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.     

Insulin-like growth factor system components in hyperparathyroidism and renal osteodystrophy

BACKGROUND: The insulin-like growth factor (IGF) system plays a key role in regulation of bone formation. In patients with renal osteodystrophy, an elevation of some IGF binding proteins (IGFBPs) has been described, but there is no study measuring serum levels of both IGF-I and IGF-II as well as IGFBP-1 to -6 in different forms of renal osteodystrophy and hyperparathyroidism. METHODS: In a cross-sectional study, we investigated 319 patients with mild (N = 29), moderate (N = 48), preuremic (N = 37), and end-stage renal failure (ESRF; N = 205). The ESRF group was treated by hemodialysis (HD; N = 148), peritoneal dialysis (PD; N = 27), or renal transplantation (RTX; N = 30). As controls without renal failure, we recruited age-matched healthy subjects (N = 87) and patients with primary hyperparathyroidism (pHPT; N = 25). Serum levels of total and free IGF-I, IGF-II, IGFBP-1 to -6, and biochemical bone markers including intact parathyroid hormone (PTH), bone alkaline phosphatase (B-ALP), and osteocalcin (OSC) were measured by specific immunometric assays. IGF system components and bone markers were correlated with clinical and bone histologic findings. Mean values +/- SEM are given. RESULTS: With declining renal function a significant increase was measured for IGFBP-1 (range 7- to 14-fold), IGFBP-2 (3- to 8-fold), IGFBP-3 (1.5- to 3-fold), IGFBP-4 (3- to 19-fold), and IGFBP-6 (8- to 25-fold), whereas IGFBP-5 levels tended to decrease (1.3- to 1. 6-fold). In contrast, serum levels of IGF-I, free IGF-I, and IGF-II remained constant in most patients. Compared with renal failure patients, pHPT patients showed a similar decline in IGFBP-5 levels and less elevated levels of IGFBP-1 (3.5-fold), IGFBP-2 (2-fold), IGFBP-3 (1.2-fold), and IGFBP-6 (4-fold) but no elevation of IGFBP-4 levels. In all subjects, free and total IGF-I levels showed significant negative correlations with IGFBP-1, IGFBP-2, and IGFBP-4 (that is, inhibitory IGF system components) and significant positive correlations with IGFBP-3 and IGFBP-5 (that is, stimulatory IGF system components). A positive correlation was observed between IGF-II and IGFBP-6. ESRF patients with mixed uremic bone disease and histologic evidence for osteopenia revealed significantly (P < 0.05) higher levels of IGFBP-2 and IGFBP-4 but lower IGFBP-5 levels. Histologic parameters of bone formation showed significant positive correlations with serum levels of IGF-I, IGF-II, and IGFBP-5. In contrast, IGFBP-2 and IGFBP-4 correlated positively with indices of bone loss. Moreover, dialysis patients with low bone turnover (N = 24) showed significantly (P < 0.05) lower levels of IGFBP-5, PTH, B-ALP, and OSC than patients with high bone turnover. CONCLUSION: Patients with primary and secondary hyperparathyroidism showed lower levels of the putative stimulatory IGFBP-5 but higher levels of IGFBP-1, -2, -3, and -6, whereas total IGF-I and IGF-II levels were not or only moderately increased. The marked increase in serum levels of IGFBP-4 appeared to be characteristic for chronic renal failure. IGFBP-5 correlated with biochemical markers and histologic indices of bone formation in renal osteodystrophy patients and was not influenced by renal function. Therefore, IGFBP-5 may gain significance as a serological marker for osteopenia and low bone turnover in long-term dialysis patients.     

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.     

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     

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.     

Serum insulin-like growth factor-I and insulin-like growth factor-binding protein-3 in localized, metastasized prostate cancer and benign prostatic hyperplasia

OBJECTIVE: Insulin-like growth factors (IGF-I and IGF-II) are important mitogenic peptides and are thought to be significant factors involved in normal and malignant cellular proliferation including benign prostatic hyperplasia (BPH) and prostate cancer (PC). In particular, the association between IGF-I and PC has received much attention. Insulin-like growth factor binding protein-3 (IGFBP-3) is the major carrier protein in serum for the IGF-I, thus is an important functional modulator of it. On the other hand, one of the functions of prostate-specific antigen (PSA) is to cleave IGFBP-3. Epidemiological studies have shown that decreased levels of serum IGFBP-3 are associated with increased PC risk. Controversial results have also been reported on the value of serum IGF-I and/or IGFBP-3 in the detection of PC, especially of metastatic PC; as increased, decreased or unchanged when compared to BPH. The aim of the present study was to investigate whether serum IGF-I and IGFBP-3 levels change in localized and metastasized PC cases compared with BPH as the control cases. METHOD: The study included 45 BPH, 24 localized PC and 19 metastasized PC cases. Serum IGF-I and IGFBP-3 levels were measured by two-site immunoradiometric assay kits, and serum total and free PSA levels were assayed by chemiluminescence method. RESULTS: Serum IGF-I levels in both localized and metastasized PC cases were similar to BPH cases (138.3 +/- 58.2, 137.7 +/- 39.0 and 147.7 +/- 44.2 ng/ml, respectively), whereas serum IGFBP-3 levels were lower in metastasized PC group than in BPH group (1,795.6 +/- 305.6 and 2,196.0 +/- 505.7 ng/ml; p = 0.005). In localized PC, serum IGFBP-3 levels (1,911.00 +/- 349.58 ng/ml) were similar to metastasized PC. There were significant correlations between serum IGFBP-3 and serum free PSA in three groups (r = -0.46, p = 0.02 for localized PC; r = -0.56, p = 0.01 for metastasized PC, and r = -0.31, p = 0.03 for BPH). CONCLUSION: These data reveal that serum IGF-I levels may not change either in localized or metastasized PC, and that decreased serum IGFBP-3 levels may be attributed to its proteolysis by PSA which is increased in PC.     

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.     

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.     

Insulin-like growth factor binding protein-3 protease activity in the urine of children with chronic renal failure

The insulin-like growth factors, IGF-1 and IGF-II, are polypeptides that potentiate cellular growth. In addition to binding to specific cell surface receptors, the IGFs bind with high affinity to a family of proteins, the insulin-like growth factor binding proteins (IGFBPs). Serum and urine IGFBP patterns are altered in individuals with chronic renal failure (CRF). We recently reported that the urinary IGFBP pattern of CRF patients is unique for increased insulin-like growth factor binding protein-1 (U-IGFBP-1) levels. In this study, we used western ligand blotting (WLB), western immunoblotting (WIB), and radioimmunoassay (RIA) to further evaluate serum and urine IGFBP profiles of children with CRF (n=14). Five patients with CRF displayed decreased serum IGFBP-3 profiles by WLB. Serum IGFBP-3 WIB profiles were remarkable for 30- and 20-kDa fragments of IGFBP-3 not seen in control serum. Serum IGFBP-3 levels, as determined by RIA, were slightly elevated. Serum levels of IGFBP-2 also were increased, although not at a level reaching statistical significance. WLB of CRF urine revealed a large increase in U-IGFBP-1 and a complete absence of urinary IGFBP-3. Recent studies of serum from pregnant women and seminal plasma have demonstrated a similar absence of intact IGFBP-3, due to the presence of a specific IGFBP-3 protease. To evaluate whether an IGFBP-3 protease accounts for the absence of intact U-IGFBP-3 in children with CRF, urine and serum samples from individuals with CRF and controls were tested. An IGFBP-3 protease assay using concentrated urine revealed the presence of two distinct proteases found only in the CRF urines. Serum IGFBP-3 protease activity was no greater in patients with CRF than in controls. We conclude that the decrease in intact urinary IGFBP-3 is due to proteolysis by an IGFBP-3 protease.     

An age-related decrease in the concentration of insulin-like growth factor binding protein-5 in human cortical bone

The skeletal contents of insulin-like growth factor-2 (IGF-II), insulin-like growth factor binding protein-5 (IGFBP-5), and insulin-like growth factor binding protein-3 (IGFBP-3) were determined in duplicate samples of human femoral cortical bone obtained from 64 subjects (44 males and 20 females) between the ages of 20 and 64 years. The results of these quantitative measurements revealed an age-related decrease in the femoral cortical content of IGFBP-5 (r=-0.272, P=0.031) in the total population. Although the femoral cortical content of IGF-II did not show a similar decrease with age, it could be correlated to the femoral cortical content of IGFBP-5 (r=0.442, P<0.001). In constrast, the femoral cortical content of IGFBP-3 did not decrease with age and could not be correlated to the femoral cortical contents of either IGFBP-5 or IGF-II. Comparisons of these results with previous measurements of insulin-like growth factor-1 (IGF-I) and transforming growth factor- (TGF-), in extracts of the same bones, showed significant cross-correlations between the femoral cortical contents of each of these growth factors and the femoral cortical contents of IGFBP-5 (r=0.625 for IGF-I versus IGFBP-5, r=0.554 for TGF- versus IGFBP-5, P<0.001 for each) but not IGFBP-3. Together, these data indicate average net losses of 60% and 29% of the femoral cortical contents of IGF-I and IGFBP-5, respectively, and apparent net losses (i.e., nonsignificant decreases) of 21% and 25% of the femoral cortical contents of IGF-II and TGF-, respectively, between the third and the sixth decades (i.e., decreases from young adult values of 75.1 pmol/g of bone for IGF-I, 124.7 pmol/g of bone for IGF-II, 0.71 pmol/g of bone for TGF-, 115.6 pmol/g of bone for IGFBP-5, and 26.2 pmol/g of bone for IGFBP-3).     

Insulin-like growth factor axis and risk of type 2 diabetes in women

IGF-I shares structural homology and in vitro metabolic activity with insulin. Laboratory models suggest that IGF-I and its binding proteins IGFBP-1 and IGFBP-2 have potentially beneficial effects on diabetes risk, whereas IGFBP-3 may have adverse effects. We therefore conducted a prospective nested case-control investigation of incident diabetes (n = 742 case subjects matched 1:1 to control subjects) and its associations with IGF-axis protein levels in the Nurses' Health Study, a cohort of middle-aged women. The median time to diabetes was 9 years. Statistical analyses were adjusted for multiple risk factors, including insulin and C-reactive protein. Diabetes risk was fivefold lower among women with baseline IGFBP-2 levels in the top versus bottom quintile (odds ratio [OR](q5-q1) = 0.17 [95% CI 0.08-0.35]; P trend < 0.0001) and was also negatively associated with IGFBP-1 levels (OR(q5-q1) = 0.37 [0.18-0.73]; P trend = 0.0009). IGFBP-3 was positively associated with diabetes (OR(q5-q1) = 2.05 [1.20-3.51]; P trend = 0.002). Diabetes was not associated with total IGF-I levels, but free IGF-I and diabetes had a significant association that varied (P interaction = 0.003) by insulin levels above the median (OR(q5-q1) = 0.48 [0.26-0.90]; P trend = 0.0001) versus below the median (OR(q5-q1) = 2.52 [1.05-6.06]; P trend < 0.05). Thus, this prospective study found strong associations of incident diabetes with baseline levels of three IGFBPs and free IGF-I, consistent with hypotheses that the IGF axis might influence diabetes risk.     

Effect of Breast Surgery on Serum Levels of Insulin-Like Growth Factors (IGF-I, IGF-II, and IGF Binding Protein-3) in Women With Benign and Malignant Breast Lesions

Background: There is evidence that insulin-like growth factors play a role in the development of breast cancer. Antiestrogens reduce circulating levels of IGF-I, but the influence of other breast cancer treatments, including surgery, is unknown and is investigated in this study.Methods: Circulating serum concentrations of IGF-I, IGF-II, and IGF binding protein-3 (IGFBP-3) were measured before and after breast surgery in 31 patients with breast cancer and 12 controls with benign breast lesions. Serum albumin was measured as a marker of the nonspecific metabolic effect of surgery.Results: Serum IGF-I, IGF-II, IGFBP-3, and albumin fell 24 hours after surgery for breast cancer but largely normalized again over the next 7 days. The fall in IGF-I and IGFBP-3 was not significant when the change in serum albumin was used as a covariate, suggesting a nonspecific effect of surgery. However, the reduction in IGF-II remained significant when adjusted for albumin and was greater after lumpectomy of malignant tumors (–8 ± 2%) compared with benign disease (2 ± 2%, P = .001). The fall in IGF-II was significantly related to the size of the removed tumor.Conclusions: Breast cancer may directly influence the serum concentration of IGF-II, possibly by direct tumor production.     

Insulin-Like Growth Factor–I Treatment to Enhance Renal Function in Advanced Chronic Renal Failure

Because of the potential for IGF-1 to enhance renal function in advanced chronic renal failure (CRF) we set out to determine whether IGF-1 can induce a sustained increase in renal function in patients with near end-stage renal failure. To this end we first examined the impact of CRF on the pharmacokinetics of IGF-1 and then we examined the effect of prolonged IGF-I treatment on the renal function of patients with an average GFR of 17mL/min/1.73m². Interestingly the metabolic clearance rate of IGF-1 in CRF subjects was similar to that in normal subjects even though the total serum IGF-1 levels rose to higher maximum levels. This increase was due to a reduced volume of IGF-1 distribution, a consequence of the elevated serum IGF binding proteins in CRF subjects. Treatment with IGF-I (60 mg/kg twice daily sc) for 31 days resulted in a 14% and 18% increase in the inulin and PAIL clearances respectively (n = 6 patients). These parameters returned to basal levels on stopping treatment. Serum immunoreactive IGFBP-3 levels fell and IGFBP-2 and -3 levels rose during IGF-1 therapy. Adverse effects were mild, of short duration and easily manage-able. Thus IGF-I pharmacokinetics are largely unchanged in CRF and the administration of IGF-1 produces a modest improvement in the GFR. These results appear to justify more extensive examination of the therapeutic role of IGF-1 in the treatment of CRF.     

Serum levels of 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D, and 25-hydroxyvitamin D in nondialyzed patients with chronic renal failure

BACKGROUND: In patients with chronic renal failure (CRF), abnormalities in vitamin D metabolism are known to be present, and several factors could contribute to the abnormalities. METHODS: We measured serum levels of three vitamin D metabolites, 1,25(OH)2D, 24, 25(OH)2D and 25(OH)D, and analyzed factors affecting their levels in 76 nondialyzed patients with CRF (serum creatinine> 1.6 and < 9.0 mg/dl), 37 of whom had diabetes mellitus (DM-CRF) and 39 of whom were nondiabetic (nonDM-CRF). RESULTS: Serum levels of 1,25(OH)2D were positively correlated with estimated creatinine clearance (CCr; r = 0.429; P < 0.0001), and levels of 24,25(OH)2D were weakly correlated with CCr (r = 0.252, P < 0.05); no correlation was noted for 25(OH)D. Serum levels of all three vitamin D metabolites were significantly and positively correlated with serum albumin. Although there were no significant differences in age, sex, estimated CCr, calcium and phosphate between DM-CRF and nonDM-CRF, all three vitamin D metabolites were significantly lower in DM-CRF than in nonDM-CRF. To analyze factors influencing vitamin D metabolite levels, we performed multiple regression analyses. Serum 25(OH)D levels were significantly and independently associated with serum albumin, presence of DM and serum phosphate (R2 = 0.599; P < 0.0001). 24,25(OH)2D levels were significantly and strongly associated with 25(OH)D (beta = 0.772; R2 = 0.446; P < 0.0001). Serum 1,25(OH)2D levels were significantly associated only with estimated CCr (R2 = 0. 409; P < 0.0001). CONCLUSIONS: These results suggest that hypoalbuminemia and the presence of DM independently affect serum 25(OH)D levels, probably via diabetic nephropathy and poor nutritional status associated with diabetes, and that 25(OH)D is actively catalyzed to 24,25(OH)2D in CRF, probably largely via extrarenal 24-hydroxylase. Serum levels of 1,25(OH)2D were significantly affected by the degree of renal failure. Thus, this study indicates that patients with CRF, particularly those with DM, should receive supplements containing the active form of vitamin D prior to dialysis.     

Characterization of insulin-like growth factors and their binding proteins in peritoneal dialysate

.Serum insulin-like growth factors (IGFs), which circulate bound to specific IGF binding proteins (IGFBPs), must exit the intravascular space before acting on target tissues. Little is known about the nature of IGF/IGFBPs in extravascular fluids of patients with chronic renal failure (CRF). Peritoneal dialysate (PD) was studied since, after a short incubation, PD contains proteins which have entered an extravascular space; thus, IGF/IGFBP forms in PD are more likely than serum forms to interact with target tissues. IGF-I and IGF-II, and IGFBPs 1 – 4, were readily identified by specific immunoassays and/or ¹²⁵iodine-IGF ligand blotting of simultaneously obtained PD and serum samples from seven CRF children; IGFBP-3 was a major IGFBP in PD as in serum. Where quantitated, IGF and IGFBP levels in PD were approximately 10% of serum concentrations. After separation of PD and serum by size-exclusion chromatography, serum had more IGFBP-3 in 150-kilodalton (kDa) than 35-kDa fractions, while PD had far less IGFBP-3 in 150-kDa than 35-kDa fractions. Immunoblot studies revealed a major 29-kDa IGFBP-3 fragment, in addition to intact 41- and 38-kDa IGFBP-3 forms, in PD and CRF serum; the 29-kDa form predominated in the 35-kDa PD fractions. These data suggest that the 29-kDa fragment is the IGFBP-3 form most likely to modulate IGF effects on target tissues of CRF individuals. Received: April 17, 1995; received in revised form September 19, 1995; accepted October 12, 1995     

Peritoneal loss of insulin-like growth factor-I and binding proteins in end-stage renal disease

The kinetics of peritoneal transport of insulin-like growth factor (IGF) system-related proteins during dialysis is not well characterized. We studied temporal changes in dialysate and serum concentrations of IGF-I and IGF-II as well as IGF binding protein (BP)-1, -2, and -3 in ten children with end-stage renal disease (ESRD) undergoing continuous cycling peritoneal dialysis (CCPD) during a 4-h peritoneal equilibration test (PET). Dialysate concentrations of IGF-I, IGF-II, and all three IGFBPs demonstrated a time-dependent increase during PET. Despite their transport, the serum concentrations of these proteins did not change significantly during the PET. Dialysate/serum ratios for IGF-I, IGF-II, and IGFBP-1, -2, and -3 were significantly increased at 2 h and increased further at 4 h, at which time values averaged 1.3±0.2%, 3.1±0.5%, 6.2±1.0%, 2.4±0.2%, and 1.3±0.2% of serum levels, respectively. The transperitoneal clearance (μl/min per 1.73 m²) of the three IGFBPs was inversely related to both their molecular weight and plasma concentration. However, peritoneal clearance of IGF-I and -II was similar to that of the larger and more-abundant IGFBP-3. Mass transfer rates (μg/h per 1.73 m²) for the IGFs and their binding proteins were directly proportional to their prevailing plasma concentration. Based on estimates of mass transfer, only a small molar excess of IGFBPs was removed from the circulation relative to the combined molar concentration of IGF-I and IGF-II. Hence, it seems unlikely that any beneficial effect of CCPD on growth in children with ESRD is mediated via a preferential loss of IGFBPs into the dialysate fluid. Received August 15, 1997; received in revised form January 7, 1998; accepted January 9, 1998     

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.     

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.