Inositol

Inositol, or more precisely myo-inositol, is a carbocyclic sugar that is abundant in brain and other mammalian tissues, mediates cell signal transduction in response to a variety of hormones, neurotransmitters and growth factors and participates in osmoregulation. It is a sugar alcohol with half the sweetness of sucrose (table sugar). It is made naturally in humans from glucose. A human kidney will produce around two grams each day. Other tissues synthesize it too, and the highest concentration is in the brain where it plays an important role making other neurotransmitters and some steroid hormones bind to their receptors. In the last 10 years, Myo-inositol gained importance in the management of PCOS due to its efficacy, safety profile and worldwide availability. Inositol, or more precisely myo-inositol, is a carbocyclic sugar that is abundant in brain and other mammalian tissues, mediates cell signal transduction in response to a variety of hormones, neurotransmitters and growth factors and participates in osmoregulation. It is a sugar alcohol with half the sweetness of sucrose (table sugar). It is made naturally in humans from glucose. A human kidney will produce around two grams each day. Other tissues synthesize it too, and the highest concentration is in the brain where it plays an important role making other neurotransmitters and some steroid hormones bind to their receptors. In the last 10 years, Myo-inositol gained importance in the management of PCOS due to its efficacy, safety profile and worldwide availability. Myo-inositol plays an important role as the structural basis for a number of secondary messengers in eukaryotic cells, the various inositol phosphates. In addition, inositol serves as an important component of the structural lipids phosphatidylinositol (PI) and its various phosphates, the phosphatidylinositol phosphate (PIP) lipids. Inositol or its phosphates and associated lipids are found in many foods, in particular fruit, especially cantaloupe and oranges. In plants, the hexaphosphate of inositol, phytic acid or its salts, the phytates, serve as phosphate stores in seed, for example in nuts and beans. Phytic acid also occurs in cereals with high bran content. Phytate is, however, not directly bioavailable to humans in the diet, since it is not digestible. Some food preparation techniques partly break down phytates to change this. However, inositol in the form of glycerophospholipids, as found in certain plant-derived substances such as lecithins is well-absorbed and relatively bioavailable. Myo-inositol (free of phosphate) was once considered a member of the vitamin B complex, called Vitamin B8 in this context. However, because it is produced by the human body from glucose, it is not an essential nutrient. The isomer myo-inositol is a meso compound, and hence optically inactive, because it has a plane of symmetry. For this reason, meso-inositol is an obsolete name for this compound. Besides myo-inositol, the other naturally occurring stereoisomers are scyllo-, muco-, D-chiro-, and neo-inositol, although they occur in minimal quantities in nature. The other possible isomers are L-chiro-, allo-, epi-, and cis-inositol. As their names denote, L- and D-chiro inositol are the only pair of inositol enantiomers, but they are enantiomers of each other, not of myo-inositol. In its most stable conformation, the myo-inositol isomer assumes the chair conformation, which moves the maximum number of hydroxyls to the equatorial position, where they are farthest apart from each other. In this conformation, the natural myo isomer has a structure in which five of the six hydroxyls (the first, third, fourth, fifth, and sixth) are equatorial, whereas the second hydroxyl group is axial. Myo-inositol is synthesized from glucose-6-phosphate (G-6-P) in two steps. First, G-6-P is isomerised by an inositol-3-phosphate synthase enzyme (for example, ISYNA1) to myo-inositol 1-phosphate, which is then dephosphorylated by an inositol monophosphatase enzyme (for example, IMPA1) to give free myo-inositol. In humans, most inositol is synthesized in the kidneys, followed by testicles, typically in amounts of a few grams per day. at the peripheral level, Myo-inositol is converted  to D-chiro-inositol by a specific epimerase. The activity of this epimerase is insulin dependent. Worthy of note, only a small quantity of Myo-inositol is converted in D-chiro-Inositol and the conversion is irreversible. Inositol, phosphatidylinositol and some of their mono- and polyphosphates function as secondary messengers in a number of intracellular signal transduction pathways. They are involved in a number of biological processes, including: In one important family of pathways, phosphatidylinositol 4,5-bisphosphate (PIP2) is stored in cellular membranes until it is released by any of a number of signalling proteins and transformed into various secondary messengers, for example diacylglycerol and inositol triphosphate.