Total IGF-I Levels Research Articles

High insulinlike growth factor I is associated with cognitive decline in Huntington disease

The somatotropic axis (growth hormone [GH] and insulinlike growth factor I [IGFI]) play a role in the cognitive deficits seen with aging, GH deficiency, and neurodegenerative disorders such as Alzheimer disease. We recently reported elevations in basal plasma GH and IGFI levels in patients with Huntington disease (HD). Here, our objective was to determine whether somatotropic axis abnormalities predicted cognitive dysfunction in HD. In this prospective cohort study of 109 patients with genetically documented HD, aged 21 to 85 years, we determined fasting blood levels of total IGFI, GH, and insulinlike factor binding protein 3 at baseline, and we used the cognitive Unified Huntington's Disease Rating Scale to assess cognitive impairment at baseline and for up to 5 years subsequently. Associations were evaluated using mixed linear model analysis. Higher plasma IGFI concentrations were associated with greater cognitive decline (beta Stroop Words, -6.01, p = 0.003; beta Stroop Color, -4.41, p = 0.01; beta Stroop Color/Words, -3.86, p = 0.02; beta Symbol Digit Modalities, -3.69, p = 0.03; and beta verbal fluency, -5.01, p = 0.03). Higher free IGFI concentrations and higher GH concentrations in men also predicted greater cognitive decline. Our findings in patients with HD suggest that a high IGFI level at baseline may be associated with greater subsequent declines in executive function and attention.

OR7,39 GH responsiveness in hypopituitary patients with very severe adult GHD using insulin, arginine or glucagon stimulation tests is associated with IGF-I SDS but not with the stimulated GH peak

levels did not differ (patients vs. controls: 701±87 vs. 572±33mg/l, P =0.17), whereas bioactive IGF-I tended to be lower in patients (5.37±0.55 vs. 6.63±0.25mg/l, P < 0.06). Conclusion: The baseline findings of elevated free GH and low bioactive IGF-I support the concept of GH resistance in uremic hemodialysis patients. Using high dose rhGH treatment it was possible to obtain normal responses in total and bioactive IGF-I levels, showing that the GH resistance may be overcome. Nevertheless, our data imply that the response of bioactive IGF-I to GH is subnormal in hemodialysis patients.

The Role of Insulin-Like Growth Factor (IGF) Binding Protein-2 in the Insulin-Mediated Decrease in IGF-I Bioactivity

ABSTRACT Context: Insulin interacts with the GH-IGF system by a reciprocal regulation of IGF-binding proteins (IGFBP) and GH, which in turn regulate insulin sensitivity via bioactive IGF-I. This network is linked to metabolic syndrome and cardiovascular diseases. Objective: We evaluated the effect of glucose and insulin on IGFBP-1-4, particularly IGFBP-2, in the regulation of bioactive IGF-I and its relation to insulin resistance. Setting: The study was conducted at an endocrinology center. Research Design and Methods: Twenty-four healthy subjects (12 men; aged 21–72 yr; body mass index 25.9 ± 0.9 kg/m2) and 19 subjects with impaired glucose tolerance (IGT; eight men; aged 26–71 yr; body mass index 28.9 ± 1.2 kg/m2 ) were prospectively studied using oral glucose tolerance test and hyperinsulinemic euglycemic clamp. Results: During the clamp, insulin decreased IGF-I bioactivity in both IGT subjects and controls (−16.2 ± 2.8 and −13.9 ± 3.3%, respectively; P &amp;lt; 0.01). In addition, insulin increased IGFBP-2 and GH and decreased IGFBP-1 and -4 but did not alter total IGF-I, IGF-II, or IGFBP-3 levels. During the oral glucose tolerance test, GH and IGFBP-1 were markedly suppressed. Subjects with IGT showed more pronounced insulin resistance and lower GH, IGFBP-1, and IGFBP-2 levels (P &amp;lt; 0.05). In multiple regression analysis, IGFBP-2 was an independent predictor of insulin sensitivity (β = 0.36, P &amp;lt; 0.05) and IGF-I bioactivity (β = −0.5, P &amp;lt; 0.05). Conclusions: Our data indicate that insulin acutely decreases IGF-I bioactivity through differential modulation of IGFBPs. Furthermore, IGFBP-2 plays a central role in the insulin-IGF system cross talk and is closely linked to insulin resistance, thereby providing a further explanation for its association with the metabolic syndrome.

The Role of Insulin-Like Growth Factor (IGF) Binding Protein-2 in the Insulin-Mediated Decrease in IGF-I Bioactivity

Insulin interacts with the GH-IGF system by a reciprocal regulation of IGF-binding proteins (IGFBP) and GH, which in turn regulate insulin sensitivity via bioactive IGF-I. This network is linked to metabolic syndrome and cardiovascular diseases. We evaluated the effect of glucose and insulin on IGFBP-1-4, particularly IGFBP-2, in the regulation of bioactive IGF-I and its relation to insulin resistance. The study was conducted at an endocrinology center. Twenty-four healthy subjects (12 men; aged 21-72 yr; body mass index 25.9 +/- 0.9 kg/m(2)) and 19 subjects with impaired glucose tolerance (IGT; eight men; aged 26-71 yr; body mass index 28.9 +/- 1.2 kg/m(2)) were prospectively studied using oral glucose tolerance test and hyperinsulinemic euglycemic clamp. During the clamp, insulin decreased IGF-I bioactivity in both IGT subjects and controls (-16.2 +/- 2.8 and -13.9 +/- 3.3%, respectively; P < 0.01). In addition, insulin increased IGFBP-2 and GH and decreased IGFBP-1 and -4 but did not alter total IGF-I, IGF-II, or IGFBP-3 levels. During the oral glucose tolerance test, GH and IGFBP-1 were markedly suppressed. Subjects with IGT showed more pronounced insulin resistance and lower GH, IGFBP-1, and IGFBP-2 levels (P < 0.05). In multiple regression analysis, IGFBP-2 was an independent predictor of insulin sensitivity (beta = 0.36, P < 0.05) and IGF-I bioactivity (beta = -0.5, P < 0.05). Our data indicate that insulin acutely decreases IGF-I bioactivity through differential modulation of IGFBPs. Furthermore, IGFBP-2 plays a central role in the insulin-IGF system cross talk and is closely linked to insulin resistance, thereby providing a further explanation for its association with the metabolic syndrome.

Bioactive IGF-I in Obesity

Bioactive IGF-I in Obesity

Ghrelin treatment protects lactotrophs from apoptosis in the pituitary of diabetic rats

Poorly controlled diabetes is associated with hormonal imbalances, including decreased prolactin production partially due to increased lactotroph apoptosis. In addition to its metabolic actions, ghrelin inhibits apoptosis in several cell types. Thus, we analyzed ghrelin's effects on diabetes-induced pituitary cell death and hormonal changes. Six weeks after onset of diabetes in male Wistar rats (streptozotocin 70 mg/kg), minipumps infusing saline or 24 nmol ghrelin/day were implanted (jugular). Rats were killed two weeks later. Ghrelin did not modify body weight or serum glucose, leptin or adiponectin, but increased total ghrelin ( P < 0.05), IGF-I ( P < 0.01) and prolactin ( P < 0.01) levels. Ghrelin decreased cell death, iNOS and active caspase-8 ( P < 0.05) and increased prolactin ( P < 0.05), Bcl-2 ( P < 0.01) and Hsp70 ( P < 0.05) content in the pituitary. In conclusion, ghrelin prevents diabetes-induced death of lactotrophs, decreasing caspase-8 activation and iNOS content and increasing anti-apoptotic pathways such as pituitary Bcl-2 and Hsp70 and serum IGF-I concentrations.

Bioactive Insulin-Like Growth Factor-I in Obesity

In obesity, total IGF-I is not reduced to the degree predicted by low GH levels, and free IGF-I levels are normal to high. Total and free IGF-I may not reflect IGF-I biological activity because immunoassays cannot account for the modifying effects of IGF binding proteins on interactions between IGF-I and its receptor. The aim of the study was to investigate the biological activity of IGF-I in obesity. We conducted a cross-sectional study at a General Clinical Research Center. Thirty-four healthy women (11 lean, 12 overweight, and 11 obese) of comparable age (overall mean, 30.7 +/- 1.3 yr) participated in the study. There were no interventions. We measured bioactive IGF-I (as measured by a kinase receptor activation assay), IGFBP-1, and GH using 6-h pools of serum collected every 10 min for 24 h, and fasting IGF-I and IGFBP-3. Mean 24-h GH (R = -0.76; P < 0.0001), total IGF-I (R = -0.36; P = 0.040), and IGFBP-1 (R = -0.41; P = 0.017) levels were inversely associated with BMI, whereas bioactive IGF-I and IGFBP-3 levels were not. Mean bioactive IGF-I was similar in the groups [2.72 +/- 0.22 (lean), 3.10 +/- 0.32 (overweight), and 2.43 +/- 0.23 [corrected] (obese) microg/liter; overall P = 0.22]. Percentage bioactive IGF-I [(bioactive/total IGF-I) x 100] was higher in obese subjects than both lean and overweight subjects (P = 0.039). Despite low GH secretion in obesity and decreasing IGFBP-1 with increasing BMI, 24-h mean bioactive IGF-I levels are not reduced in obese women and do not correlate with BMI or IGFBP-1 levels. This argues against elevated bioactive IGF-I as the etiology of reduced GH secretion through a feedback mechanism in obesity.

Intact and total insulin-like growth factor-binding protein-3 (IGFBP-3) levels in relation to breast cancer risk factors: a cross-sectional study

IntroductionLevels of insulin-like growth factor (IGF)-I and its main binding protein (IGFBP-3) have been associated with breast cancer risk among premenopausal women. However, associations of IGFBP-3 levels with breast cancer risk have been inconsistent, possibly due to the different predominant forms of circulating IGFBP-3 (intact versus fragmented) that were measured in these studies. Here, we examine the association of breast cancer risk factors with intact and total IGFBP-3 levels.MethodsThis cross-sectional study includes 737 premenopausal women recruited at screening mammography. Plasma intact and total IGFBP-3 and IGF-I levels were measured by enzyme-linked immunosorbent assay methods. Percent and absolute breast density were estimated using a computer-assisted method. The associations were evaluated using generalized linear models and Pearson (r) or Spearman (rs) partial correlation coefficients.ResultsMeans ± standard deviations of intact and total IGFBP-3 levels (ng/mL) were 1,044 ± 234 and 4,806 ± 910, respectively. Intact and total IGFBP-3 levels were correlated with age and smoking. Levels of intact IGFBP-3 were negatively correlated with waist-to-hip ratio (WHR) (r = -0.128; P = 0.0005), parity (rs = -0.078; P = 0.04), and alcohol intake (r = -0.137; P = 0.0002) and positively correlated with energy intake (r = 0.075; P = 0.04). In contrast, total IGFBP-3 levels were positively correlated with WHR (r = 0.115; P = 0.002), parity (rs = 0.089; P = 0.02), body mass index (BMI) (r = 0.115; P = 0.002), physical activity (r = 0.118; P = 0.002), and IGF-I levels (r = 0.588; P < 0.0001) and negatively correlated with percent or absolute breast density (r = -0.095; P = 0.01 and r = -0.075; P = 0.04, respectively).ConclusionOur data show that associations of some breast cancer risk factors with intact levels of IGFBP-3 are different from those with total (intact and fragmented) IGFBP-3 levels. These findings suggest that different molecular forms of IGFBP-3 may bear different relations to premenopausal breast cancer risk.

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.

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.

Normal Values of Circulating Insulin-Like Growth Factor-I Bioactivity in the Healthy Population: Comparison with Five Widely Used IGF-I Immunoassays

IGF-I immunoassays are primarily used to estimate IGF-I bioactivity. Recently an IGF-I-specific kinase receptor activation assay (KIRA) has been developed as an alternative method. However, no normative values have been established for the IGF-I KIRA. The objective of the study was to establish normative values for the IGF-I KIRA in healthy adults. This was a cross-sectional study in healthy nonfasting blood donors. Participants included 426 healthy individuals (310 males, 116 females; age range 18-79 yr). IGF-I bioactivity determined by the KIRA was measured. Results were compared with total IGF-I, measured by five different IGF-I immunoassays. Mean (+/- sd) IGF-I bioactivity was 423 (+/- 131) pmol/liter and decreased with age (beta = -3.4 pmol/liter.yr, P < 0.001). In subjects younger than 55 yr, mean IGF-I bioactivity was significantly higher in women than men. Above this age this relationship was inverse, suggesting a drop in IGF-I bioactivity after menopause. This drop was not reflected in total IGF-I levels. IGF-I bioactivity was significantly related to total IGF-I (r(s) varied between 0.46 and 0.52; P < 0.001). We established age-specific normative values for the IGF-I KIRA. We observed a significant drop in IGF-I bioactivity in women between 50 and 60 yr, which was not perceived by IGF-I immunoassays. The IGF-I KIRA, when compared with IGF-I immunoassays, theoretically has the advantage that it measures net effects of IGF-binding proteins on IGF-I receptor activation. However, it has to be proven whether information obtained by the IGF-I KIRA is clinically more relevant than measurements obtained by IGF-I immunoassays.

High insulinlike growth factor binding protein 1 level predicts incident congestive heart failure in the elderly

Low levels of insulinlike growth factor 1 (IGF-I) may influence the development of age-related cardiovascular diseases including congestive heart failure (CHF). Insulinlike growth factor binding protein 1 (IGFBP-1), which increases during catabolic states and inhibits anabolic IGF-I effects, is increased in patients with CHF and has been associated prospectively with increased mortality among older adults and survivors of myocardial infarction. We investigated the association between fasting plasma levels of IGF-I, IGFBP-1, IGFBP-3, and insulin and risk of incident CHF in the prospective Cardiovascular Health Study. From among 5,888 adults 65 years old and older in the Cardiovascular Health Study, we studied 566 incident CHF cases and 1,072 comparison subjects after exclusion of underweight individuals (body mass index <18.5 kg/m(2)) and insulin users. Hazard ratios (HRs) with 95% CIs for CHF were estimated after adjustment for age, race, sex, hypertension, systolic blood pressure, lipid levels, left ventricular hypertrophy, coronary disease, C-reactive protein, health status, diabetes, and body mass index. High baseline IGFBP-1 level was a significant predictor of CHF, independent of established CHF risk factors and inflammation markers. The HR per SD of IGFBP-1 was 1.22 (95% CI 1.07-1.39, P < .01). Relative to the lowest IGFBP-1 tertile, the HR was 1.29 (95% CI 0.96-1.74, P = .09) for the second IGFBP-1 tertile and 1.47 (95% CI 1.06-2.04; P = .02) for the highest IGFBP-1 tertile (tertile cut points 19.5 and 35.8 ng/mL). Total IGF-I, IGFBP-3, or insulin levels had no association with CHF after adjustment for CHF risk factors. High circulating IGFBP-1 level may be a CHF risk factor among older adults.

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.

Effects of a high-glucose environment on the pituitary growth hormone-releasing hormone receptor: type 1 diabetes compared with in vitro glucotoxicity

The present study investigated the effects of diabetes and high glucose on GHRH receptor (GHRH-R) mRNA and protein levels in the pituitary of diabetic rats 2, 21, and 60 days post-streptozotocin (post-STZ) administration. Two days post-STZ, the 2.5-kb GHRH-R mRNA transcript was increased. Twenty-one days post-STZ, both the 2.5- and 4-kb transcripts and a 72-kDa (125)I-GHRH-GHRH-R complex were elevated. Sixty days post-STZ, the 4-kb transcript remained increased and the 45-kDa (125)I-GHRH-GHRH-R complex (functional receptor) was decreased. Hypothalamic GHRH mRNA and serum total IGF-I levels were reduced at all three time points. To better understand the role of high glucose on GHRH-R regulation, time-course effects of 33 compared with 6 mM d-glucose (DG) were examined in cultured anterior pituitary cells from 2-mo-old healthy rats. Membrane lipoperoxidation was present in 33 mM DG, and GHRH-R mRNA levels were diminished after 24 h, Fluo-GHRH internalization was marginal after 16-24 h, and GHRH-induced cAMP levels were decreased after 24 and 48 h. Altogether, these results indicate that the increase of the 2.5-kb GHRH-R mRNA transcript in vivo could be a consequence of a decrease of hypothalamic GHRH mRNA levels in STZ rats. Since it does not affect primarily functional GHRH-R levels, the initial diminution of circulating IGF-I levels could result from a decreased GHRH-R stimulation by GHRH. Thus, the effect of glucotoxicity would be related to a decrease of functional GHRH-R protein, as observed in rats 60 days post-STZ and in cultured pituitary cells from healthy rats exposed to a high-glucose environment.

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.

Assessing the potential usefulness of IGF-related peptides and adiponectin for predicting disease risk

ObjectiveInsulin-like growth factors (IGF), their binding proteins and adiponectin have been investigated as potential blood-based biomarkers for a variety of diseases. Before these circulating proteins can be considered as biomarkers, their variation within and between individuals and between published studies must be critically assessed. The purpose of this study was to use the D-value to predict the potential usefulness of IGF-related peptides and adiponectin as biomarkers for the diagnosis of colorectal cancer (CRC). DesignIntra- and inter-individual variation of total IGF-I and -II, IGF binding protein 1 (IGFBP-1), -2 and -3 and adiponectin, was examined in 10 healthy subjects over a 5 week period. This data was analysed in conjunction with previous publications to provide a D-value, which is a theoretical value that identifies the usefulness of the analyte individually and as a panel, as a biomarker for CRC. ResultsA single measurement of total IGF-I and -II, and adiponectin provided a reproducible representation of their circulating concentrations. The D-value for total IGF-II and IGFBP-3 were 0.5 and 0.47, respectively, which corresponded to area under the curve (AUC) values of 64 and 63%. Combining these analytes into a panel only slightly improved the D-value to 0.63 (AUC was 67%). ConclusionsAlthough serum levels of total IGF-I, total IGF-II and IGFBP-3 are stable and reproducible, the D-value calculations indicate that they have limited importance when used as biomarkers of CRC.

Age-Related Alterations in Pituitary and Testicular Functions in Long-Lived Growth Hormone Receptor Gene-Disrupted Mice

The somatotropic axis, GH, and IGF-I interact with the hypothalamic-pituitary-gonadal axis in health and disease. GH-resistant GH receptor-disrupted knockout (GHRKO) male mice are fertile but exhibit delayed puberty and decreases in plasma FSH levels, testicular content of LH, and prolactin (PRL) receptors, whereas PRL levels are elevated. Because the lifespan of GHRKO mice is much greater than the lifespan of their normal siblings, it was of interest to compare age-related changes in the hypothalamic-pituitary-gonadal axis in GHRKO and normal animals. Plasma IGF-I, insulin, PRL, LH, FSH, androstenedione and testosterone levels, and acute responses to GnRH and LH were measured in young (2-4 and 5-6 months of age) and old (18-19 and 23-26 months of age) male GHRKO mice and their normal siblings. Plasma IGF-I was not detectable in GHRKO mice. Plasma PRL levels increased with age in normal mice but declined in GHRKO males, and did not differ in old GHRKO and normal animals. Plasma LH responses to acute GnRH stimulation were attenuated in GHRKO mice but increased with age only in normal mice. Plasma FSH levels were decreased in GHRKO mice regardless of age. Plasma testosterone responses to LH stimulation were attenuated in old mice regardless of genotype, whereas plasma androstenedione responses were reduced with age only in GHRKO mice. Testicular IGF-I mRNA levels were normal in young and increased in old GHRKO mice, whereas testicular concentrations and total IGF-I levels were decreased in these animals. These findings indicate that GH resistance due to targeted disruption of the GH receptor gene in mice leads to suppression of testicular IGF-I levels, and modifies the effects of aging on plasma PRL levels and responses of the pituitary and testes to GnRH and LH stimulation. Plasma testosterone levels declined during aging in normal but not in GHRKO mice, and the age-related increase in the LH responses to exogenous GnRH was absent in GHRKO mice, perhaps reflecting a delay of aging in these remarkably long-lived animals.

IGF-I measurements in the monitoring of GH therapy

Growth hormone replacement therapy has been used regularly in adult Growth hormone deficiency since the availability of recombinant GH in the 1980's. GH replacement improves quality of life, bone turnover markers, cardiovascular risk markers and adverse body composition. Originally, GH doses in replacement regimes were determined by weight and surface area and dose increases based on body composition outcomes analogous to pediatric practice. These regimens led to significant side effects related to excess GH, arthralgias, headaches and peripheral edema and IGF-I levels above the upper limit of the reference range. Newer treatment regimes therefore account for known factors affecting serum GH and IGF-I levels, i.e. age, gender, estrogen replacement and pre-treatment IGF-I levels. Monitoring is now via clinical symptomatology combined with serum total IGF-I levels, potentially this avoids excessive GH exposure and allows monitoring of compliance and dose titration. There is a lack of data relating IGF-I to biological endpoints, but analysis suggests that dose titration of IGF-I to the upper half of the age and gender related reference range is acceptable. The use of reliable IGF-I assays and extensive age and gender related reference ranges is necessary and centralized monitoring is preferable. Free IGF-I and bioavailable IGF-I measurements are available but their use in the monitoring of GH replacement remains to be determined.

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

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. 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. A case-cohort analysis was conducted among adults 65 yr and older in the Cardiovascular Health Study. 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. 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. 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.