Benzene and dopamine catechol quinones could initiate cancer or neurogenic disease

Abstract

Catechol quinones of estrogens react with DNA by 1,4-Michael addition to form depurinating N3Ade and N7Gua adducts. Loss of these adducts from DNA creates apurinic sites that can generate mutations leading to cancer initiation. We compared the reactions of the catechol quinones of the leukemogenic benzene (CAT-Q) and N-acetyldopamine (NADA-Q) with 2'-deoxyguanosine (dG) or DNA. NADA was used to prevent intramolecular cyclization of dopamine quinone. Reaction of CAT-Q or NADA-Q with dG at pH 4 afforded CAT-4-N7dG or NADA-6-N7dG, which lost deoxyribose with a half-life of 3 h to form CAT-4-N7Gua or 4 h to form NADA-6-N7Gua. When CAT-Q or NADA-Q was reacted with DNA, N3Ade adducts were formed and lost from DNA instantaneously, whereas N7Gua adducts were lost over several hours. The maximum yield of adducts in the reaction of CAT-Q or NADA-Q with DNA at pH 4 to 7 was at pH 4. When tyrosinase-activated CAT or NADA was reacted with DNA at pH 5 to 8, adduct levels were much higher (10- to 15-fold), and the highest yield was at pH 5. Reaction of catechol quinones of natural and synthetic estrogens, benzene, naphthalene, and dopamine with DNA to form depurinating adducts is a common feature that may lead to initiation of cancer or neurodegenerative disease.

Figure 1

Oxidation CAT and NADA to their respective quinones and reaction of the quinines with Ade or dG to form N3Ade and N7Gua adducts.

Figure 2

Metabolism of dopamine to form neuromelanin and depurinating DNA adducts.

Figure 3

Mass spectrum of the reaction mixture of CAT-Q with dG after 1 h at 22 °C. Inset: MS/MS of m/z 376, CAT-4-N7dG, showing the daughter ion at m/z 260, CAT-4-N7Gua.

Figure 4

Mass spectrum of the reaction mixture of NADA-Q with dG after 3 h at 22 °C. Inset: Right, MS/MS of m/z 461, NADA-6-N7dG, showing the daughter ion at m/z 345, NADA-6-N7Gua, and m/z 152, Gua. Left, MS/MS of m/z 345, NADA-6-N7Gua, showing the daughter ions at m/z 303, NADA-6-N7Gua minus the acetyl group, and m/z 152, Gua.

Figure 5

Time course of the reaction of CAT-Q with dG to form CAT-4-N7dG and its conversion to CAT-4-N7Gua. CAT (0.05M) was oxidized to CAT-Q with 3M Ag₂O in 2 ml of DMF and filtered in to 0.25M dG in 2 ml of H₂O:CH₃COOH (1:1). The pH was adjusted to 4 and the reaction continued at room temperature.

Figure 6

Time course of the reaction of NADA-Q with dG to form NADA-6-N7dG and its conversion to NADA-6-N7Gua. The same reaction conditions were used as in Figure 5, except that NADA was used instead of CAT.

Figure 7

Time course of the formation of CAT-4-N3Ade and CAT-4-N7Gua after the reaction of CAT-Q with DNA at pH 4. CAT-Q (87 µM) was reacted with 3mM DNA at pH 4 and room temperature.

Figure 8

Time course of the formation of NADA-6-N3Ade and NADA-6-N7Gua after the reaction of NADA-Q with DNA at pH 4. The same reaction conditions were used as in Figure 7, except that NADA-Q was used instead of CAT-Q.

Figure 9

Effect of pH on formation of the depurinating CAT-4-N3Ade and CAT-4-N7Gua adducts by (A) reaction of CAT-Q with DNA for 10 h and (B) tyrosinase-activated CAT with DNA for 10 h. (A) CAT-Q (87 µM) was reacted with 3 mM DNA at the indicated pH and 37° C, or (B) 87 µM CAT was reacted with 3 mM DNA in the presence of 2577 units of mushroom tyrosinase at the indicated pH and 37° C.

Figure 10

Effect of pH on formation of the depurinating NADA-6-N3Ade and NADA-6-N7Gua adducts by reaction of (A) NADA-Q with DNA for 10 h, and (B) tyrosinase-activated NADA with DNA for 10 h. The same reaction conditions were used as in Figure 9, except that (A) NADA-Q or (B) NADA was used instead of CAT-Q or CAT.