Effect of ischemia-modified albumin and dynamic thiol disulfide levels in cord blood on oxidative stress in pregnancies with intrauterine growth retardation and oligohydramnios

Authors

Abstract

Aim This study aims to evaluate both dynamic thiol-disulfide and ischemia-modified albumin (IMA) levels in pregnancies with intrauterine growth retardation and oligohydramnios.
Materials and Methods A total of 26 pregnant women with oligohydramnios and IUGR were compared with 25 pregnant women without any risk factors. The dynamic thiol-disulfide balance was determined by the new colorimetric method developed by Erel et al. IMA levels were analyzed by using the albumin cobalt binding test developed by Bar-Or et al.
Results It was found that TOS and OSI levels were higher and TAS levels were lower in the oligohydramnios group compared to the controls. Native and total thiol levels were found to be lower and statistically significant, while disulfide levels were found to be higher but not statistically significant in the study group with respect to the controls. IMA levels were found statistically significantly different between the patient and control subjects.
Discussion Our findings suggest that increased disulfide formation reduces antioxidant defenses in individuals with oligohydramnios. The balance between thiols and disulfides could be a useful marker for assessing oxidative stress in these patients and for tracking conditions associated with it.

Keywords

Introduction

Oligohydramniosis is defined as the amniotic fluid index on ultrasonography being below the 5th percentile for gestational age, the amniotic fluid volume being ≤ 5 cm, or the deepest single quadrant being < 2 cm [1]. Fetal urine is an important source of amniotic fluid in the third trimester of pregnancy, and although the underlying mechanism is not fully understood, oligohydramnios in uteroplacental insufficiency is thought to be associated with decreased fetal urine production in response to chronic fetal hypoxia[2, 3]. Along with decreased amniotic fluid volume, Chamberlain et al.[4] stated that there are connections between fetal hypoxia and acidosis, and this situation can occur in the form of stillbirth, fetal anomaly, abnormal fetal heartbeat tracing at birth, and an increase in cesarean section for fetal distress, and Chauan et al. [5] reported in their meta-analysis that oligohydramnios due to placental insufficiency increases the frequency of cesarean section due to fetal distress and the risk of a low 5th minute APGAR score (<7). In chronic fetal hypoxemia, oligohydramnios occurs together with fetal growth restriction, and the combination of these two supports the diagnosis of intrauterine growth restriction.[6] Nicolaides et al. They detected oligohydramnios in 50% of cases with intrauterine growth retardation [7]. Intrauterine growth restriction (IUGR) is 10% of the estimated fetal weight (TFA) based on gestational age, as determined on ultrasonography. It is below the percentile [8]. The frequency of fetal and perinatal mortality is observed to be increased in fetuses with IUGR [9]. It is thought that oligohydramniosis may create a source of oxidative stress (OS) in the newborn and, accordingly, increase the systemic OS load. It has been reported that reactive oxygen species (ROS) may cause oligohydramnios by causing damage to the amniotic membrane [10]. The dynamic balance between reductive and oxidative processes in physiological conditions rescues cells from the harmful production of ROS caused by the transition from physiological eu-stress to pathological oxidative di-stress or OS. Increased OS in the blood is indicated by the deterioration in the balance of total oxidative stress (TOS) and total antioxidant capacity (TAS), and the oxidative stress index (OSI). It is known that increased OS causes negative effects on macromolecules such as lipids, proteins, and DNA, and free radicals attack unsaturated fatty acids in cell membranes, causing disruption of the membrane structure and increased membrane permeability, genetic mutation on DNA, and finally enzyme inactivation [11]. There are various enzymatic and non- enzymatic defense mechanisms against the harmful effects of Reactive Oxygen Species (ROS), and one of these antioxidant mechanisms is the presence of thiols. It is known that these compounds containing sulfhydryl groups play an important role in preventing OS in cells. The primary target of intracellularly produced ROS is the thiol groups in sulfur-containing amino acids found in proteins. These thiol groups interact with ROS and form reversible disulfide bonds. These disulfide bonds are then reduced back to thiol groups by antioxidant mechanisms. Thus, a dynamic thiol/disulfide balance is achieved [12]. Research evidence suggests that OS is strongly implicated in the onset and progression of numerous disorders [12, 13, 14, 15, 16, 17, 18, 19].
Ischemia-modified albumin damages the N-terminal end of albumin as a result of increased oxidative stress, reducing the binding capacity of albumin. This modified form of albumin is called IMA [20]. This is the first study to investigate dynamic thiol disulfide balance and IMA levels in patients with oligohydramnios.

Materials and Methods

Patient and Control Group
Our study included patients aged 36-41 who were admitted to Aksaray Training and Research Hospital Maternity Unit between February 2022 and April 2022. 36 pregnant women in the gestational week and between the ages of 18-49 were included. Among the pregnant women admitted, 26 pregnant women with oligohydramniosis and IUGR were compared with 25 pregnant women without any risk factors. Medical consent was obtained from the patients included in the study in accordance with the terms of the Helsinki Declaration of Ethics. All routine laboratory parameters of the patients; hemoglobin, platelet, neutrophil, lymphocyte, hematocrit, urea creatinine, AST, ALT values , and demographic data; Age, gravida, parity, number of abortions, birth weight, baby gender, and APGAR scores were recorded. Patients below the 36th gestational week, with comorbidities, with multiple pregnancies, or with fetuses with anomalies were excluded from the study.
Sample Collection of the Study
Whole cord blood samples were taken from patients in both groups at birth in vacuum tubes containing ethylenediaminetetraacetic acid. These samples were centrifuged at 1500 rpm for 10 minutes. Then, the plasma samples were separated into Eppendorf tubes and stored in the refrigerator at -20°C until the processing time.
Biochemical Measurements TAS and TOS Measurements
Total oxidant status (TOS) and total antioxidant status (TAS) levels were measured spectrophotometrically based on the method developed by Erel [21]. Oxidative stress index (OSI). OSI (arbitrary unit) =TOS (µmol H2O2 Eq/L)/TAS (µmol Trolox Eq/L)×100 was calculated.
Measurement of Thiol/Disulfide Levels
Thiol/disulfide levels were determined by an automated spectrophotometric method as previously described by Erel and Neselioglu [22]. Disulfide levels were determined by dividing the difference obtained by subtracting native thiols from total thiols by two.
Measurement of IMA Levels
Ischemia Modified Albumin (IMA) levels were analyzed by using the albumin cobalt binding test developed by Bar-Or et al [20]. The results were expressed as absorbance units (ABSU).
Statistical Analysis
SPSS 22 (SPSS Inc., Chicago, IL, USA) program was used for statistical analysis. The Shapiro-Wilk test was used to determine whether the data showed normal distribution. Comparison of the data that was not normally distributed was determined by the Mann-Whitney U test. 0.05 was considered statistically significant.
Ethical Approval
This study was approved by the Ethics Committee of Aksaray University (Date: 2022-01-13, No: 13-SBKAEK).

Results

This study consisted of 50 people, including 25 Oligohydramnios and 25 healthy pregnant women, were included in our study. There was no significant difference between the groups in terms of age, gravity, and parity (Table 1).
Demographic data of pregnant women, including age, gestational age, birthweight, and Apgar scores of the study and control groups, are shown in Table 1.
The biochemical parameters of the study and control groups are shown in Table 2.
Native and total thiol levels were found to be significantly lower in the study group compared with the healthy pregnant subjects (p<0.001). However, disulfide levels were higher in the patient group compared with the healthy pregnant group (p= 0.132). Moreover, we found TAS levels were statistically significant between the patient and control groups (p<0.001). In addition, TOS and OSI levels were significantly different between the study and control groups (p<0.001). Additionally, serum IMA levels were significantly different between the patient and control groups (p <0.001, Table 3).

Discussion

We demonstrated that thiol levels were statistically significantly lower in patients with oligohydramnios than the healthy pregnant subjects. However, disulfide levels were higher but not statistically significant in patients with the oligohydramnios group with respect to controls. Our study also revealed that IMA levels were statistically significant in the patient group compared to the healthy controls. We also demonstrated that serum TOS and OSI levels were higher and statistically significant in patients with the study group than in healthy control subjects. However, TAS levels were lower inpatient group compared to the controls. IMA levels were higher in the study group than in the controls.
Cetin et al. [23] showed that maternal native and total thiol levels were significantly lower in the study group than in the healthy controls. However, they indicated that disulfide levels were similar between the study and control groups. They concluded that there is an impaired maternal thiol/ disulfide level in pregnancies complicated by idiopathic IUGR during the third trimester of gestation.
In another study, Yılmaz et al. [24] investigated the effects of slow-release vaginal dinoprostone on maternal and fetal OS in term pregnancies complicated by oligohydramnios, and they indicated that there was no significant difference in maternal oxidative load compared to the pre-application status. They also showed that maternal antioxidants were significantly lower in the group that received slow-release vaginal dinoprostone at the beginning of the active phase of labor than in the control group. They concluded that induction of labor with slow-release vaginal dinoprostol inserts in pregnancies with isolated oligohydramnios does not cause further OS and is safe for both mothers and neonates in terms of oxidant load by thiol/disulfide homeostasis.
Another study conducted with Kiremitli et al. [25] indicates that there was no significant difference in terms of disulfide levels. However, they found native and total thiol levels were significantly lower in the isolated oligohydramnios group than in the control group. They also investigated IMA levels and found significantly higher levels in the isolated oligohydramnios group than in the control group. They concluded that oxidative stress and ROS have a place in the pathophysiology of isolated oligohydramnios.
In the present study, native and total thiol levels were found to be significantly lower in the study group compared with the control subjects. However, disulfide levels were higher in the patient group with respect to the controls. We concluded that the decrease in serum thiol levels in the study group may be due to the continued depletion of sulfhydryl-containing antioxidant molecules to remove ROS. Moreover, TAS levels were lower in the patient group and found to be statistically significant between the patient and control groups (p<0.001). However, TOS and OSI levels were higher and found significantly different between the two groups (p<0.05). In addition, IMA levels were found to be statistically different between the patient and control groups. We hypothesized that elevated IMA concentrations could be linked to oxidative stress and an impaired capacity of the antioxidant defense system.

Limitations

Our limitation of the study is a small sample size. Large sample size studies are needed to further the prospective studies.

Conclusion

In conclusion, the results suggest an imbalance between oxidant and antioxidant mechanisms. Patients with oligohydramnios showed elevated disulfide concentrations alongside reduced native and total thiol levels, implying that disulfide formation may impair antioxidant defenses. The rise in IMA levels further reflects diminished antioxidant activity in parallel with enhanced oxidative stress, likely driven by excess ROS generation. Assessing dynamic thiol–disulfide equilibrium could therefore be useful for tracking oxidative stress in oligohydramnios and for monitoring disorders associated with it.

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