A reduced number of insulin receptors in patients with Prader-Willi syndrome

The Prader-Willi syndrome is among other features characterized by obesity and a high prevalence of glucose intolerance. The fasting plasma insulin concentration and the insulin response to glucose are often increased, indicating some insulin resistance in this disease. To investigate whether this could be due to an insulin receptor defect 7 patients with Prader-Willi syndrome, 10 normal weight subjects and 8 obese subjects were tested for the binding of [125I]insulin to monocytes. Monocytes from patients with Prader-Willi syndrome bound significantly less insulin than cells from normal subjects (P less than 0.01). However, no difference was found between Prader-Willi patients and the obese controls (P greater than 0.1). It is concluded that the insulin resistance found in Prader-Willi patients, similar to that found in obese subjects, in part, may be explained by an insulin receptor defect on target cells for insulin action.

Diurnal profile of pancreatic polypeptide, pancreatic glucagon, gut glucagon and insulin in human morbid obesity

The diurnal profiles of pancreatic glucagon, insulin, pancreatic polypeptide (PP), and enteroglucagon were studied in five obese non-diabetic subjects (195 +/- 11 per cent of ideal body weight) and in six age matched controls. All the subjects were served with ordinary mixed meals five times during the day. The obese subjects were normoglycemic but hyperinsulinemic. Both groups showed rapid increases in PP to all meals, but the PP-response was significantly impaired in the obese group during the first part of the day. Normal subjects showed significant enteroglucagon responses to all meals, and had elevated levels throughout the day. In obese subjects, levels and responses were much lower at all times. Pancreatic glucagon profiles were similar. It is concluded that the possible role of abnormalities of PP and enteroglucagon secretion in the pathogenesis of human obesity deserves further study.

Circadian profiles of insulin receptors in insulin-dependent diabetics in usual and poor metabolic control

We have characterized the 24-h changes of insulin receptors on erythrocytes from patients with insulin-dependent diabetes of long duration. These diabetics were studied both in usual and poor metabolic control. Moreover, we have examined daytime changes of insulin receptors on monocytes from newly discovered diabetics. In both erythrocyte and monocyte studies, diabetics were compared to healthy controls. At insulin tracer concentration, insulin receptor binding to erythrocytes from diabetics in usual control and normal volunteers underwent a statistically significant diurnal variation with high binding values in the early morning, low daytime values with a nadir in the late afternoon, and a peak around midnight. Even diabetics in poor metabolic control due to insulin deprivation had preserved a similar 24-h rhythm of erythrocyte insulin receptors. Insulin receptor binding to monocytes at insulin tracer concentration declined significantly during the day both in newly discovered diabetics and in healthy controls. The mechanisms responsible for the acute phase changes of insulin-receptor binding are unknown, but the receptor changes seem related to the fed state. Moreover, analysis of the temporal interrelationship between erythrocyte insulin binding and plasma insulin concentration in diabetics during the 24-h period suggests that in these patients insulin may be one of the factors determining the rapid insulin receptor regulation.

Insulin receptors in the pregnant diabetic and her newborn

To ascertain if changes in the diabetic state during pregnancy were mediated by alterations in insulin receptors, we studied insulin receptors on monocytes and erythrocytes from 18 pregnant women with insulin-dependent diabetes (IDD) during the first and third trimesters. In the first trimester, insulin binding to both cell types was similar to that in normal nonpregnant women. Moreover, insulin receptor binding remained unchanged during the third trimester even in the face of the significantly increased insulin requirement and concomitant hyperinsulinemia. Our findings suggest that changes in insulin receptors are not primarily involved in alterations of diabetic control during pregnancy. Newborns of mothers with IDD have the appearance of fetal gigantism and often suffer from neonatal hypoglycemia. To determine whether altered insulin receptor binding might contribute to these phenomena, we studied insulin receptors on monocytes and erythrocytes in infants of normal mothers (n = 21) and mothers with IDD (n = 14). Compared to adults, insulin binding to both cell types from both categories of infants was significantly increased and to the same extent. The combination of fetal hyperinsulinemia and increased receptor binding in the presence of hyperglycemia may account, at least in part, for the accelerated growth of fetuses born of diabetic mothers. Finally, the enhanced neonatal glucose tolerance of these babies may be related not only to the hyperinsulinemia but also to increased insulin sensitivity mediated, in part, by the increased insulin receptor binding.

Insulin receptor binding and receptor-mediated insulin degradation in human adipocytes

125I-insulin binding and receptor-mediated insulin degradation were studied in isolated human fat cells from subcutaneous tissue. A high albumin concentration during cell isolation and incubation protected the fragile human adipocyte from lysis. Binding of tracer was pH dependent with an optimum between 7.4 and 7.6. At 37 degrees C steady state was reached by 45 min and maintained for at least 2 h. The binding of labelled insulin in the presence of 10 mumol/l unlabelled insulin was only 1-4% of the total insulin binding. The half-maximal displacement of tracer iodoinsulin (10 pmol/l) by unlabelled insulin occurred at 0.25 nmol/l. Kinetic studies of the dissociation of labelled iodoinsulin from fat cells showed a slight acceleration in the presence of a high concentration of unlabelled insulin in the washout buffer as compared to a buffer containing no insulin. At steady state binding about 95% of the cell-associated radioactivity was extracted as iodoinsulin as judged by gel filtration. The remaining 5% co-eluted with iodotyrosine. During 60 min about 90% of the cell-associated radioactivity dissociated as iodoinsulin and the rest as iodotyrosine.

CONCLUSIONS

1) A high albumin content of buffers prevents traumatization of the human adipocyte; 2) under these conditions steady state binding of insulin is readily measured at 37 degrees C; 3) the use of a washing procedure makes the non-specific binding negligible; 4) the human adipocyte insulin receptor has a very high affinity; 5) receptor-mediated insulin degradation is minimal.

Monocyte-mediated antibody-dependent cytotoxicity. Modulation by Glycolysis and insulin

In suspensions of purified human monocytes from 14 healthy persons the antibody-dependent cell-mediated cytotoxicity (ADCC), the lactate release, and the glucose uptake were studied. In non-stimulated monocytes ADCC correlated with lactate release and glucose uptake. Following addition of insulin a dose-related rise in ADCC, lactate release, and glucose uptake was observed. For each of the three processes the maximal insulin effect was about 30%. Most of the stimulation was seen within the physiological concentration range of insulin, and the insulin concentration resulting in 50% of the maximal effect was nearly the same for ADCC, lactate release, and glucose uptake (about 100 pM). The insulin stimulation of ADCC correlated with the stimulation of lactate release and glucose uptake. An inverse correlation between the ADCC of non-stimulated monocytes and the insulin stimulation of ADCC was demonstrated. No relationship was found between monocyte maturity and any of the three variables of monocyte function, either with or without insulin. These results indicate that, for normal monocytes, the cytotoxic capacity is closely related to the glycolysis.

Effects of dietary changes on cellular insulin binding and in vivo insulin sensitivity

The effect of a low-sucrose, low-fat diet on insulin sensitivity, insulin binding to monocytes, and insulin secretion in nonketotic diabetic patients was studied. Ten obese diabetics were studied for 1 yr before and during treatment with a 1200-1500-kcal diet, whereas six diabetics of normal weight were studied for 3 mo before and after treatment with a 2200-2400-kcal diet. In the obese group, no change was found in the insulin response to i.v. injection of glucose during treatment (p greater than 0.1), but the insulin sensitivity was normalized after 1 yr (p less than 0.01). The clinical normalization and the improvement of insulin sensitivity were accompanied by a parallel normalization of the binding of insulin to monocytes (p less than 0.01). In the group of normal-weight diabetics, both the insulin sensitivity (p less than 0.05) and the insulin binding to monocytes (p less than 0.05) were normalized after a 3-mo treatment period, but the insulin secretion increased (p less than 0.05) without reaching normal values. We conclude that most nonketotic diabetic patients can be controlled by diet treatment alone. The mechanism of action of the low-fat, low-sucrose diet seems for the greatest part to be a normalization of the insulin sensitivity, which is partly caused by a normalization of the cellular insulin binding.

Increased insulin receptors after exercise in patients with insulin-dependent diabetes mellitus

Physical exercise is known to improve glucose tolerance and diminish insulin requirements in patients with well-controlled diabetes mellitus. To ascertain whether these effects of exercise are associated with alterations in insulin receptors, we studied [125I]insulin binding to erythrocytes and monocytes in athletically untrained young men with insulin-treated diabetes during three hours of postprandial bicycle exercise (nine patients) and two hours of exercise during fasting (eight patients). Compared with control periods, postprandial exercise, as well as exercise during fasting, significantly increased insulin binding to erythrocytes and monocytes at an insulin-tracer concentration of 34 pmol per liter. We suggest that similar changes occur in working muscle cells and contribute to the improved glucose tolerance induced by exercise.

Impaired cellular insulin binding and insulin sensitivity induced by high-fructose feeding in normal subjects

We have studied whether the sucrose-induced reduction of insulin sensitivity and cellular insulin binding in normal man is related to the fructose or the glucose moiety. Seven young healthy subjects were fed their usual diets plus 1000 kcal extra glucose per day and eight young healthy subjects were fed their usual diets with addition of 1000 kcal extra fructose per day. The dietary regimens continued for 1 week. Before change of diet there were no statistically significant differences between body weight and fasting plasma concentrations of glucose, insulin, and ketone bodies in the two groups studied. High-glucose feeding caused no significant changes in insulin binding or insulin sensitivity whereas high-fructose feeding was accompanied by a significant reduction both of insulin binding (P less than 0.05) and insulin sensitivity (P less than 0.05). The changes in insulin binding and insulin sensitivity correlated linearly (r = 0.52, P less than 0.01). We conclude that fructose seems to be responsible for the impaired insulin binding and insulin sensitivity induced by sucrose.

Prednisone increases the number of insulin receptors on monocytes from normal subjects

The effect of prednisone on insulin receptors on circulating monocytes was studied in 38 normal volunteers. Intake of prednisone in doses which are usually employed in clinical treatment (40 mg/day) was associated with a significant increase int the number of insulin receptors. The rise in insulin binding was maximal 7 h after the begining of the medication and it was dose related.

Decreased insulin binding to monocytes from normal pregnant women

To ascertain whether the decrease of glucose tolerance in pregnancy might be mediated by changes in insulin receptors, we have studied insulin binding to monocytes in 12 normal women during late pregnancy and 14 healthy, young, normal weight, nonpregnant female controls. The pregnant women had significantly higher fasting insulin concentrations in plasma than the controsl (18 +/- 3.5 vs. 8 +/- 1.1 microU/ml; P less than 0.01). Fasting concentrations of glucose and ketone bodies in plasma were not significantly different in the two groups. Insulin binding to monocytes from pregnant women was about 35% lower at each insulin concentration tested compared to the nonpregnant controls (P less than 0.01 at tracer insulin concentrations). Changes in cellular insulin binding were due to changes of the receptor number per cell, whereas the receptor affinity was unaffected. Insulin binding was not significantly correlated with the fasting plasma insulin in either of the two groups (P less than 0.1). Our results suggest that the deterioration of glucose tolerance in normal late pregnancy might be explained by a decrease of insulin sensitivity caused by a reduction of the number of insulin receptors.

Increased insulin sensitivity and cellular insulin binding in obese diabetics following treatment with glibenclamide

The aim of the present study was to examine the effect of glibenclamide on the insulin receptors, the insulin sensitivity and the insulin secretion in obese non-ketotic diabetics. Two groups of 9 obese diabetics were studied before and after 10 days' treatment with a 1200 kcal's diet and a 1200 kcal's diet + 10 mg/day of glibenclamide, respectively. In the group treated with diet alone we found no significant alteration of the insulin secretion pattern (P greater than 0.1). However, the insulin sensitivity increased 37% (P less than 0.01). Furthermore, the insulin binding to monocytes increased (P less than 0.01) due to a 36% rise of the binding affinity. In the group treated with glibenclamide and diet the insulin secretory pattern was unchanged, too (p greater than 0.1). The insulin sensitivity, however, increased 83% (P less than 0.01). Moreover, the insulin binding was raised (P less than 0.01) as a result of a 80% rise of the number of insulin receptors. In 4 patients who were treated with diet (1200 kcal/day) plus glibenclamide and in 5 patients who were treated with diet alone (1200 kcal/day) the insulin binding to monocytes was studied during treatment for 1 year. After 1 year we found a significantly (P less than 0.005) higher cellular insulin binding in the glibenclamide treated patients compared to the patients who got diet alone. We conclude that 1) the augmentation of the insulin sensitivity is of great importance for the normalization of the diabetic state in obese, 2) the increase in insulin binding may be of importance for the increase in insulin sensitivity, 3) glibenclamide appears to enhance the insulin sensitivity through an increase in the number of insulin receptors.

Insulin receptors, insulin secretion, and glucose disappearance rate in patients with periodic hypokalaemic paralysis

In a study of 6 male patients with periodic hypokalaemic paralysis (PHP), we found reduced insulin binding to monocytes as compared with a group of 25 normal subjects (P less than 0.1). The decreased insulin binding was caused by the decreased binding affinity. During induction of paralysis by a prolonged oral glucose load, one patient showed 24-h variations in the insulin binding to monocytes not differing from those observed in normals. After iv administration of glucose, these patients showed an elevated initial insulin response compared with the normals (P less than 0.1). However, the iv glucose tolerance tests revealed normal glucose disappearance rates. We conclude that changes in insulin receptor binding do not appear to be of pathophysiological significance for eliciting the parese attacks in PHP. However, the increased insulin response, following carbohydrate intake, might be of significance in the generation of paralytic attacks in patients with PHP.

Normalization of the insulin sensitivity and the cellular insulin binding during treatment of obese diabetics for one year

The relative importance of the insulin resistance, the decreased cellular insulin binding and the relative insulin deficiency in the pathogenesis of diabetes mellitus in obese subjects has been studied. Ten obese diabetics were studied before and during treatment for 1 year with a 1200-1500 kcal's diet. No change was found in the insulin response to iv injection of glucose during treatment (P greater than 0.1), whereas the insulin sensitivity was normalized after 1 year (P less than 0.01). In parallel to the clinical normalization and the improvement of the insulin sensitivity the insulin binding to monocytes was normalized (P less than 0.01). We conclude that both the insulin resistance and the relative insulin deficiency are of decisive importance in the pathogenesis of diabetes mellitus of the obese. The insulin receptor defect seems to be one of the major factors responsible for the insulin resistance.

The pathogenic role of an insulin-receptor defect in diabetes mellitus of the obese

I-125-insulin binding to circulating monocytes was measured in 12 obese, maturity-onset diabetic patients, in 10 obese subjects, and in 12 normal persons. The diabetic obese patients were extremely insulin resistant and had an impaired glucose tolerance, while the normoglycemic obese subjects were slightly insulin resistant and had borderline values of glucose tolerance. The insulin secretion pattern of diabetic obese patients after a glucose load differed from that of the normal and normoglycemic obese subjects, showing a low initial response.

Insulin binding to monocytes from diabetic obese patients showed a 40 per cent decrease when compared with normal persons (p <0.05). Furthermore, insulin binding to monocytes was about 20 per cent lower in diabetic obese than in normoglycemic obese subjects. However, this difference was not statistically significant (p >0.1). In the total group of persons studied, the insulin binding correlated positively to both glucose tolerance (R = 0.69, p <0.001) and insulin sensitivity (R = 0.74, p <0.001). In the separate groups we also found a statistically significant correlation between insulin binding and insulin sensitivity in normoglycemic obese (R = 0.69, p <0.05) but not in diabetic obese subjects (R = 0.36, p > 0.1)

After 10 days of treatment with a 1200-kcal. diet the diabetic patients exhibited significant increases in glucose tolerance (p < 0.01), in insulin sensitivity (p < 0.01), and in insulin binding (p < 0.01)

We conclude that a close correlation exists between insulin binding and insulin sensitivity in the three groups studied. Among obese subjects the correlation was less pronounced (statistically insignificant) in diabetic obese persons, emphasizing that, especially in this group, there are other factors of importance for the insulin resistance in addition to the receptor defect.

Insulin receptors on monocytes from patients with ketosis-prone diabetes mellitus

I-125-Insulin binding to its receptor on monocytes was measured in 30 young, insulin-treated diabetic outpatients and in 13 newly diagnosed, ketotic diabetic patients before and after insulin treatment.

In insulin-treated diabetic outpatients, insulin binding was similar on average to that of 25 age-matched normal subjects. A slight but statistically significant negative relationship was found between the insulin concentration required to displace specific binding of I-125-insulin by 50 per cent and the plasma concentration of ketone bodies (R = −0.46, p < 0.02), indicating a positive correlation between apparent receptor affinity and the plasma concentration of ketone bodies. No correlation was found between insulin binding and total plasma insulin concentration.

Insulin binding to monocytes from newly diagnosed diabetic patients exhibited large variability. Based on the initial insulin binding values and the receptor response to insulin treatment, the patients could be divided into two groups. Group 1 comprised eight diabetic subjects who had had specific cell-binding fractions at an insulin tracer concentration above the median of normal subjects before therapy; after insulin treatment for 10 days, insulin binding was restored to normal. Group 2 consisted of five diabetic patients who had had specific cell-binding fractions at a tracer level below the median of normal subjects when admitted; insulin therapy caused no significant change in insulin binding. In both groups of newly diagnosed, diabetic patients, no correlation could be found between the cellular insulin binding and the plasma concentrations of insulin and ketone bodies.

We conclude that (1) insulin-treated diabetic outpatients have normal insulin binding to monocytes; (2) among newly diagnosed, ketotic diabetics with identical metabolic presentation, some may have a raised but reversible insulin binding initially, while others seem to have defective cellular insulin binding in addition to insulin deficiency; and (3) no consistent relationships exist between the plasma levels of insulin and ketone bodies and the insulin binding on monocytes from insulin-dependent diabetics.