Utility of C-peptide for a reliable estimate of insulin secretion in children with growth hormone deficiency

Biomarkers and Diagnostic Thresholds for Congenital Hyperinsulinism

CONTEXT

Congenital Hyperinsulinism (CHI) is associated with inappropriately high levels of C-peptide in the context of hypoglycemia.

OBJECTIVE

We aimed to better clarify a diagnostic threshold value of C-peptide for children presenting with CHI.

DESIGN

This was a retrospective case-control analysis, examining all hypoglycemia screens, undertaken between 2009 and 2019 at a quaternary paediatrics unit. Plasma C-peptide, insulin, free fatty acid (FFA) and B-hydroxybutyrate (BHOB) concentrations in children diagnosed with CHI were compared with concentrations in children diagnosed with other conditions.

PATIENTS

All patients requiring hypoglycaemic screens at the quaternary children's hospital were analysed.

RESULTS

Median [C-peptide] were statistically significantly different between CHI (147) and non-CHI (72) patients, p < 0.05. The Youden Index indicated that a [C-peptide] value of 291.5 pmol/L would give the greatest optimization of sensitivity (82%) and specificity (99%) for detecting CHI. Median [insulin] differed significantly between the cohorts with a level of 64 pmol/L for CHI patients compared with 0 pmol/L with non-CHI patients (p < 0.01). Median [BOHB] was 0 μmol/L in CHI patients as compared with 2378 μmol/L for non-CHI patients (p < 0.01). Median [FFA] levels were 1910 μmol/L in the non-CHI cohort, compared with 0 in the CHI cohort (p < 0.01).

CONCLUSIONS

This study suggests that a C-peptide concentration greater than 291.5 pmol/L is diagnostic of CHI in children. C-peptide appears to offer the greatest utility as a biochemical diagnostic test for CHI and could be prioritised for laboratory analysis.

Metabolic Effects of Growth Hormone Treatment in Short Prepubertal Children: A Double-Blinded Randomized Clinical Trial

INTRODUCTION

Growth hormone (GH) is a central hormone for regulating linear growth during childhood and also highly involved in the metabolism of lipids, carbohydrates, and protein. However, few studies report on how treatment with GH during childhood influences metabolic parameters. Our aim was to investigate metabolic effects of different doses of GH in short children with GH peak levels in the low to normal range.

DESIGN

Thirty-five prepubertal short children (<-2.5 SDS), aged 7-10 years, with peak levels of GH between 7 and 14 μg/L during an arginine-insulin tolerance test, were randomized to 3 different doses (11/33/100 μg/kg/day) of GH treatment for 2 years. Auxological and metabolic investigations were performed. These included metabolites in blood and interstitial microdialysis fluid, dual-energy X-ray absorptiometry, frequently sampled intravenous glucose tolerance test (FSIVGTT), and stable isotope examinations of rates of glucose production and lipolysis.

RESULTS

At 24 months, the high-dose group (HD) had higher fasting insulin compared with the standard-dose (SD) and low-dose (LD) groups (HD: 111.7 vs. SD: 61.2 and LD: 46.0 pmol/L [p < 0.001]) and showed signs of insulin resistance (HOMA-IR, HD: 4.20 vs. SD: 2.17 and LD: 1.71 (LD) [p < 0.001]). The FSIVGTT also demonstrated higher acute insulin response (p < 0.05). Few other metabolic differences were found at 24 months, but a decreased insulin sensitivity index (Si) could already be seen at 12 months for both SD and HD compared with the LD group (p < 0.05).

CONCLUSION

Treatment with GH resulted in a dose-dependent decrease in insulin sensitivity, demonstrated by higher levels of fasting insulin and signs of insulin resistance in both HOMA indices and FSIVGTT examinations.

Serum Uric Acid Levels as an Indicator for Metabolically Unhealthy Obesity in Children and Adolescents

BACKGROUND

Metabolically healthy obesity (MHO) refers to those individuals who do not show cardiometabolic abnormalities. Our aim was to identify potential clinical and metabolic indicators that may help to distinguish between metabolically healthy and unhealthy individuals amongst overweight and obese children and adolescents.

METHODS

The study involved 246 overweight/obese and 212 normal-weight individuals enrolled in the LIFE Child study, aged between 6 and 18 years. Overweight/obese individuals without cardiovascular risk factors (fasting serum lipids, blood pressure, and glucose) were classified as MHO. Individuals meeting 1 or more criteria of cardiovascular risk factors were classified as metabolically unhealthy obesity (MUO).

RESULTS

Among the 246 overweight/obese individuals, 173 (70%) were MHO and 73 (30%) were MUO. The MHO individuals were younger, more likely to be male, and had lower BMI SDS. In the logistic regression models, uric acid (UA) SDS (OR 1.61, 95% CI 1.1-2.6, p = 0.004), waist circumference SDS (OR 2.50, 95% CI 1.2-6.4, p = 0.017), and C-peptide (OR 4.05, 95% CI 3.5-91, p = 0.003) were significant indicators of MUO.

CONCLUSION

Our results suggest that nearly one-third of overweight/obese children are already identified as MUO. Serum levels of UA can be used as an indicator of unhealthy obesity in youth, where lower levels of UA indicate a lower risk and higher levels suggest a higher risk of MUO. We note that the relevance of identifying potential indicators remains the first most important step in future clinical research.

One-hour post-load plasma glucose level is associated with a worse metabolic profile in children with GH deficiency

PURPOSE

In children, the plasma glucose value at 1 h (1hPG) during OGTT higher than 132.5 mg/dl is a predictor of alterations in glucose metabolism. We aimed to metabolically characterize GHD children according to 1hPG levels.

METHODS

Fifty-one GHD children (35 M, 16 F; mean age 8.6 years), grouped according to 1hPG, were evaluated at diagnosis and after 12 months of GH treatment (GHT) and compared with 50 matched controls at baseline. Auxological parameters, insulin-like growth factor-1 (IGF-1), glucose and insulin during OGTT, lipid profile, the oral disposition index (DIo), the homeostasis model assessment estimate of insulin resistance (Homa-IR), and the insulin sensitivity index (ISI) were evaluated.

RESULTS

At baseline, 31.4% of GHD children and 12% of controls (p = 0.016) showed 1hPG ≥ 132.5 mg/dl. The first ones showed higher mean 1hPG (p = 0.025) and LDL cholesterol (p = 0.029) and lower HDL cholesterol (p = 0.014) than controls. GHD with higher 1hPG showed a significant decrease in DIo (p < 0.001) without improvement in lipid profile after GHT, compared with children with lower 1hPG. After 12 months, the higher 1hPG group showed lower ISI Matsuda (p = 0.047) and DIo (p < 0.001) than the lower 1hPG group. 1hPG levels proved to be positively correlated with Homa-IR (p = 0.010) and LDL cholesterol (p = 0.032) and negatively with ISI Matsuda (p = 0.001) and DIo (p = 0.019). The 1hPG value at baseline was the only independent variable significantly associated with DIo at 12 months (p = 0.041).

CONCLUSIONS

1hPG level at baseline may be a useful tool to identify and properly follow up children with enhanced metabolic risk who probably need more surveillance during GHT.

IGF-1R mRNA expression is increased in obese children

OBJECTIVES

Obese children are often taller than age-matched subjects. Reports on GH and IGF-I levels in obese individuals are controversial, with normal and reduced GH-IGF-I levels having been reported in this group of patients. Thus, the aim of this study was to analyse insulin-like growth factor type 1 receptor (IGF-IR) mRNA expression in obese children.

METHODS

Forty-seven pre-pubertal children were included in this study: 29 were obese and taller than their target height, and 18 were normal eutrophic controls. Fasting blood samples were collected for IGF-IR mRNA expression in isolated lymphocytes and serum IGF-I, ALS, IGFBP-3, and IGFBP-1 concentration analysis.

RESULTS

Relative IGF-IR gene expression (2-ΔΔCT) was significantly (P=0.025) higher in obese children (median 1.87) than in controls (1.15). Fourteen of the 29 obese subjects showed 2-ΔΔCT values greater than or equal to 2, while only 2 individuals in the control group showed values above 2 (P=0.01). Obese children showed significantly (P=0.01) higher IGF-I concentrations than the control group (237ng/ml and 144ng/ml, respectively). Among obese patients, 65.5% had IGF-I values above the 75 percentile of the control group (P=0.02). ALS concentration was significantly (P=0.04) higher in the obese group, while IGFBP-3 levels were similar in obese and control children. IGFBP-1 concentration was lower in obese children, while insulin levels and HOMA-IR index were higher than in controls.

CONCLUSIONS

The higher IGF-IR mRNA expression observed in obese children, associated with the higher IGF-I and ALS and the lower IGFBP-1 levels, suggest that the higher stature observed in these children may be due to increased IGF-I bioactivity.

Glucose homeostasis in GHD children during long-term replacement therapy: a case-control study

PURPOSE

To evaluate glucose homeostasis in children with growth hormone (GH) deficiency (GHD) receiving long-term replacement therapy.

METHODS

We evaluated glucose, insulin, HOmeostasis Model Assessment (HOMA-IR), and HbA1c in 100 GHD children at diagnosis and during 5 years of therapy. One hundred healthy children comparable to patients were evaluated at baseline and after 1 and 5 years.

RESULTS

No difference was detected at baseline between GHD patients and controls in glucose (79.58 ± 9.96 vs. 77.18 ± 8.20 mg/dl), insulin (4.50 ± 3.24 vs. 4.30 ± 2.60 µU/ml), HbA1c (5.20 ± 0.31 vs. 5.25 ± 0.33%) levels, and HOMA-IR (0.93 ± 0.72 vs. 0.86 ± 0.61). One year of GH was associated with a significant increase in insulin (7.21 ± 4.84, p < 0.001) and HOMA-IR (1.32 ± 0.98, p < 0.001) in GHD children, which became different from controls (p < 0.001 and p = 0.004). These parameters did not change further during the following years of treatment in GHD subjects. In contrast, controls did not show significant changes in insulin (4.40 ± 2.60) and HOMA-IR (0.82 ± 0.60) during the first year; however, at the fifth year of the study a significant increase in insulin (6.50 ± 3.50, p = 0.004) and HOMA-IR (1.29 ± 0.54, p < 0.001) was documented, making these parameters comparable between patients and controls.

CONCLUSIONS

Our results suggest that growth hormone (GH) treatment is not associated with significant impairment of insulin sensitivity in GHD children. The slight impairment observed in GHD adolescents after long-term GH is comparable to that physiologically occurring in healthy pubertal subjects.

Glucose Metabolism in Children With Growth Hormone Deficiency

BACKGROUND

The growth hormone (GH)/insulin-like growth factor 1 (IGF-1) axis has a fundamental impact on glucose metabolism. Therefore, both untreated GH deficiency (GHD) and GH treatment (GHT) may be associated with some metabolic alterations, although the abnormalities of glucose metabolism have been investigated by relatively few studies as main outcomes.

AIM

The present review summarizes the available data on glucose metabolism in children with GHD, providing an overview of the current state of the art in order to better clarify the real metabolic impact of GHD and GHT.

METHODS

Among all the existing studies, we evaluated all original studies that fulfilled our criteria for analysis reporting parameters of glucose metabolism as the primary or secondary objective.

RESULTS

The reported impact of GHD per se on glucose metabolism is quite homogeneous, with the majority of studies reporting no significant difference in metabolic parameters between GHD children and controls. Conversely, GHT proves to be more frequently associated with a subtle form of insulin resistance, while both fasting glucose and HbA1c levels remain almost always within the normal range.

CONCLUSION

The different methods to study glucose metabolism, the heterogeneity of the populations evaluated, the different doses of GH used together with the variable duration of follow-up may be responsible for discrepancy in the results. Long-term longitudinal studies having glucose homeostasis as their primary outcome are still needed in order better to clarify the real metabolic impact of GHD and GHT in children.

More Favorable Metabolic Impact of Three-Times-Weekly versus Daily Growth Hormone Treatment in Naïve GH-Deficient Children

OBJECTIVE

To evaluate whether two different regimens of weekly injections could lead to similar auxological and metabolic effects in children with growth hormone deficiency (GHD).

DESIGN

32 GHD children (25 males, mean age 10.5 ± 2.2 yr) were randomly assigned to receive daily (group A, 16 patients) or TIW (group B, 16 patients) GHT for 12 months.

METHODS

Auxological parameters, insulin-like growth factor-I (IGF-I), glucose and insulin during OGTT, glycosylated hemoglobin (HbA1c), lipid profile, the oral disposition index (DIo), the homeostasis model assessment estimate of insulin resistance (Homa-IR), and the insulin sensitivity index (ISI).

RESULTS

After 12 months, both groups showed a significant and comparable improvement in height (p < 0.001) and IGF-I (p < 0.001). As regards the metabolic parameters, in both groups, we found a significant increase in fasting insulin (p < 0.001 and p = 0.026) and Homa-IR (p < 0.001 and p = 0.019). A significant increase in fasting glucose (p = 0.001) and a decrease in ISI (p < 0.001) and DIo (p = 0.002) were only found in group A.

CONCLUSIONS

The TIW regimen is effective and comparable with the daily regimen in improving auxological parameters and has a more favorable metabolic impact in GHD children. This trial is registered with ClinicalTrials.gov NCT03033121.