Effects of chemotherapy on bone metabolism and skeletal growth

In recent years there has been a significant increase in both acute and chronic toxicity associated with the more successful but now highly intensive chemotherapy (CT) regimens used to treat childhood cancers. The incidence of childhood cancers coincides with periods of rapid skeletal development. Consequently, short stature and osteoporosis are important long-term effects in adult survivors. Clinical data indicate that the effects of CT, including glucocorticoids, on final height are due to direct effects of these drugs on the skeleton. The multiple modes of action of CT drugs suggest a complex and diverse influence on chondrocytes, extracellular matrix and bone cells. However, only limited data demonstrate these direct effects on the proliferative capacity of growth plate chondrocytes and on key steps of endochondral ossification, the multistep process that determines rate and extent of long bone growth. Endochondral ossification requires coordinated maturation, proliferation and differentiation of growth plate chondrocytes leading to hypertrophic cells which eventually undergo apoptosis to leave a cartilaginous scaffold that is mineralized prior to the laying down of new bone. Disruption of the physiological cellular activity of growth plate chondrocytes and/or bone cells result in skeletal growth disturbances. Thus, CT drugs which disrupt normal cell division may manifest their effects on the growth plate as either a reduction in cell number and/or the loss of functional integrity of extracellular matrix. Histological and cell kinetic studies, using in vivo and in vitro models of long bone growth, are essential to increase our understanding of the cellular mechanisms involved and to finally determine how the individual growth potential might be maintained during treatment for childhood cancers.

Dexamethasone inhibits and thyroid hormone promotes differentiation of mouse chondrogenic ATDC5 cells

The effects of glucocorticoid (GC) excess, thyrotoxicosis, and hypothyroidism on linear growth indicate that growth plate chondrocytes are exquisitely sensitive to GC and thyroid hormone (T(3)). Murine ATDC5 cells undergo chondrogenesis in vitro and were used to evaluate the effects of dexamethasone (Dex) and T(3) on cell proliferation and differentiation. Immature and differentiated ATDC5 cells expressed glucocorticoid and T(3)-receptor mRNAs. Cells proliferated and organized into cartilage-like nodules after 7 days. Chondrocyte maturation progressed over 9-40 days, with increasing alkaline phosphatase (ALP) activity, secretion of an Alcian blue-positive matrix, and mineralization of cartilage-like nodules. Dex reduced cell number over the 40 day period, causing inhibition of ALP activity and matrix production with failure of mineralization. Following withdrawal of Dex, chondrocytes proliferated and re-entered the differentiation and mineralization program, indicating that GC inhibition of chondrogenesis is reversible. In contrast, T(3) reduced cell proliferation, but induced ALP activity and increased matrix secretion earlier than in control cultures. Thus, GCs and T(3) regulate growth plate chondrocyte differentiation by distinct mechanisms. GCs arrest cell proliferation, differentiation, and cartilage mineralization and maintain chondrocyte precursors in a state of quiescence with the capacity to re-enter chondrogenesis. T(3) inhibits cell proliferation but accelerates differentiation to stimulate chondrogenesis.

Growth failure in a child showing characteristics of Seckel syndrome: possible effects of IGF-I and endogenous IGFBP-3

Seckel syndrome is an autosomal-recessive disorder with a frequency of less than 1/10 000 births in which there are multiple malformations including severe short stature. We report on a patient with Seckel syndrome with a current body height of -7.5 SDS. Laboratory investigations at the age of 19 months revealed high levels of IGF-I, IGF-II and IGFBP-3. These data suggested the existence of IGF-I resistance possibly caused by impairment of the IGF-I receptor (IGF-IR) or altered IGFBPs. The purpose of this investigation was to examine whether the growth retardation in a Seckel syndrome patient is related to an alteration in the IGF system. Analysis of IGF-IR mRNA of patient's and control fibroblasts by solution hybridization/RNase protection assay did not show differences of IGF-IR transcript expression or size. Affinity crosslinking studies using [125I]-IGF-I showed normal-sized IGF-IR-ligand complexes. Mutation analysis of the complete coding regions of the IGF-I and IGF-IR genes showed no evidence of genetic alterations. Ligand blot analysis of IGFBPs secreted by the patient's fibroblasts showed stronger signals than control cells. Quantitative measurement of IGFBP-3 in cell-conditioned media was performed by radioimmunoassay (RIA) and revealed a sixfold increase when compared to control fibroblasts. We conclude that in this patient with Seckel syndrome and severe growth impairment IGF-I resistance is possibly related to altered production of IGFBP-3.

Glucocorticoids, thyroid hormone and growth hormone interactions: implications for the growth plate

Linear growth occurs during childhood and results from endochondral ossification in the growth plate. Prepubertal growth is primarily regulated by growth hormone (GH) and insulin-like growth factor (IGF)-I, with important contributions from glucocorticoids (GC) and thyroid hormone (T(3)). The somatomedin hypothesis proposed that GH stimulates hepatic IGF-I production, which then regulates growth via IGF-I receptor expressing chondrocytes in an endocrine fashion. Recent studies indicate that locally acting IGF-I is a key determinant of endochondral ossification and that GH, GC and T(3) regulate expression of IGF-I and its receptor in the growth plate directly. Analysis of hormone imbalance during childhood and studies of genetically modified mice provide support for an important GH and IGF-I autocrine/paracrine pathway and for direct effects of GC and T(3) during endochondral ossification. Thus, the epiphyseal growth plate is a key site for convergent hormone action that mediates the control of linear growth.

Thyroid status affects number and localization of thyroid hormone receptor expressing mast cells in bone marrow

Thyroid hormone (T(3)) plays a key role in endochondral ossification. The process relies on the coordinated synthesis and degradation of cartilage matrix and is disrupted in juvenile hypothyroidism, leading to abnormal skeletal development. Mast cells synthesize and store matrix-degrading enzymes. We examined whether thyroid status influences skeletal mast cell distribution in growing rats to determine whether they might modulate the actions of T(3) in bone. Tibiae were collected for histological, histochemical, immunohistochemical, and immunofluorescence analysis. Mast cells were increased throughout the bone marrow in hypothyroid rats compared with euthyroid, thyrotoxic, and hypothyroid-thyroxine replaced animals. Large numbers were present in metaphyseal marrow adjacent to the growth plate in hypothyroid animals and cells were distributed evenly throughout the marrow. Very few mast cells were present in metaphyseal marrow in other groups, but their numbers increased with increasing distance from the growth plate. T(3) receptor alpha1 (TRalpha1) was expressed in the nucleus and cytoplasm of skeletal mast cells, whereas TRalpha2 and TRbeta1 were restricted to the cytoplasm. Localization of TRs was not affected by altered thyroid status. Thus, disrupted endochondral ossification in hypothyroidism may be mediated in part by skeletal mast cells, which express TR proteins and may function as T(3) target cells.

Thyroid hormones regulate hypertrophic chondrocyte differentiation and expression of parathyroid hormone-related peptide and its receptor during endochondral bone formation

Hypothyroidism in children causes developmental abnormalities in bone and growth arrest, while thyrotoxicosis accelerates growth rate and advances bone age. To determine the effects of thyroid hormones on endochondral bone formation, we examined epiphyseal growth plates in control, hypothyroid, thyrotoxic, and hypothyroid-thyroxine (hypo-T4)-treated rats. Hypothyroid growth plates were grossly disorganized, contained an abnormal matrix rich in heparan sulfate, and hypertrophic chondrocyte differentiation failed to progress. These effects correlated with the absence of collagen X expression and increased parathyroid hormone-related protein (PTHrP) messenger RNA (mRNA) expression. In thyrotoxic growth plates, histology essentially was normal but PTHrP receptor (PTHrP-R) mRNA was undetectable. PTHrP is a potent inhibitor of hypertrophic chondrocyte differentiation that acts in a negative feedback loop with the secreted factor Indian hedgehog (Ihh) to regulate endochondral bone formation. Thyroid hormone receptor alpha1(TRalpha1), TRalpha2, and TRbeta1 proteins were localized to reserve zone progenitor cells and proliferating chondrocytes in euthyroid rat cartilage; regions in which PTHrP and PTHrP-R expression were affected by thyroid status. Thus, dysregulated Ihh/PTHrP feedback loop activity may be a key mechanism that underlies growth disorders in childhood thyroid disease.

Improvements and new potentials in pharmacological therapy of diabetes mellitus in children and adolescents

Subcutaneous insulin substitution is not physiological. Despite the many attempts using intensified insulin regimens to render current insulin substitution protocols more physiological, a nondiabetic circulating insulin profile cannot be simulated in patients with type 1 diabetes. Despite many efforts, the pharmacological treatment of type 1 diabetes consists of an unphysiological attempt to substitute only one of the hormones which are lost after beta-cell destruction, namely insulin. It is therefore mandatory to search for additional means to achieve physiological regulation of glucose homeostasis and overall metabolic status. Peptides which are being developed as additional new therapeutic compounds for type 1 diabetes include, for example, IGF-I, leptin, C-peptide and amylin. In addition, the application of insulin analogues has already been introduced into clinical practice. However, so far none of these pharmaceutical compounds has been shown to offer real clinical benefits and substantially improve metabolic control in patients with type 1 diabetes. The results of long-term clinical trials using the peptide compounds listed above for the treatment of type 1 diabetes are still not available.

Thyroid hormone acts directly on growth plate chondrocytes to promote hypertrophic differentiation and inhibit clonal expansion and cell proliferation

T3 is an important regulator of endochondral bone formation in epiphyseal growth plates. Growth arrest in juvenile hypothyroidism results from disorganization of growth plate chondrocytes and their failure to undergo hypertrophic differentiation, but it is unclear how T3 acts directly on chondrocytes or whether its actions involve other pathways. To address this issue, we investigated whether thyroid hormone receptors (TR) were localized to discrete regions of the unfused epiphysis by immunohistochemistry performed in tibial growth plates from 21-day-old rats and examined the effects of T3 on growth plate chondrocytes in agarose suspension cultures in vitro. TRalpha1, -alpha2, and -beta1 were expressed in reserve and proliferating zone chondrocytes, but not in hypertrophic cells, suggesting that progenitor cells and immature chondrocytes are the major T3 target cells in the growth plate. Chondrocytes in suspension culture expressed TRalpha1, -alpha2, and -beta1 messenger RNAs and matured by an ordered process of clonal expansion, colony formation, and terminal hypertrophic differentiation. Clonal expansion and proliferation of chondrocytes were inhibited by T3, which also induced alkaline phosphatase activity, expression of collagen X messenger RNA, and secretion of an alcian blue-positive matrix as early as 7 days after hormone stimulation. Thus, T3 inhibited chondrocyte clonal expansion and cell proliferation while simultaneously promoting hypertrophic chondrocyte differentiation. These data indicate that thyroid hormones concurrently and reciprocally regulate chondrocyte cell growth and differentiation in the endochondral growth plate.

Longitudinal analysis of maternal serum leptin levels during pregnancy, at birth and up to six weeks after birth: relation to body mass index, skinfolds, sex steroids and umbilical cord blood leptin levels

Leptin is an important regulator of body fat mass and energy expenditure during adult life. The mechanisms by which maternal and fetal weight are regulated during pregnancy are poorly understood. In order to gain more insight into a potential role of leptin during gestation, a prospective, longitudinal study was carried out to measure leptin concentrations in maternal serum of 29 healthy women during pregnancy up to 6 weeks after birth and also in umbilical cord blood of their newborns. Leptin concentrations were measured using a specific RIA. In addition, estradiol, testosterone, and sex hormone binding globulin were determined using commercially available RIAs. The mothers' skinfolds were determined at four sites using a Holtain caliper. Leptin levels increased continuously during pregnancy and reached 25.8 +/- 14.7 ng/ml at 38-40 weeks. At birth, leptin concentrations were 23.5 +/- 15.4 ng/ml. Three days after delivery a significant decrease of leptin levels to 10.6 +/- 6.0 ng/ml was observed. Six weeks after birth the leptin concentration in maternal serum was 13.8 +/- 8.6 ng/ml. At birth, maternal serum levels were significantly higher than levels in cord blood and did not correlate with leptin levels in cord blood or neonatal weight. Furthermore, leptin levels did not correlate with maternal sex steroids and sex hormone binding globulin levels. At 6-8 weeks of pregnancy, maternal leptin serum levels correlated significantly with BMI (r = 0.81). The correlation coefficients (leptin vs. BMI) dropped with increasing gestational age and at birth only a poor correlation persisted (r = 0.50). Six weeks after birth there was again a high correlation between leptin levels in maternal serum and BMI (r = 0.76). Subscapular skinfold thickness was correlated to leptin concentrations in maternal serum during the whole period of the investigation. In conclusion, maternal leptin levels continuously increased from 6-8 weeks up to 38-40 weeks of pregnancy. Maternal leptin levels decreased dramatically after birth. Six weeks after delivery, leptin levels were comparable to the values measured at the beginning of pregnancy. We hypothesize that leptin might play an important role during pregnancy and fetal development.

Diagnosis and management of juvenile hyperthyroidism in Germany: a retrospective multicenter study

This retrospective multicenter study was designed to survey the management of childhood and adolescent hyperthyroidism in six pediatric endocrinological units in Germany. Fifty-six patients aged between 1.1 and 17.0 yr (median 10.5 yr) were enrolled. Data were collected retrospectively from the patients' records by a trained pediatric endocrinologist using standardized questionnaires. After the diagnosis of hyperthyroidism was established on the basis of clinical and biological findings, treatment with antithyroid drugs (carbimazole, methimazole, thiamazole, propylthiouracil) was started in all patients. In 55/56 of the patients treated with antithyroid drugs, euthyroidism was achieved (98%). However, 26 patients (47%) were still hyperthyroid after discontinuation of the medication. Eight children with continued hyperthyroidism ultimately underwent subtotal thyroidectomy 13-136 (median 28) months after the initial diagnosis. Management principles of the participating centers were heterogeneous. As a consequence, prospective multicenter studies are urgently needed to establish clear standards for the diagnosis and therapy of childhood hyperthyroidism.

Leptin concentrations in maternal serum and amniotic fluid during the second trimenon: differential relation to fetal gender and maternal morphometry

Leptin, a hormone produced by adipocytes, provides information on the availability of fat stores to the hypothalamus and acts as an afferent satiety signal regulating appetite and energy expenditure in both rodents and humans [Zhang Y, Proenca R, Maffei M, Barone M, Leopold L, Friedman JM. Positional cloning of the mouse obese gene and its human homologue. Nature 1994;372:425-432; Sinha MK. Human leptin: the hormone of adipose tissue. Eur J Endocrinol 1997;136:461-4; Campfield LA, Smith FJ, Guisez Y, Devos R, Burn P. Recombinant mouse ob protein: evidence for a peripheral signal linking adiposity and central neural networks. Science 1995;269:546-9; Halaas JL, Gajiwala KS, Maffei M, Cohen SL, Chait BT, Rabinowitz D, Lallone RL, Burley SK, Friedman JM. Weight-reducing effects of the plasma protein encoded by the obese gene. Science 1995;269:543-6; Saladin R, De Vos P, Guerre-Millo M, Leturque A, Girard J, Staels B, Auwern J. Transient increase in obese gene expression after food intake or insulin administration. Nature 1995;377:527-9; Campfield LA, Smith FJ, Burn P. The OB protein (leptin) pathway - a link between adipose tissue mass and central neural networks. Horm Metab Res 1996;28:619-632; Blum WF, Kiess W, Rascher W, editors. Leptin - the voice of the adipose tissue. J&J Edition, JA Barth Verlag, Heidelberg, 1997]. In addition, leptin is thought to play an important role for reproduction and during gestation [Kiess W, Blum WF, Aubert ML. Leptin, puberty and reproductive function: lessons from animal studies and observations in humans. Eur J Endocrinol 1997;138:1-4; Barash IA, Cheung CC, Wigle DS, Ren H, Kabitting EB, Kuijer JL, Clifton DK, Steiner RA. Leptin is a metabolic signal to the reproductive system. Endocrinology 1996;133:3144-47; Chehab F, Lim M, Lu R. Correction of the sterility defect in homozygous obese female mice by treatment with the human recombinant leptin. Nature Genetics 1996;12:318-20; Kiess W, Schubring C, Prohaska F, Englaro P, Rascher W, Attanasio A, Blum WF. Leptin in amniotic fluid at term and at midgestation. In: Blum WF, Kiess W, Rascher W, editors. Leptin - the voice of the adipose tissue. J&J Edition, JA Barth Verlag, Heidelberg, 1997]. The purpose of this study was to gain more insight into a putative role of leptin during midgestation. Therefore we have measured leptin concentrations in maternal serum and amniotic fluid using a specific radioimmunoassay (RIA) employing human recombinant leptin for tracer and standard preparation [Blum WF, Kiess W, Rascher W, editors, Leptin - The voice of the adipose tissue. J&J Edition, JA Barth Verlag, Heidelberg, 1997; Blum WF, Englaro P, Heiman M, Attanasio Am, Kiess W, Rascher W. Clinical studies of serum leptin. In: Blum WF, Kiess W, Rascher W. Leptin - The voice of the adipose tissue. J&J Edition, JA Barth Verlag, Heidelberg, 1997; Blum WF, Englaro P, Heiman M, Attanasio AM, Kiess W, Rascher W. Plasma leptin levels in healthy children and adolescents: dependence on body mass index, body fat mass, gender, pubertal stage and testosterone. J Clin Endocrinol Metab 1997;82:2904-2910]. In addition, estriol, hCG and alphafetoprotein were measured in maternal serum. (ABSTRACT TRUNCATED)

Leptin serum concentrations in healthy neonates within the first week of life: relation to insulin and growth hormone levels, skinfold thickness, body mass index and weight

BACKGROUND AND AIMS

Leptin, the ob gene product, plays a key role in the regulation of body fat mass and weight in adult life. The mechanisms by which maternal and fetal/neonatal weight are regulated during human pregnancy and in early postnatal life are poorly understood. High leptin levels are observed in women during gestation and in cord blood at term. We have hypothesized that high leptin levels at term could represent an important feed-back indicator of nutrient supply. Subsequently, leptin could signal adipose tissue status during late gestation and during early neonatal life.

SUBJECTS AND METHODS

51 healthy newborns were studied. Clinical and auxological data (birth length, weight, and iliac, subscapular, biceps and triceps skinfold thickness) were recorded using a standardized data sheet. Venous cord blood was obtained immediately after birth in all neonates. Subsequently, capillary blood was obtained from the heel from some of the newborns when blood had to be obtained because of signs or symptoms of particular problems such as hypoglycaemia or hyperbilirubinaemia, at the following time points: two to four hours after birth in 51 infants, 56-79 h after birth in 47 infants and 99-128 h after birth in 23 of the newborns. The ratio between the sexes (girls/boys) was similar at all time points. The infants that were included in the study were subsequently found to be normal and healthy after analysis of the clinical and biochemical data. A specific ultrasensitive radioimmunoassay was used to measure leptin, while growth hormone and insulin were measured using commercially available immunoassays.

RESULTS

Gestational age was 38-42 weeks, maternal age was 21-42 years. Birth weights ranged from 2480 to 4400 g. All newborns and mothers were subsequently found to be healthy. Leptin levels in venous cord blood was 0.16-6.80 microg/l, median 3. 47 microg/l and in capillary blood shortly after birth 0.26-7.03 microg/l, median 3.89 microg/l. 56-79 h after birth leptin levels had fallen dramatically, range 0.02-1.69 microg/l, median 0.26 microg/l, while 99-128 h after birth, leptin concentrations in capillary blood (0.05-2.61 microg/l, median 0.59 microg/l) had significantly increased when compared to the levels at 56-79 h (P < 0.001). There was a significant correlation between leptin levels in umbilical vein and birth weight of the neonates (r = 0.57, P < 0.03). Multistep regression analysis revealed that weight and skinfold thickness accounted for approximately 35-70% of the variation of leptin levels. Insulin and growth hormone, and glucose and bilirubin however, had no major impact on leptin levels.

CONCLUSION

High leptin levels are present in cord blood at birth and in capillary blood shortly after birth. Since leptin levels in cord blood correlate with birth weight it is tempting to speculate that in the fetus as in later life leptin is signalling expansion of fat stores. Most importantly, we now report that leptin levels are high in the fetus but decline rapidly and dramatically after birth in healthy neonates. This may be important for the stimulation of feeding behaviour and the acquisition of energy homeostasis in the neonate.

Cloning and sequencing of the complete cDNA encoding the human insulin receptor related receptor

The insulin receptor related receptor (IRR) is a heterotetrameric transmembrane receptor with intrinsic tyrosine kinase activity. The IRR shares large homology with the insulin and the insulin-like growth factor-1 (IGF-I) receptor with regard to amino acid sequence and protein structure. So far, only a partial human sequence containing the complete 3' end has been reported, although the full-length human IRR cDNA had been used for transfection studies and functional analysis of the receptor. We have isolated a full-length human IRR cDNA and report on the 5' translated and untranslated region of the human IRR gene. The full length IRR sequence contains 4150 bases and shares a high degree of homology with the guinea pig IRR cDNA sequence and rat IRR sequences that had been reported earlier on by others. Sequencing of the IRR cDNA revealed that the human IRR cDNA contains 341 bases corresponding to the IRR 5' end in addition to the bases that had been reported on before. Also, this sequence contains the start codon of translation. The full length cDNA for the human IRR can now be used for functional expression studies and to elucidate the nature of the ligand for this receptor type.

Development of a highly sensitive nonisotopic immunoassay for the determination of salivary 17-hydroxyprogesterone: reference ranges throughout childhood and adolescence

A sensitive nonisotopic immunoassay for the determination of 17-hydroxyprogesterone (17-OHP) levels in saliva was developed. The new time-resolved fluorometric immunoassay employs a specific polyclonal anti-17-OHP antiserum immobilized onto microtiter plates, a 17-OHP-biotin conjugate as a tracer, and streptavidin-europium a as secondary probe. The lower detection limit of the assay is 23.6 pmol/L (mean -3 s of a 22-fold zero determination) corresponding to 0.39 pg/well. The coefficients of intraassay variation are 8.8, 5.3, and 8.3% at the respective concentrations of 90.9, 454.5, and 1363.5 pmol/L. The coefficients of interassay variation are 8.8, 5.3, and 8.3% at the respective concentrations. Saliva was collected in commercially available devices. Reference ranges were established using 394 saliva samples from 132 healthy children, adolescents, and adults. Morning, midday, and evening levels of 17-OHP levels in saliva varied significantly in all age groups with morning levels being higher than midday and evening levels. Saliva samples (n = 57) were also obtained from 18 children with congenital adrenal hyperplasia (CAH). Salivary 17-OHP levels in the limited number of CAH patients studied ranged from 121 to 106,050 pmol/L. In conclusion 1) a new, sensitive nonisotopic immunoassay for measurement of 17-OHP in saliva has been developed; 2) reference ranges for healthy children, adolescents, and adults have been established; 3) there is a circadian pattern of 17-OHP levels in saliva at all ages; and 4) measurement of 17-OHP in saliva should be further evaluated over a longer period of time as a potentially reliable and powerful technique to monitor metabolic control in patients with CAH. As 17-OHP levels in saliva are stable for > 10 wk at 4 degrees C, the technique is ideally suited for outpatient sampling.

Practical aspects of managing preschool children with type 1 diabetes

Day-to-day variations in diet and physical exercise, large variations in the glucose response to small changes in insulin doses, and high insulin sensitivity are characteristic of preschool children with diabetes. Hence, difficulties in achieving adequate metabolic control and stable glycaemia in preschool children are common. In addition, hypoglycaemic episodes tend to be frequent and severe in this age group. Problems identifying and treating hypoglycaemia present an additional challenge for the diabetes team and for the family caring for the young child with diabetes. Specific glucose targets are provided for this age group: premeal levels of 6-12 mmoll(-1)(110-220 mg dl(-1)) with bedtime levels above 8 mmoll(-1)(140 mg dl(-1)). It is important to note that children who suffer severe hypoglycaemic events at a young age show evidence of subtle cognitive deficits when tested during adolescence. The question of whether or not the years before pubertal onset contribute less towards the development of diabetes-related microvascular complications than do the years starting with the onset of puberty remains controversial. Twice-daily or multiple insulin injections, dietary adjustments and considerations, home blood-glucose monitoring, family education, support groups and 24-h hotline information facilities can help to achieve good metabolic control without severe hypoglycaemia in the preschool child. In general, good metabolic control without severe hypoglycaemia can be achieved using frequent counselling and a caring team approach.

Good growth despite very low levels of insulin-like growth factors

A 12.5-year-old girl presented with short stature. Insulin-like growth factor 1(IGF-I) and insulin- like growth factor binding protein (IGFBP-3) were below the 0.1 percentile. Growth hormone provocation tests disclosed normal responses to L-arginine and insulin-induced hypoglycaemia. A huge benign mesenteric cyst was discovered by abdominal ultrasound and completely removed. Subsequently, the girl showed a marked catch-up growth; however, IGF-I and IGFBP-3 remained below the 0.1 percentile.

CONCLUSION

These observations imply that growth may take place even with very low levels of insulin-like growth factors. The interpretation of low IGF-I and IGFBP-3 levels in short children still requires good clinical judgement and basic knowledge of their biological action.

Leptin as a metabolic regulator during fetal and neonatal life and in childhood and adolescence

Body weight is regulated by a feedback loop in which peripheral signals report nutritional information to an integratory center in the brain. The cloning of the ob gene is consistent with this concept and suggests that body fat content in adult rodents is regulated by a negative feedback loop centered in the hypothalamus/1-8/. In a recent report, two severely obese children with congenital leptin deficiency due to a homozygous frame-shift mutation involving the deletion of a single guanine nucleotide in codon 133 of the ob gene have been described. This discovery provides the first genetic evidence that leptin is an important regulator of energy balance in humans. However, it has become increasingly clear that apart from leptin's function in the central nervous system and in regulation of energy balance, leptin also acts in the periphery and might be important as a hormone modulating processes in regard to reproduction, glucose metabolism and insulin resistance, as well as growth and development of many tissues and organs either directly or indirectly. This report reviews some of the topics of leptin research that are of particular importance and relevance for pediatric and adolescent medicine and for pediatric endocrinology in particular.

Insulin-like growth factors (IGFs) and IGF binding proteins, serum acid-labile subunit and growth hormone binding protein in nephrotic children

We hypothesized that the increased glomerular permeability to serum proteins in the nephrotic syndrome might lead to alterations of the somatotropic hormone axis, thereby contributing to growth failure and catabolism in the nephrotic state. The insulin-like growth factors (IGF)-I and -II and the IGF binding proteins (IGFBP)-1, -2 and -3 were analyzed in serum and urine of 21 children with the nephrotic syndrome and normal glomerular filtration rate. Mean age-related serum IGF-I levels by RIA (-0.53 +/- 0.34 SD) were slightly, but significantly (P < 0.05) decreased compared with the reference population, whereas mean age-related serum IGF-II levels (0.68 +/- 0.21 SD) were slightly, but significantly (P < 0.005) increased. The urinary excretion rate of both peptides was enhanced fivefold. By RIA, mean age-related serum IGFBP-1 (2.05 +/- 0.19 SD) and, even more pronounced, IGFBP-2 (5.97 +/- 0.65 SD) were clearly elevated despite a 12-fold and 2-fold increase of the respective urinary excretion rate. There was a tight and specific correlation between age-related serum IGFBP-2 levels and the degree of the nephrotic syndrome, as estimated by serum albumin levels (r = -0.78, P < 0.0001). Serum immunoreactive IGFBP-3 levels were also elevated (1.79 +/- 0.33 SD) in nephrotic serum, due to an increase of low-molecular weight IGFBP-3 fragments. By FPLC analysis, there was a decrease of the 150 kDa IGFBP ternary complex in nephrotic serum, which in the presence of normal concentrations of the acid-labile subunit by RIA appears to be due to a reduction of intact IGFBP-3. Serum levels of the high-affinity GH binding protein that presumably reflects GH receptor status in tissues were normal. In summary, total serum IGFs in children with the nephrotic syndrome are normal, but the binding of IGFs to IGFBPs in the circulation is altered with a shift from the 150 kDa IGFBP complex to an excess of low molecular weight IGFBPs. Because increased unsaturated high-affinity IGFBPs in nephrotic serum have the ability to inhibit IGF action on target tissues by competing with the type 1 IGF receptor for IGF binding, this alteration is likely to contribute to growth failure and tissue catabolism in the nephrotic state.

Pertussis toxin sensitive G-proteins are not involved in the mitogenic signaling pathway of insulin-like growth factor-I in normal rat kidney epithelial (NRKE) cells

There is controversy as to whether or not a pertussis toxin sensitive G-protein is involved in the signaling pathway of insulin-like growth factor-I. We have used normal rat kidney epithelial (NRKE) cells to ask whether or not a pertussis toxin sensitive G-protein was involved in IGF-I stimulated DNA synthesis. NRKE cells express both IGF and IGF-II/M6P receptors and respond to IGF-I with increased thymidine incorporation into DNA. Under many circumstances incubation of cells/cell membranes with GTP analogues will inhibit binding of ligands that are linked to a G-protein-receptor pathway. However, when NRKE membrane preparations were incubated with 125I-IGF-I or 125I-IGF-II in the presence or absence of GTP gamma S, ATP and GTP, binding of the radioligands was not affected by the GTP-analogue. IGF-I and factors from serum of hypophysectomized rats (HRS) stimulated [3H]thymidine incorporation into DNA of NRKE cells. Under serum-free conditions in the presence of EGF (2 ng/ml) and PDGF (1 ng/ml) pertussis toxin over a wide range of doses had no effect upon IGF-I stimulated [3H]thymidine incorporation into DNA of NRKE cells. In addition, PT at a dose of 100 ng/ml had no effect on IGF-I(0.2-50 ng/ml) stimulated DNA synthesis of NRKE cells. However, PT at doses of 5, 50, 500, 5000 and 50,000 ng/ml was capable to ADP-ribosylate a 40 kDa protein in NRKE cell plasma membrane preparations corresponding to known PT-sensitive G-proteins. We conclude, that (1) PT-sensitive G-proteins and both IGF-I and IGF-II/M6P receptors are present in NRKE cell plasma membrane preparations, and most importantly, that (2) PT-sensitive G-proteins are not involved in the mitogenic signaling pathway of IGF-I in NRKE cells.

Insulin-like growth factor I receptor expression and function in fibroblasts from two patients with deletion of the distal long arm of chromosome 15

Most patients with deletion of the distal long arm of chromosome 15 have intrauterine growth retardation and postnatal growth deficiency in addition to developmental abnormalities. It has been proposed that the absence of one copy of the insulin-like growth factor I (IGF-I) receptor gene may play a role in the growth deficiency seen in this syndrome. To address this question we examined IGF-I receptor expression and function in fibroblasts from two patients with deletion of the distal long arm of chromosome 15 (15q26.1-->qter). Quantitative Southern blot analysis of the IGF-I receptor gene was performed on HindIII digests of fibroblast DNA. Radioactivity in the 1.7-kilobase receptor fragment in the two patients was 55% and 51% of the values in controls, consistent with the absence of one copy of the IGF-I receptor gene. IGF-I receptor messenger ribonucleic acid levels were quantitated by a solution hybridization/nuclease protection assay. Receptor messenger ribonucleic acid levels in the two patients were 45% and 52% of the values in controls. Northern blotting demonstrated normal size IGF-I receptor transcripts and affinity crosslinking of [125I]IGF-I to Triton X-100-solubilized fibroblasts demonstrated a normal size receptor in the patients. Analysis of placental membranes prepared from one patient revealed no difference in [125I]IGF-I binding. In the patients' fibroblasts, however, binding of [125I]long [R3]-IGF-I to the IGF-I receptor was significantly reduced, as assessed by the amount of radioactivity competed by the monoclonal antibody alpha IR-3 or insulin and Scatchard analysis of binding data. To assess IGF-I receptor function, stimulation of [alpha-1-14C]-methylaminoisobutyric acid transport and stimulation of [methyl-3H]thymidine incorporation into DNA by a full range of IGF-I concentrations was examined in patient and control fibroblasts. There was a significant decrease in the maximal response to IGF-I in both assays for one of the two patients when data were expressed as fold response over the basal value. However, there was no evidence for impairment of response to IGF-I in either patient's fibroblasts when data were expressed as net stimulation (maximal response minus basal). In conclusion, although IGF-I receptor expression was decreased in fibroblasts from two patients with deletion of the distal long arm of chromosome 15, we were unable to provide conclusive evidence for impairment of the biological response to IGF-I.