Insulin-like growth factor binding proteins from cultured human fibroblasts. Characterization and hormonal regulation.

Specific, high affinity insulin-like growth factor (IGF) binding proteins are secreted by human fibroblasts in culture. By multiple criteria, the species of IGF binding proteins produced by human fibroblasts are distinct from the HepG2/amniotic fluid IGF binding protein, but share many characteristics with the growth hormone-dependent IGF binding protein forms predominant in normal adult human plasma. Treatment of cultured human fibroblasts with growth hormone produced an increase in IGF binding protein activity in the medium, while addition of glucocorticoids markedly diminished IGF binding activity. Insulin, epidermal growth factor, platelet-derived growth factor, and progesterone had no effect on IGF binding activity in fibroblast media. In comparison, HepG2 IGF binding activity was enhanced by progesterone, decreased by insulin, and unaffected by growth hormone or glucocorticoid treatment. Five molecular forms of IGF binding proteins were identified by Western ligand blots in human fibroblast conditioned medium, with Mr = 41,500, 37,000, 32,000, 28,000, and 23,000. In human fibroblast conditioned medium, the Mr = 41,500 and 37,000 IGF binding protein species were abundant, as in normal human plasma, with a major Mr = 23,000 form which was a minor component in plasma.     

Immunoassay of serine-phosphorylated isoform of insulin-like growth factor (IGF) binding protein (IGFBP)-1

OBJECTIVES: Development of an ELISA for phosphorylated isoform of IGFBP-1. Serine phosphorylation is an important regulator of IGFBP-1 bioactivity, but specific immunoassays for its measurement are currently lacking. DESIGN AND METHODS: Assay design was based on a novel approach of first capturing the phosphorylated and non-phosphorylated IGFBP-1 by an anti-IGFBP-1 antibody and then selectively detecting the phosphorylated form by an anti-phosphoserine antibody. Method development involved pair-wise evaluation of the candidate antibodies and determinations of analytical performance and specificity. Specificity was monitored by reactivity with dephosphorylated IGFBP-1, with antibodies against other phosphorylated residues that are not expressed, and by comparative analysis of sample containing different IGFBP-1 phosphorylation profile. RESULTS: Analytical evaluation demonstrated acceptable performance; detection limit 0.3 microg/L, dynamic range 1.56-100 microg/L; intra- and inter-assay CVs 2.1-8.6%; mean recovery (+/-SD) 97.8+/-9.2%, and mean recovery of sample dilution 93.4+/-6.0%. The phosphorylated and total IGFBP-1 medians in non-pregnant adult serum, which mostly contain the highly phosphorylated isoform, were 11.9 and 18.6 microg/L, respectively, and the sample values were tightly correlated (r=0.99). As expected, the corresponding medians in 1st trimester (17.4 and 63.0 microg/L) and 2nd trimester (30.9 and 75.8) samples with altered IGFBP-1 phosphorylation were significantly different (p<0.001). Similarly, a fraction (1.29%) of total IGFBP-1 (13.3 mg/L) in amniotic fluids was found to be phosphorylated (0.172 mg/L). There was no reactivity with dephosphorylated IGFBP-1. CONCLUSIONS: The present ELISA is highly specific for the phosphorylated isoform of IGFBP-1 and its availability should help expedite further investigations of IGFBP-1 phosphorylation.     

Granulosa cell-derived insulin-like growth factor (IGF) binding proteins are inhibitory to IGF-I hormonal action. Evidence derived from the use of a truncated IGF-I analogue.

An increasing body of information now suggests that insulin-like growth factor (IGF) binding proteins (BPs) may serve as antigonadotropins at the level of the ovary. It is the objective of the present communication to evaluate the functional role of endogenous (granulosa cell-derived) IGFBPs by exploiting the unique properties of des(1-3)IGF-I, a naturally occurring IGF-I analogue characterized as a weak ligand of IGFBPs but not of type I IGF receptors. Given IGFBP-replete circumstances, des(1-3)IGF-I proved more potent (10-fold) than its intact counterpart in promoting the follicle stimulating hormone (FSH)-stimulated accumulation of progesterone by cultured rat granulosa cells. In contrast, des(1-3)IGF-I proved virtually equipotent to the unmodified principle under IGFBP-deplete circumstances. Taken together, these findings are in keeping with the notion and that the apparently enhanced potency of des(1-3)IGF-I (under IGFBP-replete conditions) is due to its diminished affinity for endogenously generated IGFBPs and that rat granulosa cell-derived IGFBPs are inhibitory to IGF (and thus inevitably to gonadotropin) hormonal action. Accordingly, the reported ability of gonadotropins to attenuate IGFBP release by granulosa cells may be designed to enhance the bioavailability of endogenously generated IGFs in the best interest of ovarian steroidogenesis.     

Receptors for insulinlike growth factor I are defective in fibroblasts cultured from a patient with leprechaunism.

We previously have demonstrated that fibroblasts from a patient with leprechaunism exhibited markedly decreased insulin binding to insulin receptors and that the ability of insulin to stimulate glucose incorporation in the patient's cells was greatly impaired. In addition, the insulinlike growth factor, multiplication-stimulating activity (MSA), also exhibited an impaired ability to stimulate glucose incorporation in the patient's fibroblasts, although in normal fibroblasts this response appears to be mediated by an insulinlike growth factor receptor. The present study examines 125I-labeled insulinlike growth factor I (IGF-I) binding to patient's and control fibroblasts. 125I-labeled IGF-I binds to a specific IGF-I receptor in normal fibroblasts. At steady state, binding was inhibited by unlabeled IGF-I, IGF-II, MSA III-2, MSA II, insulin, and proinsulin, in order of potency, but not by high concentrations of epidermal growth factor and human growth hormone, chemically unrelated polypeptides 125I-labeled IGF-I binding to patient's cells was decreased by approximately 75%, whereas binding of epidermal growth factor to its cell surface receptors was unaffected. Computer curve-fitting of untransformed equilibrium binding data suggests that the decreased binding resulted from a decreased Ka for IGF-I. The ability of the patient's IGF-I receptor to recognize insulin also appears to be altered. Impaired IGF-I binding by the leprechaun patient's fibroblasts may contribute to the abnormal biological response to insulinlike growth factors observed in vitro and to the in utero growth retardation.     

Intravenously injected insulin-like growth factor (IGF) I/IGF binding protein-3 complex exerts insulin-like effects in hypophysectomized, but not in normal rats.

Insulin-like growth factor (IGF) circulates in blood in two large molecular mass forms of 150 and 40 kD. Under normal conditions, most of the IGF is bound to the 150-kD complex by which it is retained in the circulation and therefore unable to exert acute insulin-like actions. The aim of this study was to answer the question whether or not IGF in the 40-kD complex is bioavailable to insulin target tissues and thus can cause acute insulin-like effects in vivo. Intravenously injected 1:1 molar recombinant human (rh) IGF I/rhIGF binding protein (BP)-3 complex lowered blood glucose and stimulated glycogen synthesis in diaphragm of hypophysectomized, but not of normal rats. The serum half-lives of the two components of the complex were similar to each other, but considerably shorter in hypox than in normal rats. On neutral gel filtration of serum both components of the injected complex appeared predominantly in the 150-kD region in normal rats. In hypox rats which lack the 150-kD complex they were found in the 40-kD region and disappeared rapidly from the circulation. We conclude that in the absence of the 150-kD complex, IGF associated with the 40-kD complex can rapidly leave the vascular compartment, reach insulin or type 1 IGF receptors and exert acute insulin-like effects.     

Increase in specific binding of insulin-like growth factor (IGF) II to type 1 IGF receptors on erythrocytes of hypopituitary children receiving growth hormone therapy

Specific receptor binding for insulin-like growth factors (IGFs) is measurable in young erythrocytes. Cells of similar age, Fraction A, can be reproducibly obtained by dextran gradient centrifugation from 5-10 ml of blood. We now report IGF-II specific binding to Fraction A erythrocytes from normal children and children with growth hormone deficiency. Normal controls (Group 1) were 5 male volunteers (14.7 +/- .6 years, mean +/- SEM) and 10 children with constitutional short stature (11.4 +/- 1.6 years) who had normal 6-hour daytime growth hormone profiles and plasma IGF-I values. Twelve growth hormone deficient children (Group 2), aged 13.7 +/- 1.1 years, had samples taken after 2 months without growth hormone therapy and again following 2 months with growth hormone (0.1 U/kg 3 times per week) therapy. The percent of total erythrocytes in Fraction A did not differ in the two groups of children. Group 1 had IGF-II specific binding of 10.2 +/- 0.6% (per 3 X 10(9) cells). IGF-II specific binding was less in Group 2 at 6.6 +/- 0.8% (p less than 0.002). With growth hormone therapy, IGF-II specific binding increased to 10.4 +/- 1.0% (p less than 0.02), a value not different from that seen in Group 1. Corresponding plasma IGF-II and IGF-I values showed a positive correlation with IGF-II specific binding (r = 0.54 and r = 0.56 respectively, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Preeclampsia is associated with alterations in insulin-like growth factor (IGF)-1 and IGF-binding proteins in Wharton's jelly of the umbilical cord.

Wharton's jelly is abundant in extracellular matrix, which is known as a storage site to concentrate and stabilise growth factors in the vicinity of cells. It was previously found that Wharton's jelly contains significant amounts of insulin-like growth factor (IGF)-1 and IGF-binding proteins (BPs). IGF-1 is a stimulator of biosynthetics of collagen and sulphated glycosaminoglycans. Preeclampsia (edema, proteinuria, hypertension (EPH)-gestosis) is accompanied by an accumulation of sulphated glycosaminoglycans in Wharton's jelly. IGF-1 and BPs may play an important role in such a remodelling of this tissue. It was decided to evaluate the alterations in amounts of IGF-1 and BPs in Wharton's jelly of newborns delivered by mothers with preeclampsia. Studies were performed on Wharton's jelly of 10 controls and 10 newborns delivered by mothers with preeclampsia (edema, proteinuria > 500 mg/l, arterial pressure: systolic > 140 mm Hg, diastolic > 90 mmHg). Radioimmunological techniques were employed to determine IGF-1 and IGF-BPs (BP-1 and BP-3). It was found that preeclampsia is associated with a decrease in IGF-1 and IGF-BP-1 in Wharton's jelly. A slight increase in IGF-BP-3 was found. Ligand blotting demonstrated that BP-3 (not BP-1) is a main component of Wharton's jelly, which binds IGF-1. Heparin drastically inhibited the binding of IGF-1 by BP-3. It is known from our previous studies that preeclampsia is associated with an increase in the amount of sulphated glycosaminoglycans (heparin, heparan sulphate, dermatan sulphate) in Wharton's jelly. This may be a factor, which prevents the binding of IGF-1 by BPs and facilitates the binding of IGF-1 to cells, stimulating them to produce sulphated glycosaminoglycans in Wharton's jelly.     

In vivo proteolysis of serum insulin-like growth factor (IGF) binding protein-3 results in increased availability of IGF to target cells.

IGF Binding Protein-3 (IGFBP-3), the major IGF carrier in the blood, undergoes limited proteolysis which reduces its affinity for IGFs, thus facilitating dissociation. The functional effects of this at the cellular level were studied by comparing two serum pools, one from healthy adults, one from women during late pregnancy when IGFBP-3 proteolysis is increased. Sera were mixed to yield identical IGF-I and IGF-II concentrations in the two pools. Western ligand and immunoblotting gave the characteristic IGFBP patterns for the two types of serum. Both pools dose-dependently stimulated DNA synthesis in cultured chick embryo fibroblasts. Stimulation by pregnancy serum was twice that by normal serum at 0.05-0.2% concentrations (P < 0.001). In the presence of excess monoclonal anti-IGF-I and -II antibodies, stimulation by both (0.1-0.2%) pools was 70-80% reduced and residual stimulation was similar. Addition of recombinant human (rh) IGFBP-3 dose-dependently depressed both pools' activity, more so for normal serum at 25 and 50 ng/ml, equally for each at 100 ng/ml. At the latter concentration, slight proteolysis of the rhIGFBP-3 was detectable in the presence of 0.2% pregnancy serum, but at 25 ng/ml, proteolysis was absent. These results suggest that IGFs are released more readily from pregnancy serum, accounting for the weaker inhibitory effect of low rhIGFBP-3 concentrations. For identical IGF concentrations, pregnancy serum's greater biological activity therefore reflects greater IGF availability to the cells. This study demonstrates the functional consequences at cellular level of serum IGFBP-3 proteolysis, underlining its significance in regulating serum IGF bioavailability.     

The effect of resistance training on serum insulin-like growth factor 1(IGF-1): A systematic review and meta-analysis

BackgroundData about the effects of resistance exercise on level of IGF-1 in the serum are conflicting. To resolve this inconsistency, we performed a systematic review and meta-analysis to precisely examine the effects of resistance exercise on the levels of serum IGF-1.MethodsPubMed, Scopus, Web of Science, and Embase databases were systematically searched from their inceptions until 10 December 2019 for randomized controlled trials (RCTs) comparing individuals who underwent resistance training and control participants. We applied a random-effects model to calculate the weighted mean difference (WMD).Results33 trials reported IGF-1 level as an outcome measure. The pooled estimate demonstrated a significant increase in IGF-1 (WMD: 10.34 ng/ml, 95 % CI: 4.93, 15.74, p = 0.000, I² = 90.3 %) after resistance training compared with the control group. Subgroup analysis demonstrated that the increase in IGF-1 levels following resistance training was only statistically significant in treatment duration ≤16 weeks (WMD: 8.04 ng/ml), participants aged more than 60 years old (WMD: 9.84 ng/ml); and in women (WMD: 17.27 ng/ml). Subsequent analysis of the relationship between participants’ age with plasma IGF-1 alterations revealed a U shape correlation in non-liner dose response, in which resistance training resulted in a declined IGF-1 level up to 40 years of age. Beyond 40 years old, the IGF-1 level was increased following resistance training.ConclusionWe have successfully demonstrated that resistance training was associated with an increased IGF-1 level among those who received the training for ≤16 weeks, among participants older than 60 years old, and among women. Further studies are warranted to clarify the mechanisms underlying the influence of resistance training on IGF-1.     

Regulation of experimental autoimmune encephalomyelitis with insulin-like growth factor (IGF-1) and IGF-1/IGF-binding protein-3 complex (IGF-1/IGFBP3).

Insulin-like growth factor (IGF)-1 is a cytokine that promotes oligodendrocyte development and myelin production. This study investigated whether treatment of chronic, relapsing murine experimental autoimmune encephalomyelitis (EAE) with IGF-1 or IGF-1 associated with its binding protein, IGFBP3, altered the course of disease. Administration of IGF-1/IGFBP3 (1-100 mg/kg per day) delayed the onset of disease in a dose-dependent manner and histologic examination showed a delay in inflammatory cells entering the central nervous system. However, once signs of EAE developed, disease was enhanced in the mice that had been given the highest dose of IGF-1/IGFBP3. Treatment with IGF-1/IGFBP3 after the onset of signs resulted in a severe relapse. Administration of free IGF-1 (10 mg/kg per day) provided mild protection when given before disease onset, but did not significantly alter the course of disease if given after disease onset. Possible mechanisms that could explain the altered disease in IGF-1/IGFBP3-treated mice included (a) IGF-1/IGFBP3 administration delayed the onset of EAE by downregulating ICAM-1 gene expression in the central nervous system, and (b) IGF-1/IGFBP3 treatment of EAE resulted in more severe disease due to enhanced expansion of encephalitogenic T cells. Although IGF-1 may enhance remyelination, these results indicate that administration of IGF-1 associated with IGFBP3 may also accentuate autoimmune demyelinating disease.     

Regulation of binding proteins for insulin-like growth factors (IGF) in humans. Increased expression of IGF binding protein 2 during IGF I treatment of healthy adults and in patients with extrapancreatic tumor hypoglycemia.

Insulin-like growth factors (IGFs) in blood form two complexes with specific binding proteins (BPs): a large, growth hormone (GH)-dependent complex with restricted capillary permeability, and a smaller complex, inversely related to GH, with high turnover of its IGF pool and free capillary permeability. The distribution of BPs and of IGFs I and II between these complexes was studied in sera from healthy adults treated with IGF I or/and GH and from patients with extrapancreatic tumor hypoglycemia. Like GH, IGF I administration raises IGF I and two glycosylation variants of IGFBP-3 in the large complex, but unlike GH drastically reduces IGF II. During IGF I infusion, IGFBP-3 appears in the small complex whose IGFBP-2 and IGF I increase three- to fivefold and fivefold, respectively. GH treatment, associated with elevated insulin levels, suppresses IGFBP-2 and inhibits its increase owing to infused IGF I. The small complex of tumor sera contains increased amounts of IGFBP-2 and -3, and two- to threefold elevated IGF II. Conclusions: low GH and/or insulin during IGF I infusion and in extrapancreatic tumor hypoglycemia enhance expression of IGFBP-2 and favor partition of IGFBP-3 into the small complex. Free capillary passage and high turnover of its increased IGF I or II pools may contribute to compensate for suppressed insulin secretion during IGF I infusion or to development of tumor hypoglycemia.     

Effects of octreotide on serum insulin-like growth factor I and insulin-like growth factor binding proteins in patients with cirrhosis

Hyperinsulinaemia and reduced insulin sensitivity are common features in patients with cirrhosis. Octreotide, a long-acting somatostatin analogue, is used in cirrhotic patients in the treatment of bleeding oesophageal varices. Octreotide has potent effects on the growth hormone (GH )/insulin-like growth factor I (IGF-I ) axis in healthy subjects, but the effects on the GH/IGF-I axis in patients with cirrhosis have been described only briefly. The effects of a 12 h infusion of octreotide (bolus 0.75 &#119 g/kg followed by 0.75 &#119 g/kg/h) in 25 subjects (normals n = 9, compensated cirrhotics n = 8, decompensated cirrhotics n = 8) were compared with those in placebo-treated controls (n = 19) during fasting conditions. IGF-I, free IGF-I, IGF binding proteins (IGFBPs), insulin, C-peptide, GH and glucose were measured. Insulin resistance was calculated using the HOMA method. Octreotide reduced levels of total IGF-I in patients with compensated cirrhosis (p = 0.03) and free IGF-I in decompensated cirrhosis (p < 0.01). Insulin resistance was significantly reduced in normal subjects, whereas the reduction in insulin resistance did not reach statistical significance in patients with cirrhosis. In normal subjects, octreotide increased the IGFBP-1 area under curve threefold (p < 0.01) and decreased IGFBP-3 levels (p < 0.01), but these effects were blunted in the cirrhotic patients. Similarly, the reduction of insulin and C-peptide was blunted in the cirrhotic patients, whereas a significant reduction in GH was demonstrated in all groups. The effects of octreotide on the GH/IGF-I axis are mitigated in patients with cirrhosis and this may be a reflection of relative hyperinsulinaemia during octreotide treatment in these patients.     

Effects of octreotide on serum insulin-like growth factor I and insulin-like growth factor binding proteins in patients with cirrhosis

Hyperinsulinaemia and reduced insulin sensitivity are common features in patients with cirrhosis. Octreotide, a long-acting somatostatin analogue, is used in cirrhotic patients in the treatment of bleeding oesophageal varices. Octreotide has potent effects on the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis in healthy subjects. but the effects on the GH/IGF-I axis in patients with cirrhosis have been described only briefly. The effects of a 12 h infusion of octreotide (bolus 0.75 microg/kg followed by 0.75 microg/kg/h) in 25 subjects (normals n=9, compensated cirrhotics n=8, decompensated cirrhotics n=8) were compared with those in placebo-treated controls (n=19) during fasting conditions. IGF-I, free IGF-I, IGF binding proteins (IGFBPs), insulin, C-peptide, GH and glucose were measured. Insulin resistance was calculated using the HOMA method. Octreotide reduced levels of total IGF-I in patients with compensated cirrhosis (p=0.03) and free IGF-I in decompensated cirrhosis (p<0.01). Insulin resistance was significantly reduced in normal subjects. whereas the reduction in insulin resistance did not reach statistical significance in patients with cirrhosis. In normal subjects, octreotide increased the IGFBP-1 area under curve threefold (p<0.01) and decreased IGFBP-3 levels (p<0.01), but these effects were blunted in the cirrhotic patients. Similarly, the reduction of insulin and C-peptide was blunted in the cirrhotic patients, whereas a significant reduction in GH was demonstrated in all groups. The effects of octreotide on the GH/IGF-I axis are mitigated in patients with cirrhosis and this may be a reflection of relative hyperinsulinaemia during octreotide treatment in these patients.     

Associations of blood levels of insulin-like growth factor (IGF)-I, IGF-II and IGF binding protein (IGFBP)-3 in schizophrenic Arab subjects.

BACKGROUND: Insulin-like growth factors (IGFs) are believed to be important in brain development and repair following neuronal damage. It is also speculated that IGFs are involved in the association of foetal and pre-adult growth with schizophrenia (SZ). METHODS: The aim of this study was to assess levels of IGF-I, IGF-II and IGF binding protein (IGFBP)-3 and their associations in male Arab patients with SZ (n=53) and healthy control subjects (HC; n=52). Anthropometric and demographic data were collected for each subject for whom blood specimens were analysed for serum lipoproteins, apolipoprotein B (apoB), IGF-I, IGF-II and IGFBP-3. RESULTS: The SZ group had lower serum total cholesterol, apoB and uric acid levels than the HC group (p<0.05). IGF-II levels were significantly higher in the SZ group (p=0.02) and correlated positively with levels of atherogenic lipoproteins--total cholesterol, low-density lipoprotein, apoB--and IGFBP-3. The pattern of correlations between the IGFs and the various parameters differed somewhat between the HC and SZ groups. CONCLUSIONS: These results demonstrate that IGF-II levels are increased in patients with SZ and show significant associations with atherogenic lipoproteins. We suggest a possible link between IGF-II metabolism and atherogenesis in SZ.     

肝硬化患者血清胰岛素样生长因子-1的变化及其临床意义

目的：研究肝硬化患者血清胰岛素样生长因子-1（IGF-1）的变化及其临床意义。方法：肝硬化患者79例，根据Child-Pugh评分分为3组，A级组21例。B级组29例。C级组29例，另选取20例正常体检者为正常组。Child-PughA、B、C级肝硬化患者再根据其入院症状分为消化道出血组与非出血组。ELISA法测定血清IGF-1值．全自动生化分析仪常规方法测定肝脏生化指标。结果：肝硬化A、B、C级组患者血清IGF-1水平与正常组比较均明显降低（P〈0.01）；肝硬化A、B、C级组间比较IGF-1水平亦有明显差异（P〈0.01或P〈0．05）；Child-PughA、B、C级肝硬化患者消化道出血组院者与非出血组IGF-1值无明显差异（P〉0.05）。结论：肝硬化患者IGF-1水平明显下降，而且其下降程度与肝脏病变程度有关；IGF-1可作为肝硬化患者肝脏功能及预后的评价指标。但是不能作为预测上消化道出血概率的指标     

Increased serum levels of insulin-like growth factor (IGF)-1 and IGF-binding protein-3 in Henoch-Schonlein purpura

beta-Phenylethylamine (beta-PEA), an endogenous amine synthesized in the brain, serves as a neuromodulator and is involved in the pathophysiology of various neurological disorders such as depression, schizophrenia, and attention-deficit hyperactivity disorder. beta-PEA fully exerts the physiological effects within the nanomolar concentration range via the trace amine receptors, but beta-PEA also causes convulsions at much higher concentrations via an as yet unknown mechanism. To investigate the electrophysiological mechanism by which beta-PEA induces convulsions, we examined the effect of beta-PEA on ionic currents passing through the cell membrane of dissociated rat cerebral cortical neurons, using a patch-clamp technique. The external application of beta-PEA suppressed ionic currents which continuously flowed when the membrane potential was held at -25 mV. The suppression was in a concentration-dependent manner and a half-maximal effective concentration was 540 muM. These currents suppressed by beta-PEA consisted of two K(+) currents: a time- and voltage-dependent K(+) current (M-current) and a leakage K(+) current. The suppression of the M-current reduces the efficacy of the current in limiting excessive neuronal firing, and the suppression of the leakage K(+) current can cause membrane depolarization and thus promote neuronal excitation. Reducing both of these currents in concert may produce neuronal seizing activity, which could conceivably underlie the convulsions induced by high-dose beta-PEA.     

Biological variation in fasting serum insulin-like growth factor binding protein-1 (IGFBP-1) among individuals with a varying glucose tolerance

Objective

To evaluate the biological variation of serum insulin-like growth factor binding protein-1 (IGFBP-1) in individuals with different degrees of glucose tolerance.

Research design and methods

IGFBP-1 was measured in 42 fasted subjects with: normal glucose tolerance (NGT = 15), impaired fasting glucose (IFG = 9), impaired glucose tolerance (IGT = 9) and type 2 diabetics (DM = 9). Short- and long-term reproducibility was determined for IGFBP-1.

Results

The longer-term reproducibility (CV) of serum IGFBP-1 was 20.9%, 29.5%, 33.1% and 48.0% for subjects with NGT, IFG, IGT and DM respectively. The results for the short-term serum IGFBP-1 yielded CVs for these same respective categories of 8.2%, 16.1%, 29.2% and 13.8%.

Conclusions

IGFBP-1 measurement was least variable in NGT individuals over both long-term and short-term intervals and variability increased with deteriorating glucose tolerance. Due to its biological variation, IGFBP-1 serum level is more reliable in normal subjects than in individuals with type 2 diabetes.     

Relationship between leptin, insulin resistance, insulin-like growth factor-1 and insulin-like growth factor binding protein-3 in patients with chronic kidney disease

This study examined the relationship between leptin, insulin-like growth factor-1 (IGF-1), IGF binding protein-3 (IGFBP-3) and insulin resistance in patients with chronic kidney disease (CKD). Levels of leptin, insulin, IGF-1, IGFBP-3 and common routine parameters were measured in 45 patients (23 males and 22 females) with CKD and 45 healthy controls matched for age, gender and body mass index. IGF-1 and IGFBP-3 levels were measured using a two-site immunoradiometric assay. Leptin levels were measured using an enzyme-linked immunosorbent assay. A homeostasis model assessment computer-solved model was used to assess insulin resistance (HOMA-IR). Levels of serum leptin, insulin, IGF-1, IGFBP-3 and HOMA-IR were significantly increased in patients with CKD compared with healthy subjects, whereas fasting blood glucose was not significantly different between the two groups. In patients with CKD, the serum leptin level was significantly correlated with IGF-1, IGFBP-3 and HOMA-IR. In conclusion, this study suggests that there is an interaction between leptin, IGF-1, IGFBP-3 and insulin resistance in patients with CKD.     

Stability of insulin-like growth factor (IGF)-I and IGF binding protein (IGFBP)-3 measured by the IMMULITE automated chemiluminescence assay system in different blood specimens

Insulin-like growth factor I (IGF-I) and IGF binding protein 3 (IGFBP-3) are measured to diagnose disorders of the somatotropic axis in children and adults. In clinical studies samples for IGF-I and IGFBP-3 measurement must often be stored for months and sent to specialized laboratories. Therefore, we tested the stability of IGF-I and IGFBP-3 in whole blood, serum and plasma from 12 volunteers at 4 degrees, 22 degrees, and 37 degrees C for several hours and at -25 degrees C for several months. The effect of only one protease inhibitor (Aprotinin = Trasylol, Bayer, Germany ) on IGF-I and IGFBP-3 measured in the automated IMMULITE assay system (DPC, Los Angeles) was tested. IGF-I and IGFBP-3 were stable in heparinized whole blood, plasma and serum at 22 degrees C up to 24 hours. IGF-I was stabilized by aprotinin for up to 72 hours at 37 degrees C. Factor concentrations were not altered after storage at -25 degrees C for at least 12 months. Recognition of IGFBP-3 fragments by the antibody used in the automated IGFBP-3 IMMULITE was excluded by measurement in 26 sera from pregnant women which usually contain IGFBP-3 fragments. In conclusion, samples for measurement of IGF-I and IGFBP-3 should be kept on ice and cooled if shipment takes more than 48 hours or alternatively 5000 IU/ml aprotinin should be added. IMMULITE assays are also valid to measure IGF-I and IGFBP-3 after at least 12 months storage at -25 degrees C.