Echinacea

Echinacea /ˌɛkɨˈneɪʃⁱə/^[1] is a genus, or group of herbaceous flowering plants in the daisy family, Asteraceae. The echinacea genus has nine species, which are commonly called coneflowers. They are endemic to eastern and central North America, where they are found growing in moist to dry prairies and open wooded areas. They have large, showy heads of composite flowers, blooming from early to late summer. The generic name is derived from the Greek word ἐχῖνος (echino), meaning "sea urchin," due to the spiny central disk. These flowering plants and their parts have different purposes. Some species are cultivated in gardens for their showy flowers, and some are traditionally used to treat and prevent common cold, flu, and other infections.^[2] Echinacea purpurea is commonly used medicinally.^[2] Two of the nine species, E. tennesseensis and E. laevigata, are listed in the United States as endangered species.^[3]

Species

The species of Echinacea are

• Echinacea angustifolia – Narrow-leaf Coneflower
• Echinacea atrorubens – Topeka Purple Coneflower
• Echinacea laevigata – Smooth Coneflower, Smooth Purple Coneflower
• Echinacea pallida – Pale Purple Coneflower
• Echinacea paradoxa – Yellow Coneflower, Bush's Purple Coneflower
• Echinacea purpurea – Purple Coneflower, Eastern Purple Coneflower
• Echinacea sanguinea – Sanguine purple Coneflower
• Echinacea simulata – Wavyleaf Purple Coneflower
• Echinacea tennesseensis – Tennessee Coneflower

Researchers at the Agricultural Research Service are using DNA analysis to help determine the number of Echinacea species. The DNA analysis allows researchers to reveal clear distinctions among species based on chemical differences in root metabolites. The research concluded that of the 40 genetically diverse populations of Echinacea studied, there were nine distinct species.

Description

Echinacea species are herbaceous, drought-tolerant perennial plants growing up to (140 cm or possibly 4 feet (grow 3-feet to over 4-feet in my front yard in the Shenandoah Valley, Va.^[4]), (reference needed) in height. They grow from taproots, except E. purpurea, which grows from a short caudex with fibrous roots. They have erect stems that in most species are unbranched. Both the basal and cauline leaves are arranged alternately. The leaves are normally hairy with a rough texture, having uniseriate trichomes (1-4 rings of cells) but sometimes they lack hairs. The basal leaves and the lower stem leaves have petioles, and as the leaves progress up the stem the petioles often decrease in length. The leaf blades in different species may have one, three or five nerves. Some species have linear to lanceolate shaped leaves, and others have elliptic- to ovate-shaped leaves; often the leaves decrease in size as they progress up the stems. Leaf bases gradually increase in width away from the petioles or the bases are rounded to heart shaped. Most species have leaf margins that are entire, but sometimes they are dentate or serrate. The flowers are collected together into single rounded heads that terminate long peduncles. The inflorescences have crateriform to hemispheric shaped involucres which are 12–40 mm wide. The phyllaries, or bracts below the flower head, are persistent and number 15–50. The phyllaries are produced in a 2–4 series. The receptacles are hemispheric to conic in shape. The paleae (chaffs on the receptacles of many Asteraceae) have orange to reddish purple ends, and are longer than the disc corollas. The paleae bases partially surrounding the cypselae, and are keeled with the apices abruptly constricted to awn-like tips. The ray florets number 8–21 and the corollas are dark purple to pale pink, white, or yellow. The tubes of the corolla are hairless or sparsely hairy, and the laminae are spreading, reflexed, or drooping in habit and linear to elliptic or obovate in shape. The abaxial faces of the laminae are glabrous or moderately hairy. The flower heads have typically 200-300 fertile, bisexual disc florets but some have more. The corollas are pinkish, greenish, reddish-purple or yellow and have tubes shorter than the throats. The pollen is normally yellow in most species, but usually white in E. pallida. The three or four-angled fruits (cypselae), are tan or bicolored with a dark brown band distally. The pappi is persistent and variously crown-shaped with 0 to 4 or more prominent teeth. x = 11.^[5]

Like all Asteraceae, the flowering structure is a composite inflorescence, with rose-colored (rarely yellow or white) florets arranged in a prominent, somewhat cone-shaped head – "cone-shaped" because the petals of the outer ray florets tend to point downward (are reflexed) once the flower head opens, thus forming a cone. Plants are generally long lived, with distinctive flowers. The common name "cone flower" comes from the characteristic center "cone" at the center of the flower. The generic name Echinacea is rooted in the Greek word ἐχῖνος (echinos), meaning sea urchin,^[6] it references the spiky appearance and feel of the flower heads.

History

Echinacea angustifolia was widely used by the North American Plains Indians for its general medicinal qualities.^[7] Echinacea was one of the basic antimicrobial herbs of eclectic medicine from the mid 19th century through the early 20th century, and its use was documented for snakebite, anthrax, and for relief of pain. In the 1930s echinacea became popular in both Europe and America as an herbal medicine. According to Wallace Sampson, MD, its modern day use as a treatment for the common cold began when a Swiss herbal supplement maker was "erroneously told" that echinacea was used for cold prevention by Native American tribes who lived in the area of South Dakota.^[8] Although Native American tribes didn't use echinacea to prevent the common cold, some Plains tribes did use echinacea to treat some of the symptoms that could be caused by the common cold: The Kiowa used it for coughs and sore throats, the Cheyenne for sore throats, the Pawnee for headaches, and many tribes including the Lakotah used it as an analgesic.^[9]

Native Americans learned of E. angustifolia by observing elk seeking out the plants and consuming them when sick or wounded, and identified those plants as elk root.^[10]

Research and marketing

Echinacea products that are marketed and studied in clinical trials vary widely in composition. They contain different species (E. purpurea, E. angustifolia, E. pallida), different plant segments (roots, flowers, extracts), different preparations (extracts and expressed juice), and different chemical compositions.^[11][12] Well-controlled clinical trials are limited, and many of them are low in quality.^{[13][14][15][16]} There are multiple scientific reviews and meta-analyses published to evaluate the peer reviewed literature on the supposed immunological effects of echinacea. However, the variability of the echinacea products used in the studies limited the comparison of effects and safety among the studies. The results are mixed, inconclusive and have not been approved for any health benefit or anti-disease activity.^[13][17]

Common cold

The evidence that showed the effectiveness of echinacea products in treating or preventing the common cold is weak.^[16][17][18]

Cancer

According to Cancer Research UK: "There is no scientific evidence to show that echinacea can help treat, prevent or cure cancer in any way. Some therapists have claimed that echinacea can help relieve side effects from cancer treatments such as chemotherapy and radiotherapy, but this has not been proved either."^[19]

Side effects

When taken by mouth, Echinacea does not usually cause side effects.^[2] One of the most extensive and systematic studies to review the safety of Echinacea products concluded that overall, "adverse events are rare, mild and reversible," with the most common symptoms being "gastrointestinal and skin-related."^[20] Such side effects include nausea, abdominal pain, diarrhea, itch, and rash. Echinacea has also been linked to rare allergic reactions, including asthma, shortness of breath, and one case of anaphylaxis.^[20][21][22] Muscle and joint pain has been associated with Echinacea, but it may have been caused by cold or flu symptoms for which the Echinacea products were administered.^[20] There are isolated case reports of rare and idiosyncratic reactions including thrombocytopenic purpura, leucopenia, hepatitis, renal failure, and atrial fibrillation, although it is not clear that these were due to Echinacea itself.^[23]

There are concerns that by stimulating immune function, Echinacea could potentially exacerbate autoimmune disease and/or decrease the effectiveness of immunosuppressive drugs, but this warning is based on theoretical considerations rather than human data.^[23] There have been no case reports of any drug interactions with Echinacea and "the currently available evidence suggests that echinacea is unlikely to pose serious health threats for patients combining it with conventional drugs."^[24]

Safety

As a matter of manufacturing safety, one investigation by an independent consumer testing laboratory found that five of eleven selected retail Echinacea products failed quality testing. Four of the failing products contained levels of phenols below the potency level stated on the labels. One failing product was contaminated with lead.^[25]

Children under 12 years old

Research studies have shown that Echinacea purpurea juice extract is safe in children 2–11 years when used up to 10 days. 7% experienced a rash after taking echinacea, which suggested an allergic reaction. There is concern that the allergic reaction could be more severe in children.^[17][26] The European Herbal Medicinal Products Committee (HMPC) and the UK Herbal Medicines Advisory Committee (HMAC) recommended against the use of echinacea containing products in children under the age of 12. Manufacturers re-labelled all oral echinacea products that had product licenses for children with a warning that they should not be given to children under 12 as a precautionary measure.^[27]

Pregnancy

Although research has not found increased risk of birth defects associated with use of echinacea during the first trimester, it is recommended that pregnant women should avoid echinacea containing products until stronger safety supporting evidence becomes available.^[17]

Lactation

It is recommended that women breastfeeding should avoid echinacea containing products due to insufficient safety information available.^[17]

General precaution

The U.S. Food and Drug Administration (FDA) recommends consumers to inform their healthcare providers about supplements they are taking as some supplements may not be risk free under certain circumstances or may interact with prescription and over-the-counter medicines.^[28]

Mechanism

Like most unrefined drugs from plant or animal origin, the constituent base for echinacea is complex, consisting of a wide variety of chemicals of variable effect and potency. Some chemicals may be directly antimicrobial, while others may work at stimulating or modulating different parts of the immune system. All species have chemical compounds called phenols, which are common to many other plants. Phenyl propanoid constituents such as cichoric acid and caftaric acid are present in E. purpurea, other phenols include echinacoside, a caffeic acid glycoside, which is found in greater levels within E. angustifolia and E. pallida roots than in other species. Many caffeic acid derivatives are ubiquitous plants constituents with little specific effects other than anti-oxidant activity. Although the phenolic constituents are poorly absorbed and have no dose–response relationship in clinical settings, their relative proportions can serve as markers for species identification and quality control of herbal remedies. Other chemical constituents that may be important in echinacea health effects include alkylamides and polysaccharides.

The immunomodulatory effects of echinacea preparations are likely caused by fat-soluble alkylamides (alkamides), which occur mostly in E. angustifolia and E. purpurea but not in E. pallida.^[29] Alkylamides bind particularly to human CB2 and to a much lesser degree to CB1 cannabinoid receptors; as a result they are implicated in a variety of modulatory functions, including immune suppression, induction of apoptosis, cell migration and inhibition of tumor necrosis factor.^[30] These alkylamides, namely, dodeca-2E,4E,8Z,10Z-tetraenoic acid isobutylamide and dodeca-2E,4E-dienoic acid isobutylamide, have similar potency to that of THC at the CB2 receptor, with THC being around 1.5 times stronger (~40 nm vs ~60 nm affinities). However, potency is dramatically less than that of THC at the psychoactive CB1 receptor (~40 nm vs ~ >1500 nm affinities).^[31]

As with any herbal preparation, individual doses may vary significantly in active chemical composition. In addition to poor process control which may affect inter- and intra-batch homogeneity, species, plant part, extraction method, and contamination or adulteration with other products all lead to variability between products.^[16][25]

Other uses

Some species of echinacea, notably E. purpurea, E. angustifolia, and E. pallida, are grown as ornamental plants in gardens.^[32] Many cultivars exist, and many of them are asexually propagated to keep them true to type.

They tolerate a wide variety of conditions, maintain attractive foliage throughout the season, and multiply rapidly. Appropriate species are used in prairie restorations. Echinacea plants also reseed in the fall. New flowers will grow where seeds have fallen from the prior year.^[33]

Echinacea extracts inhibited growth of three species of trypanosomatids: Leishmania donovani, Leishmania major, and Trypanosoma brucei.^[34]

See also

• List of ineffective cancer treatments

References

Further reading

• Mowrey, Daniel (1998). Echinacea. McGraw-Hill Professional. ISBN 978-0-87983-610-8. 

External links

Wikimedia Commons has media related to Echinacea.

Wikispecies has information related to: Echinacea

• Echinacea at DMOZ
• Website devoted to Echinacea