Doxycycline Ameliorates Vascular Endothelial and Contractile Dysfunction in the Thoracic Aorta of Diabetic Rats

Studies have shown that tetracycline class antibiotics exhibit an ameliorating action with its antioxidant property on increased oxidative stress in tissues, including heart. Since endothelial vascular dysfunction in diabetes is associated with increased oxidative stress and prevented with antioxidants, herein, we aimed to test a hypothesis whether a low-dose doxycycline treatment of diabetic rats for 4 weeks can ameliorate endothelial vascular dysfunction of thoracic aortas. Results of the present study shows that both direct and alpha receptor-mediated contractile responses as well as endothelium-dependent and endothelium-independent vasodilatory responses were preserved with low-dose doxycycline treatment (30 μmol/kg, daily; for 4 weeks) compared with untreated diabetic group. Furthermore, doxycycline treatment normalized increased lipid peroxidation and cellular glutathione level measured in plasma and prevented diabetes-induced impaired body weight gain without significant effect on high blood glucose level. Increased membrane protein level of caveolin-1, elevated ratio of PKC in particulate and cytosolic fraction, and increased protein level of cytosolic endothelin-1 in diabetic rats were also significantly prevented with doxycycline treatment. Moreover, diabetes-induced another type of oxidative stress markers in rats, matrix metalloproteinases, MMP-2, and MMP-9 were also normalized with doxycycline treatment in blood. Taken together, our data address that amelioration and/or prevention of vascular endothelial and contractile dysfunction by doxycycline is accompanied by a clear reduction in oxidative stress markers of diabetes, which provides evidence for doxycycline’s potential antioxidant action as a therapeutic agent for amelioration and/or prevention of vascular disorders in diabetic subjects.     

The influence of diabetes on cardiac β-adrenoceptor subtypes

Despite the significant developments in the treatment of diabetes mellitus, diabetic patients still continue to suffer from cardiac complications. The increase of cardiac adrenergic drive may ultimately contribute to the development and progression of diabetic cardiomyopathy. β-Adrenoceptors play an important role in the regulation of heart function. However, responsiveness of diabetic heart to β-adrenoceptor agonist stimulation is diminished. The chronotropic responses mediated by β₁-subtype, which is mainly responsible for cardiac effects of catecholamines are decreased in the atria of diabetic rats. The expression of cardiac β₁-subtype is significantly decreased in diabetic rats as well. β₂-Adrenoceptors also increase cardiac function. Although the expression of this subtype is slightly decreased in diabetic rat hearts, β₂-mediated chronotropic responses are preserved. On the other hand, functional β₃-adrenoceptor subtype was characterized in human heart. Interestingly, stimulation of cardiac β₃-adrenoceptors, on the contrary of β₁- and β₂-subtypes, mediates negative inotropic effect in human ventricular muscle. Cardiac β₃-adrenoceptors are upregulated in experimental diabetes as well as in human heart failure. These findings suggest that each β-adrenoceptor subtype may play an important role in the pathophysiology of diabetes-induced heart disease. However, it is still not known whether the changes in the expression and/or responsiveness of β-adrenoceptors are adaptive or maladaptive. Therefore, this review outlines the potential roles of these receptor subtypes in cardiac pathologies of diabetes.     

Protective Role of Antioxidants in Diabetes-Induced Cardiac Dysfunction

Cardiac dysfunction occurs during type 1 and type 2 diabetes and results from multiple parameters including glucotoxicity, lipotoxicity, fibrosis and mitochondrial uncoupling. Oxidative stress arises from an imbalance between the production of ROS and the biological system’s ability to readily detoxify the reactive intermediates. It is involved in the etiology of diabetes-induced downregulation of heart function. Several studies have reported beneficial effects of a therapy with antioxidant agents, including trace elements and other antioxidants, against the cardiovascular system consequences of diabetes. Antioxidants act through one of three mechanisms to prevent oxidant-induced cell damages. They can reduce the generation of ROS, scavenge ROS, or interfere with ROS-induced alterations. Modulating mitochondrial activity is an important possibility to control ROS production. Hence, the use of PPARα agonist to reduce fatty acid oxidation and of trace elements such as zinc and selenium as antioxidants, and physical exercise to induce mitochondrial adaptation, contribute to the prevention of diabetes-induced cardiac dysfunction. The paradigm that inhibiting the overproduction of superoxides and peroxides would prevent cardiac dysfunction in diabetes has been difficult to verify using conventional antioxidants like vitamin E. That led to use of catalytic antioxidants such as SOD/CAT mimetics. Moreover, increases in ROS trigger a cascade of pathological events, including activation of MMPs, PPARs and protein O-GlcNAcation. Multiple tools have been developed to counteract these alterations. Hence, well-tuned, balanced and responsive antioxidant defense systems are vital for proper prevention against diabetic damage. This review aims to summarize our present knowledge on various strategies to control oxidative stress and antagonize cardiac dysfunction during diabetes.     

Oxidative Stress and Diabetic Kidney Disease

The number of people with diabetic kidney disease continues to increase worldwide despite current treatments. Of the pathophysiologic mechanisms that have been identified in the development and progression of diabetic nephropathy, oxidative stress (more accurately described as increased levels of reactive oxygen species; ROS) is of major importance. The increase in ROS is due to both increased production and to decreased and/or inadequate antioxidant function. To date, human clinical trials with antioxidants have not been shown to be effective. This is likely due, at least in part, to the lack of specificity of current agents. Recent research has determined both major sources of high glucose–induced cellular ROS production as well as high glucose–induced changes in antioxidant function. Treatments targeted at one or more of the specific diabetes-induced alterations in the regulation of ROS levels will likely lead to effective treatments that prevent the development and progression of diabetic kidney disease.     

Cardiac-specific overexpression of catalase prevents diabetes-induced pathological changes by inhibiting NF-κB signaling activation in the heart

Catalase is an antioxidant enzyme that specifically catabolizes hydrogen peroxide (H₂O₂). Overexpression of catalase via a heart-specific promoter (CAT-TG) was reported to reduce diabetes-induced accumulation of reactive oxygen species (ROS) and further prevent diabetes-induced pathological abnormalities, including cardiac structural derangement and left ventricular abnormity in mice. However, the mechanism by which catalase overexpression protects heart function remains unclear. This study found that activation of a ROS-dependent NF-κB signaling pathway was downregulated in hearts of diabetic mice overexpressing catalase. In addition, catalase overexpression inhibited the significant increase in nitration levels of key enzymes involved in energy metabolism, including α-oxoglutarate dehydrogenase E1 component (α-KGD) and ATP synthase α and β subunits (ATP-α and ATP-β). To assess the effects of the NF-κB pathway activation on heart function, Bay11-7082, an inhibitor of the NF-κB signaling pathway, was injected into diabetic mice, protecting mice against the development of cardiac damage and increased nitrative modifications of key enzymes involved in energy metabolism. In conclusion, these findings demonstrated that catalase protects mouse hearts against diabetic cardiomyopathy, partially by suppressing NF-κB-dependent inflammatory responses and associated protein nitration.     

Anti-inflammatory effects of atorvastatin improve left ventricular function in experimental diabetic cardiomyopathy

Aims/hypothesis Emerging evidence suggests that statins exert beneficial effects beyond those predicted by their cholesterol-lowering actions. We investigated whether atorvastatin influences the development of left ventricular (LV) dysfunction, independently of cholesterol-lowering, in an experimental model of type 1 diabetes mellitus cardiomyopathy. Methods Streptozotocin-induced diabetic rats were treated with atorvastatin (50 mg/kg daily, orally) or with vehicle for 6 weeks. LV function was analysed using tip-catheter measurements. Cardiac stainings of TNF-α, IL-1β, intercellular adhesion molecule-1, vascular cellular adhesion molecule-1, CD11a/lymphocyte-associated antigen-1, CD11b/macrophage antigen alpha, CD18/β2-integrin, ED1/CD68, collagen I and III, and Sirius Red were assessed by digital image analysis. Ras-related C3 botulinum toxin substrate (RAC1) and ras homologue gene family, member A (RHOA) activities were determined by RAC1 glutathione-S-transferase–p21-activated kinase and rhotekin pull-down assays, respectively. Cardiac lipid peroxides were measured by a colorimetric assay. The phosphorylation state of p38 mitogen-activated protein kinase (MAPK) and endothelial nitric oxide synthase (eNOS) protein production were analysed by western blot. Results Diabetes was associated with induced cardiac stainings of TNF-α, IL-1β, cellular adhesion molecules, increased leucocyte infiltration, macrophage residence and cardiac collagen content. In contrast, atorvastatin reduced both intramyocardial inflammation and myocardial fibrosis, resulting in improved LV function. This effect was paralleled with a normalisation of diabetes-induced RAC1 and RHOA activity, in the absence of LDL-cholesterol lowering. In addition, atorvastatin decreased diabetes-induced cardiac lipid peroxide levels and p38 MAPK phosphorylation by 1.3-fold (p < 0.05) and 3.2-fold (p < 0.0005), respectively, and normalised the reduced eNOS production caused by diabetes. Conclusions/interpretation These data indicate that atorvastatin, independently of its LDL-cholesterol-lowering capacity, reduces intramyocardial inflammation and myocardial fibrosis, resulting in improved LV function in an experimental model of diabetic cardiomyopathy.     

Diabetes mellitus abrogates erythropoietin-induced cardioprotection against ischemic-reperfusion injury by alteration of the RISK/GSK-3β signaling

Recent studies reported cardioprotective effects of erythropoietin (EPO) against ischemia–reperfusion (I/R) injury through activation of the reperfusion injury salvage kinase (RISK) pathway. As RISK has been reported to be impaired in diabetes and insulin resistance syndrome, we examined whether EPO-induced cardioprotection was maintained in rat models of type 1 diabetes and insulin resistance syndrome. Isolated hearts were obtained from three rat cohorts: healthy controls, streptozotocin (STZ)-induced diabetes, and high-fat diet (HFD)-induced insulin resistance syndrome. All hearts underwent 25 min ischemia and 30 min or 120 min reperfusion. They were assigned to receive either no intervention or a single dose of EPO at the onset of reperfusion. In hearts from healthy controls, EPO decreased infarct size (14.36 ± 0.60 and 36.22 ± 4.20% of left ventricle in EPO-treated and untreated hearts, respectively, p < 0.05) and increased phosphorylated forms of Akt, ERK1/2, and their downstream target GSK-3β. In hearts from STZ-induced diabetic rats, EPO did not decrease infarct size (32.05 ± 2.38 and 31.88 ± 1.87% in EPO-treated and untreated diabetic rat hearts, respectively, NS) nor did it increase phosphorylation of Akt, ERK1/2, and GSK-3β. In contrast, in hearts from HFD-induced insulin resistance rats, EPO decreased infarct size (18.66 ± 1.99 and 34.62 ± 3.41% in EPO-treated and untreated HFD rat hearts, respectively, p < 0.05) and increased phosphorylation of Akt, ERK1/2, and GSK-3β. Administration of GSK-3β inhibitor SB216763 was cardioprotective in healthy and diabetic hearts. STZ-induced diabetes abolished EPO-induced cardioprotection against I/R injury through a disruption of upstream signaling of GSK-3β. In conclusion, direct inhibition of GSK-3β may provide an alternative strategy to protect diabetic hearts against I/R injury.     

Insulin-like growth factor I (IGF-1) supplementation prevents diabetesinduced alterations in coenzymes Q<Subscript>9</Subscript> and Q<Subscript>10</Subscript>

Diabetes, which causes enhanced oxidative stress, is a multifactorial disease that leads to deleterious effects in many organ systems within the body. Ubiquinones (coenzyme Q₉ and Q₁₀) are amphipathic molecular components of the electron transport chain that function also as endogenous antioxidants and attenuate the diabetes-induced decreases in antioxidant defense mechanisms. Insulin-like growth factor 1 (IGF-1) is considered to be an “essential surviving factor”, the level and function of which are compromised in diabetes. This study investigated the impact of IGF-1 supplementation on ubiquinone levels in a rat model of type I diabetes. Adult male Sprague-Dawley rats were divided into four groups: control, control plus IGF-1, diabetic and diabetic plus IGF-1. Diabetic animals received a single intravenous injection of streptozotocin (STZ, 55 mg/kg). IGF-1 supplementation groups received a daily intraperitoneal dose of 3 mg IGF-1 per kilogram body weight for 7 weeks. Coenzyme Q₉ and Q₁₀ levels were assessed by ultraviolet detection on high pressure liquid chromatography. STZ caused a significant reduction in body weight and an elevation in blood glucose level, which were not prevented by IGF-1 supplementation. In addition Q₉ and Q₁₀ levels in diabetic liver were significantly elevated. IGF-1 supplementation prevented liver alterations in Q₁₀ but not Q₉ levels. Q₉ and Q₁₀ levels in diabetic kidney were significantly depressed, and these deleterious effects were abolished by IGF-1 treatment. These data suggest that IGF-1 antagonizes the diabetes-induced alterations in endogenous antioxidants including coenzyme Q₁₀, and hence may have a therapeutic role in diabetes. Received: 28 March 2002 / Accepted in revised form: 5 December 2002 Correspondence to J. Ren     

Tumor necrosis factor-alpha antagonism protects from myocardial inflammation and fibrosis in experimental diabetic cardiomyopathy

To investigate the effect of anti-cytokine-based therapy in the course of diabetic cardiomyopathy, we performed a study using an anti-TNF-α monoclonal antibody treatment (mab) in Sprague male Dawley (SD) rats with streptozotocin-induced diabetic cardiomyopathy. Five days after streptozotocin injection, rats were treated with the anti-TNF-α mAb C432A for 6 weeks.At the end of the study, left ventricular (LV) function was determined by a pressure-catheter. Intercellular adhesion molecule (ICAM)-1, vascular adhesion molecule (VCAM)-1, β2-lymphocyte-integrins⁺ (CD18⁺, CD11a⁺, CD11b⁺), ED1/CD68⁺ and cytokine (TNF-α, interleukin (IL)-1β)- expressing infiltrates, total collagen content and stainings of collagen I and III were quantified by digital image analysis. LV phosphorylated and total ERK protein levels were determined by Western Blot. TNFα-antagonism reduced ICAM-1- and VCAM-1 expression and leukocyte infiltration to levels of non-diabetics and decreased macrophage residence by 3.3-fold compared with untreated diabetics. In addition, anti-TNF-α mAb-treatment decreased diabetes-induced cardiac TNF-α and IL-1β expression by 2.0-fold and 1.8- fold, respectively, and reduced the ratio of phosphorylated to total ERK by 2.7-fold. The reduction in intramyocardial inflammation was associated with a 5.4-fold and 3.6-fold reduction in cardiac collagen I and III content, respectively. This was reflected by a normalization of cardiac total collagen content to levels of non-diabetics and associated with an improved LV function. TNFα-antagonism attenuates the development of experimental diabetic cardiomyopathy associated with a reduction of intramyocardial inflammation and cardiac fibrosis.     

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

BACKGROUND: 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. METHODS: Diabetes was induced in Sprague-Dawley rats by an intravenous injection of streptozotocin (60 mg/kg). After 10 weeks of treadmill running, exogenous myocardial glucose utilization and cardiac function were determined in isolated working hearts perfused under aerobic conditions and then subjected to a 60-min period of low-flow ischemia followed by reperfusion. RESULTS: Compared to aerobically perfused sedentary control hearts, rates of myocardial glucose oxidation and glycolysis were lower in diabetic hearts. Diabetes was also characterized by a pronounced decrease in cardiac function. Following exercise training, rates of myocardial glucose oxidation and glycolysis were restored and cardiac performance was improved compared to sedentary diabetic hearts. During low-flow ischemia, the decrease in glycolysis observed in hearts of sedentary diabetic rats was attenuated following exercise training. Following ischemia, glucose oxidation and glycolysis returned to preischemic levels in all groups. However, hearts from trained diabetic animals had higher rates of glucose oxidation compared to their respective sedentary group. This was accompanied by an enhanced recovery of heart function following ischemia. CONCLUSIONS: Our results indicate that exercise training is effective in preventing the depression in myocardial glucose metabolism observed in the diabetic rat. This may explain the benefits of exercise in preventing cardiac dysfunction in diabetes.     

Myocardial performance and metabolism in non-ketotic,diabetic rat hearts: myocardial function and metabolism in vivo and in the isolated perfused heart under the influence of insulin and octanoate

Summary The influence of a non-ketonic, chronically diabetic state (60 mg/kg streptozotocin) on cardiac function and metabolism was studied under in vivo conditions by inserting a Millar-tip catheter into the left ventricle and in the model of the isolated perfused heart.In vivo heart rate and maximal left ventricular systolic pressure were reduced after a diabetes duration of 4 and 12 weeks. The maximal rise and fall in left ventricular pressure progressively declined with the duration of diabetes. The reduced myocardial function was associated with a loss in ATP and adenine nucleotides.In the perfused heart of chronically diabetic rats, heart function was also impaired and could not be restored in vitro by perfusion with glucose and insulin. In the presence of octanoate — a substrate which can be metabolized independently from insulin — heart function of diabetic rats was improved, but remained lowered as compared to controls. Since the content of myocardial creatine phosphate was reduced in diabetic hearts perfused with octanoate, these findings indicate that the suppression of cardiac performance is not only a result of an impaired glucose metabolism, but of a more general defect in energy provision and utilization.In contrast to hearts of acutely diabetic, ketotic rats most often used, the rate of lipolysis of endogenous triglycerides and the contribution of fatty acids to energy production was low in the chronically diabetic state. Inhibition of fatty acid oxidation by an inhibitor of carnitine palmitoyltransferase (CPTI) did not restore the reduced responsiveness of diabetic hearts to insulin.Analysis of intracardiac metabolites revealed that in the perfused heart of chronically diabetic rats glucose-6-phosphate and citrate do not accumulate as in hearts of ketotic, diabetic rats. Therefore, the impaired glucose metabolism presumably reflects a reduced uptake of glucose rather than in inhibition of glucolysis as in hearts of ketotic, diabetic rats.     

Diabetes-induced changes in lens antioxidant status, glucose utilization and energy metabolism: effect of DL-α-lipoic acid

Summary The study was aimed at evaluating changes in lens antioxidant status, glucose utilization, redox state of free cytosolic NAD(P)-couples and adenine nucleotides in rats with 6-week streptozotocin-induced diabetes, and to assess a possibility of preventing them by dl-α-lipoic acid. Rats were divided into control and diabetic groups treated with and without dl-α-lipoic acid (100 mg · kg body weight^–1· day^–1, i. p.). The concentrations of glucose, sorbitol, fructose, myo-inositol, oxidized glutathione, glycolytic intermediates, malate, α-glycerophosphate, and adenine nucleotides were assayed in individual lenses spectrofluorometrically by enzymatic methods, reduced glutathione and ascorbate – colorimetrically, and taurine by HPLC. Free cytosolic NAD⁺:NADH and NADP⁺:NADPH ratios were calculated from the lactate dehydrogenase and malic enzyme systems. Sorbitol pathway metabolites were found to increase, and antioxidant concentrations were reduced in diabetic rats compared with controls. The profile of glycolytic intermediates (increase in glucose 6-phosphate and fructose 6-phosphate, decrease in fructose1,6-diphosphate, increase in dihydroxyacetone phosphate, 3-phosphoglycerate, phosphoenolpyruvate, pyruvate, and no change in lactate), and 5.9-fold increase in α-glycerophosphate suggest diabetes-induced inhibition of glycolysis. Free cytosolic NAD⁺:NADH ratios, ATP levels, ATP/ADP × inorganic phosphate (P_i), and adenylate charge were reduced in diabetic rats while free cytosolic NADP⁺:NADPH ratios were elevated. Diabetes-induced changes in the concentrations of antioxidants, key glycolytic intermediates, free cytosolic NAD⁺:NADH ratios, and energy status were partially prevented by dl-α-lipoic acid, while sorbitol pathway metabolites and free cytosolic NADP⁺:NADPH ratios remained unaffected. In conclusion, diabetes-induced impairment of lens antioxidative defense, glucose intermediary metabolism via glycolysis, energy status and redox changes are partially prevented by dl-α-lipoic acid. The findings support the important role of oxidative stress in lens metabolic imbalances in diabetes. [Diabetologia (1998) 41: 1442–1450] Received: 10 November 1997 and in final revised form: 5 June 1998     

Influence of streptozotocin- and alloxan-induced diabetes on the metabolism of glycosaminoglycans

Summary GAG metabolism was investigated in rats with experimentally induced diabetes. In comparison to control animals, the uptake of³⁵S-sulfate was diminished in tissues of diabetic animals. Streptozotocin-induced diabetes showed a significant decrease in the content of GAG fractions except that of non-sulfated GAG in liver and kidney which was unchanged as compared to the control group. In rats rendered diabetic by alloxan, non-sulfated GAG increased appreciably in liver and kidney whereas highly sulfated GAG remained unchanged. In the skins of alloxan-diabetic rats both total and sulfated GAG decreased significantly. The activities of liver β-glucuronidase, β-N-acetyl glucosaminidase and cathepsin D were significantly increased in rats treated with streptozotocin and alloxan. In streptozotocin-diabetic rats, renal β-glucuronidase and β-N-acetyl glucosaminidase activities were reduced while cathepsin D activity was similar to that of controls. The renal β-N-acetyl glucosaminidase and cathepsin D activities of alloxantreated rats were not significantly different from normal but their β-glucuronidase was significantly increased. In the spleen of streptozotocin-diabetic rats all the enzymes were increased except β-N-acetyl glucosaminidase which remained unaltered. Increased excretion of uronic acid was observed in diabetic groups. These results collectively indicate that both streptozotocin- and alloxan-induced diabetes altered the synthesis and catabolism of GAG.     

Reactive oxygen species mediate a cellular ‘memory’ of high glucose stress signalling

Aims/hypothesis A long-term ‘memory’ of hyperglycaemic stress, even when glycaemia is normalised, has been previously reported in endothelial cells. In this report we sought to duplicate and extend this finding. Materials and methods HUVECs and ARPE-19 retinal cells were incubated in 5 or in 30 mmol/l glucose for 3 weeks or subjected to 1 week of normal glucose after being exposed for 2 weeks to continuous high glucose. HUVECs were also treated in this last condition with several antioxidants. Similarly, four groups of rats were studied for 3 weeks: (1) normal rats; (2) diabetic rats not treated with insulin; (3) diabetic rats treated with insulin during the last week; and (4) diabetic rats treated with insulin plus α-lipoic acid in the last week. Results In human endothelial cells and ARPE-19 retinal cells in culture, as well as in the retina of diabetic rats, levels of the following markers of high glucose stress remained induced for 1 week after levels of glucose had normalised: protein kinase C-β, NAD(P)H oxidase subunit p47phox, BCL-2-associated X protein, 3-nitrotyrosine, fibronectin, poly(ADP-ribose) Blockade of reactive species using different approaches, i.e. the mitochondrial antioxidant α-lipoic acid, overexpression of uncoupling protein 2, oxypurinol, apocynin and the poly(ADP-ribose) polymerase inhibitor PJ34, interrupted the induction both of high glucose stress markers and of the fluorescent reactive oxygen species (ROS) probe CM-H₂DCFDA in human endothelial cells. Similar results were obtained in the retina of diabetic rats with α-lipoic acid added to the last week of normalised glucose. Conclusions/interpretation These results provide proof-of-principle of a ROS-mediated cellular persistence of vascular stress after glucose normalisation.     

Carvedilol improved diabetic rat cardiac function depending on antioxidant ability

The risk for cardiovascular disease is significantly high in diabetes mellitus. Oxidative stress plays a dominant role in the pathogenesis of diabetes mellitus. Bcl-2 gene has a close connection with antagonizing oxidative stress destroy in many diseases including diabetes. Carvedilol, an adrenoceptor blocker, also has antioxidant and free radical scavenger properties. To study the effect of carvedilol on the antioxidant status and expression of Bcl-2 in healthy and diabetic hearts, we investigated carvedilol-administrated healthy and streptozotocin-induced diabetic rats. After small and large dosage (1 or 10mg/kg/d) carvedilol-administrated for 5 weeks, hemodynamic parameters, the levels of malondialdehyde (MDA), the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and expression of Bcl-2 mRNA in the cardiac tissues of all six groups were measured. Diabetic rats had higher left ventricular end diastolic pressure (LVEDP), lower maximal rate of rise/fall left ventricle pressure development and decline (+/-dP/dtmax). These parameters were improved by administration of carvedilol. Diabetic rats showed elevated MDA level and CAT activity, but lower activities of SOD and GSH-Px. Carvedilol treatment increased activities of antioxidant enzymes and expression of Bcl-2 in healthy rats as well as diabetic rats. These results indicate that carvedilol improves cardiac function via its antioxidant property in diabetic rats partly.     

Epinephrine and the Metabolic Syndrome

Epinephrine is the prototypical stress hormone. Its stimulation of all α and β adrenergic receptors elicits short-term systolic hypertension, hyperglycemia, and other aspects of the metabolic syndrome. Acute epinephrine infusion increases cardiac output and induces insulin resistance, but removal of the adrenal medulla has no consistent effect on blood pressure. Epinephrine is the most effective endogenous agonist at the β2 receptor. Transgenic mice that cannot make epinephrine and mice that lack the β2 receptor become hypertensive during exercise, presumably owing to the absence of β2-mediated vasodilatation. Epinephrine-deficient mice also have cardiac remodeling and poor cardiac responses to stress, but do not develop resting hypertension. Mice that cannot make epinephrine have a normal metabolism on a regular 14% fat diet but become hyperglycemic and insulin resistant when they eat a high fat diet. Vigorous exercise prevents diabetes in young mice and humans that overeat. However, exercise is a less effective treatment in older type 2 human diabetics and had no effect on glucose or insulin responses in older, diabetic mice. Sensitivity of the β2 receptor falls sharply with advancing age, and adrenal epinephrine release also decreases. However, treatment of older diabetic mice with a β2 adrenergic agonist improved insulin sensitivity, indicating that β2 subsensitivity can be overcome pharmacologically. Recent studies show that over the long term, epinephrine prevents hypertension during stress and improves glucose tolerance. The hyperglycemic influence of epinephrine is short-lived. Chronic administration of epinephrine and other β2 agonists improves cellular glucose uptake and metabolism. Overall, epinephrine counteracts the metabolic syndrome.     

Effect of dietary supplementation with the pyridoindole antioxidant stobadine on antioxidant state and ultrastructure of diabetic rat myocardium

Consistent with the postulated role of oxidative stress in the etiology of late diabetic complications, pharmacological interventions based on biological antioxidants have been suggested. The aim of the present study was to investigate the effect of dietary supplementation with the pyridoindole antioxidant stobadine on the myocardial antioxidant status and ultrastructure of streptozotocin-diabetic rats. Diabetic male Wistar rats were fed for 32 weeks a standard diet or a diet supplemented with stobadine (0.05% w/w). Control rats received a standard diet or stobadine-supplemented diet (0.16% w/w). Plasma levels of glucose, cholesterol and triglycerides were increased significantly by diabetes. Activities of superoxide dismutase and catalase were markedly elevated in the diabetic myocardium. Myocardial levels of conjugated dienes increased after eight months of diabetes, in spite of significantly increased myocardial α-tocopherol and coenzyme Q₉ content. The long-term treatment of diabetic animals with stobadine (i) reduced plasma cholesterol and triglyceride levels yet left the severe hyperglycemia unaffected, (ii) reduced oxidative damage of myocardial tissue as measured by conjugated dienes, (iii) reversed myocardial levels of α-tocopherol and coenzyme Q₉ to near control values, (iv) reduced elevated activity of superoxide dismutase in the diabetic myocardium, and (v) attenuated angiopathic and atherogenic processes in the myocardium as assessed by electron microscopy examination. These results are in accordance with the postulated prooxidant role of chronic hyperglycemia and provide further evidence that development of pathological changes in diabetic myocardium is amenable to pharmacological intervention by biological antioxidants. Received: 7 June 2000 / Accepted in revised form: 27 November 2000     

Effects of gender difference on cardiac myocyte dysfunction in streptozotocin-induced diabetic rats

The main characteristics of type 1 diabetic cardiomyopathy include depressed contractility and altered electrophysiological properties in ventricular myocytes. The goal of the present study was to determine the potential influence of gender in the diabetes-induced pathogenesis of ventricular myocyte function. Diabetes in both male and female rats was induced by a single intravenous injection of streptozotocin (STZ). Diabetic rats exhibited hyperglycemia and reduced body weight gain in both male and female groups. Neither contractile profiles nor activity of three types of K+ channels of ventricular myocytes was significantly different between nondiabetic male and female rats. Ventricular myocytes isolated from diabetic rats exhibited significant depression in cell contraction and relaxation, which was associated with depression of intracellular Ca2+ ([Ca2+]i) transient. The degrees of contractile depression were comparable in ventricular myocytes obtained from both male and female diabetic rats. Similarly, diabetes depressed three types of outward K+ currents (Ito, Ik, and Iss) to the same extent in both gender myocytes. These data demonstrate that in this animal model of diabetes, gender difference in cardiac myocyte functions was eliminated.     

Pharmacological Stimulation of β <Subscript>2</Subscript>-adrenergic Receptors (β <Subscript>2</Subscript>AR) Enhances Therapeutic Effectiveness of β <Subscript>1</Subscript>AR Blockade in Rodent Dilated Ischemic Cardiomyopathy

Background. We have reported that β ₂ adrenoreceptor (β ₂AR) stimulation is anti-apoptotic, and has strong beneficial effect on cardiac remodeling in an experimental model of post myocardial infarction chronic heart failure (CHF) in rats. Here we investigate whether the addition of chronic pharmacological β ₂AR stimulation enhances the therapeutic effects of β ₁AR blockade on cardiac remodeling in the same model. Methods and Results. Metoprolol, a β ₁AR blocker, given alone (β ₁) or in combination with β ₂AR agonist, fenoterol (β ₁β ₂) were administered to rats via drinking water for 6 weeks, beginning 2 weeks following permanent coronary ligation. Progressive left ventricular (LV) remodeling of untreated animals, assessed by repeated echocardiography, occurred during the observation time, i.e., 42% and 25% increases in end-systolic and end-diastolic LV volumes respectively, 27% fall in ejection fraction, and 35% infarct expansion. Pressure-volume loop analyses at 2d and 8th post infarction weeks showed continuous deterioration of systolic and diastolic functions and arterio-ventricular mismatch. Histological evaluation at the end of 8 weeks revealed the MI expansion and hypertrophy of cardiomyocytes. β ₁β ₂ prevented LV remodeling, MI expansion and cardiomyocytes hypertrophy to a greater degree than β ₁, due, in large part, to a vasodilatory effect of β ₂AR stimulation and thus improvement of arterio-ventricular mismatch. The abnormal diastolic performance improved only in β ₁β ₂. β ₁β ₂ treatment reduced myocardial apoptosis throughout myocardium, but β ₁ reduced apoptopsis only in the areas remote from MI. Conclusion. The therapeutic effects of chronic β ₁AR blockade on cardiac remodeling of heart failure are enhanced and extended when supplemented with β ₂AR stimulation. This research was supported by the Intramural Research Program of the National Institute on Aging, NIH.     

Effects of Ginkgo biloba extract and preconditioning on the diabetic rat myocardium

Summary Effects of preconditioning and Ginkgo biloba extract (EGb 761) were studied in isolated non-diabetic and diabetic ischaemic and re-perfused rat hearts. Hearts were randomly divided into five groups in both the age-matched non-diabetic and the 8-week streptozotocin-induced diabetic groups: Group I, hearts were subjected to 30 min of global ischaemia followed by 30 min of re-perfusion; Group II, one cycle of preconditioning consisting of 5 min ischaemia and 10 min re-perfusion before the induction of 30 min of ischaemia and 30 min of re-perfusion; Group III, two cycles of preconditioning; Group IV, three cycles; and Group V, four cycles before the onset of 30 min ischaemia followed by 30 min of re-perfusion. Four cycles of ischaemic preconditioning resulted in a reduction of arrhythmias in non-diabetic rats. Thus, in non-diabetics, the incidence of ventricular fibrillation and tachycardia fell from 92 % and 100 % (no preconditioning) to 33 % (p < 0.05) and 42 % (p < 0.05), respectively. Four cycles of preconditioning failed to reduce the incidence of re-perfusion arrhythmias in diabetic subjects. Preconditioning reduced the formation of oxygen free radicals measured by electron spin resonance spectroscopy, but the recovery of cardiac function was low in all non-diabetic and diabetic preconditioned groups. EGb 761 at 25 and 50 mg/kg improved cardiac function in non-preconditioned and preconditioned non-diabetic and diabetic hearts. During re-perfusion in the four-cycle preconditioned non-diabetic and diabetic groups, the amount of free radicals was reduced approximately by 50 and 70 % using 25 and 50 mg/kg of EGb 761, respectively. EGb 761 improved cardiac function after ischaemia in both non-preconditioned and preconditioned non-diabetic and diabetic rats. Our data suggest that diabetes could abolish the precondition-induced protection. [Diabetologia (1996) 39: 1255–1262] Received: 28 March 1996 and in revised form: 3 June 1996