Compton scattering by internal shields based on melanin-containing mushrooms provides protection of gastrointestinal tract from ionizing radiation

Abstract

There is a need for radioprotectors that protect normal tissues from ionizing radiation in patients receiving high doses of radiation and during nuclear emergencies. We investigated the possibility of creating an efficient oral radioprotector based on the natural pigment melanin that would act as an internal shield and protect the tissues via Compton scattering followed by free radical scavenging. CD-1 mice were fed melanin-containing black edible mushrooms Auricularia auricila-judae before 9 Gy total body irradiation. The location of the mushrooms in the body before irradiation was determined by in vivo fluorescent imaging. Black mushrooms protected 80% of mice from the lethal dose, while control mice or those given melanin-devoid mushrooms died from gastrointestinal syndrome. The crypts of mice given black mushrooms showed less apoptosis and more cell division than those in control mice, and their white blood cell and platelet counts were restored at 45 days to preradiation levels. The role of melanin in radioprotection was proven by the fact that mice given white mushrooms supplemented with melanin survived at the same rate as mice given black mushrooms. The ability of melanin-containing mushrooms to provide remarkable protection against radiation suggests that they could be developed into oral radioprotectors.

FIG. 1.

Chemical structures of melanin oligomers: (A) eumelanin; (B) pheomelanin.

FIG. 2.

Physicochemical characterization of black and white mushrooms: (A, B) Electron paramagnetic resonance of dried mushrooms: (A) black mushrooms; (B) white mushrooms (inserts show the appearance of dried mushrooms); (C–E) oxidative high-performance liquid chromatography of melanin purified from black mushrooms: (C) background solution; (D) Pyrrole-2,3-dicarboxylic acid (PDCA) standard eluting at 8 minutes; (E) melanin from black mushrooms showing PDCA peak; (F, G) results of 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay for antioxidant presence: (F) BHA positive control; (G) methanol extracts from black and white mushrooms.

FIG. 3.

Fluorescent imaging of CD-1 mice fed with white mushrooms at different times postfeeding: (A) 15 minutes, (B) 30 and (C) 60 minutes. Mice were given 1 g/kg body weight white mushrooms suspension in water via a gavage needle and imaged in a supine position under anesthesia.

FIG. 4.

Survival of irradiated CD-1 mice fed with black mushrooms and irradiated with 9 Gy Cs-137 radiation at a dose rate of 2.5 Gy/min, blood counts in the surviving mice, and histology of the gastrointestinal tract and bone marrow. (A) Kaplan–Meyer survival curves. The experiment was performed twice and was terminated at day 45; (B) white blood cell counts at day 45; (C) platelet counts; (D–H) H&E stained slides with tissues from control and irradiated mice. Left, nonirradiated controls; middle, black mushroom group; right, white mushroom supplemented with melanin. (D) stomach; (E) large intestine; (F) small intestine (SI); (G) bone marrow; (H) spleen. Original magnification: D,E,G—400, SI-200, spleen-100.

FIG. 5.

Histological analysis of SIs in irradiated CD-1 mice for dividing (Ki67) and apoptotic (TUNEL) cells and blood counts in these mice on days 0–5 after irradiation. (A) counts of Ki67-positive cells in the crypts. The insert on the left shows the villi, crypts, muscle, and cells that were counted as Ki67-positive (false-positive cells are shown with crosses); (B) counts of TUNEL-positive cells in the crypts. The insert on the left shows villi, crypts, muscle, and cells that were counted as TUNEL-positive (shown with black arrows, false-positive cells are shown with crosses); (C–G) Ki67 (upper row) and TUNEL (low row) stained slides with the tissues from the nonirradiated and irradiated mice: (C) nonirradiated group; (D) PBS; (E) white mushrooms; (F) black mushrooms; (G) white mushrooms supplemented with melanin. Original magnification 200; (H) WBC in irradiated mice on days 0–5 postirradiation; (I) platelet in irradiated mice on days 0–5 postirradiation.