CHAPTER 6

CHEMICAL COMPOUNDS OF ADAPTOGENIC SPECIES

Introduction

Allostasis and homeostasis work in concert to meet the normal, daily needs of the organism.

When an organism is exposed to chronic or severe stress, a myriad of chemical messengers interacts to

maintain a dynamic resilience. These neurotransmitters and hormones can both suppress and enhance

immune functions acting as “on” and “off” switches (Panossian et al., 1999a). Chronic or severe stressors

can overwhelm the stress response system causing dysregulation of the mediators, which has been linked to

causation of many chronic pathologies. Adaptogens can increase resistance to a wide range of stressors,

normalizing either excessive or deficient pathological conditions with minimal disturbance to normal

physiological function. These medicinal plants envision a a novel mode of action for resisting pathogenic

attack and treating stress-related conditions.

Tens of thousands of secondary plant compounds have been isolated and identified in over 20-30% of

higher plants (Wink, 1999). Plants synthesize thousands of primary and secondary plant compounds that

have a dizzying array of chemical structures. These compounds are synthesized using a relatively small

number of conserved enzymatic mechanisms. This suggests that the number of metabolites exceeds the

number of genes involved in their biosynthesis (Schwab, 2003). Most secondary metabolites are derived

from just three main pathways: acetate C2-unit (polyketides), shikimate C9-unit (phenylpropanoids), and

mevalonate C5-unit (isoprenes) (Verpoorte, 1998).

For adaptogens, finding which compounds produce adaptogenic effects has been a challenging task

because of the multitude of targets and activities of these plants. Adding to this challenge is that, compared

to synthetic drugs that are usually concentrated, single substances, plant extracts have a complex

synergistic action that has made the scientific investigation of adaptogen remedies a precipitous and

tortuous affair. Plant compounds having adaptogenic properties fall into three diverse classes of

compounds ubiquitous to the Plant Kingdom; triterpenes, phenylpropanes, and oxylipins (Panossian, 2003).

These plant constituents originate from dissimilar biosynthetic pathways, differ markedly in their chemical

structure, and involved related classes of compounds (see Table 4).

Table 4. Three classes of compounds associated with adaptogens and the biosynthetic pathways in plants.

Triterpenes (mevalonate pathway)

Triterpenoid saponins dammarane triterpene saponins, cucurbitacins

Phytosterols beta-sitosterol

Phytoecdysteroids 20-ecdysone, turkesterone

Phenylpropanes (shikimate pathway)

Flavonoids glucopyranosides, prenylated flavonoids, flavan glycosides

Lignans schizandrin, sesamin, syringaresinol

Oxylipins (acetate pathway)

hydroxylated fatty acids octadecadienoic acid

Triterpenes also include phytosterols and phytoecdysteroids, both of which are thought to have

adaptogenic roles in mammals and in humans (Slama, 1993; Bouic, 2001; Oberdorster et al., 2001). Most

adaptogen plant species contain triterpenoid saponins, in particular, Panax ginseng, Eleutherococcus

senticosus and Aralia mandshurica, genera of the Araliaceae family.

Phytosterols are synthesized from triterpenes and are ubiquitous among angiosperm species. While

the role of phytosterols in adaptogenic activity has not been emphasized in the phytotherapy literature, their

importance to nutrition is well recognized. A few recent research efforts have reported beneficial effects of

phytosterols to both normal and compromised immune systems (Bouic, 2002; Breytenbach et al., 2001).

Phytosterols are considered primary compounds and are only now becoming appreciated for having

secondary roles in plant health and defense (Lindsey et al., 2003). This group of compounds is particularly

represented by the adaptogen, Bryonia alba (Cucurbitaceae) containing eight types of sterols (Ukiya et al.,

2002).

Triterpenes are also the precursor compound for steroidal constituents that mimic insect steroids as a

defense mechanism, called phytoecdysteroids. These compounds have also not been emphasized in

phytotherapy, yet are in common use by athletes and weight lifters for the anabolic effects they produce

(Bucci, 2000). Sampling angiosperms for phytoecdysteroids have not included adaptogenic species with

the exception of the Cardueae tribe of the Asteraceae. These species are represented by Leuzea

carthamoides, Rhaponticum uniflorum, and Serratula coronata.

Phenylpropanoids comprise a large group of compounds, including flavonoids, isoflavonoids,

anthocyanins, betaines, and lignans. Flavonoids and lignans have been the main focus of adaptogenic

activity and often have attached sugars or terpene chains, being termed glucopyranosides and prenylated

flavonoids. These attached structures are likely important for bioactivity (Tziveleka et al., 2002; Galichet

and Gruissem, 2003). Phenylpropane compounds particularly emphasized in Rhodiola rosea

(Crassulaceae) are salidroside, rosavin, rosin, rosarin, and tyrosol, and the lignan, schizandrin, in

Schizandra chinensis (Magnoliaceae). The flavan glycosides, dichotosin, dichotosinin and diffutin are

characteristic of Hoppea dichotoma (Gentianaceae) and the tetraoxygenated xanthones in Hoppea fastigiata

(Peres et al., 2000).

Oxylipins are the final group of plant compounds Panossian (2003) suggests as having adaptogenic

activity. These are fatty acids that have been oxidized and display prostaglandin-like activity such as the

unsaturated polyhydroxylated fatty acids found in Bryonia alba (Cucurbitaceae) (Panossian et al., 1983;

1997; 1999). The root of this vine has been used for centuries in Armenia and in surrounding countries and

was known as the “drug for all diseases” with references to it by Hippocrates, Galen, Avicenna and other

ancient Mesopotamia figures (Panossian et al., 1997). Today it is called “loshtak” in Armenia and used to

treat a wide variety of illnesses as a registered drug in Armenia (Panossian et al., 1997). Both phytosterols

and oxylipins have traditionally been considered primary plant compounds but recently have been shown to

play secondary roles in plant signaling and defense (Blée, 1998; Tapiero et al., 2003). Thus, the separation

between primary and secondary compounds is blurred in the discussion of bioactivity of adaptogens.

Though many of these constituents are widespread among angiosperm taxa, some species, such as

Tinospora cordifolia, contain triterpenes (cordifolisides—Williamson, 2002), phytosterols (Li et al., 2003),

and phytoecdysteroids (Garcia et al., 1989; Song et al., 1991). A closer look at these compounds will

reveal their roles in plants and their activity in humans (see Table 5).

Table 5. Plant compounds believed to be responsible for adaptogenic effects and the plants containing

them.

Chemical compound Common name Latin name Citation

Triterpenoids

20-hydroxyecdysone maral root Leuzea carthamoides Pis et al., 1994

araloside spikenard Aralia mandshurica Baranov, 1982

astragaloside huang qi Astragalus membranaceus Bone, 1996

bacoside brahmi Bacopa monniera Vohora et al., 2000

cucurbitacin bryonia Bryonia alba Panossian et al., 1999

eleutheroside Siberian ginseng Eleutherococcus senticosus Baranov, 1982

ginsenoside ginseng Panax ginseng Dong et al., 2003

gypenoside jio gu lan Gynostemma pentaphyllum Tanner et al., 1999

tanshenoside bellflower Codonopsis pilosula Yuda et al., 1990

tinosporoside guruchi Tinospora cordifolia Williamson, 2002

turkesterone Swiss centaury Rhaponticum uniflorum Syrov et al., 1997

withanolide ashwagandha Withania somnifera Evans, 2002

Phenylpropanoids

dichotosin hoppea Hoppea dichotoma Wagner et al., 1994

flavonoids holy basil Ocimum sanctum Wagner et al., 1994

rosavin, rosin, rosarin rose root Rhodiola rosea Brown et al., 2002

schizandrin wu wei Schizandra chinensis Bartlova et al., 2002

Oxylipins

hydroxylated fatty acids bryonia Bryonia alba Panossian et al., 1983

hydroxylated fatty acids licorice Glycyrrhiza glabra Panossian, 2003

Terpenoids

Isoprenoid compounds (also called terpenes) are made from isopentenyl pyrophosphate (IPP) or

isoprene units. The more than 23,000 isoprenoid compounds identified so far in nature have many essential

biological functions in prokaryotes and eukaryotes (Liang et al., 2002). The enzymes that catalyze related

steps in isoprenoid biosynthesis have evolved from the likely common ancestor, prokaryotes that synthesize

hopanoids (Bohlman, 1998). Isoprene compounds are found in eubacteria, viruses, unicellular algae,

plants, fungi, and yeasts (Edwards and Ericsson, 1999). Mammals and humans can also employ isoprene

units to make triterpene compounds such as cholesterol, steroidal hormones, ubiquinone, heme, and bile

acids. Many isoprenoids have significant biological functions in nature (Liang, et al., 2002). The classes

of terpene compounds found in plants are monoterpenes, diterpenes, sesquiterpenes, triterpenes,

tetraterpenes, and polyterpenes. Plant terpenoid metabolites have been recognized as signaling molecules

in many interactions of plants with pathogens, beneficial organisms, competitors and herbivores (Bohlman

et al., 1998). Many of these compounds induce defenses against various pathogens. Others act as

pollinator attractants, insect pheromones, and hormone analogues sometimes causing endocrine disruption.

Triterpene Saponins

Though all terpenoid compounds have bioactivity in mammals and humans, it is the triterpenes that are

most important to the adaptogenic effect. Triterpenes belong to a very large group of compounds arranged

in a four or five ring configuration of 30 carbons with several oxygens attached. Triterpenes are assembled

from a C5 isoprene unit through the cytosolic mevalonate pathway to make a C30 compound and are

steroidal in nature. Cholesterol is considered a triterpene, for example. Phytosterols and phytoecdysteroids

are also triterpenes. The triterpenes are subdivided into some 20 groups, depending on their particular

structures. Triterpene compounds most often found in adaptogenic plants belong to the dammarane and

ursane/oleanane classes.

Most triterpenoid compounds in adaptogenic plants are found as saponin glycosides. This simply

refers to the attachment of various sugar molecules to the triterpene unit. These sugars are usually cleaved

off in the gut by bacteria, allowing the aglycone (triterpene) to be absorbed. Saponin glycosides have the

characteristic of reducing surface tension of water with consequent frothing. They also will strip the lipids

from your mouth if you chew on a leaf high in these compounds, acting much like soap. Many of the

triterpene saponins are designated as such by the suffix ending –side, such as ginsenoside, astragaloside,

and bacoside, named for the plant genera they were first discovered in. Some, such as the ginsenosides and

eleutherosides are designated Rx where the suffix x = a, a1, b2, c, d, e, f, g1, h1, F1, F2, F3, indicative of

the relative position of the saponin spots from top to bottom of a thin layer chromatogram.

The common occurrence of triterpenoid saponins in adaptogenic plant remedies is intriguing because

these compounds have a variety of effects that potentially could ameliorate stress pathologies. Two of the

most ubiquitous triterpenoid saponins in all plants, including adaptogens are ursolic and oleanolic acid.

Ursolic acid and its derivatives have diversified phylogenetic origins and taxonomic positions. It has been

isolated from the protective wax-like coatings of apples, pears, cranberries, prunes, and other fruits.

Ursolic acid rarely occurs without its isomer oleanolic acid. They may occur in their free acid form or as

aglycones for triterpenoid saponins that are comprised of a triterpenoid aglycone linked to one or more

sugar moieties. Ursolic and oleanolic acids are similar in pharmacological activity (Liu, 1995).

Pharmacological effects ascribed to ursolic and oleanic acids are: antitumor, antiinflammatory (Sautebin,

2000; Yamashita et al., 2002) hepatoprotective, antiulcer, antimicrobial, anti-hyperlipidemic, and antiviral.

The anticancer property of ursolic acid has been linked to a strong inhibition of both DNA polymerase and

DNA topoisomerase via competitive binding (Mizushina et al., 2003). Many other plant triterpenes exhibit

immunomodulatory and antitumor effects (Bernhardt et al., 2001), have been shown to modulate steroid

receptors (Zierau et al., 2002), act as both ligand and as suppressor of steroid hormone-mediated gene

expression, and interfere with cell messengers (Harrewijn et al., 2001).

Steroidal saponins share many structural features with steroid hormones, including the ability to insert

into cell membranes (Attele et al., 1999) and modify the composition, influence membrane fluidity (Lee et

al., 2003), and potentially affect signaling by many ligands and cofactors (Lindsey et al., 2003). For

example, it has been recently shown that ginsenoside Rg2 may have the ability to regulate serotonin

receptors (Choi et al., 2003). A recent review of the neuroactive properties of steroids suggest how some

adaptogenic compounds may relieve depression, anxiety, insomnia, and enhance cognition and memory

(Rupprecht, 2003). It is quite possible that triterpenoid compounds may modulate stress adaptation through

a nongenomic mechanism rather than through the traditional model of steroid action. That is, steroid

receptors can also be regulated through interaction with cell membrane receptors and secondary messengers

and do not always require direct binding of ligand to receptor (Wehling, 1995). Some researchers

hypothesize that since many plant compounds have similar structures as glucocorticoids (Panossian et al.,

1999) they may affect steroid receptors and endocrine response even without binding directly.

Yet another triterpenoid class of compounds having adaptogenic activity are the cucurbitacins

(Nersesyan and Collins, 2002). Cucurbitacins are predominantly found in the melon family

(Cucurbitaceae), but are also found in 20 other plant families and some fungi (Jian-Wen et al., 2002). Two

adaptogenic species of the Cucurbitaceae are Bryonia alba and Gynostemma pentaphyllum (Panossian et

al., 1997; Tanner et al., 1999). Both cucurbitacins and withanolides (a triterpene saponin found in Withania

somnifera), have an antagonistic action on insect steroid hormones at the level of the ecdysteroid receptor

(Dinan et al., 1997). Cucurbitacins have been found to inhibit the biosynthesis of DNA, RNA and protein

in cancerous cells (Witkowski et al., 1984). Cucurbitacins have also been found to diminish cortisol

binding in vitro (Witkowski and Konopa, 1981).

The ginsenosides of Panax ginseng (Araliaceae) are thought to be primarily responsible for its

adaptogenic activities. The amount of these glycosides in ginseng root varies between 0.5 and 4% (Leung

and Foster 1996). This group of steroidal saponin glycosides has a steroid skeleton with a modified side

chain at C-20 (Attele et al., 1999). The lipophilic solubility of triterpene glycosides enhances their ability

to transverse cell membranes by simple diffusion which may cause permeability of the cell membrane,

allowing exchange of ions (Melzig et al., 2001) and potentially according them the ability bind to

intracellular receptors modulating gene transcription or translation (Lee et al., 2003; Attele et al., 1999;

Yuan et al., 1998). The lipophilic properties of ginsenosides favor binding to intracellular steroid hormone

receptors, such as glucocorticoid (Chung et al., 1998) progesterone, androgen, mineralcorticoid, and

estrogen receptors (Attele et al., 1999; Lee et al., 2003).

Another hypothesis proposes that the ginsenosides and other triterpenoid saponins augment the

biosynthesis of adrenal steroid hormones by way of the pituitary (Nocerino et al., 2000; Rahman and

Sarkar, 2002). The different bioactivities of the variety of ginsenosides co-occurring in Panax ginseng

present a complex challenge. But, it is likely that the overall adaptogenic property of Panax is due to the

mixture of triterpenoid saponins, and possibly a larger mix of compounds.

Triterpenoid compounds continue to be a focus of adaptogenic plant research. Table 5 lists some

adaptogens high in triterpenoid compounds. The phytochemistry of triterpenes is not exhausted here,

however, I have tried to describe some of the important links between triterpene compounds in adaptogenic

plants and their bioactivity. I will discuss the possible mechanism of actions of these compounds further in

Chapter 7.

Phytosterols

Both triterpenes and plant sterols (phytosterols) are tetracyclic sterols with a 4-ring steroid skeleton.

Like triterpenes, phytosterols are synthesized in the mevalonate pathway. The distinction between

triterpenes and plant sterols (phytosterols) is that triterpene saponins have a 30-carbon skeleton and sterols

have a 29-27-carbon skeleton (Robbers et al., 1996). Phytosterols often occur free or as glycosides or

esters with fatty acids and make up 60-80% of the sterol mixture in almost all plants and plant tissues, with

a mixture of 6-12 other derivatives making up the remainder (Chappell, 2002). Sterols are always present

in plants as a mixture. Beta-sitosterol, along with campesterol and stigmasterol, are the most common

sterols found in plants (Lindsey et al., 2003). They serve primarily as structural components of cell and

organelle membranes, regulating the fluidity and permeability of these membranes. Seeds also contain

phytosterols with as many as 61 different sterols found in maize seedlings.

Phytosterols have also been shown to act as hormonal growth regulators in plants. Phytosterols have

been shown to be involved in membrane-associated metabolic processes and are necessary for proper

vesicle trafficking in the cell, such as signaling, regulating of transcription and translation, cellular

differentiation and cell proliferation (Piironen et al., 2000; Lindsey et al., 2003).

Humans and plants use a similar biosynthetic pathway to make sterols and thus, these have a similar

basic structure. In mammals, the steroids are derived from lanosterol, while in plants the precursor is

cycloartenol. Animal cholesterol is very similar to plant !-sitosterol. In fact, soy (Glycine max)

phytosterols are used in the semi-synthesis of pharmaceutical steroids. However, phytosterols differ in

structure from cholesterol in their side chain composition that can make them more hydrophilic.

Dietary plant sterols are extremely bioactive in humans. They are well known for their ability to

inhibit absorption of cholesterol and lowering of serum cholesterol by two main processes, preferential

uptake in the gut for plant sterols versus cholesterol, and improving elimination of cholesterol (Miettinen,

2001; Moreau et al., 2002). Other medicinal effects of plant sterols are not as well understood but it has

been reported that beta-sitosterol has anticancer, antiulcer, antidiabetic, antiinflammatory and antipyretic

properties (Gupta et al., 1996; Bouic, 2002). Phytosterols are also known to be anti-venom by producing a

conjugated derivative devoid of hemolytic activity (Mors et al., 2000). Many pentacyclic triterpenes are

also known to have anti-snake venom activity, most likely because of their similar chemical structure

(Mors et al., 2000). It has been suggested that in low doses, plant compounds such as phytosterols may be

involved in regulation of gene expression (Orzechowski et al., 2002). Some research activities report

possible synergistic activities between phytosterols. For example, the sedative activity of Perilla

fructescens is suggested to be a combined effect of both secondary and primary compounds (perillaldehyde

and stigmasterol).

Beta-sitosterol has also been found to be anthelmintic, antimutagenic, anticancerous, antiulcer,

antidiabetic, antiinflammatory, antipyretic, and analgesic. However, the antimutagenic activity of beta-

sitosterol (using a carcinogen in a test) was found to be 0.5 mg/kg for a mouse. This dose translated for

humans would provide 35 grams, and therefore not very realistic. It has been suggested that beta-sitosterol

can enhance secretion of IL-2 and gamma interferon helping to promote natural killer cells, and prime TH1

helper cells to steer the focus away from the TH2 helper cells (Bouic, 2001). The lipophilicity of

triterpenoids and phytosterols lends these compounds to easy diffusion through lipid membranes. It is

possible that these compounds can prime the tissues, increasing sensitivity to other mediators and cofactors.

Humans use cholesterol for cell multiplication. Cancer cells have a higher demand for cholesterol and

they either get it from the host or may synthesize it themselves. Researchers fed some plant sterols to

cancer cells and found that beta-sitosterol and campesterol accounted for 70% to 40% of the cell’s total

sterol content, respectively. Beta-sitosterol may be a potent inhibitor of cholesterol synthesis and has been

shown to cause apoptosis in cancer cells. That is, beta-sitosterol seems to decrease the total cholesterol

content in cancer cells and this causes the cell to stop dividing and die.

Many terpenoid metabolites in adaptogenic plants are hydroxylated such as some phytosterols. There

are over 200 natural 3-beta-monohydroxylsterols so far indexed (Hartmann, 1998). Adaptogenic activity

has recently been described for the plant sterol, !-sitosterol (Park et al., 2001; Bouic, 2002; Villasenor et

al., 2002; Chattopadhyay et al., 2003). Though phytosterol compounds are found in all plants they are

thought to play an important role in the adaptogenic properties of the following plants: Astragalus

membranaceus (Fabaceae), Bryonia alba (Cucurbitaceae), Codonopsis pilosula (Campanulaceae),

Eleutherococcus senticosus (Araliaceae), Lepidium meyenii (Brassicaceae), Ocimum sanctum (Lamiaceae),

and Rhodiola rosea (Crassulaceae). Saw palmetto (Serenoa repens, Palmaceae) seed is high in

phytosterols and has been suggested as having adaptogenic properties (Winston, 1999), though there is

little scientific research to support this hypothesis.

Phytoecdysteroids

The triterpenoid class of plant compounds includes a sterol class called phytoecdysteroids. These

compounds are derived from triterpenes and sterols in the mevalonate pathway. Phytoecdysteroids are the

subject of an intense search for compounds in plants that have a defense role against phytophagous insects

(Dinan et al., 2001). Phytoecdysteroid compounds are widely produced by plants and have either exact

chemical structure as insect steroids or are slightly derivatized versions. Phytoecdysteroids are detectable

in 5-6% of higher plant species. However, less than 2% of the world’s flora has been investigated for the

presence of ecdysteroids (Dinan, 2001; Dinan et al., 2002). Phytoecdysteroids themselves may provide a

chemical fingerprint for chemotaxonomic purposes (Dinan, 2001). It was therefore very tempting to add

this character state to the phylogeny of adaptogenic species, except for the inadequate sampling for this trait

among adaptogen species.

EcdyBase (http://ecdybase.org) is an electronic database that can be used to search for presence of

ecdysteroids in organisms. This database was consulted for presence of ecdysteroids in adaptogenic plant

species (Lafont and Wilson, 1992).

The adaptogenic species in this thesis that have been tested and found positive for presence of

phytoecdysteroids are Achryanthes bidentata (Guo et al., 2000), Tinospora cordifolia (Song et al., 1991),

Leuzea carthamoides (Brekman and Davydov, 1969; Pis et al., 1994), Rhaponticum uniflorum(Zhang et al.,

2002), and Serratula coronata (Hou et al., 1982; Gauliautdinov et al., 2000). The three latter species are

popularly cultivated in Europe with the intent to produce these compounds for dietary supplement products

(Báthori, 2002; Khodolova, 2001). None of the other adaptogenic species in this thesis were found to have

been tested for the presence of phytoecdysteroids or found to contain them. However, some related species

were found to contain phytoecdysteroids such as Tinospora capillipes (Menispermaceae), Achyranthes

fauriei, and Achyranthes rubrofusca (Amaranthaceae) (Ecdybase search, 11/25/03). There are also

intriguing examples of plants closely related to genera in this study, and used for other medicinal purposes

(not adaptogenic) which contain flavonoids, sterols and phytoecdysteroids, such as Lamium maculatum

(Lamiaceae) (Shuya et al., 2003). Atragene sibirica (Ranunculaceae) has been described as an adaptogen

(Panossian, 2003). Though Atragene sibirica has not been sampled, phytoecdysteroids have been found in

many genera of the Ranunculaceae (Dinan et al., 2002).

Since phytoecdysteroid compounds can produce an adaptogenic effect, it would therefore be likely

other adaptogenic species may also synthesize ecdysteroids. If so, the mechanism of action for adaptogenic

species may actually be due to these compounds, although it is also possible that synergism occurs with the

triterpene, phenylpropane and oxylipin compounds. Regardless, testing for phytoecdysteroids would be a

very interesting endeavor for future studies on adaptogens. Over 250 variations of ecdysteroids have been

identified so far in plants and it is theorized that there may be over 1000 possible structures (Dinan, 2001).

Chemotaxonomic analysis of phytoecdysteroids in plants seems promising according to a profiling of the

genus Silene (Caryophyllaceae) (Zibareva et al., 2002).

Phenylpropanoids

Phenylpropanoids (also termed phenolics) are derived from the aromatic amino acids, phenylalanine

and tyrosine, and include a wide variety of compounds such as stilbenes, coumarins, lignans, and lignin, as

well as flavonoids and their derivatives, isoflavonoids, flavans, and anthocyanins. Some adaptogenic plant

species are devoid of the typical dammarane triterpenoid saponins, yet high in phenylpropanoids such as

Rhodiola rosea (Crassulaceae) and Ocimum sanctum (Lamiaceae). Rhodiola species are perhaps the best

adaptogen representative of this group. Rhodiola species usually grow at high altitudes in harsh

environments. The adaptogenic properties of Rhodiola rosea have been ascribed to the phenylpropanoids,

salidroside, rosarin, rosavin, and sachaliside (Panossian et al., 1999; Tolonen et al., 2003). Another

adaptogen species, Ocimum sanctum (Lamiaceae) is also high in phenylpropanes and has been shown to

have antistress (Wagner, 1995), hypoglycemic (Chattopadhyay, 1999), immunomodulatory (seed oil)

(Mediratta et al., 2002), radioprotective (Ganasoundari et al., 1997), analgesic (Khanna and Bhatia, 2003),

hepatoprotective (Sharma et al., 2002) properties. The flavane glycosides, dichotosin, dichotosinin and

diffutin are thought to be responsible for the adaptogenic properties of Hoppea dichotoma (Gentianaceae)

(Wagner et al., 1994).

Flavonoids

Epimedium species have been shown to have a protective effect of long-term glucocorticoid exposure

(Wu et al., 1996). Some of the flavonoids in Epimedium species are prenylated. This prenyl tail is of

isoprene origin and is added during an unknown step in the biosynthetic pathway. Prenylation may be an

important distinction as prenyl structures are also found in most phytoecdysteroids and in triterpenes and

would afford a lipophilic advantage to a phenylpropanoid compound. Protein prenylation is conserved in

fungi, animals and plants and occurs post-transcriptionally. Prenylated proteins in plants have been found

to function in cellular signaling, membrane trafficking, and hormone signal transduction (Galichet and

Gruissem, 2003). While not yet found in plants, the animal enzyme, prenylcysteine lyase, can cleave the

prenyl group from a protein (Galichet and Gruissem, 2003). The current hypothesis is that prenylation

facilitates attachment of proteins to membranes. Some prenylated proteins are involved in diseases such as

cancer and Alzheimer’s. It is tempting to hypothesize that prenylation of flavonoids may assist the

adaptogenic property of some adaptogens.

Identifying the adaptogenic effect of phenylpropanoid compounds is challenging because these

compounds are ubiquitous in plants and they beneficially affect just about every tissue and system in the

human body (Havesteen, 2002). However, besides their renowned antiinflammatory and antioxidant

properties, flavonoids are also capable of gene activation (Baker, 1998) and DNA mutation and repair

(Ferguson, 2001). This gene expression activity should not be surprising since isoflavones can turn on

bacterial genes in the symbiotic relationship with legumes, and also have estrogenic activity in humans

(Dixon and Ferreira, 2002).

Flavonoids can affect the immune system in many ways, such as stimulating the production of

interferons and inducing macrophages to secrete cytokines thus alerting the immune system to pathogenic

attack (Havsteen, 2002). Flavonoids can interact with many different enzymes but especially kinases and

phosphatases that are crucial to many biosynthetic pathways and life responses (Cock et al., 2002; Owuor

and Kong, 2002). Two classes of potential cancer chemopreventive compounds, namely phenolic

compounds/antioxidants and isothiocyanates, have been shown to cause signal transduction (e.g.,

apoptosis) (Owuor and Kong, 2002).

Flavonoids can inhibit anaphylactic responses, enhance our sense of smell and taste, lower blood

pressure, and strengthen blood vessel walls by inhibiting a key enzyme in prostaglandin synthesis

(Havsteen, 2002). Flavonoids can stimulate the production of both antibodies and macrophages of the

immune system (Havsteen, 2002). Adenosine receptor activation affects many organs such as the kidneys,

heart, blood vessels, lungs, central and peripheral nervous system (Muller et al., 2002) modulates

physiological functions such as sedation, vasodilation, suppression of cardiac rate and contractility,

neurotransmitter release, inhibition of platelet aggregation and lipolysis (Muller et al., 2002). Flavonoids

are agonists of adenosine receptors in the brain (Havsteen, 2002), which are highly expressed in the brain

and GABAergic neurons (Muller et al., 2002). These receptors are involved in promotion and regulation of

sleep. Sleep disorders are prevalent in both stress dysfunction and depression. Several adaptogenic plants

have been shown to abolish suppression of bone marrow erythropoiesis caused by sleep deprivation and

increase blood cells (Provalova et al., 2002). Erythropoiesis is regulated by serotonin, norepinephrine, and

acetylcholine. The mechanism of action was suggested to involve changes in brain neurotransmitter

systems. Isoflavonoids from plants have been shown to improve cognitive function possibly by acting like

estrogen in the brain (Duffy et al., 2003). Despite the similarity between structures of steroids and

triterpenoid compounds and phytosterols, most phytoestrogens are simple phenolic compounds such as

polyphenols (Pearce et al., 2003). Thus, the classic steroidal structure is not a necessary requirement for

binding to nuclear receptors.

Phenylpropanoid compounds with adaptogenic properties are found in the following species:

Astragalus membranaceus (Fabaceae), Codonopsis pilosula (Campanulaceae), Epimedium brevicornum

and Epimedium saggitatum (Berberidaceae), Hoppea dichotoma and Hoppea fastigiata (Gentianaceae),

Ocimum sanctum (Lamiaceae), Rhodiola rosea and Rhodiola sachalinensis (Crassulaceae), and Schizandra

chinensis (Magnoliaceae).

Petal color. Kazuma et al., (2003) has suggested that flavonoid type is related to petal color. Thus,

petal color could suggest the presence of particular phenylpropanoid compounds in adaptogen species.

Further research will indicate if petal color bears out this hypothesis. Others have attempted to link

secondary plant metabolites with petal color and function for plant defense or pollination (Armbruster,

1997; Farzad et al., 2003). Petal color of the Asteraceae adaptogen species in this investigation are pink to

purple. But the main chemical compounds considered important in these species are the phytoecdysteroids,

not triterpenes, phenylpropanes or oxylipins. It is noted, however, that the majority of the petals of the 33

adaptogenic species in this investigation are white or greenish-white or yellowish-white (Table 6).

Additionally, most of these flowers are inconspicuous, so much so, that petal color was often not included

in botanical keys. This may be coincidental, though it is also very possible that petal color is related to the

biosynthesis of specific adaptogenic compounds, for example, glucopyranosides. Future research should

perhaps follow up this interesting correlation.

Table 6. Petal color of adaptogen species from this investigation.

Adaptogen Species Petal Color

Achyranthes bidentata Blume whitish-green (personal observation)

Aralia mandschurica (Rupr. & Maxim.) Seem. whitish-greenish flowers (Gleason & Cronquist,

1991)

Astragalus membranaceus Moench. cream-yellow (personal observation, 2003)

Astragalus membranaceus var. mongholicus yellow (Newman, 2003)

(Bunge) P.K. Hsiao

Bacopa monnieri (L.) Wettst. blue or white with purple veins (personal

observation)

Bryonia alba L. white to greenish-white (Culbreth, 1927)

Codonopsis lanceolata (Siebold & Zucc.) Trautv. yellow-green to pink (personal observation)

Codonopsis pilosula (Franch.) Nannf. pale green, purple-patterned (personal

observation)

Eleutherococcus senticosus (Rupr. & Maxim.) Maxim. green-white (personal observation)

Epimedium brevicornu Maxim. white (personal observation)

Epimedium koreanum Nakai white (personal observation)

Epimedium sagittatum (Siebold & Zucc.) Maxim. white-yellow (personal observation)

Glycyrrhiza glabra L. lavender to violet to blue-violet (personal

observation)

Glycyrrhiza uralensis Fisch ex. D.C. blue (Cech, 2003)

Gynostemma pentaphyllum (Thunb.) Makino greenish-white (Cech, 2003)

Hoppea dichotoma Willd. cream-colored corolla (Struwe and Albert, 2002)

Hoppea fastigiata (Grisebach) Clarke cream-coloredcorolla (Struwe and Albert, 2002)

Lepidium meyenii Walp. dirty white (Cech, 2003)

Leuzea carthamoides (Willd.) DC. pink (personal observation)

Ocimum sanctum L. white to reddish (Flora of China,

http://flora.huh.harvard.edu/china/)

Oplopanax elatus (Nakai) Nakai white (personal observation)

Panax ginseng C.A. Mey. greenish-white (personal observation)

Panax quinquefolium L. greenish-white (personal observation)

Rhaponticum uniflorum (L.) DC. purple-red (Flora of China,

http://flora.huh.harvard.edu/china/)

Rhodiola rosea L. greenish yellow or yellow (Flora of China,

http://flora.huh.harvard.edu/china/)

Rhodiola sacra (Prain ex Raym.-Hamet) S.H. Fu white (Flora of China,

http://flora.huh.harvard.edu/china/)

Rhodiola sachalinensis Boriss. yellowish (Flora of China,

http://flora.huh.harvard.edu/china/)

Schisandra chinensis (Turcz.) Baill. white (Komarov, 1937)

Serratula coronata L. purple (personal observation)

Tinospora cordifolia (Willd.) Miers yellow-green (Kirtikar, 1918)

Trichopus sempervirens (H. Perrier) Caddick & Wilkin cream or purple-brown (Caddick et al., 2002)

Trichopus zeylanicus Gaertn. cream or purple-brown (Caddick et al., 2002)

Withania somnifera (L.) Dunal greenish-yellowish (personal observation)

Lignans

Lignan is a precursor to lignin, the most common structural compound in plants. Lignan has been

found to be present in the earliest land plants (Waters, 2003). Lignans are widely distributed, though

seemingly random, and found in no less than 55 vascular plant families. Humans and other mammals

produce lignans in the gut from dietary sources, which have been shown to have phytoestrogenic properties

and are protective against cancer.

Like other phenolics, lignans have an aromatic ring and one or more hydroxyl groups. Lignans are

dimers of phenylpropanoid (C6-C3) units linked by central carbons on their side chains (MacRae and

Towers, 1984). Synthesized in plants via the shikimate pathway, lignans possess many pharmacological

actions in mammals and humans. They have been found to have antitumor, antiviral, cathartic,

antihypertensive, antimicrobial, and antifungal activity. Lignans can affect the central nervous system,

protect against liver toxins and are known to have stress-reducing effects (MacRae and Towers, 1984).

Like flavonoids, another phenylpropanoid chemical, lignans have been shown to inhibit mixed function

oxidases which are involved in detoxification and in development of more toxic metabolites.

Even though lignans are formed at the end of the shikimate pathway along with lignin, they are more

related to isoflavonoids than lignin. Lignans and isoflavones have a diphenolic structure similar to 17!-

estradiol and other hormones, which have been found to produce weak, protective estrogenic activity

(Bowey et al., 2003).

Flaxseed is among the richest source of lignans, but many seeds, nuts, whole grains, berries, fruits and

vegetables contain lignan compounds (Kilkkinen et al., 2003). The major lignans found in the diet are

syringiresinol, pinoresinol, lariciresinol, isolariciresinol, matairesinol and secoisolariciresinol (Bowey et

al., 2003). These compounds are converted by gut microflora to mammalian lignans, most notably,

enterolactone. Lignans make up the most abundant phytoestrogen compound in the Western diet.

Lignan compounds are found in the following adaptogenic plant species: Codonopsis pilosula

(Campanulaceae), Eleutherococcus senticosus (Araliaceae), Epimedium brevicornum, E. koreanum, and E.

saggitatum (Berberidaceae), and Schizandra chinensis (Magnoliaceae).

Oxylipins and Fatty Acids

The third group of compounds suggested by Panossian (2003) and others as having adaptogenic

properties is oxylipins. These are polyunsaturated fatty acids synthesized by plants via the acetate pathway

and then oxidized via the lipoxygenase pathway to produce compounds called oxylipins (Blée, 1998). The

precursor of plant oxylipins is linoleic acid. Oxylipins are believed to have a role in plants as signaling

molecules in plant resistance against insects and pathogens. Although these physiological functions in

plants are still being investigated, their biological roles seem to be comparable to those of the eicosanoid

compounds in mammals (Howe and Schilmiller, 2002). In mammals, oxylipins are synthesized primarily

from the precursor, arachidonic acid in the C20 fatty acid pathway. These compounds are involved in

inflammation, infection, allergy, and exposure to xenobiotics.

The plant oxylipins illustrated in Figure 1 have three hydroxyl (OH) groups attached. These

polyhydroxylated oxylipins from the adaptogenic species, Bryonia alba, are proposed to be responsible for

its adaptogenic activity (Panossian et al., 1981).

Human oxylipinPlant oxylipins

Figure 1. The structure of plant oxylipins is similar to human oxylipins such as leukotrienes.

As seen in Figure 1 oxylipins are structurally similar to mammalian leukotrienes and lipoxines

(Panossian et al., 1999; Panossian, 2003). The hypothesis that oxylipins have adaptogenic properties may

help explain the traditional use of some plant seeds. For example, Celastrus paniculatus, Celastraceae

(Nalini et al., 1995), Serenoa repens, Palmaceae (Winston, 1999; Bucci, 2000), Urtica dioica, Urticaceae

(Grieve, 1931), Sesamum indicum, Pedaliaceae (Holmes, 1996), and Avena sativa, Poaceae (Bucci, 2000)

have all been used in various cultures for adrenal cortex deficiency, or as rejuvenating or anabolic tonics.

These seeds are high in fatty acids. It is possible that these fatty acids may become oxidized; forming

oxylipins that then elicit localized tissue responses.

Fatty acids themselves have been shown to interact with the cell membrane, altering the conformation

of channel proteins imbedded in the membranes. Leaf et al. (2003) proposed a mechanism of action for

anti-arrhythmic properties of omega-3 fatty acids found in fish oil. This same mechanism, the intercalation

of fatty acids into the plasma membrane of cells, may help explain the adaptogenic properties of these

seeds. Others have linked polyunsaturated fatty acids to gene expression in mammalian systems (Khan and

Vanden Heuvel, 2003; Wahle et al., 2003). These hypotheses require much more research, but offer

potential mechanisms for the adaptogenic properties of some plant remedies.

One further hypothesis deserves mention. Maca root, Lepidium myenii, Brassicaceae, has been coined

the “Peruvian ginseng” because of its popular use as an aphrodisiac, to increase energy, and to promote

mental clarity. The root primarily contains alkamide compounds that are a combination of amides and fatty

acids. While fatty acids have been briefly explored there is a further mechanism not yet discussed,

peptides. Many hormones are peptides such as epinephrine, corticotropin-releasing factor (CRF), and

thyrotrophin-releasing hormone (TRH). Plants synthesize plant defensin peptides, which have a folding

pattern that shares a high similarity to defense peptides in mammals and insects (Thomma et al., 2003).

Peptides have also been shown to cause cross-reactivity and mimicry in systemic autoimmune diseases

(Fournel and Muller, 2002).

One other class of plant compound not yet investigated are plant hormes. Brassinolid has been shown

to be able to bind to the human steroid enzyme, 5!-reductase (5!R), which converts testosterone into 5!-

testosterone, the androgen with the highest affinity for the androgen receptor (Clouse, 2002; Rosati et al.,

2003). While peptides and plant hormones have not yet been suggested as a hypothesis for adaptogenic

activity, these compounds also deserve further attention.

Polysaccharides

Polysaccharides have shown immunostimulant and immunomodulatory activity by activating natural

killer cells, cytotoxic lymphocytes, interleukin 2 and helper T lymphocytes and many other cytokines

(Zhang, 2002). However, polysaccharides have not been found to have an effect on the HPA axis directly.

Rather, similar to flavonoids and fatty acids, these carbohydrate compounds seem to have a secondary

beneficial effect on HPA axis dysfunction. For example, the inulin-type oligosaccharides in Morinda

officinalis (Rubiaceae) were shown to possess an antidepressant action due to stress (Zhang et al., 2002b).

Many adaptogenic plants contain polysaccharides and oligosaccharides and are thought to play an

adaptogenic role are found in the following plant species: Achyranthes bidentata (Amaranthaceae),

Astragalus membranaceus (Fabaceae), Eleutherococcus senticosus and Panax ginseng (Araliaceae),

Codonopsis pilosula (Campanulaceae), and Epimedium brevicornum (Berberidaceae).

Table 7 illustrates the 33 adaptogenic plant species in this investigation and their main chemical

classes of compounds.

Chemotaxonomy

The largest body of work accomplished in the field of chemotaxonomy was the many volumes

published from 1966 to 1989 by Robert Hegnauer, Chemotaxonomie der Pflanzen ein Ubersicht uber die

Verbreitung und die systematische Bedeutung der Pflanzenstoff (Birkhauser Verlag, Basel, Switzerland).

More recently, Gottlieb et al. (2002) confirmed the systematic and evolutionary patterns of dicotylendon

species for food and medicine and showed that more recently evolved species are selected as medicines.

For example, in angiosperm taxa, the highest number of food species are found in more primitive orders,

whereas the highest number of medicinal species are found in the Asteridae, the most advanced order.

Many plant compounds have been applied to chemotaxonomic analysis such as: sulphated flavonoids

(Barron et al., 1988); prenylated flavonoids (Barron and Ibrahim, 1996); flavonoids in Ocimum (Grayer et

al., 2002; Vieira et al., 2003), Glycyrrhiza (Hayashi et al., 2003); glucosinolates (Fahey et al., 2001), lectins

(Fernandez-Alonso et

Table 7. Adaptogenic plant species and main chemical classes of compounds.

Triterpenes

Achyranthes

bidentata

Aralia mandshurica

Astragalus

membranaceus

Bacopa monniera

Bryonia alba

Codonopsis

pilosula

Codonopsis

lanceolata

Eleutherococcus

senticosus

Epimedium

koreanum

Glycyrrhiza glabra

Gynostemma

pentaphyllum

Leuzea

carthamoides

Ocimum sanctum

Oplopanax elatus

Panax ginseng

Panax

quinquefolium

Rhaponticum

uniflorum

Trichopus

sempervirens

Trichopus

zeylandicus

Tinospora

cordifolia

Withania somnifera

Phenylpropanoids

Achyranthes

bidentata

Astragalus

membranaceus

Codonopsis

pilosula

Eleutherococcus

senticosus

Epimedium

brevicornu

Epimedium

koreanum

Epimedium

saggitatum

Glycyrrhiza glabra

Gynostemma

pentaphyllum

Hoppea dichotoma

Hoppea fastigiata

Ocimum sanctum

Oplopanax elatus

Panax ginseng

Rhaponticum

uniflorum

Rhodiola rosea

Rhodiola

sachalinensis

Schizandra

chinensis

Sterols

Astragalus

membranaceus

Bacopa monniera

Bryonia alba

Codonopsis

pilosula

Epimedium

brevicornu

Epimedium

koreanum

Glycyrrhiza glabra

Gynostemma

pentaphyllum

Lepidium meyenii

Ocimum sanctum

Rhaponticum

uniflorum

Rhodiola

sachalinensis

Tinospora

cordifolia

Trichopus

sempervirens

Trichopus

zeylandicus

Polysaccharides

Achyranthes

bidentata

Astragalus

membranaceus

Epimedium

brevicornu

Panax ginseng

Panax

quinquefolium

Phytoecdysteroids

Achyranthes

bidentata

Leuzea

carthamoides

Rhaponticum

uniflorum

Serratula coronata

Tinospora

cordifolia

Fatty

acids/oxylipins

Bryonia alba

Lepidium meyenii

Ocimum sanctum

Panax ginseng

Alkaloid

Epimedium

brevicornu

Epimedium

koreanum

Panax ginseng

Peptides

Leuzea

carthamoides

Panax ginseng

Trichopus

sempervirens

Trichopus

zeylanicus

45

al., 2003); terpenoids in Buddleja (Houghton et al., 2003), usnic acid (Ingolfsdottir, 2002), prenylated

flavonoids (Barron and Ibrahim, 1996; Oyama et al., 1995), sequiterpenes, diterpenes and triterpenes in

conifers (Otto and Wilde, 2001), and latex in the Malpighiaceae (Vega et al., 2002). The chemotaxonomic

relevance of ecdysteroids has been researched for the following families: Ranunculaceae (Dinan et al.,

2002), Chenopodiaceae (Dinan et al., 1998), Liliaceae (Dinan et al., 2001), Centarea in Asteraceae (Sarker

et al., 1997), Gomphrena in the Amaranthaceae (Savchenko et al., 1998), Lamium in Lamiaceae

(Savchenko et al., 2001), Limonium in Plumbaginaceae (Whiting et al., 1998), and Silene in

Caryophyllaceae (Zibareva et al., 2002). Chemotaxonomy has been applied to the following Angiosperm

families: Campanulaceae (Gorovoi et al., 1971), Asteraceae, Lamiaceae (Alvarenga et al., 2001; Bohm and

Stuessy, 2001; Grayer et al., 2003), Picramnia and Alvaradoa in Picramniaceae (Jacobs, 2003), Oleaceae

(Jensen et al., 2002), Cyptolepis in Asclepiadaceae (Paulo and Houghton, 2003), Plantago in

Plantaginaceae (Ronsted et al., 2000), Codonopsis in the Campanulaceae (Wang et al., 1995), and Iris in

the Iridaceae (Williams et al., 1997). Phytosterols and oxylipins have not often been applied to

chemotaxonomy, though there are some exceptions, for example, sterols of the Caryophyllales (Patterson et

al., 1991).

Chemotaxonomy has thus been successful in revealing phylogenetic relatedness and can offer the

same for plant species with adaptogenic properties, a motivation for the present study. A new exciting

addition is a database that has been developed for the phylogenetic prediction of terpenoid skeletons in

plants, though it has not yet been translated into English (Ferreira et al., 2003).

Summary

Plants have had to cope with assaults from severe environmental conditions as well as a host of

organisms. They have done so by developing physical barriers such as thorns and thick cuticles and by

synthesizing an array of chemical compounds as well as diverse growth and defense mechanisms many of

which are conserved among various eukaryotic organisms (Clouse, 2002; Grassman et al., 2002; Menezes

and Jared, 2002). Plant compounds often affect more than one molecular target, perhaps in order to limit

the heavy cost of their production (Wink, 1999).

The complex relationship between plant compounds and activation in humans and mammals is a rich

source of investigation for the plant scientist and others. Though the chemical compounds believed to be

responsible for the adaptogenic activity are complex, there are associations between the production of

defense and growth compounds in response to symbiotic or defense roles. One area where more research is

needed, however, is the induction of plant compounds in response to both beneficial and pathogenic fungi,

bacteria, nematodes and other rhizosphere organisms (Walter et al., 2000).

Two important areas of research that are still forthcoming that relate to the study of adaptogenic plants

is the work started by Ferreira et al. (2003) and by Grassman et al. (2002). Ferreira and colleagues have

designed a program for terpenoid skeleton prediction based on botanical information. This program may

help to determine relationships between types of terpenoid compounds found in adaptogenic plants. The

reason why it is difficult at the moment to access is that it is currently written in Spanish.

My phylogenetic analysis tentatively supports the hypothesis that the majority of adaptogens are found

in more advanced angiosperm orders. Yet, low sampling of taxa with this trait is in cautious agreement.

Robyn Klein 2006 www.rrreading.com

Phylogenetic and phytochemical characteristics of plant species with adaptogenic properties

MS Thesis, 2004, Montana State University

Chapter 6 of 8