Phytochemical Composition and Antioxidant and Anti-Inflammatory Activities of Iningai Aboriginal Medicinal Plants From Central Queensland, Australia.

Abstract

Indigenous Australians possess vast ethnopharmacological knowledge of native flora and have been using it for millennia. In a collaborative initiative to document and scientifically validate this knowledge, the Tropical Indigenous Ethnobotany Centre, Australian Tropical Herbarium and the James Cook University have been working closely with traditional custodians from the Iningai community near Barcaldine, Queensland. This study aimed to evaluate crude leaf extracts from eight medicinal plant species traditionally used by the Iningai people, focusing on their phytochemical profile, antioxidant potential, cytotoxicity and anti-inflammatory activity. Phytochemical screening confirmed the presence of alkaloids, phenolics, flavonoids and terpenoids. Antioxidant activity, assessed via the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay, showed moderate to strong activity, with IC₅₀ values ranging from 37.37 ± 1.01 μg/mL to 206.50 ± 2.44 μg/mL. Cell viability assay using human peripheral blood mononuclear cells (PBMCs) showed that Pittosporum angustifolium exhibited the highest cytotoxicity, resulting 73.97% cell death, suggesting potential toxicity to human cells. Anti-inflammatory activity was evaluated in lipopolysaccharide (LPS)-stimulated PBMCs. Seven of the eight plant extracts significantly suppressed the release of proinflammatory cytokines, including tumour necrosis factor (TNF), interferon-gamma (IFN-γ), monocyte chemoattractant protein-1 (MCP-1) and interleukin (IL)-23. Overall, this study provides scientific validation for the traditional use of these eight medicinal plants by the Iningai people. The identification of key phytochemicals, antioxidant potential and anti-inflammatory properties supports their ethnopharmacological relevance. Further investigation is warranted to isolate and characterise the active compounds from the most promising species for potential development into novel therapeutic agents.