Inositol

Inositol, (of which the most prominent naturally-occurring form is myo-inositol, cis-1,2,3,5-trans-4,6-cyclohexanehexol), is a carbocyclic polyol that plays an important role as the structural basis for a number of secondary messengers in eukaryotic cells, including inositol phosphates, phosphatidylinositol (PI) and phosphatidylinositol phosphate (PIP) lipids. It is found in many foods, in particular, in cereals with high bran content, nuts, beans, and fruit, especially cantaloupe melons and oranges. Inositol is not considered a vitamin itself because it can be synthesised by the body.

Other naturally-occurring isomers (though in minimal quantities) are scyllo-, chiro-, muco-, and neo-inositol. Other possible isomers are allo-, epi-, and cis-inositol.

Myo-Inositol is classified as a member of the vitamin B complex (often referred to as vitamin B8), and is synthesized by the human body.

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Structure

The chemical formula of myo-inositol is C₆H₁₂O₆. In its most stable geometry, the inositol ring is in the chair conformation. There are nine stereoisomers, all of which may be referred to as inositol; however, the natural isomer has a structure in which the 1^st, 3^rd, 4^th, 5^th, and 6^th hydroxyls are equatorial, whereas the 2^nd hydroxyl group is axial.^[2]

Synthesis

Myo-Inositol is synthesized from glucose-6-phosphate (G-6-P) in two steps. First, G-6-P is isomerised by INYNA1 to myo-inositol 1-phosphate, which is then dephosphorylated by IMPA1 to give myo-inositol.

Function

Inositol as the basis for a number of signalling and secondary messenger molecules, is involved in a number of biological processes, including:

• Insulin signal transduction^[3]
• Cytoskeleton assembly
• Nerve guidance (Epsin)
• Intracellular calcium (Ca²⁺) concentration control^{[citation needed]}
• Cell membrane potential maintenance^{[citation needed]}
• Serotonin activity modulation
• Breakdown of fats and reducing blood cholesterol^{[citation needed]}
• Gene expression^[4][5]

Clinical implications

Some preliminary results of studies on inositol supplements show promising results for people suffering from problems such as bulimia, panic disorder, and bipolar depression.

D-chiro-inositol (DCI) has been found in two double-blind studies to be an effective treatment for many of the clinical hallmarks of polycystic ovary syndrome (PCOS), including insulin resistance, hyperandrogenism, and oligo-amenorrhea.^[6][7] The impetuses for these studies were the observed defects in DCI metabolism in PCOS and the implication of DCI in insulin signal transduction.^[8][9]

Myo-inositol has been found in double-blind studies to be an effective treatment for obsessive-compulsive disorder (OCD). It is equal in effectiveness to SSRIs and is virtually free of side-effects.^[10][11][12]

Animal studies suggest inositol reduces the severity of the osmotic demyelination syndrome if given prior to rapid correction of chronic hyponatraemia.^[13] Further study is required prior to its application in humans for this indication.

Studies from in vitro experiments, animal studies, and limited clinical experiences, claim that inositol may be used effectively against some types of cancer, in particular, when used in combination with phytic acid.^[14][15]

See also

• D-chiro-inositol
• Essential nutrient
• Inositol phosphate
• Inositol trisphosphate
• Inositol pentakisphosphate
• Inositol hexaphosphate
• Inositol triphosphate receptor
• Inositol hexanicotinate
• NOS, an energy drink containing inositol.

References