Low circulating insulin-like growth factor I bioactivity in elderly men is associated with increased mortality

Cellular senescence and sleep in childhood and adolescence: A scoping review focusing on sleep-disordered breathing

BACKGROUND

Sleep is a fundamental and complex physiological process whose duration decreases and characteristics change with age. Around 50 % of children will experience sleep disturbances at some point in their early life. Sleep disturbances can result in a number of deleterious consequences, including alterations in the levels of cellular senescence (CS) markers. CS is a complex process essential for homeostasis characterized by the irreversible loss of cell proliferation capacity; however, the accumulation of senescent cells can lead to age-related diseases.

OBJECTIVE

In this review, our objective was to gather information about the relationship between sleep duration, sleep-disordered breathing (SDB) and cellular senescence markers, namely: oxidative stress, inflammation, insulin-like growth factor 1 (IGF-1), and growth hormone (GH) in newborns, children, and teenagers.

METHODS

To achieve this, we searched six databases: MEDLINE, Scopus, LILACS, Web of Science, Embase, and SciELO, and identified 20 articles that met our inclusion criteria.

RESULTS

Our results show that better sleep quality and duration and, both the surgical and non-surgical treatment of sleep disorders are associated with a reduction in oxidative stress, inflammation, and telomeric attrition levels. Furthermore, our results also show that surgical treatment for SDB significantly reduced the levels of cellular senescence markers. Further studies need to be conducted in this area, particularly longitudinal studies, for a greater understanding of the mechanisms involved in the relationship between sleep and senescence.

CONCLUSION

Better sleep quality and duration were associated with less oxidative stress, inflammation, and telomeric attrition and a higher level of IGF-1 in children and teenagers.

Sex Does Not Affect Changes in Body Composition and Insulin-Like Growth Factor-I During US Army Basic Combat Training

ABSTRACT

Roberts, BM, Staab, JS, Caldwell, AR, Sczuroski, CE, Staab, JE, Lutz, LJ, Reynoso, M, Geddis, AV, Taylor, KM, Guerriere, KI, Walker, LA, Hughes, JM, and Foulis, SA. Sex does not affect changes in body composition and insulin-like growth factor-I during US Army basic combat training. J Strength Cond Res 38(6): e304-e309, 2024-Insulin-like growth factor 1 (IGF-I) has been implicated as a biomarker of health and body composition. However, whether changes in body composition are associated with changes in IGF-I is unclear. Therefore, we examined the relationship between body composition changes (i.e., fat mass and lean mass) and total serum IGF-I levels in a large cohort of young men ( n = 809) and women ( n = 397) attending US Army basic combat training (BCT). We measured body composition using dual energy x-ray absorptiometry and total serum IGF-I levels during week 1 and week 9 of BCT. We found that pre-BCT lean mass ( r = 0.0504, p = 0.082) and fat mass ( r = 0.0458, p = 0.082) were not associated with pre-BCT IGF-I. Body mass, body mass index, body fat percentage, and fat mass decreased, and lean mass increased during BCT (all p < 0.001). Mean (± SD ) IGF-I increased from pre-BCT (176 ± 50 ng·ml -1 ) to post-BCT (200 ± 50 ng·ml -1 , p < 0.001). Inspection of the partial correlations indicated that even when considering the unique contributions of other variables, increases in IGF-I during BCT were associated with both increased lean mass ( r = 0.0769, p = 0.023) and increased fat mass ( r = 0.1055, p < 0.001) with no sex differences. Taken together, our data suggest that although changes in IGF-I weakly correlated with changes in body composition, IGF-I, in isolation, is not an adequate biomarker for predicting changes in body composition during BCT in US Army trainees.

IGF-1 and Risk of Morbidity and Mortality From Cancer, Cardiovascular Diseases, and All Causes in EPIC-Heidelberg

CONTEXT

The functional status of organs, such as the liver, involved in IGF-1 signaling pathways influences circulating levels of IGF-1 and hence its relationship to risk of chronic disease and mortality, yet this has received limited attention.

OBJECTIVE

To examine the relationship between IGF-1 and risk of morbidity and mortality from cancer, cardiovascular diseases (CVD), and all causes, accounting for liver function.

METHODS

This study was a case-cohort design nested within EPIC-Heidelberg. IGF-1 was measured in 7461 stored serum samples collected from 1994 to 1998. Median follow-up for incident mortality events was 17.5 years. The case-cohort included a subcohort of 1810 men and 1890 women, in addition to 1668 incident cases of cancer (623 breast, 577 prostate, 202 lung, and 268 colorectal), and 1428 cases of CVD (707 myocardial infarctions and 723 strokes) and 2441 cases of death.

RESULTS

Higher IGF-1 levels showed direct associations with risks of breast (1.25; 95% CI [1.06-1.47]) and prostate (1.31; [1.09-1.57]) cancers. Restricted cubic splines plots and models including IGF-1 as quintiles revealed a U-shaped relationship between the biomarker and mortality. Participants with the lowest and the highest levels of IGF-1 experienced higher hazards of mortality from cancer, CVD, and all causes. The U-shaped form of the relationship persisted but was attenuated in analyses including only participants without any indications of liver dysfunction.

CONCLUSION

This large population-based prospective study showed that both individuals with lowest and highest levels of circulating IGF-1 were at increased risk of deaths from cancer, CVD, and all causes. For individuals with low IGF-1, the excess risks of death were more pronounced among individuals with liver cancer and cirrhosis but were also present among individuals without elevated liver enzymes.

Insulin-like Growth Factor-1 and Myocardial Remodeling in Patients with Chronic Heart Failure of Ischemic Origin

Aim. To study the presence and nature of correlations between the level of Insulin-like growth factor-1 (IGF-1) and structural and functional parameters of the heart in the development of myocardial remodeling and fibrosis in patients with chronic heart failure (CHF) of ischemic origin.Material and methods. The study included 120 men with class II-IV CHF who have history of myocardial infarction, which are divided into 3 groups depending on the CHF class. The control group included 25 healthy men. Assessment of left ventricular (LV) structural-functional state was carried out by echocardiography. Investigation of IGF-1 and N-terminal precursor indices of cerebral natriuretic peptide (NT-pro BNP) was performed by enzyme immunoassay.Results. Patients with class II CHF were hyperexpression of IGF-1, with class III CHF were registered low-normal level, with class IV CHF was established a deficiency of IGF-1. The most significant structural-geometric rearrangement of LV and significant deficit of IGF-1 recorded in patients with class IV CHF (95,6±7,02 ng/ml with class IV CHF versus 178,3±11,36 ng/ml and 124,3±9,14 ng/ml with class II and III CHF; р<0,05). In patients of class III-IV CHF, correlation relationships between IGF-1 level and echocardiographic parameters (LV myocardial mass index are established: r=-0,59, p=0,05; end systolic volume index: r=-0,55, p=0,05; value of LV ejection fraction: r=0,61, p=0,05). Significant negative correlation are established in patients with class III-IV CHF between IGF-1 level and NT-pro BNP levels (r=-0,51; р=0,05).Conclusion. The intensity of myocardial remodeling and fibrosis processes in patients with a progressive course of CHF is related to deficit of IGF-1 and is associated with a high level of activity of natriuretic peptides.

Insulin-like growth factor I sensitization rejuvenates sleep patterns in old mice

Sleep disturbances are common during aging. Compared to young animals, old mice show altered sleep structure, with changes in both slow and fast electrocorticographic (ECoG) activity and fewer transitions between sleep and wake stages. Insulin-like growth factor I (IGF-I), which is involved in adaptive changes during aging, was previously shown to increase ECoG activity in young mice and monkeys. Furthermore, IGF-I shapes sleep architecture by modulating the activity of mouse orexin neurons in the lateral hypothalamus (LH). We now report that both ECoG activation and excitation of orexin neurons by systemic IGF-I are abrogated in old mice. Moreover, orthodromical responses of LH neurons are facilitated by either systemic or local IGF-I in young mice, but not in old ones. As orexin neurons of old mice show dysregulated IGF-I receptor (IGF-IR) expression, suggesting disturbed IGF-I sensitivity, we treated old mice with AIK3a305, a novel IGF-IR sensitizer, and observed restored responses to IGF-I and rejuvenation of sleep patterns. Thus, disturbed sleep structure in aging mice may be related to impaired IGF-I signaling onto orexin neurons, reflecting a broader loss of IGF-I activity in the aged mouse brain.

Association between IGF-1 levels ranges and all-cause mortality: A meta-analysis

The association between IGF‐1 levels and mortality in humans is complex with low levels being associated with both low and high mortality. The present meta‐analysis investigates this complex relationship between IGF‐1 and all‐cause mortality in prospective cohort studies. A systematic literature search was conducted in PubMed/MEDLINE, Scopus, and Cochrane Library up to September 2019. Published studies were eligible for the meta‐analysis if they had a prospective cohort design, a hazard ratio (HR) and 95% confidence interval (CI) for two or more categories of IGF‐1 and were conducted among adults. A random‐effects model with a restricted maximum likelihood heterogeneity variance estimator was used to find combined HRs for all‐cause mortality. Nineteen studies involving 30,876 participants were included. Meta‐analysis of the 19 eligible studies showed that with respect to the low IGF‐1 category, higher IGF‐1 was not associated with increased risk of all‐cause mortality (HR = 0.84, 95% CI = 0.68–1.05). Dose–response analysis revealed a U‐shaped relation between IGF‐1 and mortality HR. Pooled results comparing low vs. middle IGF‐1 showed a significant increase of all‐cause mortality (HR = 1.33, 95% CI = 1.14–1.57), as well as comparing high vs. middle IGF‐1 categories (HR = 1.23, 95% CI = 1.06–1.44). Finally, we provide data on the association between IGF‐1 levels and the intake of proteins, carbohydrates, certain vitamins/minerals, and specific foods. Both high and low levels of IGF‐1 increase mortality risk, with a specific 120–160 ng/ml range being associated with the lowest mortality. These findings can explain the apparent controversy related to the association between IGF‐1 levels and mortality.

Telomeres: the role of shortening and senescence in major depressive disorder and its therapeutic implications

Major depressive disorder (MDD) is one of the most prevalent and debilitating psychiatric disorders, with a large number of patients not showing an effective therapeutic response to available treatments. Several biopsychosocial factors, such as stress in childhood and throughout life, and factors related to biological aging, may increase the susceptibility to MDD development. Included in critical biological processes related to aging and underlying biological mechanisms associated with MDD is the shortening of telomeres and changes in telomerase activity. This comprehensive review discusses studies that assessed the length of telomeres or telomerase activity and function in peripheral blood cells and brain tissues of MDD individuals. Also, results from in vitro protocols and animal models of stress and depressive-like behaviors were included. We also expand our discussion to include the role of telomere biology as it relates to other relevant biological mechanisms, such as the hypothalamic-pituitary-adrenal (HPA) axis, oxidative stress, inflammation, genetics, and epigenetic changes. In the text and the discussion, conflicting results in the literature were observed, especially considering the size of telomeres in the central nervous system, on which there are different protocols with divergent results in the literature. Finally, the context of this review is considering cell signaling, transcription factors, and neurotransmission, which are involved in MDD and can be underlying to senescence, telomere shortening, and telomerase functions.

Effects of resistance training on muscle strength, insulin-like growth factor-1, and insulin-like growth factor-binding protein-3 in healthy elderly subjects: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Findings regarding the effects of resistance training (RT) on muscle strength, serum level of IGF-1, and its binding proteins are contradictory. To resolve this contradiction, we performed a systematic review and meta-analysis to investigate the effects of RT on muscle strength, the levels of serum IGF-1, and IGF-binding protein-3 in the elderly and aged.

MATERIALS AND METHODS

The PubMed, CINAHL, Medline, Google Scholar, and Scopus databases and reference lists of included studies were systematically searched to identify randomized controlled trials (RCTs) comparing subjects who underwent RT and control individuals up to May 15, 2020. This study was performed following the Preferred Items for Reporting of Systematic Reviews and Meta-Analyses guidelines. We identified and analyzed 11 eligible trials in this meta-analysis.

RESULTS

Pooled data displayed an overall significant elevation in IGF-1 (mean difference (MD): 17.34 ng/ml; 95% confidence interval (CI): 7.23, 27.46) and in muscle strength in leg press (SMD: 0.82; 95% CI: 0.30, 1.34) and bench press (SMD: 0.82; 95% CI: 0.42, 1.23) following RT. By contrast, the pooled estimate showed a non-significant elevation in IGFBP-3 (MD: 0.13 ng/ml; 95% CI: - 39.39, 39.65). Subgroup analysis revealed that the elevation in serum IGF-1 levels after RT was significant only in women (MD: 19.30 ng/ml); moreover, it increased after intervention durations of both > 12 weeks (MD: 21.98 ng/ml) and of ≤ 12 weeks (MD: 15.31 ng/ml).

CONCLUSION

RT was associated with elevated muscle strength. Moreover, RT was correlated with increased serum levels of IGF-1 among women and among those who received the training for ≤ 12 weeks or > 12 weeks. Further studies are required to elucidate the mechanisms underlying the impact of RT on IGF-1, IGFBP-3, and muscle strength.

Resistance training effect on serum insulin-like growth factor 1 in the serum: a meta-analysis

BACKGROUND

The resistance exercise has drawn considerable attention to the level of insulin-like growth factor 1 in the serum. However, the relationship between resistance exercise and the level of insulin-like growth factor 1 in the serum is conflicting. This meta-analysis was performed to evaluate this relationship.

METHODS

A systematic literature search up to May 2020 was performed and 22 studies were detected with 680 subjects. They reported relationships between resistance exercise and the level of insulin-like growth factor 1 in the serum. Odds ratio (OR) with 95% confidence intervals (CIs) was calculated comparing the resistance exercise and the level of insulin-like growth factor 1 in the serum using the continuous method with a random or fixed-effect model.

RESULTS

Significantly higher insulin-like growth factor 1 was observed in subjects performing resistance training for less than 16 weeks (OR, 4.03; 95% CI, 2.49-5.57, p<.001); subjects performing resistance training for more than 16 weeks (OR, 11.55; 95% CI, 6.58-16.52, p<.001); subjects older than 60 years (OR, 11.88; 95% CI, 9.84-13.93, p<.001); females (OR, 3.87; 95% CI, 2.26-5.49, p<.001) and males (OR, 16.82; 95% CI, 7.29-26.35, p<.001). However, significantly lower insulin-like growth factor 1 was observed in subjects younger than 60 years (OR, -4.80; 95% CI, -7.74 to -1.86, p=.001).

CONCLUSIONS

However, the resistance exercise significantly increases insulin-like growth factor 1 in subjects older than 60 years, both males and females, and subjects performing resistance exercise for all any period. Surprisingly, resistance exercise significantly decreases insulin-like growth factor 1 in subjects younger than 60 years. This relationship forces us to recommend the resistance exercise to improve insulin-like growth factor 1 in serum.

The insulin-like growth factor-I receptor stimulating activity (IRSA) in health and disease

Determination of true IGF-I bioactivity in serum and other biological fluids is still a substantial challenge. The IGF-IR Kinase Receptor Activation assay (IGF-IR KIRA assay) is a novel tool to asses IGF-IR stimulating activity (IRSA) and has opened a new era in studying the IGF system. In this paper we discuss many studies showing that measuring IRSA by the IGF-IR KIRA assay often provides fundamentally different information about the IGF system than the commonly used total IGF-I immunoassays. With the IGF-IR KIRA assay phosphorylation of tyrosine residues of the IGF-IR is used as read out to quantify IRSA in unknown (serum) samples. The IGF-IR KIRA assay gives information about net overall effects of circulating IGF-I, IGF-II, IGFBPs and IGFBP-proteases on IGF-IR activation and seems especially superior to immunoreactive total IGF-I in monitoring therapeutic interventions. Although the IRSA as measured by the IGF-IR KIRA assay probably more closely reflects true bioactive IGF-I than measurements of total IGF-I in serum, the IGF-IR KIRA assay in its current form does not give information about all the post-receptor intracellular events mediated by the IGF-IR. Interestingly, in several conditions in health and disease IRSA measured by the IGF-IR KIRA assay is considerably higher in interstitial fluid and ascites than in serum. This suggests that both the paracrine (local) and endocrine (circulating) IRSA should be measured to get a complete picture about the role of the IGF system in health and disease.

Inflammation-Accelerated Senescence and the Cardiovascular System: Mechanisms and Perspectives

Low-grade chronic inflammation is a common denominator in atherogenesis and related diseases. Solid evidence supports the occurrence of an impairment in the innate and adaptive immune system with senescence, favoring the development of acute and chronic age-related diseases. Cardiovascular (CV) diseases (CVD), in particular, are a leading cause of death even at older ages. Inflammation-associated mechanisms that contribute to CVD development include dysregulated redox and metabolic pathways, genetic modifications, and infections/dysbiosis. In this review, we will recapitulate the determinants and consequences of the immune system dysfunction at older age, with particular focus on the CV system. We will examine the currently available and potential future strategies to counteract accelerated CV aging, i.e., nutraceuticals, probiotics, caloric restriction, physical activity, smoking and alcohol cessation, control of low-grade inflammation sources, senolytic and senescence-modulating drugs, and DNA-targeting drugs.

The effect of growth hormone on bioactive IGF in overweight/obese women

OBJECTIVE

Overweight/obesity is characterized by decreased growth hormone (GH) secretion whereas circulating IGF-I levels are less severely reduced. Yet, the activity of the circulating IGF-system appears to be normal in overweight/obese subjects, as estimated by the ability of serum to activate the IGF-I receptor in vitro (bioactive IGF). We hypothesized that preservation of bioactive IGF in overweight/obese women is regulated by an insulin-mediated suppression of IGF-binding protein-1 (IGFBP-1) and IGFBP-2, and by suppression of IGFBP-3, mediated by low GH. We additionally hypothesized that increases in bioactive IGF would drive changes in body composition with low-dose GH administration.

DESIGN

Cross-sectional analysis and 3-month interim analysis of a 6-month randomized, placebo-controlled study of GH administration in 50 overweight/obese women without diabetes mellitus. Bioactive IGF (kinase receptor activation assay) and body composition (DXA) were measured.

RESULTS

Prior to treatment, IGFBP-3 (r = -0.33, p = 0.02), but neither IGFBP-1 nor IGFBP-2, associated inversely with bioactive IGF. In multivariate analysis, lower IGFBP-3 correlated with lower peak stimulated GH (r = 0.45, p = 0.05) and higher insulin sensitivity (r = -0.74, p = 0.003). GH administration resulted in an increase in mean serum IGF-I concentrations (144 ± 56 to 269 ± 66 μg/L, p < 0.0001) and bioactive IGF (1.29 ± 0.39 to 2.60 ± 1.12 μg/L, p < 0.0001). The treatment-related increase in bioactive IGF, but not total IGF-I concentration, predicted an increase in lean mass (r = 0.31, p = 0.03) and decrease in total adipose tissue/BMI (r = -0.43, p = 0.003).

CONCLUSIONS

Our data suggest that in overweight/obesity, insulin sensitivity and GH have opposing effects on IGF bioactivity through effects on IGFBP-3. Furthermore, increases in bioactive IGF, rather than IGF-I concentration, predicted GH administration-related body composition changes.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00131378.

Attenuated IGF-1 predicts all-cause and cardiovascular mortality in a Black population: A five-year prospective study

BACKGROUND

Inconsistent findings are reported on whether insulin-like growth factor-1 (IGF-1) is protective or harmful in predicting hypertension, carotid wall thickness and mortality. We determined the five-year prognostic value of IGF-1 for these outcomes in a large Black population prone to hypertension and cardiovascular disease.

DESIGN

A longitudinal study as part of the PURE (Prospective Urban and Rural Epidemiology) study, North West Province, South Africa.

METHODS

We measured IGF-1 and IGF binding protein-3 (IGFBP-3) in 1038 HIV-uninfected participants (age range 32-94 years) and assessed blood pressure, carotid intima-media thickness and mortality.

RESULTS

Over five years 116 deaths occurred. Baseline IGF-1 was similar in survivors and non-survivors (p = 0.50), but tended to be higher in survivors upon adjustment for IGFBP-3 and covariates (p = 0.061). Normotensives and hypertensives (p = 0.072), and those with carotid intima-media thickness < 0.9 mm and ≥ 0.9 mm also displayed similar baseline IGF-1 (p = 0.55). Multivariable-adjusted Cox-regression indicated high IGF-1 predicting lower risk for all-cause mortality (hazard ratio 0.45; 0.23-0.88) and cardiovascular mortality (hazard ratio 0.26; 0.08-0.83) when also adjusting for IGFBP-3. When including normo- and hypertensives at baseline, high IGF-1 was related to normotension at follow-up (hazard ratio 0.68; 0.49-0.95). We found no association with carotid intima-media thickness (hazard ratio 0.59; 0.31-1.14).

CONCLUSION

In a Black South African population with low socio-economic status and harmful health behaviours, we found a protective independent association between IGF-1 and hypertension, cardiovascular and all-cause mortality, with no association with carotid wall thickness.

Insulin-Like Growth Factor-1 Receptor Deficiency in Macrophages Accelerates Atherosclerosis and Induces an Unstable Plaque Phenotype in Apolipoprotein E-Deficient Mice

BACKGROUND

We have previously shown that systemic infusion of insulin-like growth factor-1 (IGF-1) exerts anti-inflammatory and antioxidant effects and reduces atherosclerotic burden in apolipoprotein E (Apoe)-deficient mice. Monocytes/macrophages express high levels of IGF-1 receptor (IGF1R) and play a pivotal role in atherogenesis, but the potential effects of IGF-1 on their function are unknown.

METHODS AND RESULTS

To determine mechanisms whereby IGF-1 reduces atherosclerosis and to explore the potential involvement of monocytes/macrophages, we created monocyte/macrophage-specific IGF1R knockout (MΦ-IGF1R-KO) mice on an Apoe(-/-) background. We assessed atherosclerotic burden, plaque features of stability, and monocyte recruitment to atherosclerotic lesions. Phenotypic changes of IGF1R-deficient macrophages were investigated in culture. MΦ-IGF1R-KO significantly increased atherosclerotic lesion formation, as assessed by Oil Red O staining of en face aortas and aortic root cross-sections, and changed plaque composition to a less stable phenotype, characterized by increased macrophage and decreased α-smooth muscle actin-positive cell population, fibrous cap thinning, and decreased collagen content. Brachiocephalic artery lesions of MΦ-IGF1R-KO mice had histological features implying plaque vulnerability. Macrophages isolated from MΦ-IGF1R-KO mice showed enhanced proinflammatory responses on stimulation by interferon-γ and oxidized low-density lipoprotein and elevated antioxidant gene expression levels. Moreover, IGF1R-deficient macrophages had decreased expression of ABCA1 and ABCG1 and reduced lipid efflux.

CONCLUSIONS

Our data indicate that macrophage IGF1R signaling suppresses macrophage and foam cell accumulation in lesions and reduces plaque vulnerability, providing a novel mechanism whereby IGF-1 exerts antiatherogenic effects.

Selenium Status Is Positively Associated with Bone Mineral Density in Healthy Aging European Men

Objective

It is still a matter of debate if subtle changes in selenium (Se) status affect thyroid function tests (TFTs) and bone mineral density (BMD). This is particularly relevant for the elderly, whose nutritional status is more vulnerable.

Design and Methods

We investigated Se status in a cohort of 387 healthy elderly men (median age 77 yrs; inter quartile range 75–80 yrs) in relation to TFTs and BMD. Se status was determined by measuring both plasma selenoprotein P (SePP) and Se.

Results

The overall Se status in our population was low normal with only 0.5% (2/387) of subjects meeting the criteria for Se deficiency. SePP and Se levels were not associated with thyroid stimulating hormone (TSH), free thyroxine (FT4), thyroxine (T4), triiodothyronine (T3) or reverse triiodothyronine (rT3) levels. The T3/T4 and T3/rT3 ratios, reflecting peripheral metabolism of thyroid hormone, were not associated with Se status either. SePP and Se were positively associated with total BMD and femoral trochanter BMD. Se, but not SePP, was positively associated with femoral neck and ward's BMD. Multivariate linear analyses showed that these associations remain statistically significant in a model including TSH, FT4, body mass index, physical performance score, age, smoking, diabetes mellitus and number of medication use.

Conclusion

Our study demonstrates that Se status, within the normal European marginally supplied range, is positively associated with BMD in healthy aging men, independent of thyroid function. Thyroid function tests appear unaffected by Se status in this population.

IGFBP-1 predicts all-cause mortality in elderly women independently of IGF-I

OBJECTIVE

Previous studies on the insulin-like growth factor (IGF) system and mortality have shown ambiguous results. We investigated the association between IGF-I and insulin- like growth factor binding protein-1 (IGFBP-1) with all-cause mortality in an elderly female Swedish population.

DESIGN AND METHODS

A prospective cohort study of elderly women (n=338) aged between 68 and 79 years (mean age 72 years) with a mean follow-up time of 9.9 years. Baseline data in the PRIMOS (Primary Health Care and Osteoporosis) study were collected between 1999 and 2001. Data of risk factors for cardiovascular disease were collected. Death rates were registered from the Swedish Cause of Death register for the period 1999-2009. Cox regression models were used to calculate hazard ratios. IGF-I and IGFBP-1 levels were separately divided into 3 groups (high, medium and low), with cut offs at the 30th and the 70th percentiles.

RESULTS

In a fully adjusted Cox proportional hazard model, increased risk of mortality was shown for women with high serum levels of IGFBP-1, HR 3.03 (95% CI 1.64-5.63) and also with low serum levels of IGFBP-1, HR 1.98 (95% CI 1.03-3.81), compared to women with moderate levels. No significant association between IGF-I and mortality was observed.

CONCLUSIONS

High and low serum insulin-like IGFBP-1 levels were associated with an increased risk of all-cause mortality in elderly women, compared to moderate levels.

Insulin-Like Growth Factor-1 and Resistance Exercise in Community Dwelling Old Adults

BACKGROUND

Insulin-like growth factor-1 (IGF-1) is related to the preservation of lean body mass. Its decline during ageing is thought to make old adults more susceptible to sarcopenia and functional dependency. The aim of the present study was to investigate circulating total IGF-1 in old adults who engaged in a 12-weeks of progressive resistance training.

DESIGN

Intervention study.

SETTING

Community.

PARTICIPANTS

Old Icelandic adults (N = 235, 73.7 ± 5.7 years, 58.2% female).

INTERVENTION

Twelve-week resistance exercise program (3 times/week; 3 sets, 6-8 repetitions at 75-80% of the 1-repetition maximum) designed to increase strength and muscle mass of major muscle groups.

MEASUREMENTS

IGF-1.

RESULTS

At baseline IGF-1 was significantly associated with lean body mass and appendicular muscle mass (also when corrected for age, gender and various covariates). After the training IGF-1 decreased significantly from 112.1 ± 35.6 to 106.1 ± 35.2 µg/L during the course of the study. On and individual level, IGF-1 decreased in 59% and increased in 39% of the participants. Changes in IGF-1 were inversely related to changes in lean body mass (rho = -0.176, P = 0.013 ) and appendicular muscle mass (rho = -0.162, P = 0.019) also when corrected for protein intake, age, gender, and other covariates.

CONCLUSION

Serum total IGF-1 decreases after 12 weeks of resistance exercise in community dwelling old adults. When looked at IGF-1 changes for participants individually it becomes clear that IGF-1 response to resistances exercise is highly variable. Changes in IGF-1 are negatively related to changes in lean body mass during training, which supports the hypothesis that IGF-1 is redistributed from circulation into tissue during periods of active muscle building.

Changes in circulating IGF1 receptor stimulating activity do not parallel changes in total IGF1 during GH treatment of GH-deficient adults

CONTEXT

Previously we demonstrated that IGF1 receptor stimulating activity (IGF1RSA) offers advantages in diagnostic evaluation of adult GH deficiency (GHD). It is unknown whether IGF1RSA can be used to monitor GH therapy.

OBJECTIVE

To investigate the value of circulating IGF1RSA for monitoring GH therapy.

DESIGN/METHODS

106 patients (54 m; 52 f) diagnosed with GHD were included; 22 were GH-naïve, 84 were already on GH treatment and discontinued therapy 4 weeks before baseline values were established. IGF1RSA was determined by the IGF1R kinase receptor activating assay, total IGF1 by immunoassay (Immulite). GH doses were titrated to achieve total IGF1 levels within the normal range.

RESULTS

After 12 months, total IGF1 and IGF1RSA increased significantly (total IGF1 from 8.1 (95% CI 7.3-8.9) to 14.9 (95% CI 13.5-16.4) nmol/l and IGF1RSA from 115 (95% CI 104-127) to 181 (95% CI 162-202) pmol/l). After 12 months, total IGF1 normalized in 81% of patients, IGF1RSA in 51% and remained below normal in more than 40% of patients in whom total IGF1 had normalized.

CONCLUSIONS

During 12 months of GH treatment, changes in IGF1RSA did not parallel changes in total IGF1. Despite normalization of total IGF1, IGF1RSA remained subnormal in a considerable proportion of patients. At present our results have no short-term consequences for GH therapy of GHD patients. However, based on our findings we propose future studies to examine whether titrating GH dose against IGF1RSA results in a better clinical outcome than titrating against total IGF1.

Role of insulin-like growth factor 1 in stent thrombosis under effective dual antiplatelet therapy

Introduction

Accumulating evidence now indicates that insulin-like growth factors (IGF) and their regulatory proteins are growth promoters for arterial cells and mediators of cardiovascular diseases.

Aim

We hypothetised that IGF-1 levels could play a role in the development of stent thrombosis (ST), and aimed to investigate the associations between stent thrombosis under effective dual antiplatelet therapy and IGF-1 levels and other related factors such as disease severity and LV ejection fraction in patients undergoing coronary stent placement.

Material and methods

A total of 128 patients undergoing coronary stent implantation were included in the analysis. Seventy-seven patients experiencing ST in the first year after stent implantation were defined as the ST group. Fifty-one patients without ST at least 1 year after stent implantation were defined as the no-thrombosis (NT) group. The IGF-1 levels, Gensini scores, and other related factors were measured.

Results

The IGF-1 levels were significantly higher in the stent thrombosis group than in the no-thrombosis group (122.22 ±50.61 ng/ml vs. 99.52 ±46.81 ng/ml, respectively, p < 0.039). The left ventricle ejection fraction (LVEF) values were significantly lower (44.13 ±9.25% vs. 55.81 ±8.77%, p < 0.0001) and Gensini scores were significantly higher (63.74 ±26.54 vs. 48.87 ±23.7, p < 0.004) in the ST group than in the NT group, respectively. In the linear regression analysis, IGF-1, Gensini score, LVEF, total cholesterol, and triglycerides were found to be independent risk factors for ST.

Conclusions

This study revealed that the plasma IGF-1 levels, disease severity, were significantly higher and LVEF was lower in patients with ST. High IGF-1 levels may identify patients who are at increased risk for ST. Future trials are necessary to confirm these results.

Both low and high serum IGF-1 levels associate with increased risk of cardiovascular events in elderly men

CONTEXT

Most previous prospective studies suggest that low serum IGF-1 associates with increased risk of cardiovascular disease (CVD) events whereas other studies suggest that high serum IGF-1 associates with increased risk of CVD events.

OBJECTIVE

We tested the hypothesis that not only low, but also high serum IGF-1 levels associate with increased risk of CVD events in elderly men.

SETTING AND DESIGN

Serum IGF-1 levels were measured in 2901 elderly men (age 69-81 years) included in the Swedish cohort of the prospective, population-based Osteoporotic Fractures in Men Study (MrOS), Sweden cohort. Data for CVD events were obtained from national Swedish registers with no loss of followup.

RESULTS

During followup (median, 5.1 y) 589 participants experienced a CVD event. The association between serum IGF-1 and risk of CVD events was nonlinear, and restricted cubic spline Cox regression analysis revealed a U-shaped association between serum IGF-1 levels and CVD events (P < .01 for nonlinearity). Low as well as high serum IGF-1 (quintile 1 or 5 vs quintiles 2-4) significantly associated with increased risk for CVD events (hazard ratio [HR] = 1.25, 95% confidence interval, [CI], 1.02-1.54; and HR = 1.35, 95% CI 1.10-1.66, respectively). These associations remained after adjustment for prevalent CVD and multiple risk factors. High serum IGF-1 associated with increased risk of coronary heart disease (CHD) events but not with risk of cerebrovascular events.

CONCLUSIONS

Both low and high serum IGF-1 levels are risk markers for CVD events in elderly men. The association between high serum IGF-1 and CVD events is mainly driven by CHD events.

Metabolic and hormonal contributors to survival in the participants of the Mataró Ageing Study at 8 years follow-up

OBJECTIVE

Ageing is a physiological process that may be influenced by genetic factors as well as metabolic and hormonal determinants. The aim was to describe metabolic and hormonal factors related to survival in the cohort of non-institutionalized people aged >70 years old of the Mataró Ageing Study.

DESIGN AND METHODS

313 individuals were included and followed-up during 8 years. Metabolic syndrome (MS) parameters by International Diabetes Federation and ATP-III as well as hormonal factors (TSH, free-T4, growth hormone, IGF-I, ghrelin, cortisol, dehydroepiandrosterone -DHEA-, DHEAs, testosterone, SHBG, estradiol, estrone, cortisol/DHEA and cortisol/DHEAs) were studied and their relationship with survival was assessed.

RESULTS

At 8 year of follow-up, 96 out of 313 subjects (30·7%) died. No association between MS and its components and survival was found. However, when abdominal perimeter was analyzed according to distribution in quartiles and categorized by gender, the lowest and highest quartile showed higher mortality (P = 0·009; waist circumference (WC) between 98-102 cm in men and 95-102 cm in women were associated to lower mortality). In men, IGF-I, estrone, cortisol/DHEA ratio and cortisol/DHEAs ratio were lower in survivors, and in women, growth hormone and ghrelin were higher in survivors and cortisol/DHEAs ratio was lower. When Cox regression was performed for survival analysis of the whole cohort (adjusting by age, gender, tobacco consumption and WC, cortisol (B = 0·036, P = 0·033), estrone (B = 0·014, P = 0·004) and cortisol/DHEA ratio (B = 0·018, P = 0·008) were significantly associated to mortality. Sequential adjustments including additionally in the model Lawton scale, MiniNutritional Assessment and MCE showed significant association to estrone (P = 0·018).

CONCLUSIONS

Waist circumference in a U-shaped relationship, together with hormonal factors (adrenal steroids and somatotropic axis) influenced survival in individuals participating in Mataró Ageing Study.

Intraperitoneal insulin delivery to patients with type 1 diabetes results in higher serum IGF-I bioactivity than continuous subcutaneous insulin infusion

OBJECTIVE

Type 1 diabetes (T1D) is associated with low IGF-I and altered levels of IGF-binding proteins (IGFBPs) in plasma. This may be of importance for insulin sensitivity and the risk of developing diabetic complications. We hypothesized that IGF-I bioactivity is affected by the route of insulin administration and that continuous intraperitoneal insulin infusion (CIPII) has a more pronounced effect than continuous subcutaneous insulin infusion (CSII).

DESIGN AND METHODS

We compared 10 patients with T1D on CIPII with 20 age- and sex-matched patients on CSII. Blood sampling was carried out 7-9 am after an overnight fast. All patients were C-peptide negative. IGF-I bioactivity was measured in vitro using a specific IGF-I kinase receptor activation (KIRA) assay. IGF-I was also measured by immunoassay together with IGF-II, IGFBP-1 and IGFBP-2.

RESULTS

When compared with subcutaneous insulin, intraperitoneal insulin resulted in (CIPII vs CSII) higher IGF-I bioactivity (1·83 ± 0·76 vs 1·16 ± 0·24 μg/l; P = 0·02), IGF-I (120 ± 35 vs 81 ± 19 μg/l; P = 0·01) and IGF-II (1050 ± 136 vs 879 ± 110 μg/l; P = 0·02). By contrast, log-transformed IGFBP-1 was reduced (P = 0·013), whereas log-transformed IGFBP-2 was not different (P = 0·12). There was a positive correlation between IGF bioactivity and IGF-I (r = 0·69; P < 0·001) and an inverse correlation between IGF-I bioactivity and log10 IGFBP-1 (r = -0·68, P < 0·001).

CONCLUSION

The in vitro IGF-I bioactivity was higher in patients treated with CIPII compared with CSII supporting the theory that the route of insulin administration is of importance for the activity of the IGF system. Intraperitoneal insulin administration may therefore be beneficial by correcting the alterations of the IGF system in T1D.

Interaction between insulin-like growth factor-1 and atherosclerosis and vascular aging

The process of vascular aging encompasses alterations in the function of endothelial (ECs) and vascular smooth muscle cells (VSMCs) via oxidation, inflammation, cell senescence and epigenetic modifications, increasing the probability of atherosclerosis. Aged vessels exhibit decreased endothelial antithrombogenic properties, increased reactive oxygen species generation, inflammatory signaling and migration of VSMCs to the subintimal space, impaired angiogenesis and increased elastin degradation. The key initiating step in atherogenesis is subendothelial accumulation of apolipoprotein B-containing low-density lipoproteins resulting in activation of ECs and recruitment of monocytes. Activated ECs secrete 'chemokines' that interact with cognate chemokine receptors on monocytes and promote directional migration. Recruitment of immune cells establishes a proinflammatory status, further causing elevated oxidative stress, which in turn triggers a series of events including apoptotic or necrotic death of vascular and nonvascular cells. Increased oxidative stress is also considered to be a key factor in mechanisms of aging-associated changes in tissue integrity and function. Experimental evidence indicates that insulin-like growth factor-1 exerts antioxidant, anti-inflammatory and pro-survival effects on the vasculature, reducing atherosclerotic plaque burden and promoting features of atherosclerotic plaque stability.

Effects of raloxifene and estrogen on bioactive IGF1 in GH-deficient women

CONTEXT

GH action is attenuated by estrogens and selective estrogen receptor modulators (SERMs) administered orally. During GH therapy in hypopituitary women, co-treatment with raloxifene, a SERM, induced a smaller gain in lean body mass (LBM) compared with estrogen, despite an equal reduction in IGF1. As a higher IGF-binding protein-3 (IGFBP3) level was observed with raloxifene co-treatment, we hypothesize that an increase in IGFBP3 reduced IGF1 bioactivity causing the attenuated anabolic effect.

OBJECTIVE

To assess the effects of 17β-estradiol (E₂) and raloxifene on bioactive IGF1.

DESIGN

In study 1, 12 GH-deficient (GHD) women were randomized to raloxifene 120 mg/day or E₂ 4 mg/day for 1 month. In study 2, 16 GHD women were randomized to 1 month GH treatment alone (0.5 mg/day) and in combination with raloxifene (60 mg/day) or E₂ (2 mg/day). We measured bioactive IGF1, immunoreactive IGF1 and IGF2, and IGFBP3 immunoreactivity and fragmentation.

RESULTS

Raloxifene and estrogen suppressed (P<0.05) total IGF1 equally in GHD and GH-replaced hypopituitary women. In GHD patients, neither raloxifene nor estrogen affected bioactive IGF1. GH significantly increased IGF1 bioactivity, an effect attenuated by co-treatment with raloxifene (Δ -23 ± 7%, P<0.01) and estrogen (Δ -26 ± 3%, P=0.06). Total IGF1 correlated (r(2)=0.54, P<0.001) with bioactive IGF1, which represented 3.1 ± 0.2% of the total IGF1, irrespective of the treatments. Total IGF2 was unchanged by raloxifene and estrogen treatment. IGFBP3 was significantly higher during raloxifene administration, whereas no differences in IGFBP3 fragmentation were observed.

CONCLUSION

Raloxifene effect on bioactive IGF1 is similar to that of estrogen despite higher IGFBP3 levels during raloxifene administration. We conclude that the observed different effects on LBM between raloxifene and estrogen treatments cannot be explained by differences in IGF1 bioactivity.

Serum levels of bioactive IGF1 and physiological markers of ageing in healthy adults

OBJECTIVE

Senescent changes in body composition and muscle strength are accompanied by reduced production of GH and IGF1, but the causal relationship remains elusive. We speculate that serum bioactive IGF1, measured by the IGF1 kinase receptor activation assay, is closer related to human physiological ageing than total IGF1 measured by immunoassay.

DESIGN

We conducted a cross-sectional study in 150 adult males and females, between 20 and 70 years. After an overnight fasting, serum levels of bioactive IGF1, total IGF1 and IGF-binding protein 1 (IGFBP1) and IGFBP3 were assessed. Furthermore, body composition and muscle strength was measured.

RESULTS

Total IGF1 levels were higher in females (P=0.048). Bioactive IGF1 were identical in males and females (P=0.31), decreasing with age. Total IGF1 tended to decrease more with age compared with bioactive IGF1 (-1.48 vs -0.89 percent/year, P=0.052). Total body fat (TBF) was lower and BMI was higher in males (P<0.001 and P=0.005), and both increased with age. Knee extension and elbow flexion force were higher in males (P=0.001 and P=0.001), but decreased with age in both genders.  Total but not bioactive IGF1 was positively correlated to TBF, knee extension and muscle function in males. In multiple linear regression, only age predicted total IGF1, whereas age and IGFBP1 predicted bioactive IGF1.

CONCLUSIONS

Bioactive IGF1 tends to decrease to a lesser extent than total IGF1 with age and was not correlated with measures of body composition or muscle strength. Therefore, levels of circulating bioactive IGF1 does not appear to be a better biomarker of physiological ageing than total IGF1.

Growth hormone in the aging male

Secretion of growth hormone (GH) and IGF-1 levels decline during advancing years-of-life. These changes (somatopause) are associated with loss of vitality, muscle mass, physical function, together with the occurrence of frailty, central adiposity, cardiovascular complications, and deterioration of mental function. For GH treatment to be considered for anti-aging, improved longevity, organ-specific function, or quality of life should be demonstrable. A limited number of controlled studies suggest that GH supplementation in older men increases lean mass by ∼2 kg with similar reductions in fat mass. There is little evidence that GH treatment improves muscle strength and performance (e.g. walking speed or ability to climb stairs) or quality of life. The GHRH agonist (tesamorelin) restores normal GH pulsatility and amplitude, selectively reduces visceral fat, intima media thickness and triglycerides, and improves cognitive function in older persons. This report critically reviews the potential for GH augmentation during aging with emphasis on men since women appear more resistant to treatment.

Insulin-like growth factor-I (IGF-I) and clinical nutrition

IGF-I (insulin-like growth factor-I) is a peptide hormone, produced predominantly by the liver in response to pituitary GH (growth hormone), which is involved in a wide variety of physiological processes. It acts in an endocrine, paracrine and autocrine manner to promote growth. The production of IGF-I signals the availability of nutrients needed for its anabolic actions. Recently, there has been growing interest in its role in health and disease. IGF-I has long been known to be regulated by nutrition and dysregulated in states of under- and over-nutrition, its serum concentrations falling in malnutrition and responding promptly to refeeding. This has led to interest in its utility as a nutritional biomarker. A considerable evidence base supports utility for measurement of IGF-I in nutritional contexts. Its concentration may be valuable in providing information on nutritional status, prognosis and in monitoring nutritional support. However, it is insufficiently specific for use as a screening test for under nutrition as its serum concentration is influenced by many factors other than nutritional status, notably the APR (acute-phase response) and endocrine conditions. Concentrations should be interpreted along with clinical findings and the results of other investigations such as CRP (C-reactive protein). More recently, there has been interest in free IGF-I which holds promise as a nutritional marker. The present review covers nutritional regulation of IGF-I and its dysregulation in disease, then goes on to review recent studies supporting its utility as a nutritional marker in clinical contexts. Although not currently recommended by clinical guidelines, it is likely that, in time, measurement of IGF-I will become a routine part of nutritional assessment in a number of these contexts.

Associations of insulin-like growth factor-I and its binding proteins and testosterone with frailty in older men

OBJECTIVE

Ageing is associated with frailty and decreased anabolic hormones, insulin-like growth factor-I (IGF-I) and testosterone. We hypothesized that components of the IGF-I system, in conjunction with testosterone, modulate frailty risk in the elderly. We examined associations between IGF-I, its binding proteins IGFBP1 and IGFBP3 and testosterone with frailty in men.

DESIGN

Observational study of 3 447 community-dwelling men aged 70-89 years assessed in 2001-04, with 1 654 reassessed in 2008-09.

METHODS

Baseline total IGF-I, IGFBP1, IGFBP3 and testosterone were assayed. Frailty was assessed using the FRAIL scale, comprising 5 domains: fatigue; difficulty climbing stairs; difficulty walking >100 m; >5 illnesses; weight loss >5%. Men with ≥ 3 domains were considered frail.

RESULTS

At baseline, 527 men (15·3%) were frail. Frail men had lower IGFBP3 (3 630 ng/ml vs not frail: 3 800 ng/ml, P < 0·001) and comparable IGFBP1 (23·5 vs 21·5 ng/ml, P = 0·09). In multivariate analyses, higher IGFBP1 was associated with increased prevalence of frailty (highest vs lowest quartile Q4:Q1, adjusted odds ratio [OR] = 1·39, 95% CI = 1·03-1·88). New-onset frailty arose in 260 (17·5%) of 1 484 men. Lower baseline IGF-I predicted new-onset frailty (Q1:Q4 OR = 1·48, 95% CI = 1·00-2·20) as did higher IGFBP1 (Q4:Q1 OR = 1·59, 95% CI = 1·01-2·50). Men with both IGF-I and free testosterone in Q1 had greater odds of prevalent frailty (OR = 2·13, 95% CI = 1·54-2·95).

CONCLUSIONS

Older men with higher IGFBP1 level, or both lower IGF-I and testosterone, are more likely to be frail, while those with lower IGF-I and higher IGFBP1 are more likely to become frail. Components of the IGF-I system may be biomarkers or independent predictors of frailty.

Low circulating IGF-I bioactivity is associated with human longevity: findings in centenarians' offspring

Centenarians’ offspring represent a suitable model to study age-dependent variables (e.g. IGF-I) potentially involved in the modulation of the lifespan. The aim of the present study was to investigate the role of the IGF-I in human longevity. We evaluated circulating IGF-I bioactivity measured by an innovative IGF-I Kinase Receptor Activation (KIRA) Assay, total IGF-I, IGFBP-3, total IGF-II, insulin, glucose, HOMA2-B% and HOMA2-S% in 192 centenarians’ offspring and 80 offspring-controls of which both parents died relatively young. Both groups were well-matched for age, gender and BMI with the centenarians’ offspring. IGF-I bioactivity (p<0.01), total IGF-I (p<0.01) and the IGF-I/IGFBP-3 molar ratio (p<0.001) were significantly lower in centenarians’ offspring compared to offspring matched-controls. Serum insulin, glucose, HOMA2-B% and HOMA2-S% values were similar between both groups. In centenarians’ offspring IGF-I bioactivity was inversely associated to insulin sensitivity. In conclusion: 1) centenarians’ offspring had relatively lower circulating IGF-I bioactivity compared to offspring matched-controls; 2) IGF-I bioactivity in centenarians’ offspring was inversely related to insulin sensitivity. These data support a role of the IGF-I/insulin system in the modulation of human aging process.

Serum IGF1, metabolic syndrome, and incident cardiovascular disease in older people: a population-based study

OBJECTIVE

High as well as low levels of IGF1 have been associated with cardiovascular diseases (CVD). The relationship of IGF1 with (components of) the metabolic syndrome could help to clarify this controversy. The aims of this study were: i) to investigate the association of IGF1 concentration with prevalent (components of) the metabolic syndrome; and ii) to examine the role of (components of) the metabolic syndrome in the relationship between IGF1 and incident CVD during 11 years of follow-up.

METHODS

Data were used from the Longitudinal Aging Study Amsterdam, a cohort study in a representative sample of the Dutch older population (≥65 years). Data were available in 1258 subjects. Metabolic syndrome was determined using the definition of the US National Cholesterol Education Program Adult Treatment Panel III. CVD were ascertained by self-reports and mortality data.

RESULTS

Levels of IGF1 in the fourth quintile were associated with prevalent metabolic syndrome compared with the lowest quintile (odds ratio: 1.59, 95% confidence interval (CI) 1.09-2.33). The middle up to the highest quintile of IGF1 was positively associated with high triglycerides in women. Metabolic syndrome was not a mediator in the U-shaped relationship of IGF1 with CVD. Both subjects without the metabolic syndrome and low IGF1 levels (hazard ratio (HR) 1.75, 95% CI 1.12-2.71) and subjects with the metabolic syndrome and high IGF1 levels (HR 2.28, 95% CI 1.21-4.28) demonstrated increased risks of CVD.

CONCLUSIONS

In older people, high-normal IGF1 levels are associated with prevalent metabolic syndrome and high triglycerides. Furthermore, this study suggests the presence of different pathomechanisms for both low and high IGF1 levels and incident CVD.

Circulating IgGs may modulate IGF-I receptor stimulating activity in a subset of patients with Graves' ophthalmopathy

CONTEXT

There is a close association between levels of TSH binding inhibitory immunoglobulins (TBIIs) and Graves' ophthalmopathy (GO). In addition to the TSH receptor, the IGF-I receptor (IGF-IR) has been proposed to be a second autoantigen that plays a role in the pathogenesis of GO.

OBJECTIVE

The aim was to study relationships between TBII and serum IGF-IR stimulating activity in relationship to age in patients with GO.

METHODS

We performed a prospective study of 70 patients with GO (26 euthyroid, 39 subclinical hyperthyroid, 5 hyperthyroid; 8 males, 62 females; age, 47.9 ± 1.0 y). Patients were graded according to clinical activity score. IGF-IR stimulating activity was determined by IGF-IR kinase receptor activation assay; TBIIs were measured by immunoassay (Trak). Protein G magnetic beads were used to deplete serum of IgGs.

RESULTS

TBII and clinical activity score were positively related (r = 0.30; P = .01). In subjects with TBII above mean +1 SD, IGF-IR stimulating activity was positively related to age (r = 0.43; P = .05), whereas such a relationship was absent for subjects with TBII below the mean +1 SD (r = -0.04; P = .81). Depletion of IgGs from sera of patients with both TBII above the mean +1 SD and IGF-IR stimulating activity above the mean -1 SD decreased IGF-IR stimulating activity, whereas depletion in patients with TBII above the mean +1 SD but IGF-IR stimulating activity below the mean -1 SD did not change IGF-IR stimulating activity.

CONCLUSIONS

In subjects with TBII above the mean +1 SD, we observed an increase of IGF-IR stimulating activity with age. In a subgroup of these patients, depletion of IgGs significantly decreased IGF-IR stimulating activity, suggesting that, in a subset of patients with GO, IgGs may have IGF-IR stimulating activities.

Both low and high serum IGF-I levels associate with cancer mortality in older men

BACKGROUND

Although recent population-based studies suggest a U-shaped relationship between serum IGF-I concentration and all-cause mortality, the distribution of death causes underlying this association remains unclear. We hypothesized that high IGF-I levels associate with increased cancer mortality, whereas low IGF-I levels associate with increased cardiovascular disease (CVD) mortality.

METHODS

Serum IGF-I levels were measured in 2901 elderly men (mean age 75.4, range 69-81 yr) included in the prospective population-based Osteoporotic Fractures in Men Study (Sweden) study. Mortality data were obtained from central registers with no loss of follow-up. The statistical analyses included Cox proportional hazards regressions with or without a spline approach.

RESULTS

During the follow-up (mean 6.0 yr), 586 of the participants died (cancer deaths, n = 211; CVD deaths, n = 214). As expected, our data revealed a U-shaped association between serum IGF-I levels and all-cause mortality. Low as well as high serum IGF-I (quintile 1 or 5 vs. quintiles 2-4) associated with increased cancer mortality [hazard ratio (HR) = 1.86, 95% confidence interval (CI) = 1.34-2.58; and HR = 1.90, 95% CI = 1.37-2.65, respectively]. Only low serum IGF-I associated with increased CVD mortality (quintile 1 vs. quintiles 2-4, HR = 1.48, 95% CI = 1.08-2.04). These associations remained after adjustment for multiple covariates and exclusion of men who died during the first 2 yr of follow-up.

CONCLUSIONS

Our findings demonstrate that both low and high serum IGF-I levels are risk markers for increased cancer mortality in older men. Moreover, low IGF-I levels associate with increased CVD mortality.

Quantification of the GH/IGF-axis components: lessons from human studies

Originally, the circulating bioactivity of IGF-I was estimated by bioassays measuring the ability of serum to stimulate uptake of labeled sulfate or thymidine in cultures of costal cartilage or by the ability of serum to stimulate the uptake of glucose in fat tissue cultures. However, because of their laborious and unspecific nature, the original bioassays were quickly abandoned with the development of the first RIA for IGF-I in 1977. Consequently, for the past three decades the endogenous IGF-I bioactivity has been almost exclusively estimated by the use of immunoassays. Beyond any doubt, the immunoassays have provided an extensive insight into IGF-I physiology and pathophysiology. However, immunoassays ignore the presence of the IGFBPs, which are important regulators of IGF-I action in vivo. In addition, immunoassays do not consider the presence of IGF-II, which also interacts with the IGF-I receptor (IGF-IR). This aroused our interest to reintroduce the bioassay; therefore, we established a cell-based kinase receptor activation (KIRA) assay based on cells transfected with the human IGF-IR. The output signal of the KIRA assay is IGF-IR phosphorylation, and, as such, it is highly specific. Further, because detection of phosphorylated IGF-IRs is based on modern immunoassay techniques, the overall performance of the assay is close to that of a traditional IGF-I immunoassay. The first part of this review comprises a short description of the bioassay, and a more in-depth presentation of the data that have been obtained so far. It will be demonstrated that the bioassay is indeed able to yield novel information on the IGF system, most likely because it is able to integrate the different components of the IGF system into one signal: IGF-IR activation. As IGF-I, circulating GH is bound to larger proteins, the far most important GH-binding protein (GHBP) is identical to the extracellular domain of the GH receptor (GHR). Because of its origin, GHBP binds GH with the same affinity as GHR and, consequently, GHBP may affect GH bioactivity as well as pharmacokinetics. To improve our knowledge on the complex interaction between GH and GHBP in vivo, we found it of interest to develop a method for determination of free GH. To this end, we developed an ultrafiltration assay that enabled isolation of free GH in undiluted serum during approached in vivo-like conditions. The last part of this review presents our current data on free GH and its interaction with GHBP.

Hormone replacement therapy and physical function in healthy older men. Time to talk hormones?

Improving physical function and mobility in a continuously expanding elderly population emerges as a high priority of medicine today. Muscle mass, strength/power, and maximal exercise capacity are major determinants of physical function, and all decline with aging. This contributes to the incidence of frailty and disability observed in older men. Furthermore, it facilitates the accumulation of body fat and development of insulin resistance. Muscle adaptation to exercise is strongly influenced by anabolic endocrine hormones and local load-sensitive autocrine/paracrine growth factors. GH, IGF-I, and testosterone (T) are directly involved in muscle adaptation to exercise because they promote muscle protein synthesis, whereas T and locally expressed IGF-I have been reported to activate muscle stem cells. Although exercise programs improve physical function, in the long-term most older men fail to comply. The GH/IGF-I axis and T levels decline markedly with aging, whereas accumulating evidence supports their indispensable role in maintaining physical function integrity. Several studies have reported that the administration of T improves lean body mass and maximal voluntary strength in healthy older men. On the other hand, most studies have shown that administration of GH alone failed to improve muscle strength despite amelioration of the detrimental somatic changes of aging. Both GH and T are anabolic agents that promote muscle protein synthesis and hypertrophy but work through separate mechanisms, and the combined administration of GH and T, albeit in only a few studies, has resulted in greater efficacy than either hormone alone. Although it is clear that this combined approach is effective, this review concludes that further studies are needed to assess the long-term efficacy and safety of combined hormone replacement therapy in older men before the medical rationale of prescribing hormone replacement therapy for combating the sarcopenia of aging can be established.

Decline in circulating insulin-like growth factors and mortality in older adults: cardiovascular health study all-stars study

BACKGROUND

The association between changes in IGF-I and IGF binding protein (IGFBP) levels and mortality in older adults is unknown.

STUDY DESIGN

Participants were 997 persons 77 to 100 yr old enrolled in the Cardiovascular Health Study All Stars Study. Plasma levels of IGF-I, IGFBP-1, and IGFBP-3 were assessed at two study examinations (1996-1997 and 2005-2006). Mortality was assessed between 2006 and 2010.

RESULTS

Cumulative mortality (CM) was similar among individuals who had at least 10% decreases over time in IGF-I levels (CM = 29.6%), individuals who had at least 10% increases over time in IGF-I levels (CM = 24.7%), and individuals who had IGF-I levels remaining within ±10% over time (CM = 23.5%). Adjusted for age, sex, race, diabetes, body mass index, creatinine, albumin, and C-reactive protein, decreasing IGF-I level had no significant association with overall cancer mortality or noncancer mortality. Levels of IGFBP-1 increased markedly over time by 38% (median). Individuals with the largest increases in IGFBP-1 level over time had significantly increased risk of mortality. The adjusted hazard ratio per sd of IGFBP-1 change was 1.40 for overall cancer mortality (95% confidence interval = 1.10, 1.77; P = 0.01) and 1.14 for noncancer mortality (95% confidence interval = 1.02, 1.27; P = 0.02). Changes in IGFBP-3 levels were not significantly associated with mortality.

CONCLUSION

Among older adults, decreasing IGF-I level over time does not predict subsequent all-cause mortality, whereas increasing IGFBP-1 predicts increased risk of mortality.

Aging, atherosclerosis, and IGF-1

Insulin-like growth factor 1 (IGF-1) is an endocrine and autocrine/paracrine growth factor that circulates at high levels in the plasma and is expressed in most cell types. IGF-1 has major effects on development, cell growth and differentiation, and tissue repair. Recent evidence indicates that IGF-1 reduces atherosclerosis burden and improves features of atherosclerotic plaque stability in animal models. Potential mechanisms for this atheroprotective effect include IGF-1-induced reduction in oxidative stress, cell apoptosis, proinflammatory signaling, and endothelial dysfunction. Aging is associated with increased vascular oxidative stress and vascular disease, suggesting that IGF-1 may exert salutary effects on vascular aging processes. In this review, we will provide a comprehensive update on IGF-1's ability to modulate vascular oxidative stress and to limit atherogenesis and the vascular complications of aging.

Targeting the insulin-like growth factor receptor pathway in lung cancer: problems and pitfalls

The insulin-like growth factor (IGF) pathway is a complex pathway involving interactions between membrane-bound receptors, ligands, binding proteins, downstream effectors, and other receptor tyrosine kinase signaling cascades. The IGF pathway has been identified as a potential therapeutic target in non-small cell lung cancer (NSCLC) based on the following provocative factors. Preclinical observations in NSCLC have shown that this pathway is involved in tumor cell proliferation, survival, and invasiveness. In addition, IGF-1R protein expression is found in a significant number of non-small cell tumor specimens. Initial therapeutic efforts involved the development of monoclonal antibodies and tyrosine kinase inhibitors that target IGF-1R, a transmembrane receptor tyrosine kinase. Enthusiasm for targeting this pathway increased when a randomized phase II study showed that combining an anti-IGF-1R monoclonal antibody (figitumumab) with a platinum doublet resulted in a higher response rate and trends for superior progression-free survival and overall survival. Subsequently, a phase III study failed to confirm the promising results observed in the phase II trial. Currently, investigators are studying different monoclonal antibodies and tyrosine kinases targeting IGF-1R. In unselected patients, results presented thus far do not suggest efficacy of this agent. However, retrospective subgroup analyses suggest that circulating IGF-1 levels might identify patients who could benefit from treatment with an IGF-1R monoclonal antibody and may warrant further exploratory studies for predictive molecular markers. The purpose of this paper is to briefly discuss the IGF pathway and its relationship with other signaling pathways in lung cancer and to review the ongoing IGF clinical trials and efforts to identify predictive molecular markers.

Associations of IGF1 and its binding proteins with abdominal aortic aneurysm and aortic diameter in older men

OBJECTIVE

Abdominal aortic aneurysm (AAA) is most prevalent in older men. GH secretion declines with age resulting in reduced IGF1 levels. IGF1 and its binding proteins (IGFBPs) are expressed in vasculature, and lower IGF1 levels have been associated with cardiovascular risk factors and disease. However, the relationship of the IGF1 system with aortic dilation and AAA is unclear. We tested the hypothesis that circulating IGF1 and IGFBPs are associated with AAA and aortic diameter in older men.

DESIGN

A cross-sectional analysis involving 3981 community-dwelling men aged 70-89 years was performed.

METHODS

Abdominal aortic diameter was measured by ultrasound. Plasma total IGF1, IGFBP1 and IGFBP3 were measured by immunoassays.

RESULTS

After adjustment for age, body mass index, waist:hip ratio, smoking, hypertension, dyslipidemia, diabetes, coronary heart disease and serum creatinine, a higher IGF1 level was associated with AAA (odds ratio (OR)/1 s.d. increase 1.18, 95% confidence interval (CI) 1.05-1.33, P=0.006), as was the ratio of IGF1/IGFBP3 (OR=1.22, 95% CI 1.10-1.35, P<0.001). Highest IGF1 concentrations compared with lowest quintile were significantly associated with AAA (quintile (Q) 5 vs Q1: OR=1.80, 95% CI 1.20-2.70, P=0.004) as were IGF1/IGFBP3 ratios (Q5 vs Q1: OR=2.52, 95% CI 1.59-4.02, P<0.001). IGF1 and IGFBP1 were independently associated with aortic diameter (β=0.200, 95% CI 0.043-0.357, P=0.012 and β=0.274, 95% CI 0.098-0.449, P=0.002 respectively).

CONCLUSIONS

In older men, higher IGF1 and an increased ratio of IGF1/IGFBP3 are associated with AAA, while IGFBP1 is independently associated with increased aortic diameter. Components of the IGF1 system may contribute to, or be a marker for, aortic dilation in ageing men.

Effects of insulin-like growth factor 1 in preventing acute coronary syndromes: the PRIME study

OBJECTIVE

Insulin-like growth factor-1 (IGF-1) has been associated with cardiovascular risk factors and atherosclerosis. The aim of the present study was to evaluate the prognostic value of IGF-1 concentrations with respect to occurrence of well-defined coronary syndromes.

METHODS

The PRIME study is a prospective cohort having included 10,600 subjects from Northern Ireland and France. Detailed information on cardiovascular risk factors, socioeconomic and behavioural variables were collected and a cardiologic examination was performed. At 5-year follow-up, 317 incident cases of coronary events were recorded according to strict protocols. They were matched to 634 age- and centre-paired controls from the same cohort, free of coronary disease. Baseline IGF-1 concentrations were measured, together with variables of lipid and glucose metabolism and markers of vascular and systemic inflammation.

RESULTS

Baseline IGF-1 concentration was lower in subjects developing an acute coronary syndrome than in unaffected controls. IGF-1 levels correlated negatively with age, waist circumference, tobacco consumption and markers of inflammation. Subjects in the highest quartile of IGF-1 distribution had a 55% reduction in the relative risk of developing myocardial infarction and a 45% decrease for all-combined acute coronary syndromes. A similar trend, although non-significant, was noted for angina pectoris. Multiple adjustments on classical risk factors and inflammation markers did not affect IGF-1 results. Elevated levels of both IGF-1 and apo A-I conferred a significantly greater risk reduction than either one alone. However, interaction between the two markers was not significant.

CONCLUSION

Like HDL markers, high levels of IGF-1 confer protection against coronary artery disease.

Aging phenotype and its relationship with IGF-I gene promoter polymorphisms in elderly people living in Catalonia

OBJECTIVES

Genetic variations in the Insulin/IGF-I genes pathway have been related to longevity, dementia, metabolic diseases and cancer. The purpose of the present study was to investigate the 192 bp allele of IGF-I gene promoter and its relationship with metabolic syndrome (MS) components, mental and nutritional state, muscle strength and functional capacity in an aged Spanish population.

DESIGN

Population-based study (Mataró Ageing Study), including 292 subjects (144 men and 148 women, mean age 77.0±5.4). Anthropometric variables, lipid profile, glucose and blood pressure (BP) were measured; mental state (MMSE), nutritional state (MNA) and Barthel scale were performed, and were correlated to the presence of the 192 bp allele of IGF-1 gene promoter polymorphisms.

RESULTS

MS (ATP-III criteria) was found in 49.5% (41.4% in men and 57.6% in women). The 192 bp allele of IGF-I gene promoter was distributed as: 41.9% homozygous, 44.3% heterozygous and 13.9% were non-carriers of this allele. A lower prevalence of metabolic syndrome was observed in homozygous (41.9% vs 54.9% in heterozygous+non-carriers, p=0.031). Mental state (MMSE), nutritional state (MNA) and Barthel scale were better in homozygous individuals compared to heterozygous and non-carriers (p=0.015, p=0.026 and 0.047, respectively). In men, MNA was better in homozygous with no differences in MMSE and Barthel scales. In homozygous women, BP was lower (p=0.009) and Barthel scale was better (p=0.05) with no differences in MMSE and MNA.

CONCLUSION

Homozygosity for the 192 bp allele of the IGF-I gene polymorphism suggests a healthier aging condition, with less prevalence of cardiometabolic disturbances, and better mental, nutritional and functional state.

Circulating IGF-I is associated with fitness and health outcomes in a population of 846 young healthy men

CONTEXT

Insulin-like growth factor-I (IGF-I) is thought to mediate many of the beneficial outcomes of physical activity. While IGF-I has previously been shown to be positively related with aerobic fitness, few studies have examined IGF-I relationships with other fitness and health parameters. The robustness of IGF-I as a biomarker of fitness and health has yet to be fully determined.

OBJECTIVE

To determine the association of circulating IGF-I with fitness, body composition and health parameters in young, healthy men.

DESIGN AND SUBJECTS

A cross-section of 846 young, healthy Finnish men (25±5 yr, 180±6 cm, 81±13 kg). Subjects were divided into quintiles of IGF-I concentrations (Q1: lowest; Q5: highest) for statistical evaluation.

MAIN OUTCOME MEASURES

Circulating IGF-I, physical fitness: peak aerobic capacity (VO(2) peak), maximal strength of leg and arm extensors, muscle endurance (sit-ups, push-ups, and repetitive squats) and health outcome parameters (total blood cholesterol, triglyceride, high-density lipoproteins (HDL), low-density lipoproteins (LDL), systolic and diastolic blood pressure, waist circumference, % body fat, and drinking, smoking and physical activity behavior).

RESULTS

Higher IGF-I was associated with higher VO(2) peak (Q1: 39±7 vs. Q5: 44±9 mL/kg/min), sit-ups (Q1: 35±10 vs. Q5: 41±10 repetitions), push-ups (Q1: 27±13 vs. Q5: 31±14 repetitions), repetitive squats (Q2: 42±10 vs. Q5: 45±8 repetitions), HDL (Q1: 1.5±0.4 vs. Q5: 1.53±0.3 mmol/L), and lower age (Q1: 28±6 vs. Q5: 23±2 yr), %BF (Q1: 20±7 vs. Q5: 16±6%BF), waist circumference (Q1: 89±11 vs. Q5: 84±9 cm), BMI (Q1: 25.6±4 vs. Q5: 24.3m(2)/kg), diastolic blood pressure (Q1: 78.5±9 vs. Q5: 75.4±8 mm Hg), cholesterol (Q1: 4.72±0.9 vs. Q5: 4.44±0.8 mmol/L) and smoking (Q1: 44% vs. Q5: 32%). No association was observed for IGF-I and maximal leg extension (Q1: 2982±927 vs. Q5: 2932±853 N) and bench press (Q1: 895±197 vs. Q5: 919±203 N) strength, fat-free mass (Q1: 64.6±8 vs. Q5: 66.6±7 KG), LDL (2.54±0.7 vs. Q5: 2.35±0.6 mmol/L), or triglycerides (Q1: 1.05±0.6 vs. Q5: 0.99±0.5 mmol/L).

CONCLUSION

IGF-I is positively associated with aerobic fitness and muscular endurance, but not with measures of muscle strength or FFM. IGF-I is positively associated with improved health and fitness outcomes in young, healthy men.

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.

Pre-treatment levels of circulating free IGF-1 identify NSCLC patients who derive clinical benefit from figitumumab

BACKGROUND

Phase III trials of the anti-insulin-like growth factor type 1 receptor (IGF-IR) antibody figitumumab (F) in unselected non-small-cell lung cancer (NSCLC) patients were recently discontinued owing to futility. Here, we investigated a role of free IGF-1 (fIGF-1) as a potential predictive biomarker of clinical benefit from F treatment.

MATERIALS AND METHOD

Pre-treatment circulating levels of fIGF-1 were tested in 110 advanced NSCLC patients enrolled in a phase II study of paclitaxel and carboplatin given alone (PC) or in combination with F at doses of 10 or 20 mg kg(-1) (PCF10, PCF20).

RESULTS

Cox proportional hazards model interactions were between 2.5 and 3.5 for fIGF-1 criteria in the 0.5-0.9 ng ml(-1) range. Patients above each criterion had a substantial improvement in progression-free survival on PCF20 related to PC alone. Free IGF-1 correlated inversely with IGF binding protein 1 (IGFBP-1, ρ=-0.295, P=0.005), and the pre-treatment ratio of insulin to IGFBP-1 was also predictive of F clinical benefit. In addition, fIGF-1 levels correlated with tumour vimentin expression (ρ=0.594, P=0.021) and inversely with E-cadherin (ρ=-0.389, P=0.152), suggesting a role for fIGF-1 in tumour de-differentiation.

CONCLUSION

Free IGF-1 may contribute to the identification of a subset of NSCLC patients who benefit from F therapy.