The association between birth weight and capillary recruitment is independent of blood pressure and insulin sensitivity: a study in prepubertal children

Early Life Microcirculatory Plasticity and Blood Pressure Changes in Low Birth Weight Infants Born to Normotensive Mothers: A Cohort Study

BACKGROUND

Capillary rarefaction (CR) is an established hallmark of essential hypertension (EH). The aim of this study was to examine early changes in capillary density (CD) and blood pressure (BP) in low birth weight (LBW) infants who are at risk of developing EH in later life.

METHODS

We studied 77 LBW infants and 284 normal birth weight (NBW) infants, all born to mothers with normotension, in a longitudinal multicenter study. Intravital capillaroscopy was used to measure functional basal capillary density (BCD) and maximal capillary density (MCD) at birth, 3, 6, and 12 months.

RESULTS

We found that LBW infants, born preterm and at term, had a significantly higher CD at birth, then underwent significant CR in the 1st 3 months culminating in a CD similar to that seen in NBW infants. NBW infants showed a gradual reduction in CD between birth and 12 months. Non-Caucasian ethnicity and preterm birth were significant predictors of a higher CD at birth. Systolic BP in NBW infants increased significantly from birth to 3 months, and we identified a significant negative correlation between systolic BP and MCD.

CONCLUSIONS

This study has identified a process of early “accelerated capillary remodeling” in LBW infants, which corrects their higher CD at birth. This remodeling is unlikely to explain the CR seen in adult individuals with, or at risk of developing EH. Further follow-up studies are required to determine the timing and mechanisms involved in CR, which is likely to occur after the 1st year of life but before early adulthood.

Detrimental Impact of Low Birth Weight on Circulating Number and Functional Capacity of Endothelial Progenitor Cells in Healthy Children: Role of Angiogenic Factors

OBJECTIVE

To provide a comprehensive assessment of the relationship of birth weight with both endothelial progenitor cell function and angiogenic factors in children.

STUDY DESIGN

Anthropometric measures, biochemical profile, endothelial progenitor cell number, endothelial progenitor cell colony-forming units, vascular endothelial growth factor-A, and nitric oxide plasma levels of 58 children aged 7-11 years were determined.

RESULTS

A positive correlation was observed between birth weight and circulating endothelial progenitor cell number (r= 0.461; P= .001), endothelial progenitor cell colony-forming units (r= 0.512; P < .001), vascular endothelial growth factor-A (r= 0.407; P= .002), and nitric oxide (r= 0.547; P < .001) levels, whereas the adjustment for prematurity, family history of cardiovascular disease, and systolic blood pressure levels did not modify these associations.

CONCLUSION

Low birth weight was associated with a decrease in the circulating/functional capacity of endothelial progenitor cells among healthy children, independent of traditional cardiovascular risk factors. This detrimental impact was accompanied by lower circulating levels of angiogenic factors.

Microvascular Dysfunction and Hyperglycemia: A Vicious Cycle With Widespread Consequences

Microvascular and metabolic physiology are tightly linked. This Perspective reviews evidence that 1) the relationship between hyperglycemia and microvascular dysfunction (MVD) is bidirectional and constitutes a vicious cycle; 2) MVD in diabetes affects many, if not all, organs, which may play a role in diabetes-associated comorbidities such as depression and cognitive impairment; and 3) MVD precedes, and contributes to, hyperglycemia in type 2 diabetes (T2D) through impairment of insulin-mediated glucose disposal and, possibly, insulin secretion. Obesity and adverse early-life exposures are important drivers of MVD. MVD can be improved through weight loss (in obesity) and through exercise. Pharmacological interventions to improve MVD are an active area of investigation.

Capillary Rarefaction Associates with Albuminuria: The Maastricht Study

Albuminuria may be a biomarker of generalized (i.e., microvascular and macrovascular) endothelial dysfunction. According to this concept, endothelial dysfunction of the renal microcirculation causes albuminuria by increasing glomerular capillary wall permeability and intraglomerular pressure, the latter eventually leading to glomerular capillary dropout (rarefaction) and further increases in intraglomerular pressure. However, direct evidence for an association between capillary rarefaction and albuminuria is lacking. Therefore, we examined the cross-sectional association between the recruitment of capillaries after arterial occlusion (capillary density during postocclusive peak reactive hyperemia) and during venous occlusion (venous congestion), as assessed with skin capillaroscopy, and albuminuria in 741 participants of the Maastricht Study, including 211 participants with type 2 diabetes. Overall, 57 participants had albuminuria, which was defined as a urinary albumin excretion ≥30 mg/24 h. After adjustment for potential confounders, participants in the lowest tertile of skin capillary recruitment during postocclusive peak reactive hyperemia had an odds ratio for albuminuria of 2.27 (95% confidence interval, 1.07 to 4.80) compared with those in the highest tertile. Similarly, a comparison between the lowest and the highest tertiles of capillary recruitment during venous congestion yielded an odds ratio of 2.89 (95% confidence interval, 1.27 to 6.61) for participants in the lowest tertile. In conclusion, lower capillary density of the skin microcirculation independently associated with albuminuria, providing direct support for a role of capillary rarefaction in the pathogenesis of albuminuria.

Microvascular dysfunction as a link between obesity, insulin resistance and hypertension

Impaired microvascular dilatation from any cause and impaired insulin-mediated capillary recruitment in particular result in suboptimal delivery of glucose and insulin to skeletal muscle, and subsequently impairment of glucose disposal (insulin resistance). In addition, microvascular dysfunction, through functional and/or structural arteriolar and capillary drop-out, and arteriolar constriction, increases peripheral resistance and thus blood pressure. Microvascular dysfunction may thus constitute a pathway that links insulin resistance and hypertension. Overweight and obesity may be an important cause of microvascular dysfunction. Mechanisms linking overweight and obesity to microvascular dysfunction include changes in the secretion of adipokines leading to increased levels of free fatty acids and inflammatory mediators, and decreased levels of adiponectin all of which may impair endothelial insulin signaling. Microvascular dysfunction may thus constitute a new treatment target in the prevention of type 2 diabetes mellitus and hypertension.

Low Birth Weight Infants Do Not Have Capillary Rarefaction at Birth

Low birth weight predicts adult essential hypertension and is linked to increased cardiovascular mortality in adult life. A reduction in capillary density (ie, rarefaction) is a hallmark of essential hypertension, and evidence suggests that rarefaction precedes the onset of the rise in blood pressure, because it is found in normotensive individuals at high risk of developing hypertension, suggesting that rarefaction is likely to be a primary structural abnormality. We hypothesized that low birth weight infants would have significant capillary rarefaction at birth. We studied 44 low birth weight infants born to normotensive mothers (33 were born preterm, birth weight: 1823±446 g; and 11 were born at term, birth weight: 2339±177 g) and compared them with 71 infants born at term with normal weight (birth weight: 3333±519 g). We used orthogonal polarized spectroscopy to measure basal (ie, functional) and maximal (ie, structural) skin capillary densities. Low birth weight infants, whether born preterm or at term, had significantly higher functional capillary density (mean difference of 10.5 capillaries per millimeter squared; 95% CI: 6.6–14.4 capillaries per millimeter squared; P <0.0001) and higher structural capillary density (mean difference of 11.1 capillaries per millimeter squared; 95% CI: 7.6–14.5 capillaries per millimeter squared; P <0.0001) when compared with normal weight term infants. We conclude that low birth weight infants born to normotensive mothers do not have capillary rarefaction at birth. These results contradict what might have been predicted from the concept of the intrauterine origins of adult disease and suggest that microcirculatory abnormalities observed in individuals of low birth weight occur in postnatal life rather than during their intrauterine existence.

Thrombophilia mediates lowering cardiovascular risk factors in women with a history of preeclampsia

OBJECTIVE

Preeclampsia is associated with increased risk of cardiovascular disease. The aim of this pilot study was to assess whether the presence of thrombophilia results in a greater tendency to develop endothelial dysfunction and cardiovascular diseases.

METHODS

Ten women with thrombophilia were matched with 10 women without thrombophilia for a history of hypertensive disorders during pregnancy. Laboratory measurements: blood pressure, insulin sensitivity, and micro- and macrovascular function were determined.

RESULTS

Women with thrombophilia had significant lower total- and low-density cholesterol, were more insulin sensitive, and had better microvascular function.

CONCLUSION

This study suggests that thrombophilia "mediates" in lowering of cardiovascular risk factors in women with a history of preeclampsia.

The beneficial effects of breastfeeding on microvascular function in 11- to 14-year-old children

Abstract

Infant feeding practices have an impact on health in later life, although the evidence for its effects on cardiovascular health is not so clear. The aim of this study was to investigate the relationship between breastfeeding in infancy and vascular function in later childhood. Infant feeding data, together with demographic and clinical information, were obtained prospectively from a cohort of children from birth until 2 years of age. Vascular function was assessed in 159 children, now aged 11–14 years, by measuring their skin microvascular responses to iontophoretic administration of the endothelium-dependent vasodilator acetylcholine. Endothelial function was significantly better in children who had been breastfed than in those who had received infant milk formula ( p = 0.001), after adjustment for potential confounding factors. Linear regression showed that acetylcholine responses were significantly related to the duration of breastfeeding ( r = 0.30, p = 0.006). The risk of later cardiovascular disease may be reduced by exclusively breastfeeding during infancy. These findings have potential public health implications, and support policies aimed at promoting breastfeeding.

Incorporation of the fasting free fatty acid concentration into quantitative insulin sensitivity check index improves its association with insulin sensitivity in adults, but not in children

OBJECTIVE

Based on fasting insulin and glucose, several indices of insulin sensitivity have been developed in adults. Recently, it has been demonstrated that incorporation of the fasting free fatty acid (FFA) concentration improves the association with insulin sensitivity in adults. We investigated the association of clamp-derived insulin sensitivity with indices of insulin sensitivity derived from fasting blood in prepubertal children and adults, with and without incorporation of FFAs.

DESIGN AND METHODS

We studied 59 healthy adults and 29 of them are prepubertal children. We measured insulin sensitivity with the euglycemic-hyperinsulinemic clamp. Based on fasting insulin and glucose, we estimated insulin sensitivity with the homeostasis model assessment (HOMA), the quantitative insulin sensitivity check index (QUICKI), and the revised QUICKI after the incorporation of FFAs.

RESULTS

The associations of HOMA and QUICKI with clamp-derived insulin sensitivity in children (r=-0.55 and 0.54 respectively; P<0.01) were similar to those in adults (r=-0.54 and 0.53 respectively; P<0.01). However, incorporation of FFAs into the QUICKI model resulted in an increase in the association in adults, but not in children (r=0.68 and 0.48 respectively; P<0.01). Adding FFA levels to a regression model with glucose and insulin as independent variables resulted in an increase in the explained variance in clamp-derived insulin sensitivity in adults, but not in children (P value 0.004 in adults and 0.3 in children).

CONCLUSIONS

HOMA and QUICKI are associated with clamp-derived insulin sensitivity in both children and adults. Incorporating fasting levels of FFAs into the QUICKI model improves the association with clamp-derived insulin sensitivity in adults, but not in children.

Low birth weight and the developing vascular tree: a systematic review

Low birth weight (LBW) is a risk factor for hypertension, stroke and coronary heart disease in adults. Mechanisms underlying cardiovascular disease may therefore be initiated in early life. Studies to investigate the initiating events and emergence of vascular risk markers in infancy and childhood have been an area of particular interest in recent years. The aim of this review is to focus on the early development of the human vascular tree in relation to LBW. Specific characteristics, including endothelial function, intima-media thickness, microvascular density, arterial dimensions and elasticity, will be discussed. LBW due to different causes--poor foetal growth or preterm birth--results in different patterns of altered development of the vascular system, which can already be seen in infancy. Follow-up studies in children and young adults indicate that vascular compromise in many ways persists in those born either small for gestational age or prematurely.

CONCLUSION

LBW is associated with structural and functional changes in the vascular tree, which have implications for cardiovascular health in adult life.

Lower skin capillary density, normal endothelial function and higher blood pressure in children born preterm

BACKGROUND

Preterm birth is a risk factor for blood pressure (BP) elevation already at young age. The mechanisms are unknown. Low skin capillary density and impaired endothelial function characterize adults with hypertension.

OBJECTIVES

To investigate the early relationships between BP, capillary density and endothelial function after very preterm birth. Design and subjects. Clinical follow-up study of 60 healthy school children aged 7-12 years; 39 born very preterm (mean gestational age 29 weeks) and 21 control subjects born at term with normal birth weights.

METHODS

Using intravital video-microscopy, the dermal capillary densities in the fingers were measured before and during venous occlusion. Endothelial function was assessed using a Laser-Doppler technique to determine skin perfusion before and after transdermal delivery of acetylcholine, an endothelium-dependent vasodilator. Brachial BP and heart rate (HR) were also recorded.

RESULTS

Children born very preterm had lower functional capillary density than term controls (89.9 capillaries mm(-2) vs. 96.6 capillaries mm(-2), P = 0.04). During venous occlusion--measuring structural differences--this difference diminished (91.4 capillaries mm(-2) vs. 96.8 capillaries mm(-2), P = 0.12). In multivariate analysis, systolic BP (SBP) was higher in children born preterm, but SBP and capillary density did not correlate. HR was also higher in children born preterm, but did not correlate to BP or capillary density. Endothelial function did not differ between groups and did not correlate to capillary density.

CONCLUSION

Children born very preterm have lower functional skin capillary density, higher BP and higher HR. Longitudinal studies are needed to fully understand the long-term significance of these findings.

Urinary cortisol is inversely associated with capillary recruitment in women: a potential explanation for the cortisol–blood pressure relationship

The relationships of cortisol with elevated blood pressure and insulin resistance are likely to be the result of a complex interplay of different mechanisms. We hypothesize that cortisol is associated with impaired microvascular function and that this contributes to cortisol-associated high blood pressure and insulin resistance. We examined 24 h urinary free cortisol excretion in 56 healthy adults (26 women). Blood pressure was assessed by 24 h ambulatory measurements. Insulin sensitivity was determined using the hyperinsulinaemic euglycaemic clamp technique. Skin capillary recruitment after arterial occlusion was visualized with videomicroscopy and endothelium-(in)dependent vasodilation was evaluated with iontophoresis of acetylcholine and sodium nitroprusside combined with laser Doppler fluxmetry. Men were characterized by higher urinary cortisol excretion [median (interquartile range), 162 (130–194) compared with 118 (99–156) nmol/24 h, P<0.05]. In women, but not in men, urinary cortisol excretion was associated with impaired capillary recruitment (r=−0.66, P<0.001), higher systolic blood pressure (r=0.64, P<0.001) and lower insulin sensitivity (r=−0.43, P<0.05). Urinary cortisol excretion was not associated with endothelium-(in)dependent vasodilation in men or women. Regression analysis demonstrated that capillary recruitment statistically explained 37% of the association between urinary cortisol and blood pressure in women. Capillary recruitment did not explain part of the association between urinary cortisol and insulin sensitivity. In conclusion, urinary cortisol excretion is inversely associated with capillary recruitment in women, but not in men, and capillary recruitment explains part of the cortisol–blood pressure relationship. These data suggest that, in women, impairment of capillary function mediates some of the adverse effects of cortisol and thus may provide a target to prevent such adverse effects.

Altered skeletal muscle fiber composition and size precede whole-body insulin resistance in young men with low birth weight

CONTEXT

Low birth weight (LBW), a surrogate marker of an adverse fetal milieu, is linked to muscle insulin resistance, impaired insulin-stimulated glycolysis, and future risk of type 2 diabetes. Skeletal muscle mass, fiber composition, and capillary density are important determinants of muscle function and metabolism, and alterations have been implicated in the pathogenesis of insulin resistance.

OBJECTIVE

The aim of this study was to investigate whether an adverse fetal environment (LBW) induces permanent changes in skeletal muscle morphology, which may contribute to the dysmetabolic phenotype associated with LBW.

DESIGN AND SUBJECTS

Vastus lateralis muscle was obtained by percutaneous biopsy from 20 healthy 19-yr-old men with birth weights at 10th percentile or lower for gestational age (LBW) and 20 normal birth weight controls, matched for body fat, physical fitness, and whole-body glucose disposal. Myofibrillar ATPase staining was used to classify muscle fibers as type I, IIa, and IIx (formerly type IIb), and double immunostaining was performed to stain capillaries (LBW, n=8; normal birth weight, n=12).

RESULTS

LBW was associated with increased proportion of type IIx fibers (+66%; P=0.03), at the expense of decreased type IIa fibers (-22%; P=0.003). No significant change was observed in proportion of type I fibers (+16%; P=0.11). In addition, mean area of type IIa fibers was increased (+29%; P=0.01) and tended to be increased for type I fibers as well (+17%; P=0.08). Capillary density was not significantly different between groups.

CONCLUSION

Alterations in fiber composition and size may contribute to development of type 2 diabetes in individuals with LBW.

TNF-α levels are associated with skin capillary recruitment in humans: a potential explanation for the relationship between TNF-α and insulin resistance

The mechanism by which TNF-α (tumour necrosis factor-α) may cause insulin resistance is not clear. On the basis of experiments in rats, TNF-α has been suggested to cause defects in capillary function, with a decreased access of insulin and glucose to tissues. To test this hypothesis in humans, we assessed serum TNF-α concentrations, skin capillary recruitment and insulin sensitivity in a group of 37 healthy adults. In addition, we measured these variables in 21 of their prepubertal children. Serum TNF-α levels were measured by sandwich enzyme immunoassay, and insulin sensitivity was assessed with the hyperinsulinaemic euglycaemic clamp technique. Capillary recruitment during post-occlusive reactive hyperaemia was evaluated by videomicroscopy. In the adults, serum TNF-α levels were associated with both capillary recruitment (r=−0.40, P=0.02) and insulin sensitivity (r=−0.33, P=0.05). In addition, capillary recruitment was associated with insulin sensitivity (r=0.34, P=0.04). Regression analysis showed that the association between TNF-α and insulin sensitivity [−0.527 mg·kg−1 of body weight·min−1 per pmol/l per pg/ml TNF-α (95% confidence interval, −1.066 to 0.011); P=0.05] decreased by 30% after adjustment for capillary recruitment. In the children, neither capillary recruitment (r=0.33, P=0.2) nor insulin sensitivity (r=−0.24, P=0.4) was significantly associated with TNF-α. In conclusion, in adults, but not in children, serum TNF-α levels are associated with capillary recruitment during post-occlusive hyperaemia, which, in part, can explain the relationship between TNF-α and insulin resistance. Our data suggest that these relationships are initiated during growth from childhood to adulthood.

Preterm birth contributes to increased vascular resistance and higher blood pressure in adolescent girls

Preterm birth might induce permanent changes in vascular structure and function as well as in blood pressure. To elucidate this hypothesis and underlying mechanisms in girls born before term, the authors correlated neonatal data, including estradiol levels, with vascular function and structure and with blood pressure after puberty. In a case-control study design, 34 girls born before term and 32 gender- and age-matched control infants born at term were included. Pulse wave analysis was used to determine aortic pressure profiles and overall arterial compliance. Stiffness of the carotid artery and abdominal aorta was measured with ultrasonography. Pulse wave velocity in the forearm was measured with photoplethysmography. A laser Doppler technique was used to determine skin perfusion before and after transdermal delivery of acetylcholine, an endothelium-dependent vasodilator. It was found that preterm girls had significantly higher brachial and aortic blood pressure, a narrower but less stiff abdominal aorta, and lower peripheral skin blood flow than did control infants. Augmentation index, carotid stiffness, pulse wave velocity, endothelium-dependent vasodilatation, and heart rate were similar in the two groups. In the preterm group, blood pressure and vascular functions showed no association with intrauterine growth retardation or neonatal estradiol levels. In conclusion, preterm girls have higher blood pressure and an increased resistance in the vascular tree after puberty. These findings may have implications for future cardiovascular risk in the growing adult population surviving preterm birth.

Developmental determinants of blood pressure in adults

Over the past 20 years a large and varied body of research has attempted to make the case for the developmental origins of elevated adult blood pressure (BP). Experimental animal research has identified plausible biological mechanisms through which fetal nutritional insufficiency may affect adult BP. The majority of human epidemiologic studies demonstrate an inverse association of birth weight (the most commonly used marker of fetal nutrition) with adult BP and higher risk of hypertension among individuals with lower weight at birth. The most adverse BP outcomes occur among individuals who were small at birth but relatively large as adults, a finding that suggests a role for postnatal growth. We critically review the literature on proposed mechanisms and epidemiologic evidence for developmental origins of adult BP and hypertension, considering associations with birth weight, maternal nutrition during pregnancy, child growth patterns, and infant feeding.

Metals content in placentas from moderate cigarette consumers: correlation with newborn birth weight

Cigarette consumption during pregnancy produces deleterious effects in both, mother and fetus, some of them due to the presence of toxic elements in cigarette smoke, such as cadmium. Placenta constitutes a dual-purpose specimen for evaluating the pollutant burden exerted on the mother as well as on the fetus. The main objective of this study was to establish a correlation between placental concentration and distribution of some metal elements and birth weight of neonates delivered by mothers, who were either moderate smokers or nonsmokers. Forty nonsmoking and moderate smoking pregnant women paired per age, parity, weight, height and body mass index were selected. Smoking was assessed by self-reported cigarette consumption during pregnancy and urine cotinine concentration before delivery. Placental metal concentrations were evaluated by atomic absorption spectrometry (copper and cadmium) and neutron activation analysis (zinc and iron). Newborns from smokers had lower birth weights compared to infants from nonsmokers. Birth weights were correlated with placental cadmium concentrations in both, smokers and nonsmokers. Placental zinc and cadmium of smokers were mainly located at the maternal side and their levels were higher than those found in nonsmoker's placentas. In addition, all metal nutrient/pollutant ratios were decreased in the smoker group. In this first study performed in our region, we found that moderate smoking mothers deliver neonates with decreased birth weight and highly correlated to placental cadmium concentration. Decreased metal nutrient/pollutant ratios, a condition here found in smokers, may indicate a placental dysfunction, contributing to impair birth weight.

Preterm birth attenuates association between low birth weight and endothelial dysfunction

BACKGROUND

Low birth weight predisposes to later coronary disease. To further elucidate the mechanisms behind this association and their timing, vascular endothelial function-a key factor in early pathophysiology of atherosclerosis-was studied in 54 infants born either before the third trimester or at term.

METHODS AND RESULTS

All subjects were studied at 3 months of postnatal age. A laser-Doppler technique was used to measure skin perfusion before and after transdermal iontophoresis of acetylcholine (ACh; an endothelium-dependent vasodilator). In infants born at term (n=19; birth weight range: 2230 to 4205 g), maximum perfusion after ACh was 109+/-8 perfusion units (PU, mean+/-SEM) in normal-birth weight controls compared with 56+/-13 PU among those who had been small for gestational age at birth (P<0.01). In infants born preterm (n=35; birth weight range, 722 to 1868 g), ACh induced similar perfusion responses among subjects appropriate for gestational age (113+/-16 PU) and in those small for gestational age at birth (109+/-19 PU).

CONCLUSIONS

Impairment in human endothelial function associated with low birth weight occurs or emerges late in pregnancy. Very preterm birth attenuates this association. Different gene-environment interactions in the third trimester may contribute to this finding.