Insulin-Stimulated Glucose Transport in Circulating Mononuclear Cells From Nondiabetic and IDDM Subjects

The objectives of this study were 1) to evaluate glucose transport and its regulation by insulin in easily accessible human cells, 2) to investigate the glucose transporter isoforms involved, and 3) to establish whether a defect in glucose transport is associated with peripheral insulin resistance, which is common in insulin-dependent diabetes mellitus (IDDM) patients. We measured 2-deoxyglucose (2-DG) uptake in circulating mononuclear cells from 23 nondiabetic adults, 16 adults with IDDM, and 10 children with IDDM. Circulating mononuclear cells were separated from whole blood by Ficoll gradients and incubated with ± 1 nM insulin. 2-DG uptake was measured after incubation with [³H]2-DG and cell separation through corn oil-phthalate. Cytochalasin B-inhibitable 2-DG uptake (basal and insulin stimulated) was higher in control than in IDDM subjects (P < 0.001). Insulin significantly increased 2-DG uptake or 3-O-methylglucose uptake in both groups. Basal and insulin-stimulated 2-DG uptake was similar for adults and children with IDDM and did not correlate with age or body mass index in any group or disease duration, insulin dosage, or HbA_1c in IDDM. In separated monocytes and lymphocytes, 2-DG uptake increased in response to insulin only in the monocyte population. Insulin dose-response curves indicated maximal stimulation of hexose uptake at 1–2 nM insulin for both control and diabetic subjects and demonstrated a significant decrease in maximal insulin response in the latter. Immunoblotting with specific antibodies revealed that circulating mononuclear cells and separated monocytes express the GLUT1 but not the GLUT4 isoform of the glucose transporter. The immunoreactive GLUT1 content was not significantly different in monocytes from diabetic than from control adults. We conclude that 1) basal hexose uptake is significantly lower in circulating mononuclear cells from IDDM than control subjects; 2) insulin significantly increases 2-DG uptake in circulating mononuclear cells from both groups, but the absolute insulin-stimulated hexose uptake is lower in the IDDM than the control subjects; 3) the insulin response is likely mediated by GLUT1 transporters in the monocyte subpopulation; and 4) maximal insulin response is subnormal in the IDDM group, but this is not linked to a decrease in GLUT1 transporter content.