ORIGINAL PAPER
Nagoya J. Med. Sci. 83. 741–748, 2021
doi:10.18999/nagjms.83.4.741

Hypoalbuminemia is related to endothelial dysfunction
resulting from oxidative stress in parturients withpreeclampsia
Takuya Saitou1, Kazushi Watanabe1, Hiroyuki Kinoshita2, Ai Iwasaki1,
Yuki Owaki1, Hiroshi Matsushita1 and Akihiko Wakatsuki1
1

Department of Obstetrics and Gynecology, Aichi Medical University School of Medicine, Nagakute, Japan2
Department of Anesthesiology, Institute of Biomedical Sciences, Tokushima University Graduate School,
Tokushima, Japan

ABSTRACT
Serum albumin levels are inversely related with oxidative stress, but positively related with endothelial
function, in pregnant women. However, it is unclear whether hypoalbuminemia in pregnant women withpreeclampsia (PE) increases the production of oxygen-derived free radicals and impacts endothelial function.
The present study aimed to assess the relationship between serum albumin, oxidative stress, and endothelial
dysfunction in pregnant women with PE. A total of 75 women with control pregnancy (Control group, n= 30), PE (PE group, n = 24), or gestational hypertension (GH) (GH group, n = 21) were enrolled. We
assessed serum albumin levels, diacron-reactive oxygen metabolites (d-ROMs) as an oxygen-derived free
radical marker, and flow-mediated dilation (FMD) as a readout for vascular endothelial function during
the gestational period and at one month after delivery. During the gestational period, FMD was lower, but
d-ROM levels were higher, in the PE and GH groups compared with the Control group. Serum albumin
levels were lower in the PE group compared with the Control and GH groups. d-ROM levels were inversely
correlated with serum albumin levels (r = –0.54, p < 0.05) and FMD (r = –0.56, p < 0.05) in the PE
group, and negatively correlated with FMD, but not serum albumin levels, in the GH group. Serum levelsof d-ROMs and albumin, as well as FMD, were similar between groups after delivery. Our findings suggestthat reduced serum albumin levels enhance the production of oxygen-derived free radicals, resulting inimpaired maternal vascular endothelial function in parturients with PE.
Keywords: FMD, gestational hypertension, human serum albumin, oxidative stress, preeclampsia
Abbreviations:
BAP: biological antioxidant potential
BMI: body mass index
BP: blood pressured-ROMs: diacron-reactive oxygen metabolites
FMD: flow-mediated dilation
GH: gestational hypertension
JSSHP: The Japan Society for the Study of Hypertension in Pregnancy
PE: preeclampsia
SD: standard deviation

Received: December 3, 2020; accepted: March 9, 2021
Corresponding Author: Kazushi Watanabe, MD, PhD
Department of Obstetrics and Gynecology, Aichi Medical University School of Medicine, Nagakute 480-1195,
Japan
Phone: +81-561-62-3311; FAX: +81-561-62-2991; E-mail: kw446433@aichi-med-u.ac.jp
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This is an Open Access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
License. To view the details of this license, please visit (http://creativecommons.org/licenses/by-nc-nd/4.0/).

INTRODUCTION
Hypertensive disorders of pregnancy refer to a group of diseases involving hypertension inpregnancy and are a significant cause of maternal, fetal, and neonatal morbidity and mortality.1
Vasospasm, which reflects a vasomotor imbalance in maternal blood vessels, is common to
the disorders,2 and maternal endothelial dysfunction is associated with a systemic increase inoxygen-derived free radicals, resulting in oxidative stress and maternal morbidity.3 Hypertensive
disorders of pregnancy are further classified into gestational hypertension (GH), preeclampsia(PE), superimposed preeclampsia, and chronic hypertension. GH is defined as persistent denovo hypertension that develops at or after 20 weeks gestation. PE is a specific type of GH
which is accompanied by a combination of new-onset proteinuria, maternal organ dysfunction,or uteroplacental dysfunction at or after 20 weeks gestation.4 Hypoalbuminemia is a comorbidityof PE, but not GH, and results from serum albumin leaking from the maternal body via urine.
The relationship between hypoalbuminemia and the increased production of oxygen-derived free
radicals is unclear, although some studies have reported a potential association.5 We previously
reported that serum albumin reduces oxidative stress by inhibiting NADPH oxidase in humanvascular smooth muscle, and that serum albumin is inversely related to oxidative stress andpositively related to endothelial function in pregnant women.5 However, it remains unclear
whether hypoalbuminemia in pregnant women with PE increases the production of oxygen-derived
free radicals and impacts endothelial function. It is also unclear whether serum albumin levels,
production of oxygen-derived free radicals, and endothelial function change after delivery.
Here we hypothesized that hypoalbuminemia increases oxygen-derived free radical levels,
leading to vascular endothelial dysfunction in pregnant women with PE. To this end, the present
study aimed to assess relationships between serum albumin, oxidative stress, and endothelial
dysfunction in pregnant women with PE.

MATERIALS AND METHODS
Participants were 24 pregnant women with PE (PE group), 21 with GH (GH group), and 30
with uncomplicated pregnancies (Control group) who were recruited between April 1, 2010, andMarch 31, 2018, at Aichi Medical University (Aichi, Japan). Blood pressure (BP) measurements
were performed in the sitting position after a 10-minute resting period during pregnancy andat one month after delivery. GH was defined according to the Japan Society for the Study ofHypertension in Pregnancy (JSSHP) criteria, as follows: systolic BP ≥140 mmHg or diastolicBP ≥90 mmHg after 20 weeks’ gestation and hypertension normalize by 12 weeks’ postpartum.
PE was defined according to criteria of JSSHP, as follows: PE is gestational hypertension accompanied by one or more of the following new-onset conditions at or after 20 weeks’ gestation,
but all symptoms are normalized by 12 weeks’ postpartum. Proteinuria (≥300 mg protein/24
hours), other maternal organ dysfunction, or uteroplacental dysfunction.4 None of the participants
smoked, consumed alcohol or caffeine, or had a history of thyroid disease, hypertension, diabetes
mellitus, hyperlipidemia, or liver disease, and were not taking any medications known to influence lipoprotein metabolism. All control group participants underwent cesarean section due toprevious cesarean section, breech presentation, or surgery involving the uterine myometrium.
Written informed consent was obtained from each participant and the study was conducted in

743Albumin and vascular reactivity in PE

accordance with the principles of the Declaration of Helsinki. The Ethics Committee of Aichi
Medical University approved this study on November 26, 2018 (Registration No. 2018-H295).
We collected blood sample and measured FMD at the time of onset in the PE and GH groups,
and examination around 34weeks of pregnancy before cesarean section in the control group.
Blood samples were processed as previously described,6-8 and serum was stored at –80ºC
until use. Serum diacron-reactive oxygen metabolites (d-ROMs) and serum biological antioxidant
potential (BAP) were analyzed using the Free Radical Analytical System 4 (FRAS, Diacron,
Grosseto, Italy).9,10
Flow-mediated dilation (FMD) of the brachial artery was measured as a proxy for maternal
endothelial function, using a high-resolution Doppler ultrasound (Voluson E8, GE Healthcare,Zipf, Austria) with a 10-MHz transducer, as previously described.11,12 We collected blood samples
and measured FMD during pregnancy and at one month after delivery.
Statistical analyses were performed using JMP Statistical Software version 12 for Windows(SAS Institute Inc., Cary, NC). Data were expressed as mean ± standard deviation (SD). G*Powersoftware 3.1.9.3 for Windows (Heinrich-Heine-Universität, Düsseldorf, Germany) was used for
power calculations. According to the power calculations, a sample size of 24 would provide 91%
power to detect a d-ROM difference between the three groups at a significance level of 0.05
(SD = 163.0), 99% power to detect a serum albumin difference between the three groups at asignificance level of 0.05 (SD = 0.4), and 100% power to detect a FMD difference between thethree groups at a significance level of 0.05 (SD = 2.6). Patient characteristics, albumin levels,
serum d-ROM levels, and FMD before and after delivery were compared using one-way analysis
of variance followed by Fisher’s multiple comparison test. Correlations between d-ROM levels and
FMD, and between albumin and d-ROM levels, in the PE and GH groups were assessed using
single regression analysis. P<0.05 was considered statistically significant. Statistical power was
calculated using a post hoc power analysis among the Control, PE, and GH groups (significancelevel, α=0.05).

RESULTSWe analyzed 75 pregnant women (Control group, n = 30; PE group, n = 24; GH group, n =21) during the study period. Maternal age, body mass index (BMI), parity, and Gestational age
at time of study did not differ among the three groups (Table 1). Gestational age at delivery
was significantly shorter in the PE group compared to GH and Control groups (p<0.01 vs. GH,
p<0.0001 vs. Control), but did not differ between the GH and Control groups (Table 1). Neonatal
weight was significantly lower in the PE group compared to GH and Control groups (p<0.01 vs.
GH, p<0.0001 vs. Control), also significantly lower in the GH group compared to Control group(p<0.0001) (Table 1). Systolic and diastolic BP values were higher in the PE (p<0.0001) andGH (p<0.0001) groups compared with the Control group, but did not differ between the PE andGH groups (Table 1). FMD values were lower in the PE (p<0.0001) and GH (p<0.0001) groups
compared with the Control group, but did not differ between the PE and GH groups (Table 1).

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Takuya Saitou et al

Table 1

Clinical characteristics of the study population

Maternal age (year)

Control (n=30)

PE (n=24)

GH (n=21)

33.9 ± 4.2

32.8 ± 4.1

32.7 ± 4.3

Body mass index (kg/m )23.6 ± 2.2

26.3 ± 4.0

26.6 ± 4.1

Parity0.8 ± 0.7

0.7 ± 0.7

0.6 ± 0.7

Gestational age at time of study (week)

34.6 ± 1.2

34.5 ± 3.0

Gestational age at delivery (week)

38.2 ± 1.1

35.8 ± 2.6

Neonatal weight (g)3001 ± 286

2017 ± 601 a,b

2469 ± 494 a

Systolic BP (mmHg)

114.6 ± 14.4

159.0 ± 15.7

151.8 ± 7.2 a

Diastolic BP (mmHg)

71.3 ± 11.3

96.4 ± 12.1 a

93.6 ± 10.7 a

FMD (%)

9.8 ± 2.6

3.1 ± 2.6 a

3.7 ± 2.5 a2

35.6 ± 1.9
37.4 ± 2.6a,ba

BP: blood pressure
PE: preeclampsia
GH: gestational hypertension
FMD: flow mediated dilation
Data are expressed as mean ± SD.
ap<0.0001 vs. Controlbp<0.01 vs. GH
Statistical power calculated with post-hoc power analysis among the Control, PE and GH groups.
(significance level α=0.05)

Table 2 summarizes biochemical data in the Control, PE, and GH groups. Serum total protein(p<0.05 vs. Control, p<0.05 vs. GH) and albumin levels (p<0.001 vs. Control, p<0.001 vs.
GH) were lower in the PE group compared with the Control and GH groups, but did not differ
between the Control and GH groups (Table 2). Uric acid levels were higher in the PE (p<0.001)
and GH (p<0.05) groups compared with the Control group, and higher in the PE group comparedwith the GH group (p<0.05) (Table 2). Creatinine (p<0.001 vs. Control, p<0.05 vs. GH) andtriglyceride (p<0.001 vs. Control, p<0.05 vs. GH) levels were higher in the PE group comparedwith the Control and GH groups, but did not differ between the Control and GH groups (Table2). High density lipoprotein cholesterol levels were lower in the GH group compared with theControl and PE groups (p<0.05 vs. Control, p<0.05 vs. PE), but did not differ between theControl and PE groups. d-ROM levels were higher in the PE (p<0.05) and GH (p<0.05) groups
compared with the Control group, but did not differ between the PE and GH groups (Table 2).

Table 2Biochemical data before the delivery in the study population

Control (n=30)

PE (n=24)

GH (n=21)

Total protein (g/dL)

6.1 ± 0.2

5.8 ± 0.3a,c

6.1 ± 0.2

Albumin (mg/dL)

3.4 ± 0.4

2.9 ± 0.3b,d3.5 ± 0.4

Uric acid (mg/dL)

3.6 ± 0.8

6.6 ± 1.8 b,c

5.0 ± 1.7 aCreatinine (mg/dL)

0.5 ± 0.1

0.6 ± 0.2

0.5 ± 0.1

Total cholesterol (mg/dL)

238 ± 53261 ± 60234 ± 43

HDL cholesterol (mg/dL)

71 ± 1374 ± 17 c

60 ± 16 a

b,c

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Albumin and vascular reactivity in PE

LDL cholesterol (mg/dL)

115 ± 48145 ± 38

Triglyceride (mg/dL)

133 ± 54295 ± 195

122 ± 35b,c

197 ± 105

Fasting blood sugar (mg/dL)

82 ± 1181 ± 1277 ± 22d-ROMs (CARR U)

594 ± 163724 ± 124 a

725 ± 137 a

BP: blood pressure
GH: gestational hypertension
PE: preeclampsia
HDL: high density lipoprotein
LDL: low density lipoprotein
d-ROMs: diacron-reactive oxygen metabolites
Data are expressed as mean ± SD.
ap<0.05 vs Controlbp<0.001 vs Controlcp<0.05 d p<0.001 vs GH
Statistical power calculated with post-hoc power analysis among the Control, PE and GH groups.
(significance level α=0.05)

At one month after delivery, serum total protein, albumin, uric acid, creatinine, and triglyceride
levels in the PE group were normalized, and values of blood pressure, d-ROM, and FMD in the
PE and GH groups were restored to levels seen in the Control group (Table 3).

Table 3

Biochemical date at one month after the delivery

Control (n=30)

PE (n=24)

GH (n=21)

Systolic BP (mmHg)

116.8 ± 7.7

123.9 ± 8.8

124.1 ± 10.1

Diastolic BP (mmHg)

66.9 ± 9.1

73.0 ± 5.4

72.5 ± 8.3

Total protein (g/dL)

6.4 ± 0.2

6.4 ± 0.2

6.5 ± 0.2

Albumin (mg/dL)

4.2 ± 0.2

4.1 ± 0.4

4.0 ± 0.4

Uric acid (mg/dL)

4.7 ± 1.1

5.3 ± 1.0

5.4 ± 0.8

Creatinine (mg/dL)

0.6 ± 0.1

0.6 ± 0.1

0.6 ± 0.1

Total cholesterol (mg/dL)

220 ± 35

233 ± 39211 ± 32

HDL cholesterol (mg/dL)

71 ± 1366 ± 1462 ± 17

LDL cholesterol (mg/dL)

117 ± 33138 ± 25135 ± 20

Triglyceride (mg/dL)

79 ± 34

114 ± 51

96 ± 44

Fasting blood sugar (mg/dL)

81 ± 781 ± 1283 ± 6d-ROMs (CARR U)

422 ± 105357 ± 59455 ± 223

FMD (%)

9.6 ± 1.6

8.3 ± 3.2

8.0 ± 2.1

BP: blood pressure
GH: gestational hypertension
PE: preeclampsia
FMD: flow mediated dilation
d-ROMs: diacron-reactive oxygen metabolites
Data are expressed as mean ± SD.
Statistical power calculated with post-hoc power analysis among the Control, PE and GH groups.
(significance level α=0.05)

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Takuya Saitou et al

In the PE group, d-ROM levels were negatively correlated with serum albumin levels (r=–0.54,
p<0.05; Figure 1A) and FMD (r=–0.56, p<0.05; Figure 1B) during pregnancy. In the GH
group, d-ROM levels were negatively correlated with FMD (r=–0.60, p<0.01; Figure 1D), but
no correlation was observed between albumin and d-ROM levels during pregnancy (Figure 1C).

Fig. 1

Relationship between human serum albumin, concentrations of diacron reactive oxygen metabolites(d-ROMs) and flow-mediated vasodilation (FMD) in pregnant women with preeclampsia
and gestational hypertension
Fig. 1A:	Relationship between human serum albumin and concentrations of diacron reactive oxygen metabolites(d-ROMs). Closed circles represent pregnant women with preeclampsia. (r=–0.54; p<0.05)
Fig. 1B:	Relationship between concentrations of diacron reactive oxygen metabolites (d-ROMs), and flow-mediatedvasodilation (FMD). Closed circles represent pregnant women with preeclampsia. (r=–0.56; p<0.05)
Fig. 1C:	Relationship between human serum albumin and concentrations of diacron reactive oxygen metabolites(d-ROMs). Open circles represent pregnant women with gestational hypertension. (r=–0.26; p=0.42)
Fig. 1D:	Relationship between concentrations of diacron reactive oxygen metabolites (d-ROMs), and flow-mediatedvasodilation (FMD). Open circles represent pregnant women with gestational hypertension. (r=–0.60;
p<0.01)

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Albumin and vascular reactivity in PE

DISCUSSIONAlbumin is the most abundant protein in plasma and generally considered to be a multifunctional transport protein. It is thought to be the predominant circulating antioxidant in plasma, andis continuously exposed to oxidative stress.5 Serum albumin levels were lower in the PE groupcompared with the GH and Control groups, with no difference between the GH and Control
groups, in the present study. All women in the PE group during pregnancy had proteinuria, likely
reflecting protein (e.g., albumin) secretion from the body via urine.
Serum d-ROM levels in the PE and GH groups were higher during pregnancy, although thelevels did not significantly differ between the two groups. There was also a negative correlation
between levels of oxidative stress and FMD between the PE and GH groups. These results suggest that enhanced levels of serum oxidative stress may cause maternal endothelial dysfunction.
This conclusion is supported by our previous finding that an increase in oxygen-derived free
radicals during pregnancy impairs the endothelial function of patients with hypertensive disordersof pregnancy.3 A negative correlation was also found between serum albumin and d-ROM levelsin the PE group, but not in the GH group, suggesting that lower serum albumin levels may
predict higher serum levels of oxygen-derived free radicals in pregnant women with PE, but not
GH. In human vascular smooth muscle cells, albumin reportedly reduces superoxide levels by
inhibiting membrane recruitment of the NADPH oxidase cytosolic subunit p47phox, a critical
mediator of oxygen-derived free radical production in cardiovascular diseases.5,13,14 Therefore,
the reduced levels of serum albumin may, at least in part, play a role in augmenting oxidative
stress in pregnant women with PE, but not GH. Levels of serum albumin, d-ROMs, and FMD
in the PE group were restored to the normal range at one month after delivery. The recoveryof serum albumin levels may have contributed to both normalizing FMD and reducing oxidative
stress, although the underlying mechanism is unclear.
This study has some limitations. First, the sample population was small and came from asingle medical institution. Second, there was no difference in FMD among the Control, PE, andGH groups at one month after delivery. These results are somewhat inconsistent with previous
studies showing that women with a history of PE had a lower FMD at one year after delivery
and thus are at an increased risk of developing cardiovascular diseases later in life.15-21 Further
large-scale multicenter clinical studies will be needed to address the above issues.
In conclusion, reduced serum albumin levels enhance the production of oxygen-derived free
radicals, which in turn impairs maternal vascular endothelial function in parturients with PE.

ACKNOWLEDGMENTS
The authors would like to appreciate the pregnant women for taking part in this study.

DISCLOSURE
HK is a consult of IMI Co. Ltd, Koshigaya, Saitama, Japan. Other authors declare no conflictsof interest in connection with this article.

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