Therapeutic applications of the insulin-like growth factors

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.

Impaired growth and puberty in pediatric patients with inflammatory bowel disease: Etiology and treatment

Growth failure associated with delayed puberty is a unique feature in pediatric patients with inflammatory bowel disease (IBD), especially those with Crohn's disease, which has a negative effect on quality of life, emotional functioning, social functioning, and body image. Although the underlying mechanisms are not fully clear, the condition may be induced by the effects of malnutrition, inflammatory process and glucocorticoid on the growth hormone/insulin-like growth factor-1 axis or on the growth plate. Nutrition, biologic agents, intestinal resection and glucocorticoids are main treatments. Standards for monitoring and treatment of impaired growth and development in pediatric IBD patients need to be formulated. To achieve optimal growth, the efforts of hospitals, families and society are necessary.

FOXO1 content is reduced in cystic fibrosis and increases with IGF-I treatment

Cystic fibrosis-related diabetes is to date the most frequent complication in cystic fibrosis (CF). The mechanisms underlying this condition are not well understood, and a possible role of insulin resistance is debated. We investigated insulin signal transduction in CF. Total insulin receptor, IRS1, p85 PI3K, and AKT contents were substantially normal in CF cells (CFBE41o-), whereas winged helix forkhead (FOX)O1 contents were reduced both in baseline conditions and after insulin stimulation. In addition, CF cells showed increased ERK1/2, and reduced β2 arrestin contents. No significant change in SOCS2 was observed. By using a CFTR inhibitor and siRNA, changes in FOXO1 were related to CFTR loss of function. In a CF-affected mouse model, FOXO1 content was reduced in the muscle while no significant difference was observed in liver and adipose tissue compared with wild-type. Insulin-like growth factor 1 (IGF-I) increased FOXO1 content in vitro and in vivo in muscle and adipose tissue. In conclusion; we present the first description of reduced FOXO1 content in CF, which is compatible with reduced gluconeogenesis and increased adipogenesis, both features of insulin insensitivity. IGF-I treatment was effective in increasing FOXO1, thereby suggesting that it could be considered as a potential treatment in CF patients possibly to prevent and treat cystic fibrosis-related diabetes.

Cell-based assays for IGF-I bioactivity measurement: overview, limitations and current trends

Insulin-like growth factor-I (IGF-I) is an important growth promoting protein that is involved in numerous cellular responses and multiple biological systems. Although the molecular structure, function and recombinant production of IGF-I in various hosts have been the subject of much researches over the recent past, methods to determine the bioactivity of this protein have not been fully explored. Several assays have traditionally been used to measure IGF-I bioactivity, but have not become a routine laboratory practice due to the high cost involved and technical problems. Thus, there is still a need for a rapid, technically simple and accurate assay to determine IGF-I bioactivity. This review highlights the various cell-based assays currently commercially available for measuring the bioactivity of IGF-I along with their limitations. This is aimed at presenting the modern-day IGF researcher with a holistic overview of the current trends and future prospects regarding IGF-I bioactivity determinations.

Myths and truths of growth hormone and testosterone therapy in heart failure

Heart failure is a chronic clinical syndrome with very poor prognosis. Despite being on optimal medical therapy, many patients still experience debilitating symptoms and poor quality of life. In recent years, there has been a great interest in anabolic hormone replacement therapy - namely, growth hormone and testosterone - as an adjunctive therapy in patients with advanced heart failure. It has been observed that low levels of growth hormone and testosterone have been associated with increased mortality and morbidity in patients with heart failure. Animal studies and clinical trials have shown promising clinical improvement with hormonal supplementation. Growth hormone has been shown to increase ventricular wall mass, decrease wall stress, increase cardiac contractility, and reduce peripheral vascular resistance, all of which might help to enhance cardiac function, resulting in improvement in clinical symptoms. Likewise, testosterone has been shown to improve hemodynamic parameters via reduction in peripheral vascular resistance and increased coronary blood flow through vasodilation, thereby improving functional and symptomatic status. To date, growth hormone and testosterone therapy have shown some positive benefits, albeit with some concerns over adverse effects. However, large randomized controlled trials are still needed to assess the long-term safety and efficacy.

A 90-day safety study of genetically modified rice expressing rhIGF-1 protein in C57BL/6J rats

Genetically modified plants expressing disease resistance traits offer new treatment strategies for human diseases, but at the same time present a challenge in terms of food safety assessment. The present 90-day feeding study was designed to assess the safety of transgenic rice expressing the recombinant human insulin-like growth factor-1 (rhIGF-1) compared to its parental wild rice. Male and female C57BL/6J rats were given a nutritionally balanced purified diet with 20% transgenic rhIGF-1 rice or 20% parental rice for 90 days. This corresponds to a mean daily rhIGF-1 protein intake of approximately 217.6 mg/kg body weight based on the average feed consumption. In the animal study a range of biological, biochemical, clinical, microbiological and pathological parameters were examined and several significant differences were observed between groups, but none of the effects were considered to be adverse. In conclusion, no adverse or toxic effects on C57BL/6J rats were observed in the design used in this 90-day study. These results will provide valuable information for the safety assessment of genetically modified food crops.

Insulin-like growth factor-I in growth and metabolism

Deficiency of insulin-like growth factor-I (IGF-I) results in growth failure. A variety of molecular defects have been found to underlie severe primary IGF-I deficiency (IGFD), in which serum IGF-I concentrations are substantially decreased and fail to respond to GH therapy. Identification of more patients with primary or secondary IGFD is likely with investigative and diagnostic progress, particularly in the assessment of children with idiopathic short stature. Diagnosis of IGFD requires accurate and reliable IGF-I assays, adequate normative data for reference, and knowledge of IGF-I physiology for proper interpretation of data. Recombinant human IGF-I (rhIGF-I) treatment improves stature in patients with severe primary IGFD, and has also been shown to improve glycaemic control and insulin sensitivity in patients with severe insulin resistance. Ongoing studies of patients receiving rhIGF-I will allow further evaluation of the clinical utility of this treatment, with concurrent increase in our understanding of IGF-I and conditions of IGFD.

Insulin-like growth factor-I deficiency in children with growth hormone insensitivity: current and future treatment options

Growth hormone (GH) acts directly at the growth plate and through the production of insulin-like growth factor (IGF)-I. At least 50% of the hormone circulates bound to GH binding protein, and its secretion is controlled by growth hormone-releasing hormone and somatostatin. Once GH binds to two GH receptors, the janus activated kinase/signal transducers and activators of transcription (JAK/STAT) protein pathway is activated, resulting in the production of IGF-I. Serum IGF-I is produced predominantly in the liver and circulates in a 140 kDa complex, along with its binding protein, IGF binding protein 3, and acid-labile protein. Recombinant human (rh) IGF-I (mecasermin) is approved by the US FDA and the European Medicines Agency for the treatment of patients with severe primary IGF deficiency or for patients with GH1 gene deletion who have developed neutralizing antibodies to GH. It has been shown to increase growth velocity in children with either condition. In the past, there have been adverse events, particularly hypoglycemia, reported with the administration of mecasermin. However, a recent report of long-term therapy with mescasermin in children with severe IGF-I deficiency has concluded that although adverse events are common, they are rarely severe enough to interrupt or modify treatment. The serum half-life of mecasermin is shorter in patients with GH insensitivity syndrome and low serum levels of its binding protein, the insulin-like growth factor binding protein (IGFBP)-3 and acid-labile subunit, compared with the serum half-life in normal volunteers or in patients with an IGF1 gene deletion who have normal levels of IGFBP-3. Mecasermin rinfabate, a complex of rhIGF-I and rhIGFBP-3, appears to prolong the serum half-life and might counteract acute adverse events, particularly hypoglycemia, associated with the administration of mescasermin. Mecasermin rinfabate, however, is no longer available in the USA or Europe for treating conditions involving short stature, because of a legal requirement. Mecasermin has been shown to be effective in increasing height velocity and adult height in patients with severe GH resistance and in IGF1 gene deletion. There has been some interest in using mecasermin to treat patients with partial GH resistance or idiopathic short stature. At the present time, the data are insufficient to make this recommendation.

Advantages and disadvantages of GH/IGF-I combination treatment

Growth hormone (GH) is the primary regulator of insulin-like growth factor-I (IGF-I) production in a wide variety of tissues. There is much overlap in the endocrine, metabolic and anabolic effects of GH and IGF-I but both hormones have divergent effects on glucose metabolism, insulin sensitivity and differentiation of prechondrocytes. Theoretically combined administration of GH and IGF-I may be more effective than GH alone or IGF-I alone. Arguments in favor for this are: 1] Clearance of IGF-I may be markedly altered by the co-administration of GH and this will provide sustained actions of IGF-I. 2] Higher serum IGF-I levels are achieved with a combination treatment of GH and IGF-I than with GH treatment alone or IGF-I alone. In addition, combination therapy may have additive or synergistic effects. 3] The combination GH and IGF-I counteracts disadvantageous effects on glucose metabolism of either GH alone or IGF-I alone. 4] GH may exert direct actions on tissues independently from IGF-I. 5] Combination of GH and IGF-I may be more effective in improving tissue IGF-I levels. The combination therapy of GH and IGF-I might be beneficial in growth retardation, in certain specific subgroups of critically ill or catabolic patients and in the treatment of GH-deficient subjects with the metabolic syndrome and/or manifest diabetes. It is at present unknown whether an optimal balance between safety and efficacy can be achieved with the combination therapy of GH and IGF-I, since this combination has been evaluated in only a small number of patient populations and in studies of a relatively short duration. In addition, a disadvantage may be the financial costs of combination therapy of GH and IGF-I. In conclusion, there are many reasons for believing that administration of the combination therapy of GH and IGF-I could have advantages above GH alone or IGF-I alone. However, determination of whether co-administration of GH and IGF-I indeed is superior to either agent alone awaits further study.

A biologically active rhIGF-1 fusion accumulated in transgenic rice seeds can reduce blood glucose in diabetic mice via oral delivery

Human insulin-like growth factor 1(hIGF-1) is essential for cell proliferation and used therapeutically in treating various diseases including diabetes mellitus. Here, we present that a recombinant hIGF-1(rhIGF-1) was expressed fused with the C-terminus of a rice luminal binding protein and accumulated highly in rice seeds, reaching 6.8+/-0.5% of total seed protein. The rhIGF-1 fusion was demonstrated to possess biological activity to stimulate cell proliferation. Importantly, the unprocessed transgenic seeds could significantly increase plasma rhIGF-1 level and reduce blood glucose of diabetic mice via oral delivery. Further studies suggested that transgenic seeds reduced blood glucose of diabetic mice by enhancing islet cells survival and increasing insulin secretion rather than increasing insulin sensitivity. These results indicated the potential of the novel fusion expression system in production and oral delivery of biologically active small peptides for diseases.

Idiopathic short stature: management and growth hormone treatment

In the management of ISS auxological, biochemical, psychosocial and ethical elements have to be considered. In boys with constitutional delay of growth and puberty androgens are effective in increasing height and sexual characteristics, but adult height is unchanged. GH therapy is efficacious in increasing height velocity and adult height, but the inter-individual variation is considerable. The effect on psychosocial status is uncertain. Factors affecting final height gain include GH dose, height deficit in comparison to midparental height, age and first year height velocity. In case of a low predicted adult height at the onset of puberty, addition of a GnRH analogue can be considered. Although GH therapy appears safe, long-term monitoring is recommended.

Regulation of IGF-I function by proinflammatory cytokines: at the interface of immunology and endocrinology

During the past decade, the immune and endocrine systems have been discovered to interact in controlling physiologic processes as diverse as cell growth and differentiation, metabolism, and even human and animal behavior. The interaction between these two major physiological systems is a bi-directional process. While it has been well documented that hormones, including prolactin (PRL), growth hormone (GH), insulin-like growth factor-I (IGF-I), and thyroid-stimulating hormone (TSH), regulate a variety of immune events, a great deal of data have accumulated supporting the notion that cytokines from the innate immune system also affect the neuroendocrine system. Communication between these two systems coordinates processes that are necessary to maintain homeostasis. Proinflammatory cytokines often act as negative regulatory signals that temper the action of hormones and growth factors. This system of 'checks and balances' is an active, ongoing process, even in healthy individuals. Dysregulation of this process has been implicated as a potential pathogenic factor in the development of co-morbid conditions associated with several chronic inflammatory diseases, including type 2 diabetes, cardiovascular disease, cerebrovascular disease, inflammatory bowel disease, rheumatoid arthritis, major depression, and even normal aging. Over the past decade, research in our laboratory has focused on the ability of the major proinflammatory cytokines, tumor necrosis factor (TNF)alpha and interleukin (IL)-1beta, to induce a state of IGF resistance. This review will highlight these and other new findings by explaining how proinflammatory cytokines induce resistance to the major growth factor, insulin-like growth factor-I (IGF-I). We also highlight that IGF-I can induce resistance or reduce sensitivity to brain TNFalpha and discuss how TNFalpha, IL-1beta, and IGF-I interact to regulate several aspects of behavior and cognition.

Efficacy and safety of mecasermin rinfabate

There has been interest in using recombinant human (rh) insulin-like growth factor (IGF)-I (rhIGF-I) to treat short stature, either alone or in combination with its binding protein (insulin-like growth factor binding protein [IGFBP]-3). IGF-I has been shown to increase growth velocity in children with IGF deficiency, either as a result of growth hormone insensitivity syndrome (GHIS) or IGF gene deletion. However, there have been adverse events, particularly hypoglycaemia, reported with administration of unbound rhIGF-I. In addition, the serum half-life of unbound rhIGF-I is shorter when administered to patients with GHIS, who have low serum concentrations of its binding proteins IGFBP-3 and acid-labile subunit (ALS), than when administered to normal volunteers or to the patient with an IGF-I gene deletion (who had normal levels of IGFBP-3). iPlex (mecasermin rinfabate), an equimolar mixture of IGF-I and its binding protein IGFBP-3, was developed to prolong the half-life and to counteract acute adverse events (particularly hypoglycaemia) associated with administration of IGF-I. Although there are no published data on the efficacy of mecasermin rinfabate in treating growth disorders, it does appear that mecasermin rinfabate has a longer half-life in patients with GHIS than unbound IGF-I, and fewer reports of adverse events (including hypoglycaemia) when administered to patients with diabetes.

Genetic association study of growth hormone receptor and idiopathic scoliosis

Although the etiology of scoliosis is multifactorial, genetic factors play an important role. Recent linkage studies on familial idiopathic scoliosis revealed multiple putative predisposition loci. A genetic association study is complementary to linkage studies in defining the genetic basis of complex traits of diseases like idiopathic scoliosis. The onset and progression of adolescent idiopathic scoliosis is a manifestation of aberrant growth in the spine. Meanwhile, a high proportion of patients with adolescent idiopathic scoliosis have additional phenotypes, which suggest systemic growth dys-regulation during puberty. The growth hormone-insulin-like growth factor axis plays the principle role in skeletal growth regulation. Because growth hormone receptor alleles were associated with body stature and response to growth hormone treatment, we hypothesized the growth hormone receptor is a candidate predisposing and disease modifier gene for adolescent idiopathic scoliosis. Five hundred ten girls with adolescent idiopathic scoliosis and 363 normal subjects were recruited. Curve severity, arm span, and bone mineral densities were recorded. Five polymorphisms were studied by polymerase chain reaction-restriction fragment length polymorphism. All the genotype and allele frequencies were comparable between groups. The Cobb angles among patients of different genotypes were similar. The growth hormone receptor did not appear to be a predisposing gene or disease modifier gene of adolescent idiopathic scoliosis.

Molecular genetics of human growth hormone, insulin-like growth factors and their pathways in common disease

The human growth hormone gene (GH1) and the insulin-like growth factor 1 and 2 genes (IGF1 and IGF2) encode the central elements of a key pathway influencing growth in humans. This "growth pathway" also includes transcription factors, agonists, antagonists, receptors, binding proteins, and endocrine factors that constitute an intrincate network of feedback loops. GH1 is evolutionarily coupled with other genes in linkage disequilibrium in 17q24.2, and the same applies to IGF2 in 11p15.5. In contrast, IGF1 in 12q22-24.1 is not in strong linkage disequilibrium with neighbouring genes. Knowledge of the functional architecture of these regions is important for the understanding of the combined evolution and function of GH1, IGF2 and IGF1 in relation to complex diseases. A number of mutations accounting for rare Mendelian disorders have been described in GH-IGF elements. The constellation of genes in this key pathway contains potential candidates in a number of complex diseases, including growth disorders, metabolic syndrome, diabetes (notably IGF2BP2) cardiovascular disease, and central nervous system diseases, and in longevity, aging and cancer. We review these genes and their associations with disease phenotypes, with special attention to metabolic risk traits.

The role of pro-inflammatory cytokines in inflammatory bowel disease growth retardation

Childhood inflammatory bowel disease (IBD) especially those with Crohn disease is commonly complicated by faltering growth and pubertal delay. Pro-inflammatory cytokines are often elevated in IBD and may affect linear growth and puberty either systemically or at the level of the growth plate. Further study of the underlying mechanisms of the deleterious effects of cytokines on the growth plate may improve management of faltering growth in childhood IBD. Well-controlled clinical studies of the respective effect of nutritional support, immunomodulatory therapy, biological agents and growth and puberty promoting agents on managing faltering growth also require further attention.

Sensorineural hearing loss in insulin-like growth factor I-null mice: a new model of human deafness

It has been reported that mutations in the gene encoding human insulin-like growth factor-I (IGF-I) cause syndromic hearing loss. To study the precise role of IGF-I in auditory function and to hypothesize the possible morphological and electrophysiological changes that may occur in the human inner ear, we have analysed the auditory brainstem response in a mouse model of IGF-I deficiency. We show here that homozygous Igf-1(-/-) mice present an all-frequency involved bilateral sensorineural hearing loss. Igf-1(-/-) mice also present a delayed response to acoustic stimuli; this increases along the auditory pathway, indicating a contribution of the central nervous system to the hearing loss in Igf-1(-/-) mice. These results support the use of the Igf-1(-/-) mouse as a new model for the study of human syndromic deafness.

Investigational agents for the treatment of growth hormone-insensitivity syndrome

Growth hormone-insensitivity syndrome (GHIS) is usually caused by mutations in the growth hormone receptor. Recombinant IGF-I has been used to treat GHIS either alone (mecasermin) or in combination with IGF-binding protein (IGFBP)-3 (mecasermin rinfabate). IGF-I increases the growth velocity of children with IGF deficiency, which is either as a result of GHIS or an IGF-I gene deletion. Hypoglycaemia has been reported with administration of unbound IGF-I and, in addition, the serum half-life of unbound IGF-I is shorter when administered to patients with GHIS (who have low serum concentrations of its binding protein IGFBP-3) than when administered to normal volunteers or to patients with an IGF-I gene deletion (but normal IGFBP-3 levels). The IGF-I-IGFBP-3 combination was developed to prolong the half-life and counteract the acute adverse events (particularly hypoglycaemia) that are associated with administration of IGF-I. It seems that the IGF-I-IGFBP-3 combination has a longer half-life in patients with GHIS than unbound IGF-I, with fewer reports of adverse events (including hypoglycaemia) when administered to patients with diabetes. There are no studies comparing the efficacy of mecasermin with mecasermin rinfabate; both drugs have been shown to be effective but cannot be differentiated in terms of efficacy.

Effects of growth hormone (GH) and insulin-like growth factor-I therapy in patients with gene defects in the GH axis

We report on four patients (3 F) who were diagnosed as having either a 6.7 kb GH1 gene deletion, a GH1 signalling peptide mutation, or a GH receptor mutation, with particular regard to treatment modalities (GH, rhIGF-I) and final height. Patients with GH1 gene defects developed anti-GH antibodies (GH-Ab) following GH treatment. Surprisingly, growth response to GH was unrestricted in one girl, who reached a final height within her target height range, whereas her cousin with the identical genetic defect responded far less favourably. Variability in the growth inhibiting potency of GH-Ab may therefore depend on genetic disposition, specific epitopes, or induction of immunological tolerance. Growth response during rhIGF-I treatment carried out in three of the patients was moderate, but pubertal development and bone age acceleration occurred in the two patients treated at pubertal age. GH resistance, either caused by GH-Ab or GH receptor mutations, is still difficult to treat and results in a heterogeneous outcome.

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.

Emerging drugs for sarcopenia: age-related muscle wasting

Sarcopenia is the term widely used to describe the progressive loss of muscle mass with advancing age. Even before significant muscle wasting becomes apparent, ageing is associated with a slowing of movement and a gradual decline in muscle strength, factors that increase the risk of injury from sudden falls and the reliance of the frail elderly on assistance in accomplishing even basic tasks of independent living. Sarcopenia is recognised as one of the major public health problems now facing industrialised nations, and its effects are expected to place increasing demands on public healthcare systems worldwide. Although the effects of ageing on skeletal muscle are unlikely to be halted or reversed, the underlying mechanisms responsible for these deleterious changes present numerous targets for drug discovery with potential opportunities to attenuate muscle wasting, improve muscle function, and preserve functional independence. Very few drugs have been developed with sarcopenia specifically in mind. However, because many of the effects of ageing on skeletal muscle resemble those indicated in many neuromuscular disorders, drugs that target neurodegenerative diseases may also have important relevance for treating age-related muscle wasting and weakness. This review describes a selection of the emerging drugs that have been developed during the period 1997 - 2004, relevant to sarcopenia.

Characteristics of adult patients with growth hormone deficiency who underwent neurosurgery for functioning and non-functioning pituitary adenomas and craniopharyngiomas

The aim of the present study was to evaluate the characteristics of GH deficiency (GHD) in adult patients after neurosurgery for pituitary adenomas and craniopharingiomas. One hundred and one GHD patients, (42 F/59 M), aged 47.58+/-14.4 yr (mean+/-SD; range 21-78), body mass index (BMI) 28.6+/-0.6, with a history of adult-onset hypothalamic-pituitary disease, were recruited for the study. The whole group included: 45 non-functioning pituitary adenomas, 23 craniopharyngiomas, 16 PRLomas, 8 GHomas, 7 ACTHomas and 2 FSHomas; in particular 51 were macroadenomas and 27 microadenomas. At study entry, GHD diagnosis was carried out by assessing GH secretion after GHRH+arginine. All patients were submitted to the study at least 12 months after neurosurgery and, where needed, subjects were replaced with an appropriate treatment. GHD was mild in 3/101 (3%) and severe in 98/101 patients (97%). Other hormone deficiencies associated with GHD were considered: TSH, ACTH, FSH/LH, ADH. The distribution of peak GH among all patients, according to the type of disease before neurosurgery, showed that patients with Cushing disease were characterized by the presence of higher peak GH. According to the number of additional hormone deficits, the distribution of peak GH among all patients was as follows: GHD was isolated in 4/101 subjects (4%; group A), while it was associated with 1 (14/101, 14%; group B), 2 (22/101, 22%; group C), 3 (44/101, 43%; group D) and 4 hormone deficits (17/101, 16%; group E). GHD was severe in all patients in the panhypopituitaric group. Total IGF-I plasma levels in the whole group of GHD patients were 95.2+/-4.2 microg/l. In all groups of patients IGF-I was lower in subjects with severe GHD than in those with mild GHD (93.6+/-4.1 vs 148.6+/-33.6 microg/l, p<0.03). In particular, according to the type of disease presented before neurosurgery, patients with Cushing disease were characterized by the presence of higher IGF-I plasma levels compared to the other. According to the number of additional deficits, the distribution of IGF-I plasma levels was characterized by higher values when GHD was isolated than when it was associated with multiple hormone deficiencies. IGF-I plasma levels were positively associated to peak GH during GHRH+arginine (r=0.4, p<0.0005). We conclude that patients after neurosurgery approach for sellar and parasellar neoplasia, within an appropriate clinical context, and both the presence of additional pituitary hormone deficiency and low levels of IGF-I can be considered a clear GHD condition, and therefore do not require provocative tests evaluating GH secretion.

Are the metabolic effects of GH and IGF-I separable?

IGF-I mediates some, but not all of the metabolic actions of GH and it has both GH-like and insulin-like actions in vivo. GH and IGF-I both have a net anabolic effect in man enhancing whole body protein synthesis over a period of weeks and perhaps months. Both hormones favorably improve body composition in GH deficient subjects with an increase in lean body mass and decreased adiposity. This is also observed when IGF-I is given to patients with GH-receptor mutations. These compounds, however, have divergent effects on carbohydrate metabolism. A potent glucose lowering effect is typically observed after IGF-I administration, with improved insulin sensitivity with marked lowering of circulating insulin concentrations, whereas GH therapy is associated with mild compensatory hyperinsulinemia, a reflection of relative insulin resistance. The latter observation makes IGF-I a potentially more convenient anabolic agent to use in conditions where carbohydrate metabolism is more likely to be impaired. GH increases lipolysis as a direct effect of GH on the adipocyte, as well as lipid oxidation by increasing substrate availability. However IGF-I increases lipid oxidation only when given chronically, most likely as a result of chronic insulinopenia. These compounds have been tried in a variety of catabolic conditions in man and both hormones have been effective in reducing the protein wasting effects of glucocorticosteroids and mitigate some of the catabolic effects of severe hypogonadism in males. A comparison of these and other effects of these hormones is provided in this brief review. Subsequent studies are still needed to fully elucidate the safety and efficacy of IGF-I for use in humans.