Clinical StudyOxidative Stress in Women Treated with Atosiban for ImpendingPreterm Birth

Mariusz Grzesiak ,1 Zuzanna Gaj ,1,2 Rafał Kocyłowski ,1,3 Joanna Suliburska ,4

Przemysław Oszukowski ,5 Wojciech Horzelski ,6 Constantin von Kaisenberg ,7

and Maciej Banach 8

1Department of Obstetrics, Perinatology and Gynecology, Polish Mother’s Memorial Hospital-Research Institute, Lodz 93-338, Poland2Scientific Laboratory of the Center of Medical Laboratory Diagnostics and Screening, Polish Mother’s MemorialHospital-Research Institute, Lodz 93-338, Poland3PreMediCare New Med Medical Centre, Poznan 61-693, Poland4Institute of Human Nutrition and Dietetics, Poznan University of Life Sciences, Poznan 60-624, Poland5Department of Obstetrics and Perinatology, Medical University of Lodz, Zgierz 95-100, Poland6Faculty of Mathematics and Computer Science, University of Lodz, Lodz 90-238, Poland7Department of Obstetrics and Gynecology, Hannover Medical School, Hannover 30625, Germany8Department of Hypertension, Medical University of Lodz, Lodz 90-549, Poland

Correspondence should be addressed to Zuzanna Gaj; gajzuzanna@gmail.com

Received 6 July 2018; Revised 14 September 2018; Accepted 2 October 2018; Published 2 December 2018

Academic Editor: Daniela Giustarini

Copyright © 2018 Mariusz Grzesiak et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

Preterm birth is defined as delivery before 37 completed weeks of pregnancy, and it is the leading cause of neonatal morbidity andmortality. Oxidative stress is recognized as an important factor in the pathogenesis of premature labor. We conducted this analysisto investigate the safety of administration of the tocolytic drug Atosiban—a reversible, competitive antagonist of the oxytocinreceptor in the treatment of preterm birth and its impact on the level of oxidative stress in pregnant women after 48 hours oftocolytic treatment. This prospective study was conducted between March 2016 and August 2017 at the Obstetric Clinic of thePolish Mother’s Memorial Hospital Research Institute. Total oxidant status (TOS), total antioxidant status (TAS), and oxidativestress index (OSI) values as well as 3-nitrotyrosine, carbonyl, and thiol group levels were measured using an ELISA test in serumand plasma of 56 pregnant women before and after 48 hours of continuous administration of Atosiban. We found that TASlevels decreased almost twice after the 48-hour drug administration (0.936± 0.360mmol/L vs. 0.582± 0.305mmol/L, P < 0 001)while TOS increased from 18.217± 16.093μmol/L to 30.442± 30.578μmol/L (P < 0 001). We also found a significant increase inOSI index—almost a threefold increase from 0.022± 0.022 to 0.075± 0.085, P < 0 001. In addition, statistically significantdifferences in the level of carbonyl groups were found. It increased from 65.358± 31.332μmol/L to 97.982± 38.047μmol/L(P < 0 001), which indicates increased oxidation of plasma proteins. Furthermore, patients who gave birth prematurelyhad higher levels of TOS after a 48-hour drug administration than the second group with labor after 37 weeks ofpregnancy (42.803± 34.683μmol/L vs. 25.792± 27.821 μmol/L, P < 0 031). The obtained results clearly indicate that pregnantwomen during tocolytic treatment with Atosiban are in a state of increased oxidative stress and occurrence of preterm birth canbe associated with this phenomenon. This trial is registered with NCT03570294.

1. Introduction

Oxidative stress is defined as an imbalance in the productionof reactive oxygen species and the capacity of antioxidant

defenses. A moderate level of oxidative stress was foundas normal in pregnancy [1–3]. However, when increasedproduction of reactive nitrogen and oxygen species (RNSand ROS, respectively) exceeds the mother’s antioxidant

HindawiOxidative Medicine and Cellular LongevityVolume 2018, Article ID 3919106, 8 pageshttps://doi.org/10.1155/2018/3919106

potential, it can negatively affect the well-being of both themother and the fetus, leading to complications in pregnancy,as well as adverse pregnancy outcomes such as spontaneouspreterm birth and preterm premature rupture of membranes[4–9]. The modifications caused by RNS and ROS result innew functional groups such as hydroxyl or carbonyl groups,leading to fragmentation of protein, formation of protein-protein cross-linkages, disruption of the tertiary structure,and a loss of functional activity [1, 3].

Preterm labor is defined as delivery before 37 completedweeks of gestation and can affect 5–13% of all pregnanciesin high-income countries. It is the important cause of neona-tal morbidity and mortality because it can be responsible foreven 50% of neonatal morbidity and 50–75% of neonatalmortality worldwide [10]. The most common phenotype ofpreterm labor is spontaneous preterm birth of unknownetiology; however, an uncompensated increase in oxidativestress is considered as one of the important reasons forpremature birth [2, 11]. The current evidence suggests thatthe administration of tocolytic drugs can delay preterm laborfor 48 hours, thus allowing administration of corticosteroidsto stimulate production of surfactant in fetal lungs which canimprove neonatal outcome [12, 13].

Atosiban (1-(3-mercaptopropanoic acid)-2-(O-ethyl-D-tyrosine)-4-L-threonine-8-L-ornithine-oxytocin) is a revers-ible, competitive antagonist of the oxytocin receptor (OTR)and can decrease contractions and improve uterine receptiv-ity due to its ability to reduce intracytoplasmic calciumrelease and downregulate prostaglandin synthesis [14–16].Atosiban is licensed for clinical use in case of impendingpreterm birth and is commonly used in clinical practice inEurope because of its low side effect profile [17–21]. Whilea role of Atosiban in the modulation of myometrial contrac-tility is well-described, its effect on many other functions isnot so well known. Recent publications presented new dataabout its role in elevated cardiac oxidative stress in newbornrats frommothers treated with Atosiban and activation of theinflammatory pathway in the amnion which may reduce itspotency as a tocolytic drug [22–24].

We conducted this analysis to investigate the safety ofadministration of Atosiban in the treatment of preterm laborand its impact on the level of oxidative stress after 48 hours oftocolytic treatment. To the best of our knowledge, this is thefirst analysis concerning the association of Atosiban treat-ment on the total oxidant and antioxidant status in pregnantwomen suffering from threatened premature birth.

2. Material and Methods

2.1. Patients. This study was conducted between March 2016and August 2017 at the Obstetric Clinic of the PolishMother’s Memorial Hospital Research Institute which is atertiary referral hospital. The study protocol conformed tothe principles of the Helsinki Declaration and was approvedby the local Research Ethical Committee (No. 34/2014).Informed consent was obtained from all women beforeinclusion. This study was retrospectively registered withClinicalTrials.gov on 26 June 2018. Sixty-four pregnantwomen receiving prenatal care due to the risk of premature

birth who met the inclusion criteria were enrolled in thestudy. The study also involved 8 patients with twin pregnan-cies. The average results for tested biochemical parameters inthe group with twin pregnancy were very similar to theresults of the group with a single pregnancy; however, itwas decided to exclude them from the analysis to eliminateconfounding factors. The final analysis comprised 56 women.Inclusion criteria were as follows: patients between 24 and35 weeks’ gestation with intact membranes and showingevidence of premature labor. The last menstrual date orultrasonographic measurements from the first trimesterwere used to determine the gestational age. The pretermlabor was diagnosed as painful, regular, and persistentuterine contractions (no less than a 30-second duration andat least four in an hour) before the 37th week of gestationassociated with cervical changes (a cervical dilation of 1 to3 cm) and/or effacement (≥50%). Exclusion criteria includedacute fetal distress and other conditions requiring immediatedelivery (eclampsia and severe preeclampsia, abruptio pla-centa, and placenta previa) as well as chorioamnionitis,vaginal bleeding, intrauterine growth restriction, and fetalcongenital malformations. The use of any tocolytic drugsduring pregnancy before admission to the hospital also metthe exclusion criteria. The patients with circulatory systemdiseases (e.g., heart defects and hypertension), symptoms ofinfection and other diseases that may increase oxidativestress, and any other specific maternal contraindication forAtosiban treatment were also excluded. According to ourdata, none of the subjects in the study were smokers or wereusing specific antioxidant supplementation.

2.2. Tocolytic Treatment. Atosiban medication was adminis-tered after a particular patient evaluation, in accordancewith the drug characteristic medical protocol. The initialdose of Atosiban (Tractocile, Ferring Pharmaceuticals A/S,Copenhagen, Denmark) was given as a single intravenousbolus dose (6.75mg in 0.9mL isotonic sodium chloride solu-tion). This was followed immediately by intravenous infusionof 300μg/min of Atosiban in 5% glucose for 3 hours and then100μg/min for up to 48 hours. Maternal steroid therapy wasstarted right after admission to the hospital. According to themost recent recommendations from The American Collegeof Obstetricians and Gynecologists, patients were given four6mg doses of dexamethasone (Dexaven, Jelfa, Poland)administered intramuscularly every 12 hours [25].

2.3. Blood Sampling. Venous blood samples from a forearmantecubital vein were taken before and after 48 hours of con-tinuous administration of tocolytic therapy with Atosiban.Blood samples were collected into serum-separating tubesand in tubes containing EDTA (for plasma) and immediatelystored at 4°C. The plasma was then separated from the cellsby centrifugation at 1500× g for 20min, at 4°C. In order toobtain serum, the blood was centrifuged at 2500× g, at 4°Cfor 10 minutes. The serum and plasma samples were takenfor the measurement of total oxidant status (TOS), total anti-oxidant status (TAS), level of 3-nitrotyrosine (3-NT), andcarbonyl and thiol groups which were stored at −70°C inaliquots for subsequent biochemical analysis and processed

2 Oxidative Medicine and Cellular Longevity

within two months. They were thawed at room temperatureonly once at the time of analysis. All measurements wereperformed in duplicate.

2.4. Measurement of Total Oxidant and Antioxidant Status(TOS and TAS) in Serum. Total oxidant status and total anti-oxidant status values were measured by colorimetric assayaccording to a method developed by Erel [26, 27]. The TOSRel Assay Diagnostics kit (Rel Assay, Gaziantep, Turkey)was used to determine the levels of the total oxidant statusaccording to the manufacturer’s instructions. This methodis based on the iron-mediated reactions of apparently stableproducts (hydroperoxides) of the lipid peroxidation process.The oxidation of ferrous ion to ferric ion in the presence ofvarious oxidant species in serum was measured using xylenolorange. The assay was calibrated with hydrogen peroxide,and the results are expressed in terms of micromolar hydro-gen peroxide equivalent per liter (μmol H2O2 equiv./L). Thecoefficients of variation values were found less than 10%.TAS was measured by determination of the total nonenzy-matic plasma antioxidant capacity using the TAS Rel AssayDiagnostics kit (Rel Assay, Gaziantep, Turkey). In thismethod, 2,2′-azino-di-(3-ethylbenzthiazoline sulfonate) rad-ical cation (ABTS∗+, ∗ is an unpaired electron) produced bythe hydroxyl radical is used as an indicator of antioxidantactivity. The reaction was calibrated with Trolox (a water-soluble analogueof vitaminE, 6-hydroxy-2.5.7.8-tetramethyl-chroman-2-carboxylic acid), and the results were expressedas mmol Trolox equiv./L. The coefficients of variation valueswere found less than 10%.

2.5. Oxidative Stress Index (OSI) Determination. OSI wasdetermined as a TOS to TAS ratio (the resulting unit ofTAS was changed to μmol/L) and was calculated as follows:OSI (arbitrary unit) =TOS, μmol H2O2 equiv./L/TAS, andμmol Trolox equiv./L [23].

2.6. Estimation of 3-Nitrotyrosine. The competitive 3-nitrotyrosine (3-NT) ELISA Kit was used to determineprotein peroxidation in plasma (OxiSelect™ NitrotyrosineELISA Kit, Cell Biolabs Inc., San Diego, USA). 3-NT is aproduct of posttranslational modification of protein tyrosinecaused by peroxynitrite, and this modification can result inchanges in protein structure, function, and catalytic activity[28]. The absorbance was read at 450 nm against 620 nm asa reference with an ELISA reader iMark™ (Bio-Rad USA).The protein nitrotyrosine content was determined bycomparing with a standard curve that was prepared frompredetermined nitrated BSA standards (2.7 mole of nitrotyr-osine per 1 mole of BSA). The detection limit was 20 nM.

2.7. Estimation of Protein Carbonyl Groups. The measure-ment of protein carbonyl content is considered a reliablemarker of oxidative protein damage due to its long-lastingstability [28]. Protein carbonyls were measured as a parame-ter of oxidative stress in plasma after derivatization with 2,4-dinitrophenylhydrazine (DNPH) with the Carbonyl ProteinELISA Kit (Immundiagnostik AG, Bensheim, Germany)according to the instructions supplied by the manufacturer.The absorbance was read at the wavelength of 450 nm against

620 nm as a reference with an ELISA reader iMark™(Bio-Rad). The intra- and interassay coefficients of variabil-ity were found less than 6.5% and 6.2%, respectively.

2.8. Estimation of Thiol Groups. Thiol protein (sulfhydryl)status (glutathione, protein-bound, and free SH groups) wasmeasured in plasma by enzyme-linked immunosorbent assayaccording to the manual instructions (Immundiagnostik AG,Bensheim, Germany) using a modification of Ellman’smethod. Serum protein thiols react with oxygen-containingfree radicals to form disulfides; therefore, they are a goodand direct measure of the in vivo redox status in human.Absorbance was measured at 412nm against a reagent blankusing an ELISA reader Synergy H1 (BioTek, Vermont, USA).

2.9. Statistical Analysis. Statistical analyses were performedusing MedCalc for Windows, version 15.1 (MedCalcSoftware, Ostend, Belgium). The normality of data was testedusing the D’Agostino-Pearson test. The results were pre-sented as means with standard deviation (SD) or as medianwith interquartile range (25th–75th percentiles) for nonnor-mally distributed variables (gestational age at baseline, parity,gravidity, and gestational age at delivery). The baseline char-acteristics were compared depending on the assumptionsusing Student’s paired t-test for normally distributed dataor Wilcoxon’s test for paired samples for nonnormallydistributed variables. Analysis of variance (ANOVA) testswere used to examine the relationship between time of laborand levels of markers of oxidative stress. P values less than0.05 were considered statistically significant.

3. Results

Sociodemographic, obstetric, and neonatal characteristics ofthe 56 women included in the study are presented inTable 1. The mean age of the examined women was 30.9±5.4 years, 50% of patients (28/56) were nulligravida, and64% of women (36/56) were nulliparous. Atosiban wasadministered on average at 30± 2.9 weeks of pregnancy.

Table 1: Sociodemographic, obstetric, and clinical characteristics ofstudy participants.

Variables

Mothers (n = 56)Age (years)a 31± 5.3Gestation age at baseline (weeks)b 30 (28–32)

Parityb 1.59 (1–2)

Gravidityb 1 (1–2)

Gestation age at delivery (weeks)b 37 (36–39)

Children (n = 53)Male/femalec 60.4/39.6

Birth weight (g)a 2884.8± 748.8Apgar scaleb 10 (9–10)

Days of hospitalizationa 8.1± 10.1aValues are means and standard deviation (SD), bvalues are median andinterquartile range (25th–75th percentiles), and cvalues are percentage.

3Oxidative Medicine and Cellular Longevity

Looking at the results of our studies, 96% of the womentreated with Atosiban were still pregnant one week aftertreatment (54 out of 56) and the longest period from admin-istration of the drug to delivery was 14 weeks (mean 6.5± 3.5weeks). The patients gave birth on average at 36.6± 3.1 weeksof pregnancy, and 60.3% of pregnant women delivered bycesarean section, while 39.7% gave birth naturally. Despitethe fact that patients gave birth on average at 36.6 weeks ofpregnancy which could suggest preterm birth, most ofpregnant women in our study (35/53, 66%) had labored after37 completed weeks of pregnancy which confirms thetocolytic effectiveness of Atosiban. The mean birth weightof the newborns was 2884.8± 748.8 g, and they received anaverage of 8.7± 2 points on the Apgar scale. Most children(82.3%, 42/51) left the hospital during the first week oflife in good condition; two children born before the27th week of pregnancy died due to extreme prematurityand low birth weight (600 and 720 g, respectively). Onlythree children born between 28 and 31 weeks of pregnancy,due to complications related to prematurity, had to spendmore than 4 weeks in the neonatal ward. Three childrenwere lost to follow-up because their mothers gave birthin another hospital.

According to biochemical markers, both TOS and pro-tein carbonyls as well as OSI index were increased in serumcollected after 48 h therapy when compared to the serumbefore administration of Atosiban (Table 2). It was alsoshown that the total serum antioxidative potential decreasedalmost twice after a 48-hour drug administration from anaverage of 0.936± 0.360mmol/L to 0.582± 0.305mmol/L(P < 0 001). On the other hand, the total oxidation potentialincreased from the mean value of 18.217± 16.093μmol/L inthe samples taken before drug administration to the valueof 30.442± 30.578μmol/L (P < 0 001) in samples after 2 daysof continuous administration of Atosiban. The obtainedresults as well as a significant increase in OSI index whichis a cumulative marker of both oxidative and antioxidativepower (an over threefold increase from 0.022± 0.022 to0.075± 0.085, P < 0 001) clearly indicate a higher level ofoxidative stress after the treatment with Atosiban and asignificant reduction in the antioxidative capacity of theinvestigated serum. Analyses of total oxidative status, totalantioxidant status, and OSI index before and after treatmentare presented in Figures 1(a)–1(c). In addition, statistically

significant differences in the level of carbonyl groups in thetested plasma were found (Figure 1(d)). It increased from65.358±31.322μmol/L to 97.982±38.047μmol/L (P < 0 001),which indicates increased oxidation of serum proteins andtheir damage. On the other hand, we did not observe statisti-cally significant differences in the level of thiol groups. 3-NTconcentrations, an indicator of protein peroxidation andoxidative stress, were also not significantly different betweenthe groups (P = 0 230); however, the higher concentration ofthis marker was observed in the serum collected after treat-ment (40.7± 44.2 nM vs. 51.4± 44.1 nM, respectively).

An additional analysis of the levels of oxidative stressmarkers was carried out in groups of women with pre-term delivery (n = 18) and with labor after 37 weeks ofpregnancy (n = 35). Atosiban was administered at a verysimilar period of pregnancy for both groups, on average at30.1± 3.7 weeks of pregnancy in the group with pretermdelivery and at 30.2± 2.5 weeks of pregnancy in the othergroup with labor after 37 weeks of pregnancy. Patients whogave birth prematurely had higher levels of TOS after a48-hour drug administration than the second group(42.803± 34.683μmol/L vs. 25.792± 27.821μmol/L, P <0 031) (Table 3). Despite the lack of statistically significantdifferences for other markers, we also observed an increasein oxidative stress parameters (TOS and carbonyl groups)and a reduction in the antioxidative capacity (TAS) inthe compared groups before and after 48 hours of therapywith Atosiban (Table 3).

4. Discussion

In this present study, we demonstrated, for the first time, ahigher oxidative status (reflected by increased levels of TOS,OSI index, and carbonyl group level) and lower antioxidantcapacity caused by oxidative stress in the serum of pregnantwomen after tocolytic treatment. Furthermore, patientswho gave birth prematurely had higher levels of TOS after a48-hour administration of Atosiban than the second groupwith labor after 37 weeks of pregnancy, which might indicatethe influence of increased oxidative stress on preterm labor.

This study was conducted to investigate the safety ofadministration of Atosiban in the treatment of pretermlabor. Atosiban has proved to be a very effective short-term tocolytic drug which is consistent with the Polish

Table 2: Oxidative and antioxidative parameters in plasma and serum before and after 48 hours of continuous administration of tocolytictherapy with Atosiban.

Treatment with AtosibanVariable 0 hours 48 hours P value

TOS (μmol/L) 18.217± 16.093 30.442± 30.578 0.0011a

TAS (mmol/L) 0.936± 0.360 0.582± 0.305 <0.0001a

OSI (arbitrary units) 0.022± 0.022 0.115± 0.395 <0.001a

Carbonyl groups (μmol/L) 65.358± 31.322 97.982± 38.047 <0.001b

Thiol groups (μmol/L) 512.023± 121.162 516.240± 111.886 0.806a

3-Nitrotyrosine (nM) 40.8± 45.7 50.5± 44.7 0.210a

Data are presented as mean value and standard deviation. TOS: total oxidant status; TAS: total antioxidant status; OSI: oxidative stress index, aWilcoxon’s testfor paired samples, ba paired Student t-test.

4 Oxidative Medicine and Cellular Longevity

recommendations suggesting its use as the first-line drugin the treatment of preterm labor [29]. Also, our presentobservation did not confirm the reports about the adverseimpact of Atosiban on the newborns [30]. Simsek et al.[23] indicated that blockage of the oxytocin receptor maybe connected with increased fetal mortality and morbiditybecause of the elevated oxidative stress observed in theheart of the newborn rats. However, we have not foundsuch negative effects and the vast majority of neonates inour study were born in good condition. A detailed evaluationof placental and fetal circulation with assessment of cardiachemodynamic function during 48 hours of administration

of Atosiban in pregnant women carried out in our previousstudies showed that hemodynamic cardiac activity in fetusesremained unaffected after tocolytic treatment [31, 32]. It canbe explained by the fact that Atosiban crosses the placentawith an average fetal versus maternal ratio of 0.124 and itsconcentrations do not appear to accumulate in the fetus [33].

Nevertheless, we observed that treated women were in astate of increased oxidative stress after a 48-hour administra-tion of Atosiban. Unfortunately, very little is known aboutthe possible involvement of tocolytic therapy in oxidativestress damage. We demonstrated that serum and plasmasamples showed higher level of TOS and carbonyl groups as

P < 0.0011

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Figure 1: Analyses of total oxidative status (a), total antioxidant status (b), OSI index (c), and carbonyl group level (d) before and aftera 48-hour treatment with Atosiban. The horizontal lines represent the mean values.

Table 3: Analysis of levels of oxidative stress markers in groups with labor before and after 37 weeks of gestation before and after 48 hours ofcontinuous administration of tocolytic therapy with Atosiban.

Variable Birth before 37 weeks (n = 18) Birth after 37 weeks (n = 35) P value

TOS (μmol/L)0 h 24.847± 19.183 15.839± 14.135 0.060

48 h 42.803± 34.683 25.792± 27.821 0.031

TAS (mmol/L)0 h 0.937± 0.331 0.934± 0.395 0.612

48 h 0.580± 0.336 0.565± 0.305 0.636

Carbonyl groups (μmol/L)0 h 61.670± 28.555 68.606± 30.386 0.428

48 h 96.231± 37.574 101.104± 36.872 0.654

Data are presented as mean value and standard deviation. TOS: total oxidant status; TAS: total antioxidant status. Analysis of variance tests were used toexamine the relationship between time of labor and levels of markers of oxidative stress.

5Oxidative Medicine and Cellular Longevity

well as a significant increase in OSI index after tocolytictreatment. The statistically significant differences in TASlevels can also suggest that systemic antioxidant defensemechanisms are exhausted during treatment due to increasedoxidative stress. A very similar pattern was observed in thestudies conducted by Aycicek et al. [34] on active and passivematernal smoking. Cigarette smoke is a well-known riskfactor of adverse pregnancy outcomes, and exposure to thisexternal stressor agent can cause important alterations in oxi-dant and antioxidant balance and increase potent oxidativestress [3, 35]. The increased level of TOS and OSI index aswell as lower antioxidant capacity after tocolytic treatmentwith Atosiban were comparable to those observed in mater-nal serum from the active smoker group [34]. Similarly,Argüelles et al. [36] found that smoking mothers and theirnewborns had a higher concentration of the carbonyl groupand lipid peroxides and lower total antioxidant capacity inserum and umbilical cord blood than nonsmoking mothersand their newborns from the control group.

A relationship between administration of Atosiban andincrease in oxidative stress parameters was also observed inan animal research study conducted by Simsek et al. [23].They found higher levels of oxidative stress markers (TOSand OSI index) as well as a decrease in TAS level in theplasma of newborn rats in the Atosiban-treated group whencompared to the control group. This observation can be anindirect evidence of Atosiban’s involvement in a process ofincreasing levels of oxidative stress because in this studymodel, the pregnant female rats were treated only with thistocolytic drug [23]. According to Martin et al. [37], highoxidative stress level in mothers could be responsible forthe high oxidative stress level observed in newborns bydirect blood exchange in the placenta. Moreover, alsoArgüelles et al. [36] found a correlation between the oxida-tive state of the mother and the neonate, and importantly,they observed that a higher level of maternal oxidative stresscorresponds to an even higher oxidative stress in newbornumbilical cord blood.

Several studies have implicated the role of oxidativestress in preterm birth [2, 3, 5, 8, 38–40]. A high levelof systemic oxidative stress in the mother can cause pla-cental dysfunctions or other damages leading to pretermlabor [3, 8, 9, 37, 38, 41]. Most of pregnant women in ourstudy (66%) had labored after 37 completed weeks ofpregnancy; however, we found a statistically significant asso-ciation between levels of TOS and preterm birth. Patientswho gave birth prematurely had higher levels of TOS after a48-hour administration of Atosiban than the second groupwith labor after 37 weeks of pregnancy, which might indicatethe influence of increased oxidative stress on preterm labor.This is consistent with many studies measuring RNS andROS or biomarkers of oxidative stress which reportedhigher levels of these products and lower levels for antiox-idants for preterm specimens compared to term birthspecimens [5, 9, 39, 42, 43].

The limitation of this study was the relatively smallsample size used and a nonrandomized study design. More-over, all treated patients received corticosteroids which couldpotentially influence the changes in oxidative stress markers.

However, the main purpose of using tocololytics is to delaydelivery to allow the administration of a complete course ofantepartum corticosteroids so this factor could not be ruledout to examine their effect independently of each other. Wealso could not exclude the influence on women such factorsas pain, uterine contractions, and stress resulting from thethreat of premature delivery. Nevertheless, the imbalance inthe levels of oxidative stress biomarkers corresponded wellwith some previous studies regarding complications ofpregnancy and results of animal studies on Atosiban andoxidative stress. Another limitation is the lack of evaluationof dietary intake of antioxidants; however, according to ourdata, none of the subjects in the study were smokers or wereusing specific antioxidant supplementation.

5. Conclusions

In conclusion, our results can indicate that tocolytic treat-ment with Atosiban is associated with elevation of oxidativestress markers after a 48 h administration. This effect ofAtosiban may reduce its potency as a tocolytic agent andtherefore should be considered with respect to its clinicaluse, especially because of its connection with the occurrenceof premature birth. Further studies involving a large samplesize should be undertaken to examine the strength of thisobservation and can clearly give evidence to the Atosibaneffect in addition to steroids on this phenomenon. It is alsoworth considering whether the addition of antioxidanttherapy can be applied in women treated with oxytocinantagonist and whether it can increase its effectiveness.

Abbreviations

3-NT: 3-NitrotyrosineOSI: Oxidative stress indexOTR: Oxytocin receptorROS: Reactive oxygen speciesRNS: Reactive nitrogen speciesTAS: Total antioxidant statusTOS: Total oxidant status.

Data Availability

The research data used to support the findings of this studyare available from the corresponding author upon request(gajzuzanna@gmail.com, zuzanna.gaj@iczmp.edu.pl).

Conflicts of Interest

The authors declare that they have no competing interests.

Authors’ Contributions

All authors shared in the design and implementation ofthis study. All authors read and approved the final manu-script. Mariusz Grzesiak and Zuzanna Gaj contributed tothe study equally.

6 Oxidative Medicine and Cellular Longevity

Acknowledgments

The research was supported by the Polish Ministry of Scienceand Higher Education for Polish Mother’s Memorial Hospi-tal Research Institute in Lodz (Grant No. 2015/I/17-GW).

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