N-acetyl-L-cysteine inhibits 26S proteasome function: implications for effects on NF-kappaB activation

Anti-inflammatory effects of N-Acetylcysteine and Elaeagnus angustifolia extract on acute lung injury induced by λ-carrageenan in rat

N-Acetylcysteine (NAC) is a chemical compound with anti-inflammatory and antioxidant activity and acts as a free radical scavenger. Elaeagnus angustifolia (EA) is a plant native to the western part of Iran, with antioxidant and anti-inflammatory properties. The present study been taken evaluated the protective effect afforded by EA and NAC extracts on carrageenan-induced acute lung injury in Wistar rats. In this study, 42 rats were randomly assigned into seven groups. NAC and EA extracts were orally administered once/day for 21 continuous days. Pulmonary damage was induced by intratracheal injection of 100 μl of 2% λ-Carrageenan on day 21. Twenty-four hours post-surgery, the rats were euthanized and the samples were collected. Pretreatment with NAC and EA extracts reduced the total and differential cell accumulation as well as IL-6, and TNF-α cytokines. Antioxidant indicators demonstrate that in the groups receiving NAC and EA extract, MDA decreased while thiol and antioxidant capacity elevated. Treatment with NAC and EA significantly reduced Carrageenan-induced pathological pulmonary tissue injury. NAC and EA extract has protective effects on acute carrageenan-induced lung injury.

The role of topical N-acetylcysteine in ocular therapeutics

N-acetylcysteine (NAC) was first discovered as a mucolytic agent in 1960. We investigate the role of topical NAC in ocular therapeutics, including its mechanism of action, current applications, and adverse effects. A systematic search of peer-reviewed articles identified 106 references including in vitro, in vivo and clinical studies on the use of NAC in the treatment of ocular diseases. NAC can be synthetically manufactured, and its mechanisms of action include mucolysis, scavenging hydroxyl radicals, and modulation of inflammatory cascades. These unique properties contribute to the diverse applications of NAC, including its steroid-sparing potential. NAC has been used topically in the treatment of corneal wounds, chemical injuries, keratitis, dry eye disease and meibomian gland dysfunction. The clinical benefits of NAC are evident over a wide range of concentrations, the most common being 5-10% topical NAC applied four times daily. Adverse effects such as corneal necrosis are rare, but have been reported with higher doses. NAC also has potential applications in laser epithelial keratomileusis, diabetic eye disease, retinitis pigmentosa, senile nuclear cataracts, macular degeneration, and cigarette smoke-induced corneal damage. Recently, chitosan-NAC has been used as a nanocarrier for the topical administration of medications to the ocular surface. Owing to its potent antioxidant, anti-inflammatory and mucolytic properties, topical NAC has had extensive use in the treatment of ocular pathology.

Clinical influence of calcium hydroxide and N-acetylcysteine on the levels of resolvins E1 and D2 in apical periodontitis

AIM

To investigate the presence of resolvins E1 (RvE1) and D2 (RvD2) in teeth with primary endodontic infections and apical periodontitis, and to assess the influence of calcium hydroxide medication [Ca(OH)₂ ], in association with 2% chlorhexidine gel (2% CHX gel), and N-acetylcysteine (NAC) on the levels of RvE1 and RvD2 in periapical tissues.

METHODOLOGY

Thirty-six single-rooted teeth with primary endodontic infections and apical periodontitis were selected and randomly divided into three groups according to the medication: [Ca(OH)₂ ] + saline solution (SSL) [Ca(OH)₂  + SSL group] (n = 12), Ca(OH)₂  + 2% chlorhexidine gel [Ca(OH)₂  + 2% CHX gel group] (n = 12) and NAC [NAC group] (n = 12). Samples were collected from the periapical interstitial fluid at two different sampling times: before (S1) and after 14 days of intracanal medications (S2). Resolvins were measured using the enzyme-linked immunosorbent assay. Data were analysed using paired t-test, Wilcoxon test and Kruskal-Wallis test, followed by Dunn's post hoc test; all statistical tests were performed at a significance level of 5%.

RESULTS

RvE1 and RvD2 were detected in 100% of the samples (36/36) at S1 and S2. Ca(OH)₂ medication did not increase the levels of RvE1 or RvD2 (both P > 0.05); however, NAC significantly increased the levels of RvE1 and RvD2 after 14 days of treatment (P < 0.05).

CONCLUSIONS

RvE1 and RvD2 were detected in periapical tissues from teeth with root canal infections. Moreover, calcium hydroxide medication did not increase the levels of resolvins in apical periodontitis. In contrast, the use of NAC intracanal medication significantly increased the levels of RvE1 and RvD2 after 14 days of treatment.

Delayed effects of sulfur mustard on autophagy suppression in chemically-injured lung tissue

BACKGROUND

Autophagy is an intracellular hemostasis mechanism, responding to extracellular or intracellular stresses. Sulfur mustard (SM) induces cellular stress. Iranian soldiers exposed to SM gas, during the Iraq-Iran war, suffer from delayed complications even 30 years after exposure. In this study, for exploring the SM effect on autophagy pathway, gene and protein expression of autophagy markers are evaluated in the lung of SM-exposed people.

METHODS

52 FFPE lung tissues of SM-exposed people and 33 lung paraffin blocks of non-exposed patients to SM were selected. LC3 and Beclin-1 mRNA expressions were evaluated by QRT-PCR. LC3-B protein and LC3II/LC3I proteins ratio were detected by Immunohistochemistry and immunoblotting method. The collected data were analyzed in SPSS, and P value ≤ 0.05 was considered significant.

RESULTS

LC3 gene expression in SM-exposed subjects (median CT value = 4.97) increased about 4 fold compared with the control group (median CT value = 0.46, P = 0.025). Beclin-1 mRNA expression had not significant difference between two groups. After adjusting the confounding variables such as drug usage, LC3-B protein (P = 0.041) and LC3II/LC3I ratio (P = 0.044) were found significantly lower in the lung cells of SM-exposed group.

CONCLUSION

Upon exposure to SM gas, the lung cells are affected by acute cellular stress such as oxidative stress. The study results show that LC3 mRNA level increases in these patients, but, surprisingly, LC3-B protein via unknown mechanism has been down-regulated. N-acetyl cysteine and salbutamol drugs could induce the autophagy, and help to reduce the SM effects and improve the clinical condition of SM-injured patients.

Overview on the Effects of N-Acetylcysteine in Neurodegenerative Diseases

N-acetylcysteine (NAC), which is an acetylated cysteine compound, has aroused scientific interest for decades due to its important medical applications. It also represents a nutritional supplement in the human diet. NAC is a glutathione precursor and shows antioxidant and anti-inflammatory activities. In addition to the uses quoted in the literature, NAC may be considered helpful in therapies to counteract neurodegenerative and mental health diseases. Furthermore, this compound has been evaluated for its neuroprotective potential in the prevention of cognitive aging dementia. NAC is inexpensive, commercially available and no relevant side effects were observed after its administration. The purpose of this paper is to give an overview on the effects and applications of NAC in Parkinson's and Alzheimer's disorders and in neuropathic pain and stroke.

Promoter analysis and functional implications of the selenium binding protein (SBP) gene family in Arabidopsis thaliana

Selenium Βinding Protein (SBP, originally termed SBP56) was identified in mouse liver as a cytosolic protein that could bind radioactive selenium. SBPs are highly conserved proteins present in a wide array of species across all kingdoms and are likely to be involved in selenium metabolism. In Arabidopsis, the selenium binding protein (SBP) gene family comprises three genes (AtSBP1, AtSBP2 and AtSBP3). AtSBP1 and AtSBP2 are clustered in a head-to-tail arrangement on chromosome IV, while AtSBP3 is located on chromosome III. In this work, we studied the promoter activity of the Arabidopsis SBP genes, determined their tissue specificity and showed that they are differentially regulated by sodium selenite and sodium selenate. All three SBP genes are upregulated in response to externally applied selenium compounds and the antioxidant NAC selectively downregulates SBP2. Although the effect on SBP2 levels was the most prominent, in all cases, the concurrent exposure of plants to selenite and the antioxidant supressed the expression of the SBP genes. We provide evidence that (at least) SBP1 expression is tightly linked to detoxification processes related to oxidative stress, since it is downregulated in the presence of NAC in selenium-treated plants. Furthermore, our results suggest that SBP genes may participate in the mechanisms that sense redox imbalance.

Biological Activities and Potential Oral Applications of N-Acetylcysteine: Progress and Prospects

N-Acetylcysteine (NAC), a cysteine prodrug and glutathione (GSH) precursor, has been used for several decades in clinical therapeutic practices as a mucolytic agent and for the treatment of disorders associated with GSH deficiency. Other therapeutic activities of NAC include inhibition of inflammation/NF-κB signaling and expression of proinflammatory cytokines. N-Acetylcysteine is also a nonantibiotic compound possessing antimicrobial property and exerts anticarcinogenic and antimutagenic effects against certain types of cancer. Recently, studies describing potentially important biological and pharmacological activities of NAC have stimulated interests in using NAC-based therapeutics for oral health care. The present review focused on the biological activities of NAC and its potential oral applications. The potential side effects of NAC and formulations for drug delivery were also discussed, with the intent of advancing NAC-associated treatment modalities in oral medicine.

N-Acetyl-l-Cysteine Protects Astrocytes against Proteotoxicity without Recourse to Glutathione

N-acetyl-l-cysteine (NAC) exhibits protective properties in brain injury models and has undergone a number of clinical trials. Most studies of NAC have focused on neurons. However, neuroprotection may be complemented by the protection of astrocytes because healthier astrocytes can better support the viability of neurons. Here, we show that NAC can protect astrocytes against protein misfolding stress (proteotoxicity), the hallmark of neurodegenerative disorders. Although NAC is thought to be a glutathione precursor, NAC protected primary astrocytes from the toxicity of the proteasome inhibitor MG132 without eliciting any increase in glutathione. Furthermore, glutathione depletion failed to attenuate the protective effects of NAC. MG132 elicited a robust increase in the folding chaperone heat shock protein 70 (Hsp70), and NAC mitigated this effect. Nevertheless, three independent inhibitors of Hsp70 function ablated the protective effects of NAC, suggesting that NAC may help preserve Hsp70 chaperone activity and improve protein quality control without need for Hsp70 induction. Consistent with this view, NAC abolished an increase in ubiquitinated proteins in MG132-treated astrocytes. However, NAC did not affect the loss of proteasome activity in response to MG132, demonstrating that it boosted protein homeostasis and cell viability without directly interfering with the efficacy of this proteasome inhibitor. The thiol-containing molecules l-cysteine and d-cysteine both mimicked the protective effects of NAC, whereas the thiol-lacking molecule N-acetyl-S-methyl-l-cysteine failed to exert protection or blunt the rise in ubiquitinated proteins. Collectively, these findings suggest that the thiol group in NAC is required for its effects on glial viability and protein quality control.

Marine Streptomyces sp. derived antimycin analogues suppress HeLa cells via depletion HPV E6/E7 mediated by ROS-dependent ubiquitin-proteasome system

Four new antimycin alkaloids (1–4) and six related known analogs (5–10) were isolated from the culture of a marine derived Streptomyces sp. THS-55, and their structures were elucidated by extensive spectroscopic analysis. All of the compounds exhibited potent cytotoxicity in vitro against HPV-transformed HeLa cell line. Among them, compounds 6–7 were derived as natural products for the first time, and compound 5 (NADA) showed the highest potency. NADA inhibited the proliferation, arrested cell cycle distribution, and triggered apoptosis in HeLa cancer cells. Our molecular mechanic studies revealed NADA degraded the levels of E6/E7 oncoproteins through ROS-mediated ubiquitin-dependent proteasome system activation. This is the first report that demonstrates antimycin alkaloids analogue induces the degradation of high-risk HPV E6/E7 oncoproteins and finally induces apoptosis in cervical cancer cells. The present work suggested that these analogues could serve as lead compounds for the development of HPV-infected cervical cancer therapeutic agents, as well as research tools for the study of E6/E7 functions.

Evidence of a Redox-Dependent Regulation of Immune Responses to Exercise-Induced Inflammation

We used thiol-based antioxidant supplementation (n-acetylcysteine, NAC) to determine whether immune mobilisation following skeletal muscle microtrauma induced by exercise is redox-sensitive in healthy humans. According to a two-trial, double-blind, crossover, repeated measures design, 10 young men received either placebo or NAC (20 mg/kg/day) immediately after a muscle-damaging exercise protocol (300 eccentric contractions) and for eight consecutive days. Blood sampling and performance assessments were performed before exercise, after exercise, and daily throughout recovery. NAC reduced the decline of reduced glutathione in erythrocytes and the increase of plasma protein carbonyls, serum TAC and erythrocyte oxidized glutathione, and TBARS and catalase activity during recovery thereby altering postexercise redox status. The rise of muscle damage and inflammatory markers (muscle strength, creatine kinase activity, CRP, proinflammatory cytokines, and adhesion molecules) was less pronounced in NAC during the first phase of recovery. The rise of leukocyte and neutrophil count was decreased by NAC after exercise. Results on immune cell subpopulations obtained by flow cytometry indicated that NAC ingestion reduced the exercise-induced rise of total macrophages, HLA⁺ macrophages, and 11B⁺ macrophages and abolished the exercise-induced upregulation of B lymphocytes. Natural killer cells declined only in PLA immediately after exercise. These results indicate that thiol-based antioxidant supplementation blunts immune cell mobilisation in response to exercise-induced inflammation suggesting that leukocyte mobilization may be under redox-dependent regulation.

18O-Tracer Metabolomics Reveals Protein Turnover and CDP-Choline Cycle Activity in Differentiating 3T3-L1 Pre-Adipocytes

The differentiation of precursor cells into mature adipocytes (adipogenesis) has been an area of increased focus, spurred by a rise in obesity rates. Though our understanding of adipogenesis and its regulation at the cellular level is growing, many questions remain, especially regarding the regulation of the metabolome. The 3T3-L1 cell line is the most well characterized cellular model of adipogenesis. Using a time course metabolomics approach, we show that the 3T3-L1 preadipocyte metabolome is greatly altered during the first 48 hours of differentiation, where cells go through about two rounds of cell division, a process known as mitotic clonal expansion. Short-chain peptides were among several small molecules that were increased during mitotic clonal expansion. Additional indicators of protein turnover were also increased, including bilirubin, a degradation product of heme-containing proteins, and 3-methylhistidine, a post-translationally modified amino acid that is not reutilized for protein synthesis. To study the origin of the peptides, we treated differentiating preadipocytes with ¹⁸O labeled water and found that ¹⁸O was incorporated into the short chain peptides, confirming them, at least in part, as products of hydrolysis. Inhibitors of the proteasome or matrix metalloproteinases affected the peptide levels during differentiation, but inhibitors of autophagy or peptidases did not. ¹⁸O was also incorporated into several choline metabolites including cytidine 5'-diphosphocholine (CDP-choline), glycerophosphocholine, and several phosphatidylcholine species, indicative of phosphatidylcholine synthesis/degradation and of flux through the CDP-choline cycle, a hallmark of proliferating cells. ¹⁸O-Tracer metabolomics further showed metabolic labeling of glutamate, suggestive of glutaminolysis, also characteristic of proliferating cells. Together, these results highlight the utility of ¹⁸O isotope labeling in combination with metabolomics to uncover changes in cellular metabolism that are not detectable by time-resolved metabolomics.

N-acetylcysteine Protects Mice from High Fat Diet-induced Metabolic Disorders

PURPOSE

To study the effects of N-acetylcysteine (NAC, C5H9NO3S) on diet-induced obesity and obesity-related metabolic disorders.

METHODS

Six-week-old male C57BL/6 mice fed a chow or high-fat diet (HFD) were treated with NAC (2 g/L) in drinking water for 11 weeks. Its influences on body weight and food intake were manually measured, and influence on body composition were analyzed by magnetic residence imaging. Glucose meter and ELISA were used to determine serum glucose and insulin levels, as well as lipid content in the liver. The effects of NAC treatment on mRNA levels of genes involved in inflammation, thermogenesis, and lipid metabolism in various tissues were determined by real time PCR.

RESULTS

NAC supplementation inhibited the increase of fat mass and the development of obesity when mice were fed an HFD. NAC treatment significantly lowered HFD-induced macrophage infiltration, and enhanced adiponectin gene expression, resulting in reduced hyperglycemia and hyperinsulinemia, and improvement of insulin resistance. NAC oral administration suppressed hepatic lipid accumulation, as evidenced by lower levels of triglyceride and cholesterol in the liver. The beneficial effects are associated with a decrease of hepatic Pparγ and its target gene expression, and an increase in the expression of genes responsible for lipid oxidation and activation of farnesoid X receptor. Furthermore, NAC treatment also stimulates expression of thermogenic genes.

CONCLUSION

These results provide direct proof of the protective potential of NAC against HFD-induced obesity and obesity-associated metabolic disorders.

A minireview on N-acetylcysteine: An old drug with new approaches

N-acetylcysteine (NAC), a cysteine pro-drug and glutathione precursor has been used in therapeutic practices for several decades, as a mucolytic agent and for the treatment of numerous disorders including paracetamol intoxication. There is a growing interest concerning the beneficial effects of NAC against the early stages of toxicity-induced by pesticides. Nevertheless, the mechanisms underlying the therapeutic and clinical applications of NAC are not fully understood. In this review we aimed to focus on the protective effects of NAC against oxidative stress caused by pesticide in many organs. The possible mechanisms of action may be associated to its antioxidant properties. The anti-oxidative activity of NAC has been attributed to the fast reaction with free radicals as well as the restitution of reduced glutathione (GSH).

Oxidative Stress and Inflammation in Hepatic Diseases: Therapeutic Possibilities of N-Acetylcysteine

Liver disease is highly prevalent in the world. Oxidative stress (OS) and inflammation are the most important pathogenetic events in liver diseases, regardless the different etiology and natural course. N-acetyl-l-cysteine (the active form) (NAC) is being studied in diseases characterized by increased OS or decreased glutathione (GSH) level. NAC acts mainly on the supply of cysteine for GSH synthesis. The objective of this review is to examine experimental and clinical studies that evaluate the antioxidant and anti-inflammatory roles of NAC in attenuating markers of inflammation and OS in hepatic damage. The results related to the supplementation of NAC in any form of administration and type of study are satisfactory in 85.5% (n = 59) of the cases evaluated (n = 69, 100%). Within this percentage, the dosage of NAC utilized in studies in vivo varied from 0.204 up to 2 g/kg/day. A standard experimental design of protection and treatment as well as the choice of the route of administration, with a broader evaluation of OS and inflammation markers in the serum or other biological matrixes, in animal models, are necessary. Clinical studies are urgently required, to have a clear view, so that, the professionals can be sure about the effectiveness and safety of NAC prescription.

Docosahexaenoic acid induces the degradation of HPV E6/E7 oncoproteins by activating the ubiquitin-proteasome system

The oncogenic human papillomavirus (HPV) E6/E7 proteins are essential for the onset and maintenance of HPV-associated malignancies. Here, we report that activation of the cellular ubiquitin–proteasome system (UPS) by the omega-3 fatty acid, docosahexaenoic acid (DHA), leads to proteasome-mediated degradation of E6/E7 viral proteins and the induction of apoptosis in HPV-infected cancer cells. The increases in UPS activity and degradation of E6/E7 oncoproteins were associated with DHA-induced overproduction of mitochondrial reactive oxygen species (ROS). Exogenous oxidative stress and pharmacological induction of mitochondrial ROS showed effects similar to those of DHA, and inhibition of ROS production abolished UPS activation, E6/E7 viral protein destabilization, and apoptosis. These findings identify a novel role for DHA in the regulation of UPS and viral proteins, and provide evidence for the use of DHA as a mechanistically unique anticancer agent for the chemoprevention and treatment of HPV-associated tumors.

Molecular analysis of the inhibitory effect of N-acetyl-L-cysteine on the proliferation and invasiveness of pancreatic cancer cells

Preliminary studies have suggested that the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine (NAC) may be effective in inhibiting the growth of pancreatic cancer cells. In-depth cellular and molecular analyses were carried out to determine NAC's mode of action in inhibiting the growth of a well-characterized pancreatic cancer cell line (AsPC-1). Standardized assays were used to monitor cellular growth, apoptosis, levels of ROS, cellular senescence, migration, and invasiveness. Cell stiffness was measured using atomic force microscopy. Gene expression was monitored by quantitative PCR. NAC significantly inhibits the growth and metastatic potential of AsPC-1 cells by inducing cell-cycle arrest in G1 and subsequent cellular senescence and decreased invasiveness. These anticancer properties are associated with an unexpected increase in the intracellular concentrations of ROS. NAC does not decrease the susceptibility of AsPC-1 cells to the anticancer drugs gemcitabine, mitomycin C, and doxorubicin. NAC-induced changes in gene expression are consistent with the onset of mesenchymal-to-epithelial transition. In conclusion, our findings indicate that NAC induces an integrated series of responses in AsPC-1 cells that make it a highly promising candidate for development as a pancreatic cancer therapeutic.

The chemistry and biological activities of N-acetylcysteine

BACKGROUND

N-acetylcysteine (NAC) has been in clinical practice for several decades. It has been used as a mucolytic agent and for the treatment of numerous disorders including paracetamol intoxication, doxorubicin cardiotoxicity, ischemia-reperfusion cardiac injury, acute respiratory distress syndrome, bronchitis, chemotherapy-induced toxicity, HIV/AIDS, heavy metal toxicity and psychiatric disorders.

SCOPE OF REVIEW

The mechanisms underlying the therapeutic and clinical applications of NAC are complex and still unclear. The present review is focused on the chemistry of NAC and its interactions and functions at the organ, tissue and cellular levels in an attempt to bridge the gap between its recognized biological activities and chemistry.

MAJOR CONCLUSIONS

The antioxidative activity of NAC as of other thiols can be attributed to its fast reactions with OH, NO2, CO3(-) and thiyl radicals as well as to restitution of impaired targets in vital cellular components. NAC reacts relatively slowly with superoxide, hydrogen-peroxide and peroxynitrite, which cast some doubt on the importance of these reactions under physiological conditions. The uniqueness of NAC is most probably due to efficient reduction of disulfide bonds in proteins thus altering their structures and disrupting their ligand bonding, competition with larger reducing molecules in sterically less accessible spaces, and serving as a precursor of cysteine for GSH synthesis.

GENERAL SIGNIFICANCE

The outlined reactions only partially explain the diverse biological effects of NAC, and further studies are required for determining its ability to cross the cell membrane and the blood-brain barrier as well as elucidating its reactions with components of cell signaling pathways.

Liposomal Antioxidants for Protection against Oxidant-Induced Damage

Reactive oxygen species (ROS), including superoxide anion, hydrogen peroxide, and hydroxyl radical, can be formed as normal products of aerobic metabolism and can be produced at elevated rates under pathophysiological conditions. Overproduction and/or insufficient removal of ROS result in significant damage to cell structure and functions. In vitro studies showed that antioxidants, when applied directly and at relatively high concentrations to cellular systems, are effective in conferring protection against the damaging actions of ROS, but results from animal and human studies showed that several antioxidants provide only modest benefit and even possible harm. Antioxidants have yet to be rendered into reliable and safe therapies because of their poor solubility, inability to cross membrane barriers, extensive first-pass metabolism, and rapid clearance from cells. There is considerable interest towards the development of drug-delivery systems that would result in the selective delivery of antioxidants to tissues in sufficient concentrations to ameliorate oxidant-induced tissue injuries. Liposomes are biocompatible, biodegradable, and nontoxic artificial phospholipid vesicles that offer the possibility of carrying hydrophilic, hydrophobic, and amphiphilic molecules. This paper focus on the use of liposomes for the delivery of antioxidants in the prevention or treatment of pathological conditions related to oxidative stress.

Exopolysaccharide of Laetiporus sulphureus var. miniatus downregulates LPS-induced production of NO, PGE₂, and TNF-α in BV2 microglia cells via suppression of the NF-κB pathway

Our previous study showed that the exopolysaccharide (EPS) of Laetiporus sulphureus var. miniatus was well characterized and prevented cell damage in streptozotocin-induced apoptosis. However, little is known about the molecular mechanisms underlying its anti-inflammatory effects. Therefore, we attempted in this study to determine whether EPS induces a significant inhibition of pro-inflammatory mediators in lipopolysaccharide (LPS)-stimulated murine BV2 microglia cells. Our results showed that EPS significantly inhibited LPS-induced pro-inflammatory mediators, such as nitric oxide (NO), prostaglandin E(2) (PGE(2)), and tumor necrosis factor-α (TNF-α), without any significant cytotoxicity. EPS also downregulated mRNA and protein expression of inducible NO synthase (iNOS), cyclooxygenase-2 (COX-2), and TNF-α in LPS-induced BV2 microglia cells. Our data also revealed that EPS treatment significantly reduced translocation of nuclear factor-κB (NF-κB) subunit p65 and its DNA-binding activity in LPS-stimulated BV2 microglia cells. Furthermore, we confirmed by using proteasome inhibitor N-acetyl-l-cysteine (NAC), that the inhibition of NF-κB activity influenced the expression of pro-inflammatory genes in LPS-induced BV2 microglia cells. As expected, NAC suppressed the expression of iNOS, COX-2, and TNF-α by blocking proteasome-mediated degradation. Taken together, our data indicate that EPS inhibits the expression of pro-inflammatory mediators by suppressing NF-κB activity.

Protective Effects of Liposomal N-Acetylcysteine against Paraquat-Induced Cytotoxicity and Gene Expression

Paraquat (PQ) is a herbicide that preferentially accumulates in the lung and exerts its cytotoxicity via the generation of reactive oxygen species (ROS). There is no specific treatment for paraquat poisoning. Attempts have been made to increase the antioxidant status in the lung using antioxidants (e.g., superoxide dismutase, vitamin E, N-acetylcysteine) but the outcome from such treatments is limited. Encapsulation of antioxidants in liposomes improves their therapeutic potential against oxidant-induced lung damage because liposomes facilitate intracellular delivery and prolong the retention of entrapped agents inside the cell. In the present study, we compared the effectiveness of conventional N-acetylcysteine (NAC) and liposomal-NAC (L-NAC) against PQ-induced cytotoxicity and examined the mechanism(s) by which these antioxidant formulations conferred cytoprotection. The effects of NAC or L-NAC against PQ-induced cytotoxicity in A549 cells were assessed by measuring cellular PQ uptake, intracellular glutathione content, ROS levels, mitochondrial membrane potential, cellular gene expression, inflammatory cytokine release and cell viability. Pretreatment of cells with L-NAC was significantly more effective than pretreatment with the conventional drug in reducing PQ-induced cytotoxicity, as indicated by the biomarkers used in this study. Our results suggested that the delivery of NAC as a liposomal formulation improves its effectiveness in counteracting PQ-induced cytotoxicity.

Modulation of SCF beta-TrCP-dependent I kappaB alpha ubiquitination by hydrogen peroxide

Reactive oxygen species are known to participate in the regulation of intracellular signaling pathways, including activation of NF-kappaB. Recent studies have indicated that increases in intracellular concentrations of hydrogen peroxide (H(2)O(2)) have anti-inflammatory effects in neutrophils, including inhibition of the degradation of I kappaB alpha after TLR4 engagement. In the present experiments, we found that culture of lipopolysaccharide-stimulated neutrophils and HEK 293 cells with H(2)O(2) resulted in diminished ubiquitination of I kappaB alpha and decreased SCF(beta-TrCP) ubiquitin ligase activity. Exposure of neutrophils or HEK 293 cells to H(2)O(2) was associated with reduced binding between phosphorylated I kappaB alpha and SCF(beta-TrCP) but no change in the composition of the SCF(beta-TrCP) complex. Lipopolysaccharide-induced SCF(beta-TrCP) ubiquitin ligase activity as well as binding of beta-TrCP to phosphorylated I kappaB alpha was decreased in the lungs of acatalasemic mice and mice treated with the catalase inhibitor aminotriazole, situations in which intracellular concentrations of H(2)O(2) are increased. Exposure to H(2)O(2) resulted in oxidative modification of cysteine residues in beta-TrCP. Cysteine 308 in Blade 1 of the beta-TrCP beta-propeller region was found to be required for maximal binding between beta-TrCP and phosphorylated I kappaB alpha. These findings suggest that the anti-inflammatory effects of H(2)O(2) may result from its ability to decrease ubiquitination as well as subsequent degradation of I kappaB alpha through inhibiting the association between I kappaB alpha and SCF(beta-TrCP).

S-glutathionylation of the Rpn2 regulatory subunit inhibits 26 S proteasomal function

Although increased intracellular concentrations of hydrogen peroxide (H2O2) are associated with inhibition of 26 S proteasomal activity, the mechanisms responsible for such effects have not been well delineated. In the present studies, we found that direct exposure of purified 26 S proteasomes to H2O2 had negligible effects on their activity, whereas incubation with glutathione and H2O2 produced >80% decrease in chymotrypsin-like and trypsin-like activities. Rpn1 and Rpn2, which are subunits of the 19 S regulatory particle, undergo S-glutathionylation after exposure of purified 26 S proteasomes to glutathione and H2O2, as well as in HEK 293 cells and neutrophils incubated with H2O2. Increased oxidation of Rpn1 and Rpn2 cysteine thiols was also found in lung extracts from mice in which catalase was inactivated, a condition associated with augmented intracellular concentrations of H2O2 and diminished 26 S proteasomal activity. Although unoxidized Rpn2 enhanced 20 S proteolytic function in vitro, such potentiation was not found when the 20 S core particle was incubated with oxidized Rpn2. The composition of 26 S proteasomes was not altered after exposure to glutathione and H2O2, with similar amounts of Rpn1 and Rpn2 in control or oxidized 26 S proteasomal complexes. These findings identify S-glutathionylation of Rpn2 as a contributory mechanism for H2O2-induced inhibition of 26 S proteasomal function.

Imaging of radiation effects on cellular 26S proteasome function in situ

PURPOSE

The classical radiobiological paradigm is that DNA is the target for cell damage caused by ionising radiation. However, evidence is accumulating that other constituents, such as the membrane, organelles, and proteins, are also important targets. We have shown that the isolated 26S proteasome is one such target and here we wish to substantiate it within the cell, in situ.

MATERIALS AND METHODS

We used confocal microscopy to quantitatively detect and subcellularly localise radiation-induced 26S proteasome inhibition in cells expressing an ornithine decarboxylase degron that targets a fused Zoanthus species green (ZsGreen) fluorescent protein reporter specifically to the 26S proteasome.

RESULTS

Exposure of cells to a range of radiation doses, even as low as 0.05 Gy inhibited 26S activity within minutes. Initially, punctate nuclear ZsGreen fluorescence was observed that became cytoplasmic after seven hours -- a pattern distinct from the diffuse homogeneous fluorescence of cells incubated in the conventional proteasome inhibitor MG-132.

CONCLUSIONS

Our study clearly indicates that the 26S proteasome is a radiation target with physiological consequences and introduces a new perspective in mechanistic investigations of cellular responses to stresses.

Antiinflammatory effects of hydrogen peroxide in neutrophil activation and acute lung injury

RATIONALE

Although reactive oxygen species (ROS) are generally considered to be proinflammatory and to contribute to cellular and organ dysfunction when present in excessive amounts, there is evidence that specific ROS, particularly hydrogen peroxide (H(2)O(2)), may have antiinflammatory properties.

OBJECTIVES

To address the role that increases in intracellular H(2)O(2) may play in acute inflammatory processes, we examined the effects of catalase inhibition or the absence of catalase on LPS-induced inflammatory responses.

METHODS

Neutrophils from control or acatalasemic mice, or control neutrophils incubated with the catalase inhibitor aminotriazole, were treated with LPS, and levels of reactive oxygen species, proteasomal activity, NF-kappaB activation, and proinflammatory cytokine expression were measured. Acute lung injury (ALI) was produced by intratracheal injection of LPS into control, acatalasemic-, or aminotriazole-treated mice.

MEASUREMENTS AND MAIN RESULTS

Intracellular levels of H(2)O(2) were increased in acatalasemic neutrophils and in neutrophils exposed to aminotriazole. Compared with LPS-stimulated neutrophils from control mice, neutrophils from acatalasemic mice or neutrophils treated with aminotriazole demonstrated reduced 20S and 26S proteasomal activity, IkappaB-alpha degradation, NF-kappaB nuclear accumulation, and production of the proinflammatory cytokines TNF-alpha and macrophage inhibitory protein (MIP)-2. The severity of LPS-induced ALI was less in acatalasemic mice and in mice treated with aminotriazole as compared with that found in control mice.

CONCLUSIONS

These results indicate that H(2)O(2) has antiinflammatory effects on neutrophil activation and inflammatory processes, such as ALI, in which activated neutrophils play a major role.

Effects of N-acetylcysteine amide (NACA), a thiol antioxidant on radiation-induced cytotoxicity in Chinese hamster ovary cells

Ionizing radiation is known to cause tissue damage in biological systems, mainly due to its ability to produce reactive oxygen species (ROS) in cells. Many thiol antioxidants have been used previously as radioprotectors, but their application has been limited by their toxicity. In this investigation, we have explored the possible radioprotective effects of a newly synthesized thiol antioxidant, N-acetylcysteine amide (NACA), in comparison with N-acetylcysteine (NAC), a commonly used antioxidant. Protective effects of NACA and NAC were assessed using Chinese hamster ovary (CHO) cells, irradiated with 6 gray (Gy) radiation. Oxidative stress parameters, including levels of reduced glutathione (GSH), cysteine, malondialdehyde (MDA), and activities of antioxidant enzymes like glutathione peroxidase, glutathione reductase, and catalase, were measured. Results indicate that NACA was capable of restoring GSH levels in irradiated cells in a dose dependent manner. In addition, NACA prevented radiation-induced loss in cell viability. NACA further restored levels of malondialdehyde, caspase-3 activity, and antioxidant enzyme activities to control levels. Although NAC affected cells in a similar manner to NACA, its effects were not as significant. Further, NAC was also found to be cytotoxic to cells at higher concentrations, whereas NACA was non-toxic at similar concentrations. These results suggest that NACA may be able to attenuate radiation-induced cytotoxicity, possibly by its ability to provide thiols to cells.

Apoptosis induction of 2′-hydroxycinnamaldehyde as a proteasome inhibitor is associated with ER stress and mitochondrial perturbation in cancer cells

2'-Hydroxycinnamaldehyde (HCA), isolated from the stem bark of Cinnamomum cassia, and 2'-benzoyloxycinnamaldehyde (BCA), one of HCA derivatives, have antiproliferative activities on several human cancer cell lines. Our previous study suggested that reactive oxygen species (ROS) and caspase-3 are the major regulators of HCA-induced apoptosis. In the present study, we demonstrated a novel molecular target using in vitro pull-down assay by biotin-labeled HCA (biotin-HCA) in SW620 cells. We analyzed 11 differential spots of 2-dimensional gel prepared with pull-downed proteins by biotin-HCA. Among them, five spots were identified as proteasome subunits. An in vitro 26S proteasome function assay using specific fluorogenic substrates showed that HCA potently inhibits L3-like activity of the proteasome. In addition, HCA showed inhibitory action against chymotrypsin-like, trypsin-like, and PGPH-like activities. DNA microarray showed that HCA induced heat shock family and ER stress-responsive genes, which reflects the accumulation of misfolded proteins by proteasome inhibition. On western blot analysis, it was confirmed that HCA induces glucose-regulated protein, 78 kDa (GRP78) and some representative endoplasmic reticulum (ER) stress-responsive proteins. Furthermore, HCA treatment decreased mitochondrial membrane potential. The effect of HCA on cytochrome c and Bax translocation between cytosol and mitochondrial membrane was clarified using western blot analysis. These results suggest that HCA-induced apoptosis is associated with the inhibition of the proteasome activity that leads in turn to the increase of ER stress and mitochondrial perturbation.

Hydrogen peroxide induces nitric oxide and proteosome activity in endothelial cells: a bell-shaped signaling response

We investigated nitric oxide (*NO)-mediated proteosomal activation in bovine aortic endothelial cells (BAEC) treated with varying fluxes of hydrogen peroxide (H(2)O(2)) generated from glucose/glucose oxidase (Glu/GO). Results revealed a bell-shaped *NO signaling response in BAEC treated with Glu/GO (2-20 mU/ml). GO treatment (2 mU/ml) enhanced endothelial nitric oxide synthase (eNOS) phosphorylation and *NO release in BAEC. With increasing GO concentrations, phospho eNOS and *NO levels decreased. Bell-shaped responses in proteasomal function and *NO induction were observed in BAEC treated with varying levels of GO (2-10 mU/ml). Proteosomal activation induced in GO-treated BAEC was inhibited by N(omega)-nitro-L-arginine-methyl ester pretreatment, suggesting that *NO mediates proteasomal activation. Intracellular *NO induced by H(2)O(2) was detected by isolating the 4,5-diaminoflourescein (DAF-2)/*NO/O(2)-derived "green fluorescent product" using the high-performance liquid chromatography-fluorescence technique, a more rigorous and quantitative methodology for detecting the DAF-2/*NO/O(2) reaction product. Finally, the relationships between H(2)O(2) flux, proteasomal activation/inactivation, endothelial cell survival, and apoptosis are discussed.

Exposure to hydrogen peroxide diminishes NF-kappaB activation, IkappaB-alpha degradation, and proteasome activity in neutrophils

Although ROS can participate in modulating the activity of the transcriptional factor NF-kappaB and expression of NF-kappaB-dependent genes, the mechanisms involved and the roles of specific ROS have not been fully determined. In particular, individual ROS appear to have differing effects on NF-kappaB activation dependent on the cell population studied. In the present study, we examined the ability of H(2)O(2) to affect NF-kappaB activation in LPS-stimulated murine neutrophils and macrophages. Exposure of bone marrow or peritoneal neutrophils to H(2)O(2) was associated with reduced nuclear translocation of NF-kappaB and decreased production of the NF-kappaB-dependent cytokines TNF-alpha and macrophage inhibitory protein-2. H(2)O(2) treatment resulted in diminished trypsin- and chymotrypsin-like proteasome activity. The degradation of IkappaB-alpha normally found in LPS-treated neutrophils was prevented when H(2)O(2) was added to cell cultures. In contrast to the effects found in neutrophils, H(2)O(2) did not affect chymotrypsin-like proteasomal activity or cytokine production in LPS-stimulated macrophages, even though trypsin-like proteasomal activity was reduced. These results demonstrate that the effects of H(2)O(2) on NF-kappaB and proteasomal activity are cell population specific.

Redox regulation of the proteasome in T lymphocytes during aging

Proteasome is a major cellular organelle responsible for the regulated turnover of both normal and misfolded proteins. Recent reports from our laboratory have implicated lowered proteasomal chymotryptic activity to be responsible for decreased induction of the transcription factor NFkappaB in T lymphocytes during aging. In this study, we have further analyzed the basis for this decline in proteasomal function, by focusing on the role of oxidative stress. On exposure to the prooxidant BSO, both ATP-stimulatable 26S and ATP-independent 20S proteasomal catalytic activity could be down-regulated in T cells from young donors, mimicking the decline observed in T cells from the elderly. Loss in these catalytic activities, following exposure to prooxidant stimulus, also resulted in a decline in both activation-induced proliferation and degradation of the inhibitor IkappaBalpha, with concomitant increase in the accumulation of carbonylated proteins, mimicking responses seen in T cells from the elderly. Pretreatment with an antioxidant, NAC, could override prooxidant-mediated, but not age-associated, decrease in both 20S and 26S proteasomal activities. These results suggest that the decrease in proteasomal activities observed during aging may be secondary to oxidative stress and underlie immune senescence.

Signals from within: the DNA-damage-induced NF-kappaB response

An appropriate response to genotoxic stress is essential for maintenance of genome stability and avoiding the passage to neoplasia. Nuclear factor kappaB (NF-kappaB) is activated as part of the DNA damage response and is thought to orchestrate a cell survival pathway, which, together with the activation of cell cycle checkpoints and DNA repair, allows the cell in cases of limited damage to restore a normal life cycle, unharmed. In this respect, NF-kappaB is one of the main factors accounting for chemotherapy resistance and as such impedes effective cancer treatment, representing an important drug target. Despite this high clinical relevance, signalling cascades leading to DNA damage-induced NF-kappaB activation are poorly understood and the use of highly divergent experimental set-ups in the past led to many controversies in the field. Therefore, in this review, we will try to summarize the current knowledge of distinct DNA damage-induced NF-kappaB signalling pathways.

Capsaicin, a component of red peppers, inhibits the growth of androgen-independent, p53 mutant prostate cancer cells

Capsaicin is the major pungent ingredient in red peppers. Here, we report that it has a profound antiproliferative effect on prostate cancer cells, inducing the apoptosis of both androgen receptor (AR)-positive (LNCaP) and -negative (PC-3, DU-145) prostate cancer cell lines associated with an increase of p53, p21, and Bax. Capsaicin down-regulated the expression of not only prostate-specific antigen (PSA) but also AR. Promoter assays showed that capsaicin inhibited the ability of dihydrotestosterone to activate the PSA promoter/enhancer even in the presence of exogenous AR in LNCaP cells, suggesting that capsaicin inhibited the transcription of PSA not only via down-regulation of expression of AR, but also by a direct inhibitory effect on PSA transcription. Capsaicin inhibited NF-kappa activation by preventing its nuclear migration. In further studies, capsaicin inhibited tumor necrosis factor-alpha-stimulated degradation of IkappaBalpha in PC-3 cells, which was associated with the inhibition of proteasome activity. Taken together, capsaicin inhibits proteasome activity which suppressed the degradation of IkappaBalpha, preventing the activation of NF-kappaB. Capsaicin, when given orally, significantly slowed the growth of PC-3 prostate cancer xenografts as measured by size [75 +/- 35 versus 336 +/- 123 mm(3) (+/-SD); P = 0.017] and weight [203 +/- 41 versus 373 +/- 52 mg (+/-SD); P = 0.0006; capsaicin-treated versus vehicle-treated mice, respectively]. In summary, our data suggests that capsaicin, or a related analogue, may have a role in the management of prostate cancer.

Antioxidant and anti-inflammatory efficacy of NAC in the treatment of COPD: discordant in vitro and in vivo dose-effects: a review

In order to develop efficient therapeutic regimes for chronic obstructive pulmonary disease (COPD), N-acetylcysteine (NAC) has been tested as a medication which can suppress various pathogenic processes in this disease. Besides its well-known and efficient mucolytic action, NAC meets these needs by virtue of its antioxidant and anti-inflammatory modes of action. NAC is a thiol compound which by providing sulfhydryl groups, can act both as a precursor of reduced glutathione and as a direct ROS scavenger, hence regulating the redox status in the cells. In this way it can interfere with several signaling pathways that play a role in regulating apoptosis, angiogenesis, cell growth and arrest and inflammatory response. Overall, the antioxidant effects of NAC are well documented in in vivo and in vitro studies. It successfully inhibits oxidative stress at both high and low concentrations, under acute (in vitro) and chronic administration (in vivo). With regard to its anti-inflammatory action, in contrast, the effects of NAC differ in vivo and in vitro and are highly dose-dependent. In the in vitro settings anti-inflammatory effects are seen at high but not at low concentrations. On the other hand, some long-term effectiveness is reported in several in vivo studies even at low dosages. Increasing the dose seems to improve NAC bioavailability and may also consolidate some of its effects. In this way, the effects that are observed in the clinical and in vivo studies do not always reflect the success of the in vitro experiments. Furthermore, the results obtained with healthy volunteers do not always provide incontrovertible proof of its usefulness in COPD especially when number of exacerbations and changes in lung function are chosen as the primary outcomes. Despite these considerations and in view of the present lack of effective therapies to inhibit disease progression in COPD, NAC and its derivatives, because of their multiple molecular modes of action, remain promising medication once doses and route of administration are optimized.

Human Alveolar Macrophages Are Deficient in PTEN

Human alveolar macrophages play a critical role in host defense and in the development of inflammation and fibrosis in the lung. Unlike their precursor cells, blood monocytes, alveolar macrophages are long-lived and tend to be resistant to apoptotic stimuli. In this study, we examined the role of differentiation in altering baseline phosphatidylinositol (PI) 3-kinase/Akt activity. We found that differentiation increased activity of pro-survival PI 3-kinase/Akt while decreasing amounts of the negative PI 3-kinase regulator, PTEN. PTEN is a lipid phosphatase with activity against phosphatidylinositol 3,4,5-trisphosphate (PI(3,4,5)P3), the major bioactive product of PI 3-kinase. Examining in vivo differentiation of alveolar macrophages (by comparing blood monocytes to alveolar macrophages from single donors), we found that differentiation resulted in increased baseline reactive oxygen species (ROS) in the alveolar macrophages. This led to a deficiency in PTEN, increased activity of Akt, and prolonged survival of alveolar macrophages. These data support the hypothesis that alterations in ROS levels contribute to macrophage homeostasis by altering the balance between PI 3-kinase/Akt and the phosphatase, PTEN.

Nitric oxide, proteasomal function, and iron homeostasis--implications in aging and neurodegenerative diseases

In this chapter, oxidant-induced transferrin receptor-mediated iron-signaling and apoptosis are described in endothelial and neuronal cells exposed to oxidants. The role of nitric oxide in the regulation of iron homeostasis and oxidant-induced apoptosis is described. The interrelationship between oxidative stress, iron-signaling, and nitric oxide-dependent proteasomal function provides a rational mechanism that connects both oxidative and nitrative modifications.

Separation and quantification ofN-acetyl-l-cysteine andN-acetyl-cysteine-amide by HPLC with fluorescence detection

N-acetyl-l-cysteine (NAC) is a well-known antioxidant that is capable of facilitating glutathione (GSH) biosynthesis and replenishing intracellular GSH under oxidatively challenging circumstances. N-acetyl-cysteine-amide (NACA), the amide form of NAC, is a newly designed and synthesized thiol-containing compound which is believed to be more lipophilic and permeable through cell membranes than NAC. The metabolic and antioxidant effects of these compounds in vitro and in vivo are under investigation. However, an analytical method that can separate and quantify both compounds simultaneously is not yet available, to the best of our knowledge. Because of their structural similarities, the two compounds are difficult to separate using earlier HPLC methods which were designed for NAC quantification. Therefore, the goal of this work was to develop an HPLC method with fluorescence detection for simultaneous quantification of NAC and NACA in biological blood and tissue samples. A gradient HPLC program with fluorescence detection (lambda(ex) = 330 nm, lambda(em) = 376 nm) using N-(1-pyrenyl)maleimide (NPM) as the derivatizing agent was developed. The calibration curves were linear over a concentration range of 25-5000 nm (r(2) > 0.997). The coefficients of variation for within-run precision and between-run precision ranged from 0.67 to 5.23% and for accuracy ranged from 0.98 to 10.54%; the percentage relative recovery ranged from 94.5 to 102.8%. This new method provides satisfactory separation of NAC and NACA, along with other biological thiols, in 20 min with a 5 nm limit of detection (LOD) per 5 microL injection volume.

Proteasome structures affected by ionizing radiation

Exposure of cells to ionizing radiation slows the rate of degradation of substrates through the proteasome. Because the 26S proteasome degrades most short-lived cellular proteins, changes in its activity might significantly, and selectively, alter the life span of many signaling proteins and play a role in promoting the biological consequences of radiation exposure, such as cell cycle arrest, DNA repair, and apoptosis. Experiments were therefore undertaken to identify the radiation target that is associated with the proteasome. Regardless of whether they were irradiated before or after extraction and purification from human prostate cancer PC3 cells, 26S proteasomes remained intact but showed a rapid 30% to 50% dose-independent decrease in their three major enzymatic activities following exposure to 1 to 20 Gy. There was no effect on 20S proteasomes, suggesting that the radiation-sensitive target is located in the 19S cap of the 26S proteasome, rather than in the enzymatically active core. Because the base of the 19S cap contains an ATPase ring that mediates substrate unfolding, pore opening, and translocation of substrates into the catalytic chamber, we examined whether the ATPase activity of purified 26S proteasomes was affected. In fact, in vitro irradiation of proteasomes enhanced their ATPase activity. Furthermore, pretreatment with low concentrations of the free radical scavenger tempol was able to prevent both the radiation-induced decrease in proteolytic activity and the increase in ATP utilization, indicating that free radicals are mediators of these radiation-induced phenomena. Finally, we have shown that cell irradiation results in the accumulation of proteasome substrates: polyubiquitinated proteins and ornithine decarboxylase, indicating that the observed decrease in proteasome function is physiologically relevant.

Effects of dietary curcumin or N-acetylcysteine on NF-kappaB activity and contractile performance in ambulatory and unloaded murine soleus

Background

Unloading of skeletal muscle causes atrophy and loss of contractile function. In part, this response is believed to be mediated by the transcription factor nuclear factor-kappa B (NF-κB). Both curcumin, a component of the spice turmeric, and N-acetylcysteine (NAC), an antioxidant, inhibit activation of NF-κB by inflammatory stimuli, albeit by different mechanisms. In the present study, we tested the hypothesis that dietary curcumin or NAC supplementation would inhibit unloading-induced NF-κB activity in skeletal muscle and thereby protect muscles against loss of mass and function caused by prolonged unloading.

Methods

We used hindlimb suspension to unload the hindlimb muscles of adult mice. Animals had free access to drinking water or drinking water supplemented with 1% NAC and to standard laboratory diet or diet supplemented with 1% curcumin. For 11 days, half the animals in each dietary group were suspended by the tail (unloaded) and half were allowed to ambulate freely.

Results

Unloading caused a 51–53% loss of soleus muscle weight and cross-sectional area relative to freely-ambulating controls. Unloading also decreased total force and force per cross-sectional area developed by soleus. Curcumin supplementation decreased NF-κB activity measured in peripheral tissues of ambulatory mice by gel shift analysis. In unloaded animals, curcumin supplementation did not inhibit NF-κB activity or blunt the loss of muscle mass in soleus. In contrast, NAC prevented the increase in NF-κB activity induced by unloading but did not prevent losses of muscle mass or function.

Conclusion

In conclusion, neither dietary curcumin nor dietary NAC prevents unloading-induced skeletal muscle dysfunction and atrophy, although dietary NAC does prevent unloading induced NF-κB activation.

Ceramide-induced Intracellular Oxidant Formation, Iron Signaling, and Apoptosis in Endothelial Cells

Sphingolipid ceramide (N-acetylsphingosine), a bioactive second messenger lipid, was shown to activate reactive oxygen species (ROS), mitochondrial oxidative damage, and apoptosis in neuronal and vascular cells. The proapoptotic effects of tumor necrosis factor-alpha, hypoxia, and chemotherapeutic drugs were attributed to increased ceramide formation. Here we investigated the protective role of nitric oxide (.NO) during hydrogen peroxide (H(2)O(2))-mediated transferrin receptor (TfR)-dependent iron signaling and apoptosis in C(2)-ceramide (C(2)-cer)-treated bovine aortic endothelial cells (BAECs). Addition of C(2)-cer (5-20 microm) to BAECs enhanced .NO generation. However, at higher concentrations of C(2)-cer (> or =20 microm), .NO generation did not increase proportionately. C(2)-cer (20-50 microm) also resulted in H(2)O(2)-mediated dichlorodihydrofluorescein oxidation, reduced glutathione depletion, aconitase inactivation, TfR overexpression, TfR-dependent uptake of (55)Fe, release of cytochrome c from mitochondria into cytosol, caspase-3 activation, and DNA fragmentation. N(w)-Nitro-l-arginine methyl ester (l-NAME), a nonspecific inhibitor of nitricoxide synthases, augmented these effects in BAECs at much lower (i.e. nonapoptotic) concentrations of C(2)-cer. The 26 S proteasomal activity in BAECs was slightly elevated at lower concentrations of C(2)-cer (< or =10 microm) but was greatly suppressed at higher concentrations (>10 microm). Intracellular scavengers of H(2)O(2), cell-permeable iron chelators, anti-TfR receptor antibody, or mitochondria-targeted antioxidant greatly abrogated C(2)-cer- and/or l-NAME-induced oxidative damage, iron signaling, and apoptosis. We conclude that C(2)-cer-induced H(2)O(2) and TfR-dependent iron signaling are responsible for its prooxidant and proapoptotic effects and that .NO exerts an antioxidative and cytoprotective role.

A Sense of Danger from Radiation1

Tissue damage caused by exposure to pathogens, chemicals and physical agents such as ionizing radiation triggers production of generic "danger" signals that mobilize the innate and acquired immune system to deal with the intrusion and effect tissue repair with the goal of maintaining the integrity of the tissue and the body. Ionizing radiation appears to do the same, but less is known about the role of "danger" signals in tissue responses to this agent. This review deals with the nature of putative "danger" signals that may be generated by exposure to ionizing radiation and their significance. There are a number of potential consequences of "danger" signaling in response to radiation exposure. "Danger" signals could mediate the pathogenesis of, or recovery from, radiation damage. They could alter intrinsic cellular radiosensitivity or initiate radioadaptive responses to subsequent exposure. They may spread outside the locally damaged site and mediate bystander or "out-of-field" radiation effects. Finally, an important aspect of classical "danger" signals is that they link initial nonspecific immune responses in a pathological site to the development of specific adaptive immunity. Interestingly, in the case of radiation, there is little evidence that "danger" signals efficiently translate radiation-induced tumor cell death into the generation of tumor-specific immunity or normal tissue damage into autoimmunity. The suggestion is that radiation-induced "danger" signals may be inadequate in this respect or that radiation interferes with the generation of specific immunity. There are many issues that need to be resolved regarding "danger" signaling after exposure to ionizing radiation. Evidence of their importance is, in some areas, scant, but the issues are worthy of consideration, if for no other reason than that manipulation of these pathways has the potential to improve the therapeutic benefit of radiation therapy. This article focuses on how normal tissues and tumors sense and respond to danger from ionizing radiation, on the nature of the signals that are sent, and on the impact on the eventual consequences of exposure.

Supplementation of endothelial cells with mitochondria-targeted antioxidants inhibit peroxide-induced mitochondrial iron uptake, oxidative damage, and apoptosis

The mitochondria-targeted drugs mitoquinone (Mito-Q) and mitovitamin E (MitoVit-E) are a new class of antioxidants containing the triphenylphosphonium cation moiety that facilitates drug accumulation in mitochondria. In this study, Mito-Q (ubiquinone attached to a triphenylphosphonium cation) and MitoVit-E (vitamin E attached to a triphenylphosphonium cation) were used. The aim of this study was to test the hypothesis that mitochondria-targeted antioxidants inhibit peroxide-induced oxidative stress and apoptosis in bovine aortic endothelial cells (BAEC) through enhanced scavenging of mitochondrial reactive oxygen species, thereby blocking reactive oxygen species-induced transferrin receptor (TfR)-mediated iron uptake into mitochondria. Glucose/glucose oxidase-induced oxidative stress in BAECs was monitored by oxidation of dichlorodihydrofluorescein that was catalyzed by both intracellular H(2)O(2) and transferrin iron transported into cells. Pretreatment of BAECs with Mito-Q (1 microM) and MitoVit-E (1 microM) but not untargeted antioxidants (e.g. vitamin E) significantly abrogated H(2)O(2)- and lipid peroxide-induced 2',7'-dichlorofluorescein fluorescence and protein oxidation. Mitochondria-targeted antioxidants inhibit cytochrome c release, caspase-3 activation, and DNA fragmentation. Mito-Q and MitoVit-E inhibited H(2)O(2)- and lipid peroxide-induced inactivation of complex I and aconitase, TfR overexpression, and mitochondrial uptake of (55)Fe, while restoring the mitochondrial membrane potential and proteasomal activity. We conclude that Mito-Q or MitoVit-E supplementation of endothelial cells mitigates peroxide-mediated oxidant stress and maintains proteasomal function, resulting in the overall inhibition of TfR-dependent iron uptake and apoptosis.

The ubiquitin-proteasome system is responsible for cysteine-responsive regulation of cysteine dioxygenase concentration in liver

Hepatic cysteine dioxygenase (CDO) activity is a critical regulator of cellular cysteine concentration and availability of cysteine for anabolic processes and is markedly higher in animals fed diets containing excess sulfur amino acids compared with those fed levels at or below the requirement. Rat hepatocytes responded to a deficiency or excess of cysteine in the culture medium with a decrease or increase in CDO level but no change in CDO mRNA level. The cysteine analog, cysteamine, but not cysteine metabolites or thiol reagents, was also effective in increasing CDO. Inhibitors of the 26S proteasome blocked CDO degradation in cysteine-deficient cells but had little or no effect on CDO concentration in hepatocytes cultured with excess cysteine. High-molecular-mass CDO-ubiquitin conjugates were observed in cells cultured in cysteine-deficient medium, whether or not proteasome inhibitor was present, but these CDO-ubiquitin conjugates were not observed in cells cultured in cysteine-supplemented medium with or without proteasome inhibitor. Similar results were observed for degradation of recombinant CDO expressed in human heptocarcinoma cells cultured in cysteine-deficient or cysteine-supplemented medium. CDO is an example of a mammalian enzyme that is robustly regulated via its substrate, with the presence of substrate blocking the ubiquitination of CDO and, hence, the targeting of CDO for proteasomal degradation. This regulation occurs in primary hepatocytes in a manner that corresponds with changes observed in intact animals.

Alpha-synuclein up-regulation and aggregation during MPP+-induced apoptosis in neuroblastoma cells: intermediacy of transferrin receptor iron and hydrogen peroxide

1-Methyl-4-phenylpyridinium (MPP(+)) is a neurotoxin that causes Parkinson's disease in experimental animals and humans. Despite the fact that intracellular iron was shown to be crucial for MPP(+)-induced apoptotic cell death, the molecular mechanisms for the iron requirement remain unclear. We investigated the role of transferrin receptor (TfR) and iron in modulating the expression of alpha-synuclein (alpha-syn) in MPP(+)-induced oxidative stress and apoptosis. Results show that MPP(+) inhibits mitochondrial complex-1 and aconitase activities leading to enhanced H(2)O(2) generation, TfR expression and alpha-syn expression/aggregation. Pretreatment with cell-permeable iron chelators, TfR antibody (that inhibits TfR-mediated iron uptake), or transfection with glutathione peroxidase (GPx1) enzyme inhibits intracellular oxidant generation, alpha-syn expression/aggregation, and apoptotic signaling as measured by caspase-3 activation. Cells overexpressing alpha-syn exacerbated MPP(+) toxicity, whereas antisense alpha-syn treatment totally abrogated MPP(+)-induced apoptosis in neuroblastoma cells without affecting oxidant generation. The increased cytotoxic effects of alpha-syn in MPP(+)-treated cells were attributed to inhibition of mitogen-activated protein kinase and proteasomal function. We conclude that MPP(+)-induced iron signaling is responsible for intracellular oxidant generation, alpha-syn expression, proteasomal dysfunction, and apoptosis. Relevance to Parkinson's disease is discussed.

Methemoglobin is a potent activator of endothelial cells by stimulating IL-6 and IL-8 production and E-selectin membrane expression

Infection and injury are frequently accompanied by hemolysis. Endothelial cells are direct targets of free Hb or its oxidative derivatives, including methemoglobin (MHb) and hemin. This study tested whether Hb or its derivatives alter chemokine (IL-8) and cytokine (IL-6) production and the membrane expression of cell adhesion molecule (E-selectin) in human umbilical vein endothelial cells (passages 2-4, HUVECs). E-selectin membrane content and IL-6 and IL-8 release were quantified by ELISA; cellular mRNA levels were determined by RT-PCR. MHb in vitro resulted in a dose (1-50 microM)- and time (2-16 h)-dependent increase in E-selectin membrane content and IL-6 and IL-8 release in HUVECs. The stimulatory effect of MHb (12 microM) on E-selectin membrane expression and IL-6 and IL-8 release was similar to that produced after treatment with TNF-alpha (5 ng/ml) and IL-1beta (0.25 ng/ml). In contrast, Hb or hemin had no effects. As expected, MHb, Hb, and hemin markedly induced heme oxygenase-1 expression in HUVECs. Haptoglobin, cytochalasin D, and actinomycin inhibited the MHb-induced responses, whereas zinc protoporphyrin IX (a heme oxygenase inhibitor) or desferroxamine (an iron chelator) did not inhibit MHb-induced responses. MHb also increased cellular mRNA levels of E-selectin, IL-6, and IL-8. MHb treatment activated cellular NF-kappaB and NF-kappaB inhibitors; N-acetyl cysteine, SN50, and caffeic acid phenylethyl ester inhibited the MHb-induced responses. These data indicate that MHb is a potent activator of endothelial cells through NF-kappaB-mediated upregulation of cell adhesion molecule expression and chemokine and cytokine production. MHb-induced endothelial cell activation may have clinical significance after infections, hemolysis, or methemoglobinemia.

Effects of TNFalpha on expression of ICAM-1 in human airway epithelial cells in vitro: oxidant-mediated pathways and transcription factors

We demonstrate that two different cell-permeable antioxidants, pyrrolidine dithiocarbamate (PDTC) and dimethylthiourea (DMTU), inhibit TNFalpha-induced ICAM-1 surface and gene expression in primary cultures of differentiated normal human bronchial epithelial (NHBE) cells. In addition, TNFalpha stimulates binding of nuclear proteins to the nuclear factor kappa beta (NFkappaB) and the CAAT/enhancer binding protein (C/EBP) consensus sites in the ICAM-1 promoter in these cells. Because these transcription factors have been suggested to be oxidant-sensitive and important in ICAM-1 expression, the potential involvement of reactive oxygen species (ROS) in the response to TNFalpha was investigated. Interestingly, neither PDTC nor DMTU altered binding of NFkappaB complexes. In contrast, either the proteasome inhibitor carbobenzoxy-L-leucy-L-leucy-L-leucinal (MG 132) or the IkappaBalpha inhibitor BAY 11-7082 ablated TNFalpha-induced ICAM-1 gene expression and MG132 inhibited TNFalpha-induced NFkappaB complexes. Surprisingly, either PDTC or DMTU inhibited the binding of TNFalpha-enhanced C/EBP complexes to the consensus site directly adjacent to the NFkappaB site. These results suggest that although TNFalpha enhances binding of C/EBP and NFkappaB complexes in NHBE cells, C/EBP binding seems to involve an oxidant-dependent mechanism, whereas activation of NFkappaB complexes utilizes the ubiquitin-proteasome pathway, a mechanism that seems to be unaltered by the presence of antioxidants. Because interference with either signaling pathway abrogates TNFalpha-induced ICAM-1 expression, activation of both complexes seems to be involved in this response to TNFalpha, but this activation occurs via different intracellular pathways.

Evidence that glutathione depletion is a mechanism responsible for the anti-inflammatory effects of ethyl pyruvate in cultured lipopolysaccharide-stimulated RAW 264.7 cells

Ethyl pyruvate (EP), an effective scavenger of reactive oxygen species, is also an anti-inflammatory agent in a variety of in vivo and in vitro model systems. To gain a better understanding of the molecular basis for the anti-inflammatory effects of EP, we compared the pharmacological properties of EP andN-acetyl-l-cysteine (NAC), a well studied scavenger of reactive oxygen species and a precursor for the endogenous antioxidant glutathione (GSH). The studies were performed using RAW 264.7 murine macrophage-like cells that were stimulated with lipopolysaccharide (LPS). Although EP and NAC both inhibited LPS-induced nitric oxide and interleukin (IL)-6 secretion, the former compound was considerably more potent than the latter. EP markedly inhibited inducible nitric-oxide synthase, IL-6, and IL-10 mRNA induction, whereas the effects of NAC were minimal. EP inhibited LPS-induced nuclear factor-kappaB DNA binding to a much greater extent than did NAC. Both compounds inhibited LPS-induced lipid peroxidation, but the two compounds had qualitatively different effects on cellular levels of GSH. Although NAC increased GSH levels, EP had the opposite effect. The anti-inflammatory effects of EP were partially reversed when RAW 264.7 cells were treated with a cell-permeable GSH analog, glutathione ethyl ester. These data support the view that the anti-inflammatory effects of EP are mediated, at least in part, by the ability of EP to deplete cellular GSH stores. Moreover, the findings presented here suggest that an unusual combination of biochemical effects (inhibition of lipid peroxidation and GSH depletion) might account for the anti-inflammatory effects of EP.