Introduction
Herbal medicines have been used for treatment of diseases in China for thousands of years. The composition of phytochemicals in herbal medicines varies among different plant species. Phytochemicals are useful to characterize their medicinal properties of herbs. Phytochemicals may have multi-arrays of other biological significance, e.g., polyphenols, flavonoids, saponins, or carotenoids. Some of these phytochemicals are established as essential nutrients in foods and has been reported in various plants. There are at least 150 kinds of naturally occurring saponins that have been found to possess anti-cancer properties and more than 11 distinguished classes of saponins including dammaranes, tirucallanes, lupanes, hopanes, oleananes, taraxasteranes, ursanes, cycloartanes, lanostanes, cucurbitanes, and steroids.1 Due to differences in their chemical structures, saponins can display anti-tumorigenic effects on cancer cells yet active phytochemicals from herbal medicine are not easily identified. Although a number of active phytochemicals have been reported, their chemistry and reactivity and the pharmacological activities and mechanism of action and structure–function relationships at the molecular and cellular levels remain to be explored. Some special saponins with strong antitumor effects have been exhibited. Ginsenosides which are dammaranes are shown to exhibit anti-angiogenesis and inhibiting metastasis. In addition, Dioscin, one of the steroidal saponins, and its aglycone diosgenin are inducers of cell cycle arrest and apoptosis. Table 1.1 shows the medicinal properties of saponins.
Table 1.1 Medical application of selected saponins
| Family | Species | Saponins | Cancer | Ref. |
| Agavaceae | Agave
utahensis | Chlorogenin
hexasaccharide | HL-60 | Yokosuka
et al.2,
Xu et al.3 |
| Alliaceae | Allium
macrostemon
Bunge | Macrostemo-noside
O, P, Q, and R | HepG2,
MCF-7 | Yang et al.4 |
| Aslepiadceae | Cynanchum
auriculatum | Wilfoside C3N | A549 | Liu et al.5,
Kim et al.6 |
| Asparagaceae | Asparagus
gobicus | Asparanin A | HepG2 | Yang et al.7,
Wang et al.8 |
| Dioscoreaceae | Disscorea | (25S)-spirost-
5-en-3β | L929,
HeLa | Liu et al.9,
Gonzalez
et al.10 |
| Dracaenaceae | Nam ginseng | Namonins | HT-1080,
BL6 | 11, Tran
et al.12 |
| Liliaceae | Polygonatum
sibiricum
Camassia
cusickii | Neosibirico-sides
A-D TGHS-1
and 2 | MCF-7
P388 | Sy et al.13,
Ahn et al.14 |
| Solanaceae | Solanum torvum
Solanum
indicum L. | Torvosides M
Dioscin | HepG2,
MCF-7,
Colo-205,
HSC-2,
human
fibroblasts | Nartowska
et al.15,
Lu et al.16 |
Infectious diseases which are infected by microorganisms such as protozoa are of major health concern worldwide. The incidence of the disease has increased since the emergence of AIDS and Ebola diseases. In the absence of a vaccine and satisfactory drugs, there is an urgent need for novel drugs to replace or to supplement those in current use. Herbal medicines are undoubtedly a valuable source of new medicinal agents. However, active phytochemicals remain to be identified and characterized. Herbal extracts and chemically defined molecules of natural origin show various medicinal activities. It also includes about three hundred compounds isolated from higher plants and microorganisms, which are classified into chemical groups with specific biologic activity.17
Many herbal medicine-derived compounds display significant effects on body functions. They can be good candidates for drug development for treatment of various diseases including rheumatism, asthma, and atherosclerosis. Many herbal extracts and the respective active compounds isolated from natural resources for the treatment of various diseases have been reported yet individual active compounds may not display the same activity in vivo. Herbal extracts are reported to exhibit anti-viral activity against herpes simplex virus (HSV), both the types 1 and 2.18 Therefore, medicinal plants can be a good source for drug development. However, the bioactive anti-HSV molecules from the plant extracts need to be identified and tested. The mechanism of actions of the potential active anti-HSV molecule(s) requires tedious research work. Similar methodology for isolation, purification, and characterization of potential phytochemicals from other herbal medicines can be used. The most potent molecule(s) and their analogues need to undergo preclinical and toxicity evaluations before synthesis of a large amount of the bioactive molecules for medical applications. In another approach such as genomics, gene expression profiling could help to identify molecular targets of the biological activity of the active natural products that would facilitate the gene-based drug development.
Sesquiterpene
Apart from this, another common class of phytochemicals, Sesquiterpene lactones have been reported as the major phytoconstituents of Saussurea costus. Different pharmacological experiments in a number of in vitro and in vivo models have demonstrated the medicinal properties of S. costus with anti-inflammatory, anti-ulcer, anti-cancer, and hepato-protective activities.19
Flavonoids
Flavonoids are a large family of polyphenols present in herbal medicines. Six major subclasses of flavonoids, namely anthocyanidins, flavan-3-ols, flavonols, flavanones, flavones, and isoflavones.20,21 Table 1.2 shows the source of some common plant flavonols. Flavonols are the most commonly found in plants and vegetables and fruit. The biochemical properties of flavonoids influence their disposition. Their metabolites exert biological activities relevant to the health benefits in human health. Many of the biological effects of flavonoids are related to their ability to modulate cell-signaling processes and cell growth. In addition, flavonoids are shown to exhibit multi-arrays of pharmacologic activities including anti-inflammatory, anti-thrombogenic, anti-diabetic, and anti-cancer. Previous studies suggest that consumption of flavan-3-ols and anthocyanidins can exert therapeutic effects on cardiovascular disorders and type 2 diabetes mellitus. However, only a limited number of studies has reported the anti-cancer activities of flavonoids in humans but higher intake of soy isoflavones appeared to be associated with reduction in cancer risks of breast in women and prostate cancer in men. Yet the health benefits of flavonoids remain to be further investigated.
Table 1.2 Common plant flavonoids20,21
| Flavonoid Subclass | Dietary Flavonoids (aglycones) | Some Common Food Sources |
| Anthocyanidins | Cyanidin, Delphinidin,
Malvidin, Pelargonidin,
Peonidin, Petunidin | Red, blue, and purple
berries;
red and purple grapes;
red wine |
| Flavan-3-ols | Monomers (Catechins):
(+)-Catechin,
(−)-Epicatechin,
(−)-Epigallocatechin,
(+)-Gallocatechin; and
their gallate derivatives | Teas (white, green,
and oolong), grapes,
berries, apples |
Dimers and Polymers:
Proanthocyanidins# | Apples, berries,
cocoa-based products, red
grapes, red wine |
| Theaflavins, Thearubigins | Black tea |
| Flavonols | Isorhamnetin,
Kaempferol, Myricetin,
Quercetin | Onions, scallions,
kale, broccoli, apples,
berries, teas |
| Flavones | Apigenin, Luteolin,
Baicalein, Chrysin | Parsley, thyme, celery,
hot peppers |
| Flavanones | Eriodictyol, Hesperetin,
Naringenin | Citrus fruit and
juices, e.g., oranges,
grapefruits, lemons |
| Isoflavones | Daidzein, Genistein,
Glycitein, Biochanin A,
Formononetin | Soybeans, soy foods,
legumes |
Phytochemicals from cruciferous vegetables
Cruciferous vegetables, such as broccoli and cabbage, contain various sulfur-containing compounds called glucosinolates. Isothiocyanates are biologically active products of glucosinolates.22 For example, broccoli is a good source of glucoraphanin, the glucosinolate precursor of sulforaphane (SFN), and sinigrin, the glucosinolate precursor of allyl isothiocyanate (AITC).23–26 Glucosinolates are present in medicinal plants. Watercress is a rich source of gluconasturtiin, the precursor of phenethyl isothiocyanate (PEITC), while garden cress is rich in glucotropaeolin, the precursor of benzyl isothiocyanate (BITC). At pr...
