Effects of recombinant human IGF-I/IGF-binding protein-3 complex on glucose and glycerol metabolism in type 1 diabetes

IGF-1 and IGFBP3 as indirect markers of hepatic insulin resistance and their relation to metabolic syndrome parameters in liver steatosis patients

Objective. The aim of the present study was to assess insulin-like growth factor 1 (IGF-1) and IGF-binding protein 3 (IGFBP3) as markers of insulin resistance in patients with prediabetes and type 2 diabetes mellitus (TDM2). Patients and Methods. This observational clinical study included 76 obese/overweight patients at the age of 45-75 years with T2DM on oral diabetic medication and ultrasonographically or by a computerized tomography (CT) diagnosed liver steatosis. Correlation analysis was performed between plasma levels of insulin, C-peptide, IGF-1, IGFBP3 and HOMA indexes on the one hand and between plasma levels of ALT, AST, triglyceride, cholesterol, and HDL cholesterol and body mass index (BMI) of patients on the other hand. In case of significant partial correlation coefficients, a multiple linear regression model with IGF-1 and IGFBP3 used as outcome variables adjusted for age and sex groups was calculated. According to these regression models, ROC curves were prepared with HOMA index=3 used as a classificator of insulin resistance. Results. Significant correlation was found between C-peptide and IGF-1 (r=0.24, p≤0.05), C-peptide and IGFBP3 (r=0.24, p≤0.05), IGFBP3 and cholesterol (r=0.22, p≤0.05) IGFBP3 and ALT (r=0.19, p≤0.05), HOMA index and triglycerides (r=0.22, p≤0.05), and HOMA index and ALT (r=0.23, p≤0.05). Significant correlation adjusted for age and gender was found between C-peptide and IGF-1 plasma levels (R2=0.20, p<0.05) with AUROC 0.685 (p≤0.01) and C-peptide and IGFBP3 plasma levels (R2=0.28, p<0.05) with AUROC 0.684 (p≤0.01). Significant correlation adjusted for age and gender was found between triglyceride and IGFBP3 plasma levels (R2=0.28, p<0.05) with AUROC 0.616 (p≤0.01). After the distribution of patients according to their IGFBP3 levels, we found a difference between the 1st and the 4th quartiles in terms of triglyceride levels. Conclusion. Our results demonstrate a fundamental role of IGF-1 and IGFBP3 in the patho-physiology of hepatic insulin resistance and suggest them as indirect indicators of the hepatic insulin resistance.

IGF-Binding Proteins and Their Proteolysis as a Mechanism of Regulated IGF Release in the Nervous Tissue

Insulin-like growth factors 1 and 2 (IGF-1 and IGF-2) play a key role in the maintenance of the nervous tissue viability. IGF-1 and IGF-2 exhibit the neuroprotective effects by stimulating migration and proliferation of nervous cells, activating cellular metabolism, inducing regeneration of damaged cells, and regulating various stages of prenatal and postnatal development of the nervous system. The availability of IGFs for the cells is controlled via their interaction with the IGF-binding proteins (IGFBPs) that inhibit their activity. On the contrary, the cleavage of IGFBPs by specific proteases leads to the IGF release and activation of its cellular effects. The viability of neurons in the nervous tissue is controlled by a complex system of trophic factors secreted by auxiliary glial cells. The main source of IGF for the neurons are astrocytes. IGFs can accumulate as an extracellular free ligand near the neuronal membranes as a result of proteolytic degradation of IGFBPs by proteases secreted by astrocytes. This mechanism promotes interaction of IGFs with their genuine receptors and triggers intracellular signaling cascades. Therefore, the release of IGF by proteolytic cleavage of IGFBPs is an important mechanism of neuronal protection. This review summarizes the published data on the role of IGFs and IGFBPs as the key players in the neuroprotective regulation with a special focus on the specific proteolysis of IGFBPs as a mechanism for the regulation of IGF bioavailability and viability of neurons.

Insulin-Like Growth Factor 1 (IGF-1) Signaling in Glucose Metabolism in Colorectal Cancer

Colorectal cancer (CRC) is one of the most common aggressive carcinoma types worldwide, characterized by unfavorable curative effect and poor prognosis. Epidemiological data re-vealed that CRC risk is increased in patients with metabolic syndrome (MetS) and its serum components (e.g., hyperglycemia). High glycemic index diets, which chronically raise post-prandial blood glucose, may at least in part increase colon cancer risk via the insulin/insulin-like growth factor 1 (IGF-1) signaling pathway. However, the underlying mechanisms linking IGF-1 and MetS are still poorly understood. Hyperactivated glucose uptake and aerobic glycolysis (the Warburg effect) are considered as a one of six hallmarks of cancer, including CRC. However, the role of insulin/IGF-1 signaling during the acquisition of the Warburg metabolic phenotypes by CRC cells is still poorly understood. It most likely results from the interaction of multiple processes, directly or indirectly regulated by IGF-1, such as activation of PI3K/Akt/mTORC, and Raf/MAPK signaling pathways, activation of glucose transporters (e.g., GLUT1), activation of key glycolytic enzymes (e.g., LDHA, LDH5, HK II, and PFKFB3), aberrant expression of the oncogenes (e.g., MYC, and KRAS) and/or overexpression of signaling proteins (e.g., HIF-1, TGF-β1, PI3K, ERK, Akt, and mTOR). This review describes the role of IGF-1 in glucose metabolism in physiology and colorectal carcinogenesis, including the role of the insulin/IGF system in the Warburg effect. Furthermore, current therapeutic strategies aimed at repairing impaired glucose metabolism in CRC are indicated.

USP24-GSDMB complex promotes bladder cancer proliferation via activation of the STAT3 pathway

Background: Bladder cancer is the fourth and tenth most common malignancy in men and women worldwide, respectively. One of the main reasons for the unsatisfactory therapeutic control of bladder cancer is that the molecular biological mechanism of bladder cancer is complex. Gasdermin B (GSDMB) is one member of the gasdermin family and participates in the regulation of cell pyroptosis. The role of GSDMB in bladder cancer has not been studied to date. Methods: TCGA database was used to exam the clinical relevance of GSDMB. Functional assays such as MTT assay, Celigo fluorescent cell-counting assay, Annexin V-APC assay and xenografts were used to evaluate the biological role of GSDMB in bladder cancer. Mass spectrometry and immunoprecipitation were used to detect the protein interaction between GSDMB and STAT3, or GSDMB and USP24. Western blot and immunohistochemistry were used to study the relationship between USP24, GSDMB and STAT3. Results: In this study, bioinformatics analysis indicated that the mRNA expression level of GSDMB in bladder cancer tissues was higher than that in adjacent normal tissues. Then, we showed that GSDMB promoted bladder cancer progression. Furthermore, we demonstrated that GSDMB interacted with STAT3 to increase the phosphorylation of STAT3 and modulate the glucose metabolism and promote tumor growth in bladder cancer cells. Besides, we also showed that USP24 stabilized GSDMB to activate STAT3 signaling, which was blocked by the USP24 inhibitor. Conclusions: We suggested that aberrantly up-regulated GSDMB was responsible for enhancing the growth and invasion ability of bladder cancer cells. Then, we showed that GSDMB could bind to STAT3 and activate STAT3 signaling in bladder cancer. Furthermore, we also demonstrated that USP24 interacted with GSDMB and prevented GSDMB from degradation in bladder cancer cells. Therefore, the USP24/GSDMB/STAT3 axis may be a new targetable signaling pathway for bladder cancer treatment.

Glucocorticoid-insulin-like growth factor 1 (GC-IGF1) axis programming mediated hepatic lipid-metabolic in offspring caused by prenatal ethanol exposure

Prenatal ethanol exposure (PEE) could increase offspring's susceptibility to adult liver lipid-metabolism diseases. This study aimed to confirm intrauterine programming mechanism of glucocorticoid-insulin-like growth factor 1 (GC-IGF1) axis for liver dysfunction in offspring rats induced by PEE. The results showed that levels of hepatic IGF1, lipid metabolism-related enzymes (e.g. FASN and HMGCR) and serum phenotype (TG, TCH, HDL-C, and LDL-C) were low in fetal rats of PEE but high in adult offspring except for HDL-C, meanwhile, hepatic H3K9ac and expression levels of IGF1 were low in fetal rats but high in adult offspring. Furthermore, levels of serum corticosterone and hepatic glucocorticoid-activation system (mainly including expression of 11β-HSD1, GR, and C/EBPα as well as 11β-HSD1/11β-HSD2 ratio) were high in fetal rats of PEE but low or unchanged in adult offspring. The adult F2 generation of PEE maintained the same GC-IGF1 axis programming alteration as the F1 generation despite gender differences. In vitro, cortisol was proved to activate hepatocyte glucocorticoid-activation system and decrease H3K9ac and expression levels of IGF1 by GR. Therefore, PEE has a long-term effect on the offspring's liver functional development, which may be mainly related to the epigenetic programming alteration of the GC-IGF1 axis mediated by the glucocorticoid-activation system.

Intervertebral disc degeneration in mice with type II diabetes induced by leptin receptor deficiency

Background

The leptin receptor-deficient knockout (db/db) mouse is a well-established model for studying type II diabetes mellitus (T2DM). T2DM is an important risk factor of intervertebral disc degeneration (IVDD). Although the relationship between type I diabetes and IVDD has been reported by many studies, few studies have reported the effects of T2DM on IVDD in db/db mice model.

Methods

Mice were separated into 3 groups: wild-type (WT), db/db, and IGF-1 groups (leptin receptor-deficient mice were treated with insulin-like growth factor-1 (IGF-1). To observe the effects of T2DM and glucose-lowering treatment on IVDD, IGF-1 injection was used. The IVD phenotype was detected by H&E and safranin O fast green staining among db/db, WT and IGF-1 mice. The levels of blood glucose and weight in mice were also recorded. The changes in the mass of the trabecular bone in the fifth lumbar vertebra were documented by micro-computed tomography (micro-CT). Tunnel assays were used to detect cell apoptosis in each group.

Results

The weight of the mice were 27.68 ± 1.6 g in WT group, which was less than 57.56 ± 4.8 g in db/db group, and 52.17 ± 3.7 g in IGF-1 injected group (P < 0.05). The blood glucose levels were also significantly higher in the db/db mice group. T2DM caused by leptin receptor knockout showed an association with significantly decreased vertebral bone mass and increased IVDD when compared to WT mice. The db/db mice induced by leptin deletion showed a higher percentage of MMP3 expression as well as cell apoptosis in IVDD mice than WT mice (P < 0.05), while IGF-1 treatment reversed this situation (P < 0.05).

Conclusions

T2DM induced by leptin receptor knockout led to IVDD by increasing the levels of MMP3 and promoting cell apoptosis. IGF-1 treatment partially rescue the phenotype of IVDD induced by leptin receptor knockout.

Igfbp3 in grass carp (Ctenopharyngodon idellus): Molecular identification and mRNA expression under glucose, insulin and glucagon

IGFBPs play a pivotal role in regulating the physiological function of IGFs (insulin-like growth factors). As an important member of IGFBPs, IGFBP3 is involved in the regulation of physiological functions of IGFs. To investigate the functional role of Igfbp3 in a herbivorous fish species, grass carp igfbp3 (GenBank accession no. MN251843) was isolated from the liver by molecular cloning. The ORF of grass carp igfbp3 was 882 bp, which encoded 293 amino acids, and the first 22 amino acids comprised the signal peptide. The predicted molecular weight of grass carp Igfbp3 is 31.95 kDa, and the theoretical isoelectric point is 8.32. Grass carp Igfbp3 displayed a high identity with its counterparts of common carp and zebrafish. And phylogenetic tree analysis showed that the grass carp Igfbp3 was clustered into the Igfbp3 subgroups of common carp and zebrafish. Tissue distribution study showed that igfbp3 was ubiquitously expressed in all tissues examined in the present study. High expression level of igfbp3 was detected in the heart, brain and fat of grass carp. The OGTT demonstrated that igfbp3 mRNA expression was significantly elevated in the liver of grass carp in response to glucose treatment. In vitro study showed that insulin could markedly stimulated igfbp3 mRNA expression in primary grass carp hepatocytes. Moreover, igfbp3 mRNA levels were also regulated by glucagon in grass carp primary hepatocytes. These results may provide the theoretical foundation for investigating the role of Igfbp3 in fish metabolism.

The insulin like growth factor and binding protein family: Novel therapeutic targets in obesity & diabetes

Background

Recent changes in nutrition and lifestyle have provoked an unprecedented increase in the prevalence of obesity and metabolic disorders. Recognition of the adverse effects on health has prompted intense efforts to understand the molecular determinants of insulin sensitivity and dysglycemia. In many respects, actions of insulin-like growth factors (IGFs) mirror those of insulin in metabolic regulation. Unlike insulin, however, the bioactivity of IGFs is regulated by a family of seven high-affinity binding proteins (IGFBPs) which confer temporospatial modulation with implications for metabolic homeostasis. In addition, evidence is accumulating that IGF-independent actions of certain of the IGFBPs can directly modulate insulin sensitivity.

Scope of review

In this review, we discuss the experimental data indicating a critical role for IGF/IGFBP axis in metabolic regulation. We highlight key discoveries through which IGFBPs have emerged as biomarkers or putative therapeutic targets in obesity and diabetes.

Major conclusions

Growing evidence suggests that several components of the IGF-IGFBP system could be explored for therapeutic potential in metabolic disorders. Both IGFBP-1 and IGFBP-2 have been favorably linked with insulin sensitivity in humans and preclinical data implicate direct involvement in the molecular regulation of insulin signaling and adiposity respectively. Further studies are warranted to evaluate clinical translation of these findings.

Role of IGF-binding proteins in regulating IGF responses to changes in metabolism

The IGF-binding protein family contains six members that share significant structural homology. Their principal function is to regulate the actions of IGF1 and IGF2. These proteins are present in plasma and extracellular fluids and regulate access of both IGF1 and II to the type I IGF receptor. Additionally, they have functions that are independent of their ability to bind IGFs. Each protein is regulated independently of IGF1 and IGF2, and this provides an important mechanism by which other hormones and physiologic variables can regulate IGF actions indirectly. Several members of the family are sensitive to changes in intermediary metabolism. Specifically the presence of obesity/insulin resistance can significantly alter the expression of these proteins. Similarly changes in nutrition or catabolism can alter their synthesis and degradation. Multiple hormones such as glucocorticoids, androgens, estrogen and insulin regulate IGFBP synthesis and bioavailability. In addition to their ability to regulate IGF access to receptors these proteins can bind to distinct cell surface proteins or proteins in extracellular matrix and several cellular functions are influenced by these interactions. IGFBPs can be transported intracellularly and interact with nuclear proteins to alter cellular physiology. In pathophysiologic states, there is significant dysregulation between the changes in IGFBP synthesis and bioavailability and changes in IGF1 and IGF2. These discordant changes can lead to marked alterations in IGF action. Although binding protein physiology and pathophysiology are complex, experimental results have provided an important avenue for understanding how IGF actions are regulated in a variety of physiologic and pathophysiologic conditions.

Effect of insulin-like growth factor-I during the early postnatal period in intrauterine growth-restricted rats

BACKGROUND

Insulin-like growth factor-I (IGF-I) is essential for perinatal growth and development; low serum IGF-I has been observed during intrauterine growth restriction (IUGR). We investigated the effects of recombinant human (rh) IGF-I in IUGR rats during the early postnatal period.

METHODS

Intrauterine growth restriction was induced by bilateral uterine artery ligation in pregnant rats. IUGR pups were divided into two groups injected daily with rhIGF-I (2 mg/kg; IUGR/IGF-I, n = 16) or saline (IUGR/physiologic saline solution (PSS), n = 16) from postnatal day (PND) 7 to 13. Maternal sham-operated pups injected with saline were used as controls (control, n = 16). Serum IGF-I and IGF binding proteins (IGFBP) 3 and 5 were measured on PND25. The expression of Igf-i, IGF-I receptor (Igf-ir), Igfbp3, and 5 mRNA in the liver and brain was measured using real-time polymerase chain reaction on PND25. Immunohistochemical staining of the liver for IGF expression was performed.

RESULTS

Mean bodyweight on PND3 and PND25 in the IUGR pups (IUGR/IGF-I and IUGR/PSS) was significantly lower than that of the control pups. Serum IGF-I and hepatic Igf-ir mRNA in the IUGR pups were significantly lower than those in the control pups. In the IUGR/IGF-I group, hepatic Igfbp3 mRNA and liver immunohistochemical staining were increased. In the IUGR/PSS and control pups, there were no significant differences between these two groups in serum IGFBP3 and IGFBP5, hepatic Igf-i and Igfbp-5 mRNA, or brain Igf mRNA.

CONCLUSIONS

No benefits on body and brain weight gain but an effective increase in hepatic IGFBP-3 was observed after treatment with 2 mg/kg rhIGF-I during the early postnatal period.

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.

Altered liver expression of genes involved in lipid and glucose metabolism in mice with partial IGF-1 deficiency: an experimental approach to metabolic syndrome

Background

Insulin growth factor 1 (IGF-1) has multiple effects on metabolism. Much evidence suggests that the deficiency of this hormone increases insulin resistance, impairs lipid metabolism, augments oxidative damage and deregulates the neuro-hormonal axis. An inverse relationship between IGF-1 levels and the prevalence of Metabolic Syndrome (MetS) with its cardiovascular complications has been identified. However, the underlying mechanisms linking IGF-1 and MetS are still poorly understood. In order to elucidate such mechanisms, the aim of this work was to study, in mice with partial IGF-1 deficiency, liver expression of genes involved in glucose and lipid metabolism as well as serum levels of glucose, triglycerides and cholesterol, as well as liver malondialdehyde (MDA) levels, as a marker for oxidative damage.

Methods

Three experimental groups were studied in parallel: Controls (CO), wild type mice (igf-1^+/+); untreated heterozygous mice (Hz, igf-1^+/−) and Hz (igf-1^+/−) mice treated with low doses of IGF-1 for 10 days (Hz + IGF-1).

Results

A reduction of IGF-1 serum levels in the Hz group was found, which was normalized by IGF-1 therapy. Serum levels of glucose, triglycerides and cholesterol were significantly increased in the untreated Hz group as compared to both controls and Hz + IGF-1 groups. The expression of genes involved in gluconeogenesis, glycogenolysis, lipid synthesis and transport, and catabolism were altered in untreated Hz animals and the expression of most of them was normalized by IGF-1 therapy; MDA was also significantly increased in the Hz untreated group.

Conclusions

The mere partial IGF-1 deficiency is responsible for the reduction in the expression of genes involved in glucose and lipid metabolism, resulting in dyslipidemia and hyperglycemia. Such genetic alterations may seriously contribute to the establishment of MetS.

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

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

IGF-I increases markers of osteoblastic activity and reduces bone resorption via osteoprotegerin and RANK-ligand

Background

Bone is one of the major target tissues for Insulin-like Growth Factor I (IGF-I). Low doses of IGF-I were able to improve liver-associated osteopenia. In the present work, a model of partial IGF-I deficiency was used in order to provide insight into the mechanisms of the beneficial actions of IGF-I replacement therapy in bone.

Methods

Several proteins involved in osteoblastic/osteocyte and osteoclastic differentiation and activity were studied in the three experimental groups: control (CO) group (wild type mice, Igf^+/+, n = 10), heterozygous Igf^+/- group with partial IGF-I deficiency (Hz, n = 10), and heterozygous Igf^+/- mice treated with IGF-I for 10 days (Hz + IGF-I, n = 10).

Results

Data in this paper confirm that the simple partial IGF-I deficiency is responsible for osteopenia, determined by densitometry and histopathology. These findings are associated with a reduced gene expression of osteoprotegerin, sclerostin, calcitonin receptor (CTR), insulin-like growth factor binding protein 5 and RUNX2. IGF-I replacement therapy normalized CTR gene expression and reduced markers of osteoclastic activity.

Conclusions

Low doses of IGF-I constituted a real replacement therapy that normalized IGF-I serum levels improving the expression of most of these proteins closely involved in bone-forming, and reducing bone resorption by mechanisms related to osteoprotegerin, RANKL and PTH receptor.

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.

Metabolic actions of insulin-like growth factor-I in normal physiology and diabetes

Insulin-like growth factor-I (IGF-I) is closely related to insulin but has distinct metabolic actions. IGF-I is an important stimulant of protein synthesis in muscle, but it also stimulates free fatty acid use. The administration of IGF-I to patients with extreme insulin resistance results in improvement in glycemic control, and IGF-I is associated with lowering glucose and enhancing insulin sensitivity in Type 1 and Type 2 diabetes. However, patients with diabetes are also sensitive to stimulation of side effects in response to IGF-I. IGF-I coordinately links growth hormone and insulin actions and has direct effects on intermediary metabolism.

Neutrophil proteinase 3 induces diabetes in a mouse model of glucose tolerance

Type 1 diabetes is considered to be an autoimmune disease in which T cells attack pancreatic islet cells. Impaired glucose tolerance with type 2 diabetes has been classified as an obesity-associated metabolic syndrome. However, recent studies have revealed that type 2 diabetes is an autoinflammatory disease due to an imbalance of inflammatory cytokine production and related molecular components that cause inflammation. Insulin-like growth factor (IGF) and the insulin-like growth factor-binding protein-3 (IGFBP3) system are known to be involved in the development of experimental diabetic nephropathy, and urinary IGFBP3 protease activity has been observed in patients with type 2 diabetes. A serine protease was found to be responsible for the proteolytic activity in diabetic urine; however, the identity of the precise enzyme remains unknown. We investigated neutrophil proteinase 3 (PR3) to see whether it has specific enzymatic activity associated with insulin-like growth factor-1 and IGFBP3. In our study, both molecules were sufficiently degraded, which leads us to believe that PR3 may induce insulin resistance in the mouse model utilized. In addition, we found that PR3 in the urine of diabetic patients similarly affects insulin resistance. Moreover, PR3-immunized mice had an increase in glucose clearance due to inhibition of PR3 activity. As such, PR3 can be considered as an inflammatory enzyme directly linking inflammation to type 2 diabetes through downregulation of insulin-like growth factor-1/IGFBP3.

Insulin resistance in treated HIV infection

Insulin resistance (IR) was one of the first metabolic complications reported with highly active antiretroviral therapy for HIV infection. It continues to be of concern despite the introduction of newer antiretrovirals with safer metabolic profiles and is associated with inflammation and the development of diabetes mellitus. As the HIV-infected population ages, the prevalence of IR is likely to rise. Specific antiretrovirals can increase insulin resistance through two principal mechanisms, either directly by interfering with insulin signalling at the cellular level or indirectly as a consequence of defects in lipid metabolism (lipotoxocity) arising from antiretroviral toxicities such as the IR observed in those with HIV-associated lipodystrophy. There is considerable overlap between different antiretrovirals in their propensity to cause IR making it more difficult to attribute development of IR to a particular antiretroviral medication. In addition, in the setting of a generalised epidemic of obesity that exists in many populations worldwide, HIV-infected patients may be more prone to the consequences of antiretroviral-induced insulin resistance and diabetes mellitus. Optimal screening and treatment strategies for IR in treated HIV infection have not been established. In this article we review current opinion on insulin resistance in HIV and identify potential areas for future research.

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

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

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

The IGF system

The insulin-like growth factor (IGF) system plays essential role in the regulation of cell growth, proliferation and survival and affects nearly every organ system in the body. IGF-I, which has a high structural similarity to insulin, exerts growth-promoting effects, influences glucose metabolism and has neuroprotective and cardioprotective effects, partly because of its cell-proliferative and antiapoptotic properties. Aberrations in the IGF system may associate with various pathological conditions, including cancer. Insulin and its synthetic analogs are known to possess IGF-IR binding affinity, and concern has been raised about their mitogenic potential in humans. The present review summarizes the main aspects of the IGF system biology and the interactions among IGF-I, insulin, insulin analogs and their receptors.

Effects of insulin-like growth factor (IGF)-I/IGF-binding protein-3 treatment on glucose metabolism and fat distribution in human immunodeficiency virus-infected patients with abdominal obesity and insulin resistance

CONTEXT

HIV-infected patients on antiretroviral therapy are at increased risk for excess visceral adiposity and insulin resistance. Treatment with GH decreases visceral adiposity but worsens glucose metabolism. IGF-I, which mediates many of the effects of GH, improves insulin sensitivity in HIV-negative individuals.

OBJECTIVE

Our objective was to determine whether IGF-I, complexed to its major binding protein, IGF-binding protein-3 (IGFBP-3), improves glucose metabolism and alters body fat distribution in HIV-infected patients with abdominal obesity and insulin resistance.

METHODS

We conducted a pilot, open-label study in 13 HIV-infected men with excess abdominal adiposity and insulin resistance to assess the effect of 3 months of treatment with IGF-I/IGFBP-3 on glucose metabolism and fat distribution. Glucose metabolism was assessed by oral glucose tolerance test and hyperinsulinemic-euglycemic clamp. Endogenous glucose production (EGP), gluconeogenesis, whole-body lipolysis, and de novo lipogenesis (DNL) were measured with stable isotope infusions. Body composition was assessed by dual-energy x-ray absorptiometry and abdominal computed tomography scan.

RESULTS

Glucose tolerance improved and insulin-mediated glucose uptake increased significantly during treatment. EGP increased under fasting conditions, and suppression of EGP by insulin was blunted. Fasting triglycerides decreased significantly in association with a decrease in hepatic DNL. Lean body mass increased and total body fat decreased, whereas visceral adipose tissue did not change.

CONCLUSIONS

Treatment with IGF-I/IGFBP-3 improved whole-body glucose uptake and glucose tolerance, while increasing hepatic glucose production. Fasting triglycerides improved, reflecting decreased DNL, and visceral adiposity was unchanged.

IGF-I abuse in sport: current knowledge and future prospects for detection

As the tests for detecting growth hormone (GH) abuse develop further, it is likely that athletes will turn to doping with insulin-like growth factor-I (IGF-I). IGF-I mediates many of the anabolic actions of growth hormone. It stimulates muscle protein synthesis, promotes glycogen storage and enhances lipolysis, all of which make IGF-I attractive as a potential performance-enhancing agent. Pharmaceutical companies have developed commercial preparations of recombinant human IGF-I (rhIGF-I) for use in disorders of growth. The increased availability of rhIGF-I increases the opportunity for athletes to acquire supplies of the drug on the black market. The long-term effects of IGF-I administration are currently unknown but it is likely that these will be similar to the adverse effects of chronic GH abuse. The detection of IGF-I abuse is a challenge for anti-doping organisations. Research has commenced into the development of a test for IGF-I abuse based on the measurement of markers of GH action. Simultaneously, the effects of rhIGF-I on physical fitness, body composition and substrate utilisation in healthy volunteers are being investigated.

A pharmacokinetic and dosing study of intravenous insulin-like growth factor-I and IGF-binding protein-3 complex to preterm infants

In preterm infants, low levels of insulin like growth factor 1 (IGF-I) have been associated with impaired growth and retinopathy of prematurity. Our objective was to study safety and pharmacokinetics of i.v. administered rhIGF-I with its binding protein 3 (rhIGFBP-3) to preterm infants. At 3 d chronological age, an i.v. 3 h infusion of rhIGF-I/rhIGFBP-3 was administered followed by serial measurements of IGF-I and IGFBP-3. Infants were evaluated for physiologic safety measurements. The individual dose of rhIGF-I ranged from 1 to 12 microg/kg. The study was conducted at Queen Silvia Children's Hospital, Gothenburg, Sweden, between January and November 2007. Five patients (3 F) with mean (range) post menstrual age 27 wk (26-29) and birth weight 1022 g (810-1310) participated. IGF-I and IGFBP-3 levels before infusion were median (range) 18 (12-28) and 771 (651-1047) ng/mL, respectively. Immediately after study drug infusion, serum IGF-I and IGFBP-3 levels were 38 (25-59) and 838 (754-1182) ng/mL, respectively. Median (range) half-life for IGF-I and IGFBP-3 was 0.79 (0.59-1.42) and 0.87 (0.85-0.94) hours, respectively. Blood glucose, insulin, sodium, potassium, and physiologic safety measures were within normal ranges. The rhIGF-I/rhIGFBP-3 equimolar proportion was effective in increasing serum IGF-I levels and administration under these study conditions was safe and well tolerated.

A novel method incorporating gene ontology information for unsupervised clustering and feature selection

Background

Among the primary goals of microarray analysis is the identification of genes that could distinguish between different phenotypes (feature selection). Previous studies indicate that incorporating prior information of the genes' function could help identify physiologically relevant features. However, current methods that incorporate prior functional information do not provide a relative estimate of the effect of different genes on the biological processes of interest.

Results

Here, we present a method that integrates gene ontology (GO) information and expression data using Bayesian regression mixture models to perform unsupervised clustering of the samples and identify physiologically relevant discriminating features. As a model application, the method was applied to identify the genes that play a role in the cytotoxic responses of human hepatoblastoma cell line (HepG2) to saturated fatty acid (SFA) and tumor necrosis factor (TNF)-α, as compared to the non-toxic response to the unsaturated FFAs (UFA) and TNF-α. Incorporation of prior knowledge led to a better discrimination of the toxic phenotypes from the others. The model identified roles of lysosomal ATPases and adenylate cyclase (AC9) in the toxicity of palmitate. To validate the role of AC in palmitate-treated cells, we measured the intracellular levels of cyclic AMP (cAMP). The cAMP levels were found to be significantly reduced by palmitate treatment and not by the other FFAs, in accordance with the model selection of AC9.

Conclusions

A framework is presented that incorporates prior ontology information, which helped to (a) perform unsupervised clustering of the phenotypes, and (b) identify the genes relevant to each cluster of phenotypes. We demonstrate the proposed framework by applying it to identify physiologically-relevant feature genes that conferred differential toxicity to saturated vs. unsaturated FFAs. The framework can be applied to other problems to efficiently integrate ontology information and expression data in order to identify feature genes.

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A general and islet cell-enriched overexpression of IGF-I results in normal islet cell growth, hypoglycemia, and significant resistance to experimental diabetes

Insulin-like growth factor I (IGF-I) is normally produced from hepatocytes and various other cells and tissues, including the pancreas, and is known to stimulate islet cell replication in vitro, prevent Fas-mediated beta-cell destruction and delay the onset of diabetes in nonobese diabetic mice. Recently, however, the notion that IGF-I stimulates islet cell growth has been challenged by the results of IGF-I and receptor gene targeting. To test the effects of a general, more profound increase in circulating IGF-I on islet cell growth and glucose homeostasis, we have characterized MT-IGF mice, which overexpress the IGF-I gene under the metallothionein I promoter. In early reports, a 1.5-fold-elevated serum IGF-I level caused accelerated somatic growth and pancreatic enlargement. We demonstrated that the transgene expression, although widespread, was highly concentrated in the beta-cells of the pancreatic islets. Yet, islet cell percent and pancreatic morphology were unaffected. IGF-I overexpression resulted in significant hypoglycemia, hypoinsulinemia, and improved glucose tolerance but normal insulin secretion and sensitivity. Pyruvate tolerance test indicated significantly suppressed hepatic gluconeogenesis, which might explain the severe hypoglycemia after fasting. Finally, due to a partial prevention of beta-cell death against onset of diabetes and/or the insulin-like effects of IGF-I overexpression, MT-IGF mice (which overexpress the IGF-I gene under the metallothionein I promoter) were significantly resistant to streptozotocin-induced diabetes, with diminished hyperglycemia and prevention of weight loss and death. Although IGF-I might not promote islet cell growth, its overexpression is clearly antidiabetic by improving islet cell survival and/or providing insulin-like effects.

The role of IGF-I and its binding proteins in the development of type 2 diabetes and cardiovascular disease

Patients with insulin resistance and type 2 diabetes have an excessive risk of cardiovascular disease (CVD); this increased risk is not fully explained by traditional risk factors such as hypertension and dyslipidaemias. There is now compelling evidence to suggest that abnormalities of insulin-like growth factor-I (IGF-I) and one of its binding proteins, insulin-like growth factor-binding protein-1 (IGFBP-1), occur in insulin-resistant states and may be significant factors in the pathophysiology of CVD. We reviewed articles and relevant bibliographies following a systematic search of MEDLINE for English language articles between 1966 and the present, using an initial search strategy combining the MeSH terms: IGF, diabetes and CVD. Our aim was first to review the role of IGF-I in vascular homeostasis and to explore the mechanisms by which it may exert its effects. We also present an overview of the physiology of the IGF-binding proteins, and finally, we sought to summarize the evidence to date describing the changes in the insulin/IGF-I/IGFBP-1 axis that occur in type 2 diabetes and CVD; in particular, we have focused on the potential vasculoprotective effects of both IGF-I and IGFBP-1. We conclude that this system represents an interesting and novel therapeutic target in the prevention of CVD in type 2 diabetes.

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

OBJECTIVE

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

RESEARCH DESIGN AND METHODS

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

RESULTS

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

CONCLUSIONS

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