Decreased serum levels of insulin-like growth factors and IGF binding protein 3 in osteoporosis

Effects of progesterone on serum levels of IGF-1 and on femur IGF-1 mRNA in ovariectomized rats

Local and systemic insulin-like growth factors (IGFs) may be involved in the regulation of bone formation by sex hormones. The present studies describe the in vivo effects of estradiol, progesterone, or both on IGF-1 mRNA abundance in bone, serum IGF-1 levels, and bone formation. Rats were sham-operated (SHAM) or ovariectomized (OVX) at 12 weeks of age and used a week later in three experiments. First, OVX rats were treated with vehicle, estradiol, and/or medroxyprogesterone (MPA) for 3 weeks, and bone formation was assessed in the tibial metaphysis. Second, OVX rats were treated in the same manner and serum IGF-1 levels measured. Third, OVX rats were treated with an injection of vehicle, estradiol, and/or progesterone, and 24 h later, levels of IGF-1 mRNA in the femur were analyzed. The mineralized surface, mineral opposition rate, and bone formation rate (BFR) were higher in OVX than in SHAM rats. The BFR was decreased in estrogen-treated but increased in MPA-treated rats compared with vehicle-treated OVX rats. Circulating levels of IGF-1 were higher in OVX than in SHAM rats but were not affected by sex hormones in a 3-week experiment, whereas these levels were not different among groups in a 24-h experiment. Northern analysis detected 7.5 and 0.8 kb IGF-1 mRNA transcripts. The abundance of IGF-1 mRNA was higher in OVX than in SHAM rats. IGF-1 transcripts 7.5 and 0.8 kb were decreased by 72 and 29%, respectively, in estrogen-treated and increased by 44 and 43%, respectively, in progesterone-treated rats compared with vehicle-treated OVX rats. We conclude that in the short term, estrogen lowers and progesterone raises bone IGF-1 mRNA and these changes are followed by coordinated changes in bone formation rate.

Behavioral and endocrine effects of growth hormone administration in aged female rats

Growth hormone (GH) secretion declines during normal aging along with reproductive activity in mammalian species. Various behavioral changes also occur in aged animals. In these experiments we have studied the effects of GH administration on behavioral and endocrine alterations exhibited by aged (18 months old) female rats of the Sprague-Dawley strain. Animals were selected showing at least 2 weeks of cornified vaginal smears (constant estrous) and treated with GH (0.1 mg/kg SC) daily for 8 weeks. Vaginal smears performed during the drug treatment revealed a recovery of estrous cycle in 60% of animals. GH treatment was also followed by an increased acquisition of shuttle-box active avoidance behavior and a facilitated retention of passive avoidance response. Compared to saline-injected controls, female rats treated with GH also exhibited a decrease of novelty-induced excessive grooming. The endocrine pattern of GH-treated aged female rats revealed a decrease in plasma prolactin levels and an increase in luteinizing hormone and 17 beta-estradiol levels as compared to those of control animals. These results support the concept that behavioral and endocrine alterations occurring in aging are not irreversible and that GH may interfere with these changes probably by means of its trophic action on different target organs.

Serum insulin-like growth factor binding protein profiles in postmenopausal women: their correlation with bone mineral density

OBJECTIVE

The objective of this study was to evaluate the relationship between serum insulin-like growth factor binding protein profiles and bone mineral density measurements and biochemical markers of bone turnover in postmenopausal women.

STUDY DESIGN

Sera from 37 normal healthy postmenopausal women and 14 postmenopausal women with osteoporosis were analyzed for insulin-like growth factor binding proteins and osteocalcin by Western ligand blotting and radioimmunoassay, respectively. Bone mineral density measurements were performed by dual-energy x-ray absorptiometry. Urinary calcium and creatinine excretion were also determined. The data were analyzed statistically by analysis of variance and the least-squares method.

RESULTS

The serum insulin-like growth factor binding protein-2 ratio (insulin-like growth factor binding protein-2 intensity/total insulin-like growth factor binding protein intensity) in postmenopausal women with osteoporosis was significantly higher (p < 0.02) than that in normal healthy postmenopausal women, but the serum insulin-like growth factor binding protein-3 ratio in women with osteoporosis was significantly lower (p < 0.01). The serum insulin-like growth factor binding protein-2 ratio correlated negatively with the bone mineral density of the lumbar spine (p < 0.0001), femoral neck (p < 0.05), trochanter (p < 0.01), and Ward's triangle (p < 0.05), but there was a significant positive correlation between the serum insulin-like growth factor binding protein-3 ratio and the bone mineral density of the lumbar spine (p < 0.001) and trochanter (p < 0.05). No correlations between serum insulin-like growth factor binding protein levels or serum ratios and biochemical markers of bone turnover were noted.

CONCLUSION

The measurement of serum insulin-like growth factor binding protein profiles might be useful in identifying postmenopausal women at risk for osteoporosis.

Cytokines in osteoarthritis: mediators or markers of joint destruction?

OBJECTIVE

The integrity of articular cartilage is maintained by the balance between cytokine-driven anabolic and catabolic processes. Unregulated or excess influences of these molecules are thought to play a part in the pathophysiology of many joint diseases. However, the role of cytokines in osteoarthritis (OA) is not well established. Our aims are twofold: firstly to consider the evidence for the contribution of cytokines to the pathophysiology of OA and secondly to evaluate their potential as markers of disease activity in OA.

METHODS

Cytokine homeostasis, the role of catabolic and anabolic cytokines in maintaining cartilage integrity, and the contribution of such cytokines to destructive processes in OA were examined. Consideration was given to the interrelationship between cartilage, bone, and synovium in OA; metabolites produced by such structures were compared with cytokines as indicators of disease activity.

RESULTS

The evidence reviewed suggests that interleukin-1 (IL-1) and the less potent tumor necrosis factor alpha (TNF alpha) are mediators of joint damage in OA. The cytokines interleukin-6 (IL-6) and leukemia inhibitory factor (LIF) were implicted in both destructive and protective mechanisms, suggesting a dual role. Metabolites of the different components of the joint provided a better measure of disease activity than cytokines.

CONCLUSIONS

Experimental evidence is emerging that catabolic cytokines are mediators of joint damage in OA, although their usefulness as markers of disease activity is limited because of the need to monitor a wide range of ligands and their inhibitors simultaneously. In contrast, metabolites released from cells within bone, synovium, and cartilage related to disease activity and provided prognostic information.

Plasma levels of insulin-like growth factor binding protein-3 in acute trauma patients

Insulin-like growth factors (IGFs) are a family of polypeptides that regulate cell growth. Their action and bioavailability are modified by binding proteins such as IGF binding protein-3 (IGFBP-3). Plasma IGFBP-3 level was found to be growth hormone (GH)-dependent, which makes detection of IGFBP-3 useful in the evaluation of GH secretion. In the early catabolic flow phase of severe injury, when plasma levels of GH and IGF-1 are low versus uninjured levels, the role of IGFBP-3 has not been investigated. We have measured basal levels of these polypeptide hormones in 16 adult (13 men and three women aged 47 +/- 7 years) severely injured (Injury Severity Score, 32 +/- 2), hypermetabolic resting energy expenditure [REE] to basal energy expenditure [BEE] ratio, 1.30 +/- 0.05), ventilator-dependent, multiple-trauma patients within 48 to 60 hours of injury when the patients were receiving maintenance fluids without calories or nitrogen. These basal values were compared with those of 16 age-matched postabsorptive normals. In the catabolic flow phase of injury, plasma levels of GH, IGF-1, and IGFBP-3 were significantly reduced by 50%, 46%, and 45%, respectively. There was a significant linear inverse relationship between IGFBP-3 and age and also a positive correlation between IGFBP-3 and IGF-1 in both control and injured subjects. The ratio of IGFBP-3 to IGF-1 was not changed in trauma victims. Measurement of plasma IGFBP-3 levels has potential as a marker for monitoring GH therapeutic efficacy.

Prevention and treatment of osteoporosis

Because the lifetime risk of fragility fracture for a 50-year-old Caucasian woman is about 40 per cent, a whole-life strategy of osteoporosis prevention is necessary. In childhood, primary prevention of osteoporosis is based on exercise and adequate dietary calcium. In women undergoing menopause, hormone replacement therapy administered for at least ten years remains the preventive treatment of choice, and is associated with a substantial reduction in vertebral and non-vertebral fractures. Intranasal salmon calcitonin and bisphosphonates are effective alternatives, but their effects on fracture rate and their long-term safety require further evaluation. Regarding the prevention of the late bone loss leading to senile osteoporosis, there is now evidence that the reduction of the secondary hyperparathyroidism induced by calcium and vitamin D insufficiencies through the administration of calcium and vitamin D supplements significantly decreases the hip fracture incidence. There is no general consensus about the efficacy of treatment for established osteoporosis with fractures. Fluoride salts have proven their direct stimulating effects on bone formation; dosage must be moderate, and the duration of treatment should be limited to 2-3 years in order not to impair the quality of the new bone. Cyclical therapy with etidronate induces beneficial effects on bone mass in the spine, but its effect on the vertebral fracture rate is not yet established. The new bisphosphonates seem to be promising for the management of osteoporosis. Several other agents such as growth factors, silicon derivatives and strontium salts are in various stages of testing. The new definition of osteoporosis proposed by a WHO study group, no longer based on the fracture but on a low bone mass, is of major interest, because it should make possible to have a more effective therapeutic approach, before the occurrence of an irreversible degree of bone loss.

Treatment of ovariectomized rats with the complex of rhIGF-I/IGFBP-3 increases cortical and cancellous bone mass and improves structure in the femoral neck

Sixteen-week-old Sprague-Dawley rats were ovariectomized (Ovx) or sham-operated and housed for 8 weeks to develop osteopenia prior to systemic administration of rhIGF-I (0.9 and 2.6 mg/kg) alone or the rhIGF-I/IGFBP-3 (0.9, 2.6 and 7.5 mg/kg) complex. After 8 weeks of treatment, proximal femurs were fixed, embedded, and cut through the midneck region. Structural and dynamic histomorphometric analyses were performed using standard techniques. Ovx increased endocortical resorption and modeling-dependent periosteal formation which resulted in decreased cortical bone area. Despite increased bone formation, trabecular number, thickness, and area were all reduced due to increased resorption. Structural changes following Ovx included fewer struts and nodes, a higher percentage of the simpler strut forms, and reduced endocortico-trabecular connectivity. Eight weeks of treatment with rhIGF-I or rhIGF-I/IGFBP-3 promoted periosteal and endocortical bone formation and reduced the endocortical resorption induced by Ovx. Both rhIGF-I formulations stimulated bone formation on existing trabecular surfaces which increased trabecular thickness and area but not trabecular number. These treatments prevented further deterioration of the trabecular network caused by Ovx and preserved endocortico-trabecular connectivity. In summary, changes in the femoral neck following Ovx appear to be similar in rats and humans. The highest dose of rhIGF-I/IGFBP-3 used in this study showed the best results in promoting cortical and cancellous bone formation, and appears to be promising therapy for human osteopenias.

The effect of systemically administered rhIGF-I/IGFBP-3 complex on cortical bone strength and structure in ovariectomized rats

The action of systematically administered recombinant human insulinlike growth factor-I (rhIGF-I) complexed to its natural binding protein-3 (rhIGFBP-3) on cortical bone dynamic, structural, and mechanical properties was tested in previously ovariectomized (Ovx) rats. Bilateral ovariectomy or sham surgery was performed on 16-week-old female Sprague-Dawley rats. Eight weeks after surgery basal Sham and Ovx rats were killed to establish baseline cortical bone values before the initiation of treatment with rhIGF-I/IGFBP-3 complex. At that time, Ovx rats had increased body weight and body fat mass with reduced femoral BMC and BMD relative to basal Shams. Bone formation rates in Ovx rats were increased on both cortical envelopes relative to time-matched controls. The thickness of the inner lamellar bone layer and average cortical width were reduced due to increased endocortical erosion. A similar ratio between Sham and Ovx rats in body mass and composition and femoral BMC and BMD continued throughout the experiment. Sixteen weeks after surgery bone formation rates at both cortical envelopes in Ovx rats were reduced relative to Shams, but endocortical erosion remained high causing a further decrease in thickness of the inner lamellar layer. As a result of periosteal bone modeling. Ovx rats exhibited a larger femoral cross-sectional area and periosteal perimeter, as well as a thicker outer lamellar layer. Newly deposited periosteal bone increased ultimate torque values in the Ovx rats relative to Shams at 16 weeks. Treatment of Ovx rats with the rhIGF-I/IGFBP-3 complex increased body weight, lean body mass, and femoral BMC and BMD.(ABSTRACT TRUNCATED AT 250 WORDS)

The dilemma of osteoporosis in men

Hip fractures in men account for one third of all hip fractures and have a higher mortality than in women. The age-specific incidence of hip fractures is increasing so that the public health burden will increase out of proportion to the burden imposed by the increase in the numbers of elderly men in the community. Vertebral fractures are a public health problem of lesser magnitude in terms of morbidity, mortality, and cost, but they are debilitating and are seen commonly in clinical practice. (Forearm fractures should probably not be regarded as a public health problem.) The pattern of earlier gain/later loss of bone during ageing in healthy men is well documented. Peak bone mass is higher in men than women because men have bigger bones. Peak bone density is the same. The absolute amount of trabecular bone lost at the spine and iliac crest during ageing is similar in men and women. Cortical bone loss is less in men. It is less because endocortical resorption is less, and periosteal formation is greater, in men. Bone loss may accelerate in elderly men and women (rather than decelerate), perhaps because endocortical resorption and increasing cortical porosity increase the effective surface available for resorption in cortical bone. Thus, bone fragility is less in men because (a) the cross-sectional surface of the vertebral body is larger; (b) trabecular bone loss is less as a percentage of the higher peak bone mass; (c) trabecular bone loss occurs by thinning rather than perforation; and (d) periosteal appositional growth compensates for endocortical resorption by maintaining the bending strength of bone. Reduced bone density in men with fractures may be due to reduced peak bone density and bone loss. As found in women with spine fractures, men with fractures have smaller bone size. Bone loss occurs by reduced bone formation and increased bone resorption. Loss of connectivity appears to predominate in men with vertebral fractures; trabecular thinning appears to predominate in men with hip fractures. Whether men with fractures have increased bone fragility due to reduced periosteal appositional growth during ageing is unknown. The age-related decline in testosterone, adrenal androgens, growth hormone, and insulin-like growth factor 1 may be concomitants of ageing or may contribute to reduced bone-formation and bone loss. Men with vertebral fractures may be more deficient in growth hormone and insulin-like growth factor 1. Thy often have illness, hypogonadism, or illnesses associated with hypogonadism that should be sought with a high index of suspicion.(ABSTRACT TRUNCATED AT 400 WORDS)

Treatment of osteoporosis

Osteoporosis is a common disorder affecting the health of many adults. Strategies for fracture prevention include optimization of peak bone mass and prevention of bone loss at menopause and with aging. Genetic, nutritional, and life-style factors influence peak bone mass and may be used to focus preventive efforts. Once peak bone mass is reached, increased bone resorption may be the major pathogenetic factor. Calcium plus vitamin D, estrogen replacement therapy, calcitonin, and etidronate are agents currently available for treatment of osteoporosis; they act by inhibiting bone resorption. The failure of bone formation to keep pace with bone resorption also contributes to bone loss. Fluoride and intermittent parathyroid hormone therapy increase bone formation; however, more data are needed to determine efficacy. Insulin-like growth factors, transforming growth factor-beta (TGF-beta), and bone morphogenetic proteins may stimulate bone formation, but they have not yet been tested clinically. New approaches to treatment of osteoporosis will emerge as our understanding of the pathogenesis increases.

Circulating levels of insulin-like growth factor binding protein 3 (IGFBP-3) and insulin-like growth factor I (IGF-I) in perimenopausal women

The study investigated possible menopause-related changes in circulating insulin-like growth factor binding protein 3 (IGFBP-3) levels and their relationship with insulin-like growth factor I (IGF-I) plasma levels. Forty-three healthy women, aged 45-55 years, were studied (22 premenopausal and 21 postmenopausal, matched for age and body mass index); in all subjects plasma IGF-I and IGFBP-3 levels were measured by radioimmunoassay. No difference was found between mean IGFBP-3 plasma levels in the two groups studied (premenopausal 3.42 +/- 0.49 v postmenopausal 3.46 +/- 0.58 mg/l), while mean IGF-I levels were significantly lower in postmenopausal as compared with premenopausal women (136.7 +/- 37.86 v 175.7 +/- 51.91 ng/ml, p < 0.02). Multiple regression analysis showed no significant effect of age, body mass index and years since menopause on IGFBP-3 levels; however, considering the IGF-I/IGFBP-3 ratio as a possible parameter of circulating free somatomedin C, an inverse correlation was found with years since menopause (n = 43, r = -0.499, p < 0.001). We conclude that lack of oestrogen induces different effects on circulating IGF-I and IGFBP-3, possibly reflecting a real decrease in IGF-I activity.

Growth hormone-dependent insulin-like growth factor binding protein is a major determinant of bone mineral density in healthy men

To establish the major determinants of bone mass, we assessed relationships between bone mineral density (BMD) and height, weight, body mass index (BMI), muscle strength, physical capacity (VO2max), body composition, serum concentrations of insulin-like growth factor I (IGF-I), growth hormone (GH), the GH-dependent IGF binding protein (IGFBP-3), testosterone, sex hormone binding globulin (SHBG), osteocalcin, and parathyroid hormone (PTH) in 38 healthy men between 25 and 59 years of age. Values of BMD at all sites (total body, lumbar spine, and hip) were strongly correlated with IGFBP-3 (r = 0.51-0.64, p < 0.001 at all sites), and total-body BMD was also significantly correlated with IGF-I (r = 0.43, p = 0.01). BMD measurements of the total body and of the different sites of the hip were negatively correlated with age and positively with weight, BMI, muscle strength, VO2max, and fat-free weight. IGF-I and IGFBP-3 were both positively related to muscle strength and VO2max. In a stepwise forward multiple-regression analysis, the best model was obtained for the femoral neck, where IGFBP-3, GH, PTH, age, IGF-I, and BMI explained 77% of the variation in BMD. The partial regression coefficients of IGFBP-3, PTH, and BMI were all positive, whereas age, GH, and IGF-I were negatively correlated with BMD. In summary, IGFBP-3 correlated better with BMD than any other study parameter. The findings indicate that GH is of importance for bone mass and suggest that IGFBP-3 not only reflects the integrated GH secretion but also has a direct role in the endocrine regulation of bone metabolism.