Inhibition of endosomal acidification in normal cells mimics the derangements of cellular insulin and insulin-receptor metabolism observed in non—insulin-dependent diabetes mellitus

• Published in: Metabolism, clinical and experimental clinical and experimental, 1997-11, Vol.46 (11), p.1259-1265
• Main Authors: Benzi, L., Cecchetti, P., Ciccarone, A.M., Nardone, A., Merola, E., Maggiorelli, R., Campi, F., Di Cianni, G., Navalesi, R.
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Chromatography, High Pressure Liquid; Cohort Studies; Diabetes Mellitus, Type 2 - blood; Diabetes Mellitus, Type 2 - physiopathology; Diabetes. Impaired glucose tolerance; Endocrine pancreas. Apud cells (diseases); Endocrinopathies; Endocytosis - drug effects; Endocytosis - physiology; Endosomes - drug effects; Endosomes - metabolism; Etiopathogenesis. Screening. Investigations. Target tissue resistance; Humans; Insulin - analogs & derivatives; Insulin - metabolism; Iodine Radioisotopes; Ionophores - analysis; Ionophores - metabolism; Ionophores - pharmacology; Medical sciences; Middle Aged; Monensin - analysis; Monensin - metabolism; Monensin - pharmacology; Monocytes - drug effects; Monocytes - metabolism; Protein Binding - drug effects; Protein Binding - physiology; Receptor, Insulin - drug effects; Receptor, Insulin - metabolism; Reference Values; Time Factors
• ISSN: 0026-0495; 1532-8600
• DOI: 10.1016/S0026-0495(97)90227-4

Dissociation of the insulin—insulin receptor complex plays a crucial role in the processing of both insulin and the insulin receptor, and the acidification of endocytic vesicles may be the mechanism by which internalized insulin is dissociated from its receptor and properly sorted and processed. Internalized insulin—insulin receptor complexes are abnormally processed in cells from patients with non—insulin-dependent diabetes mellitus (NIDDM). Accordingly, to further investigate the mechanisms of the derangements observed in NIDDM cells, we examined the effects of the ionophore monensin, which inhibits endosomal acidification, on the cellular processing of insulin and insulin receptor in monocytes from control subjects (n = 12) and NIDDM patients (n = 14). This study confirms that monocytes from NIDDM patients, compared with cells from normal controls, had reduced binding ( P < .01), internalization ( P < .01), and degradation ( P < .01) of insulin. In addition, the release of intracellula radioactivity was slower ( P < .01), and recycling of the insulin receptor was inhibited ( P < .01). Moreover, these defects were associated with a significant ( P < .01) decrease of dissociation of the internalized insulin—insulin receptor complex. In cells from normal controls, incubation with monensin decreased insulin binding ( P < .01), but not insulin internalization. High-performance liquid chromatography (HPLC) analysis of intracellular radioactivity showed that after monensin intracellular intact insulin significantly increased ( P < .01), thus suggesting a decrease of intracellular insulin degradation. Moreover, insulin receptor recycling was completely disrupted. All of the derangements were associated with a significant decrease ( P < .01) of dissociation of insulin—insulin receptor complexes. On the contrary, in diabetic monocytes, monensin had no significant additional effect on NIDDM-linked alterations. Comparison of the results obtained in cells from NIDDM patients to those found in monensin-treated normal cells demonstrates that NIDDM and monensin gave rise to a superimposable impairment of dissociation of the intracellular insulin—insulin receptor complex, associated with similar abnormal sorting and processing of insulin and its receptor. The only defect present in NIDDM cells but not in monensin-treated cells is the decrease of insulin internalization, which thus seems independent of the action of monensin on the processing of internalized insulin—insu