Increased insulin-like growth factor I binding to red blood cells of normal prepubertal children

Red Blood Cells Store and Release Interleukin-33

Interleukin-33 (IL-33) is a member of the IL-1 cytokine superfamily that potently drives production of a variety of cytokines and contributes to the pathogenesis of inflammatory diseases. The IL-33 is a nuclear protein and is released from apoptotic or necrotic cells. Serum IL-33 levels are increased in various diseases, such as atopic dermatitis, chronic hepatitis C infection, and asthma. Here, we show that red blood cells (RBCs) are one of the major sources of plasma IL-33. The IL-33 levels are significantly increased in supernatants from lysed RBCs. Plasma IL-33 levels are increased in patients during hemolysis, and plasma IL-33 levels show a positive correlation with degree of hemolysis. The IL-33 protein and messenger RNA levels were detected in the late stages of differentiation in ex vivo primary human erythroid progenitor cell cultures, suggesting that IL-33 is expressed during maturation of RBCs. Furthermore, hemoglobin depleted red cell lysates induced IL-8 expression in human epithelial cells. This effect was attenuated in IL-33 decoy receptor expressing cells and was enhanced in IL-33 receptor expressing cells. These results suggest that erythroid progenitor cells produce IL-33 and circulating RBCs represent a major source of IL-33 that is released upon hemolysis.

Age-dependent levels of plasma neuropeptides in normal children

Several neuropeptides are secreted in high amounts in pediatric tumors such as neuroblastoma and have been used as markers of residual or recurrent disease. Plasma levels of neuropeptides might be expected to change during development, but have not been determined in normal children. We have obtained fresh plasma from cord blood of six full-term infants and from peripheral blood in 41 healthy children, ages 1 month to 21 years. Levels of six neuropeptides, vasoactive intestinal peptide (VIP), somatostatin, gastrin releasing peptide (GRP), substance P, pancreastatin and neuropeptide Y (NPY) were measured by radioimmunoassay along with insulin-like growth factor-1 (IGF-1) whose plasma levels are known to vary during development. A child with neuroblastoma was treated with the somatostatin analogue, octreotide, and the effect on plasma neuropeptides quantified. Octreotide doses of 2-3 microg/kg daily resulted in a 40-60% decrease in plasma levels of IGF-1, pancreastatin and GRP. These results are the first publication of plasma neuropeptide levels in normal children.

Erythrocyte insulin-like growth factor-L binding in younger and older males

OBJECTIVE

Insulin-like growth factor-1 (IGF-l) levels are lower in older compared with younger subjects. We tested the hypothesis that the reduction in circulating IGF-l would be accompanied by upregulation in tissue IGF-l binding in at least some tissues. We tested erythrocyte IGF-l binding since blood is an accessible tissue in humans, and there is growing evidence to suggest that erythrocyte IGF-l binding is influenced by circulating IGF-l.

DESIGN AND PATIENTS

We compared 9 healthy older males (61-68 years old) with 9 healthy younger males (15-19 years old).

MEASUREMENTS

Standard techniques were used to assay circulating IGF-l and IGF binding proteins 1-5 (IGFBPs 1-5). Erythrocyte IGF-l binding was first measured by studies in which native [125l]-IGF-l was displaced with unlabelled native IGF-l. In order to determine a possible role for IGF binding proteins (IGFBP), native [125l]-IGF-l was displaced with des-(1-3)IGF-1, which binds with IGF receptors but not IGFBPs.

RESULTS

As expected, circulating IGF-l was significantly lower in the older compared with the younger subjects. In addition, IGFBP-3 and 5 were significantly lower, and IGFBP-4 higher, in older compared with younger subjects. When native [125l]-IGF-l was displaced with unlabelled native IGF-l, the number of IGF-l binding sites per erythrocyte was higher in the older subjects (43 +/- 5 vs. 18 +/- 2, older vs. younger, respectively; P < 0.05). In contrast, when native [125l]-IGF-l was displaced with des-(1-3), IGF-l binding capacity was not different between the two age groups.

CONCLUSIONS

Erythrocyte IGF binding was increased in older compared with younger subjects. Surprisingly, the mechanism of the increase may not be a simple up regulation of IGF-l receptors in response to reduced circulating IGF-l, but possibly by an increase in the levels of as yet unidentified erythrocyte membrane-associated IGF binding proteins.

Insulin-like growth factor I receptors on blood cells: their relationship to circulating total and "free" IGF-I, IGFBP-1, IGFBP-3 and insulin levels in healthy subjects

The relationships between the insulin-like growth factor I/insulin-like growth factor binding protein (IGF-I/IGFBP) system and the IGF-I receptor characteristics on erythrocytes and PBMCs in healthy subjects in the fasting state were studied to establish whether this would be a valid way of examining IGF-I receptors in vivo. The K(d) of the IGF-I receptor on erythrocytes was positively related to circulating "free" IGF-I levels. For the IGF-I receptor on PBMCs no relationship was observed with "free" IGF-I levels. IGFBP-3 levels were inversely related to the number of IGF-I binding sites on erythrocytes and to the K(d) of the IGF-I receptor on PBMCs. Total IGF-I, insulin and IGFBP-1 levels showed no relation to the IGF-I receptor on erythrocytes and PBMCs in the fasting state. This report suggests that studies of IGF-I receptor characteristics on erythrocytes and PBMCs in the fasting state are cell-specific and cannot be extrapolated to other cell types, which may be more relevant target tissues for IGF-I action in vivo.

Modulation of IGF-I receptors by exogenous hGH treatment in constitutionally short children

OBJECTIVE

To study the in-vivo regulation of IGF-I binding sites on erythrocytes (RBC) following administration of growth hormone (hGH) to constitutionally short children. Recently, owing to biosynthetic techniques, treatment with hGH has been administered not only to children with GH deficiency but also to children with constitutional growth delay and with familial short stature.

PATIENTS AND DESIGN

Growth hormone (rhGH-Norditropin, Novo/Nordisk) was administered at a dose of 0.1 U/kg/day s.c. to 11 children with constitutional short stature. Before and at 1-2 months after initiation of treatment IGF-I binding sites and serum IGF-I were determined. Erythrocytes were separated from whole blood by centrifugation over Ficoll Hypaque and used to assess IGF-I binding sites.

RESULTS

Serum IGF-I levels increased from 14.93 +/- 1.50 nmol/l (mean +/- SEM) to 30.29 +/- 2.32 nmol/l, with a mean difference of 15.36 +/- 2.21 (P = 0.00001). Concomitantly, the number of binding sites per cell decreased from 5.77 +/- 0.81 sites per cell (m +/- SEM) to 2.10 +/- 0.36, with a mean difference of -3.67 +/- 0.76 (P = 0.0003). The dissociation constant (Kd) also decreased from 0.47 +/- 0.16 nM (m +/- SEM) to 0.10 +/- 0.02 with a mean difference of -0.37 +/- 0.16 (P = 0.02), indicating an increase in the affinity of the receptors.

CONCLUSION

Treatment of children with constitutional short stature with hGH raises the circulating IGF-I levels and down-regulates the IGF-I receptors. This study shows that IGF-I is capable of regulating its homologous receptor concentrations in vivo and it is suggested that the measurement of IGF-I binding sites on RBC may be used for the diagnosis of subtle states of resistance to IGF-I.