Serum C-peptide and osteocalcin levels in children with recently diagnosed diabetes

Association between osteocalcin and residual β-cell function in children and adolescents newly diagnosed with type 1 diabetes: a pivotal study

PURPOSE

This pivotal study aimed to evaluate circulating levels of bone remodeling markers in children and adolescents at the onset of type 1 diabetes (T1D). Additionally, we assessed their correlation with glucose control, residual β-cell function, and the severity of presentation.

METHODS

In this single-center cross-sectional study, we recruited children and adolescents newly diagnosed with T1D at our tertiary-care Diabetes Centre. Anamnestic, anthropometric, clinical, and biochemical data at T1D diagnosis were collected. Basal and stimulated C-peptide levels were assessed, along with the following bone remodeling biomarkers: osteocalcin (OC), alkaline phosphatase (ALP), parathormone (PTH), 25-OH Vitamin D (25OH-D), and the C-terminal cross-linked telopeptide of type 1 collagen (CTX).

RESULTS

We enrolled 29 individuals newly diagnosed with T1D, with a slight male prevalence (51.7%). The mean age was 8.4 ± 3.7 years. A positive correlation between OC and stimulated C-peptide (R = 0.538; p = 0.026) and between PTH and serum HCO3- (R = 0.544; p = 0.025) was found. No other correlations between bone remodeling biomarkers and clinical variables were detected.

CONCLUSION

Our data showed a positive correlation between OC levels and residual β-cell function in children and adolescents at T1D presentation. Further longitudinal studies evaluating OC levels in pediatric subjects with T1D are needed to better understand the complex interaction between bone and glucose metabolisms.

Reference limits for osteocalcin in infancy and early childhood: A longitudinal birth cohort study

OBJECTIVE

The longitudinal variations in serum levels of the hormone osteocalcin is largely unknown during infancy and early childhood. Our aim was to establish reference limits for total serum osteocalcin during specific time points from birth until 5 years of age and present those in the context of sex, breastfeeding practices and gestational age (GA).

DESIGN

Blood samples from 551 Swedish children were analysed at birth, 4, 12, 36 and 60 months of age. Total serum osteocalcin was measured using the IDS-iSYS N-MID Osteocalcin assay technique. Information about the mother, birth, anthropometrics and a food diary were collected.

RESULTS

Sex-specific and age-specific reference limits were established for the five time points. The median osteocalcin levels over time were 40.8, 90.0, 67.8, 62.2 and 80.9 μg/L for boys and 38.1, 95.5, 78.3, 73.9 and 92.6 μg/L for girls. Lower GA was associated to higher osteocalcin at birth, and ongoing breastfeeding was associated to higher osteocalcin levels.

CONCLUSION

Osteocalcin followed a wavelike pattern with low levels in the umbilical cord and a postnatal peak during the first year which then declined and rose again by the age of five. Knowledge of this wavelike pattern and association to factors as sex, breastfeeding and GA may help clinicians to interpret individual osteocalcin levels and guide in future research.

The Emerging Role of Bone-Derived Hormones in Diabetes Mellitus and Diabetic Kidney Disease

Diabetic kidney disease (DKD) causes the greatest proportion of end-stage renal disease (ESRD)-related mortality and has become a high concern in patients with diabetes mellitus (DM). Bone is considered an endocrine organ, playing an emerging role in regulating glucose and energy metabolism. Accumulating research has proven that bone-derived hormones are involved in glucose metabolism and the pathogenesis of DM complications, especially DKD. Furthermore, these hormones are considered to be promising predictors and prospective treatment targets for DM and DKD. In this review, we focused on bone-derived hormones, including fibroblast growth factor 23, osteocalcin, sclerostin, and lipocalin 2, and summarized their role in regulating glucose metabolism and DKD.

Beta cell function in participants with single or multiple islet autoantibodies at baseline in the TEDDY Family Prevention Study: TEFA

Aim

The aim of the present study was to assess beta cell function based on an oral glucose tolerance test (OGTT) in participants with single islet autoantibody or an intravenous glucose tolerance test (IvGTT) in participants with multiple islet autoantibodies.

Materials and methods

Healthy participants in Sweden and Finland, between 2 and 49.99 years of age previously identified as positive for a single (n = 30) autoantibody to either insulin, glutamic acid decarboxylase, islet antigen-2, zinc transporter 8 or islet cell antibodies or multiple autoantibodies (n = 46), were included. Participants positive for a single autoantibody underwent a 6-point OGTT while participants positive for multiple autoantibodies underwent an IvGTT. Glucose, insulin and C-peptide were measured from OGTT and IvGTT samples.

Results

All participants positive for a single autoantibody had a normal glucose tolerance test with 120 minutes glucose below 7.70 mmol/L and HbA1c values within the normal range (<42 mmol/mol). Insulin responses to the glucose challenge on OGTT ranged between 13.0 and 143 mIU/L after 120 minutes with C-peptide values between 0.74 and 4.60 nmol/L. In Swedish participants, the first-phase insulin response (FPIR) on IvGTT was lower in those positive for three or more autoantibodies (n = 13; median 83.0 mIU/L; range 20.0-343) compared to those with two autoantibodies (n = 15; median 146 mIU/L; range 19.0-545; P = .0330).

Conclusion

Participants positive for a single autoantibody appeared to have a normal beta cell function. Participants positive for three or more autoantibodies had a lower FPIR as compared to participants with two autoantibodies, supporting the view that their beta cell function had deteriorated.

Recombinant Antibodies with Unique Specificities Allow for Sensitive and Specific Detection of Uncarboxylated Osteocalcin in Human Circulation

Osteocalcin is a bone-specific protein which contains three glutamic acid residues (Glu) that undergo post-translational gamma-carboxylation. Uncarboxylated osteocalcin (ucOC) may participate in the regulation of glucose metabolism, thus measurement of ucOC could be useful in evaluating interactions between bone and glucose metabolism. We developed recombinant antibodies and immunoassay to specifically detect ucOC in human blood samples. ucOC-specific recombinant antibodies were selected from an antibody library by phage display. Four candidates were characterized, and one (Fab-AP13) was used to set up an immunoassay with a pre-existing MAb. Plasma ucOC levels were measured in subjects with normal fasting blood glucose (≤ 6 mmol/l, N = 46) or with hyperglycemia (≥ 7 mmol/l, N = 29). Further, we analyzed ucOC in age- and gender-matched patients with diagnosed type 2 diabetes (T2D, N = 49). Antibodies recognized ucOC without cross-reaction to carboxylated osteocalcin. Antibodies had unique binding sites at the carboxylation region, with Glu17 included in all epitopes. Immunoassay was set up and characterized. Immunoassay detected ucOC in serum and plasma, with on average 1.6-fold higher levels in plasma. ucOC concentrations were significantly lower in subjects with hyperglycemia (median 0.58 ng/ml, p = 0.008) or with T2D diagnosis (0.68 ng/ml, p = 0.015) than in subjects with normal blood glucose (1.01 ng/ml). ucOC negatively correlated with fasting plasma glucose in subjects without T2D (r = - 0.24, p = 0.035) but not in T2D patients (p = 0.41). Our immunoassay, based on the novel recombinant antibody, allows for specific and sensitive detection of ucOC in human circulation. Correlation between ucOC and plasma glucose suggests interactions between osteocalcin and glucose metabolism in humans.

Postnatal loss of the insulin receptor in osteoprogenitor cells does not impart a metabolic phenotype

The relationship between osteoblast-specific insulin signaling, osteocalcin activation and gluco-metabolic homeostasis has proven to be complex and potentially inconsistent across animal-model systems and in humans. Moreover, the impact of postnatally acquired, osteoblast-specific insulin deficiency on the pancreas-to-skeleton-to-pancreas circuit has not been studied. To explore this relationship, we created a model of postnatal elimination of insulin signaling in osteoprogenitors. Osteoprogenitor-selective ablation of the insulin receptor was induced after ~10 weeks of age in IR^l°^x/lox/Osx-Cre^+/- genotypic male and female mice (designated postnatal-OIRKO). At ~21 weeks of age, mice were then phenotypically and metabolically characterized. Postnatal-OIRKO mice demonstrated a significant reduction in circulating concentrations of undercarboxylated osteocalcin (ucOC), in both males and females compared with control littermates. However, no differences were observed between postnatal-OIRKO and control mice in: body composition (lean or fat mass); fasting serum insulin; HbA1c; glucose dynamics during glucose tolerance testing; or in pancreatic islet area or islet morphology, demonstrating that while ucOC is impacted by insulin signaling in osteoprogenitors, there appears to be little to no relationship between osteocalcin, or its derivative (ucOC), and glucose homeostasis in this model.