Diabetic retinopathy is associated with decreased serum levels of free IGF-I and changes of IGF-binding proteins

Integrated proteomic sample preparation with combination of on-line high-abundance protein depletion, denaturation, reduction, desalting and digestion to achieve high throughput plasma proteome quantification

In this study, we developed an integrated plasma proteome sample preparation system, by which high-abundance proteins from human plasma were first depleted by immunoaffinity column, followed by on-line middle and low-abundance proteins denaturation, reduction, desalting and tryptic digestion. To evaluate the performance of such a system, 20 μL plasma was processed automatically, followed by 1-h gradient liquid chromatography-mass spectrometry analysis (LC-MS). Compared to conventional in-solution protocols, not only the sample preparation time could be shortened from 20 h to 20 min, but also the number of identified proteins were greatly increased by 1.4-2.0 times. Such an integrated system allows us to process 36 human plasma samples per day, with more than 300 proteins and 52 FDA approved disease markers per sample being identified. With combination of such an integrated sample preparation system with label-free single-shot LC-MS/MS, the human plasma proteins could be quantified across more than 6 orders of magnitude of abundance range with high reproducibility (Pearson R = 0.99, n = 9). In addition, the relative quantification of human plasma samples from diabetic retinopathy patients and diabetic patients demonstrated the feasibility of our developed workflow for clinic plasma proteome profiling. All these results demonstrated that our developed integrated plasma proteome sample preparation system would provide a new tool for high throughput biomarker discovery.

IGFBP6 Is Downregulated in Unstable Carotid Atherosclerotic Plaques According to an Integrated Bioinformatics Analysis and Experimental Verification

Aims: To investigate the differentially expressed genes (DEGs) and molecular interaction in unstable atherosclerotic carotid plaques.

Methods: Gene expression datasets GSE41571, GSE118481, and E-MTAB-2055 were analyzed. Co-regulated DEGs in at least two datasets were analyzed with the enrichment of Gene Ontology Biological Process (GO-BP), Kyoto Encyclopedia of Genes and Genomes (KEGG), protein-protein interaction (PPI) networks, interrelationships between miRNAs/transcriptional factors, and their target genes and drug-gene interactions. The expression of notable DEGs in human carotid artery plaques and plasma was further identified.

Results: The GO-BP enrichment analysis revealed that genes associated with inflammatory response, and extracellular matrix organization were altered. The KEGG enrichment analysis revealed that upregulated DEGs were enriched in the tuberculous, lysosomal, and chemokine signaling pathways, whereas downregulated genes were enriched in the focal adhesion and PI3K/Akt signaling pathway. Collagen type I alpha 2 chain (COL1A2), adenylate cyclase 3 (ADCY3), C-X-C motif chemokine receptor 4 (CXCR4), and TYRO protein tyrosine kinase binding protein (TYROBP) might play crucial roles in the PPI networks. In drug–gene interactions, colony-stimulating factor-1 receptor had the most drug interactions. Insulin-like growth factor binding protein 6 (IGFBP6) was markedly downregulated in unstable human carotid plaques and plasma. Under a receiver operating characteristic curve analysis, plasma IGFBP6 had a significant discriminatory power (AUC, 0.894; 95% CI, 0.810–0.977), with a cutoff value of 142.08 ng/mL.

Conclusions: The genes COL1A2, ADCY3, CXCR4, and TYROBP are promising targets for the prevention of unstable carotid plaque formation. IGFBP6 may be an important biomarker for predicting vulnerable plaques.

Insulin-Like Growth Factor Binding Proteins in Autoimmune Diseases

Insulin-like growth factor binding proteins (IGFBPs) are a family of proteins binding to Insulin-like growth factors (IGFs), generally including IGFBP1, IGFBP2, IGFBP3, IGFBP4, IGFBP5, and IGFBP6. The biological functions of IGFBPs can be classified as IGFs-dependent actions and IGFs-independent effects. In this review, we will discuss the structure and function of various IGFBPs, particularly IGFBPs as potential emerging biomarkers and therapeutic targets in various autoimmune diseases, and the possible mechanisms by which IGFBPs act on the pathogenesis of autoimmune diseases.

The IGF-Axis and Diabetic Retinopathy Before and After Gastric Bypass Surgery

BACKGROUND

Laparoscopic gastric bypass (LGB) abruptly causes remission of type 2 diabetes (T2D). Such dramatic metabolic changes have previously been found to cause worsening of diabetic retinopathy (DR) and circulating insulin-like growth factor I (IGF-I) has been suggested as a causal mediator. We aimed to evaluate baseline imbalances in the circulating IGF-system and changes after LGB in patients with T2D.

METHODS

Prospective ocular examinations and measurement of the IGF-axis before and 3 and 12 months after LGB. IGF-bioactivity was measured by cell-based IGF-I receptor (IGF-IR) kinase activation assay (bioactive IGF). Total IGF-I, IGF-II and IGF binding protein (IGFBP) 1 and 3 were determined by immunoassays.

RESULTS

At baseline, 18 of 36 patients presented with DR. These patients had higher levels of bioactive IGF (p = 0.03) than patients without DR and this association was strengthened in multivariate analysis (p = 0.006). Three patients had worsening of DR, unrelated to other markers. In univariate analysis, bioactive IGF increased at 3 months (p = 0.05) but this change became insignificant in multivariate analysis (p = 0.11). IGFBP-1 increased whereas IGFBP-3 and total IGF-II decreased at the two postoperative visits (p ≤ 0.001). Total IGF-I showed no significant changes. HbA1c, glucose, HOMA-IR and lipids improved after surgery. Two patients did not complete the 12-month visit.

CONCLUSIONS

In obese T2D patients, bioactive IGF is a potential biomarker for DR and levels tended to increase 3 months after bariatric surgery. IGFBP-1 increased while IGFBP-3 and total IGF-II decreased postoperatively, but these changes were unassociated with the development of DR. Markers of the metabolic syndrome improved.

Review: Insulin-like growth factor-related proteins and diabetic complications

The insulin-like growth factor system and, in particular, insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-1 (IGFBP-1) are dysregulated in type 1 and type 2 diabetes. Serum IGF-I levels are low in both forms of diabetes, and this may be in part genetically determined. It is possible that the reduced serum levels of IGF-I are involved in the development of microvascular and macrovascular complications. Fasting serum IGFBP-1 levels are usually low in early type 2 diabetic patients with insulin resistance and hyperinsulinaemia but may be raised in patients with particularly poor glycaemic control and severe beta-cell failure. Treatment with IGF-I/binding protein complexes has been shown to improve glycaemic control in conjunction with insulin and may in future have a place in the treatment of diabetes, potentially to prevent diabetic complications. Serum IGFBP-1 determination may have utility in the assessment of cardiovascular risk and as an indicator for insulin resistance.

An ocular view of the IGF-IGFBP system

IGFs and their binding proteins have been shown to exhibit both protective and deleterious effects in ocular disease. Recent studies have characterized the expression patterns of different IGFBPs in retinal layers and within the vitreous. IGFBP-3 has roles in vascular protection stimulating proliferation, migration, and differentiation of vascular progenitor cells to sites of injury. IGFBP-3 increases pericyte ensheathment and shows anti-inflammatory effects by reducing microglia activation in diabetes. IGFBP-5 has recently been linked to mediating fibrosis in proliferative vitreoretinopathy but also reduces neovascularization. Thus, the regulatory balance between IGF and IGFBPs can have profound impact on target tissues. This review discusses recent findings of IGF and IGFBP expression in the eye with relevance to different retinopathies.

Interaction between glycaemic control and serum insulin-like growth factor 1 on the risk of retinopathy in type 2 diabetes

BACKGROUND

There is strong experimental evidence that insulin-like growth factor 1 (IGF-1) plays a role in the development of diabetic retinopathy. We carried out this study to determine the association between serum IGF-1 levels and retinopathy in patients with type 2 diabetes and whether this association is modified by the severity of hyperglycaemia.

MATERIALS AND METHODS

A total of 480 consenting patients with type 2 diabetes were enrolled between 1 August 2001 and 31 December 2002. All participants provided a medical history and underwent a physical examination, biochemical assessment and eye fundi examination. These patients were followed up in our clinics according to our national guidelines until 31 December 2009.

RESULTS

Compared with the middle tertile, increased levels of IGF-1 did not increase the risk of mild-to-moderate retinopathy (RR, 1·11; 95% CI, 0·63-1·95) and severe retinopathy (RR, 1·84; 95% CI, 0·79-8·57) at baseline. In the longitudinal analysis, increased levels of IGF-1 showed a nonsignificantly increased hazard ratio (HR) for the progression of retinopathy (HR, 1·61; 95% CI, 0·52-4·96) and severe retinopathy (HR, 1·63; 95% CI, 0·65-4·09). However, in patients with relatively good glycaemic control, there was a significantly increased risk of the progression of retinopathy (HR, 2·21; 95% CI, 1·01-5·91) and a cumulative incidence of severe retinopathy (HR, 4·82; 95% CI, 1·10-18·25) in individuals with the highest serum IGF-1 levels.

CONCLUSIONS

Our data suggested serum IGF-1 was a contributing factor in severe diabetic retinopathy and this effect may be masked by poor glycaemic control.

Peptide hormone regulation of angiogenesis

It is now apparent that regulation of blood vessel growth contributes to the classical actions of hormones on development, growth, and reproduction. Endothelial cells are ideally positioned to respond to hormones, which act in concert with locally produced chemical mediators to regulate their growth, motility, function, and survival. Hormones affect angiogenesis either directly through actions on endothelial cells or indirectly by regulating proangiogenic factors like vascular endothelial growth factor. Importantly, the local microenvironment of endothelial cells can determine the outcome of hormone action on angiogenesis. Members of the growth hormone/prolactin/placental lactogen, the renin-angiotensin, and the kallikrein-kinin systems that exert stimulatory effects on angiogenesis can acquire antiangiogenic properties after undergoing proteolytic cleavage. In view of the opposing effects of hormonal fragments and precursor molecules, the regulation of the proteases responsible for specific protein cleavage represents an efficient mechanism for balancing angiogenesis. This review presents an overview of the actions on angiogenesis of the above-mentioned peptide hormonal families and addresses how specific proteolysis alters the final outcome of these actions in the context of health and disease.

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.

Longitudinal relation between limited joint mobility, height, insulin-like growth factor 1 levels, and risk of developing microalbuminuria: the Oxford Regional Prospective Study

AIMS

To determine risk factors for development of microalbuminuria (MA) in relation to detection of limited joint mobility (LJM+) of the interphalangeal joints in a longitudinal cohort of type 1 diabetic (T1DM) subjects.

METHODS

A total of 479 T1DM subjects diagnosed <16 years were followed from diagnosis of diabetes with annual assessments consisting of assessment of LJM, measurement of HbA1c and insulin-like growth factor 1 (IGF-1), and three urine samples for albumin:creatinine ratio (ACR).

RESULTS

After a median follow up of 10.9 years, 162 subjects (35.1%) developed LJM at median age 13.0 years and duration 5.2 years. More subjects developed LJM after compared to before puberty (67.6 v 32.4%). In LJM+ compared to LJM- subjects, HbA1c (mean 10.1 (SD 1.6) v 9.6 (1.4) %)) and ACR levels (median 1.1 (range 0.2-242.9) v 0.9 (0.4-70.7) mg/mmol) were higher, and in a Cox model probability of developing LJM was related to puberty and higher HbA1c levels. ACR levels were higher after detection of LJM compared to before (median 1.2 (range 0.4-102.6) v 0.8 (0.2-181.9) mg/mmol). Probability of developing MA was related to puberty, HbA1c, female sex, and presence of LJM (a 1.9-fold increased risk). Both LJM and MA were associated with lower height SDS (LJM: mean 0.0 (SD 1.0) v 0.2 (1.1); MA: 0.0 (1.0) v 0.2 (SD 1.0)) and lower IGF-1 levels.

CONCLUSION

The development of LJM was associated with an increased risk of microalbuminuria, independent of glycaemic control. Risk for both microalbuminuria and LJM was associated with puberty, reduced growth, and reduced IGF-1 levels, and may indicate underlying shared pathogenic mechanisms.

Insulin-Like Growth Factor-1 and Its Binding Proteins, IGFBP-1 and IGFBP-3, in Adolescents with Type-1 Diabetes mellitus and Microalbuminuria

BACKGROUND/AIMS

Numerous clinical and experimental studies suggest that growth factors may contribute to the development of diabetic microvascular complications. The aim of the study was to test the hypothesis that in adolescents with type-1 diabetes mellitus and microalbuminuria (MA) there are specific disorders of serum insulin-like growth factor-1 (IGF-1) and concentrations of its binding proteins, IGFBP-1 and IGFBP-3, that could be of importance in the pathogenesis of microvascular diabetic complications.

METHODS

25 adolescents with MA, 24 adolescents with diabetes without complications, and 17 controls were examined. There were no differences with regard to age, puberty stage, HbA1c and body mass index between the groups examined. Two of the patients in the first group also had diabetic retinopathy. Serum fasting concentrations of IGF-1 and overnight urine albumin concentrations were measured by radioimmunoassay, IGFBP-1 and IGFBP-3 concentrations by immunoradiometric assay and HbA1c by high-performance liquid chromatography methods. Diabetic patients were examined by an experienced ophthalmologist and neurologist. The data were analyzed using Kruskal-Wallis ANOVA and multiple regression analysis.

RESULTS

Significantly lower IGF-1 concentrations were found in adolescents with diabetes and MA compared to diabetic patients without complications and healthy contemporaries. IGFBP-1 concentrations were significantly higher and IGFBP-3 concentrations were statistically lower in diabetic patients with MA than in patients without complications.

CONCLUSIONS

The IGF-IGFBP system is deranged in adolescents with type-1 diabetes mellitus and MA. Our results suggest the participation of circulating IGFBP-1 in the origin of diabetic complications. It could be also possible that IGFBP-3 takes part in the protection from them.

Increasing urine albumin excretion is associated with growth hormone hypersecretion and reduced clearance of insulin in adolescents and young adults with type 1 diabetes: the Oxford Regional Prospective Study

HYPOTHESIS

We previously described lower insulin-like growth factor I (IGF-I) levels in association with increased microalbuminuria (MA) risk in type 1 diabetic subjects followed from diabetes diagnosis through puberty into adulthood. By inference lower IGF-I levels may be associated with higher GH levels and changes in insulin sensitivity.

METHODS

To test this hypothesis, microalbuminuric subjects (MA+, n = 14) from the same cohort had overnight GH levels measured during euglycaemia (5 mmol/l, 01:00-07:30 h) maintained by a variable rate insulin infusion followed by a 2-step hyperinsulinaemic, euglycaemic clamp study using [6.6 2H2] glucose, and were compared to MA- controls (MA-, n = 14), matched for age (median 19.3 years, range 15.8-30.5), sex, duration of diabetes (11.1 years, range 5.1-16.4).

RESULTS

In MA+ cases GH levels, measured by the Pulsar programme, were higher (baseline; 1.8 +/- 1.4 vs. 0.7 +/- 0.5 ng/ml, P = 0.02, mean; 3.8 +/- 1.3 vs. 2.6 +/- 1.6 ng/ml, P = 0.03, maximum; 16.7 +/- 7.0 vs. 12.3 +/- 5.4, P = 0.02), despite similar HbA1(c) levels (9.8%vs. 9.6%, P = 0.6) and body or truncal fat mass. Fourier transform revealed increased GH pulse amplitude at all periodicities and overnight insulin clearance was reduced (11.7 +/- 6.9 vs. 20.1 +/- 6.5 ml/kg/min, P < 0.02). In multiple regression analysis, urine albumin excretion was associated with higher GH levels and reduced insulin clearance, independent of HbA1(c) and body composition. In female cases (n = 9), dextrose requirements were reduced during the first step of the euglycaemic clamp (1.7 +/- 0.8 vs. 2.7 +/- 1.4, P < 0.05) but no such differences existed in males or in the rate of glucose production or disposal.

CONCLUSION

The development of MA during puberty and young adulthood is associated with higher GH levels and abnormalities in insulin metabolism, particularly in females. These data extend support for our previous findings indicating a role for the GH/IGF-I axis in the pathogenesis of MA.

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

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

Low IGF-I and elevated testosterone during puberty in subjects with type 1 diabetes developing microalbuminuria in comparison to normoalbuminuric control subjects: the Oxford Regional Prospective Study

OBJECTIVE

To describe longitudinal variations in pubertal hormonal variables in subjects with and without microalbuminuria (MA).

RESEARCH DESIGN AND METHODS

Blood samples collected annually from subjects recruited at diagnosis of type 1 diabetes and followed prospectively through puberty (median follow-up 9.3 years, range 4.7-12.8) were analyzed for total and free IGF-I, IGF binding protein-1, testosterone, sex hormone-binding globulin, and HbA(1c). A total of 55 subjects who developed MA (MA(+) group) were compared with 55 age-, sex-, and duration-matched control subjects who did not develop MA (MA(-) group).

RESULTS

For female subjects, total IGF-I (MA(+) 1.2 mU/l vs. MA(-) 1.4 mU/l, P = 0.03) and free IGF-I levels (MA(+) 1,767 ng/l vs. MA(-) 2010 ng/l, P = 0.002) were lower, whereas the free androgen index (MA(+) 2.4 vs. MA(-) 2.0, P = 0.03) was higher in those with MA. These changes were less pronounced in male subjects. For both sexes, in a Cox model after adjusting for puberty, the presence of MA was associated with lower free IGF-I levels, higher testosterone standard deviation score (SDS), and poor glycemic control. We found that 22 of 55 case subjects (40%) developed persistent MA, whereas 33 (60%) had transient MA. In the persistent MA group compared with the transient and control groups, total IGF-I levels were lower (1.1 vs. 1.3 vs. 1.4 mU/l, P = 0.002) as were free IGF-I levels (1,370.9 vs. 1,907.3 vs. 1,886.7 ng/l, P < 0.001), whereas HbA(1c) levels were higher (11.8 vs. 10.3 vs. 9.9%, P < 0.001).

CONCLUSIONS

Poor glycemic control and differences in IGF-I levels and androgens, particularly in female subjects, accompany development of MA at puberty. These differences may in part account for the sexual dimorphism in MA risk during puberty and could relate to disease progression.

The relationship between the circulating IGF system and the presence of retinopathy in Type 1 diabetic patients

BACKGROUND

Patients with proliferative diabetic retinopathy (PDR) have increased vitreous levels of insulin-like growth factor (IGF)-I, IGF-II and IGF binding proteins (IGFBPs). This accumulation is probably caused by increased leakiness of the blood-retina barrier and influx of circulating IGFs and IGFBPs. To date, interest has focused on the role of circulating total IGF-I in the development of PDR, and there are only sparse data on circulating levels of free IGF-I and IGFBPs.

METHODS

We compared fasting serum samples from matched groups of Type 1 diabetic patients with no retinopathy (n = 29), non-PDR (n = 13) and PDR (n = 16). We also included matched controls (n = 26). Serum was analysed for free and total IGF-I and -II, free plus dissociable IGF-I, IGFBP-1, -2 and -3, IGFBP-1-bound IGF-I as well as IGFBP-3 proteolysis.

RESULTS

When compared with controls, diabetic patients (n = 58) showed reduced (P < 0.0005) levels of free and total IGFs, free plus dissociable IGF-I and IGFBP-3, whereas levels of IGFBP-1, IGFBP-1-bound IGF-I and IGFBP-2 were elevated. IGFBP-3 proteolysis remained unaltered. When comparing diabetic patients with different degrees of retinopathy, IGFBP-2 and IGFBP-1-bound IGF-I were the only parameters that differed significantly. Patients with retinopathy (non-PDR as well as PDR) had elevated IGFBP-2 (P < 0.03) and reduced IGFBP-1-bound IGF-I (P < 0.03), when compared with patients without retinopathy. Noteworthy, both parameters correlated (0.11 < r2 < 0.14, P < 0.02) with the severity of retinopathy.

CONCLUSION

Our study gives no evidence of a direct role of circulating free IGF-I in the development of PDR, whereas IGFBP-2 and IGFBP-1-bound IGF-I showed a relationship with the degree of retinopathy. However, further investigations are needed in order to clarify the basis and clinical relevance of this finding.

Use of somatostatin receptor ligands in obesity and diabetic complications

Somatostatin (SMS) is a potent inhibitory molecule. It inhibits both exocrine and endocrine secretory functions of the pancreas, suppresses growth hormone secretion and reduces the level of insulin-like growth factor-1. Long-acting somatostatin analogues were currently investigated for potential clinical benefits in two settings: (a) control of hyperinsulinaemia in obesity and (b) control of an excess of pro-angiogenic factors in diabetes-associated retinal complications. In two randomized, controlled trials the long-acting somatostatin analogue octreotide retarded progression of the microvascular complications in pre-proliferative and advanced stages of diabetic retinopathy. Inhibition of the early phase of insulin secretion by use of octreotide in patients with hypothalamic obesity resulted in weight loss and improved quality of life. Efficacy of octreotide correlated to residual beta-cell activity prior to the treatment. Obesity and diabetes mellitus are the most common chronic metabolic disorders in the world. The use of somatostatin analogues addressing the various hormonal imbalances of these disorders may provide a novel concept for their pharmacological treatment.