Valid measurements of total IGF concentrations in biological fluids. Recommendations from the 3rd International Symposium on Insulin-like Growth Factors.
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Body Fluids↗
Biomedical subjects
D R Clemmons
Publications and source records attributed to D R Clemmons.
Increased wound-breaking strength induced by insulin-like growth factor I in combination with insulin-like growth factor binding protein-1.
BACKGROUND: Polypeptide growth factors have been shown to accelerate wound repair in rodent animal model systems. METHODS: In this report, insulin-like growth factor I (IGF-I) and the combination of IGF-I plus insulin-like growth factor binding protein (IGFBP-1) were applied directly to linear incisions made through dorsal rat skin, and histologic analysis of breaking strength and hydroxyproline quantification were performed. RESULTS: IGF-I alone, in contrast to transforming growth factor-beta and platelet-derived growth factor, had no effect on wound-breaking strength. However, the combination of IGF-I plus IGFBP-1 significantly increased wound-breaking strength. Wound-breaking strength was increased 33% compared with wounds treated with IGF-I alone. IGFBP-1 alone had no effect. The ability to stimulate breaking strength was dependent on posttranslation modification of IGFBP-1. Phosphorylated IGFBP-1 was without effect, whereas the dephosphorylated protein was fully biologically active. This increase in wound-breaking strength induced by the combination of IGF-I and dephosphorylated IGFBP-1 was accompanied by an 67% increase in wound hydroxyproline content, whereas the combination of IGF-I and the phosphorylated form of IGFBP-1 had no effect. CONCLUSIONS: We concluded that IGF-I is a potent stimulant of incisional wound healing, but if administered without other growth factors, its effects can only be shown when it is combined with one of its specific binding proteins.
Animals↗
Insulin-like growth factor binding protein 1 stimulates cell migration and binds to the alpha 5 beta 1 integrin by means of its Arg-Gly-Asp sequence.
Insulin-like growth factor (IGF)-binding protein 1 (IGFBP-1) contains an Arg-Gly-Asp (RGD) integrin recognition sequence. In vitro mutagenesis was used to alter this RGD sequence to Trp-Gly-Asp (WGD). Migration of Chinese hamster ovary (CHO) cells expressing the wild-type protein was more than 3-fold greater in 48 hr compared with cells expressing the WGD mutant form of IGFBP-1. Similarly, wild-type IGFBP-1 added to the media of control CHO cells stimulated migration 2-fold compared with the WGD protein. A synthetic RGD-containing peptide, when added to the medium with wild-type IGFBP-1, blocked the effect of IGFBP-1 on cell migration. The addition of IGF-I to the culture medium had no effect on the migration of cells expressing IGFBP-1 or vector alone. Affinity chromatography of 125I-labeled CHO cell membrane proteins, using IGFBP-1 coupled to agarose, identified the alpha 5 beta 1 integrin (fibronectin receptor) as the only cell surface molecule capable of binding IGFBP-1 in an RGD-dependent manner. Furthermore, wild-type IGFBP-1, but not the WGD mutant form, could be coprecipitated from CHO cells with an antibody directed against the alpha 5 integrin subunit. These studies demonstrate that IGFBP-1 stimulates CHO cell migration and binds to the alpha 5 beta 1 integrin receptor, both by an RGD-dependent mechanism. The effect of IGFBP-1 on migration is independent of IGF-I and is probably mediated through the alpha 5 beta 1 integrin.
Amino Acid Sequence↗
A highly conserved insulin-like growth factor-binding protein (IGFBP-5) is expressed during myoblast differentiation.
Insulin-like growth factor-binding proteins (IGFBPs) are a family of secreted proteins that bind insulin-like growth factors I and II (IGFs I and II) and are capable of modulating IGF actions on target cells. We have shown previously that C2 myoblasts secrete a single approximately 29-kDa IGFBP during their terminal differentiation (Tollefsen, S. E., Lajara, R., McCusker, R. H., Clemmons, D. R., and Rotwein, P. (1989) J. Biol. Chem. 264, 13810-13817). In this study, we have purified the protein from C2 cell-conditioned media by conventional and IGF-affinity chromatography, cloned its cDNA by PCR-based and traditional library screening, and identified it as mouse IGFBP-5. The resultant 5561 nucleotide cDNA encodes a 252-amino acid mature protein (predicted M(r) approximately 28,400) that is 97% identical to rat and human IGFBP-5. In differentiating C2 myoblasts and in F3 azamyoblasts the > 6-kilobase IGFBP-5 mRNA accumulates concomitantly with induction of myogen mRNA, an early marker of muscle differentiation. Ligand blot analysis shows that IGFBP-5 protein is secreted within 12 h of the onset of differentiation in these cells and that it is the only IGFBP produced in several fusing skeletal muscle cell lines. In vivo, IGFBP-5 transcripts are expressed in a variety of mouse tissues including striated muscle, but, unlike other IGFBPs, it is barely detectable in liver. IGFBP-5 is more conserved than other IGFBPs in mammals; its conserved structure and sequence also extends to non-mammalian vertebrates. Hybridization of a mouse BP5 coding region probe to RNA from several chicken and Xenopus tissues demonstrated similarly sized transcripts in these species. A partial Xenopus cDNA is identical in 38/45 deduced amino acids to the mammalian proteins. Identification of an IGF-binding protein that is produced during myoblast differentiation provides a model system in which to study the potential modulatory role of IGFBPs in development.
Amino Acid Sequence↗
Role of insulin-like growth factor binding proteins in modifying IGF actions.
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Animals↗
Identification of the sites of phosphorylation in insulin-like growth factor binding protein-1. Regulation of its affinity by phosphorylation of serine 101.
Serine phosphorylation of insulin-like growth factor binding protein-1 (IGFBP-1) has been shown to alter its affinity for the insulin-like growth factors (IGF-I and IGF-II) and to modify its capacity to modulate cellular responses to the IGFs. Because of this, we determined the sites of serine phosphorylation. Purification of 32P-labeled IGFBP-1 was followed by digestion with trypsin and endoproteinase Glu-C and radiosequencing of labeled peptides. Three serines were found to be phosphorylated, with Ser101, Ser119, and Ser169 containing 70%, 5%, and 25% of the incorporated 32P, respectively. A mutated IGFBP-1, substituting alanine for serine at positions 98 and 101, was expressed in CHO cells. On nondenaturing gels, the wild type protein migrated as five isoforms (one non-phosphorylated and four phosphorylated). However, in the mutated protein, the most rapidly migrating band (a phosphorylated form) was not present. The cells containing the mutated cDNA incorporated 60% less 32P into immunoprecipitable IGFBP-1. The mutated protein had a 3-fold reduction in affinity for IGF-I compared to the wild type protein. We conclude that Ser101 represents the major site of phosphorylation containing 63% of the total 32P incorporated and that phosphorylation of Ser101 is important for maintenance of high affinity binding for this growth factor.
Alanine↗
Regulation of insulin-like growth factor-binding-protein-1, 2, 3, 4, 5, and 6: synthesis, secretion, and gene expression in estrogen receptor-negative human breast carcinoma cells.
Insulin-like growth-factors I and II (IGF-I, II) are potent mitogens for breast carcinoma proliferation. In extracellular fluids, most of the IGF-I and II is associated with specific IGF-binding proteins (IGFBPs). The role of these IGFBPs in IGF action is still not clear, but it has been demonstrated that these proteins may either enhance or inhibit IGF-mediated cellular effects. Synthesis and secretion of IGFBPs have been demonstrated in breast carcinoma cells. In this study, we examined retinoic acid (RA) and IGF-I modulation of IGFBP mRNA and IGFBP levels in two ER-negative human breast carcinoma cell lines. Treatment of MDA-MB-231 and MDA-MB-468 cells with RA increased the levels in conditioned media of a M(r) 42-46-kDa IGFBP, which was immunoprecipitated by an IGFBP-3 antibody. IGF-I also increased the accumulated levels of IGFBP-3 in the conditioned media of both cell lines. Both cell lines expressed high basal levels of IGFBP-3 mRNA; the addition of RA increased IGFBP-3 mRNA levels by 1.5-fold, whereas the addition of IGF-I had no effect on IGFBP-3 mRNA levels in either cell line. The difference in the magnitude of the RA enhancement of IGFBP-3 mRNA levels (1.5-fold) and RA stimulation of IGFBP-3 levels in conditioned media (3.5-4-fold) suggests that some of the effect of RA is at a posttranscriptional level. IGF-I increased the levels of IGFBP-2 and IGFBP-5 in conditioned media by greater than tenfold but had no effect on IGFBP-2 and IGFBP-5 mRNA levels, again suggesting the involvement of posttranscriptional controls. Pretreatment of MDA-MB-468 and MDA-MB-231 cells with IGF-I receptor antibody (alpha IR3) blocked the IGF-I effect on IGFBP-3 levels in the media in both cell lines and IGFBP-2 and IGFBP-5 secreted levels in MDA-MB-468 cell conditioned media. The addition of RA also blocked IGF-I stimulation of IGFBP-2 and IGFBP-5 levels. Cycloheximide treatment completely blocked the RA and/or IGF-I-mediated modulation of these binding proteins, suggesting that these agents enhance IGFBP-3, IGFBP-2, and IGFBP-5 synthesis and consequent secretion. MDA-MB-468 cells expressed IGFBP-5 mRNA, whereas both MDA-MB-231 and MDA-MB-468 expressed IGFBP-6 mRNA. RA enhanced IGFBP-6 gene expression by threefold in MDA-MB-231 cells, whereas IGF-1 had no effect on IGFBP-6 gene expression in either cell line.(ABSTRACT TRUNCATED AT 400 WORDS)
Blotting, Western↗
Vascular smooth muscle cells synthesize two forms of insulin-like growth factor binding proteins which are regulated differently by the insulin-like growth factors.
Vascular smooth muscle cells (SMC) synthesize insulin-like growth factor-I (IGF-I), which is a mitogen for this cell type in vitro. Since IGF binding proteins (IGFBP) modulate IGF bioactivity, we determined which IGFBPs were secreted by porcine SMC. Porcine SMC secreted 34,000 and 24,000 M(r) forms of IGFBPs which were identified as IGFBP-2 and IGFBP-4, respectively, by immunoblotting. Northern blot analysis showed single transcripts of 1.6 kb and 2.4 kb for IGFBP-2 and IGFBP-4, respectively. Secretion of IGFBP-2 was not regulated to a significant degree, with insulin, IGF-II, IGF-I, forskolin, and dibutyryl cyclic adenosine monophosphate (cAMP) inducing minimal changes in IGFBP-2 secretion of less than 30% by radioimmunoassay (RIA). Insulin increased (2.8 +/- 0.1-fold) the abundance of IGFBP-4 protein in conditioned media (CM) and increased IGFBP-4 mRNA levels. Growth factors for SMC such as platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), and transforming growth factor beta-1 (TGF beta-1) were without effect on either IGFBP-2 or -4. IGF-I treatment decreased the amount of IGFBP-4 present in CM, but a corresponding decrease in IGFBP-4 mRNA levels was not observed. In order to determine if IGFBP-4 could modulate IGF-I bioactivity, IGFBP-4 was added to pSMCs with and without IGF-I. IGF-I alone (20 ng/ml) induced a 1.6 to threefold increase in 3H-thymidine incorporation. Addition of IGFBP-4 (between 50 and 250 ng/ml) to cultures containing IGF-I (20 ng/ml) had no effect on DNA synthesis compared to that observed with IGF-I alone, while 500 ng/ml consistently caused a small decrease (15 +/- 5%; mean +/- SE). Immunoblotting of the CM obtained at the end of the 3H-thymidine assay showed a loss of intact IGFBP-4 in the cultures containing IGF-I. This corresponded with an increase in the abundance of a 16,000 M(r) immunoreactive fragment that did not bind IGF-I. Coincubation with insulin had no effect on the amount of IGFBP-4 that was converted to fragment, suggesting that the reaction was dependent upon IGF-I binding to IGFBP-4. In contrast, addition of IGFBP-4 (500 ng/ml) to human fibroblast cultures with IGF-I (20 ng/ml) almost completely inhibited the stimulatory effect of IGF-I on DNA synthesis and no increase in fragment was detected in the CM. In summary, SMC secrete IGFBP-2 and IGFBP-4, both of which have been shown to regulate IGF-mediated DNA synthesis.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
IGF binding proteins and their functions.
The insulin-like growth factor (IGF) binding proteins (IGFBPs) have several functions, including transporting the IGFs in the circulation, mediating IGF transport out of the vascular compartment, localizing the IGFs to specific cell types, and modulating both IGF binding to receptors and growth-promoting actions. The functions of IGFBPs appear to be altered by posttranslational modifications. IGFBP-3, -4, -5, and -6 have been shown to be glycosylated. Likewise all the IGFBPs have a complex disulfide bond structure that is required for maintenance of normal IGF binding. IGFBP-2, -3, -4, and -5 are proteolytically cleaved, and specific proteases have been characterized for IGFBP-3, -4, and -5. Interestingly, attachment of IGF-I or II to IGFBP-4 results in enhancement of proteolysis, whereas attachment of either growth factor to IGFBP-5 results in inhibition of proteolytic cleavage. Cleavage of IGFBP-3 results in the appearance of a 31 kDa fragment that is 50-fold reduced in its affinity for the IGF-I or IGF-II. In spite of the reduction in its affinity, this fragment is capable of potentiating the effect of IGF-I on cell growth responses; therefore, proteolysis may be a specific mechanism that alters IGFBP modulation of IGF actions. Other processes that result in a reduction in IGF binding protein affinity are associated with potentiation of cellular responses to IGF-I and -II. Specifically, the binding of IGFBP-3 to cell surfaces is associated with its ability to enhance IGF action and with a ten- to 12-fold reduction in its affinity for IGF-I and IGF-II.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Role of post translational modifications in modifying the biologic activity of insulin like growth factor binding proteins.
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Amino Acid Sequence↗
Extracellular matrix contains insulin-like growth factor binding protein-5: potentiation of the effects of IGF-I.
Insulin-like growth factor binding proteins (IGFBPs) have been shown to serve as carrier proteins for the insulin-like growth factors (IGFs) and to modulate their biologic effects. Since extracellular matrix (ECM) has been shown to be a reservoir for IGF-I and IGF-II, we examined the ECM of cultured human fetal fibroblasts and found that IGFBP-5 was incorporated intact into ECM, while mostly inert proteolytic fragments were found in the medium. In contrast, two other forms of IGFBP that are secreted by these cells were either present in ECM in minimal amounts (IGFBP-3) or not detected (IGFBP-4). Likewise, when purified IGFBPs were incubated with ECM, IGFBP-5 bound preferentially. IGFBP-5 was found to bind to types III and IV collagen, laminin, and fibronectin. Increasing salt concentrations inhibited the binding of IGFBP-5 to ECM and accelerated the release of IGFBP-5 from ECM, suggesting an ionic basis for this interaction. ECM-associated IGFBP-5 had a sevenfold decrease in affinity for IGF-I compared to IGFBP-5 in solution. Furthermore, when IGFBP-5 was present in cell culture substrata, it potentiated the growth stimulatory effects of IGF-I on fibroblasts. When IGFBP-5 was present only in the medium, it was degraded to a 22-kD fragment and had no effect on IGF-I-stimulated growth. We conclude that IGFBP-5 is present in fibroblast ECM, where it is protected from degradation and can potentiate the biologic actions of IGF-I. These findings provide a molecular explanation for the association of the IGF's with the extracellular matrix, and suggest that the binding of the IGF's to matrix, via IGFBP-5, may be important in mediating the cellular growth response to these growth factors.
Binding, Competitive↗
The insulin-like growth factors.
The recent availability of reagents to study the IGFs, their receptors, and binding proteins has led to an explosive growth in the study of IGF physiology. However, most studies to date have been descriptive, and studies delineating mechanisms of action are limited. It is apparent that most organ systems synthesize several components of the IGF system necessary for IGF to function in an autocrine or paracrine fashion and that regulation of this system occurs at the local level. However, the relative importance of locally produced IGF vs circulating IGF remains unclear. The mechanisms by which the IGFBPs modulate IGF activity are crucial to understanding this system, and identification of specific roles for each of these proteins will be required. Of critical importance is the identity of the intracellular signal transduction system by which the IGF receptor mediates the effects of the IGFs, and the delineation of mechanisms by which the IGFBPs interact with the receptor at the cellular level. It is also of interest to determine what role, if any, the IGF-II receptor plays in mediating the growth-promoting effects of the IGFs. The ubiquitous distribution of the IGFs, IGFBPs, and IGF receptors indicates that they may play a role in the regulation of coordinate growth among several tissues and cell types. Understanding the mechanisms by which these components interact to coordinate growth responses between different cell types should greatly enhance our understanding of normal growth and development.
Animals↗
Use of growth hormone and insulin-like growth factor I in catabolism that is induced by negative energy balance.
Both GH and insulin-like growth factor I (IGF-I) have been shown to promote anabolism in human volunteers that are made catabolic by caloric restriction. We have used caloric restriction as a model of controlled catabolism to test the efficacy of these agents in reversing negative nitrogen balance. Six normal volunteers underwent caloric restriction for 2-week intervals. This restriction induced negative nitrogen balance (e.g. -239 mmol/day). During the second week either IGF-I (16 micrograms/kg h) was administered by intravenous infusion for 16 h, or GH (0.05 mg/kg) was given subcutaneously daily. GH alone improved nitrogen balance by 180 mmol/day, and IGF-I improved it by 175 mmol. The two hormones had opposite effects on carbohydrate metabolism. Mean blood glucose rose approximately 26% with GH whereas it fell 37% with IGF-I and the subjects had frequent hypoglycemic episodes during the infusion. Minimal complications were observed during the 6 days of IGF-I infusion and consisted primarily of edema and jaw pain. It appeared that IGF-I was as efficacious as GH in reversing the negative nitrogen balance induced by caloric restriction and that hypoglycemia induced by IGF-I was the major limiting factor. In a second study 7 volunteers underwent the identical caloric restriction. In contrast to the first study one treatment group received the combination of GH plus IGF-I given in exactly the same doses as in the first study. A second group received IGF-I alone. The combination of GH/IGF-I was much more potent in improving nitrogen balance.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Enhancement of the anabolic effects of growth hormone and insulin-like growth factor I by use of both agents simultaneously.
The use of growth hormone (GH) as an anabolic agent is limited by its tendency to cause hyperglycemia and by its inability to reverse nitrogen wasting in some catabolic conditions. In a previous study comparing the anabolic actions of GH and IGF-I (insulin-like growth factor I), we observed that intravenous infusions of IGF-I (12 micrograms/kg ideal body wt [IBW]/h) attenuated nitrogen wasting to a degree comparable to GH given subcutaneously at a standard dose of 0.05 mg/kg IBW per d. IGF-I, however, had a tendency to cause hypoglycemia. In the present study, we treated seven calorically restricted (20 kcal/kg IBW per d) normal volunteers with a combination of GH and IGF-I (using the same doses as in the previous study) and compared its effects on anabolism and carbohydrate metabolism to treatment with IGF-I alone. The GH/IGF-I combination caused significantly greater nitrogen retention (262 +/- 43 mmol/d, mean +/- SD) compared to IGF-I alone (108 +/- 29 mmol/d; P < 0.001). GH/IGF-I treatment resulted in substantial urinary potassium conservation (34 +/- 3 mmol/d, mean +/- SE; P < 0.001), suggesting that most protein accretion occurred in muscle and connective tissue. GH attenuated the hypoglycemia induced by IGF-I as indicated by fewer hypoglycemic episodes and higher capillary blood glucose concentrations on GH/IGF-I (4.3 +/- 1.0 mmol/liter, mean +/- SD) compared to IGF-I alone (3.8 +/- 0.8 mmol/liter; P < 0.001). IGF-I caused a marked decline in C-peptide (1,165 +/- 341 pmol/liter; mean +/- SD) compared to the GH/IGF-I combination (2,280 +/- 612 pmol/liter; P < 0.001), suggesting maintenance of normal carbohydrate metabolism with the latter regimen. GH/IGF-I produced higher serum IGF-I concentrations (1,854 +/- 708 micrograms/liter; mean +/- SD) compared to IGF-I only treatment (1,092 +/- 503 micrograms/liter; P < 0.001). This observation was associated with increased concentrations of IGF binding protein 3 and acid-labile subunit on GH/IGF-I treatment and decreased concentrations on IGF-I alone. These results suggest that the combination of GH and IGF-I treatment is substantially more anabolic than either IGF-I or GH alone. GH/IGF-I treatment also attenuates the hypoglycemia caused by IGF-I alone. GH/IGF-I treatment could have important applications in diseases associated with catabolism.
Adult↗
Synthesis and regulation of insulin-like growth factor binding protein-5 in FRTL-5 cells.
FRTL-5 cells, a diploid nontransformed line of rat thyroid follicular cells, exhibit a marked mitogenic response to insulin-like growth factors (IGFs) when they are exposed to TSH. Because IGF binding proteins (IGFBPs) are important modulators of IGF actions, we investigated the capacity of FRTL-5 cells to synthesize IGFBPs. We found that FRTL-5 cell conditioned media contained a single band of approximately 31 kilodaltons on ligand blot analysis. This band represents IGFBP-5 because: 1) it can be immunostained with a specific antibody raised against human IGFBP-5; 2) by Northern analysis, total RNA from FRTL-5 cells contains a major 6-kilobase transcript when hybridized with a cDNA for rat IGFBP-5; and 3) no transcripts were observed when Northern blots of FRTL-5 cells were hybridized with complementary DNAs for rat IGFBP-1, -2, -3, -4 or -6. Conditioned media IGFBP-5 increased in response to IGF-I, IGF-II, and insulin in a dose-dependent fashion, compared with unstimulated FRTL-5 cells. At maximally effective concentrations IGF-I was 3.5- and 6-fold more potent than IGF-II and insulin, respectively. The addition of a monoclonal antibody (Sm 1.2) to IGF-I completely inhibited IGF-I stimulation of the IGFBP-5 6-kilobase transcript and the appearance of IGFBP-5 in FRTL-5 conditioned media. Stimulation of IGFBP-5 synthesis by the IGFs and insulin appeared to be regulated at the messenger RNA (mRNA) level, because each stimulated similar increases in both IGFBP-5 mRNA and media protein at maximally effective concentrations. TSH, on the other hand, inhibited basal levels of IGFBP-5 mRNA and attenuated the increase in IGFBP-5 mRNA stimulated by IGF-I. FRTL-5 cells provide a relatively uncomplicated model to study the regulation and action of IGFBP-5 and the mechanisms by which IGFs interact with this binding protein.
Animals↗
Elevated levels of insulin-like growth factor-binding protein-2 in the serum of prostate cancer patients.
We have previously documented the presence of specific insulin-like growth factor (IGF)-binding protein (IGFBPs) in seminal plasma and prostate epithelial cell-conditioned medium IGFBP-2 is the prevalent IGFBP in both fluids. To assess whether patients with prostate carcinoma have alterations in serum IGFP levels related to the production of IGFBPs by their tumors, we performed Western ligand blots (WLB) and IGFBP-2 RIA on serum samples from 32 patients with prostate carcinoma of various degrees of clinical severity and compared them to results in 16 healthy age-matched controls. We have also measured serum IGF-I and -II by RIA. The mean level of IGFBP-2 in the prostate cancer patients was 170% of control levels by WLB analysis and 195% of control levels by RIA (P < 0.01). The degree of elevation of IGFBP-2 was related to the stage of the tumor and the levels of the serum tumor marker, prostate-specific antigen. Serum IGFBP-3 levels determined by WLB and serum IGF-I and IGF-II levels measured by RIA after acid chromatography were not different among the subjects with cancer and the normal controls. We conclude that IGFBP-2, which is the main IGFBP produced by prostate epithelial cells, is elevated in the serum of patients with prostate carcinoma, and that the degree of this elevation is related to serum prostate-specific antigen levels and the stage of the tumor. We speculate that prostate-derived IGFBPs may be secreted by prostate tumors and could e of value in understanding the pathophysiology of prostatic tumor growth as well as provide potential diagnostic markers.
Blotting, Western↗
Use of insulin-like growth factor-binding protein-2 (IGFBP-2), IGFBP-3, and IGF-I for assessing growth hormone status in short children.
Insulin-like growth factor-binding protein-2 and -3 (IGFBP-2 and -3) are members of a family of proteins that are present in extracellular fluids and bind IGF-I and -II. IGFBP-2 is regulated differently from IGF-I and IGFBP-3, because its serum concentrations are elevated in some adults with GH deficiency (GHD), whereas IGF-I and IGFBP-3 concentrations are usually decreased. The purposes of this study were to define the normal range of IGFBP-2 concentrations in children, to determine its efficacy in the diagnosis of GHD, and to compare the diagnostic value of measurements of the serum GH response to provocative testing with results of measurements of IGFBP-2, IGFBP-3, and IGF-I. Mean serum IGFBP-2 concentrations ranged from 263 +/- 101 ng/mL (mean +/- SD) during infancy to 136 +/- 38 ng/mL in normal 15- to 18-yr-olds (P < 0.001), whereas IGFBP-3 increased from 1211 +/- 384 to 2781 +/- 382 ng/mL in the same age groups. Thirty-nine of 49 children with GHD and low IGF-I values (serum GH response, < or = 1 ng/mL after 2 provocative tests) had serum IGFBP-2 concentrations that were greater than 2 SD above their corresponding age-adjusted means. In contrast all 49 of these children had IGFBP-3 values that were below normal for age. Because serum IGFBP-2 concentrations are regulated by GH directly and not through IGF-I, the IGFBP-2 to IGF-I ratio was used to determine whether it improved diagnostic accuracy. Fifty of 57 GH-deficient children had IGFBP-2/IGF-I ratios that were greater than 2 SD above the mean. This included 48 of 49 children with low IGF-I and 2 of 8 children with normal IGF-I. Fifty-three of the 57 children with GHD had decreased IGFBP-3 values. Among 23 children with idiopathic short stature (ISS) who had normal responses to GH stimulation testing (serum GH, > 10 ng/mL), 7 had low IGF-I values. Of the 7, all had an increased IGFBP-2/IGF-I ratio and a low IGFBP-3 level. Of the remaining 16 children with normal IGF-I, 13 had a normal IGFBP-2/IGF-I ratio and normal IGFBP-3 values. Three had low IGFBP-3 and an increased IGFBP-2/IGF-I ratio. In 76% of the 80 short-statured patients studied, there was concordance among serum GH responses to provocative tests, IGF-I, IGFBP-2/IGF-I ratio, and IGFBP-3.(ABSTRACT TRUNCATED AT 400 WORDS)
Adolescent↗
The effect of dietary protein supplementation on insulin-like growth factors (IGFs) and IGF-binding proteins in children with shigellosis.
Nutrient deficiency causes growth failure and decreases serum insulin-like growth factor-I (IGF-I) concentrations. Because IGFBPs modulate the concentrations and availability of IGFs in serum, IGF-binding proteins (IGFBPs) were measured along with IGF-I and IGF-II before and after 21 days of refeeding in 22 undernourished Bangladeshi children (2-4 yr of age) with shigellosis. The effects of a 150 Cal/kg.day diet with a normal protein (6%; n = 10) or high protein (15%; n = 12) content were studied. The results were compared with those of 25 age-matched healthy American children (controls). Body weight gain was better in patients receiving the high protein diet than in those receiving the normal protein diet. In both groups, initial IGF-I (32 +/- 6 and 24 +/- 7 ng/mL; mean +/- SD) and IGF-II (177 +/- 15, 174 +/- 45 ng/mL) concentrations were low compared to controls (100 +/- 12 and 542 +/- 29 ng/mL, respectively; P < 0.007). After refeeding, IGF-I increased to 160 +/- 26 ng/mL on the normal protein diet and to 322 +/- 41 ng/mL on the high protein diet, exceeding values in controls (P < 0.007). IGF-II increased more than 2-fold on each diet (P < 0.007), reaching control values. IGFBP-2 concentrations before refeeding were twice those in controls (750 +/- 200 vs. 317 +/- 33 ng/mL; P < 0.007) and normalized after refeeding in the high protein group (288 +/- 32 ng/mL; P = NS), but remained elevated in the normal protein group (526 +/- 77 ng/mL; P < 0.007). IGFBP-3 levels before refeeding were low and returned to normal on each diet. IGFBP-3 proteolytic activity in serum was initially increased and declined on the high protein diet. In conclusion, protein content in the refeeding diet differentially affects IGFs and IGFBPs in young undernourished children with infection. IGF-I and IGFBP-2 seem to be particularly sensitive to dietary protein alterations. We speculate that an increase in IGF-I concentrations, normalization of IGFBP levels, and a decrease in IGFBP-3 proteolytic activity in serum may all be involved in the improved recovery and catch-up growth observed with the high protein diet.
Carrier Proteins↗