Assessing NLRP3 Inflammasome Activation by Nanoparticles

Polyethylene Terephthalate Microplastics Generated from Disposable Water Bottles Induce Interferon Signaling Pathways in Mouse Lung Epithelial Cells

Microplastics (MPs) are present in ambient air in a respirable size fraction; however, their potential impact on human health via inhalation routes is not well documented. In the present study, methods for a lab-scale generation of MPs from regularly used and littered plastic articles were optimized. The toxicity of 11 different types of MPs, both commercially purchased and in-lab prepared MPs, was investigated in lung epithelial cells using cell viability, immune and inflammatory response, and genotoxicity endpoints. The underlying mechanisms were identified by microarray analysis. Although laborious, the laboratory-scale methods generated a sufficient quantity of well characterized MPs for toxicity testing. Of the 11 MPs tested, the small sized polyethylene terephthalate (PETE) MPs prepared from disposable water bottles induced the maximum toxicity. Specifically, the smaller size PETE MPs induced a robust activation of the interferon signaling pathway, implying that PETE MPs are perceived by cells by similar mechanisms as those employed to recognize pathogens. The PETE MPs of heterogenous size and shapes induced cell injury, triggering cell death, inflammatory cascade, and DNA damage, hallmark in vitro events indicative of potential in vivo tissue injury. The study establishes toxicity of specific types of plastic materials in micron and nano size.

Role of NLRP3 inflammasome in nanoparticle adjuvant-mediated immune response

The nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain-containing 3 (NLRP3) inflammasome is pivotal in orchestrating the immune response induced by nanoparticle adjuvants. Understanding the intricate mechanisms underlying the activation of NLRP3 inflammasome by these adjuvants is crucial for deciphering their immunomodulatory properties. This review explores the involvement of the NLRP3 inflammasome in mediating immune responses triggered by nanoparticle adjuvants. It delves into the signaling pathways and cellular mechanisms involved in NLRP3 activation, highlighting its significance in modulating the efficacy and safety of nanoparticle-based adjuvants. A comprehensive grasp of the interplay between NLRP3 inflammasome and nanoparticle adjuvants holds promise for optimizing vaccine design and advancing immunotherapeutic strategies.

Nanoparticles toxicity: an overview of its mechanism and plausible mitigation strategies

Over the last decade, nanoparticles have found great interest among scientists and researchers working in various fields within the realm of biomedicine including drug delivery, gene delivery, diagnostics, targeted therapy and biomarker mapping. While their physical and chemical properties are impressive, there is growing concern about the toxicological potential of nanoparticles and possible adverse health effects as enhanced exposure of biological systems to nanoparticles may result in toxic effects leading to serious contraindications. Toxicity associated with nanoparticles (nanotoxicity) may include the undesired response of several physiological mechanisms including the distressing of cells by external and internal interaction with nanoparticles. However, comprehensive knowledge of nanotoxicity mechanisms and mitigation strategies may be useful to overcome the hazardous situation while treating diseases with therapeutic nanoparticles. With the same objectives, this review discusses various mechanisms of nanotoxicity and provides an overview of the current state of knowledge on the impact of nanotoxicity on biological control systems and organs including liver, brain, kidneys and lungs. An attempt also been made to present various approaches of scientific research and strategies that could be useful to overcome the effect of nanotoxicity during the development of nanoparticle-based systems including coating, doping, grafting, ligation and addition of antioxidants.

NLRP3 Inflammasome Inhibitors for Antiepileptogenic Drug Discovery and Development

Epilepsy is one of the most prevalent and serious brain disorders and affects over 70 million people globally. Antiseizure medications (ASMs) relieve symptoms and prevent the occurrence of future seizures in epileptic patients but have a limited effect on epileptogenesis. Addressing the multifaceted nature of epileptogenesis and its association with the Nod-like receptor family pyrin domain containing 3 (NLRP3) inflammasome-mediated neuroinflammation requires a comprehensive understanding of the underlying mechanisms of these medications for the development of targeted therapeutic strategies beyond conventional antiseizure treatments. Several types of NLRP3 inhibitors have been developed and their effect has been validated both in in vitro and in vivo models of epileptogenesis. In this review, we discuss the advances in understanding the regulatory mechanisms of NLRP3 activation as well as progress made, and challenges faced in the development of NLRP3 inhibitors for the treatment of epilepsy.

Assessing regulated cell death modalities as an efficient tool for in vitro nanotoxicity screening: a review

Nanomedicine is a fast-growing field of nanotechnology. One of the major obstacles for a wider use of nanomaterials for medical application is the lack of standardized toxicity screening protocols for assessing the safety of newly synthesized nanomaterials. In this review, we focus on less frequently studied nanomaterials-induced regulated cell death (RCD) modalities, including eryptosis, necroptosis, pyroptosis, and ferroptosis, as a tool for in vitro nanomaterials safety evaluation. We summarize the latest insights into the mechanisms that mediate these RCDs in response to nanomaterials exposure. Comprehensive data from reviewed studies suggest that ROS (reactive oxygen species) overproduction and ROS-mediated pathways play a central role in nanomaterials-induced RCDs activation. On the other hand, studies also suggest that individual properties of nanomaterials, including size, shape, or surface charge, could determine specific toxicity pathways with consequent RCD induction as well. We anticipate that the evaluation of RCDs can become one of the mechanism-based screening methods in nanotoxicology. In addition to the toxicity assessment, evaluation of necroptosis-, pyroptosis-, and ferroptosis-promoting capacity of nanomaterials could simultaneously provide useful information for specific medical applications as could be their anti-tumor potential. Moreover, a detailed understanding of molecular mechanisms driving nanomaterials-mediated induction of immunogenic RCDs will substantially aid novel anti-tumor nanodrugs development.

NLRP3 inflammasome as a sensor of micro- and nanoplastics immunotoxicity

Micro- and nanoplastics (MNPs) are emerging pollutants with scarcely investigated effects on human innate immunity. If they follow a similar course of action as other, more thoroughly investigated particulates, MNPs may penetrate epithelial barriers, potentially triggering a cascade of signaling events leading to cell damage and inflammation. Inflammasomes are intracellular multiprotein complexes and stimulus-induced sensors critical for mounting inflammatory responses upon recognition of pathogen- or damage-associated molecular patterns. Among these, the NLRP3 inflammasome is the most studied in terms of activation via particulates. However, studies delineating the ability of MNPs to affect NLRP3 inflammasome activation are still rare. In this review, we address the issue of MNPs source and fate, highlight the main concepts of inflammasome activation via particulates, and explore recent advances in using inflammasome activation for assessment of MNP immunotoxicity. We also discuss the impact of co-exposure and MNP complex chemistry in potential inflammasome activation. Development of robust biological sensors is crucial in order to maximize global efforts to effectively address and mitigate risks that MNPs pose for human health.

Immunogenic Cell Death and Role of Nanomaterials Serving as Therapeutic Vaccine for Personalized Cancer Immunotherapy

Immunogenic cell death (ICD) is a rapidly growing research area representing one of the emerging therapeutic strategies of cancer immunotherapy. ICD is an umbrella term covering several cell death modalities including apoptosis, necroptosis, ferroptosis and pyroptosis, and is the product of a balanced combination of adjuvanticity (damage-associated molecular patterns and chemokines/cytokines) and antigenicity (tumor associated antigens). Only a limited number of anti-cancer therapies are available to induce ICD in experimental cancer therapies and even much less is available for clinical use. To overcome this limitation, nanomaterials can be used to increase the immunogenicity of cancer cells killed by anti-cancer therapy, which in themselves are not necessarily immunogenic. In this review, we outline the current state of knowledge of ICD modalities and discuss achievements in using nanomaterials to increase the immunogenicity of dying cancer cells. The emerging trends in modulating the immunogenicity of dying cancer cells in experimental and translational cancer therapies and the challenges facing them are described. In conclusion, nanomaterials are expected to drive further progress in their use to increase efficacy of anti-cancer therapy based on ICD induction and in the future, it is necessary to validate these strategies in clinical settings, which will be a challenging research area.

The Relevance of Physico-Chemical Properties and Protein Corona for Evaluation of Nanoparticles Immunotoxicity-In Vitro Correlation Analysis on THP-1 Macrophages

Alongside physiochemical properties (PCP), it has been suggested that the protein corona of nanoparticles (NPs) plays a crucial role in the response of immune cells to NPs. However, due to the great variety of NPs, target cells, and exposure protocols, there is still no clear relationship between PCP, protein corona composition, and the immunotoxicity of NPs. In this study, we correlated PCP and the protein corona composition of NPs to the THP-1 macrophage response, focusing on selected toxicological endpoints: cell viability, reactive oxygen species (ROS), and cytokine secretion. We analyzed seven commonly used engineered NPs (SiO2, silver, and TiO2) and magnetic NPs. We show that with the exception of silver NPs, all of the tested TiO2 types and SiO2 exhibited moderate toxicities and a transient inflammatory response that was observed as an increase in ROS, IL-8, and/or IL-1β cytokine secretion. We observed a strong correlation between the size of the NPs in media and IL-1β secretion. The induction of IL-1β secretion was completely blunted in NLR family pyrin domain containing 3 (NLRP3) knockout THP-1 cells, indicating activation of the inflammasome. The correlations analysis also implicated the association of specific NP corona proteins with the induction of cytokine secretion. This study provides new insights toward a better understanding of the relationships between PCP, protein corona, and the inflammatory response of macrophages for different engineered NPs, to which we are exposed on a daily basis.

Hyperinflammation after anti-SARS-CoV-2 mRNA/DNA vaccines successfully treated with anakinra: Case series and literature review

The current SARS-CoV-2 pandemic diffused worldwide has encouraged the rapid development of vaccines to counter the spread of the virus. At present in Italy, 75.01% of the population completed the vaccination course (AIFA.gov.it) and very few adverse events have been recorded by now. Side-effects related to a theoretical over-reaction of the immune system in response to vaccines administration have been described, and the possibility that an autoimmune or a hyperinflammatory condition may occur was recently observed. Herein, we report four cases of hyperinflammatory syndrome with features indicative of Adult-onset Still's disease (AOSD) and macrophage activation syndrome (MAS), occurred after anti-SARS-CoV-2 vaccine injection and seen at our Unit between March and May 2021. Since interleukin (IL)-1 is one of the pivotal cytokines involved in AOSD pathogenesis, the inhibition of IL-1 is crucial in ameliorating the clinical symptoms of those patients. Moreover, it has been highlighted the central role of IL-1 as a hallmark of the hyperinflammatory status elicited by SARS-CoV-2 infection. In this case series, we successfully employed the IL-1 receptor antagonist anakinra to curb the cytokine release likely unleashed by the vaccine stimulation in potentially predisposed subjects. We also made a literature search to detect other patients with hyperinflammation temporally related to vaccines injection who benefited from IL-1 inhibition, while other AOSD/MAS-like described syndromes improved with other immunomodulatory strategies.

Targeting NLRP3 Inflammasome in the Treatment Of Diabetes and Diabetic Complications: Role of Natural Compounds from Herbal Medicine

Diabetes, a common metabolic disease with various complications, is becoming a serious global health pandemic. So far there are many approaches in the management of diabetes; however, it still remains irreversible due to its complicated pathogenesis. Recent studies have revealed that nucleotide-binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome plays a vital role in the progression of diabetes and many of its complications, making it a promising therapeutic target in pharmaceutical design. Natural derived herbal medicine, known for its utilization of natural products such as herbs or its bioactive ingredients, is shown to be able to ameliorate hyperglycemia-associated symptoms and to postpone the progression of diabetic complications due to its anti-inflammatory and anti-oxidative properties. In this review, we summarized the role of NLRP3 inflammasome in diabetes and several diabetic complications, as well as 31 active compounds that exert therapeutic effect on diabetic complications via inhibiting NLRP3 inflammasome. Improving our understanding of these promising candidates from natural compounds in herbal medicine targeting NLRP3 inflammasome inspires us the relationship between inflammation and metabolic disorders, and also sheds light on searching potential agents or therapies in the treatment of diabetes and diabetic complications.

Core Hydrophobicity of Supramolecular Nanoparticles Induces NLRP3 Inflammasome Activation

Designer nanomaterials capable of delivering immunomodulators to specific immune cells have been extensively studied. However, emerging evidence suggests that several of these nanomaterials can nonspecifically activate NLRP3 inflammasomes, an intracellular multiprotein complex controlling various immune cell functions, leading to undesirable effects. To understand what nanoparticle attributes activate inflammasomes, we designed a multiparametric polymer supramolecular nanoparticle system to modulate various surface and core nanoparticle-associated molecular patterns (NAMPs), one at a time. We also investigated several underlying signaling pathways, including lysosomal rupture-cathepsin B maturation and calcium flux-mitochondrial ROS production, to gain mechanistic insights into NAMPs-mediated inflammasome activation. Here, we report that out of the four NAMPs tested, core hydrophobicity strongly activates and positively correlates with the NLRP3 assembly compared to surface charge, core rigidity, and surface hydrophobicity. Moreover, we demonstrate different signaling inclinations and kinetics followed by differential core hydrophobicity patterns with the most hydrophobic ones exhibiting both lysosomal rupture and calcium influx early on. Altogether, this study will help design the next generation of polymeric nanomaterials for specific regulation of inflammasome activation, aiding efficient immunotherapy and vaccine delivery.

Sacubitril/valsartan (LCZ696) reduces myocardial injury following myocardial infarction by inhibiting NLRP3‑induced pyroptosis via the TAK1/JNK signaling pathway

The present study aimed to investigate the protective effects of sacubitril/valsartan (LCZ696) on ventricular remodeling in myocardial infarction (MI) and the effects of the inflammasome‑mediated inflammatory response. First, a rat model was established. Animals were then treated with LCZ696 so that the histopathological changes associated with ventricular remodeling could be investigated. The serum levels of the inflammatory factors IL‑18 and IL‑1β were also determined by ELISA. Immunofluorescence was used to investigate the ratio of pyroptosis following MI modelling. Western blotting and reverse transcription‑quantitative PCR were used to detect the relative expression levels of proteins and mRNAs in the transforming growth factor β‑activated kinase‑1 (TAK1)/JNK pathway and those associated with the NLR pyrin family domain containing 3 (NLRP3) inflammasome, respectively. The present study also investigated the regulatory mechanisms and associations between the TAK1 and JNK pathways, NOD‑, leucine‑rich repeat‑ and the NLRP3 inflammasome, in H9C2 cells and myocardial cells from the rat model of MI. LCZ696 improved MI‑induced myocardial fibrosis, rescued myocardial injury and suppressed the release of inflammatory factors. With regards to myocardial cell damage, pyroptosis in cardiomyocytes was observed. The in vitro experiments demonstrated that the overexpression of TAK1 promoted lysis of the N‑terminal of GSDMD, thereby activating the NLRP3 inflammasome and promoting the conversion of pro‑IL‑1β and pro‑IL‑18 into mature IL‑1β and IL‑18, respectively. In contrast, the silencing of TAK1 inhibited the expression levels of the NLRP3 inflammasome. In summary, LCZ696 reduced the expression levels of the NLRP3 inflammasome, suppressed inflammatory responses, improved the ventricular remodeling and exhibited protective effects in the MI heart by inhibiting the TAK1/JNK signaling pathway.

Nonclinical regulatory immunotoxicity testing of nanomedicinal products: Proposed strategy and possible pitfalls

Various nanomedicinal products (NMPs) have been reported to induce an adverse immune response, which may be related to their tendency to accumulate in or target cells of the immune system. Therefore, before their market authorization, NMPs should be thoroughly evaluated for their immunotoxic potential. Nonclinical regulatory immunotoxicity testing of nonbiological medicinal products, including NMPs, is currently performed by following the guideline S8 “Immunotoxicity Studies for Human Pharmaceuticals” of the International Council for Harmonization of Technical Requirements for Pharmaceuticals for Human Use (ICH). However, this guideline does not cover all the immunotoxicity endpoints reported for NMPs in the literature, such as complement activation related pseudo allergy, hypersensitivity and immunosuppression. In addition, ICH‐S8 does not provide any nanospecific testing considerations, which is important given their tendency to interfere with many commonly used toxicity assays. We therefore propose a nonclinical regulatory immunotoxicity assessment strategy, which considers the immunotoxicity endpoints currently missing in the ICH‐S8. We also list the known pitfalls related to the testing of NMPs and how to tackle them. Next to defining the relevant physicochemical and pharmacokinetic properties of the NMP and its intended use, the proposed strategy includes an in vitro assay battery addressing various relevant immunotoxicity endpoints. A weight of evidence evaluation of this information can be used to shape the type and design of further in vivo investigations. The final outcome of the immunotoxicity assessment can be included in the overall risk assessment of the NMP and provide alerts for relevant endpoints to address during clinical investigation.

This article is categorized under:

Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine

Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials

Surgical trauma-induced immunosuppression in cancer: Recent advances and the potential therapies

Surgical resection remains the mainstay treatment for solid cancers, especially for localized disease. However, the postoperative immunosuppression provides a window for cancer cell proliferation and awakening dormant cancer cells, leading to rapid recurrences or metastases. This immunosuppressive status after surgery is associated with the severity of surgical trauma since immunosuppression induced by minimally invasive surgery is less than that of an extensive open surgery. The systemic response to tissue damages caused by surgical operations and the subsequent wound healing induced a cascade alteration in cellular immunity. After surgery, patients have a high level of circulating damage-associated molecular patterns (DAMPs), triggering a local and systemic inflammation. The inflammatory metrics in the immediate postoperative period was associated with the prognosis of cancer patients. Neutrophils provide the first response to surgical trauma, and the production of neutrophil extracellular traps (NETs) promotes cancer progression. Activated macrophage during wound healing presents a tumor-associated phenotype that cancers can exploit for their survival advantage. In addition, the amplification and activation of myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs) or the elevated programmed death ligand-1 and vascular endothelial growth factor expression under surgical trauma, exacerbate the immunosuppression and favor of the formation of the premetastatic niche. Therapeutic strategies to reduce the cellular immunity impairment after surgery include anti-DAMPs, anti-postoperative inflammation or inflammatory/pyroptosis signal, combined immunotherapy with surgery, antiangiogenesis and targeted therapies for neutrophils, macrophages, MDSCs, and Tregs. Further, the application of enhanced recovery after surgery also has a feasible outcome for postoperative immunity restoration. Overall, current therapies to improve the cellular immunity under the special condition after surgery are relatively lacking. Further understanding the underlying mechanisms of surgical trauma-related immunity dysfunction, phenotyping the immunosuppressive cells, and developing the related therapeutic intervention should be explored.

The Nose-To-Brain Transport of Polymeric Nanoparticles Is Mediated by Immune Sentinels and Not by Olfactory Sensory Neurons

The nose-to-brain (N-to-B) transport mechanism of nanoparticles through the olfactory epithelium (OE) is not fully understood. Most research utilized nasal epithelial cell models completely deprived of olfactory cells. Aiming to shed light into key cellular pathways, in this work, for the first time, the interaction of polymeric nanoparticles in a 17-483 nm size range and with neutral and negatively and positively charged surfaces with primary olfactory sensory neurons, cortical neurons, and microglia isolated from olfactory bulb (OB), OE, and cortex of newborn rats is investigated. After demonstrating the good cell compatibility of the different nanoparticles, the nanoparticle uptake by confocal laser scanning fluorescence microscopy is monitored. Our findings reveal that neither olfactory nor forebrain neurons internalize nanoparticles. Conversely, it is demonstrated that olfactory and cortical microglia phagocytose the nanoparticles independently of their features. Overall, our findings represent the first unambiguous evidence of the possible involvement of microglia in N-to-B nanoparticle transport and the unlikely involvement of neurons. Furthermore, this approach emerges as a completely new experimental tool to screen the biocompatibility, uptake, and transport of nanomaterials by key cellular players of the N-to-B pathway in nanosafety and nanotoxicology and nanomedicine.

Immunotoxicity Considerations for Next Generation Cancer Nanomedicines

Although interest and funding in nanotechnology for oncological applications is thriving, translating these novel therapeutics through the earliest stages of preclinical assessment remains challenging. Upon intravenous administration, nanomaterials interact with constituents of the blood inducing a wide range of associated immunotoxic effects. The literature on the immunological interactions of nanomaterials is vast and complicated. A small change in a particular characteristic of a nanomaterial (e.g., size, shape, or charge) can have a significant effect on its immunological profile in vivo, and poor selection of specific assays for establishing these undesirable effects can overlook this issue until the latest stages of preclinical assessment. This work describes the current literature on unintentional immunological effects associated with promising cancer nanomaterials (liposomes, dendrimers, mesoporous silica, iron oxide, gold, and quantum dots) and puts focus on what is missing in current preclinical evaluations. Opportunities for avoiding or limiting immunotoxicity through efficient preclinical assessment are discussed, with an emphasis placed on current regulatory views and requirements. Careful consideration of these issues will ensure a more efficient preclinical assessment of cancer nanomedicines, enabling a smoother clinical translation with less failures in the future.

Toxicological assessment of nanoparticle interactions with the pulmonary system

Nanoparticle(NP)-based materials have breakthrough applications in many fields of life, such as in engineering, communications and textiles industries; food and bioenvironmental applications; medicines and cosmetics, etc. Biomedical applications of NPs are very active areas of research with successful translation to pharmaceutical and clinical uses overcoming both pharmaceutical and clinical challenges. Although the attractiveness and enhanced applications of these NPs stem from their exceptional properties at the nanoscale size, i.e. 1-1000 nm, they exhibit completely different physicochemical profiles and, subsequently, toxicological profiles from their parent bulk materials. Hence, the clinical evaluation and toxicological assessment of NPs interactions within biological systems are continuously evolving to ensure their safety at the nanoscale. The pulmonary system is one of the primary routes of exposure to airborne NPs either intentionally, via aerosolized nanomedicines targeting pulmonary pathologies such as cancer or asthma, or unintentionally, via natural NPs and anthropogenic (man-made) NPs. This review presents the state-of-the-art, contemporary challenges, and knowledge gaps in the toxicological assessment of NPs interactions with the pulmonary system. It highlights the main mechanisms of NP toxicity, factors influencing their toxicity, the different toxicological assessment methods and their drawbacks, and the recent NP regulatory guidelines based on literature collected from the research pool of NPs interactions with lung cell lines, in vivo inhalation studies, and clinical trials.

The NLRP3 p.A441V Mutation in NLRP3-AID Pathogenesis: Functional Consequences, Phenotype-Genotype Correlations and Evidence for a Recurrent Mutational Event

Objective

To determine the molecular and cellular bases of autoinflammatory syndromes in a multigenerational French family with Muckle-Wells syndrome and in a patient originating from Portugal with familial cold autoinflammatory syndrome.

Methods

Sequencing of NLRP3 exon 3 was performed in all accessible patients. Microsatellite and whole-genome single nucleotide polymorphism genotyping was used i) to test the intrafamilial segregation of the identified variant and ii) to look for a founder effect. Functional analyses included the study of i) apoptosis-associated speck-like protein containing a CARD (ASC) speck formation in HEK293T cells (stably expressing ASC-green fluorescent protein and pro-caspase 1-FLAG) transiently expressing the wild-type or mutated NLRP3 protein, ii) levels of IL-1β secreted from transfected THP-1 cells, and iii) inflammasome-related gene expression and cytokine secretion from monocytes isolated from patients in crisis (probands from the two families), related patients out of crisis, and from controls.

Results

The same heterozygous mutation (c.1322C>T, p.A441V) located in the NACHT domain, segregating with the disease within the first family, was identified in the two families. This mutation was found to be associated with different core haplotypes. NLRP3-A441V led to increased ASC speck formation and high levels of secreted IL-1β. Monocyte inflammasome-related gene expression and cytokine secretion, which were within the normal range in patients out of crisis, were found to be differentially regulated between the two probands, correlating with their phenotypic status.

Conclusion

These molecular and cellular findings, which indicate a recurrent mutational event, clearly demonstrate the pathogenicity of the p.A441V missense mutation in NLRP3-associated autoinflammatory disease and point to the interest of studying patients' primary cells to assess disease activity.

Comparative cytotoxicity of respirable surface-treated/untreated calcium carbonate rock dust particles in vitro

Calcium carbonate rock dust (RD) is used in mining to reduce the explosivity of aerosolized coal. During the dusting procedures, potential for human exposure occurs, raising health concerns. To improve RD aerosolization, several types of anti-caking surface treatments exist. The aim of the study was to evaluate cytotoxicity of four respirable RD samples: untreated/treated limestone (UL/TL), untreated/treated marble (UM/TM), and crystalline silica (SiO₂) as a positive control in A549 and THP-1 transformed human cell lines. Respirable fractions were generated and collected using FSP10 high flow-rate cyclone samplers. THP-1 cells were differentiated with phorbol-12-myristate-13-acetate (20 ng/ml, 48 h). Cells were exposed to seven different concentrations of RD and SiO₂ (0-0.2 mg/ml). RD caused a slight decrease in viability at 24 or 72 h post-exposure and were able to induce inflammatory cytokine production in A549 cells, however, with considerably less potency than SiO₂. In THP-1 cells at 24 h, there was significant dose-dependent lactate dehydrogenase, inflammatory cytokine and chemokine release. Caspase-1 activity was increased in SiO₂- and, on a lesser scale, in TM- exposed cells. To test if the increased toxicity of TM was uptake-related, THP-1 cells were pretreated with Cytochalasin D (CytD) or Bafilomycin A (BafA), followed by exposure to RD or SiO₂ for 6 h. CytD blocked the uptake and significantly decreased cytotoxicity of all particles, while BafA prevented caspase-1 activation but not cytotoxic effects of TM. Only TM was able to induce an inflammatory response in THP-1 cells, however it was much less pronounced compared to silica.