Inactivation of glutathione S-transferases by nitric oxide-derived oxidants: exploring a role for tyrosine nitration

The good Samaritan glutathione-S-transferase P1: An evolving relationship in nitric oxide metabolism mediated by the direct interactions between multiple effector molecules

Glutathione-S-transferases (GSTs) are phase II detoxification isozymes that conjugate glutathione (GSH) to xenobiotics and also suppress redox stress. It was suggested that GSTs have evolved not to enhance their GSH affinity, but to better interact with and metabolize cytotoxic nitric oxide (NO). The interactions between NO and GSTs involve their ability to bind and store NO as dinitrosyl-dithiol iron complexes (DNICs) within cells. Additionally, the association of GSTP1 with inducible nitric oxide synthase (iNOS) results in its inhibition. The function of NO in vasodilation together with studies associating GSTM1 or GSTT1 null genotypes with preeclampsia, additionally suggests an intriguing connection between NO and GSTs. Furthermore, suppression of c-Jun N-terminal kinase (JNK) activity occurs upon increased levels of GSTP1 or NO that decreases transcription of JNK target genes such as c-Jun and c-Fos, which inhibit apoptosis. This latter effect is mediated by the direct association of GSTs with MAPK proteins. GSTP1 can also inhibit nuclear factor kappa B (NF-κB) signaling through its interactions with IKKβ and Iκα, resulting in decreased iNOS expression and the stimulation of apoptosis. It can be suggested that the inhibitory activity of GSTP1 within the JNK and NF-κB pathways may be involved in crosstalk between survival and apoptosis pathways and modulating NO-mediated ROS generation. These studies highlight an innovative role of GSTs in NO metabolism through their interaction with multiple effector proteins, with GSTP1 functioning as a "good Samaritan" within each pathway to promote favorable cellular conditions and NO levels.

Alterations in the testicular parenchyma of Foxn1+/- and Foxn1-/- adult mice

Nude mice carry an autosomal recessive mutation in the Foxn1 gene and therefore are homozygous recessive animals (Foxn1 -/-). The fertility rate of homozygous male (Foxn1-/- ) is low, which seems to be related to the delay in the production of gametes at the beginning of sexual maturity. The present study evaluated the structural and organizational aspects of the testicles of homozygous and heterozygous offspring related to the Foxn1 gene in mice, describing its implications on spermatogenesis. Adult males Balb/c, Foxn1+/- and Foxn1-/- mice were used. Testes and epididymis were harvested for histological, biochemical, and sperm transit analyses. Gonadal weight was significantly lower in Foxn1+/- and Foxn1-/- animals, the same behavior was noticed for the activity of antioxidant enzymes. In addition, tubular parameters such as epithelial proportion, length, and area, as well as germ and Leydig cell's populations were significantly reduced in the aforementioned groups, leading to lower sperm production. In conclusion, our results indicate the importance of the Foxn1 in Leydig cell's function, reflecting in the preservation of spermatogenesis, thus in germ cell's population and sperm cell production.

Taxifolin, a novel food, attenuates acute alcohol-induced liver injury in mice through regulating the NF-κB-mediated inflammation and PI3K/Akt signalling pathways

CONTEXT

Taxifolin (TAX) has effective anti-inflammatory, antioxidant and hepatoprotective activities, but its potential mechanism has not been revealed.

OBJECTIVE

To evaluate the potential protective effect of TAX on acute alcohol-induced liver injury in mice.

MATERIALS AND METHODS

Alcoholic liver injury model was established by oral alcohol in mice, and randomly distributed in five groups (n = 10): Normal group (oral saline only); Alcohol group (concentration of fermented alcohol: 56%, 6 mL/kg); TAX groups, mice were orally administered with alcohol, and then TAX with doses of 20, 40, 80 mg/kg, respectively. Oral administration was conducted for 6 weeks.

RESULTS

TAX treatment illustrated that the level of alanine aminotransferase (ALT) was reduced to 65.90 ± 2.26 U/L and aspartate aminotransferase (AST) to 33.28 ± 5.62 U/L compared with alcohol group (ALT 124.51 ± 4.40 U/L, AST 61.70 ± 4.09 U/L), while superoxide dismutase (SOD) was increased to 49.81 ± 2.39 U/mg and glutathione (GSH) to 8.16 ± 0.44 μmol/g, but MDA was reversed to 2.53 ± 0.24 nmol/mg. Histopathological examination showed TAX treatment alleviated alcohol-induced hepatocyte necrosis and inflammatory infiltration. Meanwhile, Western blot and rt-PCR indicated TAX reduced IL-6 to 2.49 ± 0.25 pg/mL and TNF-α to 1.79 ± 0.20 pg/mL, and inhibiting NF-κB activation in liver. Moreover, TAX reversed alcohol-induced apoptosis by regulating the expression of PI3K/Akt and its downstream apoptotic factors.

CONCLUSIONS

The research provides novel evidence of the hepatoprotective effect of TAX on alcohol-induced liver injury, while also providing the possibility for future treatment of alcoholic liver disease.

How bad is brazilian ginseng extract for reproductive parameters in mice?

Properties attributed to the Panax ginseng are also attributed to the Brazilian ginseng, such as adaptogenic and aphrodisiac effects. There are studies demonstrating that the Brazilian ginseng (BGE) possibly increases the serum levels of testosterone and nitric oxide in mice and rats. The present study aimed to evaluate the effects of its extract on male fertility and sperm quality. Male Swiss mice (n = 60) were divided into six groups. The control animals were provided 0.5 mL of water, and 0.5 mL of water containing 7 mg/kg per day (d) sildenafil citrate. Other animals were treated with BGE at 100 mg/kg/d, 200 mg/kg/d, and 400 mg/kg/d by gavage for 42 days. Finally, animals from the last group received 200 mg/kg BGE every 3 days (3-3d) by gavage for 42 days. The results showed a reduction in the number of resistant spermatids in the testis and damage to daily sperm production, culminating in a reduction in the number of epididymal spermatozoa. Although the sperm quality decreased in all experimental animals, only males treated with BGE 100 mg/kg/d showed pre and post implantation embryo losses. We concluded that BGE alters sperm viability compromising the embryonic development after implantation.

Caracterization of glutathione S-transferase of Dermacantor marginatus and effect of the recombinant antigen as a potential anti-tick vaccine

Dermacentor marginatus is one of the main tick species in northwestern China, and is a vector of various tick-borne pathogens. Tick control method largely depends on chemical agents, but the disadvantages of using such approach would cause environmental damage and the risk of developing tick resistance to acaricides. Vaccination of tick protective antigen is an eco-friendly approach which is an alternative and promising method to mitigate tick infestation in livestock. In the study, a mu-class glutathione S-transferase (GST) sequence of D. marginatus was cloned and the recombinant protein (rDmGST) was expressed. Transcriptional level of the GST was measured together with native GST activity of the tick. Finally, A vaccine trial on rabbits against D. marginatus was proceeded to evaluate the anti-tick effect of rDmGST. Results reveled that the CDs of the D. margiantus glutathione S-transferase mu 1 gene has 669 base pair nucleotide sequence encoding a 223 amino acid. The deduced GST protein sequence had over 95 % similarity with that of D. variabilis. The rDmGST was efficiently expressed soluble and purified by His trap affinity chromatography. Enzyme activity of native GST and transcriptional profiles of the GST showed up-regulation in different stages and organs of D. marginaus during blood feeding. Polyclonal antibody reacted with rDmGST in Western blotting. Tick challenge on rDmGST inoculated rabbits showed reductions in adult female engorgement rate, total egg mass and egg hatching rate with an overall vaccine efficacy of 43.69 %. The results of the experiment indicated the GST has potential value to be an effective protective antigen of D. marginatus.

Effect of β-D-Mannuronic Acid (M2000) on Oxidative Stress Enzymes' Gene Using Healthy Donor Peripheral Blood Mononuclear Cells for Evaluating the Anti-Aging Property

OBJECTIVE

This research aimed to study the anti-aging and anti-inflammatory effects of low and high doses of the β-D-mannuronic (M2000) on gene expression of enzymes involved in oxidative stress (including SOD2, GST, GPX1, CAT, iNOS, and MPO) in peripheral blood mononuclear cells (PBMCs) of healthy donors under in vitro conditions.

METHODS

The PBMCs were separated and the RNAs were then extracted and the cDNAs synthesized, and expression levels of the mentioned genes were detected by qRT-PCR.

RESULTS

Our results indicated that the high dose of this drug could significantly reduce the expression level of the SOD2 gene compared to the lipopolysaccharide (LPS) group (p < 0.0001). Moreover, it was found that the high dose of this drug could significantly decrease the expression level of the GST gene compared to the LPS group (p < 0.0001). However, no significant reductions were observed in expression levels of the CAT and GPX1 genes compared to the LPS group. Furthermore, our data revealed that the level of iNOS and MPO gene expression was significantly reduced, in both doses of M2000, respectively, compared to the LPS group (p < 0.0001).

CONCLUSION

This research showed that M2000 as a novel NSAID with immunosuppressive properties could modify oxidative stress through lowering expression levels of the SOD2, GST, iNOS, and MPO genes compared to the healthy expression levels, with a probable reduction of the risk of developing inflammatory diseases related to age and aging.

A New Approach for the Prevention and Treatment of Cardiovascular Disorders. Molecular Hydrogen Significantly Reduces the Effects of Oxidative Stress

Cardiovascular diseases are the most common causes of morbidity and mortality worldwide. Redox dysregulation and a dyshomeostasis of inflammation arise from, and result in, cellular aberrations and pathological conditions, which lead to cardiovascular diseases. Despite years of intensive research, there is still no safe and effective method for their prevention and treatment. Recently, molecular hydrogen has been investigated in preclinical and clinical studies on various diseases associated with oxidative and inflammatory stress such as radiation-induced heart disease, ischemia-reperfusion injury, myocardial and brain infarction, storage of the heart, heart transplantation, etc. Hydrogen is primarily administered via inhalation, drinking hydrogen-rich water, or injection of hydrogen-rich saline. It favorably modulates signal transduction and gene expression resulting in suppression of proinflammatory cytokines, excess ROS production, and in the activation of the Nrf2 antioxidant transcription factor. Although H₂ appears to be an important biological molecule with anti-oxidant, anti-inflammatory, and anti-apoptotic effects, the exact mechanisms of action remain elusive. There is no reported clinical toxicity; however, some data suggests that H₂ has a mild hormetic-like effect, which likely mediate some of its benefits. The mechanistic data, coupled with the pre-clinical and clinical studies, suggest that H₂ may be useful for ROS/inflammation-induced cardiotoxicity and other conditions.

Impaired enzymatic reactive aldehyde-detoxifying capacity and glutathione peroxidase activity in the aged human arterial tissue

It is not known whether aging alters the enzymatic reactive aldehyde- and lipid hydroperoxide-detoxifying capacity of the human arterial tissue favoring vascular oxidative stress. To address this issue, we studied the specific enzymatic activities of class 1, 2 and 3 aldehyde dehydrogenase (ALDH1, ALDH2 and ALDH3), glutathione S‑transferase (isozyme A4-4, GSTA4-4) and aldose reductase (AR), namely the major reactive aldehyde-scavenging enzymes, together with the activity of the lipid hydroperoxide-removing enzyme glutathione peroxidase (GSH-Px), in superior thyroid arteries (STA) specimens obtained in the thyroid surgery setting in aged subjects (age 72.3 ± 3.6 years) and young adult controls (age 31.9 ± 3.5 years). Vascular lipid peroxidation was also studied by assessing in STA fluorescent damage products of lipid peroxidation (FDPL), which reflect oxidant-induced 4‑hydroxynonenal and lipid hydroperoxide formation. Remarkably, the activities of ALDH1, ALDH2, ALDH3, GSTA4-4, AR and GSH-Px were significantly lower, and FDPL levels higher, in the arterial tissue of the aged subjects than in that of the young adult controls. Moreover, the enzymatic activities were inversely and significantly correlated with the levels of FDPL in the arterial tissue of both the aged and young subjects, highlighting their vascular antioxidant/antilipoperoxidative role in vivo. Thus, aging impairs the enzymatic reactive aldehyde-detoxifying capacity and GSH-Px activity of the human arterial tissue eventually favoring vascular oxidative stress.

Impaired glutathione-related antioxidant defenses in the arterial tissue of diabetic patients

We studied the specific enzymatic activities of selenium-dependent (GSH-Px) and -independent (GST-Px) glutathione peroxidase, glutathione reductase (GSSG-Red), and glutathione S-transferase (GST) in internal mammary arteries (IMArt) specimens obtained during coronary artery bypass surgery in 18 patients with type 2 diabetes mellitus as compared to 18 non-diabetic controls; vascular lipid peroxidation, namely fluorescent damage products of lipid peroxidation (FDPL) as 4-hydroxynonenal-related oxidative stress indicators, was also studied. Moreover, in other 16 diabetic patients and 16 controls, total glutathione (TGlut) was determined in IMArt specimens specifically homogenized in sulfosalycilic acid to prevent vascular GSH depletion. The activities of GSH-Px, GSSG-Red, and GST were significantly lower, and FDPL levels higher, in the arterial tissue of diabetic patients than in that of controls; GST-Px was undetectable. Such enzymatic activities were inversely correlated with vascular lipid peroxidation, highlighting their antioxidant role in the arterial tissue, as were HbA1c and FDPL levels with the enzymatic activities, suggesting that glycation, oxidant species and lipoperoxidation aldehydes may be involved in glutathione-related enzyme inactivation. Further, in the diabetic patients HbA1c was correlated directly with lipid peroxidation but inversely with TGlut of the arterial tissue. In the patients considered for vascular enzymatic activities and FDPL assay, 3/4-vessel coronary artery disease (CAD) as expression of atherosclerosis severity was present in 9 diabetic patients and in 3 controls. Notably, vascular glutathione-related enzymatic activities were significantly lower, and FDPL levels higher, in the 9 diabetic patients with 3/4-vessel CAD than in the 9 without, as well as in the total of 12 patients with 3/4-vessel CAD than in the total of 24 patients without. Moreover, vascular TGlut content was significantly lower in the diabetic than in the control patients. Three/4-vessel CAD was present in 6 diabetic patients and in 2 controls considered for determination of vascular Tglut content, which was significantly lower in the diabetic patients with 3/4-vessel CAD than in those without, as well in the total of 8 patients with 3/4-vessel CAD than in the total of 24 patients without. Thus, weakened glutathione-related antioxidant capacity and oxidative stress of the arterial tissue are associated with the severity of atherosclerosis. In conclusion, impaired glutathione-related antioxidant defenses of the arterial tissue occur in diabetic patients, eventually favoring vascular oxidative stress and the severity of atherosclerosis.

Staphylococcus aureus nitric oxide synthase (saNOS) modulates aerobic respiratory metabolism and cell physiology

Nitric oxide (NO) is generated from arginine and oxygen via NO synthase (NOS). Staphylococcus aureus NOS (saNOS) has previously been shown to affect virulence and resistance to exogenous oxidative stress, yet the exact mechanism is unknown. Herein, a previously undescribed role of saNOS in S. aureus aerobic physiology was reported. Specifically, aerobic S. aureus nos mutant cultures presented with elevated endogenous reactive oxygen species (ROS) and superoxide levels, as well as increased membrane potential, increased respiratory dehydrogenase activity and slightly elevated oxygen consumption. Elevated ROS levels in the nos mutant likely resulted from altered respiratory function, as inhibition of NADH dehydrogenase brought ROS levels back to wild-type levels. These results indicate that, in addition to its recently reported role in regulating the switch to nitrate-based respiration during low-oxygen growth, saNOS also plays a modulatory role during aerobic respiration. Multiple transcriptional changes were also observed in the nos mutant, including elevated expression of genes associated with oxidative/nitrosative stress, anaerobic respiration and lactate metabolism. Targeted metabolomics revealed decreased cellular lactate levels, and altered levels of TCA cycle intermediates, the latter of which may be related to decreased aconitase activity. Collectively, these findings demonstrate a key contribution of saNOS to S. aureus aerobic respiratory metabolism.

Redox changes in the brains of reproductive female rats during aging

Reproduction is a critical and demanding phase of an animal's life. In mammals, females usually invest much more in parental care than males, and lactation is the most energetically demanding period of a female's life. Here, we tested whether oxidative stress is a consequence of reproduction in the brains of female Wistar rats. We evaluated the activities of glutathione peroxidase, glutathione S-transferase, and superoxide dismutase; H₂O₂ consumption; protein carbonylation; NO₂ & NO₃ levels; and total glutathione, as well as sex hormone levels in brain tissue of animals at 3, 6, 12, and 24months of age. Animals were grouped according to reproductive experience: breeders or non-breeders. Most of the studied parameters showed a difference between non-breeders and breeders at 12 and 24months. At 24months of age, breeders showed higher superoxide dismutase activity, H₂O₂ consumption, glutathione peroxidase activity, and carbonyl levels than non-breeders. In 12-month-old non-breeders, we observed a higher level of H₂O₂ consumption and higher superoxide dismutase and glutathione peroxidase activities than breeders. By evaluating the correlation network, we found that there were a larger number of influential nodes and positive links in breeder animals than in non-breeders, indicating a greater number of redox changes in breeder animals. Here, we also demonstrated that the aging process caused higher oxidative damage and higher antioxidant defenses in the brains of breeder female rats at 24months, suggesting that the reproduction process is costly, at least for the female brain. This study shows that there is a strong potential for a link between the cost of reproduction and oxidative stress.

Gene-environment interactions in esophageal cancer

Esophageal cancer (EC) is one of the most common malignancies in low- and medium-income countries and represents a disease of public health importance because of its poor prognosis and high mortality rate in these regions. The striking variation in the prevalence of EC among different ethnic groups suggests a significant contribution of population-specific environmental and dietary factors to susceptibility to the disease. Although individuals within a demarcated geographical area are exposed to the same environment and share similar dietary habits, not all of them will develop the disease; thus genetic susceptibility to environmental risk factors may play a key role in the development of EC. A wide range of xenobiotic-metabolizing enzymes are responsible for the metabolism of carcinogens introduced via the diet or inhaled from the environment. Such dietary or environmental carcinogens can bind to DNA, resulting in mutations that may lead to carcinogenesis. Genes involved in the biosynthesis of these enzymes are all subject to genetic polymorphisms that can lead to altered expression or activity of the encoded proteins. Genetic polymorphisms may, therefore, act as molecular biomarkers that can provide important predictive information about carcinogenesis. The aim of this review is to discuss our current knowledge on the genetic risk factors associated with the development of EC in different populations; it addresses mainly the topics of genetic polymorphisms, gene-environment interactions, and carcinogenesis. We have reviewed the published data on genetic polymorphisms of enzymes involved in the metabolism of xenobiotics and discuss some of the potential gene-environment interactions underlying esophageal carcinogenesis. The main enzymes discussed in this review are the glutathione S-transferases (GSTs), N-acetyltransferases (NATs), cytochrome P450s (CYPs), sulfotransferases (SULTs), UDP-glucuronosyltransferases (UGTs), and epoxide hydrolases (EHs), all of which have key roles in the detoxification of environmental and dietary carcinogens. Finally, we discuss recent advances in the study of genetic polymorphisms associated with EC risk, specifically with regard to genome-wide association studies, and examine possible challenges of case-control studies that need to be addressed to better understand the interaction between genetic and environmental factors in esophageal carcinogenesis.

Protective effect of artichoke leaf extract against paracetamol-induced hepatotoxicity in rats

CONTEXT

Paracetamol overdose is a predominant cause of hepatotoxicity in both humans and experimental animals.

OBJECTIVE

In this study, we investigated the protective effect of aqueous artichoke leaf extract (ALE) against paracetamol-induced liver injury in rats using N-acetylcysteine (NAC) as a reference drug.

MATERIALS AND METHODS

Rats were divided into five groups: negative control, paracetamol (2 g/kg, single oral dose), ALE (1.5 g/kg, orally for 14 d), ALE + paracetamol, and NAC (100 mg/kg) + paracetamol. Indices of liver damage (serum alanine aminotransferase and aspartate aminotransferase) were measured. Liver homogenates were analyzed for oxidative stress biomarkers (MDA, malondialdehyde; SOD activity, superoxide dismutase activity; NO, nitric oxide; GSH content, reduced glutathione), glutathione cycling (GR, glutathione reductase), and utilization (GST, glutathione-S-transferase). Apoptosis was assessed using the comet assay.

RESULTS

Paracetamol caused marked liver damage as noted by significant increased activities of serum aminotransferases (p < 0.05) as well as a significant increase in hepatic MDA and NO levels (p < 0.001) compared with the negative control group. GSH content, GR, GST, and SOD activities were decreased significantly (p < 0.001). Comet assay parameters (tail length, percentage of tailed cells, percentage of migrated DNA, and tail moment) were increased (p < 0.05), indicating apoptosis. Histopathological examination showed necrotic areas. Pre-treatment with ALE replenished hepatic GSH, reversed oxidative stress parameters, DNA damage, and necrosis induced by paracetamol.

DISCUSSION AND CONCLUSION

These results suggest that ALE may protect from paracetamol-induced liver toxicity via its antioxidant and anti-apoptotic properties.

Maltol, a food flavoring agent, attenuates acute alcohol-induced oxidative damage in mice

The purpose of this study was to evaluate the hepatoprotective effect of maltol, a food-flavoring agent, on alcohol-induced acute oxidative damage in mice. Maltol used in this study was isolated from red ginseng (Panax ginseng C.A Meyer) and analyzed by high performance liquid chromatography (HPLC) and mass spectrometry. For hepatoprotective activity in vivo, pretreatment with maltol (12.5, 25 and 50 mg/kg; 15 days) drastically prevented the elevated activities of aspartate transaminase (AST), alanine transaminase (ALT), alkaline phosphatase (ALP) and triglyceride (TG) in serum and the levels of malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) in liver tissue (p < 0.05). Meanwhile, the levels of hepatic antioxidant, such as catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) were elevated by maltol pretreatment, compared to the alcohol group (p < 0.05). Histopathological examination revealed that maltol pretreatment significantly inhibited alcohol-induced hepatocyte apoptosis and fatty degeneration. Interestingly, pretreatment of maltol effectively relieved alcohol-induced oxidative damage in a dose-dependent manner. Maltol appeared to possess promising anti-oxidative and anti-inflammatory capacities. It was suggested that the hepatoprotective effect exhibited by maltol on alcohol-induced liver oxidative injury may be due to its potent antioxidant properties.

Glutathione redox control of asthma: from molecular mechanisms to therapeutic opportunities

Asthma is a chronic inflammatory disorder of the airways associated with airway hyper-responsiveness and airflow limitation in response to specific triggers. Whereas inflammation is important for tissue regeneration and wound healing, the profound and sustained inflammatory response associated with asthma may result in airway remodeling that involves smooth muscle hypertrophy, epithelial goblet-cell hyperplasia, and permanent deposition of airway extracellular matrix proteins. Although the specific mechanisms responsible for asthma are still being unraveled, free radicals such as reactive oxygen species and reactive nitrogen species are important mediators of airway tissue damage that are increased in subjects with asthma. There is also a growing body of literature implicating disturbances in oxidation/reduction (redox) reactions and impaired antioxidant defenses as a risk factor for asthma development and asthma severity. Ultimately, these redox-related perturbations result in a vicious cycle of airway inflammation and injury that is not always amenable to current asthma therapy, particularly in cases of severe asthma. This review will discuss disruptions of redox signaling and control in asthma with a focus on the thiol, glutathione, and reduced (thiol) form (GSH). First, GSH synthesis, GSH distribution, and GSH function and homeostasis are discussed. We then review the literature related to GSH redox balance in health and asthma, with an emphasis on human studies. Finally, therapeutic opportunities to restore the GSH redox balance in subjects with asthma are discussed.

Functional impairment of rat taurine transporter by activation of nitrogen oxide through superoxide

The objective of this study was to identify the nitrogen oxide form(s) involved in the functional impairment of the rat taurine transport system. Taurine uptake activity in the rat renal brush border membrane vesicle (RBBMV) preparation or Xenopus laevis oocytes that express the rat taurine transporter was compared after the pretreatment with nitrogen oxide donors from which nitric oxide (NO) is released at different rates. The functional impairment was associated with a reduced Vmax, but did not involve an alteration in the Km, of taurine uptake in the RBBMV preparation that had been pretreated with sodium nitroprusside, a slow release nitric oxide (NO) donor. When the preparation was pretreated with S-nitroso-N-acetyl penicillamine, a rapid release NO donor, the activity of taurine uptake was unaffected. The activity was not statistically different from the control after the pretreatment with sodium nitroprusside and superoxide dismutase. Consistent with the study with RBBMV, a similar alteration in the activity of taurine uptake by NO donors was observed in oocytes expressing the transporter. Considering the fact that peroxynitrite, a highly reactive nitrogen oxide form, is formed by the reaction between NO and superoxide, the taurine transporter, and probably other transport systems as well, may be functionally impaired by peroxynitrite.

Nitric oxide metabolism in asthma pathophysiology

BACKGROUND

Asthma, a chronic inflammatory disease is typically characterized by bronchoconstriction and airway hyper-reactivity.

SCOPE OF REVIEW

A wealth of studies applying chemistry, molecular and cell biology to animal model systems and human asthma over the last decade has revealed that asthma is associated with increased synthesis of the gaseous molecule nitric oxide (NO).

MAJOR CONCLUSION

The high NO levels in the oxidative environment of the asthmatic airway lead to greater formation of reactive nitrogen species (RNS) and subsequent oxidation and nitration of proteins, which adversely affect protein functions that are biologically relevant to chronic inflammation. In contrast to the high levels of NO and nitrated products, there are lower levels of beneficial S-nitrosothiols (RSNO), which mediate bronchodilation, due to greater enzymatic catabolism of RSNO in the asthmatic airways.

GENERAL SIGNIFICANCE

This review discusses the rapidly accruing data linking metabolic products of NO as critical determinants in the chronic inflammation and airway reactivity of asthma. This article is part of a Special Issue entitled Biochemistry of Asthma.

Glutathione status in the blood of rats after reticulocytosis induced by phenylhydrazine and bleeding

In this experiment, we compared the in vivo effects of phenylhydrazine (PHZ) and bleeding treatment on the redox status and glutathione antioxidative mechanism parameters in the plasma and red blood cells (RBC) of rats. Results showed a lower level of reactive oxygen species (ROS), a higher level of lipid peroxidation and the effective antioxidative role of the glutathione system in the blood of bleeding rats. PHZ-treatment induced higher concentrations of ROS and an accumulation of oxidized glutathione in the plasma, while the glutathione system showed a satisfactory antioxidative capacity in the RBC of rats. When comparing the two anemic groups, the PHZ-treated rats showed marked oxidative stress in the plasma. .

Urinary felinine excretion in intact male cats is increased by dietary cystine

Felinine is a branched-chain sulfur amino acid present in the urine of certain Felidae, including domestic cats. The objective of the present study was to determine if additional cystine and/or dietary N would increase felinine and N-acetylfelinine excretion by intact male cats fed a low-protein (LP) diet. Feeding five adult intact male cats an LP diet (18·8 % of metabolisable energy (ME) as protein) v. a high-protein diet (38·6 % of ME as protein) resulted in a trend (P = 0·08) for decreased urinary felinine and no change in N-acetylfelinine excretion. In a 23 d study, when the LP diet was supplemented with l-cystine at 9·3 g/kg DM, urinary felinine:creatinine ratio showed a linear two-fold (121 %) increase (P < 0·01) from 0·24 (sem 0·05) to 0·53 (sem 0·13) after 10 d. Subsequent feeding of the LP diet resulted in a decrease in felinine excretion to base levels. Plasma γ-glutamylfelinylglycine concentrations were consistent with the excretion of felinine. Supplementation of the LP diet with l-cystine (9·3 g/kg DM), dispensable amino acids and arginine to a second group (n 5) also resulted in a significant (P < 0·01) but smaller (+72 %) increase in the daily felinine:creatinine ratio (0·25 (sem 0·04) to 0·43 (sem 0·05)). The degree of felinine N-acetylation within groups was unaffected by dietary addition and withdrawal of amino acids. The results indicate that felinine synthesis is regulated by cystine availability, and that arginine may be physiologically important in decreasing felinine biosynthesis in intact male cats.

Inactivation of hepatic enzymes by inhalant nitrite--in vivo and in vitro studies

We examined the effects of acute isobutyl nitrite (ISBN) exposure on the activity of several hepatic enzymes. Two strains of adult male mice (Balb/c and C57BL/6) were exposed to 900 ppm ISBN or ambient air for 45 minutes. The enzyme activity of hepatic cytochrome P450 (CYP)-mediated deethylation, glutathione S-transferase (GST), and carboxylesterase (CBE) was monitored through the substrates 3-cyano-7-ethoxycoumarin (CEC), 1-chloro-2,4-dinitrobenzene, and p-nitrophenyl acetate, respectively. Acute ISBN exposure led to a significant reduction in hepatic CYP-mediated CEC deethylation, GST, and CBE activity in Balb/c mice (of 81.5%, 74.7%, and 25.2%, respectively, vs control mice, each at P < .05) when livers were harvested immediately after inhalant exposure. The corresponding decreases in C57BL/6 mice were smaller (with reductions of 21.8%, 18.8%, and 13.3%, respectively, each at P < .05). This enzyme activity, tested in C57BL/6 mice only, returned to control values after a 24-hour period of nonexposure. Follow-up mechanistic investigations using rat liver GST indicated that ISBN-mediated enzyme inactivation was not caused by its metabolites: inorganic nitrite ion (NO2-) or nitric oxide. This inactivation could be prevented, but not reversed, by added glutathione, suggesting irreversible protein oxidation. Using different NO donors as comparative agents, we found that GST inactivation by ISBN was not associated with protein S-nitrosylation or disulfide formation, but with tyrosine nitration. Inhalant nitrite exposure, therefore, led to a significant reduction in hepatic enzyme activity in mice, possibly through tyrosine nitration of hepatic proteins. This effect raises the possibility of drug-drug metabolic interactions from inhalant nitrite abuse. However, determining the applicability of these findings to humans will require further study.

The effects of cold acclimation and nitric oxide on antioxidative enzymes in rat pancreas

Alterations of pancreatic antioxidative defense (AD) and possible nitric oxide (NO) role in AD organization of adult rats receiving l-arginine.HCl (2.25%) or N(omega)-nitro-l-arginine methyl ester (L-NAME.HCl, 0.01%) as drinking liquids and maintained at room (22+/-1 degrees C) or low (4+/-1 degrees C) temperature for 45 days were studied. For that purpose, copper, zinc- and manganese superoxide dismutase (CuZnSOD, MnSOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione S-transferase (GST) and glutathione reductase (GR) activities were determined. Cold-induced decrease of CuZnSOD was inhibited with L-NAME, while l-arginine produced the same effect as cold in both supplemented groups. Cold acclimation elevated GSH-Px activity. l-Arginine and L-NAME expressed no effect on GSH-Px in rats kept at room temperature. L-NAME additionally elevated cold-induced GSH-Px activity, l-arginine expressing a similar trend. Cold-induced increase in GST activity was inhibited by L-NAME, while l-arginine inhibited this enzyme in both supplemented groups. Cold acclimation increased GR activity in control and L-NAME-treated group and l-arginine expressed a similar trend. Neither of the treatments affected MnSOD and CAT activities. Cold-induced changes of pancreatic AD were additionally affected by the alterations in l-arginine-NO-producing pathway. Some AD changes in the same direction with l-arginine or L-NAME point to the complexity of nitrogen compounds metabolism and function, accompanied by tissue-specific response.

Role of Oxidative Stress in the Pathogenesis of Abdominal Aortic Aneurysms

The role of inflammation in the pathogenesis of abdominal aortic aneurysms (AAA) is well established. The inflammatory process leads to protease-mediated degradation of the extracellular matrix and apoptosis of smooth muscle cells (SMC), which are the predominant matrix synthesizing cells of the vascular wall. These processes act in concert to progressively weaken the aortic wall, resulting in dilatation and aneurysm formation. Oxidative stress is invariably increased in, and contributes importantly to, the pathophysiology of inflammation. Moreover, reactive oxygen species (ROS) play a key role in regulation of matrix metalloproteinases and induction of SMC apoptosis. ROS may also contribute to the pathogenesis of hypertension, a risk factor for AAA. Emerging evidence suggests that ROS and reactive nitrogen species (RNS) are associated with AAA formation in animal models and in humans. Although experimental data are limited, several studies suggest that modulation of ROS production or activity may suppress AAA formation and improve experimental outcome in rodent models. Although a number of enzymes can produce injurious ROS in the vasculature, increasing evidence points toward a role for NADPH oxidase as a source of oxidative stress in the pathogenesis of AAA.

Nitrotyrosine proteome survey in asthma identifies oxidative mechanism of catalase inactivation

Reactive oxygen species and reactive nitrogen species produced by epithelial and inflammatory cells are key mediators of the chronic airway inflammation of asthma. Detection of 3-nitrotyrosine in the asthmatic lung confirms the presence of increased reactive oxygen and nitrogen species, but the lack of identification of modified proteins has hindered an understanding of the potential mechanistic contributions of nitration/oxidation to airway inflammation. In this study, we applied a proteomic approach, using nitrotyrosine as a marker, to evaluate the oxidation of proteins in the allergen-induced murine model of asthma. Over 30 different proteins were targets of nitration following allergen challenge, including the antioxidant enzyme catalase. Oxidative modification and loss of catalase enzyme function were seen in this model. Subsequent investigation of human bronchoalveolar lavage fluid revealed that catalase activity was reduced in asthma by up to 50% relative to healthy controls. Analysis of catalase isolated from asthmatic airway epithelial cells revealed increased amounts of several protein oxidation markers, including chloro- and nitrotyrosine, linking oxidative modification to the reduced activity in vivo. Parallel in vitro studies using reactive chlorinating species revealed that catalase inactivation is accompanied by the oxidation of a specific cysteine (Cys(377)). Taken together, these studies provide evidence of multiple ongoing and profound oxidative reactions in asthmatic airways, with one early downstream consequence being catalase inactivation. Loss of catalase activity likely amplifies oxidative stress, contributing to the chronic inflammatory state of the asthmatic airway.

Reactive nitrogen species derived activation of rat liver microsomal glutathione S-transferase

The effect of reactive nitrogen species on rat liver microsomal glutathione S-transferase (MGST1) was investigated using microsomes and purified MGST1. When microsomes or the purified enzyme were incubated with peroxynitrite (ONOO(-)), the GST activity was increased to 2.5-6.5 fold in concentration-dependent manner and a small amount of the MGST1 dimer was detected. MGST1 activity was increased by ONOO(-) in the presence of high amounts of reducing agents including glutathione (GSH) and the activities increased by ONOO(-) or ONOO(-) plus GSH treatment were decreased by 30-40% by further incubation with dithiothreitol (DTT, reducing disulfide) or by sodium arsenite (reducing sulfenic acid). Furthermore, GSH was detected by HPLC from the MGST1 which was incubated with ONOO(-) plus GSH or S-nitrosoglutathione followed by DTT treatment. In addition, the MGST1 activity increased by nitric oxide (NO) donors such as S-nitrosoglutathione, S-nitrosocysteine or the non-thiol NO donor 1-hydroxy-2-oxo-3 (3-aminopropyl)-3-isopropyl was restored by the DTT treatment. Since DTT can reduce S-nitrosothiol and disulfide bond to thiol, S-nitrosylation and a mixed disulfide bond formation of MGST1 were suggested. Thus, it was demonstrated that MGST1 is activated by reactive nitrogen species through a forming dimeric protein, mixed disulfide bond, nitrosylation and sulfenic acid.

Nitric oxide mediates inactivation of glutathione S-transferase in suspension culture of Taxus cuspidata during shear stress

The importance of nitric oxide (NO) in regulating plant cell responses to environmental stresses is becoming evident. Here the possible role of NO in suspension cultures of Taxus cuspidata under shear stress was investigated in a Couette-type shear reactor. It was found that shear stress with 190 s(-1) caused NO generation in 8 h. NO formation can be inhibited by N-nitro-L-arginine, a nitric oxide synthase inhibitor. Moreover, the activity of glutathione S-transferase (GST), a principal enzyme responsible for detoxification, decreased during shear stress. This inactivation partially recovered when NOS inhibitor or NO scavenger was added into cell cultures during shear stress. Treatment with reactive nitrogen species (RNS) also caused inactivation of GST in cells. The results indicate that NO plays a crucial role in GST inactivation in Taxus cuspidata cells under shear stress.

The regulation and pharmacology of endothelial nitric oxide synthase

Nitric oxide (NO) is a small, diffusible, lipophilic free radical gas that mediates significant and diverse signaling functions in nearly every organ system in the body. The endothelial isoform of nitric oxide synthase (eNOS) is a key source of NO found in the cardiovascular system. This review summarizes the pharmacology of NO and the cellular regulation of endothelial NOS (eNOS). The molecular intricacies of the chemistry of NO and the enzymology of NOSs are discussed, followed by a review of the biological activities of NO. This information is then used to develop a more global picture of the pharmacological control of NO synthesis by NOSs in both physiologic conditions and pathophysiologic states.

Effects of flavonoids extracted from Scutellaria baicalensis Georgi on hemin–nitrite–H2O2 induced liver injury

Hemin-nitrite-H2O2 system may play a role in liver oxidative injury in some pathological events. In this paper, the effects of the three active components of the root of Scutellaria baicalensis Georgi, i.e. baicalin, baicalein and wogonin, on hemin-nitrite-H2O2 induced liver injury were studied in liver homogenate, liver microsome and human hepatoblastoma cell line HepG2 cells. It was found that hemin-nitrite-H2O2 could induce liver homogenate protein nitration, lipid peroxidation and liver microsome protein oxidation; it also caused a decrease of HepG2 cells viability. Baicalein, baicalin and wogonin could inhibit protein nitration and lipid peroxidation in liver homogenate as well as in HepG2 cells in a dose-dependent manner, the inhibition order was baicalein>baicalin>>wogonin. These three flavonoids also inhibited the oxidation of protein in liver microsome, the decrease of cell viability and the content of GSH in HepG2 cells, among which baicalin represented the most inhibitory effect. Besides, hemin-H2O2 induced cell injury could be augmented with the existence of nitrite, indicating protein nitration involved in hemin-nitrite-H2O2 induced liver injury. These results demonstrated hemin-nitrite-H2O2 could induce liver injury through oxidizing or nitrating different biomolecules. Baicalein, baicalin and wogonin could inhibit hemin-nitrite-H2O2 induced liver injury in dose-dependent manners by inhibiting oxidation and nitration.

Nitration of tyrosine 92 mediates the activation of rat microsomal glutathione s-transferase by peroxynitrite

There is increasing evidence that protein function can be modified by nitration of tyrosine residue(s), a reaction catalyzed by proteins with peroxidase activity, or that occurs by interaction with peroxynitrite, a highly reactive oxidant formed by the reaction of nitric oxide with superoxide. Although there are numerous reports describing loss of function after treatment of proteins with peroxynitrite, we recently demonstrated that the microsomal glutathione S-transferase 1 is activated rather than inactivated by peroxynitrite and suggested that this could be attributed to nitration of tyrosine residues rather than to other effects of peroxynitrite. In this report, the nitrated tyrosine residues of peroxynitrite-treated microsomal glutathione S-transferase 1 were characterized by mass spectrometry and their functional significance determined. Of the seven tyrosine residues present in the protein, only those at positions 92 and 153 were nitrated after treatment with peroxynitrite. Three mutants (Y92F, Y153F, and Y92F, Y153F) were created using site-directed mutagenesis and expressed in LLC-PK1 cells. Treatment of the microsomal fractions of these cells with peroxynitrite resulted in an approximately 2-fold increase in enzyme activity in cells expressing the wild type microsomal glutathione S-transferase 1 or the Y153F mutant, whereas the enzyme activity of Y92F and double site mutant was unaffected. These results indicate that activation of microsomal glutathione S-transferase 1 by peroxynitrite is mediated by nitration of tyrosine residue 92 and represents one of the few examples in which a gain in function has been associated with nitration of a specific tyrosine residue.

What makes an autoantigen an autoantigen?

Multiple classes of proteins are modified to tailor them for specific physiological roles. The nature of these posttranslational modifications of proteins, as well as the relationships between them including those of the immune system proteins themselves, and immune system responses are reviewed. Aspects of protein posttranslational modification and their relationship to the pathogenesis of several autoimmune diseases and primary biliary cirrhosis are highlighted.

Impairment of the activity of the xenobiotic-metabolizing enzymes arylamine N-acetyltransferases 1 and 2 (NAT1/NAT2) by peroxynitrite in mouse skeletal muscle cells

Reactive nitrogen species and their by-products, such as peroxynitrite, modulate many physiological functions of skeletal muscle. Peroxynitrite generation occuring under specific conditions, such as inflammation, may also lead to skeletal muscle dysfunction and pathologies. Arylamine N-acetyltransferases (NATs) are xenobiotic-metabolizing enzymes (XMEs) involved in the detoxification and/or metabolic activation of several drugs and chemicals. In addition to other XMEs, such as gluthatione S-transferases or cytochromes P450, NAT enzymes are expressed in skeletal muscle. We show here that functional NAT1 and NAT2 isoforms are expressed in mouse myotubes and that peroxynitrite may impair their activity in these cells. We show that this inactivation is likely due to the irreversible modification of NATs catalytic cysteine residue in vivo. Our results suggest that peroxynitrite-dependent inactivation of muscle XMEs such as NATs may contribute to muscle dysfunction by impairing the biotransformation activity of this key cellular defense enzyme system.

Peroxynitrite-derived carbonate and nitrogen dioxide radicals readily react with lipoic and dihydrolipoic acid

Alpha-lipoic acid (LA) and dihydrolipoic acid (DHLA) may have a role as antioxidants against nitric oxide-derived oxidants. We previously reported that peroxynitrite reacts with LA and DHLA with second-order rate constants of 1400 and 500 M(-1) s(-1), respectively, but indicated that these direct reactions are not fast enough to protect against peroxynitrite-mediated damage in vivo. Moreover, the mechanism of the reaction of peroxynitrite with LA has been recently challenged (J. Biol. Chem.279:9693-9697; 2004). Pulse radiolysis studies indicate that LA and DHLA react with peroxynitrite-derived nitrogen dioxide (*NO2) (k2 = 1.3 x 10(6) and 2.9 x 10(7) M(-1) s(-1), respectively) and carbonate radicals (CO(3-)) (k2 = 1.6 x 10(9) and 1.7 x 10(8) M(-1) s(-1), respectively). Carbonate radical-mediated oxidation of LA led to the formation of the potent one-electron oxidant LA radical cation. LA inhibited peroxynitrite-mediated nitration of tyrosine and of a hydrophobic tyrosine analog, N-t-BOC L-tyrosine tert-butyl ester (BTBE), incorporated into liposomes but enhanced tyrosine dimerization. Moreover, while LA competitively inhibited the direct oxidation of glutathione by peroxynitrite, it was poorly effective against the radical-mediated thiol oxidation. The mechanisms of reaction defined herein allow to rationalize the biochemistry of peroxynitrite based on direct and free radical-mediated processes and contribute to the understanding of the antioxidant actions of LA and DHLA.

Proteomic and transcriptomic analyses of macrophages with an increased resistance to oxidized low density lipoprotein (oxLDL)-induced cytotoxicity generated by chronic exposure to oxLDL

The uptake of oxidized low density lipoprotein (oxLDL) by macrophages leads to foam cell formation and fatty streaks, which represent early sites of potential atheroma development. We developed a cell culture model of chronic oxLDL exposure to determine whether hallmark parameters of oxLDL uptake and cytotoxicity are altered during foam cell formation and to determine changes in protein and mRNA expression that distinguish acute and chronic oxLDL exposure. Although the extent of oxLDL uptake did not change, a resistance to oxLDL-induced cytotoxicity was observed in the chronically exposed cells. Macrophages that have been chronically exposed to oxLDL required a 40% higher concentration of oxLDL to achieve 50% survival in a 48-h treatment relative to macrophages subjected to a single oxLDL exposure. A main feature of the differentially expressed proteome was a series of significantly overexpressed antioxidant and antioxidant-related proteins in the oxLDL-exposed cells. A large proportion of these proteins (45%) was overexpressed in the chronically exposed cells prior to the oxLDL treatment, indicative of the unique phenotype produced by the chronic treatment. Analysis of the transcriptome also revealed a broad increase in the expression of antioxidant and antioxidant-related proteins. In addition, the transcriptome experiments found an increased inflammatory response under conditions of both acute and chronic oxLDL exposure. Overall the combined functional, proteomic, and transcriptomic experiments show that macrophages respond to oxLDL by developing an oxidative stress resistance that increases and stabilizes with chronic exposure. Furthermore this protective response and the increased foam cell survival that it supports amplifies their proatherogenic role by promoting a continued inflammatory state.

Inactivation of Human Arylamine N‐Acetyltransferase 1 by Hydrogen Peroxide and Peroxynitrite

Arylamine N-acetyltransferases (NAT) are xenobiotic-metabolizing enzymes responsible for the acetylation of many arylamine and heterocyclic amines. They therefore play an important role in the detoxification and activation of numerous drugs and carcinogens. Two closely related isoforms (NAT1 and NAT2) have been described in humans. NAT2 is present mainly in the liver and intestine, whereas NAT1 is found in a wide range of tissues. Interindividual variations in NAT genes have been shown to be a potential source of pharmacological and/or pathological susceptibility. Evidence now shows that redox conditions may also contribute to overall NAT activity. This chapter summarizes current knowledge on human NAT1 regulation by reactive oxygen and nitrogen species.

Inhibition of glutathione S-transferases by thonningianin A, isolated from the African medicinal herb, Thonningia sanguinea, in vitro

There is evidence that increased expression of glutathione S-transferase (EC: 2.5.1.18, GST) is involved in resistance of tumor cells against chemotherapeutic agents. In this study we investigated the inhibitory effects of thonningianin A (Th A), a novel antioxidant isolated from the medicinal herb, Thonningia sanguinea on uncharacterized rat liver GST and human GST P1-1. Using 1-chloro-2,4-dinitrobenzene (CDNB) as substrate, rat liver cytosolic GST activity was inhibited by Th A in a concentration dependent manner with 50% inhibition concentration (IC50) of 1.1 microM. When Th A was compared with known potent GST inhibitors the order of inhibition was tannic acid>cibacron blue>hematin>Th A>ethacrynic acid with CDNB as substrate. Th A also exhibited non-competitive inhibition towards both CDNB and glutathione. Furthermore, using 1,2-dichloro-4-nitrobenzene, ethacrynic acid and 1,2-epoxy-3-(p-nitrophenoxy) propane as substrates Th A at 1.0 microM inhibited cytosolic GST by 2%, 12% and 36% respectively. Human GST P1-1 was also inhibited by Th A with an IC50 of 3.6 microM. While Th A showed competitive inhibition towards CDNB it exhibited non-competitive inhibition towards GSH of the human GST P1-1. These results suggest that Th A represents a new potent GST in vitro inhibitor.

Circadian rhythms, oxidative stress, and antioxidative defense mechanisms

Endogenous circadian and exogenously driven daily rhythms of antioxidative enzyme activities and of low molecular weight antioxidants (LMWAs) are described in various phylogenetically distant organisms. Substantial amplitudes are detected in several cases, suggesting the significance of rhythmicity in avoiding excessive oxidative stress. Mammalian and/or avian glutathione peroxidase and, as a consequence, glutathione reductase activities follow the rhythm of melatonin. Another hint for an involvement of melatonin in the control of redox processes is seen in its high-affinity binding to cytosolic quinone reductase 2, previously believed to be a melatonin receptor. Although antioxidative protection by pharmacological doses of melatonin is repeatedly reported, explanations of these findings are still insufficient and their physiological and chronobiological relevance is not yet settled. Recent data indicate a role of melatonin in the avoidance of mitochondrial radical formation, a function which may prevail over direct scavenging. Rhythmic changes in oxidative damage of protein and lipid molecules are also reported. Enhanced oxidative protein modification accompanied by a marked increase in the circadian amplitude of this parameter is detected in the Drosophila mutant rosy, which is deficient in the LMWA urate. Preliminary evidence for the significance of circadian rhythmicity in diminishing oxidative stress comes from clock mutants. In Drosophila, moderately enhanced protein damage is described for the arrhythmic and melatonin null mutant per0, but even more elevated, periodic damage is found in the short-period mutant per(s), synchronized to LD 12:12. Remarkably large increases in oxidative protein damage, along with impairment of tissue integrity and--obviously insufficient--compensatory elevations in protective enzymes are observed in a particularly vulnerable organ, the Harderian gland, of another short-period mutant tau, in the Syrian hamster. Mice deficient in the per2 gene homolog are reported to be cancer-prone, a finding which might also relate to oxidative stress. In the dinoflagellate Lingulodinium polyedrum [Gonyaulax polyedra], various treatments that cause oxidative stress result in strong suppressions of melatonin and its metabolite 5-methoxytryptamine (5-MT) and to secondary effects on overt rhythmicity. The glow maximum, depending on the presence of elevated 5-MT at the end of subjective night, decreases in a dose-dependent manner already under moderate, non-lethal oxidative stress, but is restored by replenishing melatonin. Therefore, a general effect of oxidative stress may consist in declines of easily oxidizable signaling molecules such as melatonin, and this can have consequences on the circadian intraorganismal organization and expression of overt rhythms. Recent findings on a redox-sensitive input into the core oscillator via modulation of NPAS2/BMAL1 or CLK/BMAL1 heterodimer binding to DNA indicate a direct influence of cellular redox balance, including oxidative stress, on the circadian clock.

Cloning, expression and partial characterization of a Haemaphysalis longicornis and a Rhipicephalus appendiculatus glutathione S-transferase

The ticks Haemaphysalis longicornis and Rhipicephalus appendiculatus are important parasites worldwide. The current method for control of cattle ticks involves the use of chemicals. Nevertheless, parasite resistance is an ever increasing global problem. Glutathione S-transferases (GSTs) play a central role in detoxication of xenobiotic and endogenous compounds. Several authors have noted that an increase in GST activity is associated with resistance to insecticides and acaricides. In the present study, we report the cloning and expression of GST cDNAs from H. longicornis and R. appendiculatus. In addition, we determine the effect of three acaricides (ethion, deltamethrin and diazinon) on the enzymatic activity of rGSTs.

Nitric oxide prodrugs and metallochemotherapeutics: JS-K and CB-3-100 enhance arsenic and cisplatin cytolethality by increasing cellular accumulation

Development of chemotherapeutic resistance is a major cause of pharmacologic failure in cancer treatment. One mechanism of resistance in tumor cells is the overexpression of glutathione S-transferases (GSTs) that serve two distinct roles in the development of drug resistance via the formation of glutathione conjugates with drugs for their cellular efflux, and the inhibition of the mitogen-activated protein kinase pathway. To target GST-based resistance to chemotherapeutics, a series of nitric oxide (NO)-releasing diazeniumdiolates was synthesized and shown to release NO on reaction with GST and/or glutathione. Two diazeniumdiolates, JS-K [O2-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate] and CB-3-100 [O2-(2,4-dinitrophenyl) 1-[4-(N,N-diethylcarboxamido)piperazin-1-yl]diazen-1-ium-1,2-diolate], were studied on their ability in reversing arsenic and cisplatin resistance in a rat liver cell line that is tumorigenic and shows acquired tolerance to arsenic and cisplatin, with overexpression of GSTs. The enhanced cytolethality produced by the NO donors was accompanied by increased accumulation of arsenic and platinum within cells and by enhanced activation of mitogen-activated protein kinase members c-jun-NH-kinase and extracellular signal-regulated kinase. Our data indicate that JS-K and CB-3-100 are promising lead compounds for the possible development of a novel class of adjuvant chemotherapeutic agents potentially capable of reversing arsenic and cisplatin resistance in certain tumor cells.

Lipoic Acid Protects Efficiently Only against a Specific Form of Peroxynitrite-induced Damage

The ability of the sulfur-containing compounds glutathione (GSH), glutathione disulphide (GSSG), S-methylglutathione (GSMe), lipoic acid (LA), and dihydrolipoic acid (DHLA) to protect against hypochlorous acid (HOCl)-mediated damage and peroxynitrite (ONOOH)-induced damage has been compared. Protective activity was assessed in competition assays by monitoring several detectors, i.e. dihydrorhodamine-123 (DHR-123) oxidation, alpha(1)-antiproteinase (alpha(1)-AP) inactivation, and glutathione S-transferase P1-1 (GST-P1-1) inactivation. In addition, nitration of tyrosine was measured to assess protection of the sulfur-containing compounds against ONOOH. For protection against HOCl, the efficacy of the antioxidant was controlled by the ratio of the reaction rates of the antioxidant and the detector molecule with the oxidant. The rank order of the activity of the antioxidants (GSH > DHLA approximately LA approximately GSMe > GSSG) appeared to be independent of the detector used. However, the rank order of the antioxidants against ONOOH-induced damage is strongly dependent on the detector. LA was 40 times less active than GSH in the inhibition of ONOOH-induced DHR-123 oxidation, whereas LA was 20 times more active than GSH in preventing the inhibition of GST-P1-1 by ONOOH. This points to different molecular mechanisms of ONOOH damage to DHR-123 compared with ONOOH damage to GST-P1-1. LA is a poor antioxidant in protecting against the form of ONOOH damage involved in DHR-123 oxidation. In the form of ONOOH toxicity involved in GST-P1-1 inhibition, LA is the most potent sulfur-containing antioxidant in our series. It is proposed that an intermediate product in which both sulfur atoms of LA have reacted is involved in the reaction of ONOOH with LA. The high potency of LA to protect GST-P1-1 against ONOOH might be of therapeutic interest.

Peroxynitrite irreversibly inactivates the human xenobiotic-metabolizing enzyme arylamine N-acetyltransferase 1 (NAT1) in human breast cancer cells: a cellular and mechanistic study

Arylamine N-acetyltransferases (NATs) play an important role in the detoxification and metabolic activation of a variety of aromatic xenobiotics, including numerous carcinogens. Both of the human isoforms, NAT1 and NAT2, display interindividual variations, and associations between NAT genotypes and cancer risk have been established. Contrary to NAT2, NAT1 has a ubiquitous tissue distribution and has been shown to be expressed in cancer cells. Given that the activity of NAT1 depends on a reactive cysteine that can be a target for oxidants, we studied whether peroxynitrite, a highly reactive nitrogen species involved in human carcinogenesis, could inhibit the activity of endogenous NAT1 in MCF7 breast cancer cells. We show here that exposure of MCF7 cells to physiological concentrations of peroxynitrite and to a peroxynitrite generator (3-morpholinosydnonimine N-ethylcarbamide, or SIN1) leads to the irreversible inactivation of NAT1 in cells. Further kinetic and mechanistic analyses using recombinant NAT1 showed that the enzyme is rapidly (k(inact) = 5 x 10(4) m(-1).s(-1)) and irreversibly inactivated by peroxynitrite. This inactivation is due to oxidative modification of the catalytic cysteine. We conclude that the reducing cellular environment of MCF7 cells does not sufficiently protect NAT1 from peroxynitrite-dependent inactivation and that only high concentrations of reduced glutathione could significantly protect NAT1. Thus, cellular generation of peroxynitrite may contribute to carcinogenesis and tumor progression by weakening key cellular defense enzymes such as NAT1.

Redox regulation of the human xenobiotic metabolizing enzyme arylamine N-acetyltransferase 1 (NAT1). Reversible inactivation by hydrogen peroxide

Oxidative stress is increasingly recognized as a key mechanism in the biotransformation and/or toxicity of many xenobiotics. Human arylamine N-acetyltransferase 1 (NAT1) is a polymorphic ubiquitous phase II xenobiotic metabolizing enzyme that catalyzes the biotransformation of primary aromatic amine or hydrazine drugs and carcinogens. Functional and structural studies have shown that NAT1 catalytic activity is based on a cysteine protease-like catalytic triad, containing a reactive cysteine residue. Reactive protein cysteine residues are highly susceptible to oxidation by hydrogen peroxide (H2O2) generated within the cell. We, therefore, investigated whether human NAT1 activity was regulated by this cellular oxidant. Using purified recombinant NAT1, we show here that NAT1 is rapidly (kinact = 420 m-1.min-1) inactivated by physiological concentrations of H2O2. Reducing agents, such as reduced glutathione (GSH), reverse the H2O2-dependent inactivation of NAT1. Kinetic analysis and protection experiments with acetyl-CoA, the physiological acetyl-donor substrate of the enzyme, suggested that the H2O2-dependent inactivation reaction targets the active-site cysteine residue. Finally, we show that the reversible inactivation of NAT1 by H2O2 is due to the formation of a stable sulfenic acid group at the active-site cysteine. Our results suggest that, in addition to known genetically controlled interindividual variations in NAT1 activity, oxidative stress and cellular redox status may also regulate NAT1 activity. This may have important consequences with regard to drug biotransformation and cancer risk.

Mechanism-based partial inactivation of glutathione S-transferases by nitroglycerin: tyrosine nitration vs sulfhydryl oxidation

Liver glutathione-S-transferases (GSTs) are responsible for the detoxification of electrophiles, and specifically for the metabolism of orally administered organic nitrates such as nitroglycerin (NTG). Recent studies showed that reactive nitrogen species produced by tetranitromethane (TNM), peroxynitrite, or the myeloperoxidase/H2O2/nitrite system can inactivate GST. It is not known whether NTG can similarly inactivate liver GSTs, and if shown, by what mechanism(s). We incubated purified GSTs with NTG, S-nitroso-N-acetylpenicillamine (SNAP), TNM, or vehicle (5% dextrose, D5W), followed by determination of GST activity. Incubation of GST with NTG and TNM caused significant decreases in GST activity whereas no changes were observed with SNAP or D5W. The relative GST activity (vs preincubation) was 73+/-14% for NTG, 37+/-8% for TNM, 98+/-13% for SNAP, and 98+/-9% for D5W, respectively. Exogenous glutathione (GSH) prevented both NTG- and TNM-induced changes in GST activity, consistent with the observed oxidative modification of GST, such as -SH oxidation and dimerization of oxidized GST. In contrast, NTG and TNM exhibited substantial differences in their ability to nitrate tyrosine (TYR) sites in GST. These results demonstrated that NTG can reduce the activity of its own metabolizing enzyme such as GST and this inhibitory effect of NTG was unlikely to be mediated through NO, as such, since SNAP had no effect on GST activity. The partial inactivation of GST by NTG appeared to involve -SH oxidation, but not TYR nitration. These findings provided the first evidence of mechanism-based protein inactivation by NTG, and may lend insight into the hepatic metabolism of NTG and other organic nitrates after repeated oral exposure.

Nitric oxide donor increases the efficiency of cytostatic therapy and retards the development of drug resistance

The potentiality to increase the chemotherapeutic effectiveness of some cytostatics in low, subtherapeutic doses in combination with nitric oxide (NO) donor has been shown. This type of combined therapy results in significant increase in life span and number of survivors among mice bearing leukemias P388 and L-1210. A similar effect was observed for intracerebral leukemia P388 transplantation. In this case the life span of mice treated with cyclophosphamide and NO donor increased by three times in comparison to therapy with cyclophosphamide alone. The coinjection of nitric oxide donor and cytostatics improved the antimetastatic activity of the cytostatics: the index of melanoma B16 metastasis inhibition at the cyclophosphamide monotherapy is 50%; on addition of NO donor the index is over 80%. Comparative studies of NO donor (organic nitrate) and a similar compound in which ONO(2) moieties were replaced by OH groups demonstrated that the presence of NO(2) is required for adjuvant activity of compounds and confirmed that nitric oxide modifies the antitumor effects of cytostatics. It is shown also that nitric oxide donor retards the development of drug resistance to cyclophosphamide.

Activation of microsomal glutathione s-transferase by peroxynitrite

Peroxynitrite (ONOO-) toxicity is associated with protein oxidation and/or tyrosine nitration, usually resulting in inhibition of enzyme activity. We examined the effect of ONOO- on the activity of purified rat liver microsomal glutathione S-transferase (GST) and found that the activity of reduced glutathione (GSH)-free enzyme was increased 4- to 5-fold by 2 mM ONOO-; only 15% of this increased activity was reversed by dithiothreitol. Exposure of the microsomal GST to ONOO- resulted in concentration-dependent oxidation of protein sulfhydryl groups, dimer and trimer formation, protein fragmentation, and tyrosine nitration. With the exception of sulfhydryl oxidation, these modifications of the enzyme correlated well with the increase in enzyme activity. Nitration or acetylation of tyrosine residues of the enzyme using tetranitromethane and N-acetylimidazole, respectively, also resulted in increased enzyme activity, providing additional evidence that modification of tyrosine residues can alter catalytic activity. Addition of ONOO--treated microsomal GST to microsomal membrane preparations caused a marked reduction in iron-induced lipid peroxidation, which raises the possibility that this enzyme may act to lessen the degree of membrane damage that would otherwise occur under pathophysiological conditions of increased ONOO- formation.

Enhanced activity of human IL-10 after nitration in reducing human IL-1 production by stimulated peripheral blood mononuclear cells

Nitric oxide and superoxide form the unstable compound, peroxynitrite, which can nitrate proteins and compromise function of proinflammatory cytokines at sites of inflammation. Reduced function of proinflammatory proteins such as IL-8, macrophage inflammatory protein-1alpha, and eotaxin suggest an anti-inflammatory effect of nitration. The effects of nitration on anti-inflammatory cytokines such as IL-10 are unknown. We hypothesized that peroxynitrite would modify the function of anti-inflammatory cytokines like IL-10. To test this hypothesis, the capacity of recombinant human IL-10 to inhibit production of human IL-1beta (IL-1) from LPS-stimulated human PBMC was evaluated. Human IL-10 was nitrated by incubation with peroxynitrite or by incubation with 3-morpholinosydnonimine, a peroxynitrite generator, for 2 h and then incubated with LPS-stimulated PBMC for 6 h, and IL-1 was measured in the culture supernatant fluids. Human IL-1 production was significantly lower in the peroxynitrite- or 3-morpholinosydnonimine-nitrated IL-10 group than in the IL-10 controls (p < 0.05, all comparisons). This finding demonstrates that although peroxynitrite inhibits proinflammatory cytokines, it may augment anti-inflammatory cytokines and further point to an important role for peroxynitrite in the regulation of inflammation.