Manganese Superoxide Dismutase Nitration Research Articles

The Global POLAR program: Two pivotal placebo-controlled studies of calmangafodipir used on top of modified FOLFOX6 to prevent chemotherapy-induced peripheral neuropathy (CIPN).

TPS3616 Background: Oxaliplatin (OXA), is approved in combination with 5-FU/FA (5-fluorouracil/folinic acid; FOLFOX) for metastatic as well as in adjuvant colo-rectal cancer (CRC) treatment. CIPN is a common adverse event, after OXA treatment. The incidence of chronic CIPN is approximately 15% after a cumulative dose of 780 to 850 mg/m² and 50% after a cumulative dose of 1170 mg/m². OXA induced neuropathy, results in greatly reduced nitrated manganese superoxide dismutase (MnSOD) activity. Treatment with a superoxide dismutase mimetic, such as calmangafodipir (CAL), prevents and reverses oxaliplatin-induced neuropathies. This has been demonstrated in the PLIANT study, with CAL (Glimelius et al. 2017). Methods: The POLAR program is a Phase 3, multicenter, placebo (PLC)-controlled program of CAL to prevent CIPN, recruiting in US, Europe (B, D, ES, F,ES, I and UK) and Asia (J, SK, TW and HK) and is described below; POLAR A Patients with CRC, treatment of patients with Stage III or high-risk Stage II who are indicated for adjuvant modified FOLFOX6 (mFOLFOX6) chemotherapy for up to 6 months, randomized in a 1:1 ratio, each arm n = 140: A: CAL (5 µmol/kg) + mFOLFOX6 chemotherapy B: PLC + mFOLFOX6 chemotherapy POLAR M Patients with metastatic colorectal cancer (mCRC), who are indicated for first-line mFOLFOX6 chemotherapy for at least 3 months, without any pre-planned treatment breaks and will be randomized in a 1:1:1 ratio, each arm n = 140: A: CAL (2 µmol/kg) + mFOLFOX6 chemotherapy B: CAL (5 µmol/kg) + mFOLFOX6 chemotherapy C: PLC + mFOLFOX6 chemotherapy Primary objective is to compare CAL vs PLC with respect to the proportion of patients with moderate or severe chronic CIPN. The primary endpoint is; Patient reported symptoms as proportion of patients scoring 3 or 4 in at least 1 of the first 4 items of the FACT/GOG-NTX-13 (i.e., FACT/GOG-NTX-4), targeting numbness, tingling or discomfort in hands and/or feet, assessed 9 months after the first dose of chemotherapy. In addition to conventional safety endpoints, Progressive Free Survival and Overall Survival are assessed in the POLAR M study. In the POLAR A study Disease Free Survival is one additional safety endpoint assessed. Results are expected during second half 2020. Clinical trial information: NCT03654729.

The Global POLAR program: Calmangafodipir used on top of modified FOLFOX6 (5-FU/FA and oxaliplatin) to prevent chemotherapy induced peripheral neuropathy (CIPN).

TPS722 Background: Oxaliplatin (OXA), is approved in combination with 5-FU/FA (5-fluorouracil/folinic acid; FOLFOX) for metastatic as well as in adjuvant colo-rectal cancer (CRC) treatment. CIPN is a common adverse event, after OXA treatment. The incidence of chronic CIPN is approximately 15% after a cumulative dose of 780 to 850 mg/m² and 50% after a cumulative dose of 1170 mg/m². OXA induced neuropathy, results in greatly reduced nitrated manganese superoxide dismutase (MnSOD) activity. Treatment with a superoxide dismutase mimetic, such as calmangafodipir (CAL), prevents and reverses oxaliplatin-induced neuropathies. This has been demonstrated in the PLIANT study (Glimelius et al. 2017). Methods: The POLAR program is a phase III, multicenter, placebo (PLC)-controlled program of CAL to prevent CIPN, initiated in US, Europe and Asia: POLAR A patients with CRC, treatment of patients with stage III or high-risk stage II who are indicated for adjuvant modified FOLFOX6 (mFOLFOX6) chemotherapy for up to 6 months, randomized in a 1:1 ratio, each arm n = 140: A: CAL (5 µmol/kg) + mFOLFOX6 chemotherapy B: PLC + mFOLFOX6 chemotherapy POLAR M Patients with metastatic colorectal cancer (mCRC), who are indicated for first-line mFOLFOX6 chemotherapy for at least 3 months, without any pre-planned treatment breaks and will be randomized in a 1:1:1 ratio, each arm n = 140: A: CAL (2 µmol/kg) + mFOLFOX6 chemotherapy B: CAL (5 µmol/kg) + mFOLFOX6 chemotherapy C: PLC + mFOLFOX6 chemotherapy. Primary objective is to compare CAL versus PLC with respect to the proportion of patients with moderate or severe chronic CIPN. The primary endpoint is; patient reported symptoms as proportion of patients scoring 3 or 4 in at least 1 of the first 4 items of the FACT/GOG-NTX-13 (i.e., FACT/GOG-NTX-4), targeting numbness, tingling or discomfort in hands and/or feet, assessed 9 months after the first dose of chemotherapy. In addition to conventional safety endpoints, Progressive Free Survival and Overall Survival are assessed in the POLAR M study. In the POLAR A study Disease Free Survival is one additional safety endpoint assessed. Results are expected during second half of 2020. Clinical trial information: NCT03654729.

Role of spinal peroxynitrite in remifentanil-induced hyperalgesia in rats

Objective To evaluate the role of spinal peroxynitrite in remifentanil-induced hyperalgesia in rats. Methods Thirty-two male Sprague-Dawley rats, weighing 240-260 g, aged 2-3 months, were randomly divided into 4 groups(n=8 each)using a random number table: control group(group C), remifentanil group(group R), hydrogen-rich saline group(group C+ H), and remifentanil + hydrogen-rich saline group(group R+ H). In group C, normal saline was infused for 60 min at a rate of 0.1 ml·kg-1·min-1.In group R, remifentanil was infused for 60 min at a rate of 1.0 μg·kg-1·min-1.In group R+ H, remifentanil was infused for 60 min at a rate of 1.0 μg·kg-1·min-1, and hydrogen-rich saline 10 ml/kg was intraperitoneally injected at 10 min before iv infusion.At 24 h before iv infusion and 6, 24 and 48 h after iv infusion(T0-3), the mechanical paw withdrawal threshold(MWT)and thermal paw withdrawal latency(TWL)were measured.All the rats were sacrificed after the last measurement of pain thresholds, the lumbar segment(L4-6)of the spinal cord was removed for determination of the nitrated manganese superoxide dismutase(MnSOD)expression(by immunoprecipitation and Western blot analysis), 3-nitrotyrosine(3-NT)expression(by Western blot)and spinal MnSOD activity(by spectrophotometer). Results Compared with group C, the MWT was significantly decreased, and TWL was shortened at T1-T3, the expression of spinal 3-NT and nitrated MnSOD was up-regulated, and MnSOD activity was decreased in R and R+ H groups, and no significant change was found in the parameters mentioned above in group C+ H.Compared with group R, the MWT was significantly increased, and TWL was prolonged at T1-T3, the expression of spinal 3-NT and nitrated MnSOD was down-regulated, and MnSOD activity was increased in group R+ H. Conclusion Spinal peroxynitrite is involved in the mechanism underlying remifentanil-induced hyperalgesia through inhibiting the activity of MnSOD in rats. Key words: Piperidines; Hyperalgesia; Peroxynitrite; Spinal cord

Spinal Peroxynitrite Contributes to Remifentanil-induced Postoperative Hyperalgesia via Enhancement of Divalent Metal Transporter 1 without Iron-responsive Element–mediated Iron Accumulation in Rats

Hyperalgesia is one of the negative consequences following intraoperative analgesia with remifentanil. Peroxynitrite is a critical determinant in nociceptive process. Peroxynitrite inactivates iron-sulfur cluster that results in mitochondrial dysfunction and the release of iron, leading to mitochondrial iron accumulation. Iron accumulation mediated by divalent metal transporter 1 (DMT1) plays a key role in N-methyl-D-aspartate neurotoxicity. This study aims to determine whether peroxynitrite contributes to remifentanil-induced postoperative hyperalgesia via DMT1-mediated iron accumulation. Behavior testing was performed in rat model at different time points. Three-nitrotyrosine, nitrated manganese superoxide dismutase, and DMT1 with/without iron-responsive element [DMT1(+)IRE and DMT1(-)IRE] in spinal cord were detected by Western blot and immunohistochemistry. Spinal iron concentration was measured using the Perl stain and atomic absorption spectrophotometer. Hydrogen-rich saline imparting selectivity for peroxynitrite decomposition and iron chelator was applied in mechanistic study on the roles of peroxynitrite and iron, as well as the prevention of hyperalgesia. Remifentanil induced thermal and mechanical hyperalgesia at postoperative 48 h. Compared with control, there were higher levels of 3-nitrotyrosine (mean ± SD, hyperalgesia vs. control, 1.22 ± 0.18 vs. 0.25 ± 0.05, n = 4), nitrated manganese superoxide dismutase (1.01 ± 0.1 vs. 0.19 ± 0.03, n = 4), DMT1(-)IRE (1.42 ± 0.19 vs. 0.33 ± 0.06, n = 4), and iron concentration (12.87 ± 1.14 vs. 5.26 ± 0.61 μg/g, n = 6) in remifentanil-induced postoperative hyperalgesia, while DMT1(+)IRE was unaffected. Eliminating peroxynitrite with hydrogen-rich saline protected against hyperalgesia and attenuated DMT1(-)IRE overexpression and iron accumulation. Iron chelator prevented hyperalgesia in a dose-dependent manner. Our study identifies that spinal peroxynitrite activates DMT1(-)IRE, leading to abnormal iron accumulation in remifentanil-induced postoperative hyperalgesia, while providing the rationale for the development of molecular hydrogen and "iron-targeted" therapies.

Hydrogen-rich saline prevents remifentanil-induced hyperalgesia and inhibits MnSOD nitration via regulation of NR2B-containing NMDA receptor in rats

Remifentanil administration may subsequently cause paradoxical hyperalgesia in animals and humans, but mechanisms remain unclear. Manganese superoxide dismutase (MnSOD) nitration and inactivation caused by generation of reactive oxygen species and activation of N-methyl-d-aspartate (NMDA) receptors are involved in the induction and maintenance of central neuropathic pain. Hydrogen which selectively removes superoxide has gained much attention in recent years. In this study, we investigated antinociceptive effects of hydrogen-rich saline (HRS) on remifentanil-induced postsurgical hyperalgesia in a rat model of incisional pain. HRS was injected intraperitoneally 10min before remifentanil infusion (1μgkg−1min−1 for 60min). A selective NR2B antagonist Ro25-6981 was used to investigate whether antihypernociception of HRS is associated with NMDA receptor (NMDAR). Nociception was evaluated by the paw withdrawal mechanical threshold and thermal latency respectively. Then we assessed MnSOD, NR2A and NR2B in spinal cord dorsal horn via Western blot and immunohistochemistry after nociceptive tests. Here, we found that the analgesic effect of remifentanil was followed by long-term hyperalgesia lasting at least postoperative 7days, which was accompanied with increase in NR2B expression and trafficking from cytoplasm to surface and MnSOD nitration in dorsal horn. Pretreatment with HRS (10ml/kg) significantly attenuated mechanical and thermal hyperalgesia, blocked NR2B trafficking and MnSOD nitration in dorsal horn after remifentanil infusion. Ro25-6981 not 5μg but 10 and 50μg dosage-dependently attenuated hyperalgesia, and inhibited MnSOD nitration. Hyperalgesia and MnSOD nitration were attenuated after the combination of HRS (2.5ml/kg) and Ro25-6981 (5μg). In conclusion, HRS (10ml/kg) might reverse remifentanil-induced hyperalgesia, through regulating NR2B-containing NMDAR trafficking to control MnSOD nitration and enhance MnSOD activity.

Ganoderma lucidum Polysaccharide Accelerates Refractory Wound Healing by Inhibition of Mitochondrial Oxidative Stress in Diabetes

BackgroundImpaired wound healing in diabetic patients is a serious complication with limited treatment regimens. Gene therapy of mitochondrial antioxidant enzyme manganese superoxide dismutase (MnSOD) was able to restore diabetic wound healing with suppression of O2.−. The present study was designed to determine protective effects of Ganoderma lucidum polysaccharide (Gl‐PS), as a potent inducer of MnSOD, on diabetic wound healing.Method and ResultsStreptozotocin‐induced diabetic mice with full‐thickness excisional wounds were administered with Gl‐PS (10, 50 or 250 mg/kg/day, i.g.). Gl‐PS dose‐dependently rescued the delay of wound closure and increased the mean perfusion rate around the wound in diabetic mice. Diabetic conditions markly increased mitochondrial O2.− production and nitrotyrosine formation in wound tissues, which were normalized with Gl‐PS treatment. In diabetic wound tissues, the protein level of MnSOD was unchanged whereas MnSOD activity was inhibited and its nitration was potentiated; Gl‐PS administration suppressed MnSOD nitration and increased MnSOD and glutathione peroxidase (GPx) activities. Moreover, Gl‐PS attenuated the redox enzyme p66Shc expression and phosphorylation in diabetic mice skin.ConclusionGl‐PS rescued the delayed wound healing and improved wound angiogenesis in diabetic mice, at least in part, by suppression of mitochondrial oxidative stress. This work was supported by the National Natural Science Foundation of China.

Decreases in manganese superoxide dismutase expression and activity contribute to oxidative stress in persistent pulmonary hypertension of the newborn

A rapid increase in the synthesis and release of nitric oxide (NO) facilitates the pulmonary vasodilation that occurs during birth-related transition. Alteration of this transition in persistent pulmonary hypertension of the newborn (PPHN) is associated with impaired function of endothelial nitric oxide synthase (eNOS) and an increase in oxidative stress. We investigated the hypothesis that a decrease in expression and activity of mitochondrial localized manganese superoxide dismutase (MnSOD) in pulmonary artery endothelial cells (PAEC) increases oxidative stress and impairs eNOS function in PPHN. We isolated PAEC and pulmonary arteries from fetal lambs with PPHN induced by prenatal ductus arteriosus ligation or sham ligation (control). We investigated MnSOD expression and activity, tyrosine nitration of MnSOD, and mitochondrial O(2)(-) levels in PAEC from control and PPHN lambs. We introduced exogenous MnSOD via an adenoviral vector (ad-MnSOD) transduction into PAEC and pulmonary arteries of PPHN lambs. The effect of ad-MnSOD was investigated on: mitochondrial O(2)(-) levels, MnSOD and eNOS expression and activity, intracellular hydrogen peroxide (H(2)O(2)) levels, and catalase expression in PAEC. MnSOD mRNA and protein levels and activity were decreased and MnSOD tyrosine nitration was increased in PPHN-PAEC. ad-MnSOD transduction of PPHN-PAEC increased its activity two- to threefold, decreased mitochondrial O(2)(-) levels, and increased H(2)O(2) levels and catalase expression. ad-MnSOD transduction improved eNOS expression and function and the relaxation response of PPHN pulmonary arteries. Our observations suggest that decreased MnSOD expression and activity contribute to the endothelial dysfunction observed in PPHN.

Ganoderma Lucidum Polysaccharide Accelerates Refractory Wound Healing by Inhibition of Mitochondrial Oxidative Stress in Type 1 Diabetes

Background/Aims. Refractory wounds in diabetic patients constitute a serious complication that often leads to amputation with limited treatment regimens. The present study was designed to determine the protective effect of Ganoderma lucidum polysaccharide (Gl-PS) on diabetic wound healing and investigate underlying mechanisms. Methods. Streptozotocin (STZ)-induced type 1 diabetic mice with full-thickness excisional wounds were intragastrically administered with 10, 50 or 250 mg/kg/day of Gl-PS. Results. Gl-PS dose-dependently rescued the delay of wound closure in diabetic mice. 50 and 250 mg/kg/day of Gl-PS treatment significantly increased the mean perfusion rate around the wound in diabetic mice. Diabetic conditions markly increased mitochondrial superoxide anion (O₂·^-) production, nitrotyrosine formation, and inducible nitric oxide synthase (iNOS) activity in wound tissues, which were normalized with Gl-PS treatment. In diabetic wound tissues, the protein level of manganese superoxide dismutase (MnSOD) was unchanged whereas MnSOD activity was inhibited and its nitration was potentiated; Gl-PS administration suppressed MnSOD nitration and increased MnSOD and glutathione peroxidase (GPx) activities. Moreover, Gl-PS attenuated the redox enzyme p66Shc expression and phosphorylation dose-dependently in diabetic mice skin. Conclusion. Gl-PS rescued the delayed wound healing and improved wound angiogenesis in STZ-induced type 1 diabetic mice, at least in part, by suppression of cutaneous MnSOD nitration, p66Shc and mitochondrial oxidative stress.

Acetaminophen-Induced Hepatotoxicity in Mice Occurs with Inhibition of Activity and Nitration of Mitochondrial Manganese Superoxide Dismutase

In overdose the analgesic/antipyretic acetaminophen (APAP) is hepatotoxic. Toxicity is mediated by initial hepatic metabolism to N-acetyl-p-benzoquinone imine (NAPQI). After low doses NAPQI is efficiently detoxified by GSH. However, in overdose GSH is depleted, NAPQI covalently binds to proteins as APAP adducts, and oxygen/nitrogen stress occurs. Toxicity is believed to occur by mitochondrial dysfunction. Manganese superoxide dismutase (MnSOD) inactivation by protein nitration has been reported to occur during other oxidant stress-mediated diseases. MnSOD is a critical mitochondrial antioxidant enzyme that prevents peroxynitrite formation within the mitochondria. To examine the role of MnSOD in APAP toxicity, mice were treated with 300 mg/kg APAP. GSH was significantly reduced by 65% at 0.5 h and remained reduced from 1 to 4 h. Serum alanine aminotransferase did not significantly increase until 4 h and was 2290 IU/liter at 6 h. MnSOD activity was significantly reduced by 50% at 1 and 2 h. At 1 h, GSH was significantly depleted by 62 and 80% at nontoxic doses of 50 and 100 mg/kg, respectively. No further GSH depletion occurred with hepatotoxic doses of 200 and 300 mg/kg APAP. A dose response decrease in MnSOD activity was observed for APAP at 100, 200, and 300 mg/kg. Immunoprecipitation of MnSOD from livers of APAP-treated mice followed by Western blot analysis revealed nitrated MnSOD. APAP-MnSOD adducts were not detected. Treatment of recombinant MnSOD with NAPQI did not produce APAP protein adducts. The data indicate that MnSOD inactivation by nitration is an early event in APAP-induced hepatic toxicity.

Peroxynitrite mediates active site tyrosine nitration in manganese superoxide dismutase. Evidence of a role for the carbonate radical anion.

Protein tyrosine nitration has been observed in a variety of human diseases associated with oxidative stress, such as inflammatory, neurodegenerative, and cardiovascular conditions. However, the pathways leading to nitration of tyrosine residues are still unclear. Recent studies have shown that peroxynitrite (PN), produced by the reaction of superoxide and nitric oxide, can lead to protein nitration and inactivation. Tyrosine nitration may also be mediated by nitrogen dioxide produced by the oxidation of nitrite by peroxidases. Manganese superoxide dismutase (MnSOD), which plays a critical role in cellular defense against oxidative stress by decomposing superoxide within mitochondria, is nitrated and inactivated under pathological conditions. In this study, MnSOD is shown to catalyze PN-mediated self-nitration. Direct, spectroscopic observation of the kinetics of PN decay and nitrotyrosine formation (k(cat) = 9.3 × 10(2) M(-1) s(-1)) indicates that the mechanism involves redox cycling between Mn(2+) and Mn(3+), similar to that observed with superoxide. Distinctive patterns of tyrosine nitration within MnSOD by various reagents were revealed and quantified by MS/MS analysis of MnSOD trypsin digest peptides. These analyses showed that three of the seven tyrosine residues of MnSOD (Tyr34, Tyr9, and Tyr11) were the most susceptible to nitration and that the relative amounts of nitration of these residues varied widely depending upon the nature of the nitrating agent. Notably, nitration mediated by PN, in both the presence and absence of CO2, resulted in nitration of the active site tyrosine, Tyr34, while nitration by freely diffusing nitrogen dioxide led to surface nitration at Tyr9 and Tyr11. Flux analysis of the nitration of Tyr34 by PN-CO2 showed that the nitration rate coincided with the kinetics of the reaction of PN with CO2. These kinetics and the 20-fold increase in the efficiency of tyrosine nitration in the presence of CO2 suggest a specific role for the carbonate radical anion (•CO3(-)) in MnSOD nitration by PN. We also observed that the nitration of Tyr34 caused inactivation of the enzyme, while nitration of Tyr9 and Tyr11 did not interfere with the superoxide dismutase activity. The loss of MnSOD activity upon Tyr34 nitration implies that the responsible reagent in vivo is peroxynitrite, acting either directly or through the action of •CO3(-).

Tumor necrosis factor alpha–mediated nitric oxide production enhances manganese superoxide dismutase nitration and mitochondrial dysfunction in primary neurons: an insight into the role of glial cells

Tumor necrosis factor-alpha (TNF-α), a ubiquitous pro-inflammatory cytokine, is an important mediator in the immune-neuroendocrine system that affects the CNS. The present study demonstrates that treatment with TNF-α activates microglia to increase TNF-α production in primary cultures of glial cells isolated from wild-type (WT) mice and mice deficient in the inducible form of nitric oxide synthase (iNOSKO). However, mitochondrial dysfunction in WT neurons occurs at lower concentrations of TNF-α when neurons are directly treated with TNF-α or co-cultured with TNF-α-treated microglia than iNOSKO neurons similarly treated. Immunofluorescent staining of primary neurons co-cultured with TNF-α-treated microglia reveals that the antioxidant enzyme in mitochondria, manganese superoxide dismutase (MnSOD), is co-localized with nitrotyrosine in WT but not in iNOSKO primary neuronal cells. Importantly, the percentage of surviving neurons is significantly reduced in WT neurons compared with iNOSKO neurons under identical treatment conditions. Together, the results suggest that TNF-α activates microglia to produce high levels of TNF-α and that production of nitric oxide (NO) in neurons is an important factor affecting MnSOD nitration and subsequent mitochondrial dysfunction.

Neuronal NOS‐mediated nitration and inactivation of manganese superoxide dismutase in brain after experimental and human brain injury

Manganese superoxide dismutase (MnSOD) provides the first line of defense against superoxide generated in mitochondria. SOD competes with nitric oxide for reaction with superoxide and prevents generation of peroxynitrite, a potent oxidant that can modify proteins to form 3-nitrotyrosine. Thus, sufficient amounts of catalytically competent MnSOD are required to prevent mitochondrial damage. Increased nitrotyrosine immunoreactivity has been reported after traumatic brain injury (TBI); however, the specific protein targets containing modified tyrosine residues and functional consequence of this modification have not been identified. In this study, we show that MnSOD is a target of tyrosine nitration that is associated with a decrease in its enzymatic activity after TBI in mice. Similar findings were obtained in temporal lobe cortical samples obtained from TBI cases versus control patients who died of causes not related to CNS trauma. Increased nitrotyrosine immunoreactivity was detected at 2 h and 24 h versus 72 h after experimental TBI and co-localized with the neuronal marker NeuN. Inhibition and/or genetic deficiency of neuronal nitric oxide synthase (nNOS) but not endothelial nitric oxide synthase (eNOS) attenuated MnSOD nitration after TBI. At 24 h after TBI, there was predominantly polymorphonuclear leukocytes accumulation in mouse brain whereas macrophages were the predominant inflammatory cell type at 72 h after injury. However, a selective inhibitor or genetic deficiency of inducible nitric oxide synthase (iNOS) failed to affect MnSOD nitration. Nitration of MnSOD is a likely consequence of peroxynitrite within the intracellular milieu of neurons after TBI. Nitration and inactivation of MnSOD could lead to self-amplification of oxidative stress in the brain progressively enhancing peroxynitrite production and secondary damage.

Consequences of MnSOD interactions with nitric oxide: Nitric oxide dismutation and the generation of peroxynitrite and hydrogen peroxide

The present study demonstrates that manganese superoxide dismutase (MnSOD) (Escherichia coli), binds nitric oxide (√NO) and stimulates its decay under both anaerobic and aerobic conditions. The results indicate that previously observed MnSOD-catalyzed √NO disproportionation (dismutation) into nitrosonium (NO+) and nitroxyl (NO− ) species under anaerobic conditions is also operative in the presence of molecular oxygen. Upon sustained aerobic exposure to √NO, MnSOD-derived NO− species initiate the formation of peroxynitrite (ONOO− ) leading to enzyme tyrosine nitration, oxidation and (partial) inactivation. The results suggest that both ONOO− decomposition and ONOO− -dependent tyrosine residue nitration and oxidation are enhanced by metal centre-mediated catalysis. We show that the generation of ONOO− is accompanied by the formation of substantial amounts of H2O2. MnSOD is a critical mitochondrial antioxidant enzyme, which has been found to undergo tyrosine nitration and inactivation in various pathologies associated with the overproduction of √NO. The results of the present study can account for the molecular specificity of MnSOD nitration in vivo. The interaction of √NO with MnSOD may represent a novel mechanism by which MnSOD protects the cell from deleterious effects associated with overproduction of √NO.

Adriamycin‐mediated nitration of manganese superoxide dismutase in the central nervous system: insight into the mechanism of chemobrain

Adriamycin (ADR), a potent anti-tumor agent, produces reactive oxygen species (ROS) in cardiac tissue. Treatment with ADR is dose-limited by cardiotoxicity. However, the effect of ADR in the other tissues, including the brain, is unclear because ADR does not pass the blood-brain barrier. Some cancer patients receiving ADR treatment develop a transient memory loss, inability to handle complex tasks etc., often referred to by patients as chemobrain. We previously demonstrated that ADR causes CNS toxicity, in part, via systemic release of cytokines and subsequent generation of reactive oxygen and nitrogen species (RONS) in the brain. Here, we demonstrate that treatment with ADR led to an increased circulating level of tumor necrosis factor-alpha in wild-type mice and in mice deficient in the inducible form of nitric oxide (iNOSKO). However, the decline in mitochondrial respiration and mitochondrial protein nitration after ADR treatment was observed only in wild-type mice, not in the iNOSKO mice. Importantly, the activity of a major mitochondrial antioxidant enzyme, manganese superoxide dismutase (MnSOD), was reduced and the protein was nitrated. Together, these results suggest that NO is an important mediator, coupling the effect of ADR with cytokine production and subsequent activation of iNOS expression. We also identified the mitochondrion as an important target of ADR-induced NO-mediated CNS injury.

β-Amyloid Mediated Nitration of Manganese Superoxide Dismutase: Implication for Oxidative Stress in a APP NLh/NLh X PS-1 P264L/P264L Double Knock-In Mouse Model of Alzheimer's Disease

Alzheimer's disease is a multifactorial, progressive, age-related neurodegenerative disease. In familial Alzheimer's disease, Abeta is excessively produced and deposited because of mutations in the amyloid precursor protein, presenilin-1, and presenilin-2 genes. Here, we generated a double homozygous knock-in mouse model that incorporates the Swedish familial Alzheimer's disease mutations and converts mouse Abeta to the human sequence in amyloid precursor protein and had the P264L familial Alzheimer's disease mutation in presenilin-1. We observed Abeta deposition in double knock-in mice beginning at 6 months as well as an increase in the levels of insoluble Abeta1-40/1-42. Brain homogenates from 3-, 6-, 9-, 12-, and 14-month-old mice showed that protein levels of manganese superoxide dismutase (MnSOD) were unchanged in the double knock-in mice compared to controls. Genotype-associated increases in nitrotyrosine levels were observed. Protein immunoprecipitation revealed MnSOD as a target of this nitration. Although the levels of MnSOD protein did not change, MnSOD activity and mitochondrial respiration decreased in knock-in mice, suggesting compromised mitochondrial function. The compromised activity of MnSOD, a primary antioxidant enzyme protecting mitochondria, may explain mitochondrial dysfunction and provide the missing link between Abeta-induced oxidative stress and Alzheimer's disease.

Crystal structure of nitrated human manganese superoxide dismutase: Mechanism of inactivation

A cellular consequence of the reaction of superoxide and nitric oxide is enhanced peroxynitrite levels. Reaction of peroxynitrite with manganese superoxide dismutase (MnSOD) causes nitration of the active-site residue Tyr34 and nearly complete inhibition of catalysis. We report the crystal structures at 2.4 Å resolution of human MnSOD nitrated by peroxynitrite and the unmodified MnSOD. A comparison of these structures showed no significant conformational changes of active-site residues or solvent displacement. The side chain of 3-nitrotyrosine 34 had a single conformation that extended toward the manganese with O1 of the nitro group within hydrogen-bonding distance (3.1 Å) of Nε2 of the second-shell ligand Gln143. Also, nitration of Tyr34 caused a weakening, as evidenced by the lengthening, of a hydrogen bond between its phenolic OH and Gln143, part of an extensive hydrogen-bond network in the active site. Inhibition of catalysis can be attributed to a steric effect of 3-nitrotyrosine 34 that impedes substrate access and binding, and alteration of the hydrogen-bond network that supports proton transfer in catalysis. It is also possible that an electrostatic effect of the nitro group has altered the finely tuned redox potential necessary for efficient catalysis, although the redox potential of nitrated MnSOD has not been measured.

Post-Translational Modification of Manganese Superoxide Dismutase in Acutely Rejecting Cardiac Transplants: Role of Inducible Nitric Oxide Synthase

Nitration of a critical tyrosine residue in the active site of manganese superoxide dismutase (MnSOD) can lead to enzyme inactivation. In this study, we examined the effect of inducible nitric oxide synthase (iNOS) on MnSOD expression, activity and nitration in acutely rejecting cardiac transplants. Lewis (isograft) or Wistar-Furth (allograft) donor hearts were transplanted into Lewis recipient rats. Some rats received L-N6-(1-iminoethyl) lysine (l-NIL), a specific iNOS inhibitor. Protein nitration was determined by immunohistochemical, Western blot and slot-blot analyses. MnSOD enzyme activity and gene expression were determined using Western, reverse transcriptase-polymerase chain reaction (RT-PCR) and immunoprecipitation techniques. MnSOD protein levels were decreased 50% by post-operative day 6 (POD 6), which was prevented by L-NIL. RT-PCR analysis indicated that this decrease could not be explained by any changes in MnSOD mRNA. MnSOD enzyme activity but not protein was decreased at POD 5 in untreated allografts. The loss of MnSOD activity at POD 5 was also prevented by L-NIL. Immunoreactive nitrotyrosine was apparent in untreated allografts at POD 6. Slot-blot analysis indicated that nitrotyrosine formation in allografts could be blocked by L-NIL. Nitration of MnSOD was evident upon immunoprecipitation of MnSOD followed by Western blotting for nitrotyrosine. These results suggest that the decreased MnSOD enzyme activity in acutely rejecting cardiac allografts can be attributed to a post-translational modification related to nitration arising via an iNOS-dependent pathway. This could be a potential major source of amplified oxidative stress in acute graft rejection.

Manganese superoxide dismutase (MnSOD) catalyzes NO-dependent tyrosine residue nitration

The peroxynitrite-induced nitration of manganese superoxide dismutase (MnSOD) tyrosine residue, which causes enzyme inactivation, is well established. This led to suggestions that MnSOD nitration and inactivation in vivo, detected in various diseases associated with oxidative stress and overproduction of nitric monoxide (NO), conditions which favor peroxynitrite formation, is also caused by peroxynitrite. However, our previous in vitro study demonstrated that exposure of MnSOD to NO led to NO conversion into nitrosonium (NO+) and nitroxyl (NO?) species, which caused enzyme modifications and inactivation. Here it is reported that MnSOD is tyrosine nitrated upon exposure to NO, as well as that MnSOD nitration contributes to inactivation of the enzyme. Collectively, these observations provide a compelling argument supporting the generation of nitrating species in MnSOD exposed to NO and shed a new light on MnSOD tyrosine nitration and inactivation in vivo. This may represent a novel mechanism by which MnSOD protects cell from deleterious effects associated with overproduction of NO. However, extensive MnSOD modification and inactivation associated with prolonged exposure to NO will amplify the toxic effects caused by increased cell superoxide and NO levels.

Superoxide-mediated nitration of spinal manganese superoxide dismutase: a novel pathway in N-methyl- d-aspartate-mediated hyperalgesia

N-methyl- d-aspartate (NMDA) receptors serve prominent roles in vast physio-pathological conditions including hyperalgesia (defined as augmented pain intensity in response to painful stimuli) associated with central sensitization. Using M40403 a synthetic low molecular weight superoxide dismutase mimetic that removes superoxide we show for the first time that this radical plays a key role in NMDA-mediated hyperalgesia. Intrathecal administration of NMDA in rats led to a time-dependent development of thermal hyperalgesia. Removal of superoxide with M40403 abolished NMDA-mediated hyperalgesia, while its inactive congener had no effect. Thus NMDA-mediated hyperalgesic response to heat is mediated through spinal release of superoxide. At time of near-to-maximal hyperalgesia, we observed that spinal endogenous manganese superoxide dismutase (MnSOD), the enzyme that normally keeps superoxide under well-controlled condition was nitrated, as shown by immunoprecipitation. Subsequently and as determined by biochemical analysis, nitration of MnSOD led to its deactivation as shown by the loss of the enzyme's ability to dismute and hence remove superoxide. M40403 by preventing MnSOD nitration restored its activity and inhibited the hyperalgesic response to intrathecal NMDA. Thus, superoxide-mediated nitration and deactivation of spinal MnSOD is a novel pathway of NMDA-mediated spinal hyperalgesia and hence central sensitization since it helps to maintain high levels of superoxide that in turn maintains nociceptive signaling. The broader implication of our findings is that superoxide may contribute to various forms of pain events that are driven by NMDA-receptor activation.

Quantitative assessment of tyrosine nitration of manganese superoxide dismutase in angiotensin II-infused rat kidney.

Hypertension caused by angiotensin II is characterized by an increase in tissue oxidant stress as evidenced by increased quantities of reactive oxygen and nitrogen species. Manganese superoxide dismutase (MnSOD) is a key mitochondrial antioxidant enzyme that is inactivated in conditions of oxidant stress by reacting with peroxynitrite to form 3-nitrotyrosine in its active site. The increase in 3-nitrotyrosine content in MnSOD in the kidney of angiotensin II-infused rats was assessed in this study by immunohistochemistry, Western blotting, immunoprecipitation, and HPLC with UV detection (HPLC-UV). MnSOD activity decreased approximately 50% in angiotensin II-infused rat kidneys (24 +/- 4.6 vs. 11 +/- 5.2 U/mg) without a change in protein expression. Immunohistochemical staining showed 3-nitrotyrosine predominantly in distal tubules and collecting duct cells in the angiotensin II-infused rat kidneys. By two-photon microscopy, 3-nitrotyrosine colocalized with MnSOD. Total 3-nitrotyrosine content in kidney homogenates was increased in angiotensin II-infused rat kidney [3.2 +/- 1.9 (sham treated) vs. 9.5 +/- 2.3 ng/mg protein by HPLC-UV detection]. With tracer amounts of tyrosine-nitrated recombinant MnSOD, the most sensitive technique to detect tyrosine nitration of MnSOD was immunoprecipitation from tissue with anti-MnSOD antibody, followed by detection of 3-nitrotyrosine by Western blotting or HPLC. By HPLC, 3-nitrotyrosine content of kidney MnSOD increased 13-fold after angiotensin II infusion, representing an increase from approximately one-twentieth to one-fifth of the total 3-nitrotyrosine content in sham-treated and angiotensin II-infused rat kidney, respectively. Angiotensin II-induced hypertension is accompanied by increased tyrosine nitration of MnSOD, which, because it inactivates the enzyme, may contribute to increased oxidant stress in the kidney.