Radioprotection (UV-and Gamma-rays) of DNA Molecule by Indole and Indole-derivatives

Abstract The radioprotective ability of ʟ-tryptophan, tryptamine, 3-indoleacetic and indole (10 -4 ᴍ), on UV and gamma irradiated DNA (10 -4 ᴍ) is studied. UV radioprotection is accomplished in the following order of efficiency: ʟ-Tryptophan and 3-indoleacetic acid > indole and tryptamine. The corresponding DRF measured as absorbancy loss at 260 nm, were: ʟ-Tryptophan and 3-indoleacetic acid around 3 and tryptamine and indole around l. When absorbancy loss plus changes in the patterns of the absorbancy curve were con­ sidered the DRF was: L-Tryptophan 2.53, 3-indoleacetic acid 1.54, indole 1.22 and tryptamine 0.75, respectively. For gamma radiation damage the order of radioprotection found was: Indole, ʟ-tryptophan and tryptamine > 3-indoleacetic acid. The DRF when compairing the absorbancy loss at 260 nm, were: ʟ-Tryptophan, Indole and tryptamine around 11 and 3-indoleacetic Acid around 4. When evaluating total changes in absorbancy the DRF were: Indole and ʟ-tryptophan around 6.5, tryptamine 3.7 and 3-indoleacetic 2.1. These data were correlated with measurement of the degree of molecular interactions of DNA and protectors, studied by: Spectrophotometry, m.p. determinations, circular dichroism and oriented circular dichroism, viscosity, and rate of dialysis. Also data of fluorescence and phosphorescense were considered. For gamma radioprotection a mechanism based in radical trapping, local radical trapping and partial recovery of radioprotectors is proposed. UV radioprotection is discussed considering: The close interaction of L-tryptophan with DNA which might impede dimer formation, its proton and electron donor ability. A possible (triplet-triplet) energy transfer from excited DNA to indole derivative is discussed on the basis of acetone competition and a dimer excision process considered.