The relationship among circulating insulin-like growth factor components, biochemical markers of bone turnover and bone mineral density in postmenopausal women under the age of 60

Osteosarcopenia in Reproductive-Aged Women with Polycystic Ovary Syndrome: A Multicenter Case-Control Study

CONTEXT

Osteosarcopenia (loss of skeletal muscle and bone mass and/or function usually associated with aging) shares pathophysiological mechanisms with polycystic ovary syndrome (PCOS). However, the relationship between osteosarcopenia and PCOS remains unclear.

OBJECTIVE

We evaluated skeletal muscle index% (SMI% = [appendicular muscle mass/weight (kg)] × 100) and bone mineral density (BMD) in PCOS (hyperandrogenism + oligoamenorrhea), and contrasted these musculoskeletal markers against 3 reproductive phenotypes (i): HA (hyperandrogenism + eumenorrhea) (ii); OA (normoandrogenic + oligoamenorrhea) and (iii), controls (normoandrogenic + eumenorrhea). Endocrine predictors of SMI% and BMD were evaluated across the groups.

DESIGN, SETTING, AND PARTICIPANTS

Multicenter case-control study of 203 women (18-48 years old) in New York State.

RESULTS

PCOS group exhibited reduced SMI% (mean [95% confidence interval (CI)]; 26.2% [25.1,27.3] vs 28.8% [27.7,29.8]), lower-extremity SMI% (57.6% [56.7,60.0] vs 62.5% [60.3,64.6]), and BMD (1.11 [1.08,1.14] vs 1.17 [1.14,1.20] g/cm2) compared to controls. PCOS group also had decreased upper (0.72 [0.70,0.74] vs 0.77 [0.75,0.79] g/cm2) and lower (1.13 [1.10,1.16] vs 1.19 [1.16,1.22] g/cm2) limb BMD compared to HA. Matsuda index was lower in PCOS vs controls and positively associated with SMI% in all groups (all Ps ≤ 0.05). Only controls showed associations between insulin-like growth factor (IGF) 1 and upper (r = 0.84) and lower (r = 0.72) limb BMD (all Ps < 0.01). Unlike in PCOS, IGF-binding protein 2 was associated with SMI% in controls (r = 0.45) and HA (r = 0.67), and with upper limb BMD (r = 0.98) in HA (all Ps < 0.05).

CONCLUSIONS

Women with PCOS exhibit early signs of osteosarcopenia when compared to controls likely attributed to disrupted insulin function. Understanding the degree of musculoskeletal deterioration in PCOS is critical for implementing targeted interventions that prevent and delay osteosarcopenia in this clinical population.

Age-related bone loss is associated with FGF21 but not IGFBP1 in healthy adults

What is the central question of this study? Fibroblast growth factor 21 (FGF21) plays important therapeutic roles in metabolic diseases but is associated with bone loss, through insulin-like growth factor binding protein 1 (IGFBP1), in animals. However, the effect of the FGF21-IGFBP1 axis on age-related bone loss has not been explored in humans. What is the main finding and its importance? Using 'genetically linked' parent and child family pairs, we show that the FGF21 concentration, but not the IGFBP1 concentration, is higher in older than in younger adults. Our results suggest that age-associated decline in bone mineral density is associated with FGF21 and increased bone turnover but not likely to involve IGFBP1 in healthy humans. ABSTRACT: Bone fragility increases with age. The fibroblast growth factor 21 (FGF21)-insulin-like growth factor binding protein 1 (IGFBP1) axis regulates bone loss in animals. However, the role of FGF21 in mediating age-associated bone fragility in humans remains unknown. The purpose of this study was to explore the FGF21-regulatory axis in bone turnover and the age-related decline in bone mineral density (BMD). Twenty 'genetically linked' family (parent and child) pairs were recruited. Younger adults were 22-39 years old and older adults 60-71 years old. The BMD and serum concentrations of FGF21, IGFBP1, receptor activator of nuclear factor-κB ligand (RANKL), tartrate-resistant acid phosphatase 5b (TRAP5b) and bone-specific alkaline phosphatase (BAP) were measured. Older adults had 10-18% lower BMD at the hip and spine (P < 0.008) and a twofold higher FGF21 concentration (P < 0.001). The IGFBP1 concentration was similar in younger and older adults (P = 0.961). The RANKL concentration was 44% lower (P = 0.006), whereas TRAP5b and BAP concentrations were 36 and 31% higher (P = 0.01 and P = 0.004), respectively, in older adults than in younger adults. Adjusting for sex did not affect these results. The FGF21 concentration was negatively correlated with BMD at the spine (r = -0.460, P = 0.003), but not with the IGFBP1 concentration (r = -0.144, P = 0.374). The IGFBP1 concentration was not correlated with BMD at the hip or spine (all P > 0.05). In humans, FGF21 might be involved in the age-associated decline in BMD, especially at the spine, through increased bone turnover. IGFBP1 is unlikely to be the downstream effector of FGF21 in driving the age-associated decline in BMD and in RANKL-associated osteoclast differentiation.

Role of IGF-binding proteins in regulating IGF responses to changes in metabolism

The IGF-binding protein family contains six members that share significant structural homology. Their principal function is to regulate the actions of IGF1 and IGF2. These proteins are present in plasma and extracellular fluids and regulate access of both IGF1 and II to the type I IGF receptor. Additionally, they have functions that are independent of their ability to bind IGFs. Each protein is regulated independently of IGF1 and IGF2, and this provides an important mechanism by which other hormones and physiologic variables can regulate IGF actions indirectly. Several members of the family are sensitive to changes in intermediary metabolism. Specifically the presence of obesity/insulin resistance can significantly alter the expression of these proteins. Similarly changes in nutrition or catabolism can alter their synthesis and degradation. Multiple hormones such as glucocorticoids, androgens, estrogen and insulin regulate IGFBP synthesis and bioavailability. In addition to their ability to regulate IGF access to receptors these proteins can bind to distinct cell surface proteins or proteins in extracellular matrix and several cellular functions are influenced by these interactions. IGFBPs can be transported intracellularly and interact with nuclear proteins to alter cellular physiology. In pathophysiologic states, there is significant dysregulation between the changes in IGFBP synthesis and bioavailability and changes in IGF1 and IGF2. These discordant changes can lead to marked alterations in IGF action. Although binding protein physiology and pathophysiology are complex, experimental results have provided an important avenue for understanding how IGF actions are regulated in a variety of physiologic and pathophysiologic conditions.

Insulin-like growth factors: actions on the skeleton

The discovery of the growth hormone (GH)-mediated somatic factors (somatomedins), insulin-like growth factor (IGF)-I and -II, has elicited an enormous interest primarily among endocrinologists who study growth and metabolism. The advancement of molecular endocrinology over the past four decades enables investigators to re-examine and refine the established somatomedin hypothesis. Specifically, gene deletions, transgene overexpression or more recently, cell-specific gene-ablations, have enabled investigators to study the effects of the Igf1 and Igf2 genes in temporal and spatial manners. The GH/IGF axis, acting in an endocrine and autocrine/paracrine fashion, is the major axis controlling skeletal growth. Studies in rodents have clearly shown that IGFs regulate bone length of the appendicular skeleton evidenced by changes in chondrocytes of the proliferative and hypertrophic zones of the growth plate. IGFs affect radial bone growth and regulate cortical and trabecular bone properties via their effects on osteoblast, osteocyte and osteoclast function. Interactions of the IGFs with sex steroid hormones and the parathyroid hormone demonstrate the significance and complexity of the IGF axis in the skeleton. Finally, IGFs have been implicated in skeletal aging. Decreases in serum IGFs during aging have been correlated with reductions in bone mineral density and increased fracture risk. This review highlights many of the most relevant studies in the IGF research landscape, focusing in particular on IGFs effects on the skeleton.

Associations of insulin-like growth factor-I and insulin-like growth factor binding protein-3 with bone quality in the general adult population

OBJECTIVE

Growth hormone (GH) and its main mediator, insulin-like growth factor-I (IGF-I), play a significant role in bone metabolism. The relations between IGF-I and bone mineral density (BMD) or osteoporosis have been assessed in previous studies but whether the associations are sex-specific remains uncertain. Moreover, only a few studies examined bone quality assessed by quantitative ultrasound (QUS). We aimed to investigate these associations in the general population of north-east Germany.

DESIGN AND MEASUREMENTS

Data from 1759 men and 1784 women who participated in the baseline examination of the Study of Health in Pomerania (SHIP)-Trend were used. IGF-I and IGF-binding protein-3 (IGFBP-3) concentrations were measured on the IDS-iSYS multidiscipline automated analyser (Immunodiagnostic Systems Limited). QUS measurements were performed at the heel (Achilles InSight, GE Healthcare). Sex-specific linear and multinomial logistic regression models adjusted for potential confounders were calculated.

RESULTS

Linear regression analyses revealed significant positive associations between IGF-I and IGF-I/IGFBP-3 ratio, a marker for free IGF-I, with all QUS parameters in men. Among women, we found an inverse association between IGF-I and the QUS-based fracture risk but no association with any other QUS parameter. There was no association between IGFBP-3 and the QUS-based fracture risk.

CONCLUSIONS

Our data suggest an important role of IGF-I on bone quality in men. The observed association of IGF-I with the QUS-based stiffness index and QUS-based fracture risk in this study might animate clinicians to refer patients with low IGF-I levels, particularly men, to a further evaluation of risk factors for osteoporosis and a detailed examination of the skeletal system.

Reduced bone resorption by intake of dietary vitamin D and K from tailor-made Atlantic salmon: A randomized intervention trial

Suboptimal vitamin D status is common among humans, and might increase bone resorption with subsequent negative effects on bone health. Fatty fish, including Atlantic salmon, is an important dietary vitamin D source. However, due to a considerable change in fish feed composition, the contribution of vitamin D from salmon fillet has been reduced. The main objective was to investigate if intake of vitamin D₃ enriched salmon or vitamin D₃ tablets decreased bone biomarkers (urinary N-telopeptides, deoxypyridinoline, serum bone-specific alkaline phosphatase, and osteocalcin) compared to a low vitamin D₃ intake. The 122 healthy postmenopausal women included in this 12 weeks intervention trial were randomized into four groups: three salmon groups (150 grams/two times/week) and one tablet group (800 IU vitamin D and 1000 mg calcium/day). The salmon groups also received calcium supplements. The salmon had three different vitamin D₃/vitamin K₁ combinations: high D₃+high K₁, low D₃+high K₁, or high D₃+low K₁. Increased intake of salmon containing high levels of vitamin D₃ (0.35-0.38 mg/kg/fillet) and supplements with the same weekly contribution had a positive influence on bone health as measured by bone biomarkers in postmenopausal women. Consequently, an increased level of vitamin D₃ at least to original level in feed for salmonids will contribute to an improved vitamin D₃ status and may improve human bone health.

Bone turnover and mineral density in adult thalassemic patients: relationships with growth hormone secretory status and circulating somatomedins

Previous evidence supports a role for growth hormone (GH)-insulin-like growth factor (IGF)-I deficiency in the pathophysiology of osteopenia/osteoporosis in adult thalassemia. Moreover, serum IGF-II has never been studied in this clinical condition. Thus, we elected to study the GH secretory status and the levels of circulating somatomedins, correlating these parameters with bone mineral density (BMD) and biochemical markers of bone turnover. A hundred and thirty-nine normal weight adult thalassemic patients (72 men and 67 women) were studied. Lumbar and femoral neck BMD were measured in 106/139 patients. Sixty-eight patients underwent growth hormone releasing hormone plus arginine testing. Measurement of baseline IGF-I and IGF-II was performed in all patients, while osteocalcin, C-terminal telopeptide of type I collagen (CTx), and urinary cross-linked N-telopeptides of type I collagen (NTx) were assayed in 95 of them. Femoral and lumbar osteoporosis/Z score below the expected range for age were documented in 61.3 and in 56.6 % of patients, respectively. Severe GH deficiency (GHD) was demonstrated in 27.9 % of cases, whereas IGF-I SDS was low in 86.3 %. No thalassemic patients displayed circulating levels of IGF-II below the reference range. GH peaks were positively correlated with femoral, but not lumbar, Z score. No correlations were found between GH peaks and osteocalcin, CTx and NTx. GH peaks were positively correlated with IGF-I values, which in their turn displayed a positive correlation with osteocalcin, CTx, and NTx. No correlations emerged between IGF-I values and either femoral or lumbar Z scores. No correlations were found between IGF-II and any of the following parameters: GH peaks, osteocalcin, CTx, NTx, femoral Z score, and lumbar Z score. Our study, besides providing for the first time evidence of a normal IGF-II production in thalassemia, contributes to a better understanding of the involvement of the somatotropin-somatomedin axis in the pathophysiology of bone demineralization in this disease. In particular, the contribution of GHD to femoral osteoporosis appears to be likely mediated by locally produced rather than circulating IGF-I.

Insulin-like growth factor-1 is a mediator of age-related decline of bone health status in men

OBJECTIVE

The role of insulin-like growth factor-1 (IGF-1) in bone health in men is debatable. This study aimed to determine whether IGF-1 is a mediator in age-related decline of bone health status measured by calcaneal speed of sound (SOS) in Malaysian men.

METHODS

The study recruited 279 Chinese and Malay men. Their demographic data, weight, height, calcaneal SOS were taken and fasting blood was collected for total testosterone, sex-hormone binding globulin and IGF-1 assays. The associations between the studied variables were assessed using multiple linear regression (MLR) analysis. Mediator analysis was performed using Sobel test.

RESULTS

There was a significant and parallel decrease of IGF-1 and SOS with age (p < 0.05). Serum IGF-1 was significantly and positively associated with SOS (p < 0.05) but after further adjustment for age, the significance was lost (p > 0.05). The strength of the association between age and SOS decreased after adjusting for IGF-1 level but it remained significant (p < 0.05). Sobel test revealed that IGF-1 was a significant partial mediator in the relationship between age and SOS (z = -4.3).

CONCLUSION

Serum IGF-1 is a partial mediator in the age-related decline of bone health in men as determined by calcaneal ultrasound. A prospective study should be performed to validate this relationship.

The association between insulin-like growth factor I and bone turnover markers in the general adult population

OBJECTIVES

Growth hormone (GH) and its main mediator, insulin-like growth factor I (IGF-I), play a fundamental role in human metabolism. Previous epidemiological studies investigating the association of IGF-I and bone turnover markers (BTMs) yielded conflicting results and were limited by study design or sample size. Therefore, we aimed to investigate the associations between serum levels of IGF-I or the IGF-I/IGF binging protein 3 (IGFBP-3) ratio and levels of BTMs including procollagen type 1 N-terminal propeptide (PINP), C-terminal telopeptides of type 1 collagen (CTX), and bone-specific alkaline phosphatase (BAP).

METHODS

Data from 1463 men and 1481 women who participated in the first follow-up of the Study of Health in Pomerania were used. IGF-I and IGFBP-3 levels were measured using chemiluminescent immunometric assays on an Immulite 2500 analyzer. BTM levels were measured on the IDS-iSYS Multi-Discipline Automated Analyser. Analyses of variance (ANOVA) and quantile regression models were calculated.

RESULTS

In men <55 years and premenopausal women ANOVA and quantile regression analyses revealed positive associations between IGF-I or even stronger the IGF-I/IGFBP-3 ratio and PINP [per unit increase in IGF-I/IGFBP-3 ratio in men: beta (95%-CI) 2.33 ng/ml (0.91; 3.75), p < 0.01; women: 3.63 ng/ml (2.31; 4.95), p < 0.01] or CTX [men: 20.8 ng/l (3.5; 38.0), p = 0.02; women: 12.0 ng/l (-1.2; 25.2), p = 0.07]. Furthermore in postmenopausal women, IGF-I and the IGF-I/IGFBP-3 ratio were inversely related with CTX levels, whereas an inverse U-shaped relation between IGF-I/IGFBP-3 ratio and PINP was found. Regarding BAP, we observed borderline significant associations with IGF-I or the IGF-I/IGFBP-3 ratio in older subjects only.

CONCLUSION

IGF-I levels and particularly free IGF-I, estimated by the IGF-I/IGFBP-3 ratio, are positively related with PINP as a bone formation marker and CTX as a bone resorption marker in healthy adult men younger than 55 years and premenopausal women. In older subjects the found positive as well as negative relations with BTMs have to be further investigated.

Age-related changes in serum levels of insulin-like growth factor-II and its binding proteins correlate with calcaneal bone mineral density among post-menopausal South-Indian women

BACKGROUND

Insulin-like growth factor (IGF) system components are important regulators of bone metabolism, which have a predominant role in determining bone mineral density (BMD). While the serum levels of IGF-I are regulated by various systemic hormones and growth factors, IGF-II levels reflect the skeletal production relative to physical activity, mechanical loading, aging, race etc. Though various studies have been carried out among women of different ethnic groups to understand the relationship between serum levels of IGF-II and BMD, the results seem to be quite inconclusive.

METHODS

We evaluated the same, recruiting South-Indian women who engage themselves in a wide variety of physical activities pertaining to their profession and life style.

RESULTS

Serum levels of IGF-II and IGF binding protein (IGFBP)-3 showed positive correlation with calcaneal BMD, whereas IGFBP-4 showed negative correlation. These IGF system components exhibited similar correlations with serum bone formation markers and opposite trend with bone resorption marker. While both IGF-II and IGFBP-3 levels were observed to be decreased with aging and menopause, IGFBP-4 levels increased.

CONCLUSIONS

The alterations in serum levels of IGF-II and its binding proteins due to aging and menopause could be some of the major contributors of decreased calcaneal BMD observed among elderly women.

Relationship among insulinlike growth factor I concentrations, bone mineral density, and biochemical markers of bone turnover in postmenopausal women: a population-based study

OBJECTIVE

: To assess the association among serum insulinlike growth factor I (IGF-I) concentrations, bone mineral density (BMD), and biochemical markers of bone turnover in a large group of postmenopausal women from the general population.

DESIGN

: As an extension of a larger epidemiological study, the Iranian Multicentral Osteoporosis Study, a total of 406 healthy postmenopausal women (age, 59.0 +/- 7.6 years) were randomly selected from 13 clusters in Bushehr Port. IGF-I, serum CrossLaps, degradation products of C-terminal telopeptides of type I collagen, and osteocalcin were measured by highly specific enzyme-linked immunosorbent assay. BMD was determined for the lumbar spine (L2-4) and proximal femur using dual-energy x-ray absorptiometry.

RESULTS

: The mean (+/- SD) serum IGF-I concentration for all postmenopausal women was 183.35 +/- 65.60 ng/mL. In age-adjusted analyses, there was no correlation between IGF-I and BMD at the lumbar spine and femoral neck. Compared with women in the lowest quartile of IGF-I, women in the highest quartile had a significantly greater means of osteocalcin (P = 0.04) and alkaline phosphatase (P = 0.01). Analysis by quartiles of IGF-I did not reveal an association with serum CrossLaps.

CONCLUSIONS

: Circulating IGF-I is associated with biochemical markers of bone formation, but there is no relationship among IGF-I, degradation products of C-terminal telopeptides of type I collagen, and BMD in postmenopausal women. Clearly more work will be needed before serum IGF-I can be used in clinical practice as a risk predictor for postmenopause-associated loss of bone mass.

The role of IGF-I and IGFBP-1 status and secondary hyperparathyroidism in relation to osteoporosis in elderly Swedish women

IGFBP-1 showed a strong inverse relation to the BMD values. The IGF-I values had a significant positive relation to the BMD values at all sites with the exception of the lumbar spine. The use of loop diuretics was a more important cause of secondary hyperparathyroidism than vitamin D status.

INTRODUCTION

Our aim was to investigate among elderly women the relationship to osteoporosis of calcium-regulating hormones and insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding protein-1 (IGFBP-1).

METHODS

A population-based cross-sectional study of 350 elderly women (mean age 73 years). Measurements of bone mineral density (BMD) of the left hip, lumbar spine and heel and risk markers for osteoporosis were studied.

RESULTS

The BMD values showed significant inverse relationship with the values of IGFBP-1 at all sites of measurement and significant positive relationship with the values of IGF-I at all sites with the exception of the lumbar spine. There was no significant association between the values of BMD and the values of 25-hydroxy vitamin D (25(OH)D). The use of loop diuretics was strongly and significantly associated with elevated levels of PTH >65 pg/ml (OR 4.4, P < 0.001).

CONCLUSIONS

The anabolic growth factor IGF-I and its modulating binding protein IGFBP-1 showed a stronger association with the BMD values than the calcium regulating hormones 25(OH)D and PTH. In this study the use of loop diuretics was a more important cause of secondary hyperparathyroidism than vitamin D status.

Relationships between the insulin-like growth factor I (IGF-I) receptor gene G3174A polymorphism, serum IGF-I levels, and bone mineral density in postmenopausal Korean women

We investigated the relationships between the IGF-I receptor gene G3174A polymorphism, serum IGF-I levels, and bone mineral density (BMD) in postmenopausal Korean women. The IGF-I receptor gene G3174A polymorphism was analyzed in 367 postmenopausal Korean women. Serum levels of IGF-I, bone turnover markers (osteocalcin, bone alkaline phosphatase, carboxy-terminal cross-linking telopeptide of type I collagen), and BMD at the lumbar spine and proximal femur were measured. The frequencies of the AA, GA, and GG genotypes were 10.9%, 44.1%, and 45.0%, respectively. BMD at the lumbar spine was significantly higher for the AA genotype than the other genotypes and showed an A allelic dose effect; however, no significant differences in BMD were observed at the proximal femur with respect to genotype. No differences were noted between the three genotypes in terms of serum levels of IGF-I or bone turnover markers. Women with low BMD showed a lower prevalence of the AA genotype and A allele than age-matched women with normal BMD. Women with the AA genotype were found to have about half the risk of a low BMD than women with other genotypes. In conclusion, IGF-I receptor gene G3174A polymorphism is associated with lumbar spine BMD in postmenopausal Korean women.

High serum IGFBP-2 is predictive of increased bone turnover in aging men and women

Elevated serum IGFBP-2 is associated with lower BMD in men and women. It is unknown whether IGFBP-2 serves as a negative regulator of bone metabolism by decreasing bone formation or increasing bone resorption. Studying an age-stratified community-based sample of 344 men and 276 women, IGFBP-2 was the strongest predictor of increased bone resorption among the IGF/IGFBPs studied.

INTRODUCTION

Serum insulin-like growth factor binding protein-2 (IGFBP-2), which increases with age, is a predictor of low BMD among aging men and women. However, it is unknown whether IGFBP-2 negatively influences bone metabolism by decreasing bone formation or increasing bone resorption. Few have examined the relation between the insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) with bone turnover markers.

MATERIALS AND METHODS

In an age-stratified, random sample of the community, we examined the association between serum IGF-I, IGF-II, IGFBP-1, -2, and -3, and bone turnover markers before and after adjustment for potential confounders (age, body mass index, bioavailable estradiol and testosterone, and sex hormone binding globulin). Analyses were stratified by sex and menopausal status.

RESULTS

We studied 344 men (age range, 23-90 yr) and 276 women (age range, 21-93 yr; 166 postmenopausal) not on oral contraceptives or hormone replacement. Among the IGF/IGFBPs assessed, IGFBP-2 was the strongest and most consistent predictor of bone turnover in men and women. After adjustment for potential confounders, IGFBP-2 was positively associated with osteocalcin (OC) and urine and serum N-teleopeptide (NTX) in men (r = 0.20, 0.26, and 0.23, respectively; p < 0.001), serum C-telopeptide (CTX) in premenopausal women (r = 0.28; p < 0.01), and OC, urine NTX, and serum CTX in postmenopausal women (r = 0.24, 0.33, and 0.19, respectively; p < 0.05).

CONCLUSIONS

Higher serum IGFBP-2, which is predictive of lower BMD, is associated with increased markers of bone resorption, independent of age, body mass, and sex hormones. The association between IGFBP-2 and markers of bone formation may reflect coupling with increased bone resorption, which is not adequate to maintain BMD.

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.

Sexually dimorphic regulation of hepatic isoforms of human cytochrome p450 by growth hormone

Sex differences in drug metabolism have been reported in numerous species, including humans. In rats and mice, sex-dependent differences in circulating growth hormone profiles are responsible for the differential expression of multiple sex-dependent isoforms of cytochrome P450, which is the basis for the sexual dimorphism in drug metabolism. In contrast, very little is known about sex differences in human isoforms of cytochrome P450 and their regulation by growth hormone. In this study, we have examined the effects of physiologic-like exposure doses to dexamethasone and/or pulsatile (masculine) or constant (feminine) human growth hormone on expression levels of CYP3A4, 1A2, 2D6, and 2E1 and the glucocorticoid and growth hormone receptors in hepatocyte cultures obtained from men and women donors. We report that growth hormone can regulate expression of CYP3A4, 1A2, and 2D6. The masculine-like pulsatile growth hormone profile suppresses dexamethasone-induced CYP3A4, 1A2, and 2D6, whereas the feminine-like constant profile is permissive allowing isoform expression to be equal to or greater than glucocorticoid induction alone. There are intrinsic sexual differences in hepatocytes of men and women resulting in different levels of responsiveness of CYP3A4, 1A2, and hormone receptor expression to the same sexually dimorphic growth hormone profiles. Last, although real, the sexually dimorphic effects of growth hormone on human cytochrome P450 expression are not as dramatic as those observed in rats and could easily be overlooked by the heterogeneous backgrounds of human populations.

Susceptibility for postmenopausal osteoporosis: interaction between genetic, hormonal and lifestyle factors

Although previous studies have established the importance of genetic, hormonal and lifestyle factors separately, the integral role of these factors on bone mass in postmenopausal women is still controversial. We examined the association of the collagen 1-alpha-1 gene (COLIA1) and vitamin D receptor gene (VDR) polymorphisms, s-IGF-I, s-25OHD and lifestyle factors with bone mineral density (BMD) in postmenopausal women. We determined anthropometric parameters, lifestyle factors, serum levels of IGF-I and 25OHD, the COLIA1 Sp1 (Mscl) and VDR (Bsml, Taql) polymorphisms by PCR and BMD by dual X-ray absorptiometry in 141 ambulatory postmenopausal Spanish women. There were significant linear correlations between S-25OHD and BMD and between s-IGF-I and BMD. BMD was statistically higher in active subjects. Of the three different polymorphisms, only the COLIA1 Sp1 polymorphism was significantly associated with BMD. In the logistic regression model, the COLIA1 Sp1 polymorphism, S-25OHD, s-IGF-I and physical activity variables were independently associated with osteoporosis. Our study shows that COLIA1 Sp1 polymorphism, S-25OHD and s-IGF-I serum levels and physical activity are independently associated with BMD in postmenopausal Spanish women.

The relationship among serum insulin-like growth factor-I, insulin-like growth factor-I gene polymorphism, and bone mineral density in postmenopausal women in Korea

OBJECTIVE

The objective of this study was to test the hypothesis that the cytosine-adenine polymorphism in the insulin-like growth factor-I gene is associated with serum insulin-like growth factor-I levels and bone mineral density.

STUDY DESIGN

The insulin-like growth factor-I cytosine-adenine polymorphism was analyzed in 300 postmenopausal Korean women. Serum insulin-like growth factor-I, bone alkaline phosphatase, and carboxy-terminal cross-linking telopeptide of type I collagen were measured by immunoradiometric assay and enzyme-linked immunosorbent assay. Bone mineral density at the lumbar spine and proximal femur was determined by dual energy radiograph absorptiometry.

RESULTS

Serum insulin-like growth factor-I and bone mineral density levels in women who were homozygous for a 194-base pair allele were significantly higher than those levels in the 194-base pair heterozygotes or women who did not possess the 194-base pair allele. A significantly decreased prevalence of the 194/194 genotype was observed in the combined group of women with osteopenia and osteoporosis, compared with normal women. No correlation between insulin-like growth factor-I genotypes and bone turnover markers was found.

CONCLUSION

The insulin-like growth factor-I gene cytosine-adenine polymorphism relates with circulating insulin-like growth factor-I levels and bone mineral density at the lumbar spine and proximal femur.

The contribution of IGF-I to skeletal integrity in postmenopausal women

OBJECTIVES

The pathogenic role of the decline in serum concentrations of IGF-I in postmenopausal osteoporosis is not fully elucidated. We investigated the associations among IGF-I, bone mineral density (BMD), ultrasound parameters and prevalence of vertebral fractures in postmenopausal women.

DESIGN

A cross-sectional study.

PATIENTS

One hundred and fifty-four ambulatory postmenopausal women (61 +/- 7 years) referred for osteoporosis screening.

MEASUREMENTS

IGF-I was measured by radioimmunoassay and BMD using dual-energy X-ray absorptiometry. Broadband ultrasound attenuation (BUA) and speed of sound (SOS) at calcaneus were measured by a quantitative ultrasound system.

RESULTS

IGF-I was significantly lower in osteoporotic subjects and correlated positively with BMD, BUA and SOS. After adjusting for age, years since menopause and body mass index, IGF-I accounted for 8.5% of the variance at lumbar spine BMD, 4.6% at femoral neck and 7.1% at calcaneal BUA. BUA was associated with IGF-I independently of BMD. IGF-I was lower in women with vertebral fractures (91 +/- 39 microg/l vs. 114 +/- 44 microg/l; P = 0.003). The osteoporosis densitometric criteria (t-score < or = -2.5 SD) was the most strongly independent associated variable with prevalent vertebral fractures [odds ratio (OR): 3.3 (1.4-7.6)], followed by IGF-I levels below 75th percentile [OR: 3 (1-8.8)].

CONCLUSIONS

Our study shows that IGF-I is strongly associated with bone mineral density and reflects aspects of bone quality. The contribution of IGF-I to skeletal integrity in postmenopausal women is clinically relevant.

Omega-3 polyunsaturated fatty acids and skeletal health

This minireview on skeletal biology describes the actions of prostaglandins and cytokines involved in the local regulation of bone metabolism, it documents the role of lipids in bone biology, and it presents relationships between fatty acids and other factors that impact skeletal metabolism. The data presented herein show consistent and reproducible beneficial effects of omega-3 (n-3) fatty acids on bone metabolism and bone/joint diseases. Polyunsaturated fatty acids modulate eicosanoid biosynthesis in numerous tissues and cell types, alter signal transduction, and influence gene expression. These effects have not been explored in the skeletal system. Future research on n-3 fatty acids in bone biology should focus on the following two aspects. First, the further elucidation of how n-3 fatty acids alter biochemical and molecular processes involved in bone modeling and bone cell differentiation, and second, the evaluation of the potential pharmaceutical applications of these nutraceutical fatty acids in maintaining bone mineral status and controlling inflammatory bone/joint diseases.

Changes in profiles of circulating insulin-like growth factor components during hormone replacement therapy according to the responsiveness to therapy in postmenopausal women

OBJECTIVES

Objectives of this study were (1) to evaluate the changes in the profiles of circulating insulin-like growth factor and of insulin-like growth factor-binding proteins during hormone replacement therapy and their relation with responsiveness to hormone replacement therapy and (2) to investigate the relationship between the changes in these insulin-like growth factor components and the annual changes in bone mineral density in postmenopausal women.

STUDY DESIGN

Insulin-like growth factor and insulin-like growth factor-binding proteins were measured by immunoradiometric assay and Western ligand blotting in sera from 39 postmenopausal women treated with sequential hormone replacement therapy for 1 year. Bone mineral density at the lumbar spine and the proximal portion of the femur was determined by dual-energy x-ray absorptiometry.

RESULTS

No significant change in the serum levels of insulin-like growth factor II and insulin-like growth factor-binding protein was noted during hormone replacement therapy in either the responders to therapy or the nonresponders (women with >3% bone loss per year), but serum levels of insulin-like growth factor I and proportions of insulin-like growth factor-binding proteins 1, 2, and 4 decreased during hormone replacement therapy only in the former group. Changes in insulin-like growth factor components during hormone replacement therapy did not correlate with annual bone mineral density changes.

CONCLUSION

Profiles of circulating insulin-like growth factor I and insulin-like growth factor-binding proteins might be involved in responsiveness to hormone replacement therapy, but changes in these components during hormone replacement therapy do not predict annual changes in bone mineral density.