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Self-heal extract inhibits estradiol via aryl hydrocarbon receptor

A few days ago we wrote about the anti-oestrogenic extracts in the tropical bush Bassaiopsis glomerulata, which have made their way into the bodybuilding supplement Triazole. Triazole also contains extracts of the self-heal plant [Prunella vulgaris, shown below], commonly found in Europe. In 2009 American cancer researchers published a cell and animal study in which they worked out how this substance works.

The researchers, who were funded by the American government to study herbal preparations that more and more women are using, discovered during a screening that extracts of Prunella vulgaris have an anti-oestrogenic effect. Then they looked more closely at the preparations.

The researchers exposed cells with estradiol receptors to DES, a synthetic oestrogen, and to the Prunella vulgaris extract [PV]. DES boosted the synthesis of the enzyme alkaline phosphatase, but Prunella vulgaris inhibited its synthesis. At a concentration of 50 micrograms per millilitre the extract was almost as effective as the anti-oestrogen fulvestrant [ICI]. Its trade name is Faslodex. Doctors use this to treat breast cancer.

The researchers implanted hormone-sensitive cells from humans in mice and injected them with estradiol [E]. When the mice drank tea made from Prunella vulgaris, the growth of the implanted cells halved.

How Prunella vulgaris inhibits the effect of estradiol was elucidated in experiments with estradiol-sensitive cells. In these experiments the extracts stimulated the synthesis of the enzymes CYP1A1 and CYP1B1. The first enzyme converts estradiol into 2-hydroxy-estradiol, and the second converts it into 4-hydroxy-estradiol. Both metabolites are considerably less active than estradiol, but 4-hydroxy-estradiol is an oncological worry. 4-Hydroxy-estradiol makes estradiol carcinogenic: metabolites of 4-hydroxy-estradiol can damage the DNA.

Cells synthesise more CYP1A1 and CYP1B1 if compounds interact with the aryl hydrocarbon receptor. This receptor recognises poisonous substances and reacts to them by increasing the production of detoxifying enzymes such as CYP1A1 and CYP1B1. These also deactivate estradiol. The extracts of Prunella vulgaris stimulate the aryl hydrocarbon receptor, the researchers discovered. The addition of 3-methoxy-4-nitroflavone [MNF], which blocks the aryl hydrocarbon receptor, deactivated the plant extracts.

We mentioned the word 'cancer' above. We don't think that taking supplements that contain Prunella vulgaris increase the risk of cancer. Nearly all plant extracts contain compounds that inhibit the potentially risky CYP1B1 or occupy it in some way so that it doesn’t manage to get round to transforming estradiol. This piece of wisdom is based on research done on another herbal oestrogen blocker: Ginkgo biloba. [J Steroid Biochem Mol Biol. 2006 Aug;100(4-5):167-76.]

Like Prunella vulgaris, ginkgo activates the aryl hydrocarbon receptor and thus stimulates the breakdown of estradiol via the enzyme CYP1A1. Ginkgo, however, also activates the 'bad' enzyme, CYP1B1. This is probably not such a problem. Polyphenols in gingko, like isorhamnetin, kaempferol and quercetin, are powerful inhibitors of that enzyme. [Toxicol Appl Pharmacol. 2006 May 15; 213(1): 18-26.]

The person who dreamt up Triazole was pretty clever.

Biol Reprod. 2009 Feb;80(2):375-83.

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