Pharmacological Toxicological Effects 51 Immunological Effects

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The majority of literature published about Echinacea focuses on its activity as an immunostimulant. Many of the studies focus on the activity of macrophages and Echinacea's ability to activate and stimulate immune function.

One constituent of Echinacea, the polysaccharide arabinogalactan, has been identified as a macrophage activator in vitro, causing macrophages to attack tumor cells and microorganisms. When injected into mice intraperito-neally, arabinogalactan was able to activate macrophages. Macrophage production of tumor necrosis factor (TNF)-a, interleukin (IL)-1, and interferon-B2 was increased in vitro, and production of oxygen free radicals was increased both in vitro and in vivo (6).

Three of the main active components of Echinacea, cichoric acid, polysaccharides, and alkylamides, were separated and tested at various doses in rats for phagocytic activity in alveolar macrophages and splenocytes. The alveolar macrophages from the group of rats treated with the alkylamides were the only cells to show any significant increases in phagocytic activity, phago-cytic index, TNF-a, and nitric oxide. None of the components tested had any activity on splenocytes (7).

Echinacea was fed to aging male rats and was found to cause an increase in total white cell counts during the first 2 weeks of the administration and increases in IL-2 levels in the final 5 weeks. Differential white counts were altered during the entire 8-week study, with mononuclear cells significantly increased, whereas granulocytes decreased (8).

5.2. Antimicrobial/Antiviral Effects

The focus of Echinacea research most recently has been for the treatment and prevention of URIs of varying causes. There are a number of studies using Echinacea products in the treatment of URI. Many of these show positive results with reduction of symptoms and duration of URI. Studies evaluating the preventative role of Echinacea in URI have shown less impressive results. A few reasons for the differences in efficacy may have to do with the quality of the Echinacea used in the study and study design. The treatment studies demonstrating effectiveness tend to start treatment early in the course of a URI (9).

A double-blind, placebo-controlled, randomized trial evaluating Echinacea for the treatment of colds involved 559 adult patients and three different Echinacea products (Echinaforce® [E. purpurea 95% herb and 5% root], E. purpurea concentrate, and E. purpurea root preparation). In the patients that were treated, two of the Echinacea products produced a statistically significant reduction in symptoms compared to placebo and the E. purpurea root preparation (10). In another study evaluating the prophylactic role of Echinacea, 302 patients were enrolled in a three-armed, randomized, double-blind, placebo-controlled trial. Each of the groups was given ethanolic extract of E. purpurea roots, E. angustifolia roots, or placebo for 12 weeks. They did not find a significant reduction in occurrence of URI in either treatment group; however, they speculated from their results and the results of two other similar studies that there was a 10 to 20% relative risk reduction for URI. It was concluded that larger sample sizes were needed to confirm their observation (11).

A randomized, double-blind, placebo-controlled study was done in 48 healthy patients given E. purpurea extract or placebo for 7 days and then inoculated with rhinovirus type 39. Treatment was continued for 7 more days after the inoculation. They did not find a statistically significant decrease in the rate of infection. Because of the small sample size, power analysis did not detect any differences in the frequency and severity of the illness that ensued after inoculation. However, their findings did show a trend of reduced symptoms consistent with previous studies relative to prevention of URI (12).

Eight different varieties of Echinacea were found to have antiviral activity against Herpes simplex virus (HSV) Type I in vitro. The two most potent inhibitors found were ethanol extracts of E. pallida var. sanguinea and n-hexane extracts of E. purpurea (13).

In another study, to evaluate the prophylactic action of Echinacea on Influenza virus Type A, a mixture of four herbal extracts, which included

Thujae occidentalis herb, Baptisiae tinctoriae root, E. purpurea root, and E. pallida root, were given to mice. After 6 days the mice were inoculated with Influenza virus Type A. They found a statistically significant increase in survival rate, survival time, reduced lung consolidation, and virus titer (14).

A single center, prospective, double-blind, placebo-controlled, crossover trial investigated the activity of Echinacea in humans for the treatment of recurrent genital herpes. The 1-year study involved 50 patients who were each given the product Echinaforce for 6 months and placebo for 6 months. The study found no statistically significant benefit in using Echinaforce vs placebo for frequently recurrent genital herpes (15).

5.3. Antifungal Effects

Acetylenic isobutylamides and polyacetylenes occurring in Echinacea have been shown to inhibit the growth of yeast strains of Saccharomyces cerevisiae, Candida shehata, Candida kefyr, Candida albicans, Candida steatulytica, and Candida tropicalis. This growth inhibition occurred to a greater extent under ultraviolet irradiation than without it. There are other compounds in Echinacea that are suspected to be phototoxic to microbes, but this has yet to be demonstrated (16).

Pretreatment with a polysaccharide E. purpurea extract was found to decrease morbidity and mortality in mice infected by C. albicans immunosuppresed with cyclophosphamide and cyclosporine A. They found that macrophages in the Echinacea group produced an increased amount of TNF-a. The authors state that this led to an increased resistance toward Listeria monocytogenes, C. albicans, and the intracellular parasite Leishmania enrietti (17).

5.4. Antineoplastic Activity

See also Chapter 7, Section 4.1. An investigation details the isolation of (Z)-1,8-pentadecadiene from E. angustifolia and E. pallida. This root oil constituent has inhibitory effects against Walker carcinosarcoma 256 and P-388 lymphocytic leukemia in the mouse and rat, respectively (18).

An examination of mature and precursor cells in the bone marrow and spleen was conducted to determine the activity of Echinacea in these cell's development. After an extract of Echinacea was given to mice for 1- and 2-week periods, populations of natural-killer cells and monocytes were increased in both organs, whereas other hemopoietic and immune cell populations remained at control levels. This study confirmed Echinacea's effectiveness as a nonspecific immune stimulant and suggested a prophylactic role for Echinacea in treating virus-based tumors and infection (19).

An investigation into the effects of Echinacea in mice with leukemia was performed to determine the antineoplastic activity. Two groups of mice were used; one group of mice was given a vaccine of killed erytholeukemia cells and then given live tumor cells to induce leukemia, the other group received live tumor cells. It was found that the mice that had been given the vaccine and Echinacea survived longer than the control group and the group given the vaccine alone. They found significant elevations in natural killer cells in these mice. It was concluded that combination therapy of Echinacea and vaccine prolonged the life more than the group that had received the vaccine alone (20). In an earlier study by the same investigator, it was shown that leukemic mice treated with Echinacea had a much higher survival rate than the control. The treatment group showed a 2.5-fold increase in natural killer cells in their spleens. All other major hemopoietic and immune cell lineages remained normal in the treatment group at 3 months after tumor onset. The authors concluded that the positive effects observed suggest a potential use of Echinacea in treatment of leukemia (21).

5.5. Wound Healing

Echinacea has been used topically for wound-healing. The exact mechanism is unknown but is likely caused by antihyaluronidase activity of echinacoside. A study investigating this activity found that E. pallida, which is known to contain echinacoside, had more anti-inflammatory and wound-healing activity in rats after topical application. The effects were much greater with E. pallida compared with E. purpurea and control (22).

5.6. Anti-Inflammatory Effects

Alkylamides from the roots of E. purpurea have been shown to have anti-inflammatory activity in vitro. In a study by Clifford et al., they demonstrated 36-60% and 15-46% of cyclooxygenase (COX)-I and COX-II, respectively (23).

Two in vitro studies have demonstrated anti-inflammatory activity by various Echinacea preparations. Speroni et al. showed anti-inflammatory activity attributed to echinacosides in E. pallida in rats. Another in vitro study used E. purpurea in mice that had induced paw edema. Only the higher dose used in the study downregulated COX-2 expression. The authors suggested that the anti-inflammatory properties of Echinacea are related to this inhibition (24).

5.7. Mutagenicity/Carcinogenicity

E. purpurea gave negative results in mammalian cells and bacteria in vitro and in vivo in mice mutagenicity tests. Hamster embryo cell carcinogenicity studies revealed no morphological transformations (25).

5.8. Antioxidant Effects

In an analysis of the different components of the extracts of the roots and leaves of E. purpurea, E. angustifolia, and E. pallida, all possessed anti-oxidant properties in a free-radical scavenging assay and in a lipid peroxidation assay (26).

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