Substance P identified as causative agent in tapeworm-related seizures
MedWire News: Researchers have discovered that substance P causes the seizures that can occur in patients with neurocysticercosis (NCC), a tapeworm infection of the brain.
Prema Robinson (Baylor College of Medicine, Houston, Texas, USA) and colleagues report that substance P, a neuropeptide involved in host defense, is released by the body on the death of the worms (Taenia solium) creating an inflammatory immune response. This results in the seizures that are commonly seen in patients with NCC.
As medications exist that are able to block substance P, these findings hold promise for improving treatment of such patients, says the team.
Previous research based on autopsy results has shown that substance P is present in the brains of people with NCC, but not in those without the infection.
NCC is a major cause of acquired seizures, accounting for 10% of emergency room visits for seizures in southern USA. Robinson and colleagues investigated the premise that substance P could mediate NCC-related seizures.
"Seizures are thought to result not from parasitic infection per se, but from the chronic granulomatous host response initiated by dying cysts," explain the researchers in PLoS Pathogens.
"Antiparasitic drugs can be used to kill the parasites, but the symptoms may worsen due to the host inflammatory responses being stimulated by the dying parasites."
Looking at autopsy results from five people with NCC, the researchers found that substance P was primarily found in brain areas adjacent to degenerating worms.
Intrahippocampal injection of healthy rats with substance P alone triggered severe seizures. In addition, injection of rats with brain tissue from areas adjacent to the worms in infected mice with a functioning, but not a nonfunctioning, substance P gene also triggered seizures.
However, when the rats were first injected with a substance P-receptor antagonist, prior to being injected with infected tissue, the seizures did not occur.
"Current management options for patients with moderate infections and viable cysts include antihelmintic treatment along with administration of corticosteroids to reduce inflammation and the predisposition to seizures initiated by dying parasites," say Robinson et al.
"Our finding that [substance]P causes seizures in NCC precipitated by the granulomatous response to dead or dying cysts suggest the possibility of using [substance] P receptor antagonist for seizure prophylaxis during periods of antihelmintic treatment and, perhaps, as an adjuvant or replacement for anti-epileptic drugs for the treatment and/or prevention of spontaneous seizures in NCC," they conclude.
By Helen Albert