Crucial role of apopain in the peroxynitrite-induced apoptotic DNA fragmentation

Real-Time Monitoring the Cytotoxic Effect of Andrographolide on Human Oral Epidermoid Carcinoma Cells

Andrographolide is an active diterpenoid compound extracted from Andrographis paniculata. It exhibits antiinflammatory and anticancer effects. Previous studies show that it is non-toxic to experimental animals. The leading causes of cancer are chronic inflammation and high blood glucose. This study determines the cytotoxic effect of andrographolide on cellular morphology, viability, and migration for human oral epidermoid carcinoma cell Meng-1 (OEC-M1). We use electric cell-substrate impedance sensing (ECIS) to measure the subsequent overall impedance changes of the cell monolayer in response to different concentrations of andrographolide for 24 h (10–100 µM). The results for exposure of OEC-M1 cells to andrographolide (10–100 µM) for 24 h show a concentration-dependent decrease in the overall measured resistance at 4 kHz. AlamarBlue cell viability assay and annexin V also show the apoptotic effect of andrographolide on OEC-M1 cells. A reduction in wound-healing recovery rate is observed for cells treated with 30 μM andrographolide. This study demonstrates that ECIS can be used for the in vitro screening of anticancer drugs. ECIS detects the cytotoxic effect of drugs earlier than traditional biochemical assays, and it is more sensitive and shows more detail.

AIE-based fluorescent boronate probe and its application in peroxynitrite imaging

Fluorescent probes have contributed greatly to our understanding of the biological role of peroxynitrite (ONOO^-). The ONOO^- fluorescence probe characterized by the arlyboronate received a moderate opening fluorescence response, and the borate-masked probe significantly increased the sensitivity of ONOO^-. Thus, two simple fluorescent probes (ADB and ANB) with the recognition receptor of phenyl boronate moiety were constructed for the detection of ONOO^-. The change of emission spectrum was affected differently by the electron donating (or withdrawing) of the substituents. ANB was shown to have a low sensitivity and quantum yield towards ONOO^- in aqueous solution, whereas ADB with aggregation-induced emission (AIE) process exhibited not only good sensitivity for ONOO^- with a detection limit of 75 nM, but also ADB could be used to quantitative detecting ONOO^- in response to concentrations of ONOO^- within 20 s. Importantly, ADB had good performance for the detection of exogenous ONOO^- in the RAW 264.7 cells.

Ruthenium Half-Sandwich Type Complexes with Bidentate Monosaccharide Ligands Show Antineoplastic Activity in Ovarian Cancer Cell Models through Reactive Oxygen Species Production

Ruthenium complexes are developed as substitutes for platinum complexes to be used in the chemotherapy of hematological and gynecological malignancies, such as ovarian cancer. We synthesized and screened 14 ruthenium half-sandwich complexes with bidentate monosaccharide ligands in ovarian cancer cell models. Four complexes were cytostatic, but not cytotoxic on A2780 and ID8 cells. The IC₅₀ values were in the low micromolar range (the best being 0.87 µM) and were similar to or lower than those of the clinically available platinum complexes. The active complexes were cytostatic in cell models of glioblastoma, breast cancer, and pancreatic adenocarcinoma, while they were not cytostatic on non-transformed human skin fibroblasts. The bioactive ruthenium complexes showed cooperative binding to yet unidentified cellular target(s), and their activity was dependent on reactive oxygen species production. Large hydrophobic protective groups on the hydroxyl groups of the sugar moiety were needed for biological activity. The cytostatic activity of the ruthenium complexes was dependent on reactive species production. Rucaparib, a PARP inhibitor, potentiated the effects of ruthenium complexes.

PARPs in lipid metabolism and related diseases

PARPs and tankyrases (TNKS) represent a family of 17 proteins. PARPs and tankyrases were originally identified as DNA repair factors, nevertheless, recent advances have shed light on their role in lipid metabolism. To date, PARP1, PARP2, PARP3, tankyrases, PARP9, PARP10, PARP14 were reported to have multi-pronged connections to lipid metabolism. The activity of PARP enzymes is fine-tuned by a set of cholesterol-based compounds as oxidized cholesterol derivatives, steroid hormones or bile acids. In turn, PARPs modulate several key processes of lipid homeostasis (lipotoxicity, fatty acid and steroid biosynthesis, lipoprotein homeostasis, fatty acid oxidation, etc.). PARPs are also cofactors of lipid-responsive nuclear receptors and transcription factors through which PARPs regulate lipid metabolism and lipid homeostasis. PARP activation often represents a disruptive signal to (lipid) metabolism, and PARP-dependent changes to lipid metabolism have pathophysiological role in the development of hyperlipidemia, obesity, alcoholic and non-alcoholic fatty liver disease, type II diabetes and its complications, atherosclerosis, cardiovascular aging and skin pathologies, just to name a few. In this synopsis we will review the evidence supporting the beneficial effects of pharmacological PARP inhibitors in these diseases/pathologies and propose repurposing PARP inhibitors already available for the treatment of various malignancies.

Anti-Proliferative Activities of Vasicinone on Lung Carcinoma Cells Mediated via Activation of Both Mitochondria-Dependent and Independent Pathways

Vasicinone, a quinazoline alkaloid from Adhatoda vasica Nees. is well known for its bronchodilator activity. However its antiproliferative activities is yet to be elucidated. Here-in we investigated the anti-proliferative effect of vasicinone and its underlying mechanism against A549 lung carcinoma cells. The A549 cells upon treatment with various doses of vasicinone (10, 30, 50, 70 µM) for 72 h showed significant decrease in cell viability. Vasicinone treatment also showed DNA fragmentation, LDH leakage, and disruption of mitochondrial potential, and lower wound healing ability in A549 cells. The Annexin V/PI staining showed disrupted plasma membrane integrity and permeability of PI in treated cells. Moreover vasicinone treatment also lead to down regulation of Bcl-2, Fas death receptor and up regulation of PARP, BAD and cytochrome c, suggesting the anti-proliferative nature of vasicinone which mediated apoptosis through both Fas death receptors as well as Bcl-2 regulated signaling. Furthermore, our preliminary studies with vasicinone treatment also showed to lower the ROS levels in A549 cells and have potential free radical scavenging (DPPH, Hydroxyl) activity and ferric reducing power in cell free systems. Thus combining all, vasicinone may be used to develop a new therapeutic agent against oxidative stress induced lung cancer.

Pinocembrin ex vivo preconditioning improves the therapeutic efficacy of endothelial progenitor cells in monocrotaline-induced pulmonary hypertension in rats

Pulmonary hypertension is still not curable and the available current therapies can only alleviate symptoms without hindering the progression of disease. The present study was directed to investigate the possible modulatory effect of pinocembrin on endothelial progenitor cells transplanted in monocrotaline-induced pulmonary hypertension in rats. Pulmonary hypertension was induced by a single subcutaneous injection of monocrotaline (60mg/kg). Endothelial progenitor cells were in vitro preconditioned with pinocembrin (25mg/L) for 30min before being i.v. injected into rats 2weeks after monocrotaline administration. Four weeks after monocrotaline administration, blood pressure, electrocardiography and right ventricular systolic pressure were recorded. Rats were sacrificed and serum was separated for determination of endothelin-1 and asymmetric dimethylarginine levels. Right ventricles and lungs were isolated for estimation of tumor necrosis factor-alpha and transforming growth factor-beta contents as well as caspase-3 activity. Moreover, protein expression of matrix metalloproteinase-9 and endothelial nitric oxide synthase in addition to myocardial connexin-43 was assessed. Finally, histological analysis of pulmonary arteries, cardiomyocyte cross-sectional area and right ventricular hypertrophy was performed and cryosections were done for estimation of cell homing. Preconditioning with pinocembrin provided a significant improvement in endothelial progenitor cells' effect towards reducing monocrotaline-induced elevation of inflammatory, fibrogenic and apoptotic markers. Furthermore, preconditioned cells induced a significant amelioration of endothelial markers and cell homing and prevented monocrotaline-induced changes in right ventricular function and histological analysis compared with native cells alone. In conclusion, pinocembrin significantly improves the therapeutic efficacy of endothelial progenitor cells in monocrotaline-induced pulmonary hypertension in rats.

Peroxynitrite Induces Apoptosis in Rat Aortic Smooth Muscle Cells: Possible Relation to Vascular Diseases

An emerging body of evidence is accumulating to suggest that in vivo formation of free radicals in the vasculature, such as peroxynitrite (ONOO–), and programmed cell death (i.e., apoptosis) play important roles in vascular diseases such as atherosclerosis, hypertension, and restenosis. The present study was designed to determine whether primary rat aortic smooth muscle cells (SMCs) undergo apoptosis following treatment with ONOO–. Direct exposure of primary rat aortic SMCs to ONOO– induced apoptosis in a concentration-dependent manner, as confirmed by means of quantitative fluorescence staining and TUNEL assays. ONOO–-induced apoptosis in rat aortic SMCs appears to involve activation of Ca2+-dependent endonucleases. Although the precise mechanisms by which peroxynitrite induces apoptosis in rat aortic SMCs need to be further investigated, the present, preliminary findings could be used to suggest that ONOO– formation in the vasculature may play roles in the processes of vascular diseases, such as atherosclerosis, hypertension, and restenosis, via adverse actions on blood vessels.

The PARP inhibitor PJ-34 sensitizes cells to UVA-induced phototoxicity by a PARP independent mechanism

A combination of a photosensitizer with light of matching wavelength is a common treatment modality in various diseases including psoriasis, atopic dermatitis and tumors. DNA damage and production of reactive oxygen intermediates may impact pathological cellular functions and viability. Here we set out to investigate the role of the nuclear DNA nick sensor enzyme poly(ADP-ribose) polymerase 1 in photochemical treatment (PCT)-induced tumor cell killing. We found that silencing PARP-1 or inhibition of its enzymatic activity with Veliparib had no significant effect on the viability of A431 cells exposed to 8-methoxypsoralen (8-MOP) and UVA (2.5J/cm(2)) indicating that PARP-1 is not likely to be a key player in either cell survival or cell death of PCT-exposed cells. Interestingly, however, another commonly used PARP inhibitor PJ-34 proved to be a photosensitizer with potency equal to 8-MOP. Irradiation of PJ-34 with UVA caused changes both in the UV absorption and in the 1H NMR spectra of the compound with the latter suggesting UVA-induced formation of tautomeric forms of the compound. Characterization of the photosensitizing effect revealed that PJ-34+UVA triggers overproduction of reactive oxygen species, induces DNA damage, activation of caspase 3 and caspase 8 and internucleosomal DNA fragmentation. Cell death in this model could not be prevented by antioxidants (ascorbic acid, trolox, glutathione, gallotannin or cell permeable superoxide dismutase or catalase) but could be suppressed by inhibitors of caspase-3 and -8. In conclusion, PJ-34 is a photosensitizer and PJ-34+UVA causes DNA damage and caspase-mediated cell death independently of PARP-1 inhibition.

Inputs and outputs of poly(ADP-ribosyl)ation: Relevance to oxidative stress

Oxidative stress can cause DNA breaks which induce activation of the DNA nick sensor enzyme poly(ADP-ribose) polymerase-1 (PARP-1), part of the 17 member PARP enzyme family. PARP-1 modifies target proteins by attaching to them several NAD-derived ADP-ribose units forming poly(ADP-ribose) (PAR) polymers. PARylation controls many cellular processes while intense PARylation may also lead to cell death by various mechanisms. Here we summarize the modes of activation, inhibitors and modulators of PARP-1 and review the cellular functions regulated by the enzyme.

Naringenin adds to the protective effect of L-arginine in monocrotaline-induced pulmonary hypertension in rats: favorable modulation of oxidative stress, inflammation and nitric oxide

The present study was directed to investigate the possible modulatory effect of naringenin when co-administered with L-arginine in monocrotaline-induced pulmonary hypertension in rats. Pulmonary hypertension was induced by a single subcutaneous injection of monocrotaline (60 mg/kg). L-arginine (500 mg/kg) and naringenin (50 mg/kg) were orally administered daily, alone and in combination, for 3 weeks. Mean arterial blood pressure, electrocardiography and echocardiography were then recorded and rats were sacrificed and serum was separated for determination of total nitrate/nitrite level. Right ventricles and lungs were isolated for estimation of oxidative stress markers, tumor necrosis factor-alpha, total nitrate/nitrite and transforming growth factor-beta. Myeloperoxidase and caspase-3 activities in addition to endothelial and inducible nitric oxide synthase protein expression were also determined. Moreover, histological analysis of pulmonary arteries and cardiomyocyte cross-sectional area was performed. Combined therapy provided a significant improvement in L-arginine protective effect toward preserving hemodynamic changes and alleviating oxidative stress, inflammatory and apoptotic markers induced by monocrotaline treatment. Furthermore, combined therapy prevented monocrotaline-induced changes in endothelial and inducible nitric oxide synthase protein expression as well as histological analysis compared with either treatment alone. In conclusion, naringenin significantly adds to the protective effect of L-arginine in pulmonary hypertension induced by monocrotaline in rats.

Quercetin and quercitrin protect against cytokine‑induced injuries in RINm5F β-cells via the mitochondrial pathway and NF-κB signaling

Quercetin, existing mostly in its glycoside form quercitrin, is the most widely distributed flavonoid in nature. It possesses various potential effects as an antioxidant, anti-inflammatory for cell damage of β-cells, however, studies on this topic are limited and controversial. In order to examine the effects of quercetin on type I diabetes mellitus, we investigated the role of quercetin/quercitrin in cytokine-induced β-cell injuries in RINm5F rat insulinoma cells. Cell viability, glucose-stimulated insulin secretion (GSIS), intracellular reactive oxygen species (ROS), nitric oxide (NO) and inflammation or apoptosis-associated protein expression were measured with or without quercetin/quercitrin treatment. We also compared the differences between the aglycone and the glycoside forms of quercetin, with the aim to shed some light on their structures and transportation into cells. The results showed that quercetin/quercitrin protected against cytokine-induced cell death, improved GSIS, and inhibited ROS as well as NO accumulation. These effects were associated with reduced expression of inducible nitric oxide synthases (iNOS) and inhibited translocation of nuclear factor-κB (NF-κB). Also, quercetin/quercitrin suppressed cytochrome c release from mitochondria and the following alteration of downstream proteins, suggesting that mitochondrial apoptosis was attenuated by quercetin treatment. In summary, quercetin and quercitrin are potential candidates to prevent β-cell death via the mitochondrial pathway and NF-κB signaling, and quercetin may be more efficacious than quercitrin as an anti-diabetic agent.

Gelam honey scavenges peroxynitrite during the immune response

Monocytes and macrophages are part of the first-line defense against bacterial, fungal, and viral infections during host immune responses; they express high levels of proinflammatory cytokines and cytotoxic molecules, including nitric oxide, reactive oxygen species, and their reaction product peroxynitrite. Peroxynitrite is a short-lived oxidant and a potent inducer of cell death. Honey, in addition to its well-known sweetening properties, is a natural antioxidant that has been used since ancient times in traditional medicine. We examined the ability of Gelam honey, derived from the Gelam tree (Melaleuca spp.), to scavenge peroxynitrite during immune responses mounted in the murine macrophage cell line RAW 264.7 when stimulated with lipopolysaccharide/interferon-γ (LPS/IFN-γ) and in LPS-treated rats. Gelam honey significantly improved the viability of LPS/IFN-γ-treated RAW 264.7 cells and inhibited nitric oxide production-similar to the effects observed with an inhibitor of inducible nitric oxide synthase (1400W). Furthermore, honey, but not 1400W, inhibited peroxynitrite production from the synthetic substrate 3-morpholinosydnonimine (SIN-1) and prevented the peroxynitrite-mediated conversion of dihydrorhodamine 123 to its fluorescent oxidation product rhodamine 123. Honey inhibited peroxynitrite synthesis in LPS-treated rats. Thus, honey may attenuate inflammatory responses that lead to cell damage and death, suggesting its therapeutic uses for several inflammatory disorders.

Arjunolic acid: beneficial role in type 1 diabetes and its associated organ pathophysiology

In this review article, we describe the most recent development of the beneficial effect of arjunolic acid (AA) in reducing type 1 diabetic pathophysiology. Diabetic mellitus is a serious and growing health problem worldwide. Increasing evidence suggest that oxidative stress plays a pivotal role in the pathogenesis of diabetes and its associated complications. Use of antioxidant supplements as a complimentary therapeutic approach in diabetes has, therefore, been seriously considered worldwide. AA, a natural pentacyclic triterpenoid saponin, is well known for various biological functions including antioxidant activity. It could prevent the increased production of ROS, RNS, AGEs, and the 8OHdG/2dG ratio and increase the intracellular antioxidant defence system. Signal transduction studies showed that AA could prevent hyperglycaemia induced activation of MAPKs, PKC, NF-κB signalling cascades and apoptotic cell death. Combining, AA supplements could be regarded as beneficial therapeutics in the treatment of diabetes and its associated complications.

Impaired redox signaling and mitochondrial uncoupling contributes vascular inflammation and cardiac dysfunction in type 1 diabetes: Protective role of arjunolic acid

Vascular inflammation and cardiac dysfunction are the leading causes of mortality and morbidity among the diabetic patients. Type 1 diabetic mellitus (T1DM) is associated with increased cardiovascular complications at an early stage of the disease. The purpose of the present study was to explore whether arjunolic acid (AA) plays any protective role against cardiovascular complications in T1DM and if so, what molecular pathways it utilizes for the mechanism of its protective action. Streptozotocin (STZ) was used to induce T1DM in experimental rats. Alteration in plasma lipid profile and release of membrane bound enzymes like LDH (lactate dehydrogenase) and CK (creatine kinase) established the association of hyperlipidemia and cell membrane disintegration with hyperglycemia. Hyperglycemia altered the levels of oxidative stress related biomarkers, decreased the intracellular NAD and ATP concentrations. Hyperglycemia-induced enhanced levels of VEGF, ICAM-1, MCP-1 and IL-6 in the plasma of STZ treated animals indicate vascular inflammation in T1DM. Histological studies and FACS analysis revealed that hyperglycemia caused cell death mostly via the apoptotic pathway. Investigating molecular mechanism, we observed NF-κB and MAPKs (p38 and ERK1/2) activations, mitochondrial membrane depolarization, cytochrome C release, caspase 3 activation and PARP cleavage in apoptotic cell death in the diabetic cardiac tissue. Treatment with AA (20 mg/kg body weight) reduced hyperglycemia, membrane disintegration, oxidative stress, vascular inflammation and prevented the activation of oxidative stress induced signaling cascades leading to cell death. Results suggest that AA possesses the potential to be a beneficial therapeutic agent in diabetes and its associated cardiac complications.

Roles of reactive oxygen and nitrogen species in pain

Peroxynitrite (PN; ONOO⁻) and its reactive oxygen precursor superoxide (SO; O₂•⁻) are critically important in the development of pain of several etiologies including pain associated with chronic use of opiates such as morphine (also known as opiate-induced hyperalgesia and antinociceptive tolerance). This is now an emerging field in which considerable progress has been made in terms of understanding the relative contributions of SO, PN, and nitroxidative stress in pain signaling at the molecular and biochemical levels. Aggressive research in this area is poised to provide the pharmacological basis for development of novel nonnarcotic analgesics that are based upon the unique ability to selectively eliminate SO and/or PN. As we have a better understanding of the roles of SO and PN in pathophysiological settings, targeting PN may be a better therapeutic strategy than targeting SO. This is because, unlike PN, which has no currently known beneficial role, SO may play a significant role in learning and memory. Thus, the best approach may be to spare SO while directly targeting its downstream product, PN. Over the past 15 years, our team has spearheaded research concerning the roles of SO and PN in pain and these results are currently leading to the development of solid therapeutic strategies in this important area.

Pathophysiological roles of peroxynitrite in circulatory shock

Peroxynitrite is a reactive oxidant produced from nitric oxide and superoxide, which reacts with proteins, lipids, and DNA, and promotes cytotoxic and proinflammatory responses. Here, we overview the role of peroxynitrite in various forms of circulatory shock. Immunohistochemical and biochemical evidences demonstrate the production of peroxynitrite in various experimental models of endotoxic and hemorrhagic shock both in rodents and in large animals. In addition, biological markers of peroxynitrite have been identified in human tissues after circulatory shock. Peroxynitrite can initiate toxic oxidative reactions in vitro and in vivo. Initiation of lipid peroxidation, direct inhibition of mitochondrial respiratory chain enzymes, inactivation of glyceraldehyde-3-phosphate dehydrogenase, inhibition of membrane Na+/K+ ATPase activity, inactivation of membrane sodium channels, and other oxidative protein modifications contribute to the cytotoxic effect of peroxynitrite. In addition, peroxynitrite is a potent trigger of DNA strand breakage, with subsequent activation of the nuclear enzyme poly(ADP-ribose) polymerase, which promotes cellular energetic collapse and cellular necrosis. Additional actions of peroxynitrite that contribute to the pathogenesis of shock include inactivation of catecholamines and catecholamine receptors (leading to vascular failure) and endothelial and epithelial injury (leading to endothelial and epithelial hyperpermeability and barrier dysfunction), as well as myocyte injury (contributing to loss of cardiac contractile function). Neutralization of peroxynitrite with potent peroxynitrite decomposition catalysts provides cytoprotective and beneficial effects in rodent and large-animal models of circulatory shock.

Contribution of type 1 diabetes to rat liver dysfunction and cellular damage via activation of NOS, PARP, IkappaBalpha/NF-kappaB, MAPKs, and mitochondria-dependent pathways: Prophylactic role of arjunolic acid

Diabetic mellitus, a chronic metabolic disorder, is one of the most important health problems in the world, especially in developing countries. Our earlier investigations reported the beneficial action of arjunolic acid (AA) against streptozotocin-mediated type 1 hyperglycemia. We have demonstrated that AA possesses protective roles against drug- and chemical- (environmental toxins) induced hepatotoxicity. Liver is the main organ of detoxification. The purpose of this study was to explore whether AA plays any protective role against hyperglycemic hepatic dysfunctions and, if so, what molecular pathways it utilizes for the mechanism of its protective action. In experimental rats, type 1 hyperglycemia was induced by streptozotocin. AA was administered orally at a dose of 20mg/kg body wt both before and after diabetic induction. An insulin-treated group was included in the study as a positive control for type 1 diabetes. Hyperglycemia caused a loss in body weight, reduction in serum insulin level, and increased formation of HbA(1C) as well as advanced glycation end products (AGEs). Elevated levels of serum ALT and ALP, increased production of ROS and RNS, increased lipid peroxidation, increased 8-OHdG/2-dG ratio, and decreased GSH content and cellular antioxidant defense established the hyperglycemic liver dysfunction. Activation of iNOS, IkappaBalpha/NF-kappaB, and MAPK pathways as well as signals from mitochondria were found to be involved in initiating apoptotic cell death. Hyperglycemia caused overexpression of PARP, reduction in intracellular NAD as well as ATP level, and increased DNA fragmentation in the liver tissue of the diabetic animals. Results of immunofluorescence (using anti-caspase-3 and anti-Apaf-1 antibodies), DAPI/PI staining, and DNA ladder formation and information obtained from FACS analysis confirmed the apoptotic cell death in diabetic liver tissue. Histological studies also support the experimental findings. AA treatment prevented or ameliorated the diabetic liver complications and apoptotic cell death. The effectiveness of AA in preventing the formation of ROS, RNS, HbA(1C), AGEs, and oxidative stress signaling cascades and protecting against PARP-mediated DNA fragmentation can speak about its potential uses for diabetic patients.

The anti-diabetic effect of anthocyanins in streptozotocin-induced diabetic rats through glucose transporter 4 regulation and prevention of insulin resistance and pancreatic apoptosis

Hyperglycemia, abnormal lipid and antioxidant profiles are the most usual complications in diabetes mellitus. Thus, in this study, we investigated the anti-diabetic and anti-oxidative effects of anthocyanins (ANT) from black soybean seed coats in streptozotocin (STZ)-induced diabetic rats. The administration of ANT markedly decreased glucose levels and improved heart hemodynamic function (left ventricular end diastolic pressure, +/-dp/dt parameters). ANT not only enhanced STZ-mediated insulin level decreases, but also decreased the triglyceride levels induced by STZ injection in serum. Diabetic rats exhibited a lower expression of glucose transporter 4 proteins in the membrane fractions of heart and skeletal muscle tissues, which was enhanced by ANT. In addition, ANT activated insulin receptor phosphorylation, suggesting an increased utilization of glucose by tissues. Moreover, ANT protected pancreatic tissue from STZ-induced apoptosis through regulation of caspase-3, Bax, and Bcl-2 proteins. Furthermore, ANT significantly suppressed malondialdehyde levels and restored superoxide dismutase and catalase activities in diabetic rats. Interestingly, the observed effects of ANT were superior to those of glibenclamide. Taken together, ANT from black soybean seed coat have anti-diabetic effects that are due, in part, to the regulation of glucose transporter 4 and prevention of insulin resistance and pancreatic apoptosis, suggesting a possible use as a drug to regulate diabetes.

Pharmacological evidence for a role of peroxynitrite in the pathophysiology of spinal cord injury

Evidence suggests that the reactive oxygen species peroxynitrite (PN) is an important player in the pathophysiology of acute spinal cord injury (SCI). In the present study, we examined the ability of tempol, a catalytic scavenger of PN-derived free radicals, to alleviate oxidative damage, mitochondrial dysfunction and cytoskeletal degradation following a severe contusion (200 kdyn force) SCI in female Sprague-Dawley rats. PN-mediated oxidative damage in spinal cord tissue, including protein nitration, protein oxidation and lipid peroxidation was significantly reduced by acute tempol treatment (300 mg/kg, i.p. within 5 min post-injury). Injury-induced mitochondrial respiratory dysfunction, measured after 24 h in isolated mitochondria, was partially reversed by tempol along with an attenuation of oxidative damage to mitochondrial proteins. Mitochondrial dysfunction disrupts intracellular Ca(2+) homeostasis contributing to calpain-mediated axonal cytoskeletal protein (alpha-spectrin, 280 kD) degradation. Increased levels of alpha-spectrin breakdown proteins (SBDP 145 kD and 150 kD) were significantly decreased at 24 h in tempol-treated rats indicative of spinal axonal protection. However, a therapeutic window analysis showed that the axonal cytoskeletal protective effects require tempol dosing within the first hour after injury. Nevertheless, these findings are the first to support the concept that PN is an important neuroprotective target in early secondary SCI, and that there is a mechanistic link between PN-mediated oxidative compromise of spinal cord mitochondrial function, loss of intracellular Ca(2+) homeostasis and calpain-mediated proteolytic axonal damage.

Protective effects of IRFI-042 in monensin induced neurotoxicity in chicks

Monensin, a well known ionophore antibiotic, may cause severe damage in neuronal cells by altering Na+/K+-ATPase and Ca2+-ATPase. We investigated whether IRFI-042, a synthetic analogue of vitamin E, may block lipid peroxidation in neuronal cells and protect against monensin neurotoxicity in chicks. Monensin toxicity was induced in chicks by once-daily administration (150 mg/kg by oral gavages), for 8 days. Sham animals received a saline solution and were used as controls. All animals were randomized to receive either IRFI-042 (20 mg/kg) or its vehicle. Survival rate, brain lipid peroxidation, mRNA for neuronal and inducible nitric oxide synthases (nNOS and iNOS) and brain histological evaluations, including immunohistochemical expression of nNOS and iNOS were performed. Monensin administration decreased survival rate, induced behavioural changes, increased brain lipid peroxidation, reduced brain nNOS mRNA and immunostaining and enhanced iNOS mRNA and immunostaining in the brain in chicks. IRFI-042 significantly improved the survival rate and counteracted monensin-induced changes in chick brains. Our data suggest that monensin is responsible of neurotoxicity in chicks by inducing oxidative stress/lipid peroxidation and that IRFI-042 might represent a useful pharmacological approach to protect against the neuronal damage induced by this monovalent carboxylic ionophorous polyether antibiotic.

Peroxynitrite: biochemistry, pathophysiology and development of therapeutics

Peroxynitrite--the product of the diffusion-controlled reaction of nitric oxide with superoxide radical--is a short-lived oxidant species that is a potent inducer of cell death. Conditions in which the reaction products of peroxynitrite have been detected and in which pharmacological inhibition of its formation or its decomposition have been shown to be of benefit include vascular diseases, ischaemia-reperfusion injury, circulatory shock, inflammation, pain and neurodegeneration. In this Review, we first discuss the biochemistry and pathophysiology of peroxynitrite and then focus on pharmacological strategies to attenuate the toxic effects of peroxynitrite. These include its catalytic reduction to nitrite and its isomerization to nitrate by metalloporphyrins, which have led to potential candidates for drug development for cardiovascular, inflammatory and neurodegenerative diseases.

Curcumin prevents streptozotocin-induced islet damage by scavenging free radicals: a prophylactic and protective role

Pancreatic islet cell death is the cause of deficient insulin production in diabetes mellitus. Approaches towards prevention of cell death are of prophylactic importance in control and management of hyperglycemia. Generation of oxidative stress is implicated in streptozotocin, a beta cell specific toxin-induced islet cell death. In this context, antioxidants raise an interest for therapeutic purposes. Curcumin, a common dietary spice is a well known antioxidant and hence we investigated its effect on streptozotocin-induced islet damage in vitro. Isolated islets from C57/BL6J mice were incubated with curcumin for 24 h and later exposed to streptozotocin for 8 h. The effect of streptozotocin exposure to islets was determined with respect to islet viability and functionality, cellular reactive oxygen species concentrations and levels of activated poly (ADP-ribose) polymerase-1. Cellular antioxidant potential (Cu/Zn superoxide dismutase) and advanced glycation end-product related damage was assessed to determine the metabolic status of treated and untreated islets. Islet viability and secreted insulin in curcumin pretreated islets were significantly higher than islets exposed to streptozotocin alone. Curcumin retarded generation of islet reactive oxygen species along with inhibition of Poly ADP-ribose polymerase-1 activation. Although curcumin did not cause overexpression of Cu/Zn superoxide dismutase, it prevented reduction in levels of cellular free radical scavenging enzymes. Our data shows that curcumin protects islets against streptozotocin-induced oxidative stress by scavenging free radicals. We show here for the first time, that prophylactic use of curcumin may effectively rescue islets from damage without affecting the normal function of these cellular structures.

Protein tyrosine nitration and poly(ADP-ribose) polymerase activation in N-methyl-N-nitro-N-nitrosoguanidine-treated thymocytes: implication for cytotoxicity

1-Methyl-3-nitro-1-nitrosoguanidine (MNNG) is a DNA alkylating agent. DNA alkylation by MNNG is known to trigger accelerated poly(ADP-ribose) metabolism. Various nitroso compounds release nitric oxide (NO). Therefore, we set out to investigate whether MNNG functions as NO donor and whether MNNG-derived NO or secondary NO metabolites such as peroxynitrite contribute to MNNG-induced cytotoxicity. MNNG in aqueous solutions resulted in time- and concentration-dependent NO release and nitrite/nitrate formation. Moreover, various proteins in MNNG-treated thymocytes were found to be nitrated, indicating that MNNG-derived NO may combine with cellular superoxide to form peroxynitrite, a nitrating agent. MNNG also caused DNA breakage and increased poly(ADP-ribose) polymerase activity and cytotoxicity in thymocytes. MNNG-induced DNA damage (measured by the comet assay) and thymocyte death (measured by propidium iodide uptake) was prevented by the PARP inhibitor PJ-34 and by glutathione (GSH) or N-acetylcysteine (NAC). The cytoprotection provided by PJ-34 against necrotic parameters was paralleled by increased outputs in apoptotic parameters (caspase activity, DNA laddering) indicating that PARP activation diverts apoptotic death toward necrosis. As MNNG-induced cytotoxicity showed many similarities to peroxynitrite-induced cell death, we tested whether peroxynitrite was responsible for at least part of the cytotoxicity induced by MNNG. Cell-permeable enzymic antioxidants (superoxide dismutase and catalase), the NO scavenger cPTIO or the peroxynitrite decomposition catalyst FP15 failed to inhibit MNNG-induced DNA breakage and cytotoxicity. In conclusion, MNNG induces tyrosine nitration in thymocytes. Furthermore, MNNG damages DNA by a radical mechanism that does not involve NO or peroxynitrite.

Role of iNOS-derived reactive nitrogen species and resultant nitrative stress in leukocytes-induced cardiomyocyte apoptosis after myocardial ischemia/reperfusion

Polymorphonuclear leukocyte (PMN) accumulation/activation has been implicated as a primary mechanism underlying MI/R injury. Recent studies have demonstrated that PMNs express inducible nitric oxide synthase (iNOS) and produce toxic reactive nitrogen species (RNS). However, the role of iNOS-derived reactive nitrogen species and resultant nitrative stress in PMN-induced cardiomyocyte apoptosis after MI/R remains unclear. Male adult rats were subjected to 30 min of myocardial ischemia followed by 5 h of reperfusion. Animals were randomized to receive one of the following treatments: MI/R+vehicle; MI/R+L-arginine; PMN depletion followed by MI/R+vehicle; PMN depletion followed by MI/R+L-arginine; MI/R+1400 W; MI/R+1400 W+L-arginine and MI/R+ FeTMPyP. Ischemia/reperfusion-induced and L-arginine-enhanced nitrative stress and cardiomyocyte apoptosis were determined. PMN depletion virtually abolished ischemia/reperfusion- induced PMN accumulation, attenuated ischemic/reperfusion-induced and L-arginine-enhanced nitrative stress, and reduced ischemic/reperfusion-induced and L-arginine-enhanced cardiomyocyte apoptosis (P values all <0.01). Pre-treatment with 1400 W, a highly selective iNOS inhibitor, had no effect on PMN accumulation in the ischemic/reperfused tissue. However, this treatment reduced ischemia/reperfusion-induced and L-arginine-enhanced nitrative stress and cardiomyocyte apoptosis to an extent that is comparable as that seen in PMN depletion group. Treatment with FeTMPyP, a peroxynitrite decomposition catalyst, had no effect on either PMN accumulation or total NO production. However, treatment with this ONOO(-) decomposition catalyst also reduced ischemia/reperfusion-induced and L-arginine-enhanced nitrative stress and cardiomyocyte apoptosis (P values all <0.01). These results demonstrated that ischemic/reperfusion stimulated PMN accumulation may result in cardiomyocyte injury by an iNOS-derived nitric oxide initiated and peroxynitrite-mediated mechanism. Therapeutic interventions that block PMN accumulation, inhibit iNOS activity or scavenge peroxynitrite may reduce nitrative stress and attenuate tissue injury.

Inhibition of caspase-mediated apoptosis by peroxynitrite in traumatic brain injury

In traumatic brain injury (TBI), neurons surviving the primary insult may succumb through poorly understood secondary mechanisms. In vitro, cortical neurons exposed to stretch injury exhibited enhanced vulnerability to NMDA, apoptotic-like DNA fragmentation, peroxynitrite (PN) formation, and cytoplasmic cytochrome c accumulation. Surprisingly, caspase-3 activity was undetectable by both immunoblotting and fluorogenic activity assays. Therefore, we hypothesized that PN directly inhibits caspases in these neurons. Consistent with this, stretch injury in cultured neurons elicited tyrosine nitration of procaspase-3, but not caspase-9 or Apaf-1, suggesting a direct interaction of PN with caspase-3. In an ex vivo system, PN inhibited the activity of caspase-3, and this inhibition was reversible with the addition of the sulfhydryl reducing agent dithiothreitol, indicating that PN inhibits caspases by cysteinyl oxidation. Moreover, in cultures, the PN donor 3-morpholinosydnonimine (SIN-1) blocked staurosporine-induced caspase-3 activation and its downstream effects including PARP-1 [poly-(ADP-ribose) polymerase-1] cleavage and phosphotidylserine inversion, suggesting that peroxynitrite can inhibit caspase-3-mediated apoptosis. To examine these mechanisms in vivo, rats were exposed to a lateral fluid percussion injury (FPI). FPI caused increased neuronal protein nitration that colocalized with TUNEL staining, indicating that PN was associated with neurodegeneration. Caspase-3 activity was inhibited in brain lysates harvested after FPI and was restored by adding dithiothreitol. Our data show that caspase-mediated apoptosis is inhibited in neurons subjected to stretch in vitro and to TBI in vivo, mostly because of cysteinyl oxidation of caspase-3 by PN. However, this is insufficient to prevent cell death, indicating that the TBI therapy may, at a minimum, require a combination of both anti-apoptotic and anti-oxidant strategies.

Drugs modulating the biological effects of peroxynitrite and related nitrogen species

The term "reactive nitrogen species" includes nitrogen monoxide, commonly called nitric oxide, and some other remarkable chemical entities (peroxynitrite, nitrosoperoxycarbonate, etc.) formed mostly from nitrogen monoxide itself in biological environments. Regardless of the specific mechanisms implicated in their effects, however, it is clear that an integrated pharmacological approach to peroxynitrite and related species is only just beginning to take shape. The array of affected chemical and pathological processes is extremely broad. One of the most conspicuous mechanisms observed thus far has been the scavenging of the peroxynitrite anion by molecules endowed with antioxidant activity. This discovery has in turn lent great significance to several naturally occurring and synthetic antioxidants, which usually protect not only against oxidative reactions, but also from nitrating ones, both in vitro and in vivo. This has proven to be beneficial in different tissues, especially within the central nervous system. Taking these results and those of other biochemical investigations into account, many research lines are currently in progress to establish the true potential of reactive nitrogen species deactivators in the therapy of neurological diseases, ischemia-reperfusion damage, renal failure, and lung injury, among others.

Survival pathways triggered by peroxynitrite in cells belonging to the monocyte/macrophage lineage

Peroxynitrite, a highly reactive nitrogen species, promotes in U937 cells (a promonocytic cell line) a mitochondrial permeability transition (MPT)-dependent necrosis. An initial event triggered by peroxynitrite (i.e., inhibition of complex III of the mitochondrial respiratory chain) is responsible for the time-dependent formation of H(2)O(2), essential for the occurrence of cell death. Otherwise non-toxic concentrations of peroxynitrite nevertheless commit cells to MPT-dependent necrosis, which is however prevented by a cytoprotective signaling driven by arachidonic acid (AA) released by the cytosolic PLA(2) isoform. Interestingly, the mechanism whereby delayed formation of H(2)O(2) promotes toxicity in cells exposed to intrinsically toxic concentrations of peroxynitrite is independent of the accumulation of additional damage. Cell death is in fact mediated by inhibition of the AA-dependent cytoprotective signaling. Exogenous AA, however, prevented toxicity also under these conditions. An additional point to be made is that the major findings obtained using U937 cells were reproduced in different cell types belonging to the monocyte/macrophage lineage. Hence, within the context of the inflammatory response, monocytes and macrophages may cope with peroxynitrite by using AA, a signaling molecule largely available at the inflammatory sites.

Poly(ADP-ribosyl)ation in asthma and other lung diseases

Inhibition of poly(ADP-ribosyl)ation in oxidative stress-related pathologies has recently emerged as a very effective anti-inflammatory intervention in animal models of arthritis, colitis, diabetes and shock. Recent data from three laboratories also support the role of poly(ADP-ribose) polymerase-1 (PARP-1) activation in asthma. Similarly to other inflammatory conditions, the protective effects of PARP inhibition and the PARP-1 knock out phenotype in asthma models have been attributed to inhibition of inflammatory signal transduction (mainly via NF-kappaB) and of oxidative stress-induced cell dysfunction and tissue injury. Here I discuss the complex role of poly(ADP-ribosyl)ation in the regulation of inflammatory cell migration, chemokine and cytokine production and expression of other inflammatory mediators (inducible nitric oxide synthase, matrix metalloproteinases) in asthma. The role of PARP-1 in other oxidative stress-related lung diseases such as asbestosis, silicosis, acute respiratory distress syndrome and ischemia-reperfusion injury is also reviewed.

Mechanisms of high glucose-induced apoptosis and its relationship to diabetic complications

Cellular responses to high glucose are numerous and varied but ultimately result in functional changes and, often, cell death. High glucose induces oxidative and nitrosative stress in many cell types causing the generation of species such as superoxide, nitric oxide and peroxynitrite and their derivatives. The role of these species in high glucose-mediated apoptotic cell death is relevant to the complications of diabetes such as neuropathy, nephropathy and cardiovascular disease. High glucose causes activation of several proteins involved in apoptotic cell death, including members of the caspase and Bcl-2 families. These events and the relationship between high glucose-induced oxidative stress and apoptosis are discussed here with reference to additional regulators of apoptosis such as the mitogen-activated protein kinases (MAPKs) and cell-cycle regulators.

Toluene and p-xylene induced LLC-PK1 apoptosis

Occupational exposure to organic solvents was found to be associated with development and progression of tubulo-interstitial fibrosis and chronic renal failure. However, the cellular mechanism by which this occurs remains elusive. This study was conducted to evaluate the mode of cell death in proximal tubular cells exposed to organic solvents. LLC-PK1 cell line cytotoxicity due to exposure to 1 mM of either p-xylene or toluene was compared to untreated control by cell viability, LDH release, and DNA fragmentation. Cells were exposed to solvents for 96 hrs. Toluene and p-xylene reduced cell viability and increased DNA fragmentation. LDH release was unchanged. These data indicates that long-term exposure to organic solvents is associated with proximal tubule cell apoptosis, which may be the mechanism of progressive renal fibrosis and renal failure in patients with high solvent exposure.

Mechanical traumatic injury without circulatory shock causes cardiomyocyte apoptosis: role of reactive nitrogen and reactive oxygen species

Apoptotic cell death plays a critical role in tissue injury and organ dysfunction under a variety of pathological conditions. The present study was designed to determine whether apoptosis may contribute to posttraumatic cardiac dysfunction, and if so, to investigate the mechanisms involved. Male adult mice were subjected to nonlethal traumatic injury, and cardiomyocyte apoptosis, cardiac function, and cardiac production of reactive oxygen/nitrogen species were determined. Modified Noble-Collip drum trauma did not result in circulatory shock, and the 24-h survival rate was 100%. No direct mechanical traumatic injury was observed in the heart immediately after trauma. However, cardiomyocyte apoptosis gradually increased and reached a maximal level 12 h after trauma. Significantly, cardiac dysfunction was observed 24 h after trauma in the isolated perfused heart. This was completely reversed when apoptosis was blocked by administration of a nonselective caspase inhibitor immediately after trauma. In the traumatized hearts, reactive nitrogen species (e.g., nitric oxide) and reactive oxygen species (e.g., superoxide) were both significantly increased, and maximal nitric oxide production preceded maximal apoptosis. Moreover, a highly cytotoxic reactive species, peroxynitrite, was markedly increased in the traumatic heart, and there was a significant positive correlation between cardiac nitrotyrosine content and caspase 3 activity. Our present study demonstrated for the first time that nonlethal traumatic injury caused delayed cell death and that apoptotic cardiomyocyte death contributes to posttrauma organ dysfunction. Antiapoptotic treatments, such as blockade of reactive nitrogen oxygen species generation, may be novel strategies in reducing posttrauma multiple organ failure.

Induction of programmed cell death in lily by the fungal pathogen Botrytis elliptica

SUMMARY The genus Botrytis contains necrotrophic plant pathogens that have a wide host range (B. cinerea) or are specialized on a single host species, e.g. B. elliptica on lily. In this study, it was found that B. elliptica-induced cell death of lily displays hallmark features of animal programmed cell death or apoptosis including cytoplasmic shrinkage, nuclear DNA fragmentation and the accumulation of NO as well as H(2)O(2). A pharmacological approach showed that B. elliptica-induced cell death could be modulated by serine and cysteine protease inhibitors including one caspase inhibitor. Blocking phosphatase activity stimulated cell death and concomitant lesion formation, suggesting that B. elliptica-induced cell death is mediated by kinase/phosphatase pathways. Blocking Ca(2+) influx restricted cell death. Blocking steps of sphingolipid biosynthesis delayed lily cell death for several days. B. elliptica culture filtrate (CF) was able to induce lily cell death by means of secreted proteins. Induction of cell death is necessary and sufficient for pathogenicity and host specialization because prior infiltration of B. elliptica CF enabled subsequent infection of lily by the otherwise incompatible pathogens B. cinerea and B. tulipae. The secreted B. elliptica proteins also induced cell death in some but not all Arabidopsis accessions and mutants. Arabidopsis accessions that respond to infiltration of B. elliptica CF also display cell death symptoms upon inoculation with B. elliptica conidia.

Peroxynitrite mediates calcium-dependent mitochondrial dysfunction and cell death via activation of calpains

Chondrocyte cell death is a hallmark of inflammatory and degenerative joint diseases such as rheumatoid arthritis (RA) and osteoarthritis (OA), but the molecular and cellular mechanisms involved have yet to be elucidated. Because 3-nitrotyrosine, a marker for reactive nitrogen species such as peroxynitrite, has been observed in OA and RA cartilage and has been associated with chondrocyte cell death, we investigated the mechanisms by which peroxynitrite induces cell death in human articular chondrocytes. The earliest biochemical event observed, subsequent to treatment with either peroxynitrite or the peroxynitrite generator SIN-1, was a rapid rise in intracellular calcium that lead to mitochondrial dysfunction and cell death. Although, chondrocyte death exhibited several classical hallmarks of apoptosis, including annexin V labeling, increased fraction of cells with subG1 DNA content and DNA condensation, we did not find evidence for caspase involvement either by Western blotting, fluorimetric assays, or caspase inhibition. Additionally, peroxynitrite did not inhibit cellular caspase activity. Furthermore, using other established assays of cell viability, including the MTT assay and release of lactate dehydrogenase, we found that the predominant mode of cell death involved calcium-dependent cysteine proteases, otherwise known as calpains. Our data show, for the first time, that peroxynitrite induces mitochondrial dysfunction in cells via a calcium-dependent process that leads to caspase-independent apoptosis mediated by calpains.

Reactive oxygen species induce different cell death mechanisms in cultured neurons

Apoptosis is characterized by chromatin condensation, phosphatidylserine translocation, and caspase activation. Neuronal apoptotic death involves the participation of reactive oxygen species (ROS), which have also been implicated in necrotic cell death. In this study we evaluated the role of different ROS in neuronal death. Superoxide anion was produced by incubating cells with xanthine and xanthine oxidase plus catalase, singlet oxygen was generated with rose Bengal and luminic stimuli, and hydrogen peroxide was induced with the glucose and glucose oxidase. Cultured cerebellar granule neurons died with the characteristics of apoptotic death in the presence of superoxide anion or singlet oxygen. These two conditions induced caspase activation, nuclear condensation, phosphatidylserine translocation, and a decrease in intracellular calcium levels. On the other hand, hydrogen peroxide led to a necrosis-like cell death that did not induce caspase activation, phosphatidylserine translocation, or changes in calcium levels. Cell death produced by both singlet oxygen and superoxide anion, but not hydrogen peroxide, was partially reduced by an increase in intracellular calcium levels. These results suggest that formation of specific ROS can lead to different molecular cell death mechanisms (necrosis and apoptosis) and that ROS formed under different conditions could act as initiators or executioners on neuronal death.

Peroxynitrite-induced relaxation in isolated canine cerebral arteries and mechanisms of action

The present study was undertaken to determine the vascular actions of peroxynitrite (ONOO(-)), the product of superoxide and nitric oxide (NO), in isolated canine cerebral arteries and to gain insight into its potential mechanisms of action. In the absence of any vasoactive agent, ONOO(-) (from 10(-7) to 10(-6) M) was able to reduce the basal tension. In prostaglandin F2alpha-precontracted canine basilar arterial rings, ONOO(-) elicited concentration-dependent relaxation at concentrations from 10(-8) to 10(-5) M. The effective concentrations producing approximately 50% maximal relaxation (EC(50)) to ONOO(-) were 4.06 x 10(-6) and 4.12 x 10(-6) M in intact and denuded rings, respectively (P > 0.05). No significant differences in relaxation responses were found in ring preparations with or without endothelium (P > 0.05). The presence of either 5 microM methylene blue (MB) or 5 microM 1H-[1,2,4]oxadiazolo-[4,3-alpha]quinoxalin-1-one (ODQ) significantly inhibited the relaxations induced by ONOO(-). Tetraethylammonium chloride (T-2265) significantly decreased the ONOO(-)-induced relaxations in a concentration-dependent manner. However, ONOO(-) had no effect on rings precontracted by high KCL (P > 0.05). Addition of low concentrations of calyculin A (50 nM) was able to abolish the ONOO(-)-induced relaxation. Furthermore, ONOO(-) significantly inhibited calcium-induced contractions of K(+)-depolarized canine cerebral rings in a concentration-related manner. Lastly, a variety of pharmacological agents and antagonists including L-NMMA, l-arginine, indomethacin, atropine, naloxone, diphenhydramine, cimetine, glibenclamide, haloperidol, etc., did not influence the relaxant effects of ONOO(-) on the rings. Our new results suggest that ONOO(-)-triggered relaxation, on canine cerebral arteries, is mediated by elevation of cyclic guanosine monophosphate (cGMP) levels, membrane hyperpolarization via K+ channel activation, activation of myosin light chain phosphatase activity, and interference with calcium movement and cellular membrane Ca(2+) entry.

High glucose-induced oxidative stress causes apoptosis in proximal tubular epithelial cells and is mediated by multiple caspases

Diabetic nephropathy is the leading cause of end-stage renal disease in the Western world. Poor glycemic control contributes to the development of diabetic nephropathy, but the mechanisms underlying high glucose-induced tissue injury are not fully understood. In the present study, the effect of high glucose on a proximal tubular epithelial cell (PTEC) line was investigated. Reactive oxygen species (ROS) were detected using the fluorescent probes dichlorofluorescein diacetate, dihydrorhodamine 123, and 2,3-diaminonapthalene. Peroxynitrite (ONOO-) generation and nitrite concentrations were increased after 24 h of high glucose treatment (P<0.05). LLC-PK1 cells exposed to high D-glucose (25 mM) for up to 48 h had increased DNA fragmentation (P<0.01), caspase-3 activity (P<0.001), and annexin-V staining (P<0.05) as well as decreased expression of XIAP when compared with controls (5 mM D-glucose). The ONOO- scavenger ebselen reduced DNA fragmentation and caspase-3 activity as well as the high glucose-induced nitrite production and DCF fluorescence. High glucose-induced DNA fragmentation was completely prevented by an inhibitor of caspase-3 (P<0.01) and a pan-caspase inhibitor (P<0.001). Caspase inhibition did not affect ROS generation. This study, in a PTEC line, demonstrates that high glucose causes the generation of ONOO-, leading to caspase-mediated apoptosis. Ebselen and a caspase-3 inhibitor provided significant protection against high glucose-mediated apoptosis, implicating ONOO- as a proapoptotic ROS in early diabetic nephropathy.

Peroxynitrite-induced cytotoxicity: mechanism and opportunities for intervention

Peroxynitrite is formed in biological systems when superoxide and nitric oxide are produced at near equimolar ratio. Although not a free radical by chemical nature (as it has no unpaired electron), peroxynitrite is a powerful oxidant exhibiting a wide array of tissue damaging effects ranging from lipid peroxidation, inactivation of enzymes and ion channels via protein oxidation and nitration to inhibition of mitochondrial respiration. Low concentrations of peroxynitrite trigger apoptotic death, whereas higher concentrations induce necrosis with cellular energetics (ATP and NAD) serving as switch between the two modes of cell death. Peroxynitrite also damages DNA and thus triggers the activation of DNA repair systems. A DNA nick sensor enzyme, poly(ADP-ribose) polymerase-1 (PARP-1) also becomes activated upon sensing DNA breakage. Activated PARP-1 cleaves NAD(+) into nicotinamide and ADP-ribose and polymerizes the latter on nuclear acceptor proteins. Peroxynitrite-induced overactivation of PARP consumes NAD(+) and consequently ATP culminating in cell dysfunction, apoptosis or necrosis. This cellular suicide mechanism has been implicated among others in the pathomechanism of stroke, myocardial ischemia, diabetes and diabetes-associated cardiovascular dysfunction. Here, we review the cytotoxic effects (apoptosis and necrosis) of peroxynitrite focusing on the role of accelerated ADP-ribose turnover. Regulatory mechanisms of peroxynitrite-induced cytotoxicity such as antioxidant status, calcium signalling, NFkappaB activation, protein phosphorylation, cellular adaptation are also discussed.

Peroxynitrite-induced oligodendrocyte toxicity is not dependent on poly(ADP-ribose) polymerase activation

Oligodendrocyte loss is a characteristic feature of several CNS disorders, including multiple sclerosis (MS) and spinal cord injury. However, the mechanisms responsible for oligodendrocyte destruction remain undefined. As recent studies have implicated peroxynitrite in the pathogenesis of both spinal cord injury and MS, we have examined whether peroxynitrite may mediate at least some of the oligodendrocyte damage and demyelination observed in these conditions. Primary rat oligodendrocytes were exposed to authentic peroxynitrite in vitro and assessed for cytotoxicity. Mitochondrial function, measured by the reduction of MTT to formazan, and mitochondrial membrane potential were used as indicators of cell viability. Cell death was quantitated by measuring either the release of lactate dehydrogenase from, or the uptake of propidium iodide into, damaged and dying cells. Peroxynitrite dose-dependently reduced the viability of primary oligodendrocytes and induced cell death. Furthermore, peroxynitrite significantly increased DNA strand breakage and the activity of poly(ADP-ribose) polymerase (PARP) in oligodendrocyte cultures. To identify whether PARP activation plays a role in peroxynitrite-induced oligodendrocyte toxicity, we examined the effects of the PARP inhibitors 3-aminobenzamide (3AB) and 5-iodo-6-amino-1,2-benzopyrone (INH(2)BP) on mitochondrial function and cell death in oligodendrocytes. The presence of 3AB and INH(2)BP did not protect oligodendrocytes from peroxynitrite-induced cytotoxicity. However, both compounds significantly reduced PARP activity in these cells. Primary oligodendrocytes generated from PARP-deficient mice were also highly susceptible to peroxynitrite-induced cell death. Therefore, our results show that peroxynitrite exerts cytotoxic effects on oligodendrocytes in vitro independently of PARP activation.

Nitric oxide inhibition of mitochondrial respiration and its role in cell death

Nitric oxide (NO) or its derivatives (reactive nitrogen species, RNS) inhibit mitochondrial respiration in two different ways: (i) an acute, potent, and reversible inhibition of cytochrome oxidase by NO in competition with oxygen; and, (ii) irreversible inhibition of multiple sites by RNS. NO inhibition of respiration may impinge on cell death in several ways. Inhibition of respiration can cause necrosis and inhibit apoptosis due to ATP depletion, if glycolysis is also inhibited or is insufficient to compensate. Inhibition of neuronal respiration can result in excitotoxic death of neurons due to induced release of glutamate and activation of NMDA-type glutamate receptors. Inhibition of respiration may cause apoptosis in some cells, while inhibiting apoptosis in other cells, by mechanisms that are not clear. However, NO can induce (and inhibit) cell death by a variety of mechanisms unrelated to respiratory inhibition.

Peroxynitrite reactions and formation in mitochondria

Mitochondria constitute a primary locus for the intracellular formation and reactions of peroxynitrite, and these interactions are recognized to contribute to the biological and pathological effects of both nitric oxide ((*)NO) and peroxynitrite. Extra- or intramitochondrially formed peroxynitrite can diffuse through mitochondrial compartments and undergo fast direct and free radical-dependent target molecule reactions. These processes result in oxidation, nitration, and nitrosation of critical components in the matrix, inner and outer membrane, and intermembrane space. Mitochondrial scavenging and repair systems for peroxynitrite-dependent oxidative modifications operate but they can be overwhelmed under enhanced cellular (*)NO formation as well as under conditions that lead to augmented superoxide formation by the electron transport chain. Peroxynitrite can lead to alterations in mitochondrial energy and calcium homeostasis and promote the opening of the permeability transition pore. The effects of peroxynitrite in mitochondrial physiology can be largely rationalized based on the reactivities of peroxynitrite and peroxynitrite-derived carbonate, nitrogen dioxide, and hydroxyl radicals with critical protein amino acids and transition metal centers of key mitochondrial proteins. In this review we analyze (i) the existing evidence for the intramitochondrial formation and reactions of peroxynitrite, (ii) the key reactions and fate of peroxynitrite in mitochondria, and (iii) their impact in mitochondrial physiology and signaling of cell death.

Nitric oxide-peroxynitrite-poly(ADP-ribose) polymerase pathway in the skin

In the last decade it has become well established that in the skin, nitric oxide (NO), a diffusable gas, mediates various physiologic functions ranging from the regulation of cutaneous blood flow to melanogenesis. If produced in excess, NO combines with superoxide anion to form peroxynitrite (ONOO-), a cytotoxic oxidant that has been made responsible for tissue injury during shock, inflammation and ischemia-reperfusion. The opposite effects of NO and ONOO- on various cellular processes may explain the 'double-edged sword' nature of NO depending on whether or not cellular conditions favour peroxynitrite formation. Peroxynitrite has been shown to activate the nuclear nick sensor enzyme, poly(ADP-ribose) polymerase (PARP). Overactivation of PARP depletes the cellular stores of NAD+, the substrate of PARP, and the ensuing 'cellular energetic catastrophy' results in necrotic cell death. Whereas the role of NO in numerous skin diseases including wound healing, burn injury, psoriasis, irritant and allergic contact dermatitis, ultraviolet (UV) light-induced sunburn erythema and the control of skin infections has been extensively documented, the intracutaneous role of peroxynitrite and PARP has not been fully explored. We have recently demonstrated peroxynitrite production, DNA breakage and PARP activation in a murine model of contact hypersensitivity, and propose that the peroxynitrite-PARP route represents a common pathway in the pathomechanism of inflammatory skin diseases. Here we briefly review the role of NO in skin pathology and focus on the possible roles played by peroxynitrite and PARP in various skin diseases.

Phosphate-induced chondrocyte apoptosis is linked to nitric oxide generation

An elevation in inorganic phosphate (P(i)) concentration activates epiphyseal chondrocyte apoptosis. To determine the mechanism of apoptosis, tibial chondrocytes were treated with P(i), and nitrate/nitrite (NO/NO) levels were determined. P(i) induced a threefold increase in the NO/NO concentration; inhibitors of nitric oxide (NO) synthase activity and P(i) transport significantly reduced NO/NO levels and prevented cell death. Furthermore, a dose-dependent increase in cell death was observed after exposure of chondrocytes to S-nitrosoglutathione. P(i) increased caspase 3 activity 2.7-fold. Both caspase 1 and caspase 3 inhibitors protected chondrocytes from P(i)-induced apoptosis. P(i) caused a significant decrease in the mitochondrial membrane potential, while NO synthase inhibitors maintained mitochondrial function. While P(i) caused thiol depletion, inhibition of P(i) uptake or NO generation served to maintain glutathione levels. The results suggest that NO serves to mediate key metabolic events linked to P(i)-dependent chondrocyte apoptosis.