In plants, amino acids are broken down into two groups, protein, and non-protein. There are twenty amino acids, derived from the acid hydrolysates of plant proteins (as with animal proteins). Plant proteins are essential for carrying out specific cellular functions both internally and externally. Plant proteins are seed-based store-houses for nitrogen and guard against would-be predators. Some are toxic to humans, some are of daily necessity in the human diet. Some, furthermore, have been developed into specific drugs: L-Dopa, from fava beans and other Fabaceae/Leguminosae, is used in the treatment of Parkinson's disease; L-Cysteine, found in all plants, is used in eye drops and topical antibiotics. L-Arganine stimulates the pituitary gland to release growth hormone. L-Aspartic acid is present in coffee, liquorice, sugar cane, sugar beet, and is neuro-excitatory. It is the phytochemical responsible for so-called 'sugar highs,' and is in aspartame (Harborne, 61-67).

Mucilage, therapeutically, can reduce bowel irritation, gut irritation, peristalsis, toxin absorption, cough, bronchial and urinary spasm. Mucilage can also increase expectoration (Cabrera, 35). As a gelating agent, the polysaccharide hydrocolloidal carrageenan often finds its way in ice cream; it is also used as a laxative ingredient. Perhaps the most common bulking agent derived from a polysaccharide comes from Plantago major, whose seed, the psyllium, can bulk itself up with the addition of water sufficiently to initiate peristalsis and evacuate the bowels (Tyler, 45-56).

Lipids are often a main constituent in drugs, separated by expression from the crude vegetable (plant) matter and presented as drugs in the refined state (Tyler, 82). Plant seeds are the largest source (e.g. sesame seeds,almonds, linseed) of lipids (Tyler, 83; Evans, 322).

Alkaloids are arguably the most potent therapeutic compounds and have been manufactured as various allopathic drugs, including the pain-killer morphine and the anti-malarial quinine. Derived from amino acids, alkaloids represent a varied and complex class of nitrogenous crystalline or oily compounds. Alkaloid levels in a given botanical change in the course of the day and are not homogeneous, which makes them difficult to define (Tyler et al., 186). Their presence appears to be most prevalent in the Fabaceae/Leguminosae, Papaveraceae, Ranunculaceae, Rubiaceae, Solanaceae, and Berberidacea families. Plant genera providing the highest yield of alkaloids are Nicotiana, Vinca, Strychnos, Papaver sominifera, and Rauwolfia serpentia (Evans, 545).

Pyrrolidine, tropane, or solanaceous alkaloids effect the peripheral nervous system, inhibiting the parasympathetic nervous system and stimulating the sympathetic. Pupils dilate, secretions slow, and the vagus nerve is inhibited (causing vasodilation, bronchial dilation, and reduced peristalsis) (Harborne and Baxter, 300-308).

Pyridine and piperidine alkaloids represent a class which affects the central nervous system, reduces appetite, and contains other properties usually diuretic or diaphoretic in action. Nicotine, lobeline, and coniine are examples. Coniine is extremely toxic (Harborne and Baxter, 243-254).

Pyrrolizidine alkaloids are under fire today as chemists and doctors try to determine the human hepatotoxicity of these agents which can damage liver veins, causing hepatic veno-occlusive disease (Awang, 20-22). Toxicity to livestock is demonstrated by the fact that 50% of livestock deaths occur through the ingestion of a plant that contains these alkaloids (Harborne and Baxter, 255). Because of five well-publicized deaths (one of which was the teratogenic poisoning of a fetus) following the consumption of an herb(comfrey) that had been regarded as safe, plant families in which pyrrolizidine alkaloids are most often found (Boraginacea, Asteraceae/Compositae, and Fabaceae/Leguminosae) are of immense concern to both herbalists and the FDA (Mattocks, 724).

Indole alkaloids are derived from tryptophan, and apart from the few with hallucinogenic effects, indoles such as serotonin, harmine and reserpine have a sedative effect on the central nervous system. Other constituents in this category are cytostatic, antileukemic, or are able to act on the ratio of oxygen and glucose to the cell, specifically increasing oxygen to deprived areas.

Quinoline alkaloids are named from quinoline in the cinchona plant, and refers to the quinoline alkaloids developed in the nucleus from tryptophan (Tyler et al., 202). Included in this group are quinine, the anti-malaria medication, and quinidine, which calms the heart in tachycardiasis and arrhythmia, and others. Chinchonine is an astringent and a bitter. Isoquinoline alkaloids are derived from tyrosine and phenylalanine.

The therapeutic value of this class of alkaloid differs according to the sub-categories, which include simple, benzyl, Papaveraceae, codeine, protopine, protoberberine, and ipecac isoquinolines. The protoberberines, which include berberine, hydrastine, and canadine, are anti-bacterial, anti-protozoal, astringent, tonic, bitter tasting, and respiratory, vasomotor, and circulatory stimulants (ibid.).

Terpenoids form the largest group of plant products and are the most common ingredient in volatile oils. They include camphor, Beta-carotene, and digitalin, for example, and are sometimes referred to as isoprenoids, due to the fact that all terpenoids are derived from a 5-carbon precursor isoprene (Harborne and Baxter, 552). Terpenoids are categorized as monoterpenoids and monoterpenoid lactones, sesquiterpenoids and sesquiterpenoid lactones, diterpenoids, and triterpenoids. Of these four groups, triterpenoids forms the largest. Carotenoids are formed through a head-to-tail combination of geranylgeranyl pyrophosphate, the same precursor to monoterpenoids (ibid.).

Monoterpene, sesquiterpene, and diterpene alkaloids, as well as steroidal alkaloids, are classified as alkaloids due to the presence of nitrogen in their structure. Despite that classification, those alkaloids, and some phenols as well (for instance, rotenone), may contain terpenoidal atoms or compounds or isoprenoid derivatives (ibid.).

Monoterpenoids have a head-to-tail formation of their ten-carbon precursor, geranyl pyrophosphate (Harborne and Baxter, 555). These constituents are present in volatile oils. Monoterpenoids often have a strong smell; they are the source of such scents as spearmint (carvone), bergamot and lavendar (both of which contain linalyl acetate), and sweet rose (nerol) (ibid, PD2042, PD2059, PD2065; Evans, 321). Monoterpenoids occur in insect pheromones as well. Monoterpenoids vary in pharmacological use, as expectorants, anthelmintics, anticholesteremics, insecticides, and antiseptics.

The phrase bitter principles, which refers to the bitter-tasting monoterpenoid lactones known as iridoids are also components of volatile oils and have been used to stimulate actions within the body, such as mucosal or gastric secretion. The attachment of a glucose to a hydroxyl group on the lactone ring is the determining factor in recognizing a lactone. These isoflavonoid polyphenols are sometimes also referred to as iridoid glycosides, because they are often present in glycosidic form. Iridoids usually occur in angiosperms, especially valerian, gentian, blue flag, and orris root, and can have, aside from the therapeutic actions described above, antimicrobial and antileukemic properties (Harborne and Baxter, 555, 569).

Sesquiterpenoids occur with monoterpenoids in plant essential oils, especially in the families Labiatae, Myrtaceae, Pinaceae, and Rutaceae. They also occur in micro-organisms, marine animals, fighting insects, and insect pheromonal secretions. Some are very toxic, but sesquiterpenes can be used as antifungals, carminatives, insecticides, or as an antibiotic. This latter action has been successfully demonstrated against staphylococcus areus and candida albicans, by sesquiterpenes found in marine alga (Duke, 584, Harborne and Baxter, PD2141). A sesquiterpenes found in chamomile, is an antiinflammatory agent (Harborne and Baxter, PD2123).

With the addition of a y-lactone sesquiterpenoids become sesquiterpene lactones such as those found in absynthe and arnica (Harborne and Baxter,599). The cytotoxicity of sesquiterpene lactones prevents their widespread use but encourages research into antitumor applications. Often these are the components causing contact dermatitis and some are lethal (ibid.).

Many resin acids, termed diterpenoid acids are included in this group, as are plant hormones called gibberellins. Many of the diterpenoids are toxic, similar to sesquiterpenoids, but some have antibiotic, antiviral, antiinflammatory, and bitter tonic uses (ibid). Ginkgolides, diterpenoids from the Ginkgo biloba plant, are fast becoming one of today's most highly-esteemed phytochemicals, finding use in the treatment of memory loss, allergies, asthma, brain injury, and more (DeFeudis, 1991; Harborne and Baxter, PD2447; Petkov et al., 106).

Triterpenoid saponins, or sapogenins, are plant glycosides which lather in water and are used in detergents, or as foaming agents or emulsifiers, and have enormous medical implications due to their antifungal, antimicrobial, and adaptogenic properties. Glycyrrhizin, from licorice root, is an example of a saponin used for antiinflammatory purposes in place of cortisone (Harborne and Baxter, PD2536).

Steroid saponins are similar to the sapogenins and related to the cardiac glycosides. Therapeutically, steroidal saponins their ability to interact medically and beneficially with the cardiac glycosides, sex hormones, Vitamin D, and other factors, render these phytochemicals components of great medical significance (Evans, 481). For instance, diosgenin, from Wild Yam, was used in the development of the first oral contraceptive (Harborne and Baxter, 689).

Phytosterols are necessary to plant membranes and plant cell growth. Sitosterol, stigmasterol, and campesterol are the most common (Harborne and Baxter, 712). It has been demonstrated that B-sitosterol decreases the risk of atherosclerosis by lowering plasma concentrations of LDL's (low-density lipoproteins) (Lehninger, 614). Ergosterol, combined with ultra violet light, becomes vitamin D2. Vitamin D3, mentioned in the first issue of The Protocol Journal of Botanical Medicines as a topical treatment for psoriasis, is obtained from 7-dehydrocholesterol (Tyler et al., 161).

Carotenoids, or forty-carbon tetraterpenoids, are lipid-soluble terpenes found in all forms of plants. Their value to animals comes from the splitting of the C40 molecule into the twenty-carbon isoprenoid alcohol known as Vitamin A, a process which occursafter the substance has been ingested (Guyton, 867; Harborne and Baxter, 745).

The flavonoids constitute about one-half of the eight-thousand or so recognized phenols. The rest are broken down into phenylpropanoids, anthones, stilbenoids, and quinones. The compounds have a myriad of medical functions. From the perspective of the plant kingdom, polyphenolic compounds are important contributors to the survival of plant species through the insurance of successful pollination, and also provide plants with an unpleasant taste so that possibly threatening herbivores are repelled (ibid.).

Flavonoids are molecules responsible for the color of fruit and flowers. They are beneficial to man as powerful antioxidants, stress modifiers, anti-allergic agents, anti-viral compounds and anti-carcinogens (Evans,420). Some are able to stimulate protein synthesis, and some are known antiinflammatory agents. Still others have demonstrated vaso-protective activity. Some are diuretic, antispasmodic, antibacterial,and antifungal (Harborne and Baxter, 367-415).

While some flavonoids may be classified as flavonoid glycosides, all are phenols, but flavonoids, flavonals, flavanones, isoflavones, and xanthones, all stem from flavones. Flavones have effectively been used to tone blood cell walls and bloodcells. Anthocyanidins and anthocyanins are related flavonoids. These, and flavones in general, occur most frequently as glycosides.

Isoflavones occur less frequently as glycosides, more often in their free state, and have a higher degree of structural variation(Harborne and Baxter, 415).

Tannins are polyphenolic compounds and are divided into two groups, i.e., the hydrolyzable and non-hydrolyzable tannins, and the condensed tannins. Hydrolyzable tannins are thought to be hepatotoxic with overuse; condensed tannins appear not to have this action.

In general, tannins are astringent and antiseptic. Hamamelitannin, from witch hazel bark is a source of pharmacologically-used tannin (Evans, 386-388) and often found in men's aftershave lotions. A polyphenol classified as a napthaquinone, plumbagin, for example, found in the Round Leaved Sundew (Drosera rotundifolia) a plant indigenous to coastal Maine, has shown anti-bacterial properties and continues to be researched for its anti-cancer actions (Evans, 672).

References