Diphenylacetaldehyde-generated excited states promote damage to isolated rat liver mitochondrial DNA, phospholipids, and proteins

This work studies damage to rat liver mitochondrial protein, lipid, and DNA caused by electronically excited states generated by cytochrome c-catalyzed diphenylacetaldehyde enol oxidation to triplet benzophenone. The extension of lipid peroxidation was estimated by production of thiobarbituric acid–reactive substances and by formation of Schiff bases with membrane proteins, evaluated by SDS-polyacrylamide gel electrophoresis. Concomitant with DPAA-driven mitochondrial permeabilization, extensive mtDNA fragmentation occurred and DNA adducts with aldehydes—products of fatty acid oxidation—were observed. The degree of lipid peroxidation and mtDNA alterations were significantly decreased by butylated hydroxytoluene, a potent peroxidation chain breaker. The lipid peroxidation process was also partially inhibited by the bioflavonoid rutin and urate totally prevented the mitochondrial transmembrane potential collapse. In all cases, the mitochondrial damage was dependent on the presence of phosphate ions, a putative bifunctional catalyst of carbonyl enolization. These data are consistent with the notion that triplet ketones may act like alkoxyl radicals as deleterious reactive oxygen species on biologic structures. Involvement of singlet dioxygen formed by triplet-triplet energy transfer from benzophenone in the model reaction with DPAA/cytochrome c in the presence of DCP liposomes was suggested by quenching of the accompanying chemiluminescence upon addition of histidine and lycopene.