Objective: To investigate the effects of mannose, the major component of Lycium barbarum polysaccharide, and its potential target metabolite, inositol, on mouse islet β-TC6 cells.
Methods: Different concentrations(0, 4. 6875, 9. 375, 18. 75, 37. 5, 75 and 150 μg/mL) of mannose or inositol were used to intervene β-TC6 cells for 24 hours, and the proliferation activity of cells was determined by CCK-8 method. Enzyme-linked immunosorbent assay was used to detect insulin secretion after the intervention of the β-TC6 cells from different concentration of the mannose or inositol(0, 18. 75, 75 and 150 μg/mL) combining with glucose stimulation(20 mmol/L) for 60 minutes. Pioglitazone(3. 92 mg/L) was set up as positive group, and after intervention of the mannose or inositol(0, 9. 375, 18. 75, 75 and 150 μg/mL) for 24 h, the expression levels of insulin, glucose kinase(GK), glucose transporter 4(GLUT4) and glycogen synthase(GS) mRNA were detected by real-time quantitative PCR.
Results: Compared with the control group, mannose and inositol promoted the proliferation of β-TC6 cells in a concentration-dependent manner(18. 75-150 μg/mL)(P<0. 05). Although the inositol solution of 4. 6875 μg/mL and 9. 375 μg/mL had a tendency to promote cell proliferation, there was no statistical difference(P>0. 05). After stimulation with 20 mmol/L glucose combining with different intervention concentrations(18. 75, 75 and 150 μg/mL) of mannose or inositol, no significant difference was observed in the insulin secretion of each group(P>0. 05) comparing with the control group. RT-qPCR result showed that 150 μg/mL mannose increased the expression level of GLUT4(P<0. 01) and the expression levels of GK and GLUT4 genes in the 75 μg/mL inositol group were significantly increased(P<0. 01). The expression level of GLUT4 was improved only when the concentration was decreased to 18. 75 μg/mL in inositol group(P<0. 01).
Conclusion: Mannose and inositol can improve the expression of GLUT4 mRNA, which may help to increase glucose uptake by peripheral cells. In addition, inositol can improve insulin sensitivity and glucose metabolism by increasing the expression level of GK mRNA.
Keywords: Lycium barbarum polysaccharide; diabetes mellitus; inositol; mannose; mouse islet β-TC6 cells.