Bone marrow fat content in 70 adolescent girls with anorexia nervosa: Magnetic resonance imaging and magnetic resonance spectroscopy assessment

Function and Regulation of Bone Marrow Adipose Tissue in Health and Disease: State of the Field and Clinical Considerations

Bone marrow adipose tissue (BMAT) is a metabolically and clinically relevant fat depot that exists within bone. Two subtypes of BMAT, regulated and constitutive, reside in hematopoietic-rich red marrow and fatty yellow marrow, respectively, and exhibit distinct characteristics compared to peripheral fat such as white and brown adipose tissues. Bone marrow adipocytes (BMAds) are evolutionally preserved in most vertebrates, start development after birth and expand throughout life, and originate from unique progenitor populations that control bone formation and hematopoiesis. Mature BMAds also interact closely with other cellular components of the bone marrow niche, serving as a nearby energy reservoir to support the skeletal system, a signaling hub that contributes to both local and systemic homeostasis, and a final fuel reserve for survival during starvation. Though BMAT and bone are often inversely correlated, more BMAT does not always mean less bone, and the prevention of BMAT expansion as a strategy to prevent bone loss remains questionable. BMAT adipogenesis and lipid metabolism are regulated by the nervous systems and a variety of circulating hormones. This contributes to the plasticity of BMAT, including BMAT expansion in common physiological or pathological conditions, and BMAT catabolism under certain extreme circumstances, which are often associated with malnutrition and/or systemic inflammation. Altogether, this article provides a comprehensive overview of the local and systemic functions of BMAT and discusses the regulation and plasticity of this unique adipose tissue depot in health and disease. © 2024 American Physiological Society. Compr Physiol 14:5521-5579, 2024.

Decreased Volume of Bone Marrow Adipocytes With Sparse Gelatinous Marrow Transformation in a Patient With Pancytopenia With Anorexia Nervosa: A Case Report

Patients with anorexia nervosa (AN) often have complications of hematologic abnormalities and pancytopenia, which can be fatal. In patients with AN, the rates of anemia, leukopenia, and thrombocytopenia have been reported as 16.7-39%, 7.9-39%, and 5-11%, respectively; in patients with severe AN, the rates of anemia, leukopenia, thrombocytopenia, and pancytopenia have been reported as 47-83%, 49.5-79%, 16.8-25%, and 16.4-23%, respectively. Hematologic abnormalities are often associated with morphological myeloid transformations such as hypoplasia, aplasia, and gelatinous marrow transformation (GMT). Hypocellularity, such as hypoplastic or aplastic, often results in a dry tap, whereas GMT does not usually result in this because of the aspiration of gelatinous material. Therefore, bone marrow aspiration in patients with pancytopenia with AN usually does not show a dry tap. The bone marrow adipocyte (BMA) volume increases in patients with AN, except in those with severe malnutrition. Patients with AN experiencing pancytopenia often exhibit GMT associated with atrophy of the originally increased volume of BMAs. Herein, we report the case of a patient with pancytopenia with AN who exhibited a dry tap on bone marrow aspiration. A bone marrow biopsy revealed sparse GMT with decreased BMA volume and areas of hematopoietic cells, adipocytes, and no GMT. A 13-year-old Japanese girl weighing 25.8 kg (BMI: 10.0 kg/m2) was admitted to our hospital and received nutritional therapy. The patient presented with pancytopenia and fever, prompting the conduct of bone marrow examinations. Bone marrow aspiration resulted in a dry tap, and the bone marrow biopsy revealed sparse GMT with a decreased volume of BMAs. Additionally, an area devoid of hematopoietic cells, adipocytes, or GMT was observed. Nutritional therapy resulted in weight gain and improved pancytopenia. Upon discharge, the patient weighed 40.0 kg (BMI: 15.5 kg/m2) with a normal WBC count, hemoglobin levels, and platelet count. It is significant to study hematological and bone marrow changes because patients with AN often present with hematologic abnormalities. The identification of sparse GMT, which is associated with a decrease in BMA volume and the presence of an area devoid of hematopoietic cells, adipocytes, or GMTs, is a novel finding. The improvement in pancytopenia following nutritional therapy suggests a link between myeloid transformation and malnutrition. Consequently, in patients with pancytopenia associated with AN exhibiting these bone marrow findings, nutritional therapy is necessary.

The Multifaceted Roles of Bone Marrow Adipocytes in Bone and Hematopoietic Homeostasis

Bone marrow adipose tissue (BMAT) makes up a significant portion of the marrow space, ranging from 50% to 70%, in healthy adults. It expands with aging, obesity, anorexia nervosa, and irradiation, which are conditions associated with skeletal complications or hematopoietic disorders. Therefore, BMAT has been viewed as a negative component of the bone marrow niche for decades, although the mechanisms and causative relationships have not been well-addressed. Of note, recent studies have revealed that BMAT is a multifaceted tissue that can serve as an energy reservoir to fuel osteoblasts and hematopoietic cells under stressful situations, and also acts as an endocrine/paracrine organ to suppress bone formation and support hematopoiesis at steady-state conditions. In this review, we summarize the uniqueness of BMAT, the complex findings of previous studies, and update our understanding of the physiological roles of BMAT in bone and hematopoietic metabolism based on a newly established bone marrow adipocyte-specific mouse model.

Bone in Anorexia

Anorexia nervosa is a feeding disorder involving intentional weight loss. Restricted dietary intake leads to disturbed bone metabolism due to various factors, notably endocrine, that affect bone microarchitecture and incur risk of fracture. Mild to moderate anorexia shows a paradoxical increase in bone marrow adipose tissue, whereas severe forms show gelatinous transformation known as serous atrophy of bone marrow (SABM). Imaging assessment of the mineralized and adipose components uses several techniques: dual-energy X-ray absorptiometry, computed tomography, chemical shift magnetic resonance imaging (MRI), and single-voxel MR spectroscopy. SABM induces MRI bone signal disturbances that can be hard to interpret and may hinder visualization of the fracture line.

Feasibility of joint mapping of triglyceride saturation and water longitudinal relaxation in a single breath hold applied to high fat-fraction adipose depots in the periclavicular anatomy

INTRODUCTION

Simultaneous mapping of triglyceride (TAG) saturation and tissue water relaxation may improve the characterization of the structure and function of anatomies with significant adipose tissue. While several groups have demonstrated in vivo TAG saturation imaging using MRI, joint mapping of relaxation and TAG saturation is understudied. Such mappings may avoid bias from physiological motion, if they can be done within a single breath-hold, and also account for static and applied magnetic field heterogeneity.

METHODS

We propose a transient-state/MR fingerprinting single breath-hold sequence at 3 T, a low-rank reconstruction, and a parameter estimation pipeline that jointly estimates the number of double bonds (NDB), number of methylene interrupted double bonds (NMIDB), and tissue water T1, while accounting for non-ideal radiofrequency transmit scaling and off-resonance effects. We test the proposed method in simulations, in phantom against MR spectroscopy (MRS), and in vivo regions in and around high fat fraction (FF) periclavicular adipose tissue. Partial volume and multi-peak transverse relaxation effects are explored.

RESULTS

The simulation results demonstrate accurate NDB, NMIDB, and water T1 estimates across a range of NDB, NMIDB, and T1 values. In phantoms, the proposed method's estimates of NDB and NMIDB correlate with those from MR spectroscopy (Pearson correlation ≥0.98), while the water T1 estimates are concordant with a standard phantom. The NDB and NMIDB are sensitive to partial volumes of water, showing increasing bias at FF < 40%. This bias is found to be due to noise and transverse relaxation effects. The in vivo periclavicular adipose tissue has high FF (>90%). The adipose tissue NDB and NMIDB, and muscle T1 estimates are comparable to those reported in the literature.

CONCLUSION

Robust estimation of NDB, NMIDB at high FF and water T1 across a broad range of FFs are feasible using the proposed methods. Further reduction of noise and model bias are needed to employ the proposed technique in low FF anatomies and pathologies.

Advances in Bone Marrow Imaging: Strengths and Limitations from a Clinical Perspective

Conventional magnetic resonance imaging (MRI) remains the modality of choice to image bone marrow. However, the last few decades have witnessed the emergence and development of novel MRI techniques, such as chemical shift imaging, diffusion-weighted imaging, dynamic contrast-enhanced MRI, and whole-body MRI, as well as spectral computed tomography and nuclear medicine techniques. We summarize the technical bases behind these methods, in relation to the common physiologic and pathologic processes involving the bone marrow. We present the strengths and limitations of these imaging methods and consider their added value compared with conventional imaging in assessing non-neoplastic disorders like septic, rheumatologic, traumatic, and metabolic conditions. The potential usefulness of these methods to differentiate between benign and malignant bone marrow lesions is discussed. Finally, we consider the limitations hampering a more widespread use of these techniques in clinical practice.

Identification of a stem cell mediating osteoblast versus adipocyte lineage selection

Most skeletal fragility disorders are characterized by bone loss with a concurrent gain in marrow adipocytes 1-8. This suggests that a cell that forms adipocytes at the expense of osteoblasts is central to the pathogenesis of skeletal disorders. However, this cellular point of bifurcation between adipocyte and osteoblast differentiation pathways remains unknown. Here, we identify a new cell type defined by co-expression of skeletal stem cell and adipocyte precursor markers, 9-13 (CD24+CD29+ skeletal stem cells (SSCs)), that serves as a key cellular point of bifurcation between the osteoblast and adipocyte differentiation pathways, giving rise to closely related osteoblast and adipocyte lineage-restricted precursors. CD24+CD29+SSCs comprise a small fraction of SSCs, and only this fraction displays full stemness features, including the ability to undergo serial transplantation. In line with serving as the osteoblast/adipocyte bipotent cell, the "bone to fat" tissue remodeling occurring in models of postmenopausal osteoporosis or after high fat diet exposure occur in part by reprogramming these CD24+CD29+SSCs to change their output of lineage-restricted precursors. Lastly, as subcutaneous white adipose tissue displays a similar set of CD24+CD29+ stem cells and related lineage-restricted progenitors, these findings provide a new schema explaining the stem cell basis of bone versus adipose tissue production that unifies multiple mesenchymal tissues.

Bone density and bone marrow composition in transgender girls prior to pubertal blockade: A case series

PURPOSE

To determine bone mineral density (BMD) of transgender girls before pubertal blockade, and correlate with lifestyle and clinical variables.

METHODS

Six transfemale peri-pubertal girls had knee magnetic resonance imaging (MRI) with T1-weighted images and single-voxel proton magnetic resonance spectroscopy (MRS). BMD measurements were obtained via dual-energy X-ray absorptiometry. Questionnaires about physical activity, diet, and the Eating Attitudes Test (EAT-26) were completed. The T2 relaxation rate of water (R2 = 1/T2 in s -1) was correlated with scores on surveys.

RESULTS

Three participants (50 %) had a low bone mineral density for age based on total body less head Z-score less than -2; two participants (33 %) had a low BMD for age at lumbar spine. All had EAT-26 scores below threshold for clinical concern. All participants self-reported regular exercise. Bone marrow MR variables (T1, fat fraction, unsaturation index and R2 of water) were not correlated with DXA measures.

CONCLUSIONS

Participants had low BMD on beginning pubertal blockade. Clinicians should consider monitoring BMD among youth AMAB, a group at potential risk for poor bone health.

Bone marrow adiposity in pediatric Crohn's disease

Patients with Crohn's disease often have low bone mineral density and an increased risk of osteoporosis. Although decreased bone formation can be seen at diagnosis, the underlying pathophysiology of suboptimal bone accrual remains poorly understood. We sought to evaluate a novel mechanism affecting osteogenesis in patients with Crohn's disease. In this case series, we evaluated bone marrow composition at the distal femur and proximal tibia of the left knee measured via magnetic resonance (MR) spectroscopy and relaxometry in five adolescents with the diagnosis of Crohn's disease. The subjects were enrolled prospectively between 2011 and 2013 at Boston Children's Hospital. Additional clinical information, including DXA scans to evaluate bone mineral density and body composition, and Crohn's disease history, such as glucocorticoid use and disease duration, were assessed. Healthy adolescents have persistent hematopoietic marrow with only 40 to 50 % fat in the long bone metaphyses. The current participants with Crohn's disease had increased marrow adiposity, with a mean fat fraction of 67.8 %. There appeared to be a trend towards higher fat fraction with shorter disease duration, while participants with the longest disease duration had the lowest fat fraction. Participants also had decreased bone density, increased fat mass, and lower lean mass, as assessed by DXA and compared to pediatric reference data. Our MRI results demonstrate increased marrow adiposity in children with Crohn's disease, especially early in the course of the disease. DXA may better demonstrate longer-term effects on bone. Additional studies are needed to evaluate bone marrow composition in these patients and to elucidate further the inverse relationship between marrow adipocytes and osteogenesis, as well as the relationship between bone marrow adiposity and body composition.

Anorexia Nervosa and Osteoporosis

Patients with anorexia nervosa (AN) often experience low bone mineral density (BMD) and increased fracture risk, with low body weight and decreased gonadal function being the strongest predictors of the observed bone mineral deficit and fractures. Other metabolic disturbances have also been linked to bone loss in this group of patients, including growth hormone resistance, low insulin-like growth factor-1 (IGF-1) concentrations, low leptin concentrations, and hypercortisolemia. However, these correlations lack definitive evidence of causality. Weight restoration and resumption of menstrual function have the strongest impact on increasing BMD. Other potential treatment options include bisphosphonates and teriparatide, supported by data from small clinical trials, but these agents are not approved for the treatment of low BMD in adolescents or premenopausal women with AN.

Rapid renutrition improves health status in severely malnourished inpatients with AN - score-based evaluation of a high caloric refeeding protocol in severely malnourished inpatients with anorexia nervosa in an intermediate care unit

Objective

Refeeding syndrome is a feared complication of refeeding patients with anorexia nervosa. There are now a number of controlled studies showing that refeeding with an initial high calorie count is more beneficial than cautious refeeding and is safe under continuous monitoring. However, there have yet not been studies in severe anorexia nervosa.

Method

We present an observational study in two different samples. The first sample consists of those 1075 out of a total of 3230 patients with anorexia nervosa treated in our hospital within 4 years for whom a complete admission laboratory was available and who had an age of at least 18 years at admission. A risk score was calculated from the number of pathological laboratory values out of 12 parameters indicating either refeeding syndrome or health hazards related to malnutrition. The second sample was obtained from a special ward for patients with eating disorders medically at‐risk. During the period in question, 410 patients with anorexia nervosa were treated there. 142 patients had a BMI of 13 or less and at the same time a complete data set with the mentioned 12 laboratory parameters at admission and weekly in the following 4 weeks after admission.

Results

The risk represented by the laboratory parameters is significantly and negatively correlated to BMI and much higher for the group of patients with a BMI below 13 than for those with a higher BMI (χ² sig < 0.000). The 142 patients in the special care unit gain an average of more than 4.1 kg within 4 weeks on the high‐calorie diet. With this rapid weight gain, the risk score decreases highly significantly. Neither hypophosphatemia nor rhabdomyolysis is found under phosphate substitution. Hyperhydration occurred often, which manifests itself in the drop in haematocrit by the second week.

Discussion

Under thorough medical surveillance, supplementation of phosphate and thiamine, and substitution of electrolytes whenever necessary rapid renutrition appeared to be save even in extremely malnourished inpatients with anorexia nervosa. As measured by the laboratory values, the health status of the severely malnourished patients improves significantly on a high‐calorie diet. Except for hyperhydration, there was no evidence of a refeeding syndrome.

The risk, assessed by significant laboratory parameters, increases considerably with increasingly low weight.

Rapid refeeding under medical supervision leads to rapid stabilization of health.

Under these conditions, there was no evidence of a threatening refeeding syndrome.

Even in extremely underweight patients with anorexia nervosa, rapid refeeding appears to significantly improve the risk profile.

MRI findings seen in serous atrophy of bone marrow

An 85-year-old man was referred for an MRI scan of the pelvis for further evaluation of a suspected left neck of femur fracture, which was regarded as equivocal on plain radiograph and CT. The initial MRI demonstrated unusual appearances of the visualised bone marrow and subcutaneous adipose tissue and was initially misinterpreted as a technical malfunction of the scanner. However, a repeat study on a different scanner the following day once again demonstrated the same appearances. The appearances were consistent with serous atrophy of bone marrow, a non-neoplastic disorder of the bone marrow, which is most commonly seen in severe anorexia nervosa or cachexia. These unusual, but distinct, bone marrow and subcutaneous adipose tissue appearances, which are specific to MRI, have been colloquially termed as the 'flip-flop' effect.

Fat fraction quantification of lumbar spine: comparison of T1-weighted two-point Dixon and single-voxel magnetic resonance spectroscopy in diagnosis of multiple myeloma

PURPOSE

We aimed to investigate the value of T1-weighted two-point Dixon technique and single-voxel magnetic resonance spectroscopy (MRS) in diagnosis of multiple myeloma (MM) through quantifying fat content of vertebral marrow.

METHODS

A total of 30 MM patients and 30 healthy volunteers underwent T1-weighted two-point Dixon and single-voxel MRS imaging. The fat fraction map (FFM) was reconstructed from the Dixon images using the equation FFM = Lip/In, where Lip represents fat maps and In represents in-phase images. The fat fraction (FF) of MRS was calculated by using the integral area of Lip peak divided by the sum of integral area of Lip peak and water peak.

RESULTS

FF values measured by the Dixon technique and MRS were significantly decreased in MM patients (45.99%±3.39% and 47.63%±4.38%) compared with healthy controls (64.43%±0.96% and 76.22%±1.91%) (P < 0.001 with both methods). FF values measured by Dixon technique were significantly positively correlated to those measured by MRS in MM (r = 0.837, P < 0.001) and healthy control group (r = 0.735, P < 0.001), respectively. There was no significant difference between area under the curve (AUC) obtained by the Dixon technique (0.878±0.047; range, 0.785 to 0.971; optimal cutoff, 56.35 for healthy controls vs. MM) and MRS (0.883±0.047; range, 0.791 to 0.974; optimal cutoff, 61.00 for healthy controls vs. MM). The ability of Dixon technique to differentiate MM group from healthy controls was equivalent to single-voxel MRS.

CONCLUSION

Regarding detection of fat contents in vertebral bone, T1-weighted two-point Dixon technique exhibited equivalent performance to single-voxel MRS in the diagnosis of multiple myeloma. Moreover, two-point Dixon is a more convenient and stable technique for assessing bone marrow changes in MM patients than single-voxel MRS.

Bone Health in Pediatric Patients with IBD: What Is New?

PURPOSE OF THE REVIEW

Patients with inflammatory bowel disease (IBD) have increased bone fragility, demonstrated by increased fracture risk, and often have low bone density and altered bone geometry, but the underlying pathophysiology remains poorly understood.

RECENT FINDINGS

Children and adolescents with IBD appear to have decreased bone formation, at diagnosis, which frequently improves with treatment of their underlying IBD. There is a growing body of evidence regarding how the immune system interacts with bone metabolism. There are likely multi-factorial etiologies that contribute to suboptimal bone accrual and subsequent lack of peak bone mass attainment in growing patients with IBD. There appears to be differential effects dependent upon IBD sub-type and bone compartment. Pediatric patients with IBD require recognition of several risk factors that may adversely impact their bone accrual. Future studies are necessary to further delineate the effects of IBD on pediatric bone health.

A Comprehensive Review of Complications and New Findings Associated with Anorexia Nervosa

Anorexia nervosa is a complex and deadly psychiatric disorder. It is characterized by a significant degree of both co-occurring psychiatric diseases and widespread physiological changes which affect nearly every organ system. It is important for clinicians to be aware of the varied consequences of this disorder. Given the high rate of mortality due to AN, there is a need for early recognition so that patients can be referred for appropriate medical and psychiatric care early in the course of the disorder. In this study, we present a comprehensive review of the recent literature describing medical findings commonly encountered in patients with AN. The varied and overlapping complications of AN affect pregnancy, psychological well-being, as well as bone, endocrine, gastrointestinal, cardiovascular, and pulmonary systems.

Bone Marrow Adipocytes-Role in Physiology and Various Nutritional Conditions in Human and Animal Models

In recent years, adipose tissue has attracted a lot of attention. It is not only an energy reservoir but also plays important immune, paracrine and endocrine roles. BMAT (bone marrow adipose tissue) is a heterogeneous tissue, found mostly in the medullary canal of the long bones (tibia, femur and humerus), in the vertebrae and iliac crest. Adipogenesis in bone marrow cavities is a consequence of ageing or may accompany pathologies like diabetes mellitus type 1 (T1DM), T2DM, anorexia nervosa, oestrogen and growth hormone deficiencies or impaired haematopoiesis and osteoporosis. This paper focuses on studies concerning BMAT and its physiology in dietary interventions, like obesity in humans and high fat diet in rodent studies; and opposite: anorexia nervosa and calorie restriction in animal models.

Changes in marrow adipose tissue in relation to changes in bone parameters following estradiol replacement in adolescent and young adult females with functional hypothalamic amenorrhea

CONTEXT

Low energy availability causes disruption of hypothalamic gonadotropin-releasing hormone secretion leading to functional hypothalamic amenorrhea (FHA) and hypoestrogenism, which in turn contributes to decreased bone mineral density (BMD) and increased bone marrow adipose tissue (MAT). Transdermal estradiol administration in physiologic doses increases BMD in adolescents and adults with FHA. However, the impact of estrogen replacement on MAT in relation to changes in BMD has not been studied in adolescents and young adults. We hypothesized that physiologic estrogen replacement would lead to decreases in MAT, associated with increases in BMD.

METHODS AND MATERIALS

We studied 15 adolescent and young adult females with FHA (14-25 years). All participants received a17β- estradiol transdermal patch at a dose of 0.1 mg/day (applied twice weekly) for 12 months. Participants also received cyclic progestin for 10-12 days each month. We quantified MAT (lipid/water ratio) of the fourth lumbar (L4) vertebral body and femoral diaphysis by single proton (1H)-magnetic resonance spectroscopy, and compartmental volumetric BMD of the distal radius and tibia using high-resolution peripheral quantitative computed tomography.

RESULTS

Transdermal estradiol therapy over 12 months resulted in a decrease in MAT at the lumbar (L4) vertebra from 0.92 ± 0.55 at baseline to 0.63 ± 0.29 at 12-months (p = 0.008), and an increase in radial and tibial cortical vBMD (p = 0.006, p = 0.0003). Changes in L4 MAT trended to be inversely associated with changes in radial cortical vBMD (rho = -0.47, p = 0.08).

CONCLUSION

We show that in adolescent and young adult girls with FHA, MAT decreases following transdermal estrogen therapy and these changes are associated with increased cortical vBMD.

Chronic stress and adipose tissue in the anorexic state: endocrine and epigenetic mechanisms

Although adipose tissue metabolism in obesity has been widely studied, there is limited research on the anorexic state, where the endocrine system is disrupted by reduced adipose tissue mass and there are depot-specific changes in adipocyte type and function. Stress exposure at different stages of life can alter the balance between energy intake and expenditure and thereby contribute to the pathogenesis of anorexia nervosa. This review integrates information from human clinical trials to describe endocrine, genetic and epigenetic aspects of adipose tissue physiology in the anorexic condition. Changes in the hypothalamus-pituitary-thyroid, -adrenal, and -gonadal axes and their relationships to appetite regulation and adipocyte function are discussed. Because of the role of stress in triggering or magnifying anorexia, and the dynamic but also persistent nature of environmentally-induced epigenetic modifications, epigenetics is likely the link between stress and long-term changes in the endocrine system that disrupt homoeostatic food intake and adipose tissue metabolism. Herein, we focus on the adipocyte and changes in its function, including alterations reinforced by endocrine disturbance and dysfunctional adipokine regulation. This information is critical because of the poor understanding of anorexic pathophysiology, due to the lack of suitable research models, and the complexity of genetic and environmental interactions.

Test-Retest Reliability and Correlates of Vertebral Bone Marrow Lipid Composition by Lipidomics Among Children With Varying Degrees of Bone Fragility

The reliability of lipidomics, an approach to identify the presence and interactions of lipids, to analyze the bone marrow lipid composition among pediatric populations with bone fragility is unknown. The objective of this study was to assess the test–retest reliability, standard error of measurement (SEM), and the minimal detectable change (MDC) of vertebral bone marrow lipid composition determined by targeted lipidomics among children with varying degrees of bone fragility undergoing routine orthopedic surgery. Children aged 10 to 19 years, with a confirmed diagnosis of adolescent idiopathic scoliosis (n = 13) or neuromuscular scoliosis and cerebral palsy (n = 3), undergoing posterior spinal fusion surgery at our institution were included in this study. Transpedicular vertebral body bone marrow samples were taken from thoracic vertebrae (T11, 12) or lumbar vertebrae (L1 to L4). Lipid composition was assessed via targeted lipidomics and all samples were analyzed in the same batch. Lipid composition measures were examined as the saturated, monounsaturated, and polyunsaturated index and as individual fatty acids. Relative and absolute test–retest reliability was assessed using the intraclass correlation coefficient (ICC), SEM, and MDC. Associations between demographics and index measures were explored. The ICC, SEM, and MDC were 0.81 (95% CI, 0.55–0.93), 1.6%, and 4.3%, respectively, for the saturated index, 0.66 (95% CI, 0.25–0.87), 3.5%, and 9.7%, respectively, for the monounsaturated index, and 0.60 (95% CI, 0.17–0.84), 3.6%, and 9.9%, respectively, for the polyunsaturated index. For the individual fatty acids, the ICC showed a considerable range from 0.04 (22:2n‐6) to 0.97 (18:3n‐3). Age was positively correlated with the saturated index (r² = 0.36; p = 0.014) and negatively correlated with the polyunsaturated index (r² = 0.26; p = 0.043); there was no difference in index measures by sex (p > 0.58). The test–retest reliability was moderate‐to‐good for index measures and poor to excellent for individual fatty acids; this information can be used to power research studies and identify measures for clinical or research monitoring. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Quantitative 1 H MRI and MRS of fatty acid composition

Adipose tissue as well as other depots of fat (triglycerides) are increasingly being recognized as active contributors to the human function and metabolism. In addition to the fat concentration, also the fatty acid chemical composition (FAC) of the triglyceride molecules may play an important part in diseases such as obesity, insulin resistance, hepatic steatosis, osteoporosis, and cancer. MR spectroscopy and chemical-shift-encoded imaging (CSE-MRI) are established methods for non-invasive quantification of fat concentration in tissue. More recently, similar techniques have been developed for assessment also of the FAC in terms of the number of double bonds, the fraction of saturated, monounsaturated, and polyunsaturated fatty acids, or semi-quantitative unsaturation indices. The number of papers focusing on especially CSE-MRI-based techniques has steadily increased during the past few years, introducing a range of acquisition protocols and reconstruction algorithms. However, a number of potential sources of bias have also been identified. Furthermore, the measures used to characterize the FAC using both MRI and MRS differ, making comparisons between different techniques difficult. The aim of this paper is to review MRS- and MRI-based methods for in vivo quantification of the FAC. We describe the chemical composition of triglycerides and discuss various potential FAC measures. Furthermore, we review acquisition and reconstruction methodology and finally, some existing and potential applications are summarized. We conclude that both MRI and MRS provide feasible non-invasive alternatives to the gold standard gas chromatography for in vivo measurements of the FAC. Although both are associated with gas chromatography, future studies are warranted.

Noninvasive in situ proton MRS in muscle tissue and bone marrow as a novel approach to identify previous freezing in a completely thawed cadaver

The temporary or permanent storage of human bodies in freezers following a homicide is a documented method for criminal disposal of human corpses. In these cases, the detection of characteristics which indicate that a thawed cadaver or body part was previously frozen provides crucial information for forensic casework. Previous histological and radiological approaches to detect characteristics of previous freezing are based on the formation of bubble-like gas patterns, which are difficult to distinguish from common postmortem gas formation in the course of decomposition. The objective of this study was to detect changes in the muscle tissue and in the bone marrow after freezing and thawing by means of in situ proton magnetic resonance spectroscopy (¹ H-MRS) to provide a noninvasive approach to detect postfreezing alterations in human cadavers. In this experimental study, the hind legs of seven sheep were used as substitutes for human tissue. One hind leg underwent ¹ H-MRS before and daily after storage in a deep freezer (-20°C) and complete thawing at room temperature (study group: n = 7). The opposite hind leg was kept at room temperature and was measured daily (control group: n = 7). Spectra and relaxation times were measured using single voxel measurements in the muscle tissue and in the bone marrow. ¹ H-MRS revealed several changes in the muscle tissue and in the bone marrow after freezing and thawing. A strongly reduced peak area ratio (<20) between bulk methylene and olefinic and glycerol methine and a reduced T₂ relaxation time for bulk methylene (<45 ms) measured in the bone marrow were found to be indicators that a sheep leg was previously frozen and thawed independent of the postmortem interval. Noninvasive in situ ¹ H-MRS in the bone marrow potentially provides a new method for detecting previous freezing or extreme cooling in cadavers.

Exercise Degrades Bone in Caloric Restriction, Despite Suppression of Marrow Adipose Tissue (MAT)

Marrow adipose tissue (MAT) and its relevance to skeletal health during caloric restriction (CR) is unknown: It remains unclear whether exercise, which is anabolic to bone in a calorie-replete state, alters bone or MAT in CR. We hypothesized that response of bone and MAT to exercise in CR differs from the calorie-replete state. Ten-week-old female B6 mice fed a regular diet (RD) or 30% CR diet were allocated to sedentary (RD, CR, n = 10/group) or running exercise (RD-E, CR-E, n = 7/group). After 6 weeks, CR mice weighed 20% less than RD, p < 0.001; exercise did not affect weight. Femoral bone volume (BV) via 3D MRI was 20% lower in CR versus RD (p < 0.0001). CR was associated with decreased bone by μCT: Tb.Th was 16% less in CR versus RD, p < 0.003, Ct.Th was 5% less, p < 0.07. In CR-E, Tb.Th was 40% less than RD-E, p < 0.0001. Exercise increased Tb.Th in RD (+23% RD-E versus RD, p < 0.003) but failed to do so in CR. Cortical porosity increased after exercise in CR (+28%, p = 0.04), suggesting exercise during CR is deleterious to bone. In terms of bone fat, metaphyseal MAT/ BV rose 159% in CR versus RD, p = 0.003 via 3D MRI. Exercise decreased MAT/BV by 52% in RD, p < 0.05, and also suppressed MAT in CR (-121%, p = 0.047). Histomorphometric analysis of adipocyte area correlated with MAT by MRI (R2 = 0.6233, p < 0.0001). With respect to bone, TRAP and Sost mRNA were reduced in CR. Intriguingly, the repressed Sost in CR rose with exercise and may underlie the failure of CR-bone quantity to increase in response to exercise. Notably, CD36, a marker of fatty acid uptake, rose 4088% in CR (p < 0.01 versus RD), suggesting that basal increases in MAT during calorie restriction serve to supply local energy needs and are depleted during exercise with a negative impact on bone. © 2019 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research.

Changes in Bone Marrow Adipose Tissue One Year After Roux-en-Y Gastric Bypass: A Prospective Cohort Study

Bone marrow adipose tissue (BMAT) has been postulated to mediate skeletal fragility in type 2 diabetes (T2D) and obesity. Roux-en-Y gastric bypass (RYGB) induces a substantial weight loss and resolution of comorbidities. However, the procedure induces increased bone turnover and fracture rates. No previous study has evaluated biopsy-measured BMAT fraction preoperatively and after RYGB. In this study, we aimed to investigate BMAT fraction of the hip in participants with and without T2D preoperatively and 1 year after RYGB and explore factors associated with BMAT change. Patients with morbid obesity scheduled for RYGB were examined preoperatively and 1 year after RYGB. Forty-four participants were included and preoperative examinations were possible in 35. Of these, 33 (94%) met for follow-up, 2 were excluded, and BMAT estimation was not possible in 1. Eighteen (60%) of the participants were females and 11 (37%) had T2D. Preoperative BMAT fraction was positively associated with glycosylated hemoglobin and negatively associated with areal bone mineral density (aBMD). After RYGB, BMAT fraction decreased from 40.4 ± 1.7% to 35.6 ± 12.8%, p = 0.042, or with mean percent change of 10.7% of preoperative BMAT fraction. Change in BMAT fraction was positively associated with change in body mass index (BMI) and total body fat. In females, we observed a mean percent reduction of 22.4 ± 19.6%, whereas in males BMAT increased with a mean percent of 6.8 ± 37.5%, p = 0.009. For males, changes in estradiol were associated with BMAT change; this was not observed for females. In participants with and without T2D, the mean percent BMAT reduction was 5.8 ± 36.9% and 13.5 ± 28.0%, respectively, p = 0.52. We conclude that a high BMAT seems to be associated with lower aBMD and poorer glycemic control in obese subjects. After RYGB, we observed a significant decrease in BMAT. The reduction in BMAT did not differ between participants with and without T2D, but appeared sex specific. © 2019 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc.

Medical Complications of Eating Disorders in Youth

Eating disorders affect a significant number of individuals across the life span and are found among all demographic groups (including all genders, socioeconomic statuses, and ethnicities). They can cause malnutrition, which can have significant effects on every organ system in the body. Cardiovascular complications are particularly dangerous and cause eating disorders to have the highest mortality rate of all mental illnesses. This article outlines the medical assessment and treatment of malnutrition due to disordered eating.

The Importance of Restoring Body Fat Mass in the Treatment of Anorexia Nervosa: An Expert Commentary

Anorexia nervosa is a severe mental disorder that is characterised by dietary restriction, low weight and widespread endocrine abnormalities. Whilst the importance of weight restoration has been recognised in recent guidelines, the significance of normalising body fat mass has received less attention. A recent systematic review and meta-analysis found that a minimum of 20.5% body fat mass is necessary for regular menses in women with anorexia nervosa of reproductive age. This has significant implications for both treatment and research. It is important to help the patient and carers understand that a certain level of body fat percentage is essential for optimal health, such as the return of menstruation. Further research is needed into how best to use this information to help motivation to change as part of treatment. The benefit of the return of menstruation goes beyond improved fertility: it signals the normalisation of sexual hormones, which have a widespread impact on the body and multiple pathways in the brain. Given the complex functions of adipocytes in various organs of the body, the metabolic effects of the normal body fat tissue should not be underestimated. Further research is needed to elucidate the mechanisms behind the link between minimum body fat mass, menstruation, bone and brain health in anorexia nervosa.

Marrow adipose tissue imaging in humans

Bone strength is affected not only by bone mineral density (BMD) and bone microarchitecture but also its microenvironment. Recent studies have focused on the role of marrow adipose tissue (MAT) in the pathogenesis of bone loss. Osteoblasts and adipocytes arise from a common mesenchymal stem cell within bone marrow and many osteoporotic states, including aging, medication use, immobility, over - and undernutrition are associated with increased marrow adiposity. Advancements in imaging technology allow the non-invasive quantification of MAT. This article will review magnetic resonance imaging (MRI)- and computed tomography (CT)-based imaging technologies to assess the amount and composition of MAT. The techniques that will be discussed are anatomic T1-weighted MRI, water-fat imaging, proton MR spectroscopy, single energy CT and dual energy CT. Clinical applications of MRI and CT techniques to determine the role of MAT in patients with obesity, anorexia nervosa, and type 2 diabetes will be reviewed.

Anorexia Nervosa and Bone

Anorexia nervosa (AN), a psychiatric disorder characterized by altered body image, food restriction and low body weight, is associated with low bone mineral density and increased fracture risk. Despite broadening the definition of AN in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition, the prevalence of low bone mass remains high, suggesting we continue to capture individuals at high risk for bone loss. Many of the endocrine disturbances adaptive to the state of chronic starvation are thought to be causal in impaired skeletal integrity in females and males with AN. Understanding mechanisms responsible for impaired bone quality is important given the disease's severity and chronicity. Further research is needed to formulate optimal treatment strategies to reduce fracture risk.

MECHANISMS IN ENDOCRINOLOGY: Bone marrow adiposity and bone, a bad romance?

Bone marrow adipocytes (BMA-) constitute an original and heterogeneous fat depot whose development appears interlinked with bone status throughout life. The gradual replacement of the haematopoietic tissue by BMA arises in a well-ordered way during childhood and adolescence concomitantly to bone growth and continues at a slower rate throughout the adult life. Importantly, BM adiposity quantity is found well associated with bone mineral density (BMD) loss at different skeletal sites in primary osteoporosis such as in ageing or menopause but also in secondary osteoporosis consecutive to anorexia nervosa. Since BMA and osteoblasts originate from a common mesenchymal stem cell, adipogenesis is considered as a competitive process that disrupts osteoblastogenesis. Besides, most factors secreted by bone and bone marrow cells (ligands and antagonists of the WNT/β-catenin pathway, BMP and others) reciprocally regulate the two processes. Hormones such as oestrogens, glucocorticoids, parathyroid and growth hormones that control bone remodelling also modulate the differentiation and the activity of BMA. Actually, BMA could also contribute to bone loss through the release of paracrine factors altering osteoblast and/or osteoclast formation and function. Based on clinical and fundamental studies, this review aims at presenting and discussing these current arguments that support but also challenge the involvement of BMA in the bone mass integrity.

Magnetic resonance imaging and spectroscopy evidence of efficacy for adrenal and gonadal hormone replacement therapy in anorexia nervosa

PURPOSE

Dehydroepiandrosterone (DHEA)+estrogen/progestin therapy for adolescent girls with anorexia nervosa (AN) has the potential to arrest bone loss. The primary aim of this study was to test the effects of DHEA+estrogen/progestin therapy in adolescent girls with AN on bone marrow in the distal femur using magnetic resonance imaging (MRI) and spectroscopy.

METHODS

Seventy adolescent girls with AN were enrolled in a double blind, randomized, placebo-controlled trial at two urban hospital-based programs.

INTERVENTION

Seventy-six girls were randomly assigned to receive 12months of either oral micronized DHEA or placebo. DHEA was administered with conjugated equine estrogens (0.3mg daily) for 3months, then an oral contraceptive (20μg ethinyl estradiol/ 0.1mg levonorgestrel) for 9months. The primary outcome measure was bone marrow fat by MRI and magnetic resonance spectroscopy (MRS).

RESULTS

T2 of the water resonance dropped significantly less in the active vs. placebo group over 12months at both the medial and lateral distal femur (p=0.02). Body mass index (BMI) was a significant effect modifier for T1 and for T2 of unsaturated (T2_unsat) and saturated fat (T2_sat) in the lateral distal femur. Positive effects of the treatment of DHEA+estrogen/progestin were seen primarily for girls above a BMI of about 18kg/m².

CONCLUSIONS

These findings suggest treatment with oral DHEA+estrogen/progestin arrests the age- and disease-related changes in marrow fat composition in the lateral distal femur reported previously in this population.