Octreotide stimulates insulin-like growth factor binding protein-1 (IGFBP-1) levels in acromegaly.

Insulin-like growth factors (IGFs) circulate in a complexed state with several binding proteins (BPs). Of these, IGFBP-1 is regulated by hormonal and nutritional factors. The somatostatin analogue, octreotide, has been used to effectively control hypersomaototropism in acromegaly. IGFBP-1 levels were measured by RIA in 17 acromegalic patients receiving octreotide. Serum hormone sampling was conducted hourly for 8 hr periods. Among 13 octreotide responders, mean pre-treatment basal GH, IGF-1, and IGFBP-1 levels were 19 +/- 5 micrograms/L, 1021 +/- 168 micrograms/L, and 36 +/- 8 micrograms/L respectively. One month following octreotide treatment, an acute subcutaneous injection (100 micrograms) maximally attenuated GH to 3 +/- 0.6 microgram/L (18% of control, P less than 0.03) and IGF-1 to 467 +/- 75 micrograms/L (46% of control, P less than 0.008) after 4 hrs. IGFBP-1 levels, however, were stimulated to 95 +/- 16 micrograms/L (297% of control, P less than 0.003) during the same time period. A significant increase in IGFBP-1 levels occurred within 2 hrs (158% of baseline, P less than 0.03), and was sustained until the 7th hr following injection. Insulin, a known suppressor of IGFBP-1, did not change during this time. Among the 4 octreotide non-responders, mean basal IGFBP-1 levels were 42 +/- 4 micrograms/L, and 4 hrs following octreotide administration IGFBP-1 was 40 +/- 7 micrograms/L. Octreotide induced a dynamic inverse relationship between circulating GH and IGFBP-1 levels (r = -0.73, P less than 0.001). The absence of IGFBP-1 changes in octreotide non-responders and the non-suppression of insulin in octreotide responsive patients, suggest a direct GH-mediated mechanism of IGFBP-1 regulation in octreotide treated patients with acromegaly. IGFBP-1 may be another useful marker in evaluating the response of acromegaly to octreotide treatment in patients who experience clinical benefit but equivocal GH and IGF-1 attenuation.     

Regulation of insulin-like growth factor binding protein-1 (IGFBP-1) in insulin-dependent diabetes mellitus

The aim of the present study was to characterize the effect of 44 h of hyperglycaemia on diurnal levels of insulin-like growth factor binding protein-1 (IGFBP-1), insulin-like growth factor-1 (IGF-1), growth hormone (GH) and glucagon in 7 well-controlled subjects with insulin-dependent diabetes mellitus (IDDM). Hyperglycaemia (15 mmol/l) was induced by a glucose infusion, while the degree of insulinisation was similar to that of a corresponding period with near normoglycaemia (6.9 mmol/l). Hyperglycaemia for 44 h did not alter the normal diurnal IGFBP-1 levels when the degree of insulinisation was unchanged. The diurnal secretion pattern of IGFBP-1 was preserved in both genders and without any difference between the control and hyperglycaemic periods. However, the IGFBP-1 levels were increased in these IDDM subjects despite a peripheral hyperinsulinemia. An inverse correlation was found between IGFBP-1 and peripheral insulin levels both during periods of rapid changes in IGFBP-1 and insulin concentrations (i.e. morning hours) as well as during the total 24-h sampling period. Total IGF-1 levels were low, but no further decrease was seen after 24 h of hyperglycaemia in the presence of unchanged insulin levels. In conclusion, the present study clearly shows that the increased IGFBP-1 level seen during poor metabolic control in IDDM is not caused by hyperglycaemia. Glucose levels per se do not influence either total IGF-1 or IGFBP-1 concentrations in well-insulinised diabetic patients.     

Somatostatin analog induces insulin-like growth factor binding protein-1 (IGFBP-1) expression in human hepatoma cells.

As the somatostatin analog octreotide suppresses pituitary GH secretion and circulating IGF-1 levels, we examined its effects on human hepatoma (hep G2) cells which selectively express IGFBP-1. Octreotide (60 nM) stimulated IGFBP-1 up to 4.1-fold (p < 0.001 after 24 hrs). Induction of IGFBP-1 was first detectable after 12 hrs of 6 nM octreotide (1.5-fold, p < 0.03), and was confirmed by ligand blotting. Cholera toxin and forskolin induced IGFBP-1 independently and were also additive with octreotide. IGFBP-1 mRNA expression was induced 2.7-fold by octreotide. Thus, octreotide induces basal and stimulated IGFBP-1 in hepatocytes independently of insulin and GH. As IGFBP-1 may regulate peripheral IGF-1 action, induction of IGFBP-1 represents a novel pituitary-independent mechanism for octreotide action.     

Association of total insulin-like growth factor-I, insulin-like growth factor binding protein-1 (IGFBP-1), and IGFBP-3 levels with incident coronary events and ischemic stroke

CONTEXT: Prior observational studies have demonstrated that the GH/IGF axis is associated with cardiovascular disease. However, this association has not been extensively studied among older adults. OBJECTIVE: The objective of this study was to assess the association between levels of total IGF-I and IGF binding proteins (IGFBP-1, IGFBP-3) and risk of incident coronary events and ischemic stroke. DESIGN AND PARTICIPANTS: A case-cohort analysis was conducted among adults 65 yr and older in the Cardiovascular Health Study. MAIN OUTCOME MEASURES: A total of 534 coronary events [316 nonfatal myocardial infarctions (MIs), 48 fatal MIs, and 170 fatal coronary heart disease events] and 370 ischemic strokes were identified on follow-up. Comparison subjects were 1122 randomly selected participants from the Cardiovascular Health Study. RESULTS: Mean follow-up time was 6.7 yr for coronary events, 5.6 yr for strokes, and 9.3 yr for comparison subjects. Hazard ratios (95% confidence intervals) associated with baseline levels of total IGF-I and IGFBPs were estimated using multivariate adjusted Cox proportional hazards models. Neither IGF-I nor IGFBP-1 levels predicted risk of incident coronary events or stroke. IGFBP-3 had an inverse association with risk of coronary events [adjusted hazard ratio per sd=0.88 (0.78-1.00), P=0.05] but was not associated with stroke. Exploratory analyses suggested that low IGF-I and low IGFBP-3 levels were significantly associated with higher risk of nonfatal MI (P<0.05) but not with risk of fatal MI or fatal coronary heart disease. CONCLUSION: Circulating levels of total IGF-I or IGFBP-1 were not associated with risk of total coronary events or ischemic stroke among older adults, whereas low IGFBP-3 level was associated with increased risk of incident coronary events.     

Splanchnic exchange of insulin-like growth factor binding protein-1 (IGFBP-1), IGF-I and acid-labile subunit (ALS) during normo- and hyper-insulinaemia in healthy subjects

OBJECTIVE: The main source of circulating IGF-I, insulin like growth factor binding protein-1 (IGFBP-1) and acid-labile subunit (ALS) is considered to be the liver, but their production rates have not been determined in healthy individuals. Thus, the splanchnic exchange of IGFBP-1, IGF-I, ALS and glucose were studied. STUDY DESIGN: In five overnight fasting healthy, normal weight men (mean age 29 +/- 1 years) blood samples were taken from a hepatic vein, a brachial artery and a peripheral vein in the basal state and during 3 h i.v. infusion of insulin (1.0 mU/kg/min). Normoglycaemia was maintained with a variable glucose infusion and splanchnic blood flow was determined using a constant rate indicator infusion technique. RESULTS: The basal net splanchnic glucose output amounted 0.96 +/- 0. 09 mmol/min and the splanchnic production of IGFBP-1 was 7 +/- 2 microg/min. There was a net splanchnic uptake of IGF-I (7 +/- 2 microg/min) in the basal state, while no significant splanchnic exchange of ALS was found. During the insulin infusion, insulin concentration increased from 78 +/- 12 to 660 +/- 30 pmol/l, resulting in a complete inhibition of splanchnic glucose production after 40 min of infusion. Splanchnic IGFBP-1 production rose initially to 13 +/- 4 microg/min (P < 0.05) and then gradually decreased and was completely inhibited at 180 min (P < 0.05). Insulin infusion influenced neither ALS nor IGF-I splanchnic exchange. CONCLUSION: Splanchnic production of IGFBP-1 in the basal state was demonstrated and it is completely inhibited after 180 min of hyperinsulinaemia. In contrast to what is generally held, there was no net splanchnic production of IGF-I in the basal state or during insulin stimulation.     

Close relation of fasting insulin-like growth factor binding protein-1 (IGFBP-1) with glucose tolerance and cardiovascular risk in two populations

Aims/hypothesis. Insulin resistance/hyperinsulinaemia is implicated in the development of cardiovascular disease and diabetes but its role and causal pathways are not clear. We tested the hypothesis that the insulin-like growth factor system is independently associated with cardiovascular risk within susceptible populations based on previous reports of the links between low circulating insulin-like growth factor binding protein-1 concentrations and increased macrovascular disease in Type II (non-insulin-dependent) diabetes mellitus. Methods. In a population-based study 272 subjects (142 subjects of European and 130 Pakistani of origin) underwent a 75 g oral glucose tolerance test and standardised anthropometry. Fasting concentrations of insulin-like growth factor binding protein-1 (IGFBP-1), insulin-like growth factor-I (IGF-I), insulin-like growth factor-II (IGF-II), intact insulin and lipids were measured and were related to 2-h glucose tolerance test status. Insulin sensitivity was calculated using the homeostasis model assessment (HOMA). Results. Insulin-like growth factor binding protein-1 was significantly lower in subjects with impaired glucose tolerance when compared with normal glucose tolerance in both ethnic groups (Europeans F = 6.7, p = 0.002 and Pakistanis F = 4.4, p = 0.01). Multiple linear regression modelling showed that insulin-like growth factor binding protein-1 was independently associated with 2-h glucose (β = 0.16, p = 0.009) and logistic regression indicated a 40 % reduction in risk of impaired glucose tolerance for every 2.7 ng/ml increase in the insulin-like growth factor binding protein-1 concentration [odds ratio 0.6 (CI = 0.49–0.71), p = 0.001)]. In addition, insulin-like growth factor binding protein-1 was significantly correlated negatively with several established cardiovascular factors, and positively with insulin sensitivity. Conclusion/interpretation. Insulin-like growth factor binding protein-1 is closely related to risk factors for diabetes and cardiovascular disease in people of European and Pakistani origin. It has potential use as a marker of (hepatic) insulin resistance in clinical intervention studies and further implicates the insulin-like growth factor system in the development of macrovascular disease. [Diabetologia (2001) 44: 333–339] Received: 18 May 2000 and in revised form: 22 September 2000     

Circulating levels of human insulin-like growth factor binding protein-6 (IGFBP-6) in health and disease as determined by radioimmunoassay

OBJECTIVE: Insulin-like growth factor binding protein-6 (IGFBP-6) is a relatively unknown member of a family of six specific structurally related IGF binding proteins which are involved in the modulation of the biological effects of the IGFs. A distinctive property of IGFBP-6 is its preferential affinity for IGF-II relative to IGF-I. In order to obtain more insight into the clinical significance and regulation of circulating levels of IGFBP-6 we developed a specific radioimmunoassay (RIA) for this protein. DESIGN AND PATIENTS: Selected human biological fluids and plasma from 847 normal subjects were analysed. In addition, plasma samples from patients with different disorders (i.e. GH-deficiency, acromegaly, cancer, corticosteroid-treated children suffering from different kinds of severe illness and chronic renal failure) were investigated. MEASUREMENTS: The IGFBP-6 assay is competitive, utilizing a rabbit polyclonal antibody raised against a synthetic peptide comprising amino acids 90-118 of the hIGFBP-6 sequence and an additional tyrosine residue. It is calibrated against recombinant human (rh)IGFBP-6. The 125I tracer is prepared by iodination of the synthetic peptide. There is no significant cross-reactivity with other IGFBPs and no interference with the IGFs. RESULTS: Extensive normative range values for IGFBP-6 were determined using 847 plasma samples from normal males and females, ranging from 0 to 75 years of age. IGFBP-6 levels increased gradually (about two-fold) with age. In childhood the plasma levels of IGFBP-6 in females tended to be slightly higher than those for males. For the adult population the reverse was observed. Overall, the mean +/- SD value for males was higher than that for females (149 +/- 57 vs. 139 +/- 45 micrograms/l, P < 0.004). GH status did not appear to influence IGFBP-6 level since normal levels were found for both untreated acromegalic patients and GH-deficient subjects. GH treatment of the latter group of patients did not alter IGFBP-6 in plasma. Pharmacological doses of glucocorticosteroids affected circulating IGFBP-6 levels only slightly. IGFBP-6 levels in plasma samples derived both from children with acute lymphoblastic leukaemia and from patients with various types of solid neoplasms were generally within the normal range. In contrast, plasma samples from four of six patients with non-islet cell tumour induced hypoglycaemia (NICTH) showed elevated concentrations of IGFBP-6 (SDS > 2.9). An excess of IGFBP-6 was also found in plasma of both dialysed and non-dialysed prepubertal growth retarded children with chronic renal failure (CRF) (mean SDS: 23.0 and 9.3, respectively). IGFBP-6 levels were inversely correlated with glomerular filtration rate. In a group of CRF patients who underwent renal transplantation circulating IGFBP-6 levels were markedly lower (mean SDS: 4.6). The presence of IGFBP-6 could also be demonstrated in several other human biological fluids. Low amounts were detected in saliva (3-12 micrograms/l) and breast milk (6-45 micrograms/l) while the levels in amniotic fluid and follicular fluid were comparable with those determined in normal plasma. The IGFBP-6 content of cerebrospinal fluid (CSF) ranged between 25 and 87 micrograms/l, which is rather high in relation to the relatively low concentration of total protein in this body fluid. CONCLUSIONS: Measurements of IGFBP-6 have been shown so far to be of relatively minor clinical relevance. The exceptions are chronic renal failure patients and subjects with large tumours and non-islet cell tumour induced hypoglycaemia who may exhibit elevated circulating levels of this IGFBP. The physiological significance of this observation remains to be elucidated. The possibility of quantifying IGFBP-6 by specific RIA will facilitate further in vitro and in vivo studies of its regulation and function in man.     

Plasma levels of insulin-like growth factor binding protein-4 (IGFBP-4) under normal and pathological conditions

OBJECTIVE: Insulin-like growth factor binding protein-4 (IGFBP-4) belongs to a family of six structurally related IGF-binding proteins that are involved in the modulation of the biological effects of the IGFs. In order to obtain more insight into the clinical significance and regulation of IGFBP-4 in vivo we determined the levels of this protein by a specific radioimmunoassay in the human circulation under normal and various pathological conditions. DESIGN AND PATIENTS: Selected human biological fluids and plasma samples from 804 normal healthy males and females, ranging from 0 to 78 years of age, were analysed. In addition, plasma samples from patients with several disorders (i.e. hypothyroidism, hyperthyroidism, GH-deficiency, acromegaly, cancer, chronic renal failure corticosteroid-treatment) were investigated. MEASUREMENTS: A specific RIA for hIGFBP-4 was developed, using a rabbit polyclonal antibody raised against a synthetic peptide containing amino acids 80-103 of the mature hIGFBP-4 sequence. RESULTS: In normal individuals circulating IGFBP-4 levels in males did not change with age. For females the values tended to increase slightly in older age. Overall, the mean +/- SD for males and females (189 +/- 83 microg/l and 193 +/- 72 microg/l, respectively) were not different. Normative range values of IGFBP-4 correlated weakly with those of IGF-II (r = 0.31, P < 0.001). Neither hypothyroidism nor hyperthyroidism appeared to influence circulating IGFBP-4 levels since the levels were within the normal range. Both GH status and pharmacological doses of glucocorticoids, as employed in various chronic diseases, did not seriously affect plasma IGFBP-4 either. Under conditions with increased circulating PTH levels, i.e. dialysed adult patients with chronic renal failure (CRF) and subjects with hyperparathyroidism, a weak positive relationship was noted between the plasma contents of IGFBP-4 and PTH. An excess of IGFBP-4 was found in plasma of both nondialysed and dialysed prepubertal growth retarded children with chronic renal failure (CRF) (mean SDS: 10.75 and 5.78, respectively). IGFBP-4 levels were inversely related to glomerular filtration rate. Similar results were obtained for dialysed adults with CRF. In a group of CRF children who had undergone renal transplantation, circulating IGFBP-4 levels were markedly lower (mean SDS: 3.75). There was no evidence for an increased secretion of IGFBP-4 in the circulation of most of the cancer patients with solid tumours. Several children with acute lymphoblastic leukaemia, however, showed elevated plasma IGFBP-4 levels (mean SDS: 1.27). The presence of IGFBP-4 could also be demonstrated in other human biological fluids. The highest amounts were found in amniotic fluid (391-717 microg/l) and follicular fluid (249-500 microg/l). CONCLUSIONS: Measurement of plasma IGFBP-4 has been shown so far to be of minor clinical relevance. However, the results indicate that different concentration gradients between plasma and various other body fluids may exist. Therefore, it may well be that certain pathophysiological stimuli induce significant alterations in the local turnover rate of IGFBP-4 but that they are not reflected by changes in the circulating levels. The possibility of quantifying IGFBP-4 by RIA will facilitate further in vitro and in vivo studies on its regulation and function in humans.     

Serum concentrations of insulin-like growth factor-I and insulin-like growth factor binding protein-3 in patients with chronic hepatitis

BACKGROUND: Insulin-like growth factor-I is a liver-derived humoral factor, which has important anabolic and metabolic actions and is predominantly bound by insulin-like growth factor binding protein-3. Low serum concentrations of both insulin-like growth factor-I and insulin-like growth factor binding protein-3 have been reported in patients with chronic liver disease, especially cirrhosis, but their conditions in chronic hepatitis are uncertain. The aim of this study was to evaluate the effect of chronic hepatitis on serum concentrations of insulin-like growth factor-I and insulin-like growth factor binding protein-3 and their association with hepatic inflammation activity and fibrosis. METHODS: Serum insulin-like growth factor-I and insulin-like growth factor binding protein-3 were measured by RIA (ng/ml) in 17 patients with mild to severe chronic viral hepatitis (12 chronic hepatitis C, 5 chronic hepatitis B) and 16 healthy subjects. The hepatic inflammation activity and the severity of fibrosis were evaluated using Desmet classification. RESULTS: Both insulin-like growth factor-I and insulin-like growth factor binding protein-3 levels did not correlate with inflammation activity, fibrosis or transaminase levels. In the chronic hepatitis group, insulin-like growth factor-I levels were significantly higher than the control group (mean, 263.8 +/- 27.33 versus 127.14 +/- 10.83 ng/ml, P < 0.001, respectively), whereas insulin-like growth factor binding protein-3 levels were significantly lower when compared with the controls (1643.47 +/- 60.68 versus 2728.87 +/- 284.61 ng/ml, P < 0.05, respectively). CONCLUSIONS: These results suggest that the concomitant states of serum insulin-like growth factor-I and insulin-like growth factor binding protein-3 levels in patients with chronic hepatitis may be different from cirrhotic patients and high serum IGF-I levels may be a specific finding of the stage of chronic hepatitis before developing cirrhosis.     

Serum insulin-like growth factor type 1, insulin-like growth factor-binding protein-1, and insulin-like growth factor-binding protein-3 concentrations in patients with thyroid dysfunction.

Thyroid hormones play a role in the regulation of insulin-like growth factor type 1 (IGF-1) and insulin-like growth factor-binding protein-3 (IGFBP-3) expression, and both IGF-1 and IGFBPs have been shown to be related to the function and growth of the thyroid. Our aim was to evaluate serum concentrations of IGF-1, IGFBP-1, and IGFBP-3 in patients with thyroid dysfunction before and after normalization of thyroid function. The study was performed in 86 patients with thyroid dysfunction (43 hyperthyroid and 43 hypothyroid patients) and 17 euthyroid subjects. Serum growth hormone (GH), insulin, IGF-1, IGFBP-1, and IGFBP-3 were measured in all patients before and after normalizing serum thyroid hormone concentrations. Hyperthyroid patients showed IGF-1 (198.8 +/- 17.0 microg/L) and IGFBP-3 levels (4.2 +/- 0.2 mg/L) similar to those found in the control group (217.9 +/- 20.3 microg/L and 4.2 +/- 0.3 mg/L, respectively). After therapy these levels significantly decreased to 156.6 + 11.1 microg/L (p < 0.01) and 3.3 +/- 0.1 mg/L (p < 0.001), respectively. IGFBP-1 concentrations were clearly higher than those found in controls (22.7+/- 2.6 vs. 5.7 +/- 1.5 microg/L, p < 0.001) and exhibited a significant reduction after therapy for thyroid hyperfunction (11.0 +/- 1.7 microg/L, p < 0.001). Patients with hypothyroidism showed serum concentrations of IGF-1 (161.5 +/- 13.1 microg/L, p < 0.05) and IGFBP-3 (3.2 +/- 0.3 microg/L, p < 0.05) significantly lower than those found in healthy volunteers. However, replacement therapy with levothyroxine did not induce any significant modification of these concentrations (152.6 +/- 10.6 microg/L and 3.2 +/- 0.2 mg/L, respectively). Similarly, patients with thyroid hypofunction exhibited raised levels of IGFBP-1 (15.5 +/- 0.9 microg/L, p < 0.05 vs. control group) that were significantly decreased after therapy (8.8 +/- 1.4 microg/L, p < 0.01). The results of the present study show that thyroid status affects GH/IGF axis. Hypothyroidism is associated with significant reductions of IGF-1 and IGFBP-3, and IGFBP-1 is elevated in both hypothyroidism and hyperthyroidism.     

Characterization of the enzymatic specificity of the IGF-dependent insulin-like growth factor binding protein-4 (IGFBP-4) protease

The insulin-like growth factor (IGF)-dependent IGF binding protein-4 protease secreted by cultured adult human fibroblasts was recently identified as pregnancy-associated plasma protein-A (PAPP-A). In this study we showed that in addition to human IGFBP-4 the IGF-dependent IGFBP-4 protease also digests recombinant rat IGFBP-4 into two fragments by specifically cleaving at the carboxyl-terminal side of methionine at position 131 for rat IGFBP-4. Thus the cleavage site is at the KMKV site, which is not represented in other IGFBPs. While kallikrein may cleave at this site, its action is not specific.     

Androgen receptor up-regulates insulin-like growth factor binding protein-5 (IGFBP-5) expression in a human prostate cancer xenograft

The insulin-like growth factor (IGF) binding proteins (IGFBPs) are important modulators of IGF action in many tissues including human prostate. IGFBPs and the androgen receptor (AR) are expressed in CWR22, an androgen-dependent epithelial cell human CaP xenograft that retains biological characteristics of human CaPs, including regression following androgen withdrawal and recurrent growth of AR-containing cells in the absence of testicular androgens beginning several months after castration. Northern blot and in situ hybridization analyses demonstrated that IGFBP-5 is androgen-regulated in CWR22. IGFBP-5 messenger RNA (mRNA) decreased by 90% following castration of tumor-bearing mice compared with noncastrate androgen-stimulated mice. Testosterone treatment of CWR22 tumor-bearing mice 6 or 12 days after castration increased IGFBP-5 mRNA 10- to 12-fold. Levels of other IGFBP mRNAs did not change following androgen withdrawal and replacement. IGFBP-5 protein in tumor extracts bound 125I-labeled IGF-I in ligand blot assays and the amounts of IGFBP-5 measured by immunoblotting paralleled the levels of IGFBP-5 mRNA. Androgen-induced expression of IGFBP-5 was at a maximum level within 24 h after testosterone replacement, whereas the major increase in cell proliferation as measured by Ki-67 immunostaining occurred between 24-48 h. This time course suggested IGFBP-5 may be a mediator of androgen-induced growth of CWR22. In tumors that recurred several months following castration, IGFBP-5 mRNA and protein increased to levels that approached those in androgen-stimulated CWR22 tumors from noncastrate mice. IGFBP-5 immunohistochemical staining of prostate tissue specimens from patients was stronger in androgen-dependent and androgen-independent CaP than in areas of intraepithelial neoplasia (PIN) or benign prostatic hyperplasia (BPH). IGFBP-5 mRNA in these specimens was localized predominantly to stromal cells and IGFBP-5 protein to epithelial cell membranes.     

Serum level of insulin-like growth factor-1 and insulin-like growth factor binding protein-3 in acute coronary syndromes and relationship with prognosis]

OBJECTIVE: The aim of the present study was to examine the levels of insulin-like growth factor (IGF-I) and binding protein-3 (IGFBP-3) in acute coronary syndrome (ACS) and their relationship with prognosis. METHODS: Thirty patients with ACS (22 male, 8 female) were included in our study. Patient's population included 20 patients with ST elevation myocardial infarction (STEMI) and 10 with non-ST-elevation ACS. Death, re-infarction, revascularization and malignant arrhythmia were monitored during 3 months. Study group was compared with 20 healthy subjects (Controls). Blood samples were collected in the first 24 hours and at the end of third month. Serum IGF-I and IGFBP-3 levels were determined by radioimmunoassay method. RESULTS: We found decreased level of IGF-I only in the STEMI group (105+/-84 ng/ml vs. 715+/-150 ng/ml, p<0.0001). There were no significant differences in IGFBP-3 levels between two groups. Serum IGF-I levels were significantly increased after 3rd month in the STEMI group (356+/-72 ng/ml vs. 105+/-84 ng/ml, p=0.025). There was no relationship between IGF-I, IGFBP-3 levels and cardiovascular events occurred during 90 days of follow-up. CONCLUSION: These data allows to suggest that significantly decreased level of IGF-I in STEMI group of ACSs can be used as a marker of myocardial necrosis. There was no relationship between IGF-I level and cardiovascular events occurred in 90 days, so this parameter can not be used as a negative prognostic factor.     

Expression of insulin-like growth factor binding protein-1 (IGFBP-1) mRNA in the ovine uterus throughout the oestrous cycle and early pregnancy.

Insulin-like growth factors (IGFs) are thought to be important regulators of embryonic and fetal development. The half life, distribution and action of IGFs are modulated by a family of IGF-binding proteins (IGFBP). This study investigated the pattern of IGFBP-1 expression in the ovine uterus during the oestrous cycle and early pregnancy by in situ hybridisation. Uteri were collected from 46 non-pregnant ewes throughout the oestrous cycle and from 12 pregnant ewes between days (D)13 and 22 of gestation. Samples were also obtained on D16-17 from both horns of 5 ewes with unilateral pregnancies following uterine transection. IGFBP-1 expression was quantified as optical density (OD) units from autoradiographs using a Seescan image analysis system. IGFBP-1 mRNA was confined to the luminal epithelium, with a highly significant variation in concentration according to the stage of the cycle. In non-pregnant uteri, IGFBP-1 concentrations were high throughout the late luteal phase and oestrous period, peaking at an OD of 0.76+/-0.119, but concentrations fell below the detection limit (OD<0.01) by D5 before starting to increase again between D7 and 9. During early pregnancy there was no difference in expression between non-pregnant and pregnant ewes on D13 (OD 0.76+/-0.065, n=6 vs 0.71+/-0.070, n=3). As pregnancy progressed there was a significant steady decline in IGFBP-1 expression to 0.04+/-0.02 on D22. In the transected uteri on D16-17, IGFBP-1 mRNA expression was significantly higher in the pregnant than in the non-pregnant horn (0.44+/-0.04 vs 0.10+/-0.02, n=5, P<0.01). In conclusion, the location of the IGFBP-1 suggests that it may play a role in regulating the transfer of IGFs between the endometrium and the uterine lumen. The conceptus may enhance IGFBP-1 expression during early pregnancy. Oestrogen and progesterone may regulate IGFBP-1 expression during the cycle but this requires further investigation.     

Hepatic regeneration in insulin-like growth factor binding protein-1 transgenic mice

BACKGROUND/AIMS: Partial hepatectomy results in activation of genes in the residual liver tissue which serve to restore glucose homeostasis and regenerate liver mass. Expression of insulin-like growth factor binding protein-1 (IGFBP-1) is up-regulated following partial hepatectomy and IGFBP-1 can modulate both the metabolic and mitogenic effects of insulin-like growth factor-1 (IGF-I). The aim of the study was to compare the effects of partial hepatectomy on blood glucose levels and hepatic regeneration in wild-type and transgenic mice which constitutively overexpress IGFBP-1. METHODS: Hepatic IGFBP-1 mRNA, blood glucose concentrations, liver mass and hepatic DNA synthesis were compared in sham-operated and partially hepatectomized transgenic and wild-type mice. RESULTS: Hepatic IGFBP-1 mRNA was higher in sham-operated transgenic than wild-type mice, but in both groups of mice, partial hepatectomy was associated with a significant rise in IGFBP-1 mRNA. The absolute decline in blood glucose levels following partial hepatectomy was greater in transgenic mice. Basal DNA synthesis and the response to IGF-I in isolated hepatocytes from both groups of mice were similar, and DNA synthesis in the regenerating liver in vivo was not significantly different in transgenic as compared to wild-type mice: 449.3 +/- 63.9 vs. 321.6 +/- 52.3 cpm/microgram DNA. Hepatic regeneration as measured by liver weight after hepatectomy was not different between transgenic and wild-type mice. CONCLUSIONS: Constitutive overexpression of IGFBP-1 does not enhance hepatic regeneration and does not prevent the decline in blood glucose following partial hepatectomy.     

Effect of maternal diabetes on phosphorylation of insulin-like growth factor binding protein-1 in cord serum.

AIMS: The insulin-like growth factor (IGF) system is considered important in the regulation of fetal growth. Binding of IGFs to specific binding proteins (IGFBPs) modifies their actions. In fetal blood, IGFBP-1 is the primary IGF binding protein whose phosphorylation generates proteins with different affinities for IGF-I. We studied cord serum IGFBP-1 phosphoisoform profiles in normal pregnancies and in diabetic pregnancies, which are frequently complicated by macrosomia. RESEARCH DESIGN AND METHODS: Cord serum IGFBP-1 phosphoisoform concentrations were measured at birth by two immunoenzymometric assays in 67 pregnancies complicated by Type 1 diabetes, in 28 pregnancies complicated by insulin-treated gestational diabetes, and in 62 normal pregnancies. RESULTS: Cord serum highly phosphorylated IGFBP-1 (hpIGFBP-1) concentrations were lower in pregnancies complicated by Type 1 diabetes (204 +/- 36 microg/l, P = 0.032) and in pregnancies complicated by gestational diabetes (170 +/- 28 microg/l, P = 0.031) than in controls (316 +/- 34 microg/l). Cord serum lesser phosphorylated IGFBP-1 (lpIGFBP-1) concentrations were similar in diabetic and normal pregnancies (P = 0.692 between groups by analysis of variance). Relative birth weight correlated negatively with cord serum hpIGFBP-1 and lpIGFBP-1 in diabetic pregnancies, and with cord serum lpIGFBP-1 in normal pregnancies. CONCLUSIONS: Maternal diabetes is associated with suppressed hpIGFBP-1 but unaltered lpIGFBP-1 concentrations in cord serum, suggesting that IGFBP-1 phosphoisoforms are differentially regulated in the fetus. Because hpIGFBP-1 has a higher affinity for IGF-I than does lpIGFBP-1, diabetes-related changes in fetal IGFBP-1 phosphorylation may increase IGF-I bioavailability and, consequently, stimulate fetal growth. This may partly explain the increased occurrence of macrosomia in diabetic pregnancies.     

Characterization of insulin-like growth factor binding protein-3 (IGFBP-3) binding to human breast cancer cells: kinetics of IGFBP-3 binding and identification of receptor binding domain on the IGFBP-3 molecule

Insulin-like growth factor binding protein-3 (IGFBP-3) binds to specific membrane proteins located on human breast cancer cells, which may be responsible for mediating the IGF-independent growth inhibitory effects of IGFBP-3. In this study, we evaluated IGFBP-3 binding sites on breast cancer cell membranes by competitive binding studies with IGFBP-1 through -6 and various forms of IGFBP-3, including synthetic IGFBP-3 fragments. Scatchard analysis revealed the existence of high-affinity sites for IGFBP-3 in estrogen receptor-negative Hs578T human breast cancer cells (dissociation constant (Kd) = 8.19 +/- 0.97 x 10(-9) M and 4.92 +/- 1.51 x 10(5) binding sites/cell) and 30-fold fewer receptors in estrogen receptor-positive MCF-7 cells (Kd = 8.49 +/- 0.78 x 10(-9) M and 1.72 +/- 0.31 x 10(4) binding sites/cell), using a one-site model. These data demonstrate binding characteristics of typical receptor-ligand interactions, strongly suggesting an IGFBP-3:IGFBP-3 receptor interaction. Among IGFBPs, only IGFBP-5 showed weak competition, indicating that IGFBP-3 binding to breast cancer cell surfaces is specific and cannot be attributed to nonspecific interaction with glycosaminoglycans. This was confirmed by showing that synthetic IGFBP-3 peptides containing IGFBP-3 glycosaminoglycan-binding domains competed only weakly for IGFBP-3 binding to the cell surface. Rat IGFBP-3 was 20-fold less potent in its ability to compete with human IGFBP-3(Echerichia coli), as well as 10- to 20-fold less potent for cell growth inhibition than human IGFBP-3, suggesting the existence of species specificity in the interaction between IGFBP-3 and the IGFBP-3 receptor. When various IGFBP-3 fragments were evaluated for affinity for the IGFBP-3 receptor, only those fragments that contain the midregion of the IGFBP-3 molecule were able to inhibit 125I-IGFBP-3(Escherichia coli) binding, indicating that the midregion of the IGFBP-3 molecule is responsible for binding to its receptor. These observations demonstrate that specific, high-affinity IGFBP-3 receptors are located on breast cancer cell membranes. These receptors have properties that support the notion that they may mediate the IGF-independent inhibitory actions of IGFBP-3 in breast cancer cells.     

The phosphorylation status of insulin-like growth factor-binding protein-1 in prepubertal obese children

OBJECTIVE: We measured the total and nonphosphorylated insulin-like growth factor-binding protein (IGFBP)-1 concentrations in obese children to determine the effect of obesity on the status of IGFBP-1 phosphorylation. We also measured the serum levels of insulin, total and free IGF-I, and IGFBP-3 to investigate their relationships to the IGFBP-1 phosphorylation status in obese subjects. SUBJECTS AND METHODS: Nineteen prepubertal obese and 15 age-matched control children were included in the study. The serum levels of total and nonphosphorylated IGFBP-1 were determined by noncompetitive RIAs. RESULTS: The serum levels of total and nonphosphorylated IGFBP-1 were significantly lower in the obese group (48.7+/-5.6 microgram/l, P<0.001 and 11.1+/-1.9 microgram/l, P<0.01 respectively) than in the controls (86.7+/-9.0 microgram/l and 28.8+/-6.2 microgram/l respectively). However, the ratio of nonphosphorylated IGFBP-1 to total IGFBP-1 did not differ significantly between the obese and control groups. The circulating free IGF-I level was significantly higher in the obese children than in the controls (P<0.05), while the serum levels of insulin, total IGF-I and IGFBP-3 were not significantly different between the two groups. A stepwise regression analysis of the combined group revealed that only the total IGFBP-1 level was an independent predictor of the free IGF-I concentration (P<0.001). CONCLUSION: The present study shows that both total and nonphosphorylated IGFBP-1 concentrations are decreased in obese children and the increased free IGF-I level in obese children is related to the reduced total IGFBP-1 level, but unrelated to the change in the IGFBP-1 phosphorylation status.