Mac-2 binding protein glycan isomer (M2BPGi) is a new serum biomarker for assessing liver fibrosis: more than a biomarker of liver fibrosis

Assessing liver fibrosis is important for predicting the efficacy of antiviral therapy and patient prognosis. Liver biopsy is the gold standard for diagnosing liver fibrosis, despite its invasiveness and problematic diagnostic accuracy. Although noninvasive techniques to assess liver fibrosis are becoming important, reliable serum surrogate markers are not available. A glycoproteomics study aimed at identifying such markers discovered Mac 2-Binding Protein Gylcan Isomer (M2BPGi), which is a reliable marker for assessing liver fibrosis in patients with viral hepatitis and other fibrotic liver diseases such as primary biliary cholangitis, biliary atresia, autoimmune hepatitis, and nonalcoholic fatty liver disease. M2BPGi predicts the development of hepatocellular carcinoma (HCC) in patients infected with hepatitis B and C as well as the prognosis of liver cirrhosis in those with HCC after therapy. The unique features of M2BPGi are as follows: (1) cut-off values differ for the same stages of fibrosis according to the cause of fibrosis; and (2) M2BPGi levels rapidly decrease after patients achieve a sustained antiviral response to hepatitis C virus. These observations cannot be explained if M2BPGi levels reflect the amount of fibrotic tissue. Hepatic stellate cells (HSCs) secrete M2BPGi, which may serve as a messenger between HSCs and Kupffer cells via Mac-2 (galectin 3) that is expressed in Kupffer cells during fibrosis progression. Here we show that M2BPGi is a surrogate marker for assessing HSC activation. These findings may reveal the roles of HSCs in extrahepatic fibrotic disease progression.