IGF-I Bioactivity Research Articles

BI 836845, a fully human IGF ligand neutralizing antibody, to improve the efficacy of rapamycin by blocking rapamycin-induced AKT activation.

3092 Background: Analogs of rapamycin (rapalogs) targeting mammalian target of rapamycin complex 1 (mTORC1) have shown clinical activity in several cancers. Nonetheless, preclinical and clinical data suggest that there may be intrinsic resistance to rapalogs through a feedback loop which activates upstream signaling when mTORC1 is blocked. BI 836845 is a fully human antibody, currently in phase I clinical trials, which potently neutralizes both IGF-1 and IGF-2. We tested whether BI 836845 is able to improve the efficacy of rapamycin by inhibiting upstream signaling in preclinical models. Methods: Cancer cell lines were profiled in vitro and in vivo for sensitivity to BI 836845 and rapamycin, alone or in combination. Mitogenic signaling was examined by measuring levels of phosphorylated AKT (pAKT) using Western blot analysis. IGF bioactivity was determined using a cellular IGF-1R phosphorylation ELISA. Results: The combination of BI 836845 and rapamycin was more effective than either agent alone at inhibiting the proliferation of Ewing’s sarcoma cells cultured in vitro as well as in a nude mouse xenograft model in vivo. Analysis of cell signaling upstream of mTOR demonstrated that treatment with rapamycin alone resulted in elevated pAKT, indicating feedback loop activation. BI 836845 treatment alone or in combination with rapamycin inhibited AKT phosphorylation, demonstrating that the rapamycin-induced increase in pAKT was due to elevated IGF bioactivity. Consistent with this we demonstrated that rapamycin increased IGF bioactivity in mice and that this could be inhibited by BI 836845. We extended these studies to include other cancer cell lines and profiled the correlation between improved efficacy of the combination with BI 836845 inhibition of rapamycin-induced feedback. A correlation has been observed for cancer cells derived from several indications. Conclusions: Rapamycin treatment increases AKT activation via elevated IGF ligand bioactivity. This effect can be inhibited by BI 836845, thus explaining the improved pre-clinical efficacy seen when both agents are combined. These data provide a rationale for the clinical combination of rapalogs and BI 836845.

High IGFBP2 levels are not only associated with a better metabolic risk profile but also with increased mortality in elderly men

Serum IGF-binding protein 2 (IGFBP2) concentrations are reduced in obese humans and increase after a prolonged period of fasting. We investigated the association between IGFBP2 levels and mortality together with other factors that are related to IGFBP2, including the metabolic syndrome and physical function. A prospective observational study at a clinical research center of 403 independently living elderly men (aged 73-94 years). Mortality was registered during 8.6 years of follow-up. Physical performance score (PPS), grip strength (GS), and bone mineral density (BMD) were measured. The measurements taken a baseline were: IGF1; IGFBP1, -2, and -3; IGF1 bioactivity; triiodothyronine (T(3)); and reverse T(3). Further, BMI, insulin sensitivity, cholesterol, inflammatory markers, and albumin levels were also measured. During the follow-up, 180 men died. Higher PPS, GS, and BMD were independently related to a reduced mortality (hazard ratio (HR)=0.87/point, 95% confidence interval (95% CI)=0.82-0.91, P<0.001; HR=0.96/kp, 95% CI 0.94-0.98, P<0.001; and HR=0.21/(g/cm(2)), 95% CI 0.07-0.61, P<0.01). Higher serum IGFBP2 levels were strongly related to mortality (HR=2.26/(mg/l), 95% CI 1.57-3.27, P<0.001). This was independent of comorbidity, physical function, IGF1 bioactivity, and other somatotropic parameters, including BMI and the metabolic syndrome. In addition, IGFBP2 levels were higher in subjects with nonthyroidal illness, and higher IGFBP2 levels were significantly associated with lower albumin concentrations. Despite the strong relationship between high IGFBP2 and low physical function, both were strongly and independently related to increased 8-year mortality in elderly men. IGFBP2 may be a useful biomarker integrating the nutritional status, as well as the biological effects of GH, IGF1, and insulin.

Effects of bench step exercise on arterial stiffness in post-menopausal women: Contribution of IGF-1 bioactivity and nitric oxide production

ObjectiveTo examine the effect of bench step exercise on arterial pulse wave velocity (PWV) and the associated contribution of insulin-like growth factor (IGF)-1 bioactivity and nitric oxide (NO). DesignTwenty-six elderly (post-menopausal) women were randomly allocated to a bench step exercise group or a control group. The participants in the bench step exercise group practiced a 12-week home-based bench step exercise for 10–20min, 3 times daily (i.e., for a total of 140min/week at the intensity level of lactate threshold (LT)). In addition to conventional risk factors of atherosclerosis, PWV, IGF-1/IGF binding protein (IGFBP)-3 molar ratio (an index for IGF-1 bioactivity), and urinary nitrite/nitrate (NOx) excretion were measured before and after the intervention. ResultsBMI, systolic blood pressure, fasting plasma glucose, low-density lipoprotein cholesterol, LT, and PWV were significantly improved in the bench step exercise group. A significant positive correlation between changes in PWV and IGF-1/IGFBP-3 molar ratio, and a significant negative correlation between changes in IGF-1/IGFBP-3 molar ratio and urinary NOx excretion were found in the bench step exercise group. ConclusionThe bench step exercise leads to improvements in not only the classical risk factors of atherosclerosis but also the arterial stiffness in elderly women, partly through NO production via IGF-1 bioactivity.

Addition of insulin glargine or NPH insulin to metformin monotherapy in poorly controlled type 2 diabetic patients decreases IGF-I bioactivity similarly

Aims/hypothesisThe aim of this study was to compare IGF-I bioactivity 36 weeks after the addition of insulin glargine (A21Gly,B31Arg,B32Arg human insulin) or NPH insulin to metformin therapy in type 2 diabetic patients who had poor glucose control under metformin monotherapy.MethodsIn the Lantus plus Metformin (LANMET) study, 110 poorly controlled insulin-naive type 2 diabetic patients were randomised to receive metformin with either insulin glargine (G+MET) or NPH insulin (NPH+MET). In the present study, IGF-I bioactivity was measured, retrospectively, in 104 out of the 110 initially included LANMET participants before and after 36 weeks of insulin therapy. IGF-I bioactivity was measured using an IGF-I kinase receptor activation assay.ResultsAfter 36 weeks of insulin therapy, insulin doses were comparable between the G+MET (68 ± 5.7 U/day) and NPH+MET (71 ± 6.2 U/day) groups (p = 0.68). Before insulin therapy, circulating IGF-I bioactivity was similar between the G+MET (134 ± 9 pmol/l) and NPH+MET (135 ± 10 pmol/l) groups (p = 0.83). After 36 weeks, IGF-I bioactivity had decreased significantly (p = 0.001) and did not differ between the G+MET (116 ± 9 pmol/l) and NPH+MET (117 ± 10 pmol/l) groups (p = 0.91). At baseline and after insulin therapy, total IGF-I concentrations were comparable in both groups (baseline: G+MET 13.3 ± 1.0 vs NPH+MET 13.3 ± 1.0 nmol/l, p = 0.97; and 36 weeks: 13.4 ± 1.0 vs 13.1 ± 0.9 nmol/l, p = 0.71). Total IGF-I concentration did not change during insulin therapy (13.3 ± 0.7 vs 13.3 ± 0.7 nmol/l, baseline vs 36 weeks, p = 0.86).Conclusions/interpretationAddition of insulin glargine or NPH insulin to metformin monotherapy in poorly controlled type 2 diabetic patients decreases serum IGF-I bioactivity in a similar manner.

Abstract A208: Pharmacodynamic properties and antitumor efficacy of BI 836845, a fully human IGF ligand neutralizing antibody.

Abstract Insulin-like growth factor (IGF) signaling is thought to play an important role in the development of tumors and resistance to existing cancer therapies. The proliferative and pro-survival signals driven by the IGF ligands, IGF-1 and IGF-2, are transmitted through their binding to the IGF-1 receptor (IGF-1R). In addition, IGF-2 activates the insulin receptor variant A (IR-A) that is expressed during embryonic development as well as in many cancers. To target IGF signaling for cancer therapy we have developed BI 836845, a fully human IgG1 antibody derived from an antibody phage display library that can bind to and neutralize the functions of both IGF-1 and IGF-2. Surface plasmon resonance (Biacore) analysis demonstrated that BI 836845 has an affinity (KD) of 0.07 nM and 0.8 nM for human IGF-1 and IGF-2, respectively. BI 836845 also shows comparable affinities to mouse as well as rat IGF-1 and IGF-2, allowing a comprehensive pre-clinical characterization of the pharmacodynamic properties of the antibody in these species. Cell-based ELISA assays were used to demonstrate that BI 836845 potently neutralizes the ability of IGF-1 and IGF-2 to phosphorylate the human IGF-1R. Similarly, BI 836845 inhibits phosphorylation of IR-A driven by IGF-2. BI 836845 was also shown to completely and potently inhibit IGF bioactivity in human serum samples ex vivo. Pharmacodynamic effects of BI 836845 were studied in growing rats treated intravenously once weekly with 20, 60, or 200 mg/kg antibody. Inhibition of IGF bioactivity as determined by ex vivo IGF-1R phosphorylation potential in the plasma was observed at all dose levels, despite a corresponding increase in total IGF-1 levels. An increase in total IGF-1 levels has also been seen with IGF-1R targeted antibodies in clinical studies and is thought to be due to blockade of a growth hormone mediated physiological feedback mechanism. Treatment with BI 836845 resulted in a marked dose dependent reduction of rat body weight gain at all dose levels, consistent with the known role for IGFs in normal growth and development. BI 836845 potently inhibits the in vitro proliferation of cell lines derived from various cancers, with mesenchymal-derived cancer cell lines being particularly sensitive (EC50 values in the low nanomolar range). In a model of Ewing s sarcoma, using immunodeficient nude mice subcutaneously transplanted with human RD-ES cells, twice-weekly treatment with BI 836845 resulted in partial inhibition of tumor growth. Treatment in combination with rapamycin resulted in improved efficacy at tolerated doses. In conclusion, BI 836845 is a potent IGF ligand neutralizing antibody whose pharmacological profile warrants further investigation in clinical studies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A208.

Unbound (bioavailable) IGF1 enhances somatic growth

SUMMARY Understanding insulin-like growth factor-1 (IGF1) biology is of particular importance because, apart from its role in mediating growth, it plays key roles in cellular transformation, organ regeneration, immune function, development of the musculoskeletal system and aging. IGF1 bioactivity is modulated by its binding to IGF-binding proteins (IGFBPs) and the acid labile subunit (ALS), which are present in serum and tissues. To determine whether IGF1 binding to IGFBPs is necessary to facilitate normal growth and development, we used a gene-targeting approach and generated two novel knock-in mouse models of mutated IGF1, in which the native Igf1 gene was replaced by Des-Igf1 (KID mice) or R3-Igf1 (KIR mice). The KID and KIR mutant proteins have reduced affinity for the IGFBPs, and therefore present as unbound IGF1, or 'free IGF1'. We found that both KID and KIR mice have reduced serum IGF1 levels and a concomitant increase in serum growth hormone levels. Ternary complex formation of IGF1 with the IGFBPs and the ALS was markedly reduced in sera from KID and KIR mice compared with wild type. Both mutant mice showed increased body weight, body and bone lengths, and relative lean mass. We found selective organomegaly of the spleen, kidneys and uterus, enhanced mammary gland complexity, and increased skeletal acquisition. The KID and KIR models show unequivocally that IGF1-complex formation with the IGFBPs is fundamental for establishing normal body and organ size, and that uncontrolled IGF bioactivity could lead to pathological conditions.

Serum Pregnancy-Associated Plasma Protein A in Patients With Heart Failure

Background Pregnancy-associated plasma protein A (PAPP-A) proteolyzes insulin-like growth factor (IGF)–binding proteins and thus increases IGF-1 bioactivity. PAPP-A has been reported to be involved in various pathophysiologic abnormalities; however, the clinical significance of PAPP-A has not been examined in cases of heart failure (HF). We hypothesized that PAPP-A levels might be correlated with the severity of HF. Methods and Results PAPP-A and B-type natriuretic peptide (BNP) levels were measured in 262 subjects (182 HF patients and 80 control subjects). PAPP-A levels were higher in patients with HF than in control subjects and increased with advancing New York Heart Association functional class. There were 53 cardiac events during a mean follow-up period of 796 days. PAPP-A levels were higher in patients with cardiac events than in event-free patients. Patients were divided into 3 groups on the basis of their PAPP-A and BNP levels. Kaplan-Meier analysis demonstrated that the group with both high BNP with high PAPP-A had a significantly higher cardiac event rate than other groups. Conclusions Serum PAPP-A levels were related to the severity of HF and associated with a high risk for adverse cardiac events in HF patients, suggesting that PAPP-A might be involved in the pathogenesis of HF.

Unbound (bioavailable) IGF1 enhances somatic growth

SUMMARYUnderstanding insulin-like growth factor-1 (IGF1) biology is of particular importance because, apart from its role in mediating growth, it plays key roles in cellular transformation, organ regeneration, immune function, development of the musculoskeletal system and aging. IGF1 bioactivity is modulated by its binding to IGF-binding proteins (IGFBPs) and the acid labile subunit (ALS), which are present in serum and tissues. To determine whether IGF1 binding to IGFBPs is necessary to facilitate normal growth and development, we used a gene-targeting approach and generated two novel knock-in mouse models of mutated IGF1, in which the native Igf1 gene was replaced by Des-Igf1 (KID mice) or R3-Igf1 (KIR mice). The KID and KIR mutant proteins have reduced affinity for the IGFBPs, and therefore present as unbound IGF1, or ‘free IGF1’. We found that both KID and KIR mice have reduced serum IGF1 levels and a concomitant increase in serum growth hormone levels. Ternary complex formation of IGF1 with the IGFBPs and the ALS was markedly reduced in sera from KID and KIR mice compared with wild type. Both mutant mice showed increased body weight, body and bone lengths, and relative lean mass. We found selective organomegaly of the spleen, kidneys and uterus, enhanced mammary gland complexity, and increased skeletal acquisition. The KID and KIR models show unequivocally that IGF1-complex formation with the IGFBPs is fundamental for establishing normal body and organ size, and that uncontrolled IGF bioactivity could lead to pathological conditions.

Effects of chronic slow release-lanreotide treatment on insulin-like growth factor system and metabolic parameters in acromegalic patients.

Insulin and IGF binding protein (IGFBP)-1 are linked by negative association. Somatostatin (SS) reduces insulin secretion by acting on pancreatic β-cell and also by decreasing GH secretion. SS analogues in acromegaly reduce total IGF-I levels inhibiting GH hypersecretion, but they also reduce free IGF-I bioactivity increasing IGFBP-1 levels by inducing insulin decrease. In 13 acromegalic patients we studied GH, IGF system, insulin, and glucagon levels at baseline and at 7 days, 1 and 6 months under treatment with slow release (SR)-lanreotide (LAN) (60 mg im monthly). The hormonal and metabolic response to arginine (ARG) (0.5 g/kg iv in 30 min) was also studied at each time point. LAN decreased GH, total IGF-I, and IGFBP-3 levels at each time point. Insulin and glucagon levels were reduced, while IGFBP-1 and free IGF-I levels were increased by LAN at day 7 and after 1 month only. LAN did not modify the GH, insulin, glucagon, glucose, and IGFBP-1 responses to ARG. At each time point ARG-induced insulin increase was coupled to increase in glucagon and IGFBP-1 levels. This study shows that acromegalic patients under chronic treatment with LAN display: a) inhibition of GH and total IGF-I levels, not coupled to persistent decrease in free IGF-I levels; b) persistent decrease in IGFBP- 3 but transient decrease and increase in insulin and IGFBP- 1, respectively; c) unchanged hormonal and metabolic response to ARG. Our findings also show that ARG stimulates IGFBP-1 despite marked increase in insulin secretion; this escape from the negative relationship linking insulin and IGFBP- 1 would likely reflect the ARG-induced glucagon increase.

IGF-I Bioactivity Better Reflects Growth Hormone Deficiency than Total IGF-I

GH is considered the main regulator of circulating IGF-I. Total (extractable) IGF-I is therefore routinely used for diagnosis of GH deficiency (GHD) and for monitoring treatment. Methods currently used for measurement of circulating total IGF-I may be hampered by interferences of IGF-binding proteins. Recently a kinase receptor activation assay was developed to determine IGF-I bioactivity in human serum. The principle of this assay is based on quantification of IGF-I receptor activation after stimulation with serum in vitro. The objective of the study was to investigate the diagnostic potential of IGF-I bioactivity in adults with GHD. This was a single-center observational study. Ninety-four GH-untreated patients diagnosed with GHD by GH-provocative tests were included. IGF-I bioactivity (determined by the IGF-I kinase receptor activation assay) and total IGF-I (determined by immunoassay) were measured in fasting blood samples. IGF-I bioactivity was more frequently below the normal range (<-2 sd) in untreated GH-deficient patients than total IGF-I levels (81.9 vs. 61.7%, respectively), especially in patients older than 40 years of age. IGF-I bioactivity decreased with the duration of GHD, whereas total IGF-I did not. With a decreasing number of additional pituitary deficits, total IGF-I levels more frequently remained within the normal range, whereas the percentage below the normal range was high for IGF-I bioactivity, independent of additional deficits. Determination of IGF-I bioactivity may offer advantages in the evaluation of adult GHD compared with total IGF-I as bioactivity better reflects GHD as defined by GH stimulation tests, especially in subjects older than 40 years of age.

Physical Training Leads to Improved Fitness in CKD Despite no Change in Circulating Bioactive IGF-I

Chronic kidney disease (CKD) is characterized by abnormalities in the insulin-like growth factor (IGF) system. The measurement of bioactive IGF-I in response to physical activity may provide further insight into the therapeutic potential of exercise training in CKD patients. PURPOSE: The purpose of the present study was to assess changes in the IGF system, including bioactive IGF-I,in CKD patients following a training program. METHODS: Patients (N = 21) with CKD (stage 2-4) were randomized into matched treatment and control groups. The treatment group participated in 48 weeks of progressive exercise training and dietary counseling. The control group received only usual care. Fitness measurements and blood samples for analyses of immunoreactive IGF-I, IGF-II, IGFBP-1 and -2, and bioactive IGF-I were taken at baseline, 24 weeks, and 48 weeks. Bioactive IGF-1 was assessed using the kinase receptor activation assay (KIRA). RESULTS: There were no significant differences in any of the components of the IGF system (all p- values >.05). Immunoreactive IGF-I levels correlated significantly with bioactive IGF-I at baseline (r =.50, p =.02) and at 48 weeks (r =.64, p =.01). Both VO2peak (p =.03) and total treadmill time (TT) (p =.00) increased over 48 weeks in the treatment group. CONCLUSIONS: Despite improvements in physical performance in this CKD patient population, a 48-week training program did not affect either immunoreactive or bioactive circulating IGF-I. These data suggest that if the IGF-I system is involved or mediating these positive exercise-induced adaptations in CKD patients; changes are not reflected by blood/serum measurements. Funded by the Baystate Medical Center Incubator Fund.Table

Lack of circulating bioactive and immunoreactive IGF-I changes despite improved fitness in chronic kidney disease patients following 48 weeks of physical training

Objective As known abnormalities exist in the insulin-like growth factor (IGF) system in chronic kidney disease (CKD) patients, the measurement of bioactive IGF-I may provide further insight into the therapeutic potential of long-term exercise training. Design Patients ( N = 21) with stages 3 and 4 CKD were recruited from a local nephrology practice in Springfield, MA and randomized into matched treatment and control groups. The treatment group participated in 48 weeks of supervised, progressive exercise training and dietary counseling, while the control group received only usual care. Treadmill testing, anthropometric measurements, and blood samples for analysis of immunoreactive IGF-I, IGF-II, IGFBP-1 and -2, and bioactive IGF-I were taken at baseline, 24 weeks, and 48 weeks. Results There were no significant differences in any of the components of the IGF system (all p-values > 0.05). Immunoreactive IGF-I levels correlated significantly with bioactive IGF-I at baseline ( r = 0.50, p = 0.02) and at 48 weeks ( r = 0.64, p = 0.01). There was a significant interaction between group and time for both V̇O 2peak ( p = 0.03) and total treadmill time (TT) ( p < 0.01). Conclusions Despite improvements in physical performance, a 48-week training program did not affect any of the circulating IGF system measurements. Disparities between these findings and those of other researchers reporting a biphasic response to long-term training may be explained by differences in study groups and exercise programs.

Growth hormone treatment, final height, insulin-like growth factors, ghrelin, and adiponectin in four siblings with Seckel syndrome

To report on the effect of growth hormone (GH) treatment on final height (FH) and to describe the insulin-like growth factor (IGF) system, ghrelin, and adiponectin (ADPN) in children with Seckel syndrome. Four severely growth-retarded Iraqi siblings (two girls and two boys) with Seckel syndrome were referred at ages 16.5, 14.4, 12.4, and 10.4 years. They were born at term, but their growth was retarded and birth weight ranged between 1 and 1.5 kg. The children were healthy and had a normal response to GH provocative test. Long-term GH treatment of the youngest brother and sister increased the FH by 7.2 and 3.4 cm, respectively, compared with their older brother and sister. At FH, body mass index standard deviation scores (BMISDS) ranged from -3.0 to -3.9. Serum levels of immunoreactive IGF-1, bioactive IGF-1, and IGF-binding protein 3 were all within normal to high range before GH treatment and increased after GH treatment. Fasting plasma ghrelin remained severely reduced. Despite low BMISDS, plasma ADPN was moderately reduced and showed an almost complete absence of the low-molecular-weight subform. This is the first report on the effect of GH treatment on FH in children with Seckel syndrome. GH may have increased FH. In addition to growth defects and reduced BMISDS, patients with Seckel syndrome are characterized by low fasting ghrelin levels, low total ADPN, and near deficiency of the low-molecular-weight ADPN subform. The possible significance of the hormonal changes requires further investigations.

Conventional and novel biomarkers of treatment outcome in patients with acromegaly: discordant results after somatostatin analog treatment compared with surgery

Control of disease activity in acromegaly is critical, but the biochemical definitions remain controversial. To compare traditional and novel biomarkers and health status in patients with acromegaly treated with either surgery alone or somatostatin analog (SA). Sixty-three patients in long-term remission based on normalized total IGF1 levels after surgery alone (n=36) or SA (n=27) were studied in a cross-sectional manner. The groups were comparable at diagnosis regarding demographic and biochemical variables. Each subject underwent 3 h of serum sampling including a 2-h oral glucose tolerance test (OGTT). Health status was measured by two questionnaires: EuroQoL and Acrostudy (Patient-assessed-Acromegaly symptom questionnaire (PASQ)). Total and bioactive IGF1 (μg/l) levels were similar (total: 185 ± 10 (SA) versus 171 ± 8 (surgery) (P=0.28); bioactive: 1.9 ± 0.2 vs 1.9 ± 0.1 (P=0.70)). Suppression of total and free GH (μg/l) during OGTT was blunted in the SA group (total GH(nadir): 0.59 ± 0.08 (SA) versus 0.34 ± 0.06 (surgery) (P=0.01); free GH(nadir): 0.43 ± 0.06 vs 0.19 ± 0.04 (P<0.01)). The insulin response to OGTT was delayed, and the 2-h glucose level was elevated during SA treatment (P=0.02). Disease-specific health status was better in patients after surgery (P=0.02). i) Despite similar and normalized IGF1 levels, SA treatment compared with surgery alone was associated with less suppressed GH levels and less symptom relief; ii) this discordance may be due to specific suppression of hepatic IGF1 production by SA; iii) we suggest that biochemical assessment during SA treatment should include both GH and IGF1.

Brief, high intensity exercise alters serum ghrelin and growth hormone concentrations but not IGF-I, IGF-II or IGF-I bioactivity

Exercise stimulates growth hormone (GH) release, but there are conflicting reports regarding the acute effects of exercise on circulating ghrelin and insulin-like growth factor (IGF) concentrations. This investigation examined (1) the effect of a single sprint on circulating GH, ghrelin and IGF concentrations as well as a marker of IGF-I bioactivity, and (2) whether the number of muscle actions performed during a sprint influences these responses. Seven healthy men completed 3 trials in a random order. In two exercise trials they performed a single 30-s sprint on a cycle ergometer against a resistance equivalent to either 7% (FAST) or 9% (SLOW) of their body mass. In the other they rested in the laboratory (CON). Blood samples were taken pre-, immediately post-, 10 and 30 min post-exercise, and at equivalent times in the CON trial. Total ghrelin concentrations declined after the sprint and were significantly lower after 30 min of recovery than they were pre-exercise (pre-exercise vs. 30 min; FAST, 0.62 (0.19) vs. 0.49 (0.16) μg/L, P < 0.001; SLOW, 0.59 (0.15) vs. 0.47 (0.13) μg/L, P < 0.001). GH concentrations increased in both exercise trials and were greater in the FAST than the SLOW trial. Serum concentrations of total IGF-I, free IGF-I, total IGF-II, and IGF-I bioactivity did not change after sprinting. In conclusion, sprint exercise suppresses total ghrelin concentrations and stimulates GH release but does not alter IGF concentrations or bioactivity.

Association of plasma selenium concentrations with total IGF-1 among older community-dwelling adults: The InCHIANTI study

Insulin-like growth factor (IGF-1) stimulates cell proliferation and inhibits cell apoptosis. Recent studies underline its importance as anabolic hormone and nutritional marker in older individuals. IGF-1 synthesis and bioactivity are modulated by nutritional factors including selenium intake. However, whether circulating IGF-1 levels are positively influenced by plasma selenium, one of the most important human antioxidants, is still unknown. Selenium and total IGF-1 were measured in 951 men and women ≥ 65 years from the InCHIANTI study, Tuscany, Italy. Means (SD) of plasma selenium and total IGF-1 were 0.95 (0.15) μmol/L and 113.4 (31.2)ng/mL, respectively. After adjustment for age and sex, selenium levels were positively associated with total IGF-1 (β±SE: 43.76±11.2, p=0.0001). After further adjustment for total energy and alcohol intake, serum alanine aminotransferase (ALT), congestive heart failure, selenium remained significantly associated with IGF-1 (β±SE: 36.7±12.2, p=0.003). The association was still significant when IL-6 was introduced in the model (β±SE: 40.1±12.0, p=0.0008). We found an independent, positive and significant association between selenium and IGF-1 serum levels in community dwelling older adults.

Ascites from patients with alcoholic liver cirrhosis contains higher IGF‐I bioactivity than serum

Patients with liver cirrhosis have diminished hepatic IGF-I generation, resulting in low circulating levels, whereas data on IGF-I in ascites are sparse. Therefore, we compared the IGF-system in serum and ascites from cirrhotic patients. The study comprised 43 patients (12 females) with ascites and liver function of 58 +/- 10% of normal. Serum and ascites were collected concomitantly in the fasting state. In 11 patients, second serum and ascitic samples were collected within the first week. Eleven matched controls were also included. All samples were assayed for IGF-related parameters by immunoassays and by cell-based IGF-I bioassay. As compared with controls, serum total IGF-I, total IGF-II, pro-IGF-II and bioactive IGF-I were reduced in liver patients, whereas IGF-binding protein 1 (IGFBP-1), IGFBP-2 and the soluble IGF-II receptor were elevated (P < 0.005 for all). In ascites, all IGF-related peptides but pro-IGF-II were further reduced as compared with serum (P < 0.001). By contrast, bioactive IGF-I was fourfold elevated in ascites as compared with serum (2.20 +/- 0.33 vs. 0.55 +/- 0.08 microg/l, P < 0.001). In ascites, the IGF-I bioactivity signal was completely blocked by addition of IGFBP-3. Repetitive measurements (n = 11) in ascites showed that all peptides but IGFBP-1 remained unchanged within 1 week. It is a novel observation that the in vitro bioactivity of IGF-I can be higher in fluids from an extravascular compartment than in serum, in contrast to immunoreactive levels. This supports different roles for endocrine and paracrine/autocrine IGF-I, but the pathophysiological significance of our observation remains to be clarified.

Moderate energy restriction-induced weight loss affects circulating IGF levels independent of dietary composition

Obesity is associated with major changes in the circulating IGF system. However, it is not clear to what extent the IGF system is normalized following diet, and the possible role of different types of diet is also unknown. To compare changes in the circulating IGF system following 12 weeks of moderate energy restriction (7000 kJ/day) in overweight or obese males on a high protein high red meat diet (HP) or a high carbohydrate diet (HC). Seventy-six men (mean age, 51+/-1.0 years; body mass index, 32.8+/-0.5 kg/m(2)) were allocated to matched groups treated with isocaloric diets of HP (n=34) or HC (n=42). Outcome measures were weight, body composition, IGF-related peptides, homoeostasis model assessment of insulin resistance (HOMA1-IR) and adipokines. Weight loss did not differ between diets (HP 8.5+/-0.6 kg; HC 8.2+/-0.6 kg, P>0.05). IGF-related peptides increased total IGF1 (HP 23%; HC 18%, P<0.0001), bioactive IGF1 (HP 18%; HC 15%, P<0.002), IGF1:IGF-binding protein-3 (IGFBP-3; HP 29%; HC 22%, P<0.0001) and IGFBP-1 (HP 24%; HC 25%, P<0.01). By contrast, decreases were observed in IGFBP-3 (HP -4%; HC -3%, P<0.01), pro-IGF2 (HP -3%; HC -6%, P=0.001), total IGF2 (HP -7%; HC -3%, P=0.001) and sIGF2R (HP -10%; HC -6%, P<0.005). Only IGFBP-2 increased differentially by diet (HP 34%; HC 50%, P<0.0001, diet P<0.05). Adiponectin increased in both diets, but leptin and HOMA-IR decreased (P<0.001). Weight loss induced by moderate energy restriction modulated the IGF system independent of dietary protein or red meat content. The effect of diet on IGFBP-2 appeared to have limited biological effect as total IGF2 and pro-IGF2 did not change.

Silencing of the Insulin Receptor Isoform A Favors Formation of Type 1 Insulin-Like Growth Factor Receptor (IGF-IR) Homodimers and Enhances Ligand-Induced IGF-IR Activation and Viability of Human Colon Carcinoma Cells

Insulin receptor (IR) overexpression is common in cancers, with expression of the A isoform (IR-A, exon 11-) predominating over the B isoform. The IR-A signals a proliferative, antiapoptotic response to IGF-II, which itself can be secreted by tumors to establish an autocrine proliferative loop. Therefore, IGF-II signaling via the IR-A could mediate resistance to type 1 IGF receptor (IGF-IR) inhibitory drugs that are currently in development. This study addressed the role of the IR-A, using a small interfering RNA-based approach in SW480 human colon adenocarcinoma cells that coexpress the IGF-IR. Clonogenic survival was inhibited by depletion of the IGF-IR but not the IR-A, and dual receptor depletion had no greater effect than IGF-IR knockdown alone, suggesting that the IR-A could not compensate for IGF-IR loss. IGF-IR knockdown also resulted in a decrease in viability, whereas IR-A depletion resulted in increased viability. Consistent with this, upon IR-A depletion, we found a concomitant enhancement of IGF-IR activation by IGF-I and IGF-II, reduced formation of IGF-IR:IR-A hybrid receptors and increased IGF-IR homodimer formation. Together, these results suggest that IGF bioactivity is mediated more effectively by the IGF-IR than by the IR-A or receptor hybrids and that signaling via the IGF-IR is dominant to the IR-A in colon cancer cells that express both receptors.

IGF-I Bioactivity in an Elderly Population

OBJECTIVEThere is a complex relationship between IGF-I, IGF binding proteins, growth hormone, and insulin. The IGF-I kinase receptor activation assay (KIRA) is a novel method for measuring IGF-I bioactivity in human serum. We speculated that determination of IGF-I bioactivity might broaden our understanding of the IGF-I system in subjects with the metabolic syndrome. The purpose of our study was to investigate whether IGF-I bioactivity was related to insulin sensitivity and the metabolic syndrome.RESEARCH DESIGN AND METHODSWe conducted a cross-sectional study embedded in a random sample (1,036 elderly subjects) of a prospective population-based cohort study. IGF-I bioactivity was determined by the IGF-I KIRA. Categories of glucose (in)tolerance were defined by the 2003 American Diabetes Association criteria. Insulin sensitivity was assessed by homeostasis model assessment. The Adult Treatment Panel III definition of the metabolic syndrome was used.RESULTSIn subjects with normal fasting glucose and impaired fasting glucose, IGF-I bioactivity progressively increased with increasing insulin resistance, peaked at fasting glucose levels just below 7.0 mmol/l, and dropped at higher glucose levels. Mean IGF-I bioactivity peaked when three criteria of the metabolic syndrome were present and then declined significantly when five criteria of the metabolic syndrome were present.CONCLUSIONSWe observed that IGF-I bioactivity was related to insulin sensitivity, insulin levels, and the metabolic syndrome. Our study suggests that there exists an inverse U-shaped relationship between IGF-I bioactivity and number of components of the metabolic syndrome. This observation contrasts with previous results reporting an inverse relationship between total IGF-I and components of the metabolic syndrome.