Insulin-like growth factor I stimulates lipid oxidation, reduces protein oxidation, and enhances insulin sensitivity in humans

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.

The Association Between Preoperative Insulin-Like Growth Factor 1 Levels and the Total Body Weight Loss in Women Post Laparoscopic Sleeve Gastrectomy

BACKGROUND

Despite the well-described optimal initial clinical response of sleeve gastrectomy (SG) in the treatment of obesity, some patients do not achieve optimal initial clinical response. Insulin-like growth factor-1 (IGF-1) has currently shown an association with post-bariatric surgery weight loss. This study aimed to assess the IGF-1 levels in female patients with obesity, the change after surgery, and their association with the metabolic profile and weight loss after surgery.

PATIENTS AND METHODS

This was a prospective study that was conducted on adult female patients who were recruited for SG. The patients underwent clinical and laboratory investigations that included the IGF-1 measurement. At the 1-year follow-up, the same clinical and laboratory measures were repeated.

RESULTS

This study included 100 female patients. At the 1-year follow-up, there was a statistically significant reduction in body mass index (BMI) (p < 0.001), fasting HbA1C levels (p < 0.001), and triglycerides (p < 0.001), as well as a statistically significant increase in HDL (p < 0.001) and IGF-1 (p < 0.001). Multiple regression analysis revealed that, among the patients baseline characteristics, the significant predictors for the percentage of total weight loss (%TWL) were the patients' BMI (p < 0.001) and IGF-1 levels (p < 0.001). The ROC curve showed that an IGF1 cutoff value of ≤ 23 ng/ml detected suboptimal initial clinical response, with a sensitivity of 95.35% and a specificity of 100%.

CONCLUSION

This study underscores the significant impact of SG on weight loss and metabolic improvements in female patients. Baseline IGF-1 levels emerged as a crucial predictor of optimal initial clinical response.

Detection rate of IGF-1 variants and their implication to protein binding: study of over 240,000 patients

OBJECTIVES

To determine the detection rate of IGF-1 variants in a clinical population and assess their implications.

METHODS

IGF-1 variants were detected based on their predicted mass-to-charge ratios. Most variants were distinguished by their isotopic distribution and relative retention times. A67T and A70T were distinguished with MS/MS. Patient specimens with a detected variant were de-identified for DNA sequencing to confirm the polymorphism.

RESULTS

Of the 243,808 patients screened, 1,099 patients containing IGF-1 variants were identified (0.45 %, or 4,508 occurrences per million). Seven patients were identified as homozygous or double heterozygous. Majority of variants (98 %) had amino acid substitutions located at the C-terminus (A62T, P66A, A67S, A67V, A67T, A70T). Isobaric variants A38V and A67V were detected more frequently in children than in adults. Six previously unreported variants were identified: Y31H, S33P, T41I, R50Q, R56K, and A62T. Compared with the overall population, z-score distribution of patients with IGF-1 variants was shifted toward negative levels (median z-score -1.4); however, it resembled the overall population when corrected for heterozygosity. Chromatographic peak area of some variants differed from that of the WT IGF-1 present in the same patient.

CONCLUSIONS

In the IGF-1 test reports by LC-MS, the concentrations only account for half the total IGF-1 for patients with heterozygous IGF-1 variants. An IGF-1 variant may change the binding to its receptor and/or its binding proteins, affecting its activity and half-life in circulation. Variants located in or close to the C-domain may be pathogenic. Cross-species sequence comparison indicates that A38V and A70T may have some degree of pathogenicity.

Muscular Echo-Intensity of the Quadriceps by Ultrasound Is More Related to Improvement of Gait Independence than Muscle Thickness in Older Inpatients

OBJECTIVES

This study aimed to examine whether the decrease in muscular echo-intensity of the quadriceps by ultrasound in older inpatients is related to the improvement of gait independence than the increase of muscle thickness.

DESIGN

Longitudinal study.

SETTING

Hospital-based study.

PARTICIPANTS

This study included 171 inpatients aged ≥ 65 years (median age: 84.0 [77.0-88.0], 56.1% female). Patients who were able to walk independently at hospital admission were excluded from the study.

MEASUREMENTS

Improvement of gait independence during hospital stay was assessed using the change in Functional Independence Measure (FIM) gait score (i.e., FIM gait score at hospital discharge minus FIM gait score at hospital admission) and FIM gait score at hospital discharge. Muscular echo-intensity and muscle thickness of the quadriceps were assessed at hospital admission and discharge using ultrasound images, respectively. Muscular echo-intensity has been shown to be mainly related to intramuscular adipose tissue. Multiple linear regression analysis was performed to identify the factors independently associated with the change in FIM gait score and FIM gait score at discharge.

RESULTS

Change in quadriceps echo-intensity was independently and significantly associated with the change in FIM gait score (β = -0.22, p = 0.017) and FIM gait score at hospital discharge (β = -0.21, p = 0.017). In contrast, change in quadriceps thickness was not independently and significantly associated with the change in FIM gait score (β = 0.16, p = 0.050) and FIM gait score at hospital discharge (β = 0.15, p = 0.050).

CONCLUSIONS

Our study indicates that a decrease in muscular echo-intensity of the quadriceps by ultrasound is more related to the improvement of gait independence than an increase of muscle thickness in older inpatients. Intervention for intramuscular adipose tissue of the quadriceps may be important for improving gait independence in older inpatients.

Growth Hormone and Insulin-Like Growth Factor 1 Regulation of Nonalcoholic Fatty Liver Disease

Patients with obesity have a high prevalence of nonalcoholic fatty liver disease (NAFLD), representing a spectrum of simple steatosis to nonalcoholic steatohepatitis (NASH), without and with fibrosis. Understanding the etiology of NAFLD is clinically relevant since NAFLD is an independent risk factor for diabetes and cardiovascular disease. In addition, NASH predisposes patients to the development of cirrhosis and hepatocellular carcinoma, and NASH cirrhosis represents the fastest growing indication for liver transplantation in the United States. It is appreciated that multiple factors are involved in the development and progression of NAFLD. Growth hormone (GH) and insulin-like growth factor 1 (IGF1) regulate metabolic, immune, and hepatic stellate cell function, and alterations in the production and function of GH is associated with obesity and NAFLD/NASH. Therefore, this review will focus on the potential role of GH and IGF1 in the regulation of hepatic steatosis, inflammation, and fibrosis.

Trends in insulin-like growth factor-1 levels after bariatric surgery: a systematic review and meta-analysis

According to studies, there are many inconsistencies in how IGF-1 levels change after bariatric surgery compared to before surgery, as well as its effects. These discrepancies can be attributed to various factors such as age, body mass index (BMI), and duration of intervention. Therefore, the aim of this study was to evaluate the level of insulin-like growth factor-1 (IGF-1) after bariatric surgery. A systematic review and meta-analysis based on the PRISMA guidelines was conducted from inception until 2021. From 1871 articles initially selected, 24 studies with 28 treatment arms met the eligible criteria and were included. Pooled findings from the random-effects model indicated that IGF-1 levels increased significantly [weighted mean difference (WMD) = 8.84 ng/ml; 95% confidence interval (CI) 0.30-17.39; p = 0.043] after bariatric surgery compared to before surgery. No significant heterogeneity was noted among the studies (Cochran Q test, p = 0.90, I² = 0.0%). In subgroup analysis, bariatric surgery significantly increased IGF-1 levels at age <40 years but not at age ≤40 years. Bariatric surgery is capable of increasing the IGF-1 levels compared to the period prior to surgery but with a modest clinical magnitude.

The effects of recombinant human insulin-like growth factor-1/insulin-like growth factor binding protein-3 administration on lipid and carbohydrate metabolism in recreational athletes

OBJECTIVE

Previous studies suggested that recombinant human IGF-1 (rhIGF-1) administration affects carbohydrate and lipid metabolism in healthy people and in people with diabetes. This study aimed to determine the effects of rhIGF-1/rhIGF binding protein-3 (rhIGFBP-3) administration on glucose homeostasis and lipid metabolism in healthy recreational athletes.

DESIGN AND SETTING

Randomized, double-blind, placebo-controlled rhIGF-1/rhIGFBP-3 administration study at Southampton General Hospital, UK.

PARTICIPANTS

56 recreational athletes (30 men, 26 women).

METHODS

Participants were randomly assigned to receive placebo, low-dose rhIGF-1/rhIGFBP-3 (30 mg/day) or high-dose rhIGF-1/rhIGFBP-3 (60 mg/day) for 28 days. The following variables were measured before and immediately after the treatment period: fasting lipids, glucose, insulin, C-peptide and glycated haemoglobin. The homeostatic model assessment (HOMA-IR) was used to estimate insulin sensitivity and indirect calorimetry to assess substrate oxidation rates. The general linear model approach was used to compare treatment group changes with the placebo group.

RESULTS

Compared with the placebo group, there was a significant reduction in fasting triglycerides in participants treated with high-dose rhIGF-1/rhIGFBP-3 (p = .030), but not in the low-dose group (p = .390). In women, but not in men, there were significant increases in total cholesterol (p = .003), HDL cholesterol (p = .001) and LDL cholesterol (p = .008). These lipid changes were associated with reduced fasting insulin (p = .010), C-peptide (p = .001) and HOMA-IR (p = .018) in women and reduced C-peptide (p = .046) in men.

CONCLUSIONS

rhIGF-1/rhIGFBP-3 administration for 28 days reduced insulin concentration, improved insulin sensitivity and had significant effects on lipid profile including decreased fasting triglycerides.

The Relationship between Serum Insulin-Like Growth Factor-1 Levels and Body Composition Changes after Sleeve Gastrectomy

INTRODUCTION

We previously reported that preoperative serum insulin-like growth factor-1 (IGF-1) is a predictor of total weight loss percentage (%TWL) after laparoscopic sleeve gastrectomy (LSG). IGF-1 may suppress muscle loss after surgery. IGF-1 almost accurately reflects the growth hormone (GH) secretion status, and GH has lipolytic effects. Therefore, IGF-1 may influence both the maintenance of skeletal muscle and the reduction of adipose tissue after LSG. The identification of the relationship between preoperative serum IGF-1 and body composition changes after LSG can help in understanding the pathophysiology of obesity.

METHODS

We retrospectively reviewed 72 patients with obesity who underwent LSG and were followed up for 12 months. We analyzed the relationship between preoperative serum IGF-1 levels and body composition changes after LSG. A multiple regression model was used.

RESULTS

LSG led to a significant reduction in body weight. Both body fat mass and skeletal muscle mass decreased after LSG. Preoperative serum IGF-1 levels significantly correlated with %TWL, changes in skeletal muscle mass, and body fat mass after LSG. The multiple regression model showed that preoperative serum IGF-1 levels were related to decreased body fat mass and maintaining skeletal muscle mass after LSG.

DISCUSSION/CONCLUSION

Preoperative IGF-1 measurement helps predict not only successful weight loss but also decreases body fat mass and maintains skeletal muscle mass after LSG.

Low serum insulin-like growth factor-1 level is a predictor of low total weight loss percentage after sleeve gastrectomy

BACKGROUND

Obesity is a leading cause of metabolic disorders and mortality. Laparoscopic sleeve gastrectomy (LSG) confers beneficial effects not only on weight but also on metabolic disorder development. However, some patients show insufficient weight loss after LSG. A total weight loss percentage (%TWL) <20% after LSG is defined as insufficient. The prediction of patients with insufficient weight loss after LSG before the procedure is performed may prove helpful.

OBJECTIVES

To determine predictors of %TWL after LSG.

SETTING

Longitudinal study in a university hospital.

METHODS

We retrospectively reviewed 90 obese patients who underwent LSG and were followed up for 12 months thereafter. We analyzed the relationship between %TWL and preoperative clinical parameters, such as age, sex, body mass index, lipid and glucose metabolism, and some hormones. Patients were divided into 2 groups, %TWL <20% and 20% ≤ %TWL. Multiple regression model and logistic regression models were performed.

RESULTS

LSG led to significant improvements in weight, liver, and kidney function, and lipid and glucose metabolism. The serum insulin-like growth factor-1 (IGF-1) level was significantly lower in patients with %TWL <20%. Sex, diabetes presence, body mass index, and IGF-1 were independent predictors of %TWL. Receiver operating characteristic curve analysis showed that the cutoff value of IGF-1 for %TWL <20% was 100.0ng/mL. Male sex, diabetes presence, lower preoperative BMI, and IGF-1 values were independently associated with lower %TWL (%TWL <20%).

CONCLUSIONS

Serum IGF-1 can be used to screen for patients at risk of low %TWL after LSG.

Microsatellite and Single Nucleotide Polymorphisms in the Insulin-Like Growth Factor 1 Promoter with Insulin Sensitivity and Insulin Secretion

Background

To investigate associations of the CA microsatellite and rs35767, rs5742612, and rs2288377 polymorphisms and the single nucleotide polymorphism (SNP) haplotypes with and without the CA microsatellite in the IGF1 promoter with insulin sensitivity and secretion.

Material/Methods

The CA microsatellite and SNPs were genotyped in 389 type 2 diabetes mellitus (T2DM) patients. A 75 g oral glucose tolerance test (OGTT) was given to all the participants. Associations of the genotypes and haplotypes with insulin sensitivity, insulin secretion, glucose tolerance, and insulin-like growth factor 1 (IGF1) were analyzed by ANCOVA (general linear model) and multiple linear regression, after controlling for gender, age, and BMI.

Results

The CA microsatellite, rs35767 polymorphisms, and SNP haplotypes with or without CA showed no significant association with metabolic parameters. The C allele of rs5742612 was found to be associated with decreased insulin sensitivity (HOMA-S index, β=−0.131, P=0.008; fasting insulin level, β=0.022, P=0.006) and increased insulin secretion (HOMA-B index, β=0.099, P=0.008; insulin AUC, β=0.112, P=0.012). The linear regression model also indicated that the A allele of rs2288377 was associated with decreased insulin sensitivity (HOMA-S index, β=−0.159, P=0.001; fasting insulin, β=0.143, P=0.001) and increased insulin secretion (HOMA-B index, β=0.114, P=0.017; insulin AUC, β=0.042, P=0.002).

Conclusions

The CA microsatellite and rs35767 have no genotype-related difference in insulin sensitivity or secretion. The rs5742612 and rs2288377 polymorphisms are significantly associated with insulin biology, with the TT genotype exhibiting higher insulin sensitivity and lower insulin secretion compared with carriers of the C allele and A allele, respectively, mostly attributed to the direct functional roles of the two loci.

Insulin-like growth factor-1 is a negative modulator of glucagon secretion

Glucagon secretion involves a combination of paracrine, autocrine, hormonal, and autonomic neural mechanisms. Type 2 diabetes often presents impaired glucagon suppression by insulin and glucose. Insulin-like growth factor-I (IGF-1) has elevated homology with insulin, and regulates pancreatic β-cells insulin secretion. Insulin and IGF-1 receptors share considerable structure homology and function. We hypothesized the existence of a mechanism linking the inhibition of α-cells glucagon secretion to IGF-1. Herein, we evaluated the association between plasma IGF-1 and glucagon levels in 116 nondiabetic adults. After adjusting for age gender and BMI, fasting glucagon levels were positively correlated with 2-h post-load glycaemia, HOMA index and fasting insulin, and were negatively correlated with IGF-1 levels. In a multivariable regression, the variables independently associated to fasting glucagon were circulating IGF-1 levels, HOMA index and BMI, explaining 20.7% variation. To unravel the molecular mechanisms beneath IGF-1 and glucagon association, we investigated whether IGF-1 directly modulates glucagon expression and secretion in an in vitro model of α-cells. Our data showed that IGF-1 inhibits the ability of low glucose concentration to stimulate glucagon expression and secretion via activation of the phosphatidylinositol-3-kinase/Akt/FoxO1 pathway.

Collectively, our results suggest a new regulatory role of IGF-1 on α-cells biological function.

The New Biology and Pharmacology of Glucagon

In the last two decades we have witnessed sizable progress in defining the role of gastrointestinal signals in the control of glucose and energy homeostasis. Specifically, the molecular basis of the huge metabolic benefits in bariatric surgery is emerging while novel incretin-based medicines based on endogenous hormones such as glucagon-like peptide 1 and pancreas-derived amylin are improving diabetes management. These and related developments have fostered the discovery of novel insights into endocrine control of systemic metabolism, and in particular a deeper understanding of the importance of communication across vital organs, and specifically the gut-brain-pancreas-liver network. Paradoxically, the pancreatic peptide glucagon has reemerged in this period among a plethora of newly identified metabolic macromolecules, and new data complement and challenge its historical position as a gut hormone involved in metabolic control. The synthesis of glucagon analogs that are biophysically stable and soluble in aqueous solutions has promoted biological study that has enriched our understanding of glucagon biology and ironically recruited glucagon agonism as a central element to lower body weight in the treatment of metabolic disease. This review summarizes the extensive historical record and the more recent provocative direction that integrates the prominent role of glucagon in glucose elevation with its under-acknowledged effects on lipids, body weight, and vascular health that have implications for the pathophysiology of metabolic diseases, and the emergence of precision medicines to treat metabolic diseases.

Whole-Body Protein Metabolism in Chronic Heart Failure: Relationship to Anabolic and Catabolic Hormones

BACKGROUND

Patients with chronic heart failure frequently experience profound wasting during the course of the disease, a condition termed cardiac cachexia. Although protein is the primary structural and functional component of most tissues, few studies have examined the effect of heart failure on protein metabolism. Moreover, no study has assessed the relationship of protein turnover to hormonal alterations thought to promote cachexia. Thus, our goal was to determine if whole-body protein metabolism is altered in heart failure patients and to assess the relationship of protein kinetics to circulating levels of anabolic and catabolic hormones.

METHODS

We measured whole-body protein metabolism using 13C-leucine, body composition, and circulating anabolic and catabolic hormone levels in 10 patients with chronic heart failure and 11 elderly controls.

RESULTS

No differences in leucine rate of appearance, oxidation, or nonoxidative disposal were noted between heart failure patients and controls. However, in a subgroup of patients characterized by increased resting energy expenditure for their metabolic body size (n = 4; > or = 20% above that predicted from fat-free mass), leucine rate of appearance (mean +/- SE; 146 +/- 6 micromol/min), an index of protein breakdown, tended to be higher compared with patients with normal resting energy expenditure (n = 5; 120 +/- 8 micromol/min) and controls (127 +/- 4 micromol/min; p = .06). Alterations in anabolic/catabolic hormone balance did not explain increased protein breakdown in this subgroup, and no correlations were found between hormone levels and protein breakdown in the heart failure group as a whole. In contrast, increased circulating interleukin-6 soluble receptor (r = 0.829; p < .01) and reduced insulin-like growth factor-I (r =-.751; p < .05) levels were related to greater rates of leucine oxidation in heart failure patients.

CONCLUSION

Our results demonstrate that, although increased protein turnover is not a generalized feature of heart failure, there is a subgroup of patients characterized by resting hypermetabolism and increased protein breakdown. Moreover, hormonal alterations related to the heart failure syndrome were related to increased protein oxidation.

Diagnosis, treatment and clinical perspectives of acromegaly

Acromegaly is an insidious disease of the pituitary caused by a growth hormone-secreting adenoma. Generally, the diagnosis is made rather late in the course of the disease. Currently, acromegaly can be cured in about half of the patients with the disease by expert surgery. The remainder of non-surgically cured patients often can be effectively treated with somatostatin analogs; either with the new generation of dopaminergic drugs or with Pegvisomant, a GH-receptor blocking agent. However, at the time of diagnosis many patients suffer from serious comorbidities, including hypertension, heart disease, arthrosis, sleep apnea and diabetes mellitus. Recent reports have shown that mortality risk can be normalized. Nevertheless, all efforts should be undertaken to treat comorbidities. New strategies for surgery and medical treatment are discussed.

Increased insulin-like growth factor-1 in relation to cardiovascular function in polycystic ovary syndrome: friend or foe?

The incidence of cardiovascular disease (CVD) in patients with polycystic ovary syndrome (PCOS) is very high and conventional risk factors only partially explain excessive risk of developing CVD in patients of PCOS. The pathophysiology of PCOS is very unique, and several hormonal and metabolic changes occur. Several observations suggest that serum IGF-1 levels decrease in insulin resistance, which results in IGF-1 deficiency. In patient of PCOS, close relationships have been demonstrated between insulin resistance and serum IGF-1 levels. Hyperinsulinemic insulin resistance results in a general augmentation of steroidogenesis and LH release in PCOS. The action of IGF-1 varies in different tissues possibly via autocrine or paracrine mechanisms. The increase or decrease in IGF-1 in different tissues results in differential outcomes. Several studies suggest that lowered circulating IGF-1 levels play important role in the initiation of the cardiac hypertrophic response which results in the risk of cardiovascular disease. While recent results suggests that individual with elevated IGF-1 is protected against cardiovascular disease. Thus IGF-1 shows versatile pleiotropic actions. This review provides a current perspective on increased level of IGF-1 in PCOS and also adds to the current controversy regarding the roles of IGF-1 in cardiovascular disease.

Insulin growth factor binding proteins as therapeutic targets in type 2 diabetes

INTRODUCTION

The signaling pathways of the insulin-like growth factors (IGFs) have been implicated in the aetiology of type 2 diabetes (T2D) and a number of therapeutic modalities aiming at the IGF-axis have been considered. Administration of IGF-I has been reported to improve insulin sensitivity in healthy subjects and patients with T2D. In recent years, the IGF binding proteins (IGFBPs) have also been associated with metabolic disorders, prompting the idea that IGFBPs play important roles in the pathogenesis of T2D. Thus, by virtue of their role in the regulation of IGF effects, the IGFBPs have emerged as potential biomarkers and therapeutic targets in metabolic syndromes and T2D.

AREAS COVERED

The article provides an overview on recent findings in clinical and experimental IGFBP-research and addresses the studies that have investigated the potentials of the IGFBPs as therapeutic targets in T2D.

EXPERT OPINION

There is plenty of therapeutic promise within the IGF system, but further understanding of the IGFs in T2D is necessary to avoid off-target effects. Strong evidence supports the use of IGFBPs as therapeutic targets in the treatment of T2D, and it is not difficult to foresee the use of IGFBPs as part of a combination therapy alongside other anti-diabetic drugs.

Increased Plin2 expression in human skeletal muscle is associated with sarcopenia and muscle weakness

Human aging is associated with a progressive loss of muscle mass and strength and a concomitant fat accumulation in form of inter-muscular adipose tissue, causing skeletal muscle function decline and immobilization. Fat accumulation can also occur as intra-muscular triglycerides (IMTG) deposition in lipid droplets, which are associated with perilipin proteins, such as Perilipin2 (Plin2). It is not known whether Plin2 expression changes with age and if this has consequences on muscle mass and strength. We studied the expression of Plin2 in the vastus lateralis (VL) muscle of both healthy subjects and patients affected by lower limb mobility limitation of different age. We found that Plin2 expression increases with age, this phenomenon being particularly evident in patients. Moreover, Plin2 expression is inversely correlated with quadriceps strength and VL thickness. To investigate the molecular mechanisms underpinning this phenomenon, we focused on IGF-1/p53 network/signalling pathway, involved in muscle physiology. We found that Plin2 expression strongly correlates with increased p53 activation and reduced IGF-1 expression. To confirm these observations made on humans, we studied mice overexpressing muscle-specific IGF-1, which are protected from sarcopenia. These mice resulted almost negative for the expression of Plin2 and p53 at two years of age. We conclude that fat deposition within skeletal muscle in form of Plin2-coated lipid droplets increases with age and is associated with decreased muscle strength and thickness, likely through an IGF-1- and p53-dependent mechanism. The data also suggest that excessive intramuscular fat accumulation could be the initial trigger for p53 activation and consequent loss of muscle mass and strength.

Molecular targets of omega 3 and conjugated linoleic Fatty acids - "micromanaging" cellular response

Essential fatty acids cannot be synthesized de novo by mammals and need to be ingested either with the diet or through the use of supplements/functional foods to ameliorate cardiovascular prognosis. This review focus on the molecular targets of omega 3 fatty acids and conjugated linoleic acid, as paradigmatic molecules that can be exploited both as nutrients and as pharmacological agents, especially as related to cardioprotection. In addition, we indicate novel molecular targets, namely microRNAs that might contribute to the observed biological activities of such essential fatty acids.

Redox-regulating role of insulin: the essence of insulin effect

It is well-known that insulin acts as an important hormone, controlling energy metabolism, cellular proliferation and biosynthesis of functional molecules to maintain a biological homeostasis. Over the past few years, intensive insulin therapy has been believed to be benefit for the outcome of diabetic patients, in which the suppression of oxidative stress plays a role. Moreover, insulin is accepted as a key component of glucose-insulin-potassium, a treatment which has been believed to exert significant cardiovascular protective effect via the reduction of oxidative stress. Furthermore, accumulating evidence has suggested that insulin exerts important redox-regulating actions in various insulin-sensitive target organs, implying the systematic antioxidative role of insulin as a hormone. It is time for us to revisit insulin effects, through summarizing and evaluating the novel functions of insulin and their mechanisms. This review focuses on the antioxidative effect of insulin and highlights insulin-induced regulation of various antioxidant enzymes via insulin signaling pathways and the cross talk between key transcription factors, including nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor κB (NF-κB) which are responsible for the transcription of antioxidant enzymes, leading to reduced generation of reactive oxygen species (ROS) and the enhancement of the elimination of ROS.

Normalisation of insulin-like growth factor-I does not improve insulin action in cirrhosis

BACKGROUND & AIMS

Cirrhosis of the liver is characterised by insulin resistance and low levels of insulin-like growth factor I (IGF-I). Lack of IGF-I may contribute to this insulin resistance, as IGF-I increases insulin sensitivity. This study aimed to determine the effects of normalisation of IGF-I on insulin action in cirrhosis.

METHODS

This article is a randomised sequence-crossover placebo controlled study. Eight patients with cirrhosis and eight controls were studied following treatment with IGF-I (50 μg/kg twice daily) or saline. Insulin action, glucose utilisation and endogenous glucose production were measured during the euglycaemic hyperinsulinaemic clamp.

RESULTS

The patients with cirrhosis had normal fasting glucose level, but increased levels of insulin (P < 0.05) and C-peptide (P < 0.05). Insulin resistance resulted from a defect in glycogen synthesis, whereas insulin-mediated suppression of glucose production was unaltered. In cirrhosis, IGF-I treatment normalised free (from 0.07 ± 0.01 to 0.26 ± 0.05 μg/L) and total IGF-I (from 73 ± 6 to 250 ± 39 μg/L), whereas in controls, the IGF-I level increased into the upper physiological range (free IGF-I from 0.23 ± 0.02 to 0.61 ± 0.06 μg/L; total IGF-I from 200 ± 19 to 500 ± 50 μg/L) (all P-values < 0.05). In cirrhosis, IGF-I treatment did not change fasting glucose, insulin or C-peptide levels (P > 0.05). In the controls, insulin and C-peptide levels decreased (P < 0.05). IGF-I treatment did not improve insulin sensitivity in cirrhosis.

CONCLUSIONS

Because normalisation of IGF-I levels did not affect insulin sensitivity lack of IGF-I is unlikely to result in insulin resistance in cirrhosis. IGF-I supplementation is therefore unlikely to improve insulin action in patients with cirrhosis.

Activation of proteasome by insulin-like growth factor-I may enhance clearance of oxidized proteins in the brain

The insulin-like growth factor type 1 (IGF-I) plays an important role in neuronal physiology. Reduced IGF-I levels are observed during aging and this decrease may be important to age-related changes in the brain. We studied the effects of IGF-I on total protein oxidation in brain tissues and in cell cultures. Our results indicate that in frontal cortex the level of oxidized proteins is significantly reduced in transgenic mice designed to overproduce IGF-I compared with wild-type animals. The frontal cortex of IGF-I-overproducing mice exhibited high chymotrypsin-like activity of the 20S and 26S proteasomes. The proteasome can also be activated in response to IGF-I in cell cultures. Kinetic studies revealed peak activation of the proteasome within 15 min following IGF-I stimulation. The effects of IGF-I on proteasome were not observed in R(-) cells lacking the IGF-I receptor. Experiments using specific kinase inhibitors suggested that activation of proteasome by IGF-I involves phosphatidyl inositol 3-kinase and mammalian target of rapamycin signaling. IGF-I also attenuated the increase in protein carbonyl content induced by proteasome inhibition. Thus, appropriate levels of IGF-I may be important for the elimination of oxidized proteins in the brain in a process mediated by activation of the proteasome.

Insulin-like growth factor-I in growth and metabolism

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

Isomer-specific effects of CLA on gene expression in human adipose tissue depending on PPARgamma2 P12A polymorphism: a double blind, randomized, controlled cross-over study

BACKGROUND

Peroxisome proliferator-activated receptor (PPAR)gamma is a key regulator in adipose tissue. The rare variant Pro12Ala of PPARgamma2 is associated with a decreased risk of insulin resistance. Being dietary PPARgamma ligands, conjugated linoleic acids (CLAs) received considerable attention because of their effects on body composition, cancer, atherosclerosis, diabetes, obesity and inflammation, although some effects were only demonstrated in animal trials and the results in human studies were not always consistent. In the present study effects of CLA supplementation on genome wide gene expression in adipose tissue biopsies from 11 Ala12Ala and 23 Pro12Pro men were investigated. Subjects underwent four intervention periods (4 wk) in a randomized double blind cross-over design receiving 4.25 g/d of either cis-9, trans-11 CLA, trans-10,cis-12 CLA, 1:1 mixture of both isomers or a reference linoleic acid oil preparation. After each intervention biopsies were taken, whole genome expression microarrays were applied, and genes of interest were verified by realtime PCR.

RESULTS

The following genes of lipid metabolism were regulated by CLA: LDLR, FASN, SCD, FADS1 and UCP2 were induced, while ABCA1, CD36 and CA3 were repressed. Transcription factors PPARgamma, NFAT5, CREB5 and EBF1, the adipokine NAMPT, members of the insulin signaling cascade SORBS1 and IGF1 and IL6ST were repressed, while the adipokine THBS1 and GLUT4 involved in insulin signaling were induced. Compared to trans-10,cis-12 CLA and the CLA mixture the cis-9, trans-11 CLA isomer exerted weaker effects. Only CD36 (-1.2 fold) and THBS1 (1.5 fold) were regulated. The CLA effect on expression of PPARgamma and leptin genes depends on the PPARgamma2 genotype.

CONCLUSION

The data suggest that the isomer specific influence of CLA on glucose and lipid metabolism is genotype dependent and at least in part mediated by PPARgamma.

TRIAL REGISTRATION

http://www.controlled-trials.com: ISRCTN91188075.

The insulin-like growth factor family: molecular mechanisms, redox regulation, and clinical implications

Insulin-like growth factor (IGF)-induced signaling networks are vital in modulating multiple fundamental cellular processes, such as cell growth, survival, proliferation, and differentiation. Aberrations in the generation or action of IGF have been suggested to play an important role in several pathological conditions, including metabolic disorders, neurodegenerative diseases, and multiple types of cancer. Yet the exact mechanism involved in the pathogenesis of these diseases by IGFs remains obscure. Redox pathways involving reactive oxygen species (ROS) and reactive nitrogen species (RNS) contribute to the pathogenetic mechanism of various diseases by modifying key signaling pathways involved in cell growth, proliferation, survival, and apoptosis. Furthermore, ROS and RNS have been demonstrated to alter IGF production and/or action, and vice versa, and thereby have the ability to modulate cellular functions, leading to clinical manifestations of diseases. In this review, we provide an overview on the IGF system and discuss the potential role of IGF-1/IGF-1 receptor and redox pathways in the pathophysiology of several diseases.

Arterial pulse wave velocity, inflammatory markers, pathological GH and IGF states, cardiovascular and cerebrovascular disease

Blood pressure (BP) measurements provide information regarding risk factors associated with cardiovascular disease, but only in a specific artery. Arterial stiffness (AS) can be determined by measurement of arterial pulse wave velocity (APWV). Separate from any role as a surrogate marker, AS is an important determinant of pulse pressure, left ventricular function and coronary artery perfusion pressure. Proximal elastic arteries and peripheral muscular arteries respond differently to aging and to medication. Endogenous human growth hormone (hGH), secreted by the anterior pituitary, peaks during early adulthood, declining at 14% per decade. Levels of insulin-like growth factor-I (IGF-I) are at their peak during late adolescence and decline throughout adulthood, mirror imaging GH. Arterial endothelial dysfunction, an accepted cause of increased APWV in GH deficiency (GHD) is reversed by recombinant human (rh) GH therapy, favorably influencing the risk for atherogenesis. APWV is a noninvasive method for measuring atherosclerotic and hypertensive vascular changes increases with age and atherosclerosis leading to increased systolic blood pressure and increased left ventricular hypertrophy. Aerobic exercise training increases arterial compliance and reduces systolic blood pressure. Whole body arterial compliance is lowered in strength-trained individuals. Homocysteine and C-reactive protein are two inflammatory markers directly linked with arterial endothelial dysfunction. Reviews of GH in the somatopause have not been favorable and side effects of treatment have marred its use except in classical GHD. Is it possible that we should be assessing the combined effects of therapy with rhGH and rhIGF-I? Only multiple intervention studies will provide the answer.

Growth factors and adipocytokines in prepubertal children born small for gestational age: relation to insulin resistance

OBJECTIVE

The aim of this study was to test whether being born small for gestational age (SGA) has an impact on adiponectin and leptin levels and the IGF system in relation to insulin sensitivity, taking into consideration the severity of growth restriction.

RESEARCH DESIGN AND METHODS

Serum levels of adiponectin, leptin, fasting glucose, fasting insulin (I(F)), the homeostasis model assessment insulin resistance index (HOMA-IR), IGF-1, free IGF-1, IGF-binding protein (IGFBP)-1 and -3, total cholesterol, HDL cholesterol, LDL cholesterol, and triglycerides were evaluated in 57 children at age 4-10 years. Of these, 32 had been born appropriate size for gestational age (AGA) and 25 SGA (14 in the <3rd percentile and 11 in the 3rd-10th percentile). RESULTS; The SGA 3rd-10th percentile children were already insulin resistant at prepubertal age (I(F) 39.6 +/- 16.8 vs. 27 +/- 12 pmol/l, P < 0.01, and HOMA-IR 1.4 +/- 0.6 vs. 0.95 +/- 0.42 in SGA vs. AGA children, P < 0.05). Their IGF-1 and IGFBP-3 concentrations were significantly lower than those in AGA children (160.4 +/- 66.2 vs. 207 +/- 66.8 microg/l, P < 0.05 and 2.3 +/- 0.4 vs. 3.51 +/- 1.21 mg/l in SGA vs. AGA children, P < 0.01). The SGA <3rd percentile children had higher adiponectin (15.6 +/- 5.7 mg/l, P < 0.05) and IGFBP-1 levels (113.5 +/- 33.9 microg/l, P < 0.05) than AGA children (11.3 +/- 6.6 mg/l and 90.8 +/- 24.2 microg/l, respectively) and lower IGF-1 and IGFBP-3 concentrations (162.6 +/- 68.4 microg/l, P < 0.05 and 2.4 +/- 0.7 mg/l, P < 0.01). They also had significantly lower waist circumference (P < 0.05). Leptin levels did not differ among groups, but an inverse correlation with IGFBP-1 (r = -0.55, P < 0.01) was found in the pooled SGA group.

CONCLUSIONS

Intrauterine growth restriction appears to affect the IGF axis at prepubertal age, and its severity plays a role in insulin sensitivity.

Role of IGF-1 in glucose regulation and cardiovascular disease

IGF-1 is a peptide hormone that is expressed in most tissues. It shares significant structural and functional similarities with insulin, and is implicated in the pathogenesis of insulin resistance and cardiovascular disease. Recombinant human IGF-1 has been used in Type 2 diabetes to improve insulin sensitivity and aid glycemic control. There is evidence supporting IGF-1 as a vascular protective factor and it may also be beneficial in the treatment of chronic heart failure. Further understanding of the effects of IGF-1 signaling in health and disease may lead to novel approaches to the prevention and treatment of diabetes and cardiovascular disease.

The association of insulin-like-growth factor 1 (IGF-1) with incident coronary heart disease in women: findings from the prospective British Women's Heart and Health Study

OBJECTIVE

To examine the association of insulin-like-growth factor 1 (IGF-1) with coronary heart disease (CHD) in women.

METHODS

Prospective (4 year) case-control study nested within the British Women's Heart and Health Study. With 167 cases and 333 controls. Serum IGF-1 concentrations (on serum stored at -80 degrees C for a median of 4 years) were determined using a two-site immunoenzymometric assay.

RESULTS

Among both cases and controls IGF-1 was inversely correlated with waist:hip ratio, fasting insulin, HOMA-IR, CRP, triglyceride levels and systolic blood pressure, and was positively correlated with HDL-C levels. The confounder-adjusted (age, socioeconomic position, smoking and physical activity) relative risk ratio for a 1 standard deviation (S.D.) increase in IGF-1 was 0.92 (95% CI: 0.75, 1.12) and additional adjustment for metabolic risk factors (waist:hip ratio, systolic blood pressure, high-density lipoprotein cholesterol, triglycerides, glucose, insulin and C-reactive protein) attenuated this to 0.98 (95% CI: 0.80, 1.21). There was no evidence of non-linear associations and the risk of CHD was similar across quarters of the distribution of IGF-1.

CONCLUSIONS

Despite associations with established CHD risk factors in this, and other studies, our findings suggest that higher IGF-1 levels are not associated with CHD in older British women. The contradictory evidence to date in this area highlights the need for further large-scale prospective studies and use of genetic epidemiology studies to determine the nature of the association between IGF-1 and CHD.

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.

Hypoglycemia due to paraneoplastic secretion of insulin-like growth factor-I in a patient with metastasizing large-cell carcinoma of the lung

CONTEXT

Nonpancreatic tumors may cause recurrent hypoglycemia known as nonislet cell tumor hypoglycemia. It is due to overproduction and secretion by the tumor of incompletely processed IGF-II, termed big IGF-II. We recently identified a patient with recurrent hypoglycemia and low insulin, but without elevated big IGF-II. Multiple small lung nodules were detected by computed tomography scan. An undifferentiated large-cell carcinoma was diagnosed from an axillary lymph node metastasis.

OBJECTIVE

The objective was to investigate whether the patient's hypoglycemia was due to excessive IGF-I production by the tumor.

METHODS

Serum IGF- I and IGF-II, insulin, and GH were measured by RIA; the distribution of IGFs between IGF binding protein complexes in serum was analyzed after neutral gel filtration. Tissue IGF-I was identified by immunohistochemistry and in situ hybridization, and by RT-PCR after RNA extraction.

RESULTS

Total and free serum IGF-I, but not total, free, and big IGF-II, was increased, and the IGF-I content of the two IGF binding protein complexes was elevated. Immunohistochemistry demonstrated IGF-I peptide in situ hybridization IGF-I mRNA in the lymph node metastasis. Combined GH/glucocorticoid treatment prevented hypoglycemia, but did not lower IGF-I. After chemotherapy with carboplatinum/etoposide, the lung nodules largely regressed, and serum IGF-I and the IGF-I content of the two binding protein complexes became normal. Hypoglycemia did not recur despite discontinuation of GH/glucocorticoid treatment.

CONCLUSION

Our findings are compatible with a new form of tumor hypoglycemia caused by circulating tumor-derived IGF-I.

Mechanisms of disease: metabolic effects of growth hormone and insulin-like growth factor 1

Insulin-like growth factor (IGF) 1 is a member of a family that is involved in growth, development, cell differentiation, and metabolism. IGF1, IGF2 and insulin act primarily through tyrosine-kinase-linked receptors--the IGF1 receptor (IGF1R) and insulin receptor (IR). The IGF1R binds IGF1 and IGF2 with high affinity and the IR binds insulin with high affinity; however, since both receptors share a high degree of structural and functional homology, the IGF1R can bind insulin and the IR can bind the IGFs with reduced affinity. These two receptors can, moreover, form heterodimers, which bind both ligands. Upon binding to the receptors, cascades of tyrosine and serine kinases are stimulated to facilitate growth or metabolism. The IGF2 receptor is a scavenger receptor, and is, therefore, not involved in mediation of growth or metabolic effects of the IGF family and will not be discussed in the current article. IGF1 is a major gene target of growth hormone and its product mediates many of the actions of growth hormone on growth and development; however, IGF1 has actions distinct from those of growth hormone in carbohydrate, lipid, and protein metabolism. For example, excess growth hormone causes insulin resistance and hyperglycemia, whereas IGF1 has insulin-like effects that reduce blood glucose levels and has been used experimentally to treat both type 1 and type 2 diabetes.

Glucose intolerance and insulin resistance in extremely premature newborns, and implications for nutritional management

Glucose intolerance and postnatal growth retardation are commonly seen in low-gestation newborns. In contrast to the nutrient compositions of parenteral and enteral nutrition, fetuses at equivalent gestational ages receive much more amino acids (protein) but less glucose and lipids through placental transfer.

CONCLUSION

A nutrition regime that simulates placental nutrient delivery would potentially minimize glucose intolerance and facilitate early attainment of normal growth velocity with normal body composition after preterm birth.

Association between an IGF-I gene polymorphism and body fatness: differences between generations

OBJECTIVE

A polymorphism near the promoter region of the IGF-I gene has been associated with serum IGF-I levels, body height and birth weight. In this study, we investigated whether this polymorphism is associated with body composition in young healthy subjects in two cohorts of different generations.

DESIGN

Observational study with repeated measurements.

METHODS

The study group consisted of two comparable young Dutch cohorts with a generational difference of around 20 years. The older cohort consisted of 359 subjects born between 1961 and 1965. Measurements were performed from 13 until 36 years of age. The younger cohort consisted of 258 subjects born between 1981 and 1989. Measurements were performed from 8 until 14 years of age. Height, body mass index (BMI), fat mass, fat-free mass, waist and hip circumference were compared between wild-type carriers and variant type carriers of the IGF-I polymorphism.

RESULTS

In the younger cohort, body weight, BMI, fat mass and waist circumference were significantly higher in female variant carriers of the IGF-I polymorphism. A similar trend was observed in male variant carriers. In contrast, these differences were not observed in the older cohort. Irrespective of genotype, the younger cohort showed a significantly higher total fat mass, body weight and BMI compared with the older cohort.

CONCLUSIONS

Because the differences between both genotypes were small, it seems likely that the genetic variability due to this IGF-I polymorphism impacts only slightly on body composition. Importantly, our study suggested that associations between this IGF-I promoter polymorphism and body composition possibly reflect a gene-environmental interaction of this polymorphism and that an environment that promotes obesity leads to a slightly more pronounced fat accumulation in variant carriers of this IGF-I polymorphism.

Effects of 2 wk of GH administration on 24-h indirect calorimetry in young, healthy, lean men

The present study was designed as a randomized, double-blind placebo (Plc)-controlled study to determine the effect of 2 wk of growth hormone administration (GH-adm.) on energy expenditure (EE) and substrate oxidation in healthy humans. Sixteen young healthy men were divided into two groups. The study consisted of two 24-h measurements (indirect calorimetry), separated by 2 wk of either Plc or GH injections (6 IU/day). At baseline, no significant differences were observed between the two groups in any of the measured anthropometric, hormonal, or metabolic parameters, neither did the parameters change over time in the Plc group. GH-adm. resulted in a 4.4% increase in 24-h EE (P < 0.05) and an increase in fat oxidation by 29% (P < 0.05). However, a decrease in the respiratory quotient was only observed in the postabsorptive phase after an overnight fast (0.84 +/- 0.1 to 0.79 +/- 0.1, P < 0.05). Furthermore, lean body mass (LBM) was increased by GH-adm. only [62.8 +/- 2.5 kg (baseline) vs. 64.7 +/- 2.4 kg (after), P < 0.001]. In conclusion, GH-adm. increases 24-h EE, which may be partly explained by increased LBM. Furthermore, GH-adm. stimulates fat combustion, especially in the postabsorptive state.

Insulin-like growth factor I (IGF-I) replacement therapy increases albumin concentration in liver cirrhosis: results of a pilot randomized controlled clinical trial

BACKGROUND/AIMS

Insulin-like growth factor I (IGF-I) is an anabolic hormone synthesized in the liver whose levels decrease sharply in liver cirrhosis.

METHODS

We conducted a randomized double-blind placebo-controlled clinical trial to evaluate the effect of subcutaneous administration of IGF-I (20 microg/kg/day with dose escalation to 50-100 microg/kg/day) for 4 months in patients with alcoholic or primary biliary cirrhosis (PBC) and subnormal IGF-I levels. Eight alcoholics and one PBC entered the placebo group and seven alcoholics and two PBC the treatment group. Biochemistry, body composition, muscle mass and strength, and resting energy expenditure (REE) were evaluated.

RESULTS

Total serum IGF-I and IGF-I/IGFBP-3 ratio (a surrogate marker of IGF-I biovailability) increased in the treatment group but IGF-I values still remained below normal limits in the treated patients. No differences were observed in body composition, muscle strength or muscle mass between groups. However, IGF-I therapy increased significantly serum albumin (P = 0.038) and this improvement correlated positively with variation of IGF-I/IGFBP-3 ratio. IGF-I treatment also tended to increase REE (P = 0.085); this difference was significant (P = 0.049) in the subgroup of alcoholic patients.

CONCLUSIONS

A short course of IGF-I increased albumin levels and tended to improve energy metabolism in liver cirrhosis. These findings warrant larger clinical trials to assess the clinical benefit of IGF-I in cirrhotic patients.

Rh/IGF-I/rhIGFBP-3 administration to patients with type 2 diabetes mellitus reduces insulin requirements while also lowering fasting glucose

Administration of insulin-like growth factor-I to patients with diabetes enhances insulin action and reduces the degree of hyperglycemia but it is associated with a high rate of adverse events. Infusion of the combination of rhIGFBP-3 (the principal binding protein for IGF-I in plasma) with rhIGF-I to patients with type I diabetes improved insulin sensitivity and was associated with a low incidence in side effects. In this study, 52 patients with insulin-treated type 2 diabetes received recombinant human IGF-I plus rhIGFBP-3 in one of four dosage regimens for 14 days. The four groups were: (1) continuous subcutaneous infusion of 2 mg/kg/day; (2) the same 2 mg/kg dose infused subcutaneously over 6 h between 2000 and 0200 h; (3) 1 mg/kg twice a day by bolus subcutaneous injection; (4) a single bedtime subcutaneous injection of 1 mg/kg. Across these four groups rhIGF-I/rhIGFBP-3 decreased insulin requirements between 54% and 82%. Fasting glucose decreased by 32-37%. Mean daily blood glucose (4 determinations per day) declined in all 4 groups (range 9-23% decrease). Frequent sampling for total IGF-I, free IGF-I and IGFBP-3 was performed on days 0,1,7,14 and 15. The peak total IGF-I values were increased to 4.0-4.8-fold at 16-24 h. For free IGF-I the increase varied between 7.1 and 8.2-fold and peak values were attained at 16-20 h after administration. Both the time to maximum concentration (Tmax) and the maximum free IGF-I levels (Cmax) on day 1 for all groups were substantially less than previously published studies, wherein lower doses of rhIGF-I were given without IGFBP-3. The improvement in glucose values and the degree of reduction in insulin requirement were the greatest in groups 2 and 3 and the patients in those groups had the highest free IGF-I levels. The frequency of side effects such as edema, jaw pain and arthralgias was 4% which is less than that has been reported in previous studies wherein IGF-I was administered without IGFBP-3. We conclude that rhIGF-I/rhIGFBP-3 significantly lowers insulin requirements yet improves glucose values and these changes may reflect improvement in insulin sensitivity. Coadministration of IGFBP-3 with IGF-I produces lower free IGF-I (Tmax and Cmax) levels compared to administration of IGF-I alone and is associated with relatively low incidence of side effects during 2 weeks of administration.

Pharmacologic Therapies for Acromegaly

Acromegaly is associated with insulin resistance and an increased incidence of cardiovascular disease. However, it remains unclear to what extent the effects of growth hormone (GH) excess on cardiovascular morbidity and mortality are mediated through insulin resistance versus through other direct or indirect effects of GH. Adequate control of GH excess by surgery or pharmacologic interventions is associated with decreased insulin resistance, reflected in decreased plasma insulin levels and fasting glucose levels or improved glucose tolerance. Despite divergent effects of both somatostatin and somatostatin analogs on GH, insulin and glucagon secretion, and glucose absorption, treatment with the somatostatin analogs octreotide and lanreotide has only limited effects on glucose metabolism. However, glucose sensitivity has only been formally examined using a hyperinsulinemic euglycemic clamp in a minority of these studies. Treatment with the GH-receptor antagonist pegvisomant ameliorates insulin sensitivity, reflected in decreased fasting plasma insulin levels and fasting glucose levels. Nonetheless, the effect of pegvisomant on glucose sensitivity has not been formally tested by hyperinsulinemic clamp conditions. In acromegaly, preliminary observations on new octreotide analogs with greater specificity for somatostatin-receptor subtypes indicate that these compounds achieve better control of GH hypersecretion than octreotide, but may also negatively influence insulin release. Assessment of insulin secretion and glucose levels in acromegalic patients during administration of these compounds is thus mandatory.

IGF-I concentrations are positively associated with carotid artery atherosclerosis in women

BACKGROUND

Alterations in the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis are associated with increased cardiovascular morbidity and mortality, but previous studies have yielded conflicting results. In addition, the T1169A polymorphism in the GH1 gene has been associated with IGF-I levels.

AIMS

To investigate whether IGF-I concentrations and the T1169A polymorphism of the GH1 gene are associated with cardiovascular risk factors and the intima media thickness (IMT) of the carotid artery.

METHODS

Fasting plasma IGF-I concentrations (n=1008) were measured in a large population-based OPERA (Oulu Project Elucidating Risk of Atherosclerosis) cohort. Genotype variants were determined by the restriction fragment length polymorphism method.

RESULTS

Low IGF-I concentrations associated with several cardiovascular risk factors including age, adiposity, and high triglyceride, fasting insulin and C-reactive protein concentrations in the analysis of all subjects. In the multivariate models, however, IGF-I concentrations were positively associated with the mean IMT of women (ss=0.127, P=0.009) whereas the association in men was weaker and negative (ss=-0.088, P=0.034). The 1169A allele was associated with low low-density lipoprotein cholesterol in both sexes and with low systolic blood pressure levels in women.

CONCLUSIONS

IGF-I concentrations were associated with several traditional cardiovascular risk factors. The observed gender difference in the association between IGF-I concentrations and carotid artery atherosclerosis warrants further study. The GH1 1169A allele may be associated with a favourable metabolic profile.

Free insulin-like growth factors -- measurements and relationships to growth hormone secretion and glucose homeostasis

IGF-I is a multipotent growth factor with important actions on normal tissue growth and regeneration. In addition, IGF-I has been suggested to have beneficial effects on glucose homeostasis due to its glucose lowering and insulin sensitizing actions. However, not all effects of IGF-I are considered to be favorable; thus, epidemiological studies suggest that IGF-I is also involved in the development of common cancers, atherosclerosis and type 2 diabetes. The biological actions of IGF-I are modulated by at least six IGF-binding proteins, which bind approximately 99% of the circulating IGF-I pool. So far, most in vivo studies have used serum or plasma total (extractable IGF-I) as an estimate of the bioactivity of IGF-I in vivo. However, within the last decade, validated assays for measurement of free IGF-I have been described. This review aims to discuss the current assays for free IGF-I and their advances in relation to the traditional measurement of total IGF-I. The literature overview will focus on the role of circulating free versus total IGF-I in the feedback regulation of GH release, and the possible involvement of the circulating IGF-system in glucose homeostasis.

Glucose homeostasis in abdominal obesity: hepatic hyperresponsiveness to growth hormone action

It has been suggested that (abdominally) obese individuals are hypersensitive to growth hormone (GH) action. Because GH affects glucose metabolism, this may impact glucose homeostasis in abdominal obesity. Therefore, we studied the effect of GH on glucose metabolism in abdominally obese (OB) and normal-weight (NW) premenopausal women. A 1-h intravenous infusion of GH or placebo was randomly administered to six NW [body mass index (BMI) 21.1 +/- 1.9 kg/m(2)] and six OB (BMI 35.5 +/- 1.5 kg/m(2)) women in a crossover design. Insulin, glucagon, and GH secretion were suppressed by concomitant infusion of somatostatin. Glucose kinetics were measured using a 10-h infusion of [6,6-(2)H(2)]glucose. In both groups, similar physiological GH peaks were reached by infusion of GH. GH strongly stimulated endogenous glucose production (EGP) in both groups. The percent increase was significantly greater in OB than in NW women (29.8 +/- 11.3 vs. 13.3 +/- 7.4%, P = 0.014). Accordingly, GH responsiveness, defined as the maximum response of EGP per unit GH, was increased in OB vs. NW subjects (6.0 +/- 2.1 vs. 2.2 +/- 1.5 micromol.min(-1).mU(-1).l(-1), P = 0.006). These results suggest that the liver is hyperresponsive to GH action in abdominally obese women. The role of the somatotropic ensemble in the control of glucose homeostasis in abdominal obesity is discussed.

Fat metabolism in exercise - with special reference to training and growth hormone administration

Despite abundance of fat, exclusive dependency on fat oxidation can only sustain a metabolic rate corresponding to 50-60% of VO(2max) in humans. This puzzling finding has been subject to intense research for many years. Lately, it has gained renewed interest as a consequence of increased obesity and physical inactivity imposed by Western lifestyle. Why are humans so poor at metabolizing fat? Can fat metabolism be manipulated by exercise, training, diet and hormones? And why is fat stored in specialized adipose tissue and not just as lipid droplets inside muscle cells? In the present review, human fat metabolism is discussed in relation to how human fat metabolism is designed. Limitations in this design are explored and examples of different designs for fat metabolism from animal physiology are included to illustrate these limitations. Various means of manipulating fat metabolism are discussed with special emphasis on exercise, training, growth hormone (GH) physiology and GH administration. It is concluded that fat stores, non-esterified fatty acids (NEFAs) availability and enzymes for fat oxidation can be increased substantially. However, it is almost impossible to increase fat oxidation during endurance exercise at higher intensities. It seems that, for some reason, the human being is far from optimally designed for fat oxidation during exercise. Acute GH administration has several unexpected effects on fat and carbohydrate metabolism during aerobic exercise, and future research in this area is likely to provide valuable information with respect to GH physiology and the regulation of fat and carbohydrate metabolism during aerobic exercise.