| Summary: | Salicylate-rich plants are an attractive alternative to synthetic anti-inflammatory drugs due to a better safety profile and the advantage of complementary anti-inflammatory and antioxidant effects of the co-occurring non-salicylate phytochemicals. Here, the phytochemical value and biological effects in vitro and <i>ex vivo</i> of the stems of one of such plants, <i>Gaultheria procumbens</i> L., were evaluated. The best extrahent for effective recovery of the active stem molecules was established in comparative studies of five extracts. The UHPLC-PDA-ESI-MS<sup>3</sup>, HPLC-PDA, and UV-photometric assays revealed that the selected acetone extract (AE) accumulates a rich polyphenolic fraction (35 identified constituents; total content 427.2 mg/g dw), mainly flavanols (catechins and proanthocyanidins; 201.3 mg/g dw) and methyl salicylate glycosides (199.9 mg/g dw). The extract and its model components were effective cyclooxygenase-2, lipoxygenase, and hyaluronidase inhibitors; exhibited strong antioxidant capacity in six non-cellular in vitro models (AE and procyanidins); and also significantly and dose-dependently reduced the levels of reactive oxygen species (ROS), and the release of cytokines (IL-1β, IL-8, TNF-α) and proteinases (elastase-2, metalloproteinase-9) in human neutrophils stimulated <i>ex vivo</i> by lipopolysaccharide (LPS) and <i>N</i>-formyl-L-methionyl-L-leucyl-L-phenylalanine (<i>f</i>MLP). The cellular safety of AE was demonstrated by flow cytometry. The results support the application of the plant in traditional medicine and encourage the use of AE for development of new therapeutic agents.
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