MRI-measured bone marrow adipose tissue is inversely related to DXA-measured bone mineral in Caucasian women

Bone marrow fat is increased in chronic kidney disease by magnetic resonance spectroscopy

In aging, the bone marrow fills with fat and this may lead to higher fracture risk. We show that a bone marrow fat measurement by magnetic resonance spectroscopy (MRS), a newer technique not previously studied in chronic kidney disease (CKD), is useful and reproducible. CKD patients have significantly higher bone marrow fat than healthy adults.

INTRODUCTION

Renal osteodystrophy leads to increased morbidity and mortality in patients with CKD. Traditional bone biopsy histomorphometry is used to study abnormalities in CKD, but the bone marrow, the source of osteoblasts, has not been well characterized in patients with CKD.

METHODS

To determine the repeatability of bone marrow fat fraction assessment by MRS and water-fat imaging (WFI) at four sites in patients with CKD, testing was performed to determine the coefficients of reproducibility and intraclass coefficients (ICCs). We further determined if this noninvasive technique could be used to determine if there are differences in the percent bone marrow fat in patients with CKD compared to matched controls using paired t tests.

RESULTS

The mean age of subjects with CKD was 59.8 ± 7.2 years, and the mean eGFR was 24 ± 8 ml/min. MRS showed good reproducibility at all sites in subjects with CKD and controls, with a coefficient of reproducibilities ranging from 2.4 to 13 %. MRS and WFI assessment of bone marrow fat showed moderate to strong agreement (ICC 0.6-0.7) at the lumbar spine, with poorer agreement at the iliac crest and no agreement at the tibia. The mean percent bone marrow fat at L2-L4 was 13.8 % (95 % CI 8.3-19.7) higher in CKD versus controls (p < 0.05).

CONCLUSIONS

MRS is a useful and reproducible technique to study bone marrow fat in CKD. Patients with CKD have significantly higher bone marrow fat than healthy adults; the relationship with bone changes requires further analyses.

Changes in vertebral bone marrow fat and bone mass after gastric bypass surgery: A pilot study

Bone marrow fat may serve a metabolic role distinct from other fat depots, and it may be altered by metabolic conditions including diabetes. Caloric restriction paradoxically increases marrow fat in mice, and women with anorexia nervosa have high marrow fat. The longitudinal effect of weight loss on marrow fat in humans is unknown. We hypothesized that marrow fat increases after Roux-en-Y gastric bypass (RYGB) surgery, as total body fat decreases. In a pilot study of 11 morbidly obese women (6 diabetic, 5 nondiabetic), we measured vertebral marrow fat content (percentage fat fraction) before and 6 months after RYGB using magnetic resonance spectroscopy. Total body fat mass declined in all participants (mean ± SD decline 19.1 ± 6.1 kg or 36.5% ± 10.9%, p<0.001). Areal bone mineral density (BMD) decreased by 5.2% ± 3.5% and 4.1% ± 2.6% at the femoral neck and total hip, respectively, and volumetric BMD decreased at the spine by 7.4% ± 2.8% (p<0.001 for all). Effects of RYGB on marrow fat differed by diabetes status (adjusted p=0.04). There was little mean change in marrow fat in nondiabetic women (mean +0.9%, 95% CI -10.0 to +11.7%, p=0.84). In contrast, marrow fat decreased in diabetic women (-7.5%, 95% CI -15.2 to +0.1%, p=0.05). Changes in total body fat mass and marrow fat were inversely correlated among nondiabetic (r=-0.96, p=0.01) but not diabetic (r=0.52, p=0.29) participants. In conclusion, among those without diabetes, marrow fat is maintained on average after RYGB, despite dramatic declines in overall fat mass. Among those with diabetes, RYGB may reduce marrow fat. Thus, future studies of marrow fat should take diabetes status into account. Marrow fat may have unique metabolic behavior compared with other fat depots.

A new diagnostic score to detect osteoporosis in patients undergoing lumbar spine MRI

OBJECTIVES

Signal intensity of lumbar-spine at magnetic resonance imaging (MRI) correlates to bone mineral density (BMD). Our aim was to define a quantitative MRI-based score to detect osteoporosis on lumbar-spine MRI.

METHODS

After Ethics Committee approval, we selected female patients who underwent both lumbar-spine MRI and dual-energy X-ray absorptiometry (DXA) and a reference group of 131 healthy females (20-29 years) who underwent lumbar-spine MRI. We measured the intra-vertebral signal-to-noise ratio in L1-L4. We introduced an MRI-based score (M-score), on the model of T-score. M-score diagnostic performance in diagnosing osteoporosis was estimated against DXA using receiver operator characteristic (ROC) analysis.

RESULTS

We included 226 patients (median age 65 years), 70 (31%) being osteoporotic at DXA. MRI signal-to-noise ratio correlated to BMD (r = -0.677, P < 0.001). M-score negatively correlated to T-score (r = -0.682, P < 0.001). Setting a 90%-specificity, an M-score threshold of 5.5 was found, distinguishing osteoporosis from non-osteoporosis (sensitivity 54%; ROC AUC 0.844). Thirty-one (14%) patients had a fragility fracture, with osteoporosis detected in 15 (48%) according to M-score and eight (26%) according to T-score (P = 0.016).

CONCLUSIONS

M-score obtained on lumbar spine MRI is a quantitative method correlating with osteoporosis. Its diagnostic value remains to be demonstrated on a large prospective cohort of patients.

KEY POINTS

• M-score is a quantitative score potentially screening osteoporosis on lumbar-spine MRI; • This method showed good intra- and inter-reader reproducibility; • M-score may be used for identifying patients who should undergo DXA.

Magnetic resonance imaging-measured bone marrow adipose tissue area is inversely related to cortical bone area in children and adolescents aged 5-18 years

Previous studies have shown an inverse correlation between bone marrow adipose tissue and bone mineral density in cancellous bone; however, such relationships in cortical bone are less studied, especially in children. A total of 185 healthy children and adolescents (76 females and 109 males, aged 5-18 years) were included in this study. Right femoral bone marrow adipose tissue area (BMA), right femoral cortical bone area (CBA), subcutaneous adipose tissue, visceral adipose tissue, and skeletal muscle were accessed by whole-body magnetic resonance imaging. In regression analysis with CBA as the dependent variable and BMA as the independent variable, BMA negatively contributed to CBA after adjusting for weight and total body fat or subcutaneous adipose tissue, visceral adipose tissue, and skeletal muscle (β = -0.201 to -0.272, p < 0.001). These results suggest an inverse relationship between BMA and CBA in children and adolescents after adjustment of body weight or body composition. The data support the hypothesis that a competitive relationship exists between bone and marrow fat in cortical bone and is consistent with a similar finding in cancellous bone in previous studies. Future research is needed to clarify the role of marrow fat in childhood fractures that are related to cortical bone quality.

The impact of diabetes and diabetes medications on bone health

Patients with type 2 diabetes mellitus (T2DM) have an increased risk of fragility fractures despite increased body weight and normal or higher bone mineral density. The mechanisms by which T2DM increases skeletal fragility are unclear. It is likely that a combination of factors, including a greater risk of falling, regional osteopenia, and impaired bone quality, contributes to the increased fracture risk. Drugs for the treatment of T2DM may also impact on the risk for fractures. For example, thiazolidinediones accelerate bone loss and increase the risk of fractures, particularly in older women. In contrast, metformin and sulfonylureas do not appear to have a negative effect on bone health and may, in fact, protect against fragility fracture. Animal models indicate a potential role for incretin hormones in bone metabolism, but there are only limited data on the impact of dipeptidyl peptidase-4 inhibitors and glucagon-like peptide-1 agonists on bone health in humans. Animal models also have demonstrated a role for amylin in bone metabolism, but clinical trials in patients with type 1 diabetes with an amylin analog (pramlintide) have not shown a significant impact on bone metabolism. The effects of insulin treatment on fracture risk are inconsistent with some studies showing an increased risk and others showing no effect. Finally, although there is limited information on the latest class of medications for the treatment of T2DM, the sodium-glucose co-transporter-2 inhibitors, these drugs do not seem to increase fracture risk. Because diabetes is an increasingly common chronic condition that can affect patients for many decades, further research into the effects of agents for the treatment of T2DM on bone metabolism is warranted. In this review, the physiological mechanisms and clinical impact of diabetes treatments on bone health and fracture risk in patients with T2DM are described.

Marrow fat and bone: review of clinical findings

With growing interest in the connection between fat and bone, there has been increased investigation of the relationship with marrow fat in particular. Clinical research has been facilitated by the development of non-invasive methods to measure bone marrow fat content and composition. Studies in different populations using different measurement techniques have established that higher marrow fat is associated with lower bone density and prevalent vertebral fracture. The degree of unsaturation in marrow fat may also affect bone health. Although other fat depots tend to be strongly correlated, marrow fat has a distinct pattern, suggesting separate mechanisms of control. Longitudinal studies are limited, but are crucial to understand the direct and indirect roles of marrow fat as an influence on skeletal health. With greater appreciation of the links between bone and energy metabolism, there has been growing interest in understanding the relationship between marrow fat and bone. It is well established that levels of marrow fat are higher in older adults with osteoporosis, defined by either low bone density or vertebral fracture. However, the reasons for and implications of this association are not clear. This review focuses on clinical studies of marrow fat and its relationship to bone.

Anorexia nervosa and bone metabolism

Anorexia nervosa (AN) is a psychiatric disorder characterized by self-induced starvation with a lifetime prevalence of 2.2% in women. The most common medical co-morbidity in women with AN is bone loss, with over 85% of women having bone mineral density values more than one standard deviation below an age comparable mean. The low bone mass in AN is due to multiple hormonal adaptations to under nutrition, including hypothalamic amenorrhea and growth hormone resistance. Importantly, this low bone mass is also associated with a seven-fold increased risk of fracture. Therefore, strategies to effectively prevent bone loss and increase bone mass are critical. We will review hormonal adaptations that contribute to bone loss in this population as well as promising new therapies that may increase bone mass and reduce fracture risk in AN.

Bone and fat: a relationship of different shades

Environmental and behavioral changes which occurred over the last century led simultaneously to a remarkable increase in human lifespan and to the development of health problems associated with functional impairment of organs either regulating or dependent on balanced energy metabolism. Diseases such as diabetes, obesity and osteoporosis are prevalent in our society and pose major challenges with respect to the overall health and economy. Therefore, better understanding of regulatory axes between bone and fat may provide the basis for development of strategies which will treat these diseases simultaneously and improve health and life quality of elderly.

What's the matter with MAT? Marrow adipose tissue, metabolism, and skeletal health

Marrow adipose tissue (MAT) is functionally distinct from both white and brown adipose tissue and can contribute to systemic and skeletal metabolism. MAT formation is a spatially and temporally defined developmental event, suggesting that MAT is an organ that serves important functions and, like other organs, can undergo pathologic change. The well-documented inverse relationship between MAT and bone mineral density has been interpreted to mean that MAT removal is a possible therapeutic target for osteoporosis. However, the bone and metabolic phenotypes of patients with lipodystrophy argues that retention of MAT may actually be beneficial in some circumstances. Furthermore, MAT may exist in two forms, regulated and constitutive, with divergent responses to hematopoietic and nutritional demands. In this review, we discuss the role of MAT in lipodystrophy, bone loss, and metabolism, and highlight our current understanding of this unique adipose tissue depot.

Conjugated estrogens combined with bazedoxifene: the first approved tissue selective estrogen complex therapy

Menopausal therapy with a tissue selective estrogen complex combines estrogens with a selective estrogen receptor modulator, with the goal of blending the desirable effects of estrogens on menopausal symptoms and bone with the tissue selective properties of a selective estrogen receptor modulator. The first tissue selective estrogen complex to receive regulatory approval is a combination of conjugated estrogens (CE) with bazedoxifene (BZA). Clinical trials with CE/BZA in postmenopausal women have shown improvement in vasomotor symptoms, vulvo-vaginal atrophy, and bone mineral density, without stimulation of the endometrium or breast tissue, with a generally favorable safety and tolerability profile. CE/BZA represents a new approach to the management of menopausal symptoms in women with a uterus.

Comparison of vertebral bone marrow fat assessed by 1H MRS and inphase and out-of-phase MRI among family members

Inphase and out-of-phase magnetic resonance imaging is a robust and fast method which can provide similar vertebral bone marrow fat estimation as (1)H proton magnetic resonance spectroscopy, indicating that this technique is a potentially useful tool in both research and clinical practice.

INTRODUCTION

The importance of evaluating bone marrow fat lies in the fact that osteoporosis and obesity, two disorders of body composition, are growing in prevalence. Bone fat mass can be reliably assessed using proton magnetic resonance spectroscopy ((1)H MRS), but this method is technically demanding and needs advanced post-processing unlike inphase and out-of-phase magnetic resonance imaging (MRI), which is a robust and fast method.

METHODS

We compared vertebral bone marrow fat (BMF) content assessed by inphase and out-of-phase MRI and (1)H MRS using a 1.5-T MRI scanner in mothers (n = 34, aged 49.4 years), fathers (n = 31, aged 53.1 years) and their daughters (n = 40, aged 20.3 years) who participated in the CALEX family study. Signal intensity on the inphase and out-of-phase MRI was analyzed from the same location and size of the single-voxel (1)H MRS measurement.

RESULTS

Positive correlations were found between (1)H MRS and inphase and out-of-phase MRI in the axial plane (r = 0.746, p < 0.001) and sagittal plane (r = 0.804, p < 0.001). The mean differences between (1)H MRS and inphase and out-of-phase MRI in the axial and sagittal planes were relatively small, at 4.13 and 2.67 %, and the agreement between techniques was 89.4 and 93.2 %, respectively. Girls had a significantly lower vertebral BMF than mothers and fathers with both methods (for all, p < 0.001).

CONCLUSIONS

We conclude that inphase and out-of-phase MRI can provide similar vertebral BMF estimation as (1)H MRS, indicating that this technique is a potentially useful tool in both research and clinical practice.

Comparison of the relationship between bone marrow adipose tissue and volumetric bone mineral density in children and adults

Several large-scale studies have reported the presence of an inverse relationship between bone mineral density (BMD) and bone marrow adipose tissue (BMAT) in adults. We aim to determine if there is an inverse relationship between pelvic volumetric BMD (vBMD) and pelvic BMAT in children and to compare this relationship in children and adults. Pelvic BMAT and bone volume (BV) was evaluated in 181 healthy children (5-17yr) and 495 healthy adults (≥18yr) with whole-body magnetic resonance imaging (MRI). Pelvic vBMD was calculated using whole-body dual-energy X-ray absorptiometry to measure pelvic bone mineral content and MRI-measured BV. An inverse correlation was found between pelvic BMAT and pelvic vBMD in both children (r=-0.374, p<0.001) and adults (r=-0.650, p<0.001). In regression analysis with pelvic vBMD as the dependent variable and BMAT as the independent variable, being a child or adult neither significantly contribute to the pelvic BMD (p=0.995) nor did its interaction with pelvic BMAT (p=0.415). The inverse relationship observed between pelvic vBMD and pelvic BMAT in children extends previous findings that found the inverse relationship to exist in adults and provides further support for a reciprocal relationship between adipocytes and osteoblasts.

The alliance of mesenchymal stem cells, bone, and diabetes

Bone fragility has emerged as a new complication of diabetes. Several mechanisms in diabetes may influence bone homeostasis by impairing the action between osteoblasts, osteoclasts, and osteocytes and/or changing the structural properties of the bone tissue. Some of these mechanisms can potentially alter the fate of mesenchymal stem cells, the initial precursor of the osteoblast. In this review, we describe the main factors that impair bone health in diabetic patients and their clinical impact.

Determinants of bone marrow adiposity: the modulation of peroxisome proliferator-activated receptor-γ2 activity as a central mechanism

Although the presence of adipocytes in the bone marrow is a normal physiological phenomenon, the role of these cells in bone homeostasis and during pathological states has not yet been fully delineated. As osteoblasts and adipocytes originate from a common progenitor, with an inverse relationship existing between osteoblastogenesis and adipogenesis, bone marrow adiposity often negatively correlates with osteoblast number and bone mineral density. Bone adiposity can be affected by several physiological and pathophysiological factors, with abnormal, elevated marrow fat resulting in a pathological state. This review focuses on the regulation of bone adiposity by physiological factors, including aging, mechanical loading and growth factor expression, as well as the pathophysiological factors, including diseases such as anorexia nervosa and dyslipidemia, and pharmacological agents such as thiazolidinediones and statins. Although these factors regulate bone marrow adiposity via a plethora of different intracellular signaling pathways, these diverse pathways often converge on the modulation of the expression and/or activity of the pro-adipogenic transcription factor peroxisome proliferator-activated receptor (PPAR)-γ2, suggesting that any factor that affects PPAR-γ2 may have an impact on the fat content of bone.

Divergent effects of obesity on bone health

Historically, obesity was thought to be advantageous for maintaining healthy bones due to the greater bone mineral density observed in overweight individuals. However, recent observations of increased fracture in some obese individuals have led to concern that common metabolic complications of obesity, such as type 2 diabetes, metabolic syndrome, impaired glucose tolerance, insulin resistance, hyperglycemia, and inflammation may be associated with poor bone health. In support of this hypothesis, greater visceral fat, a hallmark of insulin resistance and metabolic syndrome, is associated with lower bone mineral density. Research is needed to determine if and how visceral fat and/or poor metabolic health are causally associated with bone health. Clinicians should consider adding a marker metabolic health, such as waist circumference or fasting plasma glucose concentration, to other known risk factors for osteoporosis and fracture.

Sclerostin and Pref-1 have differential effects on bone mineral density and strength parameters in adolescent athletes compared with non-athletes

Excessive exercise can have detrimental effects on bone; however, the mechanisms leading to bone loss are not well understood. Sclerostin and preadipocyte factor (Pref)-1 are two hormones which inhibit bone formation. The present study demonstrates that these hormones may have differential effects in athletes as compared to non-athletes.

INTRODUCTION

Exercise activity is common in female adolescents, however, excessive exercise can have detrimental effects on bone mineral density (BMD). Mechanisms underlying this decrease in bone mass are not well understood. We investigated the effects of sclerostin, a potent inhibitor of bone formation via WNT signaling inhibition, and Pref-1, a suppressor of osteoblast differentiation, on BMD, bone turnover markers and bone strength in adolescent athletes.

METHODS

We studied 50 adolescents between 15-21 years of age: 17 amenorrheic athletes (AA), 17 eumenorrheic athletes (EA), and 16 nonathletic controls (NA). We measured spine and hip BMD by dual energy x-ray absorptiometry and estimated failure load and stiffness at the distal radius and tibia using micro-finite element analysis. We also measured fasting sclerostin, Pref-1, N-terminal propeptide of type 1 procollagen, and C-terminal collagen cross-links levels.

RESULTS

Sclerostin levels were higher in AA and EA compared with NA (AA: 0.42 ± 0.15 ng/mL, EA: 0.44 ± 0.09 ng/mL, NA: 0.33 ± 0.14 ng/mL; p = 0.047). In EA, sclerostin was positively associated with lumbar spine (LS) BMD and its Z-score (R = 0.52, p = 0.03 and R = 0.55, p = 0.02, respectively) whereas in NA, sclerostin was inversely associated with LS BMD (R = -0.61, p = 0.01). Pref-1 levels were similar in all three groups and there were significant inverse associations between Pref-1, BMD, and estimated bone strength in NA.

CONCLUSIONS

Sclerostin and Pref-1 may have differential effects on bone in adolescent athletes compared to non-athletes.

Gender and age groups interactions in the quantification of bone marrow fat content in lumbar spine using 3T MR spectroscopy: a multivariate analysis of covariance (Mancova)

INTRODUCTION

There is an age-related conversion of red to yellow bone marrow in the axial skeleton, with a gender-related difference less well established. Our purpose was to clarify the variability of bone marrow fat fraction (FF) in the lumbar spine due to the interaction of gender and age groups.

METHODS

44 healthy volunteers (20 males, 30-65 years old and 24 females, 30-69 years old) underwent 3T magnetic resonance spectroscopy (MRS) and conventional MRI examination of the lumbar spine; single-voxel spectrum was acquired for each vertebral body (VB). After controlling body mass index (BMI), a two-way between-groups multivariate analysis of covariance (MANCOVA) assessed the gender and age group differences in FF quantification for each lumbar VB.

RESULTS

There was a significant interaction between gender and age group, p=.017, with a large effect size (partial η(2)=.330). However the interaction explained only 33% of the observed variance. Main effects were not statistically significant. BMI was non-significantly related to FF quantification.

CONCLUSIONS

Young males showed a high FF content, which declined in the 4th decade, then increased the next 3 decades to reach a FF content just below the initial FF means. Females' FF were low in the 3rd decade, depicted an accelerated increase in the 4th decade, then a gradual increase the next 3 decades to reach a FF content similar to males' values. Our findings suggest that quantification of bone marrow FF using MRS might be used as a surrogate biomarker of bone marrow activity in clinical settings.

Whole body fat: content and distribution

Obesity and its co-morbidities, including type II diabetes, insulin resistance and cardiovascular diseases, have become one of the biggest health issues of present times. The impact of obesity goes well beyond the individual and is so far-reaching that, if it continues unabated, it will cause havoc with the economies of most countries. In order to be able to fully understand the relationship between increased adiposity (obesity) and its co-morbidity, it has been necessary to develop proper methodology to accurately and reproducibly determine both body fat content and distribution, including ectopic fat depots. Magnetic Resonance Imaging (MRI) and Spectroscopy (MRS) have recently emerged as the gold-standard for accomplishing this task. Here, we will review the use of different MRI techniques currently being used to determine body fat content and distribution. We also discuss the pros and cons of MRS to determine ectopic fat depots in liver, muscle, pancreas and heart and compare these to emerging MRI techniques currently being put forward to create ectopic fat maps. Finally, we will discuss how MRI/MRS techniques are helping in changing the perception of what is healthy and what is normal and desirable body-fat content and distribution.

The interrelationship between bone and fat: from cellular see-saw to endocrine reciprocity

The number of mature osteoblasts and marrow adipocytes in bone is influenced by the differentiation of the common mesenchymal progenitor cell towards one phenotype and away from the other. Consequently, factors which promote adipogenesis not only lead to fatty marrow but also inhibit osteoblastogenesis, resulting in decreased osteoblast numbers, diminished bone formation and, potentially, inadequate bone mass and osteoporosis. In addition to osteoblast and bone adipocyte numbers being influenced by this skewing of progenitor cell differentiation towards one phenotype, mature osteoblasts and adipocytes secrete factors which may evoke changes in the cell fate and function of each other. This review examines the endogenous factors, such as PPAR-γ2, Wnt, IGF-1, GH, FGF-2, oestrogen, the GP130 signalling cytokines, vitamin D and glucocorticoids, which regulate the selection between osteoblastogenesis and adipogenesis and the interrelationship between fat and bone. The role of adipokines on bone, such as adiponectin and leptin, as well as adipose-derived oestrogen, is reviewed and the role of bone as an energy regulating endocrine organ is discussed.

Vertebral bone marrow fat associated with lower trabecular BMD and prevalent vertebral fracture in older adults

CONTEXT

Bone marrow fat (BMF) and bone mineral density (BMD) by dual x-ray energy absorptiometry (DXA) are negatively correlated. However, little is known about the association of BMF with fracture or with separate trabecular and cortical bone compartments.

OBJECTIVE

Our objective was to assess the relationships between vertebral BMF, BMD by quantitative computed tomography, and fracture in older adults.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a cross-sectional study in the Age Gene/Environment Susceptibility-Reykjavik cohort.

MAIN OUTCOME MEASURES

Outcomes measures included vertebral BMF (L1-L4) measured with magnetic resonance spectroscopy, quantitative computed tomography and DXA scans of the hip and spine, and DXA vertebral fracture assessments. Previous clinical fracture was determined from medical records.

RESULTS

In 257 participants without recent bone-active medication use, mean age was 79 (SD 3.1) years. Mean BMF was 53.5% ± 8.1% in men and 55.0% ± 8.4% in women. Those with prevalent vertebral fracture (21 men, 32 women) had higher mean BMF in models adjusted for BMD. In separate models by sex, the difference was statistically significant only in men (57.3% vs 52.8%, P = 0.02). BMF was associated with lower trabecular volumetric BMD (vBMD) at the spine (-10.5% difference for each 1 SD increase in BMF, P < 0.01), total hip, and femoral neck, but not with cortical vBMD, in women. In men, BMF was marginally associated with trabecular spine vBMD (-6.1%, P = 0.05). Total hip and spine areal BMD (aBMD) were negatively correlated with BMF in women only.

CONCLUSION

Higher marrow fat correlated with lower trabecular, but not cortical, BMD in older women but not men. Higher marrow fat was associated with prevalent vertebral fracture in men, even after adjustment for BMD.

Femoral bone marrow adiposity and cortical bone cross-sectional areas in men with motor complete spinal cord injury

OBJECTIVES

To (1) quantify yellow and red bone marrow (BM) and cortical bone cross-sectional areas (CSAs) of the femur in persons with motor complete spinal cord injury (SCI) compared with healthy able-bodied control subjects and (2) determine the relationships between yellow and red BM, cortical CSAs, and thigh composition and measurements from dual-energy x-ray absorptiometry in men with complete SCI.

DESIGN

Cross-sectional.

SETTINGS

Clinical hospital and academic settings.

METHODS

Eight persons with motor complete SCI and 6 age-matched healthy control subjects underwent magnetic resonance imaging of both thighs to measure BM adiposity (BMA) and cortical CSA followed by whole-body dual-energy x-ray absorptiometry to measure bone mineral density and body composition for the SCI group.

RESULTS

Cortical bone CSA adjusted to total subperiosteal bone CSA was 1.5-2 times lower in men with SCI compared with able-bodied control subjects across the femoral length (P =.003). Yellow BMA CSA was 2-3 times greater in men with SCI compared with able-bodied control subjects (P < .0001). Opposite relationships were found between the yellow BMA CSA and cortical bone CSAs in men with SCI (negative association) and able-bodied control subjects (positive association). Yellow BMA was negatively associated with bone mineral density and bone mineral content and with skeletal muscle CSA and fat-free mass (P <.05) in men with SCI. Finally, yellow BMA was positively related to thigh subcutaneous adipose tissue.

CONCLUSIONS

After SCI, cortical bone CSA becomes thinner and is associated with greater accumulation of yellow BMA. Yellow BMA is associated with changes in bone CSA and bone mass, as well as increased fat mass, after SCI.

The relationships among total body fat, bone mineral content and bone marrow adipose tissue in early-pubertal girls

Investigation of the physiologic relevance of bone marrow adipose tissue (BMAT) during growth may promote understanding of the bone-fat axis and confluence with metabolic factors. The objective of this pilot investigation was two-fold: (1) to evaluate the relationships among total body fat, bone mineral content (BMC) and femoral BMAT during childhood and underlying metabolic determinants and (2) to determine if the relationships differ by race. Participants included white and non-Hispanic black girls (n=59) ages 4–10 years. Femoral BMAT volume was measured by magnetic resonance imaging, BMC and body fat by dual-energy X-ray absorptiometry. Metabolic parameters were assessed in the fasted state. Total fat and BMC were positively associated with BMAT; however, simultaneous inclusion of BMC and body fat in the statistical model attenuated the association between BMC and BMAT. Differences in BMAT volume were observed, non-Hispanic black girls exhibiting marginally greater BMAT at age eight (P=0.05) and white girls exhibiting greater BMAT at age ten (P<0.001). Metabolic parameters conferred differential impact by race, such that, a positive association for BMAT and leptin (P=0.02) and adiponectin (P=0.002) in white girls while BMAT and insulin were inversely related in non-Hispanic black girls (P=0.008). Our findings revealed a positive relationship between BMAT, body fat and BMC, although body fat, respective to leptin, contributed partly to the relationship between BMAT and BMC. Despite large differences in total fat between non-Hispanic black and white, the relationship between BMAT and BMC was similar to white girls. However, this relationship appeared to be impacted through different mechanisms according to race.

Marrow fat and bone--new perspectives

CONTEXT

There is growing interest in the relationship between bone mineral density, bone strength, and fat depots. Marrow adipose tissue, a well-established component of the marrow environment, is metabolically distinct from peripheral fat depots, but its functional significance is unknown.

OBJECTIVE

In this review, we discuss animal and human data linking the marrow adipose tissue depot to parameters of bone density and integrity as well as the potential significance of marrow adipose tissue in metabolic diseases associated with bone loss, including type 1 diabetes mellitus and anorexia nervosa. Potential hormonal determinants of marrow adipose tissue are also discussed.

CONCLUSIONS

We conclude that whereas most animal and human data demonstrate an inverse association between marrow adipose tissue and measures of bone density and strength, understanding the functional significance of marrow adipose tissue and its hormonal determinants will be critical to better understanding its role in skeletal integrity and the role of marrow adipose tissue in the pathophysiology of bone loss.

Comparison among T1-weighted magnetic resonance imaging, modified dixon method, and magnetic resonance spectroscopy in measuring bone marrow fat

INTRODUCTION

An increasing number of studies are utilizing different magnetic resonance (MR) methods to quantify bone marrow fat due to its potential role in osteoporosis. Our aim is to compare the measurements of bone marrow fat among T1-weighted magnetic resonance imaging (MRI), modified Dixon method (also called fat fraction MRI (FFMRI)), and magnetic resonance spectroscopy (MRS).

METHODS

Contiguous MRI scans were acquired in 27 Caucasian postmenopausal women with a modified Dixon method (i.e., FFMRI). Bone marrow adipose tissue (BMAT) of T1-weighted MRI and bone marrow fat fraction of the L3 vertebra and femoral necks were quantified using SliceOmatic and Matlab. MRS was also acquired at the L3 vertebra.

RESULTS

Correlation among the three MR methods measured bone marrow fat fraction and BMAT ranges from 0.78 to 0.88 (P < 0.001) in the L3 vertebra. Correlation between BMAT measured by T1-weighted MRI and bone marrow fat fraction measured by modified FFMRI is 0.86 (P < 0.001) in femoral necks.

CONCLUSION

There are good correlations among T1-weighted MRI, FFMRI, and MRS for bone marrow fat quantification. The inhomogeneous distribution of bone marrow fat, the threshold segmentation of the T1-weighted MRI, and the ambiguity of the FFMRI may partially explain the difference among the three methods.

Bone marrow mesenchymal stem cells: fat on and blast off by FGF21

Bone marrow mesenchymal stem cells (BMMSCs) are multipotent marrow stromal cells with the ability to differentiate into a variety of cell types required for tissue regeneration including osteoblasts and chondrocytes. Thus, they hold tremendous potential as powerful therapeutic strategies for the prevention and treatment of degenerative disorders including osteoporosis and osteoarthritis. The differentiation of BMMSCs into competing lineages such as osteoblasts and marrow adipocytes is regulated by various environmental cues and intrinsic signaling pathways. Here I highlight recent advances in the understanding of BMMSC function and regulation, including the interaction between BMMSCs with the hematopoietic/immune system, and the identification of novel modulators of BMMSC differentiation such as the metabolic hormone fibroblast growth factor 21 (FGF21). These new findings will further elucidate the dynamic regulation of BMMSCs in the pathophysiological control of skeletal homeostasis, and facilitate the clinical applications of BMMSCs in regenerative medicine.

Bone metabolism in obesity and weight loss

Excess body weight due to obesity has traditionally been considered to have a positive effect on bone; however, more recent findings suggest that bone quality is compromised. Both obesity and caloric restriction increase fracture risk and are regulated by endocrine factors and cytokines that have direct and indirect effects on bone and calcium absorption. Weight reduction will decrease bone mass and mineral density, but this varies by the individual's age, gender, and adiposity. Dietary modifications, exercise, and medications have been shown to attenuate the bone loss associated with weight reduction. Future obesity and weight loss trials would benefit from assessment of key hormones, adipokine and gut peptides that regulate calcium absorption, and bone mineral density and quality by using sensitive techniques in high-risk populations.

MRI-measured pelvic bone marrow adipose tissue is inversely related to DXA-measured bone mineral in younger and older adults

BACKGROUND/OBJECTIVES

Recent research has shown an inverse relationship between bone marrow adipose tissue (BMAT) and bone mineral density (BMD). There is a lack of evidence at the macro-imaging level to establish whether increased BMAT is a cause or effect of bone loss. This cross-sectional study compared the BMAT and BMD relationship between a younger adult group at or approaching peak bone mass (PBM; age 18.0-39.9 years) and an older group with potential bone loss (PoBL; age 40.0-88.0 years).

SUBJECTS/METHODS

Pelvic BMAT was evaluated in 560 healthy men and women with T1-weighted whole-body magnetic resonance imaging. BMD was measured using whole-body dual-energy X-ray absorptiometry.

RESULTS

An inverse correlation was observed between pelvic BMAT and pelvic, total and spine BMD in the younger PBM group (r=-0.419 to -0.461, P<0.001) and in the older PoBL group (r=-0.405 to -0.500, P<0.001). After adjusting for age, sex, ethnicity, menopausal status, total body fat, skeletal muscle, subcutaneous and visceral adipose tissue, neither subject group (younger PBM vs older PoBL) nor its interaction with pelvic BMAT significantly contributed to the regression models with BMD as dependent variable and pelvic BMAT as independent variable (P=0.434-0.928).

CONCLUSIONS

Our findings indicate that an inverse relationship between pelvic BMAT and BMD is present both in younger subjects who have not yet experienced bone loss and also in older subjects. These results provide support at the macro-imaging level for the hypothesis that low BMD may be a result of preferential differentiation of mesenchymal stem cells from osteoblasts to adipocytes.

Ethnic and sex differences in bone marrow adipose tissue and bone mineral density relationship

The relationship between bone marrow adipose tissue and bone mineral density is different between African Americans and Caucasians as well as between men and women. This suggests that the mechanisms that regulate the differentiation and proliferation of bone marrow stromal cells may differ in these populations.

INTRODUCTION

It has long been established that there are ethnic and sex differences in bone mineral density (BMD) and fracture risk. Recent studies suggest that bone marrow adipose tissue (BMAT) may play a role in the pathogenesis of osteoporosis. It is unknown whether ethnic and sex differences exist in the relationship between BMAT and BMD.

METHODS

Pelvic BMAT was evaluated in 455 healthy African American and Caucasian men and women (age 18-88 years) using whole-body T1-weighted magnetic resonance imaging. BMD was measured using whole-body dual-energy X-ray absorptiometry.

RESULTS

A negative correlation was observed between pelvic BMAT and total body BMD or pelvic BMD (r = -0.533, -0.576, respectively; P < 0.001). In multiple regression analyses with BMD as the dependent variable, ethnicity significantly entered the regression models as either an individual term or an interaction with BMAT. Menopausal status significantly entered the regression model with total body BMD as the dependent variable. African Americans had higher total body BMD than Caucasians for the same amount of BMAT, and the ethnic difference for pelvic BMD was greater in those participants with a higher BMAT. Men and premenopausal women had higher total body BMD levels than postmenopausal women for the same amount of BMAT.

CONCLUSIONS

An inverse relationship exists between BMAT and BMD in African American and Caucasian men and women. The observed ethnic and sex differences between BMAT and BMD in the present study suggest the possibility that the mechanisms regulating the differentiation and proliferation of bone marrow stromal cells may differ in these populations.

Marrow fat and preadipocyte factor-1 levels decrease with recovery in women with anorexia nervosa

Women with anorexia nervosa (AN) have elevated marrow fat mass despite low visceral and subcutaneous fat depots, which is inversely associated with bone mineral density (BMD). Whether marrow fat mass remains persistently elevated or decreases with recovery from AN is currently unknown. In this study, we investigated changes in marrow fat in women who have recovered from AN (AN-R). We also studied the relationship between preadipocyte factor (Pref)-1-a member of the EGF-like family of proteins and regulator of adipocyte and osteoblast differentiation-and fat depots and BMD in AN-R compared with women with AN and healthy controls (HC). We studied 29 women: 14 with active or recovered AN (30.7 + 2.2 years [mean ± SEM]) and 15 normal-weight controls (27.8 ± 1.2 years). We measured marrow adipose tissue (MAT) of the L4 vertebra and femur by (1) H-magnetic resonance spectroscopy; BMD of the spine, hip, and total body by DXA; and serum Pref-1 and leptin levels. We found that MAT of the L4 vertebra was significantly lower in AN-R compared with AN (p = 0.03) and was comparable to levels in HC. Pref-1 levels were also significantly lower in AN-R compared with AN (p = 0.02) and comparable to levels in healthy controls. Although Pref-1 was positively associated with MAT of the L4 vertebra in AN (R = 0.94; p = 0.002), we found that it was inversely associated with MAT of the L4 vertebra in HC (R = -0.71; p = 0.004). Therefore, we have shown that MAT and Pref-1 levels decrease with recovery from AN. Our data suggest that Pref-1 may have differential effects in states of nutritional deprivation compared with nutritional sufficiency.

Body composition and skeletal health: too heavy? Too thin?

The relationship between body composition and skeletal metabolism has received growing recognition. Low body weight is an established risk factor for fracture. The effect of obesity on skeletal health is less well defined. Extensive studies in patients with anorexia nervosa and obesity have illuminated many of the underlying biologic mechanisms by which body composition modulates bone mass. This review examines the relationship between body composition and bone mass through data from recent research studies throughout the weight spectrum ranging from anorexia nervosa to obesity.

Aging and bone loss: new insights for the clinician

It is well known that the underlying mechanisms of osteoporosis in older adults are different than those associated with estrogen deprivation. Age-related bone loss involves a gradual and progressive decline, which is also seen in men. Markedly increased bone resorption leads to the initial fall in bone mineral density. With increasing age, there is also a significant reduction in bone formation. This is mostly due to a shift from osteoblastogenesis to predominant adipogenesis in the bone marrow, which also has a lipotoxic effect that affects matrix formation and mineralization. We review new evidence on the pathophysiology of age-related bone loss with emphasis upon the mechanism of action of current osteoporosis treatments. New potential treatments are also considered, including therapeutic approaches to osteoporosis in the elderly that focus on the pathophysiology and potential reversal of adipogenic shift in bone.

Increased marrow adiposity in premenopausal women with idiopathic osteoporosis

CONTEXT

We have previously reported that premenopausal women with idiopathic osteoporosis based on fractures (IOP) or idiopathic low bone mineral density (ILBMD) exhibit markedly reduced bone mass, profoundly abnormal trabecular microstructure, and significant deficits in trabecular bone stiffness. Bone remodeling was heterogeneous. Those with low bone turnover had evidence of osteoblast dysfunction and the most marked deficits in microstructure and stiffness.

OBJECTIVE

Because osteoblasts and marrow adipocytes derive from a common mesenchymal precursor and excess marrow fat has been implicated in the pathogenesis of bone fragility in anorexia nervosa, glucocorticoid excess, and thiazolidinedione exposure, we hypothesized that marrow adiposity would be higher in affected women and inversely related to bone mass, microarchitecture, bone formation rate, and osteoblast number.

DESIGN

We analyzed tetracycline-labeled transiliac biopsy specimens in 64 premenopausal women with IOP or ILBMD and 40 controls by three-dimensional micro-computed tomography and two-dimensional quantitative histomorphometry to assess marrow adipocyte number, perimeter, and area.

RESULTS

IOP and ILBMD subjects did not differ with regard to any adipocyte parameter, and thus results were combined. Subjects had substantially higher adipocyte number (by 22%), size (by 24%), and volume (by 26%) than controls (P < 0.0001 for all). Results remained significant after adjusting for age, body mass index, and bone volume. Controls demonstrated expected direct associations between marrow adiposity and age and inverse relationships between marrow adiposity and bone formation, volume, and microstructure measures. No such relationships were observed in the subjects.

CONCLUSIONS

Higher marrow adiposity and the absence of expected relationships between marrow adiposity and bone microstructure and remodeling in women with IOP or ILBMD suggest that the relationships between fat and bone are abnormal; excess marrow fat may not arise from a switch from the osteoblast to the adipocyte lineage in this disorder. Whether excess marrow fat contributes to the pathogenesis of this disorder remains unclear.

Body composition and cardiovascular risk markers after remission of Cushing's disease: a prospective study using whole-body MRI

CONTEXT

Cushing's Disease (CD) alters fat distribution, muscle mass, adipokine profile, and cardiovascular risk factors. It is not known whether remission entirely reverses these changes.

OBJECTIVES

Our objective was to determine whether the adverse body composition and cardiovascular risk profile in CD change after remission.

DESIGN, SETTING, AND PATIENTS

Fourteen CD patients were studied prospectively: before surgery (active disease) and again postoperatively 6 months after discontinuing oral glucocorticoids (remission). Whole-body magnetic resonance imaging was used to examine lean and fat tissue distributions.

OUTCOME MEASURES

Body composition (skeletal muscle and fat in the visceral, bone marrow, sc, and inter-muscular compartments) and cardiovascular risk factors (serum insulin, glucose, leptin, high-molecular-weight adiponectin, C-reactive protein, and lipid profile) were measured in active CD and remission (mean 20 months after surgery).

RESULTS

Remission decreased visceral, pelvic bone marrow, sc (including trunk and limb sc), and total fat; waist circumference; and weight (P < 0.05). Remission altered fat distribution, resulting in decreased visceral/total fat (P = 0.04) and visceral fat/skeletal muscle ratios (P = 0.006). Remission decreased the absolute muscle mass (P = 0.015). Cardiovascular risk factors changed: insulin resistance, leptin, and total cholesterol decreased (P < 0.05), but adiponectin, C-reactive protein, and other lipid measures did not change.

CONCLUSIONS

CD remission reduced nearly all fat depots and reverted fat to a distribution more consistent with favorable cardiovascular risk but decreased skeletal muscle. Remission improved some but not all cardiovascular risk markers. Remission from CD dramatically improves body composition abnormalities but may still be associated with persistent cardiovascular risk.

Relationship between MRI-measured bone marrow adipose tissue and hip and spine bone mineral density in African-American and Caucasian participants: the CARDIA study

CONTEXT

An increasing number of studies suggest that bone marrow adipose tissue (BMAT) might play a role in the pathogenesis of osteoporosis. Our previous study of Caucasian women demonstrated that there is an inverse relationship between BMAT and whole-body bone mineral density (BMD). It is unknown whether visceral adipose tissue (VAT), sc adipose tissue (SAT), and skeletal muscle had an effect on the relationship between BMAT and BMD.

OBJECTIVE

In the present study we investigated the relationship between pelvic, hip, and lumbar spine BMAT with hip and lumbar spine BMD in the population-based Coronary Artery Risk Development in Young Adults (CARDIA) sample with adjustment for whole-body magnetic resonance imaging (MRI)-measured VAT, SAT, and skeletal muscle.

DESIGN

T1-weighted MRI was acquired for 210 healthy African-American and Caucasian men and women (age 38-52 yr). Hip and lumbar spine BMD were measured by dual-energy x-ray absorptiometry.

RESULTS

Pelvic, hip, and lumbar spine BMAT had negative correlations with hip and lumbar spine BMD (r = -0.399 to -0.550, P < 0.001). The inverse associations between BMAT and BMD remained strong after adjusting for demographics, weight, skeletal muscle, SAT, VAT, total adipose tissue (TAT), menopausal status, lifestyle factors, and inflammatory markers (standardized regression coefficients = -0. 296 to -0.549, P < 0.001). Among body composition measures, skeletal muscle was the strongest correlate of BMD after adjusting for BMAT (standardized regression coefficients = 0.268-0.614, P < 0.05), with little additional contribution from weight, SAT, VAT, or total adipose tissue.

CONCLUSION

In this middle-aged population, a negative relationship existed between MRI-measured BMAT and hip and lumbar spine BMD independent of demographics and body composition. These observations support the growing evidence linking BMAT with low bone density.

Risedronate inhibits bone marrow mesenchymal stem cell adipogenesis and switches RANKL/OPG ratio to impair osteoclast differentiation

BACKGROUND

Osteoporosis is accompanied by an increase in bone marrow adipose tissue. Bone marrow adipogenesis has emerged as a therapeutic target for prevention of bone loss. Amino-bisphosphonates have been widely used for treatment of osteoporosis, but the mechanism through which amino-bisphosphonates inhibit osteoporosis remains unclear. The purpose of this study is to investigate the effects of bisphosphonates on bone marrow adipogenesis and the pro-osteoclastic factors produced by adipocytes in bone marrow microenvironment.

MATERIALS AND METHODS

Human mesenchymal stem cells were obtained and purified from six volunteer donors. Each sample of cells was treated by increasing concentrations of risedronate with or without adipogenic induction for 14 d, and then droplets of the differentiated adipocytes were analyzed. The level of receptor activator of nuclear factor-κB ligand and osteoprotegerin, as well as pro-osteoclastic inflammatory factors interleukin-1, interleukin-6, and tumor necrosis factor α produced by adipocytes were evaluated by Western blot and ELISA assay. Moreover, the effect of risedronate on the activity of mammalian target of rapamycin complex 1, a key Ser/Thr kinase for initiation of adipocyte differentiation, was investigated.

RESULTS

Risedronate not only dose-dependently inhibited the bone marrow adipogenesis from human mesenchymal stem cells but also suppressed receptor activator of nuclear factor-κB ligand, not osteoprotegerin, expression in differentiated adipocytes, as well as pro-osteoclastic inflammatory factors. Furthermore, the activity of mammalian target of rapamycin complex 1 was suppressed by risedronate.

CONCLUSION

Our findings that risedronate influences the crosstalk between bone marrow adipocyte-osteoclast represent a novel mechanism for the anti-osteoporotic effects of risedronate.

The relationship between adipose tissue and bone metabolism

OBJECTIVES

The authors have set out to evaluate the literature relevant to the dynamic regulation of adipogenesis and osteogenesis.

DESIGN AND METHODS

A detailed search of the past and recent literature was conducted on Pubmed using a combination of keywords including: adipogenesis, bone marrow, hematopoiesis, mesenchymal stromal/stem cell, and osteogenesis.

RESULTS

Throughout one's lifespan, the bone marrow microenvironment provides a unique niche for mesenchymal stromal/stem cells (BMSCs) and hematopoietic stem cells (HSCs). The marrow changes as a function of biological age and pathophysiology. Historically, clinical biochemistry has observed these changes from an HSC and hematological perspective. Nevertheless, these changes also reflect the balance between BMSC adipogenic and osteogenic processes which can display an inverse or reciprocal relationship. Multiple hormonal factors and nuclear hormone receptor ligands and drugs are responsible for BMSC lineage selection. Data from a number of laboratories now implicates endocrine feedback loops between extramedullary adipose depots and the central nervous system.

CONCLUSIONS

This concise review provides a perspective on the mechanisms regulating BMSC differentiation in the context of biological aging, obesity, and osteoporosis.

Marrow fat metabolism is linked to the systemic energy metabolism

Recent advances in understanding the role of bone in the systemic regulation of energy metabolism indicate that bone marrow cells, adipocytes and osteoblasts, are involved in this process. Marrow adipocytes store significant quantities of fat and produce adipokines, leptin and adiponectin, which are known for their role in the regulation of energy metabolism, whereas osteoblasts produce osteocalcin, a bone-specific hormone that has a potential to regulate insulin production in the pancreas and adiponectin production in fat tissue. Both osteoblasts and marrow adipocytes express insulin receptor and respond to insulin-sensitizing anti-diabetic TZDs in a manner, which tightly links bone with the energy metabolism system. Metabolic profile of marrow fat resembles that of both, white and brown fat, which is reflected by its plasticity in acquiring different functions including maintenance of bone micro-environment. Marrow fat responds to physiologic and pathologic changes in energy metabolism status by changing volume and metabolic activity. This review summarizes available information on the metabolic function of marrow fat and provides hypothesis that this fat depot may acquire multiple roles depending on the local and perhaps systemic demands. These functions may include a role in bone energy maintenance and endocrine activities to serve osteogenesis during bone remodeling and bone healing.

Bone marrow fat has brown adipose tissue characteristics, which are attenuated with aging and diabetes

Fat occupies a significant portion of bone cavity however its function is largely unknown. Marrow fat expands during aging and in conditions which affect energy metabolism, indicating that fat in bone is under similar regulatory mechanisms as other fat depots. On the other hand, its location may determine specific functions in the maintenance of the environment for bone remodeling and hematopoiesis. We have demonstrated that marrow fat has a distinctive phenotype, which resembles both, white and brown adipose tissue (WAT and BAT, respectively). Marrow adipocytes express gene markers of brown adipocytes at levels characteristic for the BAT, including transcription factor Prdm16, and regulators of thermogenesis such as deiodinase 2 (Dio2) and PGC1α. The levels of expression of BAT-specific gene markers are decreased in bone of 24 mo old C57BL/6 and in diabetic yellow agouti A(vy)/a mice implicating functional changes of marrow fat occurring with aging and diabetes. Administration of antidiabetic TZD rosiglitazone, which sensitizes cells to insulin and increases adipocyte metabolic functions, significantly increased both, BAT (UCP1, PGC1α, Dio2, β3AR, Prdm16, and FoxC2) and WAT (adiponectin and leptin) gene expression in marrow of normoglycemic C57BL/6 mice, but failed to increase the expression of BAT, but not WAT, gene markers in diabetic mice. In conclusion, the metabolic phenotype of marrow fat combines both BAT and WAT characteristics. Decrease in BAT-like characteristics with aging and diabetes may contribute to the negative changes in the marrow environment supporting bone remodeling and hematopoiesis.

Short-term physical activity intervention decreases femoral bone marrow adipose tissue in young children: a pilot study

Mechanical stimulation is necessary for maximization of geometrical properties of bone mineralization contributing to long-term strength. The amount of mineralization in bones has been reciprocally related to volume of bone marrow adipose tissue and this relationship is suggested to be an independent predictor of fracture. Physical activity represents an extrinsic factor that impacts both mineralization and marrow volume exerting permissive capacity of the growing skeleton to achieve its full genetic potential. Because geometry- and shape-determining processes primarily manifest during the linear growth period, the accelerated structural changes accompanying early childhood (ages 3 to 6 y) may have profound impact on lifelong bone health. The objective of this pilot study was to determine if a short-term physical activity intervention in young children would result in augmentation of geometric properties of bone. Three days per week the intervention group (n=10) participated in 30 min of moderate intensity physical activity, such as jumping, hopping and running, and stretching activities, whereas controls (n=10) underwent usual activities during the 10-week intervention period. Femoral bone marrow adipose tissue volume and total body composition were assessed by magnetic resonance imaging and dual-energy X-ray absorptiometry, respectively, at baseline and after 10 weeks. Although after 10-weeks, intergroup differences were not observed, a significant decrease in femoral marrow adipose tissue volume was observed in those participating in physical activity intervention. Our findings suggest that physical activity may improve bone quality via antagonistic effects on femoral bone marrow adipose tissue and possibly long-term agonistic effects on bone mineralization.

Incidental vertebral lesions

Incidental vertebral lesions on imaging of the spine are commonly encountered in clinical practice. Contributing factors include the aging population, the increasing prevalence of back pain, and increased usage of MR imaging. Additionally, refinements in CT and MR imaging have increased the number of demonstrable lesions. The management of incidental findings varies among practitioners and commonly depends more on practice style than on data or guidelines. In this article we review incidental findings within the vertebral column and review management of these lesions, based on available Class III data.

Relationships of percent body fat and percent trunk fat with bone mineral density among Chinese, black, and white subjects

We examined ethnic difference in the association of body fat and trunk fat with bone mineral density (BMD) among Chinese, white, and black subjects. We found that, with greater body and trunk fat, both white and black subjects were more likely to have a low BMD than Chinese subjects.

INTRODUCTION

Ethnic differences in body fat, abdominal fat distribution, and BMD have been found in previous studies between Chinese and white subjects. However, the associations of body fat and abdominal fat distribution with BMD have not been studied, and whether the ethnic differences have an effect on these associations is unclear.

METHODS

We evaluated 1,147 subjects aged ≥ 18 years (805 Chinese, 193 whites, and 149 blacks). Percent body fat (%BF), percent trunk fat (%TF), and total and regional BMD including that of head, arm, leg, trunk, rib, spine, and pelvis were measured by dual-energy X-ray absorptiometry. Linear regression models were developed to test the association of ethnicity, %BF, and interaction between ethnicity and %BF with BMD. The models were repeated again, replacing %BF with %TF.

RESULTS

Chinese subjects showed lower BMD in total and most regions compared with black and white subjects; however, these differences were eliminated between Chinese and whites within both sexes and between Chinese and black men when age, weight, height, and %BF were added. %BF and %TF were negatively associated with most regional body BMD. The interactions between %BF, %TF, and ethnicity were found in most regional body BMD among Chinese, white, and black subjects for both men and women.

CONCLUSION

Both %BF and %TF have negative associations with BMD. With greater accumulation of %BF and %TF, both white and black subjects may experience a higher risk of low BMD than Chinese subjects.

MR spectroscopy and micro-CT in evaluation of osteoporosis model in rabbits: comparison with histopathology

PURPOSE

To explore the evidence of regular alteration of bone quality in osteoporosis dynamically examined by MRS and micro-CT, comparing with histopathology.

METHODS

Forty rabbits were allocated into two groups. Group A were used as sham. Group B underwent bilateral ovariectomy (OVX) combined with daily intramuscular methylprednisolone, underwent MR spectroscopy, micro-CT, and histopathology of L5 at 2, 4, 8, and 10 weeks after operation.

RESULTS

Fat fraction as shown by MRS in Group B was significantly increased over the time course of osteoporosis development with significant difference between two groups at 4, 8, and 10 weeks after OVX. Continuous deterioration of cancellous bone architecture in Group B, was first detected at week 4. FF value in group B correlated with micro-CT parameters. Marrow fat as measured by MR and CT was positively correlated with both the mean density and diameter of adipocytes (both of which increased over time).

CONCLUSIONS

Marrow adipogenesis occurs in synchrony with deterioration of trabecular microarchitecture.MRS may be valuable to assess the pathophysiological changes of bone marrow in osteoporosis in early stage.

KEY POINTS

MRS revealed gradually increasing bone marrow fat in rabbits rendered osteoporotic. Marrow adipogenesis occurs in synchrony with deterioration of trabecular microarchitecture. Pathology revealed an early increase in number of marrow adipocytes in osteoporosis. MRS may help assess early pathophysiological bone marrow changes in osteoporosis.

Osteoblastogenesis and adipogenesis are higher in osteoarthritic than in osteoporotic bone tissue

BACKGROUND AND AIMS

New data show that increased adipogenesis in bone marrow may decrease osteoblastogenesis, resulting in osteoporosis (OP). Runt-related transcription factor 2 (RUNX2) and peroxisome proliferator-activated receptor γ (PPARγ) are two main transcriptional regulators controlling osteoblastogenesis and adipogenesis from the same precursor cell in bone-the mesenchymal stem cell. Because osteoarthritis (OA) and OP present the opposing bone phenotype, our aim was to determine whether the expression of selected adipogenic genes is lower in OA compared to OP bone tissue.

METHODS

Bone samples were obtained from gender-matched OP (n = 54) and OA (n = 49) patients undergoing hip arthroplasty. Osteoblastogenesis and adipogenesis were estimated by gene expression analysis of RUNX2, PPARγ2 and their downstream genes.

RESULTS

In OA bone, significantly higher expression of PPARγ2 and adiponectin as well as RUNX2, osterix and osteocalcin were obtained, suggesting higher adipogenesis and osteoblastogenesis in OA than in OP. There were no differences in RUNX2/PPARγ2 and osteocalcin/adiponectin ratios between groups, suggesting similar balance of both processes. Higher perilipin 2, angiopoietin-like 4 and fatty-acid binding protein 4 mRNA levels in OP suggest activation of other transcription factors or hypoxic conditions in OP bone.

CONCLUSIONS

Regulation of bone formation by RUNX2 and PPARγ2 is modified in OA compared to OP, resulting in higher osteoblastogenesis and adipogenesis in OA. Both processes are similarly balanced in OP and OA but less active in OP.

PPARG gene promoter polymorphism is associated with non-traumatic hip fracture risk in the elderly Slovenian population: a pilot study

OBJECTIVES

Peroxisome proliferator-activated receptor γ (PPARγ), an essential transcription factor for adipogenesis, has been implicated in pathogenesis of osteoporosis. The association of three single nucleotide polymorphisms in the PPARG gene with hip fracture risk, bone mineral density (BMD) and biochemical markers of bone turnover was investigated in the elderly.

DESIGN AND METHODS

Six hundred sixty-seven elderly Slovenians were genotyped for SNPs rs12497191, rs1801282 and rs3856806. BMD and biochemical markers of bone turnover were measured. Haplotypes ACC, AGT and GCC, defined by rs12497191, rs1801282 and rs3856806 were assigned. Influence of genotype on fracture risk was assessed in 72 non-traumatic hip fracture cases and 272 controls.

RESULTS

The rs12497191 G allele alone or in haplotype was associated with lower risk of non-traumatic hip fracture and higher serum receptor activator of nuclear factor κB ligand.

CONCLUSIONS

The rs12497191 genotype could contribute to the incidence of non-traumatic hip fractures in the elderly.

Impact of intra- and extra-osseous soft tissue composition on changes in bone mineral density with weight loss and regain

Recent studies report a significant gain in bone mineral density (BMD) after diet-induced weight loss. This might be explained by a measurement artefact. We therefore investigated the impact of intra- and extra-osseous soft tissue composition on bone measurements by dual X-ray absorptiometry (DXA) in a longitudinal study of diet-induced weight loss and regain in 55 women and 17 men (19-46 years, BMI 28.2-46.8 kg/m(2)). Total and regional BMD were measured before and after 12.7 ± 2.2 week diet-induced weight loss and 6 months after significant weight regain (≥30%). Hydration of fat free mass (FFM) was assessed by a 3-compartment model. Skeletal muscle (SM) mass, extra-osseous adipose tissue, and bone marrow were measured by whole body magnetic resonance imaging (MRI). Mean weight loss was -9.2 ± 4.4 kg (P < 0.001) and was followed by weight regain in a subgroup of 24 subjects (+6.3 ± 2.9 kg; P < 0.001). With weight loss, bone marrow and extra-osseous adipose tissue decreased whereas BMD increased at the total body, lumbar spine, and the legs (women only) but decreased at the pelvis (men only, all P < 0.05). The decrease in BMD(pelvis) correlated with the loss in visceral adipose tissue (VAT) (P < 0.05). Increases in BMD(legs) were reversed after weight regain and inversely correlated with BMD(legs) decreases. No other associations between changes in BMD and intra- or extra-osseous soft tissue composition were found. In conclusion, changes in extra-osseous soft tissue composition had a minor contribution to changes in BMD with weight loss and decreases in bone marrow adipose tissue (BMAT) were not related to changes in BMD.

The role of bone marrow and visceral fat on bone metabolism

The protective effect of total fat mass on bone mineral density (BMD) has been challenged with studies showing no or negative association after adjusting for weight. Subsequently, more studies have evaluated the relationship of regional adiposity with BMD, and findings were inconsistent for central obesity. Advancements in imaging techniques enable us to directly and noninvasively study the role of adiposity on skeletal health. Visceral adiposity measured by computed tomography (CT) has consistently been shown to have negative effects on bone. Availability of magnetic resonance spectroscopy (MRS) also allows us to noninvasively quantify bone marrow fat (BMF), which has been known to be associated with osteoporosis from histomorphometric studies. Using MRS along with dual energy x-ray absorptiometry, studies have reported a detrimental role of BMF on BMD. With the increase in aging and obesity of the population, it is important to continue this effort in identifying the contribution of adipose tissues to bone quality and fracture.

Effects of risedronate on bone marrow adipocytes in postmenopausal women

SUMMARY

Aminobisphosphonates promote osteoblastogenesis while inhibiting adipogenesis in vitro. Their effect on adipogenesis in vivo remains unknown. In this study, we demonstrate that risedronate prevents marrow fat infiltration in postmenopausal women after 3 years of treatment.

INTRODUCTION

Age-related bone loss is associated with high levels of adipogenesis within the bone marrow at the expense of osteoblast population. Bisphosphonates stimulate osteoblastogenesis while inhibiting adipogenesis in vitro. In the present study, we tested whether the effect of bisphosphonates on marrow adipogenesis in vitro is also seen in vivo.

METHODS

We analyzed transiliac bone biopsies from a randomized, placebo-controlled clinical trial that evaluated the effects of risedronate treatment 5 mg/day on vertebral and non-vertebral fractures in women with postmenopausal osteoporosis. Paired bone biopsies were obtained from a subset of patients at baseline and after treatment with placebo or risedronate for 3 years (n = 14 per group). Biopsies were stained with toluidine blue and hematoxylin/eosin. Adipocyte volume/tissue volume (AV/TV), mean adipocyte number (AD(#)), and mean adipocyte diameter (AD(diam)) were quantified. Finally, expression levels of the adipogenesis transcription factor peroxisome proliferator activator gamma 2 (PPARγ2) within the bone marrow were quantified using immunohistochemistry.

RESULTS

In the placebo group, AV/TV, AD(#), and AD(diam) significantly increased after 3 years (~15%, p < 0.01). In contrast, AD(diam) remained unchanged and AV/TV and AD(#) were significantly reduced (~20%) in the risedronate group at 3 years (p < 0.01). These changes were associated with a significant reduction in PPARγ2 expression in the bone marrow of risedronate-treated women.

CONCLUSIONS

Risedronate reduces bone marrow fat in postmenopausal women. These findings are the first demonstration of an effect of bisphosphonates on marrow fat in humans in vivo. By regulating the amount of fat within the bone marrow, this effect may contribute to the beneficial effect of bisphosphonates on bone mass.

Voluntary weight loss: systematic review of early phase body composition changes

Weight loss follows when adult humans enter a phase of negative energy balance brought about by reducing energy intake and/or increasing energy expenditure. The weight loss period is usually viewed as a continuous process, ending when energy equilibrium is achieved at a lower weight or with death following depletion of fuel stores. However, growing evidence supports the expanded view that induction of negative energy balance leads to well-defined physiological effects characterized by three discrete phases (I-III). At present there are no comprehensive reviews of the 'early' phase of weight loss, a gap highlighted by recent interest in rapidly testing new treatments with short-term protocols. Herein we show from earlier reports and with new data that weight loss during phase I is: mathematically quantifiable with a t(1/2) < 1-week and 4- to 6-week duration; includes well-defined rapidly evolving body composition and energy expenditure changes; and is moderated by multiple factors including subject sex and activity level, nutrients ingested at baseline and during the negative energy balance period, and hormone and pharmacologic treatments. Our in depth review collectively characterizes phase I as a distinct weight loss period while revealing important knowledge gaps that can be filled with appropriately designed future studies.