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To the Editor:

Guha and coworkers1 reported the results of their study aiming to validate a surrogate diagnostic biomarker-based panel for the diagnosis of liver fibrosis. The authors investigated a total of 192 patients who had liver biopsies because of elevated aminotransferases and demonstrated that the Enhanced Liver Fibrosis (ELF) Panel yielded an area under the curve (AUC) of 0.90 for distinguishing severe fibrosis, 0.82 for moderate fibrosis, and 0.76 for no fibrosis.1 The ELF panel includes a series of enzyme-linked immunosorbent assay (ELISA)-based tests investigating three potential biomarkers of liver fibrosis, namely tissue inhibitor of matrix metalloproteinase 1 (TIMP1), hyaluronic acid, and aminoterminal peptide of pro-collagen III.1

Although liver biopsy followed by histologic examination remains the gold standard for the diagnosis and assessment of fibrosis, this method is invasive and has several inherent limitations and disadvantages.2 Therefore, growing efforts are being spent in the quest of biomarkers of liver fibrosis in an attempt to reduce the need for liver biopsy. Hepatic fibrosis is characterized by accumulation of extracellular matrix (including pro-collagen III and hyaluronic acid) and by increased release of tissue inhibitors of metalloproteinases (including TIMP1).3 In addition to accumulation of extracellular matrix, liver fibrosis is accompanied by increased apoptosis of hepatocytes.4 In this regard, a novel method to detect hepatocyte apoptosis consists of the measurement of the proteolytic neoepitope of the caspase substrate cytokeratin 18 in the sera of patients.5 A neoepitope in cytokeratin 18 (CK18), termed M30 antigen, becomes available at an early caspase cleavage event during apoptosis and is not detectable in vital or necrotic cells. In contrast, the cytosolic pool of uncleaved CK18 (also termed M65 antigen) is released from cells during necrosis. These findings implicate that assessments of different forms of CK18 in patient sera (M30 antigen for apoptosis and M65 antigen for necrosis) could be used to examine different cell death modes in vivo.5 Notably, we have previously demonstrated that simple measurements of M30 and M65 antigens by ELISA yielded an AUC of 0.73 and 0.74 for distinguishing advanced fibrosis from early fibrosis, respectively.6 Interestingly, a recent proteomic study has identified a few additional potential markers of liver fibrosis, including ITIH4 fragments, complement factor H-related protein 1, CD5L, Apo L1, β2GPI, and thioester-cleaved products of alpha-2 macroglobulin.7

In the light of these findings, we conclude that future efforts should be made to develop an integrated panel of biomarkers examining not only proteins involved in the enhanced extracellular matrix deposition (as in the ELF panel),1 but also in liver apoptosis.6 Addition of novel biomarkers differently expressed in liver fibrosis as identified by proteomic analysis7 may also increase the diagnostic value of the novel integrated panel. The use of biomarkers to identify patients with hepatic fibrosis may actually hold promise to develop innovative, noninvasive tests for the diagnosis of this condition, thereby reducing patient discomfort associated with invasive procedures such as liver biopsies. Moreover, it is likely to facilitate the identification of putative antifibrogenic approaches in the next few years.

References

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  • 1
    Guha IN, Parkes J, Roderick P, Chattopadhyay D, Cross R, Harris S, et al. Noninvasive markers of fibrosis in nonalcoholic fatty liver disease: validating the European Liver Fibrosis Panel and exploring simple markers. HEPATOLOGY 2008; 47: 455460.
  • 2
    Bataller R, Brenner DA. Liver fibrosis. J Clin Invest 2005; 115: 209218.
  • 3
    Friedman SL. Mechanisms of hepatic fibrogenesis. Gastroenterology 2008; 134: 16551669.
  • 4
    Török NJ. Recent advances in the pathogenesis and diagnosis of liver fibrosis. J Gastroenterol 2008; 43: 315321.
  • 5
    Cummings J, Ranson M, Butt F, Moore D, Dive C. Qualification of M30 and M65 ELISAs as surrogate biomarkers of cell death: long term antigen stability in cancer patient plasma. Cancer Chemother Pharmacol 2007; 60: 921924.
  • 6
    Yilmaz Y, Dolar E, Ulukaya E, Akgoz S, Keskin M, Kiyici M, et al. Soluble forms of extracellular cytokeratin 18 may differentiate simple steatosis from nonalcoholic steatohepatitis. World J Gastroenterol 2007; 13: 837844.
  • 7
    Gangadharan B, Antrobus R, Dwek RA, Zitzmann N. Novel serum biomarker candidates for liver fibrosis in hepatitis C patients. Clin Chem 2007; 53: 17921799.

Yusuf Yilmaz*, Engin Ulukaya†, Enver Dolar‡, * Department of Internal Medicine, Uludag University Medical School, Bursa, Turkey, † Department of Biochemistry, Uludag University Medical School, Bursa, Turkey, ‡ Department of Gastroenterology, Uludag University Medical School, Bursa, Turkey.