Abstract
Background: Inflammation and oxidative stress are key mechanisms in underlying skin conditions like psoriasis and eczema. While many plants, including Australian native plants, are proposed to target these pathways due to their phytochemical content, studies on whole extracts and their synergistic effects remain limited. Objectives: This study aimed to investigate individual and combined effects of whole plant extracts on skin protection and healing, focusing on their anti-inflammatory and antioxidant properties. Methods: The antioxidant potential of the individual and combined plant extracts were investigated on 2,2-diphenyl-1-picrylhydrazyl (DPPH) and reactive oxygen species (ROS) assay followed by luciferase assay in MCF-7 AREc32 cells for nuclear factor erythroid 2-related factor 2 (Nrf2) activation. The anti-inflammatory activities were investigated on lipopolysaccharide (LPS)-induced RAW 264.7 murine macrophages for the inhibition of nitric oxide (NO), tumour necrosis factor (TNF)-α, and interleukin (IL)-6. Synergistic interaction was determined by the combination index model (CI < 1). Combination(s) showing synergistic and optimal activity were further investigated on LPS-induced human dermal fibroblasts (HDF) cells for IL-6 inhibition and wound healing activity. Results: Three of the tested Australian native plant extracts demonstrated prominent antioxidant and anti-inflammatory activities including bitter orange, mountain pepper berry and native river mint. In particular, their three-way combination (1:1:1, w/w) showed prominent synergistic (CI < 1) in reducing NO and IL-6, along with enhanced Nrf2 activation. In LPS-inflamed HDF cells, the combination maintained synergistic inhibition of IL-6 levels and promoted wound healing response. Conclusions: These findings highlight the therapeutic potential of Australian native plant as a whole extract for skin protection and repair attributed to antioxidant and anti-inflammatory activities. The observed synergistic anti-inflammatory and antioxidant effects support their use in the development of new cosmetic formulations for skin.