The inhibition of flavoproteins by phenoxaiodonium, a new iodonium analogue

Candida albicans FRE8 encodes a member of the NADPH oxidase family that produces a burst of ROS during fungal morphogenesis

Until recently, NADPH oxidase (NOX) enzymes were thought to be a property of multicellularity, where the reactive oxygen species (ROS) produced by NOX acts in signaling processes or in attacking invading microbes through oxidative damage. We demonstrate here that the unicellular yeast and opportunistic fungal pathogen Candida albicans is capable of a ROS burst using a member of the NOX enzyme family, which we identify as Fre8. C. albicans can exist in either a unicellular yeast-like budding form or as filamentous multicellular hyphae or pseudohyphae, and the ROS burst of Fre8 begins as cells transition to the hyphal state. Fre8 is induced during hyphal morphogenesis and specifically produces ROS at the growing tip of the polarized cell. The superoxide dismutase Sod5 is co-induced with Fre8 and our findings are consistent with a model in which extracellular Sod5 acts as partner for Fre8, converting Fre8-derived superoxide to the diffusible H₂O₂ molecule. Mutants of fre8Δ/Δ exhibit a morphogenesis defect in vitro and are specifically impaired in development or maintenance of elongated hyphae, a defect that is rescued by exogenous sources of H₂O₂. A fre8Δ/Δ deficiency in hyphal development was similarly observed in vivo during C. albicans invasion of the kidney in a mouse model for disseminated candidiasis. Moreover C. albicans fre8Δ/Δ mutants showed defects in a rat catheter model for biofilms. Together these studies demonstrate that like multicellular organisms, C. albicans expresses NOX to produce ROS and this ROS helps drive fungal morphogenesis in the animal host.

We demonstrate here that the opportunistic human fungal pathogen Candida albicans uses a NADPH oxidase enzyme (NOX) and reactive oxygen species (ROS) to control morphogenesis in an animal host. C. albicans was not previously known to express NOX enzymes as these were thought to be a property of multicellular organisms, not unicellular yeasts. We describe here the identification of C. albicans Fre8 as the first NOX enzyme that can produce extracellular ROS in a unicellular yeast. C. albicans can exist as either a unicellular yeast or as multicellular elongated hyphae, and Fre8 is specially expressed during transition to the hyphal state where it works to produce ROS at the growing tip of the polarized cell. C. albicans cells lacking Fre8 exhibit a deficiency in elongated hyphae during fungal invasion of the kidney in a mouse model for systemic candidiasis. Moreover, Fre8 is required for fungal survival in a rodent model for catheter biofilms. These findings implicate a role for fungal derived ROS in controlling morphogenesis of this important fungal pathogen for public health.

Cadmium Disrupts the Balance between Hydrogen Peroxide and Superoxide Radical by Regulating Endogenous Hydrogen Sulfide in the Root Tip of Brassica rapa

Cd (cadmium) stress always alters the homeostasis of ROS (reactive oxygen species) including H₂O₂ (hydrogen sulfide) and [Formula: see text] (superoxide radical), leading to the oxidative injury and growth inhibition in plants. In addition to triggering oxidative injury, ROS has been suggested as important regulators modulating root elongation. However, whether and how Cd stress induces the inhibition of root elongation by differentially regulating endogenous H₂O₂ and [Formula: see text], rather than by inducing oxidative injury, remains elusive. To address these gaps, histochemical, physiological, and biochemical approaches were applied to investigate the mechanism for Cd to fine-tune the balance between H₂O₂ and [Formula: see text] in the root tip of Brassica rapa. Treatment with Cd at 4 and 16 μM significantly inhibited root elongation, while only 16 μM but not 4 μM of Cd induced oxidative injury and cell death in root tip. Fluorescent and pharmaceutical tests suggested that H₂O₂ and [Formula: see text] played negative and positive roles, respectively, in the regulation of root elongation in the presence of Cd (4 μM) or not. Treatment with Cd at 4 μM led to the increase in H₂O₂ and the decrease in [Formula: see text] in root tip, which may be attributed to the up-regulation of Br_UPB1s and the down-regulation of their predicted targets (four peroxidase genes). Cd at 4 μM resulted in the increase in endogenous H₂S in root tip by inducing the up-regulation of LCDs and DCDs. Treatment with H₂S biosynthesis inhibitor or H₂S scavenger significantly blocked Cd (4 μM)-induced increase in endogenous H₂S level, coinciding with the recovery of root elongation, the altered balance between H₂O₂ and [Formula: see text], and the expression of Br_UPB1s and two peroxidase genes. Taken together, it can be proposed that endogenous H₂S mediated the phytotoxicity of Cd at low concentration by regulating Br_UPB1s-modulated balance between H₂O₂ and [Formula: see text] in root tip. Such findings shed new light on the regulatory role of endogenous H₂S in plant adaptions to Cd stress.

Therapeutic strategies of diabetic nephropathy: recent progress and future perspectives

Diabetic nephropathy (DN) is one of the most common complications of diabetes with high mortality rates worldwide. The treatment of DN has posed a formidable challenge to the scientific community. Simple control of risk factors has been insufficient to cope with the progression of DN. During the process of anti-DN drug discovery, multiple pathogeneses such as oxidative stress, inflammation and fibrosis should all be considered. In this review, the pathogenesis of DN is summarized. The major context focuses on a few small molecules toward the pathogenesis available in animal models and clinical trials for the treatment of DN. The perspectives of novel anti-DN agents and the future directions for the prevention of DN are discussed.

Oxidative stress in obstructive nephropathy

Unilateral ureteric obstruction (UUO) is one of the most commonly applied rodent models to study the pathophysiology of renal fibrosis. This model reflects important aspects of inflammation and fibrosis that are prominent in human kidney diseases. In this review, we present an overview of the factors contributing to the pathophysiology of UUO, highlighting the role of oxidative stress.

Extracellular DNA: a major proinflammatory component of Pseudomonas aeruginosa biofilms

We previously demonstrated that extracellular bacterial DNA activates neutrophils through a CpG- and TLR9-independent mechanism. Biofilms are microbial communities enclosed in a polymeric matrix that play a critical role in the pathogenesis of many infectious diseases. Because extracellular DNA is a key component of biofilms of different bacterial species, the aim of this study was to determine whether it plays a role in the ability of biofilms to induce human neutrophil activation. We found that degradation of matrix extracellular DNA with DNase I markedly reduced the capacity of Pseudomonas aeruginosa biofilms to induce the release of the neutrophil proinflammatory cytokines IL-8 and IL-1beta (>75%); reduced the upregulation of neutrophil activation markers CD18, CD11b, and CD66b (p < 0.001); reduced the number of bacteria phagocytosed per neutrophil contacting the biofilm; and reduced the production of neutrophil extracellular traps. Consistent with these findings, we found that biofilms formed by the lasI rhlI P. aeruginosa mutant strain, exhibiting a very low content of matrix extracellular DNA, displayed a lower capacity to stimulate the release of proinflammatory cytokines by neutrophils, which was not decreased further by DNase I treatment. Together, our findings support that matrix extracellular DNA is a major proinflammatory component of P. aeruginosa biofilms.

Small-molecule NOX inhibitors: ROS-generating NADPH oxidases as therapeutic targets

NOX NADPH oxidases are electron-transporting membrane enzymes whose primary function is the generation of reactive oxygen species (ROS). ROS produced by NOX enzymes show a variety of biologic functions, such as microbial killing, blood pressure regulation, and otoconia formation. Strong evidence suggests that NOX enzymes are major contributors to oxidative damage in pathologic conditions. Blocking the undesirable actions of NOX enzymes, therefore, is a therapeutic strategy for treating oxidative stress-related pathologies, such as ischemia/reperfusion tissue injury, and neurodegenerative and metabolic diseases. Most currently available NOX inhibitors have low selectivity, potency, and bioavailability, precluding a pharmacologic demonstration of NOX as therapeutic targets in vivo. This review has two main purposes. First, we describe a systematic approach that we believe should be followed in the search for truly selective NOX inhibitors. Second, we present a critical review of small-molecule NOX inhibitors described over the last two decades, including recently published patents from the pharmaceutical industry. Structures, activities, and in vitro/in vivo specificity of these NOX inhibitors are discussed. We conclude that NOX inhibition is a pertinent and promising novel pharmacologic concept, but that major efforts will be necessary to develop specific NOX inhibitors suited for clinical application.

Neutrophil bleaching of GFP-expressing staphylococci: probing the intraphagosomal fate of individual bacteria

Successful host defense against bacteria such as Staphylococcus aureus (SA) depends on a prompt response by circulating polymorphonuclear leukocytes (PMN). Stimulated PMN create in their phagosomes an environment inhospitable to most ingested bacteria. Granules that fuse with the phagosome deliver an array of catalytic and noncatalytic antimicrobial peptides, while activation of the NADPH oxidase at the phagosomal membrane generates reactive oxygen species within the phagosome, including hypochlorous acid (HOCl), formed by the oxidation of chloride by the granule protein myeloperoxidase in the presence of H(2)O(2). In this study, we used SA-expressing cytosolic GFP to provide a novel probe of the fate of SA in human PMN. PMN bleaching of GFP in SA required phagocytosis, active myeloperoxidase, H(2)O(2) from the NADPH oxidase, and chloride. Not all ingested SA were bleached, and the number of cocci within PMN-retaining fluorescent GFP closely correlated with the number of viable bacteria remaining intracellularly. The percent of intracellular fluorescent and viable SA increased at higher multiplicity of infection and when SA presented to PMN had been harvested from the stationary phase of growth. These studies demonstrate that the loss of GFP fluorescence in ingested SA provides a sensitive experimental probe for monitoring biochemical events within individual phagosomes and for identifying subpopulations of SA that resist intracellular PMN cytotoxicity. Defining the molecular basis of SA survival within PMN should provide important insights into bacterial and host properties that limit PMN antistaphylococcal action and thus contribute to the pathogenesis of staphylococcal infection.

Nitric oxide production occurs downstream of reactive oxygen species in guard cells during stomatal closure induced by chitosan in abaxial epidermis of Pisum sativum

The effects of chitosan (beta-1,4 linked glucosamine, a fungal elicitor), on the patterns of stomatal movement and signaling components were studied. cPTIO (NO scavenger), sodium tungstate (nitrate reductase inhibitor) or L: -NAME (NO synthase inhibitor) restricted the chitosan induced stomatal closure, demonstrating that NO is an essential factor. Similarly, catalase (H(2)O(2) scavenger) or DPI [NAD(P)H oxidase inhibitor] and BAPTA-AM or BAPTA (calcium chelators) prevented chitosan induced stomatal closure, suggesting that reactive oxygen species (ROS) and calcium were involved during such response. Monitoring the NO and ROS production in guard cells by fluorescent probes (DAF-2DA and H(2)DCFDA) indicated that on exposure to chitosan, the levels of NO rose after only 10 min, while those of ROS increased already by 5 min. cPTIO or sodium tungstate or L: -NAME prevented the rise in NO levels but did not restrict the ROS production. In contrast, catalase or DPI restricted the chitosan-induced production of both ROS and NO in guard cells. The calcium chelators, BAPTA-AM or BAPTA, did not have a significant effect on the chitosan induced rise in NO or ROS. We propose that the production of NO is an important signaling component and participates downstream of ROS production. The effects of chitosan strike a marked similarity with those of ABA or MJ on guard cells and indicate the convergence of their signal transduction pathways leading to stomatal closure.

Induction of ASCORBATE PEROXIDASE 2 expression in wounded Arabidopsis leaves does not involve known wound-signalling pathways but is associated with changes in photosynthesis

ASCORBATE PEROXIDASE 2 (APX2) encodes a key enzyme of the antioxidant network. In excess light-stressed Arabidopsis leaves, photosynthetic electron transport (PET), hydrogen peroxide (H(2)O(2)) and abscisic acid (ABA) regulate APX2 expression. Wounded leaves showed low induction of APX2 expression, and when exposed to excess light, APX2 expression was increased synergistically. Signalling pathways dependent upon jasmonic acid (JA), chitosan and ABA were not involved in the wound-induced expression of APX2, but were shown to require PET and were preceded by a depressed rate of CO(2) fixation. This led to an accumulation of H(2)O(2) in veinal tissue. Diphenyl iodonium (DPI), which has been shown previously to be a potent inhibitor of H(2)O(2) accumulation in the veins of wounded leaves, prevented induction of APX2 expression probably by inhibition of PET. Thus, the weak induction of APX2 expression in wounded leaves may require H(2)O(2) and PET only. As in other environmental stresses, wounding of leaves resulted in decreased photosynthesis leading to increased reactive oxygen species (ROS) production. This may signal the induction of many 'wound-responsive' genes not regulated by JA-dependent or other known JA-independent pathways.