The control of mitochondrial succinate-dependent H2O2 production.

In brain mitochondria succinate activates H(2)O(2) release, concentration dependently (starting at 15 µM), and in the presence of NAD dependent substrates (glutamate, pyruvate, ß-hydroxybutyrate). We report that TCA cycle metabolites (citrate, isocitrate, α-ketoglutarate, fumarate, malate) individually and quickly inhibit H(2)O(2) release. When they are present together at physiological concentration (0.2, 0.01, 0.15, 0.12, 0.2 mM respectively) they decrease H(2)O(2) production by over 60% at 0.1-0.2 mM succinate. The degree of inhibition depends on the concentration of each metabolite. Acetoacetate is a strong inhibitor of H(2)O(2) release, starting at 10 µM and acting quickly. It potentiates the inhibition induced by TCA cycle metabolites. The action of acetoacetate is partially removed by ß-hydroxybutyrate. Removal is minimal at 0.1 mM acetoacetate, and is higher at 0.5 mM acetoacetate. We conclude that several inhibitors of H(2)O(2) release act jointly and concentration dependently to rapidly set the required level of H(2)O(2) generation at each succinate concentration.

Different effects of SNP and GSNO on mitochondrial O2 .- /H 2O2 production.

Sodium Nitroprusside (SNP) and S-Nitrosoglutathione (GSNO) differently affect mitochondrial H(2)O(2) release at Complex-I. mM SNP increases while GSNO decreases the release induced by succinate alone or added on top of NAD-linked substrates. Stimulation likely depends on Nitric Oxide ((.)NO) (released by SNP but not by GSNO) inhibiting cytochrome oxidase and mitochondrial respiration. Preincubations with SNP or high GSNO (10 mM plus DTE to increases its (.)NO release) induces an inhibition of the succinate dependent H(2)O(2) production consistent with a (.)NO dependent covalent modification. However maximal inhibition of the succinate dependent H(2)O(2) release is obtained in the presence of low GSNO (20-100 µM), but not with SNP. This inhibition appears independent of (.)NO release since µM GSNO does not affect mitochondrial respiration, or the H(2)O(2) detection systems and its effect is very rapid. Inhibition may be partly due to an increased removal of O (2) (.-) since GSNO chemically competes with NBT and cytochrome C in O (2) (.-) detection.

[Restless legs syndrome in kidney patients]. / Anxietas Tibiarum: restless legs syndrome non sempre il movimento è salute nel paziente uremico.

Restless legs syndrome (RLS) is a sensorimotor disorder characterized by a strong urge to move the legs associated with paresthesias, motor restlessness, worsening of symptoms at night, and at least partial relief by activity. RLS has a negative impact on sleep, may cause depressive and anxious states, result in poor quality of life, and be a risk factor for cardiovascular disease. RLS is frequent in patients with end-stage renal disease; in this patient population it is consistently associated with severe comorbidities. It remains an underdiagnosed clinical condition. Appropriate diagnosis and management of RLS and sleep disorders is necessary to improve the quality of life and survival of kidney patients.

Succinate is the controller of O2-/H2O2 release at mitochondrial complex I : negative modulation by malate, positive by cyanide.

Mitochondrial production of H(2)O(2) is low with NAD substrates (glutamate/pyruvate, 3 and 2 mM) (G/P) and increases over ten times upon further addition of succinate, with the formation of a sigmoidal curve (semimaximal value at 290 microM, maximal H(2)O(2) production at 600 microM succinate). Malate counteracts rapidly the succinate induced increased H(2)O(2) release and moves the succinate dependent H(2)O(2) production curve to the right. Nitric oxide (NO) and carbon monoxide (CO) are cytochrome c oxidase inhibitors which increase mitochondrial ROS production. Cyanide (CN(-)) was used to mimic NO and CO. In the presence of G/P and succinate (300 microM), CN(-) progressively increased the H(2)O(2) release rate, starting at 1.5 microM. The succinate dependent H(2)O(2) production curve was moved to the left by 30 microM CN(-). The V(max) was little modified. We conclude that succinate is the controller of mitochondrial H(2)O(2) production, modulated by malate and CN(-). We propose that succinate promotes an interaction between Complex II and Complex I, which activates O(2)(-) production.

Cultured muscle cells display defects of mitochondrial myopathy ameliorated by anti-oxidants.

The mitochondrial DNA A3243G mutation causes neuromuscular disease. To investigate the muscle-specific pathophysiology of mitochondrial disease, rhabdomyosarcoma transmitochondrial hybrid cells (cybrids) were generated that retain the capacity to differentiate to myotubes. In some cases, striated muscle-like fibres were formed after innervation with rat embryonic spinal cord. Myotubes carrying A3243G mtDNA produced more reactive oxygen species than controls, and had altered glutathione homeostasis. Moreover, A3243G mutant myotubes showed evidence of abnormal mitochondrial distribution, which was associated with down-regulation of three genes involved in mitochondrial morphology, Mfn1, Mfn2 and DRP1. Electron microscopy revealed mitochondria with ultrastructural abnormalities and paracrystalline inclusions. All these features were ameliorated by anti-oxidant treatment, with the exception of the paracrystalline inclusions. These data suggest that rhabdomyosarcoma cybrids are a valid cellular model for studying muscle-specific features of mitochondrial disease and that excess reactive oxygen species production is a significant contributor to mitochondrial dysfunction, which is amenable to anti-oxidant therapy.

Succinate modulation of H2O2 release at NADH:ubiquinone oxidoreductase (Complex I) in brain mitochondria.

Complex I (NADH:ubiquinone oxidoreductase) is responsible for most of the mitochondrial H2O2 release, both during the oxidation of NAD-linked substrates and during succinate oxidation. The much faster succinate-dependent H2O2 production is ascribed to Complex I, being rotenone-sensitive. In the present paper, we report high-affinity succinate-supported H2O2 generation in the absence as well as in the presence of GM (glutamate/malate) (1 or 2 mM of each). In brain mitochondria, their only effect was to increase from 0.35 to 0.5 or to 0.65 mM the succinate concentration evoking the semi-maximal H2O2 release. GM are still oxidized in the presence of succinate, as indicated by the oxygen-consumption rates, which are intermediate between those of GM and of succinate alone when all substrates are present together. This effect is removed by rotenone, showing that it is not due to inhibition of succinate influx. Moreover, alpha-oxoglutarate production from GM, a measure of the activity of Complex I, is decreased, but not stopped, by succinate. It is concluded that succinate-induced H2O2 production occurs under conditions of regular downward electron flow in Complex I. Succinate concentration appears to modulate the rate of H2O2 release, probably by controlling the hydroquinone/quinone ratio.

Primary cutaneous plasmacytoma after rejection of a transplanted kidney: case report and review of the literature.

Immunosuppressed organ allograft recipients are at risk of developing lymphomas and lymphoproliferative disorders as a consequence of immunosuppressive therapy and long-term antigenic stimulation from both the graft and possible viral infections. No more than 4% of the malignant tumors detected in organ recipients are plasmacytomas. Primary cutaneous plasmacytoma is a rare type of cutaneous B-cell lymphoma arising primarily in the skin. It is derived from clonally expanded plasma cells with various degrees of maturation and atypia. We report the occurrence of a solitary cutaneous plasmacytoma in a 56-year-old male patient undergoing hemodialysis after rejection of a grafted kidney. The diagnosis was made a few months after the kidney had been surgically removed. A thorough examination showed no evidence of systemic disease. Skin lesions were successfully treated with local radiotherapy. After 2 years of follow-up there were no local or systemic recurrences.

Hypoxia and succinate antagonize 2-deoxyglucose effects on glioblastoma.

Glioblastoma multiforme (GBM) are highly proliferative brain tumors characterized by a hypoxic microenvironment which controls GBM stem cell maintenance. Tumor hypoxia promotes also elevated glycolytic rate; thus, limiting glucose metabolism is a potential approach to inhibit tumor growth. Here we investigate the effects mediated by 2-deoxyglucose (2-DG), a glucose analogue, on primary GBM-derived cells maintained under hypoxia. Our results indicate that hypoxia protects GBM cells from the apoptotic effect elicited by 2-DG, which raises succinate dehydrogenase activity thus promoting succinate level decrease. As a consequence hypoxia inducible factor-1α (HIF-1α) degradation occurs and this induces GBM cells to acquire a neuronal committed phenotype. By adding succinate these effects are reverted, as succinate stabilizes HIF-1α and increases GBM stem cell fraction particularly under hypoxia, thus preserving the tumor stem cell niche. 2-DG inhibits anaerobic glycolysis altering GBM cell phenotype by forcing tumor cells into mitochondrial metabolism and by inducing differentiation.

Pericentriolar material analyses in normal esophageal mucosa, Barrett's metaplasia and adenocarcinoma.

Barrett's esophagus metaplasia is a pre-cancerous condition caused by chronic esophagitis. Chromosomal instability (CIN) is common in Barrett's cells: therefore, we investigated the possible presence of centrosomal aberrations (a main cause of CIN) by centrosomal protein immunostaining in paraffined esophageal samples of patients who developed a Barrett's adenocarcinoma. In most (55%) patients, alterations of the pericentriolar material (PCM) signals were evident and consistently marked the transition between normal epithelium to metaplasia. The alterations could even be found in adjacent native squamous epithelium, Barrett's mucosa and submucosal gland cells, as well as in the basal/epibasal layers of the mucosa and submucosal gland duct, which are the regions hosting esophageal stem and progenitor cells. These findings strongly support the hypothesis that the three esophageal histotypes (one being pathological) can have a common progenitor. Surprisingly, PCM defective signal eventually decreased with neoplastic progression, possibly to enhance the genome stability of advanced cancer cells. Importantly, PCM altered signals in Barrett's mucosa and their apparent evolution in successive histopathological steps were correlated to adenocarcinoma aggressiveness, suggesting PCM as a possible prognostic marker for tumor relapse. Extending our observations in a prospective study might help in the development of new prevention protocols for adenocarcinoma patients.

Enhanced detection of H2O2 in cells expressing horseradish peroxidase.

A new procedure for fluorescent detection of intracellular H2O2 in cells transiently expressing the catalyst Horseradish Peroxidase (HRP) is setup and validated. More specific reaction with HRP largely amplifies oxidation of the redox probes used (2',7'-dichlorodihydrofluorescein and dihydrorhodamine). Expression of HRP does not affect cell viability. The procedure reveals MAO activity, a primary intracellular H2O2 source, in monolayers of intact transfected cells. The probes oxidation rate responds specifically to the MAO activation/inhibition. Their oxidation by MAO-derived H2O2 is sensitive to intracellular H2O2 competitors: it decreases when H2O2 is removed by pyruvate and it increases when the GSH-dependent removal systems are impaired. Specific response was also measured after addition of extracellular H2O2. Oxidation of the fluorescent probes following reaction of H2O2 with endogenous HRP overcomes most criticisms in their use for intracellular H2O2 detection. The method can be applied for direct determination in plate reader and is proposed to detect H2O2 generation in physio-pathological cell models.

Comparison of temsirolimus pharmacokinetics in patients with renal cell carcinoma not receiving dialysis and those receiving hemodialysis: a case series.

BACKGROUND: Intravenous temsirolimus, an inhibitor of the mammalian target of rapamycin (mTOR), is approved for the treatment of advanced renal cell carcinoma (RCC). Sirolimus, the principal metabolite of temsirolimus in humans, also exhibits mTOR inhibitory activity. OBJECTIVE: The purpose of this study was to compare the pharmacokinetics of temsirolimus and its metabolite, sirolimus, among patients with RCC not receiving dialysis and those receiving hemodialysis. METHODS: This was a single-center, unblinded, single-dose study. Patients with histologically confirmed metastatic RCC were eligible. A single 25-mg dose of temsirolimus was administered as a 30-minute intravenous infusion during the first round of chemotherapy. Blood samples were drawn at 0 (predose), 0.5 (end of infusion), 1.5, 2.5, 5.5, 24, 72, and 144 hours after infusion. In patients receiving hemodialysis, an additional blood sample was drawn 1 hour after each treatment to compare pre- and postconcentration. Temsirolimus concentrations were assayed in blood using HPLC coupled to mass spectrometry. Pharmacokinetic parameters (C(max), T(max), t((1/2)), AUC(0-infinity), total body clearance, volume of distribution at steady state, AUC ratio [the ratio of sirolimus to temsirolimus AUCs], and AUC sum [the algebraic sum of temsirolimus and sirolimus AUCs]) were calculated and analyzed statistically. RESULTS: In total, 13 consecutive patients (11 men and 2 women; 11 not receiving dialysis and 2 receiving hemodialysis) were included. No patient refused to participate in the study. Of those not receiving dialysis, the median age was 54 years (range, 36-77 years), and of those receiving hemodialysis, the median age was 60.5 years (60-61 years). There were no significant between-group differences in the pharmacokinetic parameters of temsirolimus and sirolimus. Moreover, in patients receiving hemodialysis, blood drug concentrations assessed immediately before hemodialysis were similar to those assayed 1 hour after the treatment. CONCLUSION: This study found that after single-dose administration of 25 mg of temsirolimus as a 30-minute intravenous infusion, neither temsirolimus nor sirolimus concentrations were significantly affected in these patients with RCC receiving hemodi-alysis compared with those not receiving dialysis.

Long chain fatty acyl-CoA modulation of H(2)O (2) release at mitochondrial complex I.

Complex I is responsible for most of the mitochondrial H(2)O(2) release, low during the oxidation of the NAD linked substrates and high during succinate oxidation, via reverse electron flow. This H(2)O(2) production appear physiological since it occurs at submillimolar concentrations of succinate also in the presence of NAD substrates in heart (present work) and rat brain mitochondria (Zoccarato et al., Biochem J, 406:125-129, 2007). Long chain fatty acyl-CoAs, but not fatty acids, act as strong inhibitors of succinate dependent H(2)O(2) release. The inhibitory effect of acyl-CoAs is independent of their oxidation, being relieved by carnitine and unaffected or potentiated by malonyl-CoA. The inhibition appears to depend on the unbound form since the acyl-CoA effect decreases at BSA concentrations higher than 2 mg/ml; it is not dependent on DeltapH or Deltap and could depend on the inhibition of reverse electron transfer at complex I, since palmitoyl-CoA inhibits the succinate dependent NAD(P) or acetoacetate reduction.

Respiration-dependent removal of exogenous H2O2 in brain mitochondria: inhibition by Ca2+.

In brain mitochondria, state 4 respiration supported by the NAD-linked substrates glutamate/malate in the presence of EGTA promotes a high rate of exogenous H2O2 removal. Omitting EGTA decreases the H2O2 removal rate by almost 80%. The decrease depends on the influx of contaminating Ca2+, being prevented by the Ca2+ uniporter inhibitor ruthenium red. Arsenite is also an inhibitor (maximal effect approximately 40%, IC50, 12 microm). The H2O2 removal rate (EGTA present) is decreased by 20% during state 3 respiration and by 60-70% in fully uncoupled conditions. H2O2 removal in mitochondria is largely dependent on glutathione peroxidase and glutathione reductase. Both enzyme activities, as studied in disrupted mitochondria, are inhibited by Ca2+. Glutathione reductase is decreased by 70% with an IC50 of about 0.9 microm, and glutathione peroxidase is decreased by 38% with a similar IC50. The highest Ca2+ effect with glutathione reductase is observed in the presence of low concentrations of H2O2. With succinate as substrate, the removal is 50% less than with glutamate/malate. This appears to depend on succinate-supported production of H2O2 by reverse electron flow at NADH dehydrogenase competing with exogenous H2O2 for removal. Succinate-dependent H2O2 is inhibited by rotenone, decreased DeltaPsi, as described previously, and by ruthenium red and glutamate/malate. These agents also increase the measured rate of exogenous H2O2 removal with succinate. Succinate-dependent H2O2 generation is also inhibited by contaminating Ca2+. Therefore, Ca2+ acts as an inhibitor of both H2O2 removal and the succinate-supported H2O2 production. It is concluded that mitochondria function as intracellular Ca2+-modulated peroxide sinks.