Acetaldehyde-induced growth retardation and micro-heterogeneity of the sugar chain in transferrin synthesized by HepG2 cells.

Background: A carbohydrate-deficient transferrin (CDT) is the most useful marker of alcohol abuse; however, the mechanism of production and the pathophysiologic roles of CDT remain obscure. The effects of alcohol and its metabolites on growth and proliferation, transferrin synthesis, and phosphomannomutase enzyme activity in a human hepatoblastoma, HepG2, were examined.

Methods: HepG2 cells were treated with either ethanol at 80 mM or acetaldehyde at 400 microM. Transferrin secreted by the cells was prepared from conditioned culture medium by single-step immunoaffinity column chromatography using a goat-specific antibody against human transferrin. Phosphomannomutase and some related enzyme activities in the cell extracts were determined. Reverse transcription-polymerase chain reaction analysis of phosphomannomutase mRNA expression was also determined in HepG2 cultured with or without acetaldehyde (400 microM).

Results: HepG2 cells usually synthesized and secreted transferrin with three separated bands: main broad bands estimated to be 78 to 82 kDa, 75 kDa, and 72 kDa. The last two bands were compatible with part or the entire N-glycans-deficient transferrin (CDT) from alcoholic liver damage. Increased secretion of CDT from HepG2 correlated well with the extent of growth retardation to the level of confluent cell density. The activity of phosphomannomutase also decreased with prolongation of cellular doubling time. Furthermore, acetaldehyde treatment at 400 microM accelerated the inhibitory effect of cell growth compared with nontreated cells, and this condition facilitated CDT secretion from HepG2 cells. Determination of the enzyme activity and mRNA expression indicated that acetaldehyde showed competitive type inhibition of phosphomannomutase activity but not suppression of phosphomannomutase gene expression.

Conclusions: By culturing HepG2 cells with acetaldehyde containing media, growth inhibition-dependent increase of CDT showed good correlation with reduced enzyme activity of phosphomannomutase. Acetaldehyde facilitated growth retardation, inhibition of phosphomannomutase activity, and increased secretion of CDT. The HepG2 cell line is useful as an in vitro model to investigate the pathophysiologic state of alcoholic liver damage and mechanisms of production as well as the physiologic role of CDT.