Approaching a Unified Theory for Particle-Induced Inflammation

Lysosomal BK channels facilitate silica-induced inflammation in macrophages

BACKGROUND

Lysosomal ion channels are proposed therapeutic targets for a number of diseases, including those driven by NLRP3 inflammasome-mediated inflammation. Here, the specific role of the lysosomal big conductance Ca2+-activated K+ (BK) channel was evaluated in a silica model of inflammation in murine macrophages. A specific-inhibitor of BK channel function, paxilline (PAX), and activators NS11021 and NS1619 were utilized to evaluate the role of lysosomal BK channel activity in silica-induced lysosomal membrane permeabilization (LMP) and NLRP3 inflammasome activation resulting in IL-1β release.

METHODS

Murine macrophages were exposed in vitro to crystalline silica following pretreatment with BK channel inhibitors or activators and LMP, cell death, and IL-1β release were assessed. In addition, the effect of PAX treatment on silica-induced cytosolic K+ decrease was measured. Finally, the effects of BK channel modifiers on lysosomal pH, proteolytic activity, and cholesterol transport were also evaluated.

RESULTS

PAX pretreatment significantly attenuated silica-induced cell death and IL-1β release. PAX caused an increase in lysosomal pH and decrease in lysosomal proteolytic activity. PAX also caused a significant accumulation of lysosomal cholesterol. BK channel activators NS11021 and NS1619 increased silica-induced cell death and IL-1β release. BK channel activation also caused a decrease in lysosomal pH and increase in lysosomal proteolytic function as well as a decrease in cholesterol accumulation.

CONCLUSION

Taken together, these results demonstrate that inhibiting lysosomal BK channel activity with PAX effectively reduced silica-induced cell death and IL-1β release. Blocking cytosolic K+ entry into the lysosome prevented LMP through the decrease of lysosomal acidification and proteolytic function and increase in lysosomal cholesterol.

Respiratory and systemic impacts following MWCNT inhalation in B6C3F1/N mice

Background

A very pure multi-walled carbon nanotube (MWCNT) that was shown to have very low toxicity in vitro, was evaluated for lung and systemic effects and distribution following inhalation exposure.

Methods

B6C3F1/N mice were exposed to varying doses (0, 0.06, 0.2, and 0.6 mg/m³) of the (99.1% carbon) MWCNT by inhalation for 30 days (excluding weekends). Ten days following the last exposure, the lungs and spleen were harvested and processed for histology and immune cell population assessment. In addition, lung lavage cells and fluid were analyzed. Stimulated Raman scattering (SRS) was used to identify particles in the lungs, spleen, kidneys, liver, mediastinal and brachial lymph nodes, and olfactory bulb. Splenic tissue sections were stained with hematoxylin and eosin (H&E) for light microscopic histopathology assessment. Blood plasma was analyzed for cytokines and cathepsins. A section of the spleen was processed for RNA isolation and relative gene expression for 84 inflammation-related cytokines/chemokines.

Results

Following MWCNT exposure, particles were clearly evident in the lungs, spleens, lymph nodes and olfactory bulbs, (but not livers or kidneys) of exposed mice in a dose-dependent manner. Examination of the lavaged lung cells was unremarkable with no significant inflammation indicated at all particle doses. In contrast, histological examination of the spleen indicated the presence of apoptotic bodies within T cells regions of the white pulp area. Isolated splenic leukocytes had significant changes in various cells including an increased number of proinflammatory CD11b⁺Ly6C⁺ splenic cells. The gene expression studies confirmed this observation as several inflammation-related genes were upregulated particularly in the high dose exposure (0.6 mg/m³). Blood plasma evaluations showed a systemic down-regulation of inflammatory cytokines and a dose-dependent up-regulation of lysosomal cathepsins.

Conclusions

The findings in the lungs were consistent with our hypothesis that this MWCNT exposure would result in minimal lung inflammation and injury. However, the low toxicity of the MWCNT to lung macrophages may have contributed to enhanced migration of the MWCNT to the spleen through the lymph nodes, resulting in splenic toxicity and systemic changes in inflammatory mediators.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-021-00408-z.

The role of lysosomal ion channels in lysosome dysfunction

Lysosomes offer a unique arrangement of degradative, exocytic, and signaling capabilities that make their continued function critical to cellular homeostasis. Lysosomes owe their function to the activity of lysosomal ion channels and transporters, which maintain concentration gradients of H⁺, K⁺, Ca²⁺, Na⁺, and Cl^- across the lysosomal membrane. This review examines the contributions of lysosomal ion channels to lysosome function, showing how ion channel function is integral to degradation and autophagy, maintaining lysosomal membrane potential, controlling Ca²⁺ signaling, and facilitating exocytosis. Evidence of lysosome dysfunction in a variety of disease pathologies creates a need to understand how lysosomal ion channels contribute to lysosome dysfunction. For example, the loss of function of the TRPML1 Ca²⁺ lysosome channel in multiple lysosome storage diseases leads to lysosome dysfunction and disease pathogenesis while neurodegenerative diseases are marked by lysosome dysfunction caused by changes in ion channel activity through the TRPML1, TPC, and TMEM175 ion channels. Autoimmune disease is marked by dysregulated autophagy, which is dependent on the function of multiple lysosomal ion channels. Understanding the role of lysosomal ion channel activity in lysosome membrane permeability and NLRP3 inflammasome activation could provide valuable mechanistic insight into NLRP3 inflammasome-mediated diseases. Finally, this review seeks to show that understanding the role of lysosomal ion channels in lysosome dysfunction could give mechanistic insight into the efficacy of certain drug classes, specifically those that target the lysosome, such as cationic amphiphilic drugs.

Lung deposition patterns of MWCNT vary with degree of carboxylation

Functionalization of multi-walled carbon nanotubes (MWCNT) is known to affect the biological response (e.g. toxicity, inflammation) in vitro and in vivo. However, the reasons for these changes in vivo are not well described. This study examined the degree of MWCNT functionalization with regard to in vivo mouse lung distribution, particle retention, and resulting pathology. A commercially available MWCNT (source MWCNT) was functionalized (f-MWCNT) by systematically varying the degree of carboxylation on the particle's surface. Following a pilot study using seven variants, two f-MWCNT variants were chosen and for lung pathology and particle distribution using oropharyngeal aspiration administration of MWCNT in Balb/c mice. Particle distribution in the lung was examined at 7 and 28 days post-instillation by bright-field microscopy, CytoViva hyperspectral dark-field imaging, and Stimulated Raman Scattering (SRS) microscopy. Examination of the lung tissue by bright-field microscopy showed some acute inflammation for all MWCNT that was highest with source MWCNT. Hyperspectral imaging and SRS were employed to assess the changes in particle deposition and retention. Highly functionalized MWCNT had a higher lung burden and were more disperse. They also appeared to be associated more with epithelial cells compared to the source and less functionalized MWCNT that were mostly interacting with alveolar macrophages (AM). These results showing a slightly reduced pathology despite the extended deposition have implications for the engineering of safer MWCNT and may establish a practical use as a targeted delivery system.

Prevention of crystalline silica-induced inflammation by the anti-malarial hydroxychloroquine

Objectives: Inhalation of crystalline silica (cSiO₂) remains a significant occupational hazard and may lead to the development of silicosis. When cSiO₂ particles are phagocytized by alveolar macrophages, they cause disruption of the lysosomal membrane which results in cell death. There are currently no pharmaceutical treatments directed at this mechanism of disease; however, many existing pharmaceuticals, such as hydroxychloroquine (HCQ), become sequestered in the lysosome through an ion-trapping mechanism. The objective of this research was to determine whether HCQ can prevent cSiO₂-induced toxicity by blocking LMP in alveolar macrophages. Materials and methods: This study assessed the ability of in vitro treatment with HCQ to block toxicity and lysosomal membrane permeability in cSiO₂-exposed mouse bone-marrow derived macrophages. Additionally, C57Bl/6 mice were treated with HCQ by oral gavage before cSiO₂ exposure, and the ability of HCQ to prevent lung injury and inflammation was assessed. Results: In vitro studies demonstrated that HCQ attenuated activation of the NLRP3 inflammasome and blocked LMP. Mice treated with HCQ in vivo showed a modest trend towards decreased cSiO₂-induced toxicity. Ex vivo culture of alveolar macrophages collected from cSiO₂-treated mice showed significantly less NLRP3 inflammasome activation after in vivo exposure to HCQ. Conclusions: Our findings suggest that hydroxychloroquine blocks LMP and can significantly decrease cSiO₂-induced toxicity in vitro. HCQ may be a promising treatment for prevention of cSiO₂-induced lung damage.

Length, but Not Reactive Edges, of Cup-stack MWCNT Is Responsible for Toxicity and Acute Lung Inflammation

Multiwalled carbon nanotube (MWCNT) toxicity after inhalation has been associated with size, aspect ratio, rigidity, surface modification, and reactive oxygen species production. In this study, we investigated a series of cup-stacked MWCNT prepared as variants of the Creos 24PS. Mechanical chopping produced a short version (AR10) and graphitization to remove active reaction sites by extreme heat (2,800°C; Creos 24HT) to test the contribution of length and alteration of potential reaction sites to toxicity. The 3 MWCNT variants were tested in vitro in a human macrophage-like cell model and with C57BL/6 alveolar macrophages for dose-dependent toxicity and NLRP3 inflammasome activation. The 24PS and 24HT variants showed significant dose-dependent toxicity and inflammasome activation. In contrast, the AR10 variant showed no toxicity or bioactivity at any concentration tested. The in vivo results reflected those observed in vitro, with the 24PS and 24HT variants resulting in acute inflammation, including elevated polymorphonuclear counts, Interleukin (IL)-18, cathepsin B, and lactate dehydrogenase in isolated lung lavage fluid from mice exposed to 40 µg MWCNT. Taken together, these data indicate that length, but not the absence of proposed reaction sites, on the MWCNT influences particle bioactivity.

Imipramine blocks acute silicosis in a mouse model

BACKGROUND

Inhalation of crystalline silica is associated with pulmonary inflammation and silicosis. Although silicosis remains a prevalent health problem throughout the world, effective treatment choices are limited. Imipramine (IMP) is a FDA approved tricyclic antidepressant drug with lysosomotropic characteristics. The aim of this study was to evaluate the potential for IMP to reduce silicosis and block phagolysosome membrane permeabilization.

METHODS

C57BL/6 alveolar macrophages (AM) exposed to crystalline silica ± IMP in vitro were assessed for IL-1β release, cytotoxicity, particle uptake, lysosomal stability, and acid sphingomyelinase activity. Short term (24 h) in vivo studies in mice instilled with silica (± IMP) evaluated inflammation and cytokine release, in addition to cytokine release from ex vivo cultured AM. Long term (six to ten weeks) in vivo studies in mice instilled with silica (± IMP) evaluated histopathology, lung damage, and hydroxyproline content as an indicator of collagen accumulation.

RESULTS

IMP significantly attenuated silica-induced cytotoxicity and release of mature IL-1β from AM in vitro. IMP treatment in vivo reduced silica-induced inflammation in a short-term model. Furthermore, IMP was effective in blocking silica-induced lung damage and collagen deposition in a long-term model. The mechanism by which IMP reduces inflammation was explored by assessing cellular processes such as particle uptake and acid sphingomyelinase activity.

CONCLUSIONS

Taken together, IMP was anti-inflammatory against silica exposure in vitro and in vivo. The results were consistent with IMP blocking silica-induced phagolysosomal lysis, thereby preventing cell death and IL-1β release. Thus, IMP could be therapeutic for silica-induced inflammation and subsequent disease progression as well as other diseases involving phagolysosomal lysis.

Engineered nanomaterial-induced lysosomal membrane permeabilization and anti-cathepsin agents

Engineered nanomaterials (ENMs), or small anthropogenic particles approximately < 100 nm in size and of various shapes and compositions, are increasingly incorporated into commercial products and used for industrial and medical purposes. There is an exposure risk to both the population at large and individuals in the workplace with inhalation exposures to ENMs being a primary concern. Further, there is increasing evidence to suggest that certain ENMs may represent a significant health risk, and many of these ENMs exhibit distinct similarities with other particles and fibers that are known to induce adverse health effects, such as asbestos, silica, and particulate matter (PM). Evidence regarding the importance of lysosomal membrane permeabilization (LMP) and release of cathepsins in ENM toxicity has been accumulating. The aim of this review was to describe our current understanding of the mechanisms leading to ENM-associated pathologies, including LMP and the role of cathepsins with a focus on inflammation. In addition, anti-cathepsin agents, some of which have been tested in clinical trials and may prove useful for ameliorating the harmful effects of ENM exposure, are examined.