Simona I. Chisalita

IGF-I/insulin hybrid receptors in human endothelial cells

Vascular complications are common in diabetes. IGF-I receptors (IGF-IR) and insulin receptors (IR) in endothelial cells might respond to altered levels of IGF-I and insulin, resulting in altered endothelial function in diabetes. We therefore studied IGF-IR and IR gene expression, ligand binding, receptor protein, and phosphorylation in human umbilical vein endothelial cells (HUVEC). IGF-IR mRNA was more abundant than IR mRNA in freshly isolated HUVEC (IGF-IR/IR ratio 7.1 +/- 1.5) and in cultured HUVEC (ratio 3.5 +/- 0.51). Accordingly, specific binding of (125)I-IGF-I (0.64 +/- 0.25%) was higher than that of (125)I-insulin (0.25 +/- 0.09%). Protein was detected for both receptors and IGF-I/insulin hybrid receptors. IGF-IR phosphorylation was stimulated by 10(-10) to 10(-8) M IGF-I. IR were activated by 10(-9) to 10(-8) M insulin and IGF-I. We conclude that HUVEC express more IGF-IR than IR, and also express hybrid receptors. Both IGF-I and insulin phosphorylate their own receptors but only IGF-I seems to phosphorylate hybrid receptors.

Human microvascular endothelial cells are sensitive to IGF-I but resistant to insulin at the receptor level.

Human microvascular endothelial cells (HMVEC) are sensitive to IGF-I but insulin resistant and express several times more IGF-I receptors (IGF-IR) than insulin receptors (IR). Our aim was to investigate the mechanism of this insulin resistance in cultured HMVEC by studying receptor activation and signal propagation downstream. The IGF-IR beta-subunit and the IR beta-subunit were detected and found to co-precipitate. IRA was the major IR isoform expressed in HMVEC. IGF-I 10(-9) to 10(-8)M phosphorylated its cognate receptor beta-subunit. IGF-I also phosphorylated the IR beta-subunit at 10(-9)M. Phosphorylation of insulin receptor substrate 1 was obtained by IGF-I 10(-9) to 10(-8)M. Akt was phosphorylated by IGF-I at 10(-8) to 10(-7)M and by insulin 10(-7)M. IGF-I at 10(-8) to 10(-6)M significantly increased DNA-synthesis. We conclude that microvascular endothelial cells are sensitive to IGF-I but resistant to insulin due to a preponderance of IGF-I receptors and sequestration of insulin receptors into insulin/IGF-I hybrid receptors.

Insulin and IGF1 receptors in human cardiac microvascular endothelial cells: metabolic, mitogenic and anti-inflammatory effects

Diabetes is associated with microcirculatory dysfunction and heart failure and changes in insulin and IGF1 levels. Whether human cardiac microvascular endothelial cells (HMVEC-Cs) are sensitive to insulin and/or IGF1 is not known. We studied the role of insulin receptors (IRs) and IGF1 receptors (IGF1Rs) in metabolic, mitogenic and anti-inflammatory responses to insulin and IGF1 in HMVEC-Cs and human umbilical vein endothelial cells (HUVECs). IR and IGF1R gene expression was studied using real-time RT-PCR. Receptor protein expression and phosphorylation were determined by western blot and ELISA. Metabolic and mitogenic effects were measured as glucose accumulation and thymidine incorporation. An E-selectin ELISA was used to investigate inflammatory responses. According to gene expression and protein in HMVEC-Cs and HUVECs, IGF1R is more abundant than IR. Immunoprecipitation with anti-IGF1R antibody and immunoblotting with anti-IR antibody and vice versa, showed insulin/IGF1 hybrid receptors in HMVEC-Cs. IGF1 at a concentration of 10(-8) mol/l significantly stimulated phosphorylation of both IGF1R and IR in HMVEC-Cs. In HUVECs IGF1 10(-8) mol/l phosphorylated IGF1R. IGF1 stimulated DNA synthesis at 10(-8) mol/l and glucose accumulation at 10(-7) mol/l in HMVEC-Cs. TNF-α dramatically increased E-selectin expression, but no inflammatory or anti-inflammatory effects of insulin, IGF1 or high glucose were seen. We conclude that HMVEC-Cs express more IGF1Rs than IRs, and mainly react to IGF1 due to the predominance of IGF1Rs and insulin/IGF1 hybrid receptors. TNF-α has a pronounced pro-inflammatory effect in HMVEC-Cs, which is not counteracted by insulin or IGF1.

Increased IGF1 levels in relation to heart failure and cardiovascular mortality in an elderly population: impact of ACE inhibitors

OBJECTIVE There are conflicting results regarding the association of circulating IGF1 with cardiovascular (CV) morbidity and mortality. We assessed the relationship between IGF1 levels and heart failure (HF), ischemic heart disease (IHD), and CV mortality in an elderly population taking into account the possible impact of angiotensin converting enzyme (ACE) inhibitors. DESIGN AND METHODS A total of 851 persons aged 66-81 years, in a rural Swedish municipality, were subjected to medical history, clinical examination, electrocardiography, echocardiography, and fasting plasma samples. They were then followed for 8 years. RESULTS AND CONCLUSION Patients on ACE inhibitors had higher IGF1 levels compared with those without ACE inhibitors. In patients on ACE inhibitors, higher IGF1 values were found in patients with an ejection fraction (EF) <40% compared with EF ≥40%, in patients with higher proBNP levels in quartile 4 vs 1, and in patients with IHD when compared to those without ACE inhibitors (P<0.001). In patients without ACE inhibitors, no relationship was found between IGF1 levels and HF or IHD. In multivariate regression, only ACE inhibitors, ECG changes characteristic for IHD, and gender had a significant impact on IGF1. Patients with higher IGF1 levels in quintiles 4 and 5 compared to quintiles 1 and 2 had a 50% higher risk for CV death (P=0.03). This was significant after adjustment for well-known CV risk factors and ACE inhibitors (P=0.03). CONCLUSIONS Our results show that treatment with ACE inhibitors in an elderly population is associated with increased IGF1 levels, especially in patients with impaired cardiac function or IHD. High IGF1 levels tend to be associated with an increased risk for CV mortality.

Different Effects of Intraperitoneal and Subcutaneous Insulin Administration on the GH-IGF-1 Axis in Type 1 Diabetes

CONTEXT In type 1 diabetes mellitus, low levels of insulin-like growth factor -1 (IGF-1) and IGF binding protein-3 (IGFBP-3) and high levels of GH and IGFBP-1 are present, probably due to portal vein insulinopenia. OBJECTIVE To test the hypothesis that continuous ip insulin infusion (CIPII) has a more pronounced effect than sc insulin therapy on regulation of the GH-IGF-1 axis. DESIGN This was a prospective, observational case-control study. Measurements were performed twice at a 26-week interval. SETTING Two secondary care hospitals in the Netherlands participated in the study. PATIENTS There were a total of 184 patients, age- and gender-matched, of which 39 used CIPII and 145 sc insulin therapy for the past 4 years. OUTCOMES Primary endpoint included differences in IGF-1. Secondary outcomes were differences in GH, IGFBP-1, and IGFBP-3. RESULTS IGF-1 was higher with CIPII as compared to SC insulin therapy: 124 μg/liter (95% confidence interval [CI], 111-138) vs 108 μg/liter (95% CI 102-115) (P = .035). Additionally, IGFBP-3 concentrations were higher and IGFBP-1 and GH concentrations were lower with CIPII as compared to SC insulin therapy: 3.78 mg/liter (95% CI, 3.49-4.10) vs 3.31 mg/liter (95% CI, 3.17-3.47) for IGFBP-3, 50.9 μg/liter (95% CI, 37.9-68.2) vs 102.6 μg/liter (95% CI, 87.8-119.8) for IGFBP-1 and 0.68 μg/liter (95% CI, 0.44-1.06) vs 1.21 μg/liter (95% CI, 0.95-1.54) for GH, respectively. In multivariate analysis, IGF-1 had no significant association with HbA1c. CONCLUSIONS The GH-IGF-1 axis may be affected by the route of insulin administration with CIPII counteracting dysregulation of the GH-IGF1 axis present during sc insulin therapy.

After 6 years of intraperitoneal insulin administration IGF-I concentrations in T1DM patients are at low-normal level

OBJECTIVE Low concentrations of insulin-like growth factor-I (IGFI) have been reported in type 1 diabetes mellitus (T1DM), suggested to be due to low insulin concentrations in the portal vein. The aim was to describe the long-term course of IGFI concentrations among T1DM subjects treated with continuous intraperitoneal (IP) insulin infusion (CIPII). DESIGN Nineteen patients that participated in a randomized cross-over trial comparing CIPII and subcutaneous (SC) insulin therapy in 2006 were followed until 2012. IGF-I measurements were performed at the start of the 2006 study, after the 6 month SC- and CIPII treatment phase in 2006 and during CIPII therapy in 2012. Z-scores were calculated to compare the IGF-I concentrations with age-specific normative range values of a non-DM reference population. RESULTS In 2012, IGF-I Z-scores (-0.7; 95% confidence interval -1.3, -0.2) were significantly higher than at the start of the 2006 study (-2.5; -3.3, -1.8), the end of the SC (-2.0; -2.6, -1.5) and CIPII (-1.6; -2.1, -1.0) treatment phase with a mean difference of: 1.8 (0.9, 2.7), 1.3 (0.5, 2.1) and 0.8 (0.1, 1.6), respectively. CONCLUSION After 6 years of treatment with CIPII, IGF-I concentrations among T1DM patients increased to a level that is higher than during prior SC insulin treatment and is in the lower normal range compared to a non-DM reference population. The results of this study suggest that long-term IP insulin administration influences the IGF system in T1DM.

Proinsulin and IGFBP-1 predicts mortality in an elderly population.

BACKGROUND High IGFBP-1 in elderly subjects is related to all-cause and cardiovascular (CV) mortality. We studied the relation of IGFBP-1 to cardiometabolic risk factors and cardiovascular and all-cause mortality, and also the impact of proinsulin and insulin on this association in an unselected elderly primary health care population. HYPOTHESIS Our hypothesis was that proinsulin and insulin may have an impact on the association of high IGFBP-1 levels with all-cause and CV-mortality in elderly. DESIGN, SETTING AND PARTICIPANTS A cross-sectional and prospective study was carried out in a rural Swedish population. 851 persons aged 66-81 years were evaluated by medical history, clinical examination, electrocardiography, echocardiography, and fasting plasma samples, and were followed prospectively for up to 12 years. RESULTS At baseline, in a multivariate analysis, IGFBP-1 was associated with gender, N-terminal proBNP (NT pro-BNP), blood glucose, body mass index (BMI), insulin and proinsulin, estimated glomerular filtration rate (eGFR) and haemoglobin (Hb). During the follow-up period there were 230 deaths (27%), of which 134 (16%) were due to CV mortality. When divided into tertiles there was a significant difference for CV mortality and all-cause mortality between tertiles of IGFBP-1 and proinsulin. For insulin there was a significant difference only for all-cause mortality. After adjustment for well-known risks factors, proinsulin and IGFBP-1 had significant impact on all-cause mortality but only proinsulin on CV mortality. CONCLUSION Only proinsulin is an independent predictor for both all-cause mortality and CV mortality when comparing IGFBP-1, insulin, and proinsulin as prognostic biomarkers for CV and all-cause mortality in an elderly population.

Insulin-Like Growth Factor-1 at Diagnosis and during Subsequent Years in Adolescents with Type 1 Diabetes

Background Type 1 diabetes (T1D) in adolescents is associated with alterations in the insulin-like factor system probably caused both by a deranged metabolism and insulinopenia in the portal vein. Objective To study how the circulating IGF-1 is affected at diagnosis and during subsequent years in adolescents with T1D. Methods Ten girls and ten boys with type 1 diabetes (T1D), aged 13.0 ± 1.4 (mean ± SD) years at diagnosis, took part in the study. Blood samples were drawn at diagnosis and after 3, 9, 18, and 48 months. HbA1c, total IGF-1, and C-peptide were measured. Results At diagnosis, the patients had high HbA1c, low IGF-1, and measurable C-peptide. After the start of insulin treatment, maximal improvement in glycemic control and IGF-1 occurred within 3 months and then both tended to deteriorate, that is, HbA1c to increase and IGF-1 to decrease. C-peptide decreased with time, and after 4 years, half of the patients were C-peptide negative. At diagnosis, C-peptide correlated positively to IGF-1 (r = 0.50; p < 0.03). C-peptide correlated negatively with insulin dose (U/kg) after 18 and 48 months from diagnosis (r = −0.48; p < 0.03 and r = −0.72; p < 0.001, resp.). Conclusions In conclusion, our results show that in newly diagnosed adolescents with type 1 diabetes and deranged metabolism, the IGF-1 level is low and rapidly improves with insulin treatment but later tends to decrease concomitantly with declining endogenous insulin secretion.