Low circulating levels of insulin-like growth factor binding protein-1 (IGFBP-1) are closely associated with the presence of macrovascular disease and hypertension in type 2 diabetes

Low insulin-like growth factor-II levels predict weight gain in normal weight subjects with type 2 diabetes

PURPOSE

Insulin-like growth factor (IGF)-I and IGF-II are important in the regulation of metabolism and growth. We previously reported in normoglycemic individuals of normal weight that low circulating IGF-II predicts future weight gain. We subsequently investigated whether such relationships persisted in circumstances of type 2 diabetes.

METHODS

In 224 subjects with type 2 diabetes we assessed the association between baseline IGF-II levels and risk of weight gain (>2.0 kg) at the 5-year follow-up.

RESULTS

At follow-up, 90 participants (40.2%) gained more than 2.0 kg in body weight. For subjects (body mass index <26) at baseline, mean IGF-II levels were significantly lower in those who gained more than 2 kg in weight than in subjects of stable weight, 454 ng/mL (95% confidence interval 349-559) versus 620 ng/mL (534-705) (F=7.4, P=.01). For this subgroup low circulating IGF-II at baseline strongly correlated with weight gain (Spearman rho=-0.52, P <.001). With increasing weight, the relationship no longer prevailed. Logistic regression showed that for body mass index less than 26, individuals at baseline for each 100 ng/mL increase in baseline IGF-II there was a 47% decreased risk of gaining 2.0 kg or more in weight. Adjustment for treatment group did not materially alter this relationship. There was no difference in baseline IGF-II by treatment group. There was no difference between the group with weight gain and the group with stable weight in those who additionally received insulin or sulfonylurea treatment in the 5 years between the baseline visit and the follow-up.

CONCLUSIONS

In subjects of normal weight with type 2 diabetes, baseline IGF-II concentration is inversely related to future weight gain, independent of treatment effect, strengthening the putative role for IGF-II in regulating fat mass. We propose that IGF-II measurement has potential utility in this group for targeting such individuals for early intervention.

The IGF-I system and the renal and haemodynamic effects of losartan in normotensive patients with type 2 diabetes mellitus: a randomized clinical trial

OBJECTIVE

Losartan has been shown to protect the diabetic kidney, at least partly independent of changes in blood pressure. Imbalances in the IGF-I system are associated with the development of diabetic nephropathy. We investigated whether renal as well as haemodynamic effects of losartan are associated with changes in the IGF-I system in normotensive patients with type 2 diabetes mellitus (T2DM).

DESIGN AND PATIENTS

This randomized, double-blind placebo-controlled clinical trial involved 74 normotensive patients with T2DM and microalbuminuria. Thirty-eight patients were assigned to receive losartan and 36 patients were assigned to receive placebo for 10 weeks.

MEASUREMENTS

Serum levels of total and free IGF-I, IGFBP-3, creatinine and haemoglobin A(1c) (HbA(1c)), as well as urinary albumin excretion rate, creatinine clearance and blood pressure, were measured prior to the start of treatment and after 10 weeks of treatment.

RESULTS

At baseline, serum levels of IGFBP-3 were elevated and serum levels of free IGF-I were reduced. Losartan tended to reduce IGFBP-3 levels and to increase free IGF-I levels, although neither effect was statistically significant. These effects were more pronounced in a subanalysis of 18 losartan-treated patients with stable metabolic parameters, with a decrease in IGFBP-3 from 133.2 to 122.6 nmol/l (P=0.006) and an increase in free IGF-I levels by 8% (ns). Serum levels of total IGF-I were unaffected. The change in IGFBP-3 was inversely correlated to the change in creatinine clearance (r=-0.4; P=0.02). Total and free IGF-I inversely correlated to systolic blood pressure (r= -0.46; P=0.007 and r=0.26; P=0.14 respectively). Furthermore, changes in total IGF-I and IGFBP-3 correlated to changes in serum creatinine levels in the metabolically stable patients (r=0.58, P=0.02 and r=0.6, P=0.01, respectively). Changes in the IGF-I system were unrelated to a reduction in microalbuminuria associated with losartan.

CONCLUSIONS

Losartan lowered the elevated levels of IGFBP-3, although only significantly in the metabolically stable patients. A tendency towards an increase in free IGF-I levels was also observed, but this change was small and not statistically significant. These changes were not related to reduction in microalbuminuria, but might contribute to effects of losartan on creatinine clearance and blood pressure of losartan in normotensive patients with T2DM.

Polymorphisms in IGF-binding protein 1 are associated with impaired renal function in type 2 diabetes

The dysregulation of the IGF system has been implicated in the pathogenesis of obesity, diabetes, and diabetes complications such as nephropathy, but little is known about the genomics of the IGF system in health and disease. We genotyped 13 single nucleotide polymorphisms (SNPs) in IGFBP1 gene in 732 representative type 2 diabetic patients from the Salford Diabetes Register. Of the 13 SNPs, 8 were polymorphic and 7 of those had minor allele frequencies >0.1, one of which was in the gene promoter and one of which was nonsynonymous in exon 4. The minor alleles of these SNPs and two others were associated with a reduced prevalence of diabetic nephropathy. Haplotype analysis revealed that 97% of the genetic variation for IGFBP1 in the population sample could be accounted for using two of the "reno-protective" SNPs, with other SNPs adding little extra information. One of these two SNPs was the nonsynonymous mutation in exon 4, lying close to the integrin-binding RGD motif, which is thought to affect tissue delivery of IGF-I by IGF-binding protein 1 (IGFBP-1), possibly suggesting a "reno-protective" effect via altered IGFBP-1 binding. In conclusion, we have described the first genomic markers to be associated with diabetic microvascular complications within the human IGFBP1 gene.

Marked differences in the IGF system that are associated with migration in comparable populations of Gujaratis living in Sandwell, UK, and Gujarat, India

AIMS/HYPOTHESES

We previously reported independent links between the IGF system and the development of impaired glucose tolerance and cardiovascular risk. This study tests the hypothesis that the lifestyle change which accompanies population migration, with attendant increases in cardiovascular risk, is reflected by changes in the IGF system.

MATERIALS AND METHODS

We compared a specific Gujarati community in Sandwell, UK (n=205), with people still resident in the same villages of origin near Navsari, India (n=246). We performed anthropometry and measured fasting plasma insulin, IGF-I, insulin-like growth factor binding protein (IGFBP)-1 and IGFBP-3.

RESULTS

Daily calorie intake, BMI and WHR were significantly higher in UK Gujaratis than in Indian Gujaratis. IGFBP-1 was significantly lower in UK migrants (mean 29.5 [95% CI 25.9-33.0] vs 56.5 [50.6-62.5] microg/l; F=48.4, p<0.001). Conversely, fasting insulin, IGFBP-3 and IGF-I were all higher in UK Gujaratis (mean IGF-I 145.9 [138.1-153.6]ng/ml in UK Gujaratis and 100.9 [94.6-107.3] ng/ml in Navsari Gujaratis; F=76.6, p<0.001). These differences were still apparent when adjustment was made for BMI by location for IGF-I (F=57.4, p<0.001) and IGFBP-3 (F=5.7, p=0.02), but were no longer apparent for IGFBP-1 and insulin. At the population level, the decrease in IGFBP-1 for a given increase in insulin was significantly smaller in UK Gujaratis, suggesting greater hepatic insulin resistance in this group.

CONCLUSIONS/INTERPRETATION

Environmental factors have profound effects on circulating IGF system components and on the relationship between IGFBP-1, IGF-I and related metabolic variables. This may have long-term implications for the development of worsening glucose tolerance and cardiovascular disease.

Gender differences in the relation of insulin-like growth factor binding protein-1 to cardiovascular risk factors: a population-based study

OBJECTIVE

A possible involvement of insulin-like growth factor-I (IGF-I) and its binding protein IGFBP-1 in the pathogenesis of cardiovascular disorder has been suggested. However, few publications have addressed the gender differences in cardiovascular risk factors in relation to the IGF/IGFBP system. The aim of the present study was to study gender differences in the relationship between fasting serum levels of IGFBP-1 and cardiovascular risk factors in a normal population of men and women.

DESIGN

Cross-sectional study. Patients A normal population of 273 men and women aged 20-74 years.

MEASUREMENTS

A medical examination was performed and blood drawn in the morning after subjects had been fasting overnight. Before the examination, they were asked to fill out a questionnaire concerning lifestyle and psychosocial factors.

RESULTS

Fasting IGFBP-1 was lower in men than in women and was positively correlated to age in men but not in women. The men had in general a more disadvantageous cardiovascular risk profile than women, with several indicators of the metabolic syndrome: higher blood pressure and higher serum levels of total cholesterol, triglycerides, low density lipoprotein cholesterol (LDL-C), plasma-glucose and insulin, as well as lower IGFBP-1. Women had lower physical activity, lower consumption of alcohol, and lower values on indicators of psychosocial and mental health but had a healthier diet. Our findings indicate that low circulating levels of IGFBP-1 are associated with the well-known risk factors of cardiovascular disease; however, the association showed a different pattern for men and women. In men we found a negative association with body mass index (BMI), insulin resistance and diastolic blood pressure, and a positive association with SHBG, cortisol and testosterone. For women low IGFBP-1 appears in negative associations with BMI, waist-hip ratio (WHR), insulin resistance and testosterone, and in positive associations with SHBG and cortisol. Significant gender differences in the correlation with IGFBP-1 are seen for testosterone, cortisol, SHBG, WHR and oestradiol. For HDL-C and diastolic blood pressure the gender difference in correlation was at the limit of significance (P < 0.10).

CONCLUSION

Low circulating levels of IGFBP-1 are associated with the well-known risk factors of cardiovascular disease; however, the association showed a different pattern for men and women. The most marked gender differences in the correlation with IGFBP-1 are seen for testosterone, cortisol, SHBG, WHR, oestradiol, HDL-C and diastolic blood pressure. Our study emphasizes the importance of separate analyses for men and women. The results presented are a step towards gaining a better understanding of the gender differences in cardiovascular disease and in the regulation of IGFBP-1, though further prospective studies are needed.

Integrated Microfluidic Device for Mass Spectrometry-Based Proteomics and Its Application to Biomarker Discovery Programs

The present investigation describes the analytical performances of a microfluidic device comprising an enrichment column, a reversed-phase separation channel, and a nanoelectrospray emitter embedded altogether in polyimide layers. This configuration minimizes transfer lines and connections and reduces postcolumn peak broadening and dead volumes. This compact and versatile modular nanoLC-chip system was interfaced to both ion trap and time-of-flight mass spectrometers, and its analytical potentials were evaluated in the context of proteomics applications. The figures of merit of this system in terms of peak capacity, reproducibility, sensitivity, and linear dynamic range of peptide detection were determined using tryptic digests of complex protein extracts including albumin- and immunoglobulin-depleted rat plasma samples. The analysis of peak profiles for more than 600 peptide ions reproducibly detected across replicate nanoLC-chip-MS runs (n = 10) indicated that this system provided good reproducibility of retention time and peak intensity with RSD values of less than 0.5 and 9.1%, respectively. Variation in peptide abundance as low as 2-fold changes was identified for spiked tryptic digests present at levels of 2-5 fmol in plasma samples. Sensitivity measurements were performed on dilution series of protein digests spiked into rat plasma samples and provided a detection limit of 1-5 fmol. The modular concept of the microfluidic systems also facilitated the integration of two-dimensional chromatography (strong cation exchange/C18) thereby increasing the sample loading and selectivity of the nanoLC-chip-MS system. The application of this integrated device was evaluated for complex rat plasma samples to compare the number of protein identifications obtained using one- and two-dimensional nanoLC-chip-MS/MS.

Is premature adrenarche a risk factor for atherogenesis?

BACKGROUND

The aim of this study was to evaluate serum lipids and atherosclerosis risk in children with premature adrenarche (PA) in comparison with age-matched controls.

METHODS

Lipid profile, glucose, insulin, and insulin-like growth factor binding protein-1 (IGFBP-1) levels were studied in 24 girls with premature adrenarche and 13 healthy age-matched controls after overnight fasting.

RESULTS

The bone age, weight and body mass index were higher in the premature adrenarche group than the control group. Systolic, diastolic and mean arterial blood pressure of patients were higher than controls. The mean total cholesterol (TC), low-density lipoprotein-cholesterol (LDL-C), very low-density lipoprotein-cholesterol (VLDL-C), TC/high-density lipoprotein-cholesterol (HDL-C) and LDL-C/HDL-C ratio, and atherogenic index were significantly higher in the premature adrenarche group compared to the control group. There was no significant difference in the levels of apolipoprotein A1, apolipoprotein B and lipoprotein (a) in both groups. In the premature adrenarche group there were inverse correlations between the levels of IGFBP-1 and TC/HDL-C (rho, -0.54; P, 0.011), and LDL-C/HDL-C (rho, -0.50; P < 0.05) and atherogenic index (AI; rho, -0.54; P < 0.05). Dehydroepiandrosterone sulfate levels of the patients was negatively correlated with AI and TC/HDL-C (rho, -0.0503, P < 0.05).

CONCLUSIONS

Girls with premature adrenarche should be investigated for serum lipids, and atherogenic risk criteria should be assessed periodically in the follow up of patients with PA, as PA seems to be a risk factor for future atherosclerosis.

The impact of abnormalities in IGF and inflammatory systems on the metabolic syndrome

OBJECTIVE

Low plasma levels of IGF-I, particularly when coupled with low levels of the potentially inhibitory IGF binding protein (IGFBP)-1 and higher levels of C-reactive protein (CRP), have been implicated in the pathogenesis of metabolic syndrome X and cardiovascular disease. We report the relative contributions of IGFBP-1 and CRP to the occurrence of the metabolic syndrome in a healthy population cohort to establish the extent to which these factors may contribute to subsequent risk of cardiovascular disease.

RESEARCH DESIGN AND METHODS

The volunteers in the study were all participants in the Ely study, a continuing population-based cohort in Ely, Cambridgeshire, U.K. Of 839 individuals studied, 154 (18.4%) fulfilled criteria for the metabolic syndrome.

RESULTS

Subjects with the metabolic syndrome had lower IGFBP-1 (14.4 microg/l [95% CI 12.9-16.0] vs. 25.4 [24.1-26.7], P < 0.001) and higher CRP (1.9 mg/l [1.6-2.2] vs. 1.0 [0.9-1.1], P < 0.001). Logistic regression, adjusted for age, sex, fasting insulin, and IGF-I, demonstrated a striking 14-fold increased risk for the metabolic syndrome (odds ratio 14.1 [4.1-48.4], P < 0.001) in individuals with a CRP value in the highest tertile and IGFBP-1 levels below the median.

CONCLUSIONS

The combination of a high CRP concentration coupled with a low IGFBP-1 results in a dramatic increase in an individual's risk of having the metabolic syndrome. Further elucidation of the biological processes linking the IGF and inflammatory systems may allow the identification of novel therapeutic targets for cardiovascular risk reduction.

Screening and cloning of genes differential expressed in HepG2 cells treated with bicyclol by suppression subtractive hybridization

AIM: To construct a subtractive cDNA library of genes differential expressed in human hepatocarcinoma cell line HepG2 cells treated with bicyclol using suppression subtractive hybridization (SSH) technique and to clone genes associated with its regulation effects.

METHODS: The mRNA was isolated from HepG2 cells treated with bicyclol and dimathyl sulfoxide (DMSO), respectively, and then cDNA was synthesized. After restriction enzyme RsaI digestion, small sizes cDNA were obtained. Tester cDNA was subdivided into two portions and each was ligated with different cDNA adaptor. After tester cDNA was hybridized with driver cDNA twice and underwent nested polymerase chain reaction (PCR) twice, the DNA fragment was subcloned into T/A plasmid vectors to set up the subtractive cDNA library. Amplification of the library was carried out with E. coli strain JM109. The cDNA was sequenced and analyzed in GenBank with Blast search after colony PCR.

RESULTS: The subtractive cDNA library of genes differentially expressed in HepG2 cells treated with bicyclol was constructed successfully. The amplified library contained 46 positive clones. Colony PCR showed that these clones contained 200-1 000 bp inserts. Thirty clones were analyzed by sequencing and bioinformatics. fourteen known genes were obtained.

CONCLUSION: A subtractive cDNA library of genes differential expressed in HepG2 cells treated with bicyclol using SSH technique is constructed successfully, which brings some new clues for studying the regulation mechanism of bicyclol in vivo.

Expression, regulation, and function of IGF-1, IGF-1R, and IGF-1 binding proteins in blood vessels

The vascular insulin-like growth factor (IGF)-1 system includes the IGFs, the IGF-1 receptor (IGF-1R), and multiple binding proteins. This growth factor system exerts multiple physiologic effects on the vasculature through both endocrine and autocrine/paracrine mechanisms. The effects of IGF-1 are mediated principally through the IGF-1R but are modulated by complex interactions with multiple IGF binding proteins that themselves are regulated by phosphorylation, proteolysis, polymerization, and cell or matrix association. During the last decade, a significant body of evidence has accumulated, indicating that expression of the components of the IGF system are regulated by multiple factors, including growth factors, cytokines, lipoproteins, reactive oxygen species, and hemodynamic forces. In addition, cross-talk between the IGF system and other growth factors and integrin receptors has been demonstrated. There is accumulating evidence of a role for IGF-1 in multiple vascular pathologies, including atherosclerosis, hypertension, restenosis, angiogenesis, and diabetic vascular disease. This review will discuss the regulation of expression of IGF-1, IGF-1R, and IGF binding proteins in the vasculature and summarize evidence implicating involvement of this system in vascular diseases.

Vascular endothelial function and blood pressure homeostasis in mice overexpressing IGF binding protein-1

IGFs and their binding proteins (IGFBPs) play a significant role in metabolic regulation, and there is growing evidence that they also exert important vascular effects. IGFBP-1 contributes to glucose counterregulation, and observational studies demonstrate an inverse association between circulating IGFBP-1 levels and cardiovascular risk factors. Furthermore, IGFBP-1 levels are lower in subjects with overt macrovascular disease. We therefore hypothesized that IGFBP-1 exerts potentially beneficial effects, either directly or indirectly, on blood pressure regulation and vascular function. We tested this hypothesis using a unique transgenic mouse, which overexpresses human IGFBP-1, and explored the effect of this protein on metabolic, blood pressure, and vascular homeostasis. IGFBP-1-overexpressing mice exhibited postprandial hyperinsulinemia with preservation of glucocompetence and insulin sensitivity. Blood pressure was unchanged in the fasting state but was significantly lower in transgenic mice after a carbohydrate load. Aortic rings from IGFBP-1-overexpressing mice were hypocontractile in response to vasoconstrictors, and relaxation responses were unimpaired. Basal nitric oxide production was increased and endothelial nitric oxide synthase mRNA expression upregulated in aortae of these mice. Our data suggest that IGFBP-1 plays an important and potentially beneficial role in regulating metabolic and vascular homeostasis.