AimAquaporin-4 (AQP4), predominantly expressed in astrocytes, has been implicated in neuroinflammation through the amplification of cytokine and chemokine production. Goreisan (GRS), a traditional Japanese herbal medicine, modulates AQP4-related water homeostasis. However, its effects on AQP4-associated inflammatory processes remain unclear. This study aimed to elucidate the anti-inflammatory effects of GRS, with particular emphasis on inflammatory responses observed under AQP4-expressing conditions.MethodsIn vitro experiments were conducted using primary cultured astrocytes and AQP4-overexpressing NIH-3T3 fibroblasts stimulated with lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF-α), with or without GRS. Cytokine and chemokine expression levels were assessed by quantitative reverse transcription polymerase chain reaction, whereas ERK phosphorylation was evaluated by Western blotting. An in vivo mouse model of LPS-induced neuroinflammation was employed to assess the effects of orally administered GRS on inflammatory markers and glial activation. The contributions of individual herbal components were also examined.ResultsGRS suppressed LPS- and TNF-α-induced cytokine and chemokine mRNA expression in primary astrocytes and AQP4-expressing NIH-3T3 cells. In vivo, GRS administration reduced inflammatory cytokine expression and attenuated glial activation in the brain. GRS attenuated ERK phosphorylation under AQP4-expressing conditions, in parallel with reduced chemokine mRNA expression. Furthermore, Cinnamomi cortex, a component of GRS, was identified as a major contributor to these anti-inflammatory effects.ConclusionThese findings indicate that the effects of GRS on inflammatory gene expression and ERK activation are associated with AQP4-expressing conditions. However, the present data do not establish AQP4 as a direct or primary molecular target of GRS. Therefore, GRS may provide a potential pharmacological approach for modulating inflammatory responses observed under AQP4-expressing conditions, although further studies are required to confirm its therapeutic relevance.