Isolation, Structure, Synthesis, and Bioactivity of a Novel Putative Insulin Mediator. A Galactosamine chiro-Inositol Pseudo-Disaccharide Mn²⁺ Chelate with Insulin-like Activity

Abstract

We isolated from beef liver a putative insulin mediator termed INS-2, 1. Its structure was determined to be a novel inositol glycan pseudo-disaccharide Mn(2+) chelate containing D-chiro-inositol 2a (as pinitol) and galactosamine. Purification methods were scaled up from those previously reported to isolate an inositol glycan with similar composition from rat liver.(1) Structure of the beef liver glycan was determined by degradative chemistry and 2D NMR spectroscopy and confirmed by chemical synthesis. Its structure is 4-O-(2-amino-2-deoxy-beta-D-galactopyranosyl)-3-O-methyl-D-chiro-inositol 1 (INS-2, Figure 1). Its role as an insulin mimetic was demonstrated by its action in vivo to decrease elevated blood glucose injected to low-dose streptozotocin diabetic rats in a stereospecific and dose-dependent manner. The pseudo-disaccharide also stimulated [(14)C]glucose incorporation into [(14)C]glycogen in a dose-dependent manner in H4IIE hepatoma cells in the presence of insulin, thus enhancing insulin action. Only when chelated to Mn(2+) did it activate pyruvate dehydrogenase phosphatase in vitro in a dose-dependent manner. To our knowledge, this is the first example of a beta-1,4-linked inositol glycan consisting of D-chiro-inositol and galactosamine isolated from animal tissues with insulin mimetic actions.

Inositols prevent and reverse endothelial dysfunction in diabetic rat and rabbit vasculature metabolically and by scavenging superoxide

“…Our hypothesis is that they act metabolically by first being incorporated into precursor IPG phospholipids and͞or proteins, then subsequently cleaved into biologically active IPGs. Insulin-like actions of both biologically derived (1-3, 5-7) and chemically synthesized Myo-INS and me-DCI containing IPGs have been clearly documented (9,10). Most recently, we have demonstrated the mechanism of action of a novel galactosamine pinitol pseudodisaccharide to activate PP2C (49).…”

“…They have dose-dependent insulinlike effects on isolated adipocytes, cardiomyocytes, and diaphragms including increased glucose transport (7)(8)(9). One DCI containing IPG has been isolated from liver, and its structure has been determined and chemically synthesized (10). It is active in vivo; lowering elevated blood glucose when administered intravenously to diabetic rats (10)(11)(12).…”

“…One DCI containing IPG has been isolated from liver, and its structure has been determined and chemically synthesized (10). It is active in vivo; lowering elevated blood glucose when administered intravenously to diabetic rats (10)(11)(12). In vitro, it enhances insulin to stimulate [ 14 C]glucose incorporation into glycogen in H4IIE hepatoma cells (10).…”

“…It is active in vivo; lowering elevated blood glucose when administered intravenously to diabetic rats (10)(11)(12). In vitro, it enhances insulin to stimulate [ 14 C]glucose incorporation into glycogen in H4IIE hepatoma cells (10). It activates pyruvate dehydrogenase (PDH) phosphatase (10), phosphoprotein phosphatase PP2C directly (13), and PP1 indirectly (4,14).…”

The “Other” Inositols and Their Phosphates: Synthesis, Biology, and Medicine (with Recent Advances in myo‐Inositol Chemistry)

“…[154] A pinitol galactoside (pinitol β-1,4-galatosamine, INS-2, Figure 6, 110) isolated from beef liver has insulin mimetic properties as shown by its ability to decrease elevated blood glucose in streptozotocin diabetic rats and the stimulation of glucose incorporation into glycogen in hepatoma cells in the presence of insulin. [155] In MIN6 β cells INS-2 stimulates insulin secretion and in isolated mouse islets it potentiates glucose stimulated insulin secretion. [156] It does this through a mechanism that involves the stimulation of the protein phosphatase 2C mediated inhibition of ATP sensitive potassium channels.…”