Tom L. Broderick

Neuroprotective effects of resveratrol in Alzheimer disease pathology

Alzheimer’s disease is a chronic neurodegenerative disorder characterized by a progressive loss of cognitive and behavioral abilities. Extracellular senile plaques and intracellular neurofibrillary tangles are hallmarks of AD. Researchers aim to analyze the molecular mechanisms underlying AD pathogenesis; however, the therapeutic options available to treat this disease are inadequate. In the past few years, several studies have reported interesting insights about the neuroprotective properties of the polyphenolic compound resveratrol (3, 5, 4′-trihydroxy-trans-stilbene) when used with in vitro and in vivo models of AD. The aim of this review is to focus on the neuroprotective and antioxidant effects of resveratrol on AD and its multiple potential mechanisms of action. In addition, because the naturally occurring forms of resveratrol have a very limited half-life in plasma, a description of potential analogs aimed at increasing the bioavailability in plasma is also discussed.

Exercise training restores abnormal myocardial glucose utilization and cardiac function in diabetes

Clinical and experimental studies have shown that a reduction in myocardial glucose utilization is a factor contributing to diabetic cardiomyopathy. This study determined whether exercise training could prevent the depression in glucose utilization observed in the diabetic rat heart.

Prior meal enhances the plasma glucose lowering effect of exercise in type 2 diabetes

PURPOSE To compare the changes in plasma glucose and insulin levels in response to 1 h of exercise performed at 60% of VO(2peak) either in the fasted state or 2 h after a standardized breakfast in subjects with type 2 diabetes. METHODS Ten sedentary men with type 2 diabetes treated with oral agents and not under strict metabolic control were tested on two occasions (fasted and fed state) in a random order at a 1-wk interval. RESULTS Plasma glucose was slightly but not significantly higher at the beginning of exercise performed in the fed state versus the fasted state (12.4 +/- 1.3 vs 11.1 +/- 1.1 mmol x L(-1) respectively; mean +/- SE, P = 0.06). However, after exercise, plasma glucose levels were much lower in the fed state (7.6 +/- 1.1 mmol x L(-1)) compared with the fasted state (10.0 +/- 1.0 mmol x L(-1); P = 0.009). Insulin levels were higher at the beginning of the exercise bout performed in the fed state (177 +/- 26 vs 108 +/- 19 pmol x L(-1); P < 0.05) and during exercise. Similar respiratory exchange ratio at identical workload indicated that the difference in glycemic response was not due to differences in whole body substrate utilization. Plasma concentrations of free fatty acids, glucagon, epinephrine, and norepinephrine were also similar during both experiments. CONCLUSIONS One hour of aerobic exercise has a minimal impact on plasma glucose level when performed in fasted moderately hyperglycemic men with type 2 diabetes but induces an important decrease in plasma glucose level when performed 2 h after breakfast. Because glucose utilization increased similarly during exercise in both conditions, the higher insulin levels after the meal might have blunted glucose production, creating an imbalance between total glucose production and total peripheral utilization in the fed state in contrast to the fasted state.

Effects of Glucagon-Like Peptide-1 and Long-Acting Analogues on Cardiovascular and Metabolic Function

Although the insulinotropic role of glucagon-like peptide-1 (GLP-1) in type 2 diabetes mellitus has been substantiated, its role in cardioprotection remains largely unknown. To ascertain the role of the cardiovascular actions of GLP-1 in health and disease states necessitates a review of the current evidence as well as ongoing investigation. Of cardiovascular significance, both positive inotropic and chronotropic effects, unmodifiable by gB-adrenergic blockers, have been reportedly attributed to GLP-1 actions on the myocardium. However, the potent role of GLP-1 and its analogues in eliciting tachycardic and pressor effects should be of some concern. Aside from its reported insulinotropic activity, GLP-1 impacts the myocardium directly. Highly specific GLP-1 receptors have been identified in the heart and within the central nervous system, particularly in the nucleus tractus solitarius, a neuromodulatory centre of cardiovascular control. The occurrence of GLP-1 receptors in cardiac tissue and autonomic regions of cardiovascular control has stimulated investigation, particularly as these sites may be suitable targets for the pharmacological action of GLP-1 and long-acting analogues. Discordance on the haemodynamic consequences of GLP-1 pharmacotherapy in experimental animals and human patients has been reported in the literature. However, longterm pharmacological doses of GLP-1 have shown prolonged and beneficial actions on cardiovascular homeostasis in the adjuvant treatment of metabolic disease.

Caloric restriction restores the cardioprotective effect of preconditioning in the rat heart.

Preconditioning (PC) describes the observation that brief periods of ischemia paradoxically protect the heart and limit necrosis caused by a subsequent more prolonged period of ischemia. However, the PC response is attenuated in hearts from 9- to 12-month-old Sprague-Dawley rats, as compared to young adults. This study determined whether long-term caloric restriction (CR) could preserve the PC response, since CR increases ischemic tolerance in these hearts. Following 6 months of CR, isolated hearts underwent PC followed by ischemia and reperfusion. In contrast to control hearts in which PC response was attenuated, PC in CR hearts was clearly of benefit. In these hearts, aortic flow was increased resulting in a dramatic improvement of cardiac output. Our study suggests that CR is effective in preserving the PC response.

l-Carnitine improvement of cardiac function is associated with a stimulation in glucose but not fatty acid metabolism in carnitine-deficient hearts

OBJECTIVES Increasing myocardial carnitine content can improve heart function in patients with carnitine deficiency. We were interested in determining the effects of L-carnitine on cardiac function and substrate metabolism in a rat model of carnitine deficiency. METHODS Carnitine deficiency was induced in male Sprague-Dawley rats by supplementing the drinking water with 20 mM sodium pivalate. Control animals received an equimolar concentration of sodium bicarbonate. Following treatment, cardiac function and myocardial substrate utilization were determined in isolated working hearts perfused with glucose and relevant levels of fatty acids. To increase tissue levels of carnitine, hearts were perfused with 5 mM L-carnitine for a period of 60 min. RESULTS Hearts from sodium pivalate-treated animals demonstrated a 60% reduction in total heart carnitine content, depressions in cardiac function and rates of palmitate oxidation, and elevated rates of glycolysis compared to control hearts. Treatment with L-carnitine increased total carnitine content and reversed the depression in cardiac function seen in carnitine-deficient hearts. However, this was not associated with any improvement in palmitate oxidation. Rates of glycolysis and glucose oxidation, on the other hand, were increased with L-carnitine. CONCLUSIONS Our findings indicate that acute L-carnitine treatment is of benefit to cardiac function in this model of secondary carnitine deficiency by increasing overall glucose utilization rather than normalizing fatty acid metabolism.

Downregulation of oxytocin and natriuretic peptides in diabetes: possible implications in cardiomyopathy

Regular physical activity is beneficial in preventing the risk of cardiovascular complications of diabetes. Recent studies showed a cardioprotective role of oxytocin (OT) to induce natriuretic peptides (NPs) and nitric oxide (NO) release. It is not known if the diabetic state is associated with a reduced OT–NPs–NO system and if exercise training improves this system. To address this, we investigated the effects of treadmill running using the db/db mouse model of type 2 diabetes. Eight‐week‐old db/db mice were subjected to running 5 days per week for a period of 8 weeks. The lean db/+ littermates were used as controls. Sedentary db/db mice were obese and hyperglycaemic, and exercise training was not effective in reducing body weight and the hyperglycaemic state. Compared to control mice, db/db mice had lower heart weight and heart‐to‐body weight ratios. In these mice, this was associated with augmented cardiac apoptosis, cardiomyocyte enlargement and collagen deposits. In addition, db/db mice displayed significant downregulation in gene expression of OT (76%), OT receptors (65%), atrial NP (ANP; 43%), brain NP (BNP; 87%) and endothelial nitric oxide synthase (eNOS) (54%) in the heart (P < 0.05). Exercise training had no effect on expression of these genes which were stimulated in control mice. In response to exercise training, the significant increment of anti‐apoptotic Bcl‐2 gene expression was observed only in control mice (P < 0.05). In conclusion, downregulation of the OT–NPs–NO system occurs in the heart of the young db/db mouse. Exercise training was not effective in reversing the defect, suggesting impairment of this cardiac protective system in diabetes.

Effects of chronic caloric restriction on mitochondrial respiration in the ischemic reperfused rat heart

Dietary restriction increases life span and delays the development of age-related diseases in rodents. We have recently demonstrated that chronic dietary restriction is beneficial on recovery of heart function following ischemia. We studied whether the metabolic basis of this benefit is associated with alterations in mitochondrial respiration. Male Wistar rats were assigned to an ad libitum-fed (AL) group and a food restricted (FR) group, in which food intake was reduced to 55% of the amount consumed by the AL group. Following an 8-month period of restricted caloric intake, isolated working hearts perfused with glucose and high levels of fatty acids were subjected to global ischemia followed by reperfusion. At the end of reperfusion, total heart mitochondria was respiration was assessed in the presence of pyruvate, tricarboxylic acid intermediates, and palmitoylcarnitine. Recovery of heart function following ischemia was greater in FR hearts compared to AL hearts. Paralleling these changes in heart function was in increase in state 3 respiration with pyruvate. The respiratory control ratios in the presence of pyruvate and tricarboxylic acid intermediates were higher in FR hearts compared to AL hearts, indicating well-coupled mitochondria. Overall energy production, expressed as the ADP:O ratio and the oxidative phosphorylation rate, was also improved in FR hearts. Our results indicate that the beneficial effect of FR on recovery of heart function following ischemia is associated with changes in mitochondrial respiration.

Fatty Acid Oxidation and Cardiac Function in the Sodium Pivalate Model of Secondary Carnitine Deficiency

Carnitine-deficiency syndromes are often associated with alterations in lipid metabolism and cardiac function. The present study was designed to determine whether this is also seen in an experimental model of carnitine deficiency. Carnitine deficiency was induced in male Sprague-Dawley rats supplemented with sodium pivalate for 26 to 28 weeks. This treatment resulted in nearly a 60% depletion of myocardial total carnitine content as compared with control hearts. When isolated working hearts from these animals were perfused with 5.5 mmol/L glucose and 1.2 mmol/L palmitate and subjected to incremental increases in left-atrial filling pressures, cardiac function remained dramatically depressed. The effects of carnitine deficiency on glucose and palmitate utilization were also assessed in hearts perfused at increased workload conditions. At this workload, function was depressed in carnitine-deficient hearts, as were rates of 1.2-mmol/L [U-14C]-palmitate oxidation, when compared with control hearts (544 +/- 37 vs 882 +/- 87 nmol/g dry weight.min, P < .05). However, glucose oxidation rates from 5.5 mmol/L [U-14C]-glucose were slightly increased in carnitine-deficient hearts. To determine whether the depressed fatty acid oxidation rates were a result of reduced mechanical function in carnitine-deficient hearts, the workload of hearts was reduced. Under these conditions, mechanical function was similar among control and carnitine-deficient hearts. Palmitate oxidation rates were also similar in these hearts (526 +/- 69 v 404 +/- 47 nmol/g dry weight.min for control and carnitine-deficient hearts, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Safety and magnitude of changes in blood glucose levels following exercise performed in the fasted and the postprandial state in men with type 2 diabetes

Background Information on the extent to which acute exercise reduces blood glucose levels (BGL) in type 2 diabetes is lacking. For this reason, the effects of exercise initiated at different preexercise BGL were assessed in men with type 2 diabetes both in the fasted (FS) and the postprandial states (PS). Design and methods Forty-three men with type 2 diabetes, 12 on diet alone and 31 on hypoglycaemic agents, completed a total of 1555 exercise sessions performed in the FS and 0-1, 1-2, 2-3, 3-4, 4-5, and 5-8 h in the PS. Capillary BGL were measured before and immediately after a 1h standardized aerobic exercise session on an ergocycle at 60% of Vo2 peak. Results In the FS, there was an increase in postexercise BGL of 27 ± 21% (mean±SD; P < 0.001) when preexercise BGL was ≤ 6 mmol/l, no change when preexercise BGL were between 6 and 8 mmol/l, and a significant decrease of 12 ± 13% when preexercise BGL were >8 mmol/l (P < 0.001). In the PS, most exercise sessions were associated with significant decreases in BGL ranging between 18 ± 17 and 50 ± 12% (P < 0.001), depending on the time interval between meals and the onset of exercise. Regarding the metabolic PS, the decline in BGL was most pronounced with high preexercise BGL. Conclusions Our observations not only demonstrate that it was safe for middle-aged obese men with type 2 diabetes to exercise in the FS, but also show that the decrease in BGL during aerobic exercise was largely dependent on preexercise BGL. Eur J Cardiovasc Prev Rehabil 14: 831-836