Growth hormone secretion in Alzheimer's disease: 24-hour profile of basal levels and response to stimulation and suppression studies

Acute exercise increases circulating IGF-1 in Alzheimer's disease patients, but not in older adults without dementia

OBJECTIVES

Increased Insulin-like growth factor I (IGF-1) has been associated with improvement of cognitive function in response to exercise. Evidences indicate a role for IGF-1 in beta-amyloid clearance and reducing hyperphosphorylation tau in Alzheimer's disease (AD). There is a need to investigate the IGF-1 response to exercise in AD patients due to well-known potential effects of exercise on IGF-1. The aim of this study was to examine circulating IGF-1 levels in AD patients and older adults without dementia after acute exercise and to verify the associations among cardiorespiratory fitness, cognition and IGF-1 levels.

METHOD

Seventy-four older adults (40 older adults without dementia and 34 AD patients) participated in this study. The outcomes included IGF-1 plasma levels and performance in the submaximal exercise stress test. Secondary outcomes included cognitive functions, depressive symptoms, level of physical activity, insulin-resistance, and cholesterol. All participants performed the incremental test on a treadmill and IGF-1 was collected before and after the exercise.

RESULTS

A tendency to the difference of baseline IGF-1 plasma levels between the groups was found. After the acute exercise AD patients also presented higher levels of circulating IGF-1 compared to the Older adults without dementia. Correlations among cardiorespiratory fitness and cognitive functions were found.

CONCLUSION

The findings suggest that AD patients and older adults respond differently to acute exercise in terms of circulating IGF-1 levels. This response seems to indicate either an IGF-1 resistance or a compensatory exercise-induced to lower IGF-1 levels in AD patients. Cardiorespiratory fitness is associated with global cognition, executive function, attention and information processing speed.

Synaptic plasticity modulation by circulating peptides and metaplasticity: Involvement in Alzheimer's disease

Synaptic plasticity is a cellular process involved in learning and memory whose alteration in its two main forms (Long Term Depression (LTD) and Long Term Potentiation (LTP)), is observed in most brain pathologies, including neurodegenerative disorders such as Alzheimer's disease (AD). In humans, AD is associated at the cellular level with neuropathological lesions composed of extracellular deposits of β-amyloid (Aβ) protein aggregates and intracellular neurofibrillary tangles, cellular loss, neuroinflammation and a general brain homeostasis dysregulation. Thus, a dramatic synaptic environment perturbation is observed in AD patients, involving changes in brain neuropeptides, cytokines, growth factors or chemokines concentration and diffusion. Studies performed in animal models demonstrate that these circulating peptides strongly affect synaptic functions and in particular synaptic plasticity. Besides this neuromodulatory action of circulating peptides, other synaptic plasticity regulation mechanisms such as metaplasticity are altered in AD animal models. Here, we will review new insights into the study of synaptic plasticity regulatory/modulatory mechanisms which could influence the process of synaptic plasticity in the context of AD with a particular attention to the role of metaplasticity and peptide dependent neuromodulation.

Serum but not cerebrospinal fluid levels of insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3) are increased in Alzheimer's disease

BACKGROUND

Although insulin-like growth factor-I (IGF-I) is of importance for the adult function of the central nervous system (CNS), little is known of the significance of IGF-I in cerebrospinal fluid (CSF) in relation to Alzheimer's disease (AD).

METHODS

A cross-sectional study of 60 consecutive patients under primary evaluation of cognitive impairment and 20 healthy controls. The patients had AD dementia or mild cognitive impairment (MCI) diagnosed with AD dementia upon follow-up (n=32), stable MCI (SMCI, n=13), or other dementias (n=15). IGF-I, IGF-binding protein-3 (IGFBP-3), and insulin were measured in serum and CSF.

RESULTS

Serum IGF-I level was increased in AD patients and in patients with other dementias compared to healthy controls (P=0.01 and P<0.05, respectively). Serum IGFBP-3 concentration was increased in AD and SMCI patients compared to controls (P=0.001 and P<0.05, respectively). CSF levels of IGF-I and IGFBP-3 as well as serum and CSF levels of insulin were similar in all study groups. In the total study population (n=80), serum levels of IGF-I and IGFBP-3 correlated negatively with CSF β-amyloid₁₋₄₂ (Aβ₁₋₄₂) level (r=-0.29, P=0.01 and r=-0.27, P=0.02, respectively) and in the AD patients (n=32), the increased CSF/serum IGF-I ratio correlated positively with the CSF level of phosphorylated tau protein (P-tau; r=0.42, P=0.02).

CONCLUSION

Patients with AD as well as other dementias had high levels of IGF-I in serum but not in CSF. In AD patients, the IGF-I system was associated with biomarkers of AD disease status.

Effects of growth hormone–releasing hormone on cognitive function in adults with mild cognitive impairment and healthy older adults: results of a controlled trial

BACKGROUND

Growth hormone–releasing hormone(GHRH), growth hormone, and insulin like growth factor 1 have potent effects on brain function, their levels decrease with advancing age, and they likely play a role in the pathogenesis of Alzheimer disease. Previously, we reported favorable cognitive effects of short-term GHRH administration in healthy older adults and provided preliminary evidence to suggest a similar benefit in adults with mild cognitive impairment (MCI).

OBJECTIVE

To examine the effects of GHRH on cognitive function in healthy older adults and in adults with MCI.

DESIGN

Randomized,double-blind,placebo-controlled trial.

SETTING

Clinical Research Center, University of Washington School of Medicine in Seattle.

PARTICIPANTS

A total of 152 adults (66 with MCI) ranging in age from 55 to 87 years (mean age, 68 years); 137 adults (76 healthy participants and 61 participants with MCI) successfully completed the study.

INTERVENTION

Participants self-administered daily subcutaneous injections of tesamorelin (Theratechnologies Inc),a stabilized analog of human GHRH (1 mg/d), or placebo 30 minutes before bedtime for 20 weeks. At baseline, at weeks 10 and 20 of treatment, and after a 10-week washout(week 30), blood samples were collected, and parallel versions of a cognitive battery were administered. Before and after the 20-week intervention, participants completed an oral glucose tolerance test and a dual-energy x-ray absorptiometry scan to measure body composition.

MAIN OUTCOME MEASURES

Primary cognitive outcomes were analyzed using analysis of variance and included 3 composites reflecting executive function, verbal memory, and visual memory. Executive function was assessed with Stroop Color-Word Interference,Task Switching, the Self-Ordered Pointing Test, and Word Fluency, verbal memory was assessed with Story Recall and the Hopkins Verbal Learning Test,and visual memory was assessed with the Visual-Spatial Learning Test and Delayed Match-to-Sample.

RESULTS

The intent-to-treat analysis indicated a favorable effect of GHRH on cognition (P=.03), which was comparable in adults with MCI and healthy older adults.The completer analysis showed a similar pattern, with a more robust GHRH effect (P=.002). Subsequent analyses indicated a positive GHRH effect on executive function (P=.005) and a trend showing a similar treatment-related benefit in verbal memory(P=.08). Treatment with GHRH increased insulin like growth factor 1 levels by 117 %(P.001), which remained within the physiological range, and reduced percent body fat by 7.4%(P.001). Treatment with GHRH increased fasting insulin levels within the normal range by 35%in adults with MCI (P.001) but not in healthy adults. Adverse events were mild and were reported by 68%of GHRH treated adults and 36% of those who received placebo.

CONCLUSIONS

Twenty weeks of GHRH administration had favorable effects on cognition in both adults with MCI and healthy older adults. Longer-duration treatment trials are needed to further examine the therapeutic potential of GHRH administration on brain health during normal aging and “pathological aging.”

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00257712

Chemical modification of class II G protein-coupled receptor ligands: frontiers in the development of peptide analogs as neuroendocrine pharmacological therapies

Recent research and clinical data have begun to demonstrate the huge potential therapeutic importance of ligands that modulate the activity of the secretin-like, Class II, G protein-coupled receptors (GPCRs). Ligands that can modulate the activity of these Class II GPCRs may have important clinical roles in the treatment of a wide variety of conditions such as osteoporosis, diabetes, amyotrophic lateral sclerosis and autism spectrum disorders. While these receptors present important new therapeutic targets, the large glycoprotein nature of their cognate ligands poses many problems with respect to therapeutic peptidergic drug design. These native peptides often exhibit poor bioavailability, metabolic instability, poor receptor selectivity and resultant low potencies in vivo. Recently, increased attention has been paid to the structural modification of these peptides to enhance their therapeutic efficacy. Successful modification strategies have included d-amino acid substitutions, selective truncation, and fatty acid acylation of the peptide. Through these and other processes, these novel peptide ligand analogs can demonstrate enhanced receptor subtype selectivity, directed signal transduction pathway activation, resistance to proteolytic degradation, and improved systemic bioavailability. In the future, it is likely, through additional modification strategies such as addition of circulation-stabilizing transferrin moieties, that the therapeutic pharmacopeia of drugs targeted towards Class II secretin-like receptors may rival that of the Class I rhodopsin-like receptors that currently provide the majority of clinically used GPCR-based therapeutics. Currently, Class II-based drugs include synthesized analogs of vasoactive intestinal peptide for type 2 diabetes or parathyroid hormone for osteoporosis.

Class II G protein-coupled receptors and their ligands in neuronal function and protection

G protein-coupled receptors (GPCRs) play pivotal roles in regulating the function and plasticity of neuronal circuits in the nervous system. Among the myriad of GPCRs expressed in neural cells, class II GPCRs which couples predominantly to the Gs-adenylate cyclase-cAMP signaling pathway, have recently received considerable attention for their involvement in regulating neuronal survival. Neuropeptides that activate class II GPCRs include secretin, glucagon-like peptides (GLP-1 and GLP-2), growth hormone-releasing hormone (GHRH), pituitary adenylate cyclase activating peptide (PACAP), corticotropin-releasing hormone (CRH), vasoactive intestinal peptide (VIP), parathyroid hormone (PTH), and calcitonin-related peptides. Studies of patients and animal and cell culture models, have revealed possible roles for class II GPCRs signaling in the pathogenesis of several prominent neurodegenerative conditions including stroke, Alzheimer's, Parkinson's, and Huntington's diseases. Many of the peptides that activate class II GPCRs promote neuron survival by increasing the resistance of the cells to oxidative, metabolic, and excitotoxic injury. A better understanding of the cellular and molecular mechanisms by which class II GPCRs signaling modulates neuronal survival and plasticity will likely lead to novel therapeutic interventions for neurodegenerative disorders.

Decreased plasma insulin-like growth factor-I level in familial Alzheimer's disease patients carrying the Swedish APP 670/671 mutation

The plasma insulin-like growth factor I (IGF-I) level was determined in family members carrying the Swedish amyloid precursor protein (APP) 670/671 mutation with or without Alzheimer's disease (AD) and in age-matched controls from the same family. Plasma growth hormone (GH) and prolactin (PRL) levels were also determined. Measurement of the plasma IGF-I level by radioimmunoassay revealed a significant reduction only in the family members with AD compared to age-matched controls. However, there was no significant difference in the levels of GH and PRL between the mutation carriers with or without AD and their respective age-matched controls. These findings indicate that the mechanism(s) regulating GH and PRL were preserved and those regulating IGF-I levels might be affected in AD patients with the Swedish APP 670/671 mutation. CopyrightCopyright 1999S.KargerAG, Basel

Growth hormone therapy in elderly people: an age-delaying drug?

The aims of this review are to present a brief overview of growth hormone (GH) physiology and to summarize the studies of GH treatment in adults. Special attention has been paid to randomized controlled trials. Studies have revealed a partial deficiency of GH secretion in the elderly. GH secretion on the average declines by 14% with each decade in normal adults after 20 years of age. Aging has a central effect on the GH secretion and peripheric effect on insulin-like growth factor 1 (IGF-1) through changes in the body composition. GH administration may attenuate several important decrements in body composition and in function associated with aging. GH may also have very potent anabolic effects in surgical situations. Short-term side-effects of GH therapy include edema, carpal tunnel syndrome and arthralgia. A number of agents such as oral GH-releasing peptides (GHRPs) increase GH secretion; they may be an alternative to GH treatment in the future. Further studies of GH replacement are needed, examining issues such as dosage, tolerance and efficacy before the widespread use of GH in the elderly is advocated.