Subjects and assessment
Between January 2016 and December 2018, 107 patients with MDD were recruited (48 men and 59 women aged 18–65 years). All were patients who had been admitted to a mental health facility in Ningbo, China, and they all met the diagnostic criteria of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V). Trained psychiatrists assessed depression severity using the 17-item Hamilton Depression Rating Scale (HDRS). All patients discontinue antidepressant use for at least 2 weeks. To qualify for the study, the patients had to be able to communicate, understand the purpose of the study, and agree to participate.
The risk of suicide in patients with depression was assessed using the nurse's global assessment of suicide risk (NGASR). Patients with an NGASR score ≥ 9 (n = 60; 25 men, 35 women) were sorted into the high-suicide-risk group, while those with an NGASR score < 9 (n = 47; 23 men, 24 women) were sorted into the low-suicide-risk group. In the high-risk group, all patients had a history of suicidal ideation and suicide attempts. In the low-risk group, none of the patients had ever attempted suicide. The control group consisted of 40 volunteers (18 men, 22 women). They were excluded from the study if they had an HDRS score > 7 points, a state–trait anxiety scale score ≥ 40, any self-reported personal or family history of mental illness, or any personal history of psychotropic drug treatment. The control group matched the patient groups in terms of age, gender, and other parameters.
The exclusion criteria were as follows: severe somatic disease, ethanol or drug dependency, pregnancy or lactation, drug allergies. All subjects participated in the study voluntarily and signed the written informed consent forms. The present study was approved by the Ethics Committees of Ningbo Kangning Hospital. All experimental procedures followed the Declaration of Helsinki guidelines for human medical research.
All subjects completed the HDRS and NGASR, and all were diagnosed and rated by two trained psychiatrists. Venous blood samples (10 mL) were collected in the morning following an overnight fast and centrifuged for 5 minutes at 3,500 rpm; the serum was extracted and stored at -80ºC to await biochemical analysis.
The serum sample was taken out from the -80°C freezer, dissolved and subjected to enzyme-linked immunosorbent assay (ELISA). Serum levels of VGF were tested using VGF [SEB166Hu] ELISA kits from USCN Life Science (Wuhan, Hubei, China). We performed all experiments in duplicate, and every empty added 100 microliters sample. Absorbance readings were measured at 450 nm using a microplate reader (EnSpire; Perkin Elmer Inc., Waltham, MA), with a reference wavelength of 690 nm; the readings were then converted into concentrations by comparison with standard curve values.
Statistical analysis of the data was carried out using SPSS 22.0 software. All data are presented as mean ± SD; p-values are two-tailed, with statistical significance being set at p < 0.05. Demographic and clinical information was analyzed using one-way analysis of variance (ANOVA) for continuous variables and the chi-square test for categorical variables. By controlling factors such as age and education, analysis of covariance was used to determine the differences between the mean values of the groups. VGF levels were compared post hoc between groups. VGF values that deviated from the average value by more than three standard deviations were defined as outliers. In patients with MDD, we further analyzed the correlation between serum VGF and the following clinical variables using Pearson’s correlation: HDRS, NGASR, and demographic and clinical variables.