2.1 Screening of different groups of livery injury at different stages of HBV infection
This study randomly included 31 HBV carriers, 37 cases of chronic HBV, 83 cases of HBV-related cirrhosis (51 cases of CHC and 32 cases of DHC), and 46 cases of HCC treated in the 980th Hospital of Chinese People’s Liberation Army Joint Logistic Support Force (Hebei Province, China) from June 2015 to October 2016. The diagnoses of the patients were in accordance with the Guidelines for the Prevention and Treatment of Chronic HBV in China published in 2015 and the Diagnostic Standard for HBV Infection issued and implemented by the Ministry of Health of the People’s Republic of China. The exclusion criteria of this study for patients were: (1) autoimmune disease; (2) liver disease(s) due to other causes, such as fatty liver, alcoholic liver disease(s), or drug-induced liver disease(s); (3) underlying accompanied diseases, such as diabetes, hypertension, lung disease, heart disease, cerebrovascular disease, and kidney disease; (4) concurrence of hepatitis C virus infection; (5) with fever above 37.5°C; (6) other disease(s) and medical history that the researchers believed that might affect the experimental results; and (7) any other condition that the researchers believed was not suitable for the inclusion.
2.2 Healthy control screening
A total of 58 healthy volunteers who underwent physical examinations at the Physical Examination Center of the 980th Hospital of the Chinese People’s Liberation Army Joint Logistic Support Force from June 2015 to October 2016 were included in this study as the healthy control group. The screening criteria were: (1) healthy volunteers with their liver functions and AFP within the normal reference intervals; (2) candidates without respiratory diseases (e.g., tuberculosis), endocrine diseases (e.g., diabetes), cardiovascular diseases (e.g., hypertension), kidney diseases (e.g., kidney failure), and circulatory system diseases (e.g., leukemia); and (3) candidates with no positive clinical symptoms, no viral hepatitis infection, no smoking and alcohol consumption history, and age within 20–65 years old.
2.3 Liver function markers and demographic characteristics
All participants were asked to register their demographic information, such as name, gender, age, time of hospital visit, and clinical/hospital number, which was followed by testing and recording their biochemical and hemagglutination indices, mainly including glutamic-pyruvic transaminase (ALT), glutamic oxalacetic transaminase (AST), total bilirubin (TBil), albumin (ALB), and prothrombin time (PT) (Table 1). The ALT, AST, ALB, and TBil were detected by a P800 module automatic biochemical analyzer (Roche).
2.4 Experimental materials
Standard preparation: The ion mode detected by each substance was determined according to the corresponding value of the standard substance mass spectrometer. Table 2 shows the name and ion mode of each compound. The concentration of the standard stock solution was 5.0 mg/mL. The solvent was the mobile phase 0.1% formic acid aqueous solution (A)-acetonitrile (B), followed by diluting the concentration of each compound as 25 mg/L mixed standard working solutions, which were used for comparisons between the different preprocessing steps and methodological investigation. The internal standard solution was 2-chlorophenylalanine at a concentration of 0.1 mg/mL.
2.5 Experimental methods
2.5.1 Sample collection
In the early morning and under fasting conditions, three milliliters of peripheral venous blood were collected from each participant into a standard disposable glass tube. Within one hour, the blood samples were centrifuged at 3,500 rpm for 5 min to collect and seal 1.5 mL serum in an Eppendorf tube, with the specimen information marked on the tube surface. The serum samples were stored at −80°C for later use.
2.5.2 Pre-test process
A total of 255 serum samples of different groups were thawed at room temperature, followed by collecting 100 µL of serum and adding 20 µL of the internal standard solution (0.1 mg/mL of 2-chlorophenylalanine) and 300 µL of a 3:1 methanol/acetonitrile solution (precooled at 4°C for half an hour before usage). The serum mixtures were vortexed for 2 min, followed by 1 min sonication. After cooling at −20°C, the serum mixture was thawed at room temperature and then centrifuged at 5,000 rpm for 5 min at 4°C. The supernatant was collected and filtered through a 0.22-μm filter for later experiments.
2.5.3 Required instrument and conditions for detection
2.5.3.1 Chromatographic conditions
An Endeavorsil MT C18 column (50 × 2.1 mm, 1.8 µm) was used, with the column temperature defaulted as room temperature. The mobile phase of the column was 0.1% formic acid aqueous solution (A)-acetonitrile (B), with a 0.30 mL/min flow rate and 5 µL injection volumes. Table S1 shows the gradient elution program.
2.5.3.2 Mass spectrometry conditions
Ion source: ESI positive and negative ions were scanned simultaneously, with the scanning range of MS1 m/z 100–1,000 and MS2 m/z 50–550, the CDL temperature of 200°C, and the heating module temperature of 200°C. The drying gas flow rate was 10 L/min, and the atomizing gas flow rate was 1.5 L/min. The ion source voltages were +4.5 kV positive ion mode and −3.5 kV negative ion mode. The detector voltage was 1.70 kV, and the CID parameter was 50% collision energy. The mass calibration method based on automatic tuning was used to optimize voltage and the standard external method to calibrate the mass.
2.6 Data processing and statistical analysis
Serum samples from six groups, including the HBV carrier group, chronic hepatitis B group, CHC group, DHC group, primary HCC group, and the healthy control group were tested to obtain the data of the metabolite composition and contents. IBM SPSS 24.0 software (IBM SPSS Inc., Chicago, IL) were used for statistical analysis in this study. A non-parametric test was used to analyze the difference between groups. The diagnostic values of metabolites were analyzed by the ROC curve.