Plasma IGF-I levels and cognitive performance in older women

The neurobiology of insulin-like growth factor I: From neuroprotection to modulation of brain states

After decades of research in the neurobiology of IGF-I, its role as a prototypical neurotrophic factor is undisputed. However, many of its actions in the adult brain indicate that this growth factor is not only involved in brain development or in the response to injury. Following a three-layer assessment of its role in the central nervous system, we consider that at the cellular level, IGF-I is indeed a bona fide neurotrophic factor, modulating along ontogeny the generation and function of all the major types of brain cells, contributing to sculpt brain architecture and adaptive responses to damage. At the circuit level, IGF-I modulates neuronal excitability and synaptic plasticity at multiple sites, whereas at the system level, IGF-I intervenes in energy allocation, proteostasis, circadian cycles, mood, and cognition. Local and peripheral sources of brain IGF-I input contribute to a spatially restricted, compartmentalized, and timed modulation of brain activity. To better define these variety of actions, we consider IGF-I a modulator of brain states. This definition aims to reconcile all aspects of IGF-I neurobiology, and may provide a new conceptual framework in the design of future research on the actions of this multitasking neuromodulator in the brain.

Cyclic Glycine-Proline (cGP) Normalises Insulin-Like Growth Factor-1 (IGF-1) Function: Clinical Significance in the Ageing Brain and in Age-Related Neurological Conditions

Insulin-like growth factor-1 (IGF-1) function declines with age and is associated with brain ageing and the progression of age-related neurological conditions. The reversible binding of IGF-1 to IGF binding protein (IGFBP)-3 regulates the amount of bioavailable, functional IGF-1 in circulation. Cyclic glycine-proline (cGP), a metabolite from the binding site of IGF-1, retains its affinity for IGFBP-3 and competes against IGF-1 for IGFBP-3 binding. Thus, cGP and IGFBP-3 collectively regulate the bioavailability of IGF-1. The molar ratio of cGP/IGF-1 represents the amount of bioavailable and functional IGF-1 in circulation. The cGP/IGF-1 molar ratio is low in patients with age-related conditions, including hypertension, stroke, and neurological disorders with cognitive impairment. Stroke patients with a higher cGP/IGF-1 molar ratio have more favourable clinical outcomes. The elderly with more cGP have better memory retention. An increase in the cGP/IGF-1 molar ratio with age is associated with normal cognition, whereas a decrease in this ratio with age is associated with dementia in Parkinson disease. In addition, cGP administration reduces systolic blood pressure, improves memory, and aids in stroke recovery. These clinical and experimental observations demonstrate the role of cGP in regulating IGF-1 function and its potential clinical applications in age-related brain diseases as a plasma biomarker for-and an intervention to improve-IGF-1 function.

Association of Body Mass Index and Plant-Based Diet with Cognitive Impairment among Older Chinese Adults: A Prospective, Nationwide Cohort Study

To examine the association of body mass index (BMI) and a plant-based diet (PBD) with cognitive impairment in older adults, this cohort study used data from the Chinese Longitudinal Healthy Longevity Survey (CLHLS), a national, community-based, longitudinal, prospective study in China. Cognitive function was evaluated via the Mini-Mental State Examination (MMSE). Diet was assessed using a simplified food frequency questionnaire (FFQ), and PBD patterns were estimated using the overall plant-based diet index (PDI), the healthful plant-based diet index (hPDI), and the unhealthful plant-based diet index (uPDI). BMI was measured objectively during the physical examination. Cox proportional hazard models and restricted cubic spline analyses were used. A total of 4792 participants with normal cognition at baseline were included, and 1077 participants were identified as having developed cognitive impairment during the 24,156 person-years of follow-up. A reverse J-shaped association was observed between BMI and cognitive impairment (p = 0.005 for nonlinearity). Participants who were overweight (HR = 0.79; 95% CI 0.66–0.95) and obese (HR = 0.72; 95% CI 0.54–0.96) had a decreased risk of cognitive impairment, while those who were underweight (HR = 1.42; 95% CI 1.21–1.66) had an increased risk. Lower PDI, lower hPDI, and higher uPDI were associated with an increased risk of cognitive impairment (HR = 1.32; 95% CI 1.16–1.50 for PDI; HR = 1.46; 95% CI 1.29–1.66 for hPDI; HR = 1.21; 95% CI 1.06–1.38 for uPDI). The protective effect of being overweight on cognitive impairment was more pronounced among participants with a higher PDI (HR = 0.74; 95% CI 0.57–0.95) than those with a lower PDI (HR = 0.87; 95% CI 0.67–1.12), among participants with a higher hPDI (HR = 0.73; 95% CI 0.57–0.94) than those with a lower hPDI (HR = 0.93; 95% CI 0.72–1.10), and among participants with a lower uPDI (HR = 0.61; 95% CI 0.46–0.80) than those with a higher uPDI (HR = 1.01; 95% CI 0.80–1.27). Our results support the positive associations of overweight status, obesity, an overall PBD, and a healthful PBD with cognitive function in older adults. A lower adherence to an overall PBD, a healthful PBD, and a higher adherence to an unhealthful PBD may attenuate the protective effect of being overweight on cognitive function.

Weight spectrum and executive function in adolescents: the moderating role of negative emotions

BACKGROUND

While recent works suggested that overweight/obesity may impair executive function (EF), the overweight/obesity-EF relationship has not been well studied in adolescents. Furthermore, no research has investigated adolescent EF impairments across the weight spectrum (e.g., underweight or thinness, normal, overweight/obesity), especially those with underweight condition, with the moderating effect of negative emotions in the weight-EF association being limitedly investigated. We aimed to determine whether overall and abdominal weight spectrum associated with EF impairments and to identity whether negative emotions moderate the weight-EF link in adolescents.

METHODS

We applied a subsample of the SCHEDULE-A project. Adolescents (11-18 years) were recruited using a multi-stage cluster random sampling approach. We measured the overall and abdominal weight spectrum by body mass index z-score and waist-to-height ratio, respectively. We used the Behavior Rating Inventory of Executive Function (BRIEF) to evaluate adolescent EF in nature setting, and utilized the Depression Anxiety and Stress Scales (DASS-21) to assess three types of negative emotional status (i.e., depression, anxiety, and stress).

RESULTS

Of the 1935 adolescents, 963 (49.8%) were male. We observed that abdominal, not overall, overweight was associated with the Global Executive Composite (GEC) impairment (OR = 1.59, 95% CI 1.07-2.35), particularly for inhibit, emotion control, shift, working memory, and monitor domains. Furthermore, depression moderated the abdominal overweight-GEC association (P = 0.032 for interaction term), especially for emotional control, working memory, and initiate dimensions. Moreover, we also found abdominal thinness was associated with the Metacognition Index problem (OR = 1.33, 95% CI 1.04-1.72), particularly for plan and monitor areas.

CONCLUSIONS

Both abdominal overweight and thinness were associated with adolescent EF, and depression would be a modifiable target to improve EF in adolescents with abdominal overweight. Future longitudinal studies are needed to investigate the causal relationship between abdominal weight spectrum and EF, as well as the underlying mechanisms among adolescents suffering from depression.

From Menopause to Neurodegeneration-Molecular Basis and Potential Therapy

The impacts of menopause on neurodegenerative diseases, especially the changes in steroid hormones, have been well described in cell models, animal models, and humans. However, the therapeutic effects of hormone replacement therapy on postmenopausal women with neurodegenerative diseases remain controversial. The steroid hormones, steroid hormone receptors, and downstream signal pathways in the brain change with aging and contribute to disease progression. Estrogen and progesterone are two steroid hormones which decline in circulation and the brain during menopause. Insulin-like growth factor 1 (IGF-1), which plays an import role in neuroprotection, is rapidly decreased in serum after menopause. Here, we summarize the actions of estrogen, progesterone, and IGF-1 and their signaling pathways in the brain. Since the incidence of Alzheimer’s disease (AD) is higher in women than in men, the associations of steroid hormone changes and AD are emphasized. The signaling pathways and cellular mechanisms for how steroid hormones and IGF-1 provide neuroprotection are also addressed. Finally, the molecular mechanisms of potential estrogen modulation on N-methyl-d-aspartic acid receptors (NMDARs) are also addressed. We provide the viewpoint of why hormone therapy has inconclusive results based on signaling pathways considering their complex response to aging and hormone treatments. Nonetheless, while diagnosable AD may not be treatable by hormone therapy, its preceding stage of mild cognitive impairment may very well be treatable by hormone therapy.

Investigating the Relationship Between IGF-I, IGF-II, and IGFBP-3 Concentrations and Later-Life Cognition and Brain Volume

BACKGROUND

The insulin/insulin-like signaling (IIS) pathways, including insulin-like growth factors (IGFs), vary with age. However, their association with late-life cognition and neuroimaging parameters is not well characterized.

METHODS

Using data from the British 1946 birth cohort, we investigated associations of IGF-I, IGF-II and IGF binding protein 3 (IGFBP-3; measured at 53 and 60-64 years of age) with cognitive performance [word-learning test (WLT) and visual letter search (VLS) at 60-64 years and 69 years of age] and cognitive state [Addenbrooke's Cognitive Exam III (ACE-III) at 69-71 years of age], and in a proportion, quantified neuroimaging measures [whole brain volume (WBV), white matter hyperintensity volume (WMHV), hippocampal volume (HV)]. Regression models included adjustments for demographic, lifestyle, and health factors.

RESULTS

Higher IGF-I and IGF-II at 53 years of age was associated with higher ACE-III scores [ß 0.07 95% confidence interval (CI) (0.02, 0.12); scoreACE-III 89.48 (88.86, 90.1), respectively). IGF-II at 53 years of age was additionally associated with higher WLT scores [scoreWLT 20 (19.35, 20.65)]. IGFBP-3 at 60 to 64 years of age was associated with favorable VLS score at 60 to 64 and 69 years of age [ß 0.07 (0.01, 0.12); ß 0.07 (0.02, 0.12), respectively], higher memory and cognitive state at 69 years of age [ß 0.07 (0.01, 0.12); ß 0.07 (0.01, 0.13), respectively], and reduced WMHV [ß -0.1 (-0.21, -0.00)]. IGF-I/IGFBP-3 at 60 to 64 years of was associated with lower VLS scores at 69 years of age [ß -0.08 (-0.15, -0.02)].

CONCLUSIONS

Increased measure in IIS parameters (IGF-I, IGF-II, and IGFBP-3) relate to better cognitive state in later life. There were apparent associations with specific cognitive domains (IGF-II relating to memory; IGFBP-3 relating to memory, processing speed, and WMHV; and IGF-I/IGFBP-3 molar ratio related to slower processing speed). IGFs and IGFBP-3 are associated with favorable cognitive function outcomes.

Patients with Alzheimer's Disease Have Increased Levels of Insulin-like Growth Factor-I in Serum but not in Cerebrospinal Fluid

BACKGROUND

Insulin-like growth factor-I (IGF-I) is important for amyloid-β (Aβ) metabolism, and also interacts with the brain vasculature. In previous IGF-I studies, it has not been evaluated whether Alzheimer's disease (AD) patients had vascular comorbidities.

OBJECTIVE AND METHODS

A cross-sectional study of 40 consecutive non-diabetic AD patients and 36 healthy controls. We measured IGF-I in serum and cerebrospinal fluid (CSF) and also serum insulin. Mixed forms of AD and vascular dementia were excluded.

RESULTS

After adjustment for covariates including age, serum IGF-I level was higher in the AD group than in the controls, whereas CSF IGF-I and serum insulin were unchanged. Binary logistic regression confirmed that high serum IGF-I was associated with increased prevalence of AD [adjusted Odds Ratio (OR) = 1.83, 95% confidence interval (CI): 1.005-3.32 per standard deviation (SD) increase in serum IGF-I]. This association was more robust after exclusion of patients receiving treatment with acetylcholinesterase inhibitors or N-methyl D-aspartate (NMDA) receptor antagonists (OR = 2.23, 95 % CI: 1.10-4.48). In the total study population (n = 76) as well in the AD group (n = 40), serum IGF-I correlated negatively with CSF Aβ1-42, and CSF IGF-I correlated positively with CSF/serum albumin ratio, CSF total tau, and CSF phosphorylated tau.

CONCLUSION

In AD patients without major brain vascular comorbidities, serum but not CSF levels of IGF-I were increased after correction for covariates. This association was strengthened by exclusion of patients receiving medical treatment. Overall, the results support the notion of IGF-I resistance in mild AD dementia.

(Neuro) Peptides, Physical Activity, and Cognition

Regular physical activity (PA) improves cognitive functions, prevents brain atrophy, and delays the onset of cognitive decline, dementia, and Alzheimer’s disease. Presently, there are no specific recommendations for PA producing positive effects on brain health and little is known on its mediators. PA affects production and release of several peptides secreted from peripheral and central tissues, targeting receptors located in the central nervous system (CNS). This review will provide a summary of the current knowledge on the association between PA and cognition with a focus on the role of (neuro)peptides. For the review we define peptides as molecules with less than 100 amino acids and exclude myokines. Tachykinins, somatostatin, and opioid peptides were excluded from this review since they were not affected by PA. There is evidence suggesting that PA increases peripheral insulin growth factor 1 (IGF-1) levels and elevated serum IGF-1 levels are associated with improved cognitive performance. It is therefore likely that IGF-1 plays a role in PA induced improvement of cognition. Other neuropeptides such as neuropeptide Y (NPY), ghrelin, galanin, and vasoactive intestinal peptide (VIP) could mediate the beneficial effects of PA on cognition, but the current literature regarding these (neuro)peptides is limited.

IGF-1R Inhibitor Ameliorates Neuroinflammation in an Alzheimer's Disease Transgenic Mouse Model

Aging is a major risk factor for Alzheimer's disease (AD). Insulin-like growth factor-1 receptor (IGF-1R) regulates general aging and lifespan. However, the contribution of IGF-1 to age-related AD pathology and progression is highly controversial. Based on our previous work, AβPP/PS1 double transgenic mice, which express human mutant amyloid precursor protein (APP) and presenilin-1 (PS-1), demonstrated a decrease in brain IGF-1 levels when they were crossed with IGF-1 deficient Ames dwarf mice (df/df). Subsequently, a reduction in gliosis, amyloid-β (Aβ) plaque deposition, and Aβ_1-40/42 concentrations were observed in this mouse model. This supported the hypothesis that IGF-1 may contribute to the progression of the disease. To assess the role of IGF-1 in AD, 9-10-month-old male littermate control wild type and AβPP/PS1 mice were randomly divided into two treatment groups including control vehicle (DMSO) and picropodophyllin (PPP), a selective, competitive, and reversible IGF-1R inhibitor. The brain penetrant inhibitor was given ip. at 1 mg/kg/day. Mice were sacrificed after 7 days of daily injection and the brains, spleens, and livers were collected to quantify histologic and biochemical changes. The PPP-treated AβPP/PS1 mice demonstrated attenuated insoluble Aβ_1-40/42. Additionally, an attenuation in microgliosis and protein p-tyrosine levels was observed due to drug treatment in the hippocampus. Our data suggest IGF-1R signaling is associated with disease progression in this mouse model. More importantly, modulation of the brain IGF-1R signaling pathway, even at mid-life, was enough to attenuate aspects of the disease phenotype. This suggests that small molecule therapy targeting the IGF-1R pathway may be viable for late-stage disease treatment.

Circulating Insulin-Like Growth Factor-1 Is Positively Associated with Growth and Cognition in 6- to 9-Year-Old Schoolchildren from Ghana

BACKGROUND

Milk intake stimulates linear growth and improves cognition in children from low-income countries. These effects may be mediated through insulin-like growth factor-1 (IGF-1).

OBJECTIVE

The objective was to assess the effect of milk supplement on circulating IGF-1 and to assess IGF-1 as a correlate of growth and cognition in children.

METHODS

Secondary data on blood spot IGF-1 from a randomized, double-blind, controlled trial in 6-9-y-old children from rural Ghana were analyzed. Intervention groups received porridge with non-energy-balanced supplements: 8.8 g milk protein/d, 100 kcal/d (Milk8); 4.4 g milk and 4.4 g rice protein/d, 100 kcal/d (Milk/rice); 4.4 g milk protein/d, 48 kcal/d (Milk4); or a control (no protein, 10 kcal/d). IGF-1, length, body composition, and Cambridge Neuropsychological Test Automated Battery (CANTAB) were measured at 3.5 or 8.5 mo. Linear regressions were used to assess the effect of milk interventions on IGF-1 and IGF-1 as a correlate of growth and cognition.

RESULTS

The increase in IGF-1 was 15.3 (95% CI: 3.3, 27.3) ng/mL higher in children receiving Milk8 compared with the control. The IGF-1 increases in the isonitrogenous, isoenergetic Milk/rice or the Milk4 groups were not different from the control (P ≥ 0.49). The increase in IGF-1 was associated with improvements in 4 out of 5 CANTAB domains. The strongest associations included reductions in "mean correct latency" from Pattern Recognition Memory and "pre-extradimensional (pre-ED) shift errors" from Intra/Extradimensional Set Shift (P ≤ 0.005). In addition, change in IGF-1 was positively associated with changes in height, weight, and fat-free mass (P ≤ 0.001).

CONCLUSIONS

Intake of skimmed milk powder corresponding to one, but not half a glass of milk on school days stimulates IGF-1 in 6-9-y-old Ghanian children. IGF-1 seems to mediate the effect of milk intake on growth and cognition. The association between IGF-1 and cognition in relation to milk intake is novel and opens possibilities for dietary interventions to improve cognition.

Insulin-like Growth Factor-1 and IGF Binding Proteins Predict All-Cause Mortality and Morbidity in Older Adults

While the growth hormone/insulin-like growth factor-1 (GH/IGF-1) pathway plays essential roles in growth and development, diminished signaling via this pathway in model organisms extends lifespan and health-span. In humans, circulating IGF-1 and IGF-binding proteins 3 and 1 (IGFBP-3 and 1), surrogate measures of GH/IGF-1 system activity, have not been consistently associated with morbidity and mortality. In a prospective cohort of independently-living older adults (n = 840, mean age 76.1 ± 6.8 years, 54.5% female, median follow-up 6.9 years), we evaluated the age- and sex-adjusted hazards for all-cause mortality and incident age-related diseases, including cardiovascular disease, diabetes, cancer, and multiple-domain cognitive impairment (MDCI), as predicted by baseline total serum IGF-1, IGF-1/IGFBP-3 molar ratio, IGFBP-3, and IGFBP-1 levels. All-cause mortality was positively associated with IGF-1/IGFBP-3 molar ratio (HR 1.28, 95% CI 1.05–1.57) and negatively with IGFBP-3 (HR 0.82, 95% CI 0.680–0.998). High serum IGF-1 predicted greater risk for MDCI (HR 1.56, 95% CI 1.08–2.26) and composite incident morbidity (HR 1.242, 95% CI 1.004–1.538), whereas high IGFBP-1 predicted lower risk for diabetes (HR 0.50, 95% CI 0.29–0.88). In conclusion, higher IGF-1 levels and bioavailability predicted mortality and morbidity risk, supporting the hypothesis that diminished GH/IGF-1 signaling may contribute to human longevity and health-span.

Changes of plasma cGP/IGF-1 molar ratio with age is associated with cognitive status of Parkinson disease

OBJECTIVE

Cognitive impairment is a common feature of Parkinson disease (PD), for which age is a major contributing factor. Insulin-like growth factor-1 (IGF-1) declines with age and contributes to age-related cognitive impairment in PD. Cyclic glycine-proline (cGP) is a metabolite of IGF-1 and normalizes bioavailable IGF-1. Plasma cGP/IGF-1 molar ratio that represents bioactive IGF-1 in circulation, may associate with the cognitive status in PD.

METHODS

We examined the association of plasma cGP/IGF-1 molar ratio with the cognitive scores or age in PD patients with normal cognition (PD-N, n = 74), mild cognitive impairment (PD-MCI, n = 71), or dementia (PD-D, n = 33), and with the cognitive scores in 23 age-matched healthy controls. Plasma concentrations of IGF-1, IGF binding protein-3, and cGP were evaluated using enzyme-linked immunosorbent assay (ELISA) and high-performance liquid chromatography-mass spectrometry (HPLC-MS), respectively.

RESULTS

The cGP/IGF-1 molar ratio was positively correlated with the age of PD-N group, negatively correlated with the age of PD-D group, and not associated with the age of PD-MCI group. Independent of age, the cGP/IGF-1 molar ratio was positively correlated with the cognitive scores of healthy controls, but not in PD groups.

CONCLUSION

Old healthy people with a higher cGP/IGF-1 molar ratio showed better preserved cognition, possibly due to improved IGF-1 function. Increased cGP/IGF-1 molar ratio with age may contribute to cognitive retention in the PD-N group. The absence or reversal of such association with age in the PD-MCI and PD-D groups may indicate the conversion of cognitive status in PD, if confirmed through longitudinal investigations within the individuals with advancing cognitive impairment.

The association between serum insulin-like growth factor 1 and cognitive impairments in patients with schizophrenia

Accumulating evidence has shown that insulin-like growth factors (IGFs) are implicated in schizophrenia. Altered serum levels of IGF-1 have been found in schizophrenia patients and are associated with psychopathological symptoms. However, whether there is a relationship between IGF-1 and cognitive impairment in schizophrenia remains unknown. Thirty schizophrenia patients and 26 healthy controls were recruited for this study. The Positive and Negative Syndrome Scale was adopted to assess schizophrenic symptoms, and a battery of neuropsychological tests was employed to evaluate cognitive function. Serum IGF-1 content was determined by enzyme-linked immunosorbent assay (ELISA). We found that patients with schizophrenia performed more poorly than healthy controls in most cognitive tasks, excluding visual memory. The serum IGF-1 concentrations in schizophrenia patients were much lower than those in controls. Correlation analyses revealed that the levels of serum IGF-1 were positively correlated with executive function and attention scores in patients. Furthermore, IGF-1 was an independent contributor to deficits in executive function and attention among schizophrenia patients. Collectively, serum IGF-1 levels were significantly correlated with cognitive performance in schizophrenia patients, indicating that decreased IGF-1 levels might contribute to the pathophysiology of schizophrenia-associated cognitive impairments. The regulation of IGF-1 signaling might be a potential treatment strategy for cognitive impairments in schizophrenia.

Body mass index predicts cognitive aging trajectories selectively for females: Evidence from the Victoria Longitudinal Study

OBJECTIVE

Elevated body weight in midlife is an established risk factor for accelerated cognitive decline, impairment, and dementia. Research examining the impact of later-life body mass index (BMI) on normal cognitive aging has produced mixed results. There is a need for longitudinal designs, replication across multiple cognitive domains, and consideration of BMI effects in the context of important moderators. The present research examined (a) BMI prediction of neuropsychological performance and decline in executive function (EF), neurocognitive speed, and memory and (b) sex stratification of BMI effects.

METHOD

Participants (n = 869; 573 females; M age = 71.75, range = 53-85 years) were older adults from the Victoria Longitudinal Study. Latent growth modeling was used to examine BMI as a predictor of level and change in three latent variables of cognition. The data were then stratified by sex to test whether BMI effects differed for females and males. We adjusted for selected medical, psychosocial, and demographic characteristics.

RESULTS

Higher BMI predicted less decline in EF, neurocognitive speed, and memory. Interestingly, when the data were stratified by sex, higher BMI predicted less neuropsychological decline across domains for females only. BMI was unrelated to cognitive aging trajectories for males.

CONCLUSIONS

We found that elevated BMI was a risk-reducing factor for cognitive decline only for females. Results may be used to enhance the precision with which intervention protocols may target specific subgroups of older adults. (PsycInfo Database Record (c) 2020 APA, all rights reserved).

Association Between Weight Status and Executive Function in Young Adults

Background and objectives: To explore the association between weight status and executive function in young adults. Materials and Methods: Ninety-seven young males (age 17–26 years) underwent adiposity and body composition measurements using body composition analyzer. Inhibitory control and working memory were measured using the Cambridge Neuropsychological Test Battery (CANTAB). Results: Multiple linear regression using both unadjusted and adjusted analyses revealed no association between adiposity and body composition variables with executive tasks, apart from a significant association between skeletal muscle mass (SMM) and mean reaction time on go trial (standardized B = -0.28; p = 0.02). Multivariate analysis of covariance (MANCOVA) revealed that underweight participants presented inferior working memory compared to their normal weight (p = 0.001) or overweight peers (p = 0.008). However, according to the percentage fat quartiles (Q) participants with the highest quartile (Q4) were inferior in inhibitory control than their peers with Q2 (p = 0.04), and participants with the lowest quartile (Q1) were inferior in working memory compared with their peers with Q2 (p = 0.01) or Q3 (p = 0.02). A worse inhibitory control was observed for participants with the highest fat/SMM (Q4) compared to participants in Q3 (p = 0.03), and in contrast worse working memory was observed for participants with the lowest fat/SMM (Q1) compared to participants in Q2 (p = 0.04) or Q3 (p = 0.009). Conclusions: Low adiposity is associated with worse working memory, whereas high adiposity is associated with worse inhibitory control. Therefore, our findings show that normal adiposity, but greater SMM may have a positive impact on executive function in young adults.

A systematic review of existing peripheral biomarkers of cognitive aging: Is there enough evidence for biomarker proxies in behavioral modification interventions?: An initiative in association with the nutrition, exercise and lifestyle team of the Canadian Consortium on Neurodegeneration in Aging

Peripheral biomarkers have shown significant value in predicting brain health and may serve as a useful proxy measurement in the assessment of evidence-based lifestyle behavior modification programs, including physical activity and nutrition programs, that aim to maintain cognitive function in late life. The aim of this systematic review was to elucidate which peripheral biomarkers are robustly associated with cognitive function among relatively healthy non-demented older adults. Following the standards for systematic reviews (PICO, PRIMSA), and employing MEDLINE and Scopus search engines, 222 articles were included in the review. Based on the review of biomarker proxies of cognitive health, it is recommended that a comprehensive biomarker panel, or biomarker signature, be developed as a clinical end point for behavior modification trials aimed at enhancing cognitive function in late life. The biomarker signature should take a multisystemic approach, including lipid, immune/inflammatory, and metabolic biomarkers in the biological signature index of cognitive health.

Impact of Acute Physical Activity on Children's Divergent and Convergent Thinking: The Mediating Role of a Low Body Mass Index

While prior studies have examined the positive influence of physical activity (PA) programs on children's creative potential, they have not explored the mediating roles of psychological and physiological variables. In this study, we investigated the impact of a single dance session as a form of PA on two indicators of creative potential-divergent and convergent thinking, each of which adopts a different cognitive pathway. We also investigated the influence of a physiological condition, low body mass index (BMI), on the relation between PA and creative potential. This was a randomized controlled experiment involving 34 school children randomly assigned to either the dance intervention or a sedentary group based on their BMI profile. We measured the children's divergent and convergent thinking at pre- and post-intervention time points. Following this single PA session, we found a significant difference between divergent and convergent thinking abilities in treatment group participants with normal BMI levels and participants in the control group, but there was no difference between low BMI level treatment group participants and those in the control group. This study supported hypothesized boundary conditions for executive function improvements from PA and suggests a need for a holistic approach (involving both proper nourishment and PA) in order to facilitate improved creativity in children.

The Role of Ceramide and Sphingosine-1-Phosphate in Alzheimer's Disease and Other Neurodegenerative Disorders

Bioactive sphingolipids-ceramide, sphingosine, and their respective 1-phosphates (C1P and S1P)-are signaling molecules serving as intracellular second messengers. Moreover, S1P acts through G protein-coupled receptors in the plasma membrane. Accumulating evidence points to sphingolipids' engagement in brain aging and in neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis. Metabolic alterations observed in the course of neurodegeneration favor ceramide-dependent pro-apoptotic signaling, while the levels of the neuroprotective S1P are reduced. These trends are observed early in the diseases' development, suggesting causal relationship. Mechanistic evidence has shown links between altered ceramide/S1P rheostat and the production, secretion, and aggregation of amyloid β/α-synuclein as well as signaling pathways of critical importance for the pathomechanism of protein conformation diseases. Sphingolipids influence multiple aspects of Akt/protein kinase B signaling, a pathway that regulates metabolism, stress response, and Bcl-2 family proteins. The cross-talk between sphingolipids and transcription factors including NF-κB, FOXOs, and AP-1 may be also important for immune regulation and cell survival/death. Sphingolipids regulate exosomes and other secretion mechanisms that can contribute to either the spread of neurotoxic proteins between brain cells, or their clearance. Recent discoveries also suggest the importance of intracellular and exosomal pools of small regulatory RNAs in the creation of disturbed signaling environment in the diseased brain. The identified interactions of bioactive sphingolipids urge for their evaluation as potential therapeutic targets. Moreover, the early disturbances in sphingolipid metabolism may deliver easily accessible biomarkers of neurodegenerative disorders.

40 YEARS of IGF1: IGF1: the Jekyll and Hyde of the aging brain

The insulin-like growth factor 1 (IGF1) signaling pathway has emerged as a major regulator of the aging process, from rodents to humans. However, given the pleiotropic actions of IGF1, its role in the aging brain remains complex and controversial. While IGF1 is clearly essential for normal development of the central nervous system, conflicting evidence has emerged from preclinical and human studies regarding its relationship to cognitive function, as well as cerebrovascular and neurodegenerative disorders. This review delves into the current state of the evidence examining the role of IGF1 in the aging brain, encompassing preclinical and clinical studies. A broad examination of the data indicates that IGF1 may indeed play opposing roles in the aging brain, depending on the underlying pathology and context. Some evidence suggests that in the setting of neurodegenerative diseases that manifest with abnormal protein deposition in the brain, such as Alzheimer's disease, reducing IGF1 signaling may serve a protective role by slowing disease progression and augmenting clearance of pathologic proteins to maintain cellular homeostasis. In contrast, inducing IGF1 deficiency has also been implicated in dysregulated function of cognition and the neurovascular system, suggesting that some IGF1 signaling may be necessary for normal brain function. Furthermore, states of acute neuronal injury, which necessitate growth, repair and survival signals to persevere, typically demonstrate salutary effects of IGF1 in that context. Appreciating the dual, at times opposing 'Dr Jekyll' and 'Mr Hyde' characteristics of IGF1 in the aging brain, will bring us closer to understanding its impact and devising more targeted IGF1-related interventions.

Insulin-like Growth Factor 1 (IGF-1) as a marker of cognitive decline in normal ageing: A review

Insulin-like Growth Factor 1 (IGF-1) and its signaling pathway play a primary role in normal growth and ageing, however serum IGF-1 is known to reduce with advancing age. Recent findings suggest IGF-1 is essential for neurogenesis in the adult brain, and this reduction of IGF-1 with ageing may contribute to age-related cognitive decline. Experimental studies have shown manipulation of the GH/GF-1 axis can slow rates of cognitive decline in animals, making IGF-1 a potential biomarker of cognition, and/or its signaling pathway a possible therapeutic target to prevent or slow age-related cognitive decline. A systematic literature review and qualitative narrative summary of current evidence for IGF-1 as a biomarker of cognitive decline in the ageing brain was undertaken. Results indicate IGF-1 concentrations do not confer additional diagnostic information for those with cognitive decline, and routine clinical measurement of IGF-1 is not currently justified. In cases of established cognitive impairment, it remains unclear whether increasing circulating or brain IGF-1 may reverse or slow down the rate of further decline. Advances in neuroimaging, genetics, neuroscience and the availability of large well characterized biobanks will facilitate research exploring the role of IGF-1 in both normal ageing and age-related cognitive decline.

Lower circulating insulin-like growth factor-I is associated with better cognition in females with exceptional longevity without compromise to muscle mass and function

Mutations that reduce somatotropic signaling result in improved lifespan and health-span in model organisms and humans. However, whether reduced circulating insulin-like growth factor-I (IGF-I) level is detrimental to cognitive and muscle function in older adults remains understudied. A cross-sectional analysis was performed in Ashkenazi Jews with exceptional longevity (age ≥95 years). Cognition was assessed using the Mini-Mental State Examination and muscle function with the chair rise test, grip-strength, and gait speed. Muscle mass was estimated using the skeletal muscle index. Serum IGF-I was measured with liquid chromatography mass spectrometry. In gender stratified age-adjusted logistic regression analysis, females with IGF-I levels in the first tertile had lower odds of being cognitively impaired compared to females with IGF-I levels within the upper two tertiles, OR (95% CI) 0.39 (0.19-0.82). The result remained significant after adjustment for multiple parameters. No significant association was identified in males between IGF-I and cognition. No relationship was found between IGF-I tertiles and muscle function and muscle mass in females or males. Lower circulating IGF-I is associated with better cognitive function in females with exceptional longevity, with no detriment to skeletal muscle mass and function.

Serum IGF-1 is associated with cognitive functions in early, drug-naïve Parkinson's disease

OBJECTIVE

Cognitive deficits are common in Parkinson's disease (PD) since the early stages and many patients eventually develop dementia. Yet, occurrence of dementia in PD is unpredictable. Evidence supports the hypothesis that insulin-like growth factor-1 (IGF-1) is involved in cognitive deficits. Our aim was to evaluate the relationship between serum IGF-1 levels and neuropsychological scores in a large cohort of drug-naïve PD patients during the earliest stages of the disease.

METHODS

Serum IGF-1 levels were determined in 405 early, drug-naïve PD patients and 191 healthy controls (HC) enrolled in the Parkinson's Progression Markers Initiative (PPMI). The association between serum IGF-1 levels and neuropsychological scores was evaluated with linear regression analysis.

RESULTS

IGF-1 levels were similar in PD and HC. In PD patients the lowest IGF-1 quartile was a predictor of lower performances at the Semantic Fluency task (β = -3.46, 95%CI: -5.87 to -1.01, p = 0.005), the Symbol Digit Modalities Score (β = -2.09, 95%CI: -4.02 to -0.15, p = 0.034), and Hopkins Verbal Learning Test Retention (β = -0.05, 95%CI: -0.09 to -0.009, p = 0.019).

CONCLUSIONS

Lower serum IGF-1 levels are associated to poor performances in cognitive tasks assessing executive function, attention and verbal memory in a large cohort of early PD patients. Follow-up studies are warranted to assess if IGF-1 is related to the development of dementia in PD.

Higher Adiposity Is Associated With Slower Cognitive Decline in Hypertensive Patients: Secondary Analysis of the China Stroke Primary Prevention Trial

BACKGROUND

Obesity is a risk factor for many diseases. However, the potential association between adiposity and cognitive decline in hypertensive patients is inconclusive. We performed a secondary data analysis of the CSPPT (China Stroke Primary Prevention Trial) to examine whether adiposity is correlated with longitudinal cognitive performance in hypertensive adults.

METHODS AND RESULTS

The analysis included 16 791 patients in the CSPPT who received at least 2 cognitive assessments by the Mini-Mental State Examination (MMSE) during the follow-up (median, 4.5 years; interquartile range, 4.2-4.8 years). Outcomes included changes in MMSE scores and cognitive impairment (defined as MMSE score less than education-specific cutoff point). A marked reduction in MMSE scores at the final (compared with at the 1-year) follow-up was apparent in both men (n=4838; mean [SD] score, 0.41 [3.62]) and women (n=7190; mean [SD] score, 1.07 [4.61]; both P<0.001). Analysis using a mixed-effects model revealed an association between higher body mass index with less MMSE decline, even after controlling for demographics and comorbidities (men, β=0.0134 [SE, 0.0036]; women, β=0.0133 [SE, 0.0034]; both P<0.001). A total of 1037 men (15.3%) and 3317 women (33.1%) developed cognitive impairment. In multivariable Cox regression analyses, being obese in men (11.3% versus 18.0%; hazard ratio, 0.75; 95% confidence interval, 0.60-0.94) and women (30.1% versus 36.5%; hazard ratio, 0.82; 95% confidence interval, 0.74-0.91) was a protective factor against cognitive impairment compared with normal body mass index.

CONCLUSIONS

Higher adiposity is independently associated with slower cognitive decline in Chinese hypertensive adults.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00794885 CSPPT.

The relationship between moderate-to-vigorous physical activity and executive function among individuals with schizophrenia: differences by illness duration

OBJECTIVE

Schizophrenia is a chronic mental illness characterized by positive and negative symptoms. Cognitive impairment continues to be a core and consistent deficit. Previous studies have shown that physical activity (PA) is positively associated with cognitive performance. Thus, it may play a supportive role in mitigating cognitive impairments among individuals with schizophrenia. The aim of this study was to analyze the relationship between moderate-to-vigorous physical activity (MVPA) and executive function among adults with schizophrenia.

METHODS

The weekly amount of MVPA (assessed using accelerometers) and executive function (as per Brief Neurocognitive Assessment for Schizophrenia) of 78 adults with schizophrenia (mean [SD] age 42.4 [11.4] years; illness duration 17.0 [11.0] years; 58.2% male) were assessed in this cross-sectional study. Pearson correlations were calculated, followed by a linear regression. Participants were first analyzed together and then dichotomized on the basis of illness duration.

RESULTS

There was no significant association between MVPA and executive function, independent of the duration of illness. For individuals with < 15 years of illness, there was a significant association between weekly MVPA and working memory performance.

CONCLUSION

PA appears to be associated with executive function in some, but not all, individuals with schizophrenia.

The Somatotropic Axis in Human Aging: Framework for the Current State of Knowledge and Future Research

Mutations resulting in reduced signaling of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis are associated with increased life- and healthspan across model organisms. Similar findings have been noted in human cohorts with functional mutations in the somatotropic axis, suggesting that this pathway may also be relevant to human aging and protection from age-related diseases. While epidemiological data indicate that low circulating IGF-1 level may protect aging populations from cancer, results remain inconclusive regarding most other diseases. We propose that studies in humans and animals need to consider differences in sex, pathway function, organs, and time-specific effects of GH/IGF-1 signaling in order to better define the role of the somatotropic axis in aging. Agents that modulate signaling of the GH/IGF-1 pathway are available for human use, but before they can be implemented in clinical studies that target aging and age-related diseases, researchers need to address the challenges discussed in this Review.

Association between adiposity and cognitive function in young men: Hormonal mechanisms

OBJECTIVE

To determine the association between adiposity, hormones, and cognition in young men with abdominal obesity.

METHODS

In this cross-sectional observational study, 53 nondiabetic men with abdominal obesity (mean body mass index, 37.3 kg/m(2) ; age, 22-45 years) and normal intelligence underwent detailed measures of body composition, hormonal profiles, and cognition. Age- and education-adjusted performance in five cognitive domains was examined.

RESULTS

Total fat percentage was negatively associated with visuospatial skills (P = 0.002) and visual memory (P = 0.012). Insulin resistance (homeostatic model assessment of insulin resistance) was also negatively associated with these domains (P = 0.05 and trend, P = 0.06, respectively). Total testosterone levels were negatively associated with executive function and verbal learning and memory (P = 0.04 for each), but free testosterone was not. Sex hormone-binding globulin (SHBG) was also inversely associated with performance in these domains (P = 0.015 and trend, P = 0.09, respectively). In a stepwise regression model including percentage fat, homeostatic model assessment of insulin resistance, SHBG, and free testosterone, SHBG was the only variable selected for executive function (P = 0.05) and showed a trend for verbal learning and memory (P = 0.09).

CONCLUSIONS

Adiposity and insulin resistance were associated with worse function in visual domains. An unexpected negative association is reported between SHBG and cognitive measures, which seemed to be independent of free testosterone levels.

The Association between IGF-1 Polymorphisms, IGF-1 Serum Levels, and Cognitive Functions in Healthy Adults: The Amsterdam Growth and Health Longitudinal Study

Several studies have demonstrated an association between polymorphisms in the insulin-like growth factor-1 (IGF-1) gene and IGF-1 serum levels. IGF-1 levels have been associated with cognitive functioning in older persons and growth hormone deficient patients. The present study investigates whether IGF-1 polymorphisms, IGF-1 levels, and cognition are interconnected in healthy adults. Data of 277 participants (mean age: 42.4 years) of the Amsterdam Growth and Health Longitudinal Study on IGF-1 promoter polymorphisms, IGF-1 serum level, spatial working memory (SWM), paired associate learning (PAL), and IQ tests were analyzed. (M)ANOVAs were applied to confirm the associations between IGF-1 polymorphisms and IGF-1 levels and between IGF-1 levels and cognition. Three groups were distinguished based on specific IGF-1 polymorphism alleles: a homozygote 192 bp/192 bp genotype, a heterozygote 192 bp/x genotype, and a noncarrier x/x genotype. Although different IGF-1 levels were found for the three genotypes, performance on all cognitive tasks and IQ measures was similar. Despite the associations between IGF-1 polymorphisms and IGF-1 levels, no association was found between cognition and IGF-1 levels. It seems that IGF-1 does not play a role in the cognitive performance of healthy middle-aged adults. Possible, IGF-1 fulfills a more developmental and protective role in cognition which becomes apparent during childhood, old-age, or disease.

Metabolic and endocrine correlates of cognitive function in healthy young women

OBJECTIVE

Obesity has been associated with cognitive decline in longitudinal studies of older individuals. We hypothesized that the cognitive sequelae of obesity may be detectable in the reproductive years. In addition, we explored the hypothesis that these associations may be mediated by the hormonal milieu.

DESIGN AND METHODS

Of 49 young healthy lean and overweight women aged 20-45, we investigated the association between performance on a battery of cognitive tests, body composition parameters [body mass index, total fat, abdominal (visceral, subcutaneous, and total) adipose tissue, and muscle], and hormone levels (insulin, adiponectin, leptin, insulin-like growth factor 1 (IGF-1), estrogen, testosterone, and vitamin D).

RESULTS

We found a significant negative association between both visceral adiposity and muscle, and performance in the domain of verbal learning and memory, after controlling for age and education. Other body composition parameters showed similar trends (0.05 < P < 0.10). Additionally, the degree of insulin resistance was negatively associated with executive function domain. None of the associations between the other hormones examined (adipokines, IGF-1, gonadal hormones, and vitamin D) and cognitive function were significant.

CONCLUSION

These preliminary findings suggest a possible association between obesity and cognitive function in healthy young women of reproductive age. More research is warranted into the potential modulatory effect of insulin resistance on this association.

Insulin-like growth factor-I and insulin-like growth factor binding protein-3 in Alzheimer's disease

CONTEXT

Few large studies have been conducted to assess the relationship between circulating IGF and late-life cognition.

OBJECTIVE

The aim of the study was to assess the relationship between IGF-I and IGF binding protein-3 (IGFBP-3) serum levels and cognitive impairment, including Alzheimer's disease (AD).

METHODS

In this multicentric cross-sectional study, 694 elderly subjects (218 men, 476 women; 78.6 ± 6.7 yr old) were included; 481 had memory complaints and were diagnosed, after comprehensive cognitive assessment, with AD (n = 224) or mild cognitive impairment (MCI) (n = 257). The control group was comprised of 213 subjects without memory complaint and with normal cognition (recruited among patients' caregivers). IGF-I and IGFBP-3 serum levels were determined by ELISA.

RESULTS

IGF-I and IGFBP-3 serum levels were significantly associated with cognitive status in men (IGF-I, 137 ± 69 ng/ml for AD vs. 178 ± 88 ng/ml for MCI and 172 ± 91 ng/ml for controls, P = 0.01; IGFBP-3, 3675 ± 1542 ng/ml for AD vs. 4143 ± 1828 ng/ml for MCI and 4488 ± 1893 ng/ml for controls, P = 0.04). In women, IGFBP-3 was significantly associated with cognitive status (3781 ± 1351 ng/ml for AD vs. 4190 ± 1408 ng/ml for MCI and 4390 ± 1552 ng/ml for controls; P < 0.001), but no significant differences between groups for IGF-I occurred. After adjustment for confounding variables (age, educational level, body mass index, diabetes, apolipoprotein E ε4 status), logistic regression indicated that IGF-I [odds ratio (95% confidence interval) = 0.48 (0.26-0.88)] and IGFBP-3 [odds ratio (95% confidence interval) = 0.71 (0.52-0.97)] serum levels were independently associated with AD in men, but not in women.

CONCLUSIONS

We report a significant association between low IGF-I and IGFBP-3 serum levels and AD in men, but not in women.

Body mass index and the risk of dementia among Louisiana low income diabetic patients

Background

The association between obesity and dementia risk remains debatable and no studies have assessed this association among diabetic patients. The aim of our study was to investigate the association between body mass index (BMI) and dementia risk among middle and low income diabetic patients.

Methodology/Principal Findings

The sample included 44,660 diabetic patients (19,618 white and 25,042 African American) 30 to 96 years of age without a history of dementia in the Louisiana State University Hospital-Based Longitudinal Study. During a mean follow-up period of 3.9 years, 388 subjects developed incident dementia. The age- and sex-adjusted hazards ratios (HRs) for incident dementia at different levels of BMI (≤25, 25–26.9, 27–29.9, 30–34.9, and ≥35 kg/m²) were 1.00, 0.53 (95% CI 0.34–0.83), 0.29 (0.18–0.45), 0.37 (0.25–0.56), and 0.31 (0.21–0.48) (P_trend<0.001) in white diabetic patients, and 1.00, 1.00 (95% CI 0.62–1.63), 0.62 (0.39–0.98), 0.56 (0.36–0.86), and 0.65 (0.43–1.01) (P_trend = 0.029) in African American diabetic patients. Further adjustment for other confounding factors affected the results only slightly. There was a significant interaction between race and BMI on dementia risk (χ² = 5.52, 1df, p<0.025), such that the association was stronger in white patients. In stratified analyses, the multivariate-adjusted inverse association between BMI and risk of dementia was present in subjects aged 55–64 years, 65–74 years, and ≥75 years, in men and women, in non-smokers and smokers, and in subjects with different types of health insurance.

Conclusions/Significance

Higher baseline BMI was associated with a lower risk of dementia among diabetic patients, and this association was stronger among white than among African American diabetic patients.

IGF-1 restores visual cortex plasticity in adult life by reducing local GABA levels

The central nervous system architecture is markedly modified by sensory experience during early life, but a decline of plasticity occurs with age. Recent studies have challenged this dogma providing evidence that both pharmacological treatments and paradigms based on the manipulation of environmental stimulation levels can be successfully employed as strategies for enhancing plasticity in the adult nervous system. Insulin-like growth factor 1 (IGF-1) is a peptide implicated in prenatal and postnatal phases of brain development such as neurogenesis, neuronal differentiation, synaptogenesis, and experience-dependent plasticity. Here, using the visual system as a paradigmatic model, we report that IGF-1 reactivates neural plasticity in the adult brain. Exogenous administration of IGF-1 in the adult visual cortex, indeed, restores the susceptibility of cortical neurons to monocular deprivation and promotes the recovery of normal visual functions in adult amblyopic animals. These effects were accompanied by a marked reduction of intracortical GABA levels. Moreover, we show that a transitory increase of IGF-1 expression is associated to the plasticity reinstatement induced by environmental enrichment (EE) and that blocking IGF-1 action by means of the IGF-1 receptor antagonist JB1 prevents EE effects on plasticity processes.

Down-regulation of IGF-1/IGF-1R in hippocampus of rats with vascular dementia

Insulin-like growth factor-1 (IGF-1) has been demonstrated to have neuroprotective effects, but little is known concerning its role in vascular dementia (VaD). This study aimed to evaluate expression of IGF-1 signaling in hippocampus in rat model of VaD, and probe the underlying mechanisms. Permanent occlusion of bilateral common carotid arteries (2-VO) was used as VaD model. Learning and memory functions were declined significantly in 2-VO rats, and these impairments were further deteriorated with the prolongation of 2-VO treatment. IGF-1, IGF-1 receptor (IGF-1R), total Akt and phosphorylated Akt (p-Akt) were all measured at 1, 2 and 4 months following 2-VO injury. Compared with controls, IGF-1, IGF-1 mRNA and p-Akt expression were significantly decreased in hippocampus of 2-VO rats. However, changes of IGF-1R and total Akt levels were not significant. These results suggest that down-regulation of IGF-1 and p-Akt may contribute to the impairments of learning and memory functions after 2-VO. IGF-1/IGF-1R signaling system may involved in the onset and development of VaD.

PEGylation enhances the therapeutic potential for insulin-like growth factor I in central nervous system disorders

OBJECTIVE

Due to its potent neurotrophic activity, insulin-like growth factor I (IGF-I) has been proposed many times for therapeutic application in disorders of the central nervous system (CNS). However, insufficient brain delivery to yield beneficial central without peripheral side effects have prevented clinical development in most instances.

DESIGN

We recently reported the generation of a polyethylene-glycol modified IGF-I variant (PEG-IGF-I) with prolonged half-life and less acute side effects, but with fully maintained slow anabolic activity. Here we investigated if these beneficial properties result in improved brain availability of the drug, thereby reaching therapeutically relevant steady-state concentrations to elicit beneficial effects on neuronal function.

RESULTS

After a single subcutaneous injection, PEG-IGF-I reached much higher steady-state levels in brain tissue and cerebrospinal fluid compared with IGF-I. Two weeks treatment with PEG-IGF-I was sufficient to modulate brain plasticity processes, as judged by changes in synaptic proteins and related animal behavior. Furthermore, chronic treatment of a mouse model of brain amyloidosis with PEG-IGF-I reverted deficits in insulin/IGF-I signaling, synaptic proteins and cognitive performance.

CONCLUSIONS

Our data generate the therapeutic potential for PEG-IGF-I to treat CNS disorders by systemic drug application, and in addition scientifically support its application in disorders of synaptic function and neuronal development.

Microarray analysis of gene expression changes in the brains of NR2B-induced memory-enhanced mice

Glutamate N-methyl-D-aspartate (NMDA) receptors play a pivotal role in different forms of memory. The dysfunction of NMDA receptors contributes to the pathology of central nervous system (CNS) disorders. To further investigate the role of the NMDA receptors in brain processes, we analyzed and compared the gene expression profiles in the hippocampus of NR2B overexpression-induced memory-enhanced mice (Tg mice) with those of their wild-type littermates. Results reveal that 249 genes, which are mainly involved in neurotransmission, signal transduction, cytoskeletal structure, hormone activity, and transcription, were significantly affected in Tg mice. Interestingly, the intracellular calcium channel proteins ryanodine receptor (RyR) 1 and 3, as well as functionally related proteins such as the histidine-rich calcium-binding protein and triadin 2, were upregulated. The Homer-1c protein was also increased in Tg mice and formed a complex with the RyR protein in the mouse brain, suggesting that Homer-1c is an important modulator in both intracellular calcium signaling and overall neuronal signaling by simultaneously interacting with the NMDA receptors and RyR. Western blot and real-time PCR results show that the expression of phospho-CREB, c-fos, and the immediate-early genes Egr2 and Egr4 were also upregulated in Tg mice. The current study demonstrates that a chronic increase in the activation of NMDA receptors affected the expression of a large number of genes and may provide important clues for a better understanding of the molecular mechanism of NMDA receptor-modulated learning and memory, as well as of CNS disorders.

The GH/IGF-I Axis and Cognitive Changes across a 4-Year Period in Healthy Adults

After the age of 40, the amount of growth hormone in humans decreases. The reduced activity of the GH-IGF axis may play a role in age-related cognitive impairments. In the present study, mood and cognition of 30 healthy subjects (7 males, 23 females, aged 41–76 yr, mean age 60.9 ± 9.0) were examined twice. At baseline, we determined fasting blood levels of GH and IGF-I. Mood and cognitive status were assessed at baseline and after, on the average, 3 years and 9 months of followup. Working memory performance decreased over the years in the low IGF-group (P = .007), but not the high IGF-I group. Higher levels of GH were related with a better working memory at the second test (r = 0.42, P = .01) while higher levels of IGF-I tended to be related with a better working memory (r = 0.3, P = .06). The results suggest that higher serum levels of GH and IGF-I preserve the quality of working memory functions over the years.

Exercise and Cognitive Function: Can Working Out Train the Brain, Too?

Studies exploring the relationship between physical activity, fitness, and cognitive function vary across the lifespan in terms of both their number and the apparent strength of the associations. Studies of children are relatively few in number but generally show a positive association between physical activity and cognitive function. Studies of younger adults are even more scarce; findings are equivocal and do not support the hypothesis that greater physical activity or fitness benefits cognitive function. Studies of older adults suggest that greater physical activity and fitness may improve or at least maintain cognitive function. Increasing physical activity may improve cognitive function, especially executive function in elderly persons. A veritable handful of studies suggest that long-term strength training may have cognitive benefits for elderly persons. Regular exercise and greater aerobic fitness are associated with greater brain volume, improved neurophysiological responses to stimuli as measured by electroencephalography (EEG), and higher levels of growth factors that promote growth of brain tissue, neurogenesis, and angiogenesis. However, the findings are not unequivocal (EEG), often based on animal studies (growth factors), and the physiological significance is not well understood. Therefore, while promising, much work remains to validate these findings in humans and to determine their physiological significance for brain health and function. Current evidence does not support the cardiovascular fitness hypothesis and suggests that the neural activity during exercise itself may initiate changes in the brain, independent of the nature of the exercise. More studies are needed to establish a causal relationship, not merely associations, between exercise and cognitive function. These studies need to better quantify physical activity. Likewise, more work is needed to determine the mechanisms by which exercise alters brain function.

Quadriceps strength and executive functions in older women

OBJECTIVE

The aim of this study is to answer the question whether the strength of the knee extensor musculus quadriceps (m. quadriceps), in particular, is related to specific executive functions and whether this relationship is independent of aerobic fitness. The clinical relevance of this question is that the m. quadriceps can still be trained in older people and executive functions are the most vulnerable to processes of aging.

DESIGN

In 41 cognitively intact older women, cognitive functioning was assessed by neuropsychological tests; isometric and isotonic quadriceps strength by the Quadrisotester and the 30-sec chair-stand test, respectively; and aerobic fitness by the 6-min walk test.

RESULTS

A significant proportion of the total variance of the executive functions, attention/working memory and inhibition, were explained by isometric/isotonic knee extensor strength and aerobic fitness, respectively. Extensor muscle strength, aerobic fitness, or one or more interactions did not explain a significant proportion of the total variance of other cognitive functions.

CONCLUSIONS

These data suggest that in older women, quadriceps strength is associated with the executive function, attention/working memory, and that this effect is independent of aerobic fitness, which seems to be associated more strongly with inhibition, another executive function.

Short-term effects of replacing milk with cola beverages on insulin-like growth factor-I and insulin–glucose metabolism: a 10 d interventional study in young men

In the Western world, a trend towards increased consumption of carbonated soft drinks combined with a decreasing intake of milk is observed. This may affect circulating insulin-like growth factor I (IGF-I) and fasting insulin, as seen in pre-pubertal children. The present study was designed to reflect the trend of replacing milk with carbonated beverages in young men and to study the effects of this replacement on IGF-I, IGF-binding protein 3 (IGFBP-3), IGF-I:IGFBP-3 and glucose–insulin metabolism. A randomised, controlled crossover intervention study, in which eleven men aged 22–29 years were given a low-Ca diet in two 10 d periods with 10 d washout in between. In one period, they drank 2·5 litres of Coca Cola® per day and the other period 2·5 litres of semi-skimmed milk. Serum IGF-I, IGFBP-3 (RIA), insulin (fluoro immunoassay) and glucose (Cobas) were determined at baseline and end point of each intervention period. Insulin resistance and β-cell function were calculated with the homeostasis model assessment. A decrease in serum IGF-I was observed in the cola period compared with the milk period (P < 0·05). No effects of treatment were observed on IGFBP-3, IGF-I:IGFBP-3, insulin, glucose, insulin resistance or β-cell function. The present study demonstrates that high intake of cola over a 10 d period decreases total IGF-I compared with a high intake of milk, with no effect on glucose–insulin metabolism in adult men. It is unknown whether this is a transient phenomenon or whether it has long-term consequences.

Circulating insulin-like growth factor I and cognitive function: neuromodulation throughout the lifespan

Insulin-like growth factor I (IGF-I) is central to the somatotropic (growth hormone) axis. It promotes tissue growth and continues to have anabolic effects in adulthood. Accumulating evidence from the last decade, however, reveals that circulating levels of IGF-I also significantly affects cognitive brain function. Specifically, the decline of serum IGF-I might be associated with the age-related cognitive decline in elderly people. Moreover, psychiatric and neurological conditions characterized by cognitive impairment may be characterized by altered levels of IGF-I. Some evidence is emerging that interventions that target the GH/IGF-I axis may improve cognitive functioning, at least in deficient states. As there is evidence linking high serum IGF-I levels with cancer risk, these interventions should be carefully evaluated. On a cellular and molecular level, IGF-I may be a crucial component of neural homeostasis since disturbed IGF-I input is inevitably linked to perturbed function. Consistent with this, all nerve cells are potential targets of IGF-I actions, including neurons, glia, endothelial, epithelial, and perivascular cells. Indeed, many key cellular processes in the brain are affected by IGF-I's neurotrophic and modulatory actions. We review the regulation by IGF-I of neurotransmission and neuronal plasticity and conclude that serum IGF-I is an important mediator of neuronal growth, survival and function throughout the lifespan. The role of IGF-I in synaptic plasticity render its neurotrophic potential a key target for remediating the cognitive impairment associated with a range of neurological conditions.

Insulinlike growth factor-1, insulinlike growth factor binding protein-1, and cognitive function in older men and women

OBJECTIVES

To assess the association between insulinlike growth factor (IGF)-1 and IGF binding protein (IGFBP)-1 with three cognitive function tests in a healthy elderly population.

DESIGN

Cross-sectional analyses from the Rancho Bernardo Cohort Study.

SETTING

Southern California community of Rancho Bernardo.

PARTICIPANTS

Men (n=636) and women (n=899) from the Rancho Bernardo study (median age 74) were assessed between 1988 and 1992 for cognitive function using the Mini-Mental State Examination (MMSE), Verbal Fluency (VF) test, and Trail-Making Test Part B (Trails B). Blood samples were obtained at the same time for IGF-1 and IGFBP-1 levels. The association between biomarkers and cognitive function tests was assessed by dichotomizing tests at the clinically relevant cutoff using logistic regression and according to tertiles and continuous IGF-1 and IGFBP-1 levels using multivariate linear regression analyses.

RESULTS

The mean MMSE, VF and Trails B scores indicated better cognitive function with higher IGF-1 tertile. Multivariate analyses showed that VF and MMSE were each significantly associated with IGF-1 in a dose-response manner for men (P for trend=.001), but no cognitive function tests were related to IGF-1 in women. For men, the highest IGFBP-1 tertile was inversely and significantly different from the lowest tertile for the MMSE test only (P for trend=.02).

CONCLUSION

IGF-1 was independently and positively related to MMSE and VF in men, and IGFBP-1 was inversely associated with MMSE in men. Sex differences in the association should be further investigated.

Association between late-life body mass index and dementia: The Kame Project

OBJECTIVE

To examine the association between body mass index (BMI), waist circumference (WC), and waist-to-hip ratio (WHR) and risk of dementia and its subtypes in late life.

METHODS

Participants were members of the Kame Project, a population-based prospective cohort study of 1,836 Japanese Americans living in King County, WA, who had a mean age of 71.8 years and were dementia-free at baseline (1992-1994), and were followed for incident dementia through 2001. Cox proportional hazards models were used to estimate the risk of dementia, Alzheimer disease (AD), and vascular dementia (VaD) controlling for demographic and lifestyle characteristics and vascular comorbidities as a function of baseline BMI, WC, and WHR and change in BMI over time.

RESULTS

Higher baseline BMI was significantly associated with a reduced risk of AD (hazard ratio [HR] = 0.56, 95% confidence interval [CI] = 0.33-0.97) in the fully adjusted model. Slower rate of decline in BMI was associated with a reduced risk of dementia (HR = 0.37, 95% CI = 0.14-0.98), with the association stronger for those who were overweight or obese (HR = 0.18, 95% CI = 0.05-0.58) compared to normal or underweight (HR = 1.00, 95% CI = 0.18-5.66) at baseline.

CONCLUSION

Higher baseline body mass index (BMI) and slower declining BMI in late life are associated with a reduced risk of dementia, suggesting that low BMI or a faster decline in BMI in late life may be preclinical indicators of an underlying dementing illness, especially for those who were initially overweight or obese.

Use of serum insulin-like growth factor-I levels to predict psychiatric non-response to donepezil in patients with Alzheimer's disease

OBJECTIVE

Insulin-like growth factor-I (IGF-I) deficiency may be involved in cognitive deficits seen with aging and in neurodegenerative diseases such as Alzheimer's disease (AD). This study was aimed at investigating whether non-responder to donepezil could be predicted using decreased serum levels of IGF-I in AD patients.

DESIGN

This study involved 106 elderly subjects: 50 patients with AD and 56 age-matched controls without dementia. In patients with AD, donepezil was given orally 3 mg/day for 4 weeks and 5 mg/day for another 12 weeks. AD patients were divided into responders and non-responders based on the changes in mini-mental state examination (MMSE) scores before and 16 weeks after treatment with donepezil. Serum levels of IGF-I and atherogenic biomarkers were determined.

RESULTS

Before treatment with donepezil, there was a significant positive correlation between serum IGF-I levels and the MMSE scores in all subjects. Serum IGF-I levels and the MMSE scores were significantly lower in AD patients than in non-demented controls and were the lowest in non-responders to donepezil. Atherogenic biomarkers (LDL cholesterol, triglycerides, lipoprotein(a), lipid peroxide, apolipoprotein E, and glucose levels) did not differ significantly among these groups. On multiple logistic regression, non-responders to donepezil showed decreased serum IGF-I levels <110 ng/ml and MMSE scores <15 points before treatment.

CONCLUSIONS

These findings suggest that decreased levels of serum IGF-I combined with MMSE scores before treatment could predict non-responders to donepezil among AD patients, which may be a simple and practical method for selecting patients expected to show a response to treatment.

Central actions of liver-derived insulin-like growth factor I underlying its pro-cognitive effects

Increasing evidence indicates that circulating insulin-like growth factor I (IGF-I) acts as a peripheral neuroactive signal participating not only in protection against injury but also in normal brain function. Epidemiological studies in humans as well as recent evidence in experimental animals suggest that blood-borne IGF-I may be involved in cognitive performance. In agreement with observations in humans, we found that mice with low-serum IGF-I levels due to liver-specific targeted disruption of the IGF-I gene presented cognitive deficits, as evidenced by impaired performance in a hippocampal-dependent spatial-recognition task. Mice with serum IGF-I deficiency also have disrupted long-term potentiation (LTP) in the hippocampus, but not in cortex. Impaired hippocampal LTP was associated with a reduction in the density of glutamatergic boutons that led to an imbalance in the glutamatergic/GABAergic synapse ratio in this brain area. Behavioral and synaptic deficits were ameliorated in serum IGF-I-deficient mice by prolonged systemic administration of IGF-I that normalized the density of glutamatergic boutons in the hippocampus. Altogether these results indicate that liver-derived circulating IGF-I affects crucial aspects of mature brain function; that is, learning and synaptic plasticity, through its trophic effects on central glutamatergic synapses. Declining levels of serum IGF-I during aging may therefore contribute to age-associated cognitive loss.