cal contributes to the antidepressant action of this plant [15,24]. In human clinical studies, the hyperforin
content in St. John’s wort extracts correlated with the level of antidepressant action [27]. This chemical
appears to block synaptic reuptake of serotonin, dopamine, and norepinephrine [28]. Blocking reuptake
of neurotransmitters elevates their synaptic concentration. This is another mechanism by which synthetic
antidepressants may operate [15,24]. Although hyperforin also has antibacterial activity [23], it is uncer-
tain whether or not this compound is effective in defense functions for the plant.
C. Ginseng
The name “ginseng” can often lead to some confusion because of its use for different plants with differ-
ent phytochemical constituents. True ginsengs are plants in the genus Panax, of which Asian ginseng
(Panax ginseng) and American ginseng (Panax quinquefolium) have received the most interest for phy-
tomedicinal use [12,15,29,30]. These plants are low-growing perennial shade plants that generate a bulky
storage root that is used medicinally. On the other hand, Eleuthrococcus senticosis, a completely differ-
ent plant not even in the genus Panax, is sometimes referred to as Russian or Siberian “ginseng.” Roots
from this shrubby tree, native to regions of Siberia and northern China, were studied in the former Soviet
Union as a substitute for Asian ginseng [12,15].
Interest in the use of ginseng and Eleuthrococcusis due to their purported “adaptogen” or “tonic” ac-
tivities. Such activities are thought to increase the body’s capacity to tolerate external stresses, leading to
increased physical or mental performance [15]. For Asian ginseng, this adaptogenic activity was noted
over 3500 years ago in traditional Chinese medicine, and for American ginseng, use as an adaptogen-type
tonic was familiar to many Native American tribes [31,32]. Whereas an extensive literature documenting
adaptogenic effects in laboratory animal systems exists, results of human clinical studies have tended to
be more conflicting and variable [13,15,21,29,30]. However, there is evidence that extracts of ginseng and
Eleuthrococcuscan have an immunostimulatory effect in humans, and this may contribute to the adapto-
gen or tonic effects of these plants [15,18,21].
The major secondary products present in ginseng roots are an array of triterpene saponins, collec-
tively called ginsenosides [13,19,29,33]. The ginsenosides are glycosylated derivatives of two major
aglycones, panaxadiol and panaxatriol [12,19,33]. At present, 30 ginsenosides have been identified, of
which the ginsenosides Rb1, Rb2, Rc, Rd, Re, Rf, Rg1, and Rg2 shown in Figure 3 are considered to be
the most relevant for pharmacological activity [12,19,21,29,33]. Different ginseng species have different
proportions of ginsenosides in root tissue, and this may be related to reported differences in the pharma-
cological properties of these plant materials [20,21,30,33]. Moreover, within a particular ginseng species,
levels of particular ginsenosides can be affected by environmental factors such as soil mineral nutrient
supply [34]. From laboratory studies, it has been suggested that the pharmacological target sites for these
compounds may involve the hypothalmic-pituitary-adrenal axis because of the observed effects on serum
levels of adrenocorticotropic hormone (ACTH) and corticosterone [13]. However, it should also be noted
that the overall effects of the ginsenosides can be quite complex because of their potential for multiple ac-
tions even within a single tissue [20,30].
PHYTOMEDICINAL CHEMICAL PRODUCTION BY PLANTS 489
Figure 2 Hypericin, pseudohypericin, and hyperforin from St. John’s wort (Hypericum perforatum).
(Adapted from Ref. 12.)