Long-term hyperglycaemia impairs vascular smooth muscle cell function in women with type 1 diabetes mellitus

Arterial Stiffness and Type 1 Diabetes: The Current State of Knowledge

The most common cause of mortality among people with type 1 diabetes is cardiovascular diseases. Arterial stiffness allows predicting cardiovascular complications, cardiovascular mortality, and all-cause mortality. There are different ways to measure arterial stiffness; the gold standard is pulse wave velocity. Arterial stiffness is increased in people with type 1 diabetes compared to healthy controls. It increases with age and duration of type 1 diabetes. Arterial stiffness among people with type 1 diabetes positively correlates with systolic blood pressure, obesity, glycated hemoglobin, waist circumference, and waist to hip ratio. It has a negative correlation with the estimated glomerular filtration rate, high-density lipoprotein, and the absence of carotid plaques. The increased arterial stiffness could result from insulin resistance, collagen increase due to inadequate enzymatic glycation, and endothelial and autonomic dysfunction. The insulin-induced decrease in arterial stiffness is impaired in type 1 diabetes. There are not enough proofs to use pharmacotherapy in the prevention of arterial stiffness, but some of the medicaments got promising results in single studies, for example, renin-angiotensin-aldosterone system inhibitors, statins, and SGLT2 inhibitors. The main strategy of prevention of arterial stiffness progression remains glycemic control and a healthy lifestyle.

Cellular and molecular effects of hyperglycemia on ion channels in vascular smooth muscle

Diabetes affects millions of people worldwide. This devastating disease dramatically increases the risk of developing cardiovascular disorders. A hallmark metabolic abnormality in diabetes is hyperglycemia, which contributes to the pathogenesis of cardiovascular complications. These cardiovascular complications are, at least in part, related to hyperglycemia-induced molecular and cellular changes in the cells making up blood vessels. Whereas the mechanisms mediating endothelial dysfunction during hyperglycemia have been extensively examined, much less is known about how hyperglycemia impacts vascular smooth muscle function. Vascular smooth muscle function is exquisitely regulated by many ion channels, including several members of the potassium (K+) channel superfamily and voltage-gated L-type Ca2+ channels. Modulation of vascular smooth muscle ion channels function by hyperglycemia is emerging as a key contributor to vascular dysfunction in diabetes. In this review, we summarize the current understanding of how diabetic hyperglycemia modulates the activity of these ion channels in vascular smooth muscle. We examine underlying mechanisms, general properties, and physiological relevance in the context of myogenic tone and vascular reactivity.

Knockout of AKAP150 improves impaired BK channel-mediated vascular dysfunction through the Akt/GSK3β signalling pathway in diabetes mellitus

Vascular dysfunction resulting from diabetes is an important factor in arteriosclerosis. Previous studies have shown that during hyperglycaemia and diabetes, AKAP150 promotes vascular tone enhancement by intensifying the remodelling of the BK channel. However, the interaction between AKAP150 and the BK channel remains open to discussion. In this study, we investigated the regulation of impaired BK channel‐mediated vascular dysfunction in diabetes mellitus. Using AKAP150 null mice (AKAP150^−/−) and wild‐type (WT) control mice (C57BL/6J), diabetes was induced by intraperitoneal injection of streptozotocin. We found that knockout of AKAP150 reversed vascular remodelling and fibrosis in mice with diabetes and in AKAP150^−/− diabetic mice. Impaired Akt/GSK3β signalling contributed to decreased BK‐β₁ expression in aortas from diabetic mice, and the silencing of AKAP150 increased Akt phosphorylation and BK‐β₁ expression in MOVAS cells treated with HG medium. The inhibition of Akt activity caused a decrease in BK‐β₁ expression, and treatment with AKAP150 siRNA suppressed GSK3β expression in the nuclei of MOVAS cells treated with HG. Knockout of AKAP150 reverses impaired BK channel‐mediated vascular dysfunction through the Akt/GSK3β signalling pathway in diabetes mellitus.

MUSCLE MITOCHONDRIAL CAPACITY AND ENDURANCE IN ADULTS WITH TYPE 1 DIABETES

The impact of type 1 diabetes (T1D) on muscle endurance and oxidative capacity is currently unknown.

Purpose

Measure muscle endurance and oxidative capacity of adults with T1D compared to controls.

Methods

A cross-sectional study design with a control group was used. Subjects (19-37 years old) with T1D (n=17) and controls (n=17) were assessed with hemoglobin A1c (HbA1c) and casual glucose. Muscle endurance was measured with an accelerometer at stimulation frequencies of 2, 4, and 6 Hz for a total of nine minutes. Mitochondrial capacity was measured using near-infrared spectroscopy after exercise as the rate constant of the rate of recovery of oxygen consumption.

Results

T1D and control groups were similar in age, sex, height, and race. The T1D group had slightly higher BMI values and adipose tissue thickness over the forearm muscles. Casual glucose was 150±70 mg/dL for T1D and 98±16 mg/dL for controls (P=0.006). HbA1c of T1D subjects was 7.1±0.9% and 5.0±0.4% for controls (P<0.01). Endurance indexes at 2, 4, and 6 Hz were 94.5±5.2%, 81.8±8.4%, and 68.6±13.5% for T1D and 94.6±4.1%, 85.9±6.3%, and 68.7±15.4% for controls (p = 0.97, 0.12, 0.99, respectively). There were no differences between groups in mitochondrial capacity (T1D= 1.9±0.5 min^-1 and control=1.8±0.4 min^-1, P=0.29) or reperfusion rate (T1D= 8.8±2.8s and control=10.3±3.0s, P=0.88). There were no significant correlations between HbA1c and either muscle endurance, mitochondrial capacity or reperfusion rate.

Conclusions

Adults with T1D did not have reduced oxidative capacity, muscle endurance or muscle reperfusion rates compared to controls. HbA1c also did not correlate with muscle endurance, mitochondrial capacity or reperfusion rates. Future studies should extend these measurements to older people or people with poorly-controlled T1D.

Association Between Glucose Metabolism And Vascular Aging In Chinese Adults: A Cross-Sectional Analysis In The Tianning Cohort Study

Aim

Fasting glucose has been associated with vascular aging, but the association between HbA1c and vascular aging has been limitedly studied in Chinese and other ethnic populations. We aimed to examine this association in a large sample of Chinese adults.

Methods

In the Tianning Cohort (N=5142), fasting glucose, HbA1c, carotid-femoral pulse wave velocity (cfPWV), and pulse pressure (PP) were measured. Vascular aging was defined as having the highest quartile level of cfPWV or PP. We applied quantile regression models to examine the association between glucose metabolism and vascular aging.

Results

The median cfPWV was significantly increased as increasing quintiles of fasting glucose (β=0.14, P<0.001) and HbA1c (β=0.07, P=0.0056), respectively. Per 1-mmol/L increment of fasting glucose was significantly associated with a higher risk of having vascular aging defined by cfPWV (OR=1.05, P=0.022), PP (OR=1.06, P=0.048), or either (OR=1.08, P=0.002). Similarly, per 1% increment of HbA1c was significantly associated with a higher risk of having vascular aging defined by cfPWV (OR=1.06, P=0.044), PP (OR=1.10, P=0.012), or either (OR=1.12, P=0.042).

Conclusion

Glucose metabolism was significantly and positively associated with vascular aging in Chinese adults, but the causality is uncertain.

Hypermetabolism and impaired endothelium-dependent vasodilation in mesenteric arteries of type 2 diabetes mellitus db/db mice

Besides being a metabolic disease, diabetes is considered a vascular disease as many of the complications relate to vascular pathologies. The aim of this study was to investigate how vascular tone and reactivity and vascular cell metabolism were affected in type 2 diabetes mellitus and whether β-hydroxybutyrate could have a positive effect as alternative energy substrate. Isolated mesenteric arteries of db/db and control mice were incubated in media containing [U-¹³C]glucose or [U-¹³C]β-hydroxybutyrate, and tissue extracts were analysed by mass spectrometry. Functional characterization was performed by wire myography to assess vasodilation and vasocontraction. Hypermetabolism of glucose and β-hydroxybutyrate was observed for mesenteric arteries of db/db mice; however, hypermetabolism was significant only with β-hydroxybutyrate as energy substrate. The functional characterization showed impaired endothelial-dependent vasodilation in mesenteric arteries of the db/db mice, whereas the contractility was unaffected. This study provides evidence that the endothelial cells are impaired, whereas the vascular smooth muscle cells are more robust and seemed less affected in the db/db mouse. Furthermore, the results indicate that hypermetabolism of energy substrates may be due to adaptive changes in the mesenteric arteries.

Subclinical vascular disease in patients with diabetes is associated with insulin resistance

Patients with diabetes experience increased cardiovascular risk that is not fully explained by deficient glycemic control or traditional cardiovascular risk factors such as smoking and hypercholesterolemia. Asymptomatic patients with diabetes show structural and functional vascular damage that includes impaired vasodilation, arterial stiffness, increased intima-media thickness and calcification of the arterial wall. Subclinical vascular injury associated with diabetes predicts subsequent manifestations of cardiovascular disease, such as ischemic heart disease, peripheral artery disease and stroke. Noninvasive detection of subclinical vascular disease is commonly used to estimate cardiovascular risk associated to diabetes. Longitudinal studies in normotensive subjects show that arterial stiffness at baseline is associated with a greater risk for future hypertension independently of established risk factors. In patients with type 2 diabetes, vascular disease begins to develop during the latent phase of insulin resistance, long before the clinical diagnosis of diabetes. In contrast, patients with type 1 diabetes do not manifest vascular injury when they are first diagnosed due to insulin deficiency, as they lack the preceding period of insulin resistance. These findings suggest that insulin resistance plays an important role in the development of early vascular disease associated with diabetes. Cross-sectional and prospective studies confirm that insulin resistance is associated with subclinical vascular injury in patients with diabetes, independently of standard cardiovascular risk factors. Asymptomatic vascular disease associated with diabetes begins to occur early in life having been documented in children and adolescents. Insulin resistance should be considered a therapeutic target in order to prevent the vascular complications associated with diabetes.

Regulation of large conductance Ca2+-activated K+ (BK) channel β1 subunit expression by muscle RING finger protein 1 in diabetic vessels

The large conductance Ca(2+)-activated K(+) (BK) channel, expressed abundantly in vascular smooth muscle cells (SMCs), is a key determinant of vascular tone. BK channel activity is tightly regulated by its accessory β1 subunit (BK-β1). However, BK channel function is impaired in diabetic vessels by increased ubiquitin/proteasome-dependent BK-β1 protein degradation. Muscle RING finger protein 1 (MuRF1), a muscle-specific ubiquitin ligase, is implicated in many cardiac and skeletal muscle diseases. However, the role of MuRF1 in the regulation of vascular BK channel and coronary function has not been examined. In this study, we hypothesized that MuRF1 participated in BK-β1 proteolysis, leading to the down-regulation of BK channel activation and impaired coronary function in diabetes. Combining patch clamp and molecular biological approaches, we found that MuRF1 expression was enhanced, accompanied by reduced BK-β1 expression, in high glucose-cultured human coronary SMCs and in diabetic vessels. Knockdown of MuRF1 by siRNA in cultured human SMCs attenuated BK-β1 ubiquitination and increased BK-β1 expression, whereas adenoviral expression of MuRF1 in mouse coronary arteries reduced BK-β1 expression and diminished BK channel-mediated vasodilation. Physical interaction between the N terminus of BK-β1 and the coiled-coil domain of MuRF1 was demonstrated by pulldown assay. Moreover, MuRF1 expression was regulated by NF-κB. Most importantly, pharmacological inhibition of proteasome and NF-κB activities preserved BK-β1 expression and BK-channel-mediated coronary vasodilation in diabetic mice. Hence, our results provide the first evidence that the up-regulation of NF-κB-dependent MuRF1 expression is a novel mechanism that leads to BK channelopathy and vasculopathy in diabetes.

Is the risk and nature of CVD the same in type 1 and type 2 diabetes?

The incidence of both type 1 and type 2 diabetes is increasing globally, most likely explained by environmental changes, such as changing exposures to foods, viruses, and toxins, and by increasing obesity. While cardiovascular disease (CVD) mortality has been declining recently, this global epidemic of diabetes threatens to stall this trend. CVD is the leading cause of death in both type 1 and type 2 diabetes, with at least a two- to fourfold increased risk in patients with diabetes. In this review, the risk factors for CVD are discussed in the context of type 1 and type 2 diabetes. While traditional risk factors such as dyslipidemia, hypertension, and obesity are greater in type 2 patients than in type 1 diabetes, they explain only about half of the increased CVD risk. The role for diabetes-specific risk factors, including hyperglycemia and kidney complications, is discussed in the context of new study findings.

Determinants of vascular function in patients with type 2 diabetes

Background

Type 2 diabetes mellitus (T2DM) is independently associated with an increased risk for cardiovascular diseases that is primarily due to the early development of advanced atherosclerotic vascular changes. The aim of our study was to investigate the predictors of vascular dysfunction in T2DM patients.

Methods

We studied 165 T2DM patients without known macrovascular or microvascular disease. Standard demographic (age, gender, cardiovascular risk factors, medications), clinical (body mass index, blood pressure) and laboratory (glucose, glycated hemoglobin, lipids, renal function) parameters were included in analyses. Brachial artery flow-mediated dilation (FMD), nitrate mediated dilation (NMD) and Carotid-Femoral Pulse Wave Velocity (PWV) were measured.

Results

Median age was 66 years and duration since T2DM diagnosis was 10 years, 70% were females and 79% hypertensives, while only 10% had a glycated hemoglobin <7%. FMD was positively associated with NMD (r 0.391, P < 0.001), while PWV was inversely associated with FMD (r -0.218, P = 0.014) and NMD (r -0.309, P < 0.001). Time since diagnosis of diabetes was the single independent predictor of FMD (β -0.40, P = 0.003). Increased age and fasting glucose and the presence of hypertension were independent predictors of decreased NMD (P < 0.001). Increased age and systolic blood pressure were independently associated with increased PWV (P < 0.001).

Conclusions

In T2DM patients, impairment of endothelium-dependent vasodilation was independently associated only with longer diabetes duration while no association with other established risk factors was found. Vascular smooth muscle dysfunction and increased arterial stiffness were more prominent in older T2DM patients with hypertension. Worse glycemic control was associated with impaired vascular smooth muscle function.

Arterial stiffness is not increased in teens with early uncomplicated type 1 diabetes mellitus

People with type 1 diabetes mellitus are at an increased risk of cardiovascular mortality. Studies comparing arterial stiffness between subjects with type 1 diabetes and nondiabetic controls have provided controversial findings.We investigated brachial–ankle pulse wave velocity (baPWV) in 87 teenagers with type 1 diabetes mellitus and in 21 matched healthy controls. Our data show that baPWV was not increased in teenagers after a median illness of 5 years.

Cardiovascular disease risk in young people with type 1 diabetes

Cardiovascular disease (CVD) is the most frequent cause of death in people with type 1 diabetes (T1D), despite modern advances in glycemic control and CVD risk factor modification. CVD risk identification is essential in this high-risk population, yet remains poorly understood. This review discusses the risk factors for CVD in young people with T1D, including hyperglycemia, traditional CVD risk factors (dyslipidemia, smoking, physical activity, hypertension), as well as novel risk factors such as insulin resistance, inflammation, and hypoglycemia. We present evidence that adverse changes in cardiovascular function, arterial compliance, and atherosclerosis are present even during adolescence in people with T1D, highlighting the need for earlier intervention. The methods for investigating cardiovascular risk are discussed and reviewed. Finally, we discuss the observational studies and clinical trials which have thus far attempted to elucidate the best targets for early intervention in order to reduce the burden of CVD in people with T1D.

Association of endothelial and vascular smooth muscle dysfunction with cardiovascular risk factors, vascular complications, and subclinical carotid atherosclerosis in type 2 diabetic patients

AIM

Atherosclerosis and arteriosclerosis are mainly caused by the dysfunction of arterial components, namely, vascular endothelial cells, smooth muscle cells, and the extracellular matrix. Endothelial dysfunction is well established as a predictive surrogate marker of cardiovascular events; however, little is known regarding the clinical implications of vascular smooth muscle dysfunction for cardiovascular disease and microangiopathy. In the present study, we aimed to clarify the association of arterial dysfunction with micro-/macroangiopathy and conventional cardiovascular risk factors in 181 type 2 diabetic patients (T2DM; age ± SD, 64 ± 10 years; duration of diabetes, 12 ± 10 years).

METHODS

Flow-mediated dilatation (FMD) and nitroglycerin-mediated dilatation (NMD) were assessed to evaluate endothelial dysfunction and vascular smooth muscle dysfunction, respectively, by using a novel ultrasound device, UNEXEF18G (Unex Co. Ltd., Japan).

RESULTS

The FMD and NMD were 6.4 ± 3.9% and 13.4 ± 6.6%, respectively. No significant differences in FMD were noted between T2DM with and without micro- or macroangiopathy; however, NMD in T2DM patients with micro- and macroangiopathy was significantly lower than that in T2DM patients without angiopathy. NMD decreased with the progression of chronic kidney disease (CKD) stage (p = 0.005), but not FMD (p = 0.071). On multiple regression analysis, significant independent contributors to FMD were age, smoking, systolic blood pressure, glycosylated hemoglobin, and serum total cholesterol, while those for NMD were age, systolic blood pressure, and waist circumference.

CONCLUSION

The relationship of vascular complications and cardiovascular risk factors with NMD is different from that with FMD in type 2 diabetic patients.

Relationship of glycemia control to lipid and blood pressure lowering and atherosclerosis: the SANDS experience

OBJECTIVES

Cardiovascular disease prevention for patients with type 2 diabetes is accomplished through hypertension and dyslipidemia management. Although studies have established strategies for lowering low-density lipoprotein cholesterol (LDL-C) and blood pressure (BP), none have examined whether glycemia influences ability to achieve lipid and BP targets. This post hoc analysis from the Stop Atherosclerosis in Native Diabetics Study examines the role of baseline glycemia in achieving standard and aggressive targets and outcomes after 36 months.

METHODS

Diabetic individuals aged > 40 years with no cardiovascular events (n = 499) were randomized to aggressive versus standard targets for LDL-C, non-high-density lipoprotein cholesterol (non-HDL-C) and systolic BP (SBP). Management algorithms were used for both groups. Carotid ultrasound and echocardiography were performed at baseline and after 36 months.

RESULTS

No differences were observed in baseline hemoglobin A1c between treatment groups nor any significant change in A1c after 36 months in either group. Baseline A1c, however, was significantly and negatively related to achieving LDL-C (P = .007), non-HDL-C (P = .03) and SBP targets (P = .007) and to changes in LDL-C (P = .007), non-HDL-C (P = .03) and SBP (P = .001) in both groups. Baseline A1c failed to predict progression of carotid intima medial thickness (CIMT) (P = .42) or left ventricular mass index (LVMI) (P = .10), nor was it related to the effects of lipid and BP lowering on CIMT and LVMI over 36 months.

CONCLUSIONS

In diabetic adults with no cardiovascular disease events, A1c was negatively associated with ability to achieve LDL-C, non-HDL-C and SBP goals but was not independently related to treatment-associated changes in CIMT or LVMI over 36 months.

Intracellular Ca2+ regulating proteins in vascular smooth muscle cells are altered with type 1 diabetes due to the direct effects of hyperglycemia

Background

Diminished calcium (Ca²⁺) transients in response to physiological agonists have been reported in vascular smooth muscle cells (VSMCs) from diabetic animals. However, the mechanism responsible was unclear.

Methodology/Principal Findings

VSMCs from autoimmune type 1 Diabetes Resistant Bio-Breeding (DR-BB) rats and streptozotocin-induced rats were examined for levels and distribution of inositol trisphosphate receptors (IP₃R) and the SR Ca²⁺ pumps (SERCA 2 and 3). Generally, a decrease in IP₃R levels and dramatic increase in ryanodine receptor (RyR) levels were noted in the aortic samples from diabetic animals. Redistribution of the specific IP₃R subtypes was dependent on the rat model. SERCA 2 was redistributed to a peri-nuclear pattern that was more prominent in the DR-BB diabetic rat aorta than the STZ diabetic rat. The free intracellular Ca²⁺ in freshly dispersed VSMCs from control and diabetic animals was monitored using ratiometric Ca²⁺ sensitive fluorophores viewed by confocal microscopy. In control VSMCs, basal fluorescence levels were significantly higher in the nucleus relative to the cytoplasm, while in diabetic VSMCs they were essentially the same. Vasopressin induced a predictable increase in free intracellular Ca²⁺ in the VSMCs from control rats with a prolonged and significantly blunted response in the diabetic VSMCs. A slow rise in free intracellular Ca²⁺ in response to thapsigargin, a specific blocker of SERCA was seen in the control VSMCs but was significantly delayed and prolonged in cells from diabetic rats. To determine whether the changes were due to the direct effects of hyperglycemica, experiments were repeated using cultured rat aortic smooth muscle cells (A7r5) grown in hyperglycemic and control conditions. In general, they demonstrated the same changes in protein levels and distribution as well as the blunted Ca²⁺ responses to vasopressin and thapsigargin as noted in the cells from diabetic animals.

Conclusions/Significance

This work demonstrates that the previously-reported reduced Ca²⁺ signaling in VSMCs from diabetic animals is related to decreases and/or redistribution in the IP₃R Ca²⁺ channels and SERCA proteins. These changes can be duplicated in culture with high glucose levels.

Biphasic insulin aspart 30/70 (BIAsp 30) in the treatment of type 1 and type 2 diabetes

The pharmacological advantages of the rapid-acting analog, insulin aspart, over human insulin have contributed to the widespread prescription of the premix, biphasic insulin aspart 30/70 (BIAsp 30), in type 1 (T1DM) and type 2 diabetes (T2DM). This article reviews the available literature on the pharmacology, efficacy and safety of BIAsp 30 in T1DM and T2DM from an online search of the PubMed database. Following injection, BIAsp 30 reaches higher plasma insulin levels more quickly than human premix or basal insulin, giving effective reduction of postprandial hyperglycemia. In T1DM patients, randomized controlled trials (RCTs) have shown that HbA(1c) reduction is similar, but postprandial glycemic control is better, with BIAsp 30 than with human insulin regimens. In T2DM patients, lowering of HbA(1c) and postprandial hyperglycemia with BIAsp 30 compare favorably with optimized oral antidiabetes drug treatment, insulin glargine, and, in obese patients, human premix. An increase in minor hypoglycemia with BIAsp 30 relative to basal insulin has been reported in T2DM patients, but major and nocturnal hypoglycemia rates are generally low. Findings from RCTs in T2DM patients are supported by large observational studies. In summary, BIAsp 30 once to three times daily represents a simple and effective tool for the modern management of diabetes.