Various oscillation patterns of serum fibroblast growth factor 21 concentrations in healthy volunteers

Circadian Regulation of Endocrine Fibroblast Growth Factors on Systemic Energy Metabolism

The circadian clock is an endogenous biochemical timing system that coordinates the physiology and behavior of organisms to earth's ∼24-hour circadian day/night cycle. The central circadian clock synchronized by environmental cues hierarchically entrains peripheral clocks throughout the body. The circadian system modulates a wide variety of metabolic signaling pathways to maintain whole-body metabolic homeostasis in mammals under changing environmental conditions. Endocrine fibroblast growth factors (FGFs), namely FGF15/19, FGF21, and FGF23, play an important role in regulating systemic metabolism of bile acids, lipids, glucose, proteins, and minerals. Recent evidence indicates that endocrine FGFs function as nutrient sensors that mediate multifactorial interactions between peripheral clocks and energy homeostasis by regulating the expression of metabolic enzymes and hormones. Circadian disruption induced by environmental stressors or genetic ablation is associated with metabolic dysfunction and diurnal disturbances in FGF signaling pathways that contribute to the pathogenesis of metabolic diseases. Time-restricted feeding strengthens the circadian pattern of metabolic signals to improve metabolic health and prevent against metabolic diseases. Chronotherapy, the strategic timing of medication administration to maximize beneficial effects and minimize toxic effects, can provide novel insights into linking biologic rhythms to drug metabolism and toxicity within the therapeutical regimens of diseases. Here we review the circadian regulation of endocrine FGF signaling in whole-body metabolism and the potential effect of circadian dysfunction on the pathogenesis and development of metabolic diseases. We also discuss the potential of chrononutrition and chronotherapy for informing the development of timing interventions with endocrine FGFs to optimize whole-body metabolism in humans. SIGNIFICANCE STATEMENT: The circadian timing system governs physiological, metabolic, and behavioral functions in living organisms. The endocrine fibroblast growth factor (FGF) family (FGF15/19, FGF21, and FGF23) plays an important role in regulating energy and mineral metabolism. Endocrine FGFs function as nutrient sensors that mediate multifactorial interactions between circadian clocks and metabolic homeostasis. Chronic disruption of circadian rhythms increases the risk of metabolic diseases. Chronological interventions such as chrononutrition and chronotherapy provide insights into linking biological rhythms to disease prevention and treatment.

Metabolic Stress Index Including Mitochondrial Biomarker for Noninvasive Diagnosis of Hepatic Steatosis

BACKGROUND

Mitochondrial dysfunction with oxidative stress contributes to nonalcoholic fatty liver disease (NAFLD) progression. We investigated the steatosis predictive efficacy of a novel non-invasive diagnostic panel using metabolic stress biomarkers.

METHODS

Altogether, 343 subjects who underwent magnetic resonance imaging-based liver examinations from a population-based general cohort, and 41 patients enrolled in a biopsy-evaluated NAFLD cohort, participated in the development and validation groups, respectively. Serologic stress biomarkers were quantitated by enzyme-linked immunosorbent assay.

RESULTS

Multivariate regression showed that waist-to-hip ratio, fibroblast growth factor (FGF) 21, FGF19, adiponectin-to-leptin ratio, insulin, albumin, triglyceride, total-cholesterol, and alanine-aminotransferase were independent predictors of steatosis (rank-ordered by Wald). The area under receiver-operator characteristics curve [AUROC (95%CI)] of the metabolic stress index for steatosis (MSI-S) was 0.886 (0.85-0.92) and 0.825 (0.69-0.96) in development and validation groups, respectively. MSI-S had higher diagnostic accuracy (78.1%-81.1%) than other steatosis indices. MSI-S notably differentiated steatosis severities, while other indices showed less discrimination.

CONCLUSION

MSI-S, as a novel non-invasive index, based on mitochondrial stress biomarker FGF21 effectively predicted steatosis. Furthermore, MSI-S may increase the population that could be excluded from further evaluation, reducing unnecessary invasive investigations more effectively than other indices.

Acute sleep loss alters circulating fibroblast growth factor 21 levels in humans: A randomised crossover trial

The hormone fibroblast growth factor 21 (FGF21) modulates tissue metabolism and circulates at higher levels in metabolic conditions associated with chronic sleep-wake disruption, such as type 2 diabetes and obesity. In the present study, we investigated whether acute sleep loss impacts circulating levels of FGF21 and tissue-specific production, and response pathways linked to FGF21. A total of 15 healthy normal-weight young men participated in a randomised crossover study with two conditions, sleep loss versus an 8.5-hr sleep window. The evening before each intervention, fasting blood was collected. Fasting, post-intervention morning skeletal muscle and adipose tissue samples underwent quantitative polymerase chain reaction and DNA methylation analyses, and serum FGF21 levels were measured before and after an oral glucose tolerance test. Serum levels of FGF21 were higher after sleep loss compared with sleep, both under fasting conditions and following glucose intake (~27%-30%, p = 0.023). Fasting circulating levels of fibroblast activation protein, a protein which can degrade circulating FGF21, were not altered by sleep loss, whereas DNA methylation in the FGF21 promoter region increased only in adipose tissue. However, even though specifically the muscle exhibited transcriptional changes indicating adverse alterations to redox and metabolic homeostasis, no tissue-based changes were observed in expression of FGF21, its receptors, or selected signalling targets, in response to sleep loss. In summary, we found that acute sleep loss resulted in increased circulating levels of FGF21 in healthy young men, which may occur independent of a tissue-based stress response in metabolic peripheral tissues. Further studies may decipher whether changes in FGF21 signalling after sleep loss modulate metabolic outcomes associated with sleep or circadian disruption.

Single-Arm 8-Week Ad Libitum Self-Prepared Paleo Diet Reduces Cardiometabolic Disease Risk Factors in Overweight Adults

The paleo diet is popular among the general population due to promoted weight loss and disease prevention benefits. We examined the effectiveness of a self-administered paleo diet in improving cardiometabolic disease risk factors. Overweight, physically inactive but otherwise healthy adults (males = 4, females = 3, age 32.7 ± 4.9 years, body mass index [BMI] 29.4 ± 2.4 kg/m²) habitually eating a traditional Western diet (1853.4 ± 441.2 kcal; 34.0% carbohydrate; 41.4% fat; 19.2% protein) completed an ad libitum self-administered paleo diet for 8 weeks. Height, weight, blood pressure, and a fasting blood sample were collected pre- and post-paleo dietary intervention. Blood samples were analyzed for fasting cardiometabolic disease biomarkers-including brain-derived neurotropic factor (BDNF), fibroblast growth factor (FGF) 21, and leptin. After 8 weeks, body mass (-5.3 kg, P = .008), BMI (-1.7 kg/m², P = .002), serum leptin (-56.2%, P = .012), serum FGF21 (-26.7%, P = .002), and serum BDNF (-25.8%, P = .045) significantly decreased. Systolic and diastolic blood pressure were unchanged following the paleo dietary intervention (P > .05). Average energy intake (-412.6 kcal, P = .016) significantly decreased with the paleo dietary intervention mostly due to a reduction in carbohydrate consumption (-69.2 g; P = .003). An 8-week self-administered paleo dietary intervention was effective in improving cardiometabolic disease risk factors in a healthy, physically inactive overweight adult population.

Measuring myokines with cardiovascular functions: pre-analytical variables affecting the analytical output

In the last few years, a growing number of molecules have been associated to an endocrine function of the skeletal muscle. Circulating myokine levels, in turn, have been associated with several pathophysiological conditions including the cardiovascular ones. However, data from different studies are often not completely comparable or even discordant. This would be due, at least in part, to the whole set of situations related to the preparation of the patient prior to blood sampling, blood sampling procedure, processing and/or store. This entire process constitutes the pre-analytical phase. The importance of the pre-analytical phase is often not considered. However, in routine diagnostics, the 70% of the errors are in this phase. Moreover, errors during the pre-analytical phase are carried over in the analytical phase and affects the final output. In research, for example, when samples are collected over a long time and by different laboratories, a standardized procedure for sample collecting and the correct procedure for sample storage are acknowledged. In this review, we discuss the pre-analytical variables potentially affecting the measurement of myokines with cardiovascular functions.

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.

Response of fibroblast growth factor 21 to meal intake and insulin infusion in patients on maintenance haemodialysis

OBJECTIVE

To investigate the response of serum fibroblast growth factor 21 (FGF21) to a meal and to insulin infusion in haemodialysis (HD) patients.

DESIGN AND PATIENTS

Meal study: in a crossover design, 12 nondiabetic HD patients were randomly assigned to: (1) a non-HD day with one meal served, (2) a HD day with one meal served during HD and (3) a HD day with two meals served during and after HD, respectively. Twelve healthy controls participated in an experiment identical to the non-HD day. Insulin infusion study: in a crossover design, 11 nondiabetic HD patients were randomly assigned to receive a 4-h HD session with either: (1) no infusion, (2) glucose infusion or (3) glucose-insulin infusion. A meal was served 2 h before HD start.

RESULTS

Meal study: serum FGF21 was 23-fold higher in HD patients than controls (P < 0·001). Postprandial FGF21 decreased on all four study days (P < 0·006), but the relative reductions from baseline were significantly greater in controls (P < 0·008). Postprandial changes in FGF21 were inversely related with triglycerides (P = 0·042) and positively related with insulin-like growth factor binding protein-1 (IGFBP-1) (P < 0·001). Serum FGF21 was only associated with changes in adiponectin (P = 0·001) and free fatty acids (P = 0·04) in the healthy controls. Insulin infusion study: as compared with no infusion, glucose and glucose-insulin infusion prevented the postprandial decrease in FGF21 and resulted in higher FGF21 concentrations by up to 25% (P = 0·003).

CONCLUSIONS

Serum FGF21 was highly elevated in HD patients but the response of serum FGF21 to meal intake and insulin infusion seemed to be intact. Our results indicate that FGF21 may play an important role in short-term metabolic homoeostasis.

Circulating fibroblast growth factors as metabolic regulators--a critical appraisal

The circulating FGFs are a new group of proteins believed to function as classic hormones. With emphasis on human metabolism, we critically review current data, and propose that--although a number of questions remain--circulating FGF23 is pivotal in the control of phosphate and vitamin D metabolism, and may have additional systemic effects, particularly in chronic kidney disease; that FGF19 signaling is important for the regulation of bile acid metabolism, whereas its physiological role in promoting glucose and lipid metabolism is less well understood; and that the physiological role of circulating FGF21 in metabolic homeostasis warrants further investigation.

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.