IGF-binding protein 1 and abdominal obesity in the development of type 2 diabetes in women

Atorvastatin administration is associated with dose-related changes in IGF bioavailability

OBJECTIVE

IGF levels, their binding proteins (IGFBPs) and high-dose statin therapy have been linked to the development of diabetes. We aimed to identify whether atorvastatin caused dose-related changes in IGF proteins.

DESIGN AND METHODS

We measured IGF1, IGF2, IGFBP1 and IGFBP3 concentrations at baseline, 6 and 12 months in Protection Against Nephropathy in Diabetes with Atorvastatin trial participants with type 2 diabetes randomised to 10 mg (n=59) vs 80 mg (n=60) of atorvastatin (n=119; mean (S.D.): age 64 (10) years; 83% male; HbA1c 61 (10) mmol/mol; blood pressure 131/73 mmHg).

RESULTS

Atorvastatin was associated with overall reductions in circulating IGF1, IGF2 and IGFBP3 concentrations (P<0.05 for all changes). The adjusted mean (95% CI) between-group differences that indicate dose-related changes in IGF proteins were not significant for IGF1: -3 (-21 to 14) ng/ml; IGF2: -23 (-65 to 18) ng/ml and IGFBP3: -0.34 (-0.71 to 0.03) μg/ml, negative values indicating numerically greater lowering with high dose. The IGFBP1 concentration did not change with atorvastatin therapy overall but the adjusted mean (95% CI) between-group difference indicating a dose-related change in log IGFBP1 was highly significant -0.41 (-0.69 to 0.13, P=0.004).

CONCLUSION

IGF1, IGF2 and IGFBP3 concentrations decreased following atorvastatin therapy. A differential effect of low- vs high-dose atorvastatin on IGFBP1 concentrations was observed with likely implications for IGF bioavailability. The dose-related differential impact of atorvastatin treatment on concentration of IGF proteins merits investigation as a mechanism to explain the worsening of glucose tolerance with statin therapy.

Leptin may enhance hepatic insulin sensitivity in children and women born small for gestational age

OBJECTIVE

Children born small for gestational age (SGA) are at risk for developing type 2 diabetes. Lipodystrophy leads to early type 2 diabetes and leptin reverses the metabolic consequences of the disease. Low IGF-binding protein 1 (IGFBP1) can predict the development of type 2 diabetes. The aim of this study was to determine leptin, insulin, and IGFBP1 in children and adult women born preterm or SGA to evaluate the role of leptin as a compensatory mechanism in insulin resistance development.

METHODS

Seventy-six children (8.5-10 years, 41 girls and 35 boys) and 45 women (23-30 years) were studied. The children comprised subjects born appropriate for gestational age (<30 gestational weeks) (n=22), born SGA at term (n=23), and full-term normal-weight controls (n=31). Among the women, the corresponding figures were, n=10, n=18, and n=17 respectively. Fasting levels of IGFBP1, leptin, insulin, and IGF1 were determined and total adiponectin only in women.

RESULTS

In girls and women, term SGA subjects had higher leptin levels in relation to BMI SDS (P=0.042 and P=0.03 respectively). More than half of IGFBP1 variability was explained by leptin and insulin in children. In term SGA women, IGFBP1 level was lower compared with controls (P=0.012) and the regression line of IGFBP1 on insulin was suppressed below -1 s.d. of a reference material.

CONCLUSION

Leptin levels were elevated in term SGA girls and women, in particular in adult women, but not found in preterm girls and women. IGFBP1 was lower in term SGA women. In children, leptin and insulin were strong suppressors of IGFBP1. We speculate that higher leptin levels could be a protective event to enhance hepatic insulin sensitivity.

Effect of Ghrelin on Hepatic IGF-Binding Protein-1 Production

Ghrelin plays key roles in energy homeostasis by central and peripheral actions that include effects on insulin signalling pathways in liver. Insulin is an important inhibitor of production by hepatocytes of insulin-like growth factor-binding protein-1 (IGFBP-1) which has an endocrine role to inhibit IGF availability. The effects of ghrelin, insulin, an AMPK activator, and an AMPK inhibitor on IGFBP-1 secretion were studied in H4-II-E rat liver cells. Ghrelin (100 nM) blocked the inhibitory effect of a maximally effective concentration of insulin (10 ng/mL) on IGFBP-1 secretion during a 5 h incubation period (P < 0.001) in the absence and presence of an AMPK inhibitor. Ghrelin, alone, had no effect on IGFBP-1 production, but enhanced secretion independently of insulin under conditions of AMPK activation (P < 0.001). In conclusion, IGFBP-1 is identified as a novel target of ghrelin action in liver that may contribute to its metabolic effects in obesity.

Differences in insulin resistance markers between children born small for gestational age or born preterm appropriate for gestational age

AIM

To evaluate the impact of prenatal or postnatal compromised environment on glucose homoeostasis in children born preterm and appropriate for gestational age or small for gestational age (SGA) at term.

METHOD

Seventy-seven children (median 9.9 years, range 8.5-10) born at Karolinska Hospital were allocated to three groups: 21 subjects born before 30 weeks of gestational age (preterm), 26 SGA at term and 30 at term with appropriate birth weight (control). Anthropometric measurements were taken, and fasting blood samples for haemoglobin A1c, glucose, insulin, IGFBP-1, IGF-1 and lipid profile were taken. Glucose, insulin and IGFBP-1 samples were taken at 0, 30 and 120 min during an oral glucose tolerance test (OGTT).

RESULTS

Subjects born preterm or SGA were shorter and thinner compared with Controls. After adjustment for body mass index (BMI), the SGA group had higher basal insulin levels (p = 0.029), higher homoeostasis model assessment-insulin resistance (p = 0.012) and lower whole-body insulin sensitivity index (p = 0.007) than Controls. IGFBP-1 decrease during OGTT was attenuated in the Preterm group compared with the Control (p = 0.045) and SGA groups (p = 0.007).

CONCLUSION

The higher fasting insulin level in the SGA children, adjusted for BMI, could indicate peripheral insulin resistance. Preterm born children had reduced suppression of IGFBP-1 during OGTT, suggesting hepatic insulin resistance.

Beyond waist circumference in an adult male population of Southern Italy: Is there any role for subscapular skinfold thickness in the relationship between insulin-like growth factor-I system and metabolic parameters?

BACKGROUND

Apart from waist circumference, other adiposity measures, such as subscapular skin fold (SST), arouse growing interest due to their relationship to metabolic complications and cardiovascular risk. The IGF-I system is deregulated in obese subjects in proportion to their degree of visceral adiposity.

AIM

To examine the association among IGF-I, IGF-binding protein (BP)-1 and -3 levels and different measures of adiposity in a sample of adult male population in Southern Italy.

MATERIALS AND METHODS

A complete database for this analysis was available for 229 (age range 50-82 yr) participating at 2002-2004 Olivetti Heart Study follow-up.

RESULTS

After adjustment for age, IGF-I was inversely associated with body mass index (BMI) and waist circumference (p<0.05). IGFBP-1 was inversely associated with BMI, waist circumference, SST, homeostasis model assessment (HOMA) index, fat mass. HOMA index, age, and SST significantly predicted the IGFBP-1 plasma levels, with 24% of IGFBP-1 variability explained at a linear regression analysis.

CONCLUSIONS

IGFBP-1 inversely correlated to adiposity and HOMA index. Among adiposity indexes, SST was the best predictor of IGFBP-1 levels. The evaluation of some components of the IGF system, and simple measures of body adiposity, such as SST, may represent a further tool to better evidence phenotype profiles associated to the pathogenetic mechanism of cardiovascular risk factor clustering in male adults.

Size at birth and insulin-like growth factor-I and its binding protein-1 among infants of diabetic mothers

OBJECTIVE

to estimate the association between intrauterine fetal growth, evaluated by anthropometric measurements, and biochemical growth factors; IGF-I and IGBP-1 among IDMs.

METHODS

Cross-sectional study carried out on 69 full term IDMs who was admitted to neonatal intensive care units, Ain Shams University Hospitals. Clinical examination including anthropometric measurements; birth weight, length, head circumference, mid-arm circumference, skinfold thickness at triceps and subscapular areas and placental weight. Laboratory investigations included maternal HbA(1c) and cord blood IGF-I and IGBP-1. They were classified into three groups: 20 small for gestational age (SGA), 25 appropriate for gestational age (AGA) and 24 large for gestational age (LGA).

RESULTS

Most of SGA neonates were born to mothers with type I diabetes, while most of AGA and LGA were born to mothers with gestational diabetes. According to maternal HbA(1c), SGA and LGA neonates were born to metabolically uncontrolled mothers while AGA neonates were born to well-controlled diabetic mothers. Anthropometric measurements had significant positive correlations with IGF-I and negative correlations with IGFBP-1.

CONCLUSIONS

Good control of diabetes during pregnancy is essential to improve fetal growth. There is an opposing effect of cord blood IGF-I and IGFBP-1 on anthropometric measurements.

Insulin-like growth factor axis and risk of type 2 diabetes in women

IGF-I shares structural homology and in vitro metabolic activity with insulin. Laboratory models suggest that IGF-I and its binding proteins IGFBP-1 and IGFBP-2 have potentially beneficial effects on diabetes risk, whereas IGFBP-3 may have adverse effects. We therefore conducted a prospective nested case-control investigation of incident diabetes (n = 742 case subjects matched 1:1 to control subjects) and its associations with IGF-axis protein levels in the Nurses' Health Study, a cohort of middle-aged women. The median time to diabetes was 9 years. Statistical analyses were adjusted for multiple risk factors, including insulin and C-reactive protein. Diabetes risk was fivefold lower among women with baseline IGFBP-2 levels in the top versus bottom quintile (odds ratio [OR](q5-q1) = 0.17 [95% CI 0.08-0.35]; P trend < 0.0001) and was also negatively associated with IGFBP-1 levels (OR(q5-q1) = 0.37 [0.18-0.73]; P trend = 0.0009). IGFBP-3 was positively associated with diabetes (OR(q5-q1) = 2.05 [1.20-3.51]; P trend = 0.002). Diabetes was not associated with total IGF-I levels, but free IGF-I and diabetes had a significant association that varied (P interaction = 0.003) by insulin levels above the median (OR(q5-q1) = 0.48 [0.26-0.90]; P trend = 0.0001) versus below the median (OR(q5-q1) = 2.52 [1.05-6.06]; P trend < 0.05). Thus, this prospective study found strong associations of incident diabetes with baseline levels of three IGFBPs and free IGF-I, consistent with hypotheses that the IGF axis might influence diabetes risk.

Low serum 25-hydroxyvitamin D level predicts progression to type 2 diabetes in individuals with prediabetes but not with normal glucose tolerance

AIMS/HYPOTHESIS

Vitamin D deficiency may increase the risk of type 2 diabetes. We therefore investigated whether serum concentrations of 25-hydroxyvitamin D [25(OH)D] would predict the development of prediabetes (impaired fasting glucose, impaired glucose tolerance or the two combined) and type 2 diabetes, either on their own or when combined with serum concentrations of IGF-1 or IGF-binding protein-1 (IGFBP-1), which may interact with 25(OH)D.

METHODS

At baseline, participants aged 35-56 years without known type 2 diabetes were examined using OGTTs, 25(OH)D and IGF peptide measurements, and anthropometric and lifestyle data. Participants who had prediabetes or type 2 diabetes at follow-up 8-10 years later were selected as cases; these were then age- and sex-matched to controls with normal glucose tolerance (NGT) at both baseline and follow-up, giving a total of 980 women and 1,398 men.

RESULTS

Men but not women in the highest quartile of 25(OH)D level had a decreased OR for developing type 2 diabetes after adjustment for confounders (OR 0.52, 95% CI 0.30, 0.90), an effect accounted for by individuals with prediabetes, but not with NGT, at baseline. In both sexes, progression from prediabetes to type 2 diabetes was reduced by about 25% per 10 nmol/l increase in 25(OH)D. A high IGFBP-1 value was a better predictor of a reduced risk of type 2 diabetes than high 25(OH)D for both sexes, whereas high IGF-1 concentrations predicted a decreased risk only in men.

CONCLUSIONS/INTERPRETATION

High serum 25(OH)D concentrations predict a reduced risk of type 2 diabetes in individuals with prediabetes, but not NGT. There were no significant interactions between 25(OH)D and IGFBP-1 or IGF-1 in terms of risk of diabetes. Our data suggest that vitamin D supplementation should be evaluated for the prevention of type 2 diabetes in prediabetic individuals.

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

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

The insulin-like growth factor system, metabolic syndrome, and cardiovascular disease risk

The metabolic syndrome is a combination of metabolic and clinical features that aggregate in individuals and increase cardiovascular disease (CVD) risk considerably. It is believed, although sometimes controversially, that the underlying basis for this syndrome is insulin resistance (IR) and accompanying compensatory hyperinsulinemia. Insulin and insulin-like growth factors (IGFs) have significant homology and interact with differing affinity with the same receptors. Therefore, their actions can be complementary, and this becomes particularly significant clinico-pathologically when their circulating levels are altered. This review of currently available information attempts to answer the following questions: (1) Is there any evidence for changes in the components of the IGF system in individuals with established CVD or with increased CVD risk as with the metabolic syndrome? (2) What are the underlying mechanisms for interactions, if any, between insulin and the IGF system, in the genesis of CVD? (3) Can knowledge of the pathophysiological changes in the IGF system observed in macrosomic newborn infants and growth hormone (GH)-treated children and adults explain some of the observations in relation to the IGF system and the metabolic syndrome? (4) Can the experimental and clinical evidence adduced from the foregoing be useful in designing novel therapies for the prevention, treatment, and assignment of prognosis in metabolic syndrome-associated disease, particularly ischemic heart disease? To answer these questions, we have performed a literature review using bibliographies from PubMed, Medline, and Google Scholar published within the last 10 years. We suggest that IGF-1 levels are reduced consistently in individuals with the metabolic syndrome and its components and in those with ischemic CVD. Such changes are also seen with GH deficiency in which these changes are partially reversible with GH treatment. Furthermore, changes are seen in levels and interactions of IGF-binding proteins in these disorders, and some of these changes appear to be independent of IGF-binding capability and could potentially impact on risk for the metabolic syndrome and CVD. The promising therapeutic implications of these observations are also discussed.

Insulin sensitivity and lipid profile in prolactinoma patients before and after normalization of prolactin by dopamine agonist therapy

Hyperprolactinemia has been associated with impaired metabolism, including insulin resistance. However, the metabolic effects of elevated prolactin (PRL) levels are not completely clarified. The aim of this study was to obtain more insights of metabolic consequences in hyperprolactinemia patients. Fourteen consecutive patients, eight women and six men, aged 39.7 (±13.7) years with prolactinomas (median PRL 72 [49-131] μg/L in women and 1,260 [123-9,600] μg/L in men) were included. Anthropometric data and metabolic values were studied before and after 2 and 6 months on DA agonists (Bromocriptine [5.7 (±3.9) mg/day, n = 13] or Cabergoline [0.5 mg/week, n = 1]). Euglycemic hyperinsulinemic clamps were studied in six patients before and after 6 months of treatment. PRL normalized in all patients. Anthropometric data changed only in males with a significant decrease of median body weight (95.6 [80.7-110.1] to 83.4 [77.8-99.1] kg, P = 0.046), waist circumference and fat percentage after 6 months. LDL cholesterol was positively correlated to PRL at diagnosis (r = 0.62, P = 0.025) and decreased within 2 months (3.4 [±0.9] to 2.9 [±0.6] mmol/L, P = 0.003). Insulin, IGFBP-1 and total adiponectin levels did not change. Insulin sensitivity tended to improve after 6 months; M-value from 5.7 (±1.8) to 7.8 (±2.6) mg/kg/min, P = 0.083 and per cent improvement in M-value was correlated to per cent reduction in PRL levels (r = -0.85, P = 0.034). In conclusion, beneficial metabolic changes were seen in prolactinoma patients after treatment with DA agonists, underscoring the importance of an active treatment approach and to consider the metabolic profile in the clinical management of hyperprolactinemia patients.

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

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