Clinical Relevance of Plasma Prolylcarboxypeptidase Level in Patients with Idiopathic Acute Optic Neuritis

Objectives: This study evaluated the plasma concentration of prolylcarboxypeptidase (PRCP) and its clinical relevance in patients with idiopathic acute optic neuritis (ON). Methods: We investigated the expression of PRCP in the optic nerves of experimental autoimmune optic neuritis (EAON)-induced mice. Peripheral blood samples were collected from ON patients (n = 20) and healthy controls (n = 20). ELISA was used to measure the plasma PRCP levels. We performed measurements of visual acuity and the mean thicknesses of the macular ganglion cell layer plus inner plexiform layer (GCL+IPL) at diagnosis and 6 months after diagnosis. Results: The PRCP mRNA expression in EAON-induced mice was markedly higher than that in naïve mice. The mean plasma PRCP level was significantly higher in patients with ON than in controls. Plasma PRCP levels were negatively correlated with logMAR visual acuity at 6 months after diagnosis and differences in macular GCL+IPL thickness during an ON attack. A plasma PRCP level of 49.98 (pg/mL) predicted the recurrence of ON with a 75% sensitivity and 87.5% specificity. Conclusions: Patients with idiopathic acute ON had higher plasma PRCP levels, and this was positively correlated with final visual outcome and well-preserved macular GCL+IPL thickness during an ON attack. The increase in plasma PRCP level may reflect its compensatory secretion to counteract neuroinflammation in ON patients.