nificant because it appears that allicin (generated by alliinase activity on alliin) has a significant role in
the pharmacological activity of this medicinal plant [15,36]. In contrast, the -glutamyl-S-alkylcysteines
and cycloallin are not altered during crushing of the tissue (Ref. 36 and references therein).
Allicin appears to play a major role in the beneficial antimicrobial activity of this medicinal plant. In
this respect, crushed garlic or juice expressed from garlic cloves has been shown to have potent antimi-
crobial activity against a variety of both gram-positive and gram-negative bacteria including Escherichia,
Salmonella,Staphylococcus,Streptococcus,Klebsiella,Proteus,Bacillus,Mycobacterium, and Clostrid-
ium[15,36]. There is also substantial evidence that allicin forms the basis for garlic’s effects in lowering
blood serum cholesterol and triglyceride levels [36]. Allicin has been shown to be an inhibitor of hy-
droxymethylglutaryl coenzyme A (HMG CoA) reductase, which catalyzes a key step in cholesterol
biosynthesis [15,36]. Clinical studies have suggested that allicin may lower blood serum triglyceride lev-
els by increasing rates of lipid catabolism (Ref. 36 and references therein). Although it is clear that garlic
can decrease blood pressure in both humans and animals, this is not due to allicin and the active chemi-
cal is currently unknown [21,36].
E. Echinacea
Although there are 11 species in the genus Echinacea, this term is typically used to describe a phy-
tomedicine produced from the aerial portion of Echinacea purpurea(“purple coneflower”), roots of Echi-
nacea pallida(“pale-purple coneflower”), roots of Echinacea angustifolia(“narrow-leaf coneflower”), or
a combination of these materials [18,21]. These plants are herbaceous perennials native to North Amer-
ica and were originally used in Native American herbal traditions for wound healing, infections, and rat-
tlesnake bite [12,31]. Use of this phytomedicine was subsequently introduced to Europe in the early
1900s, and current interest lies in its use for colds, flu-like infections and upper respiratory infections
[15,21]. The best studied and effective versions of this phytomedicine involve the expressed juice of the
aerial portion of E.purpureaand an alcohol extract of E.angustifoliaroots [21]. A number of studies sug-
gest that Echinacea-based phytomedicines may be beneficial in reducing the symptoms and perhaps du-
ration of upper respiratory infections (Refs. 15 and 21 and references therein). Pharmacological studies
(350 to date) have provided strong evidence for effects of Echinaceaextracts in modulating immune
system capacity including stimulation of the phagocytic activity of human lymphocytes, stimulation of fi-
broblasts for new tissue production, increased respiration, and elevated mobility of leukocytes [15,21,38].
Extracts of Echinaceaalso appear to inhibit both tissue and bacterial hyaluronidase, and this action is
thought to aid in localization of infection, preventing its spread to other regions of the body (Refs. 21 and
38 and references therein).
The immunostimulatory activity of Echinaceapreparations appears to result from the combined ef-
fects of a complex array of constituents (Figure 5) including a series of alkylamides as isobutylamides,
caffeic acid derivatives (chicoric acid, cynarin, echinacoside—not present in E. purpurea), a series of
polyalkynes (polyacetylenes), a series of polyalkenes, and high-molecular-weight (high-MW) polysac-
charides including heteroxylans (approximate MW 35,000) and arabinorhamnogalactans (approximate
MW 45,000) [12,15,21,38]. Pharmacological studies have shown effects of the alkamides, polyalkynes,
and caffeic acid derivatives in stimulating white blood cell phagocytosis (Refs. 18 and 21 and references
therein). The high-molecular-weight polysaccharide components also appear active in stimulating phago-
cytosis as well as promoting production of interferon [21]. Furthermore, through their inhibitory effect on
5-lipoxygenase, the alkylamide constituents may provide anti-inflammatory activity. Although details of
the biosynthetic pathways of these active constituents are unknown, the hydrocarbon portions of alky-
lamides and polyalkynes most likely represent desaturation products of long-chain fatty acids (e.g., oleic
acid) shortened through -oxidation (see Ref. 19 for a discussion of these processes). Chicoric acid, cy-
narin, and echinacoside most likely arise as conjugated products of caffeic acid generated through the
shikimic acid pathway. Although factors that influence the biosynthetic pathways of these chemicals are
unknown, it has been shown that the phytomedicinal content of Echinaceacan be affected by environ-
mental conditions (soil nitrogen and potassium) and the developmental state of the plant [39].
Currently, most Echinaceaphytomedicines containing E. angustifoliaare standardized according to
their echinacoside content because the caffeic acid derivative is a marker chemical unique to Echinacea
root. However, such standardization does not consider the complex chemical interactions and possible
synergistic effects necessary for the beneficial affects of this phytomedicinal on humans.
492 BRISKIN