Serum Prolidase Activity as a Biomarker for Choroid Plexus Calcification

The choroid plexus (CP) performs multiple functions such as secretion and reabsorption. CP also acts as the blood-cerebrospinal fluid barrier. Prolidase plays an important role in collagen metabolism by degrading imidodipeptides, in which proline or hydroxyproline residue is located at the C-terminal end. Serum prolidase activity (SPA) may reflect the degree of fibrosis and inflammation. Choroid plexus calcification (CPC) is considered as the physiological calcification of the brain, and CPC is diagnosed by the presence of calcification in the anatomical region on computed tomography (CT). Here, CPC and non-calcified CP were defined by Hounsfield Units (HU) values of > 150 and < 50, respectively. We aimed to measure SPA in subjects with CPC and those with non-calcified CP. This study included 89 subjects who were admitted to the neurology clinic and underwent CT: 44 subjects with CPC and 45 subjects with non-calcified CP. The neurological examination of all subjects was normal; namely, the subjects with CPC were asymptomatic. The SPA level was significantly higher in the CPC group than that in the non-calcified CP group (p < 0.002), and there was a significant positive correlation between vitamin D and SPA levels in the CPC group. In contrast, the vitamin D and parathyroid hormone levels were higher in the CPC group, but the difference was not statically significant (p > 0.05). These findings indicate that SPA is a biomarker for CPC that may be predictive of future brain disease.