Fig. 2: Metformin induces a glucotonic effect in small intestine and colon cell lines by upregulating GLUT1 expression and enhancing glycolysis.

a qRT-PCR results of representative genes and corresponding fold changes in expression from metformin-treated rat small intestine (IEC6) and human colon (Caco-2) cell lines. b, c IEC6 and Caco-2 cell lines were incubated with vehicle (CON) or presence of biguanides, such as metformin (MET), phenformin (PHE) and buformin (BU) for 16 h, after 8-h starvation in serum-free medium, and later collected for immunoblotting of GLUT1: total proteins show that GLUT1 increases in IEC6 and Caco-2 cell lines after biguanide treatment (expression levels were normalized to β-actin) (b); membrane proteins show that GLUT1 increases in IEC6 and Caco-2 cell line plasma membranes after two representative biguanide treatment (expression levels were normalized to Na⁺/K⁺-ATPase (ATP1A1)) (c). d Immunoblots of plasma membrane lysates of organoids. ATP1A1 served as a loading control of membrane protein. e Increase in glucose uptake after metformin treatment in small intestine and colon cell lines. Glucose uptake detected of 2-deoxyglucose-6-phosphate (2DG6P). 2DG6P was normalized with MTS. Glucose uptake was abolished after GLUT1-specific inhibitor (STF-31) treatment in metformin-treated IEC6 and Caco-2 cell lines. f Increase in glucose excretion after metformin treatment in IEC6 and Caco-2 cell lines. Glucose excretion was abolished after GLUT1-specific inhibitor (STF-31) treatment in metformin-treated IEC6 and Caco-2 cell lines. All data are presented as the mean ± s.e.m. Data in a, e and f were analyzed using two-tailed Student’s t-tests; *P < 0.05, **P < 0.01, ***P < 0.001.