Chemosorption of radiometals of interest to nuclear medicine by synthetic melanins

• Published in: Nuclear medicine and biology 2008-04, Vol.35 (3), p.353-357
• Main Authors: Howell, Robertha C, Schweitzer, Andrew D, Casadevall, Arturo, Dadachova, Ekaterina A
• Format: Article
• Language: English
• Subjects: 111-Indium; 213-Bismuth; 225-Actinium; Actinium - chemistry; Adsorption; Bismuth - chemistry; Chemosorption; Cysteine - analogs & derivatives; Cysteine - chemistry; Dopamine - analogs & derivatives; Dopamine - chemistry; Gamma Rays; Indium Radioisotopes - chemistry; Levodopa - analogs & derivatives; Levodopa - chemistry; Melanin; Melanins - chemical synthesis; Melanins - chemistry; Nuclear Medicine - methods; Radiochemistry; Radiological attack; Radiology; Scintillation Counting; Tyrosine - analogs & derivatives; Tyrosine - chemistry
• ISSN: 0969-8051; 1872-9614
• DOI: 10.1016/j.nucmedbio.2007.12.006

Abstract Introduction Melanins are high-molecular-weight pigments that are ubiquitous in nature and can also be synthesized in the laboratory from a variety of precursors. Melanins possess numerous interesting physicochemical characteristics, including electromagnetic radiation absorption properties and ability to chelate metals. We have recently reported that melanin has remarkable ionizing-radiation-shielding properties, possibly because it can interact with photons via Compton scattering. We hypothesized that, if administered internally, melanin could play a beneficial role by scavenging various radionuclides, in addition to radiation shielding. Methods Three melanins were synthesized from dopamine, 3,4-dihydroxyphenylalanine ( l -Dopa) and a combination of l- cysteine and l- Dopa. For control, synthetic melanin made from tyrosine polymerization (Sigma) was used. Melanins were characterized by elemental analysis. The chemosorption of111 In,225 Ac and213 Bi by melanins was studied at 37°C for up to 48 h. Results The C-to-N molar ratios for dopamine, l- Dopa and tyrosine melanins were very close at 7.92, 8.39 and 8.48, respectively, while in mixed l- cysteine/ l- Dopa melanin, that ratio was much lower at 3.63. This mixed melanin also contained 22.33% sulfur, thus confirming incorporation of S-containing motifs into its structure. Dopamine, l- Dopa and tyrosine melanins were very similar in their abilities to decrease the activity of111 In,225 Ac and213 Bi and their radioactive daughters in supernatants by >10-fold in comparison with the starting levels, while mixed l- cysteine/ l- Dopa melanin was able to chemosorb only111 In. Conclusions We have demonstrated that synthetic melanins made of diverse precursors can chemosorb111 In,213 Bi and225 Ac, with dopamine, l- Dopa and tyrosine melanins being the most efficient towards all three of these radionuclides. Such properties of synthetic melanins can contribute to the development of the novel melanin-based radioprotective materials.