Insulin therapy increases low plasma growth hormone binding protein in children with new-onset type 1 diabetes

Growth Hormone and Counterregulation in the Pathogenesis of Diabetes

PURPOSE OF REVIEW

Canonical growth hormone (GH)-dependent signaling is essential for growth and counterregulatory responses to hypoglycemia, but also may contribute to glucose homeostasis (even in the absence of hypoglycemia) via its impact on metabolism of carbohydrates, lipids and proteins, body composition, and cardiovascular risk profile. The aim of this review is to summarize recent data implicating GH action in metabolic control, including both IGF-1-dependent and -independent pathways, and its potential role as target for T2D therapy.

RECENT FINDINGS

Experimental blockade of the GHR can modulate glucose metabolism. Moreover, the soluble form of the GH receptor (GHR, or GHBP) was recently identified as a mediator of improvement in glycemic control in patients with T2D randomized to bariatric surgery vs. medical therapy. Reductions in GHR were accompanied by increases in plasma GH, but unchanged levels of both total and free IGF-1. Likewise, hepatic GHR expression is reduced following both RYGB and VSG in rodents. Emerging data indicate that GH signaling is important for regulation of long-term glucose metabolism in T2D. Future studies will be required to dissect tissue-specific GH signaling and sensitivity and their contributions to systemic glucose metabolism.

Increasing secular trends in height and obesity in children with type 1 diabetes: JSGIT cohort

BACKGROUND

Recently, anthropometric indices in children with type 1 diabetes mellitus (T1DM) have begun to change.

OBJECTIVE

To examine secular trends in patients' anthropometric indices.

SUBJECTS

Japanese children with T1DM from the 1995, 2000, 2008 and 2013 cohorts of The Japanese Study Group of Insulin Therapy for Childhood and Adolescent Diabetes.

METHODS

We analysed serum haemoglobin A1c (HbA1c) levels, the incidence of severe hypoglycaemic events, the types and doses of insulin, height standard deviation scores (SDS), body mass index (BMI) percentiles compared with healthy Japanese children and obesity prevalence over time. We also stratified the patients according to glycaemic control levels of <58 mmol/mol (optimal), 58-75 mmol/mol (suboptimal) and ≥75 mmol/mol (high-risk).

RESULTS

Data for 513-978 patients from each of the cohorts were analysed. The incidence of severe hypoglycaemic events decreased over time (from 21 to 4.8/100 patient-years), while the proportion of insulin analogue doses increased (14.6% to 98.6%). In addition, patient height SDS (-0.22 to +0.17), BMI percentile (52.1 to 58.7) and obesity prevalence (2.1% to 5.1%) increased. Height SDS increased in all of the glycaemic control subgroups, while BMI percentile and obesity prevalence increased in the suboptimal and high-risk groups.

CONCLUSIONS

Since 1995, the average height of children with T1DM has increased in parallel with increasing insulin doses. Clinicians should be aware of increased BMI in these patients and the associated risk of developing cardiovascular disease in the future.

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 resistance, role of metformin and other non-insulin therapies in pediatric type 1 diabetes

Type 1 diabetes mellitus (T1DM) in youth is a challenging chronic medical condition. Its management should address not only the glycemic control but also insulin resistance and cardiovascular disease risk factors which are increasingly recognized to be present in youth with TID. Current knowledge on the mechanisms of insulin resistance in T1DM is reviewed. The use of adjunctive therapies that are beneficial to achieve adequate glycemic control while mitigating the effects of insulin resistance are discussed with a focus on metformin therapy and an overview of other new pharmacologic agents.

Sexual dimorphism in growth and insulin-like growth factor-I in children with type 1 diabetes mellitus

OBJECTIVE

Impaired linear growth and reduced IGF-I levels in children with type 1 diabetes (T1DM) have been related to poor metabolic control. The aim of this study was to identify additional factors which may negatively affect growth and IGF system in patients with T1DM.

DESIGN

Ninety-one T1DM children (54 males, age=: 11.73±3years, disease duration=5.6±2.1years) were studied. All children were on intensive insulin therapy: 62 children were on multiple injection therapy (MI) and 29 children on continuous subcutaneous insulin infusion (CSII).

RESULTS

Height velocity (HV) SDS and IGF-I levels were higher in females and in pubertal children [HV SDS: females=0.6±2.4 vs males=-0.45±2.3 (p=0.04); IGF-I SDS: females=-1.09±0.58 vs males=-1.4±0.6 (p=0.02); IGF-I/IGFBP-3 molar ratio: females=0.25±0.1 vs males=0.21±0.08 (p=0.04); IGF-I SDS: pre-pubertal=-1.58±0.46 vs pubertal=-1.15±0.65 (p<0.001); IGF-I/IGFBP-3 molar ratio: pre-pubertal=0.16±0.08 vs pubertal=0.26±0.09 (p<0.001)]. No differences between children on CSII or MI therapy were found. IGF-I SDS was positively related to C peptide level (p<0.001), puberty (p<0.001) and female gender (p=0.02) and negatively related to HbA1c (p=0.04). IGF-I/IGFBP-3 molar ratio was positively affected by C peptide level (p<0.001), puberty (p<0.001) and daily insulin dose (p<0.001).

CONCLUSIONS

Our results indicate that despite intensive insulin therapy, T1DM still negatively affects IGF-I secretion and linear growth. Growth impairment is more severe in males and primarily related to poor glycemic control and loss of the residual beta cell mass.

Growth abnormalities in children with type 1 diabetes, juvenile chronic arthritis, and asthma

Children and adolescents with chronic diseases are commonly affected by a variable degree of growth failure, leading to an impaired final height. Of note, the peculiar onset during childhood and adolescence of some chronic diseases, such as type 1 diabetes, juvenile idiopathic arthritis, and asthma, underlines the relevant role of healthcare planners and providers in detecting and preventing growth abnormalities in these high risk populations. In this review article, the most relevant common and disease-specific mechanisms by which these major chronic diseases affect growth in youth are analyzed. In addition, the available and potential targeting strategies to restore the physiological, hormonal, and inflammatory pattern are described.

The glomerular podocyte as a target of growth hormone action: implications for the pathogenesis of diabetic nephropathy

Involvement of the growth hormone (GH) / insulin-like growth factor 1 (IGF-I) axis in the pathogenesis of diabetic nephropathy (DN) is strongly suggested by studies investigating the impact of GH excess and deficiency on renal structure and function. GH excess in both the human (acromegaly) and in transgenic animal models is characterized by significant structural and functional changes in the kidney. In the human a direct relationship has been noted between the activity of the GH/IGF-1 axis and renal hypertrophy, microalbuminuria, and glomerulosclerosis. Conversely, states of GH deficiency or deficiency or inhibition of GH receptor (GHR) activity confer a protective effect against DN. The glomerular podocyte plays a central and critical role in the structural and functional integrity of the glomerular filtration barrier and maintenance of normal renal function. Recent studies have revealed that the glomerular podocyte is a target of GH action and that GH's actions on the podocyte could be detrimental to the structure and function of the podocyte. These results provide a novel mechanism for GH's role in the pathogenesis of DN and offer the possibility of targeting the GH/IGF-1 axis for the prevention and treatment of DN.

Development and linear growth in diabetic children receiving insulin pigment

OBJECTIVE

The aim of this study was to ascertain if there are differences in the development and linear growth between a group of diabetic children who had been receiving insulin pigment and healthy children.

METHODS

A total of 57 Chinese children with type 1 diabetes diagnosed at the age from 6 to 10 years old (26 boys and 31 girls) were included in the study. Their height and weight and development conditions were recorded until they reached their 18th birthday.

RESULTS

Diabetic children were taller than healthy children at the onset of diabetes, even though there was no significant difference between them [male height standard deviation score (SDS): 0.34 +/- 0.93, female height SDS: 0.38 +/- 0.50]. When they reached their final height, they were slightly shorter than the healthy group. However, there were still no significant differences between these two groups (male height SDS: -0.42 +/- 0.95, female height SDS: -0.60 +/- 0.98). The median age at onset of puberty, 12.62 years in boys and 11.13 years in girls, was significantly delayed in diabetic boys compared to 10.55 years in healthy boys and 9.2 years in healthy girls. The median age at menarche in diabetic girls (14.15 years) was also delayed compared with 12.27 years in healthy girls. The majority of these diabetic children were thinner than the healthy children when they were diagnosed [male body mass index (BMI): 14.45 +/- 1.35 kg/m2 vs. 16.08 +/- 0.59 kg/m2, t = -0.63, p < 0.05; female BMI: 13.50 +/- 1.87 kg/m2 vs. 15.46 +/- 0.45 kg/m2, t = -6.67, p < 0.05]; however, as they reached their final height, they became fatter, especially the girls (male BMI: 21.43 +/- 1.62 kg/m2 vs. 20.8 +/- 0.00 kg/m2, t = 1.97, p > 0.05; female BMI: 23.95 +/- 2.37 kg/m2 vs. 20.3 +/- 0.00 kg/m2, t = 8.60, p < 0.05).

CONCLUSION

Even with well-controlled glucose levels, the development of children with diabetes who had been receiving insulin pigment were still adversely affected. However, linear growth had only been slightly affected. All patients, especially girls, became fatter when they reached their final height.

Growth hormone binding protein levels in children are associated with birth weight, postnatal weight gain, and insulin secretion

Rapid infancy weight gain is associated with subsequent higher circulating insulin-like growth factor (IGF) I levels in normal children. We hypothesized that circulating levels of growth hormone binding protein (GHBP), a putative marker of GH sensitivity, may also be associated with postnatal weight gain and insulin secretion. In 751 normal children aged 7 to 8 years, we measured insulin, glucose, GHBP, IGF-I, IGF binding protein (IGFBP) 1, and IGFBP-3 levels in a fasting venous blood sample. Insulin secretion was assessed by measuring insulin and glucose levels 30 minutes after an oral glucose load. After adjustment for current weight, birth weight was inversely related to IGF-I and GHBP levels. Children with lower birth weight and rapid weight gain between birth and 3 years had higher IGF-I and GHBP levels and also lower IGFBP-1 levels than other children. Allowing for current body mass index, GHBP levels were positively related to insulin secretion. In conclusion, children who showed rapid early postnatal weight gain after low birth weight have higher levels of GHBP than other children. Increased GH sensitivity in such children could contribute to links between rapid infancy weight gain and subsequent faster rates of childhood growth and maturation.

Severe deficiencies of IGF-I, IGF-II, IGFBP-3, ALS and paradoxically high-normal bone mass in a child with insulin-resistance syndrome (Rabson-Mendenhall type)

Rabson-Mendenhall syndrome is a rare genetic disorder characterized by severe insulin resistance and hyperinsulinemia due to defects in signaling through the insulin receptor. Herein, we describe a new case of Rabson-Mendenhall syndrome in which investigations of the growth hormone (GH) - insulin-like growth factor (IGF) axis - reveal severe deficiencies in total and free insulin-like growth factor-I (IGF-I), IGF-II, IGF-binding protein-3 (IGFBP-3), and the acid labile subunit (ALS). Based on these findings, we anticipated significant bone deficits, as have been described in other clinical scenarios in which the IGF axis is significantly perturbed. Long-bone studies revealed no gross malformations. Paradoxically, DXA scanning revealed a total body bone density Z-score of +2.0 (0.8 gm/cm(2)), suggesting an overall high-normal BMD for age and a high BMD corrected for bone or height age. The mechanisms by which BMD is protected from severe deficiencies in the IGF-axis are unknown, yet may involve enhanced IGF sensitivity, increased local production of IGFs, and/or supra-physiological concentrations of insulin substituting for the actions of IGFs in bone.

Mechanisms of disease: metabolic effects of growth hormone and insulin-like growth factor 1

Insulin-like growth factor (IGF) 1 is a member of a family that is involved in growth, development, cell differentiation, and metabolism. IGF1, IGF2 and insulin act primarily through tyrosine-kinase-linked receptors--the IGF1 receptor (IGF1R) and insulin receptor (IR). The IGF1R binds IGF1 and IGF2 with high affinity and the IR binds insulin with high affinity; however, since both receptors share a high degree of structural and functional homology, the IGF1R can bind insulin and the IR can bind the IGFs with reduced affinity. These two receptors can, moreover, form heterodimers, which bind both ligands. Upon binding to the receptors, cascades of tyrosine and serine kinases are stimulated to facilitate growth or metabolism. The IGF2 receptor is a scavenger receptor, and is, therefore, not involved in mediation of growth or metabolic effects of the IGF family and will not be discussed in the current article. IGF1 is a major gene target of growth hormone and its product mediates many of the actions of growth hormone on growth and development; however, IGF1 has actions distinct from those of growth hormone in carbohydrate, lipid, and protein metabolism. For example, excess growth hormone causes insulin resistance and hyperglycemia, whereas IGF1 has insulin-like effects that reduce blood glucose levels and has been used experimentally to treat both type 1 and type 2 diabetes.

Growth hormone hypothesis and development of diabetic nephropathy in Type 1 diabetes

In Type 1 diabetes, poor glycemic control is the key predictor for the development of microalbuminuria, an established early marker of overt nephropathy. However, the role of other pathways in the development of diabetic nephropathy may also be important. The growth hormone (GH) hypothesis suggests that the GH-insulin-like growth factor (IGF)-1 axis may play an important role in this disease process. In Type 1 diabetes, the characteristic pattern of GH hypersecretion and low circulating IGF-1 levels results from hepatic GH resistance owing to the lack of portal insulin. Clinical data indicate that high GH and low IGF-1 levels reduce insulin sensitivity and worsen glycemic control. Furthermore, despite hepatic GH resistance, GH receptors at the kidney remain intact. Experimental data show that excess GH stimulates renal GH receptors and, through paracrine IGF-1 production, results in pathophysiological changes consistent with diabetic nephropathy, namely nephromegaly, glomerular hyperfiltration and eventual proteinuria. These abnormalities are reversed by intervention to block or normalize the local effects of GH and IGF-1. Although such data in humans are limited, preliminary trials show that interventions to increase IGF-1 levels and reduce GH hypersecretion improve glycemic control and insulin sensitivity in the short term. However, their effects on early nephropathy and end points, such as the prevalence of end stage renal disease, have yet to be determined.

Physiology and pathophysiology of growth hormone-binding protein: methodological and clinical aspects

Circulating GH is partly bound to a high-affinity binding protein (GHBP), which in humans is derived from cleavage of the extracellular domain of the GH receptor. The precise biological function GHBP is unknown, although a regulation of GH bioactivity appears plausible. GHBP levels are determined by GH secretory status, body composition, age, and sex hormones, but the cause-effect relationships remain unclarified. In addition to the possible in vivo significance of GHBP, the interaction between GH and GHBP has methodological implications for both GH and GHBP assays. The present review concentrates on methodological aspects of GHBP measurements, GHBP levels in certain clinical conditions with a special emphasis on disturbances in the GH-IGF axis, and discusses the possible relationship between plasma GHBP and GH receptor status in peripheral tissues.

The role of IGF-binding proteins in mediating the effects of recombinant human IGF-I on insulin requirements in type 1 diabetes mellitus

To determine the role of IGF-binding proteins in mediating the direct effects of recombinant human IGF-I on insulin requirements in type 1(insulin-dependent) diabetes mellitus, overnight changes in IGF-I, IGF-II, and IGF-binding protein-1, -2, and -3, collected under euglycemic conditions, were compared in nine subjects after double blind, randomized, sc administration of recombinant human IGF-I (40 microg/kg) or placebo at 1800 h. On both nights a somatostatin analog infusion (300 ng/kg x h) suppressed endogenous GH production, and three timed discrete GH pulses (total, 0.029 IU/kg x night) ensured identical GH levels. After recombinant human IGF-I administration, IGF-I levels and the IGF-I/IGF-binding protein-3 ratio increased [mean +/- SEM:IGF-I, 401 +/- 22 ng/ml; placebo, 256 +/- 20 ng/ml (P = 0.0002); IGF-I, 0.108 +/- 0.006; placebo, 0.074 +/- 0.004 (P = 0.0003), respectively], and insulin requirements decreased (IGF-I, 0.12 +/- 0.03; placebo, 0.23 +/- 0.03 U/kg x min; P = 0.008). The normal within-individual inverse relationships between insulin and IGF-binding protein-1 levels were observed (lag time 2 h: r = -0.34; P < 0.01). Yet despite reduced free insulin levels (8.5 +/- 1.5; placebo, 12.2 +/- 1.2 mU/liter; P = 0.03), IGF-binding protein-1 levels were reduced after recombinant human IGF-I administration (53.7 +/- 6.8; placebo, 82.2 +/- 11.8 ng/ml; P = 0.008). The largest reductions in free insulin levels after recombinant human IGF-I and thus putative improvement in insulin sensitivity occurred in subjects with the smallest increase in the plasma IGF-I/IGF-binding protein-3 ratio (r = 0.7; P = 0.03). Taken together, these data are consistent with the hypothesis that transcapillary movement of IGF-I (perhaps mediated by IGF-binding protein-1), out of the circulation facilitates altered insulin sensitivity. These data have important implications for risk-benefit assessment of recombinant human IGF-I therapy in type 1 diabetes mellitus.

Growth in the diabetic child

Insulin has an important role in the GH:IGF-I axis, and its absence leads to major endocrine disturbances, particularly during puberty. Rapid growth in the prediabetic phase occurs and may be a risk factor. Final height reflects gender and the age of onset more than specific growth factors. The influence of hepatic insulin on IGF-I bioactivity has important implications in diabetic adolescents.

Insulin as a growth factor

Various clinical syndromes illustrate the essential role of insulin in modulating somatic growth both in utero and after birth. The effect of insulin on growth is a consequence of direct effects transduced via its homologous receptor and post-receptor signaling pathways and indirect effects on other modulators of growth, such as the growth hormone-IGF axis. Recent insights into the post-receptor mechanisms of insulin signaling provide a scientific framework for the distinction between the traditional role of insulin as a major modulator of metabolism and its role as a promoter of growth.

Insulin-like growth factors (IGFs) and IGF-I treatment in the adolescent with insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) during adolescence is associated with complex derangements of the growth hormone (GH)/insulin-like growth factor (IGF) axis. Despite GH hypersecretion, IGF-I levels and IGF bioactivity are reduced. The diabetogenic effects of GH are well established, and GH hypersecretion has been implicated in the deterioration in glycemic control during adolescence and in the development of microangiopathy. Insulin deficiency or reduced portal delivery of insulin plays a central role in the development of these abnormalities, and although continuous subcutaneous insulin delivery may improve plasma IGF-I levels, it does not necessarily suppress GH levels. Recombinant IGF-I has been proposed as an adjunct to conventional insulin therapy, as restoring circulating IGF-I levels might lead to GH suppression. Placebo-controlled studies have shown a consistent reduction in GH secretion and related improvements in insulin sensitivity following a single subcutaneous IGF-I injection (40 micrograms/kg). Repeated daily subcutaneous IGF-I administration for 1 month resulted in a sustained increase in IGF-I levels, as well as a reduction in GH secretion and insulin requirements. There was no increase in hypoglycemia or other adverse effects. Recombinant IGF-I used in conjunction with insulin may therefore provide an additional approach to the management of IDDM during adolescence, allowing correction of abnormalities in the GH/IGF axis and leading to improved control and, hence, reduced risk of long-term complications. However, this hypothesis needs to be rigorously tested in long-term placebo-controlled studies.