Re-examining the potential of targeting ABHD6 in multiple sclerosis: Efficacy of systemic and peripherally restricted inhibitors in experimental autoimmune encephalomyelitis.

α/β-Hydrolase domain-containing 6 (ABHD6) contributes to the hydrolysis of the major endocannabinoid 2-arachidonoylglycerol (2-AG) in the central nervous system (CNS) and in the periphery. ABHD6 blockade has been proposed as novel strategy to treat multiple sclerosis (MS), based on the observation that the inhibitor WWL70 exerts protective anti-inflammatory effects in experimental autoimmune encephalomyelitis (EAE). According to recent data, WWL70 exhibits off-target anti-inflammatory activity in microglial cells and the potential of ABHD6 as drug target in MS remains controversial. Here we further investigated the role of ABHD6 during autoimmune demyelination by comparing the efficacy of two novel inhibitors with different CNS permeability in vivo. Preventive treatment with the systemically active inhibitor KT182 ameliorated the neurological signs of EAE during the time-course of disease. By contrast, administration of the peripherally restricted compound KT203 was ineffective in attenuating EAE symptomatology. Both inhibitors failed to improve corticospinal tract conduction latency and to attenuate inflammation at EAE recovery phase, despite being equally active at targeting brain ABHD6. Chronic administration of KT182 was associated to a partial loss of brain CB receptor coupling ability, suggesting the engagement of CB receptor-mediated mechanisms during the EAE disease progression. In cultured neurons, KT182 attenuated NMDA-stimulated excitotoxicity and mitochondrial calcium overload. However, these protective effects were not attributable to ABHD6, as they were not mimicked by the alternative inhibitors KT203, KT195 and WWL70. These results indicate that ABHD6 blockade exerts only modest therapeutic effects against autoimmune demyelination and call into question its utility as novel drug target in MS.