Serum insulin-like growth factor-I levels and potential risk of type 2 diabetes

Targeting Insulin-Like Growth Factor-I in Management of Neurological Disorders

The degradation of neurons marks as the pathological reason for onset of most of the neurological diseases although the functional deficiencies and symptoms may vary. Insulin-like growth factor-I (IGF-I) boosts regeneration of both motor and sensory neurons and thus presents as a potential treatment in management of neurological disorders. IGF-I is a pleiotropic agent which stimulates the survival and outgrowth of neurons accompanied by their motility as well as myelination by glial cells. This hormone has been found to possess neuroprotective properties which is in association with its antioxidant and mitochondrial protection activity. Studying and exploring the signaling pathways which mediate pleotropic responses intracellularly have elucidated significant therapeutic approach in treatment and management of neurological disorders by IGF-I. The current review highlights the role of IGF-I in management of major neurological disorders such as depression, Parkinson's disease, and Alzheimer's disease and also covers the mechanisms involved in the process.

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.

Serum IGFBP7 levels associate with insulin resistance and the risk of metabolic syndrome in a Chinese population

Metabolic syndrome (MetS), one of the major public health concerns, is regarded as the “common soil” of incidence of common chronic diseases and may increase the risk of type 2 diabetes. The predominant underlying mechanism of MetS is insulin resistance (IR). Additionally, previous studies have indicated that IGFBP7 has high affinity of binding with insulin and might induce IR. The objective of this study was to firstly evaluate the associations of serum IGFBP7 levels with IR and MetS with a relatively large sample and population based design. In a population based MetS case-control study, HOMA-IR was used to evaluate the insulin sensitivity and serum IGFBP7 levels were determined with chemiluminescence–linked immunoassay. As a result, the subjects of MetS and IR had higher serum levels of IGFBP7 than control healthy subjects. High serum IGFBP7 levels increased the risk of MetS and IR. Serum IGFBP7 levels were also found to be significantly correlated with metabolic-associated parameters of Waist-to-hip ratio (WHR), HDL and LDL. These findings suggest that serum IGFBP7 levels are associated with IR and MetS, providing new insight into the mechanism of IR and Mets. IGFBP7 may be a potential interventional target for IR and Mets.

Insulin-like growth factor-1 and risk of Alzheimer dementia and brain atrophy

OBJECTIVE

To relate serum insulin-like growth factor-1 (IGF-1) to risk of Alzheimer disease (AD) dementia and to brain volumes in a dementia-free community sample spanning middle and older ages.

METHODS

Dementia-free Framingham participants from generation 1 (n = 789, age 79 ± 4 years, 64% women) and generation 2 (n = 2,793, age 61 ± 9 years, 55% women; total = 3,582, age 65 ± 11 years, 57% women) had serum IGF-1 measured in 1990-1994 and 1998-2001, respectively, and were followed prospectively for incident dementia and AD dementia. Brain MRI was obtained in stroke- and dementia-free survivors of both generations 1 (n = 186) and 2 (n = 1,867) during 1999-2005. Baseline IGF-1 was related to risk of incident dementia using Cox models and to total brain and hippocampal volumes using linear regression in multivariable models adjusted for age, sex, APOE ε4, plasma homocysteine, waist-hip ratio, and physical activity.

RESULTS

Mean IGF-1 levels were 144 ± 60 μg/L in generation 1 and 114 ± 37 μg/L in generation 2. We observed 279 cases of incident dementia (230 AD dementia) over a mean follow-up of 7.4 ± 3.1 years. Persons with IGF-1 in the lowest quartile had a 51% greater risk of AD dementia (hazard ratio = 1.51, 95% confidence interval: 1.14-2.00; p = 0.004). Among persons without dementia, higher IGF-1 levels were associated with greater total brain volumes (β/SD increment in IGF-1 was 0.55 ± 0.24, p = 0.025; and 0.26 ± 0.06, p < 0.001, for generations 1 and 2, respectively).

CONCLUSION

Lower serum levels of IGF-1 are associated with an increased risk of developing AD dementia and higher levels with greater brain volumes even among middle-aged community-dwelling participants free of stroke and dementia. Higher levels of IGF-1 may protect against subclinical and clinical neurodegeneration.

Evaluation of IGFBP-7 DNA methylation changes and serum protein variation in Swedish subjects with and without type 2 diabetes

Background

Insulin-like growth factor-binding protein 7 (IGFBP-7) is able to interact with insulin-like growth factor 1 (IGF-1) as well as insulin. Previous studies have suggested that serum IGFBP-7 levels may be associated with insulin resistance in type 2 diabetes (T2D). This study aimed to evaluate IGFBP-7 serum protein and IGFBP7 DNA methylation levels in the subjects with and without T2D.

Results

A total of 340 Swedish subjects including 100 newly diagnosed T2D patients (50 women/50 men), 100 age-matched nondiabetic control subjects (50/50) and 140 treated T2D patients (54/86) were studied. Serum IGFBP-7 levels were measured with a novel ELISA. IGF1, IGFBP-1, and insulin were determined by in-house radioimmunoassays. DNA methylation levels in the IGFBP7 gene were analyzed with a bisulfite-pyrosequencing technique. Serum IGFBP-7 protein levels were similar among nondiabetic subjects, newly diagnosed, and treated T2D patients and were not correlated with IGFBP7 DNA methylation. However, IGFBP7 DNA methylation was increased in men with newly diagnosed T2D compared with nondiabetic controls (17.6% vs. 12.5%, P < 0.01). Serum IGFBP-7 levels correlated (r = 0.331, P = 0.019) with serum IGFBP-1 levels, a marker of insulin production, in men but not women with newly diagnosed T2D.

Conclusions

This study demonstrates for the first time that IGFBP7 DNA methylation levels are increased in Swedish men with newly diagnosed T2D. The correlation between IGFBP-7 and IGFBP-1 suggests that low IGFBP-7 may be associated with insulin resistance in T2D.

The impact of cow's milk-mediated mTORC1-signaling in the initiation and progression of prostate cancer

Prostate cancer (PCa) is dependent on androgen receptor signaling and aberrations of the PI3K-Akt-mTORC1 pathway mediating excessive and sustained growth signaling. The nutrient-sensitive kinase mTORC1 is upregulated in nearly 100% of advanced human PCas. Oncogenic mTORC1 signaling activates key subsets of mRNAs that cooperate in distinct steps of PCa initiation and progression. Epidemiological evidence points to increased dairy protein consumption as a major dietary risk factor for the development of PCa. mTORC1 is a master regulator of protein synthesis, lipid synthesis and autophagy pathways that couple nutrient sensing to cell growth and cancer. This review provides evidence that PCa initiation and progression are promoted by cow´s milk, but not human milk, stimulation of mTORC1 signaling. Mammalian milk is presented as an endocrine signaling system, which activates mTORC1, promotes cell growth and proliferation and suppresses autophagy. Naturally, milk-mediated mTORC1 signaling is restricted only to the postnatal growth phase of mammals. However, persistent consumption of cow´s milk proteins in humans provide highly insulinotropic branched-chain amino acids (BCAAs) provided by milk´s fast hydrolysable whey proteins, which elevate postprandial plasma insulin levels, and increase hepatic IGF-1 plasma concentrations by casein-derived amino acids. BCAAs, insulin and IGF-1 are pivotal activating signals of mTORC1. Increased cow´s milk protein-mediated mTORC1 signaling along with constant exposure to commercial cow´s milk estrogens derived from pregnant cows may explain the observed association between high dairy consumption and increased risk of PCa in Westernized societies. As well-balanced mTORC1-signaling plays an important role in appropriate prostate morphogenesis and differentiation, exaggerated mTORC1-signaling by high cow´s milk consumption predominantly during critical growth phases of prostate development and differentiation may exert long-term adverse effects on prostate health. Attenuation of mTORC1 signaling by contemporary Paleolithic diets and restriction of dairy protein intake, especially during mTORC1-dependent phases of prostate development and differentiation, may offer protection from the most common dairy-promoted cancer in men of Western societies.

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.

Functional biomarkers of depression: diagnosis, treatment, and pathophysiology

Major depressive disorder (MDD) is a heterogeneous illness for which there are currently no effective methods to objectively assess severity, endophenotypes, or response to treatment. Increasing evidence suggests that circulating levels of peripheral/serum growth factors and cytokines are altered in patients with MDD, and that antidepressant treatments reverse or normalize these effects. Furthermore, there is a large body of literature demonstrating that MDD is associated with changes in endocrine and metabolic factors. Here we provide a brief overview of the evidence that peripheral growth factors, pro-inflammatory cytokines, endocrine factors, and metabolic markers contribute to the pathophysiology of MDD and antidepressant response. Recent preclinical studies demonstrating that peripheral growth factors and cytokines influence brain function and behavior are also discussed along with their implications for diagnosing and treating patients with MDD. Together, these studies highlight the need to develop a biomarker panel for depression that aims to profile diverse peripheral factors that together provide a biological signature of MDD subtypes as well as treatment response.

Plasma levels of insulin-like growth factor-I, insulin-like growth factor binding protein-1, coenzyme Q10 and vitamin E in female populations from Poland, Serbia and Sweden

Exposure to environmental contaminants such as polycyclic aromatic hydrocarbons (PAHs), life style and nutritional status of a population are important factors that may influence normal serum levels of antioxidants and the insulin-like growth factor system. In this study we examined serum levels of insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-1(IGFBP-1), coenzyme Q10 (CoQ) and vitamin E in healthy female populations (n=4 x 100) aged 19-59 years from Poland (PL), Sweden (SE), Serbia I (SR I) and Serbia II (SR II). The last group lived in an environmental emergency area affected by the bombings of 1999 in Serbia. The Polish and SR I cohorts exhibited low IGFSD-score levels, (-2 to +/-0), compared to females from SE with IGFSD-score 0. In the SR II population, the IGFSD range was between -1 and 1. The IGFBP-1 levels of the Polish and SR I groups were lower than in the Swedish population, while the SR II levels showed a broader distribution, 20-80 microg/l. The CoQ values in the Swedish and Polish samples were around 1 nmol/ml. In contrast, the SR I cohorts exhibited higher concentrations, 1.5-3.5 nmol/ml and the SR II group had extremely low levels, <0.5 nmol/ml. The vitamin E concentrations were similar in the Polish and Swedish populations, 20-40 nmol/ml, while it was twice as high, 40-80 nmol/ml in the SR I and very low in the SR II group, which is half of the Polish and Swedish cohorts. These results suggest that different lifestyles and environmental factors affect both the IGF system and the antioxidants CoQ10 and vitamin E in female populations in Europe. The females living in the polluted area had different patterns of both the IGF and antioxidant systems. These findings may explain differences in morbidity and mortality in these countries.

Session 7: Early nutrition and later health early developmental pathways of obesity and diabetes risk

Size at birth and patterns of postnatal weight gain have been associated with adult risk for the development of type 2 diabetes in many populations, but the putative pathophysiological link remains unknown. Studies of contemporary populations indicate that rapid infancy weight gain, which may follow fetal growth restriction, is an important risk factor for the development of childhood obesity and insulin resistance. Data from the Avon Longitudinal Study of Pregnancy and Childhood shows that rapid catch-up weight gain can lead to the development of insulin resistance, as early as 1 year of age, in association with increasing accumulation of central abdominal fat mass. In contrast, the disposition index, which reflects the beta-cells ability to maintain insulin secretion in the face of increasing insulin resistance, is much more closely related to ponderal index at birth than postnatal catch-up weight gain. Infants with the lowest ponderal index at birth show a reduced disposition index at aged 8 years associated with increases in fasting NEFA levels. The disposition index is also closely related to childhood height gain and insulin-like growth factor-I (IGF-I) levels; reduced insulin secretory capacity being associated with reduced statural growth, and relatively short stature with reduced IGF-I levels at age 8 years. IGF-I may have an important role in the maintenance of beta-cell mass, as demonstrated by recent studies of pancreatic beta-cell IGF-I receptor knock-out and adult observational studies indicating that low IGF-I levels are predictive of subsequent risk for the development of type 2 diabetes. However, as insulin secretion is an important determinant of IGF-I levels, cause and effect may be difficult to establish. In conclusion, although rapid infancy weight gain and increasing rates of childhood obesity will increase the risk for the development of insulin resistance, prenatal and postnatal determinants of beta-cell mass may ultimately be the most important determinants of an individual's ability to maintain insulin secretion in the face of increasing insulin resistance, and thus risk for the development of type 2 diabetes.

Association of serum levels of IGF-I and IGFBP-1 with renal function in patients with type 2 diabetes mellitus

OBJECTIVE

Our aim was to determine whether serum Insulin-like growth factor-I (IGF-I) and Insulin-like growth factor binding protein-1 (IGFBP-1) levels were different between type 2 diabetic patients and non-diabetic control group. We also aimed to establish any relationship that might exist between the serum IGF-I and IGFBP-1 levels with the urinary albumin excretion (UAE), creatinine clearance and urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion (as a marker of renal tubular dysfunction) and other parameters (such as age, duration of diabetes, treatment, etc.) in patients with type 2 diabetes mellitus (DM).

DESIGN

Fifty-nine type 2 diabetic patients and thirty-one non-diabetic controls were included in this study.

RESULTS

Mean serum IGF-I levels in diabetic patients were lower than the non-diabetic controls (158+/-12 vs. 287+/-26microg/l), (p<0.001). Serum IGFBP-1 levels were also higher in type 2 diabetic patients compared to the control group (67+/-5 vs. 35+/-4microg/l), (p<0.001). No relationship was obtained between IGF-I and IGFBP-1 levels with neither UAE nor urinary NAG excretion. A significant negative relationship was observed between creatinine clearance and serum IGFBP-1 level (r=-0.39, p=0.004). In multiple regression analysis IGF-I was independently and negatively associated with age and insulin treatment. On the other hand, IGFBP-1 was negatively related with creatinine clearance and positively related with the duration of diabetes.

CONCLUSION

These results suggest that type 2 DM leads to a decrease in the IGF-I while elevating the IGFBP-1 levels. Further studies are needed to clarify a potential role of increased levels of IGFBP-1 in decreased creatinine clearance in type 2 DM.