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Scientific basis of Herbalism




Scientific Basis of Herbalism



As the plant kingdom evolved, different plants developed different strategies to protect themselves from a range of predators from brontosaurs to micro-organisms, and to attract assistance in reproduction. Many of these strategies were chemical: the plants became poisonous or bad-tasting to various types of predator, or sent out scents that attracted insects and other potential pollinators. Plants also developed a wide range of biochemical processes to carry out their natural functions of growth, energy conversion, and reproduction. The substances evolved in these manners necessarily have biochemical effects on animals. When humans arose, we were able to observe and test these effects, and realized that careful preparations and dosages of many plants, even some that are poisonous in their natural state could, properly applied, be useful medicines. Here I have listed, with examples, a number of the major types of pharmaceutically effective herbal chemical components: alkaloids, phenols, ketones, esters, aldehydes, iridoids, lactones and coumarins, saponins, and terpenes and terpenoids (including hydrocarbons, alcohols, sesquiterpenes, and carotenoids).

 Alkaloids

 

Opium Poppy (Papaver somniferum)

The alkaloids (a wide-ranging group of natural compounds containing basic nitrogen atoms) are generally thought to have evolved as poisonous deterrents to animals and insects. Many of the strongest herbal constituents, including a number which are still used in medicine today, are alkaloids. These include, among many others, morphine and codeine (from the opium poppy), quinine, atropine (from deadly nightshade, Atropa belladonna), scopolamine, cocaine, and ephedrine. Many alkaloids, such as the opiates, nicotine, cocaine, and caffeine, have a psychoactive effect as well as a physical one upon humans.

Alkaloids are often also responsible for both the short- and long-term toxicity of some herbs. For instance, coltsfoot (Tussilago forfara) and comfrey (Symphytum officinale) both contain pyrrolizidinic alkaloids, which can cause liver damage if taken in excessive quantities and/or over long periods of time; hence most herbalists no longer recommend that these herbs be taken internally. The higher concentration of pyrrolidizinic alkaloids in ragwort (Jacobaea vulgaris, also known as Senecio jacobaea) is the source of both this plant’s bitter taste and the well-known danger eating ragwort poses to horses and cattle.

Phenols

Clove and Tyme

Cloves & Essential oil (Syzygium aromaticum) Thyme (Thymus vulgaris)

The phenols (organic molecules with a fundamental structure of a hydroxyl group bound to an aromatic hydrocarbon ring) are an aromatic group of active compounds. These were probably evolved to discourage predation at both macro- and micro- levels, and to attract pollinating insects by scent. The phenols are highly volatile and often make up a large part of the characteristic scent of a plant or essential oil as well as producing medicinal effects.

Thymol (found in thyme) and eugenol (the chief component of the essential oil of cloves) are phenols noted for their effectiveness as disinfectants, antiseptics, anti-fungals, and anti-bacterials. Many of the major cannabinoids (medicinal and psychoactive components of cannabis) are also phenols, as is salicylic acid (a natural analgesic found in, for instance, meadowsweet and white willow bark, and the precursor to aspirin).

Ketones

Spearmint

Spearmint (Mentha spicata)

The ketones (organic molecules with a fundamental structure of an oxygen atom double-bonded to a central carbon atom) are another aromatic group of active compounds. Like the phenols, ketones are quite volatile, may form a large part of the plant or oil’s characteristic scent, and often produce medicinal effects.

Camphor (camphor tree, feverfew, and some of the artemesias and lavenders) and carvone (the main constituent of oil of spearmint; also found in the oils of caraway and dill; soothes stomach and intestinal cramping and gas and assists digestion) are two ketones which are both well-known and easily recognised by scent and taste.

Esters

Pine and Rosemary

Pine (Pinaceae) and Rosemary (Rosmarinus officinalis)

Esters are produced by the reaction of an oxoacid with a hydroxyl compound (such as an alcohol or a phenol), generally formed with a group to either side of a C-O bond. These groups may differ; some are straight-chained, some have an aromatic or cyclic structure. Most natural fats and oils are fatty acid esters; many of the esters found in plants have a low molecular weight and are aromatic, penetrative, and significant components of aromas, essential oils, and the herb’s medicinal effect. One of the best-known herbal esters is borneol acetate, an aromatic ester which is the source of pine needles’ scent and the pinelike element of the aromas of rosemary and thyme. Bornyl esters are also found in valerian roots, where they provide one component of the plant’s sedative effect; pine oil and thyme are both used as bronchial and nasal inhalants.

Aldehydes

Lemon balm

Lemon Balm (Melissa Officinalis)

Aldehydes are based around the carbonyl CO group, which is usually bonded to at least one hydrogen. The higher molecular-weight aldehydes are the source of many pleasant plant and essential oil aromas. Perhaps the best-known is citronellal, the chief constituent of citronella oil, which is also found in lemon balm and eucalyptus and has antiseptic, sedative, and insect-repelling qualities.

Iridoids

Valerian

Valerian in flower (Verbena officinalis)

Iridoids, based around a cyclopentanodihydropyran ring, are bitter-tasting defensive compounds, and the main source of what traditional herbalism calls the “bitter principle” (bitter-tasting herbs stimulate the release of gastrin, which in turn increases the production of digestive secretions such as bile, improving both appetite and digestion). Iridoidal glycosides (a sugar bonded to a non-carbohydrate structure) have been found to show antimicrobial and antileukemic activities; iridoidal glucosides (a glycoside derived from glucose) are diuretic and laxative; and valepotriates (a class of iridiodal alkaloid found in valerian root) are sedative.

Lactones and Coumarins

Elecampane root

Elecampane root (Inula helenium)

Lactones and coumarins are based around a closed ring with two or more carbons and a single oxygen molecule, with a ketone group =O bonded to one of the carbons on either side of the oxygen. Many lactones have strong mucus-moving/expectorant qualities; helenin, from elecampane root (Inula helenium), has antibacterial and antifungal effects as well, the combination of which with expectorant qualities makes elecampane one of the most useful herbs for dealing with persistent lung infections.

Sweet Woodruff

Sweet Woodruff (Galium odoratum)

Coumarins, found in meadowsweet, sweet clover, and sweet woodruff, among other herbs, are a form of bitter-tasting but sweet-scented lactone which have a number of physiological effects. They are precursors to a variety of anticoagulant drugs and rodent poisons.

Saponins

Hores chestnut and Liquorice

Horse Chestnut (Aesculus hippocastanum) & Liquorice (Glycyrrhiza glabra)


Saponins are plant glycosides with water-soluble sugars attached to a lipophilic steroid or triterpenoid, producing a soaplike foam in water-based solutions and lowering surface tension. Saponins are found in many food plants, including soybeans, asparagus, eggplants, green peppers, onions, and tea; and in a number of herbs. Many of the herbs known as wound-healers, such as calendula (Calendula officinalis) and yarrow (Achillea millefolium) are very high in saponins, as are some of the best-known expectorants, such as liquorice.

Saponins have a huge range of pharmacological effects: adaptogenic and alterative/tonic (as found in the ginsengs); antifungal and antimicrobial; capillary-strengthening (aescin, from horse chestnuts), anti-inflammatory, cholesterol-lowering, hemolytic, hepatoprotective, hormone modulation, and immune system modulation and stimulation, among other things.

Terpenes and Terpenoids

Hps and Hemp flowers

Hops (Humulus lupulus) and Hemp flowers (Cannabis sativa)

Terpenes are molecules built up from varying numbers of isoprene units (C5H6) in either rings or linked chains. Terpenoids are chemically modified (by oxidation, changes in the carbon skeleton, etc.) terpenes. Terpenes are significant biosynthetic building blocks for almost every living creature: steroids, for instance, are biologically derived from the triterpene squalene. It is therefore unsurprising that plant terpenes are one of the major sources for the pharmaceutical effects of herbs on the human body.

In plants, terpenes and terpenoids are characteristically found in resins, and often comprise a significant part of the plant’s essential oil and aroma, as well as its pharmaceutical effects. The aroma and flavour of hops, as well as their sedative effect, comes largely from terpenes, including b-carophyllene. B-carophyllene is also found in cannabis (which is very closely related to hops) and is considered a cannabinoid because it binds to cannabis receptors in the brain; it is not psychoactive, but does have anti-inflammatory effects. Many of the elements of the characteristically powerful aroma of cannabis, as well as some of its varied pharmaceutical effects, are terpenes.

Hydrocarbons

Orange and Lemon Peal

Orange and Lemon Peels

Hydrocarbons (monoterpenes with a purely hydrocarbon-based functional group) include such compounds as limonene (the main constituent of the volatile oils found in fresh citrus peels, also present in caraway, dill, fir, and the mints; expectorant and sedative).

Alcohols

Peppermint oil

Peppermint & Peppermint essential oil (Mentha x piperita)

Alcohols are monoterpenes with a hydroxyl (OH) group attached. Significant herbal alcohols include geraniol (a significant part of the sweet odour in attar of roses and lemongrass, among other plants; an insect-attractant and a very strong antiseptic); menthol (the main constituent of peppermint oil; soothes digestive-tract cramping and gas, decongestant effect on the lungs, used topically for itching, pain, and as an antiseptic); and linalool (main constituent of essential oil of coriander; also found in the lavenders and bergamot, among many others; antiseptic, fungistatic, and sedative).

Sesquiterpenes

Ginger root

Ginger root (Zingiber officinale)

Sesquiterpenes are formed from three isoprene units; structure varying. In plants, these may serve as a chemical means of competition (black walnuts, for instance, produce sesquiterpenes which makes it difficult for other plants to grow near their roots), forms of pheromones which attract insects, an aspect of the plant’s “immune system” which defends it against fungal and microbial attacks, or a defense against insect predation.

Sesquiterpenes often affect human chemistry: for instance, chamazulene (found in the blue oils of German chamomile – 







Visit : 2664 2013-03-02 11:23:43
Lables Herbalism ، Herbal plnats ، ، Scientific Basis of Herbalism ، alkaloids ، phenols ، ketones ، esters ، aldehydes ، iridoids ، lactones and coumarins ، saponins ، and terpenes and terpenoids ، hydrocarbons ، alcohols ، sesquiterpenes ، and carotenoids ، ،
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