14. Can poisonous plants or addictive substances, such as coffee, wine, spirits, etc., belong to the category of medicinal drugs?
c. In some cases, in moderate doses.
15. Find the matching pairs from among the expressions below.
a. essential oil b. fatty oil c. alcohol extract d. tar e. activated carbon
A. tinctura B. carbo C. aetheroleum D. pix E. oleum
16. Find the matching pairs from among the most common morphological expressions below.
a. cortex b. flos c. folium d. fructus e. herba f. radix g. rhizoma h. semen
A. rhizome B. grass, flowery stem C. bark D. leaf E. root F. seed
G. fruit H. flower
17. Which drug name is an example of what? a. Digitalis lanatae folium b. Calcatrippae flos c. Cardui mariani fructus
A. The drug name preserved an older plant name. B. Since there are several similar species, the plant’s full Latin name is used. C. An older drug name is preserved.
2.5. 5. Can herbs be carcinogenic (cause cancer)?
Many herbs contain carcinogenic substances, and food plants also have a 5-10% ratio of carcinogenic material. Wheat, maize, peanut, celery and different mushrooms are full of such substances. But what is more important is that they contain anti-cancer substances as well, such as Vitamin C and E, beta carotene, or the pro-vitamin of Vitamin A, etc. Fats, as in fast food, increase the risk of cancer, while fibres reduce it. Cereals, fresh fruit, and vegetables contain lots of fibre and very little fat. Where there is a hereditary cancerism in the family, there has to be caution as regards herbs, too.
Angelica is anti-cancerous, but the psoralene in it is carcinogenic. It means that an isolated active ingredient may be carcinogenic, but we never take it separately: all the substances in the plant go to the herbal infusion, and it is their combined effect that counts. Therefore it is misleading to say that certain active ingredients or elements have an unfavourable effect.
When for example one takes comfrey (Symphytum officinale), the risk of cancer is no greater than when one eats the following foods: a slice of peanut butter bread, one third of a mushroom, half a glass of a soft drink with artificial sweetener; even one hundredth of a bottle of wine or beer can be dangerous, and ethyl alcohol is also carcinogenic. In a series of experiments, laboratory animals that were given feed containing high quantities of comfrey for two years started developing cancerous tumours. Patients who regularly took greater quantities of comfrey for four months or two years respectively, eventually suffered from serious liver damage. For this reason, comfrey is prohibited in Canada. It was noted, however, that taken in the prescribed doses and for the right period, it never caused any problem. We do not take even our favourite food exclusively for years, and prescription drugs also have proper doses and application times. Thus it should not surprise us if certain herbs cannot be taken for more than a few weeks because of possible side-effects. In such cases we can continue the treatment with a different herb having different effects.
The infusion of raspberry (Rubus) contains considerable amounts of tannin, although milk neutralizes it. Raspberry leaves contain tannin, which is carcinogenic, but bearberry (Arctostaphylos uva-ursi), mullein (Verbascum), coffee, tea, mate and black pepper also contain tannin, which is held to be one of the causes of laryngeal cancer. It is no coincidence that people in Britain usually drink tea with milk, thus counteracting one of the most common side-effects of tea-drinking.
Eugenol can also be carcinogenic in allspice (Pimenta dioica), just as in clove (Syzygium aromaticum). Estragole contained in tarragon (Artemisia dracunculus) may theoretically be harmful but no cases of estragole poisoning have ever been reported.
Common coltsfoot (Tussilago farfara) has been banned in the United States because it supposedly may cause liver cancer, but the same herb is prescribed in Germany. It is true that it can cause some liver damage following illness or in case of alcoholism.
Several addictive substances and some spices have markedly positive and negative effects – coffee, tea, cocoa, coke, hop and turmeric, just to name a few. Their consumption is however not banned. Obviously, one has to know the most about what one eats and at the same time one has to be aware of one’s sensitivities.
2.6. 6. Active ingredients
In more recent textbooks, active ingredients (biologically active substances) are classified into a biogenetic system but due to practical reasons, their categorization may vary.
In the biogenetic system, substances are classified into the following five categories according to the five main metabolic pathways: saccharids, phenoloids, polyketides, terpenoids and azotoids. We hereby give a slightly more practical classification, used in most textbooks on medicinal and aromatic plants. In order to give a general overview and directions for practical application, this will suffice, given that the subject of the present textbook is not the chemistry of biologically active substances.
Saccharids, or carbohydrates. They are the primary products of photosynthesis. These natural organic compounds consist of carbon, hydrogen and oxygen atoms. They are vitally important for all human and animal organisms. Their anti-inflammatoryproperties are well-known.
This category comprises different sugars, starch, mucilage, inulin, pectine and tree-gum. Sugar alcohols are derived from simple sugars, or monosaccharides (glucose, fructose). Derivatives consisting of two or more component sugars are called oligosaccharides. Derivatives consisting of more than six (or more than ten, according to some sources; classification is rather subjective) component sugars are called polysaccharides. They can be homo-polysaccharides, like starch that consists of glucose units, or inulin that consists of fructose. Products of the partial break-down of starch are called dextrines.
Mucilage is often classified into this category although it may contain uronic acid besides simple sugars. Pectines are hetero-polysaccharides that consist of different kinds of simple sugars and contain some uronic acid. Tree-gum belongs to this category, which is usually produced as a result of pathological processes.
Glycosides may well be classified under the group of carbohydrates because one or more sugar molecules (glucose, galactose, rhamnose, mannose) are bound to a non-carbohydrate moiety (aglycone). They are water-soluble, solid, usually crystalline, organic compounds. They are bitter and have a characteristic aroma, nitrogenous ones are more toxic. Glycosides regulate heart function, are diuretic, laxative and diaphoretic.
The aglycone bound to the sugar molecule can be:
Alcoholic or phenolic OH group (O-glycosides).
Organic carbon atom (C-glycosides).
Their classification according to the aglycone part is as follows:
Cyanogenic glycosides. Phytogenic hydrogen cyanide (prussic acid) is toxic. Such examples are amigdalin in almond, peach and abricot, durrin in sorghum and Sudan grass.
Anthraquinone glycosides. They are special substances with a laxative effect, such as the active ingredients in senna and rhubarb, as well as glucofrangulin.
Steroidal glycosides or cardiac glycosides. These molecules are bound to a steroidal nucleus and contain a 5- or 6-membered lactone ring. These glycosides are found in the plant generaDigitalis, Helleborus, and Adonis.
Thioglycosides (Isothiocyanates). They are often volatile compounds, like the glycoside of mustard oil or sinalbin, sinigrin in crucifers, which break down into allyl izothiocyanate, sulfur, and nitrile.
Irridoid glycosides. They often have a bitter taste, e.g., the active ingredients of some bitter materials.
Some classifications mention indoglycosides, such as indigo.
Some lists mention non-nitrogenous glycosides, among them saponins and plant dyes. They are classified according to another system. They are the following:
Saponins (molecules with a steroidal skeleton or a triterpene skeleton) are surfactants, they produce a soap-like foam when shaken in aqueous solutions. They cause hemolysis, e. g., the saponin of Medicago alfalfa and corncockle.
Glycoretines, such as convolvulin.
Plant dyes, such as flavons and anthocyanes, e. g., luteolin, rutin, quercetin.
Other substances of undefined structure, such as vincetoxin, bryonin, and ononin
Alkaloids. They are natural compounds that contain nitrogen and combine with acids into salts. They have very strong effects. Compounds which contain nitrogen in the heterocycle and originate from amino acids are called true alkaloids. Protoalkaloids are compounds that also originate from amino acids but contain nitrogen in an aliphatic chain. Pseudoalkaloids are alkaloid-like compounds that do not originate from amino acids but contain nitrogen.
They are strong poisons, usually affecting the nervous system. They are stimulant, excitant, stupefacient and analgesic. Alkaloids are classified into major groups by their structure but we will rather list them by their common natural source, e.g., the given plant families.
- Liliaceae. Protoveratrine, colchicine and tulipin, which is similar to aconitin.
Essential oils. Essential oils are always mixtures and never homogeneous, therefore their classification is purely practical, e. g., ethereal oils, terpenes, camphors. They can be extracted by steam distillation; they are usually lipophilic and not miscible in water; they are nitrogen-free. They are digestant and bactericid. Solid or soft resins are produced from the liquid balm after the essential oil has been volatilised. Substances that are produced from essential oils usually by freeze distillation are called “camphors” in Hungary.
Characteristic ingredients of essential oils:
Monoterpenes that contain ten carbon atoms, most of which originate from geranyl-pirophosphate. Open-chain monoterpenes, e. g., myrcene, ocymene. Their alcohol derivatives are linalool and geraniol, their aldehyde derivative is citral. Cyclic monoterpenes such as menthol and carvone are produced by the cyclisation of the proto-compound.
Sesquiterpenes contain 15 carbon atoms; farnesol is an open-chain and camasulen is a cyclic sesquiterpene.
Non-terpene compounds, terpene intermediates, phenyl propane derivatives such as cinnamic aldehyde, anethole, asarone, methyl chavicole, etc.
Tannins (tannic acid, tannin). Their composition is complex; nowadays the name is used as a collective term. Some of them are derivatives of gallic acid or its derivative ellagic acid and D-glycose (the glycoside of glycose combined with tannic acids), others are catechin derivatives. Catechin tannic acids are often red, they are called phlobaphenes. The term “tannic acid” can be misleading because most of them do not contain a carboxyl group.
Their name comes from their being used for “tanning” by the leather industry. They are chemically heterogeneous phenoloids. They have an acrimonious taste and they are water-soluble. They are astringent, haemostatic and helpful in treating enteritis. The most common plants that contain high levels of tannic acid are oak, birch, heather and horse-chestnut.
Bitter materials. Their composition is unclear. They are partly water-soluble, bitter tasting, nitrogen-free substances. They are used for flavouring, preserving and colouring, they are appetitive and digestant.
Organic acids. These compounds can be found in almost all medicinal herbs. The most common organic acids are oxalic acid, citric acid, malic acid, tartaric acid, formic acid, amber acid. Salicylic acid is febrifuge, silica acid strengthens the immune system. Silica acid is contained in horse-tail, lung-wort, knot-grass, hemp-nettle, elm bark, etc.
Fat, fatty acids, waxes. Fats and fatty acids are contained mostly in fruits. Such fruits are cocoa beans, coconut, castor-oil bean, linseed, sunflower seed, etc. They differ from essential oils in that they are not volatile and are easy to dissolve in organic solvents (benzine, ether, chloroform, etc.).
Waxes are usually contained in buds, leaves and fruits of overseas plants. They are solids.
Plant dyes, flavonoids. They are substances of various structures, often bound to sugars, therefore they can also be classified as glycosides. This category comprises flavonoids, isoflavonoids, neoflavonoids, flavones, flavanones, anthocyanidin, proanthocyanidin, apigenin, silybin, chlorophyll and carotenoids. The pharmaceutical and chemical industries use them for their colouring properties. Biologically active flavonoids such as the antispasmodic apigenin and the liver-protecting silybin are often called bioflavonoids.
Milky latex. It is essentially an emulsion of the cell-fluids. It is white or yellow and may contain essential oils, resin and alkaloids. In water it swells into a sticky solution or a sticky mass. Chemically they are not uniform substances. Milky latexes of euphorbia, poppy, composite and asclepiad species are all of differing composition.
Vitamins. They are substances of different chemical compositions that are indispensable for the normal functioning of the body. Their deficiency causes diseases.
Antibiotics. According to more recent research, they occur not only in low plant forms but in some high plants as well, among others in garden-cress and other pepper wort species (Lepidium crassifolium or cartilegineum), horse-radish and celery. Antibiotics inhibit the growth and reproduction of micro-organisms and sometimes they even kill them. The best known are phytoncydes, from which allicin is contained in garlic. It has a very strong bactericidal effect, it kills even tubercle bacilli.
2.7. 7. The function of active ingredients in the vegetable kingdom
Growth regulation. E. g., the inhibition of the development of a given tissue structure, the impeding of leaf growth, the reduction of the cross-section of carrier tufts, the inhibition of germination.
Protective function. It only appears in plants attacked by some fungus. Their effect mechanism is not yet clear.
They inhibit intake (antifeddants). E. g., the azotoids of the Solanaceae family inhibit to varying degrees the growth and viability of Colorado beetle larvae. The larvae grow properly and are viable on potato and tomato, while their mortality rate is much higher on related wild species, although the species survives.
Repellents. E. g., essential oils of lavender flowers are repellents, that is why they are often used as moth repellents.
Insecticidal effect. E. g., nicotine in tobacco (Nicotiana tabacum), which was in effect used to make insecticides. It has such strong effects that nicotine-based insecticides have been banned for decades (except in the United States). The effect of pyrethrum (Chrysanthemum cinerariaefolium) was already known to the Romans and they used it as a flea powder. Since warm-blooded organisms are unaffected by it, its use is very safe. Unfortunately the active substance is unstable in light, therefore agrochemical producers manufacture pyrethrum-based insecticides with a stabilizing agent.
Attracting enemies of pests. In the case of bean and maize, they found compounds that were secreted by the plants after pest damage and sent signals to enemies of the pests. Before pest damage, these active ingredients are untraceable in the undamaged plant. Western corn rootworms that appeared and proliferated in the last decade in Hungary are trapped by Cucurbitacin traps that are produced from Cucurbitaceae.
Allelopathy. Substances occurring in plants affect the growth and development of other plants and lower organisms. These substances are evaporated by plants, secreted through the roots, washed off by precipitation or they evolve from decayed plant parts. E. g., the foliage of walnut inhibits plant growth and germination, just like goldenrod and couch grass.
Attractants (attractive substances). The repellent lavender is an attractant towards species that pollinate it. Similarly, glycosides of mustard species are repellent to most insect pests but are attractant to cabbage-butterfly.
Reserve nutritives. Especially polysaccharides, like mucilage, which can accumulate up to more than 30% in the roots of e. g., marsh mallow.
2.8. 8. Factors affecting the production of active ingredients
The level of active ingredients of a medicinal herb depends on various factors that have to be taken into account when cultivating, collecting or using them. Changes may occur within genetically determined limits but there can be large differences even within a single species.
The accumulation of active ingredients (AI) may vary depending on the plant part, therefore only those parts should be collected that have a high AI content, which can be the root, the leaf, the flower, the fruit, the bark, or the whole plant. For instance, it is common knowledge that in the case of comfrey, it is the rhizome that yields the drug but harvesting it means killing the plant itself. It is more environmental friendly to harvest the leaves and the leafy stem. Although they are less effective than the decoction of the rhizome, their harvesting does not entail killing the plant; applying it more often we can compensate for the lesser effect.
Active ingredients may undergo qualitative changes in the course of the plant’s ontogenesis or even from one time of day to another. Therefore with each plant we should be aware whether, for instance, the fruit should be harvested unripe, half-ripe or fully ripe.
Extreme environmental conditions may cause shock in plants. External factors are those factors that limit to some extent the production of active ingredients compared to the optimum. External factors that may influence production are the following.