Background: Gestational diabetes mellitus (GDM) is associated with chronic hyperglycemia, which contributes to trophoblast dysfunction and adverse pregnancy outcomes through enhanced placental inflammation and impaired insulin signaling. This study aimed to investigate the effects of Gallic acid (GA) and metformin (MET), individually and in combination, on inflammatory and insulin signaling pathways in a high glucose–induced trophoblast model.

Methods: The cytotoxic effects of GA and MET on HTR‑8 trophoblast cells were initially evaluated using the MTT assay to determine non‑toxic concentrations. The cells were then pretreated with GA and/or MET prior to exposure to high glucose conditions. The mRNA expression levels of bromodomain‑containing protein 4 (BRD4), nuclear factor‑κB (NF‑κB), tumor necrosis factor‑α (TNF‑α), interleukin‑6 (IL‑6), interleukin‑1β (IL‑1β), insulin receptor substrate‑1 (IRS‑1), and glucose transporter‑4 (GLUT‑4) were measured using quantitative real‑time PCR (qRT‑PCR).

Results: High glucose significantly increased the expression of BRD4, NF‑κB, TNF‑α, IL‑1β, and IL‑6, while decreasing GLUT‑4 and IRS‑1 levels. Pretreatment with GA, MET, or their combination reversed these changes compared with the high‑glucose group. GA alone and the combined treatment reduced IL‑1β expression, whereas only the combined treatment significantly decreased IL‑6. IRS‑1 expression increased following MET treatment and the combined GA and MET treatment.

Conclusion: GA and MET may attenuate inflammation and improve insulin signaling in trophoblast cells under high‑glucose conditions, suggesting their potential therapeutic role in managing placental dysfunction associated with GDM.