Increased 24 h mean insulin-like growth factor binding protein-3 proteolytic activity in pubertal type 1 diabetic boys

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.

Biofluid proteases profiling in diabetes mellitus

The investigation of protease relevance in biologic systems beyond catabolism of proteins and peptides to amino acids has stimulated interest as to their role in the pathogenesis of several disorders including diabetes mellitus (DM). Evaluation of proteases and the assessment of their activity in biofluids are fundamental to elucidate these proteolytic systems in DM and its related complications. In contrast to traditional immunoassay or substrate based approaches that targeted specific proteases and their inhibitors, the field of degradomics has provided a comprehensive approach to study these enzymes. Although the degradome contains over 500 proteases, very few have been associated with DM and its micro- and macrovascular complications. In this paper, we review these proteases and their respective inhibitors with emphasis on DM. It is likely that future research will expand these initial studies and look to develop high throughput automated technologies to identify and characterize biofluid proteases of diagnostic and prognostic value in other pathologies.

Lower HbA1c after 1 year, in children with type 1 diabetes treated with insulin glargine vs. NPH insulin from diagnosis: a retrospective study

OBJECTIVE

Insulin glargine offers sustained insulin delivery for 24 h. Change to glargine treatment consistently results in lower fasting glucose and fewer hypoglycemic episodes in children with type 1 diabetes compared to continuation of NPH, although glargine has not been shown to improve HbA1c in randomized trials. Studies comparing glargine and NPH in multiple injection therapy in children treated from diagnosis of type 1 diabetes are lacking.

METHODS

HbA1c and insulin requirement were compared in a retrospective study of children (7-17 yr of age) with type 1 diabetes treated from diagnosis with basal insulin glargine (n = 49) or NPH (n = 49) in a multiple injection therapy (MIT) regimen with a rapid-acting insulin analogue. Patients were followed every third month for 1 yr. HbA1c, insulin dose, and weight data were retrieved.

RESULTS

HbA1c (mean ± SD) was lower at 3-5 months (5.5 ± 0.89 vs. 6.2 ± 0.89%, p < 0.05) and 6-9 months (5.6 ± 1.14 vs. 6.6 ± 0.99%; p < 0.001) in glargine treated. After 12 months, HbA1c was significantly lower in glargine treated (6.3 ± 1.56 vs. 7.1 ± 1.28; p < 0.01). Reported total insulin doses were similar at nadir (0.5 U/kg BW × 24 h), but significantly lower at 12 months in glargine treated (0.64 ± 0.23 vs. 0.86 ± 0.3 U/kg BW × 24 h; p < 0.001).

CONCLUSIONS

HbA1c 1 yr from diagnosis was lower in children treated with glargine from start as compared with those on NPH. This observation should be viewed in the light of a significantly lower dose of total daily insulin in the glargine group.

Postprandial paradoxical IGFBP-1 response in obese patients with Type 2 diabetes

IGFs (insulin-like growth factors), which in an unbound form induce glucose and amino acid uptake, circulate bound to IGFBPs (IGF-binding proteins), which modulate their bioavailability and activity. The aim of the present study was to examine the effect of a standard meal [2301 kJ (550 kcal)] on the serum levels of IGFBP-1 in obese patients with T2DM (Type 2 diabetes mellitus), non-obese patients with T1DM (Type 1 diabetes mellitus) and healthy controls, using the artificial pancreas (Biostator®) to obtain a normal glycaemic response to the meal. IGFBP-1 levels decreased by 50% over 2 h following the meal at a similar clearance in both the healthy controls and patients with T1DM, but no significant decline was seen in the patients with T2DM, despite a several-fold increase in insulin levels. The patients with T2DM were also studied during Sandostatin® (somatostatin) infusion to decrease the inappropriate secretion of glucagon during the meal. During the 210 min of somatostatin infusion, the glucagon response was suppressed and IGFBP-1 levels were increased concomitantly with the peak in insulin levels, without any significant decrease after the meal. In conclusion, the impaired IGFBP-1 response to meal-related hyperinsulinaemia in obese patients with T2DM suggests a decreased availability of active IGF-1, leading to a decrease in glucose uptake during and after a meal in these patients. The stimulated meal response to glucagon, which contributes to postprandial hyperglycaemia, could not explain the increase in serum IGFBP-1 in these obese patients with T2DM.

Normalization of the IGF-IGFBP axis by sustained nightly insulinization in type 1 diabetes

OBJECTIVE

We sought to test the hypothesis that start of insulin glargine with sustained nightly insulin action results in changes in circulating concentrations of IGF-I and IGF binding proteins (IGFBPs) in adolescents with type 1 diabetes-changes that may support improvement of A1C.

RESEARCH DESIGN AND METHODS

Twelve pubertal adolescents with type 1 diabetes and initially on NPH insulin were studied during 12 weeks of intensified treatment with glargine.

RESULTS

Subnormal IGF-I SD scores on NPH (-1.8 +/- 0.4) rapidly increased and remained 54 +/- 9% elevated (P < 0.001) after 12 weeks on glargine. A1C decreased from 8.3 +/- 0.6% to a nadir of 6.9 +/- 0.3% (P = 0.002) at 6 weeks and correlated with changes in IGF-I (r = -0.64, P < 0.05). The increase in IGF-I did not suppress the mean overnight growth hormone (GH) secretion at 6 weeks. The mean overnight IGFBP-1 levels decreased (P = 0.035), supporting the hypothesis that the nightly hepatic insulin action was increased. Circulating IGF-I increased in the absence of changes in both GH secretion and GH receptor numbers (assessed by growth hormone binding protein), indicating that postreceptor mechanisms are involved. IGFBP-3 proteolysis was decreased.

CONCLUSIONS

Increased hepatic insulin action after start of glargine was evident from a decrease in night time IGFBP-1 concentrations. This may improve GH postreceptor signaling, resulting in increased circulating IGF-I. We suggest that even in the absence of changes in GH, increased IGF-I and decreased IGFBP-1 support the improvement of metabolic control.

Rh/IGF-I/rhIGFBP-3 administration to patients with type 2 diabetes mellitus reduces insulin requirements while also lowering fasting glucose

Administration of insulin-like growth factor-I to patients with diabetes enhances insulin action and reduces the degree of hyperglycemia but it is associated with a high rate of adverse events. Infusion of the combination of rhIGFBP-3 (the principal binding protein for IGF-I in plasma) with rhIGF-I to patients with type I diabetes improved insulin sensitivity and was associated with a low incidence in side effects. In this study, 52 patients with insulin-treated type 2 diabetes received recombinant human IGF-I plus rhIGFBP-3 in one of four dosage regimens for 14 days. The four groups were: (1) continuous subcutaneous infusion of 2 mg/kg/day; (2) the same 2 mg/kg dose infused subcutaneously over 6 h between 2000 and 0200 h; (3) 1 mg/kg twice a day by bolus subcutaneous injection; (4) a single bedtime subcutaneous injection of 1 mg/kg. Across these four groups rhIGF-I/rhIGFBP-3 decreased insulin requirements between 54% and 82%. Fasting glucose decreased by 32-37%. Mean daily blood glucose (4 determinations per day) declined in all 4 groups (range 9-23% decrease). Frequent sampling for total IGF-I, free IGF-I and IGFBP-3 was performed on days 0,1,7,14 and 15. The peak total IGF-I values were increased to 4.0-4.8-fold at 16-24 h. For free IGF-I the increase varied between 7.1 and 8.2-fold and peak values were attained at 16-20 h after administration. Both the time to maximum concentration (Tmax) and the maximum free IGF-I levels (Cmax) on day 1 for all groups were substantially less than previously published studies, wherein lower doses of rhIGF-I were given without IGFBP-3. The improvement in glucose values and the degree of reduction in insulin requirement were the greatest in groups 2 and 3 and the patients in those groups had the highest free IGF-I levels. The frequency of side effects such as edema, jaw pain and arthralgias was 4% which is less than that has been reported in previous studies wherein IGF-I was administered without IGFBP-3. We conclude that rhIGF-I/rhIGFBP-3 significantly lowers insulin requirements yet improves glucose values and these changes may reflect improvement in insulin sensitivity. Coadministration of IGFBP-3 with IGF-I produces lower free IGF-I (Tmax and Cmax) levels compared to administration of IGF-I alone and is associated with relatively low incidence of side effects during 2 weeks of administration.

Altered response of insulin-like growth factor-binding protein 1 to nutritional deprivation in type 2 diabetes mellitus

Circulating insulin-like growth factor-binding protein 1 (IGFBP-1) normally has a close inverse relationship to insulin secretion, which results in a characteristic diurnal variation. However, in type 2 diabetes the correlation with insulin may be lost and IGFBP-1 concentrations relatively increased. The aim of this study was to determine the effect of nutritional deprivation on the diurnal patterns of IGFBP-1 regulation in type 2 diabetes mellitus. After a baseline assessment period, food intake was reduced over 48 hours to 627.6 kJ/d (150 kcal/d) for 72 hours and increased again over 24 hours to baseline (refeeding). Blood samples were taken at 2-hour intervals, for 24 hours in the baseline period, 48 hours during nutritional deprivation, and 24 hours during refeeding. Six individuals with type 2 diabetes were compared with 2 groups that were selected for normal fasting glucose and insulin levels and comprised 6 obese and 6 lean subjects. During energy (caloric) restriction, fasting insulin levels decreased to a similar extent in each study group. At baseline, IGFBP-1 concentrations were similar in each of the study groups and at the end of the period of energy (caloric) restriction the 6:00 AM fasting levels had increased by 144% in the obese control group and by 245% in the lean individuals (each P < .001). In the patients with type 2 diabetes there was a blunted increase in IGFBP-1 concentrations with nutritional deprivation by 33% compared with baseline. During refeeding after nutritional deprivation the IGFBP-1 response to insulin was restored in the individuals with diabetes. In conclusion, patients with type 2 diabetes mellitus have altered IGFBP-1 regulation, relating to impaired hepatic insulin sensitivity, which improves after a period of energy (caloric) restriction.