Decreased expression of insulin-sensitive glucose transporter mRNA (GLUT-4) in adipose tissue of non-insulin-dependent diabetic and obese patients: evaluation by a simplified quantitative PCR assay

Impaired cellular uptake and utilization of glucose is the hallmark of non-insulin-dependent-diabetes (NIDDM). We have developed a quantitative assay to probe the expression of glucose-transporter genes in tissues derived from patients with NIDDM. Using the polymerase chain reaction (PCR), we assessed levels of expression of the insulin responsive glucose transporter GLUT-4 in adipose tissue of patients with NIDDM and in obese patients. We report that expression of GLUT-4 is reduced in NIDDM and in obesity associated with hyperinsulinemia and insulin resistance. These results suggest that reduction of GLUT-4 levels in the adipose cell plays an important role in the pathogenesis of insulin resistance, an early feature of NIDDM.

Treatment with a gonadotropin-releasing hormone agonist in acne or idiopathic hirsutism

Six women with acne and six women with hirsutism were treated with the GnRH analog [D-Ser(Bu(t))6] LHRH-(1-9)ethylamide (Buserelin) for 6 months (nasal spray, 1,200 micrograms/day) to suppress ovarian steroidogenesis. All women were eumenorrheic and did not demonstrate any adrenal or ovarian dysfunction. During treatment, ovarian steroids, LH and FSH decreased, while DHEA-S showed minor modifications; the clinical score for both acne and hirsutism showed a significant reduction. Moreover, acne and hirsutism were still well controlled 6 months after therapy. Gonadal function resumed in all patients after discontinuation of therapy. Three patients suffered from hot flashes from the 4th month. These data demonstrate that suppression of ovarian steroid secretion might be an efficient treatment in women suffering from acne or idiopathic hirsutism, indicating that ovarian steroids may have a key-role in the pathogenesis of these conditions.

Effects of diabetes mellitus on structural and functional properties of erythrocyte membranes

Diabetic patients present alterations in the activity of a number of enzymes of the plasma membrane. The aim of this study was to verify if the modifications of the enzymatic activities in diabetes mellitus are associated with structural alterations of the cellular membrane. By means of the freeze-fracturing technique, we studied the structure of erythrocyte membranes from 15 insulin-dependent diabetic patients (24-43 years) and 15 age-matched healthy subjects (26-47 years). The kinetic properties of the Na+/K(+)-ATPase of the same membranes were also investigated. The Na+/K(+)-ATPase of the erythrocyte plasma membrane shows an uncompetitive inhibition in the diabetic subjects. As for the freeze-fracturing results, the intramembrane particles of the erythrocyte membranes from diabetic patients appear more clustered with respect to those obtained from controls. The uncompetitive inhibition of the enzyme suggests the presence of conformational modifications of the protein. This hypothesis is supported by the freeze-fracture results which indicate that the integral protein constituents of the membrane in diabetes tend to aggregate. Modifications of the interactions between the enzymatic subunits and the membrane lipid environment might be at the basis of the Na+/K(+)-ATPase alteration in diabetes.

A novel endothelial tyrosine kinase cDNA homologous to platelet-derived growth factor receptor cDNA

Degenerate oligonucleotide primers complementary to the highly conserved subdomains III and VIII of subclass III tyrosine kinase receptors (TKr-III) were utilized to amplify rat aortic cDNA by polymerase chain reaction. Most of the cloned DNA products were rat platelet-derived growth factor receptor beta and macrophage-colony stimulating growth factor receptor cDNAs. Screening of the clones with probes coding for the receptor-specific kinase insert domain allowed the identification of a novel putative TKr-III cDNA, which hybridized with a approximately 6.1 kb mRNA with a distinctive tissue distribution. In situ hybridization on rat tissues and Northern analysis of cultured cells indicate that endothelial cells express a novel putative TKr-III mRNA.

Androgens increase insulin receptor mRNA levels, insulin binding, and insulin responsiveness in HEp-2 larynx carcinoma cells

Androgen receptors have been found in human larynx and androgens have been supposed to play an important role in promoting the growth of laryngeal carcinomas. The molecular mechanism underlaying this phenomenon is not at all understood. Aim of this work was to investigate the effects of two androgens (testosterone and dihydrotestosterone) on insulin receptor mRNA levels and insulin binding activity as well as on either metabolic or growth-promoting actions of insulin in a human larynx carcinoma cell line (HEp-2). We found that HEp-2 cells express a high affinity insulin receptor. Both androgens significantly increase insulin receptor mRNA levels and insulin receptor number in HEp-2 cells. Insulin action, evaluated either as total glucose utilization or as [3H]thymidine incorporation into DNA, significantly increased in HEp-2 treated with androgens in comparison to control cultures. Altogether, our data allow us to speculate that the increased insulin effectiveness we observed in the larynx carcinoma cell line HEp-2 after androgen treatment might be involved in the regulation of larynx cancer cells growth.

Modifications in platelet membrane transport functions in insulin-dependent diabetes mellitus and in gestational diabetes

The pathogenesis of plasma membrane alterations present in diabetes mellitus is unclear. To add new insights to the question, platelet membrane properties were evaluated in 16 women presenting impaired glucose tolerance at the 28-29th week of gestation (GDM) and in 8 women with insulin-dependent diabetes mellitus (IDDM). 15 healthy pregnant women (HPW) and 21 healthy non-pregnant (HNPW) women were the control group for GDM and IDDM, respectively. Pregnancy (HPW vs. HNPW) provoked an increase in Ca(2+)-ATPase activity and a decrease in membrane fluidity; in contrast, Na+/K(+)-ATPase, intracellular free Ca2+ concentrations, membrane cholesterol and phospholipid content did not vary. Both GDM and IDDM showed lower Na+/K(+)-ATPase activity and higher Ca2+ concentration, compared to HPW and HNPW, respectively, whereas Ca(2+)-ATPase activity was higher only in IDDM; furthermore, membrane fluidity was lower in GDM and higher in IDDM. Finally, GDM showed higher membrane cholesterol content. Both GDM and IDDM showed a very good metabolic control so that variations reported cannot be due to hyperglycemia; it is tempting to suggest that membrane variations are present before the clinical metabolic alteration. Furthermore, both GDM and IDDM were on insulin therapy, therefore: (i) insulin may be the pathogenetic factor of higher intracellular free Ca2+ concentrations and lower Na+/K(+)-ATPase activity since they both varied accordingly in GDM and IDDM, but not of (ii) changes in Ca(2+)-ATPase, membrane fluidity and cholesterol content which did not vary accordingly in GDM and IDDM.

Diabetes mellitus induces red blood cell plasma membrane alterations possibly affecting the aging process

Various alterations of red blood cell (RBC) plasma membrane appear both in diabetes mellitus and during the physiological aging process. Diabetes mellitus decreases RBC life-span; therefore, it may change the plasma membrane by acting through its effect on the aging process. In order to clarify the issue, RBCs from normal subjects and insulin-dependent diabetic patients were fractionated in five subpopulations of different mean age (fraction 1: early young RBC, fraction 5: mature RBC). Thereafter, plasma membranes were prepared and enzymatic activities, membrane fluidity and lipid peroxidation were evaluated. NA+, K(+)-ATPase activity decreased during aging and it was higher in all RBC subpopulations from normal subjects in comparison to diabetic patients. Next, lipid peroxidation and fluidity increased during aging in both the study groups; in this case, however, in all subpopulations, except for that from fraction 1, RBCs from diabetic patients showed higher membrane fluidity and lipid peroxidation in comparison to normal subjects. Data herein reported suggest that diabetes mellitus affects the plasma membrane independently of (lipid peroxidation and fluidity) or dependently on (Na+, K(+)-ATPase) its effect on aging. In the case of lipid peroxidation and fluidity diabetes mellitus seems to affect the membrane by decreasing RBC life span, whereas in the case of Na+K(+)-ATPase it seems to alter this enzymatic activity which in turn might affect RBC aging. Acetylcholinesterase activity decreased during aging in RBCs from normal subjects, but it increased in RBCs from diabetic patients; RBC subpopulation from fraction 1, on the other hand, showed similar values in normal subjects and diabetic patients. In this case the effect of diabetes mellitus appears only during aging.

Evidence that two naturally occurring human insulin receptor alpha-subunit variants are immunologically distinct

The IgG from a patient (Italy 2 [I2]) with hypoglycemia, due to autoantibodies to the insulin receptor, was purified on protein A Sepharose into two fractions that were tested in various human tissues and cells. The IgG fraction that bound protein A (absorbed IgG [IgGa]) nearly completely inhibited the binding of 125I-labeled insulin to various cells or tissues (placenta, IM-9, adipocytes, HEp-2-larynx cells, Epstein-Barr virus lymphocytes) but not greater than 50% of 125I-labeled insulin binding to human liver membranes. Conversely, both the IgG fraction from this patient, which did not bind protein A (flow-through IgG [IgGb]), and the IgGa fraction from a second similar patient (Italy 1 [I-1]) almost completely inhibited the binding of 125I-labeled insulin to liver membranes. The IgGa fraction from patient I-2 did not change receptor affinity because 50% inhibition of 125I-labeled insulin binding was not affected by either the presence or absence of these IgG fractions. Furthermore, liver binding data were not due to cross-reaction of 125I-labeled insulin to the insulinlike growth factor I receptor, and treatment of liver membranes with neuraminidase did not alter the inhibitory effect of the IgGa fraction from patient I-2 on 125I-labeled insulin binding to liver. Binding inhibition experiments performed with cells transfected with and overexpressing the -12 (human insulin receptor [HIR]-A) or the +12 (HIR-B) variant of HIR revealed that the IgGa fraction from patient I-2 inhibited 125I-labeled insulin binding to the HIR-A receptor but not to the HIR-B receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that human and porcine insulin differently affect the human insulin receptor: studies with monoclonal anti-insulin receptor antibodies

Binding studies have been carried out with radioiodinated monoclonal antibodies directed to various epitopes of the insulin receptor in order to detect differences between human and porcine insulin in the interaction with the human insulin receptor. Human insulin was more effective that porcine insulin at inhibiting the binding of 125I-MA-5 to IM-9 cells, Hep-2 human larynx cells and human placenta membranes. On the contrary, human and porcine insulin showed similar inhibitory effect on the binding of two other labeled anti-insulin receptor monoclonal antibodies, thus ruling out the possibility that results were due to experimental artifacts. Although several interpretations are possible, data reported suggest that human insulin and porcine insulin might differently affect the insulin receptor, even if, the biological significance of these findings remains unknown.

Modifications induced by gestational diabetes mellitus on cellular membrane properties

Alterations in erythrocyte plasma membrane properties (enzymatic activities and membrane fluidity) have been observed in patients affected by insulin-dependent diabetes mellitus (IDDM) and non-insulin-dependent diabetes mellitus (NIDDM). In order to verify whether these alterations are present also in gestational diabetes mellitus (GDM) we studied the plasma membranes obtained from two different cellular types (erythrocyte from both mother and cord blood and placenta syncytiothrophoblast cell) of 16 healthy pregnant women and 15 women affected by GDM. The following determinations were performed on the membrane preparations: Na+/K(+)-ATPase activity, acetyl-cholinesterase (AchE) activity, membrane fluidity and cholesterol:phospholipid ratio. We observed a reduction of both enzymatic activities and a decrease of membrane fluidity in maternal and cord blood erythrocytes and in syncytiotrophoblast plasma membranes in GDM pregnant women in comparison with controls. The cholesterol to phospholipid ratio was significantly lower in the erythrocyte membranes of women affected by GDM than in normal pregnant women, while it was increased in the cord blood erythrocyte membranes and in placental membranes in GDM in comparison with controls. The present study found, in GDM patients, a membrane alteration similar to the abnormality reported in IDDM and NIDDM (i.e. decreased Na+/K(+)-ATPase activity), while opposite modifications were observed with regard to other membrane activities and properties. The different membrane alterations observed in GDM with respect to IDDM and NIDDM might be linked to the different degree of metabolic control, on the contrary the reduced Na+/K(+)-ATPase activity might be a primary event in the pathogenesis of diabetes mellitus per se and might constitute a signal of high risk of developing the disease later in the women affected by GDM during pregnancy.

[In vitro structural aspects of the human trophoblastic cell]

Maternal- fetal exchanges are mainly regulated by trophoblast, which displays an active role during embryo growth. Trophoblast organization into a syncytial layer involves structural and functional steps that may be monitored and better elucidated by "in vitro" studies. In light of this, we have carried out morphological and biochemical analyses in order to evaluate 1) the syncytiotrophoblast formation in culture (48 h, 5-30 days) the Na+/K+ATPase activity and 3) the plasmalemmal microviscosity changes occurring during "in vitro" trophoblast production. Morphological and biochemical modulations have been pointed out.

Altered cellular Ca2+ and Na+ transport in diabetes mellitus

Platelet intracellular Ca2+ concentration ([Ca2+]i) and its response to stimuli (ADP and thrombin) were studied in 15 insulin-dependent and 22 non-insulin-dependent diabetes mellitus patients with the fluorescent probe Fura 2. The activity of Ca2(+)-ATPase and Na(+)-K(+)-ATPase, membrane fluidity, and cholesterol and phospholipid content were also determined in platelet membranes. Compared with control subjects, diabetic patients showed 1) increased platelet [Ca2+]i in the resting state, 2) higher Ca2+ levels after stimulation with thrombin and ADP, due entirely to increased resting concentrations, 3) reduced activity of Na(+)-K(+)-ATPase, 4) increased activity of Ca2(+)-ATPase, 5) higher fluidity of the platelet membrane, and 6) increased membrane concentration of total phospholipids. Na(+)-K(+)-ATPase activity was inversely related to platelet [Ca2+]i in each group studied, whereas Ca2(+)-ATPase activity was positively correlated with intracellular Ca2+ levels. The data obtained in diabetic subjects suggest an abnormality in Ca2+ and Na+ transport across the platelet membrane that might be responsible for the reported platelet hyperreactivity to stimuli in diabetes.

Beta-endorphin receptors on cultured and freshly isolated lymphocytes from normal subjects

[125I]-[D-Ala2]-beta EP*) binding to Epstein-Barr Virus (EBV) transformed B lymphocytes or to freshly isolated lymphocytes was characterized. The binding was time-, temperature- and pH-dependent; furthermore, it was reversible and cell concentration dependent. Maximum binding appeared at 15C in Tris buffer (pH 7.6) containing both BSA 0.5% and Bacitracin 0.1 mg/ml. beta EP inhibited BEP* binding to transformed lymphocytes and to freshly isolated lymphocytes by 50% at approximately 4 x 10(-8) M and 8 x 10(-9) M, respectively. Peptides representing amino-acid sequences 1-5, 1-16 and 1-17 of beta EP did not inhibit beta EP binding, neither did the opiates compounds Naloxone, Morphine, Bremazocine and Ethylketocyclazocine. On the contrary, beta EPd (6-31) inhibited beta EP* binding as effectively as beta EP, thus indicating that beta EP* binding to lymphocytes does not involve the N-terminal region of beta EP. 2 x 10(7)/ml freshly isolated lymphocytes bound 1.53 +/- 75%, whereas 2 x 10(6)/ml transformed lymphocytes bound 1.64 +/- 0.75% (mean +/- SD) beta EP* at tracer concentration. EBV transformed lymphocytes and freshly isolated lymphocytes may be useful to study beta EP receptors in humans.

An extracellular domain of the insulin receptor beta-subunit with regulatory function on protein-tyrosine kinase

Anti-insulin receptor monoclonal antibody MA-10 inhibits insulin receptor autophosphorylation of purified rat liver insulin receptors without affecting insulin binding (Cordera, R., Andraghetti, G., Gherzi, R., Adezati, L., Montemurro, A., Lauro, R., Goldfine, I. D., and De Pirro, R. (1987) Endocrinology 121, 2007-2010). The effect of MA-10 on insulin receptor autophosphorylation and on two insulin actions (thymidine incorporation into DNA and receptor down-regulation) was investigated in rat hepatoma Fao cells. MA-10 inhibits insulin-stimulated receptor autophosphorylation, thymidine incorporation into DNA, and insulin-induced receptor down-regulation without affecting insulin receptor binding. We show that MA-10 binds to a site of rat insulin receptors different from the insulin binding site in intact Fao cells. Insulin does not inhibit MA-10 binding, and MA-10 does not inhibit insulin binding to rat Fao cells. Moreover, MA-10 binding to down-regulated cells is reduced to the same extent as insulin binding. In rat insulin receptors the MA-10 binding site has been tentatively localized in the extracellular part of the insulin receptor beta-subunit based on the following evidence: (i) MA-10 binds to insulin receptor in intact rat cells; (ii) MA-10 immunoprecipitates isolated insulin receptor beta-subunits labeled with both [35S]methionine and 32P; (iii) MA-10 reacts with rat insulin receptor beta-subunits by the method of immunoblotting, similar to an antipeptide antibody directed against the carboxyl terminus of the insulin receptor beta-subunit. Moreover, MA-10 inhibits autophosphorylation and protein-tyrosine kinase activity of reduced and purified insulin receptor beta-subunits. The finding that MA-10 inhibits insulin-stimulated receptor autophosphorylation and reduces insulin-stimulated thymidine incorporation into DNA and receptor down-regulation suggests that the extracellular part of the insulin receptor beta-subunit plays a role in the regulation of insulin receptor protein-tyrosine kinase activity.

Enzymatic deglycosylation of human thyroglobulin: fluorescence studies

The interaction between the carbohydrate and the amino acid residues in human thyroglobulin has been studied. Previous reports showed that the removal of the two terminal carbohydrates of the complex chains leads to an increase in thyroglobulin binding to thyroid membranes. In our study, after enzymatic release with glycosidases of the sugar moieties from thyroglobulin, a time-dependent decrease in tryptophan fluorescence has been observed. This decrease was also associated with a shift in the emission peak from 335 to 340 nm. The strong quenching of tryptophan emission was also accompanied by a decrease in the exposure of tryptophan residues, as shown by a Stern-Volmer analysis with the neutral quencher acrylamide. These data, together with the increase in fluorescence of the dansylated deglycosylated thyroglobulin, strongly suggest that a significant conformational change of thyroglobulin follows the deglycosylation of the protein.

Species specificity of insulin binding and insulin receptor protein tyrosine kinase activity

The effect of monoclonal anti-insulin receptor antibody MA 10 on [125I]insulin binding and on insulin receptor protein tyrosine kinase activity was investigated in human and rat tissues. It was observed that MA 10 inhibits insulin binding to human, but not rat, tissues while inhibiting insulin-stimulated receptor autophosphorylation and protein tyrosine kinase activity in both human and rat tissues. These data suggest that MA 10 is directed against a region of the insulin receptor that is in between the insulin-binding domain and the beta-subunit and that in human, but not rat, tissues, this region is involved in insulin binding.

Regulation of insulin receptor-associated tyrosine kinase by a polyclonal IgG

The effect of a polyclonal anti-insulin receptor antibody (pIgG) on the insulin receptor tyrosine kinase (IRTK) activity toward poly-(Glu-Tyr) was examined using wheat germ agglutinin agarose-purified insulin receptors from rat liver membranes. The main effect of pIgG was a reduction of Vmax (from 60.8 to 31.8 pmol/min/mg), without changes of Km, when IRTK was activated by insulin. In contrast, when IRTK was activated by ATP preincubation, pIgG was unable to affect the reaction, suggesting that IRTK possesses at least two regulatory mechanisms, one of which can be affected by pIgG.

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.

Insulin-like growth factor I (IGF I) receptor autophosphorylation and kinase activity. Effect of a human polyclonal antibody (pIgG)

IGF I receptor is a tyrosine kinase capable of phosphorylating the receptor itself and other substrates. A high degree of homology does exist in tyrosine kinase domain among receptors for several polypeptide growth factor receptors and this enzymic activity has been indicated as a possible mediator of biological action. Nevertheless growth factor receptors possess peculiar specificities both in their functions and tissue distribution. A human polyclonal IgG (pIgG), previously characterized as anti insulin receptor antibody, able to inhibit insulin receptor kinase activity, was used to further investigate subunit homologies and differences in antigenicity and functional regulation between IGF I and insulin receptors, IGF I receptor tyrosine kinase was stimulated by a IGF I analog (aIGF I), produced by DNA recombinant technology, pIgG was able to inhibit IGF I receptor kinase activity, thus revealing antigenic homologies between the kinase domains of insulin and IGF I receptors. However the more pronounced inhibition of IGF I receptor-compared with insulin receptor kinase activity by pIgG suggests the existence of different regulatory mechanisms.

Inhibition of insulin and epidermal growth factor (EGF) receptor autophosphorylation by a human polyclonal IgG

The immunoglobulin G of a polyclonal antiserum (pIgG) from a patient with insulin resistance and hypoglycemia was tested for its ability to inhibit insulin binding and to affect the autophosphorylation of partially-purified insulin receptors extracted from rat liver membranes. pIgG, when added 4 hr prior to insulin, inhibited subsequent insulin binding by 50% at 30 micrograms added protein; however, insulin previously bound to the receptor could not be displaced by a 4 hr subsequent exposure of up to 70 micrograms pIgG. pIgG, independent of its effect on insulin binding, inhibited both basal and insulin-stimulated autophosphorylation of the insulin receptor in a dose-dependent manner with a half maximal effect at 3.3 to 7 micrograms protein. Furthermore, pIgG also reduced basal autophosphorylation of the EGF receptor. The effect of pIgG to inhibit basal autophosphorylation of insulin and EGF receptors, together with its ability to reduce autophosphorylation of insulin receptors fully occupied by insulin, imply that the effect of pIgG on receptor autophosphorylation is largely independent of its effect on ligand binding. Moreover, these findings suggest that pIgG may inhibit autophosphorylation by acting on domains which are similar in the insulin and EGF receptors.

Tissue-specific antibodies against the fibroblast insulin receptor in a patient with lupus nephritis and hypoglycemia

We recently reported that the serum from a patient with lupus nephritis, insulin resistance, and hypoglycemia contains multiple populations of antibodies directed at the human insulin receptor. In the present study, we found a subpopulation of antibodies (eluted from a protein A-Sepharose affinity column at pH 4.3) directed at the human fibroblast insulin receptor. When tested against human placental membranes, IM-9 lymphocytes, circulating monocytes and erythrocytes, and isolated adipocytes, the antibody subpopulation did not compete with 125I-insulin for binding to its receptor. In contrast, the antibody subpopulation competed with 125I-insulin for binding to the human fibroblast insulin receptor. This antibody subpopulation stimulated [3H]alpha-aminoisobutyric acid [( 3H]AIB) uptake to these cells. Unlike the effect of insulin, however, this regulation of transport was not antagonized by a mouse monoclonal antibody to the human insulin receptor that inhibits 125I-insulin binding. These studies indicate, therefore, that a tissue-specific antibody subpopulation can occur spontaneously in patients with antibodies to the human insulin receptor. Furthermore, they indicate the presence of anti-insulin receptor autoantibodies specifically directed against a tissue that is not primarily involved in glucose metabolism.

Human autoantibodies directed against the human, but not the rat, insulin receptor

Prior studies with monoclonal antibodies produced against the human insulin receptor in mice revealed that these antibodies may be species specific. Whether species-specific antibodies to the insulin receptor occur spontaneously in patients, however, has not been previously investigated. Recently, we found that the serum immunoglobulin G from a patient with lupus nephritis, insulin resistance, and hypoglycemia contained multiple subpopulations of antibodies directed at the human insulin receptor. We report herein that one such subpopulation has a high affinity for the human insulin receptor. This antibody subpopulation at 10 nM half-maximally inhibited [125I]insulin binding to human IM-9 lymphocytes, circulating erythrocytes and monocytes, isolated adipocytes, and placenta membranes. In contrast, this antibody subpopulation did not inhibit [125I]insulin binding to isolated rat adipocytes and hepatocytes, even at concentrations as high as 100 nM. These studies indicate that species-specific antibodies can occur spontaneously in patients with antiinsulin receptor antibodies.

Characterization of the serum from a patient with insulin resistance and hypoglycemia. Evidence for multiple populations of insulin receptor antibodies with different receptor binding and insulin-mimicking activities

The serum from a patient with lupus nephritis, insulin resistance, and hypoglycemia was studied. This serum both inhibits the binding of 125I-insulin to its receptor and has insulin-like activity on fat cells (see refs. 1 and 2). The IgG fraction from this patient's serum one-half maximally inhibited 125I-insulin binding to IM-9 cells at 1 microM, but did not markedly inhibit 125I-monoclonal antibody binding even at concentrations as high as 4 microM. The IgG was then subjected to affinity chromatography on a protein A-Sepharose column. Four protein peaks were eluted from this column by a step pH gradient from 5.5 to 2.3. Three of the four peaks inhibited 125I-insulin binding to its receptors, but none was more potent than the unfractionated IgG itself. One IgG peak, however, was able to inhibit 125I-monoclonal antibody binding at tenfold lower concentrations than the unfractionated IgG. When the ability of the four IgG fractions to stimulate 2-deoxy[3H]-D-glucose transport in rat adipocytes was studied, two fractions showed stimulatory activity. Compared with unfractionated IgG, one had a weak ability to inhibit 125I-insulin binding, but tenfold more potency to mimic insulin action. The other had a strong ability to inhibit 125I-insulin binding but less potency to mimic insulin action. These studies indicate, therefore, that the serum contains multiple populations of antibodies to the insulin receptor, or portions of the plasma membrane adjacent to the receptor, which have different biologic effects.

Red blood cell age, pyruvate kinase activity, and insulin receptors. Evidence that monocytes and RBCs may behave differently

Data emerging from insulin receptor studies performed on red blood cells (RBCs) and monocytes from the same subject are not always in agreement; dichotomy might occur since variations in mean RBC age are not taken into account or because insulin receptors on the two cell types behave differently. In the present investigation RBCs from normal male subjects were separated into five populations of different mean age by means of centrifugation of RBCs on a discontinuous gradient of buffered Percoll for 10 min at 1000 X g. Insulin binding varied significantly depending upon the RBC population tested and was closely correlated to the activity of pyruvate kinase (r2 = 0.86), a well-known marker of RBC age. These data suggested that pyruvate kinase assay might be helpful in studies of RBCs. To confirm this hypothesis, RBCs from 10 normal male subjects and 13 male patients with hemolytic anemia were studied; insulin binding was correlated to pyruvate kinase activity. By adjusting insulin binding to 2 X 10(9) RBCs/ml the range of data was abnormally high, but it became acceptable after adjusting insulin binding to pyruvate kinase activity (0.75 U/2 X 10(9) RBCs). The overall data indicated that insulin binding was highly correlated to pyruvate kinase activity (r2 = 0.82) but only slightly to reticulocyte number (r2 = 0.56) since not only reticulocytes but also erythrocytes lose receptors during maturation. Pyruvate kinase activity was measured in RBCs from normal men and from normally menstruating women at the seventh and twenty-fourth days of the cycle; results demonstrated that adjustment of data, according to mean RBC age, broadens dichotomy of monocyte and RBC data.(ABSTRACT TRUNCATED AT 250 WORDS)

Circulating anti-insulin receptor antibodies in a patient suffering from lupus nephritis and hypoinsulinemic hypoglycaemia

A 46-year-old female patient suffering from Lupus Nephritis came to our attention in 1981 for severe recurrent hypoglycaemia; she was obliged to eat every 5-7 hr to maintain glucose values not below 1.3-1.6 mM. All known causes of hypoglycaemia were excluded by performing selective angiography of the pancreas and skull, chest and abdominal computerized tomography, as well as stimulation and suppression tests. Oral glucose tolerance, tolbutamide and intravenous insulin (0.4 U/Kg b.w.) tests demonstrated that the patient was highly insulin resistant; furthermore, studies on the patient's red blood cells suggested that her insulin receptors were completely unable to bind insulin. Studies carried out to reveal the reason for this binding inhibition demonstrated that red blood cells from normal subjects as well as adipocytes from normal rats incubated with the patient's serum did not bind insulin (50% inhibition occurring at about 1:30 serum dilution). Insulin binding inhibitors were found in the fraction of the serum precipitated by ammonium sulphate. The serum cleared of IgG fraction was unable to affect insulin binding. These data demonstrate that the serum from the female patient investigated contained anti-insulin receptor antibodies blocking the binding of insulin to its receptors. Plasmapheresis improved the patient's metabolic status. The clinical picture would suggest that recurrent hypoglycaemia was caused by anti-insulin receptor antibodies acting as insulin on target cells.

Effects of prednisolone and dexamethasone in vivo and in vitro: studies of insulin binding, deoxyglucose uptake and glucose oxidation in rat adipocytes

We have studied the effects of dexamethasone and prednisolone in vitro and in vivo on insulin binding, deoxyglucose uptake and glucose oxidation in rat adipocytes. In the studies in vivo, rats were treated for 22 h with dexamethasone (30 micrograms/kg) or prednisolone (200 micrograms/kg). Following sacrifice, adipocytes were prepared and the results demonstrated that cells from prednisolone treated rats showed a 17% increase in insulin binding and increased rates of basal and insulin stimulated deoxyglucose uptake and glucose oxidation. Conversely, dexamethasone administration resulted in a 22% decrease in insulin binding, and decreased rates of deoxyglucose uptake and glucose oxidation by the cells. Thus, prednisolone and dexamethasone had opposite effects in vivo. In contrast to the opposite effects of the two glucocorticoids in vivo, dexamethasone and prednisolone (each at a concentration of 1 mumol/l) had similar effects on adipocytes in vitro. Incubation of adipocytes with the steroids did not alter insulin binding, while both agents led to a comparable decrease in the rates of basal and insulin stimulated deoxyglucose uptake and glucose oxidation. Thus, dexamethasone and prednisolone have opposite effects on adipocyte glucose metabolism in vivo but have similar effects in vitro.

Changes in insulin receptors during oral contraception

Combined estrogen/progestagen oral contraceptives (OC) have been reported to be associated with a deterioration of glucose tolerance and a decrease in insulin sensitivity; thus, since it has been suggested that steroids affect insulin receptor properties, the influence of OC on insulin receptors was investigated. The study groups were composed of nine normal menstruating women (controls), nine pill users, and two healthy women on OC for the first time. Insulin receptors on monocytes were evaluated at 7-day intervals during the 28 days between menses. Insulin receptor concentration and/or affinity did not show any variation in pill users during the test period and did not differ from values observed in controls in the luteal phase; consequently, the insulin receptor concentration in pill users is lower than that during the follicular phase or in men. The physiological variation of insulin receptor concentration and the increase of receptor affinity in the midfollicular phase, which characterize the normal menstrual cycle, are therefore abolished by OC. This effect occurs rapidly because it was also evident in the two women on OC for the first time. No difference was observed in fasting blood glucose and serum immunoreactive insulin concentrations between control subjects and pill users. The present data appear to confirm that sex steroids affect the insulin receptor and lend further support to the concept that caution must be used in clinical studies of insulin receptors when women are included. In addition, the results suggest that insulin receptors may play a role in the glucose intolerance and insulin insensitivity which have been described in pill users.

Insulin receptors on monocytes and erythrocytes from obese patients

Insulin receptors were studied in monocytes and erythrocytes [red blood cells (RBC)] isolated from 15 normal and 15 nondiabetic obese outpatients on an unrestricted diet. Insulin binding on both monocytes (P < 0.001) and RBC (P < 0.01) was higher in normal than in obese subjects due to different receptor concentrations. In some obese patients, binding to monocytes was decreased, while binding to RBC was normal. These data demonstrate that obese out-patients on an unrestricted diet have a reduced number of insulin receptors. It is suggested that interpretation of insulin binding based upon RBC should be used with caution, since a discrepancy exists in some subjects in the results obtained with these cells and monocytes.

Arginine does not influence insulin binding on circulating monocytes

Glucose ingestion, food intake or acute exercise produced rapid variations in insulin binding on monocytes. Insulin seems to play a minor or any role in this phenomenon in contrast pancreatic glucagon might be involved since it usually rises when an increase in insulin receptor affinity has been observed. To investigate the role of pancreatic glucagon we have studied the effect of arginine infusion on monocyte insulin receptor in five normal subjects. Results indicate that the aminoacid employed does not induce any change in insulin receptor affinity and concentration suggesting that the simultaneous increase in plasma insulin and pancreatic glucagon levels does not exert any action.

Differences in insulin receptors between men and menstruating women and influence of sex hormones on insulin binding during the menstrual cycle

Specific binding of [125I]insulin to circulating monocytes and erythrocytes from nine normal menstruating women and nine normal men was determined during a 28-day period (one sample every 7 days). In women, insulin binding was higher to both monocytes (P less than 0.001) and erythrocytes (P less than 0.02) in the follicular phase than in the luteal phase. In men, insulin binding to monocytes was similar to the follicular phase values for women; however, insulin binding to erythrocytes from men showed higher values than insulin binding to erythrocytes from women in both the follicular (P less than 0.001) and luteal (P less than 0.001) phases. These differences were due primarily to changes in receptor concentration rather than receptor affinity. An inverse relationship was found between insulin binding to monocytes and levels of 17 beta-estradiol, progesterone, and 17 alpha-hydroxyprogesterone; this relationship was not observed in insulin binding to erythrocytes. The present data, therefore, suggest that sex hormones may play a role in the control of insulin receptors. Furthermore, it appears that other factors exist during the follicular phase that lower insulin binding to erythrocyte insulin receptors. If insulin receptors on circulating cells reflect the behavior of the main insulin target tissues, the present data might in part explain the reduction in glucose tolerance reported by various authors in the second half of the menstrual cycle.

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.

Response of insulin receptors to oral glucose in normal subjects

Insulin binding to circulating monocytes was studied in ten male volunteers before and 1, 2, and 5 hours after the oral intake of 100 g of glucose. Results indicate an increase in the specific cell binding fraction with a change in receptor affinity 5 hours after glucose. Since the same changes appear 3 hours after food intake they are probably not directly induced by insulinemia.

Aggregation-induced stability of dexamethasone receptors in rat kidney

The stability of the dexamethasone-receptor complex of rat kidney cytosol was studied using homogenizing media of varying pH and composition. It was found that the complex is less stable with buffers usually employed for the study of steroid receptors such as Tris, EDTA etc., whereas the stability increases considerably with a solution composed of monothioglycerol 12 mmol/l and glycerol 5% in distilled water. Sepharose 4-B column chromatography revealed that the increased stability was associated with a larger form (probably an aggregate) of the receptor-steroid complex.

Specificities of rabbit anti-human insulin receptor antibodies

Human insulin receptors obtained from normal human placentae were highly purified by affinity chromatography and used to immunize rabbits. The immunological response was evaluated in order to reveal the presence of antibodies blocking the binding of insulin to monocytes of normal subjects. Since no blocking activity was found IgG from rabbits were coupled to agarose in order to evaluate the presence of antibodies directed to determinant(s) other than the insulin binding site. One rabbit was found to produce antibodies binding the insulin receptor on a site different from the insulin binding site.

The effect of food intake on insulin receptor in man

Insulin binding to circulating monocytes was studied in 22 normal volunteers before and 1, 3 and 5 h after a 1400 Kcal meal. Results indicate that 3 h after food intake there is an increase in the specific cell binding fraction (P less than 0.001) with a change in receptor affinity. Data emerging from the present study demonstrate that there are rapid changes in insulin receptor properties during the day. These changes probably play a role in the regulation of the hormonal and metabolic pattern in normal subjects.

Insulin receptors during the menstrual cycle in normal women

Specific binding of 125I-insulin to circulating monocytes from eight normal menstruating women, four postmenopausal women and four men were studied four times during a 28-day period (one sample at 7-day intervals). Data indicate the presence of a higher specific cell binding fraction in the follicular phase compared to the luteal phase due to changes in insulin receptor concentration. No changes were observed in men or postmenopausal women during the same period of time suggesting that sex hormones should be included among the factors influencing insulin receptors.