Kunal Bhattacharya

Mechanisms of carbon nanotube-induced toxicity: focus on pulmonary inflammation.

Carbon nanotubes have gained tremendous interest in a wide range of applications due to their unique physical, chemical, and electronic properties. Needless to say, close attention to the potential toxicity of carbon nanotubes is of paramount importance. Numerous studies have linked exposure of carbon nanotubes to the induction of inflammation, a complex protective response to harmful stimuli including pathogens, damaged or dying cells, and other irritants. However, inflammation is a double-edged sword as chronic inflammation can lead to destruction of tissues thus compromising the homeostasis of the organism. Here, we provide an overview of the process of inflammation, the key cells and the soluble mediators involved, and discuss research on carbon nanotubes and inflammation, including recent studies on the activation of the so-called inflammasome complex in macrophages resulting in secretion of pro-inflammatory cytokines. Moreover, recent work has shown that inflammatory cells i.e. neutrophils and eosinophils are capable of enzymatic degradation of carbon nanotubes, with mitigation of the pro-inflammatory and pro-fibrotic effects of nanotubes thus underscoring that inflammation is both good and bad.

Extracellular entrapment and degradation of single-walled carbon nanotubes

Neutrophils extrude neutrophil extracellular traps (NETs) consisting of a network of chromatin decorated with antimicrobial proteins to enable non-phagocytic killing of microorganisms. Here, utilizing a model of ex vivo activated human neutrophils, we present evidence of entrapment and degradation of carboxylated single-walled carbon nanotubes (SWCNTs) in NETs. The degradation of SWCNTs was catalyzed by myeloperoxidase (MPO) present in purified NETs and the reaction was facilitated by the addition of H2O2 and NaBr. These results show that SWCNTs can undergo acellular, MPO-mediated biodegradation and imply that the immune system may deploy similar strategies to rid the body of offending microorganisms and engineered nanomaterials.

Reactive Oxygen Species Mediated DNA Damage In Human Lung Alveolar Epithelial (A549) Cells From Exposure To Non-Cytotoxic MFI-Type Zeolite Nanoparticles

Increasing utilization of engineered nanoparticles in the field of electronics and biomedical applications demands an assessment of risk associated with deliberate or accidental exposure. Metal based nanoparticles are potentially most important of all the nanoparticles in terms of health risks. Microporous alumino-silicates and pure silicates named as zeolites and zeo-type materials with variety of structures, chemical compositions, particle sizes and morphologies have a significant number of industrial uses such as in catalysis, sorption and ion-exchange processes. In particular, the nanosized particles due to their unique properties are used in hybrid organic-inorganic materials for photography, photonics, electronics, labeling, imaging, and sensing. The aim of the current study is to investigate pure silica MFI-type zeolites nanoparticles with sizes of 50nm and 100nm (samples MFI-50 and MFI-100) under suspended conditions and their toxicological effects on human lung alveolar (A549) cells under in vitro conditions. Live cell imaging showed that the nanoparticles precipitated from the colloidal suspension of cell culture media as large agglomerates, coming in contact with the cell surface through sedimentation. A cellular proliferative capacity test showed the zeolite nanoparticles to exhibit no significant cytotoxicity below a concentration of 100μg/ml. However, both the MFI-50 and MFI-100 nanoparticles induced high intracellular reactive oxygen species (ROS) generation and elevated mitochondrial membrane potential in the A549 cells over the measured time period of 12h and at concentrations up to ≤50μg/ml. DNA fragmentation analysis using the comet assay showed that the MFI-50 and MFI-100 nanoparticles cause genotoxicity in a concentration dependent manner. Furthermore, the rate at which maximum genomic damage was caused by MFI-100 nanoparticles in the A549 cells was found to be high as compared to the MFI-50 nanoparticles. However, the damage caused by the MFI-50 nanoparticles was found to accumulate over a longer period of time as compared to MFI-100 nanoparticles. The study therefore points towards the capability of the non-cytotoxic zeolite nanoparticles to induce oxidative stress resulting in short-term altered cellular metabolism up-regulation and genomic instability. Although the damage was found to be short-lived, its persistence over longer durations, or stabilization cannot be neglected. Further studies are in progress to yield a better understanding of the mechanisms for oxidative stress and resulting cascade of events leading to genetic damage in the human lung alveolar epithelial cells following exposure to zeolite nanoparticles of different sizes.

Keeping it real: The importance of material characterization in nanotoxicology

Nanomaterials are small and the small size and corresponding large surface area of nanomaterials confers specific properties, making these materials desirable for various applications, not least in medicine. However, it is pertinent to ask whether size is the only property that matters for the desirable or detrimental effects of nanomaterials? Indeed, it is important to know not only what the material looks like, but also what it is made of, as well as how the material interacts with its biological surroundings. It has been suggested that guidelines should be implemented on the types of information required in terms of physicochemical characterization of nanomaterials for toxicological studies in order to improve the quality and relevance of the published results. This is certainly a key issue, but it is important to keep in mind that material characterization should be fit-for-purpose, that is, the information gathered should be relevant for the end-points being studied.

Dual effects of β-cyclodextrin-stabilised silver nanoparticles: enhanced biofilm inhibition and reduced cytotoxicity

The composition and mode of synthesis of nanoparticles (NPs) can affect interaction with bacterial and human cells differently. The present work describes the ability of β-cyclodextrin (β-CD) capped silver nanoparticles (AgNPs) to inhibit biofilm growth and reduce cytotoxicity. Biofilm formation of Staphylococcus epidermidis CSF 41498 was quantified by a crystal violet assay in the presence of native and capped AgNPs (Ag-10CD and Ag-20CD), and the morphology of the biofilm was observed by scanning electron microscope. The cytotoxicity of the AgNPs against HaCat cells was determined by measuring the increase in intracellular reactive oxygen species and change in mitochondrial membrane potential (ΔΨm). Results indicated that capping AgNPs with β-CD improved their efficacy against S. epidermidis CSF 41498, reduced biofilm formation and their cytotoxicity. The study concluded that β-CD is an effective capping and stabilising agent that reduces toxicity of AgNPs against the mammalian cell while enhancing their antibiofilm activity.

Single-Walled Carbon Nanotubes Inhibit the Cytochrome P450 Enzyme, CYP3A4

We report a detailed computational and experimental study of the interaction of single-walled carbon nanotubes (SWCNTs) with the drug-metabolizing cytochrome P450 enzyme, CYP3A4. Dose-dependent inhibition of CYP3A4-mediated conversion of the model compound, testosterone, to its major metabolite, 6β-hydroxy testosterone was noted. Evidence for a direct interaction between SWCNTs and CYP3A4 was also provided. The inhibition of enzyme activity was alleviated when SWCNTs were pre-coated with bovine serum albumin. Furthermore, covalent functionalization of SWCNTs with polyethylene glycol (PEG) chains mitigated the inhibition of CYP3A4 enzymatic activity. Molecular dynamics simulations suggested that inhibition of the catalytic activity of CYP3A4 is mainly due to blocking of the exit channel for substrates/products through a complex binding mechanism. This work suggests that SWCNTs could interfere with metabolism of drugs and other xenobiotics and provides a molecular mechanism for this toxicity. Our study also suggests means to reduce this toxicity, eg., by surface modification.

Nanodrugs to target articular cartilage: An emerging platform for osteoarthritis therapy

UNLABELLED Cartilage undergoes drastic structural changes during the development of osteoarthritis and cannot heal itself due to a defective chondrocyte response. Thus, much effort has been invested in the development of disease modifying drugs able to block key mediators within the cartilage matrix and biochemical pathways inside chondrocytes. However, the delivery of therapeutic agents into cartilage is ineffective. This has led to the use of cartilage-targeted nanodrugs to accumulate therapeutic agents into specific cartilage sub-compartments. This review will describe the nanodrugs targeted to specific components of cartilage matrix to generate drug reservoirs within the cartilage. The nanodrugs used as chondrocyte-specific gene delivery systems are also described. Although the use of cartilage-targeted nanodrugs in osteoarthritis is still in its infancy, these studies lay the foundation for the development of novel approaches for preventing the progression of cartilage breakdown and improving the quality of life of patients with osteoarthritis. FROM THE CLINICAL EDITOR Osteoarthritis is a degeneration of joint cartilage, which affects a large number of aging people. Current therapy for disease modification is often suboptimal. Recent research in nanomedicine has led to the design and use of nanodrugs with the aim to help reverse the disease process. In this comprehensive review, the authors described and discussed various nanodrugs in the hope that newer drugs could be discovered in the future.

Skeletal Mineralization Deficits and Impaired Biogenesis and Function of Chondrocyte‐Derived Matrix Vesicles in Phospho1–/– and Phospho1/Pit1 Double‐Knockout Mice

We have previously shown that ablation of either the Phospho1 or Alpl gene, encoding PHOSPHO1 and tissue‐nonspecific alkaline phosphatase (TNAP) respectively, lead to hyperosteoidosis, but that their chondrocyte‐derived and osteoblast‐derived matrix vesicles (MVs) are able to initiate mineralization. In contrast, the double ablation of Phospho1 and Alpl completely abolish initiation and progression of skeletal mineralization. We argued that MVs initiate mineralization by a dual mechanism: PHOSPHO1‐mediated intravesicular generation of inorganic phosphate (Pi) and phosphate transporter‐mediated influx of Pi. To test this hypothesis, we generated mice with col2a1‐driven Cre‐mediated ablation of Slc20a1, hereafter referred to as Pit1, alone or in combination with a Phospho1 gene deletion. Pit1col2/col2 mice did not show any major phenotypic abnormalities, whereas severe skeletal deformities were observed in the [Phospho1–/–; Pit1col2/col2] double knockout mice that were more pronounced than those observed in the Phospho1–/– mice. Histological analysis of [Phospho1–/–; Pit1col2/col2] bones showed growth plate abnormalities with a shorter hypertrophic chondrocyte zone and extensive hyperosteoidosis. The [Phospho1–/–; Pit1col2/col2] skeleton displayed significant decreases in BV/TV%, trabecular number, and bone mineral density, as well as decreased stiffness, decreased strength, and increased postyield deflection compared to Phospho1–/– mice. Using atomic force microscopy we found that ∼80% of [Phospho1–/–; Pit1col2/col2] MVs were devoid of mineral in comparison to ∼50% for the Phospho1–/– MVs and ∼25% for the WT and Pit1col2/col2 MVs. We also found a significant decrease in the number of MVs produced by both Phospho1–/– and [Phospho1–/–; Pit1col2/col2] chondrocytes. These data support the involvement of phosphate transporter 1, hereafter referred to as PiT‐1, in the initiation of skeletal mineralization and provide compelling evidence that PHOSPHO1 function is involved in MV biogenesis.

Cytotoxicity screening and cytokine profiling of nineteen nanomaterials enables hazard ranking and grouping based on inflammogenic potential

Abstract Engineered nanomaterials (ENMs) are being produced for an increasing number of applications. Therefore, it is important to assess and categorize ENMs on the basis of their hazard potential. The immune system is the foremost defence against foreign bodies. Here we performed cytokine profiling of a panel of nineteen representative ENMs procured from the Joint Research Centre (JRC) and commercial sources. Physicochemical characterization was performed using dynamic light scattering. The ENMs were all shown to be endotoxin content free. The human macrophage-differentiated THP.1 cell line was employed for cytotoxicity screening and based on the calculated IC50 values, the multi-walled carbon nanotubes (MWCNTs), ZnO, Ag and SiO2 NMs were found to be the most cytotoxic while single-walled carbon nanotubes (SWCNTs), TiO2, BaSO4 and CeO2 NMs, as well as the nanocellulose materials, were non-cytotoxic (at doses up to 100 µg/mL). Multiplex profiling of cytokine and chemokine secretion indicated that the TiO2, SiO2, BaSO4, CeO2 and nanocellulose materials induced potent inflammatory responses at sub-cytotoxic doses. Hierarchical clustering of cytokine responses coupled with pathway analysis demonstrated that the panel of ENMs could be segregated into two distinct groups characterized by activation and deactivation, respectively, of PPAR (peroxisome proliferator-activated receptor)/LXR (liver X receptor/retinoid X receptor) nuclear receptor pathways (NRPs). Furthermore, using rosiglitazone, a selective PPAR-γ agonist, we could show that PPAR-γ played an important role in the activation of inflammatory responses in cells exposed to TiO2 and SiO2 NMs. These studies show that ENMs of diverse chemical compositions can be grouped according to their inflammatory potential.

Geoengineering: perilous particles.

The Policy Forum “End the deadlock on governance of geoengineering research” (E. A. Parson and D. W. Keith, 15 March, p. [1278][1]) advances proposals for governmental regulation of geoengineering, the use of technologies to alter the climate in an attempt to mitigate the impacts of global