Sinapinic acid as a potential therapeutic agent for epilepsy through targeting NMDA receptors and nitrite level

Epilepsy, a widespread neural ailment considered by prolonged neuronal depolarization and repetitive discharge, has been linked to extreme stimulus of N-methyl-D-aspartate receptors (NMDARs). Despite the availability of approved anti-seizure medications (ASMs) in many developed nations, approximately 30% of epilepsy patients continue to experience drug-resistant seizures. Thus, a growing interest in discovering natural compounds as potential sources for new medications is growing. Sinapinic acid, a natural derivative of cinnamic acid found in food sources, is known for its neuroprotective properties. This study investigated how sinapinic acid interacts with NMDA receptors and its potential role in providing anticonvulsant effects. Male mice were randomly allocated into nine groups: a control group receiving normal saline (1 ml/kg), groups treated with sinapinic acid at doses of 1, 3, and 10 mg/kg, a group treated with diazepam at 10 mg/kg, a group treated with an NMDA agonist at 75 mg/kg, a group treated with an NMDA antagonist at 0.5 mg/kg, a group receiving the ineffective dose of sinapinic acid (1 mg/kg) along with the NMDA antagonist, and a group receiving the effective dose of sinapinic acid (10 mg/kg) along with the NMDA agonist. Sinapinic acid and other treatments were administered intraperitoneally 30 min prior to inducing seizures with PTZ injection. Seizure onset time was recorded following PTZ injection. Blood and brain samples were collected after anesthesia to determine serum and brain nitrite levels. Real-time PCR assessed NMDAR gene expression in the prefrontal cortex (PFC). Data were analyzed using Prism software. The time seizures began was notably extended in groups treated with sinapinic acid at doses of 3 and 10 mg/kg compared to those treated with saline (P < 0.05). Additionally, in the receiving group of an ineffective dose of sinapinic acid alongside ketamine, the beginning of seizure time was significantly prolonged compared to the group that received the ineffective dose of sinapinic acid alone (P < 0.05). Serum and prefrontal cortex (PFC) nitrite levels were significantly lower in mice treated with sinapinic acid at doses of 1, 3, and 10 mg/kg compared to the saline-treated group (P < 0.05). The gene expression of the NMDAR NR2B subunit in the PFC was decreased in groups treated with sinapinic acid at 1 and 10 mg/kg compared to the saline-treated group. Furthermore, co-administration of sinapinic acid (10 mg/kg) with NMDA resulted in significantly lower NR2A gene expression than the group treated with 10 mg/kg of sinapinic acid alone. Conversely, co-administration of ketamine with sinapinic acid (1 mg/kg) significantly increased NR2B subunit gene expression compared to the group treated with sinapinic acid at 1 mg/kg alone. Sinapinic acid showed anticonvulsant effects through reduced serum and PFC nitrite and modulation of glutamatergic signaling.