Anti-Inflammatory Effects of Ginsenoside Rg1 and Low-Dose Ginseng Extract in an Astrocyte–Microglia Co-Culture Model of Inflammation

Background: Neuroinflammation contributes to the etiopathology and symptom severity of neurodegenerative and neuropsychiatric disorders. Glial cells, especially microglia and astrocytes, play a crucial role in neuroinflammation. It has been reported that ginseng (Panax ginseng) and its bioactive component ginsenoside Rg1 exhibit anti-inflammatory effects and can improve cognitive performance in various models. However, the exact underlying mechanisms remain unclear. Methods: Astrocyte–microglia co-culture models simulating physiological (M5, 5–10% microglia) and pathological/inflammatory (M30, 30–40% microglia) conditions were treated with different concentrations of ginsenoside Rg1 (15, 30, 45 µM) or ginseng extract (derived from Korean red ginseng) at low (12.5, 25, 37.5 µg/mL) or high doses (125, 250, 375 µg/mL) for 24 h. Cell viability was assessed using the MTT assay while microglial reactivity was examined using immunocytochemistry. Astrocytic gap-junctional coupling was investigated using the scrape-loading method, and connexin 43 (Cx43) expression was analyzed using immunocytochemistry and Western blot. Results: Both Rg1 and low-dose ginseng extract reduced microglial activation under inflammatory conditions by promoting a shift in microglia from an activated to homeostatic (resting) phenotype. Rg1 preserved astrocytic gap-junctional function by preventing the inflammation-induced downregulation of Cx43 expression and enhancing Cx43-mediated gap-junctional intercellular communication. Rg1 caused a significant reduction in glial cell viability, but only at high concentrations (30 and 45 µM), under inflammatory conditions. High-dose ginseng extract showed a significant concentration-dependent reduction in glial cell viability under physiological and pathological conditions, without comparable anti-inflammatory benefits. Conclusions: This study demonstrates that low-dose ginseng and its active compound Rg1 exert anti-inflammatory effects by modulating astrocytic coupling and microglial reactivity. These results provide a novel therapeutic perspective for the use of ginseng in the treatment of neurodegenerative and neuropsychiatric diseases related to neuroinflammation.