Effects of dietary supplementation with alpha-tocopherol on myocardial infarct size and ventricular arrhythmias in a dog model of ischemia-reperfusion

Protective or Inhibitory Effect of Pharmacological Therapy on Cardiac Ischemic Preconditioning: A Literature Review

Ischemic preconditioning (IP) is an innate phenomenon, triggered by brief, non-lethal cycles of ischemia/reperfusion applied to a tissue or organ that confers tolerance to a subsequent more prolonged ischemic event. Once started, it can reduce the severity of myocardial ischemia associated with some clinical situations, such as percutaneous coronary intervention (PCI) and intermittent aortic clamping during coronary artery bypass graft surgery (CABG). Although the mechanisms underlying IP have not been completely elucidated, several studies have shown that this phenomenon involves the participation of cell triggers, intracellular signaling pathways, and end-effectors. Understanding this mechanism enables the development of preconditioning mimetic agents. It is known that a range of medications that activate the signaling cascades at different cellular levels can interfere with both the stimulation and the blockade of IP. Investigations of signaling pathways underlying ischemic conditioning have identified a number of therapeutic targets for pharmacological manipulation. This review aims to present and discuss the effects of several medications on myocardial IP.

Role of Oxidative Stress in the Genesis of Ventricular Arrhythmias

Ventricular arrhythmias, mainly lethal arrhythmias, such as ventricular tachycardia and fibrillation, may lead to sudden cardiac death. These are triggered as a result of cardiac injury due to chronic ischemia, acute myocardial infarction and various stressful conditions associated with increased levels of circulating catecholamines and angiotensin II. Several mechanisms have been proposed to underlie electrical instability of the heart promoting ventricular arrhythmias; however, oxidative stress which adversely affects ion homeostasis due to changes in the ion channel structure and function, seems to play a critical role in eliciting different types of ventricular arrhythmias. Prevention or mitigation of the severity of ventricular arrhythmias due to antioxidants has been indicated as the fundamental contribution in the field of preventive cardiology; however, novel interventions have to be developed for greater effectiveness and specificity in attenuating the adverse effects of oxidative stress. In this review, we have attempted to discuss proarrhythmic effects of oxidative stress differing in time and concentration dependence and highlight a molecular and cellular concept how it alters cardiac cell automaticity and conduction velocity sensitizing the probability of ventricular arrhythmias with resultant sudden cardiac death due to ischemic heart disease and other stressful situations. It is concluded that pharmacological approaches targeting multiple mechanisms besides oxidative stress might be more effective in the treatment of ventricular arrhythmias than current antiarrhythmic therapy.

Antioxidants in veterinary nutrition

Nutritional antioxidants have experienced a surge in research and interest in the past 20 years. this surge may be attributed to the improved methodology for investigation as well as the focus on diseases and aging processes related to oxidative stress that lend themselves to opportunistic outcomes. As such, the field of veterinary nutritional antioxidant research is also beginning to yield some interesting results, albeit, small in number compared with laboratory animals and human beings. Nonetheless, this article updates the practitioner on recent advances in research involving nutritional antioxidant applications in companion animals.

Depletion of antioxidants is associated with no-reflow phenomenon in acute myocardial infarction

BACKGROUND

No-reflow phenomenon is observed in approximately one-third of patients after percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI), and is associated with poor functional and clinical outcomes. On the other hand, the formation of free radicals in vasculature exerts deleterious effects on coronary microcirculation.

HYPOTHESIS

We hypothesized that redox state in coronary circulation may play a crucial role in no-reflow phenomenon in AMI.

METHODS

Consecutive 26 patients with first AMI who underwent primary PCI < 24 h after onset were enrolled. Before PCI, blood samples were obtained from coronary sinus to measure plasma or serum antioxidative vitamins (vitamin C, vitamin E, and beta-carotene) and antioxidative enzymes (extracellular glutathione peroxidase [GPX], superoxide dismutase, and catalase). After PCI, the corrected Thrombolysis In Myocardial Infarction (TIMI) frame count (CTFC) was measured in the target vessel. Patients with TIMI < or = 2 flow despite an optimal PCI result were designated as no-reflow group (Group NR, n = 6) and the others as reflow group (Group R, n = 20).

RESULTS

Levels of vitamin C, vitamin E, and GPX before PCI were significantly lower in Group NR than in Group R. The CTFC correlated inversely with levels of vitamin C, vitamin E, and GPX (p < 0.05).

CONCLUSIONS

Depletion of antioxidants is associated with no-reflow phenomenon in AMI. These findings strongly suggest that the redox state in coronary circulation plays an important role in the pathogenesis of no-reflow phenomenon.

Tissue damage in acute myocardial infarction: selective protection by vitamin E

A growing amount of scientific evidence supports the participation of oxygen radicals in heart disease and, consequently, a protective effect of vitamin E (VE), beta-carotene (BC), and other antioxidants. The aim of this study was to correlate plasma VE and BC concentration with the clinical course of the acute myocardial infarction (AMI). We evaluated 120 patients that were admitted at the coronary units within 12 h after the development of AMI symptoms. The AMI was diagnosed by clinical and biochemical criteria and by electrocardiography and echocardiography. Plasma VE and BC concentration was determined by high performance liquid chromatography. The patients were separated according to the plasma concentration of VE (group H, VE > 17.5 microM; group L, VE < 17.5 microM). Clinical history of patients, age, sex, associated cardiovascular risk factors, AMI localization, hemodynamic class, and the treatment received were similar between different groups. The blood levels of creatine phosphokinase (CK) evaluated either 24- or 48-h after admittance, were higher in group L than in group H (24 h: H = 436 +/- 31 U/ml vs. L = 642 +/- 84 U/ml; p < .005; 48 h: H = 242 +/- 21 U/ml; L = 423 +/- 82 U/ml, p < 0.005). The number of deflexions in the electrocardiogram at admittance (ECG-D) was significantly higher in group L than in group H (4.7 +/- 0.3 vs. 3.7 +/- 0.2; p < .005). The number of new Q waves in the ECG of release (ECG-Q) was higher in group L than in group H (2.9 +/- 0.3 vs. 2.2 +/- 0.2; p < .05). The number of segments affected in the echocardiograms (EC-S) was: L = 5.3 +/- 0.6 vs. H = 4.4 +/- 0.2; p = 0.11. No significant differences in CK levels, ECG-D, ECG-Q, and EC-S were observed when the patients were separated according their plasma BC levels. These results indicate that a high concentration of plasma VE, but not BC, was associated with a diminution in the creatine phosphokinase release and with the AMI extension.

Plasma vitamins E and C concentrations of adult patients during cardiopulmonary bypass

OBJECTIVE

This study was designed with two aims: 1) to determine if the coronary artery bypass graft (CABG) procedure alters plasma vitamin E and C concentrations of adult patients through repeated determinations of vitamin levels at time points before, during and following CABG, and 2) to assess whether plasma vitamin E concentrations reflect myocardial tissue content.

METHODS

A consecutive sample of 38 patients undergoing CABG surgery at a Midwest tertiary care hospital was enrolled. Patients receiving blood transfusions before or during surgery were excluded.

RESULTS

Plasma vitamin E/total lipid ratios rose with reperfusion, remained elevated immediately following bypass, and fell to preoperative concentrations by 24 hours. Plasma vitamin E/total cholesterol levels varied little throughout this time course. Both plasma uric acid and ascorbate concentrations (corrected for hemodilution) also rose by the preischemic interval, and remained elevated until a return to preoperative levels by 24 hours. Corrected malondialdehyde (MDA) concentrations rose by pre-ischemia but returned more quickly to preoperative levels. Atrial appendage tissue vitamin E concentrations bore a significant relationship to those of plasma prior to surgery (r=+0.49, p=0.004). Reported supplement use, plasma concentrations and body mass index contributed to the variability in atrial tissue concentrations of vitamin E.

CONCLUSIONS

In short, when not confounded by transfusions or hemodilution, several peripheral indices of antioxidants increase with the reperfusion segment of CABG procedure and return to baseline levels within 24 hours of surgery. Parallel changes in MDA were observed. The observed changes are consistent with the hypothesis that oxidative stress accompanies the ischemia-reperfusion components of the CABG procedure.

The lipid peroxidation inhibitor indenoindole H290/51 protects myocardium at risk of injury induced by ischemia-reperfusion

Lipid peroxidation contributes to myocardial reperfusion injury. The indenoindole H290/51, a lipid peroxidation inhibitor with balanced lipophilicity and a considerably higher antioxidative capacity than that of vitamin E, was tested for its myocardioprotective effect against reperfusion injury. Coronary-ligated pigs were subjected to 45 min of myocardial ischemia followed by 240 min of reperfusion. Starting five minutes prior to reperfusion, H290/51 (n = 6) or vehicle (n = 6) was retrogradely infused via a coronary vein for 30 min. The total dose of H290/51 was 1 microM in 300 ml fluid (10 ml/min). In addition to the hemodynamics, left ventricular (LV) wall segment shortening (%SS) was measured by sonomicrometry. The LV area at risk and infarct size were measured by means of Evans blue and triphenyl tetrazolium chloride staining. The hemodynamics did not change significantly during the study, and no differences were found between the two groups. In the H 290/51-treated pigs, %SS of the ischemic area recovered from 1.9% at the end of ischemia to 9.1% after 120 min (p < .05) and to 16.2% at 240 min (p < .01). There was no significant recovery in the vehicle group. The LV area at risk was approximately 20% of LV. Infarct size as a percentage of LV and of the area at risk was significantly smaller in the H290/51 group (9+/-3% and 46+/-11%) than in the control group (18+/-6%; p < .05 and 83+/-5%; p < .01). H290/51 effectively protected the myocardium at risk in the setting of myocardial ischemia followed by reperfusion. This effect was reflected by diminished infarct size and improved functional recovery.

Nitecapone is of benefit to functional performance in experimental heart transplantation

In heart transplantation, global ischemia of a graft is followed by reperfusion injury. The formation of oxygen free radicals induces arrhythmias and impairs functional recovery of the graft. This study was executed to evaluate the effect of the new antioxidant, nitecapone, on ischemia-reperfusion injury in heart transplantation in rats. Donor hearts were perfused and stored at +4 degrees C for 2 h in either Ringer's solution in the control group (C-group, n = 26) or Ringer's solution with nitecapone (NC) added (NC-group, n = 18). The donor aorta was anastomosed to the recipient's abdominal aorta and the pulmonary artery to the recipient's inferior vena cava. The grafts were classified into three categories based on the functional recovery. The rats in both groups were killed at 10, 30, or 60 min after release of the aortic clamp. Tissue samples for chemiluminescence were obtained from the left ventricle, the right ventricle, and the septum of the heart. All grafts in the NC-group (18/18) began beating after release of the aortic clamp, whereas only 50% (13/26) of the grafts in the C-group recovered (P < 0.0004). Chemiluminescence analysis showed lipid peroxidation values to be higher in the C-group than the NC-group up to 1 h after reperfusion. Also, the right ventricle samples showed lower chemiluminescence values in the NC-group than in the C-group. In conclusion, our results do not support the theory that different regions of the heart have different vulnerability to ischemia-reperfusion injuries. Nitecapone has a beneficial effect on the preservation of the grafts in terms of functional recovery.

Effect of chronic oral supplementation with alpha-tocopherol on myocardial stunning in the dog

Recent clinical and experimental studies have suggested that antioxidant supplements might actually have harmful as well as beneficial effects in the setting of cardiovascular disease. The mechanisms underlying the beneficial effects of the various antioxidants are poorly understood in humans. Reperfusion-associated myocardial injury, and particularly the phenomenon of stunning, is important because it occurs in clinical settings and may condition the prognosis after short ischemic insult. We studied the effects of chronic (3 months) alpha-tocopherol supplementation with a large oral dose (500 mg daily) on myocardial contractility (stunning) and ventricular arrhythmias in a dog model of short ischemia followed by reperfusion. Twenty dogs were randomized to either an alpha-tocopherol supplemented or a control group. After 3 months, dogs were anesthetized and underwent a 20-min coronary artery occlusion followed by reperfusion. Myocardial regional blood flow was measured by the radioactive microsphere technique and myocardial contractility by sonomicrometry. Plasma alpha-tocopherol was measured by high-performance liquid chromatography in all dogs. Twelve dogs (seven supplemented and five controls) developed ventricular fibrillation at reperfusion, showing no difference between groups. Hemodynamic parameters, blood flow in the ischemic area (collateral flow), and area at risk were similar in the two groups. Regional systolic segment shortening in the ischemic area was similar during ischemia and reperfusion in both groups, representing 41 +/- 15% (mean +/- SEM) of baseline contractility in controls and 51 +/- 8% in supplemented dogs after 150 min of reperfusion. Plasma alpha-tocopherol level was higher in supplemented than in controls (19.1 +/- 1.6 and 6.9 +/- 0.6 mg/L; p < 0.001). Thus a long-term large dose of alpha-tocopherol had no significant effect on postischaemic ventricular arrhythmias and dysfunction (myocardial stunning) in this canine model. These data suggest that if alpha-tocopherol supplementation might be useful to improve the prognosis of coronary patients, it is likely not by interfering with the stunning phenomenon.