H2O2 Mediates VEGF- and Flow-Induced Dilations of Coronary Arterioles in Early Type 1 Diabetes: Role of Vascular Arginase and PI3K-Linked eNOS Uncoupling

In diabetes, the enzyme arginase is upregulated, which may compete with endothelial nitric oxide (NO) synthase (eNOS) for their common substrate L-arginine and compromise NO-mediated vasodilation. However, this eNOS uncoupling can lead to superoxide production and possibly vasodilator hydrogen peroxide (H₂O₂) formation to compensate for NO deficiency. This hypothesis was tested in coronary arterioles isolated from pigs with 2-week diabetes after streptozocin injection. The NO-mediated vasodilation induced by flow and VEGF was abolished by NOS inhibitor L-NAME and phosphoinositide 3-kinase (PI3K) inhibitor wortmannin but was not affected by arginase inhibitor N^ω-hydroxy-nor-L-arginine (nor-NOHA) or H₂O₂ scavenger catalase in control pigs. With diabetes, this vasodilation was partially blunted, and the remaining vasodilation was abolished by catalase and wortmannin. Administration of L-arginine or nor-NOHA restored flow-induced vasodilation in an L-NAME sensitive manner. Diabetes did not alter vascular superoxide dismutase 1, catalase, and glutathione peroxidase mRNA levels. This study demonstrates that endothelium-dependent NO-mediated coronary arteriolar dilation is partially compromised in early type 1 diabetes by reducing eNOS substrate L-arginine via arginase activation. It appears that upregulated arginase contributes to endothelial NO deficiency in early diabetes, but production of H₂O₂ during PI3K-linked eNOS uncoupling likely compensates for and masks this disturbance.

Endothelial Function Assessment by Flow-Mediated Dilation Method: A Valuable Tool in the Evaluation of the Cardiovascular System

Cardiovascular diseases (CVDs) in the course of atherosclerosis are one of the most critical public health problems in the world. Endothelial cells synthesize numerous biologically active substances involved in regulating the functions of the cardiovascular system. Endothelial dysfunction is an essential element in the pathogenesis of atherosclerosis. Thus, the assessment of endothelial function in people without overt CVD allows for a more accurate estimate of the risk of developing CVD and cardiovascular events. The assessment of endothelial function is primarily used in scientific research, and to a lesser extent in clinical practice. Among the tools for assessing endothelial function, we can distinguish biochemical and physical methods, while physical methods can be divided into invasive and non-invasive methods. Flow-mediated dilation (FMD) is based on the ultrasound assessment of changes in the diameter of the brachial artery as a result of increased blood flow. FMD is a non-invasive, safe, and repeatable test, but it must be performed by qualified and experienced medical staff. The purpose of this paper is to present the literature review results on the assessment of endothelial function using the FMD method, including its methodology, applications in clinical practice and research, limitations, and future perspectives.

Effects of glucocorticoids on interstitial glucose concentrations in individuals with hematologic cancer and without known diagnosis of diabetes: a pilot study

Objective

To analyze interstitial glucose behavior during glucocorticoid use in non-diabetic patients receiving chemotherapy for hematologic malignancies.

Methods

Prospective pilot study carried out to assess interstitial glucose levels in 15 non-diabetic individuals with hematologic malignancies who received glucocorticoids in combination with chemotherapy. The FreeStyle Libre flash monitoring system (Abbott Diabetes Care) was used for up to 14 days to measure interstitial glucose.

Results

Median age and body mass index were 53 (42-61) years and 25 (23-28) kg/m² respectively. Interstitial glucose levels >180mg/dL lasting at least one hour were detected in 60% of participants. Interstitial glucose profile parameters (median and peak interstitial glucose levels and percentage of time during which interstitial glucose levels were >180mg/dL) were significantly (p<0.01) higher during glucocorticoid use (115mg/dL, 218mg/dL and 10% respectively) than after glucocorticoid discontinuation (97mg/dL, 137mg/dL and 0% respectively). Mean interstitial glucose levels increased in the afternoon and at night during glucocorticoid use.

Conclusion

This pilot study was the first to evaluate interstitial glucose levels in non-diabetic individuals using glucocorticoids in treatment of hematologic cancer. Glucocorticoid use during chemotherapy significantly increases interstitial glucose levels in these patients.

Early Endothelial Dysfunction in Type 1 Diabetes Is Accompanied by an Impairment of Vascular Smooth Muscle Function: A Meta-Analysis

Background: A large yet heterogeneous body of literature exists suggesting that endothelial dysfunction appears early in type 1 diabetes, due to hyperglycemia-induced oxidative stress. The latter may also affect vascular smooth muscles (VSM) function, a layer albeit less frequently considered in that pathology. This meta-analysis aims at evaluating the extent, and the contributing risk factors, of early endothelial dysfunction, and of the possible concomitant VSM dysfunction, in type 1 diabetes. Methods: PubMed, Web of Sciences, Cochrane Library databases were screened from their respective inceptions until October 2019. We included studies comparing vasodilatory capacity depending or not on endothelium (i.e., endothelial function or VSM function, respectively) in patients with uncomplicated type 1 diabetes and healthy controls. Results: Fifty-eight articles studying endothelium-dependent function, among which 21 studies also assessed VSM, were included. Global analyses revealed an impairment of standardized mean difference (SMD) (Cohen's d) of endothelial function: -0.61 (95% CI: -0.79, -0.44) but also of VSM SMD: -0.32 (95% CI: -0.57, -0.07). The type of stimuli used (i.e., exercise, occlusion-reperfusion, pharmacological substances, heat) did not influence the impairment of the vasodilatory capacity. Endothelial dysfunction appeared more pronounced within macrovascular than microvascular beds. The latter was particularly altered in cases of poor glycemic control [HbA_1c > 67 mmol/mol (8.3%)]. Conclusions: This meta-analysis not only corroborates the presence of an early impairment of endothelial function, even in response to physiological stimuli like exercise, but also highlights a VSM dysfunction in children and adults with type 1 diabetes. Endothelial dysfunction seems to be more pronounced in large than small vessels, fostering the debate on their relative temporal appearance.

Contribution of systemic vascular reactivity to variability in pulse volume amplitude response during reactive hyperemia

PURPOSE

The aim of the present study was to investigate why the magnitude of reactive hyperemia (RH) observed by pulse volume amplitude (PVA) after arm occlusion differs greatly among study subjects.

METHODS

Healthy subjects (n = 12) in the age range of 22-30 years participated in this study. Vascular reactivity was assessed by measuring the changes in finger PVA simultaneously in the test (occluded arm) and control arm (contralateral non-occluded arm) using two separate Photoplethysmographic sensors. Short-term HRV was computed from simultaneously acquired lead II ECG signal to monitor the changes in cardiac sympathetic nervous activity.

RESULTS

The observed coefficient of variation for inter-subject variability in PVA response in test arm during second minute of RH was 115.3%. In the control arm, significantly reduced PVA was observed during the period of occlusion as well as RH. This observation was corroborated by simultaneously acquired short-term HRV which showed a significant rise in total power (p value < 0.005) and low-frequency (LF) power (p value < 0.05) during release of occlusion when compared to the baseline. A significant positive correlation (Spearman r = 0.33; p = 0.02) was observed between % change in PVA in the control arm and in the test arm for first 3 min of RH.

CONCLUSIONS

Sympathetic activation possibly plays an important role in mediating the inter-subject variability of vascular responses during reactive hyperemia which warrants simultaneous recording of both the test and the control arm responses during RH to accurately assess endothelial function.

Endothelial function in children with a history of henoch schonlein purpura

BACKGROUND

Although Henoch-Schonlein purpura (HSP) is the most common form of systemic vasculitis in children, the long term effect of HSP on endothelial function is still not clear. The aim of our study was to evaluate the long term effect of HSP on endothelial function in children and adolescents.

METHODS

This research was an observational prospective study. The study group comprised of 19 children diagnosed with HSP. The minimum interval between the diagnosis with HSP and endothelial testing was 5 months. Endothelial function evaluation was assessed by a noninvasive technology named peripheral arterial tonometry, using an EndoPAT™ device. This method measures blood flow in the limb, in response to arterial occlusion, and calculates a Reactive Hyperemic Index (RHI) as an index of endothelial function. RHI values of the study group were compared to those of a known control group.

RESULTS

Nineteen children and adolescents with HSP underwent endothelial function studies. Endothelial function was compared to that of a known control group comprising of 23 healthy children and adolescents. The two groups had similar characteristics, including age, male to female ratio, height, weight and BMI. Mean RHI was 1.81 in the study group, and 1.87 in the control group (p = 0.18). Linear regression of the study group, showed a positive correlation between the time interval from HSP diagnosis to participation in the study, and between the RHI value (r = 0.542, p = 0.016). RHI levels were significantly higher in patients who had endothelial function measured more than 6 years since the diagnosis of HSP compared with those patients with less than 6 years follow up (1.98 + 0.74 vs. 1.38 ± 0.43 P = 0.037).

CONCLUSIONS

These results suggest that HSP causes short term endothelial dysfunction that improves with time.

Bimodal Pattern of Coronary Microvascular Involvement in Diabetes Mellitus

Background

The contribution of functionally disturbed coronary autoregulation and structurally impaired microvascular vasodilatory function to reduced coronary flow velocity reserve, reflecting impaired coronary microcirculation in diabetes mellitus (DM), has not been clearly elucidated. The objective of this study was to identify the mechanism of coronary microvascular impairment in DM in relation to duration of disease.

Methods and Results

Coronary flow velocities in the anterior descending coronary artery were assessed by transthoracic echocardiography following angiography revealing normal epicardial coronary arteries in 55 diabetic and 47 nondiabetic patients. Average peak flow velocities, coronary flow velocity reserve, and microvascular resistance in baseline and hyperemic conditions (baseline and hyperemic microvascular resistance, respectively) were assessed. Reduced coronary flow velocity reserve in patients with short duration (<10 years) of DM compared with nondiabetic patients was primarily driven by increased baseline average peak flow velocity (26.50±5.6 versus 22.08±4.31, P=0.008) in the presence of decreased baseline microvascular resistance (3.69±0.86 versus 4.34±0.76, P=0.003). In contrast, decreased coronary flow velocity reserve in patients with long‐standing (≥10 years) DM compared with nondiabetic patients was predominantly driven by reduced hyperemic average peak flow velocity (41.57±10.01 versus 53.47±11.8, P<0.001) due to increased hyperemic microvascular resistance (2.13±0.42 versus 1.69±0.39, P<0.001).

Conclusions

Both altered coronary autoregulation and impaired microvascular vasodilatory function contribute to DM‐related coronary microvascular impairment in a time‐dependent manner. DM‐induced early functional microvascular autoregulatory impairment seems to evolve into structural microvascular impairment in the initially overperfused microvascular territory at the later stage of disease.

Type 1 diabetes modulates cyclooxygenase- and nitric oxide-dependent mechanisms governing sweating but not cutaneous vasodilation during exercise in the heat

Both cyclooxygenase (COX) and nitric oxide synthase (NOS) contribute to sweating, whereas NOS alone contributes to cutaneous vasodilation during exercise in the heat. Here, we evaluated if Type 1 diabetes mellitus (T1DM) modulates these responses. Adults with (n = 11, 25 ± 5 yr) and without (n = 12, 24 ± 4 yr) T1DM performed two bouts of 30-min cycling at a fixed rate of heat production of 400 W in the heat (35°C); each followed by a 20- and 40-min recovery period, respectively. Sweat rate and cutaneous vascular conductance (CVC) were measured at four intradermal microdialysis sites treated with either 1) lactated Ringer (vehicle control site), 2) 10 mM ketorolac (nonselective COX inhibitor), 3) 10 mM N^G-nitro-l-arginine methyl ester (nonselective NOS inhibitor), or 4) a combination of both inhibitors. In nondiabetic adults, separate and combined inhibition of COX and NOS reduced exercise sweat rate (P ≤ 0.05), and the magnitude of reductions were similar across sites. In individuals with T1DM, inhibition of COX resulted in an increase in sweat rate of 0.10 ± 0.09 and 0.09 ± 0.08 mg ·: min^-1 ·: cm^-2 for the first and second exercise bouts, respectively, relative to vehicle control site (P ≤ 0.05), whereas NOS inhibition had no effect on sweating. In both groups, NOS inhibition reduced CVC during exercise (P ≤ 0.05), although the magnitude of reduction did not differ between the nondiabetic and T1DM groups (exercise 1: -28 ± 10 vs. -23 ± 8% max, P = 0.51; exercise 2: -31 ± 12 vs. -24 ± 10% max, P = 0.38). We show that in individuals with T1DM performing moderate intensity exercise in the heat, NOS-dependent sweating but not cutaneous vasodilation is attenuated, whereas COX inhibition increases sweating.

Decreased circulatory response to hypovolemic stress in young women with type 1 diabetes

OBJECTIVE

Diabetes is associated with hemodynamic instability during different situations involving acute circulatory stress in daily life. Young men with type 1 diabetes have been shown to have impaired circulatory response to hypovolemic stress. The effect of type 1 diabetes on cardiovascular response to hypovolemia in young women is unknown, however.

RESEARCH DESIGN AND METHODS

Lower body negative pressure of 30 cm H2O was used to create rapid hypovolemic stress in 15 young women with type 1 diabetes (DW) and 16 healthy women (control subjects [C]). Compensatory mobilization of venous capacitance blood (capacitance response) and net fluid absorption from tissue to blood were measured with a volumetric technique. Overall cardiovascular responses and plasma norepinephrine levels were measured.

RESULTS

Capacitance response was reduced (DW, 0.67 ± 0.05; C, 0.92 ± 0.06) and developed slower in DW (P < 0.01). Capacitance response was further reduced with increasing levels of HbA1c. Fluid absorption was almost halved in DW (P < 0.01). The initial vasoconstrictor response was reduced and developed slower in DW (P < 0.05). Arterial vasoconstriction was further reduced in the presence of microvascular complications (P < 0.05).

CONCLUSIONS

DW present with decreased and slower mobilization of venous capacitance blood and decreased net fluid absorption from tissue to blood during hypovolemic circulatory stress. Collectively, this indicates that DW are prone to hemodynamic instability, especially in the presence of microvascular complications and poor glycemic control.

Blood pressure levels but not hypertensive complications have increased in Type 1 diabetes pregnancies during 1989-2010

AIMS

The pre-pregnancy BMI and the third trimester HbA(1c) levels increased in Finnish parturients with Type 1 diabetes during 1989-2008. The aim of the present study was to investigate whether these trends have been accompanied by increases in blood pressure or hypertensive complications. Hypertension trends were analysed using the definitions of hypertension of both the American College of Obstetricians and Gynecologists and the American Diabetes Association. The associations of hypertension, as defined by the latter criteria, with perinatal complications were also studied.

METHODS

The records of a cohort of 1007 consecutive patients with Type 1 diabetes with a singleton live childbirth during 1989-2010 at the Helsinki University Central Hospital were studied.

RESULTS

The frequencies of hypertensive pregnancy complications did not change, but the mean diastolic blood pressure increased in normotensive parturients in all trimesters. The proportion of patients with systolic blood pressure > 130 mmHg or diastolic blood pressure > 80 mmHg in the first, second and third trimesters of pregnancy increased from 25 to 33%, from 26 to 35% and from 57 to 71%, respectively. Systolic blood pressure of 131-139 mmHg or diastolic blood pressure of 81-89 mmHg in the third trimester was associated with umbilical artery pH < 7.15.

CONCLUSIONS

Blood pressure of patients with Type 1 diabetes during pregnancy is increasing. A growing proportion of women with Type 1 diabetes exceed the American Diabetes Association's definition of hypertension during pregnancy.

Decreased reactivity of skin microcirculation in response to L-arginine in later-onset type 1 diabetes

OBJECTIVE

The aim of our study was to evaluate the vasodilatory effect of l-arginine infusion on the skin microcirculation and to assess the relationship between this effect and the presence of microangiopathy in patients with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Capillaroscopy was performed before and after l-arginine infusion in 48 diabetic patients (26 women and 22 men; age, 39.8 ± 6.3 years) and 24 volunteers free of any chronic disease (13 women and 11 men; age, 38.0 ± 6.7 years). The skin microcirculation reactivity, as expressed by the percentage of area covered by capillaries (coverage) and the distance between capillaries (distance), and the relationship between microcirculation reactivity and the presence of microangiopathic complications were assessed.

RESULTS

The distance before l-arginine infusion was significantly lower in patients than in controls (221 [153-311] vs. 240 [185-356] µm; P = 0.02) and did not differ after l-arginine infusion (223.5 [127-318] vs. 242.5 [181-341] µm; P = 0.27). The difference between the coverage values obtained before and after l-arginine infusion (Δcoverage) was significantly different from zero in the control group but not in the diabetes group. Patients with later onset of diabetes were characterized by decreased skin microcirculation reactivity when compared with patients with earlier onset of diabetes (-1.18 [-5.07 to 11.60] vs. 1.36 [-6.00 to 8.06]; P = 0.02) despite the higher prevalence of retinopathy in patients with earlier onset of diabetes (64% vs. 26%; P = 0.02).

CONCLUSIONS

Skin microvascular reactivity is impaired in patients with later onset of type 1 diabetes. Capillaroscopy with l-arginine infusion is useful for the identification of skin microangiopathy in type 1 diabetes.

Cardiometabolic consequences of gestational dysglycemia

The development of gestational diabetes and even milder forms of dysglycemia during pregnancy represents a maternal phenotype at increased subsequent risk for developing type 2 diabetes mellitus, metabolic syndrome, and, with time, overt cardiovascular disease. A careful and systematic dissection of the hormonal, metabolic, and vascular changes occurring in such women during pregnancy and over the postpartum years provides a unique opportunity to identify conventional and novel conditions and biomarkers whose modification may attenuate adverse long-term outcomes, particularly cardiovascular risk. The purpose of this review is to summarize current understanding of the magnitude of such risk and its potential causes, with a particular focus on postpartum alterations in endothelial and vascular smooth muscle responsiveness.

Endothelial function in women with and without a history of glucose intolerance in pregnancy

BACKGROUND/AIMS

Gestational diabetes mellitus (GDM) and milder gestational impaired glucose tolerance (GIGT) identify women who are at risk of developing cardiovascular disease. Endothelial dysfunction, as indicated by impaired flow-mediated dilatation (FMD) on brachial artery ultrasound, is an early marker of vascular disease. Thus, we sought to evaluate endothelial function in women with and without recent glucose intolerance in pregnancy.

METHODS

One-hundred and seventeen women underwent oral glucose tolerance testing (OGTT) in pregnancy, enabling stratification into those with normal gestational glucose tolerance (n = 59) and those with GDM or GIGT (n = 58). 6 years postpartum, they underwent a repeat of OGTT and brachial artery FMD studies, enabling assessment of FMD and 4 secondary vascular measures: FMD after 60 seconds (FMD60), baseline arterial diameter, peak shear rate, and reactive hyperemia.

RESULTS

There were no differences between the normal gestational glucose tolerance and GDM/GIGT groups in FMD (mean 8.5 versus 9.3%, P = 0.61), FMD60 (4.1 versus 5.1%, P = 0.33), baseline diameter (3.4 versus 3.4 mm, P = 0.66), peak shear rate (262.6 versus 274.8 s(-1), P = 0.32), and reactive hyperemia (576.6 versus 496.7%, P = 0.07). After covariate adjustment, there were still no differences between the groups.

CONCLUSION

Despite their long-term cardiovascular risk, women with glucose intolerance in pregnancy do not display endothelial dysfunction 6 years postpartum.

Hyperfiltration and effect of nitric oxide inhibition on renal and endothelial function in humans with uncomplicated type 1 diabetes mellitus

Studies of experimental diabetes mellitus (DM) suggest that increased nitric oxide (NO) bioactivity contributes to renal hyperfiltration. However, the role of NO in mediating hyperfiltration has not been fully elucidated in humans. Our aim was to examine the effect of NO synthase inhibition on renal and peripheral vascular function in normotensive subjects with uncomplicated type 1 DM. Renal function and brachial artery flow-mediated vasodilatation (FMD) were measured before and after an intravenous infusion of the NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NMMA) in 21 healthy control and 37 type 1 DM patients. Measurements in DM participants were made under clamped euglycemic conditions. The effect of l-NMMA on circulating and urinary NO metabolites (NO(x)) and cGMP and on urinary prostanoids was also determined. Baseline characteristics were similar in the two groups. For analysis, the DM patients were divided into those with hyperfiltration (DM-H, n = 18) and normal glomerular filtration rate (GFR) levels (DM-N, n = 19). Baseline urine NO(x) and cGMP were highest in DM-H. l-NMMA led to a decline in GFR in DM-H (152 ± 16 to 140 ± 11 ml·min(-1)·1.73 m(-2)) but not DM-N or healthy control participants. The decline in effective renal plasma flow in response to l-NMMA (806 ± 112 to 539 ± 80 ml·min(-1)·1.73 m(-2)) in DM-H was also exaggerated compared with the other groups (repeated measures ANOVA, P < 0.05), along with declines in urinary NO(x) metabolites and cGMP. Baseline FMD was lowest in DM-H compared with the other groups and did not change in response to l-NMMA. l-NMMA reduced FMD and plasma markers of NO bioactivity in the healthy control and DM-N groups. In patients with uncomplicated type 1 DM, renal hyperfiltration is associated with increased NO bioactivity in the kidney and reduced NO bioactivity in the systemic circulation, suggesting a paradoxical state of high renal and low systemic vascular NO bioactivity.