Fibroblast Growth Factor 21 as a Marker of Prediabetes in Patients with Non-alcoholic Fatty Liver Disease

Fibroblast growth factor 21: An emerging pleiotropic regulator of lipid metabolism and the metabolic network

Fibroblast growth factor 21 (FGF21) was originally identified as an important metabolic regulator which plays a crucial physiological role in regulating a variety of metabolic parameters through the metabolic network. As a novel multifunctional endocrine growth factor, the role of FGF21 in the metabolic network warrants extensive exploration. This insight was obtained from the observation that the FGF21-dependent mechanism that regulates lipid metabolism, glycogen transformation, and biological effectiveness occurs through the coordinated participation of the liver, adipose tissue, central nervous system, and sympathetic nerves. This review focuses on the role of FGF21-uncoupling protein 1 (UCP1) signaling in lipid metabolism and how FGF21 alleviates non-alcoholic fatty liver disease (NAFLD). Additionally, this review reveals the mechanism by which FGF21 governs glucolipid metabolism. Recent research on the role of FGF21 in the metabolic network has mostly focused on the crucial pathway of glucolipid metabolism. FGF21 has been shown to have multiple regulatory roles in the metabolic network. Since an adequate understanding of the concrete regulatory pathways of FGF21 in the metabolic network has not been attained, this review sheds new light on the metabolic mechanisms of FGF21, explores how FGF21 engages different tissues and organs, and lays a theoretical foundation for future in-depth research on FGF21-targeted treatment of metabolic diseases.

Association of hepatokines with markers of endothelial dysfunction and vascular reactivity in obese adolescents

OBJECTIVES

Obesity-induced insulin resistance (IR) is known to influence hepatic cytokines (hepatokines), including fibroblast growth factor (FGF-21), fetuin-A, and chemerin. This study aimed to investigate the association between hepatokines and markers of endothelial dysfunction and vascular reactivity in obese adolescents.

METHODS

A total of 45 obese adolescents were categorized into three groups based on glucose tolerance: normal glucose tolerance (NGT), prediabetes (PD), and type 2 diabetes (T2D). We examined the relationships between FGF-21, fetuin-A, and chemerin with endothelial markers (plasminogen activator inhibitor-1 [PAI-1], intercellular adhesion molecule-1 [ICAM-1], and vascular cell adhesion marker-1 [VCAM-1]) and vascular surrogates (brachial artery reactivity testing [BART] and peak reactive hyperemia [PRH]).

RESULTS

Obese adolescents (age 16.2±1.2 years; 62 % female, 65 % Hispanic) with NGT (n=20), PD (n=14), and T2D (n=11) had significant differences between groups in BMI; waist-hip ratio (p=0.05), systolic BP (p=0.008), LDL-C (p=0.02), PAI-1 (p<0.001). FGF-21 pg/mL (mean±SD: NGT vs. PD vs. T2D 54±42; 266±286; 160±126 p=0.006) and fetuin-A ng/mL (266±80; 253±66; 313±50 p=0.018), were significantly different while chemerin ng/mL (26±5; 31±10; 28±2) did not significantly differ between the groups. Positive correlations were found between chemerin and both PAI-1 (r=0.6; p=0.05) and ICAM-1 (r=0.6; p=0.05), FGF-21 and PAI-1 (r=0.6; p<0.001), and fetuin-A with TNFα (r=-0.4; p=0.05). Negative correlations were found between chemerin and PRH (r= -0.5; p=0.017) and fetuin-A and PRH (r=-0.4; p=0.05).

CONCLUSIONS

In our cohort, IR predicted higher FGF-21 levels suggesting a linear relationship may exist between the two parameters. Hepatokines can augment alterations in the microvascular milieu in obese adolescents as demonstrated by their associations with the markers PAI-1, ICAM-1, and PRH.

Phenotyping obesity: A focus on metabolically healthy obesity and metabolically unhealthy normal weight

Over the past 4 decades, research has shown that having a normal body weight does not automatically imply preserved metabolic health and a considerable number of lean individuals harbour metabolic abnormalities typically associated with obesity. Conversely, excess adiposity does not always equate with an abnormal metabolic profile. In fact, evidence exists for the presence of a metabolically unhealthy normal weight (MUHNW) and a metabolically healthy obese (MHO) phenotype. It has become increasingly recognised that different fat depots exert different effects on the metabolic profile of each individual by virtue of their location, structure and function, giving rise to these different body composition phenotypes. Furthermore, other factors have been implicated in the aetiopathogenesis of the body composition phenotypes, including genetics, ethnicity, age and lifestyle/behavioural factors. Even though to date both MHO and MUHNW have been widely investigated and documented in the literature, studies report different outcomes on long-term cardiometabolic morbidity and mortality. Future large-scale, observational and population-based studies are required for better profiling of these phenotypes as well as to further elucidate the pathophysiological role of the adipocyte in the onset of metabolic disorders to allow for better risk stratification and a personalised treatment paradigm.

Altered Red Blood Cell Fatty Acid and Serum Adipokine Profiles in Subjects with Obesity

BACKGROUND

Adipokines, as well as the fatty acid profile of red blood cell (RBC) membranes, are known to play important roles in the development and progression of metabolic complications induced by obesity. Thus, the objective of this study is to compare the serum adipokine profile and the RBC membrane fatty acid profile of normal-weight and obese adults, and to analyze their relationship with serum biochemical parameters.

METHODS

An observational case-control study was performed in 75 normal-weight and obese adult subjects. Biochemical serum parameters, eight serum adipokines and the RBC membrane fatty acid profiles were measured. Associations between parameters were established using regression analysis.

RESULTS

Subjects with obesity showed increased levels of leptin, fibroblast growth factor 21 (FGF21) and overexpressed nephroblastoma (NOV/CCN3), decreased adiponectin, and similar levels of vaspin and chemerin compared to normal-weight subjects. Significant positive and negative correlations were found with triglycerides and high-density lipoprotein-cholesterol (HDL-c), respectively. An increase in the total ω-6 fatty acids in the RBC membrane fatty acid profiles in subjects with obesity was observed, because of higher levels of both dihomo-γ-linolenic acid (DGLA) and arachidonic acid (AA), and decreased total ω-3 fatty acids, mainly due to lower levels of docosahexaenoic acid (DHA). The ω-6/ω-3 ratio in the RBCs was significantly higher, suggesting an inflammatory status, as was also suggested by a reduced adiponectin level. A negative association between DGLA and adiponectin, and a positive association between DHA and serum triglycerides, was observed.

CONCLUSIONS

Important alterations in serum adipokine and RBC fatty acid profiles are found in subjects with obesity.

Total serum FGF-21 levels positively relate to visceral adiposity differently from its functional intact form

Objective

Increased Fibroblast Growth Factor-21 (FGF-21) circulating levels have been described in obesity. In this observational study, we analysed a group of subjects with metabolic disorders to unravel the putative link between visceral adiposity and FGF-21 serum levels.

Methods

Total and intact serum FGF-21 concentration was measured with an ELISA assay respectively in 51 and 46 subjects, comparing FGF-21 levels in dysmetabolic conditions. We also tested Spearman's correlations between FGF-21 serum levels and biochemical and clinical metabolic parameters.

Results

FGF-21 was not significantly increased in high-risk conditions such as visceral obesity, Metabolic Syndrome, diabetes, smoking, and atherosclerosis. Waist Circumference (WC), but not BMI, positively correlated with total FGF-21 levels (r=0.31, p <0.05), while HDL-cholesterol (r=-0.29, p <0.05) and 25-OH Vitamin D (r=-0.32, p <0.05) showed a significant negative correlation with total FGF-21. ROC analysis of FGF-21 in prediction of increased WC, showed that patients with total FGF-21 level over cut-off value of 161.47 pg/mL presented with impaired FPG. Conversely, serum levels of the intact form of FGF-21 did not correlate with WC and other metabolic biomarkers.

Conclusion

Our newly calculated cut-off for total FGF-21 according to visceral adiposity identified subjects with fasting hyperglycemia. However, waist circumference correlates with total FGF-21 serum levels but does not correlate with intact FGF-21, suggesting that functional FGF-21 does not necessarily relate with obesity and metabolic features.