PSK Background

The medicinal mushroom, Coriolus versicolor has been used in traditional Chinese and Japanese medicine for centuries. Coriolus versicolor (also known scientifically as Trametes versicolor, and Polystictus versicolor, and by the common names of Yun Zhi in China, Kawaratake in Japan and Turkey’s tail in North America), belongs to a class of traditionally used mushrooms known as Basidiomycetes. Of the 20,000 species recorded, Coriolus versicolor is best known commercially for its medicinal applications1.

Coriolus versicolor contains active substances that belong to a class of immune-modulators known as biological response modifiers (BRM) or immunomodulators whose therapeutic effects are derived from their capacity to stimulate key effector pathways of the immune system. Coriolus versicolor is visible by its characteristic fan-shape leathery body marked with concentric shades of colour, and it is commonly found year round growing as overlapping clusters with a fruiting body on tree trunks and dead trees particularly in the wooded temperate climates of China, Japan and North America.

Coriolus versicolor has been traditionally harvested, dried, ground and reconstituted as a tea. The extract is recorded as being a remedy for treating a variety of symptoms associated with liver dysfunction and respiratory tract infection and for generally promoting a healthy body and spirit (Compendium of Materia Medica, AD1590), Vol 28, pp19-21(reprint edition), China Press, Beijing). In recent times, the extract is best known in Japan for use as an adjunct in the treatment of gastric and colorectal cancer.

The known therapeutic benefits of Coriolus versicolor led Japanese researchers in 1971 to isolate an active substance from shelf mushroom or cultured mycelia2. The substance was identified as a proteoglycan (also called a polysaccharopeptide) and the given name is polysaccharide-Krestin (PSK). PS-P (Polysaccharide-Peptide)3,4. was later isolated from a Chinese strain of Coriolus versicolor around 1983. Both PSK and PSP are produced (in Japan and China, respectively) in commercial quantities by fermentation of the mushroom to the mycelium stage. The mycelium biomass is then extracted with hot water and the active substance isolated by precipitation.

PSK was commercialised under the name Krestin on the Japanese market and was ranked 19th on the list of the world’s best selling medications with an annual sale in Japan worth US$357 million4. It is used primarily as an adjuvant immunotherapeutic agent in combination with standard cancer treatments such as chemotherapy, radiotherapy and surgery.

Since its discovery in 1971, over 350 scientific and clinical studies have been published demonstrating its potential benefits to a variety of diseases, especially cancer5. Similar work has been performed in China with PSP4. For simplicity in the following description, PSK has been used as a general term to include both PSK and PSP.