Chronic Kidney Disease Is Associated with Increased Plasma Levels of Fibroblast Growth Factors 19 and 21

The endocrine FGFs axis: A systemic anti-fibrotic response that could prevent pulmonary fibrogenesis?

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal disease for which therapeutic options are limited, with an unmet need to identify new therapeutic targets. IPF is thought to be the consequence of repeated microlesions of the alveolar epithelium, leading to aberrant epithelial-mesenchymal communication and the accumulation of extracellular matrix proteins. The reactivation of developmental pathways, such as Fibroblast Growth Factors (FGFs), is a well-described mechanism during lung fibrogenesis. Secreted FGFs with local paracrine effects can either exert an anti-fibrotic or a pro-fibrotic action during this pathological process through their FGF receptors (FGFRs) and heparan sulfate residues as co-receptors. Among FGFs, endocrine FGFs (FGF29, FGF21, and FGF23) play a central role in the control of metabolism and tissue homeostasis. They are characterized by a low affinity for heparan sulfate, present in the cell vicinity, allowing them to have endocrine activity. Nevertheless, their interaction with FGFRs requires the presence of mandatory co-receptors, alpha and beta Klotho proteins (KLA and KLB). Endocrine FGFs are of growing interest for their anti-fibrotic action during liver, kidney, or myocardial fibrosis. Innovative therapies based on FGF19 or FGF21 analogs are currently being studied in humans during liver fibrosis. Recent data report a similar anti-fibrotic action of endocrine FGFs in the lung, suggesting a systemic regulation of the pulmonary fibrotic process. In this review, we summarize the current knowledge on the protective effect of endocrine FGFs during the fibrotic processes, with a focus on pulmonary fibrosis.

Treatment with fibroblast growth factor 19 increases skeletal muscle fiber size, ameliorates metabolic perturbations and hepatic inflammation in 5/6 nephrectomized mice

Chronic kidney disease (CKD) is associated with osteosarcopenia, and because a physical decline in patients correlates with an increased risk of morbidity, an improvement of the musculoskeletal system is expected to improve morbi-mortality. We recently uncovered that the intestinal hormone Fibroblast Growth Factor 19 (FGF19) is able to promote skeletal muscle mass and strength in rodent models, in addition to its capacity to improve glucose homeostasis. Here, we tested the effects of a treatment with recombinant human FGF19 in a CKD mouse model, which associates sarcopenia and metabolic disorders. In 5/6 nephrectomized (5/6Nx) mice, subcutaneous FGF19 injection (0.1 mg/kg) during 18 days increased skeletal muscle fiber size independently of food intake and weight gain, associated with decreased gene expression of myostatin. Furthermore, FGF19 treatment attenuated glucose intolerance and reduced hepatic expression of gluconeogenic genes in uremic mice. Importantly, the treatment also decreased gene expression of liver inflammatory markers in CKD mice. Therefore, our results suggest that FGF19 may represent a novel interesting therapeutic strategy for a global improvement of sarcopenia and metabolic complications in CKD.

Endocrine manifestations of chronic kidney disease and their evolving management: A systematic review

BACKGROUND

Chronic Kidney Disease (CKD) shows a wide range of renal abnormalities including the excretory, metabolic, endocrine, and homeostatic function of the kidney. The prognostic impact of the 'endocrine manifestations' which are often overlooked by clinicians cannot be overstated.

METHODS AND OBJECTIVES

A systematic review was attempted to provide a comprehensive overview of all endocrine abnormalities of CKD and their evolving principles of management, searching databases of PubMed, Embase, and Scopus and covering the literature between 2002 and 2022.

RESULTS

The endocrine derangements in CKD can be attributed to a myriad of pathologic processes, in particular decreased clearance, impaired endogenous hormone production, uremia-induced cellular dysfunction, and activation of systemic inflammatory pathways. The major disorders include anemia, hyperprolactinemia, insulin resistance, reproductive hormone deficiency, thyroid hormone deficiency, and serum FGF (Fibroblast Growth Factor) alteration. Long-term effects of CKD also include malnutrition and increased cardiovascular risk. The recent times have unveiled their detailed pathogenesis and have seen an evolution in the principles of management which necessitates a revision of current guidelines.

CONCLUSION

Increased advertence regarding the pathology, impact, and management of these endocrine derangements can help in reducing morbidity as well as mortality in the CKD patients by allowing prompt individualized treatment. Moreover, with timely and appropriate intervention, a long-term reduction in complications, as well as an enhanced quality of life, can be achieved in patients with CKD.

Research Progress of Fibroblast Growth Factor 21 in Fibrotic Diseases

Fibrosis is a common pathological outcome of chronic injuries, characterized by excessive deposition of extracellular matrix components in organs, as seen in most chronic inflammatory diseases. At present, there is an increasing tendency of the morbidity and mortality of diseases caused by fibrosis, but the treatment measures for fibrosis are still limited. Fibroblast growth factor 21 (FGF21) belongs to the FGF19 subfamily, which also has the name endocrine FGFs because of their endocrine manner. In recent years, it has been found that plasma FGF21 level is significantly correlated with fibrosis progression. Furthermore, there is evidence that FGF21 has a pronounced antifibrotic effect in a variety of fibrotic diseases. This review summarizes the biological effects of FGF21 and discusses what is currently known about this factor and fibrosis disease, highlighting emerging insights that warrant further research.

Physiological and pathophysiological role of endocrine fibroblast growth factors

The endocrine subfamily of fibroblast growth factors (FGF) includes three factors: FGF19, FGF21, FGF23. They act on distal tissues through FGF receptors (FGFRs). The FGFR activation requires two cofactors: α- and β-Klotho, which are structurally related single-pass transmembrane proteins. The endocrine FGFs regulate various metabolic processes involved in the regulation of glucose and lipid metabolism as well as bile acid circulation, vitamin D modulation, and phosphate homeostasis. The FGF-FGFR dysregulation is widely implicated in the pathogenesis of various disorders. Significant alterations in plasma FGF concentration are associated with the most prevalent chronic diseases, including dyslipidemia, type 2 diabetes, cardiovascular diseases, obesity, non-alcoholic fatty liver disease, diseases of the biliary tract, chronic kidney disease, inflammatory bowel disease, osteomalacia, various malignancies, and depression. Therefore, the endocrine FGFs may serve as disease predictors or biomarkers, as well as potential therapeutic targets. Currently, numerous analogues and inhibitors of endocrine FGFs are under development for treatment of various disorders, and recently, a human monoclonal antibody against FGF23 has been approved for treatment of X-linked hypophosphatemia. The aim of this review is to summarize the current data on physiological and pathophysiological actions of the endocrine FGF subfamily and recent research concerning the therapeutic potential of the endocrine FGF pathways.

Regulation and Potential Biological Role of Fibroblast Growth Factor 21 in Chronic Kidney Disease

Chronic kidney disease (CKD) is an incurable progressive disease with the progressive impairment of kidney function, which can accelerate the progression of cardiovascular disease, increase the risk of infection, and lead to related complications such as anemia and bone disease. CKD is to a great extent preventable and treatable, and it is particularly important to improve the early diagnosis, strengthen the research underlying the mechanism of disease occurrence and development, and innovate new intervention measures. Fibroblast growth factor 21 (FGF21) belongs to one of members of endocrine FGF subfamily with evolutionarily conserved functions and performs a vital role in the regulation of energy balance and adipose metabolism. FGF21 needs to rely on β-Klotho protein to specifically bind to FGF receptor (FGFR), which activates the FGF21 signaling exerting the biological function. FGF21 is deemed as an important regulatory factor extensively modulating many cellular functions under physiologic and pathologic conditions. Although the metabolic effect of FGF21 has been extensively studied, its potential biological role in the kidney has not been generally investigated. In this review, we summarize the biological characteristics, regulation and biological function of FGF21 based on the current studies, and briefly discuss the potential relationship with chronic kidney disease.

The Saga of Endocrine FGFs

Fibroblast growth factors (FGFs) are cell-signaling proteins with diverse functions in cell development, repair, and metabolism. The human FGF family consists of 22 structurally related members, which can be classified into three separate groups based on their action of mechanisms, namely: intracrine, paracrine/autocrine, and endocrine FGF subfamilies. FGF19, FGF21, and FGF23 belong to the hormone-like/endocrine FGF subfamily. These endocrine FGFs are mainly associated with the regulation of cell metabolic activities such as homeostasis of lipids, glucose, energy, bile acids, and minerals (phosphate/active vitamin D). Endocrine FGFs function through a unique protein family called klotho. Two members of this family, α-klotho, or β-klotho, act as main cofactors which can scaffold to tether FGF19/21/23 to their receptor(s) (FGFRs) to form an active complex. There are ongoing studies pertaining to the structure and mechanism of these individual ternary complexes. These studies aim to provide potential insights into the physiological and pathophysiological roles and therapeutic strategies for metabolic diseases. Herein, we provide a comprehensive review of the history, structure–function relationship(s), downstream signaling, physiological roles, and future perspectives on endocrine FGFs.

A review on mechanism of inhibition of advanced glycation end products formation by plant derived polyphenolic compounds

Advanced glycation end products (AGEs) are naturally occurring biomolecules formed by interaction of reducing sugars with biomolecules such as protein and lipids etc., Long term high blood sugar level and glycation accelerate the formation of AGEs. Unchecked continuous formation and accumulation of AGEs are potential risks for pathogenesis of various chronic diseases. Current mode of antidiabetic therapy is based on synthetic drugs that are often linked with severe adverse effects. Polyphenolic compounds derived from plants are supposed to inhibit glycation and formation of AGEs at multiple levels. Some polyphenolic compounds regulate the blood glucose metabolism by amplification of cell insulin resistance and activation of insulin like growth factor binding protein signaling pathway. Their antioxidant nature and metal chelating activity, ability to trap intermediate dicarbonyl compounds could be possible mechanisms against glycation and AGEs formation and hence, against AGEs induced health complications. Although, few species of polyphenolic compounds are being used in in vitro trials and their in vivo study is still in progress, increasing the area of research in this field may produce a fruitful approach in management of overall diabetic complications.

Association of FGF19, FGF21 and FGF23 with carbohydrate metabolism parameters and insulin resistance in patients with chronic kidney disease

Insulin resistance (IR) is characterised by increased gluconeogenesis in the liver and the resistance of peripheral receptors to insulin. Several factors, including IR, type 2 diabetes, new-onset diabetes after transplant (NODAT) and secondary parathyroidism, are related to chronic kidney disease (CKD). These factors are associated with higher mortality due to the increased risk of cardiovascular complications. Many factors have been identified as potential markers of IR in CKD. These factors include fibroblast growth factors (FGFs), a subfamily of endocrine polypeptides. In this study, we examined the association of FGF19, FGF21 and FGF23 with selected parameters related to carbohydrate metabolism and insulin resistance in non diabetic patients with predialysis CKD and in non diabetic patients after renal transplantation. The study included 108 non diabetic subjects: 40 patients with predialysis CKD, 45 patients with CKD who had undergone renal transplantation, and 23 healthy subjects (control group). In patients who had undergone renal transplantation, concentrations of FGF23 were increased compared to the control group and patients with predialysis CKD. The highest and lowest FGF19 concentrations were observed in CKD patients and in patients who had undergone kidney transplantation, respectively. This difference was statistically significant. Leptin concentrations were higher in CKD patients compared to the control group and patients who had undergone kidney transplantation. There were no statistically significant differences in adiponectin concentrations, lean body mass or fat tissue mass between the studied groups. HOMA-IR and insulin levels were significantly increased in CKD patients and in patients who had undergone renal transplantation in comparison to the control group. The results of the study suggest the involvement of FGF in carbohydrate metabolism and insulin resistance in patients with predialysis CKD, as well as a correlation with kidney function.

Endocrine fibroblast growth factors as potential biomarkers for chronic kidney disease

INTRODUCTION

Among the family of fibroblast growth factors (FGFs), FGF19, FGF21, and FGF23 act as circulating hormones and are called endocrine FGFs. FGF19 and FGF21 regulate bile acid and energy homeostasis, respectively, whereas FGF23 regulates vitamin D and phosphate homeostasis. Accumulating evidence suggests that FGF23 plays a critical role in disturbed mineral metabolisms, left ventricular hypertrophy, immunosuppression, inflammation, among others in patients with chronic kidney disease (CKD), highlighting the potential both as a biomarker and a therapeutic target. Several studies have also examined the potential role of FGF19 and FGF21 in CKD patients.

AREAS COVERED

In this review, we present a brief overview of the biology of FGF19, FGF21, and FGF23, and summarize recent clinical and experimental studies on the pathophysiological roles of endocrine FGFs, mainly FGF23, in CKD patients.

EXPERT OPINION

Among the endocrine FGFs, FGF23 represents the most promising biomarker in CKD patients. If future studies confirm that FGF23 is directly toxic in CKD patients, FGF23 could be regarded as a therapeutic target and its measurement would be valuable if applied in clinical practice. Despite their potentially important roles, the clinical relevance of FGF19 and FGF21 in CKD patients is unclear, and much more studies are required.

FGF21: An Emerging Therapeutic Target for Non-Alcoholic Steatohepatitis and Related Metabolic Diseases

The rising global prevalence of obesity, metabolic syndrome, and type 2 diabetes has driven a sharp increase in non-alcoholic fatty liver disease (NAFLD), characterized by excessive fat accumulation in the liver. Approximately one-sixth of the NAFLD population progresses to non-alcoholic steatohepatitis (NASH) with liver inflammation, hepatocyte injury and cell death, liver fibrosis and cirrhosis. NASH is one of the leading causes of liver transplant, and an increasingly common cause of hepatocellular carcinoma (HCC), underscoring the need for intervention. The complex pathophysiology of NASH, and a predicted prevalence of 3-5% of the adult population worldwide, has prompted drug development programs aimed at multiple targets across all stages of the disease. Currently, there are no approved therapeutics. Liver-related morbidity and mortality are highest in more advanced fibrotic NASH, which has led to an early focus on anti-fibrotic approaches to prevent progression to cirrhosis and HCC. Due to limited clinical efficacy, anti-fibrotic approaches have been superseded by mechanisms that target the underlying driver of NASH pathogenesis, namely steatosis, which drives hepatocyte injury and downstream inflammation and fibrosis. Among this wave of therapeutic mechanisms targeting the underlying pathogenesis of NASH, the hormone fibroblast growth factor 21 (FGF21) holds considerable promise; it decreases liver fat and hepatocyte injury while suppressing inflammation and fibrosis across multiple preclinical studies. In this review, we summarize preclinical and clinical data from studies with FGF21 and FGF21 analogs, in the context of the pathophysiology of NASH and underlying metabolic diseases.