Effects of acute pinitol supplementation on plasma pinitol concentration, whole body glucose tolerance, and activation of the skeletal muscle insulin receptor in older humans

Abstract

Limited research with rodents and humans suggests that oral ingestion of pinitol (3- O-methyl- D- CHIRO-inositol) might positively influence glucose tolerance. This double-blinded, placebo-controlled, and cross-over study assessed the effects of acute pinitol supplementation on plasma pinitol concentration, glucose tolerance, insulin sensitivity, and activation of the skeletal muscle insulin receptor. Fifteen older, nondiabetic subjects (62+/-1 years, mean+/-SEM) completed four, 1-day trials. Subjects consumed a non-nutritive beverage with nothing (placebo) or 1,000 mg pinitol. Sixty minutes later, the subjects consumed beverages that were either energy- and carbohydrate-free (Sham) or contained 75 g glucose (OGTT). Blood samples were collected frequently over the 240-min testing period. For the OGTT trials only, vastus lateralis samples were obtained before the placebo and pinitol supplementation and 60 min after consuming the 75 g glucose beverage. Plasma pinitol concentration increased and was maintained for 240 min. Pinitol did not influence the fasting state and 180-min area under the curves for plasma glucose and insulin during the Sham and OGTT trials or hepatic (placebo 0.83+/-0.08; pinitol 0.80+/-0.08) and whole-body (placebo 6.10+/-0.54; pinitol 6.22+/-0.52) insulin sensitivities. Activation of the muscle insulin receptor was increased by 140% with glucose ingestion (Pre 0.62+/-0.12; Post 1.49+/-0.35), but pinitol did not influence this response. These results show that the pinitol supplement was quickly absorbed, but did not acutely influence indices of whole-body glucose tolerance and insulin sensitivity, or the activation of the skeletal muscle insulin receptor in older, nondiabetic humans.

Figures

Fig. 1

(A) Plasma pinitol and (B) myo-inositol concentrations over 240 min before and after acute placebo and 1 000 mg pinitol supplementation during Sham and OGTT in a subset of healthy older subjects (n = 7). Placebo and pinitol were given at minute 0 (after minute 0 blood draw) and the Sham and 75 g glucose beverages were given at minute 60 (after minute 60 blood draw). * p = 0.04, OGTT + Placebo vs. OGTT + Pinitol. UD = undetected.

Fig. 2

Urinary pinitol and myo-inositol excretions over 240 min after acute placebo and 1 000 mg pinitol supplementation during Sham (n = 13) and OGTT (n = 15) trials in healthy older subjects. * p < 0.0001, Sham vs. OGTT. UD = undetected.

Fig. 3

(A) Plasma glucose and (B) insulin concentrations before and after acute placebo and 1 000 mg pinitol supplementation during Sham (n = 13) and OGTT (n = 15) trials in healthy older subjects. The placebo and pinitol were given at minute 0 (after minute 0 blood draw) and the sham and 75 g glucose beverages were given at minute 60 (after minute 60 blood draw).

Fig. 4

Activation of the insulin receptor before (pre) placebo and 1 000 mg pinitol supplementation and 60 min after (post) 75 g glucose beverage in a subset of healthy older subjects (n = 7). The combined data contains all of the subjects for the pre (pre-placebo plus pre-pinitol, n = 14) and post (post-placebo plus post-pinitol, n = 14). * p = 0.02, Pre versus Post. IR = insulin receptor.