d-chiro-Inositol is absorbed but not synthesised in rodents

Abstract

d-chiro-inositol (DCI) and pinitol (1d-3-O-methyl-chiro-inositol) are distinctive inositols reported to possess insulin-mimetic properties. DCI-containing compounds are abundant in common laboratory animal feed. By GC–MS of 6 m-HCl hydrolysates, Purina Laboratory Rodent Diet 5001 (diet 5001) contained 0·23 % total DCI by weight with most found in the lucerne and soya meal components. In contrast, only traces ofl-chiro-inositol were observed. The DCI moiety was present in a water-soluble non-ionic form of which most was shown to be pinitol. To measure the absorption of dietary inositols, rats were fed diet 5001 in a balance study or given purified pinitol or [2H6]DCI. More than 98 % of the total DCI fed to rats as diet 5001, purified pinitol or [2H6]DCI was absorbed from the gastrointestinal tract. Rats chronically on diet 5001 consumed 921 μmol total DCI/kg body weight per d but excreted less than 5·3 % in the stools and urine, suggesting that the bulk was metabolised. The levels of pinitol or DCI in plasma, stools or urine remained relatively stable in mice fed Purina PicoLab®Rodent Diet 20 5053 over a 5-week period, whereas these values declined to very low levels in mice fed a pinitol/DCI-deficient chemically defined diet. To test whether DCI was synthesised or converted frommyo-inositol, mice were treated with heavy water or [2H6]myo-inositol. DCI was neither synthesised endogenously from2H-labelled water nor converted from [2H6]myo-inositol. DCI and pinitol in rodents appear to be derived solely from the diet.