Glycemic control prevents microvascular remodeling and increased tone in type 2 diabetes: link to endothelin-1

Intralesional Infiltrations of Arteriosclerotic Tissue Cells-Free Filtrate Reproduce Vascular Pathology in Healthy Recipient Rats

Lower-extremity arterial disease is a major health problem with increasing prevalence, often leading to non-traumatic amputation, disability and mortality. The molecular mechanisms underpinning abnormal vascular wall remodeling are not fully understood. We hypothesized on the existence of a vascular tissue memory that may be transmitted through soluble signaling messengers, transferred from humans to healthy recipient animals, and consequently drive the recapitulation of arterial wall thickening and other vascular pathologies. We examined the effects of the intralesional infiltration for 6 days of arteriosclerotic popliteal artery-derived homogenates (100 µg of protein) into rats' full-thickness wounds granulation tissue. Animals infiltrated with normal saline solution or healthy brachial arterial tissue homogenate obtained from traumatic amputation served as controls. The significant thickening of arteriolar walls was the constant outcome in two independent experiments for animals receiving arteriosclerotic tissue homogenates. This material induced other vascular morphological changes including an endothelial cell phenotypic reprogramming that mirrored the donor's vascular histopathology. The immunohistochemical expression pattern of relevant vascular markers appeared to match between the human tissue and the corresponding recipient rats. These changes occurred within days of administration, and with no cross-species limitation. The identification of these "vascular disease drivers" may pave novel research avenues for atherosclerosis pathobiology.

Intralesional Infiltrations of Cell-Free Filtrates Derived from Human Diabetic Tissues Delay the Healing Process and Recreate Diabetes Histopathological Changes in Healthy Rats

Lower limb ulcers in type-2 diabetic patients are a frequent complication that tributes to amputation and reduces survival. We hypothesized that diabetic healing impairment and other histopathologic hallmarks are mediated by a T2DM-induced tissue priming/metabolic memory that can be transferred from humans to healthy recipient animals and consequently reproduce diabetic donor’s phenotypes. We examined the effect of human T2DM tissue homogenates injected into non-diabetic rat excisional wounds. Fresh granulation tissue, popliteal artery, and peroneal nerve of patients with T2DM were obtained following amputation. Post-mammoplasty granulation and post-traumatic amputation-tissue of normal subjects acted as controls. The homogenates were intralesionally injected for 6–7 days into rats’ excisional thickness wounds. Infiltration with the different homogenates caused impaired wound closure, inflammation, nerve degeneration, and arterial thickening (all P < 0.01 vs relevant control) resembling histopathology of diabetic donor tissues. Control materials caused marginal inflammation only. Infiltration with glycated bovine albumin provoked inflammation and wound healing delay but did not induce arterial thickening. The reproduction of human diabetic traits in healthy recipient animals through a tissue homogenate support the notion on the existence of tissue metabolic memory-associated and transmissible factors, involved in the pathogenesis of diabetic complications. These may have futuristic clinical implications for medical interventions.

Cardiovascular Biomarkers and Calculated Cardiovascular Risk in Orally Treated Type 2 Diabetes Patients: Is There a Link?

The aim of the study was to test the correlation of serum levels of asymmetric dimethylarginine (ADMA), endothelin 1 (ET-1), N-terminal brain natriuretic pro-peptide (NT-proBNP), and placental growth factor (PIGF-1) with estimated cardiovascular (CV) risk. The study group was composed of 102 women and 67 men with type 2 diabetes, having their glycemic and metabolic parameters assessed. All were on oral antidiabetic drugs. Serum levels of NT-proBNP and PIGF-1 were measured by electro-hemi-luminescence on an Elecsys 2010 analyzer. Enzymatic immunoassays were used for ADMA and ET-1. The Framingham Risk Score (FRS), the UKPDS 2.0 and the ADVANCE risk engines were used to calculate cardiovascular risks while statistical analysis was performed on SPSS. Levels of PIGF-1 showed no correlation with the calculated CV risks. The same was true for ADMA, except for a weak correlation with the UKPDS-based 10-year risk for stroke (Pearsons's R=0.167, p=0.039). Plasma levels of ET-1 were correlated with the UKPDS-based 10-year risk for stroke (R=0.184, p=0.032) and fatal stroke (R=0.215, p=0.012) only. NT-proBNP was significantly correlated with all CV risk calculations: ADVANCE-based 4-yr risk (Spearman's Rho=0.521, p<0.001); UKPDS-based 10-year risk for: CHD (Rho=0.209, p=0.01), fatal CHD (Rho=0.282, p<0.001), stroke (Rho=0.482, p<0.001), fatal stroke (Rho=0.505, p<0.001); and 10-year FRS risk (Rho=0.246, p=0.002). In conclusion, ADMA and PIGF-1 did not seem useful in stratifying CV risk while ET-1 is linked to the risk of stroke, and NT-proBNP to all CV risk estimations.

Aging exacerbates impairments of cerebral blood flow autoregulation and cognition in diabetic rats

Diabetes mellitus (DM) is a leading risk factor for aging-related dementia; however, the underlying mechanisms are not well understood. The present study, utilizing a non-obese T2DN diabetic model, demonstrates that the myogenic response of the middle cerebral artery (MCA) and parenchymal arteriole (PA) and autoregulation of cerebral blood flow (CBF) in the surface and deep cortex were impaired at both young and old ages. The impaired CBF autoregulation was more severe in old than young DM rats, and in the deep than the surface cortex. The myogenic tone of the MCA was enhanced at perfusion pressure in the range of 40-100 mmHg in young DM rats but was reduced at 140-180 mmHg in old DM rats. No change of the myogenic tone of the PA was observed in young DM rats, whereas it was significantly reduced at 30-60 mmHg in old DM rats. Old DM rats had enhanced blood-brain barrier (BBB) leakage and neurodegeneration, reduced vascular density, tight junction, and pericyte coverage on cerebral capillaries in the CA3 region in the hippocampus. Additionally, DM rats displayed impaired functional hyperemia and spatial learning and short- and long-term memory at both young and old ages. Old DM rats had impaired non-spatial short-term memory. These results revealed that impaired CBF autoregulation and enhanced BBB leakage plays an essential role in the pathogenesis of age- and diabetes-related dementia. These findings will lay the foundations for the discovery of anti-diabetic therapies targeting restoring CBF autoregulation to prevent the onset and progression of dementia in elderly DM.

Hyperglycemia-induced transcriptional regulation of ROCK1 and TGM2 expression is involved in small artery remodeling in obese diabetic Göttingen Minipigs

Obesity and diabetes in humans are associated with hypertrophic remodeling and increased media:lumen ratio of small resistance arteries, which is an independent predictor of cardiovascular events. In order to minimize increases in media:lumen ratio, hypertrophic remodeling should be accompanied by outward remodeling. We aimed to investigate the mechanisms of structural remodeling in small pial arteries (PAs) and terminal mesenteric arteries (TMAs) from obese Göttingen Minipigs with or without diabetes. Göttingen Minipigs received either control diet (lean control (LC)), high fat/high fructose/high cholesterol diet (FFC), or FFC diet with streptozotocin (STZ)-induced diabetes (FFC/STZ) for 13 months. At the end of the study (20 months), we assessed body weight, fasting plasma biochemistry, passive vessel dimensions, mRNA expression (matrix metallopeptidases 2/9 (MMP2, MMP9), tissue inhibitor of metallopeptidase 1 (TIMP1), transglutaminase 2 (TGM2), Rho-kinase 1 (ROCK1), TGFβ-receptor 2 (TGFBR2), and IGF1-receptor (IGFR1) genes), and immunofluorescence in PAs and TMAs. We performed multiple linear correlation analyses using plasma values, structural data, and gene expression data. We detected outward hypertrophic remodeling in TMAs and hypertrophic remodeling in PAs from FFC/STZ animals. ROCK1 and TGM2 genes were up-regulated in PAs and TMAs from the FFC/STZ group. Passive lumen diameter (PLD) of TMAs was correlated with plasma values of glucose (GLU), fructosamine (FRA), total cholesterol (TC), and triglycerides (TGs). ROCK1 and TGM2 expressions in TMAs were correlated with PLD, plasma GLU, fructosamine, and TC. ROCK1 and TGM2 proteins were immunolocalized in the media of PAs and TMAs, and their fluorescence levels were increased in the FFC/STZ group. Hyperglycemia/hyperlipidemia is involved in regulation of ROCK1 and TGM2 expression leading to outward remodeling of small resistance arteries in obese diabetic Göttingen Minipigs.

Endothelium-dependent impairments to cerebral vascular reactivity with type 2 diabetes mellitus in the Goto-Kakizaki rat

Type 2 diabetes mellitus (T2DM) is a prevalent pathology associated with elevated cerebrovascular disease risk. We determined wall mechanics and vascular reactivity in ex vivo middle cerebral arteries (MCA) from male Goto-Kakizaki rats (GK; ~17 wk old) versus control Wistar Kyoto rats (WKY) to test the hypothesis that the diabetic environment in GK, in the absence of obesity and other comorbidities, leads to endothelial dysfunction and impaired vascular tone regulation. Dilation of MCA following challenge with acetylcholine and hypoxia was blunted in MCA from GK versus WKY, due to lower nitric oxide bioavailability and altered arachidonic acid metabolism, whereas myogenic activation and constrictor responses to serotonin were unchanged. MCA wall distensibility and cross-sectional area were not different between GK and WKY, suggesting that wall mechanics were unchanged at this age, supported by the determination that MCA dilation to sodium nitroprusside was also intact. With the use of ex vivo aortic rings as a bioassay, altered vascular reactivity determined in MCA was paralleled by relaxation responses in artery segments from GK, whereas measurements of vasoactive metabolite production indicated a loss of nitric oxide and prostacyclin bioavailability and an increased thromboxane A₂ production with both methacholine challenge and hypoxia. These results suggest that endothelium-dependent dilator reactivity of MCA in GK is impaired with T2DM, and that this impairment is associated with the genesis of a prooxidant/pro-inflammatory condition with diabetes mellitus. The restriction of vascular impairments to endothelial function only, at this age and development, provide insight into the severity of multimorbid conditions of which T2DM is only one constituent.

Coronary microvascular disease as an early culprit in the pathophysiology of diabetes and metabolic syndrome

Metabolic syndrome (MetS) is a group of cardio-metabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia; these are also a combination of independent coronary artery disease (CAD) risk factors. Alarmingly, the prevalence of MetS risk factors are increasing and a leading cause for mortality. In the vasculature, complications from MetS and type 2 diabetes (T2D) can be divided into microvascular (retinopathy and nephropathy) and macrovascular (cardiovascular diseases and erectile dysfunction). In addition to vascular and endothelial dysfunction, vascular remodeling and stiffness are also hallmarks of cardiovascular disease (CVD), and well-characterized vascular changes that are observed in the early stages of hypertension, T2D, and obesity [1-3]. In the heart, the link between obstructive atherosclerosis of coronary macrovessels and myocardial ischemia (MI) is well established. However, recent studies show that abnormalities in the coronary microcirculation are associated with functional and structural changes in coronary microvessels (classically defined as being ≤150-200μm internal diameter), which may cause or contribute to MI even in the absence of obstractive CAD. This suggests a prognostic value of an abnormal coronary microcirculation as an early sub-clinical culprit in the pathogenesis and progression of heart disease in T2D and MetS. The aim of this review is to summarize recent studies investigating the coronary microvascular remodeling in an early pre-atherosclerotic phase of MetS and T2D, and to explore potential mechanisms associated with the timing of coronary microvascular remodeling relative to that of the macrovasculature.

Abnormal myosin phosphatase targeting subunit 1 phosphorylation and actin polymerization contribute to impaired myogenic regulation of cerebral arterial diameter in the type 2 diabetic Goto-Kakizaki rat

The myogenic response of cerebral resistance arterial smooth muscle to intraluminal pressure elevation is a key physiological mechanism regulating blood flow to the brain. Rho-associated kinase plays a critical role in the myogenic response by activating Ca²⁺ sensitization mechanisms: (i) Rho-associated kinase inhibits myosin light chain phosphatase by phosphorylating its targeting subunit myosin phosphatase targeting subunit 1 (at T855), augmenting 20 kDa myosin regulatory light chain (LC₂₀) phosphorylation and force generation; and (ii) Rho-associated kinase stimulates cytoskeletal actin polymerization, enhancing force transmission to the cell membrane. Here, we tested the hypothesis that abnormal Rho-associated kinase-mediated myosin light chain phosphatase regulation underlies the dysfunctional cerebral myogenic response of the Goto-Kakizaki rat model of type 2 diabetes. Basal levels of myogenic tone, LC₂₀, and MYPT1-T855 phosphorylation were elevated and G-actin content was reduced in arteries of pre-diabetic 8-10 weeks Goto-Kakizaki rats with normal serum insulin and glucose levels. Pressure-dependent myogenic constriction, LC₂₀, and myosin phosphatase targeting subunit 1 phosphorylation and actin polymerization were suppressed in both pre-diabetic Goto-Kakizaki and diabetic (18-20 weeks) Goto-Kakizaki rats, whereas RhoA, ROK2, and MYPT1 expression were unaffected. We conclude that abnormal Rho-associated kinase-mediated Ca²⁺ sensitization contributes to the dysfunctional cerebral myogenic response in the Goto-Kakizaki model of type 2 diabetes.

Role of the Renal Microcirculation in Progression of Chronic Kidney Injury in Obesity

BACKGROUND

Obesity is largely responsible for the growing incidence and prevalence of diabetes, cardiovascular and renal diseases. Current strategies to prevent and treat obesity and its consequences have been insufficient to reverse the ongoing trends. Lifestyle modification or pharmacological therapies often produce modest weight loss which is not sustained and recurrence of obesity is frequently observed, leading to progression of target organ damage in many obese subjects. Therefore, research efforts have focused not only on the factors that regulate energy balance, but also on understanding mechanisms of target organ injury in obesity. Summary and Key Message: Microvascular (MV) disease plays a pivotal role in progressive kidney injury from different etiologies such as hypertension, diabetes, and atherosclerosis, which are all important consequences of chronic obesity. The MV networks are anatomical units that are closely adapted to specific functions of nutrition and removal of waste in every organ. Damage of the small vessels in several tissues and organs has been reported in obesity and may increase cardio-renal risk. However, the mechanisms by which obesity and its attendant cardiovascular and metabolic consequences interact to cause renal MV injury and chronic kidney disease are still unclear, although substantial progress has been made in recent years. This review addresses potential mechanisms and consequences of obesity-induced renal MV injury as well as current treatments that may provide protection of the renal microcirculation and slow progressive kidney injury in obesity.

Linagliptin reduces effects of ET-1 and TLR2-mediated cerebrovascular hyperreactivity in diabetes

AIMS

The anti-hyperglycemic agent linagliptin, a dipeptidyl peptidase-4 inhibitor, has been shown to reduce inflammation and improve endothelial cell function. In this study, we hypothesized that DPP-IV inhibition with linagliptin would improve impaired cerebral blood flow in diabetic rats through improved insulin-induced cerebrovascular relaxation and reversal of pathological cerebrovascular remodeling that subsequently leads to improvement of cognitive function.

MAIN METHODS

Male type-2 diabetic Goto-Kakizaki (GK) and nondiabetic Wistar rats were treated with linagliptin, and ET-1 plasma levels and dose response curves to ET-1 (0.1-100nM) in basilar arteries were assessed. The impact of TLR2 antagonism on ET-1 mediated basilar contraction and endothelium-dependent relaxation to acetylcholine (ACh, 1nM-1M) in diabetic GK rats was examined with antibody directed against the TLR2 receptor (Santa Cruz, 5μg/mL). The expression of TLR2 in middle cerebral arteries (MCAs) from treated rats and in brain microvascular endothelial cells (BMVEC) treated with 100nM linagliptin was assessed.

KEY FINDINGS

Linagliptin lowered plasma ET-1 levels in diabetes, and reduced ET-1-induced vascular contraction. TLR2 antagonism in diabetic basilar arteries reduced ET-1-mediated cerebrovascular dysfunction and improved endothelium-dependent vasorelaxation. Linagliptin treatment in the BMVEC was able to reduce TLR2 expression in cells from both diabetic and nondiabetic rats.

CONCLUSIONS

These results suggest that inhibition of DPPIV using linagliptin improves the ET-1-mediated cerebrovascular dysfunction observed in diabetes through a reduction in ET-1 plasma levels and reduced cerebrovascular hyperreactivity. This effect is potentially a result of linagliptin causing a decrease in endothelial TLR2 expression and a subsequent increase in NO bioavailability.

Linagliptin treatment improves cerebrovascular function and remodeling and restores reduced cerebral perfusion in Type 2 diabetes

The antihyperglycemic agent linagliptin, a dipeptidyl peptidase-4 (DPP-IV) inhibitor, has been shown to reduce inflammation and improve endothelial cell function. In this study, we hypothesized that DPP-IV inhibition with linagliptin would improve impaired cerebral perfusion in diabetic rats, as well as improve insulin-induced cerebrovascular relaxation and reverse pathological cerebrovascular remodeling. We further postulated that these changes would lead to a subsequent improvement of cognitive function. Male Type-2 diabetic and nondiabetic Goto-Kakizaki rats were treated with linagliptin for 4 wk, and blood glucose and DPP-IV plasma levels were assessed. Cerebral perfusion was assessed after treatment using laser-Doppler imaging, and dose response to insulin (10(-13) M-10(-6) M) in middle cerebral arteries was tested on a pressurized arteriograph. The impact of DPP-IV inhibition on diabetic cerebrovascular remodeling was assessed over a physiologically relevant pressure range, and changes in short-term hippocampus-dependent learning were observed using a novel object recognition test. Linagliptin lowered DPP-IV activity but did not change blood glucose or insulin levels in diabetes. Insulin-mediated vascular relaxation and cerebral perfusion were improved in the diabetic rats with linagliptin treatment. Indices of diabetic vascular remodeling, such as increased cross-sectional area, media thickness, and wall-to-lumen ratio, were also ameliorated; however, improvements in short-term hippocampal-dependent learning were not observed. The present study provides evidence that linagliptin treatment improves cerebrovascular dysfunction and remodeling in a Type 2 model of diabetes independent of glycemic control. This has important implications in diabetic patients who are predisposed to the development of cerebrovascular complications, such as stroke and cognitive impairment.

Diabetes-mediated middle cerebral artery remodeling is restored by linagliptin: Interaction with the vascular smooth muscle cell endothelin system

INTRODUCTION

Endothelin-1 (ET-1) mediates cerebrovascular remodeling in vascular smooth muscle layer of the middle cerebral arteries (MCA) in type-2 diabetic Goto-Kakizaki (GK) rats. While metformin, oral glucose lowering agent, prevent/restores vascular remodeling and reduce systemic and local ET-1 levels whether this effect was specific to metformin remained unknown. Our working hypotheses were 1) linagliptin, a DPP-IV inhibitor, can reverse diabetes-mediated cerebrovascular remodeling and this is associated with decreased ET-1, and 2) linagliptin prevents the high glucose induced increase in ET-1 and ET receptors in brain vascular smooth muscle cells (bVSMCs).

METHODS

Diabetic and non-diabetic GK rats were treated with linagliptin (4weeks). MCAs were fixed in buffered 4% paraformaldehyde and used for morphometry. Human bVSMCs incubated in normal glucose (5.5mM)/high glucose (25mM) conditions were treated with the linagliptin (100nM; 24h). ET-1 secretion and ET receptors were measured in media and cell lysate respectively. Immunostaining was performed for ET-A and ET-B receptor. ET receptors were also measured in cells treated with ET-1 (100nM) and linagliptin.

RESULTS

Linagliptin treatment regressed vascular remodeling of MCAs in diabetic animals but had no effect on blood glucose. bVSMCs in normal/high glucose condition did not show any significant difference in ET-1 secretion or ET-A and ET-B receptor expression. ET-1 treatment in high glucose condition significantly increased the ET-A receptors and this effect was inhibited by linagliptin.

CONCLUSIONS

Linagliptin is effective in reversing established pathological cerebrovascular remodeling associated with diabetes. Attenuation of the ET system could be a pleiotropic effect of linagliptin that provides vascular protection.

Linagliptin attenuates diabetes-induced cerebral pathological neovascularization in a blood glucose-independent manner: Potential role of ET-1

AIMS

We have shown that glycemic control with metformin or endothelin-1 (ET-1) inhibition with bosentan prevents and restores diabetes-mediated cerebral pathological remodeling and neovascularization. Our recent data suggest that linagliptin, a member of the dipeptidyl peptidase-4 inhibitor class of glucose-lowering agents, prevents cerebrovascular remodeling and dysfunction independent of its blood glucose lowering effects. We hypothesized that linagliptin prevents pathological neovascularization via the modulation of the ET-1 system.

MATERIALS AND METHODS

24-week old diabetic Goto-Kakizaki and nondiabetic Wistar rats were treated for 4weeks with either vehicle chow or chow containing 166mg/kg linagliptin. At termination, FITC-dextran was injected to visualize the vasculature. Brain sections were imaged by confocal microscopy for vascular density, tortuosity, vascular volume, and surface in both the cortex and striatum. Retinal acellular capillary formation was measured. Brain microvascular endothelial cells (BMVEC) isolated from control or diabetic rats were treated with linagliptin with or without ET-1 dual receptor antagonist and tested for angiogenic properties with cell migration and tube formation assays.

KEY FINDING

Linagliptin reduced all indices of cerebral neovascularization compared with control rats. In vitro, linagliptin normalized the augmented angiogenic properties of BMVECs isolated from diabetic animals and bosentan reversed this response. Cells from diabetic animals had higher ET-1 and less ETB receptors than in control cells. Linagliptin significantly decreased ET-1 levels and increased ETB receptors.

SIGNIFICANCE

ET system contributes to pathological neovascularization in diabetes as evidenced by restoration of functional angiogenesis by bosentan treatment and prevention of linagliptin-mediated improvement of angiogenesis in the in vitro model.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Abnormal Rho-associated kinase activity contributes to the dysfunctional myogenic response of cerebral arteries in type 2 diabetes

The structural and functional integrity of the brain, and therefore, cognition, are critically dependent on the appropriate control of blood flow within the cerebral circulation. Inadequate flow leads to ischemia, whereas excessive flow causes small vessel rupture and (or) blood-brain-barrier disruption. Cerebral blood flow is controlled through the interplay of several physiological mechanisms that regulate the contractile state of vascular smooth muscle cells (VSMCs) within the walls of cerebral resistance arteries and arterioles. The myogenic response of cerebral VSMCs is a key mechanism that is responsible for maintaining constant blood flow during variations in systemic pressure, i.e., flow autoregulation. Inappropriate myogenic control of cerebral blood flow is associated with, and prognostic of, neurological deterioration and poor outcome in patients with several conditions, including type 2 diabetes. Here, we review recent advances in our understanding of the role of inappropriate Rho-associated kinase activity as a cause of impaired myogenic regulation of cerebral arterial diameter in type 2 diabetes.

Ca(2+) handling alterations and vascular dysfunction in diabetes

More than 65% of patients with diabetes mellitus die from cardiovascular disease or stroke. Hyperglycemia, due to either reduced insulin secretion or reduced insulin sensitivity, is the hallmark feature of diabetes mellitus. Vascular dysfunction is a distinctive phenotype found in both types of diabetes and could be responsible for the high incidence of stroke, heart attack, and organ damage in diabetic patients. In addition to well-documented endothelial dysfunction, Ca(2+) handling alterations in vascular smooth muscle cells (VSMCs) play a key role in the development and progression of vascular complications in diabetes. VSMCs provide not only structural integrity to the vessels but also control myogenic arterial tone and systemic blood pressure through global and local Ca(2+) signaling. The Ca(2+) signalosome of VSMCs is integrated by an extensive number of Ca(2+) handling proteins (i.e. channels, pumps, exchangers) and related signal transduction components, whose function is modulated by endothelial effectors. This review summarizes recent findings concerning alterations in endothelium and VSMC Ca(2+) signaling proteins that may contribute to the vascular dysfunction found in the diabetic condition.

Immediate direct peripheral vasoconstriction in response to hyperinsulinemia and metformin in the anesthetized pig

Elevated levels of insulin have been reported to induce both an arterial vasodilation mediated by nitric oxide (NO), and vasoconstriction mediated by endothelin and reactive oxygen radicals. Metformin, used to control blood glucose levels in type 2 diabetes, has also been shown to cause NO-mediated dilation of conduit arteries. It is possible that these contradictory vascular effects are due to a non-direct action on arteries. Therefore, the direct effect of high levels of insulin and metformin infusion on resistance artery diameter was evaluated. Experiments were carried out on the anesthetized pig; blood flow and pressure were measured in the iliac artery. An adjustable snare was applied to the iliac above the pressure and flow measurement site to induce step decreases (3-4 occlusions at 5 min intervals were performed for each infusion) in blood flow, and hence iliac pressure, and the conductance (deltaflow / deltapressure) calculated. Saline, insulin (20 and 40 mUSP/l/min), and metformin (1 microg/ml/min) were infused separately downstream of the adjustable snare and their effect on arterial conductance assessed. Insulin at both infusion rates and metformin caused a significant reduction in peripheral vascular conductance. In conclusion, hyperinsulinemia and metformin infusion constrict resistance arterial vessels in vivo.

Quantitative imaging biomarkers for the evaluation of cardiovascular complications in type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is a prevalent condition in aged populations. Cardiovascular diseases are leading causes of death and disability in patients with T2DM. Traditional strategies for controlling the cardiovascular complications of diabetes primarily target a cluster of well-defined risk factors, such as hyperglycemia, lipid disorders and hypertension. However, there is controversy over some recent clinical trials aimed at evaluating efficacy of intensive treatments for T2DM. As a powerful tool for quantitative cardiovascular risk estimation, multi-disciplinary cardiovascular imaging have been applied to detect and quantify morphological and functional abnormalities in the cardiovascular system. Quantitative imaging biomarkers acquired with advanced imaging procedures are expected to provide new insights to stratify absolute cardiovascular risks and reduce the overall costs of health care for people with T2DM by facilitating the selection of optimal therapies. This review discusses principles of state-of-the-art cardiovascular imaging techniques and compares applications of those techniques in various clinical circumstances. Individuals measurements of cardiovascular disease burdens from multiple aspects, which are closely related to existing biomarkers and clinical outcomes, are recommended as promising candidates for quantitative imaging biomarkers to assess the responses of the cardiovascular system during diabetic regimens.

Dual endothelin receptor antagonism with bosentan reverses established vascular remodeling and dysfunctional angiogenesis in diabetic rats: relevance to glycemic control

AIMS

We have shown that diabetes causes cerebrovascular remodeling in part by the activation of the endothelin (ET-1) system in a glucose-dependent manner. We also reported increased yet dysfunctional cerebral angiogenesis in diabetes. Here, we tested the hypothesis that dual ET-1 receptor antagonism or glycemic control can reverse already established diabetes-induced vascular remodeling and neovascularization.

MAIN METHODS

18-week non-obese type-2 diabetic Goto-Kakizaki (GK) were treated with vehicle, metformin (300 mg/kg/day) or bosentan (100 mg/kg/day) for 4 weeks by oral gavage and compared to 10 and 18-weeks GK rats. Isolated middle cerebral artery (MCA) lumen diameter (LD), media thickness (MT), media:lumen (M:L) ratio, and cross-sectional area (CSA) were measured using pressurized arteriograph. Assessment of remodeling and angiogenesis in the brain parenchyma was achieved by three-dimensional reconstruction of fluorescently labeled images of the vasculature acquired by confocal microscopy, and measurement of neovascularization indices including vascular volume and surface area, branch density and tortuosity.

KEY FINDINGS

MCA remodeling (increased M:L ratio and CSA, but decreased LD) occurred by 18 weeks and did not progress by 22 weeks in diabetic GK rats. Metformin and bosentan partially corrected large artery remodeling. Both treatments significantly reduced all indices of neovascularization compared to untreated diabetic rats.

SIGNIFICANCE

Glycemic control or ET-1 antagonism can partially reverse diabetes-induced cerebrovascular remodeling and neovascularization. These results strongly suggest that either approach offers a therapeutic benefit and combination treatments need to be tested.

Late dual endothelin receptor blockade with bosentan restores impaired cerebrovascular function in diabetes

AIMS

Up-regulation of the endothelin (ET) system in type-2 diabetes increases contraction and decreases relaxation in basilar artery. We showed that 1) ET-receptor antagonism prevents diabetes-mediated cerebrovascular dysfunction; and 2) glycemic control prevents activation of the ET-system in diabetes. Here, our goal is to determine whether and to what extent glycemic control or ET-receptor antagonism reverses established cerebrovascular dysfunction in diabetes.

MAIN METHODS

Non-obese type-2 diabetic Goto-Kakizaki rats were administered either vehicle, metformin (300 mg/kg/day) or dual ET-receptor antagonist bosentan (100mg/kg) for 4-weeks starting at 18-weeks after established cerebrovascular dysfunction (n=5-6/group). Control group included vehicle-treated aged-matched Wistar rats. Blood glucose and pressure were monitored weekly. At termination, basilar arteries were collected and cumulative dose-response curves to ET-1 (0.1-500 nM), 5-HT (1-1000 nM) and acetylcholine (Ach, 0.1 nM-5 μM) were studied by wire myograph. Middle cerebral artery (MCA) myogenic reactivity and tone were measured using pressurized arteriograph.

KEY FINDINGS

There was no difference in ET-1 and 5-HT-mediated constrictions. Endothelium-dependent relaxation was impaired in diabetes. Bosentan improved sensitivity to Ach as well as the maximum relaxation. Myogenic-tone is decreased over the course of the disease. Both treatments improved the ability of MCAs to develop tone at 80 mm Hg and only bosentan improved the tone at higher pressures.

SIGNIFICANCE

These results suggest that contractile response is not affected by glycemic control or ET-receptor antagonism. Meanwhile, dual ET-receptor blockade is effective in partially improving endothelium-dependent relaxation and myogenic response in a blood pressure-independent manner even after established cerebrovascular dysfunction and offers therapeutic potential.

Linking the beneficial effects of current therapeutic approaches in diabetes to the vascular endothelin system

The rising epidemic of diabetes worldwide is of significant concern. Although the ultimate objective is to prevent the development and find a cure for the disease, prevention and treatment of diabetic complications is very important. Vascular complications in diabetes, or diabetic vasculopathy, include macro- and microvascular dysfunction and represent the principal cause of morbidity and mortality in diabetic patients. Endothelial dysfunction plays a pivotal role in the development and progression of diabetic vasculopathy. Endothelin-1 (ET-1), an endothelial cell-derived peptide, is a potent vasoconstrictor with mitogenic, pro-oxidative and pro-inflammatory properties that are particularly relevant to the pathophysiology of diabetic vasculopathy. Overproduction of ET-1 is reported in patients and animal models of diabetes and the functional effects of ET-1 and its receptors are also greatly altered in diabetic conditions. The current therapeutic approaches in diabetes include glucose lowering, sensitization to insulin, reduction of fatty acids and vasculoprotective therapies. However, whether and how these therapeutic approaches affect the ET-1 system remain poorly understood. Accordingly, in the present review, we will focus on experimental and clinical evidence that indicates a role for ET-1 in diabetic vasculopathy and on the effects of current therapeutic approaches in diabetes on the vascular ET-1 system.

Vascularization pattern after ischemic stroke is different in control versus diabetic rats: relevance to stroke recovery

BACKGROUND AND PURPOSE

Pre-existing diabetes mellitus worsens brain functionality in ischemic stroke. We have previously shown that type 2 diabetic rats exhibit enhanced dysfunctional cerebral neovascularization and when these rats are subjected to cerebral ischemic reperfusion injury develop hemorrhagic transformation and greater neurological deficits. However, our knowledge of vascular and functional plasticity during the recovery phase of diabetic stroke is limited. This study tested the hypothesis that vascular repair is impaired in the poststroke period in diabetes mellitus, and this is associated with poor sensorimotor and cognitive function. We further hypothesized that glycemic control prevents impaired vascularization and improves functional outcome in diabetes mellitus.

METHODS

Vascularization was assessed in the ipsilateral and contralateral hemispheres in control, diabetes mellitus and diabetes mellitus plus metformin groups 14 days after ischemic reperfusion injury, as well as in respective sham controls. Three-dimensional reconstruction of the fluorescein isothiocyanate (FITC)-stained vasculature was achieved by confocal microscopy, and stereological parameters, including vascular volume and surface area, were measured. Astrogliosis was determined by glial fibrillary acidic protein staining. The relative rates of sensorimotor recovery, cognitive decline, and spontaneous activity were assessed.

RESULTS

Vascular density in the peri-infarct area was significantly reduced in diabetes mellitus, whereas there was reparative neovascularization in control rats. Astroglial swelling and reactivity were more pronounced in diabetic stroke compared with control stroke. Diabetes mellitus blunted sensorimotor recovery and also exacerbated anxiety-like symptoms and cognitive deficits. Glycemic control started after stroke partially prevented these changes.

CONCLUSIONS

Diabetes mellitus impairs poststroke reparative neovascularization and impedes the recovery. Glycemic control after stroke can improve neurovascular repair and improve functional outcome.

Cerebral neovascularization and remodeling patterns in two different models of type 2 diabetes

We previously reported intense pial cerebral collateralization and arteriogenesis in a mild and lean model of type 2 diabetes (T2D), Goto-Kakizaki (GK) rats. Increased cerebral neovascularization differed regionally and was associated with poor vessel wall maturity. Building upon these findings, the goals of this study were to determine whether a) glycemic control prevents this erratic cerebral neovascularization in the GK model, and b) this pathological neovascularization pattern occurs in Lepr(db/db) model, which is the most commonly used model of T2D for studies involving cerebral complications of diabetes. Vascular volume, surface area and structural parameters including microvessel/macrovessel ratio, non-FITC (fluorescein) perfusing vessel abundance, vessel tortuosity, and branch density were measured by 3D reconstruction of FITC stained vasculature in GK rats or Lepr(db/db) mice. GK rats exhibited an increase in all of these parameters, which were prevented by glycemic control with metformin. In Lepr(db/db) mice, microvascular density was increased but there was no change in nonFITC-perfusing vessels. Increased PA branch density was associated with reduced branch diameter. These results suggest that T2D leads to cerebral neovascularization and remodeling but some structural characteristics of newly formed vessels differ between these models of T2D. The prevention of dysfunctional cerebral neovascularization by early glucose control suggests that hyperglycemia is a mediator of this response.

Impact of experimental diabetes on the maternal uterine vascular remodeling during rat pregnancy

Normal pregnancy is associated with an increase in uteroplacental blood flow in part due to growth and remodeling of the maternal uterine vasculature. In this study, we characterized the effect of diabetic pregnancy on vascular growth of the maternal uterine vasculature and on the passive mechanical properties of the uterine resistance arteries. Diabetes was induced in pregnant rats by injection of streptozotocin and confirmed by development of hyperglycemia. Fetuses of diabetic rats were significantly smaller and placentas larger compared to controls. Pregnancy-induced axial elongation of the mesometrial uterine vasculature was not altered by diabetes. Vascular wall thickness was unchanged between groups. Wall distensibility was increased and the rate constant of an exponential function fitted to stress-strain curve was significantly reduced demonstrating decreased wall stiffness in diabetic uterine radial arteries compared to controls. We conclude that experimental diabetes in rat pregnancy does not compromise the growth of maternal uterine vasculature but alters passive mechanical properties of the uterine radial arteries.

Metformin causes nitric oxide-mediated dilatation in a shorter time than insulin in the iliac artery of the anesthetized pig

We tested the hypothesis that metformin produces arterial dilatation indirectly, by directly exposing the endothelial surface, of an occluded test segment of the pig iliac artery in vivo, to test blood containing metformin or excess insulin, with and without the presence of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester hydrochloride. Such exposure to metformin 1 μg/mL caused the artery to dilate at constant pressure, and this was abolished when NG-nitro-L-arginine methyl ester hydrochloride was coadministered with metformin. The onset of dilatation occurred approximately 4 minutes after the commencement of endothelial exposure to metformin; this contrasts with the approximate 10 minutes required for a similar response to luminal hyperinsulinemia. After the release of flow occlusion, the subsequent flow-mediated dilatation was slightly but significantly enhanced compared with control for metformin; the effect of insulin on flow-mediated dilatation was not statistically significant. The hypothesis was disproved, as we have shown that insulin and metformin, like insulin, directly stimulate NO production by endothelium of a conduit artery; this function may be of value in delaying the atherothrombotic process. The time taken for the commencement of NO production is shorter for metformin than for insulin; the clinical relevance of this finding is unclear.

Transient mesenteric ischemia leads to remodeling of rat mesenteric resistance arteries

Mesenteric ischemia/reperfusion (I/R) is associated with high rates of morbidity and mortality. We studied the effect of mesenteric I/R on structural and mechanical properties of rat mesenteric resistance artery (MRA) that, once disrupted, might impact the outcome of this devastating clinical condition. Superior mesenteric artery from Wistar–Kyoto rats was occluded (90 min) and reperfused (24 h). The effect of tezosentan, a dual endothelin (ET)-receptor antagonist, was studied in ischemic (IO) and sham-operated (SO) animals. MRA structure and mechanics were assessed by pressure myography. Nuclei distribution, elastin content and organization, collagen I/III and ET-1 expression, ET-1 plasma levels, superoxide anion (O2⋅−) production, and mRNA levels of NAD(P)H-oxidase subunits were measured. To assess ET-1 effects on O2⋅− production, MRA from non-operated rats were incubated in culture medium with ET-1. Mesenteric I/R increased MRA wall thickness (P < 0.05) and cross-sectional area (P < 0.05) but decreased wall stiffness (P < 0.05). Arterial remodeling was paralleled by enhancement of: (i) collagen I/III expression (P < 0.01), ET-1 expression (P < 0.05), and O2⋅− formation (P < 0.01) in the vessel wall; (ii) number of internal elastic lamina (IEL) fenestrae (P < 0.05); and (iii) plasma levels of ET-1 (P < 0.05). Moreover, ET-1 increased O2⋅− (P < 0.05) production in cultured MRA. Tezosentan prevented hypertrophic remodeling and collagen I/III deposition, and enhanced O2⋅− production, but it did not affect the decreased wall stiffness after mesenteric I/R. These results indicate that 90 min occlusion/24 h reperfusion induces hypertrophic remodeling of MRA linked to ET-1-mediated increase of collagen and O2⋅−. Decreased stiffness may be associated with increased number of IEL fenestrae. The resulting MRA remodeling, initially adaptive, might become maladaptive contributing to the pathology and poor outcome of mesenteric I/R, and might be a valuable treatment target for mesenteric I/R.

Middle cerebral artery alterations in a rat chronic hypoperfusion model

Chronic cerebral hypoperfusion (CHP) induces microvascular changes that could contribute to the progression of vascular cognitive impairment and dementia in the aging brain. This study aimed to analyze the effects of CHP on structural, mechanical, and myogenic properties of the middle cerebral artery (MCA) after bilateral common carotid artery occlusion (BCCAO) in adult male Wistar rats. Sham animals underwent a similar surgical procedure without carotid artery (CA) ligation. After 15 days of occlusion, MCA and CA were dissected and MCA structural, mechanical, and myogenic properties were assessed by pressure myography. Collagen I/III expression was determined by immunofluorescence in MCA and CA and by Western blot in CA. mRNA levels for 1A1, 1A2, and 3A1 collagen subunits were quantified by quantitative real-time PCR in CA. Matrix metalloproteinase (MMP-1, MMP-2, MMP-9, and MMP-13) and hypoxia-inducible factor-1α (HIF-1α) protein expression were determined in CA by Western blot. BCCAO diminished cross-sectional area, wall thickness, and wall-to-lumen ratio. Nevertheless, whereas wall stress was increased, stiffness was not modified and myogenic response was diminished. Hypoperfusion triggered HIF-1α expression. Collagen I/III protein expression diminished in MCA and CA after BCCAO, despite increased mRNA levels for 1A1 and 3A1 collagen subunits. Therefore, the reduced collagen expression might be due to proteolytic degradation, since the expression of MMP-1 and MMP-9 increased in the CA. These data suggest that BCCAO induces hypotrophic remodeling by a mechanism that involves a reduction of collagen I/III in association with increased MMP-1 and MMP-9 and that decreases myogenic tone in major arteries supplying the brain.

Matrix metalloproteinase 13 in the ligamentum flavum from lumbar spinal canal stenosis patients with and without diabetes mellitus

BACKGROUND

Lumbar spinal canal stenosis (LSCS) is one of the most common spinal disorders in the elderly, and ligamentum flavum (LF) hypertrophy is an important cause of LSCS. Matrix metalloproteinase 13 (MMP13) can degrade fibrillar collagens and elastic microfibrils, and is involved in inflammation and fibrosis. The purpose of this study was to compare the expression of MMP13 in the LF from LSCS patients with diabetes mellitus [DM (+)] with that in the LF from patients without DM [DM (-)] and to analyze the relationship among DM, MMP13 expression, and LF hypertrophy.

METHODS

LFs from 11 DM (+) and 24 DM (-) LSCS patients were analyzed in this study. Histology analysis using hematoxylin and eosin and Masson's trichrome stain was performed for each LF. The expression of MMP13 was analyzed by quantitative real-time PCR. The thickness of LF was measured by CT.

RESULTS

In the LF from DM (+) LSCS patients, the elastic fibers were more disorganized and had lower volumes than in the LF from DM (-) LSCS patients, while more fibrotic tissue was observed in the LF from DM (+) than from DM (-) LSCS patients. MMP13 expression was significantly higher in the LF from DM (+) LSCS patients (0.46 ± 0.61 vs. 0.05 ± 0.09, P = 0.002). The LF from the DM (+) LSCS patients was significantly thicker than that from the DM (-) LSCS patients (5.0 ± 0.9 vs. 3.1 ± 0.8 mm, P < 0.01), and the thickness was correlated with the expression of MMP13 (correlation coefficient = 0.43, P = 0.01, Pearson's correlation test).

CONCLUSION

DM-related MMP13 expression can be one of the factors contributing to fibrosis and hypertrophy of the LF. Further research on the mechanism of this process may lead to new therapies for LF hypertrophy.

Pressure-independent cerebrovascular remodelling and changes in myogenic reactivity in diabetic Goto-Kakizaki rat in response to glycaemic control

AIM

We have shown hypertrophic cerebrovascular remodelling in the Goto-Kakizaki (GK) rat model of diabetes. This study tested the hypotheses that (1) vascular remodelling develops as the disease progresses and alters myogenic reactivity of resistance vessels important for regulation of cerebral blood flow (CBF), and (2) glycaemic control prevents cerebrovascular remodelling and myogenic dysfunction.

METHODS

Middle cerebral artery (MCA) lumen diameter, media : lumen (M : L) ratio, cross-sectional area (CSA) and myogenic tone were measured in 10- and 18-week-old control Wistar and diabetic GK rats using pressurized arteriograph (n = 8-14/group). Mean arterial blood pressure (MAP) was measured with telemetry (n = 5/group). Additional GK rats were treated with metformin (300 mg kg(-1) day(-1) ) for glycaemic control starting at 7 weeks after the onset of diabetes until 18 weeks (n = 9).

RESULTS

In the control group, there was no difference in remodelling indices, myogenic tone or MAP between ages. Eighteen week diabetic rats displayed increased M : L ratio and CSA, but decreased lumen diameter and myogenic tone compared to 10-week GK or 18-week control rats. MAP increased starting around 10 weeks of age and remained slightly higher in the GK rats. Glycaemic control normalized M : L ratio, CSA, lumen diameter and myogenic tone with no effect on blood pressure.

CONCLUSIONS

These findings suggest that diabetic rats develop MCA remodelling as the disease progresses but this is associated with impaired myogenic reactivity which may ultimately affect CBF. Our results also provide evidence that glycaemic control is an effective therapeutic strategy to prevent cerebrovascular remodelling and dysfunction.

Role of shear stress and stretch in vascular mechanobiology

Blood vessels are under constant mechanical loading from blood pressure and flow which cause internal stresses (endothelial shear stress and circumferential wall stress, respectively). The mechanical forces not only cause morphological changes of endothelium and blood vessel wall, but also trigger biochemical and biological events. There is considerable evidence that physiologic stresses and strains (stretch) exert vasoprotective roles via nitric oxide and provide a homeostatic oxidative balance. A perturbation of tissue stresses and strains can disturb biochemical homeostasis and lead to vascular remodelling and possible dysfunction (e.g. altered vasorelaxation, tone, stiffness, etc.). These distinct biological endpoints are caused by some common biochemical pathways. The focus of this brief review is to point out some possible commonalities in the molecular pathways in response to endothelial shear stress and circumferential wall stretch.

Internal pudendal artery from type 2 diabetic female rats demonstrate elevated endothelin-1-mediated constriction

INTRODUCTION

Diabetes is a risk factor for female sexual dysfunction (FSD). FSD has several etiologies, including a vasculogenic component that could be exacerbated in diabetes. The internal pudendal artery supplies blood to the vagina and clitoris and diabetes-associated functional abnormalities in this vascular bed may contribute to FSD.

AIM

The Goto-Kakizaki (GK) rat is a non-obese model of type 2 diabetes with elevated endothelin-1 (ET-1) activity. We hypothesize that female GK rats have diminished sexual responses and that the internal pudendal arteries demonstrate increased ET-1 constrictor sensitivity.

METHODS

Female Wistar and GK rats were used. Apomorphine (APO)-mediated genital vasocongestive arousal (GVA) was measured. Functional contraction (ET-1 and phenylephrine) and relaxation (acetylcholine, ACh) in the presence or absence of the ETA receptor antagonist (ETA R; atrasentan) or Rho-kinase inhibitor (Y-27632) were assessed in the internal pudendal and mesenteric arteries. Protein expression of ET-1 and RhoA/Rho-kinase signaling pathway was determined in the internal pudendal and mesenteric arteries.

MAIN OUTCOME MEASURE

APO-mediated GVAs; contraction and relaxation of internal pudendal and mesenteric arteries; ET-1/RhoA/Rho-kinase protein expression.

RESULTS

GK rats demonstrated no APO-induced GVAs. Internal pudendal arteries, but not mesenteric arteries, from GK rats exhibited greater contractile sensitivity to ET-1 compared with Wistar arteries. ETA R blockade reduced ET-1-mediated constriction in GK internal pudendal and mesenteric arteries. Rho-kinase inhibition reduced ET-1-mediated constriction of GK internal pudendal but not mesenteric arteries; however, it had no effect on arteries from Wistar rats. RhoA protein expression was elevated in GK internal pudendal arteries. At the highest concentrations, ACh-mediated relaxation was greater in the GK internal pudendal artery; however, no difference was observed in the mesenteric artery.

CONCLUSIONS

Female GK rats demonstrate decreased sexual responses that may be because of increased constrictor sensitivity to the ET-1/RhoA/Rho-kinase signaling in the internal pudendal artery.

Postmaximal contraction blood volume responses are blunted in obese and type 2 diabetic subjects in a muscle-specific manner

The purpose of this study was to determine whether there are differences in postisometric contraction blood volume and oxygenation responses among groups of type 2 diabetes mellitus (T2DM), obese, and lean individuals detectable using MRI. Eight T2DM patients were individually matched by age, sex, and race to non-T2DM individuals with similar body mass index (obese) and lean subjects. Functional MRI was performed using a dual-gradient-recalled echo, echo-planar imaging sequence with a repetition time of 1 s and at two echo times (TE = 6 and 46 ms). Data were acquired before, during, and after 10-s isometric dorsiflexion contractions performed at 50 and 100% of maximal voluntary contraction (MVC) force. MRI signal intensity (SI) changes from the tibialis anterior and extensor digitorum longus muscles were plotted as functions of time for each TE. From each time course, the difference between the minimum and the maximum postcontraction SI (ΔSI) were determined for TE = 6 ms (ΔSI(6)) and TE = 46 ms (ΔSI(46)), reflecting variations in blood volume and oxyhemoglobin saturation, respectively. Following 50% MVC contractions, the mean postcontraction ΔSI(6) values were similar in the three groups. Following MVC only, and in the EDL muscle only, T2DM and obese participants had ∼56% lower ΔSI(6) than the lean individuals. Also following MVC only, the ΔSI(46) response in the EDL was lower in T2DM subjects than in lean individuals. These data suggest that skeletal muscle small vessel impairment occurs in T2DM and body mass index-matched subjects, in muscle-specific and contraction intensity-dependent manners.

Vascular protection in diabetic stroke: role of matrix metalloprotease-dependent vascular remodeling

Temporary focal ischemia causes greater hemorrhagic transformation (HT) in diabetic Goto-Kakizaki (GK) rats, a model with increased cerebrovascular matrix metalloprotease (MMP) activity and tortuosity. The objective of the current study was to test the hypotheses that (1) diabetes-induced cerebrovascular remodeling is MMP dependent and (2) prevention of vascular remodeling by glucose control or MMP inhibition reduces HT in diabetic stroke. Control and GK rats were treated with vehicle, metformin, or minocycline for 4 weeks, and indices of remodeling including vascular tortuosity index, lumen diameter, number of collaterals, and middle cerebral artery (MCA) MMP activity were measured. Additional animals were subjected to 3 hours MCA occlusion/21 hours reperfusion, and infarct size and HT were evaluated as indices of neurovascular injury. All remodeling markers including MMP-9 activity were increased in diabetes. Infarct size was smaller in minocycline-treated animals. Both metformin and minocycline reduced vascular remodeling and severity of HT in diabetes. These results provide evidence that diabetes-mediated stimulation of MMP-9 activity promotes cerebrovascular remodeling, which contributes to greater HT in diabetes. Metformin and minocycline offer vascular protection, which has important clinical implications for diabetes patients who are at a fourfold to sixfold higher risk for stroke.

Short-term angiotensin-1 receptor antagonism in type 2 diabetic Goto-Kakizaki rats normalizes endothelin-1-induced mesenteric artery contraction

Endothelin (ET)-1 and angiotensin II (Ang II) are likely candidates for a key role in diabetic vascular complications. We demonstrated previously that an enhanced ET-1-induced contraction is present in mesenteric arteries from Goto-Kakizaki (GK) rats at the chronic stage of type 2 diabetes. Here, we investigated whether short-term treatment of such rats with losartan, an angiotensin type 1 receptor antagonist, might normalize the ET-1-induced contraction. In mesenteric arteries from GK rats at the chronic stage (34-38 weeks) (vs. those from age-matched control Wistar rats): (1) the ET-1-induced contraction was enhanced, (2) the levels of ET-1 and Ang II were increased, (3) ET-1-stimulated ERK2 phosphorylation was increased, and (4) the ACh-induced endothelium-dependent relaxation was reduced. Mesenteric arteries isolated from such GK rats following treatment with losartan (25mg/kg/day for 2 weeks) exhibited reduced ET-1- and Ang II-induced contractions, suppressed ET-1-stimulated ERK phosphorylation, and increased ACh-induced relaxation, while the rats exhibited normalized plasma NO metabolism and their mesenteric arteries exhibited increased basal NO formation. However, such losartan treatment did not alter the increased levels of ET-1 and Ang II seen in GK mesenteric arteries. Our data suggest that within the timescale studied here, losartan normalizes ET-1-induced mesenteric artery contraction through a suppression of ERK activities and/or by normalizing endothelial function.

Current pharmacotherapeutic concepts for the treatment of cardiovascular disease in diabetics

With the growing worldwide obesity epidemic, obesity, type 2 diabetes mellitus and hypertension leading to premature cardiovascular events, are increasingly prevalent. Diabetes mellitus is a significant public health concern and more aggressive management of the condition and its complications, particularly cardiovascular disease, is warranted. Endothelial cell dysfunction is now known to be present at the earliest stages of metabolic syndrome, and insulin resistance and may precede the clinical diagnosis of type 2 diabetes mellitus by several years. The current focus on endothelial cell function as a potential target of pharmacotherapy in the management of cardiovascular disease in diabetics seems warranted, though not all drugs currently prescribed target endothelial cell function equally. In this review, we consider the six classes of drugs currently prescribed for the treatment of hypertension as they impact endothelial cell function and advocate for the development of novel drugs that can repair the endothelium and enhance nitric oxide availability thus preventing future cardiovascular events.