**1.6. Synergy in relation to pharmacological action of phytomedicine**

Most herbs exhibit their effects on a variety of constituents, and the idea of synergy within and between them is gaining acceptance [15]. Most herbal medicines are not well documented to prove whether they are acting truly in a synergistic way or by additive effects. It is usually difficult to clinically evaluate herbal preparations without the knowledge of their synergistic effects. Biological activity may be absent in the crude drugs but may contain some components that can enhance their active components' potency. One of such examples is St. John's wort (*Hypericum perforatum*, family Hypericaceae), a clinically proven herb which has efficacy as an antidepressant. Hypericins responsible for its activity was found to be very weak, and impurities in the fraction used gave the additional results which suggest multiple (polyvalent) and synergistic effects. St. John's wort thus represents a good example of an herb which may exhibit synergism and polyvalent action [16]. The use of combinations of herbs can also result in synergism or enhancement of activity of herbal drugs. In case of multiple herb extracts, some of the herbs enhance the potency of the real effective herb, and in some cases, their constituents could reduce the toxic effects of the main herb, resulting in a safe herbal combination tolerable for consumption by the human system [17].

#### **1.7. Phytoconstituents in medicinal plants**

Phytochemicals are chemicals found in plants that protect plants against bacteria, viruses, and fungi. Eating large amount of brightly colored fruits and vegetables, whole grains/cereals, and beans containing phytochemicals may decrease the risk of developing certain cancers as well as diabetes, hypertension, and heart disease. The actions of phytochemicals vary by the type of the food and the color. They may act as antioxidants or nutrient protectors or prevent carcinogens from forming. The term phytochemical refers to a wide variety of compounds made by plants but is mainly used to describe those compounds that may affect human health. Scientists have identified thousands of phytochemicals, although only a small fraction has been studied closely. Some common examples of phytochemicals include betacarotene (with other carotenoids), vitamin C, vitamin E, and folic acid [18]. Phytochemicals have shown various physiological actions [19, 20]. Among the numerous phytochemicals in existence are the following with their usefulness:

#### **1.8. Alkaloids**

**Botanical (species)** 

**Family name**

**Local name(s)**

**Common names**

**Parts used**

**Medicinal use(s)**

**name**

33 34 35 36 37 38 39 40 [40, 52, 53].

**Table 1.**

Some common medicinal plants from Nigeria used for treating various diseases.

*Zingiber officinale*

Zingiberaceae

Atale, jinja

Ginger

Rhizome

Asthma, rheumatism, piles, hepatitis,

diuretic, headache, cold, stimulant, cough,

anthelmintic, typhoid fever, obesity, malaria

*Talinum triangulare*

Portulacaceae

Gbure, ofe bake, ntu

Water lettuce, Ceylon

Roots, leaves

spinach, fame flower,

Surinam purslane

oka

*Parkia biglobosa*

Leguminosae

Igba, igi-iru, dadawa,

West African locust bean,

Leaves, bark, fruits,

Antitumor, diabetes, high blood pressure,

malaria, tonic, wounds, mental disorder,

intestinal disorder, obesity, astringent

Anemia, scabies, schistosomiasis, fresh cuts,

high blood pressure

seeds, pulp

Dadawa tree

ogirili, dorowa

*Ocimum gratissimum*

Lamiaceae

Efinrin-nla, efinrin-aja,

Tea bush, balsam, basil

Leaves, whole plant

Antimicrobials, bronchitis, diarrhea, insect

repellant, piles, cold, cough, diabetes,

anthelmintic, hypertension, colic, fever,

convulsions

oromoba, saidoya,

nchanwu

*Newbouldia laevis*

Bignoniaceae

Akoko, ogirisi,

Tree of life, fertility tree

Leaves, bark, root

Infertility, hernia, elephantiasis, yellow fever,

14 Phytochemicals - Source of Antioxidants and Role in Disease Prevention

migraine, roundworms, cough, dysentery,

earache, stomachache

aduruku

*Morinda lucida*

Rubiaceae

Oruwo, eruwo, eze

Brimstone tree

Leaves, stem bark,

root bark

ogu, njisi

*Mentha piperita*

Lamiaceae

Mintii

Peppermint

Whole plant

Mouth wash, stomach ache, respiratory

infections, chest pains

Anticancer, malaria, heart diseases, jaundice,

flatulence, diuretic, emetic

*Lawsonia inermis*

Lythraceae

Laali, lali

Henna plant

Leaves, bark,

Spermatorrhea, malaria, astringent,

gonorrhea, ulcers, jaundice, skin diseases,

menorrhagia

flowers

These are the largest group of secondary metabolites made of ammonia compounds comprising basically nitrogen bases synthesized from amino acid building blocks having various radicals substituting one or more of the hydrogen atoms in the peptide ring, containing mostly oxygen [21]. The compounds have basic properties and are alkaline in reaction, turning red litmus paper blue. In fact, one or more nitrogen atoms that are present in an alkaloid, typically as 1°, 2°, or 3° amines, contribute to the basicity of the alkaloid. The degree of basicity varies considerably, depending on the structure of the molecule, presence, and location of the functional groups [22]. They react with acids to form crystalline salts without the production of water [21]. Alkaloids exist majorly in solid states as atropine, liquids containing carbon, hydrogen, and nitrogen.

**1.10. Saponins**

with a lipophilic triterpene derivative [33].

hypertension which usually leads to stroke [35].

**1.11. Anthraquinones**

and in dye production [37].

**1.12. Glycosides**

Saponins are a class of phytochemicals present in abundance in numerous species of plants. They are specifically amphipathic glycosides and are grouped phenomenologically by their production of soap-like foaming when shaken in aqueous solutions (phenomenology—study of structures of consciousness as experienced from the first-person point of view). They are grouped structurally by possession of one or more hydrophilic glycoside moieties combined

Phytochemicals—God's Endowment of Curative Power in Plants

http://dx.doi.org/10.5772/intechopen.77423

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Two major groups of saponins exist which are steroid and triterpene saponins. Saponins are insoluble in ether but soluble in water, and on hydrolysis, they give aglycones like glycosides. They cause hemolysis of blood and cattle poisoning as they are known to be extremely poisonous (27). Apart from causing irritation to mucous membranes, they have a bitter and acrid taste. They are soluble in alcohol and water but insoluble in solvents like benzene and n-hexane that are organic and nonpolar; therefore, they are mostly amorphous in nature. Saponins are therapeutically important because they lower bad fats in the body (hypolipidemic) and have

Saponins are known to produce inhibitory effect on inflammation [34]. Saponins help in lowering cholesterol which will subsequently reduce the risk of cardiovascular diseases such as

Anthraquinones are phenolic and glycosidic compound derivatives and are solely derived from anthracene leading to the production of variable oxidized derivatives like anthrones and anthranols [36, 21]. Industrially, anthraquinones are used for washing of bowels (laxatives)

Glycosides are the condensation products of sugars (polysaccharides inclusive) with different varieties of organic hydroxyl (occasionally thiol) compounds. Glycosides are colorless, crystalline water-soluble plant constituents found in the cell sap. Glycosides chemically contain a carbohydrate (glucose) and a noncarbohydrate part (aglycones or genin) [27, 21]. Glycosides can be readily hydrolyzed into its components with mineral acids as they are neutral in reaction and are purely bitter principles commonly found in plants of the family Genitiaceae. The action of the bitters on the gustatory nerves results in increased flow of saliva and gastric juices [27, 21]. Some of the bitter principles due to the presence of tannic acid are either used in restricting flow of blood (as astringents), function in the reduction of thyroxin, and thereby regulate cell metabolism and growth or as antiprotozoal. Examples of glycosides include cardiac glycosides which act on the heart and anthracene glycosides act as purgative and for treatment of skin diseases, while chalcone glycosides are used as anticancer agents [22]. The extracts of plants containing cyanogenetic glycosides have been reported to be useful as

anticancer potentials. Saponins work in synergy with the cardiac glycosides [22].

Alkaloids are mostly readily soluble in alcohol but are sparingly soluble in water though their salts are usually soluble in water. Their solutions are usually very bitter; alkaloids defend plants against herbivores and pathogens and are used widely as stimulants, narcotics, pharmaceuticals, and poisons because of their biological potencies [23]. Alkaloids, in nature, are found in large quantities in the seeds and roots of plants and mostly in combination with vegetable acids. Alkaloids are useful as central nervous system (CNS) stimulants and anesthetics in pharmacological applications [23].

Alkaloids also find its usefulness as pain relievers [24]. Atropine is an alkaloid used widely in medicine as an antidote to organophosphate poisoning, while caffeine stimulates CNS and respiratory systems. Caffeine also serves as an antidote to barbiturate and morphine poisoning, while emetine (from *Cephaelis ipecacuanha*) root is useful in the treatment of protozoal infections, for example, amoebic dysentery.
