Effect of glucose tolerance factor (GTF) from high chromium yeast on glucose metabolism in insulin-resistant 3T3-L1 adipocytes

Abstract

The purpose of this paper was to assess and compare the impact of GTF, CrCl₃ and Cr(pic)₃ on glucose metabolism and explore the underlying mechanism of GTF in insulin-resistant 3T3-L1 adipocytes. The insulin-resistant 3T3-L1 adipocytes were induced by incubation with insulin for 48 h. Purified GTF from high chromium yeast was used in this study, with a m/z of 769 to 712, and glutamic acid, glycine, and cysteine in an approximate ratio of 1 : 1 : 1. In addition nicotinic acid and Cr(III). GTF, CrCl₃, Cr(pic)₃ and rosiglitazone (positive control) were applied to the cells. The effective dose of GTF ranged from 0.5 μg mL⁻¹ to 1.5 μg mL⁻¹. GTF decreased cell viability significantly (P < 0.01) at doses of 3 μg mL⁻¹ or higher. Glucose consumption in insulin-resistant 3T3-L1 adipocytes induced by GTF increased significantly (P < 0.05) when incubated with GTF after 12 h. Among GTF, Cr(pic)₃ and CrCl₃, GTF stimulated glucose consumption is the greatest. In the presence of insulin, the relative expression level of insulin receptor (IR), insulin receptor substrate-1 (IRS-1), insulin receptor substrate-2 (IRS-2) and glucose transporter 4 (GLUT4) mRNA were increased by GTF by 2.4, 4.1, 0.9 and 1.1-fold, respectively, however, only IRS-1 was increased by 2.3-fold in the absence of insulin. GTF affected mRNA levels of IR and IRS-1 significantly (P < 0.01) as compared to the other two. This study not only further demonstrates that chromium containing complexes show promise in reducing insulin resistance in instances of type 2 diabetes, but also that among the chromium complexes, GTF performs the best. Additionally, new mechanistic details of how GTF affects mRNA levels of insulin signalling proteins were revealed.