We studied the internalization of [125I]insulin into circulating human monocytes, a cell type widely used for insulin binding studies. The internalization of [125I]insulin was assessed by both an acid extraction technique, which removes surface-bound insulin but not intracellular insulin, and by a trypsinization technique, which removes cell surface-bound hormone. After 5 h ofincubation at 22 C, over 40% of the total cell-associated [125I]insulin was internalized into monocytes of normal subjects. This internalization was temperature dependent; the fraction of internalized hormone was progressively decreased when the incubation with increasing concentrations of 2, 4-dinitrophenol also decreased [125I] insulin internalization, whereas dansylcadaverine, an inhibitor of transglutaminase, had no effect. Analysis by gel filtrationof the internalized labeled hormone after 4 h of incubation at 22 C indicated that 50-60% of the label was degraded insulin, but detectable intact insulin was still present. Internalization of insulin was then studied in monocytes from eight obese patients (161% of ideal body weight) with type II diabetes mellitus. After 4 h of incubation at 22 C, the specific total monocyte-associated [125I]insulin was decreased compared to that in cells from 7 normal subjects [6.02 ± 0.38% (±SE) vs. 3.91 ± 0.31% of the total; P < 0.001]. Moreover, the percentage of hormone that was internalized was also decreased from 41.4 ± 1.2% of the total to 28.9 + 1.8% (P < 0.001). In 20 nondiabetic obesesubjects, specific cell-associated [125I]insulin was reduced to 3.9 ± 0.3% (P < 0.001). However, compared to that in normal subjects, the percentage of hormone that was internalized was not decreased (39.7 ± 3.51% of the total). The present findings indicate that 1) human circulating monocytes internalize [125I]insulin; 2) this process is temperature and energy dependent; and 3) monocytes from obese type II diabetic patients have a significantly decreased ability to internalize insulin. This decreased internalization may play a role in the cellular resistance to insulin that occurs in these patients.
Insulin internalization into monocytes is decreased in patients with type II diabetes mellitus
SQUATRITO, Sebastiano;
1986-01-01
Abstract
We studied the internalization of [125I]insulin into circulating human monocytes, a cell type widely used for insulin binding studies. The internalization of [125I]insulin was assessed by both an acid extraction technique, which removes surface-bound insulin but not intracellular insulin, and by a trypsinization technique, which removes cell surface-bound hormone. After 5 h ofincubation at 22 C, over 40% of the total cell-associated [125I]insulin was internalized into monocytes of normal subjects. This internalization was temperature dependent; the fraction of internalized hormone was progressively decreased when the incubation with increasing concentrations of 2, 4-dinitrophenol also decreased [125I] insulin internalization, whereas dansylcadaverine, an inhibitor of transglutaminase, had no effect. Analysis by gel filtrationof the internalized labeled hormone after 4 h of incubation at 22 C indicated that 50-60% of the label was degraded insulin, but detectable intact insulin was still present. Internalization of insulin was then studied in monocytes from eight obese patients (161% of ideal body weight) with type II diabetes mellitus. After 4 h of incubation at 22 C, the specific total monocyte-associated [125I]insulin was decreased compared to that in cells from 7 normal subjects [6.02 ± 0.38% (±SE) vs. 3.91 ± 0.31% of the total; P < 0.001]. Moreover, the percentage of hormone that was internalized was also decreased from 41.4 ± 1.2% of the total to 28.9 + 1.8% (P < 0.001). In 20 nondiabetic obesesubjects, specific cell-associated [125I]insulin was reduced to 3.9 ± 0.3% (P < 0.001). However, compared to that in normal subjects, the percentage of hormone that was internalized was not decreased (39.7 ± 3.51% of the total). The present findings indicate that 1) human circulating monocytes internalize [125I]insulin; 2) this process is temperature and energy dependent; and 3) monocytes from obese type II diabetic patients have a significantly decreased ability to internalize insulin. This decreased internalization may play a role in the cellular resistance to insulin that occurs in these patients.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
