Phagocytosis of environmental or metabolic crystalline particles induces cytotoxicity by triggering necroptosis across a broad range of particle size and shape

Ferroptosis, necroptosis, and pyroptosis in calcium oxalate crystal-induced kidney injury

Kidney stones represent a highly prevalent urological disorder worldwide, with high incidence and recurrence rates. Calcium oxalate (CaOx) crystal-induced kidney injury serves as the foundational mechanism for the formation and progression of CaOx stones. Regulated cell death (RCD) such as ferroptosis, necroptosis, and pyroptosis are essential in the pathophysiological process of kidney injury. Ferroptosis, a newly discovered RCD, is characterized by its reliance on iron-mediated lipid peroxidation. Necroptosis, a widely studied programmed necrosis, initiates with a necrotic phenotype that resembles apoptosis in appearance. Pyroptosis, a type of RCD that involves the gasdermin protein, is accompanied by inflammation and immune response. In recent years, increasing amounts of evidence has demonstrated that ferroptosis, necroptosis, and pyroptosis are significant pathophysiological processes involved in CaOx crystal-induced kidney injury. Herein, we summed up the roles of ferroptosis, necroptosis, and pyroptosis in CaOx crystal-induced kidney injury. Furthermore, we delved into the curative potential of ferroptosis, necroptosis, and pyroptosis in CaOx crystal-induced kidney injury.

Coal dust particles can upregulate the expression of NLRP3 inflammasome components in rat alveolar macrophages through phagocytosis

Previous studies have demonstrated that silica can activate the NLRP3 inflammasome, and that macrophage phagocytosis is an essential step in this process. Although carbon is the primary component of coal dust particles, it also contains other impurities such as free silica, clay, sulfides, and carbonate minerals. Additional research is still necessary to discover if NLRP3 can be triggered due to the low silica content of coal dust particles. The purpose of this study is to investigate whether coal dust particles can induce the translation and transcription of NLRP3 inflammasome components in rat alveolar macrophages (NR8383) and whether Cytochalasin B may inhibit this process. According to the findings of our research, coal dust particles can upregulate the NLRP3 inflammasome components and IL-1β, a downstream inflammatory component. Furthermore, LPS and coal dust particles work in concert to raise the NLRP3 inflammasome components protein and transcript level in macrophages. Interestingly, the protein and transcript level of NLRP3 inflammasome components dramatically dropped when cells were concomitantly exposed to the actin polymerization inhibitor Cytochalasin B. This suggests that cellular uptake is required for coal dust particles to exert their pro-inflammatory effect.

Mechanistic studies of Ca2+-induced classical pyroptosis pathway promoting renal adhesion on calcium oxalate kidney stone formation

This study aims to investigate the role of hypercalciuria and pyroptosis in the formation of calcium oxalate kidney stones. Bioinformatics analysis was performed to compare the correlation of pyroptosis scores and cell adhesion scores between Randall's plaques and normal tissues from kidney stone patients. For the in vitro experiments, we investigated the effects of high concentrations of Ca2+ on the pyroptosis and adhesion levels of renal tubular epithelial cells and examined the adhesion levels and crystal aggregation of the cells in high Ca2+ concentrations environment by knockdown and overexpression of the key pyroptosis gene, GSDMD, and we verified the effects of Ca2+ concentration on pyroptosis and adhesion levels, kidney injury, and crystal deposition by in vivo experiments. Bioinformatic results showed that the scores of pyroptosis and cell adhesion in Randall's plaques of patients with kidney stones were significantly higher than those in normal tissues, and pyroptosis was highly positively correlated with cell adhesion. In vitro and in vivo experiments showed that high concentrations of Ca2+ activated the NLRP3/Caspase-1/GSDMD pathway of pyroptosis through ROS and up-regulated the expression of adhesion-related proteins, and GSDMD could regulate the adhesion level of renal tubular epithelial cells by mediating the level of pyroptosis, thereby affecting the adhesion and deposition of calcium oxalate crystals. Our findings reveal that the Ca2+-induced classical pyroptosis pathway may be a potential mechanism to promote calcium oxalate kidney stone formation, which provides new insights into the etiology of kidney stones.

Cell death‑related molecules and targets in the progression of urolithiasis (Review)

Urolithiasis is a high‑incidence disease caused by calcium oxalate (mainly), uric acid, calcium phosphate, struvite, apatite, cystine and other stones. The development of kidney stones is closely related to renal tubule cell damage and crystal adhesion and aggregation. Cell death, comprising the core steps of cell damage, can be classified into various types (i.e., apoptosis, ferroptosis, necroptosis and pyroptosis). Different crystal types, concentrations, morphologies and sizes cause tubular cell damage via the regulation of different forms of cell death. Oxidative stress caused by high oxalate or crystal concentrations is considered to be a precursor to a variety of types of cell death. In addition, complex crosstalk exists among numerous signaling pathways and their key molecules in various types of cell death. Urolithiasis is considered a metabolic disorder, and tricarboxylic acid cycle‑related molecules, such as citrate and succinate, are closely related to cell death and the inhibition of stone development. However, a literature review of the associations between kidney stone development, metabolism and various types of cell death is currently lacking, at least to the best of our knowledge. Thus, the present review summarizes the major advances in the understanding of regulated cell death and urolithiasis progression.

Results from omic approaches in rat or mouse models exposed to inhaled crystalline silica: a systematic review

BACKGROUND

Crystalline silica (cSiO2) is a mineral found in rocks; workers from the construction or denim industries are particularly exposed to cSiO2 through inhalation. cSiO2 inhalation increases the risk of silicosis and systemic autoimmune diseases. Inhaled cSiO2 microparticles can reach the alveoli where they induce inflammation, cell death, auto-immunity and fibrosis but the specific molecular pathways involved in these cSiO2 effects remain unclear. This systematic review aims to provide a comprehensive state of the art on omic approaches and exposure models used to study the effects of inhaled cSiO2 in mice and rats and to highlight key results from omic data in rodents also validated in human.

METHODS

The protocol of systematic review follows PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Eligible articles were identified in PubMed, Embase and Web of Science. The search strategy included original articles published after 1990 and written in English which included mouse or rat models exposed to cSiO2 and utilized omic approaches to identify pathways modulated by cSiO2. Data were extracted and quality assessment was based on the SYRCLE's Risk of Bias tool for animal studies.

RESULTS

Rats and male rodents were the more used models while female rodents and autoimmune prone models were less studied. Exposure of animals were both acute and chronic and the timing of outcome measurement through omics approaches were homogeneously distributed. Transcriptomic techniques were more commonly performed while proteomic, metabolomic and single-cell omic methods were less utilized. Immunity and inflammation were the main domains modified by cSiO2 exposure in lungs of mice and rats. Less than 20% of the results obtained in rodents were finally verified in humans.

CONCLUSION

Omic technics offer new insights on the effects of cSiO2 exposure in mice and rats although the majority of data still need to be validated in humans. Autoimmune prone model should be better characterised and systemic effects of cSiO2 need to be further studied to better understand cSiO2-induced autoimmunity. Single-cell omics should be performed to inform on pathological processes induced by cSiO2 exposure.

Bioinformatics-driven discovery of silica nanoparticles induces apoptosis and renal damage via the unfolded protein response in NRK-52E cells and rat kidney

Silica nanoparticles (SiNPs) are nanomaterials with widespread applications in drug delivery and disease diagnosis. Despite their utility, SiNPs can cause chronic kidney disease, hindering their clinical translation. The molecular mechanisms underlying SiNP-induced renal toxicity are complex and require further investigation. To address this challenge, we employed bioinformatics tools to predict the potential mechanisms underlying renal damage caused by SiNPs. We identified 1627 upregulated differentially expressed genes (DEGs) and 1334 downregulated DEGs. Functional enrichment analysis and protein-protein interaction network revealed that SiNP-induced renal damage is associated with apoptosis. Subsequently, we verified that SiNPs induced apoptosis in an in vitro model of NRK-52E cells via the unfolded protein response (UPR) in a dose-dependent manner. Furthermore, in an in vivo rat model, high-dose SiNP administration via tracheal drip caused hyalinization of the renal tubules, renal interstitial lymphocytic infiltration, and collagen fiber accumulation. Concurrently, we observed an increase in UPR-related protein levels at the onset of renal damage. Thus, our study confirmed that SiNPs induce apoptosis and renal damage through the UPR, adding to the theoretical understanding of SiNP-related kidney damage and offering a potential target for preventing and treating kidney injuries in SiNP clinical applications.

RIPK3 and kidney disease

Receptor interacting protein kinase 3 (RIPK3) is an intracellular kinase at the crossroads of cell death and inflammation. RIPK3 contains a RIP homotypic interaction motif (RHIM) domain which allows interactions with other RHIM-containing proteins and a kinase domain that allows phosphorylation of target proteins. RIPK3 may be activated through interaction with RHIM-containing proteins such as RIPK1, TRIF and DAI (ZBP1, DLM-1) or through RHIM-independent mechanisms in an alkaline intracellular pH. RIPK3 mediates necroptosis and promotes inflammation, independently of necroptosis, through either activation of NFκB or the inflammasome. There is in vivo preclinical evidence of the contribution of RIPK3 to both acute kidney injury (AKI) and chronic kidney disease (CKD) and to the AKI-to-CKD transition derived from RIPK3 deficient mice or the use of small molecule RIPK3 inhibitors. In these studies, RIPK3 targeting decreased inflammation but kidney injury improved only in some contexts. Clinical translation of these findings has been delayed by the potential of some small molecule inhibitors of RIPK3 kinase activity to trigger apoptotic cell death by inducing conformational changes of the protein. A better understanding of the conformational changes in RIPK3 that trigger apoptosis, dual RIPK3/RIPK1 inhibitors or repurposing of multiple kinase inhibitors such as dabrafenib may facilitate clinical development of the RIPK3 inhibition concept for diverse inflammatory diseases, including kidney diseases.

Carboxylated Pocoa polysaccharides inhibited oxidative damage and inflammation of HK-2 cells induced by calcium oxalate nanoparticles

The inhibitory effects of Chinese medicine Pocoa (PCPs) with different carboxyl group (-COOH) contents on oxidative damage and inflammatory response of renal epithelial cells and the influence of -COOH content in polysaccharides were investigated. HK-2 cell damage model was established by nanocalcium oxalate crystals (nanoCOM), and then PCPs with -COOH contents of 2.56% (PCP0), 7.48% (PCP1), 12.07% (PCP2), and 17.18% (PCP3) were used to protect the cells. PCPs could inhibit the damage of nanoCOM to HK-2 cells, increase cell viability, restore cytoskeleton and morphology, and improve lysosomal integrity. PCPs can reduce the oxidative stress response of nanoCOM to cells, inhibit the opening of mPTP and cell necrotic apoptosis, reduce the level of Ca2+ ions in cells, the production of ATP and MDA, and increase SOD expression. PCPs can also reduce the cellular inflammatory response caused by oxidative damage, and reduce the expression of nitric oxide (NO), inflammatory factors TNF-α, IL-6, IL-1β and MCP-1, as well as the content of inflammasome NLRP3. After protection, PCPs can inhibit the endocytosis of nanoCOM crystals by cells. With the increase in -COOH content in PCPs, its ability to inhibit nanoCOM cell damage, reduce oxidative stress, reduce inflammatory response, and inhibit crystal endocytosis increases, that is, PCP3 with the highest -COOH content, shows the best biological activity. Inhibiting cell damage and inflammation and reducing a large amount of endocytosis of crystals by cells are beneficial to inhibit the formation of kidney stones.

TIGAR protects against adenine-induced ferroptosis in human proximal tubular epithelial cells by activating the mTOR/S6KP70 axis

TP53-induced glycolysis and apoptosis regulator (TIGAR) acts as a switch for nephropathy, but its underlying mechanism is still unclear. The purpose of this study was to explore the potential biological significance and underlying mechanism of TIGAR in modulating adenine-induced ferroptosis in human proximal tubular epithelial (HK-2) cells. HK-2 cells under- or overexpressing TIGAR were challenged with adenine to induce ferroptosis. The levels of reactive oxygen species (ROS), iron, malondialdehyde (MDA), and glutathione (GSH) were assayed. Expression of ferroptosis-associated solute carrier family seven-member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4) at the level of mRNA and protein were measured by quantitative real-time-PCR and western blotting. The phosphorylation levels of proteins in the mTOR/S6KP70 pathway were determined by western blotting. Adenine overload triggered ferroptosis in HK-2 cells, as evidenced by reduced levels of GSH, SLC7A11, and GPX4, and increased levels of iron, MDA, and ROS. TIGAR overexpression repressed adenine-induced ferroptosis and induced mTOR/S6KP70 signaling. Inhibitors of mTOR and S6KP70 weakened the ability of TIGAR to inhibit adenine-induced ferroptosis. TIGAR inhibits adenine-induced ferroptosis in human proximal tubular epithelial cells by activating the mTOR/S6KP70 signaling pathway. Therefore, activating the TIGAR/mTOR/S6KP70 axis may be a treatment for crystal nephropathies.

Die hard: cell death mechanisms and their implications in nanotoxicology

Cell death is a fundamental biological process, and its fine-tuned regulation is required for life. However, the complexity of regulated cell death is often reduced to a matter of live-dead discrimination. Here, we provide a perspective on programmed or regulated cell death, focusing on apoptosis, pyroptosis, necroptosis, and ferroptosis (the latter three cell death modalities are examples of regulated necrosis). We also touch on other, recently described manifestations of (pathological) cell death including cuproptosis. Furthermore, we address how engineered nanomaterials impact on regulated cell death. We posit that an improved understanding of nanomaterial-induced perturbations of cell death may allow for a better prediction of the consequences of human exposure and could also yield novel approaches by which to mitigate these effects. Finally, we provide examples of the harnessing of nanomaterials to achieve cancer cell killing through the induction of regulated cell death.

Hyperuricemia and gout: effects on bone and articular cartilage (literature review)

Gout is a disease characterized by deposition of sodium monourate crystals in tissues which is the reason of inflammation among persons with hyperuricemia (HU). The prevalence of HU, which can be considered the first stage of gout formation, varies in different countries. Despite this, only a small number of persons with HU have been shown to develop symptoms of gout. Recent data suggest that HU is an independent risk factor for cartilage and bone damage. UA, both in the form of crystals and in a dissolved form, activates damage and potentiates cell death by releasing reactive oxygen species, activating the necroptosis pathway, neutrophil traps, synthesis of pro-inflammatory cytokines, and other pathogenetic mechanisms that cause the negative effects of HU and gout on articular cartilage and subchondral bone. The association of HU and osteoarthritis (OA) is well known and based on the common pathogenesis, but the direction of this relationship is still a debatable issue. The accumulated data suggest the need for a deeper study of the relationship of gout and asymptomatic HU with pathological processes leading to the development and progression of OA and disorders of bone metabolism.

Neutrophil-Epithelial Crosstalk During Intestinal Inflammation

Neutrophils are the most abundant leukocyte population in the human circulatory system and are rapidly recruited to sites of inflammation. Neutrophils play a multifaceted role in intestinal inflammation, as they contribute to the elimination of invading pathogens. Recently, their role in epithelial restitution has been widely recognized; however, they are also associated with bystander tissue damage. The intestinal epithelium provides a physical barrier to prevent direct contact of luminal contents with subepithelial tissues, which is extremely important for the maintenance of intestinal homeostasis. Numerous studies have demonstrated that transepithelial migration of neutrophils is closely related to disease symptoms and disruption of crypt architecture in inflammatory bowel disease and experimental colitis. There has been growing interest in how neutrophils interact with the epithelium under inflammatory conditions. Most studies focus on the effects of neutrophils on intestinal epithelial cells; however, the effects of intestinal epithelial cells on neutrophils during intestinal inflammation need to be well-established. Based on these data, we have summarized recent articles on the role of neutrophil-epithelial interactions in intestinal inflammation, particularly highlighting the epithelium-derived molecular regulators that mediate neutrophil recruitment, transepithelial migration, and detachment from the epithelium, as well as the functional consequences of their crosstalk. A better understanding of these molecular events may help develop novel therapeutic targets for mitigating the deleterious effects of neutrophils in inflammatory bowel disease.

Think Beyond Particle Cytotoxicity: When Self-Cellular Components Released After Immunogenic Cell Death Explain Chronic Disease Development

The prolonged perturbation of the immune system following the release of a plethora of self-molecules (known as damage-associated molecular patterns, DAMPs) by stressed or dying cells triggers acute and chronic pathological responses. DAMPs are commonly released after plasma membrane damage or complete rupture due to immunogenic cell death (ICD), upon numerous stressors including infectious and toxic agents. The set of DAMPs released after ICD include mature proinflammatory cytokines and alarmins, but also polymeric macromolecules. These self-intracellular components are recognized by injured and healthy surrounding cells via innate receptors, and induce upregulation of stress-response mechanisms, including inflammation. In this review, by overstepping the simple toxicological evaluation, we apply ICD and DAMP concepts to silica cytotoxicity, providing new insights on the mechanisms driving the progress and/or the exacerbation of certain SiO2–related pathologies. Finally, by proposing self-DNA as new crucial DAMP, we aim to pave the way for the development of innovative and easy-to-perform predictive tests to better identify the hazard of fine and ultrafine silica particles. Importantly, such mechanisms could be extended to nano/micro plastics and diesel particles, providing strategic advice and reports on their health issues.

Interaction between nanometer calcium oxalate and renal epithelial cells repaired with carboxymethylated polysaccharides

OBJECTIVE

Injury of renal tubular epithelial cells (HK-2) is an important cause of kidney stone formation. In this article, the repairing effect of polysaccharide (PCP0) extracted from the traditional Chinese medicine Poria cocos and its carboxymethylated derivatives on damaged HK-2 cells was studied, and the differences in adhesion and endocytosis of the cells to nanometer calcium oxalate monohydrate (COM) before and after repair were explored.

METHODS

Sodium oxalate (2.8 mmol/L) was used to damage HK-2 cells to establish a damage model, and then Poria cocos polysaccharides (PCPs) with different carboxyl (COOH) contents were used to repair the damaged cells. The changes in the biochemical indicators of the cells before and after the repair and the changes in the ability to adhere to and internalize nano-COM were detected.

RESULTS

The natural PCPs (PCP0, COOH content = 2.56%) were carboxymethylated, and three carboxylated modified Poria cocos with 7.48% (PCP1), 12.07% (PCP2), and 17.18% (PCP3) COOH contents were obtained. PCPs could repair the damaged HK-2 cells, and the cell viability was enhanced after repair. The cell morphology was gradually repaired, the proliferation and healing rate were increased. The ROS production was reduced, and the polarity of the mitochondrial membrane potential was restored. The level of intracellular Ca²⁺ ions decreased, and the autophagy response was weakened.

CONCLUSION

The cells repaired by PCPs inhibited the adhesion to nano-COM and simultaneously promoted the endocytosis of nano-COM. The endocytic crystals mainly accumulated in the lysosome. Inhibiting adhesion and increasing endocytosis could reduce the nucleation, growth, and aggregation of cell surface crystals, thereby inhibiting the formation of kidney stones. With the increase of COOH content in PCPs, its ability to repair damaged cells, inhibit crystal adhesion, and promote crystal endocytosis all increased, that is, PCP3 with the highest COOH content showed the best ability to inhibit stone formation.

Asymptomatic Hyperuricemia Promotes Recovery from Ischemic Organ Injury by Modulating the Phenotype of Macrophages

Acute organ injury, such as acute kidney injury (AKI) and disease (AKD), are major causes of morbidity and mortality worldwide. Hyperuricemia (HU) is common in patients with impaired kidney function but the impact of asymptomatic HU on the different phases of AKI/AKD is incompletely understood. We hypothesized that asymptomatic HU would attenuate AKD because soluble, in contrast to crystalline, uric acid (sUA) can attenuate sterile inflammation. In vitro, 10 mg/dL sUA decreased reactive oxygen species and interleukin-6 production in macrophages, while enhancing fatty acid oxidation as compared with a physiological concentration of 5 mg/dL sUA or medium. In transgenic mice, asymptomatic HU of 7–10 mg/dL did not affect post-ischemic AKI/AKD but accelerated the recovery of kidney excretory function on day 14. Improved functional outcome was associated with better tubular integrity, less peritubular inflammation, and interstitial fibrosis. Mechanistic studies suggested that HU shifted macrophage polarization towards an anti-inflammatory M2-like phenotype characterized by expression of anti-oxidative and metabolic genes as compared with post-ischemic AKI-chronic kidney disease transition in mice without HU. Our data imply that asymptomatic HU acts as anti-oxidant on macrophages and tubular epithelial cells, which endorses the recovery of kidney function and structure upon AKI.

Adenine overload induces ferroptosis in human primary proximal tubular epithelial cells

The pathogenesis of crystal nephropathy involves deposition of intratubular crystals, tubular obstruction and cell death. The deposition of 8-dihydroxyadenine (DHA) crystals within kidney tubules, for instance, is caused by a hereditary deficiency of adenine phosphoribosyl transferase in humans or adenine overload in preclinical models. However, the downstream pathobiological patterns of tubular cell attrition in adenine/DHA-induced nephropathy remain poorly understood. In this study, we investigated: (i) the modes of adenine-induced tubular cell death in an experimental rat model and in human primary proximal tubular epithelial cells (PTEC); and (ii) the therapeutic effect of the flavonoid baicalein as a novel cell death inhibitor. In a rat model of adenine diet-induced crystal nephropathy, significantly elevated levels of tubular iron deposition and lipid peroxidation (4-hydroxynonenal; 4-HNE) were detected. This phenotype is indicative of ferroptosis, a novel form of regulated necrosis. In cultures of human primary PTEC, adenine overload-induced significantly increased mitochondrial superoxide levels, mitochondrial depolarisation, DNA damage and necrotic cell death compared with untreated PTEC. Molecular interrogation of adenine-stimulated PTEC revealed a significant reduction in the lipid repair enzyme glutathione peroxidase 4 (GPX4) and the significant increase in 4-HNE compared with untreated PTEC, supporting the concept of ferroptotic cell death. Moreover, baicalein treatment inhibited ferroptosis in adenine-stimulated PTEC by selectively modulating the mitochondrial antioxidant enzyme superoxide dismutase 2 (SOD2) and thus, suppressing mitochondrial superoxide production and DNA damage. These data identify ferroptosis as the primary pattern of PTEC necrosis in adenine-induced nephropathy and establish baicalein as a potential therapeutic tool for the clinical management of ferroptosis-associated crystal nephropathies (e.g., DHA nephropathy, oxalate nephropathy).

Role of necroptosis of alveolar macrophages in acute lung inflammation of mice exposed to titanium dioxide nanoparticles

Titanium dioxide (TiO₂) nanoparticles are indispensable for daily life but induce acute inflammation, mainly via inhalation exposure. TiO₂ nanoparticles can be phagocytosed by alveolar macrophages (AMs) in vivo and cause necroptosis of exposed cells in vitro. However, the relationship between localization of TiO₂ nanoparticles in the lungs after exposure and their biological responses including cell death and inflammation remains unclear. This study was conducted to investigate the intra/extracellular localization of TiO₂ nanoparticles in murine lungs at 24 h after intratracheal exposure to rutile TiO₂ nanoparticles and subsequent local biological reactions, specifically necroptosis of AMs and lung inflammation. We found that TiO₂ exposure induced leukocyte migration into the alveolar region and increased the secretion of C-C motif ligand (CCL) 3 in the bronchoalveolar lavage (BAL) fluid. A combination of Raman spectroscopy and staining of cell and tissue samples confirmed that AMs phagocytose TiO₂. AMs that phagocytosed TiO₂ nanoparticles showed necroptosis, characterized by the expression of phosphorylated mixed lineage kinase domain-like protein and translocation of high mobility group box-1 from the cell nucleus to the cytoplasm. In primary cultured AMs, TiO₂ also induced necroptosis and increased the secretion of CCL3. Necroptosis inhibitors suppressed the increase in CCL3 secretion in both the BAL fluid and culture supernatant of AMs and suppressed the increase in leukocytes in the BAL fluid. These data suggest that necroptosis of AMs that phagocytose TiO₂ nanoparticles is involved as part of the mechanism by which TiO₂ induces acute lung inflammation.

DNA/RNA heteroduplex oligonucleotide technology for regulating lymphocytes in vivo

Manipulating lymphocyte functions with gene silencing approaches is promising for treating autoimmunity, inflammation, and cancer. Although oligonucleotide therapy has been proven to be successful in treating several conditions, efficient in vivo delivery of oligonucleotide to lymphocyte populations remains a challenge. Here, we demonstrate that intravenous injection of a heteroduplex oligonucleotide (HDO), comprised of an antisense oligonucleotide (ASO) and its complementary RNA conjugated to α-tocopherol, silences lymphocyte endogenous gene expression with higher potency, efficacy, and longer retention time than ASOs. Importantly, reduction of Itga4 by HDO ameliorates symptoms in both adoptive transfer and active experimental autoimmune encephalomyelitis models. Our findings reveal the advantages of HDO with enhanced gene knockdown effect and different delivery mechanisms compared with ASO. Thus, regulation of lymphocyte functions by HDO is a potential therapeutic option for immune-mediated diseases.

Centrality of Myeloid-Lineage Phagocytes in Particle-Triggered Inflammation and Autoimmunity

Exposure to exogenous particles found as airborne contaminants or endogenous particles that form by crystallization of certain nutrients can activate inflammatory pathways and potentially accelerate autoimmunity onset and progression in genetically predisposed individuals. The first line of innate immunological defense against particles are myeloid-lineage phagocytes, namely macrophages and neutrophils, which recognize/internalize the particles, release inflammatory mediators, undergo programmed/unprogrammed death, and recruit/activate other leukocytes to clear the particles and resolve inflammation. However, immunogenic cell death and release of damage-associated molecules, collectively referred to as "danger signals," coupled with failure to efficiently clear dead/dying cells, can elicit unresolved inflammation, accumulation of self-antigens, and adaptive leukocyte recruitment/activation. Collectively, these events can promote loss of immunological self-tolerance and onset/progression of autoimmunity. This review discusses critical molecular mechanisms by which exogenous particles (i.e., silica, asbestos, carbon nanotubes, titanium dioxide, aluminum-containing salts) and endogenous particles (i.e., monosodium urate, cholesterol crystals, calcium-containing salts) may promote unresolved inflammation and autoimmunity by inducing toxic responses in myeloid-lineage phagocytes with emphases on inflammasome activation and necrotic and programmed cell death pathways. A prototypical example is occupational exposure to respirable crystalline silica, which is etiologically linked to systemic lupus erythematosus (SLE) and other human autoimmune diseases. Importantly, airway instillation of SLE-prone mice with crystalline silica elicits severe pulmonary pathology involving accumulation of particle-laden alveolar macrophages, dying and dead cells, nuclear and cytoplasmic debris, and neutrophilic inflammation that drive cytokine, chemokine, and interferon-regulated gene expression. Silica-induced immunogenic cell death and danger signal release triggers accumulation of T and B cells, along with IgG-secreting plasma cells, indicative of ectopic lymphoid tissue neogenesis, and broad-spectrum autoantibody production in the lung. These events drive early autoimmunity onset and accelerate end-stage autoimmune glomerulonephritis. Intriguingly, dietary supplementation with ω-3 fatty acids have been demonstrated to be an intervention against silica-triggered murine autoimmunity. Taken together, further insight into how particles drive immunogenic cell death and danger signaling in myeloid-lineage phagocytes and how these responses are influenced by the genome will be essential for identification of novel interventions for preventing and treating inflammatory and autoimmune diseases associated with these agents.

Potentially Pathogenic Calcium Oxalate Dihydrate and Titanium Dioxide Crystals in the Alzheimer's Disease Entorhinal Cortex

Knowing that Alzheimer's disease (AD) nucleates in the entorhinal cortex (EC), samples of 12 EC specimens were probed for crystals by a protocol detecting fewer than 1/5000th of those present. Of the 61 crystals found, 31 were expected and 30 were novel. Twenty-one crystals of iron oxides and 10 atherosclerosis-associated calcium pyrophosphate dihydrate crystals were expected and found. The 30 unexpected crystals were NLRP3-inflammasome activating calcium oxalate dihydrate (12) and titanium dioxide (18). Their unusual distribution raises the possibility that some were of AD origination sites.

TRPV1 Hyperfunction Contributes to Renal Inflammation in Oxalate Nephropathy

Inflammation worsens oxalate nephropathy by exacerbating tubular damage. The transient receptor potential vanilloid 1 (TRPV1) channel is present in kidney and has a polymodal sensing ability. Here, we tested whether TRPV1 plays a role in hyperoxaluria-induced renal inflammation. In TRPV1-expressed proximal tubular cells LLC-PK₁, oxalate could induce cell damage in a time- and dose-dependent manner; this was associated with increased arachidonate 12-lipoxygenase (ALOX12) expression and synthesis of endovanilloid 12(S)-hydroxyeicosatetraenoic acid for TRPV1 activation. Inhibition of ALOX12 or TRPV1 attenuated oxalate-mediated cell damage. We further showed that increases in intracellular Ca²⁺ and protein kinase C α activation are downstream of TRPV1 for NADPH oxidase 4 upregulation and reactive oxygen species formation. These trigger tubular cell inflammation via increased NLR family pyrin domain-containing 3 expression, caspase-1 activation, and interleukin (IL)-1β release, and were alleviated by TRPV1 inhibition. Male hyperoxaluric rats demonstrated urinary supersaturation, tubular damage, and oxidative stress in a time-dependent manner. Chronic TRPV1 inhibition did not affect hyperoxaluria and urinary supersaturation, but markedly reduced tubular damage and calcium oxalate crystal deposition by lowering oxidative stress and inflammatory signaling. Taking all these results together, we conclude that TRPV1 hyperfunction contributes to oxalate-induced renal inflammation. Blunting TRPV1 function attenuates hyperoxaluric nephropathy.

Targeting nonapoptotic pathways with functionalized nanoparticles for cancer therapy: current and future perspectives

Apoptotic death evasion is a hallmark of cancer progression. In this context, past decades have witnessed cytotoxic agents targeting apoptosis. However, owing to cellular defects in the apoptotic machinery, tumors develop resistance to apoptosis-based cancer therapies. Hence, targeting nonapoptotic cell-death pathways displays enhanced therapeutic success in apoptosis-defective tumor cells. Exploitation of multifunctional properties of engineered nanoparticles may allow cancer therapeutics to target yet unexplored pathways such as ferroptosis, autophagy and necroptosis. Necroptosis presents a programmed necrotic death initiated by same apoptotic death signals that are caspase independent, whereas autophagy is self-degradative causing vacuolation, and ferroptosis is an iron-dependent form driven by lipid peroxidation. Targeting these tightly regulated nonapoptotic pathways may emerge as a new direction in cancer drug development, diagnostics and novel cancer nanotherapeutics. This review highlights the current challenges along with the advancement in this field of research and finally summarizes the future perspective in terms of their clinical merits.

6,7-Dihydroxycoumarin ameliorates crystal-induced necroptosis during crystal nephropathies by inhibiting MLKL phosphorylation

AIMS

Mineralization of crystalline particles and the formation of renal calculi contribute to the pathogenesis of crystal nephropathies. Several recent studies on the biology of crystal handling implicated intrarenal crystal deposition-induced necroinflammation in their pathogenesis. We hypothesized that 6,7-dihydroxycoumarin (DHC) inhibit intrarenal crystal cytotoxicity and necroinflammation, and ameliorate crystal-induced chronic kidney disease (CKD).

MAIN METHODS

An unbiased high content screening coupled with fluorescence microscopy was used to identify compounds that inhibit CaOx crystal cytotoxicity. The ligand-protein interactions were identified using computational models e.g. molecular docking and molecular dynamics simulations. Furthermore, mice and rat models of oxalate-induced CKD were used for in-vivo studies. Renal injury, crystal deposition, and fibrosis were assessed by histology analysis. Western blots were used to quantify the protein expression. Data were expressed as boxplots and analyzed using one way ANOVA.

KEY FINDINGS

An unbiased high-content screening in-vitro identified 6,7-DHC as a promising candidate. Further, 6,7-DHC protected human and mouse cells from calcium oxalate (CaOx) crystal-induced necroptosis in-vitro as well as mice and rats from oxalate-induced CKD in either preventive or therapeutic manner. Computational modeling demonstrated that 6,7-DHC interact with MLKL, the key protein in the necroptosis machinery, and inhibit its phosphorylation by ATP, which was evident in both in-vitro and in-vivo analyses.

SIGNIFICANCE

Together, our results indicate that 6,7-DHC possesses a novel pharmacological property as a MLKL inhibitor and could serve as a lead molecule for further development of coumarin-based novel MLKL inhibitors. Furthermore, our data identify 6,7-DHC as a novel therapeutic strategy to combat crystal nephropathies.

Effects of advanced glycation end products on dental pulp calcification

OBJECTIVE

The main aim of this study was to elucidate the effects of advanced glycation end products (AGEs) on the calcification of cultured rat dental pulp cells (RDPCs) and to investigate the crystallisation ability of glycated collagen.

MATERIALS AND METHODS

AGEs were prepared via non-enzymatic glycation of a dish coated with type I collagen using dl-glyceraldehyde. To investigate the effects of AGEs on RDPCs, we performed WST-1 and lactate dehydrogenase assays; alkaline phosphatase, Alizarin Red S and immunohistochemical staining; and real-time quantitative reverse transcription PCR. In addition, we performed crystallisation experiments on glycated collagen. All microstructures were analysed using scanning electron microscopy/energy-dispersive X-ray spectroscopy and transmission electron microscopy/diffraction pattern analysis.

RESULTS

AGEs did not affect the proliferation or differentiation of RDPCs, but enhanced the calcification rate and cytotoxicity. No major calcification-related genes or proteins were involved in these calcifications, and glycated collagen was found to exhibit a negative polarity and form calcium phosphate crystals. Cytotoxicity due to drastic changes in the concentration of pericellular ions led to dystrophic calcification, assumed to represent an aspect of diabetic pulp calcifications.

CONCLUSION

Glycated collagen-containing AGEs provide a nurturing environment for crystallisation and have a significant effect on the early calcification of RDPCs.

Oxidative stress and inflammasome activation in human rhabdomyolysis-induced acute kidney injury

Acute kidney injury (AKI) is a life-threatening complication of rhabdomyolysis. The pathophysiological mechanisms of rhabdomyolysis-induced AKI (RIAKI) have been extensively studied in the murine system, yet clinical translation of this knowledge to humans is lacking. In this study, we investigated the cellular and molecular pathways of human RIAKI. Renal biopsy tissue from a RIAKI patient was examined by quantitative immunohistochemistry (Q-IHC) and compared to healthy kidney cortical tissue. We identified myoglobin casts and uric acid localised to sites of histological tubular injury, consistent with the diagnosis of RIAKI. These pathological features were associated with tubular oxidative stress (4-hydroxynonenal staining), regulated necrosis/necroptosis (phosphorylated mixed-lineage kinase domain-like protein staining) and inflammation (tumour necrosis factor (TNF)-α staining). Expression of these markers was significantly elevated in the RIAKI tissue compared to the healthy control. A tubulointerstitial inflammatory infiltrate accumulated adjacent to these sites of RIAKI oxidative injury, consisting of macrophages (CD68), dendritic cells (CD1c) and T lymphocytes (CD3). Foci of inflammasome activation were co-localised with these immune cell infiltrate, with significantly increased staining for adaptor protein ASC (apoptosis-associated speck-like protein containing a caspase activation and recruitment domain) and active caspase-1 in the RIAKI tissue compared to the healthy control. Our clinical findings identify multiple pathophysiological pathways previously only reported in murine RIAKI, providing first evidence in humans linking deposition of myoglobin and presence of uric acid to tubular oxidative stress/necroptosis, inflammasome activation and necroinflammation.

Alum triggers infiltration of human neutrophils ex vivo and causes lysosomal destabilization and mitochondrial membrane potential-dependent NET-formation

Aluminium salts have been used in vaccines for decades. However, the mechanisms underlying their adjuvant effect are still unclear. Neutrophils, the first immune cells at the injection site, can release cellular DNA together with granular material, so‐called neutrophil extracellular traps (NETs). In mice, NETs apparently play a role in aluminium hydroxide (alum)‐adjuvant immune response to vaccines. Although no experimental data exist, this effect is assumed to be operative also in humans. As a first step to verify this knowledge in humans, we demonstrate that the injection of alum particles into human skin biopsies ex vivo leads to similar tissue infiltration of neutrophils and NET‐formation. Moreover, we characterized the mechanism leading to alum‐induced NET‐release in human neutrophils as rapid, NADPH oxidase‐independent process involving charge, phagocytosis, phagolysosomal rupture, Ca²⁺‐flux, hyperpolarization of the mitochondrial membrane, and mitochondrial ROS. Extracellular flow and inhibition experiments suggested that no additional energy from oxidative phosphorylation or glycolysis is required for NET‐release. This study suggests a so far unappreciated role for neutrophils in the initial phase of immune responses to alum‐containing vaccines in humans and provides novel insights into bioenergetic requirements of NET‐formation.

Statins ameliorate cholesterol-induced inflammation and improve AQP2 expression by inhibiting NLRP3 activation in the kidney

Background: Chronic kidney diseases (CKD) are usually associated with dyslipidemia. Statin therapy has been primarily recommended for the prevention of cardiovascular risk in patients with CKD; however, the effects of statins on kidney disease progression remain controversial. This study aims to investigate the effects of statin treatment on renal handling of water in patients and in animals on a high-fat diet.

Methods: Retrospective cohort patient data were reviewed and the protein expression levels of aquaporin-2 (AQP2) and NLRP3 inflammasome adaptor ASC were examined in kidney biopsy specimens. The effects of statins on AQP2 and NLRP3 inflammasome components were examined in nlrp3^-/- mice, 5/6 nephroectomized (5/6Nx) rats with a high-fat diet (HFD), and in vitro.

Results: In the retrospective cohort study, serum cholesterol was negatively correlated to eGFR and AQP2 protein expression in the kidney biopsy specimens. Statins exhibited no effect on eGFR but abolished the negative correlation between cholesterol and AQP2 expression. Whilst nlrp3^+/+ mice showed an increased urine output and a decreased expression of AQP2 protein after a HFD, which was moderately attenuated in nlrp3 deletion mice with HFD. In 5/6Nx rats on a HFD, atorvastatin markedly decreased the urine output and upregulated the protein expression of AQP2. Cholesterol stimulated the protein expression of NLRP3 inflammasome components ASC, caspase-1 and IL-1β, and decreased AQP2 protein abundance in vitro, which was markedly prevented by statins, likely through the enhancement of ASC speck degradation via autophagy.

Conclusion: Serum cholesterol level has a negative correlation with AQP2 protein expression in the kidney biopsy specimens of patients. Statins can ameliorate cholesterol-induced inflammation by promoting the degradation of ASC speck, and improve the expression of aquaporin in the kidneys of animals on a HFD.

A guide to crystal-related and nano- or microparticle-related tissue responses

Crystals and nano- and microparticles form inside the human body from intrinsic proteins, minerals, or metabolites or enter the body as particulate matter from occupational and environmental sources. Associated tissue injuries and diseases mostly develop from cellular responses to such crystal deposits and include inflammation, cell necrosis, granuloma formation, tissue fibrosis, and stone-related obstruction of excretory organs. But how do crystals and nano- and microparticles trigger these biological processes? Which pathomechanisms are identical across different particle types, sizes, and shapes? In addition, which mechanisms are specific to the atomic or molecular structure of crystals or to specific sizes or shapes? Do specific cellular or molecular mechanisms qualify as target for therapeutic interventions? Here, we provide a guide to approach this diverse and multidisciplinary research domain. We give an overview about the clinical spectrum of crystallopathies, about shared and specific pathomechanisms as a conceptual overview before digging deeper into the specialty field of interest.

Plasma Proteins and Platelets Modulate Neutrophil Clearance of Malaria-Related Hemozoin Crystals

Hemozoin is an insoluble crystalline pigment produced by the malaria parasite Plasmodia upon digesting host hemoglobin inside red blood cells. Red blood cell rupture releases hemozoin crystals into the circulation from where they are cleared by phagocytes such as neutrophils. We speculated that plasma proteins would affect the ability of neutrophils to clear hemozoin crystals. To test this, we cultured human blood neutrophils with hemozoin ex vivo and found that neutrophils ingested hemozoin (0.1-1 µm crystal size) in a dose-dependent manner into phagosomes and vesicles/vacuoles, resulting in morphological changes including nuclear enlargement, and vesicle formation, but not cell membrane rupture or release of neutrophil extracellular traps. The presence of human plasma significantly inhibited the ability of neutrophils to ingest hemozoin crystals. Platelet-poor plasma further inhibited the uptake of hemozoin by neutrophils. Selective exposure to fibrinogen completely replicated the plasma effect. Taken together, neutrophils cleared hemozoin crystals from the extracellular space via endocytosis into phagosomes and vesicles without inducing the release of neutrophil extracellular traps. However, human plasma components such as fibrinogen limited hemozoin clearance, whereas the presence of platelets augmented this process. These factors may influence the pro-inflammatory potential of hemozoin crystals in malaria.

B-RAFV600E Inhibitor Dabrafenib Attenuates RIPK3-Mediated Necroptosis and Promotes Functional Recovery after Spinal Cord Injury

The receptor-interacting protein kinase 3 (RIPK3) is a key regulator of necroptosis and is involved in various pathologies of human diseases. We previously reported that RIPK3 expression is upregulated in various neural cells at the lesions and necroptosis contributed to secondary neural tissue damage after spinal cord injury (SCI). Interestingly, recent studies have shown that the B-RAF^V600E inhibitor dabrafenib has a function to selectively inhibit RIPK3 and prevents necroptosis in various disease models. In the present study, using a mouse model of thoracic spinal cord contusion injury, we demonstrate that dabrafenib administration in the acute phase significantly inhibites RIPK3-mediated necroptosis in the injured spinal cord. The administration of dabrafenib attenuated secondary neural tissue damage, such as demyelination, neuronal loss, and axonal damage, following SCI. Importantly, the neuroprotective effect of dabrafenib dramatically improved the recovery of locomotor and sensory functions after SCI. Furthermore, the electrophysiological assessment of the injured spinal cord objectively confirmed that the functional recovery was enhanced by dabrafenib. These findings suggest that the B-RAF^V600E inhibitor dabrafenib attenuates RIPK3-mediated necroptosis to provide a neuroprotective effect and promotes functional recovery after SCI. The administration of dabrafenib may be a novel therapeutic strategy for treating patients with SCI in the future.

Protective effect of dabrafenib on renal ischemia-reperfusion injury in vivo and in vitro

AIMS

Ischemia-reperfusion injury (IRI) is a major cause of acute kidney injury (AKI), which can lead to poor outcome and increased risk of mortality. Dabrafenib (DAB) is an approved cancer treatment. Little is known about the effect of DAB in prevention or treatment of renal IRI.

METHODS

For in vivo experiments, C57BL/6 mice were divided into four groups: sham (no IRI, no DAB), IRI, DAB, and DAB + IRI. IRI was induced by clamping of bilateral renal pedicles for 30 min. For in vitro experiments, HK-2 cells were used to establish the hypoxia/reoxygenation (H/R) injury model, with four groups: control (no H/R, no DAB), H/R, DAB, and DAB + H/R. Renal function and renal histological changes were recorded. Expression of NGAL and KIM-1 proteins and mRNAs were determined by western blotting and qRT-PCR; secretion of inflammatory cytokines (IL-6 and TNF- α) was determined by qRT-PCR; Cell death was determined using the TUNEL assay, measurement of cleaved caspase-3, and flow cytometry. Necroptosis-related proteins were determined by western blotting.

RESULTS

In mice, DAB pretreatment improved renal function and also reduced histological injury, inflammation, cell death, and expression of necroptosis-associated proteins. In HK-2 cells, DAB significantly decreased the levels of NGAL and KIM-1, inflammatory cytokines, cell death, and necroptosis-related proteins.

CONCLUSION

Our in vitro and in vivo experiments indicated that DAB appears to alleviate renal IRI by suppressing cell death and inhibiting inflammatory responses. DAB has potential use for the clinical prevention and treatment of AKI-induced IRI.

Aconitine induces cardiomyocyte damage by mitigating BNIP3-dependent mitophagy and the TNFα-NLRP3 signalling axis

Objectives

Aconitine, the natural product extracted from Aconitum species, is widely used for the treatment of various diseases, including rheumatism, arthritis, bruises, fractures and pains. However, many studies have reported cardiotoxicity and neurotoxicity caused by aconitine, but the detailed mechanism underlying aconitine's effect on these processes remains unclear.

Materials and methods

The effects of aconitine on the inflammation, apoptosis and viability of H9c2 rat cardiomyocytes were evaluated by flow cytometry, Western blot, RNA sequencing and bioinformatics analysis.

Results

Aconitine suppressed cardiomyocyte proliferation and induced inflammation and apoptosis in a dose‐ and time‐dependent manner. These inflammatory damages could be reversed by a TNFα inhibitor and BNIP3‐mediated mitophagy. Consistent with the in vitro results, overexpression of BNIP3 in heart tissue partially suppressed the cardiotoxicity of aconitine by inhibiting apoptosis and the NLRP3 inflammasome.

Conclusions

Our findings lay a foundation for the application of a TNFα inhibitor and BNIP3 to aconitine‐induced cardiac toxicity prevention and therapy, thereby demonstrating potential for further investigation.

Docosahexaenoic Acid Suppresses Silica-Induced Inflammasome Activation and IL-1 Cytokine Release by Interfering With Priming Signal

Occupational exposure to respirable crystalline silica (cSiO₂) has been etiologically linked to human autoimmunity. Intranasal instillation with cSiO₂ triggers profuse inflammation in the lung and onset of autoimmunity in lupus-prone mice; however, dietary supplementation with the omega-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) abrogates these responses. Inflammasome activation, IL-1 cytokine release, and death in alveolar macrophages following cSiO₂ exposure are early and critical events that likely contribute to triggering premature autoimmune pathogenesis by this particle. Here we tested the hypothesis that DHA suppresses cSiO₂-induced NLRP3 inflammasome activation, IL-1 cytokine release, and cell death in the macrophage. The model used was the murine macrophage RAW 264.7 cell line stably transfected with the inflammasome adapter protein ASC (RAW-ASC). Following priming with LPS, both the canonical activator nigericin and cSiO₂ elicited robust inflammasome activation in RAW-ASC cells, as reflected by IL-1β release and caspase-1 activation. These responses were greatly diminished or absent in wild-type RAW cells. In contrast to IL-1β, cSiO₂ induced IL-1α release in both RAW-ASC and to a lesser extent in RAW-WT cells after LPS priming. cSiO₂-driven effects in RAW-ASC cells were confirmed in bone-marrow derived macrophages. Pre-incubating RAW-ASC cells with 10 and 25 μM DHA for 24 h enriched this fatty acid in the phospholipids by 15- and 25-fold, respectively, at the expense of oleic acid. DHA pre-incubation suppressed inflammasome activation and release of IL-1β and IL-1α by nigericin, cSiO₂, and two other crystals - monosodium urate and alum. DHA's suppressive effects were linked to inhibition of LPS-induced Nlrp3, Il1b, and Il1a transcription, potentially through the activation of PPARγ. Finally, nigericin-induced death was inflammasome-dependent, indicative of pyroptosis, and could be inhibited by DHA pretreatment. In contrast, cSiO₂-induced death was inflammasome-independent and not inhibited by DHA. Taken together, these findings indicate that DHA suppresses cSiO₂-induced inflammasome activation and IL-1 cytokine release in macrophages by acting at the level of priming, but was not protective against cSiO₂-induced cell death.

Cell Death in the Kidney

Apoptotic cell death is usually a response to the cell's microenvironment. In the kidney, apoptosis contributes to parenchymal cell loss in the course of acute and chronic renal injury, but does not trigger an inflammatory response. What distinguishes necrosis from apoptosis is the rupture of the plasma membrane, so necrotic cell death is accompanied by the release of unprocessed intracellular content, including cellular organelles, which are highly immunogenic proteins. The relative contribution of apoptosis and necrosis to injury varies, depending on the severity of the insult. Regulated cell death may result from immunologically silent apoptosis or from immunogenic necrosis. Recent advances have enhanced the most revolutionary concept of regulated necrosis. Several modalities of regulated necrosis have been described, such as necroptosis, ferroptosis, pyroptosis, and mitochondrial permeability transition-dependent regulated necrosis. We review the different modalities of apoptosis, necrosis, and regulated necrosis in kidney injury, focusing particularly on evidence implicating cell death in ectopic renal calcification. We also review the evidence for the role of cell death in kidney injury, which may pave the way for new therapeutic opportunities.

Extracellular traps in kidney disease

During the past decade the formation of neutrophil extracellular traps (NETs) has been recognized as a unique modality of pathogen fixation (sticky extracellular chromatin) and pathogen killing (cytotoxic histones and proteases) during host defense, as well as collateral tissue damage. Numerous other triggers induce NET formation in multiple forms of sterile inflammation, including thrombosis, gout, obstruction of draining ducts, and trauma. Whether neutrophils always die along with NET release, and if they do die, how, remains under study and is most likely context dependent. In certain settings, neutrophils release NETs while undergoing regulated necrosis-for example, necroptosis. NETs and extracellular traps (ETs) released by macrophages also have been well documented in kidney diseases-for example, in various forms of acute kidney injury. Histones released from ETs and other sources are cytotoxic and elicit inflammation, contributing to necroinflammation of the early-injury phase of acute tubular necrosis in antineutrophil cytoplasmic antibody-related renal vasculitis, anti-glomerular basement membrane disease, lupus nephritis, and thrombotic microangiopathies. Finally, acute kidney injury-related releases of dying renal cells or ETs promote remote organ injuries-for example, acute respiratory distress syndrome. In this review, we summarize what is known about the release of ETs from neutrophils and macrophages in the kidney, the available experimental evidence, and ongoing discussions in the field.

The Pyroptotic Cell Death Effector Gasdermin D Is Activated by Gout-Associated Uric Acid Crystals but Is Dispensable for Cell Death and IL-1β Release

The pyroptotic cell death effector gasdermin D (GSDMD) is required for murine models of hereditary inflammasome-driven, IL-1β-dependent, autoinflammatory disease, making it an attractive therapeutic target. However, the importance of GSDMD for more common conditions mediated by pathological IL-1β activation, such as gout, remain unclear. In this study, we address whether GSDMD and the recently described GSDMD inhibitor necrosulfonamide (NSA) contribute to monosodium urate (MSU) crystal-induced cell death, IL-1β release, and autoinflammation. We demonstrate that MSU crystals, the etiological agent of gout, rapidly activate GSDMD in murine macrophages. Despite this, the genetic deletion of GSDMD or the other lytic effector implicated in MSU crystal killing, mixed lineage kinase domain-like (MLKL), did not prevent MSU crystal-induced cell death. Consequently, GSDMD or MLKL loss did not hinder MSU crystal-mediated release of bioactive IL-1β. Consistent with in vitro findings, IL-1β induction and autoinflammation in MSU crystal-induced peritonitis was not reduced in GSDMD-deficient mice. Moreover, we show that the reported GSDMD inhibitor, NSA, blocks inflammasome priming and caspase-1 activation, thereby preventing pyroptosis independent of GSDMD targeting. The inhibition of cathepsins, widely implicated in particle-induced macrophage killing, also failed to prevent MSU crystal-mediated cell death. These findings 1) demonstrate that not all IL-1β-driven autoinflammatory conditions will benefit from the therapeutic targeting of GSDMD, 2) document a unique mechanism of MSU crystal-induced macrophage cell death not rescued by pan-cathepsin inhibition, and 3) show that NSA inhibits inflammasomes upstream of GSDMD to prevent pyroptotic cell death and IL-1β release.

Human proximal tubular cells can form calcium phosphate deposits in osteogenic culture: role of cell death and osteoblast-like transdifferentiation

Nephrocalcinosis is a clinicopathological entity characterized by microscopic calcium crystals in the renal parenchyma, within the tubular lumen or in the interstitium. Crystal binding to tubular cells may be the cause underlying nephrocalcinosis and nephrolithiasis. Pathological circumstances, such as acute cortical necrosis, may induce healthy cells to acquire a crystal-binding phenotype. The present study aimed to investigate whether human renal proximal tubular cells (HK-2 cells) can form calcium phosphate deposits under osteogenic conditions, and whether apoptosis and/or osteogenic-like processes are involved in cell calcification. HK-2 cells were cultured in standard or osteogenic medium for 1, 5, and 15 days. Von Kossa staining and ESEM were used to analyze crystal deposition. Apoptosis was investigated, analyzing caspase activation by in-cell Western assay, membrane translocation of phosphotidylserine by annexin V-FITC/propidium iodide staining, and DNA fragmentation by TUNEL assay. qRT/PCR, immunolabeling and cytochemistry were performed to assess osteogenic activation (Runx2, Osteonectin, Osteopontin and ALP), and early genes of apoptosis (BAX, Bcl-2). HK-2 cell mineralization was successfully induced on adding osteogenic medium. Calcium phosphate deposition increased in a time-dependent manner, and calcified cell aggregates exhibited characteristic signs of apoptosis. At 15 days, calcifying HK-2 cells revealed osteogenic markers, such as Runx2, ALP, osteonectin and osteopontin. Monitoring the processes at 1, 5, and 15 days showed apoptosis starting already after 5 days of osteogenic induction, when the first small calcium phosphate crystals began to appear on areas where cell aggregates were in apoptotic conditions. The cell death process proved caspase-dependent. The importance of apoptosis was reinforced by the time-dependent increase in BAX expression, starting from day 1. These findings strongly support the hypothesis that apoptosis triggered HK-2 calcification even before any calcium phosphate crystal deposition or acquisition of an osteogenic phenotype.

Systematic Overview of Solid Particles and Their Host Responses

Crystalline/particulate substances trigger a plethora of signaling events in host cells. The most prominent consequence is the inflammatory reactions that underlie crystal arthropathies, such as gout and pseudogout. However, their impact on our health was underestimated. Recent work on the role of cholesterol crystal in the development of atherosclerosis and the harm of environmental particulates has set up new frontiers in our defense against their detrimental effects. On the other hand, in the last 100 years, crystalline/particulate substances have been used with increasing frequencies in our daily lives as a part of new industrial manufacturing and engineering. Importantly, they have become a tool in modern medicine, used as vaccine adjuvants and drug delivery vehicles. Their biological effects are also being dissected in great detail, particularly with regard to their inflammatory signaling pathways. Solid structure interaction with host cells is far from being uniform, with outcomes dependent on cell types and chemical/physical properties of the particles involved. In this review, we offer a systematic and broad outlook of this landscape and a sage analysis of the complex nature of this topic.

Novel Insights into Crystal-Induced Kidney Injury

Background

The entity of crystal nephropathies encompasses a spectrum of different kidney injuries induced by crystal-formed intrinsic minerals, metabolites, and proteins or extrinsic dietary components and drug metabolites. Depending on the localization and dynamics of crystal deposition, the clinical presentation can be acute kidney injury, progressive chronic kidney disease, or renal colic.

Summary

The molecular mechanisms involving crystal-induced injury are diverse and remain poorly understood. Type 1 crystal nephropathies arise from crystals in the vascular lumen (cholesterol embolism) or the vascular wall (atherosclerosis) and involve kidney infarcts or chronic ischemia, respectively. Type 2 crystal nephropathies arise from intratubular crystal deposition causing obstruction, interstitial inflammation, and tubular cell injury. NLRP3 inflammasome and necroptosis drive renal necroinflammation in acute settings. Type 3 is represented by crystal and stone formation in the draining urinary tract, i.e., urolithiasis, causing renal colic and chronic obstruction.

Key Messages

Dissecting the types of injury is the first step towards a better understanding of the pathophysiology of crystal nephropathies. Crystal-induced acti-vation of the inflammasome and necroptosis, crystal adhesion, crystallization inhibitors, extratubulation, and granulo-ma formation are only a few of certainly many involved pathomechanisms that deserve further studies to eventually form the basis for innovative cures for these diseases.

Immune-enhancing activity of C. militaris fermented with Pediococcus pentosaceus (GRC-ON89A) in CY-induced immunosuppressed model

Background

Cordyceps militaris (C. militaris) is reported to exert various immune-activities. To enhance its activity, we fermented C.militaris with Pediococcus pentosaceus ON89A (GRC-ON89A). In this study, we investigated the immune-enhancing activity GRC-ON89A, using immunosuppressed model.

Methods

Immunosuppression was induced by intraperitoneal injection of cyclophosphamide (CY). Each group was orally administered distilled water, GRC-ON89A or GRC, respectively. The phagocytic activities against IgG -opsonized FITC particles were measured using phagocytosis assay kit. The contents β-glucan, cordycepin and SCFA were measured using β-glucan kit, liquid chromatography-mass spectrometry analysis and Gas chromatography-mass spectrometry analysis, respectively.

Results

Among GRC fermented with different probiotic strains (Pediococcus pentossaceus ON89A, Lactobacillus pentosus SC64, Weissella cibaria Sal.Cla22), GRC-ON89A induced the highest elevation of nitric oxide production and enhanced phagocytic activity of RAW 264.7 cells. In primary cultured murine macrophages from normal and CY-treated mice, GRC-ON89A increased phagocytic activity, compared to that in control cells. GRC-ON89A also significantly induced the mRNA expression of TNF-α and IL-10 and the levels of phosphorylated Lyn, Syk and MAPK. The contents of β-glucan, cordycepin and SCFA in GRC significantly increased after ON89A fermentation, compared to those in unfermented GRC.

Conclusion

These results indicate that GRC-ON89A exerted the enhanced immunostimulatory activity and contained more nutritional components, compared to unfermented GRC. Our results suggested that GRC-ON89A may be applied as an agent for immune boosting therapy in immune suppressed patients.