Angiotensin-I-converting enzyme activity in term and premature infants

Association of delayed cord clamping with acute kidney injury and two-year kidney outcomes in extremely premature neonates: a secondary analysis of the Preterm Erythropoietin Neuroprotection Trial (PENUT)

Background

Delayed cord clamping (DCC) occurs in most preterm births.

Objective

Evaluate the association of DCC with acute kidney injury (AKI) and two-year kidney outcomes.

Methods

Secondary analysis of the Preterm Erythropoietin Neuroprotection Trial of neonates born 240/7 to 276/7 weeks' gestation. AKI and two year kidney outcomes were compared in neonates with DCC (≥30 seconds after delivery) to those with early cord clamping (ECC) (<30 seconds after delivery).

Results

The incidence and severity of AKI did not differ between the DCC and ECC groups (aOR 1.17 [95%CI 0.76-1.80]). At two years corrected age, DCC was associated with a 4.5-fold times increased adjusted odds of eGFR <90 mL/min/1.73m2. No significant associations were noted between DCC and albuminuria or elevated BP.

Conclusions

DCC was not associated with decreased neonatal AKI, but was associated with higher adjusted odds of eGFR <90 mL/min/1.73m2 at two years.

Early urinary angiotensinogen excretion in critically ill neonates

INTRODUCTION

Urinary angiotensinogen is considered a reliable biomarker for intrarenal renin-angiotensin system activity. The aims of this study were to assess the urinary angiotensinogen level during the first day of life and to evaluate its correlation with renal function in critically ill neonates.

METHODS

Urinary angiotensinogen concentration during the first 24 hours of life was measured in 98 critically ill neonates. Neonatal renal function was assessed by urinary levels of cystatin-C, albumin and α1-microglobulin and urinary electrolyte excretion.

RESULTS

Urinary angiotensinogen level decreased with increasing gestational age and body weight in critically ill neonates (P<0.001). After adjustment for gestational age, urinary angiotensinogen level correlated with urinary fractional excretion of sodium and urinary levels of cystatin-C and α1-microglobulin. Multivariate linear regression identified a significant impact of urinary cystatin-C on urinary angiotensinogen level (P<0.001). Furthermore, urinary angiotensinogen was significantly increased in neonates with a urinary cystatin-C-to-creatinine ratio ⩾2500 ng/mg, which was the optimal cut-off value to predict acute kidney injury in our previous study.

CONCLUSIONS

The urinary angiotensinogen level correlates with the overall maturity of renal function during the early postnatal period in critically ill neonates and an increased urinary angiotensinogen level might reflect renal injury in immature neonates.

Programming of Hypertension

Animal models suggest that explanations for the association of low birthweight with adult hypertension may include chronic activation of the hypothalamic-pituitary-adrenal or renin-angiotensin-aldosterone axes. In humans, low birthweight predicts elevated plasma cortisol, but associations with aldosterone have not been reported. We measured aldosterone in serum samples from 205 men and 106 women from 67 to 78 years of age, from Hertfordshire, UK, for whom birthweight was recorded. Participants underwent an overnight low-dose (0.25 mg) dexamethasone suppression test and a low-dose (1 μg) ACTH (corticotropin) stimulation test and were genotyped for the -344 C/T polymorphism of the CYP11B2 gene encoding aldosterone synthase. Median aldosterone was 6.22 ng/dL (range 0.15 to 38.74) and was higher in men than women ( P <0.0001). Higher aldosterone levels after both dexamethasone and ACTH stimulation were associated with higher blood pressure ( r =0.20, P =0.001; r =0.33, P <0.0001, respectively) and with lower birthweight ( r =−0.16, P =0.008; r =−0.21, P =0.001, respectively). These associations remained significant after adjusting for age, gender, obesity, and genotype. Our findings supplement previous evidence that aldosterone is an important regulator of blood pressure and suggest that factors in early life that retard fetal growth and program activation of the hypothalamic-pituitary-adrenal axis in humans result not only in higher glucocorticoid activity but also in increased mineralocorticoid activity.

The plasma angiotensin II level increases in very low-birth weight infants with neonatal chronic lung disease

BACKGROUND

Angiotensin II (AII) has been reported to play an important role in organ fibrosis, and a local renin-angiotensin-system (RAS) has been demonstrated in the lungs. However, the relationship of the RAS to chronic lung disease of the newborn (CLD) remains obscure.

OBJECTIVE

To investigate the plasma AII levels throughout the neonatal period in very low-birth weight (VLBW) infants and examine the possible factors that might affect the AII levels.

STUDY DESIGN

The study includes 20 VLBW infants. Blood samples were collected on days 0, 7, 21 and 35 and plasma AII levels were assayed using an enzyme immunoassay. The data were analyzed by a multiple linear regression analysis with the plasma AII level as the dependent variable and significant factors determined based on a univariate analysis as independent variables.

RESULTS

The geometric mean of the plasma AII concentrations on days 0, 7, 21 and 35 was 51 pg/mL, 86 pg/mL, 132 pg/mL, and 50 pg/mL, respectively. On day 21, only CLD (p<0.01) had a highly significant association with the plasma AII level. On day 35, birth weight (p<0.05) and CLD (p<0.01) had a highly significant association with the plasma AII level. This analysis confirmed CLD to be the most significant factor associated with plasma AII level on days 21 and 35.

CONCLUSION

These findings suggest that higher levels of plasma AII in VLBW infants appear to be related to the development of CLD.

Plasma angiotensin II concentrations in the early neonatal period

BACKGROUND

There have been only a few reports on the renin-angiotensin system in low birthweight infants; in particular, plasma angiotensin II concentrations have not been studied.

AIM

To investigate plasma angiotensin II concentrations in early neonatal infants including low birthweight infants.

METHODS

Forty six patients were studied, of whom 14 weighed not less than 2500 g (normal birth weight), 16 weighed less than 2500 g but not less than 1500 g (moderately low birth weight), and 16 weighed less than 1500 g (very low birth weight). Blood samples were collected twice, on day 0 and day 7. Angiotensin II concentration was assayed using an enzyme immunoassay kit with a microplate.

RESULTS

Geometric means of angiotensin II concentrations on day 7 were 19 pg/ml in the normal birthweight group, 28 pg/ml in the moderately low birthweight group, and 76 pg/ml in the very low birthweight group. The concentrations on day 7 in the very low birthweight group were significantly higher than those in the normal birthweight and moderately low birthweight groups (p = 0.005, p = 0.031). There were significant correlations between angiotensin II concentration on day 7 and gestational age (r(s) = -0.4, p = 0.007) and birth weight (r(s) = -0.36, p = 0.016).

CONCLUSIONS

Specific physiological conditions associated with a very low birth weight are thought to be responsible for the increased concentration of angiotensin II on day 7. It is necessary to measure angiotensin II concentration for a longer period after birth and study the factors that could influence it.

The urinary activity of angiotensin-converting enzyme in preterm, full-term newborns, and children

The urinary activity of the angiotensin-converting enzyme (U(ACE)) is not yet completely documented in human neonates. We measured the U(ACE) in 36 premature neonates on the 1st day and in the 1st, 2nd, 3rd, and 4th weeks of life, in 22 full-term neonates between the 1st and 2nd days, and in 30 nursing and preschool children between 1 month and 6 years of age. The urinary excretion of sodium (U(Na)/U(Cr)) and the potassium/sodium index (U(K)/U(Na)) were analyzed in the neonates. U(ACE) was greater in premature than in full-term neonates and greater in both than in older children (p<0.001). In the premature neonates, U(ACE) peaked at the 2nd week, the U(Na)/U(Cr) index decreased, and the U(K)/U(Na) index increased between the 1st day and the 2nd week (p<0.001). The U(Na)/U(Cr) index on the 1st day and in the 1st and 2nd weeks was greater in premature than in full-term neonates (p<0.001). There was no significant correlation between the U(ACE) and the U(Na)/U(Cr) index. In conclusion, the U(ACE) profile was shown to be age dependent and related to the postnatal renal development. The increase in U(ACE) activity may reflect the high activity of the neonatal intrarenal renin-angiotensin system (RAS).

Deletion allele of angiotensin-converting enzyme is associated with increased risk and severity of bronchopulmonary dysplasia

OBJECTIVE

To explore whether the deletion (D) allele of angiotensin-converting enzyme (ACE) is associated with the risk or severity of bronchopulmonary dysplasia (BPD) among very low birth weight (BW) infants.

STUDY DESIGN

Infants with a BW < or = 1250 g were prospectively recruited. The D and I (insertion) alleles of ACE were determined using a polymerase chain reaction followed by restriction fragment length polymorphism analysis.

RESULTS

Infants with DD/DI genotype of ACE had a (mean +/- SD) birth weight (938 +/- 204 g vs 925 +/- 196 g) and gestational age (28 +/- 3 weeks vs 28 +/- 2 weeks), similar to infants with II genotype of ACE (P > .05). Infants with DD/DI genotype of ACE were more likely to have BPD than infants with II genotype (47% vs 22%, P = .025). Among infants with BPD, ACE DD/DI genotype was more common among infants with moderate or severe BPD compared with infants with mild BPD (74% vs 26%, P = .012). The number of D alleles of ACE correlated directly and positively with the severity of BPD (R = 0.23, P = .045).

CONCLUSION

The D allele of ACE is associated with an increased risk and severity of BPD among preterm infants.

Genetic polymorphisms and risk for acute renal failure in preterm neonates

Acute renal failure (ARF) affects about 10% of severely ill neonates. Recent studies have shown that genetic polymorphisms of proteins that play a role in neonatal physiology may contribute to individual susceptibility to both ARF and its risk factors. Our review summarizes the data collected to date. Studies have shown that the risk of preterm neonates for ARF is directly associated with a combination of high tumor necrosis factor-alpha producer and low interleukin-6 producer genotypes, as well as with low heat shock protein 72 producer genotype. Premature birth is itself the most important risk factor for a number of complications, including ARF, and recent studies have also shown an association between several maternal and fetal cytokine genetic polymorphisms and increased inflammatory response in preterm neonates. These polymorphisms could also be associated with increased risk for disorders such as sepsis and necrotizing enterocolitis, which lead to renal hypoperfusion and ARF. Genetic polymorphisms of the renin-angiotensin-aldosterone system have not been shown to directly influence risk for ARF. They may, however, be associated with patent ductus arteriosus, poor postnatal adaptation, and heart failure, which are all prevalent risk factors for ARF.

Angiotensin converting enzyme activity in infancy is related to birth weight

AIMS

(a) To measure infant angiotensin converting enzyme (ACE) activity in healthy term infants at birth and during the first three months of life. (b) To determine the relation between serum ACE activity and infant feeding practice during this period. (c) To investigate the relation between serum ACE activity and birth weight and other potential contributing factors including acid-base status at birth, gestation, and maternal ACE genotype.

METHODS

Prospective study of term infants, with clinical and feeding data collected from parents and medical records, and serum ACE measured in the infant at birth and 1 and 3 months of age, and in the mother at the time of birth and one to three months after birth.

RESULTS

At birth and 1 and 3 months of age, infant serum ACE activity was twice that of maternal ACE activity. Infant ACE activity at birth and 1 and 3 months did not significantly differ between breast and formula fed infants. There was a highly significant negative correlation between infant ACE activity at 3 months and birth weight (r = -0.52; p < 0.001). This persisted after the conversion of birth weights to z scores (r = -0.34; p = 0.03). ACE activity at 3 months was also related to placental weight (r = -0.30; p = 0.02) and maternal age (r = -0.30; p = 0.05). The strong correlation between serum ACE activity and birth weight z score persisted after adjustment for maternal age and placental weight (r = -0.34; p = 0.03).

CONCLUSION

As ACE is increasingly identified as a risk factor for cardiovascular disease, serum ACE activity in infancy may contribute to the link between low birth weight and later cardiovascular events.

Fetal, neonatal cord, and maternal plasma concentrations of angiotensin-converting enzyme (ACE)

OBJECTIVES

Angiotensin converting enzyme (ACE), a component of the renin-angiotensin system (RAS), catalyses the degradation of angiotensin I to angiotensin II. It was the aim of the present study to measure ACE activity in human fetal blood and to determine its changes with advancing gestational age.

METHODS

Fetal blood was sampled by cordocentesis from six control fetuses and six fetuses with Rh isoimmunisation. Cord blood was sampled from six preterm neonates, 15 neonates after spontaneous delivery at term and six neonates at term after caesarean section. In addition, maternal ACE values were determined. ACE activity was measured using the miniaturised fluorimetric method.

RESULTS

In normal fetuses (13.31+/-1.41 nmol HL/min/ml) and fetuses with Rh isoimmunisation (13.08+/-2.00 nmol HL/min/ml, p<0.05). Neonatal cord blood of preterm newborns (10.43+/-0.69 nmol HL/min/ml) and term newborns (8.99+/-0.49 nmol HL/min/ml) showed a significantly decreased ACE activity compared to the fetal controls.

CONCLUSION

We conclude that the high fetal ACE activity and the stringent regulation with advancing gestational age indicate the physiological importance of the enzyme during prenatal development.

Serum angiotensin converting enzyme in sarcoidosis--its value in present clinical practice

Angiotensin converting enzyme (ACE) has a central role in blood pressure homeostasis. It is present in low and fairly constant concentration in the serum and in high concentration in the pulmonary capillary bed. Unusually high serum angiotensin converting enzyme (SACE) activity is present in active sarcoidosis, an observation now confirmed by many investigators. In spite of its lack of specificity as a test for sarcoidosis, SACE provides a good monitor of disease activity which clinicians find useful in the management of patients with sarcoidosis. There continues to be considerable interest in SACE in sarcoidosis and with the recent development of simpler assays, more centres may be expected to offer SACE measurements as a service. In this paper we discuss the indications for estimating SACE in sarcoidosis and its relevance to current clinical practice.

Levels of renin, angiotensin I and II, angiotensin-converting enzyme and aldosterone in infancy and childhood

Basal plasma renin activity (PRA), angiotensin I and II (AI, AII), angiotensin-converting enzyme (ACE) activity and plasma aldosterone (PA) and sodium and potassium concentration were simultaneously measured in 55 healthy recumbent children aged between 1 week and 13 years. A significant (P less than 0.001) age-related decrease for PRA (r = -0.73), AI (r = -0.72), AII (r = -0.51) and PA (r = -0.71) was observed but not for ACE (r = 0.26, P = 0.06). After correction for age the correlation between PRA or PA and AI or AII was still significant (P less than 0.005). The strong correlation between AI and AII in the group as a whole (r = 0.82, P less than 0.001) and also in separate age groups, and an AI to AII ratio which was not different between the various age groups suggest that ACE activity in this age range is not rate-limiting for AII generation.

Angiotensin-converting enzyme and the renin-angiotensin system in normotensive primigravid pregnancy

In a prospective study the interactions between ACE and the renin-angiotensin system in 18 primigravid normotensive women were investigated throughout pregnancy. ACE activity was found to be depressed throughout pregnancy, rising in the last trimester and returning to non-pregnant values by 6 weeks post partum. No significant differences were found between cord arterial or venous and maternal venous ACE levels at delivery. ACE was inversely related to systolic and mean arterial blood pressures, inversely to serum sodium and urinary potassium and directly to serum potassium levels. Within the system, ACE was correlated only to aldosterone levels. In company with other components of the system ACE activity appears to be altered in pregnancy and to be influenced by similar control mechanisms. It is possible that ACE plays a modulating role on aldosterone secretion via the (des-asp1), Angiotensin I pathway.

Serum angiotensin-converting enzyme activity in normal children and in those with sarcoidosis

Serum angiotensin-converting enzyme was measured in 185 children of different ages, in 32 normal adults, in 21 children with sarcoidosis, and in 36 children with other diseases. Children had higher serum ACE volumes than did adults; an intermediate level was absorbed in adolescents. Serum ACE values did not vary according to sex. Children with sarcoidosis had significantly elevated serum ACE levels that closely reflected the activity of the disease. Our results indicate that serum ACE is useful in confirming the diagnosis of sarcoidosis in childhood, and is of greater value as a sensitive indicator for following the course of the disease and the effectiveness of steroid therapy.