TANNINS

Tannins: IntroductionTannins: pale yellow to light brown-red amorphous substances widely distributed in plants and used chiefly in tanning leather, dyeing fabric, and making ink.

Their solutions are acid and have an astringent taste.

They are isolated from oak bark, sumac, and galls.

Tannins give tea astringency, colour, and flavour.

Tannins are used industrially to clarify wine and beer, reduce viscosity of oil-well drilling mud, and they have also had medical uses

Tannins are mainly found in the cell vacuoles or in the cuticle (here cells dont interfere with plant processes: only after death and cell breakdown do they become active in metabolic processes).

Tannins are phenolic glycosides.

TANNINSHistorically, the importance of tannin-containing drugs is linked to their tanning properties (ability to transform fresh hides into leather).

Today, tanning is achieved with mineral compounds, but for several millennia, it had required exclusively the used of plant products.

These included chestnut tree tannin (Castanea sativa L.), oak tannin (Quercus robar L) in Europe, but also, in other parts of the world, tannins from Anacardiacea (Quebracho Schinopsis spp), sumacs (Rhus spp), Legumes (acacias Acacia spp) or Combretaceae (myrobalans Terminalia spp).

Some of these tannins are still prized for leathers designed for specific uses (fine leather products).

Tannins - TanningThe consequence of tanning: formation of bonds between the collagen fibres of the hide (imparts resistance to water, heat and abrasion.)

This capability of tannins to combine with macromolecules explains why they precipitate cellulose, pectins and proteins; it also explains their characteristic astringency and tartness: by precipitating the glycoproteins contained in saliva, tannins make the latter lose its lubricating power.

Morocco Tanning Pits

Tannins - Definition water-soluble phenolics of molecular weight between 500 and 3 000, which, in addition to displaying the classic reactions of phenols, can precipitate alkaloids, gelatine, and other proteins.

A more recent definition of tannins: Phenolic natural products that precipitate proteins from their aqueous solutions.

True Tannins Vs Pseudo-TanninsTrue tannins: Molecular weights of 1000-5000.

Pseudo-tannins: Gallic acid, catechins and chlorogenic acid are similar phenolic compounds: have a low molecular weight.

Tannins: Microscopy

Classification of Tannins

Classification of TanninsIn higher plants, two groups of tannins are generally distinguished, which differ by their structure, as well as their biogenic origin hydrolysable tannins and condensed tannins.

Hydrolysable Tannins: EllagitanninsGallotannins

Hydrolysable TanninsHydrolyzable tannins are hydrolyzed by weak acids or weak bases to produce carbohydrate and phenolic acids.

Examples of gallotannins are the gallic acid esters of glucose in tannic acid, (found in leaves and bark of many plant species)

Hydrolysable TanninsThey may be hydrolyzed by acids or enzymes such as tannase, (products being sugar and phenolic acids). Formed by several phenolic acids which are united by ester linkages to a central sugar (glucose) molecule.

Hydrolysable tannins are therefore esters of a sugar and phenolic acid molecules.

The phenolic acid is

in the case of gallotannins gallic acid

in the case of ellagi-tannins hexahydroxydiphenic acid (HHDP) and its oxidized derivatives (dehydrohexahydroxydiphenic acid).Ellagitannins are found in Herb Robert (Geranium species, Meadowsweet and Oak bark).

Egs of Hydrolysable TanninsGallotannins: rhubarb, cloves, red rose petals, bearberry leaves, Chinese galls, Turkish galls, hamamelis, chestnut and maple

Ellagitannins: pomegranate rind, pomegranate bark, eucalyptus leaves, some Australian kinos, chestnut (Castanea spp), and oak bark.

Gallotannins

GallotanninsGallotannins are the simplest hydrolysable tannins, containing a polyphenolic and a polyol residue.Polyol: alcohol with multiple hydroxyl groups. Most of the gallotannins isolated from plants contain a polyol residue derived from D-glucose.

Some gallotannin structures

EllagitanninsWith more than 500 natural products characterized so far, ellagitannins are the largest group of known tannins.

Ellagitannins are formed from the gallotannins by the oxidative coupling of at least two galloyl units.

Condensed TanninsAre polymers of 2 to 50 (or more) flavonoid units that are joined by carbon-carbon bonds, which are not susceptible to being cleaved by hydrolysis.

All hydrolyzable tannins and most condensed tannins are water soluble - some very large condensed tannins are insoluble.

Condensed TanninsCondensed tannins are oligomeric and polymeric proanthocyanidins consisting of coupled flavan-3-ol (catechin) units.

(oligomeric or polymeric proanthocyanidins =condensed proanthocyanidins = condensed tannins).

Biosynthetically the condensed tannins are formed by the successive condensation of the single building blocks (up to more than 50 may be included in a single condensed tannin).

The coupling pattern of the catechin units in condensed tannins can vary considerably.

NOTE: Oligomeric: a polymer that consists of 2, 3, or 4 monomeres.

Polymer: Any of numerous natural and synthetic compounds of usually high molecular weight consisting of up to millions of repeated linked units, each a relatively light and simple molecule.

Condensed Tannins/ProanthrocyanidinsThey are not readily hydrolysed to simpler molecules and they do not contain a sugar moiety (unlike hydrolysable tannins).

On treatment with acids or enzymes, condensed tannins are converted into red insoluble compounds known as phlobaphenes.

Condensed Tannins/ProanthrocyanidinsPhlobaphenes give the characteristic red colour to many drugs such as red cinchona bark, which contains these phlobatannins and their decomposition products.

These tannins are therefore sometimes called catechol tannins (as they yield catechol).

Like catechol itself, their (condensed tannin) solutions turn green with ferric chloride.

Plants rich in Condensed Tannins

Barks: cinnamon, wild cherry, cinchona, willow, acacia (wattle, mimosa), oak bark, Hamamelis.

Flowers: Lime and Hawthorn

Seeds: cocoa, guarana, kola

Fruits: cranberries, grapes, hawthorn

Leaves Hamamelis, hawthorn, tea leaves (especially green tea)

Extracts and dried juices: catechu, acacia, East Indian kino and eucalyptus kino

Complex TanninsThe structures of the complex tannins are built up from a gallotannin unit or an ellagitannin unit, and a catechin unit.

Fig: Acutissimin A, the usual representative of the complextannins.

Tannins - PropertiesWater-soluble

Also soluble in dilute alkali, alcohol, glycerol and acetone

Slightly soluble in other organic solvents.

Solutions precipitate heavy metals, alkaloids, glycosides and gelatin.

Tannins - PropertiesIf a dilute ferric chloride solution is added to an aqueous extract of hamamelis leaves (containing both types of tannins), a blue colour is produced which then changes to orange-green as more ferric chloride is added.

Free gallic acid gives an orange colour with potassium iodate.

Tannin Properties: Hydrolysable or Condensed?

With ferric salts, gallo-tannins and ellagi-tannins give blue-black precipitates.

Condensed tannins give brown-green precipitates.

Condensed tannins turn red with vanillin and HCL.

Gallo-tannins give a pink colour with potassium iodate.

Ellagitannins react (are coloured) with nitrous acid in the presence of acetic acid. Colour reaction: pink purple blue.

TLC is used to analyze extracts (visualized under UV light and with the reagents mentioned above)HPLC can also be used.

Hamamelis leaf & barkSome drugs (e.g. tea, Hamamelis leaves and Hamamelis bark) contain both hydrolysable and condensed tannins.

Pseudo-TanninsPseudo-tannins are compounds of lower molecular weight than true tannins and they do not respond to the goldbeaters skin test.

Gallic acid: rhubarb Catechins: catechu, acacia cutch, many Australian kinos, cocoa, guarana and many other drugs containing condensed tanninsChlorogenic acid: coffee (particularly unroasted) and nux Vormica (a small quantity only).Ipecacuanhic acid: ipecacuanha

Tannin FunctionTannins are of wide occurrence in plants and are usually found in greatest quantity in dead or dying cells. They exert an inhibitory effect on many enzymes due to protein precipitation and, hence, may contribute a protective function in barks and heartwoods.

Tannin SourcesCommercial tannins, as used in the leather industry, are obtained from * quebrancho, wattle, and chestnut.

Pharmaceutical tannin is prepared from oak galls and yields glucose and gallic acid on hydrolysis. Many commercial samples contain some free gallic acid. Oak galls: pharmaceutical source of tannins

* Quebrancho BarkThe name quebracho is taken from two Spanish words quebrar and hacha, meaning "to break the axe."

The bark of Quebracho consists of a thick cork layer, traditionally used as a febrifuge.

It is also used to relieve dyspnea (difficult or laboured breathing e.g from emphysema and asthma).

The bark and especially heartwood are used for tanning hides.

Tannin IncompatibilitiesClove and cinnamon contain tannins and also other principal therapeutic constituents. This may complicate extraction or produce imcompatibilities with other drugs.E.g. Many alkaloids for example are precipitated by tannins.

Tannin ExtractionTannins are extracted using water and acetone.

Optimal yields are obtained from fresh tissues or freeze-dried tissues.

Optimal yields are not obtained from dried tissues (tannins are irreversibly combined with other polymers)

After eliminating the acetone (distillation), the pigments and lipids are removed from the aqueous solution by a solvent extraction.

Ethyl acetate extraction of the aqueous solution separates the dimeric proanthrocyanidins and most gallotannins.

Polymeric proanthrocyanidins and high molecular weight gallotannins remain in the aqueous phase.

To obtain pure compounds, the appropriate chromatographic techniques are used (most often one of the gel filtrations)

Followed by reverse-phase chromatography (in water and alcohol, or water, alcohol and acetone mixures)

Medicinal Properties of TanninsTherapeutic/medicinal activities result due to the astringency properties.Tannin containing herbs (drugs) will precipitate proteins.Externally: waterproof the external layers of the skin and mucosa: Protect underlying layers.Vasoconstrictor effects on small superficial vessels

Medicinal Properties of TanninsLimits fluid loss enhance tissue regeneration in superficial wounds and burns

Internally: Anti-diarrhoealAnti-septic effects (anti-bacterial/anti-fungal) used to Rx infectious diarrhoeas and dermatitis.

Anti-oxidant Activity of TanninsHydrolysable tannins (more so than condensed tannins) are free-radical scavengers.Inhibit superoxide ion formation.Some inhibit lipoxygenaseThey do not inhibit cyclo-oxygenase.

Anti-oxidant flavonols and proanthrocyanidins from grape juice and wine are widely considered to be the main principles responsible for the preventative effect of CVD.

Enzymatic Inhibition ActionTannins may act as enzyme inhibitors.

They block 5-lipoxygenase inhibit angiotensin converting enzyme hyaluronidase activation glucosyltransferases (of microorganisms involved in cavity formation).

New (Hydrolysable) Tannin PotentialTannins, including gallo and ellagic acid (epigallitannins), are inhibitors of HIV replication.1,3,4-Tri-O-galloylquinic acid 3,5-di-O-galloyl-shikimic acid, 3,4,5-tri-O-galloylshikimic acid punicalin Punicalagin

inhibited HIV replication in infected H9 lymphocytes with little cytotoxicity. Two compounds, punicalin and punicacortein C, inhibited purified HIV reverse Transcriptase.

TANNIN CONTAINING HERBS

Turkish GallsDefinition: Turkish galls (Turkey galls, Galla): Are vegetable growths formed on the young twigs of the dyers oak, Quercus infectoria (Fagaceae). They result from the decomposition of the eggs of the gall-wasp Adleria gallaetinctoriae. If the galls are not collected and dried, the mature insect bores out of the gall and escapes.

Turkish Galls: CollectionGalls are collected by peasants of Turkey and Syria.After collection they are graded according to colour into 3 grades: blue, green and white. These are then found on the London Market.

Colour changes occur due to enzymatic secretions of insect.

Turkish GallsHistory: Ancient writers recorded the use of an infusion to test for sulphate of iron, possibly the earliest mention of an attempt to detect adulteration by chemical means.

Turkish Galls Uses & Allied DrugsUsesUsed as a source of tannic acid.Tannic acid is used as an astringent and styptic.

Used for tanning and dyeing.Ink manufacturing.

Allied DrugsChinese and Japanese Galls

Hungarian Galls

Turkish galls - Constituents50 70% tannin gallotannic acid.Tannic acid: hydrolysable tannin (consisting of gallic acid and glucose).Gallic acidEllagic acidSitosterolStarch Calcium oxalateSyringic acid (CNS-active component)

Hamamelis LeafDefinition: Witch hazel leaves consists of the dried leaves of Hamamelis virginiana, Hamamelidaceae).

It should contain no less than 30% tannins.

Hamamelis Flowers

Witch hazel leaves Hamamelis ConstituentsGallitanninsEllagitanninsFree gallic acidProanthrocyanidinsBitter principlesVolatile oil

Hamamelis - UsesAstringentHaemostatic(Both due to tannins)

Hawthorn Crataegus monogynaDefinition: Hawthorn consists of the leaves, flowers and fruits of Crataegus monogyna, (Rosaceae).

Crataegus monogyna - ConstituentsProcyanidinsFlavonoidsHyperosideVitexin rhamnoside

Crataegus Uses and Allied DrugsUsesUsed as a mild cardiac tonic, especially elderly patients.Has no toxic effects (such as Digitalis, Convallaria, and Strophanthus).

Allied DrugsOther Crataegus species.

CatechuDefinition: Gambir or pale catechu is a dried aqueous extract prepared from the leaves and young twigs of a climbing shrub, Uncaria gambir (Rubiaceae).

It should be carefully distinguished from black catechu or cutch. The plant is Native to Malaysia and Indonesia.

Catechu: UsesUses in medicine as an astringent.

Catechu: ConstituentsCatechinsCatechutannic acidCatechu redQuercetinGambir-florescin

Catechu: Allied DrugsCutch or black catechu

KinosKino: applies to a number of dried juices, rich in phlobatannins. Were formally used for their astringent properties: diarrhoea (e.g. lozenges)

Include eucalyptus kino or red gum from Eucalyptus rostrata.

Pomegranate RindDefinition: Pomegranate consists of the fruit pericarp, or the stem and bark of Punica granatum.

Punica granatum - PunicaceaeHistory: Mentioned in Bible and Quran.Used as an Ancient Medicine (Indian and Arab physicians).

Pomegranate: Actions & UsesTherapeutic category: Anti-diarrhoeal, anti-helminthic.

Uses: Bark is traditionally used to treat worms.

Dried fruit rind or fruit pulp is used to treat diarrhoea.

Active Constituents: PunicaFruit: Gallo/ellagitanninsMainly punicalin and punicalagin

Alkaloids are present in the bark, leaves and young fruit. (no alkaloids are present in the rind).

Punica granatum: PomegranatePharmacological Effects: Anti-diarrhoeal effect Tannins

Anti-helminthic effect alkaloidsThey interact strongly with the nicotinic Acetylcholine receptors: cause tapeworms to lose their grip, and are expelled from the body.

NOTE: Alkaloids are toxic and self medication may be dangerous.

Punica granatum and AlzheimersResearch conducted on mice that were given pomegranate juice, experienced 50% less degeneration of brain cells, compared to their counterparts, who drank only sweetened water.

This indicates that pomegranate juice may help cut risk of Alzheimers disease.

Punica granatum & CV HealthTests showed that pomegranate juice reduced the effects of stress on human blood vessel cells by stimulating the production of nitric oxide. This chemical is thought to help keep arteries open and keep blood flowing.

Additional research shows pomegranate juice can both reverse and prevent atherosclerosis. Researchers say the beneficial effects of pomegranate juice on hardening of the arteries are likely largely due to its high antioxidant content. The study showed that the antioxidant level in pomegranate juice was higher than that found in other fruit juices, including blueberry, cranberry, orange, and even red wine.

Punica granatum & CancerDrinking 8 ounces of pomegranate juice daily can suppress prostate cancer activity in men with recurrent prostate cancer, according to a study presented at the annual meeting of the American Urological Association in San Antonio.

A recent study at the University of WisconsinMadison using a mouse model shows that consuming pomegranates could potentially help reduce the growth and spread of lung cancer cells or even prevent lung cancer from developing.

Camellia sinensis/Thea sinensisPolyphenols strong anti-oxidant effect.Leaves: cancer preventative (Japan).Clinical trials indicate that green tea helps to promote weight loss and treat hepatitis.May prevent tooth decay.Trials show a hypotensive effect.

NB: Green-tea: caffeine needed for effects.

Cardiovascular disease, principally heart disease and stroke, are the leading cause of mortality in both men and women in all racial and ethnic groups.

The risk of atherosclerosis is increased by high blood pressure, hypertension, kidney disorders, obesity, diabetes, smoking, excessive alcohol consumption, stress, thyroid and adrenal gland problems, and lipid disorders (Crespy and Williamson 2004)

Tea contains many compounds, especially poly-phenols and epidemiologically studies show that polyphenolic compounds present in tea reduces the risk of a variety of diseases.

Catechins are the main compounds in green tea; they consist of (-)-epicatechin, (-)-epicatechin-3-gallate (ECg), (-)-epigallocatechin, (-)-epigallocatechin-3-gallate (EGCg) etc. (Graham, 1992)

THERAPEUTIC VALUES OF TANNIN METABOLITESMice consumed wine rich in phenolic components as catechin, epicatechin, gallic acid, ellagic acid showed increased antioxidant activity.

Gallic acid (GA) also showed strong antioxidant activity by preventing lipid per-oxidation.

GA is a strong antioxidant that possesses antimutagenic and anticarcinogenic activities (Shahrzad et. al., 2001)

Green tea contains: (+) gallocatechin (GC),(-) epicatechin (EC), (-) epigallocatechin (EGC),(-) epicatechingallate (ECG), (-) epigallocatechingallate (EGCG) which shows numerous biological activities including antibacterial, antioxidant, anti-tumor and cancer preventive activities.

Catechin serve as powerful antioxidant against lipid per oxidation when phospholipid bi-layers are exposed to aqueous oxygen radicals.

(+)Catechin prevents cancer (liver, lung, breast and colon cancer) in at least one of three ways:First, they can prevent the formation of carcinogens, Second, they tone up the body's natural detoxification defenses, and Finally, they suppress cancer promotion. (+)Catechin has other promising qualities: antibacterial and antiviral agent, regulating cholesterol and blood pressure, and reducing blood clotting tendencies that may cause heart attacks or strokes