Physiological and pathophysiological roles of inositols

Inositols are natural compounds involved in many biological pathways. Among them myo-inositol (myo-Ins) is the most important and widespread, and it is detectable ubiquitously in almost all biological systems. It is a very ancient molecule, defined as a prebiotic compound. d-Chiro-inositol (d-chiro-Ins), a stereoisomer of myo-Ins, is another molecule of great interest. The endogenous production of these two stereoisomers fluctuates depending on the specific tissue needs. In such a context, their transport system is another crucial component. One of the most significant activities exerted by myo-Ins and d-chiro-Ins concerns glycemia regulation. Both stereoisomers exert an insulin-mimetic activity and are also effective against insulin resistance. They also play other pivotal physiological roles, such as promoting ovulation and fertility. Besides their metabolic activity, myo-Ins and d-chiro-Ins deeply influence steroidogenesis, regulating the pools of androgens and estrogens, likely in opposite ways. Moreover, inositols in the form of inositol phosphates have the function of essential second messengers. Based on their physiological role and the pathological implications of the altered myo-Ins and d-chiro-Ins ratios, inositol therapy should be designed with two different aims: on one hand, restoring their physiological ratio; on the other hand, altering this ratio in a controlled way to achieve specific effects.