Aquaporins AQP1 and AQP4 in the cerebrospinal fluid of bacterial meningitis patients.

Aquaporins facilitate water transport through cell membranes. Due to the localization of AQP1 and AQP4 in the brain, they might contribute to cerebral edema. Our study aimed to determine whether AQP1 and AQP4 can be measured in cerebrospinal fluid (CSF), and whether there is a difference in AQP1 and AQP4 concentration between patients with bacterial meningitis (BM) and healthy controls. AQP1 and AQP4 concentrations in CSF from 35 patients with BM and 27 controls were analyzed using a commercial ELISA. The mean concentration of AQP1 in CSF was significantly elevated in patients with BM (BM: 3.8±3.4ng/ml, controls: 0.8±0.5ng/ml; p<0.001). AQP4 had a tendency to be increased, however the difference was not significant (BM: 1.8±3.1ng/ml, controls: 0.1±0.2ng/ml; p=0.092). AQP1 and AQP4 in CSF of BM patients were inversely correlated (r=-0.47, p=0.004). We could not find any other correlation between concentration of AQP1 or AQP4 in CSF and CSF leukocytes, lactate, protein, albumin CSF/serum ratio, age, a prediction score, an outcome score or the Glasgow Coma Scale at admission in patients with BM. Control patients displayed a correlation between AQP1 and the albumin CSF/serum ratio (r=0.390, p=0.040). This is the first study that detected AQP1 and AQP4 in CSF. Whether the significant elevation of AQP1 is due to a higher expression and subsequent shedding into CSF or a BM-induced cell damage needs to be determined.