A Combination of 5-(3′,4′-Dihydroxyphenyl)-γ-Valerolactone and Curcumin Synergistically Reduces Neuroinflammation in Cortical Microglia by Targeting the NLRP3 Inflammasome and the NOX2/Nrf2 Signaling Pathway

Background/Objectives: 5-(3′,4′-dihydroxyphenyl)-γ-valerolactone (γ-VL), recently identified as a predominant microbial metabolite derived from proanthocyanidins, offers benefits such as reducing inflammation, oxidative stress, and supporting brain health. Its effects on neuroinflammation and microglial activation remain largely unexplored. Curcumin, a bioactive component isolated from Curcuma longa L., is well known for its ability to reduce microglial activation and pro-inflammatory mediator production and release. While the individual effects of γ-VL and curcumin are well documented, their potential combined effects remain unexplored. This research sought to investigate the possible synergistic effects of γ-VL and curcumin in reducing microglial activation. Methods: Primary rat cortical microglia were pre-treated with γ-VL and curcumin, alone or in combination, before stimulation with LPS. An MTT assay was used to evaluate cell viability, while pro-inflammatory mediators were assessed by real-time PCR and ELISA. Nitric oxide production was evaluated with the Griess assay. SynergyFinder Plus software analyzed potential synergistic effects. Results: The combination of low micromolar concentrations of γ-VL and curcumin synergistically reduced LPS-induced microglial activation. Specifically, the combination exhibited a significantly greater ability to inhibit the production and release of pro-inflammatory factors (such as IL-1β, TNF-α, and NO) compared to each compound individually. Mechanistically, the anti-inflammatory activity was attributed to the downregulation of NLRP3 expression, and the reduction in microglial activation was linked to the modulation of the NOX2/Nrf2 signaling pathway. Conclusions: The combination of low micromolar concentrations of γ-VL and curcumin produces synergistic anti-inflammatory effects in microglia by targeting key inflammatory pathways, indicating its potential utility as a treatment strategy for neurodegenerative diseases involving microglial activation.