Polycystic ovary syndrome (PCOS) is a complex condition affecting a significant number of women in their reproductive years. Diagnosis typically involves identifying three key factors: oligo- or anovulation, clinical/biochemical hyperandrogenism, and the presence of polycystic ovaries on ultrasound. Women with PCOS often experience menstrual irregularities, infertility, and mood disorders like anxiety and depression.

While the exact cause of PCOS remains unclear, insulin resistance (IR) and subsequent hyperinsulinemia are believed to play primary roles, affecting both obese and lean individuals with the syndrome. 

Research indicates that roughly 80% of obese women with PCOS and 30–40% of lean women with PCOS experience hyperinsulinemia induced by IR, suggesting a complex interplay between insulin sensitivity and obesity in the syndrome's development. 

Altered insulin signaling in PCOS may disrupt ovarian steroidogenesis, leading to the exploration of insulin-sensitizing compounds as potential long-term treatments. Metformin has been widely studied in this regard, despite being associated with gastrointestinal discomforts. 

Recent attention has turned to two inositol stereoisomers, Myo-inositol (MI) and D-chiro-inositol (DCI), which act as insulin mediators. Both molecules play crucial roles in increasing insulin sensitivity in various tissues, thereby improving metabolic and ovulatory functions. 

While DCI restores normal insulin sensitivity in typical insulin target tissues, reducing circulating insulin and androgens and enhancing ovulation frequency, MI primarily exerts its beneficial effects at the ovarian level, enhancing insulin patterns and directly acting on ovarian functions, including steroidogenesis. 

Researchers have proposed various theories regarding the MI/DCI ratio in PCOS-affected ovaries, suggesting imbalances may contribute to excessive androgen biosynthesis. Studies have shown that the physiological MI/DCI ratio is 40:1, leading to investigations into therapies combining MI and DCI in this ratio to improve clinical outcomes in young overweight women with PCOS. 

Insulin's mechanism of action and its signal transmission to cells are well understood processes. When insulin binds to its receptor, it forms a complex that activates phosphatidylinositol-3 kinase (PI3K), an enzyme that increases the concentration of phosphoinositides (PIPs) in cells, integrating molecules into the cell membrane. 

This activation leads to four cellular processes: glucose uptake, glycogenesis, antigluconeogenesis, and antilipolysis. Additionally, PI3K activates another messenger of insulin, phosphatidylinositol, which further stimulates all metabolic activities of insulin, enhancing its action synergistically. 

Inositols play a crucial role in enhancing insulin effects and regulating intracellular functions. They include phosphoinositides (PIPs), which integrate molecules into the cell membrane, inositol polyphosphates (InsPs), which act as cytoplasmic "second" messengers, and inositol phosphoglycans (IPGs), which regulate mitochondrial metabolism. 

Inositols are stable polar molecules belonging to a family of nine hexahydroxycyclohexane stereoisomers. Initially isolated from muscles, they are found in numerous cells and tissues of mammals. In addition to insulin signal transmission, inositols are active in cellular processes such as calcium transport, association of cytoskeletal proteins, lipid metabolism, modulation of the serotoninergic pathway, cell growth, differentiation, and oocyte maturation. 

Inositol isomers have been found to play important roles in various medical conditions. For example, scyllo-inositol is implicated in neurodegenerative diseases, D-chiro-inositol (DCI) is associated with diabetes, and myo-inositol (MI) is linked to conditions like polycystic ovary syndrome (PCOS). 

MI is the most abundant inositol molecule in nature and mammalian cells, constituting 99%, with DCI making up the remaining 1%. MI can be converted into DCI by epimerization, significantly altering the concentration ratio of these molecules in different tissues. MI is found in cells in free form or bound in cell membranes, acting as a protector against hyperosmotic stress. It also regulates the activity of hormones such as follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and insulin as a second messenger. 

In mammals, a tissue-specific epimerase converts MI to DCI in an insulin-dependent manner, with different ratios of these epimers confirmed in different tissues. DCI is crucial in the insulin signaling pathway and affects molecular mechanisms related to glucose metabolism disorders. However, paradoxically, elevated DCI concentrations have been observed in women with insulin resistance (IR) and pre-eclampsia, suggesting a potential contribution of DCI to IR. 

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Ovary, insulin resistance, and hyper-androgenemia 

Ovarian function disorders in PCOS represent a growing heterogeneous, multifaceted complex entity, combined with a metabolic disorder caused by deterioration in the metabolism of carbohydrates and insulin resistance (IR). 

Insulin resistance is defined as a subnormal biological response to normal insulin levels, decreased sensitivity, or response to metabolic action of insulin. 

Clinically, insulin resistance can be described as the insufficient cell response of a known quantity of endogenous or exogenous insulin to increase glucose uptake and reduced sensitivity or answer to the metabolic effect of insulin. 

The significant association of PCO syndrome and IR is seemingly, obvious highly, complex and problematic. The frequency of association between IR and PCO according to the literature, depends on the studied population and different criteria used in the published studies. 

Although IR is significantly associated with PCO syndrome, it is not established as diagnostic criteria for PCO syndrome. Similarly, there are no general recommendations for screening for IR in patients with PCO syndrome. 

Obesity is frequently associated with PCO syndrome and plays a key role in hyperinsulinemia and IR. There are debates about interactions and relations of obesity, IR, and PCO syndrome. Accumulation of adipocytes in adipose tissue plays an important role in the endocrine function of the ovary. 

The enhanced production of leptin in adipocytes inhibits the expression of aromatase mRNA in granulosa cells, causing interruption of androgen conversion to estrogen. Production of adiponectin in adipocytes has insulin-sensitizing, anti-diabetic, and anti-inflammatory effects. 

It is unclear whether obesity is the cause of IR or worsens already-existing IR in PCO syndrome. Published data indicate that obesity is an additional circumstance that aggravates IR in patients with already previously existing IR. 

Systemic hyperinsulinism can be endogenous (obesity, gestational diabetes, diabetes type 2, extreme IR caused by mutation of the insulin receptor gene, autoantibodies on insulin receptor, insulinoma) or exogenous (diabetes mellitus type 1). 

HOMA-IR is a frequent parameter used in estimating IR in large epidemiological population studies and is calculated as a ratio of fasting insulin and glucose values. HOMA-IR can be increased in code-slender or obese patients with PCO syndrome in comparison to patients without PCO syndrome. According to the published results, cut Page of 3 9 Dr.Emanuel Paleco Institute of Medical Physics Rev .08022024 off value of HOMA-IR is 3.15 for patients with PCO syndrome, while in the general population, the defined cut-off value of HOMA-IR is 2.5. 

The assessment of insulin resistance is one of the major questions for clinicians, remaining how to distinguish wide variability in insulin-sensitive female patients in relation to insulin insensitivity and what criteria are acceptable in different ethnic groups. 

The fact is that not all women with IR have PCO syndrome, and the same IR is not present in all women with PCO syndrome. Insulin levels depend on several factors, such as metabolism and clearance of insulin, enzymatic degradation of the insulin - receptor complex, obesity, age, and androgen level. It should be taken into concern during the evaluation of the patient. 

To conclude, there might be some additional factor that leads to hyperandrogenism, which is an obligatory diagnostic criterion included in PCO syndrome and associated with hyperinsulinemia or some additional trigger. 

Hyperandrogenism has an important impact on the mechanism of PCOS, including IR, inflammation, and oxidative stress. Hyperandrogenism aggravates IR through different routes, by inhibiting insulin degradation in the liver and reduction of insulin sensitivity. Still, we need to define the necessary criterion for the diagnosis of HA as an additional trigger for the development of PCO syndrome with hyperinsulinemia. 

Insulin resistance and compensatory hyperinsulinism, contribute to increased production of androgens. Insulin has a modality as gonadotropin in the ovary triggering ovarian steroidogenesis, stimulating androgen synthesis in the adrenal glands, and modulates pulsatility of LH by increasing LH binding sites and androgen-producing response to LH. 

Hyperandrogenemia is responsible for reproductive disorders like ovulatory dysfunction, anovulation, oligomenorrhea, infertility, acne, and alopecia or hypertrichosis or hirsutism which are clinical signs of PCO syndrome. 

Hyperandogenemia is associated with obesity and increased visceral fat, which are not rare in patients with PCO syndrome. An increase in fat tissue promotes IR, HA, and hyperinsulinemia, and again, we are in the same circle of alternating disorders . 

The genomic, transcriptomic, and proteomic profile of visceral fatty tissue in women with PCO syndrome is different from that of healthy women, more similar to a man’s fatty tissue, and hence suggests the metabolic effect of HA on typical obesity in PCO syndrome. 

Beyond the multifactorial pathophysiology of PCOS, one of the hypotheses suggests a pathogenetic role of high levels of androgens that are the main cause of abdominal and visceral fatty tissue accumulation. Both stimulate IR and compensatory hyperinsulinism. Hyperinsulinism is responsible for androgen synthesis in the ovary and adrenal glands and promotes leptin-mediated inflammation in women with PCO syndrome, so the vicious circle closes. 

Heterogeneity of PCO syndrome most likely arises from obesity, abdominal fat, and IR. Central hepatic insulin resistance can be present in slender patients with PCO syndrome, while the peripheral IR is tied to adipose tissue and muscles and is characteristic of female patients who are obese. 

Since some inositols (MI, DCI) are mediators of insulin, they can potentially change the metabolism of various tissues. 

Inositols are credited with acting as a second messenger, in response to external or endocrine signals, reducing IR, improving ovarian function by reducing androgen levels, and alleviating metabolic, menstrual, and cutaneous hyperandrogenic features of PCOS. 

Noticeably, inositols are involved in the action of several endocrine systems (insulin, thyroid hormone, gonadotropins) and lipids with hormone-like activity signals (as prostaglandins). 

Myo-inositol and DCI are the two most abundant members of nine stereoisomeric inositols. The specificities of the inositols metabolism in the ovary and differences compared to other tissues are known. D-chiro inositol is synthesized in vivo by epimerization from MI, and the degree of epimerization defines insulin-dependent epimerase. 

The ratio of MI and DCI concentration in ovarian tissues is 70:1, while the ratio in women with PCOS is pathologically decreased. Type 2 diabetes mellitus, with its pathophysiological pathways, can dramatically impair DCI levels, resulting in low intracellular levels of DCI due to reduced activity of epimerase (hyperinsulinemia reduces activity of epimerase). 

In PCO syndrome, ovaries are in a state in which tissue-selective resistance to metabolic effects of insulin seems to be contradictory and associated with ovarian sensitivity to insulin unlikely liver, fat, and muscle tissue. 

In PCO syndrome with pronounced hyperinsulinemia, in the ovary, there is an accelerated conversion of MI to DCI (increased ratio, excessive synthesis of DCI) due to accelerated epimerization. As a consequence, deficiency of MI in the ovary causes specific reproductive disturbances. 

This phenomenon, called the D-chiro inositol paradox, is a rebound effect on hyperinsulinemia. The mechanism involves tissue-specific metabolic pathways that decrease the synthesis of DCI in the liver, muscles, and fat tissue as a response to hyperinsulinemia; under the same circumstances, DCI synthesis increases within the ovaries while synthesis of MI is lacking. 

Therefore, DCI is effective in treating and reducing IR but not in reducing ovarian disorders in PCO patients. 

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Treatment of reproductive disorders with inositols 

Reproductive abnormalities in PCO syndrome may appear with different clinical presentations. Disorders of ovulation, oligomenorrhea, amenorrhea, and menstrual cycle irregularities are the most common infertility causes in patients with PCO syndrome. 

The different clinical PCOS phenotypes require proper assessment of the biochemical and medical features to adopt the best pharmacological treatment and therapeutic strategy in patients with PCO syndrome. 

The aim of the pharmacological treatment may be hyperandrogenemia, oligo-ovulation, or IR. The therapeutic management and selection of the best therapy should be done upon the clinical features of the target patient and her priorities—regulation of menstrual disturbance, ovulation abnormalities, oligo-ovulation, hyperandrogenism or IR, or altogether. Before drug administration, diet and healthy lifestyle advice must be given to all patients with PCOS regardless of their weight. 

Physical activity and exercise (150 min of moderate or 75 min of intense exercise per week) play a key role in weight reduction and the prevention of obesity. That approach has been proven to be the best way to improve insulin sensitivity. 

Weight reduction with calorie intake restriction and the introduction of physical activity would be the first step in treatment for obese women diagnosed with PCO syndrome. With weight loss, the free testosterone level decreases, as does the incidence of metabolic syndrome. 

Changes in lifestyle and diet lead to lower insulin and free androgen levels, inducing the restoration of body composition, hyperandrogenism, and IR. There is very much to discover, for a better understanding of pathogenesis, how the reduction of fat tissues modifies all metabolic pathways and improvements in the metabolism of glucose or lipids, reproductive outcome, mood, quality of life, and therapy satisfaction. 

Weight reduction leads to better self-esteem. 

Hyperinsulinemia and IR are key goals of treatment in patients with PCO syndrome and include the administration of insulin-sensitizing drugs (e.g. metformin). There is still no definite cure or medication for this heterogeneous endocrine disorder with various clinical appearances. 

The routine approach after advising on lifestyle modification and weight loss is symptomatic therapy with different agents including oral antidiabetics, progesterone, contraceptives, or antiandrogens. 

The efficiency and efficacy of some other drugs as thiazolidinediones, berberine, or inositols have not been enough investigated and the effects of these drugs are still unclear in infertility treatment. 

Classic gynecological treatment in reproductive-age patients with PCO syndrome implies regulation of the menstrual cycle with the administration of combined oral hormonal contraception or progestins. 

Induction of ovulation is required in PCOS patients with anovulatory cycles if there is a desire for motherhood. The first-line treatment for ovulation induction is clomiphene citrate and letrozole, especially if it is a fertility problem tied only to anovulation without co-existing male factor or tubal obstruction. 

In the cases of combined male–female infertility, couples are treated with assisted reproductive technologies (in vitro fertilization) and stimulation of ovaries with gonadotropins. The use of gonadotropins carries significant risks of ovarian hyperstimulation, and that’s why they have indicated targeted protocols for ovarian stimulation. 

From the point of patient safety, treatment with an antagonist for ovarian stimulation and the “freez all” approach are the best options if there is ovarian hyperstimulation. Ovarian stimulation in agonistic protocol in combination with metformin can reduce the risk of hyperstimulation. 

Some patients are resistant to ovulation inductors due to persistent hyperandrogenemia, hyperestrogenemia, and IR. This abnormality is further worsened in overweight PCOS patients, especially with visceral and abdominal fatty tissues, since SHBG level is reduced due to hyperinsulinemia, and androgen levels are increasing. 

Since hyperinsulinemia stimulates androgen synthesis in patients with PCO syndrome, the attention of researchers is focused on inositol phosphoglycans as post-receptor mediators or secondary messengers of insulin signals. 

Administration of MI in patients with PCO syndrome after 12 weeks has a positive effect on the hormonal status of the patients. It has proven a significant reduction in the concentration of LH, PRL, androgens, and of LH/FSH ratio and ratio glucose/insulin. 

Increased sensitivity to insulin had been observed by reduction of HOMA-IR. In PCO patients treated with in vitro fertilization procedure and inositols it has been observed shorter duration of ovarian stimulation and minor total dose of applied gonadotropins. 

Severe ovarian hyperstimulation syndrome is significantly more often present in patients with PCO syndrome and associated with increased number of antral follicles. The positive effect of MI was observed in improved response to ovarian stimulation. 

The group of PCOS patients treated with MI had significantly more large follicles (> 16 mm) on hCG day administration, compared to control group, which had significantly more small follicles (< 12 mm). The application of MI contributes not only to the safety of infertility treatment but also to the better quality of the follicles. 

The final reproductive outcome, the proportion of conceived pregnancies and births, decreased incidence of gestational diabetes, and giving birth to eutrophic children are also significantly better in MI users. 

In patients with PCO syndrome, a higher concentration of DCI in the urine (higher elimination) and at the same time a reduced concentration in the plasma was observed compared to healthy eumenorrhoic women, while no such differences were observed for MI. 

According to the previously published data, MI supplementation improves many ovarian functions, oocyte quality, ovulation, higher chance of conception with better reproductive outcomes, as well as minor total gonadotropin dose during ovarian stimulation. 

Both stereoisomers MI and DCI additionally improve the regulation of glucose metabolism, lipid metabolism, and clinical signs of hyperandrogenemia. Thus, significant dysregulation of inositol metabolism was demonstrated in patients with PCO syndrome, which indicates a connection with hyperinsulinemia and IR. Already initial studies have proven the significant effectiveness of DCI in reducing lipid biomarkers, increasing insulin sensitivity, reducing androgen levels, and increasing the frequency of ovulation. 

These effects are mainly related to the positive systemic effect of DCI on the metabolic syndrome, but not to the effect on the ovary, while MI has proven direct positive effects on ovarian function at the cellular level. 

Administration of higher doses of DCI (2.4 g/day), seems to have a negative effect on ovarian function, more significantly in PCO patients who do not have diagnosed IR. The release of a larger amount of DCI-phosphoglycan with hyperinsulinemia stimulates the biosynthesis of testosterone in ovarian theca cells, which increases hyperandrogenemia and leads ovarian follicles to growth arrest, atresia, or even to anovulation. 

Newer published studies indicate on positive effects of combined preparations which contain both stereoisomers MI and DCI on ovarian function in patients with PCO syndrome treated with in vitro fertilization procedures. The analysis of seven factors of oocyte quality has proved the positive impact of the combined administration of MI and DCI on oocyte quality, with preparations that contained a higher concentration of DCI in relation to MI. 

The known physiological ratio of MI and DCI in the plasma is 40:1 (in the ovary 100:1), but it seems that the effect on cell quality is still more dependent on the concentration of DCI than on the physiological ratio. 

The effect of these changes on developing embryos after ICSI fertilization remains unclear, as well as the effect on conception. Studies on the preventive effect of inositol on the occurrence of gestational diabetes in the population of patients with PCO syndrome have also been published. 

The effect of MI and DCI was evaluated in the population of pregnant women diagnosed with gestational diabetes in mono-formulations or in combination. It was found that there is a significant beneficial effect on metabolic factors and reduction of IR in pregnant women diagnosed with gestational diabetes, and according to the results of the study, it has been shown that DCI has a more significant effect than MI. 

The choice of medical treatment including inositols depends on undelaying endocrinological and metabolic disorders and treatment goals. The applications of inositols showed clinical benefits in almost all outcomes compared to metformin independently and in combination with other forms of treatment for reproductive disorders. 

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Conclusions 

Inositols present fascinating potential in the realm of carbohydrate metabolism and their impact on cellular responses to insulin. Acting as crucial "messenger" molecules, they augment insulin sensitivity within targeted cells, offering a spectrum of benefits. 

Particularly noteworthy is their influence on follicle maturation, wherein inositols facilitate dominant follicle selection by curbing free androgen levels, enhancing aromatase activity, and promoting sex hormone-binding globulin (SHBG) production. 

The accumulating body of literature substantiates the favorable effects of inositols on various outcomes in patients with polycystic ovary (PCO) syndrome. Scientific evidence underscores their role in enhancing ovarian function, fostering ovulation, and ameliorating metabolic parameters, including the incidence of gestational diabetes and promoting the birth of healthy newborns. 

Both myo-inositol (MI) and D-chiro-inositol (DCI), as well as their combinations, exhibit promising effects on metabolic parameters, insulin resistance (IR), glucose metabolism regulation, and reproductive disorders. Notably, DCI demonstrates optimal efficacy in conditions characterized by pronounced IR, while MI exerts direct positive effects on ovarian function at the cellular level. 

The selection of inositol treatment—whether a single isomer or a combination—hinges upon the specific underlying disorder targeted for intervention. Each isomer and their combinations offer distinct actions and biological roles, tailored to address specific aspects of the condition under treatment. 

Clinical application of these inositol substitutes has underscored their tangible benefits, both when administered independently and when integrated with other modalities of treatment for reproductive disorders. As research advances, further elucidation of the precise mechanisms underlying their therapeutic effects will continue to refine their clinical utility and optimize patient outcomes.