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      Insulin-like growth factor-1 and its binding proteins, IGFBP-1 and IGFBP-3, in adolescents with type-1 diabetes mellitus and microalbuminuria.

      Hormone research
      Adolescent, Adult, Albuminuria, blood, complications, Blood Pressure, Diabetes Mellitus, Type 1, Diabetic Angiopathies, Female, Hemoglobin A, Glycosylated, metabolism, Humans, Insulin-Like Growth Factor Binding Protein 1, Insulin-Like Growth Factor Binding Protein 3, Insulin-Like Growth Factor I, Male, Regression Analysis

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          Abstract

          Numerous clinical and experimental studies suggest that growth factors may contribute to the development of diabetic microvascular complications. The aim of the study was to test the hypothesis that in adolescents with type-1 diabetes mellitus and microalbuminuria (MA) there are specific disorders of serum insulin-like growth factor-1 (IGF-1) and concentrations of its binding proteins, IGFBP-1 and IGFBP-3, that could be of importance in the pathogenesis of microvascular diabetic complications. 25 adolescents with MA, 24 adolescents with diabetes without complications, and 17 controls were examined. There were no differences with regard to age, puberty stage, HbA1c and body mass index between the groups examined. Two of the patients in the first group also had diabetic retinopathy. Serum fasting concentrations of IGF-1 and overnight urine albumin concentrations were measured by radioimmunoassay, IGFBP-1 and IGFBP-3 concentrations by immunoradiometric assay and HbA1c by high-performance liquid chromatography methods. Diabetic patients were examined by an experienced ophthalmologist and neurologist. The data were analyzed using Kruskal-Wallis ANOVA and multiple regression analysis. Significantly lower IGF-1 concentrations were found in adolescents with diabetes and MA compared to diabetic patients without complications and healthy contemporaries. IGFBP-1 concentrations were significantly higher and IGFBP-3 concentrations were statistically lower in diabetic patients with MA than in patients without complications. The IGF-IGFBP system is deranged in adolescents with type-1 diabetes mellitus and MA. Our results suggest the participation of circulating IGFBP-1 in the origin of diabetic complications. It could be also possible that IGFBP-3 takes part in the protection from them.

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          Most cited references22

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          Vascular endothelial growth factor/vascular permeability factor expression in a mouse model of retinal neovascularization.

          Neovascular diseases of the retina are a major cause of blindness worldwide. Hypoxia is thought to be a common precursor to neovascularization in many retinal diseases, but the factors involved in the hypoxic neovascular response have not been fully identified. To investigate the role of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) in retinal neovascularization, the expression of VEGF/VPF mRNA and protein were studied in a mouse model of proliferative retinopathy. RNA (Northern) blot analysis revealed that retinal VEGF/VPF mRNA expression increased 3-fold between 6 and 12 hr of relative retinal hypoxia and remained elevated during the development of neovascularization. In situ hybridization localized VEGF/VPF mRNA to cells bodies in the inner nuclear layer of the retina. Immunohistochemical confocal microscopy demonstrated that VEGF/VPF protein levels increase with a time course similar to that of the mRNA. The cells in the inner nuclear layer of the retina that produce VEGF/VPF were identified morphologically as Müller cells. These data suggest that VEGF/VPF expression in the retina plays a central role in the development of retinal ischemia-induced ocular neovascularization.
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            Insulin regulates the serum levels of low molecular weight insulin-like growth factor-binding protein.

            The serum levels of 34K insulin-like growth factor (IGF)-binding protein were measured by RIA in 88 type 1 diabetic patients, 9 patients with type 2 diabetes, 7 patients with insulinoma, 19 normal subjects (all after an overnight fast), and 82 normal subjects after a breakfast meal. In addition, the effect of 2- to 3-h euglycemic steady state hyperinsulinemia on serum IGF-binding protein and IGF-1 levels was studied in some subjects in each of the fasted groups. Compared with normal subjects, the mean serum IGF-binding protein levels were 4-fold (P less than 0.001) higher in type I diabetic patients treated with conventional insulin injections, 2.5-fold (P less than 0.001) higher in those treated with continuous sc insulin infusion, and 2-fold (P less than 0.05) higher in patients with type 2 diabetes. In the patients with insulinoma, the mean IGF-binding protein level was 63% below normal (P less than 0.001), and it normalized after removal of the tumor. There was a slight negative correlation between the IGF-binding protein level and insulin dose in the diabetic patients (r = -0.22; P less than 0.05). In normal subjects, serum insulin concentrations were 2-fold higher (P less than 0.001) and the IGF-binding protein level was 29% lower after a meal (P less than 0.05) than in the fasting state. Serum IGF-I concentrations were virtually identical in the type 1 and 2 diabetic patients, insulinoma patients, and normal subjects. During steady state euglycemic hyperinsulinemia, the IGF-binding protein level fell by 40-70% in each group (P less than 0.001), whereas the IGF-I level declined (P less than 0.05) in the type 2 diabetic patients only. The decline of binding protein was closely related to the baseline level (r = 0.94; P less than 0.001). No correlation was found between serum IGF-I and binding protein levels in any group. In conclusion, 1) serum 34K IGF-binding protein levels are elevated in type 1 and 2 diabetic patients and decreased in patients with insulinoma; 2) the serum binding protein, but not IGF-I concentration is decreased by acute hyperinsulinemia; and 3) these data suggest that the serum insulin concentration plays a role in regulation of the serum 34K IGF-binding protein concentration.
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              Alterations in the growth hormone-insulin-like growth factor axis in insulin dependent diabetes mellitus.

              The growth hormone (GH)-insulin-like growth factor (IGF) axis and insulin are major anabolic effectors in promoting weight gain and linear growth. These two anabolic systems are interlinked at many levels, thus abnormalities in one of these systems effect the other causing disordered metabolic homeostasis. Insufficient portal insulinization in insulin dependent diabetes mellitus (IDDM) results in hepatic GH resistance and increased production of IGF-binding proteins-1 (IGFBP-1) and IGFBP-2. GH resistance is reflected by decreased hepatic IGF-I production. In addition, changes in other GH-dependent proteins are also observed in IDDM. Increased proteolysis of IGFBP-3 results in reduction of intact IGFBP-3. Serum ALS levels are also slightly diminished in untreated diabetic patients. Hepatic resistance to GH is, at least in part, caused by diminished GH receptors as reflected by diminished circulating GHBP levels. In addition, there is also evidence from experimental and human studies suggesting post-receptor defect(s) in GH action. As a result of these changes, circulating total and free IGF-I levels are decreased during insulinopenia. Lack of negative feed-back effect of IGF-I on GH secretion causes GH hypersecretion which increases hyperglycemia by decreasing sensitivity to insulin. GH hypersecretion in poorly controlled diabetic patients may play a role in the pathogenesis of diabetic vascular complications. Most of these abnormalities in the GH-IGF axis in diabetes are reversed by effective insulinization of the patient. Addition of IGF-I treatment to insulin in adolescents with IDDM allows correction of GH hypersecretion, improves insulin sensitivity and glycemic control, and decreases insulin requirements. The effect of IGF-I treatment on diabetic complications has yet to be seen.
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