Antioxidant effects of stereoisomers of N-acetylcysteine (NAC), L-NAC and D-NAC, on angiotensin II-stimulated MAP kinase activation and vascular smooth muscle cell proliferation

A ROS-dependent mechanism promotes CDK2 phosphorylation to drive progression through S phase

Reactive oxygen species (ROS) at the right concentration promote cell proliferation in cell culture, stem cells, and model organisms. However, the mystery of how ROS signaling is coordinated with cell cycle progression and integrated into the cell cycle control machinery on the molecular level remains unsolved. Here, we report increasing levels of mitochondrial ROS during the cell cycle in human cell lines that target cyclin-dependent kinase 2 (CDK2). Chemical and metabolic interferences with ROS production decrease T-loop phosphorylation on CDK2 and so impede its full activation and thus its efficient DNA replication. ROS regulate CDK2 activity through the oxidation of a conserved cysteine residue near the T-loop, which prevents the binding of the T-loop phosphatase KAP. Together, our data reveal how mitochondrial metabolism is coupled with DNA replication and cell cycle progression via ROS, thereby demonstrating how KAP activity toward CDKs can be cell cycle regulated.

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Mitochondrial ROS drive cell cycle progression and proliferation

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Cyclin-dependent kinase 2 (CDK2) is increasingly oxidized during the cell cycle

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The oxidation state of a conserved cysteine on CDK2 regulates KAP binding

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CDK2 oxidation promotes T-loop phosphorylation and DNA replication

Raloxifene and n-Acetylcysteine Ameliorate TGF-Signalling in Fibroblasts from Patients with Recessive Dominant Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a severe skin disease caused by mutation of the COL7A1 gene. RDEB is associated with high levels of TGF-β1, which is likely to be involved in the fibrosis that develops in this disease. Endoglin (CD105) is a type III coreceptor for TGF-β1 and its overexpression in fibroblasts deregulates physiological Smad/Alk1/Alk5 signalling, repressing the synthesis of TGF-β1 and extracellular matrix (ECM) proteins. Raloxifene is a specific estrogen receptor modulator designated as an orphan drug for hereditary hemorrhagic telangiectasia, a rare vascular disease. Raloxifene stimulates endoglin synthesis, which could attenuate fibrosis. By contrast, the antioxidant N-acetylcysteine may have therapeutic value to rectify inflammation, fibrosis and endothelial dysfunction. Thus, we present here a repurposing strategy based on the molecular and functional screening of fibroblasts from RDEB patients with these drugs, leading us to propose the repositioning of these two well-known drugs currently in clinical use, raloxifene and N-acetylcysteine, to counteract fibrosis and inflammation in RDEB. Both compounds modulate the profibrotic events that may ultimately be responsible for the clinical manifestations in RDEB, suggesting that these findings may also be relevant for other diseases in which fibrosis is an important pathophysiological event.

Redox activation of DUSP4 by N-acetylcysteine protects endothelial cells from Cd²⁺-induced apoptosis

Redox imbalance is a primary cause of endothelial dysfunction (ED). Under oxidant stress, many critical proteins regulating endothelial function undergo oxidative modifications that lead to ED. Cellular levels of glutathione (GSH), the primary reducing source in cells, can significantly regulate cell function via reversible protein thiol modification. N-acetylcysteine (NAC), a precursor for GSH biosynthesis, is beneficial for many vascular diseases; however, the detailed mechanism of these benefits is still not clear. From HPLC analysis, NAC significantly increases both cellular GSH and tetrahydrobiopterin levels. Immunoblotting of endothelial NO synthase (eNOS) and DUSP4, a dual-specificity phosphatase with a cysteine as its active residue, revealed that both enzymes are upregulated by NAC. EPR spin trapping further demonstrated that NAC enhances NO generation from cells. Long-term exposure to Cd(2+) contributes to DUSP4 degradation and the uncontrolled activation of p38 and ERK1/2, leading to apoptosis. Treatment with NAC prevents DUSP4 degradation and protects cells against Cd(2+)-induced apoptosis. Moreover, the increased DUSP4 expression can redox-regulate the p38 and ERK1/2 pathways from hyperactivation, providing a survival mechanism against the toxicity of Cd(2+). DUSP4 gene knockdown further supports the hypothesis that DUSP4 is an antioxidant gene, critical in the modulation of eNOS expression, and thus protects against Cd(2+)-induced stress. Depletion of intracellular GSH by buthionine sulfoximine makes cells more susceptible to Cd(2+)-induced apoptosis. Pretreatment with NAC prevents p38 overactivation and thus protects the endothelium from this oxidative stress. Therefore, the identification of DUSP4 activation by NAC provides a novel target for future drug design.

Suppressive effects of electrochemically reduced water on matrix metalloproteinase-2 activities and in vitro invasion of human fibrosarcoma HT1080 cells

It has been demonstrated that hydrogen peroxide (H(2)O(2)) is directly associated with elevated matrix metalloproteinase-2 (MMP-2) expression in several cell lines. Electrochemically reduced water (ERW), produced near the cathode during electrolysis, and scavenges intracellular H(2)O(2) in human fibrosarcoma HT1080 cells. RT-PCR and zymography analyses revealed that when HT1080 cells were treated with ERW, the gene expression of MMP-2 and membrane type 1 MMP and activation of MMP-2 was repressed, resulting in decreased invasion of the cells into matrigel. ERW also inhibited H(2)O(2)-induced MMP-2 upregulation. To investigate signal transduction involved in MMP-2 downregulation, mitogen-activated protein kinase (MAPK)-specific inhibitors, SB203580 (p38 MAPK inhibitor), PD98059 (MAPK/extracellular regulated kinase kinase 1 inhibitor) and c-Jun NH(2)-terminal kinase inhibitor II, were used to block the MAPK signal cascade. MMP-2 gene expression was only inhibited by SB203580 treatment, suggesting a pivotal role of p38 MAPK in regulation of MMP-2 gene expression. Western blot analysis showed that ERW downregulated the phosphorylation of p38 both in H(2)O(2)-treated and untreated HT1080 cells. These results indicate that the inhibitory effect of ERW on tumor invasion is due to, at least in part, its antioxidative effect.

Ionizing radiation-induced metabolic oxidative stress and prolonged cell injury

Cellular exposure to ionizing radiation leads to oxidizing events that alter atomic structure through direct interactions of radiation with target macromolecules or via products of water radiolysis. Further, the oxidative damage may spread from the targeted to neighboring, non-targeted bystander cells through redox-modulated intercellular communication mechanisms. To cope with the induced stress and the changes in the redox environment, organisms elicit transient responses at the molecular, cellular and tissue levels to counteract toxic effects of radiation. Metabolic pathways are induced during and shortly after the exposure. Depending on radiation dose, dose-rate and quality, these protective mechanisms may or may not be sufficient to cope with the stress. When the harmful effects exceed those of homeostatic biochemical processes, induced biological changes persist and may be propagated to progeny cells. Physiological levels of reactive oxygen and nitrogen species play critical roles in many cellular functions. In irradiated cells, levels of these reactive species may be increased due to perturbations in oxidative metabolism and chronic inflammatory responses, thereby contributing to the long-term effects of exposure to ionizing radiation on genomic stability. Here, in addition to immediate biological effects of water radiolysis on DNA damage, we also discuss the role of mitochondria in the delayed outcomes of ionization radiation. Defects in mitochondrial functions lead to accelerated aging and numerous pathological conditions. Different types of radiation vary in their linear energy transfer (LET) properties, and we discuss their effects on various aspects of mitochondrial physiology. These include short and long-term in vitro and in vivo effects on mitochondrial DNA, mitochondrial protein import and metabolic and antioxidant enzymes.

Effects of post-resuscitation treatment with N-acetylcysteine on cardiac recovery in hypoxic newborn piglets

Aims

Although N-acetylcysteine (NAC) can decrease reactive oxygen species and improve myocardial recovery after ischemia/hypoxia in various acute animal models, little is known regarding its long-term effect in neonatal subjects. We investigated whether NAC provides prolonged protective effect on hemodynamics and oxidative stress using a surviving swine model of neonatal asphyxia.

Methods and Results

Newborn piglets were anesthetized and acutely instrumented for measurement of systemic hemodynamics and oxygen transport. Animals were block-randomized into a sham-operated group (without hypoxia-reoxygenation [H–R, n = 6]) and two H-R groups (2 h normocapnic alveolar hypoxia followed by 48 h reoxygenation, n = 8/group). All piglets were acidotic and in cardiogenic shock after hypoxia. At 5 min after reoxygenation, piglets were given either saline or NAC (intravenous 150 mg/kg bolus + 20 mg/kg/h infusion) via for 24 h in a blinded, randomized fashion. Both cardiac index and stroke volume of H-R controls remained lower than the pre-hypoxic values throughout recovery. Treating the piglets with NAC significantly improved cardiac index, stroke volume and systemic oxygen delivery to levels not different from those of sham-operated piglets. Accompanied with the hemodynamic improvement, NAC-treated piglets had significantly lower plasma cardiac troponin-I, myocardial lipid hydroperoxides, activated caspase-3 and lactate levels (vs. H-R controls). The change in cardiac index after H-R correlated with myocardial lipid hydroperoxides, caspase-3 and lactate levels (all p<0.05).

Conclusions

Post-resuscitation administration of NAC reduces myocardial oxidative stress and caused a prolonged improvement in cardiac function and in newborn piglets with H-R insults.

Redox control of the cell cycle in health and disease

The cellular oxidation and reduction (redox) environment is influenced by the production and removal of reactive oxygen species (ROS). In recent years, several reports support the hypothesis that cellular ROS levels could function as ''second messengers'' regulating numerous cellular processes, including proliferation. Periodic oscillations in the cellular redox environment, a redox cycle, regulate cell-cycle progression from quiescence (G(0)) to proliferation (G(1), S, G(2), and M) and back to quiescence. A loss in the redox control of the cell cycle could lead to aberrant proliferation, a hallmark of various human pathologies. This review discusses the literature that supports the concept of a redox cycle controlling the mammalian cell cycle, with an emphasis on how this control relates to proliferative disorders including cancer, wound healing, fibrosis, cardiovascular diseases, diabetes, and neurodegenerative diseases. We hypothesize that reestablishing the redox control of the cell cycle by manipulating the cellular redox environment could improve many aspects of the proliferative disorders.

Complex N-acetyl-L-cysteine compounds with biometals as self-defense factors of biological system

We studied the effects of complex N-acetyl-L-cysteine compounds with transitional biometals on the inflammatory and adaptation reactions. Some compounds were superior to known antihypoxants and actoprotectors and exhibited significant antiinflammatory activity.

NAC for noise: from the bench top to the clinic

Noise-induced hearing loss (NIHL) is an important etiology of deafness worldwide. Hearing conservation programs are in place and have reduced the prevalence of NIHL, but this disorder is still far too common. Occupational and recreational pursuits expose people to loud noise and ten million persons in the US have some degree of noise-induced hearing impairment. It is estimated that 50 million in the US and 600 million people worldwide are exposed to noise hazards occupationally. Noise deafness is still an important and frequent cause of battlefield injury in the US military. A mainstay of hearing conservation programs is personal mechanical hearing protection devices which are helpful but have inherent limitations. Research has shown that oxidative stress plays an important role in noise-induced cochlear injury resulting in the discovery that a number of antioxidant and cell death inhibiting compounds can ameliorate deafness associated with acoustic trauma. This article reviews one such compound, N-acetylcysteine (NAC), in terms of its efficacy in reducing hearing loss in a variety of animal models of acute acoustic trauma and hypothesizes what its therapeutic mechanisms of action might be based on the known actions of NAC. Early clinical trials with NAC are mentioned.

The effect of hyperoxia on reactive oxygen species (ROS) in rat petrosal ganglion neurons during development using organotypic slices

Hyperoxia, during development in rats, results in hypoxic chemosensitivity ablation, carotid body hypoplasia, and reduced chemoafferents. We hypothesized that hyperoxia increases reactive oxygen species (ROS) in cell bodies of chemoafferents. Organotypic slices of petrosal-nodose ganglia from rats at day of life (DOL) 5-6 and 17-18 were exposed to 8%, 21%, or 95% O(2) for 4 h in the presence or absence of the ROS-sensitive fluorescent indicator, CM-H(2)DCFDA, and propidium iodide was used to determine the relationship between cell death and oxygen tension. In tissue slices from DOL 5-6 rats, fluorescence intensity was 182.5 +/- 2.9 for hypoxia, 217.5 +/- 3.3 for normoxia, and 336.6 +/- 3.8 for hyperoxia, (mean +/- SEM, p < 0.001, ANOVA). Normoxia increased ROS levels by 19.2% from hypoxia (p < 0.01) with a further increase of 54.8% from normoxia to hyperoxia (p < 0.001). In tissue slices from DOL 17-18 rats, ROS levels increased with increasing oxygen tension but were less than in younger animals (p < 0.01, ANOVA). The antioxidants, NAC and TEMPO-9-AC, attenuated ROS levels and cell death. Electron microscopy demonstrated that hyperoxia damages the ultrastructure within petrosal ganglion neurons. Hyperoxic-induced increased levels of ROS in petrosal ganglion neurons may contribute to loss of hypoxic chemosensitivity during early postnatal development.

A redox cycle within the cell cycle: ring in the old with the new

In recent years, the intracellular oxidation-reduction (redox) state has gained increasing attention as a critical mediator of cell signaling, gene expression changes and proliferation. This review discusses the evidence for a redox cycle (i.e., fluctuation in the cellular redox state) regulating the cell cycle. The presence of redox-sensitive motifs (cysteine residues, metal co-factors in kinases and phosphatases) in several cell cycle regulatory proteins indicate periodic oscillations in intracellular redox state could play a central role in regulating progression from G0/G1 to S to G2 and M cell cycle phases. Fluctuations in the intracellular redox state during cell cycle progression could represent a fundamental mechanism linking oxidative metabolic processes to cell cycle regulatory processes. Proliferative disorders are central to a variety of human pathophysiological conditions thought to involve oxidative stress. Therefore, a more complete understanding of redox control of the cell cycle could provide a biochemical rationale for manipulating aberrant cell proliferation.

Nitric oxide/cGMP signaling pathway protects RAW264 cells against nitric oxide-induced apoptosis by inhibiting the activation of p38 mitogen-activated protein kinase

Nitric oxide (NO) induces apoptosis in various cells lines, while activation of the NO/cGMP signaling pathway prevents apoptosis induced by diverse stimuli, including NO. Here, we report the cytoprotective mechanisms of the NO/cGMP signaling pathway against NO-induced apoptosis in a mouse macrophage-like cell line, RAW264. Treatment with sodium nitroprusside (SNP), an NO donor, at a high-toxic concentration (4 mM) stimulated the N-terminal conformational change of Bax and its translocation to mitochondria followed by cytochrome c release and nuclear fragmentation in RAW264 cells. These changes of Bax were attenuated by pretreatment with SNP at a low-nontoxic concentration (100 microM) or dibutyryl cGMP (DBcGMP), a cell-permeable cGMP analogue. SB203580, a p38 mitogen-activated protein kinase (MAP kinase) inhibitor, blocked the effects of 4 mM SNP on Bax translocation and cell viability. Treatment with 4 mM SNP activated p38 MAP kinase and this effect was prevented by pretreatment with 100 microM SNP or DBcGMP. These findings suggest that the NO/cGMP signaling pathway inhibits NO-induced apoptosis of macrophages by suppressing the p38 MAP kinase activation, which results in N-terminal conformational change of Bax and its translocation to mitochondria.

Involvement of Aldosterone and Mineralocorticoid Receptors in Rat Mesangial Cell Proliferation and Deformability

We demonstrated recently that chronic administration of aldosterone to rats induces glomerular mesangial injury and activates mitogen-activated protein kinases including extracellular signal-regulated kinases 1/2 (ERK1/2). We also observed that the aldosterone-induced mesangial injury and ERK1/2 activation were prevented by treatment with a selective mineralocorticoid receptor (MR) antagonist, eplerenone, suggesting that the glomerular mesangium is a potential target for injuries induced by aldosterone via activation of MR. In the present study, we investigated whether MR is expressed in cultured rat mesangial cells (RMCs) and involved in aldosterone-induced RMC injury. MR expression and localization were evaluated by Western blotting analysis and fluorolabeling methods. Cell proliferation and micromechanical properties were determined by [ 3 H]-thymidine uptake measurements and a nanoindentation technique using an atomic force microscope cantilever, respectively. ERK1/2 activity was measured by Western blotting analysis with an anti-phospho–ERK1/2 antibody. Protein expression and immunostaining revealed that MR was abundant in the cytoplasm of RMCs. Aldosterone (1 to 100 nmol/L) dose-dependently activated ERK1/2 in RMCs with a peak at 10 minutes. Pretreatment with eplerenone (10 μmol/L) significantly attenuated aldosterone-induced ERK1/2 phosphorylation. Aldosterone (100 nmol/L) treatment for 30 hours increased [ 3 H]-thymidine incorporation and decreased the elastic modulus, indicating cellular proliferative and deforming effects of aldosterone, respectively. These aldosterone-induced changes in cellular characteristics were prevented by pretreatment with eplerenone or an ERK (MEK) inhibitor, PD988059 (100 μmol/L). The results indicate that aldosterone directly induces RMC proliferation and deformability through MR and ERK1/2 activation, which may contribute to the pathogenesis of glomerular mesangial injury.

Angiotensin II induces focal adhesion kinase/paxillin phosphorylation and cell migration in human umbilical vein endothelial cells

In the present study, we demonstrated that Ang II provokes a transitory enhancement of focal adhesion kinase (FAK) and paxillin phosphorylation in human umbilical endothelial cells (HUVEC). Moreover, Ang II induces a time- and dose-dependent augmentation in cell migration, but does not affect HUVEC proliferation. The effect of Ang II on FAK and paxillin phosphorylation was markedly attenuated in cells pretreated with wortmannin and LY294002, indicating that phosphoinositide 3-kinase (PI3K) plays an important role in regulating FAK activation. Similar results were observed when HUVEC were pretreated with genistein, a non-selective tyrosine kinases inhibitor, or with the specific inhibitor PP2 for Src family kinases, demonstrating the involvement of protein tyrosine kinases, and particularly Src family of tyrosine kinases, in the downstream signalling pathway of Ang II receptors. Furthermore, FAK and paxillin phosphorylation was markedly blocked after treatment of HUVEC with AG1478, a selective inhibitor of epidermal growth factor receptor (EGFR) phosphorylation. Pretreatment of cells with inhibitors of PI3K, Src family tyrosine kinases, and EGFR also decreased HUVEC migration. In conclusion, these results suggest that Ang II mediates an increase in FAK and paxillin phosphorylation and induces HUVEC migration through signal transduction pathways dependent on PI3K and Src tyrosine kinase activation and EGFR transactivation.