The diagnosis of major depressive disorder (MDD) is symptom based due to the lack of biological biomarker. p11 protein was recently found to be an important factor mediating depression-like states and antidepressant responses. The aim of the study was to assess whether p11 protein in urine can serve as a potential biomarker for major depression, and the relationship of its levels among urine, serum and cerebrospinal fluid (CSF).

We obtained urine samples from 13 drug-free MDD patients and 13 age- and gender-matched healthy controls. We also collected urine, serum and cerebrospinal fluid samples from 13 of fracture patients or cesarean section patients in the spinal anesthesia. The concentrations of p11 protein were measured using ELISA.

In MDD patients, urine levels of p11 protein were all less than the minimum detectable concentration of the ELISA kit. The urine levels of p11 were detectable only in one healthy control. In the spinal anesthesia patients, we can detect p11 concentrations in both serum and urine in only two patients. Besides, levels of p11 were detectable in the serum of one patient and urine of another patient. We were unable to measure CSF levels of p11 in all patients.

Concentrations of p11 protein in the body fluids are very low and unstable. The sensitivity of the current p11 ELISA kit is currently unsatisfactory, requiring the development of an ELISA kit of higher sensitivity to determine whether p11 in body fluids can serve as biomarker for depression.

The authors have not supplied their declaration of competing interest.