Evidence-Based and Patient-Oriented Inositol Treatment in Polycystic Ovary Syndrome: Changing the Perspective of the Disease

Polycystic ovary syndrome (PCOS)’s rate is about 6% to10% among the reproductive aged women; it is characterized by menstrual cycle irregularity with oligo-anovulation, hyperandrogenism, insulin resistance, and compensatory hyperinsulinemia. Despite the fact that the last two elements are present in a large percentage of PCOS women, they are not mandatory for the diagnosis; in order to explain the pathogenesis in these patients, it was supposed that ovarian theca cells got higher insulin sensitivity probably related to the mechanism of intracellular signalling transduction (1). Corroborating this view, it was previously demonstrated that diazoxid, which has the well-known effect of decreasing insulin levels, reduced hyperandrogenism in lean women affected by PCOS, even in the cases of normal insulin level and insulin sensitivity (2). Based on the detrimental role of insulin resistance, several insulin sensitizer drugs have been used to ameliorate PCOS symptoms and signs. Although metformin has represented the landmark of PCOS therapy in the recent past, to date several studies have tested the efficacy of Inositols, a carbocyclic polyols. Two stereoisomers, in particular Myo-inositol (MI) and D-Dhiro-inositol (DCI) showed a clinical efficacy and safety during PCOS. MI is converted in DCI by epimerase, an enzyme regulated also by insulin action. In the form of inositol-phosphoglycans (IPGs), they are involved in a non-classical insulin signalling cascade: insulin receptor is coupled by G-protein which can activate phospholipase, allowing the release of second messengers (DCI-glycan), which is able to stimulate pyruvate dehydrogenase and glycogen synthase activities, the enzyme involved in the oxidative and the non-oxidative glucose metabolism (3). On one hand, MI-IPG is able to inhibit cyclic adenosine monophosphate (cAMP) kinase and adenylyl cyclase, both involved in free fatty acid metabolism. On the other hand, DCI-IPG play a pivotal role during the binding of insulin to its receptor on cell membrane where it stimulates IPG release and starts signalling cascade. In addition, Inositols are incorporated in membrane phospholipids as phosphoinositides. Phosphatidylinositol 4, 5 bisphosphate (PtdIns-4, 5P) and phosphatidylinositol 4P (PtdIns-4P), in particular, are involved in the regulation of the cytoskeleton structure and in the regulation of cellular motility, which account also the beneficial effects of Inositol administration on sperm parameters. PtdIns-4, 5P plays a key role in controlling calcium-mediated intracellular signalling which is mandatory to address the oocytes maturation and fecundation (4).