Serum FGF-21 levels are associated with worsened radial trabecular bone microarchitecture and decreased radial bone strength in women with anorexia nervosa

Liver function linked to bone health: A bibliometric of the liver-bone axis

BACKGROUND

The liver exerts profound influence on skeletal health, while osseous tissues reciprocally modulate hepatic function. This bidirectional metabolic axis between these two organ systems plays a pivotal role in both physiological homeostasis and pathological states.

AIM

To investigate and analyze the literatures on liver-bone axis using bibliometrics.

METHODS

A comprehensive literature search pertaining to the liver-bone axis was conducted using the Science Citation Index Expanded within the Web of Science Core Collection. Subsequently, visualization and bibliometric analyses were performed utilizing VOSviewer (version 1.6.20), Citespace (version 6.2.R4), and the R programming language.

RESULTS

This comprehensive analysis encompasses 855 publications, comprising 694 articles and 161 reviews, authored by 4988 researchers from 425 institutions across 61 countries. The United States and China emerge as the leading nations in terms of publication volume. The University of California system stands out as the most influential institution in liver-bone axis research. Guanabens N is identified as the most prolific author in this field. The annual increase in publications related to the liver-bone axis underscores its growing prominence as a research focus. The study highlights key areas of investigation, including osteoporosis, bone metabolism, non-alcoholic fatty liver disease, and insulin-like growth factor-1, which represent both current and prospective hot topics within this domain.

CONCLUSION

This investigation employs bibliometric methodologies to conduct a systematic analysis of liver-bone axis literature spanning from 2001 to 2024. The exponential growth in publications over the past two decades underscores the significance of synthesizing research outcomes in this domain. Through rigorous statistical analyses, we delineate fundamental contributions to the field while providing strategic direction for emerging scholars. Furthermore, we illuminate current research trajectories and identify promising future investigative directions. Investigation of the liver-bone axis enhances our comprehension of inter-organ communication networks. Conceptualizing these organs as an integrated system provides profound insights into pathophysiological mechanisms and disease management strategies. This paradigm not only facilitates the development of sophisticated diagnostic modalities but also catalyzes the discovery of novel therapeutic agents targeting these mechanistic pathways, thereby advancing our capacity to diagnose and treat hepatic and skeletal disorders.

Associations of Serum Irisin and Fibroblast Growth Factor-21 Levels With Bone Mineral Characteristics in Eumenorrheic Adolescent Athletes With Different Training Activity Patterns

PURPOSE

To describe serum irisin and fibroblast growth factor-21 (FGF-21) concentrations in healthy female adolescents with different training activity patterns and their associations with bone mineral properties and metabolic markers.

METHODS

A total of 62 adolescent girls aged 14-18 years were recruited: 22 rhythmic gymnasts, 20 swimmers, and 20 untrained controls. Bone mineral characteristics by dual-energy X-ray absorptiometry, daily energy intake by dietary recall, serum irisin, FGF-21, undercarboxylated osteocalcin, and C-terminal telopeptide of type I collagen were measured in all girls.

RESULTS

Whole body and lumbar spine areal bone mineral density and lumbar spine bone mineral content were higher in the rhythmic gymnasts group compared with swimmers and untrained controls groups (P < .05). Serum irisin, FGF-21, undercarboxylated osteocalcin, and C-terminal telopeptide of type I collagen levels were not significantly different between the groups. In the rhythmic gymnasts group, serum FGF-21 concentration was positively correlated with lumbar spine areal bone mineral density independently of confounding factors (r = .51; P = .027).

CONCLUSIONS

Serum irisin and FGF-21 levels were not different between adolescent eumenorrheic girls with different training activity patterns. FGF-21 was positively associated with lumbar spine areal bone mineral density, which predominantly consists of trabecular bone in adolescent rhythmic gymnasts.

Effect of Fibroblast Growth Factor (FGF) 19 and 21 on Hip Geometry and Strength in Post-menopausal Osteoporosis (PMO)

Fibroblast Growth Factor (FGF) receptor signalling is important for skeletal development. The FGF19 subfamily which includes FGF19 and FGF21 are involved in bone metabolism, although their effects on bone mineral density (BMD) and bone strength remain unclear. To further characterise the influence of these two factors on the skeleton, we studied the association between circulating concentrations of FGF19 and 21 with BMD and parameters of hip geometry and strength in post-menopausal osteoporosis (PMO). The study cohort consisted of 374 women aged (mean [SD]) 68.7[12.3] years with PMO. FGF19 and FGF21 were measured in serum by ELISA. BMD was measured at the lumbar spine (LS), total hip (TH) and femoral neck (FN) (n = 277) by dual energy X-ray absorptiometry (DXA) and hip structural analysis (HSA) parameters (n = 263) at the narrow neck of the femur (NN), Intertrochanter (IT) and Femoral shaft (FS) were derived from DXA scans. FGF19 and 21 were not associated with prevalent fractures or BMD when corrected for covariates; age, BMI, smoking habits and alcohol intake. Log-transformed FGF 21 was negatively associated with HSA parameters including Outer Diameter (OD) (p = 0.019), Cross-sectional area (CSA) (p = 0.01), cross-sectional moment of inertia (CSMI) (p = 0.011), Section modulus (Z) (p = 0.002) and cortical thickness (Co Th) (p = 0.026) at the IT only. CSA, CSMI, Z and Co Th were significantly lower (p < 0.05) in women with FGF21 concentrations greater than the median (> 103.5 pg/ml). Our data suggest that FGF 21 may have potentially adverse effects on the skeleton. Further characterisation is needed, particularly as FGF 21 analogues or agonists may be used to treat obesity-related metabolic disorders.

Methionine as a regulator of bone remodeling with fasting

Caloric restriction improves metabolic health but is often complicated by bone loss. We studied bone parameters in humans during a 10-day fast and identified candidate metabolic regulators of bone turnover. Pro-collagen 1 intact N-terminal pro-peptide (P1NP), a bone formation marker, decreased within 3 days of fasting. Whereas dual-energy x-ray absorptiometry measures of bone mineral density were unchanged after 10 days of fasting, high-resolution peripheral quantitative CT demonstrated remodeling of bone microarchitecture. Pathway analysis of longitudinal metabolomics data identified one-carbon metabolism as fasting dependent. In cultured osteoblasts, we tested the functional significance of one-carbon metabolites modulated by fasting, finding that methionine - which surged after 3 days of fasting - affected markers of osteoblast cell state in a concentration-dependent manner, in some instances exhibiting a U-shaped response with both low and high concentrations driving putative antibone responses. Administration of methionine to mice for 5 days recapitulated some fasting effects on bone, including a reduction in serum P1NP. In conclusion, a 10-day fast in humans led to remodeling of bone microarchitecture, potentially mediated by a surge in circulating methionine. These data support an emerging model that points to a window of optimal methionine exposure for bone health.

Deficits in volumetric bone mineral density, bone microarchitecture, and estimated bone strength in women with atypical anorexia nervosa compared to healthy controls

OBJECTIVE

Anorexia nervosa is associated with low bone mineral density (BMD) and deficits in bone microarchitecture and strength. Low BMD is common in atypical anorexia nervosa, in which criteria for anorexia nervosa are met except for low weight. We investigated whether women with atypical anorexia nervosa have deficits in bone microarchitecture and estimated strength at the peripheral skeleton.

METHOD

Measures of BMD and microarchitecture were obtained in 28 women with atypical anorexia nervosa and 27 controls, aged 21-46 years.

RESULTS

Mean tibial volumetric BMD, cortical thickness, and failure load were lower, and radial trabecular number and separation impaired, in atypical anorexia nervosa versus controls (p < .05). Adjusting for weight, deficits in tibial cortical bone variables persisted (p < .05). Women with atypical anorexia nervosa and amenorrhea had lower volumetric BMD and deficits in microarchitecture and failure load versus those with eumenorrhea and controls. Those with a history of overweight/obesity or fracture had deficits in bone microarchitecture versus controls. Tibial deficits were particularly marked. Less lean mass and longer disease duration were associated with deficits in high-resolution peripheral quantitative computed tomography (HR-pQCT) variables in atypical anorexia nervosa.

DISCUSSION

Women with atypical anorexia nervosa have lower volumetric BMD and deficits in bone microarchitecture and strength at the peripheral skeleton versus controls, independent of weight, and particularly at the tibia. Women with atypical anorexia nervosa and amenorrhea, less lean mass, longer disease duration, history of overweight/obesity, or fracture history may be at higher risk. This is salient as deficits in HR-pQCT variables are associated with increased fracture risk.

PUBLIC SIGNIFICANCE

Atypical anorexia nervosa is a psychiatric disorder in which psychological criteria for anorexia nervosa are met despite weight being in the normal range. We demonstrate that despite weight in the normal range, women with atypical anorexia nervosa have impaired bone density, structure, and strength compared to healthy controls. Whether this translates to an increased risk of incident fracture in this population requires further investigation.

Neuroendocrine adaptations to starvation

Famine and starvation have punctuated the evolutionary past of the human species. As such, we have developed hormonal responses to undernutrition that minimize energy expenditure on processes that are not critical for the survival of the individual, such as reproduction. In this review, we discuss neuroendocrine adaptations to starvation including hypogonadotropic hypogonadism, growth hormone resistance, hypercortisolemia, and the downregulation of the hypothalamic-pituitary-thyroid axis. We review the time-course of these adaptations by describing studies involving the short-term fasting of healthy individuals as well as studies describing the hormonal changes in states of chronic undernutrition, using individuals with anorexia nervosa as a model of chronic starvation. Lastly, we review representative clinical effects of chronic undernutrition.

Fibroblast growth factor 21 and bone homeostasis

Fibroblast growth factor 21 (FGF21), a member of the FGF subfamily, is produced primarily in the liver and adipose tissue. The main function of FGF21 is to regulate energy metabolism of carbohydrates and lipids in the body through endocrine and other means, making FGF21 have potential clinical value in the treatment of metabolic disorders. Although FGF21 and its receptors play a role in the regulation of bone homeostasis through a variety of signaling pathways, a large number of studies have reported that the abuse of FGF21 and its analogues and the abnormal expression of FGF21 in vivo may be associated with bone abnormalities. Due to limited research information on the effect of FGF21 on bone metabolism regulation, the role of FGF21 in the process of bone homeostasis regulation and the mechanism of its occurrence and development have not been fully clarified. Certainly, the various roles played by FGF21 in the regulation of bone homeostasis deserve increasing attention. In this review, we summarize the basic physiological knowledge of FGF21 and the effects of FGF21 on metabolic homeostasis of the skeletal system in animal and human studies. The information provided in this review may prove beneficial for the intervention of bone diseases.

Bone marrow adipose tissue is associated with fracture history in anorexia nervosa

Although bone mineral density (BMD) is decreased and fracture risk increased in anorexia nervosa, BMD does not predict fracture history in this disorder. We assessed BMD, bone microarchitecture, and bone marrow adipose tissue (BMAT) in women with anorexia nervosa and found that only BMAT was associated with fracture history.

INTRODUCTION

Anorexia nervosa (AN) is a psychiatric disorder characterized by low body weight, low BMD, and increased risk of fracture. Although BMD is reduced and fracture risk elevated, BMD as assessed by DXA does not distinguish between individuals with versus those without prior history of fracture in AN. Despite having decreased peripheral adipose tissue stores, individuals with AN have enhanced bone marrow adipose tissue (BMAT), which is inversely associated with BMD. Whether increased BMAT is associated with fracture in AN is not known.

METHODS

We conducted a cross-sectional study in 62 premenopausal women, including 34 with AN and 28 normal-weight women of similar age. Fracture history was collected during patient interviews and BMD measured by DXA, BMAT by 1H-MRS, and parameters of bone microarchitecture by HR-pQCT.

RESULTS

Sixteen women (47.1%) with AN reported prior history of fracture compared to 11 normal-weight women (39.3%, p = 0.54). In the entire group and also the subset of women with AN, there were no significant differences in BMD or parameters of bone microarchitecture in women with prior fracture versus those without. In contrast, women with AN with prior fracture had greater BMAT at the spine and femur compared to those without (p = 0.01 for both).

CONCLUSION

In contrast to BMD and parameters of bone microarchitecture, BMAT is able to distinguish between women with AN with prior fracture compared to those without. Prospective studies will be necessary to understand BMAT's potential pathophysiologic role in the increased fracture risk in AN.

Histone Deacetylases as Modulators of the Crosstalk Between Skeletal Muscle and Other Organs

Skeletal muscle plays a major role in controlling body mass and metabolism: it is the most abundant tissue of the body and a major source of humoral factors; in addition, it is primarily responsible for glucose uptake and storage, as well as for protein metabolism. Muscle acts as a metabolic hub, in a crosstalk with other organs and tissues, such as the liver, the brain, and fat tissue. Cytokines, adipokines, and myokines are pivotal mediators of such crosstalk. Many of these circulating factors modulate histone deacetylase (HDAC) expression and/or activity. HDACs form a numerous family of enzymes, divided into four classes based on their homology to their orthologs in yeast. Eleven family members are considered classic HDACs, with a highly conserved deacetylase domain, and fall into Classes I, II, and IV, while class III members are named Sirtuins and are structurally and mechanistically distinct from the members of the other classes. HDACs are key regulators of skeletal muscle metabolism, both in physiological conditions and following metabolic stress, participating in the highly dynamic adaptative responses of the muscle to external stimuli. In turn, HDAC expression and activity are closely regulated by the metabolic demands of the skeletal muscle. For instance, NAD+ levels link Class III (Sirtuin) enzymatic activity to the energy status of the cell, and starvation or exercise affect Class II HDAC stability and intracellular localization. SUMOylation or phosphorylation of Class II HDACs are modulated by circulating factors, thus establishing a bidirectional link between HDAC activity and endocrine, paracrine, and autocrine factors. Indeed, besides being targets of adipo-myokines, HDACs affect the synthesis of myokines by skeletal muscle, altering the composition of the humoral milieu and ultimately contributing to the muscle functioning as an endocrine organ. In this review, we discuss recent findings on the interplay between HDACs and circulating factors, in relation to skeletal muscle metabolism and its adaptative response to energy demand. We believe that enhancing knowledge on the specific functions of HDACs may have clinical implications leading to the use of improved HDAC inhibitors for the treatment of metabolic syndromes or aging.

Sequential Therapy With Recombinant Human IGF-1 Followed by Risedronate Increases Spine Bone Mineral Density in Women With Anorexia Nervosa: A Randomized, Placebo-Controlled Trial

Anorexia nervosa is complicated by low bone mineral density (BMD) and increased fracture risk associated with low bone formation and high bone resorption. The lumbar spine is most severely affected. Low bone formation is associated with relative insulin-like growth factor 1 (IGF-1) deficiency. Our objective was to determine whether bone anabolic therapy with recombinant human (rh) IGF-1 used off-label followed by antiresorptive therapy with risedronate would increase BMD more than risedronate or placebo in women with anorexia nervosa. We conducted a 12-month, randomized, placebo-controlled study of 90 ambulatory women with anorexia nervosa and low areal BMD (aBMD). Participants were randomized to three groups: 6 months of rhIGF-1 followed by 6 months of risedronate ("rhIGF-1/Risedronate") (n = 33), 12 months of risedronate ("Risedronate") (n = 33), or double placebo ("Placebo") (n = 16). Outcome measures were lumbar spine (1° endpoint: postero-anterior [PA] spine), hip, and radius aBMD by dual-energy X-ray absorptiometry (DXA), and vertebral, tibial, and radial volumetric BMD (vBMD) and estimated strength by high-resolution peripheral quantitative computed tomography (HR-pCT) (for extremity measurements) and multi-detector computed tomography (for vertebral measurements). At baseline, mean age, body mass index (BMI), aBMD, and vBMD were similar among groups. At 12 months, mean PA lumbar spine aBMD was higher in the rhIGF-1/Risedronate (p = 0.03) group and trended toward being higher in the Risedronate group than Placebo. Mean lateral lumbar spine aBMD was higher, in the rhIGF-1/Risedronate than the Risedronate or Placebo groups (p < 0.05). Vertebral vBMD was higher, and estimated strength trended toward being higher, in the rhIGF-1/Risedronate than Placebo group (p < 0.05). Neither hip or radial aBMD or vBMD, nor radial or tibial estimated strength, differed among groups. rhIGF-1 was well tolerated. Therefore, sequential therapy with rhIGF-1 followed by risedronate increased lateral lumbar spine aBMD more than risedronate or placebo. Strategies that are anabolic and antiresorptive to bone may be effective at increasing BMD in women with anorexia nervosa. © 2021 American Society for Bone and Mineral Research (ASBMR).

Skeletal Muscle and Bone - Emerging Targets of Fibroblast Growth Factor-21

Fibroblast growth factor 21 (FGF21) is an atypical member of the FGF family, which functions as a powerful endocrine and paracrine regulator of glucose and lipid metabolism. In addition to liver and adipose tissue, recent studies have shown that FGF21 can also be produced in skeletal muscle. As the most abundant tissue in the human body, skeletal muscle has become increasingly recognized as a major site of metabolic activity and an important modulator of systemic metabolic homeostasis. The function and mechanism of action of muscle-derived FGF21 have recently gained attention due to the findings of considerably increased expression and secretion of FGF21 from skeletal muscle under certain pathological conditions. Recent reports regarding the ectopic expression of FGF21 from skeletal muscle and its potential effects on the musculoskeletal system unfolds a new chapter in the story of FGF21. In this review, we summarize the current knowledge base of muscle-derived FGF21 and the possible functions of FGF21 on homeostasis of the musculoskeletal system with a focus on skeletal muscle and bone.

Potential role of fibroblast growth factor 21 in the deterioration of bone quality in impaired glucose tolerance

PURPOSE

Findings on trabecular bone score (TBS), an index of bone quality, have been reported in prediabetes defined by impaired fasting glucose or HbA1c. Here, we assessed the bone mineral density (BMD) and TBS in prediabetes individuals with impaired glucose tolerance (IGT), and investigated the association of these bone parameters with serum levels of fibroblast growth factor 21 (FGF21), a hormone implicated in bone metabolism and with higher levels in IGT.

METHODS

Chinese postmenopausal women aged 55-80 years, without diabetes, were recruited from the Hong Kong Cardiovascular Risk Factor Prevalence Study in 2016-2018. Normal glucose tolerance (NGT) was defined by fasting glucose < 5.6 mmol/L and 2-h plasma glucose (2hG) < 7.8 mmol/L, and IGT by 2hG 7.8-11 mmol/L. Serum levels of FGF21 and other bone metabolism regulators were measured. Insulin sensitivity was assessed by the Matsuda index. Independent determinants of TBS were evaluated using multivariable stepwise linear regression.

RESULTS

173 individuals with NGT and 73 with IGT were included. TBS was lower in those with IGT compared to those with NGT, while BMD was comparable. Individuals with IGT had significantly higher serum FGF21 levels, which in turn showed an independent inverse relationship with TBS, attenuated after inclusion of the Matsuda index. Serum FGF21 levels, however, did not correlate with BMD.

CONCLUSION

Among Chinese postmenopausal women, bone quality was worse in IGT, despite comparable bone density. FGF21 levels showed a significant independent inverse relationship with TBS, partly attributed to insulin resistance. Whether FGF21 contributes to the impaired bone quality in IGT remains speculative.

Fibroblast Growth Factor 21 Predicts and Promotes Vascular Calcification in Haemodialysis Patients

Background

Cardiovascular disease (CVD) is the leading cause of death in haemodialysis (HD) patients. Vascular calcification (VC) is dramatically accelerated and is strongly associated with CVD events and mortality in HD patients. VC coexists with osteoporosis in many studies. Fibroblast growth factor 21 (FGF21) which is known as an adipocytokine is a new hypoglycemic strategy and is inversely related to bone mineral density.

Methods

To evaluate the contribution of FGF21 to VC in HD patients, we detected circulating FGF21 levels and measured the whole thoracic aorta calcification scores (TACS) and calcification scores of the 3 segments of thoracic aorta, including ascending thoracic aorta (ATACS), aortic arch (AoACS), and descending thoracic aorta (DTACS) of our HD patients in this cross-sectional study. In addition, we pre-incubated human aortic endothelial cells (HAECs) with FGF21 in the presence or absence of parathyroid hormone (PTH) in vitro.

Results

The median serum FGF21 level in HD patients was 11-fold higher than that in healthy controls. Ln(FGF21) was positively correlated with Ln(TACS+1), Ln(ATACS+1), Ln(AoACS+1), and Ln(DTACS+1), respectively, in HD patients. Serum FGF21 was independently associated with TACS and ATACS, AoACS, and DTACS. FGF21 which was combined with age, calcium, and intact PTH demonstrated a high area under the curve of 0.84 with optimal sensitivity (84%) and specificity (71%) for the prediction of VC in HD patients. Our vitro results showed that FGF21 enhanced the calcification effect of PTH on HAECs by increasing calcium deposition and endothelial-to-mesenchymal transition.

Conclusions

Circulating FGF21 was notably higher and was a potential predictor and promoter of VC in HD patients.

Obesity and Bone Health: A Complex Link

So far, the connections between obesity and skeleton have been extensively explored, but the results are inconsistent. Obesity is thought to affect bone health through a variety of mechanisms, including body weight, fat volume, bone formation/resorption, proinflammatory cytokines together with bone marrow microenvironment. In this review, we will mainly describe the effects of adipokines secreted by white adipose tissue on bone cells, as well as the interaction between brown adipose tissue, bone marrow adipose tissue, and bone metabolism. Meanwhile, this review also reviews the evidence for the effects of adipose tissue and its distribution on bone mass and bone-related diseases, along with the correlation between different populations with obesity and bone health. And we describe changes in bone metabolism in patients with anorexia nervosa or type 2 diabetes. In summary, all of these findings show that the response of skeleton to obesity is complex and depends on diversified factors, such as mechanical loading, obesity type, the location of adipose tissue, gender, age, bone sites, and secreted cytokines, and that these factors may exert a primary function in bone health.

Red and White Blood Cell Counts Are Associated With Bone Marrow Adipose Tissue, Bone Mineral Density, and Bone Microarchitecture in Premenopausal Women

Bone marrow adipose tissue (BMAT) resides within the bone marrow microenvironment where its function remains poorly understood. BMAT is elevated in anorexia nervosa, a disease model of chronic starvation, despite depletion of other fat depots. In addition to BMAT, the marrow microenvironment also consists of osteoblast and hematopoietic progenitors. BMAT is inversely associated with bone mineral density (BMD) in multiple populations including women with anorexia nervosa, and regulates hematopoiesis in animal models. We hypothesized that BMAT would be associated with circulating populations of hematopoietic cells (red and white blood cells) in humans and performed a post hoc analysis of two studies-a cross-sectional study and a longitudinal study-to investigate this hypothesis. We studied 89 premenopausal women cross-sectionally (median age [interquartile range], 27 [24.5, 31.7] years), including 35 with anorexia nervosa. We investigated associations between red blood cell (RBC) and white blood cell (WBC) counts and BMAT assessed by 1 H-magnetic resonance spectroscopy, BMD assessed by DXA, and bone microarchitecture assessed by HR-pQCT. In addition, we analyzed longitudinal data in six premenopausal women with anorexia nervosa treated with transdermal estrogen for 6 months and measured changes in BMAT and blood cell counts during treatment. Cross-sectionally, BMAT was inversely associated with WBC and RBC counts. In contrast, BMD and parameters of bone microarchitecture were positively associated with WBC and RBC. In women with anorexia nervosa treated with transdermal estrogen for 6 months, decreases in BMAT were significantly associated with increases in both RBC and hematocrit (rho = -0.83, p = 0.04 for both). In conclusion, we show that BMAT is inversely associated with WBC and RBC in premenopausal women, and there is a potential association between longitudinal changes in BMAT and changes in RBC. These associations warrant further study and may provide further insight into the role and function of this understudied adipose depot. © 2020 American Society for Bone and Mineral Research.

FGF21, not GCN2, influences bone morphology due to dietary protein restrictions

BACKGROUND

Dietary protein restriction is emerging as an alternative approach to treat obesity and glucose intolerance because it markedly increases plasma fibroblast growth factor 21 (FGF21) concentrations. Similarly, dietary restriction of methionine is known to mimic metabolic effects of energy and protein restriction with FGF21 as a required mechanism. However, dietary protein has been shown to be required for normal bone growth, though there is conflicting evidence as to the influence of dietary protein restriction on bone remodeling. The purpose of the current study was to evaluate the effect of dietary protein and methionine restriction on bone in lean and obese mice, and clarify whether FGF21 and general control nonderepressible 2 (GCN2) kinase, that are part of a novel endocrine pathway implicated in the detection of protein restriction, influence the effect of dietary protein restriction on bone.

METHODS

Adult wild-type (WT) or Fgf21 KO mice were fed a normal protein (18 kcal%; CON) or low protein (4 kcal%; LP) diet for 2 or 27 weeks. In addition, adult WT or Gcn2 KO mice were fed a CON or LP diet for 27 weeks. Young New Zealand obese (NZO) mice were placed on high-fat diets that provided protein at control (16 kcal%; CON), low levels (4 kcal%) in a high-carbohydrate (LP/HC) or high-fat (LP/HF) regimen, or on high-fat diets (protein, 16 kcal%) that provided methionine at control (0.86%; CON-MR) or low levels (0.17%; MR) for up to 9 weeks. Long bones from the hind limbs of these mice were collected and evaluated with micro-computed tomography (μCT) for changes in trabecular and cortical architecture and mass.

RESULTS

In WT mice the 27-week LP diet significantly reduced cortical bone, and this effect was enhanced by deletion of Fgf21 but not Gcn2. This decrease in bone did not appear after 2 weeks on the LP diet. In addition, Fgf21 KO mice had significantly less bone than their WT counterparts. In obese NZO mice dietary protein and methionine restriction altered bone architecture. The changes were mediated by FGF21 due to methionine restriction in the presence of cystine, which did not increase plasma FGF21 levels and did not affect bone architecture.

CONCLUSIONS

This study provides direct evidence of a reduction in bone following long-term dietary protein restriction in a mouse model, effects that appear to be mediated by FGF21.

Increased Expression of FGF-21 Negatively Affects Bone Homeostasis in Dystrophin/Utrophin Double Knockout Mice

Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy seen in children. In addition to skeletal muscle, DMD also has a significant impact on bone. The pathogenesis of bone abnormalities in DMD is still unknown. Recently, we have identified a novel bone-regulating cytokine, fibroblast growth factor-21 (FGF-21), which is dramatically upregulated in skeletal muscles from DMD animal models. We hypothesize that muscle-derived FGF-21 negatively affects bone homeostasis in DMD. Dystrophin/utrophin double-knockout (dKO) mice were used in this study. We found that the levels of circulating FGF-21 were significantly higher in dKO mice than in age-matched WT controls. Further tests on FGF-21 expressing tissues revealed that both FGF-21 mRNA and protein expression were dramatically upregulated in dystrophic skeletal muscles, whereas FGF-21 mRNA expression was downregulated in liver and white adipose tissue (WAT) compared to WT controls. Neutralization of circulating FGF-21 by i.p. injection of anti-FGF-21 antibody significantly alleviated progressive bone loss in weight-bearing (vertebra, femur, and tibia) and non-weight bearing bones (parietal bones) in dKO mice. We also found that FGF-21 directly promoted RANKL-induced osteoclastogenesis from bone marrow macrophages (BMMs), as well as promoted adipogenesis while concomitantly inhibiting osteogenesis of bone marrow mesenchymal stem cells (BMMSCs). Furthermore, fibroblast growth factor receptors (FGFRs) and co-receptor β-klotho (KLB) were expressed in bone cells (BMM-derived osteoclasts and BMMSCs) and bone tissues. KLB knockdown by small interfering RNAs (siRNAs) significantly inhibited the effects of FGF21 on osteoclast formation of BMMs and on adipogenic differentiation of BMMSCs, indicating that FGF-21 may directly affect dystrophic bone via the FGFRs-β-klotho complex. In conclusion, this study shows that dystrophic skeletal muscles express and secrete significant levels of FGF-21, which negatively regulates bone homeostasis and represents an important pathological factor for the development of bone abnormalities in DMD. The current study highlights the importance of muscle/bone cross-talk via muscle-derived factors (myokines) in the pathogenesis of bone abnormalities in DMD. © 2019 American Society for Bone and Mineral Research.

IGF-1 is associated with estimated bone strength in anorexia nervosa

IGF-1 and leptin are two nutritionally dependent hormones associated with low bone mass in women with anorexia nervosa. Using finite element analysis, we estimated bone strength in women with anorexia nervosa and found that IGF-1 but not leptin correlated significantly with estimated bone strength in both the radius and tibia.

PURPOSE

Women with anorexia nervosa, a psychiatric disorder characterized by self-induced starvation and low body weight, have impaired bone formation, low bone mass, and an increased risk of fracture. IGF-1 and leptin are two nutritionally dependent hormones that have been associated with low bone mass in women with anorexia nervosa. We hypothesized that IGF-1 and leptin would also be positively associated with estimated bone strength in women with anorexia nervosa.

METHODS

In this cross-sectional study of 38 women (19 with anorexia nervosa and 19 normal-weight controls), we measured serum IGF-1 and leptin and performed finite element analysis of high-resolution peripheral quantitative CT images to measure stiffness and failure load of the distal radius and tibia.

RESULTS

IGF-1 was strongly correlated with estimated bone strength in the radius (R = 0.52, p = 0.02 for both stiffness and failure load) and tibia (R = 0.55, p = 0.01 for stiffness and R = 0.58, p = 0.01 for failure load) in the women with anorexia nervosa but not in normal-weight controls. In contrast, leptin was not associated with estimated bone strength in the group of women with anorexia nervosa or normal-weight controls.

CONCLUSIONS

IGF-1 is strongly associated with estimated bone strength in the radius and tibia in women with anorexia nervosa. Further studies are needed to assess whether treatment with recombinant human IGF-1 will further improve bone strength and reduce fracture risk in this population.

Differences in Trabecular Plate and Rod Structure in Premenopausal Women Across the Weight Spectrum

CONTEXT

Premenopausal women with anorexia nervosa (AN) and obesity (OB) have elevated fracture risk. More plate-like and axially aligned trabecular bone, assessed by individual trabeculae segmentation (ITS), is associated with higher estimated bone strength. Trabecular plate and rod structure has not been reported across the weight spectrum.

OBJECTIVE

To investigate trabecular plate and rod structure in premenopausal women.

DESIGN

Cross-sectional study.

SETTING

Clinical research center.

PARTICIPANTS

A total of 105 women age 21 to 46 years: (i) women with AN (n = 46), (ii) eumenorrheic lean healthy controls (HCs) (n = 29), and (iii) eumenorrheic women with OB (n = 30).

MEASURES

Trabecular microarchitecture by ITS.

RESULTS

Mean age (±SD) was similar (28.9 ± 6.3 years) and body mass index differed (16.7 ± 1.8 vs 22.6 ± 1.4 vs 35.1 ± 3.3 kg/m2; P < 0.0001) across groups. Bone was less plate-like and axially aligned in AN (P ≤ 0.01) and did not differ between OB and HC. After controlling for weight, plate and axial bone volume fraction and plate number density were lower in OB vs HC; some were lower in OB than AN (P < 0.05). The relationship between weight and plate variables was quadratic (R = 0.39 to 0.70; P ≤ 0.0006) (i.e., positive associations were attenuated at high weight). Appendicular lean mass and IGF-1 levels were positively associated with plate variables (R = 0.27 to 0.67; P < 0.05). Amenorrhea was associated with lower radial plate variables than eumenorrhea in AN (P < 0.05).

CONCLUSIONS

In women with AN, trabecular bone is less plate-like. In women with OB, trabecular plates do not adapt to high weight. This is relevant because trabecular plates are associated with greater estimated bone strength. Higher muscle mass and IGF-1 levels may mitigate some of the adverse effects of low weight or excess adiposity on bone.

Influence of soft tissue on bone density and microarchitecture measurements by high-resolution peripheral quantitative computed tomography

High-resolution peripheral quantitative computed tomography (HR-pQCT) is a non-invasive method of measuring volumetric bone mineral density (vBMD) and microarchitecture at the distal radius and tibia. With increasing use of this technology, it is crucial to understand the potential impact of overlying soft tissue on the accuracy of HR-pQCT measures. Thus, we examined the effects of a simulated increase in adiposity (via 6- and 12-mm thick layers of overlying circumferential fat) on HR-pQCT measures of a hydroxyapatite (HA) phantom and in women (n = 20, aged 18-75 years). In the phantom, increasing the amount of overlying fat tissue led to a corresponding decrease in the mean measured density for each HA rod. In women, fat-layering led to a decrease in total vBMD (-2.9 to -3.7%, p < 0.001), cortical vBMD (-1.4% to -5.5%, p < 0.001), and estimated failure load (-1.4 to -5.7%, p = 0.002) at the radius, with similar changes in the tibia. Trabecular microarchitectural measurements were also impacted by simulated adiposity, with fat-layering leading to decreased trabecular thickness and separation and increased trabecular number at the radius (Δ's = 5 to 12%) with more pronounced differences at the tibia (Δ's = 14 to 40%). At the tibia, fat-layering also led to decreased cortical thickness and increased cortical porosity. Altogether, these results demonstrate that overlying adipose tissue can lead to artifacts in bone measurements by HR-pQCT, resulting in an underestimation of vBMD and generally, an overestimation of bone microarchitecture impairment. Therefore, soft tissue artifact should be considered when interpreting HR-pQCT results, particularly in those with high BMI and/or marked changes in adiposity.

Fibroblast growth factors in control of lipid metabolism: from biological function to clinical application

PURPOSE OF REVIEW

Several members of the fibroblast growth factor (FGF) family have been identified as key regulators of energy metabolism in rodents and nonhuman primates. Translational studies show that their metabolic actions are largely conserved in humans, which led to the development of various FGF-based drugs, including FGF21-mimetics LY2405319, PF-05231023, and pegbelfermin, and the FGF19-mimetic NGM282. Recently, a number of clinical trials have been published that examined the safety and efficacy of these novel therapeutic proteins in the treatment of obesity, type 2 diabetes (T2D), nonalcoholic steatohepatitis (NASH), and cholestatic liver disease. In this review, we discuss the current understanding of FGFs in metabolic regulation and their clinical potential.

RECENT FINDINGS

FGF21-based drugs induce weight loss and improve dyslipidemia in patients with obesity and T2D, and reduce steatosis in patients with NASH. FGF19-based drugs reduce steatosis in patients with NASH, and ameliorate bile acid-induced liver damage in patients with cholestasis. In contrast to their potent antidiabetic effects in rodents and nonhuman primates, FGF-based drugs do not appear to improve glycemia in humans. In addition, various safety concerns, including elevation of low-density lipoprotein cholesterol, modulation of bone homeostasis, and increased blood pressure, have been reported as well.

SUMMARY

Clinical trials with FGF-based drugs report beneficial effects in lipid and bile acid metabolism, with clinical improvements in dyslipidemia, steatosis, weight loss, and liver damage. In contrast, glucose-lowering effects, as observed in preclinical models, are currently lacking.

Fibroblast growth factor 21 controls mitophagy and muscle mass

BACKGROUND

Skeletal muscle is a plastic tissue that adapts to changes in exercise, nutrition, and stress by secreting myokines and myometabolites. These muscle-secreted factors have autocrine, paracrine, and endocrine effects, contributing to whole body homeostasis. Muscle dysfunction in aging sarcopenia, cancer cachexia, and diabetes is tightly correlated with the disruption of the physiological homeostasis at the whole body level. The expression levels of the myokine fibroblast growth factor 21 (FGF21) are very low in normal healthy muscles. However, fasting, ER stress, mitochondrial myopathies, and metabolic disorders induce its release from muscles. Although our understanding of the systemic effects of muscle-derived FGF21 is exponentially increasing, the direct contribution of FGF21 to muscle function has not been investigated yet.

METHODS

Muscle-specific FGF21 knockout mice were generated to investigate the consequences of FGF21 deletion concerning skeletal muscle mass and force. To identify the mechanisms underlying FGF21-dependent adaptations in skeletal muscle during starvation, the study was performed on muscles collected from both fed and fasted adult mice. In vivo overexpression of FGF21 was performed in skeletal muscle to assess whether FGF21 is sufficient per se to induce muscle atrophy.

RESULTS

We show that FGF21 does not contribute to muscle homeostasis in basal conditions in terms of fibre type distribution, fibre size, and muscle force. In contrast, FGF21 is required for fasting-induced muscle atrophy and weakness. The mass of isolated muscles from control-fasted mice was reduced by 15-25% (P < 0.05) compared with fed control mice. FGF21-null muscles, however, were significantly protected from muscle loss and weakness during fasting. Such important protection is due to the maintenance of protein synthesis rate in knockout muscles during fasting compared with a 70% reduction in control-fasted muscles (P < 0.01), together with a significant reduction of the mitophagy flux via the regulation of the mitochondrial protein Bnip3. The contribution of FGF21 to the atrophy programme was supported by in vivo FGF21 overexpression in muscles, which was sufficient to induce autophagy and muscle loss by 15% (P < 0.05). Bnip3 inhibition protected against FGF21-dependent muscle wasting in adult animals (P < 0.05).

CONCLUSIONS

FGF21 is a novel player in the regulation of muscle mass that requires the mitophagy protein Bnip3.

Low bone mineral density in anorexia nervosa: Treatments and challenges

Anorexia nervosa, a psychiatric disease predominantly affecting women, is characterized by self- induced starvation and a resultant low-weight state. During starvation, a number of hormonal adaptations - including hypothalamic amenorrhea and growth hormone resistance - allow for decreased energy expenditure during periods of decreased nutrient intake, but these very same adaptations also contribute to the medical complications associated with chronic starvation, including low bone mass. Almost 90% of women with anorexia nervosa have bone mineral density (BMD) values more than one-standard deviation below the mean of healthy women at peak bone mineral density and this disease is associated with a significantly increased risk of fracture. Although multiple therapies have been studied for the treatment of low bone mass in anorexia nervosa, there are currently no approved therapies and few promising long-term therapeutic options. This review will outline the mediators of low bone mass in anorexia nervosa, discuss therapies that have been studied for the treatment of low BMD in this disorder, and highlight the important challenges that remain, including the differences in bone modeling in adolescents with anorexia nervosa as compared to adults, necessitating that potential therapies be tested in these two populations separately, and the paucity of long-term therapeutic strategies for treating bone loss in this disorder.

Changes in marrow adipose tissue with short-term changes in weight in premenopausal women with anorexia nervosa

OBJECTIVE

In anorexia nervosa, a psychiatric disease characterized by self-induced starvation and a model of chronic undernutrition, levels of subcutaneous (SAT) and visceral (VAT) adipose tissue are low, whereas marrow adipose tissue (MAT) levels are elevated compared to normal-weight women. The reason for this paradoxical elevation of an adipose tissue depot in starvation is not known. We sought to understand changes in MAT in response to subacute changes in weight and to compare these changes with those of other fat depots and body composition parameters.

DESIGN AND METHODS

We conducted a 12-month longitudinal study including 46 premenopausal women (n = 26 with anorexia nervosa and n = 20 normal-weight controls) with a mean (s.e.m.) age of 28.2 ± 0.8 years. We measured MAT, SAT, VAT and bone mineral density (BMD) at baseline and after 12 months.

RESULTS

At baseline, SAT (P < 0.0001), VAT (P < 0.02) and BMD of the spine and hip (P ≤ 0.0002) were significantly lower and vertebral and metaphyseal MAT (P ≤ 0.001) significantly higher in anorexia nervosa compared to controls. Weight gain over 12 months was associated with increases not only in SAT and VAT, but also epiphyseal MAT (P < 0.03). Changes in epiphyseal MAT were positively associated with changes in BMD (P < 0.03).

CONCLUSIONS

In contrast to the steady state, in which MAT levels are higher in anorexia nervosa and MAT and BMD are inversely associated, short-term weight gain is associated with increases in both MAT and BMD. These longitudinal data demonstrate the dynamic nature of this fat depot and provide further evidence of its possible role in mineral metabolism.

The paradox of marrow adipose tissue in anorexia nervosa

Anorexia nervosa (AN) is a psychiatric disorder characterized by inappropriate nutrient intake resulting in low body weight. Multiple hormonal adaptations facilitate decreased energy expenditure in this state of caloric deprivation including non-thyroidal illness syndrome, growth hormone resistance, and hypogonadotropic hypogonadism. Although these hormonal adaptations confer a survival advantage during periods of negative energy balance, they contribute to the long-term medical complications associated with AN, the most common of which is significant bone loss and an increased risk of fracture. In recent years, marrow adipose tissue (MAT) has emerged as an important potential determinant of the low bone mass state characteristic of AN. Unlike subcutaneous and visceral adipose tissue depots which are low in AN, MAT levels are paradoxically elevated and are inversely associated with BMD. In this review, we discuss what is known about MAT in AN and the proposed hormonal determinants of this adipose tissue depot.

Effects of Anorexia Nervosa on Bone Metabolism

Anorexia nervosa is a psychiatric disease characterized by a low-weight state due to self-induced starvation. This disorder, which predominantly affects women, is associated with hormonal adaptations that minimize energy expenditure in the setting of low nutrient intake. These adaptations include GH resistance, functional hypothalamic amenorrhea, and nonthyroidal illness syndrome. Although these adaptations may be beneficial to short-term survival, they contribute to the significant and often persistent morbidity associated with this disorder, including bone loss, which affects >85% of women. We review the hormonal adaptions to undernutrition, review hormonal treatments that have been studied for both the underlying disorder as well as for the associated decreased bone mass, and discuss the important challenges that remain, including the lack of long-term treatments for bone loss in this chronic disorder and the fact that despite recovery, many individuals who experience bone loss as adolescents have chronic deficits and an increased risk of fracture in adulthood.

Higher serum levels of fibroblast growth factor 21 in old patients with cachexia

OBJECTIVE

Fibroblast growth factor (FGF)21 is promptly induced by short fasting in animal models to regulate glucose and fat metabolism. Data on FGF21 in humans are inconsistent and FGF21 has not yet been investigated in old patients with cachexia, a complex syndrome characterized by inflammation and weight loss. The aim of this study was to explore the association of FGF21 with cachexia in old patients compared with their healthy counterparts.

METHODS

Serum FGF21 and its inactivating enzyme fibroblast activation protein (FAP)-α were measured with enzyme-linked immunoassays. Cachexia was defined as ≥5% weight loss in the previous 3 mo and concurrent anorexia (Council on Nutrition appetite questionnaire).

RESULTS

We included 103 patients with and without cachexia (76.9 ± 5.2 y of age) and 56 healthy controls (72.9 ± 5.9 y of age). Cachexia was present in 16.5% of patients. These patients had significantly higher total FGF21 levels than controls (952.1 ± 821.3 versus 525.2 ± 560.3 pg/mL; P = 0.012) and the lowest FGF21 levels (293.3 ± 150.9 pg/mL) were found in the control group (global P < 0.001). Although FAP-α did not differ between the three groups (global P = 0.082), bioactive FGF21 was significantly higher in patients with cachexia (global P = 0.002). Risk factor-adjusted regression analyses revealed a significant association between cachexia and total (β = 649.745 pg/mL; P < 0.001) and bioactive FGF21 (β = 393.200 pg/mL; P <0.001), independent of sex, age, and body mass index.

CONCLUSIONS

Patients with cachexia exhibited the highest FGF21 levels. Clarification is needed to determine whether this is an adaptive response to nutrient deprivation in disease-related cachexia or whether the increased FGF21 values contribute to the catabolic state.

Effect of FGF-21 on implant bone defects through hepatocyte growth factor (HGF)-mediated PI3K/AKT signaling pathway

Implant bone defects are the most common phenomenon in the processes of bone transplantation. Evidences have identified that fibroblast growth factor-21 (FGF-21) encourages osteogenesis for patients with implant bone defects. The purpose of this study was to investigate the role of FGF-21 and its potential mechanism in bone mesenchymal stem cells (BMSCs). RT-PCR, Western blotting, flow cytometry, immunofluorescence and immunohistochemistry assays were performed to analyze the role of FGF-21 and intracellular signaling pathways involved in BMSCs. It was shown that FGF-21 increased viability of BMSCs. Treatment with FGF-21 decreased the apoptosis of BMSCs by decreasing pro-apoptosis protein Caspase-3. Results indicated that FGF-21 (2 mg/kg) treatment up-regulated HGF, PI3K and AKT expression in BMSCs. In addition, the protective effects of FGF-21 on BMSCs were canceled by PI3K/AKT inhibitor in BMSCs. Results found that knockdown of HGF abolished FGF-21-decreased PI3K/AKT signal pathway. Furthermore, results demonstrated that FGF-21 presented beneficial effects for implant bone defects in rat model. In conclusion, these results indicate that FGF-21 can improve implant bone defects through HGF-mediated PI3K/AKT signaling pathway in BMSCs.

Deficiency of fibroblast growth factor 21 (FGF21) promotes hepatocellular carcinoma (HCC) in mice on a long term obesogenic diet

OBJECTIVE

Non-alcoholic fatty liver (NAFL) associated with obesity is a major cause of liver diseases which can progress to non-alcoholic steatohepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Fibroblast growth factor 21 (FGF21) plays an important role in liver metabolism and is also a potential marker for NAFL. Here we aimed to test the effect of FGF21 deficiency on liver pathology in mice consuming a conventional high fat, high sucrose (HFHS) obesogenic diet for up to 52 weeks.

METHODS

C57BL6 WT and FGF21 KO mice were fed a conventional obesogenic diet and were evaluated at 16 and 52 weeks. Evaluation included metabolic assessment, liver pathology, and transcriptomic analysis.

RESULTS

With consumption of HFHS diet, FGF21 deficient mice (FGF21 KO) develop excess fatty liver within 16 weeks. Hepatic pathology progresses and at 52 weeks FGF21 KO mice show significantly worse fibrosis and 78% of mice develop HCC; in contrast only 6% of WT mice develop HCC. Well differentiated hepatocellular carcinomas in FGF21 KO mice were characterized by expanded hepatic plates, loss of reticulin network, cytologic atypia, and positive immunostaining for glutamine synthetase. Microarray analysis reveals enrichment of several fibroblast growth factor signaling pathways in the tumors.

CONCLUSIONS

In addition to attenuating inflammation and fibrosis in mice under a number of dietary challenges, we show here that FGF21 is required to limit the progression from NAFL to HCC in response to prolonged exposure to an obesogenic diet. The induction of hepatic FGF21 in response to the high fat, high sucrose obesogenic diet may play an important role in limiting progression of liver pathology from NAFL to HCC.

Bone metabolism in anorexia nervosa and hypothalamic amenorrhea

Anorexia nervosa (AN) and hypothalamic amenorrhea (HA) are states of chronic energy deprivation associated with severely compromised bone health. Poor bone accrual during adolescence followed by increased bone loss results in lifelong low bone density, degraded bone architecture, and higher risk of fractures, despite recovery from AN/HA. Amenorrhea is only one of several compensatory responses to the negative energy balance. Other hypothalamic-pituitary hormones are affected and contribute to bone deficits, including activation of hypothalamic-pituitary-adrenal axis and growth hormone resistance. Adipokines, particularly leptin, provide information on fat/energy stores, and gut hormones play a role in the regulation of appetite and food intake. Alterations in all these hormones influence bone metabolism. Restricted in scope, current pharmacologic approaches to improve bone health have had overall limited success.

Association between fibroblast growth factor 21 and bone mineral density in adults

PURPOSE

Animal-based studies have reported a decrease in bone mass resulting from high level of fibroblast growth factor 21 (FGF21). However, the correlation between plasma FGF21 levels and bone mineral density (BMD) is paradoxical in previous human-based studies, and the associations between FGF21 gene polymorphisms and BMD haven't been reported yet. Therefore, here, we evaluated plasma FGF21 levels with sufficient study samples, and performed genetic association test to reveal the physiological and genetic role of FGF21 on BMD in adults.

METHODS

Plasma and genetic samples containing 168 and 569 Han Chinese subjects, respectively, were employed in this study. Fasting plasma FGF21 levels were determined using enzyme-linked immunosorbent assay (ELISA). Regional BMD values were measured by dual energy X-ray absorptiometry (DXA). Five variants of FGF21 gene were successfully genotyped.

RESULTS

Physiological association suggested that plasma FGF21 levels were inversely correlated with BMD in femoral neck (Neck-BMD: P = 0.039) and Ward's triangle (Ward's-BMD: P = 0.002) of hip region. A FGF21 gene variant, rs490942, was significantly associated with the increase of Ward's-BMD in total (P = 0.027) and female (P = 0.016) cohorts, as well as Neck-BMD in female cohort (P = 7.45 × 10^-3). Meanwhile, eQTL results indicated that this SNP was related to the decreased level of FGF21 gene expression.

CONCLUSIONS

Taking together from both physiological and genetic levels, we suggest that FGF21 is inversely associated with regional BMD. And we haven't observed sex-specific effect in this study.

Impaired bone strength estimates at the distal tibia and its determinants in adolescents with anorexia nervosa

BACKGROUND

Altered bone microarchitecture and higher marrow adipose tissue (MAT) may reduce bone strength. High resolution pQCT (HRpQCT) allows assessment of volumetric BMD (vBMD), and size and microarchitecture parameters of bone, while 1H-magnetic resonance spectroscopy (1H-MRS) allows MAT evaluation. We have reported impaired microarchitecture at the non-weight bearing radius in adolescents with anorexia nervosa (AN) and that these changes may precede aBMD deficits. Data are lacking regarding effects of AN on microarchitecture and strength at the weight-bearing tibia in adolescents and young adults, and the impact of changes in microarchitecture and MAT on strength estimates.

OBJECTIVE

To compare strength estimates at the distal tibia in adolescents/young adults with AN and controls in relation to vBMD, bone size and microarchitecture, and spine MAT.

DESIGN AND METHODS

This was a cross-sectional study of 47 adolescents/young adults with AN and 55 controls 14-24years old that assessed aBMD and body composition using DXA, and distal tibia vBMD, size, microarchitecture and strength estimates using HRpQCT, extended cortical analysis, individual trabecular segmentation, and finite element analysis. Lumbar spine MAT (1H-MRS) was assessed in a subset of 19 AN and 22 controls.

RESULTS

Areal BMD Z-scores were lower in AN than controls. At the tibia, AN had greater cortical porosity, lower total and cortical vBMD, cortical area and thickness, trabecular number, and strength estimates than controls. Within AN, strength estimates were positively associated with lean mass, aBMD, vBMD, bone size and microarchitectural parameters. MAT was higher in AN, and associated inversely with strength estimates.

CONCLUSIONS

Adolescents/young adults with AN have impaired microarchitecture at the weight-bearing tibia and higher spine MAT, associated with reduced bone strength.

Fibroblast Growth Factor 21-Metabolic Role in Mice and Men

Since its identification in 2000, the interest of scientists in the hepatokine fibroblast growth factor (FGF) 21 has tremendously grown, and still remains high, due to a wealth of very robust data documenting this factor's favorable effects on glucose and lipid metabolism in mice. For more than ten years now, intense in vivo and ex vivo experimentation addressed the physiological functions of FGF21 in humans as well as its pathophysiological role and pharmacological effects in human metabolic disease. This work produced a comprehensive collection of data revealing overlaps in FGF21 expression and function but also significant differences between mice and humans that have to be considered before translation from bench to bedside can be successful. This review summarizes what is known about FGF21 in mice and humans with a special focus on this factor's role in glucose and lipid metabolism and in metabolic diseases, such as obesity and type 2 diabetes mellitus. We highlight the discrepancies between mice and humans and try to decipher their underlying reasons.

Eating disorders and bone metabolism in women

PURPOSE OF REVIEW

Eating Disorders are psychiatric disorders associated with a high risk for low bone mineral density (BMD) and fractures. Low BMD is a consequence of undernutrition, changes in body composition, and hormonal alterations. This review summarizes recent findings regarding novel strategies for assessing bone outcomes in patients with eating disorders, factors contributing to altered bone metabolism, and possible therapeutic strategies.

RECENT FINDINGS

Emerging research in this field suggests that not only anorexia nervosa, but also bulimia nervosa results in lower BMD compared to controls. To date studies of bone structure, and all randomized controlled trials examining the impact of various therapies on bone outcomes in anorexia nervosa, have focused on adolescent girls and women. We discuss the impact of anorexia nervosa on bone structure, and associations of resting energy expenditure, marrow adipose tissue (including the ratio of saturated to unsaturated fat), and cold activated brown adipose tissue with BMD and bone structure. Promising strategies for treatment include physiological estrogen replacement (rather than oral contraceptives) in adolescent girls with anorexia nervosa, and bisphosphonates, as well as teriparatide, in adult women with anorexia nervosa.

SUMMARY

Recent data on (i) BMD and bone structure in adolescent girls and women with eating disorders, (ii) factors that contribute to altered bone metabolism, and (iii) randomized controlled trials reporting positive effects of physiologic estrogen replacement, bisphosphonates and teriparatide on bone health, provide us with a greater understanding of the impact of eating disorders on bone and novel management strategies.

The Role of Body Weight on Bone in Anorexia Nervosa: A HR-pQCT Study

Anorexia nervosa (AN) is associated with decreased bone mineral density and increased risk of fracture. The aim of this study was to assess bone geometry, volumetric bone mineral density (vBMD), trabecular microarchitecture and estimated failure load in weight-bearing vs. non-weight-bearing bones in AN. We included twenty-five females with AN, and twenty-five female controls matched on age and height. Bone geometry, vBMD and trabecular microarchitecture were assessed using high-resolution peripheral quantitative computed tomography of the distal radius and tibia. At both sites, cortical perimeter and total bone area were similar in patients and controls. Total vBMD was lower in the AN group in the tibia (p < 0.0005) but not in the radius. In the tibia, cortical thickness was approximately 25% lower (p < 0.0005) in the AN group, whereas there was no significant difference in the radius. In terms of trabecular microarchitecture, all indices [bone volume/tissue volume (BV/TV); trabecular thickness (Tb.Th.), trabecular number (Tb.N) and trabecular spacing (Tb.Sp.)] were impaired in AN in the tibia (p values range < 0.01-0.0001). In the radius, BV/TV and Tb.N were lower (p < 0.05 and p < 0.001, respectively); Tb.Sp. was higher (p < 0.001), whereas Tb.Th. did not differ, compared to controls. Estimated failure load was lower in patients in both the radius and the tibia (p < 0.0005 and p < 0.0001, respectively), most pronounced in the tibia. In conclusion, the impairment of cortical thickness and estimated failure load were significantly more pronounced in the weight-bearing tibia, compared to the non-weight-bearing radius, implying a direct effect of low body weight on bone loss in AN.

High FGF21 levels are associated with altered bone homeostasis in HIV-1-infected patients

BACKGROUND

Fibroblast growth factor-21 (FGF21) has emerged as an important regulator of glucose, lipid, and body weight homeostasis. However, recent experimental studies have reported that increased FGF21 levels may lead to bone loss.

OBJECTIVE

To assess the relationship of serum FGF21 levels and altered bone homeostasis in HIV-1-infected patients.

DESIGN

Cross-sectional study of 137 HIV-1-infected patients and 35 healthy controls conducted at the Hospital de la Santa Creu i Sant Pau, Barcelona. Among HIV-1-infected patients, 35 were untreated (naïve), 43 were treated with antiretrovirals (HIV-1/ART) with no lipodystrophy, and 59 patients were HIV-1/ART and experienced lipodystrophy. Bone mineral density (BMD) and content (BMC) were assessed using dual-energy X-ray absorptiometry. Serum levels of FGF21, receptor activator of nuclear factor (NF)-KB ligand (RANKL), and C-telopeptide of type-I collagen (CTX-1) were measured by enzyme-linked immunosorbent assays. Serum levels of osteocalcin, osteoprotegerin, leptin, tumor necrosis factor-α, interleukin-6, interleukin-8, and monocyte chemoattractant protein-1 were determined using an antibody-linked, fluorescently labeled microsphere bead-based multiplex analysis system.

RESULTS

Alterations in bone parameters and bone homeostasis marker levels were consistent with higher turnover and bone loss in HIV-1 infected patients. FGF21 correlated negatively with BMD and BMC. FGF21 correlated positively with serum levels of osteoprotegerin and CTX-1, as well as with the CTX-1/osteocalcin ratio.

CONCLUSIONS

Elevated FGF21 levels are associated with poor bone homeostasis in HIV-1-infected patients. Increases in FGF21 serum level may be an indicator not only of metabolic derangement but it may also serve as a biomarker of altered bone homeostasis in HIV-1 infected patients.

Restrictive Eating Disorders and Skeletal Health in Adolescent Girls and Young Women

This article reviews the effects of restrictive eating disorders on bone health. The relationship between eating disorders and amenorrhea is discussed in detail. The pathologic impact of malnutrition on bone is explored by examining the results of studies using various available imaging techniques. The multiple hormonal alterations seen in adolescents and young women with anorexia nervosa are reviewed, as well as how these alterations may influence bone turnover, density, structure, and strength. The diagnostic clinical evaluation for adolescents and young women with these disorders is also outlined. Available treatment options, including those that hold promise for efficacy, as well as those we deemed to be ineffective, are considered from both the clinical and mechanistic standpoints. Finally, future research opportunities are offered, including intriguing work in the area of fat and bone interactions.

Decreased levels of Fibroblast Growth Factor 21 are correlated with improved hypoglycemia in patients with insulinoma

Fibroblast growth factor-21 (FGF-21) improves insulin sensitivity and lipid metabolism in obese or diabetic animal models and has been proposed as a potential therapeutic agent for treating T2DM, obesity, and their related complications. However, little is known about the changes of FGF21 levels in response to endogenous hyperinsulinemic hypoglycemia. To explore its relationship with parameters of glucose metabolism in patients with insulinoma, eleven subjects with pathological insulinoma and twenty-two healthy subjects were recruited for this study. Interestingly, we found that the serum FGF21 levels increased significantly in patients with insulinoma at baseline compared with the control group (381.36 ± 107.12 vs. 62.59 ± 10.48 pg/mL; P = 0.001). Furthermore, FGF21 was positively correlated with insulin (r = 0.80, P = 0.003) and proinsulin (r = 0.72, P = 0.012) in subjects with insulinoma. Multiple stepwise regression analysis showed that FGF21 was independently associated with insulin (β = 0.80, P = 0.003). In addition, FGF21 decreased significantly after surgery, and its change was still correlated positively with the changes in insulin (r = 0.61, P = 0.048) and proinsulin (r = 0.84, P = 0.001). These findings suggested that the serum FGF21 levels could be involved in a complex adaptive response to insulin secretion and glucose metabolism in humans.

FGF21 and the late adaptive response to starvation in humans

In mice, FGF21 is rapidly induced by fasting, mediates critical aspects of the adaptive starvation response, and displays a number of positive metabolic properties when administered pharmacologically. In humans, however, fasting does not consistently increase FGF21, suggesting a possible evolutionary divergence in FGF21 function. Moreover, many key aspects of FGF21 function in mice have been identified in the context of transgenic overexpression or administration of supraphysiologic doses, rather than in a physiologic setting. Here, we explored the dynamics and function of FGF21 in human volunteers during a 10-day fast. Unlike mice, which show an increase in circulating FGF21 after only 6 hours, human subjects did not have a notable surge in FGF21 until 7 to 10 days of fasting. Moreover, we determined that FGF21 induction was associated with decreased thermogenesis and adiponectin, an observation that directly contrasts with previous reports based on supraphysiologic dosing. Additionally, FGF21 levels increased after ketone induction, demonstrating that endogenous FGF21 does not drive starvation-mediated ketogenesis in humans. Instead, a longitudinal analysis of biologically relevant variables identified serum transaminases--markers of tissue breakdown--as predictors of FGF21. These data establish FGF21 as a fasting-induced hormone in humans and indicate that FGF21 contributes to the late stages of adaptive starvation, when it may regulate the utilization of fuel derived from tissue breakdown.