Mecasermin rinfabate: rhIGF-I/rhIGFBP-3 complex: iPLEX

Controversial causal association between IGF family members and osteoporosis: a Mendelian randomization study between UK and FinnGen biobanks

Objectives

Osteoporosis, a prevalent skeletal disorder characterized by reduced bone strength, is closely linked to the IGF system, crucial for skeletal metabolism. However, the precise nature of this relationship remains elusive. In this study, we employed Mendelian randomization (MR) to unravel the associations between genetically predicted serum IGF system member levels and osteoporosis.

Methods

A two-sample MR approach was employed to investigate these causal associations based on two individual datasets. Predictions of 14 serum levels of IGF system members were made using 11,036,163 relevant Single Nucleotide Polymorphisms (SNPs) within a cohort of 4,301 individuals of European descent. Genetic association estimates for osteoporosis were derived from two publicly available GWAS consortia: the Finnish consortium from the FinnGen biobank, comprising 212,778 individuals of Finnish descent (3,203 cases and 209,575 controls), and the UK consortium from the UK Biobank, including 337,159 individuals of European descent (5,266 cases and 331,893 controls).

Results

According to the UK dataset, IGF-1 levels were associated with a reduced risk of osteoporosis, as indicated by the weighted median method (Odds Ratio [OR] = 0.998, 95% CI = 0.997-1.000, P = 0.032). Additionally, higher levels of IGFBP-3 were linked to a decreased risk of osteoporosis using the Inverse-Variance Weighted (IVW) method (OR = 0.999, 95% CI = 0.998-1.000, P = 0.019), and CTGF levels exhibited a negative association with osteoporosis, as determined by the weighted median method (OR = 0.998, 95% CI = 0.996-0.999, P = 0.004). In the FinnGen dataset, IGF-1 and IGFBP-3 were not identified to be associated with osteoporosis. While, IGF-LR1 levels displayed a negative association with osteoporosis, according to the MR-Egger method (OR = 0.886, 95% CI = 0.795-0.987, P = 0.036), while CYR61 was linked to an increased risk of osteoporosis based on both the weighted median and IVW methods (OR = 1.154, 95% CI = 1.009-1.319, P = 0.037, and OR = 1.115, 95% CI = 1.022-1.215, P = 0.014, respectively).

Conclusion

This study provides compelling evidence that certain IGF family members play a role in the pathogenesis of osteoporosis between different datasets, indicating population specific causal effects between IGF family and osteoporosis. Although the results from both datasets demonstrated that IGF family involved in the pathogenesis of osteoporosis, but the responding key molecules might be various among different population. Subsequent research is warranted to evaluate the potential of these biomarkers as targets for osteoporosis prevention and treatment in specific population.

Identification of hub genes and therapeutic drugs in osteonecrosis of the femoral head through integrated bioinformatics analysis and literature mining

Osteonecrosis of the femoral head (ONFH) is a multifactorial disease leading to severely limited function. By far, the etiology and pathogenesis of ONFH are not fully understood, and surgery is the only effective way to treat ONFH. This study aims to identify hub genes and therapeutic drugs in ONFH. Two gene expression profiles were downloaded from the gene expression omnibus database, and the hub genes and candidate drugs for ONFH were identified through integrated bioinformatics analysis and cross-validated by literature mining. A total of 159 DEGs were identified. PTGS2, LRRK2, ANXA5, IGF1R, MCL1, TIMP2, LYN, CD68, CBL, and RUNX2 were validated as 10 hub genes, which has considerable implications for future genetic research and related research fields of ONFH. Our findings indicate that 85 drugs interact with ONFH, with most drugs exhibiting a positive impact on ONFH by promoting osteogenesis and angiogenesis or inhibiting microcirculation embolism, rather than being anti-inflammatory. Our study provides novel insights into the pathogenesis, prevention, and treatment of ONFH.

Receptor-Mediated Muscle Homeostasis as a Target for Sarcopenia Therapeutics

Sarcopenia is a disease characterized by age-related decline of skeletal muscle mass and function. The molecular mechanisms of the pathophysiology of sarcopenia form a complex network due to the involvement of multiple interconnected signaling pathways. Therefore, signaling receptors are major targets in pharmacological strategies in general. To provide a rationale for pharmacological interventions for sarcopenia, we herein describe several druggable signaling receptors based on their role in skeletal muscle homeostasis and changes in their activity with aging. A brief overview is presented of the efficacy of corresponding drug candidates under clinical trials. Strategies targeting the androgen receptor, vitamin D receptor, Insulin-like growth factor-1 receptor, and ghrelin receptor primarily focus on promoting anabolic action using natural ligands or mimetics. Strategies involving activin receptors and angiotensin receptors focus on inhibiting catabolic action. This review may help to select specific targets or combinations of targets in the future.

Endogenous Repair and Regeneration of Injured Articular Cartilage: A Challenging but Promising Therapeutic Strategy

Articular cartilage (AC) has a very limited intrinsic repair capacity after injury or disease. Although exogenous cell-based regenerative approaches have obtained acceptable outcomes, they are usually associated with complicated procedures, donor-site morbidities and cell differentiation during ex vivo expansion. In recent years, endogenous regenerative strategy by recruiting resident mesenchymal stem/progenitor cells (MSPCs) into the injured sites, as a promising alternative, has gained considerable attention. It takes full advantage of body's own regenerative potential to repair and regenerate injured tissue while avoiding exogenous regenerative approach-associated limitations. Like most tissues, there are also multiple stem-cell niches in AC and its surrounding tissues. These MSPCs have the potential to migrate into injured sites to produce replacement cells under appropriate stimuli. Traditional microfracture procedure employs the concept of MSPCs recruitment usually fails to regenerate normal hyaline cartilage. The reasons for this failure might be attributed to an inadequate number of recruiting cells and adverse local tissue microenvironment after cartilage injury. A strategy that effectively improves local matrix microenvironment and recruits resident MSPCs may enhance the success of endogenous AC regeneration (EACR). In this review, we focused on the reasons why AC cannot regenerate itself in spite of potential self-repair capacity and summarized the latest developments of the three key components in the field of EACR. In addition, we discussed the challenges facing in the present EACR strategy. This review will provide an increasing understanding of EACR and attract more researchers to participate in this promising research arena.

The effects of recombinant human insulin-like growth factor-1/insulin-like growth factor binding protein-3 administration on lipid and carbohydrate metabolism in recreational athletes

OBJECTIVE

Previous studies suggested that recombinant human IGF-1 (rhIGF-1) administration affects carbohydrate and lipid metabolism in healthy people and in people with diabetes. This study aimed to determine the effects of rhIGF-1/rhIGF binding protein-3 (rhIGFBP-3) administration on glucose homeostasis and lipid metabolism in healthy recreational athletes.

DESIGN AND SETTING

Randomized, double-blind, placebo-controlled rhIGF-1/rhIGFBP-3 administration study at Southampton General Hospital, UK.

PARTICIPANTS

56 recreational athletes (30 men, 26 women).

METHODS

Participants were randomly assigned to receive placebo, low-dose rhIGF-1/rhIGFBP-3 (30 mg/day) or high-dose rhIGF-1/rhIGFBP-3 (60 mg/day) for 28 days. The following variables were measured before and immediately after the treatment period: fasting lipids, glucose, insulin, C-peptide and glycated haemoglobin. The homeostatic model assessment (HOMA-IR) was used to estimate insulin sensitivity and indirect calorimetry to assess substrate oxidation rates. The general linear model approach was used to compare treatment group changes with the placebo group.

RESULTS

Compared with the placebo group, there was a significant reduction in fasting triglycerides in participants treated with high-dose rhIGF-1/rhIGFBP-3 (p = .030), but not in the low-dose group (p = .390). In women, but not in men, there were significant increases in total cholesterol (p = .003), HDL cholesterol (p = .001) and LDL cholesterol (p = .008). These lipid changes were associated with reduced fasting insulin (p = .010), C-peptide (p = .001) and HOMA-IR (p = .018) in women and reduced C-peptide (p = .046) in men.

CONCLUSIONS

rhIGF-1/rhIGFBP-3 administration for 28 days reduced insulin concentration, improved insulin sensitivity and had significant effects on lipid profile including decreased fasting triglycerides.

Lipodistrophy: a paradigm for understanding the consequences of "overloading" adipose tissue

Lipodystrophies have been recognized since at least the nineteenth century and, despite their rarity, tended to attract considerable medical attention because of the severity and somewhat paradoxical nature of the associated metabolic disease that so closely mimics that of obesity. Within the last 20 yr most of the monogenic subtypes have been characterized, facilitating family genetic screening and earlier disease detection as well as providing important insights into adipocyte biology and the systemic consequences of impaired adipocyte function. Even more recently, compelling genetic studies have suggested that subtle partial lipodystrophy is likely to be a major factor in prevalent insulin-resistant type 2 diabetes mellitus (T2DM), justifying the longstanding interest in these disorders. This progress has also underpinned novel approaches to treatment that, in at least some patients, can be of considerable therapeutic benefit.

Implications of Insulin-Like Growth Factor-1 in Skeletal Muscle and Various Diseases

Skeletal muscle is an essential tissue that attaches to bones and facilitates body movements. Insulin-like growth factor-1 (IGF-1) is a hormone found in blood that plays an important role in skeletal myogenesis and is importantly associated with muscle mass entity, strength development, and degeneration and increases the proliferative capacity of muscle satellite cells (MSCs). IGF-1R is an IGF-1 receptor with a transmembrane location that activates PI3K/Akt signaling and possesses tyrosine kinase activity, and its expression is significant in terms of myoblast proliferation and normal muscle mass maintenance. IGF-1 synthesis is elevated in MSCs of injured muscles and stimulates MSCs proliferation and myogenic differentiation. Mechanical loading also affects skeletal muscle production by IGF-1, and low IGF-1 levels are associated with low handgrip strength and poor physical performance. IGF-1 is potentially useful in the management of Duchenne muscular dystrophy, muscle atrophy, and promotes neurite development. This review highlights the role of IGF-1 in skeletal muscle, its importance during myogenesis, and its involvement in different disease conditions.

Insulin Signaling as a Key Moderator in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is an autosomal dominant genetic disease characterized by multi-system involvement. Affected organ system includes skeletal muscle, heart, gastro-intestinal system and the brain. In this review, we evaluate the evidence for alterations in insulin signaling and their relation to clinical DM1 features. We start by summarizing the molecular pathophysiology of DM1. Next, an overview of normal insulin signaling physiology is given, and evidence for alterations herein in DM1 is presented. Clinically, evidence for involvement of insulin signaling pathways in DM1 is based on the increased incidence of insulin resistance seen in clinical practice and recent trial evidence of beneficial effects of metformin on muscle function. Indirectly, further support may be derived from certain CNS derived symptoms characteristic of DM1, such as obsessive-compulsive behavior features, for which links with altered insulin signaling has been demonstrated in other diseases. At the basic scientific level, several pathophysiological mechanisms that operate in DM1 may compromise normal insulin signaling physiology. The evidence presented here reflects the importance of insulin signaling in relation to clinical features of DM1 and justifies further basic scientific and clinical, therapeutically oriented research.

Mecasermin in Insulin Receptor-Related Severe Insulin Resistance Syndromes: Case Report and Review of the Literature

Mutations in the insulin receptor (INSR) gene underlie rare severe INSR-related insulin resistance syndromes (SIR), including insulin resistance type A, Rabson–Mendenhall syndrome and Donohue syndrome (DS), with DS representing the most severe form of insulin resistance. Treatment of these cases is challenging, with the majority of DS patients dying within the first two years of life. rhIGF-I (mecasermin) has been reported to improve metabolic control and increase lifespan in DS patients. A case report and literature review were completed. We present a case involving a male patient with DS, harbouring a homozygous mutation in the INSR gene (c.591delC). Initial rhIGF-I application via BID (twice daily) injection was unsatisfactory, but continuous subcutaneous rhIGF-I infusion via an insulin pump improved weight development and diabetes control (HbA1c decreased from 10 to 7.6%). However, our patient died at 22 months of age during the course of a respiratory infection in in Libya. Currently available data in the literature comprising more than 30 treated patients worldwide seem to support a trial of rhIGF-I in SIR. rhIGF-I represents a treatment option for challenging SIR cases, but careful consideration of the therapeutic benefits and the burden of the disease is warranted. Continuous application via pump might be advantageous compared to single injections.

Use of growth hormone, IGF-I, and insulin for anabolic purpose: Pharmacological basis, methods of detection, and adverse effects

Hormones with anabolic properties such as growth hormone (GH), insulin-like growth factor-1 (IGF-I), and insulin are commonly abused among professional and recreational athletes to enhance physical ability. Performance enhancing drugs (PEDs) such as these are also commonly used by recreational athletes to improve body aesthetics. The perception of increased muscle mass due to supraphysiologic hormone supplementation, or doping, is widespread among PED users despite a paucity of evidence-based data in humans. Even still, athletes will continue to abuse PEDs in hopes of replicating anecdotal results. It is important to educate the general public and potential treating physicians of the risks of PED use, including the dangers of polypharmacy and substance dependence. It will also be important for the research community to address the common challenges associated with studying PED use such as the ethical considerations of PED administration, the general reticence of the PED-using community to volunteer information, and the constant need to improve or create new detection methods as athletes continually attempt to circumvent current methods. This review highlights the anabolic mechanisms and suggestive data implicating GH, IGF-I, and insulin for use as PEDs, the specific detection methods with cutoff ranges that may be utilized to diagnose abuse of each substance, and their respective side effects.

Continuous longitudinal infusion of rhIGF-1/rhIGFBP-3 in extremely preterm infants: Evaluation of feasibility in a phase II study

OBJECTIVE

To evaluate the feasibility of continuous longitudinal intravenous infusion of recombinant human insulin-like growth factor-1/recombinant human insulin-like growth factor binding protein-3 (rhIGF-1/rhIGFBP-3) for prevention of retinopathy of prematurity and other complications in extremely preterm infants (<28weeks' gestational age), based on initial sections of a phase II randomized controlled trial.

DESIGN

The phase II trial was designed in four sections (A-D); we report pharmacokinetic and adverse events (AEs) data pooled for Sections B and C. Infants in these study sections received rhIGF-1/rhIGFBP-3 or standard neonatal care up to postmenstrual age (weeks+days) 28+6 (Section B) or 29+6 (Section C). Dosing was variable/individualized and intended to establish serum IGF-1 within physiological intrauterine levels.

RESULTS

Nineteen infants were enrolled across Sections B/C: nine received rhIGF-1/rhIGFBP-3 and 10 standard neonatal care. Among the nine infants treated with study drug, mean (SD) dose was 95.1 (10.6)μg/kg/day and mean (SD) duration of infusion was 14.2 (6.1)days. Eight of nine (88.9%) treated infants had two or more dose changes during treatment. Mean serum IGF-1 levels during treatment were 23μg/L among treated infants compared with 14μg/L in control infants. Overall, 66.3% of IGF-1 measurements for treated infants were within target levels (20-60μg/L) versus 17.3% for control infants. Overall incidence of adverse events (AEs) was similar for treated versus control infants; AEs were generally as expected in this population, and no AEs were considered related to study treatment. There was no observed increase in infection rates (considered a possible risk with continuous intravenous infusion) between treated and control infants. Rates of hypoglycemia (considered a possible risk with IGF-1 treatment) were also similar between groups. There was one fatal serious AE of cardiac tamponade in the treated group (not considered treatment related).

CONCLUSION

Infusion of rhIGF-1/rhIGFBP-3 increased serum concentrations of IGF-1 and attainment of target levels relative to standard neonatal care. rhIGF-1/rhIGFBP-3 infusion was well tolerated with no safety signals. Although further work is required to optimize the dose regimen for attainment of physiological intrauterine levels, we believe the results reported support the feasibility of rhIGF-1/rhIGFBP-3 continuous longitudinal infusion in extremely preterm infants. The trial is registered at ClinicalTrials.gov (NCT01096784).

First-in-man study with a novel PEGylated recombinant human insulin-like growth factor-I

OBJECTIVE

This study is a first time assessment of safety and tolerability, pharmacokinetics, and pharmacodynamics of RO5046013 in human, in comparison with unmodified rhIGF-I.

DESIGN

The study was conducted as a single-center, randomized, double-blinded, placebo-controlled, single ascending dose, parallel group study in a clinical research unit in France. A total of 62 healthy volunteers participated in this clinical trial. RO5046013 was given as single subcutaneous injection, or as intravenous infusion over 48h, at ascending dose levels. The active comparator rhIGF-I was administered at 50μg/kg subcutaneously twice daily for 4days. Safety and tolerability, pharmacokinetics, and pharmacodynamics of RO5046013 were evaluated.

RESULTS

PEGylation resulted in long exposure to RO5046013 with a half-life of 140-200h. Exposure to RO5046013 increased approximately dose proportionally. RO5046013 was safe and well tolerated at all doses, injection site erythema after SC administration was the most frequent observed AE. No hypoglycemia occurred. Growth hormone (GH) secretion was almost completely suppressed with rhIGF-I administration, whereas RO5046013 caused only a modest decrease in GH at the highest dose given IV.

CONCLUSIONS

PEGylation of IGF-I strongly enhances half-life, reduces the negative GH feedback and hypoglycemia potential, and therefore offers a valuable alternative to rhIGF-I in treatment of relevant diseases.

IGF-1 as a Drug for Preterm Infants: A Step-Wise Clinical Development

BACKGROUND

Insulin-like growth factor 1 (IGF-1) is a mitogenic hormone involved in many processes such as growth, metabolism, angiogenesis and differentiation. After very preterm birth, energy demands increase while maternal supplies of nutrients and other factors are lost and the infant may become dependent on parenteral nutrition for weeks. Low postnatal IGF-1 concentrations in preterm infants are associated with poor weight gain, retinopathy of prematurity (ROP) and other morbidities. We will describe the process by which we aim to develop supplementation with recombinant human (rh) IGF-1 and its binding protein rhIGFBP-3 as a possible therapy to promote growth and maturation and reduce morbidities in extremely preterm infants.

METHODS

In order to calculate a dose of IGF-1 tolerated by neonates, a pharmacokinetic study of transfusion with fresh frozen plasma was performed, which provided a relatively low dose of IGF-1, (on average 1.4 µg/kg), that increased serum IGF-1 to levels close to those observed in fetuses and preterm infants of similar GAs. Thereafter, a Phase I 3 hours IV infusion of rhIGF-1/rhIGFBP-3 was conducted in 5 infants, followed by a Phase II study with four sections (A-D). In the Phase II, sections A-D studies, time on infusion increased and younger gestational ages were included.

RESULTS

IV infusion increased IGF-1 but with short half-life (0.5h) implying a need for continuous infusion. In order to obtain in utero levels of IGF-I, the dose was increased from 100 to 250 µg/kg/24 h and the infusion was prolonged from 3 weeks postnatal age until a postmenstrual age of 29 weeks and 6 days.

CONCLUSION

The purpose has been to ensure high-quality research into the development of a new drug for preterm infants. We hope that our work will help to establish a new standard for the testing of medications for preterm infants.

Role of IGF Binding Proteins in Regulating Metabolism

Insulin-like growth factors (IGFs) circulate in extracellular fluids bound to a family of binding proteins. Although they function in a classical manner to limit the access of the IGFs to their receptors they also have a multiplicity of actions that are independent of this property; they bind to their own receptors or are transported to intracellular and intranuclear sites to influence cellular functions that may directly or indirectly modify IGF actions. The availability of genetically modified animals has helped to determine their functions in a physiological context. These results show that many of their actions are cell type- and context-specific, and have led to a broader understanding of how these proteins function coordinately with IGF-I and -II to regulate growth and metabolism.

Doping in sport and exercise: anabolic, ergogenic, health and clinical issues

The use of doping agents is evident within competitive sport in senior and junior age groups, where they are taken by non-elite as well as elite participants. They are also taken in non-sporting contexts by individuals seeking to ‘improve’ their physique through an increase in muscle and/or decrease in fat mass. While attaining accurate data on the prevalence of their use has limitations, studies suggest the illicit use of doping agents by athletes and non-athletes may be 1–5% in the population and greater than 50% in some groups; with the prevalence being higher in males. There is conclusive evidence that some doping agents are anabolic and ergogenic. There is also evidence that the use of doping agents such as anabolic androgenic steroids, growth hormone and other anabolic agents, erythropoietin and stimulants conveys considerable health risks that include, but are not limited to: cardiovascular disease, diabetes, cancer, mental health issues, virilisation in females and the suppression of naturally produced androgens in males. This review will outline the anabolic, ergogenic and health impacts of selected doping agents and methods that may be used in both the sporting and physique development contexts. It also provides a brief tabulated overview of the history of doping and how doping agents may impact upon the analyses of clinical samples.

Insulin-like growth factor 1 receptor signaling induced by supraphysiological doses of IGF-1 in human peripheral blood lymphocytes

Insulin-like growth factor-1 (IGF-1) mediates some of growth hormone anabolic functions through its receptor, IGF-1R. Following ligand binding, intracellular signaling pathways are activated favouring proliferation, cell survival, tissue growth, development, and differentiation. IGF-1 is included in the World Anti-Doping Agency Prohibited List. While the evidence for IGF-1 as performance-enhancing substrate in healthy humans is still weak, clinical studies demonstrated that the endogenous growth hormone/IGF-1 excess is associated with cardiovascular implications. Previously, we demonstrated that human peripheral blood lymphocytes represent a suitable system to identify a gene signature, related to dihydrotestosterone or IGF-1 abuse, independent from the type of sport. In addition, in a proteomic study, we demonstrated that dihydrotestosterone hyperdosage affects cell motility and apoptosis. Here, we investigate the doping action of IGF-1 by means of a differential proteomic approach and specific protein arrays, revealing an active cytoskeletal reorganization mediated by Stat-1; moreover, IGF-1 stimulation produces a sustained activation of different signaling pathways as well as an overproduction of cytokines positively related to immune response and inflammation. In conclusion, these data indicate that, following IGF-1 hyperdosage, circulating peripheral blood lymphocytes could be more prone to transendothelial migration.

IPLEX administration improves motor neuron survival and ameliorates motor functions in a severe mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is an inherited neurodegenerative disorder and the first genetic cause of death in childhood. SMA is caused by low levels of survival motor neuron (SMN) protein that induce selective loss of α-motor neurons (MNs) in the spinal cord, resulting in progressive muscle atrophy and consequent respiratory failure. To date, no effective treatment is available to counteract the course of the disease. Among the different therapeutic strategies with potential clinical applications, the evaluation of trophic and/or protective agents able to antagonize MNs degeneration represents an attractive opportunity to develop valid therapies. Here we investigated the effects of IPLEX (recombinant human insulinlike growth factor 1 [rhIGF-1] complexed with recombinant human IGF-1 binding protein 3 [rhIGFBP-3]) on a severe mouse model of SMA. Interestingly, molecular and biochemical analyses of IGF-1 carried out in SMA mice before drug administration revealed marked reductions of IGF-1 circulating levels and hepatic mRNA expression. In this study, we found that perinatal administration of IPLEX, even if does not influence survival and body weight of mice, results in reduced degeneration of MNs, increased muscle fiber size and in amelioration of motor functions in SMA mice. Additionally, we show that phenotypic changes observed are not SMN-dependent, since no significant SMN modification was addressed in treated mice. Collectively, our data indicate IPLEX as a good therapeutic candidate to hinder the progression of the neurodegenerative process in SMA.

Insulin-like growth factor binding proteins: a structural perspective

Insulin-like growth factor binding proteins (IGFBP-1 to -6) bind insulin-like growth factors-I and -II (IGF-I and IGF-II) with high affinity. These binding proteins maintain IGFs in the circulation and direct them to target tissues, where they promote cell growth, proliferation, differentiation, and survival via the type 1 IGF receptor. IGFBPs also interact with many other molecules, which not only influence their modulation of IGF action but also mediate IGF-independent activities that regulate processes such as cell migration and apoptosis by modulating gene transcription. IGFBPs-1 to -6 are structurally similar proteins consisting of three distinct domains, N-terminal, linker, and C-terminal. There have been major advances in our understanding of IGFBP structure in the last decade and a half. While there is still no structure of an intact IGFBP, several structures of individual N- and C-domains have been solved. The structure of a complex of N-BP-4:IGF-I:C-BP-4 has also been solved, providing a detailed picture of the structural features of the IGF binding site and the mechanism of binding. Structural studies have also identified features important for interaction with extracellular matrix components and integrins. This review summarizes structural studies reported so far and highlights features important for binding not only IGF but also other partners. We also highlight future directions in which structural studies will add to our knowledge of the role played by the IGFBP family in normal growth and development, as well as in disease.

Separation of fast from slow anabolism by site-specific PEGylation of insulin-like growth factor I (IGF-I)

Insulin-like growth factor I (IGF-I) has important anabolic and homeostatic functions in tissues like skeletal muscle, and a decline in circulating levels is linked with catabolic conditions. Whereas IGF-I therapies for musculoskeletal disorders have been postulated, dosing issues and disruptions of the homeostasis have so far precluded clinical application. We have developed a novel IGF-I variant by site-specific addition of polyethylene glycol (PEG) to lysine 68 (PEG-IGF-I). In vitro, this modification decreased the affinity for the IGF-I and insulin receptors, presumably through decreased association rates, and slowed down the association to IGF-I-binding proteins, selectively limiting fast but maintaining sustained anabolic activity. Desirable in vivo effects of PEG-IGF-I included increased half-life and recruitment of IGF-binding proteins, thereby reducing risk of hypoglycemia. PEG-IGF-I was equipotent to IGF-I in ameliorating contraction-induced muscle injury in vivo without affecting muscle metabolism as IGF-I did. The data provide an important step in understanding the differences of IGF-I and insulin receptor contribution to the in vivo activity of IGF-I. In addition, PEG-IGF-I presents an innovative concept for IGF-I therapy in diseases with indicated muscle dysfunction.

New therapeutic targets for amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is one of the most devastating neurological disorders, affecting approximately half a million people worldwide. Currently there is no cure or prevention for ALS. Although ALS is a rare condition, it places a tremendous socioeconomic burden on patients, family members, caregivers and health systems.

AREAS COVERED

The review examines the mechanisms that may contribute to motor neuron degeneration in ALS, among which oxidative damage, glutatamate excitoxicity, mitochondrial dysfunction, impaired axonal transport, apoptotic cell death, growth factor deficiency, glial cell pathology and abnormal RNA metabolism are potential targets for ALS treatment. The article provides an overview of clinical trials performed to date in attempts to treat ALS with regard to molecular mechanisms and pathways they act on. It also discusses new trials based on recently developed molecular biology techniques.

EXPERT OPINION

Despite significant effectiveness of several potential therapeutics observed in preclinical trials, the results were not translatable to patients with ALS. The development of effective treatments of ALS strictly depends on understanding the primary cause of the disease. This goal will only be achieved when we identify the trigger point for motor neuron death in ALS.

Treatment with recombinant human insulin-like growth factor (rhIGF)-I/rhIGF binding protein-3 complex improves metabolic control in subjects with severe insulin resistance

OBJECTIVE

Diabetes in the context of severe insulin resistance (SIR) presents a major therapeutic challenge because conventional therapies including insulin and insulin sensitizers often fail to achieve adequate metabolic control. Adjunctive therapy with recombinant human IGF-I (rhIGF-I)/recombinant human IGF binding protein-3 (rhIGFBP-3) has been shown to improve insulin sensitivity in both type 1 and type 2 diabetes and may have a role in the treatment of SIR. We report clinical and physiological outcomes after adjunctive therapy with rhIGF-I/rhIGFBP-3 in five subjects with SIR.

RESEARCH DESIGN AND METHODS

Five females (median age, 17 yr; range, 5-37) with SIR (two with pathogenic insulin receptor mutations) were treated with 0.5-2.0 mg/kg rhIGF-I/rhIGFBP-3 using a 16-wk dose escalation protocol. Glycosylated hemoglobin was recorded monthly. At baseline and end of treatment all patients were evaluated using continuous glucose monitoring sensing and admitted for overnight GH profiling and insulin-modified stable-label iv glucose tolerance test. Changes in body composition were assessed using dual-energy x-ray absorptiometry and magnetic resonance imaging.

RESULTS

Treatment with rhIGF-I/rhIGFBP-3 was well tolerated, and all subjects reported clinical improvements with reduction in acanthosis nigricans. Glycosylated hemoglobin was reduced (8.5% pretreatment to 7.1%; P < 0.03) with a trend toward reduction in mean continuous glucose monitoring sensing glucose (10.7 vs. 8.5 mmol/liter; P = 0.08). Effects of treatment on other biochemical measures were variable, but there was a trend toward improved C-peptide responses during the iv glucose tolerance test.

CONCLUSIONS

rhIGF-I/rhIGFBP-3 is well tolerated and clinically effective in subjects with SIR.

Insulin-like growth factor I and insulin and their abuse in sport

It is believed that insulin and insulin-like growth factor I (IGF-I) are abused by professional athletes, either alone or in combination with growth hormone (GH) and anabolic steroids. The recent introduction of IGF-I to clinical practice is likely to increase its availability and abuse. Insulin and IGF-I work together with GH to control the supply of nutrients to tissues in the fasted and fed state. The actions of insulin and IGF-I that may enhance performance include increased protein anabolism and glucose uptake and storage. The detection of IGF-I and insulin abuse is challenging. There are established mass spectrometry methods for insulin analogs. The feasibility of using GH-dependent markers to detect IGF-I use is being assessed.

IGF-I abuse in sport: current knowledge and future prospects for detection

As the tests for detecting growth hormone (GH) abuse develop further, it is likely that athletes will turn to doping with insulin-like growth factor-I (IGF-I). IGF-I mediates many of the anabolic actions of growth hormone. It stimulates muscle protein synthesis, promotes glycogen storage and enhances lipolysis, all of which make IGF-I attractive as a potential performance-enhancing agent. Pharmaceutical companies have developed commercial preparations of recombinant human IGF-I (rhIGF-I) for use in disorders of growth. The increased availability of rhIGF-I increases the opportunity for athletes to acquire supplies of the drug on the black market. The long-term effects of IGF-I administration are currently unknown but it is likely that these will be similar to the adverse effects of chronic GH abuse. The detection of IGF-I abuse is a challenge for anti-doping organisations. Research has commenced into the development of a test for IGF-I abuse based on the measurement of markers of GH action. Simultaneously, the effects of rhIGF-I on physical fitness, body composition and substrate utilisation in healthy volunteers are being investigated.

A pharmacokinetic and dosing study of intravenous insulin-like growth factor-I and IGF-binding protein-3 complex to preterm infants

In preterm infants, low levels of insulin like growth factor 1 (IGF-I) have been associated with impaired growth and retinopathy of prematurity. Our objective was to study safety and pharmacokinetics of i.v. administered rhIGF-I with its binding protein 3 (rhIGFBP-3) to preterm infants. At 3 d chronological age, an i.v. 3 h infusion of rhIGF-I/rhIGFBP-3 was administered followed by serial measurements of IGF-I and IGFBP-3. Infants were evaluated for physiologic safety measurements. The individual dose of rhIGF-I ranged from 1 to 12 microg/kg. The study was conducted at Queen Silvia Children's Hospital, Gothenburg, Sweden, between January and November 2007. Five patients (3 F) with mean (range) post menstrual age 27 wk (26-29) and birth weight 1022 g (810-1310) participated. IGF-I and IGFBP-3 levels before infusion were median (range) 18 (12-28) and 771 (651-1047) ng/mL, respectively. Immediately after study drug infusion, serum IGF-I and IGFBP-3 levels were 38 (25-59) and 838 (754-1182) ng/mL, respectively. Median (range) half-life for IGF-I and IGFBP-3 was 0.79 (0.59-1.42) and 0.87 (0.85-0.94) hours, respectively. Blood glucose, insulin, sodium, potassium, and physiologic safety measures were within normal ranges. The rhIGF-I/rhIGFBP-3 equimolar proportion was effective in increasing serum IGF-I levels and administration under these study conditions was safe and well tolerated.

[Safety aspects of treatments with hrGH]

Recombinant human growth hormone (hrGH) has been used for treatment of growth hormone deficient children over 20 years and it can be considered to have an excellent safety profile. The main international surveys show few adverse drug reactions reported, specially in idiopathic growth hormone deficiency and in idiopathic short stature. With regard to cancer risk or tumor recurrence, it seems that there is no greater risk with hrGH treatment in comparison to general population. The idiopathic intracranial hypertension is a rare condition, but its incidence is higher in patients with chronic renal failure. The adverse events are rare in patients treated with hrGH, but these patients should be carefully monitored, specially those with pharmacologycal doses or with another clinical condition of greater risk.