Action of lipid peroxidation products on phosphoinositide specific phospholipase C

Phospholipase A₂-Generated Lipid Mediators in the Brain: The Good, the Bad, and the Ugly

Phospholipase A2 (PLA2) generates arachidonic acid, docosahexaenoic acid, and lysophospholipids from neural membrane phospholipids. These metabolites have a variety of physiological effects by themselves and also are substrates for the synthesis of more potent lipid mediators such as eicosanoids, platelet activating factor, and 4-hydroxynonenal (4-HNE). At low concentrations, these mediators act as second messengers. They affect and modulate several cell functions, including signal transduction, gene expression, and cell proliferation, but at high concentrations, these lipid mediators cause neurotoxicity. Among the metabolites generated by PLA2, 4-HNE is the most cytotoxic metabolite and is associated with the apoptotic type of neural cell death. Levels of 4-HNE are markedly increased in neurological disorders such as Alzheimer disease, Parkinson disease, ischemia, spinal cord trauma, and head injury. The purpose of this review is to summarize and integrate the vast literature on metabolites generated by PLA2 for a wider audience. The authors hope that this discussion will jump-start more studies not only on the involvement of PLA2 in neurological disorders but also on the importance of PLA2-generated lipid mediators in physiological and pathological processes.

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Simvastatin prevents oxygen and glucose deprivation/reoxygenation-induced death of cortical neurons by reducing the production and toxicity of 4-hydroxy-2E-nonenal

Lipid membrane peroxidation is highly associated with neuronal death in various neurodegenerative diseases including cerebral stroke. Here, we report that simvastatin decreases oxygen and glucose deprivation (OGD)/reoxygenation-evoked neuronal death by inhibiting the production and cytoxicity of 4-hydroxy-2E-nonenal (HNE), the final product of lipid peroxidation. Simvastatin markedly decreased the OGD/reoxygenation-evoked death of cortical neurons. OGD/reoxygenation increased the intracellular HNE level mostly in neuronal cells, not glial cells. Simvastatin decreased the intracellular level of HNE in neuronal cells exposed to OGD/reoxygenation. We further found that HNE induced the cytotoxicity in neuronal cells and synergistically increased the N-methyl-D-aspartate (NMDA) receptor-mediated excitotoxicity. Simvastatin largely blocked the NMDA neurotoxicity potentiated by HNE. However, simvastatin did not alter the NMDA-evoked calcium influx in the absence or presence of HNE. HNE inhibited the activity of nuclear factor-kappa B (NF-kappaB), and the cytotoxicity of HNE was in good correlation with inactivation of NF-kappaB. Simvastatin reversed the inhibition of NF-kappaB activity induced by OGD/reoxygenation or HNE. The neuroprotection by simvastatin was significantly attenuated by various NF-kappaB inhibitors, implying that simvastatin inhibits the cytotoxicity of HNE at least in part by maintaining the activity of NF-kappaB. Further understanding of the neuroprotective mechanism of simvastatin may provide a therapeutic strategy for oxidative stress-related neurodegenerative diseases.

Possible involvement of 4-hydroxynonenal in splenocyte regulated liver regeneration

Liver regeneration is a complex, systemic process regulated by humoral and cellular mechanisms. Inflammatory response to the extensive tissue damage, as in partial hepatectomy, plays important role during regeneration. Hence, it is assumed that the spleen might play a role in systemic inflammatory response involved in liver regeneration. On the other hand, liver damage and consequential regeneration are often associated with oxidative stress and lipid peroxidation. One of the end products of lipid peroxidation, 4-hydroxynonenal (HNE), is nowadays considered not only as a "second toxic messenger of free radicals" but also as a growth-regulating factor. We therefore studied in vitro interactions of the HNE-treated murine liver cells and autologous spleen cells. The spleen cells supported recovery of liver cells from the HNE cytotoxicity although spleen cells themselves exerted cytotoxic effects against the proliferating liver cells that were not treated with HNE. Our results imply that the cytokines secreted by activated immunocompetent cells may be responsible for the observed recovery of the HNE-damage liver cells, suggesting that HNE might be an important factor regulating cellular and cytokine mediated mechanisms of liver regeneration control.

4-Hydroxy-2-nonenal: a product and mediator of oxidative stress

The onset of lipid peroxidation within cellular membranes is associated with changes in their physiochemical properties and with the impairment of enzymatic functions located in the membrane environment. There is increasing evidence that aldehydic molecules generated endogenously during the process of lipid peroidation are causally involved in most of the pathophysiological effects associated with oxidative stress in cells and tissues. 4-Hydroxy-2-nonenal (HNE), among them, is believed to be largely responsible for cytopathological effects observed during oxidative stree in vivo and has achieved the status of one of the best recognized and most studied of the cytotoxic products of lipid peroxidation. In the present review, I provide a comprehensive summary of HNE, as the product and mediator or oxidative stress.

Lipid peroxidation product 4-hydroxy-2-nonenal acts synergistically with serotonin in inducing vascular smooth muscle cell proliferation

Formation of an atherosclerotic lesion is in part mediated by inflammatory and oxidative mechanisms including lipid peroxidation. To characterize the potential role of lipid peroxidation products in atherogenesis, we assessed the effect of 4-hydroxy-2-nonenal (HNE), a component of oxidatively modified lipids on vascular smooth muscle cells (VSMCs) proliferation, and its interaction with serotonin (5-hydroxytryptamine, 5-HT), a known mitogen for VSMCs. Growth-arrested rabbit VSMCs were incubated with different concentrations of HNE in the absence or presence of 5-HT. VSMCs proliferation was examined by increases in [3H]thymidine incorporation into DNA and cell number. HNE and 5-HT stimulated DNA synthesis in a dose-dependent manner. HNE had a maximal proliferative effect at a concentration of 1 microM (143% of the control) and 5-HT at 50 microM (211%). When added together, low concentrations of HNE (0.1 microM) and 5-HT (5 microM) synergistically induced DNA synthesis (273%). These effects on DNA synthesis were paralleled by an increase in cell number. A 5-HT2 receptor antagonist LY 281067 (10 microg/ml) and pertussis toxin (10 ng/ml) inhibited the mitogenic effect of 5-HT only. Protein tyrosine kinase inhibitor erbstatin A (10 microM) completely inhibited the mitogenic effect of HNE and partially that of 5-HT and the combined effect of HNE+5-HT. Protein kinase C inhibitor Ro 31-8220 (0.1 microM) completely inhibited mitogenic effects of both HNE and 5-HT, and also the combined effect of HNE+5-HT. The synergistic effect of HNE+5-HT on DNA synthesis was completely reversed by the combined use of LY 281067 (10 microg/ml) and antioxidants N-acetylcysteine (400 microM), vitamin C (200 microM), or vitamin E (20 microM). Our results suggest that HNE acts synergistically with 5-HT in inducing VSMCs proliferation. Combined use of both antiplatelet and antioxidant therapies may be useful for the prevention of VSMCs proliferative disorders associated with atherosclerosis and restenosis after angioplasty.

Induction of rat aortic smooth muscle cell growth by the lipid peroxidation product 4-hydroxy-2-nonenal

BACKGROUND

Atherosclerotic lesion formation is a complex process, in part mediated by inflammatory and oxidative mechanisms including lipid peroxidation. To further characterize the potential role of lipid peroxidation products in atherogenesis, we studied the effects of 4-hydroxy-2-nonenal (HNE) on rat aortic smooth muscle cell growth.

METHODS AND RESULTS

HNE, at concentrations of 1.0 and 2.5 micromol/L, significantly stimulated rat aortic smooth muscle cell growth as determined by cell counts, [3H]-thymidine uptake, and incorporation of bromo-deoxyuridine. To characterize the mechanism of HNE-induced mitogenesis, its effect on activation of intracellular growth signaling pathways was examined. Treatment with HNE resulted in activation of extracellular signal-regulated protein kinases ERK1 and ERK2, induction of c-fos and c-jun protein expression, and an increase in transcription factor AP-1 DNA binding activity. In addition, HNE induced expression of platelet-derived growth factor-AA (PDGF-AA) protein, and an anti-PDGF-AA antibody specifically inhibited HNE-mediated DNA synthesis, suggesting that growth factor induction may play a role in HNE-induced vascular smooth muscle cell growth. The role of redox-sensitive mechanisms in this process was further supported by the observation that HNE-induced DNA synthesis and AP-1 activation were inhibited by the antioxidants N-acetylcysteine and pyrrolidine dithiocarbamate.

CONCLUSIONS

These data demonstrate that HNE, one of several important lipid peroxidation products, induces rat aortic smooth muscle cell growth through redox-sensitive mechanisms and growth factor expression. These observations are consistent with a role for lipid peroxidation products in vascular smooth muscle cell growth in atherogenesis.

Phosphatase inhibitors potentiate 4-hydroxynonenal-induced phospholipase D activation in vascular endothelial cells

We have previously reported that endothelial cell phospholipase D (PLD), activated by 4-hydroxynonenal (4-HNE), was independent of protein kinase C activation. To determine whether PLD stimulation by 4-HNE is related to protein tyrosine phosphorylation, the effects of tyrosine kinase (Tyrk) and protein tyrosine phosphatase (PTPase) inhibitors on PLD activation were investigated. Pretreatment of bovine pulmonary artery endothelial cells (BPAEC) with Tyrk inhibitors, such as genistein, erbstatin, and herbimycin attenuated 4-HNE-induced PLD activation. Furthermore, vanadate, phenylarsine oxide, and diamide, inhibitors of PTPases, markedly increased the 4-HNE-induced PLD activation. The effects of Tyrk and PTPase inhibitors were specific towards the 4-HNE, as these agents had no effect on the agonist- or TPA-induced PLD activation. In addition to PLD activation, treatment of BPAEC with 4-HNE increased tyrosine phosphorylation of proteins including bands of molecular weights 40,000-60,000, 70,000-90,000, and 110,000-130,000. The 4-HNE-mediated increase in protein tyrosine phosphorylation was partly inhibited by genistein (100 microM). Vanadate (10 microM) pretreatment also potentiated 4-HNE-induced protein tyrosine phosphorylation. These data suggest that 4-HNE-mediated stimulation of PLD may occur as a result of activation of tyrosine kinases.