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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 4  |  Issue : 3  |  Page : 120-124

Association of serum midkine levels with insulin resistance and obesity in patients with polycystic ovarian syndrome


1 Department of Obstetrics and Gynecology, Faculty of Medicine, Çanakkale 18 Mart University, Çanakkale, Turkey
2 Department of Internal Medicine, Faculty of Medicine, Çanakkale 18 Mart University, Çanakkale, Turkey

Date of Submission21-Apr-2020
Date of Acceptance28-Jun-2020
Date of Web Publication21-Sep-2020

Correspondence Address:
Dr. Eren Pek
Department of Obstetrics and Gynecology, Çanakkale 18 Mart University Hospital, Çanakkale
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/LJMS.LJMS_30_20

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  Abstract 


Objectives: Polycystic ovarian syndrome (PCOS) is thought to be a subclinical inflammatory state with increased levels of circulating pro-inflammatory cytokines. Midkine is a pleiotropic heparin-binding neurotrophic factor with pro-inflammatory properties, and growing evidence has shown a substantial effect of midkine in inflammation. This study aimed to test whether midkine has a role in PCOS development and its relation to obesity and insulin resistance (IR). Materials and Methods: In this comparative cross-sectional study, 56 women with PCOS and 36 eumenorrheic nonhirsute, age- and body mass index (BMI)-matched women as the control group were recruited. Routine and specific (midkine) laboratory analysis and IR measurements were applied to both the study groups. Results: There were no statistically significant difference between PCOS patients and controls with regard to serum midkine levels (P = 0.412). PCOS patients were further divided into two subgroups according to BMI levels. Serum midkine levels were found to be increased in overweight PCOS patients compared with normal-weight PCOS patients (P = 0.044). Although an increasing trend was observed in respect to serum midkine levels in PCOS women with IR (Homeostatic Model Assessment-IR ≥2.5), this elevation was not statistically significant (P = 0.301). Conclusions: The positive effect of obesity on midkine levels supports the idea that midkine is probably released from adipocyte cells. IR possibly has an important role in this mechanism.

Keywords: Insulin resistance, midkine, obesity, PCOS


How to cite this article:
Beyazit F, Kamis F, Pek E, Beyazit Y. Association of serum midkine levels with insulin resistance and obesity in patients with polycystic ovarian syndrome. Libyan J Med Sci 2020;4:120-4

How to cite this URL:
Beyazit F, Kamis F, Pek E, Beyazit Y. Association of serum midkine levels with insulin resistance and obesity in patients with polycystic ovarian syndrome. Libyan J Med Sci [serial online] 2020 [cited 2020 Oct 24];4:120-4. Available from: https://www.ljmsonline.com/text.asp?2020/4/3/120/295610




  Introduction Top


Polycystic ovarian syndrome (PCOS) is an endocrine disorder primarily affecting reproductive-age women and characterized by typical ovarian morphology on ultrasound scan, oligo/anovulation, androgen excess, and insulin resistance (IR), with a prevalence of 5%–10%.[1] Although the etiology of the disease is still unelucidated, increasing evidence suggests an involvement of inflammation during disease course.[2],[3] Moreover, apart from inflammation, PCOS is also associated with other derangements closely linked with inflammation such as oxidative stress (OS) and endothelial dysfunction, thus increasing the risk of major cardiovascular events and end-organ damage, which affects the quality of life of the patient and overall health-care costs.[4],[5],[6]

Midkine is a heparin binding growth factor and has rapidly gained increasing popularity in cancer patients. It has been shown to be overexpressed in at least twenty different types of cancers. Apart from this, midkine is known to be expressed in a variety of normal body components including gastrointestinal system, kidney, spleen, lung, and thyroids.[7],[8],[9],[10] Although the role of midkine in cancer patients is well demonstrated, a number of studies propose a possible role of midkine in the inflammatory response by increasing the migration of leukocytes. Being a multifunctional cytokine, midkine fulfills different and vital parts in inflammatory conditions.[11] Furthermore, it promotes inflammatory cell responses by augmenting the migration of leukocytes, suppression of regulatory T cells (Treg), and increasing the synthesis of various chemokines. Because of its involvement in the recruitment of inflammatory cells by its promitotic, angiogenic, and antiapoptotic properties, midkine expression is enhanced in inflammatory disease states.[12] Accordingly, a potential participation of midkine in PCOS can be speculated keeping in mind the link between inflammation and PCOS. The primary outcome of the present study was to evaluate the relationship between midkine and other inflammatory markers in PCOS according to body mass index (BMI) and IR. A secondary objective of this study was to assess potential correlations between these factors and endocrine and metabolic parameters.


  Materials and Methods Top


Subjects

This cross-sectional study was conducted after approval from the institutional review board of Canakkale Onsekiz Mart University (approval no: 2016-09). Fifty-six patients aged 17–46 years and undergoing medical treatment in the outpatient gynecology clinic of Canakkale Onsekiz Mart University Hospital were recruited to this study. The study group included 56 women with a diagnosis of PCOS and 36 age- and BMI-matched healthy controls. PCOS diagnosis was based on the presence of distinct criteria proposed by the Rotterdam ESHRE/ASRM-sponsored PCOS consensus workshop in 2003.[13]

According to this consensus report, the presence of at least two of the following three features are thought to be suitable for the exact diagnosis of PCOS: oligo-ovulation and/or anovulation, clinical and/or biochemical signs of high levels of androgens, and, finally, the presence of polycystic ovaries, which is identified by ultrasonographic examination. The Rotterdam criteria were used to define polycystic ovaries, which include the presence of 12 or more follicles with a diameter of 2–9 mm within each ovary, and/or increased ovarian volume (>10 cm3). Patients with thyroid disorders, arterial hypertension, diabetes mellitus, congenital adrenal hyperplasia, Cushing syndrome, hyperprolactinemia, cardiovascular disease, severe lipid profile abnormalities with/or without antihyperlipidemic drugs, and those prescribed with gonadotropin-releasing hormone agonists/antagonists, antidiabetic agents within the previous 3 months were excluded from the present study. The control group consisted of 36 healthy, age- and BMI-matched, normally ovulating women without any metabolic, hormonal, or systemic diseases. All of the women in the control group were eumenorrheic, and all had normal ovaries on ultrasonographic examination. Moreover, the volunteers in the control group had no clinical or biochemical signs of acne, hirsutism, or hyperandrogenism.

Clinical and laboratory analyses

After 8–12 h overnight fasting, 6-ml venous blood sample was taken and centrifuged at a speed of 4000 rounds/min for 10 min to obtain serum and stored for analysis at −80°C. Routine biochemical analysis and hormone profiles including complete blood cell count and C-reactive protein (CRP) were measured for all the study participants. Biochemical tests were analyzed spectrophotometrically, using the Roche Diagnostic kits on the Cobas c501 auto-analyzer (Roche Diagnostics, IN, USA). Hormone tests were measured with the original Roche Diagnostic kits on the Cobas e601 using the electrochemiluminescence immunoassay method (Roche Diagnostics, IN, USA). All complete blood cell count measurements were applied in the hematology laboratory of our university hospital by using the same automated analyzer (Beckman Coulter, High Wycombe, United Kingdom). Serum midkine levels were tested by sandwich enzyme-linked immunosorbent assay method by using a commercially available human plasma kit (Boster Biological Technology, Pleasanton, CA, USA), according to the manufacturer's instructions. IR was estimated by Homeostatic Model Assessment of IR (HOMA-IR) as suggested by Matthews et al.[14] using serum glucose and insulin levels (HOMA-IR = fasting plasma insulin [mU/ml] × fasting plasma glucose [mg/dl]/405). The women's height and weight were measured using a standard apparatus in light indoor clothing without shoes. BMI was calculated using the following formula: BMI = weight (kg) ÷ height (m2). Women were divided into the following subgroups based on their BMI and HOMA-IR values. According to BMI, the patients were divided into overweight/obese (BMI ≥25 kg/m2) and normal weight (BMI <25 kg/m2) and according to HOMA-IR, the patients were divided into HOMA-IR <2.5 and HOMA-IR ≥2.5.

Statistical analysis

Statistical analysis was carried out using Statistical Package for Social Sciences (SPSS) version 19 software (SPSS Inc., Chicago, IL, USA). Biochemical and hormonal parameter data were presented as mean ± standard deviation for normally distributed variables. Normality of the data was determined by the Kolmogorov–Smirnov test. One-way ANOVA was used to compare normally distributed variables. A Kruskal–Wallis test was conducted to compare nonnormally distributed variables. A Mann–Whitney U test was used to compare continuous variables between the groups. Spearman's correlation coefficient analyses were performed between midkine and other hormonal and biochemical parameters. P < 0.05 was accepted as statistically significant.


  Results Top


The demographic, clinical, and biochemical data of PCOS women and controls are presented in [Table 1]. Both of the two groups were similar with respect to age and BMI levels. The mean age and BMI of PCOS patients and controls were 27.2 ± 7.0 and 27.8 ± 6.9 years and 25.7 ± 4.3 and 24.2 ± 4.4 kg/m2, respectively. Serum luteinizing hormone and testosterone levels were significantly higher in PCOS patients compared with those of controls [Table 1]. Serum midkine levels of PCOS women and controls were 14.2 ± 14.3 and 17.0 ± 17.8 pg/ml, respectively (P = 0.412).
Table 1: Demographic and laboratory parameters of polycystic ovarian syndrome women and controls

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Among women with PCOS, overweight/obese (BMI ≥25 kg/m2) group had significantly elevated midkine levels compared with normal weight (BMI <25 kg/m2) PCOS women (P = 0.044) [Table 2]. Insulin and HOMA-IR levels were also statistically significantly elevated in overweight/obese PCOS women compared with normal-weight PCOS women (P = 0.032 for insulin; P = 0.033 for HOMA-IR). According to HOMA-IR values, PCOS patients were further divided into two groups (<2.5 vs. ≥2.5). Although an increasing trend was observed with respect to serum midkine levels in HOMA-IR ≥2.5 subgroup, this elevation was not found to be statistically significant (P = 0.301) [Table 2]. No correlation was observed between serum midkine levels and other clinical and laboratory parameters [Table 3].
Table 2: Demographic and laboratory parameters of polycystic ovarian syndrome women according to body mass index and Homeostatic Model Assessment of Insulin Resistance levels

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Table 3: The correlation between serum midkine with various metabolic and hormonal parameters in polycystic ovarian syndrome patients according to body mass index

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  Discussion Top


Recent investigations suggest that subclinical inflammation has substantial involvement in the pathogenesis of PCOS.[15] Moreover, inflammatory cytokines and anti-inflammatory trace elements play vital and distinct roles in the development and maintenance of PCOS. In this context, several inflammatory cytokines and chemokines have previously been explored and used in order to be a useful prognostic and/or diagnostic parameter in inflammation-associated diseases including PCOS.[16],[17] Therefore, this study is designed because to date, no definitive role for midkine in the pathophysiology of PCOS has been attributed.

The result of our study revealed that midkine levels do not differ between PCOS women and healthy controls. However, an interesting finding was that overweight PCOS women had significantly elevated levels of midkine compared with normal-weight PCOS women. Furthermore, although we proposed that PCOS is a chronic inflammatory condition, we failed to determine any alterations in CRP and white blood cell (WBC) levels irrespective of the BMI and IR status. Thus, we found no correlation between serum midkine levels and other demographic and laboratory parameters.

The effect of obesity and overweightness on midkine levels, which is also demonstrated in the present study, suggests that adipocytes could be a major source of midkine. Indeed, obesity is closely linked with the enlarged production of inflammatory cytokines in adipose tissue that contributes to both IR and chronic inflammation. In this context, Cernkovich et al.[18] were one of the first to show that midkine is produced and secreted by adipose tissue. The authors' demonstrated that duringin vitro adipogenesis of 3T3-L1 pre-adipocytes, midkine production was distinctly elevated after the initiation of differentiation and it played a pivotal role in the 3T3-L1 pre-adipocyte clonal expansion. A recent study by Fan et al.[19] tested whether midkine is linked with increased body weight and has a role in IR. The finding suggested that midkine is expressed in adipocyte cells and is linked with increased BMI in both humans and mice.

Although the exact role of inflammation in PCOS pathogenesis is currently indistinct, it is thought that OS, which accompanies chronic low-grade inflammation, plays a major role in the disease process.[20],[21] Blagojević et al.[22] evaluated lipid status parameters, CRP and OS parameters including advanced oxidation protein products, pro/antioxidant balance, total OS, and malondialdehyde (MDA) in 114 PCOS patients. They found that PCOS patients had greater proportion of dyslipidemia, chronic inflammation, and OS compared to healthy controls. Similarly, in a recent study by Bannigida et al.,[23] serum MDA and CRP levels were found to be elevated in women with PCOS regardless of obesity, suggesting that women with PCOS have OS and elevated levels of CRP irrespective of obesity. Although we did not investigate OS markers in the present study, we investigated the levels of CRP and WBC as a marker of subclinical inflammation in PCOS patients. We found no significant differences between these subclinical markers in PCOS patients.

Midkine was first introduced as a specific tumor biomarker in the serum of several human tumors.[24] It has been demonstrated to have transforming, anti-apoptotic and mitogenic characteristics toward tumor cells as well as exhibits substantial pro-angiogenic potential. Its chemotactic effect through macrophages and neutrophils contributes to chronic inflammation, leading midkine responsible for the infiltration of transformed tissue with activated inflammatory responses.[25],[26] Accumulating evidence suggests that midkine is expressed on distinct inflammatory disease states including nephritis, encephalitis, myocarditis, arthritis, colitis, atherosclerosis, and pancreatitis.[8],[27],[28],[29],[30] Decreased leukocyte recruitment to the inflammation sites was shown to be a key mechanism attenuating chronic inflammation when midkine was absent. Moreover, midkine modulates the expression of pro-inflammatory cytokines and the expansion of regulatory T-cells. Similarly, midkine levels were not altered in the study groups. These results were contrary to our expectations. It is likely that the short life of these parameters would have affected the results or we may have missed early stages of inflammation in which all pro-inflammatory markers were elevated.

This study has some limitations that should be addressed in future studies. First, the study population was small, so the results can only be considered to be preliminary. Second, this study would have been longitudinal in design to observe clinical and hormonal parameter alterations in comparison with serum midkine levels in PCOS patients. Third, measurement of other well-known inflammatory markers including interleukin-6 and tumor necrosis factor-alpha could have been noteworthy.


  Conclusion Top


As discussed above, overweight PCOS patients have elevated midkine levels compared with normal-weight PCOS women. Increased adipose tissue existence probably has a significant effect on this mechanism, and there is a strong need for further studies that will unravel the association between obesity, IR, and midkine in PCOS patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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