Systemic treatment with the inhibitory neurotransmitter gamma-aminobutyric acid aggravates experimental autoimmune encephalomyelitis by affecting proinflammatory immune responses

Transcriptomic and proteomic analyses of multiple sclerosis (MS) lesions indicate alterations in the gamma-aminobutyric acid (GABA) inhibitory system, suggesting its involvement in the disease process. To further elucidate the role of GABA in central nervous system (CNS) inflammation in vivo, the chronic myelin oligodendrocyte glycoprotein (MOG)35-55 experimental autoimmune encephalomyelitis (EAE) model was used. Daily GABA injections (200 mg/kg) from day 3 onwards significantly augmented disease severity, which was associated with increased CNS mRNA expression levels of tumor necrosis factor alpha (TNF-α) and interleukin (IL)-6. GABA-treated mice showed enhanced MOG-dependent proliferation and were skewed towards a T helper 1 phenotype. Moreover, in vitro, the lipopolysaccharide (LPS)-induced increase in interleukin (IL)-6 production by macrophages was enhanced at low GABA concentrations (0.03-0.3 mM). In sharp contrast to exogenous GABA administration, endogenous GABA increment by systemic treatment with the GABA-transaminase inhibitor vigabatrin (250 mg/kg) had prophylactic as well as therapeutic potential in EAE. Together, these results indicate an immune amplifying role of GABA in neuroinflammatory diseases like MS.