chapter  15
Nature’s Gift to Photodynamic Medicine: Hypericin, a Herbal Photosensitizer, Is a Component of Hypericum perforatum
Pages 6

Photodynamic medicine includes both photodynamic diagnosis (PD) and photodynamic therapy (PDT) and is rather a new alternative method for clinical detection and therapy of cancer and other ailments. Their basic effects on microorganisms, however, have been known since about 100 years (Ackroyd et al., 2001). The use of light in combination with a pharmacological substance (photosensitizer) that can be activated by light is an attractive combination and led to an impressive number of scientic studies up to now. PDT fulls the requirements for a successful cancer therapy such as selective destruction of neoplastic formations and minimal toxicity towards healthy tissue (Dougherty et al., 1998). In the presence of oxygen, the photosensitizer produces cytotoxic reactive oxygen species (ROS) upon light activation at a wavelength matching its absorption maximum and a reaction is initiated by which the photosensitizer is capable of transferring the energy to the desired reactants. Because of their highly oxidative nature, the generated ROS eventually cause the destruction of tumor tissue (Brown et al., 2004). But what has this got to do with phytomedicine? Most of the photosensitizers are of synthetic origin and are based on

15.1 Introduction .................................................................................................. 279 15.2 Hypericum perforatum Extract: From an Herbal Antidepressant to the

Multifaceted Photosensitizer Hypericin .......................................................280 15.3 The Zurich Experience in Hypericum perforatum Extract and on Hypericin .................................................................................................280 15.4 Outlook ......................................................................................................... 282 References .............................................................................................................. 282

porphyrins or chlorins. More recently, however, hypericin was found to be the phototoxic component of Hypericum perforatum or St John’s wort and was subsequently considered a promising herbal photosensitizer. This is in harmony with history. Plants have been widely used in past times through intake and/or local application of their extracts to cure dermatological ailments under in¤uence of sunshine. This has been prevalent for more than 3500 years rst in ancient Egypt and later in India and in China (Wyss, 2000). We have to acknowledge that exact parameters of light dosage, serum concentration of phototoxic plant components, and other characteristics were not known in the early times. However, the principle of healing with light in combination with herbal extracts in medicine has been established a long time ago. In the future, based on white light, there could well be a renaissance under considerably improved conditions.