Protein QTL analysis of IGF-I and its binding proteins provides insights into growth biology.

The growth hormone and insulin-like growth factor (IGF) system is integral to human growth. Genome-wide association studies (GWAS) have identified variants associated with height and located near the genes in this pathway. However, mechanisms underlying these genetic associations are not understood. To investigate the regulation of the genes in this pathway and mechanisms by which regulation could affect growth, we performed GWAS of measured serum protein levels of IGF-I, IGF binding protein-3 (IGFBP-3), pregnancy-associated plasma protein A (PAPP-A2), IGF-II and IGFBP-5 in 838 children (3-18 years) from the Cincinnati Genomic Control Cohort. We identified variants associated with protein levels near IGFBP3 and IGFBP5 genes, which contain multiple signals of association with height and other skeletal growth phenotypes. Surprisingly, variants that associate with protein levels at these two loci do not colocalize with height associations, confirmed through conditional analysis. Rather, the IGFBP3 signal (associated with total IGFBP-3 and IGF-II levels) colocalizes with an association with sitting height ratio (SHR); the IGFBP5 signal (associated with IGFBP-5 levels) colocalizes with birth weight. Indeed, height-associated single nucleotide polymorphisms near genes encoding other proteins in this pathway are not associated with serum levels, possibly excluding PAPP-A2. Mendelian randomization supports a stronger causal relationship of measured serum levels with SHR (for IGFBP-3) and birth weight (for IGFBP-5) than with height. In conclusion, we begin to characterize the genetic regulation of serum levels of IGF-related proteins in childhood. Furthermore, our data strongly suggest the existence of growth-regulating mechanisms acting through IGF-related genes in ways that are not reflected in measured serum levels of the corresponding proteins.

Differential production of insulin-like growth factor-binding proteins in liver fibrosis progression.

Noninvasive methods for liver disease diagnoses offer great advantages over biopsy, but they cannot be utilized in all cases. Therefore, specific indicators for chronic liver disease management are necessary. The aim was to assess the production of insulin-like growth factor-binding proteins (IGFBPs) 1-7 and their correlation with the different stages of fibrosis in chronic hepatitis C (CHC). A prospective, cross-sectional, multicenter study was conducted. CHC patients were categorized by FibroTest® and/or FibroScan®. Serum concentrations of IGFBPs 1-7 were determined through multiple suspension arrangement array technology. Significant differences were validated by the Kruskal-Wallis and Mann-Whitney U tests. Logistic regression models were performed to assess the association between the IGFBPs and fibrosis stages. The association was determined utilizing odds ratios (ORs), and receiver operating characteristic (ROC) curves were constructed to distinguish the IGFBPs in relation to the diagnosis of fibrosis. IGFBP-1 and IGFBP-7 concentrations were higher in CHC than in the healthy individuals, whereas IGFBP-3, IGFBP-5, and IGFBP-6 were downregulated in the patients. An apparent increase of all the IGFBPs was found at fibrosis stage F4, but with different regulations. IGFBP-2, -4, -6, and -7 had the best OR, showing the relation to fibrosis progression. The ROC curves showed that IGFBP-7 was the only protein that distinguished F1 from F3 and F2 from F3. IGFBPs participate in liver fibrosis progression and could be employed as circulating novel protein panels for diagnosis and as possible therapeutic targets in liver fibrosis progression.

Interference of stress with the somatotropic axis in pigs - lights on new biomarkers.

The acceptance of animal products is increasingly associated with standardized animal welfare, which relates to appropriate animal husbandry from birth to slaughter. In particular, shipment to the slaughterhouse is considered as a critical process exposing the animals to a number of, in part severe, stressors. New biomarkers may be useful for the assessment of animal welfare. The IGF-system has been assessed in a commercial pig transport in conjunction with established markers of stress response. Furthermore, the effect of repeated restraint as an experimental model for repeated acute stress was investigated. During shipment from farm to slaughterhouse, plasma concentrations of IGFBP-3 and IGFBP-2 were significantly reduced (p < 0.01). After shipment, the plasma concentrations of IGFBP-5, glucocorticoids and IL-2 increased but decreased after lairage (p < 0.05) whereas IGF-1 decreased after shipment (p < 0.01). Repeated acute stress increased concentrations of IGFBP-3 and IGF-1 in exsanguination blood (p < 0.05). Differential IGF- signatures can indicate altered endocrine or metabolic control and thus contain complex animal-related information. The somatotropic axis may be of particular interest when established biomarkers such as cortisol, glucose, or lactate cannot be used for the assessment of animal stress or welfare.

Quantitative and Selective Analysis of Feline Growth Related Proteins Using Parallel Reaction Monitoring High Resolution Mass Spectrometry.

Today immunoassays are widely used in veterinary medicine, but lack of species specific assays often necessitates the use of assays developed for human applications. Mass spectrometry (MS) is an attractive alternative due to high specificity and versatility, allowing for species-independent analysis. Targeted MS-based quantification methods are valuable complements to large scale shotgun analysis. A method referred to as parallel reaction monitoring (PRM), implemented on Orbitrap MS, has lately been presented as an excellent alternative to more traditional selected reaction monitoring/multiple reaction monitoring (SRM/MRM) methods. The insulin-like growth factor (IGF)-system is not well described in the cat but there are indications of important differences between cats and humans. In feline medicine IGF-I is mainly analyzed for diagnosis of growth hormone disorders but also for research, while the other proteins in the IGF-system are not routinely analyzed within clinical practice. Here, a PRM method for quantification of IGF-I, IGF-II, IGF binding protein (BP) -3 and IGFBP-5 in feline serum is presented. Selective quantification was supported by the use of a newly launched internal standard named QPrEST™. Homology searches demonstrated the possibility to use this standard of human origin for quantification of the targeted feline proteins. Excellent quantitative sensitivity at the attomol/µL (pM) level and selectivity were obtained. As the presented approach is very generic we show that high resolution mass spectrometry in combination with PRM and QPrEST™ internal standards is a versatile tool for protein quantitation across multispecies.

Serum concentrations of insulin-like growth factor-binding protein 5 in Crohn's disease.

AIM: To investigate serum insulin-like growth factor-binding protein 5 (IGFBP-5) levels and intestinal IGFBP-5 expression in patients with Crohn's disease (CD). METHODS: We analyzed the serum concentrations and intestinal expression of IGFBP-5 in 42 patients with CD, of whom 26 had endoscopically or radiologically proven stricture formation. Nine of the 42 patients had active disease, with a Crohn's disease activity index > 150. Serum IGFBP-5 levels were analyzed in 20 healthy controls matched by sex and age to the CD patients. Serum IGFBP-5 was measured using an enzyme-linked immunosorbent assay. Intestinal tissue was obtained from patients through endoscopic biopsies. IGFBP-5 expression was detected using immunohistochemistry and was scored semiquantitatively. RESULTS: The median serum IGFBP-5 concentrations of CD patients were significantly lower compared with healthy controls [median 7.2 (IQR: 5.5-11.3) ng/mL vs 11.3 (8.0-44.6) ng/mL, P < 0.001]. There was no significant difference between median serum IGFBP-5 levels in CD patients with or without stricture formation [6.9 (5.5-11.3) ng/mL vs 7.8 (5.3-10.1) ng/mL, P = 0.815]. The serum IGFBP-5 levels were not significantly different between patients with active disease and inactive disease [7.2 (6.5-7.6) ng/mL vs 7.2 (5.5-11.3) ng/mL, P = 0.890]. However, a significant correlation was observed between serum IGFBP-5 levels and platelet count (PLT) (r = 0.319, P = 0.0395). No significant correlation was found between tissue IGFBP-5 immunohistochemical staining intensity scores and serum IGFBP-5 levels. No significant difference was found when comparing the serum IGFBP-5 levels among the patients with different tissue IGFBP-5 staining scores (absent/very weak, weak, moderate or strong). There was a significant correlation between tissue IGFBP-5 staining scores and white blood cell count (r = 0.391, P = 0.01) and PLT (r = 0.356, P = 0.021). CONCLUSION: Our results indicate that serum IGFBP-5 concentrations were lower in CD patients compared to healthy controls regardless of disease activity or the presence of stricture formation.

Female recruits sustaining stress fractures during military basic training demonstrate differential concentrations of circulating IGF-I system components: a preliminary study.

OBJECTIVE: Stress fracture injuries sustained during military basic combat training (BT) are a significant problem and occur at a higher rate in female recruits than male recruits. Insulin-like growth factor-I (IGF-I) is an easily measured biomarker that is involved in bone formation and positively correlated with bone mineral density, especially in women. This study examined the response of the IGF-I system between female soldiers that sustained a stress fracture (SFX, n=13) during BT and female soldiers who did not (NSFX, n=49). DESIGN: Female soldiers (n=62, 18.8 ± 0.6 yr) from 2 companies of a gender-integrated combat battalion in the Israeli Defense Forces participated in this study. Height, weight and blood draws were taken upon entry to BT (preBT) and after a four-month BT program (postBT). Stress fractures were diagnosed by bone scan. Serum was analyzed for total IGF-I, free IGF-I, IGF binding proteins (IGFBP)1-6, BAP, calcium, CTx, IL1ß, IL6, PINP, PTH, TNFα, TRAP, and 25(OH)D. Statistical differences between SFX and NSFX groups and time points were assessed by RM ANOVA with Fisher post-hoc (p≤0.05). RESULTS: The SFX group was significantly taller and had lower BMI than NSFX (p≤0.05). Serum concentrations of total IGF-I, bioavailable IGF-I, other bone biomarkers, and cytokines were not significantly different between SFX and NSFX preBT. Serum IGFBP-2 and IGFBP-5 were significantly higher in the SFX compared to the NSFX preBT (p≤0.05). In both groups, total IGF-I increased pre to postBT (p≤0.05). Additionally, a significant difference was observed in the bioavailable IGF-I response pre to postBT for both groups. The SFX group demonstrated a significant decrease in bioavailable IGF-I pre to postBT (preBT: 0.58 ± 0.58 ng/mL; postBT 0.39 ± 0.48; p≤0.05) whereas the NSFX group demonstrated a significant increase in bioavailable IGF-I pre to postBT (preBT: 0.53 ± 0.37 ng/mL; postBT: 0.63 ± 0.45; p≤0.05). CONCLUSIONS: Our study demonstrated that serum IGF-I changes during basic training and that women sustaining stress fractures during BT significantly decreased bioavailable IGF-I, whereas their uninjured counter parts increased bioavailable IGF-I. These results suggest that stress fracture susceptibility may be related to differential IGF-I system concentrations and response to physical training.

Serum concentrations of human insulin-like growth factor-1 and levels of insulin-like growth factor-binding protein-5 in patients with nonalcoholic fatty liver disease: association with liver histology.

OBJECTIVE: In this study, we aimed to investigate the relationship between the histological features of nonalcoholic fatty liver disease (NAFLD) and serum insulin-like growth factor-1 (IGF-1) and insulin-like growth factor-binding protein-5 (IGFBP-5) to determine the usefulness of this relationship in clinical practice. MATERIALS AND METHODS: Serum samples were collected from 92 patients with biopsy-proven NAFLD and 51 healthy controls and serum levels of IGF-1 and IGFBP-5 were assayed by enzyme-linked immunosorbent assay. RESULT: Serum IGFBP-5 levels were correlated with liver steatosis, fibrosis, and nonalcoholic steatohepatitis scores. IGF-1 levels were significantly decreased in patients with moderate-to-severe fibrosis compared with patients with no or mild fibrosis. CONCLUSION: Serum IGFBP-5 levels may be useful to differentiate both advanced fibrosis and definite nonalcoholic steatohepatitis from other NAFLD groups. Also, serum IGF-1 levels may be useful to differentiate advanced fibrosis in patients with NAFLD.

Effect of growth hormone administration to mature miniature Brahman cattle treated with or without insulin on circulating concentrations of insulin-like growth factor-I and other metabolic hormones and metabolites.

Previously, we determined that a primary cause of proportional stunted growth in a line of Brahman cattle was related to an apparent refractoriness in metabolic response to GH in young animals. The objective of this study was to determine the effect of administration of GH, insulin (INS), and GH plus INS to mature miniature Brahman cows (n = 6; 9.7 ± 2.06 y; 391 ± 48.6 kg) and bulls (n = 8; 9.4 ± 2.00 y; 441 ± 54.0 kg) on circulating concentrations of metabolic hormones and metabolites, primarily IGF-I and IGF-I binding proteins. We hypothesized that IGF-I secretion could be enhanced by concomitant administration of exogenous GH and INS, and neither alone would be effective. Animals were allotted to a modified crossover design that included four treatments: control (CON), GH, INS, and GH + INS. At the start of the study, one-half of the cattle were administered GH (Posilac; 14-d slow release) and the other one-half served as CON for 7 d. Beginning on day 8, and for 7 d, INS (Novolin L) was administered (0.125 IU/kg BW) twice daily (7:00 AM and 7:00 PM) to all animals; hence, the INS and GH + INS treatments. Cattle were rested for 14 d and then were switched to the reciprocal crossover treatments. Blood samples were collected at 12-hour intervals during the study. Compared with CON, GH treatment increased (P < 0.01) mean plasma concentrations of GH (11.1 vs 15.7 ± 0.94 ng/mL), INS (0.48 vs 1.00 ± 0.081 ng/mL), IGF-I (191.3 vs 319.3 ± 29.59 ng/mL), and glucose (73.9 vs 83.4 ± 2.12 mg/dL) but decreased (P < 0.05) plasma urea nitrogen (14.2 vs 11.5 ± 0.75 mg/dL). Compared with INS, GH + INS treatment increased (P < 0.05) mean plasma concentration of INS (0.71 vs 0.96 ± 0.081 ng/mL), IGF-I (228.7 vs 392.3 ± 29.74 ng/mL), and glucose (48.1 vs 66.7 ± 2.12 mg/dL), decreased (P < 0.01) plasma urea nitrogen (13.6 vs 10.4 ± 0.76 mg/dL), and did not affect GH (13.5 vs 12.7 ± 0.95 ng/mL). In the miniature Brahman model, both the GH and GH + INS treatments dramatically increased circulating concentrations of IGF-I in mature cattle, suggesting that this line of Brahman cattle is capable of responding to bioactive GH.

Prepubertal OVX increases IGF-I expression and bone accretion in C57BL/6J mice.

It is generally well accepted that the pubertal surge in estrogen is responsible for the rapid bone accretion that occurs during puberty and that this effect is mediated by an estrogen-induced increase in growth hormone (GH)/insulin-like growth factor (IGF) action. To test the cause and effect relationship between estrogen and GH/IGF, we evaluated the consequence of ovariectomy (OVX) in prepubertal mice (C57BL/6J mice at 3 wk of age) on skeletal changes and the GH/IGF axis during puberty. Contrary to our expectations, OVX increased body weight (12-18%), bone mineral content (11%), bone length (4%), bone size (3%), and serum, liver, and bone IGF-I (30-50%) and decreased total body fat (18%) at 3 wk postsurgery. To determine whether estrogen is the key ovarian factor responsible for these changes, we performed a second experiment in which OVX mice were treated with placebo or estrogen implants. In addition to observing similar results compared with our first experiment, estrogen treatment partially rescued the increased body weight and bone size and completely rescued body fat and IGF-I levels. The increased bone accretion in OVX mice was due to increased bone formation rate (as determined by bone histomorphometry) and increased serum procollagen peptide. In conclusion, contrary to the known estrogen effect as an initiator of GH/IGF surge and thereby pubertal growth spurt, our findings demonstrate that loss of estrogen and/or other hormones during the prepubertal growth period effect leads to an increase in IGF-I production and bone accretion in mice.

IGF-1 and IGF-binding proteins and bone mass, geometry, and strength: relation to metabolic control in adolescent girls with type 1 diabetes.

Children and adolescents with poorly controlled type 1 diabetes mellitus (T1DM) are at risk for decreased bone mass. Growth hormone (GH) and its mediator, IGF-1, promote skeletal growth. Recent observations have suggested that children and adolescents with T1DM are at risk for decreased bone mineral acquisition. We examined the relationships between metabolic control, IGF-1 and its binding proteins (IGFBP-1, -3, -5), and bone mass in T1DM in adolescent girls 12-15 yr of age with T1DM (n = 11) and matched controls (n = 10). Subjects were admitted overnight and given a standardized diet. Periodic blood samples were obtained, and bone measurements were performed. Serum GH, IGFBP-1 and -5, glycosylated hemoglobin (HbA(1c)), glucose, and urine magnesium levels were higher and IGF-1 values were lower in T1DM compared with controls (p < 0.05). Whole body BMC/bone area (BA), femoral neck areal BMD (aBMD) and bone mineral apparent density (BMAD), and tibia cortical BMC were lower in T1DM (p < 0.05). Poor diabetes control predicted lower IGF-1 (r(2) = 0.21) and greater IGFBP-1 (r(2) = 0.39), IGFBP-5 (r(2) = 0.38), and bone-specific alkaline phosphatase (BALP; r(2) = 0.41, p < 0.05). Higher urine magnesium excretion predicted an overall shorter, lighter skeleton, and lower tibia cortical bone size, mineral, and density (r(2) = 0.44-0.75, p < 0.05). In the T1DM cohort, earlier age at diagnosis was predictive of lower IGF-1, higher urine magnesium excretion, and lighter, thinner cortical bone (r(2) >or=0.45, p < 0.01). We conclude that poor metabolic control alters the GH/IGF-1 axis, whereas greater urine magnesium excretion may reflect subtle changes in renal function and/or glucosuria leading to altered bone size and density in adolescent girls with T1DM.

Plasma proteome profiling of a mouse model of breast cancer identifies a set of up-regulated proteins in common with human breast cancer cells.

We have applied an in-depth quantitative proteomic approach, combining isotopic labeling extensive intact protein separation and mass spectrometry, for high confidence identification of protein changes in plasmas from a mouse model of breast cancer. We hypothesized that a wide spectrum of proteins may be up-regulated in plasma with tumor development and that comparisons with proteins expressed in human breast cancer cell lines may identify a subset of up-regulated proteins in common with proteins expressed in breast cancer cell lines that may represent candidate biomarkers for breast cancer. Plasma from PyMT transgenic tumor-bearing mice and matched controls were obtained at two time points during tumor growth. A total of 133 proteins were found to be increased by 1.5-fold or greater at one or both time points. A comparison of this set of proteins with published findings from proteomic analysis of human breast cancer cell lines yielded 49 proteins with increased levels in mouse plasma that were identified in breast cancer cell lines. Pathway analysis comparing the subset of up-regulated proteins known to be expressed in breast cancer cell lines with other up-regulated proteins indicated a cancer related function for the former and a host-response function for the latter. We conclude that integration of proteomic findings from mouse models of breast cancer and from human breast cancer cell lines may help identify a subset of proteins released by breast cancer cells into the circulation and that occur at increased levels in breast cancer.

Increased serum concentration of IGFBP-4 and IGFBP-5 in healthy adults during one month's treatment with supraphysiological doses of growth hormone.

OBJECTIVES: To study the effects on insulin-like growth factor binding proteins (IGFBP)-4 and -5 after one month's treatment with supraphysiological doses of growth hormone (GH) in healthy, active young adults with a normal GH-IGF-I axis. Furthermore, the possible use of IGFBP-4 and IGFBP-5 as markers of GH doping is discussed. DESIGN: Thirty healthy, physically active volunteers (15 men and 15 women), mean age 25.9 years (range 18-35), participated in this randomized, double-blind, placebo-controlled, parallel study with three groups (n=10; 5 men and 5 women in each group). The groups comprised the following: placebo, GH 0.1IU/kg/day [0.033mg/kg/day] and GH 0.2IU/kg/day [0.067mg/kg/day]. RESULTS: Baseline levels of IGFBP-4 were higher (+20%), while IGFBP-5 levels were lower (-37%) in women than in men. IGFBP-5 levels were positively correlated to age, but no significant correlation was found for IGFBP-4. In the pooled group with active GH treatment (n=20), both IGFBP-4 and IGFBP-5 levels were increased vs. the placebo group from day 14 until end of treatment [day 28, IGFBP-4 (+40%, p<0.01) and IGFBP-5 (+61%, p <0.001)]. After inclusion of serum IGF-I as a covariate in the linear regression analysis, the associations between GH treatment and the IGFBP-4 and IGFBP-5 levels were not significant. CONCLUSIONS: This study shows that the levels of IGFBP-4 and IGFBP-5 are affected by supraphysiological GH treatment given to young, healthy, physically active adults of both genders. The present study, including relatively few subjects, does not support that IGFBP-4 and IGFBP-5 can be used as IGF-I independent markers in a forthcoming method for detecting GH doping, although, further studies are needed to investigate the potential use of IGFBP-4 and IGFBP-5 as markers of GH doping.

Effects of GH and/or sex steroids on circulating IGF-I and IGFBPs in healthy, aged women and men.

Circulating GH, IGF-I, IGFBP-3, and sex steroid concentrations decrease with age. GH or sex steroid treatment increases IGFBP-3, but little is known regarding the effects of these hormones on other IGFBPs. We assessed the effects of 26 wk of administration of GH, sex steroids, or GH + sex steroids on AM levels of IGF-I, IGFBPs 1-5, insulin, glucose, and osteocalcin and 2-h urinary excretion of deoxypyridinolline (DPD) cross-links in 53 women and 71 men aged 65-88 yr. Before treatment, in women and men, IGF-I was directly related to IGFBP-3 (P < 0.001 and P < 0.0001) and IGFBP-1 to IGFBP-2 (P = 0.0001). In women, IGFBP-1 was inversely related to insulin (P < 0.0005) and glucose (P < 0.005) and IGFBP-4 to osteocalcin (P < 0.01). IGFBP-4 and IGFBP-5 were not significantly related to DPD cross-links. GH and/or sex steroid increased IGF-I levels in both sexes, with higher concentrations in men (P < 0.001). In women, the IGF-I increment after GH was attenuated by hormone replacement therapy (HRT) coadministration (P < 0.05). Hormone administration also increased IGFBP-3. IGFBP-1 was unaffected by GH + sex steroids, whereas GH decreased IGFBP-2 by 15% in men (P < 0.05). Hormone administration did not change IGFBP-4, whereas in men IGFBP-5 increased by 20% after GH (P < 0.05) and 56% after GH + testosterone (P = 0.0003). These data demonstrate sexually dimorphic IGFBP responses to GH. Additionally, HRT attenuated or prevented GH-mediated increases in IGF-I and IGFBP-3. Whether GH and/or sex steroid administration alters local tissue production of IGFBPs and whether the latter influence autocrine or paracrine actions of IGF-I remain to be determined.

Serum levels of insulin-like growth factor (IGF); IGF-binding proteins-3, -4, and -5; and their relationships to bone mineral density and the risk of vertebral fractures in postmenopausal women.

We previously found that serum levels of insulin-like growth factor I (IGF-I) and IGF-binding protein (IGFBP)-3, but not IFGBP-2, were associated with bone mineral density (BMD) and the risk of vertebral fractures. The aim of the present study was to investigate the roles of IGFBP-4 and -5 in age-dependent bone loss and vertebral fracture risk in postmenopausal Japanese women and to compare them with those of IGF-I and IGFBP-3. One hundred and ninety-three Japanese women aged 46-88 years (mean 62.5) were enrolled in the cross-sectional study. BMD was measured at the lumbar spine, femoral neck, ultradistal radius (UDR), and total body by dual-energy X-ray absorptiometry. Serum levels of IGFBP-4 and -5 as well as IGF-I and IGFBP-3 were measured by radioimmunoassay. Serum levels of IGF-I, IGFBP-3, and IGFBP-5 declined with age, while serum IGFBP-4 increased with age. Multiple regression analysis was performed between BMD at each skeletal site and serum levels of IGF-I and IGFBPs adjusted for age, body weight, height, and serum creatinine. BMD at the UDR was significantly and positively correlated with all serum levels of IGF-I and IGFBPs measured (P < 0.01), while BMD at the femoral neck was correlated with none of them. Serum IGF-I level was significantly and positively correlated with BMD at all sites except the femoral neck (P < 0.01), while serum IGFBP-3 and -4 levels were significantly and positively correlated with only radial BMD (P < 0.01). Serum IGFBP-5 level was positively correlated with UDR BMD (P < 0.001) and negatively correlated with total BMD (P < 0.05). Serum IGF-I, IGFBP-3, and IFGBP-5 levels were significantly lower in women with vertebral fractures than in those without fractures (mean +/- SD: 97.1 +/- 32.1 vs. 143.9 +/- 40.9 ng/dl, P < 0.0001; 2.18 +/- 1.02 vs. 3.23 +/- 1.07 microg/ml, P < 0.0001; 223.6 +/- 63.3 vs. 246.5 +/- 71.5 ng/ml, P = 0.0330, respectively). When multivariate logistic regression analysis was performed with the presence of vertebral fractures as a dependent variable and serum levels of IGF-I and IGFBPs adjusted for age, body weight, height, serum creatinine, and serum alubumin as independent variables, IGF-I and IGFBP-3 were selected as indices affecting the presence of vertebral fractures [odds ratio (OR) = 0.29, 95% confidential interval (CI) 0.15-0.57 per SD increase, P = 0.0003 and OR = 0.31, 95% CI 0.16-0.61 per SD increase, P = 0.0007, respectively]. To compare the significance values, IGF-I, IGFBP-3, and age were simultaneously added as independent variables in the analysis. IGFBP-3 was more strongly associated with the presence of vertebral fractures than IGF-I and age (P = 0.0006, P = 0.0148, and P = 0.0013, respectively). Thus, after comprehensive measurements of serum levels of IGF-I and IGFBPs, it seems that serum IGF-I level is most efficiently associated with bone mass and that serum IGFBP-3 level is most strongly associated with the presence of vertebral fractures in postmenopausal women among the IGF system components examined.

Insulin-like growth factor-I (IGF-I) attenuates jejunal atrophy in association with increased expression of IGF-I binding protein-5 in parenterally fed mice.

Total parenteral nutrition (TPN) induces dramatic mucosal hypoplasia in rat small intestine that is attenuated by insulin-like growth factor-I (IGF-I). Our aim was to determine the extent of TPN-induced intestinal atrophy and its response to infusion of IGF-I in mice. Male C57BL/6 mice (18-22 g) were maintained with TPN, TPN plus co-infusion of recombinant human IGF-I [2.5 mg/(kg . d)] or oral feeding for 5 d. Body weights did not differ among the groups although serum IGF-I was increased by 78% with IGF-I infusion. IGF-I prevented the significant 25% reduction in mass of the intact small intestine due to TPN compared with oral feeding. Greater TPN-induced atrophy was noted in duodenum and jejunum than ileum. Jejunal atrophy induced by TPN reflected significant decreases in muscularis mass and concentrations of protein and DNA; mucosal cellularity was not altered by TPN. TPN induced a significant decrease in jejunal muscularis width that was reversed by IGF-I with no differences in mucosal villus height and crypt depth. Local expression of IGF-I binding protein (IGFBP)-5 positively modulates the intestinotrophic effects of IGF-I. Jejunal atrophy due to TPN and growth due to IGF-I were directly associated with expression of IGFBP-5 mRNA. TPN decreased IGFBP-5 mRNA by 60% and IGF-I increased IGFBP-5 mRNA by 200% with no change in IGF-I mRNA compared with oral feeding. In summary, TPN induces significant 25% atrophy of the mouse small intestine that is attenuated by IGF-I in association with increased expression of IGFBP-5. Compared with rats, TPN-induced atrophy is less severe and occurs primarily in the jejunal muscularis layer in mice.

Ethinylestradiol and testosterone have divergent effects on circulating IGF system components in adolescents with constitutional tall stature.

OBJECTIVE: Pharmacological doses of estrogens or testosterone are used to limit the final height of girls or boys with constitutional tall stature but the mechanism behind this growth inhibition is still debated. We therefore studied the changes in the circulating components of the insulin-like growth factor (IGF) system during high dose sex steroid therapy. DESIGN AND METHODS: Twenty three girls and twenty boys with constitutional tall stature were treated with 100 microg ethinylestradiol per day or 250 mg testosterone ester every 14 days respectively. In 19 girls and 18 boys, the levels of IGF-I, free IGF-I, IGF-II, acid-labile subunit (ALS) and IGF binding proteins (IGFBP)-2 to -6 were measured before and 3-6 months after the start of therapy (group 1). In 18 girls and 11 boys, samples were collected at the end of therapy and 3 to 6 months afterwards (group 2). Fourteen girls and nine boys belonged to both groups. All parameters were measured by radioimmunoassay or ELISA. RESULTS: Levels of IGF-I were decreased significantly by estrogen treatment but remained unchanged during testosterone treatment. Free IGF-I decreased during estrogen treatment but increased during testosterone therapy. Estrogens increased IGF-II and testosterone reduced it. The important reduction of IGFBP-2 during estrogen therapy is not reproduced by androgen therapy, neither is the stimulation by estrogens of IGFBP-4. IGFBP-3 is not modulated by either sex steroid. We found that IGFBP-6 is up-regulated by testosterone but not by estrogens; the reverse is true for ALS, which increased during estrogen treatment but remained unchanged during testosterone treatment. CONCLUSIONS: Our findings demonstrate that androgens and estrogens exert differential effects on the circulating levels of several IGF components.

Insulin-like growth factor-binding protein-5 induces a gender-related decrease in bone mineral density in transgenic mice.

IGF-binding protein-5 (IGFBP-5) is abundant in serum and bone during normal skeletal development, but levels decrease in osteoporosis. Studies have shown that IGFBP-5 stimulates markers of bone formation by potentiating IGF actions and by IGF-independent actions. To test the hypothesis that IGFBP-5 promotes the acquisition of bone mineral density (BMD), we generated transgenic (Tg) mice overexpressing Igfbp5 using a cytomegalovirus enhancer and beta-actin promoter (CMV/betaA). Tg animals showed an increase in serum IGFBP-5 concentrations by 7.7- to 3.5-fold at 3-8 wk of age, respectively. Concentrations were 6-49% higher for males compared with females in both wild-type and Tg mice. Surprisingly, BMD decreased in a gender-dependent manner, with Tg male adults affected more severely than Tg females (31.3% vs. 19.2% reduction, respectively, compared with wild-type mice, assessed by dual energy x-ray absorptiometry). Significant gender differences in BMD were confirmed by peripheral quantitative computed tomography. Histomorphometry revealed that although the bone formation rate and mineralizing surface at the periosteum decreased in Tg mice, they increased at the endosteum, suggesting opposing effects of IGFBP-5 on periosteal and endosteal osteoblasts (by altering proliferation or survival). These findings differ from previous observations in Igf1- and Igf2-null animals. In conclusion, IGFBP-5 has a significant influence on BMD acquisition and maintenance that is dependent on gender and age. The phenotype of Igfbp5 mice cannot be explained solely by IGF inhibition; thus, this study provides the first in vivo evidence, by genetic manipulation, for IGF-independent actions of IGFBP-5 in bone function. These findings have implications for the gender-biased progression of osteoporosis.

Associations of insulin-like growth factors, insulin-like growth factor binding proteins and acid-labile subunit with coronary heart disease.

OBJECTIVE: IGFs and their binding proteins (IGFBPs) are produced both systemically and locally by cells of the cardiovascular system. As growth promoters, they may play a role in atherosclerosis. DESIGN: Case-control, cross-sectional. PATIENTS: A total of 95 nondiabetic male patients with coronary heart disease (CHD) and 92 probands from the Prospective Cardiovascular Munster (PROCAM) who were below the age of 60 years and matched by age, body mass index (BMI) and smoking habits. MEASUREMENTS: We analysed the strength and independence of associations of angiographically assessed presence of CHD with BMI, systolic and diastolic blood pressure, total, high-density lipoprotein (HDL) and LDL cholesterol, triglycerides, lipoprotein(a), apolipoproteins A-I and B, total and free IGF-I, IGF-II, IGFBP-1, IGFBP-3, IGFBP-5, acid-labile subunit (ALS), insulin, C-peptide, testosterone, DHEAS and sex hormone binding globulin. RESULTS: Using multivariate statistical analysis, the presence of CHD had significant positive associations with total IGF-I, IGFBP-5, ALS and IGFBP-3. These associations were independent of each other as well as of traditional risk factors, insulin and sex hormones. CONCLUSION: These observations may indicate a pathogenetic role of the GH/IGF axis in coronary atherosclerosis.

Sustained elevation of pulsatile growth hormone (GH) secretion and insulin-like growth factor I (IGF-I), IGF-binding protein-3 (IGFBP-3), and IGFBP-5 concentrations during 30-day continuous subcutaneous infusion of GH-releasing peptide-2 in older men and women.

We test the interlinked hypotheses that in healthy older adults: 1). i.v. injection of GH-releasing peptide-2 (GHRP-2) and GHRH synergizes more in aging women than men; 2). sc infusion of both GHRP-2 (1 microg/kg.h = 1) and GHRH (1, 3, or 10) for 24 h augments GH secretion more than either agonist alone; and 3). continuous sc delivery of GHRP-2 (1) for 30 d stimulates daily GH secretion and IGF-I, IGF-binding protein-3 (IGFBP-3), and IGFBP-5. Acute two-peptide synergy was 3-fold greater in young (n = 16) than older volunteers (n = 17; P < 0.025) and was 2.3-fold higher in elderly women than men (P < 0.025). The 24-h infusion of GHRP-2 (1) combined with GHRH (3 or 10) in men and with GHRH (10) in women drove GH secretion more than GHRH alone (P