Yokukansan, a Japanese Herbal Medicine, Suppresses Substance P-Induced Production of Interleukin-6 and Interleukin-8 by Human U373 MG Glioblastoma Astrocytoma Cells

Background: Yokukansan is a traditional Japanese herbal medicine that has an antiallodynic effect in patients with chronic pain. However, the mechanisms by which yokukansan inhibits neuropathic pain are unclear. Objective: This study aimed to investigate the molecular effects of yokukansan on neuroinflammation in U373 MG glioblastoma astrocytoma cells, which express a functional high-affinity neurokinin 1 receptor (substance P receptor), and produce interleukin (IL)-6 and IL-8 in response to stimulation by substance P (SP). Methods: We assessed the effect of yokukansan on the expression of ERK1/2, P38 MAPK, nuclear factor (NF)-ΚB, and cyclooxygenase-2 (COX-2) in U373 cells by western blot assay. Levels of IL-6 and IL-8 in conditioned medium obtained after stimulation of cells with SP for 24 h were measured by enzyme-linked immunosorbent assay. All experiments were conducted in triplicate. Results were analyzed by one-way ANOVA, and significance was accepted at p < 0.05. Results: Yokukansan suppressed SP-induced production of IL-6 and IL-8 by U373 MG cells, and downregulated SP-induced COX-2 expression. Yokukansan also inhibited phosphorylation of ERK1/2 and p38 MAPK, as well as nuclear translocation of NF-ΚB, induced by SP stimulation of U373 MG cells. Conclusion: Yokukansan exhibits anti-inflammatory activity by suppressing SP-induced production of IL-6 and IL-8 and downregulating COX-2 expression in U373 MG cells, possibly via inhibition of the activation of signaling molecules, such as ERK1/2, p38 MAPK, and NF-ΚB.