Allicin protects rat cortical neurons against mechanical trauma injury by regulating nitric oxide synthase pathways

Allicin, a small molecule that is responsible for the typical smell and most of the functions of garlic, possesses a broad spectrum of pharmacological activities and is considered to have therapeutic potential in many pathologic conditions. In the present study, we investigated the potential protective effect of allicin in an in vitro model of traumatic brain injury (TBI) using primary cultured rat cortical neurons. We found that allicin treatment significantly reduced mechanical trauma-induced lactate dehydrogenase (LDH) release and inhibited apoptotic neuronal death in a dose-dependent manner. These protective effects were observed even if allicin treatment was delayed to 2h after injury. Allicin significantly decreased the expression of inducible nitric oxide synthase (iNOS) and increased the phosphorylation of endothelial NOS (eNOS) but had no effect on neuronal NOS (nNOS) expression. Allicin-induced protection in cortical neurons was augmented by iNOS and nNOS antagonists and was partly reversed by blocking eNOS phosphorylation. In addition, allicin treatment inhibited the TBI-induced activation of ERK and further enhanced the phosphorylation of Akt in TBI-injured neurons. The Akt inhibitor LY294002 attenuated the allicin-induced increase in eNOS expression and phosphorylation, whereas the ERK inhibitor PD98059 had opposite effects on the expression of iNOS and eNOS. Pretreatment with LY294002 or PD98059 partly prevented or further enhanced allicin-induced neuroprotection, respectively. Collectively, these data demonstrate that allicin treatment may be an effective therapeutic strategy for traumatic neuronal injury and that the potential underlying mechanism involves Akt- and ERK-mediated regulation of NOS pathways.