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Abstract

Propose:

To investigate the temporal relationship between plasma fibroblast growth factor 21 levels, insulin resistance, metabolic dysfunction and cardiac fibroblast growth factor 21 resistance in long-term high-fat diet–induced obese rats.

Methods:

In total, 36 male Wistar rats were fed with either a normal diet or high-fat diet for 12 weeks. Blood was collected from the tail tip, and plasma was used to determine metabolic profiles and fibroblast growth factor 21 levels. Rats were sacrificed at weeks 4, 8 and 12, and the hearts were rapidly removed for the determination of cardiac fibroblast growth factor 21 signalling pathways.

Results:

Body weight and plasma fibroblast growth factor 21 levels were increased after 4 weeks of consumption of a high-fat diet. At weeks 8 and 12, high-fat diet rats had significantly increased body weight and plasma fibroblast growth factor 21 levels, together with increased plasma insulin, HOMA index, area under the curve of glucose, plasma total cholesterol, plasma low-density lipoprotein cholesterol, serum malondialdehyde and cardiac malondialdehyde levels. However, plasma high-density lipoprotein cholesterol levels and cardiac fibroblast growth factor 21 signalling proteins (p-FGFR1 Tyr₁₅₄, p-ERK1/2 Thr₂₀₂/Tyr₂₀₄ and p-Akt Ser₄₇₃) were decreased, compared with normal diet rats.

Conclusion:

These findings suggest that plasma fibroblast growth factor 21 levels could be an early predictive biomarker prior to the development of insulin resistance, metabolic disturbance and cardiac fibroblast growth factor 21 resistance.

Keywords

Plasma fibroblast growth factor 21 levels biomarker cardiac fibroblast growth factor 21 resistance insulin resistance obesity metabolic dysfunction

Introduction

Fibroblast growth factor 21 (FGF21) is known to be a key regulator of various metabolic functions involving both glucose and fat metabolism.¹ High levels of FGF21 have been observed in the models of obese insulin-resistant animals and diabetic animals.^2,3 Clinical studies demonstrated that increased circulating FGF21 may be associated with the development of insulin resistance and metabolic syndrome.^4–6 Lee et al.⁷ found that serum FGF21 levels showed a positive correlation with lipid profiles, insulin resistance and pericardial fat volume, but the correlations were independent of obesity in metabolic syndrome patients. Moreover, a recent clinical study also suggested that higher circulating FGF21 levels could be a predictor of future adverse cardiovascular events in type 2 diabetic patients.⁸ However, currently, the temporal association between FGF21 level and insulin resistance is still unclear. Understanding this temporal association including an early detection of increases in circulating FGF21 levels could be important in the prediction and prevention of future metabolic status and adverse cardiovascular events.

We have previously reported that long-term high-fat diet (HFD) consumption caused obese insulin resistance along with cardiac autonomic imbalance in an obese insulin-resistant model, which was observed at week 8 after the start of consumption of an HFD, whereas cardiac dysfunction was observed later, at week 12 after the start of consumption of an HFD.^9,10 In addition, we also found that plasma FGF21 levels and cardiac FGF21 resistance were observed in conditions of obese insulin resistance induced by HFD consumption.^3,11 However, the temporal changes in FGF21 as well as whether alterations in levels of plasma FGF21 and cardiac FGF21 signalling pathways occur prior to or simultaneously with insulin resistance in HFD-induced obese insulin-resistant rats have never been investigated. In addition, the association between FGF21 level and other metabolic parameters and lipid profiles is still unknown.

We tested the hypothesis that increased plasma FGF21 develops prior to insulin resistance, metabolic disturbance and cardiac FGF21 resistance in HFD-induced obese insulin-resistant rats.

Materials and methods

Ethical approval

All experiments in this study were approved by the Faculty of Medicine, Chiang Mai University Institutional Animal Care and Use Committee (permit no. 006/2557), in compliance with National Institutes of Health (NIH) guidelines and in accordance with the ARRIVE guidelines for reporting experiments involving animals.

Animals and diet

In total, 36 adult male Wistar rats weighing 180–200 g were obtained from the National Animal Center, Salaya Campus, Mahidol University, Bangkok, Thailand. All rats were housed in a controlled temperature and humidity environment, with a 12:12-h light–dark cycle. Rats were fed with either a normal diet (ND: a standard laboratory rat diet, containing 19.77%E fat, CP 082, Bangkok, Thailand) or HFD (a diet containing 59.28%E fat) for 12 weeks. The ND and HFD components have been described previously.¹¹

The experiments and study protocol

After allowing 1 week for acclimatization, rats were divided into two groups and were given either ND (n = 18) or HFD (n = 18) for 12 weeks. Body weight and food intake were recorded every week. All rats were fasted for 5 h prior to being subjected to blood collection to determine all metabolic parameters. Prior to the oral glucose tolerance test (OGTT), rats were fasted overnight. At the end of the experiments (weeks 4, 8 and 12), rats were sacrificed, and hearts were removed for the determination of cardiac FGF21 signalling pathways. In addition, after euthanasia using Zoletil (zolazepam/tiletamine) 50 mg/kg combined with xylazine 3 mg/kg via intramuscular injection, the visceral fat was removed from the rats and weighed.¹²

Metabolic parameters and plasma FGF21 assessments

A commercial colorimetric assay kit (BioVision, Milpitas, CA) was used for determining the plasma high-density lipoprotein cholesterol (HDL-C) level.^11,13 Then, the Friedewald equation was used to calculate the plasma low-density lipoprotein cholesterol (LDL-C) levels.^11,14,15 A commercial colorimetric assay kit (Erba Diagnostics Mannheim GmbH, Mannheim, Germany) was used for the determination of fasting plasma glucose (FPG), plasma total cholesterol (TC) and plasma triglyceride (TG) levels.^11,14,16 The commercial sandwich enzyme-linked immunosorbent assay (ELISA) kit (LINCO research, St Charles, MO) was used to determine the plasma insulin levels.^11,13,14 The degree of insulin sensitivity was determined using the homeostasis model assessment (HOMA) index, an increase in the HOMA index indicates an increase in the insulin resistance.^11,17 Moreover, a quantitative sandwich enzyme immunoassay technique using a mouse/rat FGF21 ELISA kit (R&D systems, Inc., Minneapolis, MN) was used for the determination of plasma FGF21 levels.^11,18

OGTT and area under the curve of glucose

The OGTT was investigated at baseline and at the end of weeks 4, 8 and 12 of the dietary periods. The animals were fasted for 12 h before they underwent an OGTT. Blood was collected from a small cut at the tip of the tail immediately before 2 g/kg body weight glucose feeding via oral gavage and then blood was collected at 15, 30, 60 and 120 min after glucose feeding. The glucose analysis was performed with a colorimetric assay kit (ERBA Mannheim, Mannheim, Germany).^16,17 Moreover, the area under the curve of glucose (AUCg) was investigated from glucose curve by OGTT.^16,17

Determination of serum and cardiac malondialdehyde concentration

HPLC-based assay (Thermo Scientific, Bangkok, Thailand) was used for the determination of cardiac tissue and plasma malondialdehyde (MDA) concentrations.^9,11,13 Plasma and cardiac tissue were mixed with H₃PO₄ and thiobarbituric acid (TBA) to produce TBA reactive substances (TBARSs). The plasma and cardiac TBARS concentration were determined directly from a standard curve and reported as equivalent to the MDA concentration.^9,11,13

Determination of cardiac protein expression by western blot analysis

Cardiac tissues for determining the FGF21 signalling pathways were obtained from the fresh hearts at the LV apex.¹¹ The general procedures of western blot analysis are described in previous studies.^11,19,20 The FGF21 signalling proteins expression were determined including FGFR1 and p-FGFR1 Tyr₁₅₄ (1:200 and 1:200 dilution, respectively; Sigma–Aldrich, China); β-Klotho, ERK1/2, p-ERK1/2 Thr₂₀₂/Tyr₂₀₄, PGC-1α and β-actin (1:200, 1:1000, 1:1000, 1:1000 and 1:2000 dilution, respectively; Santa Cruz, Starr County, TX); Akt and p-Akt Ser₄₇₃ (1:1000 and 1:1000 dilution, respectively, Cell Signaling Technology, Danvers, MA).¹¹ The primary antibody was detected by horse anti-mouse immunoglobulin G (IgG) conjugate horseradish peroxidase (HRP)-linked antibody (1:2000 dilution; Cell Signalling Technology) for β-actin^11,20 and rabbit anti-goat IgG conjugate HRP-linked antibody (1:2000 dilution; Santa Cruz) for β-Klotho. Moreover, FGFR1, p-FGFR1 Tyr₁₅₄, ERK1/2, p-ERK1/2 Thr₂₀₂/Tyr₂₀₄, Akt, p-Akt Ser₄₇₃ and PGC-1α were detected by goat anti-rabbit IgG conjugate HRP-linked antibody (1:2000 dilution; Cell Signalling Technology).¹¹ The membranes were developed using the ChemiDoc touch imaging system (Bio-Rad Laboratories, Hercules, CA) on chemiluminescence mode.^11,21–24 The densitometric analysis was determined using the image J program.^11,25 Each protein expression was normalized with β-actin expression.¹¹

Statistical analysis

Data were expressed as mean ± SEM. A two-way repeated measures analysis of variance (ANOVA) was used to test the difference between group and time point. Data were analysed using SPSS statistics software version 22. A value of p < 0.05 was considered statistically significant.

Results

Metabolic dysfunction was found at weeks 8 and 12

At baseline (week 0), all metabolic parameters were similar in both the ND and HFD groups (Figure 1). At week 4, in the ND group, the body weight was significantly increased, compared to the ND group at baseline (Figure 1(a)). In the HFD group, the body weight was increased, compared to the HFD group at baseline and ND group at week 4 (Figure 1(a)).

Figure 1.

The effects of ND and HFD consumption at different time points on metabolic parameters, insulin resistance and lipid peroxidation levels (n = 6/group): (a) body weight, (b) food intake, (c) fasting plasma glucose, (d) plasma insulin, (e) HOMA index, (f) plasma TC, (g) plasma TG, (h) plasma HDL-C, (i) plasma LDL-C, (j) serum MDA levels and (k) cardiac MDA levels.

At week 8, in the ND group, the body weight was significantly increased, compared to the ND group at baseline (Figure 1(a)). In the HFD group, the body weight was increased (Figure 1(a)), along with increased plasma insulin, HOMA index, plasma TC, plasma LDL-C, serum MDA and cardiac MDA levels (Figure 1(d) to (f), (i) to (k), respectively), whereas plasma HDL-C was significantly decreased (Figure 1(h)), when compared to the HFD group at baseline and the ND group at week 8.

At week 12, in the ND group, the body weight was significantly increased when compared to the ND group at baseline (Figure 1(a)). Moreover, in the HFD group, the visceral fat weight was significantly increased when compared to the ND group (59 ± 4 g versus 30 ± 5 g, p < 0.05). In the HFD group, the body weight was increased (Figure 1(a)), along with increased plasma insulin, HOMA index, plasma TC, plasma LDL-C, serum MDA and cardiac MDA levels (Figure 1(d) to (f), (i) to (k), respectively), whereas plasma HDL-C was significantly decreased, compared to the HFD group at baseline and the ND group at week 12.

Insulin resistance was found at weeks 8 and 12

At baseline and week 4, plasma glucose curve and AUCg by OGTT at each time point were unchanged between groups (Figure 2(a), (b) and (e), respectively). At week 8 and week 12, significant increases in plasma glucose levels at 30, 60 and 120 min were found in HFD group, when compared to the ND group (Figure 2(c) and (d), respectively). Moreover, the AUCg by OGTT was increased at week 8 and week 12 in the HFD group, when compared to the ND group (Figure 2(e)).

Figure 2.

The effects of ND and HFD consumption at different time points on plasma glucose levels and AUCg by oral glucose tolerance test (OGTT; n = 6/group): (a) plasma glucose curve at baseline, (b) plasma glucose curve at week 4, (c) plasma glucose curve at week 8, (d) plasma glucose curve at week 12 and (e) AUCg.

Plasma FGF21 levels elevated precede the impairment of cardiac FGF21 signalling pathways

At week 4, significant increases in plasma FGF21 levels were found in the HFD group, compared to the ND group (Figure 3(a)). FGF21 signalling pathways including p-FGFR1 Tyr₁₅₄, FGFR1, β-Klotho, p-ERK1/2 Thr₂₀₂/Tyr₂₀₄, ERK1/2, p-Akt at Ser₄₇₃, Akt and PGC-1α expression in the HFD group showed no change, compared to the ND group (Figure 3(c) to (j), respectively). At week 8, significant increases in plasma FGF21 levels were found in the HFD group, compared to the ND group (Figure 3(a)). In addition, significant decreases in p-FGFR1 Tyr₁₅₄, p-ERK1/2 Thr₂₀₂/Tyr₂₀₄, p-Akt at Ser₄₇₃ and PGC-1α expression were found in the HFD group, compared to the ND group (Figure 3(c), (f), (h) and (j), respectively). Similar results as week 8 were observed at week 12. However, the FGFR1, β-Klotho, ERK1/2 and Akt expressions were not changed between groups (Figure 3(d), (e), (g) and (i), respectively).

Figure 3.

The temporal changes of p-FGFR1 Ser₁₅₄, FGFR1, β-Klotho, p-Erk1/2 Thr₂₀₂/Tyr₂₀₄, Erk1/2, p-Akt Ser₄₇₃, Akt and PGC1-α expression in the heart tissue after HFD consumption (n = 5–6/group): (a) plasma FGF21 levels, (b) Western bands of FGF21 signalling pathways, (c) p-FGFR1 Tyr₁₅₄, (d) FGFR1, (e) β-Klotho, (f) p-Erk1/2 Thr₂₀₂/Tyr₂₀₄, (g) Erk1/2, (h) p-Akt Ser₄₇₃, (i) Akt and (j) PGC-1α in ND and HFD rats at week 4, week 8 and week 12.

Discussion

The major findings of this study are as follows: (1) increased plasma FGF21 levels and body weight were first found after 4 weeks of HFD consumption; this occurred prior to peripheral insulin resistance and other metabolic disturbances. (2) Impaired cardiac FGF21 signalling pathways were found at week 8 and week 12 of HFD consumption.

FGF21 levels are elevated in HFD-induced obesity.^2,4 In obese individuals, excessive fat accumulation has been shown to activate FGF21 synthesis and release²⁶ via several mechanisms which involve G-protein-coupled receptor (GPR) activation²⁶ and peroxisome proliferator-activated receptor (PPAR) protein family activation²⁷ and correspond to conditions of FGF21 resistance.^2,4,28 This mechanism leads to increased plasma FGF21 in obese individuals. The temporal changes of FGF21 after HFD-induced obese insulin resistance demonstrated that FGF21 levels were increased prior to alteration of other metabolic parameters, except for body weight and visceral fat weight gain. These data suggest that FGF21 levels are associated with increase in body weight and visceral fat weight gain following HFD consumption. These changes were not observed in the ND group, indicating the influence of the amount of body fat accumulation, calorie intake and/or percentage of fat in the diet. However, future investigation is needed to give more detailed evidence concerning these findings.

Fisher et al.² reported that 22 weeks of feeding with a high-fat/high-sucrose diet in mice causes FGF21 resistance in the liver and white adipose tissues. Moreover, it has also been shown that FGF21 resistance in the heart of obese rats was found at 12 weeks after HFD feeding.^2,3,11,28,29 However, the time-course study to investigate the actual development of FGF21 resistance in the heart before 12 weeks of HFD feeding was not available. The results in this study demonstrated that the increasing plasma FGF21 levels preceded cardiac FGF21 resistance. Since the FGF21 signalling pathways in the heart play an important role in the regulation of redox homeostasis, anti-apoptosis, anti-oxidative stress, anti-inflammation and myocardial biogenesis,^30–33 the FGF21 resistance in the heart may contribute to a higher impact on the pathogenesis of cardiovascular diseases than FGF21 resistance in other tissues. Moreover, the understanding in the alteration of systemic FGF21 levels and FGF21 signalling pathways in the heart could be clinically useful especially for the cardioprotective interventions. However, this hypothesis is also still unknown and will need further investigation.

PGC1-α is an essential transcriptional coactivator and acts as an important regulators of mitochondrial metabolism in the heart.^34,35 Moreover, PGC1-α is well known to interact with a nuclear receptors PPAR family especially alpha subtype (PPAR-α) in the heart.^34,35 This interaction in the heart plays an important role in myocardial biogenesis especially for the regulation of fatty acid uptake and fatty acid β-oxidation (FAO) enzyme synthesis.^34–36 Since FAO is a primary source of ATP production for cardiac metabolism under physiological condition,^30,37 a decrease in PGC1-α expression in the heart may impair a myocardial biogenesis through a decreasing in fatty acid uptake and FAO.

FGF21 resistance remains a key focus for explaining the effects of HFD-induced FGF21 release.^2,28 This resistance to FGF21 after consumption of an HFD was characterized by increased FGF21 levels in the cited tissues and organs^2,3,28,38 along with impaired FGF21 receptor function,^2,3,28,38 plus low response to exogenous FGF21.^2,28 Although long-term HFD consumption can activate an FGF21-resistant condition, the characteristic of FGF21 resistance in each organ is specific. However, the role of HFD consumption on the characteristics of FGF21 resistance, especially in the heart, is still controversial.^3,11,28 Our present study demonstrated that cardiac FGF21 receptor function and downstream signalling pathways are still intact at week 4 in the HFD group, whereas at weeks 8 and 12 after the start of consumption of an HFD, impairment of cardiac FGF21 receptor function and downstream signalling pathways were shown. These findings suggested that the elevation of plasma FGF21 levels may be an indicator of the pre-insulin-resistant state. Moreover, high FGF21 levels may be an early predictive biomarker for the development of insulin resistance and metabolic dysfunction.

Conclusion

An early state of FGF21 resistance developed prior to insulin resistance and other metabolic disturbances, and was associated with body weight gain in HFD-fed rats. These findings suggest that increased plasma FGF21 levels could be a predictive biomarker for future development of insulin resistance and metabolic dysfunction.

Footnotes

Acknowledgements

The authors would like to thank Ms Maria Love for her editorial assistance with this article.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

This work was supported by an NSTDA Research Chair Grant from the National Science and Technology Development Agency Thailand (NC), grants from the Thailand Research Fund Royal Golden Jubilee PhD Program (PT&SC) and RTA6080003 (SC) and a Chiang Mai University Center of Excellence Award (NC).

References

Chau

Gao

Yang

et al . Fibroblast growth factor 21 regulates energy metabolism by activating the AMPK-SIRT1-PGC-1alpha pathway. Proc Natl Acad Sci U S A 2010; 107: 12553–12558.

Fisher

Chui

Antonellis

et al . Obesity is a fibroblast growth factor 21 (FGF21)-resistant state. Diabetes 2010; 59: 2781–2789.

Tanajak

Sa-Nguanmoo

Wang

et al . Fibroblast growth factor 21 (FGF21) therapy attenuates left ventricular dysfunction and metabolic disturbance by improving FGF21 sensitivity, cardiac mitochondrial redox homoeostasis and structural changes in pre-diabetic rats. Acta Physiol 2016; 217: 287–299.

Zhang

Yeung

Karpisek

et al . Serum FGF21 levels are increased in obesity and are independently associated with the metabolic syndrome in humans. Diabetes 2008; 57: 1246–1253.

Bobbert

Schwarz

Fischer-Rosinsky

et al . Fibroblast growth factor 21 predicts the metabolic syndrome and type 2 diabetes in Caucasians. Diabetes Care 2013; 36: 145–149.

Jin

Bando

Miyawaki

et al . Correlation of fibroblast growth factor 21 serum levels with metabolic parameters in Japanese subjects. J Med Invest 2014; 61: 28–34.

Lee

Lim

Hong

et al . Serum FGF21 concentration is associated with hypertriglyceridaemia, hyperinsulinaemia and pericardial fat accumulation, independently of obesity, but not with current coronary artery status. Clin Endocrinol 2014; 80: 57–64.

Ong

Januszewski

O’Connell

et al . The relationship of fibroblast growth factor 21 with cardiovascular outcome events in the Fenofibrate Intervention and Event Lowering in Diabetes study. Diabetologia 2015; 58: 464–473.

Apaijai

Pintana

Chattipakorn

et al . Cardioprotective effects of metformin and vildagliptin in adult rats with insulin resistance induced by a high-fat diet. Endocrinology 2012; 153: 3878–3885.

10.

Pongkan

Pintana

Sivasinprasasn

et al . Testosterone deprivation accelerates cardiac dysfunction in obese male rats. J Endocrinol 2016; 229: 209–220.

11.

Tanajak

Pintana

Siri-Angkul

et al . Vildagliptin and caloric restriction for cardioprotection in pre-diabetic rats. J Endocrinol 2017; 232: 189–204.

12.

Pongkan

Chattipakorn

Chronic testosterone replacement exerts cardioprotection against cardiac ischemia-reperfusion injury by attenuating mitochondrial dysfunction in testosterone-deprived rats. PLoS ONE 2015; 10: e0122503.

13.

Apaijai

Pintana

Chattipakorn

et al . Effects of vildagliptin versus sitagliptin, on cardiac function, heart rate variability and mitochondrial function in obese insulin-resistant rats. Br J Pharmacol 2013; 169: 1048–1057.

14.

Apaijai

Chinda

Palee

et al . Combined vildagliptin and metformin exert better cardioprotection than monotherapy against ischemia-reperfusion injury in obese-insulin resistant rats. PLoS ONE 2014; 9: e102374.

15.

Friedewald

Levy

Fredrickson

DS.

Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem 1972; 18: 499–502.

16.

Pratchayasakul

Kerdphoo

Petsophonsakul

et al . Effects of high-fat diet on insulin receptor function in rat hippocampus and the level of neuronal corticosterone. Life Sci 2011; 88: 619–627.

17.

Pipatpiboon

Pratchayasakul

Chattipakorn

et al . PPARgamma agonist improves neuronal insulin receptor function in hippocampus and brain mitochondria function in rats with insulin resistance induced by long term high-fat diets. Endocrinology 2012; 153: 329–338.

18.

Yan

Chen

Zhang

et al . FGF21 deletion exacerbates diabetic cardiomyopathy by aggravating cardiac lipid accumulation. J Cell Mol Med 2015; 19: 1557–1568.

19.

Palee

Weerateerangkul

Chinda

et al . Mechanisms responsible for beneficial and adverse effects of rosiglitazone in a rat model of acute cardiac ischaemia-reperfusion. Exp Physiol 2013; 98: 1028–1037.

20.

Surinkaew

Kumphune

Chattipakorn

et al . Inhibition of p38 MAPK during ischemia, but not reperfusion, effectively attenuates fatal arrhythmia in ischemia/reperfusion heart. J Cardiovasc Pharmacol 2013; 61: 133–141.

21.

Tor

Yazan

Foo

et al . Induction of apoptosis in MCF-7 cells via oxidative stress generation, mitochondria-dependent and caspase-independent pathway by ethyl acetate extract of dillenia suffruticosa and its chemical profile. PLoS ONE 2015; 10: e0127441.

22.

Liu

Niger

Koh

et al . Connexin43 mediated delivery of ADAMTS5 targeting siRNAs from mesenchymal stem cells to synovial fibroblasts. PLoS ONE 2015; 10: e0129999.

23.

Besic

Shi

Stubbs

et al . Aberrant liver insulin receptor isoform a expression normalises with remission of type 2 diabetes after gastric bypass surgery. PLoS ONE 2015; 10: e0119270.

24.

Kmiecik

Pula

Suchanski

et al . Metallothionein-3 increases triple-negative breast cancer cell invasiveness via induction of metalloproteinase expression. PLoS ONE 2015; 10: e0124865.

25.

Chinda

Sanit

Chattipakorn

et al . Dipeptidyl peptidase-4 inhibitor reduces infarct size and preserves cardiac function via mitochondrial protection in ischaemia-reperfusion rat heart. Diab Vasc Dis Res 2014; 11: 75–83.

26.

Quesada-Lopez

Cereijo

Turatsinze

et al . The lipid sensor GPR120 promotes brown fat activation and FGF21 release from adipocytes. Nat Commun 2016; 7: 13479.

27.

Dutchak

Katafuchi

Bookout

et al . Fibroblast growth factor-21 regulates PPARgamma activity and the antidiabetic actions of thiazolidinediones. Cell 2012; 148: 556–567.

28.

Patel

Adya

Chen

et al . Novel insights into the cardio-protective effects of FGF21 in lean and obese rat hearts. PLoS ONE 2014; 9: e87102.

29.

Tanajak

Letter to the editor: parameters, characteristics, and criteria for defining the term ‘FGF21 resistance’. Endocrinology 2017; 158: 1523–1524.

30.

Tanajak

Chattipakorn

Effects of fibroblast growth factor 21 on the heart. J Endocrinol 2015; 227: R13–R30.

31.

Planavila

Redondo

Hondares

et al . Fibroblast growth factor 21 protects against cardiac hypertrophy in mice. Nat Commun 2013; 4: 2019.

32.

Zhang

Huang

et al . Fibroblast growth factor 21 protects the heart from apoptosis in a diabetic mouse model via extracellular signal-regulated kinase 1/2-dependent signalling pathway. Diabetologia 2015; 58: 1937–1948.

33.

Planavila

Redondo-Angulo

Ribas

et al . Fibroblast growth factor 21 protects the heart from oxidative stress. Cardiovasc Res 2014; 106: 19–31.

34.

Duncan

JG.

Peroxisome proliferator activated receptor-alpha (PPARalpha) and PPAR gamma coactivator-1alpha (PGC-1alpha) regulation of cardiac metabolism in diabetes. Pediatr Cardiol 2011; 32: 323–328.

35.

Vega

Huss

Kelly

DP.

The coactivator PGC-1 cooperates with peroxisome proliferator-activated receptor alpha in transcriptional control of nuclear genes encoding mitochondrial fatty acid oxidation enzymes. Mol Cell Biol 2000; 20: 1868–1876.

36.

Duncan

Fong

Medeiros

et al . Insulin-resistant heart exhibits a mitochondrial biogenic response driven by the peroxisome proliferator-activated receptor-alpha/PGC-1alpha gene regulatory pathway. Circulation 2007; 115: 909–917.

37.

Lopaschuk

Ussher

Folmes

et al . Myocardial fatty acid metabolism in health and disease. Physiol Rev 2010; 90: 207–258.

38.

Sa-Nguanmoo

Tanajak

Kerdphoo

et al . FGF21 improves cognition by restored synaptic plasticity, dendritic spine density, brain mitochondrial function and cell apoptosis in obese-insulin resistant male rats. Horm Behav 2016; 85: 86–95.

Increased plasma FGF21 level as an early biomarker for insulin resistance and metabolic disturbance in obese insulin-resistant rats

Abstract

Propose:

Methods:

Results:

Conclusion:

Keywords

Introduction

Materials and methods

Ethical approval

Animals and diet

The experiments and study protocol

Metabolic parameters and plasma FGF21 assessments

OGTT and area under the curve of glucose

Determination of serum and cardiac malondialdehyde concentration

Determination of cardiac protein expression by western blot analysis

Statistical analysis

Results

Metabolic dysfunction was found at weeks 8 and 12

Insulin resistance was found at weeks 8 and 12

Plasma FGF21 levels elevated precede the impairment of cardiac FGF21 signalling pathways

Discussion

Conclusion

Footnotes

Acknowledgements

Declaration of conflicting interests

Funding

References