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1.  Does Reduced IGF-1R Signaling in Igf1r+/− Mice Alter Aging? 
PLoS ONE  2011;6(11):e26891.
Mutations in insulin/IGF-1 signaling pathway have been shown to lead to increased longevity in various invertebrate models. Therefore, the effect of the haplo- insufficiency of the IGF-1 receptor (Igf1r+/−) on longevity/aging was evaluated in C57Bl/6 mice using rigorous criteria where lifespan and end-of-life pathology were measured under optimal husbandry conditions using large sample sizes. Igf1r+/− mice exhibited reductions in IGF-1 receptor levels and the activation of Akt by IGF-1, with no compensatory increases in serum IGF-1 or tissue IGF-1 mRNA levels, indicating that the Igf1r+/− mice show reduced IGF-1 signaling. Aged male, but not female Igf1r+/− mice were glucose intolerant, and both genders developed insulin resistance as they aged. Female, but not male Igf1r+/− mice survived longer than wild type mice after lethal paraquat and diquat exposure, and female Igf1r+/− mice also exhibited less diquat-induced liver damage. However, no significant difference between the lifespans of the male Igf1r+/− and wild type mice was observed; and the mean lifespan of the Igf1r+/− females was increased only slightly (less than 5%) compared to wild type mice. A comprehensive pathological analysis showed no significant difference in end-of-life pathological lesions between the Igf1r+/− and wild type mice. These data show that the Igf1r+/− mouse is not a model of increased longevity and delayed aging as predicted by invertebrate models with mutations in the insulin/IGF-1 signaling pathway.
PMCID: PMC3223158  PMID: 22132081
2.  Liver-Derived IGF-I Regulates Mean Life Span in Mice 
PLoS ONE  2011;6(7):e22640.
Transgenic mice with low levels of global insulin-like growth factor-I (IGF-I) throughout their life span, including pre- and postnatal development, have increased longevity. This study investigated whether specific deficiency of liver-derived, endocrine IGF-I is of importance for life span.
Methods and Findings
Serum IGF-I was reduced by approximately 80% in mice with adult, liver-specific IGF-I inactivation (LI-IGF-I-/- mice), and body weight decreased due to reduced body fat. The mean life span of LI-IGF-I-/- mice (n = 84) increased 10% vs. control mice (n = 137) (Cox's test, p<0.01), mainly due to increased life span (16%) of female mice [LI-IGF-I-/- mice (n = 31): 26.7±1.1 vs. control (n = 67): 23.0±0.7 months, p<0.001]. Male LI-IGF-I-/- mice showed only a tendency for increased longevity (p = 0.10). Energy expenditure, measured as oxygen consumption during and after submaximal exercise, was increased in the LI-IGF-I-/- mice. Moreover, microarray and RT-PCR analyses showed consistent regulation of three genes (heat shock protein 1A and 1B and connective tissue growth factor) in several body organs in the LI-IGF-I-/- mice.
Adult inactivation of liver-derived, endocrine IGF-I resulted in moderately increased mean life span. Body weight and body fat decreased in LI-IGF-I-/- mice, possibly due to increased energy expenditure during exercise. Genes earlier reported to modulate stress response and collagen aging showed consistent regulation, providing mechanisms that could underlie the increased mean life span in the LI-IGF-I-/- mice.
PMCID: PMC3143189  PMID: 21799924
3.  Long-Term Health Effects of Neutering Dogs: Comparison of Labrador Retrievers with Golden Retrievers 
PLoS ONE  2014;9(7):e102241.
Our recent study on the effects of neutering (including spaying) in Golden Retrievers in markedly increasing the incidence of two joint disorders and three cancers prompted this study and a comparison of Golden and Labrador Retrievers. Veterinary hospital records were examined over a 13-year period for the effects of neutering during specified age ranges: before 6 mo., and during 6–11 mo., year 1 or years 2 through 8. The joint disorders examined were hip dysplasia, cranial cruciate ligament tear and elbow dysplasia. The cancers examined were lymphosarcoma, hemangiosarcoma, mast cell tumor, and mammary cancer. The results for the Golden Retriever were similar to the previous study, but there were notable differences between breeds. In Labrador Retrievers, where about 5 percent of gonadally intact males and females had one or more joint disorders, neutering at <6 mo. doubled the incidence of one or more joint disorders in both sexes. In male and female Golden Retrievers, with the same 5 percent rate of joint disorders in intact dogs, neutering at <6 mo. increased the incidence of a joint disorder to 4–5 times that of intact dogs. The incidence of one or more cancers in female Labrador Retrievers increased slightly above the 3 percent level of intact females with neutering. In contrast, in female Golden Retrievers, with the same 3 percent rate of one or more cancers in intact females, neutering at all periods through 8 years of age increased the rate of at least one of the cancers by 3–4 times. In male Golden and Labrador Retrievers neutering had relatively minor effects in increasing the occurrence of cancers. Comparisons of cancers in the two breeds suggest that the occurrence of cancers in female Golden Retrievers is a reflection of particular vulnerability to gonadal hormone removal.
PMCID: PMC4096726  PMID: 25020045
4.  Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers 
PLoS ONE  2013;8(2):e55937.
In contrast to European countries, the overwhelming majority of dogs in the U.S. are neutered (including spaying), usually done before one year of age. Given the importance of gonadal hormones in growth and development, this cultural contrast invites an analysis of the multiple organ systems that may be adversely affected by neutering. Using a single breed-specific dataset, the objective was to examine the variables of gender and age at the time of neutering versus leaving dogs gonadally intact, on all diseases occurring with sufficient frequency for statistical analyses. Given its popularity and vulnerability to various cancers and joint disorders, the Golden Retriever was chosen for this study. Veterinary hospital records of 759 client-owned, intact and neutered female and male dogs, 1–8 years old, were examined for diagnoses of hip dysplasia (HD), cranial cruciate ligament tear (CCL), lymphosarcoma (LSA), hemangiosarcoma (HSA), and mast cell tumor (MCT). Patients were classified as intact, or neutered early (<12 mo) or late (≥12 mo). Statistical analyses involved survival analyses and incidence rate comparisons. Outcomes at the 5 percent level of significance are reported. Of early-neutered males, 10 percent were diagnosed with HD, double the occurrence in intact males. There were no cases of CCL diagnosed in intact males or females, but in early-neutered males and females the occurrences were 5 percent and 8 percent, respectively. Almost 10 percent of early-neutered males were diagnosed with LSA, 3 times more than intact males. The percentage of HSA cases in late-neutered females (about 8 percent) was 4 times more than intact and early-neutered females. There were no cases of MCT in intact females, but the occurrence was nearly 6 percent in late-neutered females. The results have health implications for Golden Retriever companion and service dogs, and for oncologists using dogs as models of cancers that occur in humans.
PMCID: PMC3572183  PMID: 23418479
5.  Longevity effect of IGF-1R+/− mutation depends on genetic background-specific receptor activation 
Aging Cell  2013;13(1):19-28.
Growth hormone (GH) and insulin-like growth factor (IGF) signaling regulates lifespan in mice. The modulating effects of genetic background gained much attention because it was shown that life-prolonging effects in Snell dwarf and GH receptor knockout vary between mouse strains. We previously reported that heterozygous IGF-1R inactivation (IGF-1R+/−) extends lifespan in female mice on 129/SvPas background, but it remained unclear whether this mutation produces a similar effect in other genetic backgrounds and which molecules possibly modify this effect. Here, we measured the life-prolonging effect of IGF-1R+/− mutation in C57BL/6J background and investigated the role of insulin/IGF signaling molecules in strain-dependent differences. We found significant lifespan extension in female IGF-1R+/− mutants on C57BL/6J background, but the effect was smaller than in 129/SvPas, suggesting strain-specific penetrance of longevity phenotypes. Comparing GH/IGF pathways between wild-type 129/SvPas and C57BL/6J mice, we found that circulating IGF-I and activation of IGF-1R, IRS-1, and IRS-2 were markedly elevated in 129/SvPas, while activation of IGF pathways was constitutively low in spontaneously long-lived C57BL/6J mice. Importantly, we demonstrated that loss of one IGF-1R allele diminished the level of activated IGF-1R and IRS more profoundly and triggered stronger endocrine feedback in 129/SvPas background than in C57BL/6J. We also revealed that acute oxidative stress entails robust IGF-1R pathway activation, which could account for the fact that IGF-1R+/− stress resistance phenotypes are fully penetrant in both backgrounds. Together, these results provide a possible explanation why IGF-1R+/− was less efficient in extending lifespan in C57BL/6J compared with 129/SvPas.
PMCID: PMC4326867  PMID: 23898955
Genetic background; gene knockout; IGF-I; IRS; lifespan; stress resistance
6.  IGF-1 Gene Expression in Rat Colonic Mucosa After Different Exercise Volumes 
The evidence is increasing for a close link between the insulin/insulin-like growth factor (IGF) system and colon cancer prevention by physical exercise. To reveal exercise-induced alterations in colon mucosa, gene expression of IGF-1 and related genes and serum IGF-1 were investigated. Twenty male Wistar rats performed a 12 week voluntary exercise program. Nine rats served as the control group. Gene expression of IGF-1, IGF-1 receptor (IGF-1R) and IGF-binding protein 3 (IGF-BP3) were quantified by real-time RT-PCR. Circulating IGF-1 was analyzed exercise volume-dependent. Based on 3 distinguished groups with low (L-EX, <2629 m·night-1), medium (M-EX, 3003-7458 m·night-1) and high exercise volume (H-EX, >8314 m·night-1), we observed lower serum IGF-1 levels (P < 0.05) in all exercise groups as compared to the control group and IGF-1 levels declined proportional to the increase in exercise volume. A significant (p < 0.05) positive correlation was found between IGF-1 concentration and body mass (r = 0.50) and a significant negative correlation exists between body mass and exercise volume (r = -0.50). Significant differences in colonic mRNA levels of IGF-1, IGF-1R and IGF-BP3 could not be observed. Based on our data we propose that the exercise as well as the body mass reduction leads to a decrease in circulating IGF-1 and this might represent a prime link to colon cancer prevention.
Key pointsThere were significantly lower serum IGF-1 levels in all exercise groups as compared to the control group.GF-1 levels declined proportional to the increase in exercise volume.A significant positive correlation was found between IGF-1 concentration and body mass and a significant negative correlation was found between body mass and exercise volume.Significant differences in colonic mRNA levels of IGF-1, IGF-1R and IGF-BP3 could not be observed.
PMCID: PMC3794482  PMID: 24149475
Cancer prevention; IGF-1R; IGF-BP3; real-time RT PCR; physical exercise
7.  Racial Differences in the Association between Body Mass Index (BMI) and serum IGF-1, IGF-2, and IGFBP-3 
Endocrine-related cancer  2010;17(1):51.
African American (AA) race/ethnicity, lower body mass index (BMI), and higher insulin-like growth factor 1 (IGF-1) levels are associated with premenopausal breast cancer risk. This cross-sectional analysis investigated whether BMI or BMI at age 21 years contribute to racial differences in IGF-1, IGF-2, IGFBP-3, or free IGF-1. Participants included 816 white and 821 AA women between ages 40 and 79 years across a wide BMI range (18.5–40 kg/m2). Compared with white women, AA women had higher mean IGF-1 (146.3 vs. 134.4 ng/ml) and free IGF-1 (0.145 vs. 0.127) levels, and lower IGF-2 (1633.0 vs. 1769.3 ng/ml) and IGFBP-3 (3663.3 vs. 3842.5 ng/ml) levels (all p<0.01; adjusted for age, height, BMI, BMI at age 21, and menopause status). Regardless of race, IGF-1 and free IGF-1 levels sharply rose as BMI increased to 22–24 kg/m2, then declined thereafter, while IGF-2 and IGFBP-3 levels tended to rise with BMI. In contrast, BMI at age 21 was inversely associated with all IGF levels, but only among white women (p-interaction = 0.01). With the decline in IGF-1 with BMI at age 21 among whites, racial differences in IGF-1 significantly increased among women who were obese in early adulthood. In summary, BMI was associated with IGF-1 levels regardless of race/ethnicity, while obesity during childhood or young adulthood may have a greater impact on IGF-1 levels among white women. The effects of obesity throughout life on the IGF axis and racial differences in breast cancer risk require study.
PMCID: PMC2814999  PMID: 19786462
Insulin-like growth factor; obesity; race; breast cancer
8.  A polymorphic variant of the insulin-like growth factor 1 (IGF-1) receptor correlates with male longevity in the Italian population: a genetic study and evaluation of circulating IGF-1 from the "Treviso Longeva (TRELONG)" study 
BMC Geriatrics  2009;9:19.
An attenuation of the insulin-like growth factor 1 (IGF-1) signaling has been associated with elongation of the lifespan in simple metazoan organisms and in rodents. In humans, IGF-1 level has an age-related modulation with a lower concentration in the elderly, depending on hormonal and genetic factors affecting the IGF-1 receptor gene (IGF-1R).
In an elderly population from North-eastern Italy (n = 668 subjects, age range 70–106 years) we investigated the IGF-1R polymorphism G3174A (rs2229765) and the plasma concentration of free IGF-1. Frequency distributions were compared using χ2-test "Goodness of Fit" test, and means were compared by one-way analysis of variance (ANOVA); multiple regression analysis was performed using JMP7 for SAS software (SAS Institute, USA). The limit of significance for genetic and biochemical comparison was set at α = 0.05.
Males showed an age-related increase in the A-allele of rs2229765 and a change in the plasma level of IGF-1, which dropped significantly after 85 years of age (85+ group). In the male 85+ group, A/A homozygous subjects had the lowest plasma IGF-1 level. We found no clear correlation between rs2229765 genotype and IGF-1 in the females.
These findings confirm the importance of the rs2229765 minor allele as a genetic predisposing factor for longevity in Italy where a sex-specific pattern for IGF-1 attenuation with ageing was found.
PMCID: PMC2692840  PMID: 19460140
9.  Pharmacodynamic Considerations with Recombinant Human Insulin-Like Growth Factor-I in Children 
Hormone research  2005;63(5):220-227.
To report effects of weight-based recombinant human insulin-like growth factor-I (rhIGF-I) on IGF axis parameters in children with hyperinsulinism.
Open label trial with subcutaneous rhIGF-I (40 μg/kg/dose). Patients studied were children (1 month to 11 years) with diffuse hyperinsulinism (n = 7). Serial serum IGF and insulin-like growth factor binding protein (IGFBP) concentrations were measured by RIA and analyzed by linear Pearson regression.
Following the initial rhIGF-I dose, total insulin-like growth factor-I (IGF-I) rose by 56% at 30 min (p < 0.01) and 85% at 120 min (p < 0.02). Serum IGF-II, IGFBP-2, and IGFBP-3 levels did not change. Peak serum IGF-I levels within 12 h of the initial rhIGF-I dose were 167–700 mg/ml. The variable peak IGF-I response is attributable in part to IGFBP-3 differences across this pediatric age range. Models of rhIGF-I dosing based upon body surface area (BSA) or initial IGFBP-3 resulted in predictable peak serum IGF-I levels (r = 0.78; p < 0.03). Recalculating rhIGF-I dosing based upon the BSA · IGFBP-3 product correlated closely with peak IGF-I level (r = 0.85; p < 0.007).
Weight-based IGF-I dosing in this cohort resulted in variable IGF-I levels. Considering BSA and serum IGFBP-3 concentration in children is appropriate for subcutaneous IGF-I administration. A combination of these values may yield predictable individualization of rhIGF-I dosing.
PMCID: PMC3102299  PMID: 15886488
Hyperinsulinism; IGF-I dosing; rhIGF-I dosing; Pharmacokinetics; IGF-I; IGFBP
10.  Full-length huntingtin levels modulate body weight by influencing insulin-like growth factor 1 expression 
Human Molecular Genetics  2010;19(8):1528-1538.
Levels of full-length huntingtin (FL htt) influence organ and body weight, independent of polyglutamine length. The growth hormone-insulin like growth factor-1 (GH-IGF-1) axis is well established as a regulator of organ growth and body weight. In this study, we investigate the involvement of the IGF-1 pathway in mediating the effect of htt on body weight. IGF-1 expression was examined in transgenic mouse lines expressing different levels of FL wild-type (WT) htt (YAC18 mice), FL mutant htt (YAC128 and BACHD mice) and truncated mutant htt (shortstop mice). We demonstrate that htt influences body weight by modulating the IGF-1 pathway. Plasma IGF-1 levels correlate with body weight and htt levels in the transgenic YAC mice expressing human htt. The effect of htt on IGF-1 expression is independent of CAG size. No effect on body weight is observed in transgenic YAC mice expressing a truncated N-terminal htt fragment (shortstop), indicating that FL htt is required for the modulation of IGF-1 expression. Treatment with 17β-estradiol (17β-ED) lowers the levels of circulating IGF-1 in mammals. Treatment of YAC128 with 17β-ED, but not placebo, reduces plasma IGF-1 levels and decreases the body weight of YAC128 animals to WT levels. Furthermore, given the ubiquitous expression of IGF-1 within the central nervous system, we also examined the impact of FL htt levels on IGF-1 expression in different regions of the brain, including the striatum, cerebellum of YAC18, YAC128 and littermate WT mice. We demonstrate that the levels of FL htt influence IGF-1 expression in striatal tissues. Our data identify a novel function for FL htt in influencing IGF-1 expression.
PMCID: PMC2846162  PMID: 20097678
11.  Validation of serum IGF-I as a biomarker to monitor the bioactivity of exogenous growth hormone agonists and antagonists in rabbits 
Disease Models & Mechanisms  2014;7(11):1263-1273.
The development of new growth hormone (GH) agonists and growth hormone antagonists (GHAs) requires animal models for pre-clinical testing. Ideally, the effects of treatment are monitored using the same pharmacodynamic marker that is later used in clinical practice. However, intact rodents are of limited value for this purpose because serum IGF-I, the most sensitive pharmacodynamic marker for the action of GH in humans, shows no response to treatment with recombinant human GH and there is little evidence for the effects of GHAs, except when administered at very high doses or when overexpressed. As an alternative, more suitable model, we explored pharmacodynamic markers of GH action in intact rabbits. We performed the first validation of an IGF-I assay for the analysis of rabbit serum and tested precision, sensitivity, linearity and recovery using an automated human IGF-I assay (IDS-iSYS). Furthermore, IGF-I was measured in rabbits of different strains, age groups and sexes, and we monitored IGF-I response to treatment with recombinant human GH or the GHA Pegvisomant. For a subset of samples, we used LC-MS/MS to measure IGF-I, and quantitative western ligand blot to analyze IGF-binding proteins (IGFBPs). Although recovery of recombinant rabbit IGF-I was only 50% in the human IGF-I assay, our results show that the sensitivity, precision (1.7–3.3% coefficient of variation) and linearity (90.4–105.6%) were excellent in rabbit samples. As expected, sex, age and genetic background were major determinants of IGF-I concentration in rabbits. IGF-I and IGFBP-2 levels increased after single and multiple injections of recombinant human GH (IGF-I: 286±22 versus 434±26 ng/ml; P<0.01) and were highly correlated (P<0.0001). Treatment with the GHA lowered IGF-I levels from the fourth injection onwards (P<0.01). In summary, we demonstrated that the IDS-iSYS IGF-I immunoassay can be used in rabbits. Similar to rodents, rabbits display variations in IGF-I depending on sex, age and genetic background. Unlike in rodents, the IGF-I response to treatment with recombinant human GH or a GHA closely mimics the pharmacodynamics seen in humans, suggesting that rabbits are a suitable new model to test human GH agonists and antagonists.
PMCID: PMC4213730  PMID: 25239917
Pharmacodynamic marker; Acromegaly; Growth hormone deficiency; Animal model
12.  Elevated Serum Levels of IGF-1 Are Sufficient to Establish Normal Body Size and Skeletal Properties Even in the Absence of Tissue IGF-1 
Journal of Bone and Mineral Research  2010;25(6):1257-1266.
Use of recombinant insulin-like growth factor 1 (IGF-1) as a treatment for primary IGF-1 deficiency in children has become increasingly common. When untreated, primary IGF-1 deficiency may lead to a range of metabolic disorders, including lipid abnormalities, insulin resistance, and decreased bone density. To date, results of this therapy are considered encouraging; however, our understanding of the role played by IGF-1 during development remains limited. Studies on long-term treatment with recombinant IGF-1 in both children and animals are few. Here, we used two novel transgenic mouse strains to test the long-term effects of elevated circulating IGF-1 on body size and skeletal development. Overexpression of the rat igf1 transgene in livers of mice with otherwise normal IGF-1 expression (HIT mice) resulted in approximately threefold increases in serum IGF-1 levels throughout growth, as well as greater body mass and enhanced skeletal size, architecture, and mechanical properties. When the igf1 transgene was overexpressed in livers of igf1 null mice (KO-HIT), the comparably elevated serum IGF-1 failed to overcome growth and skeletal deficiencies during neonatal and early postnatal growth. However, between 4 and 16 weeks of age, increased serum IGF-1 fully compensated for the absence of locally produced IGF-1 because body weights and lengths of KO-HIT mice became comparable with controls. Furthermore, micro-computed tomography (µCT) analysis revealed that early deficits in skeletal structure of KO-HIT mice were restored to control levels by adulthood. Our data indicate that in the absence of tissue igf1 gene expression, maintaining long-term elevations in serum IGF-1 is sufficient to establish normal body size, body composition, and both skeletal architecture and mechanical function. © 2010 American Society for Bone and Mineral Research.
PMCID: PMC3153133  PMID: 20200935
IGF-1; bone; transgenic mice; IGF-1KO; micro-computed tomography; endocrine IGF-1; mechanical properties
13.  Radioimmunological determination of insulinlike growth factors I and II in normal subjects and in patients with growth disorders and extrapancreatic tumor hypoglycemia. 
Journal of Clinical Investigation  1981;68(5):1321-1330.
Serum levels of immunoreactive insulinlike growth factors (IGF) I and II were determined by a modified IGF I and a new IGF II radioimmunoassay in normal children and adults, and in patients with acromegaly, isolated growth hormone deficiency, and extrapancreatic tumor hypoglycemia. Serum samples were gel filtered by a simple routine procedure at acidic pH to dissociate and separate IGF from the IGF carrier protein. Mean immunoreactive IGF I levels (+/- SD; corrected for crossreactivity of IGF II) were 193 +/- 58 ng/ml in normal adult subjects, 712 +/- 245 ng/ml in acromegalic patients and 24 +/- 14 ng/ml in patients with isolated growth hormone deficiency. The lack of growth hormone alone, irrespective of an otherwise normal hormonal status, appears to be responsible for the drastic decrease of IGF I levels. Oversecretion of growth hormone does not increase the levels of immunoreactive IGF II: mean levels (+/- SD; corrected for crossreactivity of IGF I) in normal and acromegalic subjects are virtually identical (647 +/- 126 and 641 +/- 189 ng/ml, respectively). Apparently, normal growth hormone levels stimulate IGF II production already maximally. However in growth hormone deficiency immunoreactive IGF II is significantly decreased (252 +/- 99 ng/ml). Thus, IGF II, like IGF I, is growth hormone dependent. But in contrast to IGF I, the growth hormone dependence of IGF II seems to become apparent only at subnormal growth hormone levels. In normal children IGF I is age dependent: it is low in newborn cord sera (51 +/- 20 ng/ml) and gradually rises into the adult range with increasing age. At the onset of and during puberty mean IGF I levels lie above prepubertal values. In contrast, IGF II levels in normal children are independent of age and pubertal stage beyond the first year of life, whereas newborns have significantly lower IGF II values. Hypoglycemia resulting from extrapancreatic tumors is not associated with increased immunoreactive IGF I or II levels. IGF I is decreased in most of the sera (mean level +/- SD:56 +/- 39 ng/ml) whereas IGF II lies in the normal range (556 +/- 195 ng/ml).
PMCID: PMC370928  PMID: 7028787
14.  Reductions in serum IGF-1 during aging impair health span 
Aging Cell  2013;13(3):408-418.
In lower or simple species, such as worms and flies, disruption of the insulin-like growth factor (IGF)-1 and the insulin signaling pathways has been shown to increase lifespan. In rodents, however, growth hormone (GH) regulates IGF-1 levels in serum and tissues and can modulate lifespan via/or independent of IGF-1. Rodent models, where the GH/IGF-1 axis was ablated congenitally, show increased lifespan. However, in contrast to rodents where serum IGF-1 levels are high throughout life, in humans, serum IGF-1 peaks during puberty and declines thereafter during aging. Thus, animal models with congenital disruption of the GH/IGF-1 axis are unable to clearly distinguish between developmental and age-related effects of GH/IGF-1 on health. To overcome this caveat, we developed an inducible liver IGF-1-deficient (iLID) mouse that allows temporal control of serum IGF-1. Deletion of liver Igf -1 gene at one year of age reduced serum IGF-1 by 70% and dramatically impaired health span of the iLID mice. Reductions in serum IGF-1 were coupled with increased GH levels and increased basal STAT5B phosphorylation in livers of iLID mice. These changes were associated with increased liver weight, increased liver inflammation, increased oxidative stress in liver and muscle, and increased incidence of hepatic tumors. Lastly, despite elevations in serum GH, low levels of serum IGF-1 from 1 year of age compromised skeletal integrity and accelerated bone loss. We conclude that an intact GH/IGF-1 axis is essential to maintain health span and that elevated GH, even late in life, associates with increased pathology.
PMCID: PMC4326899  PMID: 24341939
aging; bone; growth hormone; IGF; insulin-sensitivity; LID; lifespan; liver; tumor
15.  The Effect of Acclydine in Chronic Fatigue Syndrome: A Randomized Controlled Trial 
PLoS Clinical Trials  2007;2(5):e19.
It is unclear whether insulin-like growth factor (IGF) function is involved in the pathophysiology of chronic fatigue syndrome (CFS). Unpublished data and reports in patient organization newsletters suggest that Acclydine, a food supplement, could be effective in the treatment of CFS by increasing biologically active IGF1 levels. Here we aimed to measure the IGF1 and IGF binding protein (IGFBP) 3 status of CFS patients compared to age- and gender-matched neighborhood controls, and to assess the effect of Acclydine on fatigue severity, functional impairment, and biologically active IGF1 level (IGFBP3/IGF1 ratio).
A randomized, placebo-controlled, double-blind clinical trial.
Radboud University Nijmegen Medical Centre, The Netherlands.
Fifty-seven adult patients who fulfilled the US Centers for Disease Control and Prevention criteria for CFS. IGF status of 22 CFS patients was compared to that of 22 healthy age- and gender-matched neighborhood control individuals.
Acclydine or placebo for 14 wk.
Outcome measures:
Outcomes were fatigue severity (Checklist Individual Strength, subscale fatigue severity [CIS-fatigue]), functional impairment (Sickness Impact Profile-8 [SIP-8]), and biologically active IGF1 serum concentrations. Analyses were on an intention-to-treat basis.
There was no difference in IGF status in 22 CFS patients compared to healthy age- and gender-matched control individuals. Treatment with Acclydine did not result in significant differences compared with the placebo group on any of the outcome measures: CIS-fatigue +1.1 (95% CI −4.4 to +6.5, p = 0.70), SIP-8 +59.1 (95% CI −201.7 to +319.8, p = 0.65), and IGFBP3/IGF1 ratio −0.5 (95% CI −2.8 to +1.7, p = 0.63).
We found no differences in IGF1 status in CFS patients compared to healthy matched neighborhood controls. In addition, the results of this clinical trial do not demonstrate any benefit of Acclydine over placebo in the treatment of CFS.
Editorial Commentary
Background: Chronic fatigue syndrome is a complicated and poorly understood illness. People with the condition experience tiredness that carries on for a long period of time and does not get better with rest. Other symptoms include sleeping problems, muscle and joint pains, concentration difficulties, and headaches. The causes of chronic fatigue syndrome are not known. There is evidence for the effectiveness of certain behavioral interventions, such as exercise therapy and cognitive behavioral therapy, in improving certain symptoms. However, some doctors are concerned that a food supplement called Acclydine, derived from a plant called Solanum dulcamara, is being used and promoted as a treatment for chronic fatigue syndrome when there is little evidence about the efficacy or safety of this supplement.
The researchers here carried out a randomized trial in The Netherlands, recruiting adult patients who met the internationally accepted criteria for chronic fatigue syndrome. The participants were allocated by chance to receive either 14 weeks of treatment with Acclydine together with amino acid supplements or, alternatively, placebo versions of the Acclydine and amino acid tablets. The researchers then measured participants' responses with respect to two primary outcome measures. One of these was how tired participants felt, which was measured using a subscale on a questionnaire called the Checklist Individual Strength scale (CIS-fatigue). The other primary outcome measure was “functional impairment,” which examines how well someone carries out their daily life, using the Sickness Impact Profile (SIP-8) scale. The secondary outcome measures included physical activity levels, day-to-day fatigue levels, and the levels of insulin-like growth factor 1 (IGF1) in blood, a hormone that's thought by some researchers to be related to the severity of chronic fatigue.
What the trial shows: In the trial, 57 people were randomized to receive either Acclydine plus amino acid supplements, or placebo tablets. When comparing scores on the primary outcome measures at the end of the trial, the researchers did not see significant differences between the treatment and placebo groups. Similarly, the results for secondary outcome measures in this trial did not show any significant differences between the treatment and placebo groups.
Strengths and limitations: Strengths of this study include the fact that it is one of the few properly designed studies of a product for which claims have been made of effectiveness in chronic fatigue syndrome. The study was designed as a double-blind trial, in which participants and investigators (those collecting the outcome data) did not know whether an individual received Acclydine or placebo. This procedure should help to minimize bias in assessing outcomes. A key limitation of this study is the relatively small number of participants. However, the investigators considered it unlikely that a larger trial would detect a clinically meaningful effect of Acclydine on these outcome measures for patients with chronic fatigue syndrome.
Contribution to the evidence: Systematic reviews of interventions for the treatment of chronic fatigue syndrome have found evidence for the efficacy of exercise therapy and cognitive behavioral therapy. This trial shows no evidence of efficacy of Acclydine plus amino acid supplements for the treatment of chronic fatigue.
PMCID: PMC1876596  PMID: 17525791
16.  Lipoprotein Particle Profiles Mark Familial and Sporadic Human Longevity 
PLoS Medicine  2006;3(12):e495.
Genetic and biochemical studies have indicated an important role for lipid metabolism in human longevity. Ashkenazi Jewish centenarians and their offspring have large low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles as compared with control individuals. This profile also coincided with a lower prevalence of disease. Here, we investigate whether this observation can be confirmed for familial longevity in an outbred European population and whether it can be extended to sporadic longevity in the general population.
Methods and Findings
NMR-measured lipoprotein profiles were analyzed in 165 families from the Leiden Longevity Study, consisting of 340 long-lived siblings (females >91 y, males >89 y), 511 of their offspring, and 243 partners of the offspring. Offspring had larger (21.3 versus 21.1 nm; p = 0.020) and fewer (1,470 versus 1,561 nmol/l; p = 0.011) LDL particles than their same-aged partners. This effect was even more prominent in the long-lived siblings (p < 10−3) and could be pinpointed to a reduction specifically in the concentration of small LDL particles. No differences were observed for HDL particle phenotypes. The mean LDL particle sizes in 259 90-y-old singletons from a population-based study were similar to those in the long-lived siblings and thus significantly larger than in partners of the offspring, suggesting that the relevance of this phenotype extends beyond familial longevity. A low concentration of small LDL particles was associated with better overall health among both long-lived siblings (p = 0.003) and 90-y-old singletons (p = 0.007).
Our study indicates that LDL particle profiles mark both familial and sporadic human longevity already in middle age.
Offspring of families from the Leiden Longevity Study had larger and fewer LDL particles than same-aged partners, suggesting that even in middle age LDL particle profiles are associated with longevity.
Editors' Summary
It is not clear why some people go on to live longer than others do. Some studies have shown that close relatives of long-lived people are themselves more likely to live for a long time; these findings suggest that there is probably a genetic basis for long life. However, the actual mechanisms involved have not yet been worked out. Some genes coding for proteins involved in fat metabolism, such as APOE, APOB, and CETP, have been associated with long life, suggesting a link between the way fat gets metabolized and the aging process. One study that supports this idea found that the children of 100-year-old people had larger lipoprotein particles (assemblies of proteins and fats that carry cholesterol and triglycerides in the blood) than similarly aged control individuals. However, studies such as this are very prone to “false positive” findings and therefore need to be backed up by confirmatory evidence. In addition, the previous study was performed in a very specific population (Ashkenazi Jewish people), and it is important to find out whether the findings are also true in other populations.
Why Was This Study Done?
The research group carrying out this study wanted to address several distinct questions to do with the genetics of aging. Firstly, they wanted to see if they could confirm previous findings associating large lipoprotein particles with longer life, but looking at people who were more representative of the general European population and not from a genetically isolated population. Secondly, they wanted to see whether this association applied to only long-lived people whose family members were also long-lived, or to long-lived people in general. Finally, they wanted to find out if the large lipoprotein particles were associated with better health.
What Did the Researchers Do and Find?
In the study, the researchers looked at long-lived people from across The Netherlands whose relatives were also long-lived. For this, they recruited 340 men aged over 89 and women aged over 91 into the study, all of whom had at least one similarly long-lived sister or brother. Their children (511 individuals), and the partners of their children (243 people), were also recruited into the study, with the partners acting as “controls.” The researchers also studied 259 people who had just turned 90 years old; these people were included to see whether particular characteristics of lipoproteins existed in long-lived people whose longevity did not run in families. All the participants gave blood samples, and the researchers then measured the size and amount of different lipoprotein particles in these samples. Two types of lipoprotein particles were looked at: low-density lipoprotein (LDL, often termed “bad cholesterol”) and high-density lipoprotein (HDL, sometimes called “good cholesterol”). The researchers found that the children from the long-lived people had larger and fewer LDL particles than their partners (the “control” individuals) just like their long-lived parents. Thus even though the children were not long-lived themselves, LDL particles marked the fact that they have a higher chance of becoming long-lived in the future. Similar changes in LDL particles were found for long-lived people whose relatives were not also long-lived. Interestingly, simply the level of cholesterol—the classical risk factor for cardiovascular disease—did not appear to play a role. Thus it seems that it is not the amount of cholesterol that is important in longevity but how it is packaged. Better health status was also associated with a lower proportion of small LDL particles in the blood, supporting these findings. No characteristics of the HDL particles seemed to be associated with longevity.
What Do These Findings Mean?
These findings confirm those from a previous study in Ashkenazi Jewish people that suggested that the size of LDL particles in the blood was associated with long life. The nature of this association is not clear; some studies indicated that small LDL particles increase the risk of cardiovascular disease but small LDL particles may also be harmless themselves and reflect the efficiency of other processes causally related to aging.
Additional Information.
Please access these Web sites via the online version of this summary at
Wikipedia chapter on senescence (biology of aging) (note that Wikipedia is a free Internet encyclopedia that anyone can edit)
US National Institute on Aging provides information on healthy aging, details of publicly funded research into aging, and other resources for the public
Help the Aged information on research into aging
PMCID: PMC1716190  PMID: 17194192
17.  Quantitative Ontogeny of Murine Insulin-Like Growth Factor (IGF)-I, IGF-binding Protein-3 and the IGF-related Acid-labile Subunit 
The mouse serves as an important model for insulin-like (IGF)-related research. However, lack of homologous mouse assays has prevented studies of the normal ontology of the murine IGF-system. Therefore, we developed and validated immunoaassays for murine IGF-I, IGFBP-3 and ALS and studied levels of these analytes in mice.
Using commercially available reagents, we developed and validated specific enzyme-linked immunosorbent assays (ELISAs) for murine IGF-I, IGFBP-3, and ALS. Levels of these analytes were measured in sera from CD-1 mice, male and female, sampled at 1, 2, 4, 8, 20 and 32 wks of age. In addition, sera from pregnant and post-partum CD-1 mice were also studied.
Validation of specific ELISAs for murine IGF-I, IGFBP-3 and ALS are described; all 3 assays were highly sensitive, precise and accurate. As measured by our homologous ELISA, IGF-I levels (ng/mL, mean±SD) in male mice were relatively low at 1 wk (53±8), rising sharply to peak at 8 wks of age (636±48), and gradually declining thereafter, reaching 395±64 at 32 wks. IGF-I levels in non-pregnant female mice peaked at 4 wks of age (548±77) declined at 8 wks (417±61), then recovered to plateau at 539±78 and 535±88 at 20 and 32 wks, respectively. In male mice, trends in IGFBP-3 were similar to the patterns of IGF-I. However, in non-pregnant female mice, the IGFBP-3 levels declined relatively slowly after peaking at 4-weeks of age, unlike IGF-I levels during this period. ALS levels followed the same pattern as IGF-I in both sexes. IGF-I to IGFBP-3 molar ratios (percent) were similar between sexes, rising continuously with age: ~30% at 1 wk, 80% at 4 wks, 135% at 32 wks. IGF-I was reduced in 8 wk old mice in mid-pregnancy (354±75 vs 417±61 in non-pregnant 8 wk females), reaching a nadir in late-term (146±40), and only partially recovering in the postpartum period (239±23). IGFBP-3 was also lower in late-pregnancy (1245±100 vs 1925±439) and remained depressed post-partum. In contrast to IGF-I and IGFBP-3, ALS increased more than 3-fold in mid-pregnancy (12180±1641 vs 3741±910), followed by a 4-fold decrease in late-pregnancy (2964±489), recovering postpartum (6104±1178).
We report the first ontological studies of IGF-I, IGFBP-3 and ALS in mice using newly-characterized sensitive, homologous immunoassays. Our results indicate that mice have a generally similar pattern in IGF-related axis components, with low levels early in life, increasing to peak during sexual maturation and declining thereafter. Significant gender differences in non-pregnant levels and dramatic changes during pregnancy were also found. Knowledge of the normal developmental changes in the murine IGF system and accurate tools for investigations of this system are a necessary foundation for research in this field.
PMCID: PMC2276237  PMID: 17719253
Acid-labile subunit; Insulin-like growth factor-I; Insulin-like growth factor binding-protein; Mouse insulin-like growth factor
18.  Effects of Sex and Reproductive State on Interactions between Free-Roaming Domestic Dogs 
PLoS ONE  2014;9(12):e116053.
Free-roaming dogs (Canis familiaris) are common worldwide, often maintaining diseases of domestic pets and wildlife. Management of these dogs is difficult and often involves capture, treatment, neutering and release. Information on the effects of sex and reproductive state on intraspecific contacts and disease transmission is currently lacking, but is vital to improving strategic management of their populations. We assessed the effects of sex and reproductive state on short-term activity patterns and contact rates of free-roaming dogs living in an Australian Indigenous community. Population, social group sizes and rates of contact were estimated from structured observations along walked transects. Simultaneously, GPS telemetry collars were used to track dogs' movements and to quantify the frequency of contacts between individual animals. We estimated that the community's dog population was 326±52, with only 9.8±2.5% confined to a house yard. Short-term activity ranges of dogs varied from 9.2 to 133.7 ha, with males ranging over significantly larger areas than females. Contacts between two or more dogs occurred frequently, with entire females and neutered males accumulating significantly more contacts than spayed females or entire males. This indicates that sex and reproductive status are potentially important to epidemiology, but the effect of these differential contact rates on disease transmission requires further investigation. The observed combination of unrestrained dogs and high contact rates suggest that contagious disease would likely spread rapidly through the population. Pro-active management of dog populations and targeted education programs could help reduce the risks associated with disease spread.
PMCID: PMC4277450  PMID: 25541983
19.  Insulin-like Growth Factor-1 (IGF-1): Demographic, Clinical and Laboratory Data in 120 Consecutive Adult Patients with Thalassaemia Major 
IGF-1 deficiency in TM patients in children and adolescents has been attributed to chronic anemia and hypoxia, chronic liver disease, iron overload and other associated endocrinopathies, e.g. growth hormone deficiency (GHD). Few data are available in the literature regarding adult TM patients and growth disorders. The aim of this study was to measure IGF-1 values and other clinical data in a large number of adult patients with TM to evaluate the possible relationships between them.
Patients and Methods
A cohort of 120 adult patients with TM was studied for plasma levels of IGF-1. Plasma total IGF-1 was determined by chemiluminescent immunometric assay (CLIA) method. In eleven patients (3 females) the GH response during glucagon stimulation test (GST) was also evaluated.
Fifty percent of patients (33 males and 27 females) had IGF-1 levels <- 2 SDs below normative values for healthy subjects matched for age and sex. In these patients endocrine complications and elevations of aminotransferases (ALT) were more common compared to TM patients with IGF1 > -2SDs. In multivariate regression analyses, height, weight, BMI, serum ferritin, ALT, HCV serology and left ventricular ejection fraction (LVEF) were not significantly related to IGF-1, but a significant correlation was found in females between HCV-RNA positivity and IGF-1, ALT and serum ferritin. AGHD was diagnosed in 6 (4 males) out of 11 patients (54.5%) who had glucagon stimulation tests and in 5 out of 8 (62.5%) with IGF-1 <-2SD. The mean age of patients with GHD was 39.3 years (range: 25–49 years, median: 39 years) versus 35.8 years (range: 27–45 years, median: 37.5 years) in non-GHD patients. A positive correlation between GH peak after GST and IGF-1 level was found (r: 0.6409; p: < 0.05).
In 50% of TM patients the IGF-1 levels were 2SDs below average values for healthy individuals. IGF-1 deficiency was more common in TM patients with associated endocrine complications, and a significant correlation was found in HCV-RNA positive females among IGF-1, ALT, and serum ferritin. Further data in a larger group of patients are needed to confirm whether IGF-1 level <-2 SDs may be a potential criterion for additional studies in TM patients. This datum could avoid performing GH stimulation tests in the majority of them.
PMCID: PMC4235482  PMID: 25408860
20.  Hepatoprotection and neuroprotection induced by low doses of IGF-II in aging rats 
GH and IGFs serum levels decline with age. Age-related changes appear to be associated to decreases in these anabolic hormones. We have previously demonstrated that IGF-I replacement therapy improves insulin resistance, lipid metabolism and reduces oxidative damage (in brain and liver) in aging rats. Using the same experimental model, the aim of this work was to study whether the exogenous administration of IGF-II, at low doses, acts analogous to IGF-I in aging rats.
Three experimental groups were included in this study: young healthy controls (yCO, 17 weeks old); untreated old rats (O, 103 weeks old); and aging rats treated with IGF-II (O+IGF-II, 2 μg * 100 g body weight-1 * day-1) for 30 days. Analytical parameters were determined in serum by routine laboratory methods using an autoanalyzer (Cobas Mira; Roche Diagnostic System, Basel, Switzerland). Serum levels of hormones (testosterone, IGF-I and insulin) were assessed by RIA. Serum Total Antioxidant Status was evaluated using a colorimetric assay. Mitochondrial membrane potential was evaluated using rhodamine 123 dye (adding different substrates to determine the different states). ATP synthesis in isolated mitochondria was determined by an enzymatic method.
Compared with young controls, untreated old rats showed a reduction of IGF-I and testosterone levels with a decrease of serum total antioxidant status (TAS). IGF-II therapy improved serum antioxidant capability without modifying testosterone and IGF-I circulating concentrations. In addition, IGF-II treatment reduced oxidative damage in brain and liver, improving antioxidant enzyme activities and mitochondrial function. IGF-II was also able to reduce cholesterol and triglycerides levels increasing free fatty acids concentrations.
We demonstrate that low doses of IGF-II induce hepatoprotective, neuroprotective and metabolic effects, improving mitochondrial function, without affecting testosterone and IGF-I levels.
PMCID: PMC3150260  PMID: 21733157
21.  hNAG-1 increases lifespan by regulating energy metabolism and insulin/IGF-1/mTOR signaling 
Aging (Albany NY)  2014;6(8):690-704.
Nonsteroidal anti-inflammatory drug-activated gene (NAG-1) or GDF15 is a divergent member of the transforming growth factor beta (TGF-β) superfamily and mice expressing hNAG-1/hGDF15 have been shown to be resistant to HFD-induced obesity and inflammation. This study investigated if hNAG-1 increases lifespan in mice and its potential mechanisms. Here we report that female hNAG-1 mice had significantly increased both mean and median life spans in two transgenic lines, with a larger difference in life spans in mice on a HFD than on low fat diet. hNAG-1 mice displayed significantly reduced body and adipose tissue weight, lowered serum IGF-1, insulin and glucose levels, improved insulin sensitivity, and increased oxygen utilization, oxidative metabolism and energy expenditure. Gene expression analysis revealed significant differences in conserved gene pathways that are important regulators of longevity, including IGF-1, p70S6K, and PI3K/Akt signaling cascades. Phosphorylation of major components of IGF-1/mTOR signaling pathway was significantly lower in hNAG-1mice. Collectively, hNAG-1 is an important regulator of mammalian longevity and may act as a survival factor. Our study suggests that hNAG-1 has potential therapeutic uses in obesity-related diseases where life span is frequently shorter.
PMCID: PMC4169862  PMID: 25239873
hNAG-1/GDF15; lifespan; metabolism; insulin/IGF-1/mTOR
22.  Klotho locus, metabolic traits, and serum hemoglobin in hospitalized older patients: a genetic association analysis 
Age  2011;34(4):949-968.
Klotho (KL) gene has been involved in severe alterations of physiological biochemical parameters leading to premature aging-like phenotypes and strikingly shortening lifespan. KL participates to the regulation of a number of intracellular biochemical pathways, including lipid profile and glucose metabolism. Aim of this study was to investigate the possible association between KL locus and biological parameters commonly accepted as indicators of the clinical status in hospitalized older patients. We genotyped the single-nucleotide polymorphisms (SNPs) rs9536314, rs1207568, and rs564481 at the KL locus in 594 hospitalized older patients (65–99 years), consecutively attending a geriatric ward, and tested the association of these KL variants with biological quantitative traits using analyses of covariance and genetic risk score models. Significant associations of rs9536314 with serum levels of hemoglobin, albumin, and high-density lipoprotein cholesterol (HDL-C) as well as significant associations of rs564481 with serum levels of hemoglobin, fasting insulin, and fasting glucose were observed. Gender-segregated analyses confirmed these associations, and suggested that the associations of KL genotypes with HDL-C, fasting glucose and fasting insulin levels may be driven by the female gender, while the association with serum levels of hemoglobin may be driven by the male gender. The association of KL genotypes with creatinine levels was found only in females, while the association with insulin-like growth factor-1 (IGF-1) and lymphocytes count (LC) was found only in males. The genetic risk score (GRS) models further confirmed significant associations among KL SNPs and hemoglobin, total cholesterol, and HDL-C. Gender-segregated analyses with the GRS-tagged approach confirmed the associations with HDL-C, fasting glucose, and fasting insulin levels in females, and with hemoglobin and LC in males. Our findings suggested that KL locus may influence quantitative traits such as serum levels of lipid, fasting glucose, albumin and hemoglobin in hospitalized older patients, with some gender differences suggested for creatinine, IGF-1 levels, and LC, thus being one of the genetic factors possibly contributing to age-related diseases and longevity.
PMCID: PMC3682056  PMID: 21695423
Klotho; Chromosome 13; High-density lipoprotein cholesterol; Total cholesterol; Fasting glucose; Fasting insulin; Insulin-like growth factor-1; Hemoglobin; Creatinine; Albumin; Lymphocytes
23.  Relation between insulin-like growth factor-I, body mass index, and clinical status in cystic fibrosis 
Archives of Disease in Childhood  1997;76(4):304-309.
Accepted 26 October 1996

OBJECTIVES—Despite improved nutrition and intensive treatment, subjects with cystic fibrosis have difficulty in maintaining anabolism during intercurrent infections, which can result in reduced body mass index and impaired skeletal growth. Insulin-like growth factor-I (IGF-I) and its binding protein IGFBP3 are sensitive to changes in nutritional status. The aim of this study was to determine the relation between circulating concentrations of these peptides, body mass index, and clinical status in cystic fibrosis.
METHODS—Serum concentrations of IGF-I and IGFBP3 were measured in 197 subjects (108 males, 89 females; mean age 9.69 years, range 0.41-17.9 years) and these data were analysed with respect to body mass index, pubertal stage, and clinical status as assessed by Shwachman score and forced expiratory volume in one second (FEV1 ).
RESULTS—The mean height SD score of the children studied was −0.2 (SD 1.14) and the body mass index SD score −0.26 (1.4). The body mass index SD score declined with increasing age (r=−0.18) and paralleled changes in IGF-I concentrations, which also declined. The IGF-I SD score (calculated from control data) correlated with age (r=−0.53). The abnormalities were most obvious during late puberty, when IGF-I and IGFBP3 concentrations were significantly reduced compared with those in control subjects matched for pubertal stage. The IGF-I SD score correlated with height SD score (r=0.14) and the decline in IGF-I concentrations with the fall in body mass index SD score (r=0.42). IGF-I SD scores also correlated with the Shwachman score (r=0.33) and FEV1 (r=0.17).
CONCLUSIONS—The close relation between declining IGF-I and IGFBP3 concentrations and body mass index in patients with cystic fibrosis may simply reflect poor nutritional status and insulin hyposecretion. Nevertheless, IGF-I deficiency could also contribute towards the catabolism observed in these patients, and IGF-I SD scores correlated with other measures of clinical status such as the Shwachman score and FEV1.

• The fall in body mass index with increasing age in children with cystic fibrosis parallels the decline in concentrations of IGF-I and its principal binding protein, IGFB3
• The close relation between body mass index and IGF-I concentrations in cystic fibrosis may reflect poor nutrition or insulin hyposecretion
• Nevertheless, low IGF-I concentrations may contribute directly to the fall in body mass index with increasing age
PMCID: PMC1717156  PMID: 9166020
24.  Identification of genetic determinants of IGF-1 levels and longevity among mouse inbred strains 
Aging cell  2010;9(5):823-836.
The IGF-1 signaling pathway plays an important role in regulating longevity. To identify the genetic loci and genes that regulate plasma IGF-1 levels, we intercrossed MRL/MpJ and SM/J, inbred mouse strains that differ in IGF-1 levels. Quantitative trait loci (QTL) analysis of IGF-1 levels of these F2 mice detected four QTL on chromosomes (Chrs) 9 (48 Mb), 10 (86 Mb), 15 (18 Mb) and 17 (85 Mb). Haplotype association mapping of IGF-1 levels in 28 domesticated inbred strains identified three suggestive loci in females on Chrs 2 (13 Mb), 10 (88 Mb) and 17 (28 Mb) and in males on Chrs 1 (159 Mb), 3 (52 and 58 Mb) and 16 (74 Mb). Except for the QTL on Chr 9 and 16, all loci co-localized with IGF-1 QTL previously identified in other mouse crosses. The most significant locus was the QTL on Chr 10, which contains the Igf1 gene and which had a LOD score of 31.8. Haplotype analysis among 28 domesticated inbred strains revealed a major QTL on Chr 10 overlapping with the QTL identified in the F2 mice. This locus showed three major haplotypes; strains with haplotype 1 had significantly lower plasma IGF-1 and extended longevity (P < 0.05) than strains with haplotype 2 or 3. Bioinformatic analysis, combined with sequencing and expression studies, showed that Igf1 is the most likely QTL gene, but that other genes may also play a role in this strong QTL.
PMCID: PMC3025299  PMID: 20735370
IGF-1; QTL; longevity; mouse; haplotype analysis
25.  Insulin, IGF-1 and longevity 
Aging and Disease  2010;1(2):147-157.
It has been demonstrated in invertebrate species that the evolutionarily conserved insulin and insulin-like growth factor (IGF) signaling (IIS) pathway plays a major role in the control of longevity. In the roundworm Caenorhabditis elegans, single mutations that diminish insulin/IGF-1 signaling can increase lifespan more than twofold and cause the animal to remain active and youthful much longer than normal. Likewise, substantial increases in lifespan are associated with mutations that reduce insulin/IGF-1 signaling in the fruit fly Drosophila melanogaster. In invertebrates, multiple insulin-like ligands exist that bind to a common single insulin/IGF-1 like receptor. In contrast, in mammals, different receptors exist that bind insulin, IGF-1 and IGF-2 with different affinities. In several mouse models, mutations that are associated with decreased GH/IGF-1 signaling or decreased insulin signaling have been associated with enhanced lifespan. However, the increased complexity of the mammalian insulin/IGF-1 system has made it difficult to separate the roles of insulin, GH and IGF-1 in mammalian longevity. Likewise, the relevance of reduced insulin and IGF-1 signaling in human longevity remains controversial. However, studies on the genetic and metabolic characteristics that are associated with healthy longevity and old age survival suggest that the conserved ancient IIS pathway may also play a role in human longevity.
PMCID: PMC3295030  PMID: 22396862
Insulin; IGF-1; longevity; signaling

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