Phosphoinositolglycan-Peptides from Yeast Potently Induce Metabolic Insulin Actions in Isolated Rat Adipocytes, Cardiomyocytes, and Diaphragms

Abstract

Polar headgroups of free glycosyl-phosphatidylinositol (GPI) lipids or protein-bound GPI membrane anchors have been shown to exhibit insulin-mimetic activity in different cell types. However, elucidation of the molecular mode of action of these phospho-inositolglycan (PIG) molecules has been hampered by 1) lack of knowledge of their exact structure; 2) variable action profiles; and 3) rather modest effects. In the present study, these problems were circumvented by preparation of PIG-peptides (PIG-P) in sufficient quantity by sequential proteolytic (V8 protease) and lipolytic (phosphatidylinositol-specific phospholipase C) cleavage of the GPI-anchored plasma membrane protein, Gce1p, from the yeast Saccharomyces cerevisiae. The structure of the resulting PIG-P, NH2-Tyr-Cys-Asn-ethanolamine-PO4-6(Man1-2)Man1-2Man1-+ ++6Man1-4GlcNH(2)1-6myo-inositol-1,2-cyclicPO4, was revealed by amino acid analysis and Dionex exchange chromatography of fragments generated enzymatically or chemically from the neutral glycan core and is in accordance with the known consensus structures of yeast GPI anchors. PIG-P stimulated glucose transport and lipogenesis in normal, desensitized and receptor-depleted isolated rat adipocytes, increased glycerol-3-phosphate acyltransferase activity and translocation of the glucose transporter isoform 4, and inhibited isoproterenol-induced lipolysis and protein kinase A activation in adipocytes. Furthermore, PIG-P was found to stimulate glucose transport in isolated rat cardiomyocytes and glycogenesis and glycogen synthase in isolated rat diaphragms. The concentration-dependent effects of the PIG-P reached 70-90% of the maximal insulin activity with EC50-values of 0.5-5 microM. Chemical or enzymic cleavages within the glycan or peptide portion of the PIG-P led to decrease or loss of activity. The data demonstrate that PIG-P exhibits a potent insulin-mimetic activity which covers a broad spectrum of metabolic insulin actions on glucose transport and metabolism.

Glucose Tolerance Factor – Insulin Mimetic and Potentiating Agent – A Source for a Novel Anti Diabetic Medication

“…Several groups who tried to identify the active components present in brewers' yeast, claimed that they are quinoline derivatives [70], or phosphatidylinositol glycans [71]. Other investigators tried to further purify and identify the exact structure and composition of GTF.…”

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

“…Separate classes have been identified (3), one containing D-chiro-inositol (DCI) and galactosamine (4) and a second containing myo-inositol (myo-INS) and glucosamine (1)(2)(3)(4)(5). Generated rapidly from lipid and͞or protein precursors in response to insulin, they have insulin-like effects in vitro and in vivo (1,2,4,6,7). Myo-INS phospho-glycans have been prepared by enzymatic cleavage of protein precursors and chemically synthesized (7)(8)(9).…”

“…Generated rapidly from lipid and͞or protein precursors in response to insulin, they have insulin-like effects in vitro and in vivo (1,2,4,6,7). Myo-INS phospho-glycans have been prepared by enzymatic cleavage of protein precursors and chemically synthesized (7)(8)(9). They have dose-dependent insulinlike effects on isolated adipocytes, cardiomyocytes, and diaphragms including increased glucose transport (7)(8)(9).…”

“…Myo-INS phospho-glycans have been prepared by enzymatic cleavage of protein precursors and chemically synthesized (7)(8)(9). 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).…”

Glibenclamide - profile of efficacy and safety

“…Существует масса публи-каций, свидетельствующих, что в культуре жировой и мышечной тканей глибенкламид стимулирует утилизацию глюкозы, потен-цирует липогенез и синтез гликогена, повышая чувствительность к инсулину [11][12][13][14][15][16][17]. Показано также повышение активности ти-розинкиназы инсулин-рецепторного субстрата-1 (ИРС-1), гли-когенсинтазы, фосфо-инозитол-3-фосфаткиназы (PIP-3-kinase) на фоне глибенкламида [18,19,20] …”