Mushroom Biochemistry and Medicinally Active Compounds
Many articles in the press and papers in science journals extoll the health benefits of particular mushrooms such as shiitake or reishi. However many of the compounds in these mushrooms that are being extolled are common to all mushrooms. Here is a brief description of some of them. For the most up to date research use the internet.
The mushroom cell wall is made of a layer of chitin, a layer of mannoproteins and sandwiched between them chains of ß-glucans. ß-glucans are complex polysaccharides with sugar and protein side groups. They have been shown to have a beneficial effect on the human immune system.
The precise structure of these ß-glucans varies from species to species, principally in the way the side groups are attached to the main chain. They are refered to as ß-(1-3)-glucans, ß-(1-4)-glucans, ß-(1-6)-glucans, etc. The numbers denote which carbon atoms in the sugar molecules are linked to form the ß-glucan chain. The ß-glucan polysaccharides from a number of mushrooms have been extracted and used to create drugs for cancer treatment, eg: PSK and PSP from Coriolus versicolor, Lentinan from Lentinula edodes, Sizofran from Schizophyllan commune, grifolan and maitake D-fraction from Grifola frondosa.
Mushroom ß-glucans, also known as mushroom polysaccharides, have been shown to restore normal immune function by increasing interferon-y and TNF-ß production, increasing activation of NK cells, macrophages and cytotoxic T-cells, reducing IL-4 production and inhibiting prostaglandin synthesis.
Other mushroom polysaccharides, with similar health properties, include mannans, galactans and mannogalactans.
Mushroom polysaccharides prevent oncogenesis, show anti-tumor activity through the activation of immune response, prevent tumor metastasis and improve recovery from the side effects of conventional therapy.
Ergosterol and Vitamin D
Inside the cell wall is the cell membrane. This is a phospholipid layer containing ergosterol. Ergosterol is a precursor to vitamin D2 and is converted to vitamin D2 by ultra-violet light, i.e. sun light. Just 5 minutes exposure to sunlight has been shown to increase vitamin D levels in mushrooms, and levels increase with longer exposure.
In the human intestine chitin from the mushroom cell membrane is converted to chitosan. This helps bind bile salts which influences the digestion and absorption of fats.
The cell wall and cell membrane are structural components of all mushroom cells so all mushrooms have ß-glucans, chitin and ergosterol.
Mushrooms produce compounds called secondary metabolites as by-products of primary metabolism. Secondary metabolites are not necessary for the growth of the mushroom. These accumulate over the life of the mushroom and do not degrade easily.
There are many medicinally active secondary metabolites which vary from species to species. There are toxins such as phalloidin, orellanin, gyromitrin and muscarin, hallucinogens such as psilocybin, antibiotics such as penicilin, antioxidants such as selenium compounds, statins such as lovostatin and so on.
An important group of secondary metabolites are lipids known as terpenes, mostly triterpenes in fungi. These have antioxidant and anti-inflammatory properties, inhibit histamine production and also exhibit a complementary effect with ß-glucans on the immune system. Triterpenes are bitter tasting compounds. Mushrooms high in triterpenes, such as Reishi Ganoderma lucidum, taste particularly bitter.
Bitter tasting foods have recently been found to have beneficial effects simply by virtue of being bitter. The bitterness increases the blood supply to the gut, without affecting blood pressure, to prepare it for the arrival of food and aid digestion. Many pathogens, such as bacteria, also taste bitter. The bitter taste stimulates the immune system in readiness for an attack.
These molecules, including phenolic acids, are a group of secondary metabolites from fungi and plants, secreted for protection against UV light, insects, viruses and bacteria. Phenolic compounds are an important groups of secondary metabolites because of their multifunctional properties. These compounds provide protection against several chronic diseases such as cancer, brain malfunction and several cardiovascular illnesses. Phenolic compounds have been largely recognized as natural molecules with anti-inflammatory effects.
Natural statins, in the form of lovostatin, are found in many mushrooms, such as oyster mushrooms Pleurotus spp. and chestnut mushrooms Agaricus bisporus. Lovostatin is a potent inhibitor of HMG-CoenzymeA reductase, the main rate limiting enzyme in cholesterol production. Consequently, mushrooms with lovostatin can help lower cholesterol. Dietary fibre, which in mushrooms comes from compounds such as ß-glucans, chitin and hemicellulose will also influence cholesterol formation.
Ergothioneine (Ergo) is a sulphur containing derivative of the amino acid histamine produced only by fungi and bacteria. It is a stable antioxidant that was first discovered in the fungus Ergot at the beginning of the 20th Century. It is found in many edible mushrooms including Oyster, Shiitake and Chestnut Mushrooms. It cannot be synthesised by animals and is only available from dietary sources.
In humans, Ergo has been shown to accumulate in various cells and tissues at high concentrations (100 μM to 2 mM), most abundantly in erythrocytes, bone marrow, liver, kidney, seminal fluid and the lens and cornea of eyes.
Ergo has been shown to possess numerous antioxidant and cytoprotective effects, including free radical scavenger activity, radioprotective properties, anti-inflammatory actions and protection against UV radiation or neuronal injury. The molecular mechanisms underlying these cytoprotective actions still remain largely undetermined. Ergo has also been shown to inhibit the nitration of proteins and DNA.
GABA, gamma-aminobutyric acid, is one of the major inhibitory neurotransmitters in the central nervous system and suppresses peripheral sympathetic neurotransmission. An important role for GABA in both central and peripheral nervous system is control of blood pressure. GABA also has an immune-amplifying role in neuroinflammatory diseases such as multiple sclerosis. It is found in many mushrooms especially Oyster, Cordyceps and Common Inkcaps.