Quantum Dots Elicit Hepatotoxicity through Lysosome-Dependent Autophagy Activation and Reactive Oxygen Species Production

Photodynamic therapy of cancer using graphene nanomaterials

INTRODUCTION

High incidence and fatality rates of cancer remain a global challenge. The success of conventional treatment modalities is being questioned on account of adverse effects. Photodynamic therapy (PDT) is a potential alternative. It utilizes a combination of photosensitizer (PS), light and oxygen to target the tissues locally, thereby minimizing the damage to neighboring healthy tissues. Conventional PSs suffer from poor selectivity, high hydrophobicity and sub-optimal yield of active radicals. Graphene nanomaterials (GNs) exhibit interesting particulate and photophysical properties in the context of their use in PDT.

AREA COVERED

We focus on describing the mechanistic aspects of PDT-mediated elimination of cancer cells and the subsequent development of adaptive immunity. After covering up-to-date literature on the significant enhancement of PDT capability with GNs, we have discussed the probability of combining PDT with chemo-, immuno-, and photothermal therapy to make the treatment more effective.

EXPERT OPINION

GNs can be synthesized in various size ranges, and their biocompatibility can be improved through surface functionalization and doping. These can be used as PS to generate ROS or conjugated with other PS molecules for treating deep-seated tumors. With increasing evidence on biosafety, such materials offer hope as antitumor therapeutics.

All Roads Lead to Rome: Comparing Nanoparticle- and Small Molecule-Driven Cell Autophagy

Autophagy, vital for removing cellular waste, is triggered differently by small molecules and nanoparticles. Small molecules, like rapamycin, non-selectively activate autophagy by inhibiting the mTOR pathway, which is essential for cell regulation. This can clear damaged components but may cause cytotoxicity with prolonged use. Nanoparticles, however, induce autophagy, often causing oxidative stress, through broader cellular interactions and can lead to a targeted form known as "xenophagy." Their impact varies with their properties but can be harnessed therapeutically. In this review, the autophagy induced by nanoparticles is explored and small molecules across four dimensions: the mechanisms behind autophagy induction, the outcomes of such induction, the toxicological effects on cellular autophagy, and the therapeutic potential of employing autophagy triggered by nanoparticles or small molecules. Although small molecules and nanoparticles each induce autophagy through different pathways and lead to diverse effects, both represent invaluable tools in cell biology, nanomedicine, and drug discovery, offering unique insights and therapeutic opportunities.

Golm1 facilitates the CaO2-DOPC-DSPE200-PEI -CsPbBr3 QDs -induced apoptotic death of hepatocytes through the stimulation of mitochondrial autophagy and mitochondrial reactive oxygen species production through interactions with P53/Beclin-1/Bcl-2

Mitophagy is a distinct physiological process that can have beneficial or deleterious effects in particular tissues. Prior research suggests that mitophagic activity can be triggered by CaO2-PM-CsPbBr3 QDs, yet the specific role that mitophagy plays in hepatic injury induced by CaO2-PM-CsPbBr3 QDs has yet to be established. Accordingly, in this study a series of mouse model- and cell-based experiments were performed that revealed the ability of CaO2-PM-CsPbBr3 QDs to activate mitophagic activity. Golm1 was upregulated in response to CaO2-PM-CsPbBr3 QDs treatment, and overexpressing Golm1 induced autophagic flux in the murine liver and hepatocytes, whereas knocking down Golm1 had the opposite effect. CaO2-PM-CsPbBr3 QDs were also able to Golm1 expression, in turn promoting the degradation of P53 and decreasing the half-life of this protein. Overexpressing Golm1 was sufficient to suppress the apoptotic death of hepatocytes in vitro and in vivo, whereas the knockdown of Golm1 had the opposite effect. The ability of Golm1 to promote p53-mediated autophagy was found to be associated with the disruption of Beclin-1 binding to Bcl-2, and the Golm1 N-terminal domain was determined to be required for p53 interactions, inducing autophagic activity in a manner independent of helicase activity or RNA binding. Together, these results indicate that inhibiting Golm1 can promote p53-dependent autophagy via disrupting Beclin-1 binding to Bcl-2, highlighting a novel approach to mitigating liver injury induced by CaO2-PM-CsPbBr3 QDs.

Nanotherapeutics targeting autophagy regulation for improved cancer therapy

The clinical efficacy of current cancer therapies falls short, and there is a pressing demand to integrate new targets with conventional therapies. Autophagy, a highly conserved self-degradation process, has received considerable attention as an emerging therapeutic target for cancer. With the rapid development of nanomedicine, nanomaterials have been widely utilized in cancer therapy due to their unrivaled delivery performance. Hence, considering the potential benefits of integrating autophagy and nanotechnology in cancer therapy, we outline the latest advances in autophagy-based nanotherapeutics. Based on a brief background related to autophagy and nanotherapeutics and their impact on tumor progression, the feasibility of autophagy-based nanotherapeutics for cancer treatment is demonstrated. Further, emerging nanotherapeutics developed to modulate autophagy are reviewed from the perspective of cell signaling pathways, including modulation of the mammalian target of rapamycin (mTOR) pathway, autophagy-related (ATG) and its complex expression, reactive oxygen species (ROS) and mitophagy, interference with autophagosome-lysosome fusion, and inhibition of hypoxia-mediated autophagy. In addition, combination therapies in which nano-autophagy modulation is combined with chemotherapy, phototherapy, and immunotherapy are also described. Finally, the prospects and challenges of autophagy-based nanotherapeutics for efficient cancer treatment are envisioned.

ROS-mediated NRF2/p-ERK1/2 signaling-involved mitophagy contributes to macrophages activation induced by CdTe quantum dots

Cadmium telluride (CdTe) quantum dots (QDs) have garnered significant attention for tumor imaging due to their exceptional properties. However, there remains a need for further investigation into their potential toxicity mechanisms and corresponding enhancements. Herein, CdTe QDs were observed to accumulate in mouse liver, leading to a remarkable overproduction of IL-1β and IL-6. Additionally, there was evidence of macrophage infiltration and activation following exposure to 12.5 μmol/kg body weight of QDs. To elucidate the underlying mechanism of macrophage activation, CdTe QDs functionalized with 3-mercaptopropionic acid (MPA) were utilized. In vitro experiments revealed that 1.0 μM MPA-CdTe QDs activated PINK1-dependent mitophagy in RAW264.7 macrophages. Critically, the autophagic flux remained unimpeded, as demonstrated by the absence of p62 accumulation, LC3 turnover assay results, and successful fusion of autophagosomes with lysosomes. Mechanically, QDs increased reactive oxygen species (ROS) and mitoROS by damaging both mitochondria and lysosomes. ROS, in turn, inhibited NRF2, resulting in the phosphorylation of ERK1/2 and subsequent activation of mitophagy. Notably, 1.0 μM QDs disrupted lysosomes but autophagic flux was not impaired. Eventually, the involvement of the ROS-NRF2-ERK1/2 pathway-mediated mitophagy in the increase of IL-1β and IL-6 in macrophages was confirmed using Trolox, MitoTEMPO, ML385, specific siRNAs, and lentivirus-based interventions. This study innovatively revealed the pro-inflammatory rather than anti-inflammatory role of mitophagy in nanotoxicology, shedding new light on the mechanisms of mitochondrial disorders induced by QDs and identifying several molecular targets to comprehend the toxicological mechanisms of CdTe QDs.

Molecular mechanism of nanomaterials induced liver injury: A review

The unique physicochemical properties inherent to nanoscale materials have unveiled numerous potential applications, spanning beyond the pharmaceutical and medical sectors into various consumer industries like food and cosmetics. Consequently, humans encounter nanomaterials through diverse exposure routes, giving rise to potential health considerations. Noteworthy among these materials are silica and specific metallic nanoparticles, extensively utilized in consumer products, which have garnered substantial attention due to their propensity to accumulate and induce adverse effects in the liver. This review paper aims to provide an exhaustive examination of the molecular mechanisms underpinning nanomaterial-induced hepatotoxicity, drawing insights from both in vitro and in vivo studies. Primarily, the most frequently observed manifestations of toxicity following the exposure of cells or animal models to various nanomaterials involve the initiation of oxidative stress and inflammation. Additionally, we delve into the existing in vitro models employed for evaluating the hepatotoxic effects of nanomaterials, emphasizing the persistent endeavors to advance and bolster the reliability of these models for nanotoxicology research.

Autophagy regulation by inorganic, organic, and organic/inorganic hybrid nanoparticles: Organelle damage, regulation factors, and potential pathways

The rapid development of nanotechnology requires a more thorough understanding of the potential health effects caused by nanoparticles (NPs). As a programmed cell death, autophagy is one of the biological effects induced by NPs, which maintain intracellular homeostasis by degrading damaged organelles and removing aggregates of defective proteins through lysosomes. Currently, autophagy has been shown to be associated with the development of several diseases. A significant number of research have demonstrated that most NPs can regulate autophagy, and their regulation of autophagy is divided into induction and blockade. Studying the autophagy regulation by NPs will facilitate a more comprehensive understanding of the toxicity of NPs. In this review, we will illustrate the effects of different types of NPs on autophagy, including inorganic NPs, organic NPs, and organic/inorganic hybrid NPs. The potential mechanisms by which NPs regulate autophagy are highlighted, including organelle damage, oxidative stress, inducible factors, and multiple signaling pathways. In addition, we list the factors influencing NPs-regulated autophagy. This review may provide basic information for the safety assessment of NPs.

MPA-capped CdTequantum dots induces endoplasmic reticulum stress-mediated autophagy and apoptosis through generation of reactive oxygen species in human liver normal cell and liver tumor cell

The rapid developments in nanotechnology have brought increased attention to the safety of Quantum Dots (QDs). Exploring their mechanisms of toxicity and characterizing their toxic effects in different cell lines will help us better understand and apply QDs appropriately. This study aims to elucidate the importance of reactive oxygen species (ROS) and endoplasmic reticulum (ER) stress-induced autophagy for CdTe QDs toxicity, that is, the importance of the nanoparticles in mediating cellular uptake and consequent intracellular stress effects inside the cell. The results of the study showed that cancer cells and normal cells have different cell outcomes as a result of intracellular stress effects. In normal human liver cells (L02), CdTe QDs leads to ROS generation and prolong ER stress. The subsequent autophagosome accumulation eventually triggers apoptosis by activating proapoptotic signaling pathways and the expression of proapoptotic Bax. In contrast, in human liver cancer cells (HepG2 cells), expression of UPR restrains proapoptotic signaling and downregulates Bax, and activated protective cellular autophagy, as a result of protecting these liver cancer cells from CdTe QDs-induced apoptosis. In summary, we assess the safety of CdTe QDs and recounted the molecular mechanism underlying its nanotoxicity in normal and cancerous cells. Notwithstanding, additional detailed studies on the deleterious effects of these nanoparticles in the organisms of interest are required to ensure low-risk application.

Concentration-Dependent Cellular Uptake of Graphene Oxide Quantum Dots Promotes the Odontoblastic Differentiation of Dental Pulp Cells via the AMPK/mTOR Pathway

As zero-dimension nanoparticles, graphene oxide quantum dots (GOQDs) have broad potential for regulating cell proliferation and differentiation. However, such regulation of dental pulp cells (DPSCs) with different concentrations of GOQDs is insufficiently investigated, especially on the molecular mechanism. The purpose of this study was to explore the effect and molecular mechanism of GOQDs on the odontoblastic differentiation of DPSCs and to provide a theoretical basis for the repair of pulp vitality by pulp capping. CCK-8, immunofluorescence staining, alkaline phosphatase activity assay and staining, alizarin red staining, qRT-PCR, and western blotting were used to detect the proliferation and odontoblastic differentiation of DPSC coculturing with different concentrations of GOQDs. The results indicate that the cellular uptake of low concentration of GOQDs (0.1, 1, and 10 μg/mL) could promote the proliferation and odontoblastic differentiation of DPCSs. Compared with other concentration groups, 1 μg/mL GOQDs show better ability in such promotion. In addition, with the activation of the AMPK signaling pathway, the mTOR signaling pathway was inhibited in DPSCs after coculturing with GOQDs, which indicates that low concentrations of GOQDs could regulate the odontoblastic differentiation of DPSCs by the AMPK/mTOR signaling pathway.

Monitoring leaching of Cd2+ from cadmium-based quantum dots by an Cd aptamer fluorescence sensor

Quantum Dots (QDs) have been demonstrated with outstanding optical properties and thus been widely used in many biological and biomedical studies. However, previous studies have shown that QDs can cause cell toxicity, mainly attributable to the leached Cd2+. Therefore, identifying the leaching kinetics is very important to understand QD biosafety and cytotoxicity. Toward this goal, instrumental analyses such as inductively coupled plasma mass spectrometry (ICP-MS) have been used, which are time-consuming, costly and do not provide real-time or spatial information. To overcome these limitations, we report herein a fast and cost-effective fluorescence sensor based a Cd2+-specific aptamer for real-time monitoring the rapid leaching kinetics of QDs in vitro and in living cells. The sensor shows high specificity towards Cd2+ and is able to measure the Cd2+ leached either from water-dispersed CdTe QDs or two-layered CdSe/CdS QDs. The sensor is then used to study the stability of these two types of QDs under conditions to mimic cellular pH and temperature and the results from the sensor are similar to those obtained from ICP-MS. Finally, the sensor is able to monitor the leaching of Cd2+ from QDs in HeLa cells. The fluorescence aptamer sensor described in this study may find many applications as a tool for understanding biosafety of numerous other Cd-based QDs, including leaching kinetics and toxicity mechanisms in living systems.

CdTe quantum dots trigger oxidative stress and endoplasmic reticulum stress-induced apoptosis and autophagy in rat Schwann cell line RSC96

In the current study, the cytotoxicity and mechanisms of cadmium telluride quantum dots (CdTe QDs) on RSC96 cells were evaluated by exposing different doses of CdTe QDs for 24 h. Two types of cell death, including apoptosis and autophagy, as well as two important organelles, mitochondria and endoplasmic reticulum, were focused after CdTe QDs exposure. The results showed that CdTe QDs induced apoptosis in RSC96 cells in a concentration-dependent manner; promoted the accumulation of intracellular reactive oxygen species; decreased the mitochondrial membrane potential; caused the release of cytochrome c; and also increased the expression of Bcl-2 associated X protein, caspase-3, and cytochrome c proteins and decreased the expression of Bcl-2 protein. Further results also confirmed that CdTe QDs could be internalized by RSC96 cells, and the exposure and internalization of CdTe QDs could induce excessive endoplasmic reticulum stress in the cells, and the expression levels of binding immunoglobulin protein, C/EBP homologous protein, and caspase12 proteins were increased in a concentration-dependent manner. Moreover, autophagy-related proteins LC3II, Beclin1, and P62 all increased after CdTe QDs exposure, suggesting that CdTe QDs exposure both promoted autophagosome formation and inhibited autophagosome degradation, and that CdTe QDs affected the autophagic flow in RSC96 cells. In conclusion, CdTe QDs are able to cause apoptosis and autophagy in RSC96 cells through mitochondrial and endoplasmic reticulum stress pathways, and the possible neurotoxicity of CdTe QDs should be further investigated.

Intracellular reactive oxygen species trigger mitochondrial dysfunction and apoptosis in cadmium telluride quantum dots-induced liver damage

Quantum dots (QDs), also known as semiconductor QDs, have specific photoelectricproperties which find application in bioimaging, solar cells, and light-emitting diodes (LEDs). However, the application of QDs is often limited by issues related to health risks and potential toxicity. The purpose of this study was to provide evidence regarding the safety of cadmium telluride (CdTe) QDs by exploring the detailed mechanisms involved in its hepatotoxicity. This study showed that CdTe QDs can increase reactive oxygen species (ROS) in hepatocytes after being taken up by hepatocytes, which triggers a significant mitochondrial-dependent apoptotic pathway, leading to hepatocyte apoptosis. CdTe QDs-induce mitochondrial cristae abnormality, adenosine triphosphate (ATP) depletion, and mitochondrial membrane potential (MMP) depolarization. Meanwhile, CdTe QDs can change the morphology, function, and quantity of mitochondria by reducing fission and intimal fusion. Importantly, inhibition of ROS not only protects hepatocyte viability but can also interfere with apoptosis and activation of mitochondrial dysfunction. Similarly, the exposure of CdTe QDs in Institute of Cancer Research (ICR) mice showed that CdTe QDs caused oxidative damage and apoptosis in liver tissue. NAC could effectively remove excess ROS could reduce the level of oxidative stress and significantly alleviate CdTe QDs-induced hepatotoxicity in vivo. CdTe QDs-induced hepatotoxicity may originate from the generation of intracellular ROS, leading to mitochondrial dysfunction and apoptosis, which was potentially regulated by mitochondrial dynamics. This study revealed the nanobiological effects of CdTe QDs and the intricate mechanisms involved in its toxicity at the tissue, cell, and subcellular levels and provides information for narrowing the gap between in vitro and in vivo animal studies and a safety assessment of QDs.

Reactive oxygen species trigger NF-κB-mediated NLRP3 inflammasome activation involvement in low-dose CdTe QDs exposure-induced hepatotoxicity

Cadmium telluride (CdTe) quantum dots (QDs) can be employed as imaging and drug delivery tools; however, the toxic effects and mechanisms of low-dose exposure are unclear. Therefore, this pioneering study focused on hepatic macrophages (Kupffer cells, KCs) and explored the potential damage process induced by exposure to low-dose CdTe QDs. In vivo results showed that both 2.5 μM/kg·bw and 10 μM/kg·bw could both activate KCs to cause liver injury, and produce inflammation by disturbing antioxidant levels. Abnormal liver function further verified the risks of low-dose exposure to CdTe QDs. The KC model demonstrated that low-dose CdTe QDs (0 nM, 5 nM and 50 nM) can be absorbed by cells and cause severe reactive oxygen species (ROS) production, oxidative stress, and inflammation. Additionally, the expression of NF-κB, caspase-1, and NLRP3 were decreased after pretreatment with ROS scavenging agent N-acetylcysteine (NAC, 5 mM pretreated for 2 h) and the NF-κB nuclear translocation inhibitor Dehydroxymethylepoxyquinomicin (DHMEQ, 10 μg/mL pretreatment for 4 h) respectively. The results indicate that the activation of the NF-κB pathway by ROS not only directly promotes the expression of inflammatory factors such as pro-IL-1β, TNF-α, and IL-6, but also mediates the assembly of NLRP3 by ROS activation of NF-κB pathway, which indirectly promotes the expression of NLRP3. Finally, a high-degree of overlap between the expression of the NF-κB and NLRP3 and the activated regions of KCs, further support the importance of KCs in inflammation induced by low-dose CdTe QDs.

Cyclotriphosphazene-Based "Butterfly" Fluorescence Probe for Lysosome Targeting

A cyclotriphosphazene-based "butterfly" fluorescence probe HCCP-MNI bearing two naphthalimide and morpholine units were developed for lysosome targeting. The synthesized HCCP-MNI exhibited stable fluorescence signals and was cytocompatible in the given concentration range. Co-localization experimental results showed that cells treated with the HCCP-MNI and a commercial dye (Lyso-Tracker Red DND-99) had overlapped fluorescence signals, demonstrating its targeting specificity to lysosomes. The developed HCCP-MNI may be used for cell tracking applications associated with the functionalities of lysosomes.

Surface chemistry regulates the optical properties and cellular interactions of ultrasmall MoS2 quantum dots for biomedical applications

Molybdenum disulfide quantum dots (MoS2 QDs) have drawn increasing attention owing to their distinct optical properties and potential applications in many fields such as biosensing, photocatalysis and cell imaging. Elucidating the relationship between the surface chemistry of MoS2 QDs and their optical properties as well as biological behaviors is critical for their practical applications, which remain largely unclear. Herein, by adopting a sulfur vacancy modification strategy, a toolbox of MoS2 QDs functionalized with different thiolate ligands was prepared. The effect of surface chemistry on the optical properties of MoS2 QDs was systematically explored by various spectroscopic techniques, revealing the important role of surface ligands in defining their absorption band gap and luminescence quantum yield. Furthermore, cellular experiments showed that the cytotoxicity and intracellular fate (i.e., lysosomal accumulation) of MoS2 QDs are closely related to the properties of surface ligands. Our results underscore the important roles of surface ligands in regulating the properties and biological interactions of these QDs, which will facilitate the future development of MoS2-based materials with precisely controlled functions for biomedical applications.

Toxicity of different types of quantum dots to mammalian cells in vitro: An update review

Currently, there are a great quantity type of quantum dots (QDs) that has been developed by researchers. Depending on the core material, they can be roughly divided into cadmium, silver, indium, carbon and silicon QDs. And studies on the toxicity of QDs are also increasing rapidly, but in vivo tests in model animals fail to reach a consistent conclusion. Therefore, we review the literatures dealing with the cytotoxicity of QDs in mammalian cells in vitro. After a short summary of the application characteristics of five types of QDs, the fate of QDs in cells will be discussed, ranging from the uptake, transportation, sublocation and excretion. A substantial part of the review will be focused on in vitro toxicity, in which the type of QDs is combined with their adverse effect and toxic mechanism. Because of their different luminescent properties, different subcellular fate, and different degree of cytotoxicity, we provide an overview on the balance of optical stability and biocompatibility of QDs and give a short outlook on future direction of cytotoxicology of QDs.

Differences in toxicity, mitochondrial function and miRNome in human cells exposed in vitro to Cd as CdS quantum dots or ionic Cd

Cadmium is toxic to humans, although Cd-based quantum dots exerts less toxicity. Human hepatocellular carcinoma cells (HepG2) and macrophages (THP-1) were exposed to ionic Cd, Cd(II), and cadmium sulfide quantum dots (CdS QDs), and cell viability, cell integrity, Cd accumulation, mitochondrial function and miRNome profile were evaluated. Cell-type and Cd form-specific responses were found: CdS QDs affected cell viability more in HepG2 than in THP-1; respective IC₂₀ values were ∼3 and ∼50 μg ml^-1. In both cell types, Cd(II) exerted greater effects on viability. Mitochondrial membrane function in HepG2 cells was reduced 70 % with 40 μg ml^-1 CdS QDs but was totally inhibited by Cd(II) at corresponding amounts. In THP-1 cells, CdS QDs has less effect on mitochondrial function; 50 μg ml^-1 CdS QDs or equivalent Cd(II) caused 30 % reduction or total inhibition, respectively. The different in vitro effects of CdS QDs were unrelated to Cd uptake, which was greater in THP-1 cells. For both cell types, changes in the expression of miRNAs (miR-222, miR-181a, miR-142-3p, miR-15) were found with CdS QDs, which may be used as biomarkers of hazard nanomaterial exposure. The cell-specific miRNome profiles were indicative of a more conservative autophagic response in THP-1 and as apoptosis as in HepG2.

Therapeutic Nanoparticles and Their Targeted Delivery Applications

Nanotechnology offers many advantages in various fields of science. In this regard, nanoparticles are the essential building blocks of nanotechnology. Recent advances in nanotechnology have proven that nanoparticles acquire a great potential in medical applications. Formation of stable interactions with ligands, variability in size and shape, high carrier capacity, and convenience of binding of both hydrophilic and hydrophobic substances make nanoparticles favorable platforms for the target-specific and controlled delivery of micro- and macromolecules in disease therapy. Nanoparticles combined with the therapeutic agents overcome problems associated with conventional therapy; however, some issues like side effects and toxicity are still debated and should be well concerned before their utilization in biological systems. It is therefore important to understand the specific properties of therapeutic nanoparticles and their delivery strategies. Here, we provide an overview on the unique features of nanoparticles in the biological systems. We emphasize on the type of clinically used nanoparticles and their specificity for therapeutic applications, as well as on their current delivery strategies for specific diseases such as cancer, infectious, autoimmune, cardiovascular, neurodegenerative, ocular, and pulmonary diseases. Understanding of the characteristics of nanoparticles and their interactions with the biological environment will enable us to establish novel strategies for the treatment, prevention, and diagnosis in many diseases, particularly untreatable ones.

The Current Understanding of Autophagy in Nanomaterial Toxicity and Its Implementation in Safety Assessment-Related Alternative Testing Strategies

Nanotechnology has rapidly promoted the development of a new generation of industrial and commercial products; however, it has also raised some concerns about human health and safety. To evaluate the toxicity of the great diversity of nanomaterials (NMs) in the traditional manner, a tremendous number of safety assessments and a very large number of animals would be required. For this reason, it is necessary to consider the use of alternative testing strategies or methods that reduce, refine, or replace (3Rs) the use of animals for assessing the toxicity of NMs. Autophagy is considered an early indicator of NM interactions with cells and has been recently recognized as an important form of cell death in nanoparticle-induced toxicity. Impairment of autophagy is related to the accelerated pathogenesis of diseases. By using mechanism-based high-throughput screening in vitro, we can predict the NMs that may lead to the generation of disease outcomes in vivo. Thus, a tiered testing strategy is suggested that includes a set of standardized assays in relevant human cell lines followed by critical validation studies carried out in animals or whole organism models such as C. elegans (Caenorhabditis elegans), zebrafish (Danio rerio), and Drosophila (Drosophila melanogaster)for improved screening of NM safety. A thorough understanding of the mechanisms by which NMs perturb biological systems, including autophagy induction, is critical for a more comprehensive elucidation of nanotoxicity. A more profound understanding of toxicity mechanisms will also facilitate the development of prevention and intervention policies against adverse outcomes induced by NMs. The development of a tiered testing strategy for NM hazard assessment not only promotes a more widespread adoption of non-rodent or 3R principles but also makes nanotoxicology testing more ethical, relevant, and cost- and time-efficient.

Initiation of protective autophagy in hepatocytes by gold nanorod core/silver shell nanostructures

The high reactivity of silver nanoparticles leads to their broad applications in the anti-bacterial field; however, the safety of silver nanoparticles has attracted increasing public attention. After exposure to silver nanoparticles in vivo, the liver serves as their potential deposition site; however the potential biological effects of such nanoparticles on hepatocytes at low dosages are not well understood. Here, we study the interaction between gold nanorod core/silver shell nanostructures (Au@Ag NRs) and human hepatocytes, HepG2 cells, and determine that Au@Ag NRs at sub-lethal doses can induce autophagy. After uptake, Au@Ag NRs mainly localize in the lysosomes where they release silver ions and promote the production of reactive oxygen species (ROS). The ROS then suppress the AKT-mTOR signaling pathway and activate autophagy. In addition, oxidative stress results in lysosomal impairment, causing decreased ability for lysosomal digestion. Moreover, oxidative stress also affects the structure and function of mitochondria, leading to the initiation of protective autophagy to eliminate the damaged mitochondrion. Our study shows that at sub-lethal dosages, silver nanomaterials may alter the physiological functions of hepatic cells by activating protective autophagy and cause potential health risks, indicating that cautious consideration of the safety of nanomaterials for certain applications is necessary.

Crosstalk between Autophagy and Nanomaterials: Internalization, Activation, Termination

Nanomaterials (NMs) are comprehensively applied in biomedicine due to their unique physical and chemical properties. Autophagy, as an evolutionarily conserved cellular quality control process, is closely associated with the effect of NMs on cells. In this review, the recent advances in NM-induced/inhibited autophagy (NM-phagy) are summarized, with an aim to present a comprehensive description of the mechanisms of NM-phagy from the perspective of internalization, activation, and termination, thereby bridging autophagy and nanomaterials. Several possible mechanisms are extensively reviewed including the endocytosis pathway of NMs and the related cross components (clathrin and adaptor protein 2 (AP-2), adenosine diphosphate (ADP)-ribosylation factor 6 (Arf6), Rab, UV radiation resistance associated gene (UVRAG)), three main stress mechanisms (oxidative stress, damaged organelles stress, and toxicity stress), and several signal pathway-related molecules. The mechanistic insight is beneficial to understand the autophagic response to NMs or NMs' regulation of autophagy. The challenges currently encountered and research trend in the field of NM-phagy are also highlighted. It is hoped that the NM-phagy discussion in this review with the focus on the mechanistic aspects may serve as a guideline for future research in this field.

Advances in Nanomaterials for Brain Microscopy

Microscopic imaging of the brain continues to reveal details of its structure, connectivity, and function. To further improve our understanding of the emergent properties and functions of neural circuits, new methods are necessary to directly visualize the relationship between brain structure, neuron activity, and neurochemistry. Advances in engineering the chemical and optical properties of nanomaterials concurrent with developments in deep-tissue microscopy hold tremendous promise for overcoming the current challenges associated with in vivo brain imaging, particularly for imaging the brain through optically-dense brain tissue, skull, and scalp. To this end, developments in nanomaterials offer much promise toward implementing tunable chemical functionality for neurochemical targeting and sensing, and fluorescence stability for long-term imaging. In this review, we summarize current brain microscopy methods and describe the diverse classes of nanomaterials recently leveraged as contrast agents and functional probes for microscopic optical imaging of the brain.

Review of toxicological effect of quantum dots on the liver

In recent years, quantum dots (QDs) have potential applications in technology, research and medicine. The small particle size is coupled to their unique chemical and physical properties and their excellent fluorescence characteristics. A growing number of studies have shown that QDs are distributed to secondary organs through multiple pathways, while the liver is the main reservoir of QDs. Here, we review current liver toxicity studies of QDs in vivo and in vitro. Mechanisms of hepatotoxicity are discussed and the problem of extrapolating knowledge gained from cell-based studies into animal studies is highlighted. In this context, there still exists significant discrepancies between in vitro and in vivo results, and the specific toxicity mechanism remains unclear. The hepatotoxicities of QDs are the need for a unifying protocol for reliable and realistic toxicity reports.

Cytotoxicity studies of selected cadmium-based quantum dots on 2D vs. 3D cell cultures

In our work, the cytotoxicity of selected, cadmium-based quantum dots with various surface architectures was studied on 3D spheroids.