Response of insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1) and IGFBP-3 to IGF-I treatment in severe insulin resistance

Genetic syndromes of severe insulin resistance

Insulin resistance is among the most prevalent endocrine derangements in the world, and it is closely associated with major diseases of global reach including diabetes mellitus, atherosclerosis, nonalcoholic fatty liver disease, and ovulatory dysfunction. It is most commonly found in those with obesity but may also occur in an unusually severe form in rare patients with monogenic defects. Such patients may loosely be grouped into those with primary disorders of insulin signaling and those with defects in adipose tissue development or function (lipodystrophy). The severe insulin resistance of both subgroups puts patients at risk of accelerated complications and poses severe challenges in clinical management. However, the clinical disorders produced by different genetic defects are often biochemically and clinically distinct and are associated with distinct risks of complications. This means that optimal management of affected patients should take into account the specific natural history of each condition. In clinical practice, they are often underdiagnosed, however, with low rates of identification of the underlying genetic defect, a problem compounded by confusing and overlapping nomenclature and classification. We now review recent developments in understanding of genetic forms of severe insulin resistance and/or lipodystrophy and suggest a revised classification based on growing knowledge of the underlying pathophysiology.

What is the best management strategy for patients with severe insulin resistance?

Management of severe insulin resistance (IR) is a major clinical challenge in many patients with obesity or lipodystrophy, and also in rarer patients with proven or suspected genetic defects in the insulin receptor or downstream signalling. The latter group can present at any time between birth and early adult life, with a variable clinical course broadly correlated with the severity of IR. Primary insulin signalling defects are usually associated with poor weight gain rather than obesity. Initially, extreme hyperinsulinaemia produces ovarian enlargement and hyperandrogenism in women, and often fasting or postprandial hypoglycaemia. However, any hypoglycaemia gradually evolves into insulin-resistant hyperglycaemia when beta cell function declines. Optimal management of these complex disorders depends on early diagnosis and appropriate targeting of both high and low glucose levels. In newborns, continuous nasogastric feeding may reduce harmful glycaemic fluctuations, and in older patients, acarbose may mitigate postprandial hypoglycaemia. Insulin sensitization, initially with metformin but later with trials of additional agents such as thiazolidinediones, is the mainstay of early therapy, but insulin replacement, eventually with very high doses, is required once diabetes has supervened. Preliminary data suggest that rhIGF-1 can improve survival in infants with the most severe insulin receptor defects and also improve beta cell function in older patients with milder receptoropathies. The utility of newer therapies such as glucagon-like peptide-1 agonists and dipeptidyl peptidase-IV inhibitors remains untested in this condition. Thus, management of these patients remains largely empirical, and there is a pressing need to collate data centrally to optimize treatment algorithms.

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

OBJECTIVE

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Insulin-like growth factor binding proteins in development

IGFBPs regulate growth and development by regulating IGF transport to tissues and IGF bioavailability to IGF receptors at cell membrane level. IGFBP excess leads predominantly to inhibition of IGF action and growth retardation with impaired organogenesis. Absence of human and also mouse ALS leads to decreased IGF-I levels in circulation and causes mild growth retardation. Although IGFBP KO mice demonstrate relatively minor phenotypes, the possibility of compensatory mechanisms that mask the phenotypic manifestation of lack of individual binding proteins needs to be further investigated. Recent studies of hepatic regeneration in IGFBP-1 KO mice and also with mutant IGFBP-3 Tg mice provide some limited support for the existence of IGF-independent mechanism of action in vivo.

Insulin-like growth factor-I treatment of growth disorders, diabetes mellitus and insulin resistance

Insulin-like growth factor I (IGF-I) has many potential therapeutic uses because of its varied effects--growth promotion, insulin-like influence on glucose metabolism, and neuroprotection resulting from cell-proliferative and antiapoptotic properties--but they have not been investigated systematically in clinical situations. The growth-promoting effect of recombinant human IGF-I (rhIGF-I) in the extensively studied growth hormone insensitivity syndrome (GHIS; Laron syndrome) signifies an endocrine role for the GH-IGF system. The metabolism of (adult) patients with severe insulin resistance is improved by rhIGF-I, which--together with insulin therapy--also improves metabolic control in type 1 and 2 diabetes. Further studies on IGF-I metabolic effects and growing understanding of the IGF-I-IGF-binding protein system could open new therapeutic avenues.

The effects of intensive training on insulin-like growth factor I (IGF-I) and IGF binding proteins 1 and 3 in competitive cyclists: relationships with glucose disposal

The aim of the present study was to determine whether 4 months of intensified training would result in modified plasma insulin-like growth factor I (IGF-I), insulin-like growth factor binding protein 1 (IGFBP-1) or IGFBP-3 in eight competitive cyclists and eight sedentary individuals and to define the relationships of these factors with glucose disposal. Insulin sensitivity and glucose effectiveness--that is, the fractional disappearance of glucose independent of any change in insulinaemia--were measured with the minimal model (mathematical analysis of frequently sampled intravenous glucose tolerance test). Both glucose effectiveness and insulin sensitivity were higher in the cyclists than in the sedentary individuals, but did not increase further with training. IGF-I was higher in the cyclists than in the sedentary group only after raining (P < 0.05). Plasma IGFBP-1 and IGFBP-3 increased after training (38 and 20%, respectively; P < 0.05) in the cyclists and were higher than in the sedentary individuals (P < 0.05). IGF-I was negatively correlated with insulin sensitivity before and after training (r = -0.66 and -0.67, respectively; P < 0.05) and IGFBP-1 was negatively correlated with glucose effectiveness before andafter training (r = -0.68 and -0.77, respectively; P < 0.05). Our results show that strenuous endurance training improves the somatotrope axis (growth hormone-IGF) and that IGFBP-1 may be involved in glucose homeostasis, possibly by limiting the exercise-induced increase in glucose disposal, in competitive cyclists.

Metabolic effects of insulin and insulin-like growth factor-I in endotoxemic rats during total parenteral nutrition feeding

The effects of insulin and insulin-like growth factor-I (IGF-I) on protein, energy, and glucose metabolism were examined in endotoxemic rats receiving total parenteral nutrition (TPN) for 3 days. The endotoxemic model was induced by constant infusion of lipopolysaccharide (1 mg/kg x d) for 3 days. The TPN regimen provided 200 kcal/kg x d and 1.5 g protein/kg x d. The dosage of insulin (5 mU/kg x h) and IGF-I (20 microg/kg x h), either alone or in combination, was chosen to maintain normal levels of leucine and glucose in plasma during feeding. One normal control and 4 endotoxemic groups with different treatments (saline, IGF-I, insulin, or IGF-I and insulin) were included. The effects of endotoxin were compared between the group receiving endotoxin alone and normal controls, and the effects of insulin and IGF-I were compared within the endotoxemic groups. The results show that endotoxin significantly increased the mortality and induced a hypermetabolic state, and nutrition alone could not overcome the catabolism induced by endotoxin. However, administration of insulin and IGF-I enhanced protein preservation in muscle tissue in endotoxemic rats during TPN. This effect was greater for insulin either alone or in combination with IGF-I. Insulin also significantly reduced the mortality. There were no additive effects of these two anabolic hormones on any measured parameter in these experimental conditions.

Effect of chronic treatment with octreotide nasal powder on serum levels of growth hormone, insulin-like growth factor I, insulin-like growth factor binding proteins 1 and 3 in acromegalic patients

Octreotide nasal powder is a delivery system of the somatostatin analogue developed to overcome the inconvenience of repeated subcutaneous administrations. Eight patients with clinically active acromegaly were treated for three months with octreotide nasal powder which was administered at the initial dosage of 0.125 mg tid, doubling the dosage up to 2 mg tid in order to obtain a mean GH value below 5 micrograms/l during 8 daytime hours. In 4 of these patients, treatment was prolonged till the sixth month. Blood samples were taken on days 15, 29, 43, 55, 90, 120, 150, 180 for GH, IGF-I, IGFBP-3, IGFBP-1 and insulin measurements. Before treatment, mean daytime GH and morning IGF-I serum levels were both increased but not correlated with each other. Serum IGFBP-3 levels were higher than normal and positively correlated with those of GH, IGF-I and insulin. Insulin levels were elevated and positively correlated with those of GH but not with those of IGF-I and IGFBP-1. Serum IGFBP-1 levels were in the low normal range and not correlated with any of the other parameters. Treatment with octreotide nasal powder induced in all patients a marked decrease of GH which lowered below 5 micrograms/l in 7/8 patients and IGF-I levels, which fell within the normal range in 1 patient. Serum IGFBP-3 and insulin concentrations decreased by 26% and 71%, respectively, and those of IGFBP-1 underwent an only transient increase in 5/8 patients. Opposite changes of insulin and IGFBP-1 levels, with a decrease of the former followed by an increase of the latter were noted during the 8 hours following an octreotide nasal insufflation. During chronic octreotide treatment, positive correlations were found between GH and IGF-I, GH and IGFBP-3, IGF-I and IGFBP-3, insulin and IGFBP-3 and insulin and IGF-I. An improvement of the clinical picture was registered in all patients after a few days of octreotide nasal powder administration. Treatment was well tolerated, with only mild side effects and no significant changes in the nasal mucosa, and the patients' compliance was excellent.

Zinc deficiency-induced anorexia influences the distribution of serum insulin-like growth factor-binding proteins in the rat

Zinc (Zn) deficiency can result in severe growth retardation in mammals, and in a number of animal model systems it leads to low circulating insulin-like growth factor-I (IGF-I) concentrations. Using a weanling male rat model and a number of feeding schemes, we show that in addition to lower circulating IGF-I concentrations, Zn deficiency leads to alterations in the distribution of serum IGF-binding proteins (IGFBPs). Serum from Zn-deficient animals labeled in vitro with [125I]IGF-I displayed three peaks of tracer activity: 150 kd (IGFBP-3), 37 kd (IGFBP-2 and -1), and 8 kd (free [125I]IGF-I). Relative to controls, Zn-deficient animals demonstrated more tracer binding in the 37-kd region, whereas less was found in the 150- and 8-kd peaks. Serum from chronically calorie-restricted fed animals displayed [125I]IGF-I binding profiles similar to Zn-deficient serum, implicating Zn deficiency-induced anorexia as the principle factor underlying both the lower circulating IGF-I and the alterations in IGFBP profiles. Concentrations of IGFBP-4 were unaffected by diet manipulation based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)/Western ligand blot (WLB) analysis.

The pathophysiology of the insulin-like growth factor axis in fetal growth failure: a basis for programming by undernutrition?

Recent evidence suggests that a number of adulthood conditions, including non-insulin dependent diabetes mellitus (NIDDM) and lipid and cardiovascular abnormalities are associated with intra-uterine growth retardation (IUGR). It is possible that this arises from programming of endocrine axes during development as a result of an adverse intra-uterine environment. Insulin-like growth factors (IGFs) are mitogenic polypeptides which stimulate cellular proliferation and differentiation and are important in human fetal development. The functions of IGFs are modulated by specific high affinity binding proteins (IGFBPs). IGFBP-1 is antagonistic to the insulin-like and growth promoting effects of IGF-I, and IGFBP-3 holds IGFs in the circulation by associating with IGFs and an acid labile subunit to form a ternary complex. Using specific radioimmunoassays and fetal serum obtained during diagnostic cordocentesis we have investigated the role of the IGF/IGFBP axis in human fetal development. In a study of 130 singleton pregnancies we have examined levels of immunoreactive IGFs and IGFBPs in normally grown fetuses (AGA), starved small fetuses affected by uteroplacental insufficiency (UPI), and non-starved small fetuses (SGA). IGF-I was significantly lower in the UPI group (n = 14, 7.8 +/- 0.6 micrograms l-1), than in either the SGA group (n = 22, 31.4 +/- 3.5 micrograms l-1, P = 0.0001) or the AGA group (n = 94, 36.3 +/- 1.9 micrograms l-1, P = 0.0001). IGFBP-3 showed similar changes (UPI: 682.6 +/- 50.0 micrograms l-1; SGA: 831.9 +/- 55.5 micrograms l-1; AGA: 847.7 +/- 19.8 micrograms l-1).(ABSTRACT TRUNCATED AT 250 WORDS)