Regulation of constitutive neutrophil apoptosis by the alpha,beta-unsaturated aldehydes acrolein and 4-hydroxynonenal

GSH-dependent regulation of Fas-mediated caspase-8 activation by acrolein

Activation of the cysteine protease caspase-8 by the death receptor Fas (CD95/APO-1) in B lymphoblastoid SKW6.4 cells or Jurkat T cells is associated with GSH depletion. Conversely, GSH depletion by the aldehyde acrolein (3-30 microM) was associated with inhibition of Fas-induced caspase-8 activation, although GSH depletion by buthionine sulfoximine (BSO) did not affect caspase-8 activation. In contrast to BSO, acrolein caused a loss of caspase-8 cysteine content in association with direct alkylation of caspase-8. Our findings indicate that inhibition of caspase-8 by thiol-reactive agents such as acrolein is not due to GSH depletion but caused by direct protein thiol modifications.

4-hydroxynonenal induces mitochondrial oxidative stress, apoptosis and expression of glutathione S-transferase A4-4 and cytochrome P450 2E1 in PC12 cells

An excessive and sustained increase in reactive oxygen species (ROS) production and oxidative stress have been implicated in the pathogenesis of many diseases. In the present study, we have demonstrated that 4-hydroxynonenal (4-HNE), a product of lipid peroxidation, alters glutathione (GSH) pools and induces oxidative stress in PC12 cells in culture. This increase was accompanied by alterations in subcellular ROS and glutathione (GSH) metabolisms. The GSH homeostasis was affected as both mitochondrial and extramitochondrial GSH levels, GSH peroxidase and glutathione reductase activities were inhibited and glutathione S-transferase (GST) activity was increased after 4-HNE treatment. A concentration- and time-dependent increase in cytochrome P450 2E1 (CYP 2E1) activity in the mitochondria and postmitochondrial supernatant was also observed. 4-HNE-induced oxidative stress also caused an increase in the expression of GSTA4-4, CYP2E1 and Hsp70 proteins in the mitochondria. Increased oxidative stress in PC12 cells initiated apoptosis as indicated by the release of mitochondrial cytochrome c, activation of poly-(ADP-ribose) polymerase (PARP), DNA fragmentation and decreased expression of antiapoptotic Bcl-2 proteins. Mitochondrial respiratory and redox functions also appeared to be affected markedly by 4-HNE treatment. These results suggest that HNE-induced oxidative stress and apoptosis might be associated with altered mitochondrial functions and a compromised GSH metabolism and ROS clearance.

Current concepts of redox signaling in the lungs

In the intracellular redox state (GSH/GSSG) the cell plays a key role in the regulation and potentiation of the inflammatory response in lung cells. Glutathione and thioredoxin are the important protective antioxidants in the lungs. Regulation of intracellular redox glutathione and thioredoxin levels in response to reactive oxygen/nitrogen species and in inflammation should have critical effects on different lung cells on the activation of redox sensor/signal transduction pathways and various transcription factors. Possibly via the modification of cysteine residues, oxidative stress activates multiple stress kinase pathways and transcription factors nuclear factor-kappaB and activator protein-1, which differentially regulate the genes for proinflammatory cytokines as well as the protective antioxidant genes. Emerging data suggest that protein-S-thiolation, protein-S-nitrosation, and oxidation of protein-SH (formation of sulfenic, sulfinic, and sulfonic acids) are critical in redox signaling during normal physiology and under oxidative stress in controlling the cellular processes. In this review, we discuss the recent findings in the context of redox signaling during inflammation, pathology, and the role of redox modulating agents/dietary interventions either to inhibit abnormal signaling or induce/boost the endogenous antioxidant systems. Furthermore, this also provides information as to how antioxidants are involved in redox signaling to control inflammatory and oxidative stress in the lung.