Recombinant Human Insulin-Like Growth Factor I (IGF-I): Risks and Benefits of Normalizing Blood IGF-I Concentrations

The IGF-1/GH-GLUTs-plasma glucose regulating axis in hybrid grouper (Epinephelus fuscoguttatus♀ × epinephelus lanceolatus♂) fed a high-carbohydrate diet

The carnivorous teleost fish is often intolerant to high levels of postprandial plasma glucose. This study aimed to evaluate the effects of insulin-like growth factor-1 (IGF-1) and growth hormone (GH) administrations on plasma glucose levels and expression of glucose transporters (GLUTs) in various tissues of hybrid grouper, and hence to further clarify the hormone-GLUTs-plasma glucose regulating axis. Twenty-four experimental fish (average body weight: 77.5 ± 5.4 g) were selected and injected with recombinant human IGF-1 (0.2 μg/g body weight) and PBS (0.01 mol/L) in enterocoelia, respectively, and in the GH injected experiment, the same quantity of fish (average body weight: 103.8 ± 5.8 g) were administrated with GH at a dose of 0.5 μg/g body weight or with PBS at a dose of 0.01 mol/L. Results showed that plasma glucose level was significantly (P < 0.05) declined by the IGF-1 administration but elevated by the GH administration. Plasma IGF-1 concentration was significantly (P < 0.01) elevated by the IGF-1 administration, while GH concentration did not significantly (P ≥ 0.05) respond to the GH administration. The relative mRNA levels of insulin-like growth factor-1 receptor a (IGF-Ra) in liver and muscle were decreased significantly with the IGF-1 administration, and a similar variation tendency was also found in insulin-like growth factor-1 receptor b (IGF-Rb) in liver, muscle and adipose tissues. Besides, the relative mRNA level of insulin receptor (IRS) in liver was significantly increased in the IGF-1 administrated group. After the GH administration, the mRNA levels of hepatic growth factor receptor 2 (GHR2) and IGF-1 were significantly elevated. As for GLUTs, the relative mRNA levels of GLUT1 and GLUT2 in liver were obviously elevated by the IGF-1 administration, while the mRNA level of GLUT4 in muscle was reduced. In liver, the protein levels of GLUT1, 2 and 4 were significantly elevated by the IGF-1 administration, and in adipose, only GLUT1 was observed to have a significantly increased protein level. The mRNA expression of GLUTs was less affected by the GH administration. The protein level of GLUT1 in liver was significantly reduced by the GH administration, while in adipose, it was significantly increased. The protein level of GLUT2 in liver or adipose showed an opposite variation as that of GLUT1. Overall, IGF-1 had a hypoglycemic effect on hybrid grouper, and this probably was through up-regulating the protein levels of hepatic GLUT1, 2 and 4 and adipose GLUT1. GH showed an opposite role in regulating plasma glucose level as IGF-1.

Beneficial Effect of Cissus quadrangularis Linn. on Osteopenia Associated with Streptozotocin-Induced Type 1 Diabetes Mellitus in Male Wistar Rats

Petroleum ether fraction of Cissus quadrangularis (PECQ) impact on the development of osteopenia in type 1 diabetic rat model has been evaluated. Diabetic rats were treated orally with two doses of PECQ. Another group of diabetic rats were treated with subcutaneous injection of synthetic human insulin. The cortical and trabecular bone thickness and bone strength were significantly decreased in diabetic rats. Treatment with two doses of PECQ significantly prevented these changes in diabetic rats. However, PECQ treatment (two doses) did not alter the glycemic levels in these diabetic rats. Increased levels of serum alkaline phosphatase (ALP), tartrate-resistant acid phosphatase (TRAP), and hydroxyproline were noted in diabetic rats when compared to normal control rats. The two doses of PECQ treatment further improved the serum ALP levels and significantly decreased the serum levels of TRAP and hydroxyproline. The effects of PECQ treatment on histological, biomechanical, and biochemical parameters are comparable to those of insulin. Since PECQ improves the bone health in hyperglycemic conditions by enhancing the cortical and trabecular bone growth and altering the circulating bone markers, it could be used as an effective therapy against diabetes-associated bone disorders.

Functional interaction between SNPs and microsatellite in the transcriptional regulation of insulin-like growth factor 1

A CA-repeat microsatellite in insulin-like growth factor 1 (IGF1) promoter was associated with interindividual variation of circulating IGF1 level. Previously, we reported that such association was due to variation of haplotype unit in a linkage disequilibrium block composed of microsatellite and single-nucleotide polymorphisms (SNPs), suggesting the presence of an interaction between them. In this study, reporter assays were performed to investigate the regulatory effect and interaction of genetic variants on gene expression. We used an in vitro system to compare the transcriptional activities of haplotypes (rs35767:T>C, the CA-repeat microsatellite, rs5742612:T>C, and rs2288377:T>A) in evolutionarily conserved region of IGF1 promoter. In haplotype C-T-T, a longer microsatellite had a lower transcriptional activity (17.6 ± 2.4-fold for 17 repeats and 8.3 ± 1.1-fold for 21 repeats), whereas in haplotype T-C-A, such trend could not be observed, as the microsatellite with 21 repeats had the highest transcriptional activity (17.5 ± 2.3-fold). Because the microsatellite and SNPs affected the transcriptional activity of each other, there may be an interaction between them in the regulation of IGF1 expression. For the first time, we demonstrated that a noncoding microsatellite polymorphism could act as a functional unit and interact with SNPs in the regulation of transcription in human genome.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

GENERAL SIGNIFICANCE

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

Role of the evolutionarily conserved starvation response in anorexia nervosa

This review will summarize recent findings concerning the biological regulation of starvation as it relates to anorexia nervosa (AN), a serious eating disorder that mainly affects female adolescents and young adults. AN is generally viewed as a psychosomatic disorder mediated by obsessive concerns about weight, perfectionism and an overwhelming desire to be thin. By contrast, the thesis that will be developed here is that, AN is primarily a metabolic disorder caused by defective regulation of the starvation response, which leads to ambivalence towards food, decreased food consumption and characteristic psychopathology. We will trace the starvation response from yeast to man and describe the central role of insulin (and insulin-like growth factor-1 (IGF-1))/Akt/ F-box transcription factor (FOXO) signaling in this response. Akt is a serine/threonine kinase downstream of the insulin and IGF-1 receptors, whereas FOXO refers to the subfamily of Forkhead box O transcription factors, which are regulated by Akt. We will also discuss how initial bouts of caloric restriction may alter the production of neurotransmitters that regulate appetite and food-seeking behavior and thus, set in motion a vicious cycle. Finally, an integrated approach to treatment will be outlined that addresses the biological aspects of AN.

Investigational anabolic therapies for osteoporosis

IMPORTANCE OF THE FIELD

Anabolic therapy, or stimulating the function of bone-forming osteoblasts, is the preferred pharmacological intervention for osteoporosis.

AREAS COVERED IN THIS REVIEW

We reviewed bone anabolic agents currently under active investigation. The bone anabolic potential of IGF-I and parathyroid hormone-related protein is discussed in the light of animal data and human studies. We also discuss the use of antagonists of the calcium-sensing receptor (calcilytics) as orally administered small molecules capable of transiently elevating serum parathyroid hormone (PTH). Further, we reviewed novel anabolic agents targeting members of the wingless tail (Wnt) signaling family that regulate bone formation including DKK-1, sclerostin, Thp1, and glycogen synthase kinase 3beta. We have also followed up on the promise shown by beta-blockers in modulating the activity of sympathetic nervous system, thus affecting bone anabolism. We give critical consideration to neutralizing the activity of activin A, a negative regulator of bone mass by soluble activin receptor IIA, as a strategy to promote bone formation.

WHAT THE READER WILL GAIN

Update on various strategies to promote osteoblast function currently under evaluation.

TAKE HOME MESSAGE

In spite of favorable results in experimental models, none of these strategies has yet achieved the ultimate goal of providing an alternative to injectable PTH, the sole anabolic therapy in clinical use.

Basic Mechanisms Mediating Cardiomyopathy and Heart Failure in Aging

Biological aging represents the major risk factor for the development of heart failure (HF), malignancies, and neurodegenerative diseases. While risk factors such as lifestyle patterns, genetic traits, blood lipid levels, and diabetes can contribute to its development, advancing age remains the most determinant predictor of cardiac disease. Several parameters of left ventricular function may be affected with aging, including increased duration of systole, decreased sympathetic stimulation, and increased left ventricle ejection time, while compliance decreases. In addition, changes in cardiac phenotype with diastolic dysfunction, reduced contractility, left ventricular hypertrophy, and HF, all increase in incidence with age. Given the limited capacity that the heart has for regeneration, reversing or slowing the progression of these abnormalities poses a major challenge. In this chapter, we present a discussion on the molecular and cellular mechanisms involved in the pathogenesis of cardiomyopathies and HF in aging and the potential involvement of specific genes identified as primary mediators of these diseases.

Growth hormone supplementation increased latency to tumourigenesis in Atm-deficient mice

Growth hormone (GH) is important for cell growth and differentiation, has multiple effects on lymphoid tissue and may promote blast cell proliferation and cancer development. We studied the effect of GH on longevity and tumour formation in Atm-deficient mice, an established model of the human cancer prone syndrome ataxia telangiectasia (AT). AT is a devastating recessive disorder that is characterized by progressive cerebellar ataxia, immunodeficiency, chromosomal instability and cancer susceptibility. Since AT patients also show endocrinological abnormalities the question has been raised as to whether GH therapy could be beneficial and/or increase the cancer risk in AT. We found that treatment with GH significantly increased longevity of Atm-deficient mice. In addition, GH ameliorated locomotoric behaviour and improved T-cell immunity. Thus, our data demonstrated that GH treatment is not necessarily accompanied by increased cancer development in diseases with chromosomal instability and cancer susceptibility and might be beneficial for AT patients.

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.

Erythropoietin and its carbamylated derivative prevent the development of experimental diabetic autonomic neuropathy in STZ-induced diabetic NOD-SCID mice

Autonomic neuropathy is a significant diabetic complication resulting in increased morbidity and mortality. Studies of autopsied diabetic patients and several rodent models demonstrate that the neuropathologic hallmark of diabetic sympathetic autonomic neuropathy in prevertebral ganglia is the occurrence of synaptic pathology resulting in distinctive dystrophic neurites ("neuritic dystrophy"). Our prior studies show that neuritic dystrophy is reversed by exogenous IGF-I administration without altering the metabolic severity of diabetes, i.e. functioning as a neurotrophic substance. The description of erythropoietin (EPO) synergy with IGF-I function and the recent discovery of EPO's multifaceted neuroprotective role suggested it might substitute for IGF-I in treatment of diabetic autonomic neuropathy. Our current studies demonstrate EPO receptor (EPO-R) mRNA in a cDNA set prepared from NGF-maintained rat sympathetic neuron cultures which decreased with NGF deprivation, a result which demonstrates clearly that sympathetic neurons express EPO-R, a result confirmed by immunohistochemistry. Treatment of STZ-diabetic NOD-SCID mice have demonstrated a dramatic preventative effect of EPO and carbamylated EPO (CEPO, which is neuroprotective but not hematopoietic) on the development of neuritic dystrophy. Neither EPO nor CEPO had a demonstrable effect on the metabolic severity of diabetes. Our results coupled with reported salutary effects of EPO on postural hypotension in a few clinical studies of EPO-treated anemic diabetic and non-diabetic patients may reflect a primary neurotrophic effect of EPO on the sympathetic autonomic nervous system, rather than a primary hematopoietic effect. These findings may represent a major clinical advance since EPO has been widely and safely used in anemic patients due to a variety of clinical conditions.

Amino acid infusion during anesthesia attenuates the surgery induced decline in IGF-1 and diminishes the "diabetes of injury"

Background

Surgery, commonly performed after an overnight fast, causes a postoperative decline in the anabolic and glucose lowering insulin-like growth factor-1 (IGF-1). Clinical fasting studies have exhibited a positive correlation between IGF-1 and nitrogen balance during different conditions. A perioperative amino acid infusion changes nitrogen balance and might thereby influence serum IGF-1. We hypothesized that amino acid infusion would enhance IGF-1 and thereby might influence glucose homeostasis after surgery. In this study we examined two different regimes of perioperative amino acids infusion.

Methods

24 females scheduled for abdominal hysterectomy were randomized into three groups; Ringer's solution infusion throughout anesthesia (Group B), amino acid infusion throughout anesthesia (Group C) and amino acid infusion 1 hour before anesthesia and during 1.5 hrs of surgery (Group D). Six female volunteers, who were not operated, but received the same amino acids infusion after fasting, served as controls (Group A). Fasting levels of IGF-1, Insulin-like growth factor binding protein-1 (IGFBP-1), insulin and P-glucose were studied prior to, and four days following, operation. Homeostasis model assessment (HOMA) was used as an index of insulin resistance. Non-parametric statistical methods were used.

Results

During the study the Ringer-group exhibited a decrease in IGF-1 and an increase in insulin and plasma glucose after surgery. Within the other groups there were no significant alterations over time after surgery, with the exception of a postoperative decrease in IGF-1 in group D. Group C had higher IGF-1 levels compared to group B on all days. Also, group D had higher IGF-1 levels than group B on day 2 – 4. From baseline to the first postoperative day there was a significant increase in HOMA and IGFBP-1 in groups B and C. These changes were not found in group D, in which insulin, glucose, HOMA and IGFBP-1 did not change. Amino acid infusion to the volunteers did not affect any of the variables studied.

Conclusion

Amino acid infusion during surgery attenuates the decrease in IGF-1 and diminishes the "diabetes of injury".

Insulin-like growth factors and their binding proteins in prostate cancer: Cause or consequence?☆

Insulin-like growth factors (IGFs) promote growth and survival of many types of tumor cells. Epidemiologic studies have implicated carcinogenesis with high levels of IGFs in circulation or in tissues. The levels of IGF binding proteins (IGFBPs) have been associated with reduced risk for prostate and other cancers. Experimental studies have implicated high levels of IGF-I directly and IGFBP-3 inversely in prostate cancer growth, survival, and progression. However, recent evidence suggests a much weaker association of IGF-I with prostate cancer development and a stronger antagonistic association of IGFBP-3 with prostate cancer progression. Considering the clonal heterogeneity and unpredictable progression pattern of prostate cancer, the role of any single growth factor or its regulator (IGFBP) as a single determining factor is limited. This review is a critical appraisal of the role of IGFs, IGFBP, and IGF-I receptor (the IGF axis) in both experimental and clinical prostate cancer genesis and progression.

Skeletal actions of insulin-like growth factors

Insulin-like growth factors (IGFs) promote longitudinal growth and display anabolic effects in adult bone by acting through endocrine and autocrine/paracrine mechanisms. Binding of IGF-I to its specific tyrosine-kinase receptor leads to interaction with the intracellular proteins, insulin receptor substrate-1 and -2, and the activation of distinct intracellular signaling pathways. In cartilage, IGF-I regulates the differentiation of chondrocytes and stimulates the synthesis of components of the extracellular matrix. In bone tissue, IGF-I increases the function of the differentiated osteoblasts and mediates selected anabolic actions of parathyroid hormone. Genetically modified mice, in which selected components of the IGF system were targeted in a tissue-specific fashion, have documented that circulating IGF-I is essential for physiological skeletal growth and adult bone remodeling and that local autocrine/paracrine IGF-I activities are required for optimal trabecular bone mass and mineralization. Studies in humans have indicated a correlation between serum IGF-I levels and bone mineral density. However, there is little information on the use of IGF-I in patients with metabolic bone disease.

Insulin-like growth factor I treatment for cerebellar ataxia: Addressing a common pathway in the pathological cascade?

In the present work we review evidence supporting the use of insulin-like growth factor I (IGF-I) for treatment of cerebellar ataxia, a heterogeneous group of neurodegenerative diseases of low incidence but high societal impact. Most types of ataxia display not only motor discoordination, but also additional neurological problems including peripheral nerve dysfunctions. Therefore, a feasible therapy should combine different strategies aimed to correct the various disturbances specific for each type of ataxia. For cerebellar deficits, and most probably also for other types of brain deficits, the use of a wide-spectrum neuroprotective factor such as IGF-I may prove beneficial. Intriguingly, both ataxic animals as well as human patients show altered serum IGF-I levels. While the pathogenic significance of IGF-I, if any, in this varied group of diseases is difficult to envisage, disrupted IGF-I neuroprotective signaling may constitute a common stage in the pathological cascade associated to neuronal death. Indeed, treatment with IGF-I has proven effective in animal models of ataxia. Based on this pre-clinical evidence we propose that IGF-I should be tested in clinical trials of cerebellar ataxia in those cases where either serum IGF-I deficiency (as in primary cerebellar atrophy) or loss of sensitivity to IGF-I (as in ataxia telangiectasia) has been reported. Taking advantage of the widely protective and anabolic actions of IGF-I on peripheral tissues, this neurotrophic factor may provide additional therapeutic advantages for many of the disturbances commonly associated to ataxia such as cardiopathy, muscle wasting, or immune dysfunction.

Cannabis use in sickle cell disease: a questionnaire study

Cannabinoids are increasingly being considered for the management of various painful conditions, and could be considered as an option for treating acute pain in sickle cell disease (SCD). The objective of this study was to determine the extent of use of cannabis in the community for pain and other symptom relief, and its side effects during self-administration in patients with SCD. Patients attending Central Middlesex Hospital in London were invited to complete a structured self-administered anonymous questionnaire. Eighty-six young adults with HbSS, HbSC and HbSbetathalassaemia disease (median age 30 years) participated in the study. Results showed that 31 (36%) had used cannabis in the previous 12 months to relieve symptoms associated with SCD. The main route in all but two patients was by smoking. The main reasons for use were to reduce pain in 52%, and to induce relaxation or relieve anxiety and depression in 39%. Symptoms related to sedation and mood effects were reported in 77% of patients. The majority of patients (58%) expressed their willingness to participate in studies of cannabis as a medicine. We conclude that research in the use of cannabinoids for pain relief in SCD would be both important and acceptable to adult patients.