Curcumin and Glycyrrhiza glabra Synergistically Attenuate Alzheimer's Pathology via TLR4/NF-κB-Mediated Anti-inflammatory and Redox Modulation in a D-Gal/Sodium Nitrite-Induced Mouse Model.

Abstract

This study investigates the early synergistic effects of curcumin and licorice through vertical cooperation, which can simultaneously target both the upstream and downstream components of neuroinflammation. It evaluates their neuroprotective effects and potential mechanisms in a D-galactose/sodium nitrite-induced Alzheimer's disease mouse model.Eighty C57BL/6 mice were divided into eight groups (n = 10): wild-type (WT), AD model, curcumin monotherapy (AD + CL, 100 mg/kg), G. glabra monotherapy (AD + GG, 100 mg/kg), low-dose combination (AD + COM-L, 50 + 50 mg/kg), high-dose combination (AD + COM-H, 100 + 100 mg/kg), donepezil (3 mg/kg), and SN50 (NF-κB inhibitor, 400 µg/kg). Cognitive function was assessed via Morris Water Maze in WT, AD, AD + CL, AD + GG, and AD + COM-H groups, while all groups underwent molecular analyzes. The high-dose combination most effectively restored spatial memory, reducing escape latency by ~ 43% versus monotherapies. Molecularly, it synergistically reduced tau-related proteins (MAPT, GSK-3β) and suppressed the TLR4/MyD88/NF-κB axis, lowering inflammatory mediators (IL-6, TNF-α, CXCL1, PTGS2). IL-6 was further reduced by 28.6% and 40.0% compared to curcumin and G. glabra alone, respectively. The combination also enhanced antioxidant defense (increased SOD) and anti-apoptotic capacity (upregulated BCL-2) while reducing oxidative lipid damage (lower MDA). Network pharmacology identified 40 shared AD targets, with enrichment in NF-κB and IL-17 pathways, validated experimentally. In conclusion, curcumin and G. glabra exert synergistic neuroprotection by concurrently inhibiting the TLR4/NF-κB pathway and modulating IL-17 signaling, with G. glabra potentially targeting the TLR4/HMGB1 axis and curcumin directly inhibiting NF-κB activation, forming a complementary mechanistic interplay. This multi-target action disrupts the interplay between neuroinflammation and tau pathology, underscoring the combination's therapeutic potential for AD intervention.