Leucopaxillus gentianeus

The bitter false funnelcap, Leucopaxillus gentianeus (Quél.) Kotl.

Classification

Kingdom Fungi
Phylum Basidiomycota
Class Basidiomycetes
Order Agaricales
Family Tricholomataceae
Genus Leucopaxillus

Synonyms

Agaricus amarus sensu auct.
  fide Checklist of Basidiomycota of Great Britain and Ireland (2005)
Clitocybe amara sensu auct.
  fide Checklist of Basidiomycota of Great Britain and Ireland (2005)
Clitocybe gentianea Quél.
  Mém. Soc. Émul. Montbéliard, Sér. 2 5: 341 (1873)
Lepista amara sensu auct.
  fide Checklist of Basidiomycota of Great Britain and Ireland (2005)
Leucopaxillus amarus sensu auct.
  fide Checklist of Basidiomycota of Great Britain and Ireland (2005)
Leucopaxillus amarus sensu NCL (1960)
  fide Checklist of Basidiomycota of Great Britain and Ireland (2005)
Tricholoma amarum sensu Rea (1922)
  fide Checklist of Basidiomycota of Great Britain and Ireland (2005)

Common name

Bitter false funnelcap
Bitter brown leucopaxillus
Bittermusseron (Swedish)

Description

Cap: 4-12 cm diameter, convex to plano-convex, sometimes shallowly infundibuloform, surface glabrous, reddish brown to cinnamon brown in center, becoming paler orange-yellow or yellowish-white at margin; often cracking in age; margin involute; flesh thick, white.
Gills: adnate or subdecurrent, close to crowded, narrow, white to yellowish; sometimes spotted or streaked with reddish brown in age.
Stem: 5-9 cm tall x 1-3 cm thick, cylindric to clavate, dry, fibrillose, white, arising from an  abundant mat of white mycelium.
Spores: subglobose, with amyloid warts, entire, thin-walled, 4-6 x 3.5-5.0 µm.
Spore print: white.
Odor: unpleasant, pungent; farinaceous (Wood et al., 1994)
Taste: strongly bitter.
Edibility: inedible, due to bitter taste (but not toxic).
Habitat: single or in groups on ground, usually under oak, pine and other conifers; often forming fairy rings; widely distributed over Europe and Northern and Central America; summer-fall.

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Bioactive compounds

A number of bioactive triterpenes with the cucurbitane skeleton have been isolated from L. gentianeus, including cucurbitacin B, and leucopaxillones A and B (structures shown below). Cucurbitacin B is responsible for the bitter taste of the mushroom. In the fruiting bodies, the chemical occurs mainly as tasteless fatty acid esters; upon injury these esters are rapidly cleaved enzymatically to produce cucurbitacin B, constituting a chemical defense against predators and parasites (Clericuzio et al., 2004).

cucurbitacin  B
The triterpene cucurbitacin  B, responsible for the bitter taste of L. gentianeus.
leucopaxillone A
The triterpene leucopaxillone A
leucopaxillone B
The triterpene leucopaxillone B

A later investigation revealed two new minor cucurbitane triterpenes, namely, cucurbitacin D and 16-deoxycucurbitacin B.

 cucurbitacin D
Triterpenes cucurbitacin D and16-deoxycucurbitacin B

When R1=OH and R2=H, it’s cucurbitacin D, while if R1=H and R2=acetyl, it’s 16-deoxycucurbitacin B.

Some differences were noted in the cucurbitacin triterpene profile between fruiting bodies and cultured mycelia. While cucurbitacins B and D, as well as leucopaxillones A and B, were isolated from both sources, 16-deoxycucurbitacin B and a mixture of fatty acid esters of cucurbitacin B were not found in the mycelia. Furthermore, a new triterpene, 18-deoxyleucopaxillone A, was isolated from the mycelia but not the fruiting bodies. The antiproliferative activity of the isolated triterpenes was determined against the NCI-H460 human tumor cell line, and compared with the antitumor compound topotecan, a well-known topoisomerase I inhibitor. Only cucurbitacin B (IC50 of 0.011 µg/mL) had antiproliferative activity similar to topotecan (IC50 of 0.008 µg/mL) (Clericuzio et al., 2006).

18_deoxyleucopaxilloneA
18-deoxyleucopaxillone A, isolated from the cultured mycelia of L. gentianeus.


Medicinal properties

Antibiotic activity

The mycelia and cultural filtrates of the bitter false funnelcap were tested for antibiotic activity against Bacillus cereus, Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Proteus mirabilis, Salmonella typhimurium and Candida albicans. L. gentianeus was only active against Bacillus cereus (Colletto, 1995), but in a later study also against B. cereus (Colletto and Giardino, 1996).

Antitumor effects

The in vitro growth inhibitory effects of the cucurbitane triterpenoids mentioned above was tested for their effects on the proliferation of four different human tumor cell lines (A549, CAKI-1, HepG2, MCF-7), using a 1-day MTT assay. Only cucurbitacin B was highly active against all lines, with IC50 values of 46.6, 7.1, 0.76 and 0.78 µM, respectively (Clericuzio et al., 2004).

Links

California Fungi
Patent: Method of inducing apoptosis in cancer treatment by using cucurbitacins

References

Clericuzio M, Tabasso S, Bianco MA, Pratesi G, Beretta G, Tinelli S, Zunino F, Vidari G.
Cucurbitane triterpenes from the fruiting bodies and cultivated mycelia of Leucopaxillus gentianeus.
J Nat Prod. 2006 69(12):1796-9.

Clericuzio M, Mella M, Vita-Finzi P, Zema M, Vidari G.
Cucurbitane triterpenoids from Leucopaxillus gentianeus.
J Nat Prod. 2004 67(11):1823-8.

Coletto MAB, Chiari P.
Antibiotic activity in Basidiomycetes. IX. Antibiotic activity of mycelia and cultural filtrates.
Allionia (Turin). 1995 33(0):75-9.

Coletto MAB, Giardino L.
Antibiotic activity in Basidiomycetes. X. Antibiotic activity of mycelia and cultural filtrates of 25 new strains.
Allionia (Turin). 1996 34(0):39-43.

Kotlaba F.
Distribution of Leucopaxillus gentianeus comb. nov. in Czechoslovakia and notes on its nomenclature [Engl. sum.].
Foreign Title: Rozsireni belocechratky horke-Leucopaxillus gentianeus (Quel.) comb. nov. v Ceskoslovensku a poznamky k jeji nomenklature [Engl. sum.]
Ceska Mykol. 1966 20(4):229-36.

Singer R, Smith AH.
Additional notes on the genus Leucopaxillus.
Mycologia. 1947 39(6):725-36.

Wood WF, Brandes ML, Watson RL, Jones RL, Largent DL.
Trans-2-nonenal, the cucumber odor of mushrooms.
Mycologia 1994 86(4):561-3.

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