Original Article

Endocan and Asymmetric Dimethylarginine as an Etiological Indicator in the Maternal and Umbilical Cord Serum in Pre-Eclampsia


  • Nihal Inandiklioglu
  • Emre Baser
  • Demet Aydogan Kirmizi

Received Date: 19.02.2021 Accepted Date: 28.04.2021 Med Bull Haseki 2021;59(4):308-312


Preeclampsia is a pregnancy-specific disease of unknown etiology. This study was planned to determine the place of asymmetric dimethylarginine (N, N-dimethylarginine, ADMA) and endothelial cell specific molecule-1 (ESM1, endocan) levels in etiology. The aim of this study was to determine ADMA and endocan levels in maternal and fetal umbilical cord serum of patients with preeclampsia and to evaluate them with clinical data.


This case-control study was conducted between June and December 2020. The clinical and demographic characteristics of the participants were evaluated in the department of obstetrics and gynecology. Thirty-tree women with preeclampsia and 55 healthy women in the same age group were included in our study. Serum ADMA and endocan values were determined by the ELISA method.


Maternal and umbilical cord ADMA levels in the preeclampsia group were statistically significantly higher than the control group (p=0.001, p=0.001, respectively). Likewise, the levels of the umbilical cord and maternal serum endocan were statistically significantly higher in the preeclampsia group compared to the control group (p=0.001, p=0.037, respectively).


We found that ADMA and endocan molecules associated with endothelial dysfunction in the pathogenesis of preeclampsia significantly increased in maternal and umbilical cord serum.

Keywords: N, N-dimethylarginine, preeclampsia, pregnancy, proteoglycans, umbilical cord


Preeclampsia is the accompanying of proteinuria to new-onset hypertension in pregnancy. In some preeclampsia, proteinuria may not evidently develop. Therefore, preeclampsia is the presence of one of the findings of proteinuria accompanying gestational hypertension or gestational hypertension accompanied by at least one of thrombocytopenia (platelet <100,000/mm³), renal failure (creatinine doubled from baseline or >1.1 mg/dL), liver findings [Alanine aminotransferase (ALT) or aspartate transaminase (AST) doubling the normal], cerebral findings (headache, seizure, visual disturbances) or pulmonary edema findings (1,2).

Asymmetric dimethylarginine (ADMA) is an amino acid naturally occurring in plasma and is an endogenous nitric oxide synthase (NOS) inhibitor (3). Nitric oxide (NO) is a free radical, synthesized by the NOS from L-arginine. NO regulates endothelium-dependent vasodilation, proliferation of smooth muscle cells in the vascular wall, aggregation by platelet adhesion and monocyte adhesion inhibition. It also plays a role in maintaining vascular balance and blood supply to the organs (4). Since NO is a major endothelial vasoactive mediator, ADMA is thought to play a key role in endothelial dysfunction. The endocan molecule, also known as endothelial cell-specific molecule-1 (ESM-1), is a proteoglycan synthesized from endothelial cells and detectable in serum. It is found especially in lung, kidney cells, adipocyte and endothelium (5). ADMA is associated with many conditions such as intracellular signaling, differentiation, migration, proliferation and adhesion of different cell types. Increased release of ADMA in the tissue or its level in the blood reflects endothelial activation and neovascularization, which indicates inflammation and tumor progression (6).

The main problem in preeclampsia is endothelial cell damage due to increased inflammatory response. Endothelial cell damage and subsequent endothelial dysfunction make sense of clinical findings detected in preeclampsia disease. The cause of the symptoms that play a role in preeclampsia clinic is diffuse endothelial dysfunction (7). It is thought that the molecule NO has a key role in the regulation of endothelial function. The aim of this study was to evaluate the maternal and fetal umbilical cord serum levels of ADMA and endocan molecules, which are associated with endothelial dysfunction and have different results in the literature, and to investigate the relationship between preeclampsia clinical effects and these parameters.


Study Population

This case-control study was conducted between June and December 2020. The clinical and demographic characteristics of the participants were evaluated in the department of obstetrics and gynecology. This study was approved by the Ethics Review Board of Yozgat Bozok University Faculty of Medicine (document no: 2017-KAEK-189_2020.06.23_08). The study was carried out in accordance with the principles of medical research provided by the Helsinki Declaration. Written informed consent was obtained from each participant. Preeclampsia diagnosis after the 20th week of gestation was made by blood pressure measurements taken at least four hours intervals and determined by systolic pressure above 140 mmHg and diastolic pressure above 90 mm Hg and also by measuring proteinuria in 24-hour urine ≥0.3 g; proteinuria/creatinine ratio ≥0.3 or ≥+1 proteinuria in spot urine sample (8). Diabetes mellitus, thyroid diseases, cardiovascular diseases, chronic renal failure, hyperprolactinemia, Cushing’s syndrome, congenital adrenal hyperplasia and 21-hydroxylase deficiency were accepted as exclusion criteria for the preeclampsia group. The control group was composed of normotensive 18-40 years old 370/7-406/7 w healthy singleton pregnant women. Body mass index (BMI) was calculated by dividing body weight by the square of height (kg/m²). Patients’ age, gravidity, parity, gestational weeks, systolic/diastolic blood pressure levels, protein levels in spot urine protein, hemoglobine, platelet counts, creatinine, urea, liver function markers (AST, ALT, lactate dehydrogenase), angiogenic and antiangiogenic factors sEng, sFlt and Pgf levels were recorded. Gestational weeks were determined according to the last menstrual period confirmed by ultrasonography.

Determination of Serum ADMA and Endocan Levels

Venous blood samples were taken from the participants before giving birth and taken from the umbilical cord at birth. Venous blood samples were collected in a 5 mL serum-separating vacuum tube. Blood samples were collected and centrifuged for 10 min at 2.000 g. The supernatant was quickly removed and kept frozen at -80 °C until the assays were performed. Serum ADMA (cat.no REA201/96, BioVendor, Czech Republic) and Endocan (cat. no E3160Hu, Bioassay Technology Laboratory, China) levels were measured with commercially available enzyme-linked immune sorbent assay (ELISA) kits, with a minimum detectable concentration of 0.4 µmol/L and 5 ng/L, respectively, according to the manufacturer’s instructions. Optical density values for samples and standard samples were detected on Thermo Scientific (USA) Multiscan Go Microplate Reader ELISA reader at 450 nm. The results are presented as µmol/L and ng/mL.

Statistical Analysis

Statistical analysis was performed using SPSS (version 20, SPSS Inc., Chicago, IL, USA). For each continuous variable, normality was checked by Kolmogorov-Smirnov and Shapiro-Wilk tests. The categorical variables between the groups were analyzed by using the chi-square test or Fisher’s Exact test. Comparisons between groups were applied using Student’s t-test (normally distributed data) and Mann-Whitney U test (not normally distributed data). A multivariate logistic regression analysis was performed to determine independent risk factors. A p-value of less than 0.05 was considered significant.


The demographic characteristics of the groups in our study were presented in Table 1. When the groups were compared statistically, there was no significant difference in age and BMI averages, but systolic pressure and diastolic pressure were significantly higher in the preeclampsia group (p<0.001).

Biochemical parameters and ELISA results of the study groups were presented in Table 2. Maternal serum and umbilical cord serum ADMA values were significantly higher in the preeclampsia group compared to the control group (p<0.001). Likewise, the umbilical cord and maternal serum endocan levels were found to be significantly higher in the preeclampsia group (p<0.05) (Table 2).

In the multivariate logistic regression analysis, the most important independent risk factor predicting preeclampsia was maternal ADMA [Odds ratio (OR): 6.8, 95% confidence interval (CI): 1.7-8.9], and the other independent risk factor was determined as cord endocan (OR: 3.7, 95% CI: 2.1-5.5) (Table 3). This result indicated that the rising of maternal ADMA increases the risk of preeclampsia 6.8 times, and the rising of cord endocan increases the risk of preeclampsia 3.7 times.


Endothelial dysfunction is accepted to be the basis of the pathogenesis of preeclampsia (9). It is a disease with vasospasm due to endothelial damage, activation of the coagulation system, edematous ischemic and thrombotic sequelae that progresses negatively in humoral and local control affecting blood pressure and fluid volume (10). Maternoplacental ischemic environment occurring after defective placentation causes placental factors to be released and pass into the maternal circulation. This condition initiates maternal endothelial cell damage and dysfunction. The vasodilator effect is disrupted by the anticoagulant effect of the intact endothelium, the balance of prostaglandin production and the release of NO (9,11,12). In this study, the maternal and umbilical cord serum levels of NOS inhibitor ADMA and a prostaglandin endocan were evaluated in preeclampsia patients. ADMA and endocan levels were found to be high in the maternal and umbilical cord in the preeclampsia group. Serum ADMA and endocan levels can be considered as independent risk factors for preeclampsia.

ADMA levels have been associated with many diseases such as renal diseases, Alzheimer’s, liver failure, cirrhosis, cardiovascular diseases, diabetes and preeclampsia. The inhibition of NO synthesis by ADMA causes endothelium-dependent vasodilation (3). Increased levels of ADMA have been associated with endothelial dysfunction, thus preeclampsia (13). In the study conducted by Fickling et al. (14) ADMA was associated with preeclampsia and the ADMA level was found to be significantly higher in the preeclampsia group compared to healthy pregnant women. Data supporting the same result were presented and various authors emphasized that increasing ADMA levels may play an important role in the pathogenesis of preeclampsia. These data indicated that high circulating ADMA concentration in pregnant women could be defined as a potential biomarker of preeclampsia (15-17). It has also been reported that the ADMA level decreases during normal pregnancy, decreases to a minimum at the end of the first trimester and then increases with the gestational age (18). On the other hand, it was determined that serum ADMA levels of pregnant women who developed preeclampsia were high in the first trimester and in the second trimester (19), and serum ADMA levels of pregnant women who did not develop preeclampsia and had Small for Gestational Age were normal (20). It was demonstrated that the increase in ADMA levels developed before the clinical findings of preeclampsia at 23 weeks of gestation (21). In preeclampsia studies performed in the umbilical cord serum, there are different data in the literature as in maternal serum ADMA results. Albayrak et al. (22) brought out no change in maternal serum ADMA level of the preeclampsia group, while they found the umbilical cord serum ADMA level higher than controls. In another study, both maternal serum and umbilical cord serum levels were detected to be higher in the preeclampsia group compared to the control (23). Even in the preeclampsia group, serum ADMA levels of the umbilical cord were noticed to be significantly higher in the severe preeclampsia group compared to the mild preeclampsia group (13).

Endocan is a proteoglycan secreted from vascular endothelia cells, indicative of endothelial function. It has been propounded that serum concentrations are elevated in conditions associated with endothelial activation or dysfunction. Studies have suggested that endocan can be a marker in many diseases such as tissue damage, angiogenesis, oncogenesis, inflammation, and sepsis (24). When we looked at the studies conducted with preeclampsia pregnant women in the literature, there were studies reporting that serum endocan levels were statistically higher than healthy pregnant women (5,10,11). In a meta-analysis study involving 451 preeclampsia pregnant women, it was determined that the level of endocan was higher in pregnant women with preeclampsia compared to normal healthy pregnant women (25). However, in other studies, no difference was found between serum endocan levels in the preeclampsia and the control groups (26,27). Even though the endocan protein and its expression in the maternal placenta were studied out to be higher than the control, no significant difference was found in the maternal serum level (27). A factor affecting the serum endocan level is the gestational week and it has been reported that as the gestational week increases, the serum endocan level decreases (26). A similar result was determined in patients with early onset preeclampsia, and no significant result was found (28). Moreover, no significant difference was observed between the groups with early and late preeclampsia and normotensive pregnant women (29). Schuitemaker et al. (30) highlighted that the endocan molecule has an angiogenic function in the first and second trimesters; therefore, the endocan level may be low in early-onset preeclampsia because angiogenesis is disrupted. A study on the endocan level in the fetal umbilical cord in preeclampsia patients is not included in the literature. In one of the existing studies, the umbilical cord endocan level in pregnancies complicated by intrauterine growth restriction (31) and in the other one, the umbilical cord endocan level was evaluated according to the delivery type (32). In this study, ADMA and endocan levels were found to be high in the maternal and umbilical cord in the preeclampsia group. Differences in the results of the studies may be based on the fact that they were performed without subgrouping, different samples (plasma, serum or placenta) were studied, and the number of different pregnant women.

Study Limitations

Our study has a few limitations. First, the sample size is relatively small. Second, there may be different ELISA kits used. However, evaluating both umbilical cord and maternal serum levels together is a factor that strengthens our study. At the same time, evaluating these two molecules, which are important in etiology, makes the study valuable.


In conclusion, the most important reasons for the different results between studies on ADMA and endocan include the difference in gestational week, the difference in tissue studied and the sample number. In future studies, expanding the sample size, measurements of each trimester of pregnancy, expression, protein and serum levels of maternal, placenta and umbilical cord samples and dividing preeclampsia into different subgroups according to its severity will provide more confirmed results.

Authorship Contributions

Concept: N.I., E.B., Design: N.I., E.B., Data Collection or Processing: N.I., E.B., D.A.K., Analysis or Interpretation: N.I., Literature Search: N.I., E.B., D.A.K., Writing: N.I., D.A.K.

Conflict of Interest: No conflict of interest was declared by the authors.

Financial Disclosure: The authors declared that this study received no financial support.


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