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Silybum marianum monograph.

Botanic Name

Silybum marianum (family [Compositae] Asteraceae)

Common Names

St. Mary's thistle, milk thistle, holy thistle, old lady's thistle, lady's thistle, Mary thistle, Marian thistle, true thistle, Carduus marianus.

Botanical Description

Annual or biennial that grows to 2 metres. It bears dark green leaves that are mottled with white and have toothed spiny margins. There are numerous purple flowers in large spiny heads

(1)

The achenes (fruits/seeds) are 6-8mm long, 3mm wide and 1.5mm thick. They have an outer smooth surface that is also shiny. They are usually a greyish-buff colour but can be streaked dark brown that gives an overall colour ranging from pale greyish-brown to dark chocolate brown, tapering at the base and crowned at the apex with a pale yellow collar about 1mm high. When cut transversely they show a narrow, brown outer area and two large dense white and oily cotyledons. They have a slight odour and have a bitter, oily and unpleasant taste. (2)

Part Used

Fruits (often referred to as seeds'), herb. (3) Less commonly the aerial parts. (1)

Relevant Constituents

Silymarin, a complex of at least 7 flavonolignans (Figure 2). Silybin (Figure 3) is the principal component of silymarin, sometimes referred to as silibinin. Silybin makes up more than 50% of silymarin and is made up of a mixture of two diastereoisomers, silybin A and silybin B. (4)

According to Barnes, Anderson and Phillipson (3) the constituents of Silymarin marianum are as follows:

Constituents of the Fruit

Flavolignans--between 1.5-3% silymarin (approximately 50% silibinin(= silybin)) (Figure 3), silichristin, silidianin, silimonin, isosilichristin, isosilibinin, silandrin (Figure 4), silhermin, neosilihermins A and B, 2,3-dehydrosilibinin and tritopentamers of silibinin (silybinomers).

Flavonoids--quercetin, taxifolin and dehydrokaempferol.

Lipids--between 20-30% linoleic acid, oleic acid and palmitic acid.

Sterols--cholesterol, campesterol and stigmasterol.

Other constituents--mucilages, sugars (arabinose, rhamnose, xylose, glucose), amines and saponins.

Constituents of the Leaves

Flavonoids--Apigenin, luteolin and kaempferol and their glycosides.

Other constituents--P-Sitosterol and its glucoside, and a triterpene acetate.

Silymarin is not found in the leaves.

Preparation Methods

The flavolignans can be extracted by defatting the seeds to increase their yield. The results of this defatting is then subjected to high extraction temperatures. The flavolignans are both then soluble in ethanol and water and are relatively stable up to temperatures of 100[degrees]C. (6)

Silymarin that is available in tablet form may be quite variable in bio-available flavolignans. (6)

Silybum marianum is available as a liquid extract, capsule or tablet.

Quantified levels of silymarin are recommended, of at least 25mg/ml for ethanol extracts and 10g/ml for glycerol extracts. (7)

A number of clinical trials have used a capsule (Legalon) that has been standardised equivalent to 140mg of silymarin.

Historical Information

Silybum marianum has been used as a medicine since the fourth century BCE. (8)

Theophrastus (c. 371-c. 287 BCE) mentions akorna (milk thistle) in his Enquiry Into Plants Volume II. (9)

In W. H. S. Jones' translation of Pliny the Elder's (23-79 CE) Natualis Historia Pliny discusses some of the uses of milk thistle:

The leaves, flowers or seed of this plant are of help for the treatment of wounds inflicted by scorpions, poisonous spiders, and serpents; they are also good for griping colic'. (10)

Culpeper in 1653 considered Our Lady's Thistle to be under the influence of Jupiter and to be:

'... as effectual as Carduus Benedictus for agues, and to prevent and cure infection of the plague; as also to open obstructions of the liver and spleen; and thereby as good against the jaundice. It provokes urine, breaks and expels the stone, and is good for dropsy. It is effectual also for the pain in the sides and many other inward pains and gripings. The seed and distilled water are held powerful to all the aforesaid, and besides, it is often applied both inwardly to drink and outwardly with cloths or sponges to the region of the liver to cool the distemper thereof; and to the region of the heart, against swoonings and passions of it. It cleanses the blood exceedingly, and in the spring if you please to boil the tender plant (but cut off the pricks unless you have a mind to choke yourself), it will change your blood as the season changes, and that's the way to be safe, as to change as the times change is the way to live secure; and that flatterers and weathercocks know well enough.'. (11)

There is a tradition that the milk-white veins of the leaves originated in the milk of the Virgin Mary who once fell upon a thistle. This is where the name "Our Lady's Thistle" and the Latin derivation of the species arose. (12)

Milk thistle has been eaten as a vegetable, used as a remedy for snake bite, the plague, melancholy, malaria, rabies and internal griping. It has been applied externally for the treatment of cancer. (6)

William Boericke, the noted homoeopath, in his 1901 materia medica stated that milk thistle is to be:

'... centered on the liver and portal system causing soreness, pain and jaundice. Has specific relation to the vascular system. Abuse of alcoholic beverages especially beer. Varicose veins and ulcers. Diseases in miners, associated with asthma. Disturbs sugar metabolism. Influenza, when liver is affected. Debility. Haemorrhages, especially connected with hepatic tissue'. (13)

Medicinal Actions (Contemporary Usage)

Digestive tonic (14)

Hepatoprotective (14)

Hepatotonic (14)

Antioxidant (14)

Cholagogue (14)

Cytoprotective (14)

Hepatic trophorestorative (7)

Choleretic (7)

Anti-inflammatory (3)

Antifibrotic (3)

Antitumour (3)

Toxin blockade (4).

Chelates iron (4).

Brain and cardioprotective (4)

Nephroprotective (4)

Antidiabetic (4)

Galactagogue (6)

Medicinal Indications (Contemporary Usage)

Gall bladder disorders (14)

Liver insufficiency, toxicity or cirrhosis (14)

Hepatitis (14)

Jaundice and other skin conditions involving liver dysfunction (14)

Protection of normal cells during chemotherapy (14)

Hypercholesterolaemia (14)

Nausea of pregnancy (14)

Non-alcoholic and alcoholic liver damage or disease, including fatty liver (7)

Exposure to chemical pollutants and conventional drugs (7)

Dyspeptic complaints (7)

Amantia phalloides mushroom poisoning (15)

Psoriasis (16)

Pharmacokinetics

In humans silymarin absorption rate levels vary between 20% and 50%. (17) It is slowly absorbed in the small intestine and blood levels peak two hours after taking the oral dose and it has a half-life of around 6 hours. 5-7% of what has been absorbed is excreted from the kidneys. Most stays in the liver and is incorporated into bile. (6) It undergoes phase I and especially phase II metabolism (Figure 5), undergoing many conjugation reactions, forming glucuronides which can be detected in human blood plasma. (4)

It has been shown in studies involving healthy individuals and patients with hepatic cirrhosis that the bioavailability of silybin-phosphatidylcholine complex preparation (IdB 1016) is several times greater than that of silymarin. (3)

Silymarin is not water soluble and is therefore ineffective as a tea. It is best administered as a standardised extract of 70% to 80% silymarin. (16)

Pharmacodynamics

Most studies have been performed using a standardised silymarin preparation, or its major constituent, silybin. (18)

Hepatoprotective effect

Silybum marianum been shown in vitro and in vivo to protect against the following substances:

Carbon tetrachloride

Ethanol

Paracetamol-induced liver peroxidation

Cyclosporin

Phenothiazine

Butyrophenone

Erythromycin

Amitriptyline and nortriptyline

Oestradiol

Amantia phalloides

Tacrine

Iron overload

Benzo(a)pyrene induced lung cancer

The exact mechanism of action is not fully understood, but it is believed to be that toxin blockade, antioxidant and scavenging of free radicals are the most likely reasons. (4)

Antioxidant properties

Silymarin is an antioxidant and free radical scavenger. It interacts with the cell membrane to prevent any abnormalities in the lipid fraction that is in charge of maintaining normal fluidity. (19)

Stimulation of liver regeneration

In in vitro and in vivo experiments on liver of rats showed that silibinin increases protein synthesis in a liver that has had a piece removed. (19)

Toxin blockade

Silymarin and silybin alter the structure of the hepatocyte cell membrane and other constituents may bind to the hepatocyte receptors to inhibit the binding of toxins. (4)

Chelates iron

Both silymarin and silybin have demonstrated protective effects against hepatic iron toxicity in vivo. (4)

Nephroprotective properties

Silibinin that is injected into rats prior to the administration of cisplatin (chemotherapy drug) showed protection of glomerular and proximal tubular function. (3)

Anticancer activity

Silybin (0.1-20pmol/L) inhibited the growth of ovarian cancer cells in vitro. (3)

Anti-inflammatory activity

In a rat paw oedema test silymarin administered orally reduced footpad abscesses. (3)

Brain and cardioprotective effect

In rats silybin seems to have cell death preventing properties. (4)

Antifibrotic action

In in vitro models Silybin has shown direct and indirect antifibrotic properties. (17)

Metabolic effects

In rat hepatocytes, silybin lowers glucose formation by blocking the insulin-dependant glucose transporter 4. (17)

Gastric ulcer protective effects

Silymarin given orally to rats prevented gastric ulceration induced by cold-restraint stress. (3)

Anti-diabetic effect

Silybin has reduced glucose production in rat hepatocytes. (4)

Viral hepatitis

Human studies have shown that administration of silymarin shortens treatment time in both acute and chronic hepatitis. (19)

Hepatitis induced by toxins or drugs

Human studies have shown that the liver poisoned with Amantia phalloides, phenothiazines (antipsychotic drugs) and butyrophenones (antipsychotic drugs), silymarin reduces the hepatic damage. (19)

Psoriasis

Studies have shown that silymarin improves the liver's activity in removing endotoxine, inhibiting cAMP phosphodiesterase and leukotriene synthesis. (19)

Cholesterol lowering

In two studies on rats fed a high cholesterol diet, silymarin was shown to reduce their cholesterol levels. (4)

Effects on CYP450 enzymes

There are conflicting results from various studies on what effect silymarin has on CYP450 enzymes. The reported in vitro effects seem to have no clinical relevance in vivo. (4)

Relevance of Pharmacodynamics Research to Contemporary Usage

Traditionally milk thistle has been used for disorders of the liver, spleen and gallbladder, to stimulate milk production in lactating mothers, for haemorrhoids, for dyspepsia and as a demulcent for catarrah and pleurisy. (3)

Most studies tend to focus on the hepatoprotective activity of milk thistle and its treatment of liver damage and disease. (3)

There have been many studies and clinical trials, both in vivo and in vitro that have demonstrated that a standardised equivalent of silymarin can protect and regenerate liver cells. (3-4)

In clinical use silymarin has been used with success to treat dyspepsia, toxic liver damage, environmental toxins and drugs, hepatocyte repair, supportive treatment for chronic liver diseases, alcoholic liver disease, acute viral hepatitis and hepatitis C infection. (4)

The use of milk thistle seed extract (silymarin) for the majority of medicinal actions listed above has been studied and verified by many studies and clinical trials both in vivo and in vitro. For example Braun and Cohen (4) cite more than 60 studies into the clinical use of milk thistle.

The relevance of recent research on milk thistle has mainly concentrated on the effects of silymarin on the liver, to protect hepatocytes or repair any liver damage. More studies need to be carried out on other traditional uses of milk thistle leaf (opinion of the author).

Cautions

Should not be administered during pregnancy without professional advice. [14]

Considered safe and well tolerated at recommended dosage range. (4)

At high doses (>1500 mg/day) silymarin may cause a laxative effect. Gastrointestinal adverse effects such as bloating, dyspepsia, nausea, irregular stool and diarrhoea were the most commonly noted. A small percentage of patients in clinical trials suffered pruritis, headache, exanthema, malaise, asthma and vertigo. This was similar to placebo. (19)

Both human and animal studies have shown silymarin to be non-toxic. (16)

Contraindications

None known. (7)

Known allergy to Asteraceae plant family (14)

Dosage

Dose per day           Dose per week

4.5-85 ml of 1:1       30-60 ml of 1:1
liquid extract (7)     liquid extract (7)

4.5-85 ml of 1:1       30-60 ml of 1:1
glycetract (7)         glycetract (7)


Capsule containing Silybum marianum dry fruit 7.2g standardised equivalent to silymarin 140mg. One capsule three times a day which may be reduced to twice daily as a maintenance dose. (20)

References

(1.) Van Wyk B-E, Wink M. Medicinal plants of the world an illustrated scientific guide to important medicinal plants and their uses. Portland: Timber Press; 2004.

(2.) British Herbal Medicine Association. Scientific Committee. British herbal pharmacopoeia : pharmacopoeia. British Herbal Medicine Association; 1996.

(3.) Barnes J, Anderson LA, Phillipson JD. Herbal medicines. London; Grayslake, IL: Pharmaceutical Press; 2007.

(4.) Braun L, Cohen M. Herbs & natural supplements : an evidence-based guide. Sydney: Churchill Livingstone/Elsevier; 2010.

(5.) JavedS, Kohli K, Ali M. Reassessing bioavailability of silymarin. Alternative Medicine Review. 2011 Sep;16(2):239-49.

(6.) Fisher C. Materia medica of Western herbs. [Nelson, N.Z.]: Vitex Medica; 2009.

(7.) Bone K. A clinical guide to blending liquid herbs: herbal formulations for the individual patient. Edinburgh: Churchill Livingstone; 2003.

(8.) DerMarderosian A, Beutler JA. The review of natural products : the most complete source of natural product information. 6th ed. St. Louis, Mo.: Wolters Kluwer Health: Facts and Comparisons; 2010.

(9.) Theophrastus, Hort SA. Enquiry into plants and minor works on odours and weather signs. London: William Heinemann; 1931.

(10.) Pliny, T. E. (1956). Natural History. (W. H. S. Jones, Trans.) (Vol. 7). London: William Heinemann.

(11.) Culpeper N. English physician enlarged. London: Folio Society; 2007.

(12.) Grieve M, Leyel CF, Marshall M. A modern herbal: the medicinal, culinary, cosmetic and economic properties, cultivation and folk-lore of herbs, grasses, fungi, shrubs & trees with all their modern scientific uses. New York: Dover Publications; 1982.

(13.) Boericke W. New manual of homoeopathic materia medica and repertory: including Indian drugs, nosodes, uncommon remedies, relationship, sides of the body & drug affinities. New Delhi: B. Jain Publishers; 2005.

(14.) Thomsen M, Gennat H. Phytotherapy: desk reference : a clinical handbook. Hobart: Global Natural Medicine; 2009.

(15.) Skidmore-Roth L. Mosby's handbook of herbs & natural supplements. St. Louis, Mo.: Elsevier Mosby; 2010.

(16.) Silybum marianum Monogragh. Alternative Medicine Review. 1999;4(4):272-4.

(17.) Loguercio C, Feste D. Silybin and the liver: From basic research to clinical practice. World Journal of Gastroenterolgy. 2011 May 14;17(18):2288-301.

(18.) WHO. WHO monographs on selected medicinal plants Volume 2. [Internet]. Geneva: World Health Organization;2002 [cited 2012 Mar 6]. Available from: http://site.ebrary.com/id/10040306

(19.) Ghosh A, Ghosh T, Jain S. Silymarin--A Review of the Pharmacodynamics and Bioavailability Enhancement Approaches. Journal of Pharmaceutical Science and Technology. 2010;2(10):348-55.

(20.) Madaus GmbH. (2011). Legalon [Packaging label]. Germany.

(21.) Heinrich M, Barnes J, Gibbons S, Williamson EM. Fundamentals of pharmacognosy and phytotherapy. Edinburgh; Toronto: Churchill Livingstone; 2004.

John Power | DRM, student Australian College of Natural Therapies, Advanced Diploma of Naturopathy, ATMS member 24618.
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Date:Mar 1, 2014
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