Preclinical investigation of β-caryophyllene as a therapeutic agent in an experimental murine model of Dravet syndrome

Dravet Syndrome (DS) is caused by mutations in the Scn1a gene encoding the α1 subunit of the sodium channel Nav1.1, which results in febrile seizures that progress to severe tonic-clonic seizures and associated comorbidities. Treatment with cannabidiol has been approved for the management of seizures in DS patients, but it appears to be also active against associated comorbidities. In this new study, we have investigated β-caryophyllene (BCP), a cannabinoid with terpene structure that appears to also have a broad-spectrum profile, as a useful therapy against both seizuring activity and progression of associated comorbidities. This has been studied in heterozygous conditional knock-in mice carrying a missense mutation (A1783V) in Scn1a gene expressed exclusively in neurons of the Central Nervous System (Syn-Cre/Scn1a^WT/A1783V), using two experimental approaches. In the first approach, an acute treatment with BCP was effective against seizuring activity induced by pentylenetetrazole (PTZ) in wildtype (Scn1a^WT/WT) and also in Syn-Cre/Scn1a^WT/A1783V mice, with these last animals having a greater susceptibility to PTZ. Such benefits were paralleled by a BCP-induced reduction in PTZ-induced reactive astrogliosis (labelled with GFAP) and microgliosis (labelled with Iba-1) in the prefrontal cortex and the hippocampal dentate gyrus, which were visible in both wildtype (Scn1a^WT/WT) and Syn-Cre/Scn1a^WT/A1783V mice. In the second approach, both genotypes were treated repeatedly with BCP to investigate its effects on several DS comorbidities. Thus, BCP corrected important behavioural abnormalities of Syn-Cre/Scn1a^WT/A1783V mice (e.g. delayed appearance of hindlimb grasp reflex, induction of clasping response, motor hyperactivity, altered social interaction and memory impairment), attenuated weight loss, and slightly delayed premature mortality. Again, these benefits were paralleled by a BCP-induced reduction in reactive astrogliosis and microgliosis in the prefrontal cortex and the hippocampal dentate gyrus typical of Syn-Cre/Scn1a^WT/A1783V mice. In conclusion, BCP was active in Syn-Cre/Scn1a^WT/A1783V mice against seizuring activity (acute treatment) and against several comorbidities (repeated treatment), in both cases in association with its capability to reduce glial reactivity in areas related to these behavioural abnormalities. This situates BCP in a promising position for further preclinical evaluation towards a close translation to DS patients.

Investigation in blood-brain barrier integrity and susceptibility to immune cell penetration in a mouse model of Dravet syndrome

Dravet Syndrome (DS) is a pediatric encephalopathy caused by mutations in Scn1a gene encoding the α1 subunit of the NaV1.1 voltage-gated sodium channel, which lead to early febrile seizures that progress to severe tonic-clonic seizures and several long-term behavioural comorbidities. In the present study, we have investigated whether a possible early deterioration in the blood-brain barrier (BBB) may facilitate the infiltration of immune cells to the brain parenchyma, which may contribute to these pathogenic events. In this study, conditional knock-in Scn1a-A1783V mice and their controls were used at the postnatal day (PND25): (i) to compare their levels of several immune cell populations in the bone marrow and blood; and (ii) to analyze several BBB proteins, as well as the occurrence of immune cell infiltration and endogenous immunoglobulin G (IgG) extravasation into the brain parenchyma. Our data revealed an elevation in the number of neutrophils in the blood of DS mice, but not of B- and T-cells, despite the levels of these immune cells were significantly reduced in the bone marrow. The elevated number of blood neutrophils did not apparently originate their infiltration into the hippocampus of DS mice as an immunofluorescence analysis indicated, and the same happened in B- and T-cells. However, the levels of endogenous IgG in this brain structure were significantly elevated in DS mice compared to controls, directly indicating the occurrence of extravasation into the brain parenchyma and indirectly that the BBB in DS mice may be relatively affected, a fact confirmed by the reduction in the levels of BBB-related proteins such as ZO-1 in these mice. In conclusion, our results support the occurrence of certain degree of deterioration in the BBB in DS, which may facilitate the infiltration of immune cells to the brain, then contributing to the pathogenesis in this disease.