Serum levels of insulin-like growth factor I and its binding proteins in health and disease

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

Associations of IGF1 and IGFBPs 1 and 3 with all-cause and cardiovascular mortality in older men: the Health In Men Study

OBJECTIVE

Circulating IGF1 declines with age while ill-health increases. Controversy remains whether differences in the levels of IGF1 and its binding proteins 1 and 3 (IGFBP1 and IGFBP3) determine health outcomes during ageing. We examined associations of IGF1, IGFBP1 and IGFBP3 with all-cause and cardiovascular mortality in older men.

DESIGN

We conducted a prospective cohort study of community-dwelling men aged ≥70 years.

METHODS

Plasma collected at baseline (2001-2004) was assayed for total IGF1, IGFBP1 and IGFBP3. Incidence and causes of death from time of recruitment to 31 December 2008 were ascertained using the Western Australian Data Linkage System. Cox regression analyses were performed, adjusting for conventional cardiovascular risk factors.

RESULTS

Among 3983 men followed for 5.2 years (median), 694 deaths occurred, 243 from cardiovascular disease (CVD). There was no difference in survival according to quintiles of IGF1. Increased IGFBP1 predicted increased all-cause mortality (highest versus lowest quintile: adjusted hazard ratio (HR)=1.98, 95% confidence interval (CI)=1.52-2.57, P<0.001 for trend) and increased cardiovascular mortality (HR=3.42 (2.03-5.77), P<0.001 for trend). Decreased IGFBP3 predicted increased all-cause mortality (lowest versus highest quintile: HR=1.57, 95% CI=1.23-2.01, P=0.007 for trend). Associations of IGFBP1 and IGFBP3 with all-cause mortality were not attenuated by adjustment for IGF1 levels.

CONCLUSIONS

In older men, higher IGFBP1 and lower IGFBP3 levels predict overall and CVD-related mortality, while IGF1 levels are not associated with mortality. Further studies are needed to clarify the underlying mechanisms by which IGFBP1 and IGFBP3 levels are associated with mortality risk, and whether this occurs independently of IGF1.

Association of IGF-I and IGFBP-3 with health care costs and hospitalization: results from a prospective observational study

OBJECTIVE

Previous cohort studies found robust associations of serum insulin-like growth factor I (IGF-I) and its main binding protein IGFBP-3 with increased morbidity or mortality. This study investigates the relationships between IGF-I and IGFBP-3 with health care costs and hospitalization in a general population and whether adding IGF-I or IGFBP-3 to a model of established health care predictors improves prediction.

METHODS

Data from a population-based cohort study of 3139 men and women in Germany, aged 20 to 80 years at baseline were used (median follow-up time: 5.0 years). Self-reported physician visits, length of hospital stay were used to estimate annual costs. IGF-I and IGFBP-3 were categorized at the 10th and 90th percentile, to indicate 'low', 'intermediate', and 'high' concentrations, respectively.

RESULTS

Total annual health care costs, with the major component of inpatient costs, and risk of hospitalization at baseline and follow-up were higher in subjects with low compared to intermediate IGF-I or IGFBP-3, after multivariable-adjustment. Subjects with low in contrast to intermediate IGF-I exhibited 30.6% higher annual total costs 5 years after baseline examination, corresponding to a difference in adjusted costs of EUR436.61.

CONCLUSIONS

Low IGF-I and IGFBP-3 independently predict future health care costs and hospitalization. IGF-I or IGFBP-3 might be useful to identify subjects with excess health care use. The predictive performance of cross-sectional and longitudinal models of total and inpatient costs were slightly improved by adding IGF-I or IGFBP-3 but the cost-effectiveness of inclusion into prediction models needs to be examined.

All-cause mortality and serum insulin-like growth factor I in primary care patients

OBJECTIVE

Previous population-based studies provided conflicting results regarding the association of total serum insulin-like growth factor I (IGF-I) and mortality. The aim of the present study was to assess the relation of IGF-I levels with all-cause mortality in a prospective study.

DESIGN

DETECT (Diabetes Cardiovascular Risk-Evaluation: Targets and Essential Data for Commitment of Treatment) is a large, multistage, and nationally representative study of primary care patients in Germany. The study population included 2463 men and 3603 women. Death rates were recorded by the respective primary care physician. Serum total IGF-I levels were determined by chemiluminescence immunoassays and categorized into three groups (low, moderate, and high) according to the sex- and age-specific 10th and 90th percentiles.

RESULTS

Adjusted analyses revealed that men with low [hazard ratio (HR) 1.70 (95% confidence interval [CI] 1.05-2.73), p=0.03] and high [HR 1.76 (95% CI 1.09-2.85), p=0.02] IGF-I levels had higher risk of all-cause mortality compared to men with moderate IGF-I levels. The specificity of low IGF-I and high IGF-I levels increased with lower and higher cut-offs, respectively. No such association became apparent in women.

CONCLUSIONS

The present study revealed a U-shaped relation between IGF-I and all-cause mortality in male primary care patients.

Milk intake and total dairy consumption: associations with early menarche in NHANES 1999-2004

BACKGROUND

Several components of dairy products have been linked to earlier menarche.

METHODS/FINDINGS

This study assessed whether positive associations exist between childhood milk consumption and age at menarche or the likelihood of early menarche (<12 yrs) in a U.S sample. Data derive from the National Health and Nutrition Examination Survey (NHANES) 1999-2004. Two samples were utilized: 2657 women age 20-49 yrs and 1008 girls age 9-12 yrs. In regression analysis, a weak negative relationship was found between frequency of milk consumption at 5-12 yrs and age at menarche (daily milk intake β = -0.32, P<0.10; "sometimes/variable milk intake" β = -0.38, P<0.06, each compared to intake rarely/never). Cox regression yielded no greater risk of early menarche among those who drank milk "sometimes/varied" or daily vs. never/rarely (HR: 1.20, P<0.42, HR: 1.25, P<0.23, respectively). Among the 9-12 yr olds, Cox regression indicated that neither total dairy kcal, calcium and protein, nor daily milk intake in the past 30 days contributed to early menarche. Girls in the middle tertile of milk intake had a marginally lower risk of early menarche than those in the highest tertile (HR: 0.6, P<0.06). Those in the lowest tertiles of dairy fat intake had a greater risk of early menarche than those in the highest (HR: 1.5, P<0.05, HR: 1.6, P<0.07, lowest and middle tertile, respectively), while those with the lowest calcium intake had a lower risk of early menarche (HR: 0.6, P<0.05) than those in the highest tertile. These relationships remained after adjusting for overweight or overweight and height percentile; both increased the risk of earlier menarche. Blacks were more likely than Whites to reach menarche early (HR: 1.7, P<0.03), but not after controlling for overweight.

CONCLUSIONS

There is some evidence that greater milk intake is associated with an increased risk of early menarche, or a lower age at menarche.

The effect of Helicobacter pylori and economic status on growth parameters and leptin, ghrelin, and insulin-like growth factor (IGF)-I concentrations in children

BACKGROUND

It was suggested that gastric colonization with Helicobacter pylori (H. pylori) was associated with suboptimal nutrition and growth in childhood. Furthermore, several studies indicated a relationship between H. pylori colonization and alterations in the circulating levels of growth-related molecules (GRM). Accordingly, in this study, we investigate the effect of H. pylori infection on GRMs and on the growth of healthy school children, taking into consideration the effect of their economic status (ES) and anthropometric indices of their parents.

METHODS

To acquire sociodemographic and anthropometric nutritional parameters and to detect H. pylori-specific serum IgG antibodies and growth-related molecules, we evaluated a total of 473 children attending four different primary and secondary schools in Istanbul. Subsequently, we assessed the effect of H. pylori on growth-related parameters (weight for age SDS, height for age SDS, BMI SDS, TSF, and waist-to-hip ratio) and on GRMs (leptin, ghrelin, and insulin-like growth factor-1 (IGF-1)), controlling for age, gender, family income, household crowding (HC), breastfeeding, maternal and paternal BMI SDS, and midparental height SDS with complex statistical models.

RESULTS

Of the 473 children (275 F/198 M, age 6-15 years; mean: 10.3 ± 0.1 years), 161 (34%) were H. pylori-positive. The prevalence of H. pylori was significantly higher in lower economic status (ES) groups, in children living in crowded houses, and in older age groups. Using simple statistical models, we did not find any significant associations between H. pylori infection and the growth parameters. However, in complex models for height for age SDS and for weight for age SDS, there was a significant interaction between H. pylori infection status and ES. Whereas in H. pylori-positive subjects, mid-income family children were both taller and heavier than the low-income group, there was no such an association in H. pylori-negative subjects. Among biochemical parameters, only ghrelin levels were associated with H. pylori infection in all models. Leptin levels were associated with HC in girls, whereas none of the parameters was significantly associated with leptin levels in boys. For IGF-1 levels, for boys, age and maternal BMI, and for girls, age and HC were significantly associated with IGF-1 levels.

CONCLUSION

We suggest that H. pylori may impair growth significantly only in susceptible children where unfavorable socioeconomic conditions facilitate its action, probably through mechanisms, at least in part, involving growth-related molecules.

Polymorphisms of insulin-like growth factor-1 (IGF-1) and IGF-1 receptor (IGF-1R) contribute to pathologic progression in childhood IgA nephropathy

Previous studies have suggested that insulin-like growth factor-1 (IGF-1) signaling might play an important role in renal fibrosis and regulation of the proliferation of mesangial cells and podocytes. We conducted the present study to investigate association between single nucleotide polymorphisms (SNPs) of IGF-1 (IGF-1) and IGF-1 receptor (IGF-1R) genes and childhood immunoglobulin (Ig) A nephropathy (IgAN). We analyzed five SNPs of IGF-1 and IGF-1R in 188 pediatric IgAN patients and in 263 healthy controls. We compared variations in SNPs in several sets of IgAN subgroups that were designated based on the presence of nephrotic range proteinuria (>40 mg/m2 per h), podocyte foot process effacement, and pathological progression. Genotyping of IgAN patients and controls revealed differences in IGF-1R rs2229765. Moreover, the rs2195239, rs978458, and rs1520220 SNPs of IGF-1 showed significant association with pathological progression. Thus, in the present study, we observed associations between the IGF-1/1R pathway, susceptibility to IgAN, and the pathologic progression of IgAN.

Dystroglycan modulates the ability of insulin-like growth factor-1 to promote oligodendrocyte differentiation

The adhesion receptor dystroglycan positively regulates terminal differentiation of oligodendrocytes, but the mechanism by which this occurs remains unclear. Using primary oligodendrocyte cultures, we identified and examined a connection between dystroglycan and the ability of insulin-like growth factor-1 (IGF-1) to promote oligodendrocyte differentiation. Consistent with previous reports, treatment with exogenous IGF-1 caused an increase in MBP protein that was preceded by activation of PI3K (AKT) and MAPK (ERK) signaling pathways. The extracellular matrix protein laminin was further shown to potentiate the effect of IGF-1 on oligodendrocyte differentiation. Depletion of the laminin receptor dystroglycan using siRNA, however, blocked the ability of IGF-1 to promote oligodendrocyte differentiation of cells grown on laminin, suggesting a role for dystroglycan in IGF-1-mediated differentiation. Indeed, loss of dystroglycan led to a reduction in the ability of IGF-1 to activate MAPK, but not PI3K, signaling pathways. Pharmacological inhibition of MAPK signaling also prevented IGF-1-induced increases in myelin basic protein (MBP), indicating that MAPK signaling was necessary to drive IGF-1-mediated enhancement of oligodendrocyte differentiation. Using immunoprecipitation, we found that dystroglycan, the adaptor protein Grb2, and insulin receptor substrate-1 (IRS-1), were associated in a protein complex. Taken together, our results suggest that the positive regulatory effect of laminin on oligodendrocyte differentiation may be attributed, at least in part, to dystroglycan's ability to promote IGF-1-induced differentiation.

Perspectives on concordant and discordant relations between insulin-like growth factor 1 (IGF1) and growth in fishes

Many physiological processes are modulated by the endocrine system, including growth. Insulin-like growth factor 1 is one of the primary hormones involved in growth regulation in vertebrates, including fishes. Current work on IGF1 in fishes is driven both by a desire to better understand mechanisms of growth as well as to develop a reliable index of growth rate. A review of studies relating IGF1 to growth broadly reveals positive and significant relations between IGF1 and growth; however, relations found in individual studies range from no correlation to highly significant correlations. Potential sources for this variation include both biological and methodological issues and range from differences in how growth is defined (changes in length or weight), the duration of growth assessed (weeks to months) and how growth is calculated (total change, rate, percent change); yet, these methodological concerns cannot account for all the variation found. A further review of the literature reveals a number of physiological conditions and environmental factors that might influence IGF1 level and the subsequent relation of that IGF1 level to growth rate. The term concordance is introduced to categorize factors that influence IGF1 and growth in a similar fashion, such that positive and significant relations between IGF1 and growth are maintained even though the factor stimulates changes in IGF1 level. Conversely, the term discordance is introduced to categorize factors that stimulate changes in the relations between IGF1 and growth, such that IGF1 is not an efficacious index of growth for both pre and post-stimulus fish combined. IGF1 and growth relations generally remain concordant after changes in nutrition (consumption rate or diet). Differences in IGF1 level of juvenile, maturing male and maturing female fish are common and IGF1-growth relations appear discordant between these groups. Acute changes in temperature and salinity induce discordant relations between IGF1 and growth but acclimation to persistent differences in environmental condition generally result in concordant relations. Overall, by discriminating between fish of differing physiological status and discerning and categorizing differences among environments one may effectively use IGF1 as a growth index for fishes.

Will targeting insulin growth factor help us or hurt us?: An oncologist's perspective

The insulin/insulin growth factor (IGF) pathway is a critical mediator of longevity and aging. Efforts to extend longevity by altering the insulin/IGF pathway may have varying effects on other physiological processes. Reduced insulin/IGF levels may decrease the incidence of certain cancers as well as the risk of developing metastatic disease. However, it may also increase the risk of developing cardiovascular disease as well as cardiovascular related mortality. Pursuing the right insulin/IGF pathway targets will require striking a balance between inhibiting cancer cell development and progression and avoiding damage to tissues under normal insulin/IGF-mediated control. This review will discuss the roles of the insulin/IGF pathway in aging and longevity and the development of cancer cell metastasis and considerations in taking insulin/IGF directed targets to the oncology clinic.

Maternal serum placental growth hormone, but not human placental lactogen or insulin growth factor-1, is positively associated with fetal growth in the first half of pregnancy

OBJECTIVE

To investigate if maternal levels of human placental lactogen (hPL), placental growth hormone (PGH) and insulin-like growth factor-1 (IGF-1) are associated with growth rate of the biparietal diameter (BPD) in the first half of pregnancy.

METHODS

Data on 8215 singleton fetuses from the Copenhagen First Trimester Study with measurements of BPD from ultrasound scans performed at weeks 11-14 and 17-21 of pregnancy were analyzed. Growth rate was defined as millimeters of growth/day of BPD between the two scans. Fetuses with growth rate below the 2.5(th) centile (low growth rate, n = 203) and above the 97.5(th) centile (high growth rate, n = 203) were identified. As a reference group 212 fetuses with growth rate around the median were identified (intermediate growth rate). Out of the 618 selected cases in the three growth rate groups a total of 463 cases had a blood sample taken at the time of first-trimester ultrasound (5.6% of the original sample size of 8215 pregnancies). The maternal blood serum concentrations of hPL, PGH and IGF-1 were determined in the three different growth-rate groups. Linear regression analysis without adjustment and with adjustment for known and potential confounders was used to compare serum levels between the groups.

RESULTS

Simple linear regression showed a difference in serum level of log(10) PGH between the high and intermediate growth-rate groups (P = 0.037). When adjusted for maternal weight and crown-rump length, multiple linear regression analysis confirmed this difference, as fetuses with high growth rates had a 12% (95% confidence interval, 2-20%; P = 0.009) higher maternal serum level of PGH than those with intermediate growth rates. No differences in hPL and IGF-1 levels between the three different growth-rate groups were found after simple and multiple linear regression analysis.

CONCLUSION

Maternal PGH levels are higher in women carrying fetuses with high first-trimester growth rates than in controls, both in a simple unadjusted analysis and in analyses adjusted for known and potential confounders. Thus, PGH may be involved in fetal growth regulation as early as in the first trimester of pregnancy.

Physiologically based pharmacokinetics of molecular imaging nanoparticles for mRNA detection determined in tumor-bearing mice

Disease detection and management might benefit from external imaging of disease gene mRNAs. Previously we designed molecular imaging nanoparticles (MINs) based on peptide nucleic acids complementary to cancer gene mRNAs. The MINs included contrast agents and analogs of insulin-like growth factor 1 (IGF-1). Analysis of MIN tumor uptake data showed stronger binding in tumors than in surrounding tissues. We hypothesized that MINs with an IGF-1 analog stay in circulation by binding to IGF-binding proteins. To test that hypothesis, we fit the tissue distribution results of several MINs in xenograft-bearing mice to a physiological pharmacokinetics model. Fitting experimental tissue distribution data to model-predicted mass transfer of MINs from blood into organs and tumors converged only when the parameter for MINs bound to circulating IGF-binding proteins was set to 10%-20% of the injected MIN dose. This result suggests that previous mouse imaging trials used more MINs than necessary. This prediction can be tested by a ramp of decreasing doses.

Association of serum IGF1 with endothelial function: results from the population-based study of health in Pomerania

OBJECTIVE

IGF1 mediates multiple physiological and pathophysiological responses in the cardiovascular system. The aim of this study was to analyze the association between serum IGF1 as well as IGF-binding protein 3 (IGFBP3) levels and endothelial function measured by flow-mediated dilation (FMD).

DESIGN

Cross-sectional population-based observational study.

METHODS

The study population comprised 1482 subjects (736 women) aged 25-85 years from the Study of Health in Pomerania. Serum IGF1 and IGFBP3 levels were determined by chemiluminescence immunoassays. FMD measurements were performed using standardized ultrasound techniques. FMD values below the sex-specific median were considered low.

RESULTS

In males, logistic regression analyses revealed an odds ratio (OR) of 1.27 (95% confidence interval (CI) 1.07-1.51; P=0.008) for decreased FMD for each decrement of IGF1 s.d. after adjustment for major cardiovascular confounders. In females, no significant relationship between serum IGF1 and FMD was found (OR 0.88, CI 0.74-1.05; P=0.147). After exclusion of subjects with the current use of antihypertensive medication, these findings were similar (males: OR 1.40, CI 1.12-1.75; P=0.003; females: OR 0.95, CI 0.77-1.16; P=0.595). There was no association between serum IGFBP3 levels and FMD in both sexes.

CONCLUSIONS

Low serum IGF1 levels are associated with impaired endothelial function in males. In women, serum IGF1 is not associated with endothelial function.

Growth hormone, insulin like growth factor-1, and insulin-like growth factor-binding protein-3 levels in the neonatal period: a preliminary study

BACKGROUND

Growth hormone (GH), insulinlike growth factor-1 (IGF-1), and IGF-binding protein-3 (IGFBP-3) are used in the neonatal period for evaluation of diseases such as GH deficiency, intrauterine growth restriction, and hypoglycemia. However, GH level has been reported as a single value during the neonatal period. In this study, we attempted to determine the changes of GH, IGF-1, and IGFBP-3 in the neonatal period for each week.

METHODS

One hundred and two appropriate-for-gestational age (AGA) term neonates who did not have any diseases that would interfere with GH-IGF axis were included in this cross-sectional study. Blood samples were collected and serum GH, IGF-1 and IGFBP-3 levels were measured by immunoradiometric analysis (IRMA) and weekly values were obtained for the first postnatal four weeks.

RESULTS

We showed that GH level [median (1st-3rd quartile)] decreases from the first to the fourth postnatal week [25.1 (18.5-37.4); 17.2 (13.2-22.8); 17.6 (12.2-20.2); 14.4 (6.60-19.8) ng/mL, respectively)], IGF-1 and IGFBP-3 levels [median (lst-3rd quartile)] increase [41.7 (18.0-70.0); 55.9 (39.0-103); 53.0 (40.0-97.7); 71.7 (44.3-137) and 1852 (1597-2451); 2430 (1645-2838); 2841 (2280-3675); 3018 (2151-4189) ng/mL, respectively)].

CONCLUSIONS

GH, IGF-1 and IGFBP-3 values can be evaluated for each week separately instead of for the entire neonatal period.

Insulin-like growth factors and liver cancer risk in male smokers

Background:

The liver is the primary source of circulating insulin-like growth factor (IGF)-I, yet the relation between IGFs and liver cancer is uncertain.

Methods:

In a case–cohort study within a cohort of 29 133 male smokers we examined associations of serum IGF-I and IGF binding protein (IGFBP)-3 with liver cancer (50 cases).

Results:

Nonlinear associations between liver cancer and IGF-I and IGFBP-3 were observed (P=0.04 and P<0.01, respectively), strongest association at lowest levels (odds ratio (OR)=0.2, 95% confidence interval (CI)=0.1–0.7 for 80 vs 30 ng ml⁻¹ of IGF-I; OR=0.2, 95% CI=0.1–0.6 for 1400 vs 700 ng ml⁻¹ of IGFBP-3).

Conclusions:

Low IGF-I and IGFBP-3 levels in male smokers are associated with increased risk of liver cancer.

Serum insulin-like growth factor-I and body composition in community dwelling older people

OBJECTIVES

The decline in the growth hormone/insulin-like growth factor-I (GH/IGF-I) axis during normal aging might be involved in the changes in body composition associated with increasing age. We conducted a study to investigate serum IGF-I levels across different age categories and a possible association between serum IGF-I and measurements of body composition in older people.

DESIGN

A cross-sectional analysis of community dwelling older people, which participated in a large longitudinal cohort study (Longitudinal Aging Study Amsterdam).

SUBJECTS

1319 subjects, 644 men, mean age 75.6 +/- 6.6 years and 675 women, mean age 75.4 +/- 6.6 years.

MAIN OUTCOME MEASUREMENTS

IGF-I, body mass index (BMI), waist, waist-hip ratio (WHR), fat mass, lean body mass and total bone mineral density.

RESULTS

IGF-I levels were significantly lower in the highest age categories. BMI and biceps skinfold measurements were lower in the lowest IGF-I quartile in men aged > or =75.5 years. In men with a low total physical activity score (<131 min/day), BMI, WHR and skinfolds were significantly lower in the lowest IGF-I quartile. In women with a high total physical activity score (>174 min/day), WHR was lower in the lowest IGF-I quartiles.

CONCLUSION

In this large cohort of community dwelling older people, we observed lower serum IGF-I levels in the higher age categories. A low serum IGF-I was associated with significantly lower measurements of body composition, such as BMI, skinfolds and WHR. These results do not support previous findings that high IGF-I levels are favourable for a healthy body composition in community dwelling older people.

A consensus on criteria for cure of acromegaly

OBJECTIVE

The Acromegaly Consensus Group met in April 2009 to revisit the guidelines on criteria for cure as defined in 2000.

PARTICIPANTS

Participants included 74 neurosurgeons and endocrinologists with extensive experience of treating acromegaly. EVIDENCE/CONSENSUS PROCESS: Relevant assays, biochemical measures, clinical outcomes, and definition of disease control were discussed, based on the available published evidence, and the strength of consensus statements was rated.

CONCLUSIONS

Criteria to define active acromegaly and disease control were agreed, and several significant changes were made to the 2000 guidelines. Appropriate methods of measuring and achieving disease control were summarized.

Insulin-like growth factors and risk of kidney cancer in men

BACKGROUND

Insulin-like growth factor-I (IGF-I) has been shown to increase kidney growth, glomerular filtration rate, and renal function.

METHODS

In the prospective Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) study of 29 133 Finnish male smokers aged 50-69 years, serum concentrations of IGF were measured in samples collected in 1985-1988. A total of 100 men with kidney cancer diagnosed > or =5 years after blood collection through 1997 were compared with a subcohort of 400 men; logistic regression models were used to estimate the risk of developing kidney cancer.

RESULTS

Men with IGF-I levels >113 ng ml(-1) were 59% less likely to develop kidney cancer than men with levels < or =113 ng ml(-1) (odds ratio=0.41; 95% confidence interval=0.23-0.75). The IGF binding protein-3 (IGFBP-3) levels did not alter the association. No association was observed between IGFBP-3, or molar ratio of IGF-I/IGFBP-3, and kidney cancer.

CONCLUSIONS

Low serum IGF-I levels in this cohort of older middle-aged male smokers are associated with increased kidney cancer risk, independent of IGFBP-3.

Insulin-like growth factor II in hepatocellular carcinoma

Hepatocellular carcinoma is one of the most common malignant human tumors. Hepatocarcinogenesis is a multistep process with a multifactorial etiology. Chronic hepatitis B and hepatitis C virus infection, alcohol drinking and cirrhosis of any etiology are the major risk factors for hepatocellular carcinoma. Growth factors, their receptors and related proteins are involved in the process of malignant transformation. The IGF axis is involved in the proliferation and differentiation of normal, transformed and malignant hepatocytes. In the context of hepatocarcinogenesis, IGF-II has, in particular, been investigated thoroughly. Increased IGF-II bioavailability, protease activity of IGF-binding proteins and IGF-I receptor expression, decreased expression of IGF-II receptor and IGF-binding proteins are thought to contribute to hepatocellular carcinoma genesis. This review will first focus on the role of the IGF axis in hepatocarcinogenesis. In the second part it will emphasize circulating IGF-II levels in chronic liver disease and hepatocellular carcinoma, and diagnostic application of serum IGF-II level in both small and larger hepatocellular carcinoma.

Growth hormone receptor d3-variant, insulin-like growth factor binding protein-1 -575G/A polymorphism and postnatal catch-up growth: association with parameters of glucose homeostasis in former extremely low birth weight preterm infants

BACKGROUND

Low birth weight predisposes to the development of insulin resistance. In addition to auxological parameters such as rapid catch-up growth, low IGFBP-1 serum levels in childhood have been linked to an increased risk of insulin resistance later in life. Concerning postnatal growth, we previously reported the GHRd3-variant to be associated with catch-up growth in preterm infants. In children born small for gestational age, a common IGFBP-1 promoter polymorphism -575G/A has been linked to IGFBP-1 serum levels and has been suggested to be an additional player in the interaction between the IGF-IGFBP-axis and metabolism.

STUDY DESIGN

We analyzed postnatal growth, metabolic parameters, and genotypes for the GHRd3-variant and IGFBP-1 -575G/A in 51 former extremely low birth weight preterm infants (mean age 5.9 years).

RESULTS

GHRd3 but not IGFBP-1 -575G/A was significantly associated with postnatal growth velocity. Catch-up growth, GHRd3, and IFGBP-1 -575G/A did not influence fasting insulin or HOMA-IR. However, we found significantly higher HbA1c and lower IGFBP-1 concentrations in GHRd3-carriers, a finding not seen with respect to IGFBP-1 -575G/A. Interestingly, HbA1c and IGFBP-1 levels also did not differ between children either with or without catch-up growth.

CONCLUSIONS

In addition to an association with catch-up growth, GHR exon 3 genotype significantly modulates HbA1c and IGFBP-1 concentrations in former ELBW infants. In order to confirm this observation and to clarify whether the GHRd3-variant might be considered as an independent modulator of the low birth weight infant's risk to develop insulin resistance later in life, larger studies extending to later ages are required.

Prevalence of growth hormone deficiency in Hashimoto's thyroiditis

CONTEXT

Autoimmune hypophysitis can result in GH deficiency (GHD) and is associated with other autoimmune endocrine diseases like Hashimoto's thyroiditis. Recent studies suggest a high prevalence (5%) of GHD in Hashimoto's thyroiditis.

OBJECTIVE

Our objective was to establish the prevalence of GHD in patients with treated autoimmune hypothyroidism (AIH).

PATIENTS

We included patients with spontaneous AIH [thyroid peroxidase antibodies (TPO-Ab) >or=100 kU/liter], who were adequately treated with T(4) (TSH 0.2-5.0 mU/liter). Exclusion criteria were previous I(131) treatment, thyroid surgery, or a history of hypothalamic or pituitary disease. Patients were recruited via our outpatient clinics and via patient self-help organizations.

DESIGN

We measured serum TSH, free T(4), TPO-Ab, and IGF-I. If the IGF-I concentration was below the 10th percentile of age-specific reference values, a GHRH/GH-releasing peptide (GHRP)-6 test was done. GHD was defined as a GH peak after GHRH/GHRP-6 below the 2.5th percentile of age-specific reference values.

MAIN OUTCOME MEASURES

IGF-I concentration and GH peak after GHRH/GHRP-6 test were measured.

RESULTS

From 860 patients who applied, 322 did not satisfy inclusion criteria (157 because TPO-Ab was <100 kU/liter, 165 because TSH was <0.2 or >5.0 mU/liter), and 23 had an exclusion criterion. In the remaining study population of 515 patients (476 female, 39 male), 49 patients (9.5%) had an IGF-I concentration below the 10th percentile. These patients underwent a GHRH/GHRP-6 test. Two patients had a GH peak below the 2.5th percentile.

CONCLUSION

The prevalence of GHD in Dutch patients with AIH is 0.4% (two of 515).

Obesity, growth hormone and weight loss

Growth hormone (GH) is the most important hormonal regulator of postnatal longitudinal growth in man. In adults GH is no longer needed for longitudinal growth. Adults with growth hormone deficiency (GHD) are characterised by perturbations in body composition, lipid metabolism, cardiovascular risk profile and bone mineral density. It is well established that adult GHD usually is accompanied by an increase in fat accumulation and GH replacement in adult patients with GHD results in reduction of fat mass and abdominal fat mass in particular. It is also recognized that obesity and abdominal obesity in particular results in a secondary reduction in GH secretion and subnormal insulin-like growth factor-I (IGF-I) levels. The recovery of the GH IGF-I axis after weight loss suggest an acquired defect, however, the pathophysiologic role of GH in obesity is yet to be fully understood. In clinical studies examining the efficacy of GH in obese subjects very little or no effect are observed with respect to weight loss, whereas GH seems to reduce total and abdominal fat mass in obese subjects. The observed reductions in abdominal fat mass are modest and similar to what can be achieved by diet or exercise interventions.

Growth factors as active participants in carcinogenesis: a perspective

Growth factors are low molecular peptides active in the stimulation of cell proliferation and in the regulation of embryonic development and cellular differentiation. Significant progress has been made in developing effective strategies to treat human malignancies with new chemical compounds based on a rationale directed against various components of signaling pathways. Many of these drugs target a growth factor receptor--for instance, in the form of monoclonal antibodies or inhibitors of tyrosine kinases, such as monoclonal antibodies against epidermal growth factor receptors used in treating certain types of breast cancer. Imatinib mesylate [Gleevec]) is an excellent example of mediators of signal transduction, such as tyrosine kinases. Growth factors proper are used to ameliorate various and sometimes fatal side effects of cytotoxic and/or myelosuppressive chemotherapy. Basic characteristics of several growth families are discussed with therapeutic modalities based on growth factor activity or, more often, inhibition of such activity.

Alterations of insulin-like growth factor binding protein 3 (IGFBP-3) glycosylation in patients with breast tumours

OBJECTIVES

Insulin-like growth factor binding protein-3 (IGFBP-3) is an important modulator of development and progression of breast cancer as it regulates the amount of free, physiologically active IGF-I and IGF-II. Changes in the glycosylation pattern within IGFBP-3 may affect its interaction with ligands. The aim of this study was to investigate whether such changes occur during disease progression.

DESIGN AND METHODS

IGFBP-3 in serum samples from healthy women and from women with breast tumours was characterised in terms of its concentration (IRMA), glycosylation moiety (lectin-affinity chromatography) and distribution of molecular species (immunoblotting).

RESULTS

In patients with benign tumours the concentration and carbohydrate content of IGFBP-3 was unaltered compared to healthy women. In patients with malignant tumours in most cases these two parameters were unchanged, but there were women whose concentration of IGFBP-3 was reduced and its structure was altered. In non-surviving cancer patients the concentration of IGFBP-3 was significantly reduced and these molecules contained a greater amount of biantennary complex type N-glycans having more mannose, fucose, bisecting GlcNAc and terminal sialic acid residues.

CONCLUSION

Our results showed that breast cancer progression causes alterations of IGFBP-3 glycosylation. The extent of changes increases with breast cancer severity.

Dietary predictors of the insulin-like growth factor system in adolescent females: results from the Dietary Intervention Study in Children (DISC)

BACKGROUND

The insulin-like growth factor (IGF) system is associated with the adult diet and chronic disease. Childhood diet may influence chronic disease through its effect on the IGF system; however, there is limited information describing the dietary predictors of the IGF system in adolescents.

OBJECTIVE

We examined associations between dietary food intake [fat, protein (animal and vegetable), carbohydrate, lactose, dietary fiber, calcium, zinc, and sodium] and serum IGF-I, IGF binding protein 1 (IGFBP-1), IGF binding protein 3 (IGFBP-3), and the IGF-I:IGFBP-3 molar ratio in adolescent females.

DESIGN

One hundred fifty-nine adolescent females in the Dietary Intervention Study in Children (age range: 14-18 y; 0.2-6.3 y postmenarche) were included. The dietary intake was assessed via three 24-h dietary recalls. IGF-related biomarkers were determined by using radioimmunoassays. Associations between dietary intakes and biomarkers were assessed with Pearson's correlations and multivariable linear regression. Dietary intakes and biomarkers were logarithmically transformed; thus, beta coefficients represented percentages.

RESULTS

In analyses adjusted for energy, age, and time since menarche, significant correlations (P < 0.05) were as follows: IGF-I with total protein, lactose, calcium, and sodium; IGFBP-3 with total fat (inverse), lactose, fiber, and calcium; IGF-I/IGFBP-3 with lactose and calcium; and IGFBP-1 with vegetable protein. In multivariable analyses, significant predictors of IGF-I were energy (beta = 0.14, P < 0.05) and calcium (beta = 0.14, P < 0.01), the significant predictor of IGFBP-3 was calcium (beta = 0.07, P < 0.05), and significant predictors of IGFBP-1 were vegetable protein (beta = 0.49, P < 0.05) and body mass index-for-age percentile (beta = -0.01, P < 0.001).

CONCLUSION

This study provides evidence that dietary intake affects IGF-related biomarkers-particularly elevated calcium with IGF-I and IGFBP-3 and elevated vegetable protein with IGFBP-1-and, to our knowledge, is novel in reporting these associations in adolescent females. The Dietary Intervention Study in Children was registered at clinicaltrials.gov as NCT00000459.

Lifestyle, anthropometric, and obesity-related physiologic determinants of insulin-like growth factor-1 in the Third National Health and Nutrition Examination Survey (1988-1994)

PURPOSE

Epidemiologic studies suggest that insulin-like growth factor-1 (IGF-1) is associated with obesity and, more recently, cancer. This study investigates multiple lifestyle, physiologic, and anthropometric determinants of circulating IGF-1 concentrations.

METHODS

Nationally representative data were used from the cross-sectional Third National Health and Nutrition Examination (NHANES III, 1988-1994) survey, which measured IGF-1 concentrations in blood, from a subsample of participants who were examined in the morning. After exclusion of persons with missing data, 6,058 men and women 20 years of age or older were included in the study.

RESULTS

The mean IGF-1 concentrations were 260 ng/mL in the entire population and were higher among men as compared with women (278.8 vs. 241.3 ng/mL; p<0.0001). IGF-1 decreased with increasing age (p<0.0001), body mass index (p<0.0001), and waist circumference (p<0.0001). Individuals with metabolic syndrome had lower IGF-1 concentrations after adjustment for covariates (p=0.0008). IGF-1 was inversely associated with increasing number of metabolic syndrome abnormalities (p=0.0008). All associations were stronger among women compared with men except across concentrations of glucose. IGF-1 concentrations did not vary by any other lifestyle or physiologic factors.

CONCLUSIONS

Age, adiposity, hyperglycemia, and metabolic syndrome influenced circulating IGF-1 concentrations. Diet and physical activity had no impact on IGF-1 in this nationally representative population.

Reduction of IGF-binding protein-3 as a potential marker of intra-uterine growth restriction

BACKGROUND

Growth factor-binding proteins influence the growth of infants starting in utero. Adaptation of the fetus to an adverse uterine environment is associated with changes in the growth hormone-growth factor-insulin axis.

AIMS

To evaluate serum levels of IGF-I and IGFBP-3 in small and appropriate for gestational age newborn infants.

METHODS

Fifty-four newborn infants, small (SGA, n=28) or appropriate (AGA, n=26) for gestational age were matched by gestational age and sex. Blood was collected on the first day of life, and anthropometric measurements were taken at birth. The serum levels of IGF-I and IGFBP-3 were compared, and correlated with the anthropometric measurements.

RESULTS

On the first day of life, mean serum IGFBP-3 levels were significantly lower in SGA babies and correlated with weight, length, head circumference, and ponderal index (weight/length 3) (P<0.0001). In contrast, no associations were found between IGF-I serum levels and these anthropometric measurements.

CONCLUSION

Our data show that SGA babies have significantly reduced IGFBP-3 concentrations at birth.

The current status of IGF-I assays--a 2009 update

For almost three decades, the measurement of circulating IGF-I has constituted a highly important biochemical tool in the management of GH disorders. In fact, in acromegaly the importance of circulating IGF-I has increased following the introduction of the GH receptor antagonist pegvisomant, as the use of this drug makes it impossible to use circulating GH as a monitor of disease activity. In addition, determination of circulating IGF-I constitutes a valuable scientific tool in various research areas, from epidemiological investigations through clinical trials and experimental studies. The multiple facets of IGF-I physiology and patho-physiology may explain why numerous endocrine laboratories have invested in IGF-I assays, by means of either in-house assays or commercial kits. However, despite its widespread use, the measurement of IGF-I is by no means trivial. On the contrary, the pronounced binding of IGF-I to the high-affinity IGF-binding proteins (IGFBPs) constitutes a notorious source of error, which has necessitated the development of methods that more or less successfully circumvent interference from the IGFBPs. Furthermore, there are some unsolved issues with the international standardization of the different IGF-I assays and there is no consensus regarding the procedures used when collecting and storing samples for measurement of circulating IGF-I. The aim of this review is to discuss the current state of the art of IGF-I immunoassays and to present the current analytical problems with IGF-I measurements. Finally, we would like to suggest an agenda that may be used when trying to produce internationally accepted uniform requirements for future IGF-I assays.

Insulin-like growth factor-1 (IGF-1): relation with cognitive functioning and neuroimaging marker of brain damage in a sample of hypertensive elderly subjects

IGF-1 decline has been related to age-dependent cognitive impairment and dementia. No study examined IGF-1 levels in subjects with a risk factor for brain damage such as hypertension. We investigated the relationship between IGF-1, cognitive functioning and neuroimaging in a sample of 75 hypertensive elderly subjects aged > 65. Cognitive performance were tested by mini mental state examination (MMSE), Cambridge cognitive examination (CAMDEX-R), and the frontal assessment battery (FAB). Among other indices, free IGF-1 in serum was assayed. The radial width of the temporal horn (rWTH) evaluates medial cerebral temporal lobe atrophy. Significant correlations between IGF-1 levels and both total and sub-domain scores of cognition were found. IGF-1 level was significantly lower in cognitively declined group. The lowest IGF-1 -percentile subgroup was significantly cognitively impaired. A statistically non-significant, but lower IGF-1 level was found in the sub-sample with pathologically wider rWTH. Levels of IGF-1 below 79.4 microg/l are associated with cognitive decline, whereas a level above 118 microg/l seems to be a marker of normal cognitive performance. A decreasing of IGF-1 related to a widening of the rWTH suggests an involvement of this hormone in hippocampus atrophy.

Maternal hormones during early pregnancy: a cross-sectional study

BACKGROUND

Little is known about correlates of first-trimester pregnancy hormones as in most studies maternal hormones have been measured later in gestation. We examined the associations of maternal characteristics and child sex with first-trimester maternal concentrations of four hormones implicated in breast cancer: human chorionic gonadotropin (hCG), alpha-fetoprotein (AFP), insulin-like growth factor (IGF)-I, and IGF-II.

METHODS

About 338 serum samples donated to the Northern Sweden Maternity Cohort (NSMC), 1975-2001, during the first trimester of uncomplicated pregnancies, were analyzed for the hormones of interest as a part of a case-control study. The associations of maternal characteristics and child sex with hormone concentrations were investigated by correlation, general linear regression, and multivariate regression models.

RESULTS

In the first trimester, greater maternal age was inversely correlated with IGF-I and IGF-II. In comparison with women carrying their first child, already parous women had higher IGF-I but lower hCG. Greater maternal weight and smoking were inversely correlated with hCG. No differences in hormone levels by child sex were observed.

CONCLUSIONS

Our analyses indicated that potentially modifiable maternal characteristics (maternal weight and smoking) influence first-trimester pregnancy maternal hormone concentrations.

Spuriously Elevated Serum IGF-1 in Adult Individuals with Delayed Puberty: A Diagnostic Pitfall

Serum insulin-like growth factor-1 (IGF-1) is a sensitive marker of growth hormone (GH) activity. The levels of IGF-1 vary widely, peaking during puberty and declining with advancing age. During adolescence, serum IGF-1 levels tend to correlate better with pubertal stage rather than chronological age. Here we discuss two cases of delayed puberty, both in their 20s, who presented with high serum IGF-1 but no clinical or biochemical evidence of hypersomatotropism as confirmed by appropriate GH response to an oral glucose challenge. Both individuals achieved full pubertal status with testosterone replacement therapy and their serum IGF-1 levels settled into normal age-specific range. We suggest that in chronologically adult individuals with delayed puberty, serum IGF-1 should not be interpreted on the basis of age-specific normal values but rather on their pubertal status. Furthermore, in the absence of another cause of elevated IGF-1, the expectation is that IGF-1 levels will decline towards age-normative ranges following androgen replacement therapy.

Plasma insulin-like growth factor I as predictor of progression and all cause mortality in chronic heart failure

OBJECTIVES

Insulin-like growth factor I (IGF-I) is an anabolic growth factor that seems to increase cardiac contractility. Reduced levels of IGF-I may be implicated in progression of CHF. The objective was to compare plasma IGF-I in CHF patients with healthy controls, and to examine the associations between baseline IGF-I levels, cardiac contractility and the prognosis as judged by all cause mortality and progression of CHF requiring admission to hospital.

METHODS

A prospective study comprising 194 CHF outpatients, and 169 matched controls. All patients and controls underwent echocardiographic examination at baseline. Patients were followed for a median of 30 months.

RESULTS

There was no difference in IGF-I levels between patients and controls (median and interquartile range), 78 (58-91) vs. 77 (57-94)ng/mL (P=0.92). Age-adjusted IGF-I levels were not related to left ventricular ejection fraction (LVEF) (P=0.58) or levels of N-terminal B-Type natriuretic peptide (NT-proBNP) (P=0.42). During follow-up 44 patients died and 94 were admitted to hospital due to worsening of CHF. Adjusted for cardiovascular risk factors (age, gender, NT-proBNP, lipids, diabetes mellitus, blood pressure, renal function and LVEF) IGF-I levels did not influence the overall mortality risk or the admission rate to hospital, hazard ratio (HR) (95% confidence intervals) 1.05 (0.75-1.47) (P=0.77) and 1.00 (0.80-1.26) (P=0.96), respectively per each SD increase in log IGF-I levels.

CONCLUSIONS

IGF-I levels were not reduced in patients with CHF and did not influence cardiac status at baseline or the prognosis.

Serum insulin-like growth factor-I concentration is associated with leukocyte telomere length in a population-based cohort of elderly men

CONTEXT

Both leukocyte telomere length and IGF-I are associated with the aging process. A previous in vitro study suggested that IGF-I may modulate telomerase activity in white blood cells, but little is known whether these two systems interact in vivo.

PATIENTS AND METHODS

Leukocyte telomere length was determined using a quantitative PCR assay in 2744 elderly men (mean age 75.5 yr, range 69-81 yr) included in the population-based Osteoporotic Fractures in Men-Sweden study. Serum IGF-I concentration was measured using RIA.

RESULTS

Subjects with a leukocyte telomere length in the lowest tertile group had lower serum IGF-I concentration than subjects in the two tertile groups with longer telomere lengths (P = 0.005). Logistic regression analyses showed that a higher serum IGF-I concentration was associated with a significantly reduced risk of having a leukocyte telomere length in the lowest tertile group and also after adjustment for multiple covariates (P < 0.01). Multivariate linear regression analyses demonstrated that tertile of leukocyte telomere length was positively, whereas age was negatively, associated with serum IGF-I concentration in elderly men.

CONCLUSIONS

In this large population-based, cross-sectional study, leukocyte telomere length was positively associated with serum IGF-I concentration in elderly men. The mechanisms underlying the association between serum IGF-I concentration and leukocyte telomere length remain to be determined.

Breast milk hormones and their protective effect on obesity

Data accumulated over recent years have significantly advanced our understanding of growth factors, cytokines, and hormones in breast milk. Here we deal with leptin, adiponectin, IGF-I, ghrelin, and the more recently discovered hormones, obestatin, and resistin, which are present in breast milk and involved in food intake regulation and energy balance. Little is known about these compounds in infant milk formulas. Nutrition in infancy has been implicated in the long-term tendency to obesity, and a longer duration of breastfeeding appears to protect against its development. Diet-related differences in serum leptin and ghrelin values in infancy might explain anthropometric differences and differences in dietary habits between breast-fed and formula-fed infants also later in life. However, there are still gaps in our understanding of how hormones present in breast milk affect children. Here we examine the data related to hormones contained in mother's milk and their potential protective effect on subsequent obesity.

Insulin receptor isoforms and insulin receptor/insulin-like growth factor receptor hybrids in physiology and disease

In mammals, the insulin receptor (IR) gene has acquired an additional exon, exon 11. This exon may be skipped in a developmental and tissue-specific manner. The IR, therefore, occurs in two isoforms (exon 11 minus IR-A and exon 11 plus IR-B). The most relevant functional difference between these two isoforms is the high affinity of IR-A for IGF-II. IR-A is predominantly expressed during prenatal life. It enhances the effects of IGF-II during embryogenesis and fetal development. It is also significantly expressed in adult tissues, especially in the brain. Conversely, IR-B is predominantly expressed in adult, well-differentiated tissues, including the liver, where it enhances the metabolic effects of insulin. Dysregulation of IR splicing in insulin target tissues may occur in patients with insulin resistance; however, its role in type 2 diabetes is unclear. IR-A is often aberrantly expressed in cancer cells, thus increasing their responsiveness to IGF-II and to insulin and explaining the cancer-promoting effect of hyperinsulinemia observed in obese and type 2 diabetic patients. Aberrant IR-A expression may favor cancer resistance to both conventional and targeted therapies by a variety of mechanisms. Finally, IR isoforms form heterodimers, IR-A/IR-B, and hybrid IR/IGF-IR receptors (HR-A and HR-B). The functional characteristics of such hybrid receptors and their role in physiology, in diabetes, and in malignant cells are not yet fully understood. These receptors seem to enhance cell responsiveness to IGFs.

Demographic factors influencing the GH system: Implications for the detection of GH doping in sport

Application of methods for detecting GH doping depend on being able to discriminate between abnormal levels due to doping and normal physiological levels of circulating proteins that change in response to exogenous administration. Constituents of the IGF and collagen systems have been shown to be promising markers of GH abuse. Their ultimate utility, however, depends on identification of the factors that regulate their concentrations in blood. Among these are demographic factors that are known to influence these markers in the general population. In a large cross-sectional study of the GH-responsive markers in over 1000 elite athletes from 12 countries representing 4 major ethnic groups and 10 sport types, we have shown that there is a significant negative correlation between age and all the IGF and collagen markers we studied, with a rapid decrease in early adolescence. Age was the major contribution to the variability, equivalent to >80% of the attributable variation in IGF-I and the collagen markers. The IGF axis markers were all significantly higher in women, and the collagen markers significantly higher in men, however, the contribution of gender was smaller than that of age, except for IGFBP-3 and ALS. BMI had a minor contribution to variability of the GH-responsive markers. After adjustment for the confounding influences of age, gender and BMI, the effect of ethnicity in elite athletes was trivial except for IGFBP-3 and ALS, which were both lower in Africans and higher in Caucasians. Compared to age and gender, the contribution of sport type was also modest. Our findings on the influence of age, gender, BMI and sport type have also been confirmed in a study of mostly Caucasian elite athletes in the post-competition setting. In conclusion, age and gender are the major determinants of variability for IGF-I and the collagen markers, whereas ethnicity and sport type have a minor influence. Therefore, a test based on IGF-I and the collagen markers must take age into account for men and women, and ethnicity and sport type are unlikely to be confounders for these markers.

Human insulin/IGF-1 and familial longevity at middle age

Recently, we have shown that compared to controls, long-lived familial nonagenarians (mean age: 93.4 years) from the Leiden Longevity Study displayed a lower mortality rate, and their middle-aged offspring displayed a lower prevalence of cardio-metabolic diseases, including diabetes mellitus. The evolutionarily conserved insulin/IGF-1 signaling (IIS) pathway has been implicated in longevity in model organisms, but its relevance for human longevity has generated much controversy. Here, we show that compared to their partners, the offspring of familial nonagenarians displayed similar non-fasted serum levels of IGF-1, IGFBP3 and insulin but lower non-fasted serum levels of glucose, indicating that familial longevity is associated with differences in insulin sensitivity.

The association between diet and serum concentrations of IGF-I, IGFBP-1, IGFBP-2, and IGFBP-3 in the European Prospective Investigation into Cancer and Nutrition

Circulating concentrations of insulin-like growth factor I (IGF-I) and IGF binding proteins (IGFBP) have been associated with the risk of several types of cancer. Dietary correlates of IGF-I and IGFBPs are not yet well established. The objective of this study was to assess the association between dietary intake and serum concentrations of IGF-I, IGFBP-1, IGFBP-2, and IGFBP-3 in a cross-sectional analysis of 4,731 men and women taking part in the European Prospective Investigation into Cancer and Nutrition. Diet was assessed using country-specific validated dietary questionnaires. Serum concentrations of IGF-I, IGFBP-1, IGFBP-2 and IGFBP-3 were measured, and the associations between diet and IGF-I and IGFBPs were assessed using multiple linear regression adjusting for sex, age, body mass index, smoking status, and alcohol and energy intake. Each 1 SD increment increase in total and dairy protein and calcium intake was associated with an increase in IGF-I concentration of 2.5%, 2.4%, and 3.3%, respectively (P for trend <0.001 for all) and a decrease in IGFBP-2 of 3.5%, 3.5%, and 5.4% (P for trend <0.001 for all), respectively. There were no significant associations between the intake of protein or calcium from nondairy sources and IGF-I. The results from this large cross-sectional analysis show that either the intake of dairy protein or calcium is an important dietary determinant of IGF-I and IGFBP-2 concentrations; however, we suggest that it is more likely to be protein from dairy products.

Aging in inbred strains of mice: study design and interim report on median lifespans and circulating IGF1 levels

To better characterize aging in mice, the Jackson Aging Center carried out a lifespan study of 31 genetically-diverse inbred mouse strains housed in a specific pathogen-free facility. Clinical assessments were carried out every 6 months, measuring multiple age-related phenotypes including neuromuscular, kidney and heart function, body composition, bone density, hematology, hormonal levels, and immune system parameters. In a concurrent cross-sectional study of the same 31 strains at 6, 12, and 20 months, more invasive measurements were carried out followed by necropsy to assess apoptosis, DNA repair, chromosome fragility, and histopathology. In this report, which is the initial paper of a series, the study design, median lifespans, and circulating insulin-like growth factor 1 (IGF1) levels at 6, 12, and 18 months are described for the first cohort of 32 females and 32 males of each strain. Survival curves varied dramatically among strains with the median lifespans ranging from 251 to 964 days. Plasma IGF1 levels, which also varied considerably at each time point, showed an inverse correlation with a median lifespan at 6 months (R = -0.33, P = 0.01). This correlation became stronger if the short-lived strains with a median lifespan < 600 days were removed from the analysis (R = -0.53, P < 0.01). These results support the hypothesis that the IGF1 pathway plays a key role in regulating longevity in mice and indicates that common genetic mechanisms may exist for regulating IGF1 levels and lifespan.

Genetic and epigenetic variability in the gene for IGFBP-3 (IGFBP3): correlation with serum IGFBP-3 levels and growth in short children born small for gestational age

CONTEXT

IGF-I and IGFBP-3 play a central role in fetal and postnatal growth and levels are low in short SGA children. The -202 A/C and -185 C/T SNPs are located near elements involved in directing IGFBP3 promoter activity and expression. Changes in promoter CpG methylation status affect transcription factor binding and transcriptional activation of IGFBP3 in vitro.

OBJECTIVE

To assess the relationship between IGFBP3 promoter SNPs, IGFBP-3 levels, spontaneous growth and growth response to GH treatment in short prepubertal SGA children. To assess promoter methylation status in a subgroup of short SGA subjects and controls.

PATIENTS

292 Short prepubertal SGA children, 39 short young SGA adults and 85 young adults with normal stature.

INTERVENTION

Short prepubertal SGA children received GH 1mg/m(2)/day.

OUTCOME MEASURES

Fasting levels of IGF-I and IGFBP-3, baseline and delta height SDS.

RESULTS

At baseline, IGFBP-3 levels were highest in SGA children with -202 AA genotype and lower in children with 1 or 2 copies of the C-allele (P<0.001). Children with C(-202)/C(-185) haplotype, compared to children with A(-202)/C(-185) haplotype, had lower IGFBP-3 levels (P=0.003) and were shorter (P=0.03). During GH treatment, children with C(-202)/C(-185) haplotype showed a significantly greater increase in IGFBP-3 SDS and in height SDS than children with A(-202)/C(-185) haplotype, resulting in similar IGFBP-3 levels and similar height SDS after 12 months of GH treatment. CpG methylation patterns showed a trend towards more methylation of CpGs involved in transcription factor binding in short young SGA adults compared to controls.

CONCLUSION

Polymorphic variation in the IGFBP3 promoter region is correlated with IGFBP-3 levels, spontaneous growth and response to GH treatment in short SGA children.

Association of metabolic syndrome with insulin-like growth factors among adults in the US

OBJECTIVE

To examine the association of insulin-like growth factors (IGFs) with metabolic syndrome in a nationally representative sample.

METHODS

We used data from the Third National Health and Nutrition Examination Survey. Analysis is based on participants who provided a fasting blood sample and were aged 20 years and older (n = 5,903). Participants were classified by a number of risk factors for metabolic syndrome and stratified by diabetes status.

RESULTS

Each of the components of metabolic syndrome (increased waist circumference, higher triglycerides, lower HDL cholesterol, higher blood pressure, higher fasting glucose and diabetes) was each associated with lower levels of IGF-I, IGF-BP3 and the Ratio IGF-I/IGF-BP3. Each of the metabolic syndrome components was also associated with higher levels of insulin. Participants with 3-5 components of metabolic syndrome had significantly lower IGF-I and higher IGF-BP3 levels compared to adults with 1-2 components or 0 components, after adjustment for potential confounders. Participants with diabetes had lower levels of IGF-I and IGF-BP3, and higher levels of insulin, regardless of the number of metabolic syndrome components.

CONCLUSION

These findings may prove useful to an understanding of the role of IGF-I in human disease, in particular its relation to metabolic syndrome, diabetes and potentially some cancers.

Race/ethnic variation in serum levels of IGF-I and IGFBP-3 in US adults

OBJECTIVES

The IGF axis plays a significant role in normal growth and development and variation in IGFs is associated with health outcomes. Past studies report variation in IGF levels among race/ethnic groups known to differ in disease incidence. This paper reports on race/ethnic variation in serum levels of IGF-I and IGF-BP3 in a nationally representative and ethnically diverse sample of US adults.

DESIGN

Serum IGF-I and IGFBP-3 levels from the fasting subsample (n = 6061) of respondents to the US National Health and Nutrition Examination Survey III (NHANES III) were analyzed using an IGF-I ELISA (Diagnostic Systems Laboratory (DSL) 10-5600) and an IGFBP-3 IRMA (DSL 6600). The NHANES is a combined examination and interview survey of a nationally representative sample of US adults. Regression analyses were used to estimate cross-sectional associations between the IGF axis and demographic variables.

RESULTS

In unadjusted analyses, serum IGF-I levels were higher in males than in females, and IGFBP-3 levels were higher in females than in males. Both analytes were lower in older adults. Univariate analyses indicate that serum levels of IGF-I are lower in female Non-Hispanic Whites (NHW) (256 [4.9]) and Hispanics (249 [6.6]) than in Non-Hispanic Blacks (NHB) (281 [4.9]). However, in males, IGF levels in NHWs (287 [3.6]) and NHBs (284 [4.3]) are similar and levels in Mexican-Americans are only moderately reduced (265 [3.4]). Notably, NHB's have the highest molar ratio of IGF-I:IGFBP-3 at all ages. After adjustment for age and BMI, gender and race/ethnicity differences persist.

CONCLUSIONS

These cross-sectional data support exploration of the IGF axis as an explanation for some race/ethnic differences in cancer incidence.

Expression of insulin-like growth factor system components in colorectal tissue and its relation with serum IGF levels

CONTEXT

The insulin-like growth factor (IGF)-system has been implicated in colorectal tumor carcinogenesis. Although both tumor expression levels and serum concentrations of IGF-system components are related to colorectal cancer risk, it is unknown whether IGF levels in tissue and serum are correlated.

OBJECTIVE

The objective of this study was to determine expression levels of various IGF-system components in different locations of the colorectum, and to investigate whether normal tissue IGF expression levels are correlated with serum IGF-I and IGF-II concentrations.

DESIGN

Biopsies from macroscopically normal mucosa at four locations in the colorectum (ascending, transverse, sigmoid colon, and rectum) and a fasting serum sample were obtained from 48 asymptomatic patients at increased risk of colorectal cancer. Expression levels of IGF-I, IGF-II, IGF-IR, IGF-IIR, and IGFBP-3 messenger RNA (mRNA) in tissue were quantitatively evaluated using real-time RT-PCR. Expression of IGF-IR protein in the ascending colon and rectum tissue specimens was assessed semi-quantitatively by immunohistochemistry. Serum IGF-I and IGF-II concentrations were determined using immunometric assays.

RESULTS

With the exception of IGF-IIR, mRNA levels of all the IGF-system components investigated, as well as IGF-IR protein expression, were significantly higher in the rectum compared with the ascending colon (p<or=0.001). Serum IGF-I and IGF-II concentrations did not correlate with any of the parameters studied in colorectal tissues.

CONCLUSIONS

Our results indicate that in humans IGF-system components are differentially expressed in the colorectum. Moreover, our findings suggest that local and circulating components of the IGF-system are differentially regulated. However, due to large intra-individual variation in mRNA expression, we cannot formally exclude undetected but existing routes of co-regulation.

Separation of the molecular forms of the insulin-like growth factor (IGF)-Binding proteins by affinity chromatography

Association of IGFBP-1, IGFBP-2 and IGFBP-3 with other proteins in human serum and placental cell membranes was investigated using affinity chromatography matrix with immobilized antibodies. Circulating IGFBP-1 was found to be predominantly bound to alpha(2)-macroglobulin and not in the binary complex with its ligand, IGFBP-2 complexes and/or polymers were detected, which was not acknowledged before, and IGFBP-3 molecular forms were differentiated into those that form binary/ternary complexes and those that form stable associations with other serum proteins. As for placental membranes, both IGFBP-1 dimers and high molecular mass IGFBP-1 associations, most probably with alpha(2)-macroglobulin, were recognized and resolved.

The metabolic syndrome, IGF-1, and insulin action

Recent studies have shown that insulin and insulin-like growth factor (IGF)-1 signaling are involved in the control of ageing and longevity in model organisms. Based on these studies, genes involved in the insulin/IGF-1 signaling pathway are believed to play a role in longevity throughout evolution and could also be important in determining human longevity. However, human studies have yielded conflicting and controversial results. In human, defects in insulin receptor signaling cause insulin resistance and diabetes, and IGF-1 deficiency is associated with an increased risk of cardiovascular disease and atherosclerosis. Interestingly, insulin sensitivity normally decreases during aging; however, centenarians were reported to maintain greatly increased insulin sensitivity and had a lower prevalence of the metabolic syndrome as compared to younger subjects. Additionally, a longitudinal study revealed that insulin-sensitizing hormones, including leptin and adiponectin, were significantly associated with the survival of centenarians, indicating that an efficient insulin response may influence human longevity.