Quality Standardization of Echinacea

Although Echinacea products belong to the top best-selling group of herbal products, thus far its cultivation, harvesting, and extraction are realized without profound knowledge of factors that affect its quality. Commercially available preparations of varying quality are the result.

The increasing popularity of Echinacea has raised concerns in the herbal medicine community and the media that there is a need to establish standards for Echinacea products. The diversity described above supports the need for greater efforts to provide authentic, safe, stable, and efficacious Echinacea products that are consistent from batch to batch (Bauer, 1999; Grant and Benda, 1999).

Standard quality controls with scientific criteria start with a defined species, proper cultivation and harvesting through a defined drying and extraction procedure, and end with a quantitative determination by a defined method for one or more of its active ingredients (Tierra, 1999).

Active Markers

In order to standardize Echinacea preparations, some suitable active markers must be identified in the products. Although a number of active components have been studied and identified, their mechanisms of action and bioavailability are not yet completely understood (Barrett, 2003). At present, alkamides and cichoric acid content seem to be used as quality markers for some Echinacea products. However, it is noteworthy that echinacoside, which is used frequently for standardizing E. pallida and E. angustifolia extracts, is absent from E. purpurea (). Therefore, depending on the plant species used, the active marker should be appropriate. And since the active components may act additively or synergistically, the overrating of a single compound in quality control should be avoided (Bauer, 1999).

As mentioned above, active marker levels depend on growing conditions, climate, soil quality, and harvest time, and all factors in the processing stage. Variation in the commercial samples and manufacturing process can be qualitatively and quantitatively revealed by various improved chro-matographic methods that have been used to measure content levels of typical components in the plants and products of Echinacea species.

Alkamides and Cichoric acid

Bauer (1999) described an HPLC method for identifying alkamides and cichoric acid in commercial samples of E. purpurea pressed juice preparations, and proposed standardization by analyzing alkamide and cichoric acid contents. These components are typically found in E. purpurea and show pharmacological activity. However, in the study of Al-Hassan et al. (2000), cichoric acid was not found in the pressed juice.

Alkamides have phagocyte-stimulating activity in vitro and in vivo. They were also shown in some cases to inhibit enzymes 5-lipoxygenase and cyclooxygenase, which are involved in inflammation. Cichoric acid inhibits hyaluronidase and causes stimulation of phagocyte activity in vitro and in vivo (Bauer, 1999). It is also an antioxidant protecting against free radical-induced injury and has also been shown to selectively inhibit human immunodeficiency virus type 1 integrase. However, a more recent animal study indicated that purified cichoric acid and the polysaccharide component from E. purpurea failed to exert any immunostimulatory effects in rats. These authors provided in vivo evidence that only the lipophilic alkamides (dodecatetraenoic acid isobutylamides) are the effective, nonspecific immunomodulatory agent in Echinacea plant extract. Alkamides appear to be the most active agents in terms of stimulating effect on the alveolar macrophage function (stimulating effects on TNF-α and nitric oxide production) in normal rats.

Echinacoside

Echinacoside is a polyphenolic caffeoyl derivative with antioxidant activity. It seems that the anti-inflammatory activity of E. pallida root extract depends on the presence of echinacoside. Recent studies on antiinflammatory and cicatrizing activity of Italian-grown E. pallida root extract extracted by ethanol (1:10 w/v) proved that rats treated with echinacoside or dried E. pallida extract showed significantly higher antiinflammatory and wound-healing responses than did the control or E. purpurea group. Hu and Kitts (2000) found that the methanolic extract of E. pallida root exhibited greater antioxidant activity than extracts of E. angustifolia or E. purpurea. Therefore, echinacoside could be used as the active marker of E. pallida species and its products.

Polysaccharides

Two polysaccharides (PS I, PS II) have been isolated in the aerial parts of E. purpurea (Bauer and Wagner, 1991), and Echinacea-derived polysaccharides are indeed active in certain immunological models (Barrett, 2003; Emmendorffer et al., 1999). Bodinet and Beuscher (1991) reported that the roots of E. purpurea contain arabinogalactans and arabinogalactan-containing glycoproteins that exert immunomodulating activity. They indicated that the glycoprotein-containing fractions of E. purpurea root extracts are able to induce the secretion of TNF-α, IL-1, and INF-α and -β Burger et al. (1997) also showed that the polysaccharide component of Echinacea has the effect of increasing in vitro production of TNF-α, IL-1, and IL-6 by macrophage.

More results for Echinacea polysaccharides are not from plant sources but rather from cell cultures of Echinacea. Polysaccharide components from plant sources were structurally different compared to those obtained from cell cultures. Echinacea preparations commonly contain pharmacologically insignificant amounts of polysaccharides. Therefore, more research should be undertaken if polysaccharides are to be used as an active marker for Echinacea products.

Standardization

Standardization has become a major trend in the herbal products industry as well as research organizations. The first step in conducting quality control of Echinacea products is to establish true botanical identity and safety of its raw plant material by comparison with authenticated reference plant material (ARPM), which aids in the identification of adulterants. It is expected that a “certificate of botanical identity” will eventually be required for all sales of Echinacea. For standardization of Echinacea cultivation, especially for determining optimum harvest time, practice-relevant results are needed, including botanical characteristics (macroscopic and microscopic), gross physical determinants of quality, and widely accepted quality criteria relating to chemical content. Strict quality controls are required for the Echinacea plant raw materials with regard to homogeneity and purity of the raw material, minimum content of effective components, and limit values for plant-protective agent residues and microbial contamination.

A number of quantitative standards for Echinacea roots already exist. The USP typically specifies maximum water content of 10%, total ash content of up to 7%, not more than 3% of foreign organic matter, not more than 4% of acid-soluble ash, and not more than 0.001% of heavy metals. The chemical identification of Echinacea roots has been intensively studied and could be performed by a specific procedure of the TLC test and HPLC analyses.

Numerous tests can be used to evaluate the quality and purity of end products in Echinacea. First, the physical characteristics of the extract, including appearance, pH, solubility, content of total solids, ash content, and in the case of dried extracts, particle size, may be examined. Next, appropriate quantities of desired ingredients contained in the extract may be analyzed. Chromatographic (TLC, HPLC, GC) and spectroscopic (UV, IR) analysis may be used for this (Bauer, 1999; Bauer and Remiger, 1989; Schieffer and Kohn, 2002; Wagner, 1996). Finally, the extract may be tested for impurities such as residual solvents, herbicides, pesticides, and microbial contamination (Center for Food Safety and Applied Nutrition, FDA, 1999; Roll, 2002).

Since the active ingredients in Echinacea are complex and not yet completely known, the quality of Echinacea extracts is assessed by a “fingerprint” chromatogram. The “fingerprint” chromatograms of alkamides and phenolic derivatives in the root extracts of E. angustifolia, E. pallida, and E. purpurea provide enough information to reach a reasonable conclusion about quality and could be used for comparative and relative quality assessment of Echinacea samples. A standard procedure of liquid chromatography for the analysis of total phenols and alkamides in the roots and their extracts can be found in the USP.

Some extracts are labeled and sold as standardized extracts. For example, echinacoside is the desired compound present in some Echinacea extracts (E. angustifolia or E. pallida). A capsule containing 250 mg of Echinacea extract standardized to 4% would contain 10 mg of echinacosides (Center for Food Safety and Applied Nutrition, FDA, 1999). As a standard Echinacea product, its label should indicate the related information to consumers. However, at present most Echinacea product labels give little information about which species of Echinacea was used and the amount of the active ingredient in the Echinacea remedy.

Since March 1999, the FDA has required that herbal products like Echinacea should provide labels identifying the species of the herb, the part of the plant used, and the concentration of the herb. ConsumerLab.com in the United States has published a review on testing Echinacea products. According to ConsumerLab.com, Echinacea product labels should meet the following requirements:

1. Provide all of the following information on labels (as required by the FDA):

a. The species of Echinacea (i.e., E. purpurea, E. angustifolia, or E. pallida)

b. The part of the plant used, such as root or aerial (aboveground or also referred to as the “herb”) portions μncluding stem, leaves, and flowers)

c. The form (whole herb or root, extract, or tincture)

d. The amount of Echinacea per pill or dose in grams (g) or milligrams (mg)

2. Products labeled as containing the roots of E. angustifolia and/or E. pallida are required to contain detectable levels of the specific marker compound echinacoside; products labeled as containing roots or herb of E. purpurea are required to contain detectable levels of cichoric, caftaric, and chlorogenic acids, but if they were E. purpurea-only products, they should not have more than trace levels of echinacoside.

However, even when the label indicates the chemical standard used, potency can still vary considerably. On the one hand, this is because the pharmacological activity of Echinacea may also involve the combined or synergistic actions of various compounds. On the other hand, as Gilroy et al. (2003) indicated, Echinacea samples labeled as “standardized” did not guarantee that the samples contained as much as was stated on the label. They found after an investigation of 59 commercial samples that actual contents matched contents listed on the label in only 52% of the samples. Of the 21 “standardized” preparations, 43% met the quality standard described on the label, and only four (7%) of the samples met the FDA’s labeling requirements. Clearly, a lot of scientific work aimed at the crucial task — quality control and standardization of Echinacea preparations — remains to be carried out.