Free IGF-I Research Articles

Elevated free IGF2 levels in localized, early-stage breast cancer in women

Epidemiological studies imply an association between circulating IGF1 and breast cancer, whereas the role of IGF2, which also acts on the IGF1 receptor, is less settled. This study investigates the association between IGF2 and breast cancer in patients with localized disease. The participants were women with well-characterized, early stage, localized breast cancer (n=43) and matched healthy women (n=38), from whom fasting serum levels of IGF-related peptides were measured. In patients, mean free IGF2 was increased (+57%, P<0.001), in spite of reduced total IGF2 levels (-12%, P=0.003) when compared with controls. Similar changes were seen in free IGF1 (+28%, P=0.004) and total IGF1 (-16% P=NS). Pro-IGF2 and IGF-binding protein 1 (IGFBP1) were unchanged. IGFBP2 was reduced by 22% in the patients (P=0.004). The patients showed reduced IGFBP3 protease activity and accordingly increased levels of intact IGFBP3, whereas total IGFBP3 was unchanged. Women with localized, early-stage breast cancer show elevated circulating free IGF1 and IGF2, reduced total IGF2 and alterations in IGFBPs. The changes observed despite minimal cancer disease suggest a role for the circulating IGF system in the progression of breast cancer in women.

Seasonal effects on the response of ovarian follicles to IGF1 in mares

The response of follicles to IGF1 was compared between the transition into the ovulatory season (transitional period) and the ovulatory season (ovulatory period) in eight mares using a cross-over experimental design within periods. Granulosa cells were collected from follicles 15-24 or 25-34 mm and expression of IGF1R, IGF2R, FSHR, LHCGR and PAPPA was determined by qPCR. In addition, 10 mg IGF1 or vehicle were injected into the largest follicle (transitional period) or the second largest follicle (ovulatory period) of a follicular wave before the beginning of diameter deviation between the two largest follicles (mean diameters at injection 19.2 and 20.0 mm during transitional and ovulatory periods respectively). Follicular fluid was collected 24 h after injection for determination of free IGF1, IGFBP, inhibin A and oestradiol levels. Granulosa cells from follicles 25-34 mm, but not follicles 15-24 mm, expressed higher levels of IGF1R (P=0.01), FSHR (P<0.007) and LHCGR (P=0.09) during the ovulatory period than during the transitional period, whereas IGF2R expression was higher in transitional than ovulatory follicles (P=0.06). Follicular IGFBP2 levels were not different (P>0.1) between periods and treatments, whereas IGFBP5 levels were higher (P<0.05) during the ovulatory period. Finally, IGF1 injection before the beginning of deviation induced an approximately twofold increase (P=0.01) in follicular inhibin A levels during each period and did not affect oestradiol (P>0.1). These results suggest that, as during ovulatory waves, equine follicles during transitional waves are responsive to IGF1 before the beginning of deviation and that, therefore, inadequate IGF1 responsiveness before deviation may not underlie the deficient development of dominant follicles during transition.

Cancer adds further urgency to prioritising obesity control

he increasing incidence of obesity in Australia is set to impose a major additional cancer burden at a time when population ageing alone is projected to cause unprecedented growth in cancer incidence. While obesity is frequently associated with type 2 diabetes, hypertension, lipid abnormalities and death from heart disease and stroke, there is growing evidence for its role in causing cancer. A systematic review and meta-analysis, which included the Million Women Study, investigated the link between body mass index (BMI; calculated by dividing weight in kilograms by height in metres squared) and types of cancer. 1,2 In men, a 5k g/m 2 increase in BMI was strongly associated with adenocarcinoma of the oesophagus, and thyroid, colon and renal cancers, and in women with adenocarcinoma of the oesophagus, and endometrial, gallbladder and renal cancers. There were weaker associations for melanoma and rectal cancer in men, and postmenopausal breast, thyroid and colon cancer in women. Leukaemia, myeloma and Hodgkin disease were associated in both sexes. One postulated mechanism for the link between obesity and cancer is that chronic hyperinsulinaemia results in raised levels of free IGF-I (insulin-like growth factor), with higher mean concentrations in men compared with women. This alters the environment of cells to favour cancers developing. 3 In adipocytes, androgens are converted to oestradiol, and chronic hyperinsulinaemia also reduces sex-hormone-binding globulin, leaving more oestrogen to impact on oestrogen-sensitive tissues. Further, adiponectin, a protein hormone secreted by adipocytes, is an insulin-sensitising agent that is anti-angiogenic and antiinflammatory, inversely correlated with BMI, found in higher concentrations in men than in women and, in some studies, its level is inversely associated with cancer risk. 4 Obesity is linked to 11% of colon cancers and 9% of postmenopausal breast cancers 5 — both increasingly common tumour types in Australia as a result of population ageing. With high percentages of endometrial cancer (39%), oesophageal adenocarcinoma (37%), kidney cancer (25%) and gallbladder cancer (24%) attributed to obesity and overweight, these rarer cancers may become more common as Australia’s obese population ages. 5 The risk of an obesity-related increase in cancer burden in this country is amplified, with the link between BMI and cancer compounded by a 50% increase in the number of obese or overweight Australians over the past 15 years. An estimated 7.4 million Australians are obese or overweight, including a quarter of children aged between 5 and 16 years. 6

IGF UPTAKE WITH COMPETITIVE BINDING IN ARTICULAR CARTILAGE

Experiments on the transport of radiolabeled Insulin-like Growth Factors (IGF-I and -II) into bovine articular cartilage show differential uptake depending on the relative proportion of IGF-I and -II. In this study, we present a mathematical model describing both the transport and competition of IGF-I and -II for binding sites represented by two functional groupings of IGF binding proteins (IGFBPs). The first grouping has approximately similar binding affinity to both IGF-I and -II (i.e. IGFBPs 1–5), whereas the second group has significantly higher binding preference for IGF-II compared to IGF-I (i.e. IGFBP-6). Using nonlinear least squares, it is shown that the experimental equilibrium competitive binding results can be described using a reversible Langmuir sorption isotherm involving two dominant IGFBP functional groups.After coupling the sorption model with a poromechanical continuum model, parametric studies are carried out to investigate the effect of model changes including IGF boundary conditions and the ratios of the two IGFBP functional groups. The results show that ignoring competitive binding leads to a significant overestimation of total IGF-I uptake, but an underestimation the rate of "free" (physiologically active) IGF-I within the cartilage. An increase of first group of IGFBPs (i.e. IGFBPs 1–5) as has been reported for osteoarthritis, is observed to hinder the bioavailability of free IGF-I in cartilage, even though the total IGF-I uptake is enhanced. Furthermore, the combination of dynamic compression and competitive binding is seen to enhance the IGF-I uptake within cartilage, but this enhancement is overestimated if competitive binding is neglected.

Characterization of NSCLC patients responding to anti-IGF-IR therapy

8000 Background: CP-751,871, a fully human IgG2 subtype monoclonal antibody, is a potent and specific inhibitor of the insulin-like growth factor type I receptor (IGF-IR). Methods: A comprehensive evaluation of blood and tissue markers of the IGF-IR pathway was undertaken during the conduct of phase I/II studies to evaluate the safety and efficacy of the combination of paclitaxel (T), carboplatin (C) and CP-751,871 (I) as first line treatment of advanced non-small cell lung cancer (NSCLC) patients (pts). Expression of IGF- IR and its ligands was investigated further in archival samples using tissue arrays and AQUA technology. IGF1R gene scanning was also performed. Circulating Tumor Cells (CTCs) expressing the IGF-IR were enumerated using CellTracks. Serum markers investigated included cleaved circulating IGF-IR, total and free IGF-I, IGFBP-3 and ALS. Glycemia was evaluated using fasting glucose. hGH and insulin levels were determined in a cohort of pts treated with single agent CP-751,871. Results: Blood and/or tissue samples were obtained from 190 NSCLC pts. Tissue markers were further investigated in 178 archival NSCLC specimens. Tumor IGF-IR expression was most pronounced in squamous cell carcinoma in concert with a high objective response rate to TCI in that histology (72% response rate). Two somatic mutations were identified in the beta subunit of the IGF-IR tyrosine kinase domain. One of them translated into blockade of ligand-induced receptor autophosphorylation in functional studies. CTCs expressing the IGF-IR were cleared from blood upon TCI treatment and reappeared in some patients upon disease progression. Circulating IGF-IR decreased, and IGF-1, IGFBP3 and ALS levels accumulated in serum in response to I treatment in a dose dependent manner. Importantly, sustained IGF-1 levels were observed at higher I doses, consistent with systemic IGF-IR downregulation. Hyperglycemia (glucose >250 mg/dL) was seen in 11% of NSCLC pts receiving combination TCI. It was manageable, reversible and independent of glucose levels at enrollment. hGH and glucose oscillated in parallel suggesting that hGH may play a role in the pathogenesis of I induced hyperglycemia. Conclusions: Biomarkers of the IGF-IR pathway are key elements in the development and monitoring of anti-IGF-IR therapy. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration HistoRx Inc, Immunicon, Pfizer Oncology Immunicon, Pfizer Inc, Pfizer Oncology Pfizer Oncology

Correlation between plasma cytokine/angiogenic factors (C/AF) and signaling pathways activation from baseline tumor biopsy specimens in patients with advanced non small cell lung cancer (NSCLC): Preliminary analysis from the Biomarker-based Approaches of Targeted Therapy for Lung Cancer Elimination (BATTLE) Clinical Study

8010 Background: In the first phase of BATTLE clinical study, 72 pts with advanced, previously treated NSCLC were characterized into one of four biomarker groups (BGs) based on their pre-treatment tumor biomarker profile. BGs included the following: EGFR (mutation & gene copy number), angiogenesis (VEGF and VEGFR-2 by IHC), K-ras/B-raf mutations and RXR/Cyclin D-1 (IHC and gene copy number). We performed exploratory analysis of plasma levels of 59 C/AFs to investigate potential correlation with pathway activation from pretreatment tumor specimens. Methods: 62/72 pts consented to the optional blood collection for C/AF analysis. We used multiplex bead assays to measure 53 plasma C/AFs, including VEGF, basic FGF, HGF, E-selectin, MMP-9, multiple chemokines and interleukins (IL). Total and free IGF-1, IGFBP-3, osteopontin (OPN) and sVEGFR-1&2 were measured by ELISA. To evaluate the association between plasma C/AFs and pretreatment tumor markers, Wilcoxon test was performed. Results: A significantly higher score of association was observed with OPN (p=0.005), IL-2ra (p=0.012), IL6 (p= 0.026) and IL-7 (p=0.031) in patients in the EGFR positive group, compared to those patients who were negative for this marker group. Higher IGFBP-3 was significantly associated with K-ras/B-raf mutations (p=0.007) and IL-12 (p=0.021) was significantly higher in angiogenesis positive group. Additionally, MMP-9 (p=0.017) was significantly higher in patients with negative angiogenesis markers. Conclusions: Several plasma C/AFs are associated with specific tumor derived pathway activation. This preliminary exploratory analysis suggests that broad-based plasma profiling of cytokines and angiogenic factors may be feasible approach for identifying markers of activation of tumor signaling pathways. The BATTLE clinical study continues to accrual. (funding from Department of Defense - BATTLE grant W81XWH-06–1-0303) Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration AstraZeneca AstraZeneca, Genentech

Single nucleotide polymorphisms of IGFBP-3 gene and lung cancer risk in a Korean population

Insulin-like growth factor binding protein-3 (IGFBP-3) is a putative tumor suppressor and inhibits the mitogenic and antiapoptotic activity of insulin-like growth factor (IGF) by blocking the binding to its receptors or by IGF-independent manner. Epidemiological studies have suggested that serum level of IGFBP-3 is associated with lung cancer risk. The present study was conducted to evaluate the association between single nucleotide polymorphisms (SNPs) of the IGFBP-3 gene and susceptibility to lung cancer and the effect of the SNPs on the serum levels of IGFBP-3, total IGF-I and free IGF-I in a Korean population. After a preliminary study for polymorphism screening of the promoter region of the IGFBP-3 gene in randomly selected 41 lung cancer patients, two polymorphisms (-1590 C>A; -202 A>C) were identified with PCR-based restriction fragment length polymorphism (PCR-RFLP) and SNaPshot primer extension assay in 415 Korean lung cancer patients and 415 matched normal controls. Although the genotype and allele frequency distribution of each SNP did not differ significantly between cases and controls in the single-locus analysis, we found that the polymorphisms of -1590A and -202C were associated with increased risk for lung cancer in females (-1590 C>A; adjusted OR=2.11, 95% CI=1.08-4.12, -202 A>C; adjusted OR=1.96, 95% CI=1.02-3.75, respectively) and never-smokers (-1590 C>A; adjusted OR=2.06, 95% CI=1.12-3.78, -202 A>C; adjusted OR=1.99, 95% CI=1.10-3.62, respectively) in a dominant model after stratification for gender and smoking history. Haplotype analysis showed that carriers of A-C had significantly higher risk for lung cancer in females (dominant aOR=2.05, 95% CI=1.14-3.68) and in never-smokers (codominant aOR=1.71, 95% CI=1.11-2.64 and dominant aOR=1.99, 95% CI=1.17-3.40). Functional analysis in H1703 cell line using DNA fragments containing A-C haplotype of the promoter region showed significantly decreased transcriptional activity. Furthermore, there was a negative correlation between the number of polymorphic alleles in -1590/-202 loci and serum levels of IGFBP-3 in lung cancer patients, but it was not statistically significant in the test for linear trend. These results suggest that IGFBP-3 promoter polymorphisms of -1590 C>A and -202 A>C might be a genetic risk factor for lung cancer by means of decreased IGFBP-3 expression among females or never-smoking Koreans.

Effect of Prostaglandin F2α (PGF2α) Administration on the Luteotropic and Angiogenic Factors During Functional Luteolysis in the Bovine Corpus Luteum.

The essential role of endometrium PGF2α in induction of the corpus luteum (CL) regression (luteolysis) is well documented in the cow. However, the following regulatory cascade of functional luteolysis is still not fully elucidated. The aim of the present study was therefore to determine the regulation patterns of local luteotropic factors (progesterone, oxytocin and insulin-like growth factor (IGF) family members) and angiogenic factors (vascular endothelial growth factor-A (VEGF) and angiopoietin (ANPT) family members) during functional luteolysis (first 12 h after PGF2α injection) in time-defined CL classes. Cows (n=4-5 per group) in the mid-luteal phase (days 8-12) were injected with the PGF2α-analogue (cloprostenol), and CLs were collected by transvaginal ovariectomy at 0 h, 0.5 h, 2 h, 4 h and 12 h after PGF2α injection. The mRNA expression was analyzed by a quantitative real-time PCR (Rotor-Gene 3000), and the protein concentration was evaluated by enzyme immunoassay (EIA) or radio immunoassay (RIA). Progesterone concentration in blood serum and in CL tissue as well as mRNA expression of progesterone receptor in CL tissue, were significantly downregulated at 12 h after PGF2α. Oxytocin and IGF-1 peptide concentrations rapidly declined after 0.5 h and remained at low level afterwards. The IGF binding protein (BP)-1 mRNA was strongly upregulated with the maximal level at 4 h after PGF2α. This may cause further reduction of bioactive free IGF-1 in tissue. The VEGF protein decreased also at 0.5 h, with a synchronous acute and temporal increase of angiopoietin (ANPT)-2 peptide concentrations (0.5 h and 2 h after PGF2α). The similar tendency of upregulation of ANPT-2 was found for mRNA expression level, whereas the level of ANPT-1 mRNA did not change. The results suggest that the acute decrease of the local luteotropic factors and of VEGF may play a key role during the early step of functional luteolysis. The increase of ANPT-2 after PGF2α suggests a change in vascular stability to enhance the cascade of functional luteolysis.

Leptin Does Not Mediate Short-Term Fasting-Induced Changes in Growth Hormone Pulsatility but Increases IGF-I in Leptin Deficiency States

States of acute and chronic energy deficit are characterized by increased GH secretion and decreased IGF-I levels. The objective of the study was to determine whether changes in levels of leptin, a key mediator of the adaptation to starvation, regulate the GH-IGF system during energy deficit. We studied 14 healthy normal-weight men and women during three conditions: baseline fed and 72-h fasting (to induce hypoleptinemia) with administration of placebo or recombinant methionyl human leptin (r-metHuLeptin) (to reverse the fasting associated hypoleptinemia). We also studied eight normal-weight women with exercise-induced chronic energy deficit and hypothalamic amenorrhea at baseline and during 2-3 months of r-metHuLeptin treatment. GH pulsatility, IGF levels, IGF and GH binding protein (GHBP) levels were measured. During short-term energy deficit, measures of GH pulsatility and disorderliness and levels of IGF binding protein (IGFBP)-1 increased, whereas leptin, insulin, IGF-I (total and free), IGFBP-4, IGFBP-6, and GHBP decreased; r-metHuLeptin administration blunted the starvation-associated decrease of IGF-I. In chronic energy deficit, total and free IGF-I, IGFBP-6, and GHBP levels were lower, compared with euleptinemic controls; r-metHuLeptin administration had no major effect on GH pulsatility after 2 wk but increased total IGF-I levels and tended to increase free IGF-I and IGFBP-3 after 1 month. The GH/IGF system changes associated with energy deficit are largely independent of leptin deficiency. During acute energy deficit, r-metHuLeptin administration in replacement doses blunts the starvation-induced decrease of IGF-I, but during chronic energy deficit, r-metHuLeptin administration increases IGF-I and tends to increase free IGF-I and IGFBP-3.

Low Circulating Insulin-Like Growth Factor I Bioactivity in Elderly Men Is Associated with Increased Mortality

Low IGF-I signaling activity prolongs lifespan in certain animal models, but the precise role of IGF-I in human survival remains controversial. The IGF-I kinase receptor activation assay is a novel method for measuring IGF-I bioactivity in human serum. We speculated that determination of circulating IGF-I bioactivity is more informative than levels of immunoreactive IGF-I. Our objective was to study IGF-I bioactivity in relation to human survival. DESIGN, SETTING, AND STUDY PARTICIPANTS: We conducted a prospective observational study at a clinical research center at a university hospital of 376 healthy elderly men (aged 73-94 yr). IGF-I bioactivity was determined by the IGF-I kinase receptor activation assay. Total and free IGF-I were determined by IGF-I immunoassays. Mortality was registered during follow-up (mean 82 months). During the follow-up period of 8.6 yr, 170 men (45%) died. Survival of subjects in the highest quartile of IGF-I bioactivity was significantly better than in the lowest quartile, both in the total study group [hazard ratio (HR) = 1.8; 95% confidence interval (95% CI) = 1.2-2.8; P = 0.01] as well as in subgroups having a medical history of cardiovascular disease (HR = 2.4; 95% CI = 1.3-4.3; P = 0.003) or a high inflammatory risk profile (HR = 2.3; 95% CI = 1.2-4.5; P = 0.01). Significant relationships were not observed for total or free IGF-I. Our study suggests that a relatively high circulating IGF-I bioactivity in elderly men is associated with extended survival and with reduced cardiovascular risk.

Comparison of Pancreas-Transplanted Type 1 Diabetic Patients with Portal-Venous Versus Systemic-Venous Graft Drainage: Impact on Glucose Regulatory Hormones and the Growth Hormone/Insulin–Like Growth Factor-I Axis

Pancreas grafts can be drained through the iliac vein (systemic drainage) or the portal vein. We hypothesized that normalization of portal insulin in patients with portal pancreas graft drainage stimulates the GH/IGF-I axis and thereby contributes to glucose control. We compared patients after combined kidney and pancreas transplantation with portal drainage (n = 7) to patients with systemic drainage of the pancreas graft (n = 8) and nondiabetic controls (n = 8). Overnight fasting sera were analyzed for free and total IGF-I and IGF-binding proteins. Glucose regulatory hormones were examined after an oral glucose tolerance test and GH after stimulation with GHRH. Systemic drainage led to higher basal and stimulated insulin levels than portal drainage (P < 0.05), but increments in response to oral glucose were reduced in both transplanted groups (P < 0.05 vs. controls). However, glucose tolerance was similar in all groups. Circulating free and total IGF-I and IGF-binding protein-3 were similar to control levels in the systemic drainage group but elevated in the portal drainage group (P < 0.05). Consistently, the GH response was reduced in the portal drainage group (P < 0.05 vs. controls) and correlated inversely with free IGF-I (r = -0.63, P < 0.05). Portal drainage of pancreatic endocrine secretion in pancreas graft recipients raises IGF-I and lowers GH secretion. These changes might explain that glucose regulation is maintained despite lower peripheral insulin levels, compared with patients with systemic graft drainage and nondiabetic control subjects.

TNF α and IGF‐I levels in Down Syndrome (DS)

TNF α a proinflammatory cytokine, and IGF‐I, the pleiotropic hormone have been involved in the pathogenesis of neurodegenerative diseases. Persons with DS have a number of abnormalities in their immune system. Studies showed that the neuropathology of Alzheimer disease (AD)is always present in individuals with DS 40 years of age and older. We examined levels of TNFα and IGF‐I in plasma from 41 persons with DS (45±8 years old) and 28 age‐matched healthy controls. TNFα levels were higher in DS than controls (p ≤ 0001). Total IGF‐I levels were simlar between DS and controls. However free IGF‐I levels were lower in DS than controls (p ≤ 05). The combined measurements of TNFα and IGF‐I might be useful to monitor anti‐inflammatory or neurotrophic drug effects in DS. It will be useful to determine whehter the levels are useful as biomarkers to predict early signs of AD.

Relationship between umbilical cord blood insulin-like growth factors and anthropometry in term newborns.

Birth size is associated with long-term morbidity. Insulin-like growth factor (IGF) system is the most important endocrine factor influencing fetal growth. During rapid somatic growth, free-to-total IGF-I ratio is increased, resulting in higher IGF-I bioavailability. The purpose of this study was to investigate the association of free-to-total IGF-I ratios, IGF-II, and IGF-binding protein (IGFBP)-3 umbilical cord levels with anthropometric data of term neonates. Umbilical venous plasma samples were obtained from 95 term neonates and analyzed by enzyme-linked immunosorbent assay. The large-for-gestational age (LGA) neonates had higher free IGF-I, total IGF-I, and IGFBP-3 levels than small-for-gestational age (SGA) neonates (P < 0.01, 0.001, 0.01, respectively) and higher total IGF-I and IGFBP-3 levels than appropriate-for-gestational age (AGA) neonates (P < 0.05, 0.01, respectively). The free-to-total IGF-I ratios and IGF-II levels were not different among SGA, AGA, and LGA neonates. Free IGF-I, total IGF-I, and IGFBP-3 levels were positively correlated with birth weight (r = 0.34, P < 0.001; r = 0.41, P < 0.001; r = 0.25, P < 0.05, respectively). Multiple linear regression analyses revealed that only total IGF-I levels was the independent predictive variable for birth weight. Our data suggest total IGF-I is the most important factor in the IGF system for determining fetal growth, at least near term gestation. Free-to-total IGF-I ratios may mostly be determined by total IGF-I. If birth size is associated with adult chronic metabolic diseases, total IGF-I may be involved in the pathogenesis.

Serum levels of free insulin-like growth factor-I and clinical value in healthy children

Purpose : The serum levels of total insulin-like growth factor (IGF)-I and IGF binding protein (IGFBP)- 3 reflect endogenous growth hormone (GH) secretion in healthy children. Free form of IGF-I which is suggested to have more potent biological action than complex form of IGF-I. The aim of this study is to investigate the serum levels of free IGF-I and its clinical value in healthy children. Methods : Serum levels of total IGF-I and IGFBP-3 were determined in 494 healthy children (248 boys and 246 girls) by RIA and IRMA. Serum level of free IGF-I was determined in 206 healthy children (103 boys and 103 girls) by IRMA. Results : The free IGF-I level increased with age in both sex. The free IGF-I level increased continuously between 7 and 15 years of age in boys, but decrement was noted after 14 years of age in girls. Serum total IGF-I level also increased with age in similar pattern of that of free IGF-I. There were no significant differences of mean values of the ratio of free IGF-I/total IGF-I in relation to age in both sex. And there were significant correlations between the level of free IGF-I and total IGF-I and the ratio of total IGF-I/IGFBP-3, respectively. Conclusion : In healthy children, serum free IGF-I increased with age in both sex and high free IGF-I level may play an important role in pubertal growth spurt. Our results suggest that the increased serum free IGF-I level in puberty may reflect changes in total IGF-I rather than IGFBP-3. But free IGF-I does not have more clinical value than total IGF-I because of no significant differences of mean values of the ratio of free IGF-I/total IGF-I in relation to age.

Insulin, Insulin-like Growth Factor-I, Endogenous Estradiol, and Risk of Colorectal Cancer in Postmenopausal Women

Obesity is a risk factor for colorectal cancer, and hyperinsulinemia, a common condition in obese patients, may underlie this relationship. Insulin, in addition to its metabolic effects, has promitotic and antiapoptotic activity that may be tumorigenic. Insulin-like growth factor (IGF)-I, a related hormone, shares sequence homology with insulin, and has even stronger mitogenic effects. However, few prospective colorectal cancer studies directly measured fasting insulin, and none evaluated free IGF-I, or endogenous estradiol, a potential cofactor in postmenopausal women. Therefore, we conducted a case-cohort investigation of colorectal cancer among nondiabetic subjects enrolled in the Women's Health Initiative Observational Study, a prospective cohort of 93,676 postmenopausal women. Fasting baseline serum specimens from all incident colorectal cancer cases (n = 438) and a random subcohort (n = 816) of Women's Health Initiative Observational Study subjects were tested for insulin, glucose, total IGF-I, free IGF-I, IGF binding protein-3, and estradiol. Comparing extreme quartiles, insulin [hazard ratio (HR)(q4-q1), 1.73; 95% confidence interval (CI), 1.16-2.57; P(trend) = 0.005], waist circumference (HR(q4-q1), 1.82; 95% CI, 1.22-2.70; P(trend) = 0.001), and free IGF-I (HR(q4-q1), 1.35; 95% CI, 0.92-1.98; P(trend) = 0.05) were each associated with colorectal cancer incidence in multivariate models. However, these associations each became nonsignificant when adjusted for one another. Endogenous estradiol levels, in contrast, were positively associated with risk of colorectal cancer (HR comparing high versus low levels, 1.53; 95% CI, 1.05-2.22), even after control for insulin, free IGF-I, and waist circumference. These data suggest the existence of at least two independent biological pathways that are related to colorectal cancer: one that involves endogenous estradiol, and a second pathway broadly associated with obesity, hyperinsulinemia, and free IGF-I.

Role of IGF-I in Type 2 diabetes: a focus on the mouse model

Insulin resistance, the key mechanism in Type 2 diabetes mellitus (T2DM) is also associated with the deregulation of other glucose homeostasis pathways, such as the growth hormone (GH)–IGF-I system. In this review, we summarize the endocrine and renal GH–IGF axis changes in db/db mice, a model of T2DM, and compare it with the nonobese diabetic mouse model of T1DM. In the latter, elevated circulating GH levels (associated with kidney disease) could be ameliorated with the use of GH antagonists. Contrary to that, in the obese db/db mice, serum GH and IGF-I levels are decreased and tissue levels of IGF-binding protein 1 (Igfbp1) are increased. The latter hinted again for the known inverse correlation between insulin and Igfbp1 and was mediated by changes in the transcription factor phosphorylated forkhead box O1 in obese animals. In addition, the decrease in circulating IGF-I and GH levels causes a state of low free and active IGF-I, which may further impair tissue viability (including pancreatic β-cells). Thus, further GH inhibition to modulate complications in T2DM is not indicated, but the therapeutic role of IGF-1 in this disease remains to be determined.

Growth hormone axis in chronic kidney disease

Chronic kidney disease (CKD) in children is associated with dramatic changes in the growth hormone (GH) and insulin-like growth factor (IGF-1) axis, resulting in growth retardation. Moderate-to-severe growth retardation in CKD is associated with increased morbidity and mortality. Renal failure is a state of GH resistance and not GH deficiency. Some mechanisms of GH resistance are: reduced density of GH receptors in target organs, impaired GH-activated post-receptor Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling, and reduced levels of free IGF-1 due to increased inhibitory IGF-binding proteins (IGFBPs). Treatment with recombinant human growth hormone (rhGH) has been proven to be safe and efficacious in children with CKD. Even though rhGH has been shown to improve catch-up growth and to allow the child to achieve normal adult height, the final adult height is still significantly below the genetic target. Growth retardation may persist after renal transplantation due to multiple factors, such as steroid use, decreased renal function and an abnormal GH–IGF1 axis. Those below age 6 years are the ones to benefit most from transplantation in demonstrating acceleration in linear growth. Newer treatment modalities targeting the GH resistance with recombinant human IGF-1 (rhIGF-1), recombinant human IGFBP3 (rhIGFBP3) and IGFBP displacers are under investigation and may prove to be more effective in treating growth failure in CKD.

IGF-I binding to the IGF-I receptor is affected by contaminants in commercial BSA: The contaminants are proteins with IGF-I binding properties

Objective To determine whether different albumins have an effect on IGF-I binding assays. Methods We have studied the effect of five different albumins in plate antibody capture binding assay. For IGF–IR studies the IGF–IR specific antibody 24-31 was used and for IR/IGF–IR hybrid receptors the IR specific antibody 83-7 was used. Binding to IGF–IR was studied by displacement of 125I-IGF-I with IGF-I in the absence or presence of 0.1%, 0.5% or 1% (w/v) albumin. The IR/IGF–IR hybrid receptors were studied in the presence of 0.5% (w/v) of HSA A-1887 and BSA A-7888 and with IGF-I or insulin displacement of 125I-IGF-I. The albumins used were purchased from Sigma–Aldrich. Two batches of albumins from each catalog number were tested. The albumins were: HSA A-1887, BSA A-4503, BSA A-6003, BSA A-7030, and BSA A-7888. Contaminants in the albumins were characterized as proteins with IGF-I binding properties by cross-linking to 125I-IGF-I and SDS-page analysis. Results BSA A-4503, A-7030 and A-7888 from Sigma–Aldrich contain proteins with IGF-I binding properties. These contaminants increased the determined EC50 for displacement of 125I-IGF-I from IGF–IR up to 40-fold in a BSA dependent manner. The presence of BSA-7888 in binding experiments increased the determined EC50 for IR/IGF–IR hybrid receptors 8–16-fold. Conclusions When IGF-I is characterized with respect to the effect on living cells and on binding to potential receptors unspecific binding to surfaces is often prevented by the addition of albumin in the assay. Here we report that when binding to the classical IGF–IR and IR/IGF–IR hybrid receptors are studied the measured EC50 values can be albumin dependent if it is contaminated with proteins with IGF-I binding properties. The free IGF-I concentration will be lower than estimated. Thus, the contaminated BSA preparations result in artifacts leading to misinterpretations and underestimation of the effect of IGF-I. Our results provide one possible explanation as to why different laboratories report different EC50 values for IGF-I.

Interstitial IGF-I in exercising skeletal muscle in women

To study interstitial IGF-I concentrations in resting and exercising skeletal muscle in relation to the circulating components of the IGF-IGF binding protein (IGFBP) system. Seven women performed endurance exercise with 1 leg (Ex-leg) for 1 h. The resting leg (Rest-leg) served as a control. IGF-I was determined in microdialysate (MD) and was compared with veno-arterial (v-a) concentrations of circulating IGF-IGFBP components. Median (range) basal MD-IGF-I was 0.87 (0.4-1.5) microg/l or 0.4 (0.2)% of total-IGF-I (t-IGF-I) determined in arterial serum and in the same concentration range as free dissociable IGF-I (f-IGF-I). Rest-leg MD-IGF-I decreased, reaching significance after exercise. Ex-leg MD-IGF-I was unchanged during exercise and declined after exercise at the level of significance (P = 0.05). There was a release of f-IGF-I from the Ex-leg into the circulation at the end of and shortly after exercise. A small but significant increase in circulating IGFBP-1 was detected at the end of exercise and IGFBP-1 increased further after exercise. Although interleukin-6 (IL-6) has been associated with IGFBP-3 proteolysis, the circulating molecular forms of IGFBP-3 remained unchanged in spite of an IL-6 release from the muscle compartment. Circulating IGFBP-1 is related to interstitial IGF-I in resting muscle although the temporal relationship may not be simple. Further studies should explore the role of local release of IGF-I and its impact on IGF-I activity during contraction.

Transgenic Overexpression of Pregnancy-Associated Plasma Protein-A Increases the Somatic Growth and Skeletal Muscle Mass in Mice

Although IGFs are indispensable to skeletal muscle development, little information is available regarding the mechanisms regulating the local action of IGFs in skeletal muscle tissues. Here we tested the hypothesis that pregnancy-associated plasma protein-A (PAPP-A), a member of the metalloproteinase superfamily, promotes skeletal muscle formation in vivo through degrading IGF binding proteins (IGFBPs), which increases the bioavailability of IGFs. Expression of PAPP-A is significantly increased in muscle five days after muscle injury in mice. Targeted overexpression of PAPP-A using a muscle-specific promoter significantly increased the prenatal/postnatal growth, skeletal muscle weight, and muscle fiber area in mice. These anabolic effects were reproduced using F2/F3 progeny. Free IGF-I concentration was severalfold higher in the conditioned medium (CM) of ex vivo cultured muscle from the transgenic mice, compared with the wild-type littermate muscle. Accordingly, the proliferation of C2C12 myoblasts was significantly increased in the presence of CM from cultured skeletal muscle of the transgenic mice, compared with the controls. This observed increase in myoblast proliferation was abolished on addition of noncleavable IGFBP-4 peptide, which reduced free IGF-I concentration back to the basal level of the wild-type CM. Furthermore, proliferation and differentiation of C2C12 myoblasts was increased by transient overexpression of proteolytically active PAPP-A but not by inactive mutant PAPP-A (E483/A). Collectively, we identified PAPP-A as a novel regulator of prenatal/postnatal growth and skeletal muscle formation in vivo. Moreover, our studies provide the first experimental evidence that IGFBP degradation is a key determinant in modulating the local action of IGFs in muscle.