In vitro anti-inflammatory properties of twelve Norwegian medicinal plants

Today, inflammatory diseases such as rheumatoid arthritis and inflammatory bowel disease represent a major health burden in Western societies. Such diseases are treated with drugs aiming at suppressing inflammatory symptoms. In Norway, several medicinal plants share a history of ethnomedical use towards the treatment of various inflammatory conditions which could represent sources of new anti-inflammatory drugs.

This study focused on exploring the potential of understudied traditional medicinal plants used in Norway to treat inflammation of different origin. Through phytochemical and biological screening methods, we aimed to identify plants with anti-inflammatory properties that also showed a high proportion of phenolic compounds. Based on these results, such plants would be of interest and relevance for further work including isolation and characterization of phytochemicals that could serve as novel anti-inflammatory drugs.

A systematic literature survey of historical records from the 1800s and onwards was performed searching for plants used to treat various inflammatory diseases. Twelve plants were selected and subjected to accelerated solvent extraction to obtain extracts rich in phenolic compounds, namely dichloromethane and 80 % ethanol extracts. These were studied in bioassays assessing their in vitro anti-inflammatory effects. Their ability to inhibit nitric oxide (NO) and TNF-α cytokine production was measured, and their protection against indomethacin induced damage of the intestinal epithelial barrier was evaluated using differentiated Caco-2 cells. The total phenolic content of the extracts was determined, and ¹H NMR spectroscopy and HPLC-DAD was performed for phytochemical profiling.

Several of the plants presented moderate to high bioactivity, namely Matricaria discoidea, Alnus incana, Geranium sylvaticum, Antennaria dioica, Tanacetum vulgare and Malva moschata. A stronger effect was observed among the dichloromethane extracts in NO and TNF-α inhibition, while the 80 % ethanol extracts showed greater protection of the barrier integrity. M. discoidea, A. incana and G. sylvaticum are of particular interest, presenting consistently high bioactivity. Their ¹H NMR spectra also showed a high proportion of phenolic compounds.

Both A. incana and M. discoidea are scarcely studied regarding their bioactivity and chemical composition, being potential candidates for the discovery of novel anti-inflammatory drugs. Based on the results obtained from this study, further work will focus on these two plants, including isolation of phenolic compounds and assessing their biological activities.