Evaluation of IGF system component levels and mitogenic activity of uremic serum on normal human osteoblasts

To test the hypothesis that impairment in bone formation in renal osteodystrophy in adults with chronic renal failure (CRF) might be mediated in part by alterations in circulating levels of the insulin-like growth factor (IGF) system components, we compared serum levels of IGF-I, IGF-II, IGF-binding protein (IGFBP)-3, IGFBP-4 and IGFBP-5 in adults with CRF (CRF patients with parathyroid hormone (PTH) < 100 pg/ml, PTH > 300 pg/ml and end-stage renal failure (ESRF) patients) versus age-matched controls. To evaluate the biological significance of alterations in circulating level of IGF system components, we compared the mitogenic activity of the sera on proliferation of normal human osteoblasts in vitro by using [(3)H]thymidine incorporation. We found severalfold increased serum levels of IGFBP-3 (2-fold), IGFBP-4 (5-fold) and slightly increased IGF-II levels in ESRF patients as well as a 2.6-fold increase in free IGF-I in CRF patients with PTH < 100 pg/ml. The mitogenic activity was found to be increased in serum of kidney failure patients compared to controls. This was most pronounced in CRF patients with PTH < 100 pg/ml showing also a significant increase in free IGF-I and the lowest levels of the IGF-inhibitory IGFBP-4. Our data support the hypothesis that alterations in serum levels of stimulating (i.e. free IGF-I) and inhibitory IGF system components (i.e. IGFBP-4) may influence osteoblastic cell proliferation in renal osteodystrophy.     

Down-regulation of the serum stimulatory components of the insulin-like growth factor (IGF) system (IGF-I, IGF-II, IGF binding protein [BP]-3, and IGFBP-5) in age-related (type II) femoral neck osteoporosis.

Both a decrease in bone formation and an increase in bone resorption have been implicated in the pathogenesis of age-related (type II) femoral neck osteoporosis. While the increase in the bone resorption rate has been shown to be partially related to secondary hyperparathyroidism, the mechanisms underlying the decline in bone formation have not yet been identified. The aim of the present study was to test the hypothesis that the bone formation deficit associated with type II osteoporosis might be due to secondary hyperparathyroidism and/or to a deficiency of the insulin-like growth factor (IGF) system. Circulating concentrations of IGF-I, IGF-II, IGF binding protein (IGFBP)-3, IGFBP-4, IGFBP-5, 25-hydroxycholecalciferol (25(OH)D3), and intact parathyroid hormone (PTH) were measured in 50 elderly women after sustaining a hip fracture and in 50 healthy age-matched controls. In addition, serum levels of osteocalcin (OC), skeletal alkaline phosphatase, and N-terminal procollagen peptide and urinary pyridinium cross-links were determined as markers of bone remodeling, and bone mineral density (BMD) was assessed at the proximal femur. In the patient group, serum was drawn within 18 h of the fracture and prior to surgery. Circulating protein concentrations did not change over this time frame. No difference was found between mean IGFBP-4 serum levels in the two groups studied, while mean levels of IGF-I, IGF-II, IGFBP-3, IGFBP-5, 25(OH)D3, and markers of bone formation were significantly lower (p < 0.006) in patients as compared with healthy subjects. Serum PTH and urinary pyridinium cross-links, however, were markedly increased (p < 0.001) in the osteoporotic group. In pooled data from the normal and osteoporotic populations, age-adjusted multiple regression models based on IGF-I, IGF-II, IGFBP-3, and IGFBP-5 were found to be highly predictive of serum OC (R2 = 19%, p < 0.001) and BMD of femoral neck (R2 = 49%, p < 0.0001), consistent with an effect of the anabolic IGF components on overall bone formation rate. Similar models based on 25(OH)D3 and PTH, however, were statistically unrelated to OC. To address further the potential impact of trauma on circulating IGF system components, we measured IGF system component levels in 10 male patients within 18 h following tibial fracture and in 10 age-matched normal male subjects. There was no significant difference in serum level of any of the IGF system components between the two groups. Although limited by its cross-sectional design, the present study suggests that, in addition to bone resorption resulting from secondary hyperparathyroidism, impaired bone formation associated with deficiency of the IGF system might predispose elderly women to fragility fracture of the proximal femur.     

Serum-free insulin-like growth factor I correlates with clearance in patients with chronic renal failure

Serum-free insulin-like growth factor I correlates with clearance in patients with chronic renal failure. BACKGROUND: Chronic renal failure (CRF) results in major changes in the circulating growth hormone (GH)/insulin-like growth factor (IGF) system. However, there are only limited data on changes in free IGF-I in CRF. METHODS: Matched groups of nondiabetic, nondialyzed patients with CRF (N = 25) and healthy controls (N = 13) were compared. The creatinine clearance (CCr) based on a 24-hour urine collection ranged from 3 to 59 and 89 to 148 ml/min/1.73 m2 in patients and controls, respectively. Overnight fasting serum samples were analyzed for free and total IGF-I and -II, and IGF-binding protein (IGFBP)-1, -2, and -3. Additionally, intact as well as proteolyzed IGFBP-3 was determined. RESULTS: The patients had reduced serum-free IGF-I (-53%) and increased levels of total IGF-II (40%), IGFBP-1 (546%), and IGFBP-2 (270%, P < 0.05). Serum total IGF-I and free IGF-II were normal. Also, serum levels of immunoreactive IGFBP-3 were elevated (33%, P < 0.05), but this could be explained by an increased abundance of IGFBP-3 fragments, as ligand blotting showed no difference in levels of intact IGFBP-3. Accordingly, patients had an increased proteolysis of IGFBP-3 in vivo (17%) and in vitro (7%, P < 0.05). In patients, free IGF-I levels correlated positively with CCr (r2 = 0.38, P < 0.002) and inversely with IGFBP-1 (r2 = 0.69, P < 0. 0001) and IGFBP-2 (r2 = 0.41, P < 0.0007), whereas CCr was inversely correlated with levels of IGFBP-1 (r2 = 0.48, P < 0.0001) and IGFBP-2 (r2 = 0.63, P < 0.0001). CONCLUSIONS: These data strongly support the hypothesis that CRF-related growth failure and tissue catabolism are caused by an increased concentration of circulating IGFBP-1 and -2, resulting in low serum levels of free IGF-I and thus IGF-I bioactivity. In addition, low levels of free IGF-I may explain the increased secretion of GH in CRF.     

Growth hormone resistance and inhibition of somatomedin activity by excess of insulin-like growth factor binding protein in uraemia

Insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) were studied in children with end-stage renal failure (ESRF,n=31) and chronic renal failure (n=11) with residual glomerular filtration. Somatomedin bioactivity in patient sera was found to be decreased while IGF-I and IGF-II levels by radio-immunoassay (RIA) were normal. In contrast, IGFBP-1 and IGFBP-3 levels (measured by RIA) were markedly increased in uraemia. Excess IGFBP was shown to be able to bind IGF by determination of the free IGF binding capacity. Using high-performance liquid chromatography a shift of the IGFBP-3 profile to low molecular weight components could be demonstrated in ESRF. Affinity crosslinking experiments showed that these low molecular weight IGFBP-3 immunoreactive forms are biologically active. In normal urine only IGFBP-3 forms smaller than 60 kDa were detected with a major peak at 12–20 kDa. Removal of excessive IGFBP from patient sera by affinity chromatography on an IGF-II Sepharose column resulted in a significant increase in somatomedin bioactivity. Model calculations on the interaction of IGF and IGFBP using empirical data suggested a reduction of IGF secretion in uraemia by an order of magnitude. It is concluded: (1) that renal failure causes an accumulation of low molecular weight IGFBP, (2) that the resulting excess of IGFBP acts as a somatomedin inhibitor, and (3) that in uraemia there is a relative growth hormone resistance with respect to IGF production.     

Serum insulin-like growth factors and their binding proteins in children with end-stage renal disease

Serum levels of insulin-like growth factor-I (IGF-I), IGF-II, and IGF binding protein-1 (IGFBP-1), IGFBP-2, and IGFBP-3 were measured in 54 children with end-stage renal disease (ESRD). The results were compared with their respective age-dependent normal ranges. IGFs and IGFBPs were quantified by specific radioimmunoassay. Serum IGF-I in children with ESRD tended to cluster in the low-normal range. Mean age-related serum IGF-I levels were slightly, but significantly decreased (–1.08±0.17 SDS). In view of the prevailing elevated growth hormone levels in ESRD, these serum, IGF-I levels must be interpreted as inadequately low. In contrast to IGF-I, individual serum IGF-II levels were either in the uppernormal range or clearly elevated. Mean age-related IGF-II (1.09±0.15 SDS) was lightly, but significantly elevated. Mean age-related IGFBP-1 serum levels (2.20±0.10 SDS) were moderately increased, while mean age-related serum IGFBP-2 (5.65±0.36) and IGFBP-3 levels (3.60±0.19) were markedly elevated. Affinity cross-linking of¹²⁵iodine-IGF-II to sera from patients with ESRD and immunoprecipitation with a specific antiserum showed that low molecular weight IGFBP-3 fragments in ESRD serum are capable of binding IGF. In patients with ESRD, a rapid and persistent decline of immunoreactive IGFBP-3 in response to restoration of renal function by renal transplantation was observed. This finding indicates that renal dysfunction contributes to high immunoreactive, IGFBP-3 levels in ESRD. In conclusion, the imbalance between normal total IGF levels and the excess of IGFBPs in ESRD is likely to play a role in growth failure in these children.     

The IGF/IGFBP system in relation to macroscopic bone architecture in pediatric renal transplant patients

The post-transplant bone disease of the peripheral skeleton in pediatric renal transplant recipients is characterized by an inadequately thin bone cortex in relation to muscular force. A major hormonal modulator of periosteal growth is the insulin-like growth factor (IGF)/IGF binding protein (IGFBP) system. We therefore hypothesized that the reduced cortical thickness in these patients may be due to functional IGF deficiency. To test this hypothesis, we investigated 55 patients (mean estimated glomerular filtration rate 86.3 ± 30.0 ml/min/1.73 m²) in a cross-sectional study. Parameters of macroscopic bone architecture and forearm muscle size were analyzed by peripheral quantitative computed tomography (pQCT), and serum IGF/IGFBP system components were measured by specific radioimmunoassays. The mean (± standard deviation) standardized serum IGF-I (0.20 ± 1.16 score) level was normal, while the mean IGF-II (1.16 ± 0.11 score) level was significantly elevated. Serum IGFBP-1 and IGFBP-2 levels were not altered, whereas the IGFBP-3 (1.34 ± 0.15 score) level was significantly increased. The serum IGFBP-4 level was slightly elevated (by 11%), the IGFBP-6 level was markedly (2.3-fold) elevated, while the IGFBP-5 level was comparable to that of the control. The respective age-adjusted cortical thickness at both the proximal (r = 0.407, P < 0.005) and distal (r = 0.383, P < 0.01) forearm was positively correlated with the standardized serum IGF-I level. In conclusion, the serum IGF/IGFBP system in pediatric renal transplant recipients is characterized by an increase in the levels of the inhibitory IGFBPs, IGFBP-3, -4 and -6, resulting in a functional IGF deficiency. The positive correlation of IGF-I with cortical thickness underlines the importance of this hormonal system in the modeling of bone, particularly periosteal growth.     

IGF and IGF-binding protein system in the synovial fluid of osteoarthritic and rheumatoid arthritic patients

Various arthritic disorders result from a disruption of the equilibrium between the synthesis and degradation of tissue matrix macromolecules. Growth factors, particularly insulin-like growth factor-I (IGF-I), are believed to play an important role in maintaining this equilibrium. In this study, we determined the levels of IGF-I, IGF-II, and characterized and measured the amount of IGF-binding proteins (IGFBPs) in the synovial fluid (SF) of osteoarthritis (OA), rheumatoid arthritis (RA) patients and normal individuals. Furthermore, we characterized the IGFBP found in these SFs. The levels of IGF-I, IGF-II and IGFBP-3 were determined by specific radioimmunoassays (RIAs). IGFBP identification and measurement were carried out using the Western ligand blot (WLB) technique, and characterization performed by Western immunoblot. IGFBP-3 proteolysis was analyzed by autoradiography after incubation of SF with radiolabeled IGFBP-3. Results showed a statistically significant increase (P < 0.001) in the IGF-I level in arthritic SF vs normal controls; 75 +/- 11 ng/ml and 82 +/- 11 ng/ml were recorded for RA (N = 8) and OA (N = 10), respectively, whilst normal controls (N = 9) were at 19 +/- 7 ng/ml. No difference in the level of IGF-II was recorded between the three groups studied. Human SF demonstrated the presence of IGFBP-1, -2, -3 and -4, but not that of IGFBP-5 and -6. The level of IGFBP-3 tested either by WLB or RIA was significantly higher (P < 0.001) in RA and OA patients. Moreover, a statistical and positive correlation between the levels of IGF-I and IGFBP-3 was noted. WLB analysis indicated that the amount of IGFBP-1 did not vary among the groups. The levels of IGFBP-2 and -4 were significantly increased (P < 0.02) solely in the RA SF. Further experiments demonstrated that a limited IGFBP-3 proteolysis occurred in human SF. Moreover, the ratio of total IGF over total bioactive IGFBPs was lower in RA (P < 0.05), and to a lesser extent in OA than normal specimens. This study showed the presence of four IGFBPs (1 4) in human SF for which the IGFBP-2, -3 and -4 were enhanced in arthritic fluid. Importantly, although proteolysis occurred in the SF, an increased amount of bioactive IGFBPs were present in arthritic SF, which may affect the bioavailability of IGF-I within the articular tissues.     

Serum levels of insulin-like growth factor binding protein-3 in benign and malignant breast disease.

BACKGROUND: The insulin-like growth factors IGF-I and IGF-II and their major binding protein IGFBP-3 influence the growth of breast cancer cells in vitro. Some benign non-breast tumours appear to be associated with increased serum IGFBP-3 levels which would tend to reduce bioactive-free IGF concentrations. The present study investigates whether this pattern also occurs in neoplastic breast disease. METHODS: Serum IGF-I, IGF-II and IGFBP-3 were measured by specific radioassay in 12 women with benign breast disease, 31 patients with breast cancer and in age-matched controls. RESULTS: The mean (+/-SD) serum IGFBP-3 concentration was higher in benign breast disease (3.6+/-0.7 mg/L) than in controls (2.7+/-0.6 mg/L) or in breast cancer patients (2.7+/-0.5 mg/L) (P = 0.001). Serum IGF-I and IGF-II levels were not significantly different among the groups. However, the index of free unbound IGF measured as the molar ratio of IGF-I plus IGF-II divided by IGFBP-3 was significantly lower in benign breast disease than in the other subjects. CONCLUSIONS: Either the production or clearance of IGFBP-3 is altered in benign breast disease so that there is less free IGF available to cells. This may serve to protect against malignant transformation in patients with benign breast disorders.     

Growth hormone/insulin-like growth factor system in children with chronic renal failure

Disturbances of the somatotropic hormone axis play an important pathogenic role in growth retardation and catabolism in children with chronic renal failure (CRF). The apparent discrepancy between normal or elevated growth hormone (GH) levels and diminished longitudinal growth in CRF has led to the concept of GH insensitivity, which is caused by multiple alterations in the distal components of the somatotropic hormone axis. Serum levels of IGF-I and IGF-II are normal in preterminal CRF, 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 GH levels in ESRD, these serum IGF-I levels appear inadequately low. Indeed, there is both clinical and experimental evidence for decreased hepatic production of IGF-I in CRF. This hepatic insensitivity to the action of GH may be partly the consequence of reduced GH receptor expression in liver tissue and partly a consequence of disturbed GH receptor signaling. The actions and metabolism of IGFs are modulated by specific high-affinity IGFBPs. CRF serum has an IGF-binding capacity that is increased by seven- to tenfold, leading to decreased IGF bioactivity of CRF serum despite normal total IGF levels. Serum levels of intact IGFBP-1, -2, -4, -6 and low molecular weight fragments of IGFBP-3 are elevated in CRF serum in relation to the degree of renal dysfunction, whereas serum levels of intact IGFBP-3 are normal. Levels of immunoreactive IGFBP-5 are not altered in CRF serum, but the majority of IGFBP-5 is fragmented. Decreased renal filtration and increased hepatic production of IGFBP-1 and -2 both contribute to high levels of serum IGFBP. Experimental and clinical evidence suggests that these excessive high-affinity IGFBPs in CRF serum inhibit IGF action in growth plate chondrocytes by competition with the type 1 IGF receptor for IGF binding. These data indicate that growth failure in CRF is mainly due to functional IGF deficiency. Combined therapy with rhGH and rhIGF-I is therefore a logical approach.This work was presented in part at the IPNA Seventh Symposium on Growth and Development in Children with Chronic Kidney Disease: The Molecular Basis of Skeletal Growth, 1–3 April 2004, Heidelberg, Germany     

Bone Mineral Density in Femoral Neck is Positively Correlated to Circulating Insulin-Like Growth Factor (IGF)-I and IGF-Binding Protein (IGFBP)-3 in Swedish Men

Studies on the hormonal regulation of bone metabolism in men have indicated covariation between insulin-like growth factor-I (IGF-I) and sex hormones with bone mineral density (BMD). In this study the relationships between BMD in total body, lumbar spine, femoral neck, distal and ultradistal (UD) radius and circulating levels of IGFs, IGF binding proteins (IGFBPs), and sex steroids were investigated in 55 Swedish men between 22 and 85 (52 +/- 18, mean +/- SD) years of age. BMD in total body, distal and UD radius, and femoral neck was positively correlated with serum IGF-I (r = 0.31 to 0.49), IGF-II (r = 0.32 to 0.48), IGFBP-3 (r = 0.37 to 0.53), and free androgen index (FAI) (r = 0.32 to 0.40), and negatively with IGFBP-1 (r = -0.37 to -0.41) and IGFBP-2 (r = -0.29 to -0.41) levels. A positive correlation was observed between BMD in femoral neck and estradiol/SHBG ratio (r = 0.34, P = 0.01). Age correlated negatively with serum IGF-I, IGF-II, IGFBP-3, FAI, estradiol/SHBG ratio, and BMD in total body, distal and UD radius, and femoral neck, and positively with IGFBP-1, IGFBP-2, and SHBG levels. According to stepwise multiple regression analyses, a combination of weight, IGFBP-3, and testosterone accounted for 43% of the variation in BMD in femoral neck, 34% in ultradistal radius and 48% in total body (P < 0.0001). These findings indicate that sex hormones and the different components of the IGF system are associated with BMD in Swedish men, suggesting that age-related changes in these systems could contribute to the development of osteoporosis in elderly men.     

SERUM LEVELS OF INSULIN-LIKE GROWTH FACTOR BINDING PROTEIN-3 IN BENIGN AND MALIGNANT BREAST DISEASE

Background : The insulin-like growth factors IGF-I and IGF-II and their major binding protein IGFBP-3 influence the growth of breast cancer cells in vitro. Some benign non-breast tumours appear to be associated with increased serum IGFBP-3 levels which would tend to reduce bioactive-free IGF concentrations. The present study investigates whether this pattern also occurs in neoplastic breast disease. Methods : Serum IGF-I, IGF-II and IGFBP-3 were measured by specific radioassay in 12 women with benign breast disease, 31 patients with breast cancer and in age-matched controls. Results : The mean (± SD) serum IGFBP-3 concentration was higher in benign breast disease (3.6 ± 0.7 mg/L) than in controls (2.7 ± 0.6 mg/L) or in breast cancer patients (2.7 ± 0.5 mg/L) (P = 0.001). Serum IGF-I and IGF-II levels were not significantly different among the groups. However, the index of free unbound IGF measured as the molar ratio of IGF-I plus IGF-II divided by IGFBP-3 was significantly lower in benign breast disease than in the other subjects. Conclusions : Either the production or clearance of IGFBP-3 is altered in benign breast disease so that there is less free IGF available to cells. This may serve to protect against malignant transformation in patients with benign breast disorders.     

Expression of osteotropic growth factors and growth hormone receptor in a canine distraction osteogenesis model

Osteotropic growth factors play an important role in bone metabolism. Nevertheless, knowledge about their expression in relation to distraction osteogenesis remains limited. The aim of the present study was to determine the expression of growth hormone (GH), growth hormone receptor (GHR), insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II), and bone morphogenetic protein 2 (BMP-2) in distraction-induced bone regeneration. Expression of these factors was assessed during the consolidation phase, comparing distraction osteogenesis with osteotomy-induced bone formation. Real-time PCR was performed as a semiquantitative measurement of mRNA, and the relative expression levels of these factors were determined. In addition, plasma GH profiles and plasma concentrations of IGF-I, IGF-II, and insulin-like growth factor-binding protein 4 and -6 (IGFBP-4 and -6) were measured to assess their potential systemic role during bone formation. Expression of GHR, IGF-I, and BMP-2 had significantly increased in comparison with the expression of these factors in mature bone. Expression of GHR was significantly higher in distraction-induced bone regenerate than in osteotomy-induced bone. No significant differences were found for the expression of IGF-I and BMP-2 between distraction and osteotomy. Plasma concentrations of GH, IGF-I, IGF-II, IGFBP-4, and IGFBP-6 did not demonstrate any significant differences between treatment groups and controls. Upregulation of GHR expression in distraction osteogenesis may enhance sensitivity to endogenous systemic GH and thus promote consolidation of the regenerated bone. Changes in the systemic osteotropic growth factors GH, IGF-I, IGF-II, IGFBP-4, and IGFBP-6 do not seem to be of importance during distraction osteogenesis.     

Transforming growth factor-beta regulation of the insulin-like growth factor binding protein-4 protease system in cultured human osteoblasts.

IGFBP-4 is an inhibitor of IGF-I in bone. We show that TGF-beta regulates IGFBP-4 and enhances IGF-I-stimulated growth of cultured human bone cells through increased expression of an IGFBP-4 protease, PAPP-A. This effect of TGF-beta on IGF-I bioavailability may promote local bone formation. Insulin-like growth factor binding protein (IGFBP-4) proteolysis is implicated in the regulation of local insulin-like growth factor (IGF)-I bioavailability during bone remodeling. The IGFBP-4 protease secreted by normal adult human osteoblastic (hOB) cells in culture is a novel metalloproteinase, pregnancy-associated plasma protein-A (PAPP-A). We have recently identified an inhibitor of PAPP-A, the precursor form of major basic protein (proMBP). Very little is known about the molecular regulation of this IGFBP-4 protease system. In the present study, we determined the effect of transforming growth factor (TGF)-beta and IGF-II, the two most abundant growth factors in human bone, on PAPP-A and proMBP expression in primary cultures of hOB cells. Treatment with TGF-beta resulted in time- and dose-dependent increases in PAPP-A mRNA expression, with a maximal 12-fold increase after 24 h of stimulation with 10 ng/ml TGF-beta. Increased PAPP-A levels in hOB cell-conditioned medium paralleled PAPP-A gene expression. In addition, TGF-beta completely suppressed proMBP expression. Treatment of hOB cells with IGF-II had no effect on PAPP-A or proMBP gene expression. However, IGFBP-4 proteolysis in cell-free assay was dependent on IGF-II, and there was increased IGF-II-dependent IGFBP-4 protease activity in conditioned medium from hOB cells that were treated with TGF-beta. IGF-I stimulation of hOB cell proliferation was markedly enhanced by pretreatment with TGF-beta and [Leu27]IGF-II, and this enhancement was prevented with protease-resistant IGFBP-4. In summary, TGF-beta regulates IGFBP-4 proteolysis in hOB cells through increased expression of the protease, PAPP-A, and decreased expression of the inhibitor, proMBP. However, functional activation of the IGFBP-4 protease system is dependent on IGF-II, which acts at a post-translational level. These data support a model whereby local TGF-beta and IGF-II in the bone microenvironment coordinately amplify IGF-I bioavailability through controlled IGFBP-4 proteolysis, which may be a means to promote bone formation.     

Focal induction of IGF binding proteins in proximal tubules of diabetic rat kidney.

Diabetes-associated kidney enlargement is associated with increased kidney insulinlike growth factor I (IGF-I) binding. IGF-I binds to the type I IGF receptor, which mediates most of its actions, and to specific binding proteins (IGFBPs), which modulate its actions. To explore the nature and extent of IGF-I binding in the kidney, in vitro autoradiography was used to map the distribution of IGF binding in control and diabetic rat kidney. Specificity studies were performed with increasing concentrations of unlabeled IGF-I, IGF-II, des(1-3)IGF-I (an IGF-I derivative that binds to receptors normally but with decreased affinity to binding proteins), and insulin. In control rats, diffuse binding was found throughout the kidney with increased density in the papilla. Binding specificity in the cortex and outer medulla was typical of the type I IGF receptor (IGF-I = des[1-3]IGF-I greater than IGF-II much greater than insulin). Binding in the outer medulla of diabetic kidney was typical of the type I IGF receptor. A marked focal increase in proximal tubular binding occurred in 13 of 22 postpubertal diabetic rats. Binding specificity of the proximal tubular binding was consistent with the predominance of an IGF binding protein (IGF-I = IGF-II greater than des[1-3]IGF-I with minimal displacement by insulin). Northern-blot analysis revealed increased IGFBP-1 and IGFBP-3 mRNA in cortical tissue from diabetic rats displaying increased proximal tubular binding but not from diabetic rats not displaying this phenomenon. As cell surface association of IGFBPs is linked to potentiation of IGF activity, a possible mechanism for potentiation of local IGF-I action may be provided.     

Circulating Insulin-Like Growth Factor System Changes in Women with Acute Estrogen Deficiency Induced by GnRH Agonist

This prospective longitudinal study was undertaken to examine the short-term effects (6 months) of estrogen withdrawal on the circulating IGF system. A series of 40 patients suffering from endometriosis was studied before and after a 6-month treatment period with gonadotrophin releasing hormone (GnRH) agonist and calcium, with or without nasal salmon calcitonin. The plasma concentrations of insulin-like growth factor I (IGF-I9 and insulin-like growth factor II (IGF-II) were measured by radioimmunoassay and radioreceptor assay respectively. Plasma IGF binding proteins (IGFBPs) were quantified and characterized by ligand blot and immunoblot. In all patients, a secondary hypoestrogenism was observed, including a 4% decrease in lumbar bone mineral density (L-BMD). The plasma IGF-I and IGF-II concentrations increased after treatment (24%, p < 0.0005 and 40%, p < 0.004 respectively), with no significant difference between the treatment groups. There was a positive correlation between plasma IGF-I (but not IGF-II) changes and changes in urinary deoxypyridinoline (r = 0.32, p < 0.05), urinary C telopeptide of type I collagen (r = 0.33, p < 0.04) and total plasma alkaline phosphatases (r = 0.33, p < 0.04). No correlation was found between IGF-I and L-BMD changes, while there was a positive correlation between the changes in plasma IGF-II and L-BMD (r = 0.32, p < 0.05). Ligand blot analysis revealed a significant increase in IGF-II binding to a 29–31 kilodalton region where positive staining with specific antibodies to IGFBP-3 or IGFBP-1 was observed. In conclusion, IGF-I and IGF-II plasma concentrations are both increased following a short period of treatment with a GnRH agonist. The changes in individual IGF peptides are differently correlated with changes in markers of bone remodelling and L-BMD.     

Insulin-like growth factors and risk of benign prostatic hyperplasia

BACKGROUND: Insulin-like growth factors (IGFs) have potent growth mitogenic and anti-apoptotic effects on prostate tissue, whereas IGF binding proteins (IGFBPs) inhibit growth of prostatic tissue. The IGF axis has been implicated in prostate cancer risk, but its role in benign prostatic hyperplasia (BPH) is unclear. METHODS: Plasma levels of IGF-I, IGF-II, IGFBP-1, and IGFBP-3 were determined from the fasting bloods of 206 BPH cases admitted for treatment and 306 randomly selected population controls in Shanghai, China. RESULTS: Relative to the lowest tertile, men in the highest tertile of IGF-I levels had a significantly elevated risk of BPH (odds ratio [OR] = 2.80, 95% confidence interval [95% CI] = 1.60-4.92; P(trend) < 0.001). Results for IGF-I were more pronounced after adjustment for serum androgens. In contrast, men in the highest IGFBP-3 tertile had a significantly reduced risk (OR = 0.40; 95% CI = 0.23-0.69; P(trend) < 0.001). No associations of BPH with IGF-II and IGFBP-1 were observed. CONCLUSION: As has been previously observed for prostate cancer, we found that IGF-I and IGFBP-3 are associated with BPH risk in China. Further investigation is needed to elucidate the role of the IGF axis in BPH etiology.     

Relationships of serum levels of insulinlike growth factors with indices of bone metabolism and nutritional conditions in hemodialysis patients

Insulinlike growth factor (IGF) I and IGF-II are synthesized in osteoblasts and stimulate proliferation, differentiation, and matrix synthesis in these cells. There is some evidence that IGFs act on bone cells not only by paracrine but also by endocrine pathways, suggesting that circulating IGFs may be of importance for the regulation of bone metabolism. On the other hand, the serum IGF-I level is also thought to be a good indicator of the nutritional conditions in hemodialysis patients. The present study was performed to analyze the correlations of circulating levels of IGF-I, IGF-II, IGF-binding protein (IGFBP) 1 and IGFBP-3 with biochemical markers of bone metabolism and parameters of the urea kinetic model which reflect nutritional conditions in hemodialysis patients. We also examined the differences between these relationships in male and female patients on hemodialysis. Sixty-two hemodialysis patients, 36 men (male group) and 26 women (female group), were included in this study. We measured the serum levels of IGF-I, IGF-II, IGFBP-1, and IGFBP-3. The bone mineral content (BMC) of the radius was measured by dual-energy X-ray absorptiometry. We calculated Kt/V, protein catabolic rate, and percent creatinine generation rate (%CGR). We also examined the relationships between serum levels of IGFs and BMC and the parameters of the urea kinetic model. It was found that the serum levels of IGF-I in the hemodialysis patients were almost the same as those in the control group. However, the serum levels of IGF-II, IGFBP-1, and IGFBP-3 in the hemodialysis patients were significantly higher than those in the control group. In the male group, the serum IGF-I levels showed a significant correlation with both serum intact parathyroid hormone levels and BMC, but no significant correlations between these indices were found in the female group. The serum levels of both IGF-I and IGF-II showed significant correlations with %CGR in the male group, but not in the female group. Stepwise multiple regression analysis was performed to clarify the relationship between serum levels of IGFs and BMC or %CGR. It was found that age, hemodialysis duration, serum intact parathyroid hormone levels, and sex were independent factors associated with BMC. The %CGR was associated independently with serum levels of IGF-I, and IGF-II and with the presence of diabetes mellitus. In conclusion, it is thought that serum levels of IGF-I and IGF-II can be used as indices of nutritional conditions in hemodialysis patients. However, the serum IGF-I level cannot be used as a marker of bone metabolism in hemodialysis patients.     

A potentially deleterious role of IGFBP-2 on bone density in aging men and women.

The role of the IGFs and IGFBPs on age-related changes in BMD in adult men and women is not well understood. Studying an age-stratified community based sample of 344 men and 276 women, we found higher IGFBP-2 levels to be associated with lower BMD. IGFBP-2, which increases with age in both men and women, was the strongest, most consistent predictor of BMD among the IGF/IGFBPs studied. INTRODUCTION: Insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) are important regulators of tissue growth and metabolism, but their association with BMD in adult men and women is controversial. MATERIALS AND METHODS: In an age-stratified, random sample of the community population, we examined the role of serum levels of IGF-I, IGF-II, and IGFBP-1, -2, and -3 on BMD of the proximal femur (total hip), lateral spine, midshaft, and ultradistal radius as measured by DXA. We explored the association before and after adjustment for potential confounders, including age, bioavailable estradiol and testosterone, sex hormone binding globulin (SHBG), and measures of total fat and skeletal muscle mass. RESULTS: We studied 344 men (age, 23-90 years) and 276 women (age, 21-93 years; 166 postmenopausal) not on hormone replacement or oral contraceptives. In both men and women, IGF-I and IGFBP-3 levels fell with advancing age, whereas IGFBP-2 levels tended to rise with age. There was an inverse association of IGFBP-2 with BMD at most skeletal sites in men and both premenopausal and postmenopausal women, whereas lower IGF-I and IGFBP-3 were associated with lower BMD in men and postmenopausal women only. Lower IGF-II was associated with lower BMD in men only. There were no associations between IGFBP-1 and BMD in either sex. After adjustment for age, in most cases, we found no further associations between IGF-I, IGF-II, or IGFBP-3 and BMD. In contrast, after age adjustment, higher IGFBP-2 remained a predictor of lower BMD in men and postmenopausal women at all sites except for the lateral spine (for men: r = -0.21, -0.20, and -0.19, all p < 0.001; and for postmenopausal women: r = -0.34, -0.24, and -0.25, all p < 0.01, for the total hip, midshaft, and ultradistal radius, respectively). IGFBP-2 remained an independent negative predictor of BMD in men, postmenopausal women, and all women combined after additional adjustment for bioavailable sex steroids, but not at all sites after adjustment for SHBG and muscle mass. In premenopausal women, IGFBP-2 had similar associations as seen in postmenopausal women, but they were weaker and not statistically robust. CONCLUSIONS: Among the IGF/IGFBPs in our study, IGFBP-2 was a key negative predictor of BMD among men and women, particularly postmenopausal women. Our findings suggest a potential role of the IGF/IGFBP system in regulating bone loss in aging men and women and identify a previously under-recognized, potentially deleterious role for IGFBP-2, a known inhibitor of IGF action that increases with age in both sexes. Whether the action of the IGF/IGFBP system on bone metabolism is mediated partly through its effects on muscle mass or SHBG deserves further study.     

Insulin-like growth factor binding proteins 4 and 5 and bone mineral density in elderly men and women

Insulin-like growth factor-1 (IGF-I) plays a central role in the maintenance of bone mass. To test whether two major IGF-I binding proteins, IGFBP-4 and IGFBP-5, are related to bone mineral density (BMD), we studied a sample of the Framingham Offspring Cohort participants (99 men and 101 women, ages 60-87). Serum levels of IGF-I, IGFBP-4, and IGFBP-5 were measured by previously validated radioimmunoassays (CVs approximately 10%). BMDs of the proximal femur and lumbar spine were measured using a Lunar DPX-L densitometer. In males, but not females, IGF-I and IGFBP-5 were inversely associated with age (r = 0.34 and r = -0.28, respectively; P <0.01), while IGFBP-4 levels were positively associated with age (P <0.01). Multivariate means for BMD (adjusted for age, body mass index, height, smoking, and in women, estrogen use) were computed across quartiles of IGFBP-4 and IGFBP-5 and IGFBP-4/IGFBP-5 ratio. In women, but not men, IGFBP-5 was positively associated with femoral neck BMD (P = 0.03), however, after statistical adjustment for IGF-I, this association was no longer significant. No other associations were observed for BMD at any other site. Further study is necessary for elucidation of the gender differences in the possible influence of IGF system components on bone mass.