Antiarrhythmic Effects of Some Antioxidant Vitamins in Rats Injected with Epinephrine

Vitamin E treatment in insulin-deficient diabetic rats reduces cardiac arrhythmias and mortality during severe hypoglycemia

In people with type 1 diabetes, hypoglycemia can induce cardiac arrhythmias. In rodent experiments, severe hypoglycemia can induce fatal cardiac arrhythmias, especially so in diabetic models. Increased oxidative stress associated with insulin-deficient diabetes was hypothesized to increase susceptibility to severe hypoglycemia-induced fatal cardiac arrhythmias. To test this hypothesis, Sprague-Dawley rats were made insulin deficient with streptozotocin and randomized into two groups: 1) control (n = 22) or 2) vitamin E treated (four doses of α-tocopherol, 400 mg/kg, n = 20). Following 1 week of treatment, rats were either tested for cardiac oxidative stress or underwent a hyperinsulinemic-severe hypoglycemic (10-15 mg/dL) clamp with electrocardiogram recording. As compared with controls, vitamin E-treated rats had threefold less cardiac oxidative stress, sixfold less mortality due to severe hypoglycemia, and sevenfold less incidence of heart block. In summary, vitamin E treatment and the associated reduction of cardiac oxidative stress in diabetic rats reduced severe hypoglycemia-induced fatal cardiac arrhythmias. These results indicate that in the setting of diabetes, pharmacological treatments that reduce oxidative stress may be an effective strategy to reduce the risk of severe hypoglycemia-induced fatal cardiac arrhythmias.NEW & NOTEWORTHY For people with type 1 diabetes, severe hypoglycemia can be fatal. We show in our animal model that insulin-deficient diabetic rats have fatal cardiac arrhythmias during severe hypoglycemia that are associated with increased cardiac oxidative stress. Importantly, treatment with vitamin E, to reduce oxidative stress, decreased fatal cardiac arrhythmias during severe hypoglycemia.

Effectiveness of Some Vitamins in the Prevention of Cardiovascular Disease: A Narrative Review

By virtue of their regulatory role in various metabolic and biosynthetic pathways for energy status and cellular integrity, both hydro-soluble and lipo-soluble vitamins are considered to be involved in maintaining cardiovascular function in health and disease. Deficiency of some vitamins such as vitamin A, B₆, folic acid, C, D, and E has been shown to be associated with cardiovascular abnormalities whereas supplementation with these vitamins has been claimed to reduce cardiovascular risk for hypertension, atherosclerosis, myocardial ischemia, arrhythmias, and heart failure. However, the data from several experimental and clinical studies for the pathogenesis of cardiovascular disease due to vitamin deficiency as well as therapy due to different vitamins are conflicting. In this article, we have attempted to review the existing literature on the role of different vitamins in cardiovascular disease with respect to their deficiency and supplementation in addition to examining some issues regarding their involvement in heart disease. Although both epidemiological and observational studies have shown some merit in the use of different antioxidant vitamins for the treatment of cardiovascular disorders, the results are not conclusive. Furthermore, in view of the complexities in the mechanisms of different cardiovascular disorders, no apparent involvement of any particular vitamin was seen in any specific cardiovascular disease. On the other hand, we have reviewed the evidence that deficiency of vitamin B₆ promoted KCl-induced Ca²⁺ entry and reduced ATP-induced Ca²⁺-entry in cardiomyocytes in addition to decreasing sarcolemmal (SL) ATP binding. The active metabolite of vitamin B₆, pyridoxal 5′-phosphate, attenuated arrhythmias due to myocardial infarction (MI) as well as cardiac dysfunction and defects in the sarcoplasmic reticulum (SR) Ca²⁺-transport in the ischemic-reperfused hearts. These observations indicate that both deficiency of some vitamins as well as pretreatments with different vitamins showing antioxidant activity affect cardiac function, metabolism and cation transport, and support the view that antioxidant vitamins or their metabolites may be involved in the prevention rather than the therapy of cardiovascular disease.

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.

Catecholamine response to exercise in patients with non-obstructive hypertrophic cardiomyopathy

KEY POINTS

Intense physical activity, a potent stimulus for sympathetic nervous system activation, is thought to increase the risk of malignant ventricular arrhythmias among patients with hypertrophic cardiomyopathy (HCM). As a result, the majority of patients with HCM deliberately reduce their habitual physical activity after diagnosis and this lifestyle change puts them at risk for sequelae of a sedentary lifestyle: weight gain, hypertension, hyperlipidaemia, insulin resistance, coronary artery disease, and increased morbidity and mortality. We show that plasma catecholamine levels remain stably low at exercise intensities below the ventilatory threshold, a parameter that can be defined during cardiopulmonary exercise testing, but rise rapidly at higher intensities of exercise. These findings suggest that cardiopulmonary exercise testing may be a useful tool to provide an individualized moderate-intensity exercise prescription for patients with HCM.

ABSTRACT

Intense physical activity, a potent stimulus for sympathetic nervous system activation, is thought to increase the risk of malignant ventricular arrhythmias among patients with hypertrophic cardiomyopathy (HCM). However, the impact of exercise intensity on plasma catecholamine levels among HCM patients has not been rigorously defined. We conducted a prospective observational case-control study of men with non-obstructive HCM and age-matched controls. Laboratory-based cardiopulmonary exercise testing coupled with serial phlebotomy was used to define the relationship between exercise intensity and plasma catecholamine levels. Compared to controls (C, n = 5), HCM participants (H, n = 9) demonstrated higher left ventricular mass index (115 ± 20 vs. 90 ± 16 g/m² , P = 0.03) and maximal left ventricular wall thickness (16 ± 1 vs. 8 ± 1 mm, P < 0.001) but similar body mass index, resting heart rate, peak oxygen consumption (H = 40 ± 13 vs. C = 42 ± 7 ml/kg/min, P = 0.81) and heart rate at the ventilatory threshold (H = 78 ± 6 vs. C = 78 ± 4% peak heart rate, P = 0.92). During incremental effort exercise in both groups, concentrations of adrenaline and noradrenaline were unchanged through low- and moderate-exercise intensity until reaching a catecholamine threshold (H = 82 ± 4 vs. C = 85 ± 3% peak heart rate, P = 0.86) after which levels of both molecules rose rapidly. In patients with mild non-obstructive HCM, plasma catecholamine levels remain stably low at exercise intensities below the ventilatory threshold but rise rapidly at higher intensities of exercise. Routine cardiopulmonary exercise testing may be a useful tool to provide an individualized moderate-intensity exercise prescription for patients with HCM.

Evaluating the Effect of Vitamin C on Myocardial Angiogenesis Under Oxidative Stress Induced by Exhaustive Exercise in Rat

Background: The main purpose of the present study was to assess the effects of exhaustive swimming with the consumption of a vitamin C supplement on indices of myocardial oxidative stress and gene expression related to angiogenesis. Methods: Wistar rats were randomly divided into six groups of normal (C), 100 and 200 mg/kg of vitamin C, (VC100 and VC200), exercise with 100 and 200 mg/kg of vitamin C (Ex+VC100 and Ex+VC200) and exercise without treatment (Ex). Finally, the serum activity of serum creatine phosphokinase (CK) and lactate dehydrogenase (LDH) and heart tissue oxidant/antioxidant parameters, besides gene expression of Vascular endothelial growth factor-B (VEGF-B), angiopoietin 1 (ANGPT-1) and matrix metalloproteinases 2 (MMP-2) was measured. Results: Significant increase in LDH level was seen in group Ex which was remarkably attenuated in group Ex+VC200 (p<0.001). The tissue oxidative stress was observed in group Ex where daily intake of vitamin C could remarkably regulate this property (p<0.01). Vitamin C could ameliorate significant upper gene expression of VEGF-B and MMP-2 remarkably (p<0.05). Conclusion: Oxidative condition in myocardial besides over expression of MMP-2, could be concluded as a detrimental condition resulting from exhaustive swimming that continued by the proteolytic release of CK and LDH from the muscle. Upper gene expression of VEGF-B and MMP-2 besides no changes of ANGPT-1 can be concluded as an early stage of angiogenesis. All these events were somehow attenuated by vitamin C which confirmed its beneficial effects as an antioxidant and the role of oxidation properties in the regulation of angiogenesis.

Effects of phosphodiestrase type 5 inhibitors in epinephrine-induced arrhythmia in rats: Involvement of lactate dehydrogenase and creatine kinase downregulation and adiponectin expression

Cardiac arrhythmia is a common cause of mortality, and its progression may be due to abnormal sympathetic nerve activity and catecholamine release. Besides, lactate dehydrogenase (LDH) and creatine kinase (CK) downregulation and adiponectin expression play important roles in promoting coronary artery disease. The study aimed to examine the possible cardioprotective effect of members of phosphodiesterase type 5 (PDE-5) inhibitors in epinephrine-induced arrhythmia in rats. Arrhythmia was induced by cumulative boluses of epinephrine (4, 8, 16, 32, 64, and 128 mg/kg) given at 10-min intervals. Rats were randomly allocated into five groups. Group I: Normal control group received only saline. Group II: Rats injected with epinephrine and served as arrhythmia group. Groups III, IV, and V: Rats received daily oral sildenafil (0.5 mg/kg), vardenafil (3 mg/kg), and tadalafil (10 mg/kg), respectively, for 30 days prior to epinephrine injections. Injection of epinephrine to rats decreased heart rate and QTc interval but increased RR interval and duration of arrhythmia. Epinephrine group had lower serum reduced glutathione (GSH) and adiponectin levels and higher serum malondialdehyde (MDA), nitric oxide (NO), heart LDH, and CK contents. Histopathological investigations of epinephrine group provoked necrotic changes with strong positive immunoreactivity for caspases-3. While pretreatment of rats with PDE-5 inhibitors improved GSH and adiponectin contents, ameliorated serum MDA and NO levels and heart LDH and CK contents and corrected epinephrine-induced histopathological changes. PDE-5 inhibitors may delay epinephrine-induced arrhythmia through expression of adiponectin and downregulation of heart LDH and CK.

Pharmacogenomic and clinical data link non-pharmacokinetic metabolic dysregulation to drug side effect pathogenesis

Drug side effects cause a significant clinical and economic burden. However, mechanisms of drug action underlying side effect pathogenesis remain largely unknown. Here, we integrate pharmacogenomic and clinical data with a human metabolic network and find that non-pharmacokinetic metabolic pathways dysregulated by drugs are linked to the development of side effects. We show such dysregulated metabolic pathways contain genes with sequence variants affecting side effect incidence, play established roles in pathophysiology, have significantly altered activity in corresponding diseases, are susceptible to metabolic inhibitors and are effective targets for therapeutic nutrient supplementation. Our results indicate that metabolic dysregulation represents a common mechanism underlying side effect pathogenesis that is distinct from the role of metabolism in drug clearance. We suggest that elucidating the relationships between the cellular response to drugs, genetic variation of patients and cell metabolism may help managing side effects by personalizing drug prescriptions and nutritional intervention strategies.