Residual beta-cell function more than glycemic control determines abnormalities of the insulin-like growth factor system in type 1 diabetes

Targeted serum proteomics of longitudinal samples from newly diagnosed youth with type 1 diabetes distinguishes markers of disease and C-peptide trajectory

AIMS/HYPOTHESIS

There is a growing need for markers that could help indicate the decline in beta cell function and recognise the need and efficacy of intervention in type 1 diabetes. Measurements of suitably selected serum markers could potentially provide a non-invasive and easily applicable solution to this challenge. Accordingly, we evaluated a broad panel of proteins previously associated with type 1 diabetes in serum from newly diagnosed individuals during the first year from diagnosis. To uncover associations with beta cell function, comparisons were made between these targeted proteomics measurements and changes in fasting C-peptide levels. To further distinguish proteins linked with the disease status, comparisons were made with measurements of the protein targets in age- and sex-matched autoantibody-negative unaffected family members (UFMs).

METHODS

Selected reaction monitoring (SRM) mass spectrometry analyses of serum, targeting 85 type 1 diabetes-associated proteins, were made. Sera from individuals diagnosed under 18 years (n=86) were drawn within 6 weeks of diagnosis and at 3, 6 and 12 months afterwards (288 samples in total). The SRM data were compared with fasting C-peptide/glucose data, which was interpreted as a measure of beta cell function. The protein data were further compared with cross-sectional SRM measurements from UFMs (n=194).

RESULTS

Eleven proteins had statistically significant associations with fasting C-peptide/glucose. Of these, apolipoprotein L1 and glutathione peroxidase 3 (GPX3) displayed the strongest positive and inverse associations, respectively. Changes in GPX3 levels during the first year after diagnosis indicated future fasting C-peptide/glucose levels. In addition, differences in the levels of 13 proteins were observed between the individuals with type 1 diabetes and the matched UFMs. These included GPX3, transthyretin, prothrombin, apolipoprotein C1 and members of the IGF family.

CONCLUSIONS/INTERPRETATION

The association of several targeted proteins with fasting C-peptide/glucose levels in the first year after diagnosis suggests their connection with the underlying changes accompanying alterations in beta cell function in type 1 diabetes. Moreover, the direction of change in GPX3 during the first year was indicative of subsequent fasting C-peptide/glucose levels, and supports further investigation of this and other serum protein measurements in future studies of beta cell function in type 1 diabetes.

Verapamil Prevents Decline of IGF-I in Subjects With Type 1 Diabetes and Promotes β-Cell IGF-I Signaling

Verapamil promotes functional β-cell mass and improves glucose homeostasis in diabetic mice and humans with type 1 diabetes (T1D). Now, our global proteomics analysis of serum from subjects with T1D at baseline and after 1 year of receiving verapamil or placebo revealed IGF-I as a protein with significantly changed abundance over time. IGF-I, which promotes β-cell survival and insulin secretion, decreased during disease progression, and this decline was blunted by verapamil. In addition, we found that verapamil reduces β-cell expression of IGF-binding protein 3 (IGFBP3), whereas IGFBP3 was increased in human islets exposed to T1D-associated cytokines and in diabetic NOD mouse islets. IGFBP3 binds IGF-I and blocks its downstream signaling, which has been associated with increased β-cell apoptosis and impaired glucose homeostasis. Consistent with the downregulation of IGFBP3, we have now discovered that verapamil increases β-cell IGF-I signaling and phosphorylation/activation of the IGF-I receptor (IGF1R). Moreover, we found that thioredoxin-interacting protein (TXNIP), a proapoptotic factor downregulated by verapamil, promotes IGFBP3 expression and inhibits the phosphorylation/activation of IGF1R. Thus, our results reveal IGF-I signaling as yet another previously unappreciated pathway affected by verapamil and TXNIP that may contribute to the beneficial verapamil effects in the context of T1D.

ARTICLE HIGHLIGHTS

Verapamil prevents the decline of IGF-I in subjects with type 1 diabetes (T1D). Verapamil decreases the expression of β-cell IGF-binding protein 3 (IGFBP3), whereas IGFBP3 is increased in human and mouse islets under T1D conditions. Verapamil promotes β-cell IGF-I signaling by increasing phosphorylation of IGF-I receptor and its downstream effector AKT. Thioredoxin-interacting protein (TXNIP) increases IGFBP3 expression and inhibits the phosphorylation/activation of IGF1R in β-cells. Regulation of IGFBP3 and IGF-I signaling by verapamil and TXNIP may contribute to the beneficial verapamil effects in the context of T1D.

[Diabetes mellitus and cancer: a system of insulin-like growth factors]

Diabetes mellitus and malignant tumors are among the most common and complex diseases. Epidemiological studies have shown a strong relationship between these pathologies. The causality of this relationship has not yet been unambiguously established, but a number of probable biological mechanisms have been proposed to explain it through the effects of hyperglycemia, hyperinsulinemia on the process of oncogenesis. An important role in this is played by the axis of insulin-like growth factors, their receptors and binding proteins (IGF / IGFR / IGFBP). The review provides data on the structural elements of the insulin / IGF / IGFR / IGFBP signaling axis and their internal relationships in diabetes mellitus and in the development of malignant tumors. Significant changes in the axis that occur during the formation of the diabetic environment prepare the background, which, under certain conditions, can lead to the stimulation or inhibition of tumor development. The considered signaling system, playing a significant role in the physiology of normal cells, often functions as a decisive factor in the survival of tumor cells, providing fine context-dependent regulation of many cellular processes associated with oncogenesis. However, despite many years of in-depth studies of the pathogenesis of diabetes mellitus and malignant tumors, the molecular mechanisms of the relationship between these pathologies are still largely unclear, and the internal heterogeneity of pathologies complicates research and interpretation of the results, leaving many questions.

A low serum IGF-1 is correlated with sarcopenia in subjects with type 1 diabetes mellitus: Findings from a post-hoc analysis of the iDIAMOND study

AIM

Our previous study revealed that sarcopenia was frequently observed in subjects with type 1 diabetes mellitus (T1DM). However, the factors associated with sarcopenia that are related to T1DM have not yet been clarified. Insulin-like growth factor-1 (IGF-1) has been shown to play a role in skeletal muscle growth, differentiation, and regeneration. The present study, therefore, investigated the association between the serum IGF-1 level and sarcopenia and low skeletal muscle mass in subjects with T1DM.

METHODS

This cross-sectional study enrolled subjects with T1DM (n = 168) and without diabetes (n = 59) who had had their clinical data on serum IGF-1 collected in the iDIAMOND study.

RESULTS

The z-score of serum IGF-1 was significantly lower in the subjects with T1DM than that in those without diabetes (p < 0.001). Among subjects with T1DM, the z-score of serum IGF-1 was significantly lower in sarcopenic subjects than in non-sarcopenic subjects. The multivariable logistic regression analysis showed that the serum IGF-1 z-score was an independent determinant of sarcopenia and a low skeletal muscle mass index, but not low grip strength nor slow gait speed in subjects with T1DM.

CONCLUSIONS

A low serum IGF-1 level is correlated with sarcopenia and low skeletal muscle mass in subjects with T1DM.

Insulin-Like Growth Factor Dysregulation Both Preceding and Following Type 1 Diabetes Diagnosis

Insulin-like growth factors (IGFs), specifically IGF1 and IGF2, promote glucose metabolism, with their availability regulated by IGF-binding proteins (IGFBPs). We hypothesized that IGF1 and IGF2 levels, or their bioavailability, are reduced during type 1 diabetes development. Total serum IGF1, IGF2, and IGFBP1-7 levels were measured in an age-matched, cross-sectional cohort at varying stages of progression to type 1 diabetes. IGF1 and IGF2 levels were significantly lower in autoantibody (AAb)⁺ compared with AAb^- relatives of subjects with type 1 diabetes. Most high-affinity IGFBPs were unchanged in individuals with pre-type 1 diabetes, suggesting that total IGF levels may reflect bioactivity. We also measured serum IGFs from a cohort of fasted subjects with type 1 diabetes. IGF1 levels significantly decreased with disease duration, in parallel with declining β-cell function. Additionally, plasma IGF levels were assessed in an AAb⁺ cohort monthly for a year. IGF1 and IGF2 showed longitudinal stability in single AAb⁺ subjects, but IGF1 levels decreased over time in subjects with multiple AAb and those who progressed to type 1 diabetes, particularly postdiagnosis. In sum, IGFs are dysregulated both before and after the clinical diagnosis of type 1 diabetes and may serve as novel biomarkers to improve disease prediction.

Effect of home-based strength training program on IGF-I, IGFBP-1 and IGFBP-3 in obese Latino boys participating in a 16-week randomized controlled trial

Introduction Growing evidence indicates that circulating concentrations of insulin-like growth factor 1 (IGF-I), along with IGF-I relative to IGF-binding proteins (IGFBP), are associated with an increased risk of cancer. In accord, regular exercise is linked with a lower risk of cancer. Purpose To assess the effects of a 16-week home-based strength training (HBST) program on serum IGF-I, IGFBP-1 and IGFBP-3. Methods A total of 32 obese Latino adolescent males (aged 14-18 years) were randomized into a twice-weekly HBST (n = 16) or a control group (C, n = 16) for 16 weeks. The following were measured at pre- and post-intervention: IGF-I, IGFBP-1 and IGFBP-3, glucose/insulin indices by oral and/or intravenous (IV) glucose tolerance tests, strength by one-repetition maximum (1RM), dietary intake by 3-d records, body composition by DEXA and physical activity using the Actigraph GT1X. The generalized linear model (GLM) was used to assess differences in changes among outcome measures between the HBST and C groups. Results Exercise adherence in the HBST group was 89%. IGF-1 showed a trend for significant within-subject improvements (p = 0.078) but no significant within-subject or between-subject differences for IGFBP-1, IGFBP-3 two-glucose, fasting glucose or 2-h glucose (p > 0.05). There was a significant decrease (p > 0.05) in fasting glucose in the C group (p = 0.02) and also in the intervention group (p = 0.03) between baseline and follow-up testing. A significant difference was also found in the C group for 2-h glucose with an increase at follow-up testing (p = 0.04). Conclusions Though not statistically significant (p < 0.05), the results indicated that a 16-week HBST program decreased IGF-I and increased IGFBP-1, along with IGFBP-3, concentrations among overweight/obese Latino boys. However, further studies should consider increasing either the dose or the duration of the intervention to elicit greater improvements in this at-risk pediatric population.

The association of insulin-like growth factor-1 standard deviation score and height in Chinese children with type 1 diabetes mellitus

Assessing the relationship between IGF-1 and height in type 1 diabetes children. Seventy-two type 1 diabetes children and 190 controls were recruited. The height standard deviation score of type 1 diabetes children was significantly higher than controls. The height standard deviation score was higher than the target height standard deviation score in both type 1 diabetes and controls. Serum IGF-1 levels and the IGF-1 standard deviation score were significantly lower in type 1 diabetes patients compared with controls. There was a significant difference in IGF-1 standard deviation score between the good glycemic control group and control group. The height standard deviation score was significantly correlated with C-peptide and IGF-1 levels. Furthermore, the IGF-1 standard deviation score was significantly correlated with glycemic control and C-peptide. The growth hormone/IGF-1 axis is impaired in type 1 diabetes, but height with good or poor glycemic control is not impaired.

Dysregulated growth hormone-insulin-like growth factor-1 axis in adult type 1 diabetes with long duration

CONTEXT

In type 1 diabetes (T1D), dysregulation of the GH-IGF-1 axis has been reported. Whether this is related to upper extremity impairments (UEI) is unknown.

OBJECTIVE

Examine differences in GH-IGF-1 axis between T1D on subcutaneous insulin treatment and matched controls without diabetes and possible associations between GH-IGF-1 axis and UEI.

DESIGN

Cross-sectional population-based study. Patients with T1D, onset <35 years, duration ≥ 20 years, <67 years old and controls were invited to answer questionnaires and take blood samples.

SUBJECTS

A total of 605 patients with T1D and 533 controls accepted to participate.

OUTCOMES

Fasting levels of IGF-1, IGF-1 Z-score, IGFBP-1, IGFBP-3, C-peptide, GH and UEI.

RESULTS

Patients with T1D had lower IGF-1 and IGFBP-3 and higher IGFBP-1 and GH than controls. The difference in IGF-1 persisted with age. Insulin dose was associated with increasing IGF-1 Z-score but even at a very high insulin dose (>1U/kg) IGF-1 Z-score was subnormal compared to controls. IGF-1 Z-score was unaffected by glycaemic control (HbA1c) but increased with residual insulin secretion, (C-peptide 1-99 pmol/L). IGFBP-1 was associated with fasting blood glucose, negatively in controls and positively in patients with T1D probably reflecting insulin resistance and insulin deficiency, respectively. There was no association between lower IGF-1 Z-score and UEI in T1D.

CONCLUSION

In adult T1D with fair glycaemic control, the GH-IGF-1 axis is dysregulated exhibiting GH resistance, low IGF-1 and elevated IGFBP-1. Subcutaneous insulin cannot normalize these changes while endogenous insulin secretion has marked effects on IGF-1 pointing to a role of portal insulin.

Deficiency of liver-derived insulin-like growth factor-I (IGF-I) does not interfere with the skin wound healing rate

Objective

IGF-I is a growth factor, which is expressed in virtually all tissues. The circulating IGF-I is however derived mainly from the liver. IGF-I promotes wound healing and its levels are decreased in wounds with low regenerative potential such as diabetic wounds. However, the contribution of circulating IGF-I to wound healing is unknown.

Here we investigated the role of systemic IGF-I on wound healing rate in mice with deficiency of liver-derived IGF-I (LI-IGF-I-/- mice) during normal (normoglycemic) and impaired wound healing (diabetes).

Methods

LI-IGF-I-/- mice with complete inactivation of the IGF-I gene in the hepatocytes were generated using the Cre/loxP recombination system. This resulted in a 75% reduction of circulating IGF-I. Diabetes was induced with streptozocin in both LI-IGF-I-/- and control mice. Wounds were made on the dorsum of the mice, and the wound healing rate and histology were evaluated. Serum IGF-I and GH were measured by RIA and ELISA respectively. The expression of IGF-I, IGF-II and the IGF-I receptor in the skin were evaluated by qRT-PCR. The local IGF-I protein expression in different cell types of the wounds during wound healing process was analyzed using immunohistochemistry.

Results

The wound healing rate was similar in LI-IGF-I-/- mice to that in controls. Diabetes significantly delayed the wound healing rate in both LI-IGF-I-/- and control mice. However, no significant difference was observed between diabetic animals with normal or reduced hepatic IGF-I production. The gene expression of IGF-I, IGF-II and IGF-I receptor in skin was not different between any group of animals tested. Local IGF-I levels in the wounds were similar between of LI-IGF-I-/- and WT mice although a transient reduction of IGF-I expression in leukocytes in the wounds of LI-IGF-I-/- was observed seven days post wounding.

Conclusion

Deficiency in the liver-derived IGF-I does not affect wound healing in mice, neither in normoglycemic conditions nor in diabetes.

Growth hormone and insulin-like growth factor-I axis in type 1 diabetes

The precise mechanisms relating type 1 diabetes (T1D) and poor glycemic control to the axis of growth hormone (GH), insulin like growth factor- I (IGF-I), and IGF binding protein-3 (IGFBP-3) remain to be definitively determined. GH resistance with low IGF-I as is frequently seen in patients with T1D is often related to portal hypoinsulization, and lack of upregulation of GH receptors. There are conflicting reports of the effect of a dysregulated GH/IGF-I axis on height in children and adolescents with T1D, as well as on chronic complications. This brief review discusses some of the interactions between the GH/IGF-I axis and T1D pathology, and vice-versa.

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.

Growth in patients with type 1 diabetes

PURPOSE OF REVIEW

As the incidence of type 1 diabetes (T1DM) continues to rise, complications including impairment of childhood growth remain a major concern. This review provides an overview of alterations in growth patterns before and after the onset of T1DM.

RECENT FINDINGS

Recent advances in this field include several prospective investigations of height and weight trajectories in children leading up to the development of islet autoimmunity and T1DM as well as evaluations of larger cohorts of T1DM patients to better assess predictors of altered growth. In addition, genetic and metabolic investigations have improved our understanding of the more rare severe growth impairment of Mauriac Syndrome.

SUMMARY

Despite advances in medical care of children with T1DM, growth remains suboptimal in this population and likely reflects ongoing metabolic derangement linked with classic microvascular diabetic complications.

The Effect of Hyperglycemic Hyperinsulinemia on Small-Intestinal Mucosal Protein Synthesis in Patients After Surgical Stress

Hyperglycemic hyperinsulinemia cannot stimulate intestinal protein synthesis in healthy individuals but does so in conditions characterized by an altered somatotropic axis such as diabetes. Only in a state of growth hormone resistance (high growth hormone but low insulin like growth factor [IGF-1] concentrations), extra insulin may acutely reverse the impaired, growth-hormone-induced IGF-1 release, thereby exerting anabolic actions at the intestinal tract. Growth hormone resistance can be also found in patients after surgical stress. Therefore, we wanted to test the hypothesis whether hyperglycemic hyperinsulinemia would stimulate ileal protein synthesis in the latter condition. Mass spectrometry techniques (capillary gas chromatography/combustion isotope ratio mass spectrometry) were used to directly determine the incorporation rate of 1-[(13)C]-leucine into ileal mucosal protein. All subjects had an ileostomy, which allowed easy access to the ileal mucosa, and consecutive sampling from the same tissue was performed during continuous isotope infusion (0.16 mumol/kg min). Isotopic enrichments and fractional protein synthesis were determined at baseline (period I) and after a 4-hour glucose infusion (170 mg/kg/h) or after infusion of saline (control group) (period II). In controls, ileal protein synthesis declined significantly during prolonged isotope infusion (period I: 1.11 +/- 0.14%/h, period II: 0.39 +/- 0.13%/h, p < .01). In contrast, ileal protein synthesis remained constant during glucose infusion (period I: 1.32 +/- 0.35%/h, period II: 1.33 +/- 0.21%/h, n.s. vs period I, but p < .005 vs the corresponding value at the end of period II in the control group). Using the continuous tracer infusion technique, ileal protein synthesis seemingly declines over a short time in control subjects. We found evidence that this artificial decline was due to mass effects of a rapidly turning over mucosa protein pool in which an isotopic plateau was reached during the experiment and of which the size amounted to approximately 4% of the total mixed protein pool. Maintenance of ileal protein synthesis during glucose infusion therefore indicates a rise of ileal protein synthesis in a slowly turning over protein pool. This effect in postsurgical patients would be compatible with the concept of intestinal insulin action to depend on the specific clinical state (eg, growth hormone resistance).

The influence of type 2 diabetes on serum GH and IGF-I levels in hospitalized Japanese patients

OBJECTIVE

Although serum insulin like growth factor type 1 (IGF-I) levels are negatively correlated with hemoglobin A1c (HbA1c) in patients with type 1 diabetes, this correlation is controversial in patients with type 2 diabetes mellitus (T2DM) because of the influence of multiple factors including insulin secretion and obesity. The aim of this study was to evaluate the influence of T2DM on serum growth hormone (GH) and IGF-I levels in Japanese patients, who exhibited relatively low BMI compared with white patients in the previous studies.

DESIGN

We retrospectively analysed 315 consecutive Japanese hospitalized patients with T2DM. We analysed factors correlated with changes in serum IGF-I levels and those related to diabetes.

RESULTS

The median HbA1c was 8.7% (7.4-10.2) and the median body mass index (BMI) was 26.2kg/m(2) (23.1-29.7), which was relatively low compared with the previous studies. Overall, no correlations was found between serum GH or IGF-I levels and fasting plasma glucose (FPG) or HbA1c; however, when stratified by FPG and HbA1c levels, serum IGF-I levels were significantly lower in patients with FPG≥200mg/dL than in those with FPG<200mg/dL (p=0.039). In addition, serum IGF-I levels were significantly lower in patients with HbA1c≥12% than in those with HbA1c<12% (p=0.046). Multiple linear regression analysis revealed a positive correlation between fasting C-peptide levels and serum IGF-I levels (p=0.040), whereas no correlations was found for BMI, duration of T2DM, FPG levels, or HbA1c. Moreover, patients with improved HbA1c levels during the follow up period showed a significant increase in serum IGF-I levels.

CONCLUSIONS

Serum IGF-I levels were significantly decreased in Japanese patients with uncontrolled T2DM, and impaired insulin secretion may be a mechanism underlying this effect. When diagnosing acromegaly in patients with uncontrolled diabetes, these factors should be taken into account.

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.

After 6years 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.

Type 1 diabetes patients have lower strength in femoral bone determined by quantitative computed tomography: A cross-sectional study

AIMS/INTRODUCTION

Previous studies have reported osteoporosis measured by dual-energy X-ray absorptiometry in younger patients with type 1 diabetes. Limitations of 2-D imaging, however, limit the precision of dual-energy X-ray absorptiometry for the measurement of bone mineral density and bone strength.

MATERIALS AND METHODS

Three-dimensional quantitative computed tomography was used to calculate volumetric-bone mineral density (vBMD) and strength in femoral bone subfractions. A total of 17 male type 1 diabetes patients and 18 sex-matched healthy controls aged from 18 to 49 years were investigated in the present cross-sectional study. Patients with overt nephropathy were excluded.

RESULTS

Type 1 diabetes patients had significantly lower cortical vBMD in the femoral neck, and significantly lower total vBMD, cortical thickness and cortical cross-sectional area (cortical CSA) in the intertrochanter. Bone strength estimated by the buckling ratio (an index of cortical instability) of the intertrochanter was significantly higher in type 1 diabetes patients. The following serum bone markers were comparable between the two groups: bone-specific alkaline phosphatase, N-terminal propeptide of type 1 procollagen, osteocalcin, pentosidine and homocysteine. Serum insulin-like growth factor-1 values were significantly lower in the type 1 diabetes patients than in controls. Serum insulin-like growth factor-1values were positively correlated with serum bone formation markers, and the total vBMD of the femoral neck and lumbar spine in type 1 diabetes patients.

CONCLUSIONS

The present study is the first investigation by quantitative computed tomography measurement to show cortical instability and lower vBMD in the intertrochanter of young and middle-aged type 1 diabetes patients. Low insulin-like growth factor-1 might be a causative factor for osteoporosis in type 1 diabetes.

Residual β-cell function and the insulin-like growth factor system in Danish children and adolescents with type 1 diabetes

CONTEXT

C-peptide-positive adults with type 1 diabetes (T1D) have higher circulating total and free IGF-1 and lower IGF binding protein 1 (IGFBP-1) than C-peptide-negative patients. Whether this is also the case in children remains unknown.

OBJECTIVE

The objective of the study was to examine the IGF system in children/adolescents with and without residual β-cell function (RBF).

DESIGN AND PATIENTS

This was a cross-sectional study containing 136 prepubertal (hereof 15 RBF positive) and 206 pubertal (hereof 42 RBF positive) children/adolescents with T1D for 3-6 years as well as 40 prepubertal and 30 pubertal healthy controls. RBF was evaluated by meal-stimulated C-peptide.

MAIN OUTCOME MEASURES

Fasting serum levels of bioactive IGF (ie, the ability of serum to activate the IGF-1 receptor in vitro), total IGF-1, total IGF-2, and IGFBP-1 and -3.

RESULTS

Irrespective of pubertal status, patients with T1D showed lower bioactive IGF and total IGF-1, but higher IGFBP-1 as compared with controls (P < .05). When stratified according to RBF status, a positive RBF was associated with normalization of all IGF-related peptides but IGFBP-1 in prepubertal children (P < .05), whereas none of the IGF components were normalized in prepubertal, RBF-negative children. In pubertal children, total IGF-1 and bioactive IGF remained subnormal and IGFBP-1 supranormal, irrespective of RBF status (P < .05).

CONCLUSION

Independent of pubertal status, T1D was associated with an abnormal IGF system. However, a positive RBF status appeared important but only in prepubertal children, in whom all IGF components but IGFBP-1 were normalized. We speculate that the pubertal GH surge induces insulin resistance, which overrides the stimulatory effect that an RBF may exert on the liver-derived IGF system.

The trajectory of IGF-1 across age and duration of type 1 diabetes

BACKGROUND

Individuals with type 1 diabetes may have low IGF-1, related to insulinopenia and insulin resistance. There are few longitudinal studies of IGF-1 levels to establish its pattern in type 1 diabetes with duration and age, and to examine whether IGF-1 tracks within individuals over time. We examine age and duration trends, and the relationship of IGF-1 to gender, glycaemic control, insulin level and other factors.

METHODS

Participants in the Wisconsin Diabetes Registry Study, an incident cohort study of type 1 diabetes diagnosed May 1987-April 1992, were followed for up to 18 years with IGF-1 samples up to age 45 for women and age 37 for men.

RESULTS

IGF-1 is lower with type 1 diabetes than in normative samples. Although, the pattern across age resembles that in normative samples with a peak in adolescence and slow decline after age 20, the adolescent peak is delayed for women with type 1 diabetes. There was low to moderate tracking of IGF-1 within an individual. Higher insulin dose was associated with higher IGF-1 as was puberty, and female gender. Adjusted for these factors, IGF-1 declined rapidly across early diabetes duration. Lower HbA1c was most strongly related to higher IGF-1 at Tanner stages 1 and 2.

CONCLUSIONS

IGF-1 is low in type 1 diabetes, with a delayed adolescent peak in women and is especially influenced by glycaemic control in early and pre-adolescence. High variability within an individual is likely a challenge in investigating associations between IGF-1 and long-term outcomes, and may explain contradictory findings.

Short-term effects of NPH insulin, insulin detemir, and insulin glargine on the GH-IGF1-IGFBP axis in patients with type 1 diabetes

OBJECTIVE

Insulin regulates the GH-IGF1 axis. Insulin analogs differ from human insulin in receptor affinity and possibly liver accessibility. Therefore, we compared the GH-IGF1 axis response with human NPH insulin, insulin detemir, and insulin glargine in patients with type 1 diabetes (T1D).

METHODS

A total of 17 patients (seven were women) with T1D (age of 42 (24-63) years (mean and range), BMI of 24.7 (19.5-28.3) kg/m(2), HbA1c of 7.2 (6.3-8.0) % (55 (45-64) mmol/mol), T1D duration of 26 (8-45) years) were studied using a randomized, three-period crossover design. Patients received s.c. injections of equal, individual doses of NPH, detemir, and glargine at 1800 h. Plasma glucose, serum total IGF1, bioactive IGF, IGF-binding protein (IGFBPs), and GH were measured hourly for 14 h post-injection.

RESULTS

When compared with the area under the curve (AUC) following NPH and glargine, detemir resulted in the lowest 6-14 h AUC (mean and range) of IGFBP1 (1518 (1280-1800)) vs 1621 (1367-1922) vs 1020 (860-1210) μg/l×h) and GH (17.1 (14.1-20.6) vs 15.4 (12.7-18.6) vs 10.2 (8.5-12.3) μg/l×h), but in the highest AUC of bioactive IGF (3.8 (3.5-4.2) vs 3.7 (3.4-4.0) vs 4.4 (4.1-4.8) μg/l×h) (all P<0.01). These differences were unrelated to plasma glucose. By contrast, profiles of total IGF1, IGFBP2, and IGFBP3 were comparable.

CONCLUSIONS

Independent of plasma glucose, a single dose of detemir caused larger suppression in serum IGFBP1 than NPH and glargine, whereas bioactive IGF was higher, thereby explaining the lower GH levels. Thus, detemir appears to be more liver specific than NPH insulin and glargine.

Intraperitoneal insulin infusion: treatment option for type 1 diabetes resulting in beneficial endocrine effects beyond glycaemia

Continuous intraperitoneal insulin infusion (CIPII) is a treatment option for patients with type 1 diabetes mellitus who fail to reach adequate glycaemic control despite intensive subcutaneous (SC) insulin therapy. CIPII has clear advantages over SC insulin administration in terms of pharmacokinetic and pharmacodynamic properties and has been shown to improve glycaemic regulation. Due to the delivery of insulin predominantly in the portal vein, as opposed to systemically, CIPII offers a unique research model to investigate the effects of insulin on endocrine and metabolic parameters in vivo. The aim of the present article is to provide an overview of the literature with respect to the effects of CIPII on glucose management, quality of life, complications and costs, with additional focus on metabolic and endocrine aspects. Finally, future use and research objectives are discussed.

Intraperitoneal insulin delivery to patients with type 1 diabetes results in higher serum IGF-I bioactivity than continuous subcutaneous insulin infusion

OBJECTIVE

Type 1 diabetes (T1D) is associated with low IGF-I and altered levels of IGF-binding proteins (IGFBPs) in plasma. This may be of importance for insulin sensitivity and the risk of developing diabetic complications. We hypothesized that IGF-I bioactivity is affected by the route of insulin administration and that continuous intraperitoneal insulin infusion (CIPII) has a more pronounced effect than continuous subcutaneous insulin infusion (CSII).

DESIGN AND METHODS

We compared 10 patients with T1D on CIPII with 20 age- and sex-matched patients on CSII. Blood sampling was carried out 7-9 am after an overnight fast. All patients were C-peptide negative. IGF-I bioactivity was measured in vitro using a specific IGF-I kinase receptor activation (KIRA) assay. IGF-I was also measured by immunoassay together with IGF-II, IGFBP-1 and IGFBP-2.

RESULTS

When compared with subcutaneous insulin, intraperitoneal insulin resulted in (CIPII vs CSII) higher IGF-I bioactivity (1·83 ± 0·76 vs 1·16 ± 0·24 μg/l; P = 0·02), IGF-I (120 ± 35 vs 81 ± 19 μg/l; P = 0·01) and IGF-II (1050 ± 136 vs 879 ± 110 μg/l; P = 0·02). By contrast, log-transformed IGFBP-1 was reduced (P = 0·013), whereas log-transformed IGFBP-2 was not different (P = 0·12). There was a positive correlation between IGF bioactivity and IGF-I (r = 0·69; P < 0·001) and an inverse correlation between IGF-I bioactivity and log10 IGFBP-1 (r = -0·68, P < 0·001).

CONCLUSION

The in vitro IGF-I bioactivity was higher in patients treated with CIPII compared with CSII supporting the theory that the route of insulin administration is of importance for the activity of the IGF system. Intraperitoneal insulin administration may therefore be beneficial by correcting the alterations of the IGF system in T1D.

Effects of human insulin and insulin aspart preparations on levels of IGF-I, IGFBPs and IGF bioactivity in patients with type 1 diabetes

BACKGROUND

Insulin aspart (IAsp) and its biphasic preparations BIAsp50 and BIAsp70 (containing 50% and 70% IAsp, respectively) have distinct glucose-lowering properties as compared to human insulin (HI). We investigated whether this affected the circulating IGF-system which depends on the hepatic insulin exposure.

METHODS

In a randomized, four-period crossover study, 19 patients with type 1 diabetes received identical doses (0.2 U/kg sc) of IAsp, BIAsp70, BIAsp50 and HI together with a standardized meal. Serum total IGF-I and IGFBP-1 to -3 were measured by immunoassays for nine hours post-prandially. Bioactive IGF was determined by an in-house, cell-based IGF-I receptor kinase activation (KIRA) assay.

RESULTS

Despite marked differences in peripheral insulin concentrations and plasma glucose, the four insulin preparations resulted in parallel decreases in IGFBP-1 levels during the first 3 hours, and parallel increases during the last part of the study (3-9 hours). Thus, only minor significances were seen. Insulin aspart and human insulin resulted in a lower area under the curve (AUC) during the first 3 hours as compared to BIAsp70 (p = 0.009), and overall, human insulin resulted in a lower IGFBP-1 AUC than BIAsp70 (p = 0.025). Nevertheless, responses and AUCs of bioactive IGF were similar for all four insulin preparations. Changes in levels of bioactive IGF were inversely correlated to those of IGFBP-1, increasing during the first 3 hours, whereafter levels declined (-0.83 ≤ r ≤ -0.30; all p-values <0.05).Total IGF-I and IGFBP-3 remained stable during the 9 hours, whereas IGFBP-2 changed opposite of IGFBP-1, increasing after 3-4 hours whereafter levels gradually declined. The four insulin preparations resulted in similar profiles and AUCs of total IGF-I, IGFBP-2 and IGFBP-3.

CONCLUSIONS

Despite distinct glucose-lowering properties, the tested insulin preparations had similar effects on IGF-I concentration and IGF bioactivity, IGFBP-2 and IGFBP-3 as compared to HI; only small differences in IGFBP-1 were seen and they did not affect bioactive IGF. Thus, insulin aspart containing preparation behaves as HI in regards to the circulating IGF-system. However, bioactive IGF appeared to be more sensitive to insulin exposure than total IGF-I. The physiological significance of this finding remains to be determined.

TRIAL REGISTRATION

NCT00888732.

Effects of raloxifene and estrogen on bioactive IGF1 in GH-deficient women

CONTEXT

GH action is attenuated by estrogens and selective estrogen receptor modulators (SERMs) administered orally. During GH therapy in hypopituitary women, co-treatment with raloxifene, a SERM, induced a smaller gain in lean body mass (LBM) compared with estrogen, despite an equal reduction in IGF1. As a higher IGF-binding protein-3 (IGFBP3) level was observed with raloxifene co-treatment, we hypothesize that an increase in IGFBP3 reduced IGF1 bioactivity causing the attenuated anabolic effect.

OBJECTIVE

To assess the effects of 17β-estradiol (E₂) and raloxifene on bioactive IGF1.

DESIGN

In study 1, 12 GH-deficient (GHD) women were randomized to raloxifene 120 mg/day or E₂ 4 mg/day for 1 month. In study 2, 16 GHD women were randomized to 1 month GH treatment alone (0.5 mg/day) and in combination with raloxifene (60 mg/day) or E₂ (2 mg/day). We measured bioactive IGF1, immunoreactive IGF1 and IGF2, and IGFBP3 immunoreactivity and fragmentation.

RESULTS

Raloxifene and estrogen suppressed (P<0.05) total IGF1 equally in GHD and GH-replaced hypopituitary women. In GHD patients, neither raloxifene nor estrogen affected bioactive IGF1. GH significantly increased IGF1 bioactivity, an effect attenuated by co-treatment with raloxifene (Δ -23 ± 7%, P<0.01) and estrogen (Δ -26 ± 3%, P=0.06). Total IGF1 correlated (r(2)=0.54, P<0.001) with bioactive IGF1, which represented 3.1 ± 0.2% of the total IGF1, irrespective of the treatments. Total IGF2 was unchanged by raloxifene and estrogen treatment. IGFBP3 was significantly higher during raloxifene administration, whereas no differences in IGFBP3 fragmentation were observed.

CONCLUSION

Raloxifene effect on bioactive IGF1 is similar to that of estrogen despite higher IGFBP3 levels during raloxifene administration. We conclude that the observed different effects on LBM between raloxifene and estrogen treatments cannot be explained by differences in IGF1 bioactivity.

Effect of i.p. insulin administration on IGF1 and IGFBP1 in type 1 diabetes

In type 1 diabetes mellitus (T1DM), low concentrations of IGF1 and high concentrations of IGF-binding protein 1 (IGFBP1) have been reported. It has been suggested that these abnormalities in the GH-IGF1 axis are due to low insulin concentrations in the portal vein. We hypothesized that the i.p. route of insulin administration increases IGF1 concentrations when compared with the s.c. route of insulin administration. IGF1 and IGFBP1 concentrations in samples derived from an open-label, randomized cross-over trial comparing the effects of s.c. and i.p. insulin delivery on glycaemia were determined. T1DM patients were randomized to receive either 6 months of continuous i.p. insulin infusion (CIPII) through an implantable pump (MIP 2007C, Medtronic) followed by 6 months of s.c. insulin infusion or vice versa with a washout phase in between. Data from 16 patients who had complete measurements during both treatment phases were analysed. The change in IGF1 concentrations during CIPII treatment was 10.4 μg/l (95% CI -0.94, 21.7 μg/l; P=0.06) and during s.c. insulin treatment was -2.2 μg/l (95% CI -13.5, 9.2 μg/l; P=0.69). When taking the effect of treatment order into account, the estimated change in IGF1 concentrations was found to be 12.6 μg/l (95% CI -3.1, 28.5 μg/l; P=0.11) with CIPII treatment compared with that with s.c. insulin treatment. IGFBP1 concentrations decreased to -100.7 μg/l (95% CI -143.0, -58.3 μg/l; P<0.01) with CIPII treatment. During CIPII treatment, parts of the GH-IGF1 axis changed compared with that observed during s.c. insulin treatment. This supports the hypothesis that the i.p. route of insulin administration is of importance in the IGF1 system.

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.

Quantification of the GH/IGF-axis components: lessons from human studies

Originally, the circulating bioactivity of IGF-I was estimated by bioassays measuring the ability of serum to stimulate uptake of labeled sulfate or thymidine in cultures of costal cartilage or by the ability of serum to stimulate the uptake of glucose in fat tissue cultures. However, because of their laborious and unspecific nature, the original bioassays were quickly abandoned with the development of the first RIA for IGF-I in 1977. Consequently, for the past three decades the endogenous IGF-I bioactivity has been almost exclusively estimated by the use of immunoassays. Beyond any doubt, the immunoassays have provided an extensive insight into IGF-I physiology and pathophysiology. However, immunoassays ignore the presence of the IGFBPs, which are important regulators of IGF-I action in vivo. In addition, immunoassays do not consider the presence of IGF-II, which also interacts with the IGF-I receptor (IGF-IR). This aroused our interest to reintroduce the bioassay; therefore, we established a cell-based kinase receptor activation (KIRA) assay based on cells transfected with the human IGF-IR. The output signal of the KIRA assay is IGF-IR phosphorylation, and, as such, it is highly specific. Further, because detection of phosphorylated IGF-IRs is based on modern immunoassay techniques, the overall performance of the assay is close to that of a traditional IGF-I immunoassay. The first part of this review comprises a short description of the bioassay, and a more in-depth presentation of the data that have been obtained so far. It will be demonstrated that the bioassay is indeed able to yield novel information on the IGF system, most likely because it is able to integrate the different components of the IGF system into one signal: IGF-IR activation. As IGF-I, circulating GH is bound to larger proteins, the far most important GH-binding protein (GHBP) is identical to the extracellular domain of the GH receptor (GHR). Because of its origin, GHBP binds GH with the same affinity as GHR and, consequently, GHBP may affect GH bioactivity as well as pharmacokinetics. To improve our knowledge on the complex interaction between GH and GHBP in vivo, we found it of interest to develop a method for determination of free GH. To this end, we developed an ultrafiltration assay that enabled isolation of free GH in undiluted serum during approached in vivo-like conditions. The last part of this review presents our current data on free GH and its interaction with GHBP.

Association of IGF1 with glycemic control and occurrence of severe hypoglycemia in patients with type 1 diabetes mellitus

OBJECTIVE

GH is implicated in the counter-regulatory response to hypoglycemia. We tested whether IGF1 levels are associated with occurrence of severe hypoglycemic events in patients with type 1 diabetes and whether the IGF1 concentration is influenced by glycemic control.

METHODS

A total of 228 outpatients with type 1 diabetes were included in a post hoc analysis of a 1-year observational study on severe hypoglycemia. Serum total IGF1 was measured at entry into the study. The occurrence of severe episodes of hypoglycemia, mild symptomatic, and biochemical as well as hypoglycemia awareness status was assessed. Also patients were included in a multiple regression analysis to investigate the role of HbA1c in the IGF1 concentration.

RESULTS

IGF1 levels were associated with neither severe hypoglycemia in the entire cohort (P=0.30) nor in any gender nor when confining the analysis to those with long-standing diabetes (>20 years) (n=112, P=0.68) and those with both long-standing diabetes and undetectable C-peptide (n=51, P=0.067). Levels of IGF1 were associated with neither mild symptomatic hypoglycemia (P=0.24) nor biochemical hypoglycemia (0.089) nor hypoglycemia awareness (P=0.16). At a multiple regression analysis, HbA1c was negatively associated with IGF1 (P=0.001).

CONCLUSION

In type 1 diabetes, circulating IGF1 levels are negatively associated with glycemic control. However, IGF1 levels were not associated with occurrence of hypoglycemia or hypoglycemia awareness in these patients.

Differential effects of IGF-I, IGF-II and insulin in human preadipocytes and adipocytes--role of insulin and IGF-I receptors

We compared insulin and IGF effects in adipocytes expressing IR (insulin receptors), and preadipocytes expressing IR and IGF-IR (IGF-I receptors). Treatment of adipocytes with insulin, IGF-II or IGF-I resulted in phosphorylation of IR. Order of potency was insulin>IGF-II>IGF-I. In preadipocytes IR, IGF-IR and insulin/IGF-I hybrid receptors (HR) were detected. Treatment of preadipocytes with IGF-I and IGF-II 10(-8)M resulted in activation of IGF-IR and IR whereas insulin was more potent in activating IR, with no effect on IGF-IR. In adipocytes glucose transport was 100-fold more sensitive to insulin than to IGFs and the maximal effect was higher with insulin. In preadipocytes glucose accumulation and DNA synthesis was equally sensitive to insulin and IGFs but the maximal effect was higher with IGF-I. In conclusion, insulin and IGF-I activate their cognate receptors and IGF-I also HR. IGF-II activates IR, IGF-IR and HR. Insulin and IGF-I are partial agonists to each other's receptors.

Proinsulin/C-peptide ratio, glucagon and remission in new-onset Type 1 diabetes mellitus in young adults

AIMS

After initiation of treatment in Type 1 diabetes, a period with lower insulin requirement often follows, reflecting increased insulin sensitivity and improved insulin secretion. We explored if efficiency of proinsulin processing is associated with the remission phenomenon.

METHODS

Seventy-eight patients with new-onset Type 1 diabetes were followed prospectively for 3 years. Daily insulin dosage, HbA(1c) , plasma glucose, proinsulin, C-peptide, glucagon concentrations and islet antibodies were determined at diagnosis and after 3, 6, 9, 12, 18, 24, 30 and 36 months. We studied remission, defined as an insulin dose ≤ 0.3 U kg(-1) 24 h(-1) and HbA(1c) within the normal range, in relation to the above-mentioned variables.

RESULTS

A rise and subsequent decline in plasma proinsulin and C-peptide concentrations was observed. Forty-five per cent of the patients experienced remission at one or more times, characterized by higher proinsulin and C-peptide levels, and lower proinsulin/C-peptide ratios, indicating more efficient proinsulin processing, compared with those not in remission. Non-remission also tended to be associated with higher glucagon values. Patients entering remission were more often men, had higher BMI at diagnosis, but did not differ at baseline with respect to islet antibody titres compared with patients with no remission.

CONCLUSIONS

Remissions after diagnosis of Type 1 diabetes were associated with lower proinsulin/C-peptide ratios, suggesting more efficient proinsulin processing, and tended to have lower glucagon release than non-remissions. This indicates that, in remission, the residual islets maintain a secretion of insulin and glucagon of benefit for control of hepatic glucose production.

Moderate energy restriction-induced weight loss affects circulating IGF levels independent of dietary composition

BACKGROUND

Obesity is associated with major changes in the circulating IGF system. However, it is not clear to what extent the IGF system is normalized following diet, and the possible role of different types of diet is also unknown.

OBJECTIVE

To compare changes in the circulating IGF system following 12 weeks of moderate energy restriction (7000 kJ/day) in overweight or obese males on a high protein high red meat diet (HP) or a high carbohydrate diet (HC).

DESIGN

Seventy-six men (mean age, 51+/-1.0 years; body mass index, 32.8+/-0.5 kg/m(2)) were allocated to matched groups treated with isocaloric diets of HP (n=34) or HC (n=42). Outcome measures were weight, body composition, IGF-related peptides, homoeostasis model assessment of insulin resistance (HOMA1-IR) and adipokines.

RESULTS

Weight loss did not differ between diets (HP 8.5+/-0.6 kg; HC 8.2+/-0.6 kg, P>0.05). IGF-related peptides increased total IGF1 (HP 23%; HC 18%, P<0.0001), bioactive IGF1 (HP 18%; HC 15%, P<0.002), IGF1:IGF-binding protein-3 (IGFBP-3; HP 29%; HC 22%, P<0.0001) and IGFBP-1 (HP 24%; HC 25%, P<0.01). By contrast, decreases were observed in IGFBP-3 (HP -4%; HC -3%, P<0.01), pro-IGF2 (HP -3%; HC -6%, P=0.001), total IGF2 (HP -7%; HC -3%, P=0.001) and sIGF2R (HP -10%; HC -6%, P<0.005). Only IGFBP-2 increased differentially by diet (HP 34%; HC 50%, P<0.0001, diet P<0.05). Adiponectin increased in both diets, but leptin and HOMA-IR decreased (P<0.001).

CONCLUSIONS

Weight loss induced by moderate energy restriction modulated the IGF system independent of dietary protein or red meat content. The effect of diet on IGFBP-2 appeared to have limited biological effect as total IGF2 and pro-IGF2 did not change.

Pregnancy-induced rise in serum C-peptide concentrations in women with type 1 diabetes

OBJECTIVE

The purpose of this study was to investigate whether pregnancy induces increased insulin production as a marker of improved beta-cell function in women with long-term type 1 diabetes.

RESEARCH DESIGN AND METHODS

This was a prospective study of 90 consecutive pregnant women with type 1 diabetes. At 8, 14, 21, 27, and 33 weeks blood samples were drawn for measurements of A1C, C-peptide, and serum glucose. C-peptide (detection limit: 6 pmol/l) was considered stimulated at a corresponding serum glucose concentration >or=5.0 mmol/l. GAD antibody concentration was determined at 8 and 33 weeks in 35 women.

RESULTS

C-peptide concentrations gradually increased throughout pregnancy regardless of serum glucose concentrations in the 90 women with a median duration of diabetes of 17 years (range 1-36 years). Among 35 women with paired recordings of stimulated C-peptide, C-peptide production was detectable in 15 (43%) at 8 weeks and in 34 (97%) at 33 weeks (P < 0.0001), and median C-peptide gradually increased from 6 to 11 pmol/l (P = 0.0004) with a median change of 50% (range -50 to 3,271%) during pregnancy. GAD antibodies were present in 77% with no change from 8 to 33 weeks (P = 0.85). Multivariate regression analysis revealed a positive association between the absolute increase in C-peptide concentrations during pregnancy and decreased A1C from 8 to 33 weeks (P = 0.003).

CONCLUSIONS

A pregnancy-induced increase in C-peptide concentrations in women with long-term type 1 diabetes was demonstrated, even in women with undetectable C-peptide concentrations in early pregnancy. This increase is suggestive of improved beta-cell function and was associated with improvement in glycemic control during pregnancy.

Differential lipid profile and hormonal response in type 2 diabetes by exogenous insulin aspart versus the insulin secretagogue repaglinide, at the same glycemic control

Our aim was to study, at the same glycemic control, how treatment with either the insulin secretagogue repaglinide or exogenous insulin aspart affects endogenous insulin secretion, plasma insulin and IAPP (islet amyloid polypeptide) levels, GH-IGF (growth hormone-insulin-like growth factor) axis and plasma lipoprotein concentrations in patients with type 2 diabetes. Five patients, age 65.0+/-4.1 years (mean+/-SE), body weight 82.5+/-5.0 kg, BMI (body mass index) 27.7+/-1.5 kg/m(2) were treated for 10 weeks with repaglinide or insulin aspart in a randomized, cross-over study. At the end of each treatment a 24-h metabolic profile was performed. Blood glucose, C-peptide, free human insulin, free total (human and analogue) insulin, proinsulin, IAPP, IGF-I, IGFBP-1 (IGF binding protein-1), GHBP (growth hormone binding protein) and plasma lipoprotein concentrations were measured. Similar 24-h blood glucose profiles were obtained with repaglinide and insulin aspart treatment. During the repaglinide treatment, the meal related peaks of C-peptide and free human insulin were about twofold higher than during treatment with insulin aspart. Proinsulin, GHBP were higher and IAPP levels tended to be higher during repaglinide compared to insulin aspart. Postprandial plasma total cholesterol, triglycerides and apolipoprotein B concentrations were higher on repaglinide than on insulin aspart treatment. Our results show that, at the same glycemic control, treatment with exogenous insulin aspart in comparison with the insulin secretagogue repaglinide result in a lower endogenous insulin secretion, and a tendency towards a less atherogenic postprandial lipid profile.

Long-term hyperglycaemia impairs vascular smooth muscle cell function in women with type 1 diabetes mellitus

Observations of increased stiffness in the elastic aorta in women with diabetes, but not men, emphasise the need for further analysis regarding early abnormalities in arterial wall properties of women with type 1 diabetes mellitus (DM). Ultrasound was used to study the wall properties of the distal brachial artery (BA) in 37 type 1 diabetic women (aged 22-45 years) without evident complications and in 53 controls (C). Blood samples were drawn for later analysis. Flow-mediated dilatation (FMD) was slightly lower in DM than C, 8.1+/-4.3% vs. 10.3+/-4.9% (p<0.05), and nitrate-mediated dilatation (NMD) was markedly lower, 21.7+/-6.6% vs. 31.4+/-5.7% (p<0.001). Lumen diameter, intima-media thickness and distensibility were similar in DM and C. Insulin-like growth factor (IGF-1) was lower in DM than C, 231+/-65 vs. 349+/-68 ng/ml (p<0.001). Glycosylated haemoglobin (HbA1C) and matrix metalloproteinase (MMP-9) were independent predictors of the reduced NMD in the DM. Brachial artery responsiveness to an exogenous donor of nitric oxide (NO) was markedly reduced in type 1 diabetic women despite only limited reduction in endothelium-dependent dilatation. The negative association between NMD and HbA1C suggests that long-term hyperglycaemia impairs vascular smooth muscle cell function in DM.

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.

Comparison of pancreas-transplanted type 1 diabetic patients with portal-venous versus systemic-venous graft drainage: impact on glucose regulatory hormones and the growth hormone/insulin-like growth factor-I axis

CONTEXT

Pancreas grafts can be drained through the iliac vein (systemic drainage) or the portal vein.

OBJECTIVE

We hypothesized that normalization of portal insulin in patients with portal pancreas graft drainage stimulates the GH/IGF-I axis and thereby contributes to glucose control.

METHODS

We compared patients after combined kidney and pancreas transplantation with portal drainage (n = 7) to patients with systemic drainage of the pancreas graft (n = 8) and nondiabetic controls (n = 8). Overnight fasting sera were analyzed for free and total IGF-I and IGF-binding proteins. Glucose regulatory hormones were examined after an oral glucose tolerance test and GH after stimulation with GHRH.

RESULTS

Systemic drainage led to higher basal and stimulated insulin levels than portal drainage (P < 0.05), but increments in response to oral glucose were reduced in both transplanted groups (P < 0.05 vs. controls). However, glucose tolerance was similar in all groups. Circulating free and total IGF-I and IGF-binding protein-3 were similar to control levels in the systemic drainage group but elevated in the portal drainage group (P < 0.05). Consistently, the GH response was reduced in the portal drainage group (P < 0.05 vs. controls) and correlated inversely with free IGF-I (r = -0.63, P < 0.05).

CONCLUSION

Portal drainage of pancreatic endocrine secretion in pancreas graft recipients raises IGF-I and lowers GH secretion. These changes might explain that glucose regulation is maintained despite lower peripheral insulin levels, compared with patients with systemic graft drainage and nondiabetic control subjects.

Attenuation of insulin secretion by insulin-like growth factor binding protein-1 in pancreatic beta-cells

IGFBP-1 is involved in glucohomeostasis, but the direct action of IGFBP-1 on the beta-cell remains unclear. Incubation of dispersed mouse beta-cells with IGFBP-1 for 30min inhibited insulin secretion stimulated by glucose, glucagon-like peptide 1 (GLP-1) or tolbutamide without changes in basal release of insulin and in cytosolic free Ca(2+) concentration ([Ca(2+)](i)) and NAD(P)H evoked by glucose. In contrast, IGFBP-1 augmented glucose-stimulated insulin secretion in intact islets, associated with a reduced somatostatin secretion. These results suggest a suppressive action of IGFBP-1 on insulin secretion in isolated beta-cells through a mechanism distal to energy generating steps and not involving regulation of [Ca(2+)](i). In contrast, IGFBP-1 amplifies glucose-stimulated insulin secretion in intact islets, possibly by suppressing somatostatin secretion. These direct modulatory influences of IGFBP-1 on insulin secretion may imply an important regulatory role of IGFBP-1 in vivo and in the pathogenesis of type 2 diabetes, in which loss of insulin release is an early pathogenetic event.

Elevated circulating adiponectin in type 1 diabetes is associated with long diabetes duration

OBJECTIVE

To study circulating adiponectin concentrations in relation to diabetes duration and endogenous insulin secretion in patients with type 1 diabetes.

PATIENTS

Patients with haemoglobin A1c (HbA1c) < 6% (reference range 3.6-5.4%) were selected for the study. Twenty-two men and 24 women [age 41.3 +/- 13.8 years (mean +/- SD), diabetes duration 4 months to 52 years] participated. Healthy controls (15 women and nine men, age 41.3 +/- 13.0 years) were also included. Overnight fasting serum samples were analysed for adiponectin, HbA1c, C-peptide and lipoproteins.

RESULTS

Significant positive associations were found between adiponectin concentrations and diabetes duration in univariate and multiple regression analyses. Serum adiponectin averaged 9.7 +/- 5.3 [median 8.1, interquartile range (IQR) 3.6] mg/l in patients with diabetes duration less than 10 years and 17.8 +/- 10.7 (median 14.7, IQR 7.5) mg/l in patients with longer duration (P = 0.0001). Among the patients, 24 were without detectable (< 100 pmol/l) and 22 with detectable C-peptide levels (185 +/- 91 pmol/l). C-peptide levels in controls averaged 492 +/- 177 pmol/l. HbA1c was 5.7 +/- 0.6% in patients without detectable C-peptide and 5.6 +/- 0.4% in patients with detectable C-peptide (ns). Serum adiponectin was higher in patients without detectable C-peptide than in patients with detectable C-peptide [17.3 +/- 11.1 vs. 10.6 +/- 5.8 mg/l (P < 0.005)] and in the controls [10.1 +/- 2.9 mg/l (P < 0.001 vs. patients without detectable C-peptide)].

CONCLUSIONS

The increase in circulating adiponectin concentrations in patients with type 1 diabetes appears to be strongly associated with long diabetes duration, irrespective of the metabolic control. Among other factors, a putative role for residual beta-cell function in the regulation of circulating adiponectin levels can be considered but we did not find sufficient evidence for this in the present study.

Growth hormone-IGF-I axis and growth velocity in Chinese children with type 1 diabetes mellitus

OBJECTIVE

To elucidate hormonal disturbances in patients with type 1 diabetes mellitus (DM1) with and without growth retardation.

METHODS

Patients with DM1 were divided into two groups, group A consisted of 14 patients with poor growth, and group B consisted of 24 patients with normal growth. Serum IGF-I, IGFBP-3, basal and stimulated GH, and HbA1c were measured.

RESULTS

Serum IGF-I and IGFBP-3 concentrations were significantly decreased in group A versus both groups B and controls in Tanner stages I-III; in addition, these measurements in group B were significantly lower compared to controls in Tanner stages II and III, but there was no significant difference in prepuberty. Both basal and peak serum GH were attenuated significantly in group A versus group B. Basal serum GH in group B (normal growth DM1) was significantly elevated versus the controls. There was an unambiguous negative linear regression between IGF-I and mean HbA1c in patients with DM1.

CONCLUSIONS

Growth retardation in patients with DM1 is associated with an abnormal GH-IGF-I axis and poor glycemic control.

Insulin and IGF-I action on insulin receptors, IGF-I receptors, and hybrid insulin/IGF-I receptors in vascular smooth muscle cells

Insulin and insulin-like growth factor I (IGF-I) are known to affect cardiovascular disease. We have investigated ligand binding and the dose-response relationship for insulin and IGF-I on vascular smooth muscle cells (VSMCs) at the receptor level. VSMCs from rat thoracic aorta were serum starved, stimulated with IGF-I or insulin, lysed, immunoprecipitated, and analyzed by Western blot. d-[U-(14)C]Glucose accumulation and [6-(3)H]thymidine incorporation into DNA were also measured. Specific binding of both insulin and IGF-I was demonstrated, being higher for IGF-I. Both IGF-I receptor (IGF-IR) and insulin receptor (IR) beta-subunits were detected and coprecipitated after immunoprecipitation (IP) against either of the two. No coprecipitation was found after reduction of disulphide bonds with dithiotreitol before IP. After stimulation with 10(-10)-10(-9) M IGF-I, IP of the IGF-IR, or IR beta-subunit and immunoblot with anti-phosphotyrosine antibody, we found two distinct bands indicating phosphorylation of both the IGF-IR and the IR beta-subunit. Stimulation with 10(-10)-10(-9) M insulin and IP against the IGF-IR did not show phosphorylation of either beta-subunit, whereas after IP of the IR we found phosphorylation of the IR beta-subunit. [(14)C]Glucose accumulation and [(3)H]thymidine incorporation were elevated in cells stimulated with IGF-I at 10(-10)-10(-7) M, reaching maximum by 10(-9) M. Insulin stimulation showed measurable effects only at supraphysiological concentrations, 10(-8)-10(-7) M. In conclusion, coprecipitation of both the IGF-IR and the IR beta-subunit indicates the presence of hybrid insulin/IGF-I receptors in VSMC. At a physiological concentration, insulin activates the IR but does not affect either glucose metabolism or DNA synthesis, whereas IGF-I both activates the receptor and elicits biological effect.

Lower bone mineral content in children with type 1 diabetes mellitus is linked to female sex, low insulin-like growth factor type I levels, and high insulin requirement

CONTEXT

Studies on bone mineral characteristics in children with type 1 diabetes mellitus (T1DM) have generated conflicting results.

OBJECTIVE

Our objective was to investigate bone mineral characteristics in children with T1DM and to analyze their associations with bone metabolism and the IGF-I system.

DESIGN

We recruited a cohort of Caucasian patients with T1DM for at least 3 yr and healthy children between January 2003 and June 2004.

SETTING

This was a university hospital-based study.

PARTICIPANTS

A total of 127 patients and 319 controls aged 6 to 20 yr participated.

METHODS

Dual-energy x-ray absorptiometry was performed in patients and controls. Serum bone alkaline phosphatase, CrossLaps, IGF-I, and IGF-binding protein 3 levels were determined in patients with values analyzed using our normative data from 1150 healthy children.

RESULTS

After adjustment for age, sex, pubertal stage, and body mass index sd score, total body bone mineral content (BMC)/lean body mass was significantly lower in patients than in controls (P < 0.04). This difference was a result of the differences between the girls of the two groups. Girls with T1DM had significantly lower lumbar spine and total body BMC than control girls (P = 0.002), whereas no such difference was observed in boys. Serum bone alkaline phosphatase level was significantly lower in girls than in boys (P = 0.04). Low serum IGF-I levels and the administration of large amounts of insulin were found to have independent deleterious effects on BMC for children of all ages and both sexes, whereas disease duration and glycosylated hemoglobin levels did not.

CONCLUSIONS

A sex-related difference in the impairment of bone mineral characteristics was identified in children with T1DM. Longitudinal studies are required to investigate whether boys may gain slightly less bone mass during skeletal growth.

Insulin resistance in diabetic nephropathy--cause or consequence?

Insulin resistance (IR) is associated with multiple risk factors for cardiovascular disease. Many studies have shown that IR is present in chronic renal failure (CRF), and recent evidence suggests that IR can also occur in the early stages of renal disease. Patients with diabetic nephropathy (DN) have an increase in cardiovascular mortality, and since IR may be a contributing factor, this emphasizes the importance of a detailed understanding of the mechanisms linking IR and renal dysfunction at different stages of DN. IR can be detected early on in DN, e.g. at the stage of microalbuminuria (MA) and this could indicate a common genetic trait for IR and DN. As DN progresses further, IR is aggravated and it may, in addition to other factors, possibly accelerate the decline in renal function toward end-stage renal disease (ESRD). Several potentially modifiable mechanisms including circulating hormones, neuroendocrine pathways and chronic inflammation, are said to contribute to the worsening of IR. In ESRD, uremic toxins are of major importance. In this review article, we address the association between different stages of DN and IR and attempt to summarize major findings on potential mechanisms linking DN and IR. We conclude that IR is a consequence, and potentially also a cause of DN. In addition, there are probably genetic and environmental background factors that predispose to both IR and DN.

The IGF-system is not affected by a twofold change in protein intake in patients with type 1 diabetes

OBJECTIVE

In type 1 diabetes the circulating IGF-system is altered with low IGF-I and changes in levels of IGF-binding proteins (IGFBPs) which may be of importance for the development of diabetes complications. Our aim was to study if IGF-I, as supported by experimental data in animals, can be affected by dietary protein intake.

DESIGN AND METHODS

Twelve patients with type 1 diabetes, age 37.5+/-10.0 years (mean+/-SD), diabetes duration 20.1+/-9.3 years and HbA1c 6.3+/-0.6% were allocated to isocaloric diets with either low normal protein content (LNP), (10 E%; 0.9 g protein/kg body weight) or high normal protein content (HNP) (20 E%; 1.8 g protein/kg body weight) in an open randomised cross-over study. Each diet was taken for 10 days with a wash-out period of 11 days in between. Circulating levels of total and free IGF-I and -II, IGFBP-1, -2 and -3 and GH-binding protein (GHBP) as well as ghrelin were measured with validated in-house immunoassays.

RESULTS

At day 10, urinary urea excretion was 320+/-75 mmol/24h during LNP diet compared with 654+/-159 mmol/24h during HNP diet (p<0.001). There were no changes in body weight or glycaemic control between the diets. Fasting levels of total IGF-I were 121+/-33 microg/L after LNP and 117+/-28 microg/L after HNP diet (ns) and the corresponding concentrations of IGFBP-1 were 142(141) and 132(157)mug/L [median (IQR)] (ns). There were no differences in plasma concentrations of total IGF-II, free IGF-I and -II, IGFBP-3, GHBP and ghrelin, whereas a small difference was found for IGFBP-2 (302+/-97 vs. 263+/-66 microg/L; LNP vs. HNP; p<0.04).

CONCLUSIONS

A twofold change of the dietary protein intake does not influence the altered circulating IGF-system in type 1 diabetes. In order to affect the IGF-system other interventions must be used.