Nickel (II) nitrate hexahydrate triggered canine neutrophil extracellular traps release in vitro

Ambient NO2 hinders neutrophil extracellular trap formation in rats: Assessment of the role of neutrophil autophagy

NO₂ has been known to impair immunity and exacerbate susceptibility to infectious diseases. However, scant notice has been taken of the effect of NO₂ on neutrophils. Neutrophil extracellular traps (NETs) formation is necessary for NETosis development by neutrophils as an immune system against pathogens. By analyzing the morphology and signature components of NETs, we focused for the first time on finding that 10 ppm of NO₂ exposure for 15 consecutive days can hinder the formation of NETs. Next, we used NO₂ in vivo derivatives to probe the mechanism for NETs formation in vitro. Our findings showed that NO₂ suppression of respiratory burst levels and mitogen-activated protein kinase (MAPK)/Phosphoinositide 3-kinase (PI3K)-protein kinase B (AKT) signaling was related to NO₂ reduction in NETs formation. Inhibition of phorbol myristate acetate (PMA)-induced NETs formation by NO₂ hindered autophagy, as evidenced by increased mTOR protein expression, decreased LC3 protein expression, and reduced autophagic vesicles. By activating mTOR-mediated autophagy, rapamycin (Rapa) reduced the inhibition of PMA-induced NETs by NO₂. This study will provide valuable insights into the mechanisms of immunotoxicity of NO₂, new insights into the etiology of diseases linked to NETs formation, and a theoretical basis for protection against such illnesses.

Saxitoxin induces the release of human neutrophil extracellular traps

Saxitoxin (STX) is a potent shellfish toxin found in freshwater and marine ecosystems which threatens human health by contaminating drinking water and shellfish. The formation of neutrophil extracellular traps (NETs) is a defense mechanism employed by polymorphonuclear leukocytes (PMNs) to destroy invading pathogens, and also plays a critical role in the pathogenesis of various diseases. In this study, we aimed to investigate the role of STX on human NET formation. Typical NETs-associated characteristics were detected from STX-stimulated PMNs using immunofluorescence microscopy. Moreover, NET quantification based on PicoGreen® fluorescent dye revealed that STX triggered NET formation in a concentration-dependent manner, and NET formation peaked at 120 min (with a total time of 180 min) after induction by STX. Intracellular reactive oxygen species (iROS) detection showed that iROS were significantly elevated in STX-challenged PMNs. These findings present insight into the effects of STX on human NET formation and serve as a basis for further investigations of STX immunotoxicity.

Fumonisin B1 induces chicken heterophil extracellular traps mediated by PAD4 enzyme and P2 × 1 receptor

Fumonisin B₁ (FB₁) is a common mycotoxin contamination in agricultural commodities being considered as a significant risk to human and livestock health, while the mechanism of FB₁ immunotoxicity are less understood, especially in chicken. Given that extracellular traps as a novel defense mechanism of leukocytes play an important role against foreign matters, in this study we aimed to investigate the effects of FB₁ on chicken heterophil extracellular traps (HETs) formation. Our result showed that FB₁ induced HETs release in chicken heterophils observed via immunostaining, and it was concentration-dependent during 10 to 40 μM. Moreover, in 40 μM FB₁-exposed chicken heterophils, reactive oxygen species (ROS) level was increased, while catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) activity and glutathione (GSH) content were decreased. Simultaneously, FB₁ (40 μM) activated ERK and p38 MAPK signaling pathways via increasing the phosphorylation level of ERK and p38 proteins. However, pretreatment of SB202190, U0126, and diphenyleneiodonium chloride (DPI) did not change FB₁-triggered ROS production and HETs formation, suggesting FB₁-induced HETs was a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, p38, and extracellular regulated protein kinases (ERK) signaling pathways-independent process. Inhibition of peptidyl arginine deiminase 4 (PAD4) enzyme and P2 × 1 receptor showed their vital role in 40 μM FB₁-triggered HETs. This study reported for the first time that 40 μM FB₁ induced the release of HETs in heterophils, and it was related to ROS production, PAD4, and P2 × 1, but was independent of NADPH oxidase, p38 and ERK signaling pathways, which might provide a whole novel perspective of perceiving and understanding the role of FB₁ in immunotoxicity.

Bongkrekic acid induced neutrophil extracellular traps via p38, ERK, PAD4, and P2X1-mediated signaling

Bongkrekic acid (BKA) produced by pseudomonas cocovenenans is a deadly toxin, and is mainly found in spoiled or fermented foods. However, less is known on its immunotoxicity. Neutrophil extracellular traps (NETs) are a novel effector mechanism of neutrophils against invading pathogens, but excessive NETs also contribute to tissue damage. This study aimed to investigate NET formation triggered by BKA in murine neutrophils, and describe its characteristics and potential mechanisms. Our results showed that BKA triggered NET formation via co-localization of DNA and histone or MPO by immunostaining. Moreover, BKA-triggered NET formation was dose- and time-dependent via NET quantification based on Picogreen-derived fluorescence intensities. Furthermore, BKA increased ROS production in neutrophils. Pharmacological inhibition indicated that BKA-triggered NET formation was associated with ROS-p38 and -ERK signaling pathways, but independent on NADPH oxidase. Besides, PAD4 and P2X1 receptor also mediated BKA-triggered NET formation. To our knowledge, all these findings provide for the first time an initial understanding of BKA on innate immunity, which might be helpful for further investigation on BKA immunotoxicity.

Sodium molybdate induces heterophil extracellular traps formation in chicken

Molybdenum (Mo) is not only an important rare metal that is widely used in industrial production but also an essential trace element for plants and animals. Nevertheless, in Mo polluted areas, excess Mo intake will not only cause gout in humans but also cause diarrhea in livestock and growth inhibition of chickens. Heterophils extracellular traps (HETs) are an important way to clear pathogens in the innate immune system of the chicken. However, the effects of Mo on the innate immune responses of HETs formation in chicken, and the mechanism undergoing this phenomenon remain unknown. In the study, we firstly aim to investigate the effects of sodium molybdate (Na₂MoO₄) on chicken HETs formation in vitro, and further to explore its related metabolic requirements and molecular mechanisms. Chicken heterophils were cultured with Na₂MoO₄, and Na₂MoO₄-induced HETs structures were analyzed by confocal microscopy. Moreover, Na₂MoO₄-induced HETs were quantified by Quant-iT PicoGreen® dsDNA Assay kits and fluorescence microplate. It has been shown that Na₂MoO₄ truly triggered HETs-like structures that were composed of DNA decorated with citrullinated histone 3 (citH3) and elastase. The inhibitors of NADPH oxidase, ERK_1/2 and p38 MAPK signaling pathway significantly reduced Na₂MoO₄-induced HETs formation. Further experiments on energy metabolism involving Na₂MoO₄-induced HETs formation showed that Na₂MoO₄-induced HETs release was relevant to glucose, and the inhibitors of glycolysis including 3PO, AZD23766 and 3-Bromopyuvic acid, the inhibitors of glucose transport including STF31 and Ritonavir and NSC23766 significantly decreased Na₂MoO₄-induced HETs formation_. In summary, these results demonstrate that Mo does induce chicken HETs formation in vitro, and the formation of HETs is a process relying on glucose transport 1 (GLUT1)，glucose transport 4 (GLUT4), glycolysis, and ROS production depended on the activation of NADPH oxidase, ERK_1/2 and p38 signaling pathways, which also reflects the early innate immune responses of chicken against excessive molybdenum intake.

Protective Effects of Pterostilbene on Lipopolysaccharide-Induced Acute Lung Injury in Mice by Inhibiting NF-κB and Activating Nrf2/HO-1 Signaling Pathways

Pterostilbene (PTER) is a kind of stilbene compound with biological activity isolated from plants such as red sandalwood, blueberry and grape. It has anti-tumor, anti-bacterial, anti-oxidation and other pharmacological activities. However, the underlying mechanism of the protective effect of PTER on lipopolysaccharide (LPS)-induced acute lung injury (ALI) remained not clarified. In this study, LPS was used to establish a mouse model of ALI. Bronchoalveolar lavage fluid (BALF) was collected for inflammatory cells, and the wet-to-dry weight ratio of the lungs was measured. The activities of myeloperoxidase (MPO), antioxidant indexes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and oxidation index such as malondialdehyde (MDA) in lung tissues of mice were measured by the corresponding kits. The levels of Cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), TNF-α, IL-6 and IL-1β in lung tissues of mice were detected by quantitative real-time polymerase chain reaction (qRT-PCR). The activities of Nrf2, HO-1, p-p65 and p-IκB were determined by western blotting. The results showed that the model of LPS-induced ALI was successfully replicated, and it was found that PTER could significantly improve the pathological degree of ALI such as sustained the integrity of the lung tissue structure, alleviated pulmonary interstitial edema and alveolar wall thickening, reduced infiltrated inflammatory cells. PTER could decrease the number of inflammatory cells and obviously inhibit the increase of W/D ratio caused by LPS. PTER could also significantly reduce LPS-induced MPO and MDA, and increase LPS-decreased SOD, CAT and GSH-Px in the lungs. In addition, it was also found that PTER has the ability to decrease LPS-induced production of COX-2, iNOS, TNF-α, IL-6 and IL-1β. The underlying mechanism involved in the protective effect of PTER on ALI were via activating Nrf2 and HO-1, and inhibiting the phosphorylation of p65 and IκB. These results suggested that PTER can protect LPS-induced ALI in mice by inhibiting inflammatory response and oxidative stress, which provided evidence that PTER may be a potential therapeutic candidate for LPS-induced ALI intervention.

Update of the risk assessment of nickel in food and drinking water

The European Commission asked EFSA to update its previous Opinion on nickel in food and drinking water, taking into account new occurrence data, the updated benchmark dose (BMD) Guidance and newly available scientific information. More than 47,000 analytical results on the occurrence of nickel were used for calculating chronic and acute dietary exposure. An increased incidence of post-implantation loss in rats was identified as the critical effect for the risk characterisation of chronic oral exposure and a BMDL 10 of 1.3 mg Ni/kg body weight (bw) per day was selected as the reference point for the establishment of a tolerable daily intake (TDI) of 13 μg/kg bw. Eczematous flare-up reactions in the skin elicited in nickel-sensitised humans, a condition known as systemic contact dermatitis, was identified as the critical effect for the risk characterisation of acute oral exposure. A BMDL could not be derived, and therefore, the lowest-observed-adverse-effect-level of 4.3 μg Ni/kg bw was selected as the reference point. The margin of exposure (MOE) approach was applied and an MOE of 30 or higher was considered as being indicative of a low health concern. The mean lower bound (LB)/upper bound (UB) chronic dietary exposure was below or at the level of the TDI. The 95th percentile LB/UB chronic dietary exposure was below the TDI in adolescents and in all adult age groups, but generally exceeded the TDI in toddlers and in other children, as well as in infants in some surveys. This may raise a health concern in these young age groups. The MOE values for the mean UB acute dietary exposure and for the 95th percentile UB raises a health concern for nickel-sensitised individuals. The MOE values for an acute scenario regarding consumption of a glass of water on an empty stomach do not raise a health concern.

Avermectin inhibits neutrophil extracellular traps release by activating PTEN demethylation to negatively regulate the PI3K-ERK pathway and reducing respiratory burst in carp

Excessive residual avermectin (AVM) in the environment can have toxic effects on non-target organisms. AVM can exert immunotoxicity by inducing genomic demethylation, but its effect on neutrophil extracellular traps (NETs) release in carp is unclear. In this study, carp neutrophils were pretreated with 5 μg/L AVM or 4 μM DNA demethylation inhibitor (aurintricarboxylic acid, ATA), alone or in combination, and then treated with 4 μM phorbol 12-myristate 13-acetate (PMA) to stimulate NETs release. The results showed that exposure of carp neutrophils to AVM significantly suppressed NETs release and MPO expression, increased ROS production, and dramatically reduced PMA-induced cellular respiratory burst. In addition, AVM could bind to the MBD2 molecule, markedly upregulate MBD2 expression to cause demethylation, and clearly activate PTEN expression, thereby inhibiting the expression of PI3K, AKT, Raf, MEK, and ERK. However, these effects were alleviated by ATA. In conclusion, our study showed that AVM could inhibit NETs release in carp by inducing demethylation of PTEN to negatively regulate NETs synthesis pathways and reducing respiratory burst level. Our findings clarify the mechanism of AVM immunotoxicity to fish and are of great significance for efforts to protect the ecological environment and human health.

Extracellular Traps: An Ancient Weapon of Multiple Kingdoms

The discovery, in 2004, of extracellular traps released by neutrophils has extended our understanding of the mode of action of various innate immune cells. This fascinating discovery demonstrated the extracellular trapping and killing of various pathogens by neutrophils. During the last decade, evidence has accumulated showing that extracellular traps play a crucial role in the defence mechanisms of various cell types present in vertebrates, invertebrates, and plants. The aim of this review is to summarise the relevant literature on the evolutionary history of extracellular traps used as a weapon in various kingdoms of life.

Sodium fluoride exposure triggered the formation of neutrophil extracellular traps

In recent years, numerous studies paid more attention to the molecular mechanisms associated with fluoride toxicity. However, the detailed mechanisms of fluoride immunotoxicity in bovine neutrophils remain unclear. Neutrophil extracellular traps (NETs) is a novel immune mechanism of neutrophils. We hypothesized that sodium fluoride (NaF) can trigger NETs activation and release, and investigate the related molecular mechanisms during the process. We exposed peripheral blood neutrophils to 1 mM NaF for 120 min in bovine neutrophils. The results showed that NaF exposure triggered NET-like structures decorated with histones and granule proteins. Quantitative measurement of NETs content correlated positively with the concentration of NaF. Mechanistically, NaF exposure increased reactive oxygen species (ROS) levels and phosphorylation levels of ERK, p38, whereas inhibiting the activities of superoxide dismutase (SOD) and catalase (CAT) compared with control neutrophils. NETs formation is induced by NaF and this effect was inhibited by the inhibitors diphenyleneiodonium chloride (DPI), U0126 and SB202190. Our findings described the potential importance of NaF-triggered NETs related molecules, which might help to extend the current understanding of NaF immunotoxicity.

Nanosilver induces the formation of neutrophil extracellular traps in mouse neutrophil granulocytes

As a new type of antibacterial agent, nanosilver has attracted great attention in biomedical applications. However, the safety of nanosilver to humans and the environment has not been well elucidated. The objective of this study was to investigate the influence of nanosilver on novel effector mechanism of neutrophil extracellular traps (NETs), and its possible molecular mechanisms. In this study, nanosilver (10, 20 and 40 μg/mL) was incubated with neutrophils for 90 min. Then, nanosilver-induced the release of NETs was observed by laser confocal microscopy. Nanosilver-induced NETs release was also quantitatively detected by pico Green®. In addition, the role of NADPH oxidase, extracellular signal-regulated kinase (ERK) and p38 signaling pathways in nanosilver-induced NETs release were detected by the inhibitors and pico Green®. The results indicated that nanosilver significantly activated polymorphonuclear neutrophils (PMN) to release NETs, which was a DNA-based network structure modified with histones (H3) and neutrophil elastase (NE). The inhibitors of NADPH oxidase, ERK and p38 signaling pathways significantly inhibited the formation of nanosilver-induced NETs. Furthermore, nanosilver did not alter the extracellular lactate dehydrogenase (LDH) level of PMN cells. All these results showed that nanosilver significantly induced NETs release, and the potential molecular mechanisms were correlated with reactive oxygen species (ROS) production-dependent on NADPH oxidase, ERK and p38 signaling pathways, which might provide a new perspective on nanosilver-induced excess NETs release related to the host immune damage.

Neutrophil extracellular traps promote cadmium chloride-induced lung injury in mice

Cadmium (Cd) is a ubiquitous toxic heavy metal derived mainly from industrial processes. In industrialized societies, individuals are exposed to a plethora of sources of Cd pollution. Cd can trigger serious diseases such as rheumatoid arthritis (RA) and chronic obstructive pulmonary disease (COPD) by the over-activating immune system. As an effector mechanism in innate immunity, neutrophil extracellular traps (NETs) not only play an important role in defending against infection but also lead to tissue damage. However, the role of NETs in Cd-induced lung damage process has not been previously studied. In this study, we aimed to investigate the potential effects of Cd-induced NETs on lung injury in vivo and further to clarify the molecular mechanisms of Cd-induced NETs formation. In vivo, Cd treatment destroyed the structural integrity of lung tissue and significantly increased the levels of NETs in the bronchoalveolar lavage fluid (BALF). The known NETs inhibitor DNase I ameliorated pathologic changes and significantly decreased levels of NETs in BALF, which suggesting the curial role of NETs in Cd-induced lung injury. Further investigation showed that Cd could significantly trigger NETs formation, which is composed of DNA backbone decorated with histones (H3) and neutrophils elastase (NE). The inhibitors of NADPH oxidase, ERK1/2 and p38 MAPK-signaling pathways significantly reduced the formation of NETs, and western blotting analysis also showed that Cd significantly increased the phosphorylation of p38 and ERK1/2 signaling pathways. Above results confirmed that NADPH oxidase, ERK1/2 and p38 MAPK-signaling pathways were related to Cd-induced NETs formation. In conclusion, NETs was involved in Cd-induced lung injury, and the mechanisms of Cd-induced NETs formation was via activating NADPH oxidase, ERK1/2 and p38 MAPK-signaling pathways, which might provide a new perspective in Cd-induced lung injury.

Neutrophil-Extracellular Traps, Cell-Free DNA, and Immunothrombosis in Companion Animals: A Review

Immunothrombosis is a potentially beneficial physiological process that aids innate immunity and host defense against pathogen invasion. However, this process can also be damaging when it occurs to excess or in critical blood vessels. Formation of extracellular traps by leukocytes, particularly neutrophils, is central to our understanding of immunothrombosis. In addition to degranulation and phagocytosis, extracellular traps are the third mechanism by which neutrophils combat potential pathogens. These traps consist of extracellular DNA decorated with bactericidal cellular proteins, including elastase, myeloperoxidase, and cathepsins. Neutrophils can release these structures as part of a controlled cell-death process or via a process termed vital NETosis that enables the cells to extrude DNA but remain viable. There is accumulating evidence that NETosis occurs in companion animals, including dogs, horses, and cats, and that it actively contributes to pathogenesis. Numerous studies have been published detailing various methods for identification and quantification of extracellular trap formation, including cell-free DNA, measurements of histones and proteins such as high-mobility group box-1, and techniques involving microscopy and flow cytometry. Here, we outline the present understanding of these phenomena and the mechanisms of extracellular trap formation. We critically review the data regarding measurement of NETosis in companion animals, summarize the existing literature on NETosis in veterinary species, and speculate on what therapeutic options these insights might present to clinicians in the future.