Acrolein oxidizes the cytosolic and mitochondrial thioredoxins in human endothelial cells

Acrolein is a reactive aldehyde that is a widespread environmental pollutant and can be generated endogenously from lipid peroxidation. The thioredoxin (Trx) system in endothelial cells plays a major role in the maintenance of cellular thiol redox balance, and is critical for cell survival. Normally, cells maintain the cytosolic (Trx1) and mitochondrial (Trx2) thioredoxins largely in the reduced state. In human microvascular endothelial cells, Trx1 was more sensitive than Trx2 to oxidation by acrolein. A 30-min exposure to 2.5 μM acrolein caused partial oxidation of Trx1 but not Trx2. The active site dithiol of Trx1 was essentially completely oxidized by 5 μM acrolein whereas 12.5 μM was required for complete oxidation of Trx2. Partial recovery of the Trx1 redox status was observed over a 4 h acrolein-free recovery period, with increases in the reduced form and decreases in the fully oxidized form. For cells treated with 2.5 or 5 μM acrolein the recovery did not require protein synthesis, whereas protein synthesis was required for the return of reduced Trx1 in cells treated with 12.5 μM acrolein. Pretreatment of cells with N-acetylcysteine (NAC) resulted in partial protection of Trx1 from oxidation by acrolein. In cells treated with acrolein for 30 min, followed by a 14- to 16-h acrolein-free period, small but significant cytotoxic effects were observed with 2.5 μM acrolein whereas all cells were adversely affected by ≥12.5 μM. NAC pretreatment significantly decreased the percentage of stressed cells subsequently exposed to 5 or 12.5 μM acrolein. Given the critical role of the thioredoxins in cell survival, the ability of acrolein to oxidize both thioredoxins should be taken into account for a thorough understanding of its cytotoxic effects.