A new capacity of gut microbiota: Fermentation of engineered inorganic carbon nanomaterials into endogenous organic metabolites.

Carbon-based nanomaterials (CNMs) have recently been found in humans raising a great concern over their adverse roles in the hosts. However, our knowledge of the in vivo behavior and fate of CNMs, especially their biological processes elicited by the gut microbiota, remains poor. Here, we uncovered the integration of CNMs (single-walled carbon nanotubes and graphene oxide) into the endogenous carbon flow through degradation and fermentation, mediated by the gut microbiota of mice using isotope tracing and gene sequencing. As a newly available carbon source for the gut microbiota, microbial fermentation leads to the incorporation of inorganic carbon from the CNMs into organic butyrate through the pyruvate pathway. Furthermore, the butyrate-producing bacteria are identified to show a preference for the CNMs as their favorable source, and excessive butyrate derived from microbial CNMs fermentation further impacts on the function (proliferation and differentiation) of intestinal stem cells in mouse and intestinal organoid models. Collectively, our results unlock the unknown fermentation processes of CNMs in the gut of hosts and underscore an urgent need for assessing the transformation of CNMs and their health risk via the gut-centric physiological and anatomical pathways.

Oral administration of silver nanomaterials affects the gut microbiota and metabolic profile altering the secretion of 5-HT in mice.

Due to their excellent antibacterial ability, silver nanomaterials (Ag NMs) are the most frequently used nanomaterials. Their widespread use introduces the risk of human ingestion. However, the potential toxicity of Ag NMs to the gut microbiota and their metabolic profile are yet to be fully explored. In this study, we examined the effects of Ag NMs after oral administration (0.5 mg kg-1 and 2.5 mg kg-1, 14 and 28 days) on gut homeostasis by integrating tissue imaging, 16s rRNA gene sequencing and metabolomics techniques. We uncovered that silver nanoparticles (Ag NPs) and silver nanowires (Ag NWs) altered the structure (inhibiting the proliferation of Gram-negative bacteria) and decreased the diversity of gut microbiota in mice after short-term (14 days) exposure, while the microbial community tended to recover after long-term exposure (28 days), indicating that the resistance and resilience of the gut microbiome may pose a defense against the interference by reactive, exogenous nanomaterials. Interestingly, even though the gut microbiota structure recovered after 28 days of exposure, the gut metabolites significantly changed, showing increased 1H-indole-3-carboxylic acid and elevated levels of 5-HT in the gut and blood. Collectively, our results provide a piece of evidence on the association between the ingestion of exogenous nanoparticles and gut homeostasis, especially the metabolic profile of the host. This work thus provides additional insights for the continued investigation of the adverse effects of silver nanomaterials on biological hosts.

Peripheral nerves directly mediate the transneuronal translocation of silver nanomaterials from the gut to central nervous system.

The blood circulation is considered the only way for the orally administered nanoparticles to enter the central nervous systems (CNS), whereas non-blood route-mediated nanoparticle translocation between organs is poorly understood. Here, we show that peripheral nerve fibers act as direct conduits for silver nanomaterials (Ag NMs) translocation from the gut to the CNS in both mice and rhesus monkeys. After oral gavage, Ag NMs are significantly enriched in the brain and spinal cord of mice with particle state however do not efficiently enter the blood. Using truncal vagotomy and selective posterior rhizotomy, we unravel that the vagus and spinal nerves mediate the transneuronal translocation of Ag NMs from the gut to the brain and spinal cord, respectively. Single-cell mass cytometry analysis revealed that enterocytes and enteric nerve cells take up significant levels of Ag NMs for subsequent transfer to the connected peripheral nerves. Our findings demonstrate nanoparticle transfer along a previously undocumented gut-CNS axis mediated by peripheral nerves.

Carbon Nanotubes Promote the Development of Intestinal Organoids through Regulating Extracellular Matrix Viscoelasticity and Intracellular Energy Metabolism.

The biological effect of engineered carbon nanotubes (CNTs) as beneficial biomaterials on the intestine, especially on its development, remains unclear. Here, we investigated the profitable effect of CNTs with a different graphene layer and surface modification on the 3D model of intestinal organoids and demonstrated that CNTs (50 µg/mL) promoted the development of intestinal organoids over time (0-5 days). The mechanisms involve the modulation of extracellular matrix (ECM) viscoelasticity and intracellular energy metabolism. In particular, CNTs reduced the hardness of the extracellular matrix through decreasing the elasticity and increasing the viscosity as a result of elevated metalloproteinase and binding to a protein scaffold, which activated the mechanical membrane sensors of cells, Piezo, and downstream P-p38-yes-associated protein (YAP) pathway. Moreover, CNTs altered the metabolic profile of intestinal organoids and induced increased mitochondria activity, respiration, and nutrient absorption. These mechanisms cooperated with each other to promote the proliferation and differentiation of intestinal organoids. In addition, the promoted effect of CNTs is highly dependent on the number of graphene layers, manifested as multiwalled CNTs > single-walled CNTs. Our findings highlight the CNT-intestine interaction and imply the potential of CNTs as biomaterials for intestine-associated tissue engineering.

Cellular Uptake, Stability, and Safety of Hollow Carbon Sphere-Protected Fe3O4 Nanoparticles.

Magnetic iron oxide (Fe3O4) nanoparticles (NPs) have attracted extensive attentions in biomedical fields such as magnetic resonance imaging (MRI). However, the instability and unfavorable dispersity of bare Fe3O4 NPs is a challenge for biomedical applications. Herein, we proposed a strategy using hollow carbon sphere (HCS) as a shell structure to endow Fe3O4 NPs better stability, dispersity, as well as biocompatibility. To verify intracellular behaviors and biosafety of HCSdecorated Fe3O4 nanoparticles (Fe3O4@HCS NPs), the assessment of cellular effects of these NPs based on synchrotron radiation-based techniques were done to explore detailed interaction between Fe3O4@HCS NPs and liver cells, HepG2. We found that a large number of NPs were internalized by cells in a time-dependent manner determined by inductively coupled plasma mass spectrometry (ICP-MS), which was further supported by intracellular accumulation of iron via X-ray fluorescence (XRF) imaging. Moreover, confocal imaging showed that these NPs mainly located in the lysosomes where they remained stable and undissolved within 72 hours, which was verified by chemical form characterization of iron via Fe K-edge X-ray adsorption near edge structure (XANES). With the coating shell of HCS, the release of iron ions was prevented even in acidic lysosome and the integrity of lysosomal membrane remained unchanged during the storage of NPs. As a result, Fe3O4@HCS NPs exhibited low level of oxidative stress and induced negligible cytotoxicity towards HepG2 cells. Based on the powerful techniques, we demonstrated that the carbon outer layer provides a physical barrier that helps remain excellent properties of magnetic Fe3O4 NPs and good dispersity, chemical stability, as well as biocompatibility for potential applications in biomedical fields.

Immunological Responses Induced by Blood Protein Coronas on Two-Dimensional MoS2 Nanosheets.

Two-dimensional (2D) nanosheets (NSs) have a large surface area, high surface free energy, and ultrathin structure, which enable them to more easily penetrate biological membranes and promote adsorption of drugs and proteins. NSs are capable of adsorbing a large amount of blood proteins to form NSs-protein corona complexes; however, their inflammatory effects are still unknown. Therefore, we investigated the pro-inflammatory effect of 2D model nanosheet structures, molybdenum disulfide (MoS2), and the MoS2 NSs-protein complexes with four abundant proteins in human blood, i.e., human serum albumin (HSA), transferrin (Tf), fibrinogen (Fg), and immunoglobulin G (IgG). The interactions between the NSs and the proteins were analyzed by quantifying protein adsorption, determining binding affinity, and correlating structural changes in the protein corona with the uptake of NSs by macrophages and the subsequent inflammatory response. Although all of the NSs-protein complexes induced inflammation, IgG-coated and Fg-coated NSs triggered much stronger inflammatory effects by producing and releasing more cytokines. Among the four proteins, IgG possessed the highest proportion of ß-sheets and led to fewer secondary structure changes on the MoS2 nanosheets. This can facilitate uptake and produce a stronger pro-inflammatory response in macrophages due to the recognition of an NSs-IgG complex by Fc gamma receptors and the subsequent activation of the NF-κB pathways. Our results demonstrate that the blood protein components contribute to the inflammatory effects of nanosheets and provide important insights for the nanosafety evaluation and the rational design of nanomedicines in the future.

PEG-Detachable Polymeric Micelles Self-Assembled from Amphiphilic Copolymers for Tumor-Acidity-Triggered Drug Delivery and Controlled Release.

The development of an intelligent biomaterial system that can efficiently accumulate at the tumor site and release a drug in a controlled way is very important for cancer chemotherapy. PEG is widely selected as a hydrophilic shell to acquire prolonged circulation time and enhanced accumulation at the tumor site, but it also restrains the cellular transport and uptake and leads to insufficient therapeutic efficacy. In this work, a PEG-detachable pH-responsive polymer that forms micelles from copolymer cholesterol grafted poly(ethylene glycol) methyl ether- Dlabile-poly(ß-amino ester)- Dlabile-poly(ethylene glycol) methyl ether (MPEG- Dlabile-PAE- g-Chol) is developed to overcome the aforementioned challenges based on pH value changes among normal physiological, extracellular (pHe), and intracellular (pHi) environments. PEGylated doxorubicin (DOX)-loaded polymeric micelles (DOX-PMs) can accumulate at the tumor site via an enhanced permeability and retention effect, and the PEG shell is detachable induced by cleavage of the pHe-labile linker between the PEG segment and the main chain. Meanwhile, the pHi-sensitive poly(ß-amino ester) segment is protonated and has a high positive charge. The detachment of PEG and protonation of PAE facilitate cellular uptake of DOX-PMs by negatively charged tumor cells, along with the escape from endo-/lysosome due to the "proton-sponge" effect. The DOX molecules are controlled release from the carriers at specific pH values. The results demonstrate that DOX-PMs have the capability of showing high therapeutic efficacy and negligible cytotoxicity compared with free DOX in vitro and in vivo. Overall, we anticipate that this PEG-detachable and tumor-acidity-responsive polymeric micelle can mediate effective and biocompatible drug delivery "on demand" with clinical application potential.

Stability of Ligands on Nanoparticles Regulating the Integrity of Biological Membranes at the Nano-Lipid Interface.

When nanoparticles interact with cellular or organelle membranes, the coating ligands are known to affect the integrity of the membranes, which regulate cell death and inflammation. However, the molecular mechanisms of this modulation remain unresolved. Here, we use synchrotron X-ray liquid surface scattering and molecular dynamics simulations to study interface structures between phospholipids and gold nanorods (AuNRs) coated by surfactant and polyelectrolyte. These ligands are two types of widely used surface modification with different self-assembled structures and stabilities on the surface of nanoparticles. We reveal distinct mechanisms of the ligand stability in disrupting membrane integrity. We find that the cationic surfactant ligand cetyltrimethylammonium bromide detaches from the AuNRs and inserts into phospholipids, resulting in reduced membrane thickness by compressing the phospholipids to align with the shorter ligand. Conversely, the cationic polyelectrolyte ligand poly(diallyldimethylammonium chloride) is more stable on AuNRs; although it adsorbs onto the membrane, it does not cause much impairment. The distinct coating ligand interactions with phospholipids are further verified by cellular responses including impaired lysosomal membranes and triggered inflammatory effects in macrophages. Together, the quantitative analysis of interface structures elucidates key bio-nano interactions and highlights the importance of surface ligand stability for safety and rational design of nanoparticles.