Detoxification Mechanism of α,β-Unsaturated Carbonyl Compounds in Cigarette Smoke Observed in Sheep Erythrocytes

Highly reactive α,β-unsaturated carbonyl compounds, such as acrolein (ACR), crotonaldehyde (CA) and methyl vinyl ketone (MVK), are environmental pollutants present in high concentrations in cigarette smoke. We have previously found that these carbonyl compounds in cigarette smoke extract (CSE) react with intracellular glutathione (GSH) to produce the corresponding GSH-ACR, GSH-CA and GSH-MVK adducts via Michael addition reaction. These adducts are then further reduced to the corresponding alcohol forms by intracellular aldo-keto reductases in highly metastatic mouse melanoma (B16-BL6) cells and then excreted into the extracellular fluid. This time, we conducted a similar study using sheep erythrocytes and found analogous changes in the sheep erythrocytes after exposure to CSE as those with B16-BL6 cells. This indicates similarity of the detoxification pathways of the α,β-unsaturated carbonyl compounds in sheep blood cells and B16-BL6 cells. Also, we found that the GSH-MVK adduct was reduced by aldose reductase in a cell-free solution to generate its alcohol form, and its reduction reaction was completely suppressed by pretreatment with epalrestat, an aldose reductase inhibitor, a member of the aldo-keto reductase family. In the presence of sheep blood cells, however, reduction of the GSH-MVK adduct was partially inhibited by epalrestat. This revealed that some member of the aldo-keto reductase superfamily other than aldose reductase is involved in reduction of the GSH-MVK adduct in sheep blood. These results suggest that blood cells, mainly erythrocytes are involved in reducing the inhalation toxicity of cigarette smoke via an aldo-keto reductase pathway other than that of aldose reductase.