Acute effects of insulin-like growth factor I on glucose and amino acid metabolism in the awake fasted rat. Comparison with insulin

Eye on the horizon: The metabolic landscape of the RPE in aging and disease

To meet the prodigious bioenergetic demands of the photoreceptors, glucose and other nutrients must traverse the retinal pigment epithelium (RPE), a polarised monolayer of cells that lie at the interface between the outer retina and the choroid, the principal vascular layer of the eye. Recent investigations have revealed a metabolic ecosystem in the outer retina where the photoreceptors and RPE engage in a complex exchange of sugars, amino acids, and other metabolites. Perturbation of this delicate metabolic balance has been identified in the aging retina, as well as in age-related macular degeneration (AMD), the leading cause of blindness in the Western world. Also common in the aging and diseased retina are elevated levels of cytokines, oxidative stress, advanced glycation end-products, increased growth factor signalling, and biomechanical stress - all of which have been associated with metabolic dysregulation in non-retinal cell types and tissues. Herein, we outline the role of these factors in retinal homeostasis, aging, and disease. We discuss their effects on glucose, mitochondrial, lipid, and amino acid metabolism in tissues and cell types outside the retina, highlighting the signalling pathways through which they induce these changes. Lastly, we discuss promising avenues for future research investigating the roles of these pathological conditions on retinal metabolism, potentially offering novel therapeutic approaches to combat age-related retinal disease.

Mediating Effect of Insulin-Like Growth Factor-I Underlying the Link Between Vitamin D and Gestational Diabetes Mellitus

Vitamin D was well-known to be associated with gestational diabetes mellitus (GDM). Insulin-like growth factor-I (IGF-I) has been linked to vitamin D and GDM, respectively. We hypothesize that changes in IGF-I metabolism induced by 25(OH)D3 might contribute to GDM. Therefore, we investigated the independent and combined relationships of serum 25(OH)D3 and IGF-I concentrations with GDM risk, and the mediation effect of IGF-I on 25(OH)D3. A total of 278 pregnant women (including 125 cases and 153 controls) were recruited in our current study. Maternal serum 25(OH)D3 and IGF-I were measured in the second trimester. Logistic regression models were used to estimate the associations of 25(OH)D3 and IGF-I concentrations with the risk of GDM. Mediation analyses were used to explore the mediation effect of IGF-I on the association between 25(OH)D3 and the risk of GDM. After adjusted for the confounded factors, both the third and fourth quartile of 25(OH)D3 decreased the risk of GDM (OR = 0.226; 95% CI, 0.103-0.494; OR = 0.109; 95% CI, 0.045-0.265, respectively) compared to the first quartile of 25(OH)D3. However, the third and fourth quartile of serum IGF-I (OR = 5.174; 95% CI, 2.287-11.705; OR = 12.784; 95% CI, 5.292-30.879, respectively) increased the risk of GDM compared to the first quartile of serum IGF-I. Mediation analyses suggested that 19.62% of the associations between 25(OH)D3 and GDM might be mediated by IGF-I. The lower concentration of serum 25(OH)D3 or higher IGF-I in the second trimester was associated with an increased risk of GDM. The serum IGF-I level might be a potential mediator between 25(OH)D3 and GDM.

Placental IGFBP1 levels during early pregnancy and the risk of insulin resistance and gestational diabetes

Reduced insulin sensitivity (insulin resistance) is a hallmark of normal physiology in late pregnancy and also underlies gestational diabetes mellitus (GDM). We conducted transcriptomic profiling of 434 human placentas and identified a positive association between insulin-like growth factor binding protein 1 gene (IGFBP1) expression in the placenta and insulin sensitivity at ~26 weeks gestation. Circulating IGFBP1 protein levels rose over the course of pregnancy and declined postpartum, which, together with high gene expression levels in our placenta samples, suggests a placental or decidual source. Higher circulating IGFBP1 levels were associated with greater insulin sensitivity (lesser insulin resistance) at ~26 weeks gestation in the same cohort and in two additional pregnancy cohorts. In addition, low circulating IGFBP1 levels in early pregnancy predicted subsequent GDM diagnosis in two cohorts of pregnant women. These results implicate IGFBP1 in the glycemic physiology of pregnancy and suggest a role for placental IGFBP1 deficiency in GDM pathogenesis.

Placental RNA sequencing implicates IGFBP1 in insulin sensitivity during pregnancy and in gestational diabetes

Reduced insulin sensitivity (or greater insulin resistance) is a hallmark of normal physiology in late pregnancy and also underlies gestational diabetes mellitus (GDM) pathophysiology. We conducted transcriptomic profiling of 434 human placentas and identified a strong positive association between insulin-like growth factor binding protein 1 gene (IGFBP1) expression in the placenta and insulin sensitivity at ~ 26 weeks' gestation. Circulating IGFBP1 protein levels rose over the course of pregnancy and declined postpartum, which together with high placental gene expression levels, suggests a placental source. Higher circulating IGFBP1 levels were strongly associated with greater insulin sensitivity (lesser insulin resistance) at ~ 26 weeks' gestation in the same cohort and two additional pregnancy cohorts. In addition, low circulating IGFBP1 levels in early pregnancy predicted subsequent GDM diagnosis in two cohorts. These results implicate IGFBP1 in the glycemic physiology of pregnancy and suggest a role for placental IGFBP1 deficiency in GDM pathogenesis.

IGF-1 Stimulates Glycolytic ATP Production in MCF-7L Cells

The Insulin-like Growth Factor (IGF) system in breast cancer progression has been a matter of interest for decades, but targeting this system did not result in a successful clinical strategy. The system's complexity and homology of its two receptors-insulin receptor (IR) and type 1 insulin-like growth factor receptor (IGF-1R)-are possible causes. The IGF system maintains cell proliferation and also regulates metabolism, making it a pathway to explore. To understand the metabolic phenotype of breast cancer cells, we quantified their real-time ATP production rate upon acute stimulation with ligands-insulin-like growth factor 1 (1GF-1) and insulin. MCF-7L cells express both IGF-1R and IR, while tamoxifen-resistant MCF-7L (MCF-7L TamR) cells have downregulated IGF-1R with unchanged IR levels. Treating MCF-7L cells with 5 nM IGF-1 increased the glycolytic ATP production rate, while 10 nM insulin did not affect metabolism when compared with the control. Neither treatment altered ATP production in MCF-7L TamR cells. This study provides evidence of the relationship between metabolic dysfunction, cancer, and the IGF axis. In these cells, IGF-1R, and not IR, regulates ATP production.

IGF-1 contributes to liver cancer development in diabetes patients by promoting autophagy

INTRODUCTION AND OBJECTIVES

Type 2 diabetes mellitus (T2DM) increases the occurrence and mortality of liver cancer. Insulin growth factor (IGF) plays a crucial role in the development of diabetes and liver cancer, and specifically, IGF-1 may be involved in the development of liver cancer with preexisting T2DM. Autophagy contributes to cancer cell survival and apoptosis. However, the relationship between IGF-1 and autophagy has rarely been evaluated. The purpose of this study was to investigate whether IGF-1 promotes the development of liver cancer in T2DM patients by promoting autophagy.

MATERIALS AND METHODS

Thirty-three hepatocellular carcinoma (HCC) patients with T2DM and 33 age-matched patients with HCC without T2DM were included in this study. We analyzed the expression of IGF-1 and autophagy-related LC3 and p62 mRNA and the prognosis of two groups. In vitro, we stimulated HepG2 cells with IGF-1 and then detected changes in autophagy and cell proliferation, apoptosis, and migration in the presence/absence of wortmannin, an autophagy inhibitor.

RESULTS

IGF-1 promoted autophagy, resulting in inhibition of apoptosis and induction of growth and migration of HepG2 cells. Inhibition of autophagy by wortmannin impaired IGF-1 function. Higher expression of IGF-1 was detected in HCC patients with T2DM. IGF-1 expression was higher in liver cancer tissue compared to paracancerous tissue. Elevated IGF-1 was associated with a poor prognosis in patients with HCC.

CONCLUSIONS

IGF-1 participates in the development of liver cancer by inducing autophagy. Elevated IGF-1 was a prognostic factor for patients with HCC, especially when accompanied by T2DM.

The Influence of Gestational Diabetes Mellitus upon the Selected Parameters of the Maternal and Fetal System of Insulin-Like Growth Factors (IGF-1, IGF-2, IGFBP1-3)-A Review and a Clinical Study

BACKGROUND

Gestational diabetes mellitus (GDM), defined as impaired glucose tolerance with onset or first recognition in pregnancy, increases the risk of not only maternal but also fetal and neonatal complications. Given the structural similarity of insulin-like growth factors with insulin and participation of components of the insulin-like growth factor system in glucose homeostasis, we hypothesized that the IGF axis is involved in the development of GDM complications or its pathogenesis. The aim of this study was to evaluate the effect of GDM on the selected parameters of the insulin-like growth factors (IGF-1, IGF-2, IGFBP1-3) in the maternal and fetal blood.

METHODS

The clinical material of this case-control study included 109 pregnant women and their offspring. The study group (n = 120) consisted of 60 patients with diagnosed gestational diabetes and their newborn babies. The control group (n = 98) comprised 49 healthy parturients and their offspring. We measured the concentrations of IGF-1, IGF-2, IGFBP-1, IGFBP-2, IGFBP-3, insulin and glucose made by the ELISA method in peripheral blood serum in patients suffering from GDM and pregnant women without GDM, and in the umbilical cord blood of newborn babies born to them.

RESULTS

The analysis of concentrations of IGF-1, -2 and IGFBP-3 in peripheral blood as well as umbilical cord blood did not demonstrate a statistically significant difference between the study group and the control group. Significantly lower concentration of IGFBP-1, IGFBP-2 in peripheral blood and in umbilical cord blood was detected in the study group in comparison to the control group. A statistically positive correlation between the concentration of IGF-1 in umbilical cord serum of newborn babies born to women with gestational diabetes and the length of a baby after its birth was observed.

CONCLUSIONS

Gestational diabetes mellitus does not significantly affect the concentrations of IGF-1, -2, IGFBP-3 in the peripheral blood and umbilical cord blood, but has the greatest influence on maternal and fetal IGFBP-2 concentrations. A positive correlation between the concentration of IGF-1 in umbilical cord blood and the length of a newborn suggests an influence of IGF-1 on the process of fetal development.

Mechanisms of putative IGF-I receptor resistance in active acromegaly

Acromegaly is a disease characterized by overproduction of growth hormone (GH). As a consequence of excessive GH secretion, circulating insulin-like growth factor-I (IGF-I) is elevated in active (untreated) acromegaly. IGF-I is often used as a marker of disease activity and growth hormone status in acromegaly. Although IGF-I can directly improve insulin sensitivity and glucose uptake in muscles, the excessive GH secretion in active acromegaly frequently leads to insulin resistance, glucose intolerance and even diabetes. In this review evidence will be discussed that in active acromegaly chronically elevated IGF-I, insulin and soluble Klotho (S-Klotho) levels play a pathophysiological role in the development of IGF-I receptor (IGF-IR) resistance. It is postulated that as soon as circulating IGF-I, insulin and S-Klotho rise above a certain level the IGF-IR becomes relatively resistant to actions of IGF-I. The development of a degree of IGF-IR resistance for metabolic actions may help to explain why in active acromegaly diabetogenic effects of GH predominate and are not completely counteracted and neutralized by elevated circulating levels of IGF-I. Further studies are necessary in order to support this hypothesis.

Associations between IGF1, IGFBP2 and TGFß3 Genes Polymorphisms and Growth Performance of Broiler Chicken Lines

Marker-assisted selection based on fast and accurate molecular analysis of individual genes is considered an acceptable tool in the speed-up of the genetic improvement of production performance in chickens. The objective of this study was to detect the single nucleotide polymorphisms (SNPs) in the IGF1, IGFBP2 and TGFß3 genes, and to investigate their associations with growth performance (body weight (BW) and average daily gain (ADG) at 14, 21, 28, 35 and 42 days of age) and carcass traits in broilers. Performance (carcass) data (weight before slaughter; weights of the trunk, giblets, abdominal fat, breast muscle and thigh muscle; slaughter value and slaughter percentage), as well as blood samples for DNA extraction and SNP analysis, were obtained from 97 chickens belonging to two different lines (Hubbard F15 and Cobb E) equally divided between the two sexes. The genotypes were detected using polymerase chain reaction- restriction fragment length polymorphism (PCR-RFLP) methods with specific primers and restrictase for each gene. The statistical analysis discovered significant associations (p < 0.05) between the TGFβ3 SNP and the following parameters: BW at 21, 28 and 35 days, trunk weight and slaughter value. Association analysis of BWs (at 21, 28 and 35 days) and SNPs was always significant for codominant, dominant and overdominant genetic models, showing a possible path for genomic selection in these chicken lines. Slaughter value was significant for codominant, recessive and overdominant patterns, whereas other carcass traits were not influenced by SNPs. Based on the results of this study, we suggested that the TGFβ3 gene could be used as a candidate gene marker for chicken growth traits in the Hubbard F15 and Cobb E population selection programs, whereas for carcass traits further investigation is needed.

Effect of home-based strength training program on IGF-I, IGFBP-1 and IGFBP-3 in obese Latino boys participating in a 16-week randomized controlled trial

Introduction Growing evidence indicates that circulating concentrations of insulin-like growth factor 1 (IGF-I), along with IGF-I relative to IGF-binding proteins (IGFBP), are associated with an increased risk of cancer. In accord, regular exercise is linked with a lower risk of cancer. Purpose To assess the effects of a 16-week home-based strength training (HBST) program on serum IGF-I, IGFBP-1 and IGFBP-3. Methods A total of 32 obese Latino adolescent males (aged 14-18 years) were randomized into a twice-weekly HBST (n = 16) or a control group (C, n = 16) for 16 weeks. The following were measured at pre- and post-intervention: IGF-I, IGFBP-1 and IGFBP-3, glucose/insulin indices by oral and/or intravenous (IV) glucose tolerance tests, strength by one-repetition maximum (1RM), dietary intake by 3-d records, body composition by DEXA and physical activity using the Actigraph GT1X. The generalized linear model (GLM) was used to assess differences in changes among outcome measures between the HBST and C groups. Results Exercise adherence in the HBST group was 89%. IGF-1 showed a trend for significant within-subject improvements (p = 0.078) but no significant within-subject or between-subject differences for IGFBP-1, IGFBP-3 two-glucose, fasting glucose or 2-h glucose (p > 0.05). There was a significant decrease (p > 0.05) in fasting glucose in the C group (p = 0.02) and also in the intervention group (p = 0.03) between baseline and follow-up testing. A significant difference was also found in the C group for 2-h glucose with an increase at follow-up testing (p = 0.04). Conclusions Though not statistically significant (p < 0.05), the results indicated that a 16-week HBST program decreased IGF-I and increased IGFBP-1, along with IGFBP-3, concentrations among overweight/obese Latino boys. However, further studies should consider increasing either the dose or the duration of the intervention to elicit greater improvements in this at-risk pediatric population.

Effect of different levels of tryptophan on productive performance, egg quality, blood biochemistry, and caecal microbiota of hens housed in enriched colony cages under commercial stocking density

A study was conducted to determine the tryptophan (Trp) requirement of brown hens housed in enriched colony cages. A corn and wheat-based diets with 8 levels of standardized ileal digestible (SID) Trp (0.10, 0.13, 0.16, 0.19, 0.22, 0.25, 0.28, and 0.31% of the diet) were manufactured. The diet containing SID Trp 0.10% had no supplemental Trp and was treated as control. A total of 1,344 hens were randomly allocated to 8 treatments, each having 8 replicate cages with 21 hens per cage. Body weight gain (BWG), egg production (EP), feed conversion ratio (FCR), egg quality, blood biochemistry, caecal microbial profile, and concentration of indoles were determined over a period of 16 wk. The EP was linearly improved by supplementing diet with Trp and was highest in 0.25% SID-Trp group compared to control. Trp supplementation improved (P < 0.05) FCR, overall BWG, egg shell characteristics compared to control. The microbial shift in the caecum in response to Trp supplementation was significant in response to higher than current recommendations (0.22% of SID Trp) and indicated a microbial shift towards beneficial bacteria. Indole and skatole concentrations were only significantly different (P < 0.05) when hens in control group were compared with those containing highest levels of SID-Trp. This study demonstrates that when hens are at its peak production and are reared in enriched colony cages their Trp requirement is higher than current National Research Council (1994) recommendations and 0.22% of the SID-Trp in diet can be considered as an optimal level based on regression analysis.

Insulin-Like Growth Factor Axis Biomarkers and Gestational Diabetes Mellitus: A Systematic Review and Meta-Analysis

The insulin-like growth factor (IGF) axis has been implicated in glucose homeostasis. It is plausible to hypothesize that the IGF axis is involved in the development of gestational diabetes mellitus (GDM). In a systematic review of the evidence on IGF axis biomarkers in relation to GDM, we searched the PubMed and EMBASE for publications up to May 31, 2018, on the associations of circulating IGF axis biomarkers with GDM. Eligible studies must meet the pre-specified quality assessment criteria. Meta-analyses were conducted where there were at least three studies on the same biomarker at the same gestational age window-early (<20 weeks), mid (20-29 weeks), or late (30+ weeks) gestation. Twelve studies were included (484 GDM, 1755 euglycemic pregnancies). Meta-analyses showed that GDM was consistently associated with higher IGF-I concentrations in mid-gestation (six studies) and late gestation (six studies). There were only two studies on IGF-I in early gestation and GDM with inconsistent findings. GDM was associated with lower IGFBP-2 concentrations in early, mid-, or late gestation, according to data from one or two studies. GDM was associated with higher IGFBP-3 concentrations in late gestation according to a meta-analysis of five studies. There was no association with GDM for IGFBP-3 in early or mid-gestation, according to data from one study. Other IGF axis biomarkers (IGF-II, IGFBP-1,-4,-5-6, and -7) showed no or inconsistent associations, and the data at early gestation were scanty or absent. Available evidence is suggestive but inconclusive concerning whether the IGF axis is involved in the development of GDM. More studies on IGF axis biomarkers in early gestation are warranted. If a specific IGF axis molecule is proven to be involved in the development of GDM, this may point to a new molecular target for designing interventions to reduce the incidence of GDM.

Safety, tolerability, and preliminary efficacy of an IGF-1 mimetic in patients with spinal and bulbar muscular atrophy: a randomised, placebo-controlled trial

BACKGROUND

Spinal and bulbar muscular atrophy is an X-linked neuromuscular disease caused by CAG repeat expansion in the androgen receptor gene. Patients with this disease have low concentrations of insulin-like growth factor-1 (IGF-1), and studies of overexpression and administration of IGF-1 showed benefit in a transgenic model; thus the IGF-1 pathway presents as a potential treatment target. We assessed safety, tolerability, and preliminary efficacy of BVS857, an IGF-1 mimetic, in patients with spinal and bulbar muscular atrophy.

METHODS

In this randomised, double-blind, placebo-controlled trial, we recruited patients from neuromuscular centres in Denmark (Copenhagen), Germany (Ulm), Italy (Padova), and three sites within the USA (Bethesda, MD; Irvine, CA; and Columbus, OH). Eligible patients were 18 years or older with a confirmed genetic diagnosis of spinal and bulbar muscular atrophy, were ambulatory, had symptomatic weakness, and had serum IGF-1 concentrations of 170 ng/mL or lower. Patients were randomly assigned (2:1) to study drug or placebo by a number scheme. Patients, investigators, and study personnel were masked to treatment assignment. After a safety and tolerability assessment with eight patients, BVS857 was administered once a week (0·06 mg/kg intravenously) for 12 weeks. Primary outcome measures were safety, tolerability, and the effects of BVS857 on thigh muscle volume (TMV) measured by MRI. The ratio of TMV at day 85 to baseline was analysed with ANCOVA per protocol. Secondary outcomes of muscle strength and function were measured with the Adult Myopathy Assessment Tool, lean body mass through dual energy x-ray absorptiometry, and BVS857 pharmacokinetics. This trial was registered with ClinicalTrials.gov, NCT02024932.

FINDINGS

31 patients were assessed for eligibility, 27 of whom were randomly assigned to either BVS857 treatment (n=18) or placebo (n=9), and 24 were included in the preliminary efficacy analysis (BVS857 group, n=15; placebo group, n=9). BVS857 was generally safe with no serious adverse events. No significant differences were found in adverse events between the BVS857 and placebo groups. Immunogenicity was detected in 13 (72%) of 18 patients in the BVS857 group, including crossreacting antibodies with neutralising capacity to endogenous IGF-1 in five patients. TMV decreased from baseline to day 85 in the placebo group (-3·4% [-110 cm³]) but not in the BVS857 group (0% [2 cm³]). A significant difference in change in TMV was observed in the BVS857 group versus the placebo group (geometric-mean ratio 1·04 [90% CI 1·01-1·07]; p=0·02). There were no differences between groups in measures of muscle strength and function.

INTERPRETATION

TMV remained stable in patients with spinal and bulbar muscular atrophy after being given BVS857 for 12 weeks. The intervention was associated with high incidence of immunogenicity and did not improve muscle strength or function. Additional studies might be needed to assess the efficacy of activating the IGF-1 pathway in this disease.

FUNDING

Novartis Pharmaceuticals and the US National Institutes of Health.

A novel heterozygous IGF-1 receptor mutation associated with hypoglycemia

Mutation in the insulin-like growth factor-1 receptor (IGF1R) gene is a rare cause for intrauterine and postnatal growth disorders. Patients identified with IGF1R mutations present with either normal or impaired glucose tolerance. None of the cases described so far showed hypoglycemia. We aimed to identify the genetic basis for small for gestational age, short stature and hypoglycemia over three generations in one family. The proband, a 9-year-old male, presented in infancy with recurrent hypoglycemic episodes, symmetric intrauterine growth retardation and postnatal growth retardation. Blood DNA samples from the patient, his parents, a maternal sister and maternal grandmother underwent Sanger sequencing of the IGF1R gene. Primary skin fibroblast cultures of the patient, his mother and age- and sex-matched control donors were used for gene expression and receptor functional analyses. We found a novel heterozygous mutation (c.94 + 1g > a, D1105E) affecting the splicing site of the IGF1R mRNA in the patient, his mother and his grandmother. Primary fibroblast cultures derived from the patient and his mother showed reduced proliferation and impaired activation of the IGF1R, evident by reduced IGF1R and AKT phosphorylation upon ligand binding. In conclusion, the newly identified heterozygous missense mutation in exon 1 of IGF1R (D1105E) results in impaired IGF1R function and is associated with small for gestational age, microcephaly and abnormal glucose metabolism. Further studies are required to understand the mechanisms by which this mutation leads to hypoglycemia.

Use of the hyperinsulinemic euglycemic clamp to assess insulin sensitivity in guinea pigs: dose response, partitioned glucose metabolism, and species comparisons

The guinea pig is an alternate small animal model for the study of metabolism, including insulin sensitivity. However, only one study to date has reported the use of the hyperinsulinemic euglycemic clamp in anesthetized animals in this species, and the dose response has not been reported. We therefore characterized the dose-response curve for whole body glucose uptake using recombinant human insulin in the adult guinea pig. Interspecies comparisons with published data showed species differences in maximal whole body responses (guinea pig ≈ human < rat < mouse) and the insulin concentrations at which half-maximal insulin responses occurred (guinea pig > human ≈ rat > mouse). In subsequent studies, we used concomitant d-[3-³H]glucose infusion to characterize insulin sensitivities of whole body glucose uptake, utilization, production, storage, and glycolysis in young adult guinea pigs at human insulin doses that produced approximately half-maximal (7.5 mU·min^-1·kg^-1) and near-maximal whole body responses (30 mU·min^-1·kg^-1). Although human insulin infusion increased rates of glucose utilization (up to 68%) and storage and, at high concentrations, increased rates of glycolysis in females, glucose production was only partially suppressed (~23%), even at high insulin doses. Fasting glucose, metabolic clearance of insulin, and rates of glucose utilization, storage, and production during insulin stimulation were higher in female than in male guinea pigs (P < 0.05), but insulin sensitivity of these and whole body glucose uptake did not differ between sexes. This study establishes a method for measuring partitioned glucose metabolism in chronically catheterized conscious guinea pigs, allowing studies of regulation of insulin sensitivity in this species.

Insulin-Like Growth Factor-1 Deficiency and Cirrhosis Establishment

Cirrhosis represents the final stage of chronic liver damage, which can be due to different factors such as alcohol, metabolic syndrome with liver steatosis, autoimmune diseases, drugs, toxins, and viral infection, among others. Nowadays, cirrhosis is an important health problem and it is an increasing cause of morbidity and mortality, being the 14th most common cause of death worldwide. The physiopathological pathways that lead to fibrosis and finally cirrhosis partly depend on the etiology. Nevertheless, some common features are shared in this complex mechanism. Recently, it has been demonstrated that cirrhosis is a dynamic process that can be altered in order to delay or revert fibrosis. In addition, when cirrhosis has been established, insulin-like growth factor-1 (IGF-1) deficiency or reduced availability is a common condition, independently of the etiology of chronic liver damage that leads to cirrhosis. IGF-1 deprivation seriously contributes to the progressive malnutrition of cirrhotic patient, increasing the vulnerability of the liver to establish an inflammatory and oxidative microenvironment with mitochondrial dysfunction. In this context, IGF-1 deficiency in cirrhotic patients can justify some of the common characteristics of these individuals. Several studies in animals and humans have been done in order to test the replacement of IGF-1 as a possible therapeutic option, with promising results.

Non-essential and branched-chain amino acids differentially regulate insulin-like growth factor binding protein-1 production and phosphorylation in HepG2 cells

Deprivation of branched-chain amino acids (BCAAs) induces insulin-like growth factor binding protein-1 (IGFBP-1) production in HepG2 cells, while the role of non-essential amino acids (NEAAs) remains unknown. We investigated changes in IGFBP-1 production and phosphorylation induced by NEAAs and also examined its significance on IGF-I activity in HepG2 cells. We demonstrated that decreased BCAAs and increased NEAAs stimulated phosphorylated IGFBP-1 secretion. We also revealed that decreased BCAA-to-NEAA ratios enhanced phosphorylated IGFBP-1 secretion, while changes in the total amount of amino acids (AAs) had no effect. Phosphorylation of IGF-I receptor β-subunits mediated by exogenous IGF-I in HepG2 cells was inhibited by decreased BCAAs, increased NEAAs, and decreased BCAA-to-NEAA ratios, while the total amount of AAs had no effect. In addition to BCAAs, NEAAs are also responsible for the regulation of IGFBP-1 secretion and phosphorylation in HepG2 cells. Moreover, the balance of BCAAs and NEAAs regulated IGFBP-1 secretion and phosphorylation.

Deteriorated high-fat diet-induced diabetes caused by pancreatic β-cell-specific overexpression of Reg3β gene in mice

Reg family proteins have long been implicated in islet β-cell proliferation, survival, and regeneration. In our previous study, we reported that Reg3β overexpression did not increase islet growth but prevented streptozotocin-induced islet damage by inducing specific genes. In order to explore its role in type 2 diabetes (T2D), we established high-fat diet (HFD)-induced obesity and diabetes in RIP-I/Reg3β mice. Glucose and insulin tolerance tests, immunofluorescence for insulin, eIF2α, and GLUT2 in islets, Western blots on phosphorylated AMPKα and hepatic histology were performed. Both RIP-I/Reg3β and wild-type mice gained weight rapidly and became hyperglycemic after 10 weeks on the HFD. However, the transgenic mice exhibited more significant acceleration in blood glucose levels, further deterioration of glucose intolerance and insulin resistance, and a lower intensity of insulin staining. Immunofluorescence revealed similar magnitude of islet compensation to a wild-type HFD. The normal GLUT2 distribution in the transgenic β-cells was disrupted and the staining was obviously diminished on the cell membrane. HFD feeding also caused a further decrease in the level of AMPKα phosphorylation in the transgenic islets. Our results suggest that unlike its protective effect against T1D, overexpressed Reg3β was unable to protect the β-cells against HFD-induced damage.

Central IGF-I Receptors in the Brain are Instrumental to Neuroprotection by Systemically Injected IGF-I in a Rat Model for Ischemic Stroke

AIM

Insulin-like growth factor I (IGF-I) is a neuroprotective agent in animal models of ischemic stroke. The purpose of this study was to determine whether systemically injected IGF-I exerts its neuroprotective action by binding to IGF-I receptors in the brain after crossing the blood-brain barrier, or via peripheral effects.

METHODS

To differentiate the central effects of IGF-I from systemic effects, ischemic stroke was induced in conscious male Wistar Kyoto rats by the injection of endothelin-1 adjacent to the middle cerebral artery in the right hemisphere, while either the IGF-I receptor antagonist JB-1 or vehicle was introduced into the right lateral ventricle.

RESULTS

Intravenous injection of recombinant human (rh)IGF-I resulted in 50% reduction in infarct size, which was counteracted by the central administration of JB-1. Furthermore, rhIGF-I was detected in both the ischemic and nonischemic hemisphere.

CONCLUSIONS

Systemically injected rhIGF-I passes the blood-brain barrier and protects neurons via IGF-I receptors in the brain in rats with an ischemic stroke.

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.

Changes in insulin-like growth factor-I and its binding proteins are associated with diabetes mellitus in older adults

OBJECTIVES

To determine whether changes in insulin-like growth factor (IGF) protein levels are greater in participants with type 2 diabetes mellitus or worsening glycemia than in normoglycemic individuals over a 9-year follow-up period.

DESIGN

Retrospective analysis of a cohort study.

SETTING

Participants were recruited from North Carolina, California, Maryland, and Pennsylvania.

PARTICIPANTS

Cardiovascular Health Study All Stars participants, a cohort study of community-dwelling adults aged 65 and older (N=897).

MEASUREMENTS

Plasma IGF-I, IGF binding protein (IGFBP)-1, and IGFBP-3 levels were assessed and American Diabetes Association cut-points for impaired glucose tolerance (IGT), impaired fasting glucose (IFG), and diabetes mellitus were used to classify participants at baseline (1996-97) and follow-up (2005-06).

RESULTS

At baseline, mean age was 76.3±3.6, and 18.5% had diabetes mellitus. Participants with IFG alone and IGT plus IFG had higher IGF-I levels and lower IGFBP-1 levels than those with normoglycemia or diabetes mellitus. The greatest percentage change in IGF levels occurred in those who had diabetes mellitus at baseline (9-year changes: -9.3% for IGF-I, 59.7% for IGFBP-1, -13.4% for IGFBP-3), the smallest in individuals who remained normoglycemic at follow-up (9-year changes: -3.7% for IGF-I, 25.6% for IGFBP-1, -6.4% for IGFBP-3), and intermediate in those who were normoglycemic but developed IFG at follow-up.

CONCLUSION

Degrees of glycemic impairment are associated with varying degrees of change in IGF protein levels. The changes observed in the diabetes mellitus group have been previously shown to be associated with heart failure, cancer, and noncancer mortality.

Insulin-like growth factor (IGF)-I and IGF binding proteins axis in diabetes mellitus

Increasing evidence suggests an important role of the insulin-like growth factor (IGF)-IGF binding protein (IGFBP) axis in the maintenance of normal glucose and lipid metabolism. Significant changes occur in the local IGF-I-IGFBPs environment in response to the diabetic milieu. A significant reduction of serum IGF-I levels was observed in patients with type 1 diabetes mellitus (T1DM). Inversely, considerably increased serum levels of IGF-I and IGFBP-3 levels were detected in individuals with glucose intolerance including T2DM. Recently, several prospective studies indicated that baseline levels of IGF-I and IGFBPs are associated with the development of diabetes. These findings suggest that disturbances in insulin and IGF-I-IGFBP axis can affect the development of glucose intolerance including diabetes.

Insulin-like growth factor 1, glycation and bone fragility: implications for fracture resistance of bone

Despite our extensive knowledge of insulin-like growth factor 1 (IGF1) action on the growing skeleton, its role in skeletal homeostasis during aging and age-related development of certain diseases is still unclear. Advanced glycation end products (AGEs) derived from glucose are implicated in osteoporosis and a number of diabetic complications. We hypothesized that because in humans and rodents IGF1 stimulates uptake of glucose (a glycation substrate) from the bloodstream in a dose-dependent manner, the decline of IGF1 could be associated with the accumulation of glycation products and the decreasing resistance of bone to fracture. To test the aforementioned hypotheses, we used human tibial posterior cortex bone samples to perform biochemical (measurement of IGF1, fluorescent AGEs and pentosidine (PEN) contents) and mechanical tests (crack initiation and propagation using compact tension specimens). Our results for the first time show a significant, age-independent association between the levels of IGF1 and AGEs. Furthermore, AGEs (fAGEs, PEN) predict propensity of bone to fracture (initiation and propagation) independently of age in human cortical bone. Based on these results we propose a model of IGF1-based regulation of bone fracture. Because IGF1 level increases postnatally up to the juvenile developmental phase and decreases thereafter with aging, we propose that IGF1 may play a protective role in young skeleton and its age-related decline leads to bone fragility and an increased fracture risk. Our results may also have important implications for current understanding of osteoporosis- and diabetes-related bone fragility as well as in the development of new diagnostic tools to screen for fragile bones.

The prelude on novel receptor and ligand targets involved in the treatment of diabetes mellitus

Metabolic disorders are a group of disorders, due to the disruption of the normal metabolic process at a cellular level. Diabetes Mellitus and Tyrosinaemia are the majorly reported metabolic disorders. Among them, Diabetes Mellitus is a one of the leading metabolic syndrome, affecting 5 to 7 % of the population worldwide and mainly characterised by elevated levels of glucose and is associated with two types of physiological event disturbances such as impaired insulin secretion and insulin resistance. Up to now, various treatment strategies are like insulin, alphaglucosidase inhibitors, biguanides, incretins were being followed. Concurrently, various novel therapeutic strategies are required to advance the therapy of Diabetes mellitus. For the last few decades, there has been an extensive research in understanding the metabolic pathways involved in Diabetes Mellitus at the cellular level and having the profound knowledge on cell-growth, cell-cycle, and apoptosis at a molecular level provides new targets for the treatment of Diabetes Mellitus. Receptor signalling has been involved in these mechanisms, to translate the information coming from outside. To understand the various receptors involved in these pathways, we must have a sound knowledge on receptors and ligands involved in it. This review mainly summarises the receptors and ligands which are involved the Diabetes Mellitus. Finally, researchers have to develop the alternative chemical moieties that retain their affinity to receptors and efficacy. Diabetes Mellitus being a metabolic disorder due to the glucose surfeit, demands the need for regular exercise along with dietary changes.

Action of GH on skeletal muscle function: molecular and metabolic mechanisms

Skeletal muscle is a target tissue of GH. Based on its anabolic properties, it is widely accepted that GH enhances muscle performance in sports and muscle function in the elderly. This paper critically reviews information on the effects of GH on muscle function covering structure, protein metabolism, the role of IGF1 mediation, bioenergetics and performance drawn from molecular, cellular and physiological studies on animals and humans. GH increases muscle strength by enhancing muscle mass without affecting contractile force or fibre composition type. GH stimulates whole-body protein accretion with protein synthesis occurring in muscular and extra-muscular sites. The energy required to power muscle function is derived from a continuum of anaerobic and aerobic sources. Molecular and functional studies provide evidence that GH stimulates the anaerobic and suppresses the aerobic energy system, in turn affecting power-based functional measures in a time-dependent manner. GH exerts complex multi-system effects on skeletal muscle function in part mediated by the IGF system.

Insulin-like growth factor-I (IGF-I) and clinical nutrition

IGF-I (insulin-like growth factor-I) is a peptide hormone, produced predominantly by the liver in response to pituitary GH (growth hormone), which is involved in a wide variety of physiological processes. It acts in an endocrine, paracrine and autocrine manner to promote growth. The production of IGF-I signals the availability of nutrients needed for its anabolic actions. Recently, there has been growing interest in its role in health and disease. IGF-I has long been known to be regulated by nutrition and dysregulated in states of under- and over-nutrition, its serum concentrations falling in malnutrition and responding promptly to refeeding. This has led to interest in its utility as a nutritional biomarker. A considerable evidence base supports utility for measurement of IGF-I in nutritional contexts. Its concentration may be valuable in providing information on nutritional status, prognosis and in monitoring nutritional support. However, it is insufficiently specific for use as a screening test for under nutrition as its serum concentration is influenced by many factors other than nutritional status, notably the APR (acute-phase response) and endocrine conditions. Concentrations should be interpreted along with clinical findings and the results of other investigations such as CRP (C-reactive protein). More recently, there has been interest in free IGF-I which holds promise as a nutritional marker. The present review covers nutritional regulation of IGF-I and its dysregulation in disease, then goes on to review recent studies supporting its utility as a nutritional marker in clinical contexts. Although not currently recommended by clinical guidelines, it is likely that, in time, measurement of IGF-I will become a routine part of nutritional assessment in a number of these contexts.

Human conditions of insulin-like growth factor-I (IGF-I) deficiency

Insulin-like growth factor I (IGF-I) is a polypeptide hormone produced mainly by the liver in response to the endocrine GH stimulus, but it is also secreted by multiple tissues for autocrine/paracrine purposes. IGF-I is partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions). IGF-I is a closely regulated hormone. Consequently, its logical therapeutical applications seems to be limited to restore physiological circulating levels in order to recover the clinical consequences of IGF-I deficiency, conditions where, despite continuous discrepancies, IGF-I treatment has never been related to oncogenesis. Currently the best characterized conditions of IGF-I deficiency are Laron Syndrome, in children; liver cirrhosis, in adults; aging including age-related-cardiovascular and neurological diseases; and more recently, intrauterine growth restriction. The aim of this review is to summarize the increasing list of roles of IGF-I, both in physiological and pathological conditions, underlying that its potential therapeutical options seem to be limited to those proven states of local or systemic IGF-I deficiency as a replacement treatment, rather than increasing its level upper the normal range.

Insulin-like growth factors in normal and diseased kidney

This article reviews the physiology of the insulin-like growth factor (IGF) system in the kidney and the changes and potential role of this system in selected renal diseases. The potential therapeutic uses of recombinant human IGF-I for the treatment of acute and chronic kidney failure are briefly discussed.

Hormone replacement therapy and physical function in healthy older men. Time to talk hormones?

Improving physical function and mobility in a continuously expanding elderly population emerges as a high priority of medicine today. Muscle mass, strength/power, and maximal exercise capacity are major determinants of physical function, and all decline with aging. This contributes to the incidence of frailty and disability observed in older men. Furthermore, it facilitates the accumulation of body fat and development of insulin resistance. Muscle adaptation to exercise is strongly influenced by anabolic endocrine hormones and local load-sensitive autocrine/paracrine growth factors. GH, IGF-I, and testosterone (T) are directly involved in muscle adaptation to exercise because they promote muscle protein synthesis, whereas T and locally expressed IGF-I have been reported to activate muscle stem cells. Although exercise programs improve physical function, in the long-term most older men fail to comply. The GH/IGF-I axis and T levels decline markedly with aging, whereas accumulating evidence supports their indispensable role in maintaining physical function integrity. Several studies have reported that the administration of T improves lean body mass and maximal voluntary strength in healthy older men. On the other hand, most studies have shown that administration of GH alone failed to improve muscle strength despite amelioration of the detrimental somatic changes of aging. Both GH and T are anabolic agents that promote muscle protein synthesis and hypertrophy but work through separate mechanisms, and the combined administration of GH and T, albeit in only a few studies, has resulted in greater efficacy than either hormone alone. Although it is clear that this combined approach is effective, this review concludes that further studies are needed to assess the long-term efficacy and safety of combined hormone replacement therapy in older men before the medical rationale of prescribing hormone replacement therapy for combating the sarcopenia of aging can be established.

The GH/IGF-1 system in critical illness

The Growth Hormone and Insulin-like Growth Factor-1 (IGF-1) axis plays a pivotal role in critical illness, with a derangement leading to profound changes in metabolism. Protein wasting with skeletal muscle loss, delayed wound healing, and impaired recovery of organ systems are some of the most feared consequences. The use of human recombinant Growth Hormone (rhGH) and Insulin-like Growth Factor-1 (IGF-1) - alone and in combination - has been studied extensively in preclinical and clinical trials. This article reviews the current knowlegde and clinical practice of the use of rhGh and IGF-1 in critically ill patients, with a special focus on the trauma and burns patient population.

Effect of low-intensity aerobic exercise on insulin-like growth factor-I and insulin-like growth factor-binding proteins in healthy men

Increased concentrations of circulating insulin-like growth factor-I (IGF-I) or IGF-I relative to IGF-binding proteins (IGFBPs) are associated with increased risk of developing several forms of cancer. Conversely, exercise is linked with reduced risk. This study aims to investigate the effect of a low-intensity exercise program on circulating levels of IGF-I, IGFBP-1, and IGFBP-3, in previously sedentary males. Fourteen healthy men participated in cycle ergometer training at lactate threshold intensity for 60 min/day, 5 days/week for 6 weeks. After aerobic training, insulin sensitivity improved by 20%, while fasting insulin levels decreased by 13%. Simultaneously, low-intensity aerobic training decreased the circulating levels of IGF-I by 9%, while IGFBP-1 levels increased by 16%. An interesting finding was that higher pretraining level of IGF-I was associated with greater decline in IGF-I with training. Insulin-sensitizing low-intensity aerobic exercise is thus considered to be an effective method for downregulating IGF-I and upregulating IGFBP-1 levels.

Effect of bovine somatotropin administration during the last trimester of gestation on maternal growth, and foetal and placental development in primigravid ewes

Twenty-five primigravid ewes were used in a preliminary study to investigate the effect of bovine somatotropin (bST) between 97 and 124 days of gestation, on maternaland foetal growthand development. Five ewes (reference group) were slaughteredat 96 days of gestation, and the remaining ewes were injected daily with saline (control group: no = 10) or 0·1 mg/kgbody weight of bST (bST group: no. = 10). Following bST treatment, five control- and five bST groupewes were slaughtered (slaughter group). The remaining ewes (production group) were allowed to lamb, after which the lambs were slaughtered within 2 h of birth. Bovine somatotropin reducedthe proportion of maternal body fat, but had no major impacton wool growth, maternal gain and gross skeletal measurements, and foetal growth and development. Maternal bST treatment tended to affect the number of placentomes. It should, however, be emphasized that these results are based on small numbers of animals and that further research in this area is required.

Insulin-like growth factor I and insulin and their abuse in sport

It is believed that insulin and insulin-like growth factor I (IGF-I) are abused by professional athletes, either alone or in combination with growth hormone (GH) and anabolic steroids. The recent introduction of IGF-I to clinical practice is likely to increase its availability and abuse. Insulin and IGF-I work together with GH to control the supply of nutrients to tissues in the fasted and fed state. The actions of insulin and IGF-I that may enhance performance include increased protein anabolism and glucose uptake and storage. The detection of IGF-I and insulin abuse is challenging. There are established mass spectrometry methods for insulin analogs. The feasibility of using GH-dependent markers to detect IGF-I use is being assessed.

Prolonged sleep restriction affects glucose metabolism in healthy young men

This study identifies the effects of sleep restriction and subsequent recovery sleep on glucose homeostasis, serum leptin levels, and feelings of subjective satiety. Twenty-three healthy young men were allocated to a control group (CON) or an experimental (EXP) group. After two nights of 8 h in bed (baseline, BL), EXP spent 4 h in bed for five days (sleep restriction, SR), followed by two nights of 8 h (recovery, REC). CON spent 8 h in bed throughout the study. Blood samples were taken after the BL, SR, and REC period. In EXP, insulin and insulin-to-glucose ratio increased after SR. IGF-1 levels increased after REC. Leptin levels were elevated after both SR and REC; subjective satiety remained unaffected. No changes were observed in CON. The observed increase of serum IGF-1 and insulin-to-glucose ratio indicates that sleep restriction may result in an increased risk to develop type 2 diabetes.

Short-term administration of a combination of recombinant growth hormone and insulin-like growth factor-I induces anabolism in maintenance hemodialysis

CONTEXT

Resistance to GH and IGF-I is a significant complication of severe chronic kidney disease, which contributes to muscle wasting. Pharmacological doses of recombinant human (rh) GH or rhIGF-I have been proposed to treat this catabolic condition.

OBJECTIVE

This study was undertaken to examine the potential additive anabolic effects of rhGH + rhIGF-I compared with rhIGF-I.

DESIGN

We studied eight well-nourished hemodialysis patients in a random crossover design and compared the metabolic effects of a 3-d administration of moderate dose of rhIGF-I (40 microg/kg per 12h) with an association of rhIGF-I + rhGH (50 microg/kg/d). Leucine kinetics, plasma amino acids (AAs), serum insulin, and IGF binding proteins (IGFBP)-1 and -3 were measured.

RESULTS

The net protein balance was not affected by rhIGF-I alone, whereas serum insulin and IGFBP-3 decreased (P < 0.05) and IGFBP-1 increased (P < 0.01). With the combination rhGH + rhIGF-I, an increase of IGFBP-3 (P < 0.01) and insulin (P < 0.01) as well as a decrease of IGFBP-1 (P < 0.01) occurred. Plasma essential AAs (P = 0.01) as well as the essential to nonessential AA ratio (P < 0.001) decreased. Whole-body protein net balance increased significantly (P < 0.05) with a 22% decrease in leucine oxidation and a 15% increase in nonoxidative leucine disposal.

CONCLUSIONS

In dialysis patients, rhIGF-I administration at a moderate dose has no protein metabolic effect, but the association with a moderate dose of rhGH is followed by a significant anabolic response.

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.

Growth hormone, IGF-I and insulin and their abuse in sport

There is widespread anecdotal evidence that growth hormone (GH) is used by athletes for its anabolic and lipolytic properties. Although there is little evidence that GH improves performance in young healthy adults, randomized controlled studies carried out so far are inadequately designed to demonstrate this, not least because GH is often abused in combination with anabolic steroids and insulin. Some of the anabolic actions of GH are mediated through the generation of insulin-like growth factor-I (IGF-I), and it is believed that this is also being abused. Athletes are exposing themselves to potential harm by self-administering large doses of GH, IGF-I and insulin. The effects of excess GH are exemplified by acromegaly. IGF-I may mediate and cause some of these changes, but in addition, IGF-I may lead to profound hypoglycaemia, as indeed can insulin. Although GH is on the World Anti-doping Agency list of banned substances, the detection of abuse with GH is challenging. Two approaches have been developed to detect GH abuse. The first is based on an assessment of the effect of exogenous recombinant human GH on pituitary GH isoforms and the second is based on the measurement of markers of GH action. As a result, GH abuse can be detected with reasonable sensitivity and specificity. Testing for IGF-I and insulin is in its infancy, but the measurement of markers of GH action may also detect IGF-I usage, while urine mass spectroscopy has begun to identify the use of insulin analogues.

The somatomedin hypothesis 2007: 50 years later

CONTEXT

The somatomedin/IGF hypothesis was based on the observation that GH was inactive when added to an in vitro incubation system but required a GH-dependent substance in the circulation to mediate its activity. Newer experimental evidence has led to several modifications of the hypothesis, but none of the proposed modifications accounts for all of the integrated actions of GH and IGF-I. In this paper, we propose an augmentative/counteractive modification of the existing hypothesis that takes into account all the actions of the GH-IGF system.

EVIDENCE ACQUISITION

The modification is based on experimental evidence published since the hypothesis was originally developed.

EVIDENCE SYNTHESIS

The modification is based on an integration of the results of published experimental evidence regarding the actions of GH and the IGF complex.

CONCLUSION

We propose a new augmentative/counteractive modification of the hypothesis that the actions of the GH-IGF system provide a distinct evolutionary advantage to the organism by augmenting the anabolic actions of GH while countering its potentially deleterious effects of hyperglycemia and depletion of lipid stores.

Effects of combined recombinant insulin-like growth factor (IGF)-I and IGF binding protein-3 in type 2 diabetic patients on glycemic control and distribution of IGF-I and IGF-II among serum binding protein complexes

CONTEXT

Administration of recombinant human IGF-I (rhIGF-I)/recombinant human IGF binding protein-3 (rhIGFBP-3) to patients with type 2 diabetes improves blood glucose and enhances insulin sensitivity. The changes in various components of the IGF system that occur in response to rhIGF-I/rhIGFBP-3 as well as the minimum effective dose have not been determined.

OBJECTIVES

The aim was to determine the dose of rhIGF-I/rh-IGFBP-3 necessary to achieve a significant decrease in glucose and to determine the changes that occur in the IGF-II and acid labile subunit in response to treatment.

DESIGN

A total of 39 insulin-requiring type 2 diabetics were randomized to placebo or one of six groups that received different dosages of rhIGF-I/rhIGFBP-3. After 3 d in which insulin doses were adjusted to improve glucose control, a variable insulin dosage regimen was continued, and either placebo or one of six dosages (0.125-2.0 mg/kg.d) of rhIGF-I/rhIGFBP-3 was administered for 7 d. All subjects were hospitalized, and dietary intake as well as insulin dosage were controlled with instructions to treat to normal range targets.

RESULTS

Fasting glucose was reduced in the groups that received either 1 (32 +/- 5% reduction) or 2 mg/kg.d (40 +/- 6% reduction) of the complex. Mean daily glucose (four determinations) was reduced by 26 +/- 4% in the 1 mg/kg group and by 33 +/- 5% in the 2 mg/kg group compared with 18 +/- 4% in the placebo group. Total serum IGF-I increased between 2.0 +/- 0.3- and 5.7 +/- 1.3-fold by d 8. IGFBP-3 concentrations increased significantly only in the 2 mg/kg group. IGF-II concentrations declined to values that were between 27 +/- 4% and 64 +/- 7% below baseline. Acid labile subunit concentrations declined significantly in the three highest dose groups. The sum of the IGF-I + IGF-II concentrations was significantly increased at the two highest dosages. There were very few drug-associated adverse events reported in this study with the exception of hypoglycemia, which occurred in 15 subjects who had received rhIGF-I/rhIGFBP-3 treatment.

CONCLUSIONS

Administration of rhIGF-I/rhIGFBP-3 resulted in a redistribution of the amount of IGF-I and IGF-II that bound to IGFBP-3. Fasting and mean daily blood glucose were reduced significantly in the two highest dosage groups. The results suggest that both the total concentration of IGF-I as well as its distribution in blood may determine the extent to which insulin sensitivity is enhanced.