Pharmacokinetics and bioavailability of rhIGF-I/IGFBP-3 in the rat and monkey

Systemic administration of a recombinant AAV1 vector encoding IGF-1 improves disease manifestations in SMA mice

Spinal muscular atrophy is a progressive motor neuron disease caused by a deficiency of survival motor neuron. In this study, we evaluated the efficacy of intravenous administration of a recombinant adeno-associated virus (AAV1) vector encoding human insulin-like growth factor-1 (IGF-1) in a severe mouse model of spinal muscular atrophy. Measurable quantities of human IGF-1 transcripts and protein were detected in the liver (up to 3 months postinjection) and in the serum indicating that IGF-1 was secreted from the liver into systemic circulation. Spinal muscular atrophy mice administered AAV1-IGF-1 on postnatal day 1 exhibited a lower extent of motor neuron degeneration, cardiac and muscle atrophy as well as a greater extent of innervation at the neuromuscular junctions compared to untreated controls at day 8 posttreatment. Importantly, treatment with AAV1-IGF-1 prolonged the animals' lifespan, increased their body weights and improved their motor coordination. Quantitative polymerase chain reaction and western blot analyses showed that AAV1-mediated expression of IGF-1 led to an increase in survival motor neuron transcript and protein levels in the spinal cord, brain, muscles, and heart. These data indicate that systemically delivered AAV1-IGF-1 can correct several of the biochemical and behavioral deficits in spinal muscular atrophy mice through increasing tissue levels of survival motor neuron.

Growth Hormone and Insulin-like Growth Factor 1: New Endocrine Therapies in Cardiology?

The hormones growth hormone (GH) and insulin-like growth factor 1 (IGF-1) play a dominant role in whole body growth and metabolism. This is reflected in the use of human GH (hGH) in GH-deficient children to stimulate growth and in GH-deficient adults to reduce visceral fat mass. Recent data suggest that hGH may improve cardiac function in patients with heart failure, so there is current interest in methods to raise GH-IGF levels, including the testing of agents that release GH from the pituitary, administering IGF-1, and most recently, long-acting formulations of hGH. It is hoped that this ongoing integration of cardiology and endocrinology will uncover the pathophysiology of some cardiovascular diseases and yield new treatments based on the hormones of the GH axis. (Trends Cardiovasc Med 1997;7:264-268). © 1997, Elsevier Science Inc.

Safety aspects of longitudinal administration of IGF-I/IGFBP-3 complex in neonatal mice

OBJECTIVE

Very preterm birth is associated with a high risk of morbidity. Infants born very preterm have low serum levels of insulin-like growth factor I (IGF-I), that further decrease after birth. IGF-I is essential for brain development and low serum levels have been associated with retinopathy of prematurity. The present study aimed to investigate the effects of prolonged administration of a low dose of rhIGF-I/rhIGFBP-3 on glucose levels and total body weight, as well as liver, spleen and brain weights, and gray and subcortical white matter in newborn mice.

DESIGN

The study was performed as three different trials. In all experiments C57BL/6N mice were injected with a rhIGF-I/rhIGFBP-3 complex or saline. In the first experimental trial, blood glucose levels were assessed 30 min, 1 h, 1.5 h, 3 h, 6 h, 24 h and 48 h after the rhIGF-I/rhIGFBP-3 or saline injection on postnatal day (PND) 6. In the second trial, mice were injected daily from PND 3 to 11 and sacrificed on PND 12 for analysis of IGF-I serum levels. In the third trial, body and organ weights and effects on gray and white matter were assessed on PND 18 after PND 3-11 treatments as above. Effects on gray and white matter were measured using immunoreactivity for microtubule-associated protein-2 (MAP-2), myelin basic protein (MBP), 2',3'-cyclic nucleotide 3' phosphodiesterase (CNPase), neurofilament and oligodendrocyte lineage transcription factor 2 (Olig2).

RESULTS

Blood glucose levels were unchanged in the rhIGF-I/rhIGFBP-3-treated group compared to baseline. In the control group glucose levels increased 30 min after the second saline injection; levels were not elevated at the subsequent time point. Three hours after the rhIGF-I/rhIGFBP-3 or saline, glucose levels were lower in rhIGF-I/rhIGFBP-3-treated animals than in saline treated (p=0.026). At PND 18, total body weight was higher in rhIGF-I/rhIGFBP-3-treated mice compared with controls (p<0.05), but there were no differences between groups in brain, liver or spleen weights. No differences in gray matter area were found between groups. Analyses of white matter markers showed an increased number of Olig2-positive cells in rhIGF-I/rhIGFBP-3-treated mice compared with controls (p<0.001). There were no differences between groups in terms of MBP, CNPase or neurofilament immunoreactivity.

CONCLUSIONS

Prolonged administration of rhIGF-I/rhIGFBP-3 did not have a negative impact on blood glucose levels and was beneficial for total body growth.

Open-label trial of recombinant human insulin-like growth factor 1/recombinant human insulin-like growth factor binding protein 3 in myotonic dystrophy type 1

OBJECTIVE

To evaluate the safety and tolerability of recombinant human insulin-like growth factor 1 (rhIGF-1) complexed with IGF binding protein 3 (rhIGF-1/rhIGFBP-3) in patients with myotonic dystrophy type 1 (DM1).

DESIGN

Open-label dose-escalation clinical trial.

SETTING

University medical center.

PARTICIPANTS

Fifteen moderately affected ambulatory participants with genetically proven myotonic dystrophy type 1.

INTERVENTION

Participants received escalating dosages of subcutaneous rhIGF-1/rhIGFBP-3 for 24 weeks followed by a 16-week washout period.

MAIN OUTCOME MEASURES

Serial assessments of safety, muscle mass, muscle function, and metabolic state were performed. The primary outcome variable was the ability of participants to complete 24 weeks receiving rhIGF-1/ rhIGFBP-3 treatment.

RESULTS

All participants tolerated rhIGF-1/rhIGFBP-3. There were no significant changes in muscle strength or functional outcomes measures. Lean body muscle mass measured by dual-energy x-ray absorptiometry increased by 1.95 kg (P < .001) after treatment. Participants also experienced a mean reduction in triglyceride levels of 47 mg/dL (P = .002), a mean increase in HDL levels of 5.0 mg/dL (P = .03), a mean reduction in hemoglobin A(1c) levels of 0.15% (P = .03), and a mean increase in testosterone level (in men) of 203 ng/dL (P = .002) while taking rhIGF-1/rhIGFBP-3. Mild reactions at the injection site occurred (9 participants), as did mild transient hypoglycemia (3), lightheadedness (2), and transient papilledema (1).

CONCLUSIONS

Treatment with rhIGF-1/rhIGFBP-3 was generally well tolerated in patients with myotonic dystrophy type 1. Treatment with rhIGF-1/rhIGFBP-3 was associated with increased lean body mass and improvement in metabolism but not increased muscle strength or function. Larger randomized controlled trials would be needed to further evaluate the efficacy and safety of this medication in patients with neuromuscular disease.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00233519.

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

BACKGROUND

Mecasermin rinfabate (iPLEX), comprising rhIGF-I complexed to rhIGFBP-3, was developed in an attempt to prolong the half-life of IGF-I and potentially reduce side effects. It is administered as a once-daily subcutaneous injection. Treatment with rhIGF-I has been explored in a number of growth and endocrine disorders.

OBJECTIVE

To review the published literature regarding the pharmacokinetics, safety profile and clinical efficacy of Mecasermin rinfabate.

METHODS

A comprehensive search via the NCBI PubMed portal was performed using the search terms rhIGF-I/rhIGFBP-3 complex, iPLEX and Somatokine.

RESULTS

The effects of Mecasermin rinfabate have been explored in a number of clinical situations including diabetes, severe insulin resistance, osteopaenia, burns and growth hormone insensitivity syndrome, with outcomes similar to those of rhIGF-I alone.

CONCLUSIONS

The biological effects of Mecasermin rinfabate are largely similar to those previously reported with rhIGF-I. There are little published data pertaining to pharmacokinetic properties in human subjects, and the side effect profile appears similar to that of rhIGF-I alone.

Pharmacodynamic considerations with recombinant human insulin-like growth factor-I in children

AIM

To report effects of weight-based recombinant human insulin-like growth factor-I (rhIGF-I) on IGF axis parameters in children with hyperinsulinism.

METHODS

Open label trial with subcutaneous rhIGF-I (40 microg/kg/dose). Patients studied were children (1 month to 11 years) with diffuse hyperinsulinism (n = 7). Serial serum IGF and insulin-like growth factor binding protein (IGFBP) concentrations were measured by RIA and analyzed by linear Pearson regression.

RESULTS

Following the initial rhIGF-I dose, total insulin-like growth factor-I (IGF-I) rose by 56% at 30 min (p < 0.01) and 85% at 120 min (p < 0.02). Serum IGF-II, IGFBP-2, and IGFBP-3 levels did not change. Peak serum IGF-I levels within 12 h of the initial rhIGF-I dose were 167-700 mg/ml. The variable peak IGF-I response is attributable in part to IGFBP-3 differences across this pediatric age range. Models of rhIGF-I dosing based upon body surface area (BSA) or initial IGFBP-3 resulted in predictable peak serum IGF-I levels (r = 0.78; p < 0.03). Recalculating rhIGF-I dosing based upon the BSA . IGFBP-3 product correlated closely with peak IGF-I level (r = 0.85; p < 0.007).

CONCLUSIONS

Weight-based IGF-I dosing in this cohort resulted in variable IGF-I levels. Considering BSA and serum IGFBP-3 concentration in children is appropriate for subcutaneous IGF-I administration. A combination of these values may yield predictable individualization of rhIGF-I dosing.

IGF-I/IGFBP-3 ameliorates alterations in protein synthesis, eIF4E availability, and myostatin in alcohol-fed rats

Chronic alcohol consumption decreases the concentration of the anabolic hormone IGF-I, and this change is associated with impaired muscle protein synthesis. The present study evaluated the ability of IGF-I complexed with IGF-binding protein (IGFBP)-3 to modulate the alcohol-induced inhibition of muscle protein synthesis in gastrocnemius. After 16 wk on an alcohol-containing diet, either the IGF-I/IGFBP-3 binary complex (BC) or saline was injected two times daily for three consecutive days. After the final injection of BC (3 h), plasma IGF-I concentrations were elevated in alcohol-fed rats to values not different from those of similarly treated control animals. Alcohol feeding decreased the basal rate of muscle protein synthesis by limiting translational efficiency. BC treatment of alcohol-fed rats increased protein synthesis back to basal control values, but the rate remained lower than that of BC-injected control rats. The BC partially reversed the alcohol-induced decrease in the binding of eukaryotic initiation factor (eIF)4E with eIF4G. This change was associated with reversal of the alcohol-induced dephosphorylation of eIF4G but was independent of changes in the phosphorylation of either 4E-BP1 or eIF4E. However, BC reversed the alcohol-induced increase in IGFBP-1 and muscle myostatin, known negative regulators of IGF-I action and muscle mass. Hence, exogenous IGF-I, administered as part of a BC to increase its circulating half-life, can in part reverse the decreased protein synthesis observed in muscle from chronic alcohol-fed rats by stimulating selected components of translation initiation. The data support the role of IGF-I as a mediator of chronic alcohol myopathy in rats.

Insulin-like growth factor (IGF)-I/IGF-binding protein-3 complex: therapeutic efficacy and mechanism of protection against type 1 diabetes

IGF-I regulates islet beta-cell growth, survival, and metabolism and protects against type 1 diabetes (T1D). However, the therapeutic efficacy of free IGF-I may be limited by its biological half-life in vivo. We investigated whether prolongation of its half-life as an IGF-I/IGF binding protein (IGFBP)-3 complex affords increased protection against T1D and whether this occurs by influencing T cell function and/or islet beta-cell growth and survival. Administration of IGF-I either alone or as an IGF-I/IGFBP-3 complex reduced the severity of insulitis and delayed the onset of T1D in nonobese diabetic mice, but IGF-I/IGFBP-3 was significantly more effective. Protection from T1D elicited by IGF-I/IGFBP-3 was mediated by up-regulated CCL4 and down-regulated CCL3 gene expression in pancreatic draining lymph nodes, activation of the phosphatidylinositol 3-kinase and Akt/protein kinase B signaling pathway of beta-cells, reduced beta-cell apoptosis, and stimulation of beta-cell replication. Reduced beta-cell apoptosis resulted from elevated Bcl-2 and Bcl-X(L) activity and diminished caspase-9 activity, indicating a novel role for a mitochondrial-dependent pathway of beta-cell death. Thus, IGF-I/IGFBP-3 affords more efficient protection from insulitis, beta-cell destruction, and T1D than IGF-I, and this complex may represent an efficacious therapeutic treatment for the prevention of T1D.

Systemic administration of insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) increases bone formation parameters in mice by increasing IGF bioavailability via an IGFBP-4 protease-dependent mechanism

Insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4) is a potent inhibitor of IGF actions in vitro. However, we found that systemic administration of IGFBP-4 at pharmacological doses caused a significant increase in bone formation parameters in mice by a mechanism that may involve increased IGF bioavailability via proteolysis of IGFBP-4. To evaluate the hypothesis that proteolysis of IGFBP-4 is essential for the stimulatory effects of systemically administered IGFBP-4, we produced wild-type, protease-resistant, and IGFBP-4 proteolytic fragments and evaluated their effects using biochemical markers. Protease-resistant IGFBP-4 was more potent than wild-type IGFBP-4 in inhibiting IGF-I-induced mouse osteoblast cell proliferation in vitro and in inhibiting IGF-I-induced increase in alkaline phosphatase (ALP) activity in bone extract after local administration in vivo. Systemic administration of wild-type IGFBP-4, but not protease-resistant IGFBP-4, increased serum osteocalcin, serum ALP, and ALP in skeletal extracts in a dose-dependent manner, with a maximal effect of 40% (P < 0.05) at 1.25 nmol/mouse. Systemic administration of wild-type, but not protease-resistant, IGFBP-4 increased free IGF-I levels in serum in normal mice. IGF-I, but not wild-type IGFBP-4, increased bone formation parameters in IGF-I-deficient mice. This study demonstrates that systemic administration of IGFBP-4 increases bone formation parameters in mice by increasing IGF bioavailability in the circulation via an IGFBP-4 protease-dependent mechanism.

The complex of recombinant human insulin-like growth factor-I (rhIGF-I) and its binding protein-5 (IGFBP-5) induces local bone formation in murine calvariae and in rat cortical bone after local or systemic administration

The influence of recombinant human insulin-like growth factor-I (rhIGF-I), its binding protein-5 (IGFBP-5) or their equimolar complexes on calvarial osteogenesis was investigated by quantitative radiography and histomorphometry after local administration to adult mice or mature rats. The systemic effects of these proteins were investigated in aged Sprague-Dawley rats with regard to their ability to prevent or restore bone mass in ovariectomy induced osteopenia as assessed by radiography, dual-energy X-ray absorptiometry (DEXA) analyses, peripheral computerized tomography (pQCT) and mineral analyses after daily s.c. administration for 3 or 8 weeks following a bone depletion period of 8 weeks. Bone mass of murine calvariae was significantly increased in a dose-dependent manner by the complex 7 days after discontinuation of local administration for 19 days in mice, whereas IGF-I alone expressed only weak effects. IGFBP-5 alone was ineffective in this respect. In the same model, only the complex had a weak osteogenetic potential in 7 week or 5 month old rats. Systemic long-term treatment with the complex of rhIGF-I/IGFBP-5 (2.0/7.6 mg/kg/day, s.c.) for 8 weeks resulted in significantly increased cortical thickness, area and mineral density in femoral midshaft or tibial metaphysis suggesting periosteal bone formation. This was obviously related to increased muscle strength since these effects were parallelled by increased body weight. No effect on trabecular bone occurred as demonstrated by site-specific analyses (vertebrae, proximal tibia) using DEXA, pQCT and radiography. This selective action of rhIGF-I/IGFBP-5 on periosteal bone formation is unique for an IGFBP. Femoral ash and calcium content, both corrected for tissue volume, increased slightly. However, when the increase in cortical thickness and bone mass was corrected for bone size, the effects are nearly abolished, suggesting an additional effect of bone growth. This potential deserves further evaluation in order to differentiate between effects on cortical bone via muscle strength and lack of efficacy on trabecular bone balance.

rhIGF-I/IGFBP-3 complex, but not free rhIGF-I, supports muscle protein biosynthesis in rats during semistarvation

BACKGROUND

The aim of this study was to evaluate the effect of insulin like growth factor-I (rhIGF-I) in complex with binding protein 3 (IGFBP 3) compared to the effect of free IGF-I on muscle protein biosynthesis in undernourished animals.

METHODS

Three groups of female Sprague-Dawley rats (200 g) were initially semi-starved for 3 days and then treated with saline (controls), rhIGF-I (1 microg g-1) or equimolar amounts of rhIGF-I/rhIGFBP-3 complex (5 microg g-1) i.v. twice daily for 3 days during continuous semistarvation. Protein metabolism in hind limb skeletal muscle was studied by incorporation of L-[14C-U]phenylalanine into proteins, western blot determination of translation initiation factors involved in the binding of the 40S ribosomal subunit to mRNA, and quantification of mRNA content for IGF-I, IGF-IR and GH-R. Plasma measurements of insulin, IGF-I and amino acids were also performed.

RESULTS

rhIGF-I/rhIGFBP-3, but not rhIGF-I alone, stimulated protein synthesis by 177 +/- 26% (P </= 0.05) in semi-starved rats. This stimulation was associated with dissociation of the 4E-BP1. eIF-4E complex, implicating increased binding of the 40S ribosomal subunit to mRNA, and hence increased initiation of protein synthesis in these animals. Muscle content of IGF-I mRNA was reduced in semi-starved animals, whereas IGF-I receptor mRNA was unaltered despite food restriction. Plasma concentration of IGF-I was 20% (P </= 0.05) higher in rhIGF-I/rhIGFBP-3 treated animals as compared to rats treated with saline or free IGF-I. Plasma concentrations of amino acids were increased in rhIGF-I/rhIGFBP-3 treated animals (P </= 0.05 vs. semi-starved controls).

CONCLUSION

rhIGF-I/rhIGFBP-3 (SomatoKine) was a significant stimulator of muscle protein synthesis in chronically semi-starved animals whereas IGF-I alone failed to increase protein synthesis during the same experimental conditions. This stimulation was because of increased initiation of translation, likely induced by more physiologic concentrations/kinetics of plasma IGF-I and amino acids following rhIGF-I/rhIGFBP-3 treatment, compared to IGF-I in its free form.

Greater potency of IGF-I than IGF-I/BP-3 complex in catabolic parenterally fed rats

We compared the anabolic effects of recombinant human insulin-like growth factor I (rhIGF-I, 2.5 mg/kg) and equimolar amounts of rhIGF-I prebound to rhIGF binding protein-3 (rhIGF-I/BP-3) coinfused continuously with total parenteral nutrition (TPN) solution in dexamethasone (Dex, 70 microg/day ip)-treated male rats for 6 days. The four TPN groups included control, Dex, Dex + IGF-I, and Dex+IGF-I/BP-3. Pharmacokinetic analysis indicated reduced clearance of IGF-I when infused as IGF-I/BP-3 compared with free IGF-I (0.91 +/- 0.09 vs. 2.01 +/- 0.19 ml serum/min, P < 0.001) and this was associated with significantly greater serum IGF-I concentrations in the Dex+IGF-I/BP-3 group. Despite greater total serum IGF-I levels, infusion of free IGF-I produced greater anabolic responses than IGF-I/BP-3 based on body weight, nitrogen balance, and jejunal cellularity. Treatment with free IGF-I, but not IGF-I/BP-3, significantly reduced serum insulin and glucose levels that were elevated due to Dex. There were no significant differences in liver IGF-I mRNA levels between groups. Serum IGFBP-3 levels were elevated with infusion of IGF-I/BP-3 compared with IGF-I. These results indicate greater anabolic potency of IGF-I compared with IGF-I/BP-3 when administered by continuous parenteral infusion with TPN solution in catabolic rats.

Effects of recombinant insulin-like growth factor-binding protein-4 on bone formation parameters in mice

Insulin-like growth factor (IGF)-binding protein-4 (IGFBP-4), one of the most abundant IGFBPs produced by bone cells, is a potent inhibitor of IGF actions in vitro. To evaluate the modulation of IGF actions on bone formation in vivo by IGFBP-4, we produced intact and fragment (50- to 100-fold reduced IGF affinity) forms of BP-4 and examined their local and systemic effects using biochemical markers. Local administration of IGF-I over the right parietal bone significantly increased bone extract alkaline phosphatase activity; this was completely blocked by an equimolar dose of intact IGFBP-4, but not IGFBP-4 fragment. A single sc administration of IGF-I (2 microg/g BW) significantly increased bone formation markers in both serum and skeletal extracts; surprisingly, so did intact IGFBP-4, but not fragment IGFBP-4. Subcutaneous administration of an equimolar dose of IGFBP-4 along with IGF-I did not significantly block the IGF-I effect. Administration of intact IGFBP-4 significantly increased the serum 50-kDa IGF pool and decreased the 150-kDa IGF pool without significantly changing total IGF-I. We postulate that the increase in the 50-kDa IGF pool might enhance IGFs bioavailability via a mechanism involving IGFBP-4-specific protease. This study demonstrates for the first time that a single local administration of IGFBP-4 inhibits IGF-I-induced increases in bone formation, whereas systemic administration of IGFBP-4 alone increases serum levels of bone formation markers.

Regulation of experimental autoimmune encephalomyelitis with insulin-like growth factor (IGF-1) and IGF-1/IGF-binding protein-3 complex (IGF-1/IGFBP3)

Insulin-like growth factor (IGF)-1 is a cytokine that promotes oligodendrocyte development and myelin production. This study investigated whether treatment of chronic, relapsing murine experimental autoimmune encephalomyelitis (EAE) with IGF-1 or IGF-1 associated with its binding protein, IGFBP3, altered the course of disease. Administration of IGF-1/IGFBP3 (1-100 mg/kg per day) delayed the onset of disease in a dose-dependent manner and histologic examination showed a delay in inflammatory cells entering the central nervous system. However, once signs of EAE developed, disease was enhanced in the mice that had been given the highest dose of IGF-1/IGFBP3. Treatment with IGF-1/IGFBP3 after the onset of signs resulted in a severe relapse. Administration of free IGF-1 (10 mg/kg per day) provided mild protection when given before disease onset, but did not significantly alter the course of disease if given after disease onset. Possible mechanisms that could explain the altered disease in IGF-1/IGFBP3-treated mice included (a) IGF-1/IGFBP3 administration delayed the onset of EAE by downregulating ICAM-1 gene expression in the central nervous system, and (b) IGF-1/IGFBP3 treatment of EAE resulted in more severe disease due to enhanced expansion of encephalitogenic T cells. Although IGF-1 may enhance remyelination, these results indicate that administration of IGF-1 associated with IGFBP3 may also accentuate autoimmune demyelinating disease.