Al-Azhar Assiut Medical Journal

: 2016  |  Volume : 14  |  Issue : 4  |  Page : 190--195

Contribution of indoleamine 2,3-dioxygenase in preeclampsia

Mona F.M El-Karn1, Hayam G Sayyed1, Safwat A Mohammed2, Nemah M.A Abdulrab1,  
1 Department of Medical Physiology, Faculty of Medicine, Assiut University Hospital, Assiut, Egypt
2 Department of Gynecology and Obstetrics, Faculty of Medicine, Assiut University Hospital, Assiut, Egypt

Correspondence Address:
Hayam G Sayyed
Department of Medical Physiology, Faculty of Medicine, Assiut University, Assiut 71515


Background Preeclampsia (PE) is a complex, multiorgan disease that leads to maternofetal morbidity and mortality. Increasing evidence now indicates that PE may have an immunological cause. Indoleamine 2,3-dioxygenase (IDO) is an immunomodulatory intracellular enzyme that suppresses immune response. The present study aimed to determine whether alterations in the level of IDO contribute to PE and its relation to the severity of PE. Patients and methods A case–control study was carried out on 80 pregnant women, who were divided into two groups − 40 PE patients and 40 ethnically matched, healthy, controls. Enzyme-linked immunosorbent assay was used to determine placental IDO protein concentrations. In addition, Pearson’s correlation with systolic blood pressure (as an indicator of PE severity) was estimated. Results Placental concentration of IDO was significantly lower in the PE group than in the control group, and there was an inverse association between IDO and severity of the PE. Conclusion The present study demonstrated that IDO might contribute to the pathogenesis of PE.

How to cite this article:
El-Karn MF, Sayyed HG, Mohammed SA, Abdulrab NM. Contribution of indoleamine 2,3-dioxygenase in preeclampsia.Al-Azhar Assiut Med J 2016;14:190-195

How to cite this URL:
El-Karn MF, Sayyed HG, Mohammed SA, Abdulrab NM. Contribution of indoleamine 2,3-dioxygenase in preeclampsia. Al-Azhar Assiut Med J [serial online] 2016 [cited 2020 Apr 7 ];14:190-195
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Preeclampsia (PE) is a pregnancy-associated disease that is characterized by hypertension [blood pressure (BP) >140/90 mmHg] after the 20th gestational week and proteinuria (>300 mg/l/24 h). PE may be associated with decreased platelet count, liver function impairment, renal insufficiency, development of pulmonary edema, or recent cerebral or visual disturbances [1]. PE is one of the most common pregnancy-related disorders [2], affects 2–8% of all pregnancies worldwide, and is associated with significant maternal morbidity and mortality [3],[4],[5]. The exact etiology of PE remains largely unknown, although many studies have reported that PE is secondary to placental implantation anomaly, disturbed angiogenesis, vasoconstriction, and genetic tendency, in addition to immunological intolerance among the fetus, the mother, and the placenta [6].

Multiple studies have proposed that maternal immune system dysregulation has a critical impact on the pathogenesis of PE [7]. On the contrary, Redman and Sargent [8] suggested that PE is a nonspecific, systemic, inflammatory reaction caused by placental oxidative stress.

Indoleamine 2,3-dioxygenase (IDO) is a cytosolic enzyme that catalyzes the first rate-limiting step in the cleavage tryptophan into kynurenine [9]. IDO has important immunomodulatory effects by suppressing T-cell functions by depleting tryptophan − an essential amino acid for T-cell proliferation and response [10]. IDO is produced by some alternatively activated macrophages and other immunoregulatory cells. The expression of IDO has been reported in different cell types at the fetomaternal interface [11],[12],[13]. It has been suggested that IDO plays an important role in the maintenance of self-tolerance and in the negative control of pathological and physiological immune responses [14],[15]. It is possible to suggest that IDO may be involved in the pathogenesis of PE.

This study aimed to evaluate whether alterations in placental concentration of IDO contribute to PE and its relation to the severity of PE.

 Patients and methods


The study protocol was approved by the Ethical Committee for Scientific Research (approval no: IRB00008718) at the Faculty of Medicine, Assiut University, Assiut, Egypt, and written informed consent was obtained from all participants. A total of 80 participants were enrolled for this case–control study. Inclusion criteria were as follows: patients diagnosed with PE, age between 20 and 40 years, singleton pregnancy, low parity (0–4), gestational age more than 34 weeks, and elective cesarean delivery. Exclusion criteria were as follows: patient refusal, age less than 20 and greater than 40, parity greater than 4, gestational age less than 34 weeks, pre-existing chronic hypertension, renal disease, multifetal gestation, autoimmune disease, angiopathy, maternal or fetal infection, and known fetal chromosomal or structural congenital anomalies, pregnant women in active labor, presence of diabetes, women with small-for-gestational-age fetuses, family and personal history of atopy, chronic use of medications, participants with any symptoms of infection and comorbid conditions, and complications by preterm rupture of membranes.

Participants were divided into two groups (40 patients in each group): the control group and the PE group.

According to the National Institute for Health and Care Excellence [16], the severity of PE was classified into mild, moderate, and severe on the basis of BP measurements alone: mild PE, systolic BP of 140–149 mmHg and/or diastolic BP of 90–99 mmHg; moderate PE, systolic BP of 150–159 mmHg and/or diastolic BP of 100–109 mmHg; and severe PE, systolic BP of up to 160 mmHg and/or up to diastolic BP of 110 mmHg.

Clinical analysis

History taking including maternal age at gestation (years) (as age above 40 years increases the risk of PE), gestational age, and parity as well as clinical examinations were performed, including maternal weight (as prepregnancy obesity is a risk factor for PE), height, BMI, infant birth weight (intrauterine growth retardation has been recognized a part of the diagnostic markers for PE), Apgar scores (as low placental perfusion in PE can lead to fetal distress and low Apgar scores), and placental weight.

BP was recorded as the average of two repeated measurements (6 h apart) using a mercury sphygmomanometer adapted to arm circumference. The amount of protein in urine was measured using a dipstick (it is a semiquanititative test used to detect the presence of protein in the urine).

Biochemical analysis

Placentas were collected immediately, weighed, and then whole-thickness, wedged-shaped specimens from the central to the peripheral parts of the maternal surface of the placenta were extracted. The dissected specimens were washed in ice-cold PBS, frozen in liquid nitrogen, and then stored at −70°C. Placental tissues were thawed, and 50 mg of the sample was homogenized using Glas-Col Homogenizer (Terre Haute, USA) into 2 ml of PBS, and the homogenate was then centrifuged at 10 000 rpm for 10 min by ultra centrifuge (Hettich EBA 12; Terre Haute, USA) at about 4°C.

The supernatant was used to determine IDO protein levels using an enzyme-linked immunosorbent assay kit (catalog number: 10954, sensitivity range was 0.5–100 U/l; Glory Bioscience Co. Ltd., Del Rio, Texas, USA).

Statistical analysis

Data are represented as mean±SD. Data were analyzed using statistical package for the social sciences, version 21 (SPSS; SPSS Inc., Chicago, Illinois, USA). The Kolmogorov–Smirnov test was used to determine the distribution of data, which revealed normal (parametric) distribution, and accordingly parametric tests were used. Data are expressed as mean with SD. The differences between control and PE groups were analyzed using Student’s t-test, whereas the differences between multiple parameters were analyzed through the one-way analysis of variance test. The Pearson correlation test was applied to study correlations between the placental IDO concentration and the severity of PE. All statistical tests were conducted with 95% confidence intervals, and P values 0.05 or less were considered statistically significant.


Clinical and demographic data of the studied participants

As shown in [Table 1], there were no statistically significant differences between control and PE women regarding mean maternal age and maternal height (28.80±4.50 vs. 29.30±5.10 and 157.10±3.60 vs. 155.60±3.60, respectively). On the other hand, maternal weight, maternal BMI, and maternal parity were significantly higher in PE women than in the control group (86.10±7.70 vs. 77.60±7.40, P<0.0001; 35.40±3.20 vs. 31.50±3.20, P<0.0001 and 2.44±1.10 vs. 1.60±1.40, P<0.01, respectively).{Table 1}

Regarding BP, PE patients showed significantly higher systolic and diastolic BP values as compared with the control group (158.40±20.30 vs. 119.70±6.90, P<0.0001 and 101.30±10.90 vs. 76.90±6.20, P<0.0001). In addition, albuminuria was significantly higher in PE women than in the control group.

Birth weight and Apgar score at the first minute were significantly lower in PE women than in the control group (2.82±0.42 vs. 3.13±0.41, P<0.001 and 9.17±0.78 vs. 9.65±0.90, P<0.01).

Concerning placental weight, there was a significant decrease in placental weight in women with severe PE as compared with control women, mildly PE women, and moderately PE women (312.00±44.46 vs. 564.30±101.70, P<0.001; 482.80±8.653, P<0.001, and 451.10±20.88, P<0.001) as shown in [Figure 1].{Figure 1}

Placental indoleamine 2,3-dioxygenase concentration

[Figure 2] shows significantly lower IDO concentrations in the placenta of PE women compared with control women (3.87±1.79 vs. 10.19±3.11, P<0.001). Furthermore, the concentration was negatively correlated with systolic BP (r=−0.885 and P<0.0001) and diastolic BP (r=−0.853 and P<0.0001) as shown in [Figure 3].{Figure 2}{Figure 3}


PE initiates in the placenta and exhibits a variety of maternal and fetal problems [16]. Although the etiology of PE remains unknown, there is considerable evidence that suggests it might be a result of placental abnormalities and oxidative stress [17]. Redman and Sargent [18] suggested that PE resulted from a nonspecific systemic inflammatory response, secondary to placental oxidative stress. Recent studies [19],[20],[21] have reported that PE develops when placental ischemia occurs secondary to shallow trophoblast invasion together with an immune imbalance − that is, increased proinflammatory CD4+ T cells and decreased T regulatory cells. This imbalance leads to chronic inflammation, oxidative stress, and production of proinflammatory cytokines and autoantibodies. Kudo et al. [22] suggested that increased cytokine production decreased the activity or levels of IDO in the placenta, which might be involved in the pathogenesis of PE.

The present study revealed decreased IDO concentrations in the placenta of PE patients with a concomitant inverse relationship with systolic BP, an indicator of severity of PE.

IDO is an intracellular heme-containing enzyme that cleaves the pyrrole ring of the indole nucleus of various indoleamines derivatives such as the essential amino acid tryptophan [21]. Thus, by limiting tryptophan availability in the microbial environment, it exerts antimicrobial activity [22],[23].

IDO-positive cells were detected at the maternal–fetal interface soon after implantation [24],[25] and during normal pregnancy, and it had a critical role in preventing immunological rejection of the fetal allograft during placentation [26].

In agreement with the results of the present study, Munn et al. [28] detected a decrease in IDO activity and mRNA in PE placentas. Similarly, Santoso et al. [29] demonstrated a reduction in the expression of IDO in placentas of term PE women compared with controls. In addition, Liu et al. [30] observed a marked reduction in the intensity of IDO immunostaining in PE placentas. In partial consistency with the present study, Ban et al. [31] reported a decrease in IDO protein levels and mRNA in the placenta and decidua from recurrent spontaneous abortions, and they suggested that IDO had a role in the maintenance of normal pregnancy.

Santillan et al. [32] demonstrated that pregnant mice lacked IDO and exhibited PE phenotypes, including renal histopathological dysfunction, aortic endothelial dysfunction, and intrauterine growth restriction, and they suggested that IDO has a crucial role in the pathogenesis of PE.

The impact of IDO in the pathogenesis of PE could be explained by a study by Tyler et al. [33], as they found an association between lower IDO activity and inflammatory response, and they supported the immunological activity of IDO leading to placental dysfunction. Another explanation was provided by Nishizawa et al. [34] who demonstrated reduction in the antioxidant system in relation to low IDO activity in the placentas of severely PE patients, and they proposed that oxidative stress associated with decreased IDO activity promoted the onset of PE. Previously, Myatt et al. [35] reported that IDO utilized O2− radicals to metabolize L-tryptophan. Thus, reduced IDO activity in PE might increase the bioavailability of O2− and contribute to oxidative damage in PE.

This was supported by the finding of Nishizawa et al. [34], who found that reduction in IDO activity in PE is associated with increased T-cell infiltration and increased severity of PE.

Regarding the severity of PE, based on systolic BP values, the present study showed a significant inverse relationship between the severity of PE and the IDO concentration in the placenta. Consistent with this finding, Nishizawa et al. [36] demonstrated that IDO inhibition is associated with moderate increase in BP. Similarly, Liu et al. [30] reported weak or no intensity of IDO immunostaining in women with higher maternal BP than in women with moderate or strong IDO immunostaining, indicating that IDO was related to the severity of PE.


The present study demonstrated that IDO might be a mechanism in the pathogenesis of PE. Further investigations for presymptomatic diagnosis or preventive therapy have to be carried out.

Recommendations and limitations

Further studies with larger samples might be needed to confirm the results of the present study.Evaluation of T-cell activity must be carried out instead of studying their markers.Further animal studies are recommended to study the stimulatory and inhibitory factors of IDO to evaluate its therapeutic effect in PE.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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