Igf-I and longevity

Hyperinsulinemia and Its Pivotal Role in Aging, Obesity, Type 2 Diabetes, Cardiovascular Disease and Cancer

For many years, the dogma has been that insulin resistance precedes the development of hyperinsulinemia. However, recent data suggest a reverse order and place hyperinsulinemia mechanistically upstream of insulin resistance. Genetic background, consumption of the “modern” Western diet and over-nutrition may increase insulin secretion, decrease insulin pulses and/or reduce hepatic insulin clearance, thereby causing hyperinsulinemia. Hyperinsulinemia disturbs the balance of the insulin–GH–IGF axis and shifts the insulin : GH ratio towards insulin and away from GH. This insulin–GH shift promotes energy storage and lipid synthesis and hinders lipid breakdown, resulting in obesity due to higher fat accumulation and lower energy expenditure. Hyperinsulinemia is an important etiological factor in the development of metabolic syndrome, type 2 diabetes, cardiovascular disease, cancer and premature mortality. It has been further hypothesized that nutritionally driven insulin exposure controls the rate of mammalian aging. Interventions that normalize/reduce plasma insulin concentrations might play a key role in the prevention and treatment of age-related decline, obesity, type 2 diabetes, cardiovascular disease and cancer. Caloric restriction, increasing hepatic insulin clearance and maximizing insulin sensitivity are at present the three main strategies available for managing hyperinsulinemia. This may slow down age-related physiological decline and prevent age-related diseases. Drugs that reduce insulin (hyper) secretion, normalize pulsatile insulin secretion and/or increase hepatic insulin clearance may also have the potential to prevent or delay the progression of hyperinsulinemia-mediated diseases. Future research should focus on new strategies to minimize hyperinsulinemia at an early stage, aiming at successfully preventing and treating hyperinsulinemia-mediated diseases.

PEGylation of lysine residues reduces the pro-migratory activity of IGF-I

BACKGROUND

The insulin-like growth factor (IGF) system is composed of ligands and receptors which regulate cell proliferation, survival, differentiation and migration. Some of these functions involve regulation by the extracellular milieu, including binding proteins and other extracellular matrix proteins. However, the functions and exact nature of these interactions remain incomplete.

METHODS

IGF-I variants PEGylated at lysines K27, K65 and K68, were assessed for binding to IGFBPs using BIAcore, and for phosphorylation of the IGF-IR. Furthermore, functional consequences of PEGylation were investigated using cell viability and migration assays. In addition, downstream signaling pathways were analyzed using phospho-AKT and phospho-ERK1/2 assays.

RESULTS

IGF-I PEGylated at lysines 27 (PEG-K27), 65 (PEG-K65) or 68 (PEG-K68) was employed. Receptor phosphorylation was similarly reduced 2-fold with PEG-K65 and PEG-K68 in 3T3 fibroblasts and MCF-7 breast cancer cells, whereas PEG-K27 showed a more than 10- and 3-fold lower activation for 3T3 and MCF-7 cells, respectively. In addition, all PEG-IGF-I variants had a 10-fold reduced association rate to IGF binding proteins (IGFBPs). Functionally, all PEG variants lost their ability to induce cell migration in the presence of IGFBP-3/vitronectin (VN) complexes, whereas cell viability was fully preserved. Analysis of downstream signaling revealed that AKT was preferentially affected upon treatment with PEG-IGF-I variants whereas MAPK signaling was unaffected by PEGylation.

CONCLUSION

PEGylation of IGF-I has an impact on cell migration but not on cell viability.

GENERAL SIGNIFICANCE

PEG-IGF-I may differentially modulate IGF-I mediated functions that are dependent on receptor interaction as well as key extracellular proteins such as VN and IGFBPs.

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.

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

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

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

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

The metabolic syndrome, IGF-1, and insulin action

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

IGF1 as predictor of all cause mortality and cardiovascular disease in an elderly population

BACKGROUND

IGF1 is believed to influence ageing and development of cardiovascular disease (CVD) through complex mechanisms. Reduced IGF1 levels might be causally associated with conditions accompanying ageing including development of CVD. However, in animal models reduced GH-IGF1 signalling increases lifespan. Reduced IGF1 activity might also be associated with longevity in humans.

OBJECTIVE

The objective was to investigate if plasma IGF1 levels were associated with all cause mortality, and the development of chronic heart failure (CHF) and a major CV event.

PATIENTS AND DESIGN

A population based study of 642 individuals, aged 50-89 years. Development of CHF was evaluated in 576 individuals with normal systolic function assessed by echocardiography and without the history of CHF or myocardial infarction. Development of the first major CV event was evaluated in 504 individuals with normal systolic function and without prevalent CVD. Outcomes were ascertained after 5 years using hospital discharge diagnoses.

RESULTS

Adjustment for risk factors IGF1 values in the fourth quartile versus values below the fourth quartile was associated with increased mortality (n=103), hazard ratio (HR) 1.52 (95% confidence interval (CI) 1.01-2.28; P=0.044). IGF1 in the fourth quartile was also independently associated with risk of development of CHF (n=19), HR 5.02 (95% CI 2.00-12.64; P=0.001) but showed no association with the overall incidence of major CV events (n=58), HR 1.05 (95% CI 0.59-1.90; P=0.861).

CONCLUSIONS

High IGF1 levels were independently associated with increased all cause mortality and risk of development of CHF, whereas no relation with the overall incidence of CVD was observed.

How does suppression of IGF-1 signaling by DNA damage affect aging and longevity?

Long-lived animals have evolved a robust set of defenses to maintain genomic integrity over their entire lifespan. The DNA damage response and DNA repair pathways are critical pillars of organismal defenses, minimizing somatic mutations in both post-mitotic and mitotic cells. These genomic maintenance systems not only prevent the premature emergence of cancers but may also maintain normal tissue function and organismal longevity. Genetic defects in a number of DNA repair and DNA damage response genes often leads to a dramatic increase in cancer incidence; in other cases, premature aging or progeroid syndromes may be induced. In this review, we discuss two recent reports of two nucleotide excision repair-deficient models that exhibit dramatic premature aging and shortened longevity. The DNA repair defects were also associated with a significant inhibition of the growth hormone/insulin-like growth factor 1 (GH/IGF-1) axis, an endocrine signaling pathway shown to influence aging and longevity in both vertebrates and invertebrates. Potential mechanisms of how DNA damage might affect IGF-1 signaling and aging are discussed, with a particular emphasis on the role of such signaling alterations in the adult tissue stem cell compartments.

Mineral metabolism disturbances in patients with chronic kidney disease

BACKGROUND

Kidney disease, especially chronic kidney disease (CKD), is a worldwide public health problem with serious adverse health consequences for affected individuals. Secondary hyperparathyroidism, a disorder characterized by elevated serum parathyroid hormone levels, and alteration of calcium and phosphorus homeostasis are common metabolic complications of CKD that may impact cardiovascular health.

MATERIALS AND METHODS

Here, we systematically review published reports from recent observational studies and clinical trials that examine markers of altered mineral metabolism and clinical outcomes in patients with CKD.

RESULTS

Mineral metabolism disturbances begin early during the course of chronic kidney disease, and are associated with cardiovascular disease and mortality in observational studies. Vascular calcification is one plausible mechanism connecting renal-related mineral metabolism with cardiovascular risk. Individual therapies to correct mineral metabolism disturbances have been associated with clinical benefit in some observational studies; clinical trials directed at more comprehensive control of this problem are warranted.

CONCLUSIONS

There exists a potential to improve outcomes for patients with CKD through increased awareness of the Bone Metabolism and Disease guidelines set forth by the National Kidney Foundation-Kidney Disease Outcomes Quality Initiative. Future studies may include more aggressive therapy with a combination of agents that address vitamin D deficiency, parathyroid hormone and phosphorus excess, as well as novel agents that modulate circulating promoters and inhibitors of calcification.

Control of aging and longevity by IGF-I signaling

Animal models have established the IGF-I signaling pathway as a key modulator of aging in rodents and invertebrates. Considerable evidence suggests that reduced exposure of tissue to IGF-I is associated with an extended lifespan in these species. In humans, IGF-I is linked to various age-related diseases that are limiting factors for youthful longevity. On one hand, reduced IGF-I activity is associated with significant morbidity in adulthood with an increased risk of developing cardiovascular disease, diabetes, osteoporosis and neurodegenerative diseases. On the other hand, elevated IGF-I levels have been linked to cancer risk given the role of IGF in mediating normal and malignant tissue growth. Thus, IGF is clearly involved in modulating disease of aging; however, the mechanism appears to be complex and interdependent on additional modulating factors. It is attractive to hypothesize that maximal human survival depends on tight regulation of the GH-IGF axis and maintenance of optimal IGF-I action in order to prevent morbidities associated with either deficient or excessive state. Specifically, it is possible that lower levels of IGF-I during early adulthood followed by higher levels of IGF-I later in life may be most beneficial for human longevity by addressing age-specific morbidities.