Echinacea: Background. Actions

2010

Historical Note

Echinacea was first used by Native American Sioux Indians centuries ago as a treatment for snakebite, colic, infection and external wounds, among other things. It was introduced into standard medical practice in the USA during the 1 800s as a popular anti-infective medication, which was prescribed by eclectic and traditional doctors until the 20th century. Remaining on the national list of official plant drugs in the USA until the 1940s, it was produced by pharmaceutical companies during this period. With the arrival of antibiotics, echinacea fell out of favour and was no longer considered a ‘real’ medicine for infection. Its use has re-emerged, probably because we are now in a better position to understand the limitations of antibiotic therapy and because there is growing public interest in self-care. The dozens of clinical trials conducted overseas have also played a role in its renaissance.

Common Name

Echinacea

Other Names

Echinacea angustifolia — American coneflower, black sampson, black susans, coneflower, echinaceawurzel, Indian head, kansas snakeroot, purple coneflower, purpursonnenhutkraut, racine d’echinacea, Rudbeckia angustifolia L, scurvy root, snakeroot

Echinacea purpurea Brauneria purpurea (L.) Britt., combflower, purple cone flower, red sunflower

Rudbeckia purpurea L. — Echinacea pallida, Brauneria pallida (Nutt.) Britt., pale coneflower, Rudbeckia pallida Nutt.

Botanical Name / Family

Echinacea species (family Asteraceae [Compositae])

The name ‘echinacea’ generally refers to several different plants within the genus — Echinacea purpurea, Echinacea pallida and Echinacea angustifolia.

Plant Parts Used

Root, leaf and aerial parts

Chemical Components

The most important constituents in regard to pharmacological activity are the polysaccharides, caffeic acid derivatives, alkylamides, essential oils and polyacetylenes, although there are other potentially active constituents, as well as a range of vitamins, minerals, fatty acids, resins, glycoproteins and sterols. Constituent concentrations vary depending on the species, plant part and growing conditions. In regards to the final chemical composition of an Echinacea-containing product, the drying and extraction processes further alter chemical composition.

Main Actions

Due to the wide assortment of chemical constituents found in Echinacea, it has varied pharmacological effects.

IMMUNOSTIMULANTAND IMMUNOMODULATOR

The immunostimulant activity of echinacea has been the subject of countless studies. Overall, the fresh-pressed leaf juice of Echinacea purpurea and alcoholic extracts of the roots of Echinacea pallida, Echinacea angustifolia and Echinacea purpurea have been shown to act mainly on nonspecific cellular immunity. Macrophage activation has been well demonstrated, as has stimulation of phagocytosis. Orally administered root extracts of echinacea have produced stronger effects on phagocytosis than aerial parts, with Echinacea purpurea roots producing the greatest effect, followed by that of Echinacea angustifolia and Echinacea pallida.

Activation of polymorphonuclear leukocytes and NK cells has been reported and increased numbers of T-cell and B-cell leukocytes. Research in human subjects has produced conflicting results, with some studies showing that echinacea stimulates non-specific immunity and others showing no significant effect.

It is currently believed that no one single constituent is responsible for the herb’s immunomodulating action, with the most important elements being polysaccharides, glycoproteins, alkamides and flavonoids.

ANTI-INFLAMMATORY

Echinacea purpurea has demonstrated anti-inflammatory activity in vitro and in vivo. More specifically, alkamides from the roots of Echinacea purpurea partially inhibit both COX-1 and COX-2 isoenzymes. In vivo tests identify anti-inflammatory effects also for Echinacea angustifolia and Echinacea pallida when applied topically.

Recent research has further identified that alkamides from echinacea modulate TNF-alpha mRNA expression in human monocytes/macrophages via the cannabinoid type 2 (CB2) receptor. Two alkamides that bind to the CB2 receptor more strongly than the endogenous cannabinoids have been identified. They also bind to CB1. Alkamides also potently inhibit lipopolysaccharide-induced inflammation in human whole blood and exert modulatory effects on cytokine expression in vitro. Cytokine modulation was also observed for two different echinacea extracts in a study using cytokine antibody arrays to investigate the changes in the proinflammatory cytokines and chemokines released from a cultured line of human bronchial epithelial cells exposed to rhinovirus 14. Virus infection stimulated the release of at least 31 cytokine-related molecules, an effect that was reversed by simultaneous exposure to either of the two echinacea extracts, although the patterns of response were different for the two extracts.

ANTIVIRAL

Extracts of eight taxa of the genus Echinacea were found to have antiviral activity against HSV-1 in vitro when exposed to visible and UVA light.

ANTIFUNGAL ACTIVITY

Hexane extracts of echinacea have phototoxic antimicrobial activity against fungi. The extracts inhibited growth of yeast strains of Saccharomyces cerevisiae, Candida shehata, Candida kefyr, Candida albicans, Candida steatulytica and Candida tropicalis.

Other Actions

ANTIOXIDANT

Free radical scavenging activity can be attributed to numerous antioxidant constituents found in echinacea, such as vitamin C, beta carotene, flavonoids, selenium and zinc. Herbalists consider it also to have lymphatic, blood cleansing and wound healing actions.

ANAESTHETIC

The alkylamides exert a mild anaesthetic activity, which is typically experienced as a tingling sensation on the tongue.

APOPTOSIS

Apoptosis, or programmed cell death, is a physiological, active cellular suicide process that can be modulated by various stimuli, including hormones, cytokines, growth factors, and some chemotherapeutic agents. According to one study, Echinacea purpurea was able to regulate the process of apoptosis in vivo.

CYTOCHROMES

Contradictory results have been obtained by two research groups testing the effects of echinacea on cytochrome P (CYP) activity in human volunteers. One study found that echinacea had no significant effect on CYP1A2, CYP2D6, CYP2E1 or CYP3A4 activity, whereas the other identified a significant effect on CYP3A and CYP1A2.

CHEMOPREVENTION

Several experimental studies with mice have found that treatment with echinacea reduces the incidence of tumour development. Most research has been conducted with Echinacea purpurea.