The role of allopurinol and deferoxamine in preventing pressure ulcers in pigs

Ischemia and reperfusion may be important in the pathogenesis of pressure ulcers. On the basis of this hypothesis, the effects of intermittent pressure and the anti-free radical agents allopurinol and deferoxamine were studied in a pig model in which a pressure of 150 mmHg was applied intermittently to the scapulae. Cutaneous blood flow, transcutaneous oxygen tension, skin and muscle damage, and muscle levels of adenosine triphosphate were quantified. A control group of pigs (n = 6) was untreated, the allopurinol group (n = 6) received oral allopurinol beginning 2 days before the experiment, and the deferoxamine group (n = 6) received an intramuscular injection of deferoxamine 2 hours before the experiment. Pressure (150 mmHg) was applied to the scapulae for 210 minutes, and it was relieved for 30 minutes. This 4-hour cycle was repeated continuously for 48 hours, and it resulted in pressure injuries in all animals. Allopurinol and deferoxamine improved cutaneous blood flow and tissue oxygenation, but only deferoxamine could significantly reduce cutaneous and skeletal muscle necrosis (p < 0.001). This study suggests a future role for anti-free radical agents in the reduction of pressure-induced injury.     

Oxygen radical-mediated lipid peroxidation and inhibition of Ca2+-ATPase activity of cardiac sarcoplasmic reticulum

Oxygen radicals have been implicated as important mediators of myocardial ischemic and reperfusion injury. A major product of oxygen radical formation is the highly reactive hydroxyl radical via a biological Fenton reaction. The sarcoplasmic reticulum is one of the major target organelles injured by this process. Using a oxygen radical generating system consisting of dihydroxyfumarate and Fe3+-ADP, we studied lipid peroxidation and Ca2+-ATPase of cardiac sarcoplasmic reticulum. Incubation of sarcoplasmic reticulum with dihydroxyfumarate plus Fe3+-ADP significantly inhibited enzyme activity. Addition of superoxide dismutase, superoxide dismutase plus catalase (15 micrograms/ml) or iron chelator, deferoxamine (1.25-1000 microM) protected Ca2+-ATPase activity. Time course studies showed that this system inhibited enzyme activity in 7.5 to 10 min. Similar exposure of sarcoplasmic reticulum to dihydroxyfumarate plus Fe3+-ADP stimulated malondialdehyde formation. This effect was inhibited by superoxide dismutase, catalase, singlet oxygen, and hydroxyl radical scavengers. EPR spin-trapping with 5,5-dimethyl-1-pyrroline-N-oxide verified production of the hydroxyl radical. The combination of dihydroxyfumarate and Fe3+-ADP resulted in a spectrum of hydroxyl radical spin trap adduct, which was abolished by ethanol, catalase, mannitol, and superoxide dismutase. The results demonstrate the role of oxygen radicals in causing inactivation of Ca2+-ATPase and inhibition of lipid peroxidation of the sarcoplasmic reticulum which could possibly be one of the important mechanisms of oxygen radical-mediated myocardial injury.     

Disassociation of muscle insulin signaling and insulin-stimulated glucose uptake during endotoxemia

Lipopolysaccharide (LPS) elicits a strong immune response, which leads to the release of inflammatory cytokines. Increased cytokine production has been shown to impair insulin-mediated glucose disposal. LPS can alter other factors, such as muscle blood flow and insulin signaling in the myocyte, that can influence glucose disposal. We hypothesize that LPS induced impairments in cardiovascular function contribute to the associated impairments in insulin action in vivo. Male wild-type C57BL/6J mice had a catheter implanted in the jugular vein for infusions and the carotid artery for sampling 5 days prior to the hyperinsulinemic-euglycemic clamp. Mice were treated with vehicle, low- (1 ug/gBW) or high-dose (10 ug/gBW) LPS 4 hours prior to the clamp. Muscle glucose uptake (MGU) was assessed using [2-(14)C] deoxyglucose. While both low- and high-dose LPS inhibited insulin-stimulated MGU compared to vehicle-treated mice, the impairment was more significant with the high-dose treatment (～25% in soleus and ～70% in both gastrocnemius and vastus lateralis). Interestingly, insulin signaling through the PI3-kinase pathway in the muscle was not affected by this treatment suggesting that the decrease in MGU is not directly due to impairments in muscle insulin action. Echocardiography demonstrated that high-dose LPS treatment significantly decreased stroke volume (～30%), heart rate (～35%), and cardiac output (～50%). These observations were not seen with vehicle or low-dose LPS treatment. High-dose LPS treatment also significantly decreased muscle blood flow (～70%) and whole body oxygen consumption (～50%). Thus, in vivo acute endotoxemia does not impair insulin signaling through the PI3-kinase pathway in skeletal muscle and decreased tissue blood flow likely plays a central role in the impairment of glucose uptake in the muscle.     

Role of hydroxyl radical in superoxide induced microsomal lipid peroxidation: Protective effect of anion channel blocker

Treatment of bovine pulmonary artery smooth muscle microsomes with the superoxide radical generating system hypoxanthine plus xanthine oxidase stimulated iron release, hydroxyl radical production and lipid peroxidation. Pretreatment of the microsomes with deferoxamine or dime thy lthiourea markedly inhibited lipid peroxidation, and prevented hydroxyl radical production without appreciably altering iron release. The superoxide radical generating system did not alter the ambient superoxide dismutase activity. However,addition of exogenous superoxide dismutase prevented superoxide radical induced iron release,hydroxyl radical production and lipid peroxidation. Simultaneous treatment of the microsomes with deferoxamine, dimethylthiourea or superoxide dismutase prevented hydroxyl radical production and liqid peroxidation. While deferoxamine or dimethylthiourea did not appreciably alter iron release, superoxide dismutase prevented iron release. However, addition of deferoxamine, dimethylthiourea or superoxide dismutase even 2 min after treatment did not significantly inhibit lipid peroxidation, hydroxyl radical production and iron release. Pretreatment of microsomes with the anion channel blocker 4,4’- dithiocyano 2,′- disulphonic acid stilbine did not cause any discernible change in chemiluminiscence induced by the superoxide radical generating system but markedly inhibited lipid peroxidation without appreciably altering iron release and hydroxial radical production.     

Hypoxia/reoxygenation stimulates endothelium to promote neutrophil adhesion.

An in vitro model was designed to study the role of ischemia/reperfusion and endothelium-derived oxygen free radicals on neutrophil adhesion, with particular interest in the endothelial adhesion molecules involved. Human umbilical vein endothelial cells were submitted to 5 h hypoxia followed by various times (20 min to 24 h) of reoxygenation. Human resting neutrophils were added to monolayers for the last 15 min of reoxygenation. Adherence was evaluated by myeloperoxidase assay. Under these conditions, we found an increased adhesion of neutrophils with two peaks after 20 min and 4 h reoxygenation. This was correlated with the respective expression of the preformed granule membrane protein 140 (GMP-140) and of the de novo synthesized endothelial leukocyte adhesion molecule 1 (ELAM-1) on endothelial surface. Superoxide dismutase and/or catalase, or oxypurinol added to cultures before hypoxia efficiently prevented neutrophil adhesion. These results underline the crucial role played by endothelial oxy radicals at reoxygenation in adhesion of leukocytes, which could lead to an amplification of the oxidative stress injury. The protection offered by free radical scavengers emphasizes the potential therapeutic use of antioxidants in postischemic vascular disorders.     

Synergistic induction of hydroxyl radical-induced DNA single-strand breaks by chromium(VI) compound and cigarette smoke solution

Chromium(VI) compounds and cigarette smoke are known human carcinogens. We found that K2Cr2O7 and cigarette smoke solution synergistically induced DNA single-strand breaks (0.23+/-0.04 breaks per DNA molecule) in pUC118 plasmid DNA. K2Cr2O7 alone or cigarette smoke solution alone induced much less strand breaks (0.03+/-0.01 or 0.07+/-0.02 breaks per DNA molecule, respectively). The synergistic effect was prevented by catalase and by hydroxyl radical scavengers such as deferoxamine, dimethylsulfoxide, d-mannitol, and Tris, but not by superoxide dismutase. Ascorbic acid enhanced the synergism. Glutathione inhibited strand breakage only at high concentrations. Electron spin resonance (ESR) studies using a hydroxyl radical trap demonstrated that hydroxyl radicals were generated when DNA was incubated with K2Cr2O7 and cigarette smoke solution. Hydroxyl radical adduct decreased dose-dependently when strand breakage was prevented by catalase, deferoxamine, dimethylsulfoxide, d-mannitol or Tris, but not significantly by superoxide dismutase. We also used ESR spectroscopy to study the effects of different concentration of ascorbic acid and glutathione. The results showed that hydroxyl radical, which is proposed as a main carcinogenic mechanism for both chromium(VI) compounds and cigarette smoke solution was mainly responsible for the DNA breaks they induced.     

Effect of antiperoxidative drugs on gastric damage induced by ethanol in rats

Lesion formation due to oral administration of absolute ethanol could be prevented by parenteral pretreatment with antiperoxidative drugs such as butylated hydroxytoluene (BHT), quercetin and quinacrine. Also effective were allopurinol and oxypurinol, inhibitors of xanthine oxidase, but not superoxide dismutase (SOD) and hydroxyl radical scavengers, such as sodium benzoate and dimethyl sulfoxide (DMSO). BHT, quercetin, quinacrine and sulfhydryl compounds such as reduced glutathione and cysteamine which offer gastroprotection in vivo against ethanol inhibited lipid peroxidation induced in vitro by ferrous ion in porcine gastric mucosal homogenate, but SOD, sodium benzoate, DMSO, allopurinol and oxypurinol did not. These results suggest the possibility that an active species, probably derived from free iron mobilized by the xanthine oxidase system, other than oxygen radicals such as hydroxyl radicals, contributes to lipid peroxidation and lesion formation in the gastric mucosa after absolute ethanol administration.     

Early treatment with deferoxamine limits myocardial ischemic/reperfusion injury

Oxygen-derived free radicals (the superoxide anion O2- and hydroxyl radical.OH) have been implicated in myocardial injury associated with coronary artery occlusion followed by reperfusion. Transition metals (such as iron or copper) are needed to catalyze the formation of the .OH radical and subsequent .OH-mediated lipid peroxidation, yet the role of these transition metals in the pathogenesis of myocyte necrosis remains undefined. To address this issue, 21 dogs underwent 2 h of coronary artery occlusion and 4 h of reperfusion. Each animal was randomly assigned into 1 of 3 treatment groups: 7 received the iron chelator deferoxamine beginning 30 min preocclusion, 7 received deferoxamine beginning 5 min prior to reperfusion, while 7 dogs served as saline controls. Deferoxamine effectively chelated free iron in both treatment groups (total urine iron content averaged 42 +/- 16, 662 +/- 177 and 803 +/- 2.5 micrograms in control, pretreated, and deferoxamine at reperfusion groups respectively; p less than 0.05), but had no significant effect on in vivo area at risk (AR), hemodynamic parameters, collateral blood flow during occlusion, or myocardial blood flow following reperfusion. Area of necrosis (AN) in dogs pretreated with deferoxamine (34.6 +/- 3.7% of the AR; p less than 0.05) was significantly smaller than that observed in the saline control group (55.4 +/- 4.7% of the AR). Deferoxamine administered at the time of reperfusion, however, had no significant effect on infarct size (AN/AR = 54.3 +/- 8.7%, p = NS vs. controls). Thus, early treatment with the iron chelator deferoxamine acutely reduced the extent of myocyte necrosis produced by 2 h of transient coronary artery occlusion in the canine model.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between myocardial amiodarone concentration and antiarrhythmic effect in dogs with myocardial infarction and electrically induced ventricular arrhythmias

The relationship between the antiarrhythmic effect of amiodarone and its myocardial concentration was studied in dogs with 1-week-old myocardial infarction and reproducibly inducible sustained ventricular tachycardia or ventricular fibrillation. Three groups of animals (n = 10/group) received amiodarone, 40 mg.kg-1.day-1 (low-dose amiodarone), amiodarone 60 mg.kg-1.day-1 (high-dose amiodarone), or no amiodarone (control group). After 1 week of treatment, programmed electrical stimulation was repeated, and plasma and myocardial amiodarone and desethylamiodarone concentrations were measured. In the control group, sustained ventricular tachycardia or ventricular fibrillation was induced in six dogs (p = NS) when compared with baseline data. In the low-dose amiodarone group, sustained ventricular tachycardia or ventricular fibrillation was induced only in two dogs after 1 week of treatment (p less than 0.01 vs. baseline data). Sustained ventricular tachycardia or ventricular fibrillation was induced in seven dogs after treatment with high-dose amiodarone (p = NS vs. baseline data). Plasma amiodarone concentration in the low-dose amiodarone group (2.54 +/- 1.95 micrograms/mL) was significantly less (p less than 0.01) than that in the high-dose amiodarone group (4.64 +/- 1.66 micrograms/mL). Similarly, the plasma desethylamiodarone in the low-dose amiodarone group (0.32 +/- 0.16 microgram/mL) was significantly less (p less than 0.001) than that in the high-amiodarone dose group (0.56 +/- 0.23 microgram/mL). The myocardial amiodarone concentration in the low-dose amiodarone group (49.7 +/- 23.1 micrograms/g) was significantly lower (p less than 0.001) than that in the high-dose group (98.4 +/- 32.1 micrograms/g).(ABSTRACT TRUNCATED AT 250 WORDS)     

丁苯酞对颈动脉狭窄大鼠认知功能及海马CA1区神经元凋亡的影响及相关机制研究

摘要 目的：探讨与研究丁苯酞对颈动脉狭窄大鼠认知功能及海马CA1区神经元凋亡的影响及相关机制。方法：将颈动脉狭窄大鼠大鼠（n=42）随机为三组-模型组、低剂量丁苯酞（20 mg/kg）组和高剂量丁苯酞（40 mg/kg）组,每组14只。低剂量丁苯酞组与高剂量丁苯酞组每天给予20 mg/kg、40 mg/kg丁苯酞灌胃治疗,对照组给予等剂量的生理盐水灌胃,持续21 d。结果：低剂量丁苯酞组与高剂量丁苯酞组治疗第7 d、第14 d、第21 d的BBT评分低于模型组（P<0.05）,高剂量丁苯酞组低于低剂量丁苯酞组（P<0.05）。低剂量丁苯酞组与高剂量丁苯酞组治疗第21 d、第28 d的海马CA1区神经元凋亡指数低于模型组,高剂量丁苯酞组低于低剂量丁苯酞组（P<0.05）。低剂量丁苯酞组与高剂量丁苯酞组治疗第21 d、第28 d的脑组织超氧化物歧化酶（Superoxide dismutase,SOD）活性高于模型组（P<0.05）,丙二醛（Malondialdehyde,MDA）活性低于模型组（P<0.05）,高剂量丁苯酞组与低剂量丁苯酞组对比差异都有统计学意义（P<0.05）。低剂量丁苯酞组与高剂量丁苯酞组治疗第21 d、第28 d的海马CA1区BCL2-Associated X（Bax）、B淋巴细胞瘤-2（B-cell lymphoma-2,bcl-2）蛋白相对表达水平高于模型组（P<0.05）,高剂量丁苯酞组高于低剂量丁苯酞组（P<0.05）。结论：丁苯酞在颈动脉狭窄大鼠的应用能提高海马CA1区Bax、Bcl-2蛋白的表达,抑制神经元的凋亡,改善氧化应激状态,从而提高大鼠的认知功能。     

Oxygen-based free radical generation by ferrous ions and deferoxamine

Deferoxamine accelerates the autooxidation of iron as measured by the rapid disappearance of Fe2+, the associated appearance of Fe3+, and the uptake of oxygen. Protons are released in the reaction. The formation of H2O2 was detected by the horseradish peroxidase-catalyzed oxidation of scopoletin, and the formation of hydroxyl radicals (OH.) was suggested by the formation of the OH. spin trap adduct (DMPO/OH). with the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and the generation of the methyl radical adduct on the further addition of dimethyl sulfoxide. (DMPO/OH). adduct formation was inhibited by catalase but not by superoxide dismutase. The oxidant formed converted iodide to a trichloroacetic acid-precipitable form (iodination) and was bactericidal to logarithmic phase Escherichia coli. Both iodination and bactericidal activity was inhibited by catalase and by OH. scavengers, but not by superoxide dismutase. Iodination was optimal in 5 x 10(-4) M acetate buffer, pH 5.0, and when the Fe2+ and deferoxamine concentrations were equimolar at 10(-4) M. Fe2+ could not be replaced by Fe3+, Co2+, Zn2+, Ca2+, Mg2+, or Mn2+, or deferoxamine by EDTA, diethylenetriaminepentaacetic acid, or bathophenanthroline. These findings indicate that Fe2+ and deferoxamine can act as an oxygen radical generating system, which may contribute to its biological effects in vitro and in vivo.     

Maintenance of left ventricular function (90%) after twenty-four-hour heart preservation with deferoxamine.

During 24-h in vitro heart preservation and reperfusion, irreversible tissue damage occurs caused by reactive oxygen intermediates, such as superoxide radicals, singlet oxygen, hydrogen peroxide, hydroperoxyl, hydroxyl radicals, as well as the peroxynitrite radical. Reduction of the related oxidative damage of reperfused ischemic tissue by free radical scavengers and metal chelators is of primary importance in maintaining heart function. We assessed whether deferoxamine (DFR) added to a cardioplegia solution decreased free radical formation during 24-h cold (5 degrees C) heart preservation and normothermic reperfusion (37 degrees C) in the Langendorff isolated perfused rat heart. The deferoxamine treated hearts were significantly (p less than .001) better preserved than the control hearts after 24 h of preservation with regard to recovery of left ventricular diastolic pressure, contractility (+dP/dt), relaxation (-dP/dt), creatine kinase release, and lipid peroxidation. DFR preserved cell membrane integrity and maintained 93% of left ventricular contractility. The evidence suggests that DFR reduces lipid peroxidation damage by reducing free radical formation and thereby maintaining normal coronary perfusion flow and myocardial function.     

Exercise and ovarian steroid hormones: their effects on mitochondrial respiration

The effect of exercise on mitochondria respiration was studied in gastrocnemius muscle of ovariectomized rats, pseudopregnant rats, and estrous rats. The estrous cycles were followed by vaginal smears. Rats were made pseudopregnant (PSP) by 45 s cervical stimulation with a glass rod on the day of estrous. The treadmill protocol (21 m/min, 10 grade uphill) induced a significant decrease in state 3 oxygen consumption (oxidative phosphorylation) in estrous (0.26 +/- 0.02 vs. 0.49 +/- 0.05 microatoms O min(-1) mg protein(-1)) and ovariectomized rats (0.18 +/- 0.03 vs. 0.40 +/- 0.03 microatoms O min(-1) mg protein(-1)). In contrast, pseudopregnant and progesterone-treated ovariectomized rats did not decrease state 3 nor state 4 respiratory rates. These results show that the effect of exercise on mitochondria respiration does vary according to the hormonal status.     

Reduced vulnerability of the hypertrophied rat heart to oxygen-radical injury

Effects of xanthine--xanthine oxidase produced oxygen radicals were studied in hypertrophied rat hearts in a Langendorff preparation. Heart hypertrophy was produced by banding of the abdominal aorta for 6 weeks. This resulted in a 22% increase in ventricle/body weight ratio compared with that of sham-operated controls. Perfusion with xanthine--xanthine oxidase caused contractile failure and a significant rise in the resting tension. Complete contractile failure in hypertrophied hearts was seen at 25.5 +/- 3.2 min, whereas in control hearts it happened at 14.4 +/- 5.6 min. Contractile failure due to oxygen radicals in both groups was associated with a decline in high energy phosphates, increased lipid peroxidation, and extensive structural damage. Sarcolemma in both groups became permeable to the extracellular tracer lanthanum. As compared with control, in hypertrophied hearts the malondialdehyde content, indicative of lipid peroxidation, was less by 40%; whereas superoxide dismutase, a free radical scavenger, was higher by a similar amount. These data show a greater capacity of the 6-week hypertrophied heart to withstand a free radical induced contractile failure. This delay in oxygen radical effect can be partially explained by the reduced lipid peroxide content and increased superoxide dismutase activity in the hypertrophied hearts.     

Blood flow, PO2, PCO2 and pH during progressive working contractions in a whole muscle group

Alterations in blood flow during progressive working contractions were examined to elucidate their relation to work rate in a predominantly glycolytic muscle group, i.e., m. gastrocnemius and m. plantaris, in rabbits anesthetized with urethane and chloralose. In one series of animals, the sciatic nerve was stimulated to induce plantar flexions of constant length at 2, 5 and 8% of an afterload at which only isometric tension could be developed. Another series was exercised at 30 and 50% of this value, and a third group served as non-exercised controls. Each experimental session consisted of a series of 5 min non-exercise periods followed by 6 min exercise periods, and a 10 min post-exercise period. Femoral venous blood was obtained just before the first exercise period, during the final minute of each exercise period, and 10 min after the final exercise period. The composition of venous blood samples from control animals did not change during the experimental session. Blood flow in the exercising limb increased at the lowest workload, and attained a maximum flow rate at the 5% workload. Blood gases were altered to a similar extent at all afterloads, averaging: PO2 = 4.0 +/- 0.2 kPa and PCO2 = 7.5 +/- 0.3 kPa. pH, in contrast, was lower at the heaviest afterloads (X = 7.144 +/- 0.03) compared to the lighter afterloads (X = 7.245 +/- 0.03). The blood flow and pH patterns are consistent with the glycolytic fiber type composition of this muscle group. Venous PO2 indicates that O2 delivery was adequate, even at the highest afterload.(ABSTRACT TRUNCATED AT 250 WORDS)     

Oxygen radical scavengers improve vascular patency and bone-muscle cell survival in an ischemic extremity replant model

We examined the use of oxygen radical scavengers in preventing the no-reflow phenomenon and improving bone-muscle cell survival in an ischemic extremity replant model. A total of 70 Lewis rat modified hindlimb replants were performed after specific periods of cold ischemia and intraarterial perfusion with either superoxide dismutase and catalase, specific oxygen free-radical scavengers, or a control solution. Ischemic hindlimbs treated with superoxide dismutase and catalase showed a statistically significant (p less than 0.05) improvement in vascular patency after prolonged cold ischemia when compared to controls. Histologically, experimental extremities demonstrated greater osteoblast, osteocyte, and muscle cell survival in replanted hindlimbs with patent vascular anastomoses. The perfusion of severed limbs and digits and free vascularized tissue transfers with superoxide dismutase and catalase after a period of ischemia has already occurred may prolong the ischemic "time window" tolerated for successful tissue survival.     

Oxygen radicals generated during anoxia followed by reoxygenation reduce the synthesis of tissue-type plasminogen activator and plasminogen activator inhibitor-1 in human endothelial cell culture

The effect of anoxia and reoxygenation on the synthesis and secretion of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) was studied in primary cultures of human umbilical vein endothelial cells. Sublethal anoxia, determined by trypan blue dye exclusion and lactate dehydrogenase release, was produced by cell culture under a 95% N2, 5% CO2 atmosphere for 2-24 h and was followed by reoxygenation with 95% air, 5% CO2 for 24 or 48 h. Anoxia did not alter the levels of mRNA for t-PA or PAI-1 in the cells or the secretion of t-PA or PAI-1 into the medium. At 24 h, t-PA secreted into conditioned medium was 7.0 +/- 1.4 ng/2 x 10(6) cells (n = 9) and PAI-1 was 300 +/- 13 IU/2 x 10(6) cells (n = 9), whereas the content of t-PA mRNA was 2.2 pg/micrograms of RNA and PAI-1 mRNA was 180 pg/micrograms of RNA. During reoxygenation, however, t-PA antigen and PAI-1 activity as well as mRNA for PAI-1 decreased proportionally to the duration of anoxia, to reach 27 +/- 1.0, 49 +/- 2.0, and 47 +/- 14% of control values, respectively, within 24 h of anoxia. t-PA mRNA also decreased significantly during reoxygenation following anoxia, but the extent could not be accurately quantitated. Addition, during anoxia, of a 200 micrograms/ml concentration of the superoxide anion radical scavenger superoxide dismutase or of a 5 mM concentration of the iron chelator deferoxamine mesylate prevented the subsequent decrease of t-PA antigen during reoxygenation; addition of these compounds during reoxygenation had no effect. Superoxide dismutase, but not deferoxamine mesylate, when added during anoxia prevented the subsequent decrease in PAI-1 activity. These studies suggest that the marked alteration of endothelial cell fibrinolysis during anoxia followed by reoxygenation is most likely mediated by a mechanism dependent on oxygen radicals. Impaired endothelial cell fibrinolysis may contribute to the pathophysiology of ischemia/reperfusion injury.     

N-acetylcysteine enhances muscle cysteine and glutathione availability and attenuates fatigue during prolonged exercise in endurance-trained individuals.

The production of reactive oxygen species in skeletal muscle is linked with muscle fatigue. This study investigated the effects of the antioxidant compound N-acetylcysteine (NAC) on muscle cysteine, cystine, and glutathione and on time to fatigue during prolonged, submaximal exercise in endurance athletes. Eight men completed a double-blind, crossover study, receiving NAC or placebo before and during cycling for 45 min at 71% peak oxygen consumption (VO2 peak) and then to fatigue at 92% VO2 peak. NAC was intravenously infused at 125 mg.kg(-1).h(-1) for 15 min and then at 25 mg.kg(-1).h(-1) for 20 min before and throughout exercise. Arterialized venous blood was analyzed for NAC, glutathione status, and cysteine concentration. A vastus lateralis biopsy was taken preinfusion, at 45 min of exercise, and at fatigue and was analyzed for NAC, total glutathione (TGSH), reduced glutathione (GSH), cysteine, and cystine. Time to fatigue at 92% VO2 peak was reproducible in preliminary trials (coefficient of variation 5.6 +/- 0.6%) and with NAC was enhanced by 26.3 +/- 9.1% (NAC 6.4 +/- 0.6 min vs. Con 5.3 +/- 0.7 min; P <0.05). NAC increased muscle total and reduced NAC at both 45 min and fatigue (P <0.005). Muscle cysteine and cystine were unchanged during Con, but were elevated above preinfusion levels with NAC (P <0.001). Muscle TGSH (P <0.05) declined and muscle GSH tended to decline (P=0.06) during exercise. Both were greater with NAC (P <0.05). Neither exercise nor NAC affected whole blood TGSH. Whereas blood GSH was decreased and calculated oxidized glutathione increased with exercise (P <0.05), both were unaffected by NAC. In conclusion, NAC improved performance in well-trained individuals, with enhanced muscle cysteine and GSH availability a likely mechanism.     

Endogenous triacylglycerol utilization by rat skeletal muscle during tetanic stimulation

An isolated perfused rat hindquarter preparation was used to examine the utilization of endogenous triacylglycerol (TG) during 20 min of electrical stimulation. The sciatic nerve was stimulated with maximal tetanic trains at 0.5 Hz. The isometric tension generated by the gastrocnemius-plantaris-soleus muscle group was recorded, and muscle samples were taken pre- and poststimulation. Twenty minutes of stimulation significantly reduced endogenous TG from 6.78 +/- 0.84 to 4.64 +/- 0.64 mumol X g dry wt-1 (32%) in the red gastrocnemius muscle and from 7.70 +/- 0.61 to 6.66 +/- 0.80 mumol X g dry wt-1 (13.5%) in the plantaris muscle. Although TG content decreased by 16% in the soleus (28.2 +/- 5.0 to 23.8 +/- 4.4 mumol X g-1), the change was not significant. Stimulation had no effect on white gastrocnemius TG concentration (6.84 +/- 1.22 to 6.25 +/- 1.41 mumol X g-1). Thus oxidation of TG occurred primarily in muscles with a large proportion of fast-twitch oxidative-glycolytic fibers. Calculations from measurements of muscle energy stores and fuel uptake indicated that up to 62% of the aerobic energy was provided by endogenous TG. Carbohydrate oxidation contributed up to 28% and the remaining 10% may be accounted for by the oxidation of exogenous free fatty acids originating in the perfusate or from hindquarter adipose tissue. The magnitude of the fall in TG concentration in a given muscle was inversely related to the fall in glycogen concentration.     

Free radical scavengers suppress the accumulation of platinum in the cerebral cortex

We investigated whether free radical scavengers and antioxidants inhibit the accumulation of platinum (Pt) in the cerebral cortex. Pt was detected in the cerebral cortex of mice afters administration of cisplatin and exposure to short-term hypoxia. When mice were treated with either allopurinol (20 mg/kg) or catalase (100 mg/kg) before cisplatin administration and low oxygen exposure, Pt was not detected in the cerebral cortex. However, Pt was detected in the cerebral cortex of mice pretreated with either a low dosage of allopurinol or heat-denatured catalase. Furthermore, Pt was detected in the cerebral cortex of mice preadministered vitamin C, vitamin E, or deferoxamine. Lipid peroxide levels in the cerebral cortex increased 10 min after the treatment of hypoxia, and peaked 30 min after the treatment. These results suggested that short-term hypoxia produces free radicals, which allows Pt to pass through the blood-brain barrier and accumulate in the cerebral cortex, and that the production of free radicals is reduced by the administration of either allopurinol or catalase, which prevents Pt from passing through the barrier.