugs and bioactive substances, gradually releasing therapeutic agents for progressive treatment benefits. Overall, this review delineates the synthesis, modifications and applications of nHA in various biomedical fields, shed light on the future advancements in biomaterials research.

Recent advances in nano-based drug delivery systems for treatment of liver cancer

Liver cancer is one of the aggressive primary tumors as evident by high rate of incidence and mortality. Conventional treatments (e.g. chemotherapy) suffer from various drawbacks including wide drug distribution, low localized drug concentration, and severe off-site toxicity. Therefore, they cannot satisfy the mounting need for safe and efficient cancer therapeutics, and alternative novel strategies are needed. Nano-based drug delivery systems (NDDSs) are among these novel approaches that can improve the overall therapeutic outcomes. NDDSs are designed to encapsulate drug molecules and target them specifically to liver cancer. Thus, NDDSs can selectively deliver therapeutic agents to the tumor cells and avoid distribution to off-target sites which should improve the safety profile of the active agents. Nonetheless, NDDSs should be well designed, in terms of the preparing materials, nanocarriers structure, and the targeting strategy, in order to accomplish these objectives. This review discusses the latest advances of NDDSs for cancer therapy with emphasis on the aforementioned essential design components. The review also entails the challenges associated with the clinical translation of NDDSs, and the future perspectives towards next-generation NDDSs.

Impact of inorganic/organic nanomaterials on the immune system for disease treatment

The study of nanomaterials' nature, function, and biocompatibility highlights their potential in drug delivery, imaging, diagnostics, and therapeutics. Advancements in nanotechnology have fostered the development and application of diverse nanomaterials. These materials facilitate drug delivery and influence the immune system directly. Yet, understanding of their impact on the immune system is incomplete, underscoring the need to select materials to achieve desired outcomes carefully. In this review, we outline and summarize the distinctive characteristics and effector functions of inorganic nanomaterials and organic materials in inducing immune responses. We highlight the role and advantages of nanomaterial-induced immune responses in the treatment of immune-related diseases. Finally, we briefly discuss the current challenges and future opportunities for disease treatment and clinical translation of these nanomaterials.

Anti-Cancer Activities of Nano Amorphous Calcium Phosphates toward Premalignant and Oral Cancer Cells

Despite advancements in treatment, the squamous cell carcinoma (OSCC) patient survival rate remains stagnant. Conventional therapies have limited effectiveness, necessitating novel agents. Our study aims to synthesize and characterize amorphous calcium phosphate nanoparticles (nACPs), assess their potential cytotoxic effects on premalignant and malignant OSCC cells, and investigate possible mechanisms of action. The morphological features of nACP were investigated by field emission scanning coupled with energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and particle size distribution (PSD). Then, we examined the effect of nACPs on nanoparticle uptake, cell adhesion, viability, invasion ability, cell cycle, and gene expression. nACP uptake was dose-dependent, induced limited selectivity in cytotoxicity between healthy and malignant cells, and affected cellular adhesion and invasion. Early apoptosis was the predominant type of cell death. The nACP effect on viability was verified by alterations in the genes associated with apoptosis and proliferation. A high concentration of nACP was shown to arrest the cell cycle progression in the G0/G1 phase of both malignant and premalignant cells. This type of nACP justifies the development of a strategy for its potential use as an anti-cancer agent and/or anti-cancer active carrier for various drugs in oral cancer treatments.

Challenging applicability of ISO 10993-5 for calcium phosphate biomaterials evaluation: Towards more accurate in vitro cytotoxicity assessment

Research on biomaterials typically starts with cytocompatibility evaluation, using the ISO 10993-5 standard as a reference that relies on extract tests to determine whether the material is safe (cell metabolic activity should exceed 70 %). However, the generalized approach within the standard may not accurately reflect the material's behavior in direct contact with cells, raising concerns about its effectiveness. Calcium phosphates (CaPs) are a group of materials that, despite being highly biocompatible and promoting bone formation, still exhibit inconsistencies in basic cytotoxicity evaluations. Hence, in order to test the cytocompatibility dependence on different experimental setups and material-cell interactions, we used amorphous calcium phosphate, α-tricalcium phosphate, hydroxyapatite, and octacalcium phosphate (0.1 mg/mL to 5 mg/mL) with core cell lines of bone microenvironment: mesenchymal stem cells, osteoblast-like and endothelial cells. All materials have been characterized for their physicochemical properties before and after cellular contact and once in vitro assays were finalized, groups identified as 'cytotoxic' were further analyzed using a modified Annexin V apoptosis assay to accurately determine cell death. The obtained results showed that indirect contact following ISO standards had no sensitivity of tested cells to the materials, but direct contact tests at physiological concentrations revealed decreased metabolic activity and viability. In summary, our findings offer valuable guidelines for handling biomaterials, especially in powder form, to better evaluate their biological properties and avoid false negatives commonly associated with the traditional standard approach.

Nano-ZnO-modified hydroxyapatite whiskers with enhanced osteoinductivity for bone defect repair

Hydroxyapatite (HA) whisker (HAw) represents a distinct form of HA characterized by its high aspect ratio, offering significant potential for enhancing the mechanical properties of bone tissue engineering scaffolds. However, the limited osteoinductivity of HAw hampers its widespread application. In this investigation, we observed HAw-punctured osteoblast membranes and infiltrated the cell body, resulting in mechanical damage to cells that adversely impacted osteoblast proliferation and differentiation. To address this challenge, we developed nano-zinc oxide particle-modified HAw (nano-ZnO/HAw). Acting as a reinforcing and toughening agent, nano-ZnO/HAw augmented the compressive strength and ductility of the matrix materials. At the same time, the surface modification with nano-ZnO particles improved osteoblast differentiation by reducing the mechanical damage from HAw to cells and releasing zinc ion, the two aspects collectively promoted the osteoinductivity of HAw. Encouragingly, the osteoinductive potential of 5% nano-ZnO/HAw and 10% nano-ZnO/HAw was validated in relevant rat models, demonstrating the efficacy of this approach in promoting new bone formation in vivo. Our findings underscore the role of nano-ZnO particle surface modification in enhancing the osteoinductivity of HAw from a physical standpoint, offering valuable insights into the development of bone substitutes with favorable osteoinductive properties while simultaneously bolstering matrix material strength and toughness.

Hydroxyapatite nanoparticles induced calcium overload-initiated cancer cell-specific apoptosis through inhibition of PMCA and activation of calpain

Hydroxyapatite nanoparticles (HAPNs) have been reported to specifically induce apoptosis and sustained elevation of intracellular Ca2+ concentration ([Ca2+]i) in cancer cells. However, it remains unclear whether calcium overload, the abnormal intracellular accumulation of Ca2+, is the intrinsic cause of cell apoptosis, how HAPNs specifically evoke calcium overload in cancer cells, and which potential pathways were involved in apoptosis initiation in response to calcium overload. In this study, using various cancer and normal cells, we observed a positive correlation between the degree of increased [Ca2+]i and the specific toxicity of HAPNs. Moreover, chelating intracellular Ca2+ with BAPTA-AM inhibited HAPN-induced calcium overload and apoptosis, thus demonstrating that calcium overload was the main cause of HAPN-induced cytotoxicity in cancer cells. Notably, the dissolution of particles outside the cells did not affect cell viability or [Ca2+]i. In contrast, internalized HAPNs dissolved more readily in cancer cells than in normal cells and inhibited the activity of plasma membrane calcium-ATPase solely in cancer cells to prevent extrusion of excessive Ca2+, hence leading to calcium overload in tumor cells. Upon exposure to HAPNs, the Ca2+-sensitive cysteine protease calpain was activated and then cleaved the BH3-only protein Bid. Consequently, cytochrome c was released, and caspase-9 and -3 were activated, leading to mitochondrial apoptosis. However, these effects were alleviated by the calpain inhibitor calpeptin, confirming the involvement of calpain in HANP-induced apoptosis. Therefore, our results demonstrated that calcium overload induced by HAPNs caused cancer cell-specific apoptosis by inhibiting PMCA and activating calpain in tumor cells and thus may contribute to a more comprehensive understanding of biological effects of this nanomaterial and facilitate the development of calcium overload cancer therapy.

The Combined Anti-Tumor Efficacy of Bioactive Hydroxyapatite Nanoparticles Loaded with Altretamine

In the current study, the combined anti-tumor efficacy of bioactive hydroxyapatite nano- particles (HA-NPs) loaded with altretamine (ALT) was evaluated. The well-known fact that HA has great biological compatibility was confirmed through the findings of the hemolytic experiments and a maximum IC₅₀ value seen in the MTT testing. The preparation of HA-NPs was performed using the chemical precipitation process. An in vitro release investigation was conducted, and the results demonstrated the sustained drug release of the altretamine-loaded hydroxyapatite nanoparticles (ALT-HA-NPs). Studies using the JURKAT E6.1 cell lines MTT assay, and cell uptake, as well as in vivo pharmacokinetic tests using Wistar rats demonstrated that the ALT-HA-NPs were easily absorbed by the cells. A putative synergism between the action of the Ca²⁺ ions and the anticancer drug obtained from the carrier was indicated by the fact that the ALT-HA-NPs displayed cytotoxicity comparable to the free ALT at 1/10th of the ALT concentration. It has been suggested that a rise in intracellular Ca²⁺ ions causes cells to undergo apoptosis. Ehrlich's ascites model in Balb/c mice showed comparable synergistic efficacy in a tumor regression trial. While the ALT-HA-NPs were able to shrink the tumor size by six times, the free ALT was only able to reduce the tumor volume by half.

Biomaterial-assisted tumor therapy: A brief review of hydroxyapatite nanoparticles and its composites used in bone tumors therapy

Malignant bone tumors can inflict significant damage to affected bones, leaving patients to contend with issues like residual tumor cells, bone defects, and bacterial infections post-surgery. However, hydroxyapatite nanoparticles (nHAp), the principal inorganic constituent of natural bone, possess numerous advantages such as high biocompatibility, bone conduction ability, and a large surface area. Moreover, nHAp's nanoscale particle size enables it to impede the growth of various tumor cells via diverse pathways. This article presents a comprehensive review of relevant literature spanning the past 2 decades concerning nHAp and bone tumors. The primary goal is to explore the mechanisms responsible for nHAp's ability to hinder tumor initiation and progression, as well as to investigate the potential of integrating other drugs and components for bone tumor diagnosis and treatment. Lastly, the article discusses future prospects for the development of hydroxyapatite materials as a promising modality for tumor therapy.

Hydroxyapatite Nanopowders for Effective Removal of Strontium Ions from Aqueous Solutions

Drinking water contamination has become a worldwide problem due to the highly negative effects that pollutants can have on human organisms and the environment. Hydroxyapatite (HAp) has the appropriate properties for the immobilization of various pollutants, being considered amongst the most cost-effective materials for water decontamination. The main objective of this study was to use synthesized hydroxyapatite for the elimination of Sr²⁺ ions from contaminated solutions. The hydroxyapatite used in the decontamination process was synthesized in the laboratory using an adapted method. The hydroxyapatite powder (HAp) resulting from the synthesis was analyzed both before and after the elimination of Sr²⁺ ions from contaminated solutions. The efficiency of the HAp nanoparticles in removing Sr²⁺ ions from contaminated solution was determined by batch adsorption experiments. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to study the HAp samples before and after the removal of Sr²⁺ ions. The ability of HAp nanoparticles to eliminate strontium ions from contaminated solutions was established. Moreover, the removal of Sr²⁺ ions from the contaminated aqueous solutions was highlighted by ultrasound measurements. The value of the stability parameter calculated by ultrasonic measurements after the removal of Sr²⁺ ions from the contaminated solution was similar to that of double distilled water whose stability was used as reference. The outcomes of the batch experiments and the parameters obtained from Langmuir and Freundlich models indicated that the HAp nanoparticles had a strong affinity for the elimination of Sr²⁺ ions from polluted solutions. These results emphasized that HAp nanoparticles could be excellent candidates in the development of new technologies for water remediation. More than that, the outcomes of the cytotoxic assays proved that HAp nanoparticles did not induce any noticeable harmful effects against HeLa cells and did not affect their proliferation after 1 day and 7 days of incubation.

Hydroxyapatite nanoparticles-cell interaction: New approaches to disclose the fate of membrane-bound and internalised nanoparticles

Hydroxyapatite nanoparticles are popular tools in bone regeneration, but they have also been used for gene delivery and as anticancer drugs. Understanding their mechanism of action, particularly for the latter application, is crucial to predict their toxicity. To this end, we aimed to elucidate the importance of nanoparticle membrane interactions in the cytotoxicity of MG-63 cells using two different types of nanoparticles. In addition, conventional techniques for studying nanoparticle internalisation were evaluated and compared with newer and less exploited approaches. Hydroxyapatite and magnesium-doped hydroxyapatite nanoparticles were used as suspensions or compacted as specular discs. Comparison between cells seeded on the discs and those supplemented with the nanoparticles allowed direct interaction of the cell membrane with the material to be ruled out as the main mechanism of toxicity. In addition, standard techniques such as flow cytometry were inconclusive when used to assess nanoparticles toxicity. Interestingly, the use of intracellular calcium fluorescent probes revealed the presence of a high number of calcium-rich vesicles after nanoparticle supplementation in cell culture. These structures could not be detected by transmission electron microscopy due to their liquid content. However, by using cryo-soft X-ray imaging, which was used to visualise the cellular ultrastructure without further treatment other than vitrification and to quantify the linear absorption coefficient of each organelle, it was possible to identify them as multivesicular bodies, potentially acting as calcium stores. In the study, an advanced state of degradation of the hydroxyapatite and magnesium-doped hydroxyapatite nanoparticles within MG-63 cells was observed. Overall, we demonstrate that the combination of fluorescent calcium probes together with cryo-SXT is an excellent approach to investigate intracellular calcium, especially when found in its soluble form.

Anti-melanoma effect and action mechanism of a novel chitosan-based composite hydrogel containing hydroxyapatite nanoparticles

Hydroxyapatite nanoparticles (HANPs) have been increasingly regarded and reported due to their potential anti-tumor ability. Previously, we found that the rod-like HANPs had good application potential for cutaneous melanoma (CMM). To satisfy the actual requirements in repairing post-operative skin defects and inhibiting CMM recurrence after tumorectomy, we constructed a novel chitosan/alginate (CS/Alg) hydrogel containing the aforementioned HANPs. The in vitro cell experiments confirmed that activated mitochondrial-dependent apoptosis was tightly related to the anti-tumor ability of HANPs. Specifically, we further discovered several target proteins might be involved in abnormal activating Wnt, proteoglycans in cancer, oxidative phosphorylation and p53 signaling pathways. The in vivo animal experiments demonstrated that the HANPs-loaded CS/Alg hydrogel (CS/Alg/HANPs) had a similar effect on inhibiting tumor growth as HANPs, and CS/Alg hydrogel as well as phosphate buffered saline (PBS) group (control) not showed any effect, proving the key role of HANPs. The immunohistochemical staining demonstrated a tumor inhibition via the mitochondria-mediated apoptosis pathway, consistent with the in vitro evaluation. Moreover, CS/Alg/HANPs exhibited no additional biosafety risk to the functions of major organs. Overall, this CS/Alg/HANPs hydrogel has substantial application potential for treating CMM.

Hydroxyapatite Nanoparticles for Improved Cancer Theranostics

Beyond their well-known applications in bone tissue engineering, hydroxyapatite nanoparticles (HAp NPs) have also been showing great promise for improved cancer therapy. The chemical structure of HAp NPs offers excellent possibilities for loading and delivering a broad range of anticancer drugs in a sustained, prolonged, and targeted manner and thus eliciting lower complications than conventional chemotherapeutic strategies. The incorporation of specific therapeutic elements into the basic composition of HAp NPs is another approach, alone or synergistically with drug release, to provide advanced anticancer effects such as the capability to inhibit the growth and metastasis of cancer cells through activating specific cell signaling pathways. HAp NPs can be easily converted to smart anticancer agents by applying different surface modification treatments to facilitate the targeting and killing of cancer cells without significant adverse effects on normal healthy cells. The applications in cancer diagnosis for magnetic and nuclear in vivo imaging are also promising as the detection of solid tumor cells is now achievable by utilizing superparamagnetic HAp NPs. The ongoing research emphasizes the use of HAp NPs in fabricating three-dimensional scaffolds for the treatment of cancerous tissues or organs, promoting the regeneration of healthy tissue after cancer detection and removal. This review provides a summary of HAp NP applications in cancer theranostics, highlighting the current limitations and the challenges ahead for this field to open new avenues for research.

Nano-hydroxyapatite-evoked immune response synchronized with controllable immune adjuvant release for strengthening melanoma-specific growth inhibition

Concerns about the potential systematic toxicity limit the extensive application of traditional therapeutic drugs for melanoma therapy, nano-hydroxyapatite (nHA) with good biocompatibility and anti-tumor ability could be an alternative choice. In this study, nHA was employed as an anti-tumor biomaterial due to its tumor-specific toxicity. Meanwhile, granulocyte-macrophage colony-stimulating factor (GM-CSF) served as the immune adjuvant to activate the immune response. The delivery platform was fabricated by co-encapsulation of both nHA and GM-CSF into a biocompatible thermosensitive PLGA-PEG-PLGA hydrogel. The results showed that the bio-activities of nHA and GM-CSF could be well-maintained within the hydrogel. Interestingly, the addition of nHA could attenuate the burst release of GM-CSF due to possible protein absorption capacity of nHA, which is beneficial for GM-CSF sustainable release at the tumor site, achieving boosted and prolonged anti-tumor immunity. The in vitro and in vivo data demonstrated that nHA/GM-CSF hydrogel exhibited greater potency to inhibit tumor growth via enhanced CD8⁺ T-cell response compared with hydrogel and nHA hydrogel groups, contributed by the synergistic effects of nHA and GM-CSF. Overall, the strategy combining nHA and immune adjuvant shows great promise, which largely broadens the choice of combinational therapies for melanoma. STATEMENT OF SIGNIFICANCE: Nano-hydroxyapatite (nHA) has been confirmed to specifically inhibit melanoma tumor growth and induce immune response. However, its antitumor efficiency and immunity-evoking capacity are limited. In this study, granulocyte-macrophage colony-stimulating factor (GM-CSF) was introduced to serve as the immune adjuvant. Both of them were encapsulated into a biocompatible thermosensitive PLGA-PEG-PLGA hydrogel. The addition of nHA could attenuate the burst release of GM-CSF due to the interaction with nHA, which is beneficial for GM-CSF sustainable release at tumor site, achieving boosted and prolonged anti-tumor immunity. Anti-tumor immune response could be activated due to the release of tumor-associated antigen and tumor debris induced by the specifically tumor inhibition effect of nHA and GM-CSF. The combination of nHA and GM-CSF could play synergistic inhibiting effect on tumor growth via boosting and prolonging anti-tumor immunity.

Nanotechnology-Assisted Cell Tracking

The usefulness of nanoparticles (NPs) in the diagnostic and/or therapeutic sector is derived from their aptitude for navigating intra- and extracellular barriers successfully and to be spatiotemporally targeted. In this context, the optimization of NP delivery platforms is technologically related to the exploitation of the mechanisms involved in the NP-cell interaction. This review provides a detailed overview of the available technologies focusing on cell-NP interaction/detection by describing their applications in the fields of cancer and regenerative medicine. Specifically, a literature survey has been performed to analyze the key nanocarrier-impacting elements, such as NP typology and functionalization, the ability to tune cell interaction mechanisms under in vitro and in vivo conditions by framing, and at the same time, the imaging devices supporting NP delivery assessment, and consideration of their specificity and sensitivity. Although the large amount of literature information on the designs and applications of cell membrane-coated NPs has reached the extent at which it could be considered a mature branch of nanomedicine ready to be translated to the clinic, the technology applied to the biomimetic functionalization strategy of the design of NPs for directing cell labelling and intracellular retention appears less advanced. These approaches, if properly scaled up, will present diverse biomedical applications and make a positive impact on human health.

Potential Role of Hydroxyapatite Nanocrystalline for Early Diagnostics of Ovarian Cancer

Calcification is one of the clinical and morphological manifestations of ovarian tumors and it begins at the initial stages of carcinogenesis. Thus, this process can be used for the early diagnostics of some malignant ovarian tumors. We compared the results of ultrasound and histology and found that calcifications of a size less than 200 μm are not detected by ultrasound. These calcified structures are round fragile particles of different sizes. In the EDX (Energy-dispersive X-ray spectroscopy) spectra, the main lines were from Ca and P, and the ratio of these elements corresponds to hydroxyapatite. Thus, we established that hydroxyapatite is the main mineral component of ovarian psammoma bodies and could be used for early diagnostics of ovarian malignant neoplasia.

Multifunctionality of Nanosized Calcium Apatite Dual-Doped with Li+/Eu3+ Ions Related to Cell Culture Studies and Cytotoxicity Evaluation In Vitro

Li⁺/Eu³⁺ dual-doped calcium apatite analogues were fabricated using a microwave stimulated hydrothermal technique. XRPD, FT-IR, micro-Raman spectroscopy, TEM and SAED measurements indicated that obtained apatites are single-phased, crystallize with a hexagonal structure, have similar morphology and nanometric size as well as show red luminescence. Lithium effectively modifies the local symmetry of optical active sites and, thus, affects the emission efficiency. Moreover, the hydrodynamic size and surface charge of the nanoparticles have been extensively studied. The protein adsorption (lysozyme, LSZ; bovine serum albumin, BSA) on the nanoparticle surface depended on the type of cationic dopant (Li⁺, Eu³⁺) and anionic group (OH⁻, Cl⁻, F⁻) of the apatite matrix. Interaction with LSZ resulted in a positive zeta potential, and the nanoparticles had the lowest hydrodynamic size in this protein medium. The cytotoxicity assessment was carried out on the human osteosarcoma cell line (U2OS), murine macrophages (J774.E), as well as human red blood cells (RBCs). The studied apatites were not cytotoxic to RBCs and J774.E cells; however, at higher concentrations of nanoparticles, cytotoxicity was observed against the U2OS cell line. No antimicrobial activity was detected against Gram-negative bacteria with one exception for P. aeruginosa treated with Li⁺-doped fluorapatite.

Nanocarrier-based drug delivery systems for bone cancer therapy: a review

Bone cancer is a malignant tumor that originates in the bone and destroys the healthy bone tissues. Of the various types of bone tumors, osteosarcoma is the most commonly diagnosed primary bone malignancy. The standard treatment for primary malignant bone tumors comprises surgery, chemotherapy and radiotherapy. Owing to the lack of proven treatments, different forms of alternative therapeutic approaches have been examined in recent decades. Among the new therapeutic methodologies, nanotechnology-based anticancer therapy has paved the way for new targeted strategies for bone cancer treatment and bone regeneration. They include approaches such as the co-delivery of multiple drug cargoes, the enhancement of their biodistribution and transport properties, normalizing accumulation and the optimization of drug release profiles to overcome shortcomings of the existing therapy. This review examines the standard treatments for osteosarcoma, their lacunae, and the evolving therapeutic strategies based on nanocarrier-mediated combinational drug delivery systems, and future perspectives for osteosarcoma therapy.

Synergistic Combination of Bioactive Hydroxyapatite Nanoparticles and the Chemotherapeutic Doxorubicin to Overcome Tumor Multidrug Resistance

Multidrug resistance (MDR) is one of the biggest obstacles in cancer chemotherapy. Here, a remarkable reversal of MDR in breast cancer through the synergistic effects of bioactive hydroxyapatite nanoparticles (HAPNs) and doxorubicin (DOX) is shown. DOX loaded HAPNs (DHAPNs) exhibit a 150-fold reduction in IC₅₀ compared with free DOX for human MDR breast cancer MCF-7/ADR cells, and lead to almost complete inhibition of tumor growth in vivo without obvious side effects of free DOX. This high efficacy and specificity could be attributed to multiple action mechanisms of HAPNs. In addition to acting as the conventional nanocarriers to facilitate the cellular uptake and retention of DOX in MCF-7/ADR cells, more importantly, drug-free HAPNs themselves are able to prevent drug being pumped out of MDR cells through targeting mitochondria to induce mitochondrial damage and inhibit ATP production and to trigger sustained mitochondrial calcium overload and apoptosis in MDR cancer cells while not affecting normal cells. The results demonstrate that this simple but versatile bioactive nanoparticle provides a practical approach to effectively overcome MDR.

A novel strategy for tumor therapy: targeted, PAA-functionalized nano-hydroxyapatite nanomedicine

The rapid development of nanotechnology has provided new strategies for the treatment of tumors. Nano-scale hydroxyapatite (HAP), as the main component of hard tissues in humans and vertebrates, have been found to specifically inhibit tumor cells. However, achieving controllable synthesis of HAP and endowing it with cancer cell-targeting properties remain enormous challenges. To solve this problem, we developed polyacrylic acid-coordinated hydroxyapatite nanoparticles (HAP-PAA) and further chemically grafted them with folic acid (HAP-PAA-FA) for cancer treatment in this study. The nucleation sites and steric hindrance provided by the PAA greatly inhibited the agglomeration of the nanoparticles, and at the same time, the excess functional groups further modified the surface of nanoparticles to achieve targeting efficiency. The spherical, low-crystallinity HAP-PAA nanoparticles exhibited good tumor cell lethality. After grafting the nanoparticles with folic acid for molecular targeting, their cellular uptake and specific killing ability of tumor cells were further enhanced. The HAP-PAA-FA nanoparticle system exerted a regulatory effect on the tumor microenvironment and had good biological safety. All the above results indicate that this research will broaden the application of hydroxyapatite in tumor treatment.

Hydroxyapatite nanocomposite as a potential agent in osteosarcoma PDT

Using Nanoplatforms as a hauler for photosensitizers is a bespoke paradigm to improve its bioavailability and to boost the PDT efficacy. Herein, the photodynamic cytotoxicity of methylene blue (MB) loaded on hydroxyapatite nanoparticles (HA-NPs) was tested against human osteosarcoma-derived cells (Saos-2 cell line). HA-NPs and HA-NPs loaded with MB (HA-NPs-MB) were prepared by a chemical precipitation method and characterized by TEM, Zeta potential, FTIR, and XRD. TEM images revealed that HA-NPs have a rod shape with a diameter of 14-17 nm and length around 46-64 nm. FTIR and Zeta potential confirmed the adsorption of cationic MB on HA-NPs. XRD pattern was identical to the standard XRD pattern of HA-NPs. Incubation of Saos-2 cells (24 h) with HA-NPs-MB then irradiation of cells (5 min) with a diode laser (808 nm), causes a higher decrement of cell viability (determined by MTT assay) than that caused by free MB. The LC₅₀ was 57.53 µg/mL and 86.99 µg/mL for HA-NPs-MB and free MB, respectively. Thus, the nanoformulation of MB greatly reduced the dose of MB required for effective PDT. This study also investigated the mode of cell death after incubation of cells with free MB or HA-NPs-MB composite then exposure to laser radiation. The results revealed that the majority of cells died by apoptosis while a minor fraction of cells died by necrosis, especially in the case of HA-NPs-MB. Levels of caspase-3 and death receptor-4 (DR-4) were more elevated in the case of HA-NPs-MB than free MB. The effect of the prepared nanocomposite and free MB on Raw murine macrophage (RAW 264.7) viability was also examined using the MTT assay. The results indicated that HA-NPs-MB in the presence of laser has a great cytotoxic effect on macrophage cells compared to other treatments. This may present an advantage through decreasing macrophage that promotes tumor growth. In conclusion, HA-NPs-MB nanocomposite surmounts free MB and HA-NPs in destroying macrophage cells and Saos-2 cells through apoptosis in the presence of laser irradiation. This study introduces a thorough and new insight on osteosarcoma (cancer cell line Saos-2) PDT using HA-NPs-MB exploiting the biosafety of HA-NPs.

Evaluating the Radiosensitization Effect of Hydroxyapatite Nanoparticles on Human Breast Adenocarcinoma Cell Line and Fibroblast

Background:

Nanohydroxyapatite (nHAP) exhibit anti-proliferative effects on various cancer cells. However, to date, there are only a few studies on the radiosensitization effect of nHAP. The present study aimed to investigate the possible enhancement of the radiosensitization effect of nHAP on human breast adenocarcinoma cancer (MCF-7) and fibroblast.

Methods:

nHAP was extracted from fish scales using the thermal alkaline method and characterized at Babol University of Medical Sciences (Babol, Iran) in 2017. The anti-proliferative and the radiosensitization effects of nHAP were investigated by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-Diphenyltetrazolium Bromide (MTT), clonogenic assay, and apoptosis assay. MCF-7 cells and fibroblasts were incubated with different concentrations of nHAP and at different periods. The MTT solution was added and the absorbance was measured at 570 nm. The MCF-7 cells were exposed to 0, 1.5, 3.5, and 5 Gy X-ray irradiation and incubated for 10-14 days. The data were compared using the one-way analysis of variance (ANOVA) followed by the post hoc tests (Tukey’s method).

Results:

The results showed that nHAP significantly inhibited the growth of MCF-7 cells compared with controls (P<0.001), but the difference was not statistically significant for fibroblasts (P=0.686 at 400 µg/mL at 72 hours). After 48 hours, the proliferation of MCF-7 cells and fibroblasts was inhibited by about 81% and 34% at 400 µg/mL concentration, respectively. The radiosensitization enhancement factor for MCF-7 cells and fibroblasts at a dose of 3.5 Gy and 100 μg/mL concentration were 1.87 and 1.3, respectively.

Conclusion:

nHAP can be considered as a breast cancer radiosensitization agent with limited damage to the surrounding healthy tissue.

Size-Dependent Cytotoxicity of Hydroxyapatite Crystals on Renal Epithelial Cells

Background

Hydroxyapatite (HAP) is a common component of most idiopathic calcium oxalate (CaOx) stones and is often used as a nidus to induce the formation of CaOx kidney stones.

Methods

This work comparatively studies the cytotoxicity of four kinds of HAP crystals with different sizes (40 nm to 2 μm), namely, HAP-40 nm, HAP-70 nm, HAP-1 μm, and HAP-2 μm, on human renal proximal tubular epithelial cells (HK-2).

Results

HAP crystals reduce the viability and membrane integrity of HK-2 cells in a concentration-dependent manner and consequently cause cytoskeleton damage, cell swelling, increased intracellular reactive oxygen species level, decreased mitochondrial membrane potential, increased intracellular calcium concentration, blocked cell cycle and stagnation in G0/G1 phase, and increased cell necrosis rate. HAP toxicity to HK-2 cells increases with a decrease in crystal size.

Conclusion

Cell damage caused by HAP crystals increases the risk of kidney stone formation.

Hydroxyapatite as a biomaterial - a gift that keeps on giving

The synthetic analogue to biogenic apatite, hydroxyapatite (HA) has a number of physicochemical properties that make it an attractive candidate for diagnosis, treatment of disease and augmentation of biological tissues. Here we describe some of the recent studies on HA, which may provide bases for a number of new medical applications. The content of this review is divided to different medical application modes utilizing HA, including tissue engineering, medical implants, controlled drug delivery, gene therapies, cancer therapies and bioimaging. A number of advantages of HA over other biomaterials emerge from this discourse, including (i) biocompatibility, (ii) bioactivity, (iii) relatively simple synthesis protocols for the fabrication of nanoparticles with specific sizes and shapes, (iv) smart response to environmental stimuli, (v) facile functionalization and surface modification through noncovalent interactions, and (vi) the capacity for being simultaneously loaded with a wide range of therapeutic agents and switched to bioimaging modalities for uses in theranostics. A special section is dedicated to analysis of the safety of particulate HA as a component of parenterally administrable medications. It is concluded that despite the fact that many benefits come with the usage of HA, its deficiencies and potential side effects must be addressed before the translation to the clinical domain is pursued. Although HA has been known in the biomaterials world as the exemplar of safety, this safety proves to be the function of size, morphology, surface ligands and other structural and compositional parameters defining the particles. For this reason, each HA, especially when it comes in a novel structural form, must be treated anew from the safety research angle before being allowed to enter the clinical stage.

Anti-osteosarcoma effect of hydroxyapatite nanoparticles both in vitro and in vivo by downregulating the FAK/PI3K/Akt signaling pathway

Schematic representing the anti-cancer effects of nano-HAPs both in vitro and in vivo by downregulating the FAK/PI3K/Akt signaling pathway.

Preparation and preliminary evaluation of bio-nanocomposites based on hydroxyapatites with antibacterial properties against anaerobic bacteria

Hexagonal nanocrystalline powders of the non-doped Ca₁₀(PO₄)₆(OH)₂ as well as activated with Ag⁺ and Eu³⁺ ions were synthesized by using different wet chemistry methods. Moreover, the obtained hydroxyapatite was loaded with Ag⁰, as well as nitroimidazole antimicrobials: metronidazole and tinidazole. The structural properties of the products were analyzed by X-ray diffraction (XRD), scanning (SEM) and transmission (TEM) electron microscopy as well as infrared (IR) and Raman spectroscopy. The photoluminescence properties of the Eu³⁺ and Ag⁺ co-doped Ca₁₀(PO₄)₆(OH)₂ were characterized via the PL emission, excitation spectra and the luminescence decay curve. The antimicrobial activity of the obtained materials against Prevotella bivia and Parabacteroides distasonis was studied. The cytotoxicity assessment was carried out on the human osteosarcoma cell line (U2OS) as well as human red blood cells (RBC). The choice of the in vitro model was based on the fact that U2OS is a cancer cell line derived from bone tissue which is rich in apatites that play a pivotal role in the extracellular matrix formation. RBCs are the most abundant blood cells and they are used as a cell model in the study of biocompatibility of new prepared biocompounds with potential medical applications. The obtained multifunctional materials do not exhibit the haemolytic activity, therefore, they could be used as a promising antimicrobial agent and for anaerobic bacteria.

In vitro and in vivo mechanism of hepatocellular carcinoma inhibition by β-TCP nanoparticles

Background: Studies have showed that nanoparticles have a certain anti-cancer activity and can inhibit many kinds of cancer cells. β-tricalcium phosphate nanoparticles (nano-β-TCP) displays better biodegradation, but the application and mechanism of nano-β-TCP in anti-cancer activity are still not clear. Purpose: The objective of this study was to synthesize nano-β-TCP and investigate its inhibitory properties and mechanism on hepatocellular carcinoma (HepG2) cells in vitro and in vivo. Methods: Nano-β-TCP was synthesized using ethanol-water system and characterized. The effects of nano-β-TCP on cell viability, cell uptake, intracellular oxidative stress (ROS), cell cycle and apoptosis were also investigated with HepG2 cells and human hepatocyte cells (L-02). Intratumoral injection of nano-β-TCP was performed on the xenograft liver cancer model to explore the inhibitory effect and mechanism of nano-β-TCP on liver tumors. Results: In vitro results revealed that nano-β-TCP caused reduced cell viability of HepG2 cells in a time-and dose-dependent manner. Nano-β-TCP was internalized through endocytosis and degraded in cells, resulting in obvious increase of the intracellular Ca²⁺ and PO₄ ^3- ions. Nano-β-TCP induced cancer cells to produce ROS and induced apoptosis of tumor cells by an apoptotic signaling pathways both in extrinsic and intrinsic pathway. In addition, nano-β-TCP blocked cell cycle of HepG2 cells in G0/G1 phase and disturbed expression of some related cyclins. In vivo results showed that 40 mg/kg of nano-β-TCP had no significant toxic side effects, but could effectively suppress hepatocellular carcinoma growth. Conclusion: These findings revealed the anticancer effect of nano-β-TCP and also clarified the mechanism of its inhibitory effect on hepatocellular carcinoma.

The in vitro and in vivo anti-melanoma effects of hydroxyapatite nanoparticles: influences of material factors

Background

Treatment for melanoma is a challenging clinical problem, and some new strategies are worth exploring.

Purpose

The objective of this study was to investigate the in vitro and in vivo anti-melanoma effects of hydroxyapatite nanoparticles (HANPs) and discuss the involved material factors.

Materials and methods

Five types of HANPs, ie, HA-A, HA-B, HA-C, HA-D, and HA-E, were prepared by wet chemical method combining with polymer template and appropriate post-treatments. The in vitro effects of the as-prepared five HANPs on inhibiting the viability of A375 melanoma cells and inducing the apoptosis of the cells were evaluated by Cell Counting Kit-8 analysis, cell nucleus morphology observation, flow cytometer, and PCR analysis. The in vivo anti-melanoma effects of HANPs were studied in the tumor model of nude mice.

Results

The five HANPs had different physicochemical properties, including morphology, size, specific surface area (SSA), crystallinity, and so on. By the in vitro cell study, it was found that the material factors played important roles in the anti-melanoma effect of HANPs. Among the as-prepared five HANPs, HA-A with granular shape, smaller size, higher SSA, and lower crystallinity exhibited best effect on inhibiting the viability of A375 cells. At the concentration of 200 μg/mL, HA-A resulted in the lowest cell viability (34.90%) at day 3. All the HANPs could induce the apoptosis of A375 cells, and the relatively higher apoptosis rates of the cells were found in HA-A (20.10%) and HA-B (19.41%) at day 3. However, all the HANPs showed no inhibitory effect on the viability of the normal human epidermal fibroblasts. The preliminary in vivo evaluation showed that both HA-A and HA-C could delay the formation and growth speed of melanoma tissue significantly. Likely, HA-A exhibited better effect on inhibiting the growth of melanoma tissue than HA-C. The inhibition rate of HA-A for tumor tissue growth reached 49.1% at day 23.

Conclusion

The current study confirmed the anti-melanoma effect of HANPs and provided a new idea for the clinical treatment of melanoma.

New approach to modification of poly (l-lactic acid) with nano-hydroxyapatite improving functionality of human adipose-derived stromal cells (hASCs) through increased viability and enhanced mitochondrial activity

The aim of this study was to determine the cytocompatibility of poly (l-lactide) (PLLA) scaffolds fabricated using co-rotating twin screw extrusion technique and functionalized with different concentrations of nano-hydroxyapatite (nHAp). The efforts were aimed on the designing bioactive scaffolds improving the viability and metabolic activity of human adipose-derived multipotent stromal cells (hASCs). The in vitro study was designed to determine the optimal nHAp concentration, based on analysis of hASCs morphology, adhesion rate, as well as metabolic and proliferative potential. Initially, the PLLA filled with three different concentrations of the nHAp were tested i.e. 5%, 10% and 15 wt%. The obtained results indicated that the 10 wt% nHAp in the PLLA (10% nHAp/PLLA) matrices improved the adhesion and proliferation of the hASCs, what was in good agreement with the results of tensile properties of the composites. Further, we performed profound studies regarding the cytotoxicity of 10% nHAp/PLLA. The analysis included the evaluation of the biomaterial influence on viability, apoptosis-related markers expression profile and mitochondrial function. The cytocompatibility of 10% nHAp/PLLA scaffolds toward the hASCs was confirmed. The hASCs propagated on 10% nHAp/PLLA were more viable then those propagated on the plain PLLA. The level of pro-apoptotic markers, i.e. caspase-3 and Bax in cultures on 10% nHAp/PLLA was significantly decreased. Obtained results correlated with higher mitochondrial membrane potential of hASCs in those cultures. The obtained composites may improve therapeutic potential of hASCs via directing their adhesion, enhancing proliferation and viability as well as increasing mitochondrial potential, thus may find potential application in tissue engineering.

Characterization and influence of hydroxyapatite nanopowders on living cells

Nanomaterials, such as hydroxyapatite nanoparticles show a great promise for medical applications due to their unique properties at the nanoscale. However, there are concerns about the safety of using these materials in biological environments. Despite a great number of published studies of nanoobjects and their aggregates or agglomerates, the impact of their physicochemical properties (such as particle size, surface area, purity, details of structure and degree of agglomeration) on living cells is not yet fully understood. Significant differences in these properties, resulting from different manufacturing methods, are yet another problem to be taken into consideration. The aim of this work was to investigate the correlation between the properties of nanoscale hydroxyapatite from different synthesis methods and biological activity represented by the viability of four cell lines: A549, CHO, BEAS-2B and J774.1 to assess the influence of the nanoparticles on immune, reproductive and respiratory systems.

Intracellular Interaction of Hydroxyapatite-Based Nanocrystals with Uniform Shape and Traceable Fluorescence

The intracellular interaction between osteoblasts and hydroxyapatite (HA) is of great importance for future applications of HA nanocrystals in tracing cell differentiation and bone regeneration. This research attempts to provide insight into the intracellular interaction between osteoblasts and synthetic HA nanocrystals by employing the uniform shape and fluorescence of terbium-doped HA nanocrystals jointly for the first time. When cultured for 7 days, the abundant cytoplasm of the osteoblasts could be clearly and homogeneously visualized via the green fluorescence of the internalized HA nanocrystals, which kept a uniform morphology but showed a slight size decrease and degradation; the gene expression of the osteoblasts was not obviously affected. However, on day 14, the uniform HA nanocrystals had degraded into smaller and irregular nanoparticles, and agglomeration had occurred. Meanwhile, multilayer membrane structures and vacuolization around the degraded HA particles appeared in the osteoblasts; the expression of genes largely decreased, or the genes could not be normally expressed. The results indicate that the morphology and composition change of the internalized HA nanocrystals and the microstructure change of the osteoblasts are closely related and correspond to each other. The feasible new method and insightful details will aid in future investigations of the interaction of synthetic HA nanocrystals with various cells. The results from the intracellular interaction also remind us to pay more attention to the in-depth study of HA nanoparticles used for bone repair and reconstruction.

Selective effect of hydroxyapatite nanoparticles on osteoporotic and healthy bone formation correlates with intracellular calcium homeostasis regulation

Adequate bone substitutes osseointegration has been difficult to achieve in osteoporosis. Hydroxyapatite of the osteoporotic bone, secreted by pathologic osteoblasts, had a smaller crystal size and lower crystallinity than that of the normal. To date, little is known regarding the interaction of synthetic hydroxyapatite nanoparticles (HANPs) with osteoblasts born in bone rarefaction. The present study investigated the biological effects of HANPs on osteoblastic cells derived from osteoporotic rat bone (OVX-OB), in comparison with the healthy ones (SHM-OB). A selective effect of different concentrations of HANPs on the two cell lines was observed that the osteoporotic osteoblasts had a higher tolerance. Reductions in cell proliferation, ALP activity, collagen secretion and osteoblastic gene expressions were found in the SHM-OB when administered with HANPs concentration higher than 25µg/ml. In contrast, those of the OVX-OB suffered no depression but benefited from 25 to 250µg/ml HANPs in a dose-dependent manner. We demonstrated that the different effects of HANPs on osteoblasts were associated with the intracellular calcium influx into the endoplasmic reticulum. The in vivo bone defect model further confirmed that, with a critical HANPs concentration administration, the osteoporotic rats had more and mechanically matured new bone formation than the non-treated ones, whilst the sham rats healed no better than the natural healing control. Collectively, the observed epigenetic regulation of osteoblastic cell function by HANPs has significant implication on defining design parameters for a potential therapeutic use of nanomaterials.

STATEMENT OF SIGNIFICANCE

In this study, we investigated the biological effects of hydroxyapatite nanoparticles (HANPs) on osteoporotic rat bone and the derived osteoblast. Our findings revealed a previously unrecognized phenomenon that the osteoporotic individuals could benefit from higher concentrations of HANPs, as compared with the healthy individuals. The in vivo bone defect model confirmed that, with a critical HANPs concentration administration, the osteoporotic rats had more mechanically matured new bone formation than the non-treated ones, whilst the sham rats healed no better than the natural healing control. The selective effect of HANPs might be associated with the intracellular calcium influx into the endoplasmic reticulum. Collectively, the observed epigenetic regulation by HANPs has significant implication on defining design parameters for a potential therapeutic use of nanomaterials in a pathological condition.

The Effects of Silica Nanoparticles on Apoptosis and Autophagy of Glioblastoma Cell Lines

Silica nanoparticles (SiNPs) are one of the most commonly used nanomaterials in various medical applications. However, possible mechanisms of the toxicity caused by SiNPs remain unclear. The study presented here provides novel information on molecular and cellular effects of SiNPs in glioblastoma LBC3 and LN-18 cells. It has been demonstrated that SiNPs of 7 nm, 5–15 nm and 10–20 nm induce time- and dose-dependent cytotoxicity in LBC3 and LN-18 cell lines. In contrast to glioblastoma cells, we observed only weak reduction in viability of normal skin fibroblasts treated with SiNPs. Furthermore, in LBC3 cells treated with 5–15 nm SiNPs we noticed induction of apoptosis and necrosis, while in LN-18 cells only necrosis. The 5–15 nm SiNPs were also found to cause oxidative stress, a loss in mitochondrial membrane potential, and changes in the ultrastructure of the mitochondria in LBC3 cells. Quantitative real-time PCR results showed that in LBC3 cells the mRNA levels of pro-apoptotic genes Bim, Bax, Puma, and Noxa were significantly upregulated. An increase in activity of caspase-9 in these cells was also observed. Moreover, the activation of SiNP-induced autophagy was demonstrated in LBC3 cells as shown by an increase in LC3-II/LC3-I ratio, the upregulation of Atg5 gene and an increase in AVOs-positive cells. In conclusion, this research provides novel information concerning molecular mechanisms of apoptosis and autophagy in LBC3 cells.

Interaction of hydroxyapatite nanoparticles with endothelial cells: internalization and inhibition of angiogenesis in vitro through the PI3K/Akt pathway

Nano-hydroxyapatite (nano-HAP) has been proposed as a better candidate for bone tissue engineering; however, the interactions of nano-HAP with endothelial cells are currently unclear. In this study, HAP nanoparticles (HANPs; 20 nm np20 and 80 nm np80) and micro-sized HAP particles (m-HAP; 12 μm) were employed to explore and characterize cellular internalization, subcellular distribution, effects of HANPs on endothelial cell function and underlying mechanisms using human umbilical vein endothelial cells (HUVECs) as an in vitro model. It was found that HANPs were able to accumulate in the cytoplasm, and both adhesion and uptake of the HANPs followed a function of time; compared to np80, more np20 had been uptaken at the end of the observation period. HANPs were mainly uptaken via clathrin- and caveolin-mediated endocytosis, while macropinocytosis was the main pathway for m-HAP uptake. Unexpectedly, exposure to HANPs suppressed the angiogenic ability of HUVECs in terms of cell viability, cell cycle, apoptosis response, migration and capillary-like tube formation. Strikingly, HANPs reduced the synthesis of nitric oxide (NO) in HUVECs, which was associated with the inhibition of phosphatidylinositol 3-kinase (PI3K) and phosphorylation of eNOS. These findings provide additional insights into specific biological responses as HANPs interface with endothelial cells.

Bisphosphonate-Functionalized Hydroxyapatite Nanoparticles for the Delivery of the Bromodomain Inhibitor JQ1 in the Treatment of Osteosarcoma

Osteosarcoma (OS) is one of the most common neoplasia among children, and its survival statistics have been stagnating since the combinatorial anticancer therapy triad was first introduced. Here, we report on the assessment of the effect of hydroxyapatite (HAp) nanoparticles loaded with medronate, the simplest bisphosphonate, as a bone-targeting agent and JQ1, a small-molecule bromodomain inhibitor, as a chemotherapeutic in different 2D and 3D K7M2 OS in vitro models. Both additives decreased the crystallinity of HAp, but the effect was more intense for medronate because of its higher affinity for HAp. As the result of PO₄^3--NH⁺ binding, JQ1 shielded the surface phosphates of HAp and pushed its surface charge to more positive values, exhibiting the opposite effect from calcium-blocking medronate. In contrast to the faster and more exponential release of JQ1 from monetite, its release from HAp nanoparticles followed a zero-order kinetics, but 98% of the payload was released after 48 h. The apoptotic effect of HAp nanoparticles loaded with JQ1, with medronate and with both JQ1 and medronate, was selective in 2D culture: pronounced against the OS cells and nonexistent against the healthy fibroblasts. While OS cell invasion was significantly inhibited by all of the JQ1-containing HAp formulations, that is, with and without medronate, all of the combinations of the targeting compound, medronate, and the chemotherapeutic, JQ1, delivered using HAp, but not HAp alone, inhibited OS cell migration from the tumor spheroids. JQ1 delivered using HAp had an effect on tumor migration, invasion, and apoptosis even at extremely low, subnanomolar concentrations, at which no effect of JQ1 per se was observed, meaning that this form of delivery could help achieve a multifold increase of this drug's efficacy. More than 80% of OS cells internalized JQ1-loaded HAp nanoparticles after 24 h of coincubation, suggesting that this augmentation of the activity of JQ1 may be due to the intracellular delivery and sustained release of the drug enabled by HAp. In addition to the reduction of the OS cell viability, the reduction of the migration and invasion radii was observed in OS tumor spheroids challenged with even JQ1-free medronate-functionalized HAp nanoparticles, demonstrating a definite anticancer activity of medronate alone when combined with HAp. The effect of medronate-functionalized JQ1-loaded HAp nanoparticles was most noticeable against OS cells differentiated into an osteoblastic lineage, in which case they surpassed in effect pure JQ1 and medronate-free compositions. The activity of JQ1 was mediated through increased Ezrin expression and decreased RUNX2 expression and was MYC and FOSL1 independent, but these patterns of gene expression changed in cells challenged with the nanoparticulate form of delivery, having been accompanied by the upregulation of RUNX2 and downregulation of Ezrin in OS cells treated with medronate-functionalized JQ1-loaded HAp nanoparticles.

Hydroxyapatite nanoparticle-induced mitochondrial energy metabolism impairment in liver cells: in vitro and in vivo studies

Hydroxyapatite nanoparticles (HAP-NPs) have been extensively developed as drug carriers, bone implants, coating materials, etc. in the human body. However, research focusing on the potential side effects of HAP-NPs on the mitochondria-associated energy metabolism in liver cells is lacking. In this study, HAP-NPs with a long diameter of 80 nm and a short diameter of 20 nm were evaluated for their ability to induce mitochondrial energy metabolism dysfunction in vitro and in vivo. In the in vitro system, the buffalo rat hepatocyte (BRL) cell line was directly exposed to the HAP-NPs. The results of these experiments showed that the HAP-NPs induced inhibition of mitochondrial dehydrogenase activity, which was accompanied by a decrease in the mitochondrial membrane potential (MMP). In addition, HAP-NPs elevated the hepatic levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and decreased the levels of GSH and SOD. These data indicated that HAP-NPs induced a lowered rate of electron transfer in the mitochondrial respiratory chain, accompanied by a decrease in the activity of the mitochondrial respiratory chain complexes I, II and III. Furthermore, HAP-NPs induced a decline in the enzymatic expression in the Krebs cycle. We also investigated the role of Kupffer cells (KCs, rat-derived) in the effects induced by the HAP-NPs. The supernatant from the HAP-NP-treated KCs was used to stimulate the BRL cells. We observed that the HAP-NPs had the ability to induce KC activation. The activation of KCs then led to the release of tumor necrosis factor-α (TNF-α), nitric oxide (NO) and reactive oxygen species (ROS), and induced the inhibition of mitochondrial respiratory chain complexes I, II and III in the BRL cells. In the in vivo study, the TEM examination revealed mitochondrial swelling and vacuolar degeneration in the HAP-NP-treated hepatocytes. In addition, the amount of succinate (Suc), an intermediate in the mitochondrial Krebs cycle, also declined in the ¹ H NMR spectroscopic measurements. Copyright © 2017 John Wiley & Sons, Ltd.

Cellular internalization of rod-like nano hydroxyapatite particles and their size and dose-dependent effects on pre-osteoblasts

We investigated the size/dose effects of n-HA on pre-osteoblasts, tracked the n-HA migration under TEM, and quantified extracellular and intracellular [Ca²⁺].

Investigation of luminescent mechanism: N-rich carbon dots as luminescence centers in fluorescent hydroxyapatite prepared using a typical hydrothermal process

N-Rich carbon dots (CDs) generated in the hydrothermal synthesis of HAp were trapped by growing HAp crystals to form fluorescent HAp materials.