Carbohydrate and lipid metabolism and oxidative stress parameters in patients with menstrual irregularities and obesity

The relationship between obesity and female reproductive functions has been the focus of considerable attention among researchers for many decades. Obesity has become a significant and growing public health problem [1–3]. The negative effect of insulin resistance and the associated compensatory hyperinsulinemia characteristic of obesity on androgen metabolism, the metabolism of insulin-like growth factors, and apoptosis processes are no longer in doubt [4–9]. Adipokines, especially leptin, can affect the synthesis of gonadoliberin and hypothalamic activity [10, 11], and steroidogenesis. They can also affect the endometrium's status, especially decidualization and receptivity, and possibly other associated processes. Impaired feedback mechanisms regulating the menstrual cycle are also important, primarily due to changes in transport proteins production [4]. The accumulation of excess fatty tissue affects the adrenal glands' activity, can lead to a decrease in cortisol-binding globulin production and the intensification of cortisol conversion into inactive cortisone (with a subsequent compensatory increase in cortisol synthesis). All this, due to glucocorticoids' counter insulin action, aggravates insulin resistance and leads to increased androgen synthesis in the ovaries. It is presently considered that obesity may negatively affect meiosis and embryo implantation [12; 13].

Clinical manifestations of reproductive disorders associated with excess adipose tissue accumulation vary considerably. Obesity, being the most critical risk factor, does not always lead to gynecologic pathology development. The potential protective role of the genetically determined increased clearance of sex steroids and the deposition of their excess in adipose tissue is under debate. The activity of adipose tissue enzymes involved in the extra-glandular transformation of sex steroids can also affect the reproductive system's state, which is also genetically determined [14–17].

It can be assumed that there are other mechanisms by which obesity affects the reproductive system, contributing to the diversity of clinical manifestations. Currently, the metabolomic approach is increasingly used in research, and one should bear in mind a large number of roles of any molecule in the human body. Oxidative stress, which refers to the accumulation of excessive amounts of reactive oxygen species in the body, is of great interest. Under normal physiological conditions, reactive oxygen species are involved in anti-inflammatory and antitumor protection. But under oxidative stress conditions, excessive reactive oxygen species can damage cellular proteins, lipids, and DNA. Obesity is one of the causes of chronic oxidative stress in the human body [17–24].

The present study aimed to investigate the association between oxidative stress and metabolic parameters in patients with obesity and menstrual irregularities.

Materials and methods

The study included 24 obese women aged 20–35 years with menstrual irregularities (study group) [the mean age 29.1 (26.3; 33.4) years]. The control group consisted of 15 women of the same age with obesity and regular menstrual cycle [mean age 28.7 (25.3; 32.9) years]. Exclusion criteria were hyperprolactinemia, hypothyroidism, adrenal hyperandrogenism, and diabetes mellitus.

Height and body weight were measured to calculate the bodymassindex. Fastingserumlipidprofileswereanalyzed by the colorimetric photometric method. Fasting and 2-hour post glucose load insulin and glucose levels were measured using the chemiluminescent immunoassay and photometric method, respectively. Serum levels of total testosterone and sex hormone-binding globulin (SHBG) were determined by chemiluminescence immunoassay. Free testosterone concentration was calculated. To assess the level of oxidative stress by high-performance liquid chromatography, serum concentrations of malondialdehyde, 8-OH-deoxyguanosine, coenzyme Q-10, and glutathione (reduced) were determined [23, 24].

Statistical analysis

Statistical analysis was performed using the STATISTICA 10 software. The critical level of significance when the testing statistical hypothesis was considered at p <0.05. Quantitative variables were expressed as the median (Me) and interquartile range, where Q1 was the 25th quartile, Q3 was the 75th quartile. It was found that numerical variables were not normally distributed. The statistical significance of between-group differences for continuous variables was tested with the Mann–Whitney test.

Results and discussion

In the study group, 14 patients (58.33%) had opsomenorrhea, 10 (41.66%) had hyperpolymenorrhea or abnormal uterine bleeding, 6 (25%) had a single intramural fibroid ≤5 cm in diameter. Nine (37.5%) women had a history of childbirth, three of which became pregnant after ovulation stimulation (12.5%), two (8.33%) had a miscarriage, and 4 (16.66%) had infertility. The diagnosis of polycystic ovary syndrome (PCOS) according to the Rotterdam criteria was established in 16 women (66.66%) in the study group, of whom 7 (29.16%) had phenotype A.

The body mass index ranged from 30.8 to 41.2 kg/m2 in the study group patients and from 29.7 to 40.9 kg/m2 in the control group; that is, the groups were comparable in this respect.

The study and control groups did not have statistically significant differences in lipid profile such as the concentration of total cholesterol, triglycerides, low-density lipoproteins (LDL-C), high-density lipoproteins (HDL-C) (Table 1). In both groups, there were patients with lipid disorders. Only serum levels of very-low-density lipoproteins (VLDL-C) were insignificantly but statistically significantly higher in the study group patients, which is of interest since it most likely suggests the presence of endothelial dysfunction [18]. We also did not find statistically significant differences between the groups in carbohydrate metabolism parameters, including fasting and post-load hyperinsulinemia. Only the post-load serum glucose level was slightly higher in the study group patients. Differences in the concentration of testosterone, including free testosterone, as well as SHBG also had a trend character. Perhaps a slightly different result would have been obtained using the direct determination of free testosterone. The calculation of free testosterone concentration that we used does not consider a small amount of albumin-bound hormone.

In the study group, the concentration of malonic dialdehyde, a substance formed from the arachidonic and other polyunsaturated fatty acids metabolism, was slightly but statistically significantly higher than in the control group (Table 2). Malondialdehyde interacts with phospholipids, amino acids, and nucleic acids. Determination of this substance's concentration is currently used for predicting and monitoring therapy in coronary heart disease and some kidney, infectious, and oncological diseases, and in anti-aging medicine. Current literature reports evidence about the increased concentration of this substance in patients with PCOS [22, 25]. The concentration of this oxidative stress marker is thought to be associated with lipid abnormalities. We found that its concentration increases in parallel with an increase in VLDL-C concentration in the study group, thus confirming this observation [19].

The concentration of the primary antioxidants – reduced glutathione and coenzyme Q10 – did not differ between patients groups. The same can be said about the concentration of 8-OH-deoxyguanosine, a modified nucleoside formed in a DNA molecule resulting from exposure to reactive oxygen species.

At the next study stage, we selected women with PCOS from the study group (n=16) and compared them with the control group. Table 3 shows only those variables for which the differences were statistically significant.

Patients with PCOS were characterized by the most pronounced lipid and carbohydrate metabolism abnormalities (insulin resistance), which is consistent with the literature. The decrease in SHBG production in these women naturally led to a higher calculated concentration of free testosterone.

Differences in malondialdehyde concentrations between the patients with PCOS and the control subjects were more significant than between the study and control group. Patients with PCOS also had some excess in the serum levels of 8-OH-deoxyguanosine, a modified nucleoside formed in a DNA molecule resulting from exposure to reactive oxygen species. It has mutagenic properties and is regarded as a marker of oxidative stress and risk of carcinogenesis.

Conclusion

The present study's findings suggest that oxidative stress can play a specific role in forming menstrual cycle disorders, affecting various levels of reproductive system regulation. Elucidation of the mechanisms of this negative influence can help in the development of personalized therapy. We have studied only some of the available parameters. At the same time, it is known that the antioxidant system includes many components – enzymes and low molecular weight substances, including vitamins. It seems promising to investigate these factors' whole spectrum in patients with menstrual irregularities to determine their diagnostic and prognostic value.

The most significant changes were found in patients with PCOS. Strictly speaking, they most significantly contributed to the differences between the groups. Whether patients with PCOS are more sensitive to oxidative stress or the disease itself contributes to its formation remains an open question. Insulin resistance in PCOS is tissue-specific, i.e., it is mainly related to peripheral tissues (for example, muscle), and ovarian tissues retain normal and even increased insulin sensitivity. This can be either a genetically determined feature or a consequence, for example, of active oxygen or inflammatory mediator action on tissues. The adverse effects of oxidative stress on the reproductive system may likely occur at an earlier age. Perhaps, analysis of oxidative stress parameters may be considered an additional diagnostic method in patients with PCOS in whom standard diagnostic procedures have been exhausted.