Bioavailability and pharmacokinetics of Echinacea purpurea preparations and their interaction with the immune system.

Echinacea is a widely used herbal remedy for the prevention and treatment of the common cold. Recently, many new insights concerning the molecular mode of action of the main lipophilic constituents, the alkamides, have renewed interest in this plant. In order to compare the bioavailability of alkamides from liquid and tablet preparations of E. purpurea (Echinaforce) in humans and to study the effects on ex vivo stimulated blood cells, a randomized, single-dose, crossover study with 10 (8 test, 2 placebo) volunteers has been performed. They received either 4 ml of the standardized E. purpurea (Echinaforce) tincture or 12 E. purpurea (Echinaforce) tablets or placebo. Both doses contained the same amount (0.07 mg) of the major alkamides, dodeca-2E,4E,8Z, 10E/Z-tetraenoic acid isobutylamides. Liquid chromatography electrospray ionization ion-trap mass spectrometry was used to determine the content of alkamides in serum. It was found that the arithmetic mean C(max) of dodeca-2E,4E, 8Z,10E/Z-tetraenoic acid isobutylamides absorbed after oral application of the Echinaforce tincture appeared after 30 min (0.40 ng/ml serum). In comparison, the t(max) of tablets was 45 min with a C(max) of 0.12 ng/ml. An ex vivo stimulation of blood by LPS was carried out to measure the influence of E. purpurea on the innate and adaptive immune system. Both E. purpurea preparations led to the same effects on the immune system according to the concentration of pro-inflammatory cytokines TNF-alpha and IL-8. 23 hours after oral application a significant down-regulation of TNF-alpha and IL-8 in LPS pre-stimulated whole blood was found. However, no significant changes in the concentration of IL-6 were observed. Although a quarter of the dodeca-2E,4E,8Z, 10E/Z-tetraenoic acid isobutylamides was absorbed from the tablets, the study shows that the formulations trigger the same effects on the measured immune parameters.