Coumarins and coumarin in phytotherapy

See also: coumarin in cosmetics

Coumarins are a family of natural substances widely distributed in the plant world. From a chemical point of view, these are derivatives of 5,6-benzo-2-pyrone, better known as coumarin.

The term coumarin derives from the Coumarona odorata, a legume from South America from which the molecule was first isolated back in 1820.

In the plant world, coumarins can be found both in free and glycosidic form, that is, linked as an aglycone to a sugary part. The great structural heterogeneity of these substances reflects an equally wide pharmacological-therapeutic variability.

Coumarins with phlebotonic action

The adjective phlebotonic belongs to all substances capable of increasing venous tone. Aesculin - coumarin glycoside present in horse chestnut leaves (aglycone esculetina) - decreases the permeability of capillaries (anti-edema action) and increases their resistance, improving the functionality of the vascular pathways also thanks to anti-inflammatory virtues. The same coumarin, which abounds in the flowering tops of the Sweet Clover, has shown strong anti-edematous properties in animal models; it is no coincidence that this drug is suggested, in association with flavonoids, in treatment and prophylaxis of venous insufficiency and its manifestations.

Coumarins with anticoagulant action

When, at the end of the 19th century, North American breeders introduced sweet clover (sweet clover) to their pastures and to feed their livestock, a "hemorrhagic epidemic soon appeared, which only a few years later was discovered to be linked to the use of this new forage.

During the drying of the clover, in fact, the coumarin undergoes a series of chemical transformations - partly spontaneous and partly mediated by fungi of the genus Aspergillus - which ultimately originate dicumarol. This substance interferes with the blood clotting process by blocking the vitamin k-dependent synthesis of certain clotting factors. Its derivative, warfarin, is currently used as an oral anticoagulant in the therapy of deep vein thrombosis and as a prophylaxis of pulmonary embolism and heart attack in patients with atrial fibrillation or with artificial heart valves. The same goes for another coumarin derivative, acenocoumarol, the active principle of Sintrom with a similar profile of use.

Coumarins with spasmolytic action

An example of vegetable substances with hypotensive and spasmolytic properties - therefore capable of inhibiting the spastic contraction of gastro-enteric and genito-urinary smooth muscles associated with cramp-like or colic-type pains - is given by coumarins of Viburnum prunifolium (scopoletine) and "Angelica" ("essential oil extracted from the roots).

The coumarins of Visnaga (kelina or visnadina) concentrate their spasmolytic action at the level of the smooth muscles of the coronary vessels; it is no coincidence that this plant is known for its anti-anginal properties.

Coumarins with antibacterial and antiviral action

The umbelliferone present in the aerial parts of Pilosella and in the resins of many Umbelliferae - in addition to being used as a sunscreen - has shown interesting antibiotic properties, especially against Brucella, the etiological agent of Brucellosis. The aforementioned esculetin, on the other hand, exhibits properties bacteriostatic and antifungal, while daphnoretine and 3-phenylcoumarins showed anti-hepatitis B and anti-HIV properties, respectively.

Coumarins with anti-inflammatory action

The coumarin of Sweet Clover promotes healing and tissue regeneration, thanks to the anti-edema, capillarotropic and stabilizing properties of the erythrocyte membrane (counteracts the increase in vascular permeability, a very important element in inflammatory phenomena). Esculetin, on the other hand, inhibits the synthesis of prostanoids (prostaglandins, thromboxanes and leukotrienes), molecules involved in asthmatic, allergic and inflammatory reactions.

Coumarins with photosensitizing action

Two coumarins typical of Bergamot, bergapten and psoralen, and more generally the other 6,7-furan-coumarins such as xanthoxine, have a marked photosensitizing action (they enhance the skin action of ultraviolet rays, in particular those responsible for tanning ). For this reason they are used in the so-called photodynamic therapy, used to stimulate skin pigmentation in vitiligo and to a lesser extent in psoriasis and alopecia areata. This practice consists in the oral administration or in the topical application of photosensitizing coumarin preparations, followed by exposure. to UVA radiation (320-400 nm).

Side effects of coumarins

Particular caution should be taken in the use of dried coumarin-based herbs, due to the aforementioned ability to produce dicumarol in particular situations (see fermentation of Sweet Clover). For obvious reasons, these preparations are absolutely contraindicated in patients on anticoagulant therapy (coumadin , sintrom) or antiplatelet (aspirin, clopidogrel, etc.). It must be said, however, that coumarin and other coumarins in themselves do not possess noteworthy anticoagulant activities, so on the phytotherapeutic level they should not be confused with dicumarol and its applications Therapeutic. Devil's claw, boldo, fenugreek and Chinese angelica are examples of coumarin drugs for which important episodes of drug interaction have been reported, with increased anticoagulant activity of drugs such as warfarin.

High doses of bergapten - coumarin characteristic of the essential oil of bergamot and citrus fruits in general - are mutagenic and carcinogenic; moreover, they seem to be responsible for the inhibitory activity on the CYP3A4 isoform of cytochrome P450, characteristic of grapefruit juice (which for this reason reduces the metabolism of many drugs, increasing their therapeutic activity with the risk of side effects from overdose). Due to their photosensitizing properties, 6,7-furan-coumarins are contraindicated in case of prolonged exposure to sunlight, due to the risk of photo-dermatitis, burns and melanomas.

Among the coumarin derivatives, the aflatoxins produced by molds of the genus Aspergillus starting from coumarins, play a very important toxicological role, because they significantly increase the risk of primary liver cancer. Coumarin itself is moderately toxic to the liver and kidneys.

Finally, due to their potential toxicity, coumarins are contraindicated in pregnancy and lactation.

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