Uric acid induces NADPH oxidase-independent neutrophil extracellular trap formation.

Neutrophil extracellular traps (NETs) are composed of extracellular DNA fibers with antimicrobial peptides that capture and kill microbes. NETs play a critical role in innate host defense and in autoimmune and inflammatory diseases. While the mechanism of NET formation remains unclear, reactive oxygen species (ROS) produced via activation of NADPH oxidase (Nox) are known to be an important requirement. In this study, we investigated the effect of uric acid (UA) on NET formation. UA, a well-known ROS scavenger, was found to suppress Nox-dependent ROS release in a dose-dependent manner. Low concentrations of UA significantly inhibited Nox-dependent NET formation. However, high concentrations of UA unexpectedly induced, rather than inhibited, NET formation. NETs were directly induced by UA alone in a Nox-independent manner, as revealed by experiments using control neutrophils treated with ROS inhibitors or neutrophils of patients with chronic granulomatous disease who have a congenital defect in ROS production. Furthermore, we found that UA-induced NET formation was partially mediated by NF-κB activation. Our study is the first to demonstrate the novel function of UA in NET formation and may provide insight into the management of patients with hyperuricemia.

Singlet oxygen is essential for neutrophil extracellular trap formation.

Neutrophil extracellular traps (NETs) that bind invading microbes are pivotal for innate host defense. There is a growing body of evidence for the significance of NETs in the pathogenesis of infectious and inflammatory diseases, but the mechanism of NET formation remains unclear. Previous observation in neutrophils of chronic granulomatous disease (CGD) patients, which defect NADPH oxidase (Nox) and fail to produce reactive oxygen species (ROS), revealed that ROS contributed to the formation of NETs. However, the active species were not identified. In this study, we discovered that singlet oxygen, one of the ROS, mediated Nox-dependent NET formation upon stimulation with phorbol myristate acetate. We also revealed that singlet oxygen itself could induce NET formation by a distinct system generating singlet oxygen with porfimer sodium (Photofrin) in CGD neutrophils, as well as healthy neutrophils. This was independent of Nox activation. These results show that singlet oxygen is essential for NET formation, and provide novel insights into the pathogenesis of infectious and inflammatory diseases.

Substituent effects of pterin derivatives on singlet oxygen scavenging activity.

The relationship of chemical structures of 6-formylpterin (6FP) and its derivatives with scavenging activity of singlet oxygen ((1)O(2)) was examined. First, effects of pterin derivatives on (1)O(2) released from activated human neutrophils were examined. The neutrophils, stimulated with opsonized zymosan, released (1)O(2) that was detected by chemiluminescence using a (1)O(2) specific probe, trans-1-(2'-methoxyvinyl)pyrene. 6FP and its derivatives suppressed the (1)O(2) release. 6FP and other commercially available pterin derivatives, such as biopterin and neopterin, which have different substitutions at the 6-position, suppressed the (1)O(2) release with similar extent. On the other hand, newly synthesized pterin derivatives, which have different substitutions at the 2- and/or 3-position, such as 2-amino-6-formyl-3-methylpteridin-4-one, suppressed the (1)O(2) release in a dose-dependent manner and more potently than 6FP. Then, the (1)O(2) scavenging activity of pterin derivatives was examined photochemically by direct analysis of near-infrared luminescence at 1270 nm, the most sensitive method for the detection of (1)O(2). When rose Bengal, a photosensitizer, in D(2)O solution, was irradiated by 514 nm laser beam, the emission spectrum of (1)O(2) was observed. 6FP suppressed this emission spectrum of (1)O(2), and the newly synthesized pterin derivatives with different substituent at the 2- and/or 3-position suppressed the spectrum more potently than 6FP. The order of potency was similar to that obtained from biological assays. These findings indicate that the substitutions at the 2- and/or 3-position play an important role in (1)O(2) scavenging activity of pterin derivatives.

Dasatinib induces autophagy in mice with Bcr-Abl-positive leukemia.

Dasatinib, a second-generation tyrosine kinase inhibitor, is a highly effective treatment for Bcr-Abl-positive leukemia. However, the mechanism by which dasatinib induces cell death is unclear, particularly in vivo. Autophagy is a lysosomal degradation mechanism essential for cell survival and differentiation. Autophagy also protects cells from the effects of drugs, including those used to treat leukemia. Here, we report that dasatinib induces autophagy in Bcr-Abl-positive leukemia cell lines and further show the induction of autophagy in an immunodeficient mouse model of human Bcr-Abl-positive leukemia with central nervous system (CNS) infiltration. Autophagy was induced in bone marrow (BM) as well as cerebrospinal fluid (CSF). This study is the first to show that autophagy induction is one of the mechanisms underlying cell death in leukemic cells that infiltrate the CNS. Thus, autophagy may represent a novel therapeutic target for the treatment of Bcr-Abl leukemia with CNS infiltration.

Identification of hepatic niche harboring human acute lymphoblastic leukemic cells via the SDF-1/CXCR4 axis.

In acute lymphoblastic leukemia (ALL) patients, the bone marrow niche is widely known to be an important element of treatment response and relapse. Furthermore, a characteristic liver pathology observed in ALL patients implies that the hepatic microenvironment provides an extramedullary niche for leukemic cells. However, it remains unclear whether the liver actually provides a specific niche. The mechanism underlying this pathology is also poorly understood. Here, to answer these questions, we reconstituted the histopathology of leukemic liver by using patients-derived primary ALL cells into NOD/SCID/Yc (null) mice. The liver pathology in this model was similar to that observed in the patients. By using this model, we clearly demonstrated that bile duct epithelial cells form a hepatic niche that supports infiltration and proliferation of ALL cells in the liver. Furthermore, we showed that functions of the niche are maintained by the SDF-1/CXCR4 axis, proposing a novel therapeutic approach targeting the extramedullary niche by inhibition of the SDF-1/CXCR4 axis. In conclusion, we demonstrated that the liver dissemination of leukemia is not due to nonselective infiltration, but rather systematic invasion and proliferation of leukemic cells in hepatic niche. Although the contribution of SDF-1/CXCR4 axis is reported in some cancer cells or leukemic niches such as bone marrow, we demonstrated that this axis works even in the extramedullary niche of leukemic cells. Our findings form the basis for therapeutic approaches that target the extramedullary niche by inhibiting the SDF-1/CXCR4 axis.

Edaravone directly reacts with singlet oxygen and protects cells from attack.

AIMS: Protective effects of edaravone, an approved medicine for acute brain infarction in Japan, on cell death induced by singlet oxygen (1O2) were examined. MAIN METHOD: The 1O2 scavenging activity was examined by direct analysis of near-infrared luminescence in a cell-free system and by fluorospectrometry in the presence of cells. The protective effects of edaravone on 1O2-induced cell death were examined, using rat neuronal B50 cells. Cell death was evaluated by mitochondrial respiration (MTT assay), confocal microscopy and time-lapse imaging. The chemical reaction of edaravone with 1O2 was examined by production analysis using high performance liquid chromatography (HPLC). KEY FINDINGS: When rose Bengal (RB) in D2O was irradiated by a 514nm laser beam, the signal of 1O2 was observed. Edaravone suppressed the 1O2 signal more potently than azide, a 1O2 scavenger. When B50 cells were irradiated by 525nm green light in the RB solution, production of 1O2 and induction of cell death were observed. The fluorospectrometric study and the MTT assay revealed that 100-400microM edaravone suppressed the 1O2 production and attenuated cell death in a concentration-dependent manner. Confocal microscopy and the time-lapse imaging revealed that edaravone prevented the impairment of membrane integrity and the progression of cell death induced by 1O2. The HPLC study revealed that edaravone chemically reacted with 1O2 and changed another compound. SIGNIFICANCE: Since 1O2 is possibly involved in post-ischemic neuronal damage, the clinically approved curative effects of edaravone on acute brain infarction might be attributed to its potent 1O2 scavenging activity.

Alpha-phenyl-N-tert-butyl nitrone has scavenging activity against singlet oxygen ((1)O(2)) and attenuates (1)O(2)-induced neuronal cell death.

Scavenging activity of alpha-phenyl-N-tert-butyl nitrone (PBN) against singlet oxygen ((1)O(2)) and its effects on (1)O(2)-induced neuronal cell death were examined. PBN at 1 - 4 mM dose-dependently suppressed (1)O(2) released from activated human neutrophils. PBN did not react with hydrogen peroxide or hypochlorite and did not affect myeloperoxidase activity, which are involved in the (1)O(2) formation in neutrophils. PBN also suppressed chemically generated (1)O(2) in a cell-free system. These findings collectively indicated that PBN certainly has scavenging activity against (1)O(2). Furthermore, PBN attenuated (1)O(2)-induced neuronal cell death. The well-known neuroprotective effects of PBN might be attributed to its (1)O(2)-scavenging activity.

Effects of injectable propofol emulsion on singlet oxygen released from activated human neutrophils and that chemically generated.

Effects of an injectable emulsion of propofol and its emulsifier on singlet oxygen (1O2) were examined. 1O2 released from activated human neutrophils was detected by chemiluminescence, and chemically generated 1O2 was detected by electron paramagnetic resonance (EPR). Both the propofol emulsion and the emulsifier suppressed 1O2 release from neutrophils. However, the emulsifier did not quench chemically generated 1O2, while the propofol emulsion quenched it. These results indicated that the emulsifier did not scavenge 1O2 released from neutrophils but inhibited 1O2 generation. The suppressive effects of propofol emulsion on 1O2 release from neutrophils consist of 1O2 scavenging and inhibition of 1O2 generation.