Paradoxical augmentation of bradykinin-induced vasodilatation by xanthine/xanthine oxidase-derived free radicals in isolated guinea pig heart.
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Increased generation of reactive oxygen species contribute to endothelial dysfunction in atherosclerosis, hypertension and heart failure. Recently, it was suggested that bursts of superoxide anions may inactivate endothelial surface-bound enzymes such as angiotensin converting enzyme (ACE). Here, we tested effects of xanthine/xanthine oxidase-derived superoxide anions on vascular responses and ACE activity in the isolated guinea pig heart. We analysed effects of intracoronary infusion of low concentration of xanthine oxidase (10 mU/ml) in the presence of xanthine (0,5 mM) (X/XO) on bradykinin, other endothelium-dependent and independent vasodilators (acetylcholine, ADP, SNAP), as well as vasoconstrictor responses to angiotensin I and angiotensin II. Surprisingly, X/XO significantly augmented coronary response to bradykinin without an effect on responses to ADP, acetylcholine, SNAP, angiotensin I and angiotensin II. In contrast, inhibition of ACE by perindoprilate (100 nM) resulted in augmentation of bradykinin-induced vasodilatation as well as diminution of angiotensin I-evoked vasoconstriction without an influence on other responses. In summary, in the isolated guinea pig heart, X/XO-derived free radicals selectively augmented coronary vasodilator response to bradykinin, which cannot be explained by X/XO-induced derangement of ACE. The mechanism of this paradoxical phenomenon, which might represent a defensive response of the coronary circulation to oxidative stress requires further investigations. (+info)
Fructose-1,6-biphosphate and nucleoside pool modifications prevent neutrophil accumulation in the reperfused intestine.
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Fructose-1,6-biphosphate (F16BP) attenuates ischemia/reperfusion (I/R) injury by inhibiting microvascular leukocyte adhesion or reducing neutrophil-derived oxygen free-radical production, but the causes of this action, the mechanisms in vivo, and the possible implication of nucleoside pool modifications are still controversial issues. We explored whether F16BP's inhibition of free-radical production and neutrophil recruitment is a result of its effect on adenosine (Ado) accumulation during intestinal I/R injury. The effects of F16BP administration were tested on the nucleotide/nucleoside metabolism at the end of the ischemic period and on microvascular neutrophil recruitment and free-radical production after reperfusion in vivo, in the presence or absence of Ado deaminase (ADA). Infusion of F16BP markedly increased endogenous Ado, decreased xanthine accumulation during the ischemic period, and inhibited neutrophil recruitment and subsequent neutrophil free-radical generation during reperfusion. Administration of ADA reversed these processes. The results provide strong evidence that F16BP prevents neutrophil accumulation and neutrophil free-radical generation during intestinal I/R by a key mechanism that modifies the nucleoside pool, leading to an endogenous accumulation of Ado and to a reduction of xanthine during ischemia. (+info)
OBJECTIVE: Glucose-6-phosphate dehydrogenase (G6PD), the principal source of NADPH, serves as an antioxidant enzyme to modulate the redox milieu and nitric oxide synthase activity. Deficient G6PD activity is associated with increased endothelial cell oxidant stress and diminished bioavailable nitric oxide (NO.). Therefore, we examined whether overexpression of G6PD would decrease reactive oxygen species accumulation and increase bioavailable NO. in endothelial cells. METHODS AND RESULTS: Adenoviral-mediated gene transfer of G6PD increased G6PD expression, activity, and NADPH levels in bovine aortic endothelial cells (BAECs). BAECs overexpressing G6PD demonstrated a significant reduction in reactive oxygen species accumulation when exposed to hydrogen peroxide, xanthine-xanthine oxidase, or tumor necrosis factor-alpha compared with BAECs with basal levels of G6PD. BAECs overexpressing G6PD maintained intracellular glutathione stores when exposed to oxidants because of increased activity of glutathione reductase, an effect that was not observed in endothelial cells with normal G6PD activity. Overexpression of G6PD was also associated with enhanced nitric oxide synthase activity, resulting in elevated levels of cGMP, nitrate, and nitrite, and this response was increased after stimulation with bradykinin. CONCLUSIONS: Overexpression of G6PD in vascular endothelial cells decreases reactive oxygen species accumulation in response to exogenous and endogenous oxidant stress and improves levels of bioavailable NO. (+info)
Dextromethorphan protects dopaminergic neurons against inflammation-mediated degeneration through inhibition of microglial activation.
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Inflammation in the brain has increasingly been recognized to play an important role in the pathogenesis of several neurodegenerative disorders, including Parkinson's disease and Alzheimer's disease. Inflammation-mediated neurodegeneration involves activation of the brain's resident immune cells, the microglia, which produce proinflammatory and neurotoxic factors, including cytokines, reactive oxygen intermediates, nitric oxide, and eicosanoids that impact on neurons to induce neurodegeneration. Hence, identification of compounds that prevent microglial activation may be highly desirable in the search for therapeutic agents for inflammation-mediated neurodegenerative diseases. In this study, we report that dextromethorphan (DM), an ingredient widely used in antitussive remedies, reduced the inflammation-mediated degeneration of dopaminergic neurons through inhibition of microglial activation. Pretreatment (30 min) of rat mesencephalic neuron-glia cultures with DM (1-10 micro M) reduced, in a dose-dependent manner, the microglia-mediated degeneration of dopaminergic neurons induced by lipopolysaccharide (LPS, 10 ng/ml). Significant neuroprotection by DM was also evident when DM was applied to cultures up to 60 min after the addition of LPS. The neuroprotective effect of DM was attributed to inhibition of LPS-stimulated microglial activation because DM significantly inhibited the LPS-induced production of tumor necrosis factor-alpha, nitric oxide, and superoxide free radicals. This conclusion was further supported by the finding that DM failed to prevent 1-methyl-4-phenylpyridinium- or beta-amyloid peptide (1-42)-induced dopaminergic neurotoxicity in neuron-enriched cultures. In addition, because LPS did not produce any significant increase in the release of excitatory amino acids from neuron-glia cultures and N-methyl-D-aspartate antagonist dizocilpine maleate failed to afford significant neuroprotection, it is unlikely that the neuroprotective effect of DM is mediated through N-methyl-D-aspartate receptors. These results suggest that DM may be a promising therapeutic agent for the treatment of Parkinson's disease. (+info)
Dextran sulfate protects porcine but not bovine cultured endothelial cells from free radical injury.
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Previous studies demonstrated that the polyanion dextran sulfate (DS) protects rat coronary and porcine aortic endothelium (PAE) from oxygen-derived free radical (OFR) injury due to hydrogen peroxide (H2O2) or xanthine/xanthine oxidase (X/XO). To determine if DS has a similar protective effect in bovine aortic endothelium (BAE) and bovine brain microvascular endothelium (BBME), H2O2 or X/XO was added to confluent cultures. Cell injury was assessed 1 d later by measuring the percentage of viable cells (by trypan blue exclusion) and the release of lactate dehydrogenase (LDH) into the medium. After H2O2 doses of 6.0 mM for BAE and BBME and 0.8 mM for PAE, and after X doses of 10 microM and XO doses of 0.3 U/mL for all cell types, approximately 50% of cells were viable. Cultures were pretreated with DS (0.001 to 500 microg/mL) 24 to 26 h prior to H2O2 or X/XO exposure. Pretreatment at concentrations of 0.5, 5, and 50 microg/mL significantly increased the percentage of viable cells and reduced LDH release in cultures of PAE, but not BAE or BBME, treated with H2O2. Similarly, pretreatment with DS concentrations of 5 and 50 microg/mL significantly increased the percentage of viable cells and reduced LDH release in cultures of PAE, but not BAE or BBME, treated with X/XO. Thus, DS protected porcine but not bovine endothelium. Catalase (10 U/mL) increased the percentage of viable cells and reduced LDH release in H2O2-treated BAE and BBME, suggesting that DS likely acts by a different mechanism and does not neutralize H2O2. These results suggest that the protective effect of DS on OFR-injured endothelium is species-dependent. (+info)
Energy demands during a judo match and recovery.
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OBJECTIVE: To assess energy demand during a judo match and the kinetics of recovery by measuring the metabolites of the oxypurine cascade, lipolytic activity, and glycolytic pathway. METHODS: Venous blood samples were taken from 16 national judoists (mean (SEM) age 18.4 (1.6) years), before (T(1)) and three minutes (T(2)), one hour (T(3)), and 24 hours (T(4)) after a match. A seven day diet record was used to evaluate nutrient intake. RESULTS: Nutrient analysis indicated that these athletes followed a low carbohydrate diet. Plasma lactate concentration had increased to 12.3 (1.8) mmol/l at the end of the match. An increase in the levels of extracellular markers of muscle adenine nucleotide catabolism, urea, and creatinine was observed at T(2), while uric acid levels remained unchanged. High concentrations of urea persisted for 24 hours during the recovery period. Ammonia, hypoxanthine, xanthine, and creatinine returned to control levels within the 24 hour recovery period. Uric acid concentrations rose from T(3) and had not returned to baseline 24 hours after the match. The levels of triglycerides, glycerol, and free fatty acids had increased significantly (p<0.05) after the match (T(2)) but returned to baseline values within 24 hours. Concentrations of high density lipoprotein cholesterol and total cholesterol were significantly increased after the match. CONCLUSIONS: These results show that a judo match induces both protein and lipid metabolism. Carbohydrate availability, training adaptation, and metabolic stress may explain the requirement for these types of metabolism. (+info)
Oxidative damage to mouse lens in culture. Protective effect of pyruvate.
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Studies have been conducted to examine the feasibility of preventing oxyradical-dependent oxidative stress to mouse lens in culture, using pyruvate as an antioxidant. The extent of oxidative damage to the tissue was assessed by measurement of the status of Na(+)-K(+) ATPase dependent active transport of rubidium 86Rb(+). The tissue levels of adenosine triphosphate (ATP), glutathione (GSH), malonaldehyde (MDA) and catalase were also determined. While the measurement of 86Rb(+) uptake provides an assessment of the integrity of the primary active transport system, measurement of the other components reflects the status of intracellular oxidative stress. ATP measurement also reflected on the overall status of metabolic integrity. Incubation of the lens with xanthine (XA)/xanthine oxidase (XO) system had an adverse effect on all these parameters. Incorporation of pyruvate was strikingly protective. The protective effect of pyruvate is apparently due to its ability to scavenge ROS generated in the medium with the possibility of its action on tissue metabolism as well. The findings are hence considered useful for further studies on the prevention of oxidative stress to tissues by exogenous supplementation with pyruvate, specially the human lens where the biochemistry of its antioxidant mechanisms is similar to the mouse lens, contrary to the rat lens. (+info)
Adenosine-mediated early preconditioning in mouse: protective signaling and concentration dependent effects.
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OBJECTIVES: Signaling in adenosine-mediated preconditioning is controversial. We examined roles of mitochondrial (mito) K(ATP) channels, protein kinase C (PKC) and nitric oxide (NO). METHODS: Langendorff perfused C57/Bl6 mouse hearts were subjected to 20 min ischemia and 45 min reperfusion. Effects of adenosine-mediated preconditioning were assessed in the absence and presence of signaling inhibitors. RESULTS: Control hearts recovered 70+/-2 mmHg ventricular pressure, and released 18.1+/-2.0 IU/g lactate dehydrogenase (LDH). Preconditioning with 10 microM adenosine limited necrosis (10.6+/-1.4 IU/g) without modifying contractility (72+/-2 mmHg) whereas 50 microM adenosine reduced necrosis (10.3+/-1.6 IU/g) and contractile dysfunction (91+/-2 mmHg). All protective effects of 10 and 50 microM adenosine were abrogated by mito K(ATP) channel blockade with 100 microM 5-hydroxydecanoate (5-HD) during the 'trigger' phase, but unaltered by PKC or NO synthase inhibition with 3 microM chelerythrine or 100 microM N(G)-nitro-L-arginine methyl ester (L-NAME), respectively. Protection against necrosis was eliminated by 5-HD but unaltered by chelerythrine or L-NAME during the 'mediation' phase (ischemia-reperfusion). Reduced contractile dysfunction with 50 microM adenosine was partially sensitive to 5-HD and chelerythrine, and only eliminated by co-infusion of the inhibitors. CONCLUSIONS: Adenosine-mediated preconditioning is dose-dependent with high level stimulation reducing contractile dysfunction in addition to necrosis. Preconditioning is triggered by a mito K(ATP) channel dependent process independently of PKC and NO. Subsequent protection against necrosis is also mediated by a mito K(ATP) channel dependent process independent of PKC and NO. In contrast, functional protection may be mediated by parallel mito K(ATP) and PKC dependent paths. (+info)