The Mitochondrial Interplay of Ubiquinol and Nitric Oxide in Endotoxemia

α-Lipoic acid protects kidney from oxidative stress and mitochondrial dysfunction associated to inflammatory conditions

An adequate redox status is important for maintaining mitochondrial function in inflammatory conditions. The aim of this work was to evaluate the effects of α-lipoic acid (LA) in kidney oxidative metabolism and mitochondrial function in lipopolysaccharide (LPS) treated rats. Sprague-Dawley rats (female, 45 ± 5 days old) were treated with LPS (10 mg kg(-1)) and/or LA (100 mg kg(-1)). It was observed in LPS-treated animals that the LA prevented the increase in 1.2 fold of NO production, decreased (30-40%) mitochondrial complex I-III and IV activities, and decreased (26%) membrane potential and cardiolipin oxidation (76%). No differences were observed in mitochondrial O2 consumption, mitochondrial complex II-III activity, and ATP production when LPS group was compared to LA + LPS group. Based on the improvement of mitochondrial function, the decreased production of mitochondrial NO and restoration of cardiolipin levels, this work provides a new evidence that α-lipoic acid protects kidney from oxidative stress and mitochondrial dysfunction.

Mitochondrial oxidative stress initiates visual loss in sympathetic ophthalmia

The visual loss that occurs with sympathetic ophthalmia (SO) in the absence of recognizable retinal damage and inflammatory cell infiltration is an enigma. Experimental autoimmune uveoretinitis (EAU) is an animal model used to study human endogenous uveitis. Both innate and adaptive immune responses have been well studied in the photoreceptor damage mechanism of EAU. In our studies, in the early phase of EAU, proinflammatory molecules such as tumor necrosis factor (TNF)-α and inducible nitric oxide synthase (iNOS) and the subsequent mitochondrial DNA damage, mitochondrial protein alteration, and mitochondrial dysfunction by oxidative stress were observed before retinal inflammatory cell infiltration. Our recent study shows the importance of Toll-like receptors (TLRs) in the production of proinflammatory molecules and the induction of mitochondrial oxidative stress. Thus, the innate immune responses occur first with the activation of TLRs; this activation upregulates proinflammatory molecules, leading to mitochondrial oxidative stress before retinal inflammatory cell infiltration and the subsequent adaptive immune responses. Like EAU, SO also results in photoreceptor mitochondrial oxidative damage without retinal inflammatory cell infiltration. Such damage was associated with TNF-α, TNF-α receptors, and iNOS expression in the photoreceptors, suggesting that this molecular mechanism without retinal inflammatory cell infiltration may initiate photoreceptor damage in SO.

Pro-inflammatory endothelial cell dysfunction is associated with intersectin-1s down-regulation

Background

The response of lung microvascular endothelial cells (ECs) to lipopolysaccharide (LPS) is central to the pathogenesis of lung injury. It is dual in nature, with one facet that is pro-inflammatory and another that is cyto-protective. In previous work, overexpression of the anti-apoptotic Bcl-X_L rescued ECs from apoptosis triggered by siRNA knockdown of intersectin-1s (ITSN-1s), a pro-survival protein crucial for ECs function. Here we further characterized the cyto-protective EC response to LPS and pro-inflammatory dysfunction.

Methods and Results

Electron microscopy (EM) analyses of LPS-exposed ECs revealed an activated/dysfunctional phenotype, while a biotin assay for caveolae internalization followed by biochemical quantification indicated that LPS causes a 40% inhibition in biotin uptake compared to controls. Quantitative PCR and Western blotting were used to evaluate the mRNA and protein expression, respectively, for several regulatory proteins of intrinsic apoptosis, including ITSN-1s. The decrease in ITSN-1s mRNA and protein expression were countered by Bcl-X_L and survivin upregulation, as well as Bim downregulation, events thought to protect ECs from impending apoptosis. Absence of apoptosis was confirmed by TUNEL and lack of cytochrome c (cyt c) efflux from mitochondria. Moreover, LPS exposure caused induction and activation of inducible nitric oxide synthase (iNOS) and a mitochondrial variant (mtNOS), as well as augmented mitochondrial NO production as measured by an oxidation oxyhemoglobin (oxyHb) assay applied on mitochondrial-enriched fractions prepared from LPS-exposed ECs. Interestingly, expression of myc-ITSN-1s rescued caveolae endocytosis and reversed induction of iNOS expression.

Conclusion

Our results suggest that ITSN-1s deficiency is relevant for the pro-inflammatory ECs dysfunction induced by LPS.

Protective effects of synthetic kynurenines on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism in mice

Mitochondrial complex I inhibition is thought to underlie the neurodegenerative process in Parkinson's disease (PD). Moreover, an overproduction of nitric oxide due to both cytosolic (iNOS) and mitochondrial (i-mtNOS) inducible nitric oxide synthases causes free radicals generation and oxidative/nitrosative stress, contributing to mitochondrial dysfunction and neuronal cell death. Looking for active molecules against mitochondrial dysfunction and inflammatory response in PD, we show here the effects of four synthetic kynurenines in the MPTP model of PD in mice. After MPTP administration, mitochondria from substantia nigra and, in a lesser extent, from striatum showed a significant increase in i-mtNOS activity, nitric oxide production, oxidative stress, and complex I inhibition. The four kynurenines assayed counteracted the effects of MPTP, reducing iNOS/i-mtNOS activity, and restoring the activity of the complex I. Consequently, the cytosolic and mitochondrial oxidative/nitrosative stress returned to control values. The results suggest that the kynurenines here reported represent a family of synthetic compounds with neuroprotective properties against PD, and that they can serve as templates for the design of new drugs able to target the mitochondria.

Gases in the mitochondria

Gasomodulators - nitric oxide, carbon monoxide and hydrogen sulphide - are important physiological mediators that have been implicated in disorders such as neurodegeneration and sepsis. Some of their biological functions involve the mitochondria. In particular, their inhibition of cytochrome c oxidase has received much attention as this can cause energy depletion and cytotoxicity. However, reports that cellular energy production and cell survival are maintained even in the presence of gasomodulators are not uncommon. In both cases, modulation of mitochondrial targets by the gasomodulators appears to be an important event. We provide an overview of the effects of the gasomodulators on the mitochondria.

Mitochondrial nitric oxide synthase: a masterpiece of metabolic adaptation, cell growth, transformation, and death

Mitochondria are specialized organelles that control energy metabolism and also activate a multiplicity of pathways that modulate cell proliferation and mitochondrial biogenesis or, conversely, promote cell arrest and programmed cell death by a limited number of oxidative or nitrative reactions. Nitric oxide (NO) regulates oxygen uptake by reversible inhibition of cytochrome oxidase and the production of superoxide anion from the mitochondrial electron transfer chain. In this sense, NO produced by mtNOS will set the oxygen uptake level and contribute to oxidation-reduction reaction (redox)-dependent cell signaling. Modulation of translocation and activation of neuronal nitric oxide synthase (mtNOS activity) under different physiologic or pathologic conditions represents an adaptive response properly modulated to adjust mitochondria to different cell challenges.

Photoreceptor oxidative damage in sympathetic ophthalmia

PURPOSE

To determine photoreceptor oxidative stress and damage in sympathetic ophthalmia (SO).

DESIGN

Immunohistologic study.

METHODS

Eight formalin-fixed and paraffin-embedded human globes with typical histologic features of SO and five age-matched globes without intraocular inflammation (controls) were retrieved from the Doheny Eye Institute ophthalmic pathology files. Deparaffinized sections of the globes were processed to localize tumor necrosis factor-alpha (TNF-alpha), tumor necrosis factor receptor-1 (TNF-R1), acrolein, inducible nitric oxide synthase (iNOS), and nitrotyrosine by immunolocalization method. The latter two were localized to photoreceptor mitochondria using anti-cytochrome C antibody. Apoptotic cells were detected by Terminal deoxynucleotidyl transferase biotin-dUTP Nick End Labeling (TUNEL) assay and were localized to the site of oxidative stress using antinitrotyrosine antibody.

RESULTS

Increased expression of TNF-alpha can be seen in the photoreceptor nuclear layer in all SO globes, whereas no such expression was observed in control globes. TNF-R1, iNOS, acrolein, and nitrotyrosine were immunolocalized to the inner segments of the photoreceptors in all SO globes, but only mild focal staining was observed in the control retinas. Both nitrotyrosine and iNOS immunolocalization revealed positive staining restricted primarily to mitochondria at the inner segments of the photoreceptors. Most of the TUNEL-positive cells were detected in the photoreceptors at the site of nitrotyrosine staining. In contrast, the age-matched control globes showed negative results.

CONCLUSIONS

In SO, photoreceptor mitochondrial oxidative stress occurs in the absence of leukocytic infiltration of the retina and may lead to photoreceptor apoptosis and subsequent vision loss. The oxidative stress seems to be mediated by iNOS and TNF-alpha. The current anti-inflammatory therapy combined with agents that could prevent oxidative stress may prevent photoreceptor damage in SO and may preserve vision.

Attenuation of cardiac mitochondrial dysfunction by melatonin in septic mice

The existence of an inducible mitochondrial nitric oxide synthase has been recently related to the nitrosative/oxidative damage and mitochondrial dysfunction that occurs during endotoxemia. Melatonin inhibits both inducible nitric oxide synthase and inducible mitochondrial nitric oxide synthase activities, a finding related to the antiseptic properties of the indoleamine. Hence, we examined the changes in inducible nitric oxide synthase/inducible mitochondrial nitric oxide synthase expression and activity, bioenergetics and oxidative stress in heart mitochondria following cecal ligation and puncture-induced sepsis in wild-type (iNOS(+/+)) and inducible nitric oxide synthase-deficient (iNOS(-/-)) mice. We also evaluated whether melatonin reduces the expression of inducible nitric oxide synthase/inducible mitochondrial nitric oxide synthase, and whether this inhibition improves mitochondrial function in this experimental paradigm. The results show that cecal ligation and puncture induced an increase of inducible mitochondrial nitric oxide synthase in iNOS(+/+) mice that was accompanied by oxidative stress, respiratory chain impairment, and reduced ATP production, although the ATPase activity remained unchanged. Real-time PCR analysis showed that induction of inducible nitric oxide synthase during sepsis was related to the increase of inducible mitochondrial nitric oxide synthase activity, as both inducible nitric oxide synthase and inducible mitochondrial nitric oxide synthase were absent in iNOS(-/-) mice. The induction of inducible mitochondrial nitric oxide synthase was associated with mitochondrial dysfunction, because heart mitochondria from iNOS(-/-) mice were unaffected during sepsis. Melatonin treatment blunted sepsis-induced inducible nitric oxide synthase/inducible mitochondrial nitric oxide synthase isoforms, prevented the impairment of mitochondrial homeostasis under sepsis, and restored ATP production. These properties of melatonin should be considered in clinical sepsis.

Semitelechelic HPMA copolymers functionalized with triphenylphosphonium as drug carriers for membrane transduction and mitochondrial localization

Semitelechelic HPMA (N-(2-hydroxypropyl)methacrylamide) copolymers possessing a single terminal lipophilic triphenylphosphonium (TPP) cation and fluorescent labels were synthesized to determine how the attached cation affected cellular uptake and intracellular trafficking. In vitro mitochondrial uptake fluorescence quenching assays using isolated mouse liver mitochondria indicated that only lower molecular weight (<5 kDa) BODIPY FL-labeled TPP-semitelechelic HPMA copolymers exhibited significant organelle localization or uptake. In vitro cellular uptake and intracellular trafficking was evaluated using cultured human ovarian carcinoma cells. Cells incubated with all types of TPP copolymers used in the study appeared to internalize the polymer by endocytosis only, and all of the internalized copolymer was confined to the lysosomal compartment after 24 h. Endocytotic uptake of the TPP-HPMA copolymer conjugates was rapid, suggesting that they were internalized by adsorptive endocytosis, rather than fluid-phase pinocytosis. Low-molecular weight (<5 kDa) and high-molecular weight (>5 kDa) semitelechelic copolymers, microinjected into cultured cells indicated that the TPP moiety did not significantly localize the polymers to mitochondria.

Photoreceptor mitochondrial oxidative stress in early experimental autoimmune uveoretinitis

AIMS

In early S-antigen induced experimental uveitis (EAU), photoreceptor mitochondrial proteins are nitrated prior to macrophage infiltration of the retina, suggesting that oxidative stress is an initial event in the development of EAU. We attempted to detect the oxidative stress and localise it in the EAU retina.

METHODS

Lewis rats were immunised with S-antigen in complete Freund's adjuvant (CFA). Animals were injected with CFA alone and non-immunised animals served as controls. Immunised and non-immunised animals were killed on day 5 and subsequent days. Isolated retinas were processed for inducible nitric oxide synthase (iNOS), tumour necrosis factor (TNF)alpha, interferon (IFN)gamma, interleukin (IL)Ialpha and CD28 expression by real time polymerase chain reaction. In addition, iNOS was colocalised with cytochrome c oxidase on day 5 of EAU. Oxidative stress was detected by 2', 7'-dichlorodihydrofluorescein diacetate and localised by a mitochondrial specific marker. Leucocyte and T cell infiltration in the retina/choroid was evaluated by immunohistochemistry.

RESULTS

The iNOS, TNFalpha, IFNgamma, IL1alpha and CD28 transcripts were significantly upregulated on day 5 in EAU, and iNOS was colocalised with cytochrome c oxidase in the photoreceptor mitochondria. Oxidative stress was seen primarily in the photoreceptor mitochondria. Occasional T cells were present in the retina at this stage.

CONCLUSIONS

During early EAU, mitochondrial oxidative stress is selectively noted in the photoreceptor inner segments. The oxidative stress appears to result from iNOS upregulation in the photoreceptor mitochondria and cytokine generation in the retina by a few antigen specific infiltrating T cells.

Mitochondrial Protein Nitration Primes Neurodegeneration in Experimental Autoimmune Encephalomyelitis

The mechanisms of axonal and neuronal degeneration causing visual and neurologic disability in multiple sclerosis are poorly understood. Here we explored the contribution of mitochondria to neurodegeneration in the experimental autoimmune encephalomyelitis animal model of multiple sclerosis. Oxidative injury to the murine mitochondrion preceded the infiltration of inflammatory cells, classically heralded as the mediators of demyelination and axonal injury by transection. Nitration of mitochondrial proteins affected key subunits of complexes I and IV of the respiratory chain and a chaperone critical to the stabilization and translocation of proteins into the organelle. Oxidative products were associated with loss of mitochondrial membrane potential and apoptotic cell death. Reductions in the rate of synthesis of adenosine triphosphate were severe and even greater than those associated with disorders caused by mutated mitochondrial DNA. Mitochondrial vacuolization, swelling, and dissolution of cristae occurred in axons as early as 3 days after sensitization for experimental autoimmune encephalomyelitis. Our findings implicate mitochondrial dysfunction induced by protein inactivation and mediated by oxidative stress initiates a cascade of molecular events leading to apoptosis and neurodegeneration in experimental autoimmune encephalomyelitis that is not mediated by inflammatory cells.

HO‐1 is located in liver mitochondria and modulates mitochondrial heme content and metabolism

This study investigated whether inducible heme oxygenase-1[corrected] (HO-1) [corrected] is targeted to mitochondria and its putative effects on oxidative metabolism in rat liver. Western blot and immune-electron microscopy in whole purified and fractionated organelles showed basal expression of HO-1 protein in both microsomes and mitochondria (inner membrane), accompanied by a parallel HO activity. Inducers of HO-1 increased HO-1 targeting to the inner mitochondrial membrane, which also contained biliverdin reductase, supporting that both enzymes are in the same compartmentalization. Induction of mitochondrial HO-1 was associated with a decrease of mitochondrial heme content and selective reduction of protein expression of cytochrome oxidase (COX) subunit I, which is coded by the mitochondrial genome and synthesized in the mitochondria depending on heme availability; these changes resulted in decreased COX spectrum and activity. Mitochondrial HO-1 induction was also associated with down-regulation of mitochondrial-targeted NO synthase expression and activity, resulting in a reduction of NO-dependent mitochondrial oxidant yield; inhibition of HO-1 activity reverted these effects. In conclusion, we demonstrated for the first time localization of HO-1 protein in mitochondria. It is surmised that mitochondrial HO-1 has important biological roles in regulating mitochondrial heme protein turnover and in protecting against conditions such as hypoxia, neurodegenerative diseases, or sepsis, in which substantially increased mitochondrial NO and oxidant production have been implicated.

Melatonin counteracts inducible mitochondrial nitric oxide synthase-dependent mitochondrial dysfunction in skeletal muscle of septic mice

Mitochondrial nitric oxide synthase (mtNOS) produces nitric oxide (NO) to modulate mitochondrial respiration. Besides a constitutive mtNOS isoform it was recently suggested that mitochondria express an inducible isoform of the enzyme during sepsis. Thus, the mitochondrial respiratory inhibition and energy failure underlying skeletal muscle contractility failure observed in sepsis may reflect the high levels of NO produced by inducible mtNOS. The fact that mtNOS is induced during sepsis suggests its relation to inducible nitric oxide synthase (iNOS). Thus, we examined the changes in mtNOS activity and mitochondrial function in skeletal muscle of wild-type (iNOS(+/+)) and iNOS knockout (iNOS(-/-)) mice after sepsis. We also studied the effects of melatonin administration on mitochondrial damage in this experimental paradigm. After sepsis, iNOS(+/+) but no iNOS(-/-) mice showed an increase in mtNOS activity and NO production and a reduction in electron transport chain activity. These changes were accompanied by a pronounced oxidative stress reflected in changes in lipid peroxidation levels, oxidized glutathione/reduced glutathione ratio, and glutathione peroxidase and reductase activities. Melatonin treatment counteracted both the changes in mtNOS activity and rises in oxidative stress; the indole also restored mitochondrial respiratory chain in septic iNOS(+/+) mice. Mitochondria from iNOS(-/-) mice were unaffected by either sepsis or melatonin treatment. The data suggest that inducible mtNOS, which is coded by the same gene as that for iNOS, is responsible for mitochondrial dysfunction during sepsis. The results also suggest the use of melatonin for the protection against mtNOS-mediated mitochondrial failure.

Mitochondrial nitric oxide metabolism in rat muscle during endotoxemia

In this study, heart and diaphragm mitochondria produced 0.69 and 0.77 nmol nitric oxide (NO)/min mg protein, rates that account for 67 and 24% of maximal cellular NO production, respectively. Endotoxemia and septic shock occur with an exacerbated inflammatory response that damages tissue mitochondria. Skeletal muscle seems to be one of the main target organs in septic shock, showing an increased NO production and early oxidative stress. The kinetic properties of mitochondrial nitric oxide synthase (mtNOS) of heart and diaphragm were determined. For diaphragm, the KM values for O2 and L-Arg were 4.6 and 37 microM and for heart were 3.3 and 36 microM. The optimal pH for mtNOS activity was 6.5 for diaphragm and 7.0 for heart. A marked increase in mtNOS activity was observed in endotoxemic rats, 90% in diaphragm and 30% in heart. Diaphragm and heart mitochondrial O2*- and H2O2 production were 2- to 3-fold increased during endotoxemia and Mn-SOD activity showed a 2-fold increase in treated animals, whereas catalase activity was unchanged. One of the current hypotheses for the molecular mechanisms underlying the complex condition of septic shock is that the enhanced NO production by mtNOS leads to excessive peroxynitrite production and protein nitration in the mitochondrial matrix, causing mitochondrial dysfunction and contractile failure.