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Elevated Blood Pressure in Preterm-Born Offspring Associates With a Distinct Antiangiogenic State and Microvascular Abnormalities in Adult Life

Originally publishedhttps://doi.org/10.1161/HYPERTENSIONAHA.114.04662Hypertension. 2015;65:607–614

Abstract

Preterm-born individuals have elevated blood pressure. We tested the hypothesis that this associates with an enhanced antiangiogenic circulating profile and that this association is mediated by variations in capillary density. We studied 204 adults aged 25 years (range, 20–30 years), of which 102 had been followed up prospectively since very preterm birth (mean gestational age, 30.3±2.5 weeks) and 102 were born term to uncomplicated pregnancies. A panel of circulating biomarkers, including soluble endoglin and soluble fms-like tyrosine kinase-1, were compared between groups and related to perinatal history and adult cardiovascular risk. Associations with cardiovascular phenotype were studied in 90 individuals who had undergone detailed assessment of microvascular, macrovascular, and cardiac structure and function. Preterm-born individuals had elevations in soluble endoglin (5.64±1.03 versus 4.06±0.85 ng/mL; P<0.001) and soluble fms-like tyrosine kinase-1 (88.1±19.0 versus 73.0±15.3 pg/mL; P<0.001) compared with term-born individuals, proportional to elevations in resting and ambulatory blood pressure, as well as degree of prematurity (P<0.05). Maternal hypertensive pregnancy disorder was associated with additional increases in soluble fms-like tyrosine kinase-1 (P=0.002). Other circulating biomarkers, including those of inflammation and endothelial activation, were not related to blood pressure. There was a specific graded association between soluble endoglin and degree of functional and structural capillary rarefaction (P=0.002 and P<0.001), and in multivariable analysis, there were capillary density–mediated associations between soluble endoglin and blood pressure. Preterm-born individuals exhibit an enhanced antiangiogenic state in adult life that is specifically related to elevations in blood pressure. The association seems to be mediated through capillary rarefaction and is independent of other cardiovascular structural and functional differences in the offspring.

Introduction

At present, significant advances in perinatal care have resulted in individuals born very preterm routinely surviving to adulthood.1,2 However, their early cardiovascular growth and development have occurred under unusual physiological conditions. Detailed imaging has identified that, as adults, they have a unique preterm cardiovascular phenotype, characterized by disproportionate reductions in cardiac and vascular size,39 that extends to involve the microvasculature.10

Microvascular rarefaction is a major determinant of increased vascular resistance and is associated with the development of hypertension.11,12 Indeed, pharmacological manipulation of microvascular development through pathways that include soluble endoglin (sENG), soluble fms-like tyrosine kinase-1 (sFlt-1), and vascular endothelial growth factor can induce hypertension.13,14 This occurs pathologically during onset of pregnancy complications that result in maternal hypertension, in which capillary rarefaction is linked with increases in placental-derived sENG and sFlt-1.15,16

Umbilical cord blood analysis shows that antiangiogenic factors are also increased in the fetal circulation in complicated pregnancies.17 Intriguingly, cord sera from preterm infants impairs vasculogenesis in vitro,18 and their circulating endothelial colony–forming cells express an antiangiogenic phenotype.19 Individuals born very preterm have higher blood pressure throughout early life,68,20–22 and these observations raise the possibility that an antiangiogenic milieu, potentially triggered by or related to the causes of preterm birth, underlies microvascular and blood pressure variation in preterm-born individuals. We hypothesized that these pathways are relevant to cardiovascular risk later in life, and therefore, we measured a panel of circulating angiogenic markers in adults who had been born very preterm, studied how levels vary with perinatal factors, and determined whether they are related to adult cardiovascular risk. We then identified features of the preterm cardiovascular phenotype that mediated associations between angiogenic factors and blood pressure.

Methods

Study Population

We have prospectively followed up individuals born preterm between 1982 and 1985 since recruitment at birth to randomized feeding regimes.37 Of the initial 926 subjects (birthweight, <1850 g), 240 agreed to be recontacted, of which 102 agreed to attend Oxford for detailed cardiovascular phenotyping at age 23 to 28 years.37 Compared with the original cohort, those who were followed up to adulthood had similar perinatal characteristics (Table S1 in the online-only Data Supplement) except for a small 70-g (5%) difference in birth weight, accounted for by a marginally shorter gestational age, such that the birthweight Z score does not differ. For this study, 102 young adults born term to uncomplicated pregnancies with similar age and sex distribution to the preterm-born young adults were recruited via advertisement to undergo identical investigations. Blood sampling, anthropometry, blood pressure measurements, questionnaires, and cardiovascular assessments (cardiac and macrovascular assessments) were undertaken in all participants. During an interim review, the microvascular-angiogenesis hypothesis was developed, and we amended the protocol to include ambulatory blood pressure and microvascular assessment in 30 of the 102 preterm-born adults and 60 of the 102 term-born adults (microvascular substudy). All data were coded with subject and study-specific IDs (eg, EVS001) to ensure anonymity and blinded analysis. This study was registered with ClinicalTrials.gov (NCT01487824), and the initial study protocol, as well as the subsequent amendment, was approved by the relevant ethics committee (Oxfordshire Research Ethics Committee A: 06/Q1604/118). All participants provided signed informed consent.

Main Study Measures

Perinatal Data and Cardiovascular Risk Factors

Details of perinatal data collection, cardiovascular measures, and other data collected in young adulthood at the 23- to 28-year follow-up study have previously been reported.37 In young adulthood, blood pressure was measured as the average of the last 2 of 3 brachial blood pressure recordings from an automatic digital monitor (HEM-705CP; OMRON, Osaka, Japan) with a cuff placed on the left arm after participants had rested in supine position for 10 minutes.37 Anthropometry included height, weight, and skinfold thickness. Medical and lifestyle information was collected using a questionnaire.23,24 Blood samples were drawn after a 12-hour overnight fast, centrifuged, separated within 30 minutes, and stored at −80°C. Fasting lipid and metabolic profiles, including C-reactive protein, were measured at the Oxford Hospital Biochemistry Laboratory using routine clinical quality validated assays.

Circulating Biomarkers of Angiogenesis, Inflammation, and Endothelial Activation

We quantified serum circulating vascular endothelial growth factor-A (VEGF165), sFlt-1, placental growth factor, and sENG levels with commercial enzyme-linked immunosorbent assays (Quantikine; R&D Systems Europe, Abingdon, UK). Soluble E-selectin, soluble vascular cell adhesion molecule-1 (sVCAM-1), and soluble intercellular adhesion molecule-1 (sICAM-1) were measured using Millipore MILLIPLEXMAP kits based on the Luminex xMAP platform (Millipore Corporation, Billerica, MA). Full technical details are in the online-only Data Supplement.

Additional Cardiovascular Measures

Methods for previously reported cardiac and macrovascular measures are in the online-only Data Supplement.35 Arterial stiffness was assessed by carotid-femoral pulse wave velocity using applanation tonometry (SphygmoCor Analysis System, West Ryde, Australia) and, in addition, Cardio-Ankle Vascular Index25 (Vasera; Fukuda Denshi, Tokyo, Japan) to derive a blood pressure–independent measure of arterial stiffness. Endothelial function was quantified as brachial artery flow–mediated dilatation.24 Cardiovascular magnetic resonance on a Siemens 1.5T Sonata scanner was used to quantify cardiac mass and function,5 as well as thoracic and abdominal aortic size.3,57,26

Microvascular Substudy Measures

Structural and Functional Capillary Densities

Intravital video capillaroscopy with a Leica Stereo Microscope at ×200 magnification and Schott light-emitting diode light (wavelength 450 to 610 nm, consistent with hemoglobin absorption wavelength) was used to assess microvascular structure and function on the dorsal surface of the middle phalanx of the left hand in 6 adjacent image fields at baseline and after venous occlusion. A Bosch Dinion CCD Analogue Camera relayed images to a Norban Vista black and white high-resolution monitor, which were recorded on a Sony DVO-1000MD digital video disc recorder. Calibration was performed with a 1.0 mm glass stage graticule (Knight Optical, Kent, United Kingdom), and images were analyzed with Image ProPlus. Full details of patient preparation, data acquisition, and image analysis are in the online-only Data Supplement.

Ambulatory Blood Pressure

Twenty-four-hour blood pressure monitoring was performed on the left arm using an automatic digital monitor (A&D Instruments Ltd, Tokyo, Japan). Details of device fitting and patient instructions are provided in the online-only Data Supplement.

Statistical Analysis

SPSS version 22 was used for statistical analysis. Variable normality was assessed visually from normality curves and by Shapiro–Wilk test. Comparison between groups for continuous variables was performed by 2-sided independent-sample Student t test for normally distributed data and Mann Whitney and Kruskal–Wallis tests for skewed data. Categorical variables were compared by χ2 test. Linear regression models were performed using a forced entry method. Pearson correlations (r) were used for bivariate associations and unstandardized regression coefficients (B), or standardized regression coefficients (β) were used for bivariable and multivariable regression models. One-hundred and two subjects per group provided 80% power at P=0.05 to identify a 0.38SD difference between groups. For subgroup analysis, 30 preterm-born and 60 term-born subjects provided 80% power at P=0.05 to identify a 0.62SD difference between groups. Comparisons were adjusted for age and sex. Results are presented as mean±SD. Mediation analyses were performed to determine potential causal pathways between capillary density, sENG, and 24-hour systolic blood pressure levels in preterm-born adults. Bivariable regression analyses were first performed using a forced entry method followed by multivariable regression analyses with 24-hour systolic blood pressure as the dependent variable and sENG and capillary density as independent variables. P values <0.05 were considered statistically significant.

Results

Study Population

Demographic and risk factor characteristics of the preterm- and term-born adults are presented in Table S2, with corresponding information limited to the microvascular substudy group in Table 1. There were no significant differences in the number of smokers, personal and family medical history, or lifestyle factors, such as socioeconomic status, physical activity, or diet between preterm- and term-born adults. However, preterm-born adults had a distinct metabolic profile and higher brachial blood pressure.37 In the microvascular substudy, a 10-mm Hg higher systolic blood pressure was evident on 24-hour ambulatory blood pressure monitors during both awake and sleep periods in preterm-born adults (Table 1). Of the 102 preterm-born young adults that took part in the study, 47 were delivered by prelabour cesarean section or induced (iatrogenic) delivery, of which 29 were born to hypertensive pregnancies. The remaining 55 preterm births were spontaneous (idiopathic).

Table 1. Characteristics of Microvascular Study Cohort

ParametersPreterm-Born Young Adults, n=30Term-Born Young Adults, n=60P Value
Demographics and anthropometrics
 Gestational age, wk30.5±2.739.6±0.8<0.001
 Birthweight, g1295.6±304.53411.2±319.0<0.001
 Age, y26.6±1.026.2±1.90.37
 Men, n (%)15 (50.0)30 (50.0)>0.99
 BMI, kg/m226.3±7.223.0±3.30.006
 Smokers, n (%)5 (16.7)10 (16.7)>0.99
Biochemistry
 Total cholesterol, mmol/L4.79±0.774.23±0.860.009
 HDL-C, mmol/L1.47±0.381.46±0.420.85
 LDL-C, mmol/L2.69±0.822.39±0.670.12
 Triglycerides, mmol/L1.10±0.640.86±0.330.03
 Glucose, mmol/L4.87±0.354.60±0.310.001
 Insulin, pmol/L55.1±34.836.0±18.00.002
Full 24-hour blood pressure, mm Hg
 Systolic123.3±6.4112.8±7.5<0.001
 Diastolic69.6±4.367.1±4.90.02
 Mean arterial pressure87.3±4.182.1±5.2<0.001
 Pulse pressure53.7±6.945.7±5.8<0.001
Awake blood pressure, mm Hg
 Systolic126.3±6.5116.6±8.3<0.001
 Diastolic72.9±5.270.3±5.90.05
 Mean arterial pressure90.5±4.485.7±6.10.001
 Pulse pressure53.4±7.646.3±6.1<0.001
Sleep blood pressure mm Hg
 Systolic110.3±9.2101.1±8.1<0.001
 Diastolic59.0±6.956.4±4.70.04
 Mean arterial pressure75.6±7.071.0±5.00.001
 Pulse pressure51.4±7.444.7±7.0<0.001

Values are mean±SD unless stated otherwise. P values were adjusted for age and sex. BMI indicates body mass index; HDL-C, high-density lipoprotein cholesterol; and LDL-C, low-density lipoprotein cholesterol.

Preterm Birth and Circulating Levels of Antiangiogenic and Inflammatory Biomarkers

Preterm-born adults had increased sFlt-1 and sENG levels compared with term-born individuals (P<0.001; Figure 1 and Table 2). There were no differences in vascular endothelial growth factor-A levels (P=0.36) or C-reactive protein between groups (P=0.17), but sICAM-1 and sVCAM-1 levels were significantly elevated in those born preterm (P<0.001; Table 2). The placental growth factor and soluble E-selectin levels were not detectable. In bivariable regression analyses, there was an inverse graded relationship between degree of prematurity, assessed as gestational age, and sENG and sFlt-1, with a positive relation to sICAM-1 (P<0.05). There were no graded differences with sVCAM-1 (Table S3).

Table 2. Circulating Angiogenic, Antiangiogenic, and Inflammatory Markers

Circulating BiomarkersPreterm-Born Young Adults, n=102Term-Born Young Adults, n=102P Value
Angiogenic and antiangiogenic markers
 VEGF-A, pg/mL139.5±71.3148.5±65.90.36
 sENG, ng/mL5.64±1.034.06±0.85<0.001
 sFlt-1, pg/mL88.1±19.073.0±15.3<0.001
Inflammatory markers
 CRP, mmol/L2.27±4.021.53±3.350.17
 sICAM-1, ng/mL121.3±10.9112.9±10.1<0.001
 sVCAM-1, ng/mL1187.8±271.3864.4±155.4<0.001

Values are mean±SD. P values were adjusted for age and sex. PlGF and sE-selectin were not detectable. CRP indicates C-reactive protein; PlGF, placental growth factor; sE-selectin, soluble E-selectin; sENG, soluble endoglin; sFlt-1, soluble fms-like tyrosine kinase-1; sICAM-1, soluble intercellular adhesion molecule-1; sVCAM-1, soluble vascular cell adhesion molecule-1; and VEGF-A, vascular endothelial growth factor A.

Figure 1.

Figure 1. A, Soluble endoglin (sENG) was increased in preterm-born young adults (PTYA, blue) compared with that in term-born adults (YAT, green). B, Soluble fms-like tyrosine kinase-1 (sFlt-1) in those born preterm to hypertensive pregnancy (Hyp, darker blue) was 97.7±15.9 pg/mL compared with 84.2±18.9 pg/mL in those born preterm to normotensive mothers (Norm, lighter blue), which was still significantly higher than sFlt-1 levels in term-born adults (YAT, green; 73.0±15.3 pg/mL).

To understand whether preterm birth per se or other perinatal factors accounted for these associations, we used bivariable regression analyses to identify other potentially relevant associations (Table S3). No perinatal factors apart from gestational age predicted sENG levels. Gestational hypertension during the indicated pregnancy was associated with higher offspring sFlt-1 levels but with no differences in other circulating markers (B=13.5 pg/mL per category; P=0.002, where pregnancy-induced hypertension was a dichotomous categorical variable with 1=normotensive pregnancy and 2=preeclamptic pregnancy). Figure 1B demonstrates that sFlt-1 levels in those born preterm because of maternal hypertension were 97.7±15.9 pg/mL compared with 84.2±18.9 pg/mL in those born preterm to normotensive mothers (P=0.002). sFlt-1 levels in those with a normotensive mother were still significantly elevated compared with those in term-born young adults (P<0.001). However, this difference between preterms born to a hypertensive versus normotensive pregnancy was not apparent in sENG levels (5.79±1.04 versus 5.58±1.04 ng/mL; P=0.37) that were significantly higher than those in term-born young adults (P<0.001; Figure 1A). The Apgar score at 5 minutes is also related to sFlt-1 levels (B=−1.86 pg/mL per point; P=0.05) and to sICAM-1 in young adulthood (B=−4.3 ng/mL per point; P=0.01).

In multivariable regression models, which included gestational age, birthweight, 5-minute Apgar score, gestational hypertension, and antenatal glucocorticoid exposure, gestational age remained an independent predictor for sENG (B=−0.15 ng/mL per gestational week; 95% confidence interval, −0.27 to −0.031; P=0.008), but none of the other circulating biomarkers did (Table S4). For sFlt-1, being born to a pregnancy complicated by hypertension was the main independent predictor of adult levels (B=14.7 pg/mL per category; 95% confidence interval, 6.21–23.2; P=0.001), and for sICAM-1, the association was with lower 5-minute Apgar scores (B=−21.8 ng/mL per category; 95% confidence interval; −32.4 to −11.2; P<0.001).

Adult Preterm Cardiovascular Risk Factors and Circulating Biomarkers

We then determined whether levels of these circulating markers were related to variations in cardiovascular risk factors in adult life. Both sENG and sFlt-1 were positively related to adult systolic, diastolic, and mean arterial pressures in preterm-born young adults (Table S5), and these associations were replicated with ambulatory blood pressure measures in the microvascular study subgroup (association between 24-hour systolic blood pressure and sENG was B=3.48 ng/mL per mm Hg; P=0.007 and for sFlt-1 was B=0.10 pg/mL per mm Hg; P=0.005). Figure 2 illustrates the step increase in systolic blood pressure across tertiles of sENG and sFlt-1. sVCAM-1 was positively related to insulin levels (P=0.001), with trends for association with body mass index (P=0.09) and waist-to-hip ratio (P=0.07; Table S5).

Figure 2.

Figure 2. Systolic blood pressure in preterm-born adults increased with each soluble endoglin (sENG; left, 117.4±8.6 vs 121.7±9.7 vs 127.8±10.4 mm Hg) and soluble fms-like tyrosine kinase-1 (sFlt-1; right, 118.9±8.5 vs 121.1±9.8 vs 126.7±12.0 mm Hg; P=0.006) tertile (1–3, lowest to highest).

Capillary Rarefaction, Circulating Biomarkers, and Increased Blood Pressure

We proceeded to analyses focused on circulating factors related to blood pressure. We tested the hypothesis that these factors would also be related to features of the cardiovascular phenotype previously reported to differ in preterm-born offspring, including cardiac and vascular structure and function, as well as capillary rarefaction. sENG was not related to aortic size or stiffness, cardiac structure or function, or endothelial responses, either in the full cohort or in those who took part in the microvascular substudy (Table S6). However, there were striking inverse associations between sENG and both functional (β=−0.57; P=0.002) and structural (β=−0.65; P<0.001) capillary densities in those born preterm. Preterm-born individuals had significant reductions in these microvascular parameters compared with full term–born individuals (baseline: 93.5±10.6 versus 105.2±10.6 capillaries/mm2; P<0.001 and venous occlusion: 101.8±12.7 versus 115.9±11.8 capillaries/mm2; P<0.001; Figure 3) in whom there were no associations between angiogenic factors and microvascular parameters. Although sFlt-1 was related to sENG and blood pressure, it was not associated with any of the measured cardiovascular parameters (Table S6 and Figure 4). Although sex differences did not exist in sFlt-1 or sENG levels in the preterm group, interestingly, preterm-born men were associated with a significant reduction in both functional and structural capillary densities compared with preterm-born women (P=0.04 and P=0.01). Though the numbers were small (n=15 women and n=15 women), this was consistent with the elevation in systolic blood pressure observed in men born preterm (125.3±9.6 versus 117.9±10.8; P<0.001).

Figure 3.

Figure 3. Functional (baseline) and structural (venous occlusion) capillary densities were reduced in preterm-born adults (PTYA, blue; 93.5±10.6 capillaries/mm2 and 101.8±12.7 capillaries/mm2, respectively) compared with those in term-born adults (YAT, green; 105.2±10.6 capillaries/mm2; P<0.001 and 115.9±11.8 capillaries/mm2).

Figure 4.

Figure 4. Mediation analysis to identify potential mechanisms through which increased antiangiogenic levels and capillary rarefaction are related to systolic blood pressure. Solid lines indicate significant relationships, whereas dotted lines indicate nonsignificant relationships. Bivariable regression demonstrated that soluble endoglin (sENG) is related to 24-hour systolic blood pressure and reduced functional (baseline [B]) and structural (venous occlusion [VO]) capillary densities. Soluble fms-like tyrosine kinase-1 (sFlt-1) is positively associated with systolic blood pressure but not with capillary densities. Both functional and structural capillary densities are inversely related to systolic blood pressure. In multivariable regression, associations between sENG and systolic blood pressure were diminished when functional or structural capillary densities were included, consistent with the fact that density is a relationship mediator (black arrows).

We then performed a mediation analysis within the preterm group to determine the relative hierarchies of blood pressure, capillary rarefaction, and sENG in their coassociations (Figure 4). In bivariable analyses, functional and structural capillary rarefactions were each inversely related to both resting systolic blood pressure (P=0.05 and P=0.04) and 24-hour blood pressure measures (B=−0.42 capillaries/mm2 per mm Hg; P<0.001 and B=−0.32 capillaries/mm2 per mm Hg; P=0.001). In multivariable regression, controlling for sENG levels did not alter the association between structural or functional capillary density and 24-hour systolic blood pressure (β=−0.48; P=0.05), but sENG was no longer a significant predictor of blood pressure (β=0.25; P=0.28). From this we concluded that associations between sENG levels and systolic blood pressure are mediated by capillary density.

Discussion

Preterm-born individuals have increased sFlt-1, sENG, sVCAM-1, and sICAM-1 levels in young adulthood, and of these, variation in sENG and sFlt-1 is proportional to both resting and ambulatory blood pressure levels. Of particular interest are the associations between sENG and blood pressure, which seem to be specifically related to degree of prematurity, rather than other perinatal factors, and are mediated by differences in microvascular structure and function. sFlt-1 levels were largely related to pregnancy-induced hypertension as a cause for preterm birth, and we were not able to identify any associated variations in cardiovascular phenotype. sICAM-1 seemed to be more closely related to infant condition at birth rather than prematurity per se and seemed to be relevant to metabolic function in later life. This latter association requires further investigation, but in this work, we focused on developing our mechanistic understanding of hypertension related to preterm birth.

A reduced number of capillaries, or ability to recruit capillaries, is considered a key factor underlying increased peripheral vascular resistance and is known to be a characteristic finding in patients with primary hypertension.11,12,27 Experimental elevation in blood pressure can directly lead to capillary rarefaction, most likely through an effect of increased generation of endothelial-derived reactive oxygen species on microvascular integrity.28,29 Capillary rarefaction can also antedate the onset of hypertension because reduced capillary density is observed in normotensive individuals at high risk of developing hypertension.12 However, capillary rarefaction is not a generalized observation in those predisposed to hypertension. Whereas reduced capillary number has been identified as a specific vascular abnormality in young adults with a family predisposition,30 individuals born with low birthweight do not consistently demonstrate changes in capillary density.31 We also observed a lack of association between birthweight and capillary density in our preterm study. The finding of reduced capillary density relating to preterm birth per se is more established, even when blood pressure differences are still relatively modest.32,33 Therefore, it is plausible that capillary rarefaction is a primary event in preterm-born individuals, which is established early in postnatal life.

The second and third trimesters of pregnancy are periods of rapid fetal growth with accelerated organ development, which require a quickly expanding capillary network. Premature exposure of an early third trimester fetal circulation to postnatal circulatory physiology in animal models and humans is known to have an adverse effect on development, leading to disproportionately small cardiac and vascular structure.34,35 In addition, maternal factors linked with preterm birth may be of relevance. Preterm birth is a pathophysiological event, often associated with combinations of stress, hypoxia, infection, and inflammation.1,19,36 Ligi et al19 demonstrated that the gene profile of endothelial colony–forming cells isolated from the mononuclear cell fraction obtained from cord blood, after preterm birth, exhibits a programmed shift toward increased expression of genes with antiangiogenic functions.10 Physiologically, this was sufficient for both the cells and the cord sera to impair angiogenesis in vitro.19 D’Souza et al17,3739 found that infants born later in gestation after maternal preeclampsia, a condition characterized by elevated placental-derived antiangiogenic factors in both maternal and fetal circulations, had capillary rarefaction evident at birth.40 These observations raise the possibility that the circulating angiogenic state is both altered and directly relevant to vasculogensis in the offspring both pre- and postnatally. Although we found that the association with gestational age was independent of birthweight Z score, we did not have accurate measures of fetal growth restriction or placental dysfunction in our available data set. Iatrogenic preterm delivery, which occurs in 30% of preeclamptic pregnancies, is often indicated because of fetal growth problems, as a consequence of placental dysfunction, and it remains possible that placental dysfunction may be a determinant or modifier, either in whole or in part, of some features of the long-term changes in angiogenic factors and the microvasculature we have identified.41 There is significant heterogeneity in the clinical background of premature delivery, including incidence of infection, preterm premature rupture of the membrane, and iatrogenic preterm delivery. In future studies, it will be important to establish whether the microvascular abnormalities are established postnatally because of the hemodynamic changes associated with preterm birth, and therefore of relevance to all those born preterm, or whether they vary with the prenatal clinical history. If the latter is the case, larger studies with a range of pregnancy complications will be of value to establish whether it is possible to stratify the risk of hypertension after preterm birth based on the clinical background.

We were interested to know whether there is any long-term relevance of these pathways to later cardiovascular risk. The only report of angiogenic profile in offspring of complicated pregnancies comes from Kvehaugen et al,42 who studied children aged 5 to 8 years born to pregnancies complicated by hypertension but with a high rate of preterm birth. They found no difference in sENG or sFlt-1 levels, despite differences in the mother. However, there were also no differences in blood pressure between groups, and we found a graded association between antiangiogenic factors and blood pressure. In addition, there is evidence to suggest that associations may become more evident with age. Bonamy et al10 studied slightly older children between 8 and 12 years of age and found a 6.94% reduction in resting (functional) capillary density and a 5.27% reduction in capillary density post venous occlusion (structural) compared with the 11.1% to 12.2% reduction in functional and structural capillary densities compared with term-born controls at age 25 to 28 years. By this point, both blood pressure and elevations in sENG are evident and proportional to the reductions in capillary density. Furthermore, mediation analysis suggested a pivotal role of the microcirculation in the links between the antiangiogenic profile and blood pressure in preterm-born individuals. Studies focused on this pathway will help further dissect these associations and could identify interventions of specific benefit for cardiovascular risk reduction in preterm-born offspring. Although our capillary density sex differences in the preterm group are of interest, larger study groups will be required to further explore these findings and to determine whether this is because of pathophysiological sex differences of prematurity.

A strength of our study was the detailed cardiovascular phenotyping of the cohort. This allowed us to study the importance of all the key reported features of the preterm cardiovascular phenotype, from heart to capillary, to changes in blood pressure in each individual. Differences in aortic and cardiac size did not seem relevant to blood pressure variation in individuals born preterm. However, it might be expected that these differences will adversely affect the response of the individual to risk factors, and it is possible that myocardial microvascular responses also differ. In preterm animal models, a higher incidence of heart failure has been observed in response to hypertension.43 As the microvascular hypothesis was included as an amendment to the study protocol, not all individuals underwent these investigations. Although the overall characteristics of this subgroup were similar to the full cohort, the reduced size did mean that we had insufficient subjects born to hypertensive pregnancies to study microvascular differences in this group separately. It is possible that pregnancy-induced hypertension is associated with an additional effect on capillary density in the offspring in view of their dual elevation in sENG and sFlt-1. This, and associations between the other markers and metabolic derangements, will require investigation in further, larger study cohorts.

Perspectives

This is the first demonstration of a heightened antiangiogenic state in later life in individuals who were born preterm. These findings may indicate a potential mechanistic link between an imbalance in proangiogenic and antiangiogenic factors, capillary rarefaction, and blood pressure elevation in preterm-born young adults. Whether this pathway provides a modifiable target for future prevention strategies to delay the development of hypertension in individuals born preterm is of significant future interest.

Acknowledgments

We are grateful to the volunteers who participated in these studies and all those who have previously contributed to data collection.

Footnotes

The online-only Data Supplement is available with this article at http://hyper.ahajournals.org/lookup/suppl/doi:10.1161/HYPERTENSIONAHA.114.04662/-/DC1.

Correspondence to Adam J. Lewandowski or Paul Leeson, Oxford Cardiovascular Clinical Research Facility, Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX39DU, United Kingdom. E-mail or

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Novelty and Significance

What Is New?

  • Preterm-born individuals have increased sFlt-1, sENG, sVCAM-1, and sICAM-1 levels in young adulthood.

  • Variation in sENG and sFlt-1 is proportional to both resting and ambulatory blood pressure levels.

  • The associations between sENG and blood pressure seem to be specifically related to degree of prematurity, rather than other perinatal factors, and are mediated by differences in microvascular structure and function.

  • sFlt-1 levels were largely related to pregnancy-induced hypertension as a cause for preterm birth.

What Is Relevant?

  • These findings may indicate a potential mechanistic link between an imbalance in proangiogenic and antiangiogenic factors, capillary rarefaction, and blood pressure elevation in preterm-born young adults.

Summary

This is the first demonstration of a heightened antiangiogenic state in later life in individuals who were born preterm. These findings implicate a link between an imbalance in proangiogenic and antiangiogenic factors, capillary rarefaction, and elevated blood pressure in preterm-born young adults, which may represent a novel target for intervention

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