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-minute 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 hour 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-hr 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.

The reactive aldehyde acrolein is a ubiquitous environmental pollutant and is also generated endogenously. It is a strong electrophile and reacts rapidly with nucleophiles including thiolates. This review focuses on the effects of acrolein on thioredoxin reductase (TrxR) and thioredoxin (Trx), which are major regulators of intracellular protein thiol redox balance. Acrolein causes irreversible effects on TrxR and Trx, which are consistent with the formation of covalent adducts to selenocysteine and cysteine residues that are key to their activity. TrxR and Trx are more sensitive than some other redox-sensitive proteins, and their prolonged inhibition could disrupt a number of redox-sensitive functions in cells. Among these effects are the oxidation of peroxiredoxins and the activation of apoptosis signal regulating kinase (ASK1). ASK1 promotes MAP kinase activation, and p38 activation contributes to apoptosis and a number of other acrolein-induced stress responses. Overall, the disruption of the TrxR/Trx system by acrolein could be significant early and prolonged events that affects many aspects of redox-sensitive signaling and oxidant stress.