Latent intrarenal renin-angiotensin-aldosterone system activation could persist until toddlerhood in children with a history of low birth weight

doi:10.21203/rs.3.rs-5280123/v1

Purpose

The renin-angiotensin-aldosterone system (RAAS) plays a crucial role in kidney development and the progression of chronic kidney disease (CKD). However, no studies have examined the association between RAAS and CKD in children with a history of preterm birth and low birth weight (LBW).

Methods

In first urine biomarker study, we prospectively evaluated intrarenal RAAS markers using spot urine in children, both with and without a history of LBW, who required evaluation for short stature and had no clinical kidney symptoms at registration. In second, we conducted a retrospective immunohistochemical pathological study using kidney biopsy specimens in subjects, both with and without a history of LBW, with reduced kidney function and pathological glomerular hypertrophy. Urinary angiotensinogen (AGT) was assessed as a marker of intrarenal RAAS.

Results

A total of 45 children with a median age of 5.0 years were evaluated in the prospective biomarker study. Urinary AGT/creatinine (Cr) levels were significantly higher in children with a history of LBW (n = 24) than in those without (n = 21; 12.6 vs. 6.7 µg/ng Cr, p < 0.01). In the immunohistochemical kidney pathological study, the positive area of AGT staining in the renal tubules of the subject with a history of LBW was more extensive than that of the subject without a history of LBW.

Conclusions

Our biomarker and pathological studies indicated that latent intrarenal RAAS activation in children with a history of LBW persists until toddlerhood and may contribute to the progression of CKD.

Angiotensinogen

Biomarker

Glomerular hypertrophy

Low birth weight

Preterm birth

The renin-angiotensin-aldosterone system (RAAS) plays a crucial role in renal development and the progression of chronic kidney disease (CKD).
Although preterm birth and low birth weight (LBW) are known risk factors for the development and progression of CKD, no studies have examined the association between RAAS and chronic kidney disease in children with a history of preterm birth and LBW.

What is New

In children with no clinical kidney symptoms, the urinary marker for intrarenal RAAS was significantly higher in those with a history of LBW than in those without a history of LBW.
In the immunohistochemical pathological study of children who had decreased kidney function and pathological glomerular hypertrophy, the positive area of intrarenal RAAS staining in the renal tubules of subjects with a history of LBW was more extensive than that of those without a history of LBW.
Our biomarker and pathological studies indicate that latent intrarenal RAAS activation in children with a history of LBW persists until toddlerhood and may contribute to the progression of CKD.

With advances in perinatal department care, the prognosis for preterm birth (PB) or low birth weight (LBW) infants has improved significantly. However, PB and LBW are risk factors for the development and progression of various chronic diseases [1], including chronic kidney disease (CKD), which primarily manifests as glomerular hypertrophy and tubulointerstitial fibrosis [2]. Understanding the mechanisms of CKD progression in children with a history of PB or LBW is crucial for not only improving long-term outcomes but also reducing healthcare costs associated with end-stage kidney disease management. The Development Origin of Health and Disease (DoHaD) hypothesis, which suggests that chronic diseases develop because of a mismatch between the postnatal environment and the developmental conditions of PB or LBW infants, has already been applied to CKD progression [1]. Moreover, reports have shown that nephron deficits and reduction in nephron number are involved in the progression of CKD [2,3].

The effectiveness of renin-angiotensin-aldosterone system (RAAS) inhibitors in slowing the progression of CKD has been confirmed. Similar to adult CKD patients, the frequency of introducing RAAS inhibitors in pediatric patients, whose CKD was caused by chronic nephritis or congenital kidney and urinary tract abnormalities, has been increasing [4-8]. In humans, RAAS-related genes, such as renin and angiotensinogen (AGT), are heavily involved in ureteric bud and renal collecting duct formation [9]. In particular, local RAAS only acts on kidneys and differs from circulating RAAS, which circulates throughout the body and depends on hemodynamics [10]. A report revealing that AGT is the origin of the fibrosis cascade in the renal tubulointerstitium has led to numerous subsequent molecular biological studies focusing on intrarenal RAAS in CKD. Urinary AGT, which reflects the activation of intrarenal RAAS, has been shown to be an indicator for the prognosis of kidney function [11]; moreover, gestational age and urinary AGT in neonates are significantly correlated [12].

Recently, the concept of diseases characterized by compensatory glomerular hypertrophy due to hyperfiltration, resulting from reduced nephron number, has become widespread [13]. Various background factors have been reported by many studies as potential contributors to reduced nephron number. For example, a history of PB or LBW had been shown to be associated with inadequate formation of the ureteric bud and renal collecting duct. The relationship between the RAAS, which plays a crucial role in both kidney development and the progression of CKD, and a history of PB or LBW with unknown mechanisms of CKD progression has not yet been examined. Verification of whether intrarenal local RAAS activation, which is thought to be involved during the neonatal period [12], persists into toddlerhood and adolescence in those with a history of PB or LBW before the onset of CKD would support the DoHaD hypothesis.

Here, we report prospective biomarker and retrospective immunohistochemical pathological studies to evaluate latent intrarenal RAAS activation in children with a history of LBW.

Patients

We conducted two studies. The first study was a prospective study conducted from August 2019 to December 2023 using urine biomarkers in children aged between 1 and 15 years, both with and without a history of LBW. The subjects comprised children who had no clinical kidney symptoms and had undergone evaluation for short stature on admission. The children were divided into two groups: children with and without a history of LBW. We excluded those with a genetic abnormality, bone metabolic disease, cardiopulmonary disease, congenital anomalies of the kidney and urinary tract, and CKD. We prospectively collected the following data during the evaluation for short stature: blood pressure, urinalysis (including urinary AGT, urinary neutrophil gelatinase-associated lipocalin [NGAL], urinary β2 microglobulin [β2MG]), blood examination (including serum creatinine [Cr], serum AGT, serum cystatin C [CysC]), Cr-estimated glomerular filtration rate (Cr-eGFR), CysC-estimated glomerular filtration rate (CysC-eGFR), and kidney ultrasonography findings. Because we observed variations in serum Cr levels due to muscle mass and the effects of exercise in some children, CysC-eGFR was used instead of Cr-eGFR. We also collected data on sex, gestational age, birth height, and birth weight. The immunohistochemical pathological evaluation for the second study was conducted retrospectively using renal biopsy specimens. Subjects were eligible if they had pathological glomerular hypertrophy without other types of nephritis, and the indication of their kidney biopsy was decreased kidney function with no other kidney symptoms. We selected one case with a history of LBW and one case without a history of LBW. Immunohistochemical staining of AGT was used as a marker of intrarenal RAAS, and angiotensin II (AT2) was used as a marker of systemic RAAS.

Definitions

Urine protein concentration was measured to calculate an early morning urine protein Cr (P/C) ratio. The severity of hematuria was assessed by counting the number of red blood cells (RBCs) per high-power microscopic field in a centrifuged early morning urine sample; fewer than five RBCs per high-power field indicated the absence of hematuria. We calculated the Cr-eGFR of each patient using their serum Cr and height [14]. Hypertension was defined according to the International Pediatric Hypertension Association criteria [15]. We defined birth at less than 37 weeks of gestation as PB and a birth weight of less than 2500 g as LBW. Kidney biopsies were performed by pediatric nephrologists. We measured the glomerular diameter by picking up only the glomeruli with a vascular pole. After measuring all glomeruli, we averaged the diameter of the three longest glomeruli. A mean glomerular diameter greater than 220 µm was considered glomerular hypertrophy [13].

Urinary and serum total AGT was evaluated via enzyme-linked immunosorbent assay (Immuno-Biological Laboratories Co. Ltd., Fujioka, Japan) using spot urine and serum samples. We performed immunohistochemical staining of paraffin-embedded sections of kidney biopsy samples. Immunohistochemical staining of AGT (Immuno-Biological Laboratories Co. Ltd., Fujioka, Japan) was used as a marker of intrarenal RAAS, and staining of renin and AT2 (Phoenix Pharmaceuticals, Burlingame, CA) was used as a marker of systemic RAAS.

Study design

The primary outcome for the prospective study of urine biomarkers was the difference in the level of urinary AGT/Cr in children with no clinical kidney symptoms between those with and without a history of LBW. The purpose of the pathological study using kidney biopsy specimens was to compare immunohistochemical staining of AGT and AT2 in subjects with and without a history of LBW.

Statistical analysis

The Wilcoxon rank-sum test was used to evaluate associations between categorical and continuous variables. Fisher’s exact test was used to examine associations between categorical variables. We performed all analyses using JMP version 11.0 (SAS Institute Japan Ltd., Tokyo, Japan). All data are expressed as median values (interquartile range [IQR]), and the threshold for significance was p < 0.05.

For the prospective urine biomarker study in children with a history of LBW who had no clinical kidney symptoms, we calculated a sample size of 50 children. At our institution, the number of patients who undergo evaluation for short stature with a history of LBW is approximately 20 per year. We assumed that approximately 30–40% of children would be ineligible because of non-consenting issues (i.e., 12–14 children ´ 4 years = 48–56). Therefore, to satisfy these assumptions, we calculated a sample size of 50 children over 4 years.

Clinical characteristics and results of biomarkers in the prospective biomarker study

A total of 65 children with short stature episodes were evaluated on admission to our hospital (Figure 1). Of these, 45 children (27 boys and 18 girls) were eligible for inclusion in the urine biomarker study, which comprised 24 children with a history of LBW and 21 children without a history of LBW. Among children with a history of LBW, 14 children had a history of PB.

Table 1 shows the comparison of clinical characteristics of children with and without a history of LBW. The median age of children with and without a history of LBW was 5.0 and 4.6, respectively. There were no significant differences in the sex ratio or median age between children with and without a history of LBW. None of the children had significant hematuria or proteinuria or abnormal levels of urinary NGAL/Cr. Four children (11.1%) had hypertension. Systolic blood pressure and the proportion of children with hypertension were not significantly higher in those with a history of LBW than in those without a history of LBW. Serum AGT/Cr levels differed significantly between children with and without a history of LBW. As shown in Figure 2a, urinary AGT/Cr levels were significantly higher in children with a history of LBW than in those without a history of LBW (12.6 vs. 6.7 µg/ng Cr, p < 0.01).

The comparisons of clinical characteristics of children with a history of LBW between those with and without a history of PB are shown in Table 2. None of the factors differed significantly between children with (n = 14) and without (n = 7) a history of PB except for gestational age, birth height, and birth weight. Urinary AGT/Cr levels did not differ significantly between children with and without a history of PB (Figure 2b).

Histological examination in the immunohistochemical pathological study

The first subject was a boy aged 14 years at the time of the kidney biopsy. His gestational age was 35 weeks, and his birth weight was 1468 g. He was referred to our hospital because of proteinuria determined at his school screening. He had neither hypertension nor sonographic anomalies of the kidney or urinary tract. His urinalysis showed no significant proteinuria or hematuria, and his blood examination showed decreased kidney function (Cr-eGFR: 68.9 ml/min/1.73 m²) without any other nonrenal symptoms or significant titer findings for autoimmune diseases. The second subject was a boy aged 15 years at the time of the kidney biopsy. His gestational age was 40 weeks, and his birth weight was 2900 g. He was referred to our hospital because of proteinuria confirmed at his school screening. He had no hypertension or sonographic anomalies of the kidney or urinary tract. His urinalysis showed mild proteinuria (urine P/C: 0.7 g/g Cr) and no hematuria, and his blood examination showed decreased kidney function (Cr-eGFR: 62.3 ml/min/1.73 m²) without any other nonrenal symptoms or significant titer findings for autoimmune diseases. The kidney biopsy findings of both subjects were similar. Light microscopic findings of the kidney biopsy revealed glomerular hypertrophy without crescents, glomerulosclerosis, or interstitial fibrosis. There were no significant depositions of IgG, IgA, IgM, C3, C4, C1q, or fibrinogen. Electron microscopy showed no findings of thin basement membranes or significant electron-dense deposits.

Upon immunohistochemical evaluation, the positive area of AGT staining in the renal tubules of the first subject was more extensive than that of the second subject. None of the glomeruli of either child showed AGT staining. AT2 staining was weakly positive in the renal tubules in both patients to a similar degree (Figure 3).

We showed that the levels of urinary AGT, as a marker of intrarenal RAAS, in toddler-aged children without clinical kidney symptoms who had a history of LBW were significantly higher than in those without a history of LBW. In children who had pathological glomerular hypertrophy with and without a history of LBW, kidney immunohistochemical staining of AGT was negative in the glomeruli. However, in only the child with a history of LBW, the renal tubules were AGT-positive. To the best of our knowledge, this is the first prospective study to evaluate the relationship between a biomarker of intrarenal RAAS and LBW.

It has been reported that more than 60% of nephrons are formed between 20 to 36 weeks of gestation; thus, PB is a risk factor for reduced nephron number [16]. In addition, body weight at birth and the number and size of nephron units are strongly correlated [17]. A reduction in the number of nephrons leads to glomerular hypertension and hypertrophy in the remaining nephrons, which triggers a vicious cycle of progressive loss of functioning units [18]. Suzue et al. found a significant correlation between gestational age and the level of urinary AGT in neonates [12] and concluded that immature kidney development in utero reflects a high level of the intrarenal RAAS marker. AGT, which is one of the components that make up RAAS, is secreted from the proximal tubule and induces the effect of AT2. Although renin, aldosterone, and serum AGT are established biomarkers of circulating RAAS, intrarenal RAAS has gained recent attention. Activated intrarenal RAAS plays an important role in the pathogenesis of hypertension and CKD [10]. In addition to the impact of gestational age on the level of urinary AGT in neonates, our results demonstrated that toddlers with a history of LBW before the onset of CKD have a significantly higher level of urinary AGT than those without a history of LBW. Our findings suggest that in children with a history of LBW, there is latent RAAS activation even before the onset of CKD. Our prospective cohort study on LBW subjects is currently ongoing, and we will be obtaining longitudinal urinary AGT values to examine changes in urinary AGT values beyond school age in the future. Furthermore, if any of the subjects develop CKD, we will be able to comprehensively examine how RAAS markers contribute to the development of CKD by comparing children who do and do not develop CKD.

CKD progression, induced by RAAS activation, characterized primarily by renal interstitial fibrosis, has been demonstrated in animal models. Elevated serum RAAS levels in mice have been shown to cause renal fibrotic damage [19]. Aldosterone a crucial role in organ fibrosis; it not only induces the secretion of fibrosis-promoting factors, such as plasminogen activator inhibitor-1 and transforming growth factor-β, but also causes mitochondrial damage in cultured proximal tubular cells [20]. Although fibrosis of the renal tubulointerstitium contributes considerably to the progression of CKD, it is often absent in pathological kidney tissue during the early stages of CKD. We have previously demonstrated that pathological kidney findings in children with decreased kidney function or proteinuria show compensatory glomerular hypertrophy and hyperfiltration due to a reduced number of nephrons but no tubulointerstitial fibrosis or vascular lesions [13]. Our case with a history of PB and LBW exhibited similar glomerular hypertrophy and no tubulointerstitial findings, alongside strongly positive AGT staining in the tubules. Pathologically, latent RAAS activation may affect the renal tubules before the manifestation of interstitial fibrosis. Future studies examining pathological findings of patients who exhibit fibrosis of the renal tubulointerstitium using fibrotic markers will be valuable.

Latent RAAS activation has been explored in various kidney diseases. In autosomal dominant polycystic kidney disease, a cystic disorder, hypertension occurs before the onset of CKD. In these patients, hypertension indicates the involvement of intrarenal RAAS activation before the development of CKD [21]. Additionally, Shono et al. demonstrated positive histopathological immunostaining of AGT in the kidneys of PB newborns who died of pulmonary hypoplasia and 2–10-year-old microhematuria patients with histological minor glomerular abnormalities [22]. Staining of AGT in the proximal tubule tissue of the kidney is stronger in newborns at 29 or 36 weeks gestation than in children aged 2 or 10 years. They indicated that immature kidney development could induce latent RAAS activation during the neonatal period. Our biomarker and pathological investigations revealed that latent intrarenal RAAS activation present during the neonatal period in children with a history of LBW persists until toddler age.

This study has several limitations. First, our sample of children with a history of LBW was small. Second, a direct relationship between latent intrarenal RAAS activation and CKD was not verified. Nevertheless, our findings did suggest latent intrarenal RAAS activation in toddlers with a history of LBW. Future studies should investigate intrarenal RAAS biomarkers in children with a history of PB or LBW who have developed CKD. A prospective cohort study in the same subjects is currently ongoing, which will enable such an investigation. Finally, there may have been selection bias because we only included children with a history of LBW who had short stature on admission.

In conclusion, our biomarker and pathological study indicated that latent intrarenal RAAS activation in children with a history of LBW persists until toddler age and may contribute to the progression of CKD.

AGT: angiotensinogen

AT2: angiotensin II

β2MG: β2 microglobulin

CKD: chronic kidney disease

Cr: creatinine

CysC: cystatin

DoHaD: Development Origin of Health and Disease

eGFR: estimated glomerular filtration rate

IQR: interquartile range

LBW: low birth weight

NGAL: neutrophil gelatinase-associated lipocalin

PB: preterm birth

P/C: protein creatinine ratio

RAAS: renin-angiotensin-aldosterone system

RBCs: red blood cells

Competing Interests

The authors declare no competing interests.

Funding

The study was supported by a Grant-in-Aid for Scientific Research (KAKENHI) from the Ministry of Education, Culture, Sports, Science and Technology of Japan (grant numbers 23K07242 [to SI] and Kawano Masanori Memorial Public Interest Incorporated Foundation for Promotion of Pediatrics.

Author contributions

In particular, Shingo.I. prepared the manuscript. Shingo.I., Shinya.I. and J.F. collected the clinical data. S.A., Y.K., H.K., C.U., Y.I., Y.T., T.H., T.Y., N.S., C.N. and K.N. revised the article. All the authors have read and approved the final manuscript.

Ethics approval

All procedures in this study involving human participants were performed in accordance with the ethical standards of the Takatsuki General Hospital Ethics Board. The study was conducted (approval number: 2017-75, 2019-25) in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Written informed consent was obtained from all patients’ parents according to institutional ethical guidelines.

Consent to participate

Written informed consent was obtained from all patients’ parents for this study according to institutional ethics.

Acknowledgments

The authors thank all the study participants and their families. In addition, we thank Sarina Iwabuchi, PhD, from Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript.

Data Availability Statement

The datasets generated during and/or analyzed during the current study are not publicly available, but are available from the corresponding author on reasonable request.

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Table 1 Comparison of clinical characteristics in children with or without a history of low birth weight

	All (N=45)	Children with a history of LBW (n=21)	Children without a history of LBW (n=24)	p value
	All (N=45)	Children with a history of LBW (n=21)	Children without a history of LBW (n=24)	p value
Background
Age (years)	5.0 (3.8-6.5)	5.0 (3.8-6.4)	4.6 (3.3-7.0)	0.55
Boy : Girl, n (%)	27 : 18 (60.0 % : 40.0 %)	11 : 10 (52.4 % : 47.6 %)	16 : 8 (66.7 % : 33.3 %)	0.37
Gestational week (weeks)	39.0 (35.5-39.0)	35.0 (28.5-37.0)	39.0 (39.0-40.0)	<0.0001
Birth height (cm)	45.0 (40.5-47.5)	41.0 (33.3-45.0)	47.0 (46.5-48.8)	<0.0001
Birth weight (g)	2590 (1701-2908)	1680 (834-2184)	2840 (2704-3254)	<0.0001
Blood examination
Cr-eGFR (ml/min/1.73m²)^#	124.0 (111.9-146.5)	122.3 (109.3-143.1)	124.0 (113.3-147.6)	0.49
Serum AGT (ng/mL)^##	17.2 (14.9-20.3)	17.9 (15.0-28.8)	16.5 (13.5-17.8)	0.046
Urinalysis
Hematuria, n (%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	1.0
Proteinuria, n (%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	1.0
Urinary AGT (μg/mL)	7.6 (3.3-12.1)	11.5 (5.9-16.8)	6.8 (1.8-9.9)	0.02
Urinary AGT/Cr (μg/g･Cr)	10.3 (4.7-17.9)	12.6 (9.5-21.2)	6.7 (3.3-15.5)	0.006
Urinary NGAL (ng/mL) ^†	0 (0.0-0.0)	0 (0.0-0.0)	0 (0.0-0.0)	0.84
Urinary NGAL/Cr (ng/g･Cr) ^†	0 (0.0-0.0)	0 (0.0-0.0)	0 (0.0-0.0)	0.81
Urinary β2 MG (μg/L)	113 (72-208)	172 (94-393)	106 (69-166)	0.09
Urinary β2 MG/Cr (μg/g･Cr)	0.18 (0.13-0.25)	0.25 (0.14-0.49)	0.17 (0.11-0.22)	0.10
Systolic blood pressure (mmHg)^††	100 (89-108)	103 (99-113)	97 (87-108)	0.15
Hypertension, n (%)^††	4/36 (11.1 %)	1/21 (4.8 %)	3/15 (20.0 %)	0.29
LBW; low birth weight, AGT: Angiotensinogen, CysC-eGFR; CysC-estimated glomerular filtration rate, NGAL; neutrophil gelatinase-associated lipocalin, β2 MG; β2 microglobulin, # In some children, since variations in serum Cr levels due to muscle mass and the effects of exercise were observed, CysC-eGFR was adopted instead of Cr-eGFR. ## Evaluated 43 children with data for serum angiotensinogen. † Evaluated 44 children with data for NGAL/Cr, †† Evaluated 36 children with data for systolic blood pressure

Table 2 Comparison of clinical characteristics, subdivided children with a history of LBW into those who had a history of PB and those who did not have a history of PB

	Children with a history of PB and LBW (n=14)	Children with a history of LBW but no PB (n=7)	Children with a history of PB and LBW (n=14)	Children without a history of PB nor LBW (n=24)	Children with a history of LBW but no PB (n=7)	Children without a history of PB nor LBW (n=24)
	Children with a history of PB and LBW (n=14)	Children with a history of LBW but no PB (n=7)	Children with a history of PB and LBW (n=14)	Children without a history of PB nor LBW (n=24)	Children with a history of LBW but no PB (n=7)	Children without a history of PB nor LBW (n=24)

Background
Age (years)	5.1 (3.8-6.0)	4.9 (3.8-7.3)	5.1 (3.8-6.0)	4.6 (3.3-7.0)	4.9 (3.8-7.3)	4.6 (3.3-7.0)
Boy : Girl, n (%)	8 : 6 (57.1 % : 42.9 %)	3 : 4 (42.9 % : 57.1 %)	8 : 6 (57.1 % : 42.9 %)	16 : 8 (66.7 % : 33.3 %)	3 : 4 (42.9 % : 57.1 %)	16 : 8 (66.7 % : 33.3 %)
Gestational week (weeks)	33.5 (26.8-35.3)^*	38.0 (37.0-39.0)^*	33.5 (26.8-35.3)^*	39.0 (39.0-40.0)^*	38.0 (37.0-39.0)^*	39.0 (39.0-40.0)^*
Birth height (cm)	36.0 (31.6-41.0)^*	45.0 44.9-45.5)^*	36.0 (31.6-41.0)^*	47.0 (46.5-48.8)^*	45.0 44.9-45.5)^*	47.0 (46.5-48.8)^*
Birth weight (g)	1104 (643-1691)^*	2350 (2108-2435)^*	1104 (643-1691)^*	2840 (2704-3254)^*	2350 (2108-2435)^*	2840 (2704-3254)^*
Blood examination
Cr-eGFR (ml/min/1.73m²)^#	120.7 (105.1-135.3)	140.9 (111.9-149.9)	120.7 (105.1-135.3)	124.0 (113.3-147.6)	140.9 (111.9-149.9)	124.0 (113.3-147.6)
Serum AGT (ng/mL)^##	20.3 (17.6-31.0)	15.0 (12.1-23.1)	20.3 (17.6-31.0)^*	16.5 (13.5-17.8)^*	15.0 (12.1-23.1)	16.5 (13.5-17.8)
Urinalysis
Hematuria, n (%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)
Proteinuria, n (%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)	0 (0.0%)
Urinary AGT (μg/mL)	10.4 (5.8-11.9)	14.3 (5.4-28.4)	10.4 (5.8-11.9)	6.8 (1.8-9.9)	14.3 (5.4-28.4)^*	6.8 (1.8-9.9)^*
Urinary AGT/Cr (μg/g･Cr)	11.4 (8.9-16.8)	20.4 (10.3-33.0)	11.4 (8.9-16.8)*	6.7 (3.3-15.5)^*	20.4 (10.3-33.0)^*	6.7 (3.3-15.5)^*
Urinary NGAL (ng/mL) ^†	0 (0.0-5.1)	0 (0.0-0.0)	0 (0.0-5.1)	0 (0.0-0.0)	0 (0.0-0.0)	0 (0.0-0.0)
Urinary NGAL/Cr (ng/g･Cr) ^†	0 (0.0-0.07)	0 (0.0-0.0)	0 (0.0-0.07)	0 (0.0-0.0)	0 (0.0-0.0)	0 (0.0-0.0)
Urinary β2 MG (μg/L)	139 (78-217)	446 (74-1158)	139 (78-217)	106 (69-166)	446 (74-1158)	106 (69-166)
Urinary β2 MG/Cr (μg/g･Cr)	0.17 (0.13-0.26)	0.46 (0.37-1.54)	0.17 (0.13-0.26)	0.17 (0.11-0.22)	0.46 (0.37-1.54)^*	0.17 (0.11-0.22)^*
Systolic blood pressure (mmHg) ^††	104 (100-113)	98 (91-104)	104 (100-113)	97 (87-108)	98 (91-104)	97 (87-108)
Hypertension, n (%) ^††	3/10 (30.0 %)	0/5 (0.0 %)	3/10 (30.0 %)	1/21 (4.8 %)	0/5 (0.0 %)	1/21 (4.8 %)
PB; preterm birth, LBW; low birth weight, AGT: Angiotensinogen, Cr-eGFR; Creatinine-estimated glomerular filtration rate, NGAL; neutrophil gelatinase-associated lipocalin, β2 MG; β2 microglobulin, * p<0.05, # In some children, since variations in serum Cr levels due to muscle mass and the effects of exercise were observed, CysC-eGFR was adopted instead of Cr-eGFR. ## Evaluated 43 children with data for Serum Angiotensinogen. † Evaluated 44 children with data for NGAL/Cr, †† Evaluated 33 children with data for systolic blood pressure

No competing interests reported.

Latent intrarenal renin-angiotensin-aldosterone system activation could persist until toddlerhood in children with a history of low birth weight

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