1. Introduction
Gestational diabetes mellitus (GDM) is defined as any impaired glucose tolerance, which appeared for the first time during pregnancy or was then identified [
1]. Due to the expected increase in the prevalence of GDM, it seems crucial to understand the pathogenesis of the disease itself, as well as the related complications [
2].
The system of insulin-like growth factors consists of two ligands IGF-1 and IGF-2 (insulin-like growth factor 1 and 2), two receptors IGFR-1, IGFR-2 (insulin-like growth factor receptor 1 and 2), six IGF binding proteins—IGFBP1-6 (insulin-like growth factor binding proteins 1-6) and four insulin-like growth factor binding protein-related peptides IGFBP-Rp1-4. The individual components of this system are characterized by a wide range of metabolic and mitogenic activities. The structural similarity of IGF-1 to insulin and the proven hypoglycemic effect regulated by IGFBP points to the participation of various components of this system in the regulation of glucose metabolism [
3]. On the basis of the research conducted so far, we may conclude that changes in the system of insulin-like growth factors in women with gestational diabetes mellitus exert a potential role, not only in the development of the disease itself, but also in certain complications, for example, in fetal macrosomia [
4,
5]. The studies conducted so far on insulin-like growth factors in gestational diabetes are inconsistent and focus on the assessment of IGF in either the maternal or fetal compartment [
6,
7].
The aim of this study was to evaluate the effect of GDM on the insulin-like growth factors (IGF-1, IGF-2) and insulin-like growth factor binding proteins (IGFBP 1-3) in the maternal and fetal blood.
2. Materials and Methods
The clinical material of this work included 109 women who were consecutively admitted into the Clinic of Obstetrics and Pregnancy Pathology of the Independent Public Clinical Hospital No. 1 in Lublin from 2016–2017 to deliver a baby. The study group comprised 60 patients with diagnosed GDM, as well as 60 newborns delivered by them. The control group consisted of 49 healthy parturients without coexisting diseases and their offspring (49 new-born children). All the patients, after reviewing the purpose and means of conducting the research, gave informed consent in writing for a participation in this project. The consent to carry out the research was released by the Bioethical Commission at the Medical University in Lublin (resolution number KE-0254/210/2016). The patients with diagnosed GDM were divided into two subgroups, depending on the treatment applied. In the treatment of women with GDM G1, a diabetic diet was used, also taking into consideration moderate physical effort adjusted to an advanced state of pregnancy and the pregnancy course. Whereas in the subgroup of patients with GDM G2, apart from a diabetic diet and regular physical exercise, insulin therapy was also used. GDM was diagnosed on the basis of the criteria of WHO adopted in the year 2013: “Diagnostic Criteria and Classification of Hyperglycaemia First Detected in Pregnancy” [
1].
The examination excluded patients who, on the basis of a clinical examination and the results of additional tests, were diagnosed with: chronic arterial hypertension, gestational hypertension, pre-eclampsia, eclampsia, liver diseases, endocrine disorders and autoimmune diseases, in order to avoid the impact of these diseases on the test results.
For the sake of the research, authors used samples of serum separated from peripheral blood (basilic vein), of women with at least 8 h since the last meal, at the beginning of the first period of labor, as well as umbilical cord blood taken immediately after the delivery of a baby (before delivering placenta) from the umbilical artery. The blood was sampled into disposable tubes S-Monovette type, 9 mm in volume (vacuum-aspiraton kits manufactured by Sarstedt, Germany), containing the blood clotting activator. In order to form a clot, the samples were left in an upright position for at least 30 min at room temperature. Next, they were spinned in a centrifuge (Sigma 1-6P, Polygen) for 10 min at room temperature, at the speed of 3800 rpm. The separation of serum took place under 1 h of taking the blood. The serum, obtained in such a way, was portioned in 200 μL per tube (0.5 mL), Eppendorf type (Medlab Products) and stored in a low-temperature freezer at −75 °C (Platinum Angelantoni 500, Italy) up to a year without several freezing or thawing, until the determination of concentrations.
The concentrations of IGF-1, IGF-2, IGFBP-1, IGFBP-2, IGFBP-3, insulin and glucose made by the ELISA method (Enzyme-linked Immunosorbent Assay) were measured in peripheral blood serum in the group of patients with GDM and in healthy patients, as well as in the umbilical cord blood serum of newborns born to them. Marking was made with the use of commercially available tests: IGF-1-ELISA (Enzyme Immunoassay for Quantitative Determination of human Insulin-like Growth Factor-I, Mediagnost, Germany), IGF-2-ELISA (Enzyme Immunoassay for Quantitative Determination of Human Insulin-like Growth Factor-II, Mediagnost, Germany), IGFBP-1-ELISA (Enzyme Immunoassay for quantitative Determination of human Insulin-like Growth Factor Binding Protein-1, Demeditec Diagnostics GmbH, Germany), IGFBP-2-ELISA (Enzyme Immunoassay for quantitative Determination of Insulin-like Growth Factor Binding Protein -2, Mediagnost, Germany), IGFBP-3-ELISA (Enzyme Immunoassay for Quantitative Determination of human Insulin-like Growth Factor Binding Protein -3, Mediagnost, Germany). Measurement of the absorbance was made at a wavelength of 450 nm, using a BIO-RAD microplate ELISA reader (Microplate Leader, Model 680, USA). The computer coupled with the reader by means of the Microplate Manager Version 5.2.1 program (BIO-RAD Laboratories, USA), based on the readings of light absorbance from the wells with known concentrations of standards, automatically drew standard curves on the basis of which it calculated the proteins concentration in the tested samples. All samples were assayed in triplicate. CV was <10%. Then, the insulin resistance indicator HOMA-IR (Homeostasis Model for Assessment of Insulin Resistance) was calculated, according to the following formula: HOMA-IR = glucose concentration [mmol/L] × insulin concentration [mIU/mL]/22.5.
The statistical analysis was performed using MedCalc 10.2.0.0 software. Nonsequitur was assumed at 5%. The findings, whose value was equal to p < 0.05, were considered statistically significant. The quantitative variables such as the concentration of the tested parameters (IGF-1, IGF-2, IGFBP-1, IGFBP-2, IGFBP-3, insulin, glucose) and certain demographic and clinical factors (e.g., age, body weight, BMI) were analyzed by descriptive statistics: measurement of concentration (median, mean, maximum value and minimum value) and measures of dispersion (standard deviation). Using the U–Mann–Whitney test (variables where the distribution is different from normal) or Student’s t-test (variables with normal distribution), the authors compared the distribution of values of the examined parameters (IGF-1, IGF-2, IGFBP-1, IGFBP-2, IGFBP-3, insulin, glucose) in the examined group and in the control group, and assessed a relationship with selected demografic-clinical factors in the test group. By means of Spearman’s test, the correlation between the examined parameters (IGF-1, IGF-2, IGFBP-1, IGFBP-2 and IGFBP-3) and the selected clinical factors was assessed.
3. Results
Table 1 presents a comparison of the study group (GDM) and the control group (C). The analysis of the concentrations of both IGF-1, -2 and IGFBP-3 in peripheral blood and umbilical cord blood showed no statistically significant difference between the GDM group and the Cgroup (
Table 2). A significantly lower concentration of IGFBP-1 in peripheral blood (
p = 0.0001) and umbilical cord blood (
p = 0.0443) were shown in the GDM group compared to the C group. The above, statistically significant differences were confirmed only for patients with BMI < 25 (
p = 0.0003 and
p = 0.0476, respectively). A significantly lower concentration of IGFBP-2 in peripheral blood (
p = 0.0217) and umbilical cord blood (
p = 0.0001) was shown in the GDM group compared to the C group. The above relationships were confirmed only for patients with BMI < 25 (
p = 0.0217 and
p = 0.0001, respectively). A statistically significantly higher level of insulin (
p = 0.0210) in the peripheral blood of women with GDM compared to healthy women was demonstrated (the above relationship was not confirmed in BMI subgroups); the analysis of the concentration of peripheral blood glucose in women with GDM and in healthy women showed no significant difference (
p = 0.1117). There was also observed a significantly higher median of the indicator value HOMA-IR in the GDM group compared to the C group (5.69 vs. 4.37;
p = 0.0150). However, this relationship was confirmed only in BMI > 24.99 (6.37 vs. 3.40;
p = 0.0017) (
Table 2). A significantly higher level of IGF-1 (
p = 0.0436) was found in the cord blood of newborns delivered by women suffering from GDM, who had been on a diet vs. insulin. Correlations between maternal and cord plasma IGF-1, IGF-2, IGFBP-1-3 concentrations and clinical/biochemical parameters in the GDM group are presented in
Table 3 and
Table 4. A statistically significant positive correlation was observed between the weight gain during pregnancy and the concentration of IGF-2 in the peripheral blood of women with GDM (rho = 0.263;
p = 0.0433), as well as between the concentration of IGF-1 (ng/mL) in the serum of umbilical cord blood of newborns delivered by women with GDM, and the newborn length soon after birth (rho = 0.285;
p = 0.0327) (
Figure 1). A statistically significant positive correlation was observed between the concentration of IGF-1 and IGF-2 in the peripheral blood of women with GDM and the IGF-1 concentration (rho = 0.352;
p = 0.0069), and the concentration of IGF-2 (rho = 0.644;
p < 0.0001) in the serum of umbilical cord blood of newborns delivered by women with GDM. In the study group, the drop in IGFBP-2 concentration in maternal blood was accompanied by an increase of IGF-2 in newborn’s cord blood (rho = −0.367,
p = 0.0049). There was a statistically significant negative correlation between the value of the indicator HOMA-IR, and the concentration of IGFBP-2 in the umbilical cord blood of newborns delivered by healthy women (rho = −0.28;
p = 0.0487). However, in the GDM group, such a relationship was not found. Comparisons of different IGF concentrations according to weight classification based on BMI were performed with the use of ANOVA Kruskal–Wallis test. There were no statistically significant differences in the concentrations of the tested laboratory markers depending on adult body weight classification based on BMI. Only in the case of IGFBP-1, some trend towards significantly higher values of this marker was noted in women with GDM and BMI < 25 (with desirable body weight) compared to the subjects with BMI > 24.99 (overweight) and BMI > 29.99 (obese) (118.06 vs. respectively: 72.77 and 62.40;
p = 0.0548) (
Table 5).