Experimental studies have demonstrated the beneficial effects of
tetramethylpyrazine (
TMP) against
ischemic stroke and highlighted its crucial role in anti-inflammatory activity. This study provides evidence of an alternative target for
TMP and sheds light on the mechanism of its anti-inflammatory action against ischemic
brain injury. We report a global inhibitory effect of
TMP on inflammatory cell intracerebral activation and infiltration in a rat model of permanent
cerebral ischemia. The results of immunohistochemistry, enzymatic assay, flow cytometric analysis, and cytological analysis revealed that intraperitoneal
TMP administration reduced neuronal loss, macrophage/microglia activation, brain parenchyma infiltrative neutrophils, and circulating neutrophils after
cerebral ischemia. Biochemical studies of cultured neutrophils further demonstrated that
TMP attenuated neutrophil migration, endothelium adhesion, spontaneous
nitric oxide (NO) production, and stimuli-activated NO production after
cerebral ischemia. In parallel with these anti-neutrophil phenomena,
TMP also attenuated the activities of
ischemia-induced
inflammation-associated signaling molecules, including plasma high-mobility group box-1
protein (
HMGB1) and neutrophil toll-like receptor-4 (TLR4), Akt,
extracellular signal-regulated kinase (ERK), and
inducible nitric oxide synthase. Another finding in this study was that the anti-neutrophil effect of
TMP was accompanied by a further elevated expression of
NF-E2-related factor 2 (Nrf2) and
heme oxygenase-1 (HO-1) in neutrophils after
cerebral ischemia. Taken together, our results suggest that both the promotion of endogenous anti-inflammatory defense capacity and the attenuation of pro-inflammatory responses via targeting of circulating neutrophils by elevating Nrf2/HO-1 expression and inhibiting
HMGB1/TLR4, Akt, and ERK signaling might actively contribute to
TMP-mediated neuroprotection against
cerebral ischemia.