Wasting in the acquired immune deficiency syndrome is associated with multiple defects in the serum insulin-like growth factor system

OBJECTIVE

The aim of this investigation was to characterize the GH-IGF axis of patients with AIDS associated wasting. A special emphasis was placed on determining whether IGF binding proteins (IGFBPs) of patients who have lost more than 10% of their ideal body mass are structurally different from the IGFBPs of patients with no weight loss.

DESIGN AND PATIENTS

A cross-sectional study of 11 AIDS patients was performed to determine whether the IGF system is abnormal in AIDS patients with wasting. Seven additional AIDS patients were followed longitudinally to determine whether AIDS patients experience long-term changes to their IGF system.

MEASUREMENTS

Serum levels of GH and IGF-I were measured by radioimmunoassay, IGF-II was measured by radioreceptor assay, and IGFBP-1 was measured by an enzyme linked immunoassay. IGFBP-3 and IGFBP-3 protease activity were measured by ligand blotting and a BP-3 protease assay, respectively. IGFBP-3 ternary complex formation and IGFBP-1 phosphovariants were analysed by non-denaturing PAGE.

RESULTS

AIDS patients who had lost more than 10% of their ideal body mass demonstrated a 55% reduction in serum IGF-I (81 vs 179 micrograms/l) and a 70% reduction in IGF-II (226 vs 776 micrograms/l), compared to healthy HIV negative subjects. IGF-I levels were depressed, in some patients, despite high serum levels of GH. AIDS patients who had lost more than 10% of their ideal body mass had low levels of IGFBP-3 and a reduced ability to form the IGFBP-3 ternary complex. The IGFBP-3 ternary complex could be restored only upon addition of pure IGFBP-3 and acid labile subunit to serum. Serum IGFBP-1 was increased more than threefold compared to control subjects (90 vs 24 micrograms/l). IGFBP-1 was present as a free phosphoprotein in AIDS patients with low levels of IGF-I and in a bound form when serum IGF-I levels were normal. Changes in the GH-IGF axis were sustained for up to 25 months in AIDS patients with wasting.

CONCLUSIONS

AIDS wasting is associated with a GH resistant state that results in low levels of serum IGF-I, IGF-II and IGFBP-3, elevated levels of phosphorylated IGFBP-1, and a reduced ability to form the IGFBP-3 ternary complex.

Inhibition of IGF II-induced redistribution of mannose 6-phosphate receptors by the phosphatidylinositol 3-kinase inhibitor, wortmannin

The effects of wortmannin, a selective inhibitor of phosphatidylinositol (PI)3-kinase on insulin-like growth factor II (IGF II)-induced redistribution of the 300 kDa mannose 6-phosphate/IGF II receptor (MPR 300) has been studied in human hepatoma HepG2 cells. IGF II increased the expression of MPR 300 at the cell surface threefold that was completely abolished by wortmannin at 100-300 nM. Higher concentrations of wortmannin also reduced the basal MPR 300-dependent uptake of ligands to 68% of controls. Neither the transport of two lysosomal enzymes nor the secretion of the IGF binding protein-1 were affected by wortmannin. These results show that activation of PI3-kinase plays a critical role in the IGF II-stimulated redistribution of MPR 300 initiated rather by IGF II binding to tyrosine kinase receptors than to the MPR 300.

Hyperglycemia and impaired glucose tolerance in IGF binding protein-1 transgenic mice

The insulin-like growth factors (IGFs) are present in the serum in association with high-affinity binding proteins (IGFBPs), which limit the hypoglycemic insulin-like actions of these growth factors. By utilizing the mouse phosphoglycerate kinase promoter to drive a rat genomic fragment, we developed three transgenic mouse strains that overexpressed IGFBP-1. Homozygous offspring demonstrated fasting hyperglycemia. The blood glucose values were 4.97 +/- 0.37, 4.57 +/- 0.33, and 5.58 +/- 0.50 mM for transgenic mice compared with 3.33 +/- 0.19 mM (mean +/- SE, P < 0.05) for the wild-type mice. The transgenic mice had more marked hyperglycemia after an intraperitoneal glucose challenge. The fasting serum insulin levels were significantly elevated in the transgenic mice; however, the insulin-to-glucose ratio was only modestly elevated in the fasting state and fell after a glucose challenge. Islet size and number were significantly increased; however, pancreatic insulin content was reduced (P < 0.05) compared with that of wild-type mice. The glucose response to subcutaneous insulin was similar in transgenic and wild-type mice. These data demonstrate that constitutive overexpression of IGFBP-1 results in impaired glucose tolerance with normal insulin sensitivity.

Endometrial response to hormone replacement therapy as assessed by expression of insulin-like growth factor-binding protein-1 in the endometrium

OBJECTIVE

To assess endometrial response to parenteral levonorgestrel in hormone replacement therapy by means of morphological criteria and immunohistochemical staining of insulin-like growth factor-binding protein-1 (IGFBP-1).

DESIGN

Endometrial samples were collected from 35 postmenopausal women after 12 to 22 months of continuous combined estrogen-progestin therapy. All subjects were treated with parenteral progestin. A group of 8 women was treated with a subdermal levonorgestrel-releasing implant, and 27 women had a levonorgestrel-releasing intrauterine device (IUD). Sections of formalin-fixed paraffin-embedded biopsies were used for immunohistochemistry and after hematoxylin-eosin staining for routine histologic examination.

RESULTS

Atrophic epithelium with pronounced decidual reaction in the stroma was detected by histologic examination in all endometrial samples obtained from 27 women treated with the levonorgestrel-releasing IUD. In contrast, the endometrium was proliferative in seven of eight (87.5 percent) biopsies obtained from women treated with the levonorgestrel-releasing implant. Immunoreactive IGFBP-1 was detected in decidualized stromal cells in all endometrial samples obtained during intrauterine levonorgestrel therapy, whereas only one of eight samples obtained from women treated with subdermal levonorgestrel exhibited weak staining for IGFBP-1.

CONCLUSIONS

Our data show that both the morphological and biochemical response of post- menopausal endometrium to parenteral levonorgestrel was strikingly different, depending on the route of progestin administration, and that the decidual reaction and epithelial atrophy induced by intrauterine levonorgestrel were associated with expression IGFBP-1 in decidualized stromal cells.

Serum and follicular fluid levels of insulin-like growth factor I (IGF-I), IGF-II, and IGF-binding protein-1 and -3 during the normal menstrual cycle

Insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) have important regulatory functions in ovarian follicular development. Although most studies have investigated the IGF system in ovarian cells in vitro, investigation of the IGF system in the peripheral circulation and in follicles of varying sizes throughout the menstrual cycle in large numbers of subjects has been lacking. In the current study we performed daily IGF-I, IGF-II, IGFBP-1, and IGFBP-3 measurements in 9 healthy regularly cycling volunteers throughout the menstrual cycle. In addition, we investigated IGF-I, IGF-II, IGFBP-1, and IGFBP-3 levels in 13 samples of androgen-dominant follicular fluid [FFa androstenedione to estradiol (AD:E2) ratio, > 4] and 19 samples of estrogen-dominant follicular fluid (FFe; AD:E2 ratio, 4) obtained from 21 regularly cycling subjects and in 18 samples of fluid from luteinizing follicles obtained from patients undergoing in vitro fertilization (IVF) treatment (FFivf). IGF-I, IGF-II, IGFBP-1, and IGFBP-3 were measured using two-site immunoradiometric assays. No significant day to day differences were observed in IGF-I, IGF-II, IGFBP-1, and IGFBP-3 levels across the menstrual cycle. Median IGF-II levels in FFe (630 ng/mL; range, 212-1000) were significantly higher compared to those in FFa (474 ng/mL; range, 272-603; P = 0.002). Median IGFBP-3 levels in FFe (2955 ng/mL; range, 388-3448) were also significantly higher than those in FFa (2352 ng/mL; range, 756-2604; P = 0.003). Median IGF-I (192 ng/mL; range, 29-256) and IGFBP-1 (12 ng/mL; range, 2-281) levels in FFe were not significantly different from those in FFa [149 (range, 22-232) and 21 (range, 5-32) ng/mL, respectively). In contrast, significantly lower IGFBP-1 levels were found in FFe compared to FFivf (79 ng/mL; range, 57-234; P = 0.002), whereas there was no significant difference between FFe and FFivfe IGF-I, IGF-II, or IGFBP-3 levels, respectively. IGF-II levels were correlated with follicle diameter (r = 0.52; P = 0.002), cycle day (r = 0.47; P = 0.0065), E2 levels (r = 0.53; P = 0.003), AD:E2 ratio (r = -0.58; P = 0.001), and P concentrations (r = 0.60; P = 0.001) in all follicles, whereas no such correlations were found with IGF-I. In conclusion, as circulating levels of IGF-I, IGF-II, IGFBP-1, and IGFBP-3 are not menstrual cycle dependent, it is unlikely that these growth factors and these binding proteins play an endocrine role in cyclic ovarian follicle development, although both cycle-dependent delivery to the ovary and modification of their actions locally within the ovary cannot be excluded. With regard to FF1 the findings that IGF-II levels in FF1 are elevated compared to those in FFa and correlate with follicular functional status support a role for IGF-II during development of the dominant follicle. In addition, as IGFBP-3 in estrogen-dominant follicles mirrors the rise of IGF-II, this IGFBP may be a primary regulator of IGF-II action within the estrogen-dominant follicle. Finally, the finding of elevated levels of IGFBP-1 in luteinizing (IVF) follicles suggests an important role for this peptide in corpus luteum regulation.

Retinoic acid suppresses in-vitro decidualization of human endometrial stromal cells

All-trans retinoic acid (RA) has potent effects on cell differentiation and gene expression. Previous studies have demonstrated that human endometrial stromal cells express mRNA for retinoic acid receptors (RARs) and cellular RA-binding protein-II (CRABP-II). We examined whether RA regulates stromal cell differentiation (decidualization), a critical process in preparation of the uterus for blastocyst implantation. Decidualization was induced by incubating cultured stromal cells with medroxyprogesterone acetate (MPA) and oestradiol. Decidualization was defined by the induction of prolactin, insulin-like growth factor binding protein-1 (IGFBP-1), appearance of a differentiated phenotype and changes in fibronectin expression. RA treatment significantly (P < 0.05) suppressed prolactin and IGFBP-1 production associated with stromal cells decidualization. The formation of differentiated cells was inhibited by RA, and consistent with maintenance of the undifferentiated phenotype, fibronectin mRNA content was approximately 3.5-times greater than in the absence of RA. Upon induction of decidualization, the expression of mRNA for the major RA receptor sub-types (RAR-alpha, -beta and -gamma) was maintained while the relative amounts of CRABP-II mRNA progressively decreased with differentiation. With RA treatment, RAR-alpha and RAR-gamma mRNA concentrations were approximately 70 and 25% respectively of those in cells decidualized in the absence of RA. The effects of RA appear to be partially mediated by inhibition of cAMP action. RA suppressed intracellular cAMP concentrations induced by MPA and oestradiol to approximately 35% of those in cells without RA. Addition of 50 microM dibutyryl cAMP to stromal cells treated with MPA and oestradiol only partially reversed the suppression of decidualization and prolactin release by RA. In summary, we have demonstrated that in-vitro decidualization of human endometrial stromal cells induced by MPA and oestradiol treatment is suppressed by RA.

Comparison of production of choriogonadotropin inhibitory protein, prolactin and insulin-like growth factor binding protein-1 by human decidua in vitro

We have previously demonstrated that human decidua produces a protein (decidual choriogonadotropin inhibitory protein, DCIP) that inhibits human chorionic gonadotropin (hCG) secretion from primary trophoblasts and JEG-3 choriocarcinoma cells. The present study was undertaken to examine the relationship of DCIP production to that of cell protein, prolactin (PRL) and insulin-like growth factor binding protein-1 (IGFBP-1). Term decidual cells, isolated from placental membranes by enzyme digestion and density gradient centrifugation, were incubated for 12 days in serum-free CMRL-1066 medium which was changed daily. At the end of each experiment the DCIP in the decidual culture medium was measured by bioassay: the percentage reduction, from control, of hCG production by JEG-3 cells exposed to 30% DCIP-containing decidual culture medium. Prolactin, IGFBP-1 and hCG were measured by radioimmunoassay. The DCIP activity was maximal during the first 3 days in culture. The bioactivity of decidual culture medium collected after the 5th day of culture gradually decreased and medium obtained from the final day of culture actually stimulated hCG secretion in the bioassay. Decidual cell protein gradually declined from 100% on day 1 to 56% on the last day of culture. The concentrations of protein, PRL and IGFBP-1 in the decidual culture medium gradually decreased during the first 4-6 days, followed by a rise. In contrast, glucose increased with time in culture. Production of PRL, IGFBP-1 and decidual culture medium protein exhibited a significant quadratic effect over the 12 days in culture. There was a negative relationship between decidual cell protein and glucose (r = -0.95) and a positive correlation between cell protein and protein in the decidual culture medium (r = 0.58). The DCIP activity was related to cell protein (r = 0.39), protein concentration in decidual culture medium (r = 0.36), and inversely related to the glucose level (r = -0.41). There was no relationship between DCIP activity and PRL or IGFBP-1. These results indicate that maximal DCIP production occurs during the first several days in short-term culture of decidual cells and is related to decidual-cell viability. As decidual-cell viability decreases, there is less glucose consumption in the decidual culture medium and the higher glucose levels may be responsible for the stimulatory effect of medium collected at the end of the study on JEG-3 hCG secretion.

Characterization of insulin-like growth factor binding protein-1 kinases from human hepatoma cells

The phosphorylation of insulin-like growth factor binding protein-I (IGFBP-1) alters its binding affinity for insulin-like growth factor I (IGF-I) and thus regulates the bioavailability of IGF-I for binding to the IGF-I receptor. The kinase(s) responsible for the phosphorylation of IGFBP-1 has not been identified. This study was designed to characterize the IGFBP-1 kinase activity in HepG2 human hepatoma cells, a cell line that secretes IGFBP-1 primarily as phosphorylated isoforms. IGFBP-1 kinase activity was partially purified from detergent extracts of the cells by phosphocellulose chromatography and gel filtration. Two kinases of approximate M(r) 150,000 (peak I kinase) and M(r) 50,000 (peak II kinase) were identified. Each kinase phosphorylated IGFBP-1 at serine residues that were phosphorylated by intact HepG2 cells. The kinases were distinct based on their differential sensitivity to inhibition by heparin (IC50 = 2.5 and 16.5 micrograms/ml, peak I and II kinase, respectively) and inhibition by the isoquinoline sulfonamide CKI-7 (IC50 = 50 microM and 100 microM, peak I and II kinase, respectively). In addition, a tenfold molar excess of nonradioactive GTP relative to [gamma-32P]ATP lowered the incorporation of 32P into IGFBP-1 by 80% when the reaction was catalyzed by the peak I kinase, whereas GTP had no effect on the reaction catalyzed by the peak II kinase. In the presence of polylysine, IGFBP-1 was radiolabeled by the partially purified kinase activity when [gamma-32P]GTP served as the phosphate donor indicating the presence of casein kinase II activity. Furthermore, IGFBP-1 was phosphorylated by purified casein kinase I and casein kinase II at sites phosphorylated by the peak I and II kinases. Our data suggest that at least two kinases could be responsible for the phosphorylation of IGFBP-1 in intact HepG2 cells and that the kinases are related to the casein kinase family of protein kinases.

Insulin, insulin-like growth factor-binding protein-1, and sex hormone-binding globulin in patients with Turner's syndrome: course over age in untreated patients and effect of therapy with growth hormone alone and in combination with oxandrolone

We have studied the course over age of fasting insulin, sex hormone-binding globulin (SHBG), and insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1) in untreated children with Turner's syndrome (TS) and measured the course of these parameters during therapy with GH alone and in combination with oxandrolone. Forty patients with TS, aged 3.7-16.4 yr, were investigated before any therapy. Fasting insulin levels increased significantly with chronological age, whereas SHBG and IGFBP-1 decreased with chronological age, and serum concentrations of these parameters were in the normal range. SHBG and IGFBP-1 were not coregulated by insulin in TS as previously reported under physiological conditions; IGFBP-1 was inversely correlated with insulin, but SHBG was not, and neither parameter was correlated with the other. Twenty-eight patients were further investigated 3, 6, 9, and 12 months after the start of GH monotherapy (12-18 IU/m2-week) and 3, 6, 9, and 12 months after the addition of oxandrolone (0.0625 mg/kg.day; n = 16). There was a significant increase in insulin levels during GH monotherapy and a further increase during combination therapy, with peak levels 3 months after the start of GH and combination therapy, respectively. Both SHBG and IGFBP-1 levels decreased significantly during GH monotherapy, with a further dramatic decrease after the addition of oxandrolone. Levels of free testosterone were unaffected by both treatment regimens. IGFBP-1 was inversely correlated with insulin concentrations at all time points after the start of therapy. SHBG was inversely correlated with IGF-I concentrations, but showed no relation to insulin concentrations during GH monotherapy. In conclusion, there were no abnormalities in serum concentrations of insulin, SHBG, and IGFBP-1 in untreated patients that could help to explain the retarded growth in patients with TS. All effects of combined GH and oxandrolone therapy on endocrine parameters such as insulin, SHBG, IGFBP-1 and IGF-I mimic the endocrine pattern normally observed during the pubertal growth spurt. Our data confirm the importance of insulin in the regulation of IGFBP-1, but do not point to a coregulation of IGFBP-1 and SHBG by insulin in patients with TS.

IGFBP-1 in the placenta, membranes and fetal circulation: levels at term and preterm delivery

Samples of maternal blood, amniotic fluid, placenta, fetal membranes and umbilical venous blood were collected from 59 women at vaginal delivery (32-41 weeks gestation) and 15 women at delivery by Caesarean section (37-41 weeks gestation). Umbilical vein levels of IGFBP-1 were significantly lower in deliveries prior to the onset of labour (elective Caesarean section) than those during normal vaginal delivery. These levels were, in turn, significantly lower than those delivered by emergency Caesarean section. This difference was not seen in any of the other tissues examined. Concentrations of IGFBP-1 were lower in placenta and membrane extracts from preterm deliveries than in term deliveries. This difference was not observed in maternal or fetal serum or in amniotic fluid. This study confirms that the fetal membranes are a major source of IGFBP-1 and that fetal circulating levels are raised where there is evidence of fetal hypoxia. The absence of a comparable rise in levels in placenta, membranes or amniotic fluid suggests that the origin of this increase is from fetal tissue.

Insulin-like growth factors in breast cancer

Insulin-like growth factor (IGF)-I is one of the most potent mitogens to many breast cancer cell lines in vitro. Effective growth inhibition in vitro may be achieved by antibodies to the type I IGF receptor (IGF-IR) or by using antisense strategies. Most human breast cancers express IGF-IR in vivo. Thus, different therapeutic strategies aimed at inhibiting ligand stimulation of the IGF-IR may be an attractive treatment option against breast cancer. Several drugs commonly used in breast cancer influence the IGF system both in vitro and in vivo. While antioestrogens such as tamoxifen and droloxifene reduce the expression of IGF-IR in vitro and suppress plasma levels of IGF-I but elevate IGF-binding protein-1 in vivo, megestrol acetate may reduce the delivery of IGFs to the tissues by inhibition of IGFBP-3 protease activity.

Macrophages synthesize and secrete a 25-kilodalton protein that binds insulin-like growth factor-I

Primary (thymus) and secondary (spleen) murine lymphoid tissues express a 25-kDa protein that binds IGF-I. To determine the cellular source of this insulin-like growth factor binding protein (IGFBP), 11 murine or human cell lines representing T, B, and myeloid cells at various stages of differentiation were characterized by IGF-I affinity cross-linkage and Western ligand blotting. Mature myeloid cells, but not T or B cells, secrete a 25-kDa protein that is capable of binding IGF-I. CSF-1-derived bone marrow macrophages also synthesize this 25-kDa IGFBP. Thymic macrophages, which were estimated to secrete 2 ng of binding protein/10(6) cells-h, were used in conjunction with [125I] IGF-I affinity cross-linking to develop a protein binding immunomobility-shift assay to identify which IGFBP is produced by these cells. An anti-IGFBP-4Ab, but not an anti-IGFBP-2 Ab or normal rabbit serum, shifted the [125I] IGF-IGFBP complex to a higher m.w. position, indicating that the single 25-kDa IGFBP is IGFBP-4. Northern blotting confirmed that transcripts for IGFBP-4 as well as IGF-I are expressed in thymic macrophages. A putative 278-bp IGFBP-4 cDNA fragment (residues 341-618) of rat) that contains two unique cysteine residues found only in IGFBP-4 was cloned and sequenced from thymic macrophages. These clones differed from the rat sequence at only six residues (97% homology), and the deduced amino acid sequence from the murine cDNA was identical with that of the rat sequence. Subsequent studies revealed that IGF-I stimulates DNA synthesis in thymic macrophages. However, two different IGF-I analogues differing in the amino-terminus that bind equally well to the IGF-I receptor but poorly to IGFBPs are as effective as IGF-I at 100-fold lower concentrations. These data demonstrate that murine macrophages are a source of a single 25-kDa secreted protein that binds IGF-, that the molecular identity of this protein is IGFBP-4, and that this binding protein may antagonize the extracellular effects of IGF-I.

Hormonal regulation of circulating insulin-like growth factor-binding protein-1 phosphorylation status

Insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1) normally circulates as a single, highly phosphorylated species. However, IGFBP-1 phosphorylation status can be altered, such as in pregnancy where non- and lesser phosphorylated isoforms are also present. We have examined how hormonal regulators of circulating IGFBP-1 influence its phosphorylation status and, hence, its ability to modulate IGF activity. In response to insulin-induced hypoglycemia (0.2 U/kg, iv), an increase in the highly phosphorylated isoform was observed after 5 h [16 (range, 11.5-35.5) to 77 (range, 63-250) microgram/L; 4.8-fold increase; P = 0.009], but no non- or lesser phosphorylated variants could be detected. Glucagon (1 mg, sc), increased IGFBP-1 from 27 (range, 13-36.5) to 112 (range, 100.5-129) micrograms/L (4.1-fold increase; P = 0.009) after 90 min despite preceding insulin concentrations of more than 500 pmol/L, but again the IGFBP-1 remained in the highly phosphorylated form. Regulation of IGFBP-1 phosphorylation by sex steroids was studied by comparing women receiving a combined oral contraceptive with women on no medication. Although plasma IGFBP-1 levels were significantly elevated in the treatment group [120 (range, 97.5-237.5) vs. 52 (range, 38-70) micrograms/L; P < 0.004], there was no difference in the form of IGFBP-1 present. The acute effect of somatostatin (500 micrograms/h) on IGFBP-1 phosphorylation status was also studied. Somatostatin only increased the phosphoform characteristic of normal subjects; the appearance of non- or lesser phosphorylated variants was not induced. The effect of rhIGF-I (80 or 120 micrograms, sc) on plasma IGFBP-1 was studied in three subjects with Laron's syndrome. A transient increase in the highly phosphorylated isoform of IGFBP-1 was noted; there was no rise in the non- and lesser phosphorylated isoforms also found in the plasma of Laron's syndrome subjects. These data suggest that only the highly phosphorylated species of IGFBP-1 is under hormonal control; regulation of the non- and lesser phosphorylated variants remains to be determined.

The 'dawn phenomenon' in adolescents with insulin dependent diabetes mellitus: possible contribution of insulin-like growth factor binding protein-1

OBJECTIVE

Insulin resistance increases during adolescence, and is exaggerated in patients with insulin dependent diabetes mellitus (IDDM). A relative deficiency of insulin-like growth factor-I (IGF-I) may contribute to this increased insulin requirement. Two mechanisms have been proposed: (a) increased GH secretion, caused by failure of IGF feedback control, leading to increased insulin resistance and (b) lack of insulin-like action of the IGFs which is reinforced by high plasma levels of IGFBP-1, an inhibitor of IGF action. The contribution of these two mechanisms to the 'dawn phenomenon' is assessed.

DESIGN

The two possible mechanisms were studied during the dawn rise of glucose in pubertal adolescent patients with IDDM. Two overnight studies were performed in each subject. Patients remained on the same insulin regimen throughout.

SUBJECTS

Twenty-two diabetic adolescent subjects, aged (mean +/- SEM) 14.0 +/- 0.4 years, duration of IDDM 7.9 +/- 0.8 years, were recruited. Pubertal status was: group 1 (breast stage 1-2; testicular volume < 4-8 ml) 3 male and 4 female, group 2 (breast stage 3; testicular volume 10-12 ml) 0 male 4 female, group 3 (breast stage 4-5; testicular volume 15-25 ml) 4 male and 7 female. Height standard deviation score (mean +/- SD) (-0.02 +/- 0.99) and daily insulin dose (50.4 +/- 3.1 U/day) did not change between studies. There were no differences in HbA1 (study A 11.26 +/- 0.45%, study B 11.09 +/- 0.42%).

METHODS

The subjects were admitted for the two studies 0.3 +/- 0.03 years apart. Blood samples were taken via an indwelling cannula every 20 minutes between 1900 and 0700 h.

MEASUREMENTS

GH was assayed every 20 minutes, IGFBP-1, glucose and free insulin every hour and IGF-I at 0700 h. GH, IGFBP-1, IGF-I and free insulin were measured by radioimmunoassay. IGFBPs were also analysed by Western ligand blotting techniques. GH profiles were analysed by Pulsar and results compared by paired Student's t-test. The relations between the dawn rise in glucose and the changes in IGFBP-1, GH and free insulin were examined by multiple linear regression analysis.

RESULTS

Serum IGFBP-1 levels rose overnight in the two studies (study A, from 9 +/- 1 at 2200 to 59 +/- 9 micrograms/l at 0700 h; study B, from 10 +/- 1 at 2100 to 64 +/- 14 micrograms/l at 0700 h) whilst insulin levels fell from 47 +/- 5 at 2200 to 16 +/- 2 mU/l at 0700 h (study A) and from 45 +/- 5 at 2000 to 14 +/- 2 mU/l at 0700 h (study B). Glucose levels fell from 16.0 +/- 1.0 to 9.3 +/- 0.9 mmol/l at 0400 h, and then rose to 11.9 +/- 1.1 mmol/l at 0700 h during study A, and from 13.4 +/- 1.3 to 10.1 +/- 1.1 mmol/l at 0400 h and then rose to 13.5 +/- 1.0 mmol/l at 0700 h during study B. There were no differences in GH secretion between studies (mean GH levels (mean +/- SD) (study A, 15.7 +/- 6.6 mU/l; study B, 16.2 +/- 7.1 mU/l; correlation within subjects between studies r = 0.77, P < 0.001), sum of GH peaks (study A, 189.9 +/- 90.3 mU/l; study B, 185.8 +/- 100.2 mU/l; r = 0.57, P = 0.006)). Mean GH levels varied with pubertal stage (group 1, 12.1 +/- 1.5 mU/l; group 2, 23.3 +/- 2.1 mU/l; group 3, 15.3 +/- 1.2 mU/l). Serum IGF-I levels were not different (study A, 203 +/- 12 micrograms/l; study B, 218 +/- 13 micrograms/l). REGRESSION ANALYSIS: The change in plasma glucose between 0200 and 0700 h in both studies related to free insulin, IGFBP-1 and the sum of the GH levels over the preceding hour (log glucose = 7.87 + 5.32 log IGFBP-1 (P = 0.0001) - 5.05 log free insulin (P = 0.0001) - 1.44 log GH (P = 0.004); R2 = 72%). Mean overnight GH levels did not predict the morning rise in plasma glucose.

CONCLUSION

The morning rise of IGFBP-1 and plasma glucose appear to be related in this group of subjects with IDDM and this was a consistent finding in the two studies. This relation was additive to the effect of insulin deficiency.

Androgens and insulin resistance in type 1 diabetic men

OBJECTIVE

In healthy men, both high and low serum testosterone concentrations are associated with insulin resistance, whereas low concentration of sex hormone binding globulin (SHBG) is related to reduced insulin sensitivity. The aim of our study was to examine the association of sex hormones, SHBG, dehydroepiandrosterone (DHEAS) and insulin-like growth factor binding protein-1 (IGFBP-1) on insulin sensitivity in type 1 diabetic patients.

PATIENTS

We examined 23 male patients with the mean age of 29 +/- 1 years, body mass index 22.9 +/- 0.4 kg/m2, insulin dose 47 +/- 3 units/day, glycosylated haemoglobin (HbA1c) 7.8 +/- 0.3% and duration of diabetes 13 +/- 1 years.

DESIGN

Each patient was studied with a 4-hour euglycaemic (5.5 +/- 0.1 mmol/l), hyperinsulinaemic (612 +/- 26 pmol/l) clamp with indirect calorimetry. Muscle biopsies (quadriceps femoris) for the determination of glycogen synthase were performed in 15 patients before and at the end of the clamp.

RESULTS

Insulin infusion reduced the concentrations of IGFBP-1 by 90% (P < 0.001), DHEAS by 11% (P < 0.001), and SHBG by 4% (P < 0.01), whereas free or bound testosterone levels remained unchanged. The fall in IGFBP-1 level was closely related to the basal concentration (r = 0.99, P < 0.001). Basal SHBG concentration correlated directly with total (r = 0.51, P < 0.05) and non-oxidative glucose disposal (r = 0.41, P < 0.05), and with the decrease in lipid oxidation (r = 0.47, P < 0.05) during insulin infusion. The fall in SHBG was inversely related to the mean (30-240 min) FFA concentration during hyperinsulinaemia (r = -0.64, P < 0.001). The fractional activity of glycogen synthase at the end of insulin infusion correlated directly with fasting SHBG (r = 0.71, P < 0.01) and DHEAS concentrations (r = 0.67, P < 0.01).

CONCLUSIONS

In male type 1 diabetic patients: (1) acute hyperinsulinaemia decreases IGFBP-1, DHEAS and SHBG concentrations with the greatest decline in IGFBP-1, (2) SHBG concentration is positively associated with factors indicating good insulin sensitivity, (3) association between fuel homeostasis and SHBG, DHEAS and insulin antagonists suggests a network of these factors in the regulation of insulin action in type 1 diabetic patients.

Insulin-like growth factor-I and insulin-like growth factor-binding protein-1 in Taiwanese women during normal pregnancy

Circulating levels of insulin-like growth factor-I (IGF-I) and insulin-like growth factor-binding protein-1 (IGFBP-1) in Taiwanese women during normal pregnancy were investigated. Three hundred and eighty-five pregnant women at various gestational ages and 30 nonpregnant females were recruited into the study. Serum concentrations of IGF-I and IGFBP-1 were determined by immunoradiometric assay (IRMA) and radioimmunoassay (RIA). Maternal serum levels of IGF-I increased as pregnancy progressed. Circulating IGF-I levels in women during the first trimester of pregnancy were higher than those in nonpregnant females. Serum levels of IGFBP-1 rose rapidly before 12 weeks of gestation and remained high until term. Serum IGFBP-1 levels in pregnant women during the first trimester were significantly higher than those in nonpregnant females. However, there was no difference in maternal serum IGFBP-1 levels between the second and the third trimester of pregnancy. It is concluded that serum IGF-I levels during pregnancy may be regulated by various classes of IGF-binding proteins other than IGFBP-1.

Lack of evidence for a circadian rhythm of IGFBP-1 in the mother and fetus during labour

OBJECTIVE

To determine whether the circadian rhythm of circulating levels of insulin-like growth factor binding protein-1 (IGFBP-1) is evident at the time of delivery.

DESIGN

Prospective observational study in six pregnant women and cross-sectional study in 65 women at the time of delivery.

SUBJECTS

Six pregnant women sampled over a period of 24 hours, 23 women sampled at the time of elective caesarean section, and 42 women sampled at the time of vaginal delivery.

RESULTS

In the women sampled serially over a 24 hour period there was an obvious circadian rhythm of IGFBP-1 with a peak between 01.00 and 09.00 hours. In the women sampled at the time of delivery there was no evidence for any relationship between the time of delivery and maternal or fetal levels of IGFBP-1.

CONCLUSIONS

The circadian rhythm of IGFBP-1 is not observed in women in labour. Therefore, the time of day is not an important confounding variable in studies on IGFBP-1 levels at the time of normal delivery.

Effects of maternal diabetes on fetal expression of insulin-like growth factor and insulin-like growth factor binding protein mRNAs in the rat

Maternal diabetes is associated in humans and rats with an increased risk for fetal growth abnormalities and malformations. Therefore, the effect of maternal diabetes on expression of genes that regulate fetal growth and differentiation is of considerable interest. Developmental growth is regulated in part by the expression and availability of insulin-like growth factors (IGFs). Postnatal expression of a subset of the IGFs and IGF binding proteins (IGFBPs) has been demonstrated to be regulated in response to diabetes and other metabolic conditions. We used in situ hybridization to analyze the effect of maternal diabetes, induced by streptozotocin (STZ) prior to mating, upon prenatal rat IGF and IGFBP mRNA expression. At gestational day (GD) 14, the most striking effect of maternal diabetes on fetal IGF/IGFBP gene expression was a marked increase in the abundance of IGFBP-1 mRNA within the liver primordia of fetuses isolated from diabetic dams compared to age-matched controls. This upregulation cannot be entirely due to the approximately one-half-day delay in fetal development (based on limb bud staging) associated with maternal diabetes, as there was no gross difference in the level of IGFBP-1 mRNA between GD13 and GD14 control fetal livers. In contrast, the fetal mRNA expression patterns of IGF-I, IGF-II and IGFBP-2, -3, -4, -5 and -6 were not grossly altered by maternal diabetes. These data are consistent with the hypothesis that IGFBP-1 produced within the fetal liver and secreted into fetal circulation may play a role in regulating rat fetal growth.

Protein tyrosine phosphorylation induced by epidermal growth factor and insulin-like growth factor-I in a rat clonal dental pulp-cell line

Both epidermal growth factor (EGF) and insulin-like growth factor-I (IGF-I) produce a dose-dependent stimulation in the rate of cell division in a rat clonal dental pulp-cell line (RDP 4-1). To elucidate the initial mitogen-induced cellular events that may mediate mitogenic action, the effects of EGF and IGF-I on cellular protein tyrosine phosphorylation were examined. In a dose-dependent manner, EGF (1-100 ng/ml) transiently stimulated tyrosine phosphorylation in four major proteins with apparent molecular weights of 220, 180, 140 and 120 kDa, and in five other more minor proteins (90, 80, 65, 55 and 44 kDa). IGF-I (1-100 ng/ml) dose-dependently stimulated the tyrosine phosphorylation of 160- and 140-kDa proteins, and had a smaller effect on the 80-, 65- and 44 kDa proteins. In contrast to the action of EGF, IGF-I-induced tyrosine phosphorylation was sustained for more than 60 min, particularly that of the 160-kDa phosphoprotein. From the results of specific immunoprecipitation/Western-blot analyses, the 180-kDa EGF-sensitive protein could be identified as the EGF receptor (EGF-R). Among the IGF-I-sensitive pulp cell proteins, the 160-kDa protein was identified as insulin-receptor substrate-1. Both mitogenic treatments stimulated the tyrosine phosphorylation of a weak, 44-kDa protein, which we have identified as the extracellular signal-regulated kinase-1. Despite the presence of phosphoproteins of the correct size, neither the IGF-I receptor (IGF-I-R) nor the phospholipase C gamma-isoform could be identified as tyrosine kinase substrates in either treatment. Pretreatment with the tyrosine kinase inhibitor genistein (20 micrograms/ml) significantly inhibited EGF- and IGF-I-induced tyrosine phosphorylation in permeabilized RDP 4-1 cells, and the tyrosine phosphatase inhibitor orthovanadate (1 mM) significantly prolonged the duration of the mitogen-stimulated tyrosine phosphorylation in both intact or permeabilized cells. Phorbol 12-myristate 13-acetate (100 nM), which activates protein kinase C (PKC), inhibited the tyrosine phosphorylation induced by either growth factor. This action was blocked by pretreatment with staurosporine (200 nM, 15 min), a selective PKC inhibitor. However, neither removing external Ca2+ with EGTA (1 mM) nor inducing Ca2+ influx with A23187 ionophore (2 microM) significantly altered EGF- or IGF-I-induced phosphorylation. These findings strongly suggest that authentic EGF-R and IGF-I-R on RDP 4-1 cells are coupled to complex, tyrosine kinase-mediated, intracellular signalling systems that are sensitive to a PKC-dependent mechanism. EGF- and IGF-I-induced tyrosine phosphorylation cascades may have important roles in vivo in the regulation of dental pulp-cell proliferation and ultimately may affect dentine formation.

Regulation of IGF binding proteins by FSH in human luteinizing granulosa cells

OBJECTIVE

To evaluate the regulation of the secretion of insulin-like growth factor (IGF) binding proteins (IGFBPs) by FSH in human luteinizing granulosa cells.

DESIGN AND RESULTS

Luteinizing granulosa cells were incubated with and without FSH. Levels of IGFBP-1 and -3 in the medium were measured by EIA and RIA, respectively and binding activities of these IGFBP were evaluated by Western ligand blot. FSH inhibited the secretion of IGFBP-1 dose dependently. FSH did not inhibit the secretion of immunoreactive IGFBP-3, but inhibited the binding activity of IGFBP-3. To assess the protease activity, 125I-IGFBP-3 was incubated with the cultured medium. 125I-IGFBP-3 degraded into small fragments when it was incubated with the cultured medium treated with FSH.

CONCLUSIONS

FSH enhances the action of IGF-I in human granulosa cells by inhibiting the secretion of IGFBP-1 and the binding activity of IGFBP-3 by stimulating the proteolysis of IGFBP-3.

Ethanol induces a paradoxical simultaneous increase in circulating concentrations of insulin-like growth factor binding protein-1 and insulin

The aim of this study was to examine the effect of acute alcohol intake on circulating concentrations of insulin, C-peptide, insulin-like growth factor (IGF) binding protein-1 (IGFBP-1), and plasma glucose levels. We measured these parameters for 12 hours after administration of 0, 0.5, or 1.0 g ethanol/kg body weight to nine healthy volunteers between 7:00 and 7:45 PM according to a randomized, double-blind, crossover design. Following a snack at 9:00 PM, plasma insulin (P < .05) and C-peptide (P < .01) concentrations were significantly increased at 10:00 PM in the 1.0-g group as compared with the control group. C-peptide to insulin molar ratios were significantly higher (P < .05) in both ethanol groups at 10:00 PM and 2:00 AM than in the control group. No differences were observed in plasma glucose levels between the three groups. Plasma IGFBP-1 levels showed a dose-dependent increase in the ethanol groups, and remained increased from 10:00 PM for 3 hours (P < .05 or less) at the lower dose and for 6 hours (P < .05 or less) at the higher dose. These observations indicate that ethanol-induced postprandial hyperinsulinemia is due to increased insulin secretion and that alcohol may increase hepatic insulin extraction. The lack of any effect on plasma glucose levels suggests that alcohol intake must be associated with decreased insulin sensitivity. Alcohol intake results in a paradoxical increase in peripheral concentrations of IGFBP-1 despite simultaneous hyperinsulinemia. This implies that ethanol has a direct stimulatory effect on hepatic IGFBP-1 synthesis.

Disturbed anabolic hormonal patterns in burned patients: the relation to glucagon

OBJECTIVE

Complex changes in the anabolic regulators of metabolism occur after major injury. We have studied the time course for IGF-I and IGFBP-1 after burn injury and their relations to circulating levels of other anabolic and catabolic hormones. The hormonal patterns during the onset of sepsis were also investigated.

PATIENTS

Eight patients (age 36 (6) years, mean (SEM)) with major burn injury (burn area 42 (6) %) were studied. The first 2 days since the burn were used for rehydration therapy (rehydration period), after which a complete total parenteral nutrition (TPN) period was initiated. Seven positive blood cultures, during the study period. Six of the eight survived.

MEASUREMENTS

The hormonal changes determined in the morning during the first 7 days after the burn and from day 22 to 24 were investigated. The superimposed effects of sepsis were studied by normalizing all data to the day of positive blood cultures and clinical onset of sepsis.

RESULTS

On admission, plasma levels of glucagon, IGFBP-1 and GH were elevated while levels of IGF-I were low. During the first week after the burn, morning levels of glucagon and insulin increased while levels of GH and IGF-I decreased. GH levels were still elevated compared to healthy subjects. Despite the increase in insulin levels, IGFBP-1 remained elevated. Three weeks after the burn injury, IGF-I levels were increased but still markedly below normal, while IGFBP-1 levels remained unchanged. Persistent elevations of insulin levels were combined with reductions in glucagon levels. Admission levels of IGFBP-1 correlated to nitrogen loss (negative nitrogen balance) during the first 24 hours after the burn (r = 0.84, P < 0.05). A correlation between negative nitrogen balance and glucagon levels was found during early catabolic period in the rehydration period (i.e. days 2-3, r = 0.84, P < 0.01). The relative change in IGFBP-1 levels in the rehydration period correlated to changes in glucagon levels (days 2-3 vs admission, r = 0.85, P < 0.05). The insulin/glucagon molar ratio correlated to the IGF-I/IGFBP-1 ratio during both the rehydration period (days 2-3, r = 0.77, P < 0.05) and the third week after the burn (r = 0.77, P < 0.05). During the most catabolic phase in the first week after the burn (TPN period) there was an inverse relation between IGF-I and IGFBP-I and glucagon (r = 0.83, P < 0.05). During the less catabolic third week after the burn, an inverse correlation was found between IGF-I and glucagon (r = -0.83, P < 0.05). Sepsis, superimposed upon the burn trauma, was associated with transient elevations in IGFBP-1 and reductions in insulin despite elevated levels of glucose and a further 50% increase in nitrogen losses.

CONCLUSIONS

The present findings show that marked changes is important anabolic regulating factors occur after major burn injury. Uncoupling of the GH-IGF-I axis, and the attenuation of the inhibitory effects of insulin on IGFBP-1, both contribute to the reduction in IGF-I levels and bioavailability, factors which may play an important role in post injury metabolism. Furthermore, these data suggest that the catabolic hormones (catecholamines, cortisol and glucagon), primarily glucagon seem to be involved in the modulation of IGF-I and IGFBP-1 levels following burn injury.

Activation of human insulin-like growth factor binding protein-1 gene promoter by a distal regulatory sequence in a human endometrial adenocarcinoma cell line

Insulin-like growth factor-binding protein-1 (IG-FBP-1) is the major secretory protein of decidualized human endometrium. To understand IGFBP-1 gene regulation in human endometrium, we studied the IGFBP-1 gene promoter activity in human endometrial adenocarcinoma cell line HEC-1B. Previously, we have reported that a 105-base pair (bp) ClaI/RsaI fragment, from -2732 to -2628, of IGFBP-1 promoter enhances promoter activity by 10-fold in HEC-1B cells. In this study we have characterized the activation of IGFBP-1 promoter by this distal regulatory sequence. Transient transfection assays with deletion constructs demonstrated that the activating cis-elements were located in a 59-bp fragment, from -2686 to -2628, which enhanced promoter activity 50-fold. Transient transfections and gel mobility shift assays with oligo-directed mutants revealed three cis-elements within this 59-bp region: I) ATGGGTGGGA (-2675 to -2666), II) GCTGAGCAAGTGCACAACTATCC (-2660 to -2638), and III) AGGGCGGAGT (-2637 to -2628). In nuclear extracts of HEC-1B cells, at least two proteins bound to cis-element III, one of which was transcription factor Sp1 since antibody against Sp1 caused a supershift in a gel mobility shift assay. A protein with a molecular mass of approximately 100 kilodaltons bound to cis-element I as revealed by Southwestern blotting. An unidentified protein bound to cis-element II. Mutations in cis-element I, II, and III reduced promoter activity by 37%, 86%, and 88%, respectively, indicating that there was a synergistic function among these three cis-elements.(ABSTRACT TRUNCATED AT 250 WORDS)

Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig

We have tested whether an animal with substantial amounts of both IGF-I and IGF-II in circulation, such as the guinea pig, would respond to chronic IGF infusion in the same manner as the adult rat, which has negligible amounts of IGF-II in blood. Female guinea pigs of 350 g body weight were continuously infused for 7 days with recombinant guinea pig IGF-I or -II (120 or 360 micrograms/day) or long R3 IGF-I (LR3IGF-I) (120 micrograms/day), an analogue which has much reduced affinities for IGF binding proteins. IGF-I or IGF-II infusion led to substantial increases in plasma IGF-I or IGF-II respectively in comparison with vehicle-infused animals. Nevertheless, body weight gain, feed intake, feed conversion efficiency and carcass composition were not significantly affected by any treatment (significance was deemed to be P < 0.05). Amongst the tissues examined only the fractional weight (g/kg body weight) of the adrenals was increased, and that only by the higher dose (360 micrograms/day) of IGF-I. However, the fractional weight of adrenals, gut, kidneys and spleen were significantly increased by LR3IGF-I, but again overall growth was not stimulated. A possible explanation for the lack of IGF-I effects is that total circulating IGF concentrations were not increased by these treatments. IGF-II significantly raised total IGF concentrations at the higher dose only. Plasma IGF-I was reduced by IGF-II infusion, as was plasma IGF-II by IGF-I infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Diurnal variation of sex hormone binding globulin and insulin-like growth factor binding protein-1 in women with polycystic ovary syndrome

OBJECTIVES

The aim of this study was to examine (1) the diurnal variation in SHBG and (2) the inter-relationships of insulin, IGF-I, SHBG and IGFBP-1 over 24 hours in 10 women with anovulatory PCOS and compare them with weight-matched ovulatory controls.

PATIENTS AND METHODS

The two groups comprised 10 anovulatory women with PCOS (as defined by clinical, ultrasound and biochemical criteria) and 10 weight matched controls. Serum samples were taken at two-hourly intervals for 24 hours and stored for measurement of SHBG, IGFBP-1, insulin and IGF-I. Differences between the groups were compared using the Wilcoxon ranked paired tests of the individual peak and trough concentrations in each group. The variation in insulin, IGFBP-1 and SHBG concentrations over 24 hours was tested using two-way analysis of variance with the factors time and subject. Spearman's correlation coefficient was calculated from the subjects' median value over 24 hours.

RESULTS

The median (interquartile range) body mass index (BMI) was 25.2 (22.2-29.3) in the PCOS group and 24.3 (23.2-25.7) kg/m2 in the control group. Serum testosterone (T) and LH levels were significantly raised in the PCOS group compared to the control group; T 3.8 (2.9-5.6) vs 1.9 (1.9-2.5) nmol/l (P < 0.007) and LH 12 (10-15) vs 4.1 (3.6-4.5) IU/I (P < 0.005) respectively. There was no diurnal variation in SHBG. The median (interquartile ranges) of the peak SHBG concentrations was lower in the PCOS group: 29.4 (14.9-39.4) vs 52.1 (39.4-61) nmol/l in the control group (P < 0.01). The fasting levels of insulin at 0600 h (median (interquartile ranges)) were not significantly different between the groups; 6.6 (5.4-9.8) and 6.2 (1.9-7.6) mU/l, respectively, although the peak median concentrations were significantly different; PCOS 66.1 (50.9-129.2) vs 40 (36.1-74.2) mU/l (P < 0.05). Two-way analysis of variance showed a diurnal variation in insulin concentrations in the control group (P = 0.001) but not in the PCOS group (P = 0.1). The diurnal variation in IGFBP-1 was similar in the two groups but the peak median levels were lower in the women with PCOS 54.9 (22.3-79.2) vs 71.5 (60.5-99.3) micrograms/l (P < 0.03). The decline in IGFBP-1 concentrations correlated with the increase in insulin concentrations. The IGF-I concentrations were similar in the two groups. There was a significant negative correlation between SHBG and insulin (P < 0.05) and between insulin and IGFBP-1 (P < 0.01).

CONCLUSION

This study demonstrates that there is no diurnal variation in SHBG concentrations and confirms the finding of a marked diurnal variation in the concentration of IGFBP-1. Women with PCOS who are anovulatory have an abnormal pattern of insulin secretion with an absence of diurnal variation compared to weight matched controls. This provides further evidence of the relative insulin resistance which is independent of weight found in women with anovulatory PCOS. The inverse correlations of insulin concentrations with SHBG and IGFBP-1 support the role of insulin as a possible regulator of the circulating levels of these binding proteins although the difference in the time course of their response makes it unlikely that they are co-regulated.

Modulation of inflammation-induced changes in insulin-like growth factor (IGF)-I and IGF binding protein-1 by anti-TNF antibody

The aim of the present study was to characterize changes in the insulin-like growth factor (IGF) system produced by the nonbacterial nonendotoxic inflammatory agent zymosan and to determine whether these changes were mediated by enhanced production of tumor necrosis factor (TNF). Rats were injected intraperitoneally with either zymosan or saline and studied 18 h later. Animals were pretreated with either nonimmune IgG or neutralizing anti-TNF antibody 2 h before zymosan injection. Zymosan increased the plasma concentration of TNF alpha, and this was associated with a decrease (approximately 40%) in the IGF-I concentration in plasma, liver, heart, and brain. The IGF-I content was not altered in skeletal muscle and kidney. Zymosan also increased the concentration of IGF binding protein (BP)-1 in plasma (120%), liver (90%), and muscle (470%). Circulating TNF alpha was not detectable in rats injected with anti-TNF antibody before zymosan. The neutralizing antibody prevented the zymosan-induced reduction in IGF-I in plasma and blunted the decreased observed in liver, but did not alter the decrease in heart or brain. Anti-TNF antibody also attenuated (40-60%) the increased IGFBP-1 in plasma, liver, and muscle observed in zymosan-treated rats. We conclude that zymosan-induced inflammation not only decreases IGF-I in plasma and selected tissues, but also increases IGFBP-1 in plasma, liver, and muscle, and that these alterations are due in large part to the enhanced production of TNF alpha.

Acute hyperinsulinemia, androgen homeostasis and insulin sensitivity in healthy man

The acute effects of hyperinsulinemia on androgen homeostasis and a possible association of androgens to insulin sensitivity, serum lipids and lipoproteins and to lipid oxidation were examined in 19 healthy males (27 +/- 1 yrs, body mass index 24 +/- 1 kg/m2). In each subject, a 240 min euglycemic hyperinsulinemic clamp was performed and glucose and lipid oxidation were determined by indirect calorimetry. During hyperinsulinemia serum sex hormone-binding globulin (SHBG) concentration decreased by 5% (P < 0.01), insulin-like growth factor binding protein (IGFBP-1) by 88% (P < 0.001) and dehydroepiandrosterone sulphate (DHEAS) by 12% (P < 0.001), with no change in total or free testosterone concentrations. In the basal state, IGFBP-1 and C-peptide were inversely related (r = -0.54, P < 0.05). Fasting concentrations of serum free testosterone (r = 0.59, P < 0.01) and DHEAS (r = 0.47, P < 0.05) correlated positively with serum free fatty acid (FFA) concentrations during hyperinsulinemia, but not with fasting FFA level. Lipid oxidation rate in the basal state correlated positively to the decline in SHBG (r = 0.61, P < 0.01) and DHEAS concentrations (r = 0.62, P < 0.01) during hyperinsulinemia. While the fasting serum high density lipoprotein cholesterol level correlated positively with the insulin-induced decline in DHEAS level (r = 0.58, P < 0.01), no associations were found between serum androgens and total cholesterol, low density lipoprotein cholesterol or triglyceride concentrations. Insulin sensitivity was not related to SHBG, IGFBP-1, DHEAS or testosterone concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel DNA/protein complex interacts with the insulin-like growth factor binding protein-1 (IGFBP-1) insulin response sequence and is required for maximal effects of insulin and glucocorticoids on promoter function

Glucocorticoids stimulate and insulin inhibits hepatic production of IGFBP-1 at the level of gene transcription. We previously identified contiguous insulin and glucocorticoid response sequences in the proximal rat IGFBP-1 promoter. This insulin response sequence (IRS) is palindromic (CAAAACAAACTTATTTTG) and each half resembles an IRS in the phosphoenolpyruvate carboxykinase (PEPCK) gene. We have reported that both the IGFBP-1 and PEPCK IRSs bind hepatocyte nuclear factor-3 (HNF-3) proteins [1]. We now report that IRSs from the IGFBP-1 and PEPCK, as well as an IRS which also binds HNF-3 in the rat tyrosine aminotransferase (TAT) gene, also interact with another DNA/protein complex in gel shift studies. Further, methylation interferences studies, gel shift and transient transfection studies with site-specific mutations identified a single base in the first half of the IRS that is critical both for interactions with proteins in this complex, and for maximal effects of insulin and glucocorticoids, on promoter function. Of note, a 250-fold excess of an oligo containing a C/EBP binding site (but not other AT-rich sequences) inhibits the formation of this complex in gel shift assays. Nevertheless, interactions with this C/EBP site are negligible at lower titers (< or = 100-fold excess), and antibodies against known C/EBP proteins do not react with this complex. Similarly, preincubation with CHOP, a truncated member of the C/EBP family which contains a beta-leucine zipper domain, does not prevent or alter the mobility of this novel DNA/protein complex, indicating that components of this complex do not form heterodimers with beta-ZIP proteins. We conclude that HNF-3 proteins and this novel C/EBP-related DNA/protein complex may play an important role in mediating interactions between glucocorticoids and insulin in the regulation of IGFBP-1 and perhaps multiple hepatic genes.

Regulation of IGFBP-1 in humans

IGFBP-1 secretion in humans is regulated by insulin and the counter-regulatory hormones with a high production rate and rapid turnover. The IGFBP-1 fasting levels are both genetically and environmentally determined. Serum IGFBP-1 levels may be regulated by so far unknown factors during certain conditions. The fasting IGFBP-1 level can be used as a marker of diurnal IGFBP-1 and insulin secretion.

Role of insulin-like growth factor binding proteins in the control of IGF actions

The insulin-like growth factor binding proteins have been shown to modify IGF actions. IGFBP-5 binds to extracellular matrix (ECM) and its ability to potentiate IGF activity is dependent upon the amount that is ECM associated. To determine the specific regions of IGFBP-5 that are required for ECM association, site directed mutagenesis has been used to prepare several forms of IGFBP-5. Mutants that have had the amino acids between positions 201 and 218 altered have been useful. Mutation of the lysine 211 resulted in no change in the affinity of IGFBP-5 for ECM or heparin Sepharose; however, it resulted in a major reduction in affinity for IGF-I following heparin binding. Other mutations which disrupted heparin binding also resulted in loss of this affinity shift. Most distruptive were mutations of amino acids 211, 214, 217 and 218 and 202, 206 and 207. Mutation of residues 201 plus 202 had some effect, but substitution for 207, 211, 217 and 218 had no effect. When binding to intact ECM was analyzed, similar results were obtained. This suggests that amino acids 202, 206 and 214 are definitely involved in heparin and ECM binding. When binding to proteoglycans such as tenascin and heparin sulfate proteoglycan was analyzed, similar results were obtained. IGFBP-5 also binds to other proteins in ECM, including type IV collagen and plasminogen activator inhibitor-I. Specific antisera for plasminogen activator inhibitor-1 can coprecipitate IGFBP-5. IGFBPs are degraded by specific proteases. Three proteases that degrade IGFBP-2, -4 and -5 have been characterized. They are serine proteases that cleave these proteins at basic residues. Although several well characterized serine proteases cleave IGFBP-4 or -5, the proteases in cell conditioned media appear to be distinct.

Insulin-like growth factors (IGF) and IGF binding proteins in children with chronic renal failure

The pathomechanism of growth retardation and catabolism in children with chronic renal failure (CRF) is multifactorial. Recent evidence indicates that in particular disturbances of the somatotropic hormone axis play an important pathogenic role. In preterminal CRF serum insulin-like growth factor (IGF)-I and IGF-II levels are normal, while in end-stage renal disease (ESRD), IGF-I levels are slightly decreased and IGF-II levels slightly increased. In view of the prevailing elevated growth hormone levels in ESRD, these serum IGF-I levels appear as inadequately low. Indeed, there is both clinical and experimental evidence for a decreased hepatic IGF-I production rate in CRF. This hepatic insensitivity to the action of GH is partially owing to a reduced GH receptor expression. The action and metabolism of IGFs are modulated by specific high-affinity IGF binding proteins (IGFBPs), which bind approximately 99% of circulating IGF. IGFBP-1, IGFBP-2, and low molecular weight IGFBP-3 fragments are increased in CRF serum in relation to the degree of renal dysfunction. Both decreased renal filtration, in particular of low molecular weight IGFBP-3 fragments, and increased hepatic production of IGFBP-1 and -2 contribute to high IGFBP serum levels. Experimental and clinical evidence suggests that these excessive high-affinity IGFBPs in CRF serum inhibit IGF action on target tissues by competition with the type 1 IGF receptor for IGF binding.