Increase in oxidative stress and mitochondrial impairment in hypothalamus of streptozotocin treated diabetic rat: Antioxidative effect of Withania somnifera.

Hypothalamus, the primary brain region for glucose sensing, is severely affected by oxidative stress in diabetes mellitus. Oxidative stress in this region of brain may cause severe impairment in neuronal metabolic functions. Mitochondria are prominent targets of oxidative stress and the combination of increased oxidative stress and mitochondrial dysfunctions may further decline hypothalamic neuronal functions. In the present study we examined the oxidative damage response, antioxidative responses and mitochondrial membrane permeability transition in hypothalamus of streptozotocin-treated diabetic rats. Our results show that streptozotocin significantly increases hypothalamic lipid peroxidation, protein carbonyl content while glutathione peroxidase and reduced glutathione were declined. Mitochondrial impairment marked by an increase in mitochondrial membrane permeabilization was seen following streptozotocin treatment in the hypothalamus. The oral administration of Withania somnifera root extract stabilized mitochondrial functions and prevented oxidative damage in the hypothalamus of diabetic rat. These findings suggest an increase in the oxidative stress and decline in antioxidative responses in the hypothalamus of streptozotocin treated diabetic rats. Withania somnifera root extract was found useful in reducing oxidative stress and mitochondrial impairment in hypothalamus of diabetic rat.

Efficiency of mitochondrially targeted gallic acid in reducing brain mitochondrial oxidative damage.

Oxidative stress is associated with mitochondrial impairments. Supplying mitochondria with potent antioxidants can reduce oxidative stress­induced mitochondrial impairment. Gallic acid can be used to reduce oxidative burden in mitochondria. In order to increase the bioavailability of gallic acid inside the mitochondria we synthesized mitochondrially targeted gallic acid and explored its preventive effects against sodium nitroprusside induced oxidative stress in isolated mitochondria. Our observations revealed an increase in oxidative stress,decrease in reduced glutathione in mitochondria and increase in the mitochondrial permeability pore transition due to sodium nitroprusside treatment. Pre­treatment of gallic acid and mitochondrially targeted gallic acid to sodium nitroprusside treated mitochondria not only significantly reduced the oxidative stress but also prevented mitochondrial permeability pore transition to a significant difference. Mitochondrially targeted gallic acid was found more effective in reducing oxidative stress and mitochondrial permeability pore transition than gallic acid. We conclude that mitochondrially targeted gallic acid can be used for preventing mitochondrial impairment caused by oxidative stress.

Statins lower calcium-induced oxidative stress in isolated mitochondria.

Statins are widely used cholesterol-lowering agents that exert cholesterol-independent effects including antioxidative. The present study delineates the effects of statins, atorvastatin, and simvastatin on oxidative stress and functions of mitochondria that are the primary cellular sources of oxidative stress. In isolated rat liver mitochondria, both the statins prevented calcium-induced cytochrome c release, lipid peroxidation, and opening of the mitochondrial membrane permeability transition (MPT). Both the statins decreased the activity of mitochondrial nitric oxide synthase (mtNOS), lowered the intramitochondrial ionized calcium, and increased the mitochondrial transmembrane potential. Our findings suggest that statins lower intramitochondrial ionized calcium that decreases mtNOS activity, lowers oxidative stress, prevents MPT opening, and prevents the release of cytochrome c from the mitochondria. These results provide a novel framework for understanding the antioxidative properties of statins and their effects on mitochondrial functions.

Anti-inflammatory effects of 5-HT receptor antagonist, tropisetron on experimental colitis in rats.

BACKGROUND: There is a pressing need for research that will lead to the development of new therapeutic approaches for treating inflammatory bowel disease (IBD). The aim of this study was to investigate the effects of tropisetron, a 5-Hydroxytryptamine (5-HT)-3 receptor antagonist with anti-inflammatory properties in a model of experimental colitis in rat. MATERIALS AND METHODS: Acetic acid model of colitis in rats was used. Colitis was induced by intracolonal instillation of 4% (v/v) acetic acid. One hour after induction of colitis, intraperitoneal (IP) or intrarectal (IR) tropisetron (2 mg kg(-1), either route) or dexamethasone (1 mg kg(-1), either route) was administered. The severity of colitis was assessed 24 h later using macroscopic and microscopic changes of damaged colon, measurement of inflammatory cytokines interleukin-1beta, interleukin-6 and tumour necrosis factor-alpha levels and oxidative stress markers myeloperoxidase (MPO) and malondialdehyde (MDA) in colonic tissues. RESULTS: Tropisetron decreased colonic macroscopic and microscopic damage scores. This was associated with significant reduction in both neutrophil infiltration indicated by decreased colonic MPO activity and lipid peroxidation measured by MDA content, as well as a decreased colonic inflammatory cytokines. IR tropisetron decreased colonic damage that was associated with decreased neutrophil infiltration, lipid peroxidation and colonic inflammatory cytokines. Beneficial effects of tropisetron were lower than those of dexamethasone. No significant differences were observed between IP and IR administration with the exception of MDA level more diminished by IP tropisetron and dexamethasone. CONCLUSIONS: Tropisetron exert beneficial effects in experimental rat colitis and therefore might be useful in the treatment of IBD.

Mitochondrial association of alpha-synuclein causes oxidative stress.

Alpha-synuclein is a neuron-specific protein that contributes to the pathology of Parkinson's disease via mitochondria-related mechanisms. The present study investigated possible interaction of alpha-synuclein with mitochondria and consequences of such interaction. Using SHSY cells overexpressing alpha-synuclein A53T mutant or wild-type, as well as isolated rat brain mitochondria, the present study shows that alpha-synuclein localizes at the mitochondrial membrane. In both SHSY cells and isolated mitochondria, interaction of alpha-synuclein with mitochondria causes release of cytochrome c, increase of mitochondrial calcium and nitric oxide, and oxidative modification of mitochondrial components. These findings suggest a pivotal role for mitochondria in oxidative stress and apoptosis induced by alpha-synuclein.

S-Nitrosylation of mitochondrial caspases.

Caspase-3 is a cysteine protease located in both the cytoplasm and mitochondrial intermembrane space that is a central effector of many apoptotic pathways. In resting cells, a subset of caspase-3 zymogens is S-nitrosylated at the active site cysteine, inhibiting enzyme activity. During Fas-induced apoptosis, caspases are denitrosylated, allowing the catalytic site to function. In the current studies, we sought to identify the subpopulation of caspases that is regulated by S-nitrosylation. We report that the majority of mitochondrial, but not cytoplasmic, caspase-3 zymogens contain this inhibitory modification. In addition, the majority of mitochondrial caspase-9 is S-nitrosylated. These studies suggest that S-nitrosylation plays an important role in regulating mitochondrial caspase function and that the S-nitrosylation state of a given protein depends on its subcellular localization.

Redox control of mitochondrial functions.

Redox reactions and electron flow through the respiratory chain are the hallmarks of mitochondria. By supporting oxidative phosphorylation and metabolite transport, mitochondrial redox reactions are of central importance for cellular energy conversion. In the present review, we will discuss two other aspects of the mitochondrial redox state: (i) its control of mitochondrial Ca2+ homeostasis, and (ii) the intramitochondrial formation of reactive oxygen or nitrogen species that strongly influence electron flow of the respiratory chain.

Mitochondrial nitric oxide synthase, oxidative stress and apoptosis.

Nitric oxide (NO) exerts a wide range of its biological properties via its interaction with mitochondria. By competing with O(2), physiologically relevant concentrations of NO reversibly inhibit cytochrome oxidase and decrease O(2) consumption, in a manner resembling a pharmacological competitive antagonism. The inhibition regulates many cellular functions, by e.g., regulating the synthesis of ATP and the formation of mitochondrial transmembrane potential (Delta Psi). NO regulates the oxygen consumption of both the NO-producing and the neighboring cells; thus, it can serve as autoregulator and paracrine modulator of the respiration. On the other hand, NO reacts avidly with superoxide anion (O(2)(-)) to produce the powerful oxidizing agent, peroxynitrite (ONOO(-)) which affects mitochondrial functions mostly in an irreversible manner. How mitochondria and cells harmonize the reversible effects of NO versus the irreversible effects of ONOO(-) will be discussed in this review article. The exciting recent finding of mitochondrial NO synthase will also be discussed.

Peroxynitrite formed by mitochondrial NO synthase promotes mitochondrial Ca2+ release.

Mitochondria contribute to the maintenance of the intracellular Ca2+ homeostasis by taking up and releasing the cation via separate and specific pathways. The molecular details of the release pathway are elusive but its stimulation by the cross-linking of some vicinal thiols and consequently NAD+ hydrolysis are known. Thiol cross-linking and NAD+ hydrolysis can be achieved by addition of peroxynitrite (ONOO-), the product of the reaction between superoxide (O2-) and nitric oxide (nitrogen monoxide, NO*) to mitochondria. Mitochondria contain an NO synthase (mtNOS), which is stimulated by Ca2+, and are a copious source of O2-. We show here that intramitochondrially formed ONOO- stimulates the specific, NAD+-linked Ca2+ release from mitochondria. Our findings that upon Ca2+ uptake mtNOS is stimulated, that ONOO- is formed, and that Ca2+ is subsequently released from intact mitochondria suggest the existence of a feedback loop, which prevents overloading of mitochondria with Ca2+.

Effect of chronic lithium administration on endothelium-dependent relaxation in rat aorta.

1. The effects of chronic lithium administration on the relaxant responses of rat thoracic aortic rings in the presence of indomethacin (a cyclo-oxygenase inhibitor) and/or NG-nitro-L-arginine (L-NOARG; a nitric oxide synthase inhibitor) to acetylcholine (ACh) or sodium nitroprusside were investigated in the present study. 2. Acetylcholine produced a concentration-dependent relaxation in vessels precontracted by phenylephrine (PE), while in lithium-treated rats the maximal relaxation was significantly increased. 3. Indomethacin (20 mumol/L) significantly potentiated the ACh-induced relaxation in lithium-treated and control rats. 4. NG-Nitro-L-arginine (1 mumol/L) decreased the ACh-induced relaxation in both control and lithium-treated rats. In contrast, indomethacin (20 mumol/L) reversed the inhibitory effect of L-NOARG. 5. Sodium nitroprusside produced similar concentration-dependent relaxations of vessels from both control and lithium-treated rats, which was not affected by indomethacin. In endothelium-denuded rings, indomethacin (20 mumol/L) caused a rightward shift in the concentration-contraction curve to PE. 6. These data support evidence for a possible increase in endothelium-dependent relaxation induced by ACh during long-term administration of lithium in rat aortic rings.

Mitochondrial nitric-oxide synthase stimulation causes cytochrome c release from isolated mitochondria. Evidence for intramitochondrial peroxynitrite formation.

Nitric oxide (NO) is synthesized by members of the NO synthase (NOS) family. Recently the existence of a mitochondrial NOS (mtNOS), its Ca(2+) dependence, and its relevance for mitochondrial bioenergetics was reported (Ghafourifar, P., and Richter, C. (1997) FEBS Lett. 418, 291-296; Giulivi, C., Poderoso, J. J., and Boveris, A. (1998) J. Biol. Chem. 273, 11038-11043). Here we report on the possible involvement of mtNOS in apoptosis. We show that uptake of Ca(2+) by mitochondria triggers mtNOS activity and causes the release of cytochrome c from isolated mitochondria in a Bcl-2-sensitive manner. mtNOS-induced cytochrome c release was paralleled by increased lipid peroxidation. The release of cytochrome c as well as increase in lipid peroxidation were prevented by NOS inhibitors, a superoxide dismutase mimic, and a peroxynitrite scavenger. We show that mtNOS-induced cytochrome c release is not mediated via the mitochondrial permeability transition pore because the release was aggravated by cyclosporin A and abolished by blockade of mitochondrial calcium uptake by ruthenium red. We conclude that, upon Ca(2+)-induced mtNOS activation, peroxynitrite is formed within mitochondria, which causes the release of cytochrome c from isolated mitochondria, and we propose a mechanism by which elevated Ca(2+) levels induce apoptosis.

Mitochondrial nitric oxide synthase regulates mitochondrial matrix pH.

Nitric oxide (nitrogen monoxide, NO) exerts a wide profile of its biological activities via regulation of respiration and respiration-dependent functions. The presence of nitric oxide synthase (NOS) in mitochondria (mtNOS) was recently reported by us (Ghafourifar and Richter, FEBS Lett. 418, 291-296, 1997) and others (Giulivi et al., J. Biol. Chem. 273, 11038-11043, 1998). Here we report that NO, provided by an NO donor as well as by mtNOS stimulation, regulates mitochondrial matrix pH, transmembrane potential and Ca2+ buffering capacity. Exogenously-added NO causes a dose-dependent matrix acidification. Also mtNOS stimulation, induced by loading mitochondria with Ca2+, causes mitochondrial matrix acidification and a drop in mitochondrial transmembrane potential. Inhibition of mtNOS's basal activity causes mitochondrial matrix alkalinization and provides a resistance to the sudden drop of mitochondrial transmembrane potential induced by mitochondrial Ca2+ uptake. We conclude that mtNOS plays a critical role in regulating mitochondrial delta(pH).

Increase by NO synthase inhibitor of lead-induced release of N-acetyl-beta-D-glucosaminidase from perfused rat kidney.

Urinary N-acetyl-beta-D-glucosaminidase (NAG) had been shown to be a useful early marker of renal injury such as lead nephrotoxicity. This study investigated the effect of lead acetate on nephrotoxicity and its correlation with the nitric oxide (NO) system by determining the NAG release in perfused rat kidney. Lead acetate caused a time and concentration-dependent increase in enzymuria. The effect of concurrent perfusion with lead and L-arginine (L-arg) or L-N(G)-nitro arginine methyl ester (L-NAME) [substrate and inhibitor of NO synthase respectively] in the perfusion fluid was also studied by measuring NAG activity in the perfusate kidney rat. L-arg (2 mM) has significantly decreased the lead-induced NAG release (P < 0.001), and L-NAME (0.1 mM) has significantly increased the lead-induced enzyme release in a time-dependent manner (P < 0.001). Moreover, histological studies using light microscope showed that some of the epithelial cells of the proximal convoluted tubules are degenerated or necrotic and desquamated into the lumens in rat treated with lead acetate. This change occurs at 50 microg/dl of lead acetate and was increased by addition of L-NAME to lead acetate. However, addition of L-arg had no effect on histology of lead nephrotoxicity. This may suggest that lead may interfere with the NO system in rat kidney.

Ceramide induces cytochrome c release from isolated mitochondria. Importance of mitochondrial redox state.

In the present study we show that N-acetylsphingosine (C2-ceramide), N-hexanoylsphingosine (C6-ceramide), and, to a much lesser extent, C2-dihydroceramide induce cytochrome c (cyto c) release from isolated rat liver mitochondria. Ceramide-induced cyto c release is prevented by preincubation of mitochondria with a low concentration (40 nM) of Bcl-2. The release takes place when cyto c is oxidized but not when it is reduced. Upon cyto c loss, mitochondrial oxygen consumption, mitochondrial transmembrane potential (Delta Psi), and Ca2+ retention are diminished. Incubation with Bcl-2 prevents, and addition of cyto c reverses the alteration of these mitochondrial functions. In ATP-energized mitochondria, ceramides do not alter Delta Psi, neither when cyto c is oxidized nor when it is reduced, ruling out a nonspecific disturbance by ceramides of mitochondrial membrane integrity. Furthermore, ceramides decrease the reducibility of cyto c. We conclude that the apoptogenic properties of ceramides are in part mediated via their interaction with mitochondrial cyto c followed by its release and that the redox state of cyto c influences its detachment by ceramide from the inner mitochondrial membrane.

Ceramide induces cytochrome c release from isolated mitochondria.

This chapter addresses the role of mitochondria in apoptosis. Emphasis is put on the recently observed influence of ceramides on mitochondrial functions. We report here that N-acetylsphingosine (C2-ceramide), N-hexanoylsphingosine (C6-ceramide) and, to a much lesser extent, C2-dihydroceramide, induce cytochrome c (cyt c) release from isolated rat liver mitochondria. Ceramide-induced cyt c release is prevented by a low concentration of Bcl-2. The release takes place when cyt c is oxidized, but not when it is reduced. Upon cyt c release mitochondrial oxygen consumption, mitochondrial transmembrane potential (delta psi m) and Ca2+ retention are diminished. Bcl-2 prevents, and addition of cyt c reverses, the alteration of these mitochondrial functions. In ATP-energized mitochondria ceramides do not alter delta psi m, neither when cyt c is oxidized nor when it is reduced. This rules out a non-specific disturbance by ceramides of mitochondrial-membrane integrity. It is concluded that some of the apoptogenic properties of ceramides are mediated via their interaction with mitochondrial cyt c followed by its release.

Endogenous nitric oxide modulates naloxone-precipitated withdrawal signs in a mouse model with acute cholestasis.

Cholestasis liver disease is associated with clinical and experimental findings consistent with increased opioidergic neuromodulation, increased plasma total activity, and elevated plasma enkephalin concentrations. The effect of the nitric oxide (NO) synthase inhibitor, L-nitro-arginine (L-NA, 0.03, 0.1, 0.3, 1 mg/kg), and the nitric oxide precursor, L-Arg (30 mg/kg), on antinociception induced by bile duct resection or sham operation, as well as on opioid dependence, was examined in male albino Swiss mice. Repeated (5 days) administration of L-NA attenuated signs of dependence, as assessed by naloxone (5 mg/kg)-precipitated withdrawal, and decreased the antinociception; however, L-Arg potentiated withdrawal signs and increased the antinociception. The results of this study support the involvement of the L-arginine/nitric oxide pathway in the opioidergic-dependent manifestation of cholestasis in an animal model.

Inhibition by L-NA, a nitric oxide synthase inhibitor, of naloxone-precipitated withdrawal signs in a mouse model of cholestasis.

Following the naloxone administration in bile duct resected animals, striking opioid withdrawal signs are observed due to increased opioidergic tone. Pretreatment of animals with L-nitro arginine, a nitric oxide synthase inhibitor, reduces the naloxone-precipitated withdrawal signs as well as increase the antinociception. The results of this study support evidence for the involvement of the L-arg-nitric oxide pathway in opioidergic-dependent manifestation of cholestasis in an animal model.