Long-term effect of insulin on glucose transport and insulin binding in cultured adipocytes from normal and obese humans with and without non-insulin-dependent diabetes.

Abstract

We have tested the hypothesis that in vitro exposure of insulin-resistant adipocytes with insulin results in improved insulin action. A primary culture system of adipocytes from obese subjects with or without non-insulin-dependent diabetes mellitus (NIDDM) and nonobese control subjects has been developed. The adipocytes when cultured in serum-free medium do not lose their original characteristics in regard to insulin binding and glucose transport. The adipocytes from three groups were incubated with insulin (0, 10-10 M, and lo-7 M) for 24 h at 370C, receptor-bound insuMin was dissociated, and basal and insulin (1 X 10-11_10-7 M)-stimulated glucose transport and "2I-insulin binding were determined. The 24-h insulin exposure of adipocytes from control subjects decreased basal and insulin-stimulated glucose transport. The effects of 1 X 1o-7 M insulin were more pronounced than 1 X 10-l' M insulin. Similarly, insulin exposure decreased insulin sensitivity and responsiveness of cultured adipocytes from obese and NIDDM patients. The insulin-induced reduction in insulin sensitivity and responsiveness for glucose transport in three groups were due to alterations at insulin binding and postbinding levels. In conclusion, insulin induces insulin resistance in control adipocytes and further worsens the insulin resistance of adipocytes from obese and NIDDM subjects. For insulin to improve the insulin resistance of adipocytes from NIDDM patients, either more prolonged in vitro insulin exposure and/or other hormonal factors might be required.

Mechanism of IGF-I-Stimulated Glucose Transport in Human Adipocytes: Demonstration of Specific IGF-I Receptors Not Involved in Stimulation of Glucose Transport

“…Human adipocytes were isolated by the method of Rodbell (19), whereas adipose tissue membranes (30,000 x g fraction) and partially purified solubilized receptors were prepared by the method of Livingston et al (20) as previously described from our laboratory (21,22). Glucose transport in adipocytes.…”

“…Glucose transport in adipocytes. Glucose transport in fat cells was measured by determining the uptake of [U-14 C]glucose at tracer concentration (23) as previously described (21). Fat cells at 10% lipocrit were incubated with 660 nM [U-14 C]glucose in the absence or presence of varying concentrations of insulin or IGF-I for 1 h at 37°C under 95% O 2 /5% CO 2 atmosphere in 10 mM HEPES-Krebs-Ringer bicarbonate buffer (KRBB), pH 7.4, containing 3% BSA.…”

Cellular alterations in liver, skeletal muscle, and adipose tissue responsible for insulin resistance in obesity and type II diabetes

“…We have established methods to isolate and culture human adipocytes that are responsive to insulin. 16 Basal and insulin-stimulated glucose Autoradiogram of insulin-stimulated phosphorylated human liver plasma membranes absorbed by WGAtransport were compared in freshly isolated adipocytes from lean and obese subjects without diabetes, and obese patients with NIDDM,l6 as shown in Figure 10. Basal glucose transport, expressed as glucose clearance rate per cell, in obese subjects was decreased when compared with that in lean subjects.…”

The Mammalian Glucose Transporters

“…Glucose transport is markedly impaired in tissues from obese humans (107) and animals (108). Glut 4 has been extensively studied in this abnormal metabolic state.…”