Relationship of serum leptin concentration with bone mineral density in the United States population

Obesity accelerates mouse mammary tumor growth in the absence of ovarian hormones

Obesity increases incidence and mortality of breast cancer in postmenopausal women. Mechanisms underlying this association are poorly understood. Suitable animal models are needed to elucidate potential mechanisms for this association. To determine the effects of obesity on mammary tumor growth, nonovariectomized and ovariectomized C57BL/6 mice of various body weights (lean, overweight, and obese) were implanted subcutaneously with mammary tumor cells from syngeneic Wnt-1 transgenic mice. In mice, the lean phenotype was associated with reduced Wnt-1 tumor growth regardless of ovarian hormone status. Ovariectomy delayed Wnt-1 tumor growth consistent with the known hormone responsiveness of these tumors. However, obesity accelerated tumor growth in ovariectomized but not in nonovariectomized animals. Diet-induced obesity in a syngeneic mouse model of breast cancer enhanced tumor growth, specifically in the absence of ovarian hormones. These results support epidemiological evidence that obesity is associated with increased breast cancer incidence and mortality in postmenopausal but not premenopausal women. In contrast, maintaining a lean body weight phenotype was associated with reduced Wnt-1 tumor growth regardless of ovarian hormone status.

Central control of bone remodelling

The discovery that the brain controls bone remodelling has provided a new paradigm for our understanding of bone biology. This review summarises the genetic, molecular and physiological bases for the central control of bone remodelling and discusses the future directions of this new research field of neuroskeletal biology.

Association of leptin receptor polymorphisms Lys109Arg and Gln223Arg with serum leptin profile and bone mineral density in Korean women

OBJECTIVE

The objective of the study was to examine the relationship of the LEPR Lys109Arg and Gln223Arg polymorphisms and the serum leptin profile and bone mineral density (BMD).

STUDY DESIGN

Cross-sectional study on a cohort of 145 premenopausal and 118 postmenopausal Korean women. The BMDs and serum levels of leptin, the soluble leptin receptor (sLR), and estradiol were measured, and the LEPR gene was genotyped.

RESULTS

The distributions of the LEPR Lys109Arg and Gln223Arg polymorphisms in all study subjects are as follows: Lys/Lys, 2.7%; Lys/Arg, 27.0%; Arg/Arg, 70.3%; Gln/Gln, 2.7%, Gln/Arg, 19.8%, and Arg/Arg, 77.5%, respectively. Premenopausal subjects carrying the Lys109 allele had a higher total hip BMD (P = .044) and showed a nonsignificant trend toward a higher femoral neck and lumbar BMD than the subjects without this allele.

CONCLUSION

Our study suggests the LEPR Lys109Arg polymorphism is one of the genetic determinants of the peak bone mass in Korean women.

Relationships between serum adiponectin, leptin, resistin, visfatin levels and bone mineral density, and bone biochemical markers in Chinese men

BACKGROUND

Adiponectin, leptin, resistin, and visfatin, as the main circulating peptides secreted by adipose tissue, are potential contributors to bone metabolism. We investigated whether these serum adipocytokines levels are associated with BMD and bone turnover biochemical markers in 232 Chinese men (20-80 y).

METHODS

Serum adiponectin, leptin, resistin, and visfatin levels were determined by ELISA.

RESULTS

Leptin had a positively correlation with fat mass, and remained significant after adjustment for age and BMI. There was a significant negative weak correlation between adiponectin and fat mass, and disappear after adjustment for age and BMI. Resistin and visfatin were not significantly correlated with fat mass. In the multiple linear stepwise regression analysis, lean mass and adiponectin, but not leptin, resistin and visfatin, were independent predictors of BMD. The significant positive correlations between adiponectin and bone-specific alkaline phosphatase (BAP), bone cross-linked N-telopeptides of type collagen (NTX) were found, and remained significant after adjustment for age and fat mass.

CONCLUSIONS

Adiponectin was an independent predictor of BMD in Chinese men, and positively correlated with bone turnover biochemical markers. It suggested that adiponectin exert a negative effect on bone mass in men.

IGF-1 as an early marker for low bone mass or osteoporosis in premenopausal and postmenopausal women

To find out which of the following parameters-serum levels of insulin-like growth factor 1 (IGF-1), osteoprotegerin (OPG), leptin, osteocalcin (OC), and urinary excretion of N-terminal telopeptide of type I collagen (NTx), can be used as an early marker for osteopenia/osteoporosis in women diagnosed by dual-energy X-ray absorptiometry (DXA), 282 premenopausal and 222 postmenopausal women aged 20-75 years were investigated by the measurement of bone mineral densities (BMDs) at lumbar spine (LS) and femoral neck (FN) by DXA, together with serum concentrations of IGF-1, OPG, leptin, OC, and urinary NTx. The characteristics of the earliest marker(s) were tested with the receiver operating characteristic (ROC) analysis. The area under the curve (AUC), sensitivity, and specificity parameters were determined. It was revealed that serum levels of IGF-1 and leptin changed the earliest, with both markers significantly decreasing (P < 0.0001) or increasing (P = 0.020), respectively, at age 30. However, in ROC analysis, IGF-1 was the only early parameter that had the capacity to differentiate the low bone mass/osteoporosis women from the normal ones (P < 0.0001). If the serum level of IGF-1 at 1.5 SD below its peak was adopted as a cutoff point, it could identify women with low bone mass/osteoporosis with a sensitivity of 73% and specificity of 67%. In the premenopausal women subgroup analysis, the low bone mass women (30/282, 10.6%) were older (38.2 +/- 1.7 vs. 34.5 +/- 0.5 years; P = 0.026), with lower serum levels of IGF-1 (215.1 +/- 22.4 vs. 278.8 +/- 9.4 ng/ml; P = 0.02) and less lean mass (33.1 +/- 0.6 vs. 34.8 +/- 0.2 kg; P = 0.010) than the normal ones. After controlling for age, the serum level of IGF-1 had a weak, but still significant, positive correlation with lean mass (r = 0.17, P < 0.001). In conclusion, measurement of serum IGF-1 in young women may help in the early identification of those at risk for developing low bone mass and osteoporosis.

Bone mass in prepubertal boys is associated with a Gln223Arg amino acid substitution in the leptin receptor

OBJECTIVE

The contribution of leptin to bone mass acquisition in humans remains unclear. We investigated the association of the Gln223Arg polymorphism in the leptin receptor gene (LEPR) with bone mineral content (BMC) and areal bone mineral density (aBMD) in prepubertal boys and LEPR interaction with vitamin D receptor (VDR) genotypes (Bsm1 and Fok1).

DESIGN

In a cross-sectional design with a longitudinal follow-up, dual-energy x-ray absorptiometry measurements at the lumbar spine, hip, femoral diaphysis, and radius were performed at baseline (mean age 7.4 +/- 0.4 yr) and 2 yr later in 222 healthy Caucasian males.

RESULTS

LEPR genotypes were significantly associated with baseline BMC at the hip (P = 0.017), femur diaphysis (P = 0.019), and radius (P = 0.007) and with height (P = 0.041) as well as with physical activity (P = 0.016). Associations with height and BMC at femur diaphysis and radius remained significant after 2 yr. Significant differences in 2-yr bone mass gain at the spine and femur neck were also found among LEPR genotypes. In contrast, adjusting BMC for projected bone area (aBMD) and/or weight, height, and physical activity resulted in a weak association only at the femur (P = 0.014-0.054). VDR polymorphisms were not associated with BMC or aBMD, but significant interactions occurred between VDR Fok1 and LEPR genotypes.

CONCLUSIONS

The LEPR Gln223Arg polymorphism was associated with bone mass in growing boys. The association, however, was markedly dependent on bone area, body size, and physical activity, in addition to VDR genetic variation, suggesting that the leptin system may modulate bone mass in humans mostly through indirect mechanisms.

Relation of increased leptin concentrations to history of myocardial infarction and stroke in the United States population

Leptin, an adipose tissue-derived hormone, has been linked to cardiovascular outcomes; however, data are limited in the United States population, especially women. To assess the association between leptin concentrations and history of myocardial infarction (MI) and stroke independently of traditional cardiovascular risk factors, we analyzed data from 6,239 subjects (mean age 47 years; 3,336 women) with measurements of serum leptin and full assessment of cardiovascular risk factors from the National Health and Nutrition Examination Survey (NHANES) III. Logistic regression was used to estimate the cross-sectional association of leptin concentrations (highest quartile versus lowest quartile) and history of MI, stroke, and the composite end point of MI or stroke (MI/stroke). Gender-specific models of leptin were adjusted for age, race, dyslipidemia, hypertension, diabetes, smoking, and obesity status. There were 212 men with MI/stroke (5.4%), 154 with MI (4.1%), and 82 with stroke (1.7%). There were 135 women with MI/stroke (2.6%), 74 with MI (1.5%), and 78 with stroke (1.4%). In multivariate analysis, high leptin level was significantly and independently associated with MI/stroke in men (odds ratio [OR] 2.41, 95% confidence interval [CI] 1.20 to 4.93) and women (OR 4.26, 95% CI 1.75 to 10.73); with MI in men (OR 3.16, 95% CI 1.40 to 7.37) and women (OR 3.96, 95% CI 1.29 to 12.72), and with stroke in women (OR 3.20, 95% CI 1.04 to 10.54) but not in men (OR 1.37, 95% CI 0.38 to 3.88). In conclusion, in the United States population, increased leptin concentrations are significantly associated with MI/stroke in men and women independently of traditional cardiovascular risk factors and obesity status.

Serum leptin and adiponectin are positively associated with bone mineral density at the distal radius in patients with type 2 diabetes mellitus

There have been several reports about associations of serum leptin or adiponectin with bone mineral density and biochemical markers of bone turnover. However, the precise roles of adipocytokines in bone metabolism have not been fully elucidated. We investigated the associations of serum level of leptin or adiponectin with bone mineral density, serum osteocalcin, and urinary N-terminal telopeptide of type I collagen (NTX) in 40 Japanese patients with type 2 diabetes mellitus. Bone mineral density was measured by using dual-energy x-ray absorptiometry at different sites (distal radius, femoral neck, and lumbar spine) and was expressed as z score. Multiple regression analysis revealed that there were significant positive correlations between serum leptin or adiponectin level and z score at the distal radius, but not at the femoral neck or the lumbar spine. Although no correlation was observed between serum leptin and serum osteocalcin, there was a significant negative correlation between serum leptin and urinary NTX, a marker of bone resorption. No correlation was observed between serum adiponectin and serum osteocalcin or urinary NTX. These results indicate that leptin and adiponectin may have a protective effect on bone metabolism in patients with type 2 diabetes mellitus.

The new field of neuroskeletal biology

The fields of neuroscience and bone biology have recently converged following the discovery that bone remodeling is directly regulated by the brain. This work has defined bone remodeling as one of the cardinal physiological functions of the body, subject to homeostatic regulation and integrated with the other major physiological functions by the hypothalamus. Central to this discovery was the definition of the adipocyte-derived hormone leptin as a regulator of both arms of bone remodeling, formation and resorption, through its action on the ventromedial hypothalamus and subsequently via the sympathetic nervous system to osteoblasts. The characterization of the sympathetic nervous system as a regulator of bone remodeling has led to several large clinical studies demonstrating a substantial protective effect of beta-blockers, particularly beta1-blockers, on fracture risk. Studies in model organisms have reinforced the role of the central nervous system in the regulation of bone remodeling in vivo by the identification of several additional genes, namely cocaine and amphetamine regulated transcript (Cart), melanocortin 4 receptor (Mc4R), neuropeptide Y (NPY), Y2 receptor, cannabinoid receptor CB1 (Cnbr1), and the genes of the circadian clock. These genes have several common features, including high levels of expression in the hypothalamus and the ability to regulate other major physiological functions in addition to bone remodeling including energy homeostasis, body weight, and reproduction. We review the major pathways that define the new field of neuroskeletal biology and identify further avenues of inquiry.

The relationship between birth weight leptin and bone mineral status in newborn infants

BACKGROUND

The positive relationship between fat mass, bone mass and leptin has been shown in fetal mouse cartilage/bone. It has been shown that umbilical venous leptin predicts both the size of the neonatal skeleton and its estimated volumetric mineral density.

AIMS

This study investigates how birth weight and bone mineralization correlate with leptin levels. In addition, we aimed to determine the predictive value of anthropometrics measurements and gender on variability in bone mineral status.

METHODS

Umbilical cord venous blood samples were obtained at the delivery from 100 term newborn infants. Forty of the newborn infants had birth weights appropriate for gestational age (AGA), 30 were small for gestational age (SGA) and 30 were large for gestational age (LGA). Data were acquired using the whole body dual energy X-ray obsorptiometry scanner in the first 24 h after birth.

RESULTS

Leptin concentrations were higher in LGA (36.6 +/-12.0 ng/ml; p < 0.0001), but lower in SGA (11.7 +/- 5.6 ng/ml; p < 0.001) than in AGA infants (20.3 +/- 7.6 ng/ml). Whole body bone mineral density and whole body bone mineral content were higher in LGA babies (0.442 +/- 0.025 g/cm(2), 71.6 +/- 9.0 g, p < 0.01, p < 0.001, respectively) but lower in SGA (0.381 +/- 0.027 g/cm(2), 29.1 +/- 9.1 g, p < 0.001, p < 0.001, respectively) than in AGA babies (0.426 +/- 0.022 g/cm(2), 53.7 +/- 9.6 g, respectively). The percentage of whole body bone mineral content was lower in SGA (1.3 +/- 0.3) than in AGA (1.6 +/- 0.2, p < 0.001) and LGA (1.7 +/- 0.2, p < 0.001). In stepwise linear regression analyses models; leptin is not found related to the bone indices.

CONCLUSION

Our study does not provide support for the hypothesis that leptin may play a major role in the regulation of bone metabolism in the developing skeleton.

Leptin is a negative independent predictor of areal BMD and cortical bone size in young adult Swedish men

The association between leptin and areal BMD has been controversial, and the predictive role of leptin on cortical volumetric BMD and bone size has not previously been studied. We show that leptin is a negative independent predictor of aBMD (DXA), at several measured sites, and of cortical bone size (pQCT) in a large population of young men.

INTRODUCTION

Recent findings suggest that both adipose tissue (AT) and bone mass are regulated by leptin. Previous reports studying the association between leptin and areal BMD (aBMD) have yielded conflicting results. The role of leptin on volumetric BMD (vBMD) and bone size of the cortical and trabecular bone compartments has not previously been studied.

MATERIALS AND METHODS

The Gothenburg Osteoporosis and Obesity Determinants (GOOD) study is a population-based study of 1068 men (age, 18.9 +/- 0.6 [SD] years). aBMD of the total body, lumbar spine, femoral neck, both radii, and trochanter, as well as total body AT and lean mass (LM) were measured using DXA, whereas cortical and trabecular vBMD and bone size were measured by pQCT.

RESULTS

Total body LM could explain a larger magnitude of the difference in the variation in aBMD and cortical bone size than what total body AT could (total body aBMD: LM 37.4% versus AT 8.7%; tibia cross-sectional area [CSA]: LM 46.8% versus AT 5.6%). The independent role of leptin on bone parameters was studied using a multiple linear regression model, including age, total body LM and AT, height, present physical activity, calcium intake, and smoking as covariates. Leptin was found to be a negative independent predictor of aBMD (total body: beta = -0.08, p = 0.01; lumbar spine: beta = -0.13, p < 0.01; trochanter: beta = -0.09, p = 0.01), as well as of the cortical bone size (CSA and thickness) of both the radius (CSA: beta = -0.12, p < 0.001) and tibia (CSA: beta = -0.08, p < 0.01), but not of the cortical or trabecular vBMD of these bones.

CONCLUSION

Our results indicate that LM has a greater impact on bone mass than AT. Our findings further show that leptin is a negative independent predictor of aBMD at several measured sites and of bone parameters reflecting cortical bone size, but not vBMD, in a large population of young Swedish men.

Osteoporosis in the elderly with chronic kidney disease

Considering the aging dialysis population of today, increasing our knowledge about the nature, diagnosis and the treatment of bone mineral density (BMD) problems in end-stage renal disease (ESRD) patients deserves more attention. Osteoporosis is basicly defined as a decrease in bone mass. Large epidemiological studies in general population have identified several risk factors for osteoporosis including advancing age, female gender, white race, decreased calcium intake, gastric acid suppression therapy, sedentary lifestyle, premature loss of gonadal function, decreased estrogen secretion, thin body habitus, decreased physical activity, cigarette smoking, alcohol abuse, excess glucocorticoid exposure, and possibly some genetic factors. Osteoporosis in ESRD patients is only a part of a wider spectrum of metabolic bone problems, namely uremic osteodystrophy. Therefore, its diagnosis, management and follow-up may differ from the general population and an individualization of diagnosis and definition for dialysis population may be necessary. However, standard diagnostic tools such as dual energy X-ray absorptiometry (DEXA) have been widely used for the assessment of bone mineral deficiency status in ESRD patients. Regardless of the methods, most of the studies are in concordance with a reduced BMD in HD and PD patients. Dialysis patients are known to be at increased risk for low-trauma fractures. Thinning of cortical bone, which is responsible for the largest contribution toward reduced bone mineral content in chronic renal failure results in increased fracture risk. In either normal population and dialysis patients, fracture risk is increased with age. But in dialysis patients, besides age, several other factors may also affect the degree of bone mineral deficiency, and age-BMD relationship may be blunted. Female sex, in hemodialysis patients is negatively associated with total hip BMD. While several studies have been unable to demonstrate any association between BMD and PTH levels, larger body size has been shown to have a significant positive effect on BMD in both hemodialysis and peritoneal dialysis patients. Although they have been used in small groups of chronic kidney disease (CKD) and ESRD patients, because of their potential nephrotoxicity and hypocalcemic effects, use of biphosphonates in renal patients is questionable. Currently, bone biopsy, in order to exclude adynamic bone disease is recommended before beginning treatment with bisphosphonates in chronic kidney disease and dialysis patients.

Leptin predicts BMD and bone resorption in older women but not older men: the Rancho Bernardo study

We studied the relation of leptin to bone, bone loss, and bone turnover in community-dwelling men and women. Leptin predicted higher BMD and lower bone turnover only in women. Leptin was not associated with 4-year bone loss in either sex.

INTRODUCTION

Leptin, the protein product of the obesity (OB) gene produced in fat tissue, was originally thought to be involved only in the regulation of food intake and energy balance. Recent evidence suggests that leptin may play a role in the pathophysiology of several chronic diseases. Studies of the association between leptin and bone have been numerous yet inconclusive. Only one previous longitudinal study has been reported, which showed no association of leptin with BMD after adjusting for body size.

MATERIALS AND METHODS

We report the association of serum leptin with BMD at the hip, spine, and midshaft radius in community-dwelling men (n = 498) and nonestrogen-using postmenopausal women (n = 411) 45-92 years of age. Serum leptin was measured in blood obtained between 1984 and 1987. Between 1988 and 1991, BMD was measured at the midshaft radius by single photon absorptiometry and at the femoral neck, total hip, and lumbar spine by DXA; at the same visit, height, weight, and body fat (by bioelectrical impedance analysis) were measured, and bone resorption was assessed in a subset of men (n = 286) and women (n = 241) using urine N-telopeptide (NTX). Four years later, axial BMD was remeasured in 536 participants. Sex-specific associations of leptin with BMD, NTX, and bone loss were tested using regression analysis.

RESULTS

In unadjusted analyses, leptin was associated with BMD at the femoral neck, total hip, lumbar spine, and midshaft radius in both sexes (p < 0.01). In multiple regression analyses, adjusted for age, BMI, and other bone-related factors, only women showed a graded stepwise positive association between serum leptin and BMD at all sites and a negative stepwise association with NTX (all p for trend < 0.01). Baseline leptin levels did not predict 4-year bone loss in either sex.

CONCLUSIONS

A favorable dose-dependent leptin-BMD association unexplained by obesity was observed only in women. The reason for the sex difference is unknown.

Bone metabolism in elite male rowers: adaptation to volume-extended training

We examined the effect of 6-month volume-extended training on bone metabolism in elite male rowers. Twelve elite male rowers (20.8+/-3.0 years; 192.9+/-4.7 cm; 91.9+/-5.3 kg; body fat 10.1+/-2.3%; VO2max 6.2+/-0.5 l min(-1)) participated in this study. Bone biochemical markers, hormones, bone mineral content (BMC), and bone mineral density (BMD) were assessed before and after training. Average weekly training volume was significantly higher (P<0.05) during the 6 months of heavy training compared to relative rest (11.6+/-0.4 h week(-1) vs. 16.8+/-0.6 h week(-1)), while intensity remained the same. At the end of training, only arm BMD was significantly increased by 5.7%. Osteocalcin (16.6%), insulin-like growth factor-1 (IGF-1) (20.2%) and the bioavailability IGF-1 index (17.9%) were significantly increased. Before heavy training, relationships were observed between the whole body BMD and growth hormone (r=0.64; P< or =0.02), lumbar spine BMD and 1.25(OH)2 vitamin D (r=0.69; P< or =0.04), arm BMD and testosterone (r=0.59; P< or =0.05), and arm BMD and adiponectin (r=0.59; P< or =0.05). No relationship was found between BMC or BMD and blood biochemical measures 6 months later (r=0.56; P> or =0.05). In addition, osteocalcin was related to IGF-1 (r>0.58; P<0.048) and bioavailability IGF-1 index (r>0.59; P< or =0.055) before and after training. In summary, heavy training had a moderately favorable effect on BMD. Bone tissue at specific skeleton sites is sensitive to changes in training volume even in athletes with already high BMD values. Changes in BMD and bone formation may be caused by changes in specific hormones such as IGF-1 and adiponectin in male athletes.

Leptin and its emerging role in children and adolescents

Leptin is an adipocyte-secreted hormone which plays a key role in energy homeostasis. Recent “proof of concept” studies involving leptin administration to humans support its critical role in regulating energy homeostasis, neuroendocrine and immune function as well as insulin resistance in states of energy/ caloric deprivation. Moreover, interventional studies in leptin deficient children and observational studies in normal girls and boys support a role for leptin as a permissive factor for the initiation of puberty in children. The potential clinical usefulness of leptin in several disease states in children and adolescents, including hypothalamic amenorrhea, eating disorders and syndromes of insulin resistance is still under investigation.

Physical activity in the prevention and amelioration of osteoporosis in women : interaction of mechanical, hormonal and dietary factors

Osteoporosis is a serious health problem that diminishes quality of life and levies a financial burden on those who fear and experience bone fractures. Physical activity as a way to prevent osteoporosis is based on evidence that it can regulate bone maintenance and stimulate bone formation including the accumulation of mineral, in addition to strengthening muscles, improving balance, and thus reducing the overall risk of falls and fractures. Currently, our understanding of how to use exercise effectively in the prevention of osteoporosis is incomplete. It is uncertain whether exercise will help accumulate more overall peak bone mass during childhood, adolescence and young adulthood. Also, the consistent effectiveness of exercise to increase bone mass, or at least arrest the loss of bone mass after menopause, is also in question. Within this framework, section 1 introduces mechanical characteristics of bones to assist the reader in understanding their responses to physical activity. Section 2 reviews hormonal, nutritional and mechanical factors necessary for the growth of bones in length, width and mineral content that produce peak bone mass in the course of childhood and adolescence using a large sample of healthy Caucasian girls and female adolescents for reference. Effectiveness of exercise is evaluated throughout using absolute changes in bone with the underlying assumption that useful exercise should produce changes that approximate or exceed the absolute magnitude of bone parameters in a healthy reference population. Physical activity increases growth in width and mineral content of bones in girls and adolescent females, particularly when it is initiated before puberty, carried out in volumes and at intensities seen in athletes, and accompanied by adequate caloric and calcium intakes. Similar increases are seen in young women following the termination of statural growth in response to athletic training, but not to more limited levels of physical activity characteristic of longitudinal training studies. After 9-12 months of regular exercise, young adult women often show very small benefits to bone health, possibly because of large subject attrition rates, inadequate exercise intensity, duration or frequency, or because at this stage of life accumulation of bone mass may be at its natural peak. The important influence of hormones as well as dietary and specific nutrient abundance on bone growth and health are emphasised, and premature bone loss associated with dietary restriction and estradiol withdrawal in exercise-induced amenorrhoea is described. In section 3, the same assessment is applied to the effects of physical activity in postmenopausal women. Studies of postmenopausal women are presented from the perspective of limitations of the capacity of the skeleton to adapt to mechanical stress of exercise due to altered hormonal status and inadequate intake of specific nutrients. After menopause, effectiveness of exercise to increase bone mineral depends heavily on adequate availability of dietary calcium. Relatively infrequent evidence that physical activity prevents bone loss or increases bone mineral after menopause may be a consequence of inadequate calcium availability or low intensity of exercise in training studies. Several studies with postmenopausal women show modest increases in bone mineral toward the norm seen in a healthy population in response to high-intensity training. Physical activities continue to stimulate increases in bone diameter throughout the lifespan. These exercise-stimulated increases in bone diameter diminish the risk of fractures by mechanically counteracting the thinning of bones and increases in bone porosity. Seven principles of bone adaptation to mechanical stress are reviewed in section 4 to suggest how exercise by human subjects could be made more effective. They posit that exercise should: (i) be dynamic, not static; (ii) exceed a threshold intensity; (iii) exceed a threshold strain frequency; (iv) be relatively brief but intermittent; (v) impose an unusual loading pattern on the bones; (vi) be supported by unlimited nutrient energy; and (vii) include adequate calcium and cholecalciferol (vitamin D3) availability.

Gender differences in relationships between body composition components, their distribution and bone mineral density: a cross-sectional opposite sex twin study

Numerous studies indicate that bone mineral density (BMD) is closely related to body mass and its components. Most studies have examined these relationships in women with little attention given to how these relationships differ by gender. The aims of the present study were to use the opposite sex twin model to determine if there were gender differences in the relationship between body composition and its relation to BMD and how any such differences were influenced by age. We measured body composition and bone mass by dual energy X-ray absorptiometry in 93 pairs of opposite sex twins. To examine the effect of age, they were divided into two age groups: under 50 years old (45 pairs) and over 50 years old (48 pairs). Lean mass (LM) had stronger positive relationships with the most bone variables than fat mass in both genders at all ages. Fat mass (FM) had positive relationships with total body and hip BMD in women under age 50, but not over 50. There was no significant relationship between FM and total or regional BMD in men under age 50, but men over 50 showed positive relationships between FM measures and total and some regional BMD measures. Central adiposity showed a positive relationship with BMD in men over 50 and women under 50. Fat mass (FM) and lean mass (LM) and their distribution in the body have different relationships with regional BMD in men and women that differ by age.

Bone mineral metabolism and its relationship to leptin levels in survivors of childhood leukemia and lymphoma

Leptin has important effects on bone metabolism. Possible relationships between leptin and bone mineral density were evaluated in the survivors of the childhood leukemia and lymphoma. Twenty patients were included the study. Anthropometric parameters, growth hormone response to provocative test, serum calcium, phosphorus, alkaline phosphates, osteocalcin, leptin levels, urinary calcium and deoxyypyridinoline levels, and bone mineral density were obtained. Anthropometric parameters of patients were not significantly different from those of a control group. Growth hormone provocative test was abnormal in 3 patients who received cranial radiotherapy. The osteocalcin levels and bone mineral density of patients were significantly lower than in the control group (p=.001, p=.02). Nine patients were in the osteopenic and 7 were in the osteoporotic range. The leptin levels of patients were significantly lower (p=.01) than in the control group. Bone mineral density (BMD) was significantly correlated with leptin level, age, body mass index, and Tanner stage in simple correlation analysis. However, in multivariate analysis only age was significant (p<.000, r: .752). Markers of bone metabolism, BMD, and leptin levels were not related with the growth hormone status of patients and did not present a correlation with the cumulative doses of drugs. There are a few studies evaluating the relationship between BMD and leptin levels in childhood cancer. Although this study did not find any correlation between the leptin level and BMD, detailed studies of larger numbers of patients are necessary to evaluate causes of decreased leptin level and the possible role of leptin on osteopenia observed in survivors of childhood cancer.

The relationship between blood leptin level and bone density is specific to ethnicity and menopausal status

Leptin, the obesity hormone, has been linked to bone mineralization and tumorigenesis. In addition, both bone mineral density (BMD) and postmenopausal breast cancer are associated with obesity, but the interrelationships between obesity, leptin, BMD, and breast cancer are not yet clear. In particular, there is little published research comparing white and black women in terms of these variables. We obtained blood specimens for leptin analysis from a group of 320 breast cancer patients and controls with an ethnic composition of 49% white women and 51% black women. Distal and proximal radial BMD (DBMD and PBMD) were measured by dual-energy X-ray absorptiometry, and age- and ethnicity-specific standardized scores (Z-scores) were calculated for bone density. Blood leptin levels were determined by radioimmunoassay. Blood leptin level was not linked to breast cancer risk. Leptin levels were significantly higher in black women than in white women and were also significantly higher in obese and overweight women than in normal-weight women. Black women weighed more and had a higher body mass index (BMI) than white women. After controlling for BMI, leptin was correlated with DBMD ( r = .17; P < .05) and PBMD ( r = .21; P < .05) in whites, but not in blacks. Leptin was also correlated with both distal and proximal Z-scores in postmenopausal women ( r = .14 and .13; P < .05). Thus leptin may be a predictor for BMD in a population that is prone to have a low BMD, and this relationship is independent of the effect of body weight on leptin levels. Our results suggest that ethnicity and menopausal status should be considered when comparing results from different studies.

The relationship between serum resistin, leptin, adiponectin, ghrelin levels and bone mineral density in middle-aged men

OBJECTIVE

Body weight is a significant predictor of bone mass. Hormonal factors such as sex hormones, insulin, leptin and adiponectin are thought to play a role in the mechanisms controlling the association of body weight and fat mass with bone mass. However, contradictory results have been reported for the association between serum adipocytokines and bone mineral density (BMD). We therefore examined whether the serum adipocytokine and ghrelin levels, markers of fat metabolism, are associated with BMD in male adults.

PATIENTS AND MEASUREMENTS

For 80 male adults (average age 54.5 +/- 6.4 years; average body mass index (BMI) 24.4 +/- 2.5 kg/m2), the correlations between serum resistin, leptin, adiponectin and ghrelin levels with BMD were investigated.

RESULTS

Among the adipocytokines, serum resistin levels were negatively correlated with lumbar spine BMD (r = -0.237, P = 0.05). After adjustment was made for age and BMI, log-transformed serum leptin showed a significant negative correlation with lumbar spine BMD, which was not seen on bivariate analysis (r = -0.237, P = 0.039). Femoral neck BMD was marginally associated only with serum adiponectin levels (r = -0.226, P = 0.062). In multiple regression analyses, among the adipokines, only resistin was a significant determinant of lumbar spine BMD, although the variance was small (R2 = 0.256). Serum ghrelin levels were not correlated with the BMD of either body site.

CONCLUSIONS

Serum resistin level showed a significant negative correlation with lumbar spine BMD, although the variance was small. Further studies are needed to elucidate the role of adipocytokines in bone metabolism.

Effect of different preparations of hormone therapy on lipid and glucose metabolism, coagulation factors, and bone mineral density in overweight and obese postmenopausal women

OBJECTIVE

To determine the effects of different preparations of hormone therapy (HT) on lipid and glucose metabolism, coagulation factors, and bone mineral density (BMD) in overweight and obese postmenopausal women.

DESIGN

A randomized, nonblinded, controlled study.

SETTING

Karadeniz Technical University, Department of Obstetrics and Gynecology.

PATIENT(S)

A total of 352 overweight and obese (body mass index >25 kg/m2) postmenopausal women.

INTERVENTION(S)

Ninety women received 2.5 mg of tibolone; 84 received 2 mg of E2 plus 1 mg of norethisterone acetate (E2/NETA); 90 received 0.625 mg of conjugated equine estrogen plus 2.5 mg of medroxyprogesterone acetate (CEE/MPA); and 88 did not receive any menopausal therapy (control).

MAIN OUTCOME MEASURE(S)

At baseline and after 6 months of treatment, we measured total cholesterol, triglyceride, high-density lipoprotein cholesterol (HDL), low-density lipoprotein cholesterol (LDL), insulin, glucose, factor VII, factor VIII, von Willebrand factor, antithrombin III, protein S, protein C, fibrinogen, and BMD at the lumbar spine L1-L4.

RESULT(S)

There were no statistically significant differences among the groups for any variables at baseline. After 6 months of treatment, the three regimens decreased total cholesterol, triglyceride, LDL, and fibrinogen; E2/NETA and CEE/MPA increased HDL, and tibolone decreased HDL; higher insulin concentrations were found in the control and tibolone groups. Body mass index, HDL, fibrinogen levels, and L1-L4 BMD were independent factors in the prediction of HT use.

CONCLUSION(S)

Body mass index, HDL, fibrinogen levels and L1-L4 BMD were independent factors in the prediction of HT use. Treatment with tibolone, E2/NETA, and CEE/MPA resulted in minimal improvement in lumbar spine BMD but had a beneficial effect on the procoagulation system, with minimal changes in glucose metabolism after 6 months of therapy.

Role of leptin in energy-deprivation states: normal human physiology and clinical implications for hypothalamic amenorrhoea and anorexia nervosa

Leptin is an adipocyte-secreted hormone that plays a key part in energy homoeostasis. Advances in leptin physiology have established that the main role of this hormone is to signal energy availability in energy-deficient states. Studies in animals and human beings have shown that low concentrations of leptin are fully or partly responsible for starvation-induced changes in neuroendocrine axes, including low reproductive, thyroid, and insulin-like growth factor (IGF) hormones. Disease states such as exercise-induced hypothalamic amenorrhoea and anorexia nervosa are also associated with low concentrations of leptin and a similar spectrum of neuroendocrine abnormalities. We have recently shown in an interventional, proof-of-concept study that leptin can restore ovulatory menstrual cycles and improve reproductive, thyroid, and IGF hormones and bone markers in hypothalamic amenorrhoea. Further studies are warranted to establish the safety and effectiveness of leptin for the infertility and osteoporosis associated with hypothalamic amenorrhoea, and to clarify its role in anorexia nervosa.

Relationship of serum leptin with age, body weight, body mass index, and bone mineral density in healthy mainland Chinese women

BACKGROUND

Serum leptin concentration is associated with age, fat and bone mineral density (BMD), and there are ethnic differences in physique and BMD values. The relationship between serum leptin concentration and BMD in Chinese women is presently unknown. We examined the relationship of serum leptin concentration with age, body weight, BMI and BMD in mainland Chinese women.

METHODS

Serum leptin concentration in a population of 676 Chinese females, aged 20-80 years (45.4+/-14.8 years, mean+/-S.D.), was measured using an enzyme-linked immunosorbent assay (ELISA). BMD values were measured by dual-energy X-ray absorptiometry (DXA) at a number of sites: the posteroanterior lumbar spine (PA, L1-L4), lateral lumbar spine (Lat, L2-L4), hip (including the femoral neck (FN) and total hip (T-hip)), and forearm (one-third region (RU1/3) and total region (RUT)). The relationship between changes in serum leptin concentration with age, body weight, height, body mass index (BMI) and BMD values at six sites were analyzed using 10 different regression models, and the models giving the best fit were selected.

RESULTS

The cubic regression model best described the changes in serum leptin concentration with age (R(2)=0.048, p<0.001) and body weight (R(2)=0.352, p<0.001), while the quadratic regression model was best for serum leptin concentration changes with BMI (R(2)=0.410, p<0.001); serum leptin concentration was not correlated with height. Serum leptin concentration was significantly higher in postmenopausal than premenopausal women (p<0.001). Serum leptin concentration was correlated with Lat BMD (R(2)=0.012, p<0.018), FN BMD (R(2)=0.006, p<0.041) and T-hip BMD (R(2)=0.013, p<0.004) in the whole population. In premenopausal women, leptin was positively associated with BMD except for Lat (R(2)=0.029-0.055, p<0.008); in postmenopausal women, leptin was also positively associated with AP, FN, T-hip BMD (R(2)=0.026-0.042, p<0.007). However, after adjusting for BMI not for body weight, there was no association between serum leptin concentration and age. Meanwhile, after adjustment for age, body weight and BMI, there was no association between serum leptin concentration and BMD values in premenopausal and postmenopausal women.

CONCLUSIONS

Age-related changes in serum leptin concentration is dependent on BMI, but not a direct determinant of BMD in Chinese females.

Plasma leptin concentrations in postmenopausal women with osteoporosis

Osteoporosis is less common in obese individuals with increased bone mineral density (BMD) and plasma leptin concentrations. The aim of this study was to determine the correlation between leptin levels and BMD in postmenopausal women. The study consisted of 90 postmenopausal women with a mean age of 53.45 +/- 0.87 years who visited our outpatient clinic for the evaluation of BMD. Thirty-six post-menopausal women with osteoporosis (mean age: 54.52 +/- 1.41 years and mean body mass index (BMI, kg/m2) 29.33 +/- 0.66), 30 age- and BMI-matched postmenopausal women with normal BMD, and 24 postmenopausal women (mean age: 52.79 +/- 1.48 years and mean BMI: 29.45 +/- 0.89) with osteopenic BMD were included in the study. Plasma concentrations of leptin after an overnight fast were measured by radioimmunoassay. BMD values were measured by dual-energy X-ray absorptiometry (DEXA) at the L2-L4 lumbar spine and femoral neck. The median spine BMD value in the patient group (0.67 +/- 0.08 g/cm2, mean +/- SEM) was significantly lower than that in the control group (1.02 +/- 0.25 g/cm2, mean +/- SEM) and osteopenic group (0.87 +/- 0.05 g/cm2, mean +/- SEM) (p < 0.005). The mean spine BMD value (T score -3.63 +/- 0.25, mean +/- SEM) and the mean femur neck BMD value (T score -2.55 +/- 0.18, mean +/- SEM) of the osteoporosis group were significantly lower than that in the normal BMD group (+ 0.33 +/- 0.14 and + 0.27 +/- 0.18, P < 0.001) and in the osteopenia group (-1.74 +/- 0,1 and -1.18 +/- 0.05, p < 0.005). The mean plasma leptin concentration in the osteoporotic group (17.03 +/- 1.40 ng/ml) was not significantly different from that in the normal BMD group and the osteopenia group (16.55 +/- 1.50 ng/ml; 16.16 +/- 1.60, respectively, p > 0.150). Plasma leptin concentrations were correlated with BMI in three groups (r(s) = 0.450, p = 0.025 in normal BMD group and r(s) = 0.4254, P = 0.009 in the osteoporotic group, and r(s) = 395, p = 0.015 in the osteopenia group. There was no correlation between plasma leptin concentrations and BMD values in three groups (r(s) = -0.89 in normal BMD group, r(s) = -0.124 in osteopenia group, and r(s) = -0.195 in osteoporosis group). From this study we conclude that circulating plasma leptin does not have a significant direct influence on bone mass in postmenopausal women.

Lack of independent relationship between plasma adiponectin, leptin levels and bone density in nondiabetic female adolescents

OBJECTIVES

Adiponectin has been implicated in the pathophysiology of metabolic syndrome and coronary artery disease in humans. Whether adiponectin is related to bone mineralization remains unclear in adults as well as in adolescents. In this study, we aimed to determine the relationship between plasma adiponectin, leptin concentrations and bone density, including total-body bone mineral density (BMD) and bone mineral content (BMC) in adolescence.

PATIENTS AND MEASUREMENTS

We studied 105 nondiabetic female adolescents [mean age 15.4 +/- 1.9 years, and mean body mass index (BMI), 23.1 +/- 4.0 kg/m(2)]. A venous blood sample was taken after 12 h of fasting to measure fasting plasma adiponectin and leptin levels. BMD and BMC of the whole body were measured by dual-energy X-ray absorptiometry.

RESULTS

In simple correlation analysis, plasma adiponectin and leptin levels correlated significantly with total-body BMD (r =-0.523 and r = 0.443, P < 0.001, respectively) and BMC (r =-0.471 and r = 0.396, P < 0.001, respectively). However, plasma adiponectin and leptin were related to both BMD and BMC in opposite directions. In multivariate linear regression analyses, only BMI or fat mass (FM) and Tanner stage, but not plasma adiponectin and leptin, were significantly related to BMD and BMC following adjustment for other variables.

CONCLUSIONS

The results suggest that plasma adiponectin and leptin concentrations are not related to the total-body BMD and BMC independent of the chronological age, BMI or FM, and Tanner stage in nondiabetic female adolescents, although they were highly correlated in simple correlation analyses. The biologic roles of adiponectin in bone still need further clarification.

Relationships between bone mass and circulating leptin concentrations in Hutterites

A limited number of previous studies have shown inverse associations between bone mass or density and circulating leptin in humans. Relationships between bone mass and circulating leptin in Hutterites, who have elevated bone density, are unknown. Knowledge gained from studies in mice suggests that Hutterites exhibit traits consistent with a deficiency in circulating leptin or in leptin signaling. We examined relationships between whole body (WB) and regional (lumbar, total hip, femoral neck, trochanter) bone mineral content (BMC) by dual energy X-ray absorptiometry and circulating leptin in 249 Hutterites (137 female) ages 20-55 years and 72 similarly aged non-Hutterites (37 female). We tested the hypothesis that (1) Hutterites will have low circulating leptin concentrations for a given amount of body fat compared to non-Hutterites, and (2) controlling for body fat, there will be an inverse relationship between BMC and circulating leptin among Hutterites. Hutterites had higher BMC than non-Hutterites at all skeletal sites after adjusting for site-specific bone area, age, and sex (P </= 0.02). Hutterite females had higher leptin concentrations than non-Hutterite females [geometric mean and 95% confidence interval (CI): 18.38 (17.18, 19.67) vs. 14.30 (12.55, 16.28), P </= 0.001) after adjusting for WB fat mass. Hutterite males also had higher leptin concentrations than non-Hutterite males [geometric mean and 95% CI: 6.53 (6.11, 6.98) vs. 5.62 (4.98, 6.35), P = 0.03) after adjusting for WB fat mass. We used backward stepwise regression to determine significant (P </= 0.10) covariates to include in models predicting WB and regional BMC among Hutterites (separately by sex). Subsequently, we entered leptin (log-transformed) to models to test for significance (P </= 0.05). After adjusting for covariates, leptin concentration was not a significant predictor of BMC at any site, in either sex, among Hutterites. It is possible that genetic influences that interfere with hypothalamic leptin signaling, in a manner unrelated to adipocyte leptin production, contribute to elevated Hutterite bone density.

Blood leptin and adiponectin as possible mediators of the relation between fat mass and BMD in perimenopausal women

Fat mass is a predictor of BMD; however, the mechanisms involved remain uncertain. Two adipokines, leptin and adiponectin, were examined as potential mediators of this relation in 80 perimenopausal women. Adiponectin did not exert any effect on BMD, whereas leptin exerted a negative one, with insulin acting as a confounder to this relation.

INTRODUCTION

Fat mass is an important determinant of bone density, but the mechanism involved in this relation is uncertain. Leptin and adiponectin, as circulating peptides of adipocyte origin, are potential contributors to this relation. We investigated the role of leptin and adiponectin in mediating fat mass effects on the skeleton of perimenopausal women.

MATERIALS AND METHODS

Twenty-five premenopausal and 55 postmenopausal, healthy women (42-68 years old) participated in our study. Lumbar spine BMD (BMD(L2-L4)) and total body BMC (TBBMC) were measured with DXA, leptin levels with ELISA, and adiponectin levels with radioimmunoassay (RIA). Additionally, body composition analysis was performed, as well as measurements of several hormones.

RESULTS

It was shown that serum leptin levels were negatively correlated with BMD (beta = -0.005, p = 0.027) and TBBMC (beta = -14.32, p = 0.013). The above correlation was observed only when serum insulin levels were included, as an independent variable, in the regression analysis model. Adiponectin was not significantly correlated with BMD(L2-L4) nor with TBBMC, either in the presence or absence of insulin.

CONCLUSION

Circulating adiponectin does not seem to exert any effect on bone mass. In contrast, circulating leptin showed a negative correlation with bone mass, dependent on serum insulin levels.

Fat body mass, leptin and femur bone mineral density in hip-fractured women

Fat body mass (FBM) is a strong predictor of both bone mineral density (BMD) and risk of hip fracture, but the mechanisms responsible are not completely understood. We addressed whether leptin is the link between FBM and BMD in hip-fractured women. Sixty-two of 74 women with hip fractures were evaluated. Serum leptin was measured by radioimmunoassay, 23.4+/-9.1 days (mean+/-SD) after fracture occurrence. BMD and body composition were assessed by dual-energy X-ray absorptiometry (DXA). As expected, a positive linear correlation was found between FBM and both leptin (r=0.782; p<0.001) and femur BMD measured at five sites (r value ranging from 0.293 to 0.498 depending on the site of the femur BMD assessment, p<0.05). A positive correlation between leptin and BMD measured at the intertrochanteric area (r=0.259; p<0.05) but not at the other four sites was shown. At linear multiple regression [dependent variable = femur BMD; independent variables = age, weight, height, body mass index, fracture type, term fracture-DXA, Barthel index score, FBM, lean body mass, serum PTH, serum 25(OH)vitamin D and leptin], FBM was positively associated with BMD measured at all the five sites. The association between leptin and BMD was inverse and it was significant at four of the five sites of the BMD assessment. In conclusion, in a sample of hip-fractured women, the positive association between FBM and femur BMD was not explained by serum leptin. On the contrary, after adjustment for FBM and other confounding variables, an inverse association between leptin and BMD was found.

Leptin and bone mineral density: a cross-sectional study in obese and nonobese men

Leptin has been suggested to decrease bone mineral density (BMD). This observational analysis explored the relationship between serum leptin and BMD in 327 nonobese men (controls) (body mass index 26.1 +/- 3.7 kg/m(2), age 49.9 +/- 6.0 yr) and 285 juvenile obese men (body mass index 35.9 +/- 5.9 kg/m(2), age 47.5 +/- 5.1 yr). Whole-body dual-energy x-ray absorptiometry scan measured BMD, fat mass, and lean mass. Fasting serum leptin (nanograms per milliliter) was strongly associated with fat mass (kilograms) in both controls (r = 0.876; P < 0.01) and juvenile obese (r = 0.838; P < 0.001). An inverse relation between BMD adjusted for body weight and serum leptin emerged in both the control group (r = -0.186; P < 0.01) and the juvenile obese group (r = -0.135; P < 0.05). In a multiple linear regression, fat mass, lean body mass, and occupational physical activity were positively associated with BMD in the control group, whereas in the juvenile obese, only lean body mass was positively associated with BMD and smoking negatively associated with BMD. Our study supports that leptin is inversely associated with BMD and may play a direct role in the bone metabolism in nonobese and obese Danish males, but it also stresses the fact that the strong covariation between the examined variables is a shortcoming of the cross-sectional design.

Serum leptin as a determinant of bone resorption in healthy postmenopausal women

To examine the relationships between serum leptin and bone metabolism, we measured bone mineral density (BMD) at the spine and the hip, fasting serum leptin, and osteocalcin and urinary excretion of C-terminal crosslinking telopeptide of type I collagen (CTX), as markers of bone formation and resorption, respectively, in 121 postmenopausal women aged 54 +/- 5 years. These parameters were also assessed at 6 months and 2 years of treatment with either 2.5 mg tibolone (n = 34), 1.25 mg tibolone (n = 45), or 2 mg estradiol plus 1 mg norethindrone acetate (n = 42). At baseline, serum leptin correlated positively with spine (r = 0.21, P = 0.02) and total hip (r = 0.26, P = 0.0044) BMD and negatively with CTX (r = -0.38, P < 0.0001) and osteocalcin (r = 0.21, P = 0.025). After adjustment for BMI and for fat mass, the association between serum leptin and CTX persisted with a partial correlation coefficient of -0.18 (P = 0.046) and of -0.22 (P = 0.03), respectively. Women in the highest quartile of leptin levels had 11% higher total hip (P = 0.0039) and lumbar spine BMD (P = 0.016), 21% lower osteocalcin (P = 0.01), and 38% lower CTX (P = 0.0005) than women in the lowest quartile (P < 0.05). During treatment, serum leptin levels increased (+14.7 +/- 47.3%, P = 0.019), without significant difference between the groups. This increase correlated with the increase in body weight (r = 0.46, P < 10(-4)). No correlation was found between the changes in leptin and the changes in bone parameters. In conclusion, leptin may play a role as a determinant of bone resorption in healthy, untreated postmenopausal women, but the effect of estradiol or tibolone on bone are not mediated by leptin.

Adiponectin as a novel determinant of bone mineral density and visceral fat

Growing evidence suggests that positive associations between fat mass (FM) and bone mineral density (BMD) are mediated by not only biomechanical but also biochemical factors. Adiponectin is a novel adipocyte-derived hormone that regulates energy homeostasis and has anti-inflammatory and anti-atherogenic effects. Unlike other adipokines such as leptin, adiponectin levels decrease in obesity and type 2 diabetes. The purpose of our study was to investigate associations of serum adiponectin with BMD (DXA and QCT), FM (DXA and QCT), and serum leptin and soluble leptin receptor levels in 38 women and 42 men (age 39-81, BMI 17-55, 86% with type 2 diabetes). After adjusting for age, gender, race, smoking, and diabetes status, serum adiponectin was inversely associated with areal BMD (r = -0.20 to -0.3, all P < 0.01), volumetric BMD (r = -0.35 to -0.44, all P < 0.01), and visceral fat volume (r = -0.30, P < 0.01). These associations remained significant after adjusting for whole body fat mass. The associations of adiponectin with subcutaneous fat volume, whole body FM, and serum leptin level were not significant (all P > 0.1). These data suggest that adiponectin may play a role in the protective effects of visceral fat on BMD.

Leptin, ghrelin, and proinflammatory cytokines: compounds with nutritional impact in chronic kidney disease?

Metabolic and nutritional derangements are prominent features of the uremic syndrome. Recent evidence suggest that several large-molecular-weight molecules that often are elevated in uremia, such as leptin, ghrelin, and proinflammatory cytokines, may have nutritional impact in this patient group. On the basis of present knowledge, these compounds could be regarded as suspected but not established uremic toxins. The discovery of the ob gene, its product leptin, and cerebral leptin receptors has undoubtedly widened our understanding of obesity and the underlying molecular and physiologic mechanisms that regulate food intake and body weight. Moreover, the recent discovery of leptin receptor isoforms in several peripheral organs suggests that leptin besides having a central function also has several important peripheral biological functions. Because uremic patients in general have an inappropriate elevation of circulatory leptin, further research is necessary to determine the potential biological effects of elevated leptin levels in end-stage renal disease. Also, because many symptoms and findings prevalent in the uremic syndrome are known to be associated with elevated levels of proinflammatory cytokines, such as interleukin-6, future studies are needed to evaluate the role of specific anti-inflammatory treatment strategies in malnourished uremic patients.

Genetic variation of circulating leptin is involved in genetic variation of hand bone size and geometry

Leptin is secreted primarily by the adipocytes and plays an important role in the regulation of food intake and energy expenditure. In addition to its adipostatic function, it has been demonstrated that leptin directly enhances stromal cell differentiation to osteoblasts, and since such precursor cells are potential targets for leptin, the latter could possibly mediate the relationship between obesity and bone mass and size. To address this question, we studied phenotypic and genetic correlations between the circulating levels of leptin and hand bone size (BS) and geometry (BG) of the radiographic hand in a healthy and ethnically homogeneous sample of pedigrees. We also attempted to evaluate to what extent potential leptin/BS/BG correlations are modified by an individual's obesity traits, specifically his/her BMI. Our research has shown that leptin, BMI and the corresponding bone measures are clearly inherited traits (0.46+/-0.11, 0.35+/-0.16, 0.62+/-0.12 and 0.51+/-0.09, respectively). The bivariate variance component analysis revealed very strong and significant genetic and environmental correlations between circulating leptin and BMI ( r(G)=0.86+/-0.09, r(E)=0.75+/-0.05, P<0.001). Furthermore, genetic correlations between leptin and hand bone characteristics proved inverse and statistically significant ( r(G)=-0.35+/-0.01 and -0.45+/-0.10 for BS and BG, respectively), while corresponding environmental correlations were low ( r(E)=-0.14+/-0.15 and -0.07+/-0.14) and they could be constrained to zero without significant deterioration of the model fit to the data ( P>0.10). However, despite the extremely strong relationship between leptin and BMI, we failed to detect phenotypic or genetic correlations between BMI and our two hand bone measures. Thus our study provided evidence that plasma leptin levels may be statistically significant predictor of hand bone size and geometry, and may play a physiological role in maintaining bone mass as well as in regulation of hand bone proportions.