Palbociclib with adjuvant endocrine therapy in early breast cancer (PALLAS): interim analysis of a multicentre, open-label, randomised, phase 3 study.

BACKGROUND: Palbociclib added to endocrine therapy improves progression-free survival in hormone-receptor-positive, HER2-negative, metastatic breast cancer. The PALLAS trial aimed to investigate whether the addition of 2 years of palbociclib to adjuvant endocrine therapy improves invasive disease-free survival over endocrine therapy alone in patients with hormone-receptor-positive, HER2-negative, early-stage breast cancer. METHODS: PALLAS is an ongoing multicentre, open-label, randomised, phase 3 study that enrolled patients at 406 cancer centres in 21 countries worldwide with stage II-III histologically confirmed hormone-receptor-positive, HER2-negative breast cancer, within 12 months of initial diagnosis. Eligible patients were aged 18 years or older with an Eastern Cooperative Oncology Group performance score of 0 or 1. Patients were randomly assigned (1:1) in permuted blocks of random size (4 or 6), stratified by anatomic stage, previous chemotherapy, age, and geographical region, by use of central telephone-based and web-based interactive response technology, to receive either 2 years of palbociclib (125 mg orally once daily on days 1-21 of a 28-day cycle) with ongoing standard provider or patient-choice adjuvant endocrine therapy (tamoxifen or aromatase inhibitor, with or without concurrent luteinising hormone-releasing hormone agonist), or endocrine therapy alone, without masking. The primary endpoint of the study was invasive disease-free survival in the intention-to-treat population. Safety was assessed in all randomly assigned patients who started palbociclib or endocrine therapy. This report presents results from the second pre-planned interim analysis triggered on Jan 9, 2020, when 67% of the total number of expected invasive disease-free survival events had been observed. The trial is registered with ClinicalTrials.gov (NCT02513394) and EudraCT (2014-005181-30). FINDINGS: Between Sept 1, 2015, and Nov 30, 2018, 5760 patients were randomly assigned to receive palbociclib plus endocrine therapy (n=2883) or endocrine therapy alone (n=2877). At the time of the planned second interim analysis, at a median follow-up of 23·7 months (IQR 16·9-29·2), 170 of 2883 patients assigned to palbociclib plus endocrine therapy and 181 of 2877 assigned to endocrine therapy alone had invasive disease-free survival events. 3-year invasive disease-free survival was 88·2% (95% CI 85·2-90·6) for palbociclib plus endocrine therapy and 88·5% (85·8-90·7) for endocrine therapy alone (hazard ratio 0·93 [95% CI 0·76-1·15]; log-rank p=0·51). As the test statistic comparing invasive disease-free survival between groups crossed the prespecified futility boundary, the independent data monitoring committee recommended discontinuation of palbociclib in patients still receiving palbociclib and endocrine therapy. The most common grade 3-4 adverse events were neutropenia (1742 [61·3%] of 2840 patients on palbociclib and endocrine therapy vs 11 [0·3%] of 2903 on endocrine therapy alone), leucopenia (857 [30·2%] vs three [0·1%]), and fatigue (60 [2·1%] vs ten [0·3%]). Serious adverse events occurred in 351 (12·4%) of 2840 patients on palbociclib plus endocrine therapy versus 220 (7·6%) of 2903 patients on endocrine therapy alone. There were no treatment-related deaths. INTERPRETATION: At the planned second interim analysis, addition of 2 years of adjuvant palbociclib to adjuvant endocrine therapy did not improve invasive disease-free survival compared with adjuvant endocrine therapy alone. On the basis of these findings, this regimen cannot be recommended in the adjuvant setting. Long-term follow-up of the PALLAS population and correlative studies are ongoing. FUNDING: Pfizer.

SIADH-related hyponatremia in hospital day care units: clinical experience and management with tolvaptan.

Hyponatremia (Na ˂ 135 mmol/l) is the most frequent electrolyte disorder in clinical practice, and the syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the commonest cause of hyponatremia in cancer patients. Correcting hyponatremia in these patients can reduce morbidity and mortality, increase the response to anti-cancer agents, and help reduce hospital length of stay and costs. Tolvaptan is an oral medication used to treat SIADH-related hyponatremia patients that needs to be initiated at hospital so patients can have their serum sodium monitored. If tolvaptan could be initiated in hospital day care units (DCUs), performing the same tests, hospitalization could be avoided, quality of life improved, and costs reduced. This is the first publication where a panel of oncologists are sharing their experience and making some recommendations with the use of tolvaptan to treat SIADH-related hyponatremia in DCU after collecting and examining 35 clinical cases with these type of patients. The conclusion from this retrospective observational analysis is that the use of tolvaptan in DCU is safe and effective in the therapeutic management of SIADH-related hyponatremia.

Thymbra capitata essential oil prevents cell death induced by 4-hydroxy-2-nonenal in neonatal rat cardiac myocytes.

An interdisciplinary experimental investigation on the antioxidant activity of Thymbra capitata essential oil was made. This plant is a Mediterranean culinary herb, whose essential oil antioxidant power has recently been demonstrated in vitro as one of the highest in nature. We tested if this in vitro antioxidant capacity was reproducible on biological systems using as model system primary cultures of neonatal rat cardiomyocytes treated with the lipid peroxidation product 4-hydroxy-2-nonenal. The composition and the in vitro antioxidant activity of the T. capitata essential oil were also assessed. Cell viability, mitochondrial membrane potential, and reactive oxygen species level were measured in cells treated with pathophysiologic doses of 4-hydroxy-2-nonenal (< 10 µM) or vehicle after being pre-incubated with small concentrations of the T. capitata essential oil, and the ability of small doses (< 40 ppm) to prevent the death of neonatal rat cardiomyocytes proved very remarkable. Long-term pre-incubation (12 h) with 20 ppm prevented 4-hydroxy-2-nonenal-induced cell death and avoided mitochondrial membrane potential loss and reactive oxygen species generation caused by 4-hydroxy-2-nonenal. A deleterious effect was shown at doses higher than 40 ppm. The results of this study pave the way to further analysis in animal models to achieve a deeper understanding of the in vivo antioxidant power of T. capitata essential oil.

Clinical and molecular description of two cases of neonatal diabetes secondary to mutations in PDX1.

Summary: Pancreatic dysgenesis (PD) is a rare congenital disease, with less than 100 cases reported in the literature. In most cases, patients are asymptomatic and the diagnosis is made incidentally. In this report, we present the case of two brothers with a history of intrauterine growth retardation, low birth weight, hyperglycemia, and poor weight gain. The diagnosis of PD and neonatal diabetes mellitus was made by an interdisciplinary team composed of an endocrinologist, a gastroenterologist, and a geneticist. Once the diagnosis was made, treatment with an insulin pump, pancreatic enzyme replacement therapy, and supplementation with fat-soluble vitamins was decided. The use of the insulin infusion pump facilitated the outpatient treatment of both patients. Learning points: Pancreatic dysgenesis is a relatively rare congenital anomaly; most of the time, patients are asymptomatic and are diagnosed incidentally. The diagnosis of pancreatic dysgenesis and neonatal diabetes mellitus should be made with an interdisciplinary team. Due to its flexibility, the use of an insulin infusion pump facilitated the management of these two patients.

2,3,7,8-Tetrachlorodibenzo-p-dioxin induces apoptosis by disruption of intracellular calcium homeostasis in human neuronal cell line SHSY5Y.

The persistent xenobiotic agent 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces neurotoxic effects that alters neurodevelopment and behavior both during development and adulthood. There are many ongoing efforts to determine the molecular mechanisms of TCDD-mediated neurotoxicity, the signaling pathways involved and its molecular targets in neurons. In this work, we have used SHSY5Y human neuroblastoma cells to characterize the TCDD-induced toxicity. TCDD produces a loss of viability linked to an increased caspase-3 activity, PARP-1 fragmentation, DNA laddering, nuclear fragmentation and hypodiploid (apoptotic) DNA content, in a similar way than staurosporine, a prototypical molecule of apoptosis induction. In addition, TCDD produces a decrease of mitochondrial membrane potential and an increase of intracellular calcium concentration (P < 0.05). Finally, based on the high lipophilic properties of the dioxin, we test the TCDD effect on the membrane integrity using sarcoplasmic reticulum vesicles as a model. TCDD produces calcium efflux through the membrane and an anisotropy decrease (P < 0.05) that reflects an increase in membrane fluidity. Altogether these results support the hypothesis that TCDD toxicity in SHSY5Y neuroblastoma cells provokes the disruption of calcium homeostasis, probably affecting membrane structural integrity, leading to an apoptotic process.

Adherence to the Sociedad Española de Oncología Médica (SEOM) Algorithm for the Treatment of Hyponatremia in Oncology Patients in Spain: The ALGA Study.

INTRODUCTION: The ALGA study explored adherence of Spanish treatment centers to the Sociedad Española de Oncología Médica (SEOM) treatment algorithm for oncology patients with hyponatremia that requires treatment as the main cause of hospitalization, and evaluated the impact of adherence to this algorithm on patient outcomes. METHODS: This retrospective study recruited patients aged at least 18 years with cancer, treated for at least one episode of hyponatremia secondary to the syndrome of inappropriate antidiuretic hormone secretion (SIADH). The primary outcome was the proportion of patients whose treatment adhered to the SEOM algorithm, evaluated using a pre-defined decision tree. Secondary outcomes included length of hospitalization, and time to serum sodium level improvement. Perceived center adherence to the SEOM algorithm was also assessed. RESULTS: Seventy patients from four treatment centers were included. Twenty (28.6%; 95% confidence interval [CI] 18.0, 39.2) patients on hyponatremia treatment adhered to the SEOM algorithm, with a perceived adherence of 51.0-75.0%. Algorithm adherence in candidates for chemotherapy was 36.4% (n = 8) versus 25.0% (n = 12) for non-candidates for chemotherapy. Median time to serum sodium level improvement in patients managed adherently was 80.5 h (95% CI 38.3, 331.4) versus 134.6 h (33.2, 444.9) in patients managed non-adherently. Median time to hospital discharge was 16.5 days (95% CI 8.0, 27.0) in patients managed adherently versus 9.5 days (7.0, 22.0) in patients managed non-adherently. CONCLUSION: In Spanish centers, the SEOM algorithm was adhered to in less than one-third of patients, in contrast to higher levels of perceived adherence. This requires further investigation; however, algorithm use could require further clarification, especially in non-candidates for chemotherapy.

Low levels of sodium in the blood occur in almost half of patients with cancer who are hospitalized. In some patients, this may be fatal. A care pathway was developed by the Sociedad Española de Oncología Médica in 2014 to support doctors in providing the best care for these patients. Clinical records for 70 patients with cancer at four Spanish hospitals were reviewed to determine whether treatment was given according to the care pathway. Less than one-third of patients were found to have been treated according to the pathway. Patients receiving chemotherapy were more likely to have been treated according to the pathway; however, doctors believed that more patients were treated in line with the pathway. In general, health outcomes were similar for those patients treated according to and not treated according to the pathway. The difference between doctors' belief that the pathway was followed when it might not have been needs to be examined further, say the authors. They suggest several reasons for the difference. The doctor providing feedback on whether the patient was treated according to the pathway may not have been the only doctor involved in a patient's care and may not have been aware of all the treatment choices made. Lack of clarity within the pathway may have led doctors to believe that it was being followed more often than it was. Importantly, a doctor's judgment may need to override pre-defined pathways in some situations to achieve the best outcome for the patient.

Sarcoplasmic reticulum calcium ATPase is inhibited by organic vanadium coordination compounds: pyridine-2,6-dicarboxylatodioxovanadium(V), BMOV, and an amavadine analogue.

The general affinity of the sarcoplasmic reticulum (SR) Ca (2+)-ATPase was examined for three different classes of vanadium coordination complexes including a vanadium(V) compound, pyridine-2,6-dicarboxylatodioxovanadium(V) (PDC-V(V)), and two vanadium(IV) compounds, bis(maltolato)oxovanadium(IV) (BMOV), and an analogue of amavadine, bis( N-hydroxylamidoiminodiacetato)vanadium(IV) (HAIDA-V(IV)). The ability of vanadate to act either as a phosphate analogue or as a transition-state analogue with enzymes' catalysis phosphoryl group transfer suggests that vanadium coordination compounds may reveal mechanistic preferences in these classes of enzymes. Two of these compounds investigated, PDC-V(V) and BMOV, were hydrolytically and oxidatively reactive at neutral pH, and one, HAIDA-V(IV), does not hydrolyze, oxidize, or otherwise decompose to a measurable extent during the enzyme assay. The SR Ca (2+)-ATPase was inhibited by all three of these complexes. The relative order of inhibition was PDC-V(V) > BMOV > vanadate > HAIDA-V(IV), and the IC 50 values were 25, 40, 80, and 325 microM, respectively. Because the observed inhibition is more potent for PDC-V(V) and BMOV than that of oxovanadates, the inhibition cannot be explained by oxovanadate formation during enzyme assays. Furthermore, the hydrolytically and redox stable amavadine analogue HAIDA-V(IV) inhibited the Ca (2+)-ATPase less than oxovanadates. To gauge the importance of the lipid environment, studies of oxidized BMOV in microemulsions were performed and showed that this system remained in the aqueous pool even though PDC-V(V) is able to penetrate lipid interfaces. These findings suggest that the hydrolytic properties of these complexes may be important in the inhibition of the calcium pump. Our results show that two simple coordination complexes with known insulin enhancing effects can invoke a response in calcium homeostasis and the regulation of muscle contraction through the SR Ca (2+)-ATPase.

Store-operated calcium entry in differentiated C2C12 skeletal muscle cells.

In this paper, we show further evidences for the existence of store-operated calcium entry in differentiated skeletal muscle C2C12 myotubes after Ca2+ depletion in sarcoplasmic reticulum, using thapsigargin, a potent sarcoplasmic reticulum Ca2+-ATPase inhibitor, caffeine as ryanodine receptor activator, and ATP which activates purinergic receptors. The quenching of fura 2 fluorescence emission by Mn2+ also provided evidences for store-operated calcium entry because this quenching was accelerated when sarcoplasmic reticulum was depleted of Ca2+. Ca2+ entry was sensitive to Ni2+, La3+, Gd3+ and 2-aminoethyl diphenyl borate but resistant to nifedipine, thus excluding L-type Ca2+ channels in this type of calcium entry. Our data obtained using ATP for store depletion suggest that the level of Ca2+ in internal stores could play a role in the regulation of store-operated calcium channel activity in this cell type.

Synaptosomal plasma membrane Ca(2+) pump activity inhibition by repetitive micromolar ONOO(-) pulses.

A sustained increase of intracellular free [Ca(2+)] ([Ca(2+)](i)) has been shown to be an early event of neuronal cell death induced by peroxynitrite (ONOO(-)). In this paper, chronic exposure to ONOO(-) has been simulated by treatment of rat brain synaptosomes or plasma membrane vesicles with repetitive pulses of ONOO(-) during at most 50 min, which efficiently produced nitrotyrosine formation in several membrane proteins (including the Ca(2+)-ATPase). The plasma membrane Ca(2+)-ATPase activity at near-physiological conditions (pH 7, submicromolar Ca(2+), and millimolar Mg(2+)-ATP concentrations), which plays a major role in the control of synaptic [Ca(2+)](i), can be more than 75% inhibited by a sustained exposure to micromolar ONOO(-) (e.g., to 100 pulses of 10 microM ONOO(-)). This inhibition is irreversible and mostly due to a decreased V(max), and to the 2-fold increase of the K(0.5) for Ca(2+) stimulation and about 5-fold increase of the K(M) for Mg(2+)-ATP. [Ca(2+)](i) increases to >400 nM when synaptosomes are subjected to this treatment. Reduced glutathione can afford only partial protection against the inhibition produced by micromolar ONOO(-) pulses. Therefore, inhibition of the plasma membrane Ca(2+)-pump activity during chronic exposure to ONOO(-) may account by itself for a large and sustained increase of intracellular [Ca(2+)](i) in synaptic nerve terminals.

Apoptotic cell death in cultured cardiomyocytes following exposure to low concentrations of 4-hydroxy-2-nonenal.

Lipid peroxidation (LP), induced by oxidative stress, is associated with degenerative processes. 4-Hydroxy-2-nonenal (HNE), a highly reactive diffusible product of LP, is considered by-product and mediator of oxidative stress. Its level increases under pathological conditions such as cardiovascular diseases. In this study, we partially characterized the mechanisms of HNE-mediated cytotoxicity in cardiomyocytes. After establishing that pathophysiological doses of HNE trigger cell death dependent on the incubation time and dose of HNE (LD50 = 4.4 µM), we tackled the mechanisms that underlie the cell death induced by HNE. Our results indicate that HNE rapidly increases intracellular Ca(2+); it also increases the rate of reactive oxygen species generation and causes a loss of mitochondrial membrane potential (ΔΨm) as well as a decrease in the ATP and GSH levels. Such alterations result in the activation of caspase-3 and DNA breakdown, both characteristic features of apoptotic cell death, as well as disruption of the cytoskeleton. Moreover, the nucleophilic compounds N-acetyl-cysteine and ß-mercapto-propionyl-glycine, and the synthetic antioxidant Trolox exert a potent antioxidant action against HNE damage; this suggests its use as effective compounds in order to reduce the damage occurred as consequence of cardiovascular disorders in which oxidative stress and hence LP take place.

Inhibition by 4-hydroxynonenal (HNE) of Ca2+ transport by SERCA1a: low concentrations of HNE open protein-mediated leaks in the membrane.

Exposure of sarcoplasmic reticulum membranes to 4-hydroxy-2-nonenal (HNE) resulted in inhibition of the maximal ATPase activity and Ca(2+) transport ability of SERCA1a, the Ca(2+) pump in these membranes. The concomitant presence of ATP significantly protected SERCA1a ATPase activity from inhibition. ATP binding and phosphoenzyme formation from ATP were reduced after treatment with HNE, whereas Ca(2+) binding to the high-affinity sites was altered to a lower extent. HNE reacted with SH groups, some of which were identified by MALDI-TOF mass spectrometry, and competition studies with FITC indicated that HNE also reacted with Lys(515) within the nucleotide binding pocket of SERCA1a. A remarkable fact was that both the steady-state ability of SR vesicles to sequester Ca(2+) and the ATPase activity of SR membranes in the absence of added ionophore or detergent were sensitive to concentrations of HNE much smaller than those that affected the maximal ATPase activity of SERCA1a. This was due to an increase in the passive permeability of HNE-treated SR vesicles to Ca(2+), an increase in permeability that did not arise from alteration of the lipid component of these vesicles. Judging from immunodetection with an anti-HNE antibody, this HNE-dependent increase in permeability probably arose from modification of proteins of about 150-160kDa, present in very low abundance in longitudinal SR membranes (and in slightly larger abundance in SR terminal cisternae). HNE-induced promotion, via these proteins, of Ca(2+) leakage pathways might be involved in the general toxic effects of HNE.

Vanadate induces necrotic death in neonatal rat cardiomyocytes through mitochondrial membrane depolarization.

Besides the well-known inotropic effects of vanadium in cardiac muscle, previous studies have shown that vanadate can stimulate cell growth or induce cell death. In this work, we studied the toxicity to neonatal rat ventricular myocytes (cardiomyocytes) of two vanadate solutions containing different oligovanadates distribution, decavanadate (containing decameric vanadate, V 10) and metavanadate (containing monomeric vanadate and also di-, tetra-, and pentavanadate). Incubation for 24 h with decavanadate or metavanadate induced necrotic cell death of cardiomyocytes, without significant caspase-3 activation. Only 10 microM total vanadium of either decavanadate (1 microM V 10) or metavanadate (10 microM total vanadium) was needed to produce 50% loss of cell viability after 24 h (assessed with MTT and propidium iodide assays). Atomic absorption spectroscopy showed that vanadium accumulation in cardiomyocytes after 24 h was the same when incubation was done with decavanadate or metavanadate. A decrease of 75% of the rate of mitochondrial superoxide anion generation, monitored with dihydroethidium, and a sustained rise of cytosolic calcium (monitored with Fura-2-loaded cardiomyocytes) was observed after 24 h of incubation of cardiomyocytes with decavanadate or metavanadate concentrations close to those inducing 50% loss of cell viability produced. In addition, mitochondrial membrane depolarization within cardiomyocytes, monitored with tetramethylrhodamine ethyl esther or with 3,3',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolcarbocyanine iodide, were observed after only 6 h of incubation with decavanadate or metavanadate. The concentration needed for 50% mitochondrial depolarization was 6.5 +/- 1 microM total vanadium for both decavanadate (0.65 microM V 10) and metavanadate. In conclusion, mitochondrial membrane depolarization was an early event in decavanadate- and monovanadate-induced necrotic cell death of cardiomyocytes.

Alteration of cytosolic free calcium homeostasis by SIN-1: high sensitivity of L-type Ca2+ channels to extracellular oxidative/nitrosative stress in cerebellar granule cells.

Exposure of cerebellar granule neurones in 25 mm KCl HEPES-containing Locke's buffer (pH 7.4) to 50-100 microm SIN-1 during 2 h decreased the steady-state free cytosolic Ca2+ concentration ([Ca2+]i) from 168 +/- 33 nm to 60 +/- 10 nm, whereas exposure to > or = 0.3 mm SIN-1 produced biphasic kinetics: (i) decrease of [Ca2+]i during the first 30 min, reaching a limiting value of 75 +/- 10 nm (due to inactivation of L-type Ca2+ channels) and (ii) a delayed increase of [Ca2+]i at longer exposures, which correlated with SIN-1-induced necrotic cell death. Both effects of SIN-1 on [Ca2+]i are blocked by superoxide dismutase plus catalase and by Mn(III)tetrakis(4-benzoic acid)porphyrin chloride. Supplementation of Locke's buffer with catalase before addition of 0.5-1 mm SIN-1 had no effect on the decrease of [Ca2+]i but further delayed and attenuated the increase of [Ca2+]i observed after 60-120 min exposure to SIN-1 and also protected against SIN-1-induced necrotic cell death. alpha-Tocopherol, the potent NMDA receptor antagonist (+)-MK-801 and the N- and P-type Ca2+ channels blocker omega-conotoxin MVIIC had no effect on the alterations of [Ca2+]i upon exposure to SIN-1. However, inhibition of the plasma membrane Ca2+ ATPase can account for the increase of [Ca2+]i observed after 60-120 min exposure to 0.5-1 mm SIN-1. It is concluded that L-type Ca2+ channels are a primary target of SIN-1-induced extracellular nitrosative/oxidative stress, being inactivated by chronic exposure to fluxes of peroxynitrite of 0.5-1 microm/min, while higher concentrations of peroxynitrite and hydrogen peroxide are required for the inhibition of the plasma membrane Ca2+ ATPase and induction of necrotic cell death, respectively.

Fluorescence measurements of steady state peroxynitrite production upon SIN-1 decomposition: NADH versus dihydrodichlorofluorescein and dihydrorhodamine 123.

The production of peroxynitrite during 3-morpholinosydnonimine (SIN-1) decomposition can be continuously monitored, with a sensitivity < or = 0.1 microM, from the kinetics of NADH fluorescence quenching in phosphate buffers, as well as in buffers commonly used with cell cultures, like Locke's buffer or Dulbecco's modified Eagle's medium (DMEM-F12). The half-time for peroxynitrite production during SIN-1 decomposition ranged from 14-18 min in DMEM-F12 (plus and minus phenol red) to 21.5 min in Locke's buffer and 26 min in DMEM-F12 supplemented with apotransferrin (0.1 mg/mL). The concentration of peroxynitrite reached a peak that was linearly dependent upon SIN-1 concentration, and that for 100 microM SIN-1 amounted to 1.4 +/- 0.2 microM in Locke's buffer, 3.2-3.6 microM in DMEM-F12 (plus and minus phenol red) and 1.8 microM in DMEM-F12 supplemented with apotransferrin. Thus, the maximum concentration of peroxynitrite ranged from 1.2 to 3.6% of added SIN-1. NADH was found to be less sensitive than dihydrorhodamine 123 and 2',7'-dichlorodihydrofluorescein diacetate to oxidation by H2O2, which is produced during SIN-1 decomposition in common buffers. It is shown that peroxynitrite concentration can be controlled (+/-5%) during predetermined times by using sequential SIN-1 pulses, to simulate chronic exposure of cells or subcellular components to peroxynitrite.

The NADH oxidase activity of the plasma membrane of synaptosomes is a major source of superoxide anion and is inhibited by peroxynitrite.

Plasma membrane vesicles from adult rat brain synaptosomes (PMV) have an ascorbate-dependent NADH oxidase activity of 35-40 nmol/min/(mg protein) at saturation by NADH. NADPH is a much less efficient substrate of this oxidase activity, with a Vmax 10-fold lower than that measured for NADH. Ascorbate-dependent NADH oxidase activity accounts for more than 90% of the total NADH oxidase activity of PMV and, in the absence of NADH and in the presence of 1 mm ascorbate, PMV produce ascorbate free radical (AFR) at a rate of 4.0 +/- 0.5 nmol AFR/min/(mg protein). NADH-dependent *O2- production by PMV occurs with a rate of 35 +/- 3 nmol/min/(mg protein), and is a coreaction product of the NADH oxidase activity, because: (i) it is inhibited by more than 90% by addition of ascorbate oxidase, (ii) it is inhibited by 1 micro g/mL wheat germ agglutinin (a potent inhibitor of the plasma membrane AFR reductase activity), and (iii) the KM(NADH) of the plasma membrane NADH oxidase activity and of NADH-dependent *O2- production are identical. Treatment of PMV with repetitive micromolar ONOO- pulses produced almost complete inhibition of the ascorbate-dependent NADH oxidase and *O2- production, and at 50% inhibition addition of coenzyme Q10 almost completely reverts this inhibition. Cytochrome c stimulated 2.5-fold the plasma membrane NADH oxidase, and pretreatment of PMV with repetitive 10 microm ONOO- pulses lowers the K0.5 for cytochrome c stimulation from 6 +/- 1 (control) to 1.5 +/- 0.5 microm. Thus, the ascorbate-dependent plasma membrane NADH oxidase activity can act as a source of neuronal.O2-, which is up-regulated by cytosolic cytochrome c and down-regulated under chronic oxidative stress conditions producing ONOO-.

Modulation of sarcoplasmic reticulum Ca(2+)-ATPase by chronic and acute exposure to peroxynitrite.

The Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum (SERCA), an integral membrane protein, becomes irreversibly inactivated in vitro by the addition of a single bolus of peroxynitrite with a K(0.5) of 200-300 microm, and this results in a large decrease of the ATP-dependent Ca2+ gradient across the sarcoplasmic reticulum (SR) membranes. The inactivation of SERCA is raised by treatment of SR vesicles with repetitive micromolar pulses of peroxynitrite. The inhibition of the SERCA is due to the oxidation of thiol groups and tyrosine nitration. Scavengers that react directly with peroxynitrite, such as cysteine, reduced glutathione, NADH, methionine, ascorbate or Trolox, a water-soluble analog of alpha-tocopherol, afforded significant protection. However, dimethyl sulfoxide and mannitol, two hydroxyl radical scavengers, and alpha-tocopherol did not protect SERCA from inactivation. Our results showed that the target of peroxynitrite is the cytosolic globular domain of the SERCA and that major skeletal muscle intracellular reductants (ascorbate, NADH and reduced glutathione) protected against inhibition of this ATPase by peroxynitrite.