Acetaldehyde modification of low density lipoprotein accelerates its catabolism in man

Acetaldehyde (AcA), the first metabolite in ethanol oxidation, is chemically highly reactive and binds covalently to the free amino groups of various proteins. In this study, we examined the metabolism of acetaldehyde-modified LDL (AcA-LDL) in man. LDL was isolated from human volunteers, radiolabelled with either 125I or 131I, incubated in various AcA concentrations (Aca-LDL) and injected back into the donors simultaneously with LDL incubated in identical conditions but omitting AcA (C-LDL). Acetaldehyde treatment did not change the chemical composition, electrophoretic mobility or the flotation characteristics of LDL. The proportion of free amino groups of AcA-LDL, ranging from 97 to 54.5%, was negatively correlated with the final concentration of AcA used in the incubation medium (r = -0.99, P less than 0.001). AcA modification of LDL accelerated its in vivo catabolism in man in such a way that the fractional catabolic rate (FCR) for AcA-LDL was negatively correlated with the percentage of free amino groups in AcA-LDL (r = -0.87, P less than 0.01). The clearance of AcA-LDL modified in 0.4, 2.0, 4.0 and 8.0 mM AcA was 0.9, 1.4, 2.5 and 3.7 times faster than the clearance of C-LDL, respectively. If AcA-LDL is formed in man after ethanol ingestion, its rapid clearance may be one possible mechanism for the low LDL levels observed in chronic alcohol users.