Insulin receptors on monocytes and erythrocytes from obese patients

Effect of obesity on inflammatory markers and renal functions

AIM

To examine the relationship between inflammation criteria and body mass index in otherwise-healthy obese schoolchildren and to evaluate the effect of obesity on renal functions.

METHODS

Sixty-five otherwise-healthy obese children (median age 10.8 y, range 7.1-16.5 y; median body mass index 26.8 kg/m(2), range 19.9-38.7 kg/m(2)) and 20 healthy controls (median age 12.4 y, range 10.1-17.1 y; median body mass index 18.8 kg/m(2), range 17.3-23.1 kg/m(2)) were included. Blood and urine samples were taken from every child.

RESULTS

Children in the obese and control groups had similar age and sex distributions (p>0.05). Inflammatory mediators were higher in obese children (p<0.05). A significant positive correlation was found between glomerular filtration rate and body mass index in the whole study group (r=0.39, p=0.001). A positive correlation was found between body mass index standard deviation and inflammatory mediators and glomerular filtration rate. No significant difference existed regarding protein and microalbumin excretion in the urine.

CONCLUSION

Inflammatory mediators increased significantly in obese children, and the glomerular filtration rate increased as the body mass index increased. To prevent obesity-related complications in adulthood, it is important to take measures to prevent development of obesity during childhood.

Dietary lipids influence insulin action

Insulin binding and insulin responsiveness are altered by dietary fat-induced changes in the fatty acid composition of the adipocyte plasma membrane. Feeding a high P/S diet increased polyunsaturated fatty acid content of major membrane phospholipids of adipocyte plasma membrane in normal and diabetic animals, increased membrane linoleic acid content, and prevented a decrease in arachidonic acid level in diabetic animals. The high P/S diet increased insulin binding in control animals. Animals fed the high P/S diet had significantly higher rates of insulin-stimulated glucose transport and lipogenesis than did animals fed the low P/S diet. Feeding a high P/S diet significantly increased the amount of glucose transported when expressed as a function of the specific amount of insulin bound. To determine if dietary fat-induced alterations in the fatty acid composition of skeletal muscle lipid alter insulin-dependent and basal muscle metabolism, contralateral epitrochlearis and extensor digitorum longus muscles were isolated and incubated in vitro. High levels of dietary omega-3 fatty acids reduced PGE2 and PGF2 alpha synthesis in extensor digitorum longus and epitrochlearis muscle. Insulin increased glucose and amino acid transport; the increase in glucose transport by insulin was significantly greater after consumption of the high omega-3 fatty acid diet. Rats fed high levels of omega-3 fatty acids showed reduced net protein degradation in the presence and absence of insulin due to decreased rates of protein degradation and synthesis. These experiments indicate that high levels of dietary omega-3 fatty acids alter muscle membrane composition, glucose transport, and metabolism of muscle protein. To determine if dietary fatty acids alter the onset of diabetes and insulin binding to liver nuclei in spontaneously diabetic rats, weanling rats were fed chow or semipurified diets containing 20% (w/w) fat of either high or low P/S ratio. Feeding a high P/S diet increased insulin binding to liver nuclei of control and diabetic animals. Although diet did not alter the onset of diabetes, insulin binding to liver nuclei is higher in animals at the onset of diabetes than in highly diabetic animals. Eight-week-old female C57 B 6J lean and ob/ob mice were fed semipurified diets containing 20% (w/w) fat of either high or low P/S ratio to investigate the effect of diet on specific binding of insulin to liver nuclei. Insulin binding was highest in nuclei from lean mice fed a high P/S diet. Specific binding of insulin to nuclei from obese mice was also increased by the high P/S diet, but to a lesser extent.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin binding to liver nuclei from lean and obese mice is altered by dietary fat

Insulin binding to the plasma membrane is known to be altered by modifying the membrane composition through dietary treatment. As insulin binding receptors are also present on nuclear membrane, this study was undertaken to investigate if specific binding of insulin to the liver nuclei is altered by diet. 8-wk-old female C57 B 6J lean and ob/ob mice were fed semipurified diets containing 20% (w/w) fat of either high or low polyunsaturated-to-saturated (P/S) fatty acid ratio for 4 wk. Liver nuclei were prepared, insulin binding was measured and nuclear phospholipids were isolated for lipid analysis. Insulin binding was highest in nuclei prepared from lean mice fed a high P/S diet. Specific binding of insulin to nuclei prepared from obese mice was also increased by the high P/S diet, but to a lesser extent compared to lean mice. Feeding a high P/S diet increased polyunsaturated fatty acid content of membrane phospholipids from both lean and ob/ob mice. Obese mice were characterized by higher levels of arachidonic acid and lower levels of linoleic acid in phosphatidylcholine. The present study establishes that insulin binding to liver nuclei is increased by feeding a high P/S diet, and that insulin binding to liver nuclei from obese mice is lower than from lean mice.

Red blood cell insulin receptors in health and disease

CONTENTS

Structure and characteristics of erythrocyte insulin receptor. Red blood cell age and insulin receptors. Insulin receptors in human disease states. Obesity. Chronic renal failure. Acanthosis nigricans. Miscellaneous disease states. Insulin receptors in children. Insulin receptors in women during pregnancy. Insulin binding and other hormones. Comparison of biosynthetic insulin, pancreatic human insulin and porcine insulin binding to erythrocytes. Effect of exercise on insulin binding to red blood cells of normal human volunteers. Miscellaneous insulin binding studies. Insulin internalization and degradation. Insulin and erythrocyte metabolism. Summary and conclusion.

Reduced insulin removal and erythrocyte insulin binding in obese children

To study the relationship between childhood obesity, weight loss, hyperinsulinaemia and the erythrocyte insulin receptor, we measured the plasma concentrations of immunoreactive insulin (IRI) and C-peptide and the binding of 125I-insulin to erythrocytes in 12 obese children with a mean age +/- SD of 11.4 +/- 2.5 years and a mean relative weight score +/- SD of 4.8 +/- 1.4 and 12 age-matched normal-weight children. Eight obese children were re-evaluated after 1 year's participation in a weight reduction programme. The obese children had higher fasting plasma concentrations of IRI (P less than 0.01) and C-peptide (P less than 0.05) and a lower C-peptide to IRI molar ratio (P less than 0.01) than the normal-weight children. The obese children had in addition a reduced erythrocyte insulin binding (P less than 0.05 or less) over the physiological range of circulating insulin concentration. There was a negative correlation (r = -0.60; P less than 0.01) between the insulin tracer binding and the relative weight. The weight reduction programme resulted in a decrease of 1.0 SD (P less than 0.05) in the mean relative weight score. At the end of the therapy the obese children had lower fasting blood glucose levels (P less than 0.05) and lower plasma IRI concentrations at 90 min (P less than 0.05) after an oral glucose load than at the onset of therapy. There were no significant differences between the insulin binding characteristics at the commencement and at the end of the treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte insulin receptor: normalization of binding data for the average cell age by the red cell creatine determination in obese, diabetic and acromegalic patients

Insulin binding studies performed in erythrocytes (RBC) have been employed in clinical studies assessing the status of insulin receptors at target cell tissues. However, some authors challenged this assumption on the basis of some discrepancies described in comparative studies of other cell types, probably related to populations of different cell age affecting insulin binding to RBC. We evaluated insulin binding to RBC in normal males (n = 10), non-obese diabetic males (n = 13), normal females (n = 15), obese (n = 11) and acromegalic females (n = 5), before and after correction of insulin binding data for creatine concentration in the RBC as a procedure of correction for age, since a negative correlation was described between creatine content and RBC age which also correlates inversely with % insulin binding. Insulin binding in all three groups of patients was not statistically different from corresponding values for normal males and females respectively before correction of data for creatine, but significantly reduced values were found after adjustment for creatine in accordance with published data concerning monocytes. In conclusions, the procedure of correcting insulin binding in erythrocytes by the creatine content in RBC is potentially useful for clinical investigations, since the influence of RBC age is excluded.

Characterization of differences in insulin receptors from young and old red blood cells

It has been demonstrated that young RBCs (reticulocytes and early mature erythrocytes) possess more insulin receptors than old RBCs (late mature erythrocytes) but it is not yet known whether insulin receptors on young and old RBCs are regulated similarly. In the present investigation insulin receptors on young and old RBCs have, therefore, been studied in five normal male subjects before and after 2 days dexamethasone ingestion (0.5 mg tablet every 6 h) and, in the same subjects, before and 5 h after ingestion of 75 g glucose. The results obtained clearly demonstrate that dexamethasone increases insulin receptor concentration while glucose ingestion increases both insulin receptor affinity and concentration on young RBCs. By contrast, neither stimuli modify insulin receptors on old RBCs. Studies on RBCs are usually performed on the whole RBC population not taking into account this differential responsiveness of receptors on young versus old RBCs; consequently, this phenomenon might be responsible of the fact that some data reported on RBCs are not in agreement with those reported on monocytes or adipocytes and it should be taken into consideration when using RBCs to evaluate insulin receptor regulation.

Relationship of insulin binding and insulin-stimulated tyrosine kinase activity is altered in type II diabetes

The insulin receptor contains an alpha subunit with insulin binding properties and a beta subunit with insulin-stimulated tyrosine kinase function. Preparations containing insulin and insulinlike growth factor I (IGF-I) receptors were obtained from solubilized human red cell membranes by affinity chromatography. After separate assays for insulin binding and insulin-stimulated tyrosine kinase activities, a high degree of correlation was found between these activities in preparations from normals and diabetics. Identical studies using IGF-I as the ligand showed a lesser degree of correlation. We compared 24 normal subjects and 14 untreated type II diabetics and found significant diminution in the slope of the line coupling insulin binding and insulin-stimulated kinase activities in the diabetics. This difference was not observed in a similar study of IGF-I-related activities. Compared to normal controls, untreated type II diabetics have reduced tyrosine kinase activity stimulated per unit insulin binding.

Changes in insulin receptor functions of the erythrocyte by treatment of non-insulin-dependent diabetes mellitus (NIDDM) patients with glibenclamide and diet control

The insulin binding of erythrocytes from: (i) fifteen age-matched normal subjects, (ii) ten untreated NIDDM patients and (iii) fifteen treated (glibenclamide + hypocaloric diet) NIDDM patients (all males) has been studied. A significant decrease in specific insulin binding was observed in group (ii) which improved in cases controlled after treatment (group iii). Scatchard analysis of the results suggested that changes in insulin binding were due to alteration in the number of insulin receptors on erythrocytes. The number of insulin receptors/cell was 471 in normals, 160 in diabetics and 282 in treated diabetic subjects. No significant change in the binding affinity was observed in the three groups (1.0 X 10(8), 1.2 X 10(8) and 1.1 X 10(8) M-1 in normal subjects, untreated diabetics and treated diabetics, respectively).

Insulin resistance: receptor and post-binding defects in human obesity and non-insulin-dependent diabetes mellitus

Insulin resistance is a prominent feature of three clinical conditions: obesity, impaired glucose tolerance, and non-insulin-dependent (type II) diabetes mellitus. Numerous studies over the past 15 years have provided a better understanding, from both a clinical and cellular standpoint, of the pathophysiology of these insulin-resistant states as well as of insulin action. In addition, it has recently been recognized that correction of glucose intolerance leads to an improvement in insulin secretion and a reduction in insulin resistance. Examination of the most recent data suggests that the basis for insulin resistance in these common clinical disorders is often multifactorial. In uncomplicated obesity, the cellular alterations responsible for insulin resistance appear to be at the level of the hepatic insulin receptor and in post-binding processes in peripheral target tissues. In type II diabetes, a post-binding defect(s) in peripheral tissues appears to be the primary lesion. In humans, many of the factors that mediate the changes leading to insulin resistance are still unknown and are the object of current investigations.

Insulin receptors and insulin sensitivity in normo and hyperinsulinemic obese patients

The authors have studied insulin receptors on peripheral blood monocytes and insulin sensitivity, evaluated by simultaneous infusion of glucose, insulin and somatostatin in 10 control subjects and in 20 obese patients with normal glucose tolerance. The obese patients have been divided into two groups, normo (NO) and hyperinsulinemic (HO), according to the total insulin response during OGTT. We considered HO patients with insulin response higher than M + 2DS of controls. Obese patients showed, in comparison to the controls, a lower specific binding and higher degree of insulin resistance. The subdivision of obese patients allowed us to distinguish two groups. The first was characterized by basal hyperinsulinemia, normal insulin response to the stimulus, reduced number of insulin receptors and normal or slightly reduced sensitivity. The second group showed high basal and after stimulus insulinemic values, reduced number of insulin receptors and high level of insulin resistance. When we compared the two groups of obeses we found that the first has a shorter duration of obesity and lower blood glucose values after OGTT. However both groups show the same reduction of insulin bound and the same degree of basal hyperinsulinemia. These data suggest that a reduction of insulin receptors is not the main factor responsible for insulin resistance in obesity. Furthermore, the presence of basal hyperinsulinemia and normal insulin sensitivity in our first group suggests that the modification of basal insulin concentrations is not dependent on the presence of insulin resistance.

Quality control of insulin radioreceptor assay for human erythrocytes. Effect of ageing of mono-125I-Tyr-A14-insulin preparation

The quality control of insulin radioreceptor assay for human erythrocytes is based on the storage of erythrocyte preparations in Hepes buffer of pH 8.0, containing 10 g/l of albumin and 20 mmol/l of glucose. The change of erythrocytes into spherocytes and crenated cells reduces the apparent number of insulin receptors in a relatively constant way by less than 8% a week after 10 days of storage. At the same time the dissociation constants of the insulin-receptor complex increase rapidly. Thus the use of a preparation must be limited to controlling the determination of the insulin binding sites of erythrocytes, and not to the measurement of the affinities of the receptors. When mono-125I-Tyr-A14-insulin gets old, a slow decrease in the insulin binding sites can be measured, but the dissociation constants of the insulin receptor complex are not affected.

Binding of tyrosine-A-14(125I)-monoiodoinsulin to human erythrocytes

We have studied the method for the determination of human erythrocyte insulin receptor concentrations using tyrosine-A-14-monoiodoinsulin as the labelled ligand with increasing amounts of unlabelled insulin in a saturation assay. An overnight incubation at 0-+4 degrees C was found to give the highest receptor concentrations and highest affinities for the ligand. Insulin receptor concentrations were found to be very low and lower in erythrocytes from normal females than from normal male subjects (7.0 +/- 1.9 and 10.5 +/- 1.6 receptors per erythrocyte, respectively). Our results suggest that an initially homogenous class of insulin binding sites upon exposure to insulin can appear in different forms with different binding affinities for the ligand. This was deduced from the changes in the forms of Scatchard plots when the saturation assay was performed at different times at low temperature. Variability in the forms of Scatchard plots (linear to biphasic or vice versa) in samples obtained on different occasions from the same subjects also support this view. The apparent dissociation constants (mean values) were 150 and 550 pmol/l for the linear components of the biphasic plots and 300 pmol/l for the linear plot. These values lie well within the normal plasma concentrations of insulin. Addition of spermine to the incubation mixture was shown to further accentuate the high affinity part of the Scatchard plot. The high and low affinity forms of the receptor could provide an ideal means to rapidly regulate the response to insulin.

Characterization of insulin binding to the erythroleukemia cell line K 562

The K 562 is a transformed human erythroid stemcell and is used as a target cell for NK-T-cells. In this study the presence of insulin receptors in K 562 is established. The best binding and negative cooperativity was found in the two Hepes containing buffers whereas no cooperativity was obtained in the Krebs-Ringer buffer. The calculated affinity constants and receptor number per cell varied according to the buffer. Preincubation with insulin caused a down-regulation of the insulin binding capacity. 10 ng/ml caused a lowering of the affinity, with an unchanged number of receptors. 100 ng/ml caused a decrease in receptor number with unchanged affinity. These results were found in both Hepes and Krebs-Ringer phosphate buffer. IGF-I shows cross-reactivity with the insulin receptor, with a potency of 12 and 100 times less than insulin in Krebs-Ringer phosphate buffer and G-buffer respectively. However, no specific IGF-I receptors were found. The presence of receptors on K 562 cells suggests a biological role for insulin. The different results in the different buffers, indicate that a buffer containing Hepes and/or Tris, is required to expose negative cooperativity and make the receptors more accessible to insulin.

Studies of liver insulin receptors in non-obese and obese human subjects

The insulin-binding isotherms and the structural composition of human liver insulin receptors were examined by using plasma membranes that were prepared from liver biopsies of nine non-obese and 10 obese subjects undergoing elective surgery. The insulin-binding characteristics of liver membranes from non-obese subjects were quite similar to those previously described in rat liver membranes. However, when the membranes from obese subjects were compared with the non-obese group, insulin-binding activity was reduced by 50% (P less than 0.01). The reduction in obesity resulted primarily from a decrease in total receptor number, although a small decrease in receptor affinity was also observed. Insulin binding was not correlated with sex or with the fasting plasma insulin level. The insulin-binding sites of liver membranes were affinity-labeled with 125I-insulin and the cross-linking reagent, disuccinimidyl suberate. The liver membranes from both the non-obese and the obese group had heterogenous (nonreduced) insulin-binding species of 300,000, 260,000, and 150,000 mol wt, which were again comparable to the findings reported in rat liver. Sulfhydryl reduction demonstrated a major sub-unit of 125,000 and a minor component of 40,000-45,000 in both groups. These results indicate a close similarity between the hepatic insulin receptor of man and the more intensely studied rat hepatic receptor. Obesity in human subjects is associated with a loss of hepatic insulin receptors. This alteration may contribute to the insulin resistance reported in this organ as well as to obesity-mediated glucose tolerance.

Insulin binding of human and porcine monocomponent insulin to monocytes in type 1 (insulin-dependent) diabetic patients and control subjects

In the present study insulin binding properties of human semi-synthetic and porcine insulin were compared in Type 1 (insulin-dependent) diabetic patients treated from the onset of their disease either with human semi-synthetic insulin (n = 12) or porcine insulin (n = 12) and control subjects (n = 12). In all three groups, insulin binding to circulating monocytes revealed no difference between human semi-synthetic and porcine insulin (specific insulin binding at tracer concentration: 5.7 +/- 0.5% versus 5.4 +/- 0.5% in control subjects, 5.5 +/- 0.4% versus 5.4 +/- 0.4% in Type 1 diabetic patients on porcine insulin, 5.3 +/- 0.4% versus 5.6 +/- 0.4% in Type 1 diabetic patients on human insulin). Treatment with human or porcine insulin did not have any significant influence on receptor binding properties of the two diabetic groups investigated. Absolute receptor number and affinity of both diabetic groups were within the range of healthy control subjects irrespective of treatment with human or porcine insulin.

Insulin receptors on erythrocytes in normal and obese pregnant women: comparisons to those in nonpregnant women during the follicular and luteal phases

Insulin receptors on erythrocytes were studied in nonpregnant women (n = 14) during the follicular and luteal phases, and in pregnant women in the third trimester with normal body weight (n = 14), with weight gain over 14 kg during pregnancy (n = 7), and with obesity before pregnancy (n = 7). Women with increased reticulocytes in the blood were excluded from this study. Insulin binding was slightly decreased in nonpregnant women during the luteal phase, as compared with the binding during the follicular phase. Insulin binding in normal pregnant women was comparable to that in nonpregnant women during the luteal phase. The number of receptors was reduced in those women who gained an excessive amount of body weight during pregnancy or in those pregnant women who were previously obese. These results suggest that an increased insulin resistance during pregnancy, compared to the luteal phase in nonpregnant women, cannot be explained by the changes in insulin receptors but that the reduction in insulin receptors might be one of the causes of the deterioration in carbohydrate metabolism in obese women in late pregnancy.

Insulin receptor binding and insulin action in human fat cells: effects of obesity and fasting

We have studied (125I)-insulin binding and insulin dose response relationships of (14C)-methylglucose transport conversion of (14C)-glucose to CO2 and total lipids, and lipolysis at 37 degrees C and pH 7.4 in adipocytes from obese patients before (n = 15) and after fasting for 10 days (n = 6). Studies of adipocytes from obese before fasting showed a significant reduction of insulin binding when expressed to cell surface area and rightward shifts of the insulin dose response curves (decreased insulin sensitivity) for glucose transport, glucose oxidation, lipogenesis and antilipolysis. The decreased insulin sensitivity of adipocytes from obese was most likely the functional consequence of the impaired insulin binding. Moreover, decreased maximal glucose transport capacities were present in rat cells from obese both in the basal and maximally insulin stimulated states. Similarly, the percentage response above basal level to maximal insulin stimulation of glucose oxidation and lipogenesis was impaired to these cells. The latter findings suggest post receptor defects localized both to the transport system per se and to intracellular mechanisms involved in the metabolism of glucose. Conversely, the post receptor pathways for the insulin induced antilipolysis was intact in fat cells from obese man. Studies after fasting showed an increase of adipocyte insulin binding accompanied by an increased sensitivity to the antilipolytic effect of insulin with unchanged maximal responsiveness. However, due to marked post receptor alterations, the insulin stimulated glucose utilization was severely blunted. Thus, the glucose transport system of adipocytes from all fasted subjects was totally unresponsive to insulin, while some of the fasted patients had a slight response of glucose oxidation and lipogenesis in the presence of insulin in maximally effective concentrations.