Serum trace elements and heavy metals in polycystic ovary syndrome

Abstract

Objective: We aimed to investigate the serum levels of essential trace elements copper (Cu), zinc (Zn), manganese (Mn), magnesium (Mg) and heavy metals cadmium (Cd), cobalt (Co) and lead (Pb) in the patients with polycystic ovary syndrome (PCOS). Methods: A total of 65 (35 patients with PCOS and 30 healthy controls) women were included in the study. Serum Cu, Zn, Mn, Pb, Mg, Co and Cd levels were analyzed using atomic absorption spectrophotometric method. Results: Serum Cu and Zn levels were significantly higher, but Mn and Pb levels were lower in patients with PCOS compared with the healthy participants (p < 0.01). There was no difference between patients with PCOS and the controls with respect to the serum levels of Mg, Co and Cd. Conclusions: This is the first study investigating serum Cu, Zn, Mn, Pb, Co, Mg and Cd levels in the patients with PCOS. The serum levels of trace elements and heavy metals might change in patients with PCOS. The findings in this study should be investigated with further trials in order to obtain new insights into PCOS.

Keywords

polycystic ovary syndrome trace elements heavy metals

Introduction

Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies affecting approximately 6.5–8% of the reproductive age women.^1,2 It is characterized by menstrual irregularities, clinical and/or biochemical hyperandrogenism and hyperinsulinemia.³ No one exactly knows what causes PCOS. Recent studies have indicated increased oxidative stress in the patients with PCOS.^4,5

The importance of essential trace metals in health and disease is indisputable because of their vital role in specific concentration ranges and toxicity at relatively high levels. Essential trace elements have four major functions as being stabilizers, elements of structure, essential elements for hormonal function and cofactors in enzymes.⁶

Zinc (Zn) is essential for the structure of many enzymes and plays a fundamental role in approximately 300 enzymatic reactions. It has a critical role especially in the function of metalloproteins, inducing members of oxidoreductase, hydrolase, ligase and lyase family and has coactivating functions with copper (Cu) in superoxide dismutase (SOD) or phospholipase C.⁷

Manganese (Mn) and Cu are essential micronutrients incorporated into many metalloenzymes and proteins involved in cell metabolism and regulatory pathways controlling oxidative stress.⁷ Cadmium (Cd) is a heavy metal and may have a role in the formation of reactive oxygen species (ROS).⁸ Lead (Pb) may also lead to the production of ROS by depleting glutathione (GSH) and protein-bound sulfhydryl groups and enhancing lipid peroxidation.⁹ Excessive generation of ROS is showed in patients with PCOS.^4,10,11 We thought that there might be a relationship between trace elements, heavy metals and PCOS, linked to the oxidative stress. However, we have not encountered any study evaluating neither serum essential trace elements except magnesium (Mg) nor heavy metals in women with PCOS in the English literature.

In the present study, we aimed to investigate the serum levels of essential trace elements (Cu, Zn, Mn and Mg) and heavy metals (Cd, Pb and cobalt [Co]) in patients with PCOS.

Materials and methods

Subjects

The study was conducted with 35 consecutive patients with PCOS (study group) and 30 age- and body mass index (BMI)–matched healthy women (control group) from the outpatient clinics of the Department of Obstetrics and Gynecology, Yuzuncu Yil University. First, 50 participants were recruited for each group. However, due to violation of inclusion criteria, 15 and 20 subjects were excluded from PCOS and control groups, respectively. The study was approved by the local ethics committee of the university. All the subjects provided written informed consent before participating in the study.

The diagnosis of PCOS was based on the Rotterdam criteria,¹² having two of the following three features—oligo-ovulation and/or anovulation, clinical and/or biochemical signs of hyperandrogenism and polycystic ovaries on ultrasonographic examination. Ultrasonographic examinations were performed with an 8.5-MHz vaginal transducer (Esaote, MyLab 20 Plus, Genoa, Italy).

The healthy women in the control group were selected from the people who applied only for a contraceptive counseling and who had no other complaints. They were also confirmed to be healthy by history, physical and pelvic examination and ultrasonography.

Age- and BMI-matched healthy women had regular menstrual cycles and did not have the signs of hirsutism. None of the subjects had been taking any drugs like insulin sensitizers, oral contraceptives, antiandrogens, glucocorticoids and mineral supplementations for at least 6 months before participating in the study. For both groups, the exclusion criteria included Cushing’s syndrome, androgen-secreting tumor, diabetes, congenital adrenal hyperplasia, thyroid dysfunction and hyperprolactinemia. Weight and height were measured, and BMI was calculated as weight divided by height squared (kg/m²) for each subject.

Laboratory analysis

After an overnight fast of 12 hours, 10 cc venous blood was taken from each woman during the early follicular phase (between days 3 and 5) of the spontaneous or progestin-induced menstrual cycle between 8 AM and 10 AM. The samples were kept in a cool box at +4°C and then they were transferred immediately to the laboratory. The serum samples were obtained by centrifuging blood samples at 2500 rpm for 15 min at 4°C and were stored at −80°C until analysis. The serum levels of Cu, Zn, Mn, Mg, Co, Cd and Pb were measured by atomic absorption spectrophotometer (Unicam 929, Unicam Ltd, Cambridge, UK) at the Division of Biochemistry, Department of Chemistry, Yuzuncu Yil University (Van, Turkey). Atomic absorption spectrophotometric method is an optimal choice to measure the amount of trace elements and heavy metals in serum owing to its high sensitivity and specificity.^13–15

The serum concentrations of total testosterone and dehydroepiandrosterone sulfate (DHEAS) were assessed by chemiluminescent immunoassay with an Immulite 2000 analyzer (Diagnostic Products Corp., Los Angeles, CA, USA).

Statistical analysis

Results were expressed as mean and SD. Student’s t test was performed to evaluate differences between the group means. Pearson’s correlation coefficient was used to evaluate the relationship among the variables and p < 0.05 were regarded statistically significant. Statistical analysis was performed using the Statistical Package for the Social Sciences for Windows software (version 17.0; SPSS, Inc., Chicago, IL, USA).

Results

Demographic characteristics and the comparison of serum levels of essential trace elements, heavy metals and hormones between the PCOS patients and control groups are shown in Table 1. There were no statistically significant differences between the two groups with respect to the serum Mg, Co and Cd levels. While the serum levels of Cu and Zn were higher, Mn and Pb levels were lower in PCOS patients than the controls (p < 0.01). In PCOS patients, while the mean serum Cu level was negatively correlated with BMI (r = −0.710, p < 0.01), serum Pb level was inversely correlated with total testosterone level (r = −0.543, p < 0.01). This relationship was not detected in healthy subjects.

Table 1.

Descriptive statistics and the comparison results for demographic characteristics as well as serum levels of essential trace elements, heavy metals and hormones in PCOS patients and the controls

	Patients with PCOS (n=35)	Controls (n = 30)	p	95% Confidence interval for differences
	Patients with PCOS (n=35)	Controls (n = 30)	p	Lower	Upper
Age (years)	24.25 ± 4.68	27.75 ± 5.45	0.078	−5.562	0.381
BMI (kg/m²)	21.72 ± 3.02	22.63 ± 3.08	0.451	−2.973	0.95
TT (ng/dL)	83.24 ± 37.04	45.8 ± 13.4	0.001^a	48.27	74.105
DHEAS (µg/dL)	307.81 ± 132.77	180.85 ± 80.45	0.001^a	66.82	184.89
Cu (µg/mL)	0.75 ± 0.13	0.64 ± 0.10	0.001^a	0.496	0.173
Mn (µg/dL)	0.05 ± 0.01	0.10 ± 0.07	0.001^a	−0.076	−0.026
Zn (µg/mL)	0.92 ± 0.20	0.77 ± 0.19	0.006^a	0.043	0.245
Mg (µg/mL)	15.81 ± 17.77	11.99 ± 1.29	0.253	−2.80	10.44
Pb (µg/dL)	0.45 ± 0.32	0.89 ± 0.25	0.001^a	−0.592	−0.297
Co (µg/dL)	0.03 ± 0.02	0.02 ± 0.01	0.246	−0.005	0.02
Cd (µg/dL)	0.04 ± 0.02	0.04 ± 0.01	0.758	−0.007	0.009

TT: total testosterone, PCOS: polycystic ovary syndrome, BMI: body mass index, DHEAS: dehydroepiandrosterone sulfate, Cu: copper, Mn: manganese, Zn: zinc, Mg: magnesium, Pb: lead, Co: cobalt, Cd: cadmium.

^a p < 0.05

Discussion

To the best of our knowledge, this is the first study investigating the serum levels of trace elements (except Mg) and heavy metals in PCOS, which is a multifactorial disease, and its exact cause remains a mystery.

Cu is one of the essential trace elements for human body. In this study, we found higher serum Cu level in PCOS patients (normal range, 0.7–1.5 µg/mL) than the controls (p < 0.001). In addition, Cu level was negatively correlated with BMI in patients with PCOS. In the literature, there is no study analyzing the serum Cu level and its relationship with BMI in the patients with PCOS. Cu is a cofactor of many enzymes involved in redox reactions, such as cytochrome c oxidase, ascorbate oxidase or SOD. Besides its enzymatic roles, Cu has also a role in biological systems for electron transport.¹⁶ It can induce oxidative stress by catalyzing the formation of ROS and decreasing GSH levels.^17,18 Many studies supported that increased oxidative stress may have a role in the pathogenesis of PCOS.^10,19,20 GSH depletion, resulting from the increased production of ROS, was shown in patients with PCOS.^19,21 Kuscu and Var¹¹ and Zhang et al.⁴ also demonstrated higher SOD levels in PCOS patients. Therefore, there may be a relationship between Cu and PCOS. Padilla et al. showed that deficiency of Cu increased adiposity.²² We also found an inverse relationship between serum Cu level and BMI (r = −0.71, p < 0.01). However, PCOS patients in our study were nonobese and there was no significant difference between them and the controls with respect to the BMI. In addition, total number of PCOS patients and the controls was small. Therefore, we suggest further trials to be carried out to investigate serum Cu levels and its relationship with BMI in larger groups consisted of obese and nonobese patients with PCOS.

Zn is another essential trace element and acts as a catalytic, structural and regulatory ion.²³ In addition, it plays a role as an antioxidant by contributing to the structure of the Cu-Zn SOD and maintaining the metallothionein tissue concentrations.⁷ In our study, although we found that the mean serum Zn level was higher in patients with PCOS compared with the controls (p < 0.05), Zn levels remained within the normal range (0.60–1.10 µg/mL). Since this is the first study measuring the level of Zn in PCOS patients, further studies are needed to show whether it has a role in PCOS or not.

Mn is also an essential element protecting the body against oxidative stress and is a cofactor for the metalloenzyme, which is Mn-containing SOD (MnSOD).^24,25 It neutralizes the highly reactive superoxide ions to less reactive hydrogen peroxide (H₂O₂), which is followed by its immediate conversion to H₂O by catalase and other peroxidases in the mitochondrial matrix.²⁶ In this study, the mean serum Mn levels of PCOS patients were half of the corresponding serum levels of the controls (normal range 0.09–0.29 µg/dL). Since oxidative stress is increased in PCOS, it is possible that serum Mn level is decreased as a result of consumption in the antioxidant defense system including MnSOD.

Low level of Pb exposure has a number of negative consequences for human health.²⁷ It damages cellular components by elevating levels of oxidative stress.²⁸ Although the level of Pb remained within the normal range (0–20 µg/dL), it was lower and there was an inverse correlation between serum Pb and total testosterone levels in patients with PCOS (r = −0.543, p < 0.01). In accordance with our results, Telisman et al. also showed an increase in serum testosterone level in men with occupational exposure to Pb.²⁹ However, the numbers of subjects in both the study and control groups were few and there is no other study evaluating the serum Pb level and its relationship with testosterone in PCOS patients. Further trials are needed evaluating serum Pb levels in PCOS patients.

Mg is another essential element for human body. We found that the mean serum Mg levels in patients with PCOS and the controls were similar (normal range, 12–25 µg/mL; p > 0.05) and no correlation was detected between its levels and the age, BMI, testosterone, DHEAS and the other measured trace elements and heavy metals in our study. Although Muneyyirci-Delale et al. showed a lower serum Mg level in PCOS patients,³⁰ Kauffman et al. noted no significant difference between PCOS patients and the controls with respect to its level,³¹ which is in accordance with the results of our study. Similar to our findings, the results of both of these studies did not show any correlation between the serum level of Mg, steroid hormones, age and BMI.

Both Co and Cd may interfere with DNA repair process. Co may also induce DNA damage and mediate free radical generation.²⁸ Cd is a heavy metal which is unable to generate free radicals directly but may contribute to the formation of ROS indirectly. It has also a role in the inhibition of gene expression and signal transduction.⁸ We found that there was no significant difference between serum Co (normal range, 0.1–1.2 µg/L) and Cd (normal range, <0.1 µg/dL) levels in PCOS patients and the controls. The levels of both elements were detected in normal range in each group. Therefore, we could not find any association between these elements and PCOS.

In conclusion, the serum levels of trace elements may change in patients with PCOS. The findings in this study should be investigated with further trials in order to obtain new insights into PCOS.

Footnotes

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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