Differential autophagic responses to nano-sized materials

The size-dependence and reversibility of polystyrene nanoplastics-induced lipid accumulation in mice: Possible roles of lysosomes

Nanoplastics (NPs) continue to accumulate in global aquatic and terrestrial systems, posing a potential threat to human health through the food chain and/or other pathways. Both in vivo and in vitro studies have confirmed that the liver is one of the main organs targeted for the accumulation of NPs in living organisms. However, whether exposure to NPs induces size-dependent disorders of liver lipid metabolism remains controversial, and the reversibility of NPs-induced hepatotoxicity is largely unknown. In this study, the effects of long-term exposure to environmentally relevant doses of polystyrene nanoplastics (PS-NPs) on lipid accumulation were investigated in terms of autophagy and lysosomal mechanisms. The findings indicated that hepatic lipid accumulation was more pronounced in mice exposed to 100 nm PS-NPs compared to 500 nm PS-NPs. This effect was effectively alleviated after 50 days of self-recovery for 100 nm and 500 nm PS-NPs exposure. Mechanistically, although PS-NPs exposure activated autophagosome formation through ERK (mitogen-activated protein kinase 1)/mTOR (mechanistic target of rapamycin kinase) signaling pathway, the inhibition of Rab7 (RAB7, member RAS oncogene family), CTSB (cathepsin B), and CTSD (cathepsin D) expression impaired lysosomal function, thereby blocking autophagic flux and contributing to hepatic lipid accumulation. After termination of PS-NPs exposure, lysosomal exocytosis was responsible for the clearance of PS-NPs accumulated in lysosomes. Furthermore, impaired lysosomal function and autophagic flux inhibition were effectively alleviated. This might be the main reason for the alleviation of PS-NPs-induced lipid accumulation after recovery. Collectively, we demonstrate for the first time that lysosomes play a dual role in the persistence and reversibility of hepatotoxicity induced by environmental relevant doses of NPs, which provide novel evidence for the prevention and intervention of liver injury associated with nanoplastics exposure.

Enzymatically Bioactive Nucleus Pulposus Matrix Hydrogel Microspheres for Exogenous Stem Cells Therapy and Endogenous Repair Strategy to Achieve Disc Regeneration

Exogenous stem cell therapy and endogenous repair has shown great potential in intervertebral disc regeneration. However, limited nutrients and accumulation of lactate largely impair the survival and regenerative capacity of implanted stem cells and endogenous nucleus pulposus cells (NPCs). Herein, an injectable hydrogel microsphere (LMGDNPs) have been developed by immersing lactate oxidase (LOX)-manganese dioxide (MnO2 ) nanozyme (LM) into glucose-enriched decellularized nucleus pulposus hydrogel microspheres (GDNPs) through a microfluidic system. LMGDNPs showed a delayed release profile of LOX and satisfactory enzymatic capacity in consuming lactate. Mesenchymal stem cells (MSCs) plated on LMGDNPs exhibited better cell viability than cells on GelMA and decellularized nucleus pulposus microspheres (DNP) and showed a obviously increased NPCs phenotype. LMGDNPs prevented MSCs and NPCs death and promoted extracellular matrix synthesis by exhausting lactate. It is determined that LMGDNPs promoted NPCs autophagy by activating transforming growth factor β2 overlapping transcript 1 (TGFB2-OT1), relying on the nanozyme. MSCs-loaded LMGDNPs largely preserved disc hydration and alleviated matrix degradation in vivo. Summarily, LMGDNPs promoted cell survival and matrix regeneration by providing a nutrient supply, exhausting lactate, and activating autophagy via TGFB2-OT1 and its downstream pathway and may serve as an ideal delivery system for exogenous stem cell therapy and endogenous repair.

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.

Biodegradable Antibacterial Bioorthogonal Polymeric Nanocatalysts Prepared by Flash Nanoprecipitation

Bioorthogonal activation of pro-dyes and prodrugs using transition-metal catalysts (TMCs) provides a promising strategy for imaging and therapeutic applications. TMCs can be loaded into polymeric nanoparticles through hydrophobic encapsulation to generate polymeric nanocatalysts with enhanced solubility and stability. However, biomedical use of these nanostructures faces challenges due to unwanted tissue accumulation of nonbiodegradable nanomaterials and cytotoxicity of heavy-metal catalysts. We report here the creation of fully biodegradable nanocatalysts based on an engineered FDA-approved polymer and the naturally existing catalyst hemin. Stable nanocatalysts were generated through kinetic stabilization using flash nanoprecipitation. The therapeutic potential of these nanocatalysts was demonstrated through effective treatment of bacterial biofilms through the bioorthogonal activation of a pro-antibiotic.

Perturbation of autophagy: An intrinsic toxicity mechanism of nanoparticles

Nanoparticles (NPs) have been widely used for various purposes due to their unique physicochemical properties. Such widespread applications greatly increase the possibility of human exposure to NPs in various ways. Once entering the human body, NPs may interfere with cellular homeostasis and thus affect the physiological system. As a result, it is necessary to evaluate the potential disturbance of NPs to multiple cell functions, including autophagy. Autophagy is an important cell function to maintain cellular homeostasis, and minimizing the disturbance caused by NP exposures to autophagy is critical to nanosafety. Herein, we summarized the recent research progress in nanotoxicity with particular focuses on the perturbation of NPs to cell autophagy. The basic processes of autophagy and complex relationships between autophagy and major human diseases were further discussed to emphasize the importance of keeping autophagy under control. Moreover, the most recent advances on perturbation of different types of NPs to autophagy were also reviewed. Last but not least, we also discussed major research challenges and potential coping strategies and proposed a safe-by-design strategy towards safer applications of NPs.

Size-dependent effects of polystyrene nanoplastics on autophagy response in human umbilical vein endothelial cells

Ubiquitous nanoplastics (NPs) increase exposure risks to humans through the food chain and/or other ways. However, huge knowledge gaps exist regarding the fate and adverse impact of NPs on the human cardiovascular system. Autophagy is an important catabolic pathway that disposes of cytoplasmic waste through the lysosomes. In this study, we pursued to determine the interaction and autophagy effect of polystyrene nanoplastics (PS-NPs) (100 and 500 nm in size) on human umbilical vein endothelial cells (HUVECs). The results showed both sizes of PS-NPs interacted with almost all the treated HUVECs in a time- and concentration-dependent manner, and 500 nm PS-NPs were only bound to the surface of cell membranes, whereas 100 nm PS-NPs were taken up by HUVECs and aggregated in the cytoplasm. Furthermore, exposure to 25 μg/mL of 500 nm PS-NPs for 48 h significantly increased lactate dehydrogenase release from HUVECs, while internalized 100 nm PS-NPs not only caused cell membrane damage, but also induced autophagy initiation and autophagosome formation. By a mCherry-GFP-LC3 lentivirus infection assay, we also demonstrated that autophagic flux level was impaired in response to 100 nm PS-NPs. Herein, our results provide new insight into the size-dependent internalization and autophagy response to PS-NPs in HUVECs.

An Updated Review on Implications of Autophagy and Apoptosis in Tumorigenesis: Possible Alterations in Autophagy through Engineered Nanomaterials and Their Importance in Cancer Therapy

Most commonly recognized as a catabolic pathway, autophagy is a perplexing mechanism through which a living cell can free itself of excess cytoplasmic components, i.e., organelles, by means of certain membranous vesicles or lysosomes filled with degrading enzymes. Upon exposure to external insult or internal stimuli, the cell might opt to activate such a pathway, through which it can gain control over the maintenance of intracellular components and thus sustain homeostasis by intercepting the formation of unnecessary structures or eliminating the already present dysfunctional or inutile organelles. Despite such appropriateness, autophagy might also be considered a frailty for the cell, as it has been said to have a rather complicated role in tumorigenesis. A merit in the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. In fact, several investigations on tumorigenesis have reported diminished levels of autophagic activity in tumor cells, which might result in transition to malignancy. On the contrary, autophagy has been suggested to be a seemingly favorable mechanism to progressed malignancies, as it contributes to survival of such cells. Based on the recent literature, this mechanism might also be activated upon the entry of engineered nanomaterials inside a cell, supposedly protecting the host from foreign materials. Accordingly, there is a good chance that therapeutic interventions for modulating autophagy in malignant cells using nanoparticles may sensitize cancerous cells to certain treatment modalities, e.g., radiotherapy. In this review, we will discuss the signaling pathways involved in autophagy and the significance of the mechanism itself in apoptosis and tumorigenesis while shedding light on possible alterations in autophagy through engineered nanomaterials and their potential therapeutic applications in cancer. SIGNIFICANCE STATEMENT: Autophagy has been said to have a complicated role in tumorigenesis. In the early stages of tumor formation, autophagy appears to be salutary because of its tumor-suppressing effects. On the contrary, autophagy has been suggested to be a favorable mechanism to progressed malignancies. This mechanism might be affected upon the entry of nanomaterials inside a cell. Accordingly, therapeutic interventions for modulating autophagy using nanoparticles may sensitize cancerous cells to certain therapies.

Manganese dioxide nanosheets induce mitochondrial toxicity in fish gill epithelial cells

The development and production of engineered 2D nanomaterials are expanding exponentially, increasing the risk of their release into the aquatic environment. A recent study showed 2D MnO2 nanosheets, under development for energy and biomedical applications, dissolve upon interaction with biological reducing agents, resulting in depletion of intracellular glutathione levels within fish gill cells. However, little is known concerning their toxicity and interactions with subcellular organelles. To address this gap, we examined cellular uptake, cytotoxicity and mitochondrial effects of 2D MnO2 nanosheets using an in vitro fish gill cell line to represent a target tissue of rainbow trout, a freshwater indicator species. The data demonstrate cellular uptake of MnO2 nanosheets into lysosomes and potential mechanisms of dissolution within the lysosomal compartment. MnO2 nanosheets induced severe mitochondrial dysfunction at sub-cytotoxic doses. Quantitative, single cell fluorescent imaging revealed mitochondrial fission and impaired mitochondrial membrane potential following MnO2 nanosheet exposure. Seahorse analyses for cellular respiration revealed that MnO2 nanosheets inhibited basal respiration, maximal respiration and the spare respiratory capacity of gill cells, indicating mitochondrial dysfunction and reduced cellular respiratory activity. MnO2 nanosheet exposure also inhibited ATP production, further supporting the suppression of mitochondrial function and cellular respiration. Together, these observations indicate that 2D MnO2 nanosheets impair the ability of gill cells to respond to energy demands or prolonged stress. Finally, our data demonstrate significant differences in the toxicity of the 2D MnO2 nanosheets and their microparticle counterparts. This exemplifies the importance of considering the unique physical characteristics of 2D nanomaterials when conducting safety assessments.

Reproductive toxicity of quantum dots on gonads of the fresh water crab Sinopotamon henanense

Since nano-quantum dots (QDs) are increasingly used as fluorescent dyes in biomedical sciences, the possibility of QDs contaminating aquatic environments is generally increasing. There is concern about potential toxicity of QDs. However, their risks in the aquatic environment are not entirely understood. In this study, the freshwater crab Sinopotamon henanense was exposed to cadmium telluride (CdTe) QDs by intraperitoneal injection to detect the reproductive toxicity of QDs (1/32, 1/16 and 1/4 LD₅₀; Crab was exposed for 1, 3, 5, and 7 days). After CdTe QD exposure, no significant effect was detected on the body weight and gonadosomatic index. Additionally, morphological observations showed tissue vacuolation in the testis, and inflammatory cell infiltration in the ovary. The submicroscopic structure showed that exposure to CdTe QDs damaged the organelles and cell structures of the gonads of S. henanense. Among the adverse effects, pathological changes in the nuclear membrane, mitochondria and lysosomes were particularly significant. Antioxidant enzymes responded differently to different doses of QDs. The 0.5-mg/kg dose induced superoxide dismutase activity in the testes. And in the 1-mg/kg and 4-mg/kg dose QD exposure test, the testis responded by activating glutathione peroxidase and inducing reduced glutathione and overconsuming glutathione peroxidase. Respectively, the ovaries responded by overconsuming superoxide dismutase and glutathione peroxidase and reduced glutathione. Thus, we conclude that the gonads of S. henanense were injured by CdTe QD, and male are better indicators of the toxicity of QDs than female crabs according to greater alterations in tissue structure and antioxidant enzyme in the analyses.

N-doped carbon dots triggered the induction of ROS-mediated cytoprotective autophagy in Hepa1-6 cells

Carbon dots (CDs) are an emerging fluorescent nano-imaging probe due to their unique characteristics, such as good conductivity, carbon-based chemical composition, and photochemical stability, which sets up the potential of outperforming the classic metal-based quantum dots (QDs). It is a timely effort to proactively investigate the biocompatibility feature of CDs with a view to safely utilize this emerging nanomaterial in biological systems. In this study, we assessed the safety profile of an in-house synthesized CDs in hepatocyte-like Hepa 1-6 cells, which represents an important target organ for CDs exposure through either particle uptake and/or accumulation and elimination from primary exposure sites post particle administration. We not only demonstrated a dose- and time-dependent compromised cell viability, but also observed the induction of autophagy at high concentration (i.e. 400 μg mL-1), authenticated by the conversion of microtubule-associated protein light chain 3 (LC3)-I to LC3-II. We attributed these changes as the protective mechanism by which the cells used to compensate for CDs-induced apoptosis and cytotoxicity. The involvement of autophagy was further confirmed because the cytotoxicity profile can be increased or reduced by the use of 3-MA (autophagy inhibitor) and NAC (ROS inhibitor), respectively. Collectively, our findings revealed dose-dependent moderate cytotoxicity in Hepa 1-6 cells. Mechanistic understanding of autophagy during the cellular process revealed the homeostasis when liver cells deal with CDs as an external insult.

TiO2 nanoparticles enhance the chemotherapeutic effects of 5-fluorouracil in human AGS gastric cancer cells via autophagy blockade

AIMS

Nanoparticles (NPs)-based drugs have been recently introduced to improve the efficacy of current therapeutic strategies for the treatment of cancer; however, the molecular mechanisms by which a NP interacts with cellular systems still need to be delineated. Here, we utilize the autophagic potential of TiO2 NPs for improving chemotherapeutic effects of 5-fluorouracil (5-FU) in human AGS gastric cells.

MATERIALS AND METHODS

Cell growth and viability were determined by trypan blue exclusion test and MTT assay, respectively. Vesicular organelles formation was evaluated by acridine orange staining of cells. Cell cycle and apoptosis were monitored by flow cytometry. Reactive oxygen species (ROS) level were measured by DCHF-DA staining. Autophagy was examined by q-PCR and western blotting. Molecular docking was used for studying NP interaction with autophagic proteins.

KEY FINDINGS

TiO2 NPs increase ROS production, impair lysosomal function and subsequently block autophagy flux in AGS cells. In addition, the autophagy blockade induced by non-toxic concentrations of TiO2 NPs (1 μg/ml) can promote cytotoxic and apoptotic effects of 5-FU in AGS cells.

SIGNIFICANCE

These results confirm the beneficial effects of TiO2 NPs in combination with chemotherapy in in vitro model of gastric cancer, which may pave the way to develop a possible solution to circumvent chemoresistance in cancer.

Differential effects of N-TiO2 nanoparticle and its photo-activated form on autophagy and necroptosis in human melanoma A375 cells

The manipulation of autophagy provides a new opportunity for highly effective anticancer therapies. Recently, we showed that photodynamic therapy (PDT) with nitrogen-doped titanium dioxide (N-TiO₂ ) nanoparticles (NPs) could promote the reactive oxygen species (ROS)-dependent autophagy in leukemia cells. However, the differential autophagic effects of N-TiO₂ NPs in the dark and light conditions and the potential of N-TiO_2- based PDT for the treatment of melanoma cells remain unknown. Here we show that depending on the visible-light condition, the autophagic response of human melanoma A375 cells to N-TiO₂ NPs switches between two different statuses (ie., flux or blockade) with the opposite outcomes (ie., survival or death). Mechanistically, low doses of N-TiO₂ NPs (1-100 µg/ml) stimulate a nontoxic autophagy flux response in A375 cells, whereas their photo-activation leads to the impairment of the autophagosome-lysosome fusion, the blockade of autophagy flux and consequently the induction of RIPK1-mediated necroptosis via ROS production. These results confirm that photo-controllable autophagic effects of N-TiO₂ NPs can be utilized for the treatment of cancer, particularly melanoma.

Near Infrared-Activated Dye-Linked ZnO Nanoparticles Release Reactive Oxygen Species for Potential Use in Photodynamic Therapy

Novel dye-linked zinc oxide nanoparticles (NPs) hold potential as photosensitizers for biomedical applications due to their excellent thermal- and photo-stability. The particles produced reactive oxygen species (ROS) upon irradiation with 850 nm near infrared (NIR) light in a concentration- and time-dependent manner. Upon irradiation, ROS detected in vitro in human umbilical vein endothelial cells (HUVEC) and human carcinoma MCF7 cells positively correlated with particle concentration and interestingly, ROS detected in MCF7 was higher than in HUVEC. Preferential cytotoxicity was also exhibited by the NPs as cell killing was higher in MCF7 than in HUVEC. In the absence of irradiation, dye-linked ZnO particles minimally affected the viability of cell (HUVEC) at low concentrations (<30 μg/mL), but viability significantly decreased at higher particle concentrations, suggesting a need for particle surface modification with poly (ethylene glycol) (PEG) for improved biocompatibility. The presence of PEG on particles after dialysis was indicated by an increase in size, an increase in zeta potential towards neutral, and spectroscopy results. Cell viability was improved in the absence of irradiation when cells were exposed to PEG-coated, dye-linked ZnO particles compared to non-surface modified particles. The present study shows that there is potential for biological application of dye-linked ZnO particles in photodynamic therapy.

Pro-Death or Pro-Survival: Contrasting Paradigms on Nanomaterial-Induced Autophagy and Exploitations for Cancer Therapy

Autophagy is a critical lysosome-mediated cellular degradation process for the clearance of damaged organelles, obsolete proteins, and invading pathogens and plays important roles in the pathogenesis and treatment of human diseases including cancer. While not a cell death process per se, autophagy is nevertheless intimately linked to a cell's live/die decision. Basal autophagy, operating constitutively at low levels in essentially every mammalian cell, is vital for maintaining cellular homeostasis and promotes cell survival. On the other hand, elevated level of autophagy is frequently observed in cells responding to a physical, chemical, or biological stress. This "induced" autophagy, a hallmark under a variety of pathological and pathophysiological conditions, may be either pro-death or pro-survival, two contrasting paradigms for cell fate determination. Research in our laboratory and other groups around the world over the last 15 years has revealed nanomaterials as a unique class of autophagy inducers, with the capability of elevating the cellular autophagy to extremely high levels. In this Account we focus on the contrasting cell fate decision impacted by nanomaterial-induced autophagy. First, we give a brief introduction to nanomaterial-induced autophagy and summarize our current understanding on how it affects a cell's live/die decision. Autophagy induced by nanomaterials, in most cases, promotes cell death, but a significant number of nanomaterials are also able to elicit pro-survival autophagy. Although not a common feature, some nanomaterials may induce pro-death autophagy in one cell type while eliciting pro-survival autophagy in a different cell type. The ability to control the level of the induced autophagy, and furthermore its pro-death/pro-survival nature, is critically important for nanomedicine. Second, we discuss several possible mechanistic insights on the pro-death/pro-survival decision for nanomaterial-induced autophagy. "Disrupted" autophagic processes, with a "block" or perhaps "diversion" at the various stages, may be a characteristic hallmark for nanomaterial-induced autophagy, rendering it intrinsically pro-death in nature. On the other hand, autophagy-mediated upregulation and activation of pro-survival factors or signaling pathways, overriding the intrinsic pro-death nature, may be a common mechanism for nanomaterial-induced pro-survival autophagy. In addition, cargo degradation and reactive oxygen species may also play important roles in the pro-death/pro-survival decision impacted by nanomaterial-induced autophagy. Finally, we focus on the situation where nanomaterials induce autophagy in cancer cells and summarize the different strategies in exploiting the pro-death or pro-survival nature of nanomaterial-induced autophagy to enhance the various modalities of cancer therapy, including direct cancer cell killing, chemotherapy and radiotherapy, photothermal therapy, and integrated diagnosis and therapy. While the details vary, the basic principle is simple and straightforward. If the induced autophagy is pro-death, maximize it. Otherwise, inhibit it. Effective exploitation of nanomaterial-induced autophagy has the potential to become a new weapon in our ever-increasing arsenal to fight cancer, particularly difficult-to-treat and drug-resistant cancer.

Aggregation Behavior of Nanoparticle-Peptide Systems Affects Autophagy

The aggregation of nanoparticle colloidal dispersions in complex biological environments changes the nanoparticle properties, such as size and surface area, thus affecting the interaction of nanoparticles at the interface with cellular components and systems. We investigated the effect of nanoparticle aggregation on autophagy, the main catabolic pathway that mediates degradation of nanosized materials and that is activated in response to internalization of foreign nanosized materials. We used carboxylated polystyrene nanoparticles (100 nm) and altered the nanoparticle aggregation behavior through addition of a multidomain peptide, thus generating a set of nanoparticle-peptide mixtures with variable aggregation properties. Specifically, modulating the peptide concentration resulted in nanoparticle-peptide mixtures that are well dispersed extracellularly but aggregate upon cellular internalization. We monitored the effect of internalization of nanoparticle-peptide mixtures on a comprehensive set of markers of the autophagy pathway, ranging from transcriptional regulation to clearance of autophagic substrates. The nanoparticle-peptide mixtures were found to activate the transcription factor EB, a master regulator of autophagy and lysosomal biogenesis. We also found that intracellular aggregation of nanoparticle colloidal dispersions causes blockage of autophagic flux. This study provides important insights on the effect of the aggregation properties of nanoparticles on cells and, particularly, on the main homeostatic pathway activated in response to nanoparticle internalization. These results also point to the need to control the colloidal stability of nanoparticle systems for a variety of biomedical applications.

Autophagy is a new protective mechanism against the cytotoxicity of platinum nanoparticles in human trophoblasts

Nanoparticles are widely used in commodities, and pregnant women are inevitably exposed to these particles. The placenta protects the growing fetus from foreign or toxic materials, and provides energy and oxygen. Here we report that autophagy, a cellular mechanism to maintain homeostasis, engulfs platinum nanoparticles (nPt) to reduce their cytotoxicity in trophoblasts. Autophagy was activated by nPt in extravillous trophoblast (EVT) cell lines, and EVT functions, such as invasion and vascular remodeling, and proliferation were inhibited by nPt. These inhibitory effects by nPt were augmented in autophagy-deficient cells. Regarding the dynamic state of nPt, analysis using ICP-MS demonstrated a higher accumulation of nPt in the autophagosome-rich than the cytoplasmic fraction in autophagy-normal cells. Meanwhile, there were more nPt in the nuclei of autophagy-deficient cells, resulting in greater DNA damage at a lower concentration of nPt. Thus, we found a new protective mechanism against the cytotoxicity of nPt in human trophoblasts.

Live-cell imaging of octaarginine-modified polymer dots via single particle tracking

OBJECTIVES

Nanocarriers can greatly enhance the cellular uptake of therapeutic agents to regulate cell proliferation and metabolism. Nevertheless, further application of nanocarriers is often limited by insufficient understanding of the mechanisms of their uptake and intracellular behaviour.

MATERIALS AND METHODS

Fluorescent polymer dots (Pdots) are coated with synthetic octaarginine peptides (R8) and are analysed for cellular uptake and intracellular transportation in HeLa cervical cancer cells via single particle tracking.

RESULTS

Surface modification with the R8 peptide efficiently improves both cellular uptake and endosomal escape of Pdots. With single particle tracking, we capture the dynamic process of internalization and intracellular trafficking of R8-Pdots, providing new insights into the mechanism of R8 in facilitating nanostructure-based cellular delivery. Furthermore, our results reveal R8-Pdots as a novel type of autophagy inducer.

CONCLUSIONS

This study provides new insights into R8-mediated cellular uptake and endosomal escape of nanocarriers. It potentiates biological applications of Pdots in targeted cell imaging, drug delivery and gene regulation.

Distinct autophagy-inducing abilities of similar-sized nanoparticles in cell culture and live C. elegans

Nanomaterial-induced autophagy has raised increasing concerns. A variety of nanomaterials, conventional or recently emerged, have the capability of inducing autophagy. As a consequence, it is becoming a popular belief that induction of autophagy is a common response of cells upon exposure to nanoscale materials. In order to clarify whether the "nanoscale" size is the determining factor for the nanomaterials to induce autophagy, we utilized in vitro cultured cells and an in vivo Caenorhabditis elegans (C. elegans) model to systemically investigate the autophagy-inducing ability of nanomaterials. We selected four types of representative nanomaterials with similar sizes, namely silicon nanoparticles (SiNPs), CdTe quantum dots (QDs), carbon dots (CDs) and gold nanoparticles (AuNPs). We demonstrated that, unlike most other nanomaterials tested, no autophagosome formation was detected in cultured cells or in live C. elegans with SiNP treatment. The expression of autophagy-related genes and the lipidation of LGG-1/LC3 in cells and C. elegans also remained unchanged after the treatment of SiNPs. In addition, the ability of the nanomaterials to induce autophagy appeared to correlate with those to incur subcellular organelle damage. Together, our studies demonstrate that SiNPs do not induce autophagy in vitro or in vivo in the selected model organisms and cell lines, thus clarifying that the "nanoscale" size is not the determining factor for the nanomaterials to induce autophagy. The results also suggest that the autophagy-inducing ability of most nanomaterials could be merely a reflection of their detrimental effect on cellular structures.

Designed Polymer Micelle for Clearing Amyloid Protein Aggregates via Up-Regulated Autophagy

Inhibiting protein aggregation under intra-/extracellular space and clearing protein aggregates from the brain are two critical issues for the treatment of various neurodegenerative diseases. Although a variety of anti-amyloidogenic chemicals/biochemicals have been identified for inhibiting such protein aggregation, clearing protein aggregates is a challenging issue. Here we report a designed biopolymer micelle of 15-30 nm hydrodynamic size that can clear protein aggregates from cells via an up-regulated autophagy process. The polymer has a polyaspartic acid backbone and is functionalized with fatty amine, arginine, and primary amine for inducing self-assembly, enhancing cell uptake, and up-regulating autophagy processes, respectively. The polymer micelle (PM) enters into the cell via lipid raft endocytosis, is transported to the perinuclear region where the protein oligomer/aggregate predominantly localizes, clears aggregated protein from the cell, and enhances the cell's survival against toxic protein aggregates. The designed PM may be used as a drug delivery carrier for anti-amyloidogenic drugs for enhanced efficacy in the treatment of neurodegenerative diseases.

Autophagic response to cellular exposure to titanium dioxide nanoparticles

Titanium dioxide is "generally regarded as safe" and titanium dioxide nanoparticles (TiO₂ NPs) are used in a wide variety of consumer products. Cellular exposure to TiO₂ NPs results in complex effects on cell physiology including induction of oxidative stress and impairment of lysosomal function, raising concerns about the impact of TiO₂ NPs on biological systems. We investigated the effects of TiO₂ NPs (15, 50, and 100 nm in diameter) on the lysosome-autophagy system, the main cellular catabolic pathway that mediates degradation of nanomaterials. Specifically, we monitored a comprehensive set of markers of the lysosome-autophagy system upon cell exposure to TiO₂ NPs, ranging from transcriptional activation of genes required for the formation of autophagic vesicles to clearance of autophagic substrates. This study reveals that uptake of TiO₂ NPs induces a response of the lysosome-autophagy system mediated by the transcription factor EB and consequent upregulation of the autophagic flux. Prolonged exposure to TiO₂ NPs, however, was found to induce lysosomal dysfunction and membrane permeabilization, leading to a blockage in autophagic flux. Results from this study will inform the design of TiO₂ NP based devices with specific autophagy-modulating properties.

Promoting the clearance of neurotoxic proteins in neurodegenerative disorders of ageing

Neurodegenerative disorders of ageing (NDAs) such as Alzheimer disease, Parkinson disease, frontotemporal dementia, Huntington disease and amyotrophic lateral sclerosis represent a major socio-economic challenge in view of their high prevalence yet poor treatment. They are often called 'proteinopathies' owing to the presence of misfolded and aggregated proteins that lose their physiological roles and acquire neurotoxic properties. One reason underlying the accumulation and spread of oligomeric forms of neurotoxic proteins is insufficient clearance by the autophagic-lysosomal network. Several other clearance pathways are also compromised in NDAs: chaperone-mediated autophagy, the ubiquitin-proteasome system, extracellular clearance by proteases and extrusion into the circulation via the blood-brain barrier and glymphatic system. This article focuses on emerging mechanisms for promoting the clearance of neurotoxic proteins, a strategy that may curtail the onset and slow the progression of NDAs.

TFEB-mediated activation of the lysosome-autophagy system affects the transduction efficiency of adeno-associated virus 2

Adeno-associated virus (AAV)-mediated gene transfer is an appealing therapeutic option due to AAV's safety profile. Effective delivery of AAV's genetic cargo to the nucleus, however, requires evasion of host cell barriers, including cellular clearance mechanisms mediated by the lysosome-autophagy system. We used AAV serotype 2 to monitor the autophagic response to cellular internalization of AAV and to characterize the effect of AAV-induced activation of autophagy on transgene expression. We found AAV2 internalization to induce activation of transcription factor EB, a master regulator of autophagy and lysosomal biogenesis, and upregulation of the lysosome-autophagy system. We showed that AAV2-induced activation of autophagy parallels a reduction in transgene expression, but also an increase in autophagic clearance of protein aggregates. These results can inform the design of AAV vectors with autophagy-modulating properties for applications ranging from the design of efficient gene delivery vectors to the treatment of diseases characterized by accumulation of autophagic cargo.

Oral application of carbon nanofibers in rats increases blood concentration of IL6 and IL10 and decreases locomotor activity

Carbon nanofibers (CNF) are versatile nanomaterials that are widely used in various fields of science and technology. As a consequence, animals as well as humans may be exposed to such compounds via different routes. We hypothesized that oral intake of CNF will lead to an inflammatory reaction and consequently induce behavioral impairments. To address this issue, rats were fed with 500mg/kgCNF for 14days and their locomotor activity, emotional status and cognition were quantified by testing the animals in an open field set-up, elevated plus maze and in the universal problem solving box which provides information about motivation and cognition. The behavioral tests were performed 3 times within 10days. At the end of the experiment, blood samples were collected and the plasma concentrations of IL-6, IL-8, IL-1β, IL-10 and IL-18 were measured. Our results demonstrated an inflammatory reaction determined by a significantly elevated IL-6 concentration. This, however, was counteracted by an even more pronounced increase in IL-10. The behavioral effects were restricted mainly to a decrease in locomotor activity which was significant in the open field test, as well as the elevated plus maze. Other parameters indicative of cognitive performance were not influenced and also the emotional status was largely unaffected. In conclusion, our results revealed that oral intake of 500mg/kgCNF induced some adverse effects, which, however, can be still partially compensated by the organism.

Plant Cell Wall-Penetrable, Redox-Responsive Silica Nanoprobe for the Imaging of Starvation-Induced Vesicle Trafficking

Autophagy is a self-protection process against reactive oxygen species (ROS). The intracellular level of ROS increased when cells were cultured under nutrient starvation. Antioxidants such as glutathione and ascorbic acid play an important role in ROS removal. However, the cellular redox state in the autophagic pathway is still unclear. Herein, we developed a new redox-sensitive probe with a disulfide-linked silica scaffold to enable the sensing of the reduction environment in cell organelles. This redox-responsive silica nanoprobe (ReSiN) could penetrate the plant cell wall and release fluorescent molecules in response to redox states. By applying the ReSiN to tobacco BY-2 cells and tracing the distribution of fluorescence, we found a higher reducing potential in the central vacuole than in the autolysosomes. Upon cysteine protease inhibitor (E64-c) treatment in sucrose-free medium, the disulfide-silica structures of the ReSiNs were broken down in the vacuoles but were not degraded and were accumulated in the autolysosomes. These results reveal the feasibility of our nanoprobe for monitoring the endocytic and macroautophagic pathways. These pathways merge upstream of the central vacuole, which is the final destination of both pathways. In addition, different redox potentials were observed in the autophagic pathway. Finally, the expression of the autophagy-related protein (Atg8) fused with green fluorescence protein confirmed that the ReSiN treatment itself did not induce the autophagic pathway under normal physiological conditions, indicating the versatility of this nanoprobe in studying stimuli-triggered autophagy-related trafficking.

Photodynamic N-TiO2 Nanoparticle Treatment Induces Controlled ROS-mediated Autophagy and Terminal Differentiation of Leukemia Cells

In this study, we used nitrogen-doped titanium dioxide (N-TiO₂) NPs in conjugation with visible light, and show that both reactive oxygen species (ROS) and autophagy are induced by this novel NP-based photodynamic therapy (PDT) system. While well-dispersed N-TiO₂ NPs (≤100 μg/ml) were inert, their photo-activation with visible light led to ROS-mediated autophagy in leukemia K562 cells and normal peripheral lymphocytes, and this increased in parallel with increasing NP concentrations and light doses. At a constant light energy (12 J/cm²), increasing N-TiO₂ NP concentrations increased ROS levels to trigger autophagy-dependent megakaryocytic terminal differentiation in K562 cells. By contrast, an ROS challenge induced by high N-TiO₂ NP concentrations led to autophagy-associated apoptotic cell death. Using chemical autophagy inhibitors (3-methyladenine and Bafilomycin A1), we confirmed that autophagy is required for both terminal differentiation and apoptosis induced by photo-activated N-TiO₂. Pre-incubation of leukemic cells with ROS scavengers muted the effect of N-TiO₂ NP-based PDT on cell fate, highlighting the upstream role of ROS in our system. In summary, PDT using N-TiO₂ NPs provides an effective method of priming autophagy by ROS induction. The capability of photo-activated N-TiO₂ NPs in obtaining desirable cellular outcomes represents a novel therapeutic strategy of cancer cells.

The role of hypoxia-inducible factor-1α in zinc oxide nanoparticle-induced nephrotoxicity in vitro and in vivo

Background

Zinc oxide nanoparticles (ZnO NPs) are used in an increasing number of products, including rubber manufacture, cosmetics, pigments, food additives, medicine, chemical fibers and electronics. However, the molecular mechanisms underlying ZnO NP nephrotoxicity remain unclear. In this study, we evaluated the potential toxicity of ZnO NPs in kidney cells in vitro and in vivo.

Results

We found that ZnO NPs were apparently engulfed by the HEK-293 human embryonic kidney cells and then induced reactive oxygen species (ROS) generation. Furthermore, exposure to ZnO NPs led to a reduction in cell viability and induction of apoptosis and autophagy. Interestingly, the ROS-induced hypoxia-inducible factor-1α (HIF-1α) signaling pathway was significantly increased following ZnO NPs exposure. Additionally, connective tissue growth factor (CTGF) and plasminogen activator inhibitor-1 (PAI-1), which are directly regulated by HIF-1 and are involved in the pathogenesis of kidney diseases, displayed significantly increased levels following ZnO NPs exposure in HEK-293 cells. HIF-1α knockdown resulted in significantly decreased levels of autophagy and increased cytotoxicity. Therefore, our results suggest that HIF-1α may have a protective role in adaptation to the toxicity of ZnO NPs in kidney cells. In an animal study, fluorescent ZnO NPs were clearly observed in the liver, lungs, kidneys, spleen and heart. ZnO NPs caused histopathological lesions in the kidney and increase in serum creatinine and blood urea nitrogen (BUN) which indicate possible renal possible damage. Moreover, ZnO NPs enhanced the HIF-1α signaling pathway, apoptosis and autophagy in mouse kidney tissues.

Conclusions

ZnO NPs may cause nephrotoxicity, and the results demonstrate the importance of considering the toxicological hazards of ZnO NP production and application, especially for medicinal use.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0163-3) contains supplementary material, which is available to authorized users.

Influence of multi-walled carbon nanotubes on the cognitive abilities of Wistar rats

Studies of the neurobehavioral effects of carbon nanomaterials, particularly those of multi-walled carbon nanotubes (MWCNTs), have concentrated on cognitive effects, but data are scarce. The aim of this study was to assess the influence of MWCNTs on a number of higher nervous system functions of Wistar rats. For a period of 10 days, two experimental groups were fed with MWCNTs of different diameters (MWCNT-1 group, 8-10 nm; MWCNT-2 group, 18-20 nm) once a day at a dosage of 500 mg/kg. In the open-field test, reductions of integral indications of researching activity were observed for the two MWCNT-treated groups, with a parallel significant (P<0.01) increase in stress levels for these groups compared with the untreated control group. In the elevated plus-maze test, integral indices of researching activity in the MWCNT-1 and MWCNT-2 groups reduced by day 10 by 51 and 62%, respectively, while rat stress levels remained relatively unchanged. In the universal problem solving box test, reductions in motivation and energy indices of researching activity were observed in the two experimental groups. Searching activity in the MWCNT-1 group by day 3 was reduced by 50% (P<0.01) and in the MWCNT-2 group the relevant reduction reached 11.2%. By day 10, the reduction compared with controls, was 64% (P<0.01) and 58% (P<0.01) for the MWCNT-1 and MWCNT-2 groups, respectively. In conclusion, a series of specific tests demonstrated that MWCNT-treated rats experienced a significant reduction of some of their cognitive abilities, a disturbing and worrying finding, taking into consideration the continuing and accelerating use of carbon nanotubes in medicine and science.