Tempol reduces reperfusion-induced arrhythmias in anaesthetized rats

The Effect of Piperidine Nitroxides on the Properties of Metalloproteins in Human Red Blood Cells

Nitroxides are stable, low molecular-weight radicals containing a nitroxide group that has an unpaired electron. The presence of a nitroxide group determines their redox properties. The effect of the piperidine nitroxides, Tempo, Tempol, and Tempamine, on metalloproteins (hemoglobin, superoxide dismutase, catalase) and lactate dehydrogenase in red blood cells was investigated in this research. In addition, the level of lipid peroxidation and the level of protein carbonyl groups were examined as indicators of the effect of oxidative stress. Nitroxides increased superoxide dismutase activity and oxidized hemoglobin to methemoglobin, and also slightly decreased the catalase activity of red blood cells treated with nitroxides. Tempol significantly decreased lactate dehydrogenase activity. All three nitroxides had no effect on membrane lipid peroxidation and protein oxidation. Our results confirm that nitroxides have both antioxidant and prooxidative effects in human red blood cells. The piperidine nitroxides do not initiate the oxidation of proteins and lipids in the membranes of human red blood cells.

Effect of oleuropein on myocardial dysfunction and oxidative stress induced by ischemic-reperfusion injury in isolated rat heart

Background

Studies have reported antioxidant effect of oleuropein in isolated rat heart.

Objective

This study was conducted to investigate whether perfusion of isolated rat heart with oleuropein, before induction of ischemia or at the onset of reperfusion, had any effect on the hemodynamic parameters, infarct size and biochemical factors following ischemic – reperfusion injury.

Materials and methods

Forty-eight male Wistar rats were divided into 6 groups: the control groups (Con-P and Con-T groups), O10-P and O50-P groups perfused with 10 and 50 μg/g heart oleuropein 5 min before the induction of ischemia and O10-T and O50-T groups perfused with 10 and 50 μg/g heart oleuropein at the beginning of the reperfusion, respectively. All hearts were subjected to 30 min global ischemia and 90 min reperfusion. Hemodynamic parameters were monitored throughout the experiment. The creatine kinase (CK) and malondialdehyde (MDA) level of coronary outflow were assayed and the infarct size measured at the end of reperfusion.

Results

We found hemodynamic parameters namely heart rate, left ventricular end diastolic pressure (LVEDP), left ventricular developed pressure (LVDP), ±dp/dt and coronary outflow significantly improved in all groups that received oleuropein compared to the control groups. Also, the infarct size was smaller and the coronary outflow levels of CK and MDA were lower in the oleuropein groups compared to the control groups.

Conclusions

The findings suggest that perfusion of isolated rat heart with oleuropein would lead to improved myocardial dysfunction following ischemic-reperfusion injury. Our findings confirm the antioxidant potential of oleuropein.

Prophylactic and Therapeutic Effects of Oleuropein on Reperfusion-Induced Arrhythmia in Anesthetized Rat

Background:

This study was conducted to reveal that whether i.v. injection of oleuropein, the most potent polyphenolic antioxidant in olive leaf, has any effect on the magnitude of reperfusion arrhythmia in anesthetized rats or not.

Methods:

Eighty male Wistar rats were divided into 8 groups of 10 each: groups 1 and 5 were assigned as the prophylactic and treatment control groups, groups 2 and 6 as the prophylactic and treatment groups with lidocaine (10 mg/kg), groups 3 and 4 as the prophylactic groups with 10 and 50 mg/kg oleuropein (i.v.), and groups 7 and 8 as the treatment groups with 10 and 50 mg/kg oleuropein (i.v.), respectively. Reperfusion injury was induced by 5-min regional ischemia and 15-min reperfusion of left anterior descending coronary artery. Heart rate, blood pressure, and electrocardiogram were monitored throughout the procedure.

Results:

blood pressure was significantly decreased by infusion of 50 mg/kg oleuropein in groups 4 and 8, but unlike the lidocaine as a standard anti-arrhythmic drug in groups 2 and 5 had not significant effect on heart rate. The onset of arrhythmia in groups received oleuropein (groups 3, 4, 7, and 8) was significantly delayed. The mortality rate due to irreversible ventricular fibrillation was also significantly reduced in groups 3, 4, 7, and 8. The effect of lidocaine in groups 2 and 5 was more potent than that in oleuropein group.

Conclusion:

These findings indicate that i.v. injection of oleuropein possibly through its antioxidant activity reduces the magnitude of reperfusion-induced arrhythmia.

Insulin alleviates posttrauma cardiac dysfunction by inhibiting tumor necrosis factor-α-mediated reactive oxygen species production

OBJECTIVE

Clinical evidence indicates that intensive insulin treatment prevents the incidence of multiple organ failures in surgical operation and severe trauma, but the mechanisms involved remain elusive. This study was designed to test the hypothesis that insulin may exert anti-inflammatory and antioxidative effects and thus alleviate cardiac dysfunction after trauma.

DESIGN

Prospective, randomized experimental study.

SETTING

Animal research laboratory.

SUBJECTS

Sprague Dawley rats.

INTERVENTIONS

Anesthetized rats were subjected to 200 revolutions at a rate of 35 rpm in Noble-Collip drum to induce a nonlethal mechanical trauma and were randomized to receive vehicle, insulin, and insulin + wortmannin treatments. An in vitro study was performed on cultured cardiomyocytes subjected to sham-traumatic serum (SS), traumatic serum (TS), SS + tumor necrosis factor (TNF)-α, SS + H2O2, TS + neutralizing anti-TNF-α antibody, or TS + tempol treatments.

MEASUREMENTS AND MAIN RESULTS

Immediate cardiac dysfunction occurred 0.5 hr after trauma without significant cardiomyocyte necrosis and apoptosis, while serum TNF-α and cardiac reactive oxygen species (ROS) production was increased. Importantly, incubation of cardiomyocytes with TS or SS + TNF-α significantly increased ROS generation together with dampened cardiomyocyte contractility and Ca transient, all of which were rescued by TNF-α antibody. Administration of insulin inhibited TNF-α and ROS overproduction and alleviated cardiac dysfunction 2 hours after trauma. Scavenging ROS with tempol also attenuated cardiac dysfunction after trauma, whereas insulin combined with tempol failed to further improve cardiac functional recovery compared with insulin treatment alone. Moreover, the aforementioned anti-TNF-α, antioxidative, and cardioprotective effects afforded by insulin were almost abolished by the phosphatidylinositol 3-kinase inhibitor wortmannin.

CONCLUSIONS

These results demonstrate for the first time that mechanical trauma induces a significant increase in TNF-α and ROS production, resulting in immediate cardiac dysfunction. Early posttrauma insulin treatment alleviates cardiac dysfunction by inhibiting TNF-α-mediated ROS production via a phosphatidylinositol 3-kinase/Akt-dependent mechanism.

Protective role of deoxyschizandrin and schisantherin A against myocardial ischemia-reperfusion injury in rats

Background

Our previous studies suggested that deoxyschizandrin (DSD) and schisantherin A (STA) may have cardioprotective effects, but information in this regard is lacking. Therefore, we explored the protective role of DSD and STA in myocardial ischemia–reperfusion (I/R) injury.

Methodology/Principal Findings

Anesthetized male rats were treated once with DSD and STA (each 40 µmol/kg) through the tail vein after 45 min of ischemia, followed by 2-h reperfusion. Cardiac function, infarct size, biochemical markers, histopathology and apoptosis were measured and mRNA expression of gp91^phox in myocardial tissue assessed by RT-PCR. Neonatal rat cardiomyocytes were pretreated with DSD and STA and then damaged by H₂O₂. Cell apoptosis was tested by a flow cytometric assay. Compared with the I/R group: (i) DSD and STA could significantly reduce the abnormalities of LVSP, LVEDP, ±dp/dt_max and arrhythmias, thereby showing their protective roles in cardiac function; (ii) DSD and STA could significantly attenuate the infarct size and MDA release while increasing SOD activity, suggesting a role in reducing myocardial injury; (iii) tissue morphology and myocardial textual analysis revealed that DSD and STA mitigated changes in myocardial histopathology; (iv) DSD and STA decreased apoptosis (33.56±2.58% to 10.28±2.80% and 10.98±1.99%, respectively) and caspase-3 activity in the myocardium (0.62±0.02 OD/mg to 0.38±0.02 OD/mg and 0.32±0.02 OD/mg, respectively), showing their protective effects upon cardiomyocytes; and (v) DSD and STA had similar protective effects on I/R injury as those seen with the positive control metoprolol. In vitro, DSD and STA could significantly decrease the apoptosis of neonatal cardiomyocytes.

Conclusions/Significance

These data suggest that DSD and STA can protect against myocardial I/R injury. The underlining mechanism may be related to their role in inhibiting cardiomyocyte apoptosis.

Sustained oxidative stress causes late acute renal failure via duplex regulation on p38 MAPK and Akt phosphorylation in severely burned rats

BACKGROUND

Clinical evidence indicates that late acute renal failure (ARF) predicts high mortality in severely burned patients but the pathophysiology of late ARF remains undefined. This study was designed to test the hypothesis that sustained reactive oxygen species (ROS) induced late ARF in a severely burned rat model and to investigate the signaling mechanisms involved.

MATERIALS AND METHODS

Rats were exposed to 100°C bath for 15 s to induce severe burn injury (40% of total body surface area). Renal function, ROS generation, tubular necrosis and apoptosis, and phosphorylation of MAPK and Akt were measured during 72 hours after burn.

RESULTS

Renal function as assessed by serum creatinine and blood urea nitrogen deteriorated significantly at 3 h after burn, alleviated at 6 h but worsened at 48 h and 72 h, indicating a late ARF was induced. Apoptotic cells and cleavage caspase-3 in the kidney went up slowly and turned into significant at 48 h and 72 h. Tubular cell ROS production shot up at 6 h and continuously rose during the 72-h experiment. Scavenging ROS with tempol markedly attenuated tubular apoptosis and renal dysfunction at 72 h after burn. Interestingly, renal p38 MAPK phosphorylation elevated in a time dependent manner whereas Akt phosphorylation increased during the first 24 h but decreased at 48 h after burn. The p38 MAPK specific inhibitor SB203580 alleviated whereas Akt inhibitor exacerbated burn-induced tubular apoptosis and renal dysfunction. Furthermore, tempol treatment exerted a duplex regulation through inhibiting p38 MAPK phosphorylation but further increasing Akt phosphorylation at 72 h postburn.

CONCLUSIONS

These results demonstrate that sustained renal ROS overproduction induces continuous tubular cell apoptosis and thus a late ARF at 72 h after burn in severely burned rats, which may result from ROS-mediated activation of p38 MAPK but a late inhibition of Akt phosphorylation.

Role of arachidonic acid, lipoxygenase, and mitochondrial depolarization in reperfusion arrhythmias

We have sought evidence that arachidonic acid (AA) induces mitochondrial depolarization in isolated myocytes by a lipoxygenase (LOX)-dependent mechanism and that such depolarization might contribute to arrhythmogenesis following ischemia-reperfusion injury. A method was developed for measuring mitochondrial depolarization in isolated adult rat myocytes in suspension, using tetramethylrhodamine ethyl ester. The addition of AA to myocytes resulted in mitochondrial depolarization that was inhibited by the LOX inhibitor baicalein, by the reactive oxygen species (ROS) scavenger mercaptoproprionylglycine, and by the anion channel inhibitor diisothiocyanatostilbene-disulfonic acid (DIDS). AA induced mitochondrial uncoupling and mitochondrial ATPase activity in myocytes, but both were insensitive to baicalein. We conclude that the metabolic effect of AA in myocytes puts mitochondria into an energetically compromised state where membrane potential is easily changed by the DIDS-sensitive LOX/ROS-mediated opening of an inner membrane anion channel. In an in vivo anesthetized rat model of coronary artery occlusion, baicalein was found to strongly inhibit arrhythmias induced by ischemia-reperfusion injury. Arrhythmias following ischemia-reperfusion injury have been previously associated with DIDS-sensitive ROS-mediated mitochondrial depolarization, and free fatty acids including AA were previously found to accumulate during such injury. We therefore conclude that arrhythmias following ischemia-reperfusion injury might originate from mitochondrial depolarization mediated by LOX and AA.

Protection against in vivo focal myocardial ischemia/reperfusion injury-induced arrhythmias and apoptosis by hesperidin

Among the heart diseases, ischemia and reperfusion (I/R) induced arrhythmias contribute to episodes of sudden death. Cardiac arrhythmias during ischemia reperfusion are believed to be related to oxidative stress. Therefore, the aim of this study was to examine whether treatment with hesperidin alleviates arrhythmias and infarct size in experimentally-induced myocardial I/R injury using an in vivo rat model. In this study haemodynamics parameters, markers of inflammation, biomarkers of oxidative stress and tissue nitrite level and infarct size of the heart were estimated in various groups. I/R showed a significant decrease in tissue nitrite and antioxidant level and significant increase in arrhythmias, inflammation and myocardial cell apoptosis. Treatment with hesperidin showed a significant increase in tissue nitrite, antioxidant level and reduction in inflammation, arrhythmias and apoptosis. In conclusion, the protecting effect of hesperidin in I/R induced arrhythmias is due to reduction in inflammation and oxidative stress.

Free radical scavenger specifically prevents ischemic focal ventricular tachycardia

BACKGROUND

Focal ventricular tachycardia (VT) in acute myocardial ischemia is closely related to triggered activity (TA), which may be blocked by scavenging reactive oxygen species (ROS).

OBJECTIVE

This study analyzed effects of acutely administered ROS scavenger-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) on VT in vivo and TA in vitro.

METHODS

Forty-three alpha chloralose anesthetized dogs with coronary artery occlusion were studied. Three-dimensional activation mapping helped to locate the origin of focal or reentrant VT. TEMPO (30 mg/kg intravenously) or vehicle was given. Endocardium excised from the site of origin of VT was studied using standard microelectrode techniques and measures of ROS.

RESULTS

Reentry and focal VT induction were both highly reproducible. TEMPO blocked focal VT in 6 of 11 dogs (P <.05), but 9 of 9 dogs with reentrant VT continued to have VT re-induced after TEMPO. TEMPO did not alter effective refractory period (168 +/- 3 to 171 +/- 3 ms), mean blood pressure (88 +/- 3 to 81 +/- 3 mm Hg), and size of ischemia (42% +/- 3% vs 40% +/- 4%). In vitro, TEMPO (10(-3) M, n = 14) produced no change in action potentials. Nevertheless, TA was reversibly attenuated from 5.3 +/- 1.1 to 0.4 +/- 0.4 complexes with TEMPO (n = 15, P <.05). Lucigenin-enhanced chemiluminescence and dihydroethidium staining showed increased ROS in ischemic endocardium; TEMPO dramatically reduced ROS in ischemic sites.

CONCLUSION

TEMPO, a scavenger of ROS, prevented triggered activity associated with focal VT during myocardial ischemia in areas of increased ROS. Antioxidant therapy may play an important role in blockade of focal VT under the conditions of myocardial ischemia.

Microvascular and systemic effects following top load administration of saturated carbon monoxide-saline solution

OBJECTIVE

To determine how top loads with different doses of carbon monoxide (CO)-saturated saline solutions (CO-saline) affect microvascular and systemic hemodynamics and to delineate the corresponding biochemical mechanisms.

DESIGN

Prospective study.

SETTING

University research laboratory.

SUBJECTS

Male Golden Syrian hamsters.

INTERVENTIONS

Hamsters implemented with a dorsal window chamber were given different volumes (characterized as percent of blood volume, BV) by intravenous injection of CO-saturated saline.

MEASUREMENTS AND MAIN RESULTS

Hamsters were observed until 90 mins after infusion of CO-saline solution. In the 20% BV CO-saline infusion group, observation was extended until 180 mins. Systemic variables measured included mean arterial pressure, heart rate, systemic arterial blood gases, and cardiac output and index. Microvascular hemodynamic measurements included vessel diameter, red blood cell velocity, and functional capillary density. Cyclic guanosine monophosphate (cGMP) content in the chamber tissue was measured by enzyme immunoassay. 10% BV of CO-saline increased flow maximally in the microcirculation at 30 mins after infusion (207% in arterioles and 238% in venules, p < .05 vs. baseline). Functional capillary density was significantly increased in both 10% and 15% groups (p < .05 vs. baseline), and cardiac index increased 130% (p < .05 vs. baseline) at 10 mins after 10% CO-saline infusion. There were no changes of microhemodynamic variables and functional capillary density with 2.5%, 5%, and 20% CO-saline infusion during the observation period. Microvascular hemodynamic changes by 10% CO-saline infusion were inhibited completely by L-NAME pretreatment and partially by 1H-[1,2,4]oxadiazole[4,3-a]quinoxqalin-1-one pretreatment. cGMP content in skin fold tissues was related to changes of vessel diameter.

CONCLUSIONS

Intravenous injection of CO-saturated saline caused vasodilation and improved microvascular hemodynamics in the hamster window chamber model in a dose-dependent manner. These changes were related to increased cardiac output and local cGMP content. These results support the possible use of CO-saturated solutions as a vasodilator in critical conditions.