Human insulin receptor radioimmunoassay: applicability to insulin-resistant states

A radioimmunoassay of the human insulin receptor was developed employing a potent rabbit polyclonal antibody to the human insulin receptor and a highly purified human placental insulin receptor preparation. The receptor, obtained by sequential affinity chromatography with insulin receptor monoclonal antibody-agarose and wheat germ agglutinin-agarose, was radiolabeled with 125I-Bolton-Hunter reagent at specific activities of 2,100-3,300 Ci/mmol. Over 75% of this ligand was immunoprecipitable with the polyclonal antireceptor antibody and remained immunoprecipitable for greater than 45 days. The assay was sensitive to unlabeled receptor concentrations as low as 0.2 ng/0.5 ml; unlabeled insulin did not cross-react and unlabeled insulin-like growth factor (IGF)-I receptor cross-reacted weakly. The radioimmunoassay was applicable to the measurement of insulin receptors in tissues and cells that were extracted by solubilization in 1% Triton X-100; no purification of the extracted receptor was necessary. Of the three major target tissues for insulin action studied, liver had the highest concentration of receptors (47.6 ng/mg protein); fat and muscle had lower levels. Other studies with the radioimmunoassay indicated that insulin receptors were decreased both in monocytes from obese hyperinsulinemic subjects and in fibroblasts from patients with leprechaunism.

Low-dose bedtime NPH insulin in treatment of secondary failure to glyburide

Secondary failure to oral hypoglycemic agents (OHAs) is a possible outcome for non-insulin-dependent diabetes mellitus (NIDDM) patients and poses a serious therapeutic problem. In this study, we evaluated the effect of adding a single bedtime low-dose NPH insulin injection to the previous ineffective sulfonylurea therapy in 23 NIDDM patients with true secondary failure to OHAs. This treatment schedule was conducted for 3 mo by 18 patients (78%) who completed the study. In these patients, the addition of NPH insulin (0.2 +/- 0.01 IU/kg body wt) greatly decreased fasting and postprandial plasma glucose (P less than .001) and glycosylated hemoglobin (P less than .005). No weight gain was observed in any of the patients studied. Five patients dropped out: 2 patients (9%) due to insufficient compliance, 2 patients (9%) due to the multiple insulin injections required to achieve good metabolic control, and 1 patient (4%) due to recurrent hypoglycemic episodes. No correlation was observed between glucagon-stimulated C-peptide values and amelioration of metabolic control. In conclusion, most NIDDM patients with secondary failure to OHAs may be successfully treated with the addition of a single low-dose bedtime NPH insulin injection, and residual beta-cell function evaluation is not able to predict the effectiveness of the combined treatment.

Endocytosis, recycling, and degradation of the insulin receptor. Studies with monoclonal antireceptor antibodies that do not activate receptor kinase

The endocytosis, recycling, and degradation of the insulin receptor were studied in IM-9 cells and U-937 cells by employing two monoclonal antibodies directed at the alpha subunit of the human insulin receptor, antibodies MA-5 and MA-10. Antibody MA-5 is an insulin agonist and MA-10 is an insulin antagonist (Forsayeth, J., Caro, J.F., Sinha, M.K., Maddux, B.A., and Goldfine, I.D. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 3448-3451). Both monoclonal antibodies, like insulin, induced the endocytosis of the insulin receptor within 15 min. Upon removal of extracellular ligand the internalized receptor recycled to the cell surface. At this time there was no degradation of the receptor as measured by a sensitive insulin receptor radioimmunoassay. After 20 h of incubation, insulin and MA-5, but not MA-10, induced significant receptor degradation as measured by both insulin receptor radioimmunoassay and metabolic labeling studies. These studies demonstrated, therefore, that: 1) internalization and recycling of the receptor can be induced by antireceptor monoclonal antibodies that are either insulin agonists or insulin antagonists; 2) enhanced receptor degradation can be induced by monoclonal antibodies that are insulin agonists; and 3) the process of receptor internalization does not necessarily lead to enhanced receptor degradation. Since prior studies have indicated that neither MA-5 nor MA-10 enhance insulin receptor kinase activity, the present studies also suggest that insulin receptor endocytosis and degradation induced by ligands different than insulin can occur without activation of this process.

[Chronic obstructive bronchopneumopathy and ectodermal dysplasia]

A boy, 5 year aged, admitted in intensive therapy room because affected by respiratory insufficiency, is reported. Recurrent lower respiratory tract infections and three surgical operation in the lacrimal ducts were present in the anamnesis. Clinical and radiologic features of chronic obstructive pneumonia were present. Hypotrichosis, onychodystrophy, microdontia, associated with absence of muciparous glands and greatly reduced muciparous cells of respiratory tract, were other findings.

Evidence of a defect in insulin-receptor recycling in adipocytes from older rats

Although insulin-stimulated glucose uptake is known to be decreased in adipocytes isolated from old obese rats, the cause of this defect is not totally understood. In the present study, we examined the possibility that insulin resistance is associated with defects in the intracellular processing of the insulin-receptor complex. Adipocytes were isolated from control (2-mo-old rats) and obese, insulin-resistant rats (12-mo-old rats), and the following measurements were made: 1) insulin-stimulated glucose uptake; 2) insulin binding; 3) insulin-receptor internalization and recycling; 4) accumulation of insulin within the cell; and 5) rate of loss of insulin from the cell. The results indicated that maximal insulin-stimulated glucose uptake was significantly reduced in adipocytes from obese, insulin-resistant rats (increase over basal value was 500 +/- 53% in obese rats and 1,200 +/- 96 in control rats, P less than 0.01). 125I-insulin (A14) binding (cell-associated radioactivity) and the internalization of the hormone-receptor complex were not different in the two groups of animals studied. In contrast, insulin-receptor recycling was significantly decreased in adipocytes from obese rats (72.0 +/- 6.1 vs. 93.6 +/- 2.6%, P less than 0.01). In addition, loss of intracellular radioactivity was significantly prolonged in insulin-resistant rats (t1/2 = 12.05 +/- 0.9 vs. 9.4 +/- 0.3 min, P less than 0.05). Thus adipocytes isolated from the older rats were resistant to the insulin effect on glucose uptake, and this defect was not associated with a reduction in insulin binding. However, there was a decrease in insulin receptor recycling, and this phenomenon may be related to the insulin resistance present in these cells.

Intracellular insulin processing is altered in monocytes from patients with type II diabetes mellitus

We studied total cell-associated A14-[125I]insulin radioactivity (including surface-bound and internalized radioactivity), insulin internalization, and its intracellular degradation at 37 C in monocytes from nonobese type II untreated diabetic patients (n = 9) and normal subjects (n = 7). Total cell-associated radioactivity was decreased in diabetic patients [2.65 +/- 1.21% (+/- SD) vs. 4.47 +/- 1.04% of total radioactivity; P less than 0.01]. Insulin internalization was also reduced in diabetic patients (34.0 +/- 6.8% vs. 59.0 +/- 11.3% of cell-associated radioactivity; P less than 0.01). Using high performance liquid chromatography six intracellular forms of radioactivity derived from A14-[125I] insulin were identified; 10-20% of intracellular radioactivity had approximately 300,000 mol wt and was identified as radioactivity bound to the insulin receptor, and the remaining intracellular radioactivity included intact A14-[125I]insulin, [125I]iodide, or [125I]tyrosine, and three intermediate compounds. A progressive reduction of intact insulin and a corresponding increase in iodine were found when the incubation time was prolonged. Intracellular insulin degradation was reduced in monocytes from diabetic patients; intracellular intact insulin was 65.6 +/- 18.1% vs. 37.4 +/- 18.0% of intracellular radioactivity (P less than 0.01) after 2 min and 23.6 +/- 22.3% vs. 3.9 +/- 2.3% (P less than 0.01) after 60 min in diabetic patients vs. normal subjects, respectively. In conclusion, 1) human monocytes internalize and degrade insulin in the intracellular compartment in a stepwise time-dependent manner; and 2) in monocytes from type II diabetic patients total cell-associated radioactivity, insulin internalization, and insulin degradation are significantly reduced. These defects may be related to the cellular insulin resistance present in these patients.

Insulin binding and biological activities in the FRTL-5 rat thyroid cell line

A cloned rat thyroid cell line (FRTL-5) was examined for both insulin binding and responsiveness. The characteristics of insulin binding to thyroid cells were similar to those observed in typical insulin target cells. The 125I-insulin binding was time and temperature dependent and Scatchard analysis suggested the presence of two major binding sites with high and low affinity constant (Kd = 1.4 X 10(-10) mol/L and 1.5 X 10(-9) mol/L, respectively). 125I-insulin was also internalized and degraded in a temperature-dependent manner. IGF1 was weakly effective in completing 125I-insulin binding to FRTL-5 cells (57% inhibition at 333 nmol/L), whereas noninsulin-related peptide hormones were ineffective. Exposure of FRTL-5 cells to insulin stimulated both methyl-aminoisobutyric acid (M-AIB) and 2-deoxy-D-glucose (2DG) transport. These effects were evident at 10(-9) mol/L and maximal at 10(-7) mol/L insulin. Maximal stimulation was three- to four-fold over basal value for both M-AIB and 2DG transport. These data suggest that insulin specifically binds to FRTL-5 cells and regulates different biological functions of this thyroid cell line.

[Toxic epidermal necrolysis and immunologic disorders]

The authors describe a "boiled baby", 17 months aged. The condition started acutely as an intense erythema that quickly progressed to blistering. The clinical appearance and symptomatology evoked a scalded skin. The entire cutaneous surface suffered the process. The lesions appeared after herpes-infection and were followed by knee arthritis and bronchial pneumonia. Laboratory patterns showed immunologic disorder.

Insulin internalization into monocytes is decreased in patients with type II diabetes mellitus

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 of incubation 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 temperature was reduced from 37 to 4 C. Treatment of monocytes with increasing concentrations of 2,4-dinitrophenol also decreased [125I]insulin internalization, whereas dansylcadaverine, an inhibitor of transglutaminase, had no effect. Analysis by gel filtration of 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 less than 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 less than 0.001). In 20 nondiabetic obese subjects, specific cell-associated [125I]insulin was reduced to 3.9 +/- 0.3% (P less than 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 human circulating monocytes internalize [125I]insulin; this process is temperature and energy dependent; and 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.

[Blood gas analysis and evaluation of pulmonary functional damage in bronchiolitis]

212 Sucklings affected with bronchiolitis were evaluated monitoring values of haematic gases and acid-base balance. The patients were differentiated in three groups: Hypoxemia--Hypercapnia (3.7%). Hypoxemia--Normocapnia (38.2%). Normoxemia--Hypocapnia (58.1%). Metabolic acidosis was detected in 55.1% of cases. The different value of haematic gases was correlated with entity of the pulmonary functional damage.

[Biochemical monitoring of the insufficient systemic perfusion in bronchiolitis]

Biochemical monitoring was performed on 113 sucklings affected with bronchiolitis in order to evaluate early onset of insufficient systemic perfusion. Values of haematic lactate, GPT and CPK levels in the serum, partial tension of haematic gases were evaluated on first day of hospitalization. Haemogasanalytic monitoring made it possible to differentiate two groups of infants: 21 patients with hypoxemia and 92 patients with normoxemia. Monitoring of lactatemia, CPK and GPT activity evidenced following values: hyperlactemia (66.6%), increased CPK levels (47.6%), increased GPT levels (14.2%) in the group of infants with hypoxemia. Hyperlactemia (55.4%), increased CPK levels (62%), increased GPT levels (19.5%) in the group of patients with normoxemia. These findings show no significant difference between the two groups and frequent occurrence of tissular hypoxia attributable to insufficient systemic perfusion. Moreover the results of such biochemical monitoring permit precise indication about appropriate treatment.

ATP and other nucleoside triphosphates inhibit the binding of insulin to its receptor

ATP, in a dose-dependent manner, inhibited the binding of 125I-insulin to its receptor in rat liver and human placental membranes. With rat liver plasma membranes an effect of ATP was detected at concentrations between 1.0 and 2.5 mmol/L, and maximal effects were seen at 10.0 mmol/L where binding was decreased by approximately 40%. The effect of ATP was one half-maximal within 10 minutes and maximal within 60 minutes. Scatchard analysis indicated that ATP was acting primarily to change the binding affinity of the insulin receptor. The effect of ATP was mimicked by CTP, GTP, and UTP, but not by ADP, 5'-AMP, 3'-AMP, 3'5'-cyclic AMP and adenosine. The ATP analog AMP-PNP had a potency approximately 10% that of ATP. The effect of ATP was not significantly influenced by inhibitors of phosphoprotein kinases and phosphoprotein phosphatases. In human placental membranes, ATP had a similar effect in inhibiting 125I-insulin binding to its receptor. Moreover, ATP was active in inhibiting insulin binding to purified human placental insulin receptors at 0.01 mmol/L, a concentration 1/100 of that needed for inhibiting binding to intact membranes. These studies indicate, therefore, that ATP and other nucleoside triphosphates influence the ability of the insulin receptor to bind insulin.

Effects of biguanides and sulfonylureas on insulin receptors in cultured cells

The effects of the two groups of oral agents on insulin receptors were studied in several types of cells in tissue culture: MCF-7 human breast cancer cells, IM-9 human lymphocytes, human fibroblasts, and H-35 rat hepatoma cells. In none of these cells did the four sulfonylureas tested, tolbutamide, glibenclamide (glyburide), gliclazide, and glisolamide, have any significant effects on insulin binding to its receptor. In contrast the two biguanides tested, phenformin and metformin, increased insulin binding in all cell types by 44 to 101%. These studies raise the possibility, therefore, that biguanides may have a direct effect on insulin receptors and this effect may account for the known effects of biguanides to lower elevated blood sugar levels in diabetic patients.

Metformin normalizes insulin binding to monocytes from obese nondiabetic subjects and obese type II diabetic patients

In order to evaluate the in vivo effects of biguanides on the insulin receptor, we have studied insulin binding to circulating monocytes of six normal controls, eight obese nondiabetic subjects, and six obese type II diabetic patients, both before and after 4 days of treatment with the biguanide metformin (850 mg twice daily orally). Before drug administration, 125I-insulin binding to monocytes was decreased in obese subjects and diabetic patients. After metformin administration, an increase in insulin binding to peripheral monocytes was observed in seven of eight obese nondiabetic subjects (3.57 +/- 0.43 to 4.69 +/- 0.59% bound at 10(7) monocytes, mean +/- SEM, P less than 0.01) and in all diabetic patients (3.21 +/- 0.21 to 5.22 +/- 0.34, P less than 0.01). Scatchard plots indicated that the increased binding was due to an increase in the receptor number. In contrast, no significant change in insulin binding was found in normal controls after metformin administration (5.31 +/- 0.14 and 4.70 +/- 0.12). These studies indicate that metformin normalizes the binding of insulin to its receptor in obese subjects and diabetic patients. It is suggested, therefore, that the action of metformin on the insulin receptor may be one of the mechanisms of the antidiabetic effect of this drug.

Phenformin has opposite effects on insulin and growth hormone binding to IM-9 lymphocytes

We studied simultaneously the effect of various concentrations of phenformin on insulin and growth hormone binding to IM-9 lymphocytes, a cell type known to have receptors for both these hormones. After 24 hr preincubation with phenformin at 2 x 10(-5) M, insulin binding to IM-9 cells was increased by 80.4 +/- 10.5% over control (mean +/- SE of 10 experiments). In parallel experiments HGH binding was decreased by 43.1 +/- 2.2% (mean +/- SE). This effect of phenformin was dose-dependent for both HGH and insulin binding over the concentration range 1.5 x 10(-6) M to 5 x 10(-5) M, and was already detectable 3 hr after phenformin addition. These data indicate that phenformin has an opposite effect on insulin and growth hormone binding to IM-9 cells. Several possible mechanisms might be suggested for the decrease of HGH binding sites induced by phenformin: the simultaneous opposite effect on HGH and insulin receptors raises the possibility that some metabolic event triggered by the drug is able to induce opposite changes in the binding of these two hormones with different biological activities.

Effect of metformin on insulin binding to receptors in cultured human lymphocytes and cancer cells

The effect of the biguanide metformin (dimethyl-biguanide) on insulin binding in vitro to IM-9 lymphocytes and MCF-7 human breast cancer cells was studied. Metformin significantly increased insulin binding to both cell types: maximum increment was 47.1 +/- 7.0% greater than control in IM-9 and 38.0 +/- 6.1% in MCF-7 cells. The dose-response curves indicated that the latter cell line was more sensitive to metformin, with a significant effect apparent at a metformin concentration of 7.7 x 10(-6) mol/l, similar to the levels reached in patients treated with this drug. When compared with phenformin, metformin was less active in increasing insulin binding to cultured cells, the ratio between the two drug responses being similar to that of their therapeutic dosage in patients. Insulin binding increment due to metformin was reversible, was not dependent on new protein synthesis and was evident also in IM-9 lymphocytes that had been down-regulated by pre-incubation with insulin (10(-7) mol/l). This effect of metformin on insulin binding to receptors may contribute to the hypoglycaemic effect of this agent in patients.