Human coronary microvessels in diabetes and ischaemia. Morphometric study of autopsy material

Capillary rarefaction: a missing link in renal and cardiovascular disease?

Patients with chronic kidney disease (CKD) have an increased risk for cardiovascular morbidity and mortality. Capillary rarefaction may be both one of the causes as well as a consequence of CKD and cardiovascular disease. We reviewed the published literature on human biopsy studies and conclude that renal capillary rarefaction occurs independently of the cause of renal function decline. Moreover, glomerular hypertrophy may be an early sign of generalized endothelial dysfunction, while peritubular capillary loss occurs in advanced renal disease. Recent studies with non-invasive measurements show that capillary rarefaction is detected systemically (e.g., in the skin) in individuals with albuminuria, as sign of early CKD and/or generalized endothelial dysfunction. Decreased capillary density is found in omental fat, muscle and heart biopsies of patients with advanced CKD as well as in skin, fat, muscle, brain and heart biopsies of individuals with cardiovascular risk factors. No biopsy studies have yet been performed on capillary rarefaction in individuals with early CKD. At present it is unknown whether individuals with CKD and cardiovascular disease merely share the same risk factors for capillary rarefaction, or whether there is a causal relationship between rarefaction in renal and systemic capillaries. Further studies on renal and systemic capillary rarefaction, including their temporal relationship and underlying mechanisms are needed. This review stresses the importance of preserving and maintaining capillary integrity and homeostasis in the prevention and management of renal and cardiovascular disease.

Human dermal microvascular endothelial cell morphological response to fluid shear stress

As the cells that line the vasculature, endothelial cells are continually exposed to fluid shear stress by blood flow. Recent studies suggest that the morphological response of endothelial cells to fluid shear stress depends on the endothelial cell type. Thus, the present study characterizes the morphological response of human dermal microvascular endothelial cells (HMEC-1) and nuclei to steady, laminar, and unidirectional fluid shear stress. Cultured HMEC-1 monolayers were exposed to shear stress of 0.3 dyn/cm², 16 dyn/cm², or 32 dyn/cm² for 72 h with hourly live-cell imaging capturing both the nuclear and cellular morphology. Despite changes in elongation and alignment occurring with increasing fluid shear stress, there was a lack of elongation and alignment over time under each fluid shear stress condition. Conversely, changes in cellular and nuclear area exhibited dependence on both time and fluid shear stress magnitude. The trends in cellular morphology differed at shear stress levels above and below 16 dyn/cm², whereas the nuclear orientation was independent of fluid shear stress magnitude. These findings show the complex morphological response of HMEC-1 to fluid shear stress.

Concurrent diabetes and heart failure: interplay and novel therapeutic approaches

Diabetes mellitus increases the risk of developing heart failure, and the co-existence of both diseases worsens cardiovascular outcomes, hospitalization and the progression of heart failure. Despite current advancements on therapeutic strategies to manage hyperglycemia, the likelihood of developing diabetes-induced heart failure is still significant, especially with the accelerating global prevalence of diabetes and an ageing population. This raises the likelihood of other contributing mechanisms beyond hyperglycemia in predisposing diabetic patients to cardiovascular disease risk. There has been considerable interest in understanding the alterations in cardiac structure and function in the diabetic patients, collectively termed as "diabetic cardiomyopathy". However, the factors that contribute to the development of diabetic cardiomyopathies is not fully understood. This review summarizes the main characteristics of diabetic cardiomyopathies, and the basic mechanisms that contribute to its occurrence. This includes perturbations in insulin resistance, fuel preference, reactive oxygen species generation, inflammation, cell death pathways, neurohormonal mechanisms, advanced glycated end-products accumulation, lipotoxicity, glucotoxicity, and posttranslational modifications in the heart of the diabetic. This review also discusses the impact of antihyperglycemic therapies on the development of heart failure, as well as how current heart failure therapies influence glycemic control in diabetic patients. We also highlight the current knowledge gaps in understanding how diabetes induces heart failure.

Reduced Myocardial Perfusion Reserve in Type 2 Diabetes Is Caused by Increased Perfusion at Rest and Decreased Maximal Perfusion During Stress

OBJECTIVE

To examine differences in myocardial blood flow (MBF) at rest and during stress between patients with type 2 diabetes and control subjects, and to identify potential predictors of changes in MBF at rest and during stress.

RESEARCH DESIGN AND METHODS

A cross-sectional study was conducted of 193 patients with type 2 diabetes and 20 age- and sex-matched control subjects. Cardiovascular magnetic resonance was used to evaluate left ventricular structure and function and MBF at rest and during adenosine-induced stress. MBF was derived as the mean of the flow within all segments of a midventricular slice.

RESULTS

Patients with type 2 diabetes had higher global MBF at rest (0.81 ± 0.19 mL/min/g) and lower global MBF during stress (2.4 ± 0.9 mL/min/g) than control subjects (0.61 ± 0.11 at rest, 3.2 ± 0.8 mL/min/g under stress; both P < 0.01). Patients with macroalbuminuria had lower MBF during stress (1.6 ± 0.5 mL/min/g) than did patients with microalbuminuria (2.1 ± 0.7 mL/min/g; P = 0.04), who in turn had lower MBF during stress than did normoalbuminuric patients (2.7 ± 0.9 mL/min/g; P < 0.01). Patients with severe retinopathy had lower MBF during stress (1.8 ± 0.6 mL/min/g) than patients with simplex retinopathy (2.3 ± 0.7 mL/min/g; P < 0.05) and those who did not have retinopathy (2.6 ± 1.0 mL/min/g; P < 0.05). Albuminuria and retinopathy were associated with reduced MBF during stress in a multiple regression analysis. Stress-related MBF inversely correlated with myocardial extracellular volume (P < 0.001; R ² = 0.37), a measure of diffuse myocardial fibrosis. A trend toward lower basal MBF was observed in patients treated with sodium-glucose cotransporter 2 inhibitors (P = 0.07).

CONCLUSIONS

Patients with type 2 diabetes have higher global MBF at rest and lower maximal MBF during vasodilator-induced stress than control subjects. Reduced MBF during stress is associated with diabetes complications (albuminuria and retinopathy) and is inversely correlated with diffuse myocardial fibrosis.

Effect of Hyperglycemia on Myocardial Perfusion in Diabetic Porcine Models and Humans

BACKGROUND

Diabetes mellitus (DM) causes macro- and microvasculopathy, but data on cardiac microvascular changes in large animals are scarce. We sought to determine the effect of DM on macro- and microvascular changes in diabetic pigs and humans.

METHODS

Eight domestic pigs (4 with type I diabetes and 4 controls) underwent coronary angiography with optical coherence tomography (OCT; at baseline and 1 and 2 months), coronary computed tomography angiography, cardiac magnet resonance (CMR) imaging, and histologic examination.

RESULTS

The diabetic pigs had more irregular capillaries with acellular capillaries and a smaller capillary diameter (11.7 ± 0.33 μm vs. 13.5 ± 0.53 μm; P < 0.001) than those of the control pigs. The OCT showed no significant epicardial stenosis in either group; however diabetic pigs had a greater intima-media thickness. CMR results showed that diabetic pigs had a lower relative upslope at rest (31.3 ± 5.9 vs. 37.9 ± 8.1; P = 0.011) and during stress (18.0 ± 3.0 vs. 21.6 ± 2.8; P = 0.007) than the control pigs, implying decreased myocardial perfusion. Among the 79 patients with ST elevation myocardial infarction, 25 had diabetes and they had lower myocardial perfusion on CMR as well.

CONCLUSION

DM causes microvascular remodeling and a decrease in myocardial perfusion in large animals at a very early stage of the disease course. Early and effective interventions are necessary to interrupt the progression of vascular complications in diabetic patients.

Pathophysiological significance of hepatokine overproduction in type 2 diabetes

Currently, many studies draw attention to novel secretory factors, such as adipokines or myokines, derived from the tissues that were not originally recognized as endocrine organs. The liver may contribute to the onset of various kinds of pathologies of type 2 diabetes by way of the production of secretory proteins "hepatokines." Using the comprehensive gene expression analyses in human livers, we have rediscovered selenoprotein P and LECT2 as hepatokines involved in the onset of dysregulated glucose metabolism. Overproduction of selenoprotein P, previously reported as a transport protein of selenium, induces insulin resistance and hyperglycemia in type 2 diabetic condition. Selenoprotein P also contributes to vascular complications of type 2 diabetes directly by inducing VEGF resistance in vascular endothelial cells. Notably, selenoprotein P impairs health-promoting effects of exercise by inhibiting ROS/AMPK/PGC-1α pathway in the skeletal muscle through its receptor LRP1. Overproduction of LECT2, previously reported as a neutrophil chemotactic protein, links obesity to insulin resistance in the skeletal muscle. Further studies would develop novel diagnostic or therapeutic procedures targeting hepatokines to combat over-nutrition-related diseases such as type 2 diabetes.

Down-regulation of proangiogenic microRNA-126 and microRNA-132 are early modulators of diabetic cardiac microangiopathy

AIM

Microangiopathy due to endothelial dysfunction is a major contributing factor to the development of diabetes-induced cardiovascular disease (CVD). Dysregulation of endothelial-specific microRNAs (miRs) is correlated with impaired angiogenesis and cell survival. We investigated the profile of two angiomiRs, miR-126, and miR-132, in the plasma of type 2 diabetic individuals without any known history of CVD as well as in the cardiac tissues collected from diabetics undergoing cardiac surgery.

METHODS AND RESULTS

The presence of diabetes alone significantly decreased both angiomiRs in the plasma and the myocardium. The down-regulation of angiomiRs was also associated with reduced capillaries and arterioles and increased endothelial cell apoptosis, the hallmark of microangiopathy. Importantly, a time course study in a type 2 diabetic mouse model confirmed that the down-regulation of angiomiRs preceded endothelial apoptosis as well as alterations in the density of the microvasculature. Finally, therapeutic overexpression of both angiomiRs in diabetic aortic rings and human umbilical vein endothelial cells exposed to high glucose (HG) abrogated the deleterious effects of diabetes and HG on cell survival and proliferation and restored their angiogenic potential.

CONCLUSIONS

These novel findings demonstrate that the down-regulation of angiomiRs is a major underlying mechanism for the development of microangiopathy in diabetic hearts. Therefore, therapeutic restoration of angiomiRs could become a potential approach to combat the cardiovascular complications of diabetes.

Novel skin chamber for rat ischemic flap studies in regenerative wound repair

Background

In plastic surgery, skin flap is an important approach to reconstructive wound repairs. The rat dorsal skin flap is a clinically relevant and popular animal model to investigate and evaluate flap survival and necrosis. Nonetheless, flap survival is often unstable with unpredictable outcomes, regardless of previous attempts at design modification.

Methods & Results

In the present study, we report a novel flap chamber that provides stable and reproducible outcomes by separating the dorsal skin flap from its surrounding skin by in situ immobilization. The flap chamber blocks circulation that disturbs flap ischemia from both basal and lateral sides of the flap tissue. Demarcation of skin necrosis is macroscopically evident on the flap and supported by distinct changes in histological architecture under microscopic examination. The utility of the novel skin flap chamber is further proven by applying it to the examination of flap survival in streptozotocin-induced diabetic rats with an increase in skin necrosis. The flap chamber also affords size modifications where a narrower flap chamber increases ischemia and provides manipulable therapeutic windows for studying cell therapies. Accordingly, intradermal injection of endothelial cells 3 days before flap ischemia significantly increases the survival of skin flaps.

Conclusions

The novel flap chamber not only may stabilize the skin flap and provide reproducible outcomes that overcome the shortfalls of the traditional ischemic flap but also may afford size modifications that support research designs and test therapeutic approaches to regenerative repair.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0333-0) contains supplementary material, which is available to authorized users.

Syndecan-4 shedding impairs macrovascular angiogenesis in diabetes mellitus

PURPOSE

Syndecan-4 (synd4) is a ubiquitous heparan sulfate proteoglycan cell surface receptor that modulates cell proliferation, migration, mechanotransduction, and endocytosis. The extracellular domain of synd4 sheds heavily in acute inflammation, but the shedding of synd4 in chronic inflammation, such as diabetes mellitus (DM), is still undefined. We investigated the alterations of synd4 endothelial expression in DM and the influence of impaired synd4 signaling on angiogenesis in human umbilical vein endothelial cells (HUVECs), diabetic rats, synd4 null mice, and db/db mice.

MATERIAL AND METHODS

HUVECs were incubated with advanced glycation end products (AGEs). Western blot analysis was used to determine synd4 protein expression and ELISA was used to detect soluble synd4 fragments. The concentration of synd4 in the aortic endothelia of diabetic rats was detected by immunohistochemical staining. Aortic ring assays were performed to study the process of angiogenesis in the diabetic rats and in synd4 null and db/db mice. Recombinant adenoviruses containing the synd4 gene or null were constructed to enhance synd4 aortic expression in db/db mice.

RESULTS

Western blot analysis showed decreased expression of the synd4 extracellular domain in HUVECs, and ELISA detected increased soluble fragments of synd4 in the media. Synd4 endothelial expression in the aortas of diabetic rats was decreased. Aortic ring assay indicated impaired angiogenesis in synd4 null and db/db mice, which was partially reversed by synd4 overexpression in db/db mice.

CONCLUSION

Synd4 shedding from vascular endothelial cells played an important role in the diabetes-related impairment of angiogenesis.

Using basic fibroblast growth factor nanoliposome combined with ultrasound-introduced technology to early intervene the diabetic cardiomyopathy

Basic fibroblast growth factor (bFGF)-loaded liposome (bFGF-lip) combined with ultrasound-targeted microbubble destruction (UTMD) technique was investigated to prevent diabetic cardiomyopathy (DCM). Cardiac function and myocardial ultrastructure were assessed. Terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) staining, immunohistochemistry staining, and Western blot assay were used to investigate the signal pathway underlying the expression of bFGF in DCM treatment. From Mason staining and TUNEL staining, bFGF-lip + UTMD group showed significant differences from the diabetes group and other groups treated with bFGF or bFGF-lip. The diabetes group showed similar results (myocardial capillary density, collagen volume fraction, and cardiac myocyte apoptosis index) to other bFGF treatment groups. Indexes from transthoracic echocardiography and hemodynamic evaluation also proved the same conclusion. These results confirmed that the abnormalities including diastolic dysfunctions, myocardial fibrosis, and metabolic disturbances could be suppressed by the different extents of twice-weekly bFGF treatments for 12 consecutive weeks (free bFGF or bFGF-lip +/− UTMD), with the strongest improvements observed in the bFGF-lip + UTMD group. The group combining bFGF-lip with UTMD demonstrated the highest level of bFGF expression among all the groups. The bFGF activated the PI3K/AKT signal pathway, causing the reduction of myocardial cell apoptosis and increase of microvascular density. This strategy using bFGF-lip and UTMD is a potential strategy in early intervention of DCM in diabetes.

Effect of combined treatment with rosuvastatin and protein kinase Cβ2 inhibitor on angiogenesis following myocardial infarction in diabetic rats

The aim of the present study was to investigate the effects of combined treatment with rosuvastatin and LY333531, a selective protein kinase C (PKC)β2 inhibitor, on angiogenesis under hyperglycemic conditions. Human umbilical vein endothelial cells (HUVECs) cultured in medium containing a normal or high concentration of glucose (33.3 mmol/l) were treated with rosuvastatin (0.1 µmol/l) alone or in combination with LY333531 (10 nmol/l). HUVEC migration and tube formation were assessed. Furthermore, rats with streptozotocin-induced diabetes were randomly divided into groups and treated with either rosuvastatin alone (5 mg/kg/day) or in combination with LY333531 (10 mg/kg/day) for 4 weeks following the induction of myocardial infarction (MI). Echocardiographic patterns, the extent of myocardial fibrosis, capillary density in myocardial tissue, the phosphorylation of Akt and endothelial nitric oxide synthase (eNOS), as well as the expression levels of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor 1-α (HIF‑1α) were assessed. The results from the in vitro experiment revealed that the tube-forming and migration ability of the HUVECs exposed to high-glucose medium was significantly improved in the group treated with the combination of rosuvastatin and LY333531. In vivo, the combination of rosuvastatin and LY333531 significantly improved left ventricular function, reduced the extent of myocardial fibrosis and increased myocardial capillary density compared to treatment with rosuvastatin alone. In addition, the expression levels of VEGF, and Akt and eNOS phosphorylation were significantly higher in the group exposed to the combination treatment than in the group treated with rosuvastatin alone. The results of the present study indicate that, compared to treatment with rosuvastatin alone, combined treatment with rosuvastatin and LY333531 promotes a greater level of angiogenesis in diabetic rats with MI. This effect is likely mediated through the upregulation of the VEGF‑dependent Akt/eNOS signaling pathway.

Effect of atorvastatin on the angiogenic responsiveness of coronary endothelial cells in normal and streptozotocin (STZ) induced diabetic rats

Atorvastatin, a lipid lowering agent, possesses various pleiotropic vasculoprotective effects, but its role in coronary angiogenesis is still controversial. Our objective was to study the effects of atorvastatin on the angiogenic responsiveness of coronary endothelial cells (cEC) from normal and diabetic rats. Male Wistar rats were distributed among 9 groups; (i) normal rats, (ii) 30 day diabetic rats, (iii) 60 day diabetic rats, (iv) normal rats administered a low dose of atorvastatin (1 mg/kg body mass, per oral (p.o.), for 15 days); (v) 30 day diabetic rats administered a low dose of atorvastatin; (vi) 60 day diabetic rats administered a low dose of atorvastatin; (vii) normal rats administered a high dose of atorvastatin (5 mg/kg, p.o., for 15 days); (viii) 30 day diabetic rats administered a high dose of atorvastatin; (ix) 60 day diabetic rats administered a high dose of atorvastatin. Each group was further divided into 2 subgroups, (i) sham ischemia-reperfusion and (ii) rats hearts that underwent ischemia-reperfusion. Angiogenic responsiveness the and nitric oxide (NO) releasing properties of the subgroups of cECs were studied using a chorioallantoic membrane assay and the Griess method, respectively. Atorvastatin treatment significantly increased VEGF-induced angiogenic responsiveness and the NO-releasing properties of cECs from all of the subgroups, compared with their respective non-treated subgroups except for the late-phase diabetic rat hearts that underwent ischemia-reperfusion, and the high dose of atorvastatin treatment groups. These effects of atorvastatin were significantly inhibited by pretreatment of cECs with l-NAME, wortmannin, and chelerythrine. Thus, treatment with a low dose of atorvastatin improves the angiogenic responsiveness of the cECs from normal and diabetic rats, in the presence of VEGF, via activation of eNOS-NO release.

Selenoprotein P as a diabetes-associated hepatokine that impairs angiogenesis by inducing VEGF resistance in vascular endothelial cells

AIMS/HYPOTHESIS

Impaired angiogenesis induced by vascular endothelial growth factor (VEGF) resistance is a hallmark of vascular complications in type 2 diabetes; however, its molecular mechanism is not fully understood. We have previously identified selenoprotein P (SeP, encoded by the SEPP1 gene in humans) as a liver-derived secretory protein that induces insulin resistance. Levels of serum SeP and hepatic expression of SEPP1 are elevated in type 2 diabetes. Here, we investigated the effects of SeP on VEGF signalling and angiogenesis.

METHODS

We assessed the action of glucose on Sepp1 expression in cultured hepatocytes. We examined the actions of SeP on VEGF signalling and VEGF-induced angiogenesis in HUVECs. We assessed wound healing in mice with hepatic SeP overexpression or SeP deletion. The blood flow recovery after ischaemia was also examined by using hindlimb ischaemia model with Sepp1-heterozygous-knockout mice.

RESULTS

Treatment with glucose increased gene expression and transcriptional activity for Sepp1 in H4IIEC hepatocytes. Physiological concentrations of SeP inhibited VEGF-stimulated cell proliferation, tubule formation and migration in HUVECs. SeP suppressed VEGF-induced reactive oxygen species (ROS) generation and phosphorylation of VEGF receptor 2 (VEGFR2) and extracellular signal-regulated kinase 1/2 (ERK1/2) in HUVECs. Wound closure was impaired in the mice overexpressing Sepp1, whereas it was improved in SeP (-/-)mice. SeP (+/-)mice showed an increase in blood flow recovery and vascular endothelial cells after hindlimb ischaemia.

CONCLUSIONS/INTERPRETATION

The hepatokine SeP may be a novel therapeutic target for impaired angiogenesis in type 2 diabetes.

DPP-4 inhibition attenuates cardiac dysfunction and adverse remodeling following myocardial infarction in rats with experimental diabetes

AIMS

Following myocardial infarction (MI), individuals with diabetes have a two-fold increase in the risk of heart failure, due in part to excessive loss of cardiac microvasculature. Endothelial integrity and restitution are mediated in part by stromal cell-derived factor-1α (SDF-1α), a chemokine that is elaborated by ischemic tissue but rapidly degraded by dipeptidyl peptidase-4 (DPP-4). Accordingly, we hypothesized that inhibiting this enzyme may confer benefit following myocardial infarction in the diabetic setting beyond its effect on glycemia.

METHODS AND RESULTS

Fischer F344 rats with streptozotocin (STZ)-diabetes were randomized to receive vehicle or the DPP-4 inhibitor, sitagliptin (300 mg/kg/day). Two weeks later, animals underwent experimental MI, induced by ligation of the left anterior descending coronary artery. Cardiac function was assessed by conductance catheterization and echocardiography along with cardiac structure 4 weeks post-MI. Following MI, untreated diabetic rats developed both systolic and diastolic cardiac dysfunction, in association with endothelial cell loss, fibrosis, and myocyte hypertrophy. Without affecting plasma glucose, sitagliptin treatment led to an improvement in passive left ventricular compliance, increased endothelial cell density, reduced myocyte hypertrophy, and a reduction in the abundance of collagen 1 (all P < 0.05). Systolic function was unchanged.

CONCLUSIONS

This study shows that DPP-4 inhibition attenuates several, but not all, aspects of cardiac dysfunction and adverse remodeling in the post-MI setting.

Glycation: the angiogenic paradox in aging and age-related disorders and diseases

Angiogenesis is generally a quiescent process which, however, may be modified by different physiological and pathological conditions. The "angiogenic paradox" has been described in diabetes because this disease impairs the angiogenic response in a manner that differs depending on the organs involved and disease evolution. Aging is also associated with pro- and antiangiogenic processes. Glycation, the post-translational modification of proteins, increases with aging and the progression of diabetes. The effect of glycation on angiogenesis depends on the type of glycated proteins and cells involved. This complex link could be responsible for the "angiogenic paradox" in aging and age-related disorders and diseases. Using diabetes as a model, the present work has attempted to review the age-related angiogenic paradox, in particular the effects of glycation on angiogenesis during aging.

Prognostic meaning of coronary microvascular disease in type 2 diabetes mellitus: a transthoracic Doppler echocardiographic study

BACKGROUND

The prognostic value of Doppler-derived coronary flow velocity reserve (CFVR) of the left anterior descending coronary artery in patients with type 2 diabetes with preserved left ventricular systolic function and without flow-limiting stenoses on angiography remains undetermined.

METHODS

The study sample consisted of 144 patients with type 2 diabetes (82 men; mean age 62 ± 10 years) with chest pain or angina-equivalent symptoms, no histories of coronary artery disease, and echocardiographic ejection fractions ≥ 50%. All patients underwent dipyridamole stress echocardiography with CFVR assessment of the left anterior descending coronary artery by transthoracic Doppler echocardiography and coronary angiography showing normal coronary arteries or nonobstructive coronary artery disease.

RESULTS

Mean CFVR was 2.44 ± 0.57. On individual patient analysis, 109 patients (76%) had CFVR > 2, and 35 (24%) had CFVR ≤ 2. During a median follow-up period of 29 months (interquartile range, 14-44 months), 17 hard events (five deaths, 12 nonfatal myocardial infarctions) occurred. The annual hard-event rate was 13.9% in subjects with CFVR ≤ 2 and 2.0% in those with CFVR > 2. The annual event rate associated with CFVR ≤ 2 was significantly higher both in patients with left ventricular hypertrophy (P < .0001) and in those without left ventricular hypertrophy (P = .048). On Cox analysis, CFVR ≤ 2 (hazard ratio, 11.20; 95% confidence interval, 3.07-40.92), and male sex (hazard ratio, 7.80; 95% confidence interval, 1.74-34.97) were independent prognostic indicators, whereas nonobstructive coronary artery disease was not an independent predictor of outcomes.

CONCLUSIONS

Microvascular dysfunction before the occurrence of coronary artery involvement is a strong and independent predictor of outcomes in patients with type 2 diabetes. Vasodilator stress CFVR is a suitable tool to assess microvascular dysfunction in routine clinical practice.

Diabetic cardiomyopathy: pathophysiology and clinical features

Since diabetic cardiomyopathy was first reported four decades ago, substantial information on its pathogenesis and clinical features has accumulated. In the heart, diabetes enhances fatty acid metabolism, suppresses glucose oxidation, and modifies intracellular signaling, leading to impairments in multiple steps of excitation–contraction coupling, inefficient energy production, and increased susceptibility to ischemia/reperfusion injury. Loss of normal microvessels and remodeling of the extracellular matrix are also involved in contractile dysfunction of diabetic hearts. Use of sensitive echocardiographic techniques (tissue Doppler imaging and strain rate imaging) and magnetic resonance spectroscopy enables detection of diabetic cardiomyopathy at an early stage, and a combination of the modalities allows differentiation of this type of cardiomyopathy from other organic heart diseases. Circumstantial evidence to date indicates that diabetic cardiomyopathy is a common but frequently unrecognized pathological process in asymptomatic diabetic patients. However, a strategy for prevention or treatment of diabetic cardiomyopathy to improve its prognosis has not yet been established. Here, we review both basic and clinical studies on diabetic cardiomyopathy and summarize problems remaining to be solved for improving management of this type of cardiomyopathy.

Elevated level of pro-inflammatory eicosanoids and EPC dysfunction in diabetic patients with cardiac ischemia

BACKGROUND

Circulating endothelial progenitor cells (EPCs) are recruited from the blood system to sites of ischemia and endothelial damage, where they contribute to the repair and development of blood vessels. Since numerous eicosanoids including leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) have been shown to exert potent pro-inflammatory activities, we examined their levels in chronic diabetic patients with severe cardiac ischemia in conjunction with the level and function of EPCs.

RESULTS

Lipidomic analysis revealed a diabetes-specific increase (p<0.05) in inflammatory and angiogenic eicosanoids including the 5-lipoxygenase-derived LTB (4.11±1.17 vs. 0.96±0.27 ng/ml), the lipoxygenase/CYP-derived 12-HETE (117.08±35.05 vs. 24.34±10.03 ng/ml), 12-HETrE (17.56±4.43 vs. 4.15±2.07 ng/ml), and the CYP-derived 20-HETE (0.32±0.04 vs. 0.06±0.05 ng/ml) the level of which correlated with BMI (p=0.0027). In contrast, levels of the CYP-derived EETs were not significantly (p=0.36) different between these two groups. EPC levels and their colony-forming units were lower (p<0.05) with a reduced viability in diabetic patients compared with non-diabetics. EPC function (colony-forming units (CFUs) and MTT assay) also negatively correlated with the circulating levels of HgA1C.

CONCLUSION

This study demonstrates a close association between elevated levels of highly pro-inflammatory eicosonoids, diabetes and EPC dysfunction in patients with cardiac ischemia, indicating that chronic inflammation impact negatively on EPC function and angiogenic capacity in diabetes.

Aberrant angiogenesis: The gateway to diabetic complications

Diabetes Mellitus is a metabolic cum vascular syndrome with resultant abnormalities in both micro- and macrovasculature. The adverse long-term effects of diabetes mellitus have been described to involve many organ systems. Apart from hyperglycemia, abnormalities of angiogenesis may cause or contribute toward many of the clinical manifestations of diabetes. These are implicated in the pathogenesis of vascular abnormalities of the retina, kidneys, and fetus, impaired wound healing, increased risk of rejection of transplanted organs, and impaired formation of coronary collaterals. A perplexing feature of the aberrant angiogenesis is that excessive and insufficient angiogenesis can occur in different organs in the same individual. The current article hereby reviews the molecular mechanisms including abnormalities in growth factors, cytokines, and metabolic derangements, clinical implications, and therapeutic options of dealing with abnormal angiogenesis in diabetes.

Disruption of TRPV1-mediated coupling of coronary blood flow to cardiac metabolism in diabetic mice: role of nitric oxide and BK channels

We have previously shown transient receptor potential vanilloid subtype 1 (TRPV1) channel-dependent coronary function is compromised in pigs with metabolic syndrome (MetS). However, the mechanisms through which TRPV1 channels couple coronary blood flow to metabolism are not fully understood. We employed mice lacking TRPV1 [TRPV1((-/-))], db/db diabetic, and control C57BKS/J mice to determine the extent to which TRPV1 channels modulate coronary function and contribute to vascular dysfunction in diabetic cardiomyopathy. Animals were subjected to in vivo infusion of the TRPV1 agonist capsaicin to examine the hemodynamic actions of TRPV1 activation. Capsaicin (1-100 μg·kg(-1)·min(-1)) dose dependently increased coronary blood flow in control mice, which was inhibited by the TRPV1 antagonist capsazepine or the nitric oxide synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (L-NAME). In addition, the capsaicin-mediated increase in blood flow was attenuated in db/db mice. TRPV1((-/-)) mice exhibited no changes in coronary blood flow in response to capsaicin. Vasoreactivity studies in isolated pressurized mouse coronary microvessels revealed a capsaicin-dependent relaxation that was inhibited by the TRPV1 inhibitor SB366791 l-NAME and to the large conductance calcium-sensitive potassium channel (BK) inhibitors iberiotoxin and Penetrim A. Similar to in vivo responses, capsaicin-mediated relaxation was impaired in db/db mice compared with controls. Changes in pH (pH 7.4-6.0) relaxed coronary vessels contracted to the thromboxane mimetic U46619 in all three groups of mice; however, pH-mediated relaxation was blunted in vessels obtained from TRPV1((-/-)) and db/db mice compared with controls. Western blot analysis revealed decreased myocardial TRPV1 protein expression in db/db mice compared with controls. Our data reveal TRPV1 channels mediate coupling of myocardial blood flow to cardiac metabolism via a nitric oxide-dependent, BK channel-dependent pathway that is corrupted in diabetes.

Dysregulated selectin expression and monocyte recruitment during ischemia-related vascular remodeling in diabetes mellitus

OBJECTIVE

Diabetes mellitus (DM) is associated with impaired ischemia-related vascular remodeling and also dysregulation of the inflammatory response. We sought to determine whether impaired selectin-mediated monocyte recruitment in ischemic tissues contributes to blunted ischemia-mediated angiogenesis in DM.

METHODS AND RESULTS

Contrast-enhanced ultrasound perfusion imaging and molecular imaging of endothelial P-selectin expression in the proximal hindlimb were performed at 1, 3, and 21 days after arterial ligation in wild-type and db/db mice. Ligation reduced muscle blood flow to ≈0.05 mL/minute per gram in both strains. Significant recovery of flow occurred only in wild-type mice (60%-65% of baseline flow). On molecular imaging, baseline P-selectin signal was 4-fold higher in db/db compared with wild-type mice (P<0.01) but increased minimally at day 1 after ischemia, whereas signal increased approximately 10-fold in wild-type mice (P<0.01). Immunohistology of the hindlimb skeletal muscle demonstrated severely reduced monocyte recruitment in db/db mice compared with wild-type mice. Local treatment with monocyte chemotactic protein-1 corrected the deficits in postischemic P-selectin expression and monocyte recruitment in db/db mice and led to greater recovery in blood flow.

CONCLUSION

In DM, there is dysregulation of the selectin response to limb ischemia, which leads to impaired monocyte recruitment, which may be mechanistically related to reduced vascular remodeling in limb ischemia.

Impaired neurovascular repair in subjects with diabetes following experimental intracutaneous axotomy

Diabetic complications and vascular disease are closely intertwined. Diabetes mellitus is a well-established risk factor for both large and small vessel vascular changes, and conversely other vascular risk factors confer increased risk for diabetic complications such as peripheral neuropathy, nephropathy and retinopathy. Furthermore, axons and blood vessels share molecular signals for purposes of navigation, regeneration and terminal arborizations. We examined blood vessel, Schwann cell and axonal regeneration using validated axotomy models to study and compare patterns and the relationship of regeneration among these different structures. Ten subjects with diabetes mellitus complicated by neuropathy and 10 healthy controls underwent 3 mm distal thigh punch skin biopsies to create an intracutaneous excision axotomy followed by a concentric 4-mm overlapping biopsy at different time points. Serial sections were immunostained against a pan-axonal marker (PGP9.5), an axonal regenerative marker (GAP43), Schwann cells (p75) and blood vessels (CD31) to visualize regenerating structures in the dermis and epidermis. The regenerative and collateral axonal sprouting rates, blood vessel growth rate and Schwann cell density were quantified using established stereology techniques. Subjects also underwent a chemical 'axotomy' through the topical application of capsaicin, and regenerative sprouting was assessed by the return of intraepidermal nerve fibre density through regenerative regrowth. In the healed 3 mm biopsy sites, collateral and dermal regenerative axonal sprouts grew into the central denervated area in a stereotypic pattern with collateral sprouts growing along the dermal-epidermal junction while regenerative dermal axons, blood vessels and Schwann cells grew from their transected proximal stumps into the deep dermis. Vessel growth preceded axon and Schwann cell migration into the denervated region, perhaps acting as scaffolding for axon and Schwann cell growth. In control subjects, Schwann cell growth was more robust and extended into the superficial dermis, while among subjects with diabetes mellitus, Schwann tubes appeared atrophic and were limited to the mid-dermis. Rates of collateral (P=0.0001), dermal axonal regenerative sprouting (P=0.02), Schwann cell migration (P<0.05) and blood vessel growth (P=0.002) were slower among subjects with diabetes mellitus compared with control subjects. Regenerative deficits are a common theme in diabetes mellitus and may underlie the development of neuropathy. We observed that blood vessel growth recapitulated the pattern seen in ontogeny and preceded regenerating nerve fibres, suggesting that enhancement of blood vessel growth might facilitate axonal regeneration. These models are useful tools for the efficient investigation of neurotrophic and regenerative drugs, and also to explore factors that may differentially affect axonal regeneration.

Expression and significance of fgl2 prothrombinase in cardiac microvascular endothelial cells of rats with type 2 diabetes

Microthrombosis may be involved in the pathogenesis of cardiac microangiopathy due to diabetes. Recent studies have shown that fibrinogen-like protein 2 (fgl2) plays a pivotal role in microthrombosis in viral hepatitis, acute vascular xenograft rejection and cytokine-induced fetal loss syndrome. The current study was designed to examine the expression of fgl2 in microvascular endothelial cells and investigate the effects of microthrombi due to fgl2 on cardiac function and structure in rats with type 2 diabetes. Following induction of type 2 diabetes, 24 rats were observed dynamically. Fgl2 expression and related cardiac microthrombosis were examined. Local or circulating TNF-α was measured. Coronary flow (CF) per min was calculated as an index of cardiac microcirculation. Cardiac function and morphology were evaluated. It was found that Fgl2 was highly expressed in cardiac microvascular endothelial cells of rats with type 2 diabetes, which was promoted by local or circulating TNF-α. The Fgl2 expression was associated with cardiac hyaline microthrombosis. In parallel with the fgl2 expression, CF per min, cardiac diastolic or systolic function and cardiac morphology were aggravated to some extent. It was concluded that in rats with type 2 diabetes, microthrombosis due to fgl2 contributes to the impairment of cardiac diastolic or systolic function and morphological changes.

Fenofibrate promotes ischemia-induced revascularization through the adiponectin-dependent pathway

Recent clinical trials demonstrated that PPARα agonist fenofibrate reduces cardiovascular events, including limb amputation in people with type 2 diabetes. Here, we investigated whether fenofibrate modulates the revascularization process in a mouse model of hindlimb ischemia. Treatment with fenofibrate led to acceleration of revascularization of ischemic hindlimb relative to the contralatereal limb in wild-type (WT) mice, as measured by laser Doppler blood flow and capillary density analyses. Treatment of WT mice with fenofibrate increased the serum levels of adiponectin, which has protective actions on the vasculature. Of importance, fenofibrate had no effects on the revascularization in ischemic limbs of adiponectin-deficient (APN-KO) mice. Fenofibrate stimulated the phosphorylation of AMPK and eNOS in the ischemic muscles in WT mice but not in APN-KO mice. AMPK inhibitor compound C suppressed fenofibrate-induced increase in limb perfusion and AMPK phosphorylation in ischemic muscle in WT mice without affecting adiponectin levels. NOS inhibitor l-NAME also blocked the increased blood flow of ischemic limbs in fenofibrate-treated WT mice. Our observations suggest that fenofibrate could promote revascularization in response to ischemia through adiponectin-dependent AMPK signaling.

Neovascularization in diabetes

Diabetes and its complications are a major public health burden in the developed world. The major cause of diabetic complications is abnormal growth of new blood vessels. This dysfunctional neovascularization results in significant morbidity and mortality in patients with diabetes and, as such, is a major focus of basic and clinical investigation. It has become clear that hyperglycemia disrupts tissue-level signaling in response to hypoxia and ischemia, impairs the vasculogenic potential of circulating stem cells and fundamentally alters the structure and function of key neovascularization proteins, including hypoxia-inducible factor-1. These mechanistic and pathophysiologic studies have revealed new therapeutic targets to restore normal neovascularization and to ameliorate and prevent diabetic vascular complications.

Optimization of flow reserve measurement using SPECT technology to evaluate the determinants of coronary microvascular dysfunction in diabetes

PURPOSE

The aim of this study was to validate a new method to measure regional myocardial perfusion reserve (MPR) with technetium-labelled tracers in patients with type 2 diabetes mellitus (DM2).

METHODS

A total of 40 consecutive DM2 patients without history of coronary artery disease (CAD) and 7 control subjects were recruited. Dipyridamole myocardial blood flow index (MBF) was assessed by measuring first transit counts in the pulmonary artery and myocardial count rate from gated SPECT images using (99m)Tc-labelled tracers. The corresponding MBF index was estimated 2 h later according to the same procedure. Regional myocardial perfusion reserve (MPR) was defined as the ratio between dipyridamole and baseline MBF using a 17-segment left ventricular (LV) model. Coronary flow reserve (CFR) was estimated by transthoracic contrast echo Doppler monitoring of flow velocity in the left anterior descending coronary artery (LAD) during the same session.

RESULTS

Estimated MPR was higher in control subjects than in patients (3.36 +/- 0.66 vs 1.91 +/- 0.61, respectively, p < 0.01). In patients, LAD CFR and LAD MPR were 2.01 +/- 0.78 vs 1.93 +/- 0.63, respectively (p = ns). The agreement between the two techniques was documented by their close correlation (r = 0.92, p < 0.001) and confirmed by the Bland-Altman analysis. Reversible perfusion defects occurred in 13 patients (32%) who showed similar MPR values as the remaining 27 (2.10 +/- 0.71 vs 1.83 +/- 0.71, respectively, p = ns). Finally, MPR was closely correlated with age (r = -0.50, p < 0.01) and time elapsed from the diagnosis of DM2 (r = -0.51, p < 0.01).

CONCLUSION

LV regional MPR can be accurately estimated with the broadly available single photon technology. Application of this method to DM2 patients documents the presence of a microvascular dysfunction homogeneously distributed throughout the LV walls and most frequently not associated with reversible perfusion defects.

Peroxisome proliferator-activated receptors and angiogenesis

The peroxisome proliferator-activated receptors (PPARs) are a group of three nuclear receptor isoforms, PPARalpha, PPARgamma and PPARdelta, encoded by different genes, and they form a subfamily of the nuclear receptor superfamily. The clinical interest in PPARs originates with fibrates and thiazolidinediones, which, respectively, act on PPARalpha and PPARgamma and are used to ameliorate hyperlipidaemia and hyperglycaemia in subjects with type 2 diabetes mellitus (T2DM). PPARs play a central role in these patients due to their ability to regulate the expression of numerous genes involved in glycaemic control, lipid metabolism, vascular tone and inflammation. Abnormal angiogenesis is implicated in several of the long-term complications of diabetes mellitus, characterized by vasculopathy associated with aberrant growth of new blood vessels. This pathological process plays a crucial role in diabetic retinopathy, nephropathy and neuropathy, impaired wound healing and impaired coronary collateral vessel development. In recent years, there has been increasing appreciation of the fact that PPARs might be involved in the molecular mechanisms that regulate angiogenesis through the action of growth factors and cytokines that stimulate migration, proliferation and survival of endothelial cells. During the last few years direct comparative analyses have been performed, using selective PPARs agonists, to clarify the angiogenic properties of the different members of the PPAR family. Lately, the findings provide new information to order to understand the biological, clinical and therapeutic effects of PPARs, and the role of these nuclear receptors in angiogenesis, with potentially important implications for the management of subjects affected by T2DM.

The reliability of fractional flow reserve measurement in patients with diabetes mellitus

BACKGROUND

Fractional flow reserve (FFR) is an invasive method to assess the functional significance of coronary stenoses. The value of FFR in diabetic patients is controversial because of microvascular dysfunction. The aim of this study is to investigate the effect of diabetes mellitus (DM) on FFR measurements.

METHODS

One hundred and twenty-one patients with an intermediate lesion who had undergone FFR measurement were included in the study. Lesion severity was determined by quantitative coronary angiography. The patients were divided into groups according to the presence (group 1) or absence (group 2) of DM. The patients were further categorized according to the degree of luminal narrowing caused by the lesion (40-50, 51-60, and >60%) and reference vessel diameter (> or = 2.8 and <2.8 mm). FFR measurements were compared in each category.

RESULTS

There was no difference between the FFR values of diabetic and nondiabetic patients who had coronary lesions with similar degree of luminal narrowing (0.87+/-0.08 vs. 0. 0.85+/-0.07; 0.81+/-0.08 vs. 0.82+/-0.10; 0.81+/-0.10 vs. 0.83+/-0.09, P = 0.957). In the analysis comparing FFR measurements in the categories set according to reference vessel diameter, we did not find a difference either (0.82+/-0.09 vs. 0.83+/-0.09; 0.84+/-0.09 vs. 0.82+/-0.09, P = 0.878). The DeltaFFR value, which is the difference between FFR values before and after adenosine administration, was also similar in diabetic and nondiabetic patients (8.4+/-6.0 vs. 8.4+/-5.5, P = 0.997).

CONCLUSION

The presence of DM does not have a significant impact on FFR values in coronary stenoses of intermediate severity.

Pioglitazone enhances collateral blood flow in ischemic hindlimb of diabetic mice through an Akt-dependent VEGF-mediated mechanism, regardless of PPARgamma stimulation

Background

Type 2 diabetes mellitus (T2DM) is commonly associated with both microvascular and macrovascular complications and a strong correlation exists between glycaemic control and the incidence and progression of vascular complications. Pioglitazone, a Peroxisome proliferator-activated receptor-γ (PPARγ) ligand indicated for therapy of type T2DM, induces vascular effects that seem to occur independently of glucose lowering.

Methods

By using a hindlimb ischemia murine model, in this study we have found that pioglitazone restores the blood flow recovery and capillary density in ischemic muscle of diabetic mice and that this process is associated with increased expression of Vascular Endothelial Growth Factor (VEGF). Importantly, these beneficial effects are abrogated when endogenous Akt is inhibited; furthermore, the direct activation of PPARγ, with its selective agonist GW1929, does not restore blood flow recovery and capillary density. Finally, an important collateral vessel growth is obtained with combined treatment with pioglitazone and selective PPARγ inhibitor GW9662.

Conclusion

These data demonstrate that Akt-VEGF pathway is essential for ischemia-induced angiogenic effect of pioglitazone and that pioglitazone exerts this effect via a PPARγ independent manner.

Association between maximal oxygen uptake and the heart rate corrected-QT interval in postmenopausal overweight women

BACKGROUND

Increased aerobic capacity can reduce the incidence of cardiovascular disease and the mortality rate. On the other hand, a prolonged heart rate corrected-QT (QTc) interval is associated with an increased risk of arrhythmias, cardiac sudden death and coronary artery disease.

AIMS

The association of the aerobic capacity and coronary risk factors with QTc interval was investigated in postmenopausal overweight women.

SUBJECTS AND METHODS

The subjects included 84 postmenopausal overweight women [age: 58.7+/-6.4 years, body mass index (BMI): 27.9+/-3.3] with coronary risk factors. Electrocardiogram (ECG) was recorded with a standard resting 12-lead ECG after more than 5 minutes of rest. The QTc interval was automatically calculated according to Bazett's formula. A multistage graded submaximal exercise test was performed on an electric bicycle ergometer to determine the estimated maximal oxygen uptake (VO(2)max).

RESULTS

Single correlation analysis showed the QTc interval to be positively associated with hemoglobin A(1)c (HbA(1)c), fasting glucose, fasting insulin, BMI, waist circumference, serum potassium and the number of coronary risk factors, while negatively correlated with VO(2)max. Stepwise multiple regression analysis demonstrated the strong association of the QTc interval with HbA(1)c and VO(2)max (r(2)=0.244, p<0.0001). In both patients with and without metabolic syndrome (n=15, n=69, respectively), the QTc interval was independently associated with the HbA(1)c (r(2)=0.318, p<0.05, r(2)= 0.115, p<0.05, respectively).

CONCLUSIONS

These results suggest that decreased aerobic capacity and glucose intolerance may be independent risk factors for a prolonged QTc interval, while demonstrating no relationship with metabolic syndrome.

Therapeutic angiogenesis in diabetes and hypercholesterolemia: influence of oxidative stress

Despite significant improvements in the medical, percutaneous, and surgical management, numerous patients are first seen with non-revascularizable coronary artery disease (CAD). The growth of new blood vessels to improve myocardial perfusion (i.e., therapeutic angiogenesis) is an attractive treatment option for these patients. However, the successes of angiogenic therapy, observed in preclinical studies, have not been realized in clinical trials. Increasing evidence suggests that this discrepancy between animal and human studies may be due to the nature of the substrate, or the molecular and cellular environment within which the angiogenic agent acts. Antiangiogenic influences, including endothelial dysfunction, hypercholesterolemia, and diabetes, are present in virtually all patients with advanced CAD. Recent studies have better characterized the abnormalities associated with these disease states, providing novel targets for intervention. These substrate-modifying interventions can potentially enhance the response to protein-, gene-, or cell-based angiogenic therapy. In this review, we discuss key aspects of the angiogenic process and the pathophysiologic and molecular mechanisms that contribute to an impaired angiogenic response in the setting of endothelial dysfunction, hypercholesterolemia, and diabetes, with a focus on the role of oxidative stress. Last, we briefly explore substrate modifying agents that have been evaluated in preclinical and clinical studies to improve the angiogenic response.

Diabetic cardiomyopathy

Diabetic cardiomyopathy is a distinct primary disease process, independent of coronary artery disease, which leads to heart failure in diabetic patients. Epidemiological and clinical trial data have confirmed the greater incidence and prevalence of heart failure in diabetes. Novel echocardiographic and MR (magnetic resonance) techniques have enabled a more accurate means of phenotyping diabetic cardiomyopathy. Experimental models of diabetes have provided a range of novel molecular targets for this condition, but none have been substantiated in humans. Similarly, although ultrastructural pathology of the microvessels and cardiomyocytes is well described in animal models, studies in humans are small and limited to light microscopy. With regard to treatment, recent data with thiazoledinediones has generated much controversy in terms of the cardiac safety of both these and other drugs currently in use and under development. Clinical trials are urgently required to establish the efficacy of currently available agents for heart failure, as well as novel therapies in patients specifically with diabetic cardiomyopathy.

Improved cardiac function after sirolimus-eluting stent placement in diabetic patients by pioglitazone: combination therapy with statin

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists are used as anti-diabetic drugs, and their pleiotrophic action has been reported to improve endothelial function leading to cardioprotective effects. In this study we evaluated the long-term effect of pioglitazone on cardiac function in diabetic patients after percutaneous coronary intervention (PCI) by drug-eluting stent (DES).

METHODS AND RESULTS

We investigated 54 diabetic patients who received PCI using a sirolimus-eluting stent. We excluded cases of acute myocardial infarction. They were divided into two groups: Group C received only conventional therapy (n=26) and Group P received additionally pioglitazone 15 mg/day (n=28). The left ventricular ejection fraction (LVEF) was measured by left ventriculography and analyzed before and 8 months after PCI. In Group C, LVEF did not change significantly: 55.6% vs. 56.7%, before and after PCI respectively (p=0.58). However, pioglitazone significantly improved LVEF: 54.4% vs. 60.0% (p=0.014). Multiple linear regression analysis showed that DeltaLVEF was significantly related to pioglitazone therapy (p=0.037). In particular, the combination of pioglitazone and statin improved LVEF (DeltaLVEF 9.6% with vs. 2.2% without statin).

CONCLUSIONS

Pioglitazone improved cardiac function after PCI using SES in diabetic patients, especially in combination with a statin.

Caloric restriction stimulates revascularization in response to ischemia via adiponectin-mediated activation of endothelial nitric-oxide synthase

Caloric restriction (CR) can extend longevity and modulate the features of obesity-related metabolic and vascular diseases. However, the functional roles of CR in regulation of revascularization in response to ischemia have not been examined. Here we investigated whether CR modulates vascular response by employing a murine hindlimb ischemia model. Wild-type (WT) mice were randomly divided into two groups that were fed either ad libitum (AL) or CR (65% of the diet consumption of AL). Four weeks later, mice were subjected to unilateral hindlimb ischemic surgery. Body weight of WT mice fed CR (CR-WT) was decreased by 26% compared with WT mice fed AL (AL-WT). Revascularization of ischemic hindlimb relative to the contralateral limb was accelerated in CR-WT compared with AL-WT as evaluated by laser Doppler blood flow and capillary density analyses. CR-WT mice had significantly higher plasma levels of the fat-derived hormone adiponectin compared with AL-WT mice. In contrast to WT mice, CR did not affect the revascularization of ischemic limbs of adiponectin-deficient (APN-KO) mice. CR stimulated the phosphorylation of endothelial nitric-oxide synthase (eNOS) in the ischemic limbs of WT mice. CR increased plasma adiponectin levels in eNOS-KO mice but did not stimulate limb perfusion in this strain. CR-WT mice showed enhanced phosphorylation of AMP-activated protein kinase (AMPK) in ischemic muscle, and administration of AMPK inhibitor compound C abolished CR-induced increase in limb perfusion and eNOS phosphorylation in WT mice. Our observations indicate that CR can promote revascularization in response to tissue ischemia via an AMPK-eNOS-dependent mechanism that is mediated by adiponectin.

MicroRNA-320 expression in myocardial microvascular endothelial cells and its relationship with insulin-like growth factor-1 in type 2 diabetic rats

1. The aim of the present study was to determine the role of myocardial microvascular endothelial cells (MMVEC) in impaired angiogenesis of type 2 diabetic Goto-Kakizaki (GK) rats. 2. A microRNA (miRNA) microarray was used to assess miRNA expression in MMVEC from GK and Wistar rats. Upregulation of miRNA-320 was observed in MMVEC from GK rats using real-time reverse transcription-polymerase chain reaction (RT-PCR). 3. So far, nine miRNAs have been reported to target angiogenic factors and/or receptors, including kinase insert domain containing receptor (Flk-1), insulin-like growth factor 1 (IGF-1) and insulin-like growth factor 1 receptor (IGF-1R). The predicted genes targeted by miR-320 include Flk-1, IGF-1 and IGF-1R. Western blot analysis and RT-PCR were used to analyse the protein and mRNA expression, respectively, of the putative genes IGF-1 and IGF-1R. The expression of IGF-1 and IGF-1R proteins decreased significantly in diabetic MMVEC. However, the expression of IGF-1 mRNA increased rather than decreased. The mRNA expression of IGF-1R did not differ significantly between diabetic and control MMVEC. 4. Transfection of an miR-320 inhibitor into MMVEC from GK rats confirmed that miR-320 impaired angiogenesis. The proliferation and migration of diabetic MMVEC improved after transfection of the miR-320 inhibitor. In addition, the miR-320 inhibitor significantly increased the expression of IGF-1 protein, but had no effect on the expression of IGF-1R. 5. Eleven miRNAs were upregulated in MMVEC from GK rats compared with those in Wistar rats: let-7e, miR-129, miR-291-5p, miR-320, miR-327, mir-333, miR-363-5p, miR-370, miR-494, miR-503 and miR-664. 6. The results indicate that upregulation of miR-320 in MMVEC from GK rats may be responsible for the inconsistency between the expression of IGF-1 protein and mRNA and therefore related to impaired angiogenesis in diabetes. Transfection of an miR-320 inhibitor may be a therapeutic approach for the treatment of impaired angiogenesis in diabetes.

Heart failure in the diabetic patient

This review examines the extent of the increased rate of heart failure (HF) in the diabetic patient, along with the possible causes for this increase and the poor prognosis associated with HF. Also reviewed are the therapies that are available for the treatment of diabetic HF and whether intensifying the use of these therapies might improve the worsened clinical outcomes for the patient who has diabetes.

Decreasing intracellular superoxide corrects defective ischemia-induced new vessel formation in diabetic mice

Tissue ischemia promotes vasculogenesis through chemokine-induced recruitment of bone marrow-derived endothelial progenitor cells (EPCs). Diabetes significantly impairs this process. Because hyperglycemia increases reactive oxygen species in a number of cell types, and because many of the defects responsible for impaired vasculogenesis involve HIF1-regulated genes, we hypothesized that HIF1 function is impaired in diabetes because of reactive oxygen species-induced modification of HIF1alpha by the glyoxalase 1 (GLO1) substrate methylglyoxal. Decreasing superoxide in diabetic mice by either transgenic expression of manganese superoxide dismutase or by administration of an superoxide dismutase mimetic corrected post-ischemic defects in neovascularization, oxygen delivery, and chemokine expression, and normalized tissue survival. In hypoxic fibroblasts cultured in high glucose, overexpression of GLO1 prevented reduced expression of both the EPC mobilizing chemokine stromal cell-derived factor-1 (SDF-1) and of vascular epidermal growth factor, which modulates growth and differentiation of recruited EPCs. In hypoxic EPCs cultured in high glucose, overexpression of GLO1 prevented reduced expression of both the SDF-1 receptor CXCR4, and endothelial nitric-oxide synthase, an enzyme essential for EPC mobilization. HIF1alpha modification by methylglyoxal reduced heterodimer formation and HIF1alpha binding to all relevant promoters. These results provide a basis for the rational design of new therapeutics to normalize impaired ischemia-induced vasculogenesis in patients with diabetes.

Insulin treatment enhances the myocardial angiogenic response in diabetes

OBJECTIVE

Growth factor and cell-based angiogenesis are attractive therapeutic options for diabetic patients with end-stage coronary disease. Reduced collateral vessel formation observed in diabetes is associated with increased expression of anti-angiogenic proteins, angiostatin and endostatin. The aim of this study was to determine the effects of insulin treatment on the diabetic angiogenic response to chronic myocardial ischemia.

METHODS

Yucatan miniswine were treated with alloxan (pancreatic beta-cell specific toxin, 150 mg/kg) and divided into two groups. In the diabetic group (DM, n = 8), blood glucose levels were kept greater than 250 mg/dL, and in the insulin-treated group (IDM, n = 6), intramuscular insulin was administered daily to keep blood glucose less than 150 mg/dL. A third group of age-matched swine served as nondiabetic controls (ND; n = 8). Eight weeks later, all animals underwent circumflex artery ameroid constrictor placement to induce chronic ischemia. Myocardial perfusion was assessed at 3 and 7 weeks after ameroid placement using microspheres. Microvascular function, capillary density, and myocardial expression of anti-angiogenic mediators were evaluated.

RESULTS

Diabetic animals exhibited significant impairments in endothelium-dependent microvessel relaxation to adenosine diphosphate and substance P, which were reversed in insulin-treated animals. Collateral-dependent perfusion in the ischemic circumflex territory, which was profoundly reduced in diabetic animals (-0.18 +/- 0.02 vs +0.23 +/- 0.07 mL . min(-1) . g(-1); P < .001), improved significantly with insulin treatment (0.12 +/- 0.05 mL . min(-1) . g(-1); P < .01). Myocardial expression of anti-angiogenic proteins, angiostatin and endostatin, showing a 4.3- and 3.6-fold increase in diabetic animals respectively (both P < .01 vs ND), was markedly reduced in insulin-treated animals (2.3- and 1.8-fold vs ND; both P < .01).

CONCLUSIONS

Insulin treatment successfully reversed diabetic coronary endothelial dysfunction and significantly improved the endogenous angiogenic response. These pro-angiogenic effects may be mediated through downregulation of anti-angiogenic mediators. Insulin therapy appears to be a promising modality to enhance the angiogenic response in diabetic patients.

Functional, cellular, and molecular characterization of the angiogenic response to chronic myocardial ischemia in diabetes

BACKGROUND

Ischemic heart disease is the most common cause of mortality in diabetic patients. Although therapeutic angiogenesis is an attractive option for these patients, they appear to have reduced collateral formation in response to myocardial ischemia. The aims of this study were to establish a large animal model of diabetes and chronic myocardial ischemia, evaluate the effects of diabetes on the angiogenic response, and elucidate the molecular pathways involved.

METHODS AND RESULTS

Diabetes was induced in male Yucatan miniswine using a pancreatic beta-cell specific toxin, alloxan (150 mg/kg; n=8). Age-matched swine served as controls (n=8). Eight weeks after induction, chronic ischemia was induced by ameroid constrictor placement around the circumflex coronary artery. Myocardial perfusion and function were assessed at 3 and 7 weeks after ameroid placement using isotope-labeled microspheres. Endothelial cell density and myocardial expression of angiogenic mediators was evaluated. Diabetic animals exhibited significant endothelial dysfunction. Collateral dependent perfusion and LV function were significantly impaired in diabetic animals. Diabetic animals also demonstrated reduced endothelial cell density (173+/-14 versus 234+/-23 cells/hpf, P=0.03). Expression of VEGF, Ang-1, and Tie-2 was reduced, whereas antiangiogenic proteins, angiostatin (4.4+/-0.9-fold increase, P<0.001), and endostatin (2.9+/-0.4-fold increase, P=0.03) were significantly elevated in the diabetic myocardium.

CONCLUSIONS

Diabetes results in a profound impairment in the myocardial angiogenic response to chronic ischemia. Pro- and antiangiogenic mediators identified in this study offer novel targets for the modulation of the angiogenic response in diabetes.

Role of endothelin-1, sodium hydrogen exchanger-1 and mitogen activated protein kinase (MAPK) activation in glucose-induced cardiomyocyte hypertrophy

BACKGROUND

Cardiac hypertrophy is a key structural feature of diabetic cardiomyopathy. Previous studies have shown that diabetes-induced endothelin-1 (ET-1) and sodium hydrogen exchanger-1 (NHE-1) mediate structural and functional deficits in the heart. In order to gain a mechanistic understanding of the role of ET-1 and NHE-1 in cardiomyocyte hypertrophy, we have utilized an in vitro endothelial-myocyte co-culture system to reveal cellular interactions that may arbitrate cardiomyocyte deficits in diabetes.

METHODS AND RESULTS

Rat ventricular cardiomyocytes were cultured in high glucose levels, which caused cellular hypertrophy. Hypertrophic markers, atrial natruritic peptide (ANP) and angiotensinogen (Agt), as well as inducible nitric oxide synthase (iNOS) were upregulated by high glucose. Treatment of cells with ET antagonist bosentan and NHE-1 inhibitor cariporide prevented glucose-induced cardiomyocyte hypertrophy and expression of ANP, Agt, and iNOS. Bosentan and cariporide treatment of cardiomyocytes co-cultured with endothelial cells produced a more pronounced normalization of glucose-induced changes as compared to cardiomyocyte cultured alone. To further explore the signaling mechanisms involved, we investigated the mitogen activated protein kinase (MAPK) pathway and its cross-interaction with signaling proteins known to be altered in diabetes. Our results indicate that MAPK activation is associated with cardiomyocyte hypertrophy and is inhibited by bosentan, cariporide, as well as protein kinase C inhibiton. Furthermore, MAPK activation was found to be upstream of the transcription factors, nuclear factor-kappaB and activating protein-1.

CONCLUSION

These results demonstrate that ET-1 and NHE-1 may mediate cardiomyocyte hypertrophy via MAPK activation and provide an insight into the pathogenesis of diabetic cardiomyopathy.