IGF-I) And Its Binding Proteins Research Articles

Control of follicular development and ovulation rate in pigs

There is considerable evidence that nutritional and metabolic control of follicular growth is mediated by metabolic hormones and growth factors, particularly with processes mediated by insulin-like growth factor I (IGF-I) and its binding proteins (IGFBPs). From knowledge that hormones and growth factors which can be affected by diet also positively affect ovarian function, the concept has emerged that metabolic modifiers of gonadotrophin action, rather than gonadotrophins themselves, could affect follicle development. While ovulation rate can be enhanced under certain conditions in cyclic gilts, assessing influences of metabolic modifiers on the post-lactational sow is confounded by variability in the return to oestrus after weaning. In a series of studies involving insulin administration between weaning and oestrus, successive experiments produced different results, but several measures of reproductive performance were enhanced. Administration of somatotrophin (ST) has also been shown to increase follicular development in both gilts and sows. Both insulin and ST increase IGF-I production by pig ovarian follicles, and insulin is more effective than IGF-I in reducing atresia and increasing progesterone in cultured pig follicles. Whether increases in litter size are achieved after an increase in ovulation rate involves many factors, including the quality of ova and whether the increase in ovulation rate exceeds the uterine capacity to maintain pregnancy. Given the variation in genetics and management practices, development of treatments to enhance follicle quality leading to maximal litter size is challenging.

Animal Protein Intakes during Early Life and Adolescence Differ in Their Relation to the Growth Hormone-Insulin-Like-Growth-Factor Axis in Young Adulthood1,2

Recent studies provide evidence that insulin-like-growth-factor I (IGF-I) and its binding proteins (IGFBP) IGFBP-2 and IGFBP-3 are related to the risk of several common cancers. It remains to be clarified whether their concentrations can be programmed by protein intake from different sources during growth. This study addressed the hypothesis that animal protein intakes during infancy, mid-childhood, and adolescence differ in their relevance for the growth-hormone (GH)-IGF-I axis in young adulthood. Data from the Dortmund Nutritional and Anthropometric Longitudinally Designed Study participants with at least 2 plausible 3-d weighed dietary records during adolescence (age: girls, 9–14 y; boys, 10–15 y; n = 213), around the adiposity rebound (age 4–6 y; n = 179) or early life (age 0.5–2 y; n = 130), and one blood sample in young adulthood were included in the study. Mean serum concentrations of IGF-I, IGFBP-1, IGFBP-2, and IGFBP-3 were compared between tertiles of habitual animal protein intake using multivariable regression analysis. Habitually higher animal protein intakes in females during puberty were related to higher IGF-I (P-trend = 0.005) and IGFBP-3 (P-trend = 0.01) and lower IGFBP-2 (P-trend = 0.04), but not to IGFBP-1 in young adulthood. In turn, IGF-I concentrations in young adulthood were inversely related to animal protein intakes in early life among males only (P-trend = 0.03), but not to animal protein intake around adiposity rebound (P-trend > 0.5). Our data suggest that, among females, a habitually higher animal protein intake during puberty may precipitate an upregulation of the GH-IGF-I axis, which is still discernible in young adulthood. By contrast, among males, higher animal protein intakes in early life may exert a long-term programming of the GH-IGF-I axis.

Exercise-dependent IGF-I, IGFBPs, and type I collagen changes in human peritendinous connective tissue determined by microdialysis

Microdialysis studies indicate that mechanical loading of human tendon during exercise elevates type I collagen production in tendon. However, the possibility that the insertion of microdialysis fibers per se may increase the local collagen production due to trauma has not been explored. Insulin-like growth factor I (IGF-I) and its binding proteins (IGFBPs), which are known to stimulate collagen production in animal tendons, may regulate the translation of mechanical loading to collagen synthesis. Systemic and tissue levels of IGF-I, IGFBP, and type I collagen metabolism markers [procollagen I COOH-terminal propeptide (PICP) and COOH-terminal telopeptide of type I collagen] were measured by microdialysis in peritendinous tissue of the human Achilles tendon in an exercise group (performing a 36-km run, n = 6) and a control group (no intervention, n = 6). An increase in local PICP concentration was seen in both groups after 72 h and stayed elevated in the exercise group at 96 h (P < 0.05). IGFBP-1 in both serum and dialysate increased in the exercise group immediately after exercise (P < 0.05), whereas IGFBP-3 decreased systemically (P < 0.05). Elevation of local IGFBP-4 was observed in both the control and exercise groups after 48 h (P < 0.05). Total IGF-I did not change in locally or systemically in either group. Our results indicate an increased local production of PICP in human peritendinous tissue in response to prolonged mechanical loading with part of the increase due to trauma from the sampling technique. Care must therefore be emphasized to minimize the numbers of insertions with microdialysis. We demonstrated an elevation of IGFBP-1 both systemically and peritendinously in response to prolonged acute exercise. The local increased collagen synthesis was preceded by an elevation of local concentration of IGFBP-4, suggesting that IGFBP-4 may have a key role in the IGF-axis effect on the human collagen synthesis in vivo.

Does growth hormone allow more efficient nitrogen sparing in postoperative patients requiring parenteral nutrition? A double-blind, placebo-controlled randomised trial

Growth hormone (GH) has a strong anabolic effect and is thought to be useful in improving the efficacy of parenteral nutrition (PN) to preserve muscle mass (MM) in the postoperative setting. Unfortunately, the negative clinical outcome of GH treatment in intensive care patients limits its use in this setting, but demands answers to the mechanism behind the action of this therapy. In a double-blind randomised controlled study consecutive patients after major abdominal surgery were divided into four groups of either 1/2-PN (0.13 g N/kg/day and 52% of calories as lipid) or full-strength PN (Full-PN) (0.3 g N/kg/day and 65% of calories as lipid) receiving daily injections of either GH (8-16 IU) or placebo for a period of 14 days postoperative. Outcome measures included MM derived from measures of total body potassium (40K counting) and total body nitrogen (TBN) (in vivo neutron capture technique); Fat mass from skin folds; serum insulin like growth factor-I (IGF-I) and its binding proteins (IGFBP). From 43 major upper GI surgical patients randomised 35 completed the study (one patient died from sepsis in the half-strength PN (1/2-PN)+GH group). 1/2-PN (n=11) lost TBN (P=0.001), MM (P=0.005) but not fat. Full-PN (n=9) maintained TBN, MM (P=0.056) and fat. 1/2-PN+GH (n=8) maintained TBN and fat but lost MM (P=0.038). Full-PN+GH (n=7) maintained TBN and MM but lost fat (P=0.018). Two-way ANOVA indicated that PN input (P=0.031) and not GH had a significant effect on MM. GH caused a significant rise in IGF-I levels (290+/-67 and 454+/-71 microg/l for 1/2-PN+GH and Full-PN+GH, respectively) and restored serum IGFBP3 and the acid labile subunit to normal, by the postoperative day 9. After major gastrointestinal surgery, GH causes a marked hepatic IGF-I response and nitrogen retention but its effect on body composition was more significant with a high PN input. Further, Full-PN alone was sufficient to prevent nitrogen loss and preserved MM and addition of GH does not provide further metabolic advantage.

Serum insulin-like growth factor binding protein-2 levels as an indicator of functional ability in elderly men.

In a cross-sectional study in 403 healthy, independently living elderly men (mean age 78 years), we determined which are the main physiological determinants of functional ability in the elderly, and which components of the somatotropic system contribute to the maintenance of functional ability. Functional ability was assessed by the number of problems in activities of daily living and by a measure of physical performance. Other physical characteristics included leg extensor strength, bone mineral density of total body and proximal femur, and body composition, including lean mass and fat mass. Serum insulin-like growth factor (IGF)-I and its binding proteins (IGFBP) -1, -2 and -3 concentrations were all measured by RIA. Muscle strength was related to a lower degree of disability. Further, it was positively related to physical performance and bone mineral density (all P<0.001). Fat mass influenced activities of daily living and physical performance negatively and bone mineral density positively (all P<0.001). Serum concentrations of IGF-I and IGFBP-3 were not related to any of the physical characteristics. High serum IGFBP-2 concentrations were related to a higher degree of disability (P<0.001), a lower physical performance (P=0.006), muscle strength (P=0.002), bone mineral density of proximal femur (P=0.007), lean mass and fat mass (both P<0.001). Serum insulin and IGFBP-1 concentrations were independently, positively related to lean mass (P=0.003) and fat mass (P<0.001). In independently living elderly men, functional ability appears to be determined by muscle strength (positive) and fat mass (negative). Low serum IGFBP-2 concentrations are a powerful indicator for overall good physical functional status, probably inversely reflecting the integrated sum of nutrition and the biological effects of growth hormone, IGF-I and insulin.

Effect of advanced glycation endproducts on the secretion of insulin-like growth factor-I and its binding proteins: role in osteoblast development.

In chronically uncompensated diabetes mellitus, an increase has been observed in the content of advanced glycation endproduct (AGE)-modified proteins in various tissues, including bone. This increase can lead to a local imbalance in the secretion of cytokines and growth factors, and has been implicated in the pathophysiology of the longterm complications of diabetes. We have previously shown that the proliferation and differentiation of UMR106 rat osteosarcoma and MC3T3E1 mouse calvaria-derived cell lines are regulated by AGE-modified proteins, possibly through the recognition of these AGEs by specific membrane-associated receptors. In the present study, we investigated the effects of AGE-proteins on the secretion of insulin-like growth factor-I (IGF-I) and its binding proteins (IGFBPs) by both osteoblast-like cell lines. In the case of MC3T3E1 cells, this was studied throughout their successive stages of development: proliferation, differentiation and mineralisation. For every condition, cells were incubated 24 hours with increasing concentrations of either bovine serum albumin (BSA) or AGE-BSA. IGF-I in conditioned media was separated from IGFBPs by acid gel filtration-centrifugation, and measured by radioimmunoassay. IGFBPs in conditioned media were analysed by a semi-quantitative western ligand blot. In UMR106 cells, low doses of AGE-BSA significantly decreased the secretion of both IGF-I (56% of control) and a 24 kDa IGFBP (80% of control). Results for MC3T3E1 cells, which predominantly secrete 29 kDa IGFBPs, were dependent on the stage of development. In proliferating preosteoblastic cells, AGE-BSA decreased the secretion of IGF-I (34%-37% of control) while increasing the secretion of IGFBP (124%-127% of control). On the other hand, secretion of these components of the IGF system by mature (differentiated) cells was unaffected by the presence of AGE-BSA. When these cells finally attained mineralisation, incubation with AGE-modified BSA provoked an increase both in IGFBP (131%-169% of control) and in IGF-I secretion (119%-123% of control). The presented evidence suggests that the modulation of growth and development by AGE-modified proteins, previously described for both cell lines, could be the result of an autocrine-paracrine mechanism involving the IGF-IGFBP system.

Haemodialysis with the biocompatible high permeability AN-69 membrane does not alter plasma insulin-like growth factor-I and insulin-like growth factor binding protein-3.

Insulin-like growth factor-I (IGF-I) bioactivity has been reported to be decreased in maintenance haemodialysis patients and this may affect their nutritional status. Clearances of IGF-I and its binding proteins (IGFBPs) during haemodialysis sessions using a high permeability biocompatible membrane are unknown. Five well nourished, non-diabetic adult patients were studied during one 4-h morning haemodialysis treatment using the high permeability biocompatible AN-69 dialyser. Blood was collected at the arterial and venous ports of the dialyser at 0, 1, 2 and 4 h of dialysis for haematocrit, plasma IGF-I, IGFBP-3 and insulin measurements. IGF-I, IGFBP-3 and insulin concentrations were adjusted for haemoconcentration before comparisons were made. At the beginning of the dialysis session, plasma IGF-I, IGFBP-3 and insulin levels were within the normal range (297 +/- 47 ng/ml (mean+/-SEM), 4.3 +/- 0.6 microg/ml and 11.8 +/- 3.4 microIU/ml, respectively). During the session, insulin tended to be cleared through the dialyser, whereas plasma IGF-I and IGFBP-3 values did not vary significantly. Dialysis with the high permeability AN69 membrane did not alter the main blood compounds of the IGF system in well nourished chronic haemodialysis patients, and it is unlikely that the malnutrition frequently observed in such patients would result from alterations of the IGF system during haemodialysis.

Bone turnover and growth during and after continuing chemotherapy in children with acute lymphoblastic leukemia.

Children treated for acute lymphoblastic leukemia may develop reduced bone mineral density during treatment, but there is little information on the mechanisms involved. In a prospective, longitudinal study on 15 children with ALL, we undertook serial measurements of markers of bone and collagen turnover, insulin-like growth factor (IGF)-I and its binding proteins (IGFBPs)-3 and -2 during the second year of continuing chemotherapy. In eight patients we also measured lower leg length by knemometry. Height SD scores, lower leg length velocity, IGF-I, and markers of bone collagen turnover did not differ significantly from healthy children. However, bone alkaline phosphatase, a marker of the differentiated osteoblast, was lower (mean SD score, -0.64; p < 0.0001), whereas procollagen type III N-terminal propeptide (P3NP, a marker of soft tissue collagen turnover; mean SD score, +0.93, p < 0.05), IGFBP-3 (mean SD score, +0.76; p < 0.01), and IGFBP-2 (mean SD score, +1.24, p = 0.01) were all higher than in healthy children. IGFBP-3 decreased during episodes of afebrile neutropenia (p < 0.05). Within 3 mo after completion of treatment, bone ALP increased in all eight patients, but collagen markers showed little change. IGFBP-2 returned to normal posttreatment, but P3NP and IGFBP-3 remained significantly elevated compared with healthy children (mean SD scores, +1.51 and +1.36, respectively; p < 0.01). We conclude that continuing chemotherapy was associated with normal growth and bone collagen turnover but enhanced soft tissue collagen turnover. Bone bone alkaline phosphatase was low throughout treatment, which suggests impaired osteoblast differentiation resulting from a direct effect of chemotherapy on bone. Although the effect was reversible, the long-term implications for bone health in survivors remain uncertain.

Mucus of the human olfactory epithelium contains the insulin-like growth factor-I system which is altered in some neurodegenerative diseases

Growth factors are believed to be involved in the mitotic regulation of the animal olfactory epithelium (OE). We investigated mucus covering the human OE area to see if it contained the insulin-like growth factor-I (IGF-I) and its binding proteins (IGFBPs) and to examine their behaviour in neurodegenerative diseases. Thirty patients with idiopathic late onset cerebellar ataxia (ILOCA), Parkinson's disease, and amyotrophic lateral sclerosis (ALS) and 30 age- and sex-matched healthy subjects were studied. In 10 controls, we also analyzed the mucus of the respiratory mucosa of the nose and tears. We detected IGF-I in the mucus covering the OE and Western ligand blot analysis (WLB) showed IGFBPs with an apparent Mr of 41,500/38,500, 34,000 and 24,000, which were immunoprecipitated by specific antisera to IGFBP-3, -2 and -4, respectively. Their levels were higher than those observed in the respiratory mucosa of the nose or in tears. Mucus of the OE of the patients contained significantly reduced levels of IGF-I in comparison with those of controls. The intensity of all the IGFBPs-related bands were reduced in the ILOCA, while the remaining patients had a loss in the amounts of IGFBP-3. Plasma IGF-I and IGFBPs levels were similar in patients and controls. In conclusion, our data show that mucus covering the human OE contains IGF-I and IGFBPs, suggesting that these factors have a role in the activity of the OE. The amounts are reduced in the patients' mucus, possibly reflecting a dysfunction of the OE itself.

Continuous administration of growth hormone does not prevent the decrease of IGF-I gene expression in zinc-deprived rats despite normalization of liver GH binding

To determine the role of reduced liver GH binding (GHR) in the decreased IGF-I observed in zinc-deficient (ZD) animals, we investigated the effects of GHR restoration on growth, insulin-like growth factor I (IGF-I) and its binding proteins (IGFBPs) in ZD rats. Rats were fed for 4 weeks a zinc-deficient diet (ZD Zn, 0 ppm) or a Zinc-normal diet (pair-fed or PF; Zn, 75 ppm). ZD rats received continuous s.c. infusion of bovine growth hormone (bGH) (100 microg/d) for the 4 weeks or for the last week of the study. Compared with pair-fed rats, zinc deficiency produced attenuated weight gain (-43%, P < 0.001), lower serum IGF-I and liver IGF-I mRNA (-52%, P < 0.001 and -44%, P < 0.05), lower serum IGFBPs (IGFBP-3 -66%, IGFBP-4 -48%, 34-29 kDa IGFBP cluster -53%, P < 0.05), lower liver GHR and its mRNA (-20 and -34%, P < 0.05) and lower serum growth hormone binding protein (GHBP) and its mRNA (-56 and -48%, P < 0.05; all comparisons vs PF rats). Exogenous bGH given continuously normalized the liver GHR, serum GHBP and their liver mRNAs, as well as circulating IGFBPs. Despite restoration of GHR and GHBP to normal, growth, serum IGF-I and its liver mRNA were not stimulated by GH infusion in ZD rats, indicating that IGF-I synthesis requires the presence of zinc in addition to GH, and that the lack of growth-promoting action of GH in zinc-deprived rats results from a defect beyond GH binding to its liver receptors.

Human renal fibroblasts modulate proximal tubule cell growth and transport via the IGF-I axis

To determine the paracrine interactions involved in the tubulointerstitial response to progressive renal disease, the role of insulin-like growth factor-I (IGF-I) and its binding proteins (IGFBPs) in in vitro interactions between human proximal tubule cells (PTC) and renal cortical fibroblasts (CF) were studied in primary cell culture. PTC growth and transport were increased in the presence of CF-conditioned media (CF-CM), as shown by increased thymidine incorporation, cellular protein content and sodium-hydrogen exchange (NHE) activity, to 185 +/- 31% (P < 0.01), 150 +/- 18% (P < 0.05) and 195 +/- 27% (P < 0.01) of the control values, respectively. IGF-I was produced by cultured CF at a rate of 64.6 +/- 7.5 ng/mg protein/day. Exogenous IGF-I applied to PTC provoked similar enhancement of growth and NHE activity as CF-CM and the stimulatory effect of CF-CM was blocked by specific immunoneutralization of IGF-I receptors. These receptors were threefold more abundant on PTC basolateral versus apical membranes. IGF binding proteins (IGFBP)-2 and IGFBP-3 were secreted by CF at rates of 694 +/- 88 and 1769 +/- 45 ng/mg/day, with the release of IGFBP-3 being enhanced in the presence of PTC-CM (120.0 +/- 9.7% of control, P < 0.01). Moreover, the addition of CF-CM to PTC increased cell-associated IGFBP-3 on PTC surfaces, without changes in IGF-I receptor numbers or affinity and without changes in PTC mRNA for IGFBP-3. Des(1-3)IGF-I, an analog that binds to the IGF-I receptor but not to IGFBPs, provided a less potent stimulus for PTC growth compared with IGF-I, indicating that cell-associated IGFBP-3 facilitates the action of IGF-I on PTC. The results support important paracrine roles for both IGF-I and IGFBPs in the interstitial regulation of proximal tubule growth and transport.

Protective effect of glutamine from glucocorticoid-induced muscle atrophy occurs without alterations in circulating insulin-like growth factor (IGF)-I and IGF-binding protein levels.

We investigated whether the prevention of glucocorticoid-induced muscle atrophy by glutamine infusion is associated with alterations in serum levels of insulin-like growth factor (IGF)-I and its binding proteins (IGFBPs). Hormone (cortisol acetate [CA], 100 mg/kg body wt/day) and vehicle (carboxymethyl cellulose [CMC])-treated female rats were infused with either saline or glutamine (240 mM, 0.75 ml/hr) for a 7-day period. Glutamine infusion prevented over 70% of the skeletal muscle mass loss due to the glucocorticoid injections. Serum IGF-I concentrations, which were measured by radioimmunoassay (RIA) after acid solid-phase extraction of IGFBPs, were not significantly different among groups (range of means: 373-395 ng/ml). Saline/CA treatment resulted in a 2-fold increase in circulating levels of IGFBP-3 (38- to 50-kDa bands from ligand blotting measurements) versus the saline/CMC group. Levels of 30- to 32-kDa bands were increased by approximately 3-fold in the CA-treated rats. Immunoprecipitation studies suggested that the increase in the 30- to 32-kDa binding proteins were not due to elevated levels of IGFBP-1, -2, or -5. None of the treatments significantly modified circulating levels of IGFBP-4 (24 kDa). Glutamine infusion did not reverse the effects of glucocorticoids on circulating levels of 38- to 50- and 30- to 32-kDa IGFBPs. We conclude that the attenuation of glucocorticoid-induced muscle atrophy by glutamine infusion is not associated with changes in circulating levels of IGF-I or IGFBPs.

Nutritional regulation of insulin-like growth factor-I

Several lines of evidence indicate that in the human, insulin-like growth factor-I (IGF-I) is nutritionally regulated. Both energy and protein availability are required for maintenance of IGF-I. Measurements of serum IGF-I constitute a sensitive means for monitoring the response of acutely ill patients to nutritional intervention. Serum IGF-I may also serve as a marker for evaluation of nutritional status. Our findings and those of others in animal models suggest that nutrients influence synthesis and action of IGF-I and its binding proteins (IGFBPs) at multiple levels. In fasting, liver growth hormone (GH) binding is decreased, providing one explanation for decreased IGF-I. In protein restriction, GH receptors are maintained, but there is evidence for a postreceptor defects. The latter results from pretranslational and translational defects. Amino acid availability to the hepatocytes is essential for IGF-I gene expression. Protein malnutrition not only decreases IGF-I production rate, but also enhances its serum clearance and degradation. Finally, there is evidence for selective organ resistance to the growth-promoting effects of IGF-I in protein-restricted rats.

Opposite vectorial secretion of insulin-like growth factor I and its binding proteins by pig Sertoli cells cultured in the bicameral chamber system.

A two-chamber system has been employed to investigate the vectorial secretion of insulin-like growth factor I (IGF-I) and its binding proteins (IGF-BPs) by pig Sertoli cells. The kinetics of transport of [3H]insulin as well as the transepithelial electrical resistance of filters coated with reconstituted basement membrane, in the absence of presence of Sertoli cells, indicated the formation of a functional barrier by Sertoli cells. The rates of diffusion of [125I]IGF-I or [125I]human CG were slower from the apical (AC) to the basal (BC) compartment than in the opposite direction. However, the IGF-I content and concentration in the BC was twice that seen in the AC. FSH increased the secretion of IGF-I in the BC, and therefore increased the BC/AC ratio. In contrast, most of the IGF-BPs, with apparent molecular sizes of 39-43, 34, 29 and 24 kDa, were secreted in the AC. FSH increased the secretion of IGF-BP 39-43 kDa (BP3). This is the first report of opposite vectorial secretion of IGF-I and its binding protein by any cell type.

Insulin-like growth factor binding protein measurement: Sodium dodecyl sulfate-stable complexes with insulin-like growth factor in serum prevent accurate assessment of total binding protein content by ligand blotting

The possibility that sodium dodecyl sulfate (SDS)-stable complexes of insulin-like growth factor I (IGF-I) and its binding proteins (IGF-BP) exist in rat serum has been examined by using SDS-polyacrylamide gel electrophoresis (PAGE) followed by both [ 125I]IGF-I ligand blotting and immunoblotting with antisera directed against either IGF-BP3 or IGF-I. While ligand blotting of rat serum only revealed free IGF-BP subunits ( M r ≈ 50, 35, and 30 kDa, immunoblotting with either the IGF-BP3 antiserum or IGF-I antiserum revealed major immunoreactive bands with higher molecular weights (>110, ≈100, and ≈84 kDa). The IGF-BP3 antiserum also stained the 50-kDa form of the serum IGF-BP. Specifically stained protein bands were identified by comparison with control immunoblots incubated with normal rabbit serum. Treating the serum with 0.1 n HCl prior to electrophoresis reduced the amount of high molecular weight IGF-BP3 immunoreactive species, with a concomitant increase in the amount of the 50-kDa form. A similar result was obtained if the samples were boiled prior to electrophoresis. These data indicate that not all IGF-BP IGF complexes may dissociate under normal SDS-PAGE conditions. Therefore, data obtained by using ligand blotting alone may underestimate the amount of total IGF-BP present, especially if the mixture being analyzed also contains large amounts of IGF.