Evidence for Dialdehyde/Imine Intermediate Formation During the Metabolism of Benzo[A]Pyrene-7,8-Dihydrodiol by Horseradish Peroxidase

Abstract

Several enzymatic systems can activate the proximate carcinogen benzo[a]pyrene-7,8-dihydrodiol (BP-7,8-diol) to a reactive species which results in a chemiluminescence (CL) response and genotoxic lesions. This CL response is thought to be produced by the formation of a dioxetane from BP-7,8-diol which upon ring-opening forms a highly reactive dialdehyde intermediate. When BP-7,8-diol is incubated with horseradish peroxidase (HRP) and hydrogen peroxide, the CL observed was increased and prolonged by the addition of the endogenous amine, taurine. This CL response cannot be attributed to either BP-7,8-diol-9, 10-epoxide or its interaction with taurine, but is similar to the response of a known Schiff base formation. HPLC analysis of the metabolism products of the HRP reaction with taurine using radiolabeled BP-7,8-diol showed the existence of a new UV peak with an associated radioactive peak Because aldehydes have been shown to interact with cellular macromolecules, both the increased production of photons and the formation of a new electrophilic species from this activation mechanism may cause significant DNA and/or protein damage.

Key Words:

• dialdehyde
• chemiluminescence
• peroxidase
• benzo[a]pyrene
• Schiff base
• imine