Proving that mushrooms are an essential part of the human diet
Definitions to consider while reading:
Antioxidant: Compounds that mitigate oxidation. Oxidation is a reaction that can produce free radicals, leading to cellular damage. Antioxidants such as thiols and ascorbic acid (vitamin C) terminate these reactions by donating electrons. To balance oxidative states, living organisms maintain systems with overlapping antioxidants such as glutathione, catalase, superoxide dismutase.
Blood-brain barrier: a filtering mechanism of the capillaries that carry blood to the brain and spinal cord tissue, blocking the passage of certain substances.
Cation chelator: a type of bonding of ions and molecules to metal ions. There is application of this in removing toxic metals from the body.
Glutathione: Glutathione is a tripeptide (cysteine, glycine, and glutamic acid) found in surprisingly high levels—5 millimolar—concentrations in most cells. Responsible for the following actions in the body: (Pizzorno)
Direct chemical neutralization of singlet oxygen, hydroxyl radicals, and superoxide radicals
Cofactor for several antioxidant enzymes
Regeneration of vitamins C and E
Neutralization of free radicals produced by Phase I liver metabolism of chemical toxins
One of approximately 7 liver Phase II reactions, which conjugate the activated intermediates produced by Phase I to make them water soluble for excretion by the kidneys
Transportation of mercury out of cells and the brain
Regulation of cellular proliferation and apoptosis
Vital to mitochondrial function and maintenance of mitochondrial DNA (mtDNA)
Lipid peroxidation: The oxidative degradation of lipids. It is the process in which free radicals “steal” electrons from the lipids in cell membranes, resulting in cell damage. (Wik)
Oxidative stress: disturbance in the balance between the production of reactive oxygen species (free radicals) and antioxidant defenses (Betteridge)
Pleurotus ostreatus – Oyster Mushroom
‘Constituentism’
I am not necessarily a fan of isolation and ‘constituentism’ in supplemental medicine – especially when a constituent has been isolated from its synergistic community of molecules from the whole plant or whole mushroom and is considered supposedly different than a pharmaceutical. Though, I do love to understand the individual constituents in organisms and how they work independently, in order to better understand how they work synergistically. There is also a greater understanding to be had of how animals, plants, fungi and bacteria all evolved together when we can explore specific plant and fungi constituent mechanisms with specific cellular receptors and transporters in the animal organism. A specific example of this is a compound called Ergothioneine (ERG). ERG is an amino acid derivative, specifically a crystalline betaine, derivative of histidine – the etymology explains; ergot- (found in ergot (fungus) thione- (double bond to a Sulphur) and -ine (amine containing)—basically a sulphur containing amine found in fungi. ERG is also found in Actinobacteria (gram positive bacteria that behave similar to fungi in soil, helping to decompose the organic matter of dead organisms so the molecules can be taken up by new plants, they even grow extensive mycelium like fungi and were in fact long believed to be fungi) and Cyanobacteria, commonly known as blue-green algea, (another abnormal bacteria that can actually obtain their energy from photosynthesis – they are the only photosynthetic prokaryote able to produce oxygen). (blankenfeldt)
Specific ERG transporters in the animal
We have evolved so closely with mushrooms that we have specific transporters and receptors uniquely for mushroom compounds. ERG is no exception. While we have a specific receptor for ERG, we cannot synthesize this molecule ourselves, and as I will describe later, we are discovering this compound is extremely important for human health. The ERG transporter, OCTN1, (gene: SLC22A4) is found specifically on erythrocytes, fetal liver and bone marrow, ileum of the small intestine, trachea, kidney, cerebellum, lung, monocytes, seminal vesicles and the lens and cornea of the eye (Halliwell). Interestingly, ERG transporter is concentrated in the mitochondria of cells – suggesting a role in protecting mitochondrial components from DNA damage (Paul, Halliwell). This transporter’s only known role is to sequester as much ERG within the cells as is available, and only cells with this transporter can absorb, distribute, and retain this compound (Grundermann). Researchers explored the effects when cells were depleted of this transporter, the results being that cells were more susceptible to oxidative stress, leading to mitochondrial damage, protein oxidation, and lipid peroxidation. Once taken up into the cell, ERG is extremely bioavailable and is retained for up to a month within the body.
Bioavailability of ergothioneine from mushroom consumption
Once consumed in the diet, whether it be the isolated molecule or from whole mushrooms, ERG is quickly absorbed into the blood stream. Human erythrocytes (red blood cells, RBC) contain 2-9 fold more ERG than plasma. Interestingly, concentration is lowest in early life (1-10yo), increases between 11-18yo and reaches maximum value of 3.7mg/100mL by age 18. In this study, subjects consumed 8g and 16g of mushrooms and increases in red blood cell ERG were observed. After 1 and 4hr of consumption, the 16g mushroom dose increased RBC ERG concentration compared to the control, and after only 2 hrs of 16g of mushroom consumption, RBC ERG concentration was significantly higher than the control. Variability in bioavailablity was due to genetic variations in the SLC22A4 gene (Heller, Kris-etherton, Beelman). Interestingly, mutations in the ERG transporter have been identified as a susceptibility factor for autoimmune disorders, such as rheumatoid arthritis and Crohn’s disease, as well as neurodegenerative disorders, such as dementia and Parkinson’s (Paul, Snyder).
Why do we care – Once ergothioneine is in the cell, then what happens?
Ergothioneine as an antioxidant and cytoprotectant: The distribution of ERG transporters may seem random, but on closer inspection, they seem to be present in tissues predisposed to high levels of oxidative stress and inflammation (Halliwell). In animal studies, animals who were completely deficient in ERG had higher levels of reactive oxygen species and were therefore more susceptible to oxidative stress. In vitro, ERG is a powerful scavenger of hydroxyl radical and has been shown to deactivate singlet oxygen at a higher rate than glutathione (Hseu, Servillo). Similar results were proven in vivo – rats supplemented with ERG had lower levels of lipid peroxidation and higher levels of glutathione and alpha-tocopherol. As one might surmise, ERG and glutathione seem to have an intimate relationship within the cell. Glutathione is considered the major intracellular antioxidant in almost all organisms and has important functions in detoxification and immune function. It has been proposed, based on current research, that ERG can help maintain GSH levels in the presence of oxidative burden by interacting with other cellular defense systems. The maintenance of glutathione tissue levels is important in maintaining health as depletion will impair immune function. Conveniently, mushrooms contain both glutathione and ERG. In fact, mushrooms have been observed to have higher GSH amounts than any vegetable or fruit. Grifola frondosa (Maitake), Hericium erinaceus (Lions mane), Pleurotus ostreatus (Oyster mushroom), Boletus edulis (porcini) and Lentinus edodes (shitake) containing the most, respectively (Kalaras). Considering the relationship between ERG and GSH in mushrooms, a correlation analysis found that mushrooms high in GSH were also high in ERG, specifically the caps or pileus of the mushrooms (kalaras). All this said, mushrooms are an important source for cellular antioxidants.
Cation chelator: ERG chelates divalent metal cations – specifically, Cu2, hg, Zn, Cd, Co, Fe, and Ni (Cheah, Song, Kerley). Binding these cations in the body may help prevent their participation in the generation of reactive oxygen species. For example, EGT has been found to protect DNA and protein against copper induced oxidative damage through formation of a redox-inactive EGT-Cu complex. Interestingly, the high levels of ERG in semen – due to the high concentration of ERG OCTN1 transporter on the seminal vesicles- have been shown to prevent Cu inhibition of sperm motility. There is more to be explored between the relationship of ERG and semen viability.
Ergothioneine, aging, and cognitive decline: As we age, we are more vulnerable to the oxidative stress and environmental toxins that slowly damage our DNA, making us more susceptible to neurodegeneration – one of many conditions associated with DNA damage from oxidative stress. Low levels of glutathione have been linked to certain neurodegenerative diseases including Parkinson’s disease (Wei, Shah). ERG was able to dose dependently enhance glutathione activity in the rat liver cytosol—leading researchers to postulate that declining ERG may play a role in age related decline of GSH and glutathione peroxidase. Furthermore, ERG levels were found to be lower in the elderly with early stages of dementia and in PD patients relative to age matched healthy controls (Cheah). In animal studies, oral administration of ERG protected neurons and preserved cognitive function following administration of toxic amyloid beta cisplatin or D-galactose. It is now understood that the presence of Octn1 transporter in the blood brain barrier is responsible for these neuroprotective actions. Captivatingly, researchers found that there is a direct relationship between whole blood and brain ERG levels following consumption (Cheah). It is rare for compounds to be bioavailable in this way and transported across the blood brain barrier so readily – even glutathione needs to be taken intranasal for treatment of neurodegeneration.
Ergothioneine human trial: uptake metabolism and effects
While there is undeniably a lack of human trials exploring the in vivo effects of ERG, a recent study from 2017 explored ERG uptake, metabolism, and effects on biomarkers of oxidative damage and inflammation in healthy human subjects (cheah, Tang). One of the most interesting aspects of ERG discussed in this particular article is that ERG is a tautomer. This means that it exists in two forms – thione and thiol. The thiol is a single bond to sulfur and the thione is a double bond to sulfur. The article explains that in animal physiologic conditions, ERG primarily exists as the thione tautomer – under circumstances of low stress in the body, ERG remains in its thione tautomer form and is not the first choice as an antioxidant, rather endogenous antioxidants like glutathione are preferred (glutathione is a primary antioxidant thiol in the body). When the cells undergo higher levels of oxidative stress, ERG transforms into its thiol tautomer form and is then used for extra support. Additionally, under levels of elevated stress, tissues have increased amounts of the ERG, supposedly by upregulating expression of the OCTN1 ERG transporter in response to inflammatory cytokines.
This study also found that ERG can be stored in the cells for up to a month. It is theorized that ERG is stored for an extended period of time following consumption until it is required as a stronger defense mechanism.
During administration of ERG, plasma levels significantly elevated, while whole blood levels steadily increased for up to four weeks after administration stopped (red blood cells could continue to take ERG up as needed), and the excretion of ERG in the urine remained low, indicating that ERG is absorbed and retained in the body after oral administration. While this study used pure ERG, other studies previously mentioned (Heller) prove this same high bioavailability of ERG from dietary mushrooms, and so I will consider this as true for dietary ERG.
Mushroom analyses of ergothioneine: Fruiting body or mycelium? Gilled mushrooms or polypore mushrooms?
ERG was highest in the fruiting body of Pleurotus ostreatus and in the mycelium of Pleurotus eryngii. Generally, fruiting bodies and mycelium contained different amounts of ERG, with Pleurotus genus containing the highest amounts overall (Chen). Among simple mushrooms, fruiting body of White Button had the least (1.4mg erg per 85g mushroom) and Portabella the highest (2.7mg erg per 85g mushroom). While among specialty mushrooms, Maitake had the least (16.3mg erg per 85g mushroom) and oyster the highest (26.4mg per 85g mushroom) (Dubost).
Fruiting bodies of gilled mushrooms, specifically the cap, contain the most ERG, while polypore mushrooms contain very small amounts. Interestingly, the mycelium of Ganoderma contains more ERG than the fruiting body, but still not as much as the fruiting bodies of Shitake, Matsutake, Oyster, and Maitake (Lee, Wang).
Extraction:
Hot water extraction is sufficient to extract ERG from mushrooms.
In a study that explored water extraction – temperature of water, ratio of water to mycelium and the extraction rate of ERG, the following information was found:
Most notable: at 85°C and 20:1 ratio of mycelium to water, the extraction rate of ERG was 91.2% – the least effective yield of ERG was at 78°C and a 20:1 ratio of mycelium to water. There was no difference in ERG concentration between 5 minutes and 120 minutes, so a long boil to extract EGR is not necessary (Zhang).
In Summary:
Ergothioneine is a water soluble compound that is most abundant in Oyster mushrooms. There are transporters on different tissues in the body that are highly specific to ergothioneine. Ergothioneine is readily absorbed into the blood after consumption of mushrooms and stored in tissues for up to 1 month. In times of excessive oxidative stress, ergothioneine is taken up by those tissues and used as an antioxidant. Of note: there are transporters on the blood brain barrier and there is an association with low ergothioneine and age-related cognitive decline. In a world full of environmental toxins that are mostly impossible to escape, we might as well eat more mushrooms and get some extra protection.
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