Plasma concentrations of fibroblast growth factors 19 and 21 in patients with anorexia nervosa

Comparison of Adiponectin Levels in Anorexia Nervosa, Bulimia Nervosa, Binge-Eating Disorder, Obesity, Constitutional Thinness, and Healthy Controls: A Network Meta-Analysis

Adiponectin is a protein hormone that is produced and secreted primarily by adipose tissue. The levels of adiponectin in those with eating disorders, obesity, and healthy controls have been extensively studied. However, the general picture of the differences in adiponectin levels across the mentioned conditions is still unclear and fragmented. In this study, we pooled previous studies and performed a network meta-analysis to gain a global picture of comparisons of adiponectin levels across eating disorders, obesity, constitutional thinness, and healthy controls. Electronic databases were searched for anorexia nervosa, avoidant restrictive food intake disorder, binge-eating disorder, bulimia nervosa, healthy controls, night eating syndrome, obesity, and constitutional thinness in studies where adiponectin levels were measured. A total of 4262 participants from 50 published studies were included in the network meta-analysis. Adiponectin levels were significantly higher in participants with anorexia nervosa than in healthy controls (Hedges' g = 0.701, p < 0.001). However, adiponectin levels in constitutionally thin participants were not significantly different from those of healthy controls (Hedges' g = 0.470, p = 0.187). Obesity and binge-eating disorder were associated with significantly lower adiponectin levels compared to those of healthy controls (Hedges' g = -0.852, p < 0.001 and Hedges' g = -0.756, p = 0.024, respectively). The disorders characterized by excessive increases or decreases in BMI were associated with significant changes in adiponectin levels. These results suggest that adiponectin may be an important marker of severely disequilibrated homeostasis, especially in fat, glucose, and bone metabolisms. Nonetheless, an increase in adiponectin may not simply be associated with a decrease in BMI, as constitutional thinness is not associated with a significant increase in adiponectin.

Biocompatible Macroion/Growth Factor Assemblies for Medical Applications

Growth factors are a class of proteins that play a role in the proliferation (the increase in the number of cells resulting from cell division) and differentiation (when a cell undergoes changes in gene expression becoming a more specific type of cell) of cells. They can have both positive (accelerating the normal healing process) and negative effects (causing cancer) on disease progression and have potential applications in gene therapy and wound healing. However, their short half-life, low stability, and susceptibility to degradation by enzymes at body temperature make them easily degradable in vivo. To improve their effectiveness and stability, growth factors require carriers for delivery that protect them from heat, pH changes, and proteolysis. These carriers should also be able to deliver the growth factors to their intended destination. This review focuses on the current scientific literature concerning the physicochemical properties (such as biocompatibility, high affinity for binding growth factors, improved bioactivity and stability of the growth factors, protection from heat, pH changes or appropriate electric charge for growth factor attachment via electrostatic interactions) of macroions, growth factors, and macroion-growth factor assemblies, as well as their potential uses in medicine (e.g., diabetic wound healing, tissue regeneration, and cancer therapy). Specific attention is given to three types of growth factors: vascular endothelial growth factors, human fibroblast growth factors, and neurotrophins, as well as selected biocompatible synthetic macroions (obtained through standard polymerization techniques) and polysaccharides (natural macroions composed of repeating monomeric units of monosaccharides). Understanding the mechanisms by which growth factors bind to potential carriers could lead to more effective delivery methods for these proteins, which are of significant interest in the diagnosis and treatment of neurodegenerative and civilization diseases, as well as in the healing of chronic wounds.

Associations of Circulating Irisin and Fibroblast Growth Factor-21 Levels with Measures of Energy Homeostasis in Highly Trained Adolescent Rhythmic Gymnasts

The aim of this investigation was to determine the associations of serum irisin and fibroblast growth factor-21 (FGF-21) with the measures of energy homeostasis, training stress and other energy homeostasis hormones in highly trained adolescent rhythmic gymnasts (RG). Thirty-three RG and 20 untrained controls (UC) aged 14−18 years participated in this study. Body composition, resting energy expenditure (REE), peak oxygen consumption, and different energy homeostasis hormones in serum, including irisin, FGF-21, leptin, and resistin, were measured. Irisin and FGF-21 were not significantly different (p > 0.05) between RG and UC groups. In RG, serum irisin was positively associated with REE (r = 0.40; p = 0.021) and leptin (r = 0.60; p = 0.013), while serum FGF-21 was related to body fat mass (r = 0.46; p = 0.007) and leptin (r = 0.45; p = 0.009). Irisin was related to FGF-21, independent of age, body fat, and lean masses (r = 0.36; p = 0.049) in RG. In conclusion, serum irisin concentration was associated with energy expenditure and serum FGF-21 level with energy availability measures in lean adolescent athletes, while no relationships of irisin and FGF-21 with energy status measures were observed in lean nonathletic adolescents.

Adiponectin in anorexia nervosa and its modifiers: A meta-regression study

OBJECTIVE

Adiponectin, which is secreted from adipose tissue, is a protein hormone. Although a large body of studies have found that circulating adiponectin levels increase in anorexia nervosa (AN) and caloric restriction, the effect of subtypes of AN and modifiers of adiponectin in AN are not yet known.

METHODS

A systematic search of electronic databases was performed using the search terms "adiponectin," "anorexia nervosa," and "eating disorder" up to January 2021. All studies published in peer-reviewed journals, which included cases and control groups, were selected. The main outcome was the pooled standardized mean difference (SMD) in adiponectin levels between cases and controls, using the random-effects model. Modifiers of SMD were tested via meta-regression. Heterogeneity and publication bias were evaluated.

RESULTS

Thirty-four studies met all eligibility criteria. The total sample of AN participants (Hedges' g = .765, p < .0001), and specifically the binge-eating/purging (Hedges' g = 1.211, p < .00001) and restrictive subtypes (Hedges' g = .913, p < .00001) of AN have increased adiponectin plasma levels compared with healthy controls. Meta-regression determined that insulin, IGF-1, BMI, triglyceride, resistin, glucose, IL-6 levels are significant modifiers of adiponectin levels.

DISCUSSION

Compared with controls, adiponectin levels are higher in AN overall, and specifically in the binge-eating/purging and the restrictive AN subtypes. Many of metabolic parameters of glucose metabolism and pro-inflammatory molecules modify the relationship between AN and adiponectin levels. Adipose tissue is important to maintain metabolic stability.

PUBLIC SIGNIFICANCE

Anorexia nervosa is a psychiatric disorder associated with a severe decrease in body weight and multiple metabolic abnormalities, including an increase in the hormone adiponectin. In this paper, we used meta-analysis, a powerful statistical method, to aggregate data from 34 rigorously selected research reports. This enabled us to understand the value of adiponectin to differentiate clinical subtypes of anorexia nervosa and the relations between adiponectin and other important metabolic parameters.

Growth factors in anorexia nervosa: a systematic review and meta-analysis of cross-sectional and longitudinal data

OBJECTIVES

Growth factors are signalling molecules that play roles in the survival, proliferation, migration, and differentiation of cells. Studies have found alterations in specific growth factors in anorexia nervosa (AN).

METHODS

This systematic review and meta-analysis examined articles from three databases, measuring growth factors in AN cross-sectionally and longitudinally, and in recovered AN (rec-AN) cross-sectionally. Random-effects meta-analyses were conducted for brain-derived neurotrophic factor (BDNF) and insulin growth factor-I (IGF-1) for cross-sectional and longitudinal studies.

RESULTS

A total of 82 studies were included: 56 cross-sectional (BDNF: n = 15; IGF-1: n = 41) and 24 longitudinal (BDNF: n = 5; IGF-1: n = 19) were meta-analysed and 20 studies were narratively synthesised. In cross-sectional analyses, BDNF and IGF-1 were lower in AN compared to controls, and BDNF was marginally greater in rec-AN compared to controls. In longitudinal meta-analyses, BDNF and IGF-1 increased from baseline to follow-up. Cross-sectional subgroup analyses revealed no differences in BDNF between controls and AN binge-eating/purging subtypes.

CONCLUSIONS

It is likely that the low BDNF and IGF-1 levels found in AN are consequences of starvation, which are reversible with weight restoration. The increase in BDNF and IGF-1 during therapeutic weight restoration might improve neuroplasticity, which is the basis of learning, and thus psychotherapeutic success.

Sulforaphane ameliorates non-alcoholic fatty liver disease in mice by promoting FGF21/FGFR1 signaling pathway

Most studies regarding the beneficial effect of sulforaphane (SFN) on non-alcoholic fatty liver disease (NAFLD) have focused on nuclear factor E2-related factor 2 (Nrf2). But the molecular mechanisms underlying the beneficial effect of SFN in the treatment of NAFLD remain controversial. Fibroblast growth factor (FGF) 21 is a member of the FGF family expressed mainly in liver but also in adipose tissue, muscle and pancreas, which functions as an endocrine factor and has been considered as a promising therapeutic candidate for the treatment of NAFLD. In the present study we investigated whether FGF21 was involved in the therapeutic effect of SFN against NAFLD. C57BL/6J mice were fed a high-fat diet (HFD) for 12 weeks to generate NAFLD and continued on the HFD for additional 6 weeks with or without SFN treatment. We showed that administration of SFN (0.56 g/kg) significantly ameliorated hepatic steatosis and inflammation in NAFLD mice, along with the improved glucose tolerance and insulin sensitivity, through suppressing the expression of proteins responsible for hepatic lipogenesis, while enhancing proteins for hepatic lipolysis and fatty acids oxidation. SFN administration significantly increased hepatic expression of FGFR1 and fibroblast growth factor 21 (FGF21) in NAFLD mice, along with decreased phosphorylation of p38 MAPK (the downstream of FGF21). HepG2 cells were treated in vitro with FFAs (palmitic acid and oleic acid) followed by different concentrations of SFN. We showed that the effects of SFN on FGF21 and FGFR1 protein expression were replicated in FFAs-treated HepG2 cells. Moreover, the increased FGFR1 protein occurred earlier than increased FGF21 protein. Interestingly, the rapid effect of SFN on FGFR1 protein was not regulated by the FGFR1 gene transcription. Knockdown of FGFR1 and p38 genes weakened SFN-reduced lipid deposition in FFAs-treated HepG2 cells. SFN administration in combination with rmFGF21 (1.5 mg/kg, i.p., every other day) for 3 weeks further suppressed hepatic steatosis in NAFLD mice. In conclusion, SFN ameliorates lipid metabolism disorders in NAFLD mice by upregulating FGF21/FGFR1 pathway. Our results verify that SFN may become a promising intervention to treat or relieve NAFLD.

Associations between RNA-Binding Motif Protein 3, Fibroblast Growth Factor 21, and Clinical Outcome in Patients with Stroke

Background: RNA-binding motif protein 3 (RBM3) is a cold-induced marker of good functional outcome of ischemic stroke that is promising as a protective target. Fibroblast growth factor 21 (FGF21) is an obesity- and temperature-related hormone that upregulates the expression of RBM3, which is beneficial as a recombinant treatment and has been tested under different experimental pathological conditions, including stroke. However, the interaction between RBM3 and FGF21 has not yet been tested for clinical stroke conditions. Methods: In a sample of 66 stroke patients, we analyzed the associations between the FGF21 and RBM3 serum concentrations on admission and at 72 h, body weight, maximum temperature during the first 24 h, and the outcome of patients at 3 months. We also analyzed their association with biomarkers of obesity (adiponectin and leptin) and inflammation (interleukin-6 (IL-6) and interleukin (IL-10)). Results: Higher concentrations of FGF21 on admission and RBM3 at 72 h were associated with good outcomes. Serum FGF21 and RBM3 were directly related to body mass index and inversely related to the maximum temperature during the first 24 h. We found a positive association between the FGF21 concentrations in obese patients with leptin and a negative correlation with adiponectin in non-obese participants. Conclusions: This clinical study demonstrates the association between RBM3 and FGF21 levels and the outcome of stroke patients. Although further investigations are required, these data support the pharmacological induction of RBM3 as a promising protective therapy.

Effects of interleukin-1 antagonism and corticosteroids on fibroblast growth factor-21 in patients with metabolic syndrome

Fibroblast growth factor-21 (FGF21) is elevated in patients with the metabolic syndrome. Although the exact underlying mechanisms remain ill-defined, chronic low-grade inflammation with increased Interleukin-(IL)-1β expression may be responsible. The aim of this study was to investigate effects of two different anti-inflammatory treatments (IL-1 antagonism or high-dose corticosteroids) on FGF21 in patients with the metabolic syndrome. This is a secondary analysis of two interventional studies in patients with obesity and features of the metabolic syndrome. Trial A was an interventional trial (n = 73) investigating short-term effects of the IL-1 antagonist anakinra and of dexamethasone. Trial B was a randomized, placebo-controlled, double-blinded trial (n = 67) investigating longer-term effects of IL-1 antagonism. In total, 140 patients were included in both trials. Median age was 55 years (IQR 44-66), 26% were female and median BMI was 37 kg/m² (IQR 34-39). Almost half of the patients were diabetic (45%) and had increased c-reactive protein levels of 3.4 mg/L. FGF21 levels correlated with fasting glucose levels, HOMA-index, C-peptide levels, HbA1c and BMI. Short-term treatment with anakinra led to a reduction of FGF21 levels by - 200 pg/mL (95%CI - 334 to - 66; p = 0.004). No effect was detectable after longer-term treatment (between-group difference: - 8.8 pg/mL (95%CI - 130.9 to 113.3; p = 0.89). Acute treatment with dexamethasone was associated with reductions of FGF21 by -175 pg/mL (95%CI - 236 to - 113; p < 0.001). Anti-inflammatory treatment with both, IL-1 antagonism and corticosteroids reduced FGF21 levels at short-term in individuals with the metabolic syndrome.Trial registration: ClinicalTrials.gov Identifiers NCT02672592 and NCT00757276.

Adipokines in anorexia nervosa: A systematic review and meta-analysis

OBJECTIVE

The association between adipokine dysregulation and weight loss of patients with anorexia nervosa (AN) has been long investigated, in search of a causal relationship. We sought to: a) synthesize the available evidence on potential differences between AN patients and controls with regards to adipokine measurements (namely, leptin, adiponectin, resistin, soluble leptin receptor, visfatin, vaspin and omentin), b) estimate the potential differences between constitutionally thin (CT) subjects and AN patients, and c) present the available evidence with regards to biomarker efficacy of adipokines in AN.

METHODS

A structured literature search, last updated in 2/2019, was conducted in the following databases: MEDLINE, clinicaltrials.gov, PsycINFO, PSYNDEX and WHO Registry Network. The primary outcome was the standardized mean difference of each adipokine between AN patients and controls of normal BMI. Secondary outcomes included the correlation of leptin with BMI and bone mineral density among AN patients. The study protocol is published in PROSPERO (CRD42018116767).

RESULTS

In a total of 622 screened studies, after exclusion of non-relevant articles and duplicates, 84 reports on leptin, 31 reports on adiponectin, 12 on resistin, 10 on soluble leptin receptor, 5 on visfatin, 3 on vaspin and omentin were finally included in the meta-analysis. Publication bias assessment underlined the possibility of non-significant studies being underrepresented; still, significant heterogeneity renders this statement inconclusive. Leptin [ELISA: SMD (95% CI): -3.03 (-4, -2.06)], radioimmunoassay [RIA: -3.84 (-4.71, -2.98)] and resistin [-1.67 (-2.85, -0.48)] were significantly lower in patients with AN compared with controls, whereas visfatin decrease did not reach significance (-2.03 (-4.38, 0.3). Mean adiponectin, vaspin and soluble leptin receptor levels were significantly higher. In subgroup analysis, a significantly attenuated SMD was reported in ELISA studies compared with RIA studies. Leptin was significantly lower in AN patients compared to CT subjects and BMI marginally did not appear to confound the result. In all analyses, except for the correlation of leptin with BMI in AN patients, high heterogeneity was present. Meta-regression analysis indicated a potential confounding action of controls' BMI and age on leptin SMD and between-assay differences. Publication bias assessment underlined the possibility of nonsignificant studies being underrepresented; still, further investigation did not corroborate this and significant heterogeneity renders this statement inconclusive.

CONCLUSION

A distinct profile of adipokine dysregulation is apparent in AN patients, following the anticipated pattern of low BMI. A precise estimation of the magnitude is hindered by heterogeneity, partly caused by varying assays and methodologies. Interestingly, while mean leptin levels are lower in AN subjects compared with constitutionally thin women, there is an overlap in individual levels between the two groups and therefore, they cannot be used to differentiate between these states.

The metabolic underpinning of eating disorders: A systematic review and meta-analysis of insulin sensitivity

BACKGROUND

A recent study reported a positive genetic correlation between anorexia nervosa and insulin sensitivity using data from genome-wide association studies. Epidemiological studies have, on the other hand, suggested that bulimia nervosa and binge-eating disorder are associated with decreased insulin sensitivity. The aim of this study was to conduct a systematic review and meta-analysis of insulin sensitivity across the spectrum of eating disorders.

METHODS

EMBASE, Medline, and PsycINFO were searched for all relevant studies published until January 2017, and retrieved studies were assessed for eligibility by two independent reviewers as per predefined inclusion criteria. The associations between eating disorder subtypes and insulin sensitivity were analysed separately. Individual effect sizes were standardized, and a meta-analysis was performed to calculate a pooled effect size using random effects.

RESULTS

Of 296 citations retrieved, 22 studies met the inclusion criteria, and 12 studies had appropriate data for meta-analysis. Using the random effects model, the pooled effect size (95% confidence interval) was 1.66 (0.79, 2.54) in people with anorexia nervosa (n = 340) and -0.57 (-0.80, -0.34) in people with bulimia nervosa (n = 120) and binge-eating disorders (n = 3241).

INTERPRETATION

Anorexia nervosa is associated with increased insulin sensitivity whilst bulimia nervosa and binge-eating disorders are associated with decreased insulin sensitivity. The possible mechanism underpinning these findings needs to be determined.

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 and Browning of White Adipose Tissue

Interest has been focused on differentiating anatomical, molecular, and physiological characteristics of the types of mammalian adipose tissues. White adipose tissue (WAT) and brown adipose tissue (BAT) are the two main forms of adipose tissue in humans. WAT functions as an endocrine organ and serves as a reservoir of energy in the form of triglycerides. The hormones released by WAT are called adipokines. BAT consists of a group of specialized cells with abundant uncoupling protein 1 (UCP1) in the inner mitochondrial membrane and also fulfills endocrine functions. Following the identification of functional (BAT) in human adults, there has been a great deal of interest in finding out how it is induced, its localization, and the mechanisms by which it regulates thermogenesis. Fibroblast growth factor 21 (FGF21) is a key regulator of the differentiation to brown adipocytes. The main mechanisms occur through enhancing UCP1 expression. In addition, following exposure to cold or exercise, FGF21 induces upregulation of local peroxisome proliferator-activated receptor gamma co-activator (PGC)-1-alfa and thus promotes thermogenesis in adipose tissue and skeletal muscle. FGF21 integrates several pathways allowing the regulation of human energy balance, glucose levels, and lipid metabolism. Such mechanisms and their clinical relevance are summarized in this review.

High serum levels of FGF21 are decreased in bipolar mania patients during psychotropic medication treatment and are associated with increased metabolism disturbance

Bipolar disorder (BD), a psychiatric illness, results partly as a side effect of psychotropic medications and presents a high risk of metabolic disturbance. Fibroblast growth factor 21 (FGF21) is as an important regulator in carbohydrate and lipid metabolism. In this study, we investigated the serum levels of FGF21 and analyzed its association with metabolic parameters in bipolar mania patients at pre- and post-treatment with psychotropic medications. Bipolar mania inpatients (n = 99) and healthy controls (n = 99) were included at baseline; the patients were followed up after four-week treatment. Serum levels of FGF21 and several metabolic parameters were measured by appropriate detection methods. We found that baseline serum FGF21 levels were significantly higher in bipolar manic patients when compared to that in controls. After four-week medication, FGF21 levels were found to be decreased in patients when compared to the baseline suggesting that FGF21 may be associated with the psychopathology of bipolar mania. Moreover, FGF21 levels were found to be negatively correlated with the serum triglycerides (TG), cholesterol (CHO), low-density lipoprotein cholesterol (LDL-C), apolipoprotein B (Apo B), glucose (Glu), and Body Mass Index (BMI). In addition, our data also indicates that FGF21 may monitor and/or prevent the metabolic abnormalities induced by psychotropic drugs.

Plasma fibroblast growth factor 21 levels increase with ectopic fat accumulation and its receptor levels are decreased in the visceral fat of patients with type 2 diabetes

BACKGROUND

Fibroblast growth factor 21 (FGF21) is a novel metabolic regulator that has beneficial effects on glucose and lipid metabolism. However, plasma FGF21 levels are paradoxically increased in type 2 diabetes mellitus (T2DM) and obesity, suggesting resistance to this ligand. FGF21 acts mainly on adipose tissue and ectopic fat accumulation is a typical feature in metabolic deterioration such as diabetes, metabolic syndrome, and cardiovascular disease.

OBJECTIVE

To investigate the relationship between FGF21 resistance and ectopic fat accumulation.

RESEARCH DESIGN AND METHODS

Subjects who underwent 64-slice multidetector CT (MDCT) were enrolled (n=190). Plasma FGF21 levels and MDCT data of ectopic fats at various sites were analyzed. Human visceral and subcutaneous fat tissues from abdominal and coronary artery bypass surgery were obtained. FGF21 receptor expression and postreceptor signaling in different fat deposits of both control and T2DM subjects were analyzed.

RESULTS

Plasma FGF21 levels were significantly associated with body mass index, triglyceride, homeostatic model assessment of insulin resistance, and Matsuda index. Plasma FGF21 levels were significantly higher in patients with T2DM than in the pre-diabetes and normal glucose tolerance groups. The ectopic fat phenotypes (visceral, epicardial, intrahepatic, and intramuscular fat) of T2DM were significantly higher than controls. Plasma FGF21 levels were elevated and exhibited a strong positive correlation with ectopic fat accumulation in T2DM. The expression of genes comprising the FGF21 signaling pathway was also lower in visceral fat than in subcutaneous fat in this disease.

CONCLUSIONS

Human FGF21 resistance in T2DM could result from increases in FGF21-resistant ectopic fat accumulation. Our study provides novel clinical evidence linking FGF21 resistance and T2DM pathogenesis.

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.

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.

Fibroblast growth factor 21: a regulator of metabolic disease and health span

Fibroblast growth factor 21 (FGF21) is a potent endocrine regulator with physiological effects on glucose and lipid metabolism and thus garners much attention for its translational potential for the management of obesity and related metabolic syndromes. FGF21 is mainly expressed in several metabolically active tissue organs, such as the liver, adipose tissue, skeletal muscle, and pancreas, with profound effects and therapeutic relevance. Emerging experimental and clinical data point to the demonstrated metabolic benefits of FGF21, which include, but are not limited to, weight loss, glucose and lipid metabolism, and insulin sensitivity. In addition, FGF21 also acts directly through its coreceptor β-klotho in the brain to alter light-dark cycle activity. In this review, we critically appraise current advances in understanding the physiological actions of FGF21 and its role as a biomarker of various metabolic diseases, especially type 2 diabetes mellitus. We also discuss the potentially exciting role of FGF21 in improving our health and prolonging our life span. This information will provide a fuller understanding for further research into FGF21, as well as providing a scientific basis for potentially establishing health care guidelines for this promising molecule.

Reduction in serum fibroblast growth factor-21 after gastric bypass is related to changes in hepatic fat content

BACKGROUND

Fibroblast growth factor 21 (FGF21) is elevated in obesity.

OBJECTIVES

We investigated the circulating level of FGF21 and the expression of FGF21, beta-klotho (KLB), and FGF receptor 1 (FGFR1) in adipose tissue in relation to weight, fat distribution, and Roux-en-Y gastric bypass (RYGB)-induced weight loss.

SETTING

The Department of Endocrinology at Aarhus University Hospital.

METHODS

Thirty-one obese patients were enrolled. Visceral adipose tissue volume measured by magnetic resonance imaging, hepatic fat content measured by magnetic resonance spectroscopy, and body composition measured by dual-energy x-ray absorbtiometry were determined at baseline and 12 months after RYGB. Fasting blood samples and subcutaneous and visceral adipose tissue samples were obtained. Moreover, 25 lean controls were enrolled.

RESULTS

FGF21 was significantly elevated in obese patients compared with lean patients (281±151 pg/mL versus 149±99 pg/mL, P<.05). RYGB-induced weight loss resulted in a smaller reduction in FGF21 (P = .08). However, a significant reduction was seen in obese patients with initially high FGF21 levels (42% reduction, P<.001). A significant association was found between FGF21 and hepatic fat content at baseline (r = 0.40, P<.05). Moreover, ΔFGF21 was significantly associated with Δhepatic fat content after RYGB (r = 0.39, P<.05). FGF21 mRNA was not detectable in AT from either lean or obese patients. KLB and FGFR1 were upregulated in AT in relation to obesity, and both were further increased 12 months after RYGB.

CONCLUSIONS

FGF21 is reduced in relation to weight loss in patients with initial high levels of FGF21 and this reduction is significantly associated with a reduction in hepatic fat content. Thus, changes in FGF21 after RYGB-induced weight loss are closely related to changes in liver fat content.

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.

Pancreatic Islet Responses to Metabolic Trauma

Carbohydrate, lipid, and protein metabolism are largely controlled by the interplay of various hormones, which includes those secreted by the pancreatic islets of Langerhans. While typically representing only 1% to 2% of the total pancreatic mass, the islets have a remarkable ability to adapt to disparate situations demanding a change in hormone release, such as peripheral insulin resistance. There are many different routes to the onset of insulin resistance, including obesity, lipodystrophy, glucocorticoid excess, and the chronic usage of atypical antipsychotic drugs. All of these situations are coupled to an increase in pancreatic islet size, often with a corresponding increase in insulin production. These adaptive responses within the islets are ultimately intended to maintain glycemic control and to promote macronutrient homeostasis during times of stress. Herein, we review the consequences of specific metabolic trauma that lead to insulin resistance and the corresponding adaptive alterations within the pancreatic islets.

Inside out: Bone marrow adipose tissue as a source of circulating adiponectin

The adipocyte-derived hormone adiponectin mediates beneficial cardiometabolic effects, and hypoadiponectinemia is a biomarker for increased metabolic and cardiovascular risk. Indeed, circulating adiponectin decreases in obesity and insulin-resistance, likely because of impaired production from white adipose tissue (WAT). Conversely, lean states such as caloric restriction (CR) are characterized by hyperadiponectinemia, even without increased adiponectin production from WAT. The reasons underlying this paradox have remained elusive, but our recent research suggests that CR-associated hyperadiponectinemia derives from an unexpected source: bone marrow adipose tissue (MAT). Herein, we elaborate on this surprising discovery, including further discussion of potential mechanisms influencing adiponectin production from MAT; additional evidence both for and against our conclusions; and observations suggesting that the relationship between MAT and adiponectin might extend beyond CR. While many questions remain, the burgeoning study of MAT promises to reveal further key insights into MAT biology, both as a source of adiponectin and beyond.

New adipokines

Adipose tissue is now widely recognized as "an organ" able to synthesize and secrete hundred factors collectively called adipokines. These secreted molecules exert pleiotropic actions, notably on the regulation of glucose and lipid metabolism, inflammation, reproduction, or angiogenesis. Over the past two decades, a considerable amount of work was performed on the two "star" adipokines, leptin and adiponectin, particularly because of their involvement in energy metabolism. The present review is focused on the three most recently discovered adipokines that are clearly emerging as important actors in metabolism: apelin, fibroblast growth factor-21, and neuroregulin-4. Moreover, given a number of clinical and experimental data, these three adipokines represent promising targets in the context of metabolic disorders associated with obesity.

Therapeutic potential of the endocrine fibroblast growth factors FGF19, FGF21 and FGF23

The endocrine fibroblast growth factors (FGFs), FGF19, FGF21 and FGF23, are critical for maintaining whole-body homeostasis, with roles in bile acid, glucose and lipid metabolism, modulation of vitamin D and phosphate homeostasis and metabolic adaptation during fasting. Given these functions, the endocrine FGFs have therapeutic potential in a wide array of chronic human diseases, including obesity, type 2 diabetes, cancer, and kidney and cardiovascular disease. However, the safety and feasibility of chronic endocrine FGF administration has been challenged, and FGF analogues and mimetics are now being investigated. Here, we discuss current knowledge of the complex biology of the endocrine FGFs and assess how this may be harnessed therapeutically.

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.

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

BACKGROUND

Anorexia nervosa (AN) is a psychiatric disorder characterized by self-induced starvation and low body weight. Women with AN have impaired bone formation, low bone mass and an increased risk of fracture. FGF-21 is a hormone secreted by the liver in starvation and FGF-21 transgenic mice have significant bone loss due to an uncoupling of bone resorption and bone formation. We hypothesized that FGF-21 may contribute to the low bone mass state of AN.

SUBJECTS AND METHODS

We studied 46 women: 20 with AN (median age [interquartile range]: 27.5 [25, 30.75] years) and 26 normal-weight controls (NWC) of similar age (25 [24, 28.5] years). We investigated associations between serum FGF-21 and 1) aBMD measured by dual energy X-ray absorptiometry, 2) parameters of bone microarchitecture in the distal radius and tibia measured by high-resolution peripheral quantitative CT and 3) bone strength, estimated by microfinite element analysis.

RESULTS

FGF-21 levels were similar in AN and NWC (AN: 33.1 [18.1, 117.0] pg/ml vs. NWC: 57.4 [23.8, 107.1] pg/ml; p = 0.54). There was a significant inverse association between log FGF-21 and trabecular number in the radius in both AN (R = -0.57, p < 0.01) and NWC (R=-0.53, p < 0.01) and a significant positive association between log FGF-21 and trabecular separation in the radius in AN (R = 0.50, p < 0.03) and NWC (R = 0.52, p < 0.01). Estimates of radial bone strength were inversely associated with log FGF-21 in AN (R = -0.50, p < 0.03 for both stiffness and failure load). There were no associations between FGF-21 and aBMD, cortical parameters or tibial parameters in the AN or NWC groups.

CONCLUSIONS

FGF-21 may be an important determinant of trabecular skeletal homeostasis in AN.

Serum fibroblast growth factor 21 levels are inversely associated with growth rates in infancy

BACKGROUND

Fibroblast growth factor 21 (FGF21) is a metabolic and growth regulator.

AIM

To investigate the role of FGF21 during growth in infancy.

METHODS

Blood samples for FGF21, leptin, insulin and glucose were collected from cord blood obtained from 95 preterm and term newborns (cross-sectional group), and at 6 and 12 months of life in 80 preterm and term infants (longitudinal group). Length and weight were measured at birth, 6 months, and 12 months.

RESULTS

From birth through 12 months of age, preterm infants' linear growth and weight gain were larger than those of term infants, irrespective of birth weight SDS. At birth and at 12 months, there was no difference in FGF21 levels between preterm and term infants; in contrast, at 6 months, serum FGF21 in term infants was significantly higher than that of preterm ones. In the 0-6-month period, in the whole longitudinal group, serum FGF21 was inversely correlated to the length change SDS, and such a significant inverse correlation persisted in the preterm-AGA group in the 6-12-month period. In addition, term infants who experienced length catch-up in the first 6 months of life exhibited lower serum FGF21 levels at 6 months, and those with length catch-up growth between 6 and 12 months had a greater decrease of serum FGF21 level in the same time period.

CONCLUSIONS

Our results indicate that FGF21 in infancy is inversely correlated with linear growth rate, thus suggesting that FGF21 is a negative regulator of human growth.

Fibroblast growth factor 21 is elevated in metabolically unhealthy obesity and affects lipid deposition, adipogenesis, and adipokine secretion of human abdominal subcutaneous adipocytes

OBJECTIVE

Serum concentrations of the hepatokine fibroblast growth factor (FGF) 21 are elevated in obesity, type-2 diabetes, and the metabolic syndrome. We asked whether FGF21 levels differ between subjects with metabolically healthy vs. unhealthy obesity (MHO vs. MUHO), opening the possibility that FGF21 is a cross-talker between liver and adipose tissue in MUHO. Furthermore, we studied the effects of chronic FGF21 treatment on adipocyte differentiation, lipid storage, and adipokine secretion.

METHODS

In 20 morbidly obese donors of abdominal subcutaneous fat biopsies discordant for their whole-body insulin sensitivity (hereby classified as MHO or MUHO subjects), serum FGF21 was quantified. The impact of chronic FGF21 treatment on differentiation, lipid accumulation, and adipokine release was assessed in isolated preadipocytes differentiated in vitro.

RESULTS

Serum FGF21 concentrations were more than two-fold higher in MUHO as compared to MHO subjects (457 ± 378 vs. 211 ± 123 pg/mL; p < 0.05). FGF21 treatment of human preadipocytes for the entire differentiation period was modestly lipogenic (+15%; p < 0.05), reduced the expression of key adipogenic transcription factors (PPARG and CEBPA, -15% and -40%, respectively; p < 0.01 both), reduced adiponectin expression (-20%; p < 0.05), markedly reduced adiponectin release (-60%; p < 0.01), and substantially increased leptin (+60%; p < 0.01) and interleukin-6 (+50%; p < 0.001) release.

CONCLUSIONS

The hepatokine FGF21 exerts weak lipogenic and anti-adipogenic actions and marked adiponectin-suppressive and leptin and interleukin-6 release-promoting effects in human differentiating preadipocytes. Together with the higher serum concentrations in MUHO subjects, our findings reveal FGF21 as a circulating factor promoting the development of metabolically unhealthy adipocytes.

Inflammatory cytokines and anorexia nervosa: A meta-analysis of cross-sectional and longitudinal studies

OBJECTIVE

Although inflammation is increasingly implicated in psychiatric disorders, less is known about its role in anorexia nervosa (AN), an illness with low body mass index (BMI).

METHODS

We performed a systematic PubMed literature search until 12/31/2013 and meta-analyzed cross-sectional and longitudinal studies comparing circulating pro- and anti-inflammatory cytokines between patients with anorexia nervosa (AN) and healthy controls (HCs) (1) before and (2) after weight gain, and (3) within AN patients before and after weight gain. Standardized mean differences (SMDs)± 95% confidence intervals (CIs) for results from ≥ 2 studies were calculated.

RESULTS

Of 999 initial hits, 22 studies with 924 participants (AN=512, HCs=412) were eligible. Compared to HCs, tumor necrosis factor (TNF)-alpha (SMD=0.35, 95%CI=0.09-0.61, p=0.008), interleukin (IL)1-beta (SMD=0.51, 95%CI=0.18-0.84, p=0.003), IL-6 (SMD=0.43, 95%CI=0.11-0.76, p=0.009), and TNF-receptor-II (SMD=0.42, 95%CI:0.07-0.78, p=0.02) were significantly elevated in AN, while C-reactive protein (SMD=-0.53, 95%CI=-.77, -0.28, p<0.0001) and IL-6 receptor (SMD=-0.85, 95%CI=-1.33, -0.36, p=0.0006) were significantly decreased. No differences were found for TNF-receptor I and TGF-β. Across a subset of eight longitudinal studies (AN=152, HCs=129), significant weight gain (baseline BMI=15.4 ± 1.5, endpoint BMI=18.2 ± 1.6, p<0.0001) was not associated with significant changes in TNF-α, IL-6 and IL1-β. However, after weight gain, IL-6 was not different anymore compared to HCs (SMD=0.06, 95%CI=-0.32, 0.45, p=0.75). In meta-regression, shorter illness duration (p=0.0008), but not younger age (p=0.71) significantly moderated greater IL-6 levels.

CONCLUSION

Despite abnormally low BMI, AN seems to be associated with increased inflammatory cytokines. Whether specific elevated cytokines represent trait or state markers of AN, and whether they could be treatment targets requires further study.

Endocrine FGFs: Evolution, Physiology, Pathophysiology, and Pharmacotherapy

The human fibroblast growth factor (FGF) family comprises 22 structurally related polypeptides that play crucial roles in neuronal functions, development, and metabolism. FGFs are classified as intracrine, paracrine, and endocrine FGFs based on their action mechanisms. Paracrine and endocrine FGFs are secreted signaling molecules by acting via cell-surface FGF receptors (FGFRs). Paracrine FGFs require heparan sulfate as a cofactor for FGFRs. In contrast, endocrine FGFs, comprising FGF19, FGF21, and FGF23, require α-Klotho or β-Klotho as a cofactor for FGFRs. Endocrine FGFs, which are specific to vertebrates, lost heparan sulfate-binding affinity and acquired a systemic signaling system with α-Klotho or β-Klotho during early vertebrate evolution. The phenotypes of endocrine FGF knockout mice indicate that they play roles in metabolism including bile acid, energy, and phosphate/active vitamin D metabolism. Accumulated evidence for the involvement of endocrine FGFs in human genetic and metabolic diseases also indicates their pathophysiological roles in metabolic diseases, potential risk factors for metabolic diseases, and useful biomarkers for metabolic diseases. The therapeutic utility of endocrine FGFs is currently being developed. These findings provide new insights into the physiological and pathophysiological roles of endocrine FGFs and potential diagnostic and therapeutic strategies for metabolic diseases.

Upregulation of hepatic bile acid synthesis via fibroblast growth factor 19 is defective in gallstone disease but functional in overweight individuals

BACKGROUND

Fibroblast growth factor 19 (FGF19) is an enteric hormone regulating bile acid de novo synthesis by sensing ileal bile acid flux. However, the role of FGF19 in cholelithiasis has not yet been elucidated and therefore is investigated in the present study.

METHODS

Total mRNA and protein were isolated from ileal biopsies and used for tissue expression analysis. FGF19, 7α-hydroxycholesterol (7α-OH-Chol), 27-hydroxycholesterol (27-OH-Chol), and different bile acids were determined in the blood samples.

RESULTS

FGF19 serum levels did not differ between gallstone carriers and controls but were significantly decreased in the overweight individuals (-32%, p = 0.0002), irrespective of gallstone status (normalweight to overweight controls -29%, p = 0.0017; normalweight to overweight gallstone carriers -44%, p = 0.0338), and correlated inversely with bodyweight (p < 0.0001, ρ = -0.3317). Compared to non-overweight controls, apical sodium-dependent bile acid transporter expression was significantly diminished in the non-overweight gallstone carriers (-42%, P mRNA = 0.0393; -52%, p protein = 0.0169) as well as in the overweight controls (-24%, P mRNA = 0.0148; -43%, p protein = 0.0017). FGF19 expression varied widely and was similar in all groups. A significant negative correlation was noted between 7α-OH-Chol, 27-OH-Chol, and FGF19 serum levels (p < 0.01; ρ7α-OH-Chol = -0.2155; ρ27-OH-Chol = -0.2144) in obesity.

CONCLUSION

Upregulation of hepatic bile acid synthesis via FGF 19 is defective in gallstone disease but functional in overweight individuals.

Irisin levels are lower in young amenorrheic athletes compared with eumenorrheic athletes and non-athletes and are associated with bone density and strength estimates

Irisin and FGF21 are novel hormones implicated in the “browning” of white fat, thermogenesis, and energy homeostasis. However, there are no data regarding these hormones in amenorrheic athletes (AA) (a chronic energy deficit state) compared with eumenorrheic athletes (EA) and non-athletes. We hypothesized that irisin and FGF21 would be low in AA, an adaptive response to low energy stores. Furthermore, because (i) brown fat has positive effects on bone, and (ii) irisin and FGF21 may directly impact bone, we hypothesized that bone density, structure and strength would be positively associated with these hormones in athletes and non-athletes. To test our hypotheses, we studied 85 females, 14–21 years [38 AA, 24 EA and 23 non-athletes (NA)]. Fasting serum irisin and FGF21 were measured. Body composition and bone density were assessed using dual energy X-ray absorptiometry, bone microarchitecture using high resolution peripheral quantitative CT, strength estimates using finite element analysis, resting energy expenditure (REE) using indirect calorimetry and time spent exercising/week by history. Subjects did not differ for pubertal stage. Fat mass was lowest in AA. AA had lower irisin and FGF21 than EA and NA, even after controlling for fat and lean mass. Across subjects, irisin was positively associated with REE and bone density Z-scores, volumetric bone mineral density (total and trabecular), stiffness and failure load. FGF21 was negatively associated with hours/week of exercise and cortical porosity, and positively with fat mass and cortical volumetric bone density. Associations of irisin (but not FGF21) with bone parameters persisted after controlling for potential confounders. In conclusion, irisin and FGF21 are low in AA, and irisin (but not FGF21) is independently associated with bone density and strength in athletes.

FGF21 as a Hepatokine, Adipokine, and Myokine in Metabolism and Diseases

Fibroblast growth factor (FGF) family members are mostly secreted as signaling proteins with diverse functions in development and metabolism. FGF21 is a unique FGF with metabolic, but not proliferative activities. FGF21 is mostly induced by different kinds of stress and acts though FGF receptor 1c with β-Klotho as a cofactor in an endocrine or, in parts, autocrine/paracrine manner. Hepatic FGF21 directly acts on white adipocytes to inhibit lipolysis and acts through the brain to increase systemic glucocorticoid levels and suppress physical activity in response to starvation. It also protects against dioxin toxicity. Adipocytic FGF21 induces the browning of white adipose tissue (WAT) and activates brown adipocytes in response to cold exposure. It also acts as an upstream effector of adiponectin in white adipocytes. Myocytic FGF21 protects against diet-induced obesity and insulin resistance, induces the browning of WAT, and protects against cardiac hypertrophy. In addition, Fgf21 polymorphisms are possibly related with metabolic diseases and FGF21 are biomarker of metabolic diseases. These findings indicate that FGF21 plays roles as a hepatokine, adipokine, and myokine in metabolism, injury protection, and diseases.

Serum concentrations of fibroblast growth factors 19 and 21 in women with gestational diabetes mellitus: association with insulin resistance, adiponectin, and polycystic ovary syndrome history

BACKGROUND

Fibroblast growth factor 19 (FGF19) and FGF21 are considered to be novel adipokines that improve glucose tolerance and insulin sensitivity. In the current study, we investigated serum FGF19 and FGF21 levels in patients with gestational diabetes mellitus (GDM) and explored their relationships with anthropometric and endocrine parameters.

METHOD

Serum FGF19 and FGF21 levels were determined by enzyme-linked immunosorbent assay (ELISA) in patients with GDM (n = 30) and healthy pregnant controls (n = 60) matched for maternal and gestational age. Serum FGF19 and FGF21 levels were correlated with anthropometric, metabolic, and endocrine parameters.

RESULTS

Circulating levels of FGF19 were significantly reduced in patients with GDM relative to healthy pregnant subjects, whereas FGF21 levels were increased in GDM patients. Serum FGF19 levels independently and inversely correlated with insulin resistance (increased homeostasis model assessment of insulin resistance, HOMA-IR) and were positively related to serum adiponectin in both groups. In contrast, serum FGF21 levels independently and positively correlated with insulin resistance and serum triglycerides and were inversely related to serum adiponectin. In addition, in the combined population of both groups, those women with preconception polycystic ovary syndrome (PCOS) history had the lowest levels of FGF19, which were significantly lower than those in GDM patients without PCOS history and those in controls without PCOS history.

CONCLUSIONS

Circulating FGF19 levels are reduced in GDM patients, in contrast with FGF21 levels. Both serum FGF19 and FGF21 levels are strongly related to insulin resistance and serum levels of adiponectin. Considering the different situation between FGF19 and FGF21, we suggest that reduced serum FGF19 levels could be involved in the pathophysiology of GDM, while increased serum FGF21 levels could be in a compensatory response to this disease.

Circulating levels of FGF-21 in obese youth: associations with liver fat content and markers of liver damage

OBJECTIVE

Fibroblast growth factor (FGF)-21 is highly expressed in the liver and regulates glucose and lipid metabolism in rodents. The effects of obesity and fatty liver on circulating FGF-21 levels have been described mainly in adults. Herein, we measured plasma FGF-21 levels in lean and obese adolescents with low and high hepatic fat content (HFF% <5.5% and HFF% ≥ 5.5%, respectively) and explored their relationship with hepatic fat content, measures of hepatic apoptosis, and insulin sensitivity.

METHODS

A total of 217 lean and obese adolescents with both low and high HFF% (lean = 31; obese low HFF% = 107; and obese high HFF% = 79) underwent an oral glucose tolerance test, a fast gradient magnetic resonance imaging to measure the %HFF and abdominal fat distribution. Cytokeratin 18 levels were measured as a biomarker of liver apoptosis. A subset of adolescents underwent a 2-step hyperinsulinemic-euglycemic clamp, and a liver biopsy (N = 14), to assess insulin sensitivity and steatohepatitis, respectively.

RESULTS

Compared to controls, FGF-21 levels were higher in obese youth, especially in those with high HFF (P < .001). FGF-21 significantly correlated with adiposity indexes (P < .001), visceral fat (r² = 0.240, P < .001), hepatic fat content (r² = 0.278, P < .001), cytokeratin 18 (r² = 0.217, P < .001), and alanine aminotransferase (r² = .164, P < .001). In subjects with steatoheaptitis, FGF-21 levels significantly correlated with the nonalcoholic fatty liver disease activity score (r² = 0.27, P = .04). Stepwise regression analysis indicated that these relationships are independent of body mass index, visceral fat, and insulin sensitivity. An inverse correlation was documented with insulin, hepatic resistance indexes, and adipose resistance indexes, which disappeared after adjusting for hepatic fat content.

CONCLUSIONS

Plasma FGF-21 levels are increased in obese adolescents, particularly in those with fatty liver. FGF-21 concentrations significantly and independently correlate with hepatic fat content and markers of hepatic apoptosis in obese youths.

Laparoscopic sleeve gastrectomy differentially affects serum concentrations of FGF-19 and FGF-21 in morbidly obese subjects

OBJECTIVE

Fibroblast growth factor (FGF)-19 and FGF-21 are novel metabolic regulators that improve insulin resistance and obesity in rodents. The aim of the study was to assess the effects of laparoscopic sleeve gastrectomy (LSG) on serum concentrations of FGF-19 and FGF-21 along with circulating bile acids and other relevant hormonal and biochemical parameters.

DESIGN AND METHODS

Seventeen females with obesity undergoing LSG and 15 lean healthy females were included into the study. Anthropometric and biochemical parameters, serum concentrations of FGF-19 and -21, insulin, adiponectin, leptin, C-reactive protein, resistin, amylin (total), ghrelin (active), glucagon-like peptide 1 (GLP-1, active), glucose-dependent insulinotropic peptide (GIP, total), peptide YY (PYY, total), pancreatic polypeptide (PP), and bile acids, and mRNA expression of selected adipokines and inflammatory markers in bioptic samples of subcutaneous fat were assessed at baseline and 6, 12, and 24 months after LSG.

RESULTS

LSG markedly decreased body weight, BMI, waist circumference, and insulin levels and improved systemic inflammation and lipid levels. FGF-19 concentrations increased and FGF-21 concentrations decreased after LSG along with increased adiponectin and decreased leptin, amylin, and ghrelin levels. GLP-1, GIP, PP, and circulating bile acids were not affected by LSG. PYY decreased significantly 24 months after surgery only. mRNA expression analysis in subcutaneous fat showed markedly reduced proinflammatory state.

CONCLUSIONS

Our results indicate that increased FGF-19 and decreased ghrelin concentrations could have partially contributed to the improvement of systemic inflammation and some metabolic parameters after LSG, while changes of FGF-21 are rather secondary because of weight loss.

Fibroblast growth factor 21: a novel biomarker for human muscle-manifesting mitochondrial disorders

INTRODUCTION

Diagnosis of mitochondrial disorders is challenging, because of their highly variable clinical manifestations and age-of-onset and the shortage of specific diagnostic tools. Recent molecular studies have found that serum fibroblast growth factor 21 (FGF21) has potential to be a biomarker for muscle-manifesting mitochondrial disease, as well as for follow-up of disease progression and effect of intervention.

AREAS COVERED

Serum FGF21 as a biomarker is compared to conventional serum diagnostic tools for mitochondrial disorders.

EXPERT OPINION

Mitochondrial disorders are a large group of different progressive disorders, with the age-of-onset from neonatal life to late adulthood, and symptoms originating from any organ system but sharing an underlying cause of mitochondrial dysfunction. The prevalence of these disorders is about 1:2000, varying somewhat between different countries. Serum diagnostic tools include lactate, pyruvate, their ratio, creatine kinase and amino acids. However, none of these markers are both sensitive and specific. Increased levels of FGF21 cytokine were recently found in the serum of patients, who have a muscle-manifesting mitochondrial disease, thus providing a promising, novel, sensitive and specific biomarker for these disorders.

Fibroblast growth factor 21 levels in young healthy females display day and night variations and are increased in response to short-term energy deprivation through a leptin-independent pathway

OBJECTIVE

Fibroblast growth factor (FGF)-21 is an endocrine factor with potent metabolic effects. Its day-night patterns of secretion and/or its physiological response to energy deprivation and relationship to free fatty acids (FFAs) and/or leptin remain to be fully elucidated. We aim to elucidate day-night pattern of FGF-21 levels and its relationship to FFA, to assess whether energy deprivation alters its circulating patterns, and to examine whether leptin may mediate these changes.

RESEARCH DESIGN AND METHODS

Six healthy lean females were studied for 72 h in a cross-over interventional study under three different conditions: on isocaloric diet and in a fasting state with administration of either placebo or metreleptin in physiological replacement doses. Blood samples were obtained hourly from 8:00 a.m. on day 4 until 8:00 a.m. on day 5.

RESULTS

FGF-21 exhibited day-night variation pattern during the isocaloric fed state. Fasting significantly increased FGF-21 levels (P < 0.01) via a leptin-independent pathway. Day-night variation pattern in the fed state was lost on fasting. Leptin replacement in the hypoleptinemic state restored approximate entropy of FGF-21 time series but did not alter circulating levels. FGF-21 levels were closely cross-correlated with FFA levels in all three states.

CONCLUSIONS

A day-night variation in the levels of FGF-21 exists in young lean females in the fed state. Energy deprivation increases FGF-21 levels via a leptin-independent pathway. The interaction between FGF-21 and starvation-induced lipolysis, as indicated by its close cross-correlations with FFA in both fed state and energy deprivation, needs to be studied further.

Fibroblast growth factor 21 as an emerging metabolic regulator: clinical perspectives

Fibroblast growth factor 21 (FGF21), a metabolic hormone predominantly produced by the liver, is also expressed in adipocytes and the pancreas. It regulates glucose and lipid metabolism through pleiotropic actions in these tissues and the brain. In mice, fasting leads to increased PPAR-α mediated expression of FGF21 in the liver where it stimulates gluconeogenesis, fatty acid oxidation, and ketogenesis, as an adaptive response to fasting and starvation. In the fed state, FGF21 acts as an autocrine factor in adipocytes, regulating the activity of PPAR-γ through a feed-forward loop mechanism. Administration of recombinant FGF21 has been shown to confer multiple metabolic benefits on insulin sensitivity, blood glucose, lipid profile and body weight in obese mice and diabetic monkeys, without mitogenic or other side effects. Such findings highlight the potential role of FGF21 as a therapeutic agent for obesity-related medical conditions. However, in human studies, high circulating FGF21 levels are found in obesity and its related cardiometabolic disorders including the metabolic syndrome, type 2 diabetes, non-alcoholic fatty liver disease and coronary artery disease. These findings may indicate the presence of FGF21 resistance or compensatory responses to the underlying metabolic stress, and imply the need for supraphysiological doses of FGF21 to achieve therapeutic efficacy. On the other hand, serum FGF21 has been implicated as a potential biomarker for the early detection of these cardiometabolic disorders. This review summarizes recent developments in the understanding of FGF21, from physiological and clinical perspectives.

Dysfunctions of leptin, ghrelin, BDNF and endocannabinoids in eating disorders: beyond the homeostatic control of food intake

A large body of literature documents the occurrence of alterations in the physiology of both central and peripheral modulators of appetite in acute patients with anorexia nervosa (AN) and bulimia nervosa (BN). Until more recently the role of most of the appetite modulators in the control of eating behavior was conceptualized solely in terms of their influence on homeostatic control of energy balance. However, it is becoming more and more evident that appetite modulators also affect the non-homeostatic cognitive, emotional and rewarding component of food intake as well as non food-related reward, and, recently, AN and BN have been pathophysiologically linked to dysfunctions of reward mechanisms. Therefore, the possibility exists that observed changes in appetite modulators in acute AN and BN may represent not only homeostatic adaptations to malnutrition, but also contribute to the development and/or the maintenance of aberrant non-homeostatic behaviors, such as self-starvation and binge eating. In the present review, the evidences supporting a role of leptin, ghrelin, brain-derived neurotrophic factor and endocannabinoids in the homeostatic and non-homeostatic dysregulations of patients with AN and BN will be presented. The reviewed literature is highly suggestive that changes in the physiology of these modulators may play a pivotal role in the pathophysiology of eating disorders by providing a possible link between motivated behaviors, reward processes, cognitive functions and energy balance.

Increased responses to the actions of fibroblast growth factor 21 on energy balance and body weight in a seasonal model of adiposity

The present study aimed to investigate the actions of fibroblast growth factor 21 (FGF21) on energy balance in a natural model of relative fatness, the Siberian hamster. Hamsters were studied under long days (LD) to promote weight gain, or short days to induce weight loss, and treated with rhFGF21 (3 mg/kg/day) via s.c. minipumps for 14 days. On days 7-9, detailed assessments of ingestive behaviour, metabolic gas exchange and locomotor activity were made. FGF21 caused substantial (P < 0.0001) weight loss in the fat LD state but not in the lean SD state: at the end of the study, FGF21-treated hamsters in LD lost 18% of body weight compared to vehicle controls, which is comparable to the natural body weight loss observed in SD. Epididymal fat pads, a correlate of total carcass fat content, were reduced by 19% in FGF21 treated hamsters in LD, whereas no difference was found in SD. Body weight loss in LD was associated with a reduction in food intake (P < 0.001) and a decreased respiratory exchange ratio (P < 0.001), indicating increased fat oxidation. Treatment with FGF21 maintained the normal nocturnal increase in oxygen consumption and carbon dioxide production into the early light phase in hamsters in LD, indicating increased energy expenditure, although locomotor activity was unaffected. These data suggest a greater efficacy of FGF21 in hamsters in LD compared to those in SD, which is consistent with both the peripheral and possibly central actions of FGF21 with respect to promoting a lean phenotype. The observed differences in FGF21 sensitivity may relate to day length-induced changes in adipose tissue mass.

Growth hormone level at admission and its evolution during refeeding are predictive of short-term outcome in restrictive anorexia nervosa

The growth hormone (GH)–insulin-like growth factor-1 (IGF-1) axis is dramatically altered in patients with anorexia nervosa (AN). The aim of the present study was to investigate whether GH and IGF-1 could be predictors of outcome in patients with a restrictive form of AN. Blood levels of GH, IGF-1, adipocytokines, ghrelin, insulin, glucose, and sex and thyroid hormones were measured in eleven women inpatients with AN and in ten healthy women controls. Three stages were compared during refeeding: admission (T0), when BMI reached 16 kg/m2 (T1) and at discharge when BMI reached 17.5 kg/m2 (T2). Clinical status was assessed 6 months after discharge from hospital (T3), and remission was defined by the maintenance of a BMI > or = 17.5 kg/m2. AN patients in remission (AN-R; n 6) had significantly higher GH levels at admission than those who relapsed (AN-NR; n 5) (P < 0.05). During refeeding (delta = T2 - T0), the AN-R group differed from the AN-NR group only by both GH level decrease (P < 0.05) and BMI increase (P < 0.05). In multiple regression analysis, delta GH was associated negatively and significantly and delta leptin and delta body fat mass levels were associated positively and significantly with BMI at T3 and explained 88% of its variability (r2 0.88, P < 0.05). The present study suggests that a low GH level at admission and the absence of its decrease after weight recovery could predict short-term relapse in women suffering from a restrictive form of AN.

Biological role, clinical significance, and therapeutic possibilities of the recently discovered metabolic hormone fibroblastic growth factor 21

Fibroblast growth factor 21 (FGF21), a 181 amino acid circulating protein, is a member of the FGF superfamily, with relevant metabolic actions. It acts through the interaction with specific FGF receptors and a cofactor called β-Klotho, whose expression is predominantly detected in metabolically active organs. FGF21 stimulates glucose uptake in adipocytes via the induction of glucose transporter-1. This action is additive and independent of insulin. β-Cell function and survival are preserved, and glucagon secretion is reduced by this protein, thus decreasing hepatic glucose production and improving insulin sensitivity. Lipid profile has been shown to be improved by FGF21 in several animal models. FGF21 increases energy expenditure in rodents and induces weight loss in diabetic nonhuman primates. It also exerts favorable effects on hepatic steatosis and reduces tissue lipid content in rodents. Adaptive metabolic responses to fasting, including stimulation of ketogenesis and fatty acid oxidation, seem to be partially mediated by FGF21. In humans, serum FGF21 concentrations have been found elevated in insulin-resistant states, such as impaired glucose tolerance and type 2 diabetes. FGF21 levels are correlated with hepatic insulin resistance index, fasting blood glucose, HbA1c, and blood glucose after an oral glucose tolerance test. A relationship between FGF21 levels and long-term diabetic complications, such as nephropathy and carotid atheromatosis, has been reported. FGF21 levels decreased in diabetic patients after starting therapy with insulin or oral agents. Increased FGF21 serum levels have also been found to be associated with obesity. In children, it is correlated with BMI and leptin levels, whereas in adults, FGF21 levels are mainly related to several components of the metabolic syndrome. Serum FGF21 levels have been found to be elevated in patients with ischemic heart disease. In patients with renal disease, FGF21 levels exhibited a progressive increase as renal function deteriorates. Circulating FGF21 levels seem to be related to insulin resistance and inflammation in dialysis patients. In summary, FGF21 is a recently identified hormone with antihyperglycemic, antihyperlipidemic, and thermogenic properties. Direct or indirect potentiation of its effects might be a potential therapeutic target in insulin-resistant states.

Metabolic actions of fibroblast growth factor 21

PURPOSE OF REVIEW

FGF21 has emerged as a hormone involved in energy homeostasis. A large number of recent reports have expanded the role of FGF21 from a response factor to prolonged fasting to a key hormone that regulates free fatty acid (FFAs) levels. The therapeutic role of recombinant human FGF21 for type 2 diabetes and dyslipidemia is under study.

RECENT FINDINGS

Recent evidence suggests that supraphysiological concentrations of FFAs induce FGF21 secretion (i.e., starvation and intense physical activity) through the peroxisome proliferator-activated receptor alpha (PPARα) pathway. The rise in FGF21 levels is aimed at improving energy production (ketogenesis) and utilization (oxidation) of FFAs. FGF21 increment may protect against chronic exposure to high concentrations of FFAs, which causes lipotoxicity in muscle, pancreas, and liver. In addition, FGF21 induces appetite and inhibits growth, probably as part of the adaptive starvation response. The autocrine function of FGF21 in adipose tissue increases PPARγ activity and glucose uptake. Increased plasma FGF21 levels have been found in insulin resistance states in humans. However, the reason for this rise in FGF21 values is still under study.

SUMMARY

We propose that FGF21 serves as a defense mechanism against supraphysiological concentrations of FFAs. In addition, FGF21 might have a therapeutic indication in humans.