Insulin-like growth factors (IGFs): implications for aging

Differential Plasma Proteins Identified via iTRAQ-Based Analysis Serve as Diagnostic Markers of Pancreatic Ductal Adenocarcinoma

Objective

We aimed to identify differentially expressed proteins in the plasma of patients with pancreatic cancer and control subjects, which could serve as potential tumor biomarkers.

Methods

Differentially expressed proteins were determined via isostatic labeling and absolute quantification (iTRAQ). Potential protein biomarkers were identified via enzyme-linked immunosorbent assay (ELISA) in 40 patients and 40 control subjects, and those eventually selected were further validated in 40 pancreatic cancer and normal pancreatic tissues.

Results

In total, 30 proteins displayed significant differences in expression among which 21 were downregulated and 9 were upregulated compared with the control group. ELISA revealed downregulation of peroxiredoxin-2 (PRDX2) and upregulation of alpha-1-antitrypsin (AAT), Ras-related protein Rab-2B (RAB2B), insulin-like growth factor-binding protein 2 (IGFBP2), Rho-related GTP-binding protein RhoC (RHOC), and prelamin-A/C (LMNA) proteins in 40 other samples of pancreatic cancer. Notably, only AAT, RAB2B, and IGFBP2 levels were consistent with expression patterns obtained with iTRAQ. Moreover, all three proteins displayed a marked increase in pancreatic cancer tissues. Data from ROC curve analysis indicated that the diagnostic ability of AAT, RAB2B, and IGFBP2 combined with carbohydrate antigen 19-9 (CA19-9) for pancreatic cancer was significantly greater than that of the single indexes (area under the curve (AUC): 90% vs. 75% (CA19-9), 76% (AAT), 71% (RAB2B), and 71% (IGFBP2), all P < 0.01).

Conclusion

AAT, RAB2B, and IGFBP2 could serve as effective biomarkers to facilitate the early diagnosis of pancreatic cancer.

Potential Diagnostic and Monitoring Biomarkers of Obstructive Sleep Apnea-Umbrella Review of Meta-Analyses

Obstructive sleep apnea (OSA) is a prevalent, underdiagnosed disease that imposes a significant impact on the health and wellbeing of patients and a financial burden on individuals, their families, and society. Development of new methods of testing other than an overnight sleep study, such as measurement of serum or plasma biomarkers, may provide an easier diagnostic process to identify patients with OSA and allow earlier initiation of treatment, which might prevent serious comorbidities. We conducted a systematic review and quality assessment of available meta-analyses regarding potential diagnostic and monitoring biomarkers of obstructive sleep apnea. A total of 14 sets of candidate biomarkers displayed differences in levels or concentrations in OSA patients compared to non-OSA controls, and decreased after OSA treatment: CRP, IL-6, TNF-α, Il-8, HCY, ICAM-1, VCAM-1, VEGF, TC, LDLc, HDLc, TG, leptin, MDA, ALT, AST, IGF-1, adiponectin, and cortisol. This review summarizes the evidence for OSA-associated potential biomarkers and demonstrates that the quality of available studies, as measured by AMSTAR2, is often low and associated with a high risk of bias.

Serum Levels of Insulin-like Growth Factor 1 and Insulin-like Growth Factor-binding Protein 2 as a Novel Biomarker in the Detection of Pancreatic Adenocarcinoma

BACKGROUND

Insulin-like growth factor 1 (IGF-1) and insulin-like growth factor-binding protein 2 (IGFBP-2) are proteins that belong to the IGF axis, which is involved in glucose and lipid metabolism and may as well promote carcinogenesis.

GOALS

The aim of this study was to evaluate the serum concentration levels of IGF-1 and IGFBP-2 in patients with newly diagnosed pancreatic adenocarcinoma (PDAC) to verify their possible role in the diagnosis of the disease.

STUDY

The study included 69 patients with PDAC and 20 healthy controls. The concentrations of IGF-1 and IGFBP-2 were estimated by means of ELISA. The study protocol was approved by the Bioethics Committee at the Medical University of Lodz in Poland.

RESULTS

PDAC patients compared with controls have a significantly lower mean serum IGF-1 level (45.83±30.03 vs. 70.66±60.57 ng/mL; P<0.0001). In contrast, in PDAC patients, the mean IGFBP-2 level was significantly higher compared with the control group (225.06±86.37 vs. 51.92±29.40 ng/mL; P<0.0001). The results show that, at the 0.01 sensitivity level, the IGF-1/IGFBP-2 ratio <0.85 points indicates PDAC presence. At this level of sensitivity, the test has a specificity of 0.097 (α=0.01; β=0.097; IGF-1/IGFBP-2≤0.85).

CONCLUSIONS

Our results show that IGF-1 to IGFBP-2 ratio ≤0.85 may be a powerful PDAC indicator. Further studies in this area in a larger patient group are necessary to confirm our findings.

The associations of anthropometric, behavioural and sociodemographic factors with circulating concentrations of IGF-I, IGF-II, IGFBP-1, IGFBP-2 and IGFBP-3 in a pooled analysis of 16,024 men from 22 studies

Insulin-like growth factors (IGFs) and insulin-like growth factor binding proteins (IGFBPs) have been implicated in the aetiology of several cancers. To better understand whether anthropometric, behavioural and sociodemographic factors may play a role in cancer risk via IGF signalling, we examined the cross-sectional associations of these exposures with circulating concentrations of IGFs (IGF-I and IGF-II) and IGFBPs (IGFBP-1, IGFBP-2 and IGFBP-3). The Endogenous Hormones, Nutritional Biomarkers and Prostate Cancer Collaborative Group dataset includes individual participant data from 16,024 male controls (i.e. without prostate cancer) aged 22-89 years from 22 prospective studies. Geometric means of protein concentrations were estimated using analysis of variance, adjusted for relevant covariates. Older age was associated with higher concentrations of IGFBP-1 and IGFBP-2 and lower concentrations of IGF-I, IGF-II and IGFBP-3. Higher body mass index was associated with lower concentrations of IGFBP-1 and IGFBP-2. Taller height was associated with higher concentrations of IGF-I and IGFBP-3 and lower concentrations of IGFBP-1. Smokers had higher concentrations of IGFBP-1 and IGFBP-2 and lower concentrations of IGFBP-3 than nonsmokers. Higher alcohol consumption was associated with higher concentrations of IGF-II and lower concentrations of IGF-I and IGFBP-2. African Americans had lower concentrations of IGF-II, IGFBP-1, IGFBP-2 and IGFBP-3 and Hispanics had lower IGF-I, IGF-II and IGFBP-3 than non-Hispanic whites. These findings indicate that a range of anthropometric, behavioural and sociodemographic factors are associated with circulating concentrations of IGFs and IGFBPs in men, which will lead to a greater understanding of the mechanisms through which these factors influence cancer risk.

Analysis of Four Circulating Complexes of Insulin-Like Growth Factor Binding Proteins in Human Blood during Aging

The primary role of insulin-like growth factor binding proteins (IGFBPs) is to regulate availability of IGFs for interacting with receptors, but IGFBPs perform IGF-independent actions as well. The availability and activity of IGFBPs in the circulation is influenced primarily by their concentration and structural modifications, but possibly also by interaction with major plasma proteins such as transferrin, alpha-2-macroglobulin (α2M), and fibrinogen. Four types of circulating IGFBP complexes were examined in this study by immuno- and ligand-binding assays in adults of different age. The amounts of IGFBP-3/transferrin and IGFBP-1/fibrinogen complexes were similar in middle- and old-aged persons, whereas the amounts of IGFBP-1 (or -2)/α2M monomer complexes were lower in the old-aged group and negatively correlated with total IGFBP-1 (or -2) amounts in blood. In contrast to IGFBP-1, IGFBP-2 was present in significantly greater quantities in complexes with α2M dimer than α2M monomer in older individuals. IGFBP complexes did not bind ¹²⁵I-labeled IGF-I in amounts detectable by ligand blotting. According to the results of this study, the quantities of IGFBP-1 and IGFBP-2, which interact with α2M, are age-dependent and, in the case of complexes with α2M monomer, they are negatively correlated with the total circulating levels of these two IGFBPs.

Sex Differences in Age-Related Decline of Urinary Insulin-Like Growth Factor-Binding Protein-3 Levels in Adult Bonobos and Chimpanzees

There is increasing interest in the characterization of normative senescence in humans. To assess to what extent aging patterns in humans are unique, comparative data from closely related species, such as non-human primates, can be very useful. Here, we use data from bonobos and chimpanzees, two closely related species that share a common ancestor with humans, to explore physiological markers that are indicative of aging processes. Many studies on aging in humans focus on the somatotropic axis, consisting of growth hormone (GH), insulin-like growth factors (IGFs), and IGF binding proteins (IGFBPs). In humans, IGFBP-3 levels decline steadily with increasing age. We used urinary IGFBP-3 levels as an alternative endocrine marker for IGF-I to identify the temporal pattern known to be related with age-related changes in cell proliferation, growth, and apoptosis. We measured urinary IGFBP-3 levels in samples from 71 bonobos and 102 chimpanzees. Focusing on samples from individuals aged 10 years or older, we found that urinary IGFBP-3 levels decline in both ape species with increasing age. However, in both species, females start with higher urinary IGFBP-3 levels than males, experience a steeper decline with increasing age, and converge with male levels around the age of 30-35 years. Our measurements of urinary IGFBP-3 levels indicate that bonobos and chimpanzees mirror human patterns of age-related decline in IGFBP-3 in older individuals (<10 years) of both sexes. Moreover, such as humans, both ape species show sex-specific differences in IGFBP-3 levels with females having higher levels than males, a result that correlates with sex differences in life expectancy. Using changes in urinary IGFBP-3 levels as a proxy for changes in GH and IGF-I levels that mark age-related changes in cell proliferation, this approach provides an opportunity to investigate trade-offs in life-history strategies in cross-sectional and in longitudinal studies, both in captivity and in the wild.

Relationships between IGF-1, schizophrenia, and treatment of metabolic syndrome

OBJECTIVES

The use of atypical antipsychotic drugs in patients with psychiatric illness may result in dyslipidemia, hypertension, glucose intolerance, and abdominal obesity, which are together referred to as metabolic syndrome (MS). To investigate any correlations among insulin-like growth factor-1 (IGF-1), schizophrenia, and MS, we examined the metabolic profiles of patients with schizophrenia taking atypical antipsychotics.

DESIGN

Patients with schizophrenia, their siblings, and controls participated in this study (N=50 in each group). The Structured Clinical Interview for DSM-IV Axis 1 Disorders (SCID I) and the Brief Psychiatric Rating Scale (BPRS) were administered to patients, and SCID I was administered to patients' siblings. We drew blood to measure IGF-1 levels and to determine the metabolic profiles of all participants; we also conducted anthropometric measurements.

RESULTS

There were no significant differences in IGF-1 levels between groups. By comparing IGF-1 levels with MS-related parameters, we found that IGF-1 levels were negatively correlated with triglyceride levels in the control group, and positively correlated with HDL levels in the patient group (Pearson's correlation: r=-0.291, P=0.04, and r=0.328, P=0.02, respectively). Compared to their siblings, patients with schizophrenia had a significantly different body mass index, waist circumference, and insulin resistance, and showed a trend toward a difference in glucose levels (ANOVA: P=0.004, P<0.0001, P=0.004, P=0.072, respectively).

CONCLUSION

A correlation between IGF-1 and MS may significantly influence future therapeutic strategies for MS. In order to determine the role of IGF-1 in schizophrenia, comprehensive longitudinal studies with first-episode drug-naive patients are needed.

Insulin-like growth factor I and Alzheimer´s disease: therapeutic prospects?

The search for a cure of Alzheimer's dementia is restless. In recent years, unexpected epidemiological data showing a protective effect of anti-inflammatory and cholesterol-lowering drugs gave way to clinical trials with these compounds. Now, a newly described mechanism indicating that brain amyloid clearance is modulated by serum insulin-like growth factor I may also lead to new trials with this growth factor. Insulin-like growth factor I is an abundant circulating hormone with potent central actions whose levels in serum appear to be altered in Alzheimer's patients. Amyloid clearance, a potential therapeutic target in Alzheimer's disease was mostly neglected until recent antiamyloid therapies proved to involve a peripheral amyloid sink. Although more work in animal models are required, the evidence available strongly indicates that insulin-like growth factor I therapy in Alzheimer's dementia may be addressing pathogenic processes.

Insulin-like growth factor-(IGF)-axis, inflammation, and glucose intolerance among older adults

Increasing evidence suggests that the insulin-like growth factor (IGF)-axis may play a role in glucose metabolism and may also be associated with systemic inflammation. The aim of this study was to evaluate the association of insulin-like growth factor-1 (IGF-I) and its binding proteins, IGFBP-1 and IGFBP-3, with glucose intolerance and inflammation among older adults. We conducted a cross-sectional analysis in a in a random subsample (n=922) of the Cardiovascular Health Study (CHS), a prospective cohort of men and women > or = 65 years. Mean IGFBP-1 levels were significantly lower in older adults with impaired glucose tolerance (IGT), impaired fasting glucose (IFG) and diabetes compared to those with normal fasting and post-load glucose. High IGFBP-1 was associated with a reduced prevalence of IGT and IFG; the multivariable OR between extreme quartiles of IGFBP-1 was 0.60 (95% CI: 0.37, 0.95; p-trend: 0.03) for IGT and 0.41 (95% CI: 0.26, 0.64; p-trend: <0.01) for IFG. We did not find any significant association between IGF-I and glucose intolerance in this study and the association for IGFBP-3 was less clear. However, low levels of IGF-I and IGFBP-3 were associated with increased levels of markers of inflammation including C-reactive protein and interleukin-6 levels. We conclude that among adults > or = 65 years, low IGFBP-1 levels are associated with increased prevalence of glucose intolerance. We did not confirm prior associations of low IGF-I with glucose intolerance in this cohort of older individuals.

A study of anthropomorphic and biochemical characteristics in girls with central precocious puberty and thelarche variant

BACKGROUND

Premature thelarche in later childhood may progress to central precocious puberty (CPP), which does not spontaneously resolve. Thelarche variant (TV) is a slowly progressive variant of precocious puberty.

AIM

To determine and compare levels of insulin-like growth factor-I (IGF-I), IGF binding protein-3 (IGFBP-3) and anthropomorphic measures in girls with TV and CPP.

SUBJECTS

Prepubertal controls and girls with TV and CPP.

METHODS

Chronological and bone age, weight, height, BMI, height velocity (HV), and serum IGF-I, IGFBP-3, leptin, follicle-stimulating hormone (FSH) and lutenizing hormone (LH) levels were assessed.

RESULTS

Serum IGF-I levels, HV and IGF-I/ IGFBP-3 ratio were significantly higher in girls with CPP compared to both controls and girls with TV. IGFBP-3 values for bone age (IGFBP-3BA) were significantly higher in the TV group compared to both controls and girls with CPP. FSH and LH concentrations were significantly higher in the CPP group compared to TV.

CONCLUSION

HV, IGF-I, LH and FSH levels and IGF-I/IGFBP-3 ratio are elevated in girls with CPP compared to those with TV.

Timing of puberty determines serum insulin-like growth factor-I in late adulthood

CONTEXT

IGFs may play an important role in disease etiology, especially cancer. Changes in diet can alter acute levels, but little is known about life course influences on IGF levels.

OBJECTIVE

The objective of the study was to examine the association between timing of puberty and adulthood serum IGFs (IGF-I and IGF binding protein-3).

DESIGN

This was a retrospective cohort study.

SETTING

Male pupils who attended a single school in Southern England were part of the study.

PARTICIPANTS

Participants in the study were a cohort of 1028 men born between 1927 and 1956 with anthropometric measures between 9 and 18 yr and adulthood serum IGF levels.

MAIN OUTCOME MEASURE

The study measured serum IGF-I and IGF binding protein-3 at mean age 63 yr.

RESULTS

Age at peak height velocity (APHV) was inversely associated with adult IGF-I levels. IGF-I decreased by 3.7 ng/ml (95% confidence interval 1.0-6.4, P = 0.007) for each sd increase in APHV. Prepubertal childhood height and body mass index were both inversely associated with APHV (P trend < 0.001). APHV was positively associated with adult height and inversely associated with adult body mass index. Adjustment for childhood, adult anthropometry, and other lifestyle factors did not substantially alter the association between APHV and adult IGF-I.

CONCLUSIONS

This is the first study to document an association between timing of puberty and adult IGF-I levels. A better understanding of life course determinants of the IGF system may provide new insights into disease etiology and primary prevention.

Age-associated changes of insulin action on the hydrolysis of diacylglycerol generated from phosphatidic acid

Age-related changes in insulin action on diacylglycerol (DAG) degradation was studied in rat cerebral cortex synaptosomes. The generation of monoacylglycerol (MAG) and water soluble products (WSP, glycerol plus glycerol-3-phosphate) from DAG was studied in cerebral cortex (CC) synaptosomes from adult (4-month-old) and aged (28-month-old) rats. Additionally, the effect of porcine insulin and tyrosine phosphorylation was evaluated in the same group of animals. In this study we demonstrate that the age-related increase in WSP generation was accompanied by unmodified MAG levels. In the presence of diacylglycerol lipase (DAG lipase) inhibitor, RHC-80267, a lower inhibitory effect on MAG production was observed in CC synaptosomes from aged rats with respect to that in adult membranes. Under these experimental conditions, WSP formation was only diminished in aged membranes. Insulin stimulated MAG and WSP formation at long incubation times (30 min) in adult animals, while it had an inhibitory effect in aged animals. Insulin plus vanadate (as tyrosine-phosphatase inhibitor) inhibited MAG production at short incubation times whereas the same effect was observed in aged animals at long times of incubation. WSP formation was stimulated by insulin plus vanadate both in adult and aged animals at 30 min of incubation. Our results show that insulin differentially modulates MAG and WSP production from exogenous PA in CC synaptosomes from aged rats compared with adult rats.

Endurance exercise regimens induce differential effects on brain-derived neurotrophic factor, synapsin-I and insulin-like growth factor I after focal ischemia

The optimal amount of endurance exercise required to elevate proteins involved in neuroplasticity during stroke rehabilitation is not known. This study compared the effects of varying intensities and durations of endurance exercise using both motorized and voluntary running wheels after endothelin-I-induced focal ischemia in rats. Hippocampal levels of brain-derived neurotrophic factor, insulin-like growth factor I and synapsin-I were elevated in the ischemic hemisphere even in sedentary animals suggesting an intrinsic restorative response 2 weeks after ischemia. In the sensorimotor cortex and the hippocampus of the intact hemisphere, one episode of moderate walking exercise, but not more intense running, resulted in the greatest increases in levels of brain-derived neurotrophic factor and synapsin-I. Exercise did not increase brain-derived neurotrophic factor, insulin-like growth factor I or synapsin-I in the ischemic hemisphere. In voluntary running animals, both brain and serum insulin-like growth factor I appeared to be intensity dependent and were associated with decreasing serum levels of insulin-like growth factor I and increasing hippocampal levels of insulin-like growth factor I in the ischemic hemisphere. This supports the notion that exercise facilitates the movement of insulin-like growth factor I across the blood-brain barrier. Serum corticosterone levels were elevated by all exercise regimens and were highest in rats exposed to motorized running of greater speed or duration. The elevation of corticosterone did not seem to alter the expression of the proteins measured, however, graduated exercise protocols may be indicated early after stroke. These findings suggest that relatively modest exercise intervention can increase proteins involved in synaptic plasticity in areas of the brain that likely subserve motor relearning after stroke.

Adult neurogenesis: from precursors to network and physiology

The discovery that the adult mammalian brain creates new neurons from pools of stemlike cells was a breakthrough in neuroscience. Interestingly, this particular new form of structural brain plasticity seems specific to discrete brain regions, and most investigations concern the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampal formation (HF). Overall, two main lines of research have emerged over the last two decades: the first aims to understand the fundamental biological properties of neural stemlike cells (and their progeny) and the integration of the newly born neurons into preexisting networks, while the second focuses on understanding its relevance in brain functioning, which has been more extensively approached in the DG. Here, we propose an overview of the current knowledge on adult neurogenesis and its functional relevance for the adult brain. We first present an analysis of the methodological issues that have hampered progress in this field and describe the main neurogenic sites with their specificities. We will see that despite considerable progress, the levels of anatomic and functional integration of the newly born neurons within the host circuitry have yet to be elucidated. Then the intracellular mechanisms controlling neuronal fate are presented briefly, along with the extrinsic factors that regulate adult neurogenesis. We will see that a growing list of epigenetic factors that display a specificity of action depending on the neurogenic site under consideration has been identified. Finally, we review the progress accomplished in implicating neurogenesis in hippocampal functioning under physiological conditions and in the development of hippocampal-related pathologies such as epilepsy, mood disorders, and addiction. This constitutes a necessary step in promoting the development of therapeutic strategies.

The Choroid Plexus‐Cerebrospinal Fluid System: From Development to Aging

The function of the cerebrospinal fluid (CSF) and the tissue that secretes it, the choroid plexus (CP), has traditionally been thought of as both providing physical protection to the brain through buoyancy and facilitating the removal of brain metabolites through the bulk drainage of CSF. More recent studies suggest, however, that the CP-CSF system plays a much more active role in the development, homeostasis, and repair of the central nervous system (CNS). The highly specialized choroidal tissue synthesizes trophic and angiogenic factors, chemorepellents, and carrier proteins, and is strategically positioned within the ventricular cavities to supply the CNS with these biologically active substances. Through polarized transport systems and receptor-mediated transcytosis across the choroidal epithelium, the CP, a part of the blood-CSF barrier (BCSFB), controls the entry of nutrients, such as amino acids and nucleosides, and peptide hormones, such as leptin and prolactin, from the periphery into the brain. The CP also plays an important role in the clearance of toxins and drugs. During CNS development, CP-derived growth factors, such as members of the transforming growth factor-beta superfamily and retinoic acid, play an important role in controlling the patterning of neuronal differentiation in various brain regions. In the adult CNS, the CP appears to be critically involved in neuronal repair processes and the restoration of the brain microenvironment after traumatic and ischemic brain injury. Furthermore, recent studies suggest that the CP acts as a nursery for neuronal and astrocytic progenitor cells. The advancement of our knowledge of the neuroprotective capabilities of the CP may therefore facilitate the development of novel therapies for ischemic stroke and traumatic brain injury. In the later stages of life, the CP-CSF axis shows a decline in all aspects of its function, including CSF secretion and protein synthesis, which may in themselves increase the risk for development of late-life diseases, such as normal pressure hydrocephalus and Alzheimer's disease. The understanding of the mechanisms that underlie the dysfunction of the CP-CSF system in the elderly may help discover the treatments needed to reverse the negative effects of aging that lead to global CNS failure.

Role of serum insulin-like growth factor I in mammalian brain aging

Modern societies face new public health challenges associated with an increasingly aging population. Among these, pathological conditions linked to brain aging are paramount. Old age is a risk factor for important neurological impairments such as Alzheimer's disease or stroke. Even healthy elderly people usually present with milder forms of cognitive decline. This is possibly related to less-pronounced brain deficits seen in normal aging, including the shrinkage of neurons and the dense network of neurons and glia in the central nervous system known as the neuropil, a lower neurogenetic rate, impaired angiogenesis or brain accumulation of deleterious compounds. At least in mammals, age is also associated with a decline in insulin-like growth factor-I (IGF-I) levels, a well-known neuroprotective agent. Recently, a relationship between serum IGF-I and "house-keeping" mechanisms in the brain has been evidenced in laboratory rodents. Serum IGF-I increases adult neurogenesis, sustains neuronal health through a variety of fundamental homeostatic mechanisms, participates in brain angiogenesis, contributes to brain beta-amyloid clearance and affects learning and memory. Overall, diminished trophic input resulting from decreasing serum IGF-I levels during aging likely contributes to brain senescence in mammals.

Spatial memory performances of aged rats in the water maze predict levels of hippocampal neurogenesis

Neurogenesis occurs within the adult dentate gyrus of the hippocampal formation and it has been proposed that the newly born neurons, recruited into the preexistent neuronal circuits, might be involved in hippocampal-dependent learning processes. Age-dependent spatial memory impairments have been related to an alteration in hippocampal plasticity. The aim of the current study was to examine whether cognitive functions in aged rats are quantitatively correlated with hippocampal neurogenesis. To this end, we took advantage of the existence of spontaneous individual differences observed in aged subjects in a hippocampal-dependent task, the water maze. We expected that the spatial memory capabilities of aged rats would be related to the levels of hippocampal neurogenesis. Old rats were trained in the water maze, and, 3 weeks after training, rats were injected with 5-bromo-2'-deoxyuridine (BrdUrd, 50 or 150 mg/kg) to label dividing cells. Cell proliferation was examined one day after the last BrdUrd injection, whereas cell survival and differentiation were determined 3 weeks later. It is shown that a quantitative relationship exists between learning and the number of newly generated neurons. Animals with preserved spatial memory, i.e., the aged-unimpaired rats, exhibited a higher level of cell proliferation and a higher number of new neurons in comparison with rats with spatial memory impairments, i.e., the aged-impaired rats. In conclusion, the extent of memory dysfunction in aged rats is quantitatively related to the hippocampal neurogenesis. These data reinforce the assumption that neurogenesis is involved in memory processes and aged-related cognitive alterations.

Impact of growth hormone resistance on female reproductive function: new insights from growth hormone receptor knockout mice

We examined multiple aspects of reproductive function in growth hormone receptor gene knockout (GHR-KO) and normal mice to clarify the role of growth hormone in female reproduction. In adult animals, estrous cycle duration was comparable in all mice housed individually but was significantly longer in group-housed GHR-KO females. Histological evaluation of ovaries of adult females at estrus showed that the numbers of preovulatory follicles and corpora lutea were significantly reduced in GHR-KO mice, as was the plasma estradiol level. The number of atretic preovulatory follicles was reduced in GHR gene-ablated animals. Although reverse transcription polymerase chain reaction analysis revealed reduced ovarian insulin-like growth factor I (IGF-I) mRNA expression in GHR-KO females, the expression of several steroidogenic enzyme mRNAs did not differ between groups. The numbers of active corpora lutea and uterine implantation sites were reduced in GHR-KO females at Day 7 of gestation. When young females were mated to normal males, latency to first mating and age of the female at first mating were significantly delayed in GHR-KO females, but maternal age at first conception was similar between groups. Significantly fewer virgin GHR-KO females exhibited pseudopregnancies when initially placed with vasectomized normal males than did normal female counterparts. Growth hormone resistance and IGF-I insufficiency negatively impacted 1) follicular development/ovulation rate, 2) sexual maturation, 3) production of and responsiveness to pheromonal signals, and 4) the ability of virgin females to respond to coitus by activation of luteal function. Although GHR-KO female mice are fertile, they exhibit quantitative deficits in various parameters of reproductive function.

Circulating insulin-like growth factor I mediates exercise-induced increases in the number of new neurons in the adult hippocampus

Although the physiological significance of continued formation of new neurons in the adult mammalian brain is still uncertain, therapeutic strategies aimed to potentiate this process show great promise. Several external factors, including physical exercise, increase the number of new neurons in the adult hippocampus, but underlying mechanisms are not yet known. We recently found that exercise stimulates uptake of the neurotrophic factor insulin-like growth factor I (IGF-I) from the bloodstream into specific brain areas, including the hippocampus. In addition, IGF-I participates in the effects of exercise on hippocampal c-fos expression and mimics several other effects of exercise on brain function. Because subcutaneous administration of IGF-I to sedentary adult rats markedly increases the number of new neurons in the hippocampus, we hypothesized that exercise-induced brain uptake of blood-borne IGF-I could mediate the stimulatory effects of exercise on the adult hippocampus. Thus, we blocked the entrance of circulating IGF-I into the brain by subcutaneous infusion of a blocking IGF-I antiserum to rats undergoing exercise training. The resulting inhibition of brain uptake of IGF-I was paralleled by complete inhibition of exercise-induced increases in the number of new neurons in the hippocampus. Exercising rats receiving an infusion of nonblocking serum showed normal increases in the number of new hippocampal neurons after exercise. Thus, increased uptake of blood-borne IGF-I is necessary for the stimulatory effects of exercise on the number of new granule cells in the adult hippocampus. Taken together with previous results, we conclude that circulating IGF-I is an important determinant of exercise-induced changes in the adult brain.

Transgenic mice overexpressing insulin-like growth factor-II in beta cells develop type 2 diabetes

During embryonic development, insulin-like growth factor-II (IGF-II) participates in the regulation of islet growth and differentiation. We generated transgenic mice (C57BL6/SJL) expressing IGF-II in beta cells under control of the rat Insulin I promoter in order to study the role of islet hyperplasia and hyperinsulinemia in the development of type 2 diabetes. In contrast to islets from control mice, islets from transgenic mice displayed high levels of IGF-II mRNA and protein. Pancreases from transgenic mice showed an increase in beta-cell mass (about 3-fold) and in insulin mRNA levels. However, the organization of cells within transgenic islets was disrupted, with glucagon-producing cells randomly distributed throughout the core. We also observed enhanced glucose-stimulated insulin secretion and glucose utilization in islets from transgenic mice. These mice displayed hyperinsulinemia, mild hyperglycemia, and altered glucose and insulin tolerance tests, and about 30% of these animals developed overt diabetes when fed a high-fat diet. Furthermore, transgenic mice obtained from the N1 backcross to C57KsJ mice showed high islet hyperplasia and insulin resistance, but they also developed fatty liver and obesity. These results indicate that local overexpression of IGF-II in islets might lead to type 2 diabetes and that islet hyperplasia and hypersecretion of insulin might occur early in the pathogenesis of this disease.

Actions and interactions of the IGF system in Alzheimer's disease: review and hypotheses

Insulin-like growth factors (IGF) are pleiotrophic polypeptides affecting all aspects of growth and development. The IGF system, including ligands, receptors, binding proteins and proteases is also involved in pathophysiological conditions, such as cancer and degenerative conditions. In this review, the actions and interactions of the IGF system as it relates to Alzheimer's disease will be investigated.

Insulin-like growth factor binding proteins in cerebrospinal fluid during human development and aging

We analyzed samples of insulin-like growth factor binding proteins (IGFBPs) in human cerebrospinal fluid (CSF) in neurologically normal patients from one day after birth to age 76 years. CSF samples were separated on SDS-PAGE and then transferred to nitrocellulose membranes where IGFBPs were detected by Western ligand blot using [(125)I]-IGF-II, confirming other reports where we found the presence of IGFBP-2, 3, 4, 5. The 34 kDa IGFBP-2 was present in all samples, and progressively decreased with age. A broad 28- to 30-kDa IGFBP band, having the appearance of IGFBP-5, was triphasic: faint during infancy, barely detectable at 6 months, but intense in adult and aged individuals. The 24-kDa IGFBP-4 band was only seen in neonatal CSF samples, while the IGFBP-3 doublet gradually increased during aging. Thus, these present results show that IGFBP-2, 3, 4 and 5 in CSF are developmentally regulated, suggesting roles for these molecules in the development of the nervous system.

Actions of dehydroepiandrosterone and its sulfate in the central nervous system: effects on cognition and emotion in animals and humans

Dehydroepiandrosterone (DHEA) and its sulfate ester, DHEAS, exert multiple effects in the rodent central nervous system (CNS). Most of them seem to be mediated through their non-genomic action on several neurotransmitter receptors. DHEA(S) increases neuronal excitability, enhances neuronal plasticity and also has neuroprotective properties. In line with these observations DHEA(S) treatment in rodents enhances memory in several paradigms. Even more studies show antiamnestic effects of the steroids. However, DHEA(S) has also anxiolytic and anti-aggressive properties. In humans cross-sectional and longitudinal studies suggest that DHEAS might be associated with global measures of well-being and functioning; however, a relationship with cognition could not be detected to date. Moreover, studies investigating DHEAS levels in neurodegenerative diseases have produced conflicting results. Experimental studies in elderly humans have revealed preliminary evidence for mood enhancing and antidepressant effects of DHEA treatment, while positive effects on measures of memory and attention could not be found. However, electrophysiological studies demonstrated that DHEA treatment has effects on the human CNS. Several reasons for the discrepancy between data obtained in rodents and humans are discussed and research perspectives are outlined which might help to improve interpretation of results obtained in the two species.

Effect of fenretinide on plasma IGF-I and IGFBP-3 in early breast cancer patients

Growing evidence substantiates the role of the insulin-like growth factor I (IGF-1) system in breast tumorigenesis. Retinoids have been shown to affect the IGF system several experimental models. We extended our previous data on plasma IGF-1 modulation by the synthetic retinoid fenretinide (4-HPR) and investigated the effect of the retinoid on plasma IGF binding protein (BP)-3, the major protein binding IGFs. IGF-1 and IGFBP-3 were measured on plasma samples obtained at randomization and after an interval of approximately 1 year, from 39 and 33 stage 1 breast cancer patients assigned to receive 4-HPR, and from 39 and 34 untreated controls, respectively. There was a significant decrease in plasma IGF-1 after 4-HPR administration, whereas no significant change was observed in controls. The effect of 4-HPR on IGF-1 levels was modified by menopausal status, inasmuch as the decrease in IGF-1 was particularly pronounced in pre-menopausal women, whereas the reverse was observed in untreated controls. By contrast, treatment induced an increase of IGFBP-3 with respect to controls. As a result of this dual effect, the bioavailability of IGF-1 for interaction with receptors at target levels further decreased in pre-menopausal 4-HPR treated patients compared with controls, suggesting that retinoid administration may result in lower concentrations of biologically active IGF-1. Our findings may have important implications for the clinical preventive activity of this retinoid.

Serum free IGF-I, total IGF-I, IGFBP-1 and IGFBP-3 levels in an elderly population: relation to age and sex steroid levels

BACKGROUND

Most previous studies concerning the relationship between IGF-I and age used assays measuring total IGF-I. Although free IGF-I is considered of greater biological relevance, little is known about its relationship with sex steroids levels in elderly healthy subjects.

MEASUREMENTS

In a cross-sectional study of 218 healthy people (103 men, 115 women) aged 55-80 years we measured serum total and free IGF-I, IGFBP-1 and IGFBP3 levels and sex steroids. Free androgen index and free oestradiol index were used as an indicator for free oestradiol and free testosterone levels, respectively.

RESULTS

Free IGF-I levels did not decline with age in the whole study population. Free IGF-I levels even increased in individuals above 70 years of age in comparison to those aged between 55 and 70 years (mean +/- SE 0.106 +/- 0.007 nmol/l vs. 0.086 +/- 0.004 nmol/l, P = 0.009). Total IGF-I and IGFBP-3 decreased with age (r = -0.20, P = 0.005 and r = -0.24, P = 0.001, respectively). Total IGF-I levels were positively related with free oestrogen index in both sexes. Free IGF-I did not relate to free oestrogen or androgen index. In women only, free IGF-I was related positively with DHEAS while IGFBP-1 was inversely correlated with DHEAS.

CONCLUSIONS

Free IGF-I levels do not decrease with age and are even higher in individuals above 70 years. There was no relationship between free IGF-I and free androgen or oestrogen index in either gender. We hypothesize that higher free IGF-I levels in older persons may be the consequence of selective survival in the cohort: subjects with high free IGF-I levels may live longer. The absence of a relationship between free IGF-I levels and free androgen and oestrogen indices suggests that there is no direct interaction between the biological activity of circulating IGF-I levels and sex hormone production in a healthy ageing population.

Hepatic overexpression of insulin-like growth factor-II in adulthood increases basal and insulin-stimulated glucose disposal in conscious mice

The physiological role of circulating insulin-like growth factor-II (IGF-II) in adult humans is poorly understood. We recently generated an IGF-II transgenic murine model of persistent IGF-II production (plasma IGF-II approximately 30-fold increased above normal) through over-expression of the transgene driven by the major urinary protein promoter (Rinderknecht, E., and Humbel, R. E. (1978) J. Biol. Chem. 269, 13779-13784). To determine whether in vivo insulin action is improved in these transgenic mice, we performed euglycemic insulin (18 milliunits/kg.min) clamp studies in conscious IGF-II transgenic and in age- and weight-matched control mice. Plasma glucose and insulin concentrations were significantly lower in the IGF-II transgenic compared with both control grouoff Despite decreased plasma glucose concentration, basal hepatic glucose production (HGP) and glucose clearance were increased. During the insulin clamp studies in IGF-II transgenic mice compared with control mice (a) the rates of glucose infusion and glucose uptake were increased by approximately by 65 and approximately 55%, respectively; (b) glycolysis was increased by approximately 12% while glycogen synthesis was approximately 2-fold higher; (c) while the suppression of plasma free fatty acid was similar, the increment in plasma lactate concentration was significantly higher; (d) although HGP was similarly inhibited by insulin, phosphoenolpyruvate gluconeogenesis was enhanced and accounted for a larger portion of HGP (64% versus approximately 40% in control mice). Our data suggest that the persistence of circulating IGF-II in adult mice to levels commonly observed in adult humans (50-70 nM) causes a marked improvement in peripheral (skeletal muscle) insulin action, which is not due to changes in body composition. These results suggest that circulating IGF-II may exert a regulatory role on insulin sensitivity and body composition in humans.