Medicinal, Non-medicinal, Biopesticides, Color- and Dye-Yielding Plants; Secondary Metabolites and Drug Principles; Significance of Medicinal Plants; Use of Medicinal Plants in the Systems of Traditional and Complementary and Alternative Medicines (CAMs)

Abstract

Medicinal plants are used in the treatment of different ailments. They cannot be distinguished from other plants by morphological characteristics except their pharmacological effects and contain therapeutic agents. Non-medicinal plants are morphologically similar to medicinal plants except some of the members produce active compounds that function either as poisons, pesticides, hallucinogens or teratogens. Poisonous plants produce poison, and pesticide plants are useful in pest management. Poisons and pesticides cause injury, illness, or death to a person if he tastes, smells, and gets it on skin or in eye by their local or systematic action or both. However, the boundary line between medicinal and non-medicinal poisonous, pesticide, hallucinogen plants, etc., is not sharply demarcated, e.g., Azadirachta indica, Malus sp., Prunus spp., Manihot esculenta, Abrus precatorius, Brugmansia sp., Cicuta douglasii, Colchicum autumnale, Datura spp., Digitalis purpurea, Nepenthes attenboroughii, Nerium oleander, Ricinus communis, Strophanthus gratus, Strychnos nux-vomica contain different bioactive compounds including azadirachtin, nimbin, amygdalin, linamarin, and lotaustralin (cyanogenic glycoside), abrin, ricin (ribosome-inactivating protein), aconitine (alkaloid), scopolamine, hyoscyamine, atropine (tropane alkaloids), solanine (glycoalkaloid), nerioside, oleandroside, ouabain (cardiac glycoside); saponins, strychnine (extremely bitter deadly alkaloid), etc. which may be used either as drug principles or poisons or toxins depending on dose and intention of use. Plant-derived pesticides like pyrethrin, rotenone, nicotine, strychnine, and scilliroside from Chrysanthemum cinerariifolium, Pachyrhizus erosus, Nicotina tabacum, S. nux-vomica, Drimia maritime, respectively, are widely used. Hallucinogens are psychoactive agents of natural origin and cause distortions in perceptions of reality (hallucinations) by disrupting the interaction of nerve cells and the neurotransmitter serotonin. Hallucinogens are mostly alkaloids, and mescaline, psilocin, psilocybin, ibogaine, LSD, etc. are some of the examples of common hallucinogen drugs. Topically active hallucinogens include solanaceous belladonna, henbane, mandrake, datura. Pollen from hundreds of weed, grass, and tree plant species, e.g., ragweed, maple, oak, Acacia, Bermuda grass, castor bean, red clover can trigger allergic reactions (allerginosis) in many people every year. Teratogens affect the development of an embryo, pregnancy or may cause a birth defect in the child. Diverse group of compounds, e.g., vitamin D, quinine, anagyrine, and other alkaloids aspirin, marijuana, cannabinols, etc., have shown teratogenicity compounds are synthesized by different plant of the genera including Lupinus, Veratrum, Conium, Astragalus, Nicotiana, Trachymene, Datura, Prunus, Sorghum, Senecio. Some of these plants also cause congenital defects. Natural color and dyes are obtained from plants, animals, or minerals without chemical processing. Roots, berries, bark, leaves, and wood of plants, as well as fungi and lichens, are the major natural sources. Many of the natural dyes like turmeric, annatto, and saffron are food additives and some have pharmacological effects and possible health benefits. The pharmacological effects of medicinal plants are mainly due to their secondary metabolites (e.g., alkaloids, terpenoids, phenolics, glycosides, antibiotics.) produced in the secondary metabolic pathways, which are often species specific, i.e., found in only a small set of species in a narrow phylogenetic group while the primary metabolic pathways and primary metabolites (e.g., carbohydrates, proteins, lipids, nucleic acids, and others) are ubiquitous in plant species. Innumerable numbers of medicinal herbs or their active therapeutic secondary metabolites are used in both traditional and modern systems of medicines. The secondary metabolites may be grouped as nitrogenous (e.g., alkaloids, non-protein amino acids, amines, cyanogenic glycosides, glucosinolates.) and non-nitrogenous (e.g., terpenoids, steroids, saponins, phenolics, flavonoids, polyacetylenes, polyketides, phenylpropanoids.) metabolites. Therapeutically important alkaloids include morphine and codeine from the opium poppy, cocaine from the coca plant, atropine from the deadly nightshade Belladonna, vincristine and vinblastine from the periwinkle, quinine from the bark of the cinchona, caffeine from coffee, tea, and cola plants, nicotine is present in tobacco. Monoterpenes are exemplified by the aromatic oils (e.g., menthol) contained in the leaves of some members of mint family, and pyrethroids are present in the flowers of Chrysanthemum; diterpenes paclitaxel (taxol) is found in bark of the Pacific yew tree; triterpenoids (plant steroids) phytoecdysones are a group of plant sterols are obtained from Tinospora, Asparagus; tetraterpenoids include important pigments (e.g., beta-carotene, lycopene) and are available in colored plant parts. Salicylic acid, a simple phenolic compound, can be obtained from the bark of white willow (Salix alba); isoflavones, lignin (complex phenolic macromolecule), anthocyanins, and anthocyanidins (phenolic pigments) impart pink and purple colors to flowers and fruits. Medicinal herbs include entire plant, plant parts, e.g., leaves, flowers, fruits, seeds, stems, wood, bark, roots, rhizomes, or other plant parts in entire, fragmented form as well as fresh juices, gums, fixed oils, essential oils, resins, etc. Herbal finished products include comminuted or powdered herbal materials, or extracts, tinctures, and fatty oils, and mixed herbal product. Finished and mixed herbal products may contain excipients in addition to the active ingredients. Herbal principles that have made valuable contribution to the development of modern medicine include ephedrine, digitoxin, salicin, reserpine, atropine, colchicine, quinine, codeine, vincristine, ipecac, physostigmine, sena, cocaine, capsaicin, scopolamine. Allamandin, helenalin, indicine-N-oxide, mezerien and laphacol, insulin effectors, boswellic acid, withanolides, ruscogenin, harpagoside, etc. are some therapeutically promising molecules identified recently from herbs. Artemisia annua provides new generation anti-malaria drug; bark of Prunus africana is useful for prostate cancer; Sutherlandia is important for its value to HIV/AIDS sufferers. Recent discovery like β-adrenergic and paclitaxel from Lingusticum wallichii and Taxus brevifolia, respectively, signify the role of plant as an inexhaustible treasure of modern medicines. Different traditional systems of medicine including the (i) Traditional Chinese, (ii) Ayurvedic, (iii) Unani, (iv) Homeopathy, (v) Siddah, (vi) Native North American Herbal, (vii) Western Herbal, (viii) Yoga, (ix) Naturopathy, (x) Folk medicine have been using hundreds of medicinal plants and other accessories in diagnosis, treatment, prevention, and elimination of physical, mental, or social imbalance since antiquity. Complementary and alternative medicine (CAM) is a non-mainstream medicine consisting of a wide range of healthcare practices, products, and therapies, e.g., homeopathy, naturopathy, chiropractic, magnetic field therapy, energy medicine, various forms of acupuncture, Traditional Chinese medicine, Ayurvedic medicine, Christian faith healing. Modern medicine is based on evidence and clinical proof and is practiced by medical graduates or postgraduates educated in medical college, institute, or university after completion of the prescribed medical curriculum in a stipulated period of time. Before the twentieth century, most medicines were extracted from plants (herbal medicines), and since the twentieth century, thousands of modern drugs have been synthesized from an organic compound. The active principles of herbal medicine are comparable with the contents of modern medicine, and many common drugs in use today were derived from herbal sources (e.g., aspirin from willow bark, digitalis from foxglove) and therefore, herbal medicine may not be considered as mere quackery. There are numerous advantages of herbal medicine including its effectiveness for long-standing health complaints irresponsive to traditional medicine, fewer side effects, safer to use over time, well tolerated by the patient(e.g., prescription drug vioxx-rofecoxib for arthritis was recalled due to increased risk of cardiovascular complications), inexpensive compared to modern drugs, and easy availability of herbs. However, herbal medicine and herbalist may not be proved effective for sudden, serious illnesses, serious trauma, appendicitis, or a heart attack as a conventional doctor using modern diagnostic tests, surgery, and drugs. Self-dosing with herbs, overdosing, misidentification of herbs from the wild source, interaction with prescription drugs, lack of quality assurance, etc. are some of the important disadvantages of herbal medicine.