Reactions of biogenic aldehydes with hemoglobin

The aldehyde derivatives of dopamine and serotonin, 3,4-dihydroxyphenylacetaldehyde (DOPAL) and 5-hydroxyindole-3-acetaldehyde (5-HIAL), respectively, were incubated with human hemoglobin under physiological conditions. Both DOPAL and 5-HIAL, as well as dopamine, showed a time-dependent disappearance during the incubations, whereas this was not observed with serotonin. The amounts of free aldehydes recovered after incubation with hemoglobin, as analysed by high-performance liquid chromatography with electrochemical detection, corresponded to the amounts of acid metabolites formed in enzymatic assays, when the samples instead were incubated with aldehyde dehydrogenase. Incubations with DOPAL, 5-HIAL, or dopamine, and hemoglobin also resulted in distinct increases in the absorption spectra between 250-350 nm, whereas no similar increase was observed with serotonin. Addition of sodium borohydride to the incubates, which is used to stabilize Schiff base adducts between aldehydes and proteins, resulted in reduction of DOPAL and 5-HIAL to their corresponding alcohol metabolites. However, a rapid initial disappearance of the aldehydes, as analysed from the recoveries of the alcohol metabolites, was observed, followed by a more slow disappearance rate throughout the incubation period.