Serum exosome proteome reveals the novel fibrosis marker in chronic hepatitis C patients

【Background】Although several serum markers to evaluate liver fibrosis are developed, their diagnostic abilities are insufficient compared with that of liver biopsy. We aimed to identify a novel hepatic fibrosis marker using serum exosome by proteome analysis.
【Methods and Results】Exosome was purified from serum using affinity method. Shotgun proteomic analysis using exosomes from 55 chronic hepatitis C patients (F0-1/2/3/4: 28/12/7/8) detected 1027 exosome proteins. Among them, PPBP, APCS, LPA, and ATP6V0A1 were identified as proteins whose expression levels were significantly different between patients with F1 vs F2-4, F1-2 vs F3-4, and F1-3 vs F4 (p < 0.02). We examined expression levels of these proteins using another 80 patients (F1/2/3/4: 20/20/20/20) by target proteomic analysis. PPBP and APCS were verified as exosome proteins, whose expression levels were significantly different between patients with F1 vs F2-4, F1-2 vs F3-4, and F1-3 vs F4. PPBP and APCS levels decreased in accordance with fibrosis progressed. Their expression levels in exosome were highly positively co-related with serum levels of PPBP and APCS measured by ELISA. The AUROC of serum APCS for diagnosing F4 was 0.77, and comparable with that of type IV collagen 0.756, serum PPBP 0.719, platelets 0.7, hyaluronic acid 0.692, and Fib4 index 0.635.
【Conclusion】Serum exosome proteome revealed the novel fibrosis candidate proteins. Serum APCS may be a novel biomarker to diagnose liver cirrhosis.