CSF angiotensin II and angiotensin-converting enzyme levels in anti-aquaporin-4 autoimmunity

Abstract

Background Anti-aquaporin-4 (AQP4) antibody targets perivascular astrocyte foot processes, which contain abundant angiotensinogen, a precursor of angiotensin II, angiotensin-converting enzyme (ACE) and ACE2. Objective To disclose any abnormality in the intrathecal angiotensin II metabolic pathway in Japanese patients with neuromyelitis optica (NMO) or NMO spectrum disorders (NMOs) and positive for anti-AQP4 antibody. Methods We measured CSF angiotensin II, ACE and ACE2 levels in 15 anti-AQP4 antibody-positive patients with NMO or NMOs, 21 anti-AQP4 antibody-negative multiple sclerosis (MS) patients, 32 patients with other neurological diseases (OND) and 24 non-neurologic controls, using established ELISAs. Results CSF angiotensin II levels were lower in patients with NMO/NMOs (2.01 ± 1.82 pg/ml) and those with MS (3.15 ± 1.67 pg/ml) than in the OND (5.41 ± 2.34 pg/ml) and control groups (6.71 ± 2.65 pg/ml) ( P corr < 0.005). The difference in CSF angiotensin II levels between NMO/NMOs and MS patients was nearly significant ( P uncorr = 0.052). In NMO/NMOs and MS patients, angiotensin II levels were negatively correlated with CSF/serum albumin ratio ( P < 0.05). ACE levels in CSF were lower in patients with NMO/NMOs (34.3 ± 5.61 ng/ml) than in MS patients (42.5 ± 8.19 ng/ml, P corr = 0.035) and controls (44.7 ± 4.02 ng/ml, P corr < 0.0003) while ACE2 levels were lower in NMO/NMOs (1.13 ± 0.49 ng/ml) and MS (1.75 ± 0.86 ng/ml) patients than in controls (2.76 ± 0.23 ng/ml, P corr < 0.001 for both). Conclusion CSF angiotensin II, ACE, and ACE2 levels are decreased in NMO/NMOs patients with anti-AQP4 antibody, reflecting severe destruction of perivascular astrocytes.