N-(2,3-dimercaptopropyl)phthalamidic acid (DMPA) increases polonium-210 excretion

Polonium-210 is one of the most hazardous radionuclides. As recently as 1988, there have been concerns regarding accidental exposures of humans to it. Yet, there have been no studies on the effectiveness of the newer dithiol chelating agents in increasing the excretion of this radioactive heavy metal. In order to accomplish this, a safe and effective method for determining the radioactivity of polonium-210, an alpha emitter, in the feces was developed. The excretion of polonium-210 was studied by giving male Sprague-Dawley rats 210Po (3.33 x 10(7) cpm/kg, intraperitoneal); 1 h later they were given either 5% sodium bicarbonate, N-(2,3-dimercaptopropyl)phthalamidic acid (DMPA) or meso-dimercaptosuccinic acid (DMSA) (0.20 mmol/kg, subcutaneous). Treatment was repeated daily for 12 days. DMPA and DMSA increased the urinary excretion of 210Po, as compared to control animals, 8-fold and 5-fold, respectively. DMPA increased the fecal excretion of 210Po compared to the other treatments and also decreased the level of 210Po in the spleen, a radiosensitive organ. DMPA (0.20 mmol/kg, intravenous) increased biliary levels of 210Po 5-fold compared to controls. The results indicate that DMPA has greater specificity in chelating and increasing the excretion of 210Po than DMSA.