Elucidation of Reaction Scheme Describing Malondialdehyde−Acetaldehyde−Protein Adduct Formation

Abstract

Malondialdehyde and acetaldehyde react together with proteins and form hybrid protein conjugates designated as MAA adducts, which have been detected in livers of ethanol-fed animals. Our previous studies have shown that MAA adducts are comprised of two distinct products. One adduct is composed of two molecules of malondialdehyde and one molecule of acetaldehyde and was identified as the 4-methyl-1,4-dihydropyridine-3,5-dicarbaldehyde derivative of an amino group (MDHDC adduct). The other adduct is a 1:1 adduct of malondialdehyde and acetaldehyde and was identified as the 2-formyl-3-(alkylamino)butanal derivative of an amino group (FAAB adduct). In this study, information on the mechanism of MAA adduct formation was obtained, focusing on whether the FAAB adduct serves as a precursor for the MDHDC adduct. Upon the basis of chemical analysis and NMR spectroscopy, two initial reaction steps appear to be a prerequisite for MDHDC formation. One step involves the reaction of one molecule of malondialdehyde and one of acetaldehyde with an amino group of a protein to form the FAAB product, while the other step involves the generation of a malondialdehyde-enamine. It appears that generation of the MDHDC adduct requires the FAAB moiety to be transferred to the nitrogen of the MDA-enamine. For efficient reaction of FAAB with the enamine to take place, additional experiments indicated that these two intermediates likely must be in positions on the protein of close proximity to each other. Further studies showed that the incubation of liver proteins from ethanol-fed rats with MDA resulted in a marked generation of MDHDC adducts, indicating the presence of a pool of FAAB adducts in the liver of ethanol-fed animals. Overall, these findings show that MDHDC-protein adduct formation occurs via the reaction of the FAAB moiety with a malondialdehyde-enamine, and further suggest that a similar mechanism may be operative in vivo in the liver during prolonged ethanol consumption.

Identification of a New Cross-link and Unique Histidine Adduct from Bovine Serum Albumin Incubated with Malondialdehyde

“…We have shown that MDA and acetaldehyde can react with collagen to give a potential cross-linking dihydropyridine product (3), and others (6,7) have confirmed this finding. However, under the same conditions, 70 mM MDA hardly cross-links 25 mg/ml bovine serum albumin (BSA) (8), 2 as demonstrated by the absence of an observable dimer band on SDS-PAGE gels after this time period.…”

“…Only a potentially unlikely second reaction with MDA opens the possibility of cross-linking again, probably via a dihydropyridine-type structure reported previously (3,6,8). A variety of synthetic experiments are being carried out to investigate the potential reaction mechanism proposed in Scheme 2.…”

“…On the other hand, heavy cross-linking of BSA is observed when the reaction is carried out in the presence of acetaldehyde but not acetaldehyde alone, suggesting synergy between the two reagents (8). Several MDA cross-links have been proposed involving synergy with other reactive agents, but MDA crosslinks of collagen may also involve reaction with the existing enzymatic cross-links (3).Other potential cross-links and MDA-derived adducts beyond ␤-LAA commonly require more than one MDA molecule being required to form the proposed structure, even in the presence of acetaldehyde (3,6,7,9). Such a reaction would be less likely under physiological conditions because MDA is at very low serum concentrations, and even in a "glycation hotspot," the environment of an atherosclerotic plaque (10) would be competing with many other oxidized fatty acid or sugar products for reactive lysine.…”

Surfactant lipid peroxidation damages surfactant protein A and inhibits interactions with phospholipid vesicles

“…To address the former possibility, the SP-A-mediated aggregation of auto-oxidized liposomes containing increased concentrations of lipid hydroperoxides was compared with that of nonoxidized liposomes, and no differences were found. LPO also leads to the formation of reactive aldehydes that have been shown to derivatize proteins (47,48). The addition of MDA at two to four times higher concentrations than levels reached during LPO under the conditions used had no effect on lipid aggregation rate or end point.…”

Toward an “omic” physiopathology of reactive chemicals: Thirty years of mass spectrometric study of the protein adducts with endogenous and xenobiotic compounds

“…A 3,4,5-trisubstituted 1,4-dihydropyridine structure is formed, closely resembling that of the antihypertensive Ca-channel blocker drug nifedipine (Scheme 9) (Tuma et al, 2001). It is totally speculative to wonder whether such metabolites may be physiologically occurring and may play a role in blood pressure regulation.…”