Fibroblast growth factor 21 as a biomarker for NAFLD: Integrating pathobiology into clinical practice

Abstract

Fibroblast growth factor 21 levels are increased in nonalcoholic fatty liver disease patients and are correlated with hepatic triglycerideJournal of HepatologyVol. 53Issue 5PreviewFibroblast growth factor 21 (FGF21), a hormone primarily secreted by the liver in response to peroxisome proliferator-activated receptor-α (PPARα) activation, has recently been shown to possess beneficial effects on lipid metabolism and hepatic steatosis in animal models. This study investigated the association of FGF21 with nonalcoholic fatty liver disease (NAFLD) in Chinese patients. Full-Text PDF The prevalence of non-alcoholic fatty liver disease (NAFLD) has shown a dramatic increase over recent years and is now reaching epidemic proportions. It is becoming increasingly evident that early identification of the condition is critical, as NAFLD, and in particular its more severe form non-alcoholic steatohepatitis (NASH), is linked strongly with the metabolic syndrome [[1]Hamaguchi M. Kojima T. Takeda N. Nakagawa T. Taniguchi H. Fujii K. et al.The metabolic syndrome as a predictor of non-alcoholic liver disease.Ann Intern Med. 2005; 143: 722-728Crossref PubMed Scopus (836) Google Scholar] and has been identified as an independent factor for cardiovascular disease [[2]Lakka H.M. Laaksonen D.E. Lakka T.A. Niskanen L.K. Kumpusalo E. Tuomilehto J. et al.The metabolic syndrome and total and cardiovascular disease mortality in middle-aged men.JAMA. 2002; 288: 2709-2716Crossref PubMed Scopus (3989) Google Scholar]. Furthermore there are accumulating data in relation to the progression of NASH to cirrhosis, with estimates that almost 1 in 10 liver transplants will be performed for NASH cirrhosis in the coming decades [[3]Burke A. Lucey M.R. Non-alcoholic fatty liver disease, non-alcoholic steatohepatitis and orthotopic liver transplantation.Am J Transplant. 2004; 4: 686-693Crossref PubMed Scopus (171) Google Scholar], as well as to the development of hepatocellular carcinoma [[4]Bugianesi E. Leone N. Vanni E. Marchesini G. Brunello F. Carucci P. et al.Expanding the natural history of non-alcoholic steatohepatitis: from cryptogenic cirrhosis to hepatocellular carcinoma.Gastroenterology. 2002; 123: 134-140Abstract Full Text Full Text PDF PubMed Scopus (1249) Google Scholar]. It is therefore a major public health issue. At present, a liver biopsy is the gold standard for the diagnosis and classification of NAFLD [[5]Wieckowska A. Feldstein A.E. Diagnosis of nonalcoholic fatty liver disease: invasive versus noninvasive.Semin Liver Dis. 2008; 28: 386-395Crossref PubMed Scopus (233) Google Scholar] with histological assessment carried out according to various classifications [6Kleiner D.E. Brunt E.M. Van Natta M. Behling C. Contos M.J. Cummings O.W. et al.Design and validation of a histological scoring system for nonalcoholic fatty liver disease.Hepatology. 2005; 41: 1313-1321Crossref PubMed Scopus (6900) Google Scholar, 7Brunt E.M. Janney C.G. Di Bisceglie A.M. Neuschwander-Tetri B.A. Bacon B.R. Nonalcoholic steatohepatitis: a proposal for grading and staging the histological lesions.Am J Gastroenterol. 1999; 94: 2467-2474Crossref PubMed Scopus (3074) Google Scholar, 8Matteoni C.A. Younossi Z.M. Gramlich T. Boparai N. Liu Y.C. McCullough A.J. Nonalcoholic fatty liver disease: a spectrum of clinical and pathological severity.Gastroenterology. 1999; 116: 1413-1419Abstract Full Text Full Text PDF PubMed Scopus (2750) Google Scholar]. A liver biopsy has the advantage of providing important information relating to the degree of liver damage, changes in the overall liver architecture, as well as the severity of inflammatory activity and fibrosis. However, it is an invasive test, has inherent complications, is expensive, and is operator/analyser dependent. As a result there have been ongoing efforts to identify a reliable non-invasive means of assessing the presence and severity of NAFLD in at-risk populations.In this issue of Journal of Hepatology, Li et al. [[9]Li H. Fang Q. Gao F. Fan J. Zhou J. Wang X. et al.Fibroblast growth factor 21 levels are increased in nonalcoholic fatty liver disease patients and correlated with hepatic triglyceride.J Hepatol. 2010; 53: 97-103Abstract Full Text Full Text PDF Scopus (277) Google Scholar] report the results of a study examining the potential role of fibroblast growth factor 21 (FGF21) as a biomarker for identifying the presence of NAFLD. The rationale for their study was that FGF21 had been shown to be an important regulator of hepatic glucose and lipid metabolism in animal models [[10]Nishimura T. Nakatake Y. Konishi M. Itoh N. Identification of a novel FGF, FGF21, preferentially expressed in the liver.Biochim Biophys Acta. 2000; 1492: 203-206Crossref PubMed Scopus (633) Google Scholar] and its levels tend to be elevated in obese subjects and correlated with markers of insulin resistance [[11]Chavez A.O. Molina-Carrion M. Abdul-Ghani M.A. Folli F. Defronzo R.A. Tripathy D. Circulating fibroblast growth factor-21 is elevated in impaired glucose tolerance and type 2 diabetes and correlates with muscle and hepatic insulin resistance.Diabetes Care. 2009; 32: 1542-1546Crossref PubMed Scopus (294) Google Scholar]. While the investigators’ previous work had demonstrated that FGF21 concentrations correlated with gamma glutaryl transferase (GGT) and aspartate aminotransferase (AST) levels in Chinese subjects [[12]Li H. Bao Y. Xu A. Pan X. Lu J. Wu H. et al.Serum fibroblast growth factor 21 is associated with adverse lipid profiles and gamma-glutamyltransferase but not insulin sensitivity in Chinese subjects.J Clin Endocrinol Metab. 2009; 94: 2151-2156Crossref PubMed Scopus (94) Google Scholar], the current study population consisted of 224 adult Chinese patients with a diagnosis of NAFLD based on B-mode ultrasonography and 124 controls with a normal appearing liver ultrasound. Anthropometric measurements were performed in all patients and blood samples were obtained for the determination of FGF21, ALT, and GGT, as well as markers of lipid and glucose metabolism. The FGF21 concentrations were determined by a commercially available ELISA. In addition, the group classified the degree of hepatic steatosis and measured both FGF21 and lipid concentrations in liver samples from 17 patients undergoing resection for benign liver lesions. Li and colleagues demonstrated that serum FGF21 levels were significantly higher in the NAFLD group compared to the controls, and higher in NASH patients compared to those with fatty liver. The FGF21 levels associated positively with most indices under investigation while for high density lipoprotein cholesterol there was a significant negative association. Twelve of 17 liver biopsies exhibited hepatic steatosis with FGF21 mRNA expression increasing with the degree of steatosis and with the degree of FGF21 protein expression within the liver; both plasma and hepatic FGF21 correlated with hepatic triglyceride concentrations. The authors concluded that their results support the role of FGF21 as an important regulator of hepatic lipid biochemistry and suggest that FGF21 could act as a biomarker for NAFLD.This study, along with the recent study by Dushay et al. [[15]Dushay J, Chui PC, Gopalakrishnan GS, Varela-Rey M, Crawley M, Fisher FM, Badman MK, Martinez-Chantar ML, Maratos-Flier E. Increased fibroblast growth factor 21 in obesity and nonalcoholic fatty liver disease. Gastroenterology. 2010 Aug;139(2):456–463. Epub 2010 May 5.Google Scholar], represent an important contribution to the literature as they are the first to assess plasma FGF21 levels in patients with NAFLD. With the current need for reliable biomarkers to screen and monitor patients with NAFLD, this study [[9]Li H. Fang Q. Gao F. Fan J. Zhou J. Wang X. et al.Fibroblast growth factor 21 levels are increased in nonalcoholic fatty liver disease patients and correlated with hepatic triglyceride.J Hepatol. 2010; 53: 97-103Abstract Full Text Full Text PDF Scopus (277) Google Scholar] would suggest that FGF21 could potentially fulfil this role. There are however several limitations to the current study which need to be addressed in future investigations before plasma FGF21 can be adopted as a biomarker. The most important issue is the need to correlate FGF21 with liver histology, the current gold standard for the diagnosis of NAFLD, and distinguish fatty liver from NASH. The method of classification utilised in this study, namely B-mode ultrasound, has important limitations as a means of diagnosing and determining disease severity [[13]Wieckowska A. McCullough A.J. Feldstein A.E. Noninvasive diagnosis and monitoring of nonalcoholic steatohepatitis: present and future.Hepatology. 2007; 46: 582-589Crossref PubMed Scopus (350) Google Scholar]. This may explain the large overlap in FGF21 levels between the groups as illustrated in Fig. 1 since a number of the controls, in particular those with impaired glucose tolerance may have had sub-radiological hepatic steatosis. This overlap would certainly preclude FGF21 being used as a biomarker to screen patients. A second shortcoming is the use of liver biopsies from patients undergoing resection for benign liver disease. There are several issues related to choosing this tissue for the analysis of FGF21 mRNA. The mechanism for the development of steatosis is complex and varied between different disease states and may not be the same in these cases of ‘incidental’ steatosis as for NAFLD. Another area of concern is the use of transaminase levels to classify patients with ultrasound-detected steatosis as fatty liver or NASH as this can only be determined by a liver biopsy and it has been well established that serum ALT is a poor predictor of NASH with the full spectrum of disease severity found in patients with normal transaminases [[14]Mofrad P. Contos M.J. Haque M. Sargeant C. Fisher R.A. Luketic V.A. et al.Clinical and histologic spectrum of nonalcoholic fatty liver disease associated with normal ALT values.Hepatology. 2003; 37: 1286-1292Crossref PubMed Scopus (867) Google Scholar].With NAFLD now being recognised as a major public health problem, there is certainly the need for reliable biomarkers to identify and monitor those at risk of disease progression and potentially spare them from an invasive liver biopsy. The work presented by Li and co-workers in this edition of the Journal of Hepatology suggests that FGF21 may potentially fulfil this role, as corroborated by the study by Dushay et al. that was published when this article went to press [[15]Dushay J, Chui PC, Gopalakrishnan GS, Varela-Rey M, Crawley M, Fisher FM, Badman MK, Martinez-Chantar ML, Maratos-Flier E. Increased fibroblast growth factor 21 in obesity and nonalcoholic fatty liver disease. Gastroenterology. 2010 Aug;139(2):456–463. Epub 2010 May 5.Google Scholar]. However at present, further studies are required to clarify some muddy waters and validate the results reported herein.Conflict of interestThe authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript. The prevalence of non-alcoholic fatty liver disease (NAFLD) has shown a dramatic increase over recent years and is now reaching epidemic proportions. It is becoming increasingly evident that early identification of the condition is critical, as NAFLD, and in particular its more severe form non-alcoholic steatohepatitis (NASH), is linked strongly with the metabolic syndrome [[1]Hamaguchi M. Kojima T. Takeda N. Nakagawa T. Taniguchi H. Fujii K. et al.The metabolic syndrome as a predictor of non-alcoholic liver disease.Ann Intern Med. 2005; 143: 722-728Crossref PubMed Scopus (836) Google Scholar] and has been identified as an independent factor for cardiovascular disease [[2]Lakka H.M. Laaksonen D.E. Lakka T.A. Niskanen L.K. Kumpusalo E. Tuomilehto J. et al.The metabolic syndrome and total and cardiovascular disease mortality in middle-aged men.JAMA. 2002; 288: 2709-2716Crossref PubMed Scopus (3989) Google Scholar]. Furthermore there are accumulating data in relation to the progression of NASH to cirrhosis, with estimates that almost 1 in 10 liver transplants will be performed for NASH cirrhosis in the coming decades [[3]Burke A. Lucey M.R. Non-alcoholic fatty liver disease, non-alcoholic steatohepatitis and orthotopic liver transplantation.Am J Transplant. 2004; 4: 686-693Crossref PubMed Scopus (171) Google Scholar], as well as to the development of hepatocellular carcinoma [[4]Bugianesi E. Leone N. Vanni E. Marchesini G. Brunello F. Carucci P. et al.Expanding the natural history of non-alcoholic steatohepatitis: from cryptogenic cirrhosis to hepatocellular carcinoma.Gastroenterology. 2002; 123: 134-140Abstract Full Text Full Text PDF PubMed Scopus (1249) Google Scholar]. It is therefore a major public health issue. At present, a liver biopsy is the gold standard for the diagnosis and classification of NAFLD [[5]Wieckowska A. Feldstein A.E. Diagnosis of nonalcoholic fatty liver disease: invasive versus noninvasive.Semin Liver Dis. 2008; 28: 386-395Crossref PubMed Scopus (233) Google Scholar] with histological assessment carried out according to various classifications [6Kleiner D.E. Brunt E.M. Van Natta M. Behling C. Contos M.J. Cummings O.W. et al.Design and validation of a histological scoring system for nonalcoholic fatty liver disease.Hepatology. 2005; 41: 1313-1321Crossref PubMed Scopus (6900) Google Scholar, 7Brunt E.M. Janney C.G. Di Bisceglie A.M. Neuschwander-Tetri B.A. Bacon B.R. Nonalcoholic steatohepatitis: a proposal for grading and staging the histological lesions.Am J Gastroenterol. 1999; 94: 2467-2474Crossref PubMed Scopus (3074) Google Scholar, 8Matteoni C.A. Younossi Z.M. Gramlich T. Boparai N. Liu Y.C. McCullough A.J. Nonalcoholic fatty liver disease: a spectrum of clinical and pathological severity.Gastroenterology. 1999; 116: 1413-1419Abstract Full Text Full Text PDF PubMed Scopus (2750) Google Scholar]. A liver biopsy has the advantage of providing important information relating to the degree of liver damage, changes in the overall liver architecture, as well as the severity of inflammatory activity and fibrosis. However, it is an invasive test, has inherent complications, is expensive, and is operator/analyser dependent. As a result there have been ongoing efforts to identify a reliable non-invasive means of assessing the presence and severity of NAFLD in at-risk populations. In this issue of Journal of Hepatology, Li et al. [[9]Li H. Fang Q. Gao F. Fan J. Zhou J. Wang X. et al.Fibroblast growth factor 21 levels are increased in nonalcoholic fatty liver disease patients and correlated with hepatic triglyceride.J Hepatol. 2010; 53: 97-103Abstract Full Text Full Text PDF Scopus (277) Google Scholar] report the results of a study examining the potential role of fibroblast growth factor 21 (FGF21) as a biomarker for identifying the presence of NAFLD. The rationale for their study was that FGF21 had been shown to be an important regulator of hepatic glucose and lipid metabolism in animal models [[10]Nishimura T. Nakatake Y. Konishi M. Itoh N. Identification of a novel FGF, FGF21, preferentially expressed in the liver.Biochim Biophys Acta. 2000; 1492: 203-206Crossref PubMed Scopus (633) Google Scholar] and its levels tend to be elevated in obese subjects and correlated with markers of insulin resistance [[11]Chavez A.O. Molina-Carrion M. Abdul-Ghani M.A. Folli F. Defronzo R.A. Tripathy D. Circulating fibroblast growth factor-21 is elevated in impaired glucose tolerance and type 2 diabetes and correlates with muscle and hepatic insulin resistance.Diabetes Care. 2009; 32: 1542-1546Crossref PubMed Scopus (294) Google Scholar]. While the investigators’ previous work had demonstrated that FGF21 concentrations correlated with gamma glutaryl transferase (GGT) and aspartate aminotransferase (AST) levels in Chinese subjects [[12]Li H. Bao Y. Xu A. Pan X. Lu J. Wu H. et al.Serum fibroblast growth factor 21 is associated with adverse lipid profiles and gamma-glutamyltransferase but not insulin sensitivity in Chinese subjects.J Clin Endocrinol Metab. 2009; 94: 2151-2156Crossref PubMed Scopus (94) Google Scholar], the current study population consisted of 224 adult Chinese patients with a diagnosis of NAFLD based on B-mode ultrasonography and 124 controls with a normal appearing liver ultrasound. Anthropometric measurements were performed in all patients and blood samples were obtained for the determination of FGF21, ALT, and GGT, as well as markers of lipid and glucose metabolism. The FGF21 concentrations were determined by a commercially available ELISA. In addition, the group classified the degree of hepatic steatosis and measured both FGF21 and lipid concentrations in liver samples from 17 patients undergoing resection for benign liver lesions. Li and colleagues demonstrated that serum FGF21 levels were significantly higher in the NAFLD group compared to the controls, and higher in NASH patients compared to those with fatty liver. The FGF21 levels associated positively with most indices under investigation while for high density lipoprotein cholesterol there was a significant negative association. Twelve of 17 liver biopsies exhibited hepatic steatosis with FGF21 mRNA expression increasing with the degree of steatosis and with the degree of FGF21 protein expression within the liver; both plasma and hepatic FGF21 correlated with hepatic triglyceride concentrations. The authors concluded that their results support the role of FGF21 as an important regulator of hepatic lipid biochemistry and suggest that FGF21 could act as a biomarker for NAFLD. This study, along with the recent study by Dushay et al. [[15]Dushay J, Chui PC, Gopalakrishnan GS, Varela-Rey M, Crawley M, Fisher FM, Badman MK, Martinez-Chantar ML, Maratos-Flier E. Increased fibroblast growth factor 21 in obesity and nonalcoholic fatty liver disease. Gastroenterology. 2010 Aug;139(2):456–463. Epub 2010 May 5.Google Scholar], represent an important contribution to the literature as they are the first to assess plasma FGF21 levels in patients with NAFLD. With the current need for reliable biomarkers to screen and monitor patients with NAFLD, this study [[9]Li H. Fang Q. Gao F. Fan J. Zhou J. Wang X. et al.Fibroblast growth factor 21 levels are increased in nonalcoholic fatty liver disease patients and correlated with hepatic triglyceride.J Hepatol. 2010; 53: 97-103Abstract Full Text Full Text PDF Scopus (277) Google Scholar] would suggest that FGF21 could potentially fulfil this role. There are however several limitations to the current study which need to be addressed in future investigations before plasma FGF21 can be adopted as a biomarker. The most important issue is the need to correlate FGF21 with liver histology, the current gold standard for the diagnosis of NAFLD, and distinguish fatty liver from NASH. The method of classification utilised in this study, namely B-mode ultrasound, has important limitations as a means of diagnosing and determining disease severity [[13]Wieckowska A. McCullough A.J. Feldstein A.E. Noninvasive diagnosis and monitoring of nonalcoholic steatohepatitis: present and future.Hepatology. 2007; 46: 582-589Crossref PubMed Scopus (350) Google Scholar]. This may explain the large overlap in FGF21 levels between the groups as illustrated in Fig. 1 since a number of the controls, in particular those with impaired glucose tolerance may have had sub-radiological hepatic steatosis. This overlap would certainly preclude FGF21 being used as a biomarker to screen patients. A second shortcoming is the use of liver biopsies from patients undergoing resection for benign liver disease. There are several issues related to choosing this tissue for the analysis of FGF21 mRNA. The mechanism for the development of steatosis is complex and varied between different disease states and may not be the same in these cases of ‘incidental’ steatosis as for NAFLD. Another area of concern is the use of transaminase levels to classify patients with ultrasound-detected steatosis as fatty liver or NASH as this can only be determined by a liver biopsy and it has been well established that serum ALT is a poor predictor of NASH with the full spectrum of disease severity found in patients with normal transaminases [[14]Mofrad P. Contos M.J. Haque M. Sargeant C. Fisher R.A. Luketic V.A. et al.Clinical and histologic spectrum of nonalcoholic fatty liver disease associated with normal ALT values.Hepatology. 2003; 37: 1286-1292Crossref PubMed Scopus (867) Google Scholar]. With NAFLD now being recognised as a major public health problem, there is certainly the need for reliable biomarkers to identify and monitor those at risk of disease progression and potentially spare them from an invasive liver biopsy. The work presented by Li and co-workers in this edition of the Journal of Hepatology suggests that FGF21 may potentially fulfil this role, as corroborated by the study by Dushay et al. that was published when this article went to press [[15]Dushay J, Chui PC, Gopalakrishnan GS, Varela-Rey M, Crawley M, Fisher FM, Badman MK, Martinez-Chantar ML, Maratos-Flier E. Increased fibroblast growth factor 21 in obesity and nonalcoholic fatty liver disease. Gastroenterology. 2010 Aug;139(2):456–463. Epub 2010 May 5.Google Scholar]. However at present, further studies are required to clarify some muddy waters and validate the results reported herein. Conflict of interestThe authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript. The authors who have taken part in this study declared that they do not have anything to disclose regarding funding or conflict of interest with respect to this manuscript.