Ginsenosides Rg3 and Rh2 Inhibit the Activation of AP-1 and Protein Kinase A Pathway in Lipopolysaccharide/Interferon-γ-Stimulated BV-2 Microglial Cells

Abstract

The anti-inflammatory effect of ginsenosides Rg3 and Rh2, which improves ischemic brain injury induced by middle cerebral artery occlusion, was investigated in lipopolysaccharide (LPS) and IFN-γ-induced murine BV-2 microglial cells. Ginsenoside Rh2 inhibited the production of NO, with an IC₅₀ value of 17 μM. The inhibitory effect of Rh2 on NO correlates with the decreased protein and mRNA expression of an inducible NO synthase (iNOS) gene. Additionally, ginsenoside Rh2 inhibited the expression of COX-2, pro-inflammatory TNF-α and IL-1β in BV-2 cells induced by LPS/IFN-γ, while it increased the expression of the anti-inflammatory cytokine IL-10. Electrophorectic mobility shift assays revealed that ginsenoside Rh2 significantly inhibited the LPS/IFN-γ-induced AP-1 DNA binding activity, while it enhanced the protein binding to CRE sequences. However, it did not affect NF-κB binding activity. Thus, the anti-inflammatory effect of Rh2 appears to depend on the AP-1 and protein kinase A (PKA) pathway. The anti-inflammatory effect of ginsenoside Rg3 against LPS/IFN-γ-activated BV-2 cells was less potent than that of ginsenoside Rh2. These findings suggest that the in vivo anti-ischemic effect of ginsenoside Rg3 may originate from ginsenoside Rh2, which is a main metabolite of ginsenoside Rg3 by intestinal microflora, and that of ginsenoside Rh2 may be due to its anti-inflammatory effect in brain microglia.

Abbreviations

COX:cyclooxygenase

DMEM:Dulbecco’s modified Eagle medium

ECL:enhanced chemiluminescence

EMSA:electrophoretic mobility shift assay

IFN:interferon

IL:interleukin

iNOS:inducible NO synthase

NO:nitric oxide

PKA:protein kinase A

RT-PCR:reverse transcriptase-polymerase chain reaction

TNF-α:tumor necrosis factor-alpha

Key words

Ginsenoside Rg3 - ginsenoside Rh2 - microglia - iNOS - AP-1 - PKA

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