Ra­di­a­tion Ahead? Eat a Black Mush­room!

«Week of the Fungi» on STC is a spo­radic un­der­tak­ing. This oc­ca­sional fes­ti­val is our way to hail the fall mush­room col­lect­ing sea­son in parts of the north­ern hemi­sphere. We are a bit late this year, but mush­room col­lect­ing is still pos­si­ble in many parts.

by Elio

Sup­pose that one day you have the mis­for­tune to re­ceive a strong dose of ra­di­a­tion in prepa­ra­tion for a med­ical pro­ce­dure, say a bone mar­row trans­plant. To your sur­prise, the physi­cian pre­scribes that you eat a hefty serv­ing of dark-col­ored mush­rooms about an hour be­fore­hand. Lest you think this black magic, the clin­i­cian ex­plains that this has been proven ef­fec­tive in 'clin­i­cal tri­als' in mice, sur­pris­ingly so in fact. A 2012 pa­per with the for­bid­ding ti­tle Comp­ton Scat­ter­ing by In­ter­nal Shields Based on Melanin-Con­tain­ing Mush­rooms Pro­vides Pro­tec­tion of Gas­troin­testi­nal Tract from Ion­iz­ing Ra­di­a­tion de­scribes this work. The au­thors fed mice a mush­room used in East Asian cui­sine, called Ju­das' ear, tree, or jelly ear (Au­ric­u­laria au­ric­ula-ju­dae) an hour be­fore giv­ing them a pow­er­ful 9 Gy dose with the beta emit­ter Cesium137. For per­spec­tive, any­thing over ~0.1 Gy is con­sid­ered a dan­ger­ously high dose for hu­mans. All the con­trol mice died in 13 days while ~90% of the mush­room-fed ones sur­vived. Mice fed a white mush­room (porcini) died al­most as fast as the con­trols, but those fed white mush­rooms sup­ple­mented with melanin also sur­vived.

Fig. 1. Left: Au­ric­u­laria-au­ric­ula-ju­dae (Ju­das' ear, tree ear, jelly ear). Source. Right:Bo­le­tus edulis (porcini, cep, king bo­lete). Source

Dark Fungi and Comp­ton Scat­ter­ing

And herein lies the story. Melanin, the pig­ment found in the hu­man skin among other sites, re­duces po­ten­tial dam­age caused by ion­iz­ing ra­di­a­tion. This is due to Comp­ton scat­ter­ing, a phe­nom­e­non well un­der­stood by physi­cists. Rather than try to ex­plain it, let me quote: The ra­dio­pro­tec­tive ef­fects of melanin are based on the con­trolled dis­si­pa­tion of Comp­ton elec­tron en­ergy by melanin, which re­sults in a de­creased num­ber of in­ter­ac­tions be­tween Comp­ton elec­trons and cel­lu­lar mi­lieu and the scav­eng­ing of free re­ac­tive rad­i­cals by melanin. For most of us, it's enough to know that this process can dis­si­pate ra­di­a­tion and thus re­duce its ef­fects on liv­ing things.

It has been known that some fungi, black molds and black yeasts in par­tic­u­lar, are highly re­sis­tant to radiation—witness the black walls of the en­tombed cham­ber of the "hot" Cher­nobyl re­ac­tor, which is due to their abun­dant pres­ence. We dis­cussed this be­fore (here and here), some­what in awe of these fungi that not only are re­sis­tant to a pow­er­ful lot of ra­di­a­tion but are even drawn to­wards it ("ra­diotro­pism"). And that's not all. Be­lieve it or not, they can use the ra­di­a­tion as an en­ergy source for their growth. If you find this hard to swal­low, think of this as anal­o­gous to pho­to­syn­the­sis, but in this case the en­ergy-har­vest­ing pig­ment is melanin.

Fig. 2. Melanin in black and white mush­rooms: Elec­tron para­mag­netic res­o­nance of dried mush­rooms:(A) black mush­rooms; (B) white mush­rooms (in­serts show the ap­pear­ance of the dried mush­rooms). Source

The Melanin Shield

Melanin is per­haps not the only cell com­po­nent in­volved in these re­ac­tions to ra­di­a­tion. While one study re­ported in­creased growth by melanized strains com­pared with "al­bino" un­pig­ment­ed­mu­tants, an­other one found only a small dif­fer­ence be­tween the two. But since ir­ra­di­a­tion of the black yeast Wang­iella der­mati­tidis prompts dif­fer­en­tial ex­pres­sion of up­wards of 3000 genes, there is am­ple room for other fac­tors to play a role here. I'll dis­cuss this fur­ther in the fu­ture; for now, let me re­turn to the mush­rooms and the ir­ra­di­ated mice.

Melanin, which is wide­spread among the fungi, in­clud­ing many ed­i­ble mush­rooms, has ear­lier been as­so­ci­ated with ra­dio­pro­tec­tion. It is also quite in­sol­u­ble and fairly in­di­gestible, thus likely to re­main undis­turbed in the GI tract for some time af­ter con­sump­tion. So, in ret­ro­spect, it seems al­most ob­vi­ous that feed­ing melanin-con­tain­ing mush­rooms to mice would ren­der them ra­di­a­tion resistant—but I would not have thought of it. To test this in vivo, off went these in­ves­ti­ga­tors to the near­est Trader Joe's store where they bought a sup­ply of both darkly pig­mented and white mush­rooms. A. au­ric­ula-ju­dae was a good choice for the pig­mented sam­ple be­cause it con­tains about 10% melanin by weight. While an­tiox­i­dants might also be sus­pected to play a pro­tec­tive role, the amount of an­tiox­i­dants was about the same in A. au­ric­ula-ju­dae as in the white con­trol, porcini mush­rooms.

Fig. 3. Sur­vival of ir­ra­di­ated CD‑1 mice fed with black mush­rooms, white mush­room, or white mush­rooms plus melanin and then ir­ra­di­ated with 9 Gy from Cs-137 at a dose rate of 2.5 Gy/min. Source

The au­thors de­ter­mined the res­i­dence time of the fed mush­rooms in the stom­ach and in­testines. Since the in­testines are es­pe­cially ra­diosen­si­tive, they chose for ir­ra­di­a­tion the time when the mush­room food ac­cu­mu­lated there, which was one hour post feed­ing. They fed the mice in­tra­gas­tri­cally 1 g of ground-up mush­rooms per kg body weight, an amount com­pa­ra­ble to 2–3 ounces of mush­rooms for one of us—hardly a huge amount. Some of the mice were fed melanin-con­tain­ing mush­rooms, some white mush­rooms, and some white mush­rooms sup­ple­mented with an equiv­a­lent amount of syn­thetic melanin (100mg/kg). Sur­vival af­ter ir­ra­di­a­tion in the two groups of melanin-fed mice was strik­ing. More­over, these mice showed no in­testi­nal dam­age nor any signs of apop­to­sis of in­testi­nal cells. Their bone mar­row, not shielded by the mush­rooms, was tran­siently af­fected. All of this points to the pro­tec­tion be­ing due to the melanin.

On The Hos­pi­tal Menu Some­day?

Do these re­sults with the melanin-fed mice sug­gest us­ing melanin-con­tain­ing fungi to pre­vent ra­di­a­tion dam­age in hu­mans? These stud­ies are cer­tainly en­cour­ag­ing, al­though it may not be easy to carry out the nec­es­sary clin­i­cal tri­als in hu­mans. But keep­ing in mind the low cost, ap­par­ent ef­fi­ciency, and ap­pe­tiz­ing na­ture of this pro­ce­dure, one can only hope that it will be pur­sued fur­ther. A. au­ric­ula-ju­dae grows com­monly on trees in the tem­per­ate zone (in­clud­ing in North Amer­ica) and is cul­ti­vated on a large scale in parts of Asia and Africa for both food and pur­ported med­ical value. Among its virtues, this mush­room is an im­por­tant in­gre­di­ent of Chi­nese hot and sour soup (for a good recipe, click here). It isn't overly tasty but it con­tributes a nice crunchy con­sis­tency to the dish. Porcini are an­other story. They may not be ra­dio­pro­tec­tive, but they are among the very tasti­est of wild mush­rooms. Each has its place. In­deed, in the fu­ture mush­rooms may have a place in the hos­pi­tal kitchen. Who would have thought that some day, tak­ing your med­i­cine could be a culi­nary treat?

Fig. 4. Hot and Sour Soup. Source

This story was dis­cussed in the pod­cast This Week in Mi­cro­bi­ol­ogy #67.

Ref­er­ences

Revskaya E, Chu P, How­ell RC, Schweitzer AD, Bryan RA, Har­ris M, Ger­fen G, Jiang Z, Jandl T, Kim K, Ting LM, Sell­ers RS, Dada­chova E, Casade­vall A (2012). Comp­ton scat­ter­ing by in­ter­nal shields based on melanin-con­tain­ing mush­rooms pro­vides pro­tec­tion of gas­troin­testi­nal tract from ion­iz­ing ra­di­a­tion. Can­cer Bio­ther­apy & Ra­dio­phar­ma­ceu­ti­cals, 27 (9), 570−576. PMID 23113595

Robert­son KL, Mostaghim A, Cuomo CA, Soto CM, Lebe­dev N, Bai­ley RF, Wang Z (2012). Adap­ta­tion of the black yeast Wang­iella der­mati­tidis to ion­iz­ing ra­di­a­tion: mol­e­c­u­lar and cel­lu­lar mech­a­nisms. PloS one, 7 (11). PMID 23139812