Biomedical subjects

F Giorgino

Publications and source records attributed to F Giorgino.

At least 37 records · Page 2Linked to original sources

PubMed1999

Fiber intake, serum cholesterol levels, and cardiovascular disease in European individuals with type 1 diabetes. EURODIAB IDDM Complications Study Group.

OBJECTIVE: A cross-sectional analysis of dietary fiber intake was performed in European type 1 diabetic patients enrolled in the EURODIAB IDDM Complications Study to explore its potential relationship to serum cholesterol levels and the prevalence of cardiovascular disease (CVD). RESEARCH DESIGN AND METHODS: Dietary intake was assessed by a standardized 3-day dietary record. For analysis of fiber intake (total, soluble, and insoluble) and its associations with CVD (past history or electrocardiogram abnormalities), complete data were available from 1,050 male and 1,012 female individuals. Relationships of fiber intakes to serum cholesterol levels (total, HDL, and LDL cholesterol) were examined in 926 men and 881 women with type 1 diabetes. RESULTS: Higher intakes of total fiber (g/day) were independently associated with significantly higher levels of HDL cholesterol in male (P = 0.01) and female individuals (P = 0.03). Fiber intakes of men with type 1 diabetes were also inversely related to ratios of total cholesterol to HDL cholesterol (P = 0.0001) and levels of LDL cholesterol (P = 0.0002). A protective effect of total fiber intake against CVD was observed for female subjects, where a significant trend was maintained after adjustment for potential confounders, including energy and saturated fat (P = 0.03 vs. P = 0.2 in men). Results were similar in separate analyses of soluble and insoluble fiber. CONCLUSIONS: The present study demonstrates that higher fiber intakes are independently related to beneficial alterations of the serum cholesterol pattern in men and to a lower risk for CVD in European insulin-dependent women. Beneficial effects can already be observed for fiber amounts within the range commonly consumed by outpatients with type 1 diabetes.

Adult↗

PubMed1998

Insulin-stimulated cell growth in insulin receptor substrate-1-deficient ZR-75-1 cells is mediated by a phosphatidylinositol-3-kinase-independent pathway.

In many human breast cancers and cultured cell lines, insulin receptor expression is elevated, and insulin, via its own insulin receptor, can stimulate cell growth. It has recently been demonstrated that the enzyme phosphatidylinositol-3-kinase (PI3-K) mediates various aspects of insulin receptor signaling including cell growth. In order to understand the mechanisms for insulin-stimulated cell growth in human breast cancer, we measured insulin-stimulable PI3-K activity in a non-transformed breast epithelial cell line, MCF-10A, and in two malignantly transformed cell lines, ZR-75-1 and MDA-MB157. All three cell lines express comparable amounts of insulin receptors whose tyrosine autophosphorylation is increased by insulin, and in these cell lines insulin stimulates growth. In MDA-MB157 and MCF-10A cells, insulin stimulated PI3-K activity three- to fourfold. In ZR-75-1 cells, however, insulin did not stimulate PI3-K activity. In ZR-75-1 cells PI3-K protein was present, and its activity was stimulated by epidermal growth factor, suggesting that there might be a defect in insulin receptor signaling upstream of PI3-K and downstream of the insulin receptor. Next, we studied insulin receptor substrate-1 (IRS-1), a major endogenous substrate for the insulin receptor which, when tyrosine is phosphorylated by the insulin receptor, interacts with and activates PI3-K. In ZR-75-1 cells, there were reduced levels of protein for IRS-1. In these cells, both Shc tyrosine phosphorylation and mitogen-activated protein kinase (MAP-K) activity were increased by the insulin receptor (indicating that the p21ras pathway may account for insulin-stimulated cell growth in ZR-75-1 cells). The PI3-K inhibitor LY294002 (50 microM) reduced insulin-stimulated growth in MCF-10A and MDA-MB157 cell lines, whereas it did not modify insulin effect on ZR-75-1 cell growth. The MAP-K/Erk (MEK) inhibitor PD98059 (50 microM) consistently reduced insulin-dependent growth in all three cell lines. Taken together, these data suggest that in breast cancer cells insulin may stimulate cell growth via PI3-K-dependent or-independent pathways.

Breast Neoplasms↗

PubMed1998

Divergent effects of short-term, very-low-calorie diet on insulin-like growth factor-I and insulin-like growth factor binding protein-3 serum concentrations in premenopausal women with obesity.

OBJECTIVE: Insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-3 (IGFBP-3) serum concentrations provide a good measure of the biological effects of growth hormone. The aims of the present study were to: (1) investigate the associations of IGF-I and IGFBP-3 with body fat mass and distribution, and (2) evaluate the effects of 3 weeks of very-low-calorie diet (VLCD) (318 kcal/day, with 40 g protein, 35 g carbohydrate, and 2 g fat) on IGF-I and IGFBP-3 serum concentrations. RESEARCH METHODS AND PROCEDURES: The study was performed in 21 nondiabetic premenopausal women with obesity (body mass index >27.0 kg/m2; age: ranging from 18 to 48 years). Body fat mass and distribution were measured by computed tomography. RESULTS: Before dietary treatment, IGF-I and IGFBP-3 serum concentrations were inversely associated with visceral adipose tissue (VAT) area (p<0.005 and p<0.05, respectively), but not with either total body fat or subcutaneous adipose tissue area. VLCD produced a significant decrease of body mass index (p<0.001), total body fat (p<0.001), VAT (p<0.005), subcutaneous adipose tissue (p<0.001), IGF-I concentrations (p<0.05), and an increase of IGFBP-3 serum levels (p<0.001). The association of VAT with either IGF-I or IGFBP-3 serum concentrations was not maintained following VLCD. DISCUSSION: Our study suggests that visceral adipose tissue, rather than adiposity per se, accounts for IGF-I and IGFBP-3 serum concentrations, and that rapid weight loss, possibly due to nutritional changes, results in lower IGF-I concentrations, higher IGFBP-3 concentrations, and abrogation of the inverse associations of VAT with IGF-I and IGFBP-3.

Adipose Tissue↗

PubMed1997

Interference of angiotensin-converting enzyme inhibitors on erythropoiesis in kidney transplant recipients: role of growth factors and cytokines.

BACKGROUND: Recent data indicate that factors other than erythropoietin (EPO), such as insulin-like growth factor 1 (IGF-1), can promote erythropoiesis in vitro and correct the anemia of chronic renal failure in vivo. IGF-1 is produced by the liver under growth hormone control, as well as by other sources, including the kidney. The erythropoietic role of growth factors and cytokines and their possible modulation by angiotensin-converting enzyme inhibitors (ACEI) has never been explored. METHODS: This study evaluated the serum levels of EPO, IGF-1, interleukin (IL)-2, IL-3, and granulocyte macrophage-colony-stimulating factor in 40 kidney transplanted patients with or without posttransplant erythrocytosis (PTE) and in 10 living kidney donors. Then, the effect of ACEI therapy on the above pattern was examined in patients with PTE. RESULTS: EPO and IGF-1 serum levels were significantly higher in patients with PTE than in patients without PTE and in living kidney donor subjects. ACEI therapy significantly reduced hematocrit (Hct) as well as circulating IGF-1 and EPO levels. Of note, the decrease in IGF-1 was prominent mainly in those patients whose EPO levels were not significantly modified by ACEI therapy. In all of the patients Hct levels displayed a direct relationship with circulating IGF-1 levels, but not with EPO concentration. Growth hormone did not significantly differ among the groups examined, whereas it steeply increased under ACEI. Finally, no significant difference in IL-2, IL-3, and granulocyte macrophage-colony-stimulating factor serum levels was detected. CONCLUSIONS: IGF-1 seems to play a role in the ACEI-related decrease of Hct in patients with PTE, chiefly in patients without any modification of EPO serum levels.

Adult↗

PubMed1997

Specific increase in p85alpha expression in response to dexamethasone is associated with inhibition of insulin-like growth factor-I stimulated phosphatidylinositol 3-kinase activity in cultured muscle cells.

The stimulation of phosphatidylinositol (PI) 3-kinase by insulin-like growth factor I (IGF-I) in L6 cultured skeletal muscle cells is inhibited by the glucocorticoid dexamethasone. The objective of this study was to investigate the mechanism of dexamethasone action by determining its effects on the expression of the p85alpha and p85beta regulatory subunit isoforms of PI 3-kinase, their coupling with the p110 catalytic subunit, and their association with insulin receptor substrate 1 (IRS-1) in response to IGF-I stimulation. Dexamethasone induced a 300% increase in p85alpha protein content in the L6 cultured myoblast cell line, whereas it increased p110 content by only 38% and had no effect on p85beta. The increase in p85alpha protein was associated with a coordinate increase in p85alpha mRNA. Stimulation with IGF-I induced the association of p85alpha and p85beta with IRS-1, and this was accompanied by increased amounts of the p110 catalytic subunit and markedly increased PI 3-kinase activity in IRS-1 immunoprecipitates. In cells treated with dexamethasone, greater amounts of p85alpha and lower amounts of p85beta, respectively, were found in IRS-1 immunoprecipitates, such that the alpha/beta ratio was markedly higher than in control cells. In spite of the increase in both total and IRS-1-associated p85alpha following dexamethasone treatment, IRS-1-associated p110 catalytic subunit and PI 3-kinase activity were decreased by approximately 50%. Thus, dexamethasone induces a specific increase in expression of the p85alpha regulatory subunit that is not associated with a coordinate increase in the p110 catalytic subunit of PI 3-kinase. As a consequence, in dexamethasone-treated cells, p85alpha that is not coupled with p110 competes with both p85alpha.p110 and p85beta.p110 complexes for association with IRS-1, leading to increased p85alpha but decreased p85beta, p110, and PI 3-kinase activity in IRS-1 immunoprecipitates.

Animals↗

PubMed1997

The adapter protein Grb10 associates preferentially with the insulin receptor as compared with the IGF-I receptor in mouse fibroblasts.

To identify receptor-associated proteins that may contribute to the specificity of insulin and IGF-I signaling responses, a mouse embryo library was screened using the yeast two-hybrid system. Multiple receptor-interactive clones encoding the SH2 domain of the adapter protein Grb10 were isolated. Subsequent cloning of the full-length Grb10 sequence from a mouse fat cDNA library defined a previously unknown Grb10 variant, that appears to be the predominant isoform in mouse tissues. Receptor-deficient R- cells (fibroblasts from mice with homologous disruption of the IGF-I receptor gene) and transfected R- cells expressing either insulin receptors (R-IR cells) or IGF-I receptors (R+ cells) were used to investigate the specificity of Grb10 interaction with the two related receptors. Hormone-activated insulin receptors in R-IR cells coprecipitated with three species, all recognized as Grb10 isoforms by specific Grb10 antibody. Under the same conditions, Grb10 was essentially undetectable in IGF-I receptor immunoprecipitates from stimulated R+ cells. Grb10 association with insulin receptors was maximal at 10 nM insulin stimulation and sustained from 5-10 min after hormone stimulation in R-IR cells. In conclusion, Grb10 interacts preferentially with insulin vs. IGF-I receptors in intact cells and, thus, may have a role in mediating insulin receptor-specific cellular responses.

Animals↗

PubMed1997

Lower androgenicity is associated with higher plasma levels of prothrombotic factors irrespective of age, obesity, body fat distribution, and related metabolic parameters in men.

The purpose of this study was to examine the relationships between androgenic status and plasma levels of both prothrombotic and antithrombotic factors in men, irrespective of obesity, body fat distribution, and metabolic parameters. Sixty-four apparently healthy men, 40 with a body mass index (BMI) greater than 25 kg/m2 (overweight and obese [OO]) and 24 non-obese controls with a BMI less than 25, were selected and evaluated for (1) plasma concentrations of plasminogen activator inhibitor-1 (PAI-1) antigen, PAI-1 activity, fibrinogen, von Willebrand factor (vWF) antigen, vWF activity, and factor VII (FVII) as the prothrombotic factors; (2) plasma levels of tissue plasminogen activator (TPA) antigen, protein C, and antithrombin III as the antithrombotic factors; (3) fasting plasma concentrations of insulin and glucose and the lipid pattern (triglycerides [TG] and total and high-density lipoprotein [HDL] cholesterol) as the metabolic parameters; and (4) free testosterone (FT), dehydroepiandrosterone sulfate (DHEAS), and sex hormone-binding globulin (SHBG) serum levels as the parameters of androgenicity. Body fat distribution was evaluated by the waist to hip ratio (WHR). In OO and non-obese subjects taken together, plasma levels of PAI-1 antigen, fibrinogen, and FVII were inversely associated with FT (r = .255, P < .05, r = -3.14, P < .05, and r = -.278, P < .05, respectively), and the negative relationships of both fibrinogen and FVII with FT were maintained after stepwise multiple regression analysis. Plasma concentrations of PAI-1 antigen and PAI-1 activity were also negatively correlated with SHBG (r = -.315, P < .05 and r = -.362, P < .01, respectively), and these associations held irrespective of the other parameters investigated. None of the antithrombotic and fibrinolytic factors were independently related to serum androgen levels. Subjects with a BMI higher than 25 kg/m2 had higher plasma concentrations of PAI-1 antigen, PAI-1 activity, and fibrinogen as compared with non-obese controls (P < .001, P < .001, and P < .01, respectively). In addition, in OO and control subjects as a whole, multiple stepwise regression analysis showed that the associations of BMI with PAI-1 activity, fibrinogen, vWF antigen, and vWF activity were independent of any other metabolic and hormonal parameters. Plasma concentrations of PAI-1 antigen, PAI-1 activity, and fibrinogen were also directly correlated with WHR in all subjects taken together, irrespective of the other parameters investigated. Evaluation of antithrombotic factors showed that OO subjects had higher TPA plasma concentrations than non-obese controls (P < .001), whereas protein C and antithrombin III did not differ in the two groups. TPA was also directly correlated with BMI (r = .415, P < .001) and WHR (r = .393, P < .001) in all subjects. The results of this study indicate that (1) men with lower FT serum levels have higher fibrinogen and FVII plasma concentrations, and those with lower SHBG serum levels also have higher levels of PAI-1 antigen and activity; (2) irrespective of other factors, obesity per se may account for higher concentrations of PAI-1, fibrinogen, and vWF; (3) plasma levels of PAI-1 (antigen and activity) and fibrinogen correlate independently with WHR; and (4) among the investigated antithrombotic factors (TPA antigen, protein C, antithrombin III), only TPA antigen plasma concentrations are higher in men with abdominal obesity. Thus, because of the increase in several prothrombotic factors, men with central obesity, particularly those with lower androgenicity, seem to be at greater risk for coronary heart disease (CHD). Apparently, this risk is not counteracted by a parallel increase in plasma concentrations of antithrombotic factors.

Adult↗

PubMed1997

Increase in both pro-thrombotic and anti-thrombotic factors in obese premenopausal women: relationship with body fat distribution.

OBJECTIVES: To examine the relationship of obesity, body fat distribution, and fasting plasma insulin concentrations with the plasma levels of both pro-thrombotic and anti-thrombotic factors in premenopausal women. SUBJECTS: 32 obese women with BMI > 28 and 33 age-matched non-obese = women with BMI < 25. MEASUREMENTS: (i) plasma concentrations of plasminogen activator inhibitor-1 antigen (PAI-1 Ag), plasminogen activator inhibitor-1 activity (PAI-1 activity), fibrinogen, von Willebrand factor antigen (vWF Ag), von Willebrand factor activity (vWF activity), and factor VII activity as pro-thrombotic factors; (ii) plasma concentrations of tissue plasminogen activator antigen (t-PA Ag), protein C, and antithrombin III as anti-thrombotic factors; (iii) fasting plasma insulin and glucose concentrations, and the lipid pattern (triglycerides, total and HDL-cholesterol) as metabolic parameters. The body fat distribution was evaluated by measuring the waist circumference and the waist-to-hip ratio (WHR). RESULTS: Obese subjects had higher plasma concentrations of all pro-thrombotic factors as compared to non-obese controls (PAI-1 Ag, P < 0.001; PAI-1 activity, P < 0.05; fibrinogen, P < 0.001; vWF Ag, P < 0.001; vWF activity, P < 0.05; factor VII, P < 0.05). The plasma concentrations of PAI-1 Ag and vWF Ag were directly correlated with the waist circumference independently of other metabolic and non-metabolic variables (P < 0.05). Obese women were also characterized by higher plasma concentrations of anti-thrombotic factors such as t-PA Ag and protein C as compared to non-obese controls (P < 0.001 and P < 0.001, respectively), although these factors were not independently correlated with the waist circumference or the WHR. CONCLUSION: Plasma concentrations of the pro-thrombotic factors are increased in obese women as compared to non-obese controls, and plasma levels of PAI-1 Ag and vWF Ag correlate with central fat accumulation specifically. Plasma concentrations of anti-thrombotic factors (namely protein C and t-PA Ag) are also raised in obese women, but they are not correlated with parameters of body fat distribution. The increase in protein C levels may represent a protective response partly counteracting the increase in pro-thrombotic factors in these individuals.

Adipose Tissue↗

PubMed1997

Gender differences in serum leptin in obese people: relationships with testosterone, body fat distribution and insulin sensitivity.

Testosterone levels are decreased in obese men but increased in obese women. The interplay between gonadal steroids and leptin is, at present, far from being elucidated. This study was carried out to investigate the relationship between serum leptin, plasma insulin, insulin sensitivity and free testosterone in 46 men (29 obese and 17 lean) and 65 premenopausal women (42 obese and 23 lean). In all subjects, anthropometric parameters and serum levels of insulin, leptin, free testosterone (T), dehydroepiandrosterone sulphate and sex hormone-binding globulin were measured. An oral glucose tolerance test (OGTT) and an insulin tolerance test were also performed to determine the insulin sensitivity index. Our results show a significant difference in serum leptin between lean and obese men (3.19 +/- 0.71 vs. 20.28 +/- 0.26 ng mL-1; P < 0.0005) as well as between lean and obese women (10.78 +/- 2.14 vs. 34.79 +/- 2.26 ng mL-1; P < 0.00001). Basal T concentration in the obese men was significantly lower than in the control group (18.6 +/- 1.3 vs. 23.3 +/- 1.4 ng L-1; P < 0.01), whereas in the obese women it was significantly higher than in the control group (2.0 +/- 0.2 vs. 1.3 +/- 0.1 ng L-1; P < 0.05). When multiple linear regression was performed without body mass index (BMI) in the statistical model, leptin was correlated with basal insulin (P < 0.0001), insulin sensitivity (P < 0.0001) and T (P < 0.0001) in both men and women. When BMI was included in the model as an independent variable, leptin was significantly correlated only with BMI (P < 0.0001), the degree of insulin resistance (P < 0.05) and T (only in men, P < 0.05). This study confirms that serum leptin is strongly correlated with the degree of obesity and female sex. The negative correlation between leptin and T in men, independent of BMI, is consistent with the hypothesis that T may possess an inhibitory effect on adipocyte ob gene transcription.

Adipose Tissue↗

PubMed1996

Interaction between the Grb10 SH2 domain and the insulin receptor carboxyl terminus.

Grb10 is a member of a recently identified family of adapter proteins that are thought to play a role in receptor tyrosine kinase-mediated signal transduction. We identified and isolated the Grb10 SH2 domain based on its interaction with the intracellular domain of the insulin receptor beta-subunit using the yeast two-hybrid system. The interaction was specific for the insulin receptor and the insulin-like growth factor-1 receptor, and it required a catalytically active receptor kinase domain and an intact Grb10 SH2 domain. Glutathione S-transferase fusion proteins containing the Grb10 SH2 domain associated in an insulin-dependent manner with insulin receptors from cell lysates and with purified insulin receptors. Co-precipitation experiments revealed the association of cellular Grb10 with hormone-stimulated insulin receptors in cell extracts. The Grb10 SH2 domain did not bind to an insulin receptor lacking 43 amino acids at the carboxyl terminus, and it exhibited highest affinity for a phosphopeptide containing Tyr(P)-1322. Unlike p85 and Syp, which also bind to Tyr(P)-1322, Grb10 was not found to associate with insulin receptor substrate-1. These results suggest that Grb10 is a novel insulin receptor interactive protein and provide direct evidence for an insulin receptor substrate-1-independent function of the insulin receptor carboxyl terminus in protein binding.

3T3 Cells↗

PubMed1996

Body fat accumulation is possibly responsible for lower dehydroepiandrosterone circulating levels in premenopausal obese women.

OBJECTIVE: To determine whether any androgen is independently related with parameters of body fat accumulation and distribution in obese women. DESIGN: Circulating insulin and androgen levels (total testosterone (T), free testosterone (FT), dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), androstenedione, sex hormone binding globulin (SHBG)) and the parameters of body fat accumulation and distribution (body mass index, waist-to-hip ratio, total body fat volume (TBF), visceral adipose tissue area (VAT) and subcutaneous adipose tissue area (SAT) were determined in a population of non-diabetic obese women. SUBJECTS: 28 premenopausal obese women, recruited at the Verona University Hospital Outpatient Clinic. MEASUREMENTS: TBF, VAT and SAT area were quantified by computed tomography. Hormone levels were measured by RIA. RESULTS: SHBG showed an inverse correlation with BMI (r: -0.452, P < 0.05), WHR (r: -0.388, P < 0.05), TBF (r: -0.509, P < 0.01), VAT (r: -0.378, P < 0.05) and SAT (r: -0.449, P < 0.05). DHEA was negatively associated with BMI (r: -0.376, P < 0.05), TBF (r: -0 < 0.05), VAT (r: -0.662, P < 0.001) and SAT (r: -0.401, p < 0.05). T was found to be inversely related with VAT (r: -0.401, P < 0.05). Androstenedione was positively correlated with WHR (r: 0.383, P < 0.05). DHEAS and FT did not show significant associations with BMI, WHR, or any CT-parameters. Stepwise multiple regressions were performed for all androgens: one of the age-adjusted androgens was considered as the dependent variable for each analysis, and insulin, VAT, SAT and all other androgens were entered into the regression model. DHEA was the only hormone to show an independent association (negative) with both SAT (t-value: -3.683, P < 0.01) and VAT (t-value: -2.252, P < 0.05), whereas DHEAS showed an independent positive correlation with SAT (t-value: -2.241, P < 0.05). CONCLUSIONS: Among the androgens, DHEA seems to be the most sensitive to body fat accumulation in premenopausal obese women.

Adipose Tissue↗

PubMed1995

Effects of contractile activity on tyrosine phosphoproteins and PI 3-kinase activity in rat skeletal muscle.

Insulin stimulates signaling reactions that include insulin receptor autophosphorylation and tyrosine kinase activation, insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation, and phosphatidylinositol 3-kinase (PI 3-kinase) activation. Muscle contraction has metabolic effects similar to insulin, and contraction can increase insulin sensitivity, but little is known about the molecular signals that mediate the effects of contraction. To investigate the effects of muscle contraction on insulin signaling, rats were studied after contraction of hindlimb muscles by electrical stimulation, maximal insulin injection in the absence of contraction, or contraction followed by insulin injection. Insulin increased tyrosine phosphorylation of the insulin receptor and IRS-1, whereas contraction alone had no effect. Contraction before insulin injection decreased the insulin effect on receptor and IRS-1 phosphorylation by 20-25%. Increased tyrosine phosphorylation of other proteins by insulin and/or contraction was not observed. Contraction alone had little effect on PI 3-kinase activity, but contraction markedly blunted the insulin-stimulated activation of IRS-1 and insulin receptor-immunoprecipitable PI 3-kinase. In conclusion, skeletal muscle contractile activity does not result in tyrosine phosphorylation of molecules involved in the initial steps of insulin signaling. Although contractile activity increases insulin sensitivity and responsiveness in skeletal muscle, contraction causes a paradoxical decrease in insulin-stimulated tyrosine phosphorylation and PI 3-kinase activity.

Animals↗

PubMed1995

Insulin receptor phosphorylation, insulin receptor substrate-1 phosphorylation, and phosphatidylinositol 3-kinase activity are decreased in intact skeletal muscle strips from obese subjects.

To determine whether the impaired insulin-stimulated glucose uptake in obese individuals is associated with altered insulin receptor signaling, we measured both glucose uptake and early steps in the insulin action pathway in intact strips of human skeletal muscle. Biopsies of rectus abdominus muscle were taken from eight obese and eight control subjects undergoing elective surgery (body mass index 52.9 +/- 3.6 vs 25.7 +/- 0.9). Insulin-stimulated 2-deoxyglucose uptake was 53% lower in muscle strips from obese subjects. Additional muscle strips were incubated in the basal state or with 10(-7) M insulin for 2, 15, or 30 min. In the lean subjects, tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 (IRS-1), measured by immunoblotting with anti-phosphotyrosine antibodies, was significantly increased by insulin at all time points. In the skeletal muscle from the obese subjects, insulin was less effective in stimulating tyrosine phosphorylation (maximum receptor and IRS-1 phosphorylation decreased by 35 and 38%, respectively). Insulin stimulation of IRS-1 immunoprecipitable phosphatidylinositol 3-kinase (PI 3-kinase) activity also was markedly lower in obese subjects compared with controls (10- vs 35-fold above basal, respectively). In addition, the obese subjects had a lower abundance of the insulin receptor, IRS-1, and the p85 subunit of PI 3-kinase (55, 54, and 64% of nonobese, respectively). We conclude that impaired insulin-stimulated glucose uptake in skeletal muscle from severely obese subjects is accompanied by a deficiency in insulin receptor signaling, which may contribute to decreased insulin action.

Adult↗

PubMed1995

Dexamethasone enhances insulin-like growth factor-I effects on skeletal muscle cell proliferation. Role of specific intracellular signaling pathways.

IGF-I stimulation of cell proliferation and c-Fos expression in skeletal muscle cells is markedly enhanced by dexamethasone. The effect of dexamethasone is not mediated by changes in IGF-binding proteins, as evidenced by similar effects of dexamethasone on the actions of insulin, PDGF-BB, and the IGF-I analogue long R3IGF-I. Dexamethasone also does not alter autocrine IGF-II secretion by muscle cells. To investigate the mechanism of the augmentation of IGF-I action, the effects of dexamethasone on intracellular IGF-I signaling pathways were determined. In dexamethasone-treated cells, the levels of IGF-I receptor tyrosine phosphorylation and receptor-associated phosphatidylinositol 3-kinase activity were increased. Dexamethasone-treated cells also showed increased and prolonged tyrosine phosphorylation of the Shc proteins. In contrast, dexamethasone decreased both tyrosine phosphorylation and expression of insulin receptor substrate 1 (IRS-1) and IRS-1-associated phosphatidylinositol 3-kinase activity. Thus, distinct signaling pathways activated by the IGF-I receptor in skeletal muscle cells are differentially regulated by dexamethasone. Potentiation of IGF-I action correlates with increased IGF-I receptor-associated phosphatidylinositol 3-kinase activity and tyrosine phosphorylation of Shc, but appears to be independent of activation of the IRS-1/phosphatidylinositol 3-kinase signaling pathway.

Animals↗

PubMed1994

cDNA cloning of the rat IGF I receptors: structural analysis of rat and human IGF I and insulin receptors reveals differences in alternative splicing and receptor-specific domain conservation.

IGF I and insulin receptors are homologous proteins that function in distinct physiological pathways. To define domains that might contribute to differences between IGF I and insulin receptors, we cloned the rat IGF I receptor cDNA and performed a comparative sequence analysis of specific functional domains in the two receptor types of rats and humans. Since alternative splicing has been shown to alter the activities of both IGF I and insulin receptors, we also examined the mRNA splicing patterns of the two receptors. The C-terminal region exhibits the lowest degree of amino acid homology between rat and human IGF I receptors (85%) and the tyrosine kinase domain the highest homology (98%). In the region corresponding to the CAG+/-alternative splicing site of the human IGF I receptor, a nucleotide change in the rat eliminates the alternative acceptor splice site. The rat IGF I receptor has no equivalent to the alternatively spliced exon 11 of the insulin receptor. The IGF I and insulin receptors are highly homologous in the tyrosine kinase domain (84%), but differ markedly in other specific regions (e.g., 22-26% homology in the transmembrane domain, 45% homology in the C-terminal domain). We speculate that these regions of divergent sequence may have roles in determining distinct signaling properties of IGF I and insulin receptors.

Alternative Splicing↗

PubMed1994

The free testosterone to dehydroepiandrosterone sulphate molar ratio as a marker of visceral fat accumulation in premenopausal obese women.

The aim of this paper was to investigate the relationship between sex hormones and fat distribution in premenopausal obese women. Serum concentrations of sex hormones, glucose tolerance and fat distribution were determined in a population of non-diabetic obese women, in the outpatient clinic of University Hospital, Bari, Italy. The subjects were 40 consecutive premenopausal obese women (BMI > 25). The amounts of visceral, abdominal subcutaneous, and femoral subcutaneous fat, and the visceral to abdominal subcutaneous fat ratio were measured by ultrasound techniques. Serum concentrations of total testosterone (T), free testosterone (FT), dehydroepiandrosterone sulphate (DHEAS), delta 4-androstenedione (A), 17-beta-estradiol (E2), sex hormone binding globulin (SHBG), and the FT to DHEAS molar ratio were measured during the follicular phase. Plasma glucose and insulin concentrations were evaluated during an oral glucose tolerance test. Of all sex hormones, the FT/DHEAS molar ratio was the parameter that most closely related to the amount of visceral fat (r: 0.544, P < 0.001), and this positive association was maintained (P < 0.01) after adjustment for age, BMI and insulin levels (fitted model: R2 adjusted: 0.504; F ratio: 14.73; P-value: < 0.0001). DHEAS was inversely correlated with the amount of visceral fat (r: -0.324, P < 0.05). T was inversely correlated with the amounts of both abdominal subcutaneous (r: -0.409, P < 0.01) and visceral fat (r: -0.324, P < 0.05). The FT to DHEAS molar ratio is the androgenic parameter that most closely relates to the accumulation of visceral fat in premenopausal obese women.

Adipose Tissue↗

PubMed1994

Reduced effectiveness of atrial natriuretic factor in pre-menopausal obese women.

It is well-known that the prevalence of hypertension progressively increases with body weight. Since the major physiological activities of atrial natriuretic factor (ANF) are its natriuretic, diuretic and vasodilatory effects, the aim of the present study was to investigate the ANF basal plasma levels and platelet receptor number in 15 young normotensive obese (O) and 12 age-matched normal weight healthy (C) women. ANF effectiveness was also studied in eight of the obese and seven of the control women, after an intravenous bolus of the hormone (human ANF (99-126): 0.5 mg/kg body weight). Results are expressed as means+s.d. Basal ANF plasma levels were similar between obese (18.2 +/- 9.7 pg/ml) and control women (12.3 +/- 7.7 pg/ml), whereas obese patients showed an increase density of platelet ANF-binding sites (clearance receptors) (C: 28.7 +/- 33.5 fmol/10(9) cells; O: 39.6 +/- 4.6 fmol/10(9) cells; P < 0.001), without apparent differences in receptor affinity (Kd) (C: 6.0 +/- 3.0 pM; O: 7.0 +/- 2.0 pM). The biological response to ANF, evaluated by changes of mean blood pressure levels (C: 5 +/- 1 mmHg; O: 1 +/- 1 mmHg; P < 0.001) and the percentage increase of diuresis (C: 159 +/- 52%; O: 81 +/- 62%; P < 0.01) and natriuresis (C: 205 +/- 129%; O: 99 +/- 41%; P < 0.05) was significantly reduced in obese patients. The percentage increase in sodium excretion was inversely related to the basal insulin concentrations in the obese group (r = 0.64, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Evidence for two insulin-like growth factor I receptors with distinct primary structure that are differentially expressed during development.

We have previously presented evidence for two IGF I receptor species in rat skeletal muscle. One form of IGF I receptor is selectively expressed in fetal and early postnatal life, and the second is present in both fetal and adult animals. These two IGF I receptors were shown to have similar tryptic phosphopeptide maps but to differ in beta subunit molecular weight (105,000 for the fetal vs. 95,000 for the adult type receptor). In this study, we have used specific antibodies to investigate the structural relationships between the two IGF I receptors. Anti-IGF I receptor beta subunit antibodies were generated against synthetic peptides corresponding to residues 1284-1293 and 1308-1318 of the cloned human IGF I receptor, and the capacity of these antibodies to interact with the two IGF I receptors was investigated. Both anti-peptide antibodies selectively immunoprecipitated the higher molecular weight fetal receptor and not the adult receptor from rat muscle. Human placenta and muscle were shown to contain two receptors similar to those observed in rat muscle. In human muscle, the anti-peptide antibodies and the human-specific monoclonal alpha subunit antibody alpha-IR3 also selectively immunoprecipitated the fetal type receptor. The presence of a 95,000 M(r) IGF I receptor beta subunit distinct from the insulin receptor beta subunit in human muscle was confirmed by the demonstration of an IGF I sensitive receptor with a beta subunit of this size after insulin receptor immunodepletion. These data strongly support the conclusion that the fetal and adult type IGF I receptors differ in primary structure. The fetal receptor corresponds to the cloned and sequenced IGF I receptor, and the primary structure of the adult type receptor has not yet been established.

Aging↗