Exercise and possible molecular mechanisms of protection from vascular disease and diabetes: the central role of ROS and nitric oxide

Detailed mechanistic investigation into the S-nitrosation of cysteamine

The nitrosation of cysteamine (H₂NCH₂CH₂SH) to produce cysteamine-S-nitrosothiol (CANO) was studied in slightly acidic medium by using nitrous acid prepared in situ. The stoichiometry of the reaction was H₂NCH₂CH₂SH + HNO₂ → H₂NCH₂CH₂SNO + H₂O. On prolonged standing, the nitrosothiol decomposed quantitatively to yield the disulfide, cystamine: 2H₂NCH₂CH₂SNO → H₂NCH₂CH₂S-SCH₂CH₂NH₂ + 2NO. NO₂ and N₂O₃ are not the primary nitrosating agents, since their precursor (NO) was not detected during the nitrosation process. The reaction is first order in nitrous acid, thus implicating it as the major nitrosating agent in mildly acidic pH conditions. Acid catalyzes nitrosation after nitrous acid has saturated, implicating the protonated nitrous acid species, the nitrosonium cation (NO⁺) as a contributing nitrosating species in highly acidic environments. The acid catalysis at constant nitrous acid concentrations suggests that the nitrosonium cation nitrosates at a much higher rate than nitrous acid. Bimolecular rate constants for the nitrosation of cysteamine by nitrous acid and by the nitrosonium cation were deduced to be 17.9 ± 1.5 (mol/L)^-1 s^-1 and 6.7 × 10⁴ (mol/L)^-1 s^-1, respectively. Both Cu(I) and Cu(II) ions were effective catalysts for the formation and decomposition of the cysteamine nitrosothiol. Cu(II) ions could catalyze the nitrosation of cysteamine in neutral conditions, whereas Cu(I) could only catalyze in acidic conditions. Transnitrosation kinetics of CANO with glutathione showed the formation of cystamine and the mixed disulfide with no formation of oxidized glutathione (GSSG). The nitrosation reaction was satisfactorily simulated by a simple reaction scheme involving eight reactions.

Persistence of inflammatory response to intense exercise in diabetic rats

In this study we evaluated the onset and resolution of inflammation in control and streptozotocin-induced diabetic rats subjected to a single session of intense exercise. The following measurements were carried out prior to, immediately after, and 2 and 24 hours after exercise: plasma levels of proinflammatory cytokines (TNF-α, IL-1β, IL-6, CINC-2α/β, MIP-3α, and IL-6), immunoglobulins (IgA and IgM), acute phase proteins (CRP and C3), and creatine kinase (CK) activity. We also examined the occurrence of macrophage death by measurements of macrophages necrosis (loss of membrane integrity) and DNA fragmentation. An increase was observed in the concentration of IL-1β (3.3-fold) and TNF-α (2.0-fold) and in the proportion of necrotic macrophages (4.5-fold) in diabetic rats 24 hours after exercise, while the control group showed basal measurements. Twenty-four hours after the exercise, serum CK activity was elevated in diabetic rats but not in control animals. We concluded that lesion and inflammations resulting from intense exercise were greater and lasted longer in diabetic animals than in nondiabetic control rats.

Effects of L-arginine supplementation on blood flow, oxidative stress status and exercise responses in young adults with uncomplicated type I diabetes

BACKGROUND AND AIMS

Vascular disease is the principal cause of death and disability in patients with diabetes, and endothelial dysfunction seems to be the major cause in its pathogenesis. Since L-arginine levels are diminished in conditions such as type 1 and type 2 diabetes, in this work we aimed to verify the effects of L-arginine supplementation (7 g/day) over the endothelial function and oxidative stress markers in young male adults with uncomplicated type 1 diabetes. We also investigated the influences of L-arginine administration on vascular/oxidative stress responses to an acute bout of exercise.

METHODS

Ten young adult male subjects with uncomplicated type 1 diabetes and twenty matched controls volunteered for this study. We analysed the influence of L-arginine supplementation (7 g/day during 1 week) over lower limb blood flow (using a venous occlusion plethysmography technique), oxidative stress marker (TBARS, Carbonyls), anti-oxidant parameters (uric acid and TRAP) and total tNOx in rest conditions and after a single bout of submaximal exercise (VO₂ at 10 % below the second ventilatory threshold). Data described as mean ± standard error (SE). Alpha level was P < 0.05.

RESULTS

Glycaemic control parameters were altered in type 1 diabetic subjects, such as HbA1c (5.5 ± 0.03 vs. 8.3 ± 0.4 %) and fasted glycaemia (94.8 ± 1.4 vs. 183 ± 19 mg/dL). Oxidative stress/damage markers (carbonyls and TBARS) were increased in the diabetic group, while uric acid was decreased. Rest lower limb blood flow was lower in type 1 diabetic subjects than in healthy controls (3.53 ± 0.35 vs. 2.66 ± 0.3 ml 100 ml⁻¹ min⁻¹). L-Arginine supplementation completely recovered basal blood flow to normal levels in type 1 diabetics' subjects (2.66 ± 0.3 to 4.74 ± 0.86 ml 100 ml⁻¹ min⁻¹) but did not interfere in any parameter of redox state or exercise.

CONCLUSION

Our findings highlight the importance of L-arginine for the improvement of vascular function in subjects with diabetes, indicating that L-arginine supplementation could be an essential tool for the treatment for the disease complications, at least in non-complicated diabetes. However, based on our data, it is not possible to draw conclusions regarding the mechanisms by which L-arginine therapy is inducing improvements on cardiovascular function, but this important issue requires further investigations.

Reactive oxygen and nitrogen species generation, antioxidant defenses, and β-cell function: a critical role for amino acids

Growing evidence indicates that the regulation of intracellular reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels is essential for maintaining normal β-cell glucose responsiveness. While long-term exposure to high glucose induces oxidative stress in β cells, conflicting results have been published regarding the impact of ROS on acute glucose exposure and their role in glucose stimulated insulin secretion (GSIS). Although β cells are considered to be particularly vulnerable to oxidative damage, as they express relatively low levels of some peroxide-metabolizing enzymes such as catalase and glutathione (GSH) peroxidase, other less known GSH-based antioxidant systems are expressed in β cells at higher levels. Herein, we discuss the key mechanisms of ROS/RNS production and their physiological function in pancreatic β cells. We also hypothesize that specific interactions between RNS and ROS may be the cause of the vulnerability of pancreatic β cells to oxidative damage. In addition, using a hypothetical metabolic model based on the data available in the literature, we emphasize the importance of amino acid availability for GSH synthesis and for the maintenance of β-cell function and viability during periods of metabolic disturbance before the clinical onset of diabetes.

The effect of different training programs on antioxidant status, oxidative stress, and metabolic control in type 2 diabetes

We compared the effects of 12 weeks of 3 different exercise types on type 2 diabetic (T2DM) male and female human subjects, randomly divided into 4 groups: aerobic training (AT; n = 11), strength training (ST; n = 10), combined training (CBT; n = 10), and no training (NT; n = 12). Metabolic control, anthropometric parameters, lipid and hematological profiles, kidney and liver function markers, hormones, antioxidant enzymes, and oxidative stress markers were assessed prior to and after the training programs. At baseline, fasting blood glucose and hemoglobin A(1c) in the ST group were higher than in the NT group; after the training, we no longer observed differences in these groups, suggesting an improvement on these parameters. In the AT group, catalase and superoxide dismutase activity, nitrite concentration, levels of sulfhydryl groups, and peak rate of oxygen consumption were elevated after the training (p < 0.05). No changes were observed in antioxidant enzymes or oxidative stress markers in the ST group. The levels of sulfhydryl groups diminished in the NT group (p < 0.01) and increased in the CBT group (p < 0.05). These data demonstrate that the AT program for the T2DM subjects provided important upregulation in antioxidant enzymes and increased nitric oxide bioavailability, which may help minimize oxidative stress and the development of the chronic complications of diabetes. We propose that the beneficial effects observed in the metabolic parameters of the ST group occurred in response to the poor baseline metabolic health n this group, and not necessarily in response to the training itself.

Exercise training improves the defective centrally mediated erectile responses in rats with type I diabetes

INTRODUCTION

Erectile dysfunction is a serious and common complication of diabetes mellitus. Apart from the peripheral actions, central mechanisms are also responsible for the penile erection.

AIM

The goal of the present study was to determine the impact of exercise training (ExT) on the centrally mediated erectile dysfunction in streptozotocin (STZ)-induced type I diabetic (T1D) rats.

METHODS

Male Sprague-Dawley rats were injected with STZ to induce diabetes mellitus. Three weeks after STZ or vehicle injections, rats were assigned to either ExT (treadmill running for 3-4 weeks) or sedentary groups to produce four experimental groups: control + sedentary, T1D + sedentary, control + ExT, and T1D + ExT.

MAIN OUTCOME MEASURE

After 3-4 weeks ExT, central N-methyl-D-aspartic acid (NMDA) or sodium nitroprusside (SNP)-induced penile erectile responses were measured. Neuronal nitric oxide synthase (nNOS) expression in the paraventricular nucleus (PVN) of the hypothalamus was measured by using histochemistry, real time polymerase chain reaction (PCR) and Western blot approaches.

RESULTS

In rats with T1D, ExT significantly improved the blunted erectile response, and the intracavernous pressure changes to NMDA (50 ng) microinjection within the PVN (T1D + ExT: 3.0 ± 0.6 penile erection/rat; T1D + sedentary: 0.5 ± 0.3 penile erection/rat within 20 minutes, P < 0.05). ExT improved erectile dysfunction induced by central administration of exogenous nitric oxide (NO) donor, SNP in T1D rats. Other behavior responses including yawning and stretching, induced by central NMDA and SNP microinjection were also significantly increased in T1D rats after ExT. Furthermore, we found that ExT restored the nNOS mRNA and protein expression in the PVN in T1D rats.

CONCLUSIONS

These results suggest that ExT may have beneficial effects on the erectile dysfunction in diabetes through improvement of NO bioavailability within the PVN. Thus, ExT may be used as therapeutic modality to up-regulate nNOS within the PVN and improve the central component of the erectile dysfunction in diabetes mellitus.

L-arginine is essential for pancreatic β-cell functional integrity, metabolism and defense from inflammatory challenge

In this work, our aim was to determine whether L-arginine (a known insulinotropic amino acid) can promote a shift of β-cell intermediary metabolism favoring glutathione (GSH) and glutathione disulfide (GSSG) antioxidant responses, stimulus-secretion coupling and functional integrity. Clonal BRIN-BD11 β-cells and mouse islets were cultured for 24 h at various L-arginine concentrations (0-1.15  mmol/l) in the absence or presence of a proinflammatory cytokine cocktail (interleukin 1β, tumour necrosis factor α and interferon γ). Cells were assessed for viability, insulin secretion, GSH, GSSG, glutamate, nitric oxide (NO), superoxide, urea, lactate and for the consumption of glucose and glutamine. Protein levels of NO synthase-2, AMP-activated protein kinase (AMPK) and the heat shock protein 72 (HSP72) were also evaluated. We found that L-arginine at 1.15  mmol/l attenuated the loss of β-cell viability observed in the presence of proinflammatory cytokines. L-arginine increased total cellular GSH and glutamate levels but reduced the GSSG/GSH ratio and glutamate release. The amino acid stimulated glucose consumption in the presence of cytokines while also stimulating AMPK phosphorylation and HSP72 expression. Proinflammatory cytokines reduced, by at least 50%, chronic (24 h) insulin secretion, an effect partially attenuated by L-arginine. Acute insulin secretion was robustly stimulated by L-arginine but this effect was abolished in the presence of cytokines. We conclude that L-arginine can stimulate β-cell insulin secretion, antioxidant and protective responses, enabling increased functional integrity of β-cells and islets in the presence of proinflammatory cytokines. Glucose consumption and intermediary metabolism were increased by L-arginine. These results highlight the importance of L-arginine availability for β-cells during inflammatory challenge.

High-carbohydrate high-fat diet–induced metabolic syndrome and cardiovascular remodeling in rats

The prevalence of metabolic syndrome including central obesity, insulin resistance, impaired glucose tolerance, hypertension, and dyslipidemia is increasing. Development of adequate therapy for metabolic syndrome requires an animal model that mimics the human disease state. Therefore, we have characterized the metabolic, cardiovascular, hepatic, renal, and pancreatic changes in male Wistar rats (8-9 weeks old) fed on a high-carbohydrate, high-fat diet including condensed milk (39.5%), beef tallow (20%), and fructose (17.5%) together with 25% fructose in drinking water; control rats were fed a cornstarch diet. During 16 weeks on this diet, rats showed progressive increases in body weight, energy intake, abdominal fat deposition, and abdominal circumference along with impaired glucose tolerance, dyslipidemia, hyperinsulinemia, and increased plasma leptin and malondialdehyde concentrations. Cardiovascular signs included increased systolic blood pressure and endothelial dysfunction together with inflammation, fibrosis, hypertrophy, increased stiffness, and delayed repolarization in the left ventricle of the heart. The liver showed increased wet weight, fat deposition, inflammation, and fibrosis with increased plasma activity of liver enzymes. The kidneys showed inflammation and fibrosis, whereas the pancreas showed increased islet size. In comparison with other models of diabetes and obesity, this diet-induced model more closely mimics the changes observed in human metabolic syndrome.

Progressive hyperglycemia across the glucose tolerance continuum in older obese adults is related to skeletal muscle capillarization and nitric oxide bioavailability

CONTEXT

Reduced tissue nutrient exposure may aid in the progression of glucose intolerance.

OBJECTIVE

The aim of the study was to examine peripheral tissue glucose disposal in relation to muscle capillarization and plasma nitric oxide bioavailability.

DESIGN

Participants were carefully matched for age, adiposity, and lipid status and stratified into normal (n = 20), impaired (n = 20), and type 2 diabetic (n = 20) glucose-tolerant groups.

SETTING

The study was conducted in an outpatient setting at a Clinical Research Unit.

PARTICIPANTS

Older, obese men and women (n = 60; age, 65 ± 1 yr; body mass index, 32.7 ± 0.5 kg/m(2)) participated in the study.

INTERVENTION

We performed a cross-sectional study.

MAIN OUTCOME MEASURES

Body composition, energy metabolism, aerobic fitness (maximum oxygen consumption), insulin sensitivity (glucose clamp), vastus lateralis muscle morphology, and plasma nitric oxide were assessed.

RESULTS

Although subjects were identical with respect to age, body composition, energy expenditure, and lipid status, insulin-stimulated glucose disposal and maximum oxygen consumption showed progressive decline with increasing glucose intolerance. Muscle fiber type composition and mitochondrial density were not different between groups. However, capillary density markedly declined with advancing glucose intolerance (1.86 ± 0.31, 1.70 ± 0.28, 1.42 ± 0.24 capillary/fiber; P < 0.05), a trend that was mirrored by fasting plasma nitric oxide concentrations (26.3 ± 3.6, 19.8 ± 2.3, 15.2 ± 2.1 μmol/liter; P < 0.05). Furthermore, skeletal muscle capillary density correlated with insulin sensitivity (r = 0.65; P < 0.001).

CONCLUSIONS

Impaired muscle capillarization and reduced nutrient exposure to the metabolizing tissue may play a major role in the progression of insulin resistance across the glucose tolerance continuum, independent of age, adiposity, lipid status, and resting energy metabolism. These data also highlight plasma nitric oxide as a potential surrogate marker of these impairments and may be indicative of the progression toward type 2 diabetes.

[Physical activity and endothelial dysfunction in type 2 diabetic patients: the role of nitric oxide and oxidative stress]

Type 2 diabetic patients have an increased level of systemic free radicals, which severely restrict the bioavailability of endothelium-derived nitric oxide (NO) and thus contribute to the development of an endothelial dysfunction. This review analyses the influence of physical training on molecular development mechanisms of the endothelial dysfunction and determines the significance of regular physical exercise for the endothelial function in type 2 diabetic patients. Systematic training reinforces the endogenic antioxidative capacity and results in a reduction in oxidative stress. Training - also combined with a change in diet - furthermore reduces hyperglycaemic blood sugar levels, thus curbing a major source of free radicals in diabetes. Moreover, physical exercise enhances vascular NO synthesis through an increased availability/activity of endothelial NO synthases (eNOS). Endurance, as well as resistance training with submaximal intensity or a combination of both forms of training is suitable to effectively improve the endothelial function in type 2 diabetic patients in the long term.

Extracellular heat shock proteins (eHSP70) in exercise: Possible targets outside the immune system and their role for neurodegenerative disorders treatment

The intracellular heat shock protein 70kDa (iHSP70) is a universal marker of stress protein whose expression is induced by different cell stressors, such as heat, metabolite deprivation, redox imbalances and also during physical exercise. The activation of the iHSP70 is sine qua non for the promotion of tissue repair, since the expression of this chaperone confers cytoprotection and also exerts anti-inflammatory effects. On the other hand, exercise also induces the appearance of HSP70 in the extracellular medium (eHSP70) but, so far, the eHSP70 function has been mainly attributed to the activation of the immune system, seeming to perform an opposite function from the iHSP70. Since a moderate intensity exercise bout induces a general anti-inflammatory response even in the presence of an elevated eHSP70, this protein could carry out other functions rather than immune activation. Because exercise generates heat and metabolic challenges (especially on glucose metabolism) we suggests that the motoneurons, a very active (possibly one of the most stressed cells during exercise) and also very sensitive cells to heat and glucose metabolism imbalances, could be the major sites for the eHSP70 function. Due to the importance of the iHSP70 for repair and stress adaptation, this protein must be present in abundance on the site of stress and, because of its intrinsic inability response to stress [low heat shock factor 1 (HSF-1) activation] and the structure of the motoneurons (very long cells), the iHSP70, produced on the very far nucleus, is not appropriately transported through the axon to the axon terminal, were it is required. Then, during the exercise, the released eHSP70 can be internalized by the motoneurons and act as intracellular chaperons, protecting this cell against oxidative damage, protein denaturation and many others. Since a decreased iHSP70 expression capacity is associated with neurodegeneration diseases (such as Parkinson, polyglutamine, Amyotrophic lateral sclerosis, Alzheimer's, Huntington's and many others), the understanding of the physiological function of the extracellular HSP70 could be helpful on the treatment of neurodegenerative and other neuronal diseases. Besides that, it could explain some of the beneficial effects of the pharmacological HSP70 activators and also the beneficial effects of the exercise among neuronal cells during neurodegenerative-inducing diseases.