Attenuation of oxidative damage to DNA by taurine and taurine analogs

Abstract

Taurine has been suggested to have cytoprotective actions via a number of different mechanisms. The role of taurine in protecting DNA from oxidative damage has received only limited attention. The aim of the present studies was to test the hypothesis that taurine might act to attenuate oxidative damage to DNA caused by free radicals generated by iron-stimulated catecholamine oxidation in the presence of H2O2. Calf thymus DNA (100 μg/tube) was exposed to a reaction mixture containing: ferric chloride (60 μM), H2O2 (2.8 mM) and L-dopa (100 μM). Taurine and taurine analogs were added simultaneously to determine their effects to prevent oxidative damage to DNA. The reaction was carried out for 1 hour at 37° C and terminated by rapid freezing in an ethanol/dry ice bath. The DNA was precipitated with ethanol and subsequently hydrolyzed with formic acid under vacuum. The hydroxylated bases were separated by HPLC and detected electrochemically. All experiments were replicated a minimum of 5 times. Taurine (20 mM) was found to reduce (p<0.05) damage to DNA as indexed by reductions in the formation of 5-OH-uracil (49%↓), 8-OH adenine (37%↓), and 8-OH guanine (21%↓). Taurine had minimal effects to reduce the formation of 5-OH cytosine (<7%↓). Taurine (20 mM) also increased total DNA recovery after damage 36-40% and increased total undamaged guanine ∼32%. 5-OH Uracil formation could be reduced (p<0.05) by 1 mM taurine and 8-OH-adenine formation was reduced (p<0.05) by 5 mM taurine. Studies were conducted with various amino acid analogs and total base adduct formation was reduced by 20 mM β-alanine (30%↓), lysine (58%↓) and glutathione (88%↓). When tested at 20 mM, both hypotaurine and homotaurine provided greater protection against DNA damage than taurine, whereas isethionic acid provided a similar level of protection as taurine. Using identical conditions as the assays for base hydroxylation, we tested whether inhibition of quinone formation could account for taurine's mechanism of action. Taurine (49%↓), homotaurine (24%↓) and hypotaurine (79%↓) all reduced quinone formation. Thus, inhibition of quinone formation could account for part of taurine's mechanism of action to inhibit oxidative damage, but it could not account for homotaurine's greater efficacy in preventing DNA damage. Overall, these studies show that taurine at concentrations normally found in cells can inhibit oxidative damage to DNA.