Effect of acrolein and glutathione depleting agents on thioredoxin

Acrolein is a widespread environmental pollutant that reacts rapidly with nucleophiles, especially cellular thiols. In addition to glutathione (GSH), thioredoxin (Trx) and thioredoxin reductase (TR) contain thiol groups and may react with electrophiles. In the present study, A549 cells treated with 5-25 microM acrolein for 30 min lost cellular Trx activity in a dose-dependent fashion. Over 90% of Trx activity was lost at concentrations of 25 microM or greater. In contrast, Trx protein content, as assessed by western blotting, was not altered immediately after the 30 min acrolein treatment. Both Trx activity and protein levels increased 4h after the acrolein treatment. However, Trx activity remained below control levels at 24h. A similar dose-response relationship was seen with TR in A549 cells exposed to acrolein. There was, however, a rapid recovery of TR activity such that it attained normal levels by 4h after doses < or = 75 microM acrolein. Diethyl maleate (DEM), a common but not highly specific, agent used to deplete GSH, also inactivated Trx. A 2 h exposure of A549 cells to 1 mM DEM depleted cellular GSH by ~50% and diminished Trx activity by over 67%. Lower DEM doses (0.125 mM and 0.25 mM) for 1h had no significant effect on GSH but significantly decreased Trx activity 12 and 23%, respectively. Similar to immediately after acrolein exposure, DEM did not affect Trx protein levels. A Trx-1-GFP fusion protein was transfected into A549 cells. While the fusion protein was expressed, the Trx component was inactive by the insulin reducing assay. In summary, Trx and TR are inactivated by acrolein. In addition, the GSH depleting agent DEM inactivates Trx somewhat more effectively than it depletes GSH. The Trx-1-GFP fusion protein, while readily expressed, appears to have little or no activity, perhaps because the small size of Trx-1 (12 kDa) is affected by the larger GFP.