In vivo dosimetry of aldehydes and studies on the origin of malonaldehyde

Abstract: Aldehydes are electrophilic reagents that bind to nucleophilic sites in macromolecules andmany of them have been shown to possess cytotoxic and genotoxic properties.The aim of this study was to develop an analytical method for the measurement of reactionproducts (adducts) of aldehydes with hemoglobin (Hb) and to apply this method for in vivodosimetry of endogenously formed aldehydes, particularly malonaldehyde (MA).The N-alkyl Edman method for specific cleavage of adducted N-terminal valines proved to beuseful because of a high sensitivity and since adducts from several aldehydes could bemeasured in the same sample. It was demonstrated that, in contrast to products of other aminoacids, modified valine cannot be incorporated during de novo synthesis of Hb. An artefactualbackground of adducts due to such incorporation is thus excluded. Because of chemicalinstability the adducts had to be reduced to stable products prior to the analysis.Animal experiments were carried out in order to investigate the origin of adducts observed inunexposed individuals. Increased MA production was observed in mice induced for lipidperoxidation by CCI4. Elevated MA adduct levels, and an increased susceptibility to inducedlipid peroxidation were demonstrated in mice raised on a diet based on polyunsaturated fattyacids. Factors associated with intestinal bacteria were shown to be an important source ofendogenous production of MA and also of some simple alkylators in mice. Exogenousexposures, e.g., diesel exhausts in mice and cigarette smoking in humans had no significanteffect on MA adduct levels. It seems thus likely that endogenous factors are major contributorsto lipid peroxidation and MA formation in vivo.The kinetics of the reaction of MA with N-terminal valine in Hb was studied in vitro. Thestudies on the stability of Hb and DNA adducts of MA in vivo showed that the adducts tovaline in Hb had a half-life of ca. 6 days (due to chemical instability) and the adducts toguanine in liver DNA had a half-life of ca. 12.5 days (due to repair and/or chemical instability.Based on the rate constant for the reaction and the adduct levels determined the in vivoconcentration of free MA in erythrocytes was calculated. The background concentrations offree MA in erythrocytes were ca. 3 nM in humans, ca. 10 nM in rats and ca. 70 nM in mice.This variation possibly reflects differences between species in basic metabolic rates.