Curcuma longa L. Leaf and Pseudostem Extract Suppresses Inflammation in Cytokine-Stimulated HaCaT Keratinocytes and 12-O-Tetradecanoylphorbol-13-Acetate-Induced Ear Edema in Mice

Abstract

Background: Plant-derived treatments for skin inflammation are gaining increasing interest, driven by the growing demand for safer alternatives to conventional synthetic drugs. Curcuma longa L. (turmeric) is traditionally utilized in many Asian countries for various pharmacological applications. Although the inflammation-suppressing properties of turmeric rhizomes are well established, the bioactive potential of its leaves and pseudostems remains largely unexplored. This study investigates the effects of turmeric leaf and pseudostem extract (CLE) on tumor necrosis factor (TNF)-α/interferon (IFN)-γ-stimulated HaCaT keratinocytes (HK) and 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ear edema in a mouse model.

Methods: Cell viability and intracellular ROS levels in response to CLE were assessed. The potential of CLE to suppress inflammation was evaluated by monitoring the inhibition of signaling pathways and changes in cytokine/chemokine expression through Western blotting and real-time quantitative polymerase chain reaction (RT-qPCR) analyses. CLE was also examined for its impact on skin hydration and tight junction integrity. For in vivo analysis, an ear edema model was established using female BALB/c mice (7 weeks old).

Results: CLE treatment led to a dose-dependent decline in intracellular ROS and enhanced cell viability of TNF-α/IFN-γ-stimulated HK. Treatment with CLE resulted in decreased transcription of epithelial-derived cytokines (thymic stromal lymphopoietin (TSLP), IL-25, IL-33), pro-inflammatory mediators (IL-6, IL-8, IL-13, TNF-α, IFN-γ, IL-1β), and chemokines (macrophage-derived chemokine (MDC), regulated on activation, normal T cells expressed and secreted (RANTES), thymus and activation-regulated chemokine (TARC)), along with inhibition of mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signaling proteins in stimulated HK. CLE improved expression of proteins associated with skin hydration and tight junctions, helping to preserve moisture balance and structural integrity. Moreover, CLE markedly reduced ear redness, swelling, and thickness in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced mice, while alleviating histopathological changes, including inflammatory cell infiltration and dermal thickening. Additionally, CLE effectively diminished inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and pro-inflammatory cytokine expression in the ear tissues of edema-induced mice.

Conclusions: Collectively, CLE exhibited potential as a natural anti-inflammatory agent by attenuating oxidative stress, downregulating inflammatory mediators, enhancing skin barrier function in vitro, and reducing ear edema in vivo.

Keywords: Curcuma longa; cytokines; edema; inflammation; keratinocytes.