Enhancement of endothelial function by pregnancy: inadequate response in women with type 1 diabetes

Vascular and autonomic function as early predictive biomarkers of the progression to gestational hypertension

Background

The changes in endothelial function, arterial stiffness, and heart rate variability (HRV) produced in the first trimester of pregnancy in women who develop gestational hypertension (GH) are still being investigated. Objective: to evaluate the HVR, endothelial function, and arterial stiffness changes during the first trimester of pregnancy and their relationship with the development of GH.

Methods

A group of women normotensive during the first trimester (n = 43), who later did (GH; n = 11) or did not (no-GH; n = 32) develop GH in that pregnancy, were enrolled. In the first trimester, endothelial function and arterial stiffness were evaluated through photoplethysmography. HRV, parasympathetic (PNS), and sympathetic (SNS) indexes were measured in a 5-minute continuous electrocardiogram record at rest sitting. The Griess reaction measured urinary nitrite excretion (NOx).

Results

Systolic blood pressure (SBP) values were higher in GH (no-GH: 105.8 ± 2.0 vs. GH: 112.7 ± 3.0 mmHg; p < 0.05). Endothelial function was decreased, and arterial stiffness was increased in GH. Only in GH the arterial stiffness was correlated with SBP (Pearson's r: 0.5594; 95%CI: 0.06106-0.8681; p < 0.05). In HRV, GH decreased low-frequency power and the ratio SD2/SD1. The inhibition of PNS was lower in GH. The NOx was reduced in GH (no-GH: 3.4 ± 0.4 vs. GH: 0.3 ± 0.1 μM/L; p < 0.001). NOx was correlated negatively with the SNS index only in GH.

Conclusions

Developed GH is preceded early in pregnancy by endothelial dysfunction and increased arterial stiffness. In this context, there are SNS-PNS interrelation modifications with less inhibition of PNS.

Endothelial Dysfunction in Pregnancy Complications

The endothelium, which constitutes the inner layer of blood vessels and lymphatic structures, plays an important role in various physiological functions. Alterations in structure, integrity and function of the endothelial layer during pregnancy have been associated with numerous gestational complications, including clinically significant disorders, such as preeclampsia, fetal growth restriction, and diabetes. While numerous experimental studies have focused on establishing the role of endothelial dysfunction in pathophysiology of these gestational complications, their mechanisms remain unknown. Numerous biomarkers of endothelial dysfunction have been proposed, together with the mechanisms by which they relate to individual gestational complications. However, more studies are required to determine clinically relevant markers specific to a gestational complication of interest, as currently most of them present a significant overlap. Although the independent diagnostic value of such markers remains to be insufficient for implementation in standard clinical practice at the moment, inclusion of certain markers in predictive multifactorial models can improve their prognostic value. The future of the research in this field lies in the fine tuning of the clinical markers to be used, as well as identifying possible therapeutic techniques to prevent or reverse endothelial damage.

Changes in vascular function and autonomic balance during the first trimester of pregnancy and its relationship with the new-born weight

This study aimed to evaluate vascular function changes and autonomic balance during the first trimester of pregnancy and its relationship with the new-born weight. This prospective study performed in pregnant (PG) women and after delivery (not pregnant: NPG) evaluated the endothelial function (EF) and arterial stiffness (AS) by a non-invasive method. We evaluated the heart rate variability (HRV), parasympathetic nervous system (PNS), sympathetic nervous system (SNS) indexes by electrocardiogram (5 min) and the urinary nitrite excretion (NOx). PG increased EF and NOx and decreased AS and HRV. PG decreased the PNS index and augmented the SNS index. The new-born weight positively correlated with the PNS index (Pearson's r: 0.4291; p<.05), NOx, HRV and negatively correlated with AS. In summary, in pregnancy, although haemodynamically, the SNS activation plays a compensatory role, the low rates of PNS inhibition are essential to ensure normal foetal growth.Impact StatementWhat is already known on this subject? In pregnancy, there are adaptive physiological changes in the cardiovascular system that include increases of EF and decreases AS with an SNS activation. The study of HRV lets to predict the SNS and PNS balance and how they affect blood pressure and vascular function.What the results of this study add? Although it is known that SNS activation plays a compensatory role in healthy pregnancy, this study adds the critical role of PNS. Early in pregnancy, the low rates of PNS inhibition are essential to ensure normal foetal growth.What the implications are of these findings for clinical practice and/or further research? The present results show a potential predictive value of SNS and PNS activity early in pregnancy. It will provide valuable information not only on the pregnant woman's vascular function but also on the new-born weight.

Menopausal hot flashing and endothelial function in two vascular beds: findings from a cross-sectional study of postmenopausal women

OBJECTIVE

We sought to examine the association of menopausal hot flashing with vascular reactivity in two different vascular beds in the same cohort of postmenopausal women and explore the relationship between hot flashing and cardiovascular disease (CVD) risk profile.

METHODS

A cross-sectional study of 79 healthy postmenopausal women, 23 of whom have never had menopausal hot flashes and 56 of whom have reported hot flashes. Endothelial function at a microvascular level was measured with Laser Doppler Imaging with Iontophoresis which assesses the response to both acetylcholine (Ach, endothelium dependent) and sodium-nitroprusside (SNP, endothelium independent). Reactive Hyperemia Index (RHI) was measured with peripheral arterial tonometry as a marker of endothelial function mainly at a macrovascular level. Metabolic biomarkers including insulin sensitivity were assessed.

RESULTS

Women with hot flashes had enhanced microvascular response to Ach by ∼30% (P = 0.04) and to SNP by ∼31% (P = 0.02), but lower RHI by ∼13% (P = 0.05) compared with women without flashes. Hot flashing was associated with enhanced response to SNP and lower RHI after adjustment for confounders and conventional CVD risk factors. Women with hot flashes were more insulin resistant than nonflashers (HOMAIR: 1.9 (1.2-2.6) vs 1.4 (0.8-1.9), P = 0.03).

CONCLUSIONS

Our data support the association of hot flashing with greater insulin resistance and lower macrovascular response. The paradoxical enhanced microvascular response in hot flashers could be the result of the net effect of thermoregulatory and nonnitric oxide-related pathways rather than of endothelial integrity.

Maternal microcirculation and sidestream dark field imaging: a prospective assessment of the association between labour pain and analgesia on the microcirculation of pregnant women

BACKGROUND

Pregnancy places significant demands on the cardiovascular system leading to measurable changes in the macrocirculation and potentially the microcirculation. During labour, both uterine contractions and labour pain can further impact cardiovascular status. The objective of this observational study was to compare sublingual microcirculation in labouring parturients before and after epidural analgesia.

METHODS

Healthy pregnant, labouring women requesting epidural analgesia were approached to participate. Participants with cardiovascular disease, diabetes, obesity, smoking or caffeine intake were excluded. The sidestream dark field device was applied to the sublingual mucosa obtaining images of at least 20 seconds in 5 visual fields before and after epidural analgesia. Video clips were analyzed randomly and blindly. The primary outcome was mean microvascular flow index (MFI).

RESULTS

Twelve participants completed this study. The results demonstrate no statistically significant difference in the MFI during labour pain (2.9±0.1) compared to after epidural analgesia (3.0±0.04, p = 0.31). Furthermore, there were no statistically significant differences in any secondary outcomes.

CONCLUSION

Our findings indicate that epidural analgesia may not impact sublingual microcirculation in labouring women. This agrees with literature supporting epidural analgesia as a safe, appropriate method of pain relief during labour with limited impact on peripheral macro or microcirculation.

An observational assessment of the sublingual microcirculation of pregnant and non-pregnant women

BACKGROUND

The microcirculation is responsible for distribution of blood within tissues, delivery of oxygen and other nutrients, and regulation of blood pressure. The objective of this study was to compare the sublingual microcirculation of pregnant participants to that of comparable non-pregnant volunteers.

METHODS

Two groups of participants were recruited: a group of pregnant, non-laboring women with singleton pregnancies at term gestation and a control group of age-comparable non-pregnant volunteers. A sidestream dark field imaging device was applied to the sublingual mucosal surface obtaining a steady image for at least 20 s duration, in five visual fields. The resultant five video clips per participant were analyzed blindly and at random to prevent coupling between images. The mean microvascular flow index values for each group were compared using a paired t-test.

RESULTS

Thirty-seven participants were recruited (19 pregnant, 18 non-pregnant); a single pregnant participant was withdrawn because of technical issues. Baseline characteristics were similar with the exception of weight and body mass index. The mean microvascular flow index was significantly higher in the pregnant group 2.7 ± 0.2 compared to the non-pregnant group 2.5 ± 0.3 (P = 0.021), while the perfused vessel density and proportion of perfused vessels were not significantly different (P = 0.707 and 0.403, respectively).

CONCLUSION

The microvascular flow index of pregnant women is higher than a comparable non-pregnant group, which appears to correlate with the physiological changes of pregnancy.

Serum inflammatory markers and preeclampsia in type 1 diabetes: a prospective study

OBJECTIVE

Inflammation and endothelial dysfunction have been associated with the immunobiology of preeclampsia (PE), a significant cause of adverse pregnancy outcomes. The prevalence of PE is elevated several fold in the presence of maternal type 1 diabetes mellitus (T1DM). Although cross-sectional studies of pregnancies among women without diabetes have shown altered inflammatory markers in the presence of PE, longitudinal studies of diabetic women are lacking. In maternal serum samples, we examined the temporal associations of markers of inflammation with the subsequent development of PE in women with T1DM.

RESEARCH DESIGN AND METHODS

We conducted longitudinal analyses of serum C-reactive protein (CRP), adhesion molecules, and cytokines during the first (mean ± SD, 12.2 ± 1.9 weeks), second (21.6 ± 1.5 weeks), and third (31.5 ± 1.7 weeks) trimesters of pregnancy (visits 1-3, respectively). All study visits took place before the onset of PE. Covariates were BMI, HbA1c, age of onset, duration of diabetes, and mean arterial pressure.

RESULTS

In women with T1DM who developed PE versus those who remained normotensive, CRP tended to be higher at visits 1 (P = 0.07) and 2 (P = 0.06) and was significantly higher at visit 3 (P < 0.05); soluble E-selectin and interferon-γ-inducible protein-10 (IP-10) were significantly higher at visit 3; interleukin-1 receptor antagonist (IL-1ra) and eotaxin were higher and lower, respectively, at visit 2 (all P < 0.05). These conclusions persisted following adjustment for covariates.

CONCLUSIONS

In pregnant women with T1DM, elevated CRP, soluble E-selectin, IL-1ra, and IP-10 and lower eotaxin were associated with subsequent PE. The role of inflammatory factors as markers and potential mechanisms of the high prevalence of PE in T1DM merits further investigation.

Diabetic retinopathy is related to both endothelium-dependent and -independent responses of skin microvascular flow

OBJECTIVE

Endothelial dysfunction has been hypothesized as a possible pathogenic factor in the development of diabetic retinopathy (DR). We examined the relationship of DR to endothelium-dependent and endothelium-independent responses in skin microvascular flow.

RESEARCH DESIGN AND METHODS

Participants consisted of 224 individuals with diabetes: 85 with type 1 diabetes and 139 with type 2 diabetes. Sodium nitroprusside (SNP) and acetylcholine (ACh) were delivered across the skin by iontophoresis. Laser Doppler flowmetry was used to assess the skin microcirculation response to SNP (endothelium-independent response) and ACh (endothelium-dependent response). The presence and severity of DR were graded from retinal photographs using a standard protocol.

RESULTS

Of 224 participants, 64.3% had DR. After multivariable adjustment, participants with reduced responses to SNP or ACh were more likely to have DR, with an odds ratio (OR) of 2.33 (95% CI 1.09-5.01) for SNP and 2.20 (1.05-4.61) for ACh, comparing participants with responses below and above the median values. Participants with reduced responses (below the median) to both SNP and ACh were nearly four times more likely to have DR (OR 3.86 [1.45-10.3]) than those with SNP and ACh both above the median values.

CONCLUSIONS

The presence of DR was associated with a reduction in skin microcirculation responses to iontophoresis of both SNP and ACh, suggesting that vascular processes associated with both endothelial dysfunction and endothelial function-independent mechanisms may be pathogenically related to DR.

Obesity in pregnancy: prevalence and metabolic consequences

Rates of obesity have increased exponentially worldwide to almost epidemic proportions. This is associated with a marked increase in adverse maternal and perinatal outcomes and subsequent burden on health care resources. In particular, maternal obesity is linked to numerous metabolic complications including subfertility, gestational diabetes, hypertensive disorders of pregnancy and thromboembolism with potential long-term health consequences for both mother and child. The underlying pathophysiology linking maternal obesity and adverse outcomes is complex but is likely to involve alterations in glucose and lipid metabolism, inflammation, perturbances in adipokines and vascular dysfunction all seen in obese women. Intervention studies are underway to determine whether alteration of maternal lifestyle can improve maternal and fetal outcomes.

Circulating asymmetric dimethylarginine, endothelin-1 and cell adhesion molecules in women with gestational diabetes

We measured plasma concentrations of asymmetric dimethylarginine (ADMA), endothelin-1 (ET-1), soluble vascular cell adhesion molecule-1 (sVCAM-1) and E-selectin in 56 patients with gestational diabetes (GDM), 68 pregnant women with normal glucose tolerance (NGT) and 36 healthy non-pregnant women. ADMA concentrations were markedly lower in NGT [0.48 (0.42-0.55) micromol/l] than in GDM subjects [0.50 (0.43-0.67) micromol/l] and healthy controls [0.57 (0.46-0.72) micromol/l, P = 0.005]. ET-1 levels were comparable between GDM [0.76 (0.58-0.90) pg/ml] and NGT women [0.75 (0.63-0.92) pg/ml] and significantly higher than in the non-pregnant subjects [0.62 (0.52-0.72) pg/ml, P = 0.007 and P = 0.005, respectively]. There were no differences in sVCAM-1 and E-selectin levels between the groups studied. ADMA levels were significantly associated with fasting glucose (beta = 0.23, P = 0.02) and gestational age (beta = 0.24, P = 0.01). Our results suggest that physiological adaptation to pregnancy is associated with a fall in circulating ADMA and an elevation of ET-1 concentrations, irrespective of the disturbances of glucose tolerance.

Current concepts in assessment of microvascular endothelial function using laser Doppler imaging and iontophoresis

Effective evaluation of endothelial function is a powerful tool for determining patients at risk of development and progression of cardiovascular disease. As an alternative to invasive tests of endothelial function, several noninvasive methods have been developed, including the use of laser Doppler flowmetry/imaging to measure cutaneous perfusion accompanied by iontophoresis of acetylcholine and sodium nitroprusside. It is clear from previous studies that this technique provides an easy, validated, and reproducible method for investigators to assess and monitor endothelial function in patients with a variety of pathologic conditions, but it may also be used to examine disease progression over time and responsiveness to treatment, thereby facilitating clinical trials. However, a standardization of protocols would help reduce the apparent controversy seen in the literature. With its increasing use by other groups, it is anticipated that further published studies will help to provide a better understanding of the development and progression of cardiovascular disease.

Endothelial dysfunction in diabetes mellitus

Diabetes mellitus is associated with an increased risk of cardiovascular disease, even in the presence of intensive glycemic control. Substantial clinical and experimental evidence suggest that both diabetes and insulin resistance cause a combination of endothelial dysfunctions, which may diminish the anti-atherogenic role of the vascular endothelium. Both insulin resistance and endothelial dysfunction appear to precede the development of overt hyperglycemia in patients with type 2 diabetes. Therefore, in patients with diabetes or insulin resistance, endothelial dysfunction may be a critical early target for preventing atherosclerosis and cardiovascular disease. Microalbuminuria is now considered to be an atherosclerotic risk factor and predicts future cardiovascular disease risk in diabetic patients, in elderly patients, as well as in the general population. It has been implicated as an independent risk factor for cardiovascular disease and premature cardiovascular mortality for patients with type 1 and type 2 diabetes mellitus, as well as for patients with essential hypertension. A complete biochemical understanding of the mechanisms by which hyperglycemia causes vascular functional and structural changes associated with the diabetic milieu still eludes us. In recent years, the numerous biochemical and metabolic pathways postulated to have a causal role in the pathogenesis of diabetic vascular disease have been distilled into several unifying hypotheses. The role of chronic hyperglycemia in the development of diabetic microvascular complications and in neuropathy has been clearly established. However, the biochemical or cellular links between elevated blood glucose levels, and the vascular lesions remain incompletely understood. A number of trials have demonstrated that statins therapy as well as angiotensin converting enzyme inhibitors is associated with improvements in endothelial function in diabetes. Although antioxidants provide short-term improvement of endothelial function in humans, all studies of the effectiveness of preventive antioxidant therapy have been disappointing. Control of hyperglycemia thus remains the best way to improve endothelial function and to prevent atherosclerosis and other cardiovascular complications of diabetes. In the present review we provide the up to date details on this subject.

Long-term effects of oral vitamin C supplementation on the endothelial dysfunction in the iris microvessels of diabetic rats

The current study was aimed to investigate effects of long-term supplementation of vitamin C on the iris microcirculation in streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in male Wistar-Furth rats by intravenous injection of STZ (55 mg/kg b.w.). The rats were divided into three groups: control rats (CON), STZ-induced diabetic rats (STZ), and STZ rats supplemented with vitamin C (STZ-vitC). For supplementation of vitamin C, ascorbic acid (1 g/l) was added into the drinking water. The experiments were performed at different periods (8, 12, 24 and 36 weeks) after injection of STZ. Blood glucose, tissue lipid peroxidation and plasma vitamin C were measured. To examine the endothelial function, leukocyte adhesion to the venular endothelium was evaluated in the iris post-capillaries by means of counting the number of leukocytes labeled with rhodamine 6G. Blood flow perfusion in the iris was monitored using a laser Doppler flow meter. In the STZ rats, hyperglycemia was induced with an increase in HbA(1c) and lipid peroxidation but with a decrease in the plasma vitamin C level which improved by vitamin C supplementation. The number of adherent leukocytes increased significantly, associated with reduction in the iris blood flow perfusion, at 8, 12, 24 and 36 weeks after injection of STZ. In the STZ-vitC rats, the iris blood flow perfusion was significantly increased in comparison with the STZ rats, while the leukocyte adhesion was decreased at 24 and 36 weeks. The statistical analysis shows that the leukocyte adhesion decreased with increase in the iris blood flow perfusion in STZ and STZ-vitC rats. In conclusion, vitamin supplementation suppressed leukocyte adhesion and thus endothelial dysfunction, associated with increase in iris blood flow perfusion in diabetes. The antioxidant vitamin C may be a therapeutic agent for preventing diabetic retinopathy.

Effects of Metformin on Microvascular Function and Exercise Tolerance in Women With Angina and Normal Coronary Arteries

OBJECTIVES

This study sought to determine whether metformin improves vascular function or myocardial ischemia in nondiabetic subjects.

BACKGROUND

Metformin prevents diabetes and may reduce coronary events in patients with diabetes, but effects on microvascular function and angina are not clear.

METHODS

We conducted an 8-week double-blind, randomized, placebo-controlled study of metformin 500 mg twice a day in 33 nondiabetic women with a prior history of normal coronary angiography but two consecutive positive (ST-segment depression > or =1 mm) exercise tolerance tests. All parameters were measured at baseline and at 8 weeks, together with an in vivo assessment of forearm (skin) microvascular function using laser Doppler imaging combined with iontophoresis.

RESULTS

In comparison with placebo (n = 17), metformin recipients (n = 16) showed significant reductions in weight and in homeostatic model assessment for insulin resistance (p < 0.05, intention to treat). Endothelium-dependent microvascular responses improved significantly with metformin (2-way repeated analysis of variance, p = 0.0003), but responses with placebo were unchanged (p = 0.50). A comparison of change in acetylcholine responses between metformin and placebo recipients was significant, whether analyzed by a 2-way analysis of variance (p < 0.0001) or change in area under curves (mean change +392 perfusion units, 95% confidence interval [CI] 20 to 764). Endothelium-independent responses were not altered. Maximal ST-segment depression (-0.84 mm, 95% CI -1.49 to -0.20, p = 0.013), Duke score (6.1 U, 95% CI 1.8 to 10.5, p = 0.008), and chest pain incidence (-0.11 episodes/day, 95% CI -0.22 to 0.00, p = 0.056) improved in metformin relative to placebo recipients.

CONCLUSIONS

Metformin may improve vascular function and decrease myocardial ischemia in nondiabetic women with chest pain and angiographically normal coronary arteries. Larger controlled trials of longer duration are warranted.

Changes in Endothelial Function Precede the Clinical Disease in Women in Whom Preeclampsia Develops

Endothelial dysfunction is important in the pathophysiology of preeclampsia. No study has examined endothelial function sequentially at different gestations before development of the clinical syndrome and after delivery (to compare maternal from placental influences). We sought to determine whether endothelial function changes before the clinical development of preeclampsia. We measured skin microvascular function using iontophoresis of acetylcholine and sodium nitroprusside, and laser Doppler imaging at 22, 26, 34 weeks' gestation and 6 weeks postpartum in women identified as being at increased risk of preeclampsia, based on uterine artery Doppler waveforms at 18 to 20 weeks, and controls with normal Doppler waveforms. Fifty-four women remained normotensive and preeclampsia developed in 15. In normotensive and preeclamptic women, acetylcholine responses were augmented during pregnancy compared with postpartum responses (P<0.001). Sodium nitroprusside responses were augmented during pregnancy compared with those postpartum (P<0.005) in preeclamptic women only. Microvascular responses were augmented in women in whom preeclampsia developed, compared with those in normotensive women, at 26 and 34 weeks for acetylcholine (P<0.05 and P<0.001, respectively) and at 22 and 26 weeks for sodium nitroprusside (P<0.05 and P<0.02, respectively). Postpartum acetylcholine and sodium nitroprusside responses were not significantly different between preeclamptic and normal women. Microvascular responses are enhanced during pregnancy in women in whom preeclampsia develops to a level above that seen in normotensive women. These changes precede the onset of clinical disease and might be related to a compensatory increased sensitivity of the microcirculation to nitric oxide.

Divergent metabolic and vascular phenotypes in pre-eclampsia and intrauterine growth restriction

OBJECTIVE

Pre-eclampsia (PE) and intrauterine growth restriction (IUGR) may both arise secondary to inadequate trophoblast invasion. Maternal vascular disease is evident only in PE. Little mechanistic evidence exists to explain this dichotomy.

METHODS

We employed laser Doppler imaging (LDI) to examine microvascular function in 15 women with PE and 30 healthy pregnant women matched for body mass index (BMI). We also examined 16 women with IUGR. Other factors examined included indices of inflammation, lipoproteins, leptin and insulin concentrations.

RESULTS

Women with PE had double the concentration of leptin and 30% higher triglyceride than controls. Vascular cell adhesion molecule (VCAM)-1 and interleukin (IL)-6 were also higher in women with PE, with both factors correlating with leptin independently of BMI. No difference in microvascular reactivity was observed between controls and women with PE. Women with IUGR had a four-unit smaller BMI than women with PE. When compared with controls, they also had lower low-density lipoprotein cholesterol (LDL-C) concentrations and systemic inflammatory measures were not elevated.

CONCLUSIONS

The technique of LDI is not sensitive to the vascular dysfunction of PE. However, circulating endothelial-derived factors are elevated in association with markedly elevated leptin levels. Therefore, women with IUGR may demonstrate a protective role for their 'leanness' with regard to maternal systemic inflammatory effect.