Role of the insulin-like growth factors in the endocrine control of glucose homeostasis

IGF-1 is not related to long-term outcome in hyperglycemic acute coronary syndrome patients

PURPOSE

Insulin-like growth factor-1 (IGF-1) has been associated with both protective and detrimental effects on the development of ischemic heart disease. The relationship between IGF-1 levels and major adverse cardiovascular events (MACE) in acute coronary syndrome (ACS) patients remains unclear. This study aimed to investigate the relationship between IGF-1 admission levels in hyperglycemic ACS patients and: (1) MACE over a 5 years follow-up, (2) type 2 diabetes at discharge, and (3) post-ACS myocardial infarct size and dysfunction.

METHODS

This was a post hoc analysis of the BIOMArCS-2 randomized controlled trial. From July 2008 to February 2012, 276 ACS patients with admission plasma glucose level between 140 and 288 mg/dL were included. Records of the composite of all-cause mortality and recurrent non-fatal myocardial infarction were obtained during 5 years follow-up. Venous blood samples were collected on admission. IGF-1 was measured batchwise after study completion. Oral glucose tolerance test was performed to diagnose type 2 diabetes, whereas infarct size and left ventricular function were assessed by myocardial perfusion scintigraphy (MPS) imaging, 6 weeks post-ACS.

RESULTS

Cumulative incidence of MACE was 24% at 5 years follow-up. IGF-1 was not independently associated with MACE (HR:1.00 (95%CI:0.99-1.00), p = 0.29). Seventy-eight patients (28%) had type 2 diabetes at discharge, and the highest quartile of IGF-1 levels was associated with the lowest incidence of diabetes (HR:0.40 (95%CI:0.17-0.95), p = 0.037). IGF-1 levels were not associated with post-ACS myocardial infarct size and dysfunction.

CONCLUSIONS

IGF-1 carries potential for predicting type 2 diabetes, rather than long-term cardiovascular outcomes and post-ACS myocardial infarct size and dysfunction, in hyperglycemic ACS patients.

Insulin-like growth factor axis in pregnancy and gestational diabetes mellitus

The insulin-like growth factor (IGF) is involved in the regulation of growth and metabolism. The aim of this study was to determine selected parameters of IGF system at systemic and local levels [subcutaneous (SAT) and visceral adipose tissue (VAT)] to assess its possible role in gestational diabetes mellitus (GDM). 37 pregnant women (21 with GDM and 16 without GDM) and 15 age-matched non-pregnant females were included in the study. Blood samples were taken in 28-32 and 36-38 weeks of gestation and 6-12 months after delivery. SAT and VAT samples were obtained during delivery or surgery. Compared with non-pregnant women, serum IGF-1 and IGFBP-3 were increased in both groups of pregnant women. IGF-2 was elevated only in GDM women from 36 weeks of gestation culminating 6 months after delivery (p=0.003). Serum IGFBP-3 was increased and IGFBP-4 decreased in GDM women vs. pregnant women without GDM during the whole study (IGFBP-3: p?0.001 for GDM vs. non-GDM; IGFBP-4: p=0.004 for GDM vs. non-GDM). Pregnant women with GDM had decreased mRNA expression of IGF-1, IGF-1R and IGF-2R and IGFBP-4 in VAT and IGF-1R in SAT compared to pregnant women without GDM. Changes in local activity of IGF are associated with the development of GDM.

Clinical characteristics and outcome of 467 patients with a clinically recognized eating disorder identified among 52,215 patients with type 1 diabetes: a multicenter german/austrian study

OBJECTIVE

To compare clinical characteristics and outcome of type 1 diabetes mellitus (T1DM) between patients with and without a clinically recognized eating disorder (ED).

RESEARCH DESIGN AND METHODS

A total of 52,215 T1DM patients aged 8 to <30 years from the prospective diabetes data acquisition system DPV were analyzed. A total of 467 patients had an additional diagnosis of ED according to DSM-IV criteria (anorexia nervosa [AN], n = 141 [female: 94.3%]; bulimia nervosa [BN], n = 62 [90.3%]; and EDs not otherwise specified, including binge-eating disorder [EDNOS], n = 264 [74.2%]). Groups were compared using multivariable regression. Cox proportional hazard ratios were calculated for the association between ED and retinopathy.

RESULTS

After adjustment for age, sex, and duration of diabetes, patients with ED revealed higher HbA1c (no ED vs. AN, BN, or EDNOS, respectively: 8.29 ± 0.01% [67.1 ± 0.1 mmol/mol] vs. 8.61 ± 0.15% [70.6 ± 1.6 mmol/mol], 9.11 ± 0.23% [76.1 ± 2.5 mmol/mol], or 9.00 ± 0.11% [74.9 ± 1.2 mmol/mol]) and a higher rate of pathological insulin injection sites (48.4 vs. 64.3, 64.1, or 62.1%). Furthermore, ketoacidosis (5.7 ± 0.1 vs. 12.1 ± 2.1, 18.0 ± 4.1, or 12.9 ± 1.6 events per 100 person-years) and hospitalization (54.9 ± 0.3 vs. 89.3 ± 6.0, 132.0 ± 12.7, or 91.0 ± 4.4 per 100 person-years) were more common, and duration of hospital stay was longer (4.81 ± 0.01 vs. 11.31 ± 0.21, 18.05 ± 0.48, or 8.44 ± 0.13 days per year). All P values were <0.05. Patients with BN and EDNOS had a 2.5-fold (95% CI 1.3-4.8) and a 1.4-fold (0.8-2.3) higher risk for retinopathy, whereas AN patients had no increased risk (0.9 [95% CI 0.4-2.3]).

CONCLUSIONS

Diabetes health care professionals should be aware of comorbid EDs in pediatric/young-adult T1DM patients. An ED diagnosis is associated with worse metabolic control and higher rates of diabetes complications.

The relationship between dioxin-like polychlorobiphenyls and IGF-I serum levels in healthy adults: evidence from a cross-sectional study

OBJECTIVE

Insulin-like growth factor I (IGF-I) and dioxin-like polychlorobiphenyls (DL-PCBs) have been associated with the pathogenesis of several diseases like cancer, diabetes and growth disorders. Because it has been suggested that organohalogenated contaminants could influence IGF-I levels in adults, the potential relationship between DL-PCBs and IGF-I serum levels was studied in 456 healthy adults from a representative sample of the general population of the Canary Islands (Spain).

DESIGN

Free circulating serum levels of IGF-I and IGFBP-3 were measured through an ELISA methodology, while the serum levels of the 12 DL-PCBs congeners (IUPAC numbers # 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, and 189) were measured by gas chromatography/mass spectrometry (GC-MS).

RESULTS

DL-PCBs 156 and 167, Total DL-PCBs body burden (∑PCBs: sum over the 12 measured DL-PCBs), and Total toxic burden (in terms of toxic equivalence to dioxins: ∑TEQs) showed a trend of inverse association with IGF-I serum levels in the whole studied population. After adjusting for potential confounders, including gender, body mass index (BMI), age, and IGF-binding protein-3 (IGFBP-3), younger (18-45 years) women with lower BMI (<27 kg/m(2)) and detectable levels of DL-PCB-156 showed significantly lower IGF-I levels than those in the same age and BMI subgroup with non-detectable levels of DL-PCB-156 (p<0.001). Similarly, ∑PCBs and ∑TEQs showed a tendency to an inverse association with IGF-I levels in the same group of women (p=0.017 and p=0.019 respectively).

CONCLUSIONS

These findings suggest that DL-PCBs could be involved in the regulation of the IGF-system in a way possibly influenced by gender, age and BMI. Although these results should be interpreted with caution, such circumstances could contribute to explain the development of diseases associated to the IGF system.

Biomarkers of the metabolic syndrome and breast cancer prognosis

In spite of its public health importance, our understanding of the mechanisms of breast carcinogenesis and progress is still evolving. The metabolic syndrome (MS) is a constellation of biochemical abnormalities including visceral adiposity, hyperglycemia, hyperinsulinemia, dyslipidemia and high blood pressure. The components of the MS have all been related to late-stage disease and even to a poor prognosis of breast cancer through multiple interacting mechanisms. In this review, we aim to present a summary of recent advances in the understanding of the contribution of the MS to breast cancer with the emphasis on the role of biomarkers of the MS in the prognosis of breast cancer.

IGFBP-1 protease activity and IGFBP-1 fragments in a patient with multiple myeloma

OBJECTIVE

Cleavage of IGFBPs by proteases results in IGFBP fragments that have altered IGF-binding affinity, and IGF-independent roles. We have previously purified a specific IGFBP-1 protease activity from the urine of an individual with multiple myeloma and dermatitis. The aim of this study was to determine whether IGFBP-1 protease activity and/or IGFBP-1 fragments were present in the circulation of this patient.

METHODS

The size of immunoreactive IGFBP-1 in serum samples was determined after Superose 12 chromatography. Intact IGFBP-1 and IGFBP-1 fragments were characterized in four RIAs and after SDS-PAGE.

RESULTS

Specific proteolysis of IGFBP-1 generated an N-terminal fragment (IGFBP-1(1-130)) with a predicted molecular mass of 13kDa but an apparent mass of 21kDa on SDS-PAGE. A C-terminal fragment (IGFBP-1(131-234)) produced in vitro migrated at 11.4kDa, close to its predicted size. However a C-terminal fragment of cleaved IGFBP-1 (IGFBP-1(142-234)) migrated at 14kDa on SDS-PAGE. Serum from the patient inhibited IGFBP-1 protease activity. Immunoreactive IGFBP-1 in patient serum was present at molecular masses consistent with IGFBP-1 fragments, in addition to intact IGFBP-1.

CONCLUSIONS

Specific cleavage of IGFBP-1 occurs at the tissue level and not in the circulation in a patient with multiple myeloma and dermatitis. The fragments that are generated may have endocrine roles.

Gene expression profiling of non-alcoholic steatohepatitis using gene set enrichment analysis

AIM

Non-alcoholic steatohepatitis (NASH) is a subset of non-alcoholic fatty liver disease (NAFLD) and sometimes progresses to cirrhosis and liver failure. In this study we analyzed the expression profile of genes and biological pathways involved in NASH in comparison with non-NASH by gene set enrichment analysis (GSEA) employing a DNA microarray technique.

METHODS

mRNA from liver biopsy specimens was collected from a group of NASH patients and a group of non-NASH patients. We analyzed the relative abundance of mRNA using high-density oligonucleotide microarrays containing probes for 54 675 known genes, and investigated the pathogenetic mechanisms of NASH by means of a powerful technique for analyzing molecular profiling data, GSEA.

RESULTS

The results showed that the level of expression of 27 gene sets was significantly higher and the level of expression of 25 gene sets was significantly lower in the NASH samples than in the non-NASH samples. Based on these results we created an online, publicly available, searchable database containing the data for the gene expression profiles of the NASH patients (http://www2.genome.rcast.u-tokyo.ac.jp/___/NASH/NASH_GSEA2/).

CONCLUSION

Our data revealed differences in expression of many gene sets that are involved in the pathogenesis of NASH.

Postprandial paradoxical IGFBP-1 response in obese patients with Type 2 diabetes

IGFs (insulin-like growth factors), which in an unbound form induce glucose and amino acid uptake, circulate bound to IGFBPs (IGF-binding proteins), which modulate their bioavailability and activity. The aim of the present study was to examine the effect of a standard meal [2301 kJ (550 kcal)] on the serum levels of IGFBP-1 in obese patients with T2DM (Type 2 diabetes mellitus), non-obese patients with T1DM (Type 1 diabetes mellitus) and healthy controls, using the artificial pancreas (Biostator®) to obtain a normal glycaemic response to the meal. IGFBP-1 levels decreased by 50% over 2 h following the meal at a similar clearance in both the healthy controls and patients with T1DM, but no significant decline was seen in the patients with T2DM, despite a several-fold increase in insulin levels. The patients with T2DM were also studied during Sandostatin® (somatostatin) infusion to decrease the inappropriate secretion of glucagon during the meal. During the 210 min of somatostatin infusion, the glucagon response was suppressed and IGFBP-1 levels were increased concomitantly with the peak in insulin levels, without any significant decrease after the meal. In conclusion, the impaired IGFBP-1 response to meal-related hyperinsulinaemia in obese patients with T2DM suggests a decreased availability of active IGF-1, leading to a decrease in glucose uptake during and after a meal in these patients. The stimulated meal response to glucagon, which contributes to postprandial hyperglycaemia, could not explain the increase in serum IGFBP-1 in these obese patients with T2DM.

Value of insulin-like growth factor system markers in the assessment of growth hormone status

Insulin-like growth factor-I (IGF-I) has been measured extensively in a variety of clinical settings. Total IGF-I frequently is used to assess the clinical impact of disorders of GH secretion and to monitor patients' response to therapy. It does not have sufficient precision to be used as a stand-alone test in the diagnosis of GH deficiency. Free IGF-I, IGF binding protein-3, or acid-labile subunit may provide useful information regarding GH secretion in specific conditions but are not superior to IGF-I for making the diagnosis of GH deficiency or acromegaly.

The Insulin-like Growth Factor-binding Protein 1 Gene Is a Primary Target of Peroxisome Proliferator-activated Receptors

Insulin-like growth factor-binding protein 1 (IGFBP-1) is a biomarker for metabolic and hyperproliferative diseases. At the same time, the nuclear receptors peroxisome proliferator-activated receptors (PPARs) are known for their critical role in the development of both the metabolic syndrome and various cancers. Here we demonstrate, in human hepatocellular carcinoma cells and in normal mouse liver, that IGFBP-1 mRNA expression is under the primary control of PPAR ligands. We applied an improved in silico screening approach for PPAR response elements (PPREs) and identified five candidate PPREs located within 10 kb of the transcription start site (TSS) of the IGFBP-1 gene. Chromatin immunoprecipitation assays showed that, in living cells, the genomic region containing the most proximal PPRE, at position -1200 (relative to the TSS), preferentially associates with multiple PPAR subtypes and various other components of the transcriptional apparatus, which include their heterodimerizing partner, retinoid X receptor, as well as phosphorylated RNA polymerase II, co-repressor, co-activator, and mediator proteins. Moreover, further chromatin immunoprecipitation assays demonstrated that the TSS regions of the IGFBP-1 gene and those of the related IGFBP-2, -5, and -6, but not of IGFBP-3 and -4 genes, bind PPARs as well. We also show that these additional PPAR binding genes contain a number of candidate PPREs and that their mRNA levels respond quickly to the presence of PPAR ligands, indicating that they are also primary PPAR target genes.

Insulin-like growth factor I: a predictor of long-term glucose abnormalities in patients with acute myocardial infarction

AIMS/HYPOTHESIS

Low levels of IGF-I are associated with increased risk of cardiovascular disease and type 2 diabetes. The aim of this study was to investigate the IGF-I system in patients with acute myocardial infarction (AMI) without previously known diabetes.

MATERIALS AND METHODS

One hundred and sixty-eight AMI patients were classified before hospital discharge by means of an OGTT as having NGT, IGT or newly detected type 2 diabetes. Age- and sex-matched subjects from the background population (n=185) served as the control group. The associations between fasting levels of IGF-I and IGF binding proteins 1 and 3 (IGFBP-1, IGFBP-3) and glucose metabolism during a follow-up period of 12 months were studied.

RESULTS

At hospital discharge, age-adjusted IGF-I (IGF-I SD) was significantly lower in patients with abnormal glucose tolerance (AGT=IGT or type 2 diabetes) compared with patients with NGT (p=0.014) and control subjects (p<0.001). IGF-I was strongly correlated with IGFBP-3 (r=0.730, p<0.001), which was significantly lower in patients with AGT compared with patients with NGT (p=0.009) and control subjects (p<0.001). Fasting levels of IGFBP-1 did not differ significantly between patients with NGT and AGT or between patients and control subjects. In a multiple logistic regression analysis in patients, IGF-I at hospital discharge was a significant predictor of AGT at discharge and after 12 months (adjusted odds ratio 0.29, p=0.022, and adjusted odds ratio 0.29, p=0.034, respectively).

CONCLUSIONS/INTERPRETATION

Low levels of IGF-I may be a useful predictor of abnormal glucose metabolism in patients with AMI.

The role of endogenous hormones in the etiology and prevention of breast cancer: the epidemiological evidence

Breast cancer is the most common cause of cancer death in women worldwide. Rates vary about fivefold around the world, but they are increasing in regions that until recently had low rates of disease. Despite the numerous uncertainties surrounding the etiology of breast cancer, intensive epidemiological, clinical, and genetic studies have identified a number of biological and social traits as risk factors associated with breast cancer. Principal among them is the evidence of BRCA1 and BRCA2 susceptibility genes, familial history of breast cancer, age, higher socioeconomic status, ionizing radiation, tallness in adult life, alcohol consumption, and a variety of hormone and metabolic factors. Among the hormonal influences, a relevant etiological function has been ascribed to unopposed exposure to elevated levels of estrogens and androgens. In addition, new epidemiologic evidence has indicated that among the metabolic factors, glucose metabolism, hyperinsulinemic insulin resistance, and insulin-like growth factor bioavailability may also play a role in breast cancer. These endocrine and metabolic factors may represent future targets for breast cancer prevention.

The effect of clozapine on factors controlling glucose homeostasis

BACKGROUND

This prospective study examines the effect of clozapine on factors determining glucose homeostasis.

METHOD

The sample consisted of all patients meeting DSM-IV criteria for schizophrenia who commenced clozapine treatment within the South London and Maudsley hospitals during 1 year (2000-2001). Growth hormone (GH), insulin-like growth factor-1 (IGF-1), and IGF binding protein-1 (IGFBP-1) were measured in 19 patients (10 female; mean age = 31.1 years [SD = 5.8]; 9 black British/African, 10 white British) before and after a mean of 2.5 (SD = 0.9) months of clozapine treatment.

RESULTS

Baseline IGFBP-1 was low. IGFBP-1, GH, and IGF-1 were not significantly changed by clozapine treatment.

CONCLUSIONS

Clozapine does not alter GH, IGF-1, or IGFBP-1 within 3 months of commencing treatment, indicating that alteration in glucose tolerance associated with clozapine treatment involves other mechanisms yet to be elucidated. Baseline abnormalities in IGFBP-1 indicate a preexisting susceptibility to glucoregulatory dysfunction.

Troglitazone stimulates IGF-binding protein-1 by a PPAR gamma-independent mechanism

IGFBP-1 modulates IGF availability for glucose homeostasis and it may also play a paracrine role in hepatocyte survival. IGFBP-1 is inhibited transcriptionally by insulin and is also regulated by a number of pathways that influence hepatic insulin sensitivity. The effect of the thiazolidinedione troglitazone on IGFBP-1 production was studied in HepG2 human hepatoma cells, which were found to express PPAR alpha, PPAR gamma, and PXR. Troglitazone stimulated IGFBP-1 mRNA expression 2-fold within 3h of exposure (P<0.001) and stimulated secretion up to 3-fold over a narrow dose range within 24h (P<0.001). This effect was mimicked by the PXR ligands clotrimazole and phenobarbital, but not by Wy14,643 or rosiglitazone, which are ligands for PPAR alpha and -gamma, respectively. We conclude that the effect of troglitazone on IGFBP-1 production by HepG2 cells is independent of PPAR and may involve PXR.

Insulin infusion increases levels of free IGF-I and IGFBP-3 proteolytic activity in patients after surgery

We have studied the effects of insulin on the bioavailability of insulin-like growth factor (IGF) I in insulin-resistant patients after surgery. Serum levels of total IGF-I (tIGF-I), free IGF (fIGF)-I, fIGF-II, and IGF-binding protein (IGFBP) 1 and IGFBP-3 proteolytic activity (IGFBP-3-PA), determined on the day before surgery and on the 1st postoperative day, were related to insulin sensitivity measured by a hyperinsulinemic, normoglycemic clamp. Before surgery, the decreased tIGF-I (P < 0.05) in response to insulin infusion was accompanied by an 18% reduction of IGFBP-1 (P < 0.001), while IGFBP-3-PA remained unchanged. Levels of fIGF-I and fIGF-II were not changed by insulin infusions. After surgery, IGFBP-3-PA increased (P < 0.05) during insulin infusion, and this was associated with an increase in tIGF-I (P < 0.001) and fIGF-I (P < 0.01), while no significant change was found in fIGF-II. The reduction in IGFBP-1 in response to insulin infusion was not affected by surgery. The change in IGFBP-3-PA during insulin infusion after surgery was related to the corresponding change in fIGF-I (r(2) = 0.26, P < 0.05) and postoperative insulin sensitivity (r(2) = -0.22, P < 0.05). These data suggest that increased IGFBP-3-PA during insulin infusion after surgery governs the increased levels of fIGF-I, while insulin-induced suppression of IGFBP-1 was not affected by surgery. We propose that, in catabolic, postoperative patients, increased levels of insulin from exogenous or, possibly, endogenous sources (nutritionally induced) may be a signal to increase IGF-I bioavailability by increased expression of IGFBP-3-PA to counteract further deterioration in glucose metabolism.

Stimulation of IGF-binding protein-1 secretion by AMP-activated protein kinase

Insulin-like growth factor-binding protein-1 (IGFBP-1) is stimulated during intensive exercise and in catabolic conditions to very high concentrations, which are not completely explained by known regulators such as insulin and glucocorticoids. The role of AMP-activated protein kinase (AMPK), an important signaling system in lipid and carbohydrate metabolism, in regulating IGFBP-1 was studied in H4-II-E rat hepatoma cells. Arsenic(III) oxide and 5-aminoimidazole-4-carboxamide-riboside (AICAR) were used as activators. AICAR (150 microM) stimulated IGFBP-1 secretion twofold during a 5-h incubation (P = 0.002). Insulin (100 ng/ml) inhibited IGFBP-1 by 80% (P < 0.001), but this was completely abolished in the presence of 150 microM AICAR. The effect of dexamethasone in stimulating IGFBP-1 threefold was additive to the effect of AICAR (P < 0.001) and, in the presence of AICAR, was incompletely inhibited by insulin. In conclusion AMPK is identified as a novel regulatory pathway for IGFBP-1, stimulating secretion and blocking the inhibitory effect of insulin.

Effects of peroral and transdermal oestrogen replacement therapy on glucose and insulin metabolism

OBJECTIVE

Conflicting data have been reported previously on the effects of oestrogen replacement therapy on glucose tolerance, and the effects on glycosylated haemoglobin GHbA(1c) have been studied only among diabetics. The objective of this study was to evaluate the effects on glucose and insulin metabolism among nondiabetic women and to compare the outcomes of peroral and transdermal modes of administration.

DESIGN

The effects of peroral oestradiol valerate 2 mg/day with placebo gel were compared to those of transdermal 17 beta-oestradiol gel (1 mg oestradiol/day) and placebo tablets in a randomised, double-blind, double-dummy study for six months.

PATIENTS

Seventy-nine hysterectomised, nondiabetic postmenopausal women, 39 women in the peroral oestrogen group and 40 in the gel group.

MEASUREMENTS

Oral glucose tolerance tests (OGTT) with blood glucose, serum C-peptide and insulin determinations were performed. GHbA(1c), IGF-I and IGFBP-1 were measured at baseline and after six months of therapy. In addition, insulin sensitivity and insulin secretion indices were obtained from OGTT.

RESULTS

A small significant reduction in the GHbA(1c) concentration was observed during both peroral (P < 0.05) and transdermal oestrogen therapy (P < 0.05). However, no effect on insulin sensitivity was observed. The response to a standard 75 g oral glucose load was similar in the study groups. Compared with the baseline values, the area under the curve for C-peptide decreased by 8% both in the peroral group (P < 0.05) and in the gel group (P < 0.01). The fasting and postchallenge glucose and insulin levels or insulin release indices were not significantly altered. Peroral oestrogen decreased IGF-I and increased IGFBP-1, but these findings were not associated with the changes in glucose metabolism.

CONCLUSIONS

Neither peroral nor transdermal oestradiol replacement therapy seemed to induce any negative effects on glucose metabolism over a time period of 6 months.

The impact of the GH-IGF-I axis on gonadotropin secretion: inferences from animal models

Given the tight, temporal coupling between growth and reproductive development, the idea that a common signal may regulate both adolescent growth and the initiation of puberty has been the focus of much research. Since the rate-limiting step for the onset of puberty is the appropriate hypothalamic secretion of gonadotropin-releasing hormone (GnRH), any factor important for the initiation of puberty must affect GnRH pulsatility. This review examines the hypothesis that GH and/or IGF-I are growth-related signals that regulate the release of GnRH, initiating puberty. By extension, this review also addresses the hypothesis that the GH axis also impacts GnRH and gonadotropin secretion in post-pubertal individuals and, thus, affects the maintenance of fertility in adults. The review examines data from a range of animal models employing a number of different strategies which directly manipulate the activity of either GH or IGF-I. The success of these strategies for producing the desired effects on the GH-IGF-I axis is somewhat variable. Although IGF-I may only play a permissive role in the maintenance of adult fertility, acting at the level of the gonad to increase sensitivity to gonadotropin stimulation, the data indicate that IGF-I is essential for reproductive maturation. However, in addition to its well-documented effects on the gonad, the specific mode of action of IGF-I on the neuroendocrine hypothalamus and GnRH pulsatility remains to be determined. Available evidence suggests that such action by IGF-I may be mediated through neurotransmitter effects on GnRH neurons, changing the availability of metabolic substrates for neuronal activity, or remodeling of synaptic input into GnRH neurons.

Human insulin-like growth factor (IGF) binding protein-1 inhibits IGF-I-stimulated body growth but stimulates growth of the kidney in snell dwarf mice

The actions of insulin-like growth factor-I (IGF-I) are modulated by IGF binding proteins (IGFBPs). The effects of IGFBP-1 in vivo are insufficiently known, with respect to inhibitory or stimulatory actions on IGF-induced growth of specific organs. Therefore, we studied the effects of IGFBP-1 on IGF-I-induced somatic and organ growth in pituitary-deficient Snell dwarf mice. Human GH, IGF-I, IGFBP-1, and a preequilibrated combination of equimolar amounts of IGF-I and IGFBP-1 were administered sc during 4 weeks. Treatment with IGF-I alone induced a significant increase in body length (108% of control) and weight (112%) as well as an increase in weight of the submandibular salivary glands (135%), kidneys (124%), femoral muscles (111%), testes (129%), and spleen (126%) compared with saline-treated controls. IGFBP-1 alone induced a significant increase in weight of the kidneys (152% of control). Coadministration of IGF-I with IGFBP-1 neutralized the stimulating effects of IGF-I on body length and weight as well as on the femoral muscles and testes. In contrast, the weights of the submandibular salivary glands (143%) were not significantly different from those of IGF-I-treated animals, whereas the weights of the kidneys (171%) and spleen (156%) were significantly increased compared with IGF-I-treated mice. The effect of IGFBP-1 plus IGF-I on kidney weight was not significantly greater than the effect of IGFBP-1 alone. Western ligand blotting showed induction of the IGFBP-3 doublet as well as IGFBPs with molecular masses of 24 kDa, most probably IGFBP-4, by human GH, IGF-I alone, and IGF-I in combination with IGFBP-1. Our data show that coadministration of IGFBP-1 inhibits IGF-I-induced body growth of GH-deficient mice but significantly stimulates the growth promoting effects of IGF-I on the kidneys and the spleen. These data warrant further investigation because differences in concentrations of IGFBP-1 occurring in vivo may influence IGF-I-induced anabolic processes.

Assay of a seric human hexapeptide (HWESAS) using a monoclonal antibody and ELISA

Human serum contains low-molecular-weight growth factors potentiating some in vitro biological effects of IGF-I and IGF-II and recently two peptides were mainly identified: HWESAS and WGHE. In order to determine seric HWESAS concentration, a specific monoclonal antibody against HWESAS was prepared. Its specificity was studied by inhibition tests: this antibody cross-reacts with Y-HWESAS, Cys-HWESAS. It does not react with HWESAS when its COOH is blocked, or with HWE, WGHE and tryptophan or with C3f (SSKITHRIHWESASLLR) which is a fragment of human complement containing HWESAS motif. Its affinity was measured by non competitive enzyme immunoassay (3.89+/-2.44.10(8) M(-1)). Then, this antibody was used in enzyme-linked immunosorbent assay (ELISA) and the preliminary assays were performed to detect HWESAS in serum. In contrast to healthy subjects, patients with chronic renal failure exhibited undetectable concentration of hexapeptide while after successful renal transplantation values increased to reach levels found in healthy subjects and varying according to post-operative evolution. These data are a strong hint that the kidney plays an important role in the production of this hexapeptide and underly the clinical interest of HWESAS detection in renal pathology.

IGF-I but not the IGF-I variant long R(3)IGF-I increases serum IGFBP-3 in adolescent monkeys

Previous work in rhesus monkeys has shown that both acute or chronic subcutaneous (s.c.) administration of insulin-like growth factor (IGF)-I elevates serum concentrations of IGF binding protein (IGFBP)-3. In order to determine whether an analog of IGF-I, which has a reduced affinity for the IGFBPs, has similar effects, a series of studies using adolescent female rhesus monkeys were conducted. In the first study, an s.c. injection of IGF-I (110 mg/kg;n = 6) significantly elevated serum IGFBP-3 concentrations through 7 h following treatment. In contrast, serum IGFBP-3 decreased throughout the day following an injection of Long R(3)IGF-I (110 mg/kg, s.c., n = 5). However, this decrease was not due to the analog treatment as serum IGFBP-3 also declined in a similar fashion in untreated females (n = 5) sampled on the same schedule. Serum GH levels were acutely suppressed by both IGFs but were not altered in untreated females. In the second study, serum IGFBP-3 were compared between untreated control females (n = 6) and females treated continuously by s.c. infusion with either Long R(3)IGF-I (120 mg/kg/day, s.c.;n = 5) or IGF-I (120 mg/kg/day, s.c.;n = 5) or IGF-I s.c.;n = 4). Serum IGFBP-3 was consistently elevated by IGF-I infusion, whereas levels in analog-treated monkeys were similar to those in control females. Although acute or chronic administration of Long R(3)IGF-I did not elevate serum IGFBP-3, chronic administration of the analog did not block the acute facilitating effects of IGF-I on serum IGFBP-3. The increase in serum IGFBP-3 following an acute injection of IGF-I (110 mg/kg, s.c.) was not significantly different between untreated females and females receiving a constant s.c. infusion of Long R(3)IGF-I. These data indicate either acutely or chronically administered IGF-I but not its analog Long R(3)IGF-I can elevate serum concentrations of IGFBP-3. Although the analog fails to increase serum IGFBP-3, it does not block the facilitating effects of IGF-I on concentrations of this IGFBP. Taken together, these data suggest that the increase in serum IGFBP-3 by exogenous IGF-I may not be a receptor mediated event but may be the result of IGF-I binding to IGFBP-3 and forming the binary and ternary complex, slowing IGFBP-3 degradation.

The growth hormone axis, feeding, and central allocative regulation: lessons from giant transgenic growth hormone mice

Lifetime consumption rates of male transgenic growth hormone (GH) mice and normal controls were measured on either a 38% protein diet (HP), the standard rodent diet (STD) (23.5% protein), or the standard diet supplemented with a free choice of sucrose (CARB). On STD, daily intake of normal mice increased little at sizes greater than 20 g, but larger transgenic mice ate progressively more. Both kinds of mice showed declining daily mass-specific consumption with increasing age. Transgenic mice consistently ate 13.3% less food than normal mice on a mass-specific basis across all ages. On the self-selective CARB diet, normal mice exhibited increasing age-specific daily consumption, whereas transgenic mice exhibited a trend towards age-related decline in mass-specific feeding that proved significant on the basis of body mass. Transgenic mice ingested more sucrose than standard chow and this did not vary with age. In contrast, normal mice ate less sucrose than chow and chose a declining proportion of sucrose with age. Transgenic and normal mice showed a unitary relationship of daily intake of HP in relation to body mass, resulting in constant mass-specific feeding across all ages. Transgenic GH animals, including livestock, show numerous defects that we have attributed to relative energetic stress associated with excessive allocation to lean growth. This is exacerbated by failure to offset increased demands of growth by increasing mass-specific feeding. Results presented here document altered feeding regulation in transgenic GH mice and suggest underlying mechanisms.

Effects of lifestyle and body composition on the ovary

Reduction of metabolic fuel availability below the critical level by food restriction or increased expenditure is appropriately accompanied by activations of multiple neuroendocrine-metabolic changes resulting in anovulation and amenorrhea, an important device for endogenous hypothalamic contraception. This reproductive strategy in women is required because of the enormous nutritional demand for reproductive success.

Voluntary exercise training enhances glucose transport in muscle stimulated by insulin-like growth factor I

Skeletal muscle glucose transport can be regulated by hormonal factors such as insulin and insulin-like growth factor I (IGF-I). Although it is well established that exercise training increases insulin action on muscle glucose transport, it is currently unknown whether exercise training leads to an enhancement of IGF-I-stimulated glucose transport in skeletal muscle. Therefore, we measured glucose transport activity [by using 2-deoxy-D-glucose glucose (2-DG) uptake] in the isolated rat epitrochlearis muscle stimulated by submaximally and maximally effective concentrations of insulin (0.2 and 13.3 nM) or IGF-I (5 and 50 nM) after 1, 2, and 3 wk of voluntary wheel running (WR). After 1 wk of WR, both submaximal and maximal insulin-stimulated 2-DG uptake rates were significantly (P < 0.05) enhanced (43 and 31%) compared with those of sedentary controls, and these variables were further increased after 2 (86 and 57%) and 3 wk (71 and 70%) of WR. Submaximal and maximal IGF-I-stimulated 2-DG uptake rates were significantly enhanced after 1 wk of WR (82 and 61%, and these increases did not expand substantially after 2 (71 and 58%) and 3 wk (96 and 70%) of WR. This enhancement of hormone-stimulated 2-DG uptake in WR muscles preceded any alteration in glucose transporter (GLUT-4) protein level, which increased only after 2 (24%) and 3 wk (54%) of WR. Increases in GLUT-4 protein were significantly correlated (r = 0.844) with increases in citrate synthase. These results indicate that exercise training can enhance both insulin-stimulated and IGF-I-stimulated muscle glucose transport activity and that these improvements can develop without an increase in GLUT-4 protein.

The estrogen connection: the etiological relationship between diabetes, cancer, rheumatoid arthritis and psychiatric disorders

For some considerable time, there has been a growing awareness that defective essential fatty acid metabolism plays a causal role in the pathogenesis of both schizophrenia and non-insulin-dependent diabetes mellitus (NIDDM) but the influence of defective essential fatty acid metabolism in the pathogenesis of rheumatoid arthritis and cancer is less well appreciated. An EFA deficiency, or defective EFA metabolism, negatively influences prostaglandin synthesis and glucose regulation and transport. Moreover, defective EFA metabolism negatively influences estrogen availability which contributes to the observed gender bias some of these illnesses manifest. While fluctuations of estrogen are known to contribute to the pathogenesis of these conditions, so also do fluctuations of IGF-II and there is some suggestion that IGF-II and insulin may well be inversely regulated. In addition, insulin-dependent diabetes mellitus (IDDM), rheumatoid arthritis, and schizophrenia are thought to be autoimmune disorders, while cancer is associated with immune system failure. Consequently, this paper aims to examine the pathophysiological similarities and differences between mental illness, diabetes, rheumatoid arthritis and cancer in respect of which the causal relationship that obtains between essential fatty acids, estrogen, IGF-II, glucose regulation and autoimmunity will be addressed.

Alterations in hepatic production and peripheral clearance of IGF-I after endotoxin

Lipopolysaccharide (LPS) produces a rapid and sustained reduction in the circulating concentration of insulin-like growth factor I (IGF-I), which may be responsible, in part, for the alterations in protein metabolism observed in these animals. The purpose of the present study was to determine whether this drop was due to a decreased hepatic production of IGF-I and/or an increased clearance of the peptide from the blood. Four hours after intravenous injection of LPS the plasma IGF-I concentration was decreased 50%. IGF-I release by in situ perfused livers from control rats was constant throughout the 60-min perfusion period and averaged 111 +/- 3 ng/min. In contrast, hepatic IGF-I output was decreased 46% by in vivo LPS. In contrast, livers from LPS-injected rats released more IGF binding proteins-1, -2 and -4 than did control livers. Hepatic cell isolation indicated that LPS decreased the IGF-I content in Kupffer and parenchymal cells, but not endothelial cells, by approximately 45%. Pharmacokinetic analysis of blood 125I-IGF-I decay curves indicated that the half-life for whole body clearance of 125I-IGF-I from the circulation was not altered by LPS. However, LPS increased 125I-IGF-I uptake by spleen, liver, lung, and kidney while decreasing uptake by the pancreas and gastrointestinal tract. These results indicate that the LPS-induced decrease in blood IGF-I concentration is primarily due to a reduction in hepatic production, not a change in whole body peptide clearance, and that a decreased production by both parenchymal and Kupffer cells contributes to this alteration.