Hypericin Explained

Hypericin is a naphthodianthrone, an anthraquinone derivative which, together with hyperforin, is one of the principal active constituents of Hypericum (Saint John's wort).^{[1] [2]} Hypericin is believed to act as an antibiotic, antiviral and non-specific kinase inhibitor. Hypericin may inhibit the action of the enzyme dopamine β-hydroxylase, leading to increased dopamine levels, although thus possibly decreasing norepinephrine and epinephrine.

It was initially believed that the anti-depressant pharmacological activity of hypericin was due to inhibition of monoamine oxidase enzyme. The crude extract of Hypericum is a weak inhibitor of MAO-A and MAO-B.^{[3] [4]} Isolated hypericin does not display this activity, but does have some affinity for NMDA receptors. This points in the direction that other constituents are responsible for the MAOI effect. The current belief is that the mechanism of antidepressant activity is due to the inhibition of re-uptake of certain neurotransmitters.

The large chromophore system in the molecule means that it can cause photosensitivity when ingested beyond threshold amounts. Photosensitivity is often seen in animals that have been allowed to graze on St. John's Wort. Because hypericin accumulates preferentially in cancerous tissues, it is also used as an indicator of cancerous cells. In addition, hypericin is under research as an agent in photodynamic therapy, whereby a biochemical is absorbed by an organism to be later activated with spectrum-specific light from specialized lamps or laser sources, for therapeutic purposes. The antibacterial and antiviral effects of hypericin are also believed to arise from its ability for photo-oxidation of cells and viral particles.

Hypericin derives from cyclisation of polyketides.^{[5] [6]}

The biosynthesis of hypericins is through the polyketide pathway where an octaketide chain goes through successive cyclizations and decarboxylations to form emodin anthrone which is believed to be the precursor of hypericin. Oxidization reactions yield protoforms which then are converted into hypericin and pseudohypericin. These reactions are photosensitive and take place under exposure to light and using the enzyme Hyp-1.^{[7] [8] [9] [10] [11]}

Notes and References

1. Web site: Mehta . Sweety . Pharmacognosy of St. John's Wort . Pharmaxchange.info . 2012-12-18 . 2014-02-16.
2. Web site: Hypericin: the active ingredient in Saint John's Wort. September 18, 2006. Oubre. Alondra. 1991. https://web.archive.org/web/20070928004046/http://www.delano.com/ReferenceArticles/Hypericin-Active.html . September 28, 2007 .
3. Thiede. H. M.. Walper. A.. October 1994. Inhibition of MAO and COMT by hypericum extracts and hypericin. Journal of Geriatric Psychiatry and Neurology. 7. Suppl 1 . S54–56. 10.1177/089198879400700114. 0891-9887. 7857510. 208042437 .
4. Bladt. S.. Wagner. H.. October 1994. Inhibition of MAO by fractions and constituents of hypericum extract. Journal of Geriatric Psychiatry and Neurology. 7. Suppl 1 . S57–59. 10.1177/089198879400700115. 0891-9887. 7857511. 23531061.
5. A Review of the Hypothetical Biogenesis and Regulation of Hypericin synthesis via the Polyketide Pathway in Hypericum perforatum and Experimental Methods Proposed to Evaluate the Hypothesis . Loren W. Walker . 1999 . 2011-01-04 . 2019-06-26 . https://web.archive.org/web/20190626021123/http://www.l2w.cc/pages/HYPE/index.htm . dead .
6. Polyketide Biosynthesis . Christian Hertweck . Angew. Chem. Int. Ed. . 2009 . 48 . 26 . 4688–4716 . 10.1002/anie.200806121 . 19514004.
7. Karioti A, Bilia AR . Hypericins as potential leads for new therapeutics . Int J Mol Sci . 11 . 2 . 562–594 . 2010 . 20386655 . 2852855 . 10.3390/ijms11020562 . free .
8. Falk H . From the Photosensitizer Hypericin to the Photoreceptor Stentorin- The Chemistry of Phenanthroperylene Quinones . Angew. Chem. Int. Ed. Engl. . 38 . 21 . 3116–3136 . 1999 . 10556884 . 10.1002/(SICI)1521-3773(19991102)38:21<3116::AID-ANIE3116>3.0.CO;2-S.
9. Bais HP, Vepachedu R, Lawrence CB, Stermitz FR, Vivanco JM . Molecular and biochemical characterization of an enzyme responsible for the formation of hypericin in St. John's wort (Hypericum perforatum L.) . J. Biol. Chem. . 278 . 34 . 32413–32422 . 2003 . 12799379 . 10.1074/jbc.M301681200 . free.
10. Michalska K, Fernandes H, Sikorski M, Jaskolski M . Crystal structure of Hyp-1, a St. John's wort protein implicated in the biosynthesis of hypericin . J. Struct. Biol. . 169 . 2 . 161–171 . 2010 . 19853038 . 10.1016/j.jsb.2009.10.008 .
11. Murthy HN, Kim YS, Park SY, Paek KY . Hypericins: biotechnological production from cell and organ cultures . Appl. Microbiol. Biotechnol. . 98 . 22 . 9187–9198 . 2014 . 25301586 . 10.1007/s00253-014-6119-3 . 17487401 .