Superoxide dismutase entrapped-liposomes restore the impaired endothelium-dependent relaxation of resistance arteries in experimental diabetes

Vascular endothelial dysfunction, a major mediator in diabetic cardiomyopathy

Diabetes mellitus is currently a major public health problem. A common complication of diabetes is cardiac dysfunction, which is recognized as a microvascular disease that leads to morbidity and mortality in diabetic patients. While ischemic events are commonly observed in diabetic patients, the risk for developing heart failure is also increased, independent of the severity of coronary artery disease and hypertension. This diabetes-associated clinical entity is considered a distinct disease process referred to as "diabetic cardiomyopathy". However, it is not clear how diabetes promotes cardiac dysfunction. Vascular endothelial dysfunction is thought to be one of the key risk factors. The impact of diabetes on the endothelium involves several alterations, including hyperglycemia, fatty acid oxidation, reduced nitric oxide (NO), oxidative stress, inflammatory activation, and altered barrier function. The current review provides an update on mechanisms that specifically target endothelial dysfunction, which may lead to diabetic cardiomyopathy.

Diabetes mellitus and ischemic diseases: molecular mechanisms of vascular repair dysfunction

In patients with diabetes mellitus, the ability of ischemic tissue to synchronize the molecular and cellular events leading to restoration of tissue perfusion in response to the atherosclerotic occlusion of a patent artery is markedly impaired. As a consequence, adverse tissue remodeling and the extent of ischemic injury are intensified, leading to increased morbidity and mortality. Growing evidence from preclinical and clinical studies has implicated alterations in hypoxia-inducible factor 1 levels in the abrogation of proangiogenic pathways, including vascular endothelial growth factor A/phosphoinositide 3' kinase/AKT/endothelial nitric oxide synthase and in the activation of antiangiogenic signals characterized by accumulation of advanced glycation end products, reactive oxygen species overproduction, and endoplasmic reticulum stress. In addition, the diabetic milieu shows a switch toward proinflammatory antiregenerative pathways. Finally, the mobilization, subsequent recruitment, and the proangiogenic potential of the different subsets of angiogenesis-promoting bone marrow-derived cells are markedly impaired in the diabetic environment. In this review, we will give an overview of the current understanding on the signaling molecules contributing to the diabetes mellitus-induced impairment of postischemic revascularization mainly in the setting of myocardial infarction or critical limb ischemia.

Cellular and molecular mechanisms of endothelial dysfunction in diabetes

In healthy individuals, the vascular endothelium regulates an intricate balance of factors that maintain vascular homeostasis and normal arterial function. Functional disruption of the endothelium is known to be an early event that underlies the development of subsequent cardiovascular disease (CVD) including atherosclerosis and coronary heart disease. In addition, the rising global epidemic of type 2 diabetes is a significant problem conferring a significantly higher risk of CVD to individuals in whom endothelial dysfunction is also notable. This review first summarises the role of endothelium in health and explores and evaluates the impact of diabetes on endothelial function. The characteristic features of insulin resistance and other metabolic disturbances that may underlie long-term changes in vascular endothelial function (metabolic memory) are described along with proposed cellular, molecular and epigenetic mechanisms. Through understanding the underlying mechanisms, novel targets for future therapies to restore endothelial homeostasis and 'drive' a reparative cellular phenotype are explored.

Blue native/SDS-PAGE combined with iTRAQ analysis reveals advanced glycation end-product-induced changes of synaptosome proteins in C57 BL/6 mice

Evidence shows that administration of high-level D-galactose induces the production of advanced glycation end-products (AGEs) that have been implicated in the development of diabetic complications such as neuropathy. The deterioration of learning and memory during neuropathy might be associated with the altered expression of proteins in synapse. To evaluate AGE-induced protein network alterations in synapse, blue native/SDS-PAGE and iTRAQ proteomic methods were used to screen for differentially expressed synaptic proteins of cerebral cortex in D-galactose-induced C57 BL/6 mice. In total, the expression level of 84 proteins is changed during AGE accumulation. The significantly differentially expressed proteins mainly participate in neurotransmission, energy metabolism and signal transduction pathway, suggesting that energy metabolism is damaged and neurotransmission is attenuated in synapse. The results of in vivo activities of malondialdehyde and superoxide dismutase suggested that AGE accumulation in the brain leads to the generation of reactive oxygen species. Therefore, elucidating the differentially expressed proteins underlying the AGE accumulation will open a new window to the mechanism of learning and memory impairments in neuropathy.

Role of nitrosative stress in the pathogenesis of diabetic vascular dysfunction

Here we overview the role of reactive nitrogen species (nitrosative stress) and associated pathways in the pathogenesis of diabetic vascular complications. Increased extracellular glucose concentration, a principal feature of diabetes mellitus, induces a dysregulation of reactive oxygen and nitrogen generating pathways. These processes lead to a loss of the vascular endothelium to produce biologically active nitric oxide (NO), which impairs vascular relaxations. Mitochondria play a crucial role in this process: endothelial cells placed in increase extracellular glucose respond with a marked increase in mitochondrial superoxide formation. Superoxide, when combining with NO generated by the endothelial cells (produced by the endothelial isoform of NO synthase), leads to the formation of peroxynitrite, a cytotoxic oxidant. Reactive oxygen and nitrogen species trigger endothelial cell dysfunction through a multitude of mechanisms including substrate depletion and uncoupling of endothelial isoform of NO synthase. Another pathomechanism involves DNA strand breakage and activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). PARP-mediated poly(ADP-ribosyl)ation and inhibition of glyceraldehyde-3-phosphate dehydrogenase importantly contributes to the development of diabetic vascular complications: it induces activation of multiple pathways of injury including activation of nuclear factor kappa B, activation of protein kinase C and generation of intracellular advanced glycation end products. Reactive species generation and PARP play key roles in the pathogenesis of 'glucose memory' and in the development of injury in endothelial cells exposed to alternating high/low glucose concentrations.

Role of nitrosative stress in the pathogenesis of diabetic vascular dysfunction

Here we overview the role of reactive nitrogen species (nitrosative stress) and associated pathways in the pathogenesis of diabetic vascular complications. Increased extracellular glucose concentration, a principal feature of diabetes mellitus, induces a dysregulation of reactive oxygen and nitrogen generating pathways. These processes lead to a loss of the vascular endothelium to produce biologically active nitric oxide (NO), which impairs vascular relaxations. Mitochondria play a crucial role in this process: endothelial cells placed in increase extracellular glucose respond with a marked increase in mitochondrial superoxide formation. Superoxide, when combining with NO generated by the endothelial cells (produced by the endothelial isoform of NO synthase), leads to the formation of peroxynitrite, a cytotoxic oxidant. Reactive oxygen and nitrogen species trigger endothelial cell dysfunction through a multitude of mechanisms including substrate depletion and uncoupling of endothelial isoform of NO synthase. Another pathomechanism involves DNA strand breakage and activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). PARP-mediated poly(ADP-ribosyl)ation and inhibition of glyceraldehyde-3-phosphate dehydrogenase importantly contributes to the development of diabetic vascular complications: it induces activation of multiple pathways of injury including activation of nuclear factor kappa B, activation of protein kinase C and generation of intracellular advanced glycation end products. Reactive species generation and PARP play key roles in the pathogenesis of 'glucose memory' and in the development of injury in endothelial cells exposed to alternating high/low glucose concentrations.

Implications of early structural-functional changes in the endothelium for vascular disease

By location, between the blood and tissues and the multiple functions, the endothelial cells (ECs) play a major role in securing body homeostasis. The ECs sense all variations occurring in the plasma and interstitial fluid, and respond (function of intensity), initially by modulation of their constitutive functions, then by dysfunction, expressed by temporarily altered functions and a phenotypic shift, and ultimately by injury/death. In dyslipidemia/hyperglycemia, the initial response of EC is the modulation of 2 constitutive functions: permeability and biosynthesis. Increased transcytosis of plasma beta-lipoproteins leads to their accumulation within the hyperplasic basal lamina, interaction with matrix proteins, and conversion to modified and reassembled lipoproteins (MRL). This generates a multipart inflammatory process and EC dysfunction characterized by expression of new cell adhesion molecules and MCP-1 that trigger T-lymphocytes and monocyte recruitment, diapedesis, and homing within the subendothelium where activated macrophages become foam cells. The latter, together with the subendothelial accrual of MRL, growth factors, cytokines, and chemokines, and accretion of smooth muscle cells of various sources lead to atheroma formation; in advanced disease, the EC overlaying atheroma take up lipids, become EC-derived foam cells, and the cytotoxic ambient ultimately conducts to EC apoptosis. Understanding the mechanisms of EC dysfunction is a prerequisite for EC-targeted therapy to reduce the incidence of cardiovascular diseases.

Low micromolar concentrations of copper augment the impairment of endothelium-dependent relaxation of aortae from diabetic rabbits

Both diabetes mellitus (DM) and elevated plasma copper concentrations are risk factors for cardiovascular disease (CVD). DM is associated with impaired endothelial nitric oxide (NO) and with excess superoxide (O2*-) formation. Copper is also elevated in DM and is also associated with the generation of O2*-. To explore possible interactions between DM and copper, the effect of exogenous copper (CuCl2) on endothelium-dependent relaxation and cyclic guanosine monophosphate (GMP) formation was investigated in aortae from diabetic rabbits. Rabbits were rendered diabetic by intravenous injection of alloxan. Six months after induction of DM, the aortae were excised, cut into rings, and mounted in an organ bath for isometric measurement of acetylcholine (Ach)-evoked relaxation in rings precontracted with phenylephrine (PE). In parallel studies, cyclic (c)GMP formation by aortic rings following stimulation with Ach, calcium ionophore A23187 (A23187) and sodium nitroprusside (SNP) was assessed using radioimmunoassay. The effect of copper on these parameters was then studied using the same methods. Ach-evoked relaxation and Ach- and A23187-evoked cGMP formation were significantly impaired in aortae from diabetic rabbits compared to controls, effects that were reversed with superoxide dismutase (SOD) and catalase (CAT). In contrast, there were no significant differences in SNP-stimulated relaxation or cGMP formation in aortae from diabetic rabbits compared to controls. Copper (1 to 10 micromol/L) promoted a further significant inhibition of Ach-stimulated relaxation in aortae from diabetic but not control rabbits. This reduction by copper was again reversed by SOD and CAT. We conclude that copper augments the reduction of NO bioavailability, which is already impaired in aortae from diabetic rabbits due to excess production of O2*- and H2O2. These results indicate that patients with DM may be susceptible to copper-mediated vasculopathy at much lower concentrations than those that promote vasculopathy in nondiabetic patients.