Screening of Herbal Drug extracts for inhibitory activity on inducible nitric oxide synthase (iNOS)

The inhibition of the inducible nitric oxide synthase (iNOS) turned out to be an important aspect in the field of anti-inflammatory research. Overproduction of nitric oxide (NO) induced by the enzymatic activity of iNOS in various cell types plays a role in several inflammatory and also immunoregulatory processes. [1]

In continuation of our work on anti-inflammatory herbal drugs, we herein present the results of a screening of a series of plant extracts. The plants were selected particularly with regard to their use in Traditional Chinese Medicine (TCM) as anti-inflammatory agents. The assay to elucidate the effects on inducible nitric oxide synthase (iNOS) involves the macrophage cell line RAW 264.7. Cells were stimulated with lipopolysaccharides (LPS) and interferon-gamma in presence or absence of the respective n-hexane, dichloromethane, acetone/diethylether, methanol and water extracts. The iNOS effects were determined by measuring nitrite release which is an indicator for the activity of iNOS in the cell culture supernatants by utilization of the Griess assay method. [2, 3]

Within our screening, several extracts showed promising results. The acetone/diethylether extracts from Asarum europaeum L. (Aristolochiaceae) and Minquartia guianensis Aubl. (Olacaceae) inhibited the NO production with an IC₅₀ value of ˜10µM and the acetone/diethylether extract from Cynara scolymus L. (Asteraceae) with an IC₅₀ in the range of ˜3µM. Extracts with similar effects were selected for further investigations.

Acknowledgements: The authors thank Margit Rehn (Institute of Pharmaceutical Sciences, Department of Pharmacology and Toxicology, Karl-Franzens-University) for the help in establishing the test sytem.

References: [1] Clancy, R.M. et al. (1998) Arthritis & Rheumatism 41: 1141–1151. [2] Baer, H.P., Schmidt, K. et al. (1995) Life Sci. 57: 1973–1980. [3] Dirsch, V.M. et al. (1998) Planta Med. 64: 423–426.