1.1. Sources and Usage
King Oyster is one of several Bioactive Mushroom also used as a food product with the phylogenic classification of Pleurotus eryngii. King Oyster varies from other 'Oyster' mushrooms, which are a different species (usually Pleurotus ostreatus). Pleurotus Eryngii appears to have multiple varieties; var. eryngii, var. ferulae, var. tingitanus, and var. nebrodensis although the last variety, nebrodensis, appears to have been elevated to a new species.
It is widespread in the Mediterranean, central Europe, northern Africa, and Asia. It is reported to have a pleasant taste and is used in culinary dishes.
As a mushroom, King Oyster is similar to many Herbal Supplements in the sense that it contains a variety of bioactives such as:
Eryngiolide A, an anticancer macrocyclic diterpene possibly formed from two 1,2-dihydromintlactone molecules
A hemolysin with two components, Erylysin A and Erylysin B; not heat stable at 37°C for 5 hours
Eryngase and Eryngeolysin
Bioactive peptides named Eryngin and Pleurostrin
Beta-Glucans at 20-50% of dry matter (weight after water is removed) and some other polysaccharides such as 3-O-methylated alpha-galactans and an anti-oxidant polysaccharide
Up to 8 different sterol compounds
Dietary protein, with up to 1.88-2.65% of total fresh weight as protein (and 5.3% nitrogen content)
Dietary lipids, at around 0.8% fresh weight
A minor hydrogen cyanide (HCN) content, 1-2mg/kg and lesser with cooking, in the basidiomata
Dietary Minerals such as Calcium(74.28+/-0.04mcg/g), Copper(7.474+/-0.002mcg/g), Zinc, Sodium(678+/-0.2mcg/g), Magnesium, Potassium(17.6+/-4.2mg/g), Phosphorus(9.0+/-2.6mg/g), and Sulfur(4.5+/-1.3mg/g).
It is quite unheard of to see such a large and round molecule; quite an interesting structure. It appears that two of the center molecules, the 1,2-dihydromintlactones, may unhinge at the 4 carbon and form this cyclic structure
2Interactions with Hormones
A study conducted in elk using the industrial byproducts of King Oyster mushroom (19.92% beta-glucan content in this study) noted that high doses (15% and 20%) of King Oyster in the diet, over a period of 80 days, was able to increase circulating testosterone five-fold (0.2ng/mL to 1.0ng/mL) with no influence on thyroxine, GH, or IGF. This was accompanied by an increase in monocytes (+59%, 0.22-0.35K/ul but not dose-dependent) and hematocrit (+8.9%) yet with no liver abnormalities (ALT, AST) and in increase (+13%) in HDL-C.
King Oyster does contain sterol molecules, which structurally are usually related to testosterone, but no studies have been done on the possible link.
A study in ovariectomized (without ovaries) rats with 0.3% ethanolic extract of King Oyster daily, over 75 days, appeared to slightly increase uterine weight (much less than estradiol as active control) and reduce bone loss relative to control; indicative of estrogenic effects.
When tested in vitro, 0.1ug/mL of King Oyster was equally effective as 10nM of estradiol in proliferating MCF-7 cells, a test for estrogenicity, with statistically significant increases being seen as low as 0.001ng/mL. Interestingly, when an estrogen receptor antagonist was added it significantly reduced the proliferation but 10ug/mL King Oyster still induced proliferation above control cells.
When tested against other Bioactive mushrooms at a concentration of 1.0ug/mL, King Oyster appeared to be the most estrogenic (as assessed by increased cell proliferation) of the 14 tested; nonsignificantly different than Agaracus Blazei, Grifola frondosa (Maitake), Panellus serotinus and 3 other variants of Pleurotus and also nonsignificantly different than 100nM estradiol. Agaricus bisporus appeared to be slightly suppressive of division.
3Immunology and Inflammation
An ethanolic extract of King Oyster mushroom was found at 10-50ug/mL to inhibit IL-4 transcription in antigen-stimulated mast cells in a dose-dependent manner, suggestive of suppressing an allergic response. Reduction of NFAT and NF-kB activity, COX-2 mRNA and protein level, and NF-kB translocation due to reduction of IκB-α degradation, were also seen in these cells; all of which may have been downstream from inhibiting FcεRI signalling (with SyK signalling unaffected).
Due to these inhibitory effects, less pro-inflammatory cytokines were released from antigen-stimulated mast cells such as TNF-α, IL-1 and IL-6 alongside IL-4.
In ApoE-/- mice, King Oyster at 3% of the food intake by weight for 16 weeks trended towards reducing triglycerides and total cholesterol in mice but only reached statistical significance at 12 weeks with triglycerides (and became nonsignificant at 16 weeks again). These trends were on par with the two other groups of Maitake and Bunashimeji mushrooms, yet all groups were able to reduce the area of artherosclerotic lesions with Bunashimeji being the most potent. This study appears to not be related to dietary fiber inhibiting cholesterol uptake, as dietary cholesterol was controlled (0.066%) and Bunashimeji outperformed Maitake despite Maitake having the highest fiber content.
When tested in vitro, the water extract of King Oyster appeared to be the most potent in inhibiting pancreatic lipase activity out of 8 tested medicinal mushrooms. The water and ethanolic extract brought lipase activity down to 20.8% and 89.6% of activity (respectively) while Yamabushitake scored 95.9% and 68.4% (water/ethanolic) and Maitake to 76.5% with an ethanolic extract (water extract appeared to stimulate up to 113.3%, the worst inhibitory performance) and the methanolic extract of Sparassis Cripsa getting 65.4% of control. Heat treatment (cooking) did not affect the inhibition of King Oyster with up to 60 minutes of boiling, and administration of King Oyster to rats alongside fatty acids was able to reduce the AUC of the fats by 44%, which was attributed to inhibiting absorption due to no increase in LPL levels systemically (indicative of uptake).
When fed at 3% of the diet for up to 16 weeks, King Oyster is not associated with significant changes in triglycerides but only trends towards reductions.
5Interactions with Cancer
King Oyster has been investigated for its cytotoxic effects due to belonging to the Pleurotus family, commonly associated with anti-cancer effects.
Eryngiolide A has demonstrated cytotoxicity against HeLa and HepG2 cells with IC50 values of 20.6μM and 28.6μM, respectively, which is classified as moderate cytotoxicity.
6Interactions with Oxidation
Mushrooms tend to have anti-oxidant capabilities, and when compared against 9 other species at 1mg ethanolic extract (including regular Oyster mushrooms, Pleurotus ostreatus) it was found that King Oysters scored 11.45% inhibiting on a DPPH free radical scavenging test, placing 7th out of 10 behind Morchella elata (59.22%) and Meripilus giganteus (43.12%), although ahead of regular Oyster Mushrooms (6.11%). This was given an inhibition value of 3.01 TOC (alpha-tocopherol equivalents, measured in ug/mL). A 1:3 methanolic extract of King Oyster, when tested against Morchella elata again and three new mushrooms still underperformed relatively on anti-oxidative assays.
A water extract of King Oyster has been shown, in vitro, to increase Alkaline Phosphatase activity at 0.08-10ul/mL concentrations (1.5 and 2-fold increases, respectively) and was able to delay the progression of osteoporosis ex vivo (in bones removed from mice) from 16% over 4 weeks in control to 8%. These effects may be secondary to estrogen-like activity, as a study in ovariectomized rats (to model menopause) found that 0.3% of an ethanolic extract of the fruiting bodies per day for 75 days of treatment had better bone mineral density relative to control by 14% (with estrogen at 30ug/kg being 25% higher than control).
May be useful to menopausal women for reducing the risk of osteoporosis, but appears to be estrogenic