The utility of nitric oxide (NO)-releasing silica nanoparticles as a novel antibacterial is demonstrated against Pseudomonas aeruginosa. Nitric oxide-releasing nanoparticles were prepared via co-condensation of tetraalkoxysilane with aminoalkoxysilane modified with diazeniumdiolate NO donors, allowing for the storage of large NO payloads. Comparison of the bactericidal efficacy of the NO-releasing nanoparticles to 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (PROLI/NO), a small molecule NO donor, demonstrated enhanced bactericidal efficacy of nanoparticle-derived NO and reduced cytotoxicity to healthy cells (mammalian fibroblasts). Confocal microscopy revealed that fluorescently-labeled NO-releasing nanoparticles associated with the bacteria, providing rationale for the enhanced bactericidal efficacy of the nanoparticles. Intracellular NO concentrations were measurable when the NO was delivered from nanoparticles as opposed to PROLI/NO. Collectively, these results demonstrate the advantage of delivering NO via nanoparticles for antimicrobial applications.Keywords nitric oxide; silica nanoparticle; antibacterial; bactericidal; cytotoxicity; reactive nitrogen species; reactive oxygen species Antibiotic resistance has resulted in bacterial infections becoming the most common cause of infectious disease-related death. 1,2 In the United States alone, nearly 2 million people per year acquire infections during a hospital stay, of which approximately 90,000 die. 2 The primary culprits behind such deadly infections are antibiotic-resistant pathogens, which are responsible for approximately 70% of all lethal nosocomial infections. The growing danger of life-threatening infections and the rising economic burden of resistant bacteria have created a demand for new antibacterial therapeutics.The use of nanoparticles as delivery vehicles for bactericidal agents represents a new paradigm in the design of antibacterial therapeutics. To date, most antibacterial nanoparticles have been engineered using traditional antibiotics that are either incorporated within the particle scaffold or attached to the exterior of the particle. In many cases, such particles have exhibited greater efficacy than their constituent antibiotics alone. For example, Gu et al. reported that vancomycin-capped gold nanoparticles exhibited a 64-fold improvement in efficacy over vancomycin alone. 3 Similarly, silver nanoparticles have schoenfisch@unc.edu. Supporting Information Available: Synthesis of FITC-modified silica nanoparticles, AFM analysis of nanoparticle dimensions, scavenging of NO by TSB, and confocal fluorescence microscopy images of PROLI/NO-treated P. aeruginosa cells. This material is available free of charge via the Internet at http://pubs.acs.org. NIH Public AccessAuthor Manuscript ACS Nano. Author manuscript; available in PMC 2013 February 13. shown greater antibacterial activity than silver ion (Ag + ) in solution due to the direct toxicity of the particles and tunable release of Ag + based on nanocomposite size. [4][...

Despite a detailed understanding of their metabolism, mitochondria often behave anomalously. In particular, global suppression of mitochondrial metabolism and metabolite exchange occurs in apoptosis, ischemia and anoxia, cytopathic hypoxia of sepsis and multiple organ failure, alcoholic liver disease, aerobic glycolysis in cancer cells (Warburg effect) and unstimulated pancreatic beta cells. Here, we propose that closure of voltage-dependent anion channels (VDAC) in the mitochondrial outer membrane accounts for global mitochondrial suppression. In anoxia, cytopathic hypoxia and ethanol treatment, reactive oxygen and nitrogen species, cytokines, kinase cascades and increased NADH act to inhibit VDAC conductance and promote selective oxidation of membrane-permeable respiratory substrates like short chain fatty acids and acetaldehyde. In cancer cells, highly expressed hexokinase binds to and inhibits VDAC to suppress mitochondrial function while stimulating glycolysis, but an escape mechanism intervenes when glucose-6-phosphate accumulates and dissociates hexokinase from VDAC. Similarly, glucokinase binds mitochondria of insulin-secreting beta cells, possibly blocking VDAC and suppressing mitochondrial function. We propose that glucose metabolism leads to glucose-6-phosphate-dependent unbinding of glucokinase, relief of VDAC inhibition, release of ATP from mitochondria and ATP-dependent insulin release. In support of the overall proposal, ethanol treatment of isolated rat hepatocytes inhibited mitochondrial respiration and accessibility to adenylate kinase in the intermembrane space, effects that were overcome by digitonin permeabilization of the outer membrane. Overall, these considerations suggest that VDAC is a dynamic regulator, or governator, of global mitochondrial function both in health and disease.

In Xenopus oocytes, as well as other cells, inositol-1,4,5-trisphosphate (Ins(1,4,5)P3)-induced Ca2+ release is an excitable process that generates propagating Ca2+ waves that annihilate upon collision. The fundamental property responsible for excitability appears to be the Ca2+ dependency of the Ins(1,4,5)P3 receptor. Here we report that Ins(1,4,5)P3-induced Ca2+ wave activity is strengthened by oxidizable substrates that energize mitochondria, increasing Ca2+ wave amplitude, velocity and interwave period. The effects of pyruvate/malate are blocked by ruthenium red at the Ca2+ uniporter, by rotenone at complex I, and by antimycin A at complex III, and are subsequently rescued at complex IV by ascorbate tetramethylphenylenediamine (TMPD). Our data reveal that potential-driven mitochondrial Ca2+ uptake is a major factor in the regulation of Ins(1,4,5)P3-induced Ca2+ release and clearly demonstrate a physiological role of mitochondria in intracellular Ca2+ signalling.

Mitochondrial dysfunction, secondary to excessive accumulation of Ca2+, has been implicated in cardiac injury. We here examined the action of potassium channel openers on mitochondrial Ca2+ homeostasis, as these cardioprotective ion channel modulators have recently been shown to target a mitochondrial ATP‐sensitive K+ channel. In isolated cardiac mitochondria, diazoxide and pinacidil decreased the rate and magnitude of Ca2+ uptake into the mitochondrial matrix with an IC50 of 65 and 128 μm, respectively. At all stages of Ca2+ uptake, the potassium channel openers depolarized the mitochondrial membrane thereby reducing Ca2+ influx through the potential‐dependent mitochondrial uniporter. Diazoxide and pinacidil, in a concentration‐dependent manner, also activated release of Ca2+ from mitochondria. This was prevented by cyclosporin A, an inhibitor of Ca2+ release through the mitochondrial permeability transition pore. Replacement of extramitochondrial K+ with mannitol abolished the effects of diazoxide and pinacidil on mitochondrial Ca2+, while the K+ ionophore valinomycin mimicked the effects of the potassium channel openers. ATP and ADP, which block K+ flux through mitochondrial ATP‐sensitive K+ channels, inhibited the effects of potassium channel openers, without preventing the action of valinomycin. In intact cardiomyocytes, diazoxide also induced mitochondrial depolarization and decreased mitochondrial Ca2+ content. These effects were inhibited by the mitochondrial ATP‐sensitive K+ channel blocker 5‐hydroxydecanoic acid. Thus, potassium channel openers prevent mitochondrial Ca2+ overload by reducing the driving force for Ca2+ uptake and by activating cyclosporin‐sensitive Ca2+ release. In this regard, modulators of an ATP‐sensitive mitochondrial K+ conductance may contribute to the maintenance of mitochondrial Ca2+ homeostasis.

Objective-Endothelial progenitor cells (EPCs) display a unique aptitude to promote angiogenesis and restore endothelial function of injured vessels. How progenitor cells can execute a regenerative program in the unfavorable environment of injury/inflammation-induced oxidative stress is poorly understood. We hypothesized that EPCs are resistant to oxidative stress and that this resistance is due to high expression and activity of antioxidant enzymes. 6,7 or from resident EPCs embedded within organs. 8 In contrast to differentiated mature endothelial cells, EPCs have a high proliferation potential and can be expanded extensively in vitro. 6,7,9 Transplantation of EPCs enhances vascular development by in situ differentiation and proliferation within ischemic organs. 10,11 Successful transplantation and beneficial therapeutic effect of EPCs in ischemic tissues of experimental animal models 1,2 and in humans 4,12 suggest that EPCs may exhibit a high survival potential under unfavorable conditions of ischemiareperfusion and associated oxidative stress. Methods and Results-EPCs See page 1977Excessive production of reactive oxygen species (ROS) and reactive nitrogen oxide species is an essential mechanism underlying pathogenesis of endothelial dysfunction and vascular disease. 13 Although it has been established that antioxidant enzymes, namely superoxide dismutases (SODs, converting O 2 . to H 2 O 2 ), catalase, and peroxidases (H 2 O 2 scavengers), are critical in the defense against oxidative stress, 14 the antioxidant profile of progenitor cells remains poorly understood. Here we demonstrate that human EPCs possess a unique property to withstand oxidative injury and that elevated expression of manganese superoxide dismutase (MnSOD, a mitochondria-located SOD) is a critical intrinsic mechanism protecting EPCs against oxidative stress. MethodsFor expanded Methods, please see the online section, available at http://atvb.ahajournals.org. EPC Isolation, Cell Culture, and PhenotypingThe protocol for collection and use of human blood samples was approved by the Institutional Review Board at the Mayo Clinic.EPCs from blood of 15 healthy volunteers were obtained by density Isolated mononuclear cells were plated at a density of Ϸ2ϫ10 7 cells per well on 6-well plates coated with human fibronectin (R&D Systems Inc) in endothelial growth medium-2 (EGM-2, Cambrex Corp), composed of endothelial cell basal medium-2 (EBM-2), 5% fetal bovine serum, and growth factors. Cell colonies appeared at Ϸ2 to 3 weeks. At 4 weeks, subconfluent cell colonies were passaged and cells were subsequently cultured in EGM-2. In parallel, human umbilical vein endothelial cells (HUVECs; Clonetics) and human coronary artery endothelial cells (CAECs; Clonetics) were cultured in EGM-2 with the same list of additives as used for EPCs. The majority of the experiments were performed on the cells cultured from passages 4 to 8. In some control experiments, studies were performed on the cells of passages 2 to 9. All cells studied were at similar confluence wi...

ONC201 is a first-in-class imipridone molecule currently in clinical trials for the treatment of multiple cancers. Despite enormous clinical potential, the mechanism of action is controversial. To investigate the mechanism of ONC201 and identify compounds with improved potency, we tested a series of novel ONC201 analogues (TR compounds) for effects on cell viability and stress responses in breast and other cancer models. The TR compounds were found to be ∼50–100 times more potent at inhibiting cell proliferation and inducing the integrated stress response protein ATF4 than ONC201. Using immobilized TR compounds, we identified the human mitochondrial caseinolytic protease P (ClpP) as a specific binding protein by mass spectrometry. Affinity chromatography/drug competition assays showed that the TR compounds bound ClpP with ∼10-fold higher affinity compared to ONC201. Importantly, we found that the peptidase activity of recombinant ClpP was strongly activated by ONC201 and the TR compounds in a dose- and time-dependent manner with the TR compounds displaying a ∼10–100 fold increase in potency over ONC201. Finally, siRNA knockdown of ClpP in SUM159 cells reduced the response to ONC201 and the TR compounds, including induction of CHOP, loss of the mitochondrial proteins (TFAM, TUFM), and the cytostatic effects of these compounds. Thus, we report that ClpP directly binds ONC201 and the related TR compounds and is an important biological target for this class of molecules. Moreover, these studies provide, for the first time, a biochemical basis for the difference in efficacy between ONC201 and the TR compounds.

Graft failure after liver transplantation may involve mitochondrial dysfunction. We examined whether prevention of mitochondrial injury would improve graft function. Orthotopic rat liver transplantation was performed after 18 hours' cold storage in University of Wisconsin solution and treatment with vehicle, minocycline, tetracycline, or N-methyl-4-isoleucine cyclosporin (NIM811) of explants and recipients. Serum alanine aminotransferase (ALT), necrosis, and apoptosis were assessed 6 hours after implantation. Mitochondrial polarization and cell viability were assessed by intravital microscopy. Respiration and the mitochondrial permeability transition (MPT) were assessed in isolated rat liver mitochondria. After transplantation with vehicle or tetracycline, ALT increased to 5242 U/L and 4373 U/L, respectively. Minocycline and NIM811 treatment decreased ALT to 2374 U/L and 2159 U/L, respectively (P < 0.01). Necrosis and terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) also decreased from 21.4% and 21 cells/field, respectively, after vehicle to 10.1% and 6 cells/field after minocycline and to 8.7% and 5.2 cells/field after NIM811 (P < 0.05). Additionally, minocycline decreased caspase-3 activity in graft homogenates (P < 0.05). Long-term graft survival was 27% and 33%, respectively, after vehicle and tetracycline treatment, which increased to 60% and 70% after minocycline and NIM811 (P < 0.05). In isolated mitochondria, minocycline and NIM811 but not tetracycline blocked the MPT. Minocycline blocked the MPT by decreasing mitochondrial Ca 2؉ uptake, whereas NIM811 blocks by interaction with cyclophilin D. Intravital microscopy showed that minocycline and NIM811 preserved mitochondrial polarization and cell viability after transplantation (P < 0.05). Conclusion: Minocycline and NIM811 attenuated graft injury after rat liver transplantation and improved graft survival. Minocycline and/or NIM811 might be useful clinically in hepatic surgery and transplantation. (HEPATOLOGY 2008;47:236-246.)

Exchange of information between the nucleus and cytosol depends on the metabolic state of the cell, yet the energy-supply pathways to the nuclear compartment are unknown. Here, the energetics of nucleocytoplasmic communication was determined by imaging import of a constitutive nuclear protein histone H1. Translocation of H1 through nuclear pores in cardiac cells relied on ATP supplied by mitochondrial oxidative phosphorylation, but not by glycolysis. Although mitochondria clustered around the nucleus, reducing the distance for energy transfer, simple nucleotide diffusion was insufficient to meet the energetic demands of nuclear transport. Rather, the integrated phosphotransfer network was required for delivery of high-energy phosphoryls from mitochondria to the nucleus. In neonatal cardiomyocytes with low creatine kinase activity, inhibition of adenylate kinase-catalyzed phosphotransfer abolished nuclear import. With deficient adenylate kinase, nucleoside diphosphate kinase, which secures phosphoryl exchange between ATP and GTP, was unable to sustain nuclear import. Up-regulation of creatine kinase phosphotransfer, to mimic metabolic conditions of adult cardiac cells, rescued H1 import, suggesting a developmental plasticity of the cellular energetic system. Thus, mitochondrial oxidative phosphorylation coupled with phosphotransfer relays provides an efficient energetic unit in support of nuclear transport. E fficient communication between the cytosol and nucleus is essential in cellular homeostasis, regulating proper processing of genetic and metabolic information. Central in nucleocytoplasmic exchange is the transport of macromolecules across the nuclear envelope (1, 2), a multistep process that initially proceeds by signal-mediated recognition of the macromolecule to be transported, following by docking events and, ultimately, translocation through nuclear pores (1-5). In energy-depleted cells, molecules that are actively transported into the nucleus, such as the constitutive chromatin protein histone H1, tend to accumulate on the cytosolic surface of the nuclear membrane (2, 4). While formation and docking of the transported protein, complexed with a transport receptor, may be energy-independent, the actual translocation and accumulation of molecules in the nuclear compartment against a concentration gradient may, however, require an energy source (4).Energy-consuming enzymes, including nucleoside triphosphatases, are associated with the nuclear envelope, and their activity is stimulated in the presence of the transported substrate (6, 7). Underscoring the energetic cost of nuclear transport, receptor cycling and continued signal processing mandate catalytic conversion of the guanine nucleotide-binding protein Ran from Ran-GTP to Ran-GDP, which is accomplished by the RanGTPase and the subsequent regeneration of GTP (1, 2). Yet, transport of macromolecules across the nuclear envelope that can proceed in an apparently energy-independent manner also has been reported (8, 9). This observation was, however, made i...