Increased detectability of Apolipoprotein E (ApoE) in cerebrospinal fluid samples of dogs with peracute and acute central nervous system lesions.

INTRODUCTION: Apolipoprotein E (ApoE), secreted by astrocytes and microglia after neuronal injury, is involved in neuronal regeneration and modulation of inflammatory processes. Inverse associations between ApoE and the proinflammatory mediator C-reactive protein (CRP) are described in mice, but knowledge in dogs is limited. METHODS: This study investigated ApoE levels in cerebrospinal fluid (CSF) from 141 dogs with central nervous system (CNS) diseases, including idiopathic epilepsy (n = 40), intervertebral disc herniation (IVDH, n = 40), meningoencephalitis of unknown origin (MUO, n = 30), degenerative myelopathy (n = 31), and 10 healthy controls. ApoE concentrations were measured by ELISA. CRP levels in CSF and paired serum samples were determined by immunoassay. Correlations between ApoE, clinical parameters and CRP were evaluated. We hypothesized elevated CSF ApoE in acute CNS diseases and low or undetectable levels in chronic conditions and a negative correlation between ApoE and CRP. RESULTS: ApoE was detected in 66/151 cases, of which 20 showed quantifiable levels, exclusively in diseased dogs. While dogs with peracute IVDH or high seizure frequency were significantly associated with detected ApoE, MUO cases with multiple lesions only had a trend for measurable ApoE levels. Contrary to our hypothesis, a significant positive correlation between ApoE and CRP in CSF was found, suggesting a potential modulatory role of ApoE in neuroinflammation. DISCUSSION: In conclusion, ApoE may play a role particularly during peracute and acute disease stages, while low CSF ApoE may reflect regenerative processes in affected neuronal tissue.