Effects of exogenous insulin-like growth factor I on insulin-like growth factor binding proteins in a case of growth hormone insensitivity (Laron-type)

Differential expression of IGFBPs in Laron syndrome-derived lymphoblastoid cell lines: Potential correlation with reduced cancer incidence

Laron syndrome (LS), or primary growth hormone (GH) insensitivity, is a growth disorder that results from mutation of the GH-receptor (GHR) gene leading to congenital insulin-like growth factor-1 (IGF-1) deficiency. Recent epidemiological studies have shown that LS patients are protected from cancer development. Genome-wide profiling identified genes and signaling pathways that are differentially represented in LS patients, and that may contribute to cancer protection. The present study was aimed at evaluating the hypothesis that IGF binding proteins (IGFBPs) are differentially expressed in LS, most probably as a result of low circulating levels of IGF-1. Furthermore, we postulated that IGFBPs might be differentially regulated by oxidative stress in this condition and, therefore, may contribute to cancer evasion. Our results show that IGFBP-3, which is predominantly protective, was highly expressed in LS-derived lymphoblastoid cells in comparison to control cells from the same ethnic group. On the other hand, levels of IGFBP-2, -4, -5, and -6 were diminished in LS patients, as demonstrated by RQ-PCR, Western immunoblots and confocal immunofluorescence. In addition, our data provide evidence for a pattern of IGFBP response to H₂O₂ treatment that might be associated with distinct expression of apoptosis markers (BCL2, pro-caspase-9, pro-caspase-3) in LS. In summary, differential expression of specific IGFBPs in LS might be correlated with cellular mechanisms underlying cancer protection and, probably, additional phenotypes due to congenital IGF-1 deficiency.

Extending healthy life span--from yeast to humans

When the food intake of organisms such as yeast and rodents is reduced (dietary restriction), they live longer than organisms fed a normal diet. A similar effect is seen when the activity of nutrient-sensing pathways is reduced by mutations or chemical inhibitors. In rodents, both dietary restriction and decreased nutrient-sensing pathway activity can lower the incidence of age-related loss of function and disease, including tumors and neurodegeneration. Dietary restriction also increases life span and protects against diabetes, cancer, and cardiovascular disease in rhesus monkeys, and in humans it causes changes that protect against these age-related pathologies. Tumors and diabetes are also uncommon in humans with mutations in the growth hormone receptor, and natural genetic variants in nutrient-sensing pathways are associated with increased human life span. Dietary restriction and reduced activity of nutrient-sensing pathways may thus slow aging by similar mechanisms, which have been conserved during evolution. We discuss these findings and their potential application to prevention of age-related disease and promotion of healthy aging in humans, and the challenge of possible negative side effects.

Kinetic analysis of the disposition of insulin-like growth factor 1 in healthy volunteers

PURPOSE

Insulin-like growth factor 1 (IGF-1) is predominantly bound to its specific binding proteins (IGFBPs) in circulating plasma. In the present study, pharmacokinetic analysis of IGF-1 was performed in healthy volunteers to characterize the effect of interactions with IGFBPs on IGF-1 disposition.

METHODS

Plasma concentration profiles of both free and bound IGF-1 were examined at several doses. An in vitro plasma protein binding was also analyzed.

RESULTS

The total body clearance (CLtotal) for the free IGF-1 was much higher than the creatinine clearance, suggesting that the major elimination pathway is by a route other than renal glomerular filtration. The CLtotal for the free IGF-1 exhibited a dose-dependent reduction whereas that for the sum of unbound and bound IGF-1 increased on increasing the dose. The data obtained fitted closely a one-compartment model that involved the binding and dissociation of IGF-1, as well as its biosynthesis and elimination. The estimated parameters suggest that IGF-1 exhibits high affinity binding to IGFBPs. the rate-limiting step in the overall elimination being the dissociation from IGFBPs.

CONCLUSIONS

The saturation of both the plasma protein binding and elimination accounts for the nonlinear pharmacokinetic profile. The binding to IGFBPs markedly limits both the distribution and elimination of IGF-1.

Effects of growth hormone treatment on serum levels of insulin-like growth factors (IGFs) and IGF binding proteins 1-4 in postmenopausal women

BACKGROUND AND OBJECTIVE

Insulin-like growth factor binding proteins (IGFBPs) modulate the actions and bioavailability of insulin-like growth factors (IGFs), however, their regulation in vivo is incompletely understood. In this study we investigated the effects of different doses of growth hormone (GH) on circulating levels of IGFs and IGFBPs.

DESIGN

The study was double-blind and placebo-controlled. Patients were treated with either GH in doses of 0.05, 0.10, or 0.20 lU/kg/day of placebo for one week.

PATIENTS

Forty post-menopausal women aged 52-73 years with low bone mass.

MEASUREMENTS

Serum IGF-I and IGF-II were measured by RIA while IGFBP-1-3 were measured by Western ligand blot (WLB) and compared with determinations by specific immunoassays. IGFBP-4 was measured by WLB alone.

RESULTS

Both IGF-I (P < 0.001) and IGF-II (P < 0.01) increased significantly during GH treatment. Additionally, IGFBP-1 (P < 0.001) and IGFBP-2 (P < 0.001) decreased significantly while IGFBP-3 (P < 0.001) and IGFBP-4 (P < 0.05) increased all in a dose-dependent manner. Stepwise (backwards) multiple regression analyses showed that the changes in IGF-I and IGF-II, and age correlated with the change in serum IGFBP-1. Both GH-dosage, the increase in IGF-II, and body mass index correlated with the decrease in IGFBP-2. Furthermore, the increase in serum IGF-I, IGF-II, and triiodothyronine correlated with the increase in IGFBP-3. Moreover, GH-dosage correlated with the increase in serum IGFBP-4.

CONCLUSION

GH significantly increased serum IGF-I, IGF-II, IGFBP-3, and IGFBP-4 and decreased serum IGFBP-1 and IGFBP-2 in post-menopausal women.

Laron syndrome: typical and atypical forms

Since the original description of LS by Laron in 1966, this rare condition has continued to assume an importance far beyond the number of affected cases as a unique model of GHR dysfunction. Recently, the potential of therapy with recombinant IGF-I has led to the recruitment and detailed study of patients from a heterogeneous genetic and geographical background and the realization that hereditary GH resistance is itself a heterogeneous condition, with considerable variation in clinical, biochemical and molecular features between patients. For the scientist, further study of the 'atypical' LS patient may lead to important insights into the signalling pathway between GH and IGF-I. For the clinician, the challenge lies in establishing the contribution of inherited forms of GH resistance to the group of children with idiopathic short stature, with the potential of offering therapy to these patients based on an understanding of the aetiological basis of their disorder.

The insulin-like growth factor-I/binding protein axis: physiology, pathophysiology and therapeutic manipulation

Insulin-like growth factor-I (IGF-I) is a single-chain polypeptide which has multiple metabolic actions and effects on the differentiation and proliferation of a wide variety of cell types. IGF-I has endocrine, paracrine and autocrine actions and is bound in the circulation to a complex system of binding proteins which alter its bioavailability and activity. Thus its physiology is complex and is altered in a number of pathological states. This review will discuss these states and the actual and proposed therapeutic applications of recombinant human IGF-I (rhIGF-I).

Laron dwarfism in the Arabian Gulf: a report of a sibship

Laron dwarfism is a rare inherited form of short stature. Most cases reported have been in people of Mediterranean origin, particularly Oriental Jews. We describe the first sibship in an Arab Muslim family from Kuwait in the Arabian Gulf. This type of growth hormone insensitivity is caused by defects in the growth hormone receptor gene. The recently available recombinant human insulin-like growth factor I has shown promise as a promoter of growth in children with Laron syndrome.