A CB2 inverse agonist reduced brain inflammation and neuronal death after prolonged seizures in mice | Research

The takeaway

The CB2 inverse agonist SMM-189, given after status epilepticus was stopped, prevented the seizure-induced inflammatory surge, reduced neuronal death, and improved behavioral outcomes in mice.

Epileptologists treating status epilepticus, neuroscientists studying post-seizure brain damage, and pharmacologists developing neuroprotective cannabinoid drugs.

Post-seizure CB2 inverse agonist prevented brain cytokine surge and neuronal death

What the researchers found

Status epilepticus downregulated CB1 but slightly upregulated CB2 in the hippocampus. Treatment with SMM-189 (6 mg/kg twice daily) after seizure termination prevented the brain cytokine surge, reduced neuronal death, and improved behavioral outcomes at 24 hours. SMM-189 also suppressed microglial inflammation in vitro and showed moderate neuroprotection against excitotoxicity in hippocampal cultures.

Why it matters

Current epilepsy emergency treatment focuses on stopping seizures quickly. A follow-on therapy that reduces brain damage even when given after seizures have been controlled could significantly improve outcomes for status epilepticus survivors.

The numbers in context

CB1 downregulated, CB2 slightly upregulated after SE. SMM-189 at 6 mg/kg i.p. twice daily. Prevented cytokine surge. Reduced neuronal death. Improved behavioral measures at 24 hours post-SE.

How the study worked

Kainate-induced status epilepticus in mice, terminated by diazepam after 1 hour. SMM-189 administered after seizure termination. Brain cytokines, neuronal survival, and behavior assessed at 24 hours. In vitro studies in rat primary microglia and hippocampal neuron-glia co-cultures.

What this study cannot tell us

Mouse model with chemically induced seizures. Only 24-hour outcomes assessed. Single dose regimen tested. The paradoxical finding that CB2 inverse agonism (blocking constitutive activity) rather than agonism is beneficial needs further mechanistic exploration.

How to read the evidence

Comprehensive preclinical study with in vivo and in vitro validation, but limited to acute outcomes in a chemically induced seizure model.

When this study was published

2020 animal study. Introduces a novel therapeutic concept for post-status epilepticus neuroprotection via CB2 inverse agonism.

The bigger picture

The concept of a neuroprotective "chaser" therapy that can be given after seizures are controlled addresses a critical unmet need. Many status epilepticus survivors suffer brain damage despite successful seizure termination.

Questions still open

Would longer treatment with SMM-189 provide sustained neuroprotection? Why does CB2 inverse agonism reduce inflammation when CB2 activation is typically anti-inflammatory? Could this approach work for other forms of acute brain injury?

Common questions

What is an inverse agonist?

An inverse agonist reduces the baseline activity of a receptor below its resting level, opposite to an agonist which increases activity. For CB2, inverse agonism paradoxically produced anti-inflammatory effects in this model.

Why is this different from just stopping the seizures?

Even after seizures are terminated, inflammatory and excitotoxic processes continue damaging the brain. This therapy targets that secondary damage window, potentially reducing brain injury in survivors.

Read the original research

Inverse Agonism of Cannabinoid Receptor Type 2 Confers Anti-inflammatory and Neuroprotective Effects Following Status Epileptics.

Molecular neurobiology, 57(6), 2830-2845

View on PubMed ↗Publisher’s paper ↗

Citation

Yu, Ying; Li, Lexiao; Nguyen, Davis T; Mustafa, Suni M; Moore, Bob M; Jiang, Jianxiong. (2020). Inverse Agonism of Cannabinoid Receptor Type 2 Confers Anti-inflammatory and Neuroprotective Effects Following Status Epileptics.. Molecular neurobiology, 57(6), 2830-2845. https://doi.org/10.1007/s12035-020-01923-4