Diversity of Echinacea

Echinacea diversity will be discussed in terms of its species, varieties, cultivating stage and regions, plant parts, processing of plant and products, methodology, quality, clinical trials, and legislation. The diversity is shown at the level of the following constituents that are thought to show individual or combined biological and pharmacological activity:

  • Lipophilic alkamides (dodecatetraenoic acid isobutylamides and related compounds, also called alkylamides)
  • Moderately hydrophilic phenolic caffeoyl derivatives (cichoric acid, cynarin, echinacoside, caftaric acid, chlorogenic acid, etc.)
  • Lipophilic polyalkynes and polyalkenes
  • High-molecular weight hydrophilic glycoproteins and polysaccharides including heteroxylans, fructofuranoside, and arabinogalactans.

The lipophilic alkamides and polar phenolic caffeoyl derivatives are considered to be the main pharmacologically active components in Echinacea alcohol extracts in which the polar polysaccharides are at very low level. The polysaccharides exist in expressed Echinacea juice, aqueous extract, and powdered whole herb. However, their levels in most Echinacea preparations and effects on the immune system after oral intake have been disputed.

Species

Table Species and Varieties of Genus Echinacea lists the species and varieties of Echinacea Moench (Hehantheae: Asteraceae). In the most recent publication, genus Echinacea has been reclassifled as four species and eight varieties, together with a group of introgressant hybrids. E. purpurea, E. angustifolia, and E. pallida are revised as E. purpurea (L.) Moench; E. pallida var angustifolia (DC.) Cronq.; and E. pallida var. pallida (Nutt.) Cronq..

TABLE Species and Varieties of Genus Echinacea

Binns et al. (2002)McKeown (1999)Bauer and Wagner (1991)
E. purpureaE. purpureaE. purpurea
E. pallida var. angustifoliaE. angustifolia var. angustifoliaE. angustifolia var angustifolia
E. pallida var. pallidaE. pallidaE. pallida
E. pallida var. simulataE. simulataE. simulata
E. pallida var. sanguineaE. sanguineaE. sanguinea
E. pallida var. tennesseensisE. tennesseensisE. angustifoliavar tennesseensis
E. atrorubens var atrorubensE. atrorubensE. atrorubens
E. atrorubens var neglectaE. paradoxa var. neglectaE. paradoxa var neglecta
E. atrorubens var paradoxaE. paradoxa var. paradoxaE. paradoxa var paradoxa
E. laevigataE. laevigataE. purpurea var. laevigata
 E. angustifolia var strigosaE. angustifolia var strigosa

In this post, we still use the former general names and discuss E. purpurea, E. angustifolia, and E. pallida, although certain species or varieties show the highest contents of specific phytochemicals.

The phytochemical components of various species have been analyzed and compared in a number of studies. Binns et al. (2002) published the most detailed comparison, and by using reverse-phase high-performance liquid chromatography (HPLC) have shown quantitatively the phytochemical variation in the roots and flower heads of native plant populations in genus Echinacea.

The diversity of chemical components and antioxidant capacity in the extracts of Canadian-grown E. purpurea, E. pallida, and E. angustifolia have been reported. Extracts of E. angustifolia roots could be distinguished from those of E. purpurea and E. pallida by the absence of, or only a trace of, cichoric acid, and by the presence of both cynarin and echinacoside. It should be noted that the alkamides differ greatly among species in amounts and in general chemical structure. Alkamides are present in E. purpurea and particularly as dodecatetraenoic acid isobutylamides in E. angustifolia but not in E. pallida ().

Mazza and Cottrell (1999) have analyzed and identified 70 volatile components in the plant parts of Canadian-grown E. angustifolia, E. pallida, and E. purpurea (). Some volatile compounds, such as acetaldehyde, camphene, and limonene, are present in all plant tissues irrespective of the species, while some components varied with the species and the plant parts.

Species diversity can be observed also in the alkamide content of the achene.

Variety and Other Factors

The natural variation of Echinacea within a species can have a tremendous effect on final product quality. This diversity might be due to genetic and environmental differences including variety, cultivation regions, harvest time, and cultivation or processing conditions.

In general, the wild E. angustifolia has higher echinacoside content than the cultivated one. Wills and Stuart (1999) analyzed active components in 62 commercial samples of dried root and of aerial parts of E. purpurea grown in eastern Australia.

Methodology and Laboratories

The diversity in results is also due to laboratories using different methodology and conditions.

Speroni et al. (2002) and Sloley et al. (2001) reported that echinacoside is present in E. pallida and only in traces in E. angustifolia, whereas Perry et al. (2001) reported that E. angustifolia contained more echinacoside (1.04%) than E. pallida (0.34%). As mentioned above, Binns et al. (2002) revealed new levels of some constituents in the root and flower head of wild and cultivated populations of Echinacea.

In addition, there are some inconsistencies in the results from studies on immune-regulating activity of Echinacea (). A recent study by South and Exon (2001) concluded that Echinacea preparations under some conditions may have immunosuppressive rather than immunostimulating activity. Thus, it is currently argued that characterizing Echinacea’s effects as “immunomodulation” may be more appropriate.

Schwarz et al. (2002) reported an unexpected result in a study with a double-blind, placebo-controlled crossover design, in which 40 healthy men (20 to 40 years of age) received 2 weeks of orally administered freshly pressed E. purpurea juice or placebo juice. Their study showed that compared with the placebo, E. purpurea had no effects in enhancing phagocytic activity of either polymorphonuclear leukocytes or monocytes.

Regions

Biological diversity among Echinacea species cultivated in different regions also exists. Studies carried out in China showed that the introduced Canadian E. purpurea planted in the Beijing area accumulated more cichoric acid than that planted in Canada (1.108% vs. 0.671%). The levels of the major alkamide isomer pair in E. purpurea roots were 0.04 to 0.39 mg/g in Germany and 0.8 to 3.6 mg/g in New Zealand. These differences may be caused by the geographical factors, climate, soil, and cultivation conditions, as well as preparation methodology for testing.

Plant Parts

At present, most preparations are derived from the aerial parts of E. purpurea and underground parts of E. purpurea, E. angustifoUa, or E. pallida. In an individual species or cultivar the different parts of the plant contain different levels of the active compounds. Several studies have reported that in E. purpurea, alkamide levels were much lower in leaves than in roots. Perry et al. (1997) reported that alkamide levels differed significantly among the various parts of E. purpurea. Kim et al. (2000) reported the total alkamide levels in Canadian-grown Echinacea purpurea. In roots, the level of total alkamides (2.65 to 3.28 mg/g) is much higher than that in leaves (0.10 to 0.18 mg/g).

Stuart and Wills (2000) also analyzed the distribution of alkamide and cichoric acid levels in morphological parts of E. purpurea grown in Australia and extracted with methanol. Root is a better source of alkamides, while flower and leaf are better sources of cichoric acid. The major alkamides in E. purpurea root are the isomer pair (); these two major alkamides account for about 50% of total alkamides. In Egyptian-grown E. purpurea, it was also found that these two alkamides were the major constituents in roots at all stages of development, constituting 46.4% μn fruit stage) to 75.9% μn seedling stage) of total alkamides.

Component Levels at Plant Development Stage

Growth Stage

The accumulation of phytochemicals in Echinacea varies with growth stages, species, cultivation conditions, and regions. Binns et al. (2002) have compared and defined the phytochemicals accumulating with age in all Canadian-grown species and varieties of Echinacea. Stuart and Wills (2000) investigated the change in alkamide and cichoric acid levels during the growth stages of Australian-grown E. purpurea. During the four growth stages (pre-flower, flowering, mature, senescent), the alkamide level decreased in root, stem, and leaf tissues, but increased in the flower tissue to senescence. At all stages, the alkamide level was higher in the root than in the stem or leaf. The level of cichoric acid showed no significant change during the flowering and mature stage. The cichoric acid level in stems was significantly lower than that in other tissues. El-Gengaihi et al. (1998) investigated alkamide accumulation in E. purpurea cultivated in Egypt; these authors showed that in the roots, but not in the vegetative tissues, alkamides increased and reached a maximum at the plant fruiting stage.

Berti et al. (2002) studied the effects of phonological stages; nitrogen, phosphorous, and potassium fertilization on root yield; and echinacoside and alkamide content in E. angustifolia cultivated in Chile. Results showed that echinacoside and alkamides were strongly affected by the phonological stage. Echinacoside and alkamide contents were inversely correlated with root yield. Echinacoside content was proportionally affected by potassium supply.

Flower Developmental Stages

Letchamo et al. (1999) studied the accumulation of active ingredients during the development of the flower heads of the American-grown E. purpurea. The quality of Echinacea was strongly influenced by floral development, which was divided into four stages, from early flower buds to the senescent stage. The highest content of cichoric acid was found at Stage 1, and the content of isobutylamide was highest at Stage 3 and 4. The maximum content of chlorogenic acid and echinacoside occurred at Stages 1 and 2, respectively. To obtain optimal yields of both hydrophilic and lipophilic components, Echinacea flowers should be harvested at Stage 3.

Processing Conditions

A number of recent studies have showed how varying methods of extraction, drying, and storage affect levels of active components. All these factors caused diversity in the plant material and final products. Chapter 8 in this book by Perry et al. describes these factors in detail.

As mentioned above, Echinacea contains a considerable number of phytochemicals, some of which are water soluble. Therefore, the processing methodology will affect the level of the different components extracted. The level of polysaccharides will be much lower if alcohol extraction is used during preparation.

Brovelli et al. (2001) compared two types of press to make juice from U.S.-grown E. purpurea: the hydraulic bag press and a mechanical screw press. The results showed differences not only in physical parameters but also in the chemical nature of the juices. Juice extracted by screw press had twice the concentration of cichoric acid as the juice extracted by the bag press. There was also a qualitative and quantitative difference in the alkamide fraction in favor of the screw press.

Adulteration

Over the last several years, the market for Echinacea has grown rapidly. As a result, there has been an increase in species misidentiflcation or adulteration in the Echinacea trade. Inadequate quality control means that ineffective or adulterated products can reach the market. The literature and the media have revealed examples of Echinacea preparations of poor quality and low amounts of characteristic constituents.

Roots of Parthenium integrifolium L., commonly known as American feverfew, have been found to be adulterants/substitutes for Echinacea root (Turner, 2001). Its roots are larger and easier to harvest than Echinacea roots. This adulterant/substitute can be recognized by the absence of any caffeoyl derivatives or through the presence of the sequiterpene esters cinnamoylechinadiol, cinamoylepoxyechinadiol, cinnamoylechinaxathol, and cinnamoyl dihydroxynardol.

Wolf et al. (1999) described the discrimination of the three main species of Echinacea by random amplified polymorphic DNA (RAPD) analysis. Individual Echinacea species are easily identified by RAPD analysis. Adulterations due to drug mixtures also can be detected. Laasonen et al. (2002) have developed a near-infrared reflectance spectroscopic method for the fast (analysis within 1 minute) qualitative identification of E. purpurea dried milled roots. An adulterated E. purpurea sample can be detected at a minimum of 10% adulteration.

Product Quality

The phytochemical studies on Echinacea have revealed tremendous diversity in the quality of Echinacea products derived from various sources. The potency of Echinacea products can vary from manufacturer to manufacturer and from lot to lot from a single manufacturer, all of which can be attributed to quality diversity.

Echinacea is available to consumers in many forms, including tinctures, pressed juice, liquid, tablets, pills, powders, capsules, lozenge, beverage, spray, soft gel, ointments, lotions, creams, toothpastes, and teas. In earlier publications, products for the parenteral administration of Echinacea existed in Germany (Parnham, 1996). Now, many hundreds of products are available worldwide (Bauer, 1998). Even in Australia, there are hundreds of Echinacea products listed in the Australian Register of Therapeutic Goods (ARTG) containing Echinacea alone or in combination with other herbs, vitamins, or minerals (Cameron, 1998). Tinctures or extracts of Echinacea in alcohol are the form most herbal authorities recommend. In the U.S., the most commonly used preparation is a liquid extract made from the root of E. purpurea (Kligler, 2003). In Germany, freshly pressed E. purpurea juice is popular (Bauer, 1999).

Different formulations of Echinacea preparations may have different contents of active ingredients and exert diverse pharmacological effects in the human body. Products derived from an extract containing more than 50% ethanol are not considered capable of the effects of water-soluble polysaccharides since in this concentration polysaccharides are insoluble (Stuart and Wills, 2000a). Freshly pressed Echinacea purpurea juice may contain certain levels of polysaccharides (Bauer, 1999).

Like the other herbal medicines, one problem of quality control and standardization in Echinacea products is that many countries have their own regulatory criteria and are not prepared to accept products from other countries that have been assessed by different criteria. The quality control of Echinacea thus varies by country and manufacturer. In the U.S., neither the Food and Drug Administration (FDA) nor any other federal or state agency routinely tests herbal medicines or other dietary supplements for quality prior to sale (Goldman, 2001). It was not until March 1999 that the FDA required that the labeling of herbal products provide information identifying the species of the herb, the part of the plant used, and the concentration of the herb.

Gilroy et al. (2003) investigated 59 single-herb preparations of Echinacea purchased from 11 stores in the Denver area over a 2-day period in August 2000. The samples included tablets, capsules, soft gels, and liquid. The results of thin layer chromatography (TLC) analysis showed that six samples (10%) contained no measurable Echinacea at all. The concentration of cichoric acid in the samples of the E. purpurea species ranged from 0% to 1.46%. In addition, the recommended daily dose of these samples ranged from 45 to 5,380 mg while German Commission E recommends a daily dose of 900 mg. The price per recommended dose ranged from $0.02 to 2.99.

Bauer (1999) analyzed six commercial preparations (one to four batches each) containing E. purpurea (aboveground parts) expressed juice, and found that they varied dramatically in cichoric acid and alkamide content.

In a recent issue of Consumer Reports, 12 brands of Echinacea pills on the U.S. market were compared. Levels of phenolic compound (caffeoyl-tartaric acid, chlorogenic acid, cichoric acid, and echinacoside) were assessed. Results showed that the average total percentage of phenolics varied from 0.8% to 4.5% depending on brand. Even within a brand, pills in different bottles had different levels of phenolics (Weil, 1999).

The independent ConsumerLab.com based in White Plains, New York, recently reviewed 25 commercial Echinacea products sold in the U.S., and tested them for the quality and quantity of Echinacea and levels of microbial contamination. Only 14 products (56%) passed this review. Others had inadequate labeling or lower levels of components than claimed on labels.

For 25 commercial Echinacea-containmg remedies, Osowski et al. (2000) quantified cichoric acid and alkamide contents. Results showed large differences (up to 10,000-fold) in cichoric acid or alkamide contents. Moreover, large differences among comparable products of different manufacturers and among different lots of the same product were noted.

This variation is caused in part by the enzymatic degradation by polyphenol oxidase (PPO; EC 1.14.18.1) during the processing of fresh plant material. Enzymatic degradation during extraction could reduce the measured levels of phenolic compounds by more than 50%. Nusslein et al. (2000) have investigated the causes of cichoric acid degradation in Echinacea products and recommended a process to stabilize E. purpurea products.

Clinical Trials

Because of great diversity in Echinacea product quality, it is no wonder that the results of clinical trials are inconsistent. A number of clinical trials and reviews have indicated that Echinacea preparations are efficacious in preventing and treating the common cold and other respiratory infections, while other clinical trials showed no significant effects. There are also a number of unpublished trials of Echinacea preparations with negative results. In spite of this inconsistency, clinical studies of the effect of Echinacea on the common cold remain a valid subject (); over 40 clinical studies have been published so far.

Schulten et al. (2001) reported a placebo-controlled, randomized, double-blind clinical trial evaluating the efficacy of the pressed juice from the fresh flowering E. purpurea in 80 patients with the common cold. The results showed that the duration of all symptoms was significantly reduced (9.0 days to 6.0 days) and the disease was less severe in the active treatment group than in the placebo group.

In a study by Brinkeborn et al. (1999), acute treatments of the common cold with two tablets containing crude extracts of E. purpurea (95% herb, 5% root) three times daily were shown to significantly reduce cold symptoms compared to the placebo, while a preparation of E. purpurea root did not.

Another study on the prophylactic efficacy of Echinacea was carried out in the flu season with 647 students from the University of Cologne. The result showed a 15% reduction in the number of colds in the group given Echinacea compared to the placebo group.

In a 12-week, double-blind, placebo-controlled trial, 302 healthy volunteers were given E. purpurea or E. angustifolia root extracts or a placebo pill, and any effect on prevention of upper respiratory infections was noted. Subjects taking Echinacea lasted slightly longer before suffering infection and had slightly fewer colds than those given the placebo, but the differences were not significant. Sixteen controlled clinical trials μnvolving 3,396 patients) from a total of 40 trials were chosen and evaluated in a Cochrane Library systematic review. Most trials showed positive results, suggesting that Echinacea products may have some beneficial effects on prevention and treatment of the common cold. However, quality data in about two-thirds of the trials was considered insufficient. The biggest problem is the great diversity and the unclear comparability of the investigated products. The use of different Echinacea preparations made comparability of the results difficult. It was recommended that preclinical and clinical studies with Echinacea-contaming herbal medicines should always indicate the species and plant parts used, formulation, method of extraction and quantification of potentially active components, and so on. These procedures will help to reduce inconsistencies in clinical trials and allow future research to focus on preparations that appear most promising.

Legislation, Pharmacopoeias, and Monographs

Considerable diversity also exists in the legislation, pharmacopoeias, and monographs of various countries. “There is no international consensus on how to regulate natural health products. The U.S. lists them as dietary supplements, with the onus on manufacturers to have data supporting their claims. At the other extreme, Germany regulates the products as drugs”. At present, in many countries, Echinacea is considered to be a food supplement, not a drug.

In the U.S., Echinacea is classified as a dietary supplement according to the Dietary Supplement and Health Education Act (DSHEA) approved in 1994 (FDA, 1995). Dietary supplements are treated as foods by the FDA; if they were on the market before 1994, they did not have to undergo any evaluation (Roll, 2002). Therefore, it is a manufacturer’s responsibility to ensure that Echinacea products are safe and properly labeled prior to marketing. This complicates verifying product purity, safety, and consistency. In 2001, the U.S. Pharmacopoeia (USP, 2002) created the Dietary Supplement Verification Program (DSVP) to help inform and safeguard the growing number of consumers who use dietary supplements. The program responds to the need to assure the public that dietary supplement products contain the ingredients stated on the product label (Thompson, 2001). As of March/April 2002, the botanical list in the U.S. Pharmacopoeia and National Formulary (USP-NF) had not yet included an official monograph of Echinacea products (DSVP, 2002).

In Canada, herbal products are divided into four groups under current Canadian Food and Drug regulation. Echinacea products are in the third group, which are nonprescription, traditional herb medicines (THM), intended for the self-treatment of a self-diagnosed, self-limiting condition (e.g., the use of Echinacea for the relief of sore throats due to colds). According to the Health Canada Drugs Directorate Guideline for THM such as Echinacea products (aqueous infusions and/or decoctions prepared from the dried root of E. purpurea), manufacturers follow Good Manufacturing Practice (GMP), provide a complete quantitative listing of ingredients on the label, indicate that a given product is a THM, and supply a minimum of two traditional references to support its pharmacological action for the part of the plant used.

In Australia, complementary medicine may be either “listable” or “registrable” in the Australian Register of Therapeutic Goods (ARTG). Echinacea products are listable complementary medicines that may contain only substances generally regarded as safe, and may carry only claims for the temporary relief of minor self-limiting conditions. Echinacea products are thus available in pharmacies and health food stores for consumer self-selection. Regarding Echinacea products, Australian Therapeutic Goods Administration (TGA) guides claim: “Echinacea helps support the immune system especially during the winter cold and flu season. This herb has been used traditionally for hundreds of years and now scientific evidence suggests that it may assist in supporting immune function” (TGA, 2001).

Vlietinck (2002) reported a European perspective on the elaboration of monographs on herbal medicinal products listed in the fourth edition of the European Pharmacopoeia. As of 2002, there were 106 published monographs, none of which focused on Echinacea; E. angustifolia radix, E. pallida radix, E. purpurea herba, and E. purpurea radix were among 40 monographs under study.

In Germany, Commission E of the Federal Institute of Pharmaceutical and Medicinal Products has not approved E. angustifolia herb and roots, E. pallida herb, or E. purpurea root for nonprescription drug use. Only research results from the fresh-pressed juice of E. purpurea flowering herb in 22% ethanol by volume as a preservative and from the water-alcohol extract of E. pallida roots qualified for an approved monograph. The latter preparations are recommended as a supportive treatment of recurring infections in the bronchial area and urinary tract, as well as for external use in the case of poorly healing superficial wounds (Bauer, 1999).

Echinacea products are sold as food supplements in Norway, but as herbal medicines in Sweden, Finland, and Denmark, and must be registered.