Insulin-like growth factor-II and insulin-like growth factor binding protein-2 prospectively predict longitudinal elevation of HDL-cholesterol in type 2 diabetes

RNA-Seq transcriptome profiling of Nile rat livers reveals novel insights on the anti-diabetic mechanisms of Water-Soluble Palm Fruit Extract

Water-Soluble Palm Fruit Extract (WSPFE) has been shown to confer anti-diabetic effects in the Nile rat (NR) (Arvicanthis niloticus). Liquid and powder WSPFE both deterred diabetes onset in NRs fed a high-carbohydrate (hiCHO) diet, but the liquid form provided better protection. In this study, NRs were fed either a hiCHO diet or the same diet added with liquid or powder WSPFE. Following feeding of the diets for 8 weeks, random blood glucose levels were measured to categorize NRs as either diabetes-resistant or diabetes-susceptible, based on a cut-off value of 75 mg/dL. Livers were then obtained for Illumina HiSeq 4000 paired end RNA-sequencing (RNA-Seq) and the data were mapped to the reference genome. Consistent with physiological and biochemical parameters, the gene expression data obtained indicated that WSPFE was associated with protection against diabetes. Among hepatic genes upregulated by WSPFE versus controls, were genes related to insulin-like growth factor binding protein, leptin receptor, and processes of hepatic metabolism maintenance, while those downregulated were related to antigen binding, immunoglobulin receptor, inflammation- and cancer-related processes. WSPFE supplementation thus helped inhibit diabetes progression in NRs by increasing insulin sensitivity and reducing both the inflammatory effects of a hiCHO diet and the related DNA-damage compensatory mechanisms contributing to liver disease progression. In addition, the genetic permissiveness of susceptible NRs to develop diabetes was potentially associated with dysregulated compensatory mechanisms involving insulin signaling and oxidative stress over time. Further studies on other NR organs associated with diabetes and its complications are warranted.

Associations between Insulin-Like Growth Factor Binding Protein-2 and lipoprotein kinetics in men

Low circulating concentrations of insulin-like growth factor binding protein-2 (IGFBP-2) have been associated with dyslipidemia, notably with high triglyceride (TG) levels. However, the determinants by which IGFBP-2 influences lipoprotein metabolism, especially that of TG-rich lipoproteins (TRLs), are poorly understood. Here, we aimed to assess the relationships between IGFBP-2 levels and lipoprotein production and catabolism in human subjects. Fasting IGFBP-2 concentrations were measured in the plasma of 219 men pooled from previous lipoprotein kinetics studies. We analyzed production rate and fractional catabolic rates of TRLapoB-48, and LDL-, IDL-, and VLDLapoB-100 by multicompartmental modeling of l-[5,5,5-D3] leucine enrichment data after a 12 h primed constant infusion in individuals kept in a constant nutritional steady state. Subjects had an average BMI of 30 kg/m², plasma IGFBP-2 levels of 157 ng/ml, and TG of 2.2 mmol/l. After adjustments for age and BMI, IGFBP-2 levels were negatively associated with plasma TG (r = −0.29; P < 0.0001) and positively associated with HDL-cholesterol (r = 0.26; P < 0.0001). In addition, IGFBP-2 levels were positively associated with the fractional catabolic rate of VLDLapoB-100 (r = 0.20; P < 0.01) and IDLapoB-100 (r = 0.19; P < 0.05) and inversely with the production rate of TRLapoB-48 (r = −0.28; P < 0.001). These correlations remained statistically significant after adjustments for age, BMI, and the amount of fat given during the tracer infusion. These findings show that the association between low plasma IGFBP-2 and high TG concentrations could be due to both an impaired clearance of apoB-100-containing VLDL and IDL particles and an increased production of apoB-48-containing chylomicrons. Additional studies are necessary to investigate whether and how IGFBP-2 directly impacts the kinetics of TRL.

Early pregnancy serum IGFBP-1 relates to lipid profile in overweight and obese women

Lower level of insulin-like growth factor-binding protein (IGFBP-1) has been observed in insulin resistance, while higher level of matrix metalloproteinase-8 (MMP-8) has been linked to obesity. The aim here was to study in overweight and obese women, typically manifesting with insulin resistance, whether IGFBP-1 and MMP-8 are related to and reflect systemic low-grade inflammation, metabolism and diet. Fasting serum from overweight and obese pregnant women (n = 100) in early pregnancy were analysed for IGFBP-1, phosphorylated IGFBP-1 (phIGFBP-1) and MMP-8. High-sensitivity CRP and GlycA were used as markers for low grade inflammation. GlycA and lipids were quantified using NMR. IGFBP-1 associated negatively with GlycA, evidenced by higher concentrations in the lowest quartile (median 1.53 (IQR 1.45–1.72)) compared to the highest (1.46 (1.39–1.55)) (P = 0.03). Several lipid metabolites, particularly HDL-cholesterol, correlated inversely with phIGFBP-1 (FDR<0.1). Nutritional status and diet contributed to the levels of IGFBP-1, demonstrated as an inverse correlation with maternal weight (Spearman r = -0.205, P = 0.04) and dietary intake of vitamin A (r = -0.253, P = 0.014) and a direct correlation with dietary intake of polyunsaturated fatty acids (Spearman r = 0.222, P = 0.03). MMP-8 correlated inversely with pyridoxine (r = -0.321, P = 0.002) and potassium (r = -0.220, P = 0.033). Maternal serum IGFBP-1 may contribute to maternal lipid metabolism in overweight and obese women during early pregnancy. These findings may be of importance in identification of metabolic disturbances preceding the adverse metabolic outcomes in pregnancy.

Novel cardiovascular biomarkers in patients with cardiovascular diseases undergoing intensive physical exercise

BACKGROUND

In this trial, we analyzed the plasma levels of novel biomarkers that reflect different pathophysiological pathways (sST2: mechanical strain, IGF-BP2: metabolic pathways, suPAR and GDF-15: inflammatory processes) in patients undergoing physical exercise to investigate the effects of training on their plasma concentrations.

METHODS

Plasma concentrations of novel biomarkers (sST2, IGF-BP2, suPAR and GDF-15) were analyzed by means of ELISA in patients with stable coronary artery disease (CAD) undergoing four weeks of high- and moderate-intensity training (EXCITE Trial) and in patients with one or more cardiovascular risk factors undergoing eight months of intensive physical exercise (IGF-BP2). Plasma levels of sST2 in patients undergoing eight months of intensive exercise have been published previously by our study group (1.13-fold change, P=0.045).

RESULTS

Four weeks of high-intensity exercise training resulted in a statistically significant change in the plasma level of sST2 (1.106-fold change, P=0.0054) and IGF-BP2 (1.24-fold-change, P=0.0165). Eight months of intensive exercise resulted in a significant increase of IGF-BP2 (median 61.2 ng/mL to 80.7 ng/mL, 1.319-fold change, P=0.006).

CONCLUSIONS

The significant increase of sST2 after four weeks might be a short-term effect due to the mechanical strain caused by the high-intensity training program, whereas the increase in IGF-BP2 after four weeks and eight months is likely a result of metabolic changes due to physical exercise.

MiR-29 Regulates de novo Lipogenesis in the Liver and Circulating Triglyceride Levels in a Sirt1-Dependent Manner

MicroRNAs (miRNAs) are known regulators of lipid homeostasis. We recently demonstrated that miR-29 controls the levels of circulating cholesterol and triglycerides, but the mechanisms remained unknown. In the present study, we demonstrated that systemic delivery of locked nucleic acid inhibitor of miR-29 (LNA29) through subcutaneous injection effectively suppresses hepatic expression of miR-29 and dampens de novo lipogenesis (DNL) in the liver of chow-fed mice. Next, we used mice with liver-specific deletion of Sirtuin 1 (L-Sirt1 KO), a validated target of miR-29, and demonstrated that the LNA29-induced reduction of circulating triglycerides, but not cholesterol, is dependent on hepatic Sirt1. Moreover, lipidomics analysis revealed that LNA29 suppresses hepatic triglyceride levels in a liver-Sirt1 dependent manner. A comparative transcriptomic study of liver tissue from LNA29-treated wild-type/floxed and L-Sirt1 KO mice identified the top candidate lipogenic genes and hepatokines through which LNA29 may confer its effects on triglyceride levels. The transcriptomic analysis also showed that fatty acid oxidation (FAO) genes respond differently to LNA29 depending on the presence of hepatic Sirt1. Overall, this study demonstrates the beneficial effects of LNA29 on DNL and circulating lipid levels. In addition, it provides mechanistic insight that decouples the effect of LNA29 on circulating triglycerides from that of circulating cholesterol.

Changes in IGFBP-2 levels following a one-year lifestyle modification program are independently related to improvements in plasma apo B and LDL apo B levels

BACKGROUND AND AIMS

Recent transversal studies have associated insulin-like growth factor binding protein (IGFBP)-2 levels with glucose tolerance and parameters of the lipoprotein-lipid profile. Here, we aimed at determining the longitudinal effects of a one-year lifestyle modification program on IGFBP-2 levels and to identify specific metabolic improvements impacted by the changes in IGFBP-2.

METHODS

99 middle-aged Caucasian men were involved in a lifestyle modification program consisting in personalized healthy eating and physical activity counseling, combined to elicit a daily 500 kcal deficit. Anthropometric and metabolic parameters as well as circulating IGFBP-2 levels were measured before and after one year of the lifestyle modification program.

RESULTS

The intervention triggered positive changes in many metabolic parameters and a 43% (p < 0.0001) increase of IGFBP-2 levels. Subjects with the most substantial increases in IGFBP-2 also experienced the most important metabolic improvements. Changes in IGFBP-2 levels (both absolute and relative) were correlated with markers of body fat distribution and lipoprotein-lipid profile, and independently associated with changes in LDL apolipoprotein (apo) B but not VLDL apo B concentrations. Further analyses showed that for similar changes in BMI, waist circumference and visceral adipose tissue volume, large changes in IGFBP-2 levels were required to observe improvements in LDL apo B levels.

CONCLUSIONS

The 1-year lifestyle modification program was associated with increased IGFBP-2 concentrations. Increases in IGFBP-2 levels were closely associated with reduced LDL apo B concentrations and independently of the modifications in fat mass and insulin sensitivity. Further mechanistic studies are required to assess the effects of IGFBP-2 levels on LDL metabolism.

Role of IGF-binding proteins in regulating IGF responses to changes in metabolism

The IGF-binding protein family contains six members that share significant structural homology. Their principal function is to regulate the actions of IGF1 and IGF2. These proteins are present in plasma and extracellular fluids and regulate access of both IGF1 and II to the type I IGF receptor. Additionally, they have functions that are independent of their ability to bind IGFs. Each protein is regulated independently of IGF1 and IGF2, and this provides an important mechanism by which other hormones and physiologic variables can regulate IGF actions indirectly. Several members of the family are sensitive to changes in intermediary metabolism. Specifically the presence of obesity/insulin resistance can significantly alter the expression of these proteins. Similarly changes in nutrition or catabolism can alter their synthesis and degradation. Multiple hormones such as glucocorticoids, androgens, estrogen and insulin regulate IGFBP synthesis and bioavailability. In addition to their ability to regulate IGF access to receptors these proteins can bind to distinct cell surface proteins or proteins in extracellular matrix and several cellular functions are influenced by these interactions. IGFBPs can be transported intracellularly and interact with nuclear proteins to alter cellular physiology. In pathophysiologic states, there is significant dysregulation between the changes in IGFBP synthesis and bioavailability and changes in IGF1 and IGF2. These discordant changes can lead to marked alterations in IGF action. Although binding protein physiology and pathophysiology are complex, experimental results have provided an important avenue for understanding how IGF actions are regulated in a variety of physiologic and pathophysiologic conditions.

Role of IGF Binding Proteins in Regulating Metabolism

Insulin-like growth factors (IGFs) circulate in extracellular fluids bound to a family of binding proteins. Although they function in a classical manner to limit the access of the IGFs to their receptors they also have a multiplicity of actions that are independent of this property; they bind to their own receptors or are transported to intracellular and intranuclear sites to influence cellular functions that may directly or indirectly modify IGF actions. The availability of genetically modified animals has helped to determine their functions in a physiological context. These results show that many of their actions are cell type- and context-specific, and have led to a broader understanding of how these proteins function coordinately with IGF-I and -II to regulate growth and metabolism.

IGF-Binding Proteins in Type-1 Diabetes Are More Severely Altered in the Presence of Complications

AIMS

Reduced levels of free and total insulin-like growth factor 1 (IGF-I) have been observed in type-1 diabetes (T1D) patients. The bioavailability of IGF-I from the circulation to the target cells is controlled by multifunctional IGF-binding proteins (IGFBPs). The aim of this study was to profile serum IGFBPs in T1D and its complications.

DESIGN

We measured the IGFBP levels in 3662 patient serum samples from our ongoing Phenome and Genome of Diabetes Autoimmunity (PAGODA) study. IGFBP levels of four different groups of T1D patients (with 0, 1, 2, and ≥3 complications) were compared with healthy controls.

RESULTS

Three serum IGFBPs (IGFBP-1, -2, and -6) are significantly higher in T1D patients, and these alterations are greater in the presence of diabetic complications. IGFBP-3 is lower in patients with diabetic complications. Analyses using quintiles revealed that risk of T1D complications increases with increasing concentrations of IGFBP-2 (fifth quintile ORs: 18-60, p < 10(-26)), IGFBP-1 (fifth quintile ORs: 8-20, p < 10(-15)), and IGFBP-6 (fifth quintile ORs: 3-148, p < 10(-3)). IGFBP-3 has a negative association with T1D complications (fifth quintile ORs: 0.12-0.25, p < 10(-5)).

CONCLUSION

We found that elevated serum levels of IGFBP-1, -2, and -6 were associated with T1D, and its complications and IGFBP-3 level was found to be decreased in T1D with complications. Given the known role of these IGFBPs, the overall impact of these alterations suggests a negative effect on IGF signaling.

Featured Article: Oxidative stress status and liver tissue defenses in diabetic rats during intensive subcutaneous insulin therapy

Long-term insulin delivery can reduce blood glucose variability in diabetic patients. In this study, its impact on oxidative stress status, inflammation, and liver injury was investigated. Diabetes was induced in Wistar rats with a single dose of streptozotocin (100 mg/kg). Untreated rats and rats administered Insuplant® (2 UI/200 g/day) through a subcutaneous osmotic pump for one or four weeks were compared with non-diabetic controls. Body weight, fructosamine level, total cholesterol, Insulin Growth Factor-1 (IGF-1) level, lipid peroxidation, and total antioxidant capacity were measured. Hepatic injury was determined through the measurement of glycogen content, reactive oxygen species (ROS) production, and macrophage infiltration. Liver oxidative stress status was evaluated through the measurement of superoxide dismutase (SOD), catalase (CAT), and nicotinamide adenine dinucleotide phosphate-oxidase (NADPH oxidase) expression, and p38 mitogen-activated protein kinase (p38MAPK) activation. Induction of diabetes led to increased plasma oxidative stress and inflammation. Moreover, ROS production and macrophage infiltration increased in addition to SOD, CAT, and NADPH oxidase expression. Intensive insulin therapy improved metabolic control in diabetic animals as seen by a restoration of hepatic glycogen, plasma IGF-1 levels, and a decrease in plasma oxidative stress. However, insulin treatment did not result in a decrease in acute inflammation in diabetic rats as seen by continued ROS production and macrophage infiltration in the liver, and a decrease of p38MAPK activation. These results suggest that the onset of diabetes induces liver oxidative stress and inflammation, and that subcutaneous insulin administration cannot completely reverse these changes. Targeting oxidative stress and/or inflammation in diabetic patients could be an interesting strategy to improve therapeutic options.