Physico-chemical features of engineered nanoparticles relevant to their toxicity

Abstract

Nanotoxicology studies require investigations of several physico-chemical aspects of the particle/body fluid interaction, here described by reviewing recent literature in the light of new experimental data. Current characterization mostly covers morphology and metric-related characteristics (form, chemical composition, specific surface area, primary particle size and size distribution), and is mandatory in any experimental study. To unveil toxicity mechanisms, several other physico-chemical properties relevant to (geno) toxicity need to be assessed, typically the release or quenching of radical/ROS (Reactive Oxygen Species), the presence of active metal ions, evidence of structural defects. Major tasks for physical chemists working on nanoparticles-induced genotoxicity are described with some examples: (i), Tailored preparation of the same material in different sizes; (ii) particle modification changing a single property at a time; and (iii) identification of appropriate reference materials. Phenomena occurring during the contact between nanoparticles and cellular media or biological fluids (dispersion, agglomeration/aggregation, protein adsorption) are discussed in relation to the surface properties of the nanoparticles considered.     

Interactions of nanoparticles with plasma proteins: implication on clearance and toxicity of drug delivery systems

Introduction: Intravenously injected nanoparticles, like any other foreign pathogen that enters the body, encounter multiple lines of defense intended to neutralize and eliminate the invading substance. Adsorption of plasma proteins on the nanoparticle surface is the first barrier of defense, which could lead to physical changes in the formulation, such as aggregation and charge neutralization, biochemical activation of defense cascades, and trigger elimination by multiple types of phagocytic cell.

Areas covered: In this review, recent knowledge on the mechanisms that govern the interactions of nanoparticles (micelles, liposomes, polymeric and inorganic nanoparticles) with plasma proteins is discussed. In particular, the role of the nanoparticle surface properties and protective polymer coating in these interactions is described. The mechanisms of protein adsorption on different nanoparticles are analyzed and the implications on the clearance, toxicity and efficacy of drug delivery are discussed. The review provides readers with the biological insight into the plasma/blood interactions of nanoparticles.

Expert opinion: The immune recognition of nanoparticles can seriously affect the drug delivery efficacy and toxicity. There is at present not enough knowledge on the mechanisms that dictate the nanoparticle immune recognition and stability in the biological milieu. Understanding the mechanisms of recognition will become an important part of nanoparticle design.     

In vitro evaluation of cellular response induced by manufactured nanoparticles

"Nanoparticle" is defined as the particles whose diameter in at least one dimension is less than 100 nm. Compared with fine-particles, nanoparticles have large specific surface area. There is a dramatic increase over fine-particles in chemical and physical activities, such as ion release, adsorption ability, and ROS production. These properties are important for industrial use, and many nanoparticles are already used in products familiar to consumers as sunscreens and cosmetics. However, nanoparticle properties beneficial to the industry may also induce biological influences, including toxic activities. Recently, many investigations about the toxicology of nanoparticles have been reported. In the evaluation of nanoparticles toxicity, in vitro studies give us important information, especially in terms of toxic mechanisms. In vitro studies showed that some nanoparticles induce oxidative stress, apoptosis, production of cytokines, and cell death. There are reports that cellular influences of other nanoparticles are small. There are also reports of different results, some with low and some with high influences, for the same nanoparticle. One of the causes of this inconsistency might be a diremption of the living body influence study and the characterization study. Characterization of individual nanoparticles and their dispersions are essential for in vitro evaluation of their biological effects since each nanoparticle shows unique chemical and physical properties. Particularly, the aggregation state and metal ion release ability of nanoparticles affect its cellular influences. Reports concerning the characterization in the in vitro toxicity assessment are increasing. For an accurate risk assessment of nanoparticles, in this review, we outline recent studies of in vitro evaluation of cellular influences induced by nanoparticles. Moreover, we also introduce current studies about the characterization methods of nanoparticles and their dispersions for toxicological evaluation.     

Gold nanoparticles: the importance of physiological principles to devise strategies for targeted drug delivery

Nanotechnology and its promise for clinical translation to targeted drug delivery with limited accompanying toxicity provide exciting research opportunities that demand multidisciplinary approaches. To make rapid progress in the design of nano-platforms for drug delivery and toward their use in the clinic, basic and mechanistic studies must first be tested in vitro and then progress to in vivo studies in animal models, incorporating an understanding of body functioning. Recently, gold nanoparticles (Au NPs) have gained much attention as model drug delivery platforms because of their advantageous surface characteristics that allow easy functionalization with chemical and biological molecules and also due to their apparently low toxicity. In this study we review recent in vitro and in vivo research progress with Au NPs as drug delivery platforms and suggest experimental strategies for future studies for efficacious, targeted delivery.From the Clinical EditorThe role and significance of gold nanoparticles is discussed in this comprehensive review. Au NP-s are expected to become a clinically utilized drug delivery platform enabling easy functionalization and overall low toxicity.     

Biomimetic carbon nanotubes for neurological disease therapeutics as inherent medication

Nowadays, nanotechnology is revolutionizing the approaches to different fields from manufacture to health. Carbon nanotubes (CNTs) as promising candidates in nanomedicine have great potentials in developing novel entities for central nervous system pathologies, due to their excellent physicochemical properties and ability to interface with neurons and neuronal circuits. However, most of the studies mainly focused on the drug delivery and bioimaging applications of CNTs, while neglect their application prospects as therapeutic drugs themselves. At present, the relevant reviews are not available yet. Herein we summarized the latest advances on the biomedical and therapeutic applications of CNTs in vitro and in vivo for neurological diseases treatments as inherent therapeutic drugs. The biological mechanisms of CNTs-mediated bio-medical effects and potential toxicity of CNTs were also intensely discussed. It is expected that CNTs will exploit further neurological applications on disease therapy in the near future.     

The integrated biomarker response: a suitable tool to evaluate toxicity of metal-based nanoparticles

Nanotechnology is a much promising field of science and technology with applications in a wide range of areas such as electronics, biomedical applications, energy and cosmetics. Metal-based engineered nanoparticles (ENPs) are common in many technological applications; some of the most common nanoparticles available commercially are silver, gold, copper oxide (CuO), zinc oxide (ZnO) and cadmium sulphide (CdS). The toxicity of metal-based NPs may be either due to their specific physical characteristics as NPs or to the specific toxicity of metals released from NPs under environmental conditions. In this study we evaluated the toxicity effects of a range of ENPs (Ag, Au, CuO, CdS, ZnO) along with a control containing equivalent quantities of dissolved metal on two endobenthic species: the ragworm Hediste diversicolor and the bivalve Scrobicularia plana. A suite of complementary biomarkers was used to reveal toxicity effects. A common challenge in multibiomarkers studies is to go beyond an independent interpretation of each one, and to assess a global response of individuals. The Integrated Biomarker Response (IBR) was calculated for both species exposed to the different metal-based ENPs studied or to their dissolved metal counterpart to provide efficient and easy tools for environmental managers. We evidence that metal-based NPs lead to an overall difference in biological responses from that of their dissolved counterparts. The IBR could thus be considered as an efficient tool to transfer research results to stakeholders with possible implementation for regulatory purposes.     

Approach to using mechanism-based structure activity relationship (SAR) analysis to assess human health hazard potential of nanomaterials

With the increasing use and development of engineered nanoparticles in electronics, consumer products, pesticides, food and pharmaceutical industries, there is a growing concern about potential human health hazards of these materials. A number of studies have demonstrated that nanoparticle toxicity is extremely complex, and that the biological activity of nanoparticles will depend on a variety of physicochemical properties such as particle size, shape, agglomeration state, crystal structure, chemical composition, surface area and surface properties. Nanoparticle toxicity can be attributed to nonspecific interaction with biological structures due to their physical properties (e.g., size and shape) and biopersistence, or to specific interaction with biomolecules through their surface properties (e.g., surface chemistry and reactivity) or release of toxic ions. The toxic effects of most nanomaterials have not been adequately characterized and currently, there are many issues and challenges in toxicity testing and risk assessment of nanoparticles. Based on the possible mechanisms of action and available in vitro and in vivo toxicity database, this paper proposes an approach to using mechanism-based SAR analysis to assess the relative human health hazard/risk potential of various types of nanomaterials.     

Toxicity of single-walled carbon nanotubes

Carbon nanotubes (CNTs) are an important class of nanomaterials, which have numerous novel properties that make them useful in technology and industry. Generally, there are two types of CNTs: single-walled nanotubes (SWNTs) and multi-walled nanotubes. SWNTs, in particular, possess unique electrical, mechanical, and thermal properties, allowing for a wide range of applications in various fields, including the electronic, computer, aerospace, and biomedical industries. However, the use of SWNTs has come under scrutiny, not only due to their peculiar nanotoxicological profile, but also due to the forecasted increase in SWNT production in the near future. As such, the risk of human exposure is likely to be increased substantially. Yet, our understanding of the toxicological risk of SWNTs in human biology remains limited. This review seeks to examine representative data on the nanotoxicity of SWNTs by first considering how SWNTs are absorbed, distributed, accumulated and excreted in a biological system, and how SWNTs induce organ-specific toxicity in the body. The contradictory findings of numerous studies with regards to the potential hazards of SWNT exposure are discussed in this review. The possible mechanisms and molecular pathways associated with SWNT nanotoxicity in target organs and specific cell types are presented. We hope that this review will stimulate further research into the fundamental aspects of CNTs, especially the biological interactions which arise due to the unique intrinsic characteristics of CNTs.     

Nanoparticles: a review of particle toxicology following inhalation exposure

It is expected that the rapid expansion of nanotechnology will bring many potential benefits. However, initial investigations have demonstrated that nanomaterials may adversely affect human health and the environment. By increasing the application of nanoparticles, protection of the human respiratory system from exposure to airborne nanoparticles and ultrafine particulates has become an emerging health concern. Available research has demonstrated an association between exposure to ambient airborne particulates and ultrafine particles and various adverse heath effects including increased morbidity and mortality. Nanomaterial structures are more likely to be toxic than the same materials of conventional sized samples and can be inhaled more deeply into the lungs. While the respiratory tract is considered as the primary target organ for inhaled nanoparticles, recent research has demonstrated that extrapulmonary organs are also affected. The very small size distribution and large surface area of nanoparticles available to undergo reactions may play a significant role in nanotoxicity, yet very little is known about their interactions with biological systems. This review explores the possible underlying toxicity mechanisms of nanoparticles following inhalational exposure. Nanoparticles differ from the same conventional material at a larger scale in physical, chemical and biological characteristics; therefore it is critical to recognize the potential risk of nanoparticle exposure using appropriate toxicity test methods. Current advances and limitations of toxicity assessment methods of nanoparticles are discussed highlighting the recent improvements of in vitro screening tools for the safety evaluation of the rapidly expanding area of nanotechnology.     

Pulmonary toxicity and fibrogenic response of carbon nanotubes

Abstract

Carbon nanotubes (CNTs) have been a subject of intensive research for a wide range of applications. However, because of their extremely small size and light weight, CNTs are readily inhaled into human lungs resulting in increased rates of pulmonary disorders, most notably fibrosis. Several studies have demonstrated the fibrogenic effects of CNTs given their ability to translocate into the surrounding areas in the lung causing granulomatous lesions and interstitial and sub-pleural fibrosis. However, the mechanisms underlying the disease process remain obscure due to the lack of understanding of the cellular interactions and molecular targets involved. Interestingly, certain physicochemical properties of CNTs have been shown to affect their respiratory toxicity, thereby becoming significant determinants of fibrogenesis. CNT-induced fibrosis involves a multitude of cell types and is characterized by the early onset of inflammation, oxidative stress and accumulation of extracellular matrix. Increased reactive oxygen species activate various cytokine/growth factor signaling cascades resulting in increased expression of inflammatory and fibrotic genes. Profibrotic growth factors and cytokines contribute directly to fibroblast proliferation and collagen production. Given the role of multiple players during the pathogenesis of CNT-induced fibrosis, the objective of this review is to summarize the key findings and discuss major cellular and molecular events governing pulmonary fibrosis. We also discuss the physicochemical properties of CNTs and their effects on pulmonary toxicities as well as various biological factors contributing to the development of fibrosis.     

A review of exposure and toxicological aspects of carbon nanotubes,and as additives to fire retardants in polymers

Carbon nanotubes (CNTs) have attracted considerable interest due to their unique physical, chemical, optical and electrical properties opening avenues for a large number of industrial applications. They have shown potential as fire retardant additives in polymers, reducing heat release rate and increasing time to ignition in a number of polymers. Relevant work on the types, properties and applications has been reviewed particularly considering their application in fire situations. There are concerns over the health risks associated with CNTs and many papers have likened CNTs to the health problems associated with asbestos. There are contradictions relating to the toxicity of CNTs with some papers reporting that they are toxic while others state the opposite. Directly comparing various studies is difficult because CNTs come in many combinations of size, type, purity levels and source. CNTs can potentially be released from polymers during the combustion process where human exposure may occur. While this review has shed some light regarding issues relating to toxicity under different fire scenarios much more thorough work is needed to investigate toxicity of CNTs and their evolution from CNT–polymer nanocomposites in order to reach firm conclusions.     

Current major cancer targets for nanoparticle systems

This review presents some common features of nanoparticles - activity, toxicity and biological activity. Humans are exposed to tiny particles via dust storms, volcanic ash, and other natural processes and the body systems are well adapted to protect from these potentially harmful intruders. Technological advancement has also changed the character of particulate pollution, increasing the proportion of nanometer-sized particles - "nanoparticles" and expanding the variety of chemical compositions. Studies have shown a strong correlation between particulate air pollution levels, respiratory and cardiovascular diseases, various cancers, and mortality. Adverse effects of nanoparticles on human health depend on individual factors such as genetics and existing disease, as well as exposure, and nanoparticle chemistry, size, shape, agglomeration state, and electromagnetic properties. The key to understand the toxicity of nanoparticles is their size, smaller than cells and cellular organelles, which allows them to penetrate these basic biological structures, disrupting their normal function. Examples of toxic effects include tissue inflammation, and altered cellular redox balance toward oxidation, causing abnormal function or cell death. Some of these materials have desirable characteristics for industrial applications, as nanostructured materials often exhibit beneficial properties, from UV absorbance in sunscreen to oil-less lubrication of motors. In the sense of the huge surrounding positive and negative influence of known and unknown NP-impacts it seems very important to understand and forecast the processes in the body, due to the interaction between these two sides - organism. How nanoparticles can be used as drug delivery systems and imaging devices to increase the efficacy per dose of therapeutic or imaging contrast agents; how nanoparticles will be further developed to improve their functionality in cancer treatment and imaging? How reacts the immune system of the organism after introducing nanoparticles with the aim to defeat tumors? Here the aim was to discuss the right and wrong applications of NP and to answer to some of these questions. In the mean time there will appear much more investigations because of the important application of the NP not only as drug delivery systems, but as diagnostics as well.     

Integration of inflammation,fibrosis, and cancer induced by carbon nanotubes

Abstract

Carbon nanotubes (CNTs) are nanomaterials with unique physicochemical properties that are targets of great interest for industrial and commercial applications. Notwithstanding, some characteristics of CNTs are associated with adverse outcomes from exposure to pathogenic particulates, raising concerns over health risks in exposed workers and consumers. Indeed, certain forms of CNTs induce a range of harmful effects in laboratory animals, among which inflammation, fibrosis, and cancer are consistently observed for some CNTs. Inflammation, fibrosis, and malignancy are complex pathological processes that, in summation, underlie a major portion of human disease. Moreover, the functional interrelationship among them in disease pathogenesis has been increasingly recognized. The CNT-induced adverse effects resemble certain human disease conditions, such as pneumoconiosis, idiopathic pulmonary fibrosis (IPF), and mesothelioma, to some extent. Progress has been made in understanding CNT-induced pathologic conditions in recent years, demonstrating a close interconnection among inflammation, fibrosis, and cancer. Mechanistically, a number of mediators, signaling pathways, and cellular processes are identified as major mechanisms that underlie the interplay among inflammation, fibrosis, and malignancy, and serve as pathogenic bases for these disease conditions in CNT-exposed animals. These studies indicate that CNT-induced pathological effects, in particular, inflammation, fibrosis, and cancer, are mechanistically, and in some cases, causatively, interrelated. These findings generate new insights into CNT adverse effects and pathogenesis and provide new targets for exposure monitoring and drug development against inflammation, fibrosis, and cancer caused by inhaled nanomaterials.     

A critical review of the biological mechanisms underlying the in vivo and in vitro toxicity of carbon nanotubes: The contribution of physico-chemical characteristics

Abstract

This critical review of the available human health safety data, relating to carbon nanotubes (CNTs), was conducted in order to assess the risks associated with CNT exposure. Determining the toxicity related to CNT exploitation is of great relevance and importance due to the increased potential for human exposure to CNTs within occupational, environmental and consumer settings. When this information is combined with knowledge on the likely exposure levels of humans to CNTs, it will enable risk assessments to be conducted to assess the risks posed to human health. CNTs are a diverse group of materials and vary with regards to their wall number (single and multi-walled CNTs are evident), length, composition, and surface chemistry. The attributes of CNTs that were identified as being most likely to drive the observed toxicity have been considered, and include CNT length, metal content, tendency to aggregate/agglomerate and surface chemistry. Of particular importance, is the contribution of the fibre paradigm to CNT toxicity, whereby the length of CNTs appears to be critical to their toxic potential. Mechanistic processes that are critical to CNT toxicity will also be discussed, with the findings insinuating that CNTs can exert an oxidative response that stimulates inflammatory, genotoxic and cytotoxic consequences. Consequently, it may transpire that a common mechanism is responsible for driving CNT toxicity, despite the fact that CNTs are a diverse population of materials. The similarity of the structure of CNTs to that of asbestos has prompted concern surrounding the exposure of humans, and so the applicability of the fibre paradigm to CNTs will be evaluated. It is also necessary to determine the systemic availability of CNTs following exposure, to determine where potential targets of toxicity are, and to thereby direct in vitro investigations within the most appropriate target cells. CNTs are therefore a group of materials whose useful exploitable properties prompts their increased production and utilization within diverse applications, so that ensuring their safety is of vital importance.     

Toxicity of carboxylated carbon nanotubes in endothelial cells is attenuated by stimulation of the autophagic flux with the release of nanomaterial in autophagic vesicles

Carbon nanotubes (CNTs) exhibit a number of unique properties that make them attractive for various nanomedicine applications including their intravascular use. Therefore, the vascular toxicity of CNTs is a critical safety concern and methods of CNTs toxicity modulation are of great interest. Here, we report that carboxylated multiwalled carbon nanotubes (MWCNTs) induce a decrease in viability of cultured human umbilical vein endothelial cells (HUVECs) associated with the profound accumulation of autophagosomes. This autophagosome accumulation was mTOR kinase independent and was caused by blockade of the autophagic flux rather than by activation of autophagy. Stimulation of the autophagic flux with 1 nmol/L bafilomycin A1 attenuated the cytotoxicity of carboxylated MWCNTs in HUVECs and was associated with the extracellular release of the nanomaterial in autophagic microvesicles. Thus, pharmacological stimulation of the autophagic flux may represent a new method of cytoprotection against toxic effects of nanomaterials.From the Clinical EditorThis study investigates the mechanisms of toxicity of multiwalled carbon nanutubes on human endothelial cells, concluding that pharmacological stimulation of autophagic flux may represent a new method of cytoprotection against the toxic effects of these nanomaterials.     

A review on nanotoxicity and nanogenotoxicity of different shapes of nanomaterials

Nanomaterials (NMs) generally display fascinating physical and chemical properties that are not always present in bulk materials; therefore, any modification to their size, shape, or coating tends to cause significant changes in their chemical/physical and biological characteristics. The dramatic increase in efforts to use NMs renders the risk assessment of their toxicity highly crucial due to the possible health perils of this relatively uncharted territory. The different sizes and shapes of the nanoparticles are known to have an impact on organisms and an important place in clinical applications. The shape of nanoparticles, namely, whether they are rods, wires, or spheres, is a particularly critical parameter to affect cell uptake and site‐specific drug delivery, representing a significant factor in determining the potency and magnitude of the effect. This review, therefore, intends to offer a picture of research into the toxicity of different shapes (nanorods, nanowires, and nanospheres) of NMs to in vitro and in vivo models, presenting an in‐depth analysis of health risks associated with exposure to such nanostructures and benefits achieved by using certain model organisms in genotoxicity testing. Nanotoxicity experiments use various models and tests, such as cell cultures, cores, shells, and coating materials. This review article also attempts to raise awareness about practical applications of NMs in different shapes in biology, to evaluate their potential genotoxicity, and to suggest approaches to explain underlying mechanisms of their toxicity and genotoxicity depending on nanoparticle shape.     

Overcoming the stability,toxicity, and biodegradation challenges of tumor stimuli-responsive inorganic nanoparticles for delivery of cancer therapeutics

ABSTRACT

Introduction: Stimuli-responsive nanomaterials for cancer therapy have attracted much interest recently due to their potential for improving the current standard of care. Different types of inorganic nanoparticles are widely employed for the development of these strategies, but in some cases safety concerns hinder their clinical translation. This review aims to provide an overview of the challenges that inorganic nanoparticles face regarding their stability, toxicity, and biodegradability, as well as the strategies that have been proposed to overcome them.

Areas covered: The available information about the in vitro and in vivo biocompatibility, as well as the biodegradability of the following nanoparticles, is presented and discussed: superparamagnetic iron oxide nanoparticles, gold nanoparticles, graphene and mesoporous nanoparticles made of silicon or silicon oxide. The toxicology of inorganic nanoparticles is greatly affected by many physicochemical parameters, and their surface modification emerges as the main intervention to improve their biocompatibility and tailor their performance for specific biomedical applications.

Expert opinion: Even though many different studies have been performed regarding the biological behavior of inorganic nanoparticles, long-term in vivo data is still scarce, limiting our capacity to evaluate the proposed nanomaterials for clinical use. The role of biodegradability in different therapeutic contexts is also discussed.     

SILAC-based quantitative proteomics identifies size-dependent molecular mechanisms involved in silver nanoparticles-induced toxicity

Abstract

Silver nanoparticles are currently one of the most widely used metallic nanoparticles. Due to their antibacterial properties, they are applied in textiles, house-holds items, and medical devices, among many other products. Understanding the potential toxicity associated with silver nanoparticles and the differential effect that nanoparticles of different size might induce is crucial, due to the increasing human and environmental exposure to this type of nanoparticles. In this work, we explored the different biomolecular mechanisms underlying the toxicity of silver nanoparticles in a size-dependent manner. Quantitative proteomic analysis of hepatic cells exposed to 10 and 60?nm silver nanoparticles demonstrated the alteration of a different set of proteins depending on the particle size. We demonstrated that while 10?nm silver nanoparticles induce nucleolar stress and ribosome biogenesis halt, both types of nanoparticles induce DNA damage and oxidative stress but through different pathways. In addition, both types of nanoparticles also affected cell proliferation, disrupted the cell cycle and ultimately, induced apoptosis. The alteration of different cellular mechanisms in a size-dependent manner, have relevant implications not only from a toxicity point of view, but also for the potential applications of silver nanoparticles.     

Interactions of nanoparticles with plasma proteins: implication on clearance and toxicity of drug delivery systems

INTRODUCTION: Intravenously injected nanoparticles, like any other foreign pathogen that enters the body, encounter multiple lines of defense intended to neutralize and eliminate the invading substance. Adsorption of plasma proteins on the nanoparticle surface is the first barrier of defense, which could lead to physical changes in the formulation, such as aggregation and charge neutralization, biochemical activation of defense cascades, and trigger elimination by multiple types of phagocytic cell. AREAS COVERED: In this review, recent knowledge on the mechanisms that govern the interactions of nanoparticles (micelles, liposomes, polymeric and inorganic nanoparticles) with plasma proteins is discussed. In particular, the role of the nanoparticle surface properties and protective polymer coating in these interactions is described. The mechanisms of protein adsorption on different nanoparticles are analyzed and the implications on the clearance, toxicity and efficacy of drug delivery are discussed. The review provides readers with the biological insight into the plasma/blood interactions of nanoparticles. EXPERT OPINION: The immune recognition of nanoparticles can seriously affect the drug delivery efficacy and toxicity. There is at present not enough knowledge on the mechanisms that dictate the nanoparticle immune recognition and stability in the biological milieu. Understanding the mechanisms of recognition will become an important part of nanoparticle design.     

In situ quantification of diverse titanium dioxide nanoparticles unveils selective endoplasmic reticulum stress-dependent toxicity

Although titanium dioxide nanoparticles (TiO₂ NPs) have been extensively studied, their possible impact on health due to their specific properties supported by their size and geometry, remains to be fully characterized to support risk assessment. To further document NPs biological effects, we investigated the impact of TiO₂ NPs morphology on biological outcomes. To this end, TiO₂ NPs were synthesized as nanoneedles (NNs), titanate scrolled nanosheets (TNs), gel-sol-based isotropic nanoparticles (INPs) and tested for perturbation of cellular homeostasis (cellular ion content, cell proliferation, stress pathways) in three cell types and compared to the P25. We showed that TiO₂ NPs were internalized at various degrees and their toxicity depended on both titanium content and NPs shape, which impacted on intracellular calcium homeostasis thereby leading to endoplasmic reticulum stress. Finally, we showed that a minimal intracellular content of TiO₂ NPs was mandatory to induce toxicity enlightening once more the crucial notion of internalized dose threshold beside the well-recognized dose of exposure.