Use of Mac-2 binding protein as a biomarker for nonalcoholic fatty liver disease diagnosis.

In contrast to patients with viral hepatitis, patients with nonalcoholic fatty liver disease (NAFLD) can progress to hepatocellular carcinoma during the initial stages of liver fibrosis. Development and implementation of noninvasive methods for diagnosis and progression prediction are important for effective NAFLD surveillance. Mac-2 binding protein (Mac-2bp) is a useful nonalcoholic steatohepatitis (NASH) diagnosis biomarker and a powerful prediction biomarker for NAFLD fibrosis stage. Wisteria floribunda agglutinin (WFA)-positive Mac-2bp (WFA+-M2BP) is a novel serum fibrosis biomarker for chronic hepatitis C that has clinical validity. Mac-2bp and WFA+-M2BP are also clinical NAFLD biomarker candidates. We examined the efficacy of Mac-2bp and WFA+-M2BP for NAFLD assessment using patients with biopsy-proven NAFLD (n = 510; NAFLD cohort) and subjects who received a health check-up (n = 2,122; check-up cohort). In the NAFLD cohort, we set the fibrosis predicting cutoff values as 1.80 (F1), 2.21 (F2), and 2.24 µg/mL (F3). In the subjects with fatty liver from the check-up cohort (n = 1,291), the serum Mac-2bp levels were >1.80 µg/mL in 38.6% of the subjects (n = 498), and >2.24 µg/mL in 24.6% of the subjects (n = 318). The NAFLD cohort results indicated that Mac-2bp and WFA+-M2BP were equally useful for NASH diagnosis. During the early stages of fibrosis (F1, F2), the increase in Mac-2bp was statistically significant but WFA+-M2BP did not increase. Logistic regression analysis revealed that Mac-2bp was an independent determinant for the prediction of advanced fibrosis stage (≥F2), even when adjusted for WFA+-M2BP. Immunohistochemical staining of Mac-2bp revealed that hepatocytes strongly expressed Mac-2bp in patients with NAFLD. Conclusion: Our results indicated that hepatocyte-derived Mac-2bp would be a useful single biomarker for NASH diagnosis and fibrosis stage prediction in patients with NAFLD. (Hepatology Communications 2017;1:780-791).

Establishment of mouse Mac-2 binding protein enzyme-linked immunosorbent assay and its application for mouse chronic liver disease models.

AIM: We identified Mac-2 (galectin-3) binding protein (Mac-2bp) as a novel diagnostic and liver fibrosis predicting biomarker for nonalcoholic steatohepatitis in humans. In mouse models, there are no serum biomarkers predicting liver disease severity. In this study, we developed a mouse Mac-2bp enzyme-linked immunosorbent assay (ELISA) system and determined its efficacy for predicting the severity of liver disease in mouse models, especially in non-alcoholic fatty liver disease (NAFLD) models. METHODS: We established several rat monoclonal antibodies against mouse Mac-2bp, selected two clones for the ELISA, and checked the accuracy and reproducibility of the ELISA, especially for NAFLD models and liver fibrosis models. We also investigated the relationships between serum levels and hepatic gene expression of Mac-2bp in mouse models. RESULTS: Our ELISA system had high accuracy and reproducibility (R2 = 0.999). The intra-assay and inter-assay results for the coefficient of variation were 2.0-3.7% and 1.7-6.9%, respectively. The levels of bilirubin, hemoglobin, and chyle did not affect the Mac-2bp serum levels detected by our ELISA kit. In the mouse models, serum Mac-2bp levels increased with liver disease progression (F0/F1/F2/F3, 239.1 ± 36.7 / 259.1 ± 43.0 / 457.5 ± 162.0 / 643.7 ± 116.0 ng/mL; P < 0.0001), and were significantly correlated with hepatic gene expression of Mac-2bp (R = 0.42, P < 0.0001). CONCLUSION: Our mouse Mac-2bp ELISA system effectively predicts severity of NAFLD and liver fibrosis in mouse models.

Hepatic aberrant glycosylation by N-acetylglucosaminyltransferase V accelerates HDL assembly.

Glycosylation is involved in various pathophysiological conditions. N-Acetylglucosaminyltransferase V (GnT-V), catalyzing ß1-6 branching in asparagine-linked oligosaccharides, is one of the most important glycosyltransferases involved in cancer and the immune system. Recent findings indicate that aberrant N-glycan structure can modify lipid metabolism. In this study, we investigated the effects of aberrant glycosylation by GnT-V on high-density lipoprotein cholesterol (HDL) assembly. We used GnT-V transgenic (Tg) mice and GnT-V Hep3B cell (human hepatoma cell line) transfectants. The study also included 96 patients who underwent medical health check-ups. Total serum cholesterol levels, particularly HDL-cholesterol (HDL-C) levels, were significantly increased in Tg vs. wild-type (WT) mice. Hepatic expression of apolipoprotein AI (ApoAI) and ATP-binding cassette subfamily A member 1 (ABCA1), two important factors in HDL assembly, were higher in Tg mice compared with WT mice. ApoAI and ABCA1 were also significantly elevated in GnT-V transfectants compared with mock-transfected cells. Moreover, ApoAI protein in the cultured media of GnT-V transfectants was significantly increased. Finally, we found a strong correlation between serum GnT-V activity and HDL-C concentration in human subjects. Multivariate logistic analyses demonstrated that GnT-V activity was an independent and significant determinant for serum HDL-C levels even adjusted with age and gender differences. Further analyses represented that serum GnT-V activity had strong correlation especially with the large-size HDL particle concentration. These findings indicate that enhanced hepatic GnT-V activity accelerated HDL assembly and could be a novel mechanism for HDL synthesis.

Serum Mac-2 binding protein is a novel biomarker for chronic pancreatitis.

AIM: To determine the efficacy of Mac-2 binding protein (Mac-2bp) for diagnosis of chronic pancreatitis. METHODS: Fifty-nine healthy volunteers (HV), 162 patients with chronic pancreatitis (CP), and 94 patients with pancreatic ductal adenocarcinoma (PDAC) were enrolled in this study. We measured serum Mac-2bp using our developed enzyme-linked immunosorbent assay kit. Additional biochemical variables were measured using an automated analyzer (including aminotransferase, alanine aminotransferase, γ-glutamyltransferase, alkaline phosphatase, triglyceride, C-reactive protein, and amylase levels) or chemiluminescent enzyme immunoassay (carbohydrate antigen 19-9 and carcinoembryonic antigen). The ability of Mac-2bp to predict CP diagnosis accurately was assessed using receiver operating characteristic (ROC) analyses. RESULTS: Serum Mac-2bp levels were significantly increased in CP patients compared to HV (P < 0.0001) and PDAC patients (P < 0.0001). Area under the ROC curve values of Mac-2bp for the discrimination of CP from HV and PDAC were 0.727 and 0.784, respectively. Multivariate analyses demonstrated that serum Mac-2bp levels were independent determinants for CP diagnosis from HV and PDAC patients. Immunohistological staining showed that Mac-2bp was expressed faintly in the pancreas tissues of both CP and PDAC patients. Serum aspartate aminotransferase, alanine aminotransferase, γ-glutamyltransferase, alkaline phosphatase, and triglyceride levels were significantly higher in patients with CP or PDAC. Serum Mac-2bp levels were highly correlated with protein levels of alanine aminotransferase, γ-glutamyltransferase, and C-reactive protein, but not amylase, suggesting that the damaged liver produces Mac-2bp. CONCLUSION: Measurement of serum Mac-2bp may be a novel and useful biomarker for CP diagnosis as well as liver fibrosis in the general population.

Ectopic expression of N-acetylglucosaminyltransferase V accelerates hepatic triglyceride synthesis.

AIM: Glycosylation changes induce various types of biological phenomena in human diseases. N-Acetylglucosaminyltransferase V (GnT-V) is one of the most important glycosyltransferases involved in cancer biology. Recently, many researchers have challenged studies of lipid metabolism in cancer. To elucidate the relationships between cancer and lipid metabolism more precisely, we investigated the effects of GnT-V on lipid metabolism. In this study, we investigated the effects of aberrant glycosylation by GnT-V on hepatic triglyceride production. METHODS: We compared lipid metabolism in GnT-V transgenic (Tg) mice with that of wild-type (WT) mice fed with normal chow or a choline-deficient amino acid-defined (CDAA) diet in vivo. HepG2 cells and GnT-V transfectants of Hep3B cells were used in an in vitro study. RESULTS: Serum triglyceride levels and hepatic very low-density lipoprotein (VLDL) secretion in Tg mice were significantly elevated compared with that of WT mice. Hepatic lipogenic genes (Lxrα, Srebp1, Fas and Acc) and VLDL secretion-related gene (Mttp1) were significantly higher in Tg mice. Expression of these genes was also significantly higher in GnT-V transfectants than in mock cells. Knockdown of GnT-V decreased, while both epidermal growth factor and transforming growth factor-ß1 stimulation increased LXRα gene expression in HepG2 cells. Finally, we found that the blockade of VLDL secretion by CDAA diet induced massive hepatic steatosis in Tg mice. CONCLUSION: Our study demonstrates that enhancement of hepatic GnT-V activity accelerates triglyceride synthesis and VLDL secretion. Glycosylation modification by GnT-V regulation could be a novel target for a therapeutic approach to lipid metabolism.