The effects of repeated daily recombinant human insulin-like growth factor I administration in adolescents with type 1 diabetes

AAV-mediated pancreatic overexpression of Igf1 counteracts progression to autoimmune diabetes in mice

Objective

Type 1 diabetes is characterized by autoimmune destruction of β-cells leading to severe insulin deficiency. Although many improvements have been made in recent years, exogenous insulin therapy is still imperfect; new therapeutic approaches, focusing on preserving/expanding β-cell mass and/or blocking the autoimmune process that destroys islets, should be developed. The main objective of this work was to test in non-obese diabetic (NOD) mice, which spontaneously develop autoimmune diabetes, the effects of local expression of Insulin-like growth factor 1 (IGF1), a potent mitogenic and pro-survival factor for β-cells with immunomodulatory properties.

Methods

Transgenic NOD mice overexpressing IGF1 specifically in β-cells (NOD-IGF1) were generated and phenotyped. In addition, miRT-containing, IGF1-encoding adeno-associated viruses (AAV) of serotype 8 (AAV8-IGF1-dmiRT) were produced and administered to 4- or 11-week-old non-transgenic NOD females through intraductal delivery. Several histological, immunological, and metabolic parameters were measured to monitor disease over a period of 28–30 weeks.

Results

In transgenic mice, local IGF1 expression led to long-term suppression of diabetes onset and robust protection of β-cell mass from the autoimmune insult. AAV-mediated pancreatic-specific overexpression of IGF1 in adult animals also dramatically reduced diabetes incidence, both when vectors were delivered before pathology onset or once insulitis was established. Transgenic NOD-IGF1 and AAV8-IGF1-dmiRT-treated NOD animals had much less islet infiltration than controls, preserved β-cell mass, and normal insulinemia. Transgenic and AAV-treated islets showed less expression of antigen-presenting molecules, inflammatory cytokines, and chemokines important for tissue-specific homing of effector T cells, suggesting IGF1 modulated islet autoimmunity in NOD mice.

Conclusions

Local expression of Igf1 by AAV-mediated gene transfer counteracts progression to diabetes in NOD mice. This study suggests a therapeutic strategy for autoimmune diabetes in humans.

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Local pancreatic IGF1 expression prevents spontaneous autoimmune diabetes.

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Protection achieved after one-time local administration of IGF1-encoding AAV vectors.

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Efficacious in animals treated early or once autoimmunity is already established.

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Protection through maintenance of β-cell mass and endogenous insulin secretion.

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Treatment leads to reduced infiltration and expression of immunity genes in islets.

Novel markers to detect recombinant human insulin-like growth factor-I (rhIGF-I)/rhIGF binding protein-3 (rhIGFBP-3) misuse in athletes

Insulin-like growth factor-I (IGF-I) is abused by elite athletes for its metabolic and anabolic effects. We have previously shown that it is possible to detect IGF-I misuse by measuring serum IGF-I and procollagen type III amino-terminal propeptide (P-III-NP) but a pilot study suggested measuring IGF-II, IGF binding protein-2 (IGFBP-2) and acid-labile subunit (ALS) may improve the detection of IGF-I administration. The aim of the study was to assess this in a randomized controlled trial. Twenty-six female and 30 male recreational athletes were randomized to 28 days' treatment with placebo or recombinant human (rh)IGF-I/rhIGF binding protein-3 (IGFBP-3) complex (30 mg/day or 60 mg/day), followed by 56 days' washout. IGF-II, IGFBP-2 and ALS (women only) were measured using commercial immunoassays. IGFBP-2 increased and IGF-II decreased in response to both low and high dose rhIGF-I/rhIGFBP-3 in both women and men while ALS decreased in women in response to high dose rhIGF-I/rhIGFBP-3. Two days after discontinuing treatment, significant differences remained between the three treatment groups in IGFBP-2 and IGF-II, but not ALS. Thereafter there were no significant differences between the three treatment groups in any of the markers. Combining IGF-I with IGF-II and/or IGFBP-2 improved the performance of the test to detect rhIGF-I/rhIGFBP-3 administration in both women and men. Copyright © 2016 John Wiley & Sons, Ltd.

Insulin-like growth factor-1 deficiency and metabolic syndrome

Consistent evidence associates IGF-1 deficiency and metabolic syndrome. In this review, we will focus on the metabolic effects of IGF-1, the concept of metabolic syndrome and its clinical manifestations (impaired lipid profile, insulin resistance, increased glucose levels, obesity, and cardiovascular disease), discussing whether IGF-1 replacement therapy could be a beneficial strategy for these patients. The search plan was made in Medline for Pubmed with the following mesh terms: IGF-1 and "metabolism, carbohydrate, lipids, proteins, amino acids, metabolic syndrome, cardiovascular disease, diabetes" between the years 1963-2015. The search includes animal and human protocols. In this review we discuss the relevant actions of IGF-1 on metabolism and the implication of IGF-1 deficiency in the establishment of metabolic syndrome. Multiple studies (in vitro and in vivo) demonstrate the association between IGF-1 deficit and deregulated lipid metabolism, cardiovascular disease, diabetes, and an altered metabolic profile of diabetic patients. Based on the available data we propose IGF-1 as a key hormone in the pathophysiology of metabolic syndrome; due to its implications in the metabolism of carbohydrates and lipids. Previous data demonstrates how IGF-1 can be an effective option in the treatment of this worldwide increasing condition. It has to distinguished that the replacement therapy should be only undertaken to restore the physiological levels, never to exceed physiological ranges.

Insulin and GH-IGF-I axis: endocrine pacer or endocrine disruptor?

Growth hormone/insulin-like growth factor (IGF) axis may play a role in maintaining glucose homeostasis in synergism with insulin. IGF-1 can directly stimulate glucose transport into the muscle through either IGF-1 or insulin/IGF-1 hybrid receptors. In severely decompensated diabetes including diabetic ketoacidosis, plasma levels of IGF-1 are low and insulin delivery into the portal system is required to normalize IGF-1 synthesis and bioavailability. Normalization of serum IGF-1 correlated with the improvement of glucose homeostasis during insulin therapy providing evidence for the use of IGF-1 as biomarker of metabolic control in diabetes. Taking apart the inherent mitogenic discussion, diabetes treatment using insulins with high affinity for the IGF-1 receptor may act as an endocrine pacer exerting a cardioprotective effect by restoring the right level of IGF-1 in bloodstream and target tissues, whereas insulins with low affinity for the IGF-1 receptor may lack this positive effect. An excessive and indirect stimulation of IGF-1 receptor due to sustained and chronic hyperinsulinemia over the therapeutic level required to overtake acute/chronic insulin resistance may act as endocrine disruptor as it may possibly increase the cardiovascular risk in the short and medium term and mitogenic/proliferative action in the long term. In conclusion, normal IGF-1 may be hypothesized to be a good marker of appropriate insulin treatment of the subject with diabetes and may integrate and make more robust the message coming from HbA1c in terms of prediction of cardiovascular risk.

Biochemical markers of insulin-like growth factor-I misuse in athletes: the response of serum IGF-I, procollagen type III amino-terminal propeptide, and the GH-2000 score to the administration of rhIGF-I/rhIGF binding protein-3 complex

CONTEXT

The GH-2000 and GH-2004 research groups developed a method for detecting GH misuse in athletes based on the measurement of serum IGF-I and procollagen type III amino-terminal propeptide (P-III-NP). There are reports that IGF-I is also misused by athletes, but currently there is no internationally recognized test designed to detect recombinant human IGF-I misuse.

OBJECTIVE

The objective of the study was to examine the response of serum IGF-I, P-III-NP, and the GH-2000 score to recombinant human (rh) IGF-I/rhIGF binding protein-3 (IGFBP-3) administration in recreational athletes.

DESIGN AND SETTING

This was a randomized, double-blind, placebo-controlled rhIGF-I/rhIGFBP-3 administration study at Southampton General Hospital (Southampton, United Kingdom).

PARTICIPANTS

Fifty-six recreational athletes (26 women, 30 men) participated in the study.

INTERVENTION

Participants were randomized to treatment with low-dose (30 mg/d) or high-dose (60 mg/d) rhIGF-I/rhIGFBP-3 complex or placebo for 28 days. Blood was collected throughout the drug administration and washout periods. Serum IGF-I and P-III-NP were measured using commercial immunoassays and GH-2000 scores were calculated.

RESULTS

IGF-I, P-III-NP, and the GH-2000 score rose in response to both low- and high-dose rhIGF-I/rhIGFBP-3 administration. The relative maximum response of IGF-I (approximately 4-fold increase in women and men) was greater than that of P-III-NP (40%-50% increase in women, 35%-50% increase in men). The GH-2000 formulae, which incorporate IGF-I and P-III-NP results, detected up to 61% of women and 80% of men in the rhIGF-I/rhIGFBP-3 groups but, using IGF-I concentrations alone, the sensitivity increased to 94% in both women and men during the administration period.

CONCLUSIONS

The rise in P-III-NP after rhIGF-I/rhIGFBP-3 administration is small compared with that after rhGH administration. Although rhIGF-I/rhIGFBP-3 administration can be detected using the GH-2000 score method, a test based on serum IGF-I alone provides better sensitivity.

Diabetes, growth hormone-insulin-like growth factor pathways and association to benign prostatic hyperplasia

Diabetes significantly increases the risk of benign prostatic hyperplasia (BPH) and low urinary tract symptoms (LUTS). The major endocrine aberration in connection with the metabolic syndrome is hyperinsulinemia. Insulin is an independent risk factor and a promoter of BPH. Insulin resistance may change the risk of BPH through several biological pathways. Hyperinsulinemia stimulates the liver to produce more insulin-like growth factor (IGF), another mitogen and an anti-apoptotic agent which binds insulin receptor/IGF receptor and stimulates prostate growth. The levels of IGFs and IGF binding proteins (IGFBPs) in prostate tissue and in blood are associated with BPH risk, with the regulation of circulating androgen and growth hormone. Stromal-epithelial interactions play a critical role in the development and growth of the prostate gland and BPH. Previously, we have shown that the expression of c-Jun in the fibroblastic stroma can promote secretion of IGF-I, which stimulates prostate epithelial cell proliferation through activating specific target genes. Here, we will review the epidemiologic, clinical, and molecular findings which have evaluated the relation between diabetes and development of BPH.

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.

The role of insulin-like growth factor-I and its binding proteins in glucose homeostasis and type 2 diabetes

This review addresses the possible role of the insulin-like growth factor (IGF)-axis in normal glucose homoeostasis and in the etiopathogenesis of type 2 diabetes. IGF-I, a peptide hormone, shares amino acid sequence homology with insulin and has insulin-like activity; most notably, the promotion of glucose uptake by peripheral tissues. Type 2 diabetes as well as pre-diabetic states, including impaired fasting glucose and impaired glucose tolerance, are associated cross-sectionally with altered circulating levels of IGF-I and its binding proteins (IGFBPs). Administration of recombinant human IGF-I has been reported to improve insulin sensitivity in healthy individuals as well as in patients with insulin resistance and type 2 diabetes. Further, IGF-I may have beneficial effects on systemic inflammation, a risk factor for type 2 diabetes, and on pancreatic beta-cell mass and function. There is considerable inter-individual heterogeneity in endogenous levels of IGF-I and its binding proteins; however, the relationship between these variations and the risk of developing type 2 diabetes has not been extensively investigated. Large prospective studies are required to evaluate this association.

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.

Changes in insulin sensitivity and glucose metabolism during therapy with recombinant human growth hormone in short children born small for gestational age show a negative correlation with baseline measurements

Recombinant human growth hormone (rhGH) is an effective therapy for children with short stature born small for gestational age (SGA); however, insulin resistance can develop during treatment. This retrospective analysis assessed the effect of rhGH treatment (0.067 mg/kg/day) on glucose metabolism and insulin secretion in children with short stature born SGA, and measured whether baseline characteristics correlated with changes in insulin resistance or glucose sensitivity during treatment. Baseline glucose area under the concentration-time curve (AUC) was negatively correlated with the change in glucose AUC (p<0.001). Similar negative correlations were seen between baseline insulin AUC and the change in insulin AUC during treatment (p<0.001); and between baseline HOMA-IR (homeostatic model of insulin resistance) and the change in HOMA-IR during treatment (p<0.001). Small but significant changes, not thought to be clinically significant, were seen in indicators of insulin sensitivity during rhGH treatment. Glucose levels remained within the normal range during oral glucose tolerance testing.

Normalization of the IGF-IGFBP axis by sustained nightly insulinization in type 1 diabetes

OBJECTIVE

We sought to test the hypothesis that start of insulin glargine with sustained nightly insulin action results in changes in circulating concentrations of IGF-I and IGF binding proteins (IGFBPs) in adolescents with type 1 diabetes-changes that may support improvement of A1C.

RESEARCH DESIGN AND METHODS

Twelve pubertal adolescents with type 1 diabetes and initially on NPH insulin were studied during 12 weeks of intensified treatment with glargine.

RESULTS

Subnormal IGF-I SD scores on NPH (-1.8 +/- 0.4) rapidly increased and remained 54 +/- 9% elevated (P < 0.001) after 12 weeks on glargine. A1C decreased from 8.3 +/- 0.6% to a nadir of 6.9 +/- 0.3% (P = 0.002) at 6 weeks and correlated with changes in IGF-I (r = -0.64, P < 0.05). The increase in IGF-I did not suppress the mean overnight growth hormone (GH) secretion at 6 weeks. The mean overnight IGFBP-1 levels decreased (P = 0.035), supporting the hypothesis that the nightly hepatic insulin action was increased. Circulating IGF-I increased in the absence of changes in both GH secretion and GH receptor numbers (assessed by growth hormone binding protein), indicating that postreceptor mechanisms are involved. IGFBP-3 proteolysis was decreased.

CONCLUSIONS

Increased hepatic insulin action after start of glargine was evident from a decrease in night time IGFBP-1 concentrations. This may improve GH postreceptor signaling, resulting in increased circulating IGF-I. We suggest that even in the absence of changes in GH, increased IGF-I and decreased IGFBP-1 support the improvement of metabolic control.

Therapeutic aspects of growth hormone and insulin-like growth factor-I treatment on visceral fat and insulin sensitivity in adults

Growth hormone (GH) is generally considered to exert anti-insulin actions, whereas insulin-like growth factor I (IGF-I) has insulin-like properties. Paradoxically, GH deficient adults and those with acromegaly are both predisposed to insulin resistance, but one cannot extrapolate from these pathological conditions to determine the normal metabolic roles of GH and IGF-I on glucose homeostasis. High doses of GH treatment have major effects on lipolysis, which plays a crucial role in promoting its anti-insulin effects, whereas IGF-I acts as an insulin sensitizer that does not exert any direct effect on lipolysis or lipogenesis. Under physiological conditions, the insulin-sensitizing effect of IGF-I is only evident after feeding when the bioavailability of circulating IGF-I is increased. In contrast, many studies in GH deficient adults have consistently shown that GH replacement improves the body composition profile although these studies differ considerably in terms of age, the presence or absence of multiple pituitary hormone deficiency, and whether GH deficiency was childhood or adult-onset. However, the improvement in body composition does not necessarily translate into improvements in insulin sensitivity presumably due to the anti-insulin effects of high doses of GH therapy. More recently, we have found that a very low dose GH therapy (0.1 mg/day) improved insulin sensitivity without affecting body composition in GH-deficient adults and in subjects with metabolic syndrome, and we postulate that these effects are mediated by its ability to increase free 'bioavailable' IGF-I without the induction of lipolysis. These results raise the possibility that this low GH dose may play a role in preventing the decline of beta-cell function and the development of type 2 diabetes in these "high risk" subjects.

Short-term suppression of elevated growth hormone concentrations following insulin-like growth factor 1 administration in young adults with type 1 diabetes does not alter glomerular filtration or albumin excretion rates

OBJECTIVE

Young adults with type 1 diabetes mellitus (T1DM) have increased glomerular filtration rate (GFR), which may mediate progressive renal disease and microalbuminuria. This may be secondary to low concentrations of insulin-like growth factor (IGF)-I and GH hypersecretion. We tested the hypothesis that restoration of circulating IGF-I concentrations in young adults with T1DM might suppress GH secretion, GFR and urinary albumin excretion.

DESIGN

In a randomized double blind crossover study six young adults with T1DM (three men, 19-24 years) received 7 days treatment with rhIGF-I/insulin-like growth factor binding protein (IGFBP)-3 complex (SomatoKine) 0.4 mg/kg/day and placebo. Subjects underwent overnight insulin infusion for euglycaemia, followed by determination of GFR and albumin excretion rate.

RESULTS

Following IGF-I/IGFBP-3 complex, overnight insulin requirements (0.15 vs placebo 0.21 mU/kg/min, P < 0.04), plasma insulin (77 vs placebo 152 pmol/l, P < 0.01) and mean overnight GH (2.6 vs placebo 4.8 mU/l, P < 0.04) fell. IGF-I (492 vs placebo 218 ng/ml, P < 0.01) and IGFBP-3 (4.5 vs placebo 3.9 microg/ml, P < 0.05) increased. GFR did not change (145.5 (23.9) ml/min/1.73 m(2) post-IGF-I/IGFBP-3 complex vs 152.2 (19.8) post placebo). Albumin excretion rate did not change 9.5 (5.5-16.6)mg/24 h pre- vs 11.5 (9.9-20.2) post-IGF-I/IGFBP-3 complex and 10.7 (8.1-21.2) pre- vs 11.5 (8.7-29.9) post placebo. Plasma creatinine levels were lower following IGF-I/IGFBP-3 complex (mean +/- SD, 56.2 +/- 16.8 micromol/l) vs placebo (61.5, 45.0, P < 0.02).

CONCLUSIONS

Seven days treatment with IGF-I/IGFBP-3 complex enhanced overnight insulin sensitivity and reduced GH levels, but there was no effect on glomerular hyperfiltration or albumin excretion rates.

Influence of the crosstalk between growth hormone and insulin signalling on the modulation of insulin sensitivity

Growth hormone (GH) is an important modulator of insulin sensitivity. Multiple mechanisms appear to be involved in this modulatory effect. GH does not interact directly with the insulin receptor (IR), but conditions of GH excess are associated in general with hyperinsulinemia that induces a reduction of IR levels and impairment of its kinase activity. Several post-receptor events are shared between GH and insulin. This signaling crosstalk could be involved in the diabetogenic effects of GH. The utilization of animal models of GH excess, deficiency or resistance provided evidence that the signaling pathway leading to stimulation of the phosphatidylinositol 3-kinase (PI3K)/Akt cascade is an important site of regulation, and pointed to the liver as the major site of GH-induced insulin resistance. In skeletal muscle, GH-induced insulin resistance might involve an increase in the amount of the p85 subunit of PI3K that plays a negative role in insulin signalling. GH also reduces insulin sensitivity by enhancing events that negatively modulate insulin signaling such as stimulation of serine phosphorylation of IRS-1, which prevents its recruitment to the IR and induction of the suppressor of cytokine signalling (SOCS)-1 and SOCS-3 which modulate the signalling potential of the IRS proteins. In addition, GH has been shown to decrease the expression of the insulin-sensitizing adipo-cytokines adiponectin and visfatin. Finally, genetic manipulation of mice indicated that whereas GH plays a major role in reducing insulin sensitivity, circulating IGF-I also participates in the control of insulin sensitivity and plays an important role in the hormonal balance between GH and insulin.

Therapeutic applications of the insulin-like growth factors

The potential therapeutic applications of the insulin-like growth factors (IGFs) are broad. This review focuses on treatment of humans with recombinant human IGF-I (rhIGF-I), and with a rhIGF-I/IGF binding protein-3 (IGFBP-3) complex. Several groups of patients have been treated effectively, including individuals with growth hormone insensitivity syndrome (GHIS) secondary to GH receptor deficiency, to IGF-I gene deletion, or to defects in GH signal transduction pathways, patients with type 1 and type 2 diabetes mellitus, or individuals with severe insulin resistance syndromes. In each of these conditions rhIGF-I therapy has been demonstrated to be of clear clinical benefit. Other conditions, which may potential targets for therapy with rhIGF-I or rhIGF-I/IGFBP-3, include chronic inflammatory or nutritional disorders such as Crohn's disease, juvenile chronic arthritis, or cystic fibrosis. Therapy with IGFs has not been attempted in these disorders yet, in part because of lack of adequate supplies. Recently, the newly developed rhIGF-I/IGFBP-3 complex has been used in early clinical studies. Pharmacokinetic analyses in patients with diabetes mellitus and GHIS have suggested that a more physiological profile of serum IGF-I results. Improved glycaemic control has been reported in type 1 and type 2 diabetes in adults. A therapeutic trial in naïve children with GHIS is currently under way.

Insulin resistance in the liver-specific IGF-1 gene-deleted mouse is abrogated by deletion of the acid-labile subunit of the IGF-binding protein-3 complex: relative roles of growth hormone and IGF-1 in insulin resistance

Liver IGF-1 deficient (LID) mice demonstrate a 75% reduction in circulating IGF-1 levels and a corresponding fourfold increase in growth hormone (GH) levels. At 16 weeks of age, LID mice demonstrate, using the hyperinsulinemic-euglycemic clamp, insulin insensitivity in muscle, liver, and fat tissues. In contrast, mice with a gene deletion of the acid-labile subunit (ALSKO) demonstrate a 65% reduction in circulating IGF-1 levels, with normal GH levels and no signs of insulin resistance. To further clarify the relative roles of increased GH and decreased IGF-1 levels in the development of insulin resistance, we crossed the two mouse lines and created a double knockout mouse (LID+ALSKO). LID+ALSKO mice demonstrate a further reduction in circulating IGF-1 levels (85%) and a concomitant 10-fold increase in GH levels. Insulin tolerance tests showed an improvement in insulin responsiveness in the LID+ALSKO mice compared with controls; LID mice were very insulin insensitive. Surprisingly, insulin sensitivity, while improved in white adipose tissue and in muscle, was unchanged in the liver. The lack of improvement in liver insulin sensitivity may reflect the absence of IGF-1 receptors or increased triglyceride levels in the liver. The present study suggests that whereas GH plays a major role in inducing insulin resistance, IGF-1 may have a direct modulatory role.

IGFs and IGFBPs: role in health and disease

The insulin-like growth factors (IGFs), IGF-binding proteins (IGFBPs), and IGFBP proteases are the main regulators of somatic growth and cellular proliferation. IGFs are involved in growth pre-natally and post-natally. Dysregulation of the IGF axis can lead to growth disorders such as growth hormone deficiency and acromegaly. Pre-natally, this dysregulation can lead to IUGR or macrosomia. IGFs also have an important mitogenic action and play a role in tumorigenesis and cancer. These actions are regulated by co-interactions with IGFBPs, especially IGFBP-3. In addition to somatic growth and mitogenic activity, IGFs have hypoglycaemic and insulin sensitizing actions, and their dysregulation is involved in diabetes and its complications. In this chapter, we examine the role of IGFs and IGFBPs in growth, tumorigenesis and diabetes, and discuss treatment modalities for each disease involving the GH-IGF-IGFBP axis, including discussion of current in vitro and in vivo investigations in this field.

The role of IGF-binding proteins in mediating the effects of recombinant human IGF-I on insulin requirements in type 1 diabetes mellitus

To determine the role of IGF-binding proteins in mediating the direct effects of recombinant human IGF-I on insulin requirements in type 1(insulin-dependent) diabetes mellitus, overnight changes in IGF-I, IGF-II, and IGF-binding protein-1, -2, and -3, collected under euglycemic conditions, were compared in nine subjects after double blind, randomized, sc administration of recombinant human IGF-I (40 microg/kg) or placebo at 1800 h. On both nights a somatostatin analog infusion (300 ng/kg x h) suppressed endogenous GH production, and three timed discrete GH pulses (total, 0.029 IU/kg x night) ensured identical GH levels. After recombinant human IGF-I administration, IGF-I levels and the IGF-I/IGF-binding protein-3 ratio increased [mean +/- SEM:IGF-I, 401 +/- 22 ng/ml; placebo, 256 +/- 20 ng/ml (P = 0.0002); IGF-I, 0.108 +/- 0.006; placebo, 0.074 +/- 0.004 (P = 0.0003), respectively], and insulin requirements decreased (IGF-I, 0.12 +/- 0.03; placebo, 0.23 +/- 0.03 U/kg x min; P = 0.008). The normal within-individual inverse relationships between insulin and IGF-binding protein-1 levels were observed (lag time 2 h: r = -0.34; P < 0.01). Yet despite reduced free insulin levels (8.5 +/- 1.5; placebo, 12.2 +/- 1.2 mU/liter; P = 0.03), IGF-binding protein-1 levels were reduced after recombinant human IGF-I administration (53.7 +/- 6.8; placebo, 82.2 +/- 11.8 ng/ml; P = 0.008). The largest reductions in free insulin levels after recombinant human IGF-I and thus putative improvement in insulin sensitivity occurred in subjects with the smallest increase in the plasma IGF-I/IGF-binding protein-3 ratio (r = 0.7; P = 0.03). Taken together, these data are consistent with the hypothesis that transcapillary movement of IGF-I (perhaps mediated by IGF-binding protein-1), out of the circulation facilitates altered insulin sensitivity. These data have important implications for risk-benefit assessment of recombinant human IGF-I therapy in type 1 diabetes mellitus.

Control of growth by the somatropic axis: growth hormone and the insulin-like growth factors have related and independent roles

The traditionally accepted theory has been that most of the biological effects of growth hormone (GH) are mediated by circulating (endocrine) insulin-like growth factor-I (IGF-I). This dogma was modified when it was discovered that most tissues express IGF-I that can act via an autocrine/paracrine fashion. In addition, both GH and IGF-I had independent effects on various target tissues. Using tissue-specific gene deletion of IGF-I in the liver, it has been shown that circulating IGF-I is predominantly liver-derived but is not essential for normal postnatal growth. Therefore, it is proposed that non-hepatic tissue-derived IGF-I may be sufficient for growth and development. Thus the original somatomedin hypothesis has undergone further modifications.

The somatomedin hypothesis: 2001

Since the original somatomedin hypothesis was conceived, a number of important discoveries have allowed investigators to modify the concept. Originally somatic growth was thought to be controlled by pituitary GH and mediated by circulating insulin-like growth factor-I (IGF-I, somatomedin C) expressed exclusively by the liver. With the discovery that IGF-I is produced by most, if not all, tissues, the role of autocrine/paracrine IGF-I vs. the circulating form has been hotly debated. Recent experiments using transgenic and gene-deletion technologies have attempted to answer these questions. In the liverspecific igf-1 gene-deleted mouse model, postnatal growth and development are normal despite the marked reduction in circulating IGF-I and IGF-binding protein levels; free IGF-I levels are normal. Thus, the normal postnatal growth and development in these animals may be due to normal free IGF-I levels (from as yet unidentified sources), although the role of autocrine/paracrine IGF-I has yet to be determined.

Insulin-like growth factor-I in diabetes mellitus: its physiology, metabolic effects, and potential clinical utility

Type 1 diabetes mellitus (DM) is a disease of insulin deficiency, resulting from the autoimmune-mediated destruction of pancreatic beta cells. However, as a likely consequence of intraportal insulin deficiency, patients with type 1 DM also exhibit abnormalities of the growth hormone (GH)/IGF/IGF-binding protein (IGFBP) axis, including GH hypersecretion, reduced circulating levels of insulin-like growth factor-I (IGF-I) and IGFBP-3, and elevated levels of IGFBP-1. These abnormalities not only exacerbate hyperglycemia in patients with type 1 DM, but may contribute to the pathogenesis of diabetes-specific complications, including diabetic neuropathy, nephropathy, and retinopathy. Therefore, therapeutic modalities aimed at restoring the GH-IGF-IGFBP axis are being considered. Herein, we review the efficacy of one such therapy, specifically IGF-I replacement therapy. To date, short-term beneficial metabolic effects of recombinant human IGF (rhIGF)-I therapy have been demonstrated in numerous diabetic conditions, including type 1 DM, type 2 DM, and type A insulin resistance. However, the long- term safety and metabolic efficacy of rhIGF-I therapy remains to be established. Moreover, the potential impact of rhIGF-I on the natural history of diabetic complications has yet to be explored.

Effects of low-dose recombinant human insulin-like growth factor-I on insulin sensitivity, growth hormone and glucagon levels in young adults with insulin-dependent diabetes mellitus

Despite recent interest in the therapeutic potential of recombinant human insulin-like growth factor-I (rhIGF-I) in the treatment of diabetes mellitus, its mechanism of action is still not defined. We have studied the effects of low-dose bolus subcutaneous rhIGF-I (40 microg/kg and 20 microg/kg) on insulin sensitivity, growth hormone (GH) and glucagon levels in seven young adults with insulin-dependent diabetes mellitus (IDDM) using a randomized double-blind placebo-controlled crossover study design. Each was subjected to a euglycemic clamp (5 mmol/L) protocol consisting of a variable-rate insulin infusion clamp (6:00 PM to 8:00 AM) followed by a two-dose hyperinsulinemic clamp (insulin infusion of 0.75 mU x kg(-1) x min(-1) from 8 to 10 AM and 1.5 mU x kg(-1) x min(-1) from 10 AM to 12 noon) incorporating [6,6 2H2]glucose tracer for determination of glucose production/utilization rates. Following rhIGF-I administration, the serum IGF-I level (mean +/- SEM) increased (40 microg/kg, 655 +/- 90 ng/mL, P < .001; 20 microg/kg, 472 +/- 67 ng/mL, P < .001; placebo, 258 +/- 51 ng/mL). Dose-related reductions in insulin were observed during the period of steady-state euglycemia (1 AM to 8 AM) (40 microg/kg, 48 +/- 5 pmol/L, P = .01; 20 microg/kg, 58 +/- 8 pmol/L, P = .03; placebo, 72 +/- 8 pmol/L). The mean overnight GH level (40 microg/kg, 9.1 +/- 1.4 mU/L, P = .04; 20 microg/kg, 9.6 +/- 2.0 mU/L, P = .12; placebo, 11.3 +/- 1.7 mU/L) and GH pulse amplitude (40 microg/kg, 18.8 +/- 2.9 mU/L, P = .04; 20 microg/kg, 17.0 +/- 3.4 mU/L, P > .05; placebo, 23.0 +/- 3.7 mU/L) were also reduced. No differences in glucagon, IGF binding protein-1 (IGFBP-1), acetoacetate, or beta-hydroxybutyrate levels were found. During the hyperinsulinemic clamp conditions, no differences in glucose utilization were noted, whereas hepatic glucose production was reduced by rhIGF-I 40 microg/kg (P = .05). Our data demonstrate that in subjects with IDDM, low-dose subcutaneous rhIGF-I leads to a dose-dependent reduction in the insulin level for euglycemia overnight that parallels the decrease in overnight GH levels, but glucagon and IGFBP-1 levels remain unchanged. The decreases in hepatic glucose production during the hyperinsulinemic clamp study observed the following day are likely related to GH suppression, although a direct effect by rhIGF-I cannot be entirely discounted.

Insulin-like growth factor-I and diabetes. A review

Although diabetes is a heterogeneous condition, IGF-I has been shown to improve glycaemic control and reduce insulin requirements in both IDDM and NIDDM. In IDDM, the therapeutic rationale for IGF-I is as a replacement therapy "topping up" low circulating IGF-I levels. There is now convincing evidence that this is associated with a reduction in GH secretion resulting in an improvement in insulin sensitivity and glycaemic control. The mechanism may simply be reduced GH-secretion, but pre- and post-receptor effects on insulin sensitivity are also likely. It is not clear what effect IGF-I treatment has on IGF binding proteins, but with the restoration of a more normal GH/IGF-I axis they are likely to be restored to normal concentrations which may in turn have a direct effect on glucose metabolism. In NIDDM, the mechanism of action of IGF-I remains unclear. At high doses, IGF-I may mimic insulin, but at levels resulting in unacceptable "acromegalic" IGF-I levels and side-effects. The most exciting data concerning IGF-I is with a low dose where IGF-I improves insulin sensitivity by an unknown mechanism. This may be mediated via the IGF-I receptor, by cross-reactivity with the insulin receptor, or by activation of hybrid receptors. The exact mechanism and interaction remains to be elucidated. In severe insulin-resistant states, IGF-I-treatment appears to be effective, and may be the only realistic therapeutic measure in the near future, and warrants further investigation. Detailed genetic characterization of these syndromes following treatment with IGF-I may also help to characterize the mechanism of action of IGF-I and its interactions with the insulin receptor. Thus, IGF-I appears to have a future as a therapeutic agent in treating diabetes, but long-term studies addressing safety and short-term studies addressing mechanisms are essential. With only a few pharmaceutical companies having the capability to produce IGF-I for scientific and therapeutic investigation, it is important that short-term marketing strategy does not prevent the proper exploration of this exciting peptide hormone as a therapeutic agent for all types of diabetes.

The role of IGFs in catabolism

The hypercatabolic response to trauma, extensive surgery and sepsis is characterized by an increased metabolic rate, severe muscle wasting and a negative nitrogen balance. This process of 'autocannibalism' may be in part a consequence of a disordered growth hormone (GH)/insulin-like growth factor (IGF) axis. In this chapter the normal physiology of the GH/IGF axis is first briefly reviewed. This is followed by a discussion of the changes that accompany fasting and catabolic illness, the effects of IGF-1 administration in health and disease and a comparison of the effects of IGF-1, GH and insulin on catabolism. Although initial investigations of IGF-1 administration in animals and human volunteers have often been encouraging, studies in catabolic patients have so far proved disappointing. Combined treatment with GH, IGF-1 (and insulin) or with IGF-1 and its major binding protein, may prove more effective, especially when used in conjunction with nutritional supplements such as glutamine.

Randomised placebo-controlled trial of human recombinant insulin-like growth factor I plus intensive insulin therapy in adolescents with insulin-dependent diabetes mellitus

BACKGROUND

Good glycaemic control in insulin-dependent diabetes mellitus (IDDM) to prevent complications may be difficult to achieve during adolescence, because abnormalities in production of growth hormone or insulin-like growth-factor-I (IGF-I) can lead to lower insulin sensitivity. Recombinant human IGF-I (rhIGF-I) given as an adjunct to insulin therapy in IDDM, might improve glycaemic control in adolescents; we investigated the effects of the addition of IGF-I in a randomised, double-blind, placebo-controlled trial.

METHODS

53 patients with IDDM (26 male, 27 female) with a median age of 16.1 years (range 10.8-20.6) and diabetes of more than 2 years' duration were randomly assigned subcutaneous rhIGF-I (20 or 40 microg/kg daily [n=18, n=18, respectively]) or placebo (n=17), both in addition to multiple-injection insulin therapy for 24 weeks. The primary endpoint, glycated haemoglobin (HbA1c) and routine biochemistry were measured every 4 weeks. Retinal photographs and glomerular-filtration rates were assessed at base line and at the end of the study. Data were analysed by intention to treat.

FINDINGS

With a dose of 40 microg/kg rhIGF-I daily, we found significant reductions in HbA1c compared with placebo (p=0.03), without changes in body-mass index, rate of hypoglycaemia, insulin dose, or circulating concentrations of IGF-binding proteins 1 and 3. The greatest median change in HbA1c of -0.6% (range -2.8 to -1.5%) was seen with rhIGF-I 40 microg/kg at week 12, but was not sustained at week 24. The greatest reductions in HbA1c at week 24 were seen among patients with the greatest changes in IGF-I concentrations (r=-0442, p=0.002). Retinal photographs, renal function (glomerular filtration rate and urinary albumin excretion), and routine biochemistry showed no adverse events.

INTERPRETATION

Our data confirm that rhIGF-I as an adjunct to insulin therapy can improve HbA1c values in adolescents with IDDM without overt toxic effects, but they raise questions about whether these effects can be sustained in cases of poor compliance or reduced bioefficacy.