Can Plasma Rich in Growth Factors Be Safe for Parental Use? A Safety Study in the Canine Model.

Low invasiveness is the main goal of modern surgery. The use of platelet-rich plasma (PRP) is known to be effective in a variety of applications, such as oral, maxillofacial, orthopedic, dermatologic and cosmetic surgeries. However, a potential ergogenic and carcinogenic effect of PRP derivatives by means of the insulin-like growth factor-1 (IGF-1) pathway has been suggested. Because of this notion, the purpose of this study is to assess the effect of a commercially available PRP-derivative intramuscular injection in the lumbar muscular tissue (local effect) and to determine the IGF-1 blood concentration (systemic effect) on healthy beagle dogs. Local effect was evaluated by computed tomography (CT) scan and echography, and systemic effect was calculated by blood testing on days 0, 14, 28, 42 and 56. No statistically significant changes were observed; thus, PRGF could be considered safe when using therapeutic doses.

Bioresponsive release of insulin-like growth factor-I from its PEGylated conjugate.

PEGylation of protein ligands, the attachment of polyethylene glycol (PEG) polymers to a therapeutic protein, increases therapeutics' half-life but frequently comes at the cost of reduced bioactivity. We are now presenting a bioinspired strategy leading out of this dilemma. To this end, we selected a position within insulin-like growth factor I (IGF-I) for decoration with a PEG30kDa-modified protease-sensitive peptide linker (PSL) using a combination of enzymatic and chemical bioorthogonal coupling strategies. The PSL sequence responded to matrix metalloproteinases (MMP) to provide a targeted release in diseased tissue. The IGF-PSL-PEG conjugate had different binding protein affinity, cell proliferation, and endocytosis patterns as compared to the wild type. Exposure of the conjugate to elevated levels of activated MMPs, as present in inflamed tissues, fully reestablished the wild type properties through effective PSL cleavage. In conclusion, this bioinspired approach provided a blueprint for PEGylated therapeutics combining the pharmacokinetic advantages of PEGylation, while locally restoring the full suite of biological potential of therapeutics.

Comparative Analysis of Polyethyleneimine Efficiency for Improvement of Plasmid DNA Bioavailability.

We studied the influence of the type and structure of polyethyleneimine on bioavailability and expression of plasmid DNA carrying IGF-1 gene. Polymers with different molecular weights (2.5, 10, 25, and 60 kDa) of linear and branching structure were studied. It was found that the time of polyplex circulation in the blood did not exceed 24 h and the maximum concentration of plasmid DNA was attained with complexes with a molecular weight of 60 kDa. Analysis of liver samples showed that administration of 60-kDa branched polyethyleneimine complex provides DNA protection from degradation for 4 h; in 24 h from the start of the experiment, its concentration was significantly higher than the concentration of other studied polyethyleneimines. The expression of plasmid IGF-1 DNA for this complex attained maximum in 4 h and was equal to 15.50 (7.98; 21.98) arb. units/ml. These results allow us to recommend using polyethyleneimines with branched structure and a molecular weight of 60 kDa for improving plasmid DNA protection and bioavailability.

Pharmacokinetics of IGF-1 in PAPP-A2-Deficient Patients, Growth Response, and Effects on Glucose and Bone Density.

Context: The pregnancy-associated plasma protein A2 (PAPP-A2) cleaves insulinlike growth factor binding proteins 3 and 5, releasing free insulinlike growth factor 1 (IGF-1). Homozygous mutations in PAPP-A2 result in growth failure with elevated total but low free IGF-1. Objective: To determine the 24-hour pharmacokinetic (PK) profile of free and total IGF-1 after a dose of recombinant human insulinlike growth factor 1 (rhIGF-1). We describe the growth response and effects on glucose metabolism and bone mineral density (BMD) after 1 year of rhIGF-1 therapy. Design and Patients: Three affected siblings, their heterozygous parents, and two healthy controls participated. The subjects received a dose of rhIGF-1, followed by serial blood samples collected over 24 hours. The two younger siblings were started on rhIGF-1 treatment. An oral glucose tolerance test and dual-energy X-ray absorptiometry scans were obtained at baseline and after 1 year of treatment. Results: Subcutaneous administration of rhIGF-1 increased the concentration of free and total IGF-1 in patients with PAPP-A2 deficiency. The PK profile was comparable in all participants. At baseline, all three subjects demonstrated insulin resistance and below-average BMD. Treatment with rhIGF-1 is ongoing in the youngest patient but was discontinued in his brother because of the development of pseudotumor cerebri. The treated patient had an increase in height velocity from 3.0 to 6.2 cm/y, resolution of insulin resistance, and an increase in total body BMD. Conclusions: rhIGF-1 at standard dosages resulted in similar PK characteristics in patients with PAPP-A2 deficiency, heterozygous relatives, and healthy controls. The youngest affected patient experienced a modest growth response to therapy with rhIGF-1, as well as beneficial effects on glucose metabolism and bone mass.

PEGylated insulin-like growth factor-I affords protection and facilitates recovery of lost functions post-focal ischemia.

Insulin-like growth factor-I (IGF-I) is involved in the maturation and maintenance of neurons, and impaired IGF-I signaling has been shown to play a role in various neurological diseases including stroke. The aim of the present study was to investigate the efficacy of an optimized IGF-I variant by adding a 40 kDa polyethylene glycol (PEG) chain to IGF-I to form PEG-IGF-I. We show that PEG-IGF-I has a slower clearance which allows for twice-weekly dosing to maintain steady-state serum levels in mice. Using a photothrombotic model of focal stroke, dosing from 3 hrs post-stroke dose-dependently (0.3-1 mg/kg) decreases the volume of infarction and improves motor behavioural function in both young 3-month and aged 22-24 month old mice. Further, PEG-IGF-I treatment increases GFAP expression when given early (3 hrs post-stroke), increases Synaptophysin expression and increases neurogenesis in young and aged. Finally, neurons (P5-6) cultured in vitro on reactive astrocytes in the presence of PEG-IGF-I showed an increase in neurite length, indicating that PEG-IGF-I can aid in sprouting of new connections. This data suggests a modulatory role of IGF-I in both protective and regenerative processes, and indicates that therapeutic approaches using PEG-IGF-I should be given early and where the endogenous regenerative potential is still high.

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.

Maternally Administered Cyclic Glycine-Proline Increases Insulin-Like Growth Factor-1 Bioavailability and Novelty Recognition in Developing Offspring.

Cyclic glycine-proline (cGP), a metabolite of IGF-1, is an endogenous neuropeptide that improves memory in adult rats. The presence and concentrations of endogenous cGP, and its association with IGF-1 and IGF binding protein-3 (IGFBP-3) in rat milk and plasma, were evaluated during postnatal development. Maternal-infantile transfer of cGP during lactation and its efficacy on the memory of developing offspring were also investigated. Dams were gavaged with either cGP (3 mg/kg) or saline daily from postnatal days 8-22. Concentrations of cGP were measured in dams' milk, and concentrations of cGP, IGF-1, and IGFBP-3 were measured in the plasma of dams, pups, and young adults. The recognition memory, locomotor function, and anxiety-like behavior of offspring were evaluated using behavioral tests. Endogenous cGP was detected in rat milk, and its concentration was higher during peak lactation compared with late lactation. Comparisons within control groups showed low endogenous IGF-1 and IGFBP-3 and high endogenous cGP concentrations in the plasma of male pups. The reduced IGFBP-3 and increased cGP may be a response to increase the bioavailability of IGF-1 during infancy. Exogenous cGP showed oral bioavailability and effective maternal-infantile transfer through milk. Maternally transferred cGP also led to improved recognition memory in the developing offspring, possibly through increased IGF-1 bioavailability, with no effect on locomotor activity and anxiety-like behavior. These results show that cGP is an essential endogenous peptide during early postnatal development as it improves the bioavailability of IGF-1 during infancy. Furthermore, maternal cGP supplementation offers an effective and natural route of administration for improving memory in the developing offspring.

Sustained co-delivery of BIO and IGF-1 by a novel hybrid hydrogel system to stimulate endogenous cardiac repair in myocardial infarcted rat hearts.

Dedifferentiation and proliferation of endogenous cardiomyocytes in situ can effectively improve cardiac repair following myocardial infarction (MI). 6-Bromoindirubin-3-oxime (BIO) and insulin-like growth factor 1 (IGF-1) are two potent factors that promote cardiomyocyte survival and proliferation. However, their delivery for sustained release in MI-affected areas has proved to be challenging. In the current research, we present a study on the sustained co-delivery of BIO and IGF-1 in a hybrid hydrogel system to simulate endogenous cardiac repair in an MI rat model. Both BIO and IGF-1 were efficiently encapsulated in gelatin nanoparticles, which were later cross-linked with the oxidized alginate to form a novel hybrid hydrogel system. The in vivo results indicated that the hybrid system could enhance the proliferation of cardiomyocytes in situ and could promote revascularization around the MI sites, allowing improved cardiac function. Taken together, we concluded that the hybrid hydrogel system can co-deliver BIO and IGF-1 to areas of MI and thus improve cardiac function by promoting the proliferation of cardiomyocytes and revascularization.

Drug delivery of Insulin-like growth factor I.

This review starts off outlining the control of Insulin-like growth factor I (IGF-I) kinetics in Nature and by virtue of a complex system of 6 binding proteins controlling half-life and tissue distribution of this strong anabolic peptide. In addition, alternative splicing is known to result in IGF-I variants with modulated properties in vivo and this insight is currently translated into advanced IGF-I variants for therapeutic use. Insights into these natural processes resulted in biomimetic strategies with the ultimate goal to control pharmacokinetics and have recently propelled new developments leading to optimized pharmaceutical performance of this protein in vivo. Aside from parenteral administration routes, IGF-I was successfully delivered across various epithelial barriers from liquid as well as from solid pharmaceutical forms opening novel and more convenient delivery modalities. IGF-I decoration yielded effective targeting upon systemic administration expanding the options for optimally deploying the growth factor for therapy. This review summarizes the exciting biotechnological and pharmaceutical progress seen for IGF-I delivery in recent years and critically discusses outcome in light of translational application for future IGF-I therapeutics.

IGF-1 release kinetics from chitosan microparticles fabricated using environmentally benign conditions.

The main objective of this study is to maximize growth factor encapsulation efficiency into microparticles. The novelty of this study is to maximize the encapsulated growth factors into microparticles by minimizing the use of organic solvents and using relatively low temperatures. The microparticles were fabricated using chitosan biopolymer as a base polymer and cross-linked with tripolyphosphate (TPP). Insulin like-growth factor-1 (IGF-1) was encapsulated into microparticles to study release kinetics and bioactivity. In order to authenticate the harms of using organic solvents like hexane and acetone during microparticle preparation, IGF-1 encapsulated microparticles prepared by the emulsification and coacervation methods were compared. The microparticles fabricated by emulsification method have shown a significant decrease (p<0.05) in IGF-1 encapsulation efficiency, and cumulative release during the two-week period. The biocompatibility of chitosan microparticles and the bioactivity of the released IGF-1 were determined in vitro by live/dead viability assay. The mineralization data observed with von Kossa assay, was supported by mRNA expression levels of osterix and runx2, which are transcription factors necessary for osteoblasts differentiation. Real time RT-PCR data showed an increased expression of runx2 and a decreased expression of osterix over time, indicating differentiating osteoblasts. Chitosan microparticles prepared in optimum environmental conditions are a promising controlled delivery system for cells to attach, proliferate, differentiate and mineralize, thereby acting as a suitable bone repairing material.

Safety, pharmacokinetics, and preliminary assessment of efficacy of mecasermin (recombinant human IGF-1) for the treatment of Rett syndrome.

Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder mainly affecting females and is associated with mutations in MECP2, the gene encoding methyl CpG-binding protein 2. Mouse models suggest that recombinant human insulin-like growth factor 1 (IGF-1) (rhIGF1) (mecasermin) may improve many clinical features. We evaluated the safety, tolerability, and pharmacokinetic profiles of IGF-1 in 12 girls with MECP2 mutations (9 with RTT). In addition, we performed a preliminary assessment of efficacy using automated cardiorespiratory measures, EEG, a set of RTT-oriented clinical assessments, and two standardized behavioral questionnaires. This phase 1 trial included a 4-wk multiple ascending dose (MAD) (40-120 µg/kg twice daily) period and a 20-wk open-label extension (OLE) at the maximum dose. Twelve subjects completed the MAD and 10 the entire study, without evidence of hypoglycemia or serious adverse events. Mecasermin reached the CNS compartment as evidenced by the increase in cerebrospinal fluid IGF-1 levels at the end of the MAD. The drug followed nonlinear kinetics, with greater distribution in the peripheral compartment. Cardiorespiratory measures showed that apnea improved during the OLE. Some neurobehavioral parameters, specifically measures of anxiety and mood also improved during the OLE. These improvements in mood and anxiety scores were supported by reversal of right frontal alpha band asymmetry on EEG, an index of anxiety and depression. Our data indicate that IGF-1 is safe and well tolerated in girls with RTT and, as demonstrated in preclinical studies, ameliorates certain breathing and behavioral abnormalities.

IGFALS gene dosage effects on serum IGF-I and glucose metabolism, body composition, bone growth in length and width, and the pharmacokinetics of recombinant human IGF-I administration.

CONTEXT: Acid labile subunit (ALS) deficiency, caused by IGFALS mutations, is a subtype of primary IGF-I deficiency (PIGFD) and has been associated with insulin resistance (IR) and osteopenia. Whether patients respond to recombinant human IGF-I (rhIGF-I) is unknown. OBJECTIVE AND DESIGN: This study determined the 14-hour pharmacokinetic response of free and total IGF-I and IGF binding protein 3 (IGFBP-3) to a single sc dose of rhIGF-I (120 µg/kg) in four ALS-deficient patients, compared with severe PIGFD, moderate PIGFD, and controls. Intravenous glucose tolerance tests, fasting blood levels, dual-energy X-ray absorptiometry, peripheral quantitative computed tomography, and metacarpal radiogrammetry were performed in the four patients and 12 heterozygous family members. RESULTS: IGF-I and IGFBP-3 increased above baseline (P < .05) for 2.5 hours, returning to baseline 7 hours after rhIGF-I injection. Mean (SD) IGF-I Z-score increased by 2.49 (0.90), whereas IGFBP-3 Z-score increased by 0.57 (0.10) only. IGF-I elimination rates in ALS deficiency were similar, but the IGF-I increment was lower than those for severe PIGFD. Significant gene dosage effects were found for all IGF-I peptides, height, forearm muscle size, and metacarpal width. Bone analysis showed that ALS deficiency creates a phenotype of slender bones with normal size-corrected density. Abnormal glucose handling and IR was found in three of four patients and 6 of 12 carriers. CONCLUSIONS: These gene dosage effects demonstrate that one functional IGFALS allele is insufficient to maintain normal ALS levels, endocrine IGF-I action, full growth potential, muscle size, and periosteal expansion. Similar gene dosage effects may exist for parameters of IR. Despite similar IGF-I elimination compared with severe PIGFD, ALS-deficient patients cannot mount a similar response. Alternative ways of rhIGF-I administration should be sought.

Longitudinal infusion of a complex of insulin-like growth factor-I and IGF-binding protein-3 in five preterm infants: pharmacokinetics and short-term safety.

BACKGROUND: In preterm infants, low levels of insulin-like growth factor-I (IGF-I) and IGF binding protein 3 (IGFBP-3) are associated with impaired brain growth and retinopathy of prematurity (ROP). Treatment with IGF-I/IGFBP-3 may be beneficial for brain development and may decrease the prevalence of ROP. METHODS: In a phase II pharmacokinetics and safety study, five infants (three girls) with a median (range) gestational age (GA) of 26 wk + 6 d (26 wk + 0 d to 27 wk + 2 d) and birth weight of 990 (900-1,212) g received continuous intravenous infusion of recombinant human (rh)IGF-I/rhIGFBP-3. Treatment was initiated during the first postnatal day and continued for a median (range) duration of 168 (47-168) h in dosages between 21 and 111 µg/kg/24 h. RESULTS: Treatment with rhIGF-I/rhIGFBP-3 was associated with higher serum IGF-I and IGFBP-3 concentrations (P < 0.001) than model-predicted endogenous levels. Of 74 IGF-I samples measured during study drug infusion, 37 (50%) were within the target range, 4 (5%) were above, and 33 (45%) were below. The predicted dose of rhIGF-I/rhIGFBP-3 required to establish circulating levels of IGF-I within the intrauterine range in a 1,000 g infant was 75-100 µg/kg/24 h. No hypoglycemia or other adverse effects were recorded. CONCLUSION: In this study, continuous intravenous infusion of rhIGF-I/rhIGFBP-3 was effective in increasing serum concentrations of IGF-I and IGFBP-3, and was found to be safe.

Molecular characterisation of long-acting insulin analogues in comparison with human insulin, IGF-1 and insulin X10.

AIMS/HYPOTHESIS: There is controversy with respect to molecular characteristics of insulin analogues. We report a series of experiments forming a comprehensive characterisation of the long acting insulin analogues, glargine and detemir, in comparison with human insulin, IGF-1, and the super-mitogenic insulin, X10. METHODS: We measured binding of ligands to membrane-bound and solubilised receptors, receptor activation and mitogenicity in a number of cell types. RESULTS: Detemir and glargine each displayed a balanced affinity for insulin receptor (IR) isoforms A and B. This was also true for X10, whereas IGF-1 had a higher affinity for IR-A than IR-B. X10 and glargine both exhibited a higher relative IGF-1R than IR binding affinity, whereas detemir displayed an IGF-1R:IR binding ratio of ≤ 1. Ligands with high relative IGF-1R affinity also had high affinity for IR/IGF-1R hybrid receptors. In general, the relative binding affinities of the analogues were reflected in their ability to phosphorylate the IR and IGF-1R. Detailed analysis revealed that X10, in contrast to the other ligands, seemed to evoke a preferential phosphorylation of juxtamembrane and kinase domain phosphorylation sites of the IR. Sustained phosphorylation was only observed from the IR after stimulation with X10, and after stimulation with IGF-1 from the IGF-1R. Both X10 and glargine showed an increased mitogenic potency compared to human insulin in cells expressing many IGF-1Rs, whereas only X10 showed increased mitogenicity in cells expressing many IRs. CONCLUSIONS: Detailed analysis of receptor binding, activation and in vitro mitogenicity indicated no molecular safety concern with detemir.

Quantitative analysis of exogenous IGF-1 administration of intervertebral disc through intradiscal injection.

Exogenous administration of IGF-1 has been proposed as a therapy for disc degeneration. The objectives of this study were to develop a numerical model for quantitatively analysing exogenous administration of IGF-1 into the intervertebral disc (IVD) via intradiscal injection and to investigate the effects of IGF-1 administration on distribution of glucose and oxygen in the IVD. In this study, the reversible binding reaction between IGF-1 and IGF binding proteins was incorporated into the mechano-electrochemical mixture model. The model was used to numerically analyse transport of IGF-1, glucose, oxygen and lactate in the IVD after IGF-1 administration. The enhancement of IGF-1 on lactate production was also taken into account in the theoretical model. The numerical analyses using finite element method demonstrated that the binding reactions significantly affect the time-dependent distribution of IGF-1 in the IVD. It was found that the region affected by IGF-1 was smaller and the duration of the therapeutic IGF-1 level was longer in the degenerated disc with a higher concentration of IGF binding proteins. It was also found that the IGF-1 injection can reduce glucose concentration and increase lactate accumulation (i.e., lower pH) in the IVD and these influences were regulated by the IGF-1 binding reactions. This study indicated the complexity of intradiscal administration of growth factors, which needs to be fully analysed in order to achieve a successful outcome. The new theoretical model developed in this study can serve as a powerful tool in analysing and designing the optimal treatments of growth factors for disc degeneration.

Therapeutic effects of PEGylated insulin-like growth factor I in the pmn mouse model of motoneuron disease.

Based on its potent neurotrophic and myotrophic activities, insulin-like growth factor I (IGF-I) has been proposed for treatment of neuromuscular disorders such as muscular dystrophies and amyotrophic lateral sclerosis (ALS). However, the short half life in the circulation limits its use in vivo. At least in mouse models, beneficial effects are generally only observed by dosing regimens such as minipumps or gene therapy that are difficult to translate to patients. We have developed a polyethylene glycol coupled IGF-I (PEG-IGF-I) that could circumvent these problems by longer half-life, showing all features of a therapeutic agent supporting muscular and neuronal function. Here we investigated its effects in the pmn mutant mouse, a model with typical dying-back motoneuron degeneration. In vitro, PEG-IGF-I and rhIGF-I profoundly promoted survival axonal growth of wild-type as well as pmn mutant embryonic motoneurons, suggesting that PEG-IGF-I had a fully conserved neurotrophic activity via its receptor. In vivo, treatment of pmn mutant mice with PEG-IGF-I prolonged survival, protected against late stage weight loss and significantly maintained muscle force and motor coordination. Consistently, PEG-IGF-I treatment rescued facial and lumbar motoneurons from cell death and partially preserved phrenic nerve myelinated axons. The data support that PEG-IGF-I could be used for treatment of neuromuscular diseases in a clinically feasible manner.

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.

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.

Binding and release characteristics of insulin-like growth factor-1 from a collagen-glycosaminoglycan scaffold.

Tissue engineering is a promising technique for cartilage repair, but to optimize novel scaffolds before clinical trials, it is necessary to determine their characteristics for binding and release of growth factors. Toward this goal, a novel, porous collagen-glycosaminoglycan scaffold was loaded with a range of concentrations of insulin-like growth factor-1 (IGF-1) to evaluate its potential as a controlled delivery device. The kinetics of IGF-1 adsorption and release from the scaffold was demonstrated using radiolabeled IGF-1. Adsorption was rapid, and was approximately proportional to the loading concentration. Ionic bonding contributed to this interaction. IGF-1 release was studied over 14 days to compare the release profiles from different loading groups. Two distinct phases occurred: first, a burst release of up to 44% was noted within the first 24 h; then, a slow, sustained release (13%-16%) was observed from day 1 to 14. When the burst release was subtracted, the relative percentage of remaining IGF-1 released was similar for all loading groups and broadly followed t(½) kinetics until approximately day 6. Scaffold cross-linking using dehydrothermal treatment did not affect IGF-1 adsorption or release. Bioactivity of released IGF-1 was confirmed by seeding scaffolds (preadsorbed with unlabeled IGF-1) with human osteoarthritic chondrocytes and demonstrating increased proteoglycan production in vitro.